Imbalanced bacterial community in the gums connected to Alzheimer’s infection biomarker

Imbalanced bacterial community in the gums connected to Alzheimer’s infection biomarker


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  • Source: New York University

  • Date: 12 Apr,2021

Older adults with more harmful than healthy bacteria in their gums are more likely to have evidence for amyloid beta–a key biomarker for Alzheimer’s disease–in their cerebrospinal fluid (CSF), according to new research from NYU College of Dentistry and Weill Cornell Medicine. However, this imbalance in oral bacteria was not associated with another Alzheimer’s biomarker called tau.

Periodontal disease–which affects 70 percent of adults 65 and older, according to CDC estimates–is characterized by chronic and systemic inflammation, with pockets between the teeth and gums expanding and harboring bacteria.

“The mouth is home to both harmful bacteria that promote inflammation and healthy, protective bacteria. We found that having evidence for brain amyloid was associated with increased harmful and decreased beneficial bacteria.”

Alzheimer’s disease is characterized by two hallmark proteins in the brain: amyloid beta, which clumps together to form plaques and is thought to be the primary protein deposited in the brain as Alzheimer’s develops, and tau, which builds up in nerve cells and forms tangles.

Leon is also the director of the Brain Health Imaging Institute at Weill Cornell Medicine. Participants underwent oral examinations to collect bacterial samples from under the gumline, and lumbar puncture was used to obtain CSF so as to determine the levels of amyloid beta and tau.

To estimate the brain’s manifestation of Alzheimer’s proteins, the researchers looked for lower levels of amyloid beta (which translate to higher brain amyloid levels) and higher levels of tau (which reflect greater brain tangle accumulations) in the CSF.

The mechanisms by which levels of brain amyloid accumulate and are associated with Alzheimer’s pathology are complex and only partially understood. The present study adds support to the understanding that proinflammatory diseases disrupt the clearance of amyloid from the brain, as retention of amyloid in the brain can be estimated from CSF levels. Amyloid changes are often observed decades before tau pathology or the symptoms of Alzheimer’s disease are detected.”

Mony J. de Leon, EdD, Study Senior Author and Professor, Neuroscience in Radiology

Analyzing the bacterial DNA of the samples taken from beneath the gumline under the advice of NYU College of Dentistry microbiologist Deepak Saxena, PhD, the researchers quantified bacteria known to be detrimental to oral health (e.g. Prevotella, Porphyromonas, Fretibacterium) and pro-oral health bacteria (e.g. Corynebacterium, Actinomyces, Capnocytophaga).

The results showed that individuals with an imbalance in bacteria, using a ratio favoring harmful to healthy bacteria, were more likely to have the Alzheimer’s signature of decreased CSF amyloid levels. The researchers hypothesize that since substantial levels of healthy bacteria help maintain bacterial balance and lessen inflammation, they are protective against Alzheimer’s.

“Our results reveal the value of the overall oral microbiome–not just of the role of’bad’ bacteria, but also’good’ bacteria–in modulating amyloid levels,” said Kamer. “These findings indicate that multiple oral bacteria are involved in the expression of amyloid lesions.”

The researchers didn’t find an association between gum germs and tau levels in this research, so it remains unknown whether tau lesions will develop later or when the subjects will develop the symptoms of Alzheimer’s. The researchers plan to conduct a longitudinal study and a clinical trial to test if improving gum disease –through”deep cleanings” to remove deposits of plaque and tartar from under the gumline–can alter brain amyloid and protect against Alzheimer’s disease.


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