Enhanced nitric oxide and cyclic GMP formation plays a role in the anti-platelet activity of simvastatin

Background and purpose: It has been found that 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) exert various vascular protective effects, beyond their cholesterol-lowering property, including inhibition of platelet-dependent thrombus formation. The objective of the present study was to determine whether the nitric oxide (NO)/cyclic GMP-mediated processes in platelets contribute to the anti-aggregatory activity of simvastatin. Experimental approach: After rabbit platelets were incubated with simvastatin for 5 min, aggregation was induced and the platelet aggregation, nitric oxide synthase activity, guanylyl cyclase activity, NO and cyclic GMP formation were measured appropriately. Key results: Treatment with simvastatin concentration-dependently inhibited platelet aggregation induced by collagen or arachidonic acid with an IC50 range of 52-158 mu M. We also demonstrated that simvastatin (20-80 mu M) concentration-dependently further enhanced collagen-induced NO and cyclic GMP formation through increasing NOS activity (from 2.64 +/- 0.12 to 3.52 +/- 0.21-5.10 +/- 0.14 mu mol min(-1) mg protein(-1)) and guanylyl cyclase activity (from 142.9 +/- 7.2 to 163.5 +/- 17.5-283.8 +/- 19.5 pmol min(-1) mg protein(-1)) in the platelets. On the contrary, inhibition of platelet aggregation by simvastatin was markedly attenuated (by about 50%) by addition of a nitric oxide synthase inhibitor, a NO scavenger or a NO-sensitive guanylyl cyclase inhibitor. The anti-aggregatory effects of simvastatin were significantly increased by addition of a selective inhibitor of cyclic GMP phosphodiesterase. Conclusions and implications: Our findings indicate that enhancement of a NO/cyclic GMP-mediated process plays an important role in the anti-aggregatory activity of simvastatin.