Background: Platelets play a critical role during hepatic ischemia/reperfusion (I/R). Antiplatelet strategies during liver transplantation are, however, limited because of bleeding complications. Thrombin is activated during reperfusion and regulates platelet and endothelial cell function via protease-activated receptor 4 (PAR-4). Interventions at the level of PAR-4, the main platelet receptor for thrombin, are assumed to attenuate the proinflammatory effects of thrombin without affecting blood coagulation. The aim of our study was to analyze the impact of PAR-4 blockade on platelet recruitment and microvascular injury during hepatic I/R.
Methods: C57BL/6 mice undergoing hepatic I/R (90 min/60 min and 240 min) were treated either with a selective PAR-4 antagonist TcY-NH2 or vehicle. Sham-operated animals served as controls. Recruitment of freshly isolated and fluorescence-labeled platelets and CD4 T cells was analyzed using intravital video fluorescence microscopy. Parameters of tissue injury, regeneration, and blood coagulation were assessed in tissue/blood samples.
Results: Results show that treatment with TcY-NH2 attenuated I/R-induced platelet and CD4 T-cell recruitment, improved sinusoidal perfusion failure, and reduced apoptotic and necrotic injury. The protective effect of PAR-4 blockade did not suppress hemostasis or liver regeneration.
Conclusion: Our in vivo data suggest PAR-4 as a potential target for future therapeutic strategies against platelet-mediated liver injury on transplantation.