Effect of Retraction on the Lysis of Human Clots with Fibrin Specific and Non-Fibrin Specific Plasminogen Activators

Abstract

SummaryThe effect of the serum content of human clots on their sensitivity to lysis with plasminogen activators was studied in a system composed of 125I-fibrin labeled clots immersed in buffer or in citrated plasma. The effect was studied with plasma clots before or after mechanical compression and with whole blood clots before or after retraction, using either the fibrin specific plasminogen activators recombinant tissue-type plasminogen activator (rt-PA) or recombinant single chain urokinase-type plasminogen activator (rscu-PA), and the non-fibrin specific activators recombinant two chain urokinase-type plasminogen activator (rtcu-PA), or streptokinase (SK).In a buffer milieu, all plasminogen activators had a similar fibrinolytic potency towards serum-rich clots (non-compressed plasma clots or non-retracted blood clots): 50% clot lysis in 4 h required 50 to 85 ng plasminogen activator per ml. Serum-poor clots (compressed plasma clots or retracted blood clots) were resistant to lysis in a buffer milieu but became sensitive to lysis following preincubation in plasma for 48 h. These findings indicate that plasma proteins entrapped in clots contribute significantly to their sensitivity to lysis and suggest that the amount of bound or entrapped plasminogen may be a limiting factor. In a plasma milieu, all plasminogen activators lysed serum- rich plasma or blood clots, albeit at higher concentrations (3 to 40 times higher than in the buffer milieu) and with different efficiencies: 50% clot lysis in 4 h required approximately 600 ng/ ml of rtcu-PA but 1,500 to 2,000 ng/ml of rscu-PA. These findings suggest that components of plasma are responsible for increased resistance of clots towards lysis and that the effect is variable for different plasminogen activators. Serum-poor plasma or blood clots were very resistant to lysis with non-fibrin specific agents, but became more sensitive after preincubation in plasma. However, serum-poor plasma or blood clots were sensitive to lysis with fibrin specific plasminogen activators, suggesting that during clot lysis with fibrin specific agents, plasminogen recruited from surrounding plasma may contribute significantly to clot lysis. The concentration of plasminogen activator required to obtain 50% clot lysis in a plasma milieu of compressed plasma clots or retracted blood clots was 390 and 1,600 ng/ml respectively for rt-PA and 1,100 and 3,200 ng/ml respectively for rscu-PA. These data suggest that in a plasma milieu retracted blood clots are more sensitive to lysis with fibrin specific plasminogen activators than with non-fibrin specific agents.

Ultrasound-enhanced tissue plasminogen activator thrombolysis in an in vitro porcine clot model

“…2. Sabovic et al [33] also found that serum-poor blood clots were more resistant to rt-PA thrombolysis and that plasminogen recruited from surrounding plasma contributes significantly to clot lysis. The extent of thrombolysis is dependent on rt-PA concentration and increases with increasing thrombolytic concentration until saturation above 0.05 mg/ml as shown in Fig.…”

Tissue plasminogen activator (tPA) inhibits plasmin degradation of fibrin. A mechanism that slows tPA-mediated fibrinolysis but does not require alpha 2-antiplasmin or leakage of intrinsic plasminogen.

“…In clinical situations, depletion of circulating plasminogen will result in the permeation of plasminogen-poor plasma into the front of the clot with a subsequent efflux out the back of the clot of fluid containing constituents of the coagulation milieu. Also, clot retraction may exude plasminogen-rich fluid from the clot (30). Under these conditions of low prevailing inner clot plasminogen concentrations and low plasmin generation, the interference of plasmin action on fibrin by excess tPA may be pronounced.…”

Thrombotic distal middle cerebral artery occlusion produced by topical FeCl3 application: A novel model suitable for intravital microscopy and thrombolysis studies

“…As detailed in the 'Materials and methods' section, reperfusion with tPA was not feasible when 30% FeCl 3 was used or when tPA administration was delayed for 1 hour after FeCl 3 application possibly because size and retraction of the clot had reached a state difficult to be lysed by tPA (Sabovic et al, 1989;Sabovic and Blinc, 2000). Reperfusion was obtained with early (10 minutes after FeCl 3 ) tPA administration in 12 out of 23 mice when thrombus was induced with 10% FeCl 3 .…”