A new study finds that even moderate exposure to nicotine-free smoke from e-cigarettes can stall neutrophils, the body's frontline immune cells, reducing their ability to defend against foreign invaders. The researchers say their findings provide more evidence to question the idea that e-cigarettes are safe and caution people against long-term vaping.
Since their introduction around 2007, electronic cigarettes (also known as vapes) have become extremely popular. One study estimates that the number of drug users worldwide will increase to 82 million in 2021, up from 68 million in 2020. Considered by some to be less harmful than cigarettes and used as a smoking cessation tool in some countries, the rise of e-cigarettes has spawned studies dedicated to determining their safety.
Researchers at the University of Birmingham in the UK have found in a new study that e-cigarettes can prevent neutrophils - the immune system's first line of defense against harmful foreign invaders - from functioning effectively, adding to existing evidence.
Aaron Scott, corresponding author of the study, said: "E-cigarettes are an effective, less harmful tool to help smokers quit, but our data add to the current evidence that e-cigarettes are not harmless and highlight the need to fund long-term studies of smokers."
The researchers collected blood samples from people who had never smoked or vaped, and exposed neutrophils extracted from the blood to 40 puffs of unflavored e-cigarettes (an exposure that is considered low daily exposure based on previous studies). Half of the samples were exposed to nicotine-containing vapor from the e-liquid, and the other half were exposed to vapor without nicotine.
The researchers found that in both groups of samples, with and without nicotine, the neutrophils remained alive but were trapped in place, unable to perform their normal functions.
"We found that after short, low-level exposure to e-cigarette vapor, the cells remained viable but could no longer move efficiently and perform normal protective functions," Scott said. "Interestingly, e-cigarette vapor without nicotine had the same negative effects as e-cigarette vapor that contained nicotine."
Normally, small actin filaments in neutrophils help them maintain or change shape and enable them to move or migrate toward invaders. In neutrophils exposed to e-cigarette vapor, whether containing nicotine or not, the researchers observed high concentrations of F-actin filaments. Previous research has shown that when there is too much F-actin, it affects the migration of neutrophils and their ability to take up and destroy foreign bodies.
"In health, neutrophils normally move from the blood to sites of potential harm and then use a range of protective functions to protect the lungs," said David Thickett, one of the study's co-authors. "Therefore, the observed effects of e-cigarette vapor on its mobility are of great concern and, if this occurs in vivo, would put those who regularly use e-cigarettes at a higher risk of respiratory disease."
Given the link between neutrophils and disease states, the researchers said their findings raise significant concerns.
"The effects of smoking on neutrophils are well documented, and this study further demonstrates that e-cigarettes can still have an impact on the immune system," said Liz Sapey, another co-author. "Neutrophils are strongly implicated in aging and chronic obstructive [pulmonary] disease and their relationship to tissue damage, and the effects of e-cigarettes in suppressing neutrophil activity, regardless of nicotine, may have long-term health consequences."
The study was published in the Journal of Allergy and Clinical Immunology.