Benzo[a]pyrene Enhances the Formation of 8-Hydroxy-2‘-deoxyguanosine by Ultraviolet A Radiation in Calf Thymus DNA and Human Epidermoid Carcinoma Cells

Abstract

The objective of this study is to investigate if benzo[a]pyrene (BaP) and ultraviolet (UV) radiation synergistically induce oxidative DNA damage. Calf thymus DNA was incubated with BaP and irradiated with UVB (280-320 nm) and UVA (335-400 nm). BaP substantially enhanced the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) by UVA, but only moderately increased the level of 8-OHdG by UVB. Formation of 8-OHdG proportionally correlated with both UV dose and BaP concentration. Human epidermoid carcinoma cells were incubated with 10 microg of BaP/mL for 24 h and then exposed to 10 kJ/m2 UVB and 25 kJ/m2 UVA. UVB plus BaP did not affect the level of 8-OHdG in cultured cells, whereas UVA plus BaP substantially increased 8-OHdG by over 4-fold compared to BaP and UVA controls. To confirm what reactive oxygen species (ROS) are involved in BaP plus UVA-induced oxidative DNA damage, less or more specific ROS quenchers were added to DNA solution. The results showed that only superoxide dismutase and genistein significantly quenched BaP plus UVA-induced 8-OHdG, whereas catalase, sodium azide, and mannitol exhibited no effect. Our studies suggest that BaP enhances the formation of 8-OHdG in purified DNA and cultured cells by UVA, but not by UVB, and that superoxide anion plays an important role in the synergistic induction of oxidative DNA damage.

Environmental Carcinogenic Polycyclic Aromatic Hydrocarbons: Photochemistry and Phototoxicity

“…Exposure of mammalian cells to B[a]P and fluorescent light induces 3-10 fold more 8-hydroxyguanine formation than it is carried out with B[a]P but without light (113). A similar observation by UVA light irradiation of B[a]P mixture with calf thymus DNA or with cultured human epidermoid carcinoma cells was reported by another group (145). These studies also points to the involvement of superoxide anion during the oxidation of guanine.…”

Photoirradiation of Polycyclic Aromatic Hydrocarbons with UVA Light – A Pathway Leading to the Generation of Reactive Oxygen Species, Lipid Peroxidation, and DNA Damage

“…The level of 8-OHdG adduct formed in cultured cells was much higher than that in calf thymus DNA. These results suggest that the metabolites of benzo[a]pyrene exhibit higher capability in induction of 8-OH-dG [65]. The subsequent study revealed that its metabolite, benzo[a]pyrene bay-region diolepoxide combined with UVA synergistically induced 8-OHdG in a level about 25-fold higher than benzo[a]pyrene.…”

“…Liu et al reported that benzo[a]pyrene enhances the formation of 8-OHdG formation by UVA radiation in calf thymus DNA and cultured cells [65]. The level of 8-OHdG adduct formed in cultured cells was much higher than that in calf thymus DNA.…”

Combined subcarcinogenic benzo[a]pyrene and UVA synergistically caused high tumor incidence and mutations in H‐ras gene, but not p53, in SKH‐1 hairless mouse skin

“…Thus, the combined impact of these 2 environmental factors at subcarcinogenic doses remains a challenging subject. Our previous studies demonstrated that the combination of BaP and UVA synergistically induced oxidative DNA damage in vitro 13 and in vivo 14 and BPDE-DNA adducts in vivo.…”