Deacetylation to 2-aminofluorene as a major initial reaction in the microsomal metabolism of 2-acetylaminofluorene to mutagenic products in preparations from rabbit lung and liver.

The rabbit pulmonary and hepatic microsomal pathways for the metabolism of 2-acetylaminofluorene (AAF) and 2-aminofluorene (AF) to mutagenic products were investigated by means of high performance liquid chromatography and the Salmonella mutagenicity assay. Mutagenic activity approached a maximum with increasing concentrations of AAF incubated with hepatic microsomal preparations and Salmonella; with pulmonary microsomal preparations, mutagenic activity was proportional to the concentration of AAF over the range examined. The mutagenic activities of AF exhibited typical saturation kinetics with both hepatic and pulmonary microsomal preparations. Approximately 7 times more AF than N-hydroxy-2-acetylaminofluorene (N-hydroxy-AAF) was formed in incubations of AAF (0.5 mM) with hepatic microsomal preparations. When AAF was incubated with pulmonary microsomal preparations, formation of AF, but not N-hydroxy-AAF, was detected. The inclusion of paraoxon in the pulmonary incubations blocked the formation of AF but did not lead to the recovery of any N-hydroxy-AAF. We conclude that the metabolism of AAF to mutagenic products in pulmonary microsomal preparations from rabbits is initiated primarily, if not entirely, by deacetylation of AAF to AF. The mutagenic activity of AAF with the pulmonary microsomal preparations is limited by the deacetylase activity which, like mutagenic activity, exhibits a linear relationship with the concentration of AAF. On the basis of the rates of formation of AF and N-hydroxy-AAF and their mutagenic activities, we estimate that about 60% of the hepatic metabolism of AAF to mutagenic products is dependent upon deacetylation of AAF and subsequent oxidation of the AF formed.