Effect And Mechanism Of Dexmedetomidine On Neurologic Apoptosis And Autophagy In A Rat Model Of Asphyxial Cardiac Arrest

Objective: To observe the impact of dexmedetomidine(Dex)on rats’ core temperature and neurological function after return of spontaneous circulation(ROSC)from asphyxia cardiac arrest(CA),determine the morphological change and molecular biology expression of cortical and hippocampal neurocytes 12 or 24 h after ROSC,and investigate the effects and mechanisms of Dex on apoptosis and autophagy of rat nerve cells after cardiopulmonary resuscitation.Methods: 204 male,healthy and adult SD rats were randomly divided into four groups: blank control group(BC),normal resuscitation group(N),Dex resuscitation group(D)and Dex + antogonist resuscitation group(DT).Each group has 66 except the control group being 6.After ROSC,the rats of three resuscitation groups were divided again into two subgroups: 12 h and 24 h subgroup,the sample volume of each subgroup was determined by the final survival of resuscitative rats.The CA model in rats was duplicated by asphyxia method,the rats of N group received routine medical therapy(intravenous injection of epinephrine and sodium bicarbonate)during cardiopulmonary resuscitation(CPR),D group received the intraperitoneal injection of Dex in addition to the routine CPR therapy,DT group received the intraperitoneal injection of Dex and Yohimbine in addition to the routine CPR therapy.After ROSC,core temperature of rats in every resuscitation group was monitored under a constant environment temperature of 25 ℃.At the time point of observation(12 or 24 h after ROSC),the rats were evaluated for neurological deficits scores(NDS).After scoring,the rats were quickly sacrificed and their brains were taken to obtain the cerebral hippocampus and cortex tissues,which were next observed by pathology and electron microscopy.The cerebral cortex was processed into single-cell suspension to determine the reactive oxygen species(ROS)level in the neurocytes by flow sytometer(FCM).Immunohistochemistry(IHC)was used to detect changes of caspase-3 expression in hippocampal neurocytes.The expression changes of heat shock protein 70(HSP70),Bcl-2,Bax and autophagy related protein Beclin1 in hippocampal neurocytes were detected by western-blotting(WB).Results: After resuscitation,under the constant environment temperature of 25 ℃,the core temperature of the rats in D group which were impacted by Dex,was decreased significantly compared with that in group N(P < 0.05),but the core temperature of DT group which were antagonized by Yohimbine,was no statistical difference comparing to N group.NDS in N group which were resuscitated in routine ways,was significantly lower than that in BC group(P < 0.05),NDS in D group which were injected Dex,was significantly higher than that in N group(P < 0.05),and NDS in DT group antagonized by Yohimbine was significantly lower than that in D group(P < 0.05).The damage of hippocampal neurocytes in N group was significantly worse than that in BC group under the observation of light microscope and electron microscope,but in D group the damage of hippocampal neurocytes was reduced compared with that in group N,and the damage was more obvious in DT group than that in D group.The ROS level of cortical neurocytes in N group which were resuscitated in routine ways,was significantly higher than that in BC group(P < 0.05),but in D group which were impacted by Dex,ROS level of neurocytes was decreased compared with that in N group(P < 0.05),and the ROS level of cortical neurocytes in DT group antagonized by Yohimbine was also increased compared with that in D group(P < 0.05).Caspase-3 expression in N group increased significantly compared with BC group(P < 0.05),but in D group caspase-3 expression decreased significantly compared with N group(P < 0.05),and caspase-3 expression in DT group increased significantly compared with group D(P < 0.05).Bax expression in N group increased significantly compared with BC group(P < 0.05),but in D group Bax expression decreased significantly compared with N group(P < 0.05),and Bax expression in DT group increased significantly compared with D group(P < 0.05).Beclin1 expression in N group increased significantly compared with BC group(P < 0.05),and Beclin1 expression in D group decreased significantly compared with N group(P < 0.05),but Beclin1 expression in DT group showed no significant difference compared with D group(P > 0.05).The expression of bcl-2 in N group was significantly decreased compared with that in BC group(P < 0.05),and bcl-2 expression in D group was significantly increased compared with that in N group(P < 0.05),but in DT group bcl-2 expression was not significantly different from that in D group(P > 0.05).The expression of HSP70 in N group significantly increased compared with BC group(P < 0.05),but in D group the HSP70 expression significantly increased compared with N group(P < 0.05),and the expression of HSP70 in DT group significantly decreased compared with D group(P < 0.05).Conclusion: The combined intraperitoneal injection of Dex with conventional medicine for CPR had significant hypothermia effect on resuscitated rats and significantly improved the neurological function of resuscitated rats.The mechanism was related to the pharmacology of Dex to reduce ROS levels in brain cortical neurocytes of rats after resuscitation,increase or decrease the apoptosis-related proteins expression of HSP70,caspase-3 and Bax,regulate the autophagic effect of Bcl-2-Beclin1 complex.