Can bad oral bacteria travel to the brain and trigger Parkinson's disease?

A common oral bacterium may move from the mouth to the gut and release toxins that enter the brain, damaging dopamine-producing cells linked to Parkinson's disease

According to new research, Parkinson’s disease may be influenced by bacteria that originate in the mouth.

 

A study published recently in Nature Communications shows that an oral bacterium can settle in the gut and produce a chemical that harms brain cells involved in movement control.

 

The study, titled Gut microbial production of imidazole propionate drives Parkinson’s pathologies, found higher levels of this bacterium and its toxic by-product in people with Parkinson’s disease. The chemical was shown to travel from the gut to the brain, where it damaged dopamine-producing neurons, a key feature of the disease.

 

The researchers report that this bacterium produces a metabolite called imidazole propionate, which enters the bloodstream, reaches the brain, and damages dopamine-producing neurons. These findings offer new insight into how oral and gut microbes may influence the development and progression of Parkinson’s disease.

 

What is Parkinson’s disease?

Parkinson’s disease is a progressive neurological disorder that affects movement, balance, and coordination. Classic symptoms include tremors, stiffness, slowness of movement, and problems with walking.

 

According to researchers, the centre of the disease is the loss of dopamine-producing neurons in a region of the brain called the substantia nigra. Dopamine acts as a chemical messenger that helps smooth and control movement. When these neurons die, the brain’s movement circuits begin to misfire.

What does the gut have to do with a brain disorder?

Over the past decade, multiple studies have examined the “gut–brain axis”, the two-way communication between the digestive system and the brain. People with Parkinson’s often report gut problems, such as constipation, years before motor symptoms appear.

 

Earlier research showed that the gut microbiome of people with Parkinson’s differs from that of healthy individuals, but it was unclear which microbes were involved and how they could influence the brain.

Which bacterium did researchers focus on in this study?

Streptococcus mutans, a bacterium best known for causing dental cavities, emerged as a key focus. Researchers found higher levels of this oral bacterium in the gut microbiomes of people with Parkinson’s disease.

 

This bacterium carries a specific enzyme called urocanate reductase (UrdA), which enables it to produce imidazole propionate when histidine, an amino acid, is broken down. In the study, levels of this metabolite were elevated not only in the gut but also in the blood of people with Parkinson’s.

 

Animal experiments showed that imidazole propionate can cross the blood–brain barrier. Once inside the brain, it triggered inflammation, abnormal protein clumping known as α-synuclein aggregation, and the death of dopamine-producing neurons — all hallmark features of Parkinson’s disease.

Does this mean poor oral hygiene causes Parkinson’s?

The study does not conclude that cavities or gum disease directly cause Parkinson’s disease. What it suggests is that oral bacteria, if they repeatedly enter and colonise the gut, may contribute to disease processes in susceptible individuals.

 

Parkinson’s disease is complex and influenced by genetics, ageing, environmental exposures and lifestyle factors. Oral and gut health may represent one piece of a much larger puzzle.