Background:
Infective endocarditis (IE) remains among the deadliest infectious diseases, with mortality of 15–40% despite optimal therapy. Bacterial vegetations are stabilized by a factor XIII (FXIII)–cross-linked fibrin meshwork that shelters bacteria, shields them from immune clearance, and limits antibiotic penetration. While experimental systemic fibrinolysis reduces vegetations, it is clinically untenable due to bleeding risk. Selective destabilization of cross-linked fibrin, rather than systemic clot dissolution, may therefore represent a safer therapeutic strategy in established IE.
Hypothesis:
We hypothesize that selective FXIII inhibition destabilizes cross-linked fibrin, rendering IE-associated clots susceptible to lysis and reducing bacterial incorporation, without abolishing clot formation or systemic coagulation.
Methods:
Fibrin clot stability was assessed by a turbidimetric clot-lysis assay in which plasma clots were formed with increasing ZED1301 concentrations (0.01–1 µM) plus tPA (0.125 µg/mL), and lysis was monitored as OD360nm over time. We employed our established in vitro flow-chamber system, perfusing human plasma inoculated with S. aureus under defined shear stress, and compared FXIII-depleted plasma and the direct FXIII inhibitor ZED1301 (0.1–3 µM) with control. Relative bacterial adhesion was quantified by image-based analysis (Kruskal–Wallis with Dunn's test).
Results:
FXIII depletion and pharmacological FXIII inhibition reduced S. aureus adhesion under flow. ZED1301 lowered relative bacterial adhesion dose-dependently, reaching significance at 3 µM (67.9 ± 8.2 vs control 100.0 ± 9.5; p=0.040), comparable to FXIII-depleted plasma (65.6 ± 12.0; p=0.022), whereas lower concentrations had no effect (0.1 µM: 100.3 ± 13.3; 0.3 µM: 96.0 ± 13.0; both ns). Critically, in the clot-lysis assay the direct FXIII inhibitor (at concentrations 1 µM or higher) accelerated tPA-mediated lysis of IE-relevant fibrin clots in a clear dose-dependent manner, while baseline clot formation (initial turbidity) remained unchanged across all concentrations. Thus, FXIII inhibition selectively destabilizes and lyses cross-linked fibrin clots without impairing clot formation, i.e., without systemic coagulation impairment.
Conclusion:
Selective FXIII inhibition enhances lysis of cross linked IE clots, reducing bacterial incorporation into fibrin, while preserving primary clot formation, supporting fibrin stability, rather than fibrin generation, as a safer therapeutic target in established IE.
