Ohno Akiko, Saito Yoshiro, Hanioka Nobumitsu, Jinno Hideto, Saeki Mayumi, Ando Masanori, Ozawa Shogo, Sawada Jun-ichi
Division of Environmental Chemistry, National Institute of Health Sciences, Tokyo 158-8501, Japan.
Drug Metab Dispos. 2004 Feb;32(2):235-9. doi: 10.1124/dmd.32.2.235.
Carvedilol ((+/-)-1-carbazol-4-yloxy)-3-[[2-(o-methoxyphenoxy)ethyl]amino]-2-propanol) is metabolized primarily into glucuronide conjugates. In the present study, we identified the human UDP-glucuronosyltransferase (UGT) isoforms involved in the glucuronidation of carvedilol by thin-layer chromatography using microsomes from human liver or insect cells expressing recombinant UGT isoforms. We observed two forms of carvedilol glucuronides, namely G1 and G2, in hepatic microsomes. The glucuronidation of carvedilol was catalyzed by at least three recombinant UGT isoforms: UGT1A1, UGT2B4, and UGT2B7. UGT2B4 formed both G1 and G2, whereas UGT1A1 and UGT2B7 were responsible for the formation of glucuronide G2 and G1, respectively. The enzyme kinetics for carvedilol glucuronidation by UGT1A1, UGT2B4, and UGT2B7 in addition to human liver microsomes were examined by Lineweaver-Burk analysis. The values of Km and Vmax for human liver microsomes were 26.6 microM and 106 pmol/min/mg protein for G1, and 46.0 microM and 44.5 pmol/min/mg protein for G2, respectively. The Km values for UGT1A1, UGT2B4, and UGT2B7 for G1 and G2 (22.1-55.1 microM) were comparable to those of the liver microsomes, whereas the Vmax values were in the range of 3.33 to 7.88 pmol/min/mg protein. The Km and Vmax/Km values for UGT2B4 and UGT2B7 for G1 were similar, whereas UGT2B4 had lower Km and higher Vmax/Km values for G2 compared with those of UGT1A1. These results suggest that G1 formation is catalyzed by UGT2B4 and UGT2B7, whereas G2 is formed by UGT2B4 and UGT1A1. These three hepatic UGT isoforms may have important roles in carvedilol metabolism.
卡维地洛（(+/-)-1-咔唑-4-基氧基）-3-[[2-(邻甲氧基苯氧基)乙基]氨基]-2-丙醇）主要代谢为葡糖醛酸共轭物。在本研究中，我们使用人肝脏微粒体或表达重组UGT同工型的昆虫细胞，通过薄层色谱法鉴定了参与卡维地洛葡糖醛酸化的人尿苷二磷酸葡糖醛酸基转移酶（UGT）同工型。我们在肝微粒体中观察到两种卡维地洛葡糖醛酸化物形式，即G1和G2。卡维地洛的葡糖醛酸化由至少三种重组UGT同工型催化：UGT1A1、UGT2B4和UGT2B7。UGT2B4形成G1和G2，而UGT1A1和UGT2B7分别负责葡糖醛酸化物G2和G1的形成。通过Lineweaver-Burk分析研究了UGT1A1、UGT2B4和UGT2B7以及人肝脏微粒体对卡维地洛葡糖醛酸化的酶动力学。人肝脏微粒体中G1的Km和Vmax值分别为26.6 microM和106 pmol/min/mg蛋白，G2的Km和Vmax值分别为46.0 microM和44.5 pmol/min/mg蛋白。UGT1A1、UGT2B4和UGT2B7对G1和G2的Km值（22.1 - 55.1 microM）与肝脏微粒体的Km值相当，而Vmax值在3.33至7.88 pmol/min/mg蛋白范围内。UGT2B4和UGT2B7对G1的Km和Vmax/Km值相似，而与UGT1A1相比，UGT对G2的Km值较低，Vmax/Km值较高。这些结果表明G1的形成由UGT2B4和UGT2B7催化，而G2由UGT2B以及UGT1A1形成。这三种肝脏UGT同工型可能在卡维地洛代谢中起重要作用。
