![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
DE Williams, MK Shigenaga and N Castagnoli
Department of Food Science and Technology, Oregon State University, Corvaltis 97331.
Rabbit lung microsomes metabolize (S)-nicotine primarily to (S)- nicotine delta 1',5'-iminium ion, which is the precursor of (S)- cotinine, the major urinary metabolite of (S)-nicotine in mammals. (S)- Nicotine-N'-oxide and normicotine are also produced as minor metabolites. alpha-Methylbenzylaminobenzotriazole, a mechanism-based suicide inhibitor of rabbit lung cytochromes P-450 2 and 6, inhibited (S)-nicotine oxidation in parallel with inhibition of benzphetamine N- demethylation and ethoxyresorufin O-deethylation. Pretreatment of rabbits with TCDD or Aroclor 1260 had no effect and markedly inhibited (S)-nicotine oxidation, respectively, strongly suggesting that alpha- methylbenzylaminobenzotriazole inhibition was due to inactivation of rabbit lung P-450 2. Reconstitution with cytochromes P-450 2 and 5 demonstrated that only P-450 2 was active toward (S)-nicotine, yielding predominantly the iminium ion, with smaller amounts of nornicotine, (S)- nicotine N'-oxide, and an unknown metabolite also detected. The purified rabbit lung P-450 2-catalyzed oxidation of (S)-nicotine to (S)- nicotine delta 1',5'-iminium ion exhibited a Km of 70 microM and a Vmax of 1.5 min. Covalent binding of (S)-5-3H-nicotine to rabbit lung macromolecules was dependent upon rabbit lung P-450 2-catalyzed formation of the iminium ion. Antibodies raised against P-450 2 inhibited the rabbit lung microsomal metabolism of (S)-nicotine to (S)- nicotine delta 1',5'-iminium ion by almost 95%. Titration of reconstituted P-450 2 with cytochrome b5 produced a concentration- dependent inhibition of nicotine oxidase activity. Increasing the ratio of NADH to NADPH in incubations containing lung microsomes and (S)- nicotine decreased the yield of the iminium ion, confirming the inhibitory effect of cytochrome b5 on the P-450 2-catalyzed alpha- carbon oxidation reaction. NADH alone did not support the lung microsomal metabolism of (S)-nicotine. N'-oxidation of (S]-nicotine is catalyzed by purified pig liver flavin-containing monooxygenase. A number of experiments involving the use of P-450 inhibitors, titration with NADPH-cytochrome P-450 reductase antibodies, and determination of the pH-enzyme activity profile suggested that rabbit lung flavin- containing monooxygenase contributes to a small amount of the N'-oxide produced by rabbit lung microsomes. Further examination with purified flavin-containing monooxygenase isolated from rabbit lung microsomes demonstrated that (S)-nicotine is a poor substrate for this enzyme. The low yield of N'-oxide, relative to other metabolites, in rabbit lung is uncharacteristic for most mammalian tissues and presumably reflects the unusual substrate specificity of rabbit lung flavin-containing monooxygenase.
This article has been cited by other articles:
|
|
 |
|
  L. B. von Weymarn, K. M. Brown, and S. E. Murphy Inactivation of CYP2A6 and CYP2A13 during Nicotine Metabolism J. Pharmacol. Exp. Ther., January 1, 2006; 316(1): 295 - 303. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. E. Murphy, V. Raulinaitis, and K. M. Brown NICOTINE 5'-OXIDATION AND METHYL OXIDATION BY P450 2A ENZYMES Drug Metab. Dispos., August 1, 2005; 33(8): 1166 - 1173. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S.-L. Wang, X.-Y. He, and J.-Y. Hong HUMAN CYTOCHROME P450 2S1: LACK OF ACTIVITY IN THE METABOLIC ACTIVATION OF SEVERAL CIGARETTE SMOKE CARCINOGENS AND IN THE METABOLISM OF NICOTINE Drug Metab. Dispos., March 1, 2005; 33(3): 336 - 340. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Hukkanen, P. Jacob III, and N. L. Benowitz Metabolism and Disposition Kinetics of Nicotine Pharmacol. Rev., March 1, 2005; 57(1): 79 - 115. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z. Bao, X.-Y. He, X. Ding, S. Prabhu, and J.-Y. Hong METABOLISM OF NICOTINE AND COTININE BY HUMAN CYTOCHROME P450 2A13 Drug Metab. Dispos., February 1, 2005; 33(2): 258 - 261. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. K. Krueger, M.-F. Yueh, S. R. Martin, C. B. Pereira, and D. E. Williams Characterization of Expressed Full-Length and Truncated FMO2 from Rhesus Monkey Drug Metab. Dispos., April 13, 2001; 29(5): 693 - 700. [Abstract] [Full Text]
|
|
|
|
|
|
S. Katchamart, D. M. Stresser, S. S. Dehal, D. Kupfer, and D. E. Williams Concurrent Flavin-Containing Monooxygenase Down-Regulation and Cytochrome P-450 Induction by Dietary Indoles in Rat: Implications for Drug-Drug Interaction Drug Metab. Dispos., August 1, 2000; 28(8): 930 - 936. [Abstract] [Full Text]
|
|
|
|
|
|
S. Vickers, A. D. Theoharides, B. Arison, S. K. Balani, D. Cui, C. A. Duncan, J. D. Ellis, L. M. Gorham, S. L. Polsky, T. Prueksaritanont, et al. In Vitro and In Vivo Studies on the Metabolism of Tirofiban Drug Metab. Dispos., November 1, 1999; 27(11): 1360 - 1366. [Abstract] [Full Text]
|
|
|
|
|
|
E. S. Messina, R. F. Tyndale, and E. M. Sellers A Major Role for CYP2A6 in Nicotine C-Oxidation by Human Liver Microsomes J. Pharmacol. Exp. Ther., September 1, 1997; 282(3): 1608 - 1614. [Abstract] [Full Text]
|
|
 |
 |
 |
|
 |
 |
 |
