Gut-Brain Axis in Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disorder in which gut-brain interactions, enteric alpha-synuclein (αS) pathology, and neuroimmune signals contribute to nigrostriatal degeneration. Alongside the frequent occurrence of early gastrointestinal dysfunction, findings from enteric αS pathology and epidemiological studies support the existence of a gut-first subtype of PD. This article provides an integrated review of current evidence linking gastrointestinal and brain αS pathology, gut barrier dysfunction, inflammation, and microbial imbalance in PD. We discuss how these processes may interact through the microbiota-gut-brain axis to drive neurodegeneration, and explore emerging microbiome-based therapeutic strategies including fecal microbiota transplantation, rifaximin, and probiotic approaches. We also point out future research directions, including improved enteric αS imaging and longitudinal microbiome studies starting before PD diagnosis.