Simvastatin depresses blood clotting by inhibiting activation of prothrombin, factor V, and factor XIII and by enhancing factor Va inactivation.

BACKGROUND: The mechanism of the antithrombotic action of statins is unclear. The aim of this study was to evaluate the effects of simvastatin on the coagulation process at sites of microvascular injury.

METHODS AND RESULTS: Tissue factor-initiated coagulation was assessed in blood samples collected every 30 seconds from bleeding-time wounds of 17 patients who had advanced coronary artery disease and total cholesterol levels of 224.6+/-11.8 mg/dL (mean+/-SEM). Quantitative Western blotting for time courses of fibrinogen depletion and activation of prothrombin, factor V, and factor XIII was performed before and after 3 months of simvastatin treatment (20 mg/d). Simvastatin induced reductions in total cholesterol (23%) and LDL-cholesterol (36%), which were accompanied by significant decreases in the rates of prothrombin activation (16.2+/-2.1%; P=0.004), formation of alpha-thrombin B-chain (27.4+/-1.8%; P=0.001), generation of factor Va heavy chain (29.7+/-3.1%; P=0.007) and factor Va light chain (18.9+/-1.2%; P=0.02), factor XIII activation (19.8+/-1.3%; P=0.001), and fibrinogen conversion to fibrin (72.2+/-3%; P=0.002). Posttreatment fibrinopeptides A and B concentrations, determined by using high-performance liquid chromatography, were reduced within the last 30 seconds of bleeding. The 30-kDa fragment of the factor Va heavy chain (residues 307 to 506), produced by activated protein C, and the 97-kDa fragment of the factor Va heavy chain (residues 1 to 643) were released more rapidly after simvastatin treatment. The antithrombotic actions of simvastatin showed no relationship to its cholesterol-lowering action.

CONCLUSIONS: Simvastatin treatment depresses blood clotting, which leads to reduced rates of prothrombin activation, factor Va generation, fibrinogen cleavage, factor XIII activation, and an increased rate of factor Va inactivation. These effects are not related to cholesterol reduction.