Ulinastatin Improves Endothelial Cells Injury, Attenuating Cardiac Ischemia/Reperfusion Injury via Suppressing Tissue kallikrein-kinin System Activation

Abstract Background : Ulinastatin (UIT) has been considered to have beneficial effects for patients undergoing coronary artery bypass grafting (CABG) surgery due to its anti-inflammatory properties, whereas the underlying mechanism remains unclear. Approach and Results: We established an interlink among UIT, the kallikrein-kinin system (KKS), endothelial dysfunction and cardiac inflammation in response to ischemia/reperfusion injury (IRI), using clinic investigation, in vitro and in vivo experiments, and RNA sequencing analysis. UIT was observed to inhibit the activity of tissue kallikrein (KLK1), a key enzyme of the KKS, at 24 hours after CABG surgery, which was verified in a mouse cardiac ischemia-reperfusion (I/R) model. Under normal conditions, UTI only inhibited KLK1 activity but did not affect bradykinin receptors (Bdkrs). Our in vitro and in vivo experiments revealed that UTI protected against IRI by suppressing the activation of KKS and down-regulating Bdkr-related signaling pathways including extracellular-signal–regulated kinase (ERK)/inducible nitric oxide synthase (iNOS) , which resulted in enhanced endothelial barrier function, mitigation of inflammation and edema, diminution of infarct size, ameliorated cardiac function, and decreased mortality. Inhibition of KLK1 and knockdown of bradykinin receptor 1 (Bdkrb1) not bradykinin receptor 2 (Bdkrb2) significantly prevented ERK translocation into the nucleus, reducing reperfusion-induced mouse cardiac endothelial cells (MCECs) injury. Conclusion: Our findings imply that UIT exerts a protective effect on cardiac reperfusion by suppressing the activation of KKS and highlightsthat inhibiting KLK1/Bdkrb1 is a potential intervention targeting endothelial dysfunction to ameliorate cardiac IRI.