RT Journal Article
SR Electronic
T1 Flavin-Containing Monooxygenase-MediatedN-Oxidation of the M1-Muscarinic Agonist Xanomeline
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1099
OP 1103
VO 27
IS 10
A1 Barbara J. Ring
A1 Steven A. Wrighton
A1 Susanna L. K. Aldridge
A1 Kristian Hansen
A1 Barbara Haehner
A1 Lisa A. Shipley
YR 1999
UL http://dmd.aspetjournals.org/content/27/10/1099.abstract
AB The involvement of flavin-containing monooxygenases (FMOs) in the formation of xanomeline N-oxide was examined in various human and rat tissues. Expressed FMOs formed xanomelineN-oxide at a significantly greater rate than did expressed cytochromes P-450. Consistent with the involvement of FMO in the formation of xanomeline N-oxide in human liver, human kidney, rat liver, and rat kidney microsomes, this biotransformation was sensitive to heat treatment, increased at pH 8.3, and inhibited by methimazole. The latter two characteristics were effected to a lesser extent in human kidney, rat liver, and rat kidney microsomes than were observed in human liver microsomes, suggesting the involvement of a different FMO family member in this reaction in these tissues. As additional proof of the involvement of FMO in the formation of xanomeline N-oxide, the formation of this metabolite by a characterized human liver microsomal bank correlated with FMO activity. The FMO forming xanomeline N-oxide by human kidney microsomes exhibited a 20-fold lowerKM (averageKM = 5.5 μM) than that observed by the FMO present in human liver microsomes (averageKM of 107 μM). The involvement of an FMO in the formation of xanomeline N-oxide in rat lung could not be unequivocally demonstrated. These data and those in the literature suggest that the increased prevalence ofN-oxidized metabolites of xanomeline after s.c. dosing as compared with oral dosing may be due to differences in the affinity of various FMO family members for xanomeline or to differences in exposure to xanomeline that these enzymes receive under different dosing regimens. The American Society for Pharmacology and Experimental Therapeutics