Biosynthesis and Metabolism of Cholesterol

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Biosynthesis and Metabolism of Cholesterol
HMG CoA reductase
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Biosynthesis and Metabolism of Cholesterol
liver
various tissues
Bile Acids (cholic acid, desoxy cholic acid, etc.)
Hormones (testosterone, progesterone cortisol,
estradiol, etc.)
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Anti-Hypercholesterolemic Agents
Overall Organization of the Topic

• What is arteriosclerosis?
• - Link between arteriosclerosis and cholesterol
• Lipoproteins particles
• - Structure and classification of lipoprotein
  particles
• Hyperlipidemias
• - Types and overall strategy to control
  hyperlipidemias
• Anti-hyperlipidemic Agents
• - Classes
• Statins
• Fibrates
• Bile Acid Sequestrants
• Nicotinic Acid
• Ezetimibe

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Arteriosclerosis
Arteriosclerosis is excessive formation and
deposition of endogeneous products from blood.
In 1984 a 1 drop in serum cholesterol was found
to reduce the risk to coronary heart disease
(CHD) by nearly 2.
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Lipoprotein Particles
Structure
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Lipoprotein Particles
Classification of lipoprotein particles
Composition Density Size

Chylomicrons TG gtgt C, CE Low Large
VLDL TG gt CE
IDL CE gt TG
LDL CE gtgt TG
HDL CE gt TG High Small
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Hyperlipidemia
Types of hyperlipidemias
I IIa IIb III IV V
Lipids
Cholesterol N- N- N- N-
Triglycerides N N-
Lipoproteins
Chylomicrons N N N N
VLDL N- N- N-
LDL N-
HDL N N N N-
N normal, increase decrease
slight increase slight decrease
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Strategy for Controlling Hyperlipidemia
STATINS
HMG CoA reductase
Ezetimibe
BILE ACID SEQUESTRANTS
FIBRATES
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Anti-hyperlipidemic Drugs - Statins

• Inhibit the rate limiting step in cholesterol
  biosynthesis (HMG CoA reductase)
• Lower total cholesterol and LDL
• Competitive inhibitors with affinity higher
  than the substrate (HMG CoA)
• Most used in Type IIa and IIb hyperlipidemias

trans-trans-trans
cis-trans-trans
cis-trans-cis
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Anti-hyperlipidemic Drugs - Statins
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Anti-hyperlipidemic Drugs - Statins
Rationale competitive binding
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Anti-hyperlipidemic Drugs - Statins
Pharmacokinetic properties of statins case of
cerivastatin
Bioavailabilty Dosage (mg) Protein Binding Metabolites
Atorvastatin 14 10 80 gt98 Active
Cerivastatin 60 0.2 0.3 gt99 Active
Fluvastatin 24 10 80 98 Active
Lovastatin 5 10 80 gt95
Pravastatin 17 10 40 50
Simvastatin 5 10 - 80 95
Typically all statins possess side effects. The
most dominant side effect, cited in the
withdrawal of cerivastatin, is rhabdomyolysis
(lysis of rhabdomyose) or weakening of skeletal
muscles.
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Anti-hyperlipidemic Drugs - Fibrates

• Older generation drugs introduced in 1981
• Second most useful anti-hyperlipidemic drugs
• Primarily decrease serum triglycerides
• Increase lipoprotein catabolism increase TG
  usage by the body
• Most used in Type III, IV and V hyperlipidemias

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Anti-hyperlipidemic Drugs Bile Acid Sequestrants

• Anion exchange resins
• Water insoluble and inert to digestive enzymes
• Not absorbed through the GI tract
• Positively charged nitrogens sequester bile
  acid re-absorption
• Lower serum LDL levels
• Most useful in type IIa and IIb hyperlipidemias

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Anti-hyperlipidemic Drugs Nicotinic Acid

• Administered in large doses (0.5 to 6 grams
  daily)
• Reduces triglycerides and total cholesterol
• Increases biliary secretion of cholesterol, but
  not bile acids
• Useful in Type IIa, IIb, III, IV and V
  hyperlipidemias

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Anti-hyperlipidemic Drugs Ezetimibe

• Approved in October 2002
• Reduces serum LDL, TC, and TG and increases HDL
• Prevents the absorption of cholesterol from
  diet
• Useful in Type IIa, IIb, III, IV and V
  hyperlipidemias