Inhibition of Cholesterol Synthesis by Policosanol

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DESCRIPTION (provided by applicant): Over-the-counter botanicals and nutritional supplements have gained great popularity among the public as safe and effective means to treat chronic and acute diseases, and are widely viewed as safe alternatives to prescription medicines. Hypercholesterolemia is a widespread problem for which there is great interest in alternative medicines, and policosanol is a relatively new product derived from sugar cane that has gained considerable attention as a means to reduce blood cholesterol levels. This research will investigate a possible mechanism by which policosanol decreases blood cholesterol levels. Most current evidence indicates that this mixture of long-chain alcohols inhibits or suppresses HMG-CoA reductase activity, the regulatory step in cholesterol synthesis. To test this hypothesis, the effect of policosanol on HMG-CoA reductase activity will be evaluated in cultured hepatoma cells and in whole animals, and the mechanism by which policosanol inhibits this enzyme will be determined. Preliminary studies demonstrate that policosanol does not directly inhibit HMG-CoA reductase, indicating that intracellular activation/metabolism of policosanol, or the activation of a modulatory pathway, is necessary for the suppression of this key cholesterolgenic enzyme. Studies will test the hypothesis that peroxisomal metabolism of policosanol results in the activation of AMP-kinase, which then inactivates HMG-CoA reductase by phosphorylation. An alternative hypothesis, that policosanol is metabolized to a direct inhibitor of HMG-CoA reductase, will also be tested. HMG-CoA reductase expression and activity and AMP-kinase activity will be measured in hepatoma cells and in preparations from the livers of animals treated with policosanol. Finally, to determine if peroxisomal oxidation of policosanol is necessary, the ability of policosanol to inhibit cholesterol synthesis in mice that lack peroxisomal oxidation pathways will be determined. These studies should establish a solid, mechanistic understanding of how policosanol decreases cholesterol synthesis and lowers blood cholesterol levels, and may provide a basis for predicting how the use of this compound might interact, either favorably or unfavorably, with prescription Pharmaceuticals used for the treatment of hypercholesterolemia.