Elevation of protective autophagy as a potential way for preventing developmental neurotoxicity of general anesthetics

Sevoflurane upregulates neuron death process-related Ddit4 expression by NMDAR in the hippocampus

Postoperative cognitive dysfunction (POCD) is a serious and common complication induced by anesthesia and surgery. Neuronal apoptosis induced by general anesthetic neurotoxicity is a high-risk factor. However, a comprehensive analysis of general anesthesia-regulated gene expression patterns and further research on molecular mechanisms are lacking. Here, we performed bioinformatics analysis of gene expression in the hippocampus of aged rats that received sevoflurane anesthesia in GSE139220 from the GEO database, found a total of 226 differentially expressed genes (DEGs) and investigated hub genes according to the number of biological processes in which the genes were enriched and performed screening by 12 algorithms with cytoHubba in Cytoscape. Among the screened hub genes, Agt, Cdkn1a, Ddit4, and Rhob are related to the neuronal death process. We further confirmed that these genes, especially Ddit4, were upregulated in the hippocampus of aged mice that received sevoflurane anesthesia. NMDAR, the core target receptor of sevoflurane, rather than GABAAR, mediates the sevoflurane regulation of DDIT4 expression. Our study screened sevoflurane-regulated DEGs and focused on the neuronal death process to reveal DDIT4 as a potential target mediated by NMDAR, which may provide a new target for the treatment of sevoflurane neurotoxicity.

FOXO3 Regulates Sevoflurane-Induced Neural Stem Cell Differentiation in Fetal Rats

With the increase in fetal surgeries, the effect of maternal anesthesia on progeny has attracted much attention. Our previous studies have demonstrated that 3.5% sevoflurane maternal exposure resulted in over-activated autophagy and cognitive impairment in the offspring. The autophagy activation resulted in increased apoptosis and decreased proliferation. However, the effects of sevoflurane on neural stem cell (NSC) differentiation is unclear. There is evidence that autophagy might participate in anesthesia-induced NSC differentiation. Firstly, we examined the effects of sevoflurane on NSC differentiation and explored possible mechanisms. Then, we investigated whether autophagy was related to differentiation. On gestational day 14 (G14), rats were exposed to 2% or 3.5% sevoflurane for 2 h, then markers of neurons and astrocytes, and the FOXO3 expression was measured in fetal brains 48 h later. The differentiation of NSCs was detected after autophagy inhibition by 3-MA. Changes in NSC differentiation, autophagy level, and FOXO3 were examined after administration of lithium chloride. After 3.5% sevoflurane exposure, the expressions of β-Tubulin III, NeuN, SYP, GFAP and FOXO3 increased. Autophagy inhibition alleviates improper NSC differentiation. Lithium chloride attenuated FOXO3 and autophagy activation, ameliorated NSC differentiation and the decline of Nestin expression. Our results demonstrated that maternal exposure to 3.5% sevoflurane for 2 h during the mid-trimester induced NSC differentiation in the fetal brain through the activation of FOXO3. Autophagy inhibitor or lithium chloride reversed the improper differentiation of NSCs.

Cytosolic HMGB1 Mediates Autophagy Activation in an Emulsified Isoflurane Anesthesia Cell Model

Inhalation anesthetic isoflurane may cause an increased risk of cognitive impairment. Previous studies have indicated that this cognitive decline is associated with neuroinflammation mediated by high mobility group box 1 (HMGB1). HMGB1 is released from cells and acts as a damage-associated molecule in neurodegenerative diseases. However, the effect of intracellular HMGB1 during emulsified isoflurane (EI) exposure is poorly understood. The purpose of this study was to investigate the effect of autophagy on neuroprotection, evaluate variation of HMGB1, and determine its role in autophagic flux after EI exposure in vitro. We observed that EI decreased cell viability in a concentration-dependent manner, accompanied by an increase in autophagic flux. EI exposure also elevates the HMGB1 level in cytoplasm. Further, cytosolic HMGB1 was necessary for autophagy by perturbing the beclin1-Bcl-2 interaction. Most importantly, autophagy induction by rapamycin alleviated EI-provoked cell injury, and HMGB1 knockdown induced autophagy inhibition, which exacerbated cell damage. Based on these findings, we propose that autophagic flux is sustained and upregulated in response to EI exposure by increased cytosolic HMGB1, and that autophagy activation serves as a protective mechanism against EI-induced cytotoxicity. Thus, the complex roles of HMGB1 make it pivotal in reducing EI-induced neuronal damage.

General Anesthetics Regulate Autophagy via Modulating the Inositol 1,4,5-Trisphosphate Receptor: Implications for Dual Effects of Cytoprotection and Cytotoxicity

General anesthetics are both neuroprotective and neurotoxic with unclear mechanisms. General anesthetics may control cell survival via their effects on autophagy by activation of type 1 inositol triphosphate receptor (InsP₃R-1). DT40 or SH-SY5Y cells with only or over 99% expression of InsP₃R-1 were treated with isoflurane or propofol. Cell viability was determined by MTT reduction or LDH release assays. Apoptosis was determined by measuring Caspase-3 or by TUNEL assay. Autophagy activity was determined by measuring LC3 II and P62. We evaluated mitochondrial integrity using MitoTracker Green and cytosolic ATP levels. Fura2-AM was used to measure the concentrations of cytosolic calcium ([Ca²⁺]_c). Propofol significantly increased peak and integrated calcium response (P < 0.001) in cells with InsP₃R-1 but not in cells with triple knockout of InsP₃R. Both propofol and isoflurane increased autophagy induction (P < 0.05) in an mTOR- and InsP₃R- activity dependent manner. Short exposure to propofol adequately activated InsP₃-1 to provide sufficient autophagy for cytoprotection, while prolonged exposure to propofol induced cell apoptosis via impairment of autophagy flux through over activation of InsP₃-1. Propofol damaged mitochondria and decreased cytosolic ATP. The effects of general anesthetics on apoptosis and autophagy are closely integrated; both are caused by differential activation of the type 1 InsP₃R.

Anesthetic neurotoxicity: Apoptosis and autophagic cell death mediated by calcium dysregulation

A number of findings suggested that general anesthetics induced neural cell death by apoptosis in various animal models. Although clinical evidence regarding the correlation between anesthetic exposures at young age and subsequent cognitive impairments remains unclear, repeated or consistent exposures to general anesthetics may be a potential harmful risk in developing human brains. The mechanisms underlying the anesthetic neurotoxicity have received extensive attention recently. We will attempt a brief review to summarize current understanding on the role of both apoptosis and autophagic cell death mediated by calcium dysregulation in anesthetic neurotoxicity.

Autophagy activation prevents sevoflurane-induced neurotoxicity in H4 human neuroglioma cells

AIM

The inhaled anesthetic sevoflurane may induce cognitive impairment in both animals and humans. Previous study has shown that sevoflurane triggers ER stress and may lead to apoptosis in rat hippocampal neurons. In this study, we examined whether sevoflurane caused autophagy and its contributions to sevoflurane induced neuronal cell injury.

METHODS

H4 human neuroglioma cells were exposed to 4.1% sevoflurane for 6 h. Cell viability and apoptosis ratio were assessed using a CCK8 kit and flow cytometry, respectively. Autophagosomes in the cells were detected using GFP-LC3 plasmid transfection or transmission electronic microscopy. The expression of LC3B, p62/SQSTM, C/EBP homologous protein (CHOP) and glucose-related protein 78 (GRP78) was assessed with Western blotting.

RESULTS

Sevoflurane treatment induced apoptosis and markedly increased the LC3-II level and GFP-LC3 puncta number, decreased p62 expression in H4 cells. Activation of autophagy by rapamycin (1 μmol/L) significantly reduced sevoflurane-induced apoptosis and increased cell viability, whereas inhibition of autophagy with 3-MA (5 mmol/L) caused the opposite effects. Furthermore, sevoflurane treatment markedly increased the expression of CHOP and GRP78, two hallmark proteins of ER stress. Inhibition of ER stress by 4-phenylbutyrate (500 μmol/L) abrogated sevoflurane-induced autophagy and apoptosis, and improved the viability. Moreover, sevoflurane-stimulated expression of CHOP and GRP78 was inhibited by rapamycin, but further enhanced by 3-MA.

CONCLUSION

Sevoflurane treatment induces ER stress and activates autophagy, which antagonizes sevoflurane-induced apoptosis in H4 human neuroglioma cells. The results suggest that autophagy may be a potential therapeutic target in preventing sevoflurane-induced neurotoxicity.

Adoptive Autophagy Activation: a Much-Needed Remedy Against Chemical Induced Neurotoxicity/Developmental Neurotoxicity

The profound significance of autophagy as a cell survival mechanism under conditions of metabolic stress is a well-proven fact. Nearly a decade-long research in this area has led scientists to unearth various roles played by autophagy other than just being an auto cell death mechanism. It is implicated as a vital cell survival pathway for clearance of all the aberrant cellular materials in case of cellular injury, metastasis, disease states, cellular stress, neurodegeneration and so on. In this review, we emphasise the critical role of autophagy in the environmental stressors-induced neurotoxicity and its therapeutic implications for the same. We also attempt to shed some light on the possible protective role of autophagy in developmental neurotoxicity (DNT) which is a rapidly growing health issue of the human population at large and hence a point of rising concern amongst researchers. The intimate association between DNT and neurodegenerative disorders strongly indicates towards adopting autophagy activation as a much-needed remedy for DNT.