Screening of estrogenic and antiestrogenic activities from medicinal plants

Abstract

The medicinal plant extracts commercially used in Asia were screened for their estrogenic and antiestrogenic activities in a recombinant yeast system featuring both a human estrogen receptor (ER) expression plasmid and a reporter plasmid. Pueraria lobata (flower) had the highest estrogenic relative potency (RP, 7.75 × 10⁻³; RP of 17β-estradiol = 1), followed by Amomum xanthioides (1.25 × 10⁻³). Next potent were a group consisting of Glycyrrhiza uralensis, Zingiber officinale, Rheum undulatum, Curcuma aromatica, Eriobotrya japonica, Sophora flavescens, Anemarrhena asphodeloides, Polygonum multiflorum, and Pueraria lobata (root) (ranging from 9.5 × 10⁻⁴ to 1.0 × 10⁻⁴). Least potent were Prunus persica, Lycoppus lucidus, and Adenophora stricta (ranging from 9.0 × 10⁻⁵ to 8.0 × 10⁻⁵). The extracts exerting antiestrogenic effects, Cinnamomum cassia and Prunus persica, had relative potencies of 1.14 × 10⁻³ and 7.4 × 10⁻⁴, respectively (RP of tamoxifen = 1). The solvent fractions from selected estrogenic or antiestrogenic herbs had higher estrogenic relative potencies, with their RP ranging from 9.3 × 10⁻¹ to 2.7 × 10⁻⁴ and from 8.2 × 10⁻¹ to 9.1 × 10⁻³, respectively. These results support previous reports on the efficacy of Oriental medicinal plants used or not used as phytoestrogens for hormone replacement therapy.

Introduction

The estrogen, androgen and progesterone receptors, members of the nuclear receptor (NRs) superfamily, act as nuclear transport proteins, cell cycle components, and transcription factors (Fu et al., 2003). Most cellular actions of sex steroid hormones are mediated through binding to nuclear receptors that act as ligand-inducible transcription factors (Aranda and Pascual, 2001). Estrogen plays an important role in the growth, differentiation and function of many bodily targets, including the female and male reproductive systems. Estrogen also has a variety of pharmacological functions, such as maintenance of bone mass, cardiovascular protection, and brain protection (Ciocca and Roig, 1995, Smith et al., 1996). Estrogen deficiency during menopause can lead to risk for many health problems, such as hot flushes, sleeping disorders, vaginal dryness, joint pain, mood swings, reduced bone density, cardiovascular disease, etc. (Eaker et al., 1993, Palacios, 1999, Rymer et al., 2003).

Phytoestrogens are a new category of therapeutic agents available for the prevention and treatment of diseases such as osteoporosis and breast cancer (Jordan, 2004). It has been found that natural compounds known as phytoestrogens, obtained from certain plants and possessing estrogen-like activity (Paola and David, 2002), can be used for the management of menopausal symptoms with few side effects (Thompson, 1993, Glazier and Bowman, 2001). However, many phytoestrogens and environmental xenoestrogens also have been shown to increase the risk of breast cancer in women and to affect the reproductive systems in general (Hileman, 1996). Early studies noted adverse effects on fertility in animals that had been grazing on plants rich in phytoestrogens. Today, there is a wide interest in phytoestrogens for their potential health benefits in countering menopausal symptoms (Bennetts et al., 1946, Adlercreutz and Mazur, 1997). Phytoestrogens share the basic frame of other steroid hormones, although their potencies are estimated to be approximately 1000-fold weaker than that of 17β-estradiol (Lindner, 1976). To date, more than 300 plants have been found that possess compounds with estrogenic activity (Farnsworth et al., 1975, Price and Fenwich, 1985). Several classes of phytoestrogens have been identified and studied: the hormone-like bisphenolic phytoestrogens, the isoflavonoids daidzein and genistein, coumestrol, and the lignans and matairesinols are of great interest because of their respective estrogenic, antiestrogenic, anti-carcinogenic, and antioxidant activities (Adlercreutz, 1984, Adlercreutz et al., 1982, Setchell et al., 1980, Setchell et al., 1981, Whitten and Naftolin, 1991). Moreover, these phytoestrogens are structurally and functionally similar to estrogen (Knight and Eden, 1996).

Among the in vivo and in vitro assays that have been developed to test estrogenic substances, the binding of a ligand to estrogen receptor is the simplest and is suitable for screening of estrogen and antiestrogenic substances. Yeast cells carrying the human estrogen receptor (hER) gene, estrogen response elements (ERE) and Escherichia coli β-galactosidase gene (lacZ) are very suitable for large-scale screening and sensitive analysis of estrogenic compounds, and this model system has proven useful for the assay and discovery of novel estrogenic substances in Oriental medicinal plants (Routledge and Sumpter, 1996, Breithofer et al., 1998, Zhang et al., 2005).

In this study, 94 medicinal plants commonly used in Asia were screened to determine their ability to regulate estrogenic activity, and 14 plants showed significant effects. In addition, the estrogenic activities of solvent fractions from eight selected estrogenic and two selected antiestrogenic plants, which are not well reported for estrogenic or antiestrogenic effects, were investigated in order to better assess their largely undetermined effects.