The lesser of two evils: e-cigarette exposure weakens anti-bacterial and anti-viral defenses

During cold and flu season, many of us try to boost our immune system to resist getting sick. But if you smoke, you are at a greater risk of acquiring an infection and becoming ill. Both cigarette smoke and nicotine are known to suppress the body’s immune system, which contribute to smokers being more susceptible to bacterial and viral infections. Patients with chronic obstructive pulmonary disease caused by smoking are especially prone to lung infections.

Electronic cigarettes, or e-cigarettes, are widely believed to be a healthier alternative to traditional cigarettes. While they undoubtedly cause less harm than traditional cigarettes, e-cigarettes are still hazardous to your health. A team of researchers led by Prof. Shyam Biswal at Johns Hopkins University has shown that exposure to e-cigarettes impairs your body’s ability to fight off bacterial and viral infections.

To study the effects of e-cigarette vapor on immune responses, the researchers developed the first mouse model for e-cigarette exposure. They used a modified cigarette smoke machine that regularly puffed e-cigarette vapor into a small chamber. Mice were exposed to e-cigarette vapor in the chamber for one and a half hours twice per day for two weeks. The researchers confirmed that their e-cigarette exposure set up was working effectively by monitoring blood levels of cotinine, a breakdown product of nicotine. Immediately after their final e-cigarette exposure, cotinine levels in the mice jumped to 267 ng/mL and fell to 0.6 ng/mL after 24 hours. To compare, cotinine levels in heavy smokers are often higher than 300 ng/mL.

The experimental set up used to expose mice to e-cigarette vapors (Sussan et al, 2015)
The experimental set up used to expose mice to e-cigarette vapors (Sussan et al, 2015)

When researchers infected the mice with Streptococcus pneumoniae, a common cause of lung infections, they found that mice exposed to e-cigarette had weaker anti-bacterial defenses than mice exposed to regular air in the chamber. The lungs of e-cigarette exposed mice contained three times more bacteria than lungs of unexposed mice. One of our body’s defense mechanisms against bacterial infections is to unleash white blood cells called macrophages. Macrophages destroy invading pathogens by literally gobbling them up. The lung macrophages of e-cigarette exposed mice did not eat as many bacteria as lung macrophages from unexposed mice, which means that more bacteria would be left to grow and reproduce in the lungs.

The researchers also found that exposure to e-cigarettes hindered anti-viral defenses. When e-cigarette exposed mice were infected with a low dose of the H1N1 influenza virus, they had roughly 6% more viruses in their lungs than their unexposed counterparts. The e-cigarette exposed mice were also sicker than the unexposed mice, losing more weight and showing a delayed recovery. After infection with a higher dose of H1N1, mortality in the e-cigarette exposed mice was twice as high as the unexposed mice.

Many people had previously assumed that because smoking e-cigarettes does not require combustion of tobacco, there would be very low levels of free radicals. Free radicals are toxic molecules that can damage cells by directly reacting with DNA and proteins. The researchers in this study found that e-cigarette vapor contains 700 billion free radicals per puff. Even though this is approximately 1% of the levels of free radicals in each puff of traditional cigarette smoke, it is still a significant amount.

These findings are only the first steps towards gaining a more thorough understanding of the health effects of e-cigarettes and will need to be reproduced in larger and more detailed studies. However, despite these limitations, we can say with a degree of certainty that e-cigarettes are not the guilt-free, hazard-free pleasures that their manufacturers would have you believe. Like traditional cigarettes, they can damage your cells and make you more susceptible to bacterial and viral lung infections. Whether it’s electronic or paper, the best thing for your health is still to butt out!

Sussan, T., Gajghate, S., Thimmulappa, R., Ma, J., Kim, J., Sudini, K., Consolini, N., Cormier, S., Lomnicki, S., Hasan, F., Pekosz, A., & Biswal, S. (2015). Exposure to Electronic Cigarettes Impairs Pulmonary Anti-Bacterial and Anti-Viral Defenses in a Mouse Model PLOS ONE, 10 (2) DOI: 10.1371/journal.pone.0116861


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