Markland F S, Friedrichs G S, Pewitt S R, Lucchesi B R
Department of Pharmacology, University of Michigan Medical School, Ann Arbor 48109-0632.
Circulation. 1994 Nov;90(5):2448-56. doi: 10.1161/01.cir.90.5.2448.
Thrombolytic agents used clinically rely on the activation of plasminogen to plasmin. Plasmin possesses multiple actions including increasing thrombin activity and activation of platelets. Thus, after successful thrombolytic therapy, arterial hyperactivity and reocclusion may be the result of a predominant plasmin-induced thrombogenic action at the site of the residual thrombus. Fibrolase, a direct-acting fibrinolytic enzyme from southern copperhead snake venom, induces rapid clot lysis in vitro. Fibrolase does not rely on plasminogen activation or any other bloodborne components for activity and is not inhibited by any of the rapidly acting serine proteinase inhibitors in blood.
We investigated the efficacy of fibrolase to lyse an occlusive thrombus formed in the carotid artery of the anesthetized dog. Electrolytic injury was initiated in both the right and left carotid arteries. Thirty minutes after both arteries were occluded, each vessel was infused with either fibrolase (4 mg/kg over 5 minutes) or physiological saline (over 5 minutes). In two separate groups of dogs, anisoylated plasminogen streptokinase activator complex (APSAC) (0.1 U/kg) was infused into the occluded vessel. In the artery infused with fibrolase, five of five dogs exhibited patency within 6 +/- 1 minutes of the infusion (P < .05 versus vehicle-treated artery; Fisher's exact test). In the contralateral carotid artery that received vehicle, the occlusion was maintained throughout the experimental protocol. APSAC alone lysed the thrombus in each vessel within 17 +/- 3 minutes. Five minutes after the end of fibrolase administration and in one of the groups administered APSAC, a glycoprotein (GP)IIb/IIIa antibody, 7E3 (0.8 mg/kg IV), was administered to prevent reocclusion of the patent artery. After 7E3 administration, the vessel treated with fibrolase remained patent in four of five dogs, and six of six APSAC-treated vessels were patent for the remainder of the observation period (2 hours).
These studies demonstrate that local administration of fibrolase lyses a carotid arterial thrombus rapidly without excessive hemorrhage or hemodynamic compromise. The enzyme in combination with antiplatelet therapy (7E3) offers a unique mechanism for clot dissolution and may prove useful as a clinically efficacious alternative to presently used thrombolytic agents or may act in a synergistic manner with plasminogen activators.
临床上使用的溶栓剂依赖于纤溶酶原激活为纤溶酶。纤溶酶具有多种作用，包括增加凝血酶活性和激活血小板。因此，在成功的溶栓治疗后，动脉活性过高和再闭塞可能是残留血栓部位纤溶酶诱导的主要促血栓形成作用的结果。纤维蛋白溶酶是一种来自南方铜头蛇毒液的直接作用的纤溶酶，在体外可诱导快速的血栓溶解。纤维蛋白溶酶的活性不依赖于纤溶酶原激活或任何其他血液成分，且不受血液中任何快速作用的丝氨酸蛋白酶抑制剂的抑制。
我们研究了纤维蛋白溶酶溶解麻醉犬颈动脉中形成的闭塞性血栓的疗效。在左右颈动脉均引发电解损伤。两条动脉闭塞30分钟后，向每条血管注入纤维蛋白溶酶（5分钟内注入4mg/kg）或生理盐水（5分钟内注入）。在两组不同的犬中，将茴香酰化纤溶酶原链激酶激活剂复合物（APSAC）（0.1U/kg）注入闭塞的血管。在注入纤维蛋白溶酶的动脉中，5只犬中有5只在注入后6±1分钟内血管通畅（与注入赋形剂的动脉相比，P<0.05；Fisher精确检验）。在接受赋形剂的对侧颈动脉中，在整个实验过程中闭塞均得以维持。单独使用APSAC可在17±3分钟内溶解每条血管中的血栓。在纤维蛋白溶酶给药结束后5分钟，以及在一组接受APSAC治疗的犬中，给予糖蛋白（GP）IIb/IIIa抗体7E3（0.8mg/kg静脉注射），以防止通畅动脉的再闭塞。给予7E3后，接受纤维蛋白溶酶治疗的血管在5只犬中有4只保持通畅，接受APSAC治疗的6只血管中有6只在观察期剩余时间（2小时）内保持通畅。
这些研究表明，局部给予纤维蛋白溶酶可迅速溶解颈动脉血栓，且无过度出血或血流动力学损害。该酶与抗血小板治疗（7E3）联合应用为血栓溶解提供了一种独特的机制，可能被证明是目前使用的溶栓剂的一种临床有效替代方法，或者可能与纤溶酶原激活剂协同作用。
