The Effects And Underlying Mechanisms Of Ischemic Preconditioning In Renal Ischemia Reperfusion Injury

Background:Renal ischemia reperfusion injury(IRI)inevitably occurs in renal transplantation and partial nephrectomy,which could significantly increase the morbidity,mortality,and medical resource utilization.Ischemic preconditioning(IPC)has been proposed as a potent therapeutic approach to enhance ischemia tolerance and preserve renal function;however,the underlying mechanisms remain far from understood.Part 1 Effects of Ischemic Preconditioning on the Systemic and Renal Hemodynamic Changes in Renal Ischemia Reperfusion InjuryObjectives:Explore the effects of IPC on the renal and systemic hemodynamic changes,renal function and morphology,as well the involvement of endothelial and inducible nitric oxide synthase(eNOS/iNOS),and nitric oxide(NO).Methods:Male Sprague-Dawley rats were randomly divided into five groups after right-side nephrectomy:Sham group(surgery without vascular clamping);IRI group(the left renal artery was clamped for 45 min);IPC group(pretreated with 15 min of ischemia and 10 min of reperfusion);IPC+vehicle group(administrated with 0.9%saline 5 min before IPC);and IPC+NG-nitro-L-arginine methylester(L-NAME)group(pretreated with L-NAME 5 min prior to IPC).The renal and systemic hemodynamic parameters,renal function and morphology,eNOS,iNOS,and NO expression levels in kidneys were measured at different time points after reperfusion.Results:IPC rats exhibited significant improvements in renal function,morphology,and renal artery blood flow(RABF),without obvious influence on the systemic hemodynamics and renal vein blood flow.Increased eNOS,iNOS,and NO expression levels were detected in the kidneys of IPC rats 24 h after reperfusion.Furthermore,the beneficial effects were abolished by the administration of L-NAME.Conclusions:The results suggest that IPC contributes to early restoration of RABF,probably through eNOS/iNOS-mediated NO production,thereby alleviating the renal dysfunction and histological damage caused by IRI.Part 2 Ischemic Preconditioning Protects Against Renal Ischemia Reperfusion Injury via Inducing AutophagyObjectives:Investigate the influence of IPC on autophagy in IRI kidneys,and the protective effects of autophagy in renal IRI.Methods:Male Sprague-Dawley rats were randomly divided into five groups after right-side nephrectomy:Sham group(surgery without vascular clamping);IRI group(the left renal artery was clamped for 45 min);IPC group(pretreated with 15 min of ischemia and 10 min of reperfusion);IPC+Vehicle group(administrated with PBS 10min prior to IPC);and IPC+3-methyladenine(3-MA)group(pretreated with 3-MA 10 min before IPC).The autophagy levels were measured via Western blot,immunohistochemistry,and transmission electron microscopic examination(TEME),as well as the renal function and morphology.Results:The expression levels of Beclin-1 and LC3-? in the ischemic preconditioned kidneys increased from 4h post reperfusion and peaked at 12h,which were further validated by the expression patterns of LC3 in kidney tissues through immunohistochemistry analyses and the presence of autophagosomes via TEME.Furthermore,the autophagy levels were inhibited after administration of 3-MA,meanwhile the renal function and morphology injuries worsened.Conclusions:IPC could induce autophagy in the IRI kidneys,which could contribute to the renoprotective effects of IPC.