Sepsis survivor mice exhibit a behavioral endocrine syndrome with ventral hippocampal dysfunction

Unlike other medical conditions, type 2 diabetes is a risk factor for new-onset major depression after COVID-19

OBJECTIVE

It is unclear whether pre-COVID medical conditions are risk factors for post-COVID major depressive episode (MDE). We aimed to determine which pre-COVID medical conditions are risk factors for post-COVID MDE after a hospitalization for COVID-19.

METHODS

We conducted a nested retrospective case-cohort study within a cohort of 650 patients evaluated six months after hospitalization for COVID-19 at Bicêtre hospital, France. Nine medical conditions present before COVID-19 (High blood pressure, obesity, type 2 diabetes, cardiac, respiratory and renal disease, immune deficiency, neoplasia and liver disease) were extracted from medical records. MDE was assessed using the Structured Clinical Interview for DSM-5 Disorders-Clinician Version (SCID-5-CV). Bivariate and multivariable analyses were performed to determine which pre-COVID medical conditions are independent risk factors for post-COVID new-onset MDE.

RESULTS

Patients mean age was 62.8 (15.8), 258 (39.7 %) were women; 301 (46.3 %) had high blood pressure, 205 (32.4 %) had obesity, and 186 (28.6 %) had type 2 diabetes. Thirty-six (5.5 %) patients were diagnosed with a new-onset MDE. In contrast to other medical conditions, type 2 diabetes was significantly associated with new-onset MDE (OR = 2.51 [1.19-5.29]).

CONCLUSION

Unlike other pre-COVID medical conditions, type 2 diabetes is a risk factor for post-COVID MDE. Patients with type 2 diabetes should be screened for MDE after a hospitalization for COVID-19.

Post-sepsis psychiatric disorder: Pathophysiology, prevention, and treatment

Post-sepsis psychiatric disorder, encompassing anxiety, depression, post-traumatic stress disorder and delirium, is a highly prevalent complication secondary to sepsis, resulting in a marked increase in long-term mortality among affected patients. Regrettably, psychiatric impairment associated with sepsis is frequently disregarded by clinicians. This review aims to summarize recent advancements in the understanding of the pathophysiology, prevention, and treatment of post-sepsis mental disorder, including coronavirus disease 2019-related psychiatric impairment. The pathophysiology of post-sepsis psychiatric disorder is complex and is known to involve blood-brain barrier disruption, overactivation of the hypothalamic-pituitary-adrenal axis, neuroinflammation, oxidative stress, neurotransmitter dysfunction, programmed cell death, and impaired neuroplasticity. No unified diagnostic criteria for this disorder are currently available; however, screening scales are often applied in its assessment. Modifiable risk factors for psychiatric impairment post-sepsis include the number of experienced traumatic memories, the length of ICU stay, level of albumin, the use of vasopressors or inotropes, daily activity function after sepsis, and the cumulative dose of dobutamine. To contribute to the prevention of post-sepsis psychiatric disorder, it may be beneficial to implement targeted interventions for these modifiable risk factors. Specific therapies for this condition remain scarce. Nevertheless, non-pharmacological approaches, such as comprehensive nursing care, may provide a promising avenue for treating psychiatric disorder following sepsis. In addition, although several therapeutic drugs have shown preliminary efficacy in animal models, further confirmation of their potential is required through follow-up clinical studies.

Gut-brain axis in the pathogenesis of sepsis-associated encephalopathy

The gut-brain axis is a bidirectional communication network linking the gut and the brain, overseeing digestive functions, emotional responses, body immunity, brain development, and overall health. Substantial research highlights a connection between disruptions of the gut-brain axis and various psychiatric and neurological conditions, including depression and Alzheimer's disease. Given the impact of the gut-brain axis on behavior, cognition, and brain diseases, some studies have started to pay attention to the role of the axis in sepsis-associated encephalopathy (SAE), where cognitive impairment is the primary manifestation. SAE emerges as the primary and earliest form of organ dysfunction following sepsis, potentially leading to acute cognitive impairment and long-term cognitive decline in patients. Notably, the neuronal damage in SAE does not stem directly from the central nervous system (CNS) infection but rather from an infection occurring outside the brain. The gut-brain axis is posited as a pivotal factor in this process. This review will delve into the gut-brain axis, exploring four crucial pathways through which inflammatory signals are transmitted and elevate the incidence of SAE. These pathways encompass the vagus nerve pathway, the neuroendocrine pathway involving the hypothalamic-pituitary-adrenal (HPA) axis and serotonin (5-HT) regulation, the neuroimmune pathway, and the microbial regulation. These pathways can operate independently or collaboratively on the CNS to modulate brain activity. Understanding how the gut affects and regulates the CNS could offer the potential to identify novel targets for preventing and treating this condition, ultimately enhancing the prognosis for individuals with SAE.

Corticosteroid Treatment During Sepsis Alters Hippocampal Function in Male and Female Survivors

Background

Millions of sepsis survivors annually face neuropsychiatric sequelae of their illness. Corticosteroids are frequently administered for sepsis, and their use improves neuropsychiatric outcomes, but the mechanisms are unknown. In light of prior work that has shown persistent inflammation in sepsis survivors, we hypothesized that short-term corticosteroid treatment during illness would reverse the long-term impact of sepsis on inflammatory gene expression in the hippocampus and rescue associated changes to affective behaviors.

Methods

Male and female mice underwent cecal ligation and puncture or a sham surgery to induce acute infection and were treated for 5 days with corticosterone or vehicle. Starting 2 weeks after the surgery, we performed functional phenotyping in the survivor mice followed by hippocampal RNA sequencing to identify underlying mechanisms.

Results

Long-term cecal ligation and puncture survivors exhibited anxiety-like behavior, increased central hypothalamic-pituitary-adrenal axis activity, and persistent systemic and neuroinflammation. Corticosterone treatment during illness did not reverse anxiety-like behavior or inflammation in survivors. Instead, corticosterone treatment impaired object memory and increased active coping behavior in females. History of corticosterone treatment influenced the expression of >10% of detectable transcripts in the dorsal and ventral hippocampus, including a coordinated downregulation of activity-dependent genes.

Conclusions

Corticosterone treatment during sepsis impaired memory formation in survivors and caused a lasting decrease in hippocampal neural activity, which could underlie its effect on memory. Future studies should focus on how this lasting effect of corticosteroid treatment on hippocampal activity and memory translates into improved neuropsychiatric outcomes in human sepsis survivors.

Recent advances in the study of sepsis-induced depression

Progress in medicine such as the use of anti-infective drugs and development of the advanced life support equipment has greatly improved the survival rate of patients with sepsis. However, the incidence of sepsis-related diseases is increasing. These include severe neurologic and psychologic disorders, cognitive decline, anxiety, depression, and post-traumatic stress disorder. Cerebral dysfunction occurs via multiple interacting mechanisms, with different causative pathogens having distinct effects. Because sepsis-related diseases place a substantial burden on patients and their families, it is important to elucidate the underlying pathophysiologic mechanisms to develop effective treatments.

Corticosterone enhances formation of non-fear but not fear memory during infectious illness

Introduction

Survivors of critical illness are at high risk of developing post-traumatic stress disorder (PTSD) but administration of glucocorticoids during the illness can lower that risk. The mechanism is not known but may involve glucocorticoid modulation of hippocampal- and amygdala-dependent memory formation. In this study, we sought to determine whether glucocorticoids given during an acute illness influence the formation and persistence of fear and non-fear memories from the time of the illness.

Methods

We performed cecal ligation and puncture in male and female mice to induce an acute infectious illness. During the illness, mice were introduced to a neutral object in their home cage and separately underwent contextual fear conditioning. We then tested the persistence of object and fear memories after recovery.

Results

Glucocorticoid treatment enhanced object discrimination but did not alter the expression of contextual fear memory. During context re-exposure, neural activity was elevated in the dentate gyrus irrespective of fear conditioning.

Conclusions

Our results suggest that glucocorticoids given during illness enhance hippocampal-dependent non-fear memory processes. This indicates that PTSD outcomes in critically ill patients may be improved by enhancing non-fear memories from the time of their illness.

Corticosterone enhances formation of non-fear but not fear memory during infectious illness

Survivors of critical illness are at high risk of developing post-traumatic stress disorder (PTSD) but administration of glucocorticoids during the illness can lower that risk. The mechanism is not known but may involve glucocorticoid modulation of hippocampal- and amygdalar-dependent memory formation. In this study, we sought to determine whether glucocorticoids given during an acute illness influence the formation and persistence of fear and non-fear memories from the time of the illness. We performed cecal ligation and puncture in male and female mice to induce an acute infectious illness. During the illness, mice were introduced to a neutral object in their home cage and separately underwent contextual fear conditioning. We then tested the persistence of object and fear memories after recovery. Glucocorticoid treatment enhanced object discrimination but did not alter the expression of contextual fear memory. During context re-exposure, neural activity was elevated in the dentate gyrus irrespective of fear conditioning. Our results suggest that glucocorticoids given during illness enhance hippocampal-dependent non-fear memory processes. This indicates that PTSD outcomes in critically ill patients may be improved by enhancing non-fear memories from the time of their illness.

Electroacupuncture alleviates perioperative hypothalamus-pituitary-adrenal axis dysfunction via circRNA-miRNA-mRNA networks

Electroacupuncture (EA) has long been used to alleviate surgery-induced hypothalamic-pituitary-adrenal axis dysfunction. However, its downstream gene targets in the brain remain unclear. The aim of the present study was to clarify the potential targets of EA based on RNA sequencing techniques (RNA-seq). Rats were divided into normal control (NC), hepatectomy surgery (HT), HT + EA, and HT + sham EA groups followed by RNA-seq of two representative nuclei in the hypothalamus and amygdala. Weighted Gene Co-expression Network Analysis and Gene Set Enrichment Analysis identified six gene modules associated with neuroendocrine transmitters and neural remodeling in the hypothalamus. Furthermore, circRNA-miRNA-mRNA interaction networks revealed EA-related candidate miRNAs and circRNAs, of which opioid receptor mu 1 might be an EA-specific target, and showed regulation by competing endogenous RNA. We identified the neuroendocrine circRNA-miRNA-mRNA networks through which EA has an effect on HPA axis dysfunction, thus providing potential targets and future research directions for EA treatment.

Integrated transcriptomics and metabolomics analysis of the hippocampus reveals altered neuroinflammation, downregulated metabolism and synapse in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is an intricated complication of sepsis that brings abnormal emotional and memory dysfunction and increases patients’ mortality. Patients’ alterations and abnormal function seen in SAE occur in the hippocampus, the primary brain region responsible for memory and emotional control, but the underlying pathophysiological mechanisms remain unclear. In the current study, we employed an integrative analysis combining the RNA-seq-based transcriptomics and liquid chromatography/mass spectrometry (LC-MS)-based metabolomics to comprehensively obtain the enriched genes and metabolites and their core network pathways in the endotoxin (LPS)-injected SAE mice model. As a result, SAE mice exhibited behavioral changes, and their hippocampus showed upregulated inflammatory cytokines and morphological alterations. The omics analysis identified 81 differentially expressed metabolites (variable importance in projection [VIP] > 1 and p < 0.05) and 1747 differentially expressed genes (Foldchange >2 and p < 0.05) were detected in SAE-grouped hippocampus. Moreover, 31 compounds and 100 potential target genes were employed for the Kyoto Encyclopedia of Genes and Genomes (KEGG) Markup Language (KGML) network analysis to explore the core signaling pathways for the progression of SAE. The integrative pathway analysis showed that various dysregulated metabolism pathways, including lipids metabolism, amino acids, glucose and nucleotides, inflammation-related pathways, and deregulated synapses, were tightly associated with hippocampus dysfunction at early SAE. These findings provide a landscape for understanding the pathophysiological mechanisms of the hippocampus in the progression of SAE and pave the way to identify therapeutic targets in future studies.

Neuroimmune Regulation in Sepsis-Associated Encephalopathy: The Interaction Between the Brain and Peripheral Immunity

Sepsis-associated encephalopathy (SAE), the most popular cause of coma in the intensive care unit (ICU), is the diffuse cerebral damage caused by the septic challenge. SAE is closely related to high mortality and extended cognitive impairment in patients in septic shock. At present, many studies have demonstrated that SAE might be mainly associated with blood–brain barrier damage, abnormal neurotransmitter secretion, oxidative stress, and neuroimmune dysfunction. Nevertheless, the precise mechanism which initiates SAE and contributes to the long-term cognitive impairment remains largely unknown. Recently, a growing body of evidence has indicated that there is close crosstalk between SAE and peripheral immunity. The excessive migration of peripheral immune cells to the brain, the activation of glia, and resulting dysfunction of the central immune system are the main causes of septic nerve damage. This study reviews the update on the pathogenesis of septic encephalopathy, focusing on the over-activation of immune cells in the central nervous system (CNS) and the “neurocentral–endocrine–immune” networks in the development of SAE, aiming to further understand the potential mechanism of SAE and provide new targets for diagnosis and management of septic complications.

Persisting neuroendocrine abnormalities and their association with physical impairment 5 years after critical illness

Background

Critical illness is hallmarked by neuroendocrine alterations throughout ICU stay. We investigated whether the neuroendocrine axes recover after ICU discharge and whether any residual abnormalities associate with physical functional impairments assessed 5 years after critical illness.

Methods

In this preplanned secondary analysis of the EPaNIC randomized controlled trial, we compared serum concentrations of hormones and binding proteins of the thyroid axis, the somatotropic axis and the adrenal axis in 436 adult patients who participated in the prospective 5-year clinical follow-up and who provided a blood sample with those in 50 demographically matched controls. We investigated independent associations between any long-term hormonal abnormalities and physical functional impairments (handgrip strength, 6-min walk distance, and physical health-related quality-of-life) with use of multivariable linear regression analyses.

Results

At 5-year follow-up, patients and controls had comparable serum concentrations of thyroid-stimulating hormone, thyroxine (T₄), triiodothyronine (T₃) and thyroxine-binding globulin, whereas patients had higher reverse T₃ (rT₃, p = 0.0002) and lower T₃/rT₃ (p = 0.0012) than controls. Patients had comparable concentrations of growth hormone, insulin-like growth factor-I (IGF-I) and IGF-binding protein 1 (IGFBP1), but higher IGFBP3 (p = 0.030) than controls. Total and free cortisol, cortisol-binding globulin and albumin concentrations were comparable for patients and controls. A lower T₃/rT₃ was independently associated with lower handgrip strength and shorter 6-min walk distance (p ≤ 0.036), and a higher IGFBP3 was independently associated with higher handgrip strength (p = 0.031).

Conclusions

Five years after ICU admission, most hormones and binding proteins of the thyroid, somatotropic and adrenal axes had recovered. The residual long-term abnormality within the thyroid axis was identified as risk factor for long-term physical impairment, whereas that within the somatotropic axis may be a compensatory protective response. Whether targeting of the residual abnormality in the thyroid axis may improve long-term physical outcome of the patients remains to be investigated.

Trial registration ClinicalTrials.gov: NCT00512122, registered on July 31, 2007 (https://www.clinicaltrials.gov/ct2/show/NCT00512122).

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03858-1.

Glucocorticoids and the Brain after Critical Illness

Treatment for critical illness typically focuses on a patient's short-term physical recovery; however, recent work has broadened our understanding of the long-term implications of illness and treatment strategies. In particular, survivors of critical illness have significantly elevated risk of developing lasting cognitive impairment and psychiatric disorders. In this review, we examine the role of endogenous and exogenous glucocorticoids in neuropsychiatric outcomes following critical illness. Illness is marked by acute elevation of free cortisol and adrenocorticotropic hormone suppression, which typically normalize after recovery; however, prolonged dysregulation can sometimes occur. High glucocorticoid levels can cause lasting alterations to the plasticity and structural integrity of the hippocampus and prefrontal cortex, and this mechanism may plausibly contribute to impaired memory and cognition in critical illness survivors, though specific evidence is lacking. Glucocorticoids may also exacerbate inflammation-associated neural damage. Conversely, current evidence indicates that glucocorticoids during illness may protect against the development of post-traumatic stress disorder. We propose future directions for research in this field, including determining the role of persistent glucocorticoid elevations after illness in neuropsychiatric outcomes, the role of systemic vs neuroinflammation, and probing unexplored lines of investigation on the role of mineralocorticoid receptors and the gut-brain axis. Progress toward personalized medicine in this area has the potential to produce tangible improvements to the lives patients after a critical illness, including Coronavirus Disease 2019.

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

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