Diverse Impact of E-Cigarette Aerosols on Oxidative Stress and Inflammation in Lung Alveolar Epithelial Cells (A549)

This study investigated the pro-inflammatory and pro-oxidative effects of popular electronic cigarette aerosols (ECAs) compared with conventional cigarette smoke (CS) in the cultured human alveolar epithelial cell line (A549). Using cytotoxicity assays and four ECAs, substantial differences in biological impact were observed. CS exposure led to significant declines in cell viability and pronounced morphological changes, consistent with the presence of toxic combustion byproducts. Most ECAs caused negligible cytotoxicity except for the tobacco-flavoured variant, which demonstrated marked toxicity. DNA damage and altered cell cycle profiles were minor. Oxidative stress analysis revealed stable superoxide dismutase activity but notable glutathione depletion, especially with watermelon- and strawberry-flavoured ECAs, and unaltered mitochondrial transmembrane potential, indicating the importance of individual flavour additives in cellular antioxidant defence. Inflammatory markers, such as TNF-α, NF-κB, and IL-6, were differentially elevated across the CS and ECA groups, with IL-6 consistently increased, underscoring its role in regulating epithelial cells. Advanced double fluorescence analysis revealed increased cellular heterogeneity and inflammation, which was distinct for all ECA flavours. Overall, the findings demonstrate considerable heterogeneity in biological effects among ECA flavourings and propose a simple ECA biomonitoring model. The results emphasise the necessity for individualised toxicity assessments, especially regarding subclinical inflammation and potential long-term health outcomes.