Induction of liver microsomal cytochrome P450 in cynomolgus monkeys

The aim of this study was to determine whether treatment of cynomolgus monkeys (Macaca fasicularis) with phenobarbital, beta-naphthoflavone, or dexamethasone causes an induction of microsomal crytochrome P450 (CYP) enzymes that are structurally and functionally related to rat enzymes belonging to the CYP1A, CYP2B, and CYP3A gene families. Oral treatment of male and female monkeys with phenobarbital resulted in a marked induction of a protein recognized by antibody against rat CYP2B1, as determined by Western immunoblotting. This protein, presumably a CYP2B enzyme, was not detectable in untreated monkeys, and was modestly inducible by dexamethasone but not beta-naphthoflavone. Induction of this CYP2B enzyme by phenobarbital was associated with a relatively large increase (up to 5-fold) in the rate of testosterone 16 beta-hydroxylation. Antibody, against rat CYP2B1 markedly inhibited this reaction in liver microsomes from phenobarbital-treated monkeys, but not from control monkeys. Consequently, the antibody-inhibitable rate of testosterone 16 beta-hydroxylation increased 17-fold after treatment of monkeys with phenobarbital, which is comparable with the situation in rats. In contrast to the rat CYP2B enzymes, the monkey CYP2B enzyme had little or no capacity to convert testosterone to 16 alpha-hydroxytestosterone or androstenedione, and had negligible capacity to O-dealkylate 7-pentoxyresorufin and 7-benzyloxyresorufin. Oral treatment of male and female monkeys with beta-naphthoflavone resulted in a marked induction of a protein recognized by polyclonal and monoclonal antibodies against rat CYP1A1 or against both CYP1A1 and CYP1A2. This protein was apparently a mixture of CYP1A1 and CYP1A2, neither of which was readily detectable in liver microsomes from control monkeys or monkeys treated with phenobarbital or dexamethasone. Induction of monkey CYP1A1/2 was associated with a marked increase in the O-dealkylation of 7-methoxyresorufin (up to 65-fold), the O-dealkylation of 7-ethoxyresorufin (up to 30-fold), and the N3-demethylation of caffeine (up to 17-fold), but only a 2-fold increase in benzo[a]pyrene 3-hydroxylation. Polyclonal antibodies against CYP1A1 markedly inhibited the N3-demethylation of caffeine and the O-dealkylation of 7-methoxy- and 7-ethoxyresorufin by liver microsomes from beta-naphthoflavone-treated monkeys, and partially inhibited the 3-hydroxylation of benzo[a]pyrene, indicating that monkey CYP1A1 and/or CYP1A2, like the corresponding rat enzymes, can catalyze all four reactions. Treatment of monkeys with phenobarbital resulted in a 2- to 3-fold induction of a protein recognized by antibody against rat CYP3A1. This protein (CYP3A8 or an immunochemically related enzyme) was constitutively expressed in untreated monkeys of both sexes.(ABSTRACT TRUNCATED AT 400 WORDS)