Metabolism of 1-nitropyrene by cultured rabbit alveolar macrophages and respiratory tract tissues

Abstract

The metabolism of 1-nitro[ 14C]pyrene ( 14C-1-NP; 8.1 μ m) was studied in cultured (20 hr) rabbit alveolar macrophages, lung tissue, and tracheal tissue. Metabolites from the incubation medium and from the macrophages and respiratory tract tissues were extracted and then analyzed and quantified by high-pressure liquid chromatography. The following metabolites were detected in the lung and tracheal tissue incubation medium: 1-nitropyrene-4,5-dihydrodiol, N-acetyl-1-aminopyrene, 1-aminopyrene, and 10-hydroxy-1-nitropyrene. Nitropyrene phenols (4-, 5-, 6-, 8- or 9-hydroxy-1-nitropyrene) and 3-hydroxy-1-nitropyrene were only detected in the lung and tracheal tissue and not in the incubation medium for these tissues. Minor amounts of 1-aminopyrene and 10-hydroxy-1-nitropyrene were detected in the macrophage incubation medium, and only minute quantities of 1-nitropyrene-4,5-dihydrodiol, 1-aminopyrene, and 10-hydroxy-1-nitropyrene were detected in macrophages. The total percentage of 1-NP metabolism was significantly greater in the lung and tracheal tissue (28.0 and 23.0% of the recovered 14C, respectively) than in the alveolar macrophages (6.3% of the recovered 14C). The tracheal tissue was found to have the highest activity both in 1-NP metabolism and intracellular metabolite concentration. A major portion of the 1-NP metabolites produced was released into the incubation medium. The majority of the metabolites produced by tracheal and lung tissue, 70 and 84%, respectively, were ethyl acetate extractable. The metabolites retained within the cells or tissues were also predominantly ethyl acetate extractable rather than water soluble (83% for the macrophages and trachea, 95% for the lung tissue). The metabolite profiles obtained demonstrate that metabolism by both nitro reduction and ring oxidation occurs in respiratory tissue, and a degree of tissue specificity in the formation of metabolites exists. Ring oxidation was demonstrated in the lung and tracheal tissue, but very little occurred in the macrophages.