Reduced cholesterol esterification in CaCo-2 cells by indirect action of pravastatin

In microsomal preparations of CaCo-2 cells pravastatin decreased cholesterol esterifying activity at 25 micrograms/ml to 82.5% and at 800 micrograms/ml to 56.2% of controls. Pravastatin reduced cholesteryl ester formation dose-dependently also in viable CaCo-2 cells. However, the maximal inhibition was by 90.4% at pravastatin concentration of 25 micrograms/ml, half maximal inhibition occurred between concentrations of 5 and 10 micrograms/ml. Addition of mevalonolactone, which serves as endogenous source of cholesterol, antagonized this effect. At 10 mM mevalonolactone (MVL) even doses up to 200 micrograms/ml of pravastatin were ineffective. On the other hand, pravastatin suppressed cholesteryl ester formation when acyl-CoA cholesterol acyltransferase (ACAT) (E.C. 2.3.1.26) activity was stimulated by addition of exogenous liposomal or Low Density Lipoprotein (LDL)-derived cholesterol. This inhibition was refractory to increasing amounts of exogenous cholesterol up to 400 micrograms/ml. Therefore we conclude that only excessive doses of pravastatin suppress ACAT activity directly. In viable cells the observed inhibition of cholesteryl ester formation is due to the block in de novo synthesis of cholesterol, causing a lack of substrate for ACAT and of non-sterol products of mevalonic acid. Furthermore pravastatin interferes with the esterification and/or intracellular transport only of exogenous cholesterol, confirming former results of a compartmentalized cholesterol metabolism in the enterocyte.