Cancer-causing chemicals in tobacco smoke have long been studied for their effects on DNA and DNA repair mechanisms in humans. Because of the known carcinogenicity of cigarettes, a presumably safer alternative has been developed. E-cigarettes deliver the high of cigarettes but, with just pure nicotine vaporized in a solvent, offer a much “cleaner” smoke for users. Previous research has shown that nicotine and its metabolites can also cause damage to DNA, but does this finding also apply to e-cigarette smoke (ECS)?
Moon-shong Tang, New York University School of Medicine, USA, and colleagues have studied the effects of e-cigarette smoke in mice, and in particular, the specific DNA lesions caused by ECS. Specifically, the group looked at O6-methyldeoxyguanosine (O6-medG) and γ-OH-1,N2-propanodeoxyguanosine (γ-OH-PdG) formation in lung, bladder, and heart tissue of mice that had inhaled ECS for twelve weeks. Such lesions are known to be formed after nicotine exposure. The results clearly showed that ECS induces a significant number of DNA lesions when compared to mice breathing fresh air. Not surprisingly, lung tissue was most affected, and the majority of the lesions found were γ-OH-PdG.
Additionally, the group studied the effects of ECS on DNA-repair activity in the lungs of these mice. Both nucleotide excision repair and base excision repair were found to be decreased after exposure to ECS, and concentrations of two important DNA repair proteins were also shown to be decreased. A preliminary experiment of these effects in human lung cells found that when incubated with nicotine and one of its metabolites (nicotine-derived nitrosamine ketone), the cells also showed increased DNA damage, mutation frequency, and cancer-like properties.
Further studies are needed to confirm these results, but they indicate that ECS cannot be considered harmless. Mutations such as these take many years to lead to cancer, however, long-term data on ECS effects on humans are not available, so far. In addition, this study looked only at the damage caused by nicotine vapor. However, many e-cigarettes contain flavorings which have also been shown to degrade to harmful compounds, but their effects on DNA have not yet been determined.
- E-cigarette smoke damages DNA and reduces repair activity in mouse lung, heart, and bladder as well as in human lung and bladder cells,
Hyun-Wook Lee, Sung-Hyun Park, Mao-wen Weng, Hsiang-Tsui Wang, William C. Huang, Herbert Lepor, Xue-Ru Wu, Lung-Chi Chen, Moon-shong Tang,
Proc. Natl. Acad. Sci. USA 2018, 115, E1560–E1569.