Ulinastatin attenuated cardiac ischaemia/reperfusion injury by suppressing activation of the tissue kallikrein‐kinin system

Abstract Background and Purpose Ulinastatin has beneficial effects in patients undergoing coronary artery bypass grafting (CABG) surgery due to its anti‐inflammatory properties, but the underlying mechanism remains unclear. Experimental Approach We used samples from patients undergoing CABG, a model of cardiac ischaemia–reperfusion injury (IRI) in mice and murine cardiac endothelial cell cultures to investigate links between ulinastatin, the kallikrein‐kinin system (KKS), endothelial dysfunction and cardiac inflammation in the response to ischaemia/reperfusion injury (IRI). These links were assessed using clinical investigations, in vitro and in vivo experiments and RNA sequencing analysis. Key Results Ulinastatin inhibited the activity of tissue kallikrein, a key enzyme of the KKS, at 24 h after CABG surgery, which was verified in our murine cardiac ischaemia–reperfusion model. Under normal conditions, ulinastatin only inhibited kallikrein activity but did not affect bradykinin (B 1 /B 2 ) receptors. Ulinastatin protected against IRI, in vivo and in vitro, by suppressing activation of the kallikrein‐kinin system and down‐regulating B 1 /B 2 receptor‐related signalling pathways including ERK/ iNOS, which resulted in enhanced endothelial barrier function, mitigation of inflammation and oedema, decreased infarct size, improved cardiac function and decreased mortality. Inhibition of kallikrein and knockdown of B 1 , but not B 2 receptors prevented ERK translocation into the nucleus, reducing reperfusion‐induced injury in murine cardiac endothelial cells. Conclusions and Implications Treatment with ulinastatin exerts a protective influence on cardiac reperfusion by suppressing activation of the kallikrein‐kinin system. Our findings highlight the potential of targeting kallikrein /bradykinin receptors to alleviate endothelial dysfunction, thus improving cardiac IRI.