Policosanol modulates HMG-CoA reductase activity in cultured fibroblasts

Background. Cholesterol biosynthesis is strictly controlled by 3-hydroxy-3-methylglutaryl Coenzyme A (HMG-CoA) reductase. Methods. Transfer of cultured fibroblasts to a lipid-depleted medium (LDM) up-regulates the enzyme levels. This, in turn, is followed by an accelerated biosynthesis of cholesterol, Results. Exposure of Vero fibroblasts to LDM and policosanol (0.5-50 mug/mL), a new cholesterol-lowering drug purified from sugarcane (Saccharum officinarum L.) wax, decreased in a dose-dependent manner cholesterol biosynthesis from [C-14]-acetate and H-3-water, but not from [C-14]-mevalonate. Conclusions. This suggests an effect on HMG-CoA reductase, the rate-controlling enzyme in cholesterol biosynthesis. When enzyme activity was measured in the presence of various concentrations of policosanol (0.5-50 mug/mL), reductase was not suppressed. Therefore, there was no evidence for a competitive or noncompetitive inhibition of enzyme activity. However, after treatment of intact cells with policosanol (50 mug/mL) in the presence of LDM, a suppressive effect on enzyme activity was observed, suggesting a modulatory effect of policosanol on reductase activity. The previous inhibition of enzyme up-regulation by policosanol suggests to date a depression of de novo synthesis of HMG-CoA reductase and/or stimulation of its degradation. However, the exact mechanism by which policosanol inhibits the activity of HMG-CoA reductase still remains unclear, Further studies are needed to clarify the precise mechanism of its inhibitory action on cholesterol biosynthesis. (C) 2001 IMSS. Published by Elsevier Science Inc.