by Ben Bowman
— Dental hygiene is a critical part of our daily bodily cleaning regimen. Society reminds us to brush our teeth every day, twice per day. And dentists remind us every six months that we aren’t flossing enough. But there may be an even more persuasive, and far more grave reason to break out the floss and keep those pearly whites clean. New research is beginning to suggest that the balance of bacteria that inhabit our mouths may play a role in our risk in developing the devastating brain disease, Alzheimer’s disease; specifically, when a person has the gum disease known as periodontitis.
According to the expanded Human Oral Microbiome Database (eHOMD) there are more than 750 bacterial species that make themselves a home in the human mouth. The balance of what is considered to be a healthy oral space can be shifted for a variety of reasons, including poor diet, poor oral hygiene, and excessive alcohol consumption. When conditions are shifted to a diseased state, periodontitis can manifest.
One particular bacterium that is the focus of a lot of research on how periodontitis may lead to Alzheimer’s disease is called Porphyrmonas gingivalis. P. gingivalis is a tricky little bacterium in that it is known as one of the main havoc-wreaking culprits for causing periodontitis. P. gingivalis is a gram-negative bacterium meaning that it has a two layered cell membrane (inner and outer) and because of these two lines of defense it makes it hard to eliminate via antibiotics. The idea of a gram-negative bacterium is similar to that of a castle. The walls protect what is inside, and an additional layer of protection is there in the form of the guards that stand outside of those walls in the case of an attack. And like those guards, gram negative bacteria have weaponry on the outer membrane in the form of a molecule called lipopolysaccharide (LPS). LPS can act as a bacterial toxin that can cause inflammation and septic shock in humans if it enters the blood, which is precisely what can happen during disease progression or if damage is done to the gums (think aggressive tooth brushing.) Additionally, P. gingivalis creates a protein, which we know as the plaque on our teeth.
When bacteria enter the bloodstream, known as bacteremia, our own immune system sounds the alarms via chemicals called cytokines and production of associated proteins. Similar to when an invader attacks, our body’s troops come to aid and fight back against it. But also like in combat, collateral damage can occur. This is what happens when our immune cells release chemicals that lead to inflammation throughout the body via the bloodstream. When this collateral damage is able to travel back to headquarters (the brain), some major issues arise.
Figure 1: The proposed mechanism by which P. gingivalis can produce plaque causing inflammation and damage at the gum tissue. Source: https://www.biovendor.com/blog/is-porphyromonas-gingivalis-the-main-offender-of-alzheimers-disease
These chemicals produced by our own immune cells in the face of danger, along with the plaques produced by the bacteria can have detrimental effects on the integrity of our blood brain barrier (BBB). The BBB, which is isolated from the rest of our immune system, is an additional layer of protection surrounding the brain against anything trying to enter. The BBB is weakened by the introduction of these disease associated products. The plaques from P. gingivalis and accumulation of immune cell chemicals widen the openings of the BBB and allow for bacteria and plaques to enter a space that is generally protected from any outside forces. Plaque formation can begin to stack upon each other on the brain, which is what is seen in the brains of Alzheimer’s disease patients. And while scientists are still looking to fully understand exactly how the plaques cause the BBB to weaken, a picture is beginning to form on how it occurs.
Figure 2: Here we can see how the bacteria can gain access to the bloodstream through damage gum tissue at the base of the tooth. From there, the bacteria can travel through the cardiovascular system to the brain. Source: Ryder, Mark. Journal of Periodontology
All of this information leads to a better understanding of a possible explanation for how Alzheimer’s disease can develop. The good news is, if it holds true, strides can be made in its prevention. Oral hygiene is a possible simple and effective way to keep periodontitis away. So next time the dentist tells you to floss, listen. It may end up saving your life.