Role of molecular oxygen in the generation of hydroxyl and superoxide anion radicals during enzymatic Cr(VI) reduction and its implication to Cr(VI)-induced carcinogenesis.
Electron spin resonance (ESR) spin trapping measurements provide evidence for the generation of hydroxyl radicals (*OH) in the reduction of Cr(VI) by glutathione reductase (GSSG-R) in the presence of NADPH as a cofactor. Catalase inhibited the *OH generation, while the addition of H2O2 enhanced it, indicating that the *OH radical generation involves a Fenton-like reaction. The metal chelator, deferoxamine, inhibited the *OH generation with a concomitant generation of a deferoxamine nitroxide radical. EDTA and 1,10-phenanthroline also inhibited the *OH generation. Experiments performed under argon atmosphere decreased the yield of the *OH formation, showing that molecular oxygen plays a critical role. ESR spin trapping and measurements of fluorescence change of scopoletin in the presence of horseradish peroxidase show that reduction of Cr(VI) by GSSG-R/NADPH generates superoxide anion radicals (O2*-) as well as H2O2. It can be concluded that *OH radical is generated by the reaction of H2O2 with Cr(V), which is produced by enzymatic one-electron reduction of Cr(VI). H2O2 is produced by the reduction of molecular oxygen via O2*- as an intermediate. The *OH radicals generated by these reactions are capable of causing DNA strand breaks, which can be inhibited by catalase, formate, and experiments performed under argon.
Leonard
S
S
Pathology and Physiology Research Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.
Wang
S
S
Zang
L
L
Castranova
V
V
Vallyathan
V
V
Shi
X
X
D015197:Carcinogenicity Tests; D002273:Carcinogens; D002614:Chelating Agents / Q000494:pharmacology; D002857:Chromium / Q000737:chemistry / Q000633:toxicity*; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D004249:DNA Damage; D003676:Deferoxamine / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005980:Glutathione Reductase / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry* / Q000633:toxicity; D017665:Hydroxyl Radical / Q000737:chemistry* / Q000633:toxicity; D009249:NADP / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010101:Oxygen Consumption; D013481:Superoxides / Q000737:chemistry* / Q000633:toxicity
D002273:Carcinogens; D002614:Chelating Agents; D002857:Chromium; D013481:Superoxides; D017665:Hydroxyl Radical; D009249:NADP; D004247:DNA; D006861:Hydrogen Peroxide; D005980:Glutathione Reductase; D003676:Deferoxamine; D010100:Oxygen