title: Direct and hydrogen peroxide-induced chromium(V) oxidation of deoxyribose in single-stranded and double-stranded calf thymus DNA.
abstract: Oxidative DNA damage by a model Cr(V) complex, [CrO(ehba)2]-, with and without added H2O2, was investigated for the formation of base and sugar products derived from C1', C4', and C5' hydrogen atom abstraction mechanisms. EPR studies with 5,5-dimethylpyrroline N-oxide (DMPO) have shown that Cr(V)-ehba alone can oxidize the spin trap via a direct chromium pathway, whereas reactions of Cr(V)-ehba in the presence of H2O2 generated the hydroxyl radical. Direct (or metal-centered) Cr(V)-ehba oxidation of single-stranded (ss) and double-stranded (ds) calf thymus DNA demonstrated the formation of thiobarbituric acid-reactive species (TBARS) and glycolic acid in an O2-dependent manner, consistent with abstraction of the C4' H atom. A minor C1' H atom abstraction mechanism was also observed for direct Cr(V) oxidation of DNA, but no C5' H atom abstraction product was observed. Direct Cr(V) oxidation of ss- and ds-DNA also caused the release of all four nucleic acid bases with a preference for the pyrimidines cytosine and thymine in ds-DNA, but no base release preference was observed in ss-DNA. This base release was O2-independent and could not be accounted for by the H atom abstraction mechanisms in this study. Reaction of Cr(V)-ehba with H2O2 and DNA yielded products consistent with all three DNA oxidation pathways measured, namely, C1', C4', and C5' H atom abstractions. Cr(V)-ehba and H2O2 also mediated a nonpreferential release of DNA bases with the exception of the oxidatively sensitive purine, guanine. Direct and H2O2-induced Cr(V) DNA oxidation had opposing substrate preferences, with direct Cr(V) oxidation favoring ss-DNA while H2O2-induced Cr(V) oxidative damage favored ds-DNA. These results may help explain the carcinogenic mechanism of chromium(VI) and serve to highlight the differences and similarities in DNA oxidation between high-valent chromium and oxygen-based radicals.
authors.affiliation: Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755-3564, USA.
authors.forename: K D
authors.initials: KD
authors.lastname: Sugden
authors.forename: K E
authors.initials: KE
authors.lastname: Wetterhahn
mesh_terms: D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D017608:Chromium Compounds / Q000494:pharmacology*; D004247:DNA / Q000187:drug effects*; D004249:DNA Damage / Q000187:drug effects; D004277:DNA, Single-Stranded / Q000187:drug effects*; D003855:Deoxyribose / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D008401:Gas Chromatography-Mass Spectrometry; D006016:Glycolates / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D006885:Hydroxybutyrates / Q000494:pharmacology*; D010084:Oxidation-Reduction; D011687:Purines / Q000378:metabolism; D011743:Pyrimidines / Q000378:metabolism; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism; D013950:Thymus Gland
chemical_list: D017608:Chromium Compounds; D004277:DNA, Single-Stranded; D006016:Glycolates; D006885:Hydroxybutyrates; D011687:Purines; D011743:Pyrimidines; D017392:Thiobarbituric Acid Reactive Substances; C031149:glycolic acid; C089728:2-ethyl-2-hydroxybutyric acid; D003855:Deoxyribose; D004247:DNA; D006861:Hydrogen Peroxide