Effects of Electronic Cigarette Constituents on the Human Lung: A Pilot Clinical Trial

Abstract

Electronic cigarette (e-cig) use is continuing to increase, particularly among youth never-smokers, and is used by some smokers to quit. The acute and chronic toxicity of e-cig use is unclear generally in the context of increasing reports of inflammatory-type pneumonia in some e-cig users. To assess lung effects of e-cigs without nicotine or flavors, we conducted a pilot study with serial bronchoscopies over 4 weeks in 30 never-smokers, randomized either to a 4-week intervention with the use of e-cigs containing only 50% propylene glycol (PG) and 50% vegetable glycerine or to a no-use control group. Compliance to the e-cig intervention was assessed by participants sending daily puff counts and by urinary PG. Inflammatory cell counts and cytokines were determined in bronchoalveolar lavage (BAL) fluids. Genome-wide expression, miRNA, and mRNA were determined from bronchial epithelial cells. There were no significant differences in changes of BAL inflammatory cell counts or cytokines between baseline and follow-up, comparing the control and e-cig groups. However, in the intervention but not the control group, change in urinary PG as a marker of e-cig use and inhalation was significantly correlated with change in cell counts (cell concentrations, macrophages, and lymphocytes) and cytokines (IL8, IL13, and TNFα), although the absolute magnitude of changes was small. There were no significant changes in mRNA or miRNA gene expression. Although limited by study size and duration, this is the first experimental demonstration of an impact of e-cig use on inflammation in the human lung among never-smokers.

Figure 1.. Urine propylene glycol (PG) inflammation over one month intervention.

(A) Log₁₀ transformed levels for PG in urine samples at baseline and follow-up for the control (left) and e-cig intervention (right) groups. Each dot represents one subject and paired assays for baseline and after the intervention are connected by a line. The box plot uses the median and the lower and upper quartiles (25th and 75th). (B-C) Spearman correlations of change (follow up-baseline) between PG and cell concentration, macrophages, and lymphocytes (B), and between PG and cytokines including IL-8, IL-13, and TNF-α (C) are shown in the control (left) and e-cig trial (right) groups. Significant False Positive Rate (FDR) q-values at the 0.1 level indicated by asterisks. Changes in PG and on the x-axis and change in cells (B) and cytokines (C) are on the y-axis. Note: One subject with very high baseline and follow-up PG level (likely a dietary source) was removed for analyses for changes of cells and cytokines. Subjects with red blood cell contamination were removed from the cell count analysis. In the e-cig use group, IL-13 and TNF-α were not detected at follow-up in two subjects.

Figure 2.. Principal Component Analysis (PCA) of mRNAs (A and B) and miRNAs (C) for transcripts before and after the trial for control and intervention groups.

The PCA was generated using (A) entire 33,494 mRNA transcripts analyzed, and (B) entire 2,578 miRNA transcripts analyzed. Dots represent each individual for baseline controls (blue), follow-up controls (red), baseline intervention (orange), and follow-up intervention (green).