Antihyperlipidemic medications - Lipids are heterogeneous group of compounds. These are related to fatty acids. These are insoluble in water. However, these are soluble in ether and chloroform. These are of three types:
a. Simple lipids: These are esters of alcohol and fatty acids. The fatty acids, present in diet, may be:
• Saturated fatty acids such as lauric and palmitic acids.
• Monounsaturated fatty acids such as oleic acid and palmitoleic acids.
• Polyunsaturated fatty acids such as linolenic acid and arachidonic acid; abundant in corn oil and safflower oil; have hypolipidaemic effect.
b. Compound lipids antihyperlipidemic medications: These are also esters of alcohol and fatty acids but certain other groups are also present in their structure, e.g. sulfolipids and phospholipids.
c. Neutral lipids: These are non-polar lipids such as glycerides, cholesterol and cholesterol esters. Triglycerides are composed of three fatty acids which are linked to 3-atom containing alcohol or glycerol. Cholesterol is a lipid that chemically is a sterol but not a fat.
Antihyperlipidemic medications: Apoproteins (Apos) are the surface proteins of various lipoproteins. They provide structural stability to the lipoproteins and play an important role in determining the metabolic fate of the lipoproteins on which they reside. There are 9 types of Apos, viz. Apo-A-1, ApoA-il, Apo-A-IV, Apo-B-48, Apo-B-100, Apo-CI, Apo-C-II, Apo-C-III, and Apo-E.
Cholesterol is not used for energy. It serves as a structural component of all cell membranes, as a precursor for adrenal and gonadal steroids and as precursor of hepatic bile acids. In liver, it may be stored, oxidized to bile acids or alternatively incorporated into HDL or VLDL and resecreted as lipoproteincholesterol back into circulation.
Dietary cholesterol regulates endogenous hepatic cholesterol synthesis. In liver, the cholesterol is synthesized from mevalonic acid which is obtained from reduction of acetyl coenzyme-A by 3-hydroxy-3-methyglutaryl- coenzyme-A reductase (HMC-CoA reductase) which is one of the antihyperlipidemic medications.
A small amount of cholesterol is also absorbed from the gut which is also taken up by antihyperlipidemic medications. The total intracellular cholesterol in hepatocytes provides a negative feedback for cholesterol synthesis by inhibiting HMG-CoA reductase. Due to this, synthesis of cholesterol by the liver is decreased.
Atherosclerosis (hardening of arteries due to deposition of lipoid material in the internal layers of the arteries) occurs due to elevated level of plasma lipoproteins and can lead to coronary thrombosis and infarction. Antihyperlipidemic medications used for the treatment of hyperlipidaemia are called hypolipidemic agents. The aim of the treatment is to lower the concentration of VLDL and LDL and raise HDL.