New research in mice suggests that long-term exposure to vaping liquids containing nicotine greatly increases the risk of cancer.
After breathing for 20 hours a week for more than a year, 22.5% of the mice had cancerous tumors in the lining of the lungs and 57.5% developed bladder tissue growths that may be precursors of cancer.
Meanwhile, only 5.6% of mice in a control group breathing only filtered air killed lung tumors, and none of them had bladder growth. In addition, a group of mice exposed to nicotine-free aerosol-vaping chemicals did not develop lung tumors, and only 6.3% had precancerous bladder growth.
The scientists who conducted the study emphasized that much more research is needed to determine if vaping leads to cancer in humans. But they hope their findings will be published Monday in the magazine. Proceedings of the National Academy of Sciences, will make people think twice about trying electronic cigarettes, widely perceived by teens and young adults as a safe alternative to smoking.
"Right or wrong, millions of young people are using them now, and long-term population-wide studies will not be able to report results for another decade," said the study leader. Moon-shong tang, an environmental health expert at the NYU School of Medicine.
"We needed reliable evidence to guide people in their choices, and it's not unambiguous that nicotine itself causes damage to the cells that make up organs, including lungs," said Tang, who studied how tobacco smoke promotes cancer. of lung and bladder. . "Now we can try to find measures to prevent incidents of cancer-causing electronic cigarettes."
Vaping has been linked to heart attacks, seizures and burns from explosive devices. And a growing outbreak of at least 1,080 vaping-related lung lesions It serves as a reminder that it is too early to know if electronic cigarettes are a safe alternative to smoking.
To get a better idea of the long-term effects of nicotine, Tang and his colleagues exposed 45 mice to a nicotine aerosol dissolved in isopropylene glycol and vegetable glycerin, a common vehicle for vaporizing liquids. Another group of 20 mice was exposed to the same vehicle without nicotine. For 54 weeks, the animals were subjected to aerosol mixtures for four hours a day, five days a week.
A third group of 20 mice spent time in a room with filtered ambient air. (The study was limited to 54 weeks in order to minimize the effects of age-related cancers that could have arisen regardless of exposure to electronic cigarette vapor.)
Five rats in the nicotine-exposed group died throughout the year. So did two of the mice in each of the other groups.
When the 54 weeks were up, the remaining animals were killed and the researchers examined their tissues. Nine of the 40 mice in the nicotine group had lung tumors, compared with none of the 18 mice breathing the nicotine-free aerosol and one of 18 mice exposed to filtered air. (Tang said he was not surprised to find a tumor in the control group, as mice usually increase lung cancer rates.)
In addition, the researchers found that 23 of 40 mice that inhaled the nicotine vapor developed bladder hyperplasia, an uncontrolled cell reproduction in the bladder lining that usually precedes cancer. This compares to 1 in 16 rats that inhaled nicotine-free steam and zero in 17 rats breathing filtered air. (Tissue samples from three rats were accidentally destroyed and could not be included in the analysis.)
The differences were large enough for the researchers to conclude that nicotine aerosol vaping was responsible for the increased risk of tumors. For example, mice that inhaled the nicotine mixture were eight times more likely to develop lung tumors than mice in the other two groups not exposed to nicotine.
"This is convincing and very scary," he said. Dr. Mark Litwin, the chairman of UCLA's Department of Urology. “When DNA-encoded instructions are mutilated, the cells go crazy and keep multiplying, unable to control themselves. This is a characteristic of cancer. And at a glance, this already looks like pre-cancer tissue. "
The researchers also found that some of the mice exposed to electronic cigarette vapor – with or without nicotine – developed skin or abdominal tumors, while none of their colleagues in the filtered air group did. However, these differences were small and could have been due to chance.
The work was funded by the National Institutes of Health.
At the molecular level, the results make sense. Tang's team published a survey last year showing that when nicotine is introduced into mammalian cells, innate molecules called nitrosonium ions react with nicotine to form carcinogens – both in mice and in humans.
"We can't say that electronic cigarettes definitely cause human cancer, but the mechanism at play here is very clear: the same carcinogens that other studies have shown to cause human cancer are being produced," Tang said. "We can extrapolate that with electronic cigarettes, you cause damage to your genetic material and damage your cells – and that will accumulate the more you smoke."
Electronic cigarette smoke "must be studied in more detail before it is considered safe or marketed in this way," he added.
The study had several limitations, the authors acknowledged. It included a small number of mice, and they were surrounded by steam instead of inhaling it, like electronic cigarette users.
Dr. Herbert Lepor, a study author and president of urology at NYU's Langone Health, said the team plans to use a larger group of mice to test short and long periods of exposure. The researchers also plan to take a closer look at the genetic changes associated with inhaling electronic cigarette smoke.
Experts agree that the new study does not answer the questions surrounding the current outbreak of vaping-related lung disease. But it validates concerns about the long-term effects of electronic cigarettes.
"Teens will say that vaping is safer because it eliminates all carcinogenic parts of a cigarette," said Litwin. "It turns out that this may not be the case."