Abstract: Ancylostoma caninum anticoagulant peptide 5 (AcAP5) has been reported as an FXa inhibitor. We found that this peptide showed potent inhibitory activity on activated thrombin-activatable fibrinolysis inhibitor (TAFIa), which protects the fibrin clot against lysis. This study investigated the effects of recombinant AcAP5 (rAcAP5) on fibrinolytic activity in vitro and on thrombolytic activity in vitro and in vivo. In addition, euglobulin lysis time (ELT), fibrinogen content and fibrin degradation product (FDP) in normal rat plasma were all determined to evaluate the influence of rAcAP5 on fibrinolytic activity in circulation blood. TAFIa activity was detected by colorimetry; fibrinolysis in vitro was determined with turbidimetry. Thrombolysis in vitro was measured by thrombus weight reduction; thrombolysis in vivo was conducted by arteriovenous shunt method with thrombus weight reduction. ELT, fibrinogen content and FDP were detected using routine method. rAcAP5 concentration-dependently inhibited TAFIa activity in vitro with an IC50 of 63.7 nmol/L. rAcAP5 (5-40 nmol/L) significantly accelerated urokinase-induced clot lysis of rabbit plasma and shortened fibrinolysis time (P<0.01). rAcAP5 at 1.5 μmol/L enhanced the reduced weight of thrombus induced by urokinase (P<0.05), and it also reduced thrombus weight (P<0.05) in vitro when used alone. In an arteriovenous shunt thrombolytic model, rAcAP5 (50-200 μg/kg, i.v.) dose-dependently enhanced the reduced weight of the thrombus. rAcAP5 at effective doses failed to influence ELT, fibrinogen contents and FDP in normal rat circulation plasma. In conclusion, rAcAP5 is a thrombolytic peptide, which may be attributed to its TAFIa inhibition. rAcAP5 may only exert thrombolytic activity on the thrombus site but not influence the fibrinolysis activity and fibrinogen in circulation plasma. These findings suggest that rAcAP5 is a potential thrombolytic candidate agent.

Key words: rAcAp5, TAFIa, Clot lysis, Thrombolytic activity