Researchers in the US have exposed mice to e-cigarette vapour to find that not only does it contain free radicals - DNA-damaging toxins - it also compromised their immune systems and damaged their lung tissue.

Since their introduction to the US market in 2007, e-cigarettes have enjoyed a sharp increase of popularity around the world, particularly among ex-smokers and teenagers. They've been recommended as a safer option for smokers affected by chronic obstructive pulmonary disease (COPD) - an umbrella term for a range of lung diseases including emphysema, chronic bronchitis and chronic asthma - and studies have found that e-cigarette use now outpaces cigarette use in teenagers. According to the U.S. Centres for Disease Control and Prevention, more than one-quarter million teenagers who reported never having smoked a cigarette said they used e-cigarettes in 2013.

So a team from the Johns Hopkins Bloomberg School of Public Health decided to investigate the relative safety of e-cigarette vapour to see what it does to the body. They divided their mice into two groups, placed them into inhalation chambers, and exposed them to either e-cigarette vapour from the commercial brand Njoy or clean air over a period of two weeks. The amount of e-cigarette vapour approximated average human e-cigarette consumption, which they measured by achieving blood nicotine levels in the mice that were comparable to levels that occur in the blood of human e-cigarette users. 

The two groups of mice were then each further divided into three subgroups - one received nasal drops containing Streptococcus pneumoniae, which is the type of bacteria responsible for a number of diseases, including pneumonia and sinusitis, among other illnesses; another received nasal drops containing the Influenza A virus; and the third acted as a control group, receiving no virus or bacteria.

Publishing their results in the open-access journal PLOS ONE, the team found that the mice that were exposed to e-cigarette vapour were significantly more likely to develop weakened immune responses to both bacterial and viral infections - so much so, that the diseases ended up killing some of them.

"Our findings suggest that e-cigarettes are not neutral in terms of the effects on the lungs," one of the team and  professor in the Department of Environmental Health Sciences at the Bloomberg School, Shyam Biswal, said in a press release. "We have observed that they increase the susceptibility to respiratory infections in the mouse models. This warrants further study in susceptible individuals, such as COPD patients who have switched from cigarettes to e-cigarettes or to new users of e-cigarettes who may have never used cigarettes."

"E-cigarette vapour alone produced mild effects on the lungs, including inflammation and protein damage," lead researcher and respiratory disease expert, Thomas Sussan, added. "However, when this exposure was followed by a bacterial or viral infection, the harmful effects of e-cigarette exposure became even more pronounced. The e-cigarette exposure inhibited the ability of mice to clear the bacteria from their lungs, and the viral infection led to increased weight loss and death indicative of an impaired immune response."

While it's not clear yet why the e-cigarette smoke compromised the immune systems of the mice, one possibility could be the presence of toxic free radicals, which the team found in the vapour. 

Free radicals are atoms or groups of atoms that end up with one or more unpaired electrons, which makes them highly reactive with other cellular structures. They're produced in the body when we consume things such as fried foods, alcohol, tobacco smoke, pesticides, and air pollutants, and actively damage - and sometimes kill - our cells, proteins and DNA by messing their their chemical structure. Antioxidants are the body's natural defence system against free radical damage. 

While the amount of free radicals found in the Njoy e-cigarette smoke was about 1 percent that found in cigarette smoke - cigarette smoke contains 1014 free radicals per puff - the team was surprised to find any free radicals in the vapour at all. This is because free radicals are typically associated with the combustion process involved in smoking, of which there's none in e-cigarettes. "It is possible that the heat and/or current generated during vaporisation could induce formation of radicals, and indeed, the battery output voltage has been shown to play a role in generation of other toxic chemicals," the team reports in the study.

"We were surprised by how high that number was, considering that e-cigarettes do not produce combustion products," Sussan said. "Granted, it's 100 times lower than cigarette smoke, but it's still a high number of free radicals that can potentially damage cells."

The next step would be to perform simular studies, but with cigarette smoke included for a direct comparison. As we begin to figure out the effects of e-cigarettes, we're seeing that they're in no way innocuous, and shouldn't be marketed as such. As Jacob Kastrenakes says at The Verge:

"Though it's widely expected that they'll be less harmful than traditional cigarettes, it isn't clear what the risks will be - just because the technology is so new. That's led to much debate over how strictly e-cigarettes should be regulated: loose regulations could mean e-cigs being picked up by non-smokers, exposing them to harm, while strict restrictions could prevent smokers from switching to a less-harmful alternative."

Late last year, the NSW opposition government called for an official enquiry into e-cigarettes, and in the US, things are getting particulaly complicated as the 50 states are each figuring out what to do with them. Liz Szabo at US Today reports that right now, 41 states have banned the sale of e-cigarettes to people under 18, but 17 of those have passed laws that could make it harder to regulate e-cigarettes in the same way that cigarettes are, for exampe, with heavy taxes and restrictions on public use. 

Source: The Verge