Cholesterol efflux from cells to immunopurified subfractions of human high density lipoprotein: LP-AI and LP-AI/AII.

Using immunoaffinity chromatography, we separated human high density lipoprotein (HDL) into two subfractions: LP-AI, in which all particles contain apolipoprotein A-I (apoA-I) but no apoA-II, and LP-AI/AII, in which all particles contain both apoA-I and apoA-II. To compare LP-AI and LP-AI/AII as acceptors of cell cholesterol, the isolated subfractions were diluted to 50 micrograms phospholipid/ml, and then incubated with monolayer cultures of cells in which whole-cell and lysosomal cholesterol has been labeled with 14C and 3H, respectively. We used three cell types (Fu5AH rat hepatoma cells, normal human skin fibroblasts, and rabbit aortic smooth muscle cells). When these cells were prepared to contain normal physiological quantities of cholesterol (20-35 micrograms/mg protein), LP-AI and LP-AI/AII were nearly equally efficient in promoting efflux of both whole-cell and lysosomal cholesterol. For whole-cell cholesterol, the rate constants for efflux to LP-AI and LP-AI/AII were: 0.050/h and 0.053/h, respectively, with Fu5AH cells; 0.0063/h and 0.0074/h with GM3468 human skin fibroblasts; and 0.0076/h and 0.0079/h with rabbit aortic smooth muscle cells. When cholesterol in hepatoma cells or fibroblasts was elevated two- to threefold above normal, there was still not difference in efflux of whole-cell cholesterol to LP-AI and LP-AI/AII. In longterm incubations, the net depletion of cholesterol mass from cholesterol-enriched cells was either identical with the two HDL subfractions, or somewhat greater with LP-AI/AII.(ABSTRACT TRUNCATED AT 250 WORDS)