Review spotlights gut bacteria as possible Parkinson’s treatment target

A growing body of research suggests that the gut microbiome — the community of bacteria and other microscopic organisms that live in the human digestive tract — may play key roles in the development and progression of Parkinson’s disease.

Data suggest that it may be possible to develop Parkinson’s therapies that target the gut microbiome, but many unanswered questions and scientific challenges remain before these findings can be translated into reliable treatment strategies for patients. In a new review paper, four scientists in India provided an overview of what’s currently known about the relationship between the gut microbiome and Parkinson’s, and highlighted open questions and areas where continued scientific inquiry is necessary.

The paper, “Gut microbiome immune interactions drive neuroinflammation and neurodegeneration in Parkinson’s disease,” was published in Discover Immunity.

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Gut-brain link gains attention

Parkinson’s has long been thought of as a disorder that mainly affects the brain, but new research is showing that the disease has more widespread effects on other systems within the body. In particular, studies have suggested that Parkinson’s is marked not only by damage in the brain, but also by problems involving the immune system and gut-related processes.

“Growing research indicates that [Parkinson’s] is more than simply a brain issue; it is a condition defined by ongoing communication between the [digestive system], immune system, and [brain],” the researchers wrote.

The gut microbiome plays critical roles in human health and disease that are only beginning to be understood. Many studies have suggested that the gut microbiome is dysregulated in people with Parkinson’s. Although there is considerable variation across studies, the researchers highlighted several broad patterns that have emerged across research.

In particular, Parkinson’s tends to be marked by reduced levels of bacteria that produce anti-inflammatory signaling molecules called short-chain fatty acids. At the same time, people with Parkinson’s tend to have higher levels of pro-inflammatory or endotoxin-enriched bacteria that may activate inflammatory pathways.

Collectively, these data suggest that the gut microbiome in Parkinson’s may promote a more pro-inflammatory environment throughout the body. This is noteworthy because chronic inflammation is thought to contribute to the development and progression of Parkinson’s. The researchers noted that gut bacteria may also influence brain-related processes by altering signaling in the gut’s nervous system and the nerves that connect the gut to the brain.

Gut bacteria eyed for treatment

Given that the gut microbiome seems to be involved in Parkinson’s, many researchers have begun exploring whether it might be possible to develop Parkinson’s therapies that target the gut microbiome through interventions like probiotic supplements, other microbiome-focused approaches, or dietary changes. In theory, targeting the microbiome offers a distinct advantage because gut bacteria seem to influence many different facets of the disease, which the researchers said makes microbiome-targeting therapies “inherently multimodal when compared to traditional single-target drugs.”

Even though data suggest that the gut microbiome is involved in Parkinson’s, many questions remain unanswered. Perhaps the most pressing is that, to date, it’s been impossible to prove whether changes in the gut microbiome are a cause of Parkinson’s or a consequence of the disease.

“To advance the field, well-designed longitudinal human studies are required, particularly in [early disease stage] populations, to determine whether microbiome and immune alterations are causal, contributory, or consequential,” the researchers wrote.

Technical challenges also complicate microbiome research. For example, the human microbiome is naturally highly variable from person to person, influenced by factors ranging from genetics to diet and lifestyle. This makes it hard to separate disease-related changes from natural variation. Additionally, scientists often rely on different methods to analyze the gut microbiome, which can make it hard to draw comparisons across studies. The researchers stressed the need to address these issues through large-scale research using standardized methodologies.

Researchers call for broader studies

“Advancing this field will require sustained, cross-disciplinary integration of microbiome research, immunology, neurology, and systems biology. Such collaboration is essential for refining mechanistically informed biomarkers, delineating [disease-driving] pathways, and designing clinical trials that capture the biological and [clinical variability] of patients with Parkinson’s disease,” the scientists wrote.

The researchers also noted that, since the microbiome is so naturally variable, treatments targeting gut bacteria may need to be highly personalized.

“Rather than a one-size-fits-all approach, future interventions may be tailored based on disease subtypes … as well as individual microbial, metabolic, and immune profiles. Such stratification could inform targeted therapies,” they wrote.