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

Advances in polychlorinated biphenyls-induced female reproductive toxicity

Polychlorinated biphenyls (PCBs) are a class of endocrine-disrupting chemicals (EDCs) widely present in the environment. PCBs have been of concern due to their anti/estrogen-like effects, which make them more toxic to the female reproductive system. However, there is still a lack of systematic reviews on the reproductive toxicity of PCBs in females, so the adverse effects and mechanisms of PCBs on the female reproductive system were summarized in this paper. Our findings showed that PCBs are positively associated with lower pregnancy rate, hormone disruption, miscarriage and various reproductive diseases in women. In animal experiments, PCBs can damage the structure and function of the ovaries, uterus and oviducts. Also, PCBs could produce epigenetic effects and be transferred to the offspring through the maternal placenta, causing development retardation, malformation and death of embryos, and damage to organs of multiple generations. Furthermore, the mechanisms of PCBs-induced female reproductive toxicity mainly include receptor-mediated hormone disorders, oxidative stress, apoptosis, autophagy, and epigenetic modifications. Finally, we also present some directions for future research on the reproductive toxicity of PCBs. This detailed information provided a valuable reference for fully understanding the reproductive toxicity of PCBs.

Concentrations and biomagnification of persistent organic pollutants in three granivorous food chains from an abandoned e-waste recycling site

The distinct accumulation patterns of persistent organic pollutants (POPs) among granivorous groups and the biomagnification of POPs from crops to granivorous species are still unclear. In this study, occurrence and biomagnification of POPs in three granivorous species including spotted dove (Spilopelia chinensis), scaly-breasted munia (Lonchura punctulata), and reed vole (Microtus fortis Buechner) from a former e-waste recycling site were investigated. Concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in granivorous species ranged from 41.5 to 1370 and 21.1 to 3890 ng/g lipid weight, respectively. PCBs and PBDEs were the main POPs in birds and vole, while decabromodiphenyl ethane (DBDPE) and PBDEs were predominant POPs in crops. The dominance of BDE 209 was observed in samples, with few exceptions. Biomagnification factors (BMFs) of POPs in birds and vole were measured. BMFs of most POPs in vole were higher than those in birds, indicating that POPs had greater biomagnification potential in vole. Species-specific biomagnification of POPs might be affected by many factors, such as physiochemical properties and metabolic capability of POPs. There was significant correlation between concentration ratios of POPs in muscle/air and log KOA, which demonstrated that respiratory elimination to air affects biomagnification of POPs in granivorous birds and vole.

Prenatal and postnatal exposure to polychlorinated biphenyls alter follicle numbers, gene expression, and a proliferation marker in the rat ovary

Polychlorinated biphenyls (PCBs) were used in industrial applications until they were banned in the 1970s, but they still persist in the environment. Little is known about the long-term effects of exposure to PCB mixtures on the rat ovary during critical developmental periods. Thus, this study tested whether prenatal and postnatal exposures to PCBs affect follicle numbers and gene expression in the ovaries of F1 offspring. Sprague-Dawley rats were treated with vehicle or Aroclor 1221 (A1221) at 1 mg/kg/day during embryonic days 8-18 and/or postnatal days (PND) 1-21. Ovaries from F1 rats were collected for assessment of follicle numbers and differential expression of estrogen receptor 1 (Esr1), estrogen receptor 2 (Esr2), androgen receptor (Ar), progesterone receptor (Pgr), and Ki-67 (Ki67) at PNDs 8, 32, and 60. Sera were collected for measurement of estradiol concentrations. Prenatal exposure to A1221 significantly decreased the number of primordial follicles and the total number of follicles at PND 32 compared to control. Postnatal PCB exposure borderline increased Ki67 gene expression and significantly increased Ki67 protein levels (PND 60) compared to control. Combined prenatal and postnatal PCB exposure borderline decreased Ar expression (PND 8) compared to control. However, PCB exposure did not significantly affect the expression of Pgr, Esr1, and Esr2 or serum estradiol concentrations compared to control at any time point. In conclusion, these data suggest that PCB exposure affects follicle numbers and levels of the proliferation marker Ki67, but it does not affect expression of some sex steroid hormone receptors in the rat ovary.

Biomagnification of Persistent Organic Pollutants from Terrestrial and Aquatic Invertebrates to Songbirds: Associations with Physiochemical and Ecological Indicators

Biomagnification of persistent organic pollutants (POPs) is affected by physiochemical properties of POPs and ecological factors of wildlife. In this study, influences on species-specific biomagnification of POPs from aquatic and terrestrial invertebrates to eight songbird species were investigated. The median concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in birds were 175 to 13 200 ng/g lipid weight (lw) and 62.7 to 3710 ng/g lw, respectively. Diet compositions of different invertebrate taxa for songbird species were quantified by quantitative fatty acid signature analysis. Aquatic insects had more contributions of more hydrophobic POPs, while terrestrial invertebrates had more contributions of less hydrophobic PCBs in songbirds. Biomagnification factors (BMFs) and trophic magnification factors had parabolic relationships with log K_OW and log K_OA. The partition ratios of POPs between bird muscle and air were significantly and positively correlated with log K_OA of POPs, indicating respiratory elimination as an important determinant in biomagnification of POPs in songbirds. In this study, the species-specific biomagnification of POPs in songbird species cannot be explained by stable isotopes of carbon and nitrogen and body parameters of bird species. BMFs of most studied POPs were significantly correlated with proportions of polyunsaturated fatty acids in different species of songbirds.

Use of Chicken Embryo Model in Toxicity Studies of Endocrine-Disrupting Chemicals and Nanoparticles

Lab animals such as mice and rats are widely used in toxicity research of food additive and pharmaceutics, despite the well-recognized research limitation such as the inability to simulate human neurological diseases, faster absorption of chemicals, big variations among species, and high cost when using a large number of animals. The Society of Toxicology's guidance now focuses on minimizing discomfort and distress of lab animals, finding alternative ways to reduce animal number, replacing animals with in vitro models, and complying to the animal welfare policies. The chicken embryonic model can be a better alternative to mice and rats because of its abundant availability and cost-effectiveness. It can be studied in both laboratory and natural environment, with easy manipulation in ovo or in vivo. The objective of this review paper is to evaluate the use of chicken embryonic model in toxicity evaluation for endocrine-disrupting chemicals (EDCs) and nanoparticles (NPs) by different end points to determine more comprehensive toxic responses. The end points include chicken embryonic mortality and hatchability, developmental malformation analysis, hormonal imbalance, physiological changes in endocrine organs, and antiangiogenesis. Major research methodologies using chicken embryos are also summarized to demonstrate their versatile practice and valuable application in modern toxicity evaluation of EDCs and NPs.

Chick stem cells: current progress and future prospects

Chick embryonic stem cells (cESCs) can be derived from cells obtained from stage X embryos (blastoderm stage); these have the ability to contribute to all somatic lineages in chimaeras, but not to the germ line. However, lines of stem cells that are able to contribute to the germ line can be established from chick primordial germ cells (cPGCs) and embryonic germ cells (cEGCs). This review provides information on avian stem cells, emphasizing different sources of cells and current methods for derivation and culture of pluripotent cells from chick embryos. We also review technologies for isolation and derivation of chicken germ cells and the production of transgenic birds.

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Chick embryonic stem cells (cESCs) can be derived from a variety of sources.

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cESCs can contribute to all somatic cell types but not to the germ line.

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germ cells can be isolated from early embryos, embryonic blood and gonads.

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germ cells can establish self-renewing lines and contribute to the germline.

Eggshell thinning and decreased concentrations of vitamin E are associated with contaminants in eggs of ivory gulls

The ivory gull is a high Arctic seabird species threatened by climate change and contaminant exposure. High levels of contaminants have been reported in ivory gull Pagophila eburnea eggs from Svalbard and the Russian Arctic. The present study investigated associations between high levels of contaminants (organochlorinated pesticides (OCPs), polychlorinated biphenyls (PCBs), brominated flame retardants (BFRs), perfluorinated alkyl substances (PFASs) and mercury (Hg)) and three response variables: eggshell thickness, retinol (vitamin A) and α-tocopherol (vitamin E). Negative associations were found between levels of OCPs, PCBs and BFRs and eggshell thickness (p<0.021) and α-tocopherol (p<0.023), but not with retinol (p>0.1). There were no associations between PFASs and mercury and the three response variables. Furthermore, the eggshell thickness was 7-17% thinner in the present study than in archived ivory gull eggs (≤1930). In general, a thinning above 16 to 20% has been associated with a decline in bird populations, suggesting that contaminant-induced eggshell thinning may constitute a serious threat to ivory gull populations globally.

Basic fibroblast growth factor suppresses meiosis and promotes mitosis of ovarian germ cells in embryonic chickens

Basic fibroblast growth factor (bFGF or FGF2) plays diverse roles in regulating cell proliferation, migration and differentiation during embryo development. In this study, the effect of bFGF on ovarian germ cell development was investigated in the embryonic chicken by in vitro and in vivo experiments. Results showed that a remarkable decrease in bFGF expression in the ovarian cortex was manifested during meiosis progression. With ovary organ culture, we revealed that meiosis was initiated after retinoic acid (RA) treatment alone but was decreased after combined bFGF treatment that was detected by real time RT-PCR, fluorescence immunohistochemistry and Giemsa staining. Further, no significant difference in mRNA expression of either RA metabolism-related enzymes (Raldh2 and Cyp26b1) or RA receptors was displayed after bFGF challenge. This result suggests that the suppression of bFGF on meiosis was unlikely through inhibition of RA signaling. In addition, as a mitogen, bFGF administration increased germ cell proliferation (via BrdU incorporation) in cultured organ or cells in vitro and also in developing embryos in vivo. In contrast, blockade of bFGF action by SU5402 (an FGFR1 antagonist) or inhibition of protein kinase C signaling showed inhibited effect of bFGF on mitosis. In conclusion, bFGF suppresses RA-induced entry of germ cells into meiosis to ensure embryonic ovarian germ cells to maintain at undifferentiated status and accelerate germ cell proliferation by binding with FGFR1 involving PKC activation in the chicken.

Effects of the endocrine disruptors atrazine and PCB 153 on the protein expression of MCF-7 human cells

Polychlorinated biphenyls (PCBs) and a number of pesticides can act as endocrine disrupting compounds (EDCs). These molecules exhibit hormonal activity in vivo, and can therefore interact and perturb normal physiological functions. Many of these compounds are persistent in the environment, and their bioaccumulation may constitute a significant threat for human health. Physiological abnormalities following exposure to these xenobiotic compounds go along with alterations at the protein level of individual cells. In this study, MCF-7 cells were exposed to environmentally relevant concentrations of atrazine, PCB153 (100 ppb, respectively), 17-beta estradiol (positive control, 10 nM) and a negative control (solvent) for t = 24 h (n = 3 replicates/exposure group). After trizol extraction and protein solubilization, protein expression levels were studied by 2D-DIGE. Proteins differentially expressed were excised, trypsin-digested, and identified by MALDI-ToF-ToF, followed by NCBInr database search. 2D-DIGE experiments demonstrated that 49 spots corresponding to 29 proteins were significantly differentially expressed in MCF-7 cells (>1.5-fold, P < 0.05, Student's paired t test). These proteins belonged to various cellular compartments (nucleus, cytosol, membrane), and varied in function; 88% of proteins were down-regulated during atrazine exposure, whereas 75% of proteins were up-regulated by PCB153. Affected proteins included those regulating oxidative stress such as superoxide dismutase and structural proteins such as actin or tropomyosin, which may explain morphological changes of cells already observed under the microscope. This study highlights the susceptibility of human cells to compounds with endocrine disrupting properties.

Overview of developmental and reproductive toxicity research in China: history, funding mechanisms, and frontiers of the research

Reproductive and developmental toxicology (DART) is the discipline that deals with adverse effects on male and female resulting from exposures to harmful chemical and physical agents. DART research in China boasted a long history, but presently has fallen behind the western world in education and research. The funding mechanisms for DART research in China were similar to that for other toxicological disciplines, and the funding has come from research grants and fellowships provided by national, ministerial, and provincial institutions. Finally, the frontiers of DART research in China could be summarized as follows: (1) use of model animals such as the zebrafish and roundworm, and use of cutting-edge techniques such as stem cell culture, as well as transgenic, metabonomic, and virtual screening to study the mechanisms of developmental toxicity for some important toxicants in China; (2) use of model animals and other lower-level sentinel organisms to evaluate and monitor the developmental toxicogical risk of environmental chemicals or pollutants; (3) epidemiological studies of some important reproductive hazards; (4) in-depth studying of the reproductive and developmental toxicity of some important environmental chemicals; and (5) evaluation and study of the reproductive and developmental toxicity of traditional Chinese medicines.

The chick embryo: an animal model for detection of the effects of hormonal compounds

Hormonal compounds are a class of pharmaceutical product that disrupt the endocrine system of animals and humans. Exposure to these molecules, even at low concentrations, can have severely damaging effects on the environment, to organisms, and to humans. The cumulative presence of these compounds is also characterized by synergistic effects which are difficult to estimate. They are an underestimated danger to the environment and to the human population. This paper presents an in-vivo model enabling to assessment of the real impact of exposure to hormonal compounds and the synergistic effect which can be involved. The anatomical effects of in-ovo exposure to two natural estrogen compounds (estrone and estriol, at 600 ng g(-1)) and a synthetic estrogen (ethynylestradiol, at 20 ng g(-1)) have been investigated. Estrone and estriol lead to morphological defects, mainly in the urogenital system of the developing chick embryo, whereas ethynylestradiol has fewer effects. Estriol caused persistence of Müllerian ducts in 50% of male embryos and hypertrophic oviducts in 71% of females. Estrone had the same effects but at the percentages were lower. Kidney dysfunction was also observed, but only with estrone, in both males and females. We also tested estrogenic compounds in two types of cell line which are estrogen sensitive (BG1 and MCF7) then completed and confirmed our previous in-vivo results. Seven pharmaceutical-like compounds--estrone (E1), estradiol (E2), estriol (E3), ethynylestradiol (EE(2)), carbamazepine (C), genistein (G), and bisphenol-A (BPA)--were tested alone or in mixtures. Different effects on the two cell lines were observed, indicating that endocrine compounds can act differently on this organism. Experiments also showed that these molecules have synergistic action and induce more severe effects when they are in mixtures.

Protective effects of antioxidant vitamins on Aroclor 1254-induced toxicity in cultured chicken embryo hepatocytes

Primary culture of chicken embryo hepatocytes (CEHs) was established to reveal toxicity of polychlorinated biphenyls (PCBs) and attenuating effects of antioxidants vitamin E (VE), vitamin C (VC) and vitamin A (VA) on PCBs-induced cytotoxicity. CEHs were dispersed from 14-day-old chicken embryo livers and exposed to Aroclor 1254 (A1254) in the range of 0.1-10 microg/ml, A1254 (10 microg/ml) and each vitamin (10 microg/ml) for 24 h. Cell viability was evaluated by determinations of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) leakage. The antioxidant status, namely cellular lipid peroxidation, was evaluated by measuring the thiobarbituric acid reactive substances (TBARS) and glutathion (GSH) levels and superoxide dismutase (SOD) activities. The cultured CEHs maintained normal polygonal cell shape and formed confluent monolayer after 24-h culture. A1254 (10 microg/ml) caused irreversible damage to cell membrane integrity and induced cell death in a dose-dependent manner. It induced increased TBARS production, decreased SOD activity and GSH concentration. VE, VC and VA alone or combinations of VE+VC and VE+VA significantly attenuated A1254-induced toxic effects, which suggested that lipid peroxidation was involved in the sequence of events leading to A1254-induced damage or death of the cultured CEHs. These results indicated that CEHs in serum-free culture represented a suitable model for rapid toxicity assessment of environmental pollutants such as PCBs in a visible manner. Antioxidant vitamins displayed protective effects on CEHs from A1254-induced damage through preventing lipid peroxidation.

Stimulating effects of androgen on proliferation of cultured ovarian germ cells through androgenic and estrogenic actions in embryonic chickens

The effect of androgen on germ cell proliferation was evaluated by a chicken ovarian germ-somatic cell co-culture model and the mechanisms were explored. Ovarian cells were dispersed from 18-day-old embryos, cultured in serum-free McCoy's 5A medium and challenged with testosterone (T) alone or in combinations with androgen receptor antagonist Flutamide, estrogen receptor antagonist Tamoxifen or aromatase inhibitor Letrozole for 48 h. Germ cells were identified by c-kit immunocytochemistry. The number of germ cells was counted and the proliferating cells were identified by immunocytochemistry of proliferating cell nuclear antigen (PCNA). The labeling index (LI) was determined for germ cells. Results showed that T (10(-7) to 10(-6)M) significantly increased the number of germ cells (P<0.05) and this stimulating effect was inhibited by Flutamide (10-1000 ng/ml), Tamoxifen (10-1000 ng/ml) or Letrozole (10(-9) to 10(-7)M) in a dose-dependent manner. Furthermore, PCNA-LI of germ cells displayed similar changes with the numbers of germ cells. These results indicated that T-stimulated proliferation of cultured ovarian germ cells through both, androgenic and estrogenic actions in embryonic chickens.

Toxic and hormonal effects of polychlorinated biphenyls on cultured testicular germ cells of embryonic chickens

The toxic and hormonal effects of polychlorinated biphenyls (PCBs) on testicular germ cell development were revealed with a germ-Sertoli cell co-culture model from embryonic chickens. Testicular cells were dispersed from 18-day-old embryo and exposed to Aroclor 1254 (A1254) alone and combined with alpha-tocopherol, flutamide and tamoxifen for discretion of the toxic and hormonal actions of A1254. Cell damage was evaluated by determinations of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) leakage. Results showed that 10 microg/ml A1254 induced condensed nuclear and vacuolated cytoplasm; cell exfoliated and broke into pieces as a sign of cell degeneration after treatment for 6 h. The morphological cytotoxicity was confirmed by MTT reduction and LDH leakage assays. alpha-Tocopherol attenuated the toxic effect of A1254. After culture for 48 h, A1254 (0.1-1 microg/ml) manifested obvious hormonal effect to induce germ cell proliferation, while 10 microg/ml A1254 displayed obvious toxic and hormonal effects on germ and somatic cells. Blocking of either androgen receptor by flutamide or estrogen receptor by tamoxifen inhibited hormonal effect of A1254 on germ cell proliferation and increased the cytotoxicity. The above results indicated that A1254 exposure imposed both toxic and hormonal effects on embryonic testicular germ cell proliferation, which may cause reproductive disorder and even infertility at adulthood.

Establishment of a germ-somatic cell coculture model for toxicity assessment of environmental endocrine disrupters

The objective of this study was to evaluate the effect of environmental endocrine disrupting chemicals by a germ--somatic cell coculture model in vitro. Testicular cells of 18-day-old chicken embryos were dispersed and cultured in different media. Results showed that somatic cells formed a monolayer to which germ cells adhered in the medium supplemented with insulin (Ins), transferrin (Tf), and selenite (Se) (ITS medium). However, the medium without ITS or single subtraction of Ins, Tf, or Se could not maintain cell survival in culture because many germ cells manifested apoptosis. Three known endocrine disrupters were selected to test the feasibility of this model. Aroclor 1254 (A1254, 10 microg/mL) induced condensed nuclei and vacuolated cytoplasm in germ cells, which was further confirmed by a cell proliferation assay. However, after culture for 48 h, the number of germ cells displayed a significant augment stimulated by A1254 (0.1-10 microg/mL) (P < 0.05). Similarly, 2,4-dichlorophenoxyacetic acid and busulfan displayed notable toxic effects on germ cells, and germ cell number and cell viability were significantly decreased in a dose-dependent manner (P < 0.05). The above results indicate that the chicken testicular germ-somatic cell coculture model is a simple, rapid, and veracious in vitro tool for evaluating the effect of environmental endocrine disrupters on functional basis of the cultured cells.

Effects of follicle-stimulating hormone and 17β-estradiol on proliferation of chicken embryonic ovarian germ cells in culture

The effects of follicle-stimulating hormone (FSH) and 17beta-estradiol (E2) on chicken ovarian germ cell proliferation were evaluated through a germ-somatic cell coculture model. Ovarian cells from the left ovaries of 18-day-old chicken embryos were cultured in serum-free McCoy's 5A medium at 39 degrees C and challenged with FSH (0.25-1.0 IU/mL) or E2 (10(-8)-10(-5) M) alone and in combination for 48 h. The number of germ cells was counted, and the proliferating cells were immunolocalized by a specific antibody against proliferating cell nuclear antigen (PCNA). The labeling index (LI) was determined for germ cells. Results revealed that germ cells could survive and kept proliferating under support of somatic cells. Germ cells were localized by expression of a specific antibody for stem cell factor receptor c-kit. Both FSH (0.25-1.0 IU/mL) and E2 (10(-7)-10(-5) M) alone induced a marked increase in germ cell number (P<0.05), and PCNA-LI of germ cells was greater in FSH-treated groups (0.25-1.0 IU/mL) and E2-treated groups (10(-8)-10(-5) M), compared with vehicle-treated group (P<0.05). Furthermore, FSH manifested a synergistic effect with E2 (10(-6)-10(-5) M) in stimulating germ cell proliferation. These results indicate that FSH might interact with estrogen to promote ovarian germ cell proliferation in embryonic chickens near hatching.