Cerebrospinal fluid markers of neuroinflammation in delirium: a role for interleukin-1β in delirium after hip fracture

Biomarker Predictors of Delirium in Acutely Ill Patients: A Systematic Review

Delirium is a serious and common disorder that affects up to 80% of acutely ill patients, mainly the aged. In recent years, several studies pointed out possible biomarkers that could be used alone or in combination with other resources in the diagnosis and follow-up of critically ill patients who develop delirium. In this context, a systematic review was conducted to determine the predictive value of several biomarkers in acutely (critically and noncritically) ill adult patients with delirium. Studies that used the confusion assessment method (CAM) and CAM-intensive care unit as the diagnostic method were considered. The most recent search was performed in November 2017. There was no language restriction. Initially, 626 articles were screened and 39 were included in the study. A comprehensive evaluation of the abstracts resulted in the exclusion of 202 studies, leaving 39 articles as potentially relevant. Inflammatory markers, S100β and cortisol, could predict delirium occurrence in a specific subgroup population of critically ill patients.

The INTUIT Study: Investigating Neuroinflammation Underlying Postoperative Cognitive Dysfunction

BACKGROUND/OBJECTIVES

Every year, up to 40% of the more than 16 million older Americans who undergo anesthesia/surgery develop postoperative cognitive dysfunction (POCD) or delirium. Each of these distinct syndromes is associated with decreased quality of life, increased mortality, and a possible increased risk of Alzheimer's disease. One pathologic process hypothesized to underlie both delirium and POCD is neuroinflammation. The INTUIT study described here will determine the extent to which postoperative increases in cerebrospinal fluid (CSF) monocyte chemoattractant protein 1 (MCP-1) levels and monocyte numbers are associated with delirium and/or POCD and their underlying brain connectivity changes.

DESIGN

Observational prospective cohort.

SETTING

Duke University Medical Center, Duke Regional Hospital, and Duke Raleigh Hospital.

PARTICIPANTS

Patients 60 years of age or older (N = 200) undergoing noncardiac/nonneurologic surgery.

MEASUREMENTS

Participants will undergo cognitive testing before, 6 weeks, and 1 year after surgery. Delirium screening will be performed on postoperative days 1 to 5. Blood and CSF samples are obtained before surgery, and 24 hours, 6 weeks, and 1 year after surgery. CSF MCP-1 levels are measured by enzyme-linked immunosorbent assay, and CSF monocytes are assessed by flow cytometry. Half the patients will also undergo pre- and postoperative functional magnetic resonance imaging scans. 32-channel intraoperative electroencephalogram (EEG) recordings will be performed to identify intraoperative EEG correlates of neuroinflammation and/or postoperative cognitive resilience. Eighty patients will also undergo home sleep apnea testing to determine the relationships between sleep apnea severity, neuroinflammation, and impaired postoperative cognition. Additional assessments will help evaluate relationships between delirium, POCD, and other geriatric syndromes.

CONCLUSION

INTUIT will use a transdisciplinary approach to study the role of neuroinflammation in postoperative delirium and cognitive dysfunction and their associated functional brain connectivity changes, and it may identify novel targets for treating and/or preventing delirium and POCD and their sequelae. J Am Geriatr Soc 67:794-798, 2019.

Acute transient cognitive dysfunction and acute brain injury induced by systemic inflammation occur by dissociable IL-1-dependent mechanisms

Systemic inflammation can impair cognition with relevance to dementia, delirium and post-operative cognitive dysfunction. Episodes of delirium also contribute to rates of long-term cognitive decline, implying that these acute events induce injury. Whether systemic inflammation-induced acute dysfunction and acute brain injury occur by overlapping or discrete mechanisms remains unexplored. Here we show that systemic inflammation, induced by bacterial LPS, produces both working-memory deficits and acute brain injury in the degenerating brain and that these occur by dissociable IL-1-dependent processes. In normal C57BL/6 mice, LPS (100 µg/kg) did not affect working memory but impaired long-term memory consolidation. However prior hippocampal synaptic loss left mice selectively vulnerable to LPS-induced working memory deficits. Systemically administered IL-1 receptor antagonist (IL-1RA) was protective against, and systemic IL-1β replicated, these working memory deficits. Dexamethasone abolished systemic cytokine synthesis and was protective against working memory deficits, without blocking brain IL-1β synthesis. Direct application of IL-1β to ex vivo hippocampal slices induced non-synaptic depolarisation and irreversible loss of membrane potential in CA1 neurons from diseased animals and systemic LPS increased apoptosis in the degenerating brain, in an IL-1RI-dependent fashion. The data suggest that LPS induces working memory dysfunction via circulating IL-1β but direct hippocampal action of IL-1β causes neuronal dysfunction and may drive neuronal death. The data suggest that acute systemic inflammation produces both reversible cognitive deficits, resembling delirium, and acute brain injury contributing to long-term cognitive impairment but that these events are mechanistically dissociable. These data have significant implications for management of cognitive dysfunction during acute illness.

CSF biomarkers in delirium: a systematic review

OBJECTIVE

In recent years, there has been a blossoming of studies examining cerebrospinal fluid (CSF) as a method of studying the pathophysiology of delirium. We systematically reviewed the literature for CSF studies in delirium and provide here a summary of the implications for our understanding of delirium pathophysiology. We also summarise the methods used for CSF analysis and discuss challenges and implications for future studies.

METHODS

In this systematic review, we screened MEDLINE, EMBASE, PsycINFO, Web of Science, PubMed and the Cochrane Library for articles on CSF biomarkers in delirium, published on 3 September 2016. Studies were required to use Diagnostic and Statistical Manual of Mental Disorders or International Classification of Diseases criteria for delirium or a validated tool. We excluded case reports. There were no other restrictions on study type.

RESULTS

We identified 3280 articles from our initial search, and 22 articles were included in this review. All studies were prospective, including over 400 patients with delirium and 700 controls. More than 70 different biomarkers were studied. Studies could not be compared with each other for meta-analysis because of their heterogeneity and varied widely in their risk of bias and quality assessments.

CONCLUSIONS

The 22 studies identified in this review reveal a small but growing literature, in which many of the important hypotheses in delirium pathogenesis have been examined, but from which few firm conclusions can currently be drawn. Nevertheless, the overall interpretation of the literature supports the vulnerable brain concept, that is, that biomarker evidence of, for example, Alzheimer's disease pathology and/or neuroinflammation, is associated with delirium.

CSF sodium at toxic levels precedes delirium in hip fracture patients

Delirium is an acute state of confusion and a fluctuating level of consciousness. It is precipitated by physical illness or trauma, such as pneumonia, heart infarction, or hip fracture. Delirium is common among elderly hospitalized patients, and as many as 50% of hip fracture patients may develop delirium. Delirium may precipitate dementia, but recent studies indicate that delirium is caused by unknown neurotoxic mechanisms that are different from those that are associated with dementia. Experimental studies have shown that high extracellular levels of sodium are neurotoxic. We sampled lumbar cerebrospinal fluid (CSF) from hip fracture patients during hip surgery and analyzed metal ions that influence neuronal function. Eight patients who developed delirium after surgery had 21% higher CSF sodium than 17 patients who did not develop delirium (median value 175 mmol/L; range 154-188, vs. 145 mmol/L (112-204; p < 0.008) or 39 patients who underwent elective surgery under spinal anesthesia without developing delirium (145 mmol/L; 140-149; p = 0.0004). Seven patients who had developed delirium before CSF sampling had a median CSF sodium of 150 mmol/L (144-185; p = 0.3). CSF potassium was also 21% higher in patients who developed delirium (p = 0.024), but remained within the physiological range. Serum sodium and potassium were normal in all patient groups. This study, on a small sample of patients, confirms the neurotoxic potential and clinical importance of high extracellular levels of sodium in the brain. High CSF sodium would likely affect cerebral function and could precipitate delirium; further, it could interact with dementia-specific mechanisms to precipitate dementia development.

Anesthetic Immunomodulation of the Neuroinflammation in Postoperative Cognitive Dysfunction

Postoperative delirium and cognitive dysfunction are phenomena that are associated with increases in morbidity, mortality, and resource utilization after surgery. This review scrutinized a number of studies in order to better characterize the biochemical basis for associated cognitive dysfunction and delirium, with particular focus paid to the interactions of the cholinergic system with innate immunity and how the modulation of the immune system contributes to associated neuroinflammation. Despite the clinical impact of postoperative cognitive dysfunction, evidence-based protocols for the prevention and treatment of these disorders are still lacking. Several previous trials have attempted to prevent or treat clinical manifestation by modulation of the cholinergic system with acetylcholinesterase inhibitors, the results of which have been largely ambiguous at best. As the biochemical basis of postoperative cognitive dysfunction becomes more clearly defined, future research into therapeutics based on immune modulation and treatment of neuroinflammation may prove to be very promising.

Impact of dexmedetomidine infusion during general anaesthesia on incidence of postoperative delirium in elderly patients after major non-cardiac surgery: study protocol of a randomised, double-blinded and placebo-controlled trial

INTRODUCTION

Delirium is a common complication in the elderly after surgery and is associated with worse outcomes. Multiple risk factors are related with postoperative delirium, such as exposure to general anaesthetics, pain and postoperative inflammatory response. Preclinical and clinical studies have shown that dexmedetomidine attenuated neurotoxicity induced by general anaesthetics, improved postoperative analgesia and inhibited inflammatory response after surgery. Several studies found that intraoperative use of dexmedetomidine can prevent postoperative delirium, but data were inconsistent. This study was designed to investigate the impact of dexmedetomidine administered during general anaesthesia in preventing delirium in the elderly after major non-cardiac surgery.

METHODS AND ANALYSIS

This is a randomised, double-blinded and placebo-controlled trial. 620 elderly patients (age ≥60 years) who are scheduled to undertake elective major non-cardiac surgery (with an expected duration ≥2 hours) are randomly divided into two groups. For patients in the dexmedetomidine group, a loading dose dexmedetomidine (0.6 µg/kg) will be administered 10 min before anaesthesia induction, followed by a continuous infusion at a rate of 0.5 µg/kg/hour until 1 hour before the end of surgery. For patients in the control group, normal saline will be administered with an identical rate as in the dexmedetomidine group. The primary endpoint is the incidence of delirium during the first five postoperative days. The secondary endpoints include pain intensity, cumulative opioid consumption and subjective sleep quality during the first three postoperative days, as well as the incidence of non-delirium complications and all-cause mortality within 30 days after surgery.

ETHICS AND DISSEMINATION

The study protocol was approved by the Clinical Research Ethics Committee of Peking University First Hospital (2015-987) and registered at Chinese Clinical Trial Registry (http://www.chictr.org.cn) with identifier ChiCTR-IPR-15007654. The results of the study will be presented at academic conferences and submitted to peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ChiCRR-IPR-15007654; Pre-results.

Inflammatory markers in postoperative delirium (POD) and cognitive dysfunction (POCD): A meta-analysis of observational studies

Background

The aim of this study was to summarize and discuss the similarities and differences in inflammatory biomarkers in postoperative delirium (POD) and cognitive dysfunction (POCD).

Methods

A systematic retrieval of literature up to June 2017 in PubMed, Embase, the Cochrane Library, the China National Knowledge Infrastructure database, and the Wanfang database was conducted. Extracted data were analyzed with STATA (version 14). The standardized mean difference (SMD) and the 95% confidence interval (95% CI) of each indicator were calculated using a random effect model. We also performed tests of heterogeneity, sensitivity analysis, assessments of bias, and meta-regression in this meta-analysis.

Results

A total of 54 observational studies were included. By meta-analysis we found significantly increased C-reactive protein (CRP) (9 studies, SMD 0.883, 95% CI 0.130 to 1.637, P = 0.022 in POD; 10 studies, SMD -0.133, 95% CI -0.512 to 0.246, P = 0.429 in POCD) and interleukin (IL)-6 (7 studies, SMD 0.386, 95% CI 0.054 to 0.717, P = 0.022 in POD; 16 studies, SMD 0.089, 95% CI -0.133 to 0.311, P = 0.433 in POCD) concentrations in both POD and POCD patients. We also found that the SMDs of CRP and IL-6 from POCD patients were positively correlated with surgery type in the meta-regression (CRP: Coefficient = 1.555365, P = 0.001, 10 studies; IL-6: Coefficient = -0.6455521, P = 0.086, 16 studies).

Conclusion

Available evidence from medium-to-high quality observational studies suggests that POD and POCD are indeed correlated with the concentration of peripheral and cerebrospinal fluid (CSF) inflammatory markers. Some of these markers, such as CRP and IL-6, play roles in both POD and POCD, while others are specific to either one of them.

Impact on the brain of the inflammatory response to surgery

The brain is both the orchestrator as well as the target of the innate immune system's response to the aseptic trauma of surgery. When trauma-induced inflammation is not appropriately regulated persistent neuro-inflammation interferes with the synaptic plasticity that underlies the learning and memory aspects of cognition. The complications that ensue, include postoperative delirium (POD) and postoperative cognitive dysfunction (POCD) at two poles of a constellation that is now termed perioperative neurocognitive disorders. While the relationship of acute POD to the more indolent POCD is not completely understood both can be further complicated by earlier-onset of dementia and higher mortality. How and why these disorders occur is the focus of this report. The innate immune system response to peripheral trauma signals to the brain through a regulated cascade of cellular and molecular actors producing a teleological defense mechanism, "sickness behavior," to curtail further injury and initiate repair. Sickness behavior, including disordered cognition, is terminated by neural and humoral pathways that restore homeostasis and launch the organism on a path to good health. With so many "moving parts" the innate immune system is vulnerable in clinical settings that include advanced age and lifestyle-induced diseases such as "unhealthy" obesity and the inevitable insulin resistance. Under these conditions, inflammation may become exaggerated and long-lived. Consideration is provided how to identify the high-risk surgical patient and both pharmacological (including biological compounds) and non-pharmacological strategies to customize care.

Exploring Postoperative Cognitive Dysfunction and Delirium in Noncardiac Surgery Using MRI: A Systematic Review

Surgical patients are at high risk of developing postoperative cognitive dysfunction (POCD) and postoperative delirium (POD). POCD and POD are associated with increased morbidity and mortality and worsening functional outcomes leading to severe socioeconomic consequences for the patient and the society in general. Magnetic resonance imaging (MRI) offers a unique opportunity to study the anatomy and function of the brain. MRI thus plays an important role in elucidating the neuronal component of POCD and POD. Our aim has been to systematically gather MRI findings that are related to POCD and POD. Systematic searches were conducted in PubMed, EMBASE, and PsycINFO: MRI studies investigating patients with POCD as identified by perioperative cognitive testing or patients with delirium identified postoperatively by the Confusion Assessment Method. A total of ten eligible papers were included with a total of 269 surgical patients, 36 patient controls, and 55 healthy controls who all underwent MRI examination. These studies suggested that reduction of thalamic and hippocampal volumes and reduction of cerebral blood flow may be associated with POCD, while presurgery/preexisting and postoperative white matter pathology may be associated with POD. However, the evidence from these studies is rather weak. Future MRI studies are warranted to verify the current findings.

Interleukin-6 is both necessary and sufficient to produce perioperative neurocognitive disorder in mice

BACKGROUND

Perioperative neurocognitive disorders (PND) result in long-term morbidity and mortality with no effective interventions available. Because interleukin-6 (IL-6), a pro-inflammatory cytokine, is consistently up-regulated by trauma, including after surgery, we determined whether IL-6 is a putative therapeutic target for PND in a mouse model.

METHODS

Following institutional approval, adult (12-14 weeks) male C57/Bl6 mice were pretreated with the IL-6 receptor (IL6R) blocking antibody tocilizumab prior to open tibia fracture with internal fixation under isoflurane anaesthesia. Inflammatory and behavioural responses in a trace fear conditioning (TFC) paradigm were assessed postoperatively. Separately, the effects of IL-6 administration or of depletion of bone marrow-derived monocytes (BM-DMs) with clodrolip on the inflammatory and behavioural responses were assessed. Blood brain barrier disruption, hippocampal microglial activation, and infiltration of BM-DMs were each assessed following IL-6 administration.

RESULTS

The surgery-induced decrement in freezing time in the TFC assay, indicative of cognitive decline, was attenuated by tocilizumab (P<0.01). The surgery-induced increase in pro-inflammatory mediators was significantly reduced by tocilizumab. Exogenously administered IL-6 significantly impaired freezing behaviour (P<0.05) and up-regulated pro-inflammatory cytokines; both responses were prevented by depletion of BM-DMs. IL-6 disrupted the blood brain barrier, and increased hippocampal activation of microglia and infiltration of BM-DMs.

CONCLUSIONS

IL-6 is both necessary and sufficient to produce cognitive decline. Following further preclinical testing of its perioperative safety, the IL6R blocker tocilizumab is a candidate for prevention and/or treatment of PND.

Acute Sarcopenia Secondary to Hospitalisation - An Emerging Condition Affecting Older Adults

There has been increasing interest and research into sarcopenia in community-dwelling older adults since the European Working Group on Sarcopenia in Older People (EWGSOP) agreed a consensus definition in 2010. Sarcopenia has been defined as loss of muscle mass with loss of muscle function (strength or physical performance), with measurements two Standard Deviations (SDs) below the mean of a young reference population. This definition does not necessitate longitudinal measurements, or the absence of acute illness and diagnosis can be made from single measurements. We hypothesise that hospitalisation, due to a combination of acute inflammatory burden and muscle disuse, leads to an acute decline in muscle mass and function and may lead to some individuals meeting criteria for sarcopenia, acutely, based on the EWGSOP definition. This may be partially recoverable or may lead to increased risk of developing sarcopenia long-term. We have denoted the term “acute sarcopenia” to refer to acute loss of muscle mass and function associated with hospitalisation. This review discusses some of the current available research in this context and also identifies some of the knowledge gaps and potential areas for future research.

Hypertonic saline for prevention of delirium in geriatric patients who underwent hip surgery

BACKGROUND

Postoperative delirium (POD) is a common disorder in the elderly patients, and neuroinflammation is the possible underlying mechanism. This study is designed to determine whether or not hypertonic saline (HS) pre-injection can alleviate POD in aged patients.

METHODS

This prospective study recruited 120 geriatric patients who underwent hip surgery. The patients were randomly divided into two groups: control group (NS group) and HS group. Patients in the NS group were pre-injected with 4 mL/kg isotonic saline, and those in the HS group were pre-injected with 4 mL/kg 7.5% HS. All 120 patients were then subjected to general anesthesia. Blood samples were extracted to detect the concentration of inflammatory factors, namely, IL-1β, IL-6, IL-10, and TNF-α, and the nerve injury factor S100β. Flow cytometry was used to detect the number of monocytes in peripheral venous blood and evaluate the relationship of inflammation to delirium. The nursing delirium screening scale (Nu-DESC) was used to determine cognitive function 1 to 3 days postoperatively.

RESULTS

Analysis using random-effect multivariable logistic regression indicated that HS administration before anesthesia was associated with a low risk of POD (odds ratio [OR], 0.13; 95% CI, 0.04 to 0.41; P = 0.001) and few CD14 + CD16+ monocytes (β = - 0.61; 95% CI, - 0.74 to - 0.48; P = 0.000) the following day. When the association between HS and delirium was controlled for CD14 + CD16+ monocytes, the effect size became nonsignificant (odds ratio [OR], 0.86; 95% CI, 0.14 to 5.33; P = 0.874). TNF-α was significantly associated with POD (odds ratio [OR], 1.10; 95% CI, 1.05 to 1.16; P = 0.000). However, IL-1β, IL-6, IL-10, and S100β were not significantly related to POD.

CONCLUSION

HS can alleviate POD in geriatric patients and may inhibit the secretion of inflammatory factors by monocytes.

Evaluation of early administration of simvastatin in the prevention and treatment of delirium in critically ill patients undergoing mechanical ventilation (MoDUS): a randomised, double-blind, placebo-controlled trial

BACKGROUND

Delirium in critically ill patients is associated with poor clinical outcomes. Neuroinflammation might be an important mechanism in the pathogenesis of delirium, and since simvastatin has anti-inflammatory properties it might reduce delirium. We aimed to establish whether early treatment with simvastatin would decrease the time that survivors of critical illness spent in delirium or coma.

METHODS

We undertook this randomised, double-blind, placebo-controlled trial in a general adult intensive care unit (ICU) in Watford General Hospital (Watford, UK). We enrolled critically ill patients (≥18 years) needing mechanical ventilation within 72 h of admission. We randomly assigned patients (1:1 ratio) to receive either simvastatin 80 mg or placebo daily for up to a maximum of 28 days, irrespective of coma or delirium status. We assessed delirium using the Confusion Assessment Method for the ICU (CAM-ICU). The primary outcome was number of days alive and was assessed as delirium-free and coma-free in the first 14 days after being randomly allocated to receive treatment or placebo. ICU clinical and research staff and patients were masked to treatment. We did intention-to-treat analyses with no extrapolation. This trial is registered with the International Standard Randomised Controlled Trial Registry, number ISRCTN89079989.

FINDINGS

Between Feb 1, 2013, and July 29, 2016, 142 patients were randomly assigned to receive simvastatin (n=71) or placebo (n=71), and were included in the final analysis. The mean number of days alive without delirium and without coma at day 14 did not differ significantly between the two groups (5·7 days [SD 5·1] with simvastatin and 6·1 days [5·2] with placebo; mean difference 0·4 days, 95% CI -1·3 to 2·1; p=0·66). The most common adverse event was an elevated creatine kinase concentration to more than ten times the upper limit of normal (eight [11%] in the simvastatin group vs three [4%] in the placebo group p=0·208). No patient had a serious adverse event related to the study drug.

INTERPRETATION

These results do not support the hypothesis that simvastatin modifies duration of delirium and coma in critically ill patients.

FUNDING

National Institute for Health Research.

The Alarmin HMGB1 Mediates Age-Induced Neuroinflammatory Priming

Amplified neuroinflammatory responses following an immune challenge occur with normal aging and can elicit or exacerbate neuropathology. The mechanisms mediating this sensitized or "primed" immune response in the aged brain are not fully understood. The alarmin high mobility group box 1 (HMGB1) can be released under chronic pathological conditions and initiate inflammatory cascades. This led us to investigate whether HMGB1 regulates age-related priming of the neuroinflammatory response. Here, we show that HMGB1 protein and mRNA were elevated in the hippocampus of unmanipulated aged rats (24-month-old F344XBN rats). Furthermore, aged rats had increased HMGB1 in the CSF, suggesting increased HMGB1 release. We demonstrate that blocking HMGB1 signaling with an intracisterna magna (ICM) injection of the competitive antagonist to HMGB1, Box-A, downregulates basal expression of several inflammatory pathway genes in the hippocampus of aged rats. This indicates that blocking the actions of HMGB1 might reduce age-associated inflammatory priming. To test this hypothesis, we evaluated whether HMGB1 antagonism blocks the protracted neuroinflammatory and sickness response to peripheral Escherichia coli (E. coli) infection in aged rats. ICM pretreatment of aged rats with Box-A 24 h before E. coli infection prevented the extended hippocampal cytokine response and associated cognitive and affective behavioral changes. ICM pretreatment with Box-A also inhibited aging-induced potentiation of the microglial proinflammatory response to lipopolysaccharide ex vivo Together, these results suggest that HMGB1 mediates neuroinflammatory priming in the aged brain. Blocking the actions of HMGB1 appears to "desensitize" aged microglia to an immune challenge, thereby preventing exaggerated behavioral and neuroinflammatory responses following infection.

SIGNIFICANCE STATEMENT

The world's population is aging, highlighting a need to develop treatments that promote quality of life in aged individuals. Normal aging is associated with precipitous drops in cognition, typically following events that induce peripheral inflammation (e.g., infection, surgery, heart attack). Peripheral immune stimuli cause exaggerated immune responses in the aged brain, which likely underlie these behavioral deficits. Here, we investigated whether the alarmin high mobility group box 1 (HMGB1) mediates age-associated "priming" of the neuroinflammatory response. HMGB1 is elevated in aged rodent brain and CSF. Blocking HMGB1 signaling downregulated expression of inflammatory pathway genes in aged rat brain. Further, HMGB1 antagonism prevented prolonged infection-induced neuroinflammatory and sickness responses in aged rats. Overall, blocking HMGB1 "desensitized" microglia in the aged brain, thereby preventing pathological infection-elicited neuroinflammatory responses.

Pathophysiological and behavioral effects of systemic inflammation in aged and diseased rodents with relevance to delirium: A systematic review

Delirium is a frequent outcome for aged and demented patients that suffer a systemic inflammatory insult. Animal models that reconstruct these etiological processes have potential to provide a better understanding of the pathophysiology of delirium. Therefore, we systematically reviewed animal studies in which systemic inflammation was superimposed on aged or diseased animal models. In total, 77 studies were identified. Aged animals were challenged with a bacterial endotoxin in 29 studies, 25 studies superimposed surgery on aged animals, and in 6 studies a bacterial infection, Escherichia coli (E. coli), was used. Diseased animals were challenged with a bacterial endotoxin in 15 studies, two studies examined effects of the cytokine IL-1β, and one study used polyinosinic:polycytidilic acid (poly I:C). This systematic review analyzed the impact of systemic inflammation on the production of inflammatory and neurotoxic mediators in peripheral blood, cerebrospinal fluid (CSF), and on the central nervous system (CNS). Moreover, concomitant behavioral and cognitive symptoms were also evaluated. Finally, outcomes of behavioral and cognitive tests from animal studies were compared to features and symptoms present in delirious patients.

Glial Fibrillary Acidic Protein and Ubiquitin C-Terminal Hydrolase-L1 Are Not Specific Biomarkers for Mild CT-Negative Traumatic Brain Injury

Glial fibrillary acidic protein (GFAP) and ubiquitin C-terminal hydrolase-L1 (UCH-L1) have been studied as potential biomarkers of mild traumatic brain injury (mTBI). We report the levels of GFAP and UCH-L1 in patients with acute orthopedic injuries without central nervous system involvement, and relate them to the type of extracranial injury, head magnetic resonance imaging (MRI) findings, and levels of GFAP and UCH-L1 in patients with CT-negative mTBI. Serum UCH-L1 and GFAP were longitudinally measured from 73 patients with acute orthopedic injury on arrival and on days 1, 2, 3, 7 after admission, and on the follow-up visit 3-10 months after the injury. The injury types were recorded, and 71% patients underwent also head MRI. The results were compared with those found in patients with CT-negative mTBI (n = 93). The levels of GFAP were higher in patients with acute orthopedic trauma than in patients with CT-negative mTBI (p = 0.026) on arrival; however, no differences were found on the following days. The levels of UCH-L1 were not significantly different between these two groups at any measured point of time. Levels of GFAP and UCH-L1 were not able to distinguish patients with CT-negative mTBI from patients with orthopedic trauma. Patients with orthopedic trauma and high levels of UCH-L1 or GFAP values may be falsely diagnosed as having a concomitant mTBI, predisposing them to unwarranted diagnostics and unnecessary brain imaging. This casts a significant doubt on the diagnostic value of GFAP and UCH-L1 in cases with mTBI.

Higher C-Reactive Protein Levels Predict Postoperative Delirium in Older Patients Undergoing Major Elective Surgery: A Longitudinal Nested Case-Control Study

BACKGROUND

Delirium is a common, morbid, and costly postoperative complication. We aimed to identify blood-based postoperative delirium markers in a nested case-control study of older surgical patients using a proteomics approach followed by enzyme-linked immunosorbent assay (ELISA) validation.

METHODS

The Successful Aging after Elective Surgery study enrolled dementia-free adults ≥70 years old undergoing major scheduled noncardiac surgery (N = 566; 24% delirium). Plasma was collected at four time points: preoperative, postanesthesia care unit, postoperative day 2, and 1 month postoperative. Matched pairs were selected for the independent discovery (39 pairs) and replication cohorts (36 pairs), which were subsequently combined into the pooled cohort (75 pairs). Isobaric tags for relative and absolute quantitation-based relative quantitation mass spectrometry proteomics were performed to identify the strongest delirium-related protein, which was selected for ELISA validation. Using the ELISA results, statistical analyses using nonparametric signed rank tests were performed in all cohorts examining the association between the identified protein and delirium.

RESULTS

C-reactive protein emerged from the proteomics analysis as the strongest delirium-related protein. Validation by ELISA confirmed that compared with controls, cases had significantly higher C-reactive protein levels in the discovery, replication, and pooled cohorts at the preoperative (median paired difference [MPD] 1.97 mg/L [p < .05], 0.29 mg/L, 1.56 mg/L [p < .01]), postanesthesia care unit (MPD 2.83 mg/L, 2.22 mg/L [p < .05], 2.53 mg/L [p < .01]) and postoperative day 2 (MPD 71.97 mg/L [p < .01], 35.18 mg/L [p < .05], 63.76 mg/L [p < .01]) time points, but not 1 month postoperative (MPD 2.72 mg/L, -0.66 mg/L, 1.10 mg/L).

CONCLUSIONS

Elevated preoperative and postoperative plasma levels of C-reactive protein were associated with delirium, suggesting that a preinflammatory state and heightened inflammatory response to surgery are potential pathophysiologic mechanisms of delirium.

Systemic TNF-α produces acute cognitive dysfunction and exaggerated sickness behavior when superimposed upon progressive neurodegeneration

Inflammation influences chronic neurodegeneration but its precise roles are not yet clear. Systemic inflammation caused by infection, trauma or co-morbidity can alter the brain's inflammatory status, produce acute cognitive impairments, such as delirium, and drive new pathology and accelerated decline. Consistent with this, elevated systemic TNF-α is associated with more rapid cognitive decline over 6months in Alzheimer's disease patients. In the current study we challenged normal animals and those with existing progressive neurodegeneration (ME7 prion disease) with TNF-α (i.p.) to test the hypothesis that this cytokine has differential effects on cognitive function, sickness behavior and features of underlying pathology contingent on the animals' baseline condition. TNF-α (50μg/kg) had no impact on performance of normal animals (normal brain homogenate; NBH) on working memory (T-maze) but produced acute impairments in ME7 animals similarly challenged. Plasma TNF-α and CCL2 levels were equivalent in NBH and ME7 TNF-challenged animals but hippocampal and hypothalamic transcription of IL-1β, TNF-α and CCL2 and translation of IL-1β were higher in ME7+TNF-α than NBH+TNF-α animals. TNF-α produced an exaggerated sickness behavior response (hypothermia, weight loss, inactivity) in ME7 animals compared to that in NBH animals. However a single challenge with this dose was not sufficient to produce de novo neuronal death, synaptic loss or tau hyperphosphorylation that was distinguishable from that arising from ME7 alone. The data indicate that acutely elevated TNF-α has robust acute effects on brain function, selectively in the degenerating brain, but more sustained levels may be required to significantly impact on underlying neurodegeneration.

Neuroprotective effects of HTR1A antagonist WAY-100635 on scopolamine-induced delirium in rats and underlying molecular mechanisms

BACKGROUND

Limited surveys have assessed the performance of 5-hydroxytreptamine receptor 1A and its antagonist WAY-100635 in pharmacological manipulations targeting delirium therapies. The purpose of this paper was to assess the central pharmacological activity of WAY-100635 in a rat model of scopolamine-induced delirium and its underlying mechanism.

RESULTS

A delirium rat model was established by intraperitoneal injection of scopolamine and behavioral changes evaluated through open field and elevated plus maze experiments. Concentrations of monoamines in the hippocampus and amygdalae were detected by high performance liquid chromatography. The effect of WAY-100635 on the recovery of rats from delirium was assessed by stereotactic injection of WAY-100635 and its mechanism of action determined by measuring mRNA and protein expression via real time PCR and western blotting methods. The total distance and the number of crossing and rearing in the elevated plus maze test and the time spent in the light compartment in the dark/light test of scopolamine-treated rats were significantly increased while the percentage of time spent in the open arms was decreased, showing the validity of the established delirium rat model. The measurement of the concentrations of noradrenaline, 3,4-dihydroxyphenylacetic acid, the homovanillic acid, 5-hydroxy-3-indoleacetic acid and serotonin concentrations in the cerebrospinal fluid (CSF) of scopolamine-induced delirium rats were significantly increased. The intra-hippocampus and intra-BLA injections of WAY-100635 improved the delirium-like behavior of rats by significantly reducing the expression of NLRP3 inflammasome and the release of IL1-β and IL8 into CSF.

CONCLUSIONS

Taken together, these findings indicate that WAY-100635 may exert a therapeutic effect on post-operative delirium by controlling neurotransmission as well as suppressing neuroinflammation in the central nervous system.

Perioperative cerebrospinal fluid and plasma inflammatory markers after orthopedic surgery

Background

Postoperative delirium is prevalent in older patients and associated with worse outcomes. Recent data in animal studies demonstrate increases in inflammatory markers in plasma and cerebrospinal fluid (CSF) even after aseptic surgery, suggesting that inflammation of the central nervous system may be part of the pathogenesis of postoperative cognitive changes. We investigated the hypothesis that neuroinflammation was an important cause for postoperative delirium and cognitive dysfunction after major non-cardiac surgery.

Methods

After Institutional Review Board approval and informed consent, we recruited patients undergoing major knee surgery who received spinal anesthesia and femoral nerve block with intravenous sedation. All patients had an indwelling spinal catheter placed at the time of spinal anesthesia that was left in place for up to 24 h. Plasma and CSF samples were collected preoperatively and at 3, 6, and 18 h postoperatively. Cytokine levels were measured using ELISA and Luminex. Postoperative delirium was determined using the confusion assessment method, and cognitive dysfunction was measured using validated cognitive tests (word list, verbal fluency test, digit symbol test).

Results

Ten patients with complete datasets were included. One patient developed postoperative delirium, and six patients developed postoperative cognitive dysfunction. Postoperatively, at different time points, statistically significant changes compared to baseline were present in IL-5, IL-6, I-8, IL-10, monocyte chemotactic protein (MCP)-1, macrophage inflammatory protein (MIP)-1α, IL-6/IL-10, and receptor for advanced glycation end products in plasma and in IFN-γ, IL-6, IL-8, IL-10, MCP-1, MIP-1α, MIP-1β, IL-8/IL-10, and TNF-α in CSF.

Conclusions

Substantial pro- and anti-inflammatory activity in the central neural system after surgery was found. If confirmed by larger studies, persistent changes in cytokine levels may serve as biomarkers for novel clinical trials.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0681-9) contains supplementary material, which is available to authorized users.

Cerebrospinal fluid levels of neopterin are elevated in delirium after hip fracture

BACKGROUND

The inflammatory cell product neopterin is elevated in serum before and during delirium. This suggests a role for disordered cell-mediated immunity or oxidative stress. Cerebrospinal fluid (CSF) neopterin levels reflect brain neopterin levels more closely than serum levels. Here we hypothesized that CSF neopterin levels would be higher in delirium.

METHODS

In this prospective cohort study, 139 elderly patients with acute hip fracture were recruited in Oslo and Edinburgh. Delirium was diagnosed with the confusion assessment method performed daily pre-operatively and on the first 5 days post-operatively. Paired CSF and blood samples were collected at the onset of spinal anaesthesia. Neopterin levels were measured using high-performance liquid chromatography.

RESULTS

Sixty-four (46 %) of 139 hip fracture patients developed delirium perioperatively. CSF neopterin levels were higher in delirium compared to controls (median 29.6 vs 24.7 nmol/mL, p = 0.003), with highest levels in patients who developed delirium post-operatively. Serum neopterin levels were also higher in delirium (median 37.0 vs 27.1 nmol/mL, p = 0.003). CSF neopterin remained significantly associated with delirium after controlling for relevant risk factors. Higher neopterin levels were associated with poorer outcomes (death or new institutionalization) 1 year after surgery (p = 0.02 for CSF and p = 0.03 for serum).

CONCLUSIONS

This study is the first to examine neopterin in CSF from patients with delirium. Our findings suggest potential roles for activation of cell-mediated immune responses or oxidative stress in the delirium process. High levels of serum or CSF neopterin in hip fracture patients may also be useful in predicting poor outcomes.

Fundamental role of pan-inflammation and oxidative-nitrosative pathways in neuropathogenesis of Alzheimer's disease in focal cerebral ischemic rats

Alzheimer's disease (AD) is a chronic progressive neurodegenerative condition of the brain, and it is the most common cause of dementia. Several neurobiological etiologies of AD are described in the literature. These include vascular, infectious, toxic, nutritional, metabolic, and inflammatory. However, these heterogeneous etiologies have a common denominator - viz. Inflammation and oxidative stress. Lipopolysaccharide (LPS) elevates the synthesis of proinflammatory cytokines and chemokines; chronically, together they trigger various pathological responses in the periphery and the CNS including dysfunctional memory consolidation and memory decline. Aging - the main risk factor for AD is inherently associated with inflammation. There are several age-related comorbidities that are also associated with inflammation and oxidative stress. Such co-prevailing aggravating factors, therefore, persist against a background of underlying aging-related pathology. They may converge, and their synergistic propagation may modify the disease course. A critical balance exists between homeostasis/repair and inflammatory factors; chronic, unrelenting inflammatory milieu succeeds in promoting a neuroinflammatory and neurodegenerative outcome. Extensive evidence is available that CNS inflammation is associated with neurodegeneration. LPS, proinflammatory cytokines, several mediators secreted by microglia, and oxidative-nitrosative stress in concert play a pivotal role in triggering neuroinflammatory processes and neurodegeneration. The persistent uncontrolled activity of the above factors can potentiate cognitive decline in tandem enhancing vulnerability to AD. Despite significant progress during the past twenty years, the prevention and treatment of AD have been tantalizingly elusive. Current studies strongly suggest that amelioration/prevention of the deleterious effects of inflammation may prove beneficial in preventing AD onset and retarding cognitive dysfunction in aging and AD. A concerted multi-focal therapeutic effort around the inflammation-oxidative-nitrosative stress paradigm may be crucial in preventing and treating AD. This paper informs on such relevant polypharmacy approach.

5-HT(1A) receptor antagonist improves behavior performance of delirium rats through inhibiting PI3K/Akt/mTOR activation-induced NLRP3 activity

Postoperative delirium is a common complication that often results in poor outcomes in surgical and elderly patients. Accumulating evidences suggest that the pathophysiology of delirium results from multiple neurotransmitter system dysfunctions. To further clarify the effects of the selective serotonin (5-HT) (1A) antagonist WAY-100635 on the behaviors in scopolamine induced-delirium rats and to explore the molecular mechanism, in this study, we investigated the change of monoamine levels in the cerebrospinal fluid (CSF) and different brain regions using high-performance liquid chromatography and assessed the behavioral retrieval of delirium rats treated with WAY-100635. It was found that 5-hydroxy-3-indoleacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid, and homovanillic acid concentrations in the CSF of scopolamine-induced delirium rats were significantly increased, among which 5-HIAA was also increased in hippocampus and basolateral amygdala (BLA), and 5-HT(1A) receptor was significantly higher in the hippocampuses and BLA than other brain regions. Furthermore, intrahippocampus and intra-BLA stereotactic injection of WAY-100635 improved the delirium-like behavior of rats. Mechanistically, after WAY-100635 treatment, significant reduction of IL-1β release into CSF and NOD-like receptor family, pyrin domain containing 3 (NLRP3) expression, phosphorylated phosphatidylinositol-3-kinase (PI3K), protein kinase B (AKT), and S6K was observed. Altogether, these results suggest that delirium rats induced by scopolamine may be correlated with an increased cerebral concentration of 5-HT and dopamine neurotransmitters system; the selective 5-HT(1A) antagoniszts can reverse the delirium symptoms at some extent through tendering PI3K/Akt/mammalian target of rapamycin complex 1 (mTOR) activation-induced NLRP3 activity and then reducing IL-1β release.

Fundamental role of pan-inflammation and oxidative-nitrosative pathways in neuropathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a chronic progressive neurodegenerative condition of the brain, and it is the most common cause of dementia. Several neurobiological etiologies of AD are described in the literature. These include vascular, infectious, toxic, nutritional, metabolic, and inflammatory. However, these heterogeneous etiologies have a common denominator - viz. Inflammation and oxidative stress. Lipopolysaccharide (LPS) elevates the synthesis of proinflammatory cytokines and chemokines; chronically, together they trigger various pathological responses in the periphery and the CNS including dysfunctional memory consolidation and memory decline. Aging - the main risk factor for AD is inherently associated with inflammation. There are several age-related comorbidities that are also associated with inflammation and oxidative stress. Such co-prevailing aggravating factors, therefore, persist against a background of underlying aging-related pathology. They may converge, and their synergistic propagation may modify the disease course. A critical balance exists between homeostasis/repair and inflammatory factors; chronic, unrelenting inflammatory milieu succeeds in promoting a neuroinflammatory and neurodegenerative outcome. Extensive evidence is available that CNS inflammation is associated with neurodegeneration. LPS, proinflammatory cytokines, several mediators secreted by microglia, and oxidative-nitrosative stress in concert play a pivotal role in triggering neuroinflammatory processes and neurodegeneration. The persistent uncontrolled activity of the above factors can potentiate cognitive decline in tandem enhancing vulnerability to AD. Despite significant progress during the past twenty years, the prevention and treatment of AD have been tantalizingly elusive. Current studies strongly suggest that amelioration/prevention of the deleterious effects of inflammation may prove beneficial in preventing AD onset and retarding cognitive dysfunction in aging and AD. A concerted multi-focal therapeutic effort around the inflammation-oxidative-nitrosative stress paradigm may be crucial in preventing and treating AD. This paper informs on such relevant polypharmacy approach.

Innate immune perturbations, accumulating DAMPs and inflammasome dysregulation: A ticking time bomb in ageing

Ageing has pronounced effects on the immune system, including on innate immune cells. Whilst most studies suggest that total numbers of different innate immune cell populations do not change dramatically during ageing, many of their functions such as phagocytosis, antigen presentation and inflammatory molecule secretion decline. In contrast, many endogenous damage-associated molecular patterns (DAMPs) accumulate during ageing. These include reactive oxygen species (ROS) released from damaged mitochondria, extracellular nucleotides like ATP, high mobility group box (HMGB) 1 protein, oxidized low density lipoprotein, amyloid-beta (Aβ), islet amyloid polypeptide and particulates like monosodium urate (MSU) crystals and cholesterol crystals. Some of these DAMPs trigger the activation of inflammasomes, cytosolic danger sensing signalling platforms that drive both the maturation of specific pro-inflammatory mediators such as IL-1β, as well as the initiation of pro-inflammatory pyroptotic cell death. Herein, we review the evidence that dysregulated inflammasome activation, via altered innate immune cell functions and elevated levels of DAMPs, contributes to the establishment of chronic, low-grade inflammation (characterized by elevated levels of IL-6 and C-reactive protein) and the development of age-related pathological processes.

Preoperative protein profiles in cerebrospinal fluid in elderly hip fracture patients at risk for delirium: A proteomics and validation study

BACKGROUND

A neuroinflammatory response is suggested to play an important role in delirium, a common complication in older hospitalized patients. We examined whether hip fracture patients who develop postoperative delirium have a different proteome in cerebrospinal fluid (CSF) prior to surgery.

METHODS

Patients (≥ 75 years) were admitted for hip fracture surgery. CSF was collected during spinal anaesthesia; proteins were separated using gel electrophoresis and identified with mass spectrometry. We compared the proteome of patients with and without postoperative delirium. Findings were validated in an independent, comparable cohort using immuno-assays.

RESULTS

In the derivation cohort 53 patients were included, 35.8% developed postoperative delirium. We identified differences in levels of eight CSF proteins between patients with and without subsequent delirium: complement factor C3, contactin-1, fibulin-1 and I-beta-1,3-N-acetylglucosaminyltransferase were significantly lower in patients with postoperative delirium, while neural cell adhesion molecule-2, fibrinogen, zinc-α-2-glycoprotein and haptoglobin levels were significantly higher. In the validation cohort 21.2% of 52 patients developed postoperative delirium. Immuno-assays confirmed contactin-1 results although not statistically significant. Complement factor C3 was significantly higher in patients with postoperative delirium.

CONCLUSION

Our results show the complexity of pathophysiological mechanisms involved in delirium and emphasizes the need of independent validation of findings.

GENERAL SIGNIFICANCE

This study highlights the challenges and inconsistent findings in studies of delirium, a serious complication in older patients. We analysed proteins in CSF, the most proximal fluid to the brain. All patients were free from delirium at the time of sampling.

Postoperative Delirium in the Geriatric Patient

Postoperative delirium, a common complication in older surgical patients, is independently associated with increased morbidity and mortality. Patients older than 65 years receive greater than one-third of the more than 40 million anesthetics delivered yearly in the United States. This number is expected to increase with the aging of the population. Thus, it is increasingly important that perioperative clinicians who care for geriatric patients have an understanding of the complex syndrome of postoperative delirium.

The interface between delirium and dementia in elderly adults

Delirium and dementia are two of the most common causes of cognitive impairment in older populations, yet their interrelation remains poorly understood. Previous studies have shown that dementia is the leading risk factor for delirium and that delirium is an independent risk factor for subsequent development of dementia. However, a major area of controversy is whether delirium is simply a marker of vulnerability to dementia, whether the effect of delirium is solely related to its precipitating factors, or whether delirium itself can cause permanent neuronal damage and lead to dementia. Ultimately, all of these hypotheses are likely to be true. Emerging evidence from epidemiological, clinicopathological, neuroimaging, biomarker, and experimental studies lends support to a strong relation between delirium and dementia, and to both shared and distinct pathological mechanisms. New preventive and therapeutic approaches that target delirium might offer a sought-after opportunity for early intervention, preservation of cognitive reserve, and prevention of irreversible cognitive decline in ageing.

Biomarkers of postoperative delirium and cognitive dysfunction

Elderly surgical patients frequently experience postoperative delirium (POD) and the subsequent development of postoperative cognitive dysfunction (POCD). Clinical features include deterioration in cognition, disturbance in attention and reduced awareness of the environment and result in higher morbidity, mortality and greater utilization of social financial assistance. The aging Western societies can expect an increase in the incidence of POD and POCD. The underlying pathophysiological mechanisms have been studied on the molecular level albeit with unsatisfying small research efforts given their societal burden. Here, we review the known physiological and immunological changes and genetic risk factors, identify candidates for further studies and integrate the information into a draft network for exploration on a systems level. The pathogenesis of these postoperative cognitive impairments is multifactorial; application of integrated systems biology has the potential to reconstruct the underlying network of molecular mechanisms and help in the identification of prognostic and diagnostic biomarkers.

Is there a role for monocyte chemoattractant protein-1 in delirium? Novel observations in elderly hip fracture patients

Background

Delirium is common, associated with poor outcome, but its pathophysiology remains obscure. The aim of the present study was to study a possible role of monocyte chemoattractant protein-1 (MCP-1) in the development of delirium.

Findings

A prospective cohort of 19 hip fracture patients (median age 83 years) were screened for delirium daily by validated methods. MCP-1 was measured on arrival and postoperatively. The number of patients with a raise in MCP-1 was statistically significantly higher in the group with delirium in the postoperative phase compared to the no-delirium group (5/6 vs. 1/7, p = .03).

Conclusions

MCP-1 might play a role in the development of delirium.

Co-morbidity and systemic inflammation as drivers of cognitive decline: new experimental models adopting a broader paradigm in dementia research

Dementia prevalence increases with age and Alzheimer’s disease (AD) accounts for up to 75% of cases. However, significant variability and overlap exists in the extent of amyloid-β and Tau pathology in AD and non-demented populations and it is clear that other factors must influence progression of cognitive decline, perhaps independent of effects on amyloid pathology. Coupled with the failure of amyloid-clearing strategies to provide benefits for AD patients, it seems necessary to broaden the paradigm in dementia research beyond amyloid deposition and clearance. Evidence has emerged from alternative animal model approaches as well as clinical and population epidemiological studies that co-morbidities contribute significantly to neurodegeneration/cognitive decline and systemic inflammation has been a strong common theme in these approaches. We hypothesise, and discuss in this review, that a disproportionate inflammatory response to infection, injury or chronic peripheral disease is a key determinant of cognitive decline. We propose that detailed study of alternative models, which encompass acute and chronic systemic inflammatory co-morbidities, is an important priority for the field and we examine the cognitive consequences of several of these alternative experimental approaches. Experimental models of severe sepsis in normal animals or moderate acute systemic inflammation in animals with existing neurodegenerative pathology have uncovered roles for inflammatory mediators interleukin-1β, tumour necrosis factor-α, inducible nitric oxide synthase, complement, prostaglandins and NADPH oxidase in inflammation-induced cognitive dysfunction and neuronal death. Moreover, microglia are primed by existing neurodegenerative pathology to produce exaggerated responses to subsequent stimulation with bacterial lipopolysaccharide or other inflammatory stimuli and these insults drive acute dysfunction and negatively affect disease trajectory. Chronic co-morbidities, such as arthritis, atherosclerosis, obesity and diabetes, are risk factors for subsequent dementia and those with high inflammatory status are particularly at risk. Models of chronic co-morbidities, and indeed low grade systemic inflammation in the absence of specific pathology, indicate that interleukin-1β, tumour necrosis factor-α and other inflammatory mediators drive insulin resistance, hypothalamic dysfunction, impaired neurogenesis and cognitive function and impact on functional decline. Detailed study of these pathways will uncover important mechanisms of peripheral inflammation-driven cognitive decline and are already driving clinical initiatives to mitigate AD progression through minimising systemic inflammation.