Vapour from e-cigarettes is non-toxic to human lung cells under normal usage conditions. But even when tested using extremely unrealistically high doses, e-cigarette vapour proved to be significantly less toxic to human lung cells than cigarette smoke.
Cigarette smoke was cytotoxic even at levels typically observed in real life use. And lung cells exhibited low levels of cytotoxicity only after exposing cells to a vapour amount equivalent to a day's exposure in just one hour.
'We only saw signs of cytotoxicity from the e-cigarette aerosols when we used unrealistically high levels of vapour,' explains Dr Chris Proctor, Chief Scientific Officer at British American Tobacco. 'The conservative approach we took means that it is unlikely that normal vaping use would yield cytotoxic effects, even at the low levels observed here.'
The research is published in Toxicology Mechanisms and Methods DOI: 10.1080/15376516.2016. 1217112.
Scientists at British American Tobacco used an advanced lung cell exposure system to investigate the potential adverse effects of e-cigarette vapour on airway tissue compared with cigarette smoke. A puffing machine was used with human lung cells to compare the potential cytotoxic effects of vapour with cigarette smoke in a way that mimics real-life exposures.
The cytotoxicity of the exposed cells was measured using a test called a 'neutral red uptake assay'. A neutral red uptake assay involves adding a red dye to cells. Living cells incorporate the red dye into cell components called lysosomes - the cell's waste disposal system - staining them red. As the cells begin to die, they lose the ability to incorporate this dye and the cells change in colour from red to light pink.
A commercially available e-cigarette, Vype ePen, was tested and its potential cytotoxic impact was compared to that of a 3R4F reference cigarette.
In order to elicit a cytotoxic response with the Vype e-pen e-cigarette, it was necessary to deliver an estimated daily dose of vapour to the cells in only an hour, which is unlikely to represent levels a consumer would experience. Additionally, the daily dose was calculated by assuming that 100% of vapour is deposited in the lungs.
The amount of particulate mass from the aerosols deposited on the cells' surface was also measured to prove that different amounts of smoke or vapour had reached the cells even when there was no or minimal cytotoxic response.
These tests are part of a suite of tests being developed to test novel tobacco and nicotine products and could be used to help develop standards for these products in the future.
Many in the public health community believe e-cigarettes offer great potential for reducing the public health impact of smoking. Public Health England, an executive body of the UK Department of Health, recently published a report saying that e-cigarettes are 95% safer than cigarettes. The Royal College of Physicians have said that the public can be reassured that e-cigarettes are much safer then smoking and that they should be widely promoted as an alternative to cigarettes, though they also called for more research. Cancer Research UK, Action on Smoking and Health and the British Heart Foundation are also of the view that e-cigarettes are substantially less harmful than smoking.