In vivo evidence that the lipid-regulating activity of the ACAT inhibitor CI-976 in rats is due to inhibition of both intestinal and liver ACAT.

CI-976, a new trimethoxy fatty acid anilide, is a potent and specific inhibitor of liver and intestinal acyl coenzyme A:cholesterol acyltransferase (ACAT) in vitro. Several in vivo approaches were used to determine the efficacy and sites of action of this compound in rats. CI-976 decreased non-high density lipoprotein (HDL)-cholesterol and increased HDL-cholesterol in rats with pre-established dyslipidemia. High performance gel chromatographic separation of plasma lipoproteins also revealed that CI-976, but not CL 277,082, lowered low density lipoprotein (LDL)-cholesterol and elevated HDL-cholesterol. Bay o 2752, octimibate, melinamide, and SaH 58-035 were all less potent in vivo compared to CI-976 and CL 277,082, and CI-976 produced the greatest decrease in liver cholesteryl esters. Subcutaneous (SC) administration of CI-976 was also efficacious in cholesterol-fed animals. In sucrose-fed rats, oral and SC CI-976 administration potently lowered plasma triglycerides. Hepatic cholesteryl ester accumulation in the ethinyl estradiol-treated rat was also diminished by orally administered CI-976. ACAT activity and cholesteryl ester mass were dose-dependently decreased in the livers from cholesterol-fed rats treated with CI-976, suggesting a direct effect on the liver. In both hypercholesterolemic and hypertriglyceridemic models, CI-976 also decreased plasma apoB concentrations. In other experiments radiolabeled CI-976 accumulated in the liver after multiple doses. Time-dependent changes in biliary lipid and bile acid secretion suggested that free cholesterol did not accumulate in the liver but instead was excreted as such or as bile acid. Finally, inhibition of endogenous and exogenous intestinal cholesterol absorption was demonstrated using several in vivo techniques. The combined data strongly supports the hypothesis that orally administered CI-976 inhibits both intestinal and hepatic ACAT, and that both of these enzymes may be determinants of plasma lipid concentrations in the rat.