Metabolism of the carcinogenic air pollutant 2-nitrofluorene in the isolated perfused rat lung and liver

The metabolism of 2-nitrofluorene (NF), a model substance for nitrated polycyclic aromatic hydrocarbons, was studied in the isolated perfused rat lung and liver. NF has been identified in urban air and diesel exhaust and occurs in the gas, as well as in the particulate phase. Therefore, it is conceivable that the lung represents one point of entry of this compound into the body. The lung metabolizes NF to hydroxylated NFs, mainly 9-hydroxy-NF, independently of the route of administration, (intravascular or intratracheal). After intratracheal administration, NF is rapidly excreted into the perfusate, indicating that other organs might be exposed to unmetabolized NF. The liver excretes NF metabolites as biliary glucuronides. Untreated bile is not mutagenic. However, after β-glucuronidase treatment of bile, direct-acting mutagens were detected. The mutagenic metabolites in β-glucuronidase-treated bile were the same as identified in the perfusate of the isolated lung. Since β-glucuronidase is an enzyme found in the human intestinal microflora, inhalation of NF could result in the liberation of genotoxic metabolites in the colon.