Inhibitory effect of monatepil maleate on acyl-CoA:cholesterol acyltransferase activity in the liver of cholesterol-fed Japanese monkeys

We have previously demonstrated that monatepil maleate, AJ-2615, a new calcium antagonist endowed with alpha1-adrenoceptor blocking property, has antiatherosclerotic and plasma lipid-lowering effects in Japanese monkeys fed on a cholesterol-rich diet. To clarify the mechanisms on plasma lipid-lowering action, we investigated the effect of monatepil maleate in these monkeys on hepatic acyl-CoA:cholesterol Acyltransferase (ACAT) activity. Both ACAT activity and esterified Cholesterol content in the livers of monkeys fed on a cholesterol-rich diet for 6 months significantly increased about 7- and 16-fold, respectively, as compared with those in monkeys fed on a standard diet. Monatepil maleate (30 mg/kg/day for 6 months, orally) inhibited the increases of ACAT activity and esterified Cholesterol content by 51% and 71%, respectively. In in vitro experiments, monatepil maleate inhibited ACAT activity in a concentration-dependent manner, whereas it did not affect 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity. A kinetic analysis revealed that monatepil maleate was a noncompetitive type inhibitor of ACAT. Hepatic ACAT activity was significantly correlated to hepatic esterified Cholesterol content (r = 0.775, P < .0001), to plasma very low density lipoprotein (VLDL) content (r = 0.765, P < .0001) and to plasma total Cholesterol content (r = 0.573, P < .005) in the monkeys. These results suggest that ACAT-inhibiting effect of monatepil maleate plays an important role in the reduction of hyperlipidemia.