title: Nitroreduction of nitrated and C-9 oxidized fluorenes in vitro.
abstract: Widespread environmental pollution with mutagenic and carcinogenic nitrofluorenes contributes to human health risks. Since nitroreduction leads to activation of many nitro compounds, nitroreduction of the nitrofluorene (NF) derivatives by one- and two-electron reductants was examined. Rates of nitroreduction catalyzed by xanthine oxidase (XO)/hypoxanthine and measured via stimulation of acetylated cytochrome c reduction increased with the number of nitro groups and oxidation at C-9: 9-oxo-2,4,7-triNF > 9-oxo-2,7-diNF > 2,7-diNF > 9-oxo-2-NF = 2,5-diNF > 9-hydroxy-2-NF > 2-NF. Ascorbate catalyzed one-electron reduction to nitro anion radicals which reacted with molecular O2 to yield superoxide. Rates of O2 uptake with 9-oxo-2,4,7-triNF and 9-oxo-2,7-diNF were 63 and 0.17 times those, respectively, with equivalent concentrations of nitrofurazone, a classical substrate. Superoxide formation was indicated by the approximately 75% regeneration of O2 upon addition of superoxide dismutase and catalase. 9-Oxo-2,4,7-triNF stimulated O2 uptake in the presence of XO/NADH with typical Michaelis-Menten kinetics with an apparent Km of 0.476 +/- 0.054 microM versus a Km of 6.18 +/- 0.719 microM for nitrofurazone. HPLC analyses of products from reduction catalyzed by XO or diaphorase of Clostridium with NADH showed the following trends for the rates of amine formation from 9-oxo-2,7-diNF > 2,7-diNF; 9-oxo-2-NF > 9-hydroxy-2-NF > 2-NF; 2,7-diNF > 2-NF; and 9-oxo-2,7-diNF > 9-oxo-2-NF. Little or no amine was formed in 95% O2, suggesting O2-labile intermediates. The data herein suggest that oxidation at C-9 and multiple nitro groups increase the potential for nitroreduction of the nitrofluorenes in vivo which may lead to genotoxic effects.
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, Minnesota 55455, and Veterans Affairs Medical Center, Minneapolis, Minnesota 55417, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Ritter
authors.forename: D
authors.initials: D
authors.lastname: Malejka-Giganti
mesh_terms: D000107:Acetylation; D002273:Carcinogens / Q000737:chemistry*; D003574:Cytochrome c Group / Q000378:metabolism; D005449:Fluorenes / Q000737:chemistry*; D007700:Kinetics; D009153:Mutagens / Q000737:chemistry*; D009566:Nitrates / Q000737:chemistry*; D009574:Nitro Compounds / Q000737:chemistry; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D013482:Superoxide Dismutase / Q000378:metabolism
chemical_list: D002273:Carcinogens; D003574:Cytochrome c Group; D005449:Fluorenes; D009153:Mutagens; D009566:Nitrates; D009574:Nitro Compounds; D013482:Superoxide Dismutase