Benzoyl-urokinase

For thrombolytic studies, bcnzoyl-urokinasc was chosen. The thrombolytic effect of acylated urokinase as compared to the free enzyme was measured in vitro and in vivo. The in vitro experiments were carded out in an artificial circulating system composed of a 1 -fibrin-labeled clot suspended in human plasma. The degree of thrombolysis was estimated from the released radoaedvity (fig, 12). From these experiments we concluded that the thrombolytic effect of benzoyl-urokinase is higher than that of urokinase. 

The enzymatically inactive acyl-urokinase was reactivated in plasma at 37°C with a reactivation half-time of 8 minutes (benzoyl-urokinase) or 10 hours (p-guanidinobenzoyl-urokinase). Upon administration to rabbits, urokinase was more rapidly eliminated than either acyl enzyme (Fig. 11). The results suggest that urokinase is eliminated via the binding to plasma inhibitors. Thus, it could be shown that the clearance of urokinase is modified significantly on acylation. 

The thrombolytic effect in vivo was studied in rabbits with a radioactive thrombus produced in the inferior vena cava. The radioactivity over the occluded venous segment was measured by a scintillation probe fitted with a collimator adapted to the anatomical conditions. Comparison of equivalent doses of urokinase and benzoyl-urokinase in the model of venous thrombosis showed that the acylated form of the enzyme was more active than the free enzyme [38). 

Figure 11 Fibrinolytic activity in rabbit plasma (estimated on fibrin plates) after i.v. injection of 50,000 IU/kg urokinase (U) or benzoyl-urokinase (BU) or guanidinobenzoyl-urokinase (GBU). (From Ref. 38.)...

Figure 12 Lysis of radioactive human plasma clots (related to the increase in 125I radioactivity) in a circulating plasma system by urokinase (U) and benzoyl-urokinase (BU) (50 IU/mL).

---