Abstract
Patients with severe hemophlia A and inhibitors suffer from significantly compromised clot formation as well as reduced clot stability. Recombinant factor VIIa (rFVIIa - NovoSeven®, Novo Nordisk, Bagsvaerd, Denmark) has proven safe and efficacious for securing haemostasis in hemophilia patients with inhibitors. Recently, it was proposed that the reduced thrombin generation in severe haemophilia hinders sufficient activation of factor XIII and thereby result in insufficient covalent lateralization of fibrin (Blood2005; 106: 11, Abstract 321). The present study aimed at exploring the effect of rFVIIa and rFVIIa + plasma-derived FXIII (Haematological Technologies Inc) on whole blood clot (WB) formation and WB clot stability in severe hemophilia A. In total, 14 patients with a verified FVIII:C < 0.01 IU/ml were enrolled. Ex vivo studies were performed with rFVIIa (2 μg/ml), rFVIIa+FXIII (2+10 μg/ml), and a buffer control. Dynamic WB coagulation profiles describing initiation (clotting time=CT[sec]), propagation (maximum velocity=MaxVel [mm*100/sec]) and clot strength (maximum clot firmness=MCF[mm*100]) were recorded using thrombelastography and activation with a minute amount of tissue factor (TF, Innovin, final dilution 1:50000). WB clot stability was evaluated using a reaction mixture containing TF and tPA (1nM), followed by evaluation of the MCF and the total area under the elasticity curve after 120 min analysis time (AUEC[mm*100*sec]). Data are presented as mean and Wilcoxon statistical results. In the absence of tPA, Both rFVIIa+FXIII and rFVIIa significantly shortened the CT (Buffer=1424, rFVIIa+FXIII=739 (p=0.010), rFVIIa=881, (p=0.0005)) and accelerated WB MaxVel (Buffer=3.8, rFVIIa+FXIII=10.5 (p=0.0001), rFVIIa=9.2, (p=0.0002)). The standard deviation (SD) of the CT was significant lower in WB spiked with rFVIIa+FXIII than rFVIIa (Buffer SD=697, rFVIIa+FXIII SD=289 vs rFVIIa SD=655, p=0.007). In the absence of tPA, rFVIIa+FXIII increased the MCF significantly more than rFVIIa (Buffer=4441, rFVIIa+FXIII=6414 vs rFVIIa=5943, p=0.04) and the SD of the MCF was significant lower in WB spiked with rFVIIa+FXIII than rFVIIa (Buffer SD=2174, rFVIIa+FXIII SD=331 vs rFVIIa SD=948, p=0.0006). In the presence of tPA, rFVIIa+FXIII induced higher clot strength and stability than rFVIIa alone (MCF: Buffer=1313, rFVIIa+FXIII=3295 vs rFVIIa=3023, p=0.10 (N.S.); AUEC: Buffer=3.8*106, rFVIIa+FXIII=12.8*106 vs rFVIIa=10.2*106, p=0.0269). In conclusion, both rFVIIa (2μg/mL) and FXIII (10 μg/ml) added to rFVIIa (2 μg/ml), significantly increased WB clot formation and stability in this ex vivo evaluation of the clotting potential of WB from patients with severe hemophilia A.
Regulation by tranexamic acid and thrombomodulin of hyperfibrinolysis induced by tissue plasminogen activator in human whole blood