NOS2 gene deficiency protects from sepsis-induced long-term cognitive deficits

Microglial activation and neuroinflammation in acute and chronic cognitive deficits in sepsis

Sepsis is characterised by dysregulated immune responses to infection, leading to multi-organ dysfunction and high rates of mortality. With increasing survival rates in recent years long-term neurological and psychiatric consequences have become more apparent in survivors. Many patients develop sepsis associated encephalopathy (SAE) which encompasses the profound but usually transient neuropsychiatric syndrome delirium but also new brain injury that emerges in the months and years post-sepsis. It is now clear that systemic inflammatory signals reach the brain during sepsis and that very significant neuroinflammation ensues. The major brain resident immune cell population, the microglia, has been implicated in acute and chronic cognitive dysfunction in animal models of sepsis based on a growing number of studies using bacterial endotoxin and in polymicrobial sepsis models such as cecal ligation and puncture. The current review explores the effects of sepsis on the brain, focussing on how systemic insults translate to microglial activation and neuroinflammation and how this disrupts neuronal function and integrity. We examine what has been demonstrated specifically with respect to microglial activation, revealing robust evidence for a role for neuroinflammation in sepsis-induced brain sequelae but less clear information on the extent of the specific microglial contribution to this, arising from findings using global knockout mice, non-selective drugs and treatments that equally target peripheral and central compartments. There is, nonetheless, clear evidence that microglia do become activated and do contribute to brain consequences of sepsis thus arguing for improved understanding of these neuroinflammatory processes toward the prevention and treatment of sepsis-induced brain dysfunction.

Neuroinflammatory Mechanisms of Adult Sepsis-Associated Encephalopathy: Implications for Blood-Brain Barrier Disruption and Oxidative Stress

Sepsis is a syndrome of life-threatening acute organ dysfunction caused by a dysregulated host response to infection. Sepsis-associated encephalopathy (SAE) refers to the diffuse brain dysfunction observed in sepsis cases, clinically characterized by a spectrum of neuropsychiatric manifestations ranging from delirium to coma. SAE is independently associated with increased short-term mortality and long-term neurological abnormalities, with currently no effective preventive or treatment strategies. The pathogenesis is intricate, involving disruptions in neurotransmitters, blood-brain barrier (BBB) breakdown, abnormal brain signal transmission, and oxidative stress, among others. These mechanisms interact or act in conjunction, contributing to the complexity of SAE. Scholars worldwide have made significant strides in understanding the pathogenesis of SAE, offering new perspectives for diagnosis and treatment. This review synthesizes recent mechanistic breakthroughs and clinical evidence to guide future research directions, particularly in targeting BBB restoration and oxidative stress.

Microbial Trojan Horses: Virulence Factors as Key Players in Neurodegenerative Diseases

Changes in population demographics indicate that the elderly population will reach 2.1 billion worldwide by 2050. In parallel, there will be an increase in neurodegenerative diseases such as Alzheimer's and Parkinson's. This review explores dysbiosis occurring in these pathologies and how virulence factors contribute to the worsening or development of clinical conditions, and it summarizes existing and potential ways to combat microorganisms related to these diseases. Microbiota imbalances can contribute to the progression of neurodegenerative diseases by increasing intestinal permeability, exchanging information through innervation, and even acting as a Trojan horse affecting immune cells. The microorganisms of the microbiota produce virulence factors to protect themselves from host defenses, many of which contribute to neurodegenerative diseases. These virulence factors are expressed according to the genetic composition of each microorganism, leading to a wide range of factors to be considered. Among the main virulence factors are LPS, urease, curli proteins, amyloidogenic proteins, VacA, and CagA. These factors can also be packed into bacterial outer membrane vesicles, which transport proteins, RNA, and DNA, enabling distal communication that impacts various diseases, including Alzheimer's and Parkinson's.

The Biological Changes of Synaptic Plasticity in the Pathological Process of Sepsis-associated Encephalopathy

Sepsis-associated encephalopathy (SAE) is a form of cognitive and psychological impairment resulting from sepsis, which occurs without any central nervous system infection or structural brain injury. Patients may experience long-term cognitive deficits and psychiatric disorders even after discharge. However, the underlying mechanism remains unclear. As cognitive function and mental disease are closely related to synaptic plasticity, it is presumed that alterations in synaptic plasticity play an essential role in the pathological process of SAE. Here, we present a systematic description of the pathogenesis of SAE, which is primarily driven by glial cell activation and subsequent release of inflammatory mediators. Additionally, we elucidate the alterations in synaptic plasticity that occur during SAE and comprehensively discuss the roles played by glial cells and inflammatory factors in this process. In this review, we mainly discuss the synaptic plasticity of SAE, and the main aim is to show the consequences of SAE on inflammatory factors and how they affect synaptic plasticity. This review may enhance our understanding of the mechanism underlying cognitive dysfunction and provide valuable insights into identifying appropriate therapeutic targets for SAE.

Evaluation of the Anti-Amyloid and Anti-Inflammatory Properties of a Novel Vanadium(IV)-Curcumin Complex in Lipopolysaccharides-Stimulated Primary Rat Neuron-Microglia Mixed Cultures

Lipopolysaccharides (LPS) are bacterial mediators of neuroinflammation that have been detected in close association with pathological protein aggregations of Alzheimer's disease. LPS induce the release of cytokines by microglia and mediate the upregulation of inducible nitric oxide synthase (iNOS)-a mechanism also associated with amyloidosis. Curcumin is a recognized natural medicine but has extremely low bioavailability. V-Cur, a novel hemocompatible Vanadium(IV)-curcumin complex with higher solubility and bioactivity than curcumin, is studied here. Co-cultures consisting of rat primary neurons and microglia were treated with LPS and/or curcumin or V-Cur. V-Cur disrupted LPS-induced overexpression of amyloid precursor protein (APP) and the in vitro aggregation of human insulin (HI), more effectively than curcumin. Cell stimulation with LPS also increased full-length, inactive, and total iNOS levels, and the inflammation markers IL-1β and TNF-α. Both curcumin and V-Cur alleviated these effects, with V-Cur reducing iNOS levels more than curcumin. Complementary insights into possible bioactivity mechanisms of both curcumin and V-Cur were provided by In silico molecular docking calculations on Aβ1-42, APP, Aβ fibrils, HI, and iNOS. This study renders curcumin-based compounds a promising anti-inflammatory intervention that may be proven a strong tool in the effort to mitigate neurodegenerative disease pathology and neuroinflammatory conditions.

Crosstalk between peripheral inflammation and brain: Focus on the responses of microglia and astrocytes to peripheral challenge

A growing body of evidence supports the link between peripheral inflammation and impairment of neurologic functions, including mood and cognitive abilities. The pathogenic event connecting peripheral inflammation and brain dysfunction is represented by neuroinflammation, a pathogenic phenomenon that provides an important contribution to neurodegeneration and cognitive decline also in Alzheimer's, Parkinson's, Huntington's diseases, as well as in Multiple Sclerosis. It is driven by resident brain immune cells, microglia and astrocytes, that acquire an activated phenotype in response to proinflammatory molecules moving from the periphery to the brain parenchyma. Although a huge progress has been made in clarifying cellular and molecular mechanisms bridging peripheral and central inflammation, a clear picture has not been achieved so far. Therefore, experimental models are of crucial relevance to clarify knowledge gaps in this regard. Many findings demonstrate that systemic inflammation induced by pathogen-associated molecular patterns, such as lipopolysaccharide (LPS), is able to trigger neuroinflammation. Therefore, LPS-administration is widely considered a useful tool to study this phenomenon. On this basis, the present review will focus on in vivo studies based on acute and subacute effects of systemic administration of LPS, with special attention on the state of art of microglia and astrocyte response to peripheral challenge.

Targeted rescue of synaptic plasticity improves cognitive decline in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a frequent complication of severe systemic infection resulting in delirium, premature death, and long-term cognitive impairment. We closely mimicked SAE in a murine peritoneal contamination and infection (PCI) model. We found long-lasting synaptic pathology in the hippocampus including defective long-term synaptic plasticity, reduction of mature neuronal dendritic spines, and severely affected excitatory neurotransmission. Genes related to synaptic signaling, including the gene for activity-regulated cytoskeleton-associated protein (Arc/Arg3.1) and members of the transcription-regulatory EGR gene family, were downregulated. At the protein level, ARC expression and mitogen-activated protein kinase signaling in the brain were affected. For targeted rescue we used adeno-associated virus-mediated overexpression of ARC in the hippocampus in vivo. This recovered defective synaptic plasticity and improved memory dysfunction. Using the enriched environment paradigm as a non-invasive rescue intervention, we found improvement of defective long-term potentiation, memory, and anxiety. The beneficial effects of an enriched environment were accompanied by an increase in brain-derived neurotrophic factor (BDNF) and ARC expression in the hippocampus, suggesting that activation of the BDNF-TrkB pathway leads to restoration of the PCI-induced reduction of ARC. Collectively, our findings identify synaptic pathomechanisms underlying SAE and provide a conceptual approach to target SAE-induced synaptic dysfunction with potential therapeutic applications to patients with SAE.

The endotoxin hypothesis of Alzheimer's disease

Lipopolysaccharide (LPS) constitutes much of the surface of Gram-negative bacteria, and if LPS enters the human body or brain can induce inflammation and act as an endotoxin. We outline the hypothesis here that LPS may contribute to the pathophysiology of Alzheimer's disease (AD) via peripheral infections or gut dysfunction elevating LPS levels in blood and brain, which promotes: amyloid pathology, tau pathology and microglial activation, contributing to the neurodegeneration of AD. The evidence supporting this hypothesis includes: i) blood and brain levels of LPS are elevated in AD patients, ii) AD risk factors increase LPS levels or response, iii) LPS induces Aβ expression, aggregation, inflammation and neurotoxicity, iv) LPS induces TAU phosphorylation, aggregation and spreading, v) LPS induces microglial priming, activation and neurotoxicity, and vi) blood LPS induces loss of synapses, neurons and memory in AD mouse models, and cognitive dysfunction in humans. However, to test the hypothesis, it is necessary to test whether reducing blood LPS reduces AD risk or progression. If the LPS endotoxin hypothesis is correct, then treatments might include: reducing infections, changing gut microbiome, reducing leaky gut, decreasing blood LPS, or blocking LPS response.

Ferroptosis, Pyroptosis, and Cuproptosis in Alzheimer's Disease

Alzheimer's disease (AD), the most common type of dementia, is a neurodegenerative disorder characterized by progressive cognitive dysfunction. Epidemiological investigation has demonstrated that, after cardiovascular and cerebrovascular diseases, tumors, and other causes, AD has become a major health issue affecting elderly individuals, with its mortality rate acutely increasing each year. Regulatory cell death is the active and orderly death of genetically determined cells, which is ubiquitous in the development of living organisms and is crucial to the regulation of life homeostasis. With extensive research on regulatory cell death in AD, increasing evidence has revealed that ferroptosis, pyroptosis, and cuproptosis are closely related to the occurrence, development, and prognosis of AD. This paper will review the molecular mechanisms of ferroptosis, pyroptosis, and cuproptosis and their regulatory roles in AD to explore potential therapeutic targets for the treatment of AD.

Treatment of septic encephalopathy and encephalitis - a critical appraisal

INTRODUCTION

The central nervous system is frequently involved during severe sepsis. Patients either develop septic encephalopathy characterized by delirium and coma or focal neurological signs as a consequence of septic-embolic or septic-metastatic encephalitis.

AREAS COVERED

In this review, a summary of currently available literature on established and some promising experimental treatment options for septic encephalopathy and encephalitis is provided, with a focus on the clinical utility of published studies.

EXPERT OPINION

Treatment relies on proper identification of the causative pathogen and rapidly initiated adequate empirical or (after identification of the pathogen) tailored antibiotic therapy, fluid and electrolyte management. In the presence of brain abscess(es) or mycotic aneurysm(s), surgery or interventional neuroradiology must be considered. Pharmacological approaches to prevent delirium of different etiology include the use of dexmedetomidine and (with limitations) of melatonin and its derivatives. In the absence of a specific pharmacological treatment, non-pharmacological bundles of interventions (e.g. promotion of sleep, cognitive stimulation, early mobilization and adequate therapy of pain) are of proven efficacy to prevent delirium of different etiology including sepsis. Experimental promising therapies include the use of non-bacteriolytic antibiotics and the reduction of the toxic effects of microglial activation.

The role of peripheral inflammatory insults in Alzheimer's disease: a review and research roadmap

Peripheral inflammation, defined as inflammation that occurs outside the central nervous system, is an age-related phenomenon that has been identified as a risk factor for Alzheimer's disease. While the role of chronic peripheral inflammation has been well characterized in the context of dementia and other age-related conditions, less is known about the neurologic contribution of acute inflammatory insults that take place outside the central nervous system. Herein, we define acute inflammatory insults as an immune challenge in the form of pathogen exposure (e.g., viral infection) or tissue damage (e.g., surgery) that causes a large, yet time-limited, inflammatory response. We provide an overview of the clinical and translational research that has examined the connection between acute inflammatory insults and Alzheimer's disease, focusing on three categories of peripheral inflammatory insults that have received considerable attention in recent years: acute infection, critical illness, and surgery. Additionally, we review immune and neurobiological mechanisms which facilitate the neural response to acute inflammation and discuss the potential role of the blood-brain barrier and other components of the neuro-immune axis in Alzheimer's disease. After highlighting the knowledge gaps in this area of research, we propose a roadmap to address methodological challenges, suboptimal study design, and paucity of transdisciplinary research efforts that have thus far limited our understanding of how pathogen- and damage-mediated inflammatory insults may contribute to Alzheimer's disease. Finally, we discuss how therapeutic approaches designed to promote the resolution of inflammation may be used following acute inflammatory insults to preserve brain health and limit progression of neurodegenerative pathology.

A MODIFIED SURGICAL SEPSIS MODEL SATISFYING SEPSIS-3 AND HAVING HIGH CONSISTENCY OF MORTALITY

ABSTRACT

Background : Cecal ligation and perforation (CLP) is currently considered the criterion standard model of sepsis; however, there are some deficiencies, such as low clinical relevance, inconsistency in severity grading, and an unknown proportion of CLP animals meeting the requirements of sepsis-3. Methods : Adult rats were randomly divided into the following three groups: modified CLP (M-CLP) group, CLP group, and sham group. The vital organ function of rats was evaluated 24 hours postoperatively by blood pressure, behavioral testing, histopathology, and blood test. Cytokine levels were determined by enzyme-linked immunosorbent assay, and T-cell suppression was assessed by flow cytometry. The stability of the model was evaluated by comparing the survival rates of repeated experiments in all groups from day 1 to day 14. Results : More rats in the M-CLP group met Sepsis-3 criteria than those in the CLP group 24 hours postoperatively (53.1% vs. 21.9%, P = 0.01). Rats in the M-CLP group developed more serious hepatic, pulmonary, and renal dysfunction. Similar to human sepsis, rats in the M-CLP group demonstrated more serious immunosuppression and systemic inflammation compared with the CLP group. In addition, disease development and severity, which was indicated by the stable survival rates of model animals, were more stable in the M-CLP group. Conclusions : More rats could meet Sepsis-3 criteria with this novel surgical procedure, which may reduce the number of animals needed in preclinical sepsis experiments. This stable M-CLP model may contribute to the development of new therapies.

Dysfunction of NRG1/ErbB4 Signaling in the Hippocampus Might Mediate Long-term Memory Decline After Systemic Inflammation

Accumulating evidence has suggested that a great proportion of sepsis survivors suffer from long-term cognitive impairments after hospital discharge, leading to decreased life quality and substantial caregiving burdens for family members. However, the underlying mechanism remains unclear. In the present study, we established a mouse model of systemic inflammation by repeated lipopolysaccharide (LPS) injections. A combination of behavioral tests, biochemical, and in vivo electrophysiology techniques were conducted to test whether abnormal NRG1/ErbB4 signaling, parvalbumin (PV) interneurons, and hippocampal neural oscillations were involved in memory decline after repeated LPS injections. Here, we showed that LPS induced long-term memory decline, which was accompanied by dysfunction of NRG1/ErbB4 signaling and PV interneurons, and decreased theta and gamma oscillations. Notably, NRG1 treatment reversed LPS-induced decreases in p-ErbB4 and PV expressions, abnormalities in theta and gamma oscillations, and long-term memory decline. Together, our study demonstrated that dysfunction of NRG1/ErbB4 signaling in the hippocampus might mediate long-term memory decline in a mouse model of systemic inflammation induced by repeated LPS injections. Thus, targeting NRG1/ErbB4 signaling in the hippocampus may be promising for the prevention and treatment of this long-term memory decline.

The biological alterations of synapse/synapse formation in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a common complication caused by sepsis, and is responsible for increased mortality and poor outcomes in septic patients. Neurological dysfunction is one of the main manifestations of SAE patients. Patients may still have long-term cognitive impairment after hospital discharge, and the underlying mechanism is still unclear. Here, we first outline the pathophysiological changes of SAE, including neuroinflammation, glial activation, and blood-brain barrier (BBB) breakdown. Synapse dysfunction is one of the main contributors leading to neurological impairment. Therefore, we summarized SAE-induced synaptic dysfunction, such as synaptic plasticity inhibition, neurotransmitter imbalance, and synapses loss. Finally, we discuss the alterations in the synapse, synapse formation, and mediators associated with synapse formation during SAE. In this review, we focus on the changes in synapse/synapse formation caused by SAE, which can further understand the synaptic dysfunction associated with neurological impairment in SAE and provide important insights for exploring appropriate therapeutic targets of SAE.

Assessing spatial learning and memory in mice: Classic radial maze versus a new animal-friendly automated radial maze allowing free access and not requiring food deprivation

The radial arm maze (RAM) is a common behavioral test to quantify spatial learning and memory in rodents. Prior attempts to refine the standard experimental setup have been insufficient. Previously, we demonstrated the feasibility of a fully automated, voluntary, and stress-free eight-arm RAM not requiring food or water deprivation. Here, we compared this newly developed refined RAM to a classic manual experimental setup using 24 female 10-12 weeks old C57BL/6J mice. We used a lipopolysaccharide (LPS)-induced model of systemic inflammation to examine long-term cognitive impairment for up to 13 weeks following LPS injection. Both mazes demonstrated robust spatial learning performance during the working memory paradigm. The refined RAM detected spatial learning and memory deficits among LPS-treated mice in the working memory paradigm, whereas the classic RAM detected spatial learning and memory deficits only in the combined working/reference memory paradigm. In addition, the refined RAM allowed for quantification of an animal's overall exploratory behavior and day/night activity pattern. While our study highlights important aspects of refinement of the new setup, our comparison of methods suggests that both RAMs have their respective merits depending on experimental requirements.

Central role of microglia in sepsis-associated encephalopathy: From mechanism to therapy

Sepsis-associated encephalopathy (SAE) is a cognitive impairment associated with sepsis that occurs in the absence of direct infection in the central nervous system or structural brain damage. Microglia are thought to be macrophages of the central nervous system, devouring bits of neuronal cells and dead cells in the brain. They are activated in various ways, and microglia-mediated neuroinflammation is characteristic of central nervous system diseases, including SAE. Here, we systematically described the pathogenesis of SAE and demonstrated that microglia are closely related to the occurrence and development of SAE. Furthermore, we comprehensively discussed the function and phenotype of microglia and summarized their activation mechanism and role in SAE pathogenesis. Finally, this review summarizes recent studies on treating cognitive impairment in SAE by blocking microglial activation and toxic factors produced after activation. We suggest that targeting microglial activation may be a putative treatment for SAE.

Modulation of MAPK- and PI3/AKT-Dependent Autophagy Signaling by Stavudine (D4T) in PBMC of Alzheimer’s Disease Patients

Background: Aβ₄₂ deposition plays a pivotal role in AD pathogenesis by inducing the activation of microglial cells and neuroinflammation. This process is antagonized by microglia-mediated clearance of Aβ plaques. Activation of the NLRP3 inflammasome is involved in neuroinflammation and in the impairments of Aβ-plaque clearance. On the other hand, stavudine (D4T) downregulates the NLRP3 inflammasome and stimulates autophagy-mediated Aβ-clearing in a THP-1-derived macrophages. Methods: We explored the effect of D4T on Aβ autophagy in PBMC from AD patients that were primed with LPS and stimulated with Aβ oligomers in the absence/presence of D4T. We analyzed the NLRP3 activity by measuring NLRP3-ASC complex formation by AMNIS FlowSight and pro-inflammatory cytokine (IL-1β, IL-18 and Caspase-1) production by ELISA. The phosphorylation status of p38, ERK, AKT, p70, and the protein expression of CREB, LAMP2A, beclin-1, Caspase-3 and Bcl2 were analyzed by Western blot. Results: Data showed that D4T: (1) downregulates NLRP3 inflammasome activation and the production of down-stream pro-inflammatory cytokines in PBMC; (2) stimulates the phosphorylation of AKT, ERK and p70 as well as LAMP2A, beclin-1 and Bcl2 expression and reduces Caspase-3 expression, suggesting an effect of this compound on autophagy; (3) increases phospho-CREB, which is a downstream target of p-ERK and p-AKT, inducing anti-inflammatory cytokine production and resulting in a possible decrease of Aβ-mediated cytotoxicity; and (4) reduces the phosphorylation of p38, a protein involved in the production of pro-inflammatory cytokines and tau hyperphosphorylation. Conclusions: D4T reduces the activation of the NLRP3 inflammasome, and it might stimulate autophagy as well as the molecular mechanism that modulates Aβ cytotoxicity, and D4T might reduce inflammation in the cells of AD patients. It could be very interesting to check the possible beneficial effects of D4T in the clinical scenario.

Exacerbated immune response of the brain to peripheral immune challenge in post-septic mice

BACKGROUND

Mounting evidence indicates that sepsis can induce long-lasting brain dysfunction. Recently, it has been proposed that the brain may become more sensitive to systemic inflammation if microglial cells are already primed. Microglial priming has been demonstrated in aging, traumatic brain injury, and neurodegenerative diseases. There is evidence suggesting that systemic inflammation may also prime microglia. This study aimed to investigate the brain's response to a second immune challenge in sepsis survivors and the possible role of microglial priming.

METHODS

Adult BALB/c mice were intraperitoneally (ip) injected with 5 mg/kg lipopolysaccharide (LPS) for sepsis induction. One month later, mice received a second immune challenge (LPS, 0.33 mg/kg). A cohort of mice was sacrificed 2 h post-LPS injection to measure inflammatory mediators mRNA expression. The second cohort of mice was tested on a battery of behavioral tests and then sacrificed, and brain tissues were removed for biochemical analyses.

RESULTS

Results showed that in septic mice, secondary LPS challenge induced heightened neuroinflammation compared to the control mice, as evident by a significant increase of IL-1β, TNF-α, and iNOS mRNA expression. In the immunochallenged septic mice, the anti-inflammatory cytokine IL-10 expression was also significantly increased compared to the control mice. Sepsis induction significantly disrupted the recognition ability in the novel object recognition, but the second immune challenge had no significant effect. However, immunochallenged septic mice exhibited more anxiety-like behavior in the marble burying task and intensive depressive-like behavior in the forced swim test. Additionally, the second immune challenge reduced arginase-1 levels in septic but not control mice. On the other hand, CIITA levels were increased more significantly in the LPS injected control mice compared to septic mice. Neither sepsis nor the second immune challenge significantly affected inhibitory avoidance behavior and Aβ1-42 levels in brain tissue.

CONCLUSION

Our finding suggests that low-grade immune challenge can induce exacerbated behavioral change and exaggerated inflammatory response in the brain of post-septic mice.

Cerebral dysfunctions caused by sepsis during ageing

Systemic inflammation elicited by sepsis can induce an acute cerebral dysfunction known as sepsis-associated encephalopathy (SAE). Recent evidence suggests that SAE is common but shows a dynamic trajectory over time. Half of all patients with sepsis develop SAE in the intensive care unit, and some survivors present with sustained cognitive impairments for several years after initial sepsis onset. It is not clear why some, but not all, patients develop SAE and also the factors that determine the persistence of SAE. Here, we first summarize the chronic pathology and the dynamic changes in cognitive functions seen after the onset of sepsis. We then outline the cerebral effects of sepsis, such as neuroinflammation, alterations in neuronal synapses and neurovascular changes. We discuss the key factors that might contribute to the development and persistence of SAE in older patients, including premorbid neurodegenerative pathology, side effects of sedatives, renal dysfunction and latent virus reactivation. Finally, we postulate that some of the mechanisms that underpin neuropathology in SAE may also be relevant to delirium and persisting cognitive impairments that are seen in patients with severe COVID-19.

Sepsis-Associated Encephalopathy: A Mini-Review of Inflammation in the Brain and Body

Sepsis is defined as a life-threatening multi-organ dysfunction triggered by an uncontrolled host response to infectious disease. Systemic inflammation elicited by sepsis can cause acute cerebral dysfunction, characterized by delirium, coma, and cognitive dysfunction, known as septic encephalopathy. Recent evidence has reported the underlying mechanisms of sepsis. However, the reasons for the development of inflammation and degeneration in some brain regions and the persistence of neuroinflammation remain unclear. This mini-review describes the pathophysiology of region-specific inflammation after sepsis-associated encephalopathy (SAE), clinical features, and future prospects for SAE treatment. The hippocampus is highly susceptible to inflammation, and studies that perform treatments with antibodies to cytokine receptors, such as interleukin-1β, are in progress. Future development of clinically applicable therapies is expected.

Anti-inflammatory effect of ginsenoside Rg1 on LPS-induced septic encephalopathy and associated mechanism

BACKGROUND

Sepsis frequently occurs in patients after infection and is highly associated with death. Septic encephalopathy is characterized by dysfunction of the central nervous system, of which the root cause is a systemic inflammatory response. Sepsis-associated encephalopathy is a severe disease that frequently occurs in children, resulting in high morbidity and mortality.

OBJECTIVES

In the present study, we aim to investigate the neuroprotective mechanism of ginsenoside Rg1 in response to septic encephalopathy.

METHODS

Effects of ginsenoside Rg1 on septic encephalopathy were determined by cell viability, cytotoxicity, ROS responses, and apoptosis assays and histological examination of brain. Inflammatory activities were evaluated by expression levels of IL-1β, IL-6, IL-10, TNF-α, and MCP-1 using qPCR and ELISA. Activities of signaling pathways in inflammation were estimated by the production of p-Erk1/2/Erk1/2, p-JNK/JNK, p-p38/p38, p-p65/p65, and p-IkBα/IkBα using western blot.

RESULTS

LPS simulation resulted in a significant increase in cytotoxicity, ROS responses, and apoptosis and a significant decrease in cell viability in CTX TNA2 cells, as well as brain damage in rats. Moreover, the production of IL-1β, IL-6, IL-10, TNF-α, and MCP-1 was significantly stimulated both in CTX TNA2 cells and in the brain, which confirmed the establishment of vitro and in vivo models of septic encephalopathy. The damage and inflammatory responses induced by LPS were significantly decreased by treatment with Rg1. Western blot analyses indicated Rg1 significantly decreased the production of p-Erk1/2/Erk1/2, p-JNK/JNK, p-p38/p38, p-p65/p65, and p-IkBα/IkBα in LPS-induced CTX TNA2 cells and in the brain.

CONCLUSIONS

These findings suggested that Rg1 inhibited the activation of NF-κB and MAPK signaling pathways, which activate the production of proinflammatory cytokines and chemokines. The findings of this study suggest that ginsenoside Rg1 is a candidate treatment for septic encephalopathy.

Risk of Dementia or Cognitive Impairment in Sepsis Survivals: A Systematic Review and Meta-Analysis

Background

There is growing evidence that sepsis survivors are at increased risk of developing new-onset atrial fibrillation, acute kidney injury, and neurological diseases. However, whether sepsis survivals increase the risk of dementia or cognitive impairment remains to be further explored.

Objective

The objective of this study was to determine whether sepsis survivals increase the risk of dementia or cognitive impairment.

Methods

We searched PubMed, Cochrane Library, Web of Science, and EMBASE databases for cohort studies or case-control studies from their inception to November 5, 2021. The quality of this study was assessed using the Newcastle-Ottawa Quality Assessment Scale (NOS). The Stata software (version 15.1) was used to calculate the odds ratio (OR) of dementia or cognitive impairment in sepsis survivals. Subgroup and sensitivity analyses were performed to assess the source of heterogeneity. Funnel plots and Egger's test were used to detect the publication bias.

Results

Eight studies (i.e., seven cohort studies and one case-control study) involving 891,562 individuals were included. The quality assessment results showed that the average score of NOS was over 7, and the overall quality of the included studies was high. Pooled analyses indicated that sepsis survivals were associated with an increased risk of all-cause dementia (OR = 1.62, 95% CI = 1.23-2.15, I 2 = 96.4%, p = 0.001). However, there was no obvious association between sepsis survivals and the risk of cognitive impairment (OR = 1.77, 95% CI = 0.59-5.32, I 2 = 87.4%, p = 0.306). Subgroup analyses showed that severe sepsis was associated with an increased risk of dementia or cognitive impairment (OR = 1.99, 95% CI = 1.19-3.31, I 2 = 75.3%, p = 0.008); such risk was higher than that of other unspecified types of sepsis (OR = 1.47, 95% CI = 1.04-2.09, I 2 = 97.6%, p = 0.029).

Conclusion

Sepsis survivals are associated with an increased risk of all-cause dementia but not with cognitive impairment. Appropriate management and prevention are essential to preserve the cognitive function of sepsis survivors and reduce the risk of dementia.

The potential role of dexmedetomidine on neuroprotection and its possible mechanisms: Evidence from in vitro and in vivo studies

Neurological disorders following brain injuries and neurodegeneration are on the rise worldwide and cause disability and suffering in patients. It is crucial to explore novel neuroprotectants. Dexmedetomidine, a selective α2-adrenoceptor agonist, is commonly used for anxiolysis, sedation and analgesia in clinical anaesthesia and critical care. Recent studies have shown that dexmedetomidine exerts protective effects on multiple organs. This review summarized and discussed the current neuroprotective effects of dexmedetomidine, as well as the underlying mechanisms. In preclinical studies, dexmedetomidine reduced neuronal injury and improved functional outcomes in several models, including hypoxia-induced neuronal injury, ischaemic-reperfusion injury, intracerebral haemorrhage, post-traumatic brain injury, anaesthetic-induced neuronal injury, substance-induced neuronal injury, neuroinflammation, epilepsy and neurodegeneration. Several mechanisms are associated with the neuroprotective function of dexmedetomidine, including neurotransmitter regulation, inflammatory response, oxidative stress, apoptotic pathway, autophagy, mitochondrial function and other cell signalling pathways. In summary, dexmedetomidine has the potential to be a novel neuroprotective agent for a wide range of neurological disorders.

Circadian Clock Regulates Inflammation and the Development of Neurodegeneration

The circadian clock regulates numerous key physiological processes and maintains cellular, tissue, and systemic homeostasis. Disruption of circadian clock machinery influences key activities involved in immune response and brain function. Moreover, Immune activation has been closely linked to neurodegeneration. Here, we review the molecular clock machinery and the diurnal variation of immune activity. We summarize the circadian control of immunity in both central and peripheral immune cells, as well as the circadian regulation of brain cells that are implicated in neurodegeneration. We explore the important role of systemic inflammation on neurodegeneration. The circadian clock modulates cellular metabolism, which could be a mechanism underlying circadian control. We also discuss the circadian interventions implicated in inflammation and neurodegeneration. Targeting circadian clocks could be a potential strategy for the prevention and treatment of inflammation and neurodegenerative diseases.

Systemic inflammation induced the delayed reduction of excitatory synapses in the CA3 during ageing

Sepsis-associated encephalopathy (SAE) represents diverse cerebral dysfunctions in response to pathogen-induced systemic inflammation. Peripheral exposure to lipopolysaccharide (LPS), a component of the gram-negative bacterial cell wall, has been extensively used to model systemic inflammation. Our previous studies suggested that LPS led to hippocampal neuron death and synaptic destruction in vivo. However, the underlying roles of activated microglia in these neuronal changes remained unclear. Here, LPS from two different bacterial strains (Salmonella enterica or E. coli) were compared and injected in 14- to 16-month-old mice and evaluated for neuroinflammation and neuronal integrity in the hippocampus at 7 or 63 days post-injection (dpi). LPS injection resulted in persistent neuroinflammation lasting for seven days and a subsequent normalisation by 63 dpi. Of note, increases in proinflammatory cytokines, microglial morphology and microglial mean lysosome volume were more pronounced after E. coli LPS injection than Salmonella LPS at 7 dpi. While inhibitory synaptic puncta density remained normal, excitatory synaptic puncta were locally reduced in the CA3 region of the hippocampus at 63 dpi. Finally, we provide evidence that excitatory synapses coated with complement factor 3 (C3) decreased between 7 dpi and 63 dpi. Although we did not find an increase of synaptic pruning by microglia, it is plausible that microglia recognised and eliminated these C3-tagged synapses between the two time-points of investigation. Since a region-specific decline of CA3 synapses has previously been reported during normal ageing, we postulate that systemic inflammation may have accelerated or worsened the CA3 synaptic changes in the ageing brain.

Neuroinflammation in Sepsis: Molecular Pathways of Microglia Activation

Frequently underestimated, encephalopathy or delirium are common neurological manifestations associated with sepsis. Brain dysfunction occurs in up to 80% of cases and is directly associated with increased mortality and long-term neurocognitive consequences. Although the central nervous system (CNS) has been classically viewed as an immune-privileged system, neuroinflammation is emerging as a central mechanism of brain dysfunction in sepsis. Microglial cells are major players in this setting. Here, we aimed to discuss the current knowledge on how the brain is affected by peripheral immune activation in sepsis and the role of microglia in these processes. This review focused on the molecular pathways of microglial activity in sepsis, its regulatory mechanisms, and their interaction with other CNS cells, especially with neuronal cells and circuits.

What animal models can tell us about long-term cognitive dysfunction following sepsis: A systematic review

Survivors of sepsis often develop long-term cognitive impairments. This review aimed at exploring the results of the behavioral tools and tests which have been used to evaluate cognitive dysfunction in different animal models of sepsis. Two independent investigators searched for sepsis- and cognition-related keywords. 6323 publications were found, of which 355 were selected based on their title, and 226 of these were chosen based on manuscript review. LPS was used to induce sepsis in 171 studies, while CLP was used in 55 studies. Inhibitory avoidance was the most widely used method for assessing aversive memory, followed by fear conditioning and continuous multi-trial inhibitory avoidance. With regard to non-aversive memory, most studies used the water maze, open-field, object recognition, Y-maze, plus maze, and radial maze tests. Both CLP and LPS models of sepsis were effective in inducing short- and long-term behavioral impairment. Our findings help elucidate the mechanisms involved in the pathophysiology of sepsis-induced cognitive changes, as well as the available methods and tests used to study this in animal models.

Time course of dementia following sepsis in German health claims data

Objective

We evaluated the short-, medium-, and long-term effects of sepsis on dementia incidence using German health claims data.

Methods

A total of 161,567 patients (65 years or older) were followed from 2004 to 2015 at quarterly intervals. Time since sepsis was categorized into 0 (the effective quarter of sepsis diagnosis), 1–8, and ≥9 quarters since the latest diagnosis of sepsis, taking into account admission to intensive care unit and controlling for delirium, surgery, age, sex, and comorbidities. Incident dementia was defined for all persons who did not have a validated dementia diagnosis in 2004 and 2005 and who received a first-time, valid diagnosis between 2006 and 2015.

Results

During the quarter of sepsis diagnosis, patients not admitted to intensive care had a 3.14-fold (95% CI 2.83–3.49) increased risk, and those with intensive care stay had a 2.22-fold (95% CI: 1.83–2.70) increased risk of receiving an incident dementia diagnosis compared with patients without sepsis. The impact of sepsis on incident dementia remained in the following 2 years, remitting only thereafter.

Conclusions

For sepsis survivors, medium-term dementia risk remains elevated, whereas long-term risk may reach the level of those without sepsis, even after controlling for delirium. These findings encourage identifying modifiable components of hospital and rehabilitation care.

CRISPR/Cas9-induced nos2b mutant zebrafish display behavioral abnormalities

The immunomodulatory function of nitric oxide synthase (NOS2) has been extensively studied. However, some behavioral abnormalities caused by its mutations have been found in a few rodent studies, of which the molecular mechanism remains elusive. In this research, we generated nos2b gene knockout zebrafish (nos2b^sou2/sou2 ) using CRISPR/Cas9 approach and investigated their behavioral and molecular changes by doing a series of behavioral detections, morphological measurements, and molecular analyses. We found that, compared with nos2b^+/+ zebrafish, nos2b^sou2/sou2 zebrafish exhibited enhanced motor activity; additionally, nos2b^sou2/sou2 zebrafish were characterized by smaller brain size, abnormal structure of optic tectum, reduced mRNA level of presynaptic synaptophysin and postsynaptic homer1, and altered response to sodium nitroprusside/methylphenidate hydrochloride treatment. These findings will likely contribute to future studies of behavioral regulation.

3-[(4-chlorophenyl)selanyl]-1-methyl-1H-indole ameliorates long-lasting depression- and anxiogenic-like behaviors and cognitive impairment in post-septic mice: Involvement of neuroimmune and oxidative hallmarks

Only in the last decade the long-term consequences of sepsis started to be studied and even less attention has been given to the treatment of psychological symptoms of sepsis survivors. It is estimated that 60% of sepsis survivors have psychological disturbances, including depression, anxiety, and cognitive impairment. Although the causative factors remain largely poorly understood, blood-brain barrier (BBB) disturbances, neuroinflammation, and oxidative stress have been investigated. Therefore, we sought to explore if the immunomodulatory and antioxidant selenocompound 3-[(4-chlorophenyl)selanyl]-1-methyl-1H-indole (CMI) would be able to ameliorate long-term behavioral and biochemical alterations in sepsis survivors male Swiss mice. CMI treatment (1 mg/kg, given orally for seven consecutive days) attenuated depression- and anxiogenic-like behaviors and cognitive impairment present one month after the induction of sepsis (lipopolysaccharide, 5 mg/kg intraperitoneally). Meantime, CMI treatment modulated the number of neutrophils and levels of reactive species in neutrophils, lymphocytes, and monocytes. In addition, peripheral markers of liver and kidneys dysfunction (AST, ALT, urea, and creatinine) were reduced after CMI treatment in post-septic mice. Notably, CMI treatment to non-septic mice did not alter AST, ALT, urea, and creatinine levels, indicating the absence of acute hepatotoxicity and nephrotoxicity following CMI treatment. Noteworthy, CMI ameliorated BBB dysfunction induced by sepsis, modulating the expression of inflammation-associated genes (NFκB, IL-1β, TNF-α, IDO, COX-2, iNOS, and BDNF) and markers of oxidative stress (reactive species, nitric oxide, and lipid peroxidation levels) in the prefrontal cortices and hippocampi of mice. In conclusion, we unraveled crucial molecular pathways that are impaired in post-septic mice and we present CMI as a promising therapeutic candidate aimed to manage the long-lasting behavioral alterations of sepsis survivors to improve their quality of life.

Systemic and CNS Inflammation Crosstalk: Implications for Alzheimer's Disease

After years of failed therapeutic attempts targeting beta-amyloid (Aβ) in AD, there is now increasing evidence suggesting that inflammation holds a pivotal role in AD pathogenesis and immune pathways can possibly comprise primary therapeutic targets. Inflammation is a key characteristic of numerous diseases including neurodegenerative disorders and thus not surprisingly suppression of inflammation frequently constitutes a major therapeutic strategy for a wide spectrum of disorders. Several brain-resident and peripherally-derived immune populations and inflammatory mediators are involved in AD pathophysiology, with microglia comprising central cellular player in the disease process. Systemic inflammation, mostly in the form of infections, has long been observed to induce behavioral alterations and cognitive dysfunction, suggesting for a close interaction of the peripheral immune system with the brain. Systemic inflammation can result in neuroinflammation, mainly exhibited as microglial activation, production of inflammatory molecules, as well as recruitment of peripheral immune cells in the brain, thus shaping a cerebral inflammatory milieu that may seriously impact neuronal function. Increasing clinical and experimental studies have provided significant evidence that acute (e.g. infections) or chronic (e.g. autoimmune diseases like rheumatoid arthritis) systemic inflammatory conditions may be associated with increased AD risk and accelerate AD progression. Here we review the current literature that links systemic with CNS inflammation and the implications of this interaction for AD in the context of acute and chronic systemic pathologies as acute infection and rheumatoid arthritis. Elucidating the mechanisms that govern the crosstalk between the peripheral and the local brain immune system may provide the ground for new therapeutic approaches that target the immune-brain interface and shed light on the understanding of AD.

Simvastatin Prevents Long-Term Cognitive Deficits in Sepsis Survivor Rats by Reducing Neuroinflammation and Neurodegeneration

Sepsis-associated encephalopathy causes brain dysfunction that can result in cognitive impairments in sepsis survivor patients. In previous work, we showed that simvastatin attenuated oxidative stress in brain structures related to memory in septic rats. However, there is still a need to evaluate the long-term impact of simvastatin administration on brain neurodegenerative processes and cognitive damage in sepsis survivors. Here, we investigated the possible neuroprotective role of simvastatin in neuroinflammation, and neurodegeneration conditions of brain structures related to memory in rats at 10 days after sepsis survival. Male Wistar rats (250-300 g) were submitted to cecal ligation and puncture (CLP, n = 42) or remained as non-manipulated (naïve, n = 30). Both groups were treated (before and after the surgery) by gavage with simvastatin (20 mg/kg) or an equivalent volume of saline and observed for 10 days. Simvastatin-treated rats that survived to sepsis showed a reduction in the levels of nitrate, IL1-β, and IL-6 and an increase in Bcl-2 protein expression in the prefrontal cortex and hippocampus, and synaptophysin only in the hippocampus. Immunofluorescence revealed a reduction of glial activation, neurodegeneration, apoptosis, and amyloid aggregates confirmed by quantification of GFAP, Iba-1, phospho Ser₃₉₆-tau, total tau, cleaved caspase-3, and thioflavin-S in the prefrontal cortex and hippocampus. In addition, treated animals presented better performance in tasks involving habituation memory, discriminative, and aversive memory. These results suggest that statins exert a neuroprotective role by upregulation of the Bcl-2 and gliosis reduction, which may prevent the cognitive deficit observed in sepsis survivor animals.

Prolonged Soluble Epoxide Hydrolase Reactivity in Brain Endothelial Cells Is Associated with Long Cognitive Deficits in Sepsis

Sepsis-associated encephalopathy (SAE) is known to cause long-term cognitive deficits which are related to sustained microglial activation, but the mechanisms are unclear. Recently, studies have shown soluble epoxide hydrolase (sEH) affects the chronic cognitive function or participates in long-term neuropsychiatric illness. We hypothesized that sEH may be involved in the long-term cognitive deficits of SAE. Male C57BL/6 mice were subjected to cecal ligation and puncture (CLP) and were administered vehicle or sEH inhibitor TPPU. CLP induced prolonged endothelial sEH reactivity and sustained activation of microglia in close vicinity to blood vessels at 14 days. We also observed that persistent loss of endothelial BBB function at 14 days following CLP. However, TPPU-treated septic mice exhibited improved BBB function and declined neuro-inflammation. We confirmed these beneficial effects in vitro, which indicated TPPU resulted in a significant improvement in IL-1β-induced loss of BBB integrity on hCMEC/D3 cell monolayers. Animals were also given a behavior test at 14 days after CLP. Mice showed normal basal locomotor activity in the open field compared with sham-operated animals, but performed fewer entries to the center zone, indicating increased anxiety-like behavior as avoidance of the center. TPPU-treated CLP mice showed normal crossing into the center zone during an open-field test and improved recovery of the ability to learn the novel object recognition (NOR) task compared with saline-treated CLP animals. Our data indicated that prolonged sEH reactivity in brain endothelial cells is associated with long cognitive deficits in sepsis. sEHIs such as TPPU can improve the endothelial barrier function and decrease CLP-induced long-term encephalopathy, at least in part, through anti-inflammatory effects.

NADPH oxidase 2 as a potential therapeutic target for protection against cognitive deficits following systemic inflammation in mice

BACKGROUND

Research indicates that sepsis increases the risk of developing cognitive impairment. After systemic inflammation, a corresponding activation of microglia is rapidly induced in the brain, and multiple neurotoxic factors, including inflammatory mediators (e.g., cytokines) and reactive oxygen species (e.g., superoxide), are also released that contribute to neuronal injury. NADPH oxidase (NOX) enzymes play a vital role in microglial activation through the generation of superoxide anions. We hypothesized that NOX isoforms, particularly NOX2, could exhibit remarkable abilities in developing cognitive deficits induced by systemic inflammation.

METHODS

Mice with deficits of NOX2 organizer p47phox (p47^phox-/-) and wild-type (WT) mice treated with the NOX inhibitor diphenyleneiodonium (DPI) were used in this study. Intraperitoneal lipopolysaccharide (LPS) injection was used to induce systemic inflammation. Spatial learning and memory were compared among treatment groups using the radial arm maze task. Brain tissues were collected for evaluating the transcript levels of proinflammatory cytokines, whereas immunofluorescence staining and immunoblotting were conducted to determine the percentage of activated glia (microglia and astroglia) and damaged neurons and the expression of synaptic proteins and BDNF.

RESULTS

Cognitive impairment induced by systemic inflammation was significantly attenuated in the p47^phox-/- mice compared to that in the WT mice. The p47^phox-/- mice exhibited reduced microglial and astroglial activation and neuronal damage and attenuated the induction of multiple proinflammatory cytokines, including tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and CCL2. Similar to that observed in the p47^phox-/- mice, the administration of DPI significantly attenuated the cognitive impairment, reduced the glial activation and brain cytokine concentrations, and restored the expression of postsynaptic proteins (PSD-95) and BDNF in neurons and astrocytes, compared to those in the vehicle-treated controls within 10 days after LPS injection.

CONCLUSIONS

This study clearly demonstrates that NOX2 contributes to glial activation with subsequent reduction in the expression of BDNF, synaptic dysfunction, and cognitive deficits after systemic inflammation in an LPS-injected mouse model. Our results provide evidence that NOX2 might be a promising pharmacological target that could be used to protect against synaptic dysregulation and cognitive impairment following systemic inflammation.

Enduring and Sex-specific Changes in Hippocampal Gene Expression after a Subchronic Immune Challenge

Major illnesses, including heart attack and sepsis, can cause cognitive impairments, depression, and progressive memory decline that persist long after recovery from the original illness. In rodent models of sepsis or subchronic immune challenge, memory deficits also persist for weeks or months, even in the absence of ongoing neuroimmune activation. This raises the question of what mechanisms in the brain mediate such persistent changes in neural function. Here, we used RNA-sequencing as a large-scale, unbiased approach to identify changes in hippocampal gene expression long after a subchronic immune challenge previously established to cause persistent memory impairments in both males and females. We observed enduring dysregulation of gene expression three months after the end of a subchronic immune challenge. Surprisingly, there were striking sex differences in both the magnitude of changes and the specific genes and pathways altered, where males showed persistent changes in both immune- and plasticity-related genes three months after immune challenge, whereas females showed few such changes. In contrast, females showed striking differential gene expression in response to a subsequent immune challenge. Thus, immune activation has enduring and sex-specific consequences for hippocampal gene expression and the transcriptional response to subsequent stimuli. Together with findings of long-lasting memory impairments after immune challenge, these data suggest that illnesses can cause enduring vulnerability to, cognitive decline, affective disorders, and memory impairments via dysregulation of transcriptional processes in the brain.

Dexmedetomidine protects against sepsis‑associated encephalopathy through Hsp90/AKT signaling

Sepsis‑associated encephalopathy (SAE) is characterized by neuronal apoptosis and changes in mental status. Accumulating evidence has. indicated that dexmedetomidine is capable of protecting the brain against external stimuli and improving cognitive dysfunctions. The aim of the present study was to investigate the possible neuroprotective effects of dexmedetomidine on SAE and the role of heat‑shock protein (Hsp)90/AKT signaling in an experimental model of sepsis. The SAE model was established by cecal ligation and perforation (CLP) in vivo and lipopolysaccharide (LPS) treated hippocampal neuronal cultures in vitro. It was found that dexmedetomidine inhibited caspase‑3, but increased the expression level ofBcl‑2 in CLP rats. CLP rats also exhibited a decreased level of phosphorylated AKT Thr 308 and Hsp90, and their expression could be reversed by treatment with dexmedetomidine. Additionally, application of dexmedetomidine increased cell survival and decreased neuronal apoptosis in vitro. Furthermore, the neuroprotective effects of dexmedetomidine could be reversed by 17‑AAG (a Hsp90 inhibitor), or wortmannin (a PI3K inhibitor). Analysis of TUNEL staining indicated that dexmedetomidine improved LPS‑induced neuronal apoptosis, which could be eradicated by AKT short hairpin RNA transfection, prazosin or yohimbine. Finally, dexmedetomidine ameliorated both the emotional and spatial cognitive disorders without alteration in locomotor activity. The present findings suggested that dexmedetomidine may protect the brain against SAE, and that the Hsp90/AKT pathway may be involved in this process.

Systemic inflammation impairs microglial Aβ clearance through NLRP3 inflammasome

Alzheimer's disease is the most prevalent type of dementia and is caused by the deposition of extracellular amyloid-beta and abnormal tau phosphorylation. Neuroinflammation has emerged as an additional pathological component. Microglia, representing the brain's major innate immune cells, play an important role during Alzheimer's. Once activated, microglia show changes in their morphology, characterized by a retraction of cell processes. Systemic inflammation is known to increase the risk for cognitive decline in human neurogenerative diseases including Alzheimer's. Here, we assess for the first time microglial changes upon a peripheral immune challenge in the context of aging and Alzheimer's in vivo, using 2-photon laser scanning microscopy. Microglia were monitored at 2 and 10 days post-challenge by lipopolysaccharide. Microglia exhibited a reduction in the number of branches and the area covered at 2 days, a phenomenon that resolved at 10 days. Systemic inflammation reduced microglial clearance of amyloid-beta in APP/PS1 mice. NLRP3 inflammasome knockout blocked many of the observed microglial changes upon lipopolysaccharide, including alterations in microglial morphology and amyloid pathology. NLRP3 inhibition may thus represent a novel therapeutic target that may protect the brain from toxic peripheral inflammation during systemic infection.

Activation of β2-Adrenoceptor Attenuates Sepsis-Induced Hippocampus-Dependent Cognitive Impairments by Reversing Neuroinflammation and Synaptic Abnormalities

Sepsis-associated encephalopathy induces cognitive dysfunction via mechanisms that commonly involve neuroinflammation and synaptic plasticity impairment of the hippocampus. The β2-adrenoceptor (β2-AR) is a G-protein coupled receptor that regulates immune response and synaptic plasticity, whereas its dysfunction has been implicated in various neurodegenerative diseases. Thus, we hypothesized abnormal β2-AR signaling is involved in sepsis-induced cognitive impairment. In the present study, C57BL/6 mice were subjected to cecal ligation and puncture (CLP) to mimic the clinical human sepsis-associated encephalopathy. The levels of hippocampal β2-AR, proinflammatory cytokines tumor necrosis factor (TNF-α), interleukin-1β (IL-1β), IL-6, cAMP-response element binding protein (CREB), brain derived neurotrophic factor (BDNF), post-synaptic density protein 95 (PSD95), and NMDA receptor 2 B subtypes (GluN2B) were determined at 6, 12, 24 h and 7 and 16 days after CLP. For the interventional study, mice were treated with β2-AR agonist clenbuterol in two ways: early treatment (immediately following CLP) and delayed treatment (on the 8th day following CLP). Neurobehavioral performances were assessed by open field and fear conditioning tests. Here, we found that hippocampal β2-AR expression was significantly decreased starting from 12 h and persisted until 16 days following CLP. Besides, sepsis mice also exhibited increasing neuroinflammation, down-regulated CREB/BDNF, decreasing PSD95 and GluN2B expression, and displayed hippocampus-dependent cognitive impairments. Notably, early clenbuterol treatment alleviated sepsis-induced cognitive deficits by polarizing microglia toward an anti-inflammatory phenotype, reducing proinflammatory cytokines including IL-1β, TNF-α, and up-regulating CREB/BDNF, PSD95, and GluN2B. Intriguingly, delayed clenbuterol treatment also improved cognitive impairments by normalization of hippocampal CREB/BDNF, PSD95, and GluN2B. In summary, our results support the beneficial effects of both early and delayed clenbuterol treatment, which suggests that activation of β2-AR has a translational value in sepsis-associated organ dysfunction including cognitive impairments.

Dexmedetomidine inhibits astrocyte pyroptosis and subsequently protects the brain in in vitro and in vivo models of sepsis

Sepsis is life-threatening and often leads to acute brain damage. Dexmedetomidine, an α₂-adrenoceptor agonist, has been reported to possess neuroprotective effects against various brain injury but underlying mechanisms remain elusive. In this study, in vitro and in vivo models of sepsis were used to explore the effects of dexmedetomidine on the inflammasome activity and its associated glia pyroptosis and neuronal death. In vitro, inflammasome activation and pyroptosis were found in astrocytes following lipopolysaccharide (LPS) exposure. Dexmedetomidine significantly alleviated astrocyte pyroptosis and inhibited histone release induced by LPS. In vivo, LPS treatment in rats promoted caspase-1 immunoreactivity in astrocytes and caused an increase in the release of pro-inflammatory cytokines of IL-1β and IL-18, resulting in neuronal injury, which was attenuated by dexmedetomidine; this neuroprotective effect was abolished by α₂-adrenoceptor antagonist atipamezole. Dexmedetomidine significantly reduced the high mortality rate caused by LPS challenge. Our data demonstrated that dexmedetomidine may protect glia cells via reducing pyroptosis and subsequently protect neurons, all of which may preserve brain function and ultimately improve the outcome in sepsis.

Memory deficits in males and females long after subchronic immune challenge

Memory impairments and cognitive decline persist long after recovery from major illness or injury, and correlate with increased risk of later dementia. Here we developed a subchronic peripheral immune challenge model to examine delayed and persistent memory impairments in females and in males. We show that intermittent injections of either lipopolysaccharides or Poly I:C cause memory decline in both sexes that are evident eight weeks after the immune challenge. Importantly, we observed sex-specific patterns of deficits. Females showed impairments in object recognition one week after challenge that persisted for at least eight weeks. In contrast, males had intact memory one week after the immune challenge but exhibited broad impairments in memory tasks including object recognition, and both context and tone fear conditioning several months later. The differential patterns of memory deficits in males and in females were observed without sustained microglial activation or changes in blood-brain barrier permeability. Together, these data suggest that transient neuroimmune activity results in differential vulnerabilities of females and males to memory decline after immune challenge. This model will be an important tool for determining the mechanisms in both sexes that contribute to memory impairments that develop over the weeks and months after recovery from illness. Future studies using this model will provide new insights into the role of chronic inflammation in the pathogenesis of long-lasting memory decline and dementias.

Inflammatory cytokines expression in Wilson's disease

BACKGROUND

Wilson's disease (WD) is an autosomal recessive inherited disorder of copper (Cu) metabolism. Inflammation is a self-defensive reaction aimed at eliminating or neutralizing injurious stimuli, and restoring tissue integrity. Copper deposition may lead to inflammation in the organs and tissues of WD patients.

OBJECTIVE

The aim of this study was to compare the plasma levels of inflammatory cytokines in patients with WD and healthy group, and also to assess whether inflammatory cytokines affects the clinical manifestation of WD.

METHODS

Ninety-nine patients with WD and 32 controls were recruited for this study. Ray Biotech antibody microarray was used to detect the levels of plasma inflammatory cytokines.

RESULTS AND CONCLUSION

Our results showed significant increase in T helper (Th) 1 cells (IL-2, TNF-α, and TNF-β), Th2 cells (IL-5, IL-10, and IL-13), and Th17 (IL-23) (p < 0.05). Higher plasma Th 1 cells (IL-2, TNF-α, and TNF-β), Th 2 cells (IL-13), and Th 17 (TGF-β1, IL-23) levels were found in neurological patients compared with control groups (p < 0.01). Besides, we found Th 1 cells (TNF-α and TNF-β), Th 3 (TGF-β1), and Th 17 (IL-23) levels were significantly higher in hepatic and neurological patients (p < 0.05). In addition, the higher Th1 cells (IL-2, TNF-α, and TNF-β), Th2 cells (IL-13), and Th17 (TGF-β1, IL-23) and the course of WD were associated with the severity of the neurological symptoms for WD patients. Altogether, our results indicated that dysregulation of cytokines, mainly increased expression of cytokines and chemokines, occurred in WD patients.

Long-Term Cognitive Outcomes After Sepsis: a Translational Systematic Review

Sepsis is systemic inflammatory response syndrome with a life-threatening organ dysfunction that is caused by an unbalanced host immune response in an attempt to eliminate invasive microorganisms. We posed questions, "Does sepsis survivor patients have increased risk of neuropsychiatric manifestations?" and "What is the mechanism by which sepsis induces long-term neurological sequelae, particularly substantial cognitive function decline in survivor patients and in pre-clinical sepsis models?" The studies were identified by searching PubMed/MEDLINE (National Library of Medicine), PsycINFO, EMBASE (Ovid), LILACS (Latin American and Caribbean Health Sciences Literature), IBECS (Bibliographical Index in Spanish in Health Sciences), and Web of Science databases for peer-reviewed journals that were published until January 2018. A total of 3555 papers were included in the primary screening. After that, 130 articles were selected for the study. A number of pre-clinical studies have shown an auto amplification of pro-inflammatory cytokines such as tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6 in the first few hours after sepsis induction, also increased blood-brain barrier permeability, elevated levels of matrix metalloproteinases, increased levels of damage-associated molecular patterns were demonstrated. In addition, the rodents presented long-term cognitive impairment in different behavioral tasks that were prevented by blocking the mechanism of action of these inflammatory mediators. Clinical studies have showed that sepsis survivors presented increased bodily symptoms such as fatigue, pain, visual disturbances, gastrointestinal problems, and neuropsychiatric problems compared to before sepsis. Sepsis leaves the survivors with an aftermath of physiological, neuropsychiatric, and functional impairment. Systematic review registration: CRD42017071755.

Mechanisms of action of intravenous immunoglobulin in septic encephalopathy

Acute brain dysfunction associated with sepsis is a serious complication that results in morbidity and mortality. Intravenous immunoglobulin (IVIg) treatment is known to alleviate behavioral deficits in the experimentally induced model of sepsis. To delineate the mechanisms by which IVIg treatment prevents neuronal dysfunction, an array of immunological and apoptosis markers was investigated. Our results suggest that IVIgG and IgGAM administration ameliorates neuronal dysfunction and behavioral deficits by reducing apoptotic cell death and glial cell proliferation. IgGAM treatment might suppress classical complement pathway by reducing C5a activity and proapoptotic NF-κB and Bax expressions, thereby, inhibiting major inflammation and apoptosis cascades. Future animal model experiments performed with specific C5aR and NF-κB agonists/antagonists or C5aR-deficient mice might more robustly disclose the significance of these pathways. C5a, C5aR, and NF-κB, which were shown to be the key molecules in brain injury pathogenesis in sepsis, might also be utilized as potential targets for future treatment trials of septic encephalopathy.

Neuroimmune Activation Drives Multiple Brain States

Neuroimmune signaling is increasingly identified as a critical component of neuronal processes underlying memory, emotion and cognition. The interactions of microglia and astrocytes with neurons and synapses, and the individual cytokines and immune signaling molecules that mediate these interactions are a current focus of much research. Here, we discuss neuroimmune activation as a mechanism triggering different states that modulate cognitive and affective processes to allow for appropriate behavior during and after illness or injury. We propose that these states lie on a continuum from a naïve homeostatic baseline state in the absence of stimulation, to acute neuroimmune activity and chronic activation. Importantly, consequences of illness or injury including cognitive deficits and mood impairments can persist long after resolution of immune signaling. This suggests that neuroimmune activation also results in an enduring shift in the homeostatic baseline state with long lasting consequences for neural function and behavior. Such different states can be identified in a multidimensional way, using patterns of cytokine and glial activation, behavioral and cognitive changes, and epigenetic signatures. Identifying distinct neuroimmune states and their consequences for neural function will provide a framework for predicting vulnerability to disorders of memory, cognition and emotion both during and long after recovery from illness.

S100A8/A9 Drives Neuroinflammatory Priming and Protects against Anxiety-like Behavior after Sepsis

Sepsis commonly results in acute and chronic brain dysfunction, which dramatically increases the morbidity associated with this common disease. Chronic brain dysfunction in animal models of sepsis survival is linked to persistent neuroinflammation and expression of multiple cytokines. However, we have found previously that microglia predominantly upregulate the damage associated molecule S100A8/A9 after sepsis. In this article, we show that S100A8/A9 is increased in the brains of patients who died of sepsis and that S100A8 is expressed in astrocytes and myeloid cells. Using a mouse model of sepsis survival, we show that S100A8/A9 is persistently expressed in the brain after sepsis. S100A9 expression is necessary for recruitment of neutrophils to the brain and for priming production of reactive oxygen species and TNF-α secretion in microglia and macrophages. However, despite improving these indices of chronic inflammation, S100A9 deficiency results in worsened anxiety-like behavior 2 wk after sepsis. Taken together, these results indicate that S100A8/A9 contributes to several facets of neuroinflammation in sepsis survivor mice, including granulocyte recruitment and priming of microglial-reactive oxygen species and cytokine production, and that these processes may be protective against anxiety behavior in sepsis survivors.

Bacterial Dissemination to the Brain in Sepsis

RATIONALE

Sepsis causes brain dysfunction and neuroinflammation. It is unknown whether neuroinflammation in sepsis is initiated by dissemination of bacteria to the brain and sustained by persistent infection, or whether neuroinflammation is a sterile process resulting solely from circulating inflammatory mediators.

OBJECTIVES

To determine if gut bacteria translocate to the brain during sepsis, and are associated with neuroinflammation.

METHODS

Murine sepsis was induced using cecal ligation and puncture, and sepsis survivor mice were compared with sham and unoperated control animals. Brain tissue of patients who died of sepsis was compared with patients who died of noninfectious causes. Bacterial taxa were characterized by 16S ribosomal RNA gene sequencing in both murine and human brain specimens; compared among sepsis and nonsepsis groups; and correlated with levels of S100A8, a marker of neuroinflammation using permutational multivariate ANOVA.

MEASUREMENTS AND MAIN RESULTS

Viable gut-associated bacteria were enriched in the brains of mice 5 days after surviving abdominal sepsis (P < 0.01), and undetectable by 14 days. The community structure of brain-associated bacteria correlated with severity of neuroinflammation (P < 0.001). Furthermore, bacterial taxa detected in brains of humans who die of sepsis were distinct from those who died of noninfectious causes (P < 0.001) and correlated with S100A8/A9 expression (P < 0.05).

CONCLUSIONS

Although bacterial translocation is associated with acute neuroinflammation in murine sepsis, bacterial translocation did not result in chronic cerebral infection. Postmortem analysis of patients who die of sepsis suggests a role for bacteria in acute brain dysfunction in sepsis. Further work is needed to determine if modifying gut-associated bacterial communities modulates brain dysfunction after sepsis.

Lipocalin-2 protects the brain during inflammatory conditions

Sepsis is a prevalent health issue that can lead to central nervous system (CNS) inflammation with long-term behavioral and cognitive alterations. Using unbiased proteomic profiling of over 100 different cytokines, we found that Lipocalin-2 (LCN2) was the most substantially elevated protein in the CNS after peripheral administration of lipopolysaccharide (LPS). To determine whether the high level of LCN2 in the CNS is protective or deleterious, we challenged Lcn2^-/- mice with peripheral LPS and determined effects on behavior and neuroinflammation. At a time corresponding to peak LCN2 induction in wild-type (WT) mice injected with LPS, Lcn2^-/- mice challenged with LPS had exacerbated levels of pro-inflammatory cytokines and exhibited significantly worsened behavioral phenotypes. To determine the extent of global inflammatory changes dependent upon LCN2, we performed an RNAseq transcriptomic analysis. Compared with WT mice injected with LPS, Lcn2^-/- mice injected with LPS had unique transcriptional profiles and significantly elevated levels of multiple pro-inflammatory molecules. Several LCN2-dependent pathways were revealed with this analysis including, cytokine and chemokine signaling, nucleotide-binding oligomerization domain-like receptor signaling and Janus kinase-signal transducer and activator of transcription signaling. These findings demonstrate that LCN2 serves as a potent protective factor in the CNS in response to systemic inflammation and may be a potential candidate for limiting sepsis-related CNS sequelae.

Functional and structural damage of neurons by innate immune mechanisms during neurodegeneration

Over the past decades, our view on neurodegenerative diseases has been mainly centered around neurons and their networks. Only recently it became evident that immunological processes arise alongside degenerating neurons, raising the question whether these represent just meaningless bystander reactions or in turn, contribute to pathogenesis and disease symptoms. When considering any effect of inflammatory events on the CNS one has to consider the site, duration and nature of immune activation. Likewise, one has to distinguish between mechanisms which directly impact the neuronal compartment and indirect mechanisms, which affect cells that are important for neuronal functioning and survival. As discussed in this review, both types of mechanisms may be present at the same time and additively or synergistically lead to neuronal demise. Inflammatory mediators released by the principle innate immune cells of the brain, microglia and astrocytes, can compromise the function and structure of neurons, thereby playing important roles in the pathogenesis of neurodegenerative diseases.