title: N-demethylation and N-oxidation of imipramine in rat thoracic aortic endothelial cells.
abstract: The aim of this study was to examine whether cultured rat thoracic aortic endothelial cells (TAECs) have the ability to metabolize the tertiary amine, imipramine. In rat TAECs, imipramine was biotransformed into N-demethylate and N-oxide by cytochrome P450 (CYP) and flavin-containing monooxygenase (FMO), respectively. The intrinsic clearance (V max/K m) for the N-oxide formation was approximately five times as high as that for the N-demethylate formation, indicating that oxidation by CYP was much higher than that by FMO. Moreover, we suggest that CYP2C11 and CYP3A2 are key players in the metabolism to N-demethylate in rat TAECs using the respective anti-rat CYP antibodies (anti-CYP2C11 and anti-CYP3A2). The presence of CYP2C11 and CYP3A2 proteins was also confirmed in cultured rat TAECs using a polyclonal anti-CYP antibody and immunofluorescence microscopy. In contrast, the formation rate of N-oxide at pH 8.4 was higher than that at pH 7.4. Inhibition of N-oxide formation by methimazole was found to be the best model of competitive inhibition yielding an apparent K i value of 0.80 μmol/L, demonstrating that N-oxidation was catalyzed by FMO in rat TAECs. These results suggest that rat TAEC enzymes can convert substrates of exogenous origin such as imipramine, indicating that TAECs have an important function for metabolic products, besides hepatic cells.
authors.affiliation: Department of Pharmaceutics, Faculty of Pharmaceutical Sciences, Tokushima Bunri University, 180 Yamashiro-cho, Tokushima, 770-8514, Japan.
authors.forename: Yukari
authors.initials: Y
authors.lastname: Ueda
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Yaginuma
authors.forename: Eiko
authors.initials: E
authors.lastname: Sakurai
authors.forename: Eiichi
authors.initials: E
authors.lastname: Sakurai
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D002478:Cells, Cultured; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism*; D000072467:Cytochrome P450 Family 2; D042783:Endothelial Cells / Q000378:metabolism*; D007099:Imipramine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism*; D008297:Male; D008745:Methylation; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D039181:Steroid 16-alpha-Hydroxylase / Q000378:metabolism*; D013895:Thoracic Arteries / Q000166:cytology*
chemical_list: C002921:imipramine N-oxide; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; C465260:Cyp3a2 protein, rat; D051544:Cytochrome P-450 CYP3A; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; D007099:Imipramine