TitleFlavin-containing monooxygenase S-oxygenation of a series of thioureas and thiones.
Publication TypeJournal Article
Year of Publication2014
AuthorsHenderson MC, Siddens LK, Krueger SK, J Stevens F, Kedzie K, Fang WK, Heidelbaugh T, Nguyen P, Chow K, Garst M, Gil D, Williams DE
JournalToxicol Appl Pharmacol
Date Published2014 Jul 15
KeywordsAnimals, Cell Line, Humans, Insecta, Mice, Oxidation-Reduction, Oxygenases, Thiones, Thiourea

Mammalian flavin-containing monooxygenase (FMO) is active towards many drugs with a heteroatom having the properties of a soft nucleophile. Thiocarbamides and thiones are S-oxygenated to the sulfenic acid which can either react with glutathione and initiate a redox-cycle or be oxygenated a second time to the unstable sulfinic acid. In this study, we utilized LC-MS/MS to demonstrate that the oxygenation by hFMO of the thioureas under test terminated at the sulfenic acid. With thiones, hFMO catalyzed the second reaction and the sulfinic acid rapidly lost sulfite to form the corresponding imidazole. Thioureas are often pulmonary toxicants in mammals and, as previously reported by our laboratory, are excellent substrates for hFMO2. This isoform is expressed at high levels in the lung of most mammals, including non-human primates. Genotyping to date indicates that individuals of African (up to 49%) or Hispanic (2-7%) ancestry have at least one allele for functional hFMO2 in lung, but not Caucasians nor Asians. In this study the major metabolite formed by hFMO2 with thioureas from Allergan, Inc. was the sulfenic acid that reacted with glutathione. The majority of thiones were poor substrates for hFMO3, the major form in adult human liver. However, hFMO1, the major isoform expressed in infant and neonatal liver and adult kidney and intestine, readily S-oxygenated thiones under test, with Kms ranging from 7 to 160 μM and turnover numbers of 30-40 min(-1). The product formed was identified by LC-MS/MS as the imidazole. The activities of the mouse and human FMO1 and FMO3 orthologs were in good agreement with the exception of some thiones for which activity was much greater with hFMO1 than mFMO1.

Alternate JournalToxicol. Appl. Pharmacol.
PubMed ID24727368
PubMed Central IDPMC4110205
Grant ListP30 ES000210 / ES / NIEHS NIH HHS / United States
R01 HL038650 / HL / NHLBI NIH HHS / United States
HL038650 / HL / NHLBI NIH HHS / United States