UVB in solar-simulated light causes formation of BaP-photoproducts capable of generating phosphorylated histone H2AX.

Polycyclic aromatic hydrocarbons (PAHs), wide-spread mutagenic and carcinogenic environmental pollutants, are consistently exposed to sunlight in the environment. Our previous paper showed that benzo[a]pyrene (BaP) exposed to solar-simulated light (SSL) induced phosphorylation of histone H2AX (γ-H2AX) [T. Toyooka, G. Ohnuki, Y. Ibuki, Solar-simulated light-exposed benzo[a]pyrene induces phosphorylation of histone H2AX, Mutat. Res. 650 (2008) 132-139], a marker of DNA double strand breaks. In this study, we found the ultraviolet B (UVB) region of SSL to produce photomodified BaP with high cytotoxicity and the ability to generate γ-H2AX. Degradation of BaP by SSL, resulting in an increase in cytotoxicity and the generation of γ-H2AX, was decreased by UVB-masking using a glass plate. Exposure to UVB itself increased the cytotoxicity of BaP and amount of γ-H2AX generated. Other PAHs, 1,2-benzoanthracene and 1,2:5,6-dibenzoanthracene, which absorb UVB, also showed enhanced cytotoxicity and the promoted the generation of γ-H2AX after exposure to SSL, whereas naphthalene and chrysene, which have low absorption in the UVB region, did not. These findings suggested that UVB is important for the degradation of PAHs having absorbance in this region, but that the production of genotoxic intermediates during the degradation process needs to be considered. UVB is a two-edged blade in environments, effectively degrading toxic chemicals but also producing genotoxic compounds as reactive intermediates.