title: One-electron reduction of chromium(VI) by alpha-lipoic acid and related hydroxyl radical generation, dG hydroxylation and nuclear transcription factor-kappaB activation.
abstract: Reaction of chromium(VI) with alpha-lipoic acid (reduced form, also called 1,2-dithiolane-3-pentanoic acid) generated Cr(V) and hydroxyl radical (*OH) as measured by electron spin resonance and ESR spin trapping. 5,5-Dimethyl-1-pyrroline was used as a spin trapping agent. Catalase inhibited the *OH generation and enhanced the Cr(V) formation. Superoxide dismutase had an opposite effect. H2O2 enhanced the *OH generation and decreased the Cr(V) formation in a dose-dependent manner. Metal chelators, EDTA, diethylenetriaminepentaacetic acid, deferoxamine, and 1, 10-phenanthroline inhibited *OH radical generation in the order of EDTA > 1,10-phenanthroline > DTPA > deferoxamine. Oxygen consumption measurements indicated that molecular oxygen was used to generate *OH radical in the mixture of Cr(VI) and alpha-lipoic acid. H2O2 and superoxide radical (O2-) were involved as reactive intermediates. The *OH radical was generated via Cr(V)-mediated Fenton-like reaction (Cr(V) + H2O2 --> Cr(VI) + OH- + *OH). HPLC measurements show that the *OH radical generated by this reaction is capable of generating 8-hydroxyl-2'-deoxyguanosine from 2-deoxyguanosine. Incubation of Cr(VI) with cultured Jurkat cells resulted in an activation of DNA binding activity of the nuclear factor (NF)-kappaB. Addition of alpha-lipoic acid enhanced the NF-kappaB activation, while the *OH radical scavenger, sodium formate, inhibited it, showing that alpha-lipoic acid enhanced Cr(VI)-induced NF-kappaB activation via free radical reactions. The results indicate that while alpha-lipoic acid is considered to be an antioxidant, it may be a cellular one-electron Cr(VI) reductant and could be involved in the mechanism of Cr(VI)-induced carcinogenesis.
authors.affiliation: Milton S. Hershey Medical Center, Pennsylvania State University, Hershey, Pennsylvania, 17033, USA.
authors.forename: F
authors.initials: F
authors.lastname: Chen
authors.forename: J
authors.initials: J
authors.lastname: Ye
authors.forename: X
authors.initials: X
authors.lastname: Zhang
authors.forename: Y
authors.initials: Y
authors.lastname: Rojanasakul
authors.forename: X
authors.initials: X
authors.lastname: Shi
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D002273:Carcinogens / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000378:metabolism; D003849:Deoxyguanosine / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D017665:Hydroxyl Radical / Q000737:chemistry*; D006900:Hydroxylation; D016328:NF-kappa B / Q000378:metabolism*; D010084:Oxidation-Reduction; D008063:Thioctic Acid / Q000737:chemistry*; D014407:Tumor Cells, Cultured
chemical_list: D000975:Antioxidants; D002273:Carcinogens; D004268:DNA-Binding Proteins; D016328:NF-kappa B; D002857:Chromium; C074702:chromium hexavalent ion; D017665:Hydroxyl Radical; D008063:Thioctic Acid; D003849:Deoxyguanosine