title: Development of a CD-MEKC method for investigating the metabolism of tamoxifen by flavin-containing monooxygenases and the inhibitory effects of methimazole, nicotine and DMXAA.
abstract: A selective and low-cost CD-MEKC method under acidic conditions was developed for investigating the N-oxygenation of tamoxifen (TAM) by flavin-containing monooxygenases (FMOs). The inhibitory effects of methimazole (MMI), nicotine and 5,6-dimethylxanthenone-4-acetic acid (DMXAA) on the given FMO reaction were also evaluated; 100 mM phosphate buffer (pH 8.6) was used for performing the enzymatic reaction and the separation of TAM and its metabolite tamoxifen N-oxide (TNO) was obtained with a BGE consisting of 100 mM phosphoric acid solution adjusted to pH 2.5 with triethanolamine containing 50 mM sodium taurodeoxycholate, 20 mM carboxymethyl β-CD and 20% ACN. The proposed method was applied for the kinetics study of FMO1 using TAM as a substrate probe. A Michaelis-Menten constant (K(m)) of 164.1 μM was estimated from the corrected peak area of the product, TNO. The calculated value of the maximum reaction velocity (V(max)) was 3.61 μmol/min/μmol FMO1; 50% inhibitory concentration and inhibition constant (K(i)) of MMI, the most common alternate substrate FMO inhibitor, were evaluated and the inhibitory effects of two other important FMO substrates, nicotine and DMXAA, a novel anti-tumour agent, were investigated.
authors.affiliation: Laboratory for Pharmaceutical Analysis, KU Leuven, Belgium.
authors.forename: Duygu
authors.initials: D
authors.lastname: Yeniceli
authors.forename: Xiaolan
authors.initials: X
authors.lastname: Deng
authors.forename: Erwin
authors.initials: E
authors.lastname: Adams
authors.forename: Dilek
authors.initials: D
authors.lastname: Dogrukol-Ak
authors.forename: Ann
authors.initials: A
authors.lastname: Van Schepdael
mesh_terms: D020374:Chromatography, Micellar Electrokinetic Capillary / Q000379:methods*; D003505:Cyclodextrins / Q000494:pharmacology; D006801:Humans; D008713:Methimazole / Q000494:pharmacology*; D009538:Nicotine / Q000494:pharmacology*; D010105:Oxygenases / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D015203:Reproducibility of Results; D013629:Tamoxifen / Q000032:analysis* / Q000378:metabolism; D044004:Xanthones / Q000494:pharmacology*
chemical_list: D003505:Cyclodextrins; D044004:Xanthones; C066668:vadimezan; D013629:Tamoxifen; D008713:Methimazole; D009538:Nicotine; D010105:Oxygenases; C020066:dimethylaniline monooxygenase (N-oxide forming)