Exposure to electronic cigarette smoke caused experimental models to develop lung cancer, according to a new study published online October 7 in the journal ‘Proceedings of National Academy of Sciences (PNAS)’.
This research found 22.5 percent of the mice (9 of 40) exposed to nicotine electronic cigarette smoke for 54 weeks developed lung adenocarcinomas. In parallel, none of the 20 individuals in the study exposed to the same electronic cigarette smoke without nicotine developed cancer.
Directed by Moon-shong Tang, a professor in the Departments of Environmental Medicine, Medicine and Pathology at the New York University School of Medicine, the study also found that 23 of 40 individuals (57.5 percent) exposed to smoke developed bladder hyperplasia, genetic changes that make cells more likely to multiply, which is a step toward abnormal tissue growth that occurs in cancer. Only one of the 17 mice exposed to smoke without nicotine developed hyperplasia.
Although Tang acknowledges the limitations of the study, because of the number of people involved, and because they did not inhale the smoke like humans but were surrounded by it, he points out that these results “were not intended to be compared to human diseases, but They argue that electronic cigarette smoke must be studied further before it is considered safe or marketed that way. The potential of electronic cigarette smoke as a threat to human health is not yet fully understood, ”he recalls.
The question of whether nicotine itself, separated from tobacco smoke, causes cancer is controversial due to the conflicting results of the study over time that use controversial methods.
However, almost all researchers agree that chemicals added during tobacco curing (nitrate and nitrite) can cause a reaction called nitrosation (the addition of a particle called nitrosonium ion), the authors say. It is known that this converts nicotine into nitrosamines such as NNN (N-nitrosonoricotine) and NNK (nitrosamine ketone derived from nicotine), carcinogens tested in mice and humans.
Conventional belief, Tang says, has been that the smoke from cured tobacco deposits nitrosamines in the organs and blood of a smoker, with the blood test for nitrosamine as the best measure of its potential to cause cancer.
Such tests in a 2017 study found that the levels of an NNK-related compound, called NNAL, were 95 percent lower in e-cigarette smokers than in tobacco smokers, which led some experts to conclude that A change to electronic cigarettes could save millions of lives.
Partly as a result of such public messages, 3.6 million middle and high school students in the United States have used electronic cigarettes, the authors note.
In this context, the new study finds that mammalian cells contain their own nitrosonium ions, which react directly with nicotine to form nitrosamines, including NNK. Many studies have also shown that human and mouse cells also have a broad supply of cytochrome p450, which converts more NNN and NNK into compounds that can react with DNA to form harmful adducts, they add.
Tang's team had demonstrated in an article in 'PNAS' of February 2018 that electronic cigarette smoke induces DNA damage in the lung and bladder of the experimental model, and that nitrosation in human lung and bladder cells Cultivated converts nicotine into derivatives that increase DNA mutations with the potential to transform normal cells into cancer cells.
Specifically, the previous study found that nicotine is transformed into nitrosamines, then into agents that damage DNA, which eventually form DNA adducts.
Thus, the results of the current study confirm that nicotine from electronic cigarette smoke can cause lung cancer and precancerous growth in bladders of experimental models. In addition, they argue that nicotine, once inside the cells, is converted into nitrosamines that do not leave the cells and, therefore, could never be captured by tests that measure nitrosamine levels outside the cells such as blood tests. says Tang.
"Our results support the argument that nicotine-derived DNA products are probably the main causes of carcinogenesis in models exposed to electronic cigarette smoke," says study author Herbert Lepor, the president of Langology Health Urology at New York University
"Our next step in this line of work will be to expand the number of individuals studied, shorten and prolong the time of exposure to electronic cigarettes and further investigate the genetic changes caused by electronic cigarette smoke," he concludes.