Regulation of HOXA10 expression by phytoestrogens

Comparative study of estrogenic activities of phytoestrogens using OECD in vitro and in vivo testing methods

With growing scientific interest in phytoestrogens, a number of studies have investigated the estrogenic potential of phytoestrogens in a wide variety of assay systems. However, evaluations of individual phytoestrogens with different assay systems make it difficult for predicting their relative estrogenic potency. The objective of this study was to compare estrogenic properties of fifteen known phytoestrogens using an estrogen receptor-α (ER-α) dimerization assay and Organization for Economic Cooperation and Development (OECD) standardized methods including in vitro estrogen receptor (ER) transactivation assay using VM7Luc4E2 cells and in vivo uterotrophic assay using an immature rat model. Human ER-α dimerization assay showed positive responses of eight test compounds and negative responses of seven compounds. These results were consistently found in luciferase reporter assay results for evaluating ER transactivation ability. Seven test compounds exhibiting relatively higher in vitro estrogenic activities were subjected to uterotrophic bioassays. Significant increases in uterine weights were only found after treatments with biochanin A, 8-prenylnaringenin, and coumestrol. Importantly, their uterotrophic effects were lost when animals were co-treated with antagonist of ER, indicating their ER-dependent effects in the uterus. In addition, analysis of estrogen responsive genes revealed that these phytoestrogens regulated uterine gene expressions differently compared to estrogens. Test methods used in this study provided a high consistency between in vitro and in vivo results. Thus, they could be used as effective screening tools for phytoestrogens, particularly focusing on their interactions with ER-α.

Two faces of the estrogen metabolite 2-methoxyestradiol in vitro and in vivo

2-Methoxyestradiol (2-ME), an endogenous metabolite of 17β-estradiol (E2), interacts with estrogen receptors (ERs) and microtubules, however, 2-ME has a low affinity for ERs. Furthermore, 2‑ME has been identified as a potential novel antitumor agent, combining its anti‑proliferative effects on a variety of tumor cell types with its anti‑angiogenic action. Therefore, 2‑ME is of interest due to its potential anticancer therapeutic effects. In the current study, the estrogenic effect of 2‑ME on CaBP‑9k, ERα, and progesterone receptor (PR) mRNA levels in the absence and presence of E2 and progesterone (P4) in in vivo and in vitro models was examined. In GH3 cells, the mRNA level of CaBP‑9k was induced in the E2 treatment group (concentration, 10‑9 M), and the expression of CaBP‑9k was also upregulated in the 2‑ME‑treated group (concentration, 10‑7 M). Uterine lactoferrin (Ltf) mRNA expression was also increased in the 2‑ME group [dose, 40 mg/kg body weight (BW)], which was comparable to the response with E2 (dose, 40 µg/kg BW) observed in mice. As inhibitors of ER and PR activity, ICI 182,780 and mifepristone (RU486) were observed to reverse the E2 or 2‑ME mediated increase of CaBP‑9k and Ltf mRNA expression. In addition, it was found that 2‑ME significantly decreased the levels of ERα and increased PR transcripts. Consistent with the in vitro results, the mRNA levels revealed decreased ERα and increased PR in in vivo treatment of E2 and 2‑ME. These findings demonstrate that the expression of estrogenic markers, CaBP‑9k and Ltf, is regulated by 2‑ME in in vitro and in vivo models, therefore, estrogenic activi-ties of 2-ME may be increased in females during the estrous cycle via the ER and/or PR-mediated signaling pathway.

Studying the effects of genistein on gene expression of fish embryos as an alternative testing approach for endocrine disruption

Assessment of endocrine disruption currently relies on testing strategies involving adult vertebrates. In order to minimize the use of animal tests according to the 3Rs principle of replacement, reduction and refinement, we propose a transcriptomics and fish embryo based approach as an alternative to identify and analyze an estrogenic activity of environmental chemicals. For this purpose, the suitability of 48 h and 7 days post-fertilization zebrafish and medaka embryos to test for estrogenic disruption was evaluated. The embryos were exposed to the phytoestrogen genistein and subsequently analyzed by microarrays and quantitative real-time PCR. The functional analysis showed that the genes affected related to multiple metabolic and signaling pathways in the early fish embryo, which reflect the known components of genistein's mode of actions, like apoptosis, estrogenic response, hox gene expression and steroid hormone synthesis. Moreover, the transcriptomic data also suggested a thyroidal mode of action and disruption of the nervous system development. The parallel testing of two fish species provided complementary data on the effects of genistein at gene expression level and facilitated the separation of common from species-dependent effects. Overall, the study demonstrated that combining fish embryo testing with transcriptomics can deliver abundant information about the mechanistic effects of endocrine disrupting chemicals, rendering this strategy a promising alternative approach to test for endocrine disruption in a whole organism in-vitro scale system.

Reproductive consequences of developmental phytoestrogen exposure

Phytoestrogens, estrogenic compounds derived from plants, are ubiquitous in human and animal diets. These chemicals are generally much less potent than estradiol but act via similar mechanisms. The most common source of phytoestrogen exposure to humans is soybean-derived foods that are rich in the isoflavones genistein and daidzein. These isoflavones are also found at relatively high levels in soy-based infant formulas. Phytoestrogens have been promoted as healthy alternatives to synthetic estrogens and are found in many dietary supplements. The aim of this review is to examine the evidence that phytoestrogen exposure, particularly in the developmentally sensitive periods of life, has consequences for future reproductive health.

Endocrine disruptors and spontaneous premature labor: a case control study

BACKGROUND

Premature labor is a poorly understood condition. Estrogen is thought to play a key role and therefore the labor process may be affected by endocrine disruptors. We sought to determine whether or not an environmental toxicant, DDE, or dietary derived endocrine disruptors, daidzein and genistein, are associated with spontaneous preterm labor.

METHODS

Cases were defined as primiparous patients having a preterm delivery at or before 35 weeks following the spontaneous onset of labor. Controls were defined as primiparous women who delivered on the same day as the cases but at term gestation. Over approximately 1 year, 26 cases and 52 controls were recruited. Subjects agreed to have blood tests on day one postpartum for DDE and for the phytoestrogens genistein and daidzein.

RESULTS

The mean concentration of DDE was similar in the case and control groups: 4.29 vs 4.32 ng/g lipid p = .85. In the case group, 13/26 had detectable levels of daidzein (range 0.20 - 1.56 ng/ml) compared to 25/52 controls (range 0.21 - 3.26 ng/ml). The mean concentration of daidzein was similar in cases compared to controls: 0.30 vs .34 ng/ml p = 0.91. Of the case group,14/26 had detectable levels of genistein (range 0.20 - 2.19 ng/ml) compared to 32/52 controls (range 0.21 - 2.55 ng/ml). The mean concentration of genistein was similar in cases compared to controls: 0.39 vs 0.31 ng/ml, p = 0.61.

CONCLUSION

The serum levels of DDE in this population were found to be low. There appears to be no relationship between serum concentrations of DDE, daidzein, and genistein and spontaneous preterm labor in our population. The inability to identify an effect may be related to the comparatively low concentrations of DDE in our population and the rapid and variable reduction of phytoestrogens from women in labor.