title: Stabilization versus inhibition of TAFIa by competitive inhibitors in vitro.
abstract: Two competitive inhibitors of TAFIa (activated thrombin-activable fibrinolysis inhibitor), 2-guanidinoethylmercaptosuccinic acid and potato tuber carboxypeptidase inhibitor, variably affect fibrinolysis of clotted human plasma. Depending on their concentration, the inhibitors shortened, prolonged, or had no effect on lysis in vitro. The inhibitor-induced effects were both tissue-type plasminogen activator (tPA) and TAFIa concentration-dependent. Inhibitor-dependent prolongation was favored at lower tPA concentrations. The magnitude of the prolongation increased with TAFIa concentration, and the maximal prolongation observed at each TAFIa concentration increased saturably with respect to TAFIa. A theoretical maximal prolongation of 20-fold was derived from a plot of the maximum prolongation versus TAFIa. This represents, for the first time, a measurement of the maximal antifibrinolytic potential of TAFIa in vitro. Because TAFIa spontaneously decays, the stabilization of TAFIa was investigated as a mechanism explaining the inhibitor-dependent prolongation of lysis. Both inhibitors stabilized TAFIa in a concentration-dependent, non-saturable manner. Although their KI values differed by three orders of magnitude, TAFIa was identically stabilized when the fraction of inhibitor-bound TAFIa was the same. The data fit a model whereby only free TAFIa decays. Therefore, the variable effects of competitive inhibitors of TAFIa on fibrinolysis can be rationalized in terms of free TAFIa and lysis time relative to the half-life of TAFIa.
authors.affiliation: Henderson Research Centre and McMaster University, Hamilton, Ontario L8V 1C3, Canada.
authors.forename: John B
authors.initials: JB
authors.lastname: Walker
authors.forename: Bernadette
authors.initials: B
authors.lastname: Hughes
authors.forename: Ian
authors.initials: I
authors.lastname: James
authors.forename: Peter
authors.initials: P
authors.lastname: Haddock
authors.forename: Cornelis
authors.initials: C
authors.lastname: Kluft
authors.forename: Laszlo
authors.initials: L
authors.lastname: Bajzar
mesh_terms: D001667:Binding, Competitive; D025901:Carboxypeptidase B2 / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005342:Fibrinolysis; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008962:Models, Theoretical; D010940:Plant Proteins / Q000494:pharmacology; D011480:Protease Inhibitors; D011485:Protein Binding; D013386:Succinates / Q000494:pharmacology*; D013696:Temperature; D013997:Time Factors; D010959:Tissue Plasminogen Activator / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D010940:Plant Proteins; D011480:Protease Inhibitors; D013386:Succinates; C022014:guanidinoethylmercaptosuccinic acid; D002268:Carboxypeptidases; D025901:Carboxypeptidase B2; D010959:Tissue Plasminogen Activator