Patient-derived Enterococcus mundtii and its capsular polysaccharides cause depression through the downregulation of NF-κB-involved serotonin and BDNF expression

Impacts of microbiota and its metabolites through gut-brain axis on pathophysiology of major depressive disorder

Major depressive disorder (MDD) is characterized by a high rate of recurrence and disability, which seriously affects the quality of life of patients. That's why a deeper understanding of the mechanisms of MDD pathology is an urgent task, and some studies have found that intestinal symptoms accompany people with MDD. The microbiota-gut-brain axis is the bidirectional communication between the gut microbiota and the central nervous system, which was found to have a strong association with the pathogenesis of MDD. Previous studies have focused more on the communication between the gut and the brain through neuroendocrine, neuroimmune and autonomic pathways, and the role of gut microbes and their metabolites in depression is unclear. Metabolites of intestinal microorganisms (e.g., tryptophan, kynurenic acid, indole, and lipopolysaccharide) can participate in the pathogenesis of MDD through immune and inflammatory pathways or by altering the permeability of the gut and blood-brain barrier. In addition, intestinal microbes can communicate with intestinal neurons and glial cells to affect the integrity and function of intestinal nerves. However, the specific role of gut microbes and their metabolites in the pathogenesis of MDD is not well understood. Hence, the present review summarizes how gut microbes and their metabolites are directly or indirectly involved in the pathogenesis of MDD.

Gut microbiota and inflammatory factor characteristics in major depressive disorder patients with anorexia

BACKGROUND

This study aimed to explore the gut microbiota and inflammatory factor characteristics in major depressive disorder (MDD) patients with anorexia and to analyze the correlation between gut microbiota and inflammatory factors, anorexia, and HAMD scores.

METHODS

46 MDD patients and 46 healthy controls (HC) were included in the study. The 46 MDD patients were divided into two groups according to whether they had anorexia:20 MDD without anorexia (MDA0 group) and 26 MDD with anorexia (MDA1 group). We used the Hamilton Depression Scale-24 (HAMD-24) to evaluate the depression status of all participants and 16 S ribosomal RNA (16 S rRNA)sequencing to evaluate the composition of the gut microbiota. Inflammatory factors in peripheral blood such as C-reactive protein (CRP) were detected using enzyme-linked immunosorbent assay (ELISA). Spearman's correlation analysis was used to evaluate the correlation between gut microbiota and inflammatory factors, HAMD scores, and anorexia.

RESULTS

1). CRP was significantly higher in the MDA0, MDA1, than HC. 2). An analysis of α-diversity shows: the Simpson and Pielou indices of the HC group are higher than the MDA1 group (P < 0.05). 3). The β-diversity analysis shows differences in the composition of microbial communities between the MDA0, MDA1, and HC group. 4). A correlation analysis showed that Blautia positively correlated with anorexia, HAMD scores, and CRP level, whereas Faecalibacterium, Bacteroides, Roseburia, and Parabacteroides negatively correlated with anorexia, HAMD scores, and CRP level. 5). The receiver operating characteristic (ROC) curve was drawn using the differential bacterial genera between MDD patients with or without anorexia as biomarkers to identify whether MDD patients were accompanied with anorexia, and its area under curve (AUC) was 0.85. The ROC curve was drawn using the differential bacterial genera between MDD patients with anorexia and healthy controls as biomarkers to diagnose MDD patients with anorexia, with its AUC was 0.97.

CONCLUSION

This study suggested that MDD patients with anorexia had a distinct gut microbiota compared to healthy individuals, with higher level of CRP. Blautia was more abundant in MDD patients with anorexia and positively correlated with CRP, HAMD scores, and anorexia. The gut microbiota might have influenced MDD and anorexia through the inflammatory factor CRP.

Effect of gut microbiome on serotonin metabolism: a personalized treatment approach

Several factors including diet, exercise, and medications influence the makeup of the resilient but adaptable gut microbiome. Bacteria in the gut have a significant role in the homeostasis of the neurotransmitter serotonin, also known as 5-hydroxytryptamine, involved in mood and behavior. The goal of the current work is to review the effect of the gut microbiome on serotonin metabolism, and how it can potentially contribute to the development of a personalized treatment approach for depression and anxiety. Bacterial strains provide innovative therapeutic targets that can be used for disorders, such as depression, that involve dysregulation of serotonin. Advances in bacterial genomic sequencing have increased the accessibility and affordability of microbiome testing, which unlocks a new targeted pathway to modulate serotonin metabolism by targeting the gut-brain axis. Microbiome testing can facilitate the recommendation of strain-specific probiotic supplements based on patient-specific microbial profiles. Several studies have shown that supplementation with probiotics containing specific species of bacteria, such as Bifidobacterium and Lactobacillus, can improve symptoms of depression. Further research is needed to improve the process and interpretation of microbiome testing and how to successfully incorporate testing results into guiding clinical decision-making. This targeted approach centered around the gut-brain axis can provide a novel way to personalize therapy for mental health disorders.

The Regulatory Effect of Huangshui Polysaccharides on Intestinal Microbiota and Metabolites during In Vitro Fermentation

Huangshui polysaccharides (HSPs) have attracted extensive attention recently for their biological activity and physicochemical property. This research investigated the extraction, structural characterization, and prebiotic activity of three different HSPs (HSP40-0, HSP60-0, and HSP80-0) in vitro to reveal the scientific support for the high-value utilization of Huangshui. HSPs were heteropolysaccharide with diverse structures and surface morphologies. Comprehensive analysis was conducted through 16S rRNA gene sequencing and metabolite profiling techniques, and results showed that HSPs had different potentials to regulate the gut microbiota due to their different structures; for instance, both HSP40-0 and HSP80-0 could notably increase the relative abundance of Bacteroidota, whereas HSP60-0 could increase the relative abundance of Phascolarctobacterium. In addition, HSPs upregulated beneficial differential metabolites, especially short-chain fatty acids (SCFAs). Fermentation products containing these metabolites exhibited anti-inflammatory effects on LPS-treated Caco-2 cells. This study will provide reference for exploring the relationship between the natural polysaccharide structure and the prebiotic activity and widen the application of Huangshui.

A review of the pharmacological action and mechanism of natural plant polysaccharides in depression

Depression is a prevalent mental disorder. However, clinical treatment options primarily based on chemical drugs have demonstrated varying degrees of adverse reactions and drug resistance, including somnolence, nausea, and cognitive impairment. Therefore, the development of novel antidepressant medications that effectively reduce suffering and side effects has become a prominent area of research. Polysaccharides are bioactive compounds extracted from natural plants that possess diverse pharmacological activities and medicinal values. It has been discovered that polysaccharides can effectively mitigate depression symptoms. This paper provides an overview of the pharmacological action and mechanisms, intervention approaches, and experimental models regarding the antidepressant effects of polysaccharides derived from various natural sources. Additionally, we summarize the roles and potential mechanisms through which these polysaccharides prevent depression by regulating neurotransmitters, HPA axis, neurotrophic factors, neuroinflammation, oxidative stress, tryptophan metabolism, and gut microbiota. Natural plant polysaccharides hold promise as adjunctive antidepressants for prevention, reduction, and treatment of depression by exerting their therapeutic effects through multiple pathways and targets. Therefore, this review aims to provide scientific evidence for developing polysaccharide resources as effective antidepressant drugs.

IL-6 expression-suppressing Lactobacillus reuteri strains alleviate gut microbiota-induced anxiety and depression in mice

Fecal microbiota transplantation from patients with depression/inflammatory bowel disease (PDI) causes depression with gut inflammation in mice. Here, we investigated the effects of six Lactobacillus reuteri strains on brain-derived neurotropic factor (BDNF), serotonin, and interleukin (IL)-6 expression in neuronal or macrophage cells and PDI fecal microbiota-cultured microbiota (PcM)-induced depression in mice. Of these strains, L6 most potently increased BDNF and serotonin levels in corticosterone-stimulated SH-SY5Y and PC12 cells, followed by L3. L6 most potently decreased IL-6 expression in lipopolysaccharide (LPS)-stimulated macrophages. When L1 (weakest in vitro), L3, and L6 were orally administered in mice with PcM-induced depression, L6 most potently suppressed depression-like behaviors and hippocampal TNF-α and IL-6 expression and increased hippocampal serotonin, BDNF, 5HT7, GABAARα1, and GABABR1b expression, followed by L3 and L1. L6 also suppressed TNF-α and IL-6 expression in the colon. BDNF or serotonin levels in corticosterone-stimulated neuronal cells were negatively correlated with depression-related biomarkers in PcM-transplanted mice, while IL-6 levels in LPS-stimulated macrophage were positively correlated. These findings suggest that IL-6 expression-suppressing and BDNF/serotonin expression-inducing LBPs in vitro, particularly L6, may alleviate gut microbiota-involved depression with colitis in vivo.

Regulation of colonic neuropeptide Y expression by the gut microbiome in patients with ulcerative colitis and its association with anxiety- and depression-like behavior in mice

Patients with inflammatory bowel disease (IBD), including ulcerative colitis (UC), show an increased incidence of anxiety and depression; however, the association between UC-associated psychiatric disorders and the gut microbiota is unclear. This study aimed to examine whether gut microbiota from patients with UC can alter colonic gene expression, leading to anxiety- and depression-like behavior in mice receiving fecal microbiota transplantation (FMT). RNA sequencing transcriptome analyses revealed a difference in colonic gene expression between mice receiving FMT from patients with UC (UC-FMT mice) and those receiving FMT from healthy controls (HC-FMT mice). Gene ontology analysis revealed the downregulation of neuropeptide signaling pathways, including neuropeptide Y (NPY) expression, in the colons of UC-FMT mice. The protein levels of NPY also decreased in the colon and plasma of UC-FMT mice compared to those in HC-FMT mice. The oral administration of Enterococcus mundtii (EM), a bacterium isolated from the feces of patients with UC, reduced NPY expression in the colons of mice and induced intestinal inflammation, anxiety, and depression-like behavior. Reduced NPY protein levels were also observed in the plasma and hippocampus of EM-treated mice. Intraperitoneal administration of NPY significantly alleviated anxiety- and depressive-like behaviors induced by EM in mice. Capsular polysaccharide in EM was associated with EM-induced NPY downregulation in the colon. Analysis of Gene Expression Omnibus datasets showed markedly reduced NPY expression in the inflamed colons of patients with UC compared with that in the colons of healthy controls. In summary, EM-induced reduction in the colonic expression of NPY may be associated with a decrease in hippocampal NPY and anxiety- and depression-like behavior in mice.

Cefaclor causes vagus nerve-mediated depression-like symptoms with gut dysbiosis in mice

Antibiotics are increasingly recognized as causing neuropsychiatric side effects including depression and anxiety. Alterations in central serotonin and 5-HT receptor expression are implicated in the pathogenesis of anxiety and depression, which are highly comorbid with gastrointestinal disorders. Nevertheless, it is still unclear how antibiotics can cause anxiety and depression. In this study, oral administration of cefaclor, a second-generation cephalosporin antibiotic, induced anxiety- and depression-like behaviors and colitis with gut microbiota alteration in mice. Cefaclor reduced serotonin levels and fluctuated 5-HT receptor mRNA expressions such as Htr1a, Htr1b, and Htr6 in the hippocampus. Vagotomy attenuated the cefaclor-induced anxiety- and depression-like symptoms, while the cefaclor-induced changes in gut bacteria alteration and colitis were not affected. Fluoxetine attenuated cefaclor-induced anxiety- and depression-like behaviors. Furthermore, fluoxetine decreased cefaclor-resistant Enterobacteriaceae and Enterococcaceae. Taken together, our findings suggest that the use of antibiotics, particularly, cefaclor may cause gut dysbiosis-dependent anxiety and depression through the microbiota-gut-blood-brain and microbiota-gut-vagus nerve-brain pathway. Targeting antibiotics-resistant pathogenic bacteria may be a promising therapeutic strategy for the treatment of anxiety and depression.

The Association between Gut Microbiota and Depression in the Japanese Population

Depression is a leading cause of disease worldwide. The association between gut microbiota and depression has barely been investigated in the Japanese population. We analyzed Iwaki health check-up data collected from 2017 to 2019 and constructed generalized linear mixed models. The independent variable was the relative abundance of each of the 37 gut microbiota genera that were reported to be associated with depression. The dependent variable was the presence of depression assessed by the Center for Epidemiologic Studies Depression Scale. Potential confounders, including grip strength, gender, height, weight, smoking, and drinking habits, were adjusted in the regression models. Nine genera's regression coefficients (Alistipes, Blautia, Coprococcus, Dorea, Faecalibacterium, Holdemania, Lactobacillus, Mitsuokella, and Oscillibacter) showed statistical significance after multiple comparisons adjustment. Among these nine gut bacteria genera, Alistipes, Blautia, Coprococcus, Dorea, Faecalibacterium, and Oscillibacter were reported to be associated with butyrate production in the intestine. Our results indicate that gut microbiotas may influence the depression condition of the host via the butyrate-producing process.

Vagus nerve-dependent effects of fluoxetine on anxiety- and depression-like behaviors in mice

The vagus nerve is a major pathway in the body that is responsible for regulating the activity of the parasympathetic nervous system, which plays an important role in mood disorders including anxiety and depression. Fluoxetine, also known as Prozac, is widely used to treat depression. Nevertheless, there are few studies on the vagus nerve-mediated action of fluoxetine. In this study, we aimed to investigate the vagus nerve-dependent actions of fluoxetine in mice with restraint stress-induced or antibiotics-induced anxiety- and depression-like behaviors. Compared to sham operation, vagotomy alone did not exhibit significant effects on behavioral changes and serotonin-related biomarkers in mice not exposed to stress, antibiotics, or fluoxetine. Oral administration of fluoxetine significantly alleviated anxiety- and depression-like behaviors. However, celiac vagotomy significantly attenuated the anti-depressive effects of fluoxetine. The vagotomy also inhibited the effect of fluoxetine to attenuate restraint stress- or cefaclor-induced reduction in serotonin levels and Htr1a mRNA expression in the hippocampus. These findings suggest that the vagus nerve may regulate the efficacy of fluoxetine for depression.

Lactobacillus casei and Its Supplement Alleviate Stress-Induced Depression and Anxiety in Mice by the Regulation of BDNF Expression and NF-κB Activation

Stress-induced depression and anxiety (DA) are closely connected to gastrointestinal inflammation and dysbiosis, which can suppress brain-derived neurotrophic factor (BDNF) in the brain. Herein, we isolated the BDNF expression-inducing probiotics Lactobacillus casei HY2782 and Bifidobacterium lactis HY8002 in lipopolysaccharide-stimulated SH-SY5Y cells. Then, we investigated the effects of HY2782, HY8002, anti-inflammatory L-theanine, and their supplement (PfS, probiotics-fermented L-theanine-containing supplement) on DA in mice exposed to restraint stress (RS) or the fecal microbiota of patients with inflammatory bowel disease and depression (FMd). Oral administration of HY2782, HY8002, or L-theanine alleviated RS-induced DA-like behaviors. They also decreased RS-induced hippocampal interleukin (IL)-1β and IL-6 levels, as well as NF-κB-positive cell numbers, blood corticosterone level, and colonic IL-1β and IL-6 levels and NF-κB-positive cell numbers. L-theanine more potently suppressed DA-like behaviors and inflammation-related marker levels than probiotics. However, these probiotics more potently increased RS-suppressed hippocampal BDNF level and BDNF⁺NeuN⁺ cell numbers than L-theanine. Furthermore, HY2782 and HY8002 suppressed RS-increased Proteobacteria and Verrucomicrobia populations in gut microbiota. In particular, they increased Lachnospiraceae and Lactobacillacease populations, which are closely positively associated with hippocampal BDNF expression, and suppressed Sutterellaceae, Helicobacteriaceae, Akkermansiaceae, and Enterobacteriaceae populations, which are closely positively associated with hippocampal IL-1β expression. HY2782 and HY8002 potently alleviated FMd-induced DA-like behaviors and increased FMd-suppressed BDNF, serotonin levels, and BDNF-positive neuronal cell numbers in the brain. They alleviated blood corticosterone level and colonic IL-1β α and IL-6 levels. However, L-theanine weakly, but not significantly, alleviated FMd-induced DA-like behaviors and gut inflammation. BDNF expression-inducing probiotic (HY2782, HY8002, Streptococcus thermophilus, and Lactobacillus acidophilus)-fermented and anti-inflammatory L-theanine-containing supplement PfS alleviated DA-like behaviors, inflammation-related biomarker levels, and gut dysbiosis more than probiotics or L-theanine. Based on these findings, a combination of BDNF expression-inducing probiotics with anti-inflammatory L-theanine may additively or synergistically alleviate DA and gut dysbiosis by regulating gut microbiota-mediated inflammation and BDNF expression, thereby being beneficial for DA.

Neuroprotective effects of PRG on Aβ25-35-induced cytotoxicity through activation of the ERK1/2 signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Phylloporia ribis (Schumach:Fr.)Ryvarden is a genus of needle Phellinus medicinal fungi, parasitic on the living rhizomes of hawthorn and pear trees. As a traditional Chinese medicine, Phylloporia ribis was used in folklore for long-term illness, weakness and memory loss in old age. Previous studies have shown that polysaccharides from Phylloporia ribis (PRG) significantly promoted synaptic growth in PC12 cells in a dose-dependent manner, exhibiting "NGF"-like neurotrophic activity. Aβ_25-35 damage to PC12 cells produced neurotoxicity and decreased cell survival, and PRG reduced the apoptosis rate, suggesting that PRG has neuroprotective effects. The studies confirmed that PRG had the potential to be a neuroprotective agent, but its neuroprotective mechanism remained unclear.

AIM OF THE STUDY

We aimed to elucidate the neuroprotective effects of PRG in an Aβ_25-35-induced Alzheimer's disease (AD) model.

MATERIALS AND METHODS

Highly-differentiated PC12 cells were treated with Aβ_25-35 (AD model) and PRG, and were assessed for cellular apoptosis, inflammatory factors, oxidative stress, and kinase phosphorylation.

RESULTS

The results showed that the PRG groups effectively inhibited the neurotoxicity, mainly manifested by inhibiting mitochondrial oxidative stress, attenuating neuroinflammatory responses, and improving mitochondrial energy metabolism, eventually resulting in higher cell survival. The expression of p-ERK, p-CREB and BDNF proteins was increased in the PRG groups compared to the model group, which confirmed that PRG reversed the inhibition of the ERK pathway.

CONCLUSION

We provide evidence for neuroprotection conferred by PRG and its mechanism by inhibiting ERK1/2 hyper-phosphorylation, prevention of mitochondrial stress, and subsequent prevention of apoptosis. The study highlights PRG as a promising candidate with neuroprotective effects, the potential of which can be harnessed for identifying novel therapeutic targets.