Relationship between bioavailability and hypocholesterolemic activity of YM17E, an inhibitor of ACAT, in cholesterol-fed rats

Abstract

The relationship between bioavailability and the serum cholesterol-lowering effect of YM17E, an ACAT inhibitor was investigated. Serum cholesterol levels in cholesterol-fed rats decreased after both oral and intravenous administration of YM17E. Marked inhibition of cholesterol absorption was observed after oral administration, but not after intravenous administration. YM17E and its five active metabolites were primarily distributed in the liver after intravenous administration, but in small intestine and liver after oral administration. Hepatic ACAT activity in cholesterol-fed rats was inhibited by intravenous administration. Cholesteryl ester input into plasma by Triton WR-1339 treatment to the rats was inhibited by intravenous administration of YM17E. Plasma clearance of 125I-LDL in cholesterol-fed rats increased after YM17E treatment suggesting a decrease in LDL production. These results indicate that the hypocholesterolemic effect of intravenous YM17E was due to hepatic ACAT inhibition, not an inhibition of intestinal cholesterol absorption. The contribution of ACAT inhibition in small intestine and liver on the pharmacological effect could be explained by plasma inhibitor concentration after oral or intravenous administration of YM17E. From these results, it is concluded that the change in bioavailability of ACAT inhibitors change the mechanism of hypocholesterolemic effects, shifting the relative contributions of small intestinal and hepatic ACAT inhibition.