Gum disease linked to Alzheimer's, study claims

Faith Castro
January 26, 2019

"We will have to see the outcome of this ongoing trial before we know more about its potential as a treatment for Alzheimer's". The new study is one of a growing number that suggest microbes play a role in Alzheimer's disease.

They found evidence of toxic enzymes, known as gingipains, that are released by P. gingivalis, as well as DNA from the bacterium. Additional co-authors are Guo-Jun Chen of Chongqing Medical University, PhD, and Xiaomin Wang, MD, PhD., of the Beijing Institute for Brain Disorders, Capital Medical University.

Researchers looked at brain tissue from autopsies of individuals with and without Alzheimer's disease and found a majority of those with the disease had higher levels of an enzyme called gingipains, which is produced by P. gingivalis.

However, there was also good news. Instead, they developed a small molecule that inhibits the gingipains themselves, which they showed could reduce neurodegeneration in mice injected with these enzymes.

Singhrao, who has also conducted research into the cause of Alzheimer's, had earlier discovered that the bacteria invade the brains of mice which had gum infections. In initial tests with human volunteers, a similar drug seemed safe and showed signs of improving cognition in nine participants with Alzheimer's, the company says.

"It will be important to confirm our findings in late-onset Alzheimer's disease and to define the time period over which neurofilament changes have to be assessed for optimal clinical predictability", says senior author Mathias Jucker, professor of cellular neurology at the German Center for Neurodegenerative Diseases in Tübingen who leads the DIAN study in Germany.

The study adds to evidence of a link between gum disease and dementia, but it's still not clear if gum disease bacteria actually trigger Alzheimer's, said scientists not involved in the study, BBC News reported.

Manager of Education and Outreach at the Alzheimers Association, Mayra Ligeza, spoke to the Downers Grove Library informing an audience of more than 30 people about the malignant disease. Even the brains of roughly 50 deceased, apparently dementia-free elderly people selected as controls often had lower levels of both gingipains and the proteins indicating Alzheimer's pathology.

The team measured NfL protein levels in the participants through blood samples, brain imaging and cognitive tests on average every two and half years over the last seven years. The team also examined the cerebrospinal fluid and saliva of 10 patients believed to have Alzheimer's disease, and found the P. gingivalis gene hmuY in seven, and P. gingivalis itself in all of them. "I'm much less convinced that [it] causes Alzheimer's disease", says neurobiologist Robert Moir of the Harvard University-affiliated Massachusetts General Hospital (MGH) in Boston, whose work suggests the β-amyloid protein that forms plaques in the brains of Alzheimer's patients is a protective response to microbial invaders.

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The bacteria may access the brain by infecting immune system cells or spreading through cranial nerves passing through the head and jaw, said the researchers.

Traditional broad-spectrum antibiotics would probably be ineffective against P. gingivalis in the brain, according to the research. But he stressed this won't prevent the brain from becoming infected by P. gingivalis.

Doctors have observed that gingivitis is more common among people with Alzheimer's disease, although that could be because these people find dental hygiene more challenging.

Gum disease affects an estimated 45% of the United Kingdom population, according to the British Dental Association (BDA).

The bacteria Porphyromonas gingivalis, known as Pg, lead to the gum infection chronic periodontitis, causing chronic inflammation and potential tooth loss. "This remains an area of active investigation", he said.

Experts have long warned about the negative effects of sleep deprivation, and new research suggests that people with Alzheimer's disease may be particularly affected.

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

"Despite the involvement of a virus, the [Alzheimer's] disease is apparently not contagious", she told Newsweek.

Marzi, who was not involved in the research, said in an email to CNN that if "this result can be replicated in larger cohorts and more generally in sporadic cases of Alzheimer's Disease, the blood test for NfL would indeed be a promising biomarker or diagnostic tool".

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