Enhanced intestinal protein fermentation in schizophrenia

Gut microbiome characteristics in individuals across different stages of schizophrenia spectrum disorders: A systematic review and meta-analysis

Schizophrenia (SCZ) is a complex neuropsychiatric disorder with unclear pathogenesis, limiting advances in early diagnosis and targeted interventions. Increasing evidence suggests that the gut microbiome contributed to SCZ pathophysiology, yet comprehensive characterization across illness stages remains lacking. This meta-analysis aimed to characterize gut microbial alterations across the SCZ spectrum disorder, including individuals at ultra-high risk for psychosis, first-episode psychosis (FEP) and chronic SCZ patients. A systematic search of 10 databases identified 91 case-control studies. Gut microbial outcome measures included relative abundance, alpha and beta diversity. Review Manager and R were used to analyze the data. The results showed that patients with SCZ exhibited significantly reduced alpha diversity, particularly in Shannon, Chao1, Observe and Evenness indices, compared to healthy controls. Beta diversity also differed significantly, with 88.5 % of studies reporting distinct microbial profiles across SCZ stages. Quantitative analysis revealed significantly increased relative abundance of Bacteroides and a decrease abundance of Bifidobacterium and Lactobacilli in FEP patients compared to healthy controls. Qualitative analysis further showed increasing abundance in Lactobacillus, Prevotella and Collinsella, but decreasing abundance in Faecalibacterium, Butyricicoccus, and Blautia in SCZ. Bifidobacterium exhibited stage-specific changes, decreasing in first-episode psychosis but increasing in chronic stages, while Bacteroides followed an opposite trajectory. Notably, Lactobacillus demonstrated an early upward tractor in high-risk individuals, persisting to chronic stages. This meta-analysis identified dynamic and consistent alterations in the gut microbial across the SCZ spectrum. These findings implicated the potentials of gut microbes as early indicators for identification and intervention of SCZ.

Nutrition and brain health: Implications of Mediterranean diet elements for psychiatric disorders

The Mediterranean diet is an anti-inflammatory diet now recognized for prevention and intervention against cardiometabolic disorders, although emerging literature also shows its benefits for mental health. This paper surveys literature pertinent to the Mediterranean diet with respect to schizophrenia, bipolar and unipolar depression and cognition. The National Library of Medicine database of literature was searched for publications relating to our topic through June 2024. Our results highlight the Mediterranean diet's potential role in mediating inflammation, potentially through the gut-brain axis, and its neuroprotective role against cognitive decline. Moreover, individual components of the Mediterranean diet are potentially therapeutic as well as protective, particularly fruits, vegetables, fatty fish, and whole grains. These dietary components reduce systemic inflammation, modulate gut microbiota and influence critical pathways such as moderating oxidative stress. Overall, this survey of recent literature highlights the potential of the Mediterranean diet to promote mental health and reduce the risk or severity of psychiatric and neurodegenerative disorders. The analysis underscores broader implications for the Mediterranean diet in advancing mental health outcomes and emphasizes the need for further studies and increased public education to encourage healthier eating habits and dietary interventions.

Comparative analysis of gut microbiome-derived short-chain fatty acids in patients with severe mental disorder: Insights from schizophrenia and bipolar disorder

Both schizophrenia (SZ) and bipolar disorder (BD) are associated with disruptions in the gut microbiome. Short-chain fatty acids (SCFAs), such as acetate, propionate and butyrate, are key metabolites produced by gut bacteria that influence brain function, immune responses and behaviour. We conducted a cross-sectional observational study with 123 patients (86 with SZ and 37 with BD). We analysed faecal samples for SCFA and examined associations with clinical (psychopathology and cognition), metabolic and lifestyle factors. We performed analysis of covariance to find differences in SCFA levels between diagnostic groups, adjusting for covariates. Faecal SCFA levels were numerically higher in the SZ group than in the BD group. However, after adjusting for covariates, a significant sex-by-diagnosis interaction was observed only for acetate levels. Body mass index emerged as a key predictor of SCFA levels but we observed no significant associations with other metabolic or lifestyle variables, including diet, physical activity and blood inflammatory biomarkers. Additionally, SCFA levels showed no correlation with symptom severity or cognitive performance in either group. This study is the first to compare SCFA profiles between SZ and BD, highlighting potential differences in gut microbiota-derived metabolites between these disorders. These findings suggest greater disruption of the gut-brain axis in SZ, potentially reflecting distinct pathophysiological mechanisms involving metabolic and sex-related factors. Further research, including blood SCFA measurements, could better explain the role of SCFAs and explore microbiota-targeted therapeutic strategies for SZ and BD.

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

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

Altered levels of fecal short-chain fatty acids are associated with subclinical inflammation and worse cognitive performance in patients with schizophrenia

Schizophrenia is a multi-systemic disorder that is associated with lipid profile disturbances, altered glucose homeostasis and subclinical inflammation. It has been proposed that dysfunction of the gut-brain axis might underlie these alterations. Short-chain fatty acids (SCFAs) are considered to play a pivotal role in the gut-brain axis. In this study, we aimed to compare fecal levels of SCFAs in patients with schizophrenia and healthy controls (HCs), taking into consideration their relationship with common peripheral blood alterations observed in schizophrenia. The study included 100 stable outpatients with schizophrenia and 55 HCs. The levels of SCFAs (acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, and lactic acid) in fecal samples were measured. Also, lipid profile together with the levels of C-reactive protein, glucose and insulin were determined. The levels of isovaleric acid were significantly higher in patients with schizophrenia after co-varying for age, sex, and the adherence to the Mediterranean diet. Moreover, there were significant positive correlations of the levels of valeric acid, isovaleric acid and CRP in patients with schizophrenia. In this group of participants, higher levels of isovaleric acid were associated with significantly lower scores of delayed memory after adjustment for potential covariates and interactions with CRP levels. Our results indicate that individuals with schizophrenia show altered levels of isovaleric acid that might be associated with impairments of delayed memory. The association with cognitive impairments might be independent of interactions with immune-inflammatory processes. Longitudinal and experimental studies are needed to test causal mechanisms of observed correlations.

The Role of Gut Microbiota in Anxiety, Depression, and Other Mental Disorders as Well as the Protective Effects of Dietary Components

The number of individuals experiencing mental disorders (e.g., anxiety and depression) has significantly risen in recent years. Therefore, it is essential to seek prevention and treatment strategies for mental disorders. Several gut microbiota, especially Firmicutes and Bacteroidetes, are demonstrated to affect mental health through microbiota-gut-brain axis, and the gut microbiota dysbiosis can be related to mental disorders, such as anxiety, depression, and other mental disorders. On the other hand, dietary components, including probiotics (e.g., Lactobacillus and Bifidobacterium), prebiotics (e.g., dietary fiber and alpha-lactalbumin), synbiotics, postbiotics (e.g., short-chain fatty acids), dairy products, spices (e.g., Zanthoxylum bungeanum, curcumin, and capsaicin), fruits, vegetables, medicinal herbs, and so on, could exert protective effects against mental disorders by enhancing beneficial gut microbiota while suppressing harmful ones. In this paper, the mental disorder-associated gut microbiota are summarized. In addition, the protective effects of dietary components on mental health through targeting the gut microbiota are discussed. This paper can be helpful to develop some dietary natural products into pharmaceuticals and functional foods to prevent and treat mental disorders.

The Microbiome and Mental Health Across the Lifespan

INTRODUCTION

The combined genetic material of the microorganisms in the human body, known as the microbiome, is being increasingly recognized as a major determinant of human health and disease. Although located predominantly on mucosal surfaces, these microorganisms have profound effects on brain functioning through the gut-brain axis.

METHOD

The content of the chapter is based on a study group session at the annual meeting of the American College of Neuropsychopharmacology (ACNP). The objective was to discuss the emerging relationship between the human microbiome and mental health as relevant to ACNP's interests in developing and evaluating novel neuropsychiatric treatment strategies. The focus is on specific brain disorders, such as schizophrenia, substance use, and Alzheimer's disease, as well as on broader clinical issues such as suicidality, loneliness and wisdom in old age, and longevity.

RESULTS

Studies of schizophrenia indicate that the microbiome of individuals with this disorder differs from that of non-psychiatric comparison groups in terms of diversity and composition. Differences are also found in microbial metabolic pathways. An early study in substance use disorders found that individuals with this disorder have lower levels of beta diversity in their oral microbiome than a comparison group. This measure, along with others, was used to distinguish individuals with substance use disorders from controls. In terms of suicidality, there is preliminary evidence that persons who have made a suicide attempt differ from psychiatric and non-psychiatric comparison groups in measures of beta diversity. Exploratory studies in Alzheimer's disease indicate that gut microbes may contribute to disease pathogenesis by regulating innate immunity and neuroinflammation and thus influencing brain function. In another study looking at the microbiome in older adults, positive associations were found between wisdom and alpha diversity and negative associations with subjective loneliness. In other studies of older adults, here with a focus on longevity, individuals with healthy aging and unusually long lives had an abundance of specific microorganisms which distinguished them from other individuals.

DISCUSSION

Future studies would benefit from standardizing methods of sample collection, processing, and analysis. There is also a need for the standardized collection of relevant demographic and clinical data, including diet, medications, cigarette smoking, and other potentially confounding factors. While still in its infancy, research to date indicates a role for the microbiome in mental health disorders and conditions. Interventions are available which can modulate the microbiome and lead to clinical improvements. These include microbiome-altering medications as well as probiotic microorganisms capable of modulating the inflammation in the brain through the gut-brain axis. This research holds great promise in terms of developing new methods for the prevention and treatment of a range of human brain disorders.