PD and Gut Bacteria—Is There a Link?

The vast diversity and amount of bacteria and other microorganisms we have in our gut has long been of interest to researchers. There have been many conditions, including autoimmune and neurological conditions, linked to gut bacteria and changes in gut flora. While many of these links are still being further investigated, new research has emerged in recent months specifically on PD and the gut. Two interesting and possibly influential articles have been published surrounding this lovely part of our body and its ties to PD progression and manifestation.

Using mice as a model

The first of the two studies mentioned above centers around groups of mice. In each part of the experiment, mice were divided into two groups. One group had normal gut microorganisms, and the other group was completely germ-free, and depleted of all additional bacteria and other flora. The mice were followed through three different treatment conditions. The first involved genetically modifying both types of mice to overproduce alpha-synuclein, which is a trademark protein in PD. The germ-free mice overexpressed the protein, but had no accumulation of it in the brain, nor any signs of neurological decline. The mice with the normal gut biome experienced an accumulation of the PD protein in the brain, and showed a significant cognitive decline, and PD-like symptoms.

In the second treatment set, both types of mice were still modified to overproduce alpha-synuclein, however, each set was fed long-chain fatty acids that would be made if normal gut bacteria were present. This would allow researchers to mimic the activity of the bacteria present, without it actually being there. If the germ-free mice showed symptoms, even without the original bacteria being present, it would indicate that the PD symptoms may be tied to the functions of the bacteria, not just their presence or absence. The germ-free mice did in fact show symptoms, leading researchers to continue investigating.

The final treatment involved only germ-free mice overproducing alpha-synuclein. Researchers transplanted gut bacteria from either healthy control humans, or humans with PD into the mice. In this phase of treatment, only the mice that had the gut bacteria from the individuals with PD implanted developed PD-like symptoms and showed neurological decline. This further indicated that PD manifestation and progression could be related to specific types of bacteria being present in the gut.

Moving onto humans

A more recent study published in Movement Disorders moves this research to humans. These researchers wanted to identify if gut dysbiosis, or imbalance, contributed to PD development, and sought to mediate any potentially confounding variables. The researchers utilized 197 individuals with PD, and 130 controls without PD, and controlled for confounding variables such as diet, demographics, gastrointestinal symptoms, and medications. Overall, the researchers found specific signatures within the gut biome based on dietary fruits and vegetables consumed, region of the US the individual lived in, PD status, and sex. Specifically, these signatures included altered abundances of Bifidobacteriaceae and Lactobacillaceae, among others. There were also differences found within several pathways, including the degradation of xenobiotics, and metabolism of plant-derived compounds.

Although there is still much more research to be done regarding gut bacteria and its potential association to PD, these studies, among others, seem to be headed in the right direction when it comes to uncovering this mystery and developing new treatment options!

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