Electronic cigarette aerosol induces significantly less cytotoxicity than tobacco smoke

Abstract

Electronic cigarettes (E-cigarettes) are a potential means of addressing the harm to public health caused by tobacco smoking by offering smokers a less harmful means of receiving nicotine. As e-cigarettes are a relatively new phenomenon, there are limited scientific data on the longer-term health effects of their use. This study describes a robust in vitro method for assessing the cytotoxic response of e-cigarette aerosols that can be effectively compared with conventional cigarette smoke. This was measured using the regulatory accepted Neutral Red Uptake assay modified for air–liquid interface (ALI) exposures. An exposure system, comprising a smoking machine, traditionally used for in vitro tobacco smoke exposure assessments, was adapted for use with e-cigarettes to expose human lung epithelial cells at the ALI. Dosimetric analysis methods using real-time quartz crystal microbalances for mass, and post-exposure chemical analysis for nicotine, were employed to detect/distinguish aerosol dilutions from a reference Kentucky 3R4F cigarette and two commercially available e-cigarettes (Vype eStick and ePen). ePen aerosol induced 97%, 94% and 70% less cytotoxicity than 3R4F cigarette smoke based on matched EC₅₀ values at different dilutions (1:5 vs. 1:153 vol:vol), mass (52.1 vs. 3.1 μg/cm²) and nicotine (0.89 vs. 0.27 μg/cm²), respectively. Test doses where cigarette smoke and e-cigarette aerosol cytotoxicity were observed are comparable with calculated daily doses in consumers. Such experiments could form the basis of a larger package of work including chemical analyses, in vitro toxicology tests and clinical studies, to help assess the safety of current and next generation nicotine and tobacco products.

Keywords:

• Air–liquid interface
• e-cigarettes
• lung epithelial cells
• tobacco smoke

Acknowledgements

We would like to thank Rachel Ashton for her assistance in editing the paper, Damien Breheny for reviewing the paper, Eleni Mavropoulou for her assistance with statistical analysis, Carl Vas for his guidance with e-cigarette science and technology, Andrew Baxter for his technical input specifically on the nicotine method and Mark Barber of Borgwaldt KC GmbH for his technical knowledge of the Borgwaldt RM20S exposure system.

Disclosure statement

The authors are employees of British American Tobacco (BAT). Nicoventures Ltd., UK, is a wholly-owned subsidiary of British American Tobacco.

Funding

This study was funded by BAT.