E-cigarette vaping linked to lung cancer in mice, researchers find

Maricruz Casares
Octubre 10, 2019

Researchers at New York University found that e-cigarette vapor causes lung cancer and potentially bladder cancer in mice, damaging their DNA. None of the mice exposed to e-cig smoke without nicotine developed cancer.

A related study conducted by the University of Southern California in February, found that e-cigarette users developed some of the same molecular changes in oral tissue that cause cancer in cigarette smokers. From 40 mice exposed to e-cigarette vapor with nicotine over 54 weeks, 22.5% developed lung cancer and 57.5% developed precancerous lesions on the bladder. Only one of the mice exposed to the non-nicotine e-cig smoke developed hyperplasia.

Dr. Tang admitted that there are limitations to the study - the mice were exposed to smoke outside their bodies instead of inhaling it like humans would, for example - and the results in mice can't be directly compared to the results in humans.

"It's foreseeable that if you smoke e-cigarettes, all kinds of disease comes out" over time, Moon-Shong Tang, the study's lead researcher, said in an interview. Surprisingly, one of the 17 micesthat was exposed to nicotine-free smoke got cancer. This terrifying prospect has swayed many smokers to switch to e-cigs, which are thought to be benign in comparison to cigarettes. However, while he acknowledged that more research is needed, he said that the results are "statistically very significant" and indicate that it's unlikely that e-cigarettes are safe for humans.

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This is known to convert nicotine into nitrosamines such as NNN (N-nitrosonoricotine) and NNK (nicotine-derived nitrosamine ketone), proven carcinogens in mice and humans.

The Vapor Technology Association disputed the findings of the new study, pointing to a 2015 study that found that e-cigarettes were 95% less harmful than cigarettes.

Conventional thinking, says Dr. Tang, has been that smoke from cured tobacco deposits nitrosamines into a smoker's organs and blood. Many studies have also shown that human and mouse cells also have ample supplies of cytochrome p450, which further converts NNN and NNK into compounds (e.g. formaldehyde and CH3N=NOH) that can react with DNA to form damaging adducts (e.g. gamma-OH-PdG and O6-methyl-dG), the researchers say. These are nitrosamines that deteriorate DNA and create cancer cells.

"Our results support the argument that the nicotine-derived DNA adducts are likely the main causes for carcinogenesis in mice exposed to E-cig smoke", said study author Dr. Herbert Lepor. "Our next step in this line of work will be to expand the number of mice studied, to shorten and prolong E-cigarette exposure time, and to further investigate the genetic changes caused by E-cigarette smoke". (2019) Electronic-cigarette smoke induces lung adenocarcinoma and bladder urothelial hyperplasia in mice. Note: material may have been edited for length and content.

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