IN-VIVO INDUCTION OF CYTOCHROME-P450 CYP3A EXPRESSION IN RAT LEUKOCYTES USING VARIOUS INDUCERS

Although the induction of cytochromes P450 3A (CYP3A) is relatively we ll characterized in liver, its inducibility in an easily available tis sue such as the peripheral leukocytes is not known. The purpose of thi s study was, therefore, to determine if CYP3A is inducible in vivo in peripheral leukocytes. Microsomes from rat leukocytes and liver were e xamined for CYP3A protein expression using Western blotting with a rab bit polyclonal antibody against rat CYP3A. Although CYP3A was not dete cted in control leukocytes, in vivo treatment with known CYP3A inducer s (dexamethasone, clotrimazole, phenobarbital, pregnenolone-16 alpha-c arbonitrile) resulted in CYP3A leukocyte levels of 0.2-0.8 pmol/mg pro tein. This leukocyte induction was approximately 1000-fold lower than in induced liver. Interestingly, there was an apparent linear relation ship between leukocyte and liver CYP3A contents (r(2) = 0.748, n = 29) . These results not only demonstrate for the first time that CYP3A is inducible in rat leukocytes after in vivo treatment with various CYP3A inducers, but also suggest that peripheral leukocytes could be used t o assess induction in vivo.