Synbiotics in Alzheimer's disease: mechanisms, clinical evidence, and therapeutic prospects.

Background: Growing evidence implicates gut microbiota (GM) dysbiosis in Alzheimer's disease (AD) pathogenesis via the gut-brain axis. Dysbiosis contributes to neuroinflammation, amyloid-β deposition, tau hyperphosphorylation, blood-brain barrier disruption, and cognitive decline. Synbiotics (combinations of probiotics and prebiotics) offer a promising strategy to modulate GM, potentially ameliorating these AD hallmarks through multiple mechanisms including enhanced production of neuroprotective short-chain fatty acids (SCFAs), reduced inflammation, improved gut barrier integrity, and immunomodulation.

Objective: This review critically evaluates the current evidence on the therapeutic potential of synbiotics for AD. It aims to synthesize findings from preclinical and clinical studies regarding the efficacy of synbiotics in improving cognitive function and AD pathology, elucidate the underlying biological mechanisms including GM modulation, SCFA production, immune regulation, and gut-brain signaling, and identify key challenges and future research directions for translating GM-targeted interventions into effective AD therapies.

Conclusion: Synbiotics demonstrate significant potential, particularly in early AD, by improving cognitive domains, reducing neuroinflammation and AD biomarkers, and modulating beneficial microbial metabolites. However, challenges include confounding factors, unresolved questions about causality, inconsistent results in advanced disease, and insufficient large-scale human trials. Future success hinges on rigorous longitudinal randomized controlled trials integrating multi-omics approaches, advanced in vitro models, and personalized strategies considering baseline microbiota and host genetics. While not a standalone cure, synbiotics represent a valuable component within multi-target therapeutic approaches aimed at modulating the gut-brain axis to slow AD progression.