The metabolomics of (±)-arecoline 1-oxide in the mouse and its formation by human flavin-containing monooxygenases

The alkaloid arecoline is a main constituent of areca nuts that are chewed by approximately 600 million persons worldwide. A principal metabolite of arecoline is arecoline 1-oxide whose metabolism has been poorly studied. To redress this, synthetic (+/-)-arecoline 1-oxide was administered to mice (20 mg/kg p.o.) and a metabolomic study performed on 0-12 h urine using ultra-performance liquid chromatography-coupled time-of-flight mass spectrometry (UPLC-TOFMS) with multivariate data analysis. A total of 16 mass/retention time pairs yielded 13 metabolites of (+/-)-arecoline 1-oxide, most of them novel. identity of metabolites was confirmed by tandem mass spectrometry. The principal pathways of metabolism of ()arecoline 1-oxide were mercapturic acid formation, with catabolism to mercaptan and methylmercaptan metabolites, apparent C=C double-bond reduction, carboxylic acid reduction to the aldehyde (a novel pathway in mammals), N-oxide reduction, and de-esterification. Relative percentages of metabolites were determined directly from the metabolomic data. Approximately, 50% of the urinary metabolites corresponded to unchanged ()-arecoline 1-oxide, 25% to other N-oxide metabolites, while approximately, 30% corresponded to mercapturic acids or their metabolites. Many metabolites, principally mercapturic acids and their derivatives, were excreted as diastereomers that could be resolved by UPLC-TOFMS. Arecoline was converted to arecoline 1-oxide in vitro by human flavin-containing monooxygenases FMO1 (K-M: 13.6 +/- 4.9 mu M; V-MAX: 0.114 +/- 0.01 nmol min(-1) mu g(-1) protein) and FMO3 (K-M: 44.5 +/- 8.0 mu M; V-MAX: 0.014 +/- 0.001 nmol min(-1) mu g(-1) protein), but not by FMO5 or any of 11 human cytochromes P450. This report underscores the power of metabolomics in drug metabolite mining. (c) 2006 Published by Elsevier Inc.