​Wei Jiang, a professor of Microbiology and Immunology at the Medical University of South Carolina (MUSC), has focused her research on discerning how cannabis smoking affects oral health and alters oral bacteria.

Speaking to EurekaAlert!, Wei said, “This will be the first study to investigate the cannabis-altered oral microbiome and its effects on the brain.”

Past clinical studies have noted that smoke contains compounds which affect oral health. The changes in bacteria these compounds create have been linked to cardiovascular diseases, preterm birth and Alzheimer’s disease. By allowing this bacteria to flourish, it can enter the bloodstream, subsequently damaging other organs, including the brain.

In 2021 Wei and her team released a study showing that frequent cannabis smoking alters the oral microbiome. In particular, the team found higher levels of the Actinomyces meyeri (A. meyeri) bacterium.

Wei said, “In general, the amount of A. meyeri should be very low in a healthy oral microbiome.”

The study exposed mice to A. meyeri for six months. The results showed increased inflammation and heightened levels of amyloid-beta proteins in their brains. Such proteins have previously been linked to memory loss and Alzheimer’s disease.

The new study will explore the underlying link between high levels of A. meyeri in the oral microbiome of cannabis users and brain disease.

Wei explained, “Psychological dependency on a drug can have harmful neurological effects, but we don’t know what is driving these effects in heavy cannabis users.

“We know that oral health affects your mental health. However, we don’t know exactly what role the microbiome plays.”

To investigate the effects of cannabis, the researchers will expose mice to various levels of THC and CBD. The data collected will be used to determine the effect of A. meyeri on oral bacteria.

Explaining her current hypothesis, Wei said, “We think that long-term exposure to THC, but not CBD, will increase levels of A. meyeri in saliva and lead to harmful neurological effects in mice.”

Wei’s team will also consider if humans with “cannabis use disorder” see changes within their oral microbiome and altered memory.

“We expect memory-related deficits to be associated with greater levels of A. meyeri in frequent cannabis users compared with nonusers.

“If our hypothesis is correct, a therapeutic strategy targeting A. meyeri could reduce irregularities in brain function in frequent cannabis users.

“In the future, it may also be useful to screen for certain bacteria as biomarkers of different diseases that affect the brain, such as Alzheimer’s disease.”

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