UVA Photoirradiation of Methylated Benzo[a]pyrene and Benzo[e]pyrene leading to Induction of Lipid Peroxidation

Abstract: Polycyclic aromatic hydrocarbons (PAHs) are widespread genotoxic environmental pollutants and potentially pose a health risk to humans. Although the biological and toxicological activities, including metabolism, mutagenicity and carcinogenicity of PAHs have been thoroughly studied, their phototoxicity and photo-induced biological activities have not been well examined. In this research, we studied the photoirradiation of isomeric methylbenzo[a]pyrene (MBaP) and methylbenzo[e]pyrene (MBeP) by UVA light in the presence of a lipid, methyl linoleate, and evaluated the potential of these compounds to induce lipid peroxidation. The compounds chosen for study included BaP, 3-MBaP, 4-MBaP, 6-MBaP, 7-MBaP, 10-MBaP, BeP, 4-MBeP, and 9-MBeP. The results indicate that upon photoirradiation by UVA at 7 and 21 J/cm², these compounds induced lipid peroxidation. The levels of the induced lipid peroxidation were similar among BaP and the isomeric MBaPs, and among the BeP and MBePs, with the BaP group higher than the BeP group. There was also a co-relation between the UV A light dose and the level of lipid peroxidation induced. Lipid peroxide formation was inhibited by NaN₃ (singlet oxygen and free radical scavenger) and was enhanced by the presence of deuterium oxide (D₂O) (extends singlet oxygen lifetime). These results suggest that photoirradiation of MBaPs and MBePs by UVA light generates reactive oxygen species (ROS), which induce lipid peroxidation.