Lecithin:cholesterol acyltransferase reaction on cellular lipid released by free apolipoprotein-mediated efflux.

Lecithin:cholesterol acyltransferase (LCAT) reaction was studied in free apolipoprotein-mediated cellular lipid efflux from mouse peritoneal macrophages and human skin fibroblasts. When the cells were incubated with lipid-free human apolipoproteins (apo) A-I or A-II, pre-beta high density lipoprotein (HDL) particles were generated by removing cellular cholesterol and phospholipid. Cholesterol was esterified by LCAT in such particles generated with human apoA-I, but not in those with apoA-II. The reactivity of the apoA-I-pre-beta-HDL particles with LCAT was in the same order as that in human plasma HDL and in phosphatidylcholine/cholesterol unilamellar vesicles activated by apoA-I when compared on the rate of percent cholesterol esterification. However, cholesterol efflux mediated by apoA-I was not enhanced by active cholesterol esterification in the medium from either type of cells. Thus, it is unlikely the LCAT reaction on newly generated pre-beta-HDL directly causes further cellular cholesterol efflux. In control experiments, LCAT esterified cholesterol on human plasma HDL in the cell medium regardless of its origin, either HDL or cells. Cholesterol esterification on HDL was unable to enhance cellular cholesterol efflux significantly but reduced the influx of cholesterol from HDL to cell, resulting in the increase of net efflux of cellular cholesterol, in agreement with the results previously demonstrated.