Abstract
Studies using cultures of human airway cells provide important insights into the toxicity of vaping http://ow.ly/Pj7X30kM9h3
From the authors:
M. Caruso and co-workers raise several points related to our electronic cigarette (EC) study [1]. First, they suggest that we generated EC vapour (ECV) under “extreme” experimental conditions, which could lead to overheating and thermal decomposition of E-liquids around a heated coil [2]. However, we minimised the potential effect of coil overheating by ensuring that the EC reservoir was always more than three quarters full, and by using a low power second generation EC device (3.7 V), instead of a later generation 8 V device, which would have an increased potential for substantially higher coil temperatures and under-dry conditions [2]. In addition, our use of a 4-s puff duration and 8-s interpuff interval cannot be regarded as extreme, since a recent long-term study of young vaping adults found that one inhalation pattern is multiple rapid puffs taken over very short time periods [3]. Furthermore, the production of toxins under extreme conditions in vitro does not explain why we found that a “normal” vaping session increased nasal platelet-activating factor receptor (PAFR) expression in adult volunteers.
The authors' second point is related to differences in pneumococcal adhesion compared with previous reports. Since exposure dose and duration was optimised in these in vitro studies, data are not directly comparable. For example, in our previous studies, airway cells were exposed in vitro to particulate matter [4] and welding fumes [5] for 4 h and 2 h respectively, compared to 2.5 h for exposure to ECV [1]. Since welding fume particles and fossil fuel-derived particulate matter adhere firmly to cells in vitro, we also needed an increased number of washes to remove particles before adding pneumococci. Caruso and co-workers also quote an adhesion study done by a separate group, but this group used 1×105 airway cells per well, compared to our initial seeding of 2×105 cells per well with overnight incubation to allow confluency. These experimental differences, not unsurprisingly, result in quantitative differences in pneumococcal adhesion. But the relative changes in pneumococcal adhesion between studies are broadly similar. For example, there was a median 3.1-fold increase in pneumococcal adhesion to A549 cells exposed to mild steel welding fume particles [5], compared to a 2.6- and 2.9-fold increased for nicotine-free ECV and nicotine containing ECV-exposed cells, respectively [1].
Third, M. Caruso and co-workers claim that the increase in PAFR at 5 min after a vaping session, and the lack of difference between nasal PAFR expression prior to vaping compared with healthy controls, means that our data are of “zero clinical significance”. As clearly stated throughout the paper, we measured nasal PAFR expression at 1 h post vaping, thus the (median) 6-fold increase in PAFR does not reflect either a transient or an irrelevant response. Since vapers had not inhaled ECV for 24 h before the study, and pre-vape nasal PAFR expression was not significantly different from healthy volunteers, our data are, on one hand, compatible with downregulation of nasal PAFR by 24 h. On the other hand, it is also possible that our study was underpowered for this secondary outcome. Indeed, combining nasal PAFR expression data from the healthy volunteers from the ECV study with PAFR expression data from 10 volunteers reported in our previous study of welding fumes, analysed using the same methodology [6], suggests that nasal PAFR expression in vapers is persistently increased (figure 1).
Platelet-activating factor receptor (PAFR) expression in nasal epithelial cells from vaping adults prior to experimental electronic cigarette vapour exposure (baseline) and in non-vaping controls. Non-vaping healthy controls are those recruited for vaping study [1], supplemented by controls recruited for a previous welding fume exposure study (n=10) [6]. Bar represents mean (with standard error of the mean shown) and data are analysed by unpaired t-test.
Overall our data are compatible with the recent position statement of the Forum of International Respiratory Societies that “exposure to EC aerosol in adolescence and early adulthood is not risk-free and can result in pulmonary toxicity” [7], and the recent consensus study report of the National Academies of Sciences, Engineering and Medicine, that concluded that “studies to date provide moderate evidence supporting short-term adverse effects of nicotine-containing e-cigarettes on lung defence mechanisms” [8]. Unfortunately, the studies quoted by Caruso and co-workers to support their statement that regular vaping “markedly decreases” respiratory infections (presumably compared with cigarette smoking) are not relevant to the important question of adverse health effects on young, non-smoking, people encouraged to use ECs by their attractive flavours and advertising. We therefore consider that mechanistic studies using airway cell cultures and experimental exposure of both animals and humans are critical to signposting potential toxicities, including vulnerability to bacterial airway infection. To dismiss mechanistic studies, as done for example by the authors of a 2015 report published by Public Health England [9], who concluded that the study of Sussan et al. [10] that reported defective clearance of S. pneumoniae from the lungs of mice exposed to ECV for 2 weeks “has little relevance for estimating human risk and it does not raise any new safety concerns”, is not in the spirit of the precautionary approach required when assessing environmental threats to children and young people.
Footnotes
Conflict of interest: J. Grigg reports honoraria for advisory board work from GSK and Vifor Pharmaceuticals, and honoraria for lectures from Novartis, outside the submitted work.
- Received June 27, 2018.
- Accepted June 27, 2018.
- Copyright ©ERS 2018
