Is Parkinson's Disease a Gut Problem?
POSTED ON IN Research BY Christopher Centeno
My dad died of a horrible disease called Lewy Body dementia. It's like all of the bad parts of Parkinson's mixed with all of the bad things associated with Alzheimer's. Back then, not much was known about what caused Parkinson's disease. The most bizarre thing is that as we dig deeper into what causes these diseases, instead of highlighting the brain, the focus is now shifting to the gut? Let me explain. When I first heard that the bacteria in our gut could be linked to everything from depression to Alzheimer's disease to Parkinson's disease, my biggest question as a physician was simple: how does this work? Now scientists may have found an answer and have proposed a brand-new name for the interaction: mapranosis. Before I get to the latest research, let's review some of the gut brain connections I've shared here over the past year.
Parkinson's Disease and the Gut
When you think of Parkinson's disease, the condition of the gut microbiome (the community of bacteria and other micro-organisms that live inside the intestinal tract) probably doesn't cross your mind; however, the connection between the two has become a hot topic in the research world the past couple of years. Parkinson's disease is a neurological disease that has no cure and progressively worsens over time. It's caused by less dopamine being released by a part of the brain called the substantia nigra. It can cause slowed movements and tremors, balance issues, slurred speech, dementia, and many more neurological symptoms that become more extreme and less responsive to treatment as the disease advances. Parkinson's disease occurs when nerve cells in the substantia nigra section of the midbrain begin to degenerate, decreasing the production of dopamine. This results in the uncontrolled movements, and other symptoms, that are the telltale signature of Parkinson's disease. The potential gut-brain connection in Parkinson's disease began a few years ago when certain fibers found in the brains of Parkinson's patients were also discovered in the patients' guts. In a more recent study, researchers found evidence that the gut of Parkinson's subjects was different from the gut of non-Parkinson's subjects, when mice injected with gut bacteria from Parkinson's subjects deteriorated much more rapidly than mice injected with gut bacteria from non-Parkinson's subjects. This led researchers to suggest that Parkinson's disease may actually be initiated in the gut.
Emotion and the Gut
Another link you probably wouldn't make to your gut microbiome is your ability to process emotions. However, a few months ago, another study did just that when it connected emotion processing in the frontal cortex and hippocampus areas of the brain to certain bacteria in the gut. Subjects who had more Prevotella (compared to subjects with more Bacteroides) in their gut microbiome had a lower-volume hippocampus and were more inclined to anxiety, distress, and irritability when processing emotion. Again, the research has only revealed the connection, while the mechanism for this connection is still yet to be determined.
Mapranosis: The Gut-Brain Interaction
For many proteins to properly function, there is a specific way they must be “folded.” When this process is disrupted, problems can ensue. A few months ago we looked at unfolded proteins and their association with other conditions, such as metabolic syndrome and even arthritis. It's also been well established certain brain diseases, such as Parkinson's and Alzheimer's, are associated with misfolded amyloid nerve cell proteins. To understand what these misfolded amyloid proteins are, think good proteins gone bad. They were once healthy proteins that have become unhealthy, forming in clumps and depositing plaques and wreaking havoc on otherwise healthy tissues. The new study found that amyloid proteins that are produced by certain gut microbes (bacteria, viruses, parasites, etc.) increase neuroinflammation (inflammation in the nervous system) and alter protein structure in the central nervous system, a process they called “cross-seeding.” Researchers proposed a new scientific term—mapranosis—for this interaction and suggested this mapranosis may lead to the initiation of brain disease, such as Parkinson's disease. Interestingly, researchers also identified several avenues through which microbial amyloid proteins in the gut may access or influence the central nervous system, including the vagus nerve (which runs from the medulla oblongata in the brain and branches all the way down to the colon), the GI tract itself (e.g., mouth, stomach, and intestines), and even through nerve receptors in the roof of the nose (due to the close proximity of the nasal cavity and the brain) that sense smell. All have direct connections to areas of the body, particularly the gut, that tend to harbor bacteria and other microbes, opening the door for mapranosis, or this gut-brain interaction, to occur. The upshot? It's crazy how much we don't know about the body! The idea that the bacteria in your gut may be causing havoc in your brain rewrites the medical texts once again. I'm excited to see what the next few years of gut microbiome research brings!
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