DNA adduct formation from the mutagenic air pollutant 3-nitrobenzanthrone

The environmental contaminant 3-nitrobenzanthrone (3-nitro-7H-benz[d,e]anth racen-7-one) was recently shown to be a very strong bacterial mutagen, sugg esting a new class of mutagenic compounds present in airborne particulate m atter and diesel exhaust, Using the P-32-postlabeling assay, we investigate d the capacity for 3-nitrobenzanthrone to form DNA adducts in vitro. Calf t hymus DNA was incubated with 3-nitrobenzanthrone and either xanthine oxidas e, a mammalian nitroreductase or rat liver S9 or zinc. Under these conditio ns 3-nitrobenzanthrone formed a total of seven adducts detectable by P-32-p ostlabeling. Using enrichment by butanol extraction the highest level of DN A adduct formation was found with activation by zinc (RAL: 88.4 +/- 32 per 10(8) nucleotides) followed by activation with xanthine oxidase (RAL: 75.5 +/- 12) and activation by rat liver S9 (RAL: 48.6 +/- 8). Three of the seve n adduct spots were detected in all activation systems, however different a mounts of individual spots were obtained in the different in vitro systems. The adduct pattern observed for the enzymatic incubations consisted of thr ee major spots and was essentially identical. Chemical reduction of 3-nitro benzanthrone by zinc resulted in five adduct spots whose formation was foun d to be concentration dependent, All adducts of 3-nitrobenzanthrone observe d in this study migrated primarily along a diagonal zone, typical for DNA a dducts derived from extracts of airborne particulate matter. When butanol e nrichment was compared with nuclease P1 enrichment one adduct was clearly s ensitive to the 3'-monophosphatase activity of nuclease pi. Our results dem onstrate that 3-nitrobenzanthrone binds covalently to DNA after metabolic a ctivation, forming multiple DNA adducts in vitro all of which are reduction products. These adducts may contribute to the known genotoxicity and carci nogenicity of extracts from airborne particulates. (C) 1999 Elsevier Scienc e B.V. All rights reserved.