Relationship between mevalonate pathway and arterial myocyte proliferation: in vitro studies with inhibitors of HMG-CoA reductase

The role of mevalonate and its products (isoprenoids) in the control of cellular proliferation was examined by investigating the effect of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (vastatins) on growth and on cholesterol biosynthesis of cultured arterial myocytes (SMC). Simvastatin (S) and fluvastatin (F), but not pravastatin (P), decreased the rate of growth of rat vascular SMC. The inhibition, evaluated as cell number, was dose-dependent with IC50 values of 2.8 and 2.2 muM for S and F, respectively; P (1-500 muM) was inactive. The inhibition of cell growth induced by 3.5 muM S (70% decrease) was prevented completely by the addition of 100 muM mevalonate, partially (70-85%) by the addition of 10 muM geraniol, 10 muM farnesol and 5 muM geranylgeraniol, but not by the addition of squalene, confirming the specific role of isoprenoid metabolites in regulating cell proliferation. All the tested vastatins inhibited the incorporation of [14C]acetate into cholesterol but P had 800 times lower potency than S and F. Similar results were obtained in SMC from human femoral artery. At least 80% inhibition of cholesterol synthesis was necessary to induce a decrease in SMC proliferation. To further investigate the relationship between cholesterol synthesis and cell growth, two enantiomers of F were investigated. The enantiomer more active on HMG-CoA reductase was 70- and 1.6-fold more potent on arterial myocyte proliferation than its antipode and the racemic mixture, respectively. A similar IC50 proliferation/cholesterol synthesis ratio for all the inhibitory vastatins (S, F and its enantiomers), regardless of their different potency, supports a causal relationship between the mevalonate synthetic pathway and cell proliferation.