Research into bacteria in the gut reveals how they potentially cause and affect progression of Parkinson’s

The gut microbiome is all of the microorganisms, such as bacteria and viruses, present in the gut. 

Research published in the scientific journal Nature Communications dives deeper than ever before into the gut microbiome of 490 people with Parkinson’s and 234 healthy individuals. 

Previous research has suggested that changes in the gut microbiome could be linked to Parkinson’s. Read more about the role of the gut in Parkinson’s on our blog.

The aim of the study was to investigate whether there were differences in the bacteria found in the gut in people with or without Parkinson’s.

The researchers did this by studying faecal samples from all participants, and identifying the different microorganisms present. The research used a variety of techniques to confirm that the results from the study were accurate. 

The results of the study:

• show there is an imbalance of many microorganisms in the guts of people with Parkinson’s 
• show what microorganisms cause the imbalance in the gut microbiome 
• suggest which genes and pathways may contribute to the mechanisms that cause Parkinson’s and affect its progression.

Read the full results in Nature Communications. 

The researchers identified 85 species of microorganism in the gut that are linked to people with Parkinson’s. 

Out of the 85 species connected with having Parkinson’s, 55 were increased and 29 were decreased in people with Parkinson’s compared to healthy individuals. This study confirmed changes in the gut microbiomes seen in other studies, highlighting their role in the cause of Parkinson’s. However, this study went further to connect how some changes in bacteria can affect a person's response to Parkinson’s medication and how they can influence the speed of progression of the condition.  

Some of the key confirmations and new findings are highlighted below. 

Inflammation

Some of the bacteria that were increased in people with Parkinson’s are linked to higher levels of inflammation. While inflammation is the body’s natural response to injury, high levels of inflammation can cause damage. 

Alpha-synuclein

Increases in these bacteria in the gut could potentially lead to more clumping of a protein associated with Parkinson’s, called alpha-synuclein. There were also increases in bacteria in the Parkinson’s gut which produce a molecule called Curli. Curli has been shown to increase the risk of alpha-synuclein proteins clumping together.

Medication

Another type of bacteria shown to be increased breaks down Parkinson’s medication, such as levodopa, in the gut before the medication can be absorbed. This reduces the effectiveness of some medication in the condition. 

Chemical messengers

Tyrosine is a molecule that is needed to make dopamine. Dopamine is a chemical messenger which is needed for movement and memory. Other bacteria that was increased in Parkinson’s breaks down tyrosine before it can be absorbed from the diet. This will decrease the body's ability to make dopamine, which is already in short supply in people with Parkinson’s.

Constipation

Certain bacteria release molecules which help movement in the gut, but there are  fewer of these bacteria in people with Parkinson’s. This could possibly be the reason that constipation is a common complaint in the condition.  

Neuroprotection

Another type of bacteria, also shown to be reduced in Parkinson’s, normally releases molecules which are absorbed from the gut and protects the brain against toxins. This links these bacteria not only to the cause but also to the progression of Parkinson’s.

This is the largest and most in-depth study into the microorganisms of the gut in people with Parkinson’s and provides lots of new insights, as well as confirming results from previous research. We now have a database of many microorganisms and pathways that can be studied in more specific research projects to find out how they affect people with Parkinson’s in more detail. 

The next steps could be to repeat these tests on more people from different parts of the world to see how the environment could affect the gut microbiome.

David Dexter, Associate Director of Research at Parkinson’s UK said:

“This important study has provided vital additional information on how the microbiome changes in people living with Parkinson’s. Researchers still have to answer the critical question of do these changes in gut bacteria actually cause Parkinson’s or do they develop once someone has the condition? 

“However, the key additional information this study provides is that the changes in gut bacteria can influence not only the progression of the condition but also how a person responds to their Parkinson’s medication. Further research is needed before we can suggest that rebalancing the gut in Parkinson’s to more like we see in healthy individuals will be an effective treatment for people living with Parkinson’s.”