Parkinson’s may start from bacteria in the gut, researchers say

“Desulfovibrio bacteria are (a) common bacteria in soil, water, (and) animal feces,” Per Saris, PhD, professor in the Department of Microbiology at the University of Helsinki and lead author of this study explained to Medical News Today. “We all encounter them via food, what we drink, and environmental contacts.”

“Typical for their metabolism is to produce hydrogen sulfide,” Dr. Saris continued. “They have the capacity to affect [the] production of magnetite and dehydrogenases.”

Dr. Saris said they believe hydrogen sulfide plays a role when the inflammation it causes reduces the effectiveness of the body’s hydrogen sulfide detoxification system.

“In addition, magnetite, greigite, and [or] superparamagnetic particles — all induced by Desulfovibrio bacteria — may play a role, as well as the LPS [or endotoxin] of these bacteria causing inflammation,” he added. “Other factors may also be involved — more studies are needed.”

Previous studies show an association between Desulfovibrio bacteria and inflammatory bowel disease and ulcerative colitis.

How could bacteria in the gut cause a disease of the brain?

According to Dr. Melita Petrossian, a neurologist and director of the Pacific Movement Disorders Center at Pacific Neuroscience Institute in Santa Monica, CA, it all has to do with the vagus nerve, which connects the gut with the brain.

“As (bacteria) metabolize food, they can create inflammation in the gut,” she explained to MNT. “They can cause (the) clumping together of a protein called alpha-synuclein. And those abnormal forms of alpha-synuclein can travel up the vagus nerve to the brain.”

Dr. Petrossian noted this is a more recent theory about the development of Parkinson’s via the gut.

“Prior to that, the theory was that environmental factors contributed to toxins entering through the nose, through the olfactory nerve to the olfactory bulb, and then directly back to the brainstem from there. So, these days, I think the consensus is that there’s probably a mix of where Parkinson’s comes from. For some people, it starts in the gut, and for others, it starts from the olfactory bulb.”

– Dr. Melita Petrossian, neurologist

According to Dr. Saris, for years researchers suggested a toxin or bacteria producing toxins may cause Parkinson’s disease. This is because constipation often precedes — even 10 years before — the disease’s movement disorder symptoms, when the brain is already damaged.

“Therefore, it was quite (logical) to start to study bacteria as a reason for alpha-synuclein aggregation,” Dr. Saris added.

In 2021, Dr. Saris and his research team published research showing an association between Desulfovibrio bacteria and Parkinson’s disease.

“The results of our first study suggested that Desulfovibrio bacteria may, based on correlation to Parkinson’s patients, have something to do with disease initiation,” Dr. Saris explained.

“Therefore, we isolated Desulfovibrio strains from Parkinson’s disease patients and tested if they can induce alpha-synuclein aggregation and it turned out to be the case. Clearly, they are the best candidates presently recognized that may initiate development towards Parkinson’s disease.”

Additionally, a study published in March 2023 found Desulfovibrio bacteria increased disease severity for people with Parkinson’s disease.

In this study, Dr. Saris and his team used a worm study to further examine the correlation between Desulfovibrio bacteria and Parkinson’s.

The scientists collected fecal samples from 10 Parkinson’s disease patients and their healthy spouses. The samples were checked for Desulfovibrio bacteria and if found, were isolated. The worms were then fed either the isolated Desulfovibrio bacteria or strains of E. coli bacteria.

Upon analysis, scientists found the worms fed Desulfovibrio bacteria from Parkinson’s disease patients had significantly more and larger aggregates of alpha-synuclein than the worms fed either Desulfovibrio bacteria from healthy people or E. coli.

Additionally, researchers observed worms fed Desulfovibrio bacteria from Parkinson’s disease patients died in significantly higher amounts than worms fed E. coli.

Dr. Saris said these results may be used for screening for people with high amounts of Desulfovibrio bacteria, and then for eradication treatments to help prevent Parkinson’s disease.

As for the next steps in this research, he said they are currently performing experiments in mice to verify their results.

“We (are also trying) to find out the mechanism (of) how these bacteria initiate disease using mutational studies and genome comparisons. We (are also screening) for viruses that can kill these bacteria and (looking) for bacteria that specifically inhibit Desulfovibrio. We (are also looking) for foods that inhibit Desulfovibrio.”

– Per Saris, PhD, lead researcher

MNT also spoke with Dr. Daniel Truong, neurologist, medical director, and founder of The Parkinson’s and Movement Disorder Institute at MemorialCare Orange Coast Medical Center, about this study.

He said the role of infections in the development of Parkinson’s disease is an area of active research, but currently there is no definitive answer.

“One theory is that infections may trigger or contribute to the development of Parkinson’s disease in certain individuals who are genetically predisposed to the disease,” Dr. Truong detailed. “This could occur through a variety of mechanisms, such as inflammation or the activation of the immune system.”

“Some studies have found that individuals who have had certain infections, such as those caused by the bacterium Helicobacter pylori or the influenza virus, may be at an increased risk of developing Parkinson’s disease later in life,” he added. “Other studies have suggested that chronic low-level infections, such as periodontal disease, may also be associated with a higher risk of Parkinson’s disease.”

And as up to 80% of people with Parkinson’s disease experience constipation, Dr. Truong said that can lead to the accumulation of toxins and waste products in the gut, ultimately altering the gut microbiome.

As for this current study, Dr. Truong said the next steps should include comparative genomics to identify genetic differences between the bacteria taken from people with Parkinson’s disease and without.

“As Desulfovibrio bacteria strains isolated from Parkinson’s disease patients and healthy individuals had significantly different (abilities) to induce alpha-synuclein aggregation and toxicity, further characterization of (these) Desulfovibrio bacteria strains’ different properties is needed,” he said. “Future studies are necessary to further evaluate the role of these traits in disease development.”

Because of the gut-brain connection to Parkinson’s disease, Dr. Petrossian said there are some things people can do through their diet to offer protection against the condition.

“While we don’t have proof of this, I think probably a big part of these bacterial causes of Parkinson’s … come about through misalignment of the gut microbiome,” she detailed. “And that’s most likely contributed to by the Western diet and the lack of fiber in people’s diet, and the lack of prebiotics, resulting in bacterial misalignment or bacterial overgrowth.”

Dr. Petrossian advised eating enough fiber, as well as fermented foods. However, if a person is already taking medication for Parkinson’s disease, talk to your doctor first as fermented foods may impact their medication.

“If somebody doesn’t have Parkinson’s (and) is thinking about how to prevent Parkinson’s, definitely focusing on fiber, a balanced, healthy whole diet with a good balance of fermented foods, in conjunction with exercise, sleep hygiene, social engagement, and meditation,” she added. “All those lifestyle choices do make a difference in reducing the risk of Parkinson’s disease.”

– Dr. Melita Petrossian, neurologist