Metabolic Activation of 6-Nitrochrysene in Expiants of Human Bronchus and in Isolated Rat Hepatocytes

It has previously been shown that 6-nitrochrysene can be activated to electrophilic species capable of reacting with DNA through metabolic pathways that form N-hydroxy-6-aminochrysene or trans-l,2-dihydroxy-l,2-dihydro-6-aminochrysene as critical intermediates. Since the lung is a known target tissue for the carcinogenic action of polycyclic nitroaro-matic hydrocarbons, we investigated the metabolism and DNA binding of [3H]6-nitrochrysene in 11 specimens of human bronchus. Analysis of medium from [3H]6-mtrochrysene-treated expiants indicated the presence of trans-9,10-dihydroxy-9,10-dihydro-6-nitrochrysene (0.04–330 pmol/ mg epithelial DNA), trans-l,2-dihydroxy-l,2-dihydro-6-mtrochrysene (12–1700 pmol/mg epithelial DNA), 6-aminochrysene (1.6–2200 pmol/ mg epithelial DNA), and trans-l,2-dihydroxy-l,2-dihydro-6-aminochry-sene (3.6–610 pmol/mg epithelial DNA). Both the levels and the relative proportions of these metabolites varied widely in expiants from different individuals. The amount of DNA recovered and the level of DNA modification were sufficient for adduct analysis in eight of the 11 cases for which metabolite data were obtained. Five additional bronchial specimens for which metabolite data were not obtained were also analyzed for carcino-gen-DNA adducts. The levels of binding varied from 0.06 to 30.5 pmol [3H]6-nitrochrysene bound/mg DNA (two adducts per 108 nucleotides-10 adducts per 106 nucleotides). HPLC analyses of enzymatic hydrolysates of the expiant DNA indicated that 11 of 13 cases contained adducts with retention times identical to those of adducts derived from trans-1,2-dihydroxy-l,2-dihydro-6-aminochrysene or N-hydroxy-6-aminochrysene. The adduct derived from trans-l,2-dihydroxy-l,2-dihydro-6-aminochry-sene was the major adduct detected in eight of 13 cases. The reasons for the variation in metabolism and adduct formation observed in [3H]6-nitrochrysene-treated expiants of bronchus from different donors are not known but may reflect differences in the activities of enzymes responsible for the metabolism of this compound. The influence of induction of drug metabolizing enzymes on the activation pathway of 6-nitrochrysene in an intact cell system was tested using rat hepatocytes. 6-Nitrochrysene was incubated with freshly isolated hepatocytes from rats that were either untreated or pretreated with phenobarbital, 3-methylcholanthrene or Aroclor 1254. Although the levels of adducts were similar in all cases, the pattern of DNA adducts formed in these hepatocytes was dependent on the nature of the pretreatment of the rats. As previously reported, hepatocytes from untreated rats contained adducts derived from N-hydroxy-6-aminochrysene. The same adducts were formed in hepatocytes from rats pretreated with phenobarbital. On the other hand, adducts derived from trans-l,2-dihydroxy-l,2-dihydro-6-ami-nochrysene were the predominant adducts formed in hepatocytes from rats pretreated with Aroclor 1254 or 3-methylcholanthrene.