The Brain-Gut-Axis Hypothesis (Parkinson’s Disease)

This essay is written by Jongsik Jon Chun, a professor at the Department of Biological Sciences, Seoul National University and translated by ChunLab staffs. The author is also actively engaged in R&D as a major board member at ‘ChunLab, Inc.

The Brain-Gut-Axis Hypothesis verified via Parkinson’s mice model

Autism spectrum disorder, Parkinson’s disease and Dementia are all the brain diseases that incur substantial costs not only to the individuals but also to society. Unfortunately, we do not know the exact causes of these diseases yet and there are no proper treatments. However, there have been multiple reports of patients with brain diseases experiencing discomforts in their gastrointestinal tract. Recent studies demonstrated that the brain disease is likely to have a strong correlation with our digestive organs, especially to the microbiome, the ecosystem of microorganisms in the large intestine. There are terms, “Brain-Gut-Axis” or “Gut-Brain-Axis” which indicate the gut microbiota and the brain are closely connected. Does the brain really affect the gut microbiota? Or, is it the other way around? There was a study by Professor Myung-sook Oh’s team^​1​ in the College of Pharmacy at Kyung-hee University. It provided a proof of Brain-Gut-Axis theory, and I would like to share the findings in this writing.

Parkinson’s disease is a neurodegenerative disease due to the death of the brain nerve cells that secrete dopamine which is a type of neurotransmitter. It causes slow movements, tremors and shaking on standing, muscular stiffness, shuffling gait, and bent body. Scientists use animal studies to figure out the causes and the cure for Parkinson’s disease. The common toxin used during the study is 6-hydroxydopamine(6-OHDA). When the toxin is injected into the mouse’s brain, the mouse shows similar symptoms as Parkinson’s patients. In this study, the Professor Myung-sook Oh’s team attempted to prove the Brain-Gut-Axis theory with the idea that they could closely examine the changes in the gut microbiome of the normal mouse that developed Parkinson, a well-known brain disease, after the injection of 6-OHDA.

They compared the control group with the normal mice to the Parkinson’s test group (mice injected with the toxin). The results are shown below.

(1) In terms of species diversity of the microbiome, there were no differences between the two groups

(2) However, there was a substantial (noteworthy) difference in their species compositions. The Parkinson’s test group showed a small number of Lactobacillus gasseri and Lactobacillus reuteri, and an increased number of Bacteroides acidifaciens when compared to the control group.

So, what is the implication of this study? (What can do we learn from this study?)

Although the study artificially initiated the disease, the study demonstrated Brain-Gut-Axis theory by showing that the cut microbiome compositions changed when the tested mouse developed Parkinson’s disease. However, it would be difficult to apply this study to humans directly as mice and humans carry different microbiomes. For instance, some studies showed that the increased Lactobacillus in the Parkinson tested mouse group was actually decreased in human patients (Gerhardt_2018; Hill-Burns_2017). One major difference is that Lactobacillus is a vital resident-bacillus in mice but a non-resident bacillus in adult humans. In humans, LactobacillusI enters the gut through the consumption of fermented foods such as kimchi and yogurt, and exits by defecating (Please refer to The Good Gut by Professor Sonnenburg at Stanford University).

Interestingly, Professor Mina Kwon’s team from Ulsan College of Medicine found the increased Bacteroides acidifaciens in the Parkinson tested mouse group is a species that introduced the new possibilities of curing mice obesity and mice diabetes.

Both Professor Oh and Professor Kwon used the B2B solution (EzBioCloud database and Cloud Analytics System) in their research studies.

This is a Precision Taxonomy Discovery Platform which allows the accurate classification of a bacterial species (and strain) in microbiome studies. Until now, there are more than 40,000 scientists worldwide have been using this platform and there are more than a thousand daily users.

Additionally, there have been more than eight thousand published articles referenced EzBioCloud. It would be a great honor if EzBioCloud could participate in more of the outstanding studies worldwide.