Neurodegenerative Disorders and the Gut-Microbiome-Brain Axis: A Literature Review

Neurodegenerative diseases are severe, age-related conditions with complex etiologies that result in significant morbidity and mortality. The gut microbiome, a dynamic symbiotic environment comprising commensal organisms, represents the largest reservoir of these organisms within the human body. It produces short-chain fatty acids, endogenous signals, and neuroactive compounds, which can modulate neuronal function, plasticity, and behavior. Emerging evidence suggests that the gut microbiome plays a pivotal role in neurodevelopment, aging, and brain diseases, including Alzheimer's disease, Parkinson's disease, and stroke. Communication between the gut and brain occurs through a bidirectional channel known as the gut-microbiome-brain axis, which is being explored for therapeutic potential in neurodegenerative disorders. This literature review was conducted through a comprehensive search of five electronic databases - PubMed, Scopus, Ovid Medline, Cochrane Review, and Google Scholar - from inception to June 2024, focusing on English-language studies. Keywords included "gut-brain axis", "microbiome dysbiosis", "neurodegeneration", and disorder-specific terms such as "Alzheimer's disease" and "Parkinson's disease", paired with "gut microbiome". The review examines current knowledge on the relationship between gut microbiota and neurodegenerative disorders, emphasizing potential mechanisms and therapeutic options. Results indicate that gut dysbiosis, characterized by microbial imbalance, is intricately associated with neurodegenerative disease pathogenesis by influencing immune responses, increasing blood-brain barrier permeability, and generating neurotoxic metabolites. Therapeutic approaches targeting the gut microbiome, including probiotics, prebiotics, and fecal microbiota transplantation, show promise in restoring microbial balance and slowing disease progression. However, further research is essential to validate these findings and develop effective clinical interventions.