Thrombolysis, animal models

Perfusion imaging (PI) is complementary to DWI in acute stroke assessment. In animal models, PI lesions are visible immediately after vessel occlusion and resolve rapidly after successful thrombolysis or reperfusion (Muller et al. 1995 Yenari et al. 1997). In stroke patients, serial PI studies can document... 

Gold HK, Yasuda T, Jang IK et al. (1991) Animal models for arterial thrombolysis and prevention of reocclusion. Erythrocyte-rich versus platelet-rich thrombus. Circulation 83 IV26-IV403... 

Table 2.3. ANIMAL MODELS OF ARTERIAL THROMBOSIS AND THROMBOLYSIS... 

In addition to studying the ability of fibrinogen antagonists to prevent thrombus formation, the ability of these agents to enhance the outcome of thrombolytic therapy has been studied in several animal models, in which thrombolysis alone is only partially effective and/or is followed by rapid reocclusion. These studies are summarised below. 

The present report outlines studies with fibrolase in several different animal thrombosis model systems. Infusion of fibrolase proximal to an occlusive thrombus produces rapid and effective thrombolysis in carotid (22) and renal arterial, and iliac venous thrombosis model systems (23). Recently the recombinant form of fibrolase has been purified from a yeast expression system (24). It appears to be identical in all respects to the natural enzyme and has been used successfully in the carotid arterial thrombosis model system (22). Both natural and recombinant forms of the enzyme have effective thrombolytic activity in the different animal models employed there are no observable side effects nor toxicity, and minimal or no observable hemorrhaging. 

The primary intent of the study using the canine carotid arterial thrombosis model was to determine if the recombinant enzyme could achieve thrombolysis in an experimental animal model in which a platelet-rich, occlusive arterial thrombus, develops in response to deep arterial wall injury. We found that fibrolase produced rapid thrombolysis. The experimental model is similar to one originally developed by Lucchesi in the coronary artery (30) and subsequently adapted to the carotid artery to minimize experimental loss due to ventricular fibrillation (31). The use of the carotid has the additional advantage of greater yield of experimental data, and when necessary allows the animal to serve as its own internal control, thereby facilitating the interpretation of results and simplifying statistical evaluation. This was an important consideration in the present study where r-fibrolase was in limited supply thus accounting for the need to employ relatively small animals and to administer the enzyme by local injection immediately proximal to the occlusive platelet-rich arterial thrombus. 

Venous thrombosis is produced in rats by insertion of a stainless steel wire coil into the inferior caval vein. Platelets as well as plasmatic coagulation are activated on the wire coil. Thrombus formation onto the wire is quantitated by measuring the protein content of the thrombotic material isolated. The kinetics of thrombus formation show an increase in weight and protein content within the first 30 min followed by a steady state between thrombus formation and endogenous thrombolysis leading to a constant protein content of thrombi between 1 and up to 48 h following implantation of the wire coil. Thrombosis incidence in untreated control animals in this model is 100%. The test is used to evaluate antithrombotic and thrombolytic properties of compounds in an in vivo-model of venous thrombosis in rats. 

In the iliac venous thrombosis model system six animals were studied with good lysis observed venographically in five (23). Figure 2 presents representative venograms illustrating the effectiveness of thrombolysis induced by selective application of natural fibrolase. No toxicity, little or no hemorrhaging, and no evidence of other side effects were observed in the animals studied. These studies again demonstrate the favorable therapeutic potential of native fibrolase. 

The present results demonstrate that natural fibrolase exhibits effective in vivo thrombolytic activity in several animal thrombosis model systems. Infusion of the enzyme proximal to an occlusive thrombus induced rapid and specific thrombolysis in rabbit renal arterial and iliac venous thrombosis model systems. No evidence of hemorrhaging or alterations to the hemostatic system were observed in these studies. Additionally, no toxicity was observed and no angiographic, histologic, or functional evidence of side effects were obtained. The enzyme rapidly lysed 48 hr aged thrombi in the venous thrombosis model. This suggests that one of the primary mechanisms of thrombus resistance to PA-based agents. 

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