The role of xenoestrogenic compounds in the development of breast cancer

Carcinogenic health outcomes associated with endocrine disrupting chemicals exposure in humans: A wide-scope analysis

Endocrine-disrupting chemicals (EDCs) are persistent and pervasive compounds that pose serious risks. Numerous studies have explored the effects of EDCs on human health, among which tumors have been the primary focus. However, because of study design flaws, lack of effective exposure levels of EDCs, and inconsistent population data and findings, it is challenging to draw clear conclusions on the effect of these compounds on tumor-related outcomes. Our study is the first to systematically integrate observational studies and randomized controlled trials from over 20 years and summarize over 300 subgroup associations. We found that most EDCs promote tumor development, and that exposure to residential environmental pollutants may be a major source of pesticide exposure. Furthermore, we found that phytoestrogens exhibit antitumor effects. The findings of this study can aid in the development of global EDCs regulatory health policies and alleviate the severe risks associated with EDCs exposure.

Towards replacement of animal tests with in vitro assays: a gene expression biomarker predicts in vitro and in vivo estrogen receptor activity

High-throughput transcriptomics (HTTr) has the potential to support efforts to reduce or replace some animal tests. In past studies, we described a computational approach utilizing a gene expression biomarker consisting of 46 genes to predict estrogen receptor (ER) activity after chemical exposure in ER-positive human breast cancer cells including the MCF-7 cell line. We hypothesized that the biomarker model could identify ER activities of chemicals examined by Endocrine Disruptor Screening Program (EDSP) Tier 1 screening assays in which transcript profiles of the same chemicals were examined in MCF-7 cells. For the 62 chemicals examined including 5 chemicals examined in this study using RNA-Seq, the ER biomarker model accuracy was 1) 97% for in vitro reference chemicals, 2) 76-85% for guideline uterotrophic assays, and 3) 87-88% for guideline and nonguideline uterotrophic assays. For the same chemicals, these accuracies were similar or slightly better than those of the ToxCast ER model based on 18 in vitro assays. The performance of the ER biomarker model indicates that HTTr interpreted using the ER biomarker correctly identifies active and inactive ER reference chemicals. As part of the HTTr screening program the approach could rapidly identify chemicals with potential ER bioactivities for additional screening and testing.

Glyphosate induces human breast cancer cells growth via estrogen receptors

Glyphosate is an active ingredient of the most widely used herbicide and it is believed to be less toxic than other pesticides. However, several recent studies showed its potential adverse health effects to humans as it may be an endocrine disruptor. This study focuses on the effects of pure glyphosate on estrogen receptors (ERs) mediated transcriptional activity and their expressions. Glyphosate exerted proliferative effects only in human hormone-dependent breast cancer, T47D cells, but not in hormone-independent breast cancer, MDA-MB231 cells, at 10⁻¹² to 10⁻⁶M in estrogen withdrawal condition. The proliferative concentrations of glyphosate that induced the activation of estrogen response element (ERE) transcription activity were 5-13 fold of control in T47D-KBluc cells and this activation was inhibited by an estrogen antagonist, ICI 182780, indicating that the estrogenic activity of glyphosate was mediated via ERs. Furthermore, glyphosate also altered both ERα and β expression. These results indicated that low and environmentally relevant concentrations of glyphosate possessed estrogenic activity. Glyphosate-based herbicides are widely used for soybean cultivation, and our results also found that there was an additive estrogenic effect between glyphosate and genistein, a phytoestrogen in soybeans. However, these additive effects of glyphosate contamination in soybeans need further animal study.

Endocrine disruptors provoke differential modulatory responses on androgen receptor and pregnane and xenobiotic receptor: potential implications in metabolic disorders

A systematic comparison of the impact of some potential endocrine disruptors (EDs) on modulation of androgen receptor (AR) and pregnane and xenobiotic receptor (PXR) function was conducted in a multi-step analysis. Promoter-reporter-based transcription assays were performed in conjunction with receptor dynamic studies in living cells that helped implicating the suspected EDs for their deleterious effects. We demonstrate that most of the selected EDs not only inhibit AR transcriptional activity, but also alter its subcellular dynamics. Conversely, some of these anti-androgenic compounds were potent activator of xeno-sensing nuclear receptor, PXR. Interestingly, agonist-activated AR that associates with the mitotic chromatin fails to achieve this association when bound to anti-androgenic EDs. Conclusively, most EDs (except BCH) behaved like pure antagonist for AR while as agonist for PXR. Subsequent experiments with DDT treatment in mice model indicated that in testis AR and its regulated genes PEM and ODC levels are down-regulated, whereas in liver of same mice PEM is up-regulated while AR and ODC remain unchanged. On the contrary, PXR and its regulated genes CYP3A11 and MDR1 levels in mice liver were up-regulated while in testis PXR remained unchanged, CYP3A11 up-regulated and MDR1 were down-regulated. Based on a novel "Biopit" concept it is speculated that long-term exposure to endocrine disrupting chemicals may influence the epigenetic profile of target cells via transcription factors thereby making them vulnerable to onset of chemically induced endocrine-related malignancies or metabolic disorders.

Why pesticides could be a common cause of prostate and breast cancers in the French Caribbean Island, Martinique. An overview on key mechanisms of pesticide-induced cancer

Prostate and breast cancers have become very frequent in Martinique. We previously conducted a multifactorial analysis in the French Caribbean Island, Martinique, in order to elucidate the aetiology of prostate cancer. Using a linear regression analysis, we found that the growth curves of incidence rates for Martinique and metropolitan France have been significantly diverging since 1983. Although a Caribbean genetic susceptibility factor may be involved in prostate carcinogenesis: this factor, because it could not have changed during the observation period, cannot per se account for the growing incidence of this cancer in the island. We therefore suggested that among possible environmental factors, the intensive and prolonged exposure to Carcinogenic, Mutagenic and/or Reprotoxic (CMR) or presumed CMR pesticides may account for the observed growing incidence of prostate cancer and thus may be involved in prostate carcinogenesis. In this study, we further attempt to show that due to their carcinogenic properties, pesticides and especially organochlorine pesticides may in fact be causally implicated in the growing incidence of prostate cancer in Martinique. Also, we suggest that CMR or presumed CMR pesticides may be causally involved in the growing incidence of breast cancer through a common endocrine disruption mechanism. We therefore propose that protective medical recommendations should be immediately set up and carried out by general practitioners, paediatricians, obstetricians, gynaecologists and urologists; and that public health measures of primary precaution and prevention should be urgently taken in close collaboration with health professionals in order to protect population, more especially pregnant women and children, with the final objective perhaps that these medical recommendations and public health measures will stop Martinique's cancer epidemic.

Female reproductive disorders: the roles of endocrine-disrupting compounds and developmental timing

OBJECTIVE

To evaluate the possible role of endocrine-disrupting compounds (EDCs) on female reproductive disorders emphasizing developmental plasticity and the complexity of endocrine-dependent ontogeny of reproductive organs. Declining conception rates and the high incidence of female reproductive disruptions warrant evaluation of the impact of EDCs on female reproductive health.

DESIGN

Publications related to the contribution of EDCs to disorders of the ovary (aneuploidy, polycystic ovary syndrome, and altered cyclicity), uterus (endometriosis, uterine fibroids, fetal growth restriction, and pregnancy loss), breast (breast cancer, reduced duration of lactation), and pubertal timing were identified, reviewed, and summarized at a workshop.

CONCLUSION(S)

The data reviewed illustrate that EDCs contribute to numerous human female reproductive disorders and emphasize the sensitivity of early life-stage exposures. Many research gaps are identified that limit full understanding of the contribution of EDCs to female reproductive problems. Moreover, there is an urgent need to reduce the incidence of these reproductive disorders, which can be addressed by correlative studies on early life exposure and adult reproductive dysfunction together with tools to assess the specific exposures and methods to block their effects. This review of the EDC literature as it relates to female health provides an important platform on which women's health can be improved.

Ligand structure-dependent activation of estrogen receptor alpha/Sp by estrogens and xenoestrogens

This study investigated the effects of E2, diethylstilbestrol (DES), antiestrogens, the phytoestrogen resveratrol, and the xenoestrogens octylphenol (OP), nonylphenol (NP), endosulfan, kepone, 2,3,4,5-tetrachlorobiphenyl-4-ol (HO-PCB-Cl(4)), bisphenol-A (BPA), and 2,2-bis-(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE) on induction of luciferase activity in breast cancer cells transfected with a construct (pSp1(3)) containing three tandem GC-rich Sp binding sites linked to luciferase and wild-type or variant ERalpha. The results showed that induction of luciferase activity was highly structure-dependent in both MCF-7 and MDA-MB-231 cells. Moreover, RNA interference assays using small inhibitory RNAs for Sp1, Sp3 and Sp4 also demonstrated structure-dependent differences in activation of ERalpha/Sp1, ERalpha/Sp3 and ERalpha/Sp4. These results demonstrate for the first time that various structural classes of ER ligands differentially activate wild-type and variant ERalpha/Sp-dependent transactivation, selectively use different Sp proteins, and exhibit selective ER modulator (SERM)-like activity.

Mouse N-acetyltransferase type 2, the homologue of human N-acetyltransferase type 1

There is increasing evidence that human arylamine N-acetyltransferase type 1 (NAT1, EC 2.3.1.5), although first identified as a homologue of a drug-metabolising enzyme, appears to be a marker in human oestrogen receptor positive breast cancer. Mouse Nat2 is the mouse equivalent of human NAT1. The development of mouse models of breast cancer is important, and it is essential to explore the biological role of mouse Nat2. We have therefore produced mouse Nat2 as a recombinant protein and have investigated its substrate specificity profile in comparison with human NAT1. In addition, we have tested the effects of inhibitors on mouse Nat2, including compounds which are endogenous and exogenous steroids. We show that tamoxifen, genistein and diethylstilbestrol inhibit mouse Nat2. The steroid analogue, bisphenol A, also inhibits mouse Nat2 enzymic activity and is shown by NMR spectroscopy, through shifts in proton peaks, to bind close to the active site. A three-dimensional structure for human NAT1 has recently been released, and we have used this crystal structure to generate a model of the mouse Nat2 structure. We propose that a conformational change in the structure is required in order for ligands to bind to the active site of the protein.

A novel molecular assay to discriminate transcriptional effects caused by xenoestrogens

A phenotypic definition of the term estrogen has become increasingly problematic due to the multiple modes of estrogen action which can now be defined by differing nuclear and membrane receptors for the classic ligand, 17beta-estradiol, and by the multiple signalling pathways that are consequently addressed. This has led to the term xenoestrogen being largely determined by whatever assay system is used for its definition. Here we describe a novel and simple matrix for a transfection system using MBA-MD231 and MCF-7 breast cancer cells as hosts. This matrix is able to vary the type of nuclear estrogen receptor used, and by varying the promoter-reporter construct between one using a classic estrogen response element (ERE) enhancer, and one using an enhancer element derived from the bovine oxytocin gene promoter binding an orphan nuclear receptor, direct classical effects can be neatly discriminated from non-classical and non-genomic actions of test substances. This assay matrix has been used to examine a selection of phytoestrogens and xenobiotics, thereby providing new information on the mechanism of action of some of these substances in breast cancer cells.