Sepsis-associated encephalopathy: a vicious cycle of immunosuppression

Pathogenesis of sepsis-associated encephalopathy: more than blood-brain barrier dysfunction

Sepsis-associated encephalopathy is a common neurological complication of sepsis and is responsible for higher mortality and poorer long-term outcomes in septic patients. Sepsis-associated encephalopathy symptoms can range from mild delirium to deep coma, which occurs in up to 70% of patients in intensive care units. The pathological changes in the brain associated with sepsis include cerebral ischaemia, cerebral haemorrhage, abscess and progressive multifocal necrotic leukoencephalopathy. Several mechanisms are involved in the pathogenesis of sepsis-associated encephalopathy, such as blood-brain barrier dysfunction, cerebral blood flow impairment, glial cell activation, leukocyte transmigration, and neurotransmitter disturbances. These events are interrelated and influence each other, therefore they do not act as independent factors. This review is focused on new evidence showing the pathological process of sepsis-associated encephalopathy.

Thioredoxin-Interacting Protein (TXNIP) Knockdown Protects against Sepsis-Induced Brain Injury and Cognitive Decline in Mice by Suppressing Oxidative Stress and Neuroinflammation

Sepsis-associated encephalopathy (SAE) is linked to increased morbidity and mortality rates in patients with sepsis. Increased cytokine production and neuronal apoptosis are implicated in the pathogenesis of the SAE. Neuroinflammation plays a major role in sepsis-induced brain injury. Thioredoxin-interacting protein (TXNIP), an inhibitor of thioredoxin, is associated with oxidative stress and inflammation. However, whether the TXNIP is involved in the sepsis-induced brain injury and the underlying mechanism is yet to be elucidated. Therefore, the present study was aimed at elucidating the effects of TXNIP knockdown on sepsis-induced brain injury and cognitive decline in mice. Lipopolysaccharide (LPS) was injected intraperitoneally to induce sepsis brain injury in mice. The virus-carrying control or TXNIP shRNA was injected into the lateral ventricle of the brain 4 weeks before the LPS treatment. The histological changes in the hippocampal tissues, encephaledema, and cognitive function were detected, respectively. Also, the 7-day survival rate was recorded. Furthermore, the alterations in microglial activity, oxidative response, proinflammatory factors, apoptosis, protein levels (TXNIP and NLRP3 inflammasome), and apoptosis were examined in the hippocampal tissues. The results demonstrated that the TXNIP and NLRP3 inflammasome expression levels were increased at 6, 12, and 24 h post-LPS injection. TXNIP knockdown dramatically ameliorated the 7-day survival rate, cognitive decline, brain damage, neuronal apoptosis, and the brain water content, inhibited the activation of microglia, downregulated the NLRP3/caspase-1 signaling pathway, and reduced the oxidative stress and the neuroinflammatory cytokine levels at 24 h post-LPS injection. These results suggested a crucial effect of TXNIP knockdown on the mechanism of brain injury and cognitive decline in sepsis mice via suppressing oxidative stress and neuroinflammation. Thus, TXNIP might be a potential therapeutic target for SAE patients.

Polarization of Microglia and Its Therapeutic Potential in Sepsis

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection, leaving the inflammation process without a proper resolution, leading to tissue damage and possibly sequelae. The central nervous system (CNS) is one of the first regions affected by the peripheral inflammation caused by sepsis, exposing the neurons to an environment of oxidative stress, triggering neuronal dysfunction and apoptosis. Sepsis-associated encephalopathy (SAE) is the most frequent sepsis-associated organ dysfunction, with symptoms such as deliriums, seizures, and coma, linked to increased mortality, morbidity, and cognitive disability. However, the current therapy does not avoid those patients’ symptoms, evidencing the search for a more optimal approach. Herein we focus on microglia as a prominent therapeutic target due to its multiple functions maintaining CNS homeostasis and its polarizing capabilities, stimulating and resolving neuroinflammation depending on the stimuli. Microglia polarization is a target of multiple studies involving nerve cell preservation in diseases caused or aggravated by neuroinflammation, but in sepsis, its therapeutic potential is overlooked. We highlight the peroxisome proliferator-activated receptor gamma (PPARγ) neuroprotective properties, its role in microglia polarization and inflammation resolution, and the interaction with nuclear factor-κB (NF-κB) and mitogen-activated kinases (MAPK), making PPARγ a molecular target for sepsis-related studies to come.

Protective Effects of Cannabinoid Type 2 Receptor Against Microglia Overactivation and Neuronal Pyroptosis in Sepsis-Associated Encephalopathy

Sepsis-associated encephalopathy (SAE) has close association with long-term cognitive deficits, resulting in increased mortality. The mechanism of SAE is complicate, including excessive microglial activation and neuroinflammation. Pyroptosis is a type of proinflammatory cell death program. Cannabinoid type 2 receptor (CB2R) has been proved to be effective in neuronal protection and survival promotion. Microglia play a role in CB2R mediated neuronal protection when neurons are exposed to noxious stimuli. However, the underlying mechanisms involved in this process still remain to be explored. Previous studies have demonstrated that CB2R can reduce sepsis-induced lung injury by inhibiting pyroptosis. Here, SAE model was established by cecal ligation and puncture (CLP). Open field test (OFT), novel object recognition test (NORT), and Morris water maze (MWM) test were performed to assess cognitive function. Brain samples were obtained to detect cell injury, cytokine, CB2R and pyroptosis-associated protein expression by Hematoxylin-Eosin (HE) staining, Enzyme-linked immunosorbent assay (ELISA), Western blotting and Immunofluorescence staining. CLP could induce microglia hyperactivation and neuronal pyroptosis, aggravating brain tissue destruction and cognitive dysfunction. The activation of CB2R could have a protective effect against SAE by inhibiting microglia activity and neuronal pyroptosis. This will provide a new therapeutic option for the treatment of SAE.

Insight Into Regulatory T Cells in Sepsis-Associated Encephalopathy

Sepsis-associated encephalopathy (SAE) is a diffuse central nervous system (CNS) dysfunction during sepsis, and is associated with increased mortality and poor outcomes in septic patients. Despite the high incidence and clinical relevance, the exact mechanisms driving SAE pathogenesis are not yet fully understood, and no specific therapeutic strategies are available. Regulatory T cells (T_regs) have a role in SAE pathogenesis, thought to be related with alleviation of sepsis-induced hyper-inflammation and immune responses, promotion of T helper (Th) 2 cells functional shift, neuroinflammation resolution, improvement of the blood-brain barrier (BBB) function, among others. Moreover, in a clinical point of view, these cells have the potential value of improving neurological and psychiatric/mental symptoms in SAE patients. This review aims to provide a general overview of SAE from its initial clinical presentation to long-term cognitive impairment and summarizes the main features of its pathogenesis. Additionally, a detailed overview on the main mechanisms by which T_regs may impact SAE pathogenesis is given. Finally, and considering that T_regs may be a novel target for immunomodulatory intervention in SAE, different therapeutic options, aiming to boost peripheral and brain infiltration of T_regs, are discussed.

HMGB1 augments cognitive impairment in sepsis-associated encephalopathy by binding to MD-2 and promoting NLRP3-induced neuroinflammation

BACKGROUND

Sepsis-associated encephalopathy (SAE) always manifests with severe inflammatory symptoms and cognitive impairment. High mobility group box 1 (HMGB1) is a pro-inflammatory cytokine. In this study we investigated the role of HMGB1 in SAE.

METHODS

An SAE mouse model was established through cecal ligation and puncture surgery and then injected with adenovirus short hairpin RNA (Ad-sh)-HMGB1 or Ad-sh-myeloid differentiation protein (MD-2). The cognitive impairment and pathological injury in mice of different groups were evaluated using the Morris water maze experiment, Y-maze test, tail suspension test, fear conditioning test, and haematoxylin-eosin staining. The expressions of HMGB1 (fully reduced and disulfide (ds)HMGB1), MD-2, and NLRP3 in SAE mice were determined. Then, levels of inflammatory cytokines were measured. The binding relation between HMGB1 and MD-2 was predicted and certified. Additionally, MD-2 was downregulated to verify the role of the binding of HMGB1 and MD-2 in neuroinflammation and cognitive impairment in SAE.

RESULTS

Expressions of HMGB1, MD-2, NLRP3, and inflammatory cytokines were enhanced in the SAE mouse model, which were in parallel with impaired cognitive function. HMGB1 silencing resulted in downregulated NLRP3 expression and alleviated neuroinflammation and cognitive impairment in SAE mice. Mechanically, dsHMGB1 bound to MD-2 to activate NLRP3, thereby exacerbating neuroinflammation and cognitive impairment in SAE mice. The limited binding of HMGB1 and MD-2 downregulated NLRP3 expression to alleviate neuroinflammation and cognitive impairment in SAE mice.

CONCLUSION

HMGB1 was overexpressed in SAE, and dsHMGB1 bound to MD-2 to activate NLRP3 inflammasome, inducing neuroinflammation and cognitive impairment in SAE.

Emerging Trends and Hot Spots in Sepsis-Associated Encephalopathy Research From 2001 to 2021: A Bibliometric Analysis

Study Objectives

To evaluate sepsis-associated encephalopathy (SAE) research and to quantitatively and qualitatively predict research hot spots using bibliometric analysis.

Methods

We extracted relevant publications from the Web of Science Core Collection on July 28, 2021. We investigated the retrieved data by bibliometric analysis (e.g. co-cited and cluster analysis, keyword co-occurrence) using the software CiteSpace and VOSviewer, the Online Analysis Platform of Literature Metrology (http://bibliometric.com/) and Bibliometrix to analyse and predict the trends and hot spots in this field.

Main Results

We identified 1,582 published articles and reviews on SAE from 2001 to 2021. During this period, the number of manuscripts on SAE increased steadily and peaked in 2021. The USA and China were the leading countries that had a critical impact on SAE research. Among all institutions, Vanderbilt University and Pittsburgh University held leading positions and became central in the collaboration network. Among all the journals, Critical Care Medicine published the maximum number of manuscripts in the field of SAE within 20 years. Dal-Pizzol Felipe was the most productive author (61 papers) and received the largest number of citations (930 citations). Co-citation cluster analysis revealed that the most popular terms on SAE in the manner of cluster labels were critical illness, sepsis-associated encephalopathy, polymicrobial sepsis, posterior reversible encephalopathy syndrome, rat brain, intensive care unit, prior sepsis, molecular hydrogen, inflammation drive, metabolic encephalopathies, delirium pathophysiology, and clinical neuroscience. Keyword burst detection indicated that neuroinflammation, blood-brain barrier (BBB) and mitochondria dysfunction were the current research hot spots.

Conclusions

Our study revealed that neuroinflammation, blood-brain barrier, and mitochondria dysfunction had been the research foci of SAE over the past 20 years. These have emerged as the basis for transformation from basic research to clinical application in finding effective methods for the prevention and treatment of SAE.

Regulatory T Cells: Angels or Demons in the Pathophysiology of Sepsis?

Sepsis is a syndrome characterized by life-threatening organ dysfunction caused by the dysregulated host response to an infection. Sepsis, especially septic shock and multiple organ dysfunction is a medical emergency associated with high morbidity, high mortality, and prolonged after-effects. Over the past 20 years, regulatory T cells (Tregs) have been a key topic of focus in all stages of sepsis research. Tregs play a controversial role in sepsis based on their heterogeneous characteristics, complex organ/tissue-specific patterns in the host, the multi-dimensional heterogeneous syndrome of sepsis, the different types of pathogenic microbiology, and even different types of laboratory research models and clinical research methods. In the context of sepsis, Tregs may be considered both angels and demons. We propose that the symptoms and signs of sepsis can be attenuated by regulating Tregs. This review summarizes the controversial roles and Treg checkpoints in sepsis.

Neuropsychological Outcome of Critically Ill Patients with Severe Infection

Sepsis and septic shock represent important burdens of disease around the world. Sepsis-associated neurological consequences have a great impact on patients, both in the acute phase and in the long term. Sepsis-associated encephalopathy (SAE) is a severe brain dysfunction that may contribute to long-term cognitive impairment. Its pathophysiology recognizes the following two main mechanisms: neuroinflammation and hemodynamic impairment. Clinical manifestations include different forms of altered mental status, from agitation and restlessness to delirium and deep coma. A definite diagnosis is difficult because of the absence of specific radiological and biological criteria; clinical management is restricted to the treatment of sepsis, focusing on early detection of the infection source, maintenance of hemodynamic homeostasis, and avoidance of metabolic disturbances or neurotoxic drugs.

The mechanism underlying extrapulmonary complications of the coronavirus disease 2019 and its therapeutic implication

The coronavirus disease 2019 (COVID-19) is a highly transmissible disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that poses a major threat to global public health. Although COVID-19 primarily affects the respiratory system, causing severe pneumonia and acute respiratory distress syndrome in severe cases, it can also result in multiple extrapulmonary complications. The pathogenesis of extrapulmonary damage in patients with COVID-19 is probably multifactorial, involving both the direct effects of SARS-CoV-2 and the indirect mechanisms associated with the host inflammatory response. Recognition of features and pathogenesis of extrapulmonary complications has clinical implications for identifying disease progression and designing therapeutic strategies. This review provides an overview of the extrapulmonary complications of COVID-19 from immunological and pathophysiologic perspectives and focuses on the pathogenesis and potential therapeutic targets for the management of COVID-19.

Minocycline Pretreatment Prevents Blood-Brain Barrier Disruption in Septic Rats

INTRODUCTION

The aim of the study was to explore the mechanism by which minocycline protects the blood-brain barrier (BBB) in septic rats.

METHODS

A sepsis rat model was generated in healthy, male Sprague-Dawley rats by cecal ligation and puncture (CLP). The rats were randomly divided into four groups and treated as follows: sham-operated plus normal saline (Sham + S group), CLP plus normal saline (CLP + S group), CLP plus minocycline pretreatment (CLP + M1 group), and CLP plus minocycline treatment (CLP + M2 group). Rats in the CLP + M1 group received 45 mg/kg minocycline by intraperitoneal injection every 12 h for 72 h. Rats in the Sham + S and CLP + S groups were injected with the same volume of normal saline every 12 h for 72 h. Rats in the CLP + M2 group were intraperitoneally injected with 45 mg/kg minocycline immediately after CLP and once every 12 h for 72 h. All rats were sacrificed at 72 h after operation. Tumor necrosis factor α and interleukin 6 levels, the expression of ionized calcium-binding adaptor molecule-1 (Iba-1), and the permeability of the BBB were measured. The expression of matrix metalloproteinases-9 (MMP-9) and the tight junction proteins zonula occludens-1 (ZO-1) and occludin was detected by Western blot. In addition, Evans blue (EB) staining, immunohistochemistry, and ELISA analysis were carried out.

RESULTS

Minocycline pretreatment significantly inhibited microglial activation, decreased the sepsis-induced expression of MMP-9, increased the expression of ZO-1 and occludin, and improved the permeability of the BBB. Minocycline treatment failed to inhibit microglial activation, decrease the sepsis-induced expression of MMP-9, increase the expression of ZO-1 or occluding, or improve the permeability of the BBB.

CONCLUSIONS

Minocycline pretreatment can effectively improve the altered permeability of the BBB caused by sepsis. The mechanism may be related to the inhibition of microglial activation and MMP-9 expression and increased expression of ZO-1 and occludin.

Omics of endothelial cell dysfunction in sepsis

During sepsis, defined as life-threatening organ dysfunction due to dysregulated host response to infection, systemic inflammation activates endothelial cells and initiates a multifaceted cascade of pro-inflammatory signaling events, resulting in increased permeability and excessive recruitment of leukocytes. Vascular endothelial cells share many common properties but have organ-specific phenotypes with unique structure and function. Thus, therapies directed against endothelial cell phenotypes are needed to address organ-specific endothelial cell dysfunction. Omics allow for the study of expressed genes, proteins and/or metabolites in biological systems and provide insight on temporal and spatial evolution of signals during normal and diseased conditions. Proteomics quantifies protein expression, identifies protein-protein interactions and can reveal mechanistic changes in endothelial cells that would not be possible to study via reductionist methods alone. In this review, we provide an overview of how sepsis pathophysiology impacts omics with a focus on proteomic analysis of mouse endothelial cells during sepsis/inflammation and its relationship with the more clinically relevant omics of human endothelial cells. We discuss how omics has been used to define septic endotype signatures in different populations with a focus on proteomic analysis in organ-specific microvascular endothelial cells during sepsis or septic-like inflammation. We believe that studies defining septic endotypes based on proteomic expression in endothelial cell phenotypes are urgently needed to complement omic profiling of whole blood and better define sepsis subphenotypes. Lastly, we provide a discussion of how in silico modeling can be used to leverage the large volume of omics data to map response pathways in sepsis.

Intestinal Epithelial Cell Exosome Launches IL-1β-Mediated Neuron Injury in Sepsis-Associated Encephalopathy

Background

Gut–microbiota–brain axis links the relationship between intestinal microbiota and sepsis-associated encephalopathy (SAE). However, the key mediators between them remain unclear.

Methods

Memory test was determined by Water maze. Intestinal flora was measured by 16S RNA sequencing. Neurotransmitter was detected by high-performance liquid chromatography (HPLC). Histopathology was determined by H&E, immunofluorescence (IF), and terminal-deoxynucleoitidyl transferase mediated nick end labeling (TUNEL) staining. Flow cytometry was employed to determine the proportion of macrophages.

Results

Fecal microbiota transplantation (FMT) relieved hippocampus impairment of SAE rats by inhibiting inflammation cytokine secretion, the expression of IBA-1 and neurotransmitter disturbance, and cell apoptosis and autophagy, accompanied by the reduced M1 polarization and M1 pro-inflammation factors produced by macrophages in mesenteric lymph nodes (MLNs). Actually, M1 polarization in SAE rats depended on intestinal epithelial cell (IEC)-derived exosome. GW4869-initiated inhibition of exosome secretion notably abolished M1 polarization and the secretion of IL-1β. However, GW4869-mediated improvement of hippocampus impairment was counteracted by the delivery of recombinant interleukin (IL)-1β to hippocampus. Mechanistically, IEC-derived exosome induced the excessive circulating IL-1β produced by CP-R048 macrophages, which subsequently induced damage and apoptosis of hippocampal neurons H19-7 in an autophagy-dependent manner. And reactivation of autophagy facilitates intestinal IL-1β-mediated hippocampal neuron injury.

Conclusion

Collectively, intestinal flora disturbance induced the exosome release of IECs, which subsequently caused M1 polarization in MLNs and the accumulation of circulating IL-1β. Circulating IL-1β promoted the damage and apoptosis of neurons in an autophagy-dependent manner. Possibly, targeting intestinal flora or IEC-derived exosome contributes to the treatment of SAE.

Is rosuvastatin protective against sepsis-associated encephalopathy? A secondary analysis of the SAILS trial

BACKGROUND

Sepsis is a common cause of death in emergency departments and sepsis-associated encephalopathy (SAE) is a major complication. Rosuvastatin may play a neuroprotective role due to its protective effects on the vascular endothelium and its anti-inflammatory functions. Our study aimed to explore the potential protective function of rosuvastatin against SAE.

METHODS

Sepsis patients without any neurological dysfunction on admission were prospectively enrolled in the "Rosuvastatin for Sepsis-Associated Acute Respiratory Distress Syndrome" study (SAILS trial, ClinicalTrials.gov number: NCT00979121). Patients were divided into rosuvastatin and placebo groups. This is a secondary analysis of the SAILS dataset. Baseline characteristics, therapy outcomes, and adverse drug events were compared between groups.

RESULTS

A total of 86 patients were eligible for our study. Of these patients, 51 were treated with rosuvastatin. There were significantly fewer cases of SAE in the rosuvastatin group than in the placebo group (32.1% vs. 57.1%, P=0.028). However, creatine kinase levels were significantly higher in the rosuvastatin group than in the placebo group (233 [22-689] U/L vs. 79 [12-206] U/L, P=0.034).

CONCLUSION

Rosuvastatin appears to have a protective role against SAE but may result in a higher incidence of adverse events.

Blocking HMGB1/RAGE Signaling by Berberine Alleviates A1 Astrocyte and Attenuates Sepsis-Associated Encephalopathy

As a life-threatening multiple organ dysfunction attributable to maladjusted host immune responses to infection, sepsis is usually the common pathway to serious prognosis and death for numerous infectious diseases all over the world. Sepsis-associated encephalopathy (SAE) is frequently complicated by septic conditions, and is one of the most important reasons for increased mortality and poor outcomes in septic patients which is still an urgent clinical problem need to be solved. In this research, a conspicuously discovery of treatment-related translational use for berberine was elaborated. The results revealed that berberine treatment significantly restored cognitive impairment in sepsis mice. Reduced expression levels of TNF-α, IL-1α, and C1qA were exhibited in the hippocampus of the berberine treatment group, and attenuated effect of declining neo-neuron, activation of microglia and astrocytes in the hippocampus of mice with sepsis were also found. Moreover, berberine inhibits microglia-stressed A1 astrocytes by inhibiting HMGB1 signaling was revealed, then the molecular mechanism of HMGB1/RAGE signaling inhibition leads to the better outcome of SAE was elucidated. To summarize, this research indicated that berberine targets HMGB1/RAGE signaling to inhibit microglia-stressed A1 astrocyte and neo-neuron decline, which consequently alleviates sepsis-induced cognitive impairment. Collectively, berberine may serve as potential therapeutic drug and HMGB1/RAGE signaling would be a novel target for medicine development for treating SAE.

Emodin Promotes Autophagy and Prevents Apoptosis in Sepsis-Associated Encephalopathy through Activating BDNF/TrkB Signaling

OBJECTIVE

Sepsis-associated encephalopathy (SAE) is a severe and common complication of sepsis and can induce cognitive dysfunction and apoptosis of neurons and neuroinflammation. Emodin has been confirmed to have anti-inflammatory effects. Thus, we sought to investigate the role of Emodin in SAE.

METHODS

The cecal ligation and puncture (CLP) method was used for the establishment of SAE in mice model. For treatment of Emodin, intraperitoneal injection of 20 mg/kg Emodin was performed before the surgery. The Morris water maze and open field tests were carried for measurement of cognitive dysfunction. Hematoxylin and eosin staining was for histological analysis of hippocampus. Cell apoptosis of hippocampus neurons was measured by TUNEL staining. Pro-inflammatory and anti-inflammatory cytokines in hippocampus tissue homogenate were evaluated by ELISA. BDNF/TrkB signaling-related proteins (TrkB, p-TrkB, and BDNF), autophagy-related proteins (LC3 II/I and Beclin-1), and apoptosis-related proteins (Bax, Bcl-2, and cleaved caspase-3) were detected by Western blotting.

RESULTS

Emodin significantly inhibited apoptosis and induced autophagy in hippocampal neurons of CLP-treated mice. In addition, Emodin significantly ameliorated CLP-induced cognitive dysfunction and pathological injury in mice. Meanwhile, Emodin notably inhibited CLP-induced inflammatory responses in mice via upregulation of BDNF/TrkB signaling, while the effect of Emodin was partially reversed in the presence of K252a (BDNF/TrkB signaling inhibitor).

CONCLUSION

Emodin significantly inhibited the progression of SAE via mediation of BDNF/TrkB signaling. Thus, Emodin might serve as a new agent for SAE treatment.

Brain injury, endothelial injury and inflammatory markers are elevated and express sex-specific alterations after COVID-19

Objective

Although COVID-19 is a respiratory disease, all organs can be affected including the brain. To date, specific investigations of brain injury markers (BIM) and endothelial injury markers (EIM) have been limited. Additionally, a male bias in disease severity and mortality after COVID-19 is evident globally. Sex differences in the immune response to COVID-19 may mediate this disparity. We investigated BIM, EIM and inflammatory cytokine/chemokine (CC) levels after COVID-19 and in across sexes.

Methods

Plasma samples from 57 subjects at < 48 h of COVID-19 hospitalization, and 20 matched controls were interrogated for the levels of six BIMs—including GFAP, S100B, Syndecan-1, UCHLI, MAP2 and NSE, two EIMs—including sICAM1 and sVCAM1. Additionally, several cytokines/chemokines were analyzed by multiplex. Statistical and bioinformatics methods were used to measure differences in the marker profiles across (a) COVID-19 vs. controls and (b) men vs. women.

Results

Three BIMs: MAP2, NSE and S100B, two EIMs: sICAM1 and sVCAM1 and seven CCs: GRO IL10, sCD40L, IP10, IL1Ra, MCP1 and TNFα were significantly (p < 0.05) elevated in the COVID-19 cohort compared to controls. Bioinformatics analysis reveal a stronger positive association between BIM/CC/EIMs in the COVID-19 cohort. Analysis across sex revealed that several BIMs and CCs including NSE, IL10, IL15 and IL8 were significantly (p < 0.05) higher in men compared to women. Men also expressed a more robust BIM/ EIM/CC association profile compared to women.

Conclusion

The acute elevation of BIMs, CCs, and EIMs and the robust associations among them at COVID-19 hospitalization are suggestive of brain and endothelial injury. Higher BIM and inflammatory markers in men additionally suggest that men are more susceptible to the risk compared to women.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02323-8.

Blood-Brain Barrier Disruption by Lipopolysaccharide and Sepsis-Associated Encephalopathy

As a complex multicellular structure of the vascular system at the central nervous system (CNS), the blood-brain barrier (BBB) separates the CNS from the system circulation and regulates the influx and efflux of substances to maintain the steady-state environment of the CNS. Lipopolysaccharide (LPS), the cell wall component of Gram-negative bacteria, can damage the barrier function of BBB and further promote the occurrence and development of sepsis-associated encephalopathy (SAE). Here, we conduct a literature review of the direct and indirect damage mechanisms of LPS to BBB and the relationship between these processes and SAE. We believe that after LPS destroys BBB, a large number of inflammatory factors and neurotoxins will enter and damage the brain tissue, which will activate brain immune cells to mediate inflammatory response and in turn further destroys BBB. This vicious circle will ultimately lead to the progression of SAE. Finally, we present a succinct overview of the treatment of SAE by restoring the BBB barrier function and summarize novel opportunities in controlling the progression of SAE by targeting the BBB.

Dexmedetomidine alleviates cognitive impairment by reducing blood-brain barrier interruption and neuroinflammation via regulating Th1/Th2/Th17 polarization in an experimental sepsis model of mice

Clinical studies have shown that dexmedetomidine (DEX) reduces mortality and inflammation in patients with sepsis, and ameliorates cognitive decline in both postoperative and critical care patients. This study aims to explain the neuroprotective effects provided by DEX in mice with cecal ligation and puncture (CLP)-induced polymicrobial sepsis. Mice were treated with DEX intraperitoneally three times every two hours after CLP. The survival rate, body weight, and clinical scores were recorded each day. Morris water maze (MWM) and fear conditioning tests were used to evaluate cognitive function. Blood brain barrier (BBB) permeability, hippocampal inflammation, hippocampal neural apoptosis, and T helper (Th) cell subgroups were assessed. Furthermore, Atipamezole was used to verify that the potential neuroprotective effects in the sepsis-associated encephalopathy (SAE) were mediated by DEX. Compared with the Sham group, CLP mice showed significant cognitive impairment, BBB interruption, excessive neuroinflammation, and neuronal apoptosis. These detrimental effects of CLP were attenuated by DEX. Furthermore, we found that DEX corrects peripheral Th1/Th2/Th17 shift and reduces proinflammatory cytokines in the hippocampus. Additionally, atipamezole prevented DEX's protective effect. Taken together, DEX alleviates cognitive impairments by reducing blood-brain barrier interruption and neuroinflammation by regulating Th1/Th2/Th17 polarization.

Comprehensive analysis of mRNAs, lncRNAs and circRNAs in the early phase of microglial activation

Sepsis-associated encephalopathy (SAE) is a common complication of sepsis that may seriously affect the prognosis and quality of life of patients with sepsis. Microglial activation is vital to the neuroinflammation and the pathology of SAE. In the present study, in vitro cultured BV-2 microglial cells stimulated with lipopolysaccharide (LPS) were employed as a model of microglia activation. The altered profiles of long noncoding (lnc)RNAs, circular (circ)RNAs and mRNAs in BV-2 cells after 4 h of LPS exposure were arrayed by using the Agilent competing endogenous (ce)RNA Microarray Chip. Using fold change >2 and P<0.05 as the cutoff criteria, 1,135 mRNAs and 2,488 lncRNAs were determined to be upregulated and 630 mRNAs and 744 lncRNAs to be downregulated. The number of differentially expressed circRNAs was lower, with 140 upregulated and 123 downregulated. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis of DE mRNAs suggested that inflammatory responses, as well as lipid metabolism, were involved in microglial activation. Furthermore, analyses of ceRNA networks of the lncRNA-miRNA-mRNA or circRNA-miRNA-mRNA interrelations were performed. The present study revealed a multitude of novel candidate mRNAs, lncRNAs and circRNAs involved in microglial activation, which may improve the current knowledge on neuroinflammation and provide potential therapeutic targets for SAE.

Sepsis-Induced Immunosuppression

Sepsis is expected to have a substantial impact on public health and cost as its prevalence increases. Factors contributing to increased prevalence include a progressively aging population, advances in the use of immunomodulatory agents to treat a rising number of diseases, and immune-suppressing therapies in organ transplant recipients and cancer patients. It is now recognized that sepsis is associated with profound and sustained immunosuppression, which has been implicated as a predisposing factor in the increased susceptibility of patients to secondary infections and mortality. In this review, we discuss mechanisms of sepsis-induced immunosuppression and biomarkers that identify a state of impaired immunity. We also highlight immune-enhancing strategies that have been evaluated in patients with sepsis, as well as therapeutics under current investigation. Finally, we describe future challenges and the need for a new treatment paradigm, integrating predictive enrichment with patient factors that may guide the future selection of tailored immunotherapy. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Role of Extracellular Vesicles in Cell Death and Inflammation

Extracellular vesicles (EVs) have been identified as novel mediators of intercellular communication. They work via delivering the sequestered cargo to cells in the close vicinity, as well as distant sites in the body, regulating pathophysiological processes. Cell death and inflammation are biologically crucial processes in both normal physiology and pathology. These processes are indistinguishably linked with their effectors modulating the other process. For instance, during an unresolvable infection, the upregulation of specific immune mediators leads to inflammation causing cell death and tissue damage. EVs have gained considerable interest as mediators of both cell death and inflammation during conditions, such as sepsis. This review summarizes the types of extracellular vesicles known to date and their roles in mediating immune responses leading to cell death and inflammation with specific focus on sepsis and lung inflammation.

Sepsis-Associated Encephalopathy and Blood-Brain Barrier Dysfunction

Sepsis is a life-threatening clinical condition caused by a dysregulated host response to infection. Sepsis-associated encephalopathy (SAE) is a common but poorly understood neurological complication of sepsis, which is associated with increased morbidity and mortality. SAE clinical presentation may range from mild confusion and delirium to severe cognitive impairment and deep coma. Important mechanisms associated with SAE include excessive microglial activation, impaired endothelial barrier function, and blood-brain barrier (BBB) dysfunction. Endotoxemia and pro-inflammatory cytokines produced systemically during sepsis lead to microglial and brain endothelial cell activation, tight junction downregulation, and increased leukocyte recruitment. The resulting neuroinflammation and BBB dysfunction exacerbate SAE pathology and aggravate sepsis-induced brain dysfunction. In this mini-review, recent literature surrounding some of the mediators of BBB dysfunction during sepsis is summarized. Modulation of microglial activation, endothelial cell dysfunction, and the consequent prevention of BBB permeability represent relevant therapeutic targets that may significantly impact SAE outcomes.

Relationship between miR-29a levels in the peripheral blood and sepsis-related encephalopathy

OBJECTIVE

This study aimed to explore the relationship between peripheral blood miR-29a and sepsis-related encephalopathy (SAE).

METHODS

A total of 120 patients with sepsis admitted to our hospital from March 2018 to October 2019 were selected as research subjects. They were divided into a SAE group (30 cases) and an unrelated encephalopathy group (90 cases) according to whether the patients were complicated with SAE. The levels of miR-29a in the peripheral blood, neuron-specific enolase (NSE), S100β calcium binding protein (S100β) and interleukin-6 (IL-6) in serum were determined, and the relationship between miR-29a in the peripheral blood and the diagnosis and prognosis prediction in SAE patients was analyzed.

RESULTS

Compared with the unrelated encephalopathy group, the levels of miR-29a in peripheral blood, NSE, S100β and IL-6 in serum of patients in the SAE group were elevated notably. miR-29a in the peripheral blood, and NSE, S100β, IL-6 in the serum of patients who died and survived within 28 days were detected, and the levels of these four indexes in the death group were significantly higher than those in the survival group. Correlation analysis revealed that miR-29a in the peripheral blood was positively correlated with the levels of NSE, S100β and IL-6 in serum. According to Receiver Operating Characteristic (ROC) curve analysis, miR-29a in the peripheral blood can be used as a potential biomarker to predict whether sepsis is complicated with SAE and the relative prognosis.

CONCLUSION

miR-29a is closely associated with the development of SAE, and miR-29a in the peripheral blood can be used as a potential biological index to predict whether sepsis is complicated with SAE and indications of a poor prognosis.

Role of microRNAs As Biomarkers in Sepsis-Associated Encephalopathy

Sepsis-associated encephalopathy (SAE) is a neurological complication of sepsis, characterized by brain dysfunction without any direct central nervous system infection. The diagnosis of SAE is currently a challenge. In fact, problems in making a diagnosis of SAE cause a great variability of incidence that can reach up to 70% of all septic patients. Even more, despite SAE is the most frequent type of encephalopathy occurring in critically ill patients, the molecular mechanisms that guide its progression have not been completely elucidated. On the other hand, miRNAs have proven to be excellent biomarkers for both diagnosis and prognosis, especially in brain pathologies because of their small size they can cross the blood–brain barrier easier than other biomolecules. The identification of new miRNAs as biomarkers may help to improve SAE diagnosis and prognosis and also to design new therapies for this clinical manifestation that produces diffuse cerebral dysfunction. This review is focused on SAE physiopathology and the need to have clear criteria for its diagnosis; thus, this work postulates some miRNA candidates to be used for SAE biomarkers because of their role in both, neurological damage and sepsis.

Hydrogen gas alleviates sepsis-induced neuroinflammation and cognitive impairment through regulation of DNMT1 and DNMT3a-mediated BDNF promoter IV methylation in mice

Sepsis-associated encephalopathy (SAE) can cause acute and long-term cognitive impairment and increase the mortality rate in sepsis patients, and we previously reported that 2% hydrogen gas (H2) inhalation has a therapeutic effect on SAE, but the underlying mechanism remains unclear. Dynamic DNA methylation, which catalyzed by DNA methyltransferases (DNMTs), is involved in the formation of synaptic plasticity and cognitive memory in the central nervous system. And brain-derived neurotrophic factor (BDNF), to be a key signaling component in activity-dependent synaptic plasticity, can be induced by neuronal activity accompanied by hypomethylation of its promoter IV. This study was designed to illustrate whether H2 can mediate SAE by alter the BDNF promoter IV methylation mediated by DNMTs. We established an SAE model by cecal ligation and perforation (CLP) in C57BL/6 mice. The Morris water maze test from the 4th to the 10th day after sham or CLP operations were used to evaluate mouse cognitive function. Hippocampal tissues were isolated at the 24 after sham or CLP surgery. Pro-inflammatory cytokines including tumor necrosis factor-α (TNF-α), Interleukin-6 (IL-6) and High Mobility Group Box 1 (HMGB1) were measured by enzyme-linked immunosorbent assay (ELISA). mRNA or protein levels of DNMTs (DNMT1, DNMT3a and DNMT3b), BDNF promoter IV and total BDNF were detected by RT-PCR and Western blot tests. Immunofluorescence staining were used to determine the expressions of DNMT1 and DNMT3a. The quantitative methylation analysis of the 11 CpG island of the promoter region of BDNF exon IV was determined using theAgena's MassARRAY EpiTYPER system. We found that 2% H2 inhalation can reduce pro-inflammatory factors, alleviate DNMT1, DNMT3a but not DNMT3b expression, make hypomethylation of BDNF promoter IV at 5 CpG sites, enhance the BDNF levels and then decrease escape latency but increase platform crossing times in septic mice. Our results suggest that 2% H2 inhalation may alleviate SAE through altering the regulation of BDNF promoter IV methylation which mediated by DNMT1 and DNMT3a in the hippocampus of septic mice.

Tumor necrosis factor-α small interfering RNA alveolar epithelial cell-targeting nanoparticles reduce lung injury in C57BL/6J mice with sepsis

Background

The role of tumor necrosis factor (TNF)-α small interfering (si)RNA alveolar epithelial cell (AEC)-targeting nanoparticles in lung injury is unclear.

Methods

Sixty C57BL/6J mice with sepsis were divided into normal, control, sham, 25 mg/kg, 50 mg/kg, and 100 mg/kg siRNA AEC-targeting nanoparticles groups (n = 10 per group). The wet:dry lung weight ratio, and hematoxylin and eosin staining, western blotting, and enzyme-linked immunosorbent assays for inflammatory factors were conducted to compare differences among groups.

Results

The wet:dry ratio was significantly lower in control and sham groups than other groups. TNF-α siRNA AEC-targeting nanoparticles significantly reduced the number of eosinophils, with significantly lower numbers in the 50 mg/kg group than in 25 mg/kg and 100 mg/kg groups. The nanoparticles also significantly reduced the expression of TNF-α, B-cell lymphoma-2, caspase 3, interleukin (IL)-1β, and IL-6, with TNF-α expression being significantly lower in the 50 mg/kg group than in 25 mg/kg and 100 mg/kg groups.

Conclusion

TNF-α siRNA AEC-targeting nanoparticles appear to be effective at improving lung injury-related sepsis, and 50 mg/kg may be a preferred dose option for administration.

Sepsis Induces Physical and Mental Impairments in a Mouse Model of Post-Intensive Care Syndrome

Post-intensive care syndrome (PICS) is a physical, cognitive, and mental impairment observed in intensive care unit (ICU) survivors. Although this is an emerging problem in the ICU, how sepsis induces the characteristic symptoms of PICS remains unclear. To develop a model of PICS, we induced sepsis in male C57/B6 mice via sublethal cecum slurry injection and subsequently treated them using ICU-like interventions. At 1–2 weeks post-sepsis induction, we simultaneously evaluated the abilities of the surviving mice using the following behavioral tests: (1) a grip strength test (GST) and a treadmill test for physical assessment, (2) a novel object recognition test (NORT) for cognitive assessment, and (3) an open field test (OFT) and a marble burying test (MBT) for mental assessment. The surviving mice showed a range of deficits, including muscle weakness with significantly decreased grip strength in the GST; decreased total mileage during the treadmill test; anxiety and decreased activity, with significantly decreased time in the central area, and increased duration of immobility in the OFT; and an increased number of buried marbles in the MBT. Given these physical and mental impairments in the surviving mice, our model has the potential to elucidate mechanistic insights and to discover therapeutic targets and new interventions for PICS.

Infiltrated regulatory T cells and Th2 cells in the brain contribute to attenuation of sepsis-associated encephalopathy and alleviation of mental impairments in mice with polymicrobial sepsis

Sepsis-associated encephalopathy (SAE) increases not only morbidity and mortality but has been associated with long-lasting mental impairment after hospital discharge in septic patients. Recently, studies have shown that these mental impairments are caused by infection-induced neuroinflammation. However, the role of T cells in the pathogenesis of SAE and mental impairments remains unclear. Thus, in this study, we aimed to clarify how immune cells, especially T cells, influence the development and recovery of these disorders. In the cecal slurry (CS)-induced septic mouse model, we performed three different kinds of behavioral tests, open-field test, marble burying test, and forced swimming test, and observed anxiety-like behavior in septic mice. Additionally, increased interleukin (IL)-1β and IL-6 expression levels, and infiltration of neutrophils and T cells were examined in the brain of septic mice, 10 days after sepsis onset. Twenty days after sepsis onset, the septic mice could recover the number of astrocytes. At day 30, expression levels of IL-1β and tumor necrosis factor (TNF)-α returned to normal levels in the cerebral cortex of septic mice. Interestingly, resolution of neuroinflammation and alleviation of depression were delayed in septic mice treated with FTY720, which inhibits sphingosine-1-phosphate (S1P)-dependent lymphocyte egress from lymph nodes. On analyzing the brain T cells with or without FTY720 in septic mice, the FTY720 untreated mice presented increased regulatory T cells (Treg) and Th2 cells in the brain, whereas the FTY720 treated mice demonstrated increased Th17 in the brain at day 30. Furthermore, in FTY720 treated septic mice, the number of astrocytes in the cerebral cortex remained reduced at day 30. These results suggest that infiltrated Treg and Th2 cells contribute to the attenuation SAE and alleviate SAE-induce mental disorder by resolving neuroinflammation in the chronic phase of sepsis.

Lymphocyte and NK Cell Counts Can Predict Sepsis-Associated Delirium in Elderly Patients

Background: Sepsis-associated delirium (SAD) is prevalent in elderly patients and is recognized as brain dysfunction associated with increased inflammatory response in the central nervous system during sepsis. Neuroinflammation was demonstrated to be part of its mechanism and we aimed to validate the role of immunity imbalance in a combined retrospective and prospective cohort study.

Methods: We performed a retrospective study analyzing the association between SAD and lymphocyte counts in the peripheral blood, alongside a prospective trial evaluating the quantitative changes in lymphocyte subsets and their predictive value for early diagnosis of SAD.

Results: In the retrospective study, among 1,010 enrolled adult patients (age ≥65 years), 297 patients were diagnosed with delirium during intensive care unit (ICU) stay and lymphocyte counts at ICU admission in the SAD group were significantly higher than in non-delirious counterparts (1.09 ± 0.32 vs. 0.82 ± 0.24, respectively, p = 0.001). In the prospective study, lymphocyte counts [0.83 (0.56, 1.15) vs. 0.72 (0.40, 1.06) × 10⁹/L, p = 0.020] and natural killer (NK) cell counts [96 (68, 118) vs. 56 (26, 92) cells/μl, p = 0.024] were significantly higher in the SAD group. The area under the curve value of NK cell count was 0.895 [95% confidence interval (CI): 0.857, 0.933] and of lymphocyte count was 0.728 (95% CI: 0.662, 0.795). An NK cell count cut-off value of 87 cells/ml in septic patients at ICU admission was predictive of delirium with a sensitivity of 80.2% and specificity of 80.8%.

Conclusions: We found that lymphocyte and NK cell counts were significantly higher in senior patients with SAD and that NK cell count may be valuable for the prediction of SAD within elderly patient cohorts.

INT-777 prevents cognitive impairment by activating Takeda G protein-coupled receptor 5 (TGR5) and attenuating neuroinflammation via cAMP/ PKA/ CREB signaling axis in a rat model of sepsis

BACKGROUND

Survivors of sepsis must often endure significant cognitive and behavioral impairments after discharge, but research on the relevant mechanisms and interventions remains lacking. TGR5, a member of the class A GPCR family, plays an important role in many physiological processes, and recent studies have shown that agonists of TGR5 show neuroprotective effects in a variety of neurological disorders. To date, no studies have assessed the effects of TGR5 on neuroinflammatory, cognitive, or behavioral changes in sepsis models.

METHODS

A total of 267 eight-week-old male Sprague-Dawley rats were used in this study. Sepsis was induced via cecal ligation and puncture (CLP). All animals received volume resuscitation. The rats were given TGR5 CRISPR oligonucleotide intracerebroventricularly 48 h before CLP surgery. INT-777 was administered intranasally 1 h after CLP, and the cAMP inhibitor, SQ22536, was administered intracerebroventricularly 1 h after CLP. Survival rate, bodyweight change, and clinical scores were assessed, and neurobehavioral tests, western blot, and immunofluorescence staining were performed. The cognitive function of rats was measured using the Morris water maze during 15-20 days after CLP.

RESULTS

The expression of TGR5 in the rat hippocampus was upregulated, and peaked at 3 days after CLP. The survival rate of rats after CLP was less than 50%, and the growth rate, in terms of weight, was significantly decreased. While INT-777 treatment did not improve these changes, the treatment did reduce the clinical scores of rats at 24 h after CLP. On day 15 and later, the surviving mice completed a series of behavioral tests. CLP rats showed spatial and memory deficits and anxiety-like behaviors, but INT-777 treatment significantly improved these effects. Mechanistically, immunofluorescence analysis showed that INT-777 treatment reduced the number of microglia in the hippocampus, neutrophilic infiltration, and the expression of inflammatory factors after CLP in rats. Moreover, INT-777 treatment significantly increased the expression of TGR5, cAMP, p-PKA, and p-CREB, but downregulated the expression of IL-1β, IL-6, and TNF-α. CRISPR-mediated TGR5 knockdown and SQ22536 treatment abolished the neuroprotective effects of TGR5 activation after CLP.

CONCLUSION

This study demonstrates that INT-777 treatment reduced neuroinflammation and microglial cell activation, but improved cognitive impairment in the experimental sepsis rats. TGR5 has translational potential as a therapeutic target to improve neurological outcomes in sepsis survivors.

Reducing LncRNA-5657 expression inhibits the brain inflammatory reaction in septic rats

Our preliminary study found that the long noncoding RNA (LncRNA)-5657 can reduce the expression of inflammatory factors during inflammatory reactions in rat glial cells. However, the role played by LncRNA-5657 during septic brain injury remains unclear. In the present study, rat models of septic encephalopathy were established by cecal ligation and puncture, and then the rats were treated with a hippocampal injection small hairpin RNA (shRNA) against LncRNA-5657 (sh-LnCRNA-5657). The sh-LncRNA-5657 treatment reduced the level of neuronal degeneration and necrosis in the rat hippocampus, reduced the immunoreactivities of aquaporin 4, heparanase, and metallopeptidase-9, and lowered the level of tumor necrosis factor-alpha. Glial cells were pre-treated with sh-LncRNA-5657 and then treated with 1 µg/mL lipopolysaccharide. Sh-LncRNA-5657 transfection decreased the expression of LncRNA-5657 in lipopolysaccharide-treated glial cells and decreased the mRNA and protein levels of tumor necrosis factor-alpha, interleukin-1β, and interleukin-6. These findings suggested that LncRNA-5657 expression can significantly reduce the inflammatory reaction during septic encephalopathy and induce protective effects against this disease. This study was approved by the Institutional Ethics Committee at the First Affiliated Hospital of Nanchang University of China (approval No. 2017-004) in 2017.

Prognosis of Patients with Sepsis and Non-Hepatic Hyperammonemia: A Cohort Study

Background

Hyperammonemia has been reported in some critically ill patients with sepsis who do not have hepatic failure. A significant proportion of patients with non-hepatic hyperammonemia have underlying sepsis, but the association between non-hepatic hyperammonemia and prognosis is unclear.

Material/Methods

Information about patients with sepsis and non-hepatic hyperammonemia was retrieved from the Medical Information Mart for Intensive Care-III database. Survival rates were analyzed using the Kaplan-Meier method. Multivariate logistic regression models were employed to identify prognostic factors. Receiver operating characteristic (ROC) curve analysis was used to measure the predictive ability of ammonia in terms of patient mortality.

Results

A total of 265 patients with sepsis were enrolled in this study. Compared with the non-hyperammonemia group, the patients with hyperammonemia had significantly higher rates of hospital (59.8% vs. 43.0%, P=0.007), 30-day (47.7% vs. 34.8%, P=0.036), 90-day (61.7% vs. 43.7%, P=0.004), and 1-year mortality (67.3% vs. 49.4%, P=0.004). In the survival analysis, hyperammonemia was associated with these outcomes. Serum ammonia level was an independent predictor of hospital mortality. The area under the ROC curve for the ammonia levels had poor discriminative capacity. The hyperammonemia group also had significantly lower Glasgow Coma Scale scores (P=0.020) and higher incidences of delirium (15.9% vs. 8.2%, P=0.034) and encephalopathy (37.4% vs. 19.6%, P=0.001). Intestinal infection and urinary tract infection with organisms such as Escherichia coli may be risk factors for hyperammonemia in patients who have sepsis.

Conclusions

Higher ammonia levels are associated with poorer prognosis in patients with sepsis. Ammonia also may be associated with sepsis-associated encephalopathy. Therefore, we recommend that serum ammonia levels be measured in patients who are suspected of having sepsis.

Maf1 Ameliorates Sepsis-Associated Encephalopathy by Suppressing the NF-kB/NLRP3 Inflammasome Signaling Pathway

Background

The NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome has been identified as an important mediator of blood–brain-barrier disruption in sepsis-associated encephalopathy (SAE). However, no information is available concerning the critical upstream regulators of SAE.

Methods

Lipopolysaccharide (LPS) was used to establish an in vitro model of blood–brain barrier (BBB) disruption and an in vivo model of SAE. Disruption of BBB integrity was assessed by measuring the expression levels of tight-junction proteins. NLRP3 inflammasome activation, pro-inflammatory cytokines levels, and neuroapoptosis were measured using biochemical assays. Finally, the FITC-dextran Transwell assay and Evan’s blue dye assay were used to assess the effect of Maf1 on LPS-induced endothelial permeability in vitro and in vivo.

Results

We found that Maf1 significantly suppressed the brain inflammatory response and neuroapoptosis induced by LPS in vivo and in vitro. Notably, Maf1 downregulated activation of the NF-κB/p65-induced NLRP3 inflammasome and the expression of pro-inflammatory cytokines. In addition, we found that Maf1 and p65 directly bound to the NLRP3 gene promoter region and competitively regulated the function of NLRP3 in inflammations. Moreover, overexpression of NLRP3 reversed the effects of p65 on BBB integrity, apoptosis, and inflammation in response to LPS. Our study revealed novel role for Maf1 in regulating NF-κB-mediated inflammasome formation, which plays a prominent role in SAE.

Conclusions

Regulation of Maf1 might be a therapeutic strategy for SAE and other neurodegenerative diseases associated with inflammation.

The use of fecal microbiota transplant in sepsis

Sepsis is defined as a dysregulated inflammatory response, which ultimately results from a perturbed interaction of both an altered immune system and the biomass and virulence of involved pathogens.  This response has been tied to the intestinal microbiota, as the microbiota and its associated metabolites play an essential role in regulating the host immune response to infection.  In turn, critical illness as well as necessary health care treatments result in a collapse of the intestinal microbiota diversity and a subsequent loss of health-promoting short chain fatty acids, such as butyrate, leading to the development of a maladaptive pathobiome.  These perturbations of the microbiota contribute to the dysregulated immune response and organ failure associated with sepsis.  Several case series have reported the ability of fecal microbiota transplant (FMT) to restore the host immune response and aid in recovery of septic patients.  Additionally, animal studies have revealed the mechanism of FMT rescue in sepsis is likely related to the ability of FMT to restore butyrate producing bacteria and alter the innate immune response aiding in pathogen clearance.  However, several studies have reported lethal complications associated with FMT, including bacteremia.  Therefore, FMT in the treatment of sepsis is and should remain investigational until a more detailed mechanism of how FMT restores the host immune response in sepsis is determined, allowing for the development of more fine-tuned microbiota therapies.

Can COVID-19 pandemic boost the epidemic of neurodegenerative diseases?

The pandemic of Coronavirus Disease 2019 (COVID-19) presents the world with the medical challenge associated with multifactorial nature of this pathology. Indeed COVID-19 affects several organs and systems and presents diversified clinical picture. COVID-19 affects the brain in many ways including direct infection of neural cells with SARS-CoV-2, severe systemic inflammation which floods the brain with pro-inflammatory agents thus damaging nervous cells, global brain ischaemia linked to a respiratory failure, thromboembolic strokes related to increased intravascular clotting and severe psychological stress. Often the COVID-19 is manifested by neurological and neuropsychiatric symptoms that include dizziness, disturbed sleep, cognitive deficits, delirium, hallucinations and depression. All these indicate the damage to the nervous tissue which may substantially increase the incidence of neurodegenerative diseases and promote dementia.

Hypoperfusion is a potential inducer of immunosuppressive network in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease which causes a non-reversible cognitive impairment and dementia. The primary cause of late-onset AD remains unknown although its pathology was discovered over a century ago. Recently, the vascular hypothesis of AD has received backing from evidence emerging from neuroimaging studies which have revealed the presence of a significant hypoperfusion in the brain regions vulnerable to AD pathology. In fact, hypoxia can explain many of the pathological changes evident in AD pathology, e.g. the deposition of β-amyloid plaques and chronic low-grade inflammation. Hypoxia-inducible factor-1α (HIF-1α) stimulates inflammatory responses and modulates both innate and adaptive immunity. It is known that hypoxia-induced inflammation evokes compensatory anti-inflammatory response involving tissue-resident microglia/macrophages and infiltrated immune cells. Hypoxia/HIF-1α induce immunosuppression by (i) increasing the expression of immunosuppressive genes, (ii) stimulating adenosinergic signaling, (iii) enhancing aerobic glycolysis, i.e. lactate production, and (iv) augmenting the secretion of immunosuppressive exosomes. Interestingly, it seems that these common mechanisms are also involved in the pathogenesis of AD. In AD pathology, an enhanced immunosuppression appears, e.g. as a shift in microglia/macrophage phenotypes towards the anti-inflammatory M2 phenotype and an increase in the numbers of regulatory T cells (Treg). The augmented anti-inflammatory capacity promotes the resolution of acute inflammation but persistent inflammation has crucial effects not only on immune cells but also harmful responses to the homeostasis of AD brain. I will examine in detail the mechanisms of the hypoperfusion/hypoxia-induced immunosuppressive state in general and especially, in its association with AD pathogenesis. These immunological observations support the vascular hypothesis of AD pathology.

A retrospective study of sepsis-associated encephalopathy: epidemiology, clinical features and adverse outcomes

Background

Sepsis-associated encephalopathy (SAE) is a common complication of sepsis that may result in worse outcomes. This study was designed to determine the epidemiology, clinical features, and risk factors of SAE.

Methods

This was a retrospective study of all patients with sepsis who were admitted to the Critical Care Medicine Department of Hangzhou First People’s Hospital Affiliated with Zhejiang University School of Medicine from January 2015 to December 2019.

Results

A total of 291 sepsis patients were screened, and 127 (43.6%) were diagnosed with SAE. There were significant differences in median age, proportion of underlying diseases such as hypertension, Sequential Organ Failure Assessment (SOFA) score, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, gastrointestinal infections, detection rate of Enterococcus, and 28-day mortality between the SAE and non-SAE groups. Both the SOFA score and APACHE II score were independent risk factors for SAE in patients with sepsis. All 127 SAE patients were divided into survival and non-survival groups. The age, SOFA score, and APACHE II score were independently associated with 28-day mortality in SAE patients.

Conclusion

In the present retrospective study, nearly half of patients with sepsis developed SAE, which was closely related to poor outcomes. Both the SOFA score and APACHE II score were independent risk factors for predicting the occurrence and adverse outcome of SAE.

Sepsis-associated encephalopathy and septic encephalitis: an update

INTRODUCTION

Sepsis-associated encephalopathy (SAE) and septic encephalitis (SE) are associated with increased mortality, long-term cognitive impairment, and focal neurological deficits.

AREAS COVERED

The PUBMED database was searched 2016-2020. The clinical manifestation of SAE is delirium, SE additionally is characterized by focal neurological symptoms. SAE is caused by inflammation with endothelial/microglial activation, increase of permeability of the blood-brain-barrier, hypoxia, imbalance of neurotransmitters, glial activation, axonal, and neuronal loss. Septic-embolic (SEE) and septic-metastatic encephalitis (SME) are characterized by focal ischemia (SEE) and small abscesses (SME). The continuum between SAE, SME, and SEE is documented by imaging techniques and autopsies. The backbone of treatment is rapid optimum antibiotic therapy. Experimental approaches focus on modulation of inflammation, stabilization of the blood-brain barrier, and restoration of membrane/mitochondrial function.

EXPERT OPINION

The most promising diagnostic approaches are new imaging techniques. The most important measure to fight delirium remains establishment of daily structure and adequate sensory stimuli. Dexmedetomidine and melatonin appear to reduce the frequency of delirium, their efficacy in SAE and SE remains to be established. Drugs already licensed for other indications or available as food supplements which may be effective in SAE are statins, L-DOPA/benserazide, β-hydroxybutyrate, palmitoylethanolamide, and tetracyclines or other bactericidal non-lytic antibiotics.

Exosomes in Sepsis

Sepsis is a severe state of infection with high mortality. Pathogen-associated molecular patterns and damage-associated molecular patterns (DAMPs) initiate dysregulated systemic inflammation upon binding to pattern recognition receptors. Exosomes are endosome-derived vesicles, which carry proteins, lipids and nucleic acids, and facilitate intercellular communications. Studies have shown altered contents and function of exosomes during sepsis. In sepsis, exosomes carry increased levels of cytokines and DAMPs to induce inflammation. Exosomal DAMPs include, but are not limited to, high mobility group box 1, heat shock proteins, histones, adenosine triphosphate, and extracellular RNA. Exosomes released during sepsis have impact on multiple organs, including the lungs, kidneys, liver, cardiovascular system, and central nervous system. Here, we review the mechanisms of inflammation caused by exosomes, and their contribution to multiple organ dysfunction in sepsis.

Modulation of endoplasmic reticulum stress response in gut-origin encephalopathy: Impact of vascular endothelial growth factor receptor-2 manipulation

BACKGROUND

Septic encephalopathy, the most frequent complication of sepsis, is orchestrated by a complex interplay of signals that leads to high mortality rates among intensive care unit patients. However, the role of the vascular endothelial growth factor receptor-2 (VEGFR2) in endoplasmic reticulum stress response (ERSR), during septic encephalopathy, is still elusive.

AIM

This study was aimed to examine the effect of an in-house designed/synthesized VEGFR2 antagonist, named WAG4S, on septic encephalopathy using cecal ligation and perforation (CLP).

MAIN METHODS

Rats were intraperitoneally injected with WAG-4S (1 mg/kg/d) for 7 days post-CLP.

KEY FINDINGS

In septic animals, VEGFR2 antagonism declined the expression of cortical p-VEGFR2 and p-mammalian target of rapamycin complex-1 (p-mTORC1). It also worsened the behavioral and histopathological alterations beyond CLP. However, and contrary to CLP, WAG-4S decreased the p-protein kinase R-like ER kinase (p-PERK) and eukaryotic initiation factor-2α (p-eIF2α) expression. Moreover, VEGFR2 blockade upregulated the mRNA expression of activating transcription factor-4 (ATF4), binding immunoglobulin protein/glucose-regulated protein-78 (Bip/GRP78), growth arrest and DNA damage-34 (GADD34) and spliced X-box binding protein-1 (XBP1s) above CLP. Similarly, it boosted inositol requiring enzyme-1α (IRE1α) activation and redox imbalance. In the same context, WAG-4S augmented the protein levels of CLP-induced ERSR apoptotic markers, namely C/EBP homologous protein (CHOP/GADD153), c-jun N-terminal kinase (JNK) and caspase-3.

SIGNIFICANCE

In conclusion, the PERK/eIF2α axis inhibition, during septic encephalopathy, is VEGFR2-independent, whereas the activated IRE1α/XBP1s/CHOP/JNK/caspase-3 cue promotes the ERSR execution module through VEGFR2 inhibition. This has turned VEGFR2 into a potential therapeutic target for ameliorating such an ailment.

ProBDNF promotes sepsis-associated encephalopathy in mice by dampening the immune activity of meningeal CD4+ T cells

BACKGROUND

Sepsis-associated encephalopathy (SAE) increases the mortality of septic patients, but its mechanism remains unclear. The present study aimed to investigate the roles of T lymphocytes, proBDNF, and their interaction in the pathogenesis of SAE.

METHODS

Fear conditioning tests were conducted for cognitive assessment in the lipopolysaccharide (LPS, 5 mg kg^-1)-induced septic mice. Meninges and peripheral blood were harvested for flow cytometry or qPCR. FTY720 and monoclonal anti-proBDNF antibody (McAb-proB) were used to investigate the effect of lymphocyte depletion and blocking proBDNF on the impaired cognitive functions in the septic mice.

RESULTS

In the septic mice, cognitive function was impaired, the percentage of CD4⁺ T cells were decreased in the meninges (P = 0.0021) and circulation (P = 0.0222), and pro-inflammatory cytokines were upregulated, but the anti-inflammatory cytokines interleukin (IL)-4 (P < 0.0001) and IL-13 (P = 0.0350) were downregulated in the meninges. Lymphocyte depletion by intragastrically treated FTY720 (1 mg kg^-1) for 1 week ameliorated LPS-induced learning deficit. In addition, proBDNF was increased in the meningeal (P = 0.0042) and peripheral (P = 0.0090) CD4⁺ T cells. Intraperitoneal injection of McAb-proB (100 μg) before LPS treatment significantly alleviated cognitive dysfunction, inhibited the downregulation of meningeal (P = 0.0264) and peripheral (P = 0.0080) CD4⁺ T cells, and normalized the gene expression of cytokines in the meninges. However, intra-cerebroventricular McAb-proB injection (1 μg) did not have such effect. Finally, exogenous proBDNF downregulated the percentage of CD4⁺ T cells in cultured splenocytes from septic mice (P = 0.0021).

CONCLUSION

Upregulated proBDNF in immune system promoted the pathogenesis of SAE through downregulating the circulating CD4⁺ T cells, limiting its infiltration into the meninges and perturbing the meningeal pro-/anti-inflammatory homeostasis.

Bioinformatics Analysis for Multiple Gene Expression Profiles in Sepsis

Background

This work aimed to screen key biomarkers related to sepsis progression by bioinformatics analyses.

Material/Methods

The microarray datasets of blood and neutrophils from patients with sepsis or septic shock were downloaded from Gene Expression Omnibus database. Then, differentially expressed genes (DEGs) from 4 groups (sepsis versus normal blood samples; septic shock versus normal blood samples; sepsis neutrophils versus normal controls and septic shock neutrophils versus controls) were respectively identified followed by functional analyses. Subsequently, protein–protein network was constructed, and key functional sub-modules were extracted. Finally, receiver operating characteristic analysis was conducted to evaluate diagnostic values of key genes.

Results

There were 2082 DEGs between blood samples of sepsis patients and controls, 2079 DEGs between blood samples of septic shock patients and healthy individuals, 6590 DEGs between neutrophils from sepsis and controls, and 1056 DEGs between neutrophils from septic shock patients and normal controls. Functional analysis showed that numerous DEGs were significantly enriched in ribosome-related pathway, cell cycle, and neutrophil activation involved in immune response. In addition, TRIM25 and MYC acted as hub genes in protein–protein interaction (PPI) analyses of DEGs from microarray datasets of blood samples. Moreover, MYC (AUC=0.912) and TRIM25 (AUC=0.843) had great diagnostic values for discriminating septic shock blood samples and normal controls. RNF4 was a hub gene from PPI analyses based on datasets from neutrophils and RNF4 (AUC=0.909) was capable of distinguishing neutrophil samples from septic shock samples and controls.

Conclusions

Our findings identified several key genes and pathways related to sepsis development.