Tissue-specific expression, induction, and inhibition through metabolic intermediate-complex formation of guinea pig cytochrome P450 belonging to the CYP2B subfamily

Abstract

The tissue-specific expression and induction of P450 GP-1, a constitutive form of cytochrome P450 of the guinea pig classified into the CYP2B subfamily, were studied. Prior to these studies, a P450 form (P450 GP-1 PB) was purified from phenobarbital-treated guinea pigs and the properties were compared with those of the P450 GP-1. This form was judged to be the same as P450 GP-1 existing in untreated animals by comparisons of their N-terminal amino acid sequences, peptide maps, and affinities toward anti-P450 GP-1 antibody. Immunostaining of P450 GP-1 revealed that the lung and small intestine as well as the liver of untreated guinea pigs contain P450 GP-1, while none or only small amounts of this P450 form were observed in the kidney, heart, spleen, urinary bladder, and testis. The amount of liver P450 GP-1 protein expressed in untreated guinea pigs was estimated to be 19.4% of the total cytochrome P450 and this form was increased 1.7-fold by phenobarbital treatment. Similarly, intestinal P450 GP-1 was increased by phenobarbital treatment. However, lung P450 GP-1 was not increased by the treatment. It was also observed that the liver P450 GP-1 is induced with SKF-525A to the same extent as with phenobarbital. On the other hand, dexamethasone, p,p′-dichlorodiphenyltrichloroethane, and isosafrole showed no or only a weak ability to increase the liver P450 GP-1 content. The drug-metabolizing activities in the liver microsomes of SKF-525A-pretreated guinea pigs were lower than those in phenobarbital-treated animals, although the P450 GP-1 protein was induced equally by these treatments. The low activities of SKF-525A-treated animals in the drug metabolisms were attributed to the formation of the metabolic-intermediate complex between P450 GP-1 and SKF-525A metabolite. These results permitted us to conclude that the tissue specificity in the expression of guinea pig P450 belonging to the CYP2B subfamily and the inducibility with chemicals are similar to those of rat CYP2B1, although the constitutive expression of guinea pig liver P450 GP-1 is much higher than that of CYP2B1.