Chronic e-cigarette aerosol exposure alters NRF2 and TGF-β1 signaling and enhances stem-like features in human oral and lung epithelial cells.

E-cigarette aerosols cause increased oxidative stress in vitro, in animal models, and in users, a condition linked to disease progression, including cancer. This study investigates how prolonged exposure to e-cigarette aerosols affects key cellular pathways involved in antioxidant defense and stemness. Human oral and lung epithelial cells were exposed for two weeks to e-cigarette aerosol extracts delivering 30 ng/mL nicotine, a concentration that mimics users' plasma levels. Gene and protein expression were assessed using real-time RT-PCR and western blotting analyses, respectively, while the spheroid formation assay was performed to evaluate stemness. E-cigarette exposure significantly upregulated the antioxidant regulator NRF2 and its downstream targets (e.g., SOD2, CAT, and HMOX1), while decreasing its negative regulator KEAP1. Unexpectedly, TGF-β1 protein and its downstream signaling, ERK1/2 proteins, were also elevated. Chronic exposure of cell lines to e-cigarette aerosols resulted in increased spheroid formation and elevated expression of stem cell markers (BMI1, OCT4, SNAIL, and SLUG), indicating enhanced stem-like features. Collectively, these findings demonstrate that chronic e-cigarette aerosol exposure induces concurrent activation of NRF2 and TGF-β signaling and enhances stem-like features in human oral and lung epithelial cells. These molecular and phenotypic alterations may contribute to early cellular events associated with oral and lung carcinogenesis, highlighting the need for further investigation into the long-term health consequences of sustained e-cigarette use.