title: Carcinogenic semicarbazide induces sequence-specific DNA damage through the generation of reactive oxygen species and the derived organic radicals.
abstract: Semicarbazide, a hydrazine derivative, is carcinogenic to mice but shows no or little mutagenicity in the Salmonella-microsome test. To clarify whether or not the genotoxic mechanism contributes to the non-mutagenic carcinogenicity of semicarbazide, we investigated DNA damage induced by semicarbazide using 32P-5'-end-labeled DNA fragments obtained from the c-Ha-ras-1 protooncogene and the p53 tumor suppressor gene. Semicarbazide caused DNA damage frequently at the thymine and cytosine residues in the presence of Cu(II). Catalase and bathocuproine partially inhibited DNA damage, suggesting that hydrogen peroxide plus Cu(I) participates in DNA damage. When a high concentration of semicarbazide was used in the presence of catalase, DNA damage was induced, especially at G in 5'-AG and slightly at 5'-G in GG and GGG sequences. An electron paramagnetic resonance (EPR) spectroscopic study has confirmed that the reaction of semicarbazide with Cu(II) produces carbamoyl radicals (z.rad;CONH(2)), possibly generated via the nitrogen-centered radicals of semicarbazide. Azodicarbonamide also produced carbamoyl radicals and induced DNA damage frequently at 5'-G in GG and GGG sequences, suggesting that carbamoyl radicals participate in this sequence-specific DNA damage by semicarbazide. On the basis of our previous reports, we consider that the sequence-specific DNA damage at G in 5'-AG in the present study is due to the nitrogen-centered radicals. This study has shown that semicarbazide induces DNA damage in the presence of Cu(II) through the formation of hydrogen peroxide and Cu(I). In addition, semicarbazide-derived free radicals participate in DNA damage. DNA damage induced by these reactive species may be relevant to the carcinogenicity of semicarbazide.
authors.affiliation: Radioisotope Center, Mie University School of Medicine, Edobashi 2-174, Tsu, Mie 514-8507, Japan.
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Hirakawa
authors.forename: Kaoru
authors.initials: K
authors.lastname: Midorikawa
authors.forename: Shinji
authors.initials: S
authors.lastname: Oikawa
authors.forename: Shosuke
authors.initials: S
authors.lastname: Kawanishi
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000633:toxicity*; D002417:Cattle; D002851:Chromatography, High Pressure Liquid / Q000295:instrumentation / Q000379:methods; D003300:Copper / Q000494:pharmacology; D004247:DNA / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D004249:DNA Damage / Q000502:physiology*; D003849:Deoxyguanosine / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D016166:Free Radical Scavengers / Q000494:pharmacology; D005609:Free Radicals / Q000032:analysis / Q000378:metabolism; D016158:Genes, p53 / Q000187:drug effects; D011905:Genes, ras / Q000187:drug effects; D006151:Guanosine / Q000031:analogs & derivatives* / Q000378:metabolism; D010618:Phenanthrolines / Q000494:pharmacology; D010761:Phosphorus Radioisotopes; D011401:Promoter Regions, Genetic; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012663:Semicarbazides / Q000633:toxicity*; D013379:Substrate Specificity; D013950:Thymus Gland / Q000502:physiology
chemical_list: D002273:Carcinogens; D016166:Free Radical Scavengers; D005609:Free Radicals; D010618:Phenanthrolines; D010761:Phosphorus Radioisotopes; D017382:Reactive Oxygen Species; D012663:Semicarbazides; D006151:Guanosine; C010059:carbamylhydrazine; C046215:8-hydroxyguanosine; D003300:Copper; D004247:DNA; C002478:bathocuproine; D003849:Deoxyguanosine