Parkinson's Disease and the gut microbiome

Microbiome science changes rapidly, making this an exciting, emerging field to be part of. It also means that a significant part of my week is spent deep in the latest research! I find the information I need directly from peer-reviewed medical literature, as well as preprints that can be a great source of the newest ideas to explore. And of course, it's also valuable to connect with some amazing, pioneering microbiome colleagues around the world to share our learnings from clinical practice. This means that when I come to analysing your stool test results I can feel sure my knowledge is as up-to-date as is humanly possible.

When researching a particular condition, I usually need to piece together insights from a range of microbiome studies. These can have conflicting results, often due to variations in study design. So I was delighted to find a paper published by Nature in March 2021, that analysed data from 10 different studies from around the world, to compare the microbiomes of 1,269 people in total, with and without Parkinson’s Disease. The reviewers processed the data to account for differences in study design, and all studies used 16S rRNA stool testing, which is the same technology as the Biomesight test kits I use — so the insights from this research are directly applicable to my practice.

Research has long shown people with Parkinson’s can have increased gut permeability and inflammation, as well as alterations in their microbiome profile. These are thought to result in changes in neurotransmitter production and inflammatory processes, but also other functional changes, including microglial activity. (We can think of microglia as cells that form part of a cleaning system in our brains.)

Certain bacterial species are more abundant, while others are depleted

The study showed particular patterns of microbiome alterations are associated with Parkinson's Disease. I have summarised the main findings in bullet points below (to make life easier for my microbiome colleagues)!

When analysing microbiome test results for clients who have a family history of Parkinson's Disease, I will be looking in particular at the levels of certain butyrate-producing bacteria that protect against inflammation. These bacteria have also been found at lower levels in other neuroinflammatory and neurodegenerative disorders, including multiple sclerosis (MS).

I will also be looking at whether their microbiome shows increased Akkermansia and Bifidobacteria populations, as those seem to be consistently higher in the microbiomes of people with Parkinson's. Interestingly, these kinds of bacteria are generally considered beneficial (at lower levels) with Bifidobacteria producing important neurotransmitters (primarily GABA), and yet Akkermansia is also found to be higher in people with MS.

In working with clients who have MS, I’ve seen microbiome repair to rebalance the levels of Akkermansia and butyrate producers is associated with a stabilisation and improvement in symptoms and even the prevention of new brain lesions, which has been very exciting!

The researchers also found that microbiome diversity can be increased in Parkinson's Disease. However, they suggest this is due to a decrease in the kinds of bacteria that usually dominate in a healthy microbiome, and an increase in those that are usually less abundant. This underlines why microbiome diversity cannot be used as a measure of microbiome health on its own, and needs to be considered in the context of the individual species present and the microbiome profile as a whole.

Earlier studies have also suggested that higher levels of pro-inflammatory Proteobacteria species can be associated with Parkinson's Disease, so I will be looking at those levels too, to assess a client's overall inflammatory profile.

The study showed kinds of bacteria are found in greater abundance in people with Parkinson's:

• Lactobacillus, Akkermansia, Hungatella, Alistipes and Bifidobacterium.

• Additionally, the R-7 group of the Christensenellaceae family, the genera Methanobrevibacter, Oscillobacter, Frisingicoccus, and Varibaculum were also more abundant in Parkinson's, but with smaller effect size and higher variability across studies. (Christensenella species can support the proliferation of Methanobrevibacter through cross-feeding, which may be why constipation is so common with Parkinson's.)

• Other minor increases were also observed within these families: Rikenellaeae, Porphyromonadaceae, Oscillospiraceae, and the Clostridium methylpentosum group in the Oscillospirales order

And these beneficial bacteria are found at lower levels:

• Roseburia, Blautia, Fusicatenibacter, Faecalibacterium, Moryella and Anaerostipes.

• Other Lachnospiraceae genera were also found at lower levels in some studies.

Conflicting results were found for bacteria within the Prevotellaceae family. Several studies detected these to be very depleted in Parkinson’s, while others found no differences in abundances or found them increased.

We need to consider the microbiome as a whole

While bearing these individual species in mind, it is very important to look at the overall balance of the microbiome as a whole, and consider the function of its different metabolic pathways – remembering the gut microbiome is a complex ecosystem.

Microbiome composition – and its behaviour – are also dependent on our genetics, lifestyle and diet. So it's not possible to diagnose Parkinson’s Disease from microbiome stool testing. Also, we don’t fully know how many of the microbiome changes are a cause or effect of Parkinson's symptoms, although the evidence is growing for a causal link. However, we do know — from research and clinical practice — that nourishing the beneficial species in our microbiome can boost its anti-inflammatory activity, reduce the populations of certain bacteria and change the overall shape of the community towards a health-promoting balance.

The researchers of this study conclude that microbiome disruptions are key to the development of the neurological and digestive symptoms associated with Parkinson’s Disease, suggesting microbiome interventions could have real potential in their prevention. I feel very privileged to have the chance to put their theories into practice.

REFERENCE

Romano et al (2021) Meta-analysis of the Parkinson’s disease gut microbiome suggests alterations linked to intestinal inflammation, Nature Parkinson’s Disease (2021)7:27 https://doi.org/10.1038/s41531-021-00156-z

Viola Sampson BSc is a Microbiome Analyst practising in London UK and online. You can book a consultation, or get in touch to find out more.