title: Interaction of cotinine with rat hepatic microsomal P-450. Comparison with metyrapone and immunomodulation of cotinine and metyrapone binding by monoclonal anti-cotinine antibodies.
abstract: The ability of the major nicotine metabolite, cotinine, to interact with rat liver microsomal cytochrome P-450 and the immunomodulatory effects of anti-cotinine antibodies were studied. Cotinine induced type II spectral changes with both microsomes from phenobarbital (PB)-induced rats and purified P-450 with apparent Ks values of 97 and 750 microM, respectively. In contrast, the Ks value was 0.3 microM for metyrapone and 5 microM for nicotine with both the microsomes and purified enzyme. The apparent Ki value for cotinine inhibition of 7-pentoxyresorufin O-dealkylase activity with the microsomes (87 microM) was approximately 87- and 870-fold higher than for nicotine and metyrapone, respectively. Monoclonal antibodies produced against cotinine cross-reacted equally well with metyrapone. They specifically blocked enzyme binding of both drugs based on dose-dependent inhibition of spectral changes, and reversed the metyrapone-induced inhibition of microsomal O-dealkylase activity. In contrast, antibodies to nicotine did not cross-react with cotinine or metyrapone and had no effect on their activity, although they did block the action of nicotine. These results demonstrate that cotinine binding to P-450 from PB-induced rats and inhibition of functional activity in vitro are qualitatively like the effects of metyrapone and nicotine, and that monoclonal anti-cotinine antibodies are useful molecular probes of the interactions between cotinine and metyrapone with the enzyme.
authors.affiliation: Department of Medicine, Baylor College of Medicine, Houston 77030.
authors.forename: R J
authors.initials: RJ
authors.lastname: Bjercke
authors.forename: D K
authors.initials: DK
authors.lastname: Hammond
authors.forename: H W
authors.initials: HW
authors.lastname: Strobel
authors.forename: J J
authors.initials: JJ
authors.lastname: Langone
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D003367:Cotinine / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology*; D019362:Cytochrome P-450 CYP2B1; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004790:Enzyme Induction / Q000187:drug effects; D004797:Enzyme-Linked Immunosorbent Assay; D066298:In Vitro Techniques; D007700:Kinetics; D008797:Metyrapone / Q000378:metabolism / Q000494:pharmacology*; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010088:Oxidoreductases / Q000037:antagonists & inhibitors; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013050:Spectrometry, Fluorescence
chemical_list: D000911:Antibodies, Monoclonal; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D019362:Cytochrome P-450 CYP2B1; D003367:Cotinine; D010634:Phenobarbital; D008797:Metyrapone