Metabolism and DNA binding of 1-nitro[14C]pyrene by isolated rabbit tracheal epithelial cells

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Abstract
The metabolism of 1-nitro[ 14 C]pyrene (1-NP) and the binding of its reactive intermediates to DNA and protein was examined in rabbit tracheal epithelial cells. The tracheal cells isolated by two protease digestion methods had normal cellular morphology and viability. The digestion method which demonstrated the highest rate of 1-NP metabolism and DNA binding used a 1 h incubation of the tracheas with 1% protease at 37°C. Metabolites from the incubation medium and cell lysates were extracted, analyzed and quantitated by h.p.l.c. The majority of the metabolites produced by tracheal cells were EA:AC extractable and were released to the surrounding incubation medium. The predominant metabolites identified and quantified in the medium were the ring oxidation products, a 1-NP-diol, 1-NP phenols (6- or 8-OH-1-NP), 10-OH-1-NP and 3-OH-1-NP. Major metabolites formed by nitroreduction were NAAP and 1-AMP. The metabolites retained by tracheal cells were qualitatively identical to those identified in the medium but were present at one-seventh to one-tenth of the amounts. The rate of both 1-NP metabolism and DNA binding was very high. After 4 h, 62% of the 1-NP was metabolized and 198 DNA adducts/106 nucleotides were formed. The rate of [ 14 C]1-NP-DNA adducts formation was highest at 30 min of incubation (124 adducts/10 6 nucleotides/h). These high rates of metabolism and DNA binding are consistent with the possibility that tracheal cells may be a particular target tissue for tumor induction by nitrosubstituted polycyclic aromatic hydrocarbons associated with diesel and other combustion emission particles. The preponderance of highly mutagenic 1-NP phenols as metabolites suggest that ring oxidation as well as nitroreduction may result in intermediates which form DNA adducts.