Shimizu Makiko, Nii Anna, Uno Yasuhiro, Yamazaki Hiroshi
Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Tokyo, Japan.
Joint Faculty of Veterinary Medicine, Kagoshima University, Kagoshima, Japan.
Drug Metab Dispos. 2025 Aug 5;53(9):100140. doi: 10.1016/j.dmd.2025.100140.
A family of NADPH-dependent flavin-containing monooxygenases (FMOs; EC 1.14.13.8) mediate the oxygenation of various N-containing molecules. Human FMO3 and FMO1 are the major hepatic and renal forms, respectively; monkey, dog, and pig FMO3 and FMO1 have also been identified. Triethylamine has been found in the urine of manufacturing workers. Although triethylamine was predicted to be metabolized by N-oxygenation by human FMO3 because of its classic base dissociation constant, enzymatic role of FMOs in triethylamine N-oxygenation remains to be investigated. Consequently, triethylamine N-oxygenation was investigated with FMO1/3 enzyme sources. The rate of triethylamine N-oxygenation mediated by human liver microsomes was similar to that mediated by human kidney microsomes. In contrast, the rates of triethylamine N-oxygenation by monkey, dog, and minipig liver microsomes were higher than those by kidney microsomes. Human liver microsomal triethylamine N-oxygenation was extensively suppressed by preheating liver microsomes at 45 °C for 5 minutes, suggesting a major role of FMOs in triethylamine N-oxygenation. Recombinant human, monkey, and dog FMO3 efficiently mediated triethylamine N-oxygenation, whereas only pig FMO1 exhibited this activity. Human liver microsomes and recombinant FMO3 showed similar K values for triethylamine N-oxygenation. For the 4 species tested, positive correlations were observed between the rates of FMO3-mediated triethylamine N-oxygenation and its activities toward additional probe substrates benzydamine and trimethylamine. These results suggest that human FMO3 is responsible for triethylamine N-oxygenation, with some species differences in terms of FMO-mediated triethylamine N-oxygenation in humans and animal models, eg, monkeys, dogs, and minipigs. SIGNIFICANCE STATEMENT: Human flavin-containing monooxygenase (FMO) 3 mediates the N-oxygenation of triethylamine, a basic compound of interest in human biomonitoring survey results for manufacturing workers. The substrate specificity of FMO3 for triethylamine N-oxygenation in humans, monkeys, and dogs was evident. In contrast, pig FMO1 was the predominant FMO form for the N-oxygenation of triethylamine. Human hepatic FMO3 is responsible for triethylamine N-oxygenation; however, the rate of triethylamine N-oxygenation may be slower than that of typical FMO3 probe substrate trimethylamine.
一类依赖烟酰胺腺嘌呤二核苷酸磷酸（NADPH）的含黄素单加氧酶（FMOs；酶编号EC 1.14.13.8）可介导多种含氮分子的氧化反应。人类FMO3和FMO1分别是肝脏和肾脏中的主要形式；在猴子、狗和猪中也已鉴定出FMO3和FMO1。在制造业工人的尿液中发现了三乙胺。尽管由于三乙胺的经典碱解离常数，预计其会被人类FMO3通过氮氧化作用进行代谢，但FMOs在三乙胺氮氧化中的酶促作用仍有待研究。因此，利用FMO1/3酶源对三乙胺氮氧化进行了研究。人肝微粒体介导的三乙胺氮氧化速率与肾微粒体介导的相似。相比之下，猴子、狗和小型猪肝微粒体的三乙胺氮氧化速率高于肾微粒体。将肝微粒体在45℃预热5分钟可广泛抑制人肝微粒体的三乙胺氮氧化，这表明FMOs在三乙胺氮氧化中起主要作用。重组人、猴和狗的FMO3可有效介导三乙胺氮氧化，而只有猪FMO1表现出这种活性。人肝微粒体和重组FMO3在三乙胺氮氧化方面表现出相似的K值。在所测试的4个物种中，观察到FMO3介导的三乙胺氮氧化速率与其对其他探针底物苄达明和三甲胺的活性之间呈正相关。这些结果表明，人FMO3负责三乙胺氮氧化，在人类和动物模型（如猴子、狗和小型猪）中，FMO介导的三乙胺氮氧化存在一些物种差异。意义声明：人类含黄素单加氧酶（FMO）3介导三乙胺的氮氧化，三乙胺是制造业工人人体生物监测调查结果中一种重要的碱性化合物。FMO3对人类、猴子和狗中三乙胺氮氧化的底物特异性很明显。相比之下，猪FMO1是三乙胺氮氧化的主要FMO形式。人肝脏FMO3负责三乙胺氮氧化；然而，三乙胺氮氧化的速率可能比典型的FMO3探针底物三甲胺的速率慢。
