Oxidative stress more strongly induced by ortho- than para-quinoid polycyclic aromatic hydrocarbons in A549 cells

The effect of four ortho-quinoid polycyclic aromatic hydrocarbons (PAHs) and seven para-quinoid PAHs on the viability of A549 cells were examined. The ortho-quinoid PAHs [1,2-naphthoquinone (1,2-NQ), 9,10-phenanthrenquinone (9,10-PQ), 5,6-chrysenequinone (5,6-CQ), and benzo[c]phenanthrene-5,6-quinone (B[c]P-5,6-Q)] overproduced hydrogen peroxide (H₂O₂) without being consumed themselves. These ortho-quinoid had strong cytotoxic effects except for 1,2-NQ, since of its tendency to covalently bind to thiol groups. The cytotoxicity appears to be due to the overproduction of H ₂O₂ by ortho-quinoid PAHs in a redox cycle coupled with the consumption of thiol group. In contrast, the para-quinoid PAHs were not as strong cytotoxic and did not produce H₂O₂.