PT - JOURNAL ARTICLE AU - R J Bjercke AU - D K Hammond AU - H W Strobel AU - J J Langone TI - Interaction of cotinine with rat hepatic microsomal P-450. Comparison with metyrapone and immunomodulation of cotinine and metyrapone binding by monoclonal anti-cotinine antibodies. DP - 1990 Sep 01 TA - Drug Metabolism and Disposition PG - 759--764 VI - 18 IP - 5 4099 - http://dmd.aspetjournals.org/content/18/5/759.short 4100 - http://dmd.aspetjournals.org/content/18/5/759.full SO - Drug Metab Dispos1990 Sep 01; 18 AB - 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.