Summary of Three Intestinal Bacteria Found in Dementia With Lewy Bodies Identified:
Researchers at Nagoya University Graduate School of Medicine in Japan have identified three gut bacteria – Collinsella, Ruminococcus, and Bifidobacterium – that are associated with dementia with Lewy bodies (DLB). Their findings suggest new avenues for diagnosis and treatment of this neurodegenerative disease. The researchers found similarities in gut bacteria between Parkinson’s disease and DLB, with both diseases showing decreases in short-chain fatty acid-producing bacteria and increases in bacteria that degrade the intestinal mucosa. However, they also found differences unique to DLB, including increases in Ruminococcus torques and Collinsella, and a decrease in Bifidobacterium. The researchers believe that these findings could lead to improvements in predicting and treating both Parkinson’s and DLB.
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Dementia with Lewy bodies (DLB) is a challenging form of dementia that currently has no cure. However, recent research has suggested that the gut microbiome, or the microorganisms that reside in the human digestive tract, may play a vital role in the development of DLB. Specifically, a group led by researchers at the Nagoya University Graduate School of Medicine in Japan has identified three bacteria that are involved in DLB: Collinsella, Ruminococcus, and Bifidobacterium. These findings, reported in the journal npj Parkinson’s Disease, may provide new avenues for diagnosis and treatment of DLB.
DLB is associated with abnormal deposits of alpha-synuclein, a protein in the brain that plays a role in transmitting signals between neurons. These deposits, known as Lewy bodies, affect chemicals in the brain and lead to declines in thinking, reasoning, and memory. Symptoms include confusion, memory loss, impaired movement, and visual hallucinations.
Currently, physicians find it difficult to predict which people with Parkinson’s disease will develop cognitive decline within a year and become patients with DLB. However, the researchers discovered that three intestinal bacteria, Collinsella, Ruminococcus, and Bifidobacterium, were associated with patients with DLB, providing a possible way of identifying and diagnosing this neurodegenerative disease.
Interestingly, the researchers also found similarities between the gut bacteria involved in Parkinson’s disease and DLB. In both diseases, the bacteria Akkermansia, which degrades the intestinal mucosa, increased. On the other hand, the bacteria that produce short-chain fatty acids (SCFA) in the gut decreased. Decreases in SCFA-producing bacteria have been repeatedly reported in Parkinson’s disease, Alzheimer’s disease, and ALS. This suggests that it is a common feature of neurodegenerative diseases.
In addition, the researchers found an increase in Ruminococcus torques, an increase in Collinsella, and a decrease in Bifidobacterium in patients with DLB. This was different from Parkinson’s disease patients, whose levels did not change. Importantly, the reduced levels of Bifidobacterium may suggest possible ways to treat DLB. Bifidobacterium increases brain-derived neurotrophic factor, a key protein that supports the growth, development, and maintenance of neurons in the central and peripheral nervous systems. Therefore, its decrease in DLB is likely associated with cognitive decline.
Similarly, both Ruminococcus torques and Collinsella are intestinal bacteria that carry an enzyme, the product of which regulates inflammation in a region of the brain called the substantia nigra. The substantia nigra produces dopamine, a neurotransmitter that is involved in the regulation of movement and is deficient in Parkinson’s disease. Compared to Parkinson’s disease, the levels of these bacteria were higher in people with DLB. This may explain why the effect on movement is delayed, a key feature that distinguishes DLB from Parkinson’s disease.
The researchers suggest that their findings can be used for both diagnosis and treatment. The administration of Ruminococcus torques and Collinsella in patients with Parkinson’s may delay neuroinflammation in the substantia nigra. Therapeutic intervention to increase Bifidobacterium may delay the onset and progression of DLB and reduce cognitive dysfunction.
The presence of intestinal bacteria unique to DLB may explain why some patients develop Parkinson’s disease, while others develop DLB first. Normalizing the abnormal bacteria shared between DLB and Parkinson’s disease may delay the development of both diseases. Improving the gut microbiota is a stepping stone in the treatment of dementia. The researchers hope that their findings may pave the way for the discovery of new and completely different therapeutics for DLB.
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