Evaluation of thrombomodulin/thrombin activatable fibrinolysis inhibitor function in plasma using tissue-type plasminogen activator-induced plasma clot lysis time

Background

Thrombin activatable fibrinolysis inhibitor (TAFI) is one of the most important physiological fibrinolysis inhibitors. Its inhibitory efficacy under physiological conditions remains uncertain.

Objectives

Elucidate the role of soluble thrombomodulin (sTM)/TAFI axis in the regulation of fibrinlysis.

Methods

Since thrombin is required to generate activated TAFI (TAFIa) that targets the C-terminal lysine of partially digested fibrin, a clot lysis assay is suitable for evaluating its function. Using tissue-type plasminogen activator-induced plasma clot lysis time (tPA-PCLT) together with TAFIa inhibitor and recombinant sTM (rsTM), we evaluated the specific function of TM/TAFI in the plasma milieu.

Results

tPA-PCLT values were significantly shortened by the TAFIa inhibitor. rsTM supplementation prolonged tPA-PCLT, which was shortened by the TAFIa inhibitor to a time similar to that obtained without rsTM and with the TAFIa inhibitor. Plasma obtained from patients treated with rsTM showed prolonged tPA-PCLT, which was shortened by the TAFIa inhibitor but not further prolonged by rsTM. However, no significant correlation was observed between tPA-PCLT and parameters of TM/TAFI system in the plasma.

Conclusion

The role of the TM/TAFI system in regulating fibrinolysis was successfully evaluated using TAFIa inhibitor and rsTM. Trace amounts of soluble TM in normal plasma appeared sufficient to activate TAFI and inhibit fibrinolysis. Further, a therapeutic dose of rsTM appeared sufficient to activate TAFI and regulate fibrinolysis in the plasma milieu.