Fibrolase, a fibrinolytic enzyme isolated from Agkistrodon c. contortrix (southern copperhead) venom, solubilizes fibrin primarily by rapid hydrolysis of the alpha and beta chains. Fibrolase is also an Aα, Bβ fibrinogenase. The breakdown products of fibrin and fibrinogen following incubation with fibrolase were different from those observed with plasmin. This enzyme is a metalloprotease that was inhibited by ethylenediaminetetraacetic acid. Fibrolase was inhibited by dithiothreitol, suggesting that disulfide bonds are important for catalytic activity. It was also inhibited by α2-macroglobulin, but not by the soybean or lima bean trypsin inhibitors, diisopropylfluorophosphate, or p-hydroxymercuribenzoate. Unlike thrombolytic agents such as streptokinase, fibrolase does not activate plasminogen as evidenced by the use of plasmin-specific chromogenic substrate S-2251 and by sodium do-decyl sulfate-polyacrylamide gel electrophoresis.
Fibrolase, a direct-acting fibrinolytic enzyme has been shown to cleave primarily the Aα and Bβ chains of human fibrin. We have previously reported that fibrolase also exhibits fibrinogenolytic activity and acts mainly as an α-chain fibrinogenase. In contrast to the action of streptokinase (plasminogen activator), fibrolase does not activate plasminogen. In vitro thrombolytic efficacy of fibrolase was determined by monitoring the release of radiolabel from iodinated fibrin and human blood clots. Fibrolase effectively digested the clots in a dose-dependent manner. The in vivo efficacy of fibrolase was evaluated in an animal model of arterial thrombosis. Fibrolase was found to be efficacious at dissolving femoral arterial clots following a single intravenous bolus administration. Time to reperfusion was dose dependent and similar to that observed with streptokinase. No adverse effects on blood pressure and heart rate were observed.
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