The Yin and Yang of high-density lipoprotein cholesterol.

igh-density lipoproteins (HDL) are fairly complex macomolecules consisting of a core of hydrophobic lipids cholesteryl esters and triglycerides), an envelope of phosholipids and some unesterified (free) cholesterol, and polipoproteins (apo) that ensure structural integrity, serve s ligands for protein (and possibly lipid) receptors, can act s coactivators of enzymatic reactions, and are involved in he cellular secretion of the lipoprotein. When the clinical aboratory gives a report, it refers to the mass of cholesterol ithin the specific particle (i.e., the HDL-C level). Relaively little used is the measurement of serum apoA-I levels, he major protein moiety of HDL particles, which may eflect the number of circulating HDL particles. Given the xtraordinary biological diversity of HDL particles, these easurements, HDL-C and apoA-I levels, do not provide uch functional information.