Cadmium effects on early development of chick embryos

Prenatal cadmium exposure impairs neural tube closure via inducing excessive apoptosis in neuroepithelium

Birth defects have become a public health concern. The hazardous environmental factors exposure to embryos could increase the risk of birth defects. Cadmium, a toxic environmental factor, can cross the placental barrier during pregnancy. Pregnant woman may be subjected to cadmium before taking precautionary protective actions. However, the link between birth defects and cadmium remains obscure. Cadmium exposure can induce excessive apoptosis in neuroepithelium during embryonic development progresses. Cadmium exposure activated the p53 via enhancing the adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) and reactive oxygen species' (ROS) level. And cadmium decreases the level of Paired box 3 (Pax3) and murine double minute 2 (Mdm2), disrupting the process of p53 ubiquitylation. And p53 accumulation induced excessive apoptosis in neuroepithelium during embryonic development progresses. Excessive apoptosis led to the failure of neural tube closure. The study emphasizes that environmental materials may increase the health risk for embryos. Cadmium caused the failure of neural tube closure during early embryotic day. Pregnant women may be exposed by cadmium before taking precautionary protective actions, because of cadmium concentration-containing foods and environmental tobacco smoking. This suggests that prenatal cadmium exposure is a threatening risk factor for birth defects.

Trace Metal Accumulation in Eggs of Wild Nile Crocodiles (Crocodylus niloticus) from Lake St Lucia, South Africa: Implications for Biomonitoring in a Global Biodiversity Hotspot

Nile crocodiles (Crocodylus niloticus) at Lake St Lucia, South Africa, have some of the highest blood lead (Pb) concentrations ever recorded in wildlife globally. Although exposure to Pb is known to pose major risks to wildlife reproductive success, potential impacts on crocodile reproduction at Lake St Lucia have yet to be examined. In this study, we investigated the accumulation of Pb and other trace metals (Al, V, Cr, Co, Cu, Ni, Zn and Cd) in eggs (n = 20) collected from five wild crocodile nests at Lake St Lucia. All metals analysed in this study were detected in egg contents, although concentrations varied considerably among nests and within clutches. Lead was detected in the contents of all eggs, but only at relatively low concentrations (43 ± 26 ng g^-1 dry weight). Although sampling limitations commonly associated with wild population surveys prevent a complete assessment of exposure variability, our findings suggest maternal transfer may not be a significant depuration pathway for Pb and females possibly clear Pb through other mechanisms (e.g. sequestration into claws, bone and osteoderms). Metal concentrations in eggshells and shell membranes were poorly correlated with concentrations measured in egg content and thus do not provide viable non-lethal indicators for monitoring metal exposure in Nile crocodiles. Intra-clutch variability accounted for a considerable proportion of the total variance in egg content metal concentrations, suggesting the "one egg" sampling strategy often applied in reptile studies may not be an effective biomonitoring tool for wild crocodilian populations. Although maternally derived Pb does not appear to present widespread toxicological concern at Lake St Lucia, adverse effects of Pb exposure on other reproductive functions (e.g. spermatogenesis) cannot be discounted and warrant further investigation.

Pyriproxyfen exposure induces DNA damage, cell proliferation impairments and apoptosis in the brain vesicles layers of chicken embryos

Larvicide pyriproxyfen (PPF), used in drinking water reservoirs to control Aedes mosquitoes, has already been shown as a possible cause of congenital anomalies in the central nervous system. However, the neurotoxic effects of PPF on the development of vertebrate embryos are still underexplored. Thus, the aim of this study was to investigate the effects of PPF on the morphometric parameters of the head and brain, as well as on the cell layers of the forebrain and midbrain, using embryos of Gallus domesticus as a model. Two sublethal PPF concentrations (0.01 mg/L and 10 mg/L), as defined by a survival curve, were tested. Analysis of the biometry of embryos showed significant reduction in body and brain mass and also in measurements of the head and brain. A reduction in cell layer thickness of the forebrain and midbrain was observed, accompanied by a reduction in the numerical density of cells per area. Changes in brain and head sizes and in the thickness of the cell layers of the forebrain and midbrain were significant at 10 mg/L PPF. Notably, PPF caused DNA doublestrand breaks and induced apoptosis in embryos exposed to 10 mg/L, which were accompanied by a reduction in cell proliferation. Regarding neuronal and glial differentiation, no changes were observed in the number of neurons and glial cells on the analyzed layers. Furthermore, PPF did not impact the head ossification process. These findings reveal that PPF is a strong stressor for neurodevelopment, causing damage to the cell architecture of brain vesicles.

From the Farm to the Lab: How Chicken Embryos Contribute to the Field of Teratology

Congenital anomalies and its causes, particularly, by external factors are the aim of the field called teratology. The external factors studied by teratology are known as teratogens and can be biological or environmental factors for example, chemicals, medications, recreational drugs, environmental pollutants, physical agents (e.g., X-rays and maternal hyperthermia) and maternal metabolic conditions. Proving the teratogenicity of a factor is a difficult task requiring epidemiology studies as well as experimental teratology evidence from the use of animal models, one of which is the chicken embryo. This model in particular has the advantage of being able to follow development live and in vivo, with rapid development hatching around 21 days, is cheap and easy to manipulate and to observe development. All this allows the chicken embryo to be used in drug screening studies, teratogenic evaluation and studies of mechanisms of teratogenicity. The chicken embryo shares morphological, biochemical and genetic similarities with humans as well as mammalian species, making them ideal to ascertain the actions of teratogens, as well as screen drugs to test for their safety. Pre-clinical trials for new drugs are carried out in rodents and rabbits, however, chicken embryos have been used to screen new compounds or analogs of thalidomide as well as to investigate how some drugs can lead to congenital malformations. Indeed, the chicken embryo has proved valuable in understanding how many congenital anomalies, seen in humans, arise following teratogen exposure. The aim of this review is to highlight the role of the chicken embryo as an experimental model for studies in teratology, exploring its use in drug screening studies, phenotypic evaluation and studies of teratogenic mechanisms of action. Here, we discuss many known teratogens, that have been evaluated using the chicken embryo model including some medicines, such as, thalidomide, valproic acid; recreational drugs including alcohol; environmental influences, such as viruses, specifically ZIKV, which is a newly discovered human teratogen. In addition, we discuss how the chicken embryo has provided insight on the mechanisms of teratogenesis of many compounds and also how this impact on drug safety.

Lead exposure affects cephalic morphogenesis and neural crest cells in Gallus gallus embryo

The morphogenesis of the head of vertebrates is a process that involves rapid growth and dynamic movements of various cell populations, including the neural crest cells (NCC). These pluripotent cells generated during neurulation have high proliferative and migratory capacity but xenobiotic agents can affect these migratory periods and cause congenital malformations. Lead (Pb) is the most common toxic metal in the environment and a potent teratogen that can affect growth and induce malformations. Despite the known toxic effects of Pb, there is a gap in knowledge about the impact of realistic concentrations of Pb at critical periods of early development. Here, we evaluated mortality, embryonic morphology, NCC migration, and the amount of Pb deposition in chicken embryos after 3 to 4 days of exposure. One of the most interesting observations in this study is that only about 34% of the injected Pb was present in the embryos after 4 days. We observed that exposure to Pb, even under low concentrations, increased mortality and the occurrence of malformations during embryonic development, especially in the cephalic region (CR). Although Pb was found widely distributed in the CR, no relation between its presence and the migration routes of cephalic NCC was observed. But the number of NCC and their migratory distance were reduced. These changes are consistent and explain the morphological anomalies described in this study, which also correlates with the morphofunctional abnormalities reported in the literature. Therefore, this study highlights the concern of exposure to low concentrations of this metal.

Cadmium-induced ultrastructural changes in primary target organs of developing chicken embryos (Gallus domesticus)

The aim of this study was to evaluate ultrastructural changes in kidney and liver tissue of chicken embryos exposed in ovo to cadmium. Embryonated eggs were injected on the 4^th day of incubation with cadmium at the dose of 0, 2, 4 and 8 μg/egg (80 eggs/group). The samples of kidney and liver tissues were collected from embryos at the 14th and 18th day of incubation (E14 and E18) and at hatching day (D1). The tissue structure was evaluated by transmission electron microscopy (Tecnai G2 Spirit). The results indicate that hepatocytes responded to damage caused by toxic cadmium activity with a significant disturbance in the structure of mitochondria and a considerable expansion of the lysososmal system, while glomerular cells additionally reacted with an increased proliferation of peroxisomes. The range of changes observed on the subcellular level was dependent on the dose of cadmium, embryogenesis stage and cell type.

Exposure of okadaic acid alters the angiogenesis in developing chick embryos

Okadaic acid (OA) is a common phycotoxin, which concerns diarrheic shellfish poisoning (DSP) in human being. It has been known that OA can induce disorganization in cytoskeletal architecture and cell-cell contact, cause chromosome loss, apoptosis, DNA damage and inhibit phosphatases, suggesting its potential embryotoxicity. In this paper, we found that low concentration of OA (50 nM, 100 nM and 200 nM) significantly reduced the density of vascular plexus in yolk-sac membrane (YSM) of chick embryo, while high concentration of OA (500 nM) distinctly depressed the blood vessel density in chorioallantoic membrane (CAM). After exposed to OA, MDA level and SOD activity increased significantly in CAM tissues. However, addition of vitamin C could rescue OA-suppressed angiogenesis in CAM of chick embryo. After exposure of OA, Ang-2 expression was down-regulated in CAM tissues. Taking together, we proposed that OA interfered with angiogenesis in developing chick embryo, through, at least partly, the induction of excessive ROS generation.

Association of blood heavy metals with developmental delays and health status in children

The aim of this study was to evaluate the association of blood lead, mercury, and cadmium concentrations with developmental delays and to explore the association of these concentrations with the health status of children. This study recruited 89 children with developmental delays and 89 age- and sex-matched children with typical development. Their health status was evaluated using the Pediatric Quality of Life (PedsQL) Inventory for health-related quality of life (HRQOL) and the Pediatric Outcomes Data Collection Instrument for function. Family function was also evaluated. Blood lead, mercury, and cadmium concentrations were measured using inductively coupled mass spectrometry. The children with developmental delays had a considerably poorer HRQOL, lower functional performance and family function, and a higher blood lead concentration than those with typical development. The blood lead concentration had a significantly positive association with developmental delays [odds ratio (OR) = 1.54, p < 0.01] in a dose-response manner, and it negatively correlated with PedsQL scores (regression coefficient: −0. 47 to −0.53, p < 0.05) in all the children studied. The higher blood cadmium concentration showed a significantly positive association with developmental delays (OR = 2.24, for >1.0 μg/L vs. <0.6 μg/L, p < 0.05). The blood mercury concentration was not associated with developmental delays and health status.

Oxidative stress, endocrine disruption, and malformation of Bufo gargarizans embryo exposed to sub-lethal cadmium concentrations

Thyroid hormone (TH) is critical for vertebrate postembryonic development as well as embryonic development. Chinese toad (Bufo gargarizans) embryos were exposed to different concentrations of cadmium (5, 50, 100, 200 and 500μg Cd L-1) for 7days. Malformations were monitored daily, and growth and development of embryos were measured at day 4 and 7, and type 2 and 3 iodothyronine deiodinase (Dio2 and Dio3), thyroid hormone receptors (TRα and TRβ) mRNA levels were also measured to assess disruption of TH synthesis. In addition, superoxide dismutase (SOD), glutathione peroxidase (GPx) and heat shock proteins (HSPs) mRNA expression were examined to evaluate the ability of scavenging ROS. Our results demonstrated a bimodal inhibitory effect of Cd on the embryo growth and development of Bufo gargarizans. Reduced mean stage, total length and weight were observed at 5, 50, 200 and 500, but not at 100μg Cd L-1. Embryos malformation occurred in all cadmium treatments. Morphological abnormalities of embryos are characterized by axial flexures, abdominal edema, stunted growth and fin flexure. Real-time PCR results show that exposure to cadmium down-regulated TRα and Dio3 mRNA expression and up-regulated Dio2 mRNA level. SOD and GPx mRNA expression was significantly up-regulated after cadmium exposure. We concluded that cadmium could change mRNA expression of TRα, Dio2 and Dio3 leading the inhibition of growth and development of B. gargarizans embryo, which suggests that cadmium might have the endocrine-disrupting effect in embryos. Moreover, the reduced ability of scavenging ROS induced by cadmium might be responsible for the teratogenic effects of cadmium.

Delayed vasculogenesis and impaired angiogenesis due to altered Ang-2 and VE-cadherin levels in the chick embryo model following exposure to cadmium

PURPOSE

Cadmium (Cd) causes chick embryo malformation and abnormal extra-embryonic vasculature. This study investigates the effect of Cd on vasculogenesis, quantifies extra-embryonic vascular development following exposure to cadmium acetate (CdAc).

METHODS

After 48 or 60 h incubation, chicks were explanted and treated with 50 µl of 50 µM CdAc or equimolar sodium acetate. Embryos were again incubated then re-examined 4, 8, 24 and 48 h later. Gross morphological and histological manifestations were noted. Vasculogenesis was assessed by the development of omphalomesenteric vessels from blood islands. Sinus terminalis (ST), area vasculosa (AV), vessel density and embryo crown-rump length (CRL) were measured. Ang-2 and VE-cadherin mRNA expression was analysed by RT-PCR.

RESULTS

Vasculogenesis was delayed on gross and histological examination. ST length, AV area, vessel density and CRL were significantly reduced in the Cd group. Ang-2 was increased 4 h after exposure to Cd, whereas VE-cadherin was reduced.

CONCLUSION

Cd exposure inhibits normal development of extra-embryonic vasculature in line with growth retardation of the chick embryo in association with altered expression of Ang-2 and VE-cadherin.