Metabolism and macromolecular covalent binding of [14C]-1-nitropyrene in isolated perfused and ventilated rat lungs

1-Nitropyrene (1-NP) originating from such sources as diesel exhaust emissions and coal combustion fly ash has been detected in the environment. 1-NP, in addition to being both a bacterial and mammalian mutagen, is carcinogenic in rats. The purpose of this study was to quantitate 1-NP metabolism and macromolecular covalent binding in the isolated perfused rat lung. Rat lungs were perfused with 2, 5, or 24 microM [14C]-1-NP for 90 min. Tidal volume and dynamic lung compliance were monitored continually throughout the perfusion to document the ventilatory pattern and the decay of tissue elasticity. Perfusate was sampled periodically throughout the duration of the experiment and analyzed for 1-NP metabolites with high-performance liquid chromatography. In all experiments, both dynamic lung compliance and tidal volume declined in a nearly linear manner and were approximately 60% of the initial value at the end of 90 min of perfusion. At all concentrations of [14C]-1-NP tested, less than 5 to 6% of the total amount of [14C]-1-NP added was metabolized in lungs from control and phenobarbital (PB)-treated rats. Lungs from control and PB- and 3-methylcholanthrene (3-MC)-treated rats metabolized [14C]-1-NP to oxidized, reduced, and conjugated metabolites. The major metabolites were 3-, 6-, and 8-hydroxynitropyrene. Small quantities of 10-hydroxynitropyrene, aminopyrene, and acetylaminopyrene were also detected in perfusates (less than 10% of the total metabolites). Treatment of rats with PB resulted in a 60% increase in the total metabolism of [14C]-1-NP, whereas treatment of rats with 3-MC resulted in a 10-fold increase in the rate of metabolism of [14C]-1-NP when compared to controls. Conjugate hydrolysis studies indicated that the water-soluble metabolites from lungs of control and PB- and 3-MC-treated rats consisted of hydroxynitropyrene glucuronides and hydroxynitropyrene sulfate conjugates. Quantities of 14C covalently bound to lung macromolecules after 90 min of perfusion from lungs of control and PB-treated rats were 0.06 to 0.21 nmol equivalents/g lung. However, in lungs from 3-MC-treated rats, there was a 20-fold increase in quantities of 14C covalently bound when compared to lungs from either control or PB-treated rats. The results from these studies point to the potential importance of lung metabolism in contributing to the metabolic fate of inhaled 1-NP.