Modulation of ovarian follicle maturation in Long-Evans rats exposed to polychlorinated biphenyls (PCBs) in-utero and lactationally

Prenatal exposure to persistent organic pollutants and its impact on the ovarian reserve at 12 years old in the PELAGIE mother-child cohort

Although the ovarian reserve is constituted in utero, the literature on the effects of persistent organic pollutants (POPs) during this vulnerable period on the ovarian reserve later in life is limited. We investigated whether cord blood concentrations of POPs were associated with decreased anti-Müllerian hormone (AMH, a marker of the ovarian reserve) levels in girls at the age of 12. We included 239 girls from the French mother-child PELAGIE cohort. POP concentrations of 14 organochlorine pesticides, 17 polychlorinated biphenyls (PCBs), 5 polybrominated diphenyl ethers, and 9 per-polyfluoroalkyl substances were measured on cord blood sampled at birth. During a follow-up study at 12 years old, blood samples were collected to measure AMH levels. Single-exposure associations were examined with multivariable linear regression models adjusted a priori for potential confounders. Stratification on menarche status was also performed. Mixture effects were investigated using quantile g-computation and Bayesian kernel machine regression. Overall, 16 POPs were measured in at least 30% of samples. No significant associations were found in multivariable linear regressions, except for the third tercile of exposure to PCB 180 which was statistically significantly associated with an increase in AMH levels at 12 years old (Tercile 2 v. Tercile 1: 0.13 ng/mL, 95% CI = -0.29, 0.56; Tercile 3 v. Tercile 1: 0.51 ng/mL, 95% CI = 0.02, 0.99). Additionally, in post-menarcheal girls (N = 104) only, the second tercile of p,p'-DDE was statistically significantly associated with decreased AMH levels at 12 years old (Tercile 2 v. Tercile 1: -0.61 ng/mL, 95% CI = -1.16, -0.05, Tercile 3 v. Tercile 1: 0.02 ng/mL, 95% CI = -0.51, 0.54). Both mixture models returned null associations. Despite the limited associations observed in this study, we recommend exploring these associations in larger mother-child cohorts and at older ages.

Zn and Se abrogate heavy metal mixture induced ovarian and thyroid oxido-inflammatory effects mediated by activation of NRF2-HMOX-1 in female albino rats

The thyroid is vital for the proper functioning of the female reproductive system since it regulates the metabolism and development of ovary. This is an evaluation of the essential trace elements ETE on the heavy metals mixture HMM mediated oxido-inflammatory effects in the ovary and thyroid of female albino rats. Eight groups (5 female rats /group) were treated as follows for 60 days: Group 1: Deionized water only; Group 2: (Pb, Hg, Mn and Al); Group 3: HMM + ZnCl2, 0.80 mg/kg; Group 4: HMM + Na2SeO3, 1.50 mg/kg; Group 5: HMM + ZnCl2, 0.80 mg/kg and Na2SeO3, 1.50 mg/kg combined. On day 60 animals were euthanized, ovary and thyroid were harvested and used for, MDA, NO, antioxidants, TNF-α, IL-6, HMOX-1, Caspase-3, NF-KB, NRF2, HM and histopathology. There was significant bioaccumulation of Pb, Al, Hg and MN; elevated IL-6 and TNF-α, MDA and NO, caspase-3 and NRF2, NFKB and HMOX-1 with significant decrease in antioxidants in the HMM only group in comparison to the control. Co-treatment with ETE reversed most of these effects. ETE may ameliorate HMM -induced ovarian and thyrotoxicity in female albino rats by blunting oxido-inflammatory activities.

Effects of Polychlorinated Biphenyls on Animal Reproductive Systems and Epigenetic Modifications

Polychlorinated biphenyls (PCBs) are a group of highly toxic endocrine-disrupting chemicals comprising 209 homologs. PCBs are extensively found in the environment and can induce typical estrogenic and profound, long-lasting effects on animals. In this article, the introduction of PCB residues into the environment and the pathways of PCB enrichment in animals are described. PCBs are widely deposited and eventually accumulate in human tissues and body fluids through biomagnification. PCBs can significantly decrease animal fertility and interfere with endocrine processes, leading to the development of various diseases and even cancer. The effects of PCBs on the reproductive systems of animals can also be passed to their offspring, indicating that PCBs may affect the epigenetic modification process. There is currently no treatment to effectively inhibit the toxicity of PCBs in organisms; therefore, the severity of PCB toxicity needs to be widely recognized.

Perinatal exposure to a human relevant mixture of persistent organic pollutants: Effects on mammary gland development, ovarian folliculogenesis and liver in CD-1 mice

The ability of persistent organic pollutants (POPs) with endocrine disrupting properties to interfere with the developing reproductive system is of increasing concern. POPs are transferred from dams to offspring and the high sensitivity of neonates to endocrine disturbances may be caused by underdeveloped systems of metabolism and excretion. The present study aimed to characterize the effect of in utero and lactational exposure to a human relevant mixture of POPs on the female mammary gland, ovarian folliculogenesis and liver function in CD-1 offspring mice. Dams were exposed to the mixture through the diet at Control, Low or High doses (representing 0x, 5000x and 100 000x human estimated daily intake levels, respectively) from weaning and throughout mating, gestation, and lactation. Perinatally exposed female offspring exhibited altered mammary gland development and a suppressed ovarian follicle maturation. Increased hepatic cytochrome P450 enzymatic activities indirectly indicated activation of nuclear receptors and potential generation of reactive products. Hepatocellular hypertrophy was observed from weaning until 30 weeks of age and could potentially lead to hepatotoxicity. Further studies should investigate the effects of human relevant mixtures of POPs on several hormones combined with female reproductive ability and liver function.

Effects of Chemical Mixtures on the Ovary

The ovaries play a critical role in female reproductive health because they are the site of oocyte maturation and sex steroid hormone production. The unique cellular processes that take place within the ovary make it a susceptible target for chemical mixtures. Herein, we review the available data regarding the effects of chemical mixtures on the ovary, focusing on development, folliculogenesis, and steroidogenesis. The chemical mixtures discussed include those to which women are exposed to environmentally, occupationally, and medically. Following a brief introduction to chemical mixture components, we describe the effects of chemical mixtures on ovarian development, folliculogenesis, and steroidogenesis. Further, we discuss the effects of chemical mixtures on corpora lutea and transgenerational outcomes. Identifying the effects of chemical mixtures on the ovaries is paramount to preventing and treating mixture-inducing toxicity of the ovary that has long-term consequences such as infertility and ovarian disease.

Selected persistent organic pollutants associated with the risk of primary ovarian insufficiency in women

Although some persistent organic pollutants (POPs) may not be currently in production, many of these chemicals still exist ubiquitously in the environment and continue to represent significant environmental health concern. One of the important concerns of POPs exposure may lead to the adverse reproductive consequences including primary ovarian insufficiency (POI), but the limited evidence has been reported so far. Our case-control study was performed to explore the association between serum levels of selected POPs and risk for POI in a Chinese female population, including 157 cases and 217 healthy controls. Serum concentrations of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs) and serum levels of reproductive hormones [follicle-stimulating hormone (FSH), luteinizing hormone (LH), anti-Mullerian hormone (AMH) and estradiol] were measured. The medians of dioxin-like PCBs (DL-PCBs) and p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) were significantly higher in case sera than in controls. Higher concentrations of DL-PCBs and p,p'-DDT were significantly associated with elevated risk of POI. A dose-response relationship was observed between the sum of DL-PCBs (Σ₆ DL-PCBs) and the risk of POI (p for trend = 0.003), with odds ratios for the second and third tertiles, compared with the first, of 1.31- (95% CIs: 0.67-2.57) and 3.15-fold (95% CIs: 1.63-6.10), respectively. Similar results were observed for the sum of p,p'-DDT and its metabolites (Σ₂ p,p'-DDTs). In control women, FSH levels were negatively associated with PCBs exposure, while LH had a positive association with OCPs. In patients with POI, exposure to PCBs was correlated with higher levels of LH, whereas exposure to OCPs was associated with lower levels of AMH. To the best of our knowledge, this study for the first provided evidence that exposure to PCBs and DDT could be the potential risk factors for POI in women.

Transgenerational Effects of Endocrine-Disrupting Chemicals on Male and Female Reproduction

Endocrine-disrupting chemicals are known to interfere with normal reproductive function and hormone signaling. Phthalates, bisphenol A, pesticides, and environmental contaminants such as polychlorinated biphenyls and dioxins are known endocrine-disrupting chemicals that have been shown to negatively affect both male and female reproduction. Exposure to these chemicals occurs on a daily basis owing to these compounds being found in plastics, personal care products, and pesticides. Recently, studies have shown that these chemicals may cause transgenerational effects on reproduction in both males and females. This is of concern because exposure to these chemicals prenatally or during adult life can negatively impact the reproductive health of future generations. This mini-review summarizes the endocrine-disrupting chemicals that humans are exposed to on a daily basis and what is known about the transgenerational effects that these chemicals may have on male and female reproduction.

Histopathological changes in zebrafish embryos exposed to DLPCBs extract from Zhanjiang coastal sediment

Dioxin-like polychlorinated biphenyls (DLPCBs) are ubiquitous persistent pollutants that cause adverse effects in many environmental organisms. DLPCBs in marine sediments can be absorbed by benthic organisms, bioaccumulate, and biomagnify through the food chain and threaten animal and human health. There are no reports of DLPCBs concentrations in the Zhanjiang Gulf seabed. This study was designed to investigate the concentration of DLPCBs in the Zhanjiang coastal sediment and histopathological changes in zebrafish (Diano rerio) embryos exposed to environmentally relevant concentrations of DLPCBs. Of the five sites selected, two sites TS and JSW contained DLPCBs at concentrations of 0.08 and 22.54 ng/g dry sediment, respectively. Two groups of zebrafish embryos were used. One group was exposed to 3.75, 7.5, 15, 30, and 60 mg/ml of DLPCBs extracted from the sediments sampled from the TS site and the second group to 4.375, 8.75, 17.5, 35, and 70 mg/ml of DLPCBs from JSW site from 0.75 h post-fertilization (hpf) to 96 hpf. The zebrafish exposed to 60 and 70 mg/ml of DLPCBs at 96 hpf displayed gross histopathological changes with cardiac lesions including pericardial edema being the most deleterious. Other changes observed were hydropic degeneration of gill filaments and hepatocytes, loss of intestinal folds, and uninflated swim bladder. It appears that only a few sites of the Zhanjiang gulf are contaminated with DLPCBs. This is the first report of histopathological changes in the gills, hepatocytes, intestines, heart, and the swim bladder in zebrafish embryos exposed to DLPCBs from a coastal sediment. Further studies with sampling at different stages of development are required to identify which organ/tissue is most sensitive to DLPCBs.

Endocrine disrupting chemicals and ovulation: Is there a relationship?

Although the potential for endocrine disrupting chemicals (EDCs) to disrupt female fecundity is great, few studies have assessed the threat to human reproduction. This study investigates levels of organochlorines in relation to their impact on women's menstrual cycles and ovulatory status. To address concerns of the Akwesasne Mohawk community in upstate New York regarding well-established exposure to EDCs, women's fertility and reproductive health endpoints, we recruited 215 women between the ages of 21 and 38 years to measure menstrual cycle characteristics and levels of local pollutants. Of these, 155 women collected saliva over the course of their menstrual cycle allowing for analysis of estradiol and progesterone levels and the determination of ovulatory status in relationship to their serum pollutant levels. A subset of participants (15) who did not commence cycling within a month of their enrollment were not included in the analysis, hence reducing the sample size to 140 participants. Additionally, a lipid panel, estradiol and progesterone were assessed in serum on Day 3 of the menstrual cycle. Median cycle length for women in the sample was 29 days. After aligning the cycles, 110 women were considered ovulatory and 45 (29%) anovulatory. Concentrations of groups of more persistent PCBs congeners, HCB, and p,p'-DDE did not differ significantly with ovulatory status. However, a sub-group of low-chlorinated PCB congeners, considered to be estrogenic were significantly higher among anovulatory women. These findings suggest that certain EDC's, ubiquitous in our environment, may adversely affect menstrual cycles and thus have the capacity to impair reproductive function, including likelihood of conception.

Developmental toxicity, EROD, and CYP1A mRNA expression in zebrafish embryos exposed to dioxin-like PCB126

Dioxin-like PCB126 is a persistent organic pollutant that causes a range of syndromes including developmental toxicity. Dioxins have a high affinity for aryl hydrocarbon receptor (AhR) and induce cytochrome P4501A (CYP1A). However, the role of CYP1A activity in developmental toxicity is less clear. To better understand dioxin induced developmental toxicity, we exposed zebrafish (Danio rerio) embryos to PCB126 at concentrations of 0, 16, 32, 64, and 128 μg L(-1) from 3-h post-fertilization (hpf) to 168 hpf. The embryonic survival rate decreased at 144 and 168 hpf. The fry at 96 hpf displayed gross developmental malformations, including pericardial and yolk sac edema, spinal curvature, abnormal lower jaw growth, and non-inflated swim bladder. The pericardial and yolk sac edema rate significantly increased and the heart rate declined from 96 hpf compared with the controls. PCB126 did not alter the hatching rate. To elucidate the mechanism of PCB126-induced developmental toxicity, we conducted ethoxyresorufin-O-deethylase (EROD) in vivo assay to determine CYP1A enzyme activity, and real-time PCR to study the induction of CYP1A mRNA gene expression in embryo/larval zebrafish at 24, 72, 96, and 132 hpf. In vivo EROD activity was induced by PCB126 at 16 μg L(-1) concentration as early as 72 hpf but significant increases were observed only in zebrafish exposed to 64 and 128 μg L(-1) doses (p < 0.005) at 72, 96, and 132 hpf. Induction of CYP1A mRNA expression was significantly upregulated in zebrafish exposed to 32 and 64 μg L(-1) at 24, 72, 96, and 132 hpf. Overall, the severe pericardial and yolk sac edema and reduced heart rate suggest that heart defects are a sensitive endpoint, and the general trend of dose-dependent increase in EROD activity and induction of CYP1A mRNA gene expression provide evidence that the developmental toxicity of PCB126 to zebrafish embryos is mediated by activation of AhR.

A rapid in vivo zebrafish model to elucidate oxidative stress-mediated PCB126-induced apoptosis and developmental toxicity

Dioxin-like 3,3',4,4',5-pentachlorobiphenyl (PCB126) is one of the most potent and widespread environmental pollutants. Although PCB126-induced toxicity is related to the aryl hydrocarbon receptor pathway, there is still no study that has constructed an in vivo visual model to clarify the role of the Nrf2/ARE signaling pathway in the oxidative stress mechanism of PCB126-induced toxicity. In the present study, an in vivo zebrafish model of nrf2a fused to enhanced green fluorescent protein (nrf2a-eGFP) was constructed. The zebrafish embryos microinjected with nrf2a-eGFP (72h postfertilization) were exposed to various concentrations of PCB126 (0, 25, 50, 100, 200μg/L) or 30mMN-acetylcysteine (NAC)+200μg/L PCB126. After 72h exposure, PCB126 significantly increased the malformation rates and induced eGFP expression in a dose-dependent manner in several zebrafish tissue types. The distribution of eGFP fluorescence coincided with developmental deformity sites. NAC pretreatment effectively counteracted PCB126-induced developmental toxicity including heart rate, pericardial edema, and body length. The highest PCB126 dose, 200μg/L, produced marked apoptosis in the eye, gill, and trunk detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. At 48 and 72h exposure, 200μg/L PCB126 affected glutathione metabolism as evidenced by decreased glutathione and increased glutathione disulfide concentrations, indicative of oxidative stress. These effects were also counteracted by NAC pretreatment. Furthermore, the Nrf2-regulated genes gclc, gpx, gstp1, and hmox1 were significantly induced at 24, 48, and 72h at the highest PCB126 exposures but not in the NAC-pretreated group. In addition, a significant increase in ROS generation was detected in zebrafish larvae at 72h PCB126 exposure, which might offer a link for future mechanistic studies. Collectively, these data suggest that PCB126-induced developmental toxicity and apoptosis in the nrf2a-eGFP-injected zebrafish model are due to oxidative stress mediated by disruption to glutathione metabolism and changes in Nrf2-regulated gene expression.

Very low-dose (femtomolar) 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) disrupts steroidogenic enzyme mRNAs and steroid secretion by human luteinizing granulosa cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic congener of the polyhalogenated aromatic hydrocarbons (PAH), which causes anatomical abnormalities and developmental defects, impairs ovulation and reduces fertility. TCDD's endocrine-disrupting effects are, in part, caused by a direct action at the ovary. Herein we investigated the in-vitro effects of environmentally relevant doses of TCDD on estradiol-17β (E2) production by human luteinizing granulosa cells (hLGC) obtained from women stimulated for in-vitro fertilization (IVF). TCDD at all concentrations tested (3.1fM, 3.1pM and 3.1nM) significantly decreased E2 secretion when assayed for by radioimmunoassay (RIA). Herein we confirm that TCDD alters E2 secretion by hLGC in a time-, not dose-dependent fashion and are the first to show decreases in E2 secretion with fM concentrations of TCDD. Using real-time quantitative PCR (RT-qPCR), the decreased E2 secretion correlates with a decrease in the mRNA expression levels two enzymes in the estrogen biosynthesis pathway: CYP11A1 and CYP19A1.

Aroclor 1254 impairs the development of ovarian follicles by inducing the apoptosis of granulosa cells

Aroclor 1254 impairs the development of follicle (primordial follicle excluded), possibly via the induction of apoptosis mainly in granulosa cells.

In utero and lactational exposure to PCB 118 and PCB 153 alter ovarian follicular dynamics and GnRH-induced luteinizing hormone secretion in female lambs

The effects of in utero and lactational exposure to two structurally different polychlorinated biphenyl (PCB) congeners on follicular dynamics and the pituitary-gonadal axis in female lambs were investigated. Pregnant ewes received corn oil, PCB 118, or PCB 153, and offspring was maintained until 60 days postpartum. Ovarian follicles were quantified using stereology. Plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured using radioimmunoassay before and after administration of a gonadotropin releasing hormone (GnRH) analog. PCB 118 exposure increased numbers of transitional, secondary, and the sum of secondary, early antral, and antral (Σsecondary-antral) follicles, PCB 153 exposure only increased the number of primary follicles. GnRH-induced LH levels were significantly elevated in the PCB 153 exposure group. We conclude that PCB 153 and PCB 118 alter follicular dynamics in lambs and modulate the responsiveness of the pituitary gland to GnRH.

Current advances in epigenetic modification and alteration during mammalian ovarian folliculogenesis

During the growth and development of mammalian ovarian follicles, the activation and deactivation of mass genes are under the synergistic control of diverse modifiers through genetic and epigenetic events. Many factors regulate gene activity and functions through epigenetic modification without altering the DNA sequence, and the common mechanisms may include but are not limited to: DNA methylation, histone modifications (e.g., acetylation, deacetylation, phosphorylation, methylation, and ubiquitination), and RNA-associated silencing of gene expression by noncoding RNA. Over the past decade, substantial progress has been achieved in studies involving the epigenetic alterations during mammalian germ cell development. A number of candidate regulatory factors have been identified. This review focuses on the current available information of epigenetic alterations (e.g., DNA methylation, histone modification, noncoding-RNA-mediated regulation) during mammalian folliculogenesis and recounts when and how epigenetic patterns are differentially established, maintained, or altered in this process. Based on different types of epigenetic regulation, our review follows the temporal progression of events during ovarian folliculogenesis and describes the epigenetic changes and their contributions to germ cell-specific functions at each stage (i.e., primordial folliculogenesis (follicle formation), follicle maturation, and follicular atresia).

Comparative effects of repeated administration of cadmium chloride during pregnancy and lactation and selenium protection against cadmium toxicity on some organs in immature rats' offsprings

This research comprises studies on the transfer of cadmium (CdCl(2)) from the lactating dam to the pup via milk and absorbed in the suckling, showing that cadmium is transferred to the testes, ovary, cerebellum, and thyroid gland during development. The present studies were carried out in order to assess the protective effects of selenium against cadmium toxicity in pregnant rats. On the sixth day of gestation, the females were dosed subcutaneously either with cadmium or with cadmium and selenium in the following doses (mg/kg of body weight): 0, 1 Cd, 1 Cd + 1 Se, 2 Cd, 2 Cd + 2 Se. In groups treated with cadmium, no maternal or embryonic toxicities were observed; however, an increase in testes diameters of seminiferous tubules, a progressive sloughing of germ cells, vacuolization of Sertoli cells, and Leydig cells hyperplasia were noted. The reduction in the ovary size and inhibited folliculogenesis resulted in diminution of the numbers of primordial, growing, and tertiary follicles. The pathological change in the cerebellum, the migration of granular cells from the external germinal layer to the internal granular layer, was strongly retarded. Also, the formation of many microfollicles in the thyroid gland which mimic the changes was seen in thyrotoxicosis. It also appears that selenium used at a low-enough dose could be a very effective protection against cadmium-induced developmental toxicity in the testes, ovary, cerebellum, and thyroid gland but not in the higher dose in the ovary and cerebellum.

Early life exposure to endocrine-disrupting chemicals causes lifelong molecular reprogramming of the hypothalamus and premature reproductive aging

Gestational exposure to the estrogenic endocrine disruptor methoxychlor (MXC) disrupts the female reproductive system at the molecular, physiological, and behavioral levels in adulthood. The current study addressed whether perinatal exposure to endocrine disruptors re-programs expression of a suite of genes expressed in the hypothalamus that control reproductive function and related these molecular changes to premature reproductive aging. Fischer rats were exposed daily for 12 consecutive days to vehicle (dimethylsulfoxide), estradiol benzoate (EB) (1 mg/kg), and MXC (low dose, 20 μg/kg or high dose, 100 mg/kg), beginning on embryonic d 19 through postnatal d 7. The perinatally exposed females were aged to 16-17 months and monitored for reproductive senescence. After euthanasia, hypothalamic regions [preoptic area (POA) and medial basal hypothalamus] were dissected for real-time PCR of gene expression or pyrosequencing to assess DNA methylation of the Esr1 gene. Using a 48-gene PCR platform, two genes (Kiss1 and Esr1) were significantly different in the POA of endocrine-disrupting chemical-exposed rats compared with vehicle-exposed rats after Bonferroni correction. Fifteen POA genes were up-regulated by at least 50% in EB or high-dose MXC compared with vehicle. To understand the epigenetic basis of the increased Esr1 gene expression, we performed bisulfite conversion and pyrosequencing of the Esr1 promoter. EB-treated rats had significantly higher percentage of methylation at three CpG sites in the Esr1 promoter compared with control rats. Together with these molecular effects, perinatal MXC and EB altered estrous cyclicity and advanced reproductive senescence. Thus, early life exposure to endocrine disruptors has lifelong effects on neuroendocrine gene expression and DNA methylation, together with causing the advancement of reproductive senescence.

The role of the aryl hydrocarbon receptor in the female reproductive system

In recent years, many studies have emphasized how changes in aryl hydrocarbon receptor (AHR)-mediated gene expression result in biological effects, raising interest in this receptor as a regulator of normal biological function. This review focuses on what is known about the role of the AHR in the female reproductive system, which includes the ovaries, Fallopian tubes or oviduct, uterus and vagina. This review also focuses on the role of the AHR in reproductive outcomes such as cyclicity, senescence, and fertility. Specifically, studies using potent AHR ligands, as well as transgenic mice lacking the AHR-signaling pathway are discussed from a viewpoint of understanding the endogenous role of this ligand-activated transcription factor in the female reproductive lifespan. Based on findings highlighted in this paper, it is proposed that the AHR has a role in physiological functions including ovarian function, establishment of an optimum environment for fertilization, nourishing the embryo and maintaining pregnancy, as well as in regulating reproductive lifespan and fertility. The mechanisms by which the AHR regulates female reproduction are poorly understood, but it is anticipated that new models and the ability to generate specific gene deletions will provide powerful experimental tools for better understanding how alterations in AHR pathways result in functional changes in the female reproductive system.

Overview of toxicological aspects of polybrominated diphenyl ethers: a flame-retardant additive in several consumer products

Polybrominated diphenyl ethers (PBDEs) are ubiquitous environmental contaminants due to their long half-life and widespread use as flame retardants in several consumer products, including plastics. In addition to other actions, these compounds are characterized as thyroid hormone disruptors. Thyroid hormones affect the function of nearly all tissues via their effects on cellular metabolism and the essential roles they play in differentiation and growth. Interference with thyroid hormone homeostasis by these environmental compounds, therefore, has the potential to impact development and every system in the body. Their presence in human breast milk is particularly troubling due to exposure of nursing children. The last trimester of pregnancy up to 2 years of age corresponds to a time of rapid neurodevelopment and represents a period of vulnerability to environmental insults. Rodent studies indicate that PBDEs may act as developmental neurotoxicants and effects on the reproductive system have been reported as well. Concerns exist regarding possible impacts of exposure, in particular ones which occur during development, on human health. This paper is part of a series of articles regarding contaminants in plastic and provides an overview regarding PBDEs, a class of flame-retardant additives to plastic. PBDEs possess a similar structure to the polychlorinated biphenyls (PCBs) previously used as lubricants in electrical generators and transformers until production was prohibited approximately 25 years ago. Parallels between the two compounds will be briefly made and in particular, as more epidemiological studies on PCBs are available than on PBDEs, a few examples concerning thyroid homeostasis, cognitive function and sexually dimorphic behavior in humans will be mentioned.

In utero and lactational exposures to low doses of polybrominated diphenyl ether-47 alter the reproductive system and thyroid gland of female rat offspring

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) are capable of disrupting thyroid hormone homeostasis. PBDE-47 (2,2',4,4'-tetrabromodiphenyl ether) is one of the most abundant congeners found in human breast adipose tissue and maternal milk samples.

OBJECTIVES

We evaluated the effects of developmental exposure to low doses of PBDE-47 on the female reproductive system.

METHODS

Pregnant Wistar rats were administered vehicle (peanut oil) or PBDE-47 [140 or 700 microg/kg body weight (bw)] on gestation day (GD) 6, or 5 mg 6-n-propyl-2-thiouracil (PTU)/L in the drinking water from GD7 through postnatal day (PND) 21.

RESULTS

In female offspring sacrificed on PND38, there was a significant decrease in ovarian weight after exposure to PTU or 140 microg/kg PBDE-47. Alterations in folliculogenesis were apparent: we observed a decrease in tertiary follicles and serum estradiol concentrations in the offspring exposed to either PTU or 700 microg/kg PBDE-47. PTU exposure also resulted in a decrease in primordial follicles. On PND100, persistent effects on the thyroid glands included histologic and morphometric changes after exposure to either PTU or PBDE-47. No relevant changes in reproductive indices were observed after mating the exposed F1 females with nontreated males.

CONCLUSIONS

Administration of PBDE-47 at doses relevant to human exposure led to changes in the rat female reproductive system and thyroid gland.

Autoradiographic localization of aromatic hydrocarbon receptor (AHR) in rhesus monkey ovary

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic congener of a large class of manmade pollutants that persist in the environment. TCDD exerts its toxic effects, in part, by binding to its receptor known as the aromatic hydrocarbon receptor (AHR). TCDD is estrogen modulatory and in some systems its receptor associates directly with estrogen receptors via co-activator molecules. TCDD inhibits steroid synthesis in human ovarian granulosa cells and AHR is found in these cells. We have previously shown that AHR is found in whole rhesus monkey ovary, but have yet to establish its location. In the present study, we set out to show that radiolabeled TCDD binds to monkey ovarian follicles and that this binding is receptor mediated. Ovaries from Macaca mulatta were sectioned on a cryostat at 10 micro m; and sections were incubated with either control vehicle, (3)H-TCDD, or (3)H-TCDD plus alpha-naphthoflavone (ANF), a known receptor-blocking agent. Here, we show for the first time specific binding of TCDD to the granulosa cells of antral follicles and other regions of the rhesus monkey ovary. Our data indicate a 60-fold increase in binding with (3)H-TCDD over that of control, and that this binding is reduced to the levels seen in controls with the addition of the competitive antagonist ANF. These findings support the hypothesis that TCDD directly affects primate ovarian function via the AHR.

Environmental chemicals impacting the thyroid: targets and consequences

Thyroid hormone (TH) is essential for normal brain development, but the specific actions of TH differ across developmental time and brain region. These actions of TH are mediated largely by a combination of thyroid hormone receptor (TR) isoforms that exhibit specific temporal and spatial patterns of expression during animal and human brain development. In addition, TR action is influenced by different cofactors, proteins that directly link the TR protein to functional changes in gene expression. Considering the importance of TH signaling in development, it is important to consider environmental chemicals that may interfere with this signaling. Recent research indicates that environmental chemicals can interfere with thyroid function and with TH signaling. The key issues are to understand the mechanism by which these chemicals act and the dose at which they act, and whether adaptive responses intrinsic to the thyroid system can ameliorate potential adverse consequences (i.e., compensate). In addition, several recent studies show that TRs may be unintended targets of chemicals manufactured for industrial purposes to which humans and wildlife are routinely exposed. Polychlorinated biphenyls, polybrominated diphenyl ethers, bisphenol-A, and specific halogenated derivatives and metabolites of these compounds have been shown to bind to TRs and perhaps have selective effects on TR functions. A number of common chemicals, including polybrominated biphenyls and phthalates, may also exert such effects. When we consider the importance of TH in brain development, it will be important to pursue the possibilities that these chemicals-or interactions among chemical classes-are affecting children's health by influencing TH signaling in the developing brain.

Effect of an environmentally relevant metabolized organochlorine mixture on porcine cumulus–oocyte complexes

Organochlorine compounds and their metabolites bioaccumulate and have been detected in follicular and genital tract fluids of humans and animals. This study was designed to investigate the effect of a metabolised organochlorine mixture, extracted from plasma of sows treated with an environmentally relevant organochlorine mixture in the course of a previous study, on porcine cumulus-oocyte complexes (COCs) in vitro. The major component of the metabolised mixture is 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (p,p'-DDE) at 15.1 mg/l, which accounts for 40.7% of the total extract. Polychlorinated biphenyls (PCBs) account for 30.8% of the extract and hydroxylated PCB metabolites (OH-PCBs) for 11.8%. Exposure of COCs to the metabolised mixture induced a decrease of apoptotic cumulus cells at low concentrations and an increase at higher concentrations following a U-shaped curve (p=0.0106), with the intermediate treatment (3.6 microg/l OH-PCBs) significantly reducing apoptosis compared to the extraction control (p=0.05). However, the metabolised mixture did not affect cumulus expansion, oocyte maturation, penetration, development to blastocyst, or the number of cells per blastocyst. This study also indicates that organochlorine metabolites similar in concentrations to levels found in Arctic populations can affect growing cumulus-oocyte complexes without inducing an overt toxicological response.

A dose–response study following in utero and lactational exposure to di-(2-ethylhexyl) phthalate (DEHP): Reproductive effects on adult female offspring rats

Di(2-ethylhexyl) phthalate (DEHP) is used in numerous consumer products, mainly imparting flexibility and durability to polyvinyl chloride (PVC) based plastics. It is a known reproductive and developmental toxicant in male rodents. However, data regarding effects of DEHP on female reproductive health are particularly sparse. We performed an extensive dose-response study following developmental exposure to DEHP and evaluated the effects on adult female reproductive function. Two wide ranges of doses, low and high, were tested. Female Wistar rats were treated daily with DEHP and peanut oil (vehicle control) by gavage from gestation day 6 to lactation day 21. The low doses were: 0.015, 0.045, 0.135, 0.405 and 1.215mgDEHP/kg/bw/day and the high doses were: 5, 15, 45, 135 and 405mg DEHP/kg/bw/day. At the doses tested, no effects on organ (liver, kidney, spleen, thymus, thyroid, ovary and uterus) or body weights were detected. Female offspring presented a normal pattern of estrous cyclicity with no hormonal alterations (serum estradiol and progesterone). A statistically significant increase in tertiary atretic follicles was observed at the highest dose (405mgDEHP/kg/day). Morphometric analysis indicated that uterus and vagina luminal epithelial cell height were unaffected by treatment. An increase in the number of ovarian atretic tertiary follicles was the only effect observed in adult female offspring exposed in utero and during lactation to DEHP.

Effects of developmental exposure to 2,2 ,4,4 ,5-pentabromodiphenyl ether (PBDE-99) on sex steroids, sexual development, and sexually dimorphic behavior in rats

Increasing concentrations of polybrominated flame retardants, including polybrominated diphenyl ethers (PBDEs), in breast milk cause concern about possible developmental effects in nursed babies. Because previous studies in rats have indicated effects on sex steroids and sexually dimorphic behavior after maternal exposure to polychlorinated biphenyls (PCBs), our goal in the present study was to determine if developmental exposure to 2,2 ,4,4 ,5-pentabromodiphenyl ether (PBDE-99) induces similar endocrine-mediated effects. Pregnant rats were exposed to vehicle or PBDE-99 (1 or 10 mg/kg body weight, daily during gestational days 10-18). For comparison, we also included a group exposed to the technical PCB mixture Aroclor 1254 (30 mg/kg body weight, daily). PBDE exposure resulted in pronounced decreases in circulating sex steroids in male offspring at weaning and in adulthood. Female offspring were less affected. Anogenital distance was reduced in male offspring. Puberty onset was delayed in female offspring at the higher dose level, whereas a slight acceleration was detected in low-dose males. The number of primordial/primary ovarian follicles was reduced in females at the lower dose, whereas decline of secondary follicles was more pronounced at the higher dose. Sweet preference was dose-dependently increased in PBDE-exposed adult males, indicating a feminization of this sexually dimorphic behavior. Aroclor 1254 did not alter sweet preference and numbers of primordial/primary and secondary follicles but it did affect steroid concentrations in males and sexual development in both sexes. PBDE concentrations in tissues of dams and offspring were highest on gestational day 19. These results support the hypothesis that PBDEs are endocrine-active compounds and interfere with sexual development and sexually dimorphic behavior.

Environmental toxicants and effects on female reproductive function

One of the most toxic substances known to humans, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin), is also highly pervasive in the environment. It is created naturally in volcanic eruptions and forest fires, and anthropogenically in waste incineration, chlorination processes and certain plastics manufacture. From reports of large industrial and other accidents, or from experimental studies, dioxin exposure has been correlated in animal models and/or humans with chloracne of the skin, organ cancers, hepatotoxicity, gonadal and immune changes, pulmonary and other diseases such as diabetes, skewing of the sex ratio, and infertility. We have demonstrated that the aromatic hydrocarbon receptor (AHR) that binds dioxin in tissues is localized in zebrafish, rat and rhesus monkey (Macaca mulatta) ovaries and in rat and human luteinizing granulosa cells (GC) (among other tissues), that labeled dioxin is specifically localized to granulosa cells of the ovarian follicle as observed by autoradiography, and that incubations of GC or ovarian fragments with environmentally relevant concentrations (fM to nM) of dioxin inhibit estradiol secretion significantly. Our experiments show that in human, non-human primate, rat, trout, and zebrafish ovarian tissues, dioxin inhibits estrogen synthesis at some level of the steroid biosynthetic pathway, most likely by inhibiting transcription of mRNAs for or activity of side-chain cleavage (Cyp11a1 gene) and/or aromatase (Cyp19a1 gene) enzymes, or conceivably other steroidogenic enzymes/factors. Such an untoward effect on estrogen synthesis in females exposed to dioxin environmentally may predispose them to defects in aspects of their fertility.

In utero and lactational exposure of Long-Evans rats to ammonium perchlorate (AP) disrupts ovarian follicle maturation

Ammonium perchlorate (AP) is a powerful oxidizer manufactured almost exclusively for the aerospace industry. AP salts are also used in airbags, flares, fertilizers, enamels and paints. As a result of widespread industrial use, AP has become a persistent environmental contaminant of drinking water in several U.S. states. AP ion disrupts the trapping of iodide as well as facilitates the discharge of unorganified iodide from the thyroid gland. Such disturbances in thyroid hormone concentrations during critical periods of development are then known to cause profound reproductive and developmental defects, since thyroid hormones modulate both follicular development and steroidogenesis and affect estrogen metabolism and receptor. This study was designed (1) to determine whether exposure to a low or high concentration of AP (LAP, HAP) exerts detrimental effects on follicle maturation in the Long-Evans hooded rat and (2) to determine whether the modulatory effects of AP can be ameliorated by levo-thyroxine sodium (T4) supplementation. Animals were treated via deionized drinking water on GD 7-21 with LAP (0.4 mg/kg/day) or HAP (4.0 mg/kg/day). Half of each group was also given T4 supplements via drinking water on GD 7-21. Female pups were sacrificed on postnatal days 24/25, and the ovaries were excised, fixed for histology and analyzed. The analysis included a count, measurement and classification of preantral and antral follicles in the greatest cross-sectional area of the ovary. The results indicated that treatment with the HAP significantly reduced the number of preantral follicles <50,000 microm2 and the total number of antral follicles in the <50,000, 50-100,000 and >100,000 microm2 size classes. In ovaries treated with the LAP, we observed no significant decrease in preantral follicles of any size class and only a significant reduction in the largest antral follicles. T4 only circumvented the effect on the number of small preantral and antral follicles; however, a significant diminution in the antral follicle number persisted in the mid-sized (HAP) and large (LAP, HAP)-sized classes. These data support the hypothesis that AP reduces the number of preantral and antral follicles in certain size classes in rats exposed during a critical period of development, and that T4 can attenuate the effects of AP on small preantral and antral follicles, but not on medium or large antral follicles. (T35ES007292 & ES08342.).

Estrogenic and toxic effects of polychlorinated biphenyls on cultured ovarian germ cells of embryonic chickens

Polychlorinated biphenyls (PCBs) are man-made ubiquitous pollutants that have detrimental effects on reproduction and endocrine functions in a variety of species. In the present study, estrogenic and toxic effects of PCBs on embryonic chicken ovarian development were evaluated by a germ-somatic cell co-culture system. Ovarian cells were cultured in serum-free medium and challenged with a mixture of PCBs (Aroclor 1254). Cell proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) release. Results showed that lower PCBs (0.1-1 microg/ml) manifested mainly estrogenic effect to stimulate germ cell proliferation, while higher PCBs (10 microg/ml) imposed severe toxicity on germ and somatic cells. The toxic effect of PCBs could be attenuated by an antioxidant tocopherol. PCBs induced condensed nuclear chromosome in ovarian cells and caused cell exfoliation and breakdown within initial hours of treatment. After 24 h, the estrogenic effect of PCBs began to exhibit and the survived germ cells manifested proliferation. Inhibition of the estrogenic effect of PCBs by tamoxifen led to increased toxicity on germ cells and somatic cells. These results indicate that PCBs exposure may interfere with ovarian germ cell proliferation and cause reproductive disorder via both toxic and estrogenic actions in embryonic chickens.