Zhang Yan, Hendrich Suzanne, Murphy Patricia A
Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011, USA.
J Nutr. 2003 Feb;133(2):399-404. doi: 10.1093/jn/133.2.399.
Three experiments were conducted to characterize the metabolism of isoflavones from soy milk in women: two meals in 2 wk separated by a 1-wk washout period (Experiment 1), one meal feeding (Experiment 2) and six consecutive days of feeding (Experiment 3). Urine and plasma samples were extracted directly or predigested before extraction with H-2 beta-glucuronidase/sulfatase or B-3 beta-glucuronidase so that isoflavone glucuronide and sulfate conjugates could be determined by difference. Among the three experiments, no significant differences were found in the proportion of glucuronide, sulfate and aglycone isoflavones recovered from plasma samples taken 3 h after isoflavone dosing or in 24-h urine samples taken after isoflavone dosing. In the 6-d feeding study, samples taken on d 5 and 6 did not differ significantly in isoflavone content or proportion of the metabolites studied. The percentages of daidzein and genistein glucuronides were 73 +/- 4 and 71 +/- 5% of total daidzein and genistein excreted in urine, and 62 +/- 4 and 53 +/- 6% of total daidzein and genistein present in plasma, respectively. Percentages of aglycone daidzein and genistein were 4 +/- 1 and 5 +/- 1% of total daidzein and genistein in urine, and 18 +/- 2 and 26 +/- 7% of total daidzein and genistein present in plasma, respectively. These studies showed that about one fifth of circulating isoflavones are aglycones. Concentrations of isoflavones chosen for in vitro studies should take this into account. Because the glucuronide isoflavones predominate in vivo, these metabolites should not be overlooked as possible contributors to observed effects of isoflavones.
在2周内分两餐进食，中间间隔1周的洗脱期（实验1），一餐进食（实验2）以及连续六天进食（实验3）。尿液和血浆样本在提取前直接进行提取或预先用H-2β-葡萄糖醛酸酶/硫酸酯酶或B-3β-葡萄糖醛酸酶进行消化，以便通过差值法测定异黄酮葡萄糖醛酸苷和硫酸酯共轭物。在这三项实验中，在异黄酮给药后3小时采集的血浆样本或异黄酮给药后采集的24小时尿液样本中，回收的葡萄糖醛酸苷、硫酸酯和苷元异黄酮的比例没有显著差异。在为期6天的喂养研究中，第5天和第6天采集的样本在异黄酮含量或所研究代谢物的比例方面没有显著差异。大豆苷元和染料木黄酮葡萄糖醛酸苷的百分比分别占尿液中排泄的大豆苷元和染料木黄酮总量的73±4%和71±5%，以及血浆中大豆苷元和染料木黄酮总量的62±4%和53±6%。大豆苷元和染料木黄酮苷元的百分比分别占尿液中大豆苷元和染料木黄酮总量的4±1%和5±1%，以及血浆中大豆苷元和染料木黄酮总量的18±2%和26±7%。这些研究表明，循环异黄酮中约五分之一是苷元。体外研究中选择的异黄酮浓度应考虑到这一点。由于葡萄糖醛酸苷异黄酮在体内占主导地位，这些代谢物作为异黄酮观察到的效应的可能贡献者不应被忽视。
