DNA damage, a proxy for genotoxic exposure
The γH2AX assay is tool that allows quantifying DNA damage. This is the test BAT researchers are using to determine the how much is damaged the double-strand of our genetic code.
DNA double strand breaks (DSB) are the gravest form of DNA damage in cells and reveal genetoxic exposure to an environmental factor. Such damage can lead to cancer.
No DNA damage found with e-cigarettes
The researchers show that exposure to e-cigarette aerosols did not create DNA damage at similar or greater dose than combustible cigarette. The author estimate that e-cigarette experiment lead to a dose 12 to 28 times higher than combustible cigarette smoke.
The study was conducted in vitro on lung epithelial cells exposed to e-vapor or cigarette smoke. The two e-cigarette models were a Vype eStick and a Vype ePen manufactured by Nicoventures, a subsidiary of BAT. Smoke and e-vapor were generated by a smoking machine and diluted before bathing the culture medium at a flow rate of 0.25 to 1.00 L/min. Exposure time was 2 hours after which the γH2AX assay was started. The dose of e-vapor, smoke and nicotine mass deposited at the surface of the Petri dish where the cells were incubated were determined with high precision.
A dose-effect determined with precision
Considering the higher dose and the absence of DNA damage upon exposure to e-cigarette aerosols, the authors conclude in a much safer profile for e-cigarettes than for combustible tobacco cigarettes. It is noticeable, here, that the reference level for nicotine concentration in the culture medium is ng/ml, no less than 6 orders of magnitude lower than with some previous studies that reported mg/ml, like e-liquid concentration.
In vitro studies have long received vigorous criticism because they exposed cells to aerosol levels incomparable to real vaping conditions. This point has been discussed by Konstantinos Farsalinos during the last Vapexpo event and lead the cardiologist to reject much of the results obtained by in vitro studies so far. With a tight control on the dose of aerosol delivered to the liquid medium bathing the cultured cells, reliable comparisons can be made between vaporizers and corrections applied for the dose, if needed. In this study, the “dose” stands for the mass of e-vapor deposited and also for the amont of nicotine that enters in contact with the liquid growth medium.
A precedent and controverted study
A study carried out by the Pr Weg Ongkeko from the Department of Otolaryngology-Head and Neck Surgery at the University of California, La Jolla (USA), end of 2015, concluded oppositely but also used a much more drastic protocole, exposing cells to undiluted aerosol from 48 hours to 8 weeks. Even if no information on the dose was provided by the authors, one can easily imagine how large it was, likely several orders of magnitude larger than in the present study. This Californian study reached a high popularity in the vaping community when a member of the research team, Dr J. Wang-Rodriguez, discredited herself in the media by saying: “Our study strongly suggests that electronic cigarettes are not as safe as their marketing makes them appear to the public”. Of course experts like Linda Bauld counteracted to reconnect scientists with reality and published an article in the Guardian to debunk poor reporting of this study.
A landmark publication for the scientific rigour of its approach
The conclusions drawn here by the Big Tobacco company are not surprising -I would have been baffled if they had found significant harm with their Vype. Another Big claimed the same, last year, pretending that their vaping products were innocuous but with a less convincing scientific demonstration that rather evoked product placement. What is important to retain from this BAT publication is their use of:
- Cutting edge DNA damage diagnosis,
- Advanced aerosol generation and delivery technologies that give rise to in vitro aerosol exposure systems capable of delivering aerosols to an air-liquid exposure interface (ALI).
This landmark publication illustrates what can be considered a reasonable protocol and is another demonstration that big tobacco companies are up to date with the cutting edge technologies when dealing with vaping products; previous reports already evoked their performance with vaping behavior studies and aerosol analysis.
Thorne D., Larard S., Baxter A., Meredith C., Gaça M., 2016. The comparative in vitro assessment of e-cigarette and cigarette smoke aerosols using the γH2AX assay and applied dose measurements. Toxicology Letters.