Nicotine, but not propylene glycol and vegetable glycerin (PG/VG), induces neutrophil elastase (NE) release from neutrophils. Neutrophils were isolated from peripheral blood and exposed to combinations of PG/VG, nicotine or mannitol (osmotic control) for 4 hours. (A) Representative Western blots of neutrophil secretions after incubation with the indicated e-liquid components, with Ponceau S staining as a loading control. (B) Densitometric analysis of NE and GAPDH normalized to Ponceau S staining shown as fold change compared with control. (C) NE activity in concentrated media, as measured using the fluorogenic substrate assay. *P ≤ 0.05 and **P ≤ 0.001. Data are shown as mean ± SEM. All n = 12 per group. Data were analyzed using ANOVA followed by Tukey’s test. AU = arbitrary units; MAN = mannitol; NIC = nicotine.