Human tissue-type plasminogen activator releases fibrinopeptides A and B from fibrinogen.
In five patients with venous thromboembolic disease treated with recombinant tissue-type plasminogen activator (rt-PA), there was a marked increase in the mean concentrations of fibrinopeptide A (from 0.6 to 5.9 nM; P less than 0.0001) and desarginine fibrinopeptide B (from 5.6 nM to 24.1 nM; P less than 0.01) 30 min after a bolus of rt-PA (0.6 mg/kg). Thrombin was unlikely to be responsible because the levels of desarginine fibrinopeptide B exceeded those of fibrinopeptide A and the changes occurred despite concomitant heparin therapy. The purpose of this study therefore, was to determine whether rt-PA directly releases the fibrinopeptides from fibrinogen. Incubation of rt-PA with heparinized plasma or purified fibrinogen resulted in time and dose-dependent release of both fibrinopeptide A and B. Contaminating thrombin was not responsible for this activity by the following criteria: the rate of rt-PA mediated fibrinopeptide B release was considerably faster than that of fibrinopeptide A, and fibrinopeptide release was unaffected by heparin, hirudin, or a monospecific antithrombin IgG. Aprotinin also had no effect on fibrinopeptide release, indicating that this activity was not plasmin mediated. Fibrinopeptide release was shown to be due to rt-PA because this activity was completely blocked by a monoclonal antibody against the enzyme. Further, the specificity of rt-PA for the thrombin cleavage sites on fibrinogen was confirmed by the demonstration that rt-PA released fibrinopeptide A or fibrinopeptide B from fibrinopeptide A or B-containing substrates, respectively. These studies thus demonstrate that (a) rt-PA releases fibrinopeptides A and B from fibrinogen thereby indicating that this enzyme is not specific for plasminogen, and (b) plasma fibrinopeptide A and desarginine fibrinopeptide B levels are not specific markers of thrombin action on fibrinogen in patients receiving rt-PA.
D002851:Chromatography, High Pressure Liquid; D005340:Fibrinogen / Q000378:metabolism* / Q000494:pharmacology*; D005344:Fibrinopeptide A / Q000378:metabolism*; D005345:Fibrinopeptide B / Q000494:pharmacology*; D006493:Heparin / Q000627:therapeutic use; D006801:Humans; D011994:Recombinant Proteins / Q000627:therapeutic use; D013917:Thrombin / Q000037:antagonists & inhibitors; D013923:Thromboembolism / Q000188:drug therapy; D010959:Tissue Plasminogen Activator / Q000627:therapeutic use*
D011994:Recombinant Proteins; D005344:Fibrinopeptide A; D005345:Fibrinopeptide B; D005340:Fibrinogen; D006493:Heparin; D013917:Thrombin; D010959:Tissue Plasminogen Activator