INDUCTION OF MOUSE CYTOCHROME-P450 2B ENZYMES BY AMINE METABOLITES OFMUSK XYLENE - CONTRIBUTION OF MICROSOMAL-ENZYME INDUCTION TO THE HEPATOCARCINOGENICITY OF MUSK XYLENE

Musk xylene (MX) is a synthetic nitromusk perfume ingredient that, alt hough uniformly negative in genotoxicity testing, causes liver tumors in B6C3F1 mice. MX is also capable of inducing cytochrome P450 enzymes in a manner similar to that of phenobarbital (PB), which suggests tha t epigenetic mechanisms may be involved in the carcinogenic response. At the same time, MX is metabolized in vivo by nitroreduction, a react ion catalyzed by intestinal flora that yields aromatic amine metabolit es. These amine metabolites are also capable of inactivating CYP2B10, the major cytochrome P450 enzyme induced by MX treatment. In the study reported here, the monoamine metabolites of MX, o- and p-NH2-MX, were evaluated for their potential to induce CYP2B10 and CYP1A2 mRNAs. Nor thern blot analyses indicated that both amines markedly induced CYP2B1 0 mRNA, whereas CYP1A2 mRNA, the enzyme implicated in the bioactivatio n of aromatic amines and frequently induced by aromatic amines, was in duced only slightly, a response that was not different from that seen with PB. Induction of CYP2B10 mRNA suggested that the amine metabolite s may contribute to the enzyme induction profile seen with MX treatmen t. To test this hypothesis, mice were treated with broad-spectrum anti biotics (neomycin, tetracycline, and bacitracin) to eliminate the inte stinal flora and prevent formation of o- and p-NH2-MX. In antibiotic-t reated mice treated with MX (200 mg/kg) for 4 d, no evidence of micros omal enzyme induction was observed, including no increases in liver we ight, Petal cytochrome P450 content, or CYP2B protein levels. These re sults indicate that the amine metabolites of MX are responsible for th e enzyme induction seen after MX administration, Thus, the biochemical and molecular effects of amine metabolites of MX are markedly differe nt from those of other aromatic amines but very similar to those of PB . Therefore, it appears that MX is a non-genotoxic chemical that may c ause mouse liver tumors in a manner analogous to that of PB. (C) 1997 Wiley-Liss, Inc.