HDL Metabolism and Atheroprotection: Predictive Value of Lipid Transfers

High-density lipoprotein (HDL) intravascular metabolism is complex, and the major HDL functions are esterification of cholesterol and reverse cholesterol transport, in which cholesterol from cells is excreted in bile. HDL has also several other antiatherogenic functions: antioxidative, vasodilatatory, anti-inflammatory, antiapoptotic, anti thrombotic, and anti infectious. Low HDL cholesterol is a major risk factor for cardiovas cular disease (CVD) and high HDL cholesterol may favor the many protective abilities of HDL. However, aspects of HDL function can be independent of HDL cholesterol levels, including the efflux of cholesterol from cells to HDL. Some populations show low incidence of CVD despite their low HDL cholesterol. Lipid exchange between HDL and other lipoproteins and cells is fundamental in HDL metabolism and reverse cholesterol transport. By determining HDL composition, lipid transfers can also affect HDL functions that depend on proteins that anchor on HDL particle surface. Cholesteryl ester protein (CETP) and phospholipid transfer protein facilitate lipid transfers among lipoprotein classes, but the role of the lipid transfers and transfer proteins in atherosclerosis and other diseases is not well established. CETP has become a therapeutic target because CETP inhibitors increase HDL cholesterol, but to date the clinical trials failed to show benefits for the patients. Recently, we introduced a practical in vitro assay to evaluate the simultaneous transfer from a donor nanoemulsion to HDL of unesterified and esterified cho lesterol, phospholipids, and triglycerides. Groups of subjects at different clinical, nutritional, and training conditions were tested, and among other findings, lower transfer ratios of unesterified cholesterol to HDL were predictors of the presence of CVD.