Dichlorodiphenylchloroethylene elevates cytosolic calcium concentrations and oscillations in primary cultures of human granulosa-lutein cells

The Influence of Environmental Factors on Ovarian Function, Follicular Genesis, and Oocyte Quality

Endocrine-disrupting chemicals (EDCs) exist ubiquitously in the environment. Epidemiological data suggest that the increasing prevalence of infertility may be related to the numerous chemicals. Exposure to EDCs may have significant adverse impacts on the reproductive system including fertility, ovarian reserve, and sex steroid hormone levels. This chapter covers the common exposure ways, the origins of EDCs, and their effects on ovarian function, follicular genesis, and oocyte quality. Furthermore, we will review the origin and the physiology of ovarian development, as well as explore the mechanisms in which EDCs act on the ovary from human and animal data. And then, we will focus on the bisphenol A (BPA), which has been shown to reduce fertility and ovarian reserve, as well as disrupt steroidogenesis in animal and human models. Finally, we will discuss the future direction of prevention and solution methods.

Glycosylation Pattern and in vitro Bioactivity of Reference Follitropin alfa and Biosimilars

Recombinant follicle-stimulating hormone (FSH) (follitropin alfa) and biosimilar preparations are available for clinical use. They have specific FSH activity and a unique glycosylation profile dependent on source cells. The aim of the study is to compare the originator (reference) follitropin alfa (Gonal-f®)- with biosimilar preparations (Bemfola® and Ovaleap®)-induced cellular responses in vitro. Gonadotropin N-glycosylation profiles were analyzed by ELISA lectin assay, revealing preparation specific-patterns of glycan species (Kruskal-Wallis test; p < 0.05, n = 6) and by glycotope mapping. Increasing concentrations of Gonal-f® or biosimilar (1 × 10^-3-1 × 10³ ng/ml) were used for treating human primary granulosa lutein cells (hGLC) and FSH receptor (FSHR)-transfected HEK293 cells in vitro. Intracellular cAMP production, Ca²⁺ increase and β-arrestin 2 recruitment were evaluated by BRET, CREB, and ERK1/2 phosphorylation by Western blotting. 12-h gene expression, and 8- and 24-h progesterone and estradiol synthesis were measured by real-time PCR and immunoassay, respectively. We found preparation-specific glycosylation patterns by lectin assay (Kruskal-Wallis test; p < 0.001; n = 6), and similar cAMP production and β-arrestin 2 recruitment in FSHR-transfected HEK293 cells (cAMP EC₅₀ range = 12 ± 0.9-24 ± 1.7 ng/ml; β-arrestin 2 EC₅₀ range = 140 ± 14.1-313 ± 18.7 ng/ml; Kruskal-Wallis test; p ≥ 0.05; n = 4). Kinetics analysis revealed that intracellular Ca²⁺ increased upon cell treatment by 4 μg/ml Gonal-f®, while equal concentrations of biosimilars failed to induced a response (Kruskal-Wallis test; p < 0.05; n = 3). All preparations induced both 8 and 24 h-progesterone and estradiol synthesis in hGLC, while no different EC₅₀s were demonstrated (Kruskal-Wallis test; p > 0.05; n = 5). Apart from preparation-specific intracellular Ca²⁺ increases achieved at supra-physiological hormone doses, all compounds induced similar intracellular responses and steroidogenesis, reflecting similar bioactivity, and overall structural homogeneity.

Exposure to p,p'-DDE Induces Morphological Changes and Activation of the PKCα-p38-C/EBPβ Pathway in Human Promyelocytic HL-60 Cells

Dichlorodiphenyldichloroethylene (p,p′-DDE), the most persistent metabolite of dichlorodiphenyltrichloroethane (DDT), is still present in the human population. Both are present in the bone marrow of patients with bone marrow disorders, but thus far there are no studies that assess the capability of p,p′-DDE to affect myeloid cells. The aim of this study was to determine the effect of p,p′-DDE on promyelocytic cell differentiation and intracellular pathways related to this event. p,p′-DDE induced morphological changes compatible with promyelocytic differentiation in a concentration-dependent manner. The p,p′-DDE effect on [Ca²⁺]_i, C/EBPβ protein levels, PKCα and p38 activation, and the role of oxidative stress or PLA2 was assayed. Exposure to 1.9 μg/mL of p,p′-DDE increased [Ca²⁺]_i, PKCα, p38, and C/EBPβ protein levels; the increase of nuclear C/EBPβ protein was dependent on p38. PKCα phosphorylation was dependent on PLA2 and p,p′-DDE-induced oxidative stress. p38 phosphorylation induced by p,p′-DDE was dependent on PLA2, PKC activation, and oxidative stress. These effects of p,p′-DDE at concentrations found in human bone marrow may induce alterations in immature myeloid cells and could affect their cellular homeostasis. In order to establish the risk from exposure to p,p′-DDE on the development of bone marrow disorders in humans, these effects deserve further study.

p,p'-DDE activates CatSper and compromises human sperm function at environmentally relevant concentrations

STUDY QUESTION

Is the environmental endocrine disruptor p,p′-dichlorodiphenyldichloroethylene (p,p′-DDE) able to induce non-genomic changes in human sperm and consequently affect functional sperm parameters?

SUMMARY ANSWER

p,p′-DDE promoted Ca²⁺ flux into human sperm by activating CatSper channels even at doses found in human reproductive fluids, ultimately compromising sperm parameters important for fertilization.

WHAT IS KNOWN ALREADY

p,p′-DDE may promote non-genomic actions and interact directly with pre-existing signaling pathways, as already observed in other cell types. However, although often found in both male and female reproductive fluids, its effects on human spermatozoa function are not known.

STUDY DESIGN, SIZE, DURATION

Normozoospermic sperm samples from healthy individuals were included in this study. Samples were exposed to several p,p′-DDE concentrations for 3 days at 37°C and 5% CO₂in vitro to mimic the putative continuous exposure to this toxicant in the female reproductive tract in vivo. Shorter p,p′-DDE incubation periods were also performed in order to monitor sperm rapid Ca²⁺ responses. All experiments were repeated on a minimum of five sperm samples from different individuals.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All healthy individuals were recruited at the Biosciences School, University of Birmingham, the Medical Research Institute, University of Dundee and in the Human Reproduction Service at University Hospitals of Coimbra. Intracellular Ca²⁺ concentration ([Ca²⁺]_i) was monitored by imaging single spermatozoa loaded with Oregon Green BAPTA-1AM and further whole-cell patch-clamp recordings were performed to validate our results. Sperm viability and acrosomal integrity were assessed using the LIVE/DEAD sperm vitality kit and the acrosomal content marker PSA-FITC, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

p,p′-DDE rapidly increased [Ca²⁺]_i (P < 0.05) even at extremely low doses (1 pM and 1 nM), with magnitudes of response up to 200%, without affecting sperm viability, except after 3 days of continuous exposure to the highest concentration tested (P < 0.05). Furthermore, experiments performed in a low Ca²⁺ medium demonstrated that extracellular Ca²⁺ influx was responsible for this Ca²⁺ increase (P < 0.01). Mibefradil and NNC 55-0396, both inhibitors of the sperm-specific CatSper channel, reversed the p,p′-DDE-induced [Ca²⁺]_i rise, suggesting the participation of CatSper in this process (P < 0.05). In fact, whole-cell patch-clamp recordings confirmed CatSper as a target of p,p′-DDE action by monitoring an increase in CatSper currents of >100% (P < 0.01). Finally, acrosomal integrity was adversely affected after 2 days of exposure to p,p′-DDE concentrations, suggesting that [Ca²⁺]_i rise may cause premature acrosome reaction (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study, and caution must be taken when extrapolating the results.

WIDER IMPLICATIONS OF THE FINDINGS

A novel non-genomic p,p′-DDE mechanism specific to sperm is shown in this study. p,p′-DDE was able to induce [Ca²⁺]_i rise in human sperm through the opening of CatSper consequently compromising male fertility. The promiscuous nature of CatSper activation may predispose human sperm to the action of some persistent endocrine disruptors.

STUDY FUNDING/COMPETING INTEREST(S)

The study was supported by both the Portuguese National Science Foundation (FCT; PEst-C/SAU/LA0001/2011) and the UK Wellcome Trust (Grant #86470). SM was supported by the Infertility Research Trust. RST is a recipient of a PhD fellowship from FCT (SFRH/BD/46002/2008). None of the authors has any conflict of interest to declare.

Endocrine-disrupting chemicals in ovarian function: effects on steroidogenesis, metabolism and nuclear receptor signaling

Endocrine-disrupting chemicals (EDCs) are exogenous agents with the ability to interfere with processes regulated by endogenous hormones. One such process is female reproductive function. The major reproductive organ in the female is the ovary. Disruptions in ovarian processes by EDCs can lead to adverse outcomes such as anovulation, infertility, estrogen deficiency, and premature ovarian failure among others. This review summarizes the effects of EDCs on ovarian function by describing how they interfere with hormone signaling via two mechanisms: altering the availability of ovarian hormones, and altering binding and activity of the hormone at the receptor level. Among the chemicals covered are pesticides (e.g. dichlorodiphenyltrichloroethane and methoxychlor), plasticizers (e.g. bisphenol A and phthalates), dioxins, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons (e.g. benzo[a]pyrene).

Effects of selected food phytochemicals in reducing the toxic actions of TCDD and p,p'-DDT in U937 macrophages

To assess the effectiveness of selected food phytochemicals in reducing the toxic effects of the environmental toxicants, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and p,p′-DDT (DDT), we tested the potencies of auraptene, nobiletin, zerumbone, and (±)-13-hydroxy-10-oxo-trans-11-octadecenoic acid (13-HOA) in reversing the inflammatory action of these toxicants in U937 human macrophages. Using quantitative RT–PCR as the initial screening assay, we identified antagonistic actions of zerumbone and auraptene against the action of TCDD and DDT in up-regulating the mRNA expressions of COX-2 and VEGF. The functional significance of the inhibitory action of zerumbone on COX-2 expression was confirmed by demonstrating its suppression of TCDD-induced activation of COX-2 gene expression in mouse MMDD1 cells. We tested auraptene on DDT-induced reactive oxygen species (ROS) formation in U937 macrophages and found that auraptene is a powerful agent antagonizing this action of DDT. To confirm the significance of these actions of zerumbone and auraptene at the cellular level, we assessed their influence on TCDD-induced apoptosis resistance in intact U937 macrophages and found that they are capable of reversing this action of TCDD. In conclusion, zerumbone and auraptene were identified to be the most effective agents in protecting U937 macrophages from developing these cell toxic effects of TCDD and DDT.

Environmental contaminants and human infertility: hypothesis or cause for concern?

Throughout the 1980s and 1990s the crude human birth rate (live births per 1000 population) declined, indicating reduced fertility and suggesting a potential decline in fecundity (the potential to conceive). Detection of environmental contaminants in human tissues, together with reports of a global decline in semen quality, further fueled speculation that human infertility rates are increasing and environmental toxicants are potentially important causal agents associated with this change. However, there is little compelling evidence to suggest that infertility rates amongst the general population have changed over time. Moreover, recent studies suggest a rise in the fertility rates. While several studies documented increased time to pregnancy (TTP) in exposed study populations, other investigators were not able to replicate these findings. Nevertheless, studies involving occupational exposure together with results from animal experiments lend support to the conclusion that environmental contaminants potentially adversely affect fertility. Consequently, the impact of exposure to environmental contaminants on human fertility remains controversial. To test the hypothesis that environmental contaminant exposure was associated with enhanced risk of infertility, data concerning trends in fertility and infertility rates were examined to assess the impact of exposure of developing gametes to environmental contaminants. The relationship between exposure and reproductive outcomes was then examined to illustrate the range of adverse effects for reproductive toxicants with data sets of divergent depth and reliability. Data showed that only a weak association between exposure to environmental contaminants and adverse effects on human fertility exists. However, it is postulated that evidence of chemical exposure and potential health consequences of these exposures highlight the need for further research in this area.

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.

Binding of progesterone to cell surfaces of human granulosa-lutein cells

Progesterone is produced by granulosa cells under the influence of luteinizing hormone. Nuclear progesterone receptors have been found in rat granulosa cells. Human granulosa-lutein cells rapidly respond to progesterone with an increase in intracellular calcium suggesting the existence of a nongenomic mechanism. This study was conducted to determine whether binding of progesterone to granulosa cells could occur at the membrane. Granulosa cells were obtained from an in vitro fertilization program and examined immunohistochemically with an antiserum to membrane progesterone receptors. Approximately 14-70% of freshly harvested or cultured granulosa cells of six patients showed a positive reaction to the antiserum, limited to the cell membrane. Western blot analysis of homogenates of granulosa cells and a granulosa cell tumour confirmed the presence of progesterone receptors A, B and C and low amounts of a putative membrane receptor. These results demonstrate that the plasma membranes of human granulosa cells possess binding components for progesterone which may be involved in its nongenomic mechanism of action.

Rapid effects of pesticides on human granulosa-lutein cells

Following our previous demonstration that p,p'-DDE (dichlorodiphenylchloroethylene), at environmentally relevant concentrations, can rapidly increase intracellular calcium [Ca2+]i concentrations in human granulosa-lutein cells, we examined whether other pesticides, such as Kepone, o,p-DDE and methoxychlor, have similar effects. Cultured human granulosa-lutein cells were loaded with Fura-2 AM, and changes in [Ca2+]i concentrations within small areas of single cells were studied with a dynamic digital Ca2+ imaging system. Kepone, at concentrations of 0.2-2 nmol/ml, consistently increased [Ca2+]i concentrations 2-6 times higher than baseline values within minutes of exposure. Methoxychlor at concentrations of 2.8-280 nmol/ml failed to alter [Ca2+]i levels consistently in cells from 10 patients. However, at 0.28 and 1.4 nmol/ml, increases in [Ca2+]i concentrations could be elicited by methoxychlor. The isomer o,p-DDE at 3 nmol/ml increased [Ca2+]i in granulosa cells of 11/20 patients. Pertussis toxin treatment inhibited the [Ca2+]i increases induced by estradiol, p,p'-DDE, o,p-DDE and methoxychlor, but not by Kepone or progesterone, indicating that Kepone and progesterone may act through an insensitive G protein-coupled receptor. The [Ca2+]i increases induced by Kepone also occurred in Ca2+-free medium, suggesting that [Ca2+]i mobilization occurred from the smooth endoplasmic reticulum. Thapsigargin and cyclopiazonic acid, two inhibitors of the endoplasmic reticulum Ca2+ pump, also stimulated [Ca2+]i increases but did not inhibit the Ca2+ response to all the pesticides. These results demonstrate that pesticides can have a rapid effect on human granulosa-lutein cells, and a nongenomic mechanism of action is suggested.

Involvement of calcium and calmodulin in the regulation of ovarian steroidogenesis in Atlantic croaker (Micropogonias undulatus) and modulation by Aroclor 1254

The involvement of calcium-dependent signal transduction pathways in the regulation of ovarian steroidogenesis was investigated in Atlantic croaker. Treatment with the calcium ionophores A23187 and ionomycin caused a 2- to 5-fold increase in basal steroid accumulation by croaker ovarian tissue in vitro. A23187 potentiated human chorionic gonadotropin (hCG)-induced testosterone (T) accumulation, whereas it inhibited accumulation of estradiol-17beta (E(2)) and the conversion of T to E(2), suggesting that intracellular calcium modulates aromatase enzyme activity. Gonadotropin stimulation of ovarian steroidogenesis was decreased in the presence of EGTA and inhibitors of voltage-sensitive calcium channels (VSCCs) and inositol-1,4,5-triphosphate-receptors (IP(3)Rs), indicating that releases of calcium from both intracellular and extracellular stores are components of the signal transduction pathways initiated by gonadotropin. Calmodulin is also involved in the regulation of ovarian steroidogenesis in croaker, since the calmodulin inhibitors W-7 and trifluoperazine (TFP) attenuated hCG-stimulated T and E(2) accumulation. These results are broadly similar to those reported previously in goldfish and suggest that the major calcium-dependent signaling pathways involved in gonadotropin stimulation of ovarian steroidogenesis in tetrapods are also present in teleosts. In addition, the involvement of calcium in the regulation of aromatase activity was demonstrated for the first time in a vertebrate ovary. Finally, acute exposure to 0.001-1 ppm Aroclor 1254 induced up to a 5-fold increase in hCG-stimulated E(2) accumulation, and this effect was attenuated by co-treatment with inhibitors of VSCCs and calmodulin, suggesting the existence of a novel mechanism of endocrine disruption by an environmental contaminant involving alteration of calcium-dependent signaling pathways regulating steroidogenesis.

Rapid action of pesticides on cytosolic calcium concentrations in cultures of human umbilical vein endothelial cells

Persistent metabolites of pesticides such as p,p'-DDE, at environmentally relevant concentrations, have been shown to have a rapid effect on intracellular calcium [Ca2+]i concentrations in human granulosa-lutein cells. Since endocrine disrupting substances can be transferred from the maternal circulation to the fetus the present study examined whether the pesticides, kepone, o,p-DDE, p,p'-DDE and methoxychlor, could alter cytoplasmic calcium [Ca2+]cyt concentrations in human umbilical vein endothelial (HUVE) cells. Cultured HUVE cells were loaded with Fura-2 AM and changes in [Ca2+]cyt of single cells were studied using a dynamic digital Ca2+ imaging system. Kepone and methoxychlor consistently increased [Ca2+]cyt concentrations, similar to the effects of estradiol and progesterone. p,p'-DDE increased [Ca2+]cyt concentrations in 80% of experiments whereas o,p-DDE stimulated its increases in 42%. Estrone, estriol, pregnenolone and cortisol were not effective. These results demonstrate that pesticides can have a rapid effect on HUVE cells probably through a nongenomic mechanism of action.

Non-genomic action of estradiol and progesterone on cytosolic calcium concentrations in primary cultures of human granulosa-lutein cells

BACKGROUND

The present study examined whether the sex steroids, estradiol and progesterone, could alter cytoplasmic calcium concentrations ([Ca(2+)](cyt)) in human granulosa-lutein cells.

METHODS

Human granulosa cells were obtained at the time of oocyte retrieval for IVF and cultured for 3-7 days. Cells were loaded with Fura-2 AM and changes in [Ca(2+)](cyt) of single cells were studied using a dynamic digital Ca(2+) imaging system.

RESULTS

Both estradiol and progesterone stimulated elevations of [Ca(2+)](cyt) in Ca(2+)-containing medium within seconds of exposure of the granulosa-lutein cells to the steroid, but only estradiol caused an increase in [Ca(2+)](cyt) in Ca(2+)-free medium. Both ICI-182780 and RU 486 stimulated [Ca(2+)](cyt) increases and inhibited the effects of estradiol and progesterone, respectively. Tamoxifen also induced transient increases in [Ca(2+)](cyt) concentrations but inhibited the effects of both estradiol and progesterone. The inhibitory effects of tamoxifen, ICI-182780 and RU 4486 on [Ca(2+)](cyt) responses to estradiol and progesterone could be reversed with higher concentrations of estradiol and progesterone, respectively. The [Ca(2+)](cyt) effects induced with tamoxifen could not be eliminated by prior treatment with RU 486 or ICI-182780.

CONCLUSION

These results provide strong evidence that both estradiol and progesterone as well as the steroid antagonists, tamoxifen, RU 486 and ICI-182780, can act on human granulosa-lutein cells through a non-genomic mechanism.

Environmental and occupational factors affecting fertility and IVF success

Reproductive function has been shown to be sensitive to changes in the physical, psychosocial and chemical environments. Although reproductive effects of occupational exposure to hazardous chemicals have been well documented in the literature, the potential effects of chemical contaminants at levels representative of contemporary exposures in the general population are much less certain. Evidence for adverse effects of exposure to environmental contaminants is more conclusive among the lower animals than for humans where considerable controversy remains. In addition to potential reproductive hazards of exposure to environmental contaminants, there is also evidence for adverse reproductive effects of the physical and psychosocial environments. In this review we focus on the difficulties involved in linking exposure to putative hazardous substances in environmental and occupational settings to adverse reproductive outcomes, especially success of IVF procedures. We highlight the plausibility of adverse events through animal and cell studies and the application of these results to the interpretation of human data. We consider both the male and female partners since it is essentially their combined contributions of gametes which may be affected by chemicals, which lead to successful outcomes.