Background. Streptokinase is a routinely used thrombolytic agent that is immunogenic and relatively inefficient toward platelet-rich thrombus, whereas staphylokinase is a poorly studied fibrinolytic agent. Here, the comparative immunogenicity and thrombolytic properties toward arterial platelet-rich thrombus and venous whole blood clots of streptokinase and recombinant staphylokinase were studied in baboons. Methods and Results. The inhibitory capacity of baboon plasma (in a human plasma-based clot lysis assay) was 0-39+/-0.25 mug streptokinase and 0.04-0.05 ug recombinant staphylokinase per milliliter of plasma (mean+/-SD,n=9). Intravenous infusion over 1 hour of 0.300 mg/kg of streptokinase at 0, 1,2,3, and 5 weeks in five baboons given heparin and the antiplatelet agent ridogrel increased the streptokinase-neutralizing titer from 0.22+/-0.18 mug/mL plasma at baseline to 3.8+/-4.4 mug/mL after 2 weeks (p=0.043 versus baseline by Wilcoxon signed rank test) and to 4.4+/-4.6 mug/mL after 5 weeks, whereas the thrombolytic potency toward a I-125-fibrin-labeled plasma clot inserted into an extracorporeal arteriovenous loop was reduced from 84+/-7% al baseline to 45+/-8% after 2 weeks and to 36+/-8% after 5 weeks (p<0.01 versus baseline). Administration over 1 hour of 0.065 mg/kg recombinant staphylokinase at 0, 1, 2, 3, and 5 weeks in four baboons did not induce measurable staphylokinase-neutralizing activity in three of the four animals after 5 weeks. In the fourth baboon, a staphylokinase-neutralizing activity of 0.8 and 1.5 mug/mL was found at 3 and 5 weeks, respectively. Repeated staphylokinase administration was not associated with inhibition of clot lysis (43+/-4% lysis at baseline, 52+/-9% at 3 weeks, and 61+/-14% at 5 weeks; p=NS versus baseline). Repeated administration of streptokinase but not of staphylokinase caused a marked (>50%) decrease in blood pressure, requiring administration of steroids and intravenous fluids, and a marked increase in leukocyte count and hemoglobin concentration. Intravenous infusion of streptokinase or recombinant staphylokinase over 1 hour in doses ranging between 0 and 1.0 mg/kg in three groups of four baboons each induced dose-dependent lysis of a I-125-fibrin-labeled autologous jugular vein blood clot (50% lysis requiring 0.140 mg/kg streptokinase and (1.058 mg/kg recombinant staphylokinase, representing equimolar amounts of 3.25 nmol/kg) without systemic fibrinogen depletion. The thrombolytic potency toward platelet-rich arterial thrombus of streptokinase and recombinant staphylokinase were studied in a femoral arterial eversion graft model. Arterial recanalization with recombinant staphylokinase was more frequent and more persistent than with streptokinase (all p<0.05). Intravenous infusion of 1.0 mg/kg streptokinase or 0.25 mg/kg recombinant staphylokinase in two groups of four baboons each given intravenous heparin (200-unit bolus and 50 units . kg-1 . hr-1) and aspirin (10 mg/kg) did not produce a significant prolongation of the median template bleeding time. Conclusions. Recombinant staphylokinase has a thrombolytic potency toward jugular vein blood clots in baboons comparable to that of streptokinase, but it is less immunogenic and less allergenic and it does not induce resistance to lysis upon repeated administration; it is significantly more efficient than streptokinase for the dissolution of platelet-rich arterial eversion graft thrombi. Recombinant staphylokinase, which can be easily obtained in active form by expression in Escherichia coli, may constitute a potentially useful alternative to streptokinase for the treatment of acute myocardial infarction.
