DNA adducts and mutagenic specificity of the ubiquitous environmental pollutant 3‐nitrobenzanthrone in Muta Mouse

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Abstract
3‐nitrobenzanthrone (3‐NBA) is an extremely potent mutagen in the Salmonella reversion assay and a suspected human carcinogen identified in diesel exhaust and in ambient airborne particulate matter. To evaluate the in vivo mutagenicity of 3‐NBA, we analyzed the mutant frequency (MF) in the cII gene of various organs (lung, liver, kidney, bladder, colon, spleen, and testis) in lambda/lacZ transgenic mice (Muta Mouse) after intraperitoneal treatment with 3‐NBA (25 mg/kg body weight injected once a week for 4 weeks). Increases in MF were found in colon, liver, and bladder, with 7.0‐, 4.8‐, and 4.1‐fold increases above the control value, respectively, whereas no increase in MF was found in lung, kidney, spleen, and testis. Simultaneously, induction of micronuclei in peripheral blood reticulocytes was observed. The sequence alterations in the cII gene recovered from 41 liver mutants from 3‐NBA‐treated mice were compared with 32 spontaneous mutants from untreated mice. Base substitution mutations predominated for both the 3‐NBA‐treated (80%) and the untreated (81%) groups. However, the proportion of G:C→T:A transversions in the mutants from 3‐NBA‐treated mice was higher (49% vs. 6%) and the proportion of G:C→A:T transitions was lower than those from untreated mice (10% vs. 66%). The increase in MF in the liver was associated with strong DNA binding by 3‐NBA, whereas in lung, in which there was no increase in MF, a low level of DNA binding was observed (268.0–282.7 vs. 8.8–15.9 adducts per 108 nucleotides). DNA adduct patterns with multiple adduct spots, qualitatively similar to those formed in vitro after activation of 3‐NBA with nitroreductases and in vivo in rats, were observed in all tissues examined. Using high‐pressure liquid cochromatographic analysis, we confirmed that all major 3‐NBA‐DNA adducts produced in vivo in mice are derived from reductive metabolites bound to purine bases (70–80% with deoxyguanosine and 20–30% with deoxyadenosine in liver). These results suggest that G:C→T:A transversions induced by 3‐NBA are caused by misreplication of adducted guanine residues through incorporation of adenine opposite the adduct (A‐rule). Environ. Mol. Mutagen. 43:186–195, 2004.

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