Long-term users of electronic cigarettes might face increased susceptibility to pneumonia and other lung infections, according to early research in cells, mice, and humans.
The studies suggest that, just like conventional cigarette smoke, inhaled e-cigarette vapor increases the risk of airway bacterial infection.
When researchers examined the effects of e-cigarette vapor exposure on airway epithelial cells expressing platelet-activating factor receptors (PAFRs), they found that vaping increased pneumococcal adhesion to the cells.
Senior author Jonathan Grigg, MD, of Queen Mary University of London, explained that while pneumococcal bacteria can be present in airways without causing illness, they can also invade the airway lining and cause pneumonia or septicemia.
The research was published online Feb. 8 in the
"We know that exposure to traditional cigarette smoke helps these bacteria stick to airway lining cells, increasing the risk of infection. We wanted to see whether or not e-cigarettes might have the same effect," Grigg told Ƶ.
In a comprehensive review of more than 800 studies, published last month, the National Academies of Sciences, Engineering and Medicine concluded that while vaping is certainly safer than smoking conventional cigarettes, the health effects of long-term use remain largely unknown.
The newly published research adds to the growing evidence that inhaling e-cigarette vapor has the potential to damage health, Grigg said.
Earlier research by the investigators showed that PAFRs help pneumococcal bacteria adhere to airway cells, and that PAFR levels increase when airways are exposed to cigarette smoke, passive smoke, pollution, and other inhalants.
They began their latest research by looking at the cells lining the human nose in the laboratory. Some cells were exposed to e-cigarette vapor, with and without nicotine, while others were not exposed.
Cells exposed to either the e-cigarette vapor with nicotine or without it expressed PAFR at levels three times higher than those seen in the non-exposed cells.
When the researchers introduced pneumococcal bacteria to these cells, they found that exposure to e-cigarette vapor with or without nicotine doubled the amount of bacteria sticking to the airways.
When the researchers tested the effects of e-cigarette vapor exposure in mice, they once again found that inhaled exposure to e-cigarette vapor increased PAFR levels on airway lining cells. Exposure also increased pneumococcal bacteria in the respiratory tract after infection.
PAFR levels in the cells lining the nose were also examined in 10 regular users of e-cigarettes containing nicotine, as well as one person who regularly used e-cigarettes without nicotine and six people who did not vape.
Baseline PAFR levels in the airways of all 17 volunteers were measured and then the vapers were asked to take at least 10 puffs on their e-cigarette during a 5-minute span.
One hour after vaping, PAFR levels on the airway cells had increased threefold, compared to no increase in non-exposed controls.
The finding of a PAFR expression increase in users of both nicotine and non-nicotine containing e-cigarettes suggests a need for studies comparing nasal PAFR responses to nicotine- and non-nicotine vapor, as well as nicotine nasal spray, the researchers wrote.
They cited several study limitations, including lack of data on whether e-cigarette vapor-induced nasal PAFR expression induced pneumococcal infection in humans. The study also didn't address effects of e-cigarette vapor on adhesion of non-pneumococcal pathogens "that co-opt PAFR to adhere to human cells including non-typeable Haemophilus influenzae, Acinetobacter baumannii, and some strains of Pseudomonas aeruginosa and Neisseria meningitides."
Commenting on the study, European Respiratory Society president Mina Gaga, MD, PhD, said that while e-cigarettes are very new, "[s]tudies like this one give us early warning of what the risks might be."
"The adverse effects of tobacco smoking are not evident immediately. They usually develop after years of exposure, so we need to do more research and follow users over time to see what the long-term health effects may be," she noted in a written statement.
Disclosures
Funding for this research ws provided by Queen Mary University of London, and others.
Primary Source
European Respiratory Journal
Myashita L, et al. "E-cigarette vapour enhances pneumococcal adherence to airway epithelial cells" Eur Resp J 2018; DOI: 10.1183/13993003.01592-2017.