A recent study published in PlosOne reports seemingly alarming effects of electronic cigarette liquids with and without nicotine on human lung epithelial cells. Exposure of the cells for 24 or 48 hours to e-liquids resulted in increased expression of a proinflammatory cytokine (IL-6), enhanced the susceptibility of the cells to infection by human rhinovirus, and reduced the expression levels of host defense molecules. From these data, the authors conclude that the inhalation of e-liquids may have deleterious health effects of on the lung.
Link to the article: http://www.plosone.org/annotation/listThread.action?root=81975
This conclusion is in striking conflict with the tremendously positive experiences countless users of electronic cigarettes have reported in internet forums and social networks. Nonetheless, health authorities will certainly appreciate the result as another allegedly strong argument against electronic cigarettes. Therefore, I started surveys in two German vaping forums, asking for changes in the frequency of airway infections after switching from smoking to vaping. The results are published as a comment to the article on the PlosOne website: http://www.plosone.org/annotation/listThread.action?root=81975j
Since reader comments in scientific journals are hardly noticed by the public, I am posting my comment in the blog as well, hoping for wider distribution of its content.
Electronic Cigarettes and Airway Infections: The User Experience
The authors report that exposure of human lung epithelial cells to e-cigarette liquids promotes IL-6 production and rhinovirus infection. The effects were enhanced in the presence of nicotine. Based on these observations the authors conclude that the inhalation of e-liquids with or without nicotine may have deleterious health effects on the lung .
The obvious question raised by this study is the translation of the cell culture experiments to the inhalation of e-liquid vapor. This is an important point because the conclusions of the present study may have a major impact on the assessment and regulation of e-cigarettes.
To tentatively address this issue, a survey has been carried out in two pertinent German internet forums:
Most of the active members of these forums use high-performance second and third generation devices. The survey was limited to users who had reduced their tobacco consumption by ≥95% since at least two months. They were asked to vote for one of the following statements (here translated to English):
Since I have been switching to e-cigarettes the frequency of airway infections is
o not markedly changed
Participants were explicitly requested to restrict their answers to the common cold and disregard potential effects on other types of infections or related lung diseases such as asthma or COPD. Besides simple voting, participants had the possibility to report their experience verbally in the respective threads of the forums, which are publicly accessible (in German language).
The survey was started September 24, 2014 and is still open. The data presented reflect the state on September 26, 2 p.m. CET. At this time point, 307 votes had been received. Of those 207 (67.4%) reported on reduced frequency, 89 (29.0%) observed no changes and 11 (3.6%) noticed an increased incidence of airway infections. Many users voting for reduced incidence verbally reported dramatic reductions of both frequency and severity of infections. On the other hand, most of the participants who had not seen any changes said that they did not considerably suffer from airway infections while still smoking and that this condition has remained unchanged after switching to e-cigarettes.
The survey is relatively small, relies on self-evaluation of the participants, and was not controlled for potentially relevant parameters such as time elapsed since switching or associated changes in lifestyle. Nevertheless the data are very clear and strongly suggest that switching from smoking to the inhalation of e-liquids does not increase but rather decreases the frequency of airway infections. This result is not particularly surprising in view of the well known immune suppressive effects of tobacco smoking, resulting in increased susceptibility of smokers to infections of the respiratory tract . The data provide further evidence for the health benefits associated with the switch from tobacco smoking to vaping reported previously .
Obviously, the data do not allow judging the effects of e-liquid inhalation compared to breathing clean air. However, as e-cigarettes are almost exclusively used by former smokers as an alternative to tobacco cigarettes, the effects of e-liquids on non-smokers are irrelevant.
The result of this survey indicates that the cell culture model used by Wu et al. does not reflect the consequences of e-liquid inhalation by humans. Presumably incubation of lung epithelial cells for up to 48 hours with e-liquids does not adequately mimic the effects of inhaled vapor. Moreover, the authors were apparently mistaken about the final nicotine concentrations in their experiments. According to the Material and Methods section of their paper, cells were incubated with up to 0.3% (v/v) of liquid containing 18 mg of nicotine per ml. Though not explicitly stated in the manuscript, this dilution would result in 54 µg/ml final. The authors state “the final nicotine concentrations were within the serum nicotine range of e-cigarette users.” However, a serum nicotine concentration of 54 µg/ml is far above the lethal threshold of 2-4 µg/ml . Concentrations of 20 ng/ml or less were measured in plasma or serum of volunteers upon inhalation of nicotine containing e-liquids [5, 6]. Thus, the nicotine concentrations applied by Wu et al. are three orders of magnitude higher than typical nicotine plasma levels.
In summary, the reported experience of e-cigarette users indicates that the switch from smoking to vaping does not increase the incidence of airway infections. Instead, most users, who had frequently suffered from severe infections while smoking, reported on substantial improvement. In view of this result and the widely documented health benefits associated with the switch from tobacco products to e-cigarettes , lung specialists should not unsettle their patients. Rather, they should motivate smokers unable to quit otherwise to take advantage of a comparably harmless way of nicotine consumption.
1. Wu Q, Jiang DJ, Minor M and Chu HW (2104) Electronic cigarette liquid increases inflammation and virus infection in primary human airway epithelial cells. PLoS One e108342. http://www.ncbi.nlm.nih.gov/pubmed/25244293
2. Feldman C and Anderson R (2013) Cigarette smoking and mechanisms of susceptibility to infections of the respiratory tract and other organ systems. J Infect 67: 169-184. http://www.ncbi.nlm.nih.gov/pubmed/23707875
3. Farsalinos KE, Romagna G, Tsiapras D, Kyrzopoulos S and Voudris V (2014) Characteristics, perceived side effects and benefits of electronic cigarette use: A worldwide survey of more than 19,000 consumers. Int J Environ Res Public Health 11: 4356-4373. http://www.ncbi.nlm.nih.gov/pubmed/24758891
4. Mayer B (2014) How much nicotine kills a human? Tracing back the generally accepted lethal dose to dubious self-experiments in the nineteenth century. Arch Toxicol 88: 5-7. http://www.ncbi.nlm.nih.gov/pubmed/24091634
5. Vansickel AR and Eissenberg T (2013) Electronic cigarettes: Effective nicotine delivery after acute administration. Nicotine Tob Res 15: 267-270. http://www.ncbi.nlm.nih.gov/pubmed/22311962
6. Farsalinos KE, Spyrou A, Tsimopoulou K, Stefopoulos C, Romagna G and Voudris V (2014) Nicotine absorption from electronic cigarette use: comparison between first and new-generation devices. Sci Rep 4: Art. 4133. http://www.ncbi.nlm.nih.gov/pubmed/24569565
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