[Effect of isoflavones in regulating the transcription of target genes through estrogen receptors]

Diverse animal models to examine potential role(s) and mechanism of endocrine disrupting chemicals on the tumor progression and prevention: Do they have tumorigenic or anti-tumorigenic property?

Acting as hormone mimics or antagonists in the interaction with hormone receptors, endocrine disrupting chemicals (EDCs) have the potentials of disturbing the endocrine system in sex steroid hormone-controlled organs and tissues. These effects may lead to the disruption of major regulatory mechanisms, the onset of developmental disorders, and carcinogenesis. Especially, among diverse EDCs, xenoestrogens such as bisphenol A, dioxins, and di(2-ethylhexyl)phthalate, have been shown to activate estrogen receptors (ERs) and to modulate cellular functions induced by ERs. Furthermore, they appear to be closely related with carcinogenicity in estrogen-dependant cancers, including breast, ovary, and prostate cancers. In in vivo animal models, prenatal exposure to xenoestrogens changed the development of the mouse reproductive organs and increased the susceptibility to further carcinogenic exposure and tumor occurence in adults. Unlike EDCs, which are chemically synthesized, several phytoestrogens such as genistein and resveratrol showed chemopreventive effects on specific cancers by contending with ER binding and regulating normal ER action in target tissues of mice. These results support the notion that a diet containing high levels of phytoestrogens can have protective effects on estrogen-related diseases. In spite of the diverse evidences of EDCs and phytoestrogens on causation and prevention of estrogen-dependant cancers provided in this article, there are still disputable questions about the dose-response effect of EDCs or chemopreventive potentials of phytoestrogens. As a wide range of EDCs including phytoestrogens have been remarkably increasing in the environment with the rapid growth in our industrial society and more closely affecting human and wildlife, the potential risks of EDCs in endocrine disruption and carcinogenesis are important issues and needed to be verified in detail.

Estrogen-like activities of saikosaponin-d in vitro: a pilot study

Saikosaponin-d (SSd), a saponin derivative with a similar structure to estradiol, was extracted from Bupleurum falcatum L. (Umbelliferae). It was found that SSd stimulated the proliferation of MCF-7 cells by using MCF-7 cell proliferation assay. Cell-cycle analysis revealed that the proliferation-stimulating effect was associated with a marked increase in the number of MCF-7 cells in S phase. These actions of SSd were dose-dependent at doses ranging from 10nM to 10 microM and could be significantly inhibited by the specific estrogen receptor (ER) antagonist ICI-182780. Co-incubation of MCF-7 cells with 1 microM of ER antagonist ICI-182780 abolished the inductive effects of SSd on estrogen response element (ERE)-luciferase activity, suggesting that the estrogenic effects of SSd were mediated through the estrogen receptors. To evaluate the relative involvement of estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) in mediating the actions of SSd, ER-negative human cervical carcinoma (HeLa) cells were cotransfected with the ERE-luciferase reporter construct and either ERalpha or ERbeta construct. The results showed that SSd could activate ERE-luciferase activity via the ERalpha-mediated pathway in a dose-dependent manner (10 nM to 10 microM); whereas, the activation of ERbeta-mediated ERE-luciferase activity by SSd only occurred at a high concentration (10 microM). Furthermore, the ERalpha protein and mRNA levels were increased by treatment with SSd within 24h. These data support our hypothesis that SSd acts as a weak phytoestrogen. Presumably, the estrogenic effect of SSd is mediated by the estrogen receptor.