S9 induction by the combined treatment with cyclohexanol and albendazole

Cyclohexanol (CH) is an industrial solvent capable of inducing cytochrome P450 (CYP) enzymes including the CYP2E and CYP2B subfamilies. S9 from CH treated rats is able to activate several N-nitrosamines that are poorly activated by Aroclor 1254, phenobarbital/beta -naphthoflavone (PB/NF) or 3-methylcholanthrene S9 fractions into mutagens detected by the Salmonella typhimurium Ames test. Additionally, albendazole (ABZ) is a widely used anthelmintic drug and a potent inducer of the CYP1A subfamily. Since CYP1A, -2B and -2E subfamilies are implicated in the activation of several environmental mutagens/carcinogens, we studied CYP induction in the rat liver by the combined effect of these two compounds, and used S9 derived from it in the Salmonella/microsome assay to compare with S9 obtained from Aroclor or PB/NF treated rats. Total CYP content in hepatic microsomes was induced by Aroclor, but not by any of the other chemical combinations. Western blot and enzymatic activity analysis revealed quantitative but not qualitative differences in the CYP subfamilies present in the different microsomal fractions; all of the chemicals used increased the levels of CYP1A1/2, CYP2B1/2 and CYP2E1 with respect to control microsomes. CYP3A was not modified by the different treatments. When tested in the Ames test, Aroclor S9 and PB/NF S9 were the most effective in the activation of benzo[a]pyrene and 3-methylcholanthrene which are metabolized mainly by CYP1A1; additionally, the highest mutagenic potency of 2-aminofluorene and N-nitrosodipropylamine, which are activated by CYP1A2 and CYP2B, respectively, were obtained with PB/NF S9. All these compounds were also activated when CH/ABZ S9 was used as the exogenous source of metabolism. Mutagens like N-nitrosopyrrolidine and N-nitrosodimethylamine, activated by CYP2E1, were detected only when CH/ABZ S9 was used, and the effectiveness of the different S9 fractions in activating cyclophosphamide decreased in the following order: Aroclor = PB/NF > CH/ABZ > control. From these experiments we can conclude that the individual CYP- inducing properties of ABZ and CH complement each other when the two compounds are administered in conjunction and that the resulting S9 fraction is able to activate several known mutagens in the Ames test.