Summary
Recombinant human soluble thrombomodulin (rhsTM) was compared with various anticoagulants
for in vitro anticoagulant effects on thrombin generation, clotting time, and thromboelastography.
rhsTM as well as APC reduced the level 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-deficient plasma and was closely associated with the inhibitory effect
on prothrombinase and factor Va. On the other hand, hirudin and argatroban delayed
the time to reach the level of the peak, without reducing it. rhsTM and other anticoagulants
except for activated protein C (APC) were found to have concentration-dependent anticoagulant
activity by conventional clotting tests. However, the concentration of rhsTM for clotting
time was slightly affected by anti-protein C antibody. Moreover, the concentration
of rhsTM required to inhibit thrombin activity directly was 50 times higher than that
needed to inhibit thrombin generation. The effect of rhsTM on clot development was
compared with that of other anticoagulants by thromboelastography; rhsTM reduced the
growth of the clot but had little effect on the time to activate clotting, while the
other anticoagulants had the opposite effect. This 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 factor Va inactivation
and prothrombinase inhibition.
Keywords
Soluble thrombomodulin - thrombin generation - thromboelastography - activated protein
C - argatroban - hirudin - heparin
