Department of Pharmaceutical Sciences, Massachusetts College of Pharmacy and Health Sciences, Boston, Massachusetts, USA.
Drug Metab Dispos. 2011 Apr;39(4):693-702. doi: 10.1124/dmd.110.036004. Epub 2010 Dec 21.
Oxymetazoline (6-tert-butyl-3-(2-imidazolin-2-ylmethyl)-2,4-dimethylphenol) has been widely used as a nonprescription nasal vasoconstrictor for >40 years; however, its metabolic pathway has not been investigated. This study describes the in vitro metabolism of oxymetazoline in human, rat, and rabbit liver postmitochondrial supernatant fraction from homogenized tissue (S9) fractions and their microsomes supplemented with NADPH. The metabolites of oxymetazoline identified by liquid chromatography (LC)/UV/tandem mass spectrometry (MS/MS), included M1 (monohydroxylation of the t-butyl group), M2 (oxidative dehydrogenation of the imidazoline to an imidazole moiety), M3 (monohydroxylation of M2), M4 (dihydroxylation of oxymetazoline), and M5 (dihydroxylation of M2). Screening with nine human expressed cytochromes P450 (P450s) identified CYP2C19 as the single P450 isoform catalyzing the formation of M1, M2, and M3. Glutathione conjugates of oxymetazoline (M6) and M2 (M7) were identified in the liver S9 fractions, indicating the capability of oxymetazoline to undergo bioactivation to reactive intermediate species. M6 and M7 were not detected in those liver S9 incubations without NADPH. Cysteine conjugates (M8 and M9) derived from glutathione conjugates and hydroxylated glutathione conjugates (M10 and M11) were also identified. The reactive intermediate of oxymetazoline was trapped with glutathione and N-acetyl cysteine and identified by LC/MS/MS. M6 was isolated and identified by one-dimensional or two-dimensional NMR as the glutathione conjugate of a p-quinone methide. We have shown the tendency of oxymetazoline to form p-quinone methide species via a bioactivation mechanism involving a CYP2C19-catalyzed two-electron oxidation. Nevertheless, we conclude that the formation of this reactive species might not be a safety concern for oxymetazoline nasal products because of the typical low-dose and brief dosage regimen limited to nasal delivery.
奥昔布宁（6-叔丁基-3-（2-咪唑啉-2-基甲基）-2,4-二甲基苯酚）作为一种非处方鼻腔血管收缩剂已被广泛使用超过 40 年；然而，其代谢途径尚未被研究。本研究描述了奥昔布宁在人、大鼠和兔肝线粒体后上清液（S9）级分及其用 NADPH 补充的微粒体中的体外代谢。通过液相色谱（LC）/紫外线/串联质谱（MS/MS）鉴定的奥昔布宁代谢物包括 M1（叔丁基的单羟基化）、M2（咪唑啉氧化脱氢为咪唑部分）、M3（M2 的单羟基化）、M4（奥昔布宁的双羟基化）和 M5（M2 的双羟基化）。用九种人表达的细胞色素 P450（P450s）进行筛选，鉴定出 CYP2C19 是催化 M1、M2 和 M3 形成的单一 P450 同工酶。奥昔布宁的谷胱甘肽缀合物（M6）和 M2 的谷胱甘肽缀合物（M7）在肝 S9 级分中被鉴定，表明奥昔布宁有能力发生生物转化形成反应性中间产物。在没有 NADPH 的肝 S9 孵育中未检测到 M6 和 M7。还鉴定了源自谷胱甘肽缀合物和羟化谷胱甘肽缀合物的半胱氨酸缀合物（M8 和 M9）。用 LC/MS/MS 鉴定用谷胱甘肽和 N-乙酰半胱氨酸捕获的奥昔布宁的反应性中间产物。通过一维或二维 NMR 将 M6 鉴定为 p-醌亚甲基的谷胱甘肽缀合物。我们已经表明，奥昔布宁通过涉及 CYP2C19 催化的两电子氧化的生物活化机制倾向于形成 p-醌亚甲基物种。然而，我们得出结论，由于典型的低剂量和短暂的剂量方案仅限于鼻腔给药，因此这种反应性物质的形成可能不是奥昔布宁鼻用产品的安全问题。
