INHIBITION OF ACYL-COA-CHOLESTEROL ACYLTRANSFERASE DECREASES APOLIPOPROTEIN B-100-CONTAINING LIPOPROTEIN SECRETION FROM HEPG2 CELLS

There is evidence that the overproduction of apoB-100-containing lipop roteins by the liver is the underlying event in some forms of dyslipop roteinemia. This metabolic status is associated to an increased risk o f developing premature coronary artery disease CAD. The conclusions fr om previous studies suggested that the availability to the hepatocytes of cholesterol that is readily esterified is an important determinant for VLDL and LDL secretion. In the present study, we set out to inves tigate the effect of the specific stimulation and inhibition of the ra te-limiting enzyme of the cholesterol esterification, acyl-CoA:cholest erol acyl-transferase (ACAT, E.C. 2.3.1.26), on the lipid and on the a poB-100 secretion rate from a human hepatoma cell line (HepG2). When t he specific ACAT inhibitor FCE 27677 (10(-5) M) was added to the cultu res, a decrease of the cellular cholesteryl ester content and at the s ame time a significant reduction of the neutral lipids and of the apoB -100 secretion rate were noticed. The stimulation of ACAT by 25-hydrox ycholesterol (20 mu g/ml) caused a 4-fold increase of the cellular cho lesteryl ester content and a 2-fold increase of the lipoprotein secret ion rate. FCE 27677 (10(-5) M to 10(-7) M) prevented the effects elici ted by the oxysterol. On the contrary, lovastatin (10(-6) M) and gemfi brozil (10(-6) M) had no effect. The analysis of the lipid and of the apolipoprotein composition of the lipoproteins secreted in the medium revealed that ACAT inhibition had the dual effect of both decreasing t he number of apoB-100-containing lipoproteins secreted as well as thei r cholesteryl ester load. Altogether, these data support the idea of a close relationship between ACAT activation, leading to increased chol esteryl ester availability, and apoB-100-containing lipoprotein secret ion. It is speculated that ACAT inhibitors may prove useful for the tr eatment of human dyslipoproteinemias caused by the hepatic overproduct ion of apoB-100-containing lipoproteins.