The interplay between the gut-brain axis and the microbiome: A perspective on psychiatric and neurodegenerative disorders

Abstract

What is the effect of our gut microbial flora on brain? Does the gut microbiome have any role in the causation of psychiatric and neurodegenerative diseases? Does the effect of gut microbiota traverse the gut-brain axis? Questions like these have captured the interest and imagination of the scientific community for quite some time now. Research in the quest for answers to these questions, to unravel the potential role of the microbiota inhabiting the gut in controlling brain functions, has progressed manifold over the last two decades. Although the possibility of microbiome as a key susceptibility factor for neurological disorders viz. Parkinson’s disease, Alzheimer’s disease, multiple sclerosis, and autism spectrum disorder has bolstered by an increase in the clinical and preclinical evidence, the field is still in its infancy. Given the fact that the diversity of the gut microbiota is affected by various factors including the diet and exercise, the interpretation of such data becomes all the more difficult. Also, such studies have been mostly conducted on animal models, so there is a need for randomized controlled trials in human subjects, corroborated by longitudinal studies, to establish if modulating the gut microbiota can unravel novel therapeutic interventions. Exploring the genomic, metagenomic and metabolomic data from clinical subjects with psychiatric and neurological diseases can prove to be a helpful guide in individual treatment selection.

Exploring the Influence of Gut–Brain Axis Modulation on Cognitive Health: A Comprehensive Review of Prebiotics, Probiotics, and Symbiotics

“…Ongoing studies aim to deepen our understanding of the interactions within the microbiome–gut–brain axis, particularly exploring mechanisms between the gastrointestinal tract and the nervous system [ 122 , 156 , 157 , 158 , 159 , 160 , 161 , 162 , 163 , 164 , 165 , 166 , 167 , 168 , 169 , 170 , 171 ]. Future research should focus on more precise analyses and explorations of the composition of gut microbiota, identifying which strains are dominantly associated with conditions such as anxiety, depression, Parkinson’s disease, and other psychiatric and cognitive disorders, including Alzheimer’s disease [ 172 , 173 , 174 , 175 , 176 , 177 , 178 , 179 , 180 , 181 , 182 , 183 , 184 ]. Areas that remain less explored, such as the various negative associations of different bacterial strains, including inflammatory diseases, neuroinflammation, and metabolic disorders or postpartum depression, require further investigation for a deeper understanding.…”

From Gut Microbiota to Brain Waves: The Potential of the Microbiome and EEG as Biomarkers for Cognitive Impairment

“…These conditions have been linked to various diseases such as diabetes, obesity, cardiovascular disease, cancer, and inflammatory bowel disease. More recent studies have also unveiled a connection between the gut microbiome and the development of several neurological disorders, including depression, multiple sclerosis, ALS, Parkinson’s disease, and AD [ 16 , 17 , 18 , 19 , 72 , 87 , 88 , 89 ]. The gut microbiome communicates with the brain through the gut–brain axis, a bidirectional communication pathway that integrates the gut’s functions with the cognitive and emotional centers of the brain [ 20 , 85 ].…”

Alzheimer’s disease and microorganisms: the non-coding RNAs crosstalk

“…In particular, Porphyromonas gingivalis (P. gingivalis), a periodontal pathogen, has been detected in the brains of AD patients and is associated with neurotoxicity. P. gingivalis triggers toll-like receptor (TLR-2) and TLR-4 signaling, leading to the activation of TNF-α and interleukine-1 (IL-1) through bacterial LPS and an increase in miRNA-9 expression (upregulation), ultimately alleviating inflammation (Ishida et al, 2017;Dominy et al, 2019;Bashir and Khan, 2022). LPS also induces the long non-coding RNA (lncRNA) MALAT1 in gingival fibroblasts, leading to pro-inflammatory states.…”