title: Synthesis of depurinating DNA adducts formed by one-electron oxidation of 7H-dibenzo[c,g]carbazole and identification of these adducts after activation with rat liver microsomes.
abstract: It is hypothesized that 7H-dibenzo[c,g]carbazole (DBC) is metabolically activated by one-electron oxidation in accordance with its propensity to be easily oxidized to its radical cation. Iodine oxidation of DBC produces a radical cation that subsequently binds to nucleophilic groups of dG or Ade. Oxidation of DBC in the presence of dG products three adducts: DBC-5-N7Gua, DBC-6-N7Gua, and DBC-6-C8Gua, whereas in the presence of Ade, four adducts are obtained: DBC-5-N7Ade, DBC-5-N3Ade, DBC-5-N1Ade, and DBC-6-N3Ade. Formation of these adducts demonstrates that the DBC radical cation reacts at C-5 or C-6 with the reactive nucleophiles N-7 and C-8 of dG and N-7, N-3, and N-1 of Ade. Formation DNA adducts by DBC was studied by using horesradish peroxidase or 3-methylcholanthrene-induced rat liver microsomes for activation. Identification of the biologically-formed depurinating adducts was achieved by comparison of their retention times on HPLC in two different solvent systems and by matrix-assisted laser desorption ionization (MALDI) mass spectrometry. Quantitation of the adducts formed by rat liver microsomes shows that 96% are depurinating adducts, DBC-5-N7Gua (11%), DBC-6-N7Gua (32%), and DBC-5-N7Ade (53%), and 4% are unidentified stable adducts. Activation of DBC by horseradish peroxidase affords 32% stable unidentified adducts and 68% depurinating adducts: 19% DBC-5-N7Gua, 13% DBC-6-N7Gua, 27% DBC-5-N7Ade, and 9% DBC-5-N3Ade. Thus, activation of DBC by cytochrome P450 predominantly forms depurinating adducts by one-electron oxidation.
authors.affiliation: Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha, USA.
authors.forename: L
authors.initials: L
authors.lastname: Chen
authors.forename: P D
authors.initials: PD
authors.lastname: Devanesan
authors.forename: J
authors.initials: J
authors.lastname: Byun
authors.forename: J K
authors.initials: JK
authors.lastname: Gooden
authors.forename: M L
authors.initials: ML
authors.lastname: Gross
authors.forename: E G
authors.initials: EG
authors.lastname: Rogan
authors.forename: E L
authors.initials: EL
authors.lastname: Cavalieri
mesh_terms: D000818:Animals; D002227:Carbazoles / Q000737:chemistry / Q000378:metabolism*; D002273:Carcinogens / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D018736:DNA Adducts / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism*; D004583:Electrons; D007455:Iodine; D009682:Magnetic Resonance Spectroscopy; D008862:Microsomes, Liver / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D051381:Rats; D016339:Spectrometry, Mass, Fast Atom Bombardment; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D002227:Carbazoles; D002273:Carcinogens; D018736:DNA Adducts; D007455:Iodine; C013478:7H-dibenzo(c,g)carbazole