Summary
Bypassing inhibitors in haemophilia patients is limited to activated (a) Factor(F)VII
products. We introduced “FVa activity augmentation” as another bypassing strategy
and studied effects of an engineered FVa variant designated superFVa. Procoagulant and clot stabilising properties of superFVa and recombinant human (rh)FVIIa, either alone or in combination, were studied
in thrombin generation and clot lysis assays in normal human plasma (NHP) with or
without anti-FVIII inhibitors, in haemophilia plasma, and in FVIII-deficient mice
or in wild-type mice with anti-FVIII inhibitors. SuperFVa was as effective as rhFVIIa to improve thrombin generation or clot lysis. Furthermore,
procoagulant effects were significantly enhanced when these compounds were combined.
RhFVIIa at 40 nM (a therapeutic concentration) improved thrombin generation mildly,
but markedly improved thrombin generation when combined with a low concentration (e.
g. 3 nM) of superFVa. In clot lysis studies, the concentration of rhFVIIa to normalise clot lysis times
could be reduced by 100-fold (e. g. from 40 nM to 0.4 nM) when combined with a low
concentration (0.37 nM) of superFVa. In haemostasis studies of FVIII-deficient mice, blood loss was dose-dependently
reduced by either superFVa or rhFVIIa. SuperFVa (200 U/kg) corrected mean blood loss indistinguishably from rhFVIII. Blood loss
correction by rhFVIIa was greatly improved when combined with superFVa. Similar blood loss correction results were observed for therapies in wild-type
mice after infusion with anti-FVIII inhibitors. Thus, superFVa may be an effective procoagulant agent in the setting of haemophilia with inhibitors
and it merits further evaluation for new bypassing strategies.
Supplementary Material to this article is available online at www.thrombosis-online.com.
Keywords
Haemophilia - Factor VIII - Factor V - bleeding - haemostasis - inhibitors