Enhancement of recombinant tissue plasminogen activator-induced reperfusion by recombinant tick anticoagulant peptide, a selective factor Xa inhibitor, in a canine model of femoral arterial thrombosis

Abstract

Tick anticoagulant peptide (TAP) is a 60 amino acid protein originally isolated from the soft tick, Ornithodoros moubata, which exhibits potent anticoagulant properties due to its selective inhibition of blood coagulation factor Xa. We evaluated a recombinant version of TAP (rTAP) for its ability to accelerate recombinant tissue plasminogen activator (rt-PA) -mediated lysis of an occlusive thrombus and prevent acute reocclusion in a canine model of femoral artery thrombosis. An occlusive thrombus was formed by insertion of a thrombogenic copper coil into the femoral artery of anesthetized dogs. Blood flow velocity was monitored directly and continuously by Doppler flowmetry. 60 min after occlusion, dogs received an i.v. infusion of either saline or rTAP (0.5, 2.5 or 8.0 μg/kg/min), followed 45 min later by rt-PA (0.8 mg/kg, i.v. over 90 min; n=8/group). The saline and rTAP infusions were discontinued 1 h after stopping the rt-PA. All dogs achieved reperfusion, with a time to reperfusion in the saline-treated (vehicle) group (administered rt-PA alone) of 61 ±7 min. The time to reperfusion was slightly decreased in the 0.5ug/kg/min rTAP group (47±4min, p=NS). In the groups administered rTAP at 2.5 and 8.0 ug/kg/min, significant reductions in the time to reperfusion were observed (28±4 and 32±5mins, respectively, p<0.05). Following termination of the rt-PA, all vehicle dogs reoccluded in 37±11 min. The lowest dose of rTAP, 0.5 ug/kg/min, had no effect on either the reocclusion incidence or time (8/8 in 39±7min). In contrast, the two higher doses of rTAP maintained vessel patency in all dogs during the rTAP infusion period and dramatically delayed the time to reocclusion. However, 7/8 dogs eventually reoccluded in 117±12 and 140±9min for the groups receiving rTAP infusions of 2.5 and 8.0 ug/kg/min, respectively. Maximal elevations in activated partial thromboplastin time or template bleeding time associated with the rTAP administration were only 1.3- and 1.1-fold of baseline values, respectively. The dramatic effect of factor Xa inhibition on the efficacy of rt-PA-mediated reperfusion and acute reocclusion following rt-PA suggests that factor Xa inhibition may represent a potentially useful therapeutic adjunct to thrombolytic therapy.