Tong Zeen, Li Hongshan, Goljer Igor, McConnell Oliver, Chandrasekaran Appavu
Drug Safety and Metabolism, Biotransformation Division, Wyeth Research, Collegeville, PA 19426, USA.
Drug Metab Dispos. 2007 Dec;35(12):2203-10. doi: 10.1124/dmd.107.016972. Epub 2007 Sep 17.
Glucuronidation, which may take place on the phenolic hydroxyl and carboxyl groups, is a major pathway of metabolism for thyroxine (T4) and triiodothyronine (T3). In this study, a liquid chromatography/mass spectrometry (LC/MS) method was developed to separate phenolic and acyl glucuronides of T4 and T3. The method was used to collect the phenolic glucuronide of T4 for definitive characterization by NMR and to determine effects of incubation pH, species differences, and human UDP-glucuronosyltransferases (UGTs) involved in the formation of the glucuronides. Formation of T4 phenolic glucuronide was favored at pH 7.4, whereas formation of T4 acyl glucuronide was favored at pH 6.8. All the UGTs examined catalyzed the formation of T4 phenolic glucuronide except UGT1A4; the highest activity was detected with UGT1A3, UGT1A8, and UGT1A10, followed by UGT1A1 and UGT2B4. Formation of T3 phenolic glucuronide was observed in the order of UGT1A8 > UGT1A10 > UGT1A3 > UGT1A1; trace activity was observed with UGT1A6 and UGT1A9. UGT1A3 was the major isoform catalyzing the formation of T4 and T3 acyl glucuronides. In liver microsomes, phenolic glucuronidation was the highest in mice for T4 and in rats for T3 and lowest in monkeys for both T4 and T3. Acyl glucuronidation was highest in humans and lowest in mice for T4 and T3. Phenolic glucuronidation was higher than acyl glucuronidation for T4 in humans; in contrast, the acyl glucuronidation was slightly higher than phenolic glucuronidation for T3. UGT activities were lower toward T3 than T4 in all the species. The LC/MS method was a useful tool in studying glucuronidation of T4 and T3.
葡萄糖醛酸化反应可发生在酚羟基和羧基上，是甲状腺素（T4）和三碘甲状腺原氨酸（T3）的主要代谢途径。在本研究中，开发了一种液相色谱/质谱（LC/MS）方法来分离T4和T3的酚类葡萄糖醛酸苷和酰基葡萄糖醛酸苷。该方法用于收集T4的酚类葡萄糖醛酸苷，通过核磁共振（NMR）进行明确表征，并确定孵育pH值、物种差异以及参与葡萄糖醛酸苷形成的人尿苷二磷酸葡萄糖醛酸基转移酶（UGT）的作用。T4酚类葡萄糖醛酸苷的形成在pH 7.4时更有利，而T4酰基葡萄糖醛酸苷的形成在pH 6.8时更有利。除UGT1A4外，所有检测的UGT均催化T4酚类葡萄糖醛酸苷的形成；UGT1A3、UGT1A8和UGT1A10的活性最高，其次是UGT1A1和UGT2B4。T3酚类葡萄糖醛酸苷的形成顺序为UGT1A8 > UGT1A10 > UGT1A3 > UGT1A1；UGT1A6和UGT1A9观察到微量活性。UGT1A3是催化T4和T3酰基葡萄糖醛酸苷形成的主要同工型。在肝微粒体中，T4的酚类葡萄糖醛酸化在小鼠中最高，T3的酚类葡萄糖醛酸化在大鼠中最高，T4和T3的酚类葡萄糖醛酸化在猴子中最低。T4和T3的酰基葡萄糖醛酸化在人类中最高，在小鼠中最低。人类中T4的酚类葡萄糖醛酸化高于酰基葡萄糖醛酸化；相反，T3的酰基葡萄糖醛酸化略高于酚类葡萄糖醛酸化。在所有物种中，UGT对T3的活性低于对T4的活性。LC/MS方法是研究T4和T3葡萄糖醛酸化的有用工具。
