To review the evidence showing an association between gut microbiome (GM) dysbiosis and Parkinson's disease (PD), with an emphasis on the mechanisms by which GM dysbiosis may be involved in PD pathophysiology.

A literature review was conducted using PubMed to identify studies that evaluated the differences between GM of PD patients and of healthy individuals. Also, studies that investigated the mechanisms by which GM changes might trigger or influence PD pathogenesis were reviewed.

There are significant changes in GM of PD patients as compared to that of healthy individuals, which cause decreased production of neuroprotective factors such as short-chain fatty acids (SCFA) and ghrelin. Such changes also increase the release of bacterial neurotoxins including lipopolysaccharide, epoxomicin, and β-N-methylamino-L-alanine into the systemic circulation which might potentiate nigral dopaminergic degeneration given the disrupted blood-brain barrier in PD.

GM changes might be related to the underlying pathophysiology of PD via different mechanisms. A better understanding of the consequences of GM changes, especially those taking place in the ENS and CNS, can help identify the key factors triggering α-synucleinopathy, and provide potential targets for clinical trials to test potential disease-modifying agents for PD including SCFA, probiotics, Tumor Necrosis Factor-alpha antagonists and recombinant ghrelin.