Lipids and atherosclerosis

Atherosclerosis is the leading cause of death in North America and within the next two decades will be the leading cause worldwide. Atherosclerosis is characterized by vascular obstruction from the deposits of plaque, resulting in reduced blood flow. Plaque rupture and the consequent thrombosis may lead to sudden blockage of the arteries and cause heart attack. High serum lipid levels, especially the elevated level of low-density lipoprotein (LDL), have been shown to be strongly related to the development of atherosclerosis. It is generally accepted that atherosclerotic lesions are initiated via an enhancement of LDL uptake by monocytes and macrophages. In the liver, uptake of plasma LDL is mediated via specific LDL receptors, but a scavenger receptor system is employed by macrophages. Plasma LDL must be modified prior to uptake by macrophages. Analysis of the lipid content in the oxidatively modified LDL from hyperlipidemic patients revealed that the level of lysophosphatidylcholine was greatly elevated, and the high level of the lysolipid was shown to impair the endothelium-dependent relaxation of the blood vessels. In a separate study, we showed that a high level of homocysteine caused the increase in cholesterol production and apolipoprotein B-100 secretion in hepatic cells. Statins have been used effectively to control the production of cholesterol in the liver, and recently, ezetimibe has been shown to supplement the efficacy of statins by inhibiting cholesterol absorption. The factor of elevated levels of triglyceride-rich lipoproteins in association with depressed high-density lipoproteins, usually in the context of insulin resistance, is an important contributor to atherosclerosis and can be effectively treated with fibric acid derivatives. In hyperhomocysteinemia, folic acid supplements may have a role in the control of cholesterol by reducing the plasma homocysteine level.