Compositional and functional alterations in the oral and gut microbiota in patients with psychosis or schizophrenia: A systematic review

Abstract

Background: Gut and oral microbiota are intrinsically linked to human health. Recent studies suggest a direct link with mental health through bidirectional gut–brain pathways. Emerging evidence suggests that the composition and/or function of intestinal microbiome differs in those with psychosis and schizophrenia as compared with controls. There is relatively little research on the predicted or actual functional alterations associated with the composition of oral and gut microbiota in patients with psychosis. We will perform a systematic review and meta-analysis to identify, evaluate and if possible, combine the published literature on compositional alterations in the oral and gut microbiota in patients with psychosis or schizophrenia compared with healthy controls. We also aim to explore the potential functional impact of any compositional changes. Methods: Original studies involving humans and animals using a case-control, cohort or cross-sectional design will be included. The electronic databases PsycINFO, EMBASE, Web of Science, PubMed/MEDLINE and Cochrane will be systematically searched. Quantitative analyses will be performed using random-effects meta-analyses to calculate mean difference with 95% confidence intervals. Discussion: Changes in microbiota composition in psychosis and schizophrenia have been correlated with alternations in brain structure and function, altered immunity, altered metabolic pathways and symptom severity. Changes have also been identified as potential biomarkers for psychosis that might aid in diagnosis. Understanding how predicted or actual functional alterations in microbial genes or metabolic pathways influence symptomatic expression and downstream clinical outcomes may contribute to the development of microbiome targeted interventions for psychosis. Registration: The study is prospectively registered in PROSPERO, the International Prospective Register of Systematic Reviews (CRD42021260208).

Differences in Alpha Diversity of Gut Microbiota in Neurological Diseases

“…Furthermore, the ROC curve analysis showed that alpha diversity was able to diagnose AD, schizophrenia, and MS. These results demonstrate dysregulation and alteration in gut microbiota in AD, schizophrenia, and MS, which had been confirmed in the previous studies (Murray et al, 2021 ; Cantoni et al, 2022 ). Dysregulation of gut microbiota could facilitate the occurrence and development of neurological diseases, in which the “gut microbiota-brain” axis might play an important role (Almeida et al, 2020 ).…”

Is There a Link between Oropharyngeal Microbiome and Schizophrenia? A Narrative Review

“…The authors added that it could be explain by a decrease immune surveillance in the gut. This point gives us another hypothesis for the OBA: the link between oral microbiome and schizophrenia could be made throughout the gut microbiota [ 50 ].…”

“…They added that this pointing to the relation between oral resident bacteria and gut bacteria, suggesting that oral resident bacteria in a synergistic manner may colonize the gut in schizophrenic patients. A study is currently underway to clarify the relationship between the composition of the oral and intestinal microbiota in patients with psychosis or schizophrenia and healthy controls [ 50 ].…”

Maternal Supplementation with N-Acetylcysteine Modulates the Microbiota-Gut-Brain Axis in Offspring of the Poly I:C Rat Model of Schizophrenia

“…Furthermore, these patients may also display an increased intestinal permeability [ 38 ]. To date, nearly a dozen studies have reported differences in the microbiome between healthy individuals and patients at different stages of the disease [ 39 , 40 ]. Nevertheless, their results are not consistent, especially when analyzing bacterial components in a higher taxonomic order.…”