Toxicity assessment of 6PPD-quinone in human lung cells: Insights from BEAS-2B and A549 cell lines

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), an environmental transformation product of the rubber tire antioxidant 6PPD, is increasingly detected in urban environments, yet its impact on human health. This study investigated toxicological effects of 6PPD-Q in two human lung cells: BEAS-2B (a transformed bronchial epithelial cell) and A549 (a lung adenocarcinoma cell). Cells were exposed to 6PPD-Q at concentrations of 5 to 80 ng/mL and effects on cell viability, oxidative stress by generation of reactive oxygen species (ROS), disruption of antioxidant defense response, oxidative DNA damage as determined by formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG), and biotransformation 6PPD-Q were determined. Results showed a biphasic response with an increase in cell viability at lower concentrations, suggesting an adaptive cellular response. ROS production and levels of 8-OHdG significantly increased, indicating an imbalance in redox status and induction of oxidative DNA damage. Two phase I hydroxylation products, 6PPD-Q-4-OH (TPOH1) and 6PPD-Q-phenyl-OH (TPOH2), were identified. In A549 cells, TPOH1 was only in the media, while TPOH2 was found both inside cells and in the media. Moreover, mRNA expression analysis revealed upregulation of metabolism- and oxidative stress-related genes and inflammatory cytokines. These findings suggest that 6PPD-Q may trigger oxidative stress and inflammation in lung cells. This study highlights the effects of 6PPD-Q on lung cells and underscores the need for further research on its long-term impact on human respiratory health.