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Differentiated induction of cytochrome P450b/e and P450p mRNAs by dose of phenobarbital in primary cultures of adult rat hepatocytes. 1990

T A Kocarek, and E G Schuetz, and P S Guzelian
Department of Medicine, Medical College of Virginia, Richmond 23298.

Phenobarbital induces cytochromes P450 (P450s) of not only the class IIB gene subfamily (i.e., P450b and P450e) but also the class IIIA gene subfamily (P450p and P450pcn2). To determine whether coinduction of these structurally dissimilar gene products involves the same mechanism, we examined the dose dependency of phenobarbital induction of the mRNAs for these four P450s in a new responsive system for primary monolayer cultures of adult rat hepatocytes on Matrigel, a reconstituted basement membrane. Two-day treatments of the cultures with phenobarbital produced marked dose-dependent increases in the levels of P450b, P450e, and P450p mRNAs, which reached maximal inductions ranging from 11- to greater than 193-fold. Although the dose-response relationships for the inductions of P450b and P450e mRNAs by phenobarbital were similar (ED50 = 1.5 x 10(-5) and 5.7 x 10(-6) M, respectively), the dose-response curve for the induction of P450p mRNA was positioned distinctly to the right (ED50 = 3.0 x 10(-4) M). This difference reflects a potency ratio of 20-fold for P450p/P450b mRNA induction. Phenobarbital also produced a weak dose-dependent induction of P450pcn2 mRNA, with a potency (ED50 = 3.4 x 10(-5) M) intermediate between those for P450b/e and P450p. In a similar experiment using two phenobarbital-like inducers, (trans)nonachlor and clotrimazole, the relative inductions of P450b, P450e, P450p, and P450pcn2 mRNAs proved to be similar to those produced by phenobarbital (P450p/P450b potency ratios = 14- and 16-fold, respectively). These findings provide strong further evidence in support of the newly emerging concept that "phenobarbital" induction of the responsive class IIB and class IIIA P450 isozymes likely reflects multiple mechanisms.

UI MeSH Term Description Entries
D007527 Isoenzymes Structurally related forms of an enzyme. Each isoenzyme has the same mechanism and classification, but differs in its chemical, physical, or immunological characteristics. Alloenzyme,Allozyme,Isoenzyme,Isozyme,Isozymes,Alloenzymes,Allozymes
D008099 Liver A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances. Livers
D008297 Male Males
D010634 Phenobarbital A barbituric acid derivative that acts as a nonselective central nervous system depressant. It potentiates GAMMA-AMINOBUTYRIC ACID action on GABA-A RECEPTORS, and modulates chloride currents through receptor channels. It also inhibits glutamate induced depolarizations. Phenemal,Phenobarbitone,Phenylbarbital,Gardenal,Hysteps,Luminal,Phenobarbital Sodium,Phenobarbital, Monosodium Salt,Phenylethylbarbituric Acid,Acid, Phenylethylbarbituric,Monosodium Salt Phenobarbital,Sodium, Phenobarbital
D011919 Rats, Inbred Strains Genetically identical individuals developed from brother and sister matings which have been carried out for twenty or more generations or by parent x offspring matings carried out with certain restrictions. This also includes animals with a long history of closed colony breeding. August Rats,Inbred Rat Strains,Inbred Strain of Rat,Inbred Strain of Rats,Inbred Strains of Rats,Rat, Inbred Strain,August Rat,Inbred Rat Strain,Inbred Strain Rat,Inbred Strain Rats,Inbred Strains Rat,Inbred Strains Rats,Rat Inbred Strain,Rat Inbred Strains,Rat Strain, Inbred,Rat Strains, Inbred,Rat, August,Rat, Inbred Strains,Rats Inbred Strain,Rats Inbred Strains,Rats, August,Rats, Inbred Strain,Strain Rat, Inbred,Strain Rats, Inbred,Strain, Inbred Rat,Strains, Inbred Rat
D002478 Cells, Cultured Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others. Cultured Cells,Cell, Cultured,Cultured Cell
D003577 Cytochrome P-450 Enzyme System A superfamily of hundreds of closely related HEMEPROTEINS found throughout the phylogenetic spectrum, from animals, plants, fungi, to bacteria. They include numerous complex monooxygenases (MIXED FUNCTION OXYGENASES). In animals, these P-450 enzymes serve two major functions: (1) biosynthesis of steroids, fatty acids, and bile acids; (2) metabolism of endogenous and a wide variety of exogenous substrates, such as toxins and drugs (BIOTRANSFORMATION). They are classified, according to their sequence similarities rather than functions, into CYP gene families (>40% homology) and subfamilies (>59% homology). For example, enzymes from the CYP1, CYP2, and CYP3 gene families are responsible for most drug metabolism. Cytochrome P-450,Cytochrome P-450 Enzyme,Cytochrome P-450-Dependent Monooxygenase,P-450 Enzyme,P450 Enzyme,CYP450 Family,CYP450 Superfamily,Cytochrome P-450 Enzymes,Cytochrome P-450 Families,Cytochrome P-450 Monooxygenase,Cytochrome P-450 Oxygenase,Cytochrome P-450 Superfamily,Cytochrome P450,Cytochrome P450 Superfamily,Cytochrome p450 Families,P-450 Enzymes,P450 Enzymes,Cytochrome P 450,Cytochrome P 450 Dependent Monooxygenase,Cytochrome P 450 Enzyme,Cytochrome P 450 Enzyme System,Cytochrome P 450 Enzymes,Cytochrome P 450 Families,Cytochrome P 450 Monooxygenase,Cytochrome P 450 Oxygenase,Cytochrome P 450 Superfamily,Enzyme, Cytochrome P-450,Enzyme, P-450,Enzyme, P450,Enzymes, Cytochrome P-450,Enzymes, P-450,Enzymes, P450,Monooxygenase, Cytochrome P-450,Monooxygenase, Cytochrome P-450-Dependent,P 450 Enzyme,P 450 Enzymes,P-450 Enzyme, Cytochrome,P-450 Enzymes, Cytochrome,Superfamily, CYP450,Superfamily, Cytochrome P-450,Superfamily, Cytochrome P450
D004305 Dose-Response Relationship, Drug The relationship between the dose of an administered drug and the response of the organism to the drug. Dose Response Relationship, Drug,Dose-Response Relationships, Drug,Drug Dose-Response Relationship,Drug Dose-Response Relationships,Relationship, Drug Dose-Response,Relationships, Drug Dose-Response
D004790 Enzyme Induction An increase in the rate of synthesis of an enzyme due to the presence of an inducer which acts to derepress the gene responsible for enzyme synthesis. Induction, Enzyme
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia

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