Co-Administration of Factor XIII with Hemostatic Agents in Hemophilia Promotes Clot Stability and Composition

Hemophilia A results from the absence, deficiency, or inhibition of factor VIII. Bleeding is treated with use of two broad classes of hemostatic agents; replacement factors (recombinant or plasma-derived human FVIII [FVIII] or factor IX) or bypassing agents (recombinant activated factor VIIa [rFVIIa], plasma-derived anti-inhibitor coagulant complex [FEIBA], or recombinant porcine FVIII [rpFVIII]). Despite treatment with hemostatic agents, some hemophilia patients experience refractory bleeding. Factor XIII-A₂B₂ (FXIII) is a thrombin-activated protransglutaminase. Activated FXIII (FXIIIa) crosslinks fibrin to stabilize clots and increase red blood cell retention during clot contraction, and therefore, clot weight; these functions have been specifically associated with fibrin alpha-chain crosslinking and production of high molecular weight (HMW) crosslinked fibrin species. Although pilot studies have indicated that in hemophilia co-administration of FXIII with hemostatic agents improves hemostasis, the biochemical mechanisms evoked during co-administration have yet to be elucidated. We hypothesize that co-administration of FXIII with hemostatic agents enhances hemostasis in hemophilia by accelerating FXIII activation, increasing fibrin crosslinking, and improving the composition of contracted clots.

We first analyzed in vitrotissue factor-activated coagulation in FVIII-deficient plasmas (n=5) with or without buffer (normal saline with 0.75% bovine serum albumin), plasma-derived FXIII (2 U/mL), and/or recombinant human FVIII (1 U/mL). Reactions were performed at 37°C and quenched with urea/EDTA at varying time points. Clot lysates were separated on 10% Tris-glycine gels, blotted, probed for FXIII(a) and fibrin(ogen), and analyzed by densitometry. Compared to buffer, FXIII, or FVIII-treated hemophilic plasma, FVIII+FXIII co-treatment increased the formation rate and level of FXIIIa. Furthermore, compared to buffer or FXIII-treated hemophilic plasma, both FVIII-treatment and FVIII+FXIII co-treatment increased the formation rate and level of crosslinked fibrin species (gamma chain and HMW species). Notably, compared to FVIII-treatment (alone), FVIII+FXIII co-treatment increased the formation rate and level of HMW crosslinked fibrin species.

Next, we analyzed clot formation in whole blood obtained from untreated FVIII-deficient (n=2) or FVIII-inhibitor (n=6) patients. Citrated whole blood was pre-incubated at 37°C for 30 minutes with or without buffer, FXIII (2 U/mL), rFVIIa (25 nM), FEIBA (1 U/mL), or rpFVIII (1 U/mL), alone and in combination with FXIII, and clot formation was triggered with tissue factor and recalcification. In thrombelastography assays, compared to buffer or FXIII-treated hemophilic whole blood, rFVIIa, FEIBA, and rpFVIII treatments alone or with FXIII co-treatment shortened the time to clot formation (clot time [R]). Compared to buffer, FXIII, FEIBA or rpFVIII-treated hemophilic whole blood, rFVIIa-treatment (alone) and co-treatment with rFVIIa+FXIII or FEIBA+FXIIII increased clot stability (area under the elastic curve). In whole blood clot contraction assays, compared to buffer, FXIII, rFVIIa, FEIBA, or rpFVIII-treated hemophilic whole blood, co-treatment with rFVIIa+FXIII, FEIBA+FXIII, or rpFVIII+FXIII significantly increased clot weight.

Our data show that in hemophilic plasmas, co-administration of FXIII with hemostatic agents accelerates FXIIIa activation, resulting in accelerated and increased HMW species formation. Furthermore, in hemophilic whole blood, co-administration of FXIII with hemostatic agents improved clot biophysical characteristics and increased clot weight. Collectively, these data suggest co-administration of FXIII with conventional hemostatic agents may promote clot stability and improve the composition of contracted clots by enhancing fibrin alpha-chain crosslinking.