Serotonergic neurotransmission mediated cognitive dysfunction in two mouse models of sepsis-associated encephalopathy

BACKGROUND

Patients with sepsis-associated encephalopathy (SAE) often exhibit cognitive impairments. Despite this, the underlying mechanisms of SAE remain largely unexplored. Here, we explored the role of serotonergic neurotransmission in cognitive dysfunction of two mouse models of SAE.

METHODS

The mouse models of SAE were established by injection of lipopolysaccharide (LPS, 10 mg/kg, intraperitoneal) and cecal ligation puncture (CLP) respectively. Barnes maze, new object recognition test and open field test were used to evaluate the effects of fluoxetine (selective serotonin reuptake inhibitor) and cyproheptadine (nonselective 5-HT2 receptor antagonist) on cognition and motor activity of mice. Additionally, WAY100635 (5-HT1A receptor antagonist) was co-administered with fluoxetine to explore the mechanism underlying effect of fluoxetine on cognitive impairments of SAE. Enzyme-linked immunosorbent assay (ELISA) was performed to determine 5-HT levels in hippocampus, brainstem and frontal lobe of experimental groups.

RESULTS

Both LPS-induced sepsis and CLP induced sepsis resulted in a notable learning deficit. Fluoxetine ameliorated, while cyproheptadine aggravated, cognitive impairment in two classic mouse models of SAE. The cognition-enhancing effect of fluoxetine is reversed by WAY100635. Decreased 5-HT levels in hippocampus, brainstem and frontal lobe were observed in LPS septic model and CLP septic model. Notably, both fluoxetine and cyproheptadine significantly increased 5-HT levels in those brain regions in LPS septic model. Additionally, fluoxetine significantly increased 5-HT levels in frontal lobe of CLP septic model.

CONCLUSIONS

Our study demonstrated that serotonergic neurotransmission plays a significant role in mechanisms underlying cognitive impairment in SAE. These findings contribute to identification of novel targets to prevent and arrest cognitive impairment in SAE.

Potential of piperine for neuroprotection in sepsis-associated encephalopathy

AIMS

Sepsis-associated encephalopathy (SAE) is a common complication that increases mortality and leads to long-term cognitive impairment in sepsis survivors. However, no specific or effective therapy has been identified for this complication. Piperine is an alkaloid known for its anti-inflammatory, antioxidant, and neuroprotective properties, which are important characteristics for treatment of SAE. The objective of this study was to evaluate the neuroprotective effect of piperine on SAE in C57BL/6 mice that underwent cecum ligation and perforation surgery (CLP).

MAIN METHODS

C57BL/6 male mice were randomly assigned to groups that underwent SHAM surgery or CLP. Mice in the CLP group were treated with piperine at doses of 20 or 40 mg/kg for short- (5 days) or long-term (10 days) periods after CLP.

KEY FINDINGS

Our results revealed that untreated septic animals exhibited increased concentrations of IL-6, TNF, VEGF, MMP-9, TBARS, and NLRP3, and decreased levels of BDNF, sulfhydryl groups, and catalase in the short term. Additionally, the levels of carbonylated proteins and degenerated neuronal cells were increased at both time points. Furthermore, short-term and visuospatial memories were impaired. Piperine treatment reduced MMP-9 activity in the short term and decreased the levels of carbonylated proteins and degenerated neuronal cells in the long term. It also lowered IL-6 and TBARS levels at both time points evaluated. Moreover, piperine increased short-term catalase and long-term BDNF factor levels and improved memory at both time points.

SIGNIFICANCE

In conclusion, our data demonstrate that piperine exerts a neuroprotective effect on SAE in animals that have undergone CLP.

Elevated Intracranial Pressure Level Is a Risk Factor for Sepsis-associated Encephalopathy: A Prospective Cohort Study

BACKGROUND/AIM

Cerebral edema is common in patients with sepsis-associated encephalopathy (SAE) and is a major cause of elevated intracranial pressure (ICP); however, the relationship between elevated ICP and SAE is unclear. The aim of this study was to investigate the association between optic nerve sheath diameter (ONSD), a surrogate of ICP, and the incidence of SAE.

PATIENTS AND METHODS

A prospective observational study was performed in a medical-surgical adult intensive care unit (ICU). All patients in the ICU who were consecutively diagnosed with sepsis during the study period were evaluated for eligibility. Ultrasound measurements of ONSD were performed within 6 h of enrollment and every two days thereafter until the patient developed SAE. Clinical and blood test data were collected throughout this period. Patients underwent a daily conscious and cognitive assessment. SAE was diagnosed as delirium or Glasgow Coma Scale (GCS) <15 points. Multivariate modified Poisson regression analysis was performed to identify risk factors for SAE.

RESULTS

A total of 123 patients with sepsis were included in the analysis. 58 patients (47.2%) developed SAE. The levels of ONSD0 (the first measured value) and ONSDmax (the maximum measured value) in the SAE group were significantly higher than those in the non-SAE group (5.23±0.52 mm vs. 5.85±0.54 mm for ONSD0 and 5.41±0.46 mm vs. 6.09±0.58 mm for ONSDmax, respectively; all p-values <0.001). The area under the curves (AUCs) for the ONSD0 and ONSDmax values in predicting SAE were 0.801 (95%CI=0.723-0.880, p<0.001) and 0.829 (95%CI=0.754-0.903, p<0.001), respectively. A higher ONSD0 level was significantly associated with an increased risk of SAE (adjusted risk ratio 3.241; 95%CI=1.686-6.230, p<0.001).

CONCLUSION

The levels of ONSD correlate with risk of SAE, indicating that increased ICP level is an independent risk factor for the development of SAE. Dynamic monitoring of ONSD/ICP has a high predictive value for SAE. Measures to prevent increases in ICP are helpful to reduce the incidence of SAE in sepsis patients.

The spectrum of sepsis-associated encephalopathy: a clinical perspective

Sepsis-associated encephalopathy is a severe neurologic syndrome characterized by a diffuse dysfunction of the brain caused by sepsis. This review provides a concise overview of diagnostic tools and management strategies for SAE at the acute phase and in the long term. Early recognition and diagnosis of SAE are crucial for effective management. Because neurologic evaluation can be confounded by several factors in the intensive care unit setting, a multimodal approach is warranted for diagnosis and management. Diagnostic tools commonly employed include clinical evaluation, metabolic tests, electroencephalography, and neuroimaging in selected cases. The usefulness of blood biomarkers of brain injury for diagnosis remains limited. Clinical evaluation involves assessing the patient's mental status, motor responses, brainstem reflexes, and presence of abnormal movements. Electroencephalography can rule out non-convulsive seizures and help detect several patterns of various severity such as generalized slowing, epileptiform discharges, and triphasic waves. In patients with acute encephalopathy, the diagnostic value of non-contrast computed tomography is limited. In septic patients with persistent encephalopathy, seizures, and/or focal signs, magnetic resonance imaging detects brain injury in more than 50% of cases, mainly cerebrovascular complications, and white matter changes. Timely identification and treatment of the underlying infection are paramount, along with effective control of systemic factors that may contribute to secondary brain injury. Upon admission to the ICU, maintaining appropriate levels of oxygenation, blood pressure, and metabolic balance is crucial. Throughout the ICU stay, it is important to be mindful of the potential neurotoxic effects associated with specific medications like midazolam and cefepime, and to closely monitor patients for non-convulsive seizures. The potential efficacy of targeted neurocritical care during the acute phase in optimizing patient outcomes deserves to be further investigated. Sepsis-associated encephalopathy may lead to permanent neurologic sequelae. Seizures occurring in the acute phase increase the susceptibility to long-term epilepsy. Extended ICU stays and the presence of sepsis-associated encephalopathy are linked to functional disability and neuropsychological sequelae, underscoring the necessity for long-term surveillance in the comprehensive care of septic patients.

HSPB8 up-regulation alleviates cognitive dysfunction in a mouse model of sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is associated with a higher risk of cognitive deficits; however, its potential mechanisms are still unknow. Recently, researches show that HSPB8, a family of small heat shock proteins, affects cognitive function and ameliorates sepsis-induced dysfunction. However, the role of HSPB8 in SAE-associated cognitive impairment has not been elucidated. In this study, we found that HSPB8 expression was up-regulated in the brain of mice with lipopolysaccharide-induced sepsis. HSPB8 overexpression alleviated cognitive decline in SAE mice. In addition, exogenous HSPB8 exerts neuroprotective effects and salvages synaptic function via regulating NRF1/TFAM-induced mitochondrial biogenesis and DRP1-mediate mitochondrial fission in a lipopolysaccharide-induced mouse model. Furthermore, HSPB8 overexpression inhibits IBA1 and NLRP3 activation in the SAE model. Overexpression of HSPB8 may be an efficient treatment for relieving SAE-related cognitive decline.

Sex, sepsis and the brain: defining the role of sexual dimorphism on neurocognitive outcomes after infection

Sexual dimorphisms exist in multiple domains, from learning and memory to neurocognitive disease, and even in the immune system. Male sex has been associated with increased susceptibility to infection, as well as increased risk of adverse outcomes. Sepsis remains a major source of morbidity and mortality globally, and over half of septic patients admitted to intensive care are believed to suffer some degree of sepsis-associated encephalopathy (SAE). In the short term, SAE is associated with an increased risk of in-hospital mortality, and in the long term, has the potential for significant impairment of cognition, memory, and acceleration of neurocognitive disease. Despite increasing information regarding sexual dimorphism in neurologic and immunologic systems, research into these dimorphisms in sepsis-associated encephalopathy remains critically understudied. In this narrative review, we discuss how sex has been associated with brain morphology, chemistry, and disease, sexual dimorphism in immunity, and existing research into the effects of sex on SAE.

CLINICAL PHENOTYPES OF SEPSIS-ASSOCIATED ENCEPHALOPATHY: A RETROSPECTIVE COHORT STUDY

ABSTRACT

Background: Sepsis-associated encephalopathy (SAE) is a dysfunction of the central nervous system experienced during sepsis with variable clinical and pathophysiologic features. We sought to identify distinct SAE phenotypes in relation to clinical outcomes. Methods: The Medical Information Mart for Intensive Care IV (MIMIC-IV) database and the eICU database were used to conduct a retrospective cohort study. Adult sepsis patients were included and SAE was defined as having a Glasgow Coma Scale (GCS) score ˂15 or delirium. The following our clinical phenotypes were defined as: ischemic-hypoxic, metabolic, mixed (ischemic-hypoxic and metabolic), and unclassified. The primary outcome was in-hospital mortality. Results: The study enrolled 4,120 sepsis patients, 2,239 from MIMIC-IV (including 1,489 patients with SAE, 67%), and 1,881 from eICU (1,291, 69%). For the SAE cohort, 2,780 patients in total were enrolled (median age, 67 years; interquartile range, 56-76.8; 1,589 (57%) were male; median GCS score was 12 [8-14]; median Sequential Organ Failure Assessment score was 6 [4-9]). The SAE phenotype distributions between the MIMIC-IV and eICU cohorts were as follows (39% vs. 35% ischemic-hypoxic, P = 0.043; 38% vs. 40% metabolic, P = 0.239; 15% vs. 15% mixed, P = 0.972; 38% vs. 40% unclassified, P = 0.471). For the overall cohort, the in-hospital mortality for patients with ischemic-hypoxic, metabolic, mixed, or unclassified phenotypes was 33.9% (95% confidence interval, 0.3-0.37), 28.4% (0.26-0.31), 41.5% (0.37-0.46), and 14.2% (0.12-0.16), respectively. In the multivariable logistic analysis, the mixed phenotype was associated with the highest risk of in-hospital mortality after adjusting for age, sex, GCS, and modified Sequential Organ Failure Assessment score (adjusted odds ratio, 2.11; 95% confidence interval, 1.67-2.67; P < 0.001). Conclusions: Four SAE phenotypes had different clinical outcomes. The mixed phenotype had the worst outcomes. Further understanding of these phenotypes in sepsis may improve trial design and targeted SAE management.

Prognostic role of serum ammonia in patients with sepsis-associated encephalopathy without hepatic failure

Objectives

Our previous study shows that serum ammonia in sepsis patients without hepatic failure is associated with a poor prognosis. The relationship between serum ammonia level and the prognosis of sepsis-associated encephalopathy (SAE) patients without hepatic failure remains unclear. We aimed to explore the relationship between serum ammonia levels and the prognosis of patients with SAE.

Materials and methods

This study is a retrospective cohort study. We collected 465 patients with SAE admitted to the intensive care unit (ICU) from Medical Information Mart for Intensive Care IV (MIMIC IV) from 2008 to 2019. Patients with SAE were divided into a survival group (369 patients) and a non-survival group (96 patients). We used the Wilcoxon signed-rank test and the multivariate logistic regression analysis to analyze the relationship between serum ammonia levels and the prognosis of patients with SAE. R software was used to analyze the dataset.

Results

The primary outcome was the relationship between serum ammonia level and hospital mortality of SAE. The secondary outcomes were the relationship between serum ammonia level and hospital stays, simplified acute physiology score (SAPS II), Charlson, Glasgow coma scale (GCS), sequential organ failure assessment (SOFA), and lactate level of SAE. The mortality of patients with SAE was 20.6%. The serum ammonia level was not significantly associated with hospital mortality, longer hospital stays, higher SAPS II and Charlson scores, and lower GCS of patients with SAE. The serum ammonia level was associated with higher SOFA scores and lactate levels in patients with SAE. The SAPS II and Charlson scores were independent risk factors for death in patients with SAE.

Conclusion

Serum ammonia level was associated with higher SOFA scores and lactate levels in patients with SAE. In addition, the SAPS II and Charlson scores can be used to assess the prognosis of patients with SAE. Therefore, we should closely monitor serum ammonia, SAPS II, and Charlson levels in patients with SAE.

Metabolic Reprogramming of Microglia in Sepsis-Associated Encephalopathy: Insights from Neuroinflammation

Sepsis-associated encephalopathy (SAE) is a diffuse brain dysfunction caused by sepsis that manifests as a range of brain dysfunctions from delirium to coma. It is a relatively common complication of sepsis associated with poor patient prognosis and mortality. The pathogenesis of SAE involves neuroinflammatory responses, neurotransmitter dysfunction, blood-brain barrier (BBB) disruption, abnormal blood flow regulation, etc. Neuroinflammation caused by hyperactivation of microglia is considered to be a key factor in disease development, which can cause a series of chain reactions, including BBB disruption and oxidative stress. Metabolic reprogramming has been found to play a central role in microglial activation and executive functions. In this review, we describe the pivotal role of energy metabolism in microglial activation and functional execution and demonstrate that the regulation of microglial metabolic reprogramming might be crucial in the development of clinical therapeutics for neuroinflammatory diseases like SAE.

[Research Progress in Clinical Electrophysiological Assessment of Patients with Sepsis-Associated Encephalopathy]

Sepsis-associated encephalopathy(SAE) caused by infections outside the central nervous system always presents extensive brain damage.It is common in clinical practice and associated with a poor prognosis.There are problems in the assessing and diagnosing of SAE.Many factors,such as sedation and mechanical ventilation,make it difficult to assess SAE,while electrophysiological examination may play a role in the assessment.We reviewed the studies of electrophysiological techniques such as electroencephalography and somatosensory evoked potentials for monitoring SAE,hoping to provide certain evidence for the clinical evaluation and diagnosis of SAE.

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.

Senkyunolide I Protects against Sepsis-Associated Encephalopathy by Attenuating Sleep Deprivation in a Murine Model of Cecal Ligation and Puncture

Sepsis may lead to sleep deprivation, which will promote the development of neuroinflammation and mediate the progression of sepsis-associated encephalopathy (SAE). Senkyunolide I, an active component derived from an herb medicine, has been shown to provide a sedative effect to improve sleep. However, its role in sepsis is unclear. The present study was performed to investigate whether Senkyunolide I protected against SAE in a murine model of cecal ligation and puncture (CLP). Here, we showed that Senkyunolide I treatment improved the 7-day survival rate and reduced the excessive release of cytokines including TNF-α, IL-6, and IL-1β. A fear conditioning test was performed, and the results showed that Senkyunolide I attenuated CLP-induced cognitive dysfunction. Senkyunolide I treatment also decreased the phosphorylation levels of inflammatory signaling proteins, including p-ERK, p-JNK, p-P38, and p-P65, and the level of inflammatory cytokines, including TNF-α, IL-6, and IL-1β, in the hippocampus homogenate. Sleep deprivation was attenuated by Senkyunolide I administration, as demonstrated by the modification of the BDNF and c-FOS expression. When sleep deprivation was induced manually, the protective effect of Senkyunolide I against inflammatory responses and cognitive dysfunction was reversed. Our data demonstrated that Senkyunolide I could protect against sepsis-associated encephalopathy in a murine model of sepsis via relieving sleep deprivation.

Widespread time-dependent changes in tissue cytokine concentrations in brain regions during the acute phase of endotoxemia in mice

Sepsis-associated encephalopathy (SAE) is a diffuse brain dysfunction induced by the systemic response to infection in septic patients. In the present study, we modeled SAE by administering lipopolysaccharide (LPS) intraperitoneally to mice at a concentration of 3.0 mg/kg. We investigated regional preferences for cytokine-mediated brain reactions to endotoxemia and at what time point brain inflammation begins, as well as what cytokines are involved in acute brain reactions. Brains were divided into seven parts: cortex (CTX), olfactory system (Olf), hippocampus (Hip), striatum (Str), diencephalon (Die), brain stem (BS), and cerebellum (CBL). In each brain region, we determined the tissue concentrations of 11 cytokines: CCL2, CCL3, CCL11, CXCL1, CXCL2, CXCL9, CXCL10, G-CSF, IL-1β, IL-6, and TNF-α, in mice injected with LPS or saline, at 1, 4, and 24 h after injection using multiplex cytokine assays. Every brain region responded with the production of multiple cytokines to LPS-induced systemic inflammation during the acute phase (4-24 h) after LPS injection. IL-6, CCL2, CCL3, CXCL1, CXCL2, CXCL9, and TNF-α were "early cytokines" that increased only at 4 h but not at 24 h after LPS injection in most brain regions. CCL11, CXCL10, and G-CSF were "late cytokines" that were elevated up to 24 h after LPS injection in selected brain regions. The regions Olf, Hip, and Die were the most responsive to endotoxemia; these regions produced ten cytokines and continued to produce three "late cytokines" up to 24 h after LPS injection. Str was the least responsive to endotoxemia. The widespread nature of brain cytokine production explains the characteristics of SAE. Further studies on the roles of CCL11, CXCL10, and G-CSF may be especially important in terms of potential prevention of SAE between 4 and 24 h after the onset of sepsis.

Policies and strategies to prevent patient falls in hospital

Emeritus Professor Alan Glasper, University of Southampton, discusses polices and strategies used by nurses to minimise patient falls in hospital.

Mitochondria-Targeted Peptide Reverses Mitochondrial Dysfunction and Cognitive Deficits in Sepsis-Associated Encephalopathy

Sepsis-associated encephalopathy (SAE) is associated with increased mortality, morbidity, and long-term cognitive impairments. Its pathophysiology remains to be determined and an effective pharmacologic treatment is lacking. The goal of this study was to investigate the effects of the mitochondria-targeted peptide SS-31 on mitochondrial function and cognitive deficits in SAE mice. C57BL/6 male mice were randomly divided into sham, sham + SS-31, cecal ligation and puncture (CLP), and CLP + SS-31 groups. Peptide SS-31 (5 mg/kg) was intraperitoneally administrated immediately after operation and afterwards once daily for six consecutive days. Surviving mice were subjected to behavioral tests and the hippocampus was collected for biochemical analysis 7 days after operation. The results showed that CLP resulted in high mortality rate and cognitive deficits, representative characteristics of SAE. A physiological mechanistic investigation revealed that mitochondrial function of hippocampus was severely impaired, coupled with reactive oxygen species (ROS) generation, triggering neuronal apoptosis and inflammation. Notably, administration of peptide SS-31 protected the integrity of mitochondria, reversed the mitochondrial dysfunction, inhibited the apoptosis resulting from the release of cytochrome c, diminished the response of inflammation, and ultimately reversed the behavior deficits in the SAE mice. In conclusion, our data demonstrate that daily treatment with mitochondria-targeted peptide SS-31 reduces mortality rate and ameliorates cognitive deficits, which is possibly through a mechanism of reversing mitochondrial dysfunction and partial inhibition of neuronal apoptosis and inflammation in the hippocampus of the SAE mice.