The Protective Effect And Partial Mechanism Of Dexmedetomidine On Renal Ischemia/Reperfusion(Hypoxia/Reoxygenation) Injury

BackgroundDexmedetomidine(Dex),served as a highly selective a2 adrenoceptor agonist,is characterized by analgesia,sedationand anxiolytic property.It has been shown that Dex has advantages in reducing anesthetic requirements,enhancing hemodynamic stability and providing sedation following cardiac surgery.As its wide application in cardiac surgery under CPB,Dex has shown significant effect on reducing the postoperative lung and brain injury,However,the safety and effect on of Dex for renal protection is controversial.Sugita S et al.have reported that continuous infusion of Dex alleviates renal ischemia reperfusion injury in rat kidney while Kari et al.have suggested that intravenous Dex does not show protective effect on the renal function but only increases the uriary output.Acute kidney injury is a global public health concern associated with high morbidity,mortality,and healthcare costs.Cardiac surgery under cardiopulmonary bypass,is the main cause for the thrombosis,abnormal physiological perfusion and local kidney ischemia hypoxia injury,which may progress to different degrees of acute kidney injury,AKI is commonly occurred after cardiac surgery under CPB,which brings about adverse outcomes and high treatment costs.Cardiac valve replacement is a common type of cardiac surgery,and clinical study has demonstrated that valvular heart surgery is an independent risk factor for AKI.The early diagnosis and intervention of AKI in patients subjected to cardiac valve replacement under CPB is crucial.Renal protection should be put on the schedule during cardiac surgery under cardiopulmonary bypass,and anesthetic drug improvement may be an available and important strategy.Whether Dex is able to attenuate the renal injury in patients undergoing cardiac valve replacement under CPB remained to be solved.Endoplasmic reticulum is the largest organelle in eukaryotic cells and plays an important role in maintaining homeostasis.When the cell's demand for the function of the endoplasmic reticulum exceeds its own capacity,unfolded or misfolded proteins accumulate in the endoplasmic reticulum(ER)and the pathological state of the steady imbalance of calcium ions called endoplasmic reticulum stress(ERS).Studies have shown that moderate ERS is a kind of self protection mechanism,cells by activating unfolded protein reactions,temporarily inhibit protein synthesis,promote protein folding correctly,strengthen unfolded or misfolded proteins degradation,restore endoplasmic reticulum steady state to maintain cell survival.However,excessive or prolonged ERS may lead to cells apoptosis or necrosis,resulting in organ and tissue damage.ER stress can be triggered by various stimuli,such as ischemia,hypoxia,oxidative stress,glucose starvation,and elevated protein synthesis.what is one of the important ways to activate cell apoptosis.A lot of study shows that ERS was involved in the reperfusion injury of vital organs such as heart,brain and kidney,But whether ERS is involved in the kidney protection of Dex is unclear.Oxidative stress mediated by ROS is involved in the pathogenesis of I/R injury.Oxygen free radical is one of the important factors that induce renal ischemia reperfusion injury.Oxygen free radicals can react with lipid peroxidation of unsaturated fatty acids in biofilms to damage the body tissue cells.Oxygen free radicals also participate in cell signal transduction and regulate apoptosis.ObjectivesPart I clinical study:1.To measure the levels of BUN,Cr,NGAL,IL-18.The urine output during operation and the post-operative complication of acute kidney injury(AKI)were recorded.to explore the effect of Dex on renal function and the incidence of AKI in patients with cardiac valve replacement under cardiopulmonary bypass.2.To measure the level of MDA and the SOD activity,to explore whether the lipid peroxidation is involved in the effect of Dex on renal function and the incidence of AKI in patients with cardiac valve replacement under cardiopulmonary bypass.Part II cultured cells experiment1.To measure the cell viability and cell apoptosis,to explore the protective effects of Dex on the apoptosis of renal tubular epithelial cells induced by hypoxia/reoxygenation2.To measure the the expression of GRP78,CHOP,caspase-12,cleaved caspase-3,the level of MDA and the activity of SOD,to explore the potential mechanism of ERS and lipid peroxidation in the protection of Dex.MethodsPart I clinical study:The effect of dexmedetomidine on the postoperative incidence rate of acute kidney injury and renal function in patients undergoing cardiac valve replacement under cardiopulmonary bypass:A double-blind randomized controlled trialWe designed a prospective,randomized,placebo-controlled,single-center,parallel-arm double-blind trial.Patients were randomly divided into Dex group and Placebo group.Dex(0.6?g.kg-1)was administered in patients of Dex group at 15 min before anesthesia induction,followed by a treatment of 0.2 ?g.kg-1.h-1 Dex until the end of operation.Patients in Placebo group were treated with normal saline equally.The levels of serum urea nitrogen(BUN),creatinine(Cr),neutrophil gelatinase-associated lipocalin(NGAL),IL-18,MDA level and SOD activity were tested before anesthesia induction(T1)and after operation at 0,12 h,24 h and 72 h(T2-5).The urine output during operation and the post-operative complication of acute kidney injury(AKI)were recorded.Part ? cultured cells experimentRole of endoplasmic reticulum stress pathway in dexmedetomidine on hypoxia/reoxygenation in human renal tubular epithelial cellsHuman renal tubular epithelial cells(HK-2 cells)cultured in vitro were randomly divided into 4 groups(n=5 each)using a random number table:control group(group C):the cells were incubated for 28 h in an incubator filled with normoxia at 37?;the Dexmedetomidine group:Dexmedetomidine 0.1nmol/L(final concentrations)was added to the culture medium and the cells were incubated for 2 h,and then incubated for 28 h in an incubator filled with normoxia at 37?:H/R group:the cells were incubated in an anaerobic chamber for 24 h at 37 ? and then incubated for 4 h in an incubator filled with normoxia at 37?;the Dexmedetomidine + H/R group:the cells was incubated for 2 h in the culture medium containing Dexmedetomidine 0.1 nmol/L(final concentrations)and then incubated in an anaerobic chamber for 24 h at 37 ? and then incubated for 4 h in an incubator filled with normoxia at 37?.After treatment in each group,the cell viability was measured by MTT assay,cell apoptosis was measured using flow cytometry,Compared with group H/R,the cell survival rate increased and apoptosis rate decreased.The expression of glucose-regulated protein 78(GRP78)and C/EBP homologous protein(CHOP),caspase-12,cleaved caspase-3 were determined by western blot.The level of malondialdehyde(MDA)and the activity of superoxide dismutase(SOD)were detected.ResultsPart I clinical study:Finally,72 patients were included in our study.The baseline demographic characteristics were similar between the two groups(P>0.05).Besides,there was no significant difference in surgical characteristics,and duration of aortic occlusion and CPB between the two groups(P>0.05).Compared with the levels at T1,the plasma levels of BUN and Cr at T5 were significantly increased in both two groups.The levels of serum NGAL and urine IL-18 in both two groups were significantly elevated at T3 and T4,the plasma level of MDA was increased and the plasma activity of SOD was declined significantly at T2 and T3(P<0.05).For Placebo group,the levels of BUN and Cr at T5 were significantly higher than Dex group,the level of serum NGAL at T3 and T4 was significantly higher,the plasma level of MDA was significantly higher and the plasma activity of SOD at T2 and T3 was significantly lower than Dex group(P<0.05).Compared with Placebo group,the incidence of AKI was significantly decreased,and the urine volume during the entire process of surgery was obviously increased in Dex group(P<0.05).Part ? cultured cells experimentCompared with group C,the cell viability was significantly decreased,the cell apoptotic rate was increased in groups H/R and Dex + H/R(P<0.05).Compared with group H/R,the cell viability was significantly increased and the cell apoptotic rate was significantly decreased in each Dex+ H/R group.Compared with group C,SOD activity was significantly decreased and the concentration of MDA were increased,and the expression of GRP78,CHOP,caspase-12 and cleaved caspase-3 were up-regulated in groups H/R and Dex + H/R.Compared with group H/R,the SOD activity was significantly increased,the concentration of MDA was decreased,and the expression of GRP78,CHOP,caspase-12 and cleaved caspase-3 were down-regulated in group Dex + H/R(P<0.05).ConclusionsPart ? clinical study:1.Dex may attenuate the renal injury and decrease the incidence of AKI in patients undergoing cardiac valve replacement under cardiopulmonary bypass.2.lipid peroxidation is involved in the mechanism of the effect of Dex on renal function in patients with cardiac valve replacement under cardiopulmonary bypass.Part ? cultured cells experiment1.Dexmedetomidine can inhibit H/R induced apoptosis in human renal tubular epithelial cells.2.Endoplasmic reticulum stress pathway is involved in the mechanism of Dex inhibit H/R induced apoptosis in human renal tubular epithelial cells.