Anesthesia, surgery, illness and Alzheimer's disease

Mechanisms of comorbidity between Alzheimer's disease and pain

Clinical studies have revealed a significant correlation between pain and neurodegenerative diseases, particularly Alzheimer's disease (AD). However, due to cognitive and speech impairments, AD patients, especially those in moderate to severe stages, are often overlooked in pain management. The challenges in obtaining pain-related information from this population exacerbate the issue. Although recent clinical research has increasingly recognized the comorbidity of AD and pain, the pathological alterations and interactive mechanisms underlying this relationship remain inadequately explored. This review provides a comprehensive analysis of the clinical features and pathological mechanisms of AD with and without pain comorbidity. It examines underlying processes, including neuroinflammation, peripheral-central immune interactions, and neurotransmitter dynamics. Furthermore, it highlights current pain assessment and management strategies in AD patients. By offering a theoretical framework, this review aims to support the development of effective pain management approaches and serve as a reference for clinical interventions targeting AD-associated pain. HIGHLIGHTS: The comorbidity between AD and CP encompasses multiple interrelated biological pathways, such as neurodegeneration and inflammatory responses. The damage to neurons and synapses in AD patients influences the brain regions responsible for processing pain, thereby reducing the pain response. Neuroinflammation plays a vital role in the development of both AD and CP. Enhanced inflammatory responses have an impact on the CNS and promote sensitization. Common neurotransmitter alterations exist in the comorbidity of AD and CP, influencing cognition, emotion, and pain perception.

Deep brain stimulation of thalamic nucleus reuniens promotes neuronal and cognitive resilience in an Alzheimer's disease mouse model

The mechanisms that confer cognitive resilience to Alzheimer's Disease (AD) are not fully understood. Here, we describe a neural circuit mechanism underlying this resilience in a familial AD mouse model. In the prodromal disease stage, interictal epileptiform spikes (IESs) emerge during anesthesia in the CA1 and mPFC regions, leading to working memory disruptions. These IESs are driven by inputs from the thalamic nucleus reuniens (nRE). Indeed, tonic deep brain stimulation of the nRE (tDBS-nRE) effectively suppresses IESs and restores firing rate homeostasis under anesthesia, preventing further impairments in nRE-CA1 synaptic facilitation and working memory. Notably, applying tDBS-nRE during the prodromal phase in young APP/PS1 mice mitigates age-dependent memory decline. The IES rate during anesthesia in young APP/PS1 mice correlates with later working memory impairments. These findings highlight the nRE as a central hub of functional resilience and underscore the clinical promise of DBS in conferring resilience to AD pathology by restoring circuit-level homeostasis.

New strategy of using double-network hydrogel extravascular stent for preventing venous graft restenosis after coronary artery bypass grafting

OBJECTIVE

Effective therapies for the prevention of vein graft failure, which frequently occurs in coronary artery bypass grafting (CABG) due to intimal hyperplasia (IH), are still lacking. Here, we investigated the effects of the perivenous application of double-network hydrogel on vein grafts in carotid artery bypass grafting in a rabbit model.

METHODS

Healthy New Zealand white rabbits were randomized into the following groups: no graft, graft, or graft + Double-network hydrogel external stent (DNHES). The rabbits' carotid artery was bypassed via the jugular vein. Double-network hydrogel external stent was wrapped around the jugular graft after the anastomoses were completed. Blood flow parameters and tissue histology of the vein grafts were evaluated.

RESULTS

Compared with the untreated vein grafts at 12 weeks after the surgery, the DNHES significantly improved graft flow, attenuated intimal and medial thickening, reduced the anti-proliferating cell nuclear antigen proliferation index of the vein grafts, decreased the mRNA and protein expression of Mitogen-Activated Protein Kinase (MAPK) and Transforming Growth Factor-β (TGF-β), and increased the mRNA and protein expression of endothelial Nitric Oxide Synthase (eNOS).

CONCLUSION

The perivenous application of DNHES exerts beneficial effects on vein grafts, reduces the inflammatory response in carotid artery bypass grafting in a rabbit model, and appears to be a safe and promising strategy to prevent vein graft failure.

Perioperative Neurocognitive Disorders in Adults Requiring Cardiac Surgery: Screening, Prevention, and Management

Neurocognitive changes are the most common complication after cardiac surgery, ranging from acute postoperative delirium to prolonged postoperative neurocognitive disorder. Changes in cognition are distressing to patients and families and associated with worse outcomes overall. This review outlines definitions and diagnostic criteria, risk factors for, and mechanisms of Perioperative Neurocognitive Disorders and offers strategies for preoperative screening and perioperative prevention and management of neurocognitive complications.

IL-33/ST2 axis promotes remodeling of the extracellular matrix and drives protective microglial responses in the mouse model of perioperative neurocognitive disorders

Anesthesia and surgery induce cognitive impairment via uncertain mechanisms. Increasing evidence has suggested that microglial activity mediated by IL-33 /ST2 plays a critical role in immune regulation and inflammatory responses. Yet, the implications for microglia activity mediated by IL-33 in perioperative neurocognitive disorders (PND) are not well established. We showed that IL-33 and ST2 were downregulated in the hippocampus after anesthesia and surgery, and the expression of aggrecan, remodeling by microglia, was upregulated. Meanwhile, the expression of pro-inflammatory cytokines (IL-6 and IL-1β) and M1-like microglia marker (iNOS) increased, and the expression of M2-like microglia marker (CD206) decreased. Notably, the administration of IL-33 attenuated neuroinflammation and shifted the polarization of microglia in the hippocampus after anesthesia and surgery. Furthermore, IL-33 treatment rescued the increase of aggrecan, loss of dendritic spines, and impairment of LTP, improving cognitive performance. In conclusion, our study suggests that microglia activity mediated by IL-33/ST2 plays a vital role in cognitive impairments after anesthesia and surgery, which may serve as a therapeutic target for PND.

Effect of preoperative tropisetron treatment on postoperative cognitive function: A retrospective cohort study

To investigate the effect of preoperative tropisetron treatment on postoperative cognitive function on the basis of patients' Mini-Cog scale scores. In this retrospective cohort study, data were retrieved from the medical record database. This research did not involve concerns with patient safety and violation of their interests, and therefore, no ethical review was required. Depending on tropisetron exposure status, patients were assigned to the exposure group (86 patients) and the non-exposure group (74 patients). Patients in the exposure and non-exposure groups were administered tropisetron (10 mg; intravenously 15 minutes before operation) and other antiemetics, respectively. Data on the patients' demographic characteristics, American society of Anesthesiologists (ASA) classification, comorbid underlying diseases, sleep quality, education level, anesthesia method, duration of fasting, intraoperative blood loss and fluid replacement, intraoperative minimum and maximum systolic blood pressures (SBPs), intraoperative minimum and maximum diastolic blood pressures (DBPs), postoperative Mini-Cog scale (a simple intelligence status assessment scale) score, and postoperative visual analogue scale (VAS) pain score were collected in both the groups. The postoperative Mini-Cog score (as an indicator of cognitive function) and the rate of postoperative cognitive impairment were compared between the exposure and non-exposure groups. A multifactorial logistic regression equation was constructed to analyze the factors associated with impaired cognitive function in the postoperative period. The postoperative cognitive impairment rate in the exposure group was significantly lower than that in the non-exposure group (3.5% vs 16.2%; P < .05). Multifactorial logistic regression analysis suggested that tropisetron was a protective factor for postoperative cognitive function, with a statistically significant effect (odds ratio [OR] = 5.04, 95% confidence interval [CI] = 1.31-19.4). Preoperative tropisetron exposure significantly reduces the incidence of postoperative cognitive impairment in patients, and it is a protective factor for postoperative cognitive function.

Orthopedic Surgery Causes Gut Microbiome Dysbiosis and Intestinal Barrier Dysfunction in Prodromal Alzheimer Disease Patients: A Prospective Observational Cohort Study

OBJECTIVE

To investigate gut microbiota and intestinal barrier function changes after orthopedic surgery in elderly patients with either normal cognition (NC) or a prodromal Alzheimer disease phenotype (pAD) comprising either subjective cognitive decline (SCD) or amnestic mild cognitive impairment (aMCI).

BACKGROUND

Homeostatic disturbances induced by surgical trauma and/or stress can potentially alter the gut microbiota and intestinal barrier function in elderly patients before and after orthopedic surgery.

METHODS

In this prospective cohort study, 135 patients were subject to preoperative neuropsychological assessment and then classified into: NC (n=40), SCD (n=58), or aMCI (n=37). Their gut microbiota, bacterial endotoxin (lipopolysaccharide), tight junction (TJ) protein, and inflammatory cytokines in blood were measured before surgery and on postsurgical day 1, 3, and 7 (or before discharge).

RESULTS

The short-chain fatty acid (SCFA)-producing bacteria were lower while the gram-negative bacteria, lipopolysaccharide and TJ were higher preoperatively in both the SCD and aMCI (pAD) groups compared with the NC group. After surgery, a decrease in SCFA-producing bacteria, and an increase in both gram-negative bacteria and plasma claudin were significant in the pAD groups relative to the NC group. SCFA-producing bacteria were negatively correlated with TJ and cytokines in pAD patients on postsurgical day 7. Furthermore, surgery-induced perioperative metabolic stress and inflammatory responses were associated with gut microbiota alterations.

CONCLUSIONS

Surgery exacerbates both preexisting microbiota dysbiosis and intestinal barrier dysfunction in pAD patients, all of which may be associated with systemic inflammation and, in turn, may lead to further cognitive deterioration.

Extended anesthesia exposure for abdominal and pelvic procedures in older adults with colorectal cancer: Associations with chart dementia diagnoses

BACKGROUND

We hypothesized that cumulative anesthesia exposure over the course of routine treatment of colorectal cancer in older adults can increase long-term risk of Alzheimer's disease (AD), Alzheimer's disease-related dementias (ADRD), and other chronic neurocognitive disorders (CND).

METHODS

We conducted a SEER-Medicare-based retrospective cohort study of 84,770 individuals age 65 years and older diagnosed with colorectal cancer between 1998 and 2007 using a proportional hazards model with inverse probability weighted estimators. The primary exploratory variable was a time-variant measure of cumulative anesthesia exposure for abdominal and pelvic procedures, updated continuously.

RESULTS

Our primary outcomes, AD and ADRD, occurred in 6005/84,770 (7.1%) and 14,414/83,444 (17.3%) individuals respectively. No statistically significant association was found between cumulative anesthesia exposure and AD (hazard ratio [HR], 0.993; 95% CI, 0.973-1.013). However, it was moderately associated with the risk of ADRD (HR, 1.016; 95% CI, 1.004-1.029) and some secondary outcomes including most notably: cerebral degeneration (HR, 1.048; 95% CI, 1.033-1.063), hepatic encephalopathy (HR, 1.133; 95% CI, 1.101-1.167), encephalopathy-not elsewhere classified (HR,1.095; 95% CI: 1.076-1.115), and incident/perioperative delirium (HR, 1.022; 95% CI, 1.012-1.032). Furthermore, we observed an association between perioperative delirium and increased risk of AD (HR, 2.05; 95% CI, 1.92-2.09).

CONCLUSION

Cumulative anesthesia exposure for abdominal and pelvic procedures was not associated with increased risk of AD directly and had a small but statistically significant association with ADRD and a number of other CNDs. Cumulative anesthesia exposure was also associated with perioperative delirium, which had an independent adverse association with AD risk.

Hypercholesterolemia aggravates sevoflurane-induced cognitive impairment in aged rats by inducing neurological inflammation and apoptosis

We aimed to explore the effects of hypercholesterolemia on sevoflurane-induced cognitive impairment in aged rats and the underlying mechanism(s). Aged rats were administrated with high-fat diet, sevoflurane, or both. Thereafter, the plasma levels of total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) were evaluated. The Morris water maze task was performed to evaluate the spatial learning and memory ability of rats. Moreover, Nissl and Evans blue staining were conducted to test nerve damage and detect the blood-brain barrier permeability, respectively. The percentage of apoptotic cells was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling assay. The messenger RNA expression of inflammatory factors and protein expression of microglial activation markers and apoptosis-related proteins were tested by real-time polymerase chain reaction, enzyme-linked immunosorbent assay, or western blot analysis, respectively. High-fat diet induced high levels of TC, TG, and LDL but decreased levels of HDL. However, sevoflurane had no effects on these levels. In contrast, sevoflurane significantly induced the impairment of learning and memory, nerve damage, neuroinflammatory damage, and neuronal apoptosis. Hypercholesterolemia exacerbated the sevoflurane-induced impairment in aged rats. These results suggested that hypercholesterolemia aggravates sevoflurane-induced cognitive impairment in aged rats, possibly by inducing neurological inflammation and apoptosis.

Surgical Trauma in Mice Modifies the Content of Circulating Extracellular Vesicles

Surgical interventions rapidly trigger a cascade of molecular, cellular, and neural signaling responses that ultimately reach remote organs, including the brain. Using a mouse model of orthopedic surgery, we have previously demonstrated hippocampal metabolic, structural, and functional changes associated with cognitive impairment. However, the nature of the underlying signals responsible for such periphery-to-brain communication remains hitherto elusive. Here we present the first exploratory study that tests the hypothesis of extracellular vesicles (EVs) as potential mediators carrying information from the injured tissue to the distal organs including the brain. The primary goal was to investigate whether the cargo of circulating EVs after surgery can undergo quantitative changes that could potentially trigger phenotypic modifications in the target tissues. EVs were isolated from the serum of the mice subjected to a tibia surgery after 6, 24, and 72 h, and the proteome and miRNAome were investigated using mass spectrometry and RNA-seq approaches. We found substantial differential expression of proteins and miRNAs starting at 6 h post-surgery and peaking at 24 h. Interestingly, one of the up-regulated proteins at 24 h was α-synuclein, a pathogenic hallmark of certain neurodegenerative syndromes. Analysis of miRNA target mRNA and corresponding biological pathways indicate the potential of post-surgery EVs to modify the extracellular matrix of the recipient cells and regulate metabolic processes including fatty acid metabolism. We conclude that surgery alters the cargo of circulating EVs in the blood, and our results suggest EVs as potential systemic signal carriers mediating remote effects of surgery on the brain.

Surgery Performed Under Propofol Anesthesia Induces Cognitive Impairment and Amyloid Pathology in ApoE4 Knock-In Mouse Model

Background: Postoperative cognitive dysfunction (POCD) following anesthesia and surgery is a common and severe complication, especially in elderly patients. A pre-existing cognitive impairment may impart susceptibility to further cognitive dysfunction; the mechanism remains unclear. We hypothesized that the specific impacts of anesthesia and surgery on individuals with preclinical Alzheimer’s disease (AD) may render them more susceptible to an increase in the risk of cognitive impairment. The aim of this study was to compare the cognitive impairment between normal adult mice and those with preclinical AD after propofol anesthesia and surgery.

Methods: We performed abdominal surgery in cognitively pre-symptomatic, 5-month-old male mice with sporadic AD (apolipoprotein E4 allele, ApoE4-KI) and age-matched (C57BL/6J) controls. Propofol anesthesia (170 mg/kg) was induced via retro-orbital injection over 2 h. Morris water maze (MWM) and Y-maze tests were conducted 2 days before and 2, 4, and 7 days after surgery. The mean escape latencies and spontaneous alternation percentages were the major outcomes. Neuronal apoptosis in hippocampal sections was evaluated using the terminal dUTP nick-end labeling (TUNEL) assay. Hippocampal amyloid beta (Aβ) levels were assessed via quantitative immunohistochemistry (IHC).

Results: The control mice exhibited increased mean escape latencies of MWM at postoperative 2 and 4, but not at day 7; ApoE4-KI mice exhibited such increases at postoperative days 2, 4 and 7. Significant differences between ApoE4-KI and control mice in terms of the mean escape latencies were evident at days 2 and 7 (both P < 0.05). However, performance on a non-hippocampal memory tasks (Y-maze test) did not differ. More TUNEL-positive neurons were evident in the hippocampal CA3 region of ApoE4-KI mice at postoperative days 2 and 4, but not at day 7 compared to the control group (both P < 0.05). IHC revealed significantly elevated Aβ deposition in the hippocampal CA3 region of ApoE4-KI mice at postoperative days 4 and 7 compared to control mice (both P < 0.05).

Conclusions: Propofol anesthesia followed by surgery induced persistent changes in cognition, and pathological hippocampal changes in pre-symptomatic, but vulnerable AD mice. It would be appropriate to explore whether preclinical AD patients are more vulnerable to POCD development.

Cognitive reserve and Alzheimer's biological continuum: clues for prediction and prevention of dementia

Cognitive reserve is originally an epidemiological concept that encompasses individual abilities to cope with changes. It is considered the result of a balance between processes of cellular damage and repair, and its description raised much interest in predicting and preventing cognitive decline in aging and Alzheimer's disease (AD). In this study, we discussed the concept of cognitive reserve considering the recent definition of AD as a biological continuum and suggest that the protection of cognitive reserve may result from efficient synaptic plasticity mechanisms. Despite pathological changes of AD appearing very early during life, long before the onset of cognitive symptoms, different variables act together to keep repair mechanisms effective guaranteeing successful aging if environmental enrichment is maintained.

Resting-state functional connectivity in early postanaesthesia recovery is characterised by globally reduced anticorrelations

BACKGROUND

A growing body of literature addresses the possible long-term cognitive effects of anaesthetics, but no study has delineated the normal trajectory of neural recovery attributable to anaesthesia alone in adults. We obtained resting-state functional MRI scans on 72 healthy human volunteers between ages 40 and 80 (median: 59) yr before, during, and after general anaesthesia with sevoflurane, in the absence of surgery, as part of a larger study on cognitive function postanaesthesia.

METHODS

Region-of-interest analysis, independent component analysis, and seed-to-voxel analysis were used to characterise resting-state functional connectivity and to differentiate between correlated and anticorrelated connectivity before, during, and after general anaesthesia.

RESULTS

Whilst positively correlated functional connectivity remained essentially unchanged across these perianaesthetic states, anticorrelated functional connectivity decreased globally by 35% 1 h after emergence from general anaesthesia compared with baseline, as seen by the region-of-interest analysis. This decrease corresponded to a consistent reduction in expression of canonical resting-state networks, as seen by independent component analysis. All measures returned to baseline 1 day later.

CONCLUSIONS

The normal perianaesthesia trajectory of resting-state connectivity in healthy adults is characterised by a transient global reduction in anticorrelated activity shortly after emergence from anaesthesia that returns to baseline by the following day.

CLINICAL TRIAL REGISTRATION

NCT02275026.

Postoperative neurocognitive disorders

A decline in cognitive function is a frequent complication of major surgery. Postoperative cognitive impairments have generally been divided into short- (postoperative delirium) and long-term disturbances (postoperative cognitive dysfunction [POCD]). Long-term impairments are often subtle and overlooked. They need to be objectively assessed using neuropsychological tests to be diagnosed. Although POCD has been the subject of considerable research over the past decades, it remains uncertain why some patients do not return to preoperative levels of cognitive function. Surgery and anesthesia have both been implicated to play a role in POCD development, and certain patient-related factors, such as advanced age and low preoperative baseline cognitive function, have consistently been found to predict postoperative cognitive decline. This article will present an overview of POCD and its etiology and provide advice on possible strategies on its prevention.

Surgery-induced cognitive dysfunction is alleviated through triggering receptor expressed on myeloid cells 2

Neuroinflammation plays a key role in perioperative neurocognitive disorders (PND). Increased evidences indicate that triggering receptor expressed on myeloid cells 2 (TREM2) can mitigate inflammatory response in the brain, and the aim of this study is to investigate whether TREM2 is involved in surgery-induced cognitive dysfunction in adult mice. We used adult C57BL/6 mice subjected to intramedullary fixation surgery, and found that surgery did not impair the motor ability of mice, but worsened the learning and memory function, and reduced the expression of TREM2. Meanwhile, up-regulated TREM2 expression in the brain of mice, induced by selective TREM2 agonist HSP60, significantly improved the learning and memory, alleviated the neuroinflammation, and decreased the neuronal cell apoptosis in mice. Meanwhile, TREM2-siRNA abolished the increased expression of TREM2 induced by HSP60, and reversed all the HSP60-induced beneficial effects. Therefore, our study indicated that up-regulation of TREM2 alleviated neuroinflammation and improved learning and memory function after surgery in mice.

Intravenous parecoxib for early postoperative cognitive dysfunction in elderly patients: evidence from a meta-analysis

BACKGROUND

Inflammation plays a key role in the etiology and pathology of postoperative cognitive dysfunction (POCD). Cyclooxygenase (COX)-2 inhibitor parecoxib is used for the treatment of acute pain due to its potent anti-inflammatory and analgesic effects. Herein, we evaluated the efficacy and safety of parecoxib on early POCD in geriatric patients.

OBJECTIVE

This study was performed to evaluate the efficacy and safety of parecoxib for early postoperative cognitive dysfunction (POCD) in elderly patients.

METHODS

Comprehensive literature search based on six electronic databases was applied to retrieve all related randomized controlled trials (RCTs). Two independent reviewers screened each article for eligibility according to the predetermined inclusion criteria. The Cochrane's Tool was applied to evaluate the methodological quality of included studies. RevMan 5.3 was used to conduct meta-analysis.

RESULTS

Eight RCTs comprising a total of 1106 subjects prepared for orthopedic surgical operation were selected. All the identified RCTs were conducted in China. The methodological qualities of included studies were judged to be medium to high. The integrated data showed that perioperative intravenous parecoxib could remarkably reduce the incidence of POCD with improved Mini-Mental State Examination (MMSE) score. Parecoxib could significantly reduce the concentrations of interleukin-6, but results regarding the changes in tumor necrosis factor-alpha, C-reactive protein, and S100β levels remained inconsistent.

CONCLUSION

Perioperative parecoxib administration is effective in reducing the incidence of POCD and improving the MMSE score compared with control. However, the beneficial effect of parecoxib has been tested only in the Chinese population. Future RCTs in western countries with larger-scale and more comprehensive neurological tests are needed.

EVALUATION OF PAIN SYNDROME AND EFFICIENCY OF PAIN MANAGEMENT IN LUMBAR SPINE SURGERY

Multimodal analgesia for lumbar spine surgery is still a controversial problem, because of possible fusion problems, significant neuropathic component of pain, and influence of anesthesia type. Aim of the study was to assess the efficacy of pain management after lumbar spine surgery considering characteristics of pain, type of anesthesia and analgesic regimen. Material and methods. 254 ASA I-II patients with degenerative lumbar spine disease were enrolled into prospective study. Patients were operated either under spinal anesthesia (SA) or total intravenous anesthesia (TIVA). In postoperative period patients got either standard pain management (SPM – paracetamol±morphine) or multimodal analgesia (MMA – paracetamol+parecoxib+pregabalin±morphine). Results. We revealed neuropathic pain in 53.9 % of patients, who were elected for lumbar spine surgery. VAS pain score in patients with neuropathic pain was higher, than in patients with nociceptive pain. Total intravenous anesthesia was associated with greater opioid consumption during the first postoperative day. Multimodal analgesia based on paracetamol, parecoxib and pregabalin allowed to decrease requirements for opioids, postoperative nausea and dizziness. Pregabalin used for evening premedication had equipotential anxiolytic effect as phenazepam without postoperative cognitive disturbances. Conclusions. Multimodal analgesia is opioid-sparing technique that allows to decrease complications. Spinal anesthesia is associated to a decreased opioid consumption in the 1st postoperative day.

Age and Sex Influence the Hippocampal Response and Recovery Following Sepsis

Although in-hospital mortality rates for sepsis have decreased, survivors often experience lasting physical and cognitive deficits. Moreover, older adults are more vulnerable to long-term complications associated with sepsis. We employed a murine model to examine the influence of age and sex on the brain’s response and recovery following sepsis. Young (~ 4 months) and old (~ 20 months) mice (C57BL/6) of both sexes underwent cecal ligation and puncture (CLP) with restraint stress. The hippocampal transcriptome was examined in age- and sex-matched controls at 1 and 4 days post-CLP. In general, immune- and stress-related genes increased, while neuronal, synaptic, and glial genes decreased 1 day after CLP-induced sepsis. However, specific age and sex differences were observed for the initial responsiveness to sepsis as well as the rate of recovery examined on day 4. Young females exhibited a muted transcriptional response relative to young males and old females. Old females exhibited a robust shift in gene transcription on day 1, and while most genes recovered, genes linked to neurogenesis and myelination continued to be downregulated by day 4. In contrast, old males exhibited a more delayed or prolonged response to sepsis, such that neuronal and synaptic genes continued to decrease while immune response genes continued to increase on day 4. These results suggest that aging is associated with delayed recovery from sepsis, which is particularly evident in males.

Special Considerations for the Aging Brain and Perioperative Neurocognitive Dysfunction

Postoperative delirium and postoperative cognitive dysfunction (POCD) occur commonly in older adults after surgery and are frequently underrecognized. Delirium has been associated with worse outcomes, and both delirium and cognitive dysfunction increase the risk of long-term cognitive decline. Although the pathophysiology of delirium and POCD have not been clearly defined, risk factors for both include increasing age, lower levels of education, and baseline cognitive impairment. In addition, developing delirium increases the risk of POCD. This article examines interventions that may reduce the risk of developing delirium and POCD and improve long-term recovery and outcomes in the vulnerable older population.

The anaesthetic xenon partially restores an amyloid beta-induced impairment in murine hippocampal synaptic plasticity

BACKGROUND

It is controversially discussed whether general anaesthesia increases the risk of Alzheimer's disease (AD) or accelerates its progression. One important factor in AD pathogenesis is the accumulation of soluble amyloid beta (Aβ) oligomers which affect N-methyl-d-aspartate (NMDA) receptor function and abolish hippocampal long-term potentiation (LTP). NMDA receptor antagonists, at concentrations allowing physiological activation, can prevent Aβ-induced deficits in LTP. The anaesthetics xenon and S-ketamine both act as NMDA receptor antagonists and have been reported to be neuroprotective. In this study, we investigated the effects of subanaesthetic concentrations of these drugs on LTP deficits induced by different Aβ oligomers and compared them to the effects of radiprodil, a NMDA subunit 2B (GluN2B)-selective antagonist.

METHODS

We applied different Aβ oligomers to murine brain slices and recorded excitatory postsynaptic field potentials before and after high-frequency stimulation in the CA1 region of hippocampus. Radiprodil, xenon and S-ketamine were added and recordings evoked from a second input were measured.

RESULTS

Xenon and radiprodil, applied at low concentrations, partially restored the LTP deficit induced by pre-incubated Aβ_1-42. S-ketamine showed no effect. None of the drugs tested were able to ameliorate Aβ_1-40-induced LTP-deficits.

CONCLUSIONS

Xenon administered at subanaesthetic concentrations partially restored Aβ_1-42-induced impairment of LTP, presumably via its weak NMDA receptor antagonism. The effects were in a similar range than those obtained with the NMDA-GluN2B antagonist radiprodil. Our results point to protective properties of xenon in the context of pathological distorted synaptic physiology which might be a meaningful alternative for anaesthesia in AD patients.

Association between exposure to anaesthesia and surgery and long-term cognitive trajectories in older adults: report from the Mayo Clinic Study of Aging

BACKGROUND

The link between exposure to general anaesthesia and surgery (exposure) and cognitive decline in older adults is debated. We hypothesised that it is associated with cognitive decline.

METHODS

We analysed the longitudinal cognitive function trajectory in a cohort of older adults. Models assessed the rate of change in cognition over time, and its association with exposure to anaesthesia and surgery. Analyses assessed whether exposure in the 20 yr before enrolment is associated with cognitive decline when compared with those unexposed, and whether post-enrolment exposure is associated with a change in cognition in those unexposed before enrolment.

RESULTS

We included 1819 subjects with median (25th and 75th percentiles) follow-up of 5.1 (2.7-7.6) yr and 4 (3-6) cognitive assessments. Exposure in the previous 20 yr was associated with a greater negative slope compared with not exposed (slope: -0.077 vs -0.059; difference: -0.018; 95% confidence interval: -0.032, -0.003; P=0.015). Post-enrolment exposure in those previously unexposed was associated with a change in slope after exposure (slope: -0.100 vs -0.059 for post-exposure vs pre-exposure, respectively; difference: -0.041; 95% confidence interval: -0.074, -0.008; P=0.016). Cognitive impairment could be attributed to declines in memory and attention/executive cognitive domains.

CONCLUSIONS

In older adults, exposure to general anaesthesia and surgery was associated with a subtle decline in cognitive z-scores. For an individual with no prior exposure and with exposure after enrolment, the decline in cognitive function over a 5 yr period after the exposure would be 0.2 standard deviations more than the expected decline as a result of ageing. This small cognitive decline could be meaningful for individuals with already low baseline cognition.

Delineating the Trajectory of Cognitive Recovery From General Anesthesia in Older Adults: Design and Rationale of the TORIE (Trajectory of Recovery in the Elderly) Project

BACKGROUND

Mechanistic aspects of cognitive recovery after anesthesia and surgery are not yet well characterized, but may be vital to distinguishing the contributions of anesthesia and surgery in cognitive complications common in the elderly such as delirium and postoperative cognitive dysfunction. This article describes the aims and methodological approach to the ongoing study, Trajectory of Recovery in the Elderly (TORIE), which focuses on the trajectory of cognitive recovery from general anesthesia.

METHODS

The study design employs cognitive testing coupled with neuroimaging techniques such as functional magnetic resonance imaging, diffusion tensor imaging, and arterial spin labeling to characterize cognitive recovery from anesthesia and its biological correlates. Applying these techniques to a cohort of age-specified healthy volunteers 40-80 years of age, who are exposed to general anesthesia alone, in the absence of surgery, will assess cognitive and functional neural network recovery after anesthesia. Imaging data are acquired before, during, and immediately after anesthesia, as well as 1 and 7 days after. Detailed cognitive data are captured at the same time points as well as 30 days after anesthesia, and brief cognitive assessments are repeated at 6 and 12 months after anesthesia.

RESULTS

The study is underway. Our primary hypothesis is that older adults may require significantly longer to achieve cognitive recovery, measured by Postoperative Quality of Recovery Scale cognitive domain, than younger adults in the immediate postanesthesia period, but all will fully recover to baseline levels within 30 days of anesthesia exposure. Imaging data will address systems neuroscience correlates of cognitive recovery from general anesthesia.

CONCLUSIONS

The data acquired in this project will have both clinical and theoretical relevance regardless of the outcome by delineating the mechanism behind short-term recovery across the adult age lifespan, which will have major implications for our understanding of the effects of anesthetic drugs.

Inhalational Anesthetics Induce Neuronal Protein Aggregation and Affect ER Trafficking

Anesthetic agents have been implicated in the causation of neurological and cognitive deficits after surgery, the exacerbation of chronic neurodegenerative disease, and were recently reported to promote the onset of the neurologic respiratory disease Congenital Central Hypoventilation Syndrome (CCHS), related to misfolding of the transcription factor Phox2B. To study how anesthetic agents could affect neuronal function through alterations to protein folding, we created neuronal cell models emulating the graded disease severity of CCHS. We found that the gas anesthetic isoflurane and the opiate morphine potentiated aggregation and mislocalization of Phox2B variants, similar to that seen in CCHS, and observed transcript and protein level changes consistent with activation of the endoplasmic reticulum (ER) unfolded protein response. Attenuation of ER stress pathways did not result in a correction of Phox2B misfolding, indicating a primary effect of isoflurane on protein structure. We also observed that isoflurane hindered the folding and activity of proteins that rely heavily on ER function, like the CFTR channel. Our results show how anesthetic drugs can alter protein folding and induce ER stress, indicating a mechanism by which these agents may affect neuronal function after surgery.

[The efficacy of prevention of postoperative cognitive dysfunction in cardiac surgeries with the use of the cerebrolysin]

AIM

To assess the efficacy of postoperative cytoprotection with cerebrolysin in cardiac surgeries without using cardiopulmonary bypass and to analyze the changes in the blood circulation in the postoperative period in groups with- and without cerebrolysin preconditioning.

MATERIAL AND METHODS

Thirty-eight patients, who underwent coronary and mammaro-coronary bypass grafting without using cardiopulmonary bypass, were included in the study. Fifteen patients received cerebrolysin before surgery.

RESULTS AND CONCLUSION

Cerebrolysin improved cognitive test scores. Positive changes on anxiety and depression scales were observed as well. In the group of patients treated with cerebrolysin, quantitative parameters of the cerebral blood flow were in stable condition, with a slight increase on the 10th day after surgery, which may indicate increasing stress resistance of cells of the central nervous system after appropriate pharmacological protection.

Impact of Inflammation on the Blood-Neural Barrier and Blood-Nerve Interface: From Review to Therapeutic Preview

A number of nervous system disorders are characterized by a state of inflammation (neuroinflammation) in which members of the innate immune system, most notably mast cells and microglia-acting as single entities and in unison-produce inflammatory molecules that play major roles. A neuroinflammatory environment can weaken not only blood-nerve and blood-brain barrier (BBB) integrity but also that of the blood-spinal cord barrier. Mast cells, with their distribution in peripheral nerves and the central nervous system, are positioned to influence blood-nerve barrier characteristics. Being close also to the perivasculature and on the brain side of the BBB, the mast cell is well positioned to disrupt BBB function. Interestingly, tissue damage and/or stress activates homeostatic mechanisms/molecules expressed by mast cells and microglia, and includes N-acylethanolamines. Among the latter, N-palmitoylethanolamine has distinguished itself as a key component in supporting homeostasis of the organism against external stressors capable of provoking inflammation. This review will discuss the pathobiology of neuroinflammation with emphasis on mast cells and microglia, their roles in BBB health, and novel therapeutic opportunities, including nanoscale delivery for targeting these immune cells with a view to maintain the BBB.

Anesthesia, brain changes, and behavior: Insights from neural systems biology

Long-term consequences of anesthetic exposure in humans are not well understood. It is possible that alterations in brain function occur beyond the initial anesthetic administration. Research in children and adults has reported cognitive and/or behavioral changes after surgery and general anesthesia that may be short lived in some patients, while in others, such changes may persist. The changes observed in humans are corroborated by a large body of evidence from animal studies that support a role for alterations in neuronal survival (neuroapoptosis) or structure (altered dendritic and glial morphology) and later behavioral deficits at older age after exposure to various anesthetic agents during fetal or early life. The potential of anesthetics to induce long-term alterations in brain function, particularly in vulnerable populations, warrants investigation. In this review, we critically evaluate the available preclinical and clinical data on the developing and aging brain, and in known vulnerable populations to provide insights into potential changes that may affect the general population of patients in a more, subtle manner. In addition this review summarizes underlying processes of how general anesthetics produce changes in the brain at the cellular and systems level and the current understanding underlying mechanisms of anesthetics agents on brain systems. Finally, we present how neuroimaging techniques currently emerge as promising approaches to evaluate and define changes in brain function resulting from anesthesia, both in the short and the long-term.

Lasting impact of general anaesthesia on the brain: mechanisms and relevance

General anaesthesia is usually considered to safely induce a reversible brain state allowing the performance of surgery under optimal conditions. An increasing number of clinical and experimental observations, however, suggest that anaesthetic drugs, especially when they are administered at the extremes of age, can trigger long-term morphological and functional alterations in the brain. Here, we review available mechanistic data linking general-anaesthesia exposure to impaired cognitive performance in both young and mature nervous systems. We also provide a critical appraisal of the translational value of animal models and highlight the important challenges that need to be addressed to strengthen the link between laboratory work and clinical investigations in the field of anaesthesia-neurotoxicity research.

Neuroinflammation, Mast Cells, and Glia: Dangerous Liaisons

The perspective of neuroinflammation as an epiphenomenon following neuron damage is being replaced by the awareness of glia and their importance in neural functions and disorders. Systemic inflammation generates signals that communicate with the brain and leads to changes in metabolism and behavior, with microglia assuming a pro-inflammatory phenotype. Identification of potential peripheral-to-central cellular links is thus a critical step in designing effective therapeutics. Mast cells may fulfill such a role. These resident immune cells are found close to and within peripheral nerves and in brain parenchyma/meninges, where they exercise a key role in orchestrating the inflammatory process from initiation through chronic activation. Mast cells and glia engage in crosstalk that contributes to accelerate disease progression; such interactions become exaggerated with aging and increased cell sensitivity to stress. Emerging evidence for oligodendrocytes, independent of myelin and support of axonal integrity, points to their having strong immune functions, innate immune receptor expression, and production/response to chemokines and cytokines that modulate immune responses in the central nervous system while engaging in crosstalk with microglia and astrocytes. In this review, we summarize the findings related to our understanding of the biology and cellular signaling mechanisms of neuroinflammation, with emphasis on mast cell-glia interactions.

Neurocognitive Adverse Effects of Anesthesia in Adults and Children: Gaps in Knowledge

Numerous preclinical and clinical studies investigating the neurodevelopmental and neurocognitive effects of exposure to anesthesia and the combination of anesthesia and surgery have demonstrated histopathological and both temporary and long-term cognitive and behavioral effects at the extremes of the human age spectrum. Increasing coverage in the lay press for both our youngest and oldest patient populations has led to heightened concerns regarding the potential harmful side effects of almost all commonly used anesthetic drug regimens. Although the majority of information regarding anesthetic risks in the developing brain derives from preclinical work in rodents, research involving the aged brain has identified a well-defined postoperative cognitive phenotype in humans. While preclinical and clinical data appear to support some association between anesthesia and surgery and the development of detrimental cognitive changes in both the developing and the aged brain, correlation between anesthesia and surgery and poor neurological outcomes does not imply causation. Given this information, no single anesthetic or group of anesthetics can be recommended over any other in terms of causing or preventing negative neurocognitive outcomes in either population. This review summarizes the growing body of preclinical and clinical literature dedicated to the detrimental effects of anesthesia on both the developing and the aging brain.

Specialized Pro-Resolving Mediators from Omega-3 Fatty Acids Improve Amyloid-β Phagocytosis and Regulate Inflammation in Patients with Minor Cognitive Impairment

In this review we discuss the immunopathology of Alzheimer's disease (AD) and recent advances in the prevention of minor cognitive impairment (MCI) by nutritional supplementation with omega-3 fatty acids. Defective phagocytosis of amyloid-β (Aβ) and abnormal inflammatory activation of peripheral blood mononuclear cells (PBMCs) are the two key immune pathologies of MCI and AD patients. The phagocytosis of Aβ by PBMCs of MCI and AD patients is universally defective and the inflammatory gene transcription is heterogeneously deregulated in comparison to normal subjects. Recent studies have discovered a cornucopia of beneficial anti-inflammatory and pro-resolving effects of the specialized proresolving mediators (SPMs) resolvins, protectins, maresins, and their metabolic precursors. Resolvin D1 and other mediators switch macrophages from an inflammatory to a tissue protective/pro-resolving phenotype and increase phagocytosis of Aβ. In a recent study of AD and MCI patients, nutritional supplementation by omega-3 fatty acids individually increased resolvin D1, improved Aβ phagocytosis, and regulated inflammatory genes toward a physiological state, but only in MCI patients. Our studies are beginning to dissect positive factors (adherence to Mediterranean diet with omega-3 and exercise) and negative factors (high fat diet, infections, cancer, and surgeries) in each patient. The in vitro and in vivo effects of omega-3 fatty acids and SPMs suggest that defective phagocytosis and chronic inflammation are related to defective production and/or defective signaling by SPMs in immune cells.

Evidence of an association between brain cellular injury and cognitive decline after non-cardiac surgery

BACKGROUND

Postoperative cognitive dysfunction (POCD) is common after non-cardiac surgery, but the mechanism is unclear. We hypothesized that decrements in cognition 1 month after non-cardiac surgery would be associated with evidence of brain injury detected by elevation of plasma concentrations of S100β, neuron-specific enolase (NSE), and/or the brain-specific protein glial fibrillary acid protein (GFAP).

METHODS

One hundred and forty-nine patients undergoing shoulder surgery underwent neuropsychological testing before and then 1 month after surgery. Plasma was collected before and after anaesthesia. We determined the relationship between plasma biomarker concentrations and individual neuropsychological test results and a composite cognitive functioning score (mean Z-score).

RESULTS

POCD (≥-1.5 sd decrement in Z-score from baseline) was present in 10.1% of patients 1 month after surgery. There was a negative relationship between higher plasma GFAP concentrations and lower postoperative composite Z-scores {estimated slope=-0.14 [95% confidence interval (CI) -0.24 to -0.04], P=0.005} and change from baseline in postoperative scores on the Rey Complex Figure Test copy trial (P=0.021), delayed recall trial (P=0.010), and the Symbol Digit Modalities Test (P=0.004) after adjustment for age, sex, history of hypertension and diabetes. A similar relationship was not observed with S100β or NSE concentrations.

CONCLUSIONS

Decline in cognition 1 month after shoulder surgery is associated with brain cellular injury as demonstrated by elevated plasma GFAP concentrations.

Haloperidol Suppresses NF-kappaB to Inhibit Lipopolysaccharide-Induced Pro-Inflammatory Response in RAW 264 Cells

Background

Haloperidol, a tranquilizing agent, is administered both to treat symptoms of psychotic disorders and to sedate agitated and delirious patients. Notably, haloperidol has been suggested to inhibit the immune response through unknown mechanisms. We hypothesized that the sedative modulates the immune response via NF-κB.

Material/Methods

Using flow cytometry, we analyzed the effects of haloperidol on expression CD80 and CD86 in RAW 264 cells and in primary macrophages derived from bone marrow. Secretion of interleukin (IL)-1β, IL-6, and IL-12 p40 was measured by enzyme-linked immunosorbent assay. In addition, NF-κB activation was evaluated using a reporter assay based on secretory embryonic alkaline phosphatase. Finally, synthetic antagonists were used to identify the dopamine receptor that mediates the effects of haloperidol.

Results

Haloperidol inhibited NF-κB activation, and thereby suppressed expression of CD80, as well as secretion of IL-1β, IL-6, and IL-12 p40. CD80 and IL-6 levels were similarly attenuated by a D2-like receptor antagonist, but not by a D1-like receptor antagonist.

Conclusions

The data strongly suggest that haloperidol inhibits the immune response by suppressing NF-κB signaling via the dopamine D2 receptor.

Association of Mild Cognitive Impairment With Exposure to General Anesthesia for Surgical and Nonsurgical Procedures: A Population-Based Study

OBJECTIVE

To examine whether exposure to general anesthesia for operations and procedures after the age of 40 years is associated with incident mild cognitive impairment (MCI) in elderly patients.

PATIENTS AND METHODS

A population-based, prospective cohort of Olmsted County, Minnesota, residents aged 70 to 89 years at enrollment, underwent baseline and 15-month interval evaluations that included the Clinical Dementia Rating scale, a neurologic evaluation, and neuropsychological testing. Anesthesia records after the age of 40 years until last evaluation for MCI were abstracted. Proportional hazards regression, adjusting for other known MCI risk factors, was used to assess whether exposure to surgical general anesthesia after the age of 40 years is associated with the incidence of MCI.

RESULTS

Of 1731 participants (mean age, 79 years), 536 (31.0%) developed MCI during a median follow-up of 4.8 years. Anesthesia exposure was not associated with MCI when analyzed as a dichotomous variable (any vs none; adjusted hazard ratio [HR], 1.07; 95% CI, 0.83-1.37; P=.61), the number of exposures (adjusted HR, 1.05; 95% CI, 0.78-1.42; adjusted HR, 1.12; 95% CI, 0.86-1.47; and adjusted HR, 1.02; 95% CI, 0.76-1.34, for 1, 2-3, and ≥4 exposures compared with no exposure as the reference; P=.73), or the total cumulative duration of exposure (adjusted HR, 1.00; 95% CI, 0.98-1.01, per 60-minute increase; P=.83). In secondary sensitivity analyses, anesthesia after 60 years of age was associated with incident MCI (adjusted HR, 1.25; 95% CI, 1.02-1.55; P=.04), as was exposure in the previous 20 and 10 years.

CONCLUSION

We found no significant association between cumulative exposure to surgical anesthesia after 40 years of age and MCI. However, these data do not exclude the possibility that anesthetic exposures occurring later in life may be associated with an increase in the rate of incident MCI.

Preoperative Cognitive and Frailty Screening in the Geriatric Surgical Patient: A Narrative Review

PURPOSE

The identification of older patients who may have deficits in cognitive or functional domains will become more pressing as increasing numbers of these patients present for preoperative evaluations. The number of older adults with deficiencies in these areas is projected to grow, and more of these patients will present for assessment in preoperative clinics with the expectation that surgeries will be performed.

METHODS

We review current outcomes data for preoperative cognitive impairment and frailty.

FINDINGS

We point to a number of directions research is taking as systems for the prevention of postoperative cognitive and functional decline are being developed. We also discuss the current status of screening and examine potential instruments that can be used in the setting of the preanesthesia clinic.

IMPLICATIONS

Clinicians may anticipate that geriatric screening tools focused on cognitive and functional domains will play a direct role in the ongoing evolution of presurgical assessment and triage.

Surgery is associated with ventricular enlargement as well as cognitive and functional decline

INTRODUCTION

In preclinical studies, surgery/anesthesia contribute to cognitive decline and enhance neuropathologic changes underlying Alzheimer's disease (AD). Nevertheless, the link between surgery, anesthesia, apolipoprotein E ε4 (APOE ε4), and AD remains unclear.

METHODS

We performed a retrospective cohort analysis of two prospective longitudinal aging studies. Mixed-effects statistical models were used to assess the relationship between surgical/anesthetic exposure, the APOE genotype, and rate of change in measures of cognition, function, and brain volumes.

RESULTS

The surgical group (n = 182) experienced a more rapid rate of deterioration compared with the nonsurgical group (n = 345) in several cognitive, functional, and brain magnetic resonance imaging measures. Furthermore, there was a significant synergistic effect of anesthesia/surgery exposure and presence of the APOE ε4 allele in the decline of multiple cognitive and functional measures.

DISCUSSION

These data provide insight into the role of surgical exposure as a risk factor for cognitive and functional decline in older adults.

Cerebral mast cells contribute to postoperative cognitive dysfunction by promoting blood brain barrier disruption

Trauma induced neuroinflammation plays a key role in the development of postoperative cognitive dysfunction (POCD). The blood-brain barrier (BBB), a highly specialized endothelial layer, is exquisitely sensitive to inflammatory insults, which can result in numerous neurocognitive syndromes. While brain mast cells are the "first responder" in the injury, the functional interactions between mast cells and the BBB remain poorly understood. Our results demonstrate that tibial fracture surgery can induce cognitive impairment relating to an inflammatory response and destabilization of the BBB. Disodium cromoglycate (cromolyn)--which acts as a mast cell stabilizer--inhibited this effect. Specifically, cromolyn resulted in ameliorated cognitive ability, decrease of inflammatory cytokines and increase of BBB stability. Taken together, these results suggest that activated mast cells contributed to central nervous system inflammation and cognitive dysfunction by promoting BBB disruption, and interactions between mast cells and the BBB could constitute a new and unique therapeutic target for POCD.

Exposure to general anesthesia and the risk of dementia

Exposure to anesthesia and surgery has been hypothesized to increase the risk of developing Alzheimer's disease (AD). While the exact pathogenesis of AD remains unknown, it potentially involves specific proteins (eg, amyloid beta and tau) and neuroinflammation. A growing body of preclinical evidence also suggests that anesthetic agents interact with the components that mediate AD neuropathology at multiple levels. However, it remains unclear whether anesthesia and surgery are associated with an increased risk of AD in humans. To date, there have not been randomized controlled trials to provide evidence for such a causal relationship. Besides, observational studies showed inconsistent results. A meta-analysis of 15 case-control studies revealed no statistically significant association between general anesthesia and the development of AD (pooled odds ratio [OR] =1.05; P=0.43). However, a few retrospective cohort studies have demonstrated that exposure to anesthesia and surgery is associated with an increased risk of AD. Thus, well-designed studies with longer follow-up periods are still needed to define the role of anesthesia in relation to the development of AD.

Pre-administration of curcumin prevents neonatal sevoflurane exposure-induced neurobehavioral abnormalities in mice

Sevoflurane, a commonly used inhaled anesthetic, can induce neuronal apoptosis in the developing rodent brain and correlate with functional neurological impairment later in life. However, the mechanisms underlying these deleterious effects of sevoflurane remain unclear and no effective treatment is currently available. Herein, the authors investigated whether curcumin can prevent the sevoflurane anesthesia-induced cognitive impairment in mice. Six-day-old C57BL/6 mice were exposed to 3% sevoflurane 2h daily for 3 consecutive days and were treated with curcumin at the dose of 20 mg/kg or vehicle 30 min before the sevoflurane anesthesia from postnatal days 6 (P6) to P8. Cognitive functions were evaluated by open field, Morris water maze, and fear conditioning tests on P61, P63-69, and P77-78, respectively. In another separate experiment, mice were killed on day P8 or P78, and the brain tissues were harvested and then subjected to biochemistry studies. Our results showed that repeated neonatal sevoflurane exposure led to significant cognitive impairment later in life, which was associated with increased neuronal apoptosis, neuroinflammation, oxidative nitrosative stress, and decreased memory related proteins. By contrast, pre-administration of curcumin ameliorated early neuronal apoptosis, neuroinflammation, oxidative nitrosative stress, memory related proteins, and later cognitive dysfunction. In conclusion, our data suggested that curcumin pre-administration can prevent the sevoflurane exposure-induced cognitive impairment later in life, which may be partly attributed to its ability to attenuate the neural apoptosis, inflammation, and oxidative nitrosative stress in mouse brain.

Prolonged neuroinflammation after lipopolysaccharide exposure in aged rats

Inflammation is a hallmark of several disease states ranging from neurodegeneration to sepsis but is also implicated in physiological processes like ageing. Non-resolving inflammation and prolonged neuroinflammation are unclear processes implicated in several conditions, including ageing. In this study we studied the long-term effects of endotoxemia, as systemic lipopolysaccharide (LPS) injection, focusing on the role of astrocyte activation and cytokine release in the brain of aged rats. A single dose of LPS (2 mg/kg) or 0.9% saline was injected intraperitoneally in aged rats. Levels of pro-inflammatory cytokines (TNFα and IL-1β) and NF-κB p65 activation were measured systemically and in hippocampal tissue. Astrocytes and cytokines release in the CNS were detected via double immunofluorescence staining at different time-points up to day 30. Serum levels of TNFα and IL-1β were significantly increased acutely after 30 minutes (p<0.001) and up to 6 hours (p<0.001) following LPS-injection. Centrally, LPS-treated rats showed up-regulated mRNA expression and protein levels of pro-inflammatory cytokines in the hippocampus. These changes associated with astrogliosis in the hippocampus dentate gyrus (DG), IL-1β immunoreactivity and elevated NF-κB p65 expression up to day 30 post LPS exposure. Overall, these data demonstrate that LPS induces prolonged neuroinflammation and astrocyte activation in the hippocampus of aged rats. Hippocampal NF-κB p65 and excessive astrocytes-derived IL-1β release may play a pivotal role in regulating long-lasting neuroinflammation.

Cerebral protection: inflammation, endothelial dysfunction, and postoperative cognitive dysfunction

PURPOSE OF REVIEW

Postoperative cognitive dysfunction (POCD) is a well recognized perioperative syndrome, with approximately 15% of patients over the age of 60 years displaying objectively measured decrease in cognitive function as a consequence of anesthesia and surgery. The exact cause, however, remains unknown. This review aims to update anesthesiologists on the recent advancements in the understanding of the pathophysiology of POCD.

RECENT FINDINGS

Recent evidence suggests that the observed predilection to POCD is likely mediated by a neuro-inflammatory response - with surgery being a major contributing factor. The blood-brain barrier, a highly specialized endothelial layer, is exquisitely sensitive to an inflammatory insult and implicated in the cause of other neurocognitive syndromes also characterized by neuro-inflammation such as cerebral malaria. Inflammatory changes may disrupt the blood-brain barrier and facilitate migration of macrophages into the brain, damaging synapses and neurones and ultimately lead to POCD. This review explores the important question of causality - the potential relationship between inflammation, endothelial dysfunction, and postoperative cognitive decline.

SUMMARY

Recent research points to a central role of a neuro-inflammatory cascade in POCD, with endothelial dysfunction potentially aggravating the insult. Investigating the genomic and molecular mechanisms that underlie the intervariation in the inflammatory response to surgery, improving the identification of appropriate endothelial and inflammatory biomarkers, and developing endothelial modulatory and anti-inflammatory (prevention and resolution) strategies are key areas of future translational research. This is important as the elderly, who show increased susceptibility to this and other perioperative illness syndromes, represent an ever-increasing proportion of patients presenting for surgery.

Hereditary vulnerabilities to post-operative cognitive dysfunction and dementia

In view of multiple prospective investigations reporting an incidence of 10% or greater in elderly patients after cardiac and non-cardiac procedures, it is surprising that no families, twins or even individual cases have been reported with persistent post-operative cognitive dysfunction (POCD) or post-operative dementia (POD) that is otherwise unexplained. As POCD and POD research has shifted in recent years from surgical and anesthetic variables to predictors of intrinsic, patient-specific susceptibility, a number of markers based on DNA sequence variation have been investigated. Nevertheless, no heritable, genomic indices of persistent POCD or post-operative dementia lasting 3 months or longer after surgery have been identified to date. The present manuscript surveys challenges confronting the search for markers of heritable vulnerability to POCD and POD, and proposes steps forward to be taken now, including the addition of surgical and anesthetic descriptors to ongoing longitudinal dementia protocols and randomized clinical trials (RCTs) comprising serial psychometric testing, and a fresh focus on phenotypes and genotypes shared between outliers with "extreme" POCD and POD traits.

Perioperative delirium and its relationship to dementia

A number of serious clinical cognitive syndromes occur following surgery and anesthesia. Postoperative delirium is a behavioral syndrome that occurs in the perioperative period. It is diagnosed through observation and characterized by a fluctuating loss of orientation and confusion. A distinct syndrome that requires formalized neurocognitive testing is frequently referred to as postoperative cognitive dysfunction (POCD). There are serious concerns as to whether either postoperative delirium or postoperative cognitive dysfunction leads to dementia. These concerns are reviewed in this article.

Surgery upregulates high mobility group box-1 and disrupts the blood-brain barrier causing cognitive dysfunction in aged rats

AIM

Postoperative cognitive dysfunction (POCD) is a growing and largely underestimated problem without defined etiology. Herein, we sought to determine the relationship between cognitive decline, blood-brain barrier (BBB) permeability, and inflammation, namely high mobility group box-1 (HMGB1), after surgery in aged rats.

METHODS

Aged rats were randomly assigned as surgery group (n = 45, splenectomy under general anesthesia), anesthesia (n = 45, 2% isoflurane for 2 h), and naïve control (n = 15). Markers of inflammation were measured in plasma and brain. Blood-brain barrier ultrastructure and permeability were measured by transmission electron microscope (TEM) and IgG immunohistochemistry. Cognitive function was assessed in a reversal learning version of the Morris water maze (MWM).

RESULTS

Surgical trauma under general anesthesia caused distinct changes in systemic and central proinflammatory cytokines. Levels of HMGB1 and the receptor for advanced glycation end products (RAGE) were significantly upregulated in the hippocampus of operated animals. Immunohistochemistry and TEM showed BBB disruption induced by surgery and anesthesia. These molecular changes were associated with cognitive impairment in latency with the MWM up to postoperative day 3.

CONCLUSIONS

HMGB1 and RAGE signaling appear pivotal mediators of surgery-induced cognitive decline and may contribute to the changes in BBB permeability after peripheral surgical trauma.