Boards and Beyond: Biochemistry A Companion Book to the Boards and Beyond Website Jason Ryan, MD, MPH Version Date: 1-11-2018
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Table of Contents DNA Structure Purine Metabolism Pyrimidine Metabolism Glucose Glycolysis Gluconeogenesis Gluconeogenesi s Glycogen HMP Shunt Fructose and Galactose Pyruvate Dehydrogenase TCA Cycle Electron Transport Chain Fatty Acids Ketone Bodies
1 5 10 16 19 25 29 34 38 42 46 50 55 61
Ethanol Metabolism Exercise and Starvation Inborn Errors of Metabolism Metabolis m Amino Acids Phenylalanine Phenylala nine and Tyrosine Other Amino Acids Ammonia B Vitamins B12 and Folate Other Vitamins Lipid Metabolism Hyperlipidemia Hyperlipide mia Lipid Drugs Lysosomal Storage Diseases
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63 67 73 78 82 89 95 101 109 113 121 127 130 135
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DNA •
•
•
Contains genetic code Nucleus of eukaryotic eukaryotic cells Cytoplasm of prokaryotic cells
DNA Structure Jason Ryan, MD, MPH
DNA Structure •
•
•
DNA Vocabulary
Sugar (ribose) backbone Nitrogenous base Phosphate bonds
•
•
•
Nucleotides •
•
Nucleotide/Nucleoside Nitrogenous base Purine/Pyrimidine
Nucleoside vs. Nucleotide
DNA:Polymer Nucleotide: Monomer
•
Nucleotide •
Nitrogenous base
Pentose sugar
•
Sugar
•
Nitrogenous base
•
Phosphate group
•
Phosphate group
•
Ribonucleotide
•
Deoxyribonucleotide Binhtruong/Wikipedia
1
Adenosine Monophosphate
Nucleoside •
Base and sugar
•
No phosphate group
Wikipedia/Public i c Domain
Nitrogenous Bases
Nucleotides
Pyrimidines
Cytidine Cytosine
Thymine
Thymidine
Uridine
Uracil
Purines
Adenine
Guanine
Adenosine
Nucleotides •
•
•
Guanosine
Base Pairing
Synthesized as monophosphates
•
Converted to triphosphate form Added to DNA •
DNA •
Adenine-Thymine
•
Guanine-Cytosine
RNA •
Adenine-Uracil
•
Guanine-Cytosine
More C-G bonds = ↑ Melting temperature DeoxyadenosineTriphosphate
DNA Methylation •
•
•
•
Bacterial DNA Methylation
Methyl group added to cytosine
•
•
Occurs in segments with CG patterns (“CG islands”)
•
Both strands
•
•
Inactivates transcription (“epigenetics”) Human DNA: ~70% methylated Unmethylated CG stimulate immune response
Cytosine
•
5-methylcytosine
2
Bacteria methylate cytos ine and adenine Methylation protects bacteria from viruses (phages) Non-methylated DNA destroyed by endonucleases “Restriction-modification systems”
Chromatin
Nucleosome
•
Found in nucleus of eukaryotic cells
•
Key protein: Histones
•
DNA plus proteins = chromatin
•
Units of histones plus DNA = nucleosomes
•
Chromatin condenses into chromosomes
Histones •
Peptides •
•
•
Drug-Induced Lupus •
H1, H2A, H2B, H2B, H3, H4
•
Contain basic amino acids •
High content of lysine, arginine
•
Positively charged
•
Binds negatively charged phosphate backbone
•
•
H1 distinct from others •
Not in nucleosome core
•
Larger, more basic
•
Ties beads on string together
Chromatin Types •
•
Fever, Fever, joint pains, rash after s tarting drug Anti-histone antibodies (>95% cases) Contrast with anti-dsDNA in classic classic lupus
Classic drugs: •
Hydralazine
•
Procainamide
•
Isoniazid
Heterochromatin
•
Acetylation
•
Condensed
•
Acetyl group added to lysine
•
Gene sequences not transcribed (varies by cell)
•
Relaxes chromatin for transcription
•
Significant DNA methylation methylation
•
Euchromatin •
Less condensed
•
Transcription
•
Significant histone acetylation
Acetyl Group
Histone Acetylation
Deacetylation •
3
Reverse effect
Lysine
Histone deacetylase deacetylase inhibitors
Epigenetics
HDACs
Histone Acetylation
•
Potential therapeutic effects
•
Anti-cancer
•
Huntington’s disease
•
Transcription
Transcription
•
Increased expression of HDACs some some tumors Movement disorder
•
Abnormal huntingtin protein
•
Gain of function mutation (mutant protein)
•
Possible mechanism: histone deacetylation
•
Leads to neuronal cell death in striatum striatum
gene silencing
DNA Methylation Dokmanovic et al. Histone deacetylase inhibitors: overview and perspectives Mol Cancer Res. 2007 Oct;5(10):981-9.
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Nucleotides Pyrimidines
Cytidine
Purine Metabolism
Thymidine
Uridine
Purines
Jason Ryan, MD, MPH
Adenosine
Nucleotide Roles •
•
•
Sources of Nucleotides
RNA and DNA monomers Energy: ATP Physiologic mediators •
cAMP levels blood flow
•
cGMP
•
•
•
•
•
Diet (exogenous) Biochemical synthesis (endogenous) •
Direct synthesis
•
Salvage
second messenger
Key Points •
Guanosine
Purine Synthesis
Ribonucleic acids (RNA) synthesized first
•
RNA converted to deoxy ribonucleic ribonucleic acids (DNA) Different pathways for purines versus pyrimidines All nitrogen comes from amino acids
•
Goal is to create AMP and GMP Ingredients: •
Ribose phosphate (HMP Shunt)
•
Amino acids
•
Carbons (tetrahydrofolate, CO2)
Adenosine
5
Guanosine
Purine Synthesis •
Purine Synthesis •
Step 1: Create PRPP
Hypoxanthine
Step 2: Create IMP
Amino Acids Folate CO2
5-Phosphoribosyl-1-pyrophosphate (PRPP)
Ribose5-phosphate
5-Phosphoribosyl-1-pyrophosphate (PRPP)
Purine Synthesis
Purine Synthesis •
•
N N 6
Nitrogen Sources N
Glycine 6
6 unit, 3 double bonds
5 N
5 unit, 2 double bonds
N
Aspartate
N
N
N N Glutamine Adenine
Guanine
Hypoxanthine
Purine Synthesis
N
Purine Synthesis
N 6
Carbon Sources
5 N
CO2
N
•
Glycine
Step 3: Create AMP and GMP
N Tetrahydrofolate
N
Adenosine-MP
N
Tetrahydrofolate
Inosine monophosphate monophosphate (IMP)
N
*Key Point Folate contributes to formation of purines
Guanosine-MP
6
5 N
N
N
Two rings with two nitrogens: •
Inosine monophosphate monophosphate (IMP)
Purine Synthesis
Purine Synthesis
Summary
Regulation
•
•
Starts with ribose phosphate from HMP shunt Key intermediates are PRPP and IMP
IMP/AMP/GMP
Glutamine-PRPP amidotransferase
AMP 5-Ribose Phosphate
PRPP
5-Ribose Phosphate
IMP
PRPP
AMP IMP GMP
GMP Aspartate Glycine Glutamine THF CO2
Purine Synthesis
Deoxyribonucleotides
Drugs & D iseases •
Ribonucleotide Reductase
ADP
•
dADP
Ribavirin (antiviral) •
Inhibits IMP dehydrogenase dehydrogenase
•
Blocks conversion I MP to GMP
•
Inhibits synthesis guanine nucleotides (purines)
Mycophenolate •
GDP
(immunosuppressant)
Inhibits IMP dehydrogenase dehydrogenase
dGDP
Purine Fates
Purine Salvage •
•
•
Adenine
Guanine
Salvages bases: adenine, guanine, hypoxanthine Converts back into nucleotides: AMP, GMP, GMP, IMP Requires PRPP
Hypoxanthine
Uric Acid Salvage
5-Phosphoribosyl-1-pyrophosphate (PRPP)
Excretion
7
Purine Salvage
Purine Salvage
Hypoxanthine Hypoxanthineand an d Guanine
Adenine
Hypoxanthine
Adenine PRPP
Inosine monophosphate monophosphate (IMP)
HGPRT Hypoxanthine-Guanine phosphoribosyltransferase
Adenosine-MP
APRT Adenine phosphoribosyltransferase
Guanine PRPP Guanosine-MP PRPP
Purine Salvage
Purine Salvage
Drugs & Diseases
Drugs & Diseases
•
6-Mercaptopurine
•
Azathioprine
•
Chemotherapy agent
•
Immunosuppressant
•
Mimics hypoxanthine/guanine hypoxanthine/guanine
•
Converted to 6-MP
•
Added to PRPP by HGPRT
•
Inhibits multiple steps in de novo synthesis
•
↓IMP/AMP/GMP
Thioinosinic acid
+ PRPP
6-MP
Azathioprine
6-MP
Purine Breakdown
Purine Breakdown *SCID
Hypoxanthine
Xanthine Oxidase Xanthine Oxidase
Xanthine
Adenosine-MP
APRT Uric Acid
Adenosine Deaminase Adenosine
Inosine Purine nucleoside phosphorylase
Guanase
Guanine Adenine
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Hypoxanthine
Purine Salvage •
Gout
Purine Salvage
Xanthine Oxidase
Drugs & Diseases Hypoxanthine
Drugs & Diseases •
Uric Acid
Azathioprine and 6-MP
•
Excess uric acid
•
•
Crystal deposition in joints pain, swelling, redness
•
Metabolized by xanthine oxidase Caution with allopurinol allopurinol
•
Can occur from overproduction overproduction of uric acid
•
May boost effects
•
High cell turnover (trauma, chemotherapy)
•
May increase toxicity
•
Consumption of purine-rich foods (meat, ( meat, seafood) seafood)
•
Treatment: inhibit xanthine oxidase (allopurinol (allopurinol)) Xanthine Oxidase
6-MP
Purine Salvage Drugs & Diseases •
•
Lesch-Nyhan syndrome •
X-linked absence of HGPRT
•
Excess uric acid production (“juvenile gout”)
•
Excess de novo purine synthesis ( ↑PRPP,↑IMP ↑PRPP, ↑IMP )
•
Neurologic impairment (mechanism unclear)
•
Hypotonia, chorea
•
Classic feature: self mutilating behavior (biting, scratching)
•
No treatment
Classic presentation •
Male child with motor symptoms, self- mutilation, gout
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Thiouric acid (inactive)
Nucleotides Pyrimidines
Pyrimidine Metabolism
Thymidine
Cytidine
Uridine
Purines
Jason Ryan, MD, MPH
Adenosine
Pyrimidine Synthesis Synthesis
Pyrimidine Synthesis
•
Goal is to create CMP, CMP, UMP, UMP, TMP
•
•
Ingredients:
•
•
Ribose phosphate (HMP Shunt)
•
Amino acids
•
Carbons (tetrahydrofolate, CO2)
Guanosine
Step 1: Make carbamoyl phosphate Note: ring formed first then ribose sugar added
ATP
Glutamine
ADP
CO2
Carbamoyl Phosphate
Carbamoylphosphate synthetase II Cytidine
Thymidine
Pyrimidine Synthesis Synthesis •
UMP
Uridine
Pyrimidine Synthesis Synthesis
Step 2: Make orotic acid
•
Step 3: Make UMP UMP Synthase
Aspartate
Orotic Acid Carbamoyl Phosphate
Uridine-MP Orotic Acid
5-Phosphoribosyl-1-pyrophosphate (PRPP)
10
Pyrimidine Ring
Key Point •
•
Two nitrogens/four carbons
UMP synthesized first CMP, TMP TMP derived from UMP Carbamoyl Phosphate
CMP Carbamoyl Phosphate
Glutamine
Cytosine
C
Orotic Acid
N
C
C
C
Aspartate
UMP Uracil TMP
UMP Synthase Bifunctional
N Thymine
Pyrimidine Synthesis Synthesis
Pyrimidine Synthesis Synthesis
Drugs and Diseases
Drugs and Diseases
•
Orotic aciduria
•
Key findings
•
Autosomal recessive
•
Orotic acid in urine
•
Defect in UMP synthase
•
Megaloblastic anemia
•
Buildup of orotic acid
•
No B12/folate response
•
Loss of pyrimidines
•
Growth retardation
•
Orotic Acid
Treatment: •
Uridine
•
Bypasses UMP synthase
Orotic Acid
Ornithine transcarbamylase transcarbamylase
Cytidine
OTC •
•
•
•
•
•
Key urea cycle enzyme Combines carbamoyl phosphate with ornithine Makes citrulline OTC deficiency increased carbamoyl phosphate
↑ carbamoyl phosphate ↑ orotic acid confuse with orotic aciduria Don’t confuse •
Both have orotic aciduria
•
OTC only: ↑ ammonia levels (urea cycle dysfunction)
•
Ammonia
Uridine-MP
Uridine-TP ATP
encephalopathy encephalopathy (baby with lethargy, coma)
11
Cytidine-TP
Pyrimidine Synthesis
Thymidine
Drugs and Diseases •
Ara-C (Cytarabine or cytosine arabinoside) •
Chemotherapy agent
•
Converted to araCTP
•
Mimics dCTP (pyrimidine analog)
•
Inhibits DNA polymerase
•
•
•
Only used in DNA thymidine is only required nucleotide Deoxy thymidine Synthesized from deoxyuridine deoxyuridine
H
Thymidine
Ara-C
dCytidine
Pyrimidine Synthesis
Thymidine •
Drugs and Diseases
Step 1: Convert UMP to dUDP
Uridine-MP
Uridine
•
deoxyuridine-DP
Uridine-DP
Hydroxyurea •
Inhibits ribonucleotide reductase
•
Blocks formation of deoxynucleotides deoxynucleotides (RNA intact!)
•
Rarely used for malignancy
•
Can be used for polycythemia vera, essential thrombocytosis
•
Used in sickle cell anemia
•
Causes increased fetal hemoglobin levels (mechanism unclear) unclear)
Ribonucleotide Reductase
Thymidine •
•
Thymidine
Step 2: Convert dUDP to dUMP Step 3: Convert dUMP to dTMP
Thymidylate Synthase
1 Carbon added
dTMP
dUMP
Thymidylate Synthase deoxyuridine-MP (dUMP)
deoxythymidine-MP (dTMP) Source of 1 carbon N5, N10 Tetrahydrofolate Tetrahydrofolate
12
Folate Compounds
Folate Compounds
Folate Tetrahydrofolate
Dihydrofolate
N5, N10 Tetrahydrofolate
Tetrahydrofolate
Pyrimidine Synthesis
Thymidine
Drugs and Diseases •
Thymidylate Synthase dUridine-MP
Thymidine-MP
DHF
N5, N10 T etrahydrofolate etrahydrofolate
5-FU •
Chemotherapy agent
•
Mimics uracil
•
Converted to 5-FdUMP 5-FdUMP (abnormal dUMP)
•
Covalently binds N5,N10 TFH and thymidylate synthase
•
Result: inhibition thymidylate synthase
•
Blocks dTMP synthesis (“thymineless death”)
Folate
Dihydrofolate Reductase
THF
Uracil
* Folate = 1 carbon carriers
Pyrimidine Synthesis
Pyrimidine Synthesis
Drugs and Diseases
Drugs and Diseases
•
Methotrexate
•
Sulfonamides antibiotics
•
Chemotherapy agent, immunosuppressant immunosuppressant
•
Bacteria cannot absorb folic acid
•
Mimics DHF
•
Synthesize THF from para-aminobenzoic acid (PABA)
•
Inhibits dihydrofolate reductase
•
Sulfonamides mimic PABA
•
Blocks synthesis dTMP
•
Block THF synthesis
•
Rescue with leucovorin leucovorin (folinic acid; converted toTHF)
•
↓ THF formation
•
No effect human cells (dietary (dietary folate)
Folate
↓ dTMP (loss of DNA synthesis)
Methotrexate Fdardel/Wikipedia
13
Pyrimidine Synthesis
Bacterial THF Synthesis PABA Dihydropteroate Synthase
Drugs and Diseases •
Sulfonamides
Dihydropteroic Acid
Folate deficiency
↓ DNA production
•
Main effect: loss of dTMP pr oduction
•
RNA production relatively intact (does not require require thymidine)
•
Macrocytic anemia (fewer but larger RBCs)
•
Neural tube defects in pregnancy
Dihydrofolic Acid Trimethoprim
Dihydrofolate Reductase THF
DNA
Vitamin B12
Vitamin B12 •
Thymidylate Synthase
•
•
dUridine-MP
Thymidine-MP
DHF
N5, N10 T etrahydrofolate etrahydrofolate
N5 Methyl THF
THF
•
Required to regenerate THF from N5-Methy l THF Deficiency = “Methyl folate trap” Loss of dTMP synthesis (megaloblastic anemia) Neurological dysfunction (demyelination)
Folate
Dihydrofolate Reductase
B12
Homocysteine Homocysteine and MMA MMA
B12 versus Folate Deficiency Deficiency •
Folate
N5-Methyl THF
THF
B12 •
Homocysteine
•
Both folate and B12 required required to covert to methionine
•
Elevated homocysteine in both deficiencies
Methylmalonic Acid •
Methionine
Methylmalonic Acid (MMA)
B12
Homocysteine
Succinyl CoA
Methymalonyl CoA
14
B12 also converts M MA to succinyl CoA
•
B12 deficiency = ↑ methylmalonic acid (MMA) level
•
Folate deficiency = normal MMA level
B12 versus versus Folate Deficiency Deficiency
Megaloblastic Anemia •
•
•
•
Anemia (↓Hct) Large RBCs (↑MCV) Hypersegmented neutrophils Commonly caused by defective DNA production •
15
Folate deficiency
•
B12 (neuro symptoms, MMA)
•
Orotic aciduria
•
Drugs (MTX, 5-FU, hydroxyurea)
•
Zidovudine (HIV NRTIs)
Carbs •
•
“watered carbon” Carbohydrate = “wateredcarbon” Most have formula Cn(H2O)m
Glucose
Glucose C6H12O6
Jason Ryan, MD, MPH
Wikipedia/Public Domain
Carbs •
•
Carbs
Monosaccharides (C6H12O6) Glucose, Fructose, Galactose
•
•
•
•
Disaccharides = 2 monosaccharides Broken down to monosaccharides in GI tract Lactose(galactose Lactose (galactose + glucose); lactase Sucrose(fructose Sucrose (fructose + glucose); sucrase
Glucose
Lactose
Complex Carbs •
Polysaccharides: polymers of monosaccharides
•
Starch •
•
Plant polysaccharide polysaccharide (glucose polymers)
•
Glycogen
•
Cellulose
•
Glucose
Animal polysaccharide polysaccharide (also glucose polymers)
•
Plant polysaccharide of glucose molecules
•
Different bonds from starch
•
Cannot be broken down down by animals
•
“Fiber” in diet improved bowel function
16
All carbohydra tes broken down into: •
Glucose
•
Fructose
•
Galactose
Glucose Metabolism
Glucose Metabolism •
Glucose
Anaerobic Metabolism
TCA Cycle
HMP Shunt
Lactate
H2O/CO2
Ribose/ NADPH
Fatty Acid Synthesis
•
Fatty Acids
•
Most varied use of glucose
•
TCA cycle for ATP
•
Glycogen synthesis
Glycogen
Glucose Metabolism
Brain
•
Red blood cells
•
Constant use of glucose glucose for TCA cycle (ATP)
•
No mitochondria
•
Little glycogen storage
•
Use glucose for anaerobic anaerobic metabolism (make ATP)
•
Generate lactate
•
Also use glucose for HMP shunt (NADPH)
Muscle/heart •
TCA cycle (ATP)
•
Transport into cells heavily influenced influenced by insulin
•
More insulin more glucose uptake
•
Mostly converts glucose to fatty acids
•
Store glucose as glycogen
•
Like muscle, uptake influenced influenced by insulin
•
Glucose Entry into Cells •
•
Glycogenesis
Glucose Metabolism •
Liver
Glucose GI Absorption GI Lumen
Na+ independent entry •
14 different tr ansporters described
•
GLUT-1 to GLUT-14
•
Varies by tissue (i.e. GLUT-1 in RBCs) Glucose absorbed from low
•
Intestinal epithelium
•
Interstitium/Blood
2 Na+ SGLT 1 Glucose
Na+ dependent entry •
Adipose tissue
high concentration
Renal tubules
↑[Glucose] Na+
GLUT ATP
↓[Glucose]
Na+
17
GLUT 2 Glucose
Proximal Tubule
Glucose Entry into Cells
Lumen (Urine)
Interstitium/Blood
•
Na+ Na+ Glucose
ATP •
K+
•
Glucose
18
GLUT-1 •
Insulin independent (uptake when [glucose]high)
•
Brain, RBCs
GLUT-4 •
Insulin dependent
•
Fat tissue, tissue, skeletal muscle
GLUT-2 •
Insulin independent
•
Bidirectional (gluconeogenesis)
•
Liver, kidney
•
Intestine (glucose OUT of epithelial cells to portal vein)
•
Pancreas
Glycolysis •
•
•
•
Used by all cells of the body Sequence of reactions that occurs in cytoplasm Convertsglucose Converts glucose(6 (6 carbons) to pyruvate (3 carbons) Generates ATP and NADH
Glycolysis Jason Ryan, MD, MPH
NADH
Glycolysis
Nicotinamide adenine dinucleotide •
Two nucleotides
•
Carrieselectrons
•
NAD+ •
•
Glucose Glucose-6-phosphate Fructose-6-phosphate Fructose-1,6-bisphosphate
Accepts electrons
Glyceraldehyde-3-phosphate
NADH •
Donates electrons
•
Can donate to electron transport chain
Dihydroxyacetone Phosphate
1,3-bisphosphoclycerate ATP
3-phosphoglycerate 2-phosphoglycerate Phosphoenolpyruvate Pyruvate
Glycolysis
Hexokinase vs. Glucokinase
Priming Stage •
•
Uses energy (consumes 2 ATP) First and last reactions most critical
•
Glucose ATP Glucose-6-phosphate Fructose-6-phosphate ATP Fructose-1,6-bisphosphate
19
Hexokinase •
Found in most tissues
•
Strongly inhibited by G6P
•
Blocks cells from hording glucose
•
Insulin = no effect
•
Low Km (usually operates operates max)
•
Low Vm (max is not that that high)
Glucose ATP -
ADP Glucose-6-phosphate
Hexokinase
Hexokinase vs. Glucokinase V = Vm* [S] Km + [S]
•
Glucokinase Found in liver and pancreas
•
Vmax
Hexokinase Low Km Quickly Reach Vm Vm low
V
ATP
•
NOT inhibited by G6P
•
Induced by insulin
•
Insulin promotes transcription
•
•
Glucose -
ADP
Inhibited by F6P (overcome by ↑glucose) Glucose-6-phosphate High Km (rate varies with glucose)
Fructose-6-phosphate
[S] *Enzyme inactive when (1) low glucose and (2) high F6P
Glucokinase
Glucokinase regulatory protein
High Vm liver after meals
(GKRP) V = Vm* [S] Km + [S]
Vmax
•
Activity varies with [glucose]
•
•
Glucokinase High Km High Vm
V
Translocates glucokinase to nucleus Result: inactivation of enzyme Fructose 6 phosphate: •
•
Sigmoidal Curve Cooperativity
GKRP binds glucokinase
nucleus (inactive)
Glucose: •
Competes with GKRP GKRP for GK binding
•
Glucokinase GK
cytosol (active)
GKRP
F-6-P
Nucleus GKRP
[S] GK
Hexokinase vs. Glucokinase •
•
Glucokinase Deficiency
Low blood sugar
•
•
Hexokinase working (no inhibition G6P)
•
Glucokinase inactive (rate α glucose; low insulin)
•
Glucose to tissues, tissues, not li ver
High blood sugar •
• •
Glucose
•
•
Glucose
•
ATP
Hexokinase inactive inactive (inhibited by G6P) Glucokinase working (high glucose, glucose, high insulin) insulin) ADP Liver will store glucose as glycogen Glucose-6-phosphate
Fructose-6-phosphate
20
Results inhyperglycemia in hyperglycemia Pancreasless Pancreas less sensitive to glucose Mild hyperglycemia Often exacerbated by pregnancy
Regulation of Glycolysis
Phosphofructokinase-1 •
•
•
•
Phosphofructokinase-1
Rate limiting step forglycolysis
•
Consumes 2nd ATP in priming stage Irreversible Commits glucose to glycolysis •
•
HMP shunt, glycogen synthesis synthesis no long possible
Key inhibitors (lessglycolysis) •
Citrate (TCA cycle)
•
ATP
Key inducers (moreglycolysis) •
AMP
•
Fructose 2,6 bisphosphate (insulin)
Fructose-6-phosphate ATP
Fructose-6-phosphate ATP
ADP Fructose-1,6-bisphosphate ADP Fructose-1,6-bisphosphate
Fructose 2,6 Bisphosphate
Insulin and Glucagon
Regulation of Glycolysis
G
I PFK2 Fructose-6-phosphate
F-2,6-bisphosphate Fructose 1,6 Bisphosphatase2
PFK1
AC
-
Fructose 1,6 Bisphosphatase1
cAMP
+ P PFK2/FBPase2
Fructose-1,6-bisphosphate PKA
On/off switch glycolysis ↑ = glycolysis (on) ↓ = no glycolysis (gluconeogenesis)
PFK2/FBPase2
Fructose 2,6 Bisphosphate
Fructose 2,6 Bisphosphate
Regulation of Glycolysis
Regulation of Glycolysis
Fed State
Fasting State
Insulin
Glucagon
↑Insulin ↑F 2,6 BP
PFK2
↑ F 2,6 BP
↓ F 2,6 BP
F6P
↓Insulin ↓F 2,6 BP
PFK2 F6P F2,6BPase P
F2,6BPase +
-
F 1,6 BP
F 1,6 BP
21
Glycolysis
Glycolysis
Splitting Stage
Energy Stage
Glyceraldehyde-3-phosphate NAD+
•
•
Fructose 1,6-phosphate to two molecules GAP Reversible for gluconeogenesis gluconeogenesis
•
•
•
Starts with GAP
NADH
Two ATP pe r GAP Total per glucose = 4
3-phosphoglycerate 2-phosphoglycerate
Fructose-1,6-bisphosphate Glyceraldehyde-3-phosphate
1,3-bisphosphoclycerate ATP
Anaerobic Metabolism (no O2) 2 ATP (net)
Dihydroxyacetone Phosphate
Phosphoenolpyruvate ATP
Pyruvate
NADH NAD+
Glycolysis Pyruvate kinase •
Inhibited by AT by ATP, P,alanine
•
Activated by fructose 1,6 BP •
•
Phosphoenolpyruvate
Not reversible
•
•
Pyruvate Kinase
ATP
•
•
Skeletal muscles can degrade protein for energy Produce alanine blood liver Liver converts alanine to glucose
Pyruvate
“Feed forward” activation
Glucagon/epinephrine
Glucose/ Glycogen
Glucose
•
Phosphorylation
•
Inactivation of pyruvate kinase
•
Slows glycolysis/favors gluconeogenesis
Urea
Pyruvate
Pyruvate
Amino Acids
Alanine
Liver
Glycolysis Energy Stage
TCA Cycle
Alanine Cycle
Energy Stage •
Lactate
Alanine Alanine transaminase transaminase ( ALT) ALT)
NADH
Phosphoenolpyruvate
Muscle
Glyceraldehyde-3-phosphate NAD+
•
Lactate dehydrogenase (LDH) •
•
•
Pyruvate Lactate
ATP
Plasma elevations common •
Hemolysis
•
Myocardial infarction
•
Some tumors
Pleuraleffusions •
Pyruvate Kinase
•
•
•
Pyruvate
Limited supply NAD+ Must regenerate O2 present •
LDH •
1,3-bisphosphoclycerate 3-phosphoglycerate
NAD (mitochondria)
2-phosphoglycerate
O2 absent •
Lactate
NADH
NADH
Phosphoenolpyruvate
NADH NAD+ via LDH
NAD+ Acetyl-CoA
Pyruvate
Transudate vs. exudate
NADH NAD+ TCA Cycle
22
Lactate
TCA Cycle
Lactic Acidosis •
•
•
•
•
Muscle Cramps
↓O2 ↓ pyruvate entry into TCA cycle ↑ lactic acid production ↓pH, ↓HCO3 Elevated anion gap acidosis Sepsis, bowel ischemia, seizures
•
•
•
•
Too much exercise too much NAD consumption •
Exceed capacity capacity of TCA cycle/electron transport
•
Elevated NADH/NAD ratio
Favors pyruvate lactate pH falls in muscles cramps Distance runners: lots of mitochondria (bigger, too)
Pyruvate Lactate Dehydrogenase Lactate
TCA Cycle
Pyruvate Kinase Deficiency •
•
Autosomalrecessivedisorder RBCsmost RBCsmost effected •
•
•
2,3 Bisphosphoglycerate Bisphosphoglycerate •
•
No mitochondria
•
•
Require PK for anaerobic metabolism
•
Loss of ATP
•
Membrane failure phagocytosis in spleen
•
•
•
Usually presents as newborn Extravascular hemolysis
•
Disease severity ranges based on enzyme activity
2-phosphoglycerate
Pyruvate
Energy Yield from Glucose
Easier to release O2 100
Right Shift ↑BPG (Also ↑ Co2, Temp, H+)
25 75
No TCA cycle
Sacrific es ATPfrom ATPfromglycolysis 2,3 BPG alters Hgb binding
1,3-bisphosphoglycerate
BPG ATP Mutase 3-phosphoglycerate
Lactate
Right Curve Shifts
50
2,3 BPG
ATP
Splenomegaly
n o 75 i t a r u t a S 50 % b H
No mitochondria
Glyceraldehyde-3-phosphate
Phosphoenolpyruvate
•
25
Created from diverted 1,3 BPG Used by RBCs
100
pO2 (mmHg)
23
•
ATP generated depends on cells/oxygen
•
Highest yield with O2 and mitochondria •
Allows pyruvate to enter enter TCA cycle
•
Converts pyruvate/NADH
ATP
TCA Cycle
Summary
Energy from Glucose
Glucose
Key Steps •
Regulation •
Oxygen and Mitochondria Glucose + 6O2 32/30 ATP+ ATP+ 6CO2 + 6 H2O 32 ATP = malate-aspartate shu ttle (liver, heart) 30 ATP = glycerol-3-phosphate shuttle (muscle)
•
No Oxygen or No Mitochondria Glucose 2 ATP + 2 Lactate + 2 H2O
Glucose-6-phosphate Fructose-6-phosphate AMP F2,6BP Fructose-1,6-bisphosphate Fructose-1,6-bisphosphate
#1: Hexokinase/Glucokinase
•
#2: PFK1
•
#3: Pyruvate Kinase
Irreversible
Glyceraldehyde-3-phosphate
•
Glucose
G6P (Hexo/Glucokinase)
•
F6P F 1,6 BP (PFK1)
•
PEP pyruvate (pyruvate kinase)
1,3-bisphosphoclycerate 3-phosphoglycerate 2-phosphoglycerate Phosphoenolpyruvate ATP Alanine
*RBCs = no mitochondria
Summary
Glucose
ATP
Key Steps •
•
Glucose-6-phosphate
ATPexpended expended •
Glucose
•
F6P
G6P
F1,6BP
Fructose-6-phosphate
ATP
Fructose-1,6-bisphosphate
ATPgenerated generated 3PG
•
1,3BPG
•
PEP pyruvate
Glyceraldehyde-3-phosphate 1,3-bisphosphoclycerate ATP 3-phosphoglycerate 2-phosphoglycerate Phosphoenolpyruvate ATP
Pyruvate
24
Pyruvate
Gluconeogenesis
Glucose Glucose-6-phosphate
•
Glucose from other carbons
•
Sources of glucose
Gluconeogenesis
Fructose-6-phosphate Fructose-1,6-bisphosphate
•
Pyruvate
•
Lactate
•
Amino acids
•
Propionate (odd chain fats)
•
Glycerol (fats)
Glyceraldehyde-3-phosphate 1,3-bisphosphoclycerate 3-phosphoglycerate
Jason Ryan, MD, MPH
2-phosphoglycerate Phosphoenolpyruvate Pyruvate
Liver
Glucose
Pyruvate
Glucose
Liver
Pyruvate
Pyruvate Cori Cycle
Alanine Cycle
Pyruvate Carboxylase Lactate
Alanine
↓ATP Gluconeogenesis
Gluconeogenesis
Acetyl-Coa
↑ATP Acetyl-Coa
*Pyruvatecarboxylase inactive without Acetyl-Coa TCA Cycle
Gluconeogenesis •
ATP TCA Cycle
Gluconeogenesis
Step #1: Pyruvate Phosphoenolpyruvate
•
Step #1: Pyruvate Phosphoenolpyruvate Mitochondria
ATP CO2
Pyruvate Pyruvate Carboxylase
GTP Oxaloacetate (OAA)
Cytosol
Malate Shuttle Phosphoenolpyruvate (PEP)
Pyruvate
PEP Carboxykinase
Pyruvate Carboxylase
Biotin
25
Oxaloacetate (OAA)
Phosphoenolpyruvate (PEP)
PEP Carboxykinase
Pyruvate Carboxylase Deficiency
Biotin •
Cofactor for carboxylation enzymes •
All add 1-carbon group via CO 2
•
Pyruvate carboxylase
•
Acetyl-CoA carboxylase
•
•
Very rare
•
Presents in infancy with failure to thrive
•
•
Propionyl-CoA carboxylase
Elevatedpyruvate lactate Lactic acidosis
Deficiency •
Very rare (vitamin widely distributed)
•
Massive consumption raw egg whites (avidin)
•
Dermatitis, glossitis, loss of appetite, nausea
Gluconeogenesis •
•
Gluconeogenesis Fructose-6-phosphate
Step #2: •
Fructose 1,6 bisphosphate
•
Rate limiting step
Fructose 6 phosphate phosphate Phosphofructokinase-1 Phosphofructokinase -1
Fructose-1,6-bisphosphate
Fructose-6-phosphate
Phosphofructokinase-1
Fructose 1,6 bisphosphatase 1
Fructose 1,6 bisphosphatase 1 ATP AMP Fructose 2,6 bisphosphate
Fructose-1,6-bisphosphate
Fructose 2,6 Bisphosphate
Fructose 2,6 Bisphosphate
Regulation of Glycolysis/Gluconeogenesis
Regulation of Gluconeogenesis •
PFK2 Fructose-2,6-bisphosphate
•
Fructose-6-phosphate
Fructose 1,6 Bisphosphatase 2 PFK1
•
Fructose 1,6 Bisphosphatase 1
Fructose-1,6-bisphosphate
On/off switch glycolysis ↑ = glycolysis (on) ↓ = no glycolysis (gluconeogenesis)
26
Levels rise with high insulin (fed state) Levels fall with high glucagon (fasting state) Drivesglycolysis versusgluconeogenesis gluconeogenesis
PFK1 vs. F 1,6 BPtase1 Phosphofr uctokinase-1 Glycolysis
Gluconeogenesis
Fructose 1,6 Bisphosphat ase Gluconeogenesis
•
•
•
Step #3: Glucose 6-phosphate Glucose Occurs mainly in liver and kidneys Other organs shunt G6P glycogen
Glucose-6 Phosphate
Fructose-6-phosphate
Fructose 1,6 Bisphosphate1
PFK1
Glucose Glucose-6 Phosphatase
Endoplasmic Reticulum
Fructose-1,6-bisphosphate
Gluconeogenesis
Hormonal Control Glucose Glucagon
+
Glucose
Glucose-6-phosphate Glucose-6-phosphate
F2,6BP
Insulin/ Glucagon
Fructose-6-phosphate
AMP
Glucagon
(↓F2,6BP) +
Fructose-6-phosphate
Fructose-1,6-bisphosphate
ATP
Fructose-1,6-bisphosphate
Phosphoenolpyruvate
Phosphoenolpyruvate
Glucagon
Acetyl CoA Pyruvate
Pyruvate
Gluconeogenesis
Hormones
Glucose
Substrates
•
Fructose-1,6-bisphosphate Glyceraldehyde-3-phosphate Glyceraldehyde-3-phosphate
Dihydroxyacetone Dihydroxyacetone Phosphate
•
Odd Chain Fatty Acids PEP
OAA Lactate
Pyruvate
Propionyl CoA Amino Acids
x
Glycerol
Alanine
27
Insulin •
Shuts down gluconeogenesis gluconeogenesis (favors glycolysis)
•
Action via F 2,6, BP
Glucagon (opposite of insulin)
Other Hormones •
•
•
Epinephrine •
Raises blood glucose
•
Gluconeogenesis and glycogen breakdown
Cortisol •
Increases gluconeogenesis enzymes
•
Hyperglycemia common side effect steroid drugs
Thyroid hormone •
Increases gluconeogenesis
28
Glycogen •
•
•
•
•
Glycogen
•
Storage form of glucose Polysaccharide Repeating units of glucose Most abundant in muscle, liver
Lin Mei/Flikr
Muscle: glycogen for own use Liver: glycogen for body
Jason Ryan, MD, MPH
Glycogen Synthesis
Glycogen Synthesis
Glucose-6-phosphate
Glucose ATP Hexokinase/ Glucokinase
Glucose-1-phosphate UTP
ADP Glycogen
UDP-glucose pyrophosphorylase
Glucose-6-phosphate
UDP-Glucose Glycogen Synthase Unbranched Glycogen Glycolysis
Branching Enzyme Branched Glycogen
Glycogen Breakdown
Glycogen Breakdown Glucose-6 PhosphataseGlucose-6-phosphate
•
Glycolysis
•
Removes glucose molecules from glycogen polymer
•
Creates glucose-1-phosphate glucose-1-phosphate
•
Glucose-1-phosphate
α1,4 glucosidase (lysosomes)
Phosphorylase
•
UDP-Glucose
Glycogen phosphorylase
•
Debranching Enzyme
Branched Glycogen (α1,6)
29
Stabilized by vitamin B6
Debranching enzyme •
Unbranched Glycogen (α1,4)
Stops when glycogen branches decreased to 2-4 linked glucose molecules (limit ( limit dextrins) dextrins )
Cleaves limit dextrins
Debranching Enzyme
Hormonal Regulation Glycogen
Glucagon Epinephrine
Insulin
Glucose
Hormonal Regulation
Hormonal Regulation
Glycogen
Glucagon Epinephrine
Glycogen
P
Glucagon Epinephrine
Insulin
Enzyme Phosphorylation
Insulin
P
Glycogen Phosphorylase
Glycogen Synthase
Glycogen Phosphorylase
Glucose
Glycogen Synthase
Glucose
Epinephrine and Glucagon
Insulin
Glycogen Phosphorylase
Glycogen Phosphorylase Gluc
Epi
I
Adenyl
+ cAMP
Cyclase
+
P Glycogen Phosphorylase
Tyrosine Kinase
Glycogen Breakdown
Protein Phosphatase 1
P
Glycogen Phosphokinase A
Glycogen Phosphorylase
P GPKinase A
Protein Phosphatase 1
PKA
GPKinase A
30
Glycogen Breakdown
P
Epinephrine and Glucagon
Insulin
Glycogen Synthase
GlycogenSynthase Gluc
Epi
I
Adenyl
+
Cyclase
+
Tyrosine Kinase
cAMP Glycogen Synthase
Protein Phosphatase 1
Inhibition Glycogen Synthesis
P
Glycogen Synthase
Protein Phosphatase 1
Glycogen Synthase
PKA
P
Muscle Contraction
Glycogen Synthase
P Glycogen Synthesis
Glycogen Regulation
Glycogen Phosphorylase
Glycogen ATP Glucose
P Glycogen Phosphorylase
Glycogen Phosphorylase
Glycogen Breakdown
Glycogen Synthase
Glucose 6-P
AMP
Calcium/Calmodulin
GPKinase A
Glucose
Glycogen Storage Diseases
Glycogen as Fuel
•
Ingested Glucose
•
•
r h / g e s o c u l G
•
•
Glycogen
0
8
16
Gluconeogenesis (proteins/fatty acids)
24
36
Hours
31
Most autosomal recessive Defective breakdown of glycogen Liver: hypoglycemia Muscle: weakness More than 14 described
Von Gierke’s Disease
Von Gierke’s Disease
Glycogen Storage Disease Type I
Glycogen Storage Disease Type I
•
Glucose-6-phosphatase deficiency (Type Ia) •
•
•
•
•
Type Ib: Glucose transporter deficiency
Presents in infancy: 2-6 months of age Severe hypoglycemia between meals
Diagnosis: •
DNA testing (preferred)
•
Liver biopsy (historical test)
•
Treatment: Cornstarch (glucose polymer)
•
Avoid sucrose, lactose, fructose, galactose
•
Lethargy
•
Seizures
•
Feed into glycolysis pathways
•
Lactic acidosis (Cori cycle)
•
Cannot be metabolized to glucose via gluconeogenesis gluconeogenesis
•
Worsen accumulation of glucose 6-phosphate
Enlarged liver (excess glycogen) •
Can lead to liver failure
Pompe’s Disease
Pompe’s Disease
Glycogen Storage Disease Type II
Glycogen Storage Disease Type II
•
Acid alpha-glucosidase deficiency •
•
•
•
•
Also “lysosomal acid maltase”
Accumulation of glycogen in lysosomes •
Classic form presents in infancy Severe disease often death in infancy/childhood
•
•
•
Enlarged muscles •
Cardiomegaly
•
Enlarged tongue
Hypotonia Liver enlargement (often from heart failure) No metabolic problems (hypoglycemia) Death from heart failure
Cori’s Disease
Cori’s Disease
Glycogen Storage Disease Type III
Glycogen Storage Disease Type III
•
Debranching enzyme deficiency
•
Similar to type I except:
Classic presentation: •
Infant or child with hypoglycemia/hepatome hypoglycemia/hepatomegaly galy
Milder hypoglycemia
•
Hypotonia/weakness
•
No lactic acidosis (Cori cycle intact)
•
Possible cardiomyopathy with hypertrophy
•
Muscle involvement (glycogen accumulation) accumulation)
•
•
•
Key point: Gluconeogenesis is intact
32
McArdle’s Disease Glycogen Storage Disease Type V •
Muscle glycogen phosphorylase deficiency •
Myophosphorylase deficiency
•
Skeletal muscle has unique isoform of G-phosphorylase
•
Glycogen not properly broken down in muscle cells
•
Usuallypresentsin adolescence/early adulthood •
Exercise intolerance, fatigue, cramps
•
Poor endurance, muscle swelling, swelling, and weakness
•
Myoglobinuria and CK release (especially with exercise) exercise)
•
Urine may turn dark after exercise
33
HMP Shunt •
Series of reactions that goes by several names: •
•
Hexose monophosphate monophosphate shunt
•
Pentose phosphate pathway
•
6-phosphogluconate 6-phosphogluconate pathway
Glucose6-phosphate “shunted” away fromglycoly sis
HMP Shunt Jason Ryan, MD, MPH
Glucose
HMP Shunt
HMP Shunt
Glucose-6-phosphate Fructose-6-phosphate
•
Fructose-1,6-bisphosphate •
Glyceraldehyde-3-phosphate 1,3-bisphosphoclycerate
Synthesizes: •
NADPH (many uses)
•
Ribose 5-phosphate (nucleotide synthesis)
Two key clinical correlations: •
G6PD deficiency
•
Thiamine deficiency (transketolase)
3-phosphoglycerate 2-phosphoglycerate Phosphoenolpyruvate Pyruvate
HMP Shunt
HMP Shunt •
•
Oxidative Reactions
All reactions occur in cytosol Two phases: •
Oxidative: irreversible, rate-limiting
•
Reductive: reversible
Glucose-6 PhosphateDehydrogenase Glucose Ribulose-5 Phosphate
CO2
6 phosphogluconolactone
Glucose-6-phosphate
NADPH NADPH
Glucose Ribulose-5 Phosphate
Glucose-6-phosphate Ribose-5 Phos Phos hate hate
Fructose-6-phosphate
34
NADP+
NADPH
NADP+
HMP Shunt
Transketolase
Reductive Reactions
NADPH Glucose Ribulose-5 Phosphate
•
Transfers a carbon unit to create F-6-phosphate
•
Requires thiamine (B1) as a co-factor
•
Wernicke-Korsakoff syndrome
Glucose-6-phosphate Ribose-5 Phos Phos hate hate
Transketolase
Abnormal transketolase may predispose
•
Affected individuals may have abnormal binding to thiamine
Fructose-6-phosphate
NADPH
Ribose-5-Phosphate
Nicotinamide adenine dinucleotide phosphate
Purine Nucleotides Adenosine, Guanosine
Ribose5-phosphate
•
•
Similar structure to NADH
•
Not used for oxidative phosphorylation (ATP)
Pyrimidine Nucleotides Cytosine, Uridine, Thymidine
NADH
NADPH Uses •
•
•
•
•
Respiratory Burst
Used in “reductive” reactions
•
Releases hydrogen to form NADP+ Use #1: Co-factor in fatty acid, steroid synthesis •
NADPH
•
Liver, mammary glands, testis, adrenal cortex
Phagocytes generate H2O2 to kill bacteria •
“Oxygen dependent” killing
•
“Oxygen independent”: independent”: low pH, enzymes
Uses three key enzymes: •
Use #2:Phagocytosis #2: Phagocytosis Use #3: Protection from oxidative oxidative damag e
35
NADPH oxidase
•
Superoxide dismutase
•
Myeloperoxidase
CGD
Respiratory Burst O2
Chronic Granulomatous Disease •
NADPH
•
NADPH Oxidase
•
NADP+
•
O2-
Catalase (+) bacteriabreakdown bacteria breakdown H2O2
•
Five organisms cause almost all CGD infections:
Myeloperoxidase
Cl-
•
Bacterial Death
Phagocytes use despite enzyme deficiency deficiency
•
Superoxide Dismutase H2O2
Loss of function of NADPH oxidase Phagocytes cannot generate H 2O2 Catalase (-) bacteria generate th eir own H 2O2
•
Host cells have no H 2O2 to use recurrent infections Staph aureus, Pseudomonas, Pseudomonas, Serratia, Nocardia, Aspergillus
HOCl Source: UpToDate
G6PD Deficiency
Glutathione
Glucose-6-Phosphate Dehydrogenase
Erythrocytes
•
•
NADPH required for normal red blood cell function H2O2 generation triggered in RBCs •
•
•
Trigger
H2O2
Infections
•
Drugs
•
Fava beans
Glutathione
Glutathione Peroxidase
Need NADPH to degrade H2O2 Absence of required NADPH hemolysis
H2O
NADP+
Glutathione Reductase
Glutathione Disulfide
NADPH + H+
G6PD Deficiency
G6PD Deficiency
Glucose-6-Phosphate Dehydrogenase
Glucose-6-Phosphate Dehydrogenase
•
•
•
X-linked disorder (males)
•
•
•
•
Most common human enzyme disorder High prevalence in Africa, in Africa,Asia, Asia, the Mediterranean
•
•
HMP Shunt Requires G6PD
Classic findings: Heinz bodies and bite cells Heinz bodies: oxidized Hgb precipitated in RBCs Bite cells: phagocytic removal by splenic macrophages
May protect against malaria
Recurrent hemolysis after exposure to trigger May present as dark urine Other HMP functions usually okay •
Nucleic acids, fatty acids, acids, etc.
Heinz bodies Bite cells
36
G6PD Deficiency
G6PD Deficiency
Triggers
Diagnosis and Treatment
•
•
•
Infection: Macrophages generate free radicals Fava beans: Contain oxidants
•
Drugs: •
•
•
Antibiotics (sulfa (sulfa drugs, drugs , dapsone, nitrofurantoin, INH) •
Anti-malarials (primaquine, quinidine)
Diagnosis: •
Fluorescent spot test
•
Detects generation of NADPH fromNADP
•
Positive test if blood spot fails to fluoresce fluoresce under UVlight
Treatment: •
Aspirin, acetaminophen (rare)
37
Avoidance of triggers
Fructose and Galactose •
•
Isomers of glucose (same formula: C6H12O6) Galactose (and glu cose) taken up by SGLT1 •
Fructose and Galactose
Na+ dependent transporter
•
Fructose taken up by facilitated diffusion GLUT-5
•
All leave enterocytes by GLUT-2
Jason Ryan, MD, MPH
Carbohydrate Carbohydrate GI Absorption GI Lumen
Fructose
Interstitium/Blood
•
Commonly found in sucrose (glucose + fructose) Glucose
2 Na+ SGLT 1 Glucose
Glucose-6-phosphate
Glucose GLUT Galactose 2 Fructose
Galactose
Fructose-6-phosphate
GLUT 5 Fructose
Fructose-1,6-bisphosphate Na+
Glyceraldehyde3-phosphate
ATP
Glyceraldehyde
Dihydroxyacetone Phosphate
Fructose-1-Phosphate
Fructose
Na+
Fructose
Fructose Glyceraldehyde3-phosphate Triokinase
Glyceraldehyde
Glucose
Special Point Dihydroxyacetone Phosphate Aldolase B
Glucose-6-phosphate
Phosphofructokinase-1 Rate-limiting step: glycolysis ATP
Fructose-1,6-bisphosphate Glyceraldehyde-3-phosphate
Fructose
Fructose-1-Phosphate Fructokinase (liver)
Fructose-6-phosphate
Fructose bypasses PFK-1 Rapid metabolism
Dihydroxyacetone Phosphate
1,3-bisphosphoclycerate 3-phosphoglycerate
Fructose-1-Phosphate
2-phosphoglycerate Phosphoenolpyruvate Pyruvate
38
Fructose
Fructose
Essential Fructosuria
Glucose
Special Point Hexokinase Initial enzyme glycolysis
Glucose-6-phosphate •
Fructose
Hexokinase can metabolize small amount of fructose
Fructose-6-phosphate
•
•
Fructose-1,6-bisphosphate
Glyceraldehyde-3-phosphate
•
Dihydroxyacetone Phosphate
Deficiency offructokinase of fructokinase Benign condition Fructose not taken up by liver cells Fructose appears in urine (depending on intake)
1,3-bisphosphoclycerate 3-phosphoglycerate 2-phosphoglycerate Phosphoenolpyruvate Pyruvate
Hereditary Fructose Intolerance •
•
•
Hereditary Fructose Intolerance
Deficiency of aldolase B Build-up of fructose 1-phosphate Depletion of ATP
↑Fructose-1-Phosphate
↓ATP
↓Gluconeogenesis
Hypoglycemia/ Vomiting
Hereditary Fructose Intolerance •
•
•
•
•
•
Liver Failure
Glucose Fructose
Baby just weaned from breast milk
NADPH
39
NADH
Sorbitol Aldose Reductase
Avoid fructose, sucrose, sorbitol
NAD+
NADP+
Glucose
Hypoglycemia (seizures)
Enlarged liver Part of newborn screening panel Treatment: •
Hepatomegaly
Polyol Pathway
Failure to thrive Symptoms after feeding •
↓Glycogen Breakdown
Fructose Sorbitol Dehydrogenase
Galactose
Galactose
•
Commonly found in lactose(glucose lactose (glucose + galactose)
•
Converted to glucose 6-phosphate
Galactose ATP
Galactokinase
Galactose 1-Phosphate
UDP-Glucose
Galactose Galactose 1-Phosphate Uridyltransferase (GALT)
Galactose 1-Phosphate
Glucose
Glucose 1-Phosphate
Glycogen
Glucose 6-Phosphate
Glycolysis
Glucose 1-Phosphate
Classic Galactosemia •
•
•
•
Polyol Pathway
Deficiency of galactose 1-phosphate uridyltransf erase Autosomalrecessivedisorder Galactose-1-phosphate accumulates in cells
NADPH
NAD+
NADP+
Sorbitol
Glucose
Aldose Reductase
Classic Galactosemia •
•
Often first few days of life
•
Shortly after consumption of milk
Liver accumulation galactose/galactitol •
•
Liver failure
•
Jaundice
•
Hepatomegaly
•
Failure to thrive
Galactitol
Classic Galactosemia
Presents in infancy •
Fructose Sorbitol Dehydrogenase
Leads to accumulation of galactitol in cells
Galactose
Cataracts if untreated
40
NADH
•
Screening: GALT enzyme activity assay
•
Treatment: avoid galactose galactose
Galactokinase Deficiency •
•
•
•
Milder form of galactosemia Galactose not taken up by cells Accumulates in blood and urine Main problem: cataractsas cataractsas child/young adult •
May present as vision problems
41
Pyruvate •
Pyruvate Dehydrogenase
End product of glycolysis
Liver
Glucose
Glucose
Liver
Pyruvate Alanine Cycle
Cori Cycle
Jason Ryan, MD, MPH Lactate
Alanine Gluconeogenesis
Pyruvate •
•
•
Pyruvate Pyruvate
Transported into mitochondria for: •
Entry into TCA cycle
•
Gluconeogenesis
Acetyl-Coa
Pyruvate Dehydrogenase Complex
Pyruvate Carboxylase
Outer membrane: a voltage-gated porin complex Inner: mitochondrial pyruvate carrier (MPC)
Gluconeogenesis
Acetyl-Coa
ATP TCA Cycle
Pyruvate Dehydrogenase Complex •
•
Pyruvate Dehydrogenase Complex O
Complex of 3 enzymes •
Pyruvate dehydrogenase (E1)
•
Dihydrolipoyl transacetylase (E2)
•
Dihydrolipoyl dehydrogenase (E3)
CO2
Pyruvate
E1 OH
Requires 5 co-factors •
NAD+
•
FAD+
•
Coenzyme A (CoA)
•
Thiamine
•
Lipoic acid
CH3-C-COO-
Thiamine-PP Thiamine -PP
CH3-CH-TPP CoA NADH
NAD
E1
E3
E3 E2 FAD+
42
E2
Acetyl-CoA O
Lipoic Acid
CH3-C-Lipoic Acid
Thiamine
Thiamine Deficiency
PDH Cofactors •
Vitamin B1
•
•
Converted to thiamine pyrophosphate (TPP)
•
•
Co-factor for four enzymes
•
Pyruvate dehydrogenase
•
•
dehydrogenase (TCA cycle) α-ketoglutarate dehydrogenase
•
Dry type: polyneuritis, muscle weakness
•
α-ketoacid dehydrogenase (branched chain amino acids)
•
Wet type: type: tachycardia, hig h-output heart failure, failure, edema
•
Transketolase ( HMP shunt)
ATP
•
•
Wernicke-Korsakoff syndrome •
Alcoholics (malnourished, poor absorption vitamins)
•
Confusion, confabulation
AMP Thiamine pyrophospate
FAD+
Thiamine and Glucose •
Underdeveloped areas
•
Thiamine
•
↓ production of ATP ↑ aerobic tissues affected most (nerves/heart) Beriberi
PDH Cofactors
Malnourished patients: ↓glucose↓thiamine ↓glucose↓thiamine If glucose given first unable to metabolize Case reports of worsening Wernicke-Korsakoff
•
•
•
Synthesized fromriboflavin from riboflavin (B2) Added to adenosine FAD+ Accepts 2 electrons FADH2
Riboflavin
NAD+
Coenzyme A
PDH Cofactors
PDH Cofactors
•
•
Carries electrons as NADH Synthesized from niacin (B3) •
•
Niacin
•
•
Niacin: synthesized from tryptophan
•
Flavin Adenine Dinucleotide
Also a nucleotide coenzy me (NAD, FAD) Synthesized frompantothenic from pantothenic acid (B5) Accepts/donates Accepts/donates acyl groups
Used in electron transport
Pantothenic Acid Coenzyme A
Nicotinamide Adenine Dinucleotide
Acetyl-CoA
43
Lipoic Acid
B Vitamins •
•
•
•
PDH Cofactors
* All water soluble * All wash out quickly from body (not stored in liver like B12)
B1: Thiamine
•
B2: Riboflavi n (FAD) B3: Niacin (NAD)
•
•
B5: Pantothenic Acid (CoA)
PDH Regulation •
•
Inhibited byarsenic by arsenic •
Poison (metal)
•
Binds to lipoic acid inhibits PDH (like thiamine deficiency)
•
Oxidized to arsenous oxide: smells like garlic (breath)
•
Non-specific symptoms: vomiting, diarrhea, coma, coma, death
PDH Complex Deficiency
PDH Kinase: phosphorylates enzyme inactivation PDH phosphatase: dephosphorylation activation
•
•
•
•
↑NAD/NADH ↑ADP Ca2+
Bonds with lysine lipoamide Co-factor for E2
P
•
Rare inborn error of metabolism Pyruvate shunted to alanine, lactate Often X linked Most common cause: mutations in PDHA1 gene Codes for E1-alpha subunit
PDH
PDH
E1
↑ACoA ↑ATP Active
Inactive
PDH Complex Deficiency •
•
Mitochondrial Disorders
Key findings (infancy): •
Poor feeding
•
Growth failure
•
Developmental delays
•
•
•
Elevated alanine
•
Lactic acidosis
Inborn error of metabolism All cause severelactic acidosis Key examples: •
Labs: •
α
44
Pyruvate dehydrogenase complex deficiency
•
Pyruvate carboxylase deficiency
•
Cytochrome oxidase deficiencies deficiencies
PDH Complex Deficiency
Ketogenic Amino Acids
Treatment •
•
Thiamine, lipoic acid (optimize remaining PDH) Ketogenic diet •
Low carbohydrates (reduces lactic acidosis)
•
High fat
•
Ketogenic amino acids: Lysine and leucine
•
Drives ketone production (instead of glucose) glucose)
Acetoacetate Leucine
Acetyl-CoA Lysine
45
TCA Cycle Tricarboxylic Acid Cycle, Krebs Cycle, Citric Acid Cycle •
•
•
Metabolic pathway Converts acetyl-CoA CO2 Derives energy from reactions
TCA Cycle Jason Ryan, MD, MPH
TCA Cycle
TCA Cycle
Tricarboxylic Acid Cycle, Krebs Cycle, Citric Acid Cycle •
•
All reactions occur in mitochondria Produces: •
NADH
GTP
•
CO2
Citrate
Oxaloacetate
NADH, FADH2 electron transport chain (ATP)
•
Acetyl-CoA
Malate
Isocitrate CO2 NADH α-ketoglutarate
Fumarate FADH2 Succinate
CO2 NADH
Succinyl-CoA
GTP
Citrate Synthesis •
•
•
Fasting State
6 Carbon structure Oxaloacetate (4C) + Acetyl-CoA (2C) Inhibited by ATP by ATP
•
•
•
Oxaloacetate used for gluconeogenesis oxaloacetatefor TCA cycle ↓ oxaloacetatefor Acetyl-CoA (fatty acids) Ketone bodies
Special Points: Inhibits PFK1 (glycolysis) Activates ACoA carboxylase (fatty acid synthesis)
Acetyl-CoA
Pyruvate
Acetyl-CoA
Ketones
Citrate
Oxaloacetate Synthase
Glucose
Citrate
Citrate
Oxaloacetate Synthase
CoA
Citrate CoA
ATP
46
α-Ketoglutarate
Isocitrate •
•
•
•
Isomer of citrate Enzyme: aconitase
•
•
Forms intermediate (cis-aconitate) then isocitrate Inhibited by fluoroacetate: rat poison •
Citrate
Rate limiting step of TCA cycle Inhibited by: •
ATP
•
NADH
Activated by: •
ADP
•
Ca++
Isocitrate Isocitrate Dehydrogenase
α-ketoglutarate
Isocitrate
Succinyl-CoA •
•
•
Succinate
α-ketoglutarate dehydrogenase complex Similar to pyruvate dehydrogenase complex Cofactors: •
Thiamine
•
CoA
•
NAD
•
FADH
•
Lipoic acid
•
Succinyl-CoA synthase
Succinyl-CoA
Succinate
Succinyl-CoA NADH
α-ketoglutarate
CoA GTP
CoA
α-KG Dehydrogenase Ca++
Succinyl-CoA
CO2 NADH
Fumarate •
•
•
Fumarate
Succinate dehydrogenase Unique enzyme: embedded mitochondrial membrane Functions as complex II electron transport Succinate
•
FAD+
Complex II Fumarate
CO2 NADH
Succinate Dehydrogenase
FADH2
Electron Transport
47
Also produced several other pathways •
Urea cycle
•
Purine synthesis (formation of IMP)
•
Amino acid breakdown: phenylalanine, phenylalanine, tyrosine
Malate and Oxaloacetate NADH
Malate Shuttle •
Malate “shuttles” molecules cytosol mitochondria
•
Key points:
Oxaloacetate
Malate dehydrogenase dehydrogenase •
Malate Fumarase
•
Malate can cross mitochondrial membrane (transporter)
•
NADH and oxaloacetate oxaloacetate cannot cross
Two key uses: •
Transfer of NADH into mitochondria
•
Transfer of oxaloacetate OUT of mitochondria NADH
Fumarate
Oxaloacetate
Malate dehydrogenase dehydrogenase
Malate
Malate Shuttle •
Malate Shuttle
Use #1: Transfer of NADH Aspartate
•
OAA
α-KG
Gluconeogenesis
Malate NADH
Glut
+
NAD
Use #2: Transfer of oxaloacetate
OAA
Malate +
NADH
Cytosol
NAD
Cytosol
Mitochondria Aspartate
α-KG
OAA Glut
Mitochondria OAA
Malate NADH
NAD+
NAD+
NADH
TCA Intermediates
Succinyl CoA Odd Chain Fatty Acids Branched Chain Amino Acids Acids
Fatty Acids
Amino Glucose Acids Oxaloacetate
Malate
TCA Cycle (α-KG)
Citrate
Malate
Isocitrate
Amino Acids
Methylmalonyl CoA
Succinyl-CoA
α-ketoglutarate
Fumarate
Succinate
TCA Cycle (succinate)
Succinyl-CoA
48
Heme Synthesis
TCA Cycle Key Points •
Pyruvate Dehydrogenase Acetyl-CoA Pyruvate
TCA Cycle
Inhibited by: •
ATP, ATP,Acetyl-CoA, NADH NADH
ATP
•
NADH
•
Acetyl CoA
•
Citrate
•
Succinyl CoA
NADH Oxaloacetate
Citrate synthase
ATP NADH
ATP Citrate
Malate
Citrate
Isocitrate
Isocitrate Dehydrogenase Fumarate
α-KG Dehydrogenase
FADH2 Succinate
CO2 NADH
Succinyl-CoA
GTP
TCA Cycle
TCA Cycle
Key Points •
CO2
NADH α-ketoglutarate
NADH SuccinylCoA
Acetyl-CoA
Pyruvate
Activated by: •
ADP
•
Calcium
NADH Citrate
Oxaloacetate ADP Ca++
Malate
Isocitrate Isocitrate Dehydrogenase
Ca++
Fumarate
α-KG Dehydrogenase
FADH2 Succinate GTP
49
CO2 NADH α-ketoglutarate
Succinyl-CoA
CO2 NADH
Aerobic Metabolism Cytosol Mitochondria GTP
Electron Transport Chain
NADH NADH NADH
Acetyl CoA
2 ATP
ATP
FADH2
Pyruvate Glucose Pyruvate
NADH
2 NADH
Jason Ryan, MD, MPH
NADH
Acetyl CoA
ATP
NADH FADH2 GTP
Malate Shuttle Aspartate
α-KG
Glycerol Glycerol Phosphate Shuttle Shuttle
OAA
Malate NADH
Glut
Glycerol Phosphate Dehydrogenase Dihydroxyacetone Glycerol phosphate Phosphate
NAD+
Cytosol
NADH
NAD+
Cytosol Glycerol cehraot le PhGoly sp orso pgheanteas DeP hh yd Dehydreogenase
Mitochondria Aspartate
α-KG
OAA Glut
Malate NADH
NAD+
Mitochondria FAD
Electron Transport
FADH2
Electron Transport Complexes Cytosol
•
•
•
•
•
•
Extract electrons from NADH/FADH2 Transfer to oxygen( oxygen (aerobic respiration) In process, generate/capture energy NADH NAD+ + H+ + 2eFADH2 FAD + + 2 H+ + 2e2e- + 2H+ + ½O2 H2O
Outer Membrane Inner Membrane Space
I
50
II
III
IV
Inner Membrane
Complex I •
•
•
Complex I
NADH Dehydrogenase
•
OxidizesNADH Oxidizes NADH (NADH NAD+) Transfers electrons to coenzyme Q(ubiquinone) Q (ubiquinone)
•
•
CoQ shuttles electrons to complex III Pumps H+ into intermembrane space Key intermediates: •
Flavin mononucleotide (FMN)
•
Iron sulfur compounds (FeS)
e-
CoQ
NADH
NADH
Electron Transport
•
•
Outer Membrane
•
•
H+
e-
FeS
No good data to support this use
Inner Membrane
III
H+
Complex II •
•
Complex III
Succinate dehydrogenase (TCA cycle) Electrons from succinate FADH2 CoQ
•
•
•
FAD+
Succinate
II FADH2
Fumarate
CoQ
Some data indicate statins decrease CoQ levels Hypothesized to contribute to statin myopathy CoQ 10 supplements may help in theory
eCoQ
I
FMN
e-
CoQ 10 Supplements Supplements Cytosol
Inner Membrane Space
e-
e-
CoQ
Succinate Dehydrogenase
51
Cytochrome bc 1 complex Transfers electrons CoQ cytochrome c
Pumps H+ to intermembrane space
Electron Transport
Cytochromes Cytosol •
•
Outer Membrane Inner Membrane Space
H+
e-
Cyt c
•
Iron plus porphyrin ring
•
Hgb: mostly Fe2+
•
e-
•
IV
III
Inner Membrane
Class ofproteins of proteins Contains a hemegroup hemegroup
Cytochromes: Fe2+Fe3+ Oxidation state changes with electron transport
•
Electron transport: a, b, c
•
Cytochrome P450: drug metabolism
H+
Complex IV •
•
•
•
•
Electron Transport Cytosol
Cytochromea Cytochrome a + a3 Cytochrome c oxidase(reacts oxidase (reacts with oxygen) Contains copper (Cu) Electrons and O 2 H2O Also pumps H+
Outer Membrane Inner Membrane Space
H+ H+ H+
H+ H+
H+ H+
HH++ H+
H+ H+ H+ H+
H+ + + H+H+ H+ H + H H+H+ H+ H+ H+ + + H+ H+ H+H H H+ H+ H+ H+
H+
CoQ
I
II
III
Cyt c
H+ + H+ H+ H H+
H2O
O2
Phosphorylation •
•
Inner Membrane
IV
Oxidative Phosphorylation Cytosol
Two ways to produce ATP: •
Substrate level phosphorylation
•
Oxidative phosphorylation
Outer Membrane
Substrate level phosphorylation (via enzyme): Phosphoenolpyruvate
Inner Membrane Space
ADP
ATP
H+
H+
H+
H+ H+
H+ H+ H+
H+
H+ H+
H+
+ H+ H H+ H+ + + H+ H H+ H
ATP Synthase Pyruvate ADP
52
ATP
Inner Membrane
ATP Synthase
P/O Ratio
•
Complex V
•
•
Converts proton (charge) gradient ATP
•
•
ATP per mol ecule O2 Classically had to be an integer
•
“electrochemical gradient”
•
3 per NADH
•
“proton motive force”
•
2 per FADH2
Protons move down gradient (“chemiosmosis”)
•
Newer estimates •
2.5 per NADH
•
1.5 per FADH2
Hinkle P. P/O ratios of mitochondrial oxidative phosphorylation. Biochimica et Biophysica Biophysica Act 1706 (Jan 2005) 1-11
Aerobic Energy Production 30/32 ATP per glucose
Drugs and Poisons •
Cytosol Mitochondria
Acetyl CoA
2 ATP
GTP (1ATP) NADH NADH NADH
•
•
11 ATP
Two ways ways to disrupt oxidative phosphory lation #1: Block/inhibit electron transport #2: Allow H+ to leak out of inner membrane space •
“Uncoupling” of electron transport/oxidative transport/oxidative phosphorylation
FADH2
Pyruvate Glucose Pyruvate
NADH Acetyl CoA
2 NADH Malate Glycerol-3-P
2 NADH (6) 2 FADH2 (4)
NADH NADH FADH2
11 ATP
GTP (1 ATP)
Inhibitors •
•
Rotenone (insecticide)
•
•
Binds complex I
•
Prevents electron transfer (reduction) to CoQ
•
•
Antimycin A (antibiotic) •
•
Cyanide Poisoning
•
Complex III (bc1 complex) complex)
•
Complex IV •
•
•
Carbon monoxide (binds a3 in Fe 2+ state – competes with O 2) Cyanide (binds a3 in Fe
3+
state)
53
CNS: Headache, confusion Cardiovascular: Cardiovascular: Initial tachycardia, hypertension hypertension Respiratory: Initial tachypnea Bright red venous blood: ↑O2 content Almond smell Anaerobic metabolism:lactic metabolism: lacticacidosis
Cyanide Poisoning •
•
Uncoupling Agents Cytosol
Nitroprusside : treatment of hypertensive emergencies •
Contains five cyanide groups per per molecule
•
Toxic Toxic l evels with prolonged infusions
Outer Membrane Inner Membrane Space
Treatment: Nitrites (amyl nitrite) •
•
Converts Fe2+ Fe3+ in Hgb (methemoglobin)
H+
H+
H+
H+ H+
H+ H+ H+
H+
H+ H+
H+
+ H+ H H+ H+H+ + H+ H H
+
3+
Fe in Hgb binds cyanide, protects mitochondria ATP Synthase
ADP
Uncoupling Agents •
•
•
Oligomycin A
2,4 dinitrophenol (DNP)
•
Aspirin (overdose) (overdose)
•
Brownfat •
Newborns (also (also hibernating animals)
•
Uncoupling protein 1 (UCP-1, thermogenin)
•
Sympathetic stimulation (NE, β receptors) lipolysis
•
•
Electron transport heat (not ATP)
All lead to production of heat
54
Macrolide antibiotic Inhibits ATPsynthase Protons cannot move through enzyme
•
Protons trapped in intermembrane space
•
Oxidative phosphorylation stops
•
ATP cannot be generated
ATP
Inner Membrane
Lipids •
•
•
Mostly carbon and hydrogen Not soluble in water Many types: •
Fatty Acids Jason Ryan, MD, MPH
Lipids Glycerol
•
•
•
•
Triglyceride
Vocabulary
•
•
Cholesterol
•
Phospholipids
•
Steroids
•
Glycolipids
Most lipids degraded to free fatty acids in intestine Enterocytes conv ert FAs totriacylglycerol totriacylglycerol Chylomicronscarry Chylomicronscarry through plasma TAG degraded back to f ree fatty acids •
Lipoprotein lipase
•
Endothelial surfaces of capillaries
•
Abundant in adipocytes and muscle tissue
More Vocabulary
“Saturated” fat (or fatty acid)
•
Trans fat
•
Contains no double bonds
•
Double bonds (unsaturated) (unsaturated) can be trans or cis
•
“Saturated” with hydrogen
•
Most natural fats have cis configuration
•
Usually solid at room temperature
•
Trans from partial hydrogenation (food processing method)
•
Raise LDL cholesterol
•
Can increase LDL, lower HDL
“Unsaturated” fat •
•
Triacylglycerol (triglycerides)
•
Fatty Acid and Triglycerides Fatty Acid
•
Fatty acids
•
•
Contains at least one double bond
“Monounsaturated:” One double bond “Polyunsaturated:” More than one double bond
Omega-3 fatty acids •
Type of polyunsaturated fat
•
Found in fish oil
•
Lower triglyceride levels
eicosapentaenoic acid (EPA)
55
Fatty Acid Metabolism •
•
•
Fatty Acid Synthesis
Fattyacids synthesis
•
•
Liver, mammary glands, adipose tissue (small amount)
•
Excess carbohydrates and proteins
fatty acids
Fatty acid storage •
Adipose tissue
•
Stored as triglycerides
•
In high energy states (fed state): •
Lots of acetyl-CoA acetyl-CoA
•
Lots of ATP ATP
•
Inhibition of isocitrate dehydrogenase dehydrogenase (TCA cycle)
Result:High Result: High citrate level
Fatty acid breakdown
Acetyl-CoA
•
β-oxidation
•
Acetyl CoA TCA cycle ATP
ATP Isocitrate Dehydrogenase
Citrate Oxaloacetate Synthase
Citrate CoA
Fatty Acid Synthesis
Fatty Acid Synthesis
•
Step 1: Citrate to cytosol via citrate shuttle
•
•
Key point: Acetyl-CoA cannot cross membrane
•
Step 2: Citrate converted to acetyl-CoA Net effect: Excess acetyl-CoA moved to cytosol
Citrate Cytosol Mitochondria
ATP-Citrate Lyase
Acetyl-CoA
ATP Isocitrate Dehydrogenase
Citrate Oxaloacetate Synthase
Acetyl-CoA
Citrate CoA ATP
ADP
Oxaloacetate
Citrate CoA
Fatty Acid Synthesis •
•
Biotin
Step 3: Acetyl-CoA converted to malonyl-CoA Rate limiting step
•
Glucagon Epinephrine
Insulin
+
-
All add 1-carbon group via CO2
•
Pyruvate carboxylase
•
-
Acetyl-CoA Carboxylase Malonyl-CoA
Acetyl-CoA
•
•
β-oxidation Citrate
Cofactor for carboxylation enzymes
CO2 Biotin Daniel W. Foster. Malonyl CoA: the regulator of fatty acid synthesis and oxidation J Clin Invest. 2012;122(6):1958– 1959.
56
Acetyl-CoA carboxylase Propionyl-CoA carboxylase
Fatty Acid Synthesis •
•
•
•
•
Fatty Acid Storage
Step #4: Synthesis of palmitate Enzyme: fatty acid synthase Uses carbons from acetyl CoA and malonyl CoA Creates 16 carbon fatty acid RequiresNADPH RequiresNADPH (HMP Shunt)
•
Palmitate can be modified to other fatty acids
•
Used by various tissues based on needs
•
Stored as triacylglycerols triacylglycerols in adipose tissue
Palmitate
Fatty Acid Breakdown
Fatty Acid Breakdown •
•
•
Fatty Acid
Key enzyme: Hormone sensitive lipase Removes fatty acids f rom TAGin adipocytes Activatedby glucagonand glucagonand epinephrine
Hormone Sensitive Lipase Triacylglycerol
Liver Glycerol
Glycerol
Fatty Acid Breakdown
Glucose Glucose-6-phosphate
•
Fructose-6-phosphate
•
Fructose-1,6-bisphosphate Glyceraldehyde-3-phosphate
Dihydroxyacetone Phosphate Glycerol-3-Phosphate Dehydrogenase
1,3-bisphosphoclycerate 3-phosphoglycerate
•
Glycerol-3-Phosphate Glycerol Kinase
2-phosphoglycerate Phosphoenolpyruvate Pyruvate
Glycerol
57
Fatty acids transported via albumin Taken Taken up by tissues Not used by: •
RBCs: RBCs: Glycolysis only (no mitochondria)
•
Brain: Brain: Glucose and ketones ketones only
β-oxidation
Fatty Acid Breakdown •
•
•
β-oxidation Removal of 2-carbon units from fatty acids Produces acetyl-Co A, NADH, FADH2
•
Step #1: Convert fatty acid to fatty acyl CoA ATP Fatty Acid
Fatty acyl CoA
R—C—OH
Long Chain Fatty Acyl CoA synthetase
O
β-oxidation •
•
•
•
ADP
CoA
R—C—CoA O
Carnitine Shuttle
Step #2: Transport fatty acyl CoA inner mitochondria Uses carnitine shuttle
Cytosol Inner Membrane Space
Carnitine in diet Also synthesized from lysine and methionine •
Only liver, kidney can synthesize de novo novo
•
Muscle and heart depend on diet or other tissues tissues
Fatty acyl CoA
Malonyl-CoA Carnitine Palmitoyl Transferase-1
-
Acyl Carnitine
Fatty acyl CoA R—C—CoA
Carnitine
R—C—Carnitine
O
O
Mitochondrial Matrix R—C—CoA CoA
O Fatty acyl CoA
Carnitine
Carnitine Deficiencies •
•
•
Malnutrition
•
Liver disease
•
Increased requirements (trauma, burns, pregnancy) pregnancy)
•
Hemodialysis (↓ synthesis; loss through membranes)
•
•
•
Major consequence: •
Inability to transport LCFA to mitochondria
•
Accumulation of LCFA LCFA in cells
Acyl Carnitine
Carnitine Deficiencies Deficiencies
Several potential secondary causes •
CPT-2
Low serumcarnitine serum carnitine and acylcarnitine levels
58
Muscleweakness, Muscle weakness, especially during exercise Cardiomyopathy Hypoketotic hypoglycemiawhen hypoglycemia when fasting •
Tissues overuse glucose glucose
•
Poor ketone synthesis without without fatty acid breakdown
Primary systemic carnitine deficiency
β-oxidation
•
Mutation affecting carnitine uptake into cells
•
•
Infantile phenotype presents first two year of life
•
•
Encephalopathy
•
Hepatomegaly
•
Hyperammonemia (liver dysfunction)
•
•
•
Hypoketotic hypoglycemia
•
Low serum carnitine: carnitine: kidneys cannot resorb carnitine
•
Reduced carnitine levels in muscle, liver, liver, and heart
Step #3: Begin “cycles” of beta oxidation Removes two carbons Shortens chain by two Generates NADH, FADH2, Acetyl CoA
β carbon CoA-S
α carbon
β-oxidation
Acyl-CoA Dehydrogenase
•
First step in a cycle involves acyl-CoA dehydrogenase
•
Adds a double bond between α and β carbons
•
β carbon CoA-S
•
α carbon
Family of four enzymes •
Short
•
Medium
•
Long
•
Very-long chain fatty acids
Well described deficiency of medium chain enzyme
FAD Acyl-CoA dehydrogenase FADH2
CoA-S
MCAD Deficiency
MCAD Deficiency
Medium Chain Acyl-CoA Dehydrogenase
Medium Chain Acyl-CoA Dehydrogenase
•
•
•
•
•
Autosomalrecessivedisorder Poor oxidation 6-10 carbon fatty acids Severehypoglycemia Severehypoglycemia without ketones Dicarboxylic acids 6-10 carbons in urine
•
•
•
Highacylcarnitinelevels
Dicarboxylic Acid
59
Gluconeogenesis shutdown •
Pyruvate carboxylase depends depends on Acetyl-CoA
•
Acetyl-CoA levels low in absence β-oxidation
Exacerbated in fasting/infection Treatment: Avoid fasting
Odd Chain Fatty Acids •
•
•
Propionyl CoA
β-oxidation proceeds until 3 carbons remain Propionyl-CoA Succinyl-CoA TCA cycle Key point: Odd chain FA glucose
•
•
Common pathway to TCA cycle Elevated methylmal onic acid seen in B12 deficiency
Biotin
Propionyl-CoA
MethylMalonyl-CoA
S-CoA Propionyl-CoA
Propionyl-CoA Carboxylase (Biotin)
Amino Acids Isoleucine Valine Threonine Methionine
Methylmalonic Acidemia •
•
•
•
Deficiency of Methylmalonyl-CoA mutase Anion gap metabolic acidosis CNS dysfunction Often fatal early in life
Methylmalonyl-CoA
Methylmalonyl-CoA mutase
Succinyl-CoA
B12 S-CoA
Succinyl-CoA B12
Succinyl-CoA
S-CoA
Isomers
60
Odd Chain Fatty Acids Cholesterol
TCA Cycle
Ketone Bodies •
•
•
•
•
Ketone Bodies
Alternative fuel source for some cells Fasting/starvation fatty acids to liver Fatty acids acetyl-CoA ↑ acetyl-CoA exceeds capacity TCA cycle Acetyl-CoA shunted toward ketone bodies Fatty Acids
Acetyl-CoA
KetoneBodies
Jason Ryan, MD, MPH
TCA Cycle
Ketone Body Synthesis
Ketolysis
CH3—C—CoA Acetyl-CoA
Acetyl-CoA
O
•
•
CH3—CH2—C—CoA Acetoacetyl-CoA OH HMG-CoA
O
O
Constant low level synthesis synthesis
•
↑ synthesis in fasting when FA levels are high
•
Used by muscle, heart
•
Brain can also use ketone bodies
•
Livercannot Liver cannotuse use ketone bodies
3
Acetoacetate
•
•
O-—C—CH2— C—CH2—C—CoA O O CH
O-—C—CH2— C—O-
3-hydroxybutyrate/acetoacetate ATP Liver releases ketones into plasma
H CH3—C—
Spares glucose for the brain
O-
CH2—C— OH
CH3—C—CH3 Acetone O
O
3-Hydroxybutyrate
Ketolysis
Big Picture 3-Hydroxybutyrate
•
•
NADH
•
Acetoacetate
Fatty Acids
Acetoacetyl CoA
Acetyl-CoA TCA Cycle
Brain cannot use fatty acids Ketone bodies allow use of fatty acid energy by brain Also used by other tissues: preserve glucose for brain
Liver
Ketone Bodies
Brain
Acetyl-CoA
Acetyl-CoA TCA Cycle Schönfeld P, Reiser G. Why does brain metabolism not favor burning of fatty acids to provide energy? Journal of Cerebral Blood Flow & Metabolism (2013) 33, 1493 – 1499
61
Ketoacidosis •
•
•
Diabetes
Ketone bodies have low pKa
•
Release H+ at plasma pH ↑ ketones anion gap metabolic acidosis
•
•
•
•
3-Hydroxybutyrate
Acetoacetate
•
H O-—C—CH2— C—OO
Low insulin High fatty acid utilization Oxaloacetate depleted TCA cycle stalls
↑ acetyl-CoA Ketone production
Acetyl-CoA
CH3 —C—CH2—C—O-
O
OH
Fatty Acids
Ketones
Glucose
O NADH
Oxaloacetate Malate
Alcoholism
Urinary Ketones
•
EtOH metabolism: excess NADH
•
Oxaloacetate shunted to malate
•
•
•
•
Acetyl-CoA
Ketones
NADH
Oxaloacetate
Normally no ketones in urine
•
Elevated urine ketones:
•
Stalls TCA cycle ↑ acetyl-CoA Ketone production Also ↓ gluconeogenesis
•
Citrate
Malate dehydrogenase dehydrogenase
Malate
62
Any produced
utilized
•
Poorly controlled diabetes (insufficient insulin)
•
DKA
•
Prolonged starvation
•
Alcoholism
Citrate
Ethanol Metabolism
NAD+
Ethanol Metabolism
NAD+
NADH
Aldehyde Dehydrogenase
Alcohol Dehydrogenase
Jason Ryan, MD, MPH Ethanol
NADH
Acetaldehyde
Acetate
Cytosol Mitochondria
Ethanol Metabolism
NADH Stalls TCA Cycle Acetyl-CoA
•
•
Excessive alcohol consumption leads to problems: •
CNS depressant
•
Hypoglycemia
•
Ketone body formation (ketosis)
•
Lactic acidosis
•
Accumulation of fatty acids
•
Hyperuricemia
•
Hepatitis and cirrhosis
Citrate
Oxaloacetate
NADH Isocitrate
Malate
Isocitrate Dehydrogenase Fumarate
Trigger for all biochemical problems is ↑NADH
CO2
α-ketoglutarate
NADH
NADH
α-KG Dehydrogenase Succinate
NADH Stalls TCA Cycle •
•
•
•
•
Gluconeogenesis inhibited •
•
•
Ketones
Gluconeogenesis NADH
Oxaloacetate
CO2 NADH
Ethanol and Hypoglycemia
NADH shunts oxaloacetate to malate ↑ acetyl-CoA Ketone production Also ↓ gluconeogenesis hypoglycemia Acetyl-CoA
Succinyl-CoA
Citrate
Malate dehydrogenase NAD+
Malate
63
Oxaloacetate shunted to malate
Glycogenimportant Glycogen important source of fasting glucose Danger of low glucose when glycogen low •
Drinking without eating
•
Drinking afterrunning
Ketones from Acetate •
•
•
Ketosis from Ethanol
Liver: Acetate acetyl-CoA TCA cycle stalled due to high NADH
Glucose Amino Acids Fatty Acids
Acetyl-CoA ketones NAD+
NADH
Acetaldehyde
Limited supply NAD+
•
Depleted by EtOH metabolism
•
TCA Cycle
Accumulation of Fatty Acids
Glyceraldehyde-3-phosphate NAD+
•
•
Acetate
Acetate
Lactic Acidosis
•
Ethanol
Ketones
Acetyl-CoA Aldehyde Dehydrogenase
Ketones
Acetyl-CoA
NADH 1,3-bisphosphoclycerate 3-phosphoglycerate
Overwhelms electron transport Pyruvate shunted to lactate Regenerates NAD+
2-phosphoglycerate
•
High levels NADH stalls beta oxidation •
Beta oxidation generates generates NADH (like TCA cycle)
•
Requires NAD+
•
Inhibited when NADH is high
Result: ↓ FA breakdown
Phosphoenolpyruvate NADH -
Pyruvate NADH NAD+
•
PDH Lactate
β-oxidation
-
TCA Cycle
Accumulation Accumulation of Fatty Acids •
Accumulation of Fatty Acids
Stalled TCA cycle ↑ fatty acid synthesis
•
•
Citrate
Rate limiting step of fatty acid synthesis Favored when citrate high from slow TCA cycle
Fatty Acids
Cytosol Mitochondria
β-oxidation Acetyl-CoA
Citrate Oxaloacetate Synthase
Citrate
NADH
-
+
Acetyl-CoA Carboxylase Malonyl-CoA
Acetyl-CoA
TCA Cycle
Citrate
CO2
CoA
Biotin
64
Accumulation of Fatty Acids •
•
•
Accumulation of Fatty Acids
Malate accumulation also cont ributes to FA levels
•
Used to generate NADPH NADPH favors fatty acid synthesis
•
•
•
Fatty acid synthase Uses carbons from acetyl CoA and malonyl CoA Creates 16 carbon fatty acid palmitate Requires NADPH
Acetyl-CoA
Pyruvate NADPH
Malic Enzyme
NADH
Oxaloacetate
Citrate
NAD+
Palmitate
Malate
Glycerol
Fatty Acids and Ethanol
Glucose Glucose-6-phosphate Fructose-6-phosphate
Acetyl-CoA
Citrate
Fatty Acids
Fructose-1,6-bisphosphate Glyceraldehyde-3-phosphate
TCA Cycle
1,3-bisphosphoclycerate
NAD+ 3-phosphoglycerate
NADPH
Malate
Dihydroxyacetone Phosphate NADH Glycerol-3-Phosphate
Pyruvate
Dehydrogenase
Glycerol-3-Phosphate
2-phosphoglycerate Phosphoenolpyruvate Pyruvate
Fatty Liver •
Glycerol
Uric Acid
Seen in alcoholism due to buildup of triglycerides
•
Urate and lactate compete for excretion •
•
•
•
65
Excreted by proximal tubule of nephron
↑ lactate in plasma = ↓ excretion ↑ uric acid gout attack Alcohol a well-described trigger for gout
Hepatitis and Cirrhosis •
•
•
•
•
Hepatitis and Cirrhosis
High NADH slows ethanol metabolism Result:buildup Result: buildup of acetaldehyde
•
Microsomal ethanol-oxidizing system (MEOS)
•
Alternative pathway for ethanol
Toxic to liver cells Acute: Inflammation Alcoholic hepatitis •
Chronic: Scar tissue Cirrhosis
•
NAD+
NADH
•
Acetyl-CoA
Acetaldehyde
Aldehyde Dehydrogenase
•
Normally metabolizes small amount of ethanol ethanol
•
Becomes important with excessiveconsumption
Cytochrome P450-dependent pathway in liver Generates acetaldehyde and acetate Consumes NADPH and Oxygen
•
Oxygen: generates free radicals
•
NADPH: glutathione cannot be regenerated •
Acetate
Loss of protection from oxidative stress
Alcohol Dehydrogenase Ethanol
•
Zero order kinetics (constant rate)
•
Also metabolizes methanol and ethylene glycol
•
Inhibited by fomepizole (antizol) •
Alcohol Dehydrogenase
Treatment for methanol/ethylene methanol/ethylene glycol intoxication +
NAD
+
NAD
NADH
Methanol
NADH
Alcohol Dehydrogenase
Ethylene Glycol Ethanol
Acetaldehyde
Acetate
Aldehyde Dehydrogenase •
•
•
NAD+
NADH
Ethanol
•
•
•
NADH
•
Aldehyde Dehydrogenase
Alcohol Dehydrogenase Acetaldehyde
Glycolaldehyde
Alcohol Flushing
Inhibited by disulfiram (antabuse) Acetaldehyde accumulates Triggers catecholamine release Sweating, flushing, flushing, palpitations, nausea, vomiting NAD+
Formaldehyde
Aldehyde Dehydrogenase
Alcohol Dehydrogenase
•
Acetaldehyde
Acetate
66
Skin flushing when consuming alcohol Due to slow metabolism of acetaldehyde Common among Asian populations •
Japan, China, Korea Korea
•
Inherited deficiency aldehyde dehydrogenase dehydrogenase 2 (ALDH2)
Possible ↑risk esophageal esophageal and oropharyngeal cancer
Exercise •
•
Exercise and Starvation
•
•
Rapidly depl etes ATP in muscles Duration, intensity depends on other fuels Glycogen Glucose TCA cycle available but slow Short term needs met by creatine
Glycogen
Glucose
Jason Ryan, MD, MPH Pyruvate
Lactate
Creatine
Creatinine
•
Present in muscles as asphosphocreatine phosphocreatine
•
•
Source of phosphate groups
•
•
•
•
TCA Cycle
Important for heart and muscles Can donate to ADP ATP Reserve when ATP falls rapidly in early exer cise
•
Amount of creatinine proportional to muscle mass Excreted by kidneys Creatine Kinase
Creatine Kinase
Creatine
Spontaneous conversion creatinine
Phosphocreatine
Creatine
Phosphocreatine
Creatinine
ATP and Creatine
Calcium and Exercise
•
Consumed within seconds of exercise
•
•
Used for short, intense exertion
•
•
•
•
•
Heavy lifting
•
Sprinting
•
Exercise for longer time re quires other pathways Slower metabolism Result: Exercise intensity diminishes with time
67
Calcium release from muscles stimulates metabolism Activates glycogenolysis Activates TCA cycle
Calcium Activation
Calcium Activation
Glycogen Breakdown
TCA Cycle
Acetyl-CoA
Pyruvate
NADH Citrate
Oxaloacetate
P Glycogen Phosphorylase Calcium/Calmodulin
Glycogen Breakdown
ADP Ca++
Malate
Isocitrate Isocitrate Dehydrogenase
Glycogen Phosphokinase A
Fumarate
α-KG Dehydrogenase
FADH2 Succinate
Succinyl-CoA
GTP
•
40-yard 40-yard sprint
Aerobic exercise •
Long distance running
•
Co-ordinated effort by organ systems
•
Multiple potential sources sources of energy
•
•
Anaerobic exercise •
Sprinting, weight lifting
•
Purely a muscular effort
•
Blood vessels in muscles muscles compressed during peak contraction
•
Muscle cells isolated from body
•
Muscle relies on it’s own fuel stores
•
ATP and creatine phosphate (consumed in seconds) Glycogen •
Metabolized to lactate (anaerobic (anaerobic metabolism)
•
TCA cycle too slow
Fast pace cannot be maintained •
Creatinine phosphate consumed consumed
•
Lactate accumulates
Moderate Aerobic Exercise
Intense Aerobic Exercise
1-mile run
Marathon
•
•
•
•
ATP and creatine phosphate (consumed in seconds) Glycogen: metabolized to CO 2 (aerobic metabolism) Slower pace than sprint •
Decrease lactate production production
•
Allow time for TCA cycle and oxidative phosphorylation
•
•
•
•
•
“Carbohydrateloading” “Carbohydrateloading” by runners •
CO2 NADH
Anaerobic Exercise
Types of Exercise •
CO2
NADH α-ketoglutarate
Ca++
•
Increases muscle glycogen content
•
68
Co-operation between muscle, liver, adipose tissue ATP and creatine phosphate (consumed in seconds) Muscle glycogen: metabolized to CO 2 Liver glycogen: Assists muscles produces glucose Often all glycogen consumed during race Conversion to metabolism of fatty acids •
Slower process
•
Maximum speed of running reduced
Elite runners condition to use glycogen/fatty acids
Intense Aerobic Exercise
Intense Aerobic Exercise Exercise
Fatty Acid Metabolism
Fatty Acid Metabolism
•
Malonyl-CoA levels fall
Fatty acyl CoA
Cytosol
Glucagon Epinephrine -
Inner Membrane Space
β-oxidation
Fatty acyl CoA
-
Acetyl-CoA Carboxylase
R—C—CoA O
Malonyl-CoA
Acetyl-CoA
Carnitine Palmitoyl Transferase-1
Malonyl-CoA -
Acyl Carnitine R—C—Carnitine
Carnitine
O
Mitochondrial Matrix R—C—CoA
CO2 Biotin
CoA
O Fatty acyl CoA
Muscle Cramps
CPT-2
Muscle Cramps
Acyl Carnitine
Glyceraldehyde-3-phosphate NAD+
•
•
•
•
Too much exercise ↑ NAD consumption •
Exceed capacity capacity of TCA cycle/electron transport
•
Elevated NADH/NAD ratio
Favors pyruvate lactate pH falls in muscles cramps Distance runners: lots of mitochondria •
•
Limited supply NAD+
•
Must regenerate
•
O2 present
•
O2 absent
•
•
NADH
NADH
1,3-bisphosphoclycerate 3-phosphoglycerate
NAD (mitochondria)
2-phosphoglycerate Phosphoenolpyruvate
NADH NAD+ via LDH
Bigger, too
Pyruvate NADH NAD+
Fed State •
•
•
Lactate
Insulin Effects
Glucose, amino acids absorbed into blood
•
Lipids into chylomicrons lymph blood Insulin secretion
Glycogen synthesis •
•
•
Beta cells of pancreas
•
•
Stimulated by glucose, parasympathetic parasympathetic system
•
•
69
Liver, muscle
Increases glycolysis Inhibits gluconeogenesis Promotes glucose adipose tissue Used to form triglycerides
•
Promotes uptake of amino acids by muscle
•
Stimulates protein synthesis/inhibits breakdown
TCA Cycle
Insulin in the Liver •
Insulin and Glycolys Glycolysis is
Glucokinase •
Found in liver and pancreas
•
Induced by insulin insulin
•
Insulin promotes transcription
ATP
Glucose
PFK2 F-2,6-bisphosphate
Fructose-6-phosphate Fructose 1,6 Bisphosphatase2
ADP
PFK1
Glucose-6-phosphate
Fructose 1,6 Bisphosphatase1
Fructose-1,6-bisphosphate
On/off switch glycolysis ↑ = glycolysis (on) ↓ = no glycolysis (gluconeogenesis)
Insulin and Fatty Acids
Insulin and Glycogen Glycogen Glycogen
•
Acetyl-CoA converted to malonyl-CoA
•
Rate limiting step Glucagon Epinephrine
Insulin Glucagon Epinephrine
β-oxidation
Insulin Citrate
Glycogen Phosphorylase
Glycogen Synthase
Acetyl-CoA Carboxylase Malonyl-CoA
Acetyl-CoA
Glucose
-
-
+
CO2 Biotin
Fasting/Starvation •
•
•
Fasting/Starvation
Glucose levels fall few hours after a meal
•
Decreased insulin Increased glucagon
Key effect of glucagon •
•
70
Glycogen breakdown in liver
•
Maintains glucose levels in plasma
•
Dominant source glucose between meals
Other effects •
Inhibits fatty acid synthesis
•
Stimulates release of fatty acids acids from adipose tissue
•
Stimulates gluconeogenesis
Starvation
Glucose Sources
Alanine Cycle
Ingested Glucose
Muscle
Liver
NH 4+
NH 4+
r h / g e s o c u l G
Glycogen
Gluconeogenesis Alanine Lactate Glycerol Odd Chain FAs
Glutamate Key Point #1: Glycogenexhausted after ~24 hours
Pyruvate
Alanine
Alanine
α-KG
α-KG Glucose
0
8
16
24
Key Point #2: Glucose levels maintained in fasting by many sources
36
Hours
Glutamate
Pyruvate
Glucose
Key Point: Peripheral tissue alanine glucose
Starvation
Starvation
Cori Cycle
Glycerol
Glucose Glucose-6-phosphate Fructose-6-phosphate Fructose-1,6-bisphosphate
Glyceraldehyde-3-phosphate
Dihydroxyacetone Phosphate
1,3-bisphosphoclycerate 3-phosphoglycerate
Glycerol-3-Phosphate Dehydrogenase
Glycerol-3-Phosphate Glycerol Kinase
2-phosphoglycerate Phosphoenolpyruvate Petaholmes/Wikipedia
Pyruvate
Starvation
Starvation
Odd Chain Fatty Acids
Fuel Sources of Tissues
•
•
•
β-oxidation proceeds until 3 carbons remain Propionyl-CoA Succinyl-CoA TCA cycle Key point: Only odd ch ain FA glucose
•
•
•
•
Succinyl-CoA S-CoA Propionyl-CoA
Propionyl-CoA Carboxylase (Biotin)
71
Glycerol
Glycolysis slows (low insulin levels) Less glucose utilized by muscle/liver muscle/liver Shift to fatty acid beta oxidation for fuel Spares glucose andmaintains and maintainsglucoselevels
Malnutrition •
Malnutrition
Kwashiorkor
•
•
Inadequate protein intake intake
•
Hypoalbuminemia
•
Swollen legs, abdomen
edema
Hypoglycemia in Children •
•
•
Marasmus •
Inadequate energy intake
•
Insufficient total calories
•
Kwashiorkor without edema
•
Muscle, fat wasting
Hypoketotic Hypoglycemia
Occurswith metabolic metabolicdisorders Glycogen storage diseases
•
•
Lack of ketones in setting of ↓ glucose during fasting Occursin mitochondrial disorders
•
Hypoglycemia
•
Loss of beta oxidation and and gluconeogenesis
•
Ketosis
•
FFA
•
Usually after overnight fast
•
Pyruvate oxaloacetate
•
Tissues overuse glucose hypoglycemia
Hereditary fructose intolerance •
Deficiency of aldolase B
•
Build-up of fructose 1-phosphate
•
Depletion of ATP
•
Usually a baby just weaned weaned from breast milk
Hypoketotic Hypoglycemia •
Carnitine deficiency
•
MCAD deficiency
•
Low serum carnitine and acylcarnitine levels
•
Medium chain acyl-CoA dehydrogenase dehydrogenase
•
Dicarboxylic acids 6-10 carbons carbons in urine
•
High acylcarnitine levels
72
beta oxidation ketones (beta oxidation)
glucose (gluconeogenesis)
Inborn Errors in Metabolism Metabolism •
•
Inborn Errors of Metabolism
•
Glycogen storage diseases Galactosemia
•
•
•
Failure to thrive, hypotonia
Lab findings suggest diagnosis: •
Newborn Hypoglycemia •
Often present in newborn period Often non-specific features: •
•
Jason Ryan, MD, MPH
•
Defects in me tabolic pathways
Hypoglycemia
•
Ketosis
•
Hyperammonemia
•
Lactic acidosis
Glycogen Storage Diseases •
Hereditary fructose intolerance Organic acidemias Disorders of fatty acid metabolism
•
Some have no hypoglycemia •
Only affect muscles
•
McArdle’s Disease (type V)
•
Pompe’s Disease (type II)
Hypoglycemia seen in others •
Von Gierke’s Disease (Type I)
•
Cori’s Disease (Type III)
Glucose
Glycogen Storage Diseases •
•
•
Glycogen Storage Storage Diseases
Fasting hypoglycemia
•
Von Gierke’s Disease (Type I)
•
Hours after eating
•
Severe hypoglycemia
•
Not in post-prandial period
•
Lactic acidosis
Ketosis
•
Cori’s Disease (Type III)
•
Absence of glucose during fasting
•
Gluconeogenesis intact
•
Fatty acid breakdown (NOT a fatty acid disorder)
•
Mild hypoglycemia
•
Ketone synthesis
•
No lactic acidosis
Cori Cycle
Hepatomegaly •
Glycogen buildup in liver
Petaholmes/Wikipedia
73
HFI
HFI
Hereditary Fructose Intolerance
Hereditary Fructose Intolerance
•
•
•
•
•
•
•
•
Deficiency of aldolase B Build-up of fructose 1-phosphate
•
Starts after weaned from breast milk
•
“Reducing sugars” in urine
•
Depletion of ATP Loss of gluconeogenesis and glycogenolysis Hypoglycemia
No fructose in breast milk
•
Glucose, fructose, galactose galactose
•
Reducing sugars in urine with hypoglycemia hypoglycemia
Lactic acidosis Ketosis Hepatomegaly (glycogen buildup)
Classic Galactosemia
Classic Galactosemia
•
Deficiency of galactose 1-phosphate uridyltransferase uridyltr ansferase
•
Vomiting/diarrhea after feeding
•
Galactose-1-phosphate accumulates
•
Similar presentation to HFI
•
•
•
•
Depletion of ATP 1st few days of life Breast milk contains lactose Lactose = galactose + glucose
•
Hypoglycemia
•
Lactic acidosis
•
Ketosis
•
Hepatomegaly (glycogen buildup)
•
“Reducing sugars” in urine
Organic Acidemias Hypoglycemia Lactic Acidosis Ketosis
•
•
After feedings Galactosemia HFI
•
Fasting Glycogen Storage Diseases
Abnormal metabolism of organic acids •
Propionic acid
•
Methylmalonic acid
Buildup of organic acids in blood/urine Hyperammonemia
Propionic Acid
74
Methylmalonic Acid
Succinyl-CoA •
•
•
Organic Acidemias
Common pathway to TCA cycle
•
Many substances metabolized to propionyl-CoA Propionyl-CoA Methylmalonyl-CoA
•
Poor feeding, vomiting, hypotonia, lethargy
•
Hypoglycemia ketosis
Biotin
Propionyl-CoA
Methylmalonyl-CoA
Succinyl-CoA
•
B12
•
•
Amino Acids
Complex mechanism
•
Liver damage
↓ gluconeogenesis
Anion gap metabolic acidosis Hyperammonemia Elevated urine/plasma organic acids
TCA Cycle
Propionic Acidemia
Methylmalonic Acidemia
Deficiency of proipionyl-CoA carboxylase
•
Succinyl-CoA S-CoA Propionyl-CoA
•
Odd Chain
Isoleucine Fatty Acids Valine Threonine Cholesterol Methionine
•
Onset in newborn period (weeks-months)
Deficiency of methylmalonyl-CoA mutase
Methylmalonyl-CoA
Methylmalonyl-CoA mutase
Succinyl-CoA
B12
Propionyl-CoA Carboxylase (Biotin)
S-CoA
S-CoA
Isomers
Propionic Acid
Methylmalonic Acid
Maple Syrup Urine Disease
Fatty Acid Disorders
•
Branched chain amino acid disorder
•
Carnitine deficiency
•
Deficiency of α-ketoacid dehydrogenase
•
MCAD deficiency
•
•
•
Multi-subunit complex
•
Medium-chain-acyl-CoA dehydrogenase
•
Cofactors: Thiamine, lipoic acid
•
Beta oxidation enzyme
Amino acids and α-ketoacids in plasma/urine α-ketoacid of isoleucine gives urine sweet smell
Valine
Leucine
•
Isoleucine
75
Both cause hypoketotic hypoglycemiawhen hypoglycemia when fasting
•
Lack of fatty acid breakdown
•
Overutilization of glucose hypoglycemia
low ketone bodies
•
Lack of acetyl-CoA for gluconeogenesis gluconeogenesis
Fatty Acid Disorders •
Symptoms with fasting or illness
•
Usually 3 months to 2 years •
•
•
Primary Carnitine Deficiency •
Frequent feedings < 3months 3months prevent fasting
Failure to thrive, altered consciousness, hypotonia Hepatomegaly
•
Cardiomegaly
•
Hypoketotic hypoglycemia
•
•
Carnitine necessary for carnitine shuttle •
Links with fatty acids forming acylcarnitine
•
Moves fatty acids into mitochondria mitochondria for metabolism
Muscle weakness, cardiomyopathy Lowcarnitineand acylcarnitinelevels
R—C—CoA O
Acyl-CoA
+
R
Acylcarnitine Acylcarnitine
Carnitine
MCAD Deficiency Medium Chain Acyl-CoA Dehydrogenase •
Poor oxidation 6-10 carbon fatty acids
•
Dicarboxylicacids 6-10 carbons in urine
•
Highacylcarnitinelevels
•
Hypoketotic Hypoglycemia
Seen when beta oxidation impaired
Carnitine Deficiency Low carnitine levels Low acyl-carnitine levels
MCAD Deficiency High acylcarnitine levels Dicarboxylic acids
Dicarboxylic Acid
OTC Deficiency
Urea Cycle Disorders •
•
•
•
•
•
Ornithine transcarbamylase deficiency
Onset in newborn period (first 24 to 48 hours)
•
Feeding protein load symptoms Poor feeding, vomiting, lethargy May lead to seizures
•
•
Most common urea cycle disorder ↑ carbamoyl phosphate ↑ orotic acid (derived from carbamoyl phosphate) Ornithine
Lab tests: Isolated severe hyperammonemia •
Normal < 50 mcg/dl
•
Urea disorder may be > 1000
NH4+
Carbamoyl Transcarbamylase Phosphate
Urea Cycle
No other major metabolic derangements Glutamine
Carbamoyl Phosphate
Orotic Acid
PyrimidineSynthesis
76
Pyrimidines (U, C, G)
Orotic Aciduria •
•
•
•
•
Mitochondrial Disorders
Disorder of pyrimidine synthesis
•
Also has orotic aciduria Normalammonialevels No somnolence, seizures
•
•
•
Major features: Megaloblastic anemia, poor growth
Inborn errors of metabolism Loss of ability to metabolize pyruvate acetyl CoA All cause severe lactic acidosis All cause elevated alanine (amino acid) •
•
Pyruvate shunted to alanine and lactate
Pyruvate dehydrogenase complex deficiency
Alanine
PDH Complex Deficiency
Pyruvate •
Pyruvate Dehydrogenase
End product of glycolysis
•
•
Liver
Glucose
Glucose
Liver
Pyruvate Cori Cycle
Alanine Cycle
•
Lactate
Alanine Gluconeogenesis
Acetyl-Coa
TCA Cycle
Hypoglycemia Failure to thrive Acidosis Urinary Sugars
Galactosemia HFI
↑ Organic acids ↑ NH3
↓ Ketones
Fatty Acid Disorder
↑NH3 Urea Cycle Defect
↑ Ketones Glycogen Storage Disease
Organic Acidemia
↑Lactate ↑Alanine
Mitochondrial Disorder
77
Pyruvate shunted to alanine, lactate Key findings (infancy): •
Poor feeding
•
Growth failure
•
Developmental delays
Labs: •
Elevated alanine
•
Lactic acidosis
•
No hypoglycemia
Amino Acids •
•
Building blocks (monomers) of proteins All contain amine group and carboxylicacid
Amino Acids Jason Ryan, MD, MPH
Glycine
pKa
Amino Acids •
•
log acid dissociation constant
All except glycine have L- and D- configurations Only L-amino acids used in human proteins
CH3 O H3N - C - C H OL - alanine
O O-
HA A- + H+
CH3 C – C - NH3
pH = pKa + log
[A-]
[HA]
H
pKa = pH - log
D - alanine
[A-]
[HA]
pKa
HA A- + H+
pKa
[A-] pKa: pH - log
•
H+ H+ H+
H+
Acetic acid (C2O2H) pKa = 4.75
pH>pKa A- >> AH
High pH (i.e. 12.0)
pH
O-
H+ H+ H+ H+H+ H+ H+ H+H+ H+ H+H+H+ H+ H+ H+
H+ H+ H+ H+H+ H+ H+ H+H+ H+ H+H+H+ H+ H+ H+
Low pH (i.e. 1.0)
78
pH <4.75
pH >4.75 H+ H+ H+ H+
pKa •
pKa
Ammonia (NH3) pKa = 9.4
•
•
Amino acids: multiple acid-base regions Each has different pKa
H H
H
N+ H
N
H+ H+ H+ H+H+ H+ H+H+ H+ H+ H+H H+ H+ H+ H+
COOH COO- + H+
H
H
pH >9.4 (NH3)
pH <9.4 (NH4+)
H+ H+ H+
H+
pKa •
R
R
H
R
R
NH3+
NH2 + H+
Usually low pKa < 4.0 At normal pH (7.4): COO-
Usually high pKa > 9.0 At normal pH (7.4): NH 3+
Titration Curves pKa3
Some side chains have pKa (3 pKa values!)
pKa2 pKa2
pH pKa=10.53 pKa1
pKa1
NaOH
pKa=2.18
pKa=8.95
NaOH
R
O H2N - C - C H OH
Lysine
Charge at Normal pH •
•
H+ H+ H+ H+H+ H+ H+H+ H+ H+ H+H+ H+ H+ H+ H+
Charge at Normal pH
Normal plasma pH=7.4 AA charge (+/-) depends on pKa values pKa=2.01
pKa=12.48
O-
+NH 3
OpKa=9.6
NH3+
pKa=2.2
pKa=9.04
NH3+
Arginine
Glycine
79
Basic Amino Acids
Histones •
pKa=2.01
pKa=12.48 +NH 3
O Arginine *most basic AA
NH3+
Contain basicamino basic amino acids •
High content of lysine, arginine
•
Positively charged
•
Binds negatively charged phosphate phosphate backbone DNA
pKa=9.04 Adenosine Monophosphate
pKa=10.53 Both +1 charge at normal pH Remove 1H+ from solution Raise pH (basic)
pKa=8.95 pKa=2.18 Lysine
Wikipedia/Public i c Domain
Histidine •
•
Acidic Amino Acids pKa=3.18
Considered a “basic” amino acid Side chain pKa close to plasma pH
pKa=2.10
OO-
NH3+
pKa=9.82
pKa=1.82 Aspartate
O-
pKa=6.00
pKa=4.07
pKa=2.10
O-
O-
NH3+
NH3+
pKa=9.17
pKa=9.47
Glutamate
Hydrophobic Amino Acids
Sickle Cell Anemia •
Methionine
Proline
Leucine
Tryptophan
Alanine
Substitution of polar glutamate for nonpolar valinein valine in hemoglobin protein
Glycine
-O
Phenylalanine Valine
Valine
Isoleucine
80
Glutamate
Proline •
•
Essential Amino Acids
Rigid structure (ring) formed from amino group and side chain
•
•
Nine amino acids must be supplied by diet Cannot be synthesized de novo by cells
Lysine
Used in collagen
Histidine
Leucine
Tryptophan
Threonine
Isoleucine
Phenylalanine
Proline
Glucogenic vs. Ketogenic •
•
•
Methionine
Glucogenic vs. Ketogenic Pyruvate
Glucogenic amino acids: •
Can be converted to pyruvate or TCA cycle inter mediates
•
Can become glucose via gluconeogenesis
Acetyl-CoA
Ketogenic amino acids •
Convert to ketone bodies and acetyl CoA
•
Cannot become glucose glucose
Glucose
Oxaloacetate
Most amino acids are either: •
Glucogenic
•
Glucogenic and ketogenic ketogenic
Valine
TCA Cycle
Ketogenic Amino Acids *both essential
Acetoacetate Leucine
Acetyl-CoA Lysine
81
Ketone Bodies
Phenylalanine Phenylalanin e and Tyrosine •
Phenylalanine and Tyrosine
•
•
Dopamine, Norepinephrine, Epinephrine
•
Thyroid hormone, Melanin
•
Metabolism: several important vitamins/cofactors
•
Three metabolic disorders:
Jason Ryan, MD, MPH
Phenylalanine
Key amino acids for synthesis of:
•
Phenylketonuria (PKU)
•
Albinism
•
Alkaptonuria
Phenylalanine
Alanine with a phenyl group added
•
Converted to tyrosine (non-essential amino acid)
Phenylalanine
Alanine
Phenylalanine Hydroxylase
Tyrosine
Phenylalanine Tetrahydrobiopterin
Tetrahydrobiopterin
Phenylalanine
BH4 •
Cofactor for phenylalanine metabolism NAD+
Phenylalanine Hydroxylase
NADH Dihydropteridine Reductase
Phenylalanine
BH4
BH2
Tyrosine
Dihydropteridine Reductase
NAD+ Tetrahydrobiopterin BH4
Dihydrobiopterin BH2
82
NADH
Phenylketonuria
Phenylketonuria
PKU
PKU
•
•
•
•
Deficiency of phenylalanine hydroxylase activity •
Defective enzyme (classic PKU)
•
Defective/deficient BH4 cofactor cofactor
•
Metabolites of phenylalanine toxicity
Most common inborn error of metabolism Phenyllactate
Accumulation Accumulation of phenylalanine Deficiency of tyrosine (sometimes low normal) Phenylpyruvate
Phenylacetate
Phenylalanine Phenylketones
Phenylketonuria
Phenylketonuria
Signs and Symptoms
Treatment
•
•
Musty smell in urine from phenylalanine metabolites CNS Symptoms
Aspartame (aspartate + phenylalanine)
•
Restriction of phenylalanine
•
Found in most proteins (essential amino acid)
•
Seizures
•
Synthetic amino acids mixtures use for food
•
Tremor
•
Phenylalanine level monitored
•
No aspartame (Equal/NutraSweet)
•
Tyrosine becomes essential
Pale skin, fair hair,blue eyes •
Lack of tyrosine conversion to melanin
Phenylketonuria
Phenylketonuria •
Dietary modification
Mental retardation
•
•
•
Screening
Maternal PKU •
Occurs in women with PKU who consume phenylalanine
•
High levels of phenylalanine phenylalanine acts as a teratogen
•
Baby born with microcephaly, congenital heart defects
•
Newborn measurement of phenylalanine level
•
Done 2-3 days after birth •
83
Maternal enzymes may normalize levels levels at birth
Phenylketonuria
Phenylketonuria
BH4 Deficiency
BH4 Deficiency
•
Rare (2%) cause of PKU
•
•
Defective BH4
•
Elevated phenylalanine Also decreased synthesis of:
•
Often due to defective dihydropteridine reductase
•
Epinephrine, Norepinephrine
•
Also impaired BH4 synthesis
•
Serotonin
•
Dopamine (↑prolactin)
BH4
Phenylketonuria
Tyrosine Hormones
BH4 Deficiency •
Treatment: •
Dietary restriction of phenylalanine
•
Tyrosine supplementation (now essential) essential)
•
Supplementation of BH4
•
L-dopa, carbidopa
•
5-hydroxytryptophan
dopamine serotonin
Dopamine
Norepinephrine
Epinephrine
Tyrosine
Tyrosine Metabolism
Tyrosine Metabolism Metyrosine
Tyrosine Hydroxylase Tyrosine
DOPA
Dopamine
Norepinephrine
Epinephrine
Tyrosine
BH4
BH2
Dihydroxyphenylalanine (DOPA)
Dihydropteridine Reductase
NAD+
84
NADH
Tyrosine Metabolism Carbidopa
Levodopa/Carbidopa
B6
DOPA Decarboxylase Dopamine
DOPA Decarboxylase
L-Dihydroxyphenylalanine (L-DOPA)
CNS
Dihydroxyphenylalanine (DOPA)
Blood Brain Barrier
Dopamine Carbidopa L-DOPA
B6
Tyrosine Metabolism
Dopamine
Tyrosine Metabolism SAM
Vitamin C
Dopamine Β-hydroxylase Dopamine
DOPA Decarboxylase
Phenylethanolamine N-methyltransferase Norepinephrine
Norepinephrine
Epinephrine
S-A S-Adenosyl Methionine
S-A S-Adenosyl Methionine
SAM
SAM
•
•
Cofactor that donates methyl groups Synthesized fr om ATP and methionine
•
•
Methionine similar to homocysteine SAM – methyl group – adenosine = Homocysteine
Methionine
ATP Methionine Homocysteine SAM
85
S-Adenosyl S-Adenosyl Methionine
S-A S-Adenosyl Methionine
SAM
SAM •
•
Need to regenerate methionine to maintain SAM Requires folate and vitamin B12
Phenylethanolamine N-methyltransferase Epinephrine
Norepinephrine
Folate
N5-Methyl THF
Adenosine
THF
B12 Homocysteine
SAM
Methionine
Homocysteine SAM
S-Adenosyl Methionine
Tyrosine Metabolism
SAM
Phenylethanolamine N-methyltransferase BH4
Epinephrine
Norepinephrine
Tyrosine
B6 DOPA
VitC Do pamine
SAM Norepinephri ne
Epinephrine
Adenosine
ATP SAM
B12/Folate
Homocysteine
Methionine
Thyroxine (T4)
Melanin •
•
•
Iodine
Pigment i n skin, hair, eyes Synthesized by melanocytes Polymer of repeating units made from tyrosine Melanin Tyrosinase
Tyrosine
Thyroxine (T4) Tyrosine
86
DOPA quinone
Oculocutaneous Oculocutaneous albinism
Oculocutaneous albinism
(OCA)
(OCA)
•
•
•
•
•
Most commonly from deficiency of:
•
Seen in Chediak-Higashi Syndrome
•
Tyrosinase (OCA Type I)
•
Immunodeficiency
•
Tyrosine transporters (OCA Type II)
•
OCA Type II: Transporter defect
Decreased/absent melanin
•
Pale skin, blond hair, blue eyes ↑ risk of sunburns ↑ risk of skincancer
Ocular albinism: •
Rare variant, blue eyes only
Alkaptonuria
Tyrosine Breakdown
Ochronosis •
Fumarate Homogentisic Acid
•
•
Oxidase Tyrosine Homogentisic Acid (HGA)
Deficiency of homogentisic acid oxidase Autosomal recessive ↑ homogentisic homogentisic acid
•
Polymerization dark pigment
•
Pigment deposited in connective tissue (ochronosis)
Acetoacetate
*Tyrosine (and phenylalanine) ketogenic and glucogenic
Alkaptonuria
Alkaptonuria
Ochronosis
Ochronosis
•
Classic finding: dark urine when left standing •
•
•
•
Diagnosis
•
Treatment:
polymerization
•
Arthritis(large Arthritis (large joints: knees, hips) •
•
Fresh urine normal
Severe arthritis may be crippling
•
Black pigment in cartilage, joints ClassicX-ray finding:calcification calcificationintervertebraldiscs
•
Urine discoloration in infancy
•
Other symptoms later in life (20-30 years)
87
Elevated HGA in urine/plasma Dietary restriction (tyrosine and phenylalanine)
Catecholamine Breakdown •
Monoamines: Dopamine, norepinephrine, epinephrine
•
Degradation via two enzymes:
•
•
•
•
Monamine oxidase (MAO): (MAO) : Amine COOH
•
Catechol-O-methyltransferase Catechol-O-methyltra nsferase (COMT): (COMT) : Methyl to oxygen
Tyrosine Hormones
COMT MAO
Epi, Norepi Vanillylmandelic acid (VMA) Dopamine Homovanillic acid (HVA) HVA and VMA excreted in urine
COMT Dopamine
Tyrosine Hormones Norepinephrine
•
Normetanephrine •
MAO
MAO Dihydroxymandelic Acid
Homovanillic Acid (HVA)
Pheochromocytoma •
COMT
MAO
COMT
Vanillylmandelic acid (VMA)
•
Tumor generating catecholamines Majority of metabolism is intratumoral Metanephrines often measured for diagnosis •
Metanephrine and normetanephrine normetanephrine
•
24hour urine collection
Older test: 24 hour collection of VMA
MAO MAO Epinephrine
COMT
Metanephrine
Pharmacology
Tyramine Tyramine
•
•
Parkinson's •
Selegiline: MAO-b inhibitor inhibitor
•
Entacapone, tolcapone: COMT inhibitors
•
↑ dopamine levels
•
Naturally occurring substance
•
Sympathomimetic (causes sympathetic activation)
•
•
Depression •
•
MAO inhibitors (Tranylcypromine, Phenelzine)
↑ dopamine, NE, serotonin levels
Normally metabolized GI tract Patients on MAOi tyramine in blood
•
Hypertensive Hypertensive crisis
•
“Cheeseeffect” “Cheese effect” •
Cheese, red wine, some meats
Dopamine
88
Amino Acids •
•
•
•
•
Other Amino Acids
•
•
Jason Ryan, MD, MPH
•
Tryptophan
Tryptophan Niacin, serotonin, melatonin Histidine Histamine Glycine Heme Arginine Creatine, urea, nitric oxide Glutamate GABA Branched chain amino acids (Maple syrup urine) Homocysteine (homocystinuria) Cysteine (cystinuria)
Tryptophan Tryptophan Hydroxylase
5-Hydroxytryptophan
BH4 Tryptophan
Dihydropteridine Reductase
NAD+
Carcinoid Syndrome Caused by GI tumors that secrete serotonin
•
Altered tryptophan metabolism
•
•
Normally ~1% tryptophan
•
Up to 70% in patients patients with carcinoid syndrome
•
Tryptophan deficiency deficiency (pellagra) reported
BH2
Tryptophan
Serotonin 5-hydroxytryptamine (5-HT)
•
5-Hydroxytryptophan
NADH
Serotonin Breakdown •
Metabolism viamonoamine via monoamine oxidase •
serotonin
•
•
Same enzyme: dopamine/epinephrine/norepinephrine
MAO inhibitors used in depression (↑serotonin) ↑ Urinary 5-HIAA in carcinoid syndrome
Serotonin effects •
Diarrhea (serotonin stimulates GI motility)
•
↑ fibroblast growth and fibrogenesis fibrogenesis valvular lesions
•
Flushing (other mediators also) also)
Monoamine Oxidase (MAO)
Serotonin 5-hydroxytytamine (5-HT)
89
5-hydroxyindole acetaldehyde (5-HT)
5-Hydroxyindoleacetic acid (5-HIAA)
Tryptophan
Tryptophan Vitamin B6 NADH
NADPH
Tryptophan Tryptophan
Serotonin 5-hydroxytytamine (5-HT)
Niacin Melatonin
Hartnup Disease •
•
•
•
Hartnup Disease
Absence of AA transporter in proximal tubule Autosomal recessive Loss of tryptophan in urine
•
Symptomsfrom niacindeficiency niacin deficiency
•
Histidine
Pellagra •
Hyperpigmented rash
•
Exposed areas of skin
•
Red tongue (glossitis)
•
Diarrhea and vomiting
•
CNS: dementia, encephalopathy encephalopathy
•
“Dermatitis, diarrhea, dementia”
Treatment: •
High protein diet
•
Niacin
Glycine Vitamin B6
•
•
Important amino acid for heme synthesis All carbon and nitrogen from glycineor glycine or succinyl CoA
Histidine Decarboxylase
Histidine
CO2
Histamine
Heme
90
Porphyrin Ring
Arginine
Glutamate
Creatine (muscle)
Vitamin B6
Glutamate Decarboxylase
Arginine Glutamate
Urea (urea cycle)
Excitatory Neurotransmitter
Nitric Oxide Synthase
Gamma-aminobutyric acid GABA
Inhibitory Neurotransmitter
Arginine + NADPH Citrulline + Nitric Oxide + NADP+
Branched Chain Amino Amino Acids
Branched Chain Amino Amino Acids Decarboxylation
•
Essential amino acids
•
Primarily metabolized by muscle cells
•
Metabolism depends on α-ketoacid dehydrogenase •
Transamination
Valine
Succinyl-CoA
Isoleucine
Succinyl-CoA Acetyl-CoA
Leucine
Acetyl-CoA Acetoacetate
Branched-chain α-ketoacid dehydrogenase complex (BCKDC)
•
Similar to pyruvate dehydrogenase complex
•
E1, E2, E3 subunits
•
Cofactors: Thiamine, lipoic acid
Valine
Leucine
α-ketoacid dehydrogenase
Isoleucine
Maple Syrup Urine Disease •
•
•
•
•
•
Dehydrogenation
Maple Syrup Urine Disease
Deficiency of α-ketoacid dehydrogenase
•
Autosomal recessive Five phenotypes Classic MSUD most common (E1, E2, E3 deficiency)
•
•
•
↑ branched chain AA’s and α-ketoacids in plasma α-ketoacid of isoleucine gives urine sweet smell
•
•
91
Neurotoxicity is main problem MSUD Primarily due to accumulation of leucine: leucine : “leucinosis” Classic MSUD occurs in 1 st few days of life Lethargy and irritability Apnea, seizures Signs of cerebral edema
Maple Syrup Urine Disease •
•
Homocysteine
Diagnosis:
•
•
Elevated branched chain amino acid levels in plasma
•
Valine, leucine, isoleucine
•
•
Treatment:
Cysteine: non-essential •
•
Dietary restriction of branched-chain amino acids acids
•
Monitoring plasma amino acid concentrations
•
Homocysteine, Homocysteine , cysteine, cysteine , andmethionine and methionine related Methionine: essential
•
•
Thiamine supplementation
Synthesized from methionine
Homocysteine: non-standard Transsulfuration pathway •
Methionine homocysteine
Methionine Valine
Leucine
cysteine
Cysteine
Homocysteine
Isoleucine
Homocysteine
Homocysteine Methyl (CH3)
Methionine
ATP
Adenosine
S-Adenosylmethionine SAM
Homocysteine SAM
Homocysteine Cystathionine
Succinyl CoA
α-ketobutyrate
Homocysteine N5-methyl Tetrahydrofolate
Tetrahydrofolate
Serine
Folate
B12 MethionineSynthase
Cystathionine Synthase (B6) Methionine
SAM
Homocysteine
Cystathionine
Cystathionine Synthase (B6)
Cysteine Homocysteine
92
Cysteine
Homocysteine Levels
Homocystinuria
•
Normal: 5-15 micromoles/liter
•
Severe hyperhomocyste inemia: >100micromoles/lit er
•
Mild-moderate Mild-moderate elevations:
•
Defects in homocysteine metabolism enzymes
•
Autosomal recessive disorders
•
Can be caused caused by vitamin deficiencies: B12/folate, B6
•
May be associated with ↑ risk CV disease
•
No data on lowering levels levels to lower risk
Homocystinuria •
Homocystinuria
Common symptoms (mechanisms unclear) •
Lens dislocation
•
Long limbs, chest chest deformities
•
Osteoporosis in childhood childhood
•
Mental retardation
•
Blood clots
•
Early atherosclerosis (stroke, MI)
Homocysteine Elevations •
Classic homocystinuria:
•
Dietary treatment:
•
Cystathionine β synthase (CBS) deficiency
•
Avoid methionine
•
Increase cysteine (now essential) essential)
•
Vitamin B6 supplementation supplementation (some patients “B6 responders”)
Homocysteine
Less common causes •
•
Methionine synthase deficiency Defective metabolism folate/B12 MTHFR gene mutations
Methylene tetrahydrofolate reductase (MTHFR) N5-methyl Tetrahydrofolate
Tetrahydrofolate
Folate
•
B12 MethionineSynthase
Methionine
SAM
Homocysteine
Cystathionine
Cystathionine Synthase (B6)
93
Cysteine
Cystinuria •
•
•
•
•
Cystine: Two cysteine molecules linked together Cystinuria:autosomalrecessive disorder
↓ reabsorption cystine by proximal tubule of nephron Main problem: kidney stones Prevention: methionine free diet
Cystine
94
Amino Acid Breakdown •
•
•
Ammonia
No storage form of amino acids Unused amino acids broken down Amino group removed NH3 + α-keto acid
R
Jason Ryan, MD, MPH
•
•
NH4+
Amino Acid Breakdown
Toxic to body Transferred to liver in a non-toxic structure Converted by liver to urea (non-toxic) for excretion
•
•
Usual 1st step: removal of nitrogen by transamination Amino group passed to glutamate
R
Amino acid
Glutamate
R
O
H3N - C - C
Aminotransferases
•
O
α-keto acid
O=C - C O-
•
O-
Aminotransferases
Transfer nitrogen from amino acids to glutamate All require vitamin B6 as cofactor Two used as liver function tests: •
Alanine aminotransferase (ALT)
•
Aspartate aminotransferase (AST)
O
O=C - C O-
α-ketoglutarate
•
+
O-
Ammonia •
R
O
H3 N - C - C
α-ketoglutarate
Glutamate
AST
Aspartate
95
Oxaloacetate
Glutamate •
•
•
Glutamine
Two methods for transfer of nitrogen from glutamate to liver for excretion in urea cycle
•
•
#1: Glutamine synthesis #2: Alanine cycle
•
Non-toxic Transfers nitrogen to liver for excretion Glutamine synthetase found in most tissues
Glutamate
Liver
Glutamine Glutamine Synthetase
NH4 +
Glutamine •
Alanine Cycle
In liver, glutamine converted back to glutamate
•
•
NH 4+
Glutamate
Urea Cycle
Used by muscles to transfer nitrogen to liver Glutamate nitrogen alanine Alanine
Glutamate
Glutamate Dehydrogenase
NH4+
ALT
Glutaminase
α-ketoglutarate Glutamine
α-ketoglutarate
Pyruvate
Alanine Cycle •
•
Alanine Cycle
Alanine to liver pyruvate Nitrogen transferred back to glutamate
•
NH 4+
Glutamate
Alanine
Glutamate
Nitrogen removed from glutamate
Glutamate Dehydrogenase
ALT
α-ketoglutarate
α-ketoglutarate
Pyruvate
96
Urea Cycle
Alanine Cycle
Mitochondrial Disorders
Muscle
Liver
Pyruvate
Alanine
Alanine
Often deficient metabolism of pyruvate
Ammonia
•
Carbon dioxide
•
Aspartate
Pyruvate carboxylase deficiency
•
Pyruvate dehydrogenase deficiency
Elevatedalanine Elevatedalanineand and lactate
Glucose
Urea Cycle
Ammonia (NH4+) Urea Excretion in urine Urea synthesized from: •
•
Pyruvate
Urea Cycle •
•
•
Glutamate
α-KG
α-KG Glucose
•
Inborn errors of metabolism
NH4+
NH 4+ Glutamate
•
•
•
NH 4+
First reaction (and 2nd) in mitochondria Rate limiting step
NH
+
4
CarbamoylPhosphate Synthetase I
CO2 CO2 2 ATP
Urea
2 ADP
Carbamoyl Phosphate
Aspartate
N-acetylglutamate •
•
•
•
•
•
Pyrimidine Synthesis
Allosteric activator
•
Carbamoyl phosphate synthetase II
Carbamoyl Phosphate Synthetase I Enzyme will not function without this cofactor Synthesized from glutamate and acetyl CoA
↑ protein (fed state) ↑ N-acetylglutamate Used to regulate urea cycle
ATP
Glutamine
ADP
CO2 Carbamoyl phosphate synthetase II
97
Carbamoyl Phosphate
Urea Cycle •
Urea Cycle
Second reaction also in mitochondria Ornithine Transcarbamylase
NH4+ Carbamoyl Phosphate Synthetase I
Carbamoyl Phosphate
Ornithine Carbamoyl Phosphate Transcarbamylase
Citrulline
CO2 Mitochondria
+
Cytosol Ornithine
Citrulline Ornithine
Urea Cycle
Citrulline
Aspartate ATP
Carbamoyl Phosphate
•
Citrulline
Ornithine
•
Non-standard amino acid - not encoded by genome Incorporated into proteins via post-translational modification
•
More incorporation in inflammation
•
Anti-citrulline antibodies used in rheumatoid arthritis
Argininosuccinate
•
Anti-cyclic citrullinated peptide antibodies (anti-CCP)
•
Up to 80% of patients with RA
Urea Arginine Fumarate
Hyperammonemia
Hyperammonemia •
•
Symptoms
Results from any disruption urea cycle •
Commonly seen in advanced advanced liver disease
•
Rare cause: urea cycle disorders
•
•
•
↑ ammonia can deplete α-ketoglutarate (TCA cycle)
•
•
NH4 +
Citrulline
Glutamine Synthase
Glutamate Dehydrogenase
Glutamine
Glutamate NH4 +
α-ketoglutarate
98
Main effect onCNS on CNS Can lead to cerebral edema Tremor (asterixis) Memory impairment Slurredspeech
•
Vomiting
•
Can progress to coma
Hyperammonemia
Hyperammonemia
Treatment
Treatment: Enzyme deficiencies only
•
•
STEAK
Low protein diet Lactulose
•
Ammonium Detoxicants •
Sodium phenylbutyrate (oral)
•
Synthetic disaccharide (laxative) (laxative)
•
Sodium phenylacetate-sodium phenylacetate-sodium benzoate (IV)
•
Colon breakdown by bacteria bacteria to fatty acids
•
Conjugate with glutamine
Lowers colonic pH; favors formation of NH 4+ over NH3 NH4+ not absorbed trapped in colon
•
Excreted in the urine
•
•
•
•
Result: ↓plasma ammonia concentrations
removal of nitrogen/ammonia
Arginine supplementation •
Urea cycle disorders make arginine essential
OTC Deficiency
OTC Deficiency
Ornithine transcarbamylase deficiency
Ornithine transcarbamylase deficiency
•
•
•
•
•
Most common urea cycle disorder
•
X linked recessive ↑ carbamoyl phosphate ↑ ammonia
•
•
↑ orotic acid (derived from carbamoyl phosphate)
•
CMP Carbamoyl Phosphate
Glutamine
Orotic Acid
•
Presents in infancy or childhood •
Depends on severity of defect
•
If severe, occurs after first several feedings (protein)
Symptoms from hyperammonemia Somnolence, poor feeding Seizures Vomiting, lethargy,coma
UMP TMP
PyrimidineSynthesis
UMP Synthase Bifunctional
OTC Deficiency
Citrullinemia
Ornithine transcarbamylase deficiency •
confuse with orotic aciduria Don’t confuse •
Disorder of pyrimidine synthesis synthesis
•
Also has orotic aciduria
•
OTC only: ↑ ammonia levels (urea cycle dysfunction)
•
Ammonia
•
•
•
•
encephalopathy encephalopathy (child with lethargy, coma)
99
Deficiency of argininosuccinate synthase Elevated citrulline Low arginine Hyperammonemia
Other Urea Cycle Disorders •
•
•
•
Deficiencies of each enzyme described All autosomal recessive except OTC deficiency All cause hyperammonemia Build-up of urea cycle intermediates
100
B Vitamins •
8 Vitamins: B1, B2, B3, B5, B6, B7, B9, B12
•
All watersoluble water soluble
•
B Vitamins
•
Contrast with non-B vitamins
•
Most fat soluble (except (except C)
Most wash out quickly if deficient in diet •
Deficiency in weeks to months
•
Exception is B12: stored in liver (mainly), also muscles
Jason Ryan, MD, MPH
Thiamine
B Vitamins •
•
•
Vitamin B1
Used in many different metabolic pathways pathways Deficiencies: greatest effect on rapidly growing tissues Common symptoms •
Dermatitis (skin)
•
Glossitis (swelling/redness (swelling/redness of tongue)
•
Diarrhea (GI tract)
•
Cheilitis (skin breakdown at corners of lips)
•
Converted to thiamine pyrophosphate (TPP)
•
Co-factor for four enzymes •
Pyruvate dehydrogenase
•
dehydrogenase (TCA cycle) α-ketoglutarate dehydrogenase
•
acids) α-ketoacid dehydrogenase (branched chain amino acids)
•
Transketolase (HMP shunt) shunt)
Thiamine
ATP
AMP Thiamine pyrophosphate pyrophosphate
Pyruvate Dehydrogenase Complex
Pyruvate Pyruvate
•
Complex of 3 enzymes (E1, E2, E3)
•
Requires 5 co-factors
•
Pyruvate Dehydrogenase Complex
•
Acetyl-Coa
Pyruvate dehydrogenase (E1) Thiamine (B1)
•
FAD+ (B2)
•
NAD+ (B3)
•
Coenzyme A (B5)
•
Lipoic acid
E1 E3 E2
TCA Cycle
101
α-KG Dehydrogenase •
Branched Chain Amino Amino Acids
TCA cycle
•
•
Metabolism depends on α-ketoacid dehydrogenase Deficiency: Maple Syrup Urine Disease
α-ketoglutarate CoA
α-KG Dehydrogenase CO2 NADH
Succinyl-CoA
Valine
Transketolase •
Transfers a carbon unit to create F-6-phosphate
•
Wernicke-Korsakoff syndrome •
Isoleucine
Thiamine Deficiency
HMP Shunt
•
Leucine
•
Beriberi •
Underdeveloped areas
Abnormal transketolase may predispose
•
Dry type: polyneuritis, muscle weakness
Affected individuals may have abnormal binding to thiamine
•
Wet type: type: tachycardia, high-output heart failure, failure, edema
•
NADPH
•
Glucose Ribulose-5 Phosphate
Wernicke-Korsakoff syndrome
Glucose-6-phosphate
Alcoholics (malnourished, poor absorption vitamins)
•
Confusion, confabulation
•
Ataxia
•
Ophthalmoplegia (blurry vision)
Ribose-5 Phos Phos hate hate
Transketolase
Fructose-6-phosphate
Riboflavin
Thiamine and Glucose •
•
•
Vitamin B2
Malnourished patients: ↓glucose↓thiamine ↓glucose↓thiamine
•
If glucose given first unable to metabolize Case reports of worsening Wernicke-Korsakoff
•
•
•
Added to adenosine FAD+ Accepts 2 electrons FADH2 FAD+required bydehydrogenases by dehydrogenases Electrontransportchain
Riboflavin
102
Flavin Adenine Dinucleotide
Electron Transport
Riboflavin
Complex I
Deficiency
•
•
TransferselectronsNADH Coenzyme Q Key intermediates: Flavin mononucleotide (FMN)
•
•
•
e-
e-
NADH
FMN
e-
FeS
•
•
•
•
Inflammation of lips
•
Cracks in skin at corners of mouth
vascularization (rare) Corneal vascularization
Tryptophan
Vitamin B3 Used NADH, NADPH
Cheilitis
CoQ
Niacin •
Deficiency very rare Dermatitis, glossitis
Niacin
Used in electron transport NAD+requiredbydehydrogenases by dehydrogenases
•
Niacin: can be synthesized from tryptophan
•
Conversion requires vitamin B6 B6 NADH
NADPH
Tryptophan Niacin Nicotinamide Adenine Dinucleotide
Niacin
Niacin
Vitamin B3
Vitamin B3
•
Grains, milk, meats, liver
•
Deficiency: Pellagra
•
Not found incorn in corn
•
Four D’s
•
Corn-based diets deficiency
•
•
Dermatitis
•
Diarrhea
•
Dementia
•
Death
Skin findings •
103
Sun-exposed areas
•
Initially like bad sunburn
•
Blisters, scaling
•
Dorsal surfaces of the hands
•
Face, neck, arms, and feet
Niacin Deficiency •
Hartnup Disease
INH therapy(tuberculosis) therapy (tuberculosis) •
INH ↓B6 activity
•
↓B6 activity ↓Niacin (from tryptophan)
•
Hartnup disease
•
Carcinoid syndrome
•
•
•
•
Niacin
Carcinoid Syndrome •
•
Vitamin B3
Caused by GI tumors that secrete serotonin •
•
Diarrhea, flushing, cardiac cardiac valve disease
•
Also used to treat hyperlipidemia Direct effects on lipolysis (unrelated NAD/NADP)
Altered tryptophan metabolism
•
Normally ~1% tryptophan
•
Up to 70% in patients patients with carcinoid syndrome
serotonin
•
Tryptophan deficiency deficiency (pellagra) reported
Pantothenic Acid
Niacin Excess •
Absence of AA transporter in proximal tubule Autosomal recessive Loss of tryptophan in urine Symptomsfrom niacindeficiency niacin deficiency
Vitamin B5
Facial flushing •
Seen with niacin tr eatment for hyperlipidemia
•
Stimulates release of prostaglandins in skin
•
Face turns red, warm
•
Can blunt with aspirin (inhibits prostaglandin) prior to Niacin
•
Fades with time
•
•
Used in coenzyme A CoA required by dehydrogenases/other dehydrogenases /other enzymes
Pantothenic Acid
Acetyl-CoA
104
Coenzyme A
Pantothenic Acid
β-oxidation •
Vitamin B5
Step #1: Convert fatty acid to fatty acyl CoA
•
•
ATP Fatty Acid
ADP
CoA
R—C—OH O
•
•
Fatty acyl CoA Long Chain Fatty Acyl CoA synthetase
•
•
GI symptoms: Nausea, vomiting, cramps Numbness, paresthesias (“burningfeet ”) ”) Necrosis of adrenal glands seen in animal studies
R—C—CoA O
Pyridoxal phosphate phosphate
Vitamin B6 •
Widely distributed in foods Deficiency very rare
Vitamin B6
Three compounds
PyridoxalPhosphate
•
Pyridoxine (plants)
•
Pyridoxal, pyridoxamine (animals)
•
Co-factor in many different reactions
•
Aminotransferas e reactions (amino (aminoacids) acids) α-ketoglutarate
All converted to pyridoxal phosphate
Glutamate
AST
Pyridoxamine
Pyridoxal
Aspartate
Pyridoxine
Pyridoxal phosphate
Oxaloacetate
Cystathionine
Neurotransmitters
Dopamine Methionine Norepinephrine
B6
SAM
Homocysteine
Cystathionine
Cystathionine Synthase (B6)
Epinephrine Serotonin GABA
105
Cysteine
Pyridoxal phosphate
Pyridoxal phosphate
Histamine Synthesis
Glycogen Breakdown Glucose-6
Vitamin B6
PhosphataseGlucose-6-phosphate
Glycolysis
B6 Glucose-1-phosphate
Histidine Decarboxylase
UDP-Glucose
Histidine
CO2
Glycogen phosphorylase
Histamine Unbranched Glycogen (α1,4) Debranching Enzyme
Branched Glycogen (α1,6)
Pyridoxal phosphate phosphate
Pyridoxal phosphate
Niacin Synthesis
Heme Synthesis
•
•
•
Niacin can be synthesized from tryptophan
•
Requires B6 B6 deficiency Niacin deficiency
•
•
NADH
Required for synthesis γ-aminolevulinic acid (ALA) Necessary to synthesize heme Deficiency can result in sideroblastic anemia •
Iron cannot be incorporated incorporated into heme
•
Iron accumulates in RBC cytoplasm
Succinyl-CoA
NADPH
Tryptophan
ALA
Heme
Niacin Glycine
Isoniazid
Oral Contraceptives Contraceptives
INH •
•
•
•
•
Tuberculosis drug Similar to B6 structure Forms inactive pyridoxalphosphate Result: relative B6 deficiency
•
•
•
Must supplement B6 when takin INH
Pyridoxal
INH
106
Increase vitamin B6 requirements Mechanism unclear Deficiency Deficiency symptoms very rare
Vitamin B6 Deficiency
Vitamin B6 Toxicity
•
Very rare
•
Only B-vitamin with potential toxicity
•
CNS symptoms
•
Occurs with massive intake
•
Sensory neuropathy
•
•
Seizures
•
Confusion
•
Neuropathy
•
Glossitis, oral ulcers
Biotin
•
Pain/numbness in legs
•
Sometimes difficulty walking walking
Gluconeogenesis
Vitamin B7 •
Usually supplementation supplementation (not dietary)
Cofactor for carboxylationenzymes carboxylationenzymes •
All add 1-carbon group via CO2
•
Pyruvate carboxylase
•
Acetyl-CoA carboxylase
•
Propionyl-CoA carboxylase
ATP CO2
Pyruvate Pyruvate Carboxylase ABC Enzymes Enzymes ATP Biotin CO2
Fatty Acid Synthesis •
Oxaloacetate (OAA)
Biotin
Odd Chain Fatty Acids
Acetyl-CoA converted to malonyl-CoA
•
Propionyl-CoA Succinyl-CoA TCA cycle ATP CO2
Propionyl-CoA Carboxylase (Biotin)
ATP CO2 Biotin
Methylmalonyl-CoA
Propionyl-CoA
Malonyl-CoA
Acetyl-CoA
S-CoA
S-CoA
Acetyl-CoA Carboxylase
Amino Acids Valine Methionine Isoleucine Threonine
107
Odd Chain Fatty Acids
Succinyl-CoA
Biotin
B Vitamins: Absorption
Vitamin B7 •
Deficiency •
Very rare (vitamin widely distributed)
•
Massive consumption raw egg whites (avidin)
•
Dermatitis, glossitis, loss of appetite, appetite, nausea
108
•
All absorbed from diet in small intestine
•
Most injejunum in jejunum
•
Exception is B12: terminal ileum
Folate (B9) and Vitamin B12 •
•
Folate and Vitamin B12
•
Both used in synthesis of thymidine (DNA) Both used in metabolism of homocysteine Deficiency of either vitamin: •
↓ DNA synthesis (megaloblastic anemia)
•
↑ homocysteine
Jason Ryan, MD, MPH
Homocysteine
Thymidine-MP
S-Adenosyl Methionine
Thymidine
SAM Thymidylate Synthase
dUridine-MP
•
Cofactor that donates methyl groups
•
Synthesized fr om ATPand methionine
Thymidine-MP
Methionine DHF
N5, N10 T etrahydrofolate etrahydrofolate
Folate ATP
N5 Methyl THF
B12
Dihydrofolate Reductase
THF
SAM
Methionine
Homocysteine
S-Adenosyl Methionine
Methionine Regeneration Regeneration
SAM
Vitamin B12
Folate
CH3
N5-methyl etrahydrofolate
Tetrahydrofolate Adenosine B12
MethionineSynthase
ATP SAM
B12/Folate
Homocysteine Methionine
Methionine
109
SAM
Homocysteine
Thymidine
Megaloblastic Anemia •
Thymidylate Synthase
•
•
dUridine-MP
Thymidine-MP
•
Anemia (↓Hct) Large RBCs (↑MCV) Hypersegmented neutrophils Commonly caused by defective DNA production •
DHF
N5, N10 Tetrahydrofolate
N5 Methyl THF
B12
Homocysteine
THF
Folate
Folate deficiency
•
B12
•
Orotic aciduria
•
Drugs (MTX, 5-FU, hydroxyurea)
•
Zidovudine (HIV NRTIs)
Dihydrofolate Reductase
Methionine
Folate Compounds
Folate Compounds
Folate Tetrahydrofolate
Dihydrofolate
N5, N10 Tetrahydrofolate
Tetrahydrofolate
Folate •
Absorbed in the jejunum
•
Increased requirements in pregnancy/lactation •
Increased cell division more metabolic demand
•
Lack of folate neural tube defects
Folate Deficiency •
110
Commonly seen in alcoholics •
Decreased intake
•
Poor absorption
Cobalamin
Folate Deficiency •
Vitamin B12
Poor absorption/utilization certain drugs •
Phenytoin
•
Trimethoprim
•
Methotrexate
•
•
Plasma
Trimethoprim Methotrexate
B12 Neuropathy
Vitamin B12
•
One major role unique from folate Odd chain fatty acid metabolism
•
•
•
Conversion to succinyl CoA
•
Deficiency: ↑levels methylmalonic acid
•
Probably contributes to peripheral neuropathy
•
•
Found i n meats meats
Phenytoin
Cobalamin •
Only synthesized by bacteria
•
Folate
Dihydrofolate Reductase
THF
•
GI Tract
Folate
DHF
Large, complex structure (corrin ring) Contains element cobalt
•
•
Myelin synthesis affected in B12 deficiency Peripheral neuropathy not seen in folate deficiency
Subacute combined degeneration (SCD) Involvesdorsal Involvesdorsalspinalcolumns Defective myelinformation myelin formation (unclear mechanism) Bilateral symptoms
•
Legs >> arms
•
Paresthesias
•
•
•
Ataxia Loss of vibration and position sense Can progress: severe weakness, paraplegia
Odd Chain Fatty Acids
Odd Chain Fatty Acids
Vitamin B12
Vitamin B12
Methylmalonyl-CoA
Methylmalonyl-CoA mutase
↑MMA: hallmark of B12 Deficiency Not seen in folate deficiency deficiency
Succinyl-CoA
B12 S-CoA
S-CoA
Methylmalonic Acid Isomers Biotin
Propionyl-CoA
Methylmalonyl-CoA
Methylmalonyl-CoA mutase
Succinyl-CoA
B12 TCA Cycle
Amino Acids Isoleucine Valine Threonine Methionine
S-CoA
Odd Chain Fatty Acids Cholesterol
111
S-CoA
Cobalamin
Pernicious Anemia
Vitamin B12 •
•
Liver stores years worth of vitamin B12 Deficiency from poor diet very rare
•
•
Autoimmune destruction of gastric parietal cells
•
Loss of secretion of intrinsicfactor
•
IF necessary for B12 absorption terminal ileum
B12/Cobalamin
Pernicious Anemia •
•
Other deficiency causes
Chronic inflammation of gastric body More common among women Complex immunology
•
Ileum resection/dysfunction
•
Loss of intrinsic factor from stomach
•
Diphyllobothrium latum
•
•
Crohn’s disease Gastric bypass
•
Antibodies against parietal cells
•
Antibodies against intrinsic factor
•
Type II hypersensitivity features
•
Helminth (tapeworm)
•
Also autoreactive CD4 T-cells
•
Transmission from eating infected fish
•
Consumes B12
•
Associatedwith HLA-DR antigens
•
Associated withgastric with gastric adenocarcinoma
B12 Deficiency
B12 Deficiency
Diagnosis
Treatment
•
•
•
•
Low serum B12
•
High serum methylmalonic acid Antibodies to intrinsic factor (pernicious anemia) Schilling test •
Classic diagnostic test for pernicious anemia
•
Oral radiolabeled B12
•
IM B12 to saturate liver r eceptors
•
Normal result: Radiolabeled Radiolabeled B12 detectable to urine
•
Can repeat with oral IF
•
•
112
Liquid injection available Often given SQ/IM Should see increase in reticulocytes
Non-B Vitamins •
•
Vitamins A, C, D, E, and K Most fat soluble •
Only exception is C
•
Contrast with B vitamins: All water soluble
Other Vitamins Jason Ryan, MD, MPH Vitamin A Vitamin D
Fat Soluble Vitamin
Fat Malabsorption
Absorption •
•
•
•
•
Formmicelles Form micellesin in jejunum •
Clusters of lipids
•
Hydrophobic gr oups inside
•
Hydrophilic groups outside
•
Leads to deficiencies of fat-soluble vitamins
•
Abnormal bile or pancreatic secretion
•
•
Absorbed by enterocytes
•
Packaged into chylomicrons Secretedinto lymph Carried to liver as chylomicron remnants
Vitamin A •
•
Retinol = Vitamin A Retinoids
Loss of A, D, E, and K
Disease or resection of intestine Key Causes •
Cystic fibrosis (lack of pancreatic enzymes)
•
Celiac sprue
•
Crohn’s disease
•
Primary biliary cirrhosis
•
Primary sclerosing cholangitis
Beta Carotene Vitamin A
•
Family of structures
•
Derived from vitamin A
•
Important for vision, vision, growth, epithelial tissues
•
Key retinoids: r etinal, retinoic acid acid
•
•
•
•
113
Pro-vitamin A (a carotenoid) Major source of vitamin A in diet Cleaved into retinal Antioxidant Antioxidant properties •
Similar to vitamin C, vitamin E
•
Protects against free radical damage
•
May reduce ri sk of cancers cancers and other diseases
Retinal •
•
•
Retinoic Acid
Found in visual pigments Rods, cones in retina
•
•
Rhodopsin = light-sensitive protein receptor •
Generates nerve impulses based on light
•
Contains retinal
Binds with receptors in nucleus
•
•
•
•
Limit/control keratin production
•
Retinoic acid (or similar) used in treatment of psoriasis
•
Deficiency: dry skin
Important example:mucous example: mucous •
•
Dietary sources
Limit/control mucous production production epithelial cells
Vitamin A
Vitamin A •
Acts like a hormone
Regulates/controls protein synthesis Important example:keratin example: keratin
Deficiency Vitamin A
•
Visualsymptoms
•
Found in liver
•
Night blindness (often first sign)
•
Dark green and yellow vegetables
•
Xerophthalmia (keratinization of cornea
•
Many people under-consume under-consume vitamin A
•
Stored in liver (years to develop deficiency)
Keratinization •
•
Skin: thickened, dry skin
Growth failure in children
Vitamin A
Vitamin A
Therapy
Therapy
•
•
Measles
•
blindness)
AML – M3 subtype (acute promyelocytic leukemia)
•
Mechanism not clear clear
•
All-trans-retinoic acid (ATRA/tretinoin) (ATRA/tretinoin)
•
Used in resource-limited countries
•
Synthetic derivative of retinoic acid
•
Induces malignant cells to complete complete differentiation
•
Become non-dividing mature granulocytes/macrophage granulocytes/macrophagess
Skin disorders •
Psoriasis
•
Acne
114
Vitamin A
Isotretinoin
Excess
Accutane
•
•
•
•
Hypervitaminosis A Usually from chronic, excessive supplements
•
•
Dry, itchy skin Enlarged liver
Vitamin C •
•
•
•
Highly teratogenic
•
OCP and/or pregnancy test prior to Rx
Iron Absorption
Ascorbic Acid •
Only water-solubl e non-B vitamin
•
Antioxidant Antioxidant properties
Found in fruits and vegetables Three key roles: •
•
Absorption of iron
•
Collagen synthesis
•
Dopamine synthesis •
Collagen Synthesis •
•
•
•
13-cis-retinoic acid Effectivefor acne
Heme iron •
Found in meats
•
Easily absorbed
Non-heme iron •
Absorbed in Fe2+ state
•
Aided by vitamin C
•
Important for vegans
Vitamin C Fe3+
Heme
Fe2+
Methemoglobinemia •
Fe3+ iron in heme
•
Rx: Vitamin C
Duodenal Epithelial Cell
Tyrosine Metabolism
Post-translational modification of collagen Hydroxylationofspecific proline and lysine residues Occurs in endoplasmic reticulum Deficiency ↓ collagen scurvy
Vitamin C
Dopamine Β-hydroxylase Dopamine Proline Fe2+
Fe3+
Hydroxyproline
Vitamin C
115
Norepinephrine
Scurvy •
•
•
•
•
Vitamin C deficiency syndrome Defective collagensynthesis collagen synthesis Sore gums, loose teeth Fragile blood vessels easy bruising
•
•
•
•
Nausea, vomiting, diarrhea
•
Iron overload
Common on long sea voyages voyages Sailors ate limes to prevent scurvy (“Limey”)
•
Predisposed patients
•
Frequent transfusions, hemochromatosis hemochromatosis
Kidney stones •
Calcium oxalate stones
•
Vitamin C can be metabolized metabolized into oxalate
Seen with “tea and toast ” diet (no fruits/vegetables)
Vitamin D
Smoking •
•
•
Historicaldisorder •
•
Vitamin C Excess
Increased vitamin C requirements Likely due to antioxidant properties Deficient levels common
•
Vitamin D2 is ergocalcifero l •
•
•
Vitamin D Activation
Found in plants
Vitamin D3 is cholecalciferol cholecalciferol •
Scurvy or definite symptoms rare
D3
Found in fortified milk
Two sou rces D3: •
Diet
•
Sunlight (skin synthesizes D3)
D2
Vitamin D Activation 25carbon
•
Vitamin D3 from sun/food inert •
•
•
•
No biologic activity
•
Must be hydroxylated to become active Step 1: 25 hydroxylation
•
Occurs in liver
•
Step 2: 1 hydroxylation
•
•
Constant activity
•
Occurs in kidney
•
Regulated by PTH
1 carbon
116
Liver: Converts to 25-OH Vitamin D (calcidiol) Kidney: Converts to 1,25-OH2 Vitamin D (calcitriol (calcitriol)) 1,25-OH2 Vitamin D = active form
Vitamin D Activation •
•
Vitamin D and the Kidney
25-OH Vitamin D = storage form •
Constantly produced produced by liver
•
Available for activation by kidney as needed
•
•
Proximal tubule converts vitamin D to active form Can occur independent of kidney in sarcoidosis •
Leads to hypercalcemia
Serum [25-OH VitD] best indicator vitamin D status •
Long half-life
•
Liver production not regulated regulated
PTH + 1α - hydroxylase 1,25-OH Vitamin D 2 25-OH Vitamin D
Vitamin D Function •
•
Vitamin D Deficiency
GI: ↑Ca2+and P043-absorption
•
Poor GI absorption Ca2+and P043-
•
Major mechanism of clinical effects
•
Hypophosphatemia
•
Raises Ca, increases bone mineralization
•
Hypocalcemia (tetany,seizures )
Bone: ↑Ca2+ and P043- resorption
•
Bone: poor mineralization
•
Process of demineralizing bones
•
Adults: Osteomalacia
•
Paradoxical effect
•
Children: Rickets
•
Occurs at abnormally high levels
Suda T et al. Bone effects of vitamin D - Discrepancies between in vivo and in vitro studies Arch Biochem Biophys. 2012 Jul 1;523(1):22-9
Osteomalacia
Rickets
• Children and adults • Occurs in areas of bone turnover
•
•
Bone remodeling constantly occurring
•
Osteoclasts clear bone
•
Osteoblasts lay down new bone (“osteoid”)
•
↓ Vitamin D = ↓mineralization of newly formed bone
Deficient mineralization of growth plate
•
Growth plate processes
Bone pain/tenderness pain/tenderness
•
Fractures
•
Chondrocytes hypertrophy/proliferate
•
Vascularinvasion mineralization
•
↓ Vitamin D:
•
Clinical features
•
• Clinical features •
Only occurs in children
•
• PTH levels very high bone density • CXR: Reduced bone
117
Growth plate thickens without mineralization
•
Bone pain
•
Distal forearm/knee most affected (rapid growth)
•
Delayed closure fontanelles
•
Bowing of femur/tibia (classic X-ray finding)
Vitamin D
Vitamin D in Renal Failure
Sources
Sick Kidneys
•
Natural sources: •
↑Phosphate
↓1,25-OH2 Vitamin D •
•
↓Ca from plasma
Oily fish (salmon)
•
Liver
•
Egg yolk
Most milk fortified with vitamin D Rickets largely eliminated due to fortification
↓Ca from gut
Hypocalcemia
↑PTH
Vitamin D
Vitamin D
Breast Feeding
Excess
•
Breast milk low in vitamin D •
•
•
•
•
Even if mother has sufficient levels
Lower in women with dark skin Most infants get little sun exposure Exclusively breast fed infants supplementation
•
•
•
Hypervitaminosis D •
Massive consumption calcitriol supplements
•
Sarcoidosis
•
Granulomatous macrophages macrophages express 1α-hydroxylase
Hypercalcemia, hypercalciuria Kidney stones Confusion
Vitamin E
Vitamin E
Tocopherol
Tocopherol
•
Antioxidant
•
Key role in protecting RBCs from oxidative damage
•
118
Deficiency Deficiency very rare •
Hemolytic anemia
•
Muscle weakness
•
Ataxia
•
Loss of proprioception/vibration
Vitamin E •
•
Vitamin K
Least toxic of fat soluble vitamins Very high dosages reported to inhibit vitamin K •
•
•
Warfarin users may see INR rise
•
Vitamin K •
Vitamin K
Forms γ-carboxyglutamate (Gla) residues
Glutamate Residue
Vitamin K
N—CH2—C CH2
O
CH2
γ carbon
Activates clotting factors in liver Vitamin K dependent factors: II, VII, IX, X, C, S Post-translational Post-translational modification modificationby by vitamin K
•
γ-carboxyglutamate (Gla) Residue
•
Found in green, leafy vegetables (K1 form) •
Cabbage, kale, spinach spinach
•
Also egg yolk, liver
Also synthesized by GI bacteria (K2 form)
N—CH2—C
+
CH2
γ carboxylation carboxylation
-OOC
COO-
O
CH2 COO-
CO2 Activated Clotting Clotting Factor
Precursor
Warfarin
Vitamin K Deficiency
Vitamin KAntagonist Epoxide Reductase
-
Warfarin
•
•
Reduced Vitamin K
Oxidized Vitamin K N—CH2—C
N—CH2—C
CH2
CH2 O
O
CH2
CH2
-OOC
COOPrecursor
•
COO-
CO2 Activated Clotting Clotting Factor
119
Results in bleeding(“coagulopathy”) Deficiency of vitamin K-dependent factors Key lab findings: •
Elevated PT/INR
•
Can see elevated elevated PTT (less sensitive)
•
Normal bleeding time
•
Dietary deficiency rare
•
GI bacteria produce sufficient quantities
Vitamin K Deficiency
Zinc
Causes •
•
•
Warfarin therapy (deficient action) Antibiotics Antibiotics
•
•
Cofactor for many (100+) enzymes
•
Deficiency in children
•
Decrease GI bacteria bacteria
•
Poor growth
•
May alter warfarin dose requirement
•
Impaired sexualdevelopment
Newborn babies
•
Sterile GI tract at birth
•
Poor wound healing
•
Insufficient vitamin K in breast milk
•
Loss of taste (required by taste buds) buds)
•
Risk of neonatal hemorrhage
•
Immune dysfunction (required for cytokine production)
•
Babies given IM vitamin K at birth
•
Dermatitis: red skin, pustules (patients on TPN)
Acrodermatitis enteropathica
Found in meat, chicken Absorbed mostly in duodenum (similar to iron) Risk factors for deficiency •
Alcoholism (low zinc associated associated with cirrhosis)
•
Chronic renal disease disease
•
Malabsorption
•
•
•
•
•
Zinc fingers •
Protein segments that contain zinc •
•
•
•
Deficiency in children/adul ts
•
Zinc •
•
“Domain,” “Motif”
Found in proteins that bind proteins, RNA, DNA Often bind specific DNA sequences Influence/modify genes and gene activity
120
Rare, autosomal recessive disease Zinc absorption impaired Mutations in gene for zinc transportation Dermatitis •
Hyperpigmented (often red) skin
•
Classically perioral and perianal perianal
•
Also in arms/legs
Other symptoms •
Loss of hair, diarrhea, poor growth
•
Immune dysfunction (recurrent infections)
Lipids •
•
•
Mostly carbon and hydrogen Not soluble in water Many types: •
Lipid Metabolism Jason Ryan, MD, MPH
Lipids
Fatty acids
•
Triacylglycerol (triglycerides)
•
Cholesterol
•
Phospholipids
•
Steroids
•
Glycolipids
Lipids Glycerol
Fatty Acid
Triglyceride
Cholesterol
Lipoproteins Particles of lipids and proteins •
•
•
•
•
Chylomicrons
Low
High
Density
Very low-density lipoprotein (VLDL) Intermediate-density lipoprotein(IDL) Low density lipoproteins (LDL) VLDL
High-density lipoprotein (HDL) Large
HDL
Small Size
121
LDL
Apolipoproteins •
•
•
Absorption of Fatty Acids
Proteins that bind lipids Found in lipoproteins Various functions: •
Surface receptors
•
Co-factors for enzymes enzymes
Absorption of Cholesterol •
Cholesteryl esters formed in enterocytes
•
Acyl-CoAcholesterolacyltransferase( ACA ACAT T)
•
•
•
Fatty acids Triglycerides
•
Packaged into chylomicronsby chylomicronsby intestinal cells
•
To lymph blood stream
Cholesteryl Esters Fatty Acid
Packaged into chylomicrons by intestinal cells To lymph blood stream Cholesterol Enterocyte
ACAT
Chylomicrons
Free Cholesterol
Cholesteryl esters
Cholesteryl Ester
Lipoprotein Lipase
Apolipoprotein B48 •
•
•
LPL
Found only on chylomicrons
•
Contains 48% of apo-B protein Required forsecretion for secretion from enterocytes
•
•
Extracellularenzyme Extracellularenzyme Anchored to capillarywalls Mostly found in adipose tissue, muscle, and heart •
•
•
•
122
Not in liver liver has hepatic lipase
Converts triglycerides triglycerides fatty acids (and glycerol) Fatty acids used for storage (adipose) (adipose) or fuel Requiresapo Requires apo C-II for activation
Other Apolipoproteins Apolipoproteins
Chylomicrons Adipocytes
•
•
•
C-II
Liver
•
Co-factor for lipoprotein lipase
•
Carried by: Chylomicrons, VLDL/IDL Fatty Acids
Apo E •
Binds to liver receptors
•
Required for uptake of remnants
Chylomicron Remnants
Lipoprotein Lipase
Both fromHDL from HDL Fatty Acids
Skeletal Muscle
Chylomicrons
Chylomicron Remnants •
•
•
•
Summary
Apo-E receptors on liver Takeup remnants via recept or-mediated endocyt osis Usually only present after meals (clear 1-5hrs)
•
•
•
Milky appearance
•
Secreted from enterocytes with Apo48 Pick up Apo C-II and ApoE from HDL Carry triglycerides and cholesteryl esters Deliver triglycerides to cells •
•
Return to liver as chylomicron remnants •
Cholesterol Synthesis •
•
Acetoacetyl-CoA HMG-CoA Synthase HMG-CoA HMG-CoA Reductase
3-hydroxy-3-methylglutaryl-coe 3-hydroxy-3-methylglutaryl-coenzyme nzyme A
ApoE receptors on liver
Lipid Transport
Only the liver can synthesize cholesterol Acetyl-CoA
Lipoprotein lipase stimulates (C-II co-factor) breakdown
Mevalonate
Cholesterol Mevalonate
123
Liver secretes two main lipoproteins: •
VLDL
•
HDL
HDL •
•
•
HDL
Scavenger lipoprotein
•
Lecithin-cholesterol acyl transferase (LCAT (LCAT))
•
Brings cholesterol back to liver
•
Esterifies cholesterol in HDL; packs esters densely in core
•
“Reverse transport”
•
Activated by A-I by A-I
Secreted as small “nascent” HDL particle Key apolipoproteins: A-I, C-II, ApoE
•
Cholesteryl ester transfer protein (CETP (CETP))
•
Carries cholesterol back to liver
•
Exchanges esters (HDL) for triglycerides (VLDL)
A-I
C-II
A-I
TG
HDL HDL
Apo E
CE
VLDL •
•
•
VLDL
Transport lipoprotein
•
Secreted by liver (nascent VLDL) Carriestriglycerides,cholesteroltotissues
•
•
B100
B100
Changes during circulation #1: LPL removes triglycerides triglycerides #2: CETP in HDL removes triglycerides from VLDL
C-II
B100
VLDL
VLDL
Apo E
HDL
VLDL
IDL •
•
TG C
C
C-II
C-II
B100 LPL CETP
TG Apo E
•
VLDL /LDL
CETP
TG IDL
Hepatic Lipase
Formed from VLDL Hepatic lipase removes triglycerides HDL removes C-II and ApoE B100
•
•
•
•
B100 TG HL
C
C-II IDL
Apo E
TG TG
Apo E C-II
LDL
HDL
124
Found inliver in liver capillaries Similar function to LPL (releases fatty acids) Very important for IDL LDL conversion Absence HL absence IDL/LDL conversion
Apo E
LDL •
•
•
Small amount of triglycerides High concentration of cholesterol/cholesteryl esters Transfers cholesterol cholesterol to cells with LDL receptor •
•
Foam Cells •
Macrophages filled with cholesterol
•
Foundin atherosclerotic atheroscleroticplaques
•
Contain LDL receptors and LDL
Receptor-mediated endocytosis
LDL receptors recognize B100
B100 TG
LDL
Lipoprotein Composition
Summary C-II B-100
VLDL
LPL CETP
C-II
B-100
IDL Apo E
Apo E
FFA
HL LDL B-100
C-II
Apo E
HDL A-I
Lipoprotein(a)
Abetalipoproteinemia
Lp(a) •
•
•
•
•
Modified form of LDL Contains large glycoprotei n apolipoprot ein(a) Elevated levels risk factor for cardiovascular disease Not routinely measured
•
Autosomalrecessivedisorder
•
Defect in MTP
•
MTP forms/secretes lipoproteins with apo-B
•
No proven therapy for high levels
125
Microsomal triglyceride transfer transfer protein
•
Chylomicrons from intestine (B48)
•
VLDL from liver (B100)
Abetalipoproteinemia
Abetalipoproteinemia
Clinical Features
Lab Findings
•
Presents in infancy •
•
•
•
Steatorrhea
•
Abdominal distension
•
Failure to thrive
•
•
•
Fat-soluble vitamin deficiencies •
Especially vitamin E (ataxia, (ataxia, weakness, hemolysis)
•
Vitamin A (poor vision)
Low or zero VLDL/ILD/LDL Very low triglyceride and total cholesterol levels Low vitamin E levels Acanthocytosis •
Lipid accumulation in enterocytes on biopsy
126
Abnormal RBC membrane lipids
Lipid Measurements Measurements •
•
•
•
Total Cholesterol LDL-C HDL-C TG
Hyperlipidemia
Friedewald Formula
Jason Ryan, MD, MPH
LDL-C = Total Chol – HDL-C - TG 5
Secondary Hyperlipidemia
Hyperlipidemia •
•
•
Elevated total cholesterol, LDL, or triglycerides Risk factor for coronary disease and stroke Modifiable – often related to lifestyle factors •
Sedentary lifestyle
•
Saturated and trans-fatty acid foods
•
Lack of fiber
Signs of Hyperlipidemia •
•
•
Signs of Hyperlipidemia
Most patients have no signs/symptoms
•
Physical findings occur in patients with severe ↑lipids Usually familial syndrome •
•
127
Xanthomas •
Plaques of lipid-laden histiocytes
•
Appear as skin bumps or on eyelids
Tendinous Xanthoma •
Lipid deposits in tendons
•
Common in Achilles Achilles
Cornealarcus •
Lipid deposit in cornea
•
Seen on fundoscopy
Pancreatitis •
•
•
Familial Dyslipidemias
Elevatedtriglycerides(>1000) acute pancreatitis
•
Exact mechanism unclear May involve increased chylomicronsin chylomicronsin plasma •
Chylomicrons usually formed after meals and cleared
•
Always present when triglycerides > 1000mg/dL
•
May obstruct capillaries ischemia
•
Vessel damage can can expose triglycerides to pancreatic lipases
•
Triglycerides breakdown free fatty acids
•
Acid tissue injury pancreatitis
•
•
•
Familial Dyslipidemias •
•
•
•
•
•
Familial Dyslipidemias
Type I – Hyperchylomicronemia SevereLPL dysfunction •
•
Type II - Familial Hypercholesterolemia •
Autosomal dominant
LPL deficient
•
Few or zero LDL receptors
LPL co-factor deficient (apolipoprotein C-II)
•
Very high LDL (>300 heterozygote; >700 homozygote)
•
Tendon xanthomas, corneal corneal arcus
•
Severe atherosclerosis (can have MI in 20s)
Recurrent pancreatitis Enlarged liver, xanthomas Treatment: Very low fat diet •
Reports of normal lifespan
•
No apparent ↑risk atherosclerosis
ApoE and Alzheimer’s
Familial Dyslipidemias •
Type I – Hyperchylomicronemia Autosomal recessive ↑↑↑TG (>1000; milky plasma appearance) ↑↑↑ chylomicrons
Type III – Familial Dysbetalipoproteinemia •
Apo-E2 subtype of Apo-E
•
Poorly cleared by liver
•
Accumulation of chylomicron remnants andVLDL (collectively know as β-lipoproteins) Usually mild (TC>300 mg/dl)
•
Xanthomas
•
Premature coronary disease
•
ApoE4 •
Elevated total cholesterol cholesterol and triglycerides
•
ApoE2 •
•
•
•
128
Decreased risk of Alzheimer’s Increased risk of Alzheimer’s
Familial Dyslipidemias •
Type IVHypertriglyceridemia IV Hypertriglyceridemia •
Autosomal dominant
•
VLDL overproduction or impaired catabolism catabolism
•
↑TG (200-500)
•
↑VLDL
•
Associated with diabetes type II
•
Often diagnosed on routine screening bloodwork
•
Increased coronary risk/premature coronary disease disease
129
The “Cholesterol Panel” “Lipid Panel” •
Total Cholesterol
•
LDL-C
•
•
HDL-C TG
Lipid Drugs
Friedewald Formula
Jason Ryan, MD, MPH
LDL = Total Chol – HDL - TG 5
LDL Cholesterol •
•
•
•
•
HDL Cholesterol
“Bad” cholesterol Associated with CV risk <100 mg/dl very good >200 mg/dl high Evidence that treating high levels reduces risk
•
•
•
•
Trigylcerides •
•
•
•
“Good”c holesterol Inversely associated with risk <45mg/dl low Little evidence that raising low levels reduces risk
Pancreatitis
Normal TG level <150mg/dl
•
Levels > 1000 can cause pancreatitis Elevated TG levels modestly associated with CAD Little evidence that lowering high levels reduces risk
•
•
130
Elevatedtriglycerides acute pancreatitis Exact mechanism unclear May involve increased chylomicronsin chylomicronsin plasma •
Chylomicrons usually formed after meals and cleared
•
Always present when triglycerides > 1000mg/dL
•
May obstruct capillaries ischemia
•
Vessel damage can can expose triglycerides to pancreatic lipases
•
Triglycerides breakdown free fatty acids
•
Acid tissue injury pancreatitis
Guidelines
Treating Hyperlipidemia •
•
•
•
Lipid Drug Therapy
Usually treat elevated LDL-C with statins
•
Rarely treat elevated TG or low HDL-C Secondary prevention •
Patients with coronary or vascular disease
•
Strong evidence that lipid lowering lowering drugs benefit
•
Primary prevention •
Not all patients benefit the same
•
Benefit depends on risk of CV disease
•
Treating TG or HDL •
•
•
Old Cholesterol Guidelines set LDL-C goal •
Diabetes or CAD: Goal LDL <100
•
2 or more risk factors: Goal LDL <130
•
0 or 1 risk factor: Goal LDL <160
New guidelines require risk calculator •
Treat patients if risk above limit (usually 5%/year)
•
No LDL goal
Statins 1st line majority of hyperlipidemia patients
Treating TG or HDL HDL
Rarely treat for TG or HDL alone Many LDL drugs improve TG/HDL Few data showing a benefit of treatment
•
•
Triglycerides •
>500
•
High Non-HDL cholesterol cholesterol (TC – HDL)
Low HDL •
Statins
Lipid Lowering Drugs •
•
•
•
•
•
Patients with established CAD
Lovastatin, Atorvastatin, Simvastatin
Statins Niacin Fibrates Absorption blockers
•
•
•
•
Bile acid resins Omega-3 fatty acids
•
•
•
Diet/exercise/weight loss = GREAT way to reduce cholesterol levels and CV risk
•
3-hydroxy-3-methylglutaryl-coenz 3-hydroxy-3-methylglutaryl-coenzyme yme A HMG-CoA
Act on liver liver synthesis HMG-CoA reductase inhibitors ↓cholesterol synthesis in liver ↑LDL receptors in liver Major effect: ↓ LDL decrease Some ↓TG,↑HDL ↓TG,↑HDL Excellent outcomes data (↓MI/Death) ↑LFTs
HMG-CoA Reductase
Mevalonate
131
Statin Muscle Problems •
•
•
•
•
Statin Muscle Problems
Many muscle symptoms associated with statins
•
Mechanism poorly understood Low levels of coenzymeQ coenzyme Q in muscles Many patients take CoQ 10 supplements
•
Hydrophilicstatins Pravastatin, fluvastatin, rosuvastatin
•
May cause l ess myalgias
•
•
Myositis
•
Rhabdomyolysis
•
•
Like myalgias, increased CK
•
Weakness, muscle pain, dark urine
•
CKs in 1000s
•
Acute renal failure death
•
↑risk with some drugs (cyclosporine, gemfibrozil)
Statins metabolized by liver P450 system Interactions with other drugs Inhibitorsincrease ↑ risk LFTs/myalgias •
i.e. grapefruit juice
Atorvastatin, Atorvastatin, simvastatin, simvastatin, lovastatin
Niacin •
Normal CK levels
•
•
Lipophilic statins •
Weakness, soreness
•
P450
Statins
•
•
•
Theoretical benefit for muscle aches on statins
Hydrophilic Hydrophilic vs. Lipophilic •
Myalgias
Niacin
Complex, incompletely understood mechanism Overall effect: LDL ↓↓ HDL ↑↑ Often used when HDL is low
↓FA mobilization
↓TG
132
↓VLDL
↓HDL breakdown
↓LDL
↑HDL
Niacin •
Niacin
Major side effects is flushing
•
Hyperglycemia
•
Stimulates release of prostaglandins i n skin
•
Insulin resistance (mechanism incompletely understood) understood)
•
Face turns red, warm
•
Avoid in diabetes
•
Can blunt with aspirin (inhibits prostaglandin) prior to Niacin
•
Fades with time
•
Hyperuricemia
Fibrates
Fibrates
Gemfibrozil, clofibrate, bezafibrate, fenofibrate
Gemfibrozil, clofibrate, bezafibrate, fenofibrate
•
Activate PPAR-a
•
Side effects
•
Modifies gene transcription
•
Myositis (Rhabdo with gemfibrozil; caution with statins)
•
↑ activity lipoprotein lipase
•
↑LFTs
•
↑ liver fatty acid oxidation
•
Cholesterol gallstones
↓ VLDL
•
Major overall effect TG breakdown
•
Used for patients with very high triglycerides
Absorption blockers
Absorption blockers
Ezetimibe
Ezetimibe
•
•
•
Blocks cholesterol absorption
•
Works at intestinal brush border Blocksdietary cholesterolabsorption cholesterolabsorption •
Highly selective for cholesterol
•
Does not affect affect fat-soluble vitamins, triglycerides
•
•
•
•
•
133
Result: ↑LDL receptors on liver Modest reduction LDL Some ↓TG,↑HDL ↓TG,↑HDL Weak data on hard outcomes (MI, death) ↑LFTs Diarrhea
Bile Acid Resins
Omega-3 Fatty Acids
Cholestyramine, colestipol, colesevelam •
•
Old drugs; rarely used Prevent intestinal reabsorption bile •
•
•
•
•
•
•
Cholesterol bile GI tract
reabsorption
Resins lead to more bile excretion in stool Liver converts cholesterol bile to makeup losses Modest lowering LDL Miserable for patients: Bloating, bad taste Can’t absorb absorb certain fat soluble vitamins Cholesterol gallstones
eicosapentaenoic acid (EPA)
docosahexaenoic docosahexaenoic acid (DHA)
Wikipedia/Public Domain
PCSK9 Inhibitors
Omega-3 Fatty Acids •
•
•
•
•
•
•
•
Alirocumab, Evolocumab
Found in fish oil Consumption associated with ↓CV events Incorporated into cell membranes
•
•
PCSK9 degradation of LDL receptors
•
Lowers triglycerides triglycerides (~25 to 30%) Modest ↑ HDL
•
Commercial supplements available (Lovaza) GI side effects: nausea, diarrhea, “fishy” taste
Alirocumab, Evolocumab
•
FDA approval in 2015
•
Reduce VLDL production
PCSK9 Inhibitors •
•
Given by subcutaneous injection Results in significant LDL reductions (>60%) Major adverse effect is injection site skin reaction Some association with memory problems
134
•
Binds to LDL receptor
•
LDL receptor transported to lysosome
Alirocumab/Evolocumab: Antibodies Inactivate PCSK9 •
↓ LDL-receptor degradation
•
↑ LDL receptors receptors on hepatocytes
•
↓ LDL cholesterol cholesterol in plasma
Lysosomes •
•
Lysosomal Storage Diseases
•
Membrane-bound organelles of cells Contain enzymes Breakdown numerous biological structures •
•
Proteins, nucleic acids, carbohydrates, lipids
Digest obsolete components of the cell
Jason Ryan, MD, MPH
Sphingolipids
Lysosomal Storage Diseases •
•
•
Absence of lysosomal enzyme Inability to breakdown complex molecules Accumulation disease
•
Most autosomal recessive
•
Most have no treatment or cure
•
•
Sphingosine: Sphingosine : long chain “aminoalcohol” “amino alcohol” Addition of fatty acid to NH2 = Ceramide
Sphingosine
Ceramide
Ceramide Trihexoside
Ceramide Derivatives •
•
•
•
Globotriaosylceramide (Gb3)
Modification of “head group” on ceramide Yields glycosphingolipids, glycosphingolipids,sulfatides,others Very important structures fornerve for nerve tissue Lack of breakdown accumulation liver, liver, spleen
•
•
•
Three sugar head group on ceramide Broken down by α-galactosidase A Fabry’s Disease •
Deficiency of α-galactosidase A
•
Accumulation of ceramide trihexoside
Head Group
Ceramide
Ceramide
135
Glucose
Galactose
Galactose
Fabry’s Disease •
X-linked recessive disease
•
Slowlyprogressivesymptoms
•
Fabry’s Disease •
Neuropathy
•
Skin:angiokeratomas Skin: angiokeratomas
•
Begins child earlyadulthood
•
Fabry’s Disease •
•
•
Small dark, red to purple raised spots
•
Dilated surface capillaries
Decreased sweat
Fabry’s Disease
Renal disease •
Classically pain in limbs, hands, feet
•
Proteinuria, renal failure
CNS problems •
TIA/Stroke (early age) age)
Cardiac disease •
Left ventricular hypertrophy
•
Heart failure
Fabry’s Disease •
Often misdiagnosed initially
•
Enzyme replacement therapy available •
Fabry’s Disease •
Recombinant Recombinant galactosidase
Classic case •
Child with pain in hands/feet
•
Lack of sweat sweat
•
Skin findings
Deficiency of α-galactosidase A Accumulation of ceramide trihexoside
136
Gaucher’s Disease
Glucocerebroside •
•
•
Glucose head group on ceramide Broken down byglucocerebrosidase by glucocerebrosidase Gaucher’s
•
•
disease
•
Deficiency of glucocerebrosidase glucocerebrosidase
•
Accumulation of glucocerebroside glucocerebroside
•
•
Gaucher’s Disease •
•
•
Bone Crises
Hepatosplenomegaly: •
•
Splenomegaly: Splenomegaly: most common initial sign
•
Bones •
Marrow: Anemia, thrombocytopenia, thrombocytopenia, rarely leukopenia
•
Often easy bruising from low platelets
•
Avascular necrosis of joints joints (joint collapse)
•
•
Severe bone pain Due to bone infarction (ischemia) Infiltration of Gaucher cells in intramedullary space Intense pain, often with fever (like sickle cell)
CNS (rare, neuropathic forms of disease) •
Gaze palsy
•
Dementia
•
Ataxia
Gaucher’s Disease •
Most common lysosomal storage disease Autosomal recessive More common among Ashkenazi among Ashkenazi Jewishpopulation Jewish population Lipids accumul ate in spleen, liver, bones
Gaucher’s Disease
Type I
•
Type II
•
Most common form
•
Presents in infancy with marked CNSsymptoms
•
Presents childhood to adult
•
Death <2yrs
•
Minimal CNS dysfunction
•
Hepatosplenomegaly, Hepatosplenomegaly, bruising, anemia, joint problems
•
Normal lifespan possible
•
Enzyme replacement therapy
•
Synthetic (recombinant DNA) glucocerebrosidase
•
Type III •
137
Childhood onset; onset; progressive dementia; dementia; shortened lifespan
Gaucher’s Disease •
Sphingomyelin
Classic case: •
Child of Ashkenazi Jewish descent
•
Splenomegaly on exam exam
•
Anemia
•
Bruising (lowplatelets)
•
Joint pain/fractures
•
Phosphate-nitrogen head group
•
Broken down by sphingomyelinase
•
Niemann-Pick disease
•
Deficiency of acid sphingomyelinase (ASM) •
Accumulation of sphingomyelin sphingomyelin
Deficiency of glucocerebrosidase Accumulation of glucocerebroside
Niemann-Pick Disease •
•
•
•
•
Niemann-Pick Disease
Autosomal recessive More common among Ashkenazi among AshkenaziJewishpopulation Jewish population Splenomegaly, Splenomegaly, neurol ogic deficits
•
Hepatosplenomegaly
•
Progressiv e neuroimpairment
•
Multiple subtypes of disease Presents in infancy to adulthood based on type
•
•
Cherry Red Spot •
2° thrombocytopenia
•
Weakness: will worsen over over time
•
Classic presentation: child that loses motor skills
Pathology •
Large macrophages with lipids
•
“Foam cells ”
•
Spleen, bone marrow
Severe forms: death <3-4yrs
Niemann-Pick Disease
Seen in many conditions:
•
Classic case:
•
Niemann-Pick
•
Previously well, healthy child
•
Tay-Sachs
•
Weakness, loss of motor skills
•
Central retinal artery artery occlusion
•
Enlarged liver or spleen on physical exam
•
Cherry red spot
Deficiency of sphingomyelinase Accumulation of sphingomyelin
138
Krabbe’s Disease
Galactocerebroside •
Galactose head group
•
Autosomal Recessive
•
Broken down bygalactocerebrosidase by galactocerebrosidase
•
Usually presents <6 months of age
•
•
Major component of myelin Krabbe’s Disease
•
•
•
Deficiency of galactocerebrosidase galactocerebrosidase
•
Developmental delay
•
Abnormal metabolism of galactocerebroside galactocerebroside
•
Eventually floppy limbs, loss of head head control
•
•
•
•
Globoid Cells •
•
Only neuro symptoms Progressive weakness
Globe-shaped cells
•
Often more than one nucleus
Often fever without infection Usually death <2 years
Gangliosides
Krabbe:globoidcell leukodystrophy leukodystrophy Globoid cells in neuronal tissue •
Absent reflexes Optic atrophy: vision loss
•
Contain head group with NANA
•
Names GM1, GM2, GM3 GM3
•
•
•
•
N-acetylneuraminic acid (also called sialic acid) G-ganglioside M= # of NANA’s (m=mono) 1,2,3= Sugar sequence NANA
Ceramide
Glucose
Galactose
Galactose
GM2
Tay-Sachs Disease •
Tay-Sachs Disease
Deficiency of hexosaminidase A •
Breaks down down GM2 ganglioside
•
Accumulation of GM2 ganglioside
•
More common among Ashkenazi among AshkenaziJewishpopulation Jewish population
•
Most common form presents 3-6 months of age
•
Progressive neurodegeneration •
•
Weakness
•
Exaggerated startle reaction reaction
•
Progresses to seizures, vision/hearing loss, paralysis
•
Usually death in childhood
Cherry red spot •
•
139
Slow development
•
No hepatosplenomegaly hepatosplenomegaly (contrast with Niemann-Pick)
Classic path finding: lysosomes with onion skinning
Tay-Sachs Disease •
Sulfatides
Classic presentation: •
3-6 month old infant
•
Ashkenazi Jewish descent descent
•
Developmental delay
•
Exaggerated startle response
•
Cherry Red spot
•
Galactocerebroside Galactocerebroside+ sulfuricacid
•
Major component of myelin
•
•
Broken down by arylsulfatase A Metachromatic leukodystrophy •
Deficiency of arylsulfatase A
•
Accumulation of sulfatides sulfatides
Deficiency of hexosaminidase A Accumulation of GM2 ganglioside
Metachromatic leukodystrophy
Sphingolipidoses Weakness
•
•
•
•
Autosomal recessive Childhood to adult onset based on subtype •
Most common type presents ~ 2 years of age
•
Contrast with Krabbe’s: present < 6 months
Hand/Feet Pain ↓ sweat Rash
Ataxia: Gait problems; falls Hypotonia: Speech problems
•
Dementia can develop
•
Most children do not survive childhood
Fabry’s
Spleen Anemia Fractures
Gaucher’s
Sphingosine Fatty Acids Ceramides
Glycosaminoglycans •
Also called mucopolysaccharides
•
Long polysaccharides
•
•
Baby Cherry Spot Ashkenazi No spleen
~ 2 years old Ataxia
Older child Liver/spleen Cherry Spot
Baby No Cherry Spot
Tay Sachs
Metachromatic Leukodystrophy
Krabbe’s Niemann Pick
Glycosaminoglycans
Repeating disaccharide units An amino sugar and an uronic acid
L-iduronate Heparan Sulfate L-iduronate
N-acetylglucosamine Dermatan Sulfate
Chondroitin Sulfate
140
Hurler’s and Hunter’s
Hurler’s Syndrome
•
Metabolic disorders
•
Autosomal recessive
•
Inability to breakdown heparan and dermatan
•
Deficiency of α-L-iduronidase
•
•
Diagnosis: mucopolysaccharides in urine Types of mucopolysaccharidosis •
Hurler’s: Type I
•
Hunter’s: Type II
•
Total of 7 types
•
•
•
•
•
•
Facial abnormalities (“coarse” features) Shortstature
•
Mental retardation
•
Hepatosplenomegaly
Hurler’s Syndrome
Dysostosis Multiplex •
Accumulation of heparan and dermatan sulfate Symptoms usually in 1st year of life
Radiographic findings in Hurler’s Enlarged skull Abnormal ribs, spine
•
Corneal clouding
•
Ear,sinus, pulmonar y infections
•
Airway obstruction and sleep apnea
•
•
•
•
•
Tracheal cartilage abnormalities
Inclusion Cell Disease
X-linked recessive
•
Deficiency of iduronate 2-sulfatase (IDS) Similar to Hurler’s except: •
Thick secretions
I-cell I-cell Disease
Hunter’s Syndrome •
Abnormal size arrangement of collagen fibers
Subtype ofmucolipidosis of mucolipidosis disorders •
•
Later onset (1-2years) (1-2years)
•
Combined features of sphingolipid and mucopolysaccharide mucopolysaccharide
Named for inclusions on light microscopy Similar to Hurler’s Onset in 1st year of life (some features present at birth)
•
No corneal clouding
•
•
Behavioral problems
•
Growth failure
•
Learning difficulty
•
Coarse facial features
•
Trouble sitting still (can mimic ADHD)
•
Hypotonia/Motor delay
•
Often aggressive behavior
•
Frequent respiratory infections
•
Clouded corneas
141
•
Joint abnormalities
•
Dysostosis multiplex
Pompe’s Disease
I-cell I-cell Disease Inclusion Cell Disease
Glycogen Storage Disease Type II Mannose-6-Phosphate
•
Lysosomal enzymes synthesized normally
•
Failure of processing in Golgiapparatus Golgi apparatus
•
•
Mannose-6-phosphate NOT added to lysosome proteins
•
M6P directs enzymes to lysosome
•
Result: enzymes secreted outside of cell Deficient intracellular enzyme levels (WBCs, fibroblasts)
•
Increased extracellular enzyme levels levels (plasma)
•
Multiple enzymes abnormal
•
Intracellular inclusions in lymphocytes lymphocytes and fibroblasts
Acid alpha-glucosidase alpha-glucosidasedeficiency
•
Accumulation of glycogen in lysosomes
•
•
•
Key findings: •
•
142
Also “lysosomal acid maltase”
Classic form presents in infancy Severe disease often death in infancy/childhood
