Musk xylene induces and inhibits mouse hepatic cytochrome P-450 2B enzymes.

The purpose of this work was to characterize the effects of musk xylene on mouse hepatic microsomal enzyme activities. Male B6C3F1 mice were dosed for 7 days at 0 or 200 mg musk xylene/kg after which microsomes were prepared. Musk xylene treatment increased liver weight by 40%, caused hepatocellular hypertrophy and increased total cytochrome P-450 2-fold over control. Microsomes from musk xylene-treated mice showed increased activity for the dealkylation of ethoxy- and methoxyresorufin, results consistent with increased CYP1A1 and 1A2 protein levels determined by Western blotting. No increase in pentoxyresorufin-O-dealkylation activity was seen, but musk xylene treatment markedly increased CYP2B protein levels. Preliminary in vitro studies showed that musk xylene inhibited mouse CYP2B enzymes (IC50 approximately 1 microM), but did not affect the activities of CYP1A1 or 1A2. This inhibition was not NADPH-dependent. These results indicate that, in mice, musk xylene causes generalized hepatic changes similar to classical CYP2B inducers. However, musk xylene is also a potent inhibitor of the CYP2B enzymes.