Combinations of recombinant staphylokinase (STA) and single-chain urokinase-type plasminogen activator (scuPA) induce synergistic thrombolysis in vitro
R. Aisina, L. Mukhametova, K. Gershkovich, S. Varfolomeyev (Moscow, Russia)
Time: 17:15 - 18:15
Objective: STA binds to fibrin-bound plasminogen (Pg). Conversion of inactive equimolar Pg*STA complex to active plasmin(Pm)*STA complex is a rate-limited step that is accelerated by the product. ScuPA has affinity only for molecules of Pg which are bound to the inner COOH-terminal lysines of partially degraded fibrin and it activates Pg directly. Since STA and scuPA are distinguished by mechanism of Pg activation and fibrin-selectivity of thrombolytic action, their combinations can induce a synergistic thrombolysis. In this work, thrombolytic and side effects of combinations of STA and scuPA were studied in vitro.
Methods: Kinetics of plasma clots lysis and depletion of plasma proteins (Pg, fibrinogen and alpha2-antiplasmin) levels under the action of different concentrations of STA, scuPA and their combinations were monitored.
Results: Equieffective doses which caused 50% clot lysis in 4 h were found to be 30 nM STA and 75 nM scuPA. To reveal a potential synergistic effect, simultaneous and sequential combinations of various doses of STA and scuPA were studied. Equieffective doses of STA, scuPA and their combinations which caused the same specified effects in 2 or 4 h were analyzed by the algebraic fractional method. Synergism of STA and scuPA was found at total concentrations of the agents of 25 to 65 nM. The synergistic of thrombolysis was more pronounced at simultaneous combinations of the agents than at subsequent addition of STA followed by scuPA (in 30 min). The maximal 3.5-4-fold increase in thrombolysis was observed for combinations of 10-15 nM STA and 15-35 nM scuPA as compared with the expected thrombolysis, obtained by summarizing of the effects of the individual agents. The synergistic combinations of STA and scuPA caused the significant less depletion of Pg, fibrinogen and alpha2-antiplasmin levels in plasma, as compared with the expected effects.
Conclusion: The synergy of STA and scuPA is connected with an initial formation of COOH-terminal lysine.residues on fibrin surface under the action of STA, that leads to the increase in Pg activation by scuPA and formation of tcuPA. As a result of Pg activation by tcuPA, concentration of plasmin and Pm*STA complex increases. Because of all these reactions proceed on fibrin surface, the combinations of STA and scuPA cause the enhanced thrombolytic effect at the reduced side effects.