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Hamid Boulares, Ph.D. Department of Pharmacology, LSUHSC, Tel: 568-2304 Lipid Lowering Agents.

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Presentation on theme: "Hamid Boulares, Ph.D. Department of Pharmacology, LSUHSC, Tel: 568-2304 Lipid Lowering Agents."— Presentation transcript:

1 Hamid Boulares, Ph.D. Department of Pharmacology, LSUHSC, Tel: Lipid Lowering Agents

2 LIPID TRANSPORT - Overview Chylomicrons: Chylomicrons: large lipoprotein particles that transport dietary lipids from the intestines to other locations in the body. They are one of the 5 major groups of lipoproteins (chylomicrons, VLDL, IDL, LDL, HDL) which enable fats and cholesterol to move within the water based solution of the blood stream. Chylomicron remnant: Chylomicron remnant: Once triglyceride stores are distributed, the chylomicron returns APOC2 (but keeps APOE) back to the HDL and thus becomes a chylomicron remnant. APOB48 and APOE are important to identify the chylomicron remnant in the liver for endocytosis and breakdown. IDL IDL: intermediate Density VLDL VLDL: Very low Density HDL HDL: High Density LCAT LCAT: Lecithin-Acetyl-CoA C-acyltransferase Atherosclerosis

3 Lipoproteins and Their Structure Surface Surface: monolayer of polar lipids, unesterified cholesterol and apolipoproteins Apolipoproteins Apolipoproteins: Add stability to structure; act as ligands for cell surface receptors or co-factors for enzymatic reactions Core Core: Cholesteryl esters (cholesterol esterified to fatty acid ), TG

4 Characteristics of Lipoproteins ApoE VLDL VLDL : endogenous triglycerides; catabolized by lipoprotein lipase (LPL), short half- life IDL IDL: cholesteryl esters, converted to LDL by hepatic lipase LDL LDL: apoB-mediated uptake by LDL receptor, long half-life HDL HDL: phospholipids cholesteryl esters, removed by hepatic scavenger receptor B secreted to bile, steroid synthesis, VLDL synthesis.

5 Plasma Lipoproteins: Classes & Functions Very Low Density Lipoprotein (VLDL ) Synthesized in liver Transport endogenous triglycerides to peripheral tissue 90% lipid, 10% protein Metabolized by LPL Apo B-100 Receptor binding Apo C-II LPL activator Apo E Remnant receptor binding

6 Plasma Lipoproteins: Classes & Functions Intermediate Density Lipoprotein (IDL) Synthesized from VLDL during VLDL degradation Triglyceride transport and precursor to LDL –Apo B-100 Receptor binding –Apo C-II LPL activator –Apo E Receptor binding

7 Plasma Lipoproteins: Classes & Functions Low Density Lipoprotein (LDL ) –Synthesized from IDL –Cholesterol transport –78% lipid, 58% cholesterol & CE –Apo B-100 Receptor binding

8 LDL receptor Characterized by Michael Brown and Joseph Goldstein (Nobel prize winners in 1985) Receptor also called B/E receptor because of its ability to recognize particles containing both Apo B and E Activity occurs mainly in the liver Receptor recognizes apo E more readily than apo B-100 FYI

9 Dyslipidemia and atherosclerosis Many clinical trials demonstrate that increase of LDL levels induce formation of atherosclerosis plaques. Gordon T et al. Am J Med 1977;62: Risk of CHD LDL-C (mg/dL) HDL-C (mg/dL) For any level of LDL-C, HDL-C is inversely related to CHD risk Slide source:

10 DiseaseLipid Profile PrevalenceEtiology Primary Hypercholesterolemia Familial Hypercholesterolemia  LDL 1:500 (+/-)  LDL Receptor Familial Defective ApoB100  LDL 1:100  ApoB100 binding to LDLR Polygenic Hypercholesterolemia  Chol Commonunknown Primary Hypertriglyceridemia Familial Hypertriglyceridemia  TG  HDL  VLDL Common  VLDL breakdown  VLDL synthesis Mixed Hyperlipidemia Familial Combined Hyperlipidemia  LDL  TG  HDL 1:100Unknown, dominant inheritance Disorders of HDL metabolism Polygenic low HDL  HDL CommonObesity, diabetes high carb diets Familial hypoalphalipoproteinemia  HDL 1:100Unknown, dominant inheritance Genetic Causes of Dyslipidemia

11 Hypertriglyceridemia Hypertriglyceridemia (VLDL) Diabetes, oral contraceptives (estrogen), hypothyroidism, hypopituitarism, high sugar diet and high alcohol intake ( increased production and decreased clearance of VLDL ). Hypercholesterolemia Hypercholesterolemia (LDL) High cholesterol (fat) diet, hypopitutarism and hypothyroidism (decreased LDL receptors). Secondary Hyperlipidemia

12 Classification of Lipoprotein Analysis Results (mg/dl) Total Cholesterol: <200 desirable borderline high >240 high LDL Cholesterol: <100 optimal near/above optimal borderline high high >190 very high HDL Cholesterol: <40 low >60 high Triglycerides: <150 normal high high >500 very high

13 Modes to reduce lipid levels Modes to reduce lipid levels: 1. Therapeutic lifestyle changes. - improved diet: reduce the intake of saturated fat to < 7% of calories. - reduce the cholesterol intake to < 200 mg/day. - weight reduction - increased physical activity 2. Medication.

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15 Cholestyramine and Colestipol and Colesevelam Lipid Lowering Drugs: Anion-Exchange Resins Sequester bile acids (BA) in the gut hence blocking enterohepatic cycling of BA Usually used in combination with a statin Major side effects – bitter taste, nausea constipation Important interactions – bind polar drugs such as warfarin, digoxin, thyroxine and statins: give 1 hr before resin

16 STATINS Increased LDL Uptake STATINS Mechanism of Action Mechanism of Action HMG CoA reductase

17 Lipid Lowering Drugs: STATINS 1.Fungal metabolites: Lovostatin ( MEVACOR), Simvastatin ( ZOCOR), Provastatin ( PRAVACHOL) 2. Synthetic derivatives Fluvastatin ( LESCOL), Atorvastatin (LIPITOR) and Rosuvastatin ( CRESTOR) but effective with once daily administration 3.They have short half-lives (~2 hours except atorvastatin at 14h) but effective with once daily administration slightly higher efficacy if given at night 4.All have slightly higher efficacy if given at night 5.All except pravastatin are metabolised through CYP enzymes in the liver which is the source of important drug-drug interactions (e.g. with warfarin) 6.Major side effects: 6.Major side effects: Hepatitis and myositis ( inflammation of the muscles)

18 Fatal Rhabdomyolysis with Statins The major adverse effect of clinical significance associated with statin use is myopathy Rhabdomyolysis; Breakdown of muscle proteins (myoglobin, creatine kinase) that leads to renal toxicity. Symptoms include muscle pain and weakness and dark urine due to muscle catabolism Reason for Cerivastatin (Baycol) withdrawal from the market (~20-fold greater risk compared to other statins ) Risk increased by combination with:Risk increased by combination with: –Fibrates especially for gemfibrozil/cerivastatin –Nicotinic acid –Protease Inhibitors (HAART therapy)-Highly Active AntiRetroviral Therapy

19 Pleiotropic effects of statins on the vasculature Clinical Science Clin. Sci. (2003) 105, Clinical Science Clin. Sci. (2003) 105,

20 Lipid Lowering Agents: Nicotinic Acid (Niacin)  hepatic VLDL synthesis by inhibiting adipose tissue lipolysis  VLDL clearance by  LPL activity Is the licensed agent with largest impact on HDL (30-50%  ) Lowers lipoproteins VLDL, IDL, LDL (by ~ 30%) Usually employed in combination with fibrate, resin or statin Major side effects  Flushing – prostaglandin mediated  Skin drying & GI intolerance  Exacerbates gout (  uric acid secretion), diabetes (promotes insulin resistance) and peptic ulcers

21 Lipid Lowering Drugs: Fibrates  Important interactions  increased risk of myopathy  in dose requirements (~30%) for warfarin- fibrates displace warfarin from albumin Act as PPAR  ligands- multiple changes  ApoA   HDL  LPL  FA uptake and oxidation in muscle cells  FA oxidation in hepatocytes and  TG synthesis Net Effects  VLDL (TG),  LDL and  HDL Absorbed efficiently (>90%) when given with a meal but not on an empty stomach Main side effects  GI intolerance  1-2%  in the incidence of gallstones due to  cholesterol synthesis Gemfibrozil and Fenofibrate

22 Novel inhibitor of intestinal cholesterol transporter - inhibits intestinal cholesterol uptake and transport by ~ 50% Metabolite has 400x the potency of parent compound and prolongs action by enterohepatic cycling No important adverse effects OR significant drug interactions Unlike resins does not raise TG - synergism with statins (e.g. ezetimibe/simvastatin, marketed as Vytorin and Inegy) NPCIL1: Niemann-Pick Cl-like channel 1 protein Lipid Lowering Drugs: EZETIMIBE

23 Progression of Drug Therapy in Primary Prevention If LDL goal not achieved, intensify LDL-lowering therapy If LDL goal not achieved, intensify drug therapy or refer to a lipid specialist Monitor response and adherence to therapy Start statin or bile acid resin or nicotinic acid Consider higher dose of statin or add a bile acid sequestrant or nicotinic acid 6 wks Q 4-6 mo If LDL goal achieved, treat other lipid risk factors Initiate LDL- lowering drug therapy

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