Parkinson’s disease is a progressive brain disorder that affects millions of people worldwide.
It is best known for movement problems such as shaking, muscle stiffness, slower movement and difficulty with balance, although it can also affect sleep, mood, thinking and digestion.
The disease develops when important nerve cells in the brain become damaged or die. Many of these cells normally produce dopamine, a chemical that helps the brain control smooth and coordinated movement.
Scientists still do not know exactly why Parkinson’s begins in most people. Genetics can increase risk, but inherited changes explain only a minority of cases, which has led researchers to investigate environmental factors and changes elsewhere in the body.
One area receiving growing attention is the gut. The human digestive system contains trillions of bacteria and other microorganisms, collectively known as the gut microbiome, and researchers increasingly suspect that changes in this community may influence the brain.
A team led by Professor Per Saris at the University of Helsinki in Finland has focused on bacteria called Desulfovibrio. These bacteria can live in the human intestine and produce substances that may affect nearby cells and other microorganisms.
In earlier research, the team reported that people with Parkinson’s disease were more likely to carry higher amounts of Desulfovibrio in their gut than people without the disease. Greater amounts of the bacteria were also associated with more severe Parkinson’s symptoms.
To investigate whether this association could have a biological explanation, the scientists turned to tiny laboratory worms called Caenorhabditis elegans. These worms are widely used in medical research because scientists can study basic biological processes in them relatively quickly.
The researchers were particularly interested in alpha-synuclein, a protein found naturally in the nervous system. In Parkinson’s disease, alpha-synuclein can fold incorrectly and collect into abnormal clumps, which are strongly linked to damage in brain cells.
The team collected Desulfovibrio bacteria from the stool of people with Parkinson’s disease and from healthy individuals. They then fed these different bacterial strains to worms that had been genetically modified to produce human alpha-synuclein.
Worms exposed to Desulfovibrio taken from people with Parkinson’s developed significantly more and larger alpha-synuclein clumps than worms exposed to bacteria from healthy people. The worms receiving bacteria from Parkinson’s patients were also more likely to die.
The findings suggest that particular strains of Desulfovibrio may encourage the harmful buildup of alpha-synuclein. The researchers proposed that substances produced by these bacteria, including hydrogen sulfide and compounds that can promote oxidative stress, could contribute to the process.
However, the study does not prove that these bacteria cause Parkinson’s disease in humans. Experiments in worms cannot fully reproduce the complexity of the human gut and brain, and people with Parkinson’s may have changes in their gut bacteria for many reasons, including diet, constipation, medication and the disease itself.
Researchers therefore need much more evidence before treatments aimed at Desulfovibrio could be recommended. Future studies may examine whether reducing certain bacterial strains changes alpha-synuclein buildup or Parkinson’s risk in animals and eventually in people.
The research was published in 2023 in the peer-reviewed journal Frontiers in Cellular and Infection Microbiology. The study adds to growing evidence that the connection between the gut and brain may be important in understanding Parkinson’s disease.
If scientists eventually confirm that specific gut bacteria contribute to Parkinson’s, the discovery could open new possibilities for identifying people at risk or developing treatments that target the microbiome. For now, however, there is no evidence that probiotics, antibiotics or other attempts to change gut bacteria can prevent Parkinson’s disease.
The findings offer an intriguing clue rather than a final answer. Understanding why Parkinson’s begins will likely require scientists to piece together genetics, environmental exposures, immune responses, gut health and changes in the brain over many years.
If you care about Parkinson’s disease, please read studies that Vitamin B may slow down cognitive decline, and Mediterranean diet could help lower risk of Parkinson’s.
For more health information, please see recent studies about how wheat gluten might be influencing our brain health, and Olive oil: a daily dose for better brain health..
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