Parkinson’s disease, a neurological disorder marked by tremors, stiffness and slowed movement, may have a surprising link to oral bacteria that find their way into the gut.
A new study by scientists at the Pohang University of Science and Technology in South Korea has shown how these microbes and the substances they produce can influence the brain and contribute to the disease.
The research, published in the journal Nature Communications, found that the oral bacterium Streptococcus mutans was more abundant in the gut microbiome of people with Parkinson’s compared to healthy individuals.
This bacterium, which is also known for causing dental cavities, produces an enzyme called urocanate reductase (UrdA). The enzyme generates a metabolite named imidazole propionate (ImP), which was found at higher levels in the gut and blood of Parkinson’s patients.
Once in circulation, ImP was shown to reach the brain, where it contributed to the death of dopamine-producing neurons, a key feature of the disorder.
In experiments with mice, the introduction of S. mutans or genetically modified E. coli producing UrdA led to increased levels of ImP in both blood and brain. The animals displayed classic Parkinson’s symptoms including motor difficulties, neuroinflammation, neuronal loss and abnormal accumulation of the protein alpha-synuclein.
The study also revealed that these damaging effects were linked to activation of a protein complex called mTORC1. When the mice were treated with a drug that blocks this pathway, there was a clear reduction in inflammation, neuronal damage, alpha-synuclein clumping and motor problems.
According to the researchers, the findings provide fresh insight into the connection between the oral-gut microbiome and the brain. They suggest that focusing on the microbes and their metabolites could help in the search for new treatments for Parkinson’s disease.
