The Role Of Mitochondria In General Anesthesia-induced Neurotoxicity And Cognitive Deficits And Its Mechanism

General anesthesia has been reported to induce widespread neurotoxicity and cognitive deficits in aging or developing mammals.Mitochondria are supposed to be the most vulnerable initial target of this disorder.Mitochondrial dysfunction is important in the development and progression of several degenerative diseases,including Alzheimer’s disease,Parkinson’s disease and Huntington’s disease,known to be plagued by severe cognitive decline.However,the role of mitochondria in general anesthesia and effective pharmacologic agents targeted on mitochondria during general anesthesia exposure are lacking.In this study,we hypothesized that mitochondrial abnormalities are involved in the early pathogenesis of general anesthesia-induced neurotoxicity and cognitive deficits.We determined in aging mice or developing rats the effects of isoflurane,a general inhalation anesthetic,on mitochondrial function and morphology and cognition.We further investigated the protective effects of mitochondrion-targeted protectant SS-31 in mitochondria,hippocampus,and cognition and the underlying mechanism.Section 1:The role of mitochondria in general anesthesia-induced neurotoxicity and cognitive deficits in aging mice and its mechanism1.Effects of isoflurane on mitochondrial function and synaptic plasticity in aging mice:[Abstract]Objective:To investigate the effects of isoflurane and mitochondrion-targeted protectant SS-31 on mitochondrial function and synaptic plasticity in aging mice.Methods:Fifteen-month-old male C57BL/6 mice were randomly assigned to one of the following four groups(n=14/group):control,control+ SS-31,isoflurane,and isoflurane+SS-31.Mice were exposed to 1.5%isoflurane or 30%oxygen for two hours following intraperitoneal administration of mitochondrion-targeted peptide SS-31 or vehicle with 30 min interval.The hippocampus was immediately removed for biochemical assays after gas inhalation.Behavioral tests were evaluated by the open field test and fear conditioning 24 hours after the experiment.Results:We showed that cognitive deficits induced by exposure of the aging mice to isoflurane were accompanied by mitochondrial dysfunction in hippocampus due to loss of the enzymatic activity of complex 1.This loss resulted in the increase of reactive oxygen species production,decrease of ATP production and mitochondrial membrane potential,and opening of mitochondrial permeability transition pore.Further,we provided evidence that the BDNF signaling pathway was involved in this process to regulate synaptic plasticity-related proteins,for instance,downregulation of synapsin 1,PSD-95 and p-CREB,and upregulation of NR2A,NR2B,CaMKⅡa and CaMKⅡβ.Of note,the isoflurane-induced cognitive deficits were rescued by SS-31 through reversal of mitochondrial dysfunction,which facilitated the regulation of BDNF signaling including the expression reversal of aforementioned important synaptic-signaling proteins in aging mice.Conclusion:Our data demonstrate that reversing mitochondrial dysfunction by SS-31 enhances BDNF signaling pathway and synaptic plasticity,and provides protective effects on cognitive function,thereby support the notion that SS-31 may have therapeutic benefits for elderly humans undertaking anesthesia.2.Effects of isoflurane on mitochondria-related inflammation and apoptosis in aging mice:[Abstract]Objective:To determine in aging mice the effects of isoflurane and mitochondrion-targeted antioxidant SS-31 on mitochondria-related inflammation and apoptosis in aging mice.Methods:Fifteen-month-old male C57BL/6 mice were randomly assigned to one of the following four groups(n=18/group):control,control+SS-31,isoflurane,and isoflurane+SS-31.Mice were exposed to 1.5%isoflurane or 30%oxygen for two hours following intraperitoneal administration of mitochondrion-targeted peptide SS-31 or vehicle with 30 min interval.The hippocampus was immediately removed for biochemical assays and immunohistochemical analyses after gas inhalation.Behavioral tests were evaluated by the open field test and fear conditioning 24 hours after the experiment.Results:The results showed that isoflurane induced hippocampus-dependent memory deficit,which was associated with mitochondrial dysfunction including reduced ATP contents,increased ROS levels,and mitochondrial swelling.Treatment with SS-31 significantly ameliorated isoflurane-induced cognitive deficits through the improvement of mitochondrial integrity and function.Mechanistically,SS-31 treatment suppressed pro-inflammatory responses by decreasing the levels of NF-κB,NLRP3,caspase 1,IL-1β,and TNF-α;and inhibited the apoptotic pathway by decreasing the Bax/Bcl-2 ratio,reducing the release of cytochrome C,and blocking the cleavage of caspase 3.Conclusion:Our results indicate that isoflurane-induced cognitive deficits may be attenuated by mitochondrion-targeted antioxidants,such as SS-31.Therefore,SS-31 may have therapeutic potentials in preventing injuries from oxidative stresses that contribute to anesthetic-induced neurotoxicity.Section 2:The role of mitochondria in general anesthesia-induced neurotoxicity and cognitive deficits in developing rats and its mechanismEffects of isoflurane on long-term mitochondrial morphogenesis and cognition in developing rats:[Abstract]Objective:This study explores the effects of isoflurane and mitochondrion-targeted antioxidant SS-31 on mitochondrial morphogenesis and cognition in developing rats.Methods:Rat pups at PND 7(n=24/group)were randomly assigned to one of following four treatment protocols:control,control+SS-31,isoflurane,and isoflurane+SS-31.SS-31(5 mg/kg)or phosphate-buffered saline(PBS)was intraperitoneally administered to the pups with a volume of 0.4 ml/kg 30 min before oxygen or isoflurane inhalation.The hippocampus was immediately removed for biochemical assays.Histopathological studies were conducted at PND 21,and behavioral tests were performed at PND 40 or 60.Results:We found that early exposure to isoflurane caused remarkable reactive oxygen species accumulation,mitochondrial deformation,and neuronal apoptosis in hippocampus.The injury occurrence ultimately gave rise to long-term cognitive deficits in developing rats.Interestingly,pretreatment with SS-31 not only provided protective effect against oxidative stress and mitochondrial damages,but also attenuated isoflurane-induced cognitive deficits.Conclusion:Our data support the notion that mitochondrial damage is an early and long lasting event of GA-induced injury and suggest that SS-31 might have clinically therapeutic benefits for pediatric patients undertaking GA.SummaryIn this study,we found that:1.Isoflurane anesthesia induced abnormalities of mitochondrial function and morphology which evidenced by reduction of ETC complex I activity,ATP generation and MMP level;opening of mPTP;swelling of mitochondria with disorganized and vacuolated in cristae;condensed mitochondria with degenerative changes;and decrease in mitochondrial density.2.Isoflurane anesthesia caused severe ROS generation and oxidative stress,leading to the subsequent activations of mitochondrial ROS-related NLRP3-caspase 1 inflammatory signal pathway and Cyt C-caspase 3 apoptotic pathway,ultimately,gave rise to neuroapoptosis.3.Isoflurane anesthesia caused down regulations of BDNF/p-TrkB pathway and synaptic-signaling proteins synapsin 1 and PSD-95,and inhibition of NMDA-CaMKII-CREB pathway,which is key to both memory consolidation and synaptic plasticity.4.Isoflurane induced neurotoxicity with injury of hippocampal neurons,and impairment of learning and memory.5.Mitochondrion-targeted protectant SS-31 ameliorated isoflurane-induced mitochondrial injuries,inhibited oxidative stress,inflammation and apoptosis,consolidated BDNF/TrkB and NMDA-CaMKII-CREB pathway,ultimately improved cognition.ConclusionIsoflurane GA induces impairments of mitochondrial function and morphology,increased oxidative stress,upregulation of neuronal inflammation and apoptosis,changes of synaptic plasticity,and ultimately cognitive deficits.SS-31 has the protective effects on mitochondria,neurons and cognition.Our results also give the evidences that mitochondria are the earliest target for GA and directly improving mitochondrial function and morphogenesis ameliorates isoflurane-induced neurotoxicity and cognitive deficits.This work suggests a new strategy to benefit the developing-and/or aging patients who need GA for surgery.