The spectrum of enzymes involved in activation of 2-aminoanthracene varies with the metabolic system applied

Abstract

The aim of this study was to estimate the involvement of cytochrome P450s (CYPs) in the metabolic activation of 2-aminoanthracene (2AA) by use of metabolic systems such as liver S9 or hepatocytes from untreated and β-naphthoflavone (BNF)- or phenobarbital (PB)-treated rats. Metabolic activation was determined in the Salmonella reverse mutation assay (Ames test). Unexpectedly, both enzyme inducers, BNF and PB, significantly decreased the mutagenicity of 2AA activated by S9 fractions. 2AA mutagenicity was detected in the presence of cytochrome P450 inhibitors such as α-naphthoflavone (ANF), clotrimazole and N-benzylimidazole to study the contribution of CYP isoenzymes to the activation process. ANF significantly decreased the activation of 2AA by S9 from untreated rats. In contrast, ANF significantly increased the metabolic activation of 2AA by S9 from BNF- and PB-treated rats. The enhanced mutagenicity was not altered by co-incubation with clotrimazole and ANF. Pre-incubation of 2AA in the presence of N-benzylimidazole significantly increased the activation of 2AA by S9 from BNF- and PB-treated rats, which suggests that CYPs play minor role in 2AA metabolic activation by rat liver S9 fractions. In contrast with the results described above, BNF treatment of rats significantly enhanced the activation of 2AA by hepatocytes. ANF attenuated the extent of this activation suggesting that different enzymes play a major role in the activation processes in these metabolic systems. Our results indicate that identification of mutagenic hazard by use of the Ames test may depend on the metabolic system applied.