| Abstract: | This study examines whether chemical components from diesel exhaust particulates react with DNA to form covalently bound adducts. Experiments in this report describe the in vitro reaction of purified DNA with a dichloromethane extract of diesel exhaust particulates in the absence or presence of enzyme activation by rat liver microsomes. The reactivity of the particle extract was compared to that of benzoa]pyrene metabolites using low temperature fluorescence techniques which detect small quantities of polycyclic aromatic compounds bound to DNA. Incubation of DNA with the particle extract in the presence of microsomal enzymes produced no detectable fluorescent adducts in contrast to model experiments using benzoa]pyrene. However, addition of the particle extract to incubation mixtures containing benzoa]pyrene markedly decreased formation of benzoa]pyrene-DNA adducts because the particle extract inhibits microsomal enzymes which activate benzoa]pyrene and other polycyclic aromatic hydrocarbons. In the absence of microsomal enzymes, fluorescent material was detected in DNA exposed to high concentrations of the particle extract, but probably not as a result of covalent binding because the mutagenic activity of the particle extract remained unchanged during prolonged incubation with DNA. This stability is in contrast to the rapid decrease in mutagenic activity of benzoa]pyrene-4,5-oxide during incubation with DNA. Thus, direct mutation of bacteria by the particle extract may require activation by bacterial enzymes as is known to occur with nitroaromatic compounds. |
