Differential Modulation of Plasminogen Activator Mediated Thrombolysis By Recombinant Thrombomodulin and Activated Protein C

Introduction:

Urokinase (UK) and tissue plasminogen activator (tPA) mediate thrombolytic actions by activating endogenous plasminogen. Thrombomodulin (TM) complexes with thrombin to activate Protein C and thrombin activatable fibrinolysis inhibitor (TAFI). Activated Protein C (APC) modulates coagulation by digesting factors V and VIII and activates fibrinolysis by decreasing PAI-1 functionality. Since the thrombin/thrombomodulin complex regulates both TAFI functionality and protein C activation, rTM modulates the fibrinolytic process by multiple mechanisms.

Aim:

To compare the effects of rTM and APC on urokinase and tPA mediated thrombolysis utilizing thromboelastography.

Materials and methods:

Native whole blood was activated using a diluted intrinsic activator (APTT reagent, Triniclot). The modulation of thrombolysis by tPA and UK (Abbott, Chicago, USA) was studied by supplementing these agents to whole blood and monitoring TEG profiles for 3 hours. To investigate effect of APC (Haematologic Technologies, VT, USA) and rTM (Asahi Kasai Pharma, Tokyo, Japan) these agents were also supplemented to the activated blood at a concentration range of 0.02 - 3.0 ug/ml. The modulation of tPA and UK induced thrombolysis by APC and rTM was studied in terms of thromboelastograph patterns. In addition, the effect of both APC and rTM on plasma based systems supplemented with tPA was also investigated.

Results:

In comparison to rTM, APC produced a stronger anticoagulant effect in terms of r time, k time, angle and MA. Fibrinolysis was assessed in terms of LY30 (%) and LY60 (%). At concentrations of up to 3.0ug/ml rTM and APC did not produce any direct fibrinolytic effects. APC also produced strong augmentation of the lytic of effects of tPA and urokinase in a concentration dependent fashion. rTM at lower concentrations produced stabilization of clot resisting fibrinolysis. In the plasma based system, APC exhibited a stronger interaction with tPA in comparison to rTM.

Conclusion:

These studies demonstrate the differential anticoagulant and procoagulant effects of APC and rTM. APC is a stronger anticoagulant than rTM and facilitates thrombolysis. rTM is a weaker anticoagulant and modulates clot stability branding it resistant to fibrinolysis. These observations suggest that while APC may impair hemostasis, rTM restores hemostasis via TAFI activation. The dual mode of action of the rTM may contribute to the regulation of fibrinolysis in facilitating hemostatic balance in both physiologic and pathologic states.

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