In a paper about to be published in the American Journal of Respiratory and Critical Care Medicine, researchers from the University of North Carolina at Chapel Hill report what they believe to be the first study to use human airway samples to examine the effects of electronic cigarettes (e-cigarettes).
E-cigarettes are battery-operated devices that produce an inhalable aerosol mixture of chemicals that includes nicotine, flavorings, and other substances. Some mixtures do not include nicotine.
At present, there are more than 460 different e-cigarette brands for sale in the United States.
Devices come in many different forms, several of which resemble conventional cigarettes, pipes, and cigars, while others resemble pens and USB memory sticks. Others may look quite different, such as those with fillable tanks.
'Confusion' about e-cigarette safety
A recent population study that found that e-cigarette use is linked to smoking cessation suggests that around 2.4 percent of U.S. adults are regular users.
E-cigarette use has been growing particularly quickly among teenagers. Between 2011 and 2015, the proportion of U.S. high-school students using e-cigarettes rose from 1.5 to 16.0 percent, while among middle-school students, it rose from 0.6 percent to 5.3 percent.
In 2016, there were more than 2 million middle- and high-school students using e-cigarettes.
"There is confusion about whether e-cigarettes are 'safer' than cigarettes because the potential adverse effects of e-cigarettes are only beginning to be studied," explains senior study author Mehmet Kesimer, Ph.D., an associate professor of pathology.
For their investigation, Prof. Kesimer and his colleagues tested sputum samples taken from 15 regular users of e-cigarettes, 14 current smokers of conventional cigarettes, and 15 non-smokers who had never used either type of cigarette. They confirmed the smoking status of the participants from tests of blood and urine samples.
'Signature of harm' in the lungs
Results showed that e-cigarettes produce a unique immune response in the lungs that "indicate[s] that the effects of e-cigarettes are overlapping with yet distinct from those observed in otherwise healthy cigarette smokers."
The airway samples from the e-cigarette users had markers of abnormal "neutrophilic response and altered mucin secretion," note the authors.
Neutrophils are an abundant type of white blood cell that play an important role in maintaining and protecting the airways. However, if disrupted, they can raise the risk of inflammation-related lung diseases such as cystic fibrosis and chronic obstructive pulmonary disease.
Users of both e-cigarettes and conventional cigarettes also showed significant increases in mucin secretions, particularly of mucin 5AC. Mucins are proteins in the mucus that lines the airways and protects their cells from damage. The overproduction of mucin 5AC has been linked to chronic bronchitis, asthma, and other such lung conditions.
The study's results also showed that both e-cigarette users and conventional smokers showed considerable increases in markers of oxidative stress and more active defense mechanisms that are typical of lung disease. These markers included "aldehyde-detoxification and oxidative-stress-related proteins, thioredoxin (TXN), and matrix metalloproteinase-9 (MMP9)."
The researchers point out that a weakness of their study is the fact that among the 15 e-cigarette users, there were five who said that they occasionally smoked conventional tobacco cigarettes, and 12 who said that they had smoked them in the past.
The team concludes, nevertheless, that e-cigarettes have a "signature of harm" in the lungs that, although it has some unique features, shares some similarities with that of conventional cigarettes.
"Our results suggest that e-cigarettes might be just as bad as cigarettes."
Prof. Mehmet Kesimer