Dynamics of fibrin clot lysis under flow conditions by erythrocyte-linked tPA

Summary form only given. Tissue plasminogen activator (tPA) triggers plasmin generation and subsequent blood clot dissolution. However, its therapeutic use is limited by an extremely short blood half-life. Previous studies by our group have shown that the half-life of tPA can be prolonged considerably by employing erythrocytes as natural carriers of tPA and that RBC carriage of tPA facilitates fibrinolysis of the nascent clot. In the present work we characterized the lysis of the nascent clots by RBC-tPA complex under flow conditions using an original in vitro model. Normal human RBC or RBC conjugated with activase (ACT, wild-type tPA) were entrapped in nascent plasma clots formed under venous flow conditions (62.5 s^-1). Video-microscopy was used to compare formation and lysis of both RBC and RBC-tPA containing clots in separate flow chambers. Both types of clots displayed similar clot formation time (10-15 min). However, while clots containing normal RBC did not degrade even after a 90 min perfusion with buffer, degradation of the clots containing RBC-tPA was observed within 15 min. Lysis quantification with radiolabelled fibrinogen demonstrated that a 40 min perfusion of buffer over the RBC-tPA clot reduced its fibrin content and red cell content by 70% and 85%, respectively. In contrast, no changes in fibrin and red cell count were detected in the control clot. These data support the notion that RBC carriage of plasminogen activators may be useful for thromboprophylaxis.