Effects of calpain on sevoflurane-induced aged rats hippocampal neuronal apoptosis

Sevoflurane exposure accelerates the onset of cognitive impairment via promoting p-Drp1S616-mediated mitochondrial fission in a mouse model of Alzheimer's disease

Sevoflurane is an inhalational anesthetic widely used in clinical settings. Accumulating evidence has shown that sevoflurane exposure may impair cognitive function, potentially contributing to Alzheimer's disease (AD)-related changes. However, the underlying mechanism remains poorly understood. In the present study, 4-month-old 5xFAD mice were used to investigate the effect of sevoflurane exposure on cognitive decline by Y-maze test and novel object recognition test. We found that sevoflurane exposure promoted the appearance of cognitive impairment of 5xFAD mice, accompanied with the deterioration of Aβ accumulation, synaptic defects, and neuroinflammation. Additionally, sevoflurane was also found to aggravate mitochondrial fission of 5xFAD mice, as indicated by the further upregulated expression of p-Drp1S616. Moreover, sevoflurane significantly increased mitochondrial damage and dysfunction of AD models both in vitro and in vivo experiments. Seahorse XF analysis further indicated that sevoflurane exposure facilitated a metabolic shift from oxidative phosphorylation to glycolysis. Further rescue experiments revealed that a key mechanism underlying sevoflurane-induced cognitive impairment was the excessive mitochondrial fission, as supported by the result that the mitochondrial fission inhibitor Mdivi-1 counteracted the sevoflurane-mediated deteriorative effects in 5xFAD mice. These findings provided evidence for a new mechanism of sevoflurane exposure accelerating AD-related cognitive decline.

Necroptosis involved in sevoflurane-induced cognitive dysfunction in aged mice by activating NMDA receptors increasing intracellular calcium

Perioperative neurocognitive disorders are a common surgical and postanesthesia complication. Necroptosis contributes to the emergence of various neurological disorders. We conjecture that cognitive impairment is associated with necroptosis of hippocampal neurons, which is mediated by NMDA receptors leading to cytoplasmic calcium imbalance. C57BL/6 J male mice ( 18 months) were randomly divided into the C ( control group), S ( sevoflurane group), S+M ( sevoflurane plus the NMDA receptor antagonist memantine group) and S+N ( sevoflurane plus necrostatin-1) group. We exposed the mice to 3% sevoflurane for 2 h a day for three consecutive days in the S, S+M and S+N groups. Memantine ( 20 mg/kg) or Nec-1 ( 10 mg/kg) was injected intraperitoneally 1 h before sevoflurane anesthesia in the S+M or S+N group. We used the animal behavior tests to evaluate the cognitive function. Pathological damage, the rate of necroptosis, [Ca2+]i, and the expression of necroptosis-related proteins were evaluated. The cognitive function tests, pathological damage, the rate of necroptosis, the expression of necroptosis-related proteins, NMDAR2A and NMDAR2B were significantly different in the S group ( P < 0.05). Alleviated pathological damage, decreased the rate of necroptosis and down-regulated the expression of necroptosis-related proteins occurred in the S+M and S+N group ( P < 0.05). The lower elevated [Ca2+]i, expression of NMDAR2A and NMDAR2B were found in the S+M group. Our findings highlighted sevoflurane-induced cognitive dysfunction is associated with an imbalance in cytoplasmic calcium homeostasis by activating NMDA receptors, which causes hippocampus neurons to undergo necroptosis and ultimately affects cognitive performance in aged mice.

taVNS Alleviates Sevoflurane-Induced Cognitive Dysfunction in Aged Rats Via Activating Basal Forebrain Cholinergic Neurons

Postoperative cognitive dysfunction (POCD) is a common complication of central nervous system after anesthesia or surgery. Sevoflurane, an inhalation anesthetic, may inhibit cholinergic pathway that induce neuronal death and neuroinflammation, ultimately leading to POCD. Transauricular vagus nerve stimulation (taVNS) has neuroprotective effects in POCD rats, but the mechanisms related to cholinergic system have not been revealed. Sprague-Dawley rats were anesthetized with sevoflurane to construct the POCD model. The immunotoxin 192-IgG-saporin (192-sap) selectively lesioned cholinergic neurons in the basal forebrain, which is the major source of cholinergic projections to hippocampus. After lesion, rats received 5 days of taVNS treatment (30 min per day) starting 24 h before anesthesia. Open field test and Morris water maze were used to test the cognitive function. In this study, rats exposed to sevoflurane exhibited cognitive impairment that was attenuated by taVNS. In addition, taVNS treatment activated cholinergic system in the basal forebrain and hippocampus, and downregulated the expression of apoptosis- and necroptosis-related proteins, such as cleaved Caspase-3 and p-MLKL, in the hippocampus. Meanwhile, the activation of Iba1⁺ microglial by sevoflurane was reduced by taVNS. 192-sap blocked the cholinergic system activation in the basal forebrain and hippocampus and inhibited taVNS-mediated neuroprotection and anti-inflammation effects in the hippocampus. Generally, our study indicated that taVNS might alleviate sevoflurane-induced hippocampal neuronal apoptosis, necroptosis and microglial activation though activating cholinergic system in the basal forebrain.

Promotion of a synthetic degradation of activated STAT6 by PARP-1 inhibition: roles of poly(ADP-ribosyl)ation, calpains and autophagy

Background

We reported that PARP-1 regulates genes whose products are crucial for asthma, in part, by controlling STAT6 integrity speculatively through a calpain-dependent mechanism. We wished to decipher the PARP-1/STAT6 relationship in the context of intracellular trafficking and promoter occupancy of the transcription factor on target genes, its integrity in the presence of calpains, and its connection to autophagy.

Methods

This study was conducted using primary splenocytes or fibroblasts derived from wild-type or PARP-1^−/− mice and Jurkat T cells to mimic Th2 inflammation.

Results

We show that the role for PARP-1 in expression of IL-4-induced genes (e.g. gata-3) in splenocytes did not involve effects on STAT6 phosphorylation or its subcellular trafficking, rather, it influenced its occupancy of gata-3 proximal and distal promoters in the early stages of IL-4 stimulation. At later stages, PARP-1 was crucial for STAT6 integrity as its inhibition, pharmacologically or by gene knockout, compromised the fate of the transcription factor. Calpain-1 appeared to preferentially degrade JAK-phosphorylated-STAT6, which was blocked by calpastatin-mediated inhibition or by genetic knockout in mouse fibroblasts. The STAT6/PARP-1 relationship entailed physical interaction and modification by poly(ADP-ribosyl)ation independently of double-strand-DNA breaks. Poly(ADP-ribosyl)ation protected phosphorylated-STAT6 against calpain-1-mediated degradation. Additionally, our results show that STAT6 is a bonafide substrate for chaperone-mediated autophagy in a selective and calpain-dependent manner in the human Jurkat cell-line. The effects were partially blocked by IL-4 treatment and PARP-1 inhibition.

Conclusions

The results demonstrate that poly(ADP-ribosyl)ation plays a critical role in protecting activated STAT6 during Th2 inflammation, which may be synthetically targeted for degradation by inhibiting PARP-1.

Sevoflurane exposure causes neuronal apoptosis and cognitive dysfunction by inducing ER stress via activation of the inositol 1, 4, 5-trisphosphate receptor

The role of the inositol 1, 4, 5-trisphosphate receptor (IP3R) in hippocampal neuronal apoptosis and cognitive dysfunction induced by sevoflurane is currently unclear. Therefore, in this study, we investigated the role of the IP3R in endoplasmic reticulum (ER) stress and hippocampal neuronal apoptosis induced by sevoflurane in aged rats and isolated hippocampal neurons using both in vivo and in vitro experiments, including bioinformatics, functional enrichment analysis, gene set enrichment analysis, hematoxylin, and eosin staining, TUNEL assay, flow cytometry, western blot analysis and transmission electron microscopy. Furthermore, behavioral assessment was performed with the Morris water maze test. We identified 232 differentially expressed genes induced by sevoflurane exposure, including 126 upregulated genes and 106 downregulated genes. Sevoflurane exposure caused cognitive impairment and neuronal injury, and increased p-IP3R levels and ER stress. An IP3R inhibitor, 2-APB, suppressed these changes, while an IP3R agonist, FK-506, aggravated these changes. Together, these findings suggest that sevoflurane exposure causes marked cognitive dysfunction in aged rats and neuronal injury in isolated hippocampal neurons by activating the IP3R and inducing cytoplasmic calcium overload, thereby resulting in ER stress and hippocampal neuronal apoptosis. GRAPHICAL ABSTRACT.

Electro-Acupuncture Pretreatment Ameliorates Anesthesia and Surgery-Induced Cognitive Dysfunction Via Inhibiting Mitochondrial Injury and nEuroapoptosis in Aged Rats

Postoperative cognitive dysfunction (POCD) remains one of the most common complications following anesthesia and surgery (AS) in the elderly population. Calcium-mediated mitochondrial injury has been proved to induce cognitive impairment in a variety of neurologic diseases. In the current study we determined whether electro-acupuncture (EA) pretreatment ameliorated AS-induced POCD in aged rats, as well as the underlying mechanism. Eighty SD rats (18 months, male) were randomly assigned into four groups (n = 20): C, C + EA, POCD and EA + POCD. Rats in Group POCD and EA + POCD were subjected to exploratory laparotomy under sevoflurane anesthesia. Rats of Group C + EA and EA + POCD received a 5-day EA stimulation at Hegu, Neiguan and Zusanli acupoints before AS. At 3rd day after AS, open field test along with Morris water maze test were employed to examine the cognitive function of aged rats. Then hippocampal tissues were stripped and hippocampal neuronal amount, expression level of cleaved caspase-9 level, cytochrome c (Cyt C), cleaved caspase-3 level, Bcl-2, Bax, ROS expression level, apoptosis rate, mitochondrial membrane potential (MMP), cytosolic calcium concentration ([Ca²⁺]c), opening level of mitochondrial permeability transition pore (mPTP) and ultrastructure of hippocampal neurons were detected separately. EA pretreatment inhibited AS-induced cognitive dysfunction. Furthermore, EA pretreatment decreased level of [Ca²⁺]c, MMP, mPTP, ROS and hippocampal mitochondrial disruption and enhanced neuronal amount. In addition, EA pretreatment notably reduced the AS-induced increased level of cleaved caspase-9, cleaved caspase-3 and expression of Cyt c, Bax/Bcl-2 ratio, as well as neuronal apoptosis rate in aged rats. EA pretreatment ameliorates AS-induced POCD in aged rats, the potential mechanism may be associated with inhibiting calcium overload and ameliorating mitochondrial injury and neuroapoptosis in hippocampal neurons.

Necrostatin-1 Against Sevoflurane-Induced Cognitive Dysfunction Involves Activation of BDNF/TrkB Pathway and Inhibition of Necroptosis in Aged Rats

Postoperative cognitive dysfunction (POCD) induced by anesthesia or surgery has become a common complication in the aged population. Sevoflurane, a clinical inhalation anesthetic, could stimulate calcium overload and necroptosis to POCD. In addition, necroptosis inhibitor necrostatin-1 (Nec-1) alleviated cognitive impairment caused by multiple causes, including postoperative cognitive impairment. However, whether Nec-1 exerts a neuroprotective effect on POCD via calcium and necroptosis remains unclear. We anesthetized Sprague-Dawley rats with sevoflurane to construct the POCD model and to explore the mechanism underlying neuroprotective effects of Nec-1 in POCD. Rats were treated with Nec-1 (6.25 mg/kg) 1 h prior to anesthesia. Open field test and Morris water maze were employed to detect the cognitive function. In this study, rats exposed to sevoflurane displayed cognitive dysfunction without changes in spontaneous activity; however, the sevoflurane-induced POCD could be relieved by Nec-1 pretreatment. Nec-1 decreased sevoflurane-induced calcium overload and calpain activity in the hippocampus. In addition, Nec-1 alleviated the expression of p-RIPK1, RIPK1, p-RIPK3, RIPK3, p-MLKL and MLKL. Furthermore, Nec-1 remarkably increased BDNF and p-TrkB/TrkB expression in the hippocampus of aged rats. Ultimately, our research manifests evidence that Nec-1 may play a neuroprotective role against sevoflurane-induced cognitive impairment via the increase of BDNF/TrkB and suppression of necroptosis-related pathway.

P300 Inhibition Improves Cell Apoptosis and Cognition Impairment Induced by Sevoflurane Through Regulating IL-17A Activation

BACKGROUND

Sevoflurane (Sev) is a rapidly acting, potent inhalation anesthetic with rapid uptake and elimination. But many studies have shown that Sev could result in cognition dysfunction in adolescent or aging patients. Now, therapeutic targeting with IL-17A antibody has shown a promising effect on Sev-induced cognition impairment. In the study we report that P300 inhibition could act as an alternative approach to decrease IL-17A activity.

METHODS

SHSY5Y cells were treated with Sev and cell apoptosis was evaluated by Annexin V-FITC/PI staining. The expression of P300 and IL-17A were assessed by Western blotting. Water maze tests were conducted in order to assess the cognitive function.

RESULTS

We found that P300 and IL-17A were activated in SHSY5Y cells treated with Sev. P300 inhibitor C646 could reduce the apoptosis induced by Sev through decreasing IL-17A avtivity. Furthermore, IL-17A expression was upregulated after neurons were transfected with P300 expression plasmid and IL-17A expression was downregulated after neurons were incubated with P300 inhibitor C646. P300 overexpression could upregulate the promoter activity of IL-17A. Finally, in a rat model treated with Sev, we also found C646 to significantly improve the cognition impairment through the IL-17A pathway.

CONCLUSIONS

These data show that P300 will potentially be a new drug target for the therapy of cognition impairment caused by Sev.

Apoptosis inhibition is involved in improvement of sevoflurane-induced cognitive impairment following normobaric hyperoxia preconditioning in aged rats

Sevoflurane, a commonly used anesthetic agent has been confirmed to induce cognitive impairment in aged rats. Normobaric hyperoxia preconditioning has been demonstrated to induce neuroprotection in rats. The present study aimed to determine whether normobaric hyperoxia preconditioning could ameliorate cognitive deficit induced by sevoflurane and the possible mechanism by which it may exert its effect. A total of 66, 20-month-old male Sprague-Dawley rats were randomly divided into 3 groups (n=22 each): Rats in the control (C) and sevoflurane anesthesia (S) groups received no normobaric hyperoxia preconditioning before sevoflurane exposure, rats in the normobaric hyperoxia pretreatment (HO) group received normobaric hyperoxia preconditioning before sevoflurane exposure (95% oxygen for 4 continuous h daily for 6 consecutive days). The anesthesia rats (S and HO groups), were exposed to 2.5% sevoflurane for 5 h, while the sham anesthesia rats (C group) were exposed to no sevoflurane. The neurobehavioral assessment was performed using a Morris water maze test, the expressions of the apoptosis proteins were determined using western blot analysis, and the apoptosis rate and cytosolic calcium concentration were measured by flow cytometry. Normobaric hyperoxia preconditioning improved prolonged escape latency and raised the number of platform crossings induced by sevoflurane in the Morris water maze test, increased the level of bcl-2 protein, and decreased the level of bax and active caspase-3 protein, the apoptosis rate and cytosolic calcium concentration in the hippocampus 24 h after sevoflurane exposure. The findings of the present study may imply that normobaric hyperoxia preconditioning attenuates sevoflurane-induced spatial learning and memory impairment, and this effect may be partly related to apoptosis inhibition in the hippocampus. In conclusion, normobaric hyperoxia preconditioning may be a promising strategy against sevoflurane-induced cognitive impairment by inhibiting the hippocampal neuron apoptosis.

Sevoflurane increases intracellular calcium to induce mitochondrial injury and neuroapoptosis

Sevoflurane is commonly used in clinical anesthesia. However, some reports indicated that Sevoflurane could induce mitochondrial injury and neuroapoptosis. Although the mechanism remains unclear, evidence points to the increase of intracellular calcium after administration of Sevoflurane. Herein, we sought whether the increment of intracellular Ca2+ caused by Sevoflurane administration could induce mitochondrial injury and apoptosis in primary neurons of the hippocampus. Fluo-4-acetoxymethyl ester Ca2+ probe was used for measuring intracellular Ca2+ concentrations. LDH assay, CCK-8 assay, and Western blotting were performed to confirm Sevoflurane-induced neuroapoptosis. ROS, mPTP, and ATP production were assayed to reveal mitochondrial injury. Our results indicated that Sevoflurane increased intracellular Ca2+ and neuronal death. Sevoflurane also elevated ROS and the opening of mPTP, and decreased ATP production in neurons. The expression of cytochrome c, cleaved caspase-9, cleaved caspase-3, and the ratio of Bax/Bcl-2 were also increased. By using calcium channel blocker Nimodipine, the increase of intracellular Ca2+ was attenuated, and the death rate of neurons, the ROS and opening of mPTP, decreased ATP production, the expressions of cytochrome c, cleaved caspase-9, cleaved caspase-3 and the ratio of Bax/Bcl-2 were alleviated. Our study suggested that Sevoflurane could increase intracellular Ca2+ to induce mitochondrial injury and mitochondria-mediated neuroapoptosis in neurons.

AMPK-SIRT1-PGC1α Signal Pathway Influences the Cognitive Function of Aged Rats in Sevoflurane-Induced Anesthesia

To understand the effect of AMP-activated protein kinase (AMPK)-SIRT1 (silent information regulator 1)-PPARγ coactivator-1α (PGC1α) signaling pathway on the cognitive function of sevoflurane-anesthetized aged rats. Aged rats were divided into Normal group, Sevo group (Sevoflurane anesthesia), Sevo + AICAR (the AMPK activator) group, Sevo + EX527 group (the AMPK inhibitor), and Sevo + AICAR + EX527 group. The cognitive function of rats was determined by the Morris water maze. Hippocampal neuronal apoptosis was evaluated by TUNEL and Fluoro-Jade C (FJC) staining, and the expression of cleaved caspase-3 was detected by immunohistochemistry. ROS, SOD, and MDA levels and the fluorescence intensity of GFAP in the hippocampus were assayed. The mitochondrial membrane potential (MMP), mitochondrial mass, ATP level, and the expression of AMPK-SIRT1-PGC1α were determined by the corresponding methods. Rats in the Sevo group manifested significant extension in the escape latency, with fewer platform crossings; and meanwhile, the apoptotic rate, the number of FJC-positive cells, and the fluorescence intensity of GFAP of neurons were elevated, with up-regulation of cleaved caspase-3. Moreover, the level of MDA and ROS was increased evidently, with significant down-regulation of SOD activity, ATP, mitochondrial mass and MMP levels, and AMPK, SIRT1 and PGC-1α protein expressions. However, sevoflurane-induced changes above were improved after the administration of AICAR, and EX527 could reverse AICAR-induced improvements in Sevo-anesthetized aged rats. Activating AMPK-SIRT1-PGC1α pathway can improve the cognitive function and mitigate the neuronal injury in Sevo-anesthetized aged rats by antagonizing the oxidative stress and maintaining the mitochondrial function.

Key miRNAs associated with memory and learning disorder upon exposure to sevoflurane determined by RNA sequencing

The study aimed to identify differentially expressed microRNAs (miRNAs/miRs) and explore the mechanisms governing impaired memory and learning ability in developing brains exposed to sevoflurane. A total of six 7‑day‑old male ICR mice were randomly assigned into the sevoflurane anesthesia group (treated with 2.4% sevoflurane) or control group (treated with normal saline solution at the same dose). After 14 days, the mice were subjected to a Morris water maze experiment. Then, the animals were sacrificed and hippocampus tissues were isolated. RNAs in hippocampus tissues were sequenced and the differential miRNA expression profiles were identified by a bioinformatics approach. The learning and memory function of mice were significantly affected by sevoflurane exposure. A total of 18 miRNAs were found to be significantly affected by sevoflurane administration. Their target genes clustered into different functional groups, such as 'dephosphorylation', 'vesicle localization' and the 'Wnt signaling pathway'. miR‑101b‑3p was closely related with 'chromatin binding' and 'protein serine/threonine kinase activity'. The most represented pathways for miRNAs included 'neuroactive ligand‑receptor interaction' (miR‑1187), 'long‑term depression' (miR‑425‑5p), 'FoxO signaling pathway' (miR‑425‑5p) and the 'neurotrophin signaling pathway' (miR‑467a‑3p). miR‑467a‑3p (degree=89), miR‑101b‑3p (degree=59), and miR‑1187 (degree=51) were the hub nodes in the miRNA regulatory network. The Wnt signaling pathway, miR‑467a‑3p, miR‑1187 and miR‑101b‑3p may be therapeutic targets for preventing cognitive impairments induced by sevoflurane.

Sevoflurane promotes the proliferation of HUVECs by activating VEGF signaling

The vascular endothelium plays an essential role in vascular disease and cardiovascular diseases. The effects and underlying mechanisms of sevoflurane on vascular endothelial growth factor (VEGF) in human endothelial cells have not been elucidated. The MTT colorimetric assay was used to determine HUVEC activity at different concentrations (1 and 3%, respectively) of sevoflurane for different time-points (12, 24 and 48 h, respectively). The regulation of sevoflurane on the mRNA levels of VEGFa, VEGFb, VEGFc and VEGFR1, 2, 3 was analyzed by real-time PCR. When VEGFR2 was inhibited by axitinib, VEGFR2 protein expression was determined by western blotting, and the cell viability was assessed by MTT analysis. The results revealed that sevoflurane increased cell viability in a dose- and time-dependent manner. Sevoflurane significantly upregulated VEGFA mRNA expression only. In addition, sevoflurane increased the expression of VEGFR2 at the mRNA and protein levels, whereas sevoflurane did not modulate the mRNA expression of VEGFR1 and VEGFR3. Furthermore, sevoflurane failed to increase the mRNA and protein expression of VEGFR2 when VEGFR2 was inhibited by axitinib, an inhibitor of VEGF receptors. In conclusion, sevoflurane may be a promising agent against endothelium dysfunction-caused vascular disease by activating the VEGF-A/VEGFR2 signaling pathway.

The Effect of Chronic Fluorosis on Calcium Ions and CaMKIIα, and c-fos Expression in the Rat Hippocampus

This study investigated neurotoxicity of chronic fluorosis in the rat hippocampus. Newly weaning, male, Sprague-Dawley (SD) rats were administered 15, 30, and 60 mg/L sodium fluoride (NaF) solution (fluorine ion concentration 8.25, 16.50, and 33.00 mg/L, respectively), and tap water, for 18 months. The neurotoxicological mechanism was examined with a focus on intracellular calcium overload. Results showed that as the fluoride concentration increased, calcium ion concentration [Ca²⁺], the expression of calcium/calmodulin-dependent protein kinase II α (CaMKIIα), and the expression of catus proto-oncogene protein c-fos (c-fos) all tend to increase. Compared to the control group, Ca²⁺, CaMKIIα, and c-fos significantly increased (P < 0.05) in the moderate-fluoride and the high-fluoride groups. These results indicate that Ca²⁺/CaMKIIα/c-fos channel signal may be the molecular mechanism of central nervous system damage caused by chronic fluoride intoxication. Moreover, elevated Ca²⁺ concentration in the hippocampus may be the initiating factor of neuronal apoptosis induced by fluoride.

Protective effect of vitexin reduces sevoflurane-induced neuronal apoptosis through HIF-1α, VEGF and p38 MAPK signaling pathway in vitro and in newborn rats

Previous studies have demonstrated that Vitexin possesses antihypertensive, anti-inflammatory and potential anticancer effects. The present study aimed to investigate whether the protective effect of vitexin protects against sevoflurane-induced neuronal apoptosis and the underlying mechanisms of this protective effect. The results demonstrated that Vitexin pretreatment significantly reduced neuronal apoptosis, and inhibited caspase-3 activity, apoptosis regulator BAX protein expression and malondialdehyde levels in sevoflurane-induced newborn rats. In addition, Vitexin pretreatment increased superoxide dismutase and glutathione peroxidase activity. Furthermore, it was revealed that treatment with vitexin induced hypoxia inducible factor 1α subunit (HIF-1α) and vascular endothelial growth factor (VEGF) protein expression, and suppressed phosphorylated-p38 MAP kinase (p38) protein expression in sevoflurane-induced newborn rat. Together, the results of the current study suggest that the protective effect of vitexin reduces sevoflurane-induced neuronal apoptosis through HIF-1α-, VEGF- and p38-associated signaling pathways in newborn rats.

Cognitive Impairment and Endoplasmic Reticulum Stress Induced by Repeated Short-Term Sevoflurane Exposure in Early Life of Rats

Sevoflurane is one of the most commonly used volatile anaesthetics for children, but the safety of prolonged or repeated clinical use of sevoflurane in infants or children is controversial. Here, we investigated the effects of sevoflurane on rats in early life and the time scale of those effects. Our behavioral results indicated that repeated short-term exposure of new-born rats to sevoflurane caused learning and memory impairment, while a single exposure of rats to sevoflurane was relatively safe. Further mechanistic investigation revealed that repeated sevoflurane exposure impaired long-term potentiation (LTP), downregulated the expression of certain synaptogenesis-related proteins (GluR1, PSD95) and upregulated proteins related to endoplasmic reticulum (ER) stress in the hippocampus. An ER stress inhibitor, tauroursodeoxycholic acid (TUDCA), reversed the changes in the levels of synaptic plasticity proteins. Our results provide new evidence for the clinical concerns regarding repeated sevoflurane anesthesia.

Cyclin-dependent kinase 5/Collapsin response mediator protein 2 pathway may mediate sevoflurane-induced dendritic development abnormalities in rat cortical neurons

Sevoflurane has been reported to induce neurotoxicity and cognitive impairment in the developing brains. However, the underlying molecular mechanisms remain poorly understood. Recent studies have demonstrated aberrant cyclin-dependent kinase 5 (CDK5) activity is implicated in inhaled anesthetic-induced neurotoxicity. CDK5/CRMP2 signaling is involved in the cortical and hippocampal dendritic development. The aim of present study is to investigate whether the CDK5/CRMP2 pathway mediates sevoflurane-induced dendritic development abnormalities. Rat primary cortical neurons were treated with 4% sevoflurane for 6h, the CDK5 inhibitor roscovitine or the vehicle (0.3% DMSO) was administered 12h before sevoflurane or carrying gases exposure. Cortical neurons were harvested for further analysis 0h, 12h and 24h after exposure. Sevoflurane exposure for 6h did not reduce cell viability and slightly increased the expression of cleaved caspase-3. Sevoflurane induced abnormal CDK5 activation by increasing the expression of its activator p25 and promoted the phosphorylation of CRMP2 (Ser522). The increased phospho-CRMP2 (Ser522) was mainly distributed in the cytoplasm of cortical neurons. Sevoflurane significantly reduced the number of primary dendrites and the number of branching points; whereas it did not influence the total dendritic length. Suppression of CDK5 activation with roscovitine attenuated neuronal apoptosis, hyperphosphorylation of CRMP2 (Ser522) and dendritic development abnormalities induced by sevoflurane. Our results indicate that activation of the CDK5/CRMP2 pathway may mediate sevoflurane-induced dendritic development abnormalities in the cortical neurons. The physiological significance of these findings remains to be determined.