CELLULAR CHOLESTEROL ESTER ACCUMULATION INDUCED BY FREE CHOLESTEROL-RICH LIPID DISPERSIONS

The influence of lipoprotein composition on free cholesterol (FC) esterification and accumulation of esterified cholesterol (EC) was studied in cells of Fu5AH rat hepatoma exposed to culture media supplemented with FC-lecithin dispersions having mol ratios of FC to phospholipid (FC/P) ranging from 0.6-2.8. In the presence of normal human serum, FC-lecithin dispersions with a FC/P > 1 stimulated both the esterification of FC and the accumulation of cellular EC. Dispersions with FC/P values of .apprx. 1 had no effect on either FC esterification or the accumulation of EC when compared to cells grown in the absence of lipid dispersions. No stimulation of cellular response was obtained when FC-rich dispersions were added to cells in the absence of serum; stimulation was observed when cells were exposed to isolated human serum lipoproteins (very low density, low density and high density). With each lipoprotein, FC-lecithin dispersions with FC/P values < 1 inhibited cholesteryl ester accumulation, FC-rich dispersions stimulated, and dispersions with FC/P values of .apprx. 1 had an effect equivalent to that of isolated lipoproteins alone. These studies establish that cellular FC esterification and EC content are not influenced solely by the FC concentration of medium, but rather respond to the ratio of FC to phospholipid. Serum lipoproteins may participate in the transfer of FC carried by FC-rich lecithin dispersions to cells.