title: High-performance liquid chromatographic assay for human liver microsomal omeprazole metabolism.
abstract: Assays for the measurement of omeprazole metabolites in plasma and urine have been reported, but when applied to the determination of omeprazole metabolites formed by human liver microsomal incubations there were obvious limitations in sensitivity. The present high-performance liquid chromatographic (HPLC) assay, which comprises extraction, evaporation and reconstitution, is several-fold more sensitive with a limit of detection of approximately 2 pmol (2 nM in incubate) for omeprazole sulphone and 25 pmol (25 nM in incubate) for hydroxyomeprazole. Extraction efficiency is essentially quantitative and is highly reproducible (coefficient of variation = 2.1% for both metabolites). The assay is linear over a wide range of concentrations and the formation of the metabolites is linear with respect to both time (to 15 min) and protein concentration (to 1.5 mg/ml). Two minor metabolites, one of which was identified tentatively as 5-O-desmethylomeprazole, were also formed by human liver microsomes and could be determined by this method. Preliminary studies of the formation of omeprazole sulphone and hydroxyomeprazole showed that the formation kinetics in human liver microsomes were biphasic for both metabolites, suggesting that at least two different cytochrome P450 isoforms are involved in their formation.
authors.affiliation: Astra Hässle AB, Mölndal, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Andersson
authors.forename: P O
authors.initials: PO
authors.lastname: Lagerstrøm
authors.forename: J O
authors.initials: JO
authors.lastname: Miners
authors.forename: M E
authors.initials: ME
authors.lastname: Veronese
authors.forename: L
authors.initials: L
authors.lastname: Weidolf
authors.forename: D J
authors.initials: DJ
authors.lastname: Birkett
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D009853:Omeprazole / Q000032:analysis / Q000378:metabolism* / Q000493:pharmacokinetics; D013056:Spectrophotometry, Ultraviolet; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; D039181:Steroid 16-alpha-Hydroxylase; D009853:Omeprazole