Adverse Effects of Electronic Cigarettes on the Disease-Naïve Oral Microbiome
January 30, 2022 7 minutes read
By Lindsey N. Clark, MD, and Taimur K. Mian, MD
Dr. Clark is a PGY-1 Psychiatry Resident at Community Health Network, Indianapolis.
Dr. Mian is a Psychiatry Clinical Faculty Member at Community Health Network, Indianapolis.
SYNOPSIS: A robust metagenomic comparison study of the effects of electronic cigarettes on oral microbiomes suggested that the unique aerosol component of electronic cigarettes poses increased risk to development of oral cavity disease.
SOURCE: Ganesan SM, Dabdoub SM, Nagaraja HN, et al. Adverse effects of electronic cigarettes on the disease-naïve oral microbiome. Sci Adv 2020;6:eaaz0108.
The oral cavity hosts a diverse group of bacterial communities, with more than 1,000 species across seven phyla. Imbalances in the oral microbiome communities and increased inflammatory responses to oral bacteria have been associated with diseases, such as periodontitis, dental caries tooth loss, and oropharyngeal cancer.
The effects of cigarette use, chewing tobacco, and alcohol consumption on the oral cavity have been studied widely, with results showing these habits offset the healthy balance of oral bacterial communities and create the potential for harmful bacterial species to be introduced into the oral cavity, increasing the risk for disease development.1,2 However, the effects of e-cigarettes on the oral microbiome, and their potential for harm, remain understudied. Considering e-cigarettes are relatively novel because they deliver nicotine in a unique heated aerosol component, more insight into their effects on the oral microbiome is needed to determine their risk for oral cavity illness.
Ganesan et al analyzed the subgingival microbiomes across e-cigarette users, smokers, and nonsmokers. They recruited 123 individuals considered systemically and periodontally healthy. Periodontal health, or gingival inflammation assessment, was defined as attachment loss of < 1, fewer than three sites with 4 mm of probe depths, and a bleeding index of < 20%. Systemic health was established using the American Society of Anesthesiologists Physical Status Classification. Participants were placed in one of five groups based on their tobacco use status: smoker, nonsmoker, e-cigarette user, former smoker currently using e-cigarettes, and concomitant cigarette and e-cigarette user. Current smoking was defined as at least a five-pack-year history. Nonsmokers were defined as people who consumed fewer than 100 cigarettes in their lifetimes. Those in the e-cigarette category used the product daily for at least three months, with at least one cartridge per day, or 1 mL of liquid per day. Sample size was determined to have at least an 80% chance of detecting clades of bacterial genes that differed in abundance by 1%. Exclusion criteria consisted of presence of controlled or uncontrolled diabetes; HIV infection; use of immunosuppressant medication, bisphosphonates, steroids, antibiotic therapy, or oral prophylactic procedures within the past three months; and fewer than 20 teeth in dentition.
Subgingival plaque samples using sterile endodontic paper points and gingival crevicular fluid collections were taken from each participant at 15 sites within the oral cavity. Bacterial DNA was isolated from the paper point samples and quantified using Qiagen DNA MiniAmp kits and Qubit fluorometers. Phylogenetic profiles for each participant’s oral microbiome were created using Kraken v1.1 software and complete genome data lists from the Human Oral Microbiome Database. Each phylogenetic profile then was tested for alpha (within-group) and beta (between-group) genetic diversity using PhyloToAST v1.4 and QIIME v1.9.
For quality control, all DNA samples were sequenced in two runs, and samples were randomly assigned to each run. Each participant’s gingival crevicular fluid samples also were used to determine cytokine assays, measuring levels of interferon-gamma (INF-gamma), interleukin 2 (IL-2), IL-4, IL-6, IL-8, IL-10, granulocyte-macrophage colony stimulating factor (GM-CSF), and tumor necrosis factor-alpha (TNF-alpha). To assess and compare the genetic variability and gene clustering in the oral microbiome community between each participant cohort, Ganesan et al generated principal coordinate analysis (PCoA) plots using the software PhyloToAST (PcoA.py). The significance of identified genetic clustering in participant cohorts was determined using permutational multivariate analysis of variance (MANOVA) (adonis function, vegan package for R). Additionally, the relative abundance of functional genes across participant cohorts was assessed using linear discriminant analysis (LDA) (scikit-learn v0.18.0). Wilk’s lambda was used to test for significance of LDA identified functional gene clustering.
Overall, Ganesan et al compared oral microbiomes of 20 e-cigarette users, 25 nonsmokers, 25 current cigarette smokers, 25 former smokers, and 25 dual users. E-cigarette users were age 21 to 35 years, predominantly white, and reported using e-cigarettes products with 6 mg to 18 mg of nicotine. Interpretation of PCoA and LDA plots revealed three significantly different oral microbial profiles of e-cigarette users, smokers, and nonsmokers (P = 0.008, MANOVA/Wilks). There was no significant microbial profile difference between e-cigarette users, dual users, and former smokers who had switched to e-cigarettes (P = 0.27 and 0.35).
Further nonmetric multidimensional scaling analysis of variance in the user groups showed the duration of e-cigarette use (< 6 months vs. > 10 months) was the strongest source of variation, with nicotine concentration and type of flavoring not contributing to variations seen in the oral microbial profiles. Furthermore, 70% of the metagenome in e-cigarette users was shared by more than 80% of subjects, whereas the smoker and nonsmoker cohorts only shared 40% and 50% of their metagenomes, respectively. This presence of a large, core microbiome present in most e-cigarette users that differed significantly from the microbiome of smokers and nonsmokers suggests the aerosol effects of e-cigarettes alters the oral cavity bacterial community via different mechanisms than traditional cigarettes.
Additionally, the metagenome profile of e-cigarette users showed more genes related to virulence factors vs. smokers and nonsmokers (P < 0.05), including cell wall and capsular polysaccharides, peptidoglycan, and lipopolysaccharide biosynthesis, stress response, quorum sensing and biofilm formation, and resistance to antibiotics and toxic compounds. These findings suggest the unique oral bacterial community found in e-cigarette users could increase exposure to bacterial factors that cause disease in human hosts. Further analysis of the cytokine assays taken from the participant’s gingival crevicular fluid showed those who used e-cigarettes had significantly higher levels of proinflammatory cytokines IL-2, IL-6, GM-CSF, TNF-alpha, and INF-gamma, and lower levels of anti-inflammatory cytokine IL-10 (P < 0.05, Dunn’s test). These findings suggest the e-cigarette user microbial profile creates a higher inflammatory burden and response vs. cigarette users and nonsmokers.
Cigarette users showed a similar increase in proinflammatory cytokines vs. never-smokers as well with increases in cytokines IL-2, IL-6, and IL-8, TNF-alpha, and INF-gamma, and lower levels of IL-10. The authors noted this difference may suggest that while both e-cigarette and cigarette use increase inflammatory response cytokines in the oral microbiome, different biological pathways are involved.
COMMENTARY
Ultimately, this study shows e-cigarette use can shift the oral microbiome community to a state with more exposure to bacterial virulence factors and increased host inflammatory response, both states that can predispose an individual to oral cavity diseases. The authors noted while no e-cigarette users had been diagnosed with periodontitis, the functional genetic profile of their oral microbiome “bore remarkable resemblance to individuals with periodontitis.”3,4 Ganesan et al hypothesized the glycerol and glycol components of e-cigarette aerosol may serve as a nutrient source for bacteria, altering the microbial profile and biofilm structures in the oral cavity of e-cigarette users.
While e-cigarettes have been on the market for 17 years, and studies have begun to show the potential for harmful effects on the respiratory system, little remains known about their effect on the oral cavity and the oral microbiome.5,6 Because the heated aerosol contains fewer harmful chemicals than an ignited tobacco device, it has been suggested their use is safer than cigarettes, and they often have been advertised as a smoking cessation device.7 However, studies show the biggest user group of e-cigarettes is a young population taking up e-cigarette use as a new habit vs. a tool for smoking cessation. One study revealed 20% of high schoolers in the United States admitted to trying e-cigarettes at least once a month.8 Considering these numbers, physicians are incredibly likely to encounter a young patient who is using e-cigarettes recreationally. Physicians should consider the results of the Ganesan et al study, along with the growing body of literature, which demonstrate that e-cigarettes expose users to a unique aerosol-nicotine compound that may increase the risk for oral cavity disease. Talking to patients about e-cigarette use and the effects on their oral health may be beneficial for reducing the risks of developing oral cavity diseases associated with e-cigarette use.
REFERENCES
- Börnigen D, Ren B, Pickard R, et al. Alterations in oral bacterial communities are associated with risk factors for oral and oropharyngeal cancer. Sci Rep 2017;7:17686.
- Wade WG. Oral microbiome in health and disease. Pharmacol Res 2013;69:137-143.
- Dabdoub SM, Ganesan SM, Kumar PS. Comparative metagenomics reveals taxonomically idiosyncratic yet functionally congruent communities in periodontitis. Sci Rep 2016;6:38993.
- Duran-Pinedo AE, Chen T, Teles R, et al. Community-wide transcription of the oral microbiome in subjects with and without periodontitis. ISME J 2014;8:1659-1672.
- Gotts JE, Jordt S, McConnell R, Tarran R. What are the respiratory effects of e-cigarettes? BMJ 2019;366:l5275.
- Mukhopadhyay S, Mehrad M, Dammert P, et al. Lung biopsy findings in severe pulmonary illness associated with e-cigarette use (vaping): A report of eight cases. Am J Clin Pathol 2020;153:30-39.
- Pulvers K, Nollen NL, Rice M, et al. Effect of pod e-cigarettes vs. cigarettes on carcinogen exposure among African American and Latinx smokers. JAMA Netw Open 2020;3:e2026324.
- Wang TW, Neff LJ, Park-Lee E, et al. E-cigarette use among middle and high school students — United States, 2020. MMWR Morb Mortal Wkly Rep 2020;69:1310-1312.
A robust metagenomic comparison study of the effects of electronic cigarettes on oral microbiomes suggested that the unique aerosol component of electronic cigarettes poses increased risk to development of oral cavity disease.
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