E-cigarette use is associated with significant changes in immune-related gene expression in the nasal mucosa similar to those reported in cigarette smokers, according to findings from a prospective study that compared gene-expression profiles in nonsmokers, cigarette smokers, and e-cigarette users.
Vapers showed decreased expression of a large number of immune-related genes, including all genes found to be decreased in cigarette smokers.
The findings do not imply that e-cigarette use has the same health impact as cigarette smoking, but they do suggest that vaping may have, as yet, unidentified effects on health, Ilona Jaspers, PhD, of the University of North Carolina School of Medicine, Chapel Hill, and colleagues wrote in the American Journal of Physiology.
"Despite the common perception that vaping e-cigarettes is a safe alternative to cigarettes, the data shown here demonstrate the need for further studies related to changes in respiratory immune health induced by vaping e-cigarettes."
In an email exchange with MedPage Today, Jaspers noted that the effect on gene expression among e-cigarette users in the study was actually greater than among cigarette smokers: "Our study collected observational data, and therefore we cannot speculate on whether and/or how e-cigarette use affects the overall health of these individuals. However, our observations demonstrate that e-cigarette use has an impact on the expression of genes associated with regulating immune responses and that these effects are broader than those seen in cigarette smokers," she said.
Studies have repeatedly shown cigarette smoking and secondhand smoke exposure to be associated with immune suppression and an increased risk for respiratory and bacterial infection.
"Even in otherwise healthy subjects, smoking or secondhand smoke exposure is associated with enhanced susceptibility to microbial infections as well as enhanced infection associated severity and morbidity," the researchers wrote. "Smoking broadly suppresses multiple host defense mechanisms including epithelial cell responses and recruitment and activation of innate immune cells, such as neutrophils, macrophages, and natural killer cells."
Previous studies by Jaspers and colleagues showed that cigarette smoke exposure modified the ability of epithelial cells to mount an effective type I interferon response to viral infections and produce the cytokines needed to activate immune cells -- "effectively compromising innate immune host defense responses."
For their latest study, the team recruited healthy adults age 50 and younger who were either nonsmokers (n=13 ), active cigarette smokers (n=14), or active e-cigarette users who reported vaping for at least the last 6 months (n=12). Dual cigarette and e-cigarette users were excluded from the study, and nonsmokers had very little, if any, exposure to secondhand smoke.
Smokers and e-cigarette users kept journals documenting their cigarette or e-cigarette use, and urine and blood samples were taken and analyzed to confirm nicotine levels and biomarkers relevant to tobacco exposure. At 3 to 4 weeks post-enrollment, the researchers took samples from the nasal passages of each participant to analyze immune response gene expression.
Smoking cigarettes or vaping e-cigarettes was associated with decreased expression of specific immune-related genes. All genes with decreased expression in cigarette smokers (n=53) were also decreased in e-cigarette smokers, along with an additional 305 unique genes.
E-cigarette users showed a greater suppression of genes common with those changed in cigarette smokers: "This was particularly apparent for suppressed expression of transcription factors, such as EGR1, which was functionally associated with decreased expression of five target genes in cigarette smokers and 18 target genes in e-cigarette users," the researchers wrote.
"Taken together, these data indicate that vaping e-cigarettes is associated with decreased expression of a large number of immune-related genes, which are consistent with immune suppression at the level of the nasal mucosa."
Nine of the e-cigarette smokers in the study had previously been cigarette smokers, and three had not previously smoked cigarettes. This, and the small sample size, were cited as study limitations. The researchers noted that previous comparisons of the gene expression profiles of smokers and former smokers suggest that some smoking-induced gene expression changes may be irreversible.
"Thus, it is possible that the 53 genes decreased in both cigarette smokers and e-cigarette users are derived from the cigarette smoking history common to both groups, which are not reversed by switching to e-cigarettes."
Jaspers said that the team will soon examine flu vaccine response among e-cigarette users in an effort to determine if users have a modified immune response to the nasal live attenuated influenza vaccine.
"In our previous studies we had already demonstrated that cigarette smokers have suppressed immune responses in the context of the nasal live attenuated influenza virus vaccine, and our upcoming research study was designed to expand these observations to e-cigarette users."
This research was supported by grants from the NIH and the FDA Center for Tobacco Products.
The researchers declared no relevant relationships with industry related to this work.
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