The role of iron in reactive oxygen species generation from diesel exhaust particles

Diesel exhaust particles (DEP) are known to produce reactive oxygen species (ROS), which induce oxidative stress and inflammation in the lung and respiratory tract. DEP are composed of polycyclic aromatic hydrocarbons (PAH) and their derivatives, redox active semi-quinones, and trace amounts of heavy metals. ROS production was measured by thiobarbituric acid-reactive substances of deoxyribose (TBARS) formation from DEP samples obtained from Korea (DEP-KO), and the Standard Reference Material (SRM) 2975 to explore the role of transition metals. Both DEP-KO and SRM2975 had similar amounts of transition metals, whereas DEP-KO contained more iron, but less copper and zinc, than SRM2975. The water-soluble fraction from SRM2975, but not that from DEP-KO, had a broad absorption in the visible region, but not from DEP-KO, obscuring an accurate absorption measurement of TBARS. Fluorescence measurements of TBARS generation in a water-soluble extract showed that SRM2975 produces more TBARS, but the addition of hydrogen peroxide (H2O2) generated more TBARS in DEP-KO than in SRM2975, consistent with the higher amounts of iron in DEP-KO. The incubation of DEP with iron chelators inhibited the production of TBARS. Finally, a novel use of the fluorogenic spin trap probe, proxyl fluorescamine, enabled the detection of the ROS production from both DEP-KO and SRM2975. Our findings suggested that careful consideration is needed to measure TBARS production in DEP, and that iron in DEP seems to be more important than other transition metals in H2O2-induced ROS generation.