Chemical and Biochemical Aspects of Nitroarene Mutagenicity

Abstract

<p> Nitroarenes are the nitro-functionalized derivatives of polycyclic aromatic hydrocarbons (PAH) which are found in a variety of environmental matrices, and are potential human carcinogens. The 1997 discovery of a potent mutagen, 3-nitrobenzanthrone, in diesel exhaust has renewed interest in these compounds. Theoretically- and experimentally-determined characteristics of nitroarenes have been explored as predictors of their mutagenic potencies in the Ames reversion assay. In this multifaceted project, the relationships of these parameters and rates of nitroarene metabolism to the mutagenic potencies of 11 nitroarenes in Salmonella typhimurium strain YG1021 were explored.</p> <p> Ab initio calculations at the HF/3-21G level were performed for these molecules. Calculated NO2 dihedral angles and εLUMO values were smaller in magnitude than those previously determined by lower quality semi-empirical and STO-3G ab initio calculations, and showed poor correlations with nitroarene mutagenicity. Molecular negative electrostatic potential surfaces for the nitroarenes studied possessed two regions which, when placed in a common orientation in 3-dimensional space, suggested specific binding contacts within the active site of the nitroarene-activating enzyme nitroreductase.</p> <p> An efficient GC-MS method was developed for the analysis of organic extracts from Salmonella incubations with nitroarenes in the determination of relative rates of metabolism, and employed a two-stage solid phase extraction sample clean-up scheme. The rates of nitroarene metabolism for six nitroarenes, whose mutagenic potencies ranged over two orders of magnitude, ranged from 450 to 3600 pmol/hr/mL Salmonella culture at 25°C and showed a good correlation with mutagenicity.</p> <p> The results of this work suggest that mutagenic potency is a direct result of intermediate accumulation, and cast serious doubts on the reported correlations between nitroarene physicochemical properties and mutagenic potencies. This study underscores the need for the in-depth examination of the characteristics of nitroarene intermediates as an explanation of nitroarene mutagenic potencies.</p>