Inflammasome signaling affects anxiety- and depressive-like behavior and gut microbiome composition

Gut dysbiosis-induced vitamin B6 metabolic disorder contributes to chronic stress-related abnormal behaviors in a cortisol-independent manner

Chronic stress can result in various conditions, including psychological disorders, neurodegenerative diseases, and accelerated brain aging. Gut dysbiosis potentially contributes to stress-related brain disorders in individuals with chronic stress. However, the causal relationship and key factors between gut dysbiosis and brain disorders in chronic stress remain elusive, particularly under non-sterile conditions. Here, using a repeated restraint stress (RRS) rat model, we show that sequential transplantation of the cecal contents of different RRS stages to normal rats reproduced RRS-induced core phenotypes, including abnormal behaviors, increased peripheral blood corticosterone and inflammatory cytokines, and a unique gut microbial phenotype. This core phenotypic development was effectively inhibited with probiotic supplement. The RRS-induced unique gut microbial phenotypes at the genus level were positively or negatively associated with the levels of 20 plasma metabolites, including vitamin B6 metabolites 4-pyridoxic acid and 4-pyridoxate. Vitamin B6 supplement during RRS alleviated weight loss, abnormal behaviors, peripheral inflammation, and neuroinflammation, but did not affect the peripheral corticosterone levels in chronic stressed rats. Dampening inflammatory signaling via knocking out caspase 11 or caspase 1 inhibitor abolished RRS-induced abnormal behaviors and peripheral and neuroinflammation but did not decrease peripheral corticosterone in mice. These findings show that gut dysbiosis-induced vitamin B6 metabolism disorder is a new non-hypothalamic-pituitary-adrenal axis mechanism of chronic stress-related brain disorders. Both probiotics and vitamin B6 supplement have potential to be developed as therapeutic strategies for preventing and/or treating chronic stress-related illness.

Peripheral mitochondrial DNA as a neuroinflammatory biomarker for major depressive disorder

In the pathogenesis of major depressive disorder, chronic stress-related neuroinflammation hinders favorable prognosis and antidepressant response. Mitochondrial DNA may be an inflammatory trigger, after its release from stress-induced dysfunctional central nervous system mitochondria into peripheral circulation. This evidence supports the potential use of peripheral mitochondrial DNA as a neuroinflammatory biomarker for the diagnosis and treatment of major depressive disorder. Herein, we critically review the neuroinflammation theory in major depressive disorder, providing compelling evidence that mitochondrial DNA release acts as a critical biological substrate, and that it constitutes the neuroinflammatory disease pathway. After its release, mitochondrial DNA can be carried in the exosomes and transported to extracellular spaces in the central nervous system and peripheral circulation. Detectable exosomes render encaged mitochondrial DNA relatively stable. This mitochondrial DNA in peripheral circulation can thus be directly detected in clinical practice. These characteristics illustrate the potential for mitochondrial DNA to serve as an innovative clinical biomarker and molecular treatment target for major depressive disorder. This review also highlights the future potential value of clinical applications combining mitochondrial DNA with a panel of other biomarkers, to improve diagnostic precision in major depressive disorder.

Nitrate ameliorates alcohol-induced cognitive impairment via oral microbiota

Alcohol use is associated with cognitive impairment and dysregulated inflammation. Oral nitrate may benefit cognitive impairment in aging through altering the oral microbiota. Similarly, the beneficial effects of nitrate on alcohol-induced cognitive decline and the roles of the oral microbiota merit investigation. Here we found that nitrate supplementation effectively mitigated cognitive impairment induced by chronic alcohol exposure in mice, reducing both systemic and neuroinflammation. Furthermore, nitrate restored the dysbiosis of the oral microbiota caused by alcohol consumption. Notably, removing the oral microbiota led to a subsequent loss of the beneficial effects of nitrate. Oral microbiota from donor alcohol use disordered humans who had been taking the nitrate intervention were transplanted into germ-free mice which then showed increased cognitive function and reduced neuroinflammation. Finally, we examined 63 alcohol drinkers with varying levels of cognitive impairment and found that lower concentrations of nitrate metabolism-related bacteria were associated with higher cognitive impairment and lower nitrate levels in plasma. These findings highlight the protective role of nitrate against alcohol-induced cognition impairment and neuroinflammation and suggest that the oral microbiota associated with nitrate metabolism and brain function may form part of a "microbiota-mouth-brain axis".

Repeated Administration of a Full-Spectrum Cannabidiol Product, Not a Cannabidiol Isolate, Reverses the Lipopolysaccharide-Induced Depressive-Like Behavior and Hypolocomotion in a Rat Model of Low-Grade Subchronic Inflammation

Background: Mounting evidence suggests that the phytocannabinoid cannabidiol (CBD) holds promise as an antidepressant agent in conditions underlined by inflammation. Full-spectrum CBD extracts might provide greater behavioral efficacy than CBD-only isolates and might require lower doses to achieve the same outcomes due to the presence of other cannabinoids, terpenes, and flavonoids. However, investigations in this area remain limited. Methods: We evaluated the behavioral response to the administration for 7 days of 15 and 30 mg/kg of a CBD isolate and a full-spectrum CBD product in a rat model of subchronic lipopolysaccharide (LPS, 0.5 mg/kg/day/7 days, intraperitoneal)-induced depressive-like and sickness behavior. The forced swim test was used to assess depressive-like behavior, the open field test (OFT) to assess locomotion, and the elevated plus maze to assess anxiety-like behavior. Results: The full-spectrum CBD extract at both doses, but not the CBD isolate, reversed the LPS-induced depressive-like behavior in the forced swim test. Moreover, the full-spectrum CBD extract at the higher dose but not the CBD isolate restored the subchronic LPS-induced hypolocomotion in the OFT. Repeated administration of both formulations elicited an anxiogenic-like trend in the elevated plus maze. Conclusion: Full-spectrum CBD products might have greater therapeutic efficacy in resolving inflammation-induced depressive and sickness behavior compared to a CBD-only isolate.

The Role of Mitochondrial Dysfunction-Mediated Changes in Immune Cytokine Expression in the Pathophysiology and Treatment of Major Depressive Disorder

Recent studies have demonstrated an association between major depressive disorder (MDD) and both mitochondrial dysfunction and alterations in pro-inflammatory cytokine expression, suggesting that such changes may be key drivers of MDD pathogenesis. Mechanistically, changes in mitochondrial function are related to endoplasmic reticulum stress, reactive oxygen species production, oxidative phosphorylation, apoptosis, and disrupted calcium ion homeostasis, all of which trigger the activation of signaling cascades that affect the expression of pro-inflammatory cytokines, including tumor necrosis factor alpha, interleukin 1, interleukin 6, and interferons. Certain factors present in the gut microbiota ecosystem can influence communication between microorganisms and the brain through the neuroendocrine, immune, and autonomic nervous systems, thereby altering mitochondrial function and cytokine production. This review article explores the means through which mitochondria regulate immune cytokine expression and the role of mitochondrial dysfunction in the pathogenesis and treatment of MDD to provide new perspectives for the diagnosis of this disease and the development of novel therapeutic interventions with greater efficacy and improved safety profiles.

Transcranial ultrasound stimulation ameliorates dextran sulphate sodium-induced colitis and behavioural disorders by suppressing the inflammatory response in the brain

Inflammatory bowel disease (IBD) is associated with neuroinflammation, which may contribute to an increased risk of neurodegenerative disorders. This research investigated the potential of transcranial low-intensity pulsed ultrasound (LIPUS) to mitigate colonic inflammation induced by dextran sulphate sodium (DSS), focusing on its effects via the brain-gut axis. Colitis and neuroinflammation were induced in mice by administering 3% (wt/vol) DSS for 7 days. Subsequently, the brain was subjected to LIPUS stimulation at intensities of 0.5 or 1.0 W/cm² for 3 days. Biological samples were analyzed using real-time polymerase chain reaction, western blot, enzyme-linked immunosorbent assay, and histological observation. Behavioural dysfunctions were assessed using the open field test, novel object recognition task, and Y-maze test. The alteration in gut microbiota composition was assessed through 16S rRNA sequencing. LIPUS therapy notably alleviated colitis symptoms and suppressed inflammation in both the colon and hippocampus of DSS-exposed mice. Compared with the group treated only with DSS, the LIPUS treatment showed decreased crypt destruction and partial epithelial barrier preservation. Moreover, LIPUS preserved intestinal barrier function by upregulating the levels of occludin and zonula occludens, decreasing the levels of lipopolysaccharide (LPS) and LPS-binding protein in serum, and ameliorating behavioural disorders. Further analysis indicated that LIPUS did not significantly transform the composition of the intestinal microbiota, but the microbial community showed some differences from the community in the DSS-only treatment group. This study demonstrates that transcranial LIPUS stimulation could be a novel therapeutic strategy for IBD and neuroinflammation via regulation of inflammatory interactions across brain-gut axis.

Weizmannia coagulans BC99 Improve Cognitive Impairment Induced by Chronic Sleep Deprivation via Inhibiting the Brain and Intestine's NLRP3 Inflammasome

Weizmannia coagulans BC99, a Gram-positive, spore-forming, lactic acid-producing bacterium is renowned for its resilience and health-promoting properties, W. coagulans BC99 survives harsh environments, including high temperatures and gastric acidity, enabling effective delivery to the intestines. The consequences of chronic sleep deprivation (SD) include memory deficits and gastrointestinal dysfunction. In this study, a chronic sleep deprivation cognitive impairment model was established by using a sleep deprivation instrument and W. coagulans BC99 was given by gavage for 4 weeks to explore the mechanism by which BC99 improves cognitive impairment in sleep-deprived mice. BC99 improved cognitive abnormalities in novel object recognition tests induced by chronic sleep deprivation and showed behavior related to spatial memory in the Morris water maze test. W. coagulans BC99 reduced the heart mass index of sleep-deprived mice, increased the sleep-related neurotransmitters 5-HT and DA, decreased corticosterone and norepinephrine, and increased alpha diversity and community similarity. It reduced the abundance of harmful bacteria such as Olsenella, increased the abundance of beneficial bacteria such as Lactobacillus and Bifidobacterium, and promoted the production of short-chain fatty acids (SCFAs). W. coagulans BC99 also inhibits LPS translocation and the elevation of peripheral inflammatory factors by maintaining the integrity of the intestinal barrier and inhibiting the expression of the NLRP3 signaling pathway in the jejunum, thereby inhibiting the NLRP3 inflammasome in the brain of mice and reducing inflammatory factors in the brain, providing a favorable environment for the recovery of cognitive function. The present study confirmed that W. coagulans BC99 ameliorated cognitive impairment in chronic sleep-deprived mice by improving gut microbiota, especially by promoting SCFAs production and inhibiting the NLRP3 signaling pathway in the jejunum and brain. These findings may help guide the treatment of insomnia or other sleep disorders through dietary strategies.

Genetic overlap between schizophrenia and constipation: insights from a genome-wide association study in a European population

BACKGROUND

Patients with schizophrenia (SCZ) experience constipation at significantly higher rates compared with the general population. This relationship suggests a potential genetic overlap between these two conditions.

METHODS

We analyzed genome-wide association study (GWAS) data for both SCZ and constipation using a five-part approach. The first and second parts assessed the overall and local genetic correlations using methods such as linkage disequilibrium score regression (LDSC) and heritability estimation from summary statistics (HESS). The third part investigated the causal association between the two traits using Mendelian randomization (MR). The fourth part employed conditional/conjunctional false discovery rate (cond/conjFDR) to analyze the genetic overlap with different traits based on the statistical theory. Finally, an LDSC-specifically expressed gene (LDSC-SEG) analysis was conducted to explore the tissue-level associations.

RESULTS

Our analyses revealed both overall and specific genetic correlations between SCZ and constipation at the genomic level. The MR analysis suggests a positive causal relationship between SCZ and constipation. The ConjFDR analysis confirms the genetic overlap between the two conditions and identifies two genetic risk loci (rs7583622 and rs842766) and seven mapped genes (GPR75-ASB3, ASB3, CHAC2, ERLEC1, GPR75, PSME4, and ACYP2). Further investigation into the functions of these genes could provide valuable insights. Interestingly, disease-related tissue analysis revealed associations between SCZ and constipation in eight brain regions (substantia nigra, anterior cingulate cortex, hypothalamus, cortex, hippocampus, cortex, amygdala, and spinal cord).

CONCLUSION

This study provides the first genetic evidence for the comorbidity of SCZ and constipation, enhancing our understanding of the pathophysiology of both conditions.

Abdominal ultrasound stimulation alleviates DSS-induced colitis and behavioral disorders in mice by mediating the microbiota-gut-brain axis balance

Inflammatory bowel disease (IBD) has the potential to induce neuroinflammation, which may increase the risk of developing neurodegenerative disorders. Ultrasound stimulation to the abdomen is a potential treatment for dextran sulfate sodium (DSS)-induced acute colitis. The present study aimed to investigate whether abdominal low-intensity pulsed ultrasound (LIPUS) can alleviate DSS-induced neuroinflammation through the microbiota-gut-brain axis. Male mice were fed DSS to induce ulcerative colitis. LIPUS stimulation was then applied to the abdomen at intensities of 0.5 and 1.0 ​W/cm2. Mouse biological samples were analyzed, and behavior was evaluated. [18F]FEPPA PET/CT imaging was employed to track and quantify inflammation in the abdomen and brain. Changes in the gut microbiota composition were analyzed using 16S rRNA sequencing. Abdominal LIPUS significantly inhibited the DSS-induced inflammatory response, repaired destroyed crypts, and partially preserved the epithelial barrier. [18F]FEPPA accumulation in the colitis-induced neuroinflammation in the abdomen and specific brain regions significantly decreased after LIPUS treatment. LIPUS maintained intestinal integrity by increasing zonula occludens and occludin levels, reduced lipopolysaccharide-binding protein and lipopolysaccharide levels in the serum, and improved behavioral dysfunctions. Moreover, LIPUS, at an intensity of 0.5 ​W/cm2, reshaped the gut microbiota in colitis-induced mice by increasing the relative abundance of the Firmicutes and decreasing the relative abundance of the Bacteroidota. Our findings demonstrated that abdominal LIPUS stimulation has the potential to be a novel therapeutic strategy to improve colitis-induced behavioral disorders through microbiota-gut-brain axis signaling.

Nasal administration of mitochondria relieves depressive- and anxiety-like behaviors in male mice exposed to restraint stress through the suppression ROS/NLRP3/caspase-1/IL-1β signaling pathway

Neuroinflammation and oxidative stress are known to be implicated in the pathogenesis of depression. Exogenous mitochondrial transplantation has exhibited beneficial effects for treating neurological disorders. Hence, this research aimed to evaluate the impact of nasal administration of mitochondria on neuroinflammation and oxidative stress in mouse models displaying depressive- and anxiety-like behaviors caused by restraint stress (RS). Thirty male BALB/c mice were divided into control, RS, and RS + 340 µg of mitochondrial. Mice were subjected to RS using an immobilization falcon tube (2 h/day) for 2 weeks except for the control group. We conducted two behavioral tests to evaluate anxiety-like behaviors: elevated plus maze (EPM) and open field test (OFT). Tail suspension test (TST) was implemented to assess depressive-like behavior. ATP and reactive oxygen species (ROS) levels were measured in the hippocampus. Besides, serum corticosterone (CORT) levels were evaluated using the ELISA method. The expression of NLRP3 inflammasome, caspase-1 (Cas-1), and IL-1β was tested by western blot. We found that mitotherapy increased the time spent in the center of OFT and open arms of the EPM, while it diminished immobility time in TST. Mitochondrial administration considerably attenuated ROS generation and CORT levels and restored ATP levels. Additionally, mitotherapy prevented RS-induced upregulation of IL-1β, cleaved Cas1/Pro Cas1 ratio, and NLRP3/1 in the hippocampus of mice. These findings suggested that the beneficial effects of intranasal mitochondria on depression and anxiety may be attributed to suppression of the ROS/NLRP3/IL-1β/caspase-1 signaling pathway.

Neuroinflammation and pathways that contribute to tourette syndrome

Tourette syndrome (TS), a neurological and psychological disease, typically exhibit motor and phonic tics. The pathophysiology of TS remains controversial. Currently, the recognized pathogenesis of TS is the imbalance of neurotransmitters, involving abnormality of the cortex-striatum-thalamus-cortex circuit. Recently, clinical researches demonstrate that triggers such as infection and allergic reaction could lead to the onset or exacerbation of tic symptoms. Current studies have also suggested that neural-immune crosstalk caused by inflammation is also associated with TS, potentially leading to the occurrence of tics by inducing neurotransmitter abnormalities. Herein, we review inflammation-related factors contributing to the occurrence of TS as well as the mechanisms by which immune-inflammatory pathways mediate the onset of TS. This aims to clarify the pathogenesis of TS and provide a theoretical basis for the treatment of TS.

Administration time modify the anxiolytic and antidepressant effects of inulin via gut-brain axis

An imbalance in the microbiota-gut-brain axis exerts an essential effect on the pathophysiology of depressive and anxiety disorders. Our previous research revealed that the timing of inulin administration altered its effects on chronic unpredictable mild stress (CUMS)-induced anxiety and depression. However, it is still unclear if the gut-brain axis is primarily responsible for these effects. In this study, fecal microbiota transplantation (FMT) confirmed that inulin administration at different times alleviated CUMS-induced anxiety- and depression-like behaviors via the gut-brain axis. The time of administration seemed to modify the anxiolytic and antidepressant effects of inulin, and inulin intervention in the evening was more pronounced in inhibiting the inflammatory responses than that of morning inulin intervention. Serum metabolomics analysis showed that the main differential metabolites, including fenofibric acid, 4'-Hydroxyfenoprofen glucuronide and 5-(4-Hydroxybenzyl)thiazolidine-2,4-dione may be vital for the anxiolytic and antidepressant effects of different inulin treatment times. Our results suggested that inulin administration in the evening was more effective in alleviating the inflammatory responses and improving amino acids metabolism. This study provides a new potential link between the microbiota-gut-brain axis and chrono-nutrition, demonstrating that a more appropriate administration time results in a better intervention effect.

Targeted microbiota dysbiosis repair: An important approach to health management after spinal cord injury

Current research primarily focuses on the pathological mechanisms of spinal cord injury (SCI), seeking to promote spinal cord repair and restore motorial and sensory functions by elucidating mechanisms of cell death or axonal regeneration. However, SCI is almost irreversible, and patients often struggle to regain mobility or self-care abilities after injuries. Consequently, there has been significant interest in modulating systemic symptoms following SCI to improve patients' quality of life. Neuron axonal disconnection and substantial apoptotic events following SCI result in signal transmission loss, profoundly impacting various organ and systems, including the gastrointestinal tract. Dysbiosis can lead to severe bowel dysfunction in patients, substantially lowering their quality of life and significantly reducing life expectancy of them. Therefore, researches focusing on the restoration of the gut microbiota hold promise for potential therapeutic strategies aimed at rehabilitation after SCI. In this paper, we explore the regulatory roles that dietary fiber, short-chain fatty acids (SCFAs), probiotics, and microbiota transplantation play in patients with SCI, summarize the potential mechanisms of post-SCI dysbiosis, and discuss possible strategies to enhance long-term survival of SCI patients. We aim to provide potential insights for future research aimed at ameliorating dysbiosis in SCI patients.

Role of the gut microbiome in psychological symptoms associated with inflammatory bowel diseases

The brain-gut axis constitutes the basis for the bidirectional communication between the central nervous system and the gastrointestinal tract driven by neural, hormonal, metabolic, immunological, and microbial signals. Alterations in the gut microbiome composition as observed in inflammatory bowel diseases can modulate brain function and emerging empirical evidence has indicated that interactions among the brain-gut microbiome-axis seem to play a significant role in the pathogenesis of both inflammatory bowel diseases and psychiatric disorders and their comorbidity. Yet, the immunological and molecular mechanisms underlying the co-occurrence of inflammatory bowel diseases and psychological symptoms are still poorly understood. The aim of this narrative review is to highlight contemporary empirical findings supporting a pivotal role of the gut microbiome in the pathophysiology of highly prevalent neuropsychiatric symptoms in inflammatory bowel diseases such as fatigue, depression, and anxiety. Finally, we focus on microbiome modulation as potential treatment option for comorbid neuropsychiatric symptoms in immune-mediated diseases and especially in inflammatory bowel diseases. High-quality clinical trials are required to clarify how microbiome modulation through dietary interventions or probiotic, prebiotic or synbiotic treatment can be used clinically to improve mental health and thus quality of life of patients with inflammatory bowel diseases.

New perspectives on microbiome-dependent gut-brain pathways for the treatment of depression with gastrointestinal symptoms: from bench to bedside

Patients with depression are more likely to have chronic gastrointestinal (GI) symptoms than the general population, but such symptoms are considered only somatic symptoms of depression and lack special attention. There is a chronic lack of appropriate diagnosis and effective treatment for patients with depression accompanied by GI symptoms, and studying the association between depression and GI disorders (GIDs) is extremely important for clinical management. There is growing evidence that depression is closely related to the microbiota present in the GI tract, and the microbiota-gut-brain axis (MGBA) is creating a new perspective on the association between depression and GIDs. Identifying and treating GIDs would provide a key opportunity to prevent episodes of depression and may also improve the outcome of refractory depression. Current studies on depression and the microbially related gut-brain axis (GBA) lack a focus on GI function. In this review, we combine preclinical and clinical evidence to summarize the roles of the microbially regulated GBA in emotions and GI function, and summarize potential therapeutic strategies to provide a reference for the study of the pathomechanism and treatment of depression in combination with GI symptoms.

The microbiome's influence on the neurobiology of opioid addiction and brain connectivity

BACKGROUND

Opioids are the most effective and potent analgesics available for acute pain management. With no viable alternative for treating chronic or post operative pain, it is not surprising that over 10 million people misuse opioids. This study explores the developmental influence of the microbiome on resistance to opioid addictive behavior and functional connectivity.

METHODS

Female germ free reared (GFR) mice were compared to wild-type (WT) mice, before and after conventionalization using conditioned place preference (CPP) with oxycodone (OXY) exposure. Functional connectivity data were collected providing site-specific analysis for over 140 different brain areas.

RESULTS

GFR mice showed significant reduction in CPP after OXY exposure. When GFR mice are conventionalized CPP reward behavior mirrors WT mice. Functional connectivity data shows significant differences across several brain regions e.g., thalamus, hippocampus, and sensory cortices between GFR and WT before and after conventionalization. Prior to conventionalization GFR mice showed hyperconnectivity that became less organized and more global after conventionalization. Sequencing of the fecal microbiome of the GFR mice before conventionalization showed an absence of normal murine gut microbiome members, but the presence of Corynebacterium, Staphylococcus, Paenibacillus, and Turicibacter.

CONCLUSION

The implications suggest the microbiome has a direct impact on the development of reward seeking behavior. With the widespread number of opioid receptors found in the gut, studying the interaction between the microbiota and substance use disorder may lead to a better understanding of the mechanisms that lead to the development of addiction as well as potential treatments.

Metformin reprograms tryptophan metabolism via gut microbiome-derived bile acid metabolites to ameliorate depression-Like behaviors in mice

As an adjunct therapy, metformin enhances the efficacy of conventional antidepressant medications. However, its mode of action remains unclear. Here, metformin was found to ameliorate depression-like behaviors in mice exposed to chronic restraint stress (CRS) by normalizing the dysbiotic gut microbiome. Fecal transplants from metformin-treated mice ameliorated depressive behaviors in stressed mice. Microbiome profiling revealed that Akkermansia muciniphila (A. muciniphila), in particular, was markedly increased in the gut by metformin and that oral administration of this species alone was sufficient to reverse CRS-induced depressive behaviors and normalize aberrant stress-induced 5-hydroxytryptamine (5-HT) metabolism in the brain and gut. Untargeted metabolomic profiling further identified the bile acid metabolites taurocholate and deoxycholic acid as direct A. muciniphila-derived molecules that are, individually, sufficient to rescue the CRS-induced impaired 5-HT metabolism and depression-like behaviors. Thus, we report metformin reprograms 5-HT metabolism via microbiome-brain interactions to mitigate depressive syndromes, providing novel insights into gut microbiota-derived bile acids as potential therapeutic candidates for depressive mood disorders from bench to bedside.

Beyond metabolic messengers: Bile acids and TGR5 as pharmacotherapeutic intervention for psychiatric disorders

Psychiatric disorders pose a significant global health challenge, exacerbated by the COVID-19 pandemic and insufficiently addressed by the current treatments. This review explores the emerging role of bile acids and the TGR5 receptor in the pathophysiology of psychiatric conditions, emphasizing their signaling within the gut-brain axis. We detail the synthesis and systemic functions of bile acids, their transformation by gut microbiota, and their impact across various neuropsychiatric disorders, including major depressive disorder, general anxiety disorder, schizophrenia, autism spectrum disorder, and bipolar disorder. The review highlights how dysbiosis and altered bile acid metabolism contribute to the development and exacerbation of these neuropsychiatric disorders through mechanisms involving inflammation, oxidative stress, and neurotransmitter dysregulation. Importantly, we detail both pharmacological and non-pharmacological interventions that modulate TGR5 signaling, offering potential breakthroughs in treatment strategies. These include dietary adjustments to enhance beneficial bile acids production and the use of specific TGR5 agonists that have shown promise in preclinical and clinical settings for their regulatory effects on critical pathways such as cAMP-PKA, NRF2-mediated antioxidant responses, and neuroinflammation. By integrating findings from the dynamics of gut microbiota, bile acids metabolism, and TGR5 receptor related signaling events, this review underscores cutting-edge therapeutic approaches poised to revolutionize the management and treatment of psychiatric disorders.

Therapeutic effects of exercise on depression: The role of microglia

Major depressive disorderadversely affects mental health. Traditional therapeutic approaches, including medication, psychological intervention, and physical therapy, exert beneficial effects on depression. However, these approaches are associated with some limitations, such as high cost, adverse reactions, recurrent episodes, and low patient adherence. Previous studies have demonstrated that exercise therapy can effectively mitigate depressive symptoms, although the underlying mechanism has not been elucidated. Recent studies have suggested that depression is a microglial disease. Microglia regulate the inflammatory response, synaptic plasticity, neurogenesis, kynurenine pathway and the activation of hypothalamic-pituitary-adrenal axis, all of which affect depression. Exercise therapy is reported to shift the balance of microglial M1/M2 polarization in the hippocampus, frontal lobe, and striatum, suppressing the release of pro-inflammatory factors and consequently alleviating behavioral deficits in animal models of depression. Further studies are needed to examine the specific effects of different exercise regimens on microglia to identify the exercise regimen with the best therapeutic effect.

Investigating the Potential Therapeutic Mechanisms of Puerarin in Neurological Diseases

Plants and their derived phytochemicals have a long history of treating a wide range of illnesses for several decades. They are believed to be the origin of a diverse array of medicinal compounds. One of the compounds found in kudzu root is puerarin, a isoflavone glycoside commonly used as an alternative medicine to treat various diseases. From a biological perspective, puerarin can be described as a white needle crystal with the chemical name of 7-hydroxy-3-(4-hydroxyphenyl)-1-benzopyran-4-one-8-D-glucopyranoside. Besides, puerarin is sparingly soluble in water and produces no color or light yellow solution. Multiple experimental and clinical studies have confirmed the significant therapeutic effects of puerarin. These effects span a wide range of pharmacological effects, including neuroprotection, hepatoprotection, cardioprotection, immunomodulation, anticancer properties, anti-diabetic properties, anti-osteoporosis properties, and more. Puerarin achieves these effects by interacting with various cellular and molecular pathways, such as MAPK, AMPK, NF-κB, mTOR, β-catenin, and PKB/Akt, as well as different receptors, enzymes, and growth factors. The current review highlights the molecular mechanism of puerarin as a neuroprotective agent in the treatment of various neurodegenerative and neurological diseases. Extensive cellular, animal, and clinical research has provided valuable insights into its effectiveness in conditions such as Alzheimer's disease, Parkinson's disease, epilepsy, cerebral stroke, depression, and more.

Microbiota-Gut-Brain Axis in Psychiatry: Focus on Depressive Disorders

Purpose of Review

Gut microbiota contribute to several physiological processes in the host. The composition of the gut microbiome is associated with different neurological and neurodevelopmental diseases. In psychiatric disease, stress may be a major factor leading to gut microbiota alterations. Depressive disorders are the most prevalent mental health issues worldwide and patients often report gastrointestinal symptoms. Accordingly, evidence of gut microbial alterations in depressive disorders has been growing. Here we review current literature revealing links between the gut microbiome and brain function in the context of depression.

Recent Findings

The gut-brain axis could impact the behavioral manifestation of depression and the underlying neuropathology via multiple routes: the HPA axis, immune function, the enteric nervous system, and the vagus nerve. Furthermore, we explore possible therapeutic interventions including fecal microbiota transplant or probiotic supplementation in alleviating depressive symptoms.

Summary

Understanding the mechanisms by which bidirectional communication along the gut-brain axis can be dysregulated in patients with depression could lead to the development of personalized, microbiome-targeted therapies for the treatment of this disorder.

Gut microbiota in health and disease: advances and future prospects

The gut microbiota plays a critical role in maintaining human health, influencing a wide range of physiological processes, including immune regulation, metabolism, and neurological function. Recent studies have shown that imbalances in gut microbiota composition can contribute to the onset and progression of various diseases, such as metabolic disorders (e.g., obesity and diabetes) and neurodegenerative conditions (e.g., Alzheimer's and Parkinson's). These conditions are often accompanied by chronic inflammation and dysregulated immune responses, which are closely linked to specific forms of cell death, including pyroptosis and ferroptosis. Pathogenic bacteria in the gut can trigger these cell death pathways through toxin release, while probiotics have been found to mitigate these effects by modulating immune responses. Despite these insights, the precise mechanisms through which the gut microbiota influences these diseases remain insufficiently understood. This review consolidates recent findings on the impact of gut microbiota in these immune-mediated and inflammation-associated conditions. It also identifies gaps in current research and explores the potential of advanced technologies, such as organ-on-chip models and the microbiome-gut-organ axis, for deepening our understanding. Emerging tools, including single-bacterium omics and spatial metabolomics, are discussed for their promise in elucidating the microbiota's role in disease development.

AdipoRon exerts an antidepressant effect by inhibiting NLRP3 inflammasome activation in microglia via promoting mitophagy

Depression is a serious mental disorder that threatens patients' physical and mental health worldwide. The activation of the NLR family pyrin domain-containing 3 (NLRP3) inflammasome is essential for microglia-mediated neuroinflammation and neuronal damage in depression. Numerous pathophysiological factors, such as mitochondrial dysfunction and impaired mitophagy, have an essential role in activating the NLRP3 inflammasome. AdipoRon is a potent adiponectin receptor agonist; however, its antidepressant effects have not been thoroughly investigated. In this study, we found that AdipoRon ameliorated depression-like behavior and neuronal damage induced by chronic unpredictable mild stress (CUMS). Further research demonstrated that AdipoRon inhibited the activation of the NLRP3 inflammasome and protected hippocampal neurons from microglial cytotoxicity by promoting mitophagy, increasing the clearance of damaged mitochondria, and reducing mtROS accumulation. Importantly, inhibition of mitophagy attenuated the antidepressant and neuroprotective effects of AdipoRon. Overall, these findings indicate that AdipoRon alleviates depression by inhibiting NLRP3 inflammasome activation in microglia via improving mitophagy.

Chronic corticosterone exposure causes anxiety- and depression-related behaviors with altered gut microbial and brain metabolomic profiles in adult male C57BL/6J mice

Chronic exposure to glucocorticoids in response to long-term stress is thought to be a risk factor for major depression. Depression is associated with disturbances in the gut microbiota composition and peripheral and central energy metabolism. However, the relationship between chronic glucocorticoid exposure, the gut microbiota, and brain metabolism remains largely unknown. In this study, we first investigated the effects of chronic corticosterone exposure on various domains of behavior in adult male C57BL/6J mice treated with the glucocorticoid corticosterone to evaluate them as an animal model of depression. We then examined the gut microbial composition and brain and plasma metabolome in corticosterone-treated mice. Chronic corticosterone treatment resulted in reduced locomotor activity, increased anxiety-like and depression-related behaviors, decreased rotarod latency, reduced acoustic startle response, decreased social behavior, working memory deficits, impaired contextual fear memory, and enhanced cued fear memory. Chronic corticosterone treatment also altered the composition of gut microbiota, which has been reported to be associated with depression, such as increased abundance of Bifidobacterium, Turicibacter, and Corynebacterium and decreased abundance of Barnesiella. Metabolomic data revealed that long-term exposure to corticosterone led to a decrease in brain neurotransmitter metabolites, such as serotonin, 5-hydroxyindoleacetic acid, acetylcholine, and gamma-aminobutyric acid, as well as changes in betaine and methionine metabolism, as indicated by decreased levels of adenosine, dimethylglycine, choline, and methionine in the brain. These results indicate that mice treated with corticosterone have good face and construct validity as an animal model for studying anxiety and depression with altered gut microbial composition and brain metabolism, offering new insights into the neurobiological basis of depression arising from gut-brain axis dysfunction caused by prolonged exposure to excessive glucocorticoids.

The inflammatory underpinning of depression: An historical perspective

Over the last thirty years, substantial evidence has accumulated in support of the hypothesis that dysregulation of inflammatory processes plays a critical role in the pathophysiology of depression. This review traces the evolution of research supporting this link, discussing key findings from several major investigative fronts: Alterations in inflammatory markers associated with depression; Mood changes following the exogenous administration of inflammatory challenges; The anti-inflammatory properties of traditional antidepressants and the promising antidepressant effects of anti-inflammatory drugs. Additionally, it explores how inflammatory processes interact with specific brain regions and neurochemical systems to drive depressive pathology. A thorough analysis of the 100 most-cited experimental studies on the topic ensures a comprehensive, transparent and unbiased collection of references. This methodological approach offers a panoramic view of the inflammation-depression nexus, shedding light on the complexity of its mechanisms and their connections to psychiatric categorizations, symptoms, demographics, and life events. Synthesizing insights from this extensive research, the review presents an integrative model of the biological foundations of inflammation-associated depression. It posits that we have reached a critical juncture where the translation of this knowledge into personalized immunomodulatory treatments for depression is not just possible, but imperative.

Association between major depressive disorder and gut microbiota dysbiosis

OBJECTIVE

Major depressive disorder (MDD) affects 300 million people globally. Because dysbiosis may alter the central nervous system, it plays a potential role in this disorder. Dysbiosis is characterized by a decrease in microbial diversity and an increase in proinflammatory species. The human gut microbiota refers to the trillions of microbes, such as bacteria, that live in the human gut. The purpose of this study was to compare the gut microbiota of patients with MDD with that of healthy controls.

METHODS

This case-control study involved 35 MDD cases and 35 healthy age- and sex-matched controls. Stool samples were collected and subjected to quantitative real-time PCR. Four intestinal bacterial phyla (firmicutes, bacteroidetes, actinobacteria, and proteobacteria) were investigated by 16SrRNA analysis.

RESULTS

The findings indicated a relative abundance of bacteroidetes to firmicutes in the control and case groups was 0.66 vs. 1.33, respectively (p < .05). There were no significant differences in actinobacteria or proteobacteria among those in the MDD group compared to the healthy control group.

CONCLUSIONS

Gut microbiota dysbiosis may contribute to the onset of depression, underscoring the importance of understanding the relationship between MDD and gut microbiota. Firmicutes, which produce short-chain fatty acids, are crucial for intestinal health. However, dysbiosis can disrupt the gut microbiota, impacting the central nervous system and contributing to the onset of depression.

Microglia and gut microbiota: A double-edged sword in Alzheimer's disease

The strong association between gut microbiota (GM) and brain functions such as mood, behaviour, and cognition has been well documented. Gut-brain axis is a unique bidirectional communication system between the gut and brain, in which gut microbes play essential role in maintaining various molecular and cellular processes. GM interacts with the brain through various pathways and processes including, metabolites, vagus nerve, HPA axis, endocrine system, and immune system to maintain brain homeostasis. GM dysbiosis, or an imbalance in GM, is associated with several neurological disorders, including anxiety, depression, and Alzheimer's disease (AD). Conversely, AD is sustained by microglia-mediated neuroinflammation and neurodegeneration. Further, GM and their products also affect microglia-mediated neuroinflammation and neurodegeneration. Despite the evidence connecting GM dysbiosis and AD progression, the involvement of GM in modulating microglia-mediated neuroinflammation in AD remains elusive. Importantly, deciphering the mechanism/s by which GM regulates microglia-dependent neuroinflammation may be helpful in devising potential therapeutic strategies to mitigate AD. Herein, we review the current evidence regarding the involvement of GM dysbiosis in microglia activation and neuroinflammation in AD. We also discuss the possible mechanisms through which GM influences the functioning of microglia and its implications for therapeutic intervention. Further, we explore the potential of microbiota-targeted interventions, such as prebiotics, probiotics, faecal microbiota transplantation, etc., as a novel therapeutic strategy to mitigate neuroinflammation and AD progression. By understanding and exploring the gut-brain axis, we aspire to revolutionize the treatment of neurodegenerative disorders, many of which share a common theme of microglia-mediated neuroinflammation and neurodegeneration.

Christensenella minuta mitigates behavioral and cardiometabolic hallmarks of social defeat stress

Psychological stress during early development and adolescence may increase the risk of psychiatric and cardiometabolic comorbidities in adulthood. The gut microbiota has been associated with mental health problems such as depression and anxiety and with cardiometabolic disease, but the potential role of the gut microbiota in their comorbidity is not well understood. We investigated the effects and mode of action of the intestinal bacterium Christensenella minuta DSM 32891 on stress-induced mental health and cardiometabolic disturbances in a mouse model of social defeat stress. We demonstrate that administered C. minuta alleviates chronic stress-induced depressive, anxiogenic and antisocial behavior. These effects are attributed to the bacterium's ability to modulate the hypothalamic-pituitary-adrenal axis, which mediates the stress response. This included the oversecretion of corticosterone and the overexpression of its receptors, as well as the metabolism of dopamine (DA) and the expression of its receptors (D1, D2L and D2S). Additionally, C. minuta administration reduced chronically induced inflammation in plasma, spleen and some brain areas, which likely contribute to the recovery of physical and behavioral function. Furthermore, C. minuta administration prevented chronic stress-induced cardiovascular damage by regulating key enzymes mediating liver fibrosis and oxidative stress. Finally, C. minuta increased the abundance of bacteria associated with mental health. Overall, our study highlights the potential of microbiota-directed interventions to alleviate both the physical and mental effects of chronic stress.

The role of the microbiota-gut-brain axis in methamphetamine-induced neurotoxicity: Disruption of microbial composition and short-chain fatty acid metabolism

Methamphetamine (METH) abuse is associated with significant neurotoxicity, high addiction potential, and behavioral abnormalities. Recent studies have identified a connection between the gut microbiota and METH-induced neurotoxicity and behavioral disorders. However, the underlying causal mechanisms linking the gut microbiota to METH pathophysiology remain largely unexplored. In this study, we employed fecal microbiota transplantation (FMT) and antibiotic (Abx) intervention to manipulate the gut microbiota in mice administered METH. Furthermore, we supplemented METH-treated mice with short-chain fatty acids (SCFAs) and pioglitazone (Pio) to determine the protective effects on gut microbiota metabolism. Finally, we assessed the underlying mechanisms of the gut-brain neural circuit in vagotomized mice. Our data provide compelling evidence that modulation of the gut microbiome through FMT or microbiome knockdown by Abx plays a crucial role in METH-induced neurotoxicity, behavioral disorders, gut microbiota disturbances, and intestinal barrier impairment. Furthermore, our findings highlight a novel prevention strategy for mitigating the risks to both the nervous and intestinal systems caused by METH, which involves supplementation with SCFAs or Pio.

A clinical trial of the effects of cocoa rich chocolate on depression and sleep quality in menopausal women

In this triple-blind, randomized clinical trial, 60 menopausal women between the ages of 45 and 65 were randomized to receive 78% dark chocolate (12 g/day) or milk chocolate (12 g/day) for eight weeks. The primary outcome was depression scores. Secondary outcomes included sleep quality and anthropometric indices. ANCOVA with baseline adjustment showed that the mean depression score after the intervention in the group receiving dark chocolate was significantly reduced compared to the milk chocolate group (mean difference: -2.3; 95% confidence interval: -3.9 to -0.8; p = 0.003; Cohen's d = -0.54). However, no statistically significant difference in the overall sleep quality score and its subdomains was observed between the two groups after the intervention (p > 0.05). Furthermore, after the intervention, there was no statistically significant difference between the two groups in terms of anthropometric indices, including weight (p = 0.075), BMI (p = 0.137), waist circumference (p = 0.463), and hip circumference (p = 0.114). The study suggests that consuming 78% dark chocolate for eight weeks may contribute to improvements in depression scores, but it does not appear to improve sleep quality or anthropometric indices.Trial registration: IRCT20220926056046N1; December 2022.

Efficacy of bifidobacterium-related preparations on depression: the first meta-analysis

Currently, depression-induced suicide has emerged as the primary contributor to the worldwide burden of disability. However, the prevailing drug treatment not only suffers from delayed effectiveness and limited efficacy, but also there are withdrawal symptoms and rebound phenomenon. Consequently, there is an imperative to investigate safer and more efficient treatments to ameliorate the clinical manifestations of depression. At present, there is increased evidence that probiotics can improve the symptoms of depression, but the existing studies use many and mixed types of probiotics, and it is impossible to determine the specific efficacy of bifidobacteria in the treatment of depression. This review will systematically review the effects of bifidobacteria on the treatment effect of depression, Meta-analysis showed that Bifidobacterium-related preparations effectively improved depressive symptoms in patients with depression. This study represents the initial meta-analysis conducted on the use of bifidobacteria-related agents for treating depression. The objective was to determine the effect of bifidobacteria-related preparations on improving depressive symptoms. We found that Bifidobacterium and its related agents can effectively reduce depression scale scores in patients with depression, suggesting the need for further research into this potential strategy for the prevention and treatment of depression.

The impact of neuroinflammation on neuronal integrity

Neuroinflammation, characterized by a complex interplay among innate and adaptive immune responses within the central nervous system (CNS), is crucial in responding to infections, injuries, and disease pathologies. However, the dysregulation of the neuroinflammatory response could significantly affect neurons in terms of function and structure, leading to profound health implications. Although tremendous progress has been made in understanding the relationship between neuroinflammatory processes and alterations in neuronal integrity, the specific implications concerning both structure and function have not been extensively covered, with the exception of perspectives on glial activation and neurodegeneration. Thus, this review aims to provide a comprehensive overview of the multifaceted interactions among neurons and key inflammatory players, exploring mechanisms through which inflammation influences neuronal functionality and structural integrity in the CNS. Further, it will discuss how these inflammatory mechanisms lead to impairment in neuronal functions and architecture and highlight the consequences caused by dysregulated neuronal functions, such as cognitive dysfunction and mood disorders. By integrating insights from recent research findings, this review will enhance our understanding of the neuroinflammatory landscape and set the stage for future interventions that could transform current approaches to preserve neuronal integrity and function in CNS-related inflammatory conditions.

Relationships between the gut microbiome and brain functional alterations in first-episode, drug-naïve patients with major depressive disorder

OBJECTIVE

Increasing evidence has shown that the microbiota-gut-brain axis (MGB) is involved in the mechanism of major depressive disorder (MDD). However, the relationship between the gut microbiome and brain function in MDD patients has not been determined. Here, we intend to identify specific changes in the gut microbiome and brain function in first-episode, drug-naïve MDD patients and then explore the associations between the two omics to elucidate how the MGB axis plays a role in MDD development.

METHODS

We recruited 38 first-episode, drug-naïve MDD patients and 37 healthy controls (HC). The composition of the fecal microbiome and neural spontaneous activity alterations were examined using 16S rRNA gene amplicon sequencing analysis and regional homogeneity (ReHo). Spearman correlation analyses were conducted to assess the associations between the gut microbiome and brain function.

RESULTS

Compared with HC, MDD patients exhibited distinct alterations in the gut microbiota and elevated ReHo in the frontal regions. In the MDD group, a positive relationship was noted between the relative abundance of Blautia and the HAMD-17 and HAMA scores, as well as between the relative abundance of Oxalobacteraceae and the HAMD-17 score. The relative abundances of Porphyromonadaceae and Parabacteroides were negatively correlated with the ReHo values of frontal regions.

LIMITATIONS

Our study utilized a cross-sectional design, and the number of subjects was relatively small.

CONCLUSION

We found that some specific gut microbiomes were associated with frontal function, and others were associated with clinical symptoms in MDD patients, which may support the role of the MGB axis underlying MDD.

Prenatal Gut Microbiota Predicts Temperament in Offspring at 1-2 Years

The purpose of this study was to explore whether prenatal gut microbiota (GM) and its functions predict the development of offspring temperament. A total of 53 mothers with a 1-year-old child and 41 mothers with a 2-year-old child were included in this study using a mother-infant cohort from central China. Maternal fecal samples collected during the third trimester were analyzed using 16S rRNA V3-V4 gene sequences. Temperament of the child was measured by self-reported data according to the primary caregiver. The effects of GM in mothers on offspring's temperament were evaluated using multiple linear regression models. The results demonstrated that the alpha diversity index Simpson of prenatal GM was positively associated with the activity level of offspring at 1 year (adj. P = .036). Bifidobacterium was positively associated with high-intensity pleasure characteristics of offspring at 1 year (adj. P = .031). Comparatively, the presence of Bifidobacterium found in the prenatal microbiome was associated with low-intensity pleasure characteristics in offspring at 2 years (adj. P = .031). There were many significant associations noted among the functional pathways of prenatal GM and temperament of offspring at 2 years. Our findings support the maternal-fetal GM axis in the setting of fetal-placental development with subsequent postnatal neurocognitive developmental outcomes, and suggest that early childhood temperament is in part associated with specific GM in the prenatal setting.

Prenatal Stress and Ethanol Exposure: Microbiota-Induced Immune Dysregulation and Psychiatric Risks

Changes in maternal gut microbiota due to stress and/or ethanol exposure can have lasting effects on offspring's health, particularly regarding immunity, inflammation response, and susceptibility to psychiatric disorders. The literature search for this review was conducted using PubMed and Scopus, employing keywords and phrases related to maternal stress, ethanol exposure, gut microbiota, microbiome, gut-brain axis, diet, dysbiosis, progesterone, placenta, prenatal development, immunity, inflammation, and depression to identify relevant studies in both preclinical and human research. Only a limited number of reviews were included to support the arguments. The search encompassed studies from the 1990s to the present. This review begins by exploring the role of microbiota in modulating host health and disease. It then examines how disturbances in maternal microbiota can affect the offspring's immune system. The analysis continues by investigating the interplay between stress and dysbiosis, focusing on how prenatal maternal stress influences both maternal and offspring microbiota and its implications for susceptibility to depression. The review also considers the impact of ethanol consumption on gut dysbiosis, with an emphasis on the effects of prenatal ethanol exposure on both maternal and offspring microbiota. Finally, it is suggested that maternal gut microbiota dysbiosis may be significantly exacerbated by the combined effects of stress and ethanol exposure, leading to immune system dysfunction and chronic inflammation, which could increase the risk of depression in the offspring. These interactions underscore the potential for novel mental health interventions that address the gut-brain axis, especially in relation to maternal and offspring health.

The effects of chronic, continuous β-funaltrexamine pre-treatment on lipopolysaccharide-induced inflammation and behavioral deficits in C57BL/6J mice

BACKGROUND

Inflammation and neuroinflammation are integral to the progression and severity of many diseases and are strongly associated with cardiovascular disease, cancer, autoimmune disorders, neurodegenerative disease, and neuropsychiatric disorders. These diseases can be difficult to treat without addressing the underlying inflammation, and, as such, a growing need has arisen for pharmaceutical treatments that target inflammatory mediators and signaling pathways. Our lab has investigated the therapeutic potential of the irreversible µ-opioid antagonist β-funaltrexamine (β-FNA) and discovered that acute treatment ameliorates inflammation in astrocytes in vitro and inhibits central and peripheral inflammation and reduces anxiety- and sickness-like behavior in male C57BL/6J mice. Now, our investigation has expanded to investigate the chronic pre-treatment effects of β-FNA on lipopolysaccharide (LPS)-induced inflammation and behavior in male C57BL/6J mice.

RESULTS

Micro-osmotic drug pumps were surgically inserted into the subcutaneous intrascapular space of male C57BL/6J mice. β-FNA or saline vehicle was continuously administered for seven days. On the sixth day, mice were given intraperitoneal injections of LPS or saline. An elevated plus maze test, followed by a forced swim test, were administered 24 h post-injection to measure sickness-, anxiety- and depressive-like behavior. Immediately after testing, frontal cortex, hippocampus, spleen, and plasma were collected. Levels of inflammatory chemokines C-C motif chemokine ligand 2 (CCL2) and C-X-C motif chemokine ligand 10 (CXCL10) were measured in tissues by enzyme-linked immunosorbent assay (ELISA). Quantitative reverse transcription polymerase chain reaction (RT-qPCR) was used to assess expression of the enzyme indoleamine 2, 3-dioxygenase 1 (IDO1) and the NLR family pyrin domain-containing protein 3 (NRLP3) inflammasome in frontal cortex and spleen tissues. Chronic pre-treatment robustly decreased inflammation in the hippocampus, frontal cortex, and spleen and reduced or abolished anxiety- and sickness-like behavior (e.g., increased time spent motionless, increased time spent in a contracted position, and reduced distance moved). However, treatment with β-FNA alone increased both inflammation in the frontal cortex and anxiety-like behavior.

CONCLUSION

These findings provide novel insights into the anti-inflammatory and behavior-modifying effects of chronic β-FNA pre-treatment and continue to support the therapeutic potential of β-FNA under inflammatory conditions.

Microglia Caspase11 non-canonical inflammasome drives fever

AIM

Animals exhibit physiological changes designed to eliminate the perceived danger, provoking similar symptoms of fever. However, a high-grade fever indicates poor clinical outcomes. Caspase11 (Casp11) is involved in many inflammatory diseases. Whether Casp11 leads to fever remains unclear. In this study, we investigate the role of the preoptic area of the hypothalamus (PO/AH) microglia Casp11 in fever.

METHODS

We perform experiments using a rat model of LPS-induced fever. We measure body temperature and explore the functions of peripheral macrophages and PO/AH microglia in fever signaling by ELISA, immunohistochemistry, immunofluorescence, flow cytometry, macrophage depletion, protein blotting, and RNA-seq. Then, the effects of macrophages on microglia in a hyperthermic environment are observed in vitro. Finally, adeno-associated viruses are used to knockdown or overexpress microglia Casp11 in PO/AH to determine the role of Casp11 in fever.

RESULTS

We find peripheral macrophages and PO/AH microglia play important roles in the process of fever, which is proved by macrophage and microglia depletion. By RNA-seq analysis, we find Casp11 expression in PO/AH is significantly increased during fever. Co-culture and conditioned-culture simulate the induction of microglia Casp11 activation by macrophages in a non-contact manner. Microglia Casp11 knockdown decreases body temperature, pyrogenic factors, and inflammasome, and vice versa.

CONCLUSION

We report that Casp11 drives fever. Mechanistically, peripheral macrophages transmit immune signals via cytokines to microglia in PO/AH, which activate the Casp11 non-canonical inflammasome. Our findings identify a novel player, the microglia Casp11, in the control of fever, providing an explanation for the transmission and amplification of fever immune signaling.

Therapeutic modulation of the kynurenine pathway in severe mental illness and comorbidities: A potential role for serotonergic psychedelics

Mounting evidence points towards a crucial role of the kynurenine pathway (KP) in the altered gut-brain axis (GBA) balance in severe mental illness (SMI, namely depression, bipolar disorder, and schizophrenia) and cardiometabolic comorbidities. Preliminary evidence shows that serotonergic psychedelics and their analogues may hold therapeutic potential in addressing the altered KP in the dysregulated GBA in SMI and comorbidities. In fact, aside from their effects on mood, psychedelics elicit therapeutic improvement in preclinical models of obesity, metabolic syndrome, and vascular inflammation, which are highly comorbid with SMI. Here, we review the literature on the therapeutic modulation of the KP in the dysregulated GBA in SMI and comorbidities, and the potential application of psychedelics to address the altered KP in the brain and systemic dysfunction underlying SMI and comorbidities. Psychedelics might therapeutically modulate the KP in the altered GBA in SMI and comorbidities either directly, via altering the metabolic pathway by influencing the rate-limiting enzymes of the KP and affecting the levels of available tryptophan, or indirectly, by affecting the gut microbiome, gut metabolome, metabolism, and the immune system. Despite promising preliminary evidence, the mechanisms and outcomes of the KP modulation with psychedelics in SMI and systemic comorbidities remain largely unknown and require further investigation. Several concerns are discussed surrounding the potential side effects of this approach in specific cohorts of individuals with SMI and systemic comorbidities.

Gut-Brain Axis: Role of Microbiome, Metabolomics, Hormones, and Stress in Mental Health Disorders

The influence of gut microbiome, metabolites, omics, hormones, and stress on general and mental health is increasingly being recognized. Ancient cultures recognized the importance of diet and gut health on the overall health of an individual. Western science and modern scientific methods are beginning to unravel the foundations and mechanisms behind some of the ancient beliefs and customs. The gut microbiome, an organ itself, is now thought to influence almost all other organs, ranging from the brain to the reproductive systems. Gut microbiome, metabolites, hormones, and biological sex also influence a myriad of health conditions that range from mental health disorders, obesity, gastrointestinal disorders, and cardiovascular diseases to reproductive health. Here, we review the history and current understanding of the gut-brain axis bidirectional talk in various mental health disorders with special emphasis on anxiety and depressive disorders, whose prevalence has increased by over 50% in the past three decades with COVID-19 pandemic being the biggest risk factor in the last few years. The vagal nerve is an important contributor to this bidirectional talk, but other pathways also contribute, and most remain understudied. Probiotics containing Lactobacillus and Bifidobacterium species seem to have the most impact on improvement in mental health symptoms, but the challenge appears to be maintaining sustained levels, especially since neither Lactobacillus nor Bifidobacterium can permanently colonize the gut. Ancient endogenous retroviral DNA in the human genome is also linked to several psychiatric disorders, including depression. These discoveries reveal the complex and intricately intertwined nature of gut health with mental health disorders.

Genetic prediction of blood metabolites mediating the relationship between gut microbiota and Alzheimer's disease: a Mendelian randomization study

Background

Observational studies have suggested an association between gut microbiota and Alzheimer's disease (AD); however, the causal relationship remains unclear, and the role of blood metabolites in this association remains elusive.

Purpose

To elucidate the causal relationship between gut microbiota and AD and to investigate whether blood metabolites serve as potential mediators.

Materials and methods

Univariable Mendelian randomization (UVMR) analysis was employed to assess the causal relationship between gut microbiota and AD, while multivariable MR (MVMR) was utilized to mitigate confounding factors. Subsequently, a two-step mediation MR approach was employed to explore the role of blood metabolites as potential mediators. We primarily utilized the inverse variance-weighted method to evaluate the causal relationship between exposure and outcome, and sensitivity analyses including Contamination mixture, Maximum-likelihood, Debiased inverse-variance weighted, MR-Egger, Bayesian Weighted Mendelian randomization, and MR pleiotropy residual sum and outlier were conducted to address pleiotropy.

Results

After adjustment for reverse causality and MVMR correction, class Actinobacteria (OR: 1.03, 95% CI: 1.01-1.06, p = 0.006), family Lactobacillaceae (OR: 1.03, 95% CI: 1.00-1.05, p = 0.017), genus Lachnoclostridium (OR: 1.03, 95% CI: 1.00-1.06, p = 0.019), genus Ruminiclostridium9 (OR: 0.97, 95% CI: 0.94-1.00, p = 0.027) and genus Ruminiclostridium6 (OR: 1.03, 95% CI: 1.01-1.05, p = 0.009) exhibited causal effects on AD. Moreover, 1-ribosyl-imidazoleacetate levels (-6.62%), Metabolonic lactone sulfate levels (2.90%), and Nonadecanoate (19:0) levels (-12.17%) mediated the total genetic predictive effects of class Actinobacteria on AD risk. Similarly, 2-stearoyl-GPE (18:0) levels (-9.87%), Octadecanedioylcarnitine (C18-DC) levels (4.44%), 1-(1-enyl-stearoyl)-2-oleoyl-GPE (p-18:0/18:1) levels (38.66%), and X-23639 levels (13.28%) respectively mediated the total genetic predictive effects of family Lactobacillaceae on AD risk. Furthermore, Hexadecanedioate (C16-DC) levels (5.45%) mediated the total genetic predictive effects of genus Ruminiclostridium 6 on AD risk; Indole-3-carboxylate levels (13.91%), X-13431 levels (7.08%), Alpha-ketoglutarate to succinate ratio (-13.91%), 3-phosphoglycerate to glycerate ratio (15.27%), and Succinate to proline ratio (-14.64%) respectively mediated the total genetic predictive effects of genus Ruminiclostridium 9 on AD risk.

Conclusion

Our mediation MR analysis provides genetic evidence suggesting the potential mediating role of blood metabolites in the causal relationship between gut microbiota and AD. Further large-scale randomized controlled trials are warranted to validate the role of blood metabolites in the specific mechanisms by which gut microbiota influence AD.

Multimodal brain-derived subtypes of Major depressive disorder differentiate patients for anergic symptoms, immune-inflammatory markers, history of childhood trauma and treatment-resistance

An estimated 30 % of Major Depressive Disorder (MDD) patients exhibit resistance to conventional antidepressant treatments. Identifying reliable biomarkers of treatment-resistant depression (TRD) represents a major goal of precision psychiatry, which is hampered by the clinical and biological heterogeneity. To uncover biologically-driven subtypes of MDD, we applied an unsupervised data-driven framework to stratify 102 MDD patients on their neuroimaging signature, including extracted measures of cortical thickness, grey matter volumes, and white matter fractional anisotropy. Our novel analytical pipeline integrated different machine learning algorithms to harmonize data, perform data dimensionality reduction, and provide a stability-based relative clustering validation. The obtained clusters were characterized for immune-inflammatory peripheral biomarkers, TRD, history of childhood trauma and depressive symptoms. Our results indicated two different clusters of patients, differentiable with 67 % of accuracy: one cluster (n = 59) was associated with a higher proportion of TRD, and higher scores of energy-related depressive symptoms, history of childhood abuse and emotional neglect; this cluster showed a widespread reduction in cortical thickness (d = 0.43-1.80) and volumes (d = 0.45-1.05), along with fractional anisotropy in the fronto-occipital fasciculus, stria terminalis, and corpus callosum (d = 0.46-0.52); the second cluster (n = 43) was associated with cognitive and affective depressive symptoms, thicker cortices and wider volumes. Multivariate analyses revealed distinct brain-inflammation relationships between the two clusters, with increase in pro-inflammatory markers being associated with decreased cortical thickness and volumes. Our stratification of MDD patients based on structural neuroimaging identified clinically-relevant subgroups of MDD with specific symptomatic and immune-inflammatory profiles, which can contribute to the development of tailored personalized interventions for MDD.

Probiotics and the microbiota-gut-brain axis in neurodegeneration: Beneficial effects and mechanistic insights

Neurodegenerative diseases (NDs) are a group of heterogeneous disorders with a high socioeconomic burden. Although pharmacotherapy is currently the principal therapeutic approach for the management of NDs, mounting evidence supports the notion that the protracted application of available drugs would abate their dopaminergic outcomes in the long run. The therapeutic application of microbiome-based modalities has received escalating attention in biomedical works. In-depth investigations of the bidirectional communication between the microbiome in the gut and the brain offer a multitude of targets for the treatment of NDs or maximizing the patient's quality of life. Probiotic administration is a well-known microbial-oriented approach to modulate the gut microbiota and potentially influence the process of neurodegeneration. Of note, there is a strong need for further investigation to map out the mechanistic prospects for the gut-brain axis and the clinical efficacy of probiotics. In this review, we discuss the importance of microbiome modulation and hemostasis via probiotics, prebiotics, postbiotics and synbiotics in ameliorating pathological neurodegenerative events. Also, we meticulously describe the underlying mechanism of action of probiotics and their metabolites on the gut-brain axis in different NDs. We suppose that the present work will provide a functional direction for the use of probiotic-based modalities in promoting current practical treatments for the management of neurodegenerative-related diseases.

Baseline gut microbiota profiles affect treatment response in patients with depression

The role of the gut microbiota in the pathophysiology of depression has been explored in numerous studies, which have confirmed that the baseline gut microbial profiles of patients with depression differ from those of healthy individuals. The gut microbiome affects metabolic activity in the immune and central nervous systems and regulates intestinal ecology through the neuroendocrine system. Additionally, baseline changes in the gut microbiota differed among patients with depression who demonstrated varying treatment response. Currently, probiotics are an emerging treatment for depression; however, the efficacy of modulating the gut microbiota in the treatment of depression remains uncertain. Additionally, the mechanisms by which changes in the gut microbiota affect treatment response in patients with depression remain unclear. In this review, we aimed to summarize the differences in the baseline gut microbiota between the remission and non-remission groups after antidepressant therapy. Additionally, we summarized the possible mechanisms that may contribute to antidepressant resistance through the effects of the gut microbiome on the immune and nervous systems, various enzymes, bioaccumulation, and blood-brain barrier, and provide a basis for treating depression by targeting the gut microbiota.

Differential Reshaping of Skin and Intestinal Microbiota by Stocking Density and Oxygen Availability in Farmed Gilthead Sea Bream (Sparus aurata): A Behavioral and Network-Based Integrative Approach

Fish were kept for six weeks at three different initial stocking densities and water O2 concentrations (low-LD, 8.5 kg/m3 and 95-70% O2 saturation; medium-MD, 17 kg/m3 and 55-75% O2 saturation; high-HD, 25 kg/m3 and 60-45% O2 saturation), with water temperature increasing from 19 °C to 26-27 °C. The improvement in growth performance with the decrease in stocking density was related to changes in skin and intestinal mucosal microbiomes. Changes in microbiome composition were higher in skin, with an increased abundance of Alteromonas and Massilia in HD fish. However, these bacteria genera were mutually exclusive, and Alteromonas abundance was related to a reactive behavior and systemic growth regulation via the liver Gh/Igf system, while Massilia was correlated to a proactive behavior and a growth regulatory transition towards muscle rather than liver. At the intestinal level, microbial abundance showed an opposite trend for two bacteria taxa, rendering in a low abundance of Reyranella and a high abundance of Prauserella in HD fish. This trend was correlated with up-regulated host gene expression, affecting the immune response, epithelial cell turnover, and abiotic stress response. Most of the observed responses are adaptive in nature, and they would serve to infer new welfare indicators for increased stress resilience.

Ameliorated Effects of Fucoidan on Dextran Sulfate Sodium-Induced Ulcerative Colitis and Accompanying Anxiety and Depressive Behaviors in Aged C57BL/6 Mice

Fucoidan has shown better effects on the improvement of acute ulcerative colitis (UC). However, the specific mechanisms by which fucoidan improves UC-related behavioral disorders in aged mice, especially its effect on the gut-brain axis, remain to be further explored. C57BL/6 male mice aged 8 months were gavaged with 400 or 100 mg/kg bw day fucoidan for five consecutive weeks, with UC being induced by ad libitum to dextran sulfate sodium (DSS) solution in the fifth week. The results showed that fucoidan ameliorated UC and accompanying anxiety- and depressive-like behaviors with downregulated expressions of (NOD)-like receptor family and pyrin domain-containing 3 (NLRP3), apoptosis-associated speck-like protein (ASC), cysteine aspartate-specific protease-1 (Caspase-1) and interlekin-1β (IL-1β), and elevated mRNA levels of brain-derived neurotrophic factor (Bdnf) and postsynaptic-density protein 95 (Psd-95) in cortex and hippocampus. Furthermore, fucoidan improved the permeability of intestinal barrier and blood-brain barrier and restored the abnormal structure of the gut microbiota with a significantly decreased ratio of Firmicutes to Bacteroidota (F/B) and obviously increased abundance of Akkermansia. As a diet-derived bioactive ingredient, fucoidan might be a better alternative for the prevention of UC and accompanying anxiety- and depressive-like behaviors.

Antidepressant-like effects of hyperoside on chronic stress-induced depressive-like behaviors in mice: Gut microbiota and short-chain fatty acids

BACKGROUND

The antidepressant effect of hyperoside (HYP), which is the main component of Hypericum perforatum, is not established. This study aimed to determine the effects of HYP on depression.

METHODS

The antidepressant-like effect of HYP was studied in mice induced by chronic restraint stress (CRS). The effects of HYP on behavior, inflammation, neurotransmitters, gut microbiota, and short-chain fatty acids (SCFAs) were studied in CRS mice.

RESULTS

HYP improved depressive-like behavior in mice induced by CRS. Nissl staining analysis showed that HYP improved neuronal damage in CRS mice. Western blot (WB) analysis showed that HYP increased the expression levels of BDNF and PSD95 in the hippocampus of CRS mice. The results of ELISA showed that HYP down-regulated the expression levels of IL-6, IL-1β, TNF-α, and CORT in the hippocampus, blood, and intestinal tissues of mice and up-regulated the expression levels of 5-HT and BDNF. Hematoxylin and eosin (HE) staining results indicate that HYP can improve the intestinal histopathological injury of CRS mice. The results of 16S rRNA demonstrated that HYP attenuated the dysbiosis of the gut microbiota of depressed mice, along with altering the concentration of SCFAs.

LIMITATIONS

In the present study, direct evidence that HYP improves depressive behaviors via gut microbiota and SCFAs is lacking, and only female mice were evaluated, which limits the understanding of the effects of HYP on both sexes.

CONCLUSIONS

HYP can improve CRS-induced depressive-like behaviors in mice, which is associated with regulating the gut microbiota and SCFAs concentration.

Brain-gut photobiomodulation restores cognitive alterations in chronically stressed mice through the regulation of Sirt1 and neuroinflammation

BACKGROUND

Chronic stress is an important risk factor for the development of major depressive disorder (MDD). Recent studies have shown microbiome dysbiosis as one of the pathogenic mechanisms associated with MDD. Thus, it is important to find novel non-pharmacological therapeutic strategies that can modulate gut microbiota and brain activity. One such strategy is photobiomodulation (PBM), which involves the non-invasive use of light.

OBJECTIVE/HYPOTHESIS

Brain-gut PBM could have a synergistic beneficial effect on the alterations induced by chronic stress.

METHODS

We employed the chronic unpredictable mild stress (CUMS) protocol to induce a depressive-like state in mice. Subsequently, we administered brain-gut PBM for 6 min per day over a period of 3 weeks. Following PBM treatment, we examined behavioral, structural, molecular, and cellular alterations induced by CUMS.

RESULTS

We observed that the CUMS protocol induces profound behavioral alterations and an increase of sirtuin1 (Sirt1) levels in the hippocampus. We then combined the stress protocol with PBM and found that tissue-combined PBM was able to rescue cognitive alterations induced by CUMS. This rescue was accompanied by a restoration of hippocampal Sirt1 levels, prevention of spine density loss in the CA1 of the hippocampus, and the modulation of the gut microbiome. PBM was also effective in reducing neuroinflammation and modulating the morphology of Iba1-positive microglia.

LIMITATIONS

The molecular mechanisms behind the beneficial effects of tissue-combined PBM are not fully understood.

CONCLUSIONS

Our results suggest that non-invasive photobiomodulation of both the brain and the gut microbiome could be beneficial in the context of stress-induced MDD.

Standard rodent diets differentially impact alcohol consumption, preference, and gut microbiome diversity

Alcohol use disorder (AUD) is a complex and widespread disease with limited pharmacotherapies. Preclinical animal models of AUD use a variety of voluntary alcohol consumption procedures to recapitulate different phases of AUD, including binge alcohol consumption and dependence. However, voluntary alcohol consumption in mice is widely variable, making it difficult to reproduce results across labs. Accumulating evidence indicates that different brands of commercially available rodent chow can profoundly influence alcohol intake. In this study, we investigated the effects of three commercially available and widely used rodent diet formulations on alcohol consumption and preference in C57BL/6 J mice using the 24 h intermittent access procedure. The three brands of chow tested were LabDiet 5,001 (LD5001), LabDiet 5,053 (LD5053), and Teklad 2019S (TL2019S) from two companies (Research Diets and Envigo, respectively). Mice fed LD5001 and LD5053 displayed higher levels of alcohol consumption and preference compared to mice fed TL2019S. We also found that alcohol consumption and preference could be rapidly switched by changing the diet 48 h prior to alcohol administration. Sucrose, saccharin, and quinine preferences were not altered, suggesting that the diets did not alter sweet and bitter taste perception. We also found that mice fed LD5001 displayed increased quinine-resistant alcohol intake compared to mice fed TL2019S, suggesting that diets could influence the development of compulsive behaviors such as alcohol consumption. We profiled the gut microbiome of water- and alcohol-drinking mice that were maintained on different diets and found significant differences in bacterial alpha- and beta-diversities, which could impact the gut-brain axis signaling and alcohol consumption.

Exploring the potential of drug repurposing for treating depression

Researchers are interested in drug repurposing or drug repositioning of existing pharmaceuticals because of rising costs and slower rates of new medication development. Other investigations that authorized these treatments used data from experimental research and off-label drug use. More research into the causes of depression could lead to more effective pharmaceutical repurposing efforts. In addition to the loss of neurotransmitters like serotonin and adrenaline, inflammation, inadequate blood flow, and neurotoxins are now thought to be plausible mechanisms. Because of these other mechanisms, repurposing drugs has resulted for treatment-resistant depression. This chapter focuses on therapeutic alternatives and their effectiveness in drug repositioning. Atypical antipsychotics, central nervous system stimulants, and neurotransmitter antagonists have investigated for possible repurposing. Nonetheless, extensive research is required to ensure their formulation, effectiveness, and regulatory compliance.

High-fat diet, microbiome-gut-brain axis signaling, and anxiety-like behavior in male rats

Obesity, associated with the intake of a high-fat diet (HFD), and anxiety are common among those living in modern urban societies. Recent studies suggest a role of microbiome-gut-brain axis signaling, including a role for brain serotonergic systems in the relationship between HFD and anxiety. Evidence suggests the gut microbiome and the serotonergic brain system together may play an important role in this response. Here we conducted a nine-week HFD protocol in male rats, followed by an analysis of the gut microbiome diversity and community composition, brainstem serotonergic gene expression (tph2, htr1a, and slc6a4), and anxiety-related defensive behavioral responses. We show that HFD intake decreased alpha diversity and altered the community composition of the gut microbiome in association with obesity, increased brainstem tph2, htr1a and slc6a4 mRNA expression, including in the caudal part of the dorsomedial dorsal raphe nucleus (cDRD), a subregion previously associated with stress- and anxiety-related behavioral responses, and, finally, increased anxiety-related defensive behavioral responses. The HFD increased the Firmicutes/Bacteroidetes ratio relative to control diet, as well as higher relative abundances of Blautia, and decreases in Prevotella. We found that tph2, htr1a and slc6a4 mRNA expression were increased in subregions of the dorsal raphe nucleus in the HFD, relative to control diet. Specific bacterial taxa were associated with increased serotonergic gene expression in the cDRD. Thus, we propose that HFD-induced obesity is associated with altered microbiome-gut-serotonergic brain axis signaling, leading to increased anxiety-related defensive behavioral responses in rats.