Metabolic activation of nitropyrenes and diesel particulate extracts

The aim of this research was to investigate the possible risks of genotoxicity associated with human exposure to diesel engine emissions. We sought to identify and evaluate the critical components of such emissions by using a variety of short-term biological systems. Adducts formed between benzo[a]pyrene and DNA in several short-term test systems have been thoroughly investigated. Although benzo[a]pyrene has long been used as an index of the potential carcinogenicity of polycyclic aromatic hydrocarbon mixtures and is present in diesel engine emissions, it may not be the best measure of the carcinogenicity of these emissions if, indeed, they are confirmed to exert such an effect in humans. Certain nitroarenes, known to be present in diesel particulate extracts, are very potent mutagens in the Ames assay. The major adducts formed in Salmonella typhimurium with 1-nitropyrene (Howard and Beland 1982) and 1,8-dinitropyrene (Andrews et al. 1986; Fifer et al. 1986) have been identified. We undertook, therefore, a comparison of the DNA adducts formed between 1-nitropyrene, 1,3-dinitropyrene, 1,6-dinitropyrene, and 1,8-dinitropyrene and cellular DNA in various systems, including human bronchial segments, in rabbit lung and trachea, and mouse embryo fibroblast C3H/10T1/2 cells, with those reported to be formed in S. typhimurium. In these studies, we administered radiolabeled nitropyrenes, analogous to the treatments previously employed for testing benzo[a]pyrene, and isolated and digested the modified DNA. We then compared elution times, by high-pressure liquid chromatography, of the radioactive adducts with synthetic standards. Not all combinations of exposures were undertaken, since the direction of the investigations changed to include studies on adducts formed in animals exposed to diesel engine emissions themselves. Of the samples studied, metabolism of 1-nitropyrene was most evident in the human bronchial tissue. Little metabolism was evident in duodenal and colonic samples. Mouse C3H/10T1/2 embryo fibroblasts showed no detectable metabolism of, DNA adduct formation with, or transformation by 1-nitropyrene. DNA adducts were detected in cells exposed to 1,8-dinitropyrene and traces of adducts were formed with either 1,3-dinitropyrene or 1,6-dinitropyrene. Measurements of DNA adducts formed after treatment with [4,5,9,10-3H]-1-nitropyrene in rabbit tracheal samples showed that only about 2 to 15 percent of the associated radiolabel could be accounted for as the previously identified C-8 adduct. To facilitate the quantification of adduct levels that might occur in humans and laboratory animals exposed to the nitroarenes in diesel engine emissions, antisera were prepared against DNA modified with 1-nitrosopyrene.(ABSTRACT TRUNCATED AT 400 WORDS)