Endocrine disrupting chemicals and reproductive disorders in women, men, and animal models.

This chapter covers the known effects of endocrine disrupting chemicals (EDCs) on reproductive disorders. The EDCs represented are highly studied, including plasticizers (bisphenols and phthalates), chemicals in personal care products (parabens), persistent environmental contaminants (polychlorinated biphenyls), and chemicals in pesticides or herbicides. Both female and male reproductive disorders are reviewed in the chapter. Female disorders include infertility/subfertility, irregular reproductive cycles, early menopause, premature ovarian insufficiency, polycystic ovarian syndrome, endometriosis, and uterine fibroids. Male disorders include infertility/subfertility, cryptorchidism, and hypospadias. Findings from both human and animal studies are represented.

Prenatal exposure to an environmentally relevant phthalate mixture accelerates biomarkers of reproductive aging in a multiple and transgenerational manner in female mice.

Phthalates are known endocrine-disrupting chemicals that are found in many consumer products. Our laboratory previously developed a relevant phthalate mixture consisting of six phthalates and found that it disrupted female fertility in mice. However, it is unknown if prenatal exposure to phthalate mixtures can accelerate reproductive aging and if this occurs in multiple generations. Thus, we tested the hypothesis that prenatal exposure to a mixture of phthalates accelerates biomarkers of reproductive aging in multiple generations of female mice. Pregnant CD-1 mice were orally dosed with vehicle control or a phthalate mixture (20 µg/kg/day-500 mg/kg/day) daily from gestational day 10 to birth. Adult F1 females born to these dams were used to create the F2 and F3 generations by mating them with unexposed males. At 13 months, estrous cyclicity was monitored and ovaries and sera were collected for analysis. In the F1 generation, the mixture decreased testosterone and inhibin B levels, but increased follicle-stimulating hormone and luteinizing hormone levels compared to control. In the F2 generation, the phthalate mixture decreased the percent of antral follicles and testosterone hormone levels compared to control. In the F3 generation, prenatal exposure to the phthalate mixture increased ovarian weight, increased the time in metestrus/diestrus, altered follicle numbers, and decreased the levels of luteinizing hormone compared to control. Collectively, these data suggest that prenatal exposure to a phthalate mixture may accelerate several biomarkers of reproductive aging in a multi- and transgenerational manner in female mice.

Prenatal exposure to a phthalate mixture leads to multigenerational and transgenerational effects on uterine morphology and function in mice.

Phthalates are commonly used plasticizers and additives that are found in plastic containers, children's toys and medical equipment. Phthalates are classified as endocrine-disrupting chemicals and exposure to phthalates has been associated with several human health risks including reproductive defects. Most studies focus on a single phthalate; however, humans are exposed to a mixture of phthalates daily. We hypothesized that prenatal exposure to an environmentally relevant phthalate mixture would lead to changes in uterine morphology and function in mice in a multi-generational manner. To test this hypothesis, pregnant CD-1 dams were orally dosed with vehicle or a phthalate mixture (20 µg/kg/day, 200 µg/kg/day, 200 mg/kg/day, and 500 mg/kg/day) from gestational day 10.5 to parturition. The mixture contained 35 % diethyl phthalate, 21 % di-(2-ethylhexyl) phthalate, 15 % dibutyl phthalate, 15 % diisononyl phthalate, 8% diisobutyl phthalate, and 5% benzylbutyl phthalate. The F1 pups were maintained and mated to produce two more generations (F2 and F3). At the age of 13 months, all females were euthanized and tissue samples were collected in diestrus. Our results showed that exposure to a phthalate mixture caused a decrease in progesterone levels in the treated groups in the F2 generation. The 200 mg/kg/day treatment group showed a decreased and increased luminal epithelial cell proliferation in the F1 and F2 generations respectively. In addition, these mice in the F2 generation had reduced Hand2 expression in the sub-epithelial stroma compared to the controls. A higher incidence of multilayered luminal epithelium and large dilated endometrial glands were observed in the phthalate mixture exposed groups in all generations. The mixture also caused a higher incidence of smooth muscle actin expression and collagen deposition in the endometrium compared to controls. Collectively, our results demonstrate that prenatal exposure to an environmentally relevant phthalate mixture can have adverse effects on female reproductive functions.

Mechanisms of action of agrochemicals acting as endocrine disrupting chemicals.

Agrochemicals represent a significant class of endocrine disrupting chemicals that humans and animals around the world are exposed to constantly. Agrochemicals can act as endocrine disrupting chemicals through a variety of mechanisms. Recent studies have shown that several mechanisms of action involve the ability of agrochemicals to mimic the interaction of endogenous hormones with nuclear receptors such as estrogen receptors, androgen receptors, peroxisome proliferator activated receptors, the aryl hydrocarbon receptor, and thyroid hormone receptors. Further, studies indicate that agrochemicals can exert toxicity through non-nuclear receptor-mediated mechanisms of action. Such non-genomic mechanisms of action include interference with peptide, steroid, or amino acid hormone response, synthesis and degradation as well as epigenetic changes (DNA methylation and histone modifications). This review summarizes the major mechanisms of action by which agrochemicals target the endocrine system.

Prenatal Exposure to Di(2-Ethylhexyl) Phthalate Causes Long-Term Transgenerational Effects on Female Reproduction in Mice.

Di(2-ethylhexyl) phthalate (DEHP) is a plasticizer in many consumer products. Although DEHP is a known endocrine disruptor, little is known about the effects of DEHP exposure on female reproduction. Thus, this study tested the hypothesis that prenatal DEHP exposure affects follicle numbers, estrous cyclicity, and hormone levels in multiple generations of mice. Pregnant CD-1 mice were orally dosed with corn oil (vehicle control) or DEHP (20 and 200 µg/kg/d and 500 and 750 mg/kg/d) from gestational day 11 until birth. The F1 females were mated with untreated males to create the F2 generation, and the F2 females were mated with untreated males to create the F3 generation. At 1 year, ovaries, hormones, and estrous cycles were analyzed in each generation. Prenatal DEHP exposure altered estrous cyclicity (750 mg/kg/d), increased the presence of ovarian cysts (750 mg/kg/d), and decreased total follicle numbers (750 mg/kg/d) in the F1 generation. It also decreased anogenital distance (200 µg/kg/d) and altered follicle numbers (200 µg/kg/d and 500 mg/kg/d) in the F2 generation, and it altered estrous cyclicity (20 and 200 µg/kg/d and 500 and 750 mg/kg/d) and decreased folliculogenesis (200 µg/kg/d and 500 mg/kg/d) in the F3 generation. Further, prenatal DEHP increased estradiol levels (F1 and F3), decreased testosterone levels (F1, F2, and F3), decreased progesterone levels (F2), altered gonadotropin hormone levels (F1 and F3), and decreased inhibin B levels (F1 and F3). Collectively, these data show that prenatal exposure to DEHP has multigenerational and transgenerational effects on female reproduction and it may accelerate reproductive aging.

Bisphenol A Exposure, Ovarian Follicle Numbers, and Female Sex Steroid Hormone Levels: Results From a CLARITY-BPA Study.

Bisphenol A (BPA) is an industrial chemical found in thermal receipts and food and beverage containers. Previous studies have shown that BPA can affect the numbers and health of ovarian follicles and the production of sex steroid hormones, but they often did not include a wide range of doses of BPA, used a small sample size, focused on relatively short-term exposures to BPA, and/or did not examine the consequences of chronic BPA exposure on the ovaries or steroid levels. Thus, this study was designed to examine the effects of a wide range of doses of BPA on ovarian morphology and sex steroid hormone production. Specifically, this study tested the hypothesis that prenatal and continuous BPA exposure reduces ovarian follicle numbers and sex steroid hormone levels. To test this hypothesis, rats were dosed with vehicle, ethinyl estradiol (0.05 and 0.5 µg/kg body weight/d), or BPA (2.5, 25, 250, 2500, and 25,000 µg/kg body weight/d) from gestation day 6 until 1 year as part of the Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA). Ovaries and sera were collected on postnatal days 1, 21, and 90, and at 6 months and 1 year. The ovaries were subjected to histological evaluation of follicle numbers and the sera were subjected to measurements of estradiol and progesterone. Collectively, these data indicate that BPA exposure at some doses and time points affects ovarian follicle numbers and sex steroid levels, but these effects are different than those observed with ethinyl estradiol exposure and some previous studies on BPA.

Prenatal Exposure to DEHP Induces Premature Reproductive Senescence in Male Mice.

Di-(2-ethylhexyl) phthalate (DEHP) is the most commonly used phthalate, and it is an endocrine-disrupting chemical. This study tested a hypothesis that prenatal exposure to DEHP lays the foundation for premature gonadal dysfunction and subsequent reproductive senescence in male mice. Pregnant female CD-1 mice were orally dosed with vehicle control (tocopherol-stripped corn oil) or with 20 µg/kg/day, 200 µg/kg/day, 500 mg/kg/day, or 750 mg/kg/day of DEHP from gestational day 11 to birth. Overall, the prenatal DEHP exposure did not cause any overt physical health problems in male offspring, as no significant differences in their body nor gonadal weight were seen up to the age of 23 months. However, an age- and dose-dependent gonadal dysfunction was observed. As early as 7 months of age, the 750 mg/kg/day group of mice exhibited significantly reduced fertility. At 19 months of age, 86% of the 750 mg/kg/day mice became infertile, whereas only 25% of the control mice were infertile. At this age, all of the DEHP-exposed mice had lower serum testosterone levels, higher serum estradiol levels, and higher LH levels compared with control mice. Histological evaluations showed that mice prenatally exposed to DEHP displayed a wide array of gonadal and epididymal abnormalities such as increased germ cell apoptosis, degenerative seminiferous tubules, oligozoospermia, asthenozoospermia, and teratozoospermia in comparison to age-matching control mice. In summary, this study shows that prenatal exposure to DEHP induces premature reproductive senescence in male mice.