Hanioka Nobumitsu, Isobe Takashi, Kinashi Yu, Tanaka-Kagawa Toshiko, Jinno Hideto
Department of Biochemical Toxicology, Yokohama University of Pharmacy, 601 Matano-cho, Totsuka-ku, Yokohama, 245-0066, Japan.
Faculty of Pharmaceutical Sciences, Okayama University, 1-1-1 Tsushima-naka, Kita-ku, Okayama, 700-8530, Japan.
Arch Toxicol. 2016 Jul;90(7):1651-7. doi: 10.1007/s00204-015-1619-1. Epub 2015 Oct 29.
Mono(2-ethylhexyl) phthalate (MEHP) is an active metabolite of di(2-ethylhexyl) phthalate (DEHP) and has endocrine-disrupting effects. MEHP is metabolized into glucuronide by UDP-glucuronosyltransferase (UGT) enzymes in mammals. In the present study, the hepatic and intestinal glucuronidation of MEHP in humans, dogs, rats, and mice was examined in an in vitro system using microsomal fractions. The kinetics of MEHP glucuronidation by liver microsomes followed the Michaelis-Menten model for humans and dogs, and the biphasic model for rats and mice. The K m and V max values of human liver microsomes were 110 µM and 5.8 nmol/min/mg protein, respectively. The kinetics of intestinal microsomes followed the biphasic model for humans, dogs, and mice, and the Michaelis-Menten model for rats. The K m and V max values of human intestinal microsomes were 5.6 µM and 0.40 nmol/min/mg protein, respectively, for the high-affinity phase, and 430 µM and 0.70 nmol/min/mg protein, respectively, for the low-affinity phase. The relative levels of V max estimated by Eadie-Hofstee plots were dogs (2.0) > mice (1.4) > rats (1.0) ≈ humans (1.0) for liver microsomes, and mice (8.5) > dogs (4.1) > rats (3.1) > humans (1.0) for intestinal microsomes. The percentages of the V max values of intestinal microsomes to liver microsomes were mice (120 %) > rats (57 %) > dogs (39 %) > humans (19 %). These results suggest that the metabolic abilities of UGT enzymes expressed in the liver and intestine toward MEHP markedly differed among species, and imply that these species differences are strongly associated with the toxicity of DEHP.
邻苯二甲酸单（2-乙基己基）酯（MEHP）是邻苯二甲酸二（2-乙基己基）酯（DEHP）的一种活性代谢产物，具有内分泌干扰作用。在哺乳动物中，MEHP通过尿苷二磷酸葡萄糖醛酸基转移酶（UGT）代谢为葡萄糖醛酸苷。在本研究中，使用微粒体组分在体外系统中检测了人、犬、大鼠和小鼠中MEHP的肝脏和肠道葡萄糖醛酸化作用。肝脏微粒体对MEHP进行葡萄糖醛酸化的动力学在人和犬中遵循米氏模型，在大鼠和小鼠中遵循双相模型。人肝脏微粒体的K m和V max值分别为110 µM和5.8 nmol/分钟/毫克蛋白。肠道微粒体的动力学在人、犬和小鼠中遵循双相模型，在大鼠中遵循米氏模型。人肠道微粒体在高亲和力阶段的K m和V max值分别为5.6 µM和0.40 nmol/分钟/毫克蛋白，在低亲和力阶段分别为430 µM和0.70 nmol/分钟/毫克蛋白。通过伊迪-霍夫斯泰 plots法估计的V max相对水平，对于肝脏微粒体，犬（2.0）>小鼠（1.4）>大鼠（1.0）≈人（1.0）；对于肠道微粒体，小鼠（8.5）>犬（4.1）>大鼠（3.1）>人（1.0）。肠道微粒体V max值相对于肝脏微粒体V max值的百分比为小鼠（120%）>大鼠（57%）>犬（39%）>人（19%）。这些结果表明，肝脏和肠道中表达的UGT酶对MEHP的代谢能力在不同物种之间存在显著差异，这意味着这些物种差异与DEHP的毒性密切相关。
