Does recombinant factor VIIa, apart from overall hemostasis, regulate TAFI dependent fibrinolysis? In vitro analysis using overall hemostasis potential (OHP) assay.

Abstract

Using the recently developed overall hemostatic potential (OHP) assay, we investigated the effects of different concentrations of recombinant factor VIIa on overall hemostasis and on thrombin activatable fibrinolysis inhibitor (TAFI) dependent fibrinolysis in different factor deficient plasmas. rFVIIa increased OHP in FV, FVIII and FIX deficient plasmas but not up to the levels in normal pooled plasma (NPP). Maximal levels were found at 2.4 microg/mL of rFVIIa, while higher doses did not further increase OHP. In FXII deficient plasma, OHP is higher than in NPP and addition of rVIIa further increased it. Even very high concentrations of rFVIIa (9.6 microg/mL) did not induce a significant increase of OHP in NPP. Higher concentrations of rVIIa down-regulated fibrinolysis in FVIII, FIX and FXI deficient plasmas to values obtained in NPP. Using potato tuber carboxy-peptidase inhibitor (PTCI), a specific inhibitor of TAFI, it was found that TAFI's influence on fibrinolysis down-regulation in FVIII and FIX deficient plasmas increased after addition of higher concentrations of rFVIIa. From this in vitro study it seems that rFVIIa in a concentration of 2.4 microg/mL improves overall hemostasis in FV, FVIII and FIX deficient plasmas. rFVIIa, even at very high (supra-therapeutic) concentrations, does not induce hypercoagulability either in NPP or in deficient plasmas. Higher concentrations of rVIIa induce, at least partly, TAFI dependent down-regulation of fibrinolysis in FVIII and FIX deficient plasmas. These results, together with some previous ex vivo studies, point to OHP assay as a possible diagnostic tool for evaluating the hemostatic effects of rFVIIa.