The effects of two acylcoenzyme a: Cholesterol acyltransferase (ACAT) inhibitors, cyclandelate and a non-hydrolysable ether analogue, benzyl3,3,5-trimethylcyclohexanol on low density lipoprotein metabolism in macrophages and hepatocytes

Abstract

Cyclandelate (3,3,5,-trimethylcyclohexanylmandelate) caused a dose-dependent decrease in the metabolism of radioiodinated low density lipoprotein [ 125I-LDL] by J774 mouse macrophages. This was probably an indirect effect dur to the inhibition of cholesterol esterification by the cells rather than a direct one one the interaction of LDL with its receptor, since no inhibition was seen in cells which had been cholesterol-depleted by prior incubation with lipoprotein-depleted serum for 48 hr. Cyclandelate also inhibited immediately de novo synthesis of cholesterol from [1- 14C]acetate in J774 cells, suggesting a direct action of the drug on an enzyme of the cholesterol biosynthetic pathway. The drug was an efficient inhibitor of hamster and rat intestinal acylcoenzyme A: cholesterol acyltransferase (ACAT) activity in vitro with an ic 50 of 20 μM. Addition of cyclandelate to the diet of meal-fed rats caused a marked inhibition of the rate of appearance of dietary [4- 14C]cholesterol in the plasma. A nonhydrolysable ether analogue of cyclandelate, benzyl3,3,5-trimethylcyclohexanol, was prepared to compare hepatic and extrahepatic actions of the two molecules. The analogue inhibited cholesterol esterification in J774 cells, transformed human macrophages U937 and human umbilical vein endothelial cells with an ic 50 of 20 μM and had effects similar to those of cyclandelate on 125I-LDL metabolism in J774 cells. Differences between the analogue and cyclandelate were seen in hepatocytes and hepatic microsomal fractions, where preincubation with the analogue inhibited cholesterol esterification in both systems while cyclandelate had no inhibitory action in either. Consequently, preincubation of rat hepatocytes with benzyl3,3,5-trimethylcyclohexanol for 17 hr caused a marked decrease in the binding of 125I-LDL to the cells, whereas binding to cells preincubated with cyclandelate was the same as to control cells.