High-fat diet aggravates postoperative cognitive dysfunction in aged mice

Lactiplantibacillus plantarum 1008 Promotes Reproductive Function and Cognitive Activity in Aged Male Mice with High-Fat-Diet-Induced Obesity by Altering Metabolic Parameters and Alleviating Testicular Oxidative Damage, Inflammation and Apoptosis

The effects of Lactiplantibacillus plantarum 1008 (LP1008) on age-related cognitive impairment and skeletal muscle atrophy have been reported previously. However, its role in obesity- and age-related hypogonadism has yet to be explored. This study investigates the therapeutic efficacy of low- and high-dose LP1008 in a high-fat-diet-fed male mouse model. Mice at 37 weeks of age were fed a standard diet (n = 8) or a 45% high-fat diet for 28 weeks, and the high-fat-diet-fed mice were divided into vehicle, low-dose and high-dose LP1008 groups (n = 8 per group) on the basis of the treatment administered for an additional 8 weeks. We found that LP1008 suppressed the increases in total cholesterol levels and liver function parameters and alleviated histological changes in the brain, ileum, gastrocnemius muscle and testes. In terms of reproductive function, LP1008 attenuated the decreases in sperm quality, sperm maturity, testosterone levels and levels of enzymes involved in testosterone biosynthesis. Furthermore, LP1008 altered impairments in spatial learning and memory and induced slight alterations in the gut microbiota. Moreover, LP1008 exerted antioxidant, anti-inflammatory and anti-apoptotic effects in aged, obese male mice. LP1008 reversed diet-induced obesity, age-related reproductive dysfunction and pathological damage by increasing testosterone levels and altering the gut microbiome through the regulation of mediators involved in oxidative stress, apoptosis and inflammation.

Intermittent fasting alleviates postoperative cognitive dysfunction by reducing neuroinflammation in aged mice

Elderly individuals undergoing surgical procedures are often confronted with the peril of experiencing postoperative cognitive dysfunction (POCD). Prior research has demonstrated the exacerbating effect of sevoflurane anesthesia on neuroinflammation, which can further deteriorate the condition of POCD in elderly patients. Intermittent fasting (IF) restricts food consumption to a specific time window and has been demonstrated to ameliorate cognitive dysfunction induced by neuropathic inflammation. We subjected 18-month-old male mice to 16 hours of fasting and 8 hours of unrestricted eating over a 24-hour period for 0, 1, 2, and 4 weeks, followed by abdominal exploration under sevoflurane anesthesia. In this study, we aim to explore the potential impact of IF on postoperative cognitive function in aged mice undergoing sevoflurane surgery through the preoperative implementation of IF measures. The findings indicate two weeks of IF leads to a significant enhancement of learning and memory capabilities in mice following surgery. The cognitive performance, as determined by the novel object recognition and Morris water maze tests, as well as the synaptic plasticity, as measured by in vivo electrophysiological recordings, has demonstrated marked improvements. Furthermore, the administration of IF markedly enhances the expression of synaptic-associated proteins in hippocampal neurons, concomitant with a decreasing expression of pro-inflammatory factors and a reduced density of microglial cells within the hippocampal brain region. To summarize, the results of this study indicate that IF may mitigate inflammation in the hippocampal area of the brain. Furthermore, IF appears to provide a safeguard against cognitive impairment and synaptic plasticity impairment brought on by sevoflurane anesthesia.

Middle aged CAMKII-Cre:Cbsfl/fl mice: a new model for studying perioperative neurocognitive disorders

Postoperative complications, such as perioperative neurocognitive disorders (PND), have become a major issue affecting surgical outcomes. However, the mechanism of PND remains unclear, and stable animal models of middle-aged PND are lacking. S-adenosylmethionine (SAM), a cystathionine beta-synthase (CBS) allosteric activator, can reduce the level of plasma homocysteine and prevent the occurrence of PND. However, the time and resource-intensive process of constructing models of PND in elderly animals have limited progress in PND research and innovative therapy development. The present study aimed to construct a stable PND model in middle-aged CAMKII-Cre:Cbsfl/fl mice whose Cbs was specifically knocked out in CAMKII positive neurons. Behavioral tests showed that these middle-aged mice displayed cognitive deficits which were aggravated by exploratory laparotomy under isoflurane anesthesia. Compared with typical PND mice which were 18-month-old, these middle-aged mice showed similar cognitive deficits after undergoing exploratory laparotomy under isoflurane anesthesia. Though there was no significant difference in the number of neurons in either the hippocampus or the cortex, a significant increase in numbers of microglia and astrocytes in the hippocampus was observed. These indicate that middle-aged CAMKII-Cre:Cbsfl/fl mice can be used as a new PND model for mechanistic studies and therapy development for PND.

Post-operative cognitive dysfunction is exacerbated by high-fat diet via TLR4 and prevented by dietary DHA supplementation

Post-operative cognitive dysfunction (POCD) is an abrupt decline in neurocognitive function arising shortly after surgery and persisting for weeks to months, increasing the risk of dementia diagnosis. Advanced age, obesity, and comorbidities linked to high-fat diet (HFD) consumption such as diabetes and hypertension have been identified as risk factors for POCD, although underlying mechanisms remain unclear. We have previously shown that surgery alone, or 3-days of HFD can each evoke sufficient neuroinflammation to cause memory deficits in aged, but not young rats. The aim of the present study was to determine if HFD consumption before surgery would potentiate and prolong the subsequent neuroinflammatory response and memory deficits, and if so, to determine the extent to which these effects depend on activation of the innate immune receptor TLR4, which both insults are known to stimulate. Young-adult (3mo) & aged (24mo) male F344xBN F1 rats were fed standard chow or HFD for 3-days immediately before sham surgery or laparotomy. In aged rats, the combination of HFD and surgery caused persistent deficits in contextual memory and cued-fear memory, though it was determined that HFD alone was sufficient to cause the long-lasting cued-fear memory deficits. In young adult rats, HFD + surgery caused only cued-fear memory deficits. Elevated proinflammatory gene expression in the hippocampus of both young and aged rats that received HFD + surgery persisted for at least 3-weeks after surgery. In a separate experiment, rats were administered the TLR4-specific antagonist, LPS-RS, immediately before HFD onset, which ameliorated the HFD + surgery-associated neuroinflammation and memory deficits. Similarly, dietary DHA supplementation for 4 weeks prior to HFD onset blunted the neuroinflammatory response to surgery and prevented development of persistent memory deficits. These results suggest that HFD 1) increases risk of persistent POCD-associated memory impairments following surgery in male rats in 2) a TLR4-dependent manner, which 3) can be targeted by DHA supplementation to mitigate development of persistent POCD.

J147 affects cognition and anxiety after surgery in Zucker rats

Vulnerable patients are at risk for neuroinflammation-mediated post-operative complications, including depression (POD) and cognitive dysfunction (POCD). Zucker rats, expressing multiple risk factors for post-operative complications in humans, may provide a clinically relevant model to study pathophysiology and explore potential interventions. J147, a newly developed anti-dementia drug, was shown to prevent POCD in young healthy rats, and improved early post-surgical recovery in Zucker rats. Aim of the present study was to investigate POCD and the therapeutic potential of J147 in male Zucker rats. Risk factors in the Zucker rat strain were evaluated by comparison with lean littermates. Zucker rats were subjected to major abdominal surgery. Acute J147 treatment was provided by a single iv injection (10 mg/kg) at the start of surgery, while chronic J147 treatment was provided in the food (aimed at 30 mg/kg/day), starting one week before surgery and up to end of protocol. Effects on behavior were assessed, and plasma, urine and brain tissue were collected and processed for immunohistochemistry and molecular analyses. Indeed, Zucker rats displayed increased risk factors for POCD, including obesity, high plasma triglycerides, low grade systemic inflammation, impaired spatial learning and decreased neurogenesis. Surgery in Zucker rats reduced exploration and increased anxiety in the Open Field test, impaired short-term spatial memory, induced a shift in circadian rhythm and increased plasma neutrophil gelatinase-associated lipocalin (NGAL), microglia activity in the CA1 and blood brain barrier leakage. Chronic, but not acute J147 treatment reduced anxiety in the Open Field test and protected against the spatial memory decline. Moreover, chronic J147 increased glucose sensitivity. Acute J147 treatment improved long-term spatial memory and reversed the circadian rhythm shift. No anti-inflammatory effects were seen for J147. Although Zucker rats displayed risk factors, surgery did not induce extensive POCD. However, increased anxiety may indicate POD. Treatment with J147 showed positive effects on behavioral and metabolic parameters, but did not affect (neuro)inflammation. The mixed effect of acute and chronic treatment may suggest a combination for optimal treatment.

Age-Related Perioperative Neurocognitive Disorders: Experimental Models and Druggable Targets

With the worldwide increase in life span, surgical patients are becoming older and have a greater propensity for postoperative cognitive impairment, either new onset or through deterioration of an existing condition; in both conditions, knowledge of the patient's preoperative cognitive function and postoperative cognitive trajectory is imperative. We describe the clinical utility of a tablet-based technique for rapid assessment of the memory and attentiveness domains required for executive function. The pathogenic mechanisms for perioperative neurocognitive disorders have been investigated in animal models in which excessive and/or prolonged postoperative neuroinflammation has emerged as a likely contender. The cellular and molecular species involved in postoperative neuroinflammation are the putative targets for future therapeutic interventions that are efficacious and do not interfere with the surgical patient's healing process.

Amelioratory Effect of Melatonin on Cognition Dysfunction Induced by Sevoflurane Anesthesia in Aged Mice

Background

Postoperative cognitive dysfunction (POCD) can be described as a clinical phenomenon characterized by cognitive impairment in patients, particularly elderly patients, after anesthesia and surgery. Researchers have focused on the probable effect of general anesthesia drugs on cognitive functioning status in older adults. Melatonin is an indole-type neuroendocrine hormone with broad biological activity and potent anti-inflammatory, anti-apoptotic, and neuroprotective effects. This study investigated the effects of melatonin on cognitive behavior in aged mice anesthetized with sevoflurane. In addition, melatonin's molecular mechanism was determined.

Objectives

This study aimed to investigate the mechanisms of melatonin against sevoflurane-induced neurotoxicity.

Methods

A total of 94 aged C57BL/6J mice were categorized into different groups, namely control (control + melatonin (10 mg/kg)), sevoflurane (sevoflurane + melatonin (10 mg/kg)), sevoflurane + melatonin (10 mg/kg) + phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) inhibitor LY294002 (30 mg/kg), and sevoflurane + melatonin (10 mg/kg) + mammalian target of rapamycin (mTOR) inhibitor (10 mg/kg). The open field and Morris water maze tests were utilized to assess the neuroprotective effects of melatonin on sevoflurane-induced cognitive impairment in aged mice. The expression levels of the apoptosis-linked proteins, PI3K/Akt/mTOR signaling pathway, and pro-inflammatory cytokines in the brain's hippocampus region were determined using the Western blotting technique. The apoptosis of the hippocampal neurons was observed using the hematoxylin and eosin staining technique.

Results

Neurological deficits in aged, sevoflurane-exposed mice were significantly decreased after melatonin treatment. Mechanistically, melatonin treatment restored sevoflurane-induced down-regulated PI3K/Akt/mTOR expression and significantly attenuated sevoflurane-induced apoptotic cells and neuroinflammation.

Conclusions

The findings of this study have highlighted the neuroprotective effect of melatonin on sevoflurane-induced cognitive impairment via regulating the PI3K/Akt/mTOR pathway, which might be effective in the clinical treatment of elderly patients with anesthesia-induced POCD.

High-fat diet-associated cognitive decline: Is zinc finger protein 1 (ZPR1) the molecular connection?

Zinc finger protein 1 (ZPR1) is required for cellular replication and viability. Recently, ZPR1 variant rs964184 has been repeatedly linked to high plasma triglyceride levels, metabolic syndrome, type 2 diabetes mellitus (T2DM), and nonalcoholic fatty liver disease (NAFLD), suggesting its involvement in lipid metabolism. This article attempts to explain how ZPR1 contributes to the mechanism of high-fat diet-associated cognitive decline through three premises: i) high-fat diet results in cognitive decline, ii) ZPR1 deficiency also results in cognitive decline, and iii) high-fat diet results in ZPR1 deficiency. Therefore, ZPR1 has the potential to be the connection between high-fat diet and cognitive decline. The two modalities of cognitive decline caused by low concentrations of ZPR1 are reduced brain-derived growth factor (BDNF) synthesis and neuron death, both occurring in the hippocampus. Downregulation of ZPR1 may lead to decreased synthesis of BDNF due to reduced concentrations of peroxisome proliferator-activated receptor-gamma (PPAR-γ), tropomyosin receptor kinase B (Trk B), and cAMP response element-binding protein (CREB), resulting in reduced ability to form and retain long-term memory as well as reduced neuroplasticity. Likewise, low concentrations of ZPR1 facilitate neuron death by producing lower amount of spinal motor neuron (SMN) protein, causing genomic instability, activating mixed-lineage protein kinase 3 (MLK3), mitogen-activated protein kinase 7 (MKK7), and c-Jun N-terminal kinase 3 (JNK3) signal cascade, and ultimately resulting in the activation of Caspase 3.

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ZPR1 plays an important role in cell division and viability.

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ZPR1 variant rs964184 has been linked to dysregulation of lipid metabolism.

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High-fat diet can reduce ZPR1 to induce hippocampal neuronal death.

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High-fat diet correlates with cognitive decline.

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ZPR1 may mediate high-fat diet-induced cognitive decline.

Alterations in the gut microbiota contribute to cognitive impairment induced by the ketogenic diet and hypoxia

Many genetic and environmental factors increase susceptibility to cognitive impairment (CI), and the gut microbiome is increasingly implicated. However, the identity of gut microbes associated with CI risk, their effects on CI, and their mechanisms remain unclear. Here, we show that a carbohydrate-restricted (ketogenic) diet potentiates CI induced by intermittent hypoxia in mice and alters the gut microbiota. Depleting the microbiome reduces CI, whereas transplantation of the risk-associated microbiome or monocolonization with Bilophila wadsworthia confers CI in mice fed a standard diet. B. wadsworthia and the risk-associated microbiome disrupt hippocampal synaptic plasticity, neurogenesis, and gene expression. The CI is associated with microbiome-dependent increases in intestinal interferon-gamma (IFNg)-producing Th1 cells. Inhibiting Th1 cell development abrogates the adverse effects of both B. wadsworthia and environmental risk factors on CI. Together, these findings identify select gut bacteria that contribute to environmental risk for CI in mice by promoting inflammation and hippocampal dysfunction.

Inflammation and Insulin Resistance as Risk Factors and Potential Therapeutic Targets for Alzheimer's Disease

Overnutrition and modern diets containing high proportions of saturated fat are among the major factors contributing to a low-grade state of inflammation, hyperglycemia and dyslipidemia. In the last decades, the global rise of type 2 diabetes and obesity prevalence has elicited a great interest in understanding how changes in metabolic function lead to an increased risk for premature brain aging and the development of neurodegenerative disorders such as Alzheimer's disease (AD). Cognitive impairment and decreased neurogenic capacity could be a consequence of metabolic disturbances. In these scenarios, the interplay between inflammation and insulin resistance could represent a potential therapeutic target to prevent or ameliorate neurodegeneration and cognitive impairment. The present review aims to provide an update on the impact of metabolic stress pathways on AD with a focus on inflammation and insulin resistance as risk factors and therapeutic targets.

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.

11β-HSD1 Inhibition Rescues SAMP8 Cognitive Impairment Induced by Metabolic Stress

Ageing and obesity have been shown to increase the risk of cognitive decline and Alzheimer's disease (AD). Besides, elevated glucocorticoid (GCs) levels cause metabolic stress and have been associated with the neurodegenerative process. Direct pieces of evidence link the reduction of GCs caused by the inhibition of 11β-HSD type 1 (11β-HSD1) with cognitive improvement. In the present study, we investigated the beneficial effects of 11β-HSD1 inhibitor (i) RL-118 after high-fat diet (HFD) treatment in the senescence-accelerated mouse prone 8 (SAMP8). We found an improvement in glucose intolerance induced by HFD in mice treated with RL-118, a significant reduction in 11β-HSD1 and glucocorticoid receptor (GR) protein levels. Furthermore, specific modifications in the FGF21 activation after treatment with 11β-HSD1i, RL-118, which induced changes in SIRT1/PGC1α/AMPKα pathway, were found. Oxidative stress (OS) and reactive oxygen species (ROS), as well as inflammatory markers and microglial activation, were significantly diminished in HFD mice treated with 11β-HSD1i. Remarkably, treatment with 11β-HSD1i altered PERK pathway in both diet groups, increasing autophagy only in HFD mice group. After RL-118 treatment, a decrease in glycogen synthase kinase 3 (GSK3β) activation, Tau hyperphosphorylation, BACE1 protein levels and the product β-CTF were found. Increases in the non-amyloidogenic secretase ADAM10 protein levels and the product sAPPα were found in both treated mice, regardless of the diet. Consequently, beneficial effects on social behaviour and cognitive performance were found in treated mice. Thus, our results support the therapeutic strategy of selective 11β-HSD1i for the treatment of age-related cognitive decline and AD.

Effects of Memantine in a Mouse Model of Postoperative Cognitive Dysfunction

Persistent impairment in cognitive functioning postoperatively is reported by clinical and animal studies, and is labeled as postoperative cognitive dysfunction (POCD). Evidence points to an exaggerated neuroinflammatory response resulting from peripheral systemic inflammation after surgery, with subsequent cytokine-induced glutamatergic excitotoxicity and synaptic impairment. These immunological changes, among many others, are also observed in Alzheimer’s disease. Memantine is an N-methyl-D-aspartate receptor (NMDAR) antagonist commonly used to treat Alzheimer’s disease. Surprisingly, little research exists on the role of memantine in preventing POCD. The purpose of this study is to investigate the effects of memantine on a spectrum of cognitive functions postoperatively. Mice were divided into 3 groups and each received treatment for 4 weeks. Placebo groups received a placebo then underwent either a sham procedure or a laparotomy procedure. The memantine group received memantine hydrochloride then underwent a laparotomy procedure. Cognitive tests were performed on postoperative days (POD) 1 and 7. Compared to sham-operated mice, placebo groups that underwent a laparotomy procedure showed impaired memory in the Morris water maze test, higher anxiety-like behavior in the open field and the elevated plus maze tests, increased depression-like behavior in the tail suspension test, and lack of preference for social novelty in the three-chamber test. On the other hand, memantine-treated mice that underwent a laparotomy procedure showed enhanced memory on POD7, improved depression-like behavior on POD1 and POD7, enhanced preference for social novelty on POD1, and no improvement in anxiety-like behavior. These findings suggest a potential protective effect of memantine in mice postoperatively on memory, depression-like behavior, and preference for social novelty.

Obesity caused by a high-fat diet regulates the Sirt1/PGC-1α/FNDC5/BDNF pathway to exacerbate isoflurane-induced postoperative cognitive dysfunction in older mice

Objectives: To investigate the effects of obesity caused by high-fat diet (HFD) on postoperative cognitive dysfunction (POCD) and expression of the Sirt1/PGC-1α/FNDC5/BDNF pathway in the hippocampus of older mice. Methods: Fifty-six 15-month-old male C57BL/6 mice were randomly divided into eight groups - ad libitum control (ALC), ad libitum surgery (ALS), ad libitum surgery with PBS (ALS + PBS), ad libitum surgery with resveratrol (ALS + Res), HFD control (HFC), HFD surgery (HFS), HFD surgery with PBS (HFS + PBS), HFD surgery with resveratrol (HFS + Res). Surgery group mice were exposed to isoflurane before tibial fracture internal fixation. Open field tests and fear conditioning were performed to test motor ability and memory. The levels of expression of Sirt1, PGC-1α, FNDC5, and BDNF were detected using western blot and immunofluorescence. Results: The results of the open field tests indicated there were no between-group differences in motor ability and anxiety. The results of the fear conditioning indicated that the memory of the HFC group and HFS group mice were significantly worse compared with the ALC group and ALS group mice, respectively. There were parallel decreases in expression of the Sirt1/PGC-1α/FNDC5/BDNF pathway in the hippocampi of the HFC and HFS group mice. Resveratrol treatment attenuated the memory loss by increasing hippocampal Sirt1 expression. Expression of the PGC-1α/FNDC5/ BDNF pathway in the CA1 area of the hippocampus was upregulated after resveratrol treatment. Conclusion: An HFD exacerbates POCD in older mice. This change was related to HFD inhibition of expression of the Sirt1/PGC-1α/FNDC5/BDNF pathway in the hippocampus. Resveratrol pretreatment reversed the memory loss via upregulation of this pathway.