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  • Writer's pictureNatalie Wilcox

Parkinson's Disease and the Gut

In the medical community there is a massive movement revolving around tiny microorganisms. Healthy gut bacteria has been linked with many conditions from depression (Winter et al., 2018), to celiac disease (Valitutti et al., 2019) and Parkinson’s Disease (PD) (Hill-Burns et al., 2017). This is hardly the first time the gastrointestinal (GI) system has been linked to PD. Oftentimes some of the first symptoms of PD are constipation and intestinal inflammation which may be linked to a decrease in gut bacteria diversity.

Stomach problems, intestinal microorganisms, and a brain-based condition seem to be very separate entities within the body, however they are all linked through the Enteric Nervous System (ENS). The ENS is a large branch of the peripheral nervous system that can control the function of the GI tract independently from the brain. Having a decreased diversity of gut bacteria has been linked to dysfunction in the ENS, and may explain the cause of GI problems with brain diseases (Camilleri, 2019). Overall a large quantity and variety of different bacteria in the gut is a good recipe for a healthy immune system, body, and brain.

This may on the surface sound counter intuitive. Don’t we take antibiotics to get rid of bacteria in our gut that is making us sick? Well, yes and no. Some bacteria, like the kind living on the egg salad that’s been left out too long at the barbeque, can make you sick. However, the majority of bacteria that lives in your gut isn’t harmful and can be helpful. For example, microbes in the gut have been linked to the majority of the production of serotonin in the body. Serotonin is an incredibly important neurotransmitter that conveys messages between areas of the body and brain, and is best known for being associated with the feeling of happiness (Ridaura and Belkaid, 2015). There are many theories around why people may have a decreased microbiome: too many antibiotics, not enough bacteria exposure in early childhood, or a diet with limited diversity. No matter the reason, losing diversity in gut bacteria can have detrimental effects on the whole body, including the brain.

In March of 2021, Nature published an article conducting a meta-analysis of the many studies that had looked into the relationship between the loss of specific gut bacteria and Parkinson’s Disease. By analyzing the data collected and accounting for variation in study methods, they were able to determine one thing for certain, people with PD all had an altered microbiome. The meta-analysis sought to find out if there were consistencies between the studies in the way that the microbiomes had been altered. The article states that variation in sample collection and testing methods could account for the heterogeneity of findings but found an association between the prevalence of Parkinson’s Disease and loss of specific bacteria. Results showed that overall the Parkinson’s samples had a lower abundance of Roseburia, Fusicatenibacter, Blautia, Anaerostipes, and Faecalibacterium, the same bacteria found to be missing in the guts of people with Multiple Sclerosis. The results also showed a higher abundance of Lactobacillus, Akkermansia, Hungatella, and Bifidobacterium which are also raised in Crohn’s Disease.

These changes in bacterial health have a direct relationship on neurotransmitters, specifically the production of glutamate. In the brain glutamate plays a key role in the transmission of motor signals, therefore a decrease in its availability can be linked to the disjointed movement often characteristic of Parkinson’s Disease (Romano et al., 2021).


Resources

Camilleri M., Leaky gut: mechanisms, measurement and clinical implications in humans

Gut 2019;68:1516-1526.

Hill-Burns, E.M., Debelius, J.W., Morton, J.T., Wissemann, W.T., Lewis, M.R., Wallen, Z.D., Peddada, S.D., Factor, S.A., Molho, E., Zabetian, C.P., Knight, R. and Payami, H. (2017), Parkinson's disease and Parkinson's disease medications have distinct signatures of the gut microbiome. Mov Disord., 32: 739-749. https://doi.org/10.1002/mds.26942

Ridaura, V., & Belkaid, Y. (2015). Gut Microbiota: The Link to Your Second Brain. Cell, 161(2), 193-194. doi:10.1016/j.cell.2015.03.033

Romano, S., Savva, G.M., Bedarf, J.R. et al. Meta-analysis of the Parkinson’s disease gut microbiome suggests alterations linked to intestinal inflammation. npj Parkinsons Dis. 7, 27 (2021). https://doi.org/10.1038/s41531-021-00156-z

Valitutti, Cucchiara, & Fasano. (2019). Celiac Disease and the Microbiome. Nutrients, 11(10), 2403. MDPI AG. Retrieved from http://dx.doi.org/10.3390/nu11102403

Winter, G., Hart, R., Charlesworth, R. & Sharpley, C. (2018). Gut microbiome and depression: what we know and what we need to know. Reviews in the Neurosciences, 29(6), 629-643. https://doi.org/10.1515/revneuro-2017-0072




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