BACKGROUND: The altered gut microbiota substantially impacts the onset and progression of Alzheimer's disease (AD) and Parkinson's disease (PD), the two most widely studied neurodegenerative conditions. Microbiome-derived metabolites have been increasingly associated with disease onset, progression, and therapeutic targets in neurodegenerative disorders. Exploring the diagnostic and therapeutic implications of gut microbiome-derived biomarkers is critical to advancing our understanding and management of neurodegeneration.
METHODOLOGY: We systematically reviewed both clinical and preclinical studies published from 2010 to 2025. Studies examining gut microbiota composition, microbial-derived metabolites, or therapeutic interventions targeting the gut microbiome were included. Identification of gut microbiome alterations, discovery of microbial or metabolite-based biomarkers, association with disease onset or progression, and/or therapeutic effects on cognitive, neurological, or inflammatory outcomes were evaluated.
RESULT: Short-chain fatty acids(SCFAs) such as butyrate and acetate were found to be noninvasive biomarkers in patients with Alzheimer's disease (AD), mild cognitive impairment (MCI), and Parkinson's disease (PD). Lower SCFA levels correlated with cognitive decline. Diagnostic accuracy improved when SCFA combinations were used, with AUCs ranging from 0.75 to 0.87. Trimethylamine N-oxide(TMAO) levels showed inconsistent associations, with both elevated and reduced levels linked to disease risk. Therapeutic approaches targeting gut microbiota, including probiotics, prebiotics, dietary changes, and fecal microbiota transplantation, demonstrated cognitive benefits and modulation of gut-brain signaling pathways.
CONCLUSION: Overall, gut-derived biomarkers offer a promising avenue for early diagnosis and novel therapeutic approaches in AD and PD, while acknowledging that evidence in other neurodegenerative diseases remains limited through modulation of the gut-brain axis.
