REGULATION OF THE CONCENTRATION OF PRE-BETA HIGH-DENSITY-LIPOPROTEIN IN NORMAL PLASMA BY CELL-MEMBRANES AND LECITHIN-CHOLESTEROL ACYLTRANSFERASE ACTIVITY

A minor fraction of plasma high-density lipoprotein (prebeta-1 HDL) has been shown to promote cholesterol efflux from peripheral cell membranes [Castro, G. R., & Fielding, C. J. (1988) Biochemistry 27, 25-29]. When isolated native plasma is incubated at 37-degrees-C, this fraction is specifically decreased. On the other hand, the level of plasma prebeta-1 HDL is fully protected in the presence of even very low levels of fibroblasts, vascular smooth muscle cells, or macrophages. Blood cells were completely inactive in maintaining plasma prebeta-1 HDL levels in the absence of peripheral cells, even at the relatively high levels present in whole blood. The loss of prebeta-1 observed in isolated plasma was dependent upon lecithin-cholesterol acyltransferase (LCAT) activity. These data suggest that reverse cholesterol transport catalyzed by prebeta-1 HDL, and subsequent LCAT-mediated cholesterol esterification, is directly dependent upon the interaction between this HDL species and competent peripheral cells.