Protective Effects And Mechanisms Of Dexmedetomidine On Myocardial Injury Induced By Hepatic Cold Ischemia Reperfusion

China is one of the countries with the highest incidence of liver disease.Decompensated liver cirrhosis,liver cancer,liver failure result in irreversible liver damage,eventually developed into end-stage liver disease.At present,liver transplantation?LT?is the only effective treatment for end-stage liver disease.Cold ischemia-reperfusion of the liver is an inevitable pathophysiological process during liver transplantation,which not only leads to liver injury but also causes myocardial injury.Myocardial injury is one of the main causes of postoperative death.Dexmedetomidine?Dex?is a highly selective ?2-adrenoreceptor agonist with dose dependent analgesic,sedative,anxiolytic and inhibition of sympathetic nerve.Dex has been widely used in clinical anesthesia.The existing literature confirms that Dex has a protective effect on myocardial injury induced by myocardial ischemia-reperfusion.But there is few researches studying the protective effects of Dex against myocardial injury induced by liver cold ischemia-reperfusion and its mechanism is not clear.Therefore,we conduct this research to identify the effect of Dex and provide the mechanism for it.We divided this research into 2 parts:Part one:The clinical research of protective effects of Dex against myocardial injury induced by liver cold ischemia-reperfusionObjective To investigate the effects of dexmedetomidine on myocardial injury in adult patients undergoing liver transplantation?LT?.Methods This study was approved by the hospital ethics committee?approval number: 2016N0038KY?,and signed the informed consent of the patient or family.Sixty ASA II or III patients aged 42-63 yr,body mass index 18-25 kg/m2 scheduled for liver transplantation were randomly divided into 2 groups?n=30?: control group?group C?and dexmedetomidine group?group D?.In this study,all cases were treated with classic unturn-flowing orthotopic liver transplantation and all patients were successfully completed surgery.Anesthesia was induced with intravenous midazolam 0.1 mg/kg,etomidate 0.3 mg/kg,sufentanil 1 ?g/kg and cisatracurium 0.15 mg/kg.Mechanical ventilation parameters were set as follows: respiratory rate of 10 to 14 times/min,a tidal volume of 8-10 ml/kg,and a fraction of inspired oxygen with a ratio of 1:2.The endtidal carbon dioxide?PETCO2?was maintained at 35–40 mm Hg.The central venous pressure?CVP?and the mean pulmonary artery pressure?MPAP?were monitored by three lumen central venous catheter and Swan-Ganz catheter.Stroke volume variation?SVV?and cardiac output?CO?were monitored by Flo Trac/Vigileo.Anesthesia was maintained with the target controlled infusion of propofol 2-4?g/ml,intravenous infusion of remifentanil 0.1–0.2 ?g/kg per min and with cisatracurium,which was given at a rate of 1-2?g/kg per min and then supplied with 1% to 2% inhalation of sevoflurane.The BIS was monitored between 40 and 50 during surgery.Intraoperative hemoglobin maintained more than 80 g/L.The plasma was injected according to the coagulation function.The Dex group received an initial bolus dose of dexmedetomidine 0.5 ?g/kg over 12 min,followed immediately by a continuous infusion of 0.5 ?g/kg/h.The Dex infusion started after the induction of anesthesia and continued till the end of surgery.The same volum of normal saline was i.v injected in group C.HR,MAP,CVP,MPAP,SVV and CO were recorded after the induction of anesthesia and at skin incision and 30 min of anhepatic phase and 30 min of neohepatic stage and the end of surgery.Blood samples were taken from the central vein after the induction of anesthesia?T₀,baseline?,at 30 min after anhepatic phase?T₁?,30 min of neohepatic stage?T₂?and the end of surgery?T3?and 4h?T4?and 24h?T5?after operation for the determination of serum tumor necrosis factor-??TNF-??,interleukin-6?IL-6?,interleukin-10?IL-10?,high mobility group box 1 protein?HMGB1?,heart-type fatty acid binding protein?H-FABP?,cardiac troponin I?c Tn I?,myoglobin?Myo?,N-terminal pro-brain natriuretic peptide?NT-pro BNP?,creatine kinase-MB?CK-MB?concentrations and lactate dehydrogenase?LDH?,alpha-hydroxybutyrate dehydrogenase??-HBDH?activities.Blood samples were taken from the radial artery for blood gas analysis at T₀-5.The dosage of vasoactive agent was recorded during surgry.The incidence rate of postreperfusion syndrome?PRS?,myocardial ischemia,bradycardia,premature ventricular contraction,atrial fibrillation,ventricular tachycardia and myocardial infarction was recorded.Extubation time and ICU stay time were recorded.Results?1?Hemodynamic changes: Compared with the baseline value,HR was significantly increased from skin incision to the end of surgery,MAP was significantly increased at skin incision,30 min of neohepatic stage and the end of surgery and decreased at 30 min of anhepatic phase,CVP,MPAP and CO were significantly decreased at 30 min of anhepatic phase and increased at 30 min of neohepatic stage and the end of surgery,SVV was significantly increased at 30 min of anhepatic phase and decreased at 30 min of neohepatic stage in both groups?P<0.05?.Compared with group C,HR was significantly decreased from skin incision to the end of surgery,MAP was decreased at skin incision in group D?P<0.05?.?2?Changes of serum cytokines: Compared with T₀,the serum concentrations of TNF-?,IL-6 and IL-10 were significantly increased at T₁-5,the serum concentration of HMGB1 was significantly increased at T₂-5 in both groups?P<0.05?.Compared with group C,the serum concentrations of TNF-? and IL-6 were significantly decreased at T₁-5,the serum concentration of IL-10 was significantly increased at T₁-5,the serum concentration of HMGB1 was decreased at T₂-5 in group D?P<0.05?.?3?Changes of myocardial injury markers: Compared with T₀,levels of serum H-FABP,c Tn I,Myo,NT-pro BNP,CK-MB,LDH and ?-HBDH were significantly increased at T₂-5 in both groups?P<0.05?.Compared with group C,levels of serum H-FABP,c Tn I,Myo,NT-pro BNP,CK-MB,LDH and ?-HBDH were significantly decreased at T₂-5 in group D?P<0.05?.?4?Comparison of other indicators: Compared with group C,the dosage of vasoactive agent was significantly decreased in group D?P<0.05?.There was no significant difference in the incidence rate of PRS,bradycardia,premature ventricular contraction,atrial fibrillation,myocardial infarction and extubation time,ICU stay time and blood gas analysis at T₀-5 between the two groups?P>0.05?.Conclusion Intravenous infusion of dexmedetomidine can reduce the intraoperative application of vasoactive drugs and decrease the incidence rate of myocardial ischemia and ventricular tachycardia and inhibit inflammatory reaction and ameliorate myocardial injury induced by liver cold ischemia-reperfusion during LT.Part two:Protective effects and mechanisms of Dex on myocardial injury induced by hepatic cold ischemia reperfusion in ratsObjective To investigate the effects of dexmedetomidine on myocardial injury in rats undergoing liver cold ischemia reperfusion.Methods Forty healthy male Sprague-Dawley rats,weighing 220-250 g,aged 8-10 weeks,were randomly divided into 5 groups?n=8 each?using a random number table: sham operation group?group Sham?,liver cold ischemia reperfusion group?group Model?,dexmedetomidine group?group Dex?,atipamezole group?group Atip?,JAK2 kinase inhibitor AG490 group?group AG490?.In group Dex,rats received dexmedetomidine 100?g/kg 30 min before establishing model;In group Atip,rats received atipamezole 500?g/kg 30 min prior to dexmedetomidine treatment;In group AG490,rats received AG490 10mg/kg 30 min before establishing model.At 8h of reperfusion,blood samples were collected from the infra-hepatic vena cava for determination of serum TNF-?,IL-6,HMGB1,CK-MB,c Tn I and H-FABP levels by ELISA.After blood sampling,the rats were sacrificed,and hearts were harvested for examination of histopathological changes?with light microscope?and for determination of malondialdehyde?MDA?content?using thiobarbituric acid method?and superoxide dismutase?SOD?activity?by xanthine oxidase method?,expression of activated caspase-3?by immuno-histochemistry?,and apoptotic cells?using TUNEL?.Apoptotic rate was calculated.The expression of phosphorylations of JAK2,STAT₁ and STAT3 were assessed by Western blot.Results Compared with group Sham,the levels of TNF-?,IL-6,HMGB1,CK-MB,c Tn I and H-FABP were significantly increased,the MDA content was increased,the SOD activity was decreased,apoptotic rate was increased,Pathological damage aggravated,and the expression of activated caspase-3,p-JAK2,p-STAT₁ and p-STAT3 were up-regulated in other groups?P<0.05?;Compared with group Model,the levels of TNF-?,IL-6,HMGB1,CK-MB,c Tn I and H-FABP were significantly decreased,the MDA content was decreased,the SOD activity was increased,apoptotic rate was decreased,Pathological damage alleviated,and the expression of activated caspase-3,p-JAK2,p-STAT₁ and p-STAT3 were down-regulated in group Dex and AG490?P<0.05?;Compared with group Dex,the levels of TNF-?,IL-6,HMGB1,CK-MB,c Tn I and H-FABP were significantly increased,the MDA content was increased,the SOD activity was decreased,apoptotic rate was increased,Pathological damage aggravated,and the expression of activated caspase-3,p-JAK2,p-STAT₁ and p-STAT3 were up-regulated in group Atip?P<0.05?.Conclusion Dexmedetomidine can ameliorate myocardial injury induced by liver cold ischemia-reperfusion in rats,and the mechanism is related to its anti-inflammatory,antioxidant and inhibition of activation of JAK/STAT pathway.