Currently 3.6 million Junior and high school students use e-cigarettes as a result of messaging that suggests they are void of significant health risks. Recently however new concerns have been raised about the risk of e-cigarettes based on reports of direct lung toxicity.
Investigators from NYU have now reported that exposure to e-cigarette smoke caused mice to develop lung cancer according to a new study published in the prestigious Proceedings of National Academy of Sciences. The study found that 22% of mice exposed to e-cigarette smoke with nicotine for 54 weeks developed lung adenocarcinomas. None of the 20 mice from the study exposed to the same e-cigarette smoke without nicotine developed cancer. (1)
The study also found that 57% of mice exposed to e-cigarette smoke developed pre-cancerous changes in cells that line the bladder.
According to the study author, Dr. Tang “Tobacco smoke is among the most dangerous environmental agents to which humans are routinely exposed, but the potential of e-cigarette smoke as a threat to human health is not yet fully understood.” Our study results in mice were not meant to be compared to human disease, but instead argue that e-cigarette smoke must be more thoroughly studied before it is deemed safe or marketed that way.”
Nicotine and Nitrosamines
The question of whether nicotine itself, separate from tobacco smoke, causes cancer is controversial because of conflicting study results over time that used oft-criticized methods. Almost all researchers agree, however, that chemicals added during the curing of tobacco—nitrate and nitrite—can cause a reaction called nitrosation, or the addition of a particle called a nitrosonium ion, the authors say.
This is known to convert nicotine into nitrosamines such as N-nitrosonoricotine (NNN) and nicotine-derived nitrosamine ketone (NNK), which are proven carcinogens in mice and humans.
Conventional thinking, says Dr. Tang, has been that smoke from cured tobacco deposits nitrosamines into a smoker’s organs and blood. Nitrosamine blood tests are the best measure of their potential to cause cancer. Such tests in a previous study found that levels of a compound related to NNK, called NNAL, were 95 percent lower in e-cigarette smokers than in tobacco smokers, leading some experts to conclude that a switch to e-cigarettes might save millions of lives. (3)
Dr. Tang’s team had shown previously that e-cigarette smoke induces DNA damage in the mouse lung and bladder, and that nitrosation in cultured human lung and bladder cells converts nicotine into derivatives that increase DNA code changes, or mutations, with the potential to transform normal cells into cancer cells. Specifically, the earlier study found that nicotine is transformed into nitrosamines, then into DNA damaging agents, which ultimately form DNA adducts. (4)
The current study results confirm that nicotine from e-cigarette smoke can cause cancer in the lungs, and precancerous growth in the bladders, of mice. Furthermore, the results argue that nicotine, once inside cells, is converted into nitrosamines that do not leave cells and, therefore, could never be captured by tests that measure nitrosamine levels outside of cells, for example blood tests, says Dr. Tang.
Further research will focus on expanding the number of mice studied, to shorten and prolong e-cigarette exposure times, and to further investigate the genetic changes caused by e-cigarette smoke.