CHARACTERIZATION OF PHOSPHOLIPIDS IN PRE-ALPHA HDL - SELECTIVE PHOSPHOLIPID EFFLUX WITH APOLIPOPROTEIN-A-I

Previously, we have shown that lipid-free apoA-I, when incubated with fibroblasts, will produce lipoproteins of pre-alpha mobility (Asztalos , B. F., et al, 1997, Arterioscler. Thromb, Vasc. Biol. 17: 1630-1636) . In order to understand the nature of these pre-alpha particles, we f urther characterized their lipid content. The pre-alpha particles are high density lipoproteins, having a median density of 1.08 g/ml, They have a surface charge of -18.45 mV, The phospholipid composition of th ese particles showed that they have 4% each of phosphatidyl ethanolami ne and inositol; 69% phosphatidyl choline and 18% sphingomyelin. This phospholipid composition is different from those of plasma HDL (81% ph osphatidyl choline, 13% sphingomyelin), plasma membrane on the fibrobl asts, and whole fibroblast phospholipid. To demonstrate that the pre-a lpha mobility resides in the lipids, lipids from pre-alpha lipoprotein s were reconstituted with lipid-free apoA-I. The resultant particles r etained their pre-alpha mobility. We conclude that apoA-I may react wi th specific regions of plasma membrane to acquire this unusual lipid c omposition and that pre-alpha mobility is caused in part by the unusua l phospholipid composition.