Gut Microbiome and Its Role in Parkinson's Disease

Parkinson's disease (PD) afflicted more than 8.5 million people globally in 2019, as the prevalence of the condition more than doubled during the preceding 25 years. Both non-motor symptoms, such as mood disorders and cognitive impairment, and motor symptoms, such as tremors and rigidity, are indicative of this progressive neurodegenerative disease. Recent data indicates a significant role for the gut microbiome in PD pathogenesis and progression, emphasizing the microbiota-gut-brain axis. In compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement, this systematic review summarizes our current knowledge about the function of the gut microbiome in PD, highlighting recurrent microbial alterations and assessing microbiome-based treatment strategies. The review revealed several consistent patterns in the gut microbiota of PD patients, including reduced microbial diversity and specific taxonomic alterations, including a drop in Firmicutes abundance and an increase in Proteobacteria abundance. Functional changes in the gut microbiome, such as altered short-chain fatty acid (SCFA) production and tryptophan metabolism, were also noted. These microbial changes were observed even in early-stage and drug-naïve PD patients, suggesting they are not merely a consequence of disease progression or medication use. The review highlighted potential mechanisms linking gut microbiome alterations to PD, including increased intestinal permeability, neuroinflammation, and modulation of alpha-synuclein aggregation. Probiotics, prebiotics, and fecal microbiota transplantation are a few interventions that try to modify the gut microbiome and might be possible to halt the advancement of PD and enhance patients' quality of life with the condition. Future research should focus on establishing causality through large-scale longitudinal studies, standardizing microbiome analysis methods, and exploring personalized microbiome-based therapies.