Sevoflurane induces neurotoxicity in the developing rat hippocampus by upregulating connexin 43 via the JNK/c-Jun/AP-1 pathway

A conductive polymer restores connexin43 expression through the suppression of mitogen-activated protein kinases to improve intercellular communication and alleviate atrial fibrillation

Conductive biomaterials have shown promising results for correcting pathological cardiac electrical signaling. However, their mechanisms of operation are still largely unclear. One reason behind disrupted cardiac intercellular communication, though, is lowered expression of the gap junction protein connexin43 (Cx43), which may be alleviated by conductive biomaterials. In this study, we aimed to test this hypothesis, using the self-doping conductive biomaterial poly-3-amino-4-methoxybenzoic acid-gelatin (PAMB-G). An in vitro model was established, in which cardiomyocytes (CMs) were treated with anisomycin, while the in vivo model involved anisomycin-treated mice subjected to electrical pacing to induce atrial fibrillation (AF). Cx43 expression, Ca2+ transient propagation, and CM electrical conduction in vitro, as well as the in vivo effects of PAMB-G on AF, were evaluated; additionally, the underlying molecular mechanisms were identified. We found that anisomycin, at different concentrations, down-regulated Cx43; this was counteracted by PAMB-G, which restored proper Cx43 expression, coupled with improved Ca2+ signal and electrical conduction. Cx43 restoration was due to PAMB-G suppressing anisomycin-induced activation of MAPKs P38 and JNK, which are involved in phosphorylating Cx43 for degradation. Similar observations were also found in vivo, where a PAMB-G patch acted against anisomycin-induced Cx43 downregulation and impaired atrial cell communication, subsequently alleviating pacing-induced AF. Therefore, PAMB-G suppresses MAPKs, in turn upregulating Cx43, leading to improved electrical signal transduction. As a result, modulating the MAPK-Cx43 pathway, such as with PAMB-G, could serve as a potential therapeutic strategy for cardiac arrhythmia. STATEMENT OF SIGNIFICANCE: Disruption of atrial intercellular gap junction channels, comprised of connexins, leads to atrial fibrillation (AF), the most prevalent arrhythmia, with poor clinical outcomes. Current AF treatments are associated with adverse effects, and only focus on managing symptoms, thereby necessitating innovative treatment strategies. One such strategy is conductive biomaterials, which show promising results for correcting pathological cardiac electrical signaling. We synthesized a self-doping conductive biomaterial, poly-3-amino-4-methoxybenzoic acid-gelatin (PAMB-G), and found that it counteracts against anisomycin-induced connexin43 (Cx43) downregulation, subsequently improving cardiac electrical conduction and alleviating pacing-induced AF. This is owed to PAMB-G suppressing anisomycin-associated activation of mitogen-activated kinases P38 and JNK, which are involved in phosphorylating Cx43 for degradation. Therefore, PAMB-G modulation of MAPK-Cx43 pathway could aid in cardiac arrhythmia treatment.

Dexmedetomidine alleviates sevoflurane-induced neurotoxicity during late pregnancy by modulating apoptotic pathways and BDNF receptor expression

To investigate the associations between the neurotoxicity of sevoflurane and the neuroprotection provided by dexmedetomidine, we measured apoptotic gene and protein expression, brain-derived neurotrophic factor (BDNF) levels, and receptor expression, and neuronal apoptosis. Pregnant rats were treated with dexmedetomidine, 2.5% sevoflurane for 6 h, or a combination of 2.5% sevoflurane for 6 h with dexmedetomidine on gestational day 18 (G18). The apoptotic genes and proteins expression, BDNF and receptor expression, and neuronal apoptosis were assessed in offspring hippocampi on postnatal day 1 (P1) and P41. Dendritic spine density, synaptophysin protein fluorescence staining, and cognitive function were evaluated on P41. Maternal sevoflurane exposure increased Bax mRNA and protein expression, decreased Bcl-2 mRNA and protein expression, enhanced neuronal apoptosis, decreased the ratio of mature BDNF (mBDNF) to proBDNF, reduced mBDNF and tropomyosin receptor kinase B (TrkB) protein expression, and increased p75 neurotrophin receptor (p75NTR) protein expression in the hippocampi of neonatal rats. In juvenile rats, maternal sevoflurane exposure reduced mBDNF and TrkB protein expression, dendritic spine density, the proportion of time spent in the target quadrant, and the number of crossings over the platform while increasing escape latency in the Morris water maze. All abnormalities induced by maternal sevoflurane exposure, except for mBDNF levels on P41, were alleviated by dexmedetomidine. Dexmedetomidine mitigates sevoflurane-induced neuronal development abnormalities and cognitive impairments during late pregnancy by improving hippocampal Bcl-2 and Bax mRNA and protein expression, as well as proBDNF-p75NTR and mBDNF-TrkB protein expression in offspring.

Comparative analysis of BAG1 and BAG2: Insights into their structures, functions and implications in disease pathogenesis

As BAG family members, Bcl-2 associated athanogene family protein 1 (BAG1) and 2 (BAG2) are implicated in multiple cellular processes, including apoptosis, autophagy, protein folding and homeostasis. Although structurally similar, they considerably differ in many ways. Unlike BAG2, BAG1 has four isoforms (BAG1L, BAG1M, BAG1S and BAG1 p29) displaying different expression features and functional patterns. BAG1 and BAG2 play different cellular functions by interacting with different molecules to participate in the regulation of various diseases, including cancer/tumor and neurodegenerative diseases. Commonly, BAG1 acts as a protective factor to predict a good prognosis of patients with some types of cancer or a risk factor in some other cancers, while BAG2 is regarded as a risk factor to promote cancer/tumor progression. In neurodegenerative diseases, BAG2 commonly acts as a neuroprotective factor. In this review, we summarized the differences in molacular structure and biological function between BAG1 and BAG2, as well as the influences of them on pathogenesis of diseases, and explore the prospects for their clinical therapy application by specifying the activators and inhibitors of BAG1 and BAG2, which might provide a better understanding of the underlying pathogenesis and developing the targeted therapy strategies for diseases.

Inhalation of hydrogen gas mitigates sevoflurane-induced neuronal apoptosis in the neonatal cortex and is associated with changes in protein phosphorylation

Inhalation of hydrogen (H2) gas is therapeutically effective for cerebrovascular diseases, neurodegenerative disorders, and neonatal brain disorders including pathologies induced by anesthetic gases. To understand the mechanisms underlying the protective effects of H2 on the brain, we investigated the molecular signals affected by H2 in sevoflurane-induced neuronal cell death. We confirmed that neural progenitor cells are susceptible to sevoflurane and undergo apoptosis in the retrosplenial cortex of neonatal mice. Co-administration of 1-8% H2 gas for 3 h to sevoflurane-exposed pups suppressed elevated caspase-3-mediated apoptotic cell death and concomitantly decreased c-Jun phosphorylation and activation of the c-Jun pathway, all of which are induced by oxidative stress. Anesthesia-induced increases in lipid peroxidation and oxidative DNA damage were alleviated by H2 inhalation. Phosphoproteome analysis revealed enriched clusters of differentially phosphorylated proteins in the sevoflurane-exposed neonatal brain that included proteins involved in neuronal development and synaptic signaling. H2 inhalation modified cellular transport pathways that depend on hyperphosphorylated proteins including microtubule-associated protein family. These modifications may be involved in the protective mechanisms of H2 against sevoflurane-induced neuronal cell death.

Boswellic acid and apigenin alleviate methotrexate-provoked renal and hippocampal alterations in rats: Targeting autophagy, NOD-2/NF-κB/NLRP3, and connexin-43

The neuronal and renal deteriorations observed in patients exposed to methotrexate (MTX) therapy highlight the need for medical interventions to counteract these complications. Boswellic acid (BA) and apigenin (APG) are natural phytochemicals with prominent neuronal and renal protective impacts in various ailments. However, their impacts on MTX-provoked renal and hippocampal toxicity have not been reported. Thus, the present work is tailored to clarify the ability of BA and APG to counteract MTX-provoked hippocampal and renal toxicity. BA (250 mg/kg) or APG (20 mg/kg) were administered orally in rats once a day for 10 days, while MTX (20 mg/kg, i.p.) was administered once on the sixth day of the study. At the histopathological level, BA and APG attenuated MTX-provoked renal and hippocampal aberrations. They also inhibited astrocyte activation, as proven by the inhibition of glial fibrillary acidic protein (GFAP). These impacts were partially mediated via the activation of autophagy flux, as proven by the increased expression of beclin1, LC3-II, and the curbing of p62 protein, alongside the regulation of the p-AMPK/mTOR nexus. In addition, BA and APG displayed anti-inflammatory features as verified by the damping of NOD-2 and p-NF-κB p65 to reduce TNF-α, IL-6, and NLRP3/IL-1β cue. These promising effects were accompanied with a notable reduction in one of the gap junction proteins, connexin-43 (Conx-43). These positive impacts endorse BA and APG as adjuvant modulators to control MTX-driven hippocampal and nephrotoxicity.

MANF Alleviates Sevoflurane-Induced Cognitive Impairment in Neonatal Mice by Modulating Microglial Activation and Polarization

The precise mechanism underlying sevoflurane-induced neurotoxicity and cognitive impairment remains largely unknown. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a neuroprotective factor that has shown promise in various neurological disorders. However, its impact on sevoflurane-induced alterations has not been investigated. Thus, the objective of this study was to examine the effect of MANF in mitigating sevoflurane-induced neurotoxicity in young mice. Anesthesia with 3% sevoflurane 2 h daily was administered to young mice on postnatal day (P) 3, 6 and 9. We also constructed mono-macrophage-specific MANF knockout (MKO) mice in the mechanistic studies. Finally, the recombinant human MANF (rhMANF, 20 μg) protein was intraperitoneally administrated to neonatal mice before the sevoflurane anesthesia and the cognitive function, levels of pro-inflammatory cytokine and synapse-associated protein PSD95, the status of neural apoptosis, microglia activation and oxidative stress in hippocampus of the mice were investigated. The sevoflurane anesthesia increased the expression of endogenous MANF in the hippocampus, especially in microglia. MKO upregulated the expression of tumor necrosis factor-α (TNF-α), accelerated the neural apoptosis and the activation of microglia in hippocampus in young mice. MANF reversed the sevoflurane-induced cognitive impairment and inhibited the upregulation of TNF-α, the neural apoptosis and the reduction of the postsynaptic density protein-95 (PSD95) induced by sevoflurane anesthesia. Also, pretreatment with MANF alleviated the sevoflurane-induced activation of microglia and oxidative stress. Our current results demonstrated that MANF ameliorated neurotoxicity induced by the sevoflurane anesthesia in young mice, and such protective effect was associated with inhibition of microglia activation and neuroinflammation.

TAK1 Reduces Surgery-induced Overactivation of RIPK1 to Relieve Neuroinflammation and Cognitive Dysfunction in Aged Rats

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a common clinical complication in elderly patients, but its underlying mechanism remains unclear. Receptor-interacting protein kinase 1 (RIPK1), a key molecule mediating necroptosis and regulated by transforming growth factor β-activated kinase 1 (TAK1), was reported to be associated with cognitive impairment in several neurodegenerative diseases. This study was conducted to investigate the possible role of TAK1/RIPK1 signalling in POCD development following surgery in rats.

METHODS

Young (2-month-old) and old (24-month-old) Sprague-Dawley rats were subjected to splenectomy under isoflurane anaesthesia. The young rats were treated with the TAK1 inhibitor takinib or the RIPK1 inhibitor necrostatin-1 (Nec-1) before surgery, and old rats received adeno-associated virus (AAV)-TAK1 before surgery. The open field test and contextual fear conditioning test were conducted on postoperative day 3. The changes in TNF-α, pro-IL-1β, AP-1, NF-κB p65, pRIPK1, pTAK1 and TAK1 expression and astrocyte and microglia activation in the hippocampus were assessed.

RESULTS

Old rats had low TAK1 expression and were more susceptible to surgery-induced POCD and neuroinflammation than young rats. TAK1 inhibition exacerbated surgery-induced pRIPK1 expression, neuroinflammation and cognitive dysfunction in young rats, and this effect was reversed by a RIPK1 inhibitor. Conversely, genetic TAK1 overexpression attenuated surgery-induced pRIPK1 expression, neuroinflammation and cognitive dysfunction in old rats.

CONCLUSION

Ageing-related decreases in TAK1 expression may contribute to surgery-induced RIPK1 overactivation, resulting in neuroinflammation and cognitive impairment in old rats.

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.

Tripartite motif 72 inhibits apoptosis and mitochondrial dysfunction in neural stem cells induced by anesthetic sevoflurane by activating PI3K/AKT pathway

Anesthetics exposure induces neurocognitive deficits during brain development and impairs self-renewal and differentiation of neural stem cells (NSCs). Tripartite motif 72 (TRIM72, also known as mitsugumin 53, MG53) is involved in tissue repair and plasma membrane damage repair. The neuroprotective effect of TRIM72 against sevoflurane-induced neurotoxicity of NSCs was investigated in this study. First, human NSCs were exposed to different concentrations of sevoflurane. Results showed that TRIM72 was downregulated in sevoflurane-treated NSCs. Exposure to sevoflurane reduced cell viability in NSCs. Second, sevoflurane-treated NSCs were stimulated with recombinant human TRIM72 (rhTRIM72). Treatment with rhTRIM72 enhanced the cell viability in sevoflurane-treated NSCs. Moreover, treatment with a rhTRIM72-attenuated sevoflurane-induced increase in caspase-3 activity in NSCs. Third, JC-1 aggregates were deceased and JC-1 monomer was increased in sevoflurane-treated NSCs, which were reversed by rhTRIM72. Furthermore, rhTRIM72 also weakened sevoflurane-induced decrease in superoxide dismutase and glutathione peroxidase and increase in malondialdehyde and reactive oxygen species in NSCs. Finally, reduced phosphorylation levels of protein kinase B (AKT) and phosphatidylinositol 3-kinase (PI3K) in sevoflurane-treated NSCs were upregulated by rhTRIM72. In conclusion, TRIM72 inhibited cell apoptosis and reduced the mitochondria membrane potential of sevoflurane-treated NSCs through activation of the PI3K/AKT pathway.

Research progress on molecular mechanisms of general anesthetic-induced neurotoxicity and cognitive impairment in the developing brain

General anesthetics-induced neurotoxicity and cognitive impairment in developing brains have become one of the current research hotspots in the medical science community. The underlying mechanisms are complex and involve various related molecular signaling pathways, cell mediators, autophagy, and other pathological processes. However, few drugs can be directly used to treat neurotoxicity and cognitive impairment caused by general anesthetics in clinical practice. This article reviews the molecular mechanism of general anesthesia-induced neurotoxicity and cognitive impairment in the neonatal brain after surgery in the hope of providing critical references for the treatments of clinical diseases.

Insulin signaling in the central nervous system, a possible pathophysiological mechanism of anesthesia-induced delayed neurocognitive recovery/postoperative neurocognitive disorder: a narrative review

INTRODUCTION

Impairment in neurocognitive functions ranges between delayed neurocognitive recovery (DNR) and postoperative neurocognitive disorders (pNCD). Incidence varies from 11% after noncardiac surgery to 60% after cardiac surgery.

AREAS COVERED

Insulin receptors (IRs) signaling pathway in the central nervous system (CNS) could be a possible pathophysiological mechanism of anesthesia-induced DNR/pNCD and perioperative intranasal insulin administration could be a preventive approach. This hypothesis is supported by the following evidence: effects of IRs-CNS signaling pathway on neuromodulation; higher incidence of DNR/pNCD in patients with insulin resistance; neurotoxicity of IRs signaling pathways after anesthetic exposure; improvement of neurocognitive impairment after insulin exposure. This narrative review was conducted after a literature search of PubMed, EMBASE and SCOPUS online medical data performed in May 2022.

EXPERT OPINION

Perioperative intranasal insulin is shown to be protective and future studies should address: the role of insulin as a neuromodulator; its integration into neuroprotection approaches; patient populations that might benefit from this approach; a well-defined protocol of intranasal insulin administration in a perioperative background and other disciplines; and possible collateral effects.

Mechanistic insight into sevoflurane-associated developmental neurotoxicity

With the development of technology, more infants receive general anesthesia for surgery, other interventions, or clinical examination at an early stage after birth. However, whether general anesthetics can affect the function and structure of the developing infant brain remains an important, complex, and controversial issue. Sevoflurane is the most-used anesthetic in infants, but this drug is potentially neurotoxic. Short or single exposure to sevoflurane has a weak effect on cognitive function, while long or repeated exposure to general anesthetics may cause cognitive dysfunction. This review focuses on the mechanisms by which sevoflurane exposure during development may induce long-lasting undesirable effects on the brain. We review neural cell death, neural cell damage, impaired assembly and plasticity of neural circuits, tau phosphorylation, and neuroendocrine effects as important mechanisms for sevoflurane-induced developmental neurotoxicity. More advanced technologies and methods should be applied to determine the underlying mechanism(s) and guide prevention and treatment of sevoflurane-induced neurotoxicity.

1. We discuss the mechanisms underlying sevoflurane-induced developmental neurotoxicity from five perspectives: neural cell death, neural cell damage, assembly and plasticity of neural circuits, tau phosphorylation, and neuroendocrine effects. 2. Tau phosphorylation, IL-6, and mitochondrial dysfunction could interact with each other to cause a nerve damage loop. 3. miRNAs and lncRNAs are associated with sevoflurane-induced neurotoxicity.

Repeated exposure to sevoflurane in neonatal rats impairs cognition in adulthood via the PKA-CREB-BDNF signaling pathway

Sevoflurane (Sev) anesthesia is widely used in pediatrics due to its low blood-gas partition coefficient and lack of pungency. However, Sev treatment may lead to cognitive dysfunction in later life. The current study administered Sev to neonatal rats to investigate the effects of Sev treatment on cognitive performance in adulthood. In total, 6-day-old rats received 3% Sev for 2 h daily for 3 consecutive days. The cognitive function of rats in adulthood was evaluated in 56-day-old rats by Morris water maze test. The hippocampal neuron morphology was observed by Nissl staining. Hippocampal brain-derived neurotrophic factor (BDNF) levels were measured by ELISA. The protein expression of protein kinase A (PKA), cAMP response element binding protein (CREB), phosphorylated-CREB (p-CREB) and BDNF in hippocampus were assessed by western blotting. The water maze results demonstrated that neonatal treatment with Sev resulted in a significant impairment of cognition in 56-day-old adult rats. Behavioral analysis revealed that Sev treatment increased latency to first pass the platform and decreased residence in target quadrants and across platform frequency compared with the control group in Morris water maze tests. Furthermore, compared with the control group, neonatal exposure to Sev reduced the number of neurons and the concentration of BDNF in the hippocampus, a brain region important for learning and memory. Additionally, Sev significantly decreased the expression of PKA, p-CREB, BDNF and the p-CREB/CREB ratio. Treatment with bucladesine, a selective PKA agonist, partially reversed the deleterious effects of Sev. In summary, the results indicated that PKA-CREB-BDNF signaling served an important role in the cognitive decline caused by neonatal exposure to Sev.

Effects of sevoflurane general anesthesia during early pregnancy on AIM2 expression in the hippocampus and parietal cortex of Sprague-Dawley offspring rats

The aim of the present study was to investigate the effect of exposure to sevoflurane general anesthesia during early pregnancy on interferon-inducible protein AIM2 (AIM2) expression in the hippocampus and parietal cortex of the offspring Sprague-Dawley (SD) rats. A total of 18 SD rats at a gestational age of 5-7 days were randomly divided into three groups: i) A control group (control); ii) 2-h sevoflurane general anesthesia, group 1 (S1); and iii) 4-h sevoflurane general anesthesia, group 2 (S2). The six offspring rats in each group were maintained for 30 days and assessed by Morris water maze testing. Brain specimens were collected from offspring rats 30 days after birth. Changes in the structural morphology of neurons in the hippocampus and parietal cortex were observed using hematoxylin and eosin staining. Nissl bodies in the hippocampus and parietal cortex were observed by Nissl staining. The expression of glial fibrillary acidic protein (GFAP), AIM2, CD45 and IL-1β was detected by immunohistochemistry and the protein levels of CD45, IL-1β, pro-caspase-1 and caspase-1 p10 were detected by western blotting. Compared with the control group, offspring rats in the S1 and S2 groups exhibited poor long-term learning and memory ability and experienced different degrees of damage to both the hippocampus and parietal cortex. The expression levels of GFAP, AIM2, CD45, IL-1β, caspase-1 and caspase-1 p10 in the offspring of both the S1 and the S2 groups were significantly increased (P<0.05) compared with offspring of the control group. Moreover, compared with the offspring of the S1 group, hippocampal and parietal cortex injury in the offspring of the S2 group was further aggravated, and the expression of GFAP, AIM2, CD45, IL-1β, pro-caspase-1 and cleaved-caspase-1 was significantly increased (P<0.05). In conclusion, sevoflurane general anesthesia in SD rat early pregnancy promoted the expression of AIM2 and the inflammatory response in the hippocampus and parietal cortex of offspring rats.

Expression Signature of lncRNAs and mRNAs in Sevoflurane-Induced Mouse Brain Injury: Implication of Involvement of Wide Molecular Networks and Pathways

Sevoflurane, one of the most commonly used pediatric anesthetics, was found to cause developmental neurotoxicity. To understand specific risk groups and develop countermeasures, a better understanding of its mechanisms is needed. We hypothesize that, as in many other brain degeneration pathways, long non-coding RNAs (lncRNAs) are involved in the sevoflurane-induced neurotoxicity. Postnatal day 7 (PD7) mice were exposed to 3% sevoflurane for 6 h. To quantify neurotoxicity in these mice, we (1) detected neural apoptosis through analysis of caspase 3 expression level and activity and (2) assessed long-term learning ability via the Morris water maze at PD60. To elucidate specific mechanisms, profiles of 27,427 lncRNAs and 18,855 messenger RNAs (mRNAs) in mouse hippocampi were analyzed using microarray assays. Sevoflurane-induced abnormal lncRNA and mRNA expression-associated function pathways were predicted by bioinformatic analysis. We found that sevoflurane induced significant neurotoxicity, causing acute neuroapoptosis and abnormal expression of 148 mRNAs and 301 lncRNAs on PD7 in mouse hippocampus. Additionally, exposed mice exhibited impaired memory on PD60. Bioinformatic analysis predicted that the dysregulated mRNAs, which are highly correlated with their co-expressed dysregulated lncRNAs, might be involved in 34 neurodegenerative signaling pathways (e.g., brain cell apoptosis and intellectual developmental disorder). Our study reveals for the first time that neonatal exposure to 3% sevoflurane induces abnormal lncRNA and mRNA expression profiles. These dysregulated lncRNAs/mRNAs form wide molecular networks that might contribute to various functional neurological disease pathways in the hippocampus, resulting in the observed acute apoptosis and impaired long-term memory.

Prenatal sevoflurane exposure: Effects of iron metabolic dysfunction on offspring cognition and potential mechanism

For decades, the neurotoxicity caused by anesthetics in mammalian brain development has gained increasing attention. Exposure to anesthetics leads to neurotoxicity and apoptosis of nerve cells, which in turn induces cognitive dysfunction. Although most of the data came from animal studies, general anesthetics have been shown to have adverse effects on cognitive function in infants and young children in recent years. This concern has led to a number of retrospective studies that observed an association between general anesthesia in pregnant women and neurobehavioral problems in fetuses or offspring. Every year, many pregnant women undergo non-obstetric anesthesia due to various reasons such as traffic accidents, fetal interventions, acute appendicitis, symptomatic cholelithiasis, and trauma. A matter of concern for these pregnant women is whether anesthesia has a detrimental effect on fetal brain development in the womb and whether the fetus has cognitive impairment after birth. In humans, the association of anesthetic exposure in infants with the long-term impairment of neurologic functions has been reported in several retrospective clinical studies. Recently, we have found that sevoflurane anesthesia during pregnancy in mice-induced cognitive impairment in the offspring by causing iron deficiency and inhibiting myelinogenesis. Sevoflurane is a commonly used general anesthetic in the hospitals, which can induce neurotoxicity and cause cognitive impairment in fetuses, infants, children, and adults. However, the exact mechanism of sevoflurane-induced damage to the central nervous system (CNS) is not fully understood. Based on our recent results, this paper reviewed the effects of sevoflurane on cognitive impairment and pathological changes such as neurogenesis, neuronal apoptosis, and iron metabolism dysfunction in the offspring.

AMPK‑SIRT1 pathway dysfunction contributes to neuron apoptosis and cognitive impairment induced by sevoflurane

The anesthetic sevoflurane (Sev) is widely used because of its low blood-gas partition coefficient and lack of pungency. However, the application of Sevmay lead to cognitive impairment later in life. Previous results have indicated that exposure to Sev-induced neuronal apoptosis and cognitive dysfunction in a rat model, but much work remains to elucidate the mechanism. In the present study, inhibition in the AMP-activated protein kinase/Sirtuin 1 (AMPK/SIRT1) signaling pathway and a decrease in AMPK/SIRT1 activity was found to occur concomitantly in neuronal apoptosis induced by Sev. AICAR, an activator of AMPK, was able to suppress Sev-induced neuronal apoptosis and SIRT1 activity reduction in vitro. Further animal studies also showed that AICAR treatment blocked the deleterious cognition and AMPK/SIRT1 activity reduction in the cognition impairment rats induced by Sev. Taken together, it was concluded that the AMPK/SIRT1 signaling pathway mediates neuronal apoptosis and cognition impairment induced by Sev. The study provides evidence that AMPK activation ameliorates Sev-induced cognitive deficits.

Epigenetic modulation of the MAPK pathway prevents isoflurane-induced neuronal apoptosis and cognitive decline in aged rats

Isoflurane is a broadly used inhalation anesthetic that causes cognitive impairment in rodent models as well as humans. Although previous studies suggested an association between isoflurane exposure and neuro-inflammation, apoptosis and mitochondrial dysfunction, the pathogenesis of isoflurane-induced cognitive decline remains elusive. In the present study, 22-month-old male Sprague-Dawley male rats (n=96) were divided into three groups: Control (Cont), isoflurane (ISO) and MS-275 pre-treated groups. The rats were sacrificed following exposure to isoflurane and a cognitive test. The hippocampus of each animal was harvested for quantitative PCR, TUNEL staining and western blot analysis. Histone deacetylases (HDAC)-1, -2 and -3 exhibited a significant increase at the gene and protein expression levels, whereas negligible mRNA expressions were observed for genes HDAC 4-11 (P>0.05; compared with Cont). Pre-treatment with the HDAC inhibitor MS-275 significantly inhibited the increase in TUNEL-positive cells induced by isoflurane exposure (70.72% decrease; P<0.001; compared with ISO). Furthermore, MS-275 significantly decreased caspase-3 and Bax expression levels while increasing Bcl-2 protein expression. The isoflurane-induced changes in the MAPK pathway signaling proteins ERK1/2, JNK and p38 were also reversed with MS-275 pre-treatment. Finally, in a Morris water maze test, the time to find a hidden platform was reduced in MS-275 pre-treated rats, compared with the ISO group. Therefore, the present study provided insight into the effect of isoflurane exposure on neuronal apoptosis pathways, as well as cognitive decline via epigenetic programming of MAPK signaling in aged rats.

Sevoflurane prevents vulnerable plaque disruption in apolipoprotein E-knockout mice by increasing collagen deposition and inhibiting inflammation

BACKGROUND

Sevoflurane may reduce the occurrence of major adverse cardiovascular events (MACCEs) in surgical patients, although the mechanisms are poorly understood. We hypothesised that sevoflurane stabilises atherosclerotic plaques by inhibiting inflammation and enhancing prolyl-4-hydroxylase α1 (P4Hα1), the rate-limiting subunit for the P4H enzyme essential for collagen synthesis.

METHODS

We established a vulnerable arterial plaque model in apolipoprotein E-knockout mice (ApoE^-/-) fed a high-fat diet that underwent daily restraint/noise stress, with/without a single prior exposure to sevoflurane for 6 h (1-3%; n=30 per group). In vitro, smooth muscle cells (SMCs) were incubated with tumour necrosis factor-alpha in the presence/absence of sevoflurane. Immunohistochemistry, immunoblots, and mRNA concentrations were used to quantify the effect of sevoflurane on plaque formation, expression of inflammatory cytokines, P4Hα1, and collagen subtypes in atherosclerotic plaques or isolated SMCs.

RESULTS

In ApoE^-/- mice, inhalation of sevoflurane 1-3% for 6 h reduced the aortic plaque size by 8-29% in a dose-dependent manner, compared with control mice that underwent restraint stress alone (P<0.05); this was associated with reduced macrophage infiltration and lower lipid concentrations in plaques. Sevoflurane reduced gene transcription and protein expression levels of pro-inflammatory cytokines (≥69-75%; P<0.05) and matrix metalloproteinases (≥39-65%; P<0.05) at both gene transcription and protein levels, compared with controls. Sevoflurane dose dependently increased Types I and III collagen deposition through enhanced protein expression of P4Hα1, both in vivo and in vitro (0.7-3.3-fold change; P<0.05).

CONCLUSIONS

Sevoflurane dose dependently promotes plaque stabilisation and decreases the incidence of plaque disruption in ApoE^-/- mice by increasing collagen deposition and inhibiting inflammation. These mechanisms may contribute to sevoflurane reducing MACCE.

Research progress and treatment strategies for anesthetic neurotoxicity

Every year, a large number of infants and young children worldwide are administered general anesthesia. Whether general anesthesia adversely affects the intellectual development and cognitive function of children at a later date remains controversial. Many animal experiments have shown that general anesthetics can cause nerve damage during development, affect synaptic plasticity, and induce apoptosis, and finally affect learning and memory function in adulthood. The neurotoxicity of pediatric anesthetics (PAN) has received extensive attention in the field of anesthesia, which has been listed as a potential problem affecting public health by NFDA of the United States. Previous studies on rodents and non-human primates indicate that inhalation of anesthetics early after birth can induce long-term and sustained impairment of learning and memory function, as well as changes in brain function. Many anti-oxidant drugs, dexmedetomidine, as well as a rich living environment and exercise have been proven to reduce the neurotoxicity of anesthetics. In this paper, we summarize the research progress, molecular mechanisms and current intervention measures of anesthetic neurotoxicity.

PNU282987 alleviates Aβ-induced anxiety and depressive-like behaviors through upregulation of α7nAChR by ERK-serotonin receptors pathway

Patients with Alzheimer's disease often undergo anxiety and depression. Our previous studies have shown that α7nAChR protects against Aβ-induced neurotoxicity via downregulation of p38 and JNK MAPKs, but the role of α7nAChR on Aβ-induced anxiety and depressive-like behaviors and the effect of α7nAChR on the regulation of MAPKs pathways remain unknown. To examine the effects of α7nAChR and MAPKs pathways on Aβ-induced anxiety and depression-like behaviors and to explore their relationships between them, elevated plus maze, open field and forced swim tests were performed. Protein levels of 5-HT_1A receptor, 5-HT_2C receptor, α7nAChR, t-ERK1/2 and p-ERK1/2 in the amygdala were analyzed by western blotting and immunostaining. Our study found out that Aβ oligomers induced anxiety and depression-like behaviors in C56BL/6 mice with open field, elevated plus maze and forced swim tests. However, activation of α7nAChR or inhibition of ERK pathways showed significant antidepressant and anxiolytic-like effects on Aβ-injected mice. Moreover, Aβ significantly decreased the level of 5-HT_1A receptor but increased the level of 5-HT_2C receptor in the basolateral amygdala. Treatment with α7nAChR agonist PNU282987 or ERK inhibitor U0126 reversed Aβ-induced 5-HT_1A and 5-HT_2C receptor changes. Moreover, activation of α7nAChR inhibited ERK pathway in the amygdala of Aβ_1-42-injected mice. Our study provides a new insight into the mechanism of α7nAChR in Aβ-induced depression and anxiety-related symptoms through the regulation of ERK1/2 pathway and the potential association with serotonin receptors. Together, our data suggests that α7nAChR is protective against Aβ-induced anxiety and depression-like behaviors in mice.

GluN2A-selective positive allosteric modulator-nalmefene-flumazenil reverses ketamine-fentanyl-dexmedetomidine-induced anesthesia and analgesia in rats

Anesthetics are used to produce hypnosis and analgesic effects during surgery, but anesthesia for a long time after the operation is not conducive to the recovery of animals or patients. Therefore, finding appropriate treatments to counter the effects of anesthetics could enhance postoperative recovery. In the current study, we discovered the novel role of a GluN2A-selective positive allosteric modulator (PAM) in ketamine-induced anesthesia and investigated the effects of the PAM combined with nalmefene and flumazenil (PNF) in reversing the actions of an anesthetic combination (ketamine-fentanyl-dexmedetomidine, KFD). PAM treatment dose-dependently decreased the duration of the ketamine-induced loss of righting reflex (LORR). Compared with those in the KFD group, the duration of LORR and the analgesic effect of the KFD + PNF group were obviously decreased. Meanwhile, successive administration of PNF and KFD had no adverse effects on the cardiovascular and respiratory systems. Both the KFD group and the KFD + PNF group showed no changes in hepatic and renal function or cognitive function in rats. Moreover, the recovery of motor coordination of the KFD + PNF group was faster than that of the KFD group. In summary, our results suggest the potential application of the PNF combination as an antagonistic treatment strategy for anesthesia.

Involvement of homodomain interacting protein kinase 2-c-Jun N-terminal kinase/c-Jun cascade in the long-term synaptic toxicity and cognition impairment induced by neonatal Sevoflurane exposure

Sevoflurane is one of the most widely used anesthetics with recent concerns rising about its pediatric application. The synaptic toxicity and mechanisms underlying its long‐term cognition impairment remain unclear. In this study, we investigated the expression and roles of homeodomain interacting protein kinase 2 (HIPK2), a stress activating kinase involved in neuronal survival and synaptic plasticity, and its downstream c‐Jun N‐terminal kinase (JNK)/c‐Jun signaling in the long‐term toxicity of neonatal Sevoflurane exposure. Our data showed that neonatal Sevoflurane exposure results in impairment of memory, enhancement of anxiety, less number of excitatory synapses and lower levels of synaptic proteins in the hippocampus of adult rats without significant changes of hippocampal neuron numbers. Up‐regulation of HIPK2 and JNK/c‐Jun was observed in hippocampal granular neurons shortly after Sevoflurane exposure and persisted to adult. 5‐((6‐Oxo‐5‐(6‐(piperazin‐1‐yl)pyridin‐3‐yl)‐1,6‐dihydropyridin‐3‐yl)methylene)thiazolidine‐2,4‐dione trifluoroacetate, antagonist of HIPK2, could significantly rescue the cognition impairment, decrease in long‐term potentiation, reduction in spine density and activation of JNK/c‐Jun induced by Sevoflurane. JNK antagonist SP600125 partially restored synapse development and cognitive function without affecting the expression of HIPK2. These data, in together, revealed a novel role of HIPK2‐JNK/c‐Jun signaling in the long‐term synaptic toxicity and cognition impairment of neonatal Sevoflurane exposure, indicating HIPK2‐JNK/c‐Jun cascade as a potential target for reducing the synaptic toxicity of Sevoflurane.

Cover Image for this issue: doi: 10.1111/jnc.14757.

Claudin-15 overexpression inhibits proliferation and promotes apoptosis of Schwann cells in vitro

Our previous experiments have discovered that Claudin-15 was up-regulated in Schwann cells of the distal nerve stumps of rat models of sciatic nerve injury. However, how Claudin-15 affects Schwann cell function is still unknown. This study aimed to identify the effects of Claudin-15 on proliferation and apoptosis of Schwann cells cultured in vitro and explore the underlying mechanisms. Primary Schwann cells were obtained from rats. Claudin-15 in Schwann cells was knocked down using siRNA (siRNA-1 group) compared with the negative control siRNA transfection group (negative control group). Claudin-15 in Schwann cells was overexpressed using pGV230-Claudin-15 plasmid (pGV230-Claudin-15 group). The pGV230 transfection group (pGV230 group) acted as the control of the pGV230-Claudin-15 group. Cell proliferation was analyzed with EdU assay. Cell apoptosis was analyzed with flow cytometric analysis. Cell migration was analyzed with Transwell inserts. The mRNA and protein expressions were analyzed with quantitative polymerase chain reaction assay and western blot assay. The results showed that compared with the negative control group, cell proliferation rate was up-regulated; p-AKT/AKT ratio, apoptotic rate, p-c-Jun/c-Jun ratio, mRNA expression of protein kinase C alpha, Bcl-2 and Bax were down-regulated; and mRNA expression of neurotrophins basic fibroblast growth factor and neurotrophin-3 were increased in the siRNA-1 group. No significant difference was found in cell migration between the negative control and siRNA-1 groups. Compared with the pGV230 group, the cell proliferation rate was down-regulated; apoptotic rate, p-c-Jun/c-Jun ratio and c-Fos protein expression increased; mRNA expression of protein kinase C alpha and Bax decreased; and mRNA expressions of neurotrophins basic fibroblast growth factor and neurotrophin-3 were up-regulated in the pGV230-Claudin-15 group. The above results demonstrated that overexpression of Claudin-15 inhibited Schwann cell proliferation and promoted Schwann cell apoptosis in vitro. Silencing of Claudin-15 had the reverse effect and provided neuroprotective effect. This study was approved by the Experimental Animal Ethics Committee of Jilin University of China (approval No. 2016-nsfc001) on March 5, 2016.

Long non-coding RNA Peg13 attenuates the sevoflurane toxicity against neural stem cells by sponging microRNA-128-3p to preserve Sox13 expression

BACKGROUND

Exposure to anesthetics during brain development may impair neurological function, however, the mechanisms underlying anesthetic neurotoxicity are unclear. Recent studies indicate that long non-coding RNAs (lncRNAs) are crucial for regulating the functional brain development during neurogenesis. This study aimed to determine the regulatory effects and potential mechanisms of lncRNA Peg13 (Peg13) on sevoflurane exposure-related neurotoxicity against neural stem cells (NSCs).

METHODS

Mouse embryotic NSCs were isolated and their self-renewal and differentiation were characterized by immunofluorescence. NSCs were exposed to 4.1% sevoflurane 2 h daily for three consecutive days. The potential toxicities of sevoflurane against NSCs were evaluated by neurosphere formation, 5-ethynyl-2'-deoxyuridine (EdU) incorporation and flow cytometry assays. The Peg13, miR-128-3p and Sox13 expression in NSCs were quantified. The potential interactions among Peg13, miR-128-3p and Sox13 were analyzed by luciferase reporter assay. The effects of Peg13 and/or miR-128-3p over-expression on the sevoflurane-related neurotoxicity and Sox13 expression were determined in NSCs.

RESULTS

The isolated mouse embryotic NSCs displayed potent self-renewal ability and differentiated into neurons, astrocytes and oligodendrocytes in vitro, which were significantly inhibited by sevoflurane exposure. Sevoflurane exposure significantly down-regulated Peg13 and Sox13, but enhanced miR-128-3p expression in NSCs. Transfection with miR-128-3p mimics, but not the control, significantly mitigated the Peg13 or Sox13-regulated luciferase expression in 293T cells. Peg13 over-expression significantly reduced the sevoflurane-related neurotoxicity and increased Sox13 expression in NSCs, which were mitigated by miR-128-3p transfection.

CONCLUSION

Such data indicated that Peg13 mitigated the sevoflurane-related neurotoxicity by sponging miR-128-3p to preserve Sox13 expression in NSCs.

Neurodevelopmental Effect of General Anesthesia on the Pediatric Patient

In this article, the authors review the animal and human data on the recent studies looking at the neurotoxicity of general anesthesia in the pediatric population. Animal studies in rodents and non-human primates demonstrate neurotoxic effects when exposed to general anesthesia at a young age. However, prospective clinical studies in humans do not show significant differences in intelligence quotient outcomes in children younger than 3 years with isolated and/or short exposures. Current studies are investigating alternatives to minimize the potential side effects, including the addition of protective agents to the anesthetic mix. Understanding the findings regarding the laboratory and clinical studies on the effects of general anesthesia is important in guiding both patient care and parent education. This is particularly relevant in the care of children with ophthalmic conditions such as trauma, congenital cataract, and congenital glaucoma, which may require urgent surgery and early anesthetic exposure. [J Pediatr Ophthalmol Strabismus. 2019;56(6):349-353.].

Cognitive impairment and transcriptomic profile in hippocampus of young mice after multiple neonatal exposures to sevoflurane

Children with repeated inhalational anesthesia may develop cognitive disorders. This study aimed to investigate the transcriptome-wide response of hippocampus in young mice that had been exposed to multiple sevoflurane in the neonatal period. Mice received 3% sevoflurane for 2 h on postnatal day (PND) 6, 8, and 10, followed by arterial blood gas test on PND 10, behavioral experiments on PND 31–36, and RNA sequencing (RNA-seq) of hippocampus on PND 37. Functional annotation and protein-protein interaction analyses of differentially expressed genes (DEGs) and quantitative reverse transcription polymerase chain reaction (qPCR) were performed. Neonatal sevoflurane exposures induced cognitive and social behavior disorders in young mice. RNA-seq identified a total of 314 DEGs. Several enriched biological processes (ion channels, brain development, learning, and memory) and signaling pathways (oxytocin signaling pathway and glutamatergic, cholinergic, and GABAergic synapses) were highlighted. As hub-proteins, Pten was involved in nervous system development, synapse assembly, learning, memory, and behaviors, Nos3 and Pik3cd in oxytocin signaling pathway, and Cdk16 in exocytosis and phosphorylation. Some top DEGs were validated by qPCR. This study revealed a transcriptome-wide profile in mice hippocampus after multiple neonatal exposures to sevoflurane, promoting better understanding of underlying mechanisms and investigation of preventive strategies.

Knockdown of long noncoding RNA WNT5A-AS restores the fate of neural stem cells exposed to sevoflurane via inhibiting WNT5A/Ryk-ROS signaling

Long noncoding RNAs (lncRNAs) have been implicated in neurogenesis. LncRNA WNT5A-AS is upregulated in neural stem cells (NSCs), the proliferation of which is inhibited by sevoflurane. Thus, we hypothesized that knocking down of lncRNA WNT5A-AS may restore the fate of NSCs exposed to sevoflurane. To test this hypothesis, NSCs obtained from postnatal Sprague-Dawley rats were exposed to 2.4% sevoflurane or control gas for 6 h. Bioinformatics analysis, quantitative PCR and RNA interference technology were used to identify the properties of lncRNA WNT5A-AS. Cell proliferation was assessed using counting a Cell Counting Kit-cell 8 assay, a 5-ethynyl-2'-deoxyuridine incorporation assay, and a plate cloning assay. Cell survival was detected by flow cytometry, which was also used to examine the levels of reactive oxygen species (ROS) and the cell cycle. The levels of WNT5A and receptor tyrosine kinase (Ryk) were measured via Western blotting. LncRNA WNT5A-AS was identified to have low coding potency and to be located on the antisense strand of WNT5A. The level of upregulated lncRNA WNT5A-AS was positively correlated with that of WNT5A in response to sevoflurane exposure. The knockdown of lncRNA WNT5A-AS promoted the proliferation and survival of NSCs, whereas it suppressed the WNT5A/Ryk-ROS signaling and drove cell cycle processes. Taken together, findings strongly suggest that the inhibition of lncRNA WNT5A-AS can rescue the fate of NSCs. In addition, WNT5A/Ryk-ROS signaling might be a downstream target of lncRNA WNT5A-AS.

Proteomics analysis of HSV-1-induced alterations in mouse brain microvascular endothelial cells

Herpes simplex virus 1 (HSV-1) is a predominant cause of herpes simplex encephalitis (HSE), leading to a high mortality rate and severe neurological sequelae worldwide. HSE is typically accompanied by the blood-brain barrier (BBB) disruption, but the underlying mechanisms are unclear. To explore the disruption mechanisms of the BBB, quantitative analysis of the cellular proteome was carried out to investigate the proteomic changes that occur after infection. In this study, bEnd.3 cells were infected with HSV-1, followed by liquid chromatography-tandem mass spectrometry. A total of 6761 proteins were identified in three independent mass spectrometry analyses. Compared to the uninfected cells, 386 and 293 differentially expressed proteins were markedly upregulated or downregulated, respectively. Bioinformatic analysis showed that the activator protein-1 factor, including Fos, Jun, and ATF family proteins and cell adhesion molecules were significantly changed. Further validation of the changes observed for these proteins was carried out by western blotting and quantitative real-time PCR. Transendothelial electrical resistance (TEER) studies were performed to explore the effects of ATF3, Fra1, or JunB overexpression on the function of bEnd.3 cells. Characterization of the differential expression of these proteins in bEnd.3 cells will facilitate further exploration of BBB disruption upon HSV-1 infection.

Effect of ERK inhibitor on corneal neovascularization induced by alkali burn in mice and its mechanism

The objective of this study is to explore the effect of extracellular signal–regulated kinase (ERK) inhibitors on corneal neovascularization induced by alkali burn in mice and its mechanism. A total of 30 standard diet (SD) healthy mice were divided into normal group, alkali burn group, and inhibitor group. Normal group was not treated. Alkali burn group and inhibitor group were used to establish corneal neovascularization model induced by alkali burn. After successful modeling, ERK inhibitor was used to intervene in inhibitor group, and saline of equal volume was used in normal group and alkali burn group. The area of corneal neovascularization was calculated and the expression of vascular endothelial growth factor (VEGF), c-Fos, c-Jun, ERK1/2, and p-ERK1/2 protein in cornea tissue of three groups of mice was detected. The relative expression of vascular area, length, VEGF, c-Fos, c-Jun, ERK1/2, and p-ERK1/2 protein in cornea tissue of mice in alkali burn group was significantly higher than that in normal group and inhibitor group. The relative expression of vascular area, length, VEGF, c-Fos, c-Jun, ERK1/2, and p-ERK1/2 protein in cornea tissue of mice in inhibitor group was higher than that in normal group, and the expression level of PEDF was lower than that in normal group ( P < 0.05). ERK inhibitors inhibit the formation of corneal neovascularization by inhibiting the expression of VEGF, c-Fos, and c-Jun proteins through the action of ERK signaling pathway.

Dexmedetomidine Ameliorates the Neurotoxicity of Sevoflurane on the Immature Brain Through the BMP/SMAD Signaling Pathway

Numerous studies have demonstrated that general anesthetics might damage the nervous system, thus, the effect of general anesthetics on the developing brain has attracted much attention. Dexmedetomidine (Dex) exhibits a certain neuroprotective effect, but the mechanism is obscure. In our study, pregnant rats on gestational day 20 (G20) were exposed to 3% sevoflurane for 2 h or 4 h, and the neuronal apoptosis in hippocampal CA1 region of the offspring rats was detected by quantification of TUNEL positive cells and cleaved-caspase3 (cl-caspase3). Different doses of Dex were intraperitoneally injected before sevoflurane anesthesia; then, the expression of apoptotic-related proteins including BCL-2, BAX and cl-caspase3 as well as amyloid precursor protein (APP, a marker of axonal injury), p-CRMP-2 and CRMP-2 were measured at postnatal days 0, 1and 3 (P0, P1, and P3, respectively). As an antagonist of the bone morphgenetic proteins (BMP) receptor, DMH1 was co-administered with sevoflurane plus Dex to investigate whether BMP/SMAD is associated with the neuroprotective effects of Dex. The results showed that prenatal sevoflurane anesthesia for 4 h activated apoptosis transiently, as manifested by the caspase3 activity peaked on P1 and disappeared on P3. In addition, the expressions of APP and p-CRMP-2/CRMP-2 in postnatal rat hippocampus were significantly increased, which revealed that prenatal sevoflurane anesthesia caused axonal injury of offspring. The long-term learning and memory ability of offspring rats was also impaired after prenatal sevoflurane anesthesia. These damaging effects of sevoflurane could be mitigated by Dex and DMH1 reversed the neuroprotective effect of Dex. Our results indicated that prenatal exposure to 3% sevoflurane for 4 h increased apoptosis and axonal injury, even caused long-term learning and memory dysfunction in the offspring rats. Dex dose-dependently reduced sevoflurane- anesthesia-induced the neurotoxicity by activating the BMP/SMAD signaling pathway.