Is there a link between parkinson’s disease and gut microbiota?

Parkinson’s disease affects more than 1% of people over 60. It is the second most frequent neurodegenerative disease in the world. Previous studies have established a link between gut microbiota disruption (dysbiosis (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) ) and the development of this disease through the gut-brain axis, but no definite conclusion has been reached regarding a specific bacterial composition associated to the disease.

Dysbiosis observed in patients with Parkinson’s

In recent studies conducted in 80 patients with several degrees of Parkinson’s, their gut microbiota was compared to that of 72 healthy persons. A dysbiosis was brought to light: the intestinal flora of patients displayed a higher abundance of bacterial species belonging to the Lactobacillaceae, Enterobacteriaceae and Enterococcaceae families, and a lower abundance of Lachnospiraceae. The more severe the disease was, the more apparent this difference as regards to Enterobacteriaceae and Lachnospiraceae, and the more important the motor disorders were. This is why researchers believed that these two bacterial families were correlated to the disease’s progression.

Neurotoxic inflammation

In the patients under investigation, the composition of the gut microbiota was affected by several parameters associated to the disease (duration, development stage, use of anti-Parkinson drugs), although they do not act on one specific bacterial family. The patients also displayed disrupted activity of neurotransmitters, i.e. molecules involved in mood regulation (serotonin, dopamine and norepinephrine); and they also produced more lipopolysaccharides, substances generating an inflammation that may damage neurons when they cross the intestinal barrier and the blood-brain barrier (that protects the brain from the surrounding blood). Although this scientific breakthrough is undeniable, it still needs to be further investigated (link between dysbiosis and gut inflammation, role of neurotransmitters in the gut-brain communication...).