Single sevoflurane exposure increases methyl-CpG island binding protein 2 phosphorylation in the hippocampus of developing mice

Sevoflurane-induced cognitive effect on α7-nicotine receptor and M1 acetylcholine receptor expression in the hippocampus of aged rats

BACKGROUND

Sevoflurane treatment increases the incidence of postoperative cognitive dysfunction (POCD), and patients with POCD show a decline in cognitive abilities compared to preoperative levels.

OBJECTIVES

This study aimed to investigate whether the activation of α7 nicotinic acetylcholine receptor (α7nAChR) and the expression of M1 acetylcholine receptor (mAChR M1) in the hippocampus affects the cognitive function of aged rats.

METHODS

Forty-eight Sprague-Dawley (SD) rats of 1-week- and 12-months-old were divided into eight groups: four groups for α7nAChR and four groups for mAChR M1, respectively. All SD rats received 1.0-02% sevoflurane for α7nAChR and 1.0-02% sevoflurane for mAChR M1 for 2-6 h, respectively. The Y-maze test was used to assess the ability to learn and memory after receiving sevoflurane for 7 days at the same moment portion. RT-PCR was used to determine the expression of α7nAChR and mAChR M1 in the hippocampus of rats.

RESULTS

The α7nAChR mitigated the formation of sevoflurane-induced memory impairment by modulating the translocation of NR2B from the intracellular reservoir to the cell surface reservoir within the hippocampus. Next, sevoflurane-induced decline of cognitive function and significantly decreased mAChR M1 expression at mRNA levels.

CONCLUSION

α7nAChR regulates the trafficking of NR2B in the hippocampus of rats via the Src-family tyrosine kinase (SFK) pathway. This regulation is associated with cognitive deficits induced by sevoflurane in hippocampal development. Sevoflurane affects the cognitive function of rats by suppressing the mAChR M1 expression at mRNA levels in the hippocampus.

Sevoflurane induces neurotoxic effects on developing neurons through the WNK1/NKCC1/Ca2+ /Drp-1 signalling pathway

Children repeatedly exposed to anaesthesia have a high risk of cognitive impairment, but the mechanism of its regulation in this context is unknown. The objective of this study was to investigate the possible toxic mechanism of sevoflurane through the WNK1/NKCC1/Ca²⁺ /Drp-1 signalling pathway. The hippocampal neuronal HT22 cell line was used in this study. The intervention group was treated with the WNK1 inhibitor WNK-463, CaN inhibitor FK506 and Drp-1 inhibitor Mdivi-1 respectively in the medium for 30 min before sevoflurane anaesthesia. The sevofluane group and all intervention group treated with 4.1% sevoflurane for 6 h. Compared with the control group, sevoflurane treatment decreased cell viability and increased cellular apoptosis. Our study found that WNK-463, FK506 and Mdivi-1 can all alleviate the sevoflurane-induced reduction in cell viability, decrease the cell apoptosis. In addition, WNK-463 pretreatment could inhibit the increase of WNK1 kinase and NKCC1 protein concentration caused by sevoflurane. Further, sevoflurane anaesthesia causes intracellular calcium overload, increases the expression of CaN and induces the dephosphorylation of Drp-1 protein at ser637, while CaN inhibitor FK506 pretreatment could reduce the dephosphorylation of Drp-1. Therefore, the WNK1/NKCC1/Ca²⁺ /Drp-1 signalling pathway plays an important role in sevoflurane-related neurotoxicity. Reducing intracellular calcium influx may be one of the important mechanism to ameliorate sevoflurane toxicity.

Neonatal exposure to sevoflurane impairs preference for social novelty in C57BL/6 female mice at early-adulthood

Social interaction deficit is core symptom of children with autism, owing to interaction of genetic predisposition and environmental toxins. Sevoflurane could induce neurotoxicity in developing brain in rodent models. This study aims to investigate whether sevoflurane anesthesia in neonatal period could impair social behaviors in male and female mice. Twenty-eight male and thirty-one female mice were randomly assigned to receive 3.0% sevoflurane or 60% oxygen on postnatal day 6. They were tested for social interaction behaviors at one- and two-month-old. In addition, the cortex and hippocampus of neonatal mice undergoing sevoflurane anesthesia were harvested for immunoblotting analysis. As a result, both male and female mice undergoing sevoflurane anesthesia showed strong sociability and weak preference for social novelty at juvenile age. In addition, the male mice developed normal preference for social novelty at early-adulthood; However, the female mice remained weak preference for social novelty. Furthurmore, sevoflurane anesthesia could decrease the levels of PSD95 but not Neuroligin-1 in the hippocampus but not cortex of neonatal mice. In conclusion, sevoflurane anesthesia in neonatal period could disturb development of social memory and impair preference for social novelty in female mice at early-adulthood, with the potential mechanism of decreasing PSD95 expression in the hippocampus of C57BL/6 mice.

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.

Histone H3K9 Trimethylation Downregulates the Expression of Brain-Derived Neurotrophic Factor in the Dorsal Hippocampus and Impairs Memory Formation During Anaesthesia and Surgery

Brain-derived neurotrophic factor (BDNF) is essential for cognitive and memory functions. Abnormal BDNF expression in the central nervous system may impair these functions. Anaesthesia and surgery can induce perioperative neurocognitive disorders (PND). Clinical studies show that BDNF expression is decreased in patients presenting with cognitive impairment after anaesthesia and surgery. However, the molecular mechanism is still unclear. Epigenetic regulation plays an important role in cognition. The hypermethylation of H3K9 is crucial for transcriptional silencing and the onset of cognitive disorders. Here, we hypothesised that H3K9 trimethylation repressed BDNF expression and impaired memory formation or recall during anaesthesia and surgery. Laparotomy under isoflurane inhalation anaesthesia, behavioural tests, Western blotting, quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR), chromatin immunoprecipitation (ChIP), and immunohistochemistry were used in this study. BDNF expression was decreased in the hippocampus after anaesthesia and surgery. Cognitive impairment affected memory formation but not recall. The trimethylation of H3K9 downregulated BDNF expression. The overexpression of BDNF or use of exogenous BDNF improved the impairment of memory formation caused by anaesthesia and surgery. Therefore, inhibiting H3K9 trimethylation and increasing the expression of BDNF may help prevent PND in the clinical setting.

Effects of Branched-Chain Amino Acid Supplementation on Spontaneous Seizures and Neuronal Viability in a Model of Mesial Temporal Lobe Epilepsy

BACKGROUND

The essential branched-chain amino acids (BCAAs) leucine, isoleucine, and valine have recently emerged as a potential novel treatment for medically refractory epilepsy. Blood-derived BCAAs can readily enter the brain, where they contribute to glutamate biosynthesis and may either suppress or trigger acute seizures. However, the effects of BCAAs on chronic (ie, spontaneous recurrent) seizures and epilepsy-associated neuron loss are incompletely understood.

MATERIALS AND METHODS

Sixteen rats with mesial temporal lobe epilepsy were randomized into 2 groups that could drink, ad libitum, either a 4% solution of BCAAs in water (n=8) or pure water (n=8). The frequency and relative percent of convulsive and nonconvulsive spontaneous seizures were monitored for a period of 21 days, and the brains were then harvested for immunohistochemical analysis.

RESULTS

Although the frequency of convulsive and nonconvulsive spontaneous recurrent seizures over a 3-week drinking/monitoring period were not different between the groups, there were differences in the relative percent of convulsive seizures in the first and third week of treatment. Moreover, the BCAA-treated rats had over 25% fewer neurons in the dentate hilus of the hippocampus compared with water-treated controls.

CONCLUSIONS

Acute BCAA supplementation reduces seizure propagation, whereas chronic oral supplementation with BCAAs worsens seizure propagation and causes neuron loss in rodents with mesial temporal lobe epilepsy. These findings raise the question of whether such supplementation has a similar effect in humans.

Relevance of experimental paradigms of anesthesia induced neurotoxicity in the mouse

Routine general anesthesia is considered to be safe in healthy individuals. However, pre-clinical studies in mice, rats, and monkeys have repeatedly demonstrated that exposure to anesthetic agents during early post-natal periods can lead to acute neurotoxicity. More concerning, later-life defects in cognition, assessed by behavioral assays for learning and memory, have been reported. Although the potential for anesthetics to damage the neonatal brain is well-documented, the clinical significance of the pre-clinical models in which damage is induced remains quite unclear. Here, we systematically evaluate critical physiological parameters in post-natal day 7 neonatal mice exposed to 1.5% isoflurane for 2–4 hours, the most common anesthesia induced neurotoxicity paradigm in this animal model. We find that 2 or more hours of anesthesia exposure results in dramatic respiratory and metabolic changes that may limit interpretation of this paradigm to the clinical situation. Our data indicate that neonatal mouse models of AIN are not necessarily appropriate representations of human exposures.

Neurotoxicity of anesthetics: Mechanisms and meaning from mouse intervention studies

Volatile anesthetics are widely used in human medicine and generally considered to be safe in healthy individuals. In recent years, the safety of volatile anesthesia in pediatric patients has been questioned following reports of anesthetic induced neurotoxicity in pre-clinical studies. These studies in mice, rats, and primates have demonstrated that exposure to anesthetic agents during early post-natal periods can cause acute neurotoxicity, as well as later-life cognitive defects including deficits in learning and memory. In recent years, the focus of many pre-clinical studies has been on identifying candidate pathways or potential therapeutic targets through intervention trials. These reports have shed light on the mechanisms underlying anesthesia induced neurotoxicity as well as highlighting the challenges of pre-clinical modeling of anesthesia induced neurotoxicity in mice. Here, we summarize the data derived from intervention studies in neonatal mouse models of anesthetic exposure and provide an overview of mechanisms proposed to mediate anesthesia induced neurotoxicity in mice based on these reports. The majority of these studies implicate one of three mechanisms: reactive oxygen species (ROS) mediated stress and signaling, growth/nutrient signaling, or direct neuronal modulation.

Propofol Regulates Neural Stem Cell Proliferation and Differentiation via Calmodulin-Dependent Protein Kinase II/AMPK/ATF5 Signaling Axis

BACKGROUND

Propofol can cause degeneration of developing brain cells and subsequent long-term learning or memory impairment. However, at the early stage of embryonic development, the molecular mechanism of propofol-induced inhibition in neural stem cells (NSCs) neurogenesis is still unclear. The aim of this study was to determine the role of propofol in NSCs neurogenesis and, more importantly, to explore the underlying mechanism.

METHODS

First, a single intraperitoneal injection of propofol was performed in pregnant mice, and 6 hours after administration of propofol, the hippocampus RNA and the protein of the embryos' brains was extracted to analyze the expression of neuron-specific markers. Second, the primary NSCs were isolated from the hippocampus of mouse embryonic brain and then treated with propofol for cell viability, immunostaining, and transwell assays; more importantly, we performed RNA sequencing (RNA-seq) and q-reverse transcription polymerase chain reaction assays to identify genes regulated by propofol; the Western blot, small interfering RNA (SiRNA), and luciferase reporter assays were used to study the effects of propofol on calmodulin-dependent protein kinase (CaMk) II/5' adenosine monophosphate-activated protein kinase (AMPK)/activating transcription factor 5 (ATF5) signaling pathway.

RESULTS

Our results indicated that propofol treatment could inhibit the proliferation, migration, and differentiation of NSCs. The results of RNA-seq assays showed that propofol treatment resulted in downregulation of a group of Ca-dependent genes. The following mechanism studies showed that propofol regulates the proliferation, differentiation, and migration of NSCs through the CaMkII/phosphorylation of serine at amino acid position 485 (pS485)/AMPK/ATF5 signaling pathway.

CONCLUSIONS

The results from study demonstrated that propofol inhibits the proliferation, differentiation, and migration of NSCs, and these effects are partially mediated by CaMkII/pS485/AMPK/ATF5 signaling pathway.

Role of α7nAChR-NMDAR in sevoflurane-induced memory deficits in the developing rat hippocampus

Detrimental effects of volatile anaesthetics, including sevoflurane, on the structure and function of the developing brain have been reported. The internalization of N-methyl-D-aspartate receptors (NMDARs) contributes to anaesthetic neurotoxicity. Both nicotinic acetylcholine receptors (nAChRs) and NMDAR play a critical role in the development of the nervous system. Moreover, nAChR can interact with NMDAR, and previous studies have demonstrated modulation of NMDAR by nAChR. In our study, we used an α7 nicotinic acetylcholine receptor (α7nAChR) agonist and α7nAChR antagonist to explore the role of α7nAChR and NMDAR in sevoflurane-induced long-term effects on memory and dendritic spine both in vivo and in vitro. The results revealed that the activation of α7nAChR attenuated the development of sevoflurane-induced memory deficit and dendritic spine changes, which might be by regulating NR2B-containing NMDAR trafficking from the intracellular pool to the cell surface pool in the hippocampus. Moreover, we demonstrated that α7nAChR could regulate NR2B-containing NMDAR via Src-family tyrosine kinase (SFK). Thus, our current study indicates that the trafficking of NR2B-containing NMDAR is regulated by α7nAChR via SFK in neonatal rat hippocampus, which may be secondary to sevoflurane-induced cognitive deficits in the developing hippocampus.

Pink1 attenuates propofol-induced apoptosis and oxidative stress in developing neurons

BACKGROUND

The underlying mechanisms of propofol-induced neurotoxicity in developing neurons are still not completely understood. We examined the role of PTEN-induced kinase 1 (Pink1), an antioxidant protein, in propofol-induced apoptosis in developing neurons.

MATERIALS AND METHODS

Primary hippocampal neurons isolated from neonatal Sprague-Dawley rats were exposed to propofol 20 μM for 2, 4, 6 and 12 h. Subsequently, neurons underwent overexpression and knockdown of Pink1, followed by propofol exposure (20 μM, 6 h). Neuron apoptosis was detected by terminal transferase deoxyuridine triphosphate-biotin nick-end labeling (TUNEL). Reactive oxygen species (ROS) production in neurons was detected by using a 2,7-dichlorodihydro-fluorescein diacetate probe and target protein or mRNA levels were analyzed by Western blotting or real-time polymerase chain reaction.

RESULTS

Propofol treatment time-dependently increased the number of TUNEL-positive neurons and the expression levels of cleaved caspase-3 and B-cell lymphoma 2 (BcL-2) associated X protein, but decreased expression levels of BcL-2. Furthermore, propofol treatment time-dependently reduced the expression levels of Pink1 mRNA and protein. ROS production and the markers of oxidative stress, 2,4-dinitrophenol and 4-hydroxynonenal, were increased by propofol treatment. However, these propofol-induced changes were significantly restored by Pink1 overexpression.

CONCLUSIONS

Pink1 plays an important role in neuronal apoptosis induced by propofol. Our results may provide some new insights in propofol-induced neurotoxicity in developing neurons.

Recent Insights Into Molecular Mechanisms of Propofol-Induced Developmental Neurotoxicity: Implications for the Protective Strategies

Mounting evidence has demonstrated that general anesthetics could induce developmental neurotoxicity, including acute widespread neuronal cell death, followed by long-term memory and learning abnormalities. Propofol is a commonly used intravenous anesthetic agent for the induction and maintenance of anesthesia and procedural and critical care sedation in children. Compared with other anesthetic drugs, little information is available on its potential contributions to neurotoxicity. Growing evidence from multiple experimental models showed a similar neurotoxic effect of propofol as observed in other anesthetic drugs, raising serious concerns regarding pediatric propofol anesthesia. The aim of this review is to summarize the current findings of propofol-induced developmental neurotoxicity. We first present the evidence of neurotoxicity from animal models, animal cell culture, and human stem cell-derived neuron culture studies. We then discuss the mechanism of propofol-induced developmental neurotoxicity, such as increased cell death in neurons and oligodendrocytes, dysregulation of neurogenesis, abnormal dendritic development, and decreases in neurotrophic factor expression. Recent findings of complex mechanisms of propofol action, including alterations in microRNAs and mitochondrial fission, are discussed as well. An understanding of the toxic effect of propofol and the underlying mechanisms may help to develop effective novel protective or therapeutic strategies for avoiding the neurotoxicity in the developing human brain.

Role of histone acetylation in long-term neurobehavioral effects of neonatal Exposure to sevoflurane in rats

Human studies, and especially laboratory studies, provide evidence that early life exposure to general anesthesia may affect neurocognitive development via largely unknown mechanisms. We explored whether hippocampal histone acetylation had a role in neurodevelopmental effects of sevoflurane administered to neonatal rats. Male Sprague-Dawley rats were exposed to 3% sevoflurane or were subjected to maternal separation only for 2h daily at postnatal days 6, 7, and 8. The histone deacetylase inhibitor, sodium butyrate (250mg/kg, intraperitoneally), or saline was administered starting 2h prior to anesthesia or maternal separation and continued daily until the end of behavioral tests, which were performed between postnatal days 33 and 50. Upon completion of the behavioral tests, the brain tissues were harvested for further analysis. Rats neonatally exposed to sevoflurane exhibited decreased freezing time in the fear conditioning contextual test and increased escape latency, decreased time in target quadrant, and number of platform crossings in the Morris water maze test. The sevoflurane-exposed rats had lower hippocampal density of dendritic spines, reduced levels of the brain-derived neurotrophic factor, c-fos protein, microtubule-associated protein 2, synapsin1, postsynaptic density protein 95, pCREB/CREB, CREB binding protein, and acetylated histones H3 and H4, and increased levels of histone deacetylases 3 and 8. These neurobehavioral abnormalities were normalized in the sevoflurane-exposed rats treated with sodium butyrate. Our findings provide evidence that neonatal exposure to sevoflurane induces neurobehavioral abnormalities and long-lasting alterations in histone acetylation; normalization of histone acetylation may alleviate the neurodevelopmental side effects of the anesthetic.

MicroRNAs: New Players in Anesthetic-Induced Developmental Neurotoxicity

Growing evidence demonstrates that prolonged exposure to general anesthetics during brain development induces widespread neuronal cell death followed by long-term memory and learning disabilities in animal models. These studies have raised serious concerns about the safety of anesthetic use in pregnant women and young children. However, the underlying mechanisms of anesthetic-induced neurotoxicity are complex and are not well understood. MicroRNAs are endogenous, small, non-coding RNAs that have been implicated to play important roles in many different disease processes by negatively regulating target gene expression. A possible role for microRNAs in anesthetic-induced developmental neurotoxicity has recently been identified, suggesting that microRNA-based signaling might be a novel target for preventing the neurotoxicity. Here we provide an overview of anesthetic-induced developmental neurotoxicity and focus on the role of microRNAs in the neurotoxicity observed in both human stem cell-derived neuron and animal models. Aberrant expression of some microRNAs has been shown to be involved in anesthetic-induced developmental neurotoxicity, revealing the potential of microRNAs as therapeutic or preventive targets against the toxicity.