Background: Coagulation factor XIII (FXIII) is a key player in clot structural stability and lysis catalysing crosslinking reactions of fibrin. FXIII has been associated with increased risk of coronary artery disease and myocardial infarction, although there are few studies focused on ischemic stroke.

Aims: The purpose of this study is to evaluate the impact of FXIII in a mouse model of ischemic stroke by analysing cerebral infarct size and functional outcome, and its involvement in ex-vivo thrombus formation and lysis.

Methods: We performed a ferric chloride-induced distal middle cerebral artery occlusion stroke model in mice (n=26) treated with FXIII inhibitor (ZED1301, Zedira) or vehicle. Infarct size and neurological test were evaluated 24h after stroke. In addition, thromboelastometry (ROTEM) with FXIII inhibitor and tPA was performed on both, human and mice blood samples, to evaluate the influence of FXIII on thrombus stiffness and lysis. Finally, fibrin networks were generated ex-vivo and the effect of active FXIII (FXIIIa) and alpha-2-antiplasmin (a2-AP) on fibrin crosslinking and lysis were studied using confocal microscopy.

Results: Animals treated with FXIII inhibitor presented lower infarct size and improved motor coordination compared to vehicle 24h after stroke, without concomitant intracranial bleeds (Figure 1). In ROTEM analysis, FXIII inhibitor (20µM) significantly delayed clot formation time (CFT) and decreased the maximum clot firmness (MCF) in both human and mice blood. In the presence of tPA, lysis time was shorter in samples treated with FXIII inhibitor. Fibrin crosslinking, determined by confocal microscopy, was increased and Tenecteplase (TNK) lysis was decreased (15.7µm²/s vs 26.5 µm²/s) after addition of FXIIIa (Figure 2). Moreover, when a2-AP was cross-linked to fibrin by FXIIIa, TNK lysis activity was further reduced (4.1 µm²/s).

Ferric chloride-induced stroke model in mice. A) Experimental design. B) Brain infarct size in mice treated with FXIII inhibitor (4,7mM) and control group. C) Coat hanger test during the first 5 seconds at baseline and 24h after stroke. *p<0.05

Effect of FXIII on fibrin clot formation and lysis. A) Representative ROTEM® tracing (TEMogram) of human blood samples treated or not with FXIII inhibitor (20µM) in the presence and absence of tPA (250 U/mL). B) The clot formation time (CFT), maximum clot firmness (MCF) and the alpha angle, which describe clot kinetics, of mice blood samples treated or not with FXIII inhibitor (20µM). C) Confocal images of fibrin networks (left) and lysis activity of both, tPA and TNK, on fibrin crosslinked meshwork with FXIIIa and a2AP. FXIIIa: active Factor XIII. a2AP: apha-2-antiplasmin. TNK: Tenecteplase. *p<0.05 and **p<0.01 vs control.

Conclusions: Our results suggest a possible role for FXIII in thrombus stabilization and resistance to revascularization treatments resulting in increased infarct size in experimental ischemic stroke.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/factor-xiii-increases-cerebral-infarct-size-by-promoting-thrombus-stabilization-and-resistance-to-revascularization-treatments-in-ischemic-stroke/