Although most people do not associate oral diseases with serious health problems, there is increasing evidence showing that oral bacteria play an important role in systemic diseases such as colon cancer and heart disease. Now, new research from the Forsyth Institute shows a link between periodontal (gum) disease and the formation of amyloid plaque, a hallmark of Alzheimer’s disease.
In their article, ‘Microglial Cell Response to Experimental Periodontal Disease’, published in the Journal of Neuroinflammation, Forsyth scientists and colleagues at Boston University show that gum disease can cause changes in brain cells called microglial cells, which are responsible for defending the brain from amyloid plaque. This plaque is a type of protein that is associated with cell death and cognitive decline in people with Alzheimer’s. The study provides important information about how oral bacteria reach the brain and the role of neuroinflammation in Alzheimer’s disease.
“We knew from one of our earlier studies that inflammation associated with gum disease activates an inflammatory response in the brain,” said Dr. Alpdogan Kantarci, a senior member of Forsyth’s staff and lead author of the study. “In this study, we asked the question, can oral bacteria cause a change in brain cells?”
This is how oral bacteria make us lose protection against amyloid plaque
The microglial cells that the researchers studied are a type of white blood cell responsible for digesting amyloid plaque. The Forsyth scientists discovered that when exposed to oral bacteria, microglial cells become overstimulated and eat too much. “They basically became obese,” Dr. Kantarci said. “They couldn’t digest the plaque formations anymore.”
The finding is important in showing the impact of gum disease on systemic health. Gum disease causes lesions to develop between the gums and teeth. The area of this lesion is the size of your palm. Dr. Kantarci explained: “It’s an open wound that allows bacteria from the mouth to enter the bloodstream and circulate to other parts of the body.” These bacteria can cross the blood-brain barrier and stimulate microglial cells in the brain.
Microglial cells are responsible for digesting amyloid plaque. When exposed to oral bacteria, they become overstimulated and eat too much, so they can no longer digest the plaque formations.
Using mouse oral bacteria to cause gum disease in laboratory mice, the scientists were able to track the progression of periodontal disease in mice and confirm that the bacteria had traveled to the brain.
They then isolated microglial cells from the brain and exposed them to oral bacteria. This exposure stimulated microglial cells, activated neuroinflammation, and changed the way microglial cells dealt with amyloid plaques.
“Recognizing how oral bacteria cause neuroinflammation will help us develop much more targeted strategies,” said Dr. Kantarci. “This study suggests that in order to prevent neuroinflammation and neurodegeneration, it will be critical to control oral inflammation associated with periodontal disease. The mouth is part of the body and if inflammation and oral infection are not taken care of, systemic diseases, such as Alzheimer’s, cannot be prevented in a reproducible way.
This study is the first time that scientists caused periodontal disease with mouse-specific bacteria and were able to study the effects of the same species’ oral microbiome on the brain. Having bacteria and cells of the same species brings the test closer to replicating what the process looks like in humans.
Source: Forsyth Institute
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