E-cigarette aerosol exposure modulates crystalline silica-induced fibrotic responses in the lungs

Pulmonary toxicity of e-cigarettes (e-cigs), particularly their combined effects with occupational exposures like crystalline silica (S), remains largely unexplored. This study evaluated the combined effects, molecular mechanisms, and differential responses in the lungs following co-exposure to e-cig aerosols and S. Subchronic silicosis was established by oropharyngeal aspiration of S (0.2 g/kg) into C57BL/6 mice. Mice were exposed to filtered air, S, or e-cig (E) + S with endpoints evaluated 28 days post-exposure. The count median diameter of e-cig aerosols generated for our mice exposure was 0.771 µm (GSD = 2.33). Enhanced pause (Penh) values increased significantly in male E + S group and female S and E + S groups, compared to their respective air controls, during the first and second weeks of exposure. Histological evaluations (hematoxylin and eosin and Masson's trichrome staining) revealed significantly increased fibrosis scores in both male and female S and E + S groups compared to respective air controls. Hematological analysis revealed a significant decrease in neutrophil counts/percentage in female E + S mice compared to S alone. Cytokine analysis revealed a significant increase in keratinocyte chemoattractant (KC) levels in male S and E + S groups compared to air controls, while in female mice, KC expression increased significantly in the E + S group compared to S alone. Protein analysis revealed distinct sex-specific changes in key protein markers associated with fibrosis and epithelial-mesenchymal transition. Taken together, these findings indicate that S-induced lung fibrosis with or without e-cig exposure occurred in both male and female mice, with different underlying molecular mechanisms.