EFFECT OF A NEW ACYL-COENZYME A-CHOLESTEROL ACYLTRANSFERASE INHIBITOR, HL-004, ON CHOLESTEROL ESTERIFICATION AND LIPID-METABOLISM IN HEP G2CELLS

We studied the effect of a new acyl-coenzyme A:cholesterol acyltransfe rase (ACAT) inhibitor, HL-004, on intracellular cholesterol metabolism in the human hepatoma cell line Hep G2. Culture of Hep G2 cells in th e presence of HL-004 at the concentrations of 10(-7) mol/L and 10(-6) mol/L resulted in pronounced inhibition of the incorporation of radio- labeled [H-3]cholesterol (20% decrease at 10(-7) mol/L and 80% decreas e at 10(-6) mol/L) and [C-14]oleate into intracellular cholesterol est er (CE). This inhibition was dose dependent and became evident at grea ter than or equal to 3 hours of culture. The intracellular CE mass als o began to decline at 3 hours. The secretion of radioactive CE in the non-high-density lipoprotein (HDL) fraction, but not the HDL fraction, of the culture medium was inhibited in proportion to the decrease in CE production. The free cholesterol level, however, remained unchanged both in the cells and in the medium. In contrast, the effect of the d rug on the incorporation of radioactivity from [C-14]sodium acetate in to free cholesterol and from [H-3]glycerol into triglycerides or phosp holipids was not marked, suggesting no potential to exert any other si gnificant effect on hepatic lipid metabolism. In conclusion, the prese nt study demonstrated that HL-004 was incorporated into liver cells, s pecifically inhibited ACAT, and suppressed the secretion of lipoprotei n CE from the liver.