Mechanisms of DNA damage by chromium(V) carcinogens.
Reactions of bis(2-ethyl-2-hydroxy-butanato)oxochromate(V) with pUC19 DNA, single-stranded calf thymus DNA (ss-ctDNA), a synthetic oligonucleotide, 5'-GATCTATGGACTTACTTCAAGGCCGGGTAATGCTA-3' (35mer), deoxyguanosine and guanine were carried out in Bis-Tris buffer at pH 7.0. The plasmid DNA was only nicked, whereas the single-stranded DNA suffered extensive damage due to oxidation of the ribose moiety. The primary oxidation product was characterized as 5-methylene-2-furanone. Although all four bases (A, C, G and T) were released during the oxidation process, the concentration of guanine exceeds the other three. Orthophosphate and 3'-phosphates were also detected in this reaction. Likewise, the synthetic oliogomer exhibits cleavage at all bases with a higher frequecncy at G sites. This increased cleavage at G sites was more apparent after treating the primary oxidation products with piperidine, which may indicate base oxidation as well. DNA oxidation is shown to proceed through a Cr(V)-DNA intermediate in which chromium(V) is coordinated through the phosphodiester moiety. Two alternative mechanisms for DNA oxidation by oxochromate(V) are proposed to account for formation of 5-methylene-2-furanone, based on hydrogen abstraction or hydride transfer from the C1' site of the ribose followed by hydration and two successive beta-eliminations. It appears that phosphate coordination is a prerequisite for DNA oxidation, since no reactions between chromium(V) and deoxyguanosine or guanine were observed. Two other additional pathways, hydrogen abstraction from C4' and guanine base oxidation, are also discussed.
Bose
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Department of Chemistry, Kent State University, Kent, OH 44242, USA. rbose@Platinum.kent.edu
Fonkeng
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Moghaddas
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Stroup
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D000818:Animals; D001483:Base Sequence; D002273:Carcinogens / Q000494:pharmacology*; D002417:Cattle; D002857:Chromium / Q000494:pharmacology*; D004249:DNA Damage; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000187:drug effects*; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000235:genetics; D005663:Furans / Q000032:analysis; D015394:Molecular Structure; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry* / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010957:Plasmids / Q000737:chemistry / Q000187:drug effects*; D013950:Thymus Gland
D002273:Carcinogens; D004277:DNA, Single-Stranded; D005663:Furans; D009838:Oligodeoxyribonucleotides; D009942:Organometallic Compounds; D002857:Chromium; C037354:protoanemonin; C083520:bis(2-hydroxy-2-ethylbutanoato)oxochromate(V)