4-Hydroxytamoxifen-induced cytotoxicity and bisphenol A: competition for estrogen receptors in human breast cancer cell lines

Diethylhexyl Phthalate and Bisphenol A Promote Vincristine and Tamoxifen Resistance in Vitro

Environmental estrogen active compounds are strong determinants of estrogen receptor (ER)-positive breast cancers, and increased evidence indicates their contribution to chemotherapy resistance. In the current study, the efficacy of vincristine and tamoxifen, with the presence of diethylhexyl phthalate (DEHP) and bisphenol A (BPA) and the possible involvement of estrogen and estrogen receptor-related mechanisms, was evaluated in an ER+ mammary tumor cancer cell line, MCF-7. Chemotherapeutics tamoxifen as an estrogen receptor modulator and vincristine as an antimitotic compound were selected for evaluation against the presence of common endocrine disrupters. BPA and DEHP preincubation at their proliferative concentrations for 4 h was found to decrease the cytotoxicity of vincristine. mRNA and protein expression of ESR1 and ESR 2 were decreased by vincristine, while this decrease was reversed by DEHP and BPA. Both BPA and DEHP were able to interfere with the cytotoxic activity of vincristine against MCF-7 cells through ESR1 and ESR2. This study provides in vitro toxicological evidence for vincristine resistance and its relation to estrogen active environmental pollutants in ER+ breast cancer cells.

Concentrations of perfluoroalkyl substances and bisphenol A in newborn dried blood spots and the association with child behavior

Experimental studies suggest that prenatal exposure to endocrine disrupting chemicals interferes with developmental processes in the fetal brain. Yet, epidemiological evidence is inconclusive. In a birth cohort (2008-2010, upstate New York), we quantified concentrations of perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and bisphenol A (BPA) in stored newborn dried blood spots using liquid chromatography/tandem mass spectrometry. Mothers reported on children's behavior using the Strengths and Difficulties Questionnaire at age 7 (650 singletons and 138 twins). Difficulties in total behavior (i.e., emotional, conduct, hyperactivity, and peer problems) and prosocial behavior were classified using validated cut-offs. We used logistic regression with generalized estimating equations to estimate the odds of having difficulties per exposure category. In total, 111 children (12.1%) had total behavioral difficulties and 60 (6.5%) had difficulties in prosocial behavior. The median (interquartile range) of PFOS, PFOA, and BPA were 1.74 ng/ml (1.33), 1.12 ng/ml (0.96), and 7.93 ng/ml (10.79), respectively. Higher PFOS levels were associated with increased odds of having behavioral difficulties (OR per SD of log PFOS = 1.30, 95%CI: 1.03-1.65). We observed associations between PFOS in the highest relative to the lowest quartile and behavioral difficulties (OR for PFOS_1.14-1.74 = 1.65, 95%CI: 0.84-3.34; PFOS_1.75-2.47 = 1.73, 95%CI: 0.87-3.43; and PFOS_>2.47 = 2.47, 95%CI: 1.29-4.72 compared to PFOS_<1.41). The associations between higher concentrations of PFOS and behavioral difficulties at age 7 years were driven by problems in conduct and emotional symptoms. Higher PFOA levels were associated with difficulties in prosocial behavior (OR = 1.35, 95%CI: 1.03-1.75). There was an inverse association between BPA concentrations and difficulties in prosocial behavior but only in the 2nd and 4th quartiles. We found no interactions between sex and chemical concentrations. Increasing prenatal exposure to PFOS and PFOA, as reflected in neonatal concentrations, may pose risk for child behavioral difficulties.

Disruption in Thyroid Signaling Pathway: A Mechanism for the Effect of Endocrine-Disrupting Chemicals on Child Neurodevelopment

Thyroid hormones are crucial in normal brain development. Transient and mild thyroid hormone insufficiency in pregnancy is also associated with impaired neurodevelopment in the offspring (e.g., 3-4 IQ score loss in association with maternal free thyroxine in the lowest fifth percentile). While inadequate iodine intake remains the most common underlying cause of mild thyroid hormone insufficiency in vulnerable populations including pregnant women, other factors such as exposure to environmental contaminants have recently attracted increasing attention, in particular in interaction with iodine deficiency. Endocrine-disrupting chemicals (EDCs) are natural and synthetic substances with ubiquitous exposure in children and adults including pregnant women. EDCs interfere, temporarily or permanently, with hormonal signaling pathways in the endocrine system by binding to hormone receptors and modifying gene expression. Other mechanisms involve alterations in production, metabolism, and transfer of hormones. Experimental studies have shown that exposures to EDCs affect various brain processes such as neurogenesis, neural differentiation and migration, as well as neural connectivity. Neuroimaging studies confirm brain morphological abnormalities (e.g., cortical thinning) consistent with neurodevelopmental impairments as a result of EDC exposures at standard use levels. In this review, we provide an overview of present findings from toxicological and human studies on the anti-thyroid effect of EDCs with a specific attention to fetal and early childhood exposure. This brief overview highlights the need for additional multidisciplinary studies with a focus on thyroid disruption as an underlying mechanism for developmental neurotoxicity of EDC, which can provide insight into modifiable risk factors of developmental delays in children.

Nonsteroidal estrogen receptor isoform-selective biphenyls

Estrogen receptor (ER) has been a therapeutic target to treat ER-positive breast cancer, most notably by agents known as selective estrogen receptor modulators (SERMs). However, resistance and severe adverse effects of known drugs gave impetus to the search for newer agents with better therapeutic profile. ERα and ERβ are two isoforms sharing 56% identity and having different physiological functions and expressions in various tissues. Only two residues differ in the active sites of the two isoforms motivating us to design isoform-selective ligands. Guided by computational docking and molecular dynamics simulations, we have designed, synthesized, and tested, substituted biphenyl-2,6-diethanones and their derivatives as potential agents targeting ERα. Four of the molecules synthesized exhibited preferential cytotoxicity in ERα+ cell line (MCF-7) compared to ERβ+ cell line (MDA-MB-231). Molecular dynamics (MD) in combination with molecular mechanics-generalized Born surface area (MM-GBSA) methods could account for binding selectivity. Further cotreatment and E-screen studies with known ER ligands-estradiol (E₂ ) and tamoxifen (Tam)-indicated isoform-selective anti-estrogenicity in ERα+ cell line which might be ER-mediated. ERα siRNA silencing experiments further confirmed the ER selective nature of ligands.

The relationship between urinary bisphenol A levels and meningioma in Chinese adults

BACKGROUND

Estrogen has been implicated as a risk factor for meningioma. Bisphenol A (BPA), a widely used synthetic xenoestrogen, has already been reported to be associated with several estrogen-sensitive tumors.

METHOD

An exploratory association study of 243 meningioma cases and 258 frequency-matched healthy controls was conducted, using subjects from a hospital-based study to demonstrate the association of urine BPA concentration and the risk of meningioma. The specimens and data of patients were collected at Union Hospital, Wuhan, China, from 2009 to 2010.

RESULTS

A positive association between increasing levels of urinary BPA and meningioma was observed, independent of confounding factors such as gender, age, race, body mass index, HRT use, BMI, and family history of cancer. Compared to quartile 1 (referent), the multivariate-adjusted odds ratio of meningioma associated with quartile 4 was 1.45 (95 % CI, 1.02-1.98) (P trend = 0.03).

CONCLUSION

In this case-control study from China, a clear association between urinary BPA concentrations and diagnosis of meningioma was detected.

Bisphenol A, an endocrine-disrupting chemical, and brain development

Bisphenol A (BPA) is an endocrine-disrupting chemical, widely used in various industries and the field of dentistry. The consequent increase in BPA exposure among humans has led us to some concerns regarding the potential deleterious effects on reproduction and brain development. The emphasis of this review is on the effects of prenatal and lactational exposure to low doses of BPA on brain development in mice. We demonstrated that prenatal exposure to BPA affected fetal murine neocortical development by accelerating neuronal differentiation/migration during the early embryonic stage, which was associated with up- and down-regulation of the genes critical for brain development, including the basic helix-loop-helix transcription factors. In the adult mice brains, both abnormal neocortical architecture and abnormal corticothalamic projections persisted in the group exposed to the BPA. Functionally, BPA exposure disturbed murine behavior, accompanied with a disrupted neurotransmitter system, including monoamines, in the postnatal development period and in adult mice. We also demonstrated that epigenetic alterations in promoter-associated CpG islands might underlie some of the effects on brain development after exposure to BPA.

Activation of the mTOR pathway by low levels of xenoestrogens in breast epithelial cells from high-risk women

Breast cancer is an estrogen-driven disease. Consequently, hormone replacement therapy correlates with disease incidence. However, increasing male breast cancer rates over the past three decades implicate additional sources of estrogenic exposure including wide spread estrogen-mimicking chemicals or xenoestrogens (XEs), such as bisphenol-A (BPA). By exposing renewable, human, high-risk donor breast epithelial cells (HRBECs) to BPA at concentrations that are detectable in human blood, placenta and milk, we previously identified gene expression profile changes associated with activation of mammalian target of rapamycin (mTOR) pathway genesets likely to trigger prosurvival changes in human breast cells. We now provide functional validation of mTOR activation using pairwise comparisons of 16 independent HRBEC samples with and without BPA exposure. We demonstrate induction of key genes and proteins in the PI3K-mTOR pathway--AKT1, RPS6 and 4EBP1 and a concurrent reduction in the tumor suppressor, phosphatase and tensin homolog gene protein. Altered regulation of mTOR pathway proteins in BPA-treated HRBECs led to marked resistance to rapamycin, the defining mTOR inhibitor. Moreover, HRBECs pretreated with BPA, or the XE, methylparaben (MP), surmounted antiestrogenic effects of tamoxifen showing dose-dependent apoptosis evasion and induction of cell cycling. Overall, XEs, when tested in benign breast cells from multiple human subjects, consistently initiated specific functional changes of the kind that are attributed to malignant onset in breast tissue. Our observations demonstrate the feasibility of studying renewable human samples as surrogates and reinforce the concern that BPA and MP, at low concentrations detected in humans, can have adverse health consequences.

Prenatal exposure to bisphenol A affects adult murine neocortical structure

Prenatal exposure to low-doses of bisphenol A (BPA) has been shown to affect murine neocortical development by accelerating neuronal differentiation/migration through disrupting thyroid hormone function. We therefore studied whether prenatal exposure to low-doses of BPA affected organization of adult neocortical structures. Pregnant mice were injected with 20 microg/kg of BPA daily from embryonic day 0.5 (E0.5) and bromodeoxyuridine (BrdU) was injected at E12.5, E14.5 and at E16.5, and the fetal brains were analyzed after birth. The BrdU-positive cells labeled at E14.5 were significantly increased in the Vth and VIth cortical layers of BPA-treated mice at postnatal 3 weeks (P3W), whereas they were confined to the IVth layer of control mice, though such differences disappeared at P12W. The thalamocortical projections demonstrated by DiI-labeling were abnormal at P3W and P12W in BPA-treated mice. These results indicate that BPA might affect not only neocortical development but also thalamocortical connections.

Murine neocortical histogenesis is perturbed by prenatal exposure to low doses of Bisphenol A

Bisphenol A (BPA) has been shown to disrupt thyroid hormone function. We therefore studied whether prenatal exposure to low-doses of BPA affects the morphology and the expression of some genes related to brain development in the murine fetal neocortex. Pregnant mice were injected subcutaneously with 20 microg/kg of BPA daily from embryonic day 0 (E0). Control animals received vehicle alone. For evaluating cell proliferation, neuronal differentiation and migration, bromodeoxyuridine (BrdU) was injected intraperitoneally into pregnant mice with various regimens and the brains were processed for immunohistochemistry. The total RNA was extracted from the embryonic telencephalon at various embryonic stages. The BrdU-labeled cells examined 1 hour after BrdU injection showed no differences between the BPA-treated and control groups (n = 10, each), which indicated that the proliferation of precursor cells was not affected. The BrdU-labeled cells, analysed 2 days after BrdU injection, were decreased in the ventricular zone of BPA-treated mice at E14.5 and E16.5, whereas they were increased in the cortical plate at E14.5 as compared with those in control mice (n = 10, each). Furthermore, the expression of Math3, Ngn2, Hes1, LICAM, and THRalpha was significantly upregulated at E14.5 in the BPA-treated group. These results suggested that BPA might disrupt normal neocortical development by accelerating neuronal differentiation/migration.

A Role for Sulfation-Desulfation in the Uptake of Bisphenol A into Breast Tumor Cells

Bisphenol A (BPA) is a widely used plasticizer whose estrogenic properties may impact hormone-responsive disorders and fetal development. In vivo, BPA appears to have greater activity than is suggested by its estrogen receptor (ER) binding affinity. This may be a result of BPA sulfation/desulfation providing a pathway for selective uptake into hormone-responsive cells. BPA is a substrate for estrogen sulfotransferase, and bisphenol A sulfate (BPAS) and disulfate are substrates for estrone sulfatase. Although the sulfated xenobiotics bind poorly to the ER, both stimulated the growth of receptor-positive breast tumor cells. Treatment of MCF-7 cells with BPAS leads to desulfation and uptake of BPA. No BPAS is found inside the cells. These findings suggest a mechanism for the selective uptake of BPA into cells expressing estrone sulfatase. Therefore, sulfation may increase the estrogenic potential of xenobiotics.