Dysregulation of the gut–brain axis in schizophrenia and bipolar disorder

Abstract

Purpose of review Schizophrenia (SCZ) and bipolar disorder are severe mental disorders, both placing a significant burden on individuals' wellbeing and global health generally. The complex interaction of multiple mechanisms, underlying these disorders, still needs further elucidation. Increased activation of components of the immune system may be involved, including alterations in intestinal permeability and gut microbiome. Probiotics, defined as living microorganisms conferring health benefits to the host when administered in adequate amounts, seem to have supportive therapeutic effect in psychiatric disorders. The authors in this review provide an overview of this emerging research field and summarize both the publicated microbiome studies in SCZ and bipolar disorder and the current clinical research using probiotic supplementation in patients diagnosed with these disorders. Recent findingsThe current data indicate that there are differences in the microbiome in SCZ and bipolar disorder patients as compared with healthy controls. Part of these differences may be induced by medication use, others by smoking and other lifestyle factors. Correlations between microbiome quantification and symptom severity have been observed in cross-sectional studies, but unfortunately, no replicated findings so far. Probiotic supplementation was shown not only to alleviate gastrointestinal complaints but also reduce symptom severity, rehospitalization rates and cognitive improvement. Replication of improvement of cognition is needed. SummaryDifferences in microbiome have been shown in both SCZ and bipolar disorder in comparison to healthy controls. Evidence that probiotics can improve psychiatric functioning is still very limited.

Characterization of Early Life Stress-Affected Gut Microbiota

“…We have previously reported that changes in the gut microbiota of pregnant mice result in changes in the gut microbiota of the offspring and increases of anxious behavior [ 11 ]. Alterations of gut microbiota in several mental disorders, such as autism spectrum disorder (ASD), schizophrenia, and depression, have also been reported [ 12 , 13 , 14 ]. In particular, patients with ASD and schizophrenia show impairment of social behaviors as a symptom.…”

“…In particular, patients with ASD and schizophrenia show impairment of social behaviors as a symptom. The alterations of many bacterial abundances such as Bifidobacterium, Lactobacillus, Bacteroides, Ruminococcaceae, or Verrucomicrobia have been reported in patients with ASD or schizophrenia [ 12 , 14 , 15 , 16 ], which suggests the possibility that the gut–brain axis may affect social behavior. In addition, stress reportedly affects gut microbiota [ 17 ].…”

Exploring the role of ketone bodies in the diagnosis and treatment of psychiatric disorders

“…A further benefit of the KD is its ability to alter the gut microbiome, which in the context of the evolving understanding of the gut-brain axis in psychiatric research ( 44–46 ) could prove particularly meaningful. In terms of overall balance of gut microbiota, there are a series of studies covering a range of age groups that demonstrate the KD’s positive impact on dysbiosis ( 47–49 ).…”

Exploring the Role and Potential of Probiotics in the Field of Mental Health: Major Depressive Disorder

“…Clinical trials have demonstrated the efficacy of probiotic supplementation in ameliorating mental illness. The clinical efficacy of probiotics coupled with their lack of detrimental side effects and stigmatization make them a promising therapeutic intervention in mental disorders [26][27][28][29]. Although existing clinical trials are limited and more substantial research outcomes are needed, probiotics are a noteworthy therapeutic intervention as far as the mental health domain is concerned.…”