Effects of endocrine disrupting compounds on the pathology and oestrogen receptor alpha and beta distribution in the uterus and cervix of ewe lambs

Actions of Bisphenol A on Different Feto-Maternal Compartments Contributing to Preterm Birth

Preterm birth remains to be one of the most prevalent obstetric complications worldwide. Since there are multiple etiological factors associated with this disease process, an integrative literature search in PubMed and Scopus databases on possible mechanism of action and effect of bisphenols on exposure on human or animal placental samples in preterm birth was conducted. From 2332 articles on initial literature search, 63 studies were included for full data extraction. Altogether, several pathways were shown to be possibly affected by bisphenols, leading to dysregulations in structural and endocrine foundation in the placenta, potential induction of senescence and failure of decidualization in the decidua, and possible propagation of inflammation in the fetal membranes. Combined, these actions may eventually counteract bisphenol-induced relaxation of the myometrium and promote contractility alongside fetal membrane weakening. In totality, these individual impairments in gestation-critical processes may lead to failure of maintenance of pregnancy, and thus effecting preterm birth.

Neonatal exposure to a glyphosate-based herbicide alters the uterine differentiation of prepubertal ewe lambs

The exposure to endocrine-disrupting compounds (EDCs), such as glyphosate-based herbicides (GBHs), during early life might alter female fertility. The aim of the present study was to evaluate the effects of neonatal exposure to a GBH on sheep uterine development. To achieve this, Friesian ewe lambs were exposed to GBH (2 mg/kg of body weight/day; n = 12) or vehicle (controls; n = 10) through s.c. injections, from postnatal day (PND) 1 to PND14; on PND45, the uteri were obtained to evaluate histomorphological and molecular parameters. Morphological parameters were determined by picrosirius-hematoxylin staining. Protein expression of Ki67 (as a cell proliferation marker), p27, and molecules involved in uterine organogenetic differentiation was measured by immunohistochemistry. We also determined the mRNA expression of the IGF molecular pathway by RT-PCR. Although histomorphology was not modified, the uteri of GBH-exposed ewe lambs showed lower cell proliferation, together with higher p27 protein expression. In addition, the uteri of GBH-exposed ewe lambs showed increased gene expression of insulin-like growth factor binding protein 3 (IGFBP-3), decreased expression of ERα in the luminal (LE) and glandular (GE) epithelia and in the subepithelial stroma (SS), and lower PR expression in the LE but higher in the GE and SS. In addition, GBH treatment decreased the uterine expression of Wnt5a in the GE, of Wnt7a in the SS, of β-catenin in the LE and GE, of Hoxa10 in the SS, and of Foxa2 in the GE as compared with controls. In conclusion, neonatal exposure to GBH decreased cell proliferation and altered the expression of molecules that control proliferation and development in the uterus. All these changes might have adverse consequences on uterine differentiation and functionality, affecting the female reproductive health of sheep. GBH may be responsible for uterine subfertility, acting as an EDC.

Neonatal exposure to a glyphosate-based herbicide alters the histofunctional differentiation of the ovaries and uterus in lambs

The aim of the present study was to compare the effect of oral and subcutaneous exposure to a glyphosate-based herbicide (GBH) on the female reproductive system, specifically in the ovaries and uterus of prepubertal lambs. To this end, ewe lambs were exposed to a s.c. (n: 5) or an oral (n: 5) environmentally relevant dose of GBH (2 mg/kg/day) or to vehicle (controls, n: 12), from postnatal day (PND) 1 to PND14. Serum glyphosate and aminomethylphosphonic acid (AMPA) concentrations were measured on PND15 and PND45. The ovaries and uterus were obtained and weighed on PND45. Ovarian follicular dynamics and uterine morphological features were determined by picrosirius-hematoxylin staining. The proliferation marker Ki67 was evaluated by immunohistochemistry in ovarian and uterine samples. Glyphosate but not AMPA was detected in serum of exposed lambs on PND15, whereas neither glyphosate nor AMPA were detected on PND45. Controls were negative for glyphosate and AMPA on PND15 and PND45. GBH exposure did not affect ovarian or uterine weight. However, on PND45, the ovary of GBH-exposed lambs showed altered follicular dynamics, increased proliferation of granulosa and theca cells, and decreased mRNA expression of FSHR and GDF9, whereas their uterus showed decreased cell proliferation but no alterations in the histomorphology or gene expression. In conclusion, GBH exposure altered the ovarian follicular dynamics and gene expression, and the proliferative activity of the ovaries and uterus of lambs. It is noteworthy that all the adverse effects found in the ovaries and uterus of both GBH-exposed groups were similar, independently of the administration route.

Epigenetics and developmental programming of welfare and production traits in farm animals

The concept that postnatal health and development can be influenced by events that occur in utero originated from epidemiological studies in humans supported by numerous mechanistic (including epigenetic) studies in a variety of model species. Referred to as the 'developmental origins of health and disease' or 'DOHaD' hypothesis, the primary focus of large-animal studies until quite recently had been biomedical. Attention has since turned towards traits of commercial importance in farm animals. Herein we review the evidence that prenatal risk factors, including suboptimal parental nutrition, gestational stress, exposure to environmental chemicals and advanced breeding technologies, can determine traits such as postnatal growth, feed efficiency, milk yield, carcass composition, animal welfare and reproductive potential. We consider the role of epigenetic and cytoplasmic mechanisms of inheritance, and discuss implications for livestock production and future research endeavours. We conclude that although the concept is proven for several traits, issues relating to effect size, and hence commercial importance, remain. Studies have also invariably been conducted under controlled experimental conditions, frequently assessing single risk factors, thereby limiting their translational value for livestock production. We propose concerted international research efforts that consider multiple, concurrent stressors to better represent effects of contemporary animal production systems.

Estrogen and glucocorticoid receptor agonists and antagonists in oocytes modulate the pattern of expression of genes that encode nuclear receptor proteins in very early stage rainbow trout (Oncorhynchus mykiss) embryos

Previous studies show that changes in estrogen (ER) and glucocorticoid receptor (GR) function in rainbow trout (Oncorhynchus mykiss) oocytes modulate the growth performance phenotype of embryo and juvenile progeny; the present study was undertaken to determine whether this altered growth performance is associated with changes in the expression of several growth-related genes in early-stage embryos. Unfertilized oocytes were incubated in the presence of various combinations of GR and ER agonists and antagonists; the oocytes were then fertilized and the expression of genes that encode for six nuclear receptor superfamily (NRS) proteins (GR1, GR2, ERα, ERβ, TRα, and TRβ) and the two IGF peptides (IGF1 and IGF2) were measured in the 7-, 13-, and 26-dpf embryos. By day 26 of embryogenesis, the expression of the six NRS-related genes of interest and that of igf2 were significantly enhanced in embryos reared from ER agonist- or ER antagonist-treated oocytes, regardless of whether the GR agonist, cortisol, was also included in the initial oocyte incubation medium. Conversely, the igf1 expression pattern among treatment groups was significantly enhanced in the cortisol-only treatment group and in the ER antagonist and GR antagonist groups that were co-incubated with cortisol. Additionally, in the ER agonist treatment groups igf1 expression was significantly inhibited when cortisol was included in the oocyte incubation medium. The findings show that a single in ovo exposure to the receptor agonists/antagonists markedly changed the programming of the expression of NRS-related and IGF-related genes of the early-stage trout embryos.

Environmental induction of the fetal epigenome

The healthy adult is the result of successful interaction between the maternal environment and the developing fetal epigenome. The Barker hypothesis first suggested that in utero exposure to the maternal environment impacts adult health and disease. Since the origin of this theory, numerous studies have lent further support. Epigenomic alteration involves DNA methylation and histone modifications. Pregnancy, when the epigenome is typically actively programmed, is a vulnerable time, when exposures may have the most profound epigenetic effect. Recent advances have allowed an understanding of the extent and mechanism by which environmental exposures alter the epigenome of the fetus. Healthcare providers who treat and counsel reproductive-age women are in a unique position to protect against these epigenetic alterations and therefore prevent adverse impact on the developing fetus that may manifest throughout life.

Photoperiod modulates access of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) to the brain and its effect on gonadotropin and thyroid hormones in adult ewes

The effects of photoperiod on the cerebrospinal fluid (CSF) concentration of six ortho-substituted polychlorinated biphenyls (PCBs: PCB28, PCB52, PCB101, PCB138, PCB153, and PCB180), the effects of an orally administered low dose of PCB153 (0.3mg/kg, three times a week for three weeks) on PCBs and thyroid hormones (THs) concentrations in the CSF and plasma, and the release of luteinizing hormone (LH) were determined in ovariectomized, estradiol-implanted ewes (2.5 years old) maintained indoors under artificial long day (LD, 16L: 8D) and short day (SD, 8L: 16D) conditions. Concentrations of two PCBs (PCB28 and PCB153) in the plasma and four PCBs in the CSF (PCB101, PCB138, PCB153, and PCB180) were significantly higher during LD than SD. Following PCB153 treatment, its concentration in the plasma was higher in SD (1.2 ± 0.3 ng/ml) than LD (0.2 ± 0.05 ng/ml), but similar in the CSF (10.2 ± 3.7 pg/ml vs. 13 ± 0.7 pg/ml) under both photoperiods. During SD, the concentration of PCB153 in the CSF was higher in treated animals than controls, while no differences were noted under LD. These findings indicate that in ewes, exposure of the brain to more highly chlorinated, ortho-substituted PCBs may be modulated by photoperiod. PCB153 treatment had no effect on plasma THs, but reduced total triiodothyronine concentration during LD and free thyroxine during SD in the CSF. Under both photoperiods, PCB153 reduced basal plasma LH and reinforced the inhibition of pulsatile LH release during LD. As PCB153 reduced LH and THs (which are involved in the seasonal control of reproduction in ewes), it may have a braking effect on seasonal transitions between active and inactive phases of reproduction.

Masculinization of the distal tubular and external genitalia in female sheep with prenatal androgen exposure

Prenatal exposure to endogenous or exogenous androgens alters the development of the female reproductive tract. Although lesions in ovaries and external genitalia of androgenized female sheep have been reported, lesions of the tubular genitalia have not. Testosterone propionate (TP) or dihydrotestosterone (DHT) was administered by intramuscular injection twice weekly to 32 ewes from 30 to 90 days of pregnancy. The ewes lambed normally. The reproductive tracts from 24 treated and 13 control postpubertal female offspring were examined at 10 months of age. The ovaries, oviducts, and uteri were grossly and histologically normal in both TP- and DHT-exposed sheep. However, in the DHT-treated sheep, the uterus connected to a misshapen, saccular vagina that opened into the urethra; in the TP-treated sheep, it ended in a blind sac. In both TP- and DHT-treated sheep, the urethra was approximately 5 times longer than that of control sheep, and it resembled a male urethra with bilateral male accessory genital glands. The urethra terminated in a fully developed penis in both TP- and DHT-treated sheep, and a scrotal sac was present (without testes). These results show that prenatal exposure of female sheep to exogenous androgens results in masculinization of the tubular and external genitalia.

Expression of genes for oestrogen and progesterone receptors in the cervix of anoestrous ewes treated with gonadotrophin releasing hormone with or without progesterone priming

The aim was to determine the oestrogens receptor alpha (ERα) mRNA and the binding capacity of oestrogens (ER) and progesterone receptor (PR) in the cervix of anoestrous ewes treated with gonadotrophin-releasing hormone (GnRH) with or without progesterone (P) priming, at the expected time of induced ovulation and early luteal phase. In Experiment 1, ewes were treated with P for 10 days (n=4), with nine micro-doses of GnRH followed by a GnRH bolus injection (n=4), or with P plus GnRH treatments (n=3), and tissues were harvested either without treatment (n=4), when P was removed, or 24h after the GnRH bolus injection. In Experiment 2, ewes were treated with the same GnRH or P plus GnRH treatments and tissues were harvested on Day 1 (n=12) or Day 5 (n=10) after the GnRH bolus injection. In the cranial cervix, the P treatment decreased and the GnRH treatment (after P treatment) increased the ERα mRNA, ER and PR concentrations (P<0.002). The ERα mRNA and ER concentrations were greater on Day 1, than on Day 5 in P plus GnRH treated ewes (P<0.0005). In the caudal cervix, lesser ERα mRNA, ER and PR concentrations than cranial cervix were found (P<0.0001). In conclusion, the ERα transcriptional activity and ER and PR binding capacity were strongly influenced by P and/or GnRH treatments in the cranial cervix, while the steroid receptors binding capacity remained unchanged in the caudal cervix of anoestrous ewes at the expected time of induced ovulation and early luteal phase.

Bisphenol-A exposure in utero leads to epigenetic alterations in the developmental programming of uterine estrogen response

Bisphenol-A (BPA) is a nonsteroidal estrogen that is ubiquitous in the environment. The homeobox gene Hoxa10 controls uterine organogenesis, and its expression is affected by in utero BPA exposure. We hypothesized that an epigenetic mechanism underlies BPA-mediated alterations in Hoxa10 expression. We analyzed the expression pattern and methylation profile of Hoxa10 after in utero BPA exposure. Pregnant CD-1 mice were treated with BPA (5 mg/kg IP) or vehicle control on d 9-16 of pregnancy. Hoxa10 mRNA and protein expression were increased by 25% in the reproductive tract of mice exposed in utero. Bisulfite sequencing revealed that cytosine-guanine dinucleotide methylation was decreased from 67 to 14% in the promoter and from 71 to 3% in the intron of Hoxa10 after in utero BPA exposure. Decreased DNA methylation led to an increase in binding of ER-alpha to the Hoxa10 ERE both in vitro as and in vivo as determined by EMSA and chromatin immunoprecipitation, respectively. Diminished methylation of the ERE-containing promoter sequence resulted in an increase in ERE-driven gene expression in reporter assays. We identify altered methylation as a novel mechanism of BPA-induced altered developmental programming. Permanent epigenetic alteration of ERE sensitivity to estrogen may be a general mechanism through which endocrine disruptors exert their action.

An Updated Weight of the Evidence Evaluation of Reproductive and Developmental Effects of Low Doses of Bisphenol A

There is controversy over whether low doses of bisphenol A (BPA, CAS no. 80-05-7) cause reproductive and developmental effects in humans. We update the 2004 weight-of-evidence assessment of an expert panel convened by Harvard's Center for Risk Analysis by critically evaluating over 50 additional studies published between April 2002 and February 2006 that examine in vivo reproductive and developmental toxicity in mammals at doses <or=5 mg/kg-d. Our findings are consistent with the Harvard study: some statistically significant findings in rats and mice exist but they are generally countered by more numerous studies showing no effect for similar endpoints. No effect is marked or consistent across species, doses, and time points. Some mouse studies report morphological changes in testes and sperm and some non-oral mouse studies report morphological changes in female reproductive organs. Owing to lack of first-pass metabolism, results from non-oral studies are of limited relevance to oral human exposure. Human biomonitoring indicates exposures lower than the "low" doses in the reviewed animal studies. Reports of human health impact are very limited and inconsistent. Taken together, the weight of evidence does not support the hypothesis that low oral doses of BPA adversely affect human reproductive and developmental health.

Effects of ethanol extracts from Adzuki bean (Phaseolus angularis Wight.) and Lima bean (Phaseolus lunatus L.) on estrogen and progesterone receptor phenotypes of MCF-7/BOS cells

In this study, the possible molecular mechanisms involved in the estrogen-like activities of ethanol extracts from two common Chinese legumes, i.e. Adzuki bean (Phaseolus angularis Wight.) and Lima bean (Phaseolus lunatus L.) were investigated. Reverse transcription-polymerase chain reaction (RT-PCR) measurement and western blot analysis were conducted to detect the functional mRNA and protein expressions, while immunofluorescence was used to determine the estrogen receptor (ER) intracellular distribution in the MCF-7/BOS cell line. The results indicated that (1) both mRNA and protein levels of progesterone receptor (PR) in the cell line increased after 48 h treatment with the extracts compared with those in the control; (2) Adzuki and Lima bean extracts might alter the ER intracellular distributions in two different manners: for the Adzuki bean, the ER appeared in both cytoplasm and nucleus, while for the Lima bean, it exhibited the same pattern as that of estradiol in which the ER almost disappeared in the nucleus and mainly occurred in the cytoplasm. Above all, the results showed a novel pattern of ER intracellular distribution in the MCF-7/BOS cell line upon exposure to Adzuki bean extract, suggesting that different pathways were involved in the estrogen-like activities of the ethanol extracts of Adzuki bean and Lima bean.

Xenoestrogen exposure imprints expression of genes (Hoxa10) required for normal uterine development

The developing reproductive tract is sensitive to endocrine perturbation. Bisphenol A (BPA), a xenoestrogen, is a common component of food storage plastics and dental composites. We tested the ability of BPA to alter expression of HOXA10, a gene necessary for uterine development. A dose-response increase in HOXA10 mRNA expression was demonstrated in Ishikawa cells treated with 0.1 nM to 25 microM BPA. To determine whether in utero BPA exposure resulted in a lasting alteration of uterine HOXA10 expression, mice were treated with 0.5-5.0 mg/kg BPA on gestational days 9-16. A dose-responsive increase was seen in stromal cell HOXA10 expression in 2- and 6-week-old mice exposed in utero. To discern the mechanism of BPA action, the HOXA10 estrogen response element (ERE) and autoregulatory element (ARE) were tested for BPA responsiveness. BPA drove luciferase expression from HOXA10-ERE and ARE reporter constructs. HOXA10 ERE mediated induction was blocked by ER antagonist ICI, while HOXA10 ARE induction was blocked by either ICI or HOXA10 antisense. BPA affects HOXA10 expression through the HOXA10 ERE and indirectly through the ARE. BPA initially alters HOXA10 expression through the ERE, however, the response is imprinted and uncoupled from estrogen stimulation in the adult. Several xenoestrogens alter HOX gene expression, indicating that HOX genes are a common target of endocrine disruption. In utero exposure to a xenoestrogen produces reproductive tract alterations by imprinting essential developmental regulatory genes.

Steroid hormones acutely regulate expression of a Nudix protein-encoding gene in the endometrial epithelium of sheep

Steroid hormones regulate endometrial gene expression to meet the needs of developing embryos. Our hypothesis is that steroid hormones transiently induce expression of genes in the endometrial epithelium to make the uterine environment different between the earliest days of pregnancy. We identified one such gene product using differential display-polymerase chain reactions. The gene product that was strongly induced in ewes between day 3 and 6 of the estrous cycle was cloned and sequenced to identify it as encoding a member of the Nudix family of hydrolase enzymes. Northern blot analyses indicated that NUDT16 mRNA concentrations were elevated 10-fold in the endometrium of sheep from day 5 to 9 of the estrous cycle and returned to basal levels by day 11. In assays of RNA samples from 15 different tissues from an adult ewe, the concentrations of NUDT16 mRNA were greatest in endometrium. In situ hybridization localized NUDT16 mRNA exclusively to the endometrial epithelial cells of the glands and uterine lumen. In ovariectomized ewes, NUDT16 mRNA was induced by a regimen of alternating estrogen and progesterone therapy designed to mimic the hormonal experiences of a ewe at day 6 of the estrous cycle. The final estrogen treatment in the regimen was critical to the expression of NUDT16 as well as progesterone receptor and estrogen receptor-beta genes. Characterization of the NUDT16 gene identified putative steroid hormone response elements, which can now be investigated to understand its unique pattern of regulation in the earliest days of pregnancy.

Differential estradiol effects on estrogen and progesterone receptors expression in the oviduct and cervix of immature ewes

In order to study the effect of estradiol-17beta (E2) on estrogen (E) and progesterone (P) receptors expression in oviduct and cervix of lambs, their respective transcripts (ERalpha mRNA and PR mRNA) were determined by solution hybridization and the receptor proteins (ER and PR) by binding assays after E2 treatments. Lambs (n=4 in each group) were not treated or treated with one, two or three i.m. injections of E2 (1 microg/kg) at 24 h of interval. Tissues were obtained 12 or 24 h after the last E2 injection. Estradiol treatments increased ERalpha mRNA and PR mRNA concentrations in an organ-dependent manner: transitory in the oviduct while maintained in the cervix. The E2 effect on the oviductal and cervical ER and PR concentrations were biphasic, with an initial reduction of receptors content that was followed by restoration. The ER restoration in oviduct was earlier than in the cervix. In summary, this study shows that E2 treatments may exert an inductive effect in ERalpha mRNA and PR mRNA levels and a biphasic effect in ER and PR concentrations in oviduct and cervix of immature ewe. These E2 effects varied in timing and strength depending on the organ of the reproductive tract.

Differential effects of the endocrine-disrupting compounds bisphenol-A and octylphenol on gonadotropin secretion, in prepubertal ewe lambs

This study examined the effects of long-term exposure to the endocrine-disrupting compounds (EDCs) Bisphenol-A (BPA) and Octylphenol (OP) on gonadotrophin secretion in pre-pubertal female sheep. Four-week-old, female lambs were randomly allocated to four groups (n=6), and twice each week treated with i.m. injections of either corn oil (vehicle controls), diethylstilbestrol (DES; 0.175mg/kg), BPA (3.5mg/kg) or OP (3.5mg/kg). After 5 weeks of treatment, animals were ovariectomized (ovx) and ovary weights recorded. Two weeks later, blood samples were collected from lambs every 15min for 6h, for LH pulse analysis. Animals were then euthanased and adrenal and kidney weight recorded. An age-related increase in tonic LH secretion was noted in Control, BPA- and OP-treated lambs, but was absent in DES-treated lambs. Following ovx, LH secretion increased in all except DES-treated lambs; FSH concentrations increased in all groups. BPA and DES significantly suppressed LH pulse frequency (C: 6.7+/-0.3pulses/6h, DES: 1.5+/-0.8pulses/6h, BPA: 2.3+/-0.8pulses/6h) and amplitude (C: 7.1+/-1.0ng/ml, DES: 1.9+/-0.6ng/ml, BPA: 1.6+/-0.4ng/ml). OP had no effect on LH secretion (Frequency: 5.8+/-0.5pulses/6h, amplitude: 8.0+/-2.0ng/ml). Ovary weight was similar among all groups. Results show that chronic in vivo exposure of prepubertal female lambs to BPA, at levels lower than those reported previously, can have significant effects on LH secretion that are comparable to those seen following exposure to the known xenoestrogen, DES. Exposure to an equal dose of the EDC OP, over the equivalent period of time was without effect on gonadotropin secretion in the prepubertal ewe lamb. These results indicate that exposure of prepubertal female lambs to the EDC BPA can induce significant effects on gonadotropin secretion, the potential long-term effects of exposure and the effects of these changes on reproductive performance and efficacy, therefore, merit further study.

The role of sex steroid receptors in sheep female reproductive physiology

Cell responsiveness to steroid hormones is related to the number and affinity of its receptors, thus factors affecting steroid expression will influence tissue sensitivity and functionality. The present review discusses the role of oestrogen and progesterone receptors in sheep female reproductive physiology. The mechanism of steroid hormone action in the target cell is introduced first; the tissue distribution, physiological functions and regulation of oestrogen receptor subtypes and progesterone receptor isoforms in ruminants are reported. The role of steroid receptors in target tissues (with emphasis on the uterus and pituitary gland) during different physiological events is addressed in an attempt to clarify oestrogen and progesterone actions in different developmental and reproductive stages: prepubertal period, oestrous cycle, pregnancy, post-partum period and seasonal anoestrus. The present review shows how the distinct reproductive stages are accompanied by dramatic changes in uterine receptor expression. The role of oestrogen and progesterone receptors in the molecular mechanism responsible for premature luteolysis that results in subnormal luteal function is discussed. Finally, the effect of nutrition on sex steroid receptor expression and the involvement on reproductive performance is reported.