The inhibitory effect of recombinant human soluble thrombomodulin on initiation and extension of coagulation - A comparison with other anticoagulants

Recombinant human soluble thrombomodulin (rhsTM) was compared with various anticoagulants for in vitro anticoagulant effects on thrombin generation, c lotting time, and thromboelastography. rhsTM as well as APC reduced the lev el of the peak of the thrombin generation curve, but we did not observe any time-delay to reach the peak. This effect of rhsTM was diminished in PC-de ficient plasma and was closely associated with the inhibitory effect on pro thrombinase and factor Va. On the other hand, hirudin and argatroban delaye d the time to reach the level of the peak, without reducing it. rhsTM and o ther anticoagulants except for activated protein C (APC) were found to have concentration-dependent anticoagulant activity by conventional clotting te sts. However, the concentration of rhsTM for clotting time was slightly aff ected by anti-protein C antibody. Moreover, the concentration of rhsTM requ ired to inhibit thrombin activity directly was 50 times higher than that ne eded to inhibit thrombin generation. The effect of rhsTM on clot developmen t was compared with that of other anticoagulants by thromboelastography; rh sTM reduced the growth of the clot but had little effect on the time to act ivate clotting, while the other anticoagulants had the opposite effect. Thi s effect of rhsTM was completely abolished by the addition of anti-protein C or anti-protein S antibody. These findings suggest that rhsTM attenuates blood clotting by reducing the level of generated thrombin through protein C activation and subsequent fa ctor Va inactivation and prothrombinase inhibition.