Miles Kristini K, Stern Stephan T, Smith Philip C, Kessler Fay K, Ali Shazia, Ritter Joseph K
Department of Pharmacology and Toxicology, Virginia Commonwealth University, Medical College of Virginia Campus, 1217 E. Marshall Street, Richmond, VA 23298-0613, USA.
Drug Metab Dispos. 2005 Oct;33(10):1513-20. doi: 10.1124/dmd.105.004663. Epub 2005 Jul 20.
Mycophenolic acid (MPA; 1,3-dihydro-4-hydroxy-6-methoxy-7-methyl-3-oxo-5-isobenzylfuranyl)-4-methyl-4-hexenoate), the active metabolite of the immunosuppressant prodrug, mycophenolate mofetil, undergoes glucuronidation to its 7-O-glucuronide as a primary route of metabolism. Because differences in glucuronidation may influence the efficacy and/or toxicity of MPA, we investigated the MPA UDP-glucuronosyltransferase (UGT) activities of human liver microsomes (HLMs) and rat liver microsomes with the goal of identifying UGTs responsible for MPA catalysis. HLMs (n = 23) exhibited higher average MPA glucuronidation rates (14.7 versus 6.0 nmol/mg/min, respectively, p < 0.001) and higher apparent affinity for MPA (K(m) = 0.082 mM versus 0.20 mM, p < 0.001) compared with rat liver microsomes. MPA UGT activities were reduced >80% in liver microsomes from Gunn rats. To identify the active enzymes, human and rat UGT1A enzymes were screened for MPA-glucuronidating activity. UGT1A9 was the only human liver-expressed UGT1A enzyme with significant activity and exhibited both high affinity (K(m) = 0.077 mM) and high activity (V(max) = 28 nmol x min(-1) x mg(-1)). Spearman correlation analyses revealed a stronger relationship between HLM MPA UGT activities and 1A9-like content (r(2) = 0.79) relative to 1A1 (r(2) = 0.20), 1A4-like (r(2) = 0.22), and 1A6 (r(2) = 0.41) protein. A different profile was observed for rat with three active liver-expressed UGT1A enzymes: 1A1 (medium affinity/capacity), 1A6 (low affinity/medium capacity), and 1A7 (high affinity/capacity). Our data suggest that UGT1A enzymes are the major contributors to hepatic MPA metabolism in both species, but 1A9 is dominant in human, whereas 1A1 and 1A7 are likely the principal mediators in control rat liver. This information should be useful for interpretation of MPA pharmacokinetic and toxicity data in clinical and animal studies.
霉酚酸（MPA；1,3 - 二氢 - 4 - 羟基 - 6 - 甲氧基 - 7 - 甲基 - 3 - 氧代 - 5 - 异苄基呋喃基）-4 - 甲基 - 4 - 己烯酸酯）是免疫抑制剂前药霉酚酸酯的活性代谢产物，其主要代谢途径是葡萄糖醛酸化生成7 - O - 葡萄糖醛酸苷。由于葡萄糖醛酸化的差异可能会影响MPA的疗效和/或毒性，我们研究了人肝微粒体（HLM）和大鼠肝微粒体中MPA UDP - 葡萄糖醛酸基转移酶（UGT）的活性，目的是确定负责MPA催化的UGT。与大鼠肝微粒体相比，HLM（n = 23）表现出更高的平均MPA葡萄糖醛酸化速率（分别为14.7对6.0 nmol/mg/min，p < 0.001）和对MPA更高的表观亲和力（K(m) = 0.082 mM对0.20 mM，p < 0.001）。来自Gunn大鼠的肝微粒体中MPA UGT活性降低了80%以上。为了确定活性酶，对人和大鼠的UGT1A酶进行了MPA葡萄糖醛酸化活性筛选。UGT1A9是唯一在人肝脏中表达且具有显著活性的UGT1A酶，表现出高亲和力（K(m) = 0.077 mM）和高活性（V(max) = 28 nmol·min(-1)·mg(-1)）。Spearman相关性分析显示，相对于1A1（r(2) = 0.20）、1A4样（r(2) = 0.22）和1A6（r(2) = 0.41）蛋白，HLM MPA UGT活性与1A9样含量之间的关系更强（r(2) = 0.79）。在大鼠中观察到不同的情况，有三种在肝脏中表达的活性UGT1A酶：1A1（中等亲和力/能力）、1A6（低亲和力/中等能力）和1A7（高亲和力/能力）。我们的数据表明，UGT1A酶是这两个物种肝脏中MPA代谢的主要贡献者，但1A9在人类中占主导地位，而1A1和1A7可能是对照大鼠肝脏中的主要介导者。这些信息对于解释临床和动物研究中的MPA药代动力学和毒性数据应该是有用的。
