The effects of a cocarcinogen, ferric oxide, on the metabolism of benzo[a]pyrene in the isolated perfused lung

Abstract

An isolated perfused New Zealand rabbit lung preparation was used to investigate the effects of a cocarcinogen, ferric oxide (Fe ₂ O ₃ ), on the metabolism of benzo[a]pyrene (BaP), a ubiquitous potent carcinogen that has been associated with the increased incidence of human bronchiogenic carcinoma in occupational and urban settings. [ ¹⁴ C]‐BaP was administered intratracheally to an isolated perfused lung (IPL) preparation with and without Fe ₂ O ₃ after intraperitoneal pretreatment of the whole animal with BaP or intratracheal pretreatment of the whole animal with Fe ₂ O ₃ and/or BaP. BaP and its metabolites were isolated from serial blood samples up to 180 min after administration of [ ¹⁴ C]BaP to the IPL. BaP and its metabolites were also isolated from lung tissue, washout fluid, macrophage, and trachea bronchi at the end of the perfusion at 180 min. Patterns of BaP metabolites were determined by chromatographic techniques and liquid scintillation counting.

Fe ₂ O ₃ pretreatment to the whole animal or administration of Fe ₂ O ₃ to the IPL altered BaP metabolism by the perfused lung. Fe ₂ O ₃ pretreatment to the whole animal resulted in an increase in the total rate of appearance of metabolites of BaP in the blood (ng/g lung·h), while Fe ₂ O ₃ administration to the IPL resulted in a decrease in the total rate of appearance of BaP metabolites in the blood and inhibited the effect of pretreatment. Administration of Fe ₂ O ₃ with BaP to the IPL with or without Fe ₂ O ₃ pretreatment to the whole animal, or BaP administration to the IPL preceded by Fe ₂ O ₃ pretreatment to the whole animal, enhanced dihydrodiol formation and depressed formation of water‐soluble metabolites. Since dihydrodiol formation is considered to be the active pathway of BaP metabolism, these data suggest that pulmonary exposure to a known cocarcinogen, Fe ₂ O ₃ , in the presence of BaP results in increased production of dihydrodiols of BaP, which may be further metabolized to the ultimate carcinogenic form(s) of BaP. Therefore, Fe ₂ O ₃ can enhance the metabolic activation of BaP by the lung, as well as act as a carrier for penetration and retention of BaP in the lung.