Mechanism of the Inhibition of Cholesterol Absorption by DL-Melinamide: Inhibition of Cholesterol Esterification

In order to elucidate the mechanism of action of DL-melinamide [DL-MA, N-(α-methylbenzyl)linoleamide], an inhibitor of cholesterol absorption, the effect of DL-MA on esterification of cholesterol in the mucosa of rabbit small intestine was studied. DL-MA inhibited acyl CoA:cholesterol acyltransferase (ACAT, EC 2.3.1.26) activity in the mucosal microsomes, with 50% inhibition occurring at approximately 0.5 μM. On the other hand, DL-MA had no effect on the cholesterol esterase (EC 3.1.1.13) activity in the mucosal cytosol. Kinetic studies indicate that DL-MA is an uncompetitive inhibitor of ACAT. D-MA, one of the two optical isomers of DL-MA, was found to be a more effective inhibitor of ACAT than L-MA, another isomer. This finding indicates that the inhibition of cholesterol absorption by DL-MA depends on the inhibition of ACAT by this compound, in view of the fact that D-MA is a more effective inhibitor of cholesterol absorption than L-MA.