Endocrine Disrupting Chemicals : Interaction with Estrogen Receptors an in vitro Assessment of Endocrine Activity Potential

Abstract

The endocrine system is a complex set of hormone-producing glands that regulate biological processes in the body from conception through adulthood into old age, including the development of brain and nervous apparatus, the growth and the function of the reproductive system, as well as the metabolism and blood sugar levels. Furthermore, estrogen, one of these hormones, regulate a variety of biological processes, influencing growth, differentiation and function of target tissues, where they interact with nuclear estrogen receptors (ERs), ERa and ERb, which act as transcription factors. Moreover, in the environment there are exogenous agents which could interfere with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body. These endocrine disrupting chemicals (EDC) might interfere and disrupt the physiological hormonal pathway, acting also on ERs. In this study we investigated the estrogen-like properties of four xenoestrogens, classified as enviromental contaminants (diethylstilbestrol, hexestrol, coumestrol, phosalone), on human MCF-7 cells, using a combination of proliferative assay, gene and protein expression of estrogen receptors and protein modulation of estrogen-responsive genes, like c-myc and p21. All tested compounds showed a proliferative effect in MCF-7 cells and acted as ligands for estrogen receptors; moreover, they act as cell-cycle modulators. We observed that proliferative response of MCF-7 cells, after treatment with tested compounds, is in agreement with the rank of potency predicted by other tests (QSARs analysis, receptor binding assay and transactivation assay) confirming that the described test is a predictive tool to assess estrogenic activity.Moreover, we analysed estrogen receptor modulation. The most relevant result was the up-regulation of the ERb in response to the treatment with 10µM phosalone, the compound that induced the least proliferative effect. ERb might attenuate ERa-induced proliferation and affects cell-cycle progression. Furthermore, c-myc and p21 modulation indicate that the observed proliferative effect correlates with c-myc induction, while p21 was not affected ruling out a contribution to proliferation limiting effects. These results suggest analysing both in vitro proliferation and molecular endpoints, to estimate the effet of xenoestrogens.