Streptokinase and APSAC inhibit platelet aggregation in vitro by fibrinogenolysis: Effect of plasma fibrinogen degradation products X and E

Abstract

Summary Streptokinase (SK) in vitro can both activate and inhibit platelets. Inhibition has been ascribed either to proteolysis of membrane glycoproteins (GPs) or to the inhibitory effect of fibrinogen degradation products (FgDPs). Addition of a low concentration of SK (300 U/ml) to human citrated platelet rich plasma (cPRP) has been shown to lead to an aggregation defect, related to fibrinogenolysis, without discernible changes in the glycoprotein IIb/IIIa complex. In the present study, similar results were obtained with SK (300–5000 U/ml), and the acylated plasminogen streptokinase activator complex (APSAC) (0.01 U/ml). The aggregation defects appeared to be related to the extent of fibrinogenolysis. The knowledge of the FgDPs profile might help in the understanding of this aggregation defect. We have chosen to generate the FgDPs in plasma by activating plasminogen with SK 300 U/ml, 15 min at 37°C. Fragments X and E were separated by gel filtration and identified by electrophoresis and immunoblot. The effects of the fractions containing fragments X and E on aggregation were studied using human washed platelets resuspended in Tyrode buffer, 2 mM Ca++, 1 mM Mg++, after stimulation with ADP (10−5 mol/l). The results (expressed as percentage of the response obtained with intact fibrinogen) were: 72%±18 (p In conclusion, our data confirm and extend previous observations on the mechanisms of platelet aggregation inhibition by SK or APSAC. The main factor of platelet inhibition in plasma appears to be the FgDP E.