Mitophagy impairment is involved in sevoflurane-induced cognitive dysfunction in aged rats

TLR3 deletion inhibits programmed necrosis of brain cells in neonatal mice with sevoflurane-induced cognitive dysfunction

This research aimed to explore the influence of TLR deletion on sevoflurane-induced postoperative cognitive dysfunction in neonatal mice. Herein, WT and TLR3 KO neonatal mice, each with 24, were randomly divided into control group, sevoflurane group, and TLR3^−/−+sevoflurane group. The hippocampal neurons of WT, TLR3 KO and RIP3 KO neonatal mice in C group, SEV group, TLR3^−/−+SEV group and RIP3^−/−+SEV group were extracted for in vitro experiments. The results revealed the degeneration and necrosis of nerve cells in SEV group. Microscopic findings indicated that nerve cells showed shrinkage and nuclear hyperchromatism, along with lessening or even disappearance of nuclei and enlargement of cell spaces, and apoptotic cells in the brain tissues were evidently increased. Compared with SEV group, TLR3^−/−+SEV group displayed reductions in these phenomena. Additionally, SEV group showed the reduced SHP2 expression and the increased expressions of proteins associated with TLR signaling pathway and apoptosis. Furthermore, there were no obvious differences in the expressions of such proteins in hippocampal neurons between RIP3^−/−+SEV and TLR3^−/−+SEV groups. The results confirmed that inhibiting RIP3 phosphorylation and suppressing TLR3 expressions exerted the same influence on the expressions of these proteins in the hippocampus of neonatal mice with sevoflurane-induced cognitive dysfunction. Based on these, it is speculated that TLR3 influences neonatal mice with sevoflurane-induced cognitive dysfunction probably by regulating RIP3 phosphorylation.

TREM2 ameliorates anesthesia and surgery-induced cognitive impairment by regulating mitophagy and NLRP3 inflammasome in aged C57/BL6 mice

Postoperative cognitive dysfunction (POCD) is a major postoperative complication. Triggering receptor expressed on myeloid cells 2 (TREM2) exerts a neuroprotective function against neuro-inflammatory responses. The present study investigated the role of TREM2 in anesthesia and surgery-induced cognitive impairment and the potential related mechanism. Our results revealed that TREM2 was downregulated, coupled with activation of the NLRP3 inflammasome and subsequent IL-1β expression on postoperative day 3. A corresponding decline in PSD-95 and BDNF was found at the same time point. The key regulator of mitophagy PINK1 and Parkin protein levels were significantly decreased following surgery and anesthesia. TREM2 overexpression partially reversed postoperative cognitive impairment and enhanced PSD-95 and BDNF expression. TREM2 overexpression also improved mitophagy function and inhibited activation of the NLRP3 inflammasome and associated production of IL-1β. Our findings demonstrate that TREM2 rescues anesthesia and surgery-induced spatial learning and memory impairment and neuro-inflammation in aged C57/BL6 mice, which may be at least partially mediated through the activation of mitophagy and subsequent inhibition of the NLRP3 inflammasome.

Neuroinflammation as the Underlying Mechanism of Postoperative Cognitive Dysfunction and Therapeutic Strategies

Postoperative cognitive dysfunction (POCD) is a common neurological complication following surgery and general anesthesia, especially in elderly patients. Severe cases delay patient discharge, affect the patient’s quality of life after surgery, and are heavy burdens to society. In addition, as the population ages, surgery is increasingly used for older patients and those with higher prevalences of complications. This trend presents a huge challenge to the current healthcare system. Although studies on POCD are ongoing, the underlying pathogenesis is still unclear due to conflicting results and lack of evidence. According to existing studies, the occurrence and development of POCD are related to multiple factors. Among them, the pathogenesis of neuroinflammation in POCD has become a focus of research in recent years, and many clinical and preclinical studies have confirmed the correlation between neuroinflammation and POCD. In this article, we reviewed how central nervous system inflammation occurred, and how it could lead to POCD with changes in peripheral circulation and the pathological pathways between peripheral circulation and the central nervous system (CNS). Furthermore, we proposed some potential therapeutic targets, diagnosis and treatment strategies at the cellular and molecular levels, and clinical applications. The goal of this article was to provide a better perspective for understanding the occurrence of POCD, its development, and preventive strategies to help manage these vulnerable geriatric patients.

Role of BDNF/ProBDNF Imbalance in Postoperative Cognitive Dysfunction by Modulating Synaptic Plasticity in Aged Mice

Postoperative cognitive dysfunction (POCD) is a disturbing neurological complication in patients undergoing anesthesia and surgical procedures. Brain-derived neurotrophic factor (BDNF) and its precursor proBDNF binding to their corresponding receptors tyrosine kinase (TrkB) and p75 neurotrophin receptor (p75NTR) exert quite an opposite biological function in neuron survival and synaptic function. This study aimed to demonstrate the critical role of the BDNF/proBDNF ratio in modulating synaptic plasticity, which further leads to anesthesia-/surgery-induced POCD. It also showed that the exogenous BDNF or p75NTR inhibitor could ameliorate cognitive dysfunction. In detail, 16-month-old C57BL/6 mice were subjected to a stabilized tibial fracture surgery with isoflurane anesthesia to establish the POCD animal model. The mice were then microinjected with either p75NTR inhibitor or exogenous BDNF into the dorsal hippocampus. Behavioral experiments were performed by open field and fear conditioning tests (FCTs). Western blotting was also used to measure the expression levels of BDNF, proBDNF, TrkB, p-TrkB, p75NTR, and synapse proteins. Golgi staining and electrophysiology were applied to evaluate the neuronal synaptic plasticity. Here, we demonstrated that anesthesia/surgery induced a reduction of BDNF/proBDNF, which negatively regulates the synaptic function in hippocampus, subsequently leading to cognitive impairment in aged mice. P75NTR inhibitor and exogenous BDNF could attenuate cognitive deficits by rescuing the dendritic spine loss and long-term potentiation (LTP) via altering the BDNF/proBDNF ratio. This study unveiled that the BDNF/proBDNF ratio in the hippocampus played a key role in anesthesia-/surgery-induced POCD. Thereby, tuning the ratio of BDNF/proBDNF is supposed to be a promising therapeutic target for POCD.

Sevoflurane Effects on Neuronal Energy Metabolism Correlate with Activity States While Mitochondrial Function Remains Intact

During general anesthesia, alterations in neuronal metabolism may induce neurotoxicity and/or neuroprotection depending on the dose and type of the applied anesthetic. In this study, we investigate the effects of clinically relevant concentrations of sevoflurane (2% and 4%, i.e., 1 and 2 MAC) on different activity states in hippocampal slices of young Wistar rats. We combine electrophysiological recordings, partial tissue oxygen (p_tiO₂) measurements, and flavin adenine dinucleotide (FAD) imaging with computational modeling. Sevoflurane minimally decreased the cerebral metabolic rate of oxygen (CMRO₂) while decreasing synaptic transmission in naive slices. During pharmacologically induced gamma oscillations, sevoflurane impaired network activity, thereby decreasing CMRO₂. During stimulus-induced neuronal activation, sevoflurane decreased CMRO₂ and excitability while basal metabolism remained constant. In this line, stimulus-induced FAD transients decreased without changes in basal mitochondrial redox state. Integration of experimental data and computer modeling revealed no evidence for a direct effect of sevoflurane on key enzymes of the citric acid cycle or oxidative phosphorylation. Clinically relevant concentrations of sevoflurane generated a decent decrease in energy metabolism, which was proportional to the present neuronal activity. Mitochondrial function remained intact under sevoflurane, suggesting a better metabolic profile than isoflurane or propofol.

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.

ACSL4 contributes to sevoflurane-induced ferroptotic neuronal death in SH-SY5Y cells via the 5' AMP-activated protein kinase/mammalian target of rapamycin pathway

Background

Acyl-CoA synthetase long chain family member 4 (ACSL4) has been reported to serve as a major player in the progress of ferroptosis in various diseases. Nevertheless, the functional role and mechanism of ACSL4 in sevoflurane (sev)-induced neuronal death has never been elucidated.

Methods

Cell viability was assessed using Cell Counting Kit-8 (CCK-8). Iron levels, reactive oxygen species (ROS) production, and malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), and glutathione (GSH) content were determined to assess ferroptosis level. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and western blot were undertaken for the measurement of gene expression.

Results

Sev hindered the viability of SH-SY5Y cells and suppression of ferroptosis by ferrostatin-1 (Fer-1) mitigated sev-induced inhibition of SH-SY5Y cell viability. Sev treatment increases the Fe²⁺ level and decreases the mRNA levels of SLC7A11 and GPX4 in SH-SY5Y cells. Sev increased the expression of ACSL4. Moreover, silencing of ACSL4 could abrogate sev-induced cell damage, as evidenced by increases in cell viability, GPX4 protein levels, and decreases in iron levels, ROS production, and MDA and 4-HNE content. Remarkably, sev hindered the activation of the 5' AMP-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) signaling, which was diminished by knockdown of ACSL4. Moreover, inhibition of the AMPK/mTOR signaling by compound C could mitigate the protective effect of ACSL4 silencing against sev-induced ferroptotic cell death.

Conclusions

Downregulation of ACSL4 restrained sev-induced ferroptotic cell death via AMPK/mTOR signaling, providing the basis for an approach to alleviate sev-induced postoperative cognitive dysfunction (POCD).

A National Population Cohort Study Showed That Exposure to General Anesthesia in Early Childhood Is Associated with an Increase in the Risk of Developmental Delay

This study investigated the relationship between exposure to general anesthesia (GA) and the risk of cognitive and mental disorders. This study has thus investigated the relationships between exposure to GA before the age of 3 and subsequent cognitive and mental disorders in a national-wide research sample. We obtained our subjects from the National Health Insurance Research Database (NHIRD) of Taiwan, which was based on the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). Children in the hospital aged less than 3 years old were included if there was GA exposure or not during the period of year 1997 to 2008. Cox proportional hazard regression models adjusted for potential confounding factors were used to estimate the relative magnitude of the risk associated with GA exposure. The cohort contained 2261 subjects with GA and 4522 children without GA as a comparison group. GA exposure group had a higher rate of developmental delay than in the without GA group (hazard ratio 1.46, p < 0.0001). There was no significant difference in the overall incidence of ADHD, autism and intellectual disability between the GA-exposed group and the comparison cohort. In conclusion, this study reported that children exposed to GA early before the age of three had a small association with increased risk of development delay thereafter.

ApoE transiently regulates hippocampus amyloid-beta deposition to stable learning and memory ability in adult rats exposed in sevoflurane

Objective

Post-operative cognitive dysfunction (POCD) is a common central nervous system complication after surgery. Inhaled anesthetic sevoflurane is thought to have harmful effects on the developing and aged nerves, but its effects on adults' nervous system are less studied and the mechanism is not clear.

Methods

Male adult rats were divided into control group and sevoflurane group. Rats from sevoflurane group were received 3.2% sevoflurane + carrier gas (1 L/min O2+1 L/min air) for 2 h, while control group received carrier gas for 2 h. Each group was subsequently divided into 3 subgroups according to the Day 1, Day 3, Day 7 after sevoflurane anesthesia. Morris Water Maze, amyloid-beita (Abeta) and apolipoprotein E (ApoE) mRNA in hippocampus were analyzed. Then, adult ApoE-/- rats were also divided into control group and sevoflurane group. Each group was divided into 3 subgroups according to Day 1, Day 3 and Day 7. Abeta mRNA and protein expression in hippocampus were analyzed.

Results

Compared with the control group, hippocampal Abeta mRNA and protein expression in rats from sevoflurane group significantly increased in hippocampus on Day 7, while ApoE mRNA and protein expression increased on Day 1 and Day 3. There was no difference in times of crossing platforms, time during platform, times across platform quadrant and time percent during platform quadrant between each group. Compared with the control group, hippocampal Abeta and ApoE-/- rats in sevoflurane group did not change.

Conclusion

ApoE modulates hippocampal Abeta deposition and stabilizes learning and memory ability in adult rats after sevoflurane exposure, but this effect is not constant.

Regulation of glial cell-derived neurotrophic factor in sevoflurane-induced neuronal apoptosis by long non-coding RNA CDKN2B-AS1 as a ceRNA to adsorb miR-133

OBJECTIVE

To investigate the regulatory mechanism of sevoflurane-induced neuronal apoptosis through analyzing the expression of glial cell-derived neurotrophic factor (GDNF) mediated by miR-133, sponged by long non-coding RNA (lncRNA) CDKN2B-AS1.

METHODS

An in vitro cell injury model was established by using different concentrations of sevoflurane and primary hippocampal neurons. Cell proliferation was detected by Cell Counting Kit-8 (CCK-8); caspase-3 and caspase-9 activities were detected by colorimetry, and apoptotic cells were determined by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Fluorescence in situ hybridization (FISH) analysis was used to detect localized expression of CDKN2B antisense RNA 1 (CDKN2B-AS1), and dual-luciferase reporter assay was employed to verify the correlation of CDKN2B-AS1 and miR-133, and of miR-133 and GDNF. The expression of CDKN2B-AS1, miR-133, and GDNF mRNA in the cell injury model were measured by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Western blot was utilized to detect the expression of GDNF protein in the cell injury model.

RESULTS

In the cell injury model, CDKN2B-AS1 was highly expressed in the cytoplasm, and CDKN2B-AS1 and GDNF were downregulated and miR-133 was upregulated as detected by qRT-PCR (all P<0.05). The connections between CDKN2B-AS1 and miR-133, and between miR-133 and GDNF were confirmed. That is, CDKN2B-AS1 regulated the expression of GDNF by adsorbing miR-133 (all P<0.05). In cells treated with sevoflurane, overexpression of CDKN2B-AS1 could inhibit caspase-3 and caspase-9 activities and the degree of apoptosis. miR-133 could partially alleviate the effect of overexpressing CDKN2B-AS1 on cells, and si-GDNF the effect of miR-133 inhibitor (all P<0.05).

CONCLUSION

lncRNA CDKN2B-AS1 can up-regulate the expression of GDNF, inhibit neuronal apoptosis, and ease the toxic effect of sevoflurane on neural cells by acting as a sponge to adsorb miR-133.

Involvement of Mitochondrial Dynamics and Mitophagy in Sevoflurane-Induced Cell Toxicity

General anesthesia is a powerful and indispensable tool to ensure the accomplishment of surgical procedures or clinical examinations. Sevoflurane as an inhalational anesthetic without unpleasant odor is commonly used in clinical practice, especially for pediatric surgery. However, the toxicity caused by sevoflurane has gained growing attention. Mitochondria play a key role in maintaining cellular metabolism and survival. To maintain the stability of mitochondrial homeostasis, they are constantly going through fusion and fission. Also, damaged mitochondria need to be degraded by autophagy, termed as mitophagy. Accumulating evidence proves that sevoflurane exposure in young age could lead to cell toxicity by triggering the mitochondrial pathway of apoptosis, inducing the abnormalities of mitochondrial dynamics and mitophagy. In the present review, we focus on the current understanding of mitochondrial apoptosis, dynamics and mitophagy in cell function, the implications for cell toxicity in response to sevoflurane, and their underlying potential mechanisms.

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.

Repeated propofol exposure-induced neuronal damage and cognitive impairment in aged rats by activation of NF-κB pathway and NLRP3 inflammasome

BACKGROUND

Elderly patients receive propofol at regular intervals for sedation during gastrointestinal endoscopy. However, the link between cognition and intermittent propofol exposure remains unclear. Thus, we used aged rats to investigate the effect of propofol on cognition.

METHODS

The study included two parts. In the first part, aged (18-20 months old) male Sprague-Dawley rats underwent intermittent intraperitoneal injection of propofol (200 mg/kg) or intralipid, every 9 days or once a day. In the second part, some aged rats received intraperitoneal injection of Bay 11-7082 (1 mg/kg), a specific inhibitor of NF-κB, 30 min before propofol injection. Memory tests were performed to evaluate cognition 24 h after the entire treatment. The hippocampal neuronal damage was assessed by TUNEL staining. The hippocampal levels of p-NF-κB p65, NLRP3, caspase-1 p20, and cleaved caspase-3 were detected by western blotting. The hippocampal and serum levels of IL-1β, IL-6, and TNF-α were evaluated using ELISA.

RESULTS

There were no differences in the behavioral tests, hippocampal neuronal damage, and neuroinflammation between groups given intralipid and propofol treatment every 9 days. However, repeated propofol treatment once a day promoted activation of NF-κB and the NLRP3 inflammasome, inducing cognitive impairment and neuroinflammation. Interestingly, pretreatment with Bay-11-7082 not only inhibited NF-κB/NLRP3 inflammasome activation, but also attenuated neuronal damage and cognitive dysfunction in aged rats exposed to daily propofol treatment.

CONCLUSIONS

Intermittent propofol treatment every 9 days may be safe for aged rats. However, propofol treatment once a day could impair the cognition of aged rats, partly through the activation of the NF-κB pathway and NLRP3 inflammasome, which may be a potential targets for the treatment of cognitive impairment in elderly patients.