Impact of E-Cigarette Aerosols on Oxidative Stress and Inflammation in Lung Alveolar Epithelial Cells (A549): The Role of Subclinical Inflammation

This study investigated the proinflammatory and prooxidative effects of popular electronic cigarette (EC) aerosols compared with conventional cigarette smoke (CS) in cultured human alveolar epithelial cell line (A549). Using cytotoxicity assays and four EC extracts, 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 EC extracts 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 ECs, 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 CS and EC groups, with IL-6 consistently increased, underscoring its role in epithelial cell regulation. Advanced double fluorescence analysis highlighted increased cellular heterogeneity and inflammation, distinct for all EC flavours. Overall, the findings demonstrate considerable heterogeneity in biological effects among EC flavourings and propose a simple biomonitoring model. The results emphasise the necessity for individualised toxicity assessments, especially regarding potential long-term health outcomes.