Cytochrome P450 isozyme induction by methyl ethyl ketone and m-xylene in rat liver.

The rat hepatic cytochrome P450 induction pattern caused by administration of a high peroral dose of methyl ethyl ketone (MEK, 1.4 ml/kg once daily for 3 consecutive days) and m-xylene (1.0 ml/kg X 3) was studied by catalytic activity and immunoblotting techniques. MEK caused a marked increase in the amount of P450 isozymes belonging to the phenobarbital- and ethanol-inducible P450 subfamilies P450IIB and P450IIE, respectively. Catalytic activities linked with these isozymes, pentoxyresorufin O-depentylase (P450IIB), aniline hydroxylase, and N-nitrosodimethylamine N-demethylase (P450IIE), were also increased (18.0-, 5.4-, and 2.4-fold, respectively). The activity of ethoxyresorufin O-deethylase, which is predominantly linked with the polycyclic aromatic hydrocarbon-inducible P450 isozymes, was also increased 2.3-fold without an apparent increase in the amount of the respective P450 protein (P450IA). m-Xylene caused a similar induction pattern with less effect on P450IIE. Simultaneous administration of MEK and m-xylene resulted in an additive or, in the case of pentoxyresorufin O-depentylase, a potentiating effect on P450-linked catalytic activities. These data indicate that MEK and m-xylene elicit a qualitatively similar induction of P450 isozymes, which may play a role in the metabolic interactions of these compounds.