Study links gum disease-causing bacteria to Alzheimer's

Researchers say they've found more evidence linking bacteria found in a common type of gum disease to dementia. A new study, published in the journal Science Advances, found a key pathogen associated with chronic periodontal disease in the brains of people with Alzheimer's disease.

The study authors say these results, plus additional testing in mice, provide "solid evidence" of a link between the two diseases and may offer a potential new way to treat Alzheimer's. The devastating illness affects 47 million people worldwide, and there is no cure.

However, Alzheimer's experts not involved in the research caution that it is too early to tell how strong this association is, or whether it could lead to effective treatments.

What the new study found

Scientists from Cortexyme, Inc., a privately held, clinical-stage pharmaceutical company, analyzed the brain tissues of patients with Alzheimer's disease and found evidence of Porphyromonas gingivalis, the bacteria associated with gum disease.

Further tests in mice found that this bacteria could travel from the mouth to the brain and increased production of amyloid beta, a protein strongly associated with Alzheimer's.

In addition to the Porphyromonas gingivalis, the researchers found toxic enzymes produced by the bacteria called gingipains in the neurons of patients with Alzheimer's. Higher levels gingipain were associated with tau and ubiquitin, two other proteins involved in the development of Alzheimer's. 

The team also tested drugs in mice aimed at clearing the harmful bacteria and blocking its toxic enzymes. In these lab experiments, scientists were able to reduce the number of Porphyromonas gingivalis bacteria in the infected brains, block the production of toxic proteins, and halt degeneration in the brain.

The researchers hope this will provide the basis for developing a new therapy that could one day treat humans in a similar way.

"The findings of this study offer evidence that P. gingivalis and gingipains in the brain play a central role in the pathogenesis [development] of AD [Alzheimer's disease], providing a new conceptual framework for disease treatment," the study authors write.

Research on infections and Alzheimer's disease

This is not the first study to show a relationship between gum disease and Alzheimer's.

A 2017 study out of Taiwan found that people with chronic gum disease lasting 10 years had a 70 percent increased risk for developing Alzheimer's. Another small study published in 2016 in the journal PLOS ONE found gum disease was associated with a six-fold increase in the rate of cognitive decline in people with mild to moderate dementia.

Other research has looked at whether various bacterial, viral, or fungal infections may play a role in Alzheimer's, but there is currently not enough evidence to say.

"The idea that bacteria and viruses may play a part in brain disease like Alzheimer's is not necessarily new," Rebecca Edelmayer, Ph.D., director of scientific engagement for the Alzheimer's Association, told CBS News. "But what this paper suggests is really an association and not causation and that should be very clearly emphasized when we're talking about studies like this. More research is needed to really identify a causative role for microbes."

In other words, it's unknown whether gum disease increases the risk of Alzheimer's or if people with dementia have an increased risk of gum disease because of poor oral care.

Edelmayer also cautions not to put too much weight on drugs tested in mice. "It really will be important to see how this plays out in human randomized controlled trials, which is the gold standard for understanding whether a therapeutic targeting something like the P. gingivalis mechanism would actually be effective," she said.

Could good oral care help prevent Alzheimer's?

While taking care of your teeth and gums is an important part of healthy aging, Edelmayer says it's too early to say if those steps could help prevent Alzheimer's disease.

Of course, there are many factors that go into someone's individual risk of developing dementia. The Alzheimer's Association has a campaign called "10 Ways to Love Your Brain" to help people lower their risk.

"We think a lot about things like diet, exercise, a good management of cardiovascular health, getting good sleep. All of these things could potentially play a role as a lifestyle intervention for decreasing your risk of developing cognitive decline," Edelmayer said.

She notes that good oral health could one day fall into one of these categories if there's more evidence to show that gum disease actually increases the risk for developing dementia.

Still, Edelmayer says with so much still unknown about the disease, studies like this are important for gaining a better understanding of Alzheimer's.

"I think the research really reinforces the complexity of Alzheimer's disease," she said. "It highlights the importance of sharing information and experiments and data like this very freely and widely across the research community so this robust discussion about this kind of science takes place."