Analysis of gut microbiota diversity and auxiliary diagnosis as a biomarker in patients with schizophrenia: A cross-sectional study

Gut microbiome and schizophrenia: insights from two-sample Mendelian randomization

Growing evidence suggests a potential link between the gut microbiome and schizophrenia. However, it is unclear whether the gut microbiome is causally associated with schizophrenia. We performed two-sample bidirectional Mendelian randomization to detect bidirectional causal relationships between gut microbiome and schizophrenia. Summary genome-wide association study (GWAS) datasets of the gut microbiome from the MiBioGen consortium (n = 18,340) and schizophrenia (n = 130,644) were utilized in our study. Then a cohort of sensitive analyses was followed to validate the robustness of MR results. We identified nine taxa that exerted positive causal effects on schizophrenia (OR: 1.08-1.16) and six taxa that conferred negative causal effects on schizophrenia (OR: 0.88-0.94). On the other hand, the reverse MR analysis showed that schizophrenia may increase the abundance of nine taxa (OR: 1.03-1.08) and reduce the abundance of two taxa (OR: 0.94). Our study unveiled mutual causal relationships between gut microbiome and schizophrenia. The findings may provide evidence for the treatment potential of gut microbiomes in schizophrenia.

Prebiotic Treatment in People With Schizophrenia

BACKGROUND

Preliminary evidence suggests that people with schizophrenia have decreased relative abundance of butyrate-producing bacteria in the gut microbiota. Butyrate plays a critical role in maintaining the integrity of the gut-blood barrier and has a number of anti-inflammatory effects. This proof-of-concept study was designed to assess whether the addition of the oligofructose-enriched inulin (OEI) prebiotic: Prebiotin could increase the production of butyrate.

METHODS

Twenty-seven people who met the criteria for either Diagnostic and Statistical Manual of Mental Disorders, 5th Edition, schizophrenia or schizoaffective disorder were entered into a 10-day, double-blind, placebo-controlled, randomized clinical trial. The study was conducted on an inpatient unit to standardize the participant diet and environment. Participants were randomized to either OEI (4 g, 3 times a day) or a placebo (4 g of maltodextrin, 3 times a day). In order to assess the effect of OEI treatment on butyrate levels, participants underwent pretreatment and posttreatment OEI challenges. The primary outcome measure was relative change in postchallenge plasma butyrate levels after 10 days of OEI treatment.

RESULTS

In both the intent-to-treat and completer analyses, OEI treatment was associated with a greater number of participants who met the OEI challenge responder criteria than those treated with placebo. OEI treatment was also associated with an increase in baseline butyrate levels (effect size for the group difference in the change of baseline butyrate levels was 0.58).

CONCLUSIONS

We were able to demonstrate that treatment with the prebiotic OEI selectively increased the level of plasma butyrate in people with schizophrenia.Trial registration:ClinicalTrials.gov identifier NCT03617783.

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.

Altered gut microbiota and systemic immunity in Chinese patients with schizophrenia comorbid with metabolic syndrome

BACKGROUND

Metabolic syndrome (MetS) is highly prevalent in individuals with schizophrenia (SZ), leading to negative consequences like premature mortality. Gut dysbiosis, which refers to an imbalance of the microbiota, and chronic inflammation are associated with both SZ and MetS. However, the relationship between gut dysbiosis, host immunological dysfunction, and SZ comorbid with MetS (SZ-MetS) remains unclear. This study aims to explore alterations in gut microbiota and their correlation with immune dysfunction in SZ-MetS, offering new insights into its pathogenesis.

METHODS AND RESULTS

We enrolled 114 Chinese patients with SZ-MetS and 111 age-matched healthy controls from Zhejiang, China, to investigate fecal microbiota using Illumina MiSeq sequencing targeting 16 S rRNA gene V3-V4 hypervariable regions. Host immune responses were assessed using the Bio-Plex Pro Human Cytokine 27-Plex Assay to examine cytokine profiles. In SZ-MetS, we observed decreased bacterial α-diversity and significant differences in β-diversity. LEfSe analysis identified enriched acetate-producing genera (Megamonas and Lactobacillus), and decreased butyrate-producing bacteria (Subdoligranulum, and Faecalibacterium) in SZ-MetS. These altered genera correlated with body mass index, the severity of symptoms (as measured by the Scale for Assessment of Positive Symptoms and Scale for Assessment of Negative Symptoms), and triglyceride levels. Altered bacterial metabolic pathways related to lipopolysaccharide biosynthesis, lipid metabolism, and various amino acid metabolism were also found. Additionally, SZ-MetS exhibited immunological dysfunction with increased pro-inflammatory cytokines, which correlated with the differential genera.

CONCLUSION

These findings suggested that gut microbiota dysbiosis and immune dysfunction play a vital role in SZ-MetS development, highlighting potential therapeutic approaches targeting the gut microbiota. While these therapies show promise, further mechanistic studies are needed to fully understand their efficacy and safety before clinical implementation.

Investigating the Impacts of Diet, Supplementation, Microbiota, Gut-Brain Axis on Schizophrenia: A Narrative Review

Schizophrenia is a disease with a complex etiology that significantly impairs the functioning of patients. In recent years, there has been increasing focus on the importance of the gut microbiota in the context of the gut-brain axis. In our study, we analyzed data on the gut-brain axis in relation to schizophrenia, as well as the impacts of eating habits, the use of various supplements, and diets on schizophrenia. Additionally, the study investigated the impact of antipsychotics on the development of metabolic disorders, such as diabetes, dyslipidemia, and obesity. There may be significant clinical benefits to be gained from therapies supported by supplements such as omega-3 fatty acids, B vitamins, and probiotics. The results suggest the need for a holistic approach to the treatment of schizophrenia, incorporating both drug therapy and dietary interventions.

Association of gut dysbiosis with first‑episode psychosis (Review)

The gut‑microbiota‑brain axis is a complex bidirectional communication system linking the gastrointestinal tract to the brain. Changes in the balance, composition and diversity of the gut‑microbiota (gut dysbiosis) have been found to be associated with the development of psychosis. Early‑life stress, along with various stressors encountered in different developmental phases, have been shown to be associated with the abnormal composition of the gut microbiota, leading to irregular immunological and neuroendocrine functions, which are potentially responsible for the occurrence of first‑episode psychosis (FEP). The aim of the present narrative review was to summarize the significant differences of the altered microbiome composition in patients suffering from FEP vs. healthy controls, and to discuss its effects on the occurrence and intensity of symptoms in FEP.

Microbiota-brain axis: Exploring the role of gut microbiota in psychiatric disorders - A comprehensive review

Mental illness is a hidden epidemic in modern science that has gradually spread worldwide. According to estimates from the World Health Organization (WHO), approximately 10% of the world's population suffers from various mental diseases each year. Worldwide, financial and health burdens on society are increasing annually. Therefore, understanding the different factors that can influence mental illness is required to formulate novel and effective treatments and interventions to combat mental illness. Gut microbiota, consisting of diverse microbial communities residing in the gastrointestinal tract, exert profound effects on the central nervous system through the gut-brain axis. The gut-brain axis serves as a conduit for bidirectional communication between the two systems, enabling the gut microbiota to affect emotional and cognitive functions. Dysbiosis, or an imbalance in the gut microbiota, is associated with an increased susceptibility to mental health disorders and psychiatric illnesses. Gut microbiota is one of the most diverse and abundant groups of microbes that have been found to interact with the central nervous system and play important physiological functions in the human gut, thus greatly affecting the development of mental illnesses. The interaction between gut microbiota and mental health-related illnesses is a multifaceted and promising field of study. This review explores the mechanisms by which gut microbiota influences mental health, encompassing the modulation of neurotransmitter production, neuroinflammation, and integrity of the gut barrier. In addition, it emphasizes a thorough understanding of how the gut microbiome affects various psychiatric conditions.

Gut microbiota signatures of vulnerability to food addiction in mice and humans

OBJECTIVE

Food addiction is a multifactorial disorder characterised by a loss of control over food intake that may promote obesity and alter gut microbiota composition. We have investigated the potential involvement of the gut microbiota in the mechanisms underlying food addiction.

DESIGN

We used the Yale Food Addiction Scale (YFAS) 2.0 criteria to classify extreme food addiction in mouse and human subpopulations to identify gut microbiota signatures associated with vulnerability to this disorder.

RESULTS

Both animal and human cohorts showed important similarities in the gut microbiota signatures linked to food addiction. The signatures suggested possible non-beneficial effects of bacteria belonging to the Proteobacteria phylum and potential protective effects of Actinobacteria against the development of food addiction in both cohorts of humans and mice. A decreased relative abundance of the species Blautia wexlerae was observed in addicted humans and of Blautia genus in addicted mice. Administration of the non-digestible carbohydrates, lactulose and rhamnose, known to favour Blautia growth, led to increased relative abundance of Blautia in mice faeces in parallel with dramatic improvements in food addiction. A similar improvement was revealed after oral administration of Blautia wexlerae as a beneficial microbe.

CONCLUSION

By understanding the crosstalk between this behavioural alteration and gut microbiota, these findings constitute a step forward to future treatments for food addiction and related eating disorders.

16S rRNA gene sequencing reveals altered gut microbiota in young adults with schizophrenia and prominent negative symptoms

BACKGROUND

Gut dysbiosis has been established as a characteristic of schizophrenia (SCH). However, the signatures regarding SCH patients with prominent negative symptoms (SCH-N) in young adults have been poorly elucidated.

METHODS

Stool samples were obtained from 30 young adults with SCH-N, 32 SCH patients with prominent positive symptoms (SCH-P) along with 36 healthy controls (HCs). Microbial diversity and composition were analyzed by 16S rRNA gene sequencing. Meanwhile, psychiatric symptoms were assessed by the positive and negative syndrome scale (PANSS).

RESULTS

There is a significant difference in β-diversity but not α-diversity indexes among the three groups. Moreover, we found a higher abundance of Fusobacteria and Proteobacteria phyla and a lower abundance of Firmicutes phyla in SCH-N when compared with HC. Besides, we identified a diagnostic potential panel comprising six genera (Coprococcus, Monoglobus, Prevotellaceae_NK3B31_group, Escherichia-Shigella, Dorea, and Butyricicoccus) that can distinguish SCH-N from HC (area under the curve = 0.939). However, the difference in microbial composition between the SCH-N and SCH-P is much less than that between SCH-N and the HC, and SCH-N and SCH-P cannot be effectively distinguished by gut microbiota.

CONCLUSION

The composition of gut microbiota was changed in the patients with SCH-N, which may help in further understanding of pathogenesis in young adults with SCH-N.

The relationship between the gut microbiota and oxidative stress in the cognitive function of schizophrenia: A pilot study in China

Cognitive impairment is a core symptom of schizophrenia. The gut microbiota (GM) and oxidative stress may play important roles in the pathophysiological mechanisms of cognitive impairment. This study aimed to explore the relationship between GM and oxidative stress in the cognitive function of schizophrenia. GM obtained by 16S RNA sequencing and serum superoxide dismutase (SOD) levels from schizophrenia patients (N = 68) and healthy controls (HCs, N = 72) were analyzed. All psychiatric symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS). Cognitive function was assessed using the MATRICS Consensus Cognitive Battery (MCCB). Correlation analysis was used to explore the relationship between GM, SOD, and cognitive function. Machine learning models were used to identify potential biomarkers. Compared to HCs, the relative abundances of Collinsella, undefined Ruminococcus, Lactobacillus, Eubacterium, Mogibacterium, Desulfovibrio, Bulleidia, Succinivibrio, Corynebacterium, and Atopobium were higher in patients with schizophrenia, but Faecalibacterium, Anaerostipes, Turicibacter, and Ruminococcus were lower. In patients with schizophrenia, the positive factor, general factor, and total score of MCCB positively correlated with Lactobacillus, Collinsella, and Lactobacillus, respectively; SOD negatively correlated with Eubacterium, Collinsella, Lactobacillus, Corynebacterium, Bulleidia, Mogibacterium, and Succinivibrio, but positively correlated with Faecalibacterium, Ruminococcus, and MCCB verbal learning index scores; Faecalibacterium and Turicibacter were positively correlated with MCCB visual learning index scores and speed of processing index scores, respectively. Our findings revealed a correlation between SOD and GM and confirmed that cognitive dysfunction in patients with schizophrenia involves abnormal SOD levels and GM changes.

An Innovative Probiotic-Based Supplement to Mitigate Molecular Factors Connected to Depression and Anxiety: An In Vitro Study

The gut-brain axis is a bidirectional relationship between the microbiota and the brain; genes related to the brain and gut synaptic formation are similar. Research on the causal effects of gut microbiota on human behavior, brain development, and function, as well as the underlying molecular processes, has emerged in recent decades. Probiotics have been shown in several trials to help reduce anxiety and depressive symptoms. Because of this, probiotic combinations have been tested in in vitro models to see whether they might modulate the gut and alleviate depression and anxiety. Therefore, we sought to determine whether a novel formulation might affect the pathways controlling anxiety and depression states and alter gut barrier activities in a 3D model without having harmful side effects. Our findings indicate that B. bifidum novaBBF7 10 mg/mL, B. longum novaBLG2 5 mg/mL, and L. paracasei TJB8 10 mg/mL may influence the intestinal barrier and enhance the synthesis of short-chain fatty acids. Additionally, the probiotics studied did not cause neuronal damage and, in combination, exert a protective effect against the condition of anxiety and depression triggered by L-Glutamate. All these findings show that probiotics can affect gut function to alter the pathways underlying anxiety and depression.

Approach to the diagnosis and management of dysbiosis

All microorganisms like bacteria, viruses and fungi that reside within a host environment are considered a microbiome. The number of bacteria almost equal that of human cells, however, the genome of these bacteria may be almost 100 times larger than the human genome. Every aspect of the physiology and health can be influenced by the microbiome living in various parts of our body. Any imbalance in the microbiome composition or function is seen as dysbiosis. Different types of dysbiosis are seen and the corresponding symptoms depend on the site of microbial imbalance. The contribution of the intestinal and extra-intestinal microbiota to influence systemic activities is through interplay between different axes. Whole body dysbiosis is a complex process involving gut microbiome and non-gut related microbiome. It is still at the stage of infancy and has not yet been fully understood. Dysbiosis can be influenced by genetic factors, lifestyle habits, diet including ultra-processed foods and food additives, as well as medications. Dysbiosis has been associated with many systemic diseases and cannot be diagnosed through standard blood tests or investigations. Microbiota derived metabolites can be analyzed and can be useful in the management of dysbiosis. Whole body dysbiosis can be addressed by altering lifestyle factors, proper diet and microbial modulation. The effect of these interventions in humans depends on the beneficial microbiome alteration mostly based on animal studies with evolving evidence from human studies. There is tremendous potential for the human microbiome in the diagnosis, treatment, and prognosis of diseases, as well as, for the monitoring of health and disease in humans. Whole body system-based approach to the diagnosis of dysbiosis is better than a pure taxonomic approach. Whole body dysbiosis could be a new therapeutic target in the management of various health conditions.

The emerging roles of microbiota-derived extracellular vesicles in psychiatric disorders

Major depressive disorder, schizophrenia, and bipolar disorder are three major psychiatric disorders that significantly impact the well-being and overall health of patients. Some researches indicate that abnormalities in the gut microbiota can trigger certain psychiatric diseases. Microbiota-derived extracellular vesicles have the ability to transfer bioactive compounds into host cells, altering signaling and biological processes, ultimately influencing the mental health and illness of the host. This review aims to investigate the emerging roles of microbiota-derived extracellular vesicles in these three major psychiatric disorders and discusses their roles as diagnostic biomarkers and therapies for these psychiatric disorders.

Transplantation of gut microbiota derived from patients with schizophrenia induces schizophrenia-like behaviors and dysregulated brain transcript response in mice

Schizophrenia (SCZ), as a neurodevelopmental disorder and devastating disease, affects approximately 1% of the world population. Although numerous studies have attempted to elucidate the causes of SCZ occurrence, it is not clearly understood. Recently, the emerging roles of the gut microbiota in a range of brain disorders, including SCZ, have attracted much attention. While the molecular mechanism of gut microbiota in regulating the pathogenesis of SCZ is still lacking. Here, we first confirmed the difference of gut microbiome between SCZ patients and healthy controls, and then, we performed fecal microbiota transplantation (FMT) to clarify the roles of SCZ patients-derived microbiota in a specific pathogen free (SPF) mice model. 16 S rDNA sequencing confirmed that a significant difference of gut microbiome was present between two groups of FMT mice, which has a similar trend with the above human gut microbiome. Furthermore, we found that transplantation of fecal microbiota from SCZ patients into SPF mice was sufficient to induce schizophrenia-like (SCZ-like) symptoms, such as deficits in sociability and hyperactivity. Furthermore, the brains of mice colonized with SCZ microbiota displayed dysregulated transcript response and alternative splicing of SCZ-relevant genes. Moreover, 10 key genes were identified to be correlated with SCZ by an integrative transcriptome data analysis. Finally, 4 key genes were identified to be correlated with the 12 differential genera between two groups of FMT mice. Our results thus demonstrated that the gut microbiome might modify the transcriptomic profile in the brain, thereby modulating social behavior, and our present study can help better understand the link between gut microbiota and SCZ pathogenesis through the gut-brain axis.

Neuroinflammation and Schizophrenia: New Therapeutic Strategies through Psychobiotics, Nanotechnology, and Artificial Intelligence (AI)

The prevalence of schizophrenia, affecting approximately 1% of the global population, underscores the urgency for innovative therapeutic strategies. Recent insights into the role of neuroinflammation, the gut-brain axis, and the microbiota in schizophrenia pathogenesis have paved the way for the exploration of psychobiotics as a novel treatment avenue. These interventions, targeting the gut microbiome, offer a promising approach to ameliorating psychiatric symptoms. Furthermore, advancements in artificial intelligence and nanotechnology are set to revolutionize psychobiotic development and application, promising to enhance their production, precision, and effectiveness. This interdisciplinary approach heralds a new era in schizophrenia management, potentially transforming patient outcomes and offering a beacon of hope for those afflicted by this complex disorder.

Alterations of the gut microbiota in patients with schizophrenia

Introduction

Schizophrenia is a complex psychiatric disorder, of which molecular pathogenesis remains largely unknown. Accumulating evidence suggest that gut microbiota may affect brain function via the complex gut-brain axis, which may be a potential contributor to schizophrenia. However, the alteration of gut microbiota showed high heterogeneity across different studies. Therefore, this study aims to identify the consistently altered gut microbial taxa associated with schizophrenia.

Methods

We conducted a systematic search and synthesis of the up-to-date human gut microbiome studies on schizophrenia, and performed vote counting analyses to identify consistently changed microbiota. Further, we investigated the effects of potential confounders on the alteration of gut microbiota.

Results

We obtained 30 available clinical studies, and found that there was no strong evidence to support significant differences in α-diversity and β-diversity between schizophrenic patients and healthy controls. Among 428 differential gut microbial taxa collected from original studies, we found that 8 gut microbial taxa were consistently up-regulated in schizophrenic patients, including Proteobacteria, Gammaproteobacteria, Lactobacillaceae, Enterobacteriaceae, Lactobacillus, Succinivibrio, Prevotella and Acidaminococcus. While 5 taxa were consistently down-regulated in schizophrenia, including Fusicatenibacter, Faecalibacterium, Roseburia, Coprococcus and Anaerostipes.

Discussion

These findings suggested that gut microbial changes in patients with schizophrenia were characterized by the depletion of anti-inflammatory butyrate-producing genera, and the enrichment of certain opportunistic bacteria genera and probiotics. This study contributes to further understanding the role of gut microbiota in schizophrenia, and developing microbiota-based diagnosis and therapy for schizophrenia.

The Gut Microbiome and Mental Health

The gut microbiome has been well researched in the past few years and may be a target for treating mental illness. Trillions of bacteria in the digestive system work with the brain, immune function, and endocrine pathways. This gut microbiome ecosystem mediates the interaction between the human being and the environment making its inclusion in holistic nursing essential. Changes in normal balance of the gut microbiome occur with diet, antibiotics and other medications, stress, cancer treatment, geography and environment, and current illnesses. When the microbiome is challenged a "dysbiotic" state leads to inadequate production of needed neurotransmitters such as serotonin and dopamine. Research has shown links between the dysbiosis, and the inflammatory response system that are known to contribute to depression, anxiety, and schizophrenia. Understanding the role of the gut microbiome can be beneficial to holistic nurses, providing a new tool to prevent, treat, or reduce symptoms of mental illness and improve general immune function. This innocuous holistic approach to mental wellness is becoming an important evidenced-based approach.

Associations of the Gut Microbiome With Treatment Resistance in Schizophrenia

Importance

There is growing interest in the role of gut microbiome composition in schizophrenia. However, lifestyle factors are often neglected, and few studies have investigated microbiome composition in treatment-resistant schizophrenia.

Objective

To explore associations between the gut microbiome and schizophrenia diagnosis, treatment resistance, clozapine response, and treatment-related adverse effects while adjusting for demographic and lifestyle factors.

Design, Setting, and Participants

In this case-control study of adults aged 20 to 63 years, stool samples and data on demographic characteristics, lifestyle, and medication use were collected and gut microbiome measures obtained using shotgun metagenomics. Participants with a schizophrenia diagnosis were referred through psychiatric inpatient units and outpatient clinics. Data were collected for 4 distinct groups: control individuals without a psychiatric diagnosis (past or present), individuals with treatment-responsive schizophrenia taking nonclozapine antipsychotic medications, clozapine-responsive individuals with treatment-resistant schizophrenia, and clozapine-nonresponsive individuals with treatment-resistant schizophrenia. Participants were recruited between November 2020 and November 2021. Control individuals were recruited in parallel through posters and online advertisements and matched for age, sex, and body mass index (BMI) to the individuals with schizophrenia. Participants were excluded if taking antibiotics in the past 2 months, if unable to communicate in English or otherwise follow study instructions, were pregnant or planning to become pregnant, or had any concomitant disease or condition making them unsuited to the study per investigator assessment. Data were analyzed from January 2022 to March 2023.

Main Outcomes and Measures

Omics relationship matrices, α and β diversity, and relative abundance of microbiome features.

Results

Data were collected for 97 individuals (71 [74%] male; mean [SD] age, 40.4 [10.3] years; mean [SD] BMI, 32.8 [7.4], calculated as weight in kilograms divided by height in meters squared). Significant microbiome associations with schizophrenia were observed at multiple taxonomic and functional levels (eg, common species: b2, 30%; SE, 13%; adjusted P = .002) and treatment resistance (eg, common species: b2, 27%; SE, 16%; adjusted P = .03). In contrast, limited evidence was found for microbiome associations with clozapine response, constipation, or metabolic syndrome. Significantly decreased microbial richness was found in individuals with schizophrenia compared to control individuals (t95 = 4.25; P < .001; mean [SD] for control individuals, 151.8 [32.31]; mean [SD] for individuals with schizophrenia, 117.00 [36.2]; 95% CI, 18.6-51.0), which remained significant after a covariate and multiple comparison correction. However, limited evidence was found for differences in β diversity (weighted UniFrac) for schizophrenia diagnosis (permutational multivariate analysis of variance [PERMANOVA]: R2, 0.03; P = .02), treatment resistance (R2, 0.02; P = .18), or clozapine response (R2, 0.04; P = .08). Multiple differentially abundant bacterial species (19) and metabolic pathways (162) were found in individuals with schizophrenia, which were primarily associated with treatment resistance and clozapine exposure.

Conclusions and Relevance

The findings in this study are consistent with the idea that clozapine induces alterations to gut microbiome composition, although the possibility that preexisting microbiome differences contribute to treatment resistance cannot be ruled out. These findings suggest that prior reports of microbiome alterations in individuals with chronic schizophrenia may be due to medication or lifestyle factors and that future studies should incorporate these variables in their design and interpretation.

Probiotic, prebiotic, synbiotic and fermented food supplementation in psychiatric disorders: A systematic review of clinical trials

The use of probiotics, prebiotics, synbiotics or fermented foods can modulate the gut-brain axis and constitute a potentially therapeutic intervention in psychiatric disorders. This systematic review aims to identify current evidence regarding these interventions in the treatment of patients with DSM/ICD psychiatric diagnoses. Forty-seven articles from 42 studies met the inclusion criteria. Risk of bias was assessed in all included studies. Major depression was the most studied disorder (n = 19 studies). Studies frequently focused on schizophrenia (n = 11) and bipolar disorder (n = 5) and there were limited studies in anorexia nervosa (n = 4), ADHD (n = 3), Tourette (n = 1), insomnia (n = 1), PTSD (n = 1) and generalized anxiety disorder (n = 1). Except in MDD, current evidence does not clarify the role of probiotics and prebiotics in the treatment of mental illness. Several studies point to an improvement in the immune and inflammatory profile (e.g. CRP, IL6), which may be a relevant mechanism of action of the therapeutic response identified in these studies. Future research should consider lifestyle and dietary habits of patients as possible confounders that may influence inter-individual treatment response.

Microbial composition, functionality, and stress resilience or susceptibility: unraveling sex-specific patterns

BACKGROUND

Following exposure to traumatic stress, women are twice as likely as men to develop mood disorders. Yet, individual responses to such stress vary, with some people developing stress-induced psychopathologies while others exhibit resilience. The factors influencing sex-related disparities in affective disorders as well as variations in resilience remain unclear; however, emerging evidence suggests differences in the gut microbiota play a role. In this study, using the single prolonged stress (SPS) model of post-traumatic stress disorder, we investigated pre- and post-existing differences in microbial composition, functionality, and metabolites that affect stress susceptibility or resilience in each sex.

METHODS

Male and female Sprague-Dawley rats were randomly assigned to control or SPS groups. Two weeks following SPS, the animals were exposed to a battery of behavioral tests and decapitated a day later. Based on their anxiety index, they were further categorized as SPS-resilient (SPS-R) or SPS-susceptible (SPS-S). On the day of dissection, cecum, and selected brain tissues were isolated. Stool samples were collected before and after SPS, whereas urine samples were taken before and 30 min into the SPS.

RESULTS

Before SPS exposure, the sympathoadrenal axis exhibited alterations within male subgroups only. Expression of tight junction protein claudin-5 was lower in brain of SPS-S males, but higher in SPS-R females following SPS. Across the study, alpha diversity remained consistently lower in males compared to females. Beta diversity revealed distinct separations between male and female susceptible groups before SPS, with this separation becoming evident in the resilient groups following SPS. At the genus level, Lactobacillus, Lachnospiraceae_Incertae_Sedis, and Barnesiella exhibited sex-specific alterations, displaying opposing abundances in each sex. Additionally, sex-specific changes were observed in microbial predictive functionality and targeted functional modules both before and after SPS. Alterations in the microbial short-chain fatty acids (SCFAs), were also observed, with major and minor SCFAs being lower in SPS-susceptible males whereas branched-chain SCFAs being higher in SPS-susceptible females.

CONCLUSION

This study highlights distinct pre- and post-trauma differences in microbial composition, functionality, and metabolites, associated with stress resilience in male and female rats. The findings underscore the importance of developing sex-specific therapeutic strategies to effectively address stress-related disorders. Highlights SPS model induces divergent anxiety and social behavioral responses to traumatic stress in both male and female rodents. SPS-resilient females displayed less anxiety-like behavior and initiated more interactions towards a juvenile rat than SPS-resilient males. Sex-specific pre-existing and SPS-induced differences in the gut microbial composition and predictive functionality were observed in susceptible and resilient rats. SPS-resilient males displayed elevated cecal acetate levels, whereas SPS-susceptible females exhibited heightened branched-chain SCFAs.

Dysregulation of Microbiota in Patients With First-Episode Psychosis Is Associated With Symptom Severity and Treatment Response

BACKGROUND

The gut microbiome has been implicated in the pathogenesis of mental disorders where the gut-brain axis acts as a bidirectional communication network.

METHODS

Herein, we investigated the compositional and functional differences of gut microbiome between patients with first-episode psychosis (FEP) (n = 26) and healthy control participants (n = 22) using whole-genome shotgun sequencing. In addition, we assessed the oral microbiome in patients with FEP (n = 13) and listed their taxonomic diversity.

RESULTS

Our findings suggest that there is a dysbiosis of gut microbiota in patients with FEP. Relative abundance of Bifidobacterium adolescentis, Prevotella copri, and Turicibacter sanguinis was markedly increased (linear discriminant analysis scores [log10] > 1, and Mann-Whitney U test; false discovery rate-adjusted p values < .05) in the FEP group compared with the healthy control participants. Pathway analysis indicated that several metabolic pathways, particularly deoxyribonucleotide biosynthesis, branched-chain amino acid biosynthesis, tricarboxylic acid cycle, and fatty acid elongation and biosynthesis, were dysregulated in the FEP group compared with the healthy control group. In addition, this preliminary study was able to identify specific gut microbes (at baseline) that were predictive of weight gain in the FEP group at a 1-year follow-up. Bacteroides dorei, Bifidobacterium adolescentis, Turicibacter sanguinis, Roseburia spp., and Ruminococcus lactaris were positively associated (eXtreme gradient boosting, XGBoost regression model, Shapley additive explanations, R2 = 0.82) with weight gain.

CONCLUSIONS

Our findings may suggest the involvement of gut microbiota in the pathogenesis of psychosis. The benefit of modulation of the gut microbiome in the treatment of psychotic disorders should be explored further.

Scrutinizing microbiome determinism: why deterministic hypotheses about the microbiome are conceptually ungrounded

This paper addresses the topic of determinism in contemporary microbiome research. I distinguish two types of deterministic claims about the microbiome, and I show evidence that both types of claims are present in the contemporary literature. First, the idea that the host genetics determines the composition of the microbiome which I call "host-microbiome determinism". Second, the idea that the genetics of the holobiont (the individual unit composed by a host plus its microbiome) determines the expression of certain phenotypic traits, which I call "microbiome-phenotype determinism". Drawing on the stability of traits conception of individuality (Suárez in Hist Philos Life Sci 42:11, 2020) I argue that none of these deterministic hypotheses is grounded on our current knowledge of how the holobiont is transgenerationally assembled, nor how it expresses its phenotypic traits.

Gut microbial diversity moderates polygenic risk of schizophrenia

Background

Schizophrenia (SCZ) is a heritable disorder with a polygenic architecture, and the gut microbiota seems to be involved in its development and outcome. In this study, we investigate the interplay between genetic risk and gut microbial markers.

Methods

We included 159 first-episode, drug-naïve SCZ patients and 86 healthy controls. The microbial composition of feces was characterized using the 16S rRNA sequencing platform, and five microbial α-diversity indices were estimated [Shannon, Simpson, Chao1, the Abundance-based Eoverage Estimator (ACE), and a phylogenetic diversity-based estimate (PD)]. Polygenic risk scores (PRS) for SCZ were constructed using data from large-scale genome-wide association studies. Effects of microbial α-diversity, microbial abundance, and PRS on SCZ were evaluated via generalized linear models.

Results

We confirmed that PRS was associated with SCZ (OR = 2.08, p = 1.22×10-5) and that scores on the Shannon (OR = 0.29, p = 1.15×10-8) and Simpson (OR = 0.29, p = 1.25×10-8) indices were inversely associated with SCZ risk. We found significant interactions (p < 0.05) between PRS and α-diversity indices (Shannon, Simpson, and PD), with the effects of PRS being larger in those exhibiting higher diversity compared to those with lower diversity. Moreover, the PRS effects were larger in individuals with a high abundance of the genera Romboutsia, Streptococcus, and Anaerostipes than in those with low abundance (p < 0.05). All three of these genera showed protective effects against SCZ.

Conclusion

The current findings suggest an interplay between the gut microbiota and polygenic risk of SCZ that warrants replication in independent samples. Experimental studies are needed to determine the underpinning mechanisms.

Mendelian randomization study revealed a gut microbiota-neuromuscular junction axis in myasthenia gravis

A growing number of studies have implicated that gut microbiota abundance is associated with myasthenia gravis (MG). However, the causal relationship underlying the associations is still unclear. Here, we aim to investigate the causal effect of gut microbiota on MG using Mendelian randomization (MR) method. Publicly available Genome-wide association study (GWAS) summary-level data for gut microbiota and for MG were extracted. Inverse variance weighted was used as the main method to analyze causality. The robustness of the results was validated with sensitivity analyses. Our results indicated that genetically predicted increased phylum Lentisphaerae (OR = 1.319, p = 0.026), class Lentisphaerae (OR = 1.306, p = 0.044), order Victivallales (OR = 1.306, p = 0.044), order Mollicutes (OR = 1.424, p = 0.041), and genus Faecalibacterium (OR = 1.763, p = 0.002) were potentially associated with a higher risk of MG; while phylum Actinobacteria (OR = 0.602, p = 0.0124), class Gammaproteobacteria (OR = 0.587, p = 0.036), family Defluviitaleaceae (OR = 0.695, p = 0.047), family Peptococcaceae (OR = 0.698, p = 0.029), and family Family XIII (OR = 0.614, p = 0.017) were related to a lower risk of MG. The present study provides genetic evidence for the causal associations between gut microbiota and MG, thus suggesting novel insights into the gut microbiota-neuromuscular junction axis in the pathogenesis of MG.

Relationships among the gut microbiome, brain networks, and symptom severity in schizophrenia patients: A mediation analysis

The microbiome-gut-brain axis (MGBA) plays a critical role in schizophrenia (SZ). However, the underlying mechanisms of the interactions among the gut microbiome, brain networks, and symptom severity in SZ patients remain largely unknown. Fecal samples, structural and functional magnetic resonance imaging (MRI) data, and Positive and Negative Syndrome Scale (PANSS) scores were collected from 38 SZ patients and 38 normal controls, respectively. The data of 16S rRNA gene sequencing were used to analyze the abundance of gut microbiome and the analysis of human brain networks was applied to compute the nodal properties of 90 brain regions. A total of 1,691,280 mediation models were constructed based on 261 gut bacterial, 810 nodal properties, and 4 PANSS scores in SZ patients. A strong correlation between the gut microbiome and brain networks (r = 0.89, false discovery rate (FDR) -corrected p < 0.05) was identified. Importantly, the PANSS scores were linearly correlated with both the gut microbiome (r = 0.5, FDR-corrected p < 0.05) and brain networks (r = 0.59, FDR-corrected p < 0.05). The abundance of genus Sellimonas significantly affected the PANSS negative scores of SZ patients via the betweenness centrality of white matter networks in the inferior frontal gyrus and amygdala. Moreover, 19 significant mediation models demonstrated that the nodal properties of 7 brain regions, predominately from the systems of visual, language, and control of action, showed significant mediating effects on the PANSS scores with the gut microbiome as mediators. Together, our findings indicated the tripartite relationships among the gut microbiome, brain networks, and PANSS scores and suggested their potential role in the neuropathology of SZ.

An updated overview on the relationship between human gut microbiome dysbiosis and psychiatric and psychological disorders

There is a lot of evidence establishing that nervous system development is related to the composition and functions of the gut microbiome. In addition, the central nervous system (CNS) controls the imbalance of the intestinal microbiota, constituting a bidirectional communication system. At present, various gut-brain crosstalk routes have been described, including immune, endocrine and neural circuits via the vagal pathway. Several empirical data have associated gut microbiota alterations (dysbiosis) with neuropsychiatric diseases, such as Alzheimer's disease, autism and Parkinson's disease, and with other psychological disorders, like anxiety and depression. Fecal microbiota transplantation (FMT) therapy has shown that the gut microbiota can transfer behavioral features to recipient animals, which provides strong evidence to establish a causal-effect relationship. Interventions, based on prebiotics, probiotics or synbiotics, have demonstrated an important influence of microbiota on neurological disorders by the synthesis of neuroactive compounds that interact with the nervous system and by the regulation of inflammatory and endocrine processes. Further research is needed to demonstrate the influence of gut microbiota dysbiosis on psychiatric and psychological disorders, and how microbiota-based interventions may be used as potential therapeutic tools.

The importance of the gut microbiome and its signals for a healthy nervous system and the multifaceted mechanisms of neuropsychiatric disorders

Increasing evidence links the gut microbiome and the nervous system in health and disease. This narrative review discusses current views on the interaction between the gut microbiota, the intestinal epithelium, and the brain, and provides an overview of the communication routes and signals of the bidirectional interactions between gut microbiota and the brain, including circulatory, immunological, neuroanatomical, and neuroendocrine pathways. Similarities and differences in healthy gut microbiota in humans and mice exist that are relevant for the translational gap between non-human model systems and patients. There is an increasing spectrum of metabolites and neurotransmitters that are released and/or modulated by the gut microbiota in both homeostatic and pathological conditions. Dysbiotic disruptions occur as consequences of critical illnesses such as cancer, cardiovascular and chronic kidney disease but also neurological, mental, and pain disorders, as well as ischemic and traumatic brain injury. Changes in the gut microbiota (dysbiosis) and a concomitant imbalance in the release of mediators may be cause or consequence of diseases of the central nervous system and are increasingly emerging as critical links to the disruption of healthy physiological function, alterations in nutrition intake, exposure to hypoxic conditions and others, observed in brain disorders. Despite the generally accepted importance of the gut microbiome, the bidirectional communication routes between brain and gut are not fully understood. Elucidating these routes and signaling pathways in more detail offers novel mechanistic insight into the pathophysiology and multifaceted aspects of brain disorders.

Causal effects of gut microbiota on sepsis and sepsis-related death: insights from genome-wide Mendelian randomization, single-cell RNA, bulk RNA sequencing, and network pharmacology

BACKGROUND

Gut microbiota alterations have been implicated in sepsis and related infectious diseases, but the causal relationship and underlying mechanisms remain unclear.

METHODS

We evaluated the association between gut microbiota composition and sepsis using two-sample Mendelian randomization (MR) analysis based on published genome-wide association study (GWAS) summary statistics. Sensitivity analyses were conducted to validate the robustness of the results. Reverse MR analysis and integration of GWAS and expression quantitative trait loci (eQTL) data were performed to identify potential genes and therapeutic targets.

RESULTS

Our analysis identified 11 causal bacterial taxa associated with sepsis, with increased abundance of six taxa showing positive causal relationships. Ten taxa had causal effects on the 28-day survival outcome of septic patients, with increased abundance of six taxa showing positive associations. Sensitivity analyses confirmed the robustness of these associations. Reverse MR analysis did not provide evidence of reverse causality. Integration of GWAS and eQTL data revealed 76 genes passing the summary data-based Mendelian randomization (SMR) test. Differential expression of these genes was observed between sepsis patients and healthy individuals. These genes represent potential therapeutic targets for sepsis. Molecular docking analysis predicted potential drug-target interactions, further supporting their therapeutic potential.

CONCLUSION

Our study provides insights for the development of personalized treatment strategies for sepsis and offers preliminary candidate targets and drugs for future drug development.

Characteristics of gut microbiota and metabolic phenotype in patients with major depressive disorder based on multi-omics analysis

Depression is a chronic, relapsing mental illness, often accompanied by loss of appetite, increased fatigue, insomnia and poor concentration. Here, we performed serum and urine metabolomics and fecal 16S rDNA sequencing studies on 57 unmedicated patients with major depressive disorder (MDD) and 57 healthy controls to characterize the metabolic and flora profile of MDD patients. We observed significant differences in serum and urinary metabolome between MDD patients and healthy individuals. Specifically, glycerophospholipid metabolism, primary bile acid biosynthesis and linoleic acid metabolism were significantly disordered in serum, and aminoacyl-tRNA biosynthesis, arginine biosynthesis, purine metabolism, phenylalanine metabolism, alanine, aspartate and glutamate metabolism, and pyrimidine metabolism were significantly impaired in urine. On this basis, we identified four potential diagnostic biomarkers for carnitine and four fatty acid classes in serum and urine, respectively. In addition, we observed significant disturbances of the gut microbiota in MDD patients. Spearman correlation analysis showed that imbalances in the gut microbiota were associated with metabolic disturbances, suggesting an important role of the gut microbiota in the pathogenesis of MDD. Our study provides a theoretical basis for further understanding of the pathogenesis of depression and for future clinical diagnosis and screening, as well as a basis for targeting the gut flora to optimize its structure for the prevention and treatment of depression.

Our Mental Health Is Determined by an Intrinsic Interplay between the Central Nervous System, Enteric Nerves, and Gut Microbiota

Bacteria in the gut microbiome play an intrinsic part in immune activation, intestinal permeability, enteric reflex, and entero-endocrine signaling. The gut microbiota communicates with the central nervous system (CNS) through the production of bile acids, short-chain fatty acids (SCFAs), glutamate (Glu), γ-aminobutyric acid (GABA), dopamine (DA), norepinephrine (NE), serotonin (5-HT), and histamine. A vast number of signals generated in the gastrointestinal tract (GIT) reach the brain via afferent fibers of the vagus nerve (VN). Signals from the CNS are returned to entero-epithelial cells (EES) via efferent VN fibers and communicate with 100 to 500 million neurons in the submucosa and myenteric plexus of the gut wall, which is referred to as the enteric nervous system (ENS). Intercommunications between the gut and CNS regulate mood, cognitive behavior, and neuropsychiatric disorders such as autism, depression, and schizophrenia. The modulation, development, and renewal of nerves in the ENS and changes in the gut microbiome alter the synthesis and degradation of neurotransmitters, ultimately influencing our mental health. The more we decipher the gut microbiome and understand its effect on neurotransmission, the closer we may get to developing novel therapeutic and psychobiotic compounds to improve cognitive functions and prevent mental disorders. In this review, the intricate control of entero-endocrine signaling and immune responses that keep the gut microbiome in a balanced state, and the influence that changing gut bacteria have on neuropsychiatric disorders, are discussed.

A Pilot Interaction Analysis of Gut Microbiota and Peripheral Markers of Aging in Severe Psychiatric Disorders: A Role for Lachnoclostridium?

Excessive predominance of pathological species in the gut microbiota could increase the production of inflammatory mediators at the gut level and, via modification of the gut-blood barrier, at the systemic level. This pro-inflammatory state could, in turn, increase biological aging that is generally proxied by telomere shortening. In this study, we present findings from a secondary interaction analysis of gut microbiota, aging, and inflammatory marker data from a cohort of patients with different diagnoses of severe mental disorders. We analyzed 15 controls, 35 patients with schizophrenia (SCZ), and 31 patients with major depressive disorder (MDD) recruited among those attending a community mental health center (50 males and 31 females, mean and median age 46.8 and 46.3 years, respectively). We performed 16S rRNA sequencing as well as measurement of telomere length via quantitative fluorescence in situ hybridization and high-sensitivity C-reactive protein. We applied statistical modeling with logistic regression to test for interaction between gut microbiota and these markers. Our results showed statistically significant interactions between telomere length and gut microbiota pointing to the genus Lachnostridium, which remained significantly associated with a reduced likelihood of MDD even after adjustment for a series of covariates. Although exploratory, these findings show that specific gut microbiota signatures overexpressing Lachnoclostridium and interacting with biological aging could modulate the liability for MDD.

Effects of low-frequency rTMS combined with risperidone on the gut microbiome in hospitalized patients with chronic schizophrenia

Repetitive transcranial magnetic stimulation (rTMS) has been widely used in treating schizophrenia (SCH). However, the effects of the low frequency of rTMS combined with antipsychotics on the gut microbiome in chronic SCH have been poorly investigated. In the present study, psychiatric symptoms were assessed and the stool samples obtained from 33 adult patients with chronic SCH (at baselinephase), 27 after 2 weeks of treatment (rTMS combined with risperidone, SCH-2W), and 37 healthy controls (HC) were analyzed by 16S rRNA gene sequencing. We found that the reduction of phylum Proteobacteria, family Enterobacteriaceae and genera Escherichia-Shigella as well as the increase of genera norank_f_Lachnospiraceae might be related to the antipsychotic effect of rTMS combined with risperidone. These findings indicate that the brain-gut-microbiota axis might be involved in the therapeutic effect of rTMS combined with antipsychotic drugs.

The Gut-Organ Axis within the Human Body: Gut Dysbiosis and the Role of Prebiotics

The human gut microbiota (GM) is a complex microbial ecosystem that colonises the gastrointestinal tract (GIT) and is comprised of bacteria, viruses, fungi, and protozoa. The GM has a symbiotic relationship with its host that is fundamental for body homeostasis. The GM is not limited to the scope of the GIT, but there are bidirectional interactions between the GM and other organs, highlighting the concept of the "gut-organ axis". Any deviation from the normal composition of the GM, termed "microbial dysbiosis", is implicated in the pathogenesis of various diseases. Only a few studies have demonstrated a relationship between GM modifications and disease phenotypes, and it is still unknown whether an altered GM contributes to a disease or simply reflects its status. Restoration of the GM with probiotics and prebiotics has been postulated, but evidence for the effects of prebiotics is limited. Prebiotics are substrates that are "selectively utilized by host microorganisms, conferring a health benefit". This study highlights the bidirectional relationship between the gut and vital human organs and demonstrates the relationship between GM dysbiosis and the emergence of certain representative diseases. Finally, this article focuses on the potential of prebiotics as a target therapy to manipulate the GM and presents the gaps in the literature and research.

Compositional and Functional Alterations in Intestinal Microbiota in Patients with Psychosis or Schizophrenia: A Systematic Review and Meta-analysis

BACKGROUND AND HYPOTHESIS

Intestinal microbiota is intrinsically linked to human health. Evidence suggests that the composition and function of the microbiome differs in those with schizophrenia compared with controls. It is not clear how these alterations functionally impact people with schizophrenia. We performed a systematic review and meta-analysis to combine and evaluate data on compositional and functional alterations in microbiota in patients with psychosis or schizophrenia.

STUDY DESIGN

Original studies involving humans and animals were included. The electronic databases PsycINFO, EMBASE, Web of Science, PubMed/MEDLINE, and Cochrane were systematically searched and quantitative analysis performed.

STUDY RESULTS

Sixteen original studies met inclusion criteria (1376 participants: 748 cases and 628 controls). Ten were included in the meta-analysis. Although observed species and Chao 1 show a decrease in diversity in people with schizophrenia compared with controls (SMD = -0.14 and -0.66 respectively), that did not reach statistical significance. We did not find evidence for variations in richness or evenness of microbiota between patients and controls overall. Differences in beta diversity and consistent patterns in microbial taxa were noted across studies. We found increases in Bifidobacterium, Lactobacillus, and Megasphaera in schizophrenia groups. Variations in brain structure, metabolic pathways, and symptom severity may be associated with compositional alterations in the microbiome. The heterogeneous design of studies complicates a similar evaluation of functional readouts.

CONCLUSIONS

The microbiome may play a role in the etiology and symptomatology of schizophrenia. Understanding how the implications of alterations in microbial genes for symptomatic expression and clinical outcomes may contribute to the development of microbiome targeted interventions for psychosis.

Ileal Dysbiosis Is Associated with Increased Acoustic Startle in the 22q11.2 Microdeletion Mouse Model of Schizophrenia

Recent studies involving transplantation of feces from schizophrenia (SCZ) patients and their healthy controls into germ-free mice have demonstrated that the gut microbiome plays a critical role in mediating SCZ-linked physiology and behavior. To date, only one animal model (a metabotropic glutamate receptor 5 knockout) of SCZ has been reported to recapitulate SCZ-linked gut dysbiosis. Since human 22q11.2 microdeletion syndrome is associated with increased risk of SCZ, we investigated whether the 22q11.2 microdeletion ("Q22") mouse model of SCZ exhibits both SCZ-linked behaviors and intestinal dysbiosis. We demonstrated that Q22 mice display increased acoustic startle response and ileal (but not colonic) dysbiosis, which may be due to the role of the ileum as an intestinal region with high immune and neuroimmune activity. We additionally identified a negative correlation between the abundance of a Streptococcus species in the ilea of Q22 mice and their acoustic startle response, providing early evidence of a gut-brain relationship in these mice. Given the translational relevance of this mouse model, our work suggests that Q22 mice could have considerable utility in preclinical research probing the relationship between gut dysbiosis and the gut-brain axis in the pathogenesis of SCZ.

Probiotics, Live Biotherapeutic Products (LBPs), and Gut-Brain Axis Related Psychological Conditions: Implications for Research and Dietetics

It is well-known that probiotics have key roles in the crosstalk between the gut and brain in terms of nutrition and health. However, when investigating their role in nutrition and health, it can be important to discriminate probiotics used as foods, food supplements, or drugs. For clarification of this terminology, the Food and Drug Administration (FDA) has established a new "live biotherapeutic products" (LBP) category, expressing pharmaceutical expectations and to reduce confusion in the literature. Growing evidence advises that the community of microorganisms found in the gut microbiota is associated with psychological conditions. Hence, it is thought that LBPs may positively affect depression, anxiety, bipolar disorder, and schizophrenia by reducing inflammation, improving gut microbiota, and balancing gut neurometabolites. This review focuses on the specific position of probiotics as LBPs in psychological conditions. Condition-specific potential pathways and mechanisms of LBPs and the prominent strains are discussed in the light of novel studies for future research, dietetic and pharmaceutical applications.

The Role of the Microbiome in First Episode of Psychosis

The relationship between the gut-brain-microbiome axis has gained great importance in the study of psychiatric disorders, as it may represent a new target for their treatment. To date, the available literature suggests that the microbiota may influence the pathophysiology of several diseases, including psychosis. The aim of this review is to summarize the clinical and preclinical studies that have evaluated the differences in microbiota as well as the metabolic consequences related to psychosis. Current data suggest that the genera Lactobacillus and Megasphaera are increased in schizophrenia (SZ), as well as alterations in the glutamate-glutamine-GABA cycle, serum levels of tryptophan, kynurenic acid (KYNA), and short-chain fatty acids (SCFAs). There are still very few studies on early-onset psychosis, thus more studies are needed to be able to propose targeted therapies for a point when the disease has just started or has not yet progressed.

Gut Microbiome Composition and Its Association with Sleep in Major Psychiatric Disorders

INTRODUCTION

Sleep disturbances are highly prevalent across most major psychiatric disorders. Alterations in the hypothalamic-pituitary-adrenal axis, neuroimmune mechanisms, and circadian rhythm disturbances partially explain this connection. The gut microbiome is also suspected to play a role in sleep regulation, and recent studies suggest that certain probiotics, prebiotics, synbiotics, and fecal microbiome transplantation can improve sleep quality.

METHODS

We aimed to assess the relationship between gut-microbiota composition, psychiatric disorders, and sleep quality in this cross-sectional, cross-disorder study. We recruited 103 participants, 63 patients with psychiatric disorders (major depressive disorder [n = 31], bipolar disorder [n = 13], psychotic disorder [n = 19]) along with 40 healthy controls. Sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI). The fecal microbiome was analyzed using 16S rRNA sequencing, and groups were compared based on alpha and beta diversity metrics, as well as differentially abundant species and genera.

RESULTS

A transdiagnostic decrease in alpha diversity and differences in beta diversity indices were observed in psychiatric patients, compared to controls. Correlation analysis of diversity metrics and PSQI score showed no significance in the patient and control groups. However, three species, Ellagibacter isourolithinifaciens, Senegalimassilia faecalis, and uncultured Blautia sp., and two genera, Senegalimassilia and uncultured Muribaculaceae genus, were differentially abundant in psychiatric patients with good sleep quality (PSQI >8), compared to poor-sleep quality patients (PSQI ≤8).

CONCLUSION

In conclusion, this study raises important questions about the interconnection of the gut microbiome and sleep disturbances.

When the microbiome helps the brain-current evidence

The gut microbiota-brain axis has been recognized as a network of connections that provides communication between the gut microflora and both central and autonomic nervous system. The gut microbiota alteration has been targeted for therapy in various neurodegenerative and psychiatric disbalances. Psychobiotics are probiotics that contribute beneficially to the brain function and the host mental health as a result of an interaction with the commensal gut bacteria, although their mechanism of action has not been completely revealed. In this state-of-art review, the findings about the potential therapeutic effects of the psychobiotics alone or in combination with conventional medicine in the treatment of neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease, as well as in some psychiatric diseases like depression, schizophrenia, and bipolar disorder, have been summarized. The evidence of the psychobiotics therapeutic outcomes obtained in preclinical and clinical trials have been given respectively for the observed neurodegenerative and psychiatric disorders.

Effects of Ecologically Relevant Concentrations of Cadmium on the Microbiota, Short-Chain Fatty Acids, and FFAR2 Expression in Zebrafish

Exposure to cadmium (Cd) can affect neurodevelopment and results in increased potential of developing neurodegenerative diseases during the early developmental stage of organisms, but the mechanisms through which exposure to environmentally relevant concentrations of Cd lead to developmental neurotoxicity remain unclear. Although we know that microbial community fixations overlap with the neurodevelopmental window during early development and that Cd-induced neurodevelopmental toxicity may be related to the disruption of microorganisms during early development, information on the effects of exposure to environmentally relevant Cd concentrations on gut microbiota disruption and neurodevelopment is scarce. Therefore, we established a model of zebrafish exposed to Cd (5 µg/L) to observe the changes in the gut microbiota, SCFAs, and free fatty acid receptor 2 (FFAR₂) in zebrafish larvae exposed to Cd for 7 days. Our results indicated that there were significant changes in the gut microbial composition due to the exposure to Cd in zebrafish larvae. At the genus level, there were decreases in the relative abundances of Phascolarctobacterium, Candidatus Saccharimonas, and Blautia in the Cd group. Our analysis revealed that the acetic acid concentration was decreased (p > 0.05) while the isobutyric acid concentration was increased (p < 0.05). Further correlation analysis indicated a positive correlation between the content of acetic acid and the relative abundances of Phascolarctobacterium and Candidatus Saccharimonas (R = 0.842, p < 0.01; R = 0.767, p < 0.01), and a negative correlation between that of isobutyric acid and the relative abundance of Blautia glucerasea (R = -0.673, p < 0.05). FFAR₂ needs to be activated by SCFAs to exert physiological effects, and acetic acid is its main ligand. The FFAR₂ expression and the acetic acid concentration were decreased in the Cd group. We speculate that FFAR₂ may be implicated in the regulatory mechanism of the gut-brain axis in Cd-induced neurodevelopmental toxicity.

Emerging epigenetic dynamics in gut-microglia brain axis: experimental and clinical implications for accelerated brain aging in schizophrenia

Brain aging, which involves a progressive loss of neuronal functions, has been reported to be premature in probands affected by schizophrenia (SCZ). Evidence shows that SCZ and accelerated aging are linked to changes in epigenetic clocks. Recent cross-sectional magnetic resonance imaging analyses have uncovered reduced brain reserves and connectivity in patients with SCZ compared to typically aging individuals. These data may indicate early abnormalities of neuronal function following cyto-architectural alterations in SCZ. The current mechanistic knowledge on brain aging, epigenetic changes, and their neuropsychiatric disease association remains incomplete. With this review, we explore and summarize evidence that the dynamics of gut-resident bacteria can modulate molecular brain function and contribute to age-related neurodegenerative disorders. It is known that environmental factors such as mode of birth, dietary habits, stress, pollution, and infections can modulate the microbiota system to regulate intrinsic neuronal activity and brain reserves through the vagus nerve and enteric nervous system. Microbiota-derived molecules can trigger continuous activation of the microglial sensome, groups of receptors and proteins that permit microglia to remodel the brain neurochemistry based on complex environmental activities. This remodeling causes aberrant brain plasticity as early as fetal developmental stages, and after the onset of first-episode psychosis. In the central nervous system, microglia, the resident immune surveillance cells, are involved in neurogenesis, phagocytosis of synapses and neurological dysfunction. Here, we review recent emerging experimental and clinical evidence regarding the gut-brain microglia axis involvement in SCZ pathology and etiology, the hypothesis of brain reserve and accelerated aging induced by dietary habits, stress, pollution, infections, and other factors. We also include in our review the possibilities and consequences of gut dysbiosis activities on microglial function and dysfunction, together with the effects of antipsychotics on the gut microbiome: therapeutic and adverse effects, role of fecal microbiota transplant and psychobiotics on microglial sensomes, brain reserves and SCZ-derived accelerated aging. We end the review with suggestions that may be applicable to the clinical setting. For example, we propose that psychobiotics might contribute to antipsychotic-induced therapeutic benefits or adverse effects, as well as reduce the aging process through the gut-brain microglia axis. Overall, we hope that this review will help increase the understanding of SCZ pathogenesis as related to chronobiology and the gut microbiome, as well as reveal new concepts that will serve as novel treatment targets for SCZ.

The Effect of Probiotic Supplementation on the Gut-Brain Axis in Psychiatric Patients

The pathophysiology of several psychiatric diseases may entail disturbances in the hypothalamic-pituitary-adrenal (HPA) axis and metabolic pathways. Variations in how these effects present themselves may be connected to individual variances in clinical symptoms and treatment responses, such as the observation that a significant fraction of participants do not respond to current antipsychotic drugs. A bidirectional signaling pathway between the central nervous system and the gastrointestinal tract is known as the microbiota-gut-brain axis. The large and small intestines contain more than 100 trillion microbial cells, contributing to the intestinal ecosystem's incredible complexity. Interactions between the microbiota and intestinal epithelium can alter brain physiology and affect mood and behavior. There has recently been a focus on how these relationships impact mental health. According to evidence, intestinal microbiota may play a role in neurological and mental illnesses. Intestinal metabolites of microbial origin, such as short-chain fatty acids, tryptophan metabolites, and bacterial components that might stimulate the host's immune system, are mentioned in this review. We aim to shed some on the growing role of gut microbiota in inducing/manipulating several psychiatric disorders, which may pave the way for novel microbiota-based therapies.

Serum Metabolic Profile in Schizophrenia Patients With Antipsychotic-Induced Constipation and Its relationship With Gut Microbiome

BACKGROUND AND HYPOTHESIS

Antipsychotics (APs), the cornerstone of schizophrenia treatment, confer a relatively high risk of constipation. However, the mechanisms underpinning AP-induced constipation are poorly understood. Thus, we hypothesized that (1) schizophrenia patients with AP-induced constipation have distinct metabolic patterns; (2) there is more than one mechanism at play in producing this adverse drug effect; and (3) AP-associated changes in the gut microbiome are related to the altered metabolic profiles.

STUDY DESIGN

Eighty-eight schizophrenia patients, including 44 with constipation (C) and 44 matched patients without constipation (NC), were enrolled in this study. Constipation was diagnosed by Rome IV criteria for constipation and colonic transit time using radiopaque markers (ROMs) while severity was evaluated with the Bristol Stool Form Scale (BSS) and Constipation Assessment Scale (CAS). Fasting blood samples were drawn from all participants and were subjected to non-targeted liquid chromatography-mass spectrometry (LC-MS) metabolomic analysis.

STUDY RESULTS

Eleven metabolites were significantly altered in AP-induced constipation which primarily disturbed sphingolipid metabolism, choline metabolism, and sphingolipid signaling pathway (P value < .05, FDR < 0.05). In the C group, changes in the gut bacteria showed a certain degree of correlation with 2 of the significantly altered serum metabolites and were associated with alterations in choline metabolism.

CONCLUSIONS

Our findings indicated that there were disturbances in distinct metabolic pathways that were associated with AP-induced constipation. In addition, this study presents evidence of a link between alterations in the gut microbiome and host metabolism which provides additional mechanistic insights on AP-induced constipation.

Comparison of gut microbiome profile in patients with schizophrenia and healthy controls - A plausible non-invasive biomarker?

The human gut microbiome regulates brain function through the microbiome-gut-brain axis and is implicated in several neuropsychiatric disorders. However, the relationship between the gut microbiome and the pathogenesis of schizophrenia (SCZ) is poorly defined, and very few studies have examined the effect of antipsychotic treatment response. We aim to study the differences in the gut microbiota among drug-naïve (DN SCZ) and risperidone-treated SCZ patients (RISP SCZ), compared to healthy controls (HCs). We recruited a total of 60 participants, from the clinical services of a large neuropsychiatric hospital, which included DN SCZ, RISP SCZ and HCs (n = 20 each). Fecal samples were analyzed using 16s rRNA sequencing in this cross-sectional study. No significant differences were found in taxa richness (alpha diversity) but microbial composition differed between SCZ patients (both DN and RISP) and HCs (PERMANOVA, p = 0.02). Linear Discriminant Analysis Effect Size (LEfSe) and Random Forest model identified the top six genera, which significantly differed in abundance between the study groups. A specific genus-level microbial panel of Ruminococcus, UCG005, Clostridium_sensu_stricto_1 and Bifidobacterium could discriminate SCZ patients from HCs with an area under the curve (AUC) of 0.79, HCs vs DN SCZ (AUC: 0.68), HCs vs RISP SCZ (AUC: 0.93) and DN SCZ vs RISP SCZ (AUC: 0.87). Our study identified distinct microbial signatures that could aid in the differentiation of DN SCZ, RISP SCZ, and HCs. Our findings contribute to a better understanding of the role of the gut microbiome in SCZ pathophysiology and suggest potential targeted interventions.

Schizophrenia as autoimmune disease: Involvement of Anti-NCAM antibodies

Understanding the etiopathogenesis of schizophrenia has always been an unsolved puzzle for modern medicine. This seems to be due to both disease complexity and lack of sufficient knowledge regarding the biological and non-biological anomalies that exhibit schizophrenia subjects. However, dysregulated immunity is a commonly identified feature in affected individuals. Thus, recently, a hallmark study showed causality relationship between anti-NCAM antibodies and schizophrenia-related behaviors in mice. NCAM plays crucial role in neurodevelopment during early life and neuroplasticity against different stressors during adulthood, and its dysfunction in schizophrenia is increasingly proven. The present review provides the main evidence that support the contribution of autoimmunity and NCAM abnormalities in the development of schizophrenia. Furthermore, it introduces five hypotheses that may explain the mechanism by which anti-NCAM antibodies are produced in the context of schizophrenia: (i) molecular mimicry, (ii) gut dysbiosis, (iii) viral infection, (iv) exposure to environmental pollutants, (v) and NCAM production anomalies.

Schizophrenia and obesity: May the gut microbiota serve as a link for the pathogenesis?

Schizophrenia (SZ) places a tremendous burden on public health as one of the leading causes of disability and death. SZ patients are more prone to developing obesity than the general population from the clinical practice. The development of obesity frequently causes poor psychiatric outcomes in SZ patients. In turn, maternal obesity during pregnancy has been associated with an increased risk of SZ in offspring, suggesting that these two disorders may have shared neuropathological mechanisms. The gut microbiota is well known to serve as a major regulator of bidirectional interactions between the central nervous system and the gastrointestinal tract. It also plays a critical role in maintaining physical and mental health in humans. Recent studies have shown that the dysbiosis of gut microbiota is intimately associated with the onset of SZ and obesity through shared pathophysiological mechanisms, particularly the stimulation of immune inflammation. Therefore, gut microbiota may serve as a common biological basis for the etiology in both SZ and obesity, and the perturbed gut-brain axis may therefore account for the high prevalence of obesity in patients with SZ. On the basis of these findings, this review provides updated perspectives and intervention approaches on the etiology, prevention, and management of obesity in SZ patients by summarizing the recent findings on the role of gut microbiota in the pathogenesis of SZ and obesity, highlighting the role of gut-derived inflammation.

Brain Structure and Function: Insights from Chemical Neuroanatomy

We present a brief historical and epistemological outline of investigations on the brain’s structure and functions. These investigations have mainly been based on the intermingling of chemical anatomy, new techniques in the field of microscopy and computer-assisted morphometric methods. This intermingling has enabled extraordinary investigations to be carried out on brain circuits, leading to the development of a new discipline: “brain connectomics”. This new approach has led to the characterization of the brain’s structure and function in physiological and pathological conditions, and to the development of new therapeutic strategies. In this context, the conceptual model of the brain as a hyper-network with a hierarchical, nested architecture, arranged in a “Russian doll” pattern, has been proposed. Our investigations focused on the main characteristics of the modes of communication between nodes at the various miniaturization levels, in order to describe the brain’s integrative actions. Special attention was paid to the nano-level, i.e., to the allosteric interactions among G protein-coupled receptors organized in receptor mosaics, as a promising field in which to obtain a new view of synaptic plasticity and to develop new, more selective drugs. The brain’s multi-level organization and the multi-faceted aspects of communication modes point to an emerging picture of the brain as a very peculiar system, in which continuous self-organization and remodeling take place under the action of external stimuli from the environment, from peripheral organs and from ongoing integrative actions.

Gut microbes and host behavior: The forgotten members of the gut-microbiome

The gut microbiota refers to an entire population of microorganisms that colonize the gut. This community includes viruses, prokaryotes (bacteria and archaea), and eukaryotes (fungi and parasites). Multiple studies in the last decades described the significant involvement of gut bacteria in gut-brain axis communication; however, the involvement of other members of the gut microbiota has been neglected. Recent studies found that these 'forgotten' members of the gut microbiota may also have a role in gut-brain communication, although it is still unclear whether they have a direct effect on the brain or if their effects are mediated by gut bacteria. Here, we provide concrete suggestions for future research to tease out mechanisms of the microbiota-gut-brain axis. This article is part of the Special Issue on "Microbiome & the Brain: Mechanisms & Maladies".

Shotgun metagenomics reveals abnormal short-chain fatty acid-producing bacteria and glucose and lipid metabolism of the gut microbiota in patients with schizophrenia

Evidence has shown that the gut microbiota is closely related to the pathogenesis of schizophrenia, but temporal changes in the gut microbiota of patients with schizophrenia (SZ) during treatment remain unclear. Here, to evaluate temporal changes in the gut microbiota in schizophrenia, we performed whole-genome shotgun metagenomics on fecal samples from 36 healthy controls (HCs) and 19 baseline-period patients, and followed up with patients upon treatment. Compared to that in HCs, beta diversity in SZ was significantly distinct. The genera Bacteroides, Prevotella and Clostridium were the top 3 altered genera between SZ and HCs, and the Bacteroides-Prevotella ratio was significantly increased in SZ. Thirty-three percent of differentially abundant species were short-chain fatty acid (SCFA)-producing bacteria. Functional analysis showed that glucose and lipid metabolism of the gut microbiota was decreased in SZ compared with those in HCs. The abundances of two rate-limiting enzymes in glucose and lipid metabolism, phosphofructokinase (PFK) and acetyl-CoA carboxylase (ACC), were significantly decreased in SZ, and differentially abundant metabolism-related enzymes were significantly associated with SCFA-producing bacteria. Next, we found that the abundance of SCFA-producing bacteria also changed after treatment and that Clostridium was significantly negatively correlated with the total positive and negative syndrome scale (PANSS) score in patients. Functional analysis showed that glycoside hydrolase family 30 incrementally increased in abundance during treatment and were significantly associated with SCFA-producing bacteria. Our findings help to provide evidence for the role of gut microbiota in the occurrence and development of schizophrenia.

Elucidating gut microbiota-hippocampus interactions in emerging psychosis: A new perspective for the development of early interventions for memory impairments

Hippocampal dysregulation might be a key pathophysiological factor for memory impairments in psychosis. Contemporary models particularly postulate that an imbalance of hippocampal glutamate and GABA leads to impaired memory and may thus serve as a therapeutic target to improve memory deficits. However, currently available interventions in early stages of psychosis do not explicitly target hippocampal pathology. A novel approach for manipulating hippocampus-dependent memory processes is provided via the gut microbiota. In this perspective article, we first recapitulate compelling evidence for emerging hippocampus pathology during the development of psychosis. The following sections emphasize the critical role of the gut microbiota in hippocampus plasticity and memory, and summarize existing evidence of gut microbiota alterations in different stages of psychosis. Finally, we propose a novel conceptual roadmap for future studies deciphering gut microbiota-hippocampus synergisms in emerging psychosis and argue that specific microbial supplementation might be promising for improving hippocampus-dependent memory deficits in early stages of psychosis.