A new study finds that long-term exposure to periodontal bacteria leads to inflammation and degeneration in brain neurons in mice similar to the effects of Alzheimer’s disease in humans.
Periodontitis is a common but preventable gum infection that damages the soft tissue and bone supporting the tooth. As the immune system reacts and toxins are released, inflammation occurs. Without treatment, the infection eventually leads to tooth loss.
The study, published in the journal PLOS ONE, suggests that periodontal disease may be an initiator of Alzheimer’s, which currently has no cure.
“Other studies have demonstrated a close association between periodontitis and cognitive impairment, but this is the first study to show that exposure to the periodontal bacteria results in the formation of senile plaques that accelerate the development of neuropathology found in Alzheimer’s patients,” said Dr. Keiko Watanabe, professor of periodontics at the University of Illinois at Chicago (UIC) College of Dentistry and corresponding author on the study.
“This was a big surprise,” Watanabe said. “We did not expect that the periodontal pathogen would have this much influence on the brain, or that the effects would so thoroughly resemble Alzheimer’s disease.”
To investigate the effect of this bacteria on brain health, the researchers established chronic periodontitis in 10 wild-type mice. Another group of 10 mice served as controls. After 22 weeks of repeated oral application of the bacteria to the study group, the researchers studied the brain tissue of the mice and compared brain health.
The researchers discovered that the mice continuously exposed to the bacteria had significantly higher amounts of accumulated amyloid beta — a senile plaque found in the brain tissue of Alzheimer’s patients. The periodontitis mice also had more brain inflammation and fewer intact neurons due to degeneration.
These results were further supported by amyloid beta protein analysis as well as RNA analysis which showed greater gene expression associated with inflammation and degeneration in the periodontitis mice. DNA from the periodontal bacteria was also found in the brain tissue of these mice, and a bacterial protein was observed inside their neurons.
“Our data not only demonstrate the movement of bacteria from the mouth to the brain, but also that chronic infection leads to neural effects similar to Alzheimer’s,” Watanabe said.
The researchers say these findings are extremely important, partly because they used a wild-type mouse model; most mice used to study Alzheimer’s are transgenic mice, which have been genetically altered to more strongly express genes associated with the senile plaque and enable Alzheimer’s development.
“Using a wild-type mouse model added strength to our study because these mice were not primed to develop the disease, and use of this model gives additional weight to our findings that periodontal bacteria may kick-start the development of the Alzheimer’s,” Watanabe said.
Understanding the triggers and risk factors for the development of Alzheimer’s is critical to the development of treatments, say the researchers, particularly when it comes to sporadic, or late-onset disease, which makes up more than 95 percent of cases and has largely unknown causes and mechanisms.
While the results are significant for the scientific community, Watanabe said there are lessons for everyone.
“Oral hygiene is an important predictor of disease, including diseases that happen outside the mouth,” she said. “People can do so much for their personal health by taking oral health seriously.”