Comparative reduction of 1-nitro-3-nitrosopyrene and 1-nitro-6-nitrosopyrene: implications for the tumorigenicity of...

Dinitropyrenes are mutagenic environmental pollutants. Of these compounds, 1,6-dinitropyrene is a potent tumorigen while 1,3-dinitropyrene appears to be weakly or non-tumorigenic. Two-electron reduction of dinitropyrenes yields nitro-nitrosopyrenes, which have been shown previously to be the major aerobic metabolites of these compounds in vitro. Further reduction of nitrosopyrenes is required for their activation to a DNA-reactive N-hydroxylamines. In this work, 1-nitro-3-nitrosopyrene was synthesized and the electrochemical and enzyme-catalyzed reduction of 1-nitro-3-nitrosopyrene has been compared with that of 1-nitro-6-nitrosopyrene. As determined by cyclic voltammetry, the reduction potentials of 1-nitro-3-nitrosopyrene, 1-nitro-6-nitrosopyrene and their parent dinitropyrenes were similar, although 1-nitro-3-nitrosopyrene did have a slightly more negative cathodic peak potential than the other three compounds. The NADPH-mediated reduction of 1-nitro-6-nitrosopyrene to intermediates which reduce succinoylated cytochrome c was faster than that of 1-nitro-3-nitrosopyrene. In the presence of rat liver microsomes or cytosol, the reduction of 1-nitro-6-nitrosopyrene was faster than that of 1-nitro-3-nitrosopyrene. These differences in the rates of nitro-nitrosopyrene reduction may be one factor contributing to the lower tumorigenic potential of 1,3-dinitropyrene relative to 1,6-dinitropyrene.