Author(s): A R TALL
Variation of HDL cholesterol levels in man shows a strong inverse relationship to the incidence of atherosclerotic vascular disease. Thus the regulation of HDL cholesterol levels has been the subject of intense investigation. Human genetic differences in cholesteryl ester transfer protein and hepatic lipase illustrate the importance of these factors in the normal catabolism of HDL, while metabolic and population studies show that lipoprotein lipase activity plays a central role in the transfer of lipids and apoproteins into HDL. Metabolic turnover studies in humans suggest that variations in the fractional catabolism of the HDL structural proteins, apoA-I and apoA-II, account for much of the variation of HDL levels in human populations. Although the catabolism of these apolipoproteins is poorly understood, changes in the core lipid composition of HDL may lead to changes in catabolism of the HDL proteins. The core lipid composition of HDL appears to be determined by lipid transfer processes, and the activities of lipoprotein and hepatic lipase. Thus many genetic and environmental factors that influence HDL levels appear to operate by changing the activities of the lipases or the lipid transfer process.