EVIDENCE THAT THE PROTEIN-C ACTIVATION PATHWAY AMPLIFIES THE INHIBITION OF THROMBIN GENERATION BY RECOMBINANT HUMAN THROMBOMODULIN IN PLASMA

Thrombomodulin (TM) is a cofactor for the thrombin-catalyzed activatio n of anticoagulant protein C. However, we have no evidence that thromb omodulin actually activates protein C during blood coagulation process ing, nor do we know whether this activated protein C acts as an antico agulant. We studied the inhibitory action of recombinant human soluble TM (rhs-TM) on thrombin generation in whole plasma. Human plasma was activated with small amounts of tissue factor using phospholipid vesic les in place of activated platelets. Thrombin generation was observed. The addition of only 2 nM of rhs-TM prevented rapid generation of thr ombin and reduced the total amount of thrombin generated. In order to study the influence of the protein C activation pathway on this inhibi tory action of rhs-TM, protein C-depleted plasma was used. rhs-TM had little inhibitory effect on protein C-depleted plasma. However, the ad dition of protein C caused a delay in thrombin generation and a reduct ion of the maximum thrombin concentration. We concluded that the antic oagulant activity of rhs-TM was amplified by the protein C activation pathway.