Induction of estrogen-responsive gene transcription in the embryo, larval, juvenile and adult life stages of zebrafish as biomarkers of short-term exposure to endocrine disrupting chemicals

Female zebrafish (Danio rerio) exposure to polystyrene nanoplastics induces reproductive toxicity in mother and their offspring

Nanoplastics (NPs) have been commonly detected in aquatic ecosystems, and their negative effects on aquatic organisms have raised concerns in the scientific community and general public. The acute toxicity, neurotoxicity, and metabolic toxicity induced by NPs on fishes have been reported by many studies, although less attention has been focused on how mother exposed to NPs affected their offspring in aquatic organisms. Here, female zebrafish (F0) were exposed to 0, 200 and 2000 μg/L polystyrene nanoplastics (PS-NPs) for 42 d, with their offspring (F1) reared in clear water until sexual maturity. The results showed that PS-NPs were detected in various organs of F0 and F1. PS-NPs exposure significantly decreased gonadal 17-estradiol (E2), while increasing testosterone (T) contents. Lower levels of cyp19a1a, lhr and erα expressions in the 2000 μg/L group were consistent with a reduced number of mature oocytes (MO), but an increase in perinucleolar oocytes (PO). Interestingly, the expression of vtg was only up-regulated by 200 μg/L PS-NPs. After exposure, the egg production was dramatically reduced, but the hatching rate and heartbeat of F1 embryos from treated females were significantly higher than those observed in females from the control group. Maternal PS-NPs exposure significantly decreased the E2 and T levels in F1 adults, while PS-NPs exposure significantly up-regulated the sox9a but down-regulated the foxl2a in F1 larvae of 30 days post fertilization (dpf). This study showed that PS-NPs caused reproductive toxicity by changing the hypothalamic-pituitary-gonadal (HPG) axis-related genes, impairing the reproductive capacity of female zebrafish, affecting the development and disrupting the endocrine function of F1. These results suggested that PS-NPs had adverse effects on fish reproductive system both in the directly exposed generation and in their unexposed offspring.

Toxic effects of environmental concentration Bisphenol AF exposure on the survival, growth and reproduction of adult male Oryzias curvinotus

Bisphenol AF (BPAF) is a novel environmental endocrine disruptor, and is widely detected in the aquatic environment, which is a potential threat to the health of fish. In this study, male Oryzias curvinotus were exposed to environmental concentrations (0.93 and 9.33 μg/L) of BPAF for 21 days. The effects of BPAF on survival, growth, reproduction, liver and testis histology, and gene transcriptional profiles of O. curvinotus were investigated. The results showed that the survival rate of male O. curvinotus slight decrease with increasing BPAF concentration, and there was no significant effect on body length, body weight, and K-factor. BPAF (9.33 μg/L) caused significant changes in testicular structure and reduced spermatid count in O. curvinotus. Changes in transcript levels of some antioxidant-related genes in gills and liver following BPAF exposure, imply an effect of BPAF on the immune system. After BPAF exposure, chgs and vtgs were up-regulated, validating the estrogenic effect of BPAF. In the hypothalamic - pituitary - gonadal axis (HPG) results, erα, erγ and cyp19a1b were all up-regulated in the brain, and the 0.93 μg/L BPAF group was more up-regulated than the 9.33 μg/L BPAF group. In testis, BPAF significantly up-regulated the mRNA expression level of cyp17a1 and cyp11b, while significantly down-regulated mRNA expression level of cyp11a, and cyp19a1 was significantly down-regulated only in the 0.93 μg/L BPAF group. In conclusion, environmental levels of BPAF have adverse effects on the survival and reproduction of O. curvinotus, and the potential toxic effects of environmental levels of BPAF cannot be ignored.

Use of All-Male cyp17a1-Deficient Zebrafish (Danio rerio) for Evaluation of Environmental Estrogens

Natural and synthetic environmental estrogens (EEs) are widespread and have received extensive attention. Our previous studies demonstrated that depletion of the cytochrome P450 17a1 gene (cyp17a1) leads to all-testis differentiation phenotype in zebrafish and common carp. In the present study, cyp17a1-deficient zebrafish with defective estrogen biosynthesis were used for the evaluation of EEs, as assessed by monitoring vitellogenin (vtg) expression. A rapid and sensitive assessment procedure was established with the 3-day administration of estradiol (E2), followed by examination of the transcriptional expression of vtgs in our cyp17a1-deficient fish. Compared with the control fish, a higher E2-mediated vtg upregulation observed in cyp17a1-deficient zebrafish exposed to 0.1 μg/L E2 is known to be estrogen receptor-dependent and likely due to impaired in vivo estrogen biosynthesis. The more responsive vtg expression in cyp17a1-deficient zebrafish was observed when exposed to 200 and 2000 μg/L bisphenol A (BPA) and perfluoro-1-octanesulfonate (PFOS). The estrogenic potentials of E2, BPA, and PFOS were compared and assessed by the feminization effect on ovarian differentiation in cyp17a1-deficient zebrafish from 18 to 50 days postfertilization, based on which a higher sensitivity of E2 in ovarian differentiation than BPA and PFOS was concluded. Collectively, through the higher sensitivity to EEs and the capacity to distinguish chemicals with different estrogenic potentials exhibited by the all-male cyp17a1-deficient zebrafish with impaired estrogen biosynthesis, we demonstrated that they can be used as an excellent in vivo model for the evaluation of EEs. Environ Toxicol Chem 2024;43:1062-1074. © 2024 SETAC.

Hepatic Transcriptomic Responses to Ethinylestradiol in Two Life Stages of Japanese Quail

Chemical risk assessment for avian species typically depends on information from toxicity tests performed in adult birds. Early-life stage (ELS) toxicity tests have been proposed as an alternative, but incorporation of these data into existing frameworks will require knowledge about the similarities/differences between ELS and adult responses. The present study uses transcriptomics to assess hepatic gene expression in ELS and adult Japanese quail following exposure to ethinylestradiol (EE2). Prior to incubation, ELS quail were dosed with measured EE2 concentrations of 0.54, 6.3, and 54.2 µg/g egg weight via air cell injection. Adult quail were fed a single dose of EE2 at nominal concentrations of 0, 0.5, and 5 mg/kg body weight by gavage. Liver tissue was collected from five to six individuals per dose group at mid-incubation for ELS quail and 4 days after dosing for adults. A total of 283 and 111 differentially expressed genes (DEGs) were detected in ELS and adult quail, respectively, 16 of which were shared across life stages. Shared DEGs included estrogenic biomarkers such as vitellogenin genes and apovitellenin-1. For the dose groups that resulted in the highest number of DEGs (ELS, 6.3 µg/g; adult, 5 mg/kg), 21 and 35 Kyoto Encyclopedia of Genes and Genomes pathways were enriched, respectively. Ten of these pathways were shared between life stages, including pathways involved with signaling molecules and interaction and the endocrine system. Taken together, our results suggest conserved mechanisms of action following estrogenic exposure across two life stages, with evidence from differential expression of key biomarker genes and enriched pathways. The present study contributes to the development and evaluation of ELS tests and toxicogenomic approaches and highlights their combined potential for screening estrogenic chemicals. Environ Toxicol Chem 2022;41:2769-2781. © 2022 SETAC.

Biomarker Responses, Gene Expression Alterations, and Histological Changes in Zebrafish (Danio rerio) After In Vivo Exposure to Polychlorinated Diphenyl Ethers

Polychlorinated diphenyl ethers (PCDEs) have been detected in various aquatic matrices, which pose potential threats to aquatic ecosystem security. In this work, both micro and macro analysis methods were used to assess the toxicity of PCDEs to zebrafish. Results indicated that after in vivo PCDE exposure, the oxidative stress and related gene of Danio rerio were significantly changed. The higher concentration or longer exposure time could cause more severe oxidative stress in zebrafish tissues. Compared with among the five tested compounds, more obvious changes in the level of oxidative biomarkers of lower chlorinated PCDEs’ (4-mono-CDE and 4,4′-di-CDE) exposure groups were observed. The integrated biomarker response analysis and gene expression results also indicate a similar trend. Histopathological observation suggested that 4,4′-di-CDE could render liver nuclei enlargement and necrosis, hepatocyte vacuolation, and the development inhibition of ovarian cells. Transmission electron microscope photos showed that 4,4′-di-CDE caused organelle damage in the liver and ovary, including the rupture of the endoplasmic reticulum, swelling of mitochondria, and condensation of chromatin in the liver and mitochondria disappeared significantly in the ovary. The degree of damage is enhanced with the increasing exposure doses. In addition, PCDEs also significantly altered vitellogenin content and related gene (vtg1) expression, suggesting that PCDEs may be estrogen endocrine disruptors. Overall, these results provided some valuable toxicological data of PCDEs on aquatic species.

Summary of 17 chemicals evaluated by OECD TG229 using Japanese Medaka, Oryzias latipes in EXTEND 2016

In June 2016, the Ministry of the Environment of Japan announced a program "EXTEND2016" on the implementation of testing and assessment for endocrine active chemicals, consisting of a two-tiered strategy. The aim of the Tier 1 screening and the Tier 2 testing is to identify the impacts on the endocrine system and to characterize the adverse effects to aquatic animals by endocrine disrupting chemicals detected in the aquatic environment in Japan. For the consistent assessment of the effects on reproduction associated with estrogenic, anti-estrogenic, androgenic, and/or anti-androgenic activities of chemicals throughout Tier 1 screening to Tier 2 testing, a unified test species, Japanese medaka (Oryzias latipes), has been used. For Tier 1 screening, the in vivo Fish Short-Term Reproduction Assay (OECD test guideline No. 229) was conducted for 17 chemicals that were nominated based on the results of environmental monitoring, existing knowledge obtained from a literature survey, and positive results in reporter gene assays using the estrogen receptor of Japanese medaka. In the 17 assays using Japanese medaka, adverse effects on reproduction (i.e., reduction in fecundity and/or fertility) were suggested for 10 chemicals, and a significant increase of hepatic vitellogenin in males, indicating estrogenic (estrogen receptor agonistic) potency, was found for eight chemicals at the concentrations in which no overt toxicity was observed. Based on these results, and the frequency and the concentrations detected in the Japanese environment, estrone, 4-nonylphenol (branched isomers), 4-tert-octylphenol, triphenyl phosphate, and bisphenol A were considered as high priority candidate substances for the Tier 2 testing.

Fluorescent Reporter Zebrafish Line for Estrogenic Compound Screening Generated Using a CRISPR/Cas9-Mediated Knock-in System

An increasing number of compounds in our diet and environment are being identified as estrogenic, causing serious and detrimental effects on human, animal, and ecosystem health. Time- and cost-effective biological tools to detect and screen these compounds with potential high-throughput capabilities are in ever-growing demand. We generated a knock-in zebrafish transgenic line with enhanced green fluorescent protein (EGFP) driven by the regulatory region upstream of vitellogenin 1 (vtg1), a well-studied biomarker for estrogenic exposure, using CRISPR/Cas9 technology. Exposure to 17β-estradiol (E2: 0-625 nM) starting at 4-h post-fertilization in dechorionated embryos resulted in the significant induction of hepatic EGFP with ≥5 nM E2 as early as 3-days post-fertilization. Concentration- and time-dependent increase in the percentage of hepatic EGFP-positive larvae and extent of fluorescence expression, categorized into 3 expression levels, were observed with E2 exposure. A strong correlation between the levels of EGFP mRNA, vtg1 mRNA, and EGFP fluorescence levels were detected. Image analysis of the area and intensity of hepatic EGFP fluorescence resulted in high-fidelity quantitative measures that could be used in automated screening applications. In addition, exposure to bisphenol A (0-30 μM) resulted in quantitative responses showing promise for the use of this transgenic line to assess estrogenic activity of endocrine-disrupting chemicals. These results demonstrate that this novel knock-in zebrafish reporter allows for distinct screening of in vivo estrogenic effects, endpoints of which can be used for laboratory testing of samples for estimation of possible human and environmental risks.

A review of the influences of microplastics on toxicity and transgenerational effects of pharmaceutical and personal care products in aquatic environment

PPCPs (pharmaceutical and personal care products) and microplastics (MPs) are two types of emerging pollutants that are ubiquitous and widely concerned in the environment. Both of them can accumulate in fish or aquatic invertebrates and transfer to offspring, thereby producing toxic effects on both parents and offspring, in which the characteristics of MPs also enable them to adsorb PPCPs thus producing carrier effects. In this study, we have conducted a comprehensive review of MPs and PPCPs and found that MPs can act as a carrier of PPCPs to influence the bioaccumulation of PPCPs. MPs and PPCPs have toxicity and transgenerational effects on both fish and aquatic invertebrates in many aspects, and MPs can also affect the toxicity and transgenerational effects of PPCPs due to their carrier effects. This paper revealed that MPs may have an important impact on the bioavailability of PPCPs and the interaction between MPs and PPCPs is a hot topic in future research. This study also puts forward the shortcomings of the current research and related suggestions, and relevant research should be carried out as soon as possible to provide the basis for the prevention and treatment of fresh water.

Orbencarb induces lethality and organ malformation in zebrafish embryos during development

Thiocarbamates are one of the components of pesticides that target weeds by inhibiting adenosine triphosphate (ATP) synthesis. Orbencarb, one of the isomeric thiocarbamates applied to wheat, maize, and soybean, has been found to have toxic effects on mammals and marine ecosystems. Although the toxicity ranges of orbencarb in different organisms are known, specific studies on the environmental contamination and harmful effects of orbencarb on non-target organisms are scarce. In this study, we observed that orbencarb induced embryotoxicity during zebrafish development as well as apoptosis and reactive oxygen species (ROS) production in the intestine. It was further observed that orbencarb decreased the viability of the embryos and simultaneously affected the heart rate and vessel formation. Orbencarb decreased the mRNA levels of ccnd1, ccne1, cdk2, and cdk6 and induced abnormal development of the eyes, brain, yolk sac, and spinal cord in zebrafish embryos. Orbencarb also hampered vasculogenesis in the zebrafish embryos by inhibiting the mRNA expression of flt1, flt4, kdr, and vegfc. Collectively, these results suggested that orbencarb is embryotoxic and disrupts the normal growth of zebrafish embryos by inducing the generation of ROS and hampering vasculogenesis.

Determination and reduced life expectancy model and molecular docking analyses of estrogenic potentials of 17β-estradiol, bisphenol A and nonylphenol on expression of vitellogenin gene (vtg1) in zebrafish

This study determined and evaluated the estrogenic potentials on hepatic vitellogenin gene (vtg1) of adult male zebrafish which were exposed to low level concentrations (ng/L-μg/L levels) of individual and binary mixtures of 17β-estradiol (E₂), bisphenol A (BPA) and nonylphenol (NP) through the use of reduced life expectancy (RLE) model and molecular docking analysis. The order of in vivo estrogenic potentials of individual and binary exposure of E₂, BPA and NP was as follows: E₂+BPA＞E₂＞E₂+NP＞BPA＞BPA + NP >>>NP. Binary mixtures of E₂, BPA and NP had weak synergistic effects under the exposure concentration ranges. With the expression of hepatic vtg1 gene, the hepatic toxicity was analyzed by using the RLE model. All plots of the linear RLE model had negative slopes indicating that EC₅₀ was negatively correlated with the natural logarithm of exposure time (lnET₅₀). The RLE model analyses can be useful to evaluate the exposure time effects of zebrafish by using EC₅₀ as toxicity endpoint. Molecular docking analysis revealed that the interaction potential of E₂ (Binding energy: -10.1 kcal/mol) for the zebrafish ERα-LBD was the most potent (stable), followed by BPA (-8.0 kcal/mol) and NP (-6.8 kcal/mol). Molecular docking analysis can be useful to understand interactive effects of E₂, BPA and NP.

Developmental toxicity of the fungicide ziram in zebrafish (Danio rerio)

Ziram is a broad spectrum pesticide that belongs to the class of dimethyl-dithiocarbamate (DTC) fungicides. The objectives of this study were to assess the effects of ziram in developing zebrafish. Ziram was highly toxic to zebrafish embryos, with a 96-h LC₅₀ value of 1082.54 nM (∼0.33 mg/L). Zebrafish embryos at 6 h post-fertilization (hpf) were exposed to solvent control (0.1% DMSO), or one dose of 1, 10, 100, and 1000 nM ziram for 96 h. Ziram induced lethality in a dose-dependent manner, decreased hatching rate and heartbeat, and caused wavy deformities at 72 and 96 hpf at 100 and 1000 nM. Basal oxygen consumption rates of zebrafish at 24 hpf were decreased with 1000 nM, suggesting that ziram affects oxidative phosphorylation. We also measured the expression of transcripts associated with the oxidative stress response (sod1 and sod2) and dopamine receptor signaling at ∼96 h of exposure. There was no difference in the expression of genes related to oxidative stress, nor those related to the dopamine system. Locomotor activity was also assessed in larval zebrafish (7 dpf), and ziram increased total activity, the velocity in light zone, and total distance moved at 10 nM, while it decreased the mean time spent in the dark zone at 1 and 10 nM. Behavioral responses were dependent upon the time point and clutch examined. These data demonstrate that ziram negatively impacts embryonic development (i.e. mortality, hatching, heartbeat and notochord development) of zebrafish, decreases basal respiration of embryos, and alters behavioral responses in larvae.

Contribution of G protein-coupled estrogen receptor 1 (GPER) to 17β-estradiol-induced developmental toxicity in zebrafish

Exposure to 17β-estradiol (E2) influences the regulation of multiple signaling pathways, and E2-mediated disruption of signaling events during early development can lead to malformations such as cardiac defects. In this study, we investigated the potential role of the G-protein estrogen receptor 1 (GPER) in E2-induced developmental toxicity. Zebrafish embryos were exposed to E2 from 2h post fertilization (hpf) to 76 hpf with subsequent transcriptional measurements of heart and neural crest derivatives expressed 2 (hand2), leucine rich repeat containing 10 (lrrc10), and gper at 12, 28 and 76 hpf. Alteration in the expression of lrrc10, hand2 and gper was observed at 12 hpf and 76 hpf, but not at 28 hpf. Expression of these genes was also altered after exposure to G1 (a GPER agonist) at 76 hpf. Expression of lrrc10, hand2 and gper all coincided with the formation of cardiac edema at 76 hpf as well as other developmental abnormalities. While co-exposure of G1 with G36 (a GPER antagonist) rescued G1-induced abnormalities and altered gene expression, co-exposure of E2 with G36, or ICI 182,780 (an estrogen receptor antagonist) did not rescue E2-induced cardiac deformities or gene expression. In addition, no effects on the concentrations of downstream ER and GPER signaling molecules (cAMP or calcium) were observed in embryo homogenates after E2 treatment. These data suggest that the impacts of E2 on embryonic development at this stage are complex and may involve multiple receptor and/or signaling pathways.

Interpretation of fish biomarker data for identification, classification, risk assessment and testing of endocrine disrupting chemicals

Chemical induced changes in fish biomarkers vitellogenin (VTG), secondary sex characteristics (SSC), and sex ratio indicate modes/mechanisms of action (MOAs) of EAS (estrogen, androgen and steroidogenesis) pathways. These biomarkers could be used for defining MOAs and the causal link between MOAs and adverse effects in fish for the identification of endocrine disrupting chemicals (EDCs). This paper compiled data sets of 150 chemicals for VTG, 57 chemicals for SSC and 38 chemicals for sex ratio in fathead minnow, medaka and zebrafish. It showed 1) changes in fish biomarkers can indicate the MOAs as anticipated; 2) in addition to EAS pathways, chemicals with non-EAS pathways induced changes in fish biomarkers; 3) responses of fish biomarkers did not always follow the anticipated patterns of EAS pathways. These responses may result from the interaction of chemical-induced multiple MOAs and confounding factors like fish diet, infection, culture conditions, general toxicity and stress response. The complex response of fish biomarkers to a chemical of interest requires EDC testing at multiple biological levels. Interpretation of fish biomarker data should be combined with relevant information at different biological levels, which is critical for defining chemical specific MOAs. The utility of fish biomarker data for identification, classification, PBT assessment, risk assessment, and testing of EDCs in the regulatory context was discussed. This paper emphasizes the importance of fish biomarker data in the regulatory context, a weight of evidence approach for the interpretation of fish biomarker data and the need for defining levels of evidence for the identification of EDCs.

Acute and short-term developmental toxicity of cyhalofop-butyl to zebrafish (Danio rerio)

Cyhalofop-butyl is an aryloxyphenoxypropionate post-emergence herbicide widely used around the world in agriculture. The acute toxicity of cyhalofop-butyl to embryos, larvae (12 and 72 h post-hatching), and adult zebrafish, as well as the short-term developmental toxicity of cyhalofop-butyl to embryo and sac-fry stages, was tested. The results showed that the 96-h LC50 values of cyhalofop-butyl to embryos, 12 h post-hatching larvae, 72 h post-hatching larvae, and adult fish were 2.03, 0.58, 1.42, and 3.49 mg/L, respectively, suggesting zebrafish early life stages were more sensitive to cyhalofop-butyl than adult stage. Cyhalofop-butyl would inhibit the spontaneous movement, heartbeat, hatching rate of embryos, and the body length of surviving larvae of zebrafish at 1.00 mg/L or higher concentrations. Morphological abnormalities, including pericardial edema, yolk sac edema, deformation of tail, and deformation of spine, were induced by cyhalofop-butyl. The results indicated that cyhalofop-butyl had significant negative impacts on zebrafish at different life stages, and spontaneous movement and hatching rate were sensitive endpoints for assessing short-term developmental toxicity of cyhalofop-butyl.

Long-term effects of bisphenol AF (BPAF) on hormonal balance and genes of hypothalamus-pituitary-gonad axis and liver of zebrafish (Danio rerio), and the impact on offspring

Bisphenol AF (BPAF) is one of the analogues of bisphenol A (BPA) and is widely used as a raw material in the plastics industry. The potential toxicity to fish from exposure to BPAF in the aquatic environment is largely unknown. In this study, zebrafish (Danio rerio) were exposed to BPAF at 5, 25 and 125 μg L(-1), from 4 hour-post-fertilization (hpf) to 120 day-post-fertilization (dpf), representing the period from embryo to adult. The levels of plasma hormones were measured and the expression of selected representative genes along the hypothalamus-pituitary-gonad (HPG) axis and liver were examined. The concentration of 17β-estradiol (E2) was significantly increased in male and female fish and a significant decrease of testosterone (T) was observed in male fish. The mRNA expression of genes along the HPG axis and in liver tissues in F0 generation fish demonstrated that the steroid hormonal balances of zebrafish were modulated through the alteration of steroidgenesis. The significant decrease of egg fertilization among offspring indicates the possibility of sperm deterioration of parent following exposure to BPAF. The higher occurrence of malformation and lower survival rate in the offspring from the exposure group suggested a possibility of maternal transfer of BPAF, which could be responsible for the increased prevalence of adverse health signs in the offspring. The hatching delay in 5 μg L(-1) BPAF indicated that parental exposure to environmentally relevant concentration of BPAF would result in delayed hatching of the offspring. A potential consequence of adverse effects in the offspring by BPAF deserves further investigation.

Effect of trifloxystrobin on hatching, survival, and gene expression of endocrine biomarkers in early life stages of medaka (Oryzias latipes)

Trifloxystrobin is a systemic broad-spectrum foliar strobilurin fungicides that enters the aquatic environment during agricultural application. It is highly toxic and poses a potential risk to aquatic organisms, whereas the effect on the development of early life stages of fish are unclear. In this study, hatchability, time to hatching, and larval mortality were measured. Additionally, the expression of biomarker genes, including those involved in sex hormone pathways (er, vtg, cyp17, and cyp19a), thyroid hormone pathways (trα and dio2), and aryl hydrocarbon receptor pathways (ahr and cyp1a), was determined after embryos of medaka (Oryzias latipes) were exposed to different levels of trifloxystrobin (0, 0.1, 1, 10, and 100 μg/L) for 28 days. The results showed that there were significant differences between controls and the 100 μg/L treatment group in both hatchability and time to hatching of fertilized eggs (p<0.05). Larval mortality was significantly increased in the 0.1, 1, and 10 μg/L treatment groups (p<0.05). These results indicate that embryonic and larval development may be affected by trifloxystrobin exposure. Moreover, the mRNA levels of the er gene were significantly up-regulated at levels of trifloxystrobin above 1 μg/L treatment groups. Up-regulation of vtg, cyp17, and cyp19a mRNA levels was observed in the larvae at the lower concentration treatment groups. The mRNA levels of cyp1a genes were significantly up-regulated at all of the treatment groups. These results suggest that trifloxystrobin is a potential endocrine disruptor through effects on the sex hormone pathway and xenobiotic metabolism. The changes in cyp1a expression can be used as a highly sensitive biomarker to assess trifloxystrobin contamination in the early life stages of fish.

Environmental fate and ecological risks of nonylphenols and bisphenol A in the Cape D'Aguilar Marine Reserve, Hong Kong

Nonylphenols (NPs) and bisphenol A (BPA) are the most common endocrine disruptors detected in the coastal waters of Hong Kong. The Cape D'Aguilar Marine Reserve (CAMR), the only marine reserve in Hong Kong is close to urbanized areas, thus the resident marine organisms are inevitably influenced by partially treated wastewater from adjacent sewage treatment plants (STPs). Elevated levels of NPs and BPA were detected in all seawater, sediment and biota samples collected from the CAMR. Estrogenic activities of seawater from the CAMR, and sludge and sewage from a nearby STP were assessed using yeast estrogen screen assay. We found aromatase, estrogen receptor and vitellogenin genes in the marine medaka fish Oryzias melastigma were significantly up-regulated after exposure to the reserve's seawater. According to a tissue-residue-based probabilistic risk assessment, the marine species living in the CAMR are having 35% and 21% of chance to be at risk due to exposure to NPs and BPA, respectively.

Embryonic exposure to carbendazim induces the transcription of genes related to apoptosis, immunotoxicity and endocrine disruption in zebrafish (Danio rerio)

Carbendazim is one of the most widespread environmental contaminant that can cause major concern to human and animal reproductive system. To date, very few studies have been conducted on the toxic effect of carbendazim in the non-target organism zebrafish (Danio rerio). The study presented here aimed to assess how carbendazim triggers apoptosis, immunotoxicity and endocrine disruption pathways in zebrafish during its embryo development. Our results demonstrated that the expression patterns of many key genes involved in cell apoptosis pathway (e.g. P53, Mdm2, Bbc3 and Cas8) were significantly up-regulated upon the exposure to carbendazim at the concentration of 500 μg/L, while the Bcl2 and Cas3 were down-regulated at the same concentration, interestingly, the expression level of Ogg1 decreased at all the exposure concentrations. It was also observed that the mRNA levels of CXCL-C1C, CCL1, IL-1b and TNFα which were closely related to the innate immune system, were affected in newly hatched zebrafish after exposed to different concentrations of carbendazim. Moreover, the expression of genes that are involved in the hypothalamic-pituitary-gonadal/thyroid (HPG/HPT) axis including VTG, ERα, ERβ2, Dio1, Dio2, Thraa and Thrb were all down-regulated significantly after the exposure to carbendazim. The expression levels of two cytochrome P450 aromatases CYP19a and CYP19b were increased significantly after 20 and 100 μg/L carbendazim exposure, respectively. Taken together, our results indicated that carbendazim had the potential to induce cell apoptosis and cause immune toxicity as well as endocrine disruption in zebrafish during the embryo developmental stage. The information presented here also help to elucidate the environmental risks caused by the carbendazim-induced toxicity in aquatic organisms.

Embryonic exposure to butachlor in zebrafish (Danio rerio): endocrine disruption, developmental toxicity and immunotoxicity

Butachlor is a chloroacetanilide herbicide widely employed in weeding important crops. Recently, the study of the possible toxic effects of butachlor in non-target organisms has increased substantially. However, the endocrine disruption, developmental toxicity and immunotoxicity effects of butachlor in fish have not been fully investigated in previous studies. In the present study, zebrafish embryos were exposed to a range of butachlor concentrations from 4 to 20 μM to evaluate the embryonic toxicity of butachlor until 84 hours postfertilization (hpf). The results demonstrated that butachlor was highly toxic to zebrafish embryos, hindering the hatching process, resulting in a series of malformations and followed by mortality. The malformations observed included pericardial edema (PE) and yolk sac edema (YSE), which showed concentration-dependent responses. The analysis of endocrine gene transcription indicated that butachlor significantly induced the expression of the estrogen-responsive gene Vtg1 but had no effect on the expression of the ERα gene. The innate immune system appeared to be another possible target of butachlor. At 72 hpf, butachlor significantly up-regulated the innate immune system-related genes, including IL-1β, CC-chem, CXCL-C1c and IL-8. These data suggest that butachlor causes developmental toxicity, endocrine disruption and immune toxicity in the zebrafish embryo. Bidirectional interactions between the endocrine system and the immune system might be present, and further studies are needed to determine these possible pathways.

Alternatives to in vivo tests to detect endocrine disrupting chemicals (EDCs) in fish and amphibians--screening for estrogen, androgen and thyroid hormone disruption

Endocrine disruption is considered a highly relevant hazard for environmental risk assessment of chemicals, plant protection products, biocides and pharmaceuticals. Therefore, screening tests with a focus on interference with estrogen, androgen, and thyroid hormone pathways in fish and amphibians have been developed. However, they use a large number of animals and short-term alternatives to animal tests would be advantageous. Therefore, the status of alternative assays for endocrine disruption in fish and frogs was assessed by a detailed literature analysis. The aim was to (i) determine the strengths and limitations of alternative assays and (ii) present conclusions regarding chemical specificity, sensitivity, and correlation with in vivo data. Data from 1995 to present were collected related to the detection/testing of estrogen-, androgen-, and thyroid-active chemicals in the following test systems: cell lines, primary cells, fish/frog embryos, yeast and cell-free systems. The review shows that the majority of alternative assays measure effects directly mediated by receptor binding or resulting from interference with hormone synthesis. Other mechanisms were rarely analysed. A database was established and used for a quantitative and comparative analysis. For example, a high correlation was observed between cell-free ligand binding and cell-based reporter cell assays, between fish and frog estrogenic data and between fish embryo tests and in vivo reproductive effects. It was concluded that there is a need for a more systematic study of the predictive capacity of alternative tests and ways to reduce inter- and intra-assay variability.

Macondo crude oil from the Deepwater Horizon oil spill disrupts specific developmental processes during zebrafish embryogenesis

Background

The Deepwater Horizon disaster was the largest marine oil spill in history, and total vertical exposure of oil to the water column suggests it could impact an enormous diversity of ecosystems. The most vulnerable organisms are those encountering these pollutants during their early life stages. Water-soluble components of crude oil and specific polycyclic aromatic hydrocarbons have been shown to cause defects in cardiovascular and craniofacial development in a variety of teleost species, but the developmental origins of these defects have yet to be determined. We have adopted zebrafish, Danio rerio, as a model to test whether water accumulated fractions (WAF) of the Deepwater Horizon oil could impact specific embryonic developmental processes. While not a native species to the Gulf waters, the developmental biology of zebrafish has been well characterized and makes it a powerful model system to reveal the cellular and molecular mechanisms behind Macondo crude toxicity.

Results

WAF of Macondo crude oil sampled during the oil spill was used to treat zebrafish throughout embryonic and larval development. Our results indicate that the Macondo crude oil causes a variety of significant defects in zebrafish embryogenesis, but these defects have specific developmental origins. WAF treatments caused defects in craniofacial development and circulatory function similar to previous reports, but we extend these results to show they are likely derived from an earlier defect in neural crest cell development. Moreover, we demonstrate that exposure to WAFs causes a variety of novel deformations in specific developmental processes, including programmed cell death, locomotor behavior, sensory and motor axon pathfinding, somitogenesis and muscle patterning. Interestingly, the severity of cell death and muscle phenotypes decreased over several months of repeated analysis, which was correlated with a rapid drop-off in the aromatic and alkane hydrocarbon components of the oil.

Conclusions

Whether these teratogenic effects are unique to the oil from the Deepwater Horizon oil spill or generalizable for most crude oil types remains to be determined. This work establishes a model for further investigation into the molecular mechanisms behind crude oil mediated deformations. In addition, due to the high conservation of genetic and cellular processes between zebrafish and other vertebrates, our work also provides a platform for more focused assessment of the impact that the Deepwater Horizon oil spill has had on the early life stages of native fish species in the Gulf of Mexico and the Atlantic Ocean.

PCR-ELISA detection of estrogen receptor β mRNA expression and plasma vitellogenin induction in juvenile sole (Solea solea) exposed to waterborne 4-nonylphenol

In this study, the effect of 4-nonylphenol (4NP) on reproductive axis of sole (Solea solea) has been investigated by using selected biomarkers of estrogenic effects: vitellogenin (VTG) and estrogen receptor β (ERβ) mRNA. Furthermore, an enzyme linked immunosorbent assay (ELISA) detection system of reverse transcriptase-polymerase chain reaction (RT-PCR) products for the analysis of sole ERβ mRNA expression was developed and validated. The proposed method allows large-scale analyses of different mRNAs in fast and not expensive way. Our results have demonstrated that the PCR-ELISA method developed shows high sensitivity, good reproducibility and also the potential for semi-quantitative analysis of hepatic ERβ mRNAs. Both plasma VTG level and ERβ mRNA expression were increased in tested animals following a short exposure to environmental relevant concentrations (10(-6)M) of 4NP, confirming the functional role of ERβ in the regulation of xenoestrogens-induced production of VTG. The methodology provided in the present study together with the preliminary results on the hepatic expression of ERβ may be useful in environmental xenoestrogens monitoring studies, using flatfish as "sentinel" species.

PFOS elicits transcriptional responses of the ER, AHR and PPAR pathways in Oryzias melastigma in a stage-specific manner

Perfluorooctane sulfonate (PFOS) is widely distributed in seawater. However, the effects of PFOS on important receptors involved in the toxicity of POPs have not been fully defined, especially for the embryonic stages of marine fish. In this study, we examined the transcriptional responses and PFOS accumulation in the marine medaka embryos at the early and late developmental stages of 4 and 10 dpf upon PFOS exposure (1, 4, and 16mg/L). PFOS accumulated in the embryos, and the embryonic burdens of PFOS at 10 dpf were markedly higher than those at 4 dpf. Moreover, thirteen genes involved in three important POPs-related receptor pathways, including ER, AHR and PPAR, were cloned and investigated. The mRNA expression levels of ERα and ERγ were not significantly altered, but the estrogenic marker genes were downregulated upon PFOS exposure at 4 dpf. Conversely, ERs and related marker genes all were significantly upregulated at 10 dpf. The expressions of ARNT and cyp1a were both upregulated at 4 dpf, while no obvious changes were detected at 10 dpf. The expressions of cyp19a and cyp19b were regulated by PFOS in a stage-specific manner. PFOS produced different effects on three isoforms of PPAR. PPARα and PPARβ were first inhibited at 4 dpf and were induced at 10 dpf. PFOS did not elicit a change in PPARγ expression at either stage. In conclusion, this study showed that PFOS has an estrogenic activity and endocrine-disruptive properties. Meanwhile, PFOS could elicit transcriptional responses on POPs-related pathways in a stage-specific manner.