Protective Effects And Mechanisms Of Dexmedetomidine On Kidney And Lung Injury Induced By Renal Ischemia-reperfusion

Acute kidney injury(AKI) or Acute renal failure(ARF) induced by renal ischemia reperfusion(IR) is a common complication during perioperation, which is usually associated with increased duration of hospital stay, healthcare cost and mortality. Recent investigations demonstrated that despite improvements in dialysis technology and advances in supportive care, the morbidity and mortality associated with AKI has remained unchanged over the past two decades. AKI rarely occurs in isolation and is usually accomplicated by extrarenal organ pathologic injury and dysfunction. The lung, as an organ with large microcapillary network, is highly susceptible to injury caused by circulating pro-inflammatory mediators from kidney inflicted with ischemia reperfusion. The mortality rate of combined ARF and acute lung injury (ALI) could be up to 80%. Unfortunately, currently more effective methods to reduce renal ischemia reperfusion injury(IRI) and its induced ALI are still deficiency and anticipated. Therefore, it is significantly and necessarily to explore more better curative methods to reduce them.Recently, some studies have proved that apoptosis in tubular epithelium and immune inflammatory reaction mediated via TLR4 are the critical mechanisms leading to renal IRI. Trigger of anti-apoptosis signal cascade to reduce epithelia apoptosis or inhibition of TLR4 signaling to relieve inflammation are becoming a novel strategy to ameliorate renal IRIDexmedetomeding(Dex), applied in ICU sedation and clinical anesthesia currently, is a highly potent?2 adrenergic agonist with sedative, analgesic, hemodynamic stabilizing and diuretic effects. Some recent experiments demonstrated that Dex was able to activate protective signaling pathway to reduce neural cell apoptosis, it also could reduce myocardial infarct size and improve perioperative cardiac function as well as exert anti-inflammatory effects and improve survival rate by decreasing pro-inflammatory mediators during sedation for sepsis. Therefore, it may be naturally speculated that Dex can probably provide kidney and lung protection to improve mortality following renal IRI. The purpose of this research is to verify the hypothesis and further explore related mechanisms.Methods1. C57BL/6J mice were subjected to bilateral renal IR with or without Dex treatment and then followed by HE staining for renal histopathological assessment, TUNEL staining for tubular cell apoptosis evaluation, biochemical analysis for renal function, immuohistochemistry and Western blot for expression of kidney TLR4, ILISA for plasma HMGB1 level. The mortality was assessed after right renal IR and left nephrectomy with or without Dex treatment.2. HK2 were subcultured and the effects of Dex on HK2 injury induced by OGD were evaluated by MTT assay. Protein expressions of total Akt and phosphorylation Akt(pAkt) in HK2 with Dex treatment were determined by Western blot.3. Lungs were obtained from C57BL/6J mice subjected to bilateral renal IR with or without Dex treatment and then followed by HE staining for histopathological assessment, lung wet/dry ratio evaluation, biochemical analysis for MPO activity, RT-PCR and FQ-PCR for mRNA expression of ICAM-1and TNF-?.Results1. Increased kidney histopathological injury, tubular cell apoptosis and plasma creatinin and urea level were detected after renal ischemia 25 min and reperfuse 24 h. Pre- or post-treatment with Dex 25?g/kg resulted in 53% and 38% reduction in damage, 72% and 58% reduction in cell apoptosis as well as significant decrease in plasma creatinin and urea level.?2 adrenoceptor antagonist Atipamezole(Atip) 250?g/kg abrogated renal protective effects of Dex.2. Expression of TLR4 proteins and plasma HMGB1 level were increased after renal ischemia 25 min and reperfuse 24 h. Pre-treatment with Dex 25?g/kg downregulated them. Atip 250?g/kg reversed the downregulated effects of Dex on TLR4 and HMGB1.3. Long-term survival was noted in 70% and 60% of animal treated with Dex before and after renal IRI within 7 day. By contrast, animal not treated with Dex or receiving Atip combined Dex fared much worse. Within 3 day, 65% of these animals were dead and no animal survived beyond 5 day.4. HK2 viability analysis using MTT assay showed a time-dependent induction of injury with marked cell death(60% reduction in viability) occurring after 180-min OGD. Incubating HK2 with Dex(0.001, 0.01 and 0.1 nM) before OGD exposure dose- dependently inhibited injury. Treatment with 0.1 nM Dex increased cell viability to 94%. The cytoprotective effect of Dex was abolished by co-treatment with Atip 1 nM.5. HK2 incubated with media containing 0.1 nM Dex for 5, 10, 20, 30, 45 min. pAkt was increased at all time points and peaked after 20 min whereas total Akt were not altered. Atip 1 nM reduced but not completely abolish Dex induced upregulation of pAkt. PI3-Akt inhibitor LY294002(50?M) rather than MAPK inhibitor PD98059 (50?M) completely abolished Dex-induced activation of Akt.6. Bilateral renal ischemia 45 min followed by 6 h reperfusion induced histopathological injury, 3.5 fold increasing of lung wet/dry ratio, 1 fold increasing of MPO activity, 7 and 10 fold upregulation of mRNA expression of ICAM-1 and TNF-?in lung. Pre- or post-treatment with Dex resulted in about one third decreasing of lung wet/dry ratio, 58% and 16% decline of MPO activity, moreover significantly inhibited mRNA overexpression of CAM-1 and TNF-?and ameliorated lung injury. Atip abrogated the downregulated effects of Dex on wet/dry ration and MPO activity but failed to reverse the downregulated effects of Dex on ICAM-1 and TNF-?mRNA.Conclusions1. Dex provides renoprotection against ischemia-reperfusion injury in C57BL/6J mice.2. It is main renoprotective mechanism that Dex inhibits cell apoptosis and downregulates protein expression of TLR4 and plasma level of HMGB1 via activating?2 adrenoceptor.3. Dex is able to reduce HK2 injury induced by OGD and the activation of PI3K-Akt signaling via?2 adrenoceptor dependent and independent pathway is probably the main mechanism.4. Dex attenuates remote lung injury induced by renal ischemia-reperfusion in C57BL/6J mice.5. The mechanism of Dex'pulmonary protection is that lung inflammation may be ameliorated via triggering?2 adrenoceptor dependent and independent signal pathway.