Aerosols from electronic cigarettes (e-cigarettes) affect biomarkers in oral cells in laboratory cultures, suggesting an increased risk for diseases such as oral cancer, researchers say.
"This study shows they can be harmful to the oral cavity and should not be considered a safe alternative to tobacco smoking," Diana Messadi, DDS, PhD, told Medscape Medical News.
Dr Messadi, a professor of dentistry at the University of California, Los Angeles, and colleagues published the finding May 25 in PLOS One.
As e-cigarettes become more popular, experts have clashed over whether they provide more benefits or harm. Advocates argue that they can help smokers quit or shift to a less harmful mode of nicotine consumption. Detractors say e-cigarettes may encourage people to begin inhaling toxic substances for the first time.
"We got interested because [of] public health advertisements around the world that e-cigarettes are healthier than tobacco cigarettes," said Dr Messadi.
In particular, Dr Messadi said support for e-cigarettes from public health officials in the United Kingdom attracted her attention. "That was the debate that really triggered our interest in e-cigarettes."
In the typical e-cigarette, a battery-powered heating element atomizes a liquid containing nicotine, propylene glycol or glycerin, and flavorings. The user inhales this aerosol.
Some studies have shown that e-cigarettes can reduce the number of cigarettes consumed by smokers without significant adverse effects, but long-term effects are unclear, Dr Messadi and colleagues report.
Other research has shown that menthol-flavored e-cigarette liquids can reduce cell proliferation and viability in cultures and impair immune functions in mice, they write.
To better understand the effects of e-cigarettes, the researchers cultured normal human oral keratinocytes. They built a puffing machine to push clean air through e-cigarettes through the front air hole. They impinged the aerosols into the culture media for 10 minutes and found that the longer the puff, the greater the concentration of aerosols.
As controls, they cultivated a second set of cells without aerosols, and a third set with fumed silica impinged in its media.
Using an adenosine triphosphate assay as a measure, they found that significantly fewer of the cells exposed to e-cigarette aerosols were viable (P < .05) than were the untreated cells. Of the cells exposed to fumed silica, more were viable than the cells exposed to e-cigarette aerosols, but fewer were viable than the untreated cells.
Intracellular glutathione levels were also lower in the cells exposed to e-cigarette aerosols and the cells exposed to fumed silica compared with the untreated cells. Glutathione helps protect cells from the oxidative stress believed to lead to cancer in tobacco smokers.
The cells exposed to e-cigarette aerosols also expressed more heme oxygenase than the untreated cells. High levels of this enzyme may be correlated with inflammation.
The finding suggests e-cigarettes may increase the risk for periodontal disease as well as cancer, Dr Messadi said.
The researchers plan to proceed with experiments in animals and ultimately to see whether e-cigarette aerosols cause cancer or other diseases.
"E-cigarettes are pretty recent in use, so it's still early to detect any oral changes in patients," Dr Messadi explained. "You need years of use before you find any changes. But basically translating it to patient care is our ultimate aim."
On the basis of what she knows now, she said, clinicians should counsel their nonsmoking patients to avoid e-cigarettes. "Especially, they should discourage adolescents and young adults from starting e-cigarettes if they never smoked," she said.
"For adults who want to stop smoking, I tell them if it stops them from smoking, it's good, but in the long run they also have to stop using it."
She noted that the US Food and Drug Administration has not approved e-cigarettes for smoking cessation.
The new study reinforces the evidence that e-cigarettes pose a risk to the user, said Nelson Rhodus, DMD, MPH, a distinguished professor of oral medicine and otolaryngology at the University of Minnesota in Minneapolis.
"There is a misperception among patients that if they have stopped using regular cigarettes and started using e-cigarettes that they don't have risk, and that's not true," said Dr Rhodus, who was not involved in the study.
Even if the ingredients in the aerosol were not toxic, using e-cigarettes might still cause harm, he said. "Just the act of inhaling something over the oral mucosa has an effect in drying out the tissue," he said.
Researchers at the University of Minnesota are conducting similar studies and getting similar results, he said.
However, he cautioned that the effects on humans cannot be definitively determined by studying cells cultured in a laboratory. "Human beings are more complex, and there are other factors, and some of these might be protective factors," he said.
The authors and Dr Rhodus have disclosed no relevant financial relationships.
PLoS ONE. 2016;11:e0154447. Full text
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Cite this: E-Cigarettes Aerosols Damage Oral Cells in Laboratory - Medscape - Jul 15, 2016.