Abstract
Parkinson’s disease is a chronic neurodegenerative disease characterized by the accumulation of misfolded alpha-synuclein protein (Lewy bodies) in dopaminergic neurons of the substantia nigra and other related circuitry, which contribute to the development of both motor (bradykinesia, tremors, stiffness, abnormal gait) and non-motor symptoms (gastrointestinal issues, urinogenital complications, olfaction dysfunction, cognitive impairment). Despite tremendous progress in the field, the exact pathways and mechanisms responsible for the initiation and progression of this disease remain unclear. However, recent research suggests a potential relationship between the commensal gut bacteria and the brain capable of influencing neurodevelopment, brain function and health. This bidirectional communication is often referred to as the microbiome–gut–brain axis. Accumulating evidence suggests that the onset of non-motor symptoms, such as gastrointestinal manifestations, often precede the onset of motor symptoms and disease diagnosis, lending support to the potential role that the microbiome–gut–brain axis might play in the underlying pathological mechanisms of Parkinson’s disease. This review will provide an overview of and critically discuss the current knowledge of the relationship between the gut microbiota and Parkinson’s disease. We will discuss the role of α-synuclein in non-motor disease pathology, proposed pathways constituting the connection between the gut microbiome and the brain, existing evidence related to pre- and probiotic interventions. Finally, we will highlight the potential opportunity for the development of novel preventative measures and therapeutic options that could target the microbiome–gut–brain axis in the context of Parkinson’s disease.
Highlights
Parkinson’s disease (PD) is the second most common neurodegenerative disorder with an estimated prevalence of approximately 1% among individuals over the age of 65 (Nussbaum, 2003)
Results of this study demonstrated normalized distal colon motility following treatment, an important factor associated with maintenance of a balanced microbiome – presenting a potential novel early intervention for PD, given the frequent early onset of GI symptoms related to gut motility such as constipation, which warrants further investigation
It is a continuously progressing field of study, which is complicated by the multitude of factors mediating the potential influence of the gut microbiome on PD including diet and lifestyle habits, levels of inflammation, presence of comorbidities, and use of supplements or medications, etc
Summary
Parkinson’s disease (PD) is the second most common neurodegenerative disorder with an estimated prevalence of approximately 1% among individuals over the age of 65 (Nussbaum, 2003). Animals raised in GF conditions have demonstrated increased BBB permeability through decreased expression of tight junction proteins, potentially due to a lack of bacterial-derived SCFAs, capable of improvement following colonization with commensal microbiota (Ma et al, 2019) Taken together, these studies suggest the inherent presence of a bidirectional pathway between the gut and the brain, mediated by the microbiota, is vital for proper nervous system maturation and function. Another such study among individuals with inflammatory bowel syndrome (144,018 individuals with IBD and 720,090 matched controls) reported a 78% reduction in the incidence of PD among the population when anti-TNF therapy was previously utilized to TABLE 1 | Summary of recent pre- and probiotic studies related to Parkinson’s disease in humans
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