Age-dependent postoperative cognitive impairment and Alzheimer-related neuropathology in mice

Microbiota-gut-brain axis in perioperative neurocognitive and depressive disorders: Pathogenesis to treatment

An increasing number of people undergo anesthesia and surgery. Perioperative neurocognitive and depressive disorders are common central nervous system complications with similar pathogeneses. These conditions pose a deleterious threat to human health and a significant societal burden. In recent years, numerous studies have focused on the role of the gut microbiota and its metabolites in the central nervous system via the gut-brain axis. Its involvement in perioperative neurocognitive and depressive disorders has attracted considerable attention. This review aimed to elucidate the role of the gut microbiota and its metabolites in the pathogenesis of perioperative neurocognitive and depressive disorders, as well as the value of targeted interventions and treatments.

Mechanism research on microRNA-669f-5p/deoxycytidylate deaminase axis mediating sevoflurane-induced cognitive dysfunction in aged mice

OBJECTIVE

To investigate the role of the microRNA (miRNA)-669f-5p/deoxycytidylate deaminase (Dctd) axis in sevoflurane inducing cognitive dysfunction in aged mice.

METHODS

Sixty-six C57BL/6J mice were used in the experiment model and were randomly divided into the sevoflurane group and the control group. The mice in the sevoflurane group were anesthetised with 3.4% sevoflurane, whereas those in the control group were air-treated for the same period. The study was then performed using bioinformatics sequencing, as well as in vitro and in vivo validation.

RESULTS

The mice in the sevoflurane group showed significant cognitive impairments in terms of a decrease in both spatial learning and memory abilities. Experimental doses of miR-669f-5p agonist exhibited no obvious effect on cognitive function following sevoflurane inhalation, but inhibiting the expression of miR-669f-5p could alleviate the impairments. Based on the results of the bioinformatics sequencing, miR-669f-5p/Dctd and the toll-like receptor (TLR) signalling pathway could be the key miRNA, gene and pathway leading to postoperative cognitive dysfunction following sevoflurane inhalation. The aged mice showed significantly increased expression of miR-669f-5p in the hippocampus following sevoflurane inhalation, and upregulating/inhibiting its expression could increase/decrease TLR expression in the hippocampus. Furthermore, miR-669f-5p could reduce the expression of the Dctd gene by binding to its 3'untranslated region.

CONCLUSION

The miR-669f-5p/Dctd axis plays an important role in sevoflurane inducing cognitive dysfunction in aged mice, providing a new direction for further development of therapeutic strategies concerning the prevention and treatment of cognitive dysfunction associated with sevoflurane anaesthesia.

Anesthesia/surgery activate MMP9 leading to blood-brain barrier disruption, triggering neuroinflammation and POD-like behavior in aged mice

Anesthesia and surgery activate matrix metalloproteinase 9 (MMP9), leading to blood-brain barrier (BBB) disruption and postoperative delirium (POD)-like behavior, especially in the elderly. Aged mice received intraperitoneal injections of either the MMP9 inhibitor SB-3CT, melatonin, or solvent, and underwent laparotomy under 3 % sevoflurane anesthesia(anesthesia/surgery). Behavioral tests were performed 24 h pre- and post-operatively. Serum and cortical tissue levels of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) were measured using ELISA. Levels of PDGFRβ, MMP9, tight junction, Mfsd2a, caveolin-1, synaptophysin, and postsynaptic densin (PSD)-95 proteins in the prefrontal cortex were assayed using Western blotting. BBB permeability was assessed by detecting IgG in the prefrontal cortex and serum S100β levels. Anesthesia/surgery-induced peripheral inflammation activated MMP9, which in turn injured pericytes and tight junctions and increased transcytosis, thereby disrupting the BBB. Impaired BBB allowed the migration of peripheral inflammation into the central nervous system (CNS), thereby inducing neuroinflammation, synaptic dysfunction, and POD-like behaviors. However, MMP9 inhibition reduced pericyte and tight junction injury and transcytosis, thereby preserving BBB function and preventing the migration of peripheral inflammation into the CNS, thus attenuating synaptic dysfunction and POD-like behavior. In addition, to further validate the above findings, we showed that melatonin exerted similar effects through inhibition of MMP9. The present study shows that after anesthesia/surgery, inflammatory cytokines upregulation is involved in regulating BBB permeability in aged mice through activation of MMP9, suggesting that MMP9 may be a potential target for the prevention of POD.

A53T α-synuclein mutation increases susceptibility to postoperative delayed neurocognitive recovery via hippocampal Ang-(1-7)/MasR axis

Delayed neurocognitive recovery (dNCR) is a common complication in geriatric surgical patients. The impact of anesthesia and surgery on patients with neurodegenerative diseases, such as Parkinson's disease (PD) or prion disease, has not yet been reported. In this study, we aimed to determine the association between a pre-existing A53T genetic background, which involves a PD-related point mutation, and the development of postoperative dNCR. We observed that partial hepatectomy induced hippocampus-dependent cognitive deficits in 5-month-old A53T transgenic mice, a model of early-stage PD without cognitive deficits, unlike in age-matched wild-type (WT) mice. We respectively examined molecular changes at 6 h, 1 day, and 2 days after partial hepatectomy and observed that cognitive changes were accompanied by weakened angiotensin-(1-7)/Mas receptor [Ang-(1-7)/MasR] axis, increased alpha-synuclein (α-syn) expression and phosphorylation, decreased methylated protein phosphatase-2A (Me-PP2A), and prompted microglia M1 polarization and neuronal apoptosis in the hippocampus at 1 day after surgery. Nevertheless, no changes in blood-brain barrier (BBB) integrity or plasma α-syn levels in either A53T or WT mice. Furthermore, intranasal administration of selective MasR agonist AVE 0991, reversed the mentioned cognitive deficits in A53T mice, enhanced MasR expression, reduced α-syn accumulation and phosphorylation, and attenuated microglia activation and apoptotic response. Our findings suggest that individuals with the A53T genetic background may be more susceptible to developing postoperative dNCR. This susceptibility could be linked to central α-syn accumulation mediated by the weakened Ang-(1-7)/MasR/methyl-PP2A signaling pathway in the hippocampus following surgery, independent of plasma α-syn level and BBB.

Involvement of Fgf2-mediated tau protein phosphorylation in cognitive deficits induced by sevoflurane in aged rats

OBJECTIVE

Anesthetics have been linked to cognitive alterations, particularly in the elderly. The current research delineates how Fibroblast Growth Factor 2 (Fgf2) modulates tau protein phosphorylation, contributing to cognitive impairments in aged rats upon sevoflurane administration.

METHODS

Rats aged 3, 12, and 18 months were subjected to a 2.5% sevoflurane exposure to form a neurotoxicity model. Cognitive performance was gauged, and the GEO database was employed to identify differentially expressed genes (DEGs) in the 18-month-old cohort post sevoflurane exposure. Bioinformatics tools, inclusive of STRING and GeneCards, facilitated detailed analysis. Experimental validations, both in vivo and in vitro, examined Fgf2's effect on tau phosphorylation.

RESULTS

Sevoflurane notably altered cognitive behavior in older rats. Out of 128 DEGs discerned, Fgf2 stood out as instrumental in regulating tau protein phosphorylation. Sevoflurane exposure spiked Fgf2 expression in cortical neurons, intensifying tau phosphorylation via the PI3K/AKT/Gsk3b trajectory. Diminishing Fgf2 expression correspondingly curtailed tau phosphorylation, neurofibrillary tangles, and enhanced cognitive capacities in aged rats.

CONCLUSION

Sevoflurane elicits a surge in Fgf2 expression in aging rats, directing tau protein phosphorylation through the PI3K/AKT/Gsk3b route, instigating cognitive aberrations.

Anesthesia and dementia: An up-to-date review of the existing literature

Concerns around the impact of anesthesia on cognitive decline and dementia, including Alzheimer's Disease (AD), have been increasing and recently attracting considerable attention in the research community. One unanswered question is whether anesthesia is a risk factor of dementia, specifically AD type dementia. A large body of evidence, coming from in vivo and in vitro models, suggests that exposure to anesthetic agents may increase the risk of AD through mechanisms of action similar to AD's neuropathology. In terms of clinical studies, our knowledge of the relationship between anesthesia and dementia is based on limited data, with most studies suggesting that there is no association. The aim of this paper was therefore to outline recent clinical studies exploring this controversial relationship and discuss future directions in terms of study design and potential areas of study. As the aging population and the prevalence of dementia and AD increases, we need a better understanding of anesthesia as a risk factor for neurodegeneration through well-designed studies. Despite the controversy, there seems to be little evidence to support that anesthesia itself or other surgical and patient factors can cause or accelerate AD.

Calcium regulation by SERC-A before and during Alzheimer disease

There are many factors involved in the incidence of Alzheimer’s disease that, in combination, impede or hinder normal neuronal functions. Little is currently known about calcium regulation before and during the disease. Internal instability of calcium levels is associated with increased vascular risk, a prevalent condition in a high number of individuals already compromised by Alzheimer’s disease. This review provides a reevaluation of the molecular mechanism of the sarcoendoplasmic reticulum calcium ATPase (SERC-A) in the disease and discusses salient aspects of voltage-gated calcium channel function; in these way new alternatives could be open for its treatment. These regulation mechanisms are clinically relevant since the irregular functions of SERC+A has been implicated in pathologies of brain function.

fRNC: Uncovering the dynamic and condition-specific RBP-ncRNA circuits from multi-omics data

The RNA binding protein (RBP) and non-coding RNA (ncRNA) interacting networks are increasingly recognized as the main mechanism in gene regulation, and are tightly associated with cellular malfunction and disease. Here, we present fRNC, a systems biology tool to uncover the dynamic spectrum of RBP-ncRNA circuits (RNC) by integrating transcriptomics, interactomics and proteomics data. fRNC constructs the RBP-ncRNA network derived from CLIP-seq or PARE experiments. Given scoring on nodes and edges according to differential analysis of expression data, it finds an RNC containing global maximum significant RBPs and ncRNAs. Alternatively, it can also capture the locally maximum scoring RNC according to user-defined starting nodes with the greedy search. When compared with existing tools, fRNC can detect more accurate and robust sub-network with scalability. As shown in the cases of esophageal carcinoma, breast cancer and Alzheimer's disease, fRNC enables users to analyze the collective behaviors between RBP and the interacting ncRNAs, and reveal novel insights into the disease-associated processes. The fRNC R package is available at https://github.com/BioinformaticsSTU/fRNC.

Perioperative considerations in patients with chemotherapy-induced cognitive impairment: a narrative review

Patients with cancer may suffer from a decline in their cognitive function after various cancer therapies, including surgery, radiation, and chemotherapy, and in some cases, this decline in cognitive function persists even years after completion of treatment. Chemobrain or chemotherapy-induced cognitive impairment, a well-established clinical syndrome, has become an increasing concern as the number of successfully treated cancer patients has increased significantly. Chemotherapy-induced cognitive impairment can originate from direct neurotoxicity, neuroinflammation, and oxidative stress, resulting in alterations in grey matter volume, white matter integrity, and brain connectivity. Surgery has been associated with exacerbating the inflammatory response associated with chemotherapy and predisposes patients to develop postoperative cognitive dysfunction. As the proportion of patients living longer after these therapies increases, the magnitude of impact and growing concern of post-treatment cognitive dysfunction in these patients has also come to the fore. We review the clinical presentation, potential mechanisms, predisposing factors, diagnostic methods, neuropsychological testing, and imaging findings of chemotherapy-induced cognitive impairment and its intersection with postoperative cognitive dysfunction.

Reactive oxygen species contribute to delirium-like behavior by activating CypA/MMP9 signaling and inducing blood-brain barrier impairment in aged mice following anesthesia and surgery

Postoperative delirium (POD) is common in the elderly and is associated with poor clinical outcomes. Reactive oxygen species (ROS) and blood-brain barrier (BBB) damage have been implicated in the development of POD, but the association between these two factors and the potential mechanism is not clear. Cyclophilin A (CypA) is a specifically chemotactic leukocyte factor that can be secreted in response to ROS, which activates matrix metalloproteinase 9 (MMP9) and mediates BBB breakdown. We, therefore, hypothesized that ROS may contribute to anesthesia/surgery-induced BBB damage and delirium-like behavior via the CypA/MMP9 pathway. To test these hypotheses, 16-month-old mice were subjected to laparotomy under 3% sevoflurane anesthesia (anesthesia/surgery) for 3 h. ROS scavenger (N-acetyl-cysteine) and CypA inhibitor (Cyclosporin A) were used 0.5 h before anesthesia/surgery. A battery of behavior tests (buried food test, open field test, and Y maze test) was employed to evaluate behavioral changes at 24 h before and after surgery in the mice. Levels of tight junction proteins, CypA, MMP9, postsynaptic density protein (PSD)-95, and synaptophysin in the prefrontal cortex were assessed by western blotting. The amounts of ROS and IgG in the cortex of mice were observed by fluorescent staining. The concentration of S100β in the serum was detected by ELISA. ROS scavenger prevented the reduction in TJ proteins and restored the permeability of BBB as well as reduced the levels of CypA/MMP9, and further alleviated delirium-like behavior induced by anesthesia/surgery. Furthermore, the CypA inhibitor abolished the increased levels of CypA/MMP, which reversed BBB damage and ameliorated delirium-like behavior caused by ROS accumulation. Our findings demonstrated that ROS may participate in regulating BBB permeability in aged mice with POD via the CypA/MMP9 pathway, suggesting that CypA may be a potential molecular target for preventing POD.

HDAC6 Inhibition Alleviates Anesthesia and Surgery-Induced Less Medial Prefrontal-Dorsal Hippocampus Connectivity and Cognitive Impairment in Aged Rats

To investigate the underlying mechanisms of postoperative cognitive dysfunction and the impairment of medial prefrontal cortex-hippocampus connectivity. Postoperative cognitive dysfunction frequently affects elderly following surgery. The role of inter-brain-region connectivity abnormality after anesthesia and surgery on postoperative cognitive dysfunction development remains unclear. Medial prefrontal cortex-hippocampus connectivity of aged and adult rats was evaluated by injecting neurotracer biotinylated dextranamine (BDA) into bilateral hippocampus 3 days before partial hepatectomy, and biotinylated dextranamine positive cells of medial prefrontal cortex 2 days after hepatectomy were counted. HDAC6 shRNA was injected into medial prefrontal cortex and hippocampus bilaterally before hepatectomy or an HDAC6 activity inhibitor Tubastatin A was administered systemically after hepatectomy. Neuroinflammation and HDAC6 down-target ac-tubulin in medial prefrontal cortex and hippocampus were detected. Learning and memory of rats were evaluated by Barnes Maze task during 2-5 days after surgery and delayed matching-to-place water maze task during 10-23 days after surgery. Compared to the age-matched normal controls, anesthesia and surgery significantly decreased BDA-positive neurons in medial prefrontal cortex of aged rats, but not young adult rats. Local HDAC6 knockdown and systemic HDAC6 inhibition both increased BDA-positive neurons number of medial prefrontal cortex, alleviated learning and memory impairment in the Barnes Maze task and water maze task, decreased HDAC6 expression, inflammatory cytokines, astrocyte and microglial activation, and increased ac-tubulin expression in aged rats which received surgery. Our data indicated that anesthesia and surgery impaired medial prefrontal cortex-hippocampus connectivity and cognition which was associated with HDAC6 overexpression.

Esketamine alleviates postoperative cognitive decline via stimulator of interferon genes/ TANK-binding kinase 1 signaling pathway in aged rats

BACKGROUND

Postoperative cognitive decline (POCD) is a common complication after surgery and anesthesia among the elderly. Yet the potential mechanism of POCD remains ambiguous, with limited therapeutic measures currently available. Ketamine has been reported to attenuate POCD after cardiac surgery. Herein, we tried to determine the effect of esketamine (the S-enantiomer of ketamine) on POCD and the possible molecular mechanisms.

METHODS

We investigated the effects of esketamine (10 mg/kg) on POCD using an exploratory laparotomy model in aged SD rats (24 months). Open field, novel object recognition, and morris water maze tests were performed on day 30 post-surgery. 24 h or 30 d post-surgery, brain tissue from the hippocampus and ventromedial prefrontal cortex (vmPFC) was harvested and subjected to histopathology and molecular biology analysis. During the in vitro experiment, primary astrocytes from the hippocampus and vmPFC were exposed to lipopolysaccharide (LPS) to investigate the pathological changes in astrocytes during the process of POCD.

RESULTS

Our results indicated that exploratory laparotomy could induce significant cognitive and memory decline, accompanied by A2-type astrocytes phenotype loss and increased expression of neuron Aβ-42, astrocytes GABA, stimulator of interferon genes (STING) and TANK-binding kinase 1 (TBK1). In addition, LPS exposure significantly decreased the mitochondrial membrane potential and upregulated the level of pyroptosis-associated proteins, including cleaved caspase-1 and IL-18. Notably, treatment with esketamine reversed these abnormalities in vivo and vitro. However, ADU-S100, a special STING activator, suppressed the protective effects of esketamine to a certain extent. Finally, C-176, an antagonist of STING, further enhanced the protective effects of esketamine against POCD.

CONCLUSIONS

Findings of our study suggest that esketamine can alleviate surgery-induced POCD in rats via inhibition of the STING/TBK1 signaling pathway.

Progress in the correlation of postoperative cognitive dysfunction and Alzheimer's disease and the potential therapeutic drug exploration

Postoperative cognitive dysfunction (POCD) is a decrease in mental capacity that can occur days to weeks after a medical procedure and may become permanent and rarely lasts for a longer period of time. With the continuous development of research, various viewpoints in academic circles have undergone subtle changes, and the role of anesthesia depth and anesthesia type seems to be gradually weakened; Alzheimer's disease (AD) is a latent and progressive neurodegenerative disease in the elderly. The protein hypothesis and the synaptic hypothesis are well-known reasons. These changes will also lead to the occurrence of an inflammatory cascade. The exact etiology and pathogenesis need to be studied. The reasonable biological mechanism affecting brain protein deposition, neuroinflammation, and acetylcholine-like effect has a certain relationship between AD and POCD. Whereas there is still further uncertainty about the mechanism and treatment, and it is elusive whether POCD is a link in the continuous progress of AD or a separate entity, which has doubts about the diagnosis and treatment of the disease. Therefore, this review is based on the current common clinical characteristics of AD and POCD, and pathophysiological research, to search for their common points and explore the direction and new strategies for future treatment.

Correlation between microRNA-320 and postoperative delirium in patients undergoing tibial fracture internal fixation surgery

Background

Although the incidence of postoperative delirium (POD) in the elderly after surgery are rising as individuals are living longer, the pathogenesis of POD remains poorly understood. It has been suggested that miRNA-320 may play a role in POD based on animal study and human study.

Methods

We first carried out an animal study, and designed and conducted a human study based on the result of animal study. The aged rats were randomly assigned to five groups: the control (C), anesthesia and surgery (AS), saline (NS), agomir-320 (AG), and antagomir-320 (AT) groups. Postoperative spatial learning and memory in rats were analyzed by the Morris water maze and the open field tests. The plasma levels of insulin-like growth factor-1 (IGF-1), amyloid precursor protein (APP) proteins, miRNA320 and IGF-1mRNA were measured by ELISA and qRT-PCR, respectively. A total of 240 Chinese Han patients over 65 years who underwent tibial fracture internal fixation were included in the PNDABLE study. POD cases and non-POD controls (1:1 matched) were selected by an anesthesiologist using Confusion Assessment Method.

Results

For Group AS, the escape latency was significantly longer and the ratio of time spent in the target quadrant was significantly reduced, APP and miR-320 were upregulated and IGF-1mRNA was downregulated compared with Group C. For Group AG, the escape latency was significantly longer and the ratio of time spent in the target quadrant was significantly reduced, APP and miR-320 were upregulated and IGF-1mRNA was downregulated compared with Group AS. For Group AT, the escape latency was significantly reduced and the ratio of time spent in the target quadrant was significantly longer, APP and miR-320 were downregulated and IGF-1mRNAwas upregulated compared with Group AS. Compared with NPOD patients, the expressions of plasma miR-320 and APP protein were increased and the expression of plasma IGF-1 mRNA was decreased in POD patients after surgery.

Conclusions

MiRNA-320 might play a role in up-regulating the levels of IGF-1mRNA and APP protein, which offered a new target for POD treatment.

Trial registration

Correlation of perioperative neurocognitive disorders with lifestyle and biomarkers. ChiCTR2000033439. Registered 1 June 2020.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-022-01612-w.

Dysfunction of EAAT3 Aggravates LPS-Induced Post-Operative Cognitive Dysfunction

Numerous results have revealed an association between inhibited function of excitatory amino acid transporter 3 (EAAT3) and several neurodegenerative diseases. This was also corroborated by our previous studies which showed that the EAAT3 function was intimately linked to learning and memory. With this premise, we examined the role of EAAT3 in post-operative cognitive dysfunction (POCD) and explored the potential benefit of riluzole in countering POCD in the present study. We first established a recombinant adeno-associated-viral (rAAV)-mediated shRNA to knockdown SLC1A1/EAAT3 expression in the hippocampus of adult male mice. The mice then received an intracerebroventricular microinjection of 2 μg lipopolysaccharide (LPS) to construct the POCD model. In addition, for old male mice, 4 mg/kg of riluzole was intraperitoneally injected for three consecutive days, with the last injection administered 2 h before the LPS microinjection. Cognitive function was assessed using the Morris water maze 24 h following the LPS microinjection. Animal behavioral tests, as well as pathological and biochemical assays, were performed to clarify the role of EAAT3 function in POCD and evaluate the effect of activating the EAAT3 function by riluzole. In the present study, we established a mouse model with hippocampal SLC1A1/EAAT3 knockdown and found that hippocampal SLC1A1/EAAT3 knockdown aggravated LPS-induced learning and memory deficits in adult male mice. Meanwhile, LPS significantly inhibited the expression of EAAT3 membrane protein and the phosphorylation level of GluA1 protein in the hippocampus of adult male mice. Moreover, riluzole pretreatment significantly increased the expression of hippocampal EAAT3 membrane protein and also ameliorated LPS-induced cognitive impairment in elderly male mice. Taken together, our results demonstrated that the dysfunction of EAAT3 is an important risk factor for POCD susceptibility and therefore, it may become a promising target for POCD treatment.

Gut-Brain Axis: Possible Role of Gut Microbiota in Perioperative Neurocognitive Disorders

Aging is becoming a severe social phenomenon globally, and the improvements in health care and increased health awareness among the elderly have led to a dramatic increase in the number of surgical procedures. Because of the degenerative changes in the brain structure and function in the elderly, the incidence of perioperative neurocognitive disorders (PND) is much higher in elderly patients than in young people following anesthesia/surgery. PND is attracting more and more attention, though the exact mechanisms remain unknown. A growing body of evidence has shown that the gut microbiota is likely involved. Recent studies have indicated that the gut microbiota may affect postoperative cognitive function via the gut-brain axis. Nonetheless, understanding of the mechanistic associations between the gut microbiota and the brain during PND progression remains very limited. In this review, we begin by providing an overview of the latest progress concerning the gut-brain axis and PND, and then we summarize the influence of perioperative factors on the gut microbiota. Next, we review the literature on the relationship between gut microbiota and PND and discuss how gut microbiota affects cognitive function during the perioperative period. Finally, we explore effective early interventions for PND to provide new ideas for related clinical research.

The Mechanisms of Sevoflurane-Induced Neuroinflammation

Sevoflurane is one of the most commonly used inhaled anesthetics due to its low blood gas coefficient, fast onset, low airway irritation, and aromatic smell. However, recent studies have reported that sevoflurane exposure may have deleterious effects on cognitive function. Although neuroinflammation was most widely mentioned among the established mechanisms of sevoflurane-induced cognitive dysfunction, its upstream mechanisms have yet to be illustrated. Thus, we reviewed the relevant literature and discussed the most mentioned mechanisms, including the modulation of the microglial function, blood–brain barrier (BBB) breakdown, changes in gut microbiota, and ease of cholinergic neurotransmission to help us understand the properties of sevoflurane, providing us new perspectives for the prevention of sevoflurane-induced cognitive impairment.

Dysfunction of the Glymphatic System as a Potential Mechanism of Perioperative Neurocognitive Disorders

Perioperative neurocognitive disorder (PND) frequently occurs in the elderly as a severe postoperative complication and is characterized by a decline in cognitive function that impairs memory, attention, and other cognitive domains. Currently, the exact pathogenic mechanism of PND is multifaceted and remains unclear. The glymphatic system is a newly discovered glial-dependent perivascular network that subserves a pseudo-lymphatic function in the brain. Recent studies have highlighted the significant role of the glymphatic system in the removal of harmful metabolites in the brain. Dysfunction of the glymphatic system can reduce metabolic waste removal, leading to neuroinflammation and neurological disorders. We speculate that there is a causal relationship between the glymphatic system and symptomatic progression in PND. This paper reviews the current literature on the glymphatic system and some perioperative factors to discuss the role of the glymphatic system in PND.

Ginkgolide B‑mediated therapeutic effects on perioperative neurocognitive dysfunction are associated with the inhibition of iNOS‑mediated production of NO

Perioperative neurocognitive dysfunction (PND) is a prevalent neurological complication after anesthesia and surgery. Ginkgolide B (GB) has been suggested to improve lipopolysaccharide-induced learning and memory impairment. The present study aimed to investigate whether GB serves a protective role against PND by inhibiting inducible nitric oxide synthase (iNOS) and nitric oxide (NO). Abdominal surgery was performed on 10- to 12-week-old male C57BL/6 mice under isoflurane anesthesia. Prior to surgery, 1400W (a specific iNOS inhibitor) and GB were administered via intraperitoneal injection. Open field and fear conditioning tests were conducted to assess cognitive function on postoperative days 1 and 3. Biochemical assays were performed to evaluate alterations in NO, malondialdehyde (MDA) and superoxide dismutase (SOD) levels. Western blotting was performed to measure iNOS expression in the hippocampus on postoperative day 1. In addition, hematoxylin and eosin staining was performed to detect the neuronal morphology in the hippocampus. Following treatment with 1400W or GB, surgery-induced cognitive dysfunction was improved. Compared with the control group, the surgery group exhibited significant overproduction of iNOS and MDA in the hippocampus on postoperative day 1. Higher levels of NO were also detected in the hippocampus and prefrontal cortex of the surgery group on postoperative day 1. Furthermore, pretreatment with 1400W or GB significantly inhibited the surgery-induced elevation of NO and MDA in brain tissues. Moreover, GB pretreatment significantly inhibited surgery-induced downregulation of SOD and upregulation of iNOS. Surgery-induced increases in neuronal loss and the Bax/Bcl-2 ratio in the hippocampus were significantly inhibited by pretreatment with GB. Collectively, the results of the present study demonstrated that the therapeutic effects of GB on PND were associated with inhibition of iNOS-induced NO production, increased SOD, and the alleviation of neuronal loss and apoptosis.

Atorvastatin attenuates surgery-induced BBB disruption and cognitive impairment partly by suppressing NF-κB pathway and NLRP3 inflammasome activation in aged mice

In clinic, perioperative neurocognitive disorder is becoming a common complication of surgery in old patients. Neuroinflammation and blood-brain barrier (BBB) disruption are important contributors for cognitive impairment. Atorvastatin, as a strong HMG-CoA reductase inhibitor, has been widely used in clinic. However, it remains unclear whether atorvastatin could prevent anesthesia and surgery-induced BBB disruption and cognitive injury by its anti-inflammatory property. In this study, aged C57BL/6J mice were used to address this question. Initially, the mice were subject to atorvastatin treatment for 7 days (10 mg/kg). After a simple laparotomy under 1.5% isoflurane anesthesia, Morris water maze was performed to assess spatial learning and memory. Western blot analysis, immunohistochemistry, and enzyme-linked immunosorbent assay were used to examine the inflammatory response, BBB integrity, and cell apoptosis. Terminal-deoxynucleotidyl transferase mediated nick end labeling assay was used to assess cell apoptosis. The fluorescein sodium and transmission electron microscopy were used to detect the permeability and structure of BBB. The results showed that anesthesia and surgery significantly injured hippocampal-dependent learning and memory, which was ameliorated by atorvastatin. Atorvastatin could also reverse the surgery-induced increase of systemic and hippocampal cytokines, including IL-1β, TNF-α, and IL-6, accompanied by inhibiting the nuclear factor kappa-B (NF-κB) pathway and Nucleotide-Binding Oligomerization Domain, or Leucine Rich Repeat and Pyrin Domain Containing 3 (NLRP3) inflammasome activation, as well as hippocampal neuronal apoptosis. In addition, surgery triggered an increase of BBB permeability, paralleled by a decrease of the ZO-1, occludin, and Claudin 5 proteins in the hippocampus. However, atorvastatin treatment could protect the BBB integrity from the impact of surgery, by up-regulating the expressions of ZO-1, occludin, and Claudin 5. These findings suggest that atorvastatin exhibits neuroprotective effects on cognition in aged mice undergoing surgery.

Inhibitory effect of desflurane on degranulation of mast cells induced by lateral ventricular injection of stimulator-C48/80 in C57BL/6 male mice

Inhalation of anesthetic agents have been observed to confer neuroprotection for decades. The present study was intended to determine whether desflurane (DES) prohibits mast cells (MCs) from degranulation induced by lateral ventricular injection (LVC) with Compound 48/80 (C48/80) in C57BL/6. Total 100 mice were recruited to this study, but only 88 male mice (20–24 weeks) were survived from the procedure, and randomized and allocated into four groups: (A) the saline group; (B) the C48/80 group; (C) the sodium cromoglycate (CRO + C48/80) group; (D) 7.5% DES preconditioning for 2 h + C48/80 lateral ventricular injection (DES + C48/80) group. The slices of mice brain thalamus were performed for toluidine blue staining (MCs) and immunochemistry (fluorescence of Iba1 and GFAP, respectively), and brain tissues were extracted to probe IL-6, TNF-α, NF-κB (p65), and TLR4 against GAPDH by western blotting. Our results demonstrated that administration of C48/80 provoked degranulation of mast cells at thalamus, increasing the fluorescence intensities of Iba1 and GFAP, and over-expressing IL-6, TNF-α, NF-κB(p65), and TLR4. However, pre-conditioning inhalation of DES prohibited MCs from degranulation, diminishing the fluorescent intensities of Iba1 and GFAP, decreasing expressed levels of IL-6, TNF-α, NF-κB(p65), as well as TLR4. It suggests inhalation DES could inhibit the neuroinflammation and deactivate glial and astrocytes via direct prohibiting degranulation of MCs at thalamus in the central nervous system (CNS).

Gene-Specific DNA Methylation Linked to Postoperative Cognitive Dysfunction in Apolipoprotein E3 and E4 Mice

BACKGROUND

Geriatric surgical patients are at higher risk of developing postoperative neurocognitive disorders (NCD) than younger patients. The specific mechanisms underlying postoperative NCD remain unknown, but they have been linked to genetic risk factors, such as the presence of APOE4, compared to APOE3, and epigenetic modifications caused by exposure to anesthesia and surgery.

OBJECTIVE

To test the hypothesis that compared to E3 mice, E4 mice exhibit a more pronounced postoperative cognitive impairment associated with differential DNA methylation in brain regions linked to learning and memory.

METHODS

16-month-old humanized apolipoprotein-E targeted replacement mice bearing E3 or E4 were subjected to surgery (laparotomy) under general isoflurane anesthesia or sham. Postoperative behavioral testing and genome-wide DNA methylation were performed.

RESULTS

Exposure to surgery and anesthesia impaired cognition in aged E3, but not E4 mice, likely due to the already lower cognitive performance of E4 prior to surgery. Cognitive impairment in E3 mice was associated with hypermethylation of specific genes, including genes in the Ephrin pathway implicated in synaptic plasticity and learning in adults and has been linked to Alzheimer's disease. Other genes, such as the Scratch Family Transcriptional Repressor 2, were altered after surgery and anesthesia in both the E3 and E4 mice.

CONCLUSION

Our findings suggest that the neurocognitive and behavioral effects of surgery and anesthesia depend on baseline neurocognitive status and are associated with APOE isoform-dependent epigenetic modifications of specific genes and pathways involved in memory and learning.

Evaluation of the Effect of Dexmedetomidine on Postoperative Cognitive Dysfunction through Aβ and Cytokines Analysis

Postoperative cognitive dysfunction is a common postoperative neurological complication in elderly patients, and has some relationship with neuroinflammation. some studies have shown ability of dexmedetomidine to improve cognitive performance in elderly individuals who underwent thoracic surgery. Therefore, our study hypothesized that dexmedetomidine treatment may reduce the incidence of POCD in elderly patients.In addition,this study detected the antineuroinflammatory effects of dexmedetomidine by β-amyloid aggregation inhibitors and release of cytokines in elderly patients . The results show that dexmedetomidine used during operation can inhibit the postoperative release of Aβ and cytokines in elderly patients, and dexmedetomidine used during operation can reduce the incidence of postoperative cognitive dysfunction, with dose-dependence. These results provide a clinical application direction for clinical anesthesiologists and ICU physicians.

lncRNAs Are Involved in Sevoflurane Anesthesia-Related Brain Function Modulation through Affecting Mitochondrial Function and Aging Process

Long noncoding RNAs (lncRNAs) play important roles in brain function modulation and neurodegenerative diseases. However, whether lncRNA regulations are involved in the mechanisms of perioperative neurocognitive disorders, especially in anesthesia-related brain dysfunction, remain unknown. Therefore, we explored the expression and regulation pattern profiles of lncRNAs in the hippocampus of aged rats after sevoflurane anesthesia. Three lncRNAs and 772 protein-coding genes were identified by microarray analysis and evidenced by in vitro and in vivo experiments as differentially expressed. Functional annotation and differentially expressed- (DE-) lncRNA-mRNA coexpression networks reveal that DE-lncRNAs are associated with mitochondrial dysfunction and oxidative stress, aging-related metabolism alterations, DNA damage, and apoptosis, as well as neurodegenerative features during sevoflurane anesthesia. These results suggest that lncRNAs play roles in general anesthesia-related brain function modulation during the perioperative context and provide insights into the lncRNA-related modulation mechanisms and targets.

Graphene oxide improves postoperative cognitive dysfunction by maximally alleviating amyloid beta burden in mice

Rationale: Graphene oxide (GO) based nanomaterials have shown potential for the diagnosis and treatment of amyloid-β (Aβ)-related diseases, mainly on Alzheimer's disease (AD). However, these nanomaterials have limitations. How GO is beneficial to eliminate Aβ burden, and its physiological function in Aβ-related diseases, still needs to be investigated. Moreover, postoperative cognitive dysfunction (POCD) is an Aβ-related common central nervous system complication, however, nanomedicine treatment is lacking.

Methods: To evaluate the effects of GO on Aβ levels, HEK293T-APP-GFP and SHSY5Y-APP-GFP cells are established. Intramedullary fixation surgery for tibial fractures under inhalation anesthesia is used to induce dysfunction of fear memory in mice. The fear memory of mice is assessed by fear conditioning test.

Results: GO treatment maximally alleviated Aβ levels by simultaneously reducing Aβ generation and enhancing its degradation through inhibiting β-cleavage of amyloid precursor protein (APP) and improving endosomal Aβ delivery to lysosomes, respectively. In postoperative mice, the hippocampal Aβ levels were significantly increased and hippocampal-dependent fear memory was impaired. However, GO administration significantly reduced hippocampal Aβ levels and improved the cognitive function of the postoperative mice.

Conclusion: GO improves fear memory of postoperative mice by maximally alleviating Aβ accumulation, providing new evidence for the application of GO-based nanomedicines in Aβ-related diseases.

A Novel Individual-based Determination of Postoperative Cognitive Dysfunction in Mice

Postoperative cognitive dysfunction (POCD) is a significant clinical issue. Aging is a risk factor for POCD. It is known that not every patient develops POCD. This situation shall be similar in animals. Determination of POCD is individual-based in humans but group-based in animal studies. This difference prevents effective evaluation of biomarkers and interventions for POCD in preclinical studies. The objective of this study was to determine whether individual animal could be assessed for POCD by a system similar to that for patients. Seven-week old CD1 and 18-month old C57BL/6 male mice were subjected to right carotid arterial exposure under isoflurane anesthesia. Mice were evaluated by Barnes maze and fear conditioning either post-surgery alone or both prior to surgery and post-surgery. Surgery increased the time to identify the target box in Barnes maze when tested one day or 8 days after the training sessions and reduced freezing behavior in fear conditioning test. This phenomenon occurred in 7-week old animals with and without evaluation before the surgery and in 18-month old mice evaluated before and after surgery. Based on the method and criteria used for a human whose cognition was evaluated before and after surgery to assess individual decline of cognition, 7 in 21 mice in the surgical group and 1 in 21 mice in control group of 7-week old mice had cognitive dysfunction. Among 18-month old mice, 13 in 21 mice in the surgical group and 2 in 20 mice in the control group had cognitive dysfunction. The incidence of cognitive dysfunction in mice with surgery was higher than that in control mice no matter whether young adult (P = 0.045) or old mice (P < 0.001) were considered. These results indicate that surgery induces POCD in mice. Individual animal-based assessment can be used to identify animals with POCD.

Anesthesia plus surgery in neonatal period impairs preference for social novelty in mice at the juvenile age

Anesthetic sevoflurane could induce neurotoxicity in developing brain and cause adverse neurobehavioral outcomes in mice, including inattention, social interaction deficit, and learning and memory impairment. However, there is less data on the effect of anesthesia plus surgery on social interaction behavior. Therefore, we investigated whether the combination of anesthesia and surgical stimulation could induce behavioral and biochemical changes in mice. Firstly, the six-day-old mice were received either 3% sevoflurane anesthesia or abdominal surgery under sevoflurane anesthesia. Then, these mice were scheduled to social interaction test in three-chambered social paradigm at one-month-old. In addition, the brain tissues of neonatal mice were harvested at 24 h after treatment, for measuring the levels of OXTR and NMDAR1 in Western blot analysis. We found that neonatal anesthesia with sevoflurane in a clinically-relevant dosage could not induce social interaction deficit. Nevertheless, anesthesia plus surgery was able to impair preference for social novelty in mice. Moreover, anesthesia plus surgery decreased the levels of OXTR in hippocampus and cortex of mice, as well as NMDAR1 in hippocampus. Collectively, these results suggested that anesthesia plus surgery could impair social novelty preference, but not sociability in mice, and that social memory might be more vulnerable than social affiliation in biological property. Furthermore, reduction in the levels of cortex OXTR and hippocampus NMDAR1 could be associated with social recognition memory in mice.

Genome-Wide Screen of the Hippocampus in Aged Rats Identifies Mitochondria, Metabolism and Aging Processes Implicated in Sevoflurane Anesthesia

Previous studies have shown multiple mechanisms and pathophysiological changes after anesthesia, and genome-wide studies have been implemented in the studies of brain aging and neurodegenerative diseases. However, the genome-wide gene expression patterns and modulation networks after general anesthesia remains to be elucidated. Therefore, whole transcriptome microarray analysis was used to explore the coding gene expression patterns in the hippocampus of aged rats after sevoflurane anesthesia. Six hundred and thirty one upregulated and 183 downregulated genes were screened out, then 44 enriched terms of biological process, 16 of molecular function and 18 of the cellular components were identified by Gene Ontology (GO) and KEGG analysis. Among them, oxidative stress, metabolism, aging, and neurodegeneration were the most enriched biological processes and changed functions. Thus, involved genes of these processes were selected for qPCR verification and a good consistency was confirmed. The potential signaling pathways were further constructed including mitochondrion and oxidative stress-related Hifs-Prkcd-Akt-Nfe2l2-Sod1 signaling, multiple metabolism signaling (Scd2, Scap-Hmgcs2, Aldh18a1-Glul and Igf1r), as well as aging and neurodegeneration related signaling (Spidr-Ercc4-Cdkn1a-Pmaip1 and Map1lc3b). These results provide potential therapeutic gene targets for brain function modulation and memory formation process after inhaled anesthesia in the elderly, which could be valuable for preventing postoperative brain disorders and diseases, such as perioperative neurocognitive disorders (PND), from the genetic level in the future.

Muscle Injury Induces Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is a major complication affecting patients of any age undergoing surgery. This syndrome impacts everyday life up to months after hospital discharge, and its pathophysiology still remains unclear. Translational research focusing on POCD is based on a wide variety of rodent models, such as the murine tibial fracture, whose severity can limit mouse locomotion and proper behavioral assessment. Besides, influence of skeletal muscle injury, a lesion encountered in a wide range of surgeries, has not been explored in POCD occurrence. We propose a physical model of muscle injury in CX3CR1^GFP/+ mice (displaying green fluorescent microglial cells) to study POCD, with morphological, behavioral and molecular approaches. We highlighted: alteration of short- and long-term memory after muscle regeneration, wide microglial reactivity in the brain, including hippocampus area, 24 hours after muscle injury, and an alteration of central brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF) balance, 28 days after muscle injury. Our results suggest for the first time that muscle injury can have early as well as late impacts on the brain. Our CX3CR1^GFP/+ model can also facilitate microglial investigation, more specifically their pivotal role in neuroinflammation and synaptic plasticity, in the pathophysiology of POCD.

Inflammasome and Cognitive Symptoms in Human Diseases: Biological Evidence from Experimental Research

Cognitive symptoms are prevalent in the elderly and are associated with an elevated risk of developing dementia. Disease-driven changes can cause cognitive disabilities in memory, attention, and language. The inflammasome is an innate immune intracellular complex that has a critical role in the host defense system, in that it senses infectious pathogen-associated and endogenous danger-associated molecular patterns. An unbalanced or dysregulated inflammasome is associated with infectious, inflammatory, and neurodegenerative diseases. Due to its importance in such pathological conditions, the inflammasome is an emerging drug target for human diseases. A growing number of studies have revealed links between cognitive symptoms and the inflammasome. Several studies have shown that reducing the inflammasome component mitigates cognitive symptoms in diseased states. Therefore, understanding the inflammasome regulatory mechanisms may be required for the prevention and treatment of cognitive symptoms. The purpose of this review is to discuss the current understanding of the inflammasome and its relationships with cognitive symptoms in various human diseases.

Anesthesia and surgery induce age-dependent changes in behaviors and microbiota

The neuropathogenesis of postoperative delirium remains mostly unknown. The gut microbiota is implicated in the pathogenesis of neurological disorders. We, therefore, set out to determine whether anesthesia/surgery causes age-dependent gut microbiota dysbiosis, changes in brain IL-6 level and mitochondrial function, leading to postoperative delirium-like behavior in mice. Female 9 or 18 months old mice received abdominal surgery under 1.4% isoflurane for two hours. The postoperative delirium-like behavior, gut microbiota, levels of brain IL-6, PSD-95 and synaptophysin, and mitochondrial function were determined by a battery of behavioral tests, 16s rRNA sequencing, ELISA, Western blot and Seahorse XFp Extracellular Flux Analyzer. Intragastric administration of Lactobacillus (10 days) and probiotic (20 days) were used to mitigate the anesthesia/surgery-induced changes. Anesthesia/surgery caused different alterations in gut microbiota, including change rate of reduction in the levels of gut lactobacillus, between the 18 and 9 months old mice. The anesthesia/surgery induced greater postoperative delirium-like behavior, increased brain IL-6 levels, decreased PSD-95 and synaptophysin levels, and mitochondrial dysfunction in 18 than 9 months old mice. Treatments with Lactobacillus and probiotic mitigated the anesthesia/surgery-induced changes. These data suggest that microbiota dysbiosis may contribute to neuropathogenesis of postoperative delirium and treatment with Lactobacillus or a probiotic could mitigate postoperative delirium.

Exogenous hydrogen sulfide alleviates surgery-induced neuroinflammatory cognitive impairment in adult mice by inhibiting NO signaling

Background

To investigate the effect and mechanisms of exogenous hydrogen sulfide in surgery-induced neuroinflammatory cognitive dysfunction.

Methods

C57BL/6 J male mice (n = 140) were used and randomly divided into seven groups: the sham group, surgery group, GYY4137 group, L-NAME group, surgery+GYY4137 group, surgery +L-NAME group, and surgery+GYY4137 + L-NAME group. After the interventions, open field tests (OFT) and the Morris water maze (MWM) test were conducted to evaluate learning and memory abilities in the mice. ELISAs, nitrate reductase assays, and Western blots (WB) were conducted to evaluate interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), nitric oxide (NO), inducible nitric oxide synthase (iNOS), malondialdehyde (MDA), and antioxidant enzyme superoxide dismutase (SOD) levels. Furthermore, the expression level of microglial marker ionized calcium binding adaptor molecule 1 (IBA) in the hippocampal CA1 and CA3 areas was detected by an immunohistochemical (IHC) assay and apoptotic cells were observed using terminal deoxynucleotidyl transferase dUTP end-labeling (TUNEL) staining kits.

Results

We found that surgery induced neuroinflammatory cognitive dysfunction, oxidative stress, microglial activation, and cell apoptosis in the hippocampus. Moreover, following surgery, NO and iNOS levels were elevated in the hippocampus. Notably, all the effects caused by surgery were reversed by the H₂S donor GYY4137 or the iNOS inhibitor N(gamma)-nitro-L-arginine methyl ester (L-NAME). However, the combined application of GYY4137 and L-NAME was not superior to treatment with either agent alone and the effect of GYY4137 was similar to that of L-NAME.

Conclusion

The long-acting hydrogen sulfide donor GYY4137 had an ability to reversed the cognitive deficits and inflammation caused by carotid artery exposure surgery. This implies that NO signaling pathways might participate in this process. These results indicate that exogenous H₂S may be a promising therapy for POCD.

Neuroinflammation and Perioperative Neurocognitive Disorders

Neuroinflammation has become a key hallmark of neurological complications including perioperative pathologies such as postoperative delirium and longer-lasting postoperative cognitive dysfunction. Dysregulated inflammation and neuronal injury are emerging from clinical studies as key features of perioperative neurocognitive disorders. These findings are paralleled by a growing body of preclinical investigations aimed at better understanding how surgery and anesthesia affect the central nervous system and possibly contribute to cognitive decline. Herein, we review the role of postoperative neuroinflammation and underlying mechanisms in immune-to-brain signaling after peripheral surgery.

Anesthesiology and cognitive impairment: a narrative review of current clinical literature

Background

The impact of general anesthesia on cognitive impairment is controversial and complex. A large body of evidence supports the association between exposure to surgery under general anesthesia and development of delayed neurocognitive recovery in a subset of patients. Existing literature continues to debate whether these short-term effects on cognition can be attributed to anesthetic agents themselves, or whether other variables are causative of the observed changes in cognition. Furthermore, there is conflicting data on the relationship between anesthesia exposure and the development of long-term neurocognitive disorders, or development of incident dementia in the patient population with normal preoperative cognitive function. Patients with pre-existing cognitive impairment present a unique set of anesthetic considerations, including potential medication interactions, challenges with cooperation during assessment and non-general anesthesia techniques, and the possibility that pre-existing cognitive impairment may impart a susceptibility to further cognitive dysfunction.

Main body

This review highlights landmark and recent studies in the field, and explores potential mechanisms involved in perioperative cognitive disorders (also known as postoperative cognitive dysfunction, POCD). Specifically, we will review clinical and preclinical evidence which implicates alterations to tau protein, inflammation, calcium dysregulation, and mitochondrial dysfunction. As our population ages and the prevalence of Alzheimer’s disease and other forms of dementia continues to increase, we require a greater understanding of potential modifiable factors that impact perioperative cognitive impairment.

Conclusions

Future research should aim to further characterize the associated risk factors and determine whether certain anesthetic approaches or other interventions may lower the potential risk which may be conferred by anesthesia and/or surgery in susceptible individuals.

Autophagy Dysfunction and mTOR Hyperactivation Is Involved in Surgery: Induced Behavioral Deficits in Aged C57BL/6J Mice

Autophagy is crucial for cell survival, development, division, and homeostasis. The mammalian target of rapamycin (mTOR), which is the foremost negative controller of autophagy, plays a key role in many endogenous processes. The present study investigated whether rapamycin can ameliorate surgery-induced cognitive deficits by inhibiting mTOR and activating autophagy in the hippocampus. Both adult and aged C57BL/6J mice received an intraperitoneal injection of rapamycin (10 mg/kg/day) for 5 days per week for one and a half months. Mice were then subjected to partial hepatectomy under general anesthesia. Behavioral performance was assessed on postoperative days 3, 7, and 14. Hippocampal autophagy-related (Atg)-5, phosphorylated mTOR, and phosphorylated p70S6K were examined at each time point. Brain derived neurotrophic factor (BDNF), synaptophysin, and tau hyperphosphorylation (T396) in the hippocampus were also examined. Surgical trauma and anesthesia exacerbated spatial learning and memory impairment in aged mice on postoperative days 3 and 7. Following partial hepatectomy, the levels of phosphorylated mTOR, phosphorylated 70S6K, and phosphorylated tau were all increased in the hippocampus. A corresponding decline in BDNF and synaptophysin were observed. Rapamycin treatment restored autophagy function, attenuated phosphorylation of tau protein, and increased BDNF and synaptophysin expression in the hippocampus of surgical mice. Furthermore, surgery and anesthesia induced spatial learning and memory impairments were also reversed by rapamycin treatment. Autophagy impairments and mTOR hyperactivation were detected along with surgery-induced behavioral deficits. Inhibiting the mTOR signaling pathway with rapamycin successfully ameliorated surgery-related cognitive impairments by sustaining autophagic degradation, inhibiting tau hyperphosphorylation, and increasing synaptophysin and BDNF expression.

Plasma amyloid beta level changes in aged mice with cognitive dysfunction following sevoflurane exposure

INTRODUCTION

Previous studies have stated that cognitive impairment induced by anesthetics was associated with amyloid beta (Aβ). However, few researchers have investigated the transport of Aβ inside and outside of the brain.

AIM

We attempted to probe the effects of sevoflurane on cognitive functions, the plasma Aβ, and transporters of Aβ in aged mice. The receptor for advanced glycation end-products (RAGE) is an Aβ influx protein, and Low-density lipoprotein receptor-related protein-1 (LRP-1) is an Aβ efflux protein.

METHODS

Aged mice were divided into the control group and the sevoflurane group. The mice were exposed to 100% oxygen or 2.5% sevoflurane for 2 h. The abilities of spatial learning and memory in mice were tested using the Morris water maze. Aβ concentrations of plasma were measured with enzyme-linked immunosorbent assay kits. The RAGE and LRP-1 gene levels in the brain were assessed with quantitative polymerase chain reaction, and the protein levels were determined by western blot analysis. The locations of RAGE in the brain were confirmed via immunofluorescence.

RESULTS

In the sevoflurane group mice, the escape latency was increased on the 5th day of training, and the time spent in the target quadrant was decreased on the 7th day after anesthesia. Sevoflurane reduced the concentration of plasma Aβ1-40. In addition, sevoflurane increased both gene and protein levels of RAGE in the brain, and increased RAGE proteins co-localized with the hippocampal vascular endothelial cells.

CONCLUSION

RAGE over-expression in the hippocampal vascular endothelial cells possibly resulted in the excessive transport of the plasma Aβ1-40 into the brain after treatment with sevoflurane, which was associated with sevoflurane-induced cognitive dysfunction in aged mice.

MiR-190a potentially ameliorates postoperative cognitive dysfunction by regulating Tiam1

BACKGROUND

Postoperative cognitive dysfunction (POCD) affects a large number of post-surgery patients, especially for the elderly. However, the etiology of this neurocognitive disorder is largely unknown. Even if several studies have reported a small number of miRNAs as the essential modulatory factors in POCD, these findings are still rather limited. The aim of current study was to screen the POCD-related miRNAs in the hippocampus tissues and investigate the target genes of differentially expressed miRNAs and their biological functions underlying POCD pathophysiology.

METHODS

The miRNA microarray was used to find the abnormal expression of miRNAs in the hippocampus tissues from the POCD model mice to normal mice (Discovery cohort, 3 vs 3). The nominal significant results were validated in an independent sample of hippocampus tissues of 10 mice based on same miRNA microarray (Replication cohort, 5 vs 5). Expression level of the most significantly abnormal miRNA was further validated by real-time quantitative polymerase chain reaction (PCR). To determine the expression pattern among miRNAs and genes and detect the interactions, we conducted a weighted gene co-expression network analysis (WGCNA) in the miRNAs and genes expression data from hippocampus tissue of wild type mice (n = 24). The target genes of miRNAs were predicted using the miRWalk3.0 software. Furthermore, we used the ClueGO software to decipher the pathways network and reveal the biological functions of target genes of miRNAs.

RESULTS

We found that nine miRNAs showed significant associations with POCD in both datasets. Among these miRNAs, mmu-miR-190a-3p was the most significant one. By performing WGCNA analysis, we found 25 co-expression modules, of which mmu-miR-190a-3p was significantly anti-correlated with red module. Moreover, in the red module, 314 genes were significantly enriched in four pathways such as axon guidance and calcium signaling pathway, which are well-documented to be associated with psychiatric disorders and brain development. Also, 169 of the 314 genes were highly correlated with mmu-miR-190a-3p, and four genes (Sphkap, Arhgef25, Tiam1, and Ntrk3) had putative binding sites at 3'-UTR of mmu-miR-190a-3p. Based on protein-protein network analysis, we detected that Tiam1 was a central gene regulated by the mmu-miR-190a-3p.

CONCLUSIONS

Taken together, we conclude that mmu-miR-190a-3p is involved in the etiology of POCD and may serve as a novel predictive indicator for POCD.

Identification of the Potential Key Long Non-coding RNAs in Aged Mice With Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is a significant complication of surgery, particularly in elderly patients. Emerging researches showed that long non-coding RNA (lncRNA) may play a vital role in the pathogenesis of POCD. Here we aimed to identify potential key lncRNAs involved in the development of POCD. LncRNA and mRNA expression profiles in hippocampal tissues from POCD and control mice were analyzed by microarray assay. Gene ontology (GO) and KEGG pathway enrichment analyses were conducted to probe the functions of dysregulated genes. Then, important factors of the mainly affected biological processes were measured in the hippocampus. Correlated coding–non-coding co-expression (CNC) networks were constructed. Finally, the potential key pairs of lncRNA and target mRNA implicated in POCD were probed. Our data showed that 868 differentially expressed lncRNAs and 690 differentially expressed mRNAs were identified in total. GO and KEGG analyses indicated that the differentially expressed genes were mainly associated with inflammatory and apoptotic signaling pathways. Surgery-induced inflammatory cytokines and apoptosis were significantly increased in hippocampal tissues of aged mice. In CNC network analysis, we found that LncRNA uc009qbj.1 was positively correlated with apoptosis-associated gene Vrk2 level. LncRNA ENSMUST00000174338 correlated positively with expression of the inflammation and apoptosis-associated gene Smad7. LncRNA NONMMUT00000123687 mediated gene expression by binding the inflammation-regulated transcription factor Meis2. Our results suggested that these potential key lncRNAs and mRNAs may play a crucial role in the development of POCD through mediating neuronal inflammation or apoptosis.

Central cholinergic neuronal degeneration promotes the development of postoperative cognitive dysfunction

Postoperative cognitive dysfunction (POCD) is consistently associated with increased morbidity and mortality. However, its mechanism remains poorly understood. We hypothesized that central cholinergic neuronal degeneration facilitates the development of POCD. The impact of anesthesia/surgery (appendectomy) on learning and memory and the levels of choline acetyltransferase (ChAT), acetylcholinesterase (AChE), vesicular acetylcholine transporter (VAChT), and choline transporter (CHT) in adult and aged mice were measured. Separate cohorts were analyzed after pretreatment with donepezil, an AChE inhibitor, in aged mice or with murine-p75-saporin (mu-p75-sap), a cholinergic-specific immunotoxin, in adult mice. Morris Water Maze was used to measure the learning and memory changes after anesthesia/surgery. Western blot was used to measure the changes in the protein levels of the biomarkers of the central cholinergic system. We found that anesthesia/surgery-induced memory decline and attenuation of central cholinergic biomarkers (ChAT and VAChT) in aged mice but not in adult mice. Donepezil pretreatment reduced central cholinergic impairment in the aged mice and prevented learning and memory declines after anesthesia/surgery. In contrast, when central cholinergic neurons were pre-injured with mu-p75-sap, cognitive dysfunction developed in the adult mice after anesthesia/surgery. These data suggest that central cholinergic neuronal degeneration facilitates the development of POCD.

Sex and genetic differences in postoperative cognitive dysfunction: a longitudinal cohort analysis

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a common postoperative complication experienced by patients aged 65 years and older, and these older adults comprise more than one third of the surgical patients in the USA. Because not everyone with a history of exposure to surgery and anesthesia develops POCD, there are likely major biological risk factors involved. There are important gaps in our knowledge regarding whether genetic makeup, biological sex, or other Alzheimer's disease risk factors predispose older adults to developing POCD. We set out to determine whether biological sex and Apolipoprotein E-ε4 (APOE4) carrier status increase the risk of developing POCD in older adults.

METHODS

We performed a cohort analysis of 1033 participants of prospective longitudinal aging studies. Participants underwent regular cognitive test batteries and we compared the annual rate of change over time in various cognitive measures in the women exposed to surgery and general anesthesia compared to the men exposed to surgery and general anesthesia. Mixed-effects statistical models were used to assess the relationship between biological sex, APOE4 carrier status, surgery and anesthesia exposure, and the rate of change in cognitive test scores.

RESULTS

When comparing all men (n = 89) and women (n = 164) who had surgery, there were no significant sex differences in postoperative cognitive outcomes. However, men with an APOE4 allele performed significantly worse on cognitive testing following surgery and anesthesia than women APOE4 carriers, even after adjusting for age, education level, and comorbidities.

CONCLUSIONS

Older men with APOE4 allele may be more vulnerable to postoperative cognitive dysfunction than older women with APOE4 allele.

Sevoflurane enhanced the clearance of Aβ1-40 in hippocampus under surgery via up-regulating AQP-4 expression in astrocyte

The neurotoxicity of anesthetics on developing brain has been a focused issue for years. However, controversy exists between human and animal studies and surgery may be a potential reason for this. The discovery of glymphatic system, a pathway eliminating soluble substance from central nervous system (CNS), together with recent evidence that surgery-induced Aβ increase contributes to cognition dysfunction made us rethink about the influence of anesthetics on cognitive function. The function of glymphatic system was proved to be enhanced by sleep and sedation, so we assumed that under clinical situation Aβ1-40 whose accumulation played important role in cognitive dysfunction was increased by surgery and eliminated from CNS by glymphatic system. The function of glymphatic system is facilitated by aquaporin-4 (AQP-4), a water channel expressed in highly polarized manor in astrocytic endfeet, whose transcription is regulated by nuclear factor of activated T cells 5 (NFAT5). Our results suggest that under brief operation and sevoflurane exposure, surgery may be the main cause of Aβ increase and sevoflurane increase the elimination of Aβ by up-regulating AQP-4 which is the key component in glymphatic system.

Postoperative cognitive dysfunction in the aged: the collision of neuroinflammaging with perioperative neuroinflammation

The aging population is burgeoning globally and this trend presents great challenges to the current healthcare system as the growing number of aged individuals receives procedures of surgery and anesthesia. Postoperative cognitive dysfunction (POCD) is a severe postoperative neurological sequela. Advanced age is considered as an independent risk factor of POCD. Mounting evidence have shown that neuroinflammation plays an essential role in POCD. However, it remains debatable why this complication occurs highly in the aged individuals. As known, aging itself is the major common high-risk factor for age-associated disorders including diabetes, cardiovascular disease, cancer, and neurodegenerative diseases. Chronic low-grade neuroinflammation (dubbed neuroinflammaging in the present paper) is a hallmark alternation and contributes to age-related cognitive decline in the normal aging. Interestingly, several lines of findings show that the neuroinflammatory pathogenesis of POCD is age-dependent. It suggests that age-related changes, especially the neuroinflammaging, are possibly associated with the postoperative cognitive impairment. Understanding the role of neuroinflammaging in POCD is crucial to elucidate the mechanism of POCD and develop strategies to prevent or treat POCD. Here the focus of this review is on the potential role of neuroinflammaging in the mechanism of POCD. Lastly, we briefly review promising interventions for this neurological sequela.

Identification of the Potential Key Long Non-coding RNAs in Aged Mice With Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is a significant complication of surgery, particularly in elderly patients. Emerging researches showed that long non-coding RNA (lncRNA) may play a vital role in the pathogenesis of POCD. Here we aimed to identify potential key lncRNAs involved in the development of POCD. LncRNA and mRNA expression profiles in hippocampal tissues from POCD and control mice were analyzed by microarray assay. Gene ontology (GO) and KEGG pathway enrichment analyses were conducted to probe the functions of dysregulated genes. Then, important factors of the mainly affected biological processes were measured in the hippocampus. Correlated coding-non-coding co-expression (CNC) networks were constructed. Finally, the potential key pairs of lncRNA and target mRNA implicated in POCD were probed. Our data showed that 868 differentially expressed lncRNAs and 690 differentially expressed mRNAs were identified in total. GO and KEGG analyses indicated that the differentially expressed genes were mainly associated with inflammatory and apoptotic signaling pathways. Surgery-induced inflammatory cytokines and apoptosis were significantly increased in hippocampal tissues of aged mice. In CNC network analysis, we found that LncRNA uc009qbj.1 was positively correlated with apoptosis-associated gene Vrk2 level. LncRNA ENSMUST00000174338 correlated positively with expression of the inflammation and apoptosis-associated gene Smad7. LncRNA NONMMUT00000123687 mediated gene expression by binding the inflammation-regulated transcription factor Meis2. Our results suggested that these potential key lncRNAs and mRNAs may play a crucial role in the development of POCD through mediating neuronal inflammation or apoptosis.

Isoflurane anesthesia impairs the expression of immune neuromodulators in the hippocampus of aged mice

Cognitive dysfunction is one of the most common postoperative complications experienced by older patients after anesthesia and surgery but the cause remains unknown. Immune molecules are essential for many aspects of neural homeostasis, including learning and memory, and an imbalance in immune neuromodulators is implicated in the development of neural dysfunction. Aging alters the control of neuroinflammatory cascades and general anesthetics are immunosuppressants. Therefore, we hypothesized that general anesthesia disturbs neuroimmune signaling in an age-dependent fashion. We tested this hypothesis by examining gene expression of key immune neuromodulators including IL-1β, TNFα, and CCL2 in the hippocampus of young adult (3 mo) and aged (20 mo) mice following isoflurane anesthesia. We show that isoflurane anesthesia increases expression of these signaling molecules in the hippocampus of young adult mice but decreases it in the hippocampus of old mice. Furthermore, anesthetized old mice had an amplified hippocampal neuroimmune response to systemically administered lipopolysaccharide compared to age-matched carrier controls. Together, these data indicate that isoflurane anesthesia disrupts hippocampal neuroimmune mediator gene expression in the old brain and suggests a potential mechanism by which general anesthesia can contribute to disordered neuronal homeostasis and post-anesthesia cognitive disability in older subjects.

Surgery, neuroinflammation and cognitive impairment

Trauma experienced during surgery can contribute to the development of a systemic inflammatory response that can cause multi-organ dysfunction or even failure. Post-surgical neuroinflammation is a documented phenomenon that results in synaptic impairment, neuronal dysfunction and death, and impaired neurogenesis. Various pro-inflammatory cytokines, such as TNFα, maintain a state of chronic neuroinflammation, manifesting as post-operative cognitive dysfunction and post-operative delirium. Furthermore, elderly patients with post-operative cognitive dysfunction or delirium are three times more likely to experience permanent cognitive impairment or dementia. We conducted a narrative review, considering evidence extracted from various databases including Pubmed, MEDLINE and EMBASE, as well as journals and book reference lists. We found that further pre-clinical and well-powered clinical studies are required to delineate the precise pathogenesis of post-operative delirium and cognitive dysfunction. Despite the burden of post-operative neurological sequelae, clinical studies investigating therapeutic agents, such as dexmedetomidine, ibuprofen and statins, have yielded conflicting results. In addition, evidence supporting novel therapeutic avenues, such as nicotinic and HMGB-1 targeting and remote ischaemic pre-conditioning, is limited and necessitates further investigation.

Inhibiting RIPK1 Limits Neuroinflammation and Alleviates Postoperative Cognitive Impairments in D-Galactose-Induced Aged Mice

Neuroinflammation plays a critical role in the pathogenesis of postoperative cognitive dysfunction (POCD) of the elderly patients. Receptor-interacting protein kinase1 (RIPK1) is a key molecular switch modulating inflammation, apoptosis and necroptosis. Here, we investigated whether inhibiting RIPK1 by necrostatin-1 (Nec-1) could limit neuroinflammation and attenuate POCD in D-Galactose (D-Gal)-induced aged mice. The mice were subjected to anesthesia and partial hepatectomy, and necrostatin-1 was administered intraperitoneally 1 h prior to anesthesia and surgery. Cognitive function and movement were tested 24 h after surgery by open field, Barnes maze and puzzle box. The hippocampal tissues were collected to detect the following: neuroinflammation (Iba-1, IL-1α, IL-1β, TNF-α), Necroptosis (Propidium Iodide (PI) labeling, RIPK1, nuclear transcription factor kappa B (NF-κB) and neuroplasticity (doublecortin (DCX), NR2B, GluA1, GluA2). We found that anesthesia and surgery induced a significant deficit in spatial memory acquisition and impairment of executive function and memory to simple task in D-Galactose-induced aged mice. Inhibiting RIPK1 by necrostatin-1 strikingly mitigated cognitive impairment and alleviated postoperative amplified neuroinflammation, necroptosis and GluA1 loss in hippocampus. These suggest that targeting RIPK1 by necrostatin-1 may serve as a promising therapeutics for prevention of POCD in elderly patients.

Central cholinergic system mediates working memory deficit induced by anesthesia/surgery in adult mice

BACKGROUND

Postoperative cognitive dysfunction (POCD) is consistently associated with increased morbidity and mortality, which has become a major concern of patients and caregivers. Although POCD occurs mainly in aged patients, it happens at any age. Previous studies demonstrated that anesthesia/surgery had no effects on reference memory of adult mice. However, whether it impairs working memory remains unclear. Working memory deficit would result in many deficits of executive function. We hypothesized that anesthesia/surgery impaired the working memory of adult mice and the central cholinergic system was involved.

METHOD

Tibial fracture internal fixation under the anesthesia of isoflurane was performed in two-month-old C57BL/6 mice. Two days later, the spatial reference memory and working memory were measured by a Morris Water Maze (MWM). Donepezil, an inhibitor of acetylcholinesterase (AChE), was administered in another cohort mice for 4 weeks. Then, the working memory was measured by MWM 2 days after anesthesia/surgery. Western blot was used to detect the protein levels of acetylcholine transferase (ChAT), AChE, vesicular acetylcholine transporter (VAChT), and choline transporter (ChT) in the prefrontal cortex (PFC).

RESULTS

We found that anesthesia/surgery had no effects on the reference memory, but it impaired the working memory in adult mice. Meanwhile, we also found that the protein level of ChAT in PFC decreased significantly compared with that in control group. Donepezil pretreatment prevented working memory impairment and the decrease of the protein levels of ChAT induced by anesthesia/surgery.

CONCLUSION

These results suggest that anesthesia/surgery leads to working memory deficits in adult mice and central cholinergic system impairment is involved.

Nanogels of dual inhibitor-modified hyaluronic acid function as a potent inhibitor of amyloid β-protein aggregation and cytotoxicity

Inhibition of amyloid β-protein (Aβ) aggregation is considered as a promising strategy for the prevention and treatment of Alzheimer’s disease. Epigallocatechin-3-gallate (EGCG) and curcumin have been recognized as effective inhibitors of Aβ aggregation. Herein, we proposed dual-inhibitor modification of hyaluronic acid (HA) to explore the synergistic effect of the two inhibitors. EGCG-modified HA (EHA) formed dispersed hydrogel structures, while EGCG-curcumin bi-modified HA (CEHA) self-assembled into nanogels like curcumin-modified HA (CHA). Thioflavin T fluorescent assays revealed that the inhibitory effect of CEHA was 69% and 55% higher than EHA and CHA, respectively, and cytotoxicity assays showed that the viability of SH-SY5Y cells incubated with Aβ and CEHA was 28% higher than that with Aβ and the mixture of EHA and CHA. These results clearly indicate the synergism of the two inhibitors. It is considered that the difference in the hydrophobicities of the two inhibitors made the bi-modification of HA provide a favorable CEHA nanostructure that coordinated different inhibition effects of the two inhibitors. This research indicates that fabrication of dual-inhibitor nanosystem is promising for the development of potent agents against Aβ aggregation and cytotoxicity.