How Mouth Bacteria Can Crawl Into Your Brain and Destroy It

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Neuro Athletes,

Little did I know that your mouth can be the gateway to several health problems that extend beyond a toothache or cavity.

Primer.

Alzheimer’s disease (AD) - a condition that often involves the accumulation of two types of proteins called amyloid and tau in the brain- has been linked to oral health. AD patients exhibit neuroinflammation consistent with infection, including microglial activation, inflammasome activation, complement activation, and altered cytokine profiles. However, new research is showing that another important cause of neuroinflammation may be peripheral infections such as periodontitis.

Although a number of bacteria can be recovered from this disease, the keystone pathogen that causes periodontal and gingival diseases is Porphyromonas gingivalis.

Porphyromonas gingivalis: An Overview

Porphyromonas gingivalis, a prominent component of oral microorganism communities, is the main pathogen that causes periodontitis.

Periodontal disease represents a group of oral inflammatory infections initiated by oral pathogens which exist as a complex biofilms on the tooth surface and cause destruction to tooth supporting tissues. The severity of this disease ranges from mild and reversible inflammation of the gingiva (gingivitis) to chronic destruction of connective tissues, the formation of periodontal pocket and ultimately result in loss of teeth. 

The link

Porphyromonas gingivalis is a bacterium that is a member of the normal oral microbiota but may overgrow and thrive uncontrollably under conditions of poor oral hygiene or habitual smoking and alcohol consumption and can leak from the gum into the blood circulation and potentially infiltrate the blood-brain-barrier (BBB). The provocative findings are the latest in a wave of research suggesting microbial infections may play a role in Alzheimer’s disease. 

The idea is that as periodontitis breaks down cells in the gums. P. gingivalis is able to break into the rest of the body from there, it can travel to more distant organs and establish bacterial colonies and places it’s not meant to be including, as animal studies have confirmed, the brain. There P. gingivalis releases toxins and that's when things start to get really messy.

The thinking is that these toxins compromise the tissue structure around the bacterial colonies which makes the brain's protective barrier leaky, damages cells, and impacts cell's ability to function correctly. So in response to that compounds that are associated with the damage, like amyloid beta could form an act like a scab over these wounds, there's even evidence that suggests P. gingivalis can make it harder for the brain to get rid of this stuff.

To explore whether the bacteria were actually causing Alzheimer’s as opposed to it just being a related factor, researchers rubbed the gums of healthy mice with P. gingivalis to produce an infection. After six weeks the researchers examined the animals brains and found the presence of the bacteria along with higher than normal levels of β-amyloid protein and dying neurons. The P. gingivalis bacteria had damaged tau proteins which contributed to the formation of tangles in the brain, a common characteristic of Alzheimer’s.

In a second part of the experiment, mice were given a drug that removes P. gingivalis from the brain. This reduced brain inflammation, stopped β-amyloid production and neurodegeneration and even began to repair damaged neurons. While an antibiotic known to kill this type of bacteria also did this, it was not as effective initially, and the bacteria quickly became resistant. Scientists hope that in the future these results will lead to a treatment for the Alzheimer’s or even possibly a vaccine that prevents it.

Let’s sum it up

• BBB dysfunction is an important hallmark of AD which can be caused by neuroinflammation.

• An important cause of neuroinflammation may be P. gingivalis which reaches the brain after systemic spread from its primary habitat – the periodontal pocket, established under ‘chronic’ periodontitis. 

• Although P. gingivalis is not be the sole organism that can enter the brain, it has the preference to initiate dysbiosis even at low concentrations.

Take Away: What Does This Mean For Me?

I wouldn’t be running to your local physicians office telling them about the times you missed a brush or floss however with most guidelines, consistency is of utmost importance. “The main conclusion we still have is: brush and floss” James Noble, a neurologist at Columbia University who has studied the link between periodontal disease and Alzheimer’s.

You may always have billions of bacteria in your mouth, but with good oral hygiene practices and regular dental visits, you limit the risk of P. gingivalis causing periodontal disease.

Tell me the truth. How often do you floss?

I am neurotic about my flossing. I actually carry dental floss with me and run to the bathroom after a meal at a fancy restaurant to floss my teeth. Is that weird?

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Dr. David Rabin- a Board-Certified Psychiatrist, Neuroscientist, and inventor who studies resilience and the impact of chronic stress in our day-to-day lives.

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That’s it for this week! Hit me up if you have any stories, feedback, or insights to share. Otherwise, see you next week!