Walle T, Otake Y, Galijatovic A, Ritter J K, Walle U K
Department of Cell and Molecular Pharmacology and Experimental Therapeutics, Medical University of South Carolina, Charleston 29425, USA.
Drug Metab Dispos. 2000 Sep;28(9):1077-82.
The UDP-glucuronosyltransferases (UGTs) have long been known to be inducible by various chemicals, including drugs, although the extent of induction in general has been modest. In the present study, we determined the ability of the dietary flavonoid chrysin to induce UGT activity, protein and mRNA. When pretreating human hepatoma Hep G2 cells with 25 microM chrysin, the glucuronidation of chrysin itself increased 4.2-fold when measured in the intact cell and 14-fold in the cell homogenate, i.e., autoinduction. Microsomes from chrysin-treated cells probed with specific antibodies in Western analyses showed marked induction of the UGT1A family of proteins. Isoform-specific induction of the important hepatic UGT1A1 protein was observed but not of UGT1A6 or UGT2B7. The strong induction of UGT1A1 was confirmed by Northern analyses of total RNA as well as mRNA, using a specific probe. UGT1A1 message as well as protein was detectable also in untreated Hep G2 cells. In catalytic activity assays with recombinant UGT1A1, 1A4, 1A6 and 1A9, chrysin was found to be a high affinity substrate for UGT1A1 (K(m) 0.35 microM). Catalytic activity was also found for UGT1A9 and 1A6 but not for 1A4. Further studies demonstrated a 20-fold induction of the glucuronidation of bilirubin by the chrysin-treated cells and a 7. 9-fold induction of the glucuronidation of the oral contraceptive drug ethinylestradiol, two of the best known and specific UGT1A1 substrates, demonstrating the potential importance of this induction. In view of these findings, it will be important to extend these studies to other dietary flavonoids.
长期以来，人们已知UDP - 葡萄糖醛酸基转移酶（UGTs）可被包括药物在内的各种化学物质诱导，尽管总体诱导程度适中。在本研究中，我们测定了膳食类黄酮白杨素诱导UGT活性、蛋白质和mRNA的能力。用25 microM白杨素预处理人肝癌Hep G2细胞时，在完整细胞中测定，白杨素自身的葡萄糖醛酸化增加了4.2倍，在细胞匀浆中增加了14倍，即自身诱导。在蛋白质免疫印迹分析中，用特异性抗体检测白杨素处理细胞的微粒体，结果显示UGT1A蛋白家族有明显诱导。观察到重要的肝脏UGT1A1蛋白有同工型特异性诱导，但UGT1A6或UGT2B7没有。使用特异性探针，通过总RNA以及mRNA的Northern分析证实了UGT1A1的强烈诱导。在未处理的Hep G2细胞中也可检测到UGT1A1的信息和蛋白质。在用重组UGT1A1、1A4、1A6和1A9进行的催化活性测定中，发现白杨素是UGT1A1的高亲和力底物（K(m) 0.35 microM）。还发现UGT1A9和1A6有催化活性，但1A4没有。进一步研究表明，白杨素处理的细胞使胆红素葡萄糖醛酸化诱导了20倍，使口服避孕药炔雌醇葡萄糖醛酸化诱导了7.9倍，这两种是最知名且特异的UGT1A1底物，证明了这种诱导的潜在重要性。鉴于这些发现，将这些研究扩展到其他膳食类黄酮很重要。
