Short-Term and Long-Term Effects of Electronic Cigarettes on Mouse Lungs Following Nose-Only Exposures

Health effects of electronic cigarettes (ECs) remain unknown, despite their popularity. We have determined that ECs produce highly reactive free radicals that could potentially cause damage in exposed tissues, mainly lungs. Goal for this study was to investigate the short- and long-term effects of ECs in mouse lungs. We focused on evaluating lung functions, oxidative stress related markers, and lung injury following nose-only exposures in male and female mice after 4- and 12-week periods. The EC exposure was modeled in vivo using nose-only exposures to C57BL/6 mice. For all studies, E-liquid (60:40; PG:VG) aerosols were compared to sham (compressed air) and to very low non-nicotine cigarette smoke (CS) controls in both sexes. Oxidative stress biomarkers (GSH, 8-Isoprostane, REDD1, and pGSK3β) and their selected downstream (RPS6) as well as upstream (AKT) target proteins in addition to pH2AX were measured by Western blot analysis. Lung function in mice was assessed by flexiVent and the injury scores were calculated following lung histology. Changes in cytology were also observed in cytospins from bronchoalveolar lavage (BALF). The lung injury (LI) score following 12-week exposures was significantly higher with EC and CS in female mice. Higher cell counts in BALF were mainly observed in CS exposed males and females at 4 and 12 weeks. 8-Isoprostane levels were significantly higher in EC and CS exposed males at 12 weeks. pGSK3β/GSK3β was low in males and higher in female mice at 4 weeks, and this difference was more pronounced at 12 weeks in CS exposed mice. Some mice exposed to EC and CS also showed DNA damage, as measured by pH2AX/H2AX expression. Based on the LI score, ECs were placed in between compressed air and CS. Our results showed the differentially expressed inflammation and oxidative stress/damage-related pathways from in vivo exposures to EC aerosols vs CS that could be an effective strategy for identifying EC relevant biomarkers of exposure and potential harm.