Electronic cigarettes (e-cigarettes) are battery powered devices that deliver aerosols, which often contain nicotine, as well as flavorings, propylene glycol and glycerin. Many e-cigarettes look like cigarettes and the aerosols are inhaled like cigarette smoke. 4 to 6% of UK and 8 to 10% of US smokers have used e-cigarettes, and they are increasingly used in younger age groups without prior smoking history.
E-cigarettes are marketed as a ‘safer’ substitute to cigarettes, delivering nicotine without the toxic products of cigarette smoke, and are recommended to reduce smoking. This is supported by the Royal College of Physicians and Public Health England, who encourage e-cigarettes as a strategy for cigarette smoking cessation.
While e-cigarettes are considered less risky than cigarettes, they may still damage the lungs. E-cigarette aerosols typically contain nicotine, additives and other contaminants that can affect normal lung biology, and in vitro studies have shown that e-cigarettes can modify lung epithelial and endothelial cell biology. However, these have not been confirmed in vivo.
We designed our study to examine the effects of e-cigarettes on lung biology in those who have never smoked (‘never-smokers’). Ten volunteer never-smokers were included, with seven using e-cigarettes with nicotine, and three using e-cigarettes without. A small sample was used for ethical reasons, since the effects of e-cigarette exposure were unknown.
Even in such a small study population, the results showed clear changes equivalent to smoking two cigarettes in all three cell populations sampled.
Volunteers were assessed on day 1 with a questionnaire and chest x-ray, and their vital signs, O2 saturation, and lung function were checked. Three cell populations were sampled: plasma endothelial microparticles (EMPs), the small airway epithelium, and alveolar macrophages. One week later, subjects inhaled 10 puffs from e-cigarettes, waited 30 min, and inhaled another 10 puffs. Immediately after each exposure, the questionnaire and vital sign and O2 saturation tests were repeated. Two hours later, the remaining tests were repeated, and mRNA on the lung samples was sequenced.
Even in such a small study population, the results showed clear changes equivalent to smoking two cigarettes in all three cell populations sampled. This doesn’t show that e-cigarettes cause lung disease, but suggests e-cigarettes are not harmless, and that it may be premature for doctors to recommend their use before further study.
Our study demonstrates that e-cigarette exposure results in elevated levels of pulmonary capillary endothelial microparticles and transcriptome changes in lung small airway epithelium and in alveolar macrophages. We aren’t aware of any previous assessments of lung biology following e-cigarette exposure in never-smokers, but this is consistent with previous studies on e-cigarette use in smokers. These reported increased coughing and respiratory difficulties and decreased exhaled nitric oxide, as well as altered mucin secretions and a unique lung immune response in e-cigarette users.
Studying the possible adverse effects of e-cigarettes on lung health is complicated. There are many brands of e-cigarettes, with a variety of flavors and other additives in addition to nicotine. Further, because nicotine is addictive, it is not ethical to study long-term e-cigarette exposure in never-smokers. This means many studies on e-cigarettes are carried out in ex-cigarette smokers, whose lungs are already compromised to some degree.
Despite these challenges, our data suggests that even limited, acute exposure to e-cigarettes dysregulates biology of the human lung in vivo. Whether this results in lung disease can only be evaluated by large scale, long-term studies of individuals who have used only e-cigarettes. Such a study is currently challenging to conduct, as most e-cigarette users have previously been exposed to cigarette smoke exposure.
However, the observed biological changes in these cell populations suggest that e-cigarette may not be as safe as we assume. Therefore, recommending e-cigarettes as safer alternatives to cigarette smoking should be considered carefully until further studies are conducted.