Dornstauder E, Jisa E, Unterrieder I, Krenn L, Kubelka W, Jungbauer A
Institute of Applied Microbiology, University of Agricultural Sciences, Muthgasse 18, A-1190 Vienna, Austria.
J Steroid Biochem Mol Biol. 2001 Jul;78(1):67-75. doi: 10.1016/s0960-0760(01)00075-9.
Isoflavones are the most potent estrogenic compounds in red clover extracts. Standardized extracts have been discussed as an alternative for hormone replacement therapy. Variation due to extraction procedure and natural seasonal variation and variations originating from agricultural conditions have prevented the large scale use of such phytochemicals. An improved extraction procedure and careful analysis of the raw material yielded in a highly standardized preparation (Menoflavon) with an average isoflavone content of approximately 9% (dry weight) determined by HPLC. The estrogenic activity has been further evaluated by a yeast two plasmid system using estrogen receptor alpha (ER alpha) and estrogen receptor beta (ER beta). An estrogenic activity corresponding to a transactivational capacity of ca. 18 microg 17 beta-estradiol per g red clover extract for ER alpha and ca. 78 microg 17 beta-estradiol per g red clover for ER beta was obtained. The difference is explained by the higher affinity of ER beta to isoflavones than that observed for ER alpha. Calculation of potency from isoflavone content measured by HPLC yielded a comparable potency to that experimentally determined by the bioassay. The high content of isoflavones as well as the higher transactivational potency for ER beta than ER alpha make these extracts interesting candidates for HRT.
异黄酮是红三叶草提取物中最具活性的雌激素类化合物。标准化提取物已被讨论作为激素替代疗法的一种替代物。由于提取过程、自然季节变化以及源自农业条件的变化，阻碍了此类植物化学物质的大规模使用。一种改进的提取方法以及对原材料的仔细分析，得到了一种高度标准化的制剂（Menoflavon），通过高效液相色谱法测定其平均异黄酮含量约为9%（干重）。通过使用雌激素受体α（ERα）和雌激素受体β（ERβ）的酵母双质粒系统进一步评估了雌激素活性。对于ERα，每克红三叶草提取物的雌激素活性相当于约18微克17β - 雌二醇的反式激活能力；对于ERβ，每克红三叶草提取物的雌激素活性相当于约78微克17β - 雌二醇的反式激活能力。这种差异的解释是，ERβ对异黄酮的亲和力高于ERα。根据高效液相色谱法测定的异黄酮含量计算效力，得到的效力与生物测定实验确定的效力相当。异黄酮的高含量以及ERβ比ERα更高的反式激活效力，使得这些提取物成为激素替代疗法的有趣候选物。
