Comparison of the effects of e-cigarette vapor vs cigarette smoke on lung function and inflammation in mice

Electronic cigarettes (e-cigarettes) are advertised as a new smoking cessation tool and an alternative to cigarette smoking, aiming to limit smoking-related illnesses. However, concerns about their safety and toxicity have been raised. In spite of widespread use, only a limited number of studies on their effects in the respiratory system exist. We aimed to compare the effects of e-cigarette vapor vs cigarette smoke in the lungs of mice. Methods: C57BL/6 mice were exposed for 3 days or 4 weeks to air, cigarette smoke (CS) or e-cigarette vapor from i) propylene glycol/vegetable glycerol (1:1; PGVG), ii) PGVG with flavor (tobacco blend 1%; PGVG-F), or iii) PGVG with nicotine (18 mg/ml; PGVG-N). Results: After 3 days, BALF cellularity was increased (mostly macrophages) in all groups compared to air-breathing mice. After 4 weeks, BALF cellularity was elevated only in the CS and PGVG-F mice. Using a forced oscillation technique we observed that 3 day exposure to PGVG resulted in increased tissue elasticity and airway resistance compared to air-exposed mice. In the 4 week groups, airway elasticity was increased only in the CS and PGVG-F. Airway resistance in response to metacholine was increased in the CS and PGVG-F groups. Markers of oxidative stress and inflammation (protein carbonyls, malondialdehyde, interleukin-1β and -6) after 4 weeks were increased only in CS mice. Conclusions: Our findings suggest that after prolonged use, e-cigarettes trigger milder inflammatory responses and respiratory perturbations and that the flavor added was responsible for most of the observed damage.