Regulation of Plasma High-Density Lipoprotein Levels by the ABCA1 Transporter and the Emerging Role of High-Density Lipoprotein in the Treatment of Cardiovascular Disease

High-density lipoproteins (HDL) protect against cardiovascular disease. HDL removes and transports excess cholesterol from peripheral cells to the liver for removal from the body. HDL also protects low-density lipoproteins (LDL) from oxidation and inhibits expression of adhesion molecules in endothelial cells, preventing monocyte movement into the vessel wall. The ABCA1 transporter regulates intracellular cholesterol levels in the liver and in peripheral cells by effluxing excess cholesterol to lipid-poor apoA-I to form nascent HDL, which is converted to mature alpha-HDL by esterification of cholesterol to cholesteryl esters (CE) by lecithin cholesterol acyltransferase. The hepatic ABCA1 transporter and apoA-I are major determinants of levels of plasma alpha-HDL cholesterol as well as poorly lipidated apoA-I, which interact with ABCA1 transporters on peripheral cells in the process of reverse cholesterol transport. Cholesterol in HDL is transported directly back to the liver by HDL or after transfer of CE by the cholesteryl ester transfer protein (CETP) by the apoB lipoproteins. Current approaches to increasing HDL to determine the efficacy of HDL in reducing atherosclerosis involve acute HDL therapy with infusions of apoA-I or apoA-I mimetic peptides and chronic long-term therapy with selective agents to increase HDL, including CETP inhibitors.