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GABA-modulating bacteria of the human gut microbiota.
The gut microbiota affects many important host functions, including the immune response and the nervous system1. However, while substantial progress has been made in growing diverse microorganisms of the microbiota2, 23-65% of species residing in the human gut remain uncultured3,4, which is an obstacle for understanding their biological roles. A likely reason for this unculturability is the absence in artificial media of key growth factors that are provided by neighbouring bacteria in situ5,6. In the present study, we used co-culture to isolate KLE1738, which required the presence of Bacteroides fragilis to grow. Bioassay-driven purification of B. fragilis supernatant led to the isolation of the growth factor, which, surprisingly, is the major inhibitory neurotransmitter GABA (γ-aminobutyric acid). GABA was the only tested nutrient that supported the growth of KLE1738, and a genome analysis supported a GABA-dependent metabolism mechanism. Using growth of KLE1738 as an indicator, we isolated a variety of GABA-producing bacteria, and found that Bacteroides ssp. produced large quantities of GABA. Genome-based metabolic modelling of the human gut microbiota revealed multiple genera with the predicted capability to produce or consume GABA. A transcriptome analysis of human stool samples from healthy individuals showed that GABA-producing pathways are actively expressed by Bacteroides, Parabacteroides and Escherichia species. By coupling 16S ribosmal RNA sequencing with functional magentic resonance imaging in patients with major depressive disorder, a disease associated with an altered GABA-mediated response, we found that the relative abundance levels of faecal Bacteroides are negatively correlated with brain signatures associated with depression.
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Obesity and Depression: A Pathophysiotoxic Relationship.
Obesity and depression are two of the most prevalent diseases with increasing trends worldwide; it has been some time since the first epidemiological associations were first described. Currently, there is abundant evidence showing the physiology and the molecular aspects that intersect the biology of both ailments. This narrative review aims to synthesize current evidence on the epidemiology and shared pathophysiology of obesity and major depressive disorder, emphasizing convergent inflammatory, neuroendocrine, metabolic, genetic, and gut-brain mechanisms. We aggregate evidence for a bidirectional relationship mediated by: (1) chronic low-grade inflammation (elevated CRP, IL-6, TNF-α; microglial activation); (2) HPA axis dysregulation (hyper/corticosteronemia, impaired feedback, altered CRH/ACTH signaling); (3) metabolic and neurotrophic signaling deficits (insulin and leptin resistance, dysregulated adipokines such as leptin/adiponectin, impaired BDNF and synaptic plasticity); (4) lipid-derived neurotoxicity and mitochondrial stress (saturated fatty acids, ceramides, oxidative stress); and (5) gut-brain axis perturbations (microbiota dysbiosis, increased intestinal permeability, LPS-driven endotoxemia, altered short-chain fatty acids and tryptophan-kynurenine metabolism). We highlight how these convergent pathways promote neuroinflammation and mood dysregulation in individuals with obesity and summarize clinical consequences for screening, integrated management, and targeted interventions that modulate immune, neuroendocrine, metabolic, and microbial processes. Finally, we outline priorities for identifying shared biomarkers and advancing personalized strategies via multi-omics and systems medicine to improve prevention, diagnosis, and treatment.
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Neurobiology of Resilience: Interface Between Mind and Body.
Stress-related neuropsychiatric disorders, such as major depressive disorder and posttraumatic stress disorder, exact enormous socioeconomic and individual consequences. Resilience, the process of adaptation in the face of adversity, is an important concept that is enabling the field to understand individual differences in stress responses, with the hope of harnessing this information for the development of novel therapeutics that mimic the body's natural resilience mechanisms. This review provides an update on the current state of research of the neurobiological mechanisms of stress resilience. We focus on physiological and transcriptional adaptations of specific brain circuits, the role of cellular and humoral factors of the immune system, the gut microbiota, and changes at the interface between the brain and the periphery, the blood-brain barrier. We propose viewing resilience as a process that requires the integration of multiple central and peripheral systems and that elucidating the underlying neurobiological mechanisms will ultimately lead to novel therapeutic options.
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Implications of neurogenesis in depression through BDNF: rodent models, regulatory pathways, gut microbiota, and potential therapy.
Major Depressive Disorder (MDD) is a prevalent psychiatric disorder with a profound impact on global health, necessitating a deeper understanding of its pathophysiology. This review synthesizes current evidence linking neurogenesis, particularly in the hippocampal region, with MDD. Accumulating data showed a significant reduction of neurogenesis in the hippocampal region of both MDD patients and various MDD rodent models. We highlight the role of brain-derived neurotrophic factor (BDNF) and its associated signaling pathways in regulating neurogenesis and depressive symptoms. Additionally, the influence of gut microbiota on the neurogenesis in depression is presented, offering a novel perspective on environmental modulation of neurogenesis. This review also underscores the potential antidepressant interventions targeting neurogenesis and BDNF's regulation, such as therapeutic benefits of environmental enrichment, physical activity, and pharmacological agents in enhancing neurogenesis and alleviating depressive symptoms. Together, this systemic review provides a foundation for future research aiming at developing personalized treatments by targeting neurogenesis in MDD, potentially leading to novel biomarkers and therapeutic strategies.
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Multi-omics analyses of the gut microbiome, fecal metabolome, and multimodal brain MRI reveal the role of Alistipes and its related metabolites in major depressive disorder.
BACKGROUND: Compelling evidence claims that gut microbial dysbiosis may be causally associated with major depressive disorder (MDD), with a particular focus on Alistipes. However, little is known about the potential microbiota-gut-brain axis mechanisms by which Alistipes exerts its pathogenic effects in MDD. METHODS: We collected data from 16S rDNA amplicon sequencing, untargeted metabolomics, and multimodal brain magnetic resonance imaging from 111 MDD patients and 102 healthy controls. We used multistage linked analyses, including group comparisons, correlation analyses, and mediation analyses, to explore the relationships between the gut microbiome (Alistipes), fecal metabolome, brain imaging, and behaviors in MDD. RESULTS: Gut microbiome analysis demonstrated that MDD patients had a higher abundance of Alistipes relative to controls. Partial least squares regression revealed that the increased Alistipes was significantly associated with fecal metabolome in MDD, involving a range of metabolites mainly enriched for amino acid, vitamin B, and bile acid metabolism pathways. Correlation analyses showed that the Alistipes-related metabolites were associated with a wide array of brain imaging measures involving gray matter morphology, spontaneous brain function, and white matter integrity, among which the brain functional measures were, in turn, associated with affective symptoms (anxiety and anhedonia) and cognition (sustained attention) in MDD. Of more importance, further mediation analyses identified multiple significant mediation pathways where the brain functional measures in the visual cortex mediated the associations of metabolites with behavioral deficits. CONCLUSION: Our findings provide a proof of concept that Alistipes and its related metabolites play a critical role in the pathophysiology of MDD through the microbiota-gut-brain axis.
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Gut microbiota and major depressive disorder: A systematic review and meta-analysis.
BACKGROUND: Growing attention has been paid to the field of gut microbiota for mental disorders over the last decade. However, to our knowledge, no studies have conducted systematic reviews on the association between gut microbiota and major depressive disorder (MDD) in both interventional and non-interventional studies. METHODS: We conducted a systematic review and meta-analysis of 16 studies (10 observational [701 participants] and six interventional trials [302 participants]) examining gut microbiota in patients with MDD. The primary outcome measures were differences in the profile of microbiota in the observational studies, and symptom changes for depression between pre- and post-intervention with probiotics in the interventional trials. RESULTS: In the observational studies, significant reductions in several taxa at the family and genus levels were observed in patients with MDD compared to non-depressed controls. In the interventional studies with probiotics, a significant improvement was found in depressive symptomatology compared to controls (SMD = -1.62, 95% CI = -2.73 to -0.51, p< 0.01). LIMITATIONS: Lack of consideration of the effects of diet and pharmacotherapy was a possible limitation. CONCLUSIONS: Our results indicate that several taxa at the family and genus levels, specifically family Prevotellaceae, genus Corprococcus, and Faecalibacterium, were decreased in MDD compared to non-depressed controls in observational studies, and depressive symptoms were improved compared to controls in interventional studies with probiotics. Due to the limited number of studies, further studies considering diet and pharmacotherapy are needed to explore the relationships between gut microbiota and MDD in humans.
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Effects of Probiotic NVP-1704 on Mental Health and Sleep in Healthy Adults: An 8-Week Randomized, Double-Blind, Placebo-Controlled Trial.
The human gut microbiome is closely linked to mental health and sleep. We aimed to verify the efficacy and safety of probiotic NVP-1704, a mixture of Lactobacillus reuteri NK33 and Bifidobacterium adolescentis NK98, in improving stress, depression, anxiety, and sleep disturbances, along with the measurement of some blood biomarkers. A total of 156 healthy adults with subclinical symptoms of depression, anxiety, and insomnia were retrospectively registered and randomly assigned to receive either NVP-1704 (n = 78) or a placebo (n = 78) for eight weeks. Participants completed the Stress Response Inventory, Beck's Depression and Anxiety Inventory, Pittsburg Sleep Quality Index, and Insomnia Severity Index at baseline, at four and eight weeks of treatment. Pre- and post-treatment blood tests for biomarkers were conducted. After intervention, gut microbiota composition was quantified by pyrosequencing the bacterial 16S rRNA gene. The NVP-1704 group had a more significant reduction in depressive symptoms at four and eight weeks of treatment, and anxiety symptoms at four weeks compared to the placebo group. Those receiving NVP-1704 also experienced an improvement in sleep quality. NVP-1704 treatment led to a decrease in serum interleukin-6 levels. Furthermore, NVP-1704 increased Bifidobacteriaceae and Lactobacillacea, whereas it decreased Enterobacteriaceae in the gut microbiota composition. Our findings suggest that probiotic NVP-1704 could be beneficial for mental health and sleep.
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The gut microbiome from middle-aged women with depression modulates depressive-like behaviors and plasma fatty acid metabolism in female middle-aged mice.
BACKGROUND: Intestinal dysbacteriosis has frequently been involved in the context of depression. Nonetheless, only scant information is available about the features and functional changes of gut microbiota in female middle-aged depression (MAD). OBJECTIVE: This study aims to explore whether there are characteristic changes in the gut microbes of female MAD and whether these changes are associated with depressive-like behaviors. Meanwhile, this study observed alterations in the lipid metabolism function of gut microbes and further examined changes in plasma medium- and long-chain fatty acids (MLCFAs) in mice that underwent fecal microbiota transplantation (FMT). METHODS: Stool samples obtained from 31 MAD, along with 24 healthy individuals (HC) were analyzed by 16 S rRNA gene sequencing. Meanwhile, 14-month-old female C57BL/6J mice received antibiotic cocktails and then oral gavage of the microbiota suspension of MAD or HC for 3 weeks to reconstruct gut microbiota. The subsequent depressive-like behaviors, the composition of gut microbiota, as well as MLCFAs in the plasma were evaluated. RESULTS: A noteworthy disruption in gut microbial composition in MAD individuals compared to HC was observed. Several distinct bacterial taxa, including Dorea, Butyricicoccus, and Blautia, demonstrated associations with the demographic variables. A particular microbial panel encompassing 49 genera effectively differentiated MAD patients from HC (AUC = 0.82). Fecal microbiome transplantation from MAD subjects led to depressive-like behaviors and dysfunction of plasma MLCFAs in mice. CONCLUSIONS: These findings suggest that microbial dysbiosis is linked to the pathogenesis of MAD, and its role may be associated with the regulation of MLCFAs metabolism.
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The Role of Probiotics and Their Metabolites in the Treatment of Depression.
Depression is a common and complex mental and emotional disorder that causes disability, morbidity, and quite often mortality around the world. Depression is closely related to several physical and metabolic conditions causing metabolic depression. Studies have indicated that there is a relationship between the intestinal microbiota and the brain, known as the gut-brain axis. While this microbiota-gut-brain connection is disturbed, dysfunctions of the brain, immune system, endocrine system, and gastrointestinal tract occur. Numerous studies show that intestinal dysbiosis characterized by abnormal microbiota and dysfunction of the microbiota-gut-brain axis could be a direct cause of mental and emotional disorders. Traditional treatment of depression includes psychotherapy and pharmacotherapy, and it mainly targets the brain. However, restoration of the intestinal microbiota and functions of the gut-brain axis via using probiotics, their metabolites, prebiotics, and healthy diet may alleviate depressive symptoms. Administration of probiotics labeled as psychobiotics and their metabolites as metabiotics, especially as an adjuvant to antidepressants, improves mental disorders. It is a new approach to the prevention, management, and treatment of mental and emotional illnesses, particularly major depressive disorder and metabolic depression. For the effectiveness of antidepressant therapy, psychobiotics should be administered at a dose higher than 1 billion CFU/day for at least 8 weeks.
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Association between soft drink consumption and depression mediated by gut microbiome: a perspective.
This perspective synthesises current evidence on the association between soft drink consumption and depression, with emphasis on the gut microbiome as a potential mediating mechanism. PubMed, Scopus, and Google Scholar were searched using the following terms: 'soft drinks', 'sugar-sweetened beverages', 'carbonated beverages', 'soda', 'depression', 'depressive symptoms', 'mental health', 'gut microbiome', 'microbiota', and 'gut-brain axis'. Peer-reviewed original articles published in English between January 2000 and October 2025 were included if they involved human participants of any age (sample size ≥50 for observational studies), assessed soft drink or sugar-sweetened beverage consumption, and measured depression diagnosis, depressive symptoms, or depression severity. Associations between soft drink consumption and increased depression risk were consistently shown across multiple study designs and populations. Evidence for artificially sweetened beverages was less consistent and suggested potentially distinct, non-sugar-related pathways. A multicentre cohort study of 932 participants revealed that soft drink consumption predicted the major depressive disorder diagnosis (odds ratio = 1.081), with stronger effects in women (odds ratio = 1.167). Eggerthella partially mediated the soft drink-depression association, explaining approximately 4% of the association. Soft drink consumption is associated with increased depression risk through multiple biological pathways involving inflammation, metabolic dysregulation, and gut microbiome alterations. Modest effect sizes suggest the involvement of multiple interconnected mechanisms. Public health interventions to limit sugar-sweetened beverage consumption are recommended to improve physical and mental health. Healthcare providers should consider dietary assessment and counselling as part of depression prevention and treatment strategies.