New research out of the U.S. suggests the saliva microbiome of chronic weed smokers with cannabis use disorder could be associated with central nervous system (CNS) abnormalities that can affect the brain, spinal cord, and nerves found throughout the body.
A microbiome relates to the microorganisms in a particular environment. In the case of saliva, it comprises bacteria shed from oral surfaces.
“This is the first study to reveal that long-term oral cannabis exposure is associated with oral enrichment of Actinomyces meyeri (A. meyeri) and its contributions to CNS abnormalities,” notes the study in the December 2021 issue of The Lancet.
A. meyeri, which resides on mucosal surfaces, has been defined as a disease-causing microorganism and an infrequent cause of human actinomycosis, a rare bacterial infection.
To find out if there was an association, mice were orally inoculated with three types of live bacteria — namely A. meyeri, Actinomyces odontolyticus, a rare bacterial infection in humans with only 46 cases reported from its discovery in 1958, and Neisseria elongata, which is a constituent of the normal oral flora.
The inoculation was conducted twice a week for six months. The idea was to mimic human conditions, the study points out.
What researchers found was that cannabis smoking in humans was associated with oral microbial dysbiosis, generally defined as a reduction in microbial diversity and the loss of beneficial bacteria.
Subjects experienced the biggest increases in Streptococcus, bacteria commonly found in the throat and on the skin, and Actinomyces, which are part of the normal flora of the mouth and gastrointestinal tract, and the biggest decreases in Neisseria, a large genus of bacteria that colonize the mucosal surfaces of many animals, compared to non-cannabis smokers.
Furthermore, investigators found a link between first cannabis use and A. meyeri. The bacterium “was highly enriched in the saliva from chronic cannabis smokers compared to those of non-smokers, and its oral enrichment was associated with the age of first cannabis use,” they write in the study.
Looking at directly administering the bacterium without cannabis or its components, researchers found it “could elicit an alteration in the oral-microbiome-brain axis in a mouse model.”
That axis refers to the network of connections involving multiple biological systems that allow bidirectional communication between oral bacteria and the brain.
In the long term, “oral inoculation of A. meyeri bacterium to mice resulted in behavioral changes, macrophage infiltration and increased Aβ 42 protein production.” Aβ42, which is an amino acid product, has been found to be a core biomarker for the diagnosis of Alzheimer’s Disease.
Authors suggest study findings “may help develop novel treatments targeting the microbiota (which are pathogenic microorganisms found in and on all multicellular organisms) or its active molecules for prevention or treatment of some neurological abnormalities.”
A study from 2014 found actinomycosis is a rare chronic disease caused by Actinomyces spp., which are part of the normal flora of the oral cavity and respiratory tract. “Preventive measures, such as reduction of alcohol abuse and improvement of dental hygiene, may limit occurrence of pulmonary, cervicofacial and CNS actinomycosis.”
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