Comparative studies on the inhibitory spectrum of recombinant hirudin, DuP 714 and heparin on thrombin and factor Xa generation in biochemically defined systems.

The effect of antithrombotic drugs on the generation of serine proteases was studied in a biochemically defined system in which the prothrombin complex concentrate Konyne provided the necessary coagulation factors in the absence of plasma. The amount of thrombin and factor Xa generation was measured with a chromogenic substrate on a microcentrifugal analyzer. Furthermore, the assay was modified by supplementation with either purified antithrombin III or factor V. The synthetic peptide Ac-(D)Phe-Pro-boroArg-OH (DuP 714) was shown to be the most effective inhibitor of thrombin and also had strong inhibitor actions against factor Xa generation. Recombinant hirudin (rH) was nearly as active as DuP 714 on thrombin generation, however, it was less effective on factor Xa generation. With rH no concentration-dependent inhibition of factor Xa generation was found, i.e. over a wide range of concentration it only produced a steady inhibition of about 40-50% without further increase. The addition of AT-III to the system did not influence the action of DuP 714 or rH, but it strongly increased the inhibitory effects of unfractionated heparin (PMH) as well as of a low molecular weight heparin (LMWH) on both thrombin and factor Xa generation. The addition of factor V to the assay system did not cause any changes in the activity of all agents on protease generation.