title: Regulation by alpha 2-antiplasmin and fibrin of the activation of plasminogen with recombinant staphylokinase in plasma.
abstract: The effects of alpha 2-antiplasmin and fibrin on the activation of plasminogen by recombinant staphylokinase (STAR) were studied in an effort to elucidate further the molecular basis of the fibrin-specificity of this fibrinolytic agent. In purified systems consisting of 1.5 mumol/L intact or low-M(r) plasminogen and 3 mumol/L alpha 2-antiplasmin, at 37 degrees C and in the absence of fibrin, STAR did not induce plasminogen activation and plasmin-alpha 2-antiplasmin complex (PAP) formation. Addition of a purified fibrin clot (30% vol at a concentration of 3 mg/mL) to mixtures containing intact plasminogen caused approximately 40% plasminogen activation within 2 hours, whereas in mixtures containing low-M(r) plasminogen, no activation was observed. In contrast, 10 nmol/L streptokinase (SK) induced 74% to 100% plasminogen activation within 2 hours in mixtures containing either intact or low-M(r) plasminogen, in both the absence and the presence of fibrin. In citrated human plasma in the absence of fibrin, 30 nmol/L STAR did not induce measurable plasminogen activation and PAP formation (< 1.5% within 2 hours), whereas addition of a plasma clot (12% vol) resulted in complete clot lysis and conversion of 19% +/- 8% of the plasminogen to PAP within 2 hours. Addition of a second plasma clot produced 23% +/- 2% additional plasminogen activation. Equipotent concentrations for plasma clot lysis of SK (100 nmol/L) induced 54% +/- 11% plasminogen activation in the absence and 49% +/- 16% in the presence of fibrin. Addition of 50 mmol/L 6-aminohexanoic acid (6-AHA) abolished the effect of fibrin on plasminogen activation with STAR, but not on activation with SK. In alpha 2-antiplasmin-depleted human plasma in the absence of fibrin, 30 nmol/L STAR did not induce fibrinogen breakdown (> 90% residual fibrinogen after 6 hours), whereas 30 nmol/L preformed plasmin-STAR complex induced extensive fibrinogen degradation (70% within 20 minutes). Thus, in the absence of fibrin, alpha 2-antiplasmin inhibits the activation of plasminogen by STAR, by preventing generation of active plasmin-STAR complex. Fibrin stimulates plasminogen activation by STAR via mechanisms involving the lysine-binding sites of plasminogen, probably by facilitating the generation of plasmin-STAR complex and by delaying its inhibition at the clot surface.
authors.affiliation: Center for Thrombosis and Vascular Research, University of Leuven, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Silence
authors.forename: D
authors.initials: D
authors.lastname: Collen
authors.forename: H R
authors.initials: HR
authors.lastname: Lijnen
mesh_terms: D000933:Antifibrinolytic Agents; D005337:Fibrin / Q000494:pharmacology*; D005341:Fibrinolysin / Q000378:metabolism / Q000494:pharmacology*; D005342:Fibrinolysis / Q000187:drug effects; D006801:Humans; D008666:Metalloendopeptidases / Q000097:blood*; D010958:Plasminogen / Q000378:metabolism*; D011994:Recombinant Proteins / Q000097:blood; D000979:alpha-2-Antiplasmin / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D000933:Antifibrinolytic Agents; D011994:Recombinant Proteins; D000979:alpha-2-Antiplasmin; C037742:plasmin-plasmin inhibitor complex; D005337:Fibrin; D010958:Plasminogen; D005341:Fibrinolysin; D008666:Metalloendopeptidases; C022653:auR protein, Staphylococcus aureus