Differences in the inhibition of coagulation factor XIII-A from animal species revealed by Michael Acceptor- and thioimidazol based blockers

IntroductionThe A-subunit of blood coagulation factor XIII is a pro-transglutaminase, which cross-links α- and γ-fibrin-chains in its activated form. Selective inhibitors against FXIII-A may be desirable drugs to prevent the development of thromboses. Animal models are generally used for proof of principle and for toxicological studies in drug development. The aim of the study was to investigate the specificity of a set of FXIII-A-blockers against FXIII-A from different species, i.e. human, dog, mouse, rat and pig. Thus the usefulness of different animal species for FXIII-A-blocker drug development should be evaluated.Materials and MethodsFXIII-A proteins were recombinantly produced in insect cells and purified to homogeneity. They were characterized by SDS- and native PAGE, a transamidase assay and isopeptidase assay. The inhibition second-order rate constants of different irreversible inhibitors were determined using the isopeptidase assay.ResultsAll FXIII-A species were able to assemble with recombinant human FXIII-B into a heterotetrameric complex. Kinetic parameters of FXIII-A species were determined. Second-order rate constants for FXIII-A inhibition by two irreversible inhibitors were determined and differed considerably. FXIII-A species of dog, mouse and rat were inhibited in a manner similar to human FXIII-A. Pig FXIII-A however was resistant to a previously described non-peptidic inhibitor. Furthermore, the results showed considerably better inhibition with the novel peptide-based inhibitor compared to the non-peptidic compound.ConclusionsOur data shows that biochemical interspecies comparison studies are a prerequisite for animal studies. Peptide-derived inhibitors carrying a Michael Acceptor Pharmacophore (MAP) are a promising new class of FXIII-A-inhibitors.