Thirdhand vaping exposures are associated with pulmonary and systemic inflammation in a mouse model

Abstract

Thirdhand smoke (THS) is the accumulation of secondhand smoke on surfaces that ages with time. THS exposure is a potential health threat to children, partners of smokers, and workers in environments with current or past smoking, and needs further investigation. In this study, we hypothesized that thirdhand Electronic Nicotine Delivery Systems (ENDS) exposures elicit lung and systemic inflammation due to resuspended particulate matter (PM) and inorganic compounds that remain after active vaping has ceased. To test our hypothesis, we exposed C57BL/6J mice to cotton towels contaminated with ENDS aerosols from unflavored vape fluid (6 mg nicotine in 50/50 propylene glycol/vegetable glycerin) for 1h/day, five days/week, for three weeks. We assessed protein levels in serum and bronchoalveolar lavage fluid (BALF) using a multiplex protein assay. The mean ± sd for PM₁₀ and PM_2.5 measurements in exposed mouse cages were 8.3 ± 14.0 and 4.6 ± 7.5 μg/m³, compared to 6.1 ± 11.2 and 3.7 ± 6.6 μg/m³ in control cages respectively. Two compounds, 4-methyl-1, 2-dioxolane and 4-methyl-cyclohexanol, were detected in vape fluid and on ENDS-contaminated towels, but not on control towels. Mice exposed to ENDS-contaminated towels had lower levels of serum Il-7 (P = 0.022, n = 7), and higher levels of Il-13 in the BALF (P = 0.006, n = 7) than those exposed to control towels (n = 6). After adjusting for sex and age, Il-7 and Il-13 levels were still associated with thirdhand vaping exposure (P = 0.010 and P = 0.017, respectively). This study provides further evidence that thirdhand ENDS aerosols can contaminate surfaces, and subsequently influence lung and systemic health upon exposure.

Keywords: E-cigarettes; blood cytokines; lung cytokines; mouse model; organic chemicals; particulate matter; thirdhand smoke; vaping.

Figure 1.

The sample chamber of the inhalation exposure system with aerosol generated onto towels (i); To assess differences in PM concentrations, UPAS V2+ air samplers were placed in a subset of exposed and control mouse cages in (ii); Finally, ENDS-contaminated and control towels were placed in clean mouse cages, and mice were placed on towels 1hr/day, 5 days a week over a three-week period (iii). ENDS: electronic nicotine delivery systems; PM: particulate matter.

Figure 2.

Time series plots of real-time PM₁₀ (A) and PM_2.5 (B) measurements taken during one of the experimental periods. Real-time samplers were turned on but programmed to start logging data around 9:45am. Air samplers were placed side-by-side on a lab bench with one or two personnel working in the room. Towel samples were exposed to ENDS aerosols for one hour from ~ 9:45 am till ~ 10:45 am, while controls were kept in an airtight Ziplock bag. Then, ENDS-contaminated towels were also placed in airtight Ziplock bags and transported to the vivarium by 11:15 am. New mouse cages were set up, and towels and samplers were placed in the cages before introducing the respective group of mice into the new cages by 11:25 am. Then, at approximately 12:25 pm, air samplers were turned off, mice were placed in their home cages and the towels were placed back into the Ziplock bags.

Figure 3.

Wilcoxon rank sum tests of proportions of chemicals identified in ENDS contaminated vs. control towels. Test statistics are provided for chemicals with ≥ 1.5-fold change higher proportion in ENDS-contaminated towels compared to control towels. Compounds with pink dots are > 2.0-fold change with P values < 0.05. ENDS: electronic nicotine delivery systems.

Figure 4.

Boxplots of proportions (or ratios) of 2,5-dimethylfuran (A) and 4-methyl-1,2-dioxolane (B) identified in ENDS-contaminated vs. control towels. These ratios are derived from the AUC values for chemicals detected in each sample towel sample. ENDS: electronic nicotine delivery systems.

Figure 5.

Mean (± standard deviation) of Il-7 levels in serum (A) and Il-13, Il-1β and Il-12p70 levels in (BALF, B, C, and D, respectively) of male and female mice exposed to towels with ENDS aerosol contamination. n = 2 each for all males and females in the exposed and control groups at 75 days. n = 3 and n = 2 for exposed and control males, respectively, at 48 days at the time of sacrifice. BALF: bronchoalveolar lavage fluid; ENDS: electronic nicotine delivery systems.