Induction of specific cytochrome P-450 isozymes by methylenedioxyphenyl compounds and antagonism by 3-methylcholanthrene.
Two methylenedioxyphenyl compounds, isosafrole (5-propenyl-1,3-benzodioxole) and an analog, 5-t-butyl-1,3-benzodioxole (BD), differ markedly as inducers of cytochrome P-450 isozymes in rat liver microsomes. Isosafrole is a mixed-type inducer, inducing P-450b, P-450c, and P-450d. In contrast, BD is a phenobarbital-type inducer, increasing P-450b, but producing little or no increase in P-450c or P-450d. Similarly, isosafrole increases the amount of translatable mRNA for P-450b, c and d, while BD induces only the mRNA for P-450b. Dimethylation of the methylene bridge carbon of BD to give 2,2-dimethyl-5-t-butyl-1,3-benzodioxole (DBD) blocks the formation of NADPH-reduced Type III metabolite-P-450 complexes in vitro, and diminishes but does not abolish the ability of the compound to induce P-450b. Western blots of microsomes from isosafrole and BD-treated rat livers confirm that in contrast to isosafrole, BD does not induce P-450d or P-450c. However, the antibody to P-450d recognizes two new polypeptides (approximately 50K Mr) from sodium dodecyl sulfate-polyacrylamide gels of liver microsomes from BD-treated rats. These polypeptides are not observed in control, isosafrole, 3-methylcholanthrene (3-MC), or DBD-treated rats. They are intensified by coadministration of 3-MC with BD and may represent either modified isozyme-metabolite adducts or degradation products of P-450d. However, the polypeptides could not be generated in vitro by addition of BD to 3-MC-induced microsomes with NADPH under conditions which produced spectral metabolite complexes, or in a reconstituted system with P-450d. The two methylenedioxyphenyl compounds do not form stable metabolite complexes with the same P-450 isozymes. BD formed distinct spectral metabolite complexes in vitro with both P-450b and P-450c but not with P-450d in a reconstituted system. In contrast, isosafrole forms metabolite complexes with all three isozymes. Coadministration of 3-MC with BD blocked induction of P-450b by 80% and produced a similar repression of its translatable mRNA. This finding indicates that 3-MC type inducers not only induce certain cytochrome P-450 isozymes, but also repress synthesis of other isozymes.
D000818:Animals; D002474:Cell-Free System; D003101:Collodion; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004149:Dioxoles / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D004790:Enzyme Induction / Q000187:drug effects; D007120:Immunochemistry; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology*; D008862:Microsomes, Liver / Q000201:enzymology; D011132:Polyribosomes / Q000201:enzymology; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D012451:Safrole / Q000494:pharmacology; D013053:Spectrophotometry
D065607:Cytochrome P-450 Enzyme Inhibitors; D004149:Dioxoles; D007527:Isoenzymes; C037778:2,2-dimethyl-5-tert-butyl-1,3-benzodioxole; D008748:Methylcholanthrene; C037776:5-tert-butyl-1,3-benzodioxole; D003101:Collodion; D003577:Cytochrome P-450 Enzyme System; D012451:Safrole; C015959:isosafrole