Effect of SMP-500, a novel acyl-coA:cholesterol acyltransferase inhibitor, on the cholesterol esterification and its hypocholesterolemic properties

We investigated the effects of SMP-500, a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, on ACAT activities in the liver and intestine, and in macrophages. We measured its effects on the serum cholesterol levels and hepatic cholesterol content in mice, rabbits and hamsters. SMP-500 inhibited ACAT activities in rabbit liver and small intestine microsomes with IC(50) values of 72 and 84 nmol/l, respectively, and acted as a competitive inhibitor of rabbit liver ACAT. SMP-500 potently inhibited cholesterol esterification in rat peritoneal macrophages (IC(50) = 15 nmol/l). In high-fat and high-cholesterol diet-fed mice and in high-cholesterol diet-fed rabbits, SMP-500 reduced the serum cholesterol levels and the hepatic cholesterol content. SMP-500 also reduced the serum and hepatic cholesterol in normal chow-fed hamsters in a dose-dependent manner. In all the animal models, SMP-500 reduced the hepatic free cholesterol content as well as the total and esterified cholesterol. Administered orally, SMP-500 had a direct inhibitory effect on hepatic ACAT activity. These results indicate that SMP-500 is a potent and competitive ACAT inhibitor and may have a therapeutic potential for treating hypercholesterolemia and atherosclerosis.