42 - Hydroxyl Radical Production and DNA Damage via Photolysis by Sunlight of the Genotoxic Hydroxamic Acid Intermediate of Polyaromatic Amine Carcinogen

Abstract

The hydroxyl radical (●OH) has been considered to be one of the most reactive oxygen species produced in biological systems, which can cause DNA, protein, and lipid oxidation. N-hydroxy-2-acetamidofluorene (N-OH-AAF) has been identified as a major genotoxic metabolite of 2-nitroflurene, a polyaromatic amine carcinogen commonly found in diesel exhaust. The carcinogenicity of N-OH-AAF has been mainly attributed to the formation of DNA adducts via aryl nitrenium ion. Recently, we found, unexpectedly, that exposure of N-OH-AAF to sunlight can induce the formation of not only DNA single and double strand breaks, but also 8-OHdG, both of which were inhibited by the typical ●OH scavengers (DMSO and ethanol), but not by the classic iron and copper chelating agents. ESR secondary radical spin-trapping with DMPO and fluorescent studies with terephthalic acid confirmed that ●OH was indeed generated from N-OH-AAF photolysis, with the formation of the characteristic DMPO/•OH and the fluorescent 2-hydroxyterephthalic acid, respectively. This is the first report that the highly reactive ●OH can be readily produced via homolysis of N-OH-AAF by sunlight, which represents a new mechanism of ●OH production that does not require redox-active metal ions, and provide a new perspective to understand the molecular mechanism for the carcinogenicity of polycyclic aromatic amines.