Attenuation of cell cycle progression by 2,3,7,8-tetrachlorodibenzo-p-dioxin eliciting ovulatory blockade in gonadotropin-primed immature rats

Endocrine Disrupting Chemicals in Polycystic Ovary Syndrome: The Relevant Role of the Theca and Granulosa Cells in the Pathogenesis of the Ovarian Dysfunction

Polycystic ovary syndrome (PCOS) is the most common heterogeneous endocrine disorder among women of reproductive age. The pathogenesis of PCOS remains elusive; however, there is evidence suggesting the potential contribution of genetic interactions or predispositions combined with environmental factors. Among these, endocrine disrupting chemicals (EDCs) have been proposed to potentially contribute to the etiology of PCOS. Granulosa and theca cells are known to cooperate to maintain ovarian function, and any disturbance can lead to endocrine disorders, such as PCOS. This article provides a review of the recent knowledge on PCOS pathophysiology, the role of granulosa and theca cells in PCOS pathogenesis, and the evidence linking exposure to EDCs with reproductive disorders such as PCOS.

Endocrine Disruption of the Follicle-Stimulating Hormone Receptor Signaling During the Human Antral Follicle Growth

An increasing number of pollutants with endocrine disrupting potential are accumulating in the environment, increasing the exposure risk for humans. Several of them are known or suspected to interfere with endocrine signals, impairing reproductive functions. Follicle-stimulating hormone (FSH) is a glycoprotein playing an essential role in supporting antral follicle maturation and may be a target of disrupting chemicals (EDs) likely impacting female fertility. EDs may interfere with FSH-mediated signals at different levels, since they may modulate the mRNA or protein levels of both the hormone and its receptor (FSHR), perturb the functioning of partner membrane molecules, modify intracellular signal transduction pathways and gene expression. In vitro studies and animal models provided results helpful to understand ED modes of action and suggest that they could effectively play a role as molecules interfering with the female reproductive system. However, most of these data are potentially subjected to experimental limitations and need to be confirmed by long-term observations in human.

Environmental toxicant exposure and menstrual cycle length

PURPOSE OF REVIEW

This review seeks to evaluate the impact of environmental exposures on the menstrual cycle length detailing timing of exposure on pathophysiology.

RECENT FINDINGS

Recent literature has examined the relationship between menstrual cycle length and environmental exposures including air pollutants, parabens, and polybrominated biphenyls.

SUMMARY

Research is limited but suggest importance of further research in evaluating environmental exposures and menstrual cycle length.

Changes in the expression of genes involved in the ovarian function of rats caused by daily exposure to 3-methylcholanthrene and their prevention by α-naphthoflavone

Daily exposure to low doses of 3-methylcholanthrene (3MC) during the pubertal period in rats disrupts both follicular growth and ovulation. Thus, to provide new insights into the toxicity mechanism of 3MC in the ovary, here we investigated the effect of daily exposure to 3MC on selected ovarian genes, the role of the aryl hydrocarbon receptor (AhR) and the level of epigenetic remodeling of histone post-transcriptional modifications. Immature rats were daily injected with 3MC (0.1 or 1 mg/kg) and mRNA expression of genes involved in different ovarian processes were evaluated. Of the 29 genes studied, 18 were up-regulated, five were down-regulated and six were not altered. To assess whether AhR was involved in these changes, we used the chromatin immunoprecipitation assay. 3MC increased AhR binding to promoter regions of genes involved in Notch signaling (Hes1, Jag1), activation of primordial follicles (Cdk2), cell adhesion (Icam1), stress and tumor progression (Dnajb6), apoptosis (Bax, Caspase-9) and expression of growth and transcription factors (Igf2, Sp1). Studying the trimethylation and acetylation of histone 3 (H3K4me3 and H3K9Ac, respectively) of these genes, we found that 3MC increased H3K4me3 in Cyp1a1, Jag1, Dnajb6, Igf2, Notch2, Adamts1, Bax and Caspase-9, and H3K9Ac in Cyp1a1, Jag1, Cdk2, Dnajb6, Igf2, Icam1, and Sp1. Co-treatment with α-naphthoflavone (αNF), a specific antagonist of AhR, prevented almost every 3MC-induced changes. Despite the low dose used in these experiments, daily exposure to 3MC induced changes in both gene expression and epigenomic remodeling, which may lead to premature ovarian failure.

Transcriptional profiling of porcine granulosa cells exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a toxic man-made chemical compound contaminating the environment. An exposure of living organisms to TCDD may result in numerous disorders, including reproductive pathologies. The aim of the current study was to examine the effects of TCDD on the transcriptome of porcine granulosa cell line AVG-16. By employing next-generation sequencing (NGS) we aimed to identify genes potentially involved in the mechanism of TCDD action and toxicity in porcine granulosa cells. The AVG-16 cells were treated with TCDD (100 nM) for 3, 12 or 24 h, and afterwards total cellular RNA was isolated and sequenced. In TCDD-treated cells we identified 141 differentially expressed genes (DEGs; p_adjusted < 0.05 and log2 fold change ≥1.0). The DEGs were assigned to GO term, covering biological processes, molecular functions and cellular components. Due to the large number of genes with altered expression, in the current study we analyzed only the genes involved in follicular growth, development and functioning. The obtained results showed that TCDD may affect ovarian follicle fate by influencing granulosa cell cycle, proliferation and DNA repair. The demonstrated over-time changes in the quantity and quality of genes being affected by TCDD treatment showed that the effects of TCDD on granulosa cells changed dramatically between 3-, 12- and 24-h of cell culture. This finding indicate that timing of gene expression measurement is critical for drawing correct conclusions on detailed relationships between the TCDD-affected genes and resulting intracellular processes. These conclusions have to be confirmed and extended by research involving proteomic and functional studies.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Effect of tocopherol and acetylsalicylic acid on the biochemical indices of blood in dioxin-exposed rats

New sources of dioxins and increased dioxin concentrations in the environment, coupled with their increased bioavailability along the food chain and accumulation in adipose tissues, contribute to various adverse long-term biological effects. The purpose of the study was to determine whether tocopherol protects the CNS by decreasing the pro-inflammatory influence of free radicals generated by TCDD; whether acetylsalicylic acid inhibits the production of inflammatory mediators; and whether the combined administration of tocopherol and acetylsalicylic acid to TCDD-exposed rats has a potential CNS-protective effect. The study included 117 rats divided into 8 groups: 75 female and 12 male Buffalo rats aged 8-10 weeks, weighing 140-160 g; as well as 30 female rats aged 6 weeks and weighing 120 g, which were the offspring of females from each study group. In the experiment, the following substances were used: 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), dosed at 5 μg/kg BW and 12.5 μg/kg BW, diluted in a 1% DMSO solution at the concentration of 1 μg/ml; α-tocopherol acetate, dosed at 30 mg/kg BW, in 0.2 ml of oil solution; and acetylsalicylic acid, 50mg/kg BW, suspended in 0.5 ml of starch solution, administered orally using a feeding tube. Pleurisy was induced by an injection of 0.15 ml of 1% carrageenin solution. The use of tocopherol reduces the adverse effects of the inflammatory reaction induced by TCDD. Administering tocopherol improves protein metabolism by reducing protein catabolism, and raises γ-globulin fraction levels. Combined acetylsalicylic acid and tocopherol suppress catabolic processes accompanying inflammation.

Effects of Endocrine-Disrupting Chemicals on the Ovary

Endocrine-disrupting chemicals (EDCs) are found abundantly in the environment, resulting in daily human exposure. This is of concern because many EDCs are known to target the female reproductive system and, more specifically, the ovary. In the female, the ovary is the key organ responsible for reproductive and endocrine functions. Exposure to EDCs is known to cause many reproductive health problems such as infertility, premature ovarian failure, and abnormal sex steroid hormone levels. Some EDCs and their effects on adult ovarian function have been studied extensively over the years, whereas the effects of others remain unclear. This review covers what is currently known about the effects of selected EDCs (bisphenol A, methoxychlor, 2,3,7,8-tetrachlorodibenzo-p-dioxin, phthalates, and genistein) on the adult ovary and the mechanisms by which they act upon the ovary, focusing primarily on their effects on folliculogenesis and steroidogenesis. Furthermore, this review discusses future directions needed to better understand the effects of EDCs, including the need to examine the effects of multiple and more consistent doses and to study different mechanisms of action.

The aryl hydrocarbon receptor is constitutively active in advanced prostate cancer cells

Background

Distant prostate cancers are commonly hormone refractory and exhibit increased growth no longer inhibited by androgen deprivation therapy. Understanding all molecular mechanisms contributing to uncontrolled growth is important to obtain effective treatment strategies for hormone refractory prostate cancers (HRPC). The aryl hydrocarbon receptor (AhR) affects a number of biological processes including cell growth and differentiation. Several studies have revealed that exogenous AhR ligands inhibit cellular proliferation but recent evidence suggests AhR may possess intrinsic functions that promote cellular proliferation in the absence of exogenous ligands.

Methods/Results

qRT-PCR and western blot analysis was used to determine AhR mRNA and protein expression in hormone sensitive LNCaP cells as well as hormone refractory DU145, PC3 and PC3M prostate cancer cell lines. LNCaP cells express AhR mRNA and protein at a much lower level than the hormone refractory cell models. Cellular fractionation and immunocytochemistry revealed nuclear localization of AhR in the established hormone refractory cell lines while LNCaP cells are devoid of nuclear AhR protein. qRT-PCR analysis used to assess basal CYP1B1 levels and a xenobiotic responsive element binding assay confirmed ligand independent transcriptional activity of AhR in DU145, PC3 and PC3M cells. Basal CYP1B1 levels were decreased by treatment with specific AhR inhibitor, CH223191. An in vitro growth assay revealed that CH223191 inhibited growth of DU145, PC3 and PC3M cells in an androgen depleted environment. Immunohistochemical staining of prostate cancer tissues revealed increased nuclear localization of AhR in grade 2 and grade 3 cancers compared to the well differentiated grade 1 cancers.

Conclusions

Together, these results show that AhR is constitutively active in advanced prostate cancer cell lines that model hormone refractory prostate cancer. Chemical ablation of AhR signaling can reduce the growth of advanced prostate cancer cells, an effect not achieved with androgen receptor inhibitors or growth in androgen depleted media.

Inhibition of constitutive aryl hydrocarbon receptor (AhR) signaling attenuates androgen independent signaling and growth in (C4-2) prostate cancer cells

The aryl hydrocarbon receptor is a member of the basic-helix-loop-helix family of transcription factors. AhR mediates the biochemical and toxic effects of a number of polyaromatic hydrocarbons such as 2,3,7,8,-tetrachloro-dibenzo-p-dioxin (TCDD). AhR is widely known for regulating the transcription of drug metabolizing enzymes involved in the xenobiotic metabolism of carcinogens and therapeutic agents, such as cytochrome P450-1B1 (CYP1B1). Additionally, AhR has also been reported to interact with multiple signaling pathways during prostate development. Here we investigate the effect of sustained AhR signaling on androgen receptor function in prostate cancer cells. Immunoblot analysis shows that AhR expression is increased in androgen independent (C4-2) prostate cancer cells when compared to androgen sensitive (LNCaP) cells. RT-PCR studies revealed constitutive AhR signaling in C4-2 cells without the ligand induced activation required in LNCaP cells. A reduction of AhR activity by short RNA mediated silencing in C4-2 cells reduced expression of both AhR and androgen responsive genes. The decrease in androgen responsive genes correlates to a decrease in phosphorylated androgen receptor and androgen receptor expression in the nucleus. Furthermore, the forced decrease in AhR expression resulted in a 50% decline in the growth rate of C4-2 cells. These data indicates that AhR is required to maintain hormone independent signaling and growth by the androgen receptor in C4-2 cells. Collectively, these data provide evidence of a direct role for AhR in androgen independent signaling and provides insight into the molecular mechanisms responsible for sustained androgen receptor signaling in hormone refractory prostate cancer.