(By Dr. Joseph D. Lim and Dr. Kenneth Lester Lim, BS-MMG, DDM, MSc-OI)
THE ORAL cavity, aka the oral microbiome, plays a critical role in maintaining oral health.
Changes in the oral environment in the mouth may disrupt the balance of microbes, increasing the risk of being infected with diseases.
This is true with smoking, either with tobacco, cigarettes or marijuana.
Little is known about how long-term marijuana use affects the microbes and researchers at the Medical University of South Carolina ventured to find out.
Dr. Wei Jiang, an immunologist, led a study to explore the effects of cannabis use on the oral microbiome.
Her co-researcher is Matthew Greseth, a postdoctoral student in the Department of Biochemistry and Molecular Biology and Assistant Director of Science Communications initiatives in the College of Graduate Studies.
The research team screened the saliva of long-term cannabis users and found increased levels of Actinomyces meyeri in the mouth that correlated with the length of cannabis use.
Increased levels of bacteria may lead to disorders of the immune system.
To assess how high levels of A. meyeri affect the immune system, Jiang’s team gave mice A. meyeri through the mouth and observed an increase in the levels of b-amyloid in the brain, one of the proteins associated with Alzheimer’s disease.
It suggests that long-term cannabis use alters brain health, according to the study published in EBioMedicine.
“I think the most exciting aspect of our work is the link between the oral microbiome and brain health,” said Dr. Jiang. “To prove this link, we went beyond the typical associative studies in humans and conducted a causal study in mice.”
Smoking upsets the balance of microbes in the oral cavity. Smoking marijuana is known to influence neural functioning, and some of its components, such as tetrahydrocannabinol, can affect the immune system.
To analyze changes to the oral microbiome in the context of marijuana use, Dr. Jiang analyzed the saliva of chronic cannabis smokers and compared them with the saliva of tobacco smokers and nonsmokers.
The researchers identified similar changes in several bacterial species between smokers and nonsmokers; however, A. meyeri was uniquely changed in cannabis smokers.
According to Mr. Greseth, the Actinomyces family of bacteria, of which A. meyeri is a member, are commensal bacteria of the oral cavity, but they can also become opportunistic pathogens. Smoking can cause disruptions in the oral mucosa that may lead to bacterial fragments or even whole bacteria migrating into the circulatory system, where they can influence the immune system, he said.
Dr. Jiang found increased levels of antibodies against A. meyeri in the plasma of cannabis smokers.
To find out in detail how A. meyeri influences brain health, the researchers inoculated mice with A. meyeri. These mice exhibited reduced activity, increased migration of macrophages into the brain and increased levels of b-amyloid. These results suggest that long-term cannabis use alters brain health, especially the build-up of toxic b-amyloid protein, which is associated with Alzheimer’s disease and other dementias.
The presence of immune cells in the brain may lead to altered brain function, presumably through persistent brain inflammation, which can impair brain function. Unexpectedly, however, macrophages stimulated by A. meyeri did not result in an inflammatory response but did induce macrophage migration to the brain.
“That’s a puzzle,’’ Dr. Jiang pointed out. ‘In general, people think that if you activate macrophages and they migrate to the brain, they produce pro-inflammatory signals that result in brain inflammation and eventually brain dysfunction.”
However, she continued, brain dysfunction can also occur without the conventional inflammatory signals.
Marijuana use may cause dementia but may also help people who already have the condition, said Mr. Greset.
This paradox, he said, may be due to the frequency of use, duration of use or heavy versus light use – all of which warrants further investigation.
Dr. Jiang and her research team would like to investigate further how A. meyeri causes amyloid protein production in the brain and develop an inhibitor to this process.
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Dr. Joseph D. Lim is the former Associate Dean of the College of Dentistry, University of the East; former Dean, College of Dentistry, National University; Past President and Honorary Fellow of the Asian Oral Implant Academy; Honorary Fellow of the Japan College of Oral Implantologists; and Honorary Life Member of the Thai Association of Dental Implantology. For questions on dental health, e-mail jdlim2008@gmail.com or text 0917-8591515.
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Dr. Kenneth Lester Lim, BS-MMG, DDM, MSc-OI, graduated Doctor of Dental Medicine, University of the Philippines College of Dentistry, Manila, 2011; Bachelor of Science in Marketing Management, De la Salle University, Manila, 2002; and Master of Science (MSc.) in Oral Implantology, Goethe University, Frankfurt, Germany, 2019. He is an Associate professor; Fellow, International Congress of Oral Implantologists; Member, American Academy of Implant Dentistry and Philippine College of Oral Implantologists. For questions on dental health, e-mail limdentalcenter@gmail.com/PN
