Hypolipidemic and antioxidant activity of the novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor KY-455 in rabbits and hamsters

The hypolipidemic and antioxidant effects of N-(4,6-dimethyl-1-pentylindolin-7-yl)-2,2-dimethylpropanamide (CAS 178469-71-1, KY-455), a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, were examined in hyperlipidemic rabbits and normolipidemic hamsters. KY-455 inhibited rabbit intestinal, hepatic, macrophage and adrenal ACAT with IC50 values of 0.4, 0.9, 2.9 and 4.1 micromol/l, respectively. KY-455 also inhibited rabbit plasma and LDL-peroxidation (IC50: 0.4 and 1.7 micromol/l, respectively). In rabbits fed a high-cholesterol diet, treatment with KY-455 (30 mg/kg/day) for 8 days markedly lowered serum esterified, free, low-density lipoprotein (LDL)-cholesterol, and hepatic esterified cholesterol levels. KY-455 tended to inhibit ex vivo hepatic ACAT activity 5 h after the final administration. KY-455 also inhibited ex vivo peroxidation of plasma lipids 1 and 5 h after the final administration in rabbits. In normolipidemic hamsters fed a regular diet, treatment with KY-455 (30 mg/kg, twice a day) for 4 days significantly reduced serum esterified, free and LDL-cholesterol, and hepatic esterified and free cholesterol levels. A single administration of KY-455 (30 mg/kg) significantly inhibited ex vivo hepatic ACAT activity in hamsters. In conclusion, KY-455 showed in vitro inhibitory effects on LDL-peroxidation and macrophage ACAT activity at similar concentrations, and in vivo hypolipidemic and ex vivo antioxidative effects at the same dose. Long-term administration of KY-455 is expected to prevent the progress of atherosclerosis by lowering plasma lipid levels, inhibiting both LDL-oxidation and accumulation of cholesterol in macrophages.