title: Induction of 8-hydroxydeoxyguanosine in DNA by chromium(III) plus hydrogen peroxide and its prevention by scavengers.
abstract: The capability of Cr(III) to induce DNA lesions generated by oxidative damage was investigated in this study by examining the formation of 8-hydroxydeoxyguanosine (8-OHdG) in calf thymus DNA by CrCl3 and/or H2O2 in 10 mM phosphate buffer. In the presence of 0.5 mM H2O2, the formation of 8-OHdG markedly increased with increasing CrCl3 concentration. In contrast, H2O2 or CrCl3 alone did not cause any increase in 8-OHdG level above background. The amount of 8-OHdG induced by CrCl3 plus H2O2 was time dependent; its generation increased linearly over an incubation period of 90 min. The formation of 8-OHdG was unfavorable in an acidic solution (pH < 6); the highest level of 8-OHdG was observed at pH 7-8. Scavengers of reactive oxygen species markedly inhibited the formation of 8-OHdG by CrCl3 plus H2O2; the inhibition effect was sodium azide > D-mannitol > Tris-HCl at an equal concentration. The induction of 8-OHdG by CrCl3 plus H2O2 remained unchanged in D2O. Moreover, an addition of catalase (2.2 U/ml) to the reaction mixture completely inhibited the formation of 8-OHdG by CrCl3/H2O2, whereas only 22% of that formation was inhibited by superoxide dismutase (11 U/ml). A large amount of bovine serum albumin (1.1 mg/ml) could reduce the formation of 8-OHdG by CrCl3 plus H2O2, thereby implying that Cr(III)-mediated DNA-protein crosslinks are unfavorable for 8-OHdG formation. Furthermore, ascorbate could prevent the formation of 8-OHdG by CrCl3 plus H2O2; the extent of prevention increased with increasing ascorbate concentration (10 microM-3 mM). Thus, ascorbate acts as a free radical scavenger in the CrCl3/H2O2 system. The above findings suggest that Cr(III)/H2O2 could generate oxidative damage to DNA, possibly through a Fenton-like reaction, i.e. Cr(III)+H2O2-->Cr(IV)+.OH+OH-. This study also indicates that Cr(III), previously considered as the ultimate kinetically stable species of Cr(VI) metabolites, is capable of inducing carcinogenic lesions through interaction with a cellular oxygen species.
authors.affiliation: Department of Life Sciences, National Tsing Hua University, Taipei, Taiwan, Republic of China.
authors.forename: T C
authors.initials: TC
authors.lastname: Tsou
authors.forename: C L
authors.initials: CL
authors.lastname: Chen
authors.forename: T Y
authors.initials: TY
authors.lastname: Liu
authors.forename: J L
authors.initials: JL
authors.lastname: Yang
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D002417:Cattle; D002857:Chromium / Q000633:toxicity*; D004247:DNA / Q000187:drug effects* / Q000378:metabolism; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000378:metabolism; D016166:Free Radical Scavengers / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000633:toxicity*; D017382:Reactive Oxygen Species
chemical_list: D016166:Free Radical Scavengers; D017382:Reactive Oxygen Species; D002857:Chromium; D000080242:8-Hydroxy-2'-Deoxyguanosine; D004247:DNA; D006861:Hydrogen Peroxide; D003849:Deoxyguanosine; D001205:Ascorbic Acid