Bioassay of phytoestrogen in herbal medicine used for postmenopausal disorder using transformed MCF-7 cells

It is well known that plants contain substances with oestrogen activity comparable to that in animals. In animals, oestrogens are steroid hormones while plants contain oestrogen with various chemical characteristics, referred to as phytoestrogens. These especially, may be responsible for part of the effects of Chinese herbal prescriptions for postmenopausal disorders in which oestrogen deficiency is considered the primary cause. In addition, the presence or absence of oestrogen activity in herbal medicine is considered extremely important for patients in whom oestrogen administration is contraindicated. The most important action of oestrogen is the transcriptional regulation of specific genes via oestrogen receptors (ER). Therefore, we have established a highly sensitive bioassay system by placing oestrogen responsive elements (ERE) upstream to the reporter gene, and have used this assay to determine the oestrogen activity in herbal medicine. As a result, phytoestrogens were found in many Chinese herbal prescriptions for postmenopausal disorder, and some prescriptions were considered to effectively administer hormone replacement therapy (HRT). However, since oestrogen activities in most Chinese herbal prescriptions were thought to be weak, it was considered that these prescriptions improved postmenopausal disorder based on a mechanism differing from that of oestrogen replacement therapy.