It refers to increased levels of lipids in the blood, including cholesterol and triglycerides.
Hyperlipidemia
It is defined as elevated levels of low-density lipoprotein (LDL) cholesterol and triacylglycerols and with low levels of high-density lipoprotein (HDL) cholesterol.
Causes: cigarette smoking, hypertension, obesity, and diabetes, lack of exercise and consumption of a diet containing excess saturated fatty acids.
Hyperlipidemias can also result from a single inherited gene defect in lipoprotein metabolism or, more commonly, from a combination of genetic and lifestyle factors. Anti-hyperlipidemic drugs must be taken. When therapy is terminated, plasma lipid levels return to pretreatment levels.
Pathophysiological factors:
Preventions: Quit smoking; maintain a healthy body weight, Increase physical activity.
Treatment:
3-Hydroxy-3-methylglutaryl (HMG) coenzyme A (COA) reductase inhibitors commonly known as statins, lower elevated levels LDL cholesterol, resulting in a substantial reduction in coronary events and death from CHD. This group of antihyperlipidemic agents inhibits the first committed enzymatic step of cholesterol synthesis, and they are the first-line and more effective treatment for patients with elevated LDL cholesterol. Therapeutic benefits include improvement of coronary endothelial function, plaque stabilization, inhibition of platelet thrombus formation, and anti-inflammatory activity. The value of lowering the level of cholesterol with statin drugs has been now demonstrated in 1) men with hyperlipidemia but no known CHD, p2) atients with CHD with or without hyperlipidemia, and 3) men and women with average total and LDL cholesterol levels and no known CHD.
Mechanism of action: Lovastatin, simvastatin, atorvastatin, pravastatin, fluvastatin, and rosuvastatin are analogs of HMG; it is the precursor of cholesterol. Simvastatin and Lovastatin are lactones that are hydrolyzed to the active drug. Fluvastatin and Pravastatin are active as such. Because of their strong affinity for the enzyme, all compete effectively to inhibit HMG CoA reductase, the rate-limiting step in cholesterol synthesis. By inhibiting de novo cholesterol synthesis, they deplete the intracellular supply of cholesterol. Atorvastatin and Rosuvastatin are the most potent LDL cholesterol lowering statin drugs, followed by simvastatin, pravastatin and then lovastatin and fluvastatin.
Therapeutic uses: All types of hyperlipidemias.
Pharmacokinetics: At the doses of 30 to 50 percent of lovastatin and simvastatin are absorbed orally. Pravastatin and fluvastatin are almost completely absorbed after oral administration; Similarly, Fluvastatin and pravastatin are active as such, whereas lovastatin and simvastatin must be hydrolyzed to their acid forms. Due to first-pass metabolism, the primary action of these drugs is on the liver. All are biotransformed. Excretion through feces and the bile, but some urinary elimination also occurs. Their half-lives range from 1.5 to 2 hours
Adverse effects: Myopathy and rhabdomyolysis, abnormalities in liver functioning,
Contraindications: These drugs are contraindicated in nursing mothers and during pregnancy. they should not be used in children or teenagers.
2. Nicotinic acid (Niacin): Niacin can reduce LDL levels by 10-20% and is the most effective agent for increasing HDL levels. Niacin can be used in combination with statins, and a fixed-dose combination of lovastatin and long-acting niacin is available.
Mechanism of action: Niacin strongly inhibits the lipolysis in adipose tissue at gram doses, the primary producer of circulating free fatty acids. The liver normally utilizes these circulating fatty acids as a major precursor for triacylglycerol synthesis. Thus, niacin causes a decrease in liver triacylglycerol synthesis, which is required for VLDL production. LDL (the cholesterol-rich lipoprotein) is derived from VLDL in the plasma. Therefore, a reduction in the VLDL concentration also results in a decreased plasma LDL concentration. Thus, both plasma triacylglycerol (in VLDL) and cholesterol (in VLDL and LDL) are lowered. Furthermore, niacin treatment increases HDL cholesterol levels. Moreover, by boosting secretion of tissue plasminogen activator and lowering the level of plasma fibrinogen, niacin can reverse some of the endothelial cell dysfunction contributing to thrombosis associated with atherosclerosis and hypercholesterolemia.
Therapeutic uses: Niacin lowers plasma levels of both cholesterol and triacylglycerol and used in the treatment of Hyperlipidemias and severe hypercholesterolemias.
Pharmacokinetics: Niacin, it’s a nicotinamide derivative, administered orally. It is converted in the body as a nicotinamide, which is incorporated into the cofactor nicotinamide-adenine dinucleotide (NAD+) and other metabolites are excreted in the urine.
Adverse effects: pruritus, intense cutaneous flush, nausea and abdominal pain, hyperuricemia and gout. Impaired glucose tolerance and hepatotoxicity.
Fibrates: Fenofibrate and gemfibrozil
Fenofibrate and gemfibrozil are derivatives of fibric acid that lower serum triacylglycerols and increase HDL levels. Both have the same mechanism of action. However, fenofibrate is more effective than gemfibrozil in lowering plasma LDL cholesterol and triglyceride levels.
Mechanism of action: The peroxisome proliferator activated receptors (PPARs) are members of the nuclear receptor supergene family that regulates lipid metabolism. PPARs functions as a ligand-activated transcription factor. Upon binding to its natural ligand (fatty acids or eicosanoids) or hypolipidemic drugs, PPARs are activated. They then bind to peroxisome proliferator response elements, which are localized in numerous gene promoters. In particular, PPARs regulates the expression of genes encoding for proteins involved in lipoprotein structure and function.
Therapeutic uses: Treatment of hyper-triacylglycerolemias, Fenofibrate and gemfibrozil are particularly useful in treating Type III hyperlipidemia.
Pharmacokinetics: Both drugs are completely absorbed after an oral dose. Gemfibrozil and fenofibrate widely distributed, bound to albumin, undergo extensive biotransformation and are excreted in the urine as their glucuronide conjugates.
Adverse effects: Lithiasis, mild gastrointestinal disturbances, Myositis, Myopathy and rhabdomyolysis.
Bile acid sequestrants: Bile acid sequestrants (resins) have significant LDL cholesterol lowering effects, although the benefits are less than those observed with statins.
Mechanism of action: Cholestyramine, colesevelam and colestipol, are anion-exchange resins that bind negatively charged bile acids and bile salts in the small intestine. The resin/bile acid complex is excreted in the feces, thus preventing the bile acids from returning to the liver by the enterohepatic circulation. Lowering the bile acid concentration causes hepatocytes to increase conversion of cholesterol to bile acids, resulting in a replenished supply of these compounds, which are essential components of the bile. Consequently, the intracellular cholesterol concentration decreases, which activate an increased hepatic uptake of cholesterol-containing LDL particles, leading to a fall in plasma LDL.The final outcome of this sequence of events is a decreased total plasma cholesterol concentration.
Therapeutic uses: The bile acid binding resins are the drugs of choice in treating Type IIa and Type IIb hyperlipidemias. Cholestyramine can also relieve pruritus caused by accumulation of bile acids in patients with biliary obstruction.
Pharmacokinetics: These drugs taken orally. Because they are insoluble in water and are very large molecular weights (greater than 106), they are neither absorbed nor metabolically altered by the intestine. Instead, they are totally excreted in the feces.
Adverse effects: Nausea, constipation, flatulence
Cholesterol absorption inhibitors:
Ezetimibe selectively inhibits intestinal absorption of dietary and biliary cholesterol in the small intestine, leading to a decrease in the delivery of intestinal cholesterol to the liver. This causes a reduction of hepatic cholesterol stores and an increase in clearance of cholesterol from the blood. Ezetimibe lowers LDL cholesterol by 17 percent and triacylglycerols by 6 percent, and it increases HDL cholesterol by 1.3 percent. Ezetimibe is primarily metabolized in the small intestine and liver via glucuronide conjugation (a Phase II reaction), with subsequent biliary and renal excretion. Both ezetimibe and ezetimibe-glucuronide are slowly eliminated from plasma, with a half-life of approximately 22 hours. Ezetimibe has no clinically meaningful effect on the plasma concentrations of the fat-soluble vitamins A, D, and E. Patients with moderate to severe hepatic insufficiency should not be treated with ezetimibe.
Combination drug therapy: It is often necessary to employ two antihyperlipidemic drugs to achieve treatment goals in plasma lipid levels. For example, in Type II hyperlipidemia, patients are commonly treated with a combination of niacin plus a bile acid binding agent, such as cholestyramine.
Cholestrol, statins
