Oxidative stress generated DNA damage by 6PPD and other tyre additives in A549 human lung epithelial cells

Tyre additives such as p-phenylenediamines (PPDs) and benzothiazoles (BTs) are ubiquitous in the environment. They have been frequently detected in urban air and have been detected in the human body. However, few studies have examined the toxicological effects in human cells. In this study we perform cytotoxicity, oxidative stress and DNA damage assays on A549 human alveolar lung cells with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), diphenyl-p-phenylenediamine (DPPD), 1,3-benzothiazole (BTZ) and 2-mercaptobenzothiazole (MBT). It was found that all additives were able to cause glutathione (GSH) depletion and induce DNA strand breaks after 24 h exposure in a concentration-dependent manner. The presence of N-acetyl-L-cysteine (NAC), a GSH precursor, mitigated both GSH depletion and DNA damage from 6PPD. Although the tested concentrations of tyre additives exceeded typical levels reported for ambient air, these additives have been detected in wastewater, road runoff and road dust. Therefore, human exposure can occur through multiple routes, including inhalation, ingestion, and dermal absorption, ultimately reaching alveolar cells either directly via the lungs or indirectly through the bloodstream.