Developmental toxicity of endocrine disruptors in early life stages of zebrafish, a genetic and embryogenesis study

Mutation of brain aromatase disrupts spawning behavior and reproductive health in female zebrafish

Aromatase (Cyp19a1) is the steroidogenic enzyme that converts androgens into bioactive estrogens, and hence is in a pivotal position to mediate reproduction and sexual behavior. In teleosts, there are two aromatase paralogs: cyp19a1a that is highly expressed in granulosa and Leydig cells in the gonads with critical function in sexual differentiation of the ovary, and cyp19a1b that is highly expressed in radial glial cells in the brain with unknown roles in reproduction. Cyp19a1 ^-/- mutant zebrafish lines were used to investigate the importance of the cyp19a1 paralogs for spawning behavior and offspring survival and early development. Mutation of cyp19a1b was found to increase the latency to the first oviposition in females. Mutation of cyp19a1b in females also increased the number of eggs spawned; however, significantly more progeny died during early development resulting in no net increase in female fecundity. This finding suggests a higher metabolic cost of reproduction in cyp19a1b ^-/- mutant females. In males, the combined mutation of both cyp19a1 paralogs resulted in significantly lower progeny survival rates, indicating a critical function of cyp19a1 during early larval development. These data establish the specific importance of cyp19a1b for female spawning behavior and the importance of the cyp19a1 paralogs for early larval survival.

Embryo developmental toxicity in marine medaka (Oryzias melastigma) due to parental and embryonic 17α-ethinylestradiol exposure

The synthetic estrogen 17α-ethinylestradiol (EE2) is a common component of hormone therapy and oral contraceptives and has been widely used for nearly 60 years. Numerous studies have shown that exposure to EE2 can affect embryonic development in a number of fish species. The effects of parental and embryonic EE2 exposure on embryo developmental toxicity and the underlying molecular mechanisms, however, have rarely been examined. In this study, embryos collected from parental EE2-exposed adult fish were examined to assess EE2-induecd toxicity during embryo development. The rate of embryo development including heart rate, hatching rate, and larval locomotion were measured to assess embryo developmental toxicity. The embryonic transcriptome was used to delineate the related developmental toxicity pathways. Our results suggest that parental and embryonic EE2 exposure resulted in growth retardation including a reduction in embryo heart rate, a delay in the appearance eye pigmentation, decreased hatching rate and impaired larval locomotion. In addition, gene ontology (GO) enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and Ingenuity Pathway Analysis (IPA) of transcriptome revealed that these impairments are controlled by estrogen receptor and related to eye structure, neuronal and synaptic structure, and behaviour. The key factors identified, including PRKAA2, APOB, EPHB2, OXTR, NR2E3, and POU4F2, could serve as biomarkers for assessing EE2-induced embryo developmental toxicity. For the first time, our results show that eye pigmentation is a potentially sensitive marker of EE2-induced embryo developmental toxicity.

Endocrine disrupting chemicals in the environment: Environmental sources, biological effects, remediation techniques, and perspective

Endocrine disrupting chemicals (EDCs) have been identified as emerging contaminants, which poses a great threat to human health and ecosystem. Pesticides, polycyclic aromatic hydrocarbons, dioxins, brominated flame retardants, steroid hormones and alkylphenols are representative of this type of contaminant, which are closely related to daily life. Unfortunately, many wastewater treatment plants (WWTPs) do not treat EDCs as targets in the normal treatment process, resulting in EDCs entering the environment. Few studies have systematically reviewed the related content of EDCs in terms of occurrence, harm and remediation. For this reason, in this article, the sources and exposure routes of common EDCs are systematically described. The existence of EDCs in the environment is mainly related to human activities (Wastewater discharges and industrial activities). The common hazards of these EDCs are clarified based on available toxicological data. At the same time, the mechanism and effect of some mainstream EDCs remediation technologies (such as adsorption, advanced oxidation, membrane bioreactor, constructed wetland, etc.) are separately mentioned. Moreover, our perspectives are provided for further research of EDCs.

Effects of 17α-Ethinylestradiol (EE2) exposure during early life development on the gonadotropic axis ontogenesis of the European sea bass, Dicentrarchus labrax

Exposure of young organisms to oestrogenic endocrine disrupting chemicals (EDCs) can elicit adverse effects, particularly on the reproductive function. In fish, as in other vertebrates, reproduction is controlled by the neuroendocrine gonadotropic axis, whose components are mainly regulated by sex steroids and may then be targets for EDCs. In the present study, we investigated the effects of a xenoestrogen exposure on the ontogenesis of the gonadotropic axis in European sea bass. After exposure of hatching larvae for 8 days to 17α-ethinylestradiol (EE2) (0.5 nM and 50 nM), gene expression for kisspeptins (kiss1, kiss2), gonadotropin-releasing hormones (gnrh1, gnrh2, gnrh3), gonadotropin beta subunits (lhβ and fshβ) and brain type aromatase (cyp19a1b) were measured using quantitative real-time PCR. Our results demonstrate that EE2 strongly stimulated the expression of brain type aromatase (cyp19a1b) in sea bass larvae. In addition, EE2 exposure also affected the mRNA levels of kiss1, gnrh1 and gnrh3 by inducing a downregulation of these genes during the early developmental stages, while no effect was seen in gnrh2, lhβ and fshβ. These results reinforce the idea that the larval development is a sensitive critical period in regard to endocrine disruption and that the gonadotropic axis in the developing sea bass is sensitive to xenoestrogen exposure.

Behavioural impairment and oxidative stress by acute exposure of zebrafish to a commercial formulation of tebuconazole

Tebuconazole is a systemic follicular fungicide known to cause diverse problems in non-target organisms namely associated to the pure active ingredient. As such, the objective of this work was to evaluate developmental changes induced by a tebuconazole commercial formulation to a non-target animal model. Zebrafish embryos at ± 2 h post-fertilization were exposed to tebuconazole wettable powder concentrations (0.05, 0.5 and 5 mg L^-1) for 96 h with developmental toxicity assessed throughout the exposure period and biochemical parameters evaluated at the end of the exposure. Behavioural assessment (spatial exploration and response to stimuli) was conducted 24 h after the end of the exposure. While no developmental and physiological alterations were observed, exposure to tebuconazole resulted in an increased generation of reactive oxidative species at the 0.05 and 0.5 mg L^-1 concentrations and a decreased GPx activity at the 0.5 mg L^-1 concentration suggesting a potential protection mechanism. There was also a change in the avoidance-escape behaviour supporting an anxiolytic effect suggesting possible alterations in the central nervous system development demanding further studies.

Cyclophosphamide affects eye development and locomotion in zebrafish (Danio rerio)

Cyclophosphamide (CP) is a broad-spectrum anticancer drug and has been frequently detected in aquatic environments due to its incomplete removal by wastewater treatment facilities and slow degradation in waters. Its toxicity in fish remains largely unknown. In this study, zebrafish eggs <4 h post fertilization (hpf) were exposed to CP at the concentrations from 0.5 to 50.0 μg/L until 168 hpf, and its toxicity was evaluated by biochemical, transcriptomic, and behavioral approaches. The results showed that malformation and mortality rates increased with CP concentrations. The 7-day malformation EC₅₀ and mortality (LC₃₀) by CP were calculated to be 86.8 μg/L and 7.5 mg/L, respectively. Inhibited startle response (light to dark) (a minimal of 19%) and reduced swimming velocity (a minimal of 30%) were observed in the CP-exposed larvae. The thicknesses of retinal ganglion layer, inner plexiform layer, and inner nuclear layer in the retina were increased after exposure to CP. Meanwhile, exposure to CP increased karyorrhexis and karyolysis in the liver tissue. Transcriptomic analysis identified 607 differentially expressed genes (DEGs) (159 up-regulated and 448 down-regulated). A significant reduction in the transcripts of sgk1 (the FoxO pathway), jun (the MAPK pathway), and diabloa (apoptosis pathway) were observed in the CP-treated larvae. This study has demonstrated that low concentrations of CP cause malformation, reduced swimming capacity, histopathological alterations in the retina and liver tissues, and interference on transcriptional expressions of key genes associated with different pathways. The ecological risk of CP and other anticancer drugs to aquatic organisms merits future investigation.

The antidepressant venlafaxine perturbs cardiac development and function in larval zebrafish

Venlafaxine, a selective serotonin and norepinephrine reuptake inhibitor, is a highly prescribed antidepressant and is detected at µg/L concentrations in waterways receiving municipal wastewater effluents. We previously showed that early-life venlafaxine exposure disrupted the normal development of the nervous system and reduces larval activity in zebrafish (Danio rerio). However, it is unclear whether the reduced swimming activity may be associated with impaired cardiac function. Here we tested the hypothesis that zygotic exposure to venlafaxine impacts the development and function of the larval zebrafish heart. Venlafaxine (0, 1 or 10 ng) was administered by microinjection into freshly fertilized zebrafish embryos (1-4 cell stage) to assess heart development and function during early-life stages. Venlafaxine deposition in the zygote led to precocious development of the embryo heart, including the timing of the first heartbeat, increased heart size, and a higher heart rate at 24- and 48-hours post-fertilization (hpf). Also, waterborne exposure to environmental levels of this antidepressant during early development increased the heart rate at 48 hpf of zebrafish larvae mimicking the zygotic deposition. The venlafaxine-induced higher heart rate in the embryos was abolished in the presence of NAN-190, an antagonist of the 5HT_1A receptor. Also, heart rate dropped below control levels in the 10 ng, but not 1 ng venlafaxine group at 72 and 96 hpf. An acute stressor reduced the venlafaxine-induced heart rate at 48 hpf but did not affect the already reduced heart rate at 72 and 96 hpf in the 10 ng venlafaxine group. Our results suggest that the higher heart rate in the venlafaxine group may be due to an enhanced serotonin stimulation of the 5HT_1A receptor. Taken together, early-life venlafaxine exposure disrupts cardiac development and has the potential to compromise the cardiovascular performance of larval zebrafish.

Reproductive health and endocrine disruption in smallmouth bass (Micropterus dolomieu) from the Lake Erie drainage, Pennsylvania, USA

Smallmouth bass Micropterus dolomieu were sampled from three sites within the Lake Erie drainage (Elk Creek, Twentymile Creek, and Misery Bay, an embayment in Presque Isle Bay). Plasma, tissues for histopathological analyses, and liver and testes preserved in RNALater® were sampled from 30 smallmouth bass (of both sexes) at each site. Liver and testes samples were analyzed for transcript abundance with Nanostring nCounter® technology. Evidence of estrogenic endocrine disruption was assessed by the presence and severity of intersex (testicular oocytes; TO) and concentrations of plasma vitellogenin in male fish. Abundance of 17 liver transcripts associated with reproductive function, endocrine activity, and contaminant detoxification pathways and 40 testes transcripts associated with male and female reproductive function, germ cell development, and steroid biosynthesis were also measured. Males with a high rate of TO (87-100%) and plasma vitellogenin were noted at all sites; however, TO severity was greatest at the site with the highest agricultural land cover. Numerous transcripts were differentially regulated among the sites and patterns of transcript abundance were used to better understand potential risk factors for estrogenic endocrine disruption. The results of this study suggest endocrine disruption is prevalent in this region and further research would benefit to identify the types of contaminants that may be associated with the observed biological effects.

Exposure to aluminium causes behavioural alterations and oxidative stress in the brain of adult zebrafish

Aluminium (Al) water pollution is an increasing environmental problem. Accordingly, this study aimed to find out more about its toxic effects on aquatic organisms. Adult zebrafish were exposed to 11 mg/L of Al and the behavioural responses and its correlation with brain oxidative stress, antioxidant-defences, changes in metabolism and neurotransmission were assessed at 10, 15 and 20 days of exposure. The behavioural and locomotory responses, suggest an increase in the anxiety state, especially observed in animals exposed to Al for 15 days. The reactive oxygen species increased in a time-dependent trend, while the oxidative damage varied over exposure time. The activity of antioxidant enzymes, as superoxide dismutase, glutathione peroxidase and glutathione S-transferases, and the metallothioneins levels increased after short-term exposures and tended to decrease or stabilize at longer times. The results contribute to understand the toxic mechanisms activated by Al highlighting correlations like behavioural disorders and oxidative state.

Inhibition of swim bladder inflation in Japanese medaka (Oryzias latipes) embryos following exposure to select pharmaceuticals alone and in combination

This study leveraged the Japanese medaka fish embryo model for the assessment of effects of select contaminants on early development in fish. Fish embryos were exposed to various pharmaceutical contaminants including synthetic hormones and non-steroidal anti-inflammatory drugs and their effects on development were observed. Initial screening determined that swim bladder inflation failure was the most common endpoint detected. Swim bladder inflation failure was first explored in a study demonstrating that medaka require access to the air-water interphase to inflate their swim bladders in a time-dependent manner, and swim bladder inflation failure was correlated with mortality. Fish embryos were exposed 24-hours post fertilization until hatch to concentration ranges of various pharmaceutical contaminants including: 17β-estradiol, 17α-ethinylestradiol, and levonorgestrel (1 to 1000 µg/L), or diclofenac (0.32 to 100 mg/L). The main effect observed across all four compounds was a significant increase in failure of swim bladder inflation with increasing exposure concentration (24 to 72-hours post-hatch). Following single compound experiments combinatorial exposures using no-observed-effect concentrations were conducted. The main effect observed was a significant decrease in inflation success 24-hours post-hatch following a binary mixture of levonorgestrel and 17α-ethinylestradiol, as well as a significant decrease in swim bladder inflation success at all times following exposure to a quaternary mixture of all four compounds. This study demonstrated that embryonic exposure to pharmaceutical compounds, both alone and in combination, resulted in failure of swim bladder inflation in larval Japanese medaka.

A comprehensive review on environmental toxicity of azole compounds to fish

BACKGROUND

Azoles are considered as one of the most efficient fungicides for the treatment of humans, animals, and plant fungal pathogens. They are of significant clinical importance as antifungal drugs and are widely used in personal care products, ultraviolet stabilizers, and in aircraft for its anti-corrosive properties. The prevalence of azole compounds in the natural environment and its accumulation in fish raises questions about its impact on aquatic organisms.

OBJECTIVES

The objective of this paper is to review the scientific studies on the effects of azole compounds in fish and to discuss future opportunities for the risk evaluation.

METHODS

A systematic literature search was conducted on Web of Science, PubMed, and ScienceDirect to locate peer-reviewed scientific articles on occurrence, environmental fate, and toxicological impact of azole fungicides on fish.

RESULTS

Studies included in this review provide ample evidence that azole compounds are not only commonly detected in the natural environment but also cause several detrimental effects on fish. Future studies with environmentally relevant concentrations of azole alone or in combination with other commonly occurring contaminants in a multigenerational study could provide a better understanding.

CONCLUSION

Based on current knowledge and studies reporting adverse biological effects of azole on fish, considerable attention is required for better management and effective ecological risk assessment of these emerging contaminants.

The effects of norethindrone on the ontogeny of gene expression along the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes in zebrafish (Danio rerio)

Little is known about the molecular effects of progestins on the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes in fish prior to sexual differentiation. In this study, the effects of norethindrone (NET) on the ontogeny of HPG- and HPA-related genes in zebrafish embryo/early larvae prior to sexual differentiation were evaluated. Embryo/larvae were exposed to different concentrations (5, 50, 500 ng/L) of NET for 6 days. The levels of the transcripts of the genes closely related to the HPG and HPA axes were determined daily during 3 stages (embryo, embryo/larvae transition, and early larvae). The results showed that most genes were up-regulated and the ontogeny of genes in the HPA axis was earlier than that of HPG axis, especially for the upstream genes of both the HPG (gnrh2, gnrh3, fshb, lhb) and the HPA (crh, pomc, star) axes. In contrast, the transcriptional expressions of genes of the cortisol/stress pathway (cyp11b, mr) were inhibited and those of the progesterone pathway were not affected. More importantly, NET exposure induced the expressions of the genes (esr1, vtg1, hsd17b3, hsd11b2, ar) that are closely related to the steroid hormone pathways in the embryos/larvae stages, implying a precocious effects of NET in zebrafish. This study demonstrates that NET alters the expression of HPA- and HPG-axes related genes in zebrafish at early stages, pointing to the need for the same type of analysis during the zebrafish gonadal differentiation window.

Impacts of bisphenol A analogues on zebrafish post-embryonic brain

Bisphenol A (BPA) is a widely studied and well-recognised endocrine-disrupting chemical, and one of the current issues is its safe replacement by various analogues. Using larva zebrafish as a model, the present study reveals that moderate and chronic exposure to BPA analogues such as bisphenol S, bisphenol F and bisphenol AF may also affect vertebrate neurodevelopment and locomotor activity. Several parameters of embryo-larval development were investigated, such as mortality, hatching, number of mitotically active cell, as defined by 5-bromo-2'-deoxyuridine incorporation and proliferative cell nuclear antigen labelling, aromatase B protein expression in radial glial cell and locomotor activity. Our results show that exposure to several bisphenol analogues induced an acceleration of embryo hatching rate. At the level of the developing brain, a strong up-regulation of the oestrogen-sensitive Aromatase B was also detected in the hypothalamic region. This up-regulation was not associated with effects on the numbers of mitotically active progenitors nor differentiated neurones in the preoptic area and in the nuclear recessus posterior of the hypothalamus zebrafish larvae. Furthermore, using a high-throughput video tracking system to monitor locomotor activity in zebrafish larvae, we show that some bisphenol analogues, such as bisphenol AF, significantly reduced locomotor activity following 6 days of exposure. Taken together, our study provides evidence that BPA analogues can also affect the neurobehavioural development of zebrafish.

Transcriptome analysis of testis reveals the effects of developmental exposure to bisphenol a or 17α-ethinylestradiol in medaka (Oryzias latipes)

Endocrine disrupting chemicals (EDCs) can induce abnormalities in organisms via alteration of molecular pathways and subsequent disruption of endocrine functions. Bisphenol A (BPA) and 17α-ethinylestradiol (EE2) are ubiquitous EDCs in the environment. Many aquatic organisms, including fish, are often exposed to varying concentrations of BPA and EE2 throughout their lifespan. Both BPA and EE2 can activate estrogenic signaling pathways and cause adverse effects on reproduction via alteration of pathways associated with steroidogenesis. However, transcriptional pathways that are affected by chronic exposure to these two ubiquitous environmental estrogens during embryonic, larval, and juvenile stages are not clearly understood. In the present study, we examined transcriptional alterations in the testis of medaka fish (Oryzias latipes) chronically exposed to a low concentration of BPA or EE2. Medaka were exposed to BPA (10 μg/L) or EE2 (0.01 μg/L) from 8 h post-fertilization (as embryos) to adulthood 50 days post fertilization (dpf), and transcriptional alterations in the testis were examined by RNA sequencing (RNA-seq). Transcriptomic profiling revealed 651 differentially expressed genes (DEGs) between BPA-exposed and control testes, while 1475 DEGs were found between EE2-exposed and control testes. Gene ontology (GO) analysis showed a significant enrichment of "intracellular receptor signaling pathway", "response to steroid hormone" and "hormone-mediated signaling pathway" in the BPA-induced DEGs, and of "cilium organization", "microtubule-based process" and "organelle assembly" in the EE2-induced DEGs. Pathway analysis showed significant enrichment of "integrin signaling pathway" in both treatment groups, and of "cadherin signaling pathway", "Alzheimer disease-presenilin pathway" in EE2-induced DEGs. Single nucleotide polymorphism (SNP) and insertion-deletion (Indel) analysis found no significant differences in mutation rates with either BPA or EE2 treatments. Taken together, global gene expression differences in testes of medaka during early stages of gametogenesis were responsive to chronic BPA and EE2 exposure.

Toxic effects of a mancozeb-containing commercial formulation at environmental relevant concentrations on zebrafish embryonic development

The toxicological knowledge of mancozeb (MZ)-containing commercial formulations on non-target species is scarce and limited. Therefore, the objective of this work was to represent a realistic application scenario by evaluating the toxicity of environmental relevant and higher concentrations of a commercial formulation of MZ using zebrafish embryos. Following determination of the 96-h LC₅₀ value, the embryos at the blastula stage (~ 2 h post-fertilisation, hpf) were exposed to 0.5, 5, and 50 μg L^-1 of the active ingredient (~ 40× lower than the 96-h LC₅₀). During the exposure period (96 h), lethal, sublethal, and teratogenic parameters, as well as behaviour analysis, at 120 hpf, were assayed. Biochemical parameters such as oxidative stress-linked enzymes (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR)), reactive oxygen species (ROS) levels, and glutathione levels (GSH and GSSG), as well as the activity of degradation (glutathione S-transferase (GST) and carboxylesterase (CarE)), neurotransmission (acetylcholinesterase (AChE)), and anaerobic respiration (lactate dehydrogenase (LDH))-related enzymes, were analysed at the end of the exposure period. Exposed embryos showed a marked decrease in the hatching rate and many malformations (cardiac and yolk sac oedema and spinal torsions), with a higher prevalence at the highest concentration. A dose-dependent decreased locomotor activity and a response to an aversive stimulus, as well as a light-dark transition decline, were observed at environmental relevant concentrations. Furthermore, the activities of SOD and GR increased while the activity of GST, AChE, and MDA contents decreased. Taken together, the involvement of mancozeb metabolites and the generation of ROS are suggested as responsible for the developmental phenotypes. While further studies are needed to fully support the hypothesis presented, the potential cumulative effects of mancozeb-containing formulations and its metabolites could represent an environmental risk which should not be disregarded.

The Effects of 17α-Ethinylestradiol on the Heart Rate of Embryonic Japanese Medaka (Oryzias latipes)

Estrogen toxicity has been an area of priority in aquatic toxicology over the last 20 yr. Currently, estrogen toxicity is primarily linked to classical estrogen signaling, the interaction of estrogen receptors alpha and beta (ERα and ERβ). Recent evidence has indicated that a rapid, nongenomic, nonclassical estrogen signaling pathway exists via the G protein-coupled estrogen receptor (GPER), which is expressed in many biological systems, with roles in the cardiovascular system. The objective of the present study was to investigate the effect of 17α-ethinylestradiol (EE2) on the heart rate of embryonic Japanese medaka (Oryzias latipes). A significant decrease (bradycardia) in embryonic heart rate was observed at all treatment concentrations (0.1, 1, 10, 100, and 1000 ng/L EE2) at 144, 168, and 192 h postfertilization (hpf; p ≤ 0.05), whereas 120 and 216 hpf embryos experienced a significant decrease from the control at 10, 100, and 1000 ng/L EE2 and 0.1, 100, and 1000 ng/L EE2, respectively (p ≤ 0.05). In addition, using select estrogen receptor modulators, it was demonstrated that estrogen-induced bradycardia appears to be linked to GPER and not ERα and ERβ. The present study highlights GPER as a novel and alternative mode of action for EE2 toxicity at environmentally relevant concentrations. Environ Toxicol Chem 2020;39:904-912. © 2020 SETAC.

Parental exposure to bisphenol A affects pharyngeal cartilage development and causes global transcriptomic changes in zebrafish (Danio rerio) offspring

BACKGROUND

As one of the most common endocrine-disrupting chemicals (EDCs), bisphenol A (BPA) is a threat to aquatic ecosystems. Despite a rich literature addressing the adverse effects of BPA on various systems in fish models, the potential impact of parental BPA exposure on offspring pharyngeal cartilage development is poorly understood.

METHODS

Adult zebrafish (F0) were exposed to BPA (1.0 μM) or control for 7 days. Eggs (F1) were collected and exposed to BPA (control, 0.05, 0.1, 1, 10 μM) until 120 h post-fertilization. Histomorphometrical essay was used to quantitatively and qualitatively assess the effects of BPA on pharyngeal cartilage development. RNA sequencing (RNA-seq) was used to discover differentially expressed genes (DEGs), and KEGG pathway and GO enrichment analysis were performed to interpret functional ontology.

RESULTS

Parental BPA exposure affected hatchability and heart rates of F1 progeny. By pathology analysis, parental BPA exposure caused craniofacial deformity, characterized by wider angles of cartilage elements, disrupted pharyngeal chondrocytes and promoted apoptosis and elongation of head length. RNA-seq suggested that many DEGs were involved in multiple biological processes and signaling pathways; defense responses, reactive oxygen species metabolic process, apoptosis, p53 signaling pathway and MAPK signaling pathway were closely associated with the toxicity of parental BPA exposure.

CONCLUSIONS

Parental BPA exposure affected chondrogenesis in the viscerocranium of zebrafish offspring and led to global transcriptomic changes involved in apoptosis, hyperplasia and oxidative stress. These newly identified gene expression patterns, pathways and gene networks of zebrafish eleutheroembryos after early-life waterborne BPA exposure, may lead to severe and permanent morphological and functional consequences.

Overview of the analysis, occurrence and ecological effects of hormones in lake waters in Asia

Hormones are natural and synthetic compounds that are now being detected in the aquatic environment. Many lakes in Asia are important water sources that may be affected by these emerging contaminants. Lakes are drains and reservoirs of watersheds that are altered by changing land use and environmental conditions. While there are several studies on the detection of hormones in lakes, these studies were mostly done in China. Limited information is available on the presence of these contaminants in the lakes in other Asian countries. Hormones in the lake water come from discharge waters in urban areas, farm runoffs, and effluents of wastewater and sewage treatment plants. Hormones contamination in water has been shown to affect the reproduction and growth of certain aquatic organisms. In this review, a background on the chemical nature and physiological functions of hormones is provided and the existing knowledge on the occurrence and ecological impacts of hormones in lakes is described. The available analytical methods for sampling, analyte extraction and instrumental analysis are outlined. This overview provides insights on the current conditions of lakes that may be impacted by hormones contamination. Understanding the levels and possible ecological consequences will address the issues on these emerging contaminants especially in the Asian environment. This will elicit discussions on improving guidelines on wastewater discharges and will drive future research directions.

Associations Between Behavioral Effects of Bisphenol A and DNA Methylation in Zebrafish Embryos

Endocrine-disrupting contaminants have been associated with aberrant changes in epigenetic pathways in animals. In this study, zebrafish embryos were exposed bisphenol A (BPA) to search for associations between behavior and epigenetic mechanisms in fish. For concentration-dependent responses, embryos were exposed to a range of BPA concentrations (0.1 nM to 30 μM). Embryos were analyzed for locomotor activity at 3-, 4-, and 5-days post fertilization (dpf) in response to changing light conditions. Based on concentration-dependent effects on behavior and gene expression, 10 μM BPA [from 24 to 96 hours post fertilization (hpf)] was used for a whole-genome bisulfite sequencing (WGBS) study searching for genome-wide impacts on DNA methylation. Over the examined concentration ranges, hyperactivity was demonstrated for exposures to 0.001 μM BPA in comparison to embryos exposed to lower or higher BPA concentrations. Transcriptional analysis showed significant effects at >0.01 μM BPA for two genes related to DNA methylation (dnmt1, cbs). BPA exposure did not significantly affect global DNA methylation, but 20,474 differentially methylated (DM) sites in 4,873 genes were identified by WGBS analysis. Most DM sites were identified within gene bodies. The genes with the most DM sites were all protocadherin 2 gamma subfamily genes, related to axon targeting, synaptic development and neuronal survival. KEGG pathways most significantly affected by BPA exposure were phosphatidylinositol signaling system, followed by VEGF and MAPK signaling pathways. This study shows that BPA can affect zebrafish embryo swimming activity at very low concentrations as well as affecting numerous methylated sites in genes which are overrepresented in functionally relevant metabolic pathways. In conclusion, altered methylation patterns of genes associated with nervous system development might lead to abnormal swimming activity.

The endocrine disruptor, 17α-ethinyl estradiol, alters male mate choice in a freshwater fish

Among the handful of studies on the behavioural effects of endocrine disrupting chemicals (EDCs), only a few have set out to disentangle the mechanisms underpinning behavioural changes. In fish, previous studies have shown that both visual and chemical cues play an important role in mate choice. As such, contaminant-induced changes in either transmission or perception of mate choice cues could have direct implications for individual's fitness. One widespread contaminant of environmental concern is 17α-ethinyl estradiol (EE2), a synthetic estrogen used in the contraceptive pill. Here, we investigated the impacts of EE2 exposure (28 days; measured concentration 14 ng/L) on visual and chemical communication in wild guppies (Poecilia reticulata). Using a standard dichotomous mate choice assay, we first gave individual males (either control or EE2-exposed) the opportunity to court two size-matched females (one control and one EE2-exposed) using only visual cues. We then introduced chemical cues of females (control and EE2-exposed) to the trial tank. We found that there was no significant effect of EE2-treatment on total time males spent associating with the females, when given only visual cues. There was, however, a significant effect on male courtship behaviour, with both control and EE2-exposed males spending more time performing 'sigmoid' displays towards the visual cues of control females compared to EE2-exposed females. When males were presented with both visual and chemical female cues simultaneously, we found that males spent more time courting control females that were paired with EE2-chemical cues. Not only does our study uncover a previously unknown behavioural impact of EE2-exposure on chemical cues, but demonstrates that EE2-exposure can exert complex effects on visual and chemical communication in a mate choice context. Finally, we contribute to the discussion of intraspecific variability by providing data on the potential trade-offs underpinning contaminant-induced behavioural changes.

Associations Between Behavioral Effects of Bisphenol A and DNA Methylation in Zebrafish Embryos

Endocrine-disrupting contaminants have been associated with aberrant changes in epigenetic pathways in animals. In this study, zebrafish embryos were exposed bisphenol A (BPA) to search for associations between behavior and epigenetic mechanisms in fish. For concentration-dependent responses, embryos were exposed to a range of BPA concentrations (0.1 nM to 30 μM). Embryos were analyzed for locomotor activity at 3-, 4-, and 5-days post fertilization (dpf) in response to changing light conditions. Based on concentration-dependent effects on behavior and gene expression, 10 μM BPA [from 24 to 96 hours post fertilization (hpf)] was used for a whole-genome bisulfite sequencing (WGBS) study searching for genome-wide impacts on DNA methylation. Over the examined concentration ranges, hyperactivity was demonstrated for exposures to 0.001 μM BPA in comparison to embryos exposed to lower or higher BPA concentrations. Transcriptional analysis showed significant effects at >0.01 μM BPA for two genes related to DNA methylation (dnmt1, cbs). BPA exposure did not significantly affect global DNA methylation, but 20,474 differentially methylated (DM) sites in 4,873 genes were identified by WGBS analysis. Most DM sites were identified within gene bodies. The genes with the most DM sites were all protocadherin 2 gamma subfamily genes, related to axon targeting, synaptic development and neuronal survival. KEGG pathways most significantly affected by BPA exposure were phosphatidylinositol signaling system, followed by VEGF and MAPK signaling pathways. This study shows that BPA can affect zebrafish embryo swimming activity at very low concentrations as well as affecting numerous methylated sites in genes which are overrepresented in functionally relevant metabolic pathways. In conclusion, altered methylation patterns of genes associated with nervous system development might lead to abnormal swimming activity.

Impact on growth, oxidative stress, and apoptosis-related gene transcription of zebrafish after exposure to low concentration of arsenite

Low concentrations of arsenic (As) contamination in aquatic environment is a worldwide issue, which is of great concern. To evaluate the impact of low concentrations of As on zebrafish, we measured the growth, antioxidant enzymes including superoxide dismutase (SOD) and catalase (CAT), oxidative damage (malondialdehyde, MDA) and apoptosis-related genes (nrf2, p53 and c-jun) of adult zebrafish after exposing to different AsIII concentrations (0, 10, 50, 100 or 150 μg L^-1) for 28 d. Results indicated that exposure to low AsIII concentrations decreased the zebrafish weight by 14%, increased the activities of SOD and CAT by 23-41% and 31-59%, decreased the contents of MDA by 29-54%, and modulated transcription of apoptosis related genes. Our study showed that chronic exposure to AsIII concentrations <150 μg L^-1 generated oxidative stress and damage on zebrafish, and altered apoptosis-related genes in zebrafish.

Comparison of steroidogenic gene expression in mummichog (Fundulus heteroclitus) testis tissue following exposure to aromatizable or non-aromatizable androgens

Androgens are a recognized class of endocrine disrupting compounds with the ability to impact reproductive status in aquatic organisms. The current study utilized in vitro exposure of mummichog (Fundulus heteroclitus) testis tissue to either the aromatizable androgen 17α-methyltestosterone (MT) or the non-aromatizable androgen 5α-dihydrotestosterone (DHT) over the course of 24 h to determine if there were differential effects on steroidogenic gene expression. Testis tissue was exposed to androgen concentrations of 10^-12 M, 10^-9 M and 10^-6 M for 6, 12, 18 or 24 h, after which a suite of steroidogenic genes, including steroidogenic acute regulatory protein, 3β-hydroxysteroid dehydrogenase (3βhsd) and cytochrome P450 17A1 (cyp17a1), were quantified using real-time polymerase chain reaction. Both androgens affected steroidogenic gene expression, with most alterations occurring at the 24-hour time point. The gene with the highest fold-change, and shortest interval to expression alteration, was 3βhsd for both androgens. Potential differences between the two model androgens were observed in increased expression of cyp17a1 and 11β-hydroxysteroid dehydrogenase (11βhsd), which were only altered after exposure to DHT and in expression levels of cytochrome P450 11A1 (cyp11a1), which was upregulated by MT but not altered by DHT. Results from this study show both androgens interact at the gonadal level of the hypothalamus-pituitary-gonadal axis and may possess some distinct gene expression impacts. These data strengthen the current research initiatives of establishing in vitro test systems that allow toxic potential of untested chemicals to be predicted from molecular perturbations.

Toxicity and non-harmful effects of the soya isoflavones, genistein and daidzein, in embryos of the zebrafish, Danio rerio

Based on the assumed oestrogenic and apoptotic properties of soya isoflavones (genistein, daidzein), and following the current OECD test-guidelines and principle of 3Rs, we have studied the potential toxicity of phytochemicals on the zebrafish embryos test (ZFET). For this purpose, zebrafish embryos at 2-3 h post-fertilisation (hpf) were exposed to both soya isoflavones (from 1.25 mg/L to 20 mg/L) and assayed until 96 hpf. Lethal and sub-lethal endpoints (mortality, hatching rates and malformations) were estimated in the ZFET, which was expanded to potential gene expression markers, determining the lowest observed effect (and transcriptional) concentrations (LOEC, LOTEC), and the no-observable effect (and transcriptional) concentrations (NOEC, NOTEC). The results revealed that genistein is more toxic (LC50-96 hpf: 4.41 mg/L) than daidzein (over 65.15 mg/L). Both isoflavones up-regulated the oestrogen (esrrb) and death receptors (fas) and cyp1a transcript levels. Most thyroid transcript signals were up-regulated by genistein (except for thyroid peroxidase/tpo), and the hatching enzyme (he1a1) was exclusively up-regulated by daidzein (from 1.25 mg/L onwards). The ZFET proved suitable for assessing toxicant effects of both isoflavones and potential disruptions (i.e. oestrogenic, apoptotic, thyroid, enzymatic) during the embryogenesis and the endotrophic larval period.

Assaying uptake of endocrine disruptor compounds in zebrafish embryos and larvae

To study the effects of environmental endocrine disruptor compounds (EDCs) on aquatic animals, embryos and larvae are typically incubated in water containing defined concentrations of EDCs. However, the amount of EDC uptake into the animal is often difficult to determine. Using radiolabeled estradiol ([³H]E2), we previously developed a rapid, straightforward assay to measure estradiol uptake from water into zebrafish embryos and larvae. Here, we extend this approach to measure the uptake of two additional EDCs, bisphenol A (BPA) and ethinyl estradiol (EE2). As with E2, the uptake of each compound by individual larvae was low (<6%), and increased with increasing concentration, duration, and developmental stage. We found that E2 and EE2 had similar uptake under equivalent exposure conditions, while BPA had comparatively lower uptake. One application of this assay is to test factors that influence EDC uptake or efflux. It has been suggested that persistent organic pollutants (POPs) inhibit ABC transporters that may normally efflux EDCs and their metabolites, inducing toxicity in aquatic organisms. We measured [³H]E2 levels in zebrafish in the presence or absence of the POP PDBE-100, and cyclosporine A, a known inhibitor of ABC transporters. Neither chemical significantly affected [³H]E2 levels in zebrafish, suggesting that zebrafish maintain estradiol efflux in the presence of PDBE-100, independently of cyclosporine A-responsive transporters. These uptake results will be a valuable reference for EDC exposure studies in developing zebrafish, and provide a rapid assay to screen for chemicals that influence estrogen-like EDC levels in vivo.

Ketamine induction of p53-dependent apoptosis and oxidative stress in zebrafish (Danio rerio) embryos

Ketamine is a widely used pharmaceutical that has been detected in water sources worldwide. Zebrafish embryos were used in this study to investigate the oxidative stress and apoptotic signals following a 24h exposure to different ketamine concentrations (0, 50, 70 and 90 mg L^-1). Early blastula embryos (∼2 h post fertilisation-hpf) were exposed for 24 h and analysed at 8 and 26 hpf. Reactive oxygen species and apoptotic cells were identified in vivo, at 26 hpf. Enzymatic activities (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), lactate dehydrogenase (LDH) and acetylcholinesterase (AChE)), glutathione levels (oxidised (GSSG) and reduced (GSH)), oxidative damage (lipid peroxidation (LPO) and protein carbonyls (CO)) as well as oxidative stress (gclc, gstp1, sod1 and cat), apoptosis (casp3a, casp6, casp8, casp9, aifm1 and tp53) and cell proliferation (pcna) related-genes were evaluated at 8 and 26 hpf. Caspase (3 and 9) activity was also determined at both time-points by colorimetric methods. Superoxide dismutase (SOD), catalase (CAT), glutathione levels (GSSG), caspase-9 and reactive oxygen species (ROS) were shown to be affected by ketamine exposure while in vivo analysis showed no difference in ROS. A significant up-regulation of superoxide dismutase (sod1) and catalase (cat) genes expression was also perceived. Ketamine-induced apoptosis was observed in vivo and confirmed by the apoptotic-related genes up-regulation. The overall results suggest that ketamine induced oxidative stress and apoptosis through the involvement of p53-dependent pathways in zebrafish embryos which could be important for the evaluation of the overall risk of ketamine in aquatic environments.

Atrazine affects craniofacial chondrogenesis and axial skeleton mineralization in zebrafish (Danio rerio)

Atrazine is a commonly used herbicide that has previously been implicated as an endocrine-disrupting compound. Previous studies have shown that estrogenic endocrine-disrupting compounds affect the development of the heart, cartilage, and bone in zebrafish ( Danio rerio). To determine whether atrazine has effects similar to other endocrine disruptors, zebrafish embryos were treated with a range of atrazine concentrations. Atrazine treatment at a low concentration of 0.1 µM resulted in significant differences in craniofacial cartilage elements, while concentrations ≥1 µM led to decreased survival and increased heart rates. Fish treated with ≥1 µM atrazine also developed with delayed vertebrae mineralization. Higher concentrations of atrazine caused gross craniofacial defects and decreased hatching rates. Further studies into the molecular pathways disrupted in these developmental processes could shed light on a link between endocrine-disrupting compounds and developmental abnormalities.

The Primodos components Norethisterone acetate and Ethinyl estradiol induce developmental abnormalities in zebrafish embryos

Primodos was a hormone pregnancy test used between 1958-1978 that has been implicated with causing a range of birth defects ever since. Though Primodos is no longer used, it's components, Norethisterone acetate and Ethinyl estradiol, are used in other medications today including treatments for endometriosis and contraceptives. However, whether Primodos caused birth defects or not remains controversial, and has been little investigated. Here we used the developing zebrafish embryo, a human cell-line and mouse retinal explants to investigate the actions of the components of Primodos upon embryonic and tissue development. We show that Norethisterone acetate and Ethinyl estradiol cause embryonic damage in a dose and time responsive manner. The damage occurs rapidly after drug exposure, affecting multiple organ systems. Moreover, we found that the Norethisterone acetate and Ethinyl estradiol mixture can affect nerve outgrowth and blood vessel patterning directly and accumulates in the forming embryo for at least 24 hrs. These data demonstrate that Norethisterone acetate and Ethinyl estradiol are potentially teratogenic, depending on dose and embryonic stage of development in the zebrafish. Further work in mammalian model species are now required to build on these findings and determine if placental embryos also are affected by synthetic sex hormones and their mechanisms of action.

Growth, blood health, antioxidant status and immune response in juvenile yellow catfish Pelteobagrus fulvidraco exposed to α-ethinylestradiol (EE2)

Triplicate groups of juvenile yellow catfish Pelteobagrus fulvidraco were exposed to three levels of α-ethinylestradiol (EE2) (0, 0.1 and 1 ng L^-1) for 56 days. Fish survival rate (>93.33%) was not different among experimental groups. Weight gain and specific growth rate of fish exposed to EE2 were higher than those of control fish. Hepatosomatic index of fish exposed to 1 ng L^-1 EE2 was the highest. Serum total protein, albumin, globulin, alanine aminotransferase, aspartate transaminase, cholesterol and triglyceride increased with increasing EE2 exposure levels. Liver total anti-oxidative capacity, malondialdehyde content and lysozyme activity of fish exposed to EE2 were higher than those of control fish. Phagocytic indices of fish exposed to 1 ng L^-1 EE2 was lower than that of control fish. This study indicates that although EE2 exposure can promote the growth of yellow catfish in short-term, EE2 exerts its toxic effects by inducing reactive oxygen species generation and malondialdehyde accumulation, leading to blood deterioration and interfering with immune response.

Genotyping live fish larvae: Non-lethal and noninvasive DNA isolation from 3-5 day old hatchlings

Genotyping fish larvae is a valuable technique for numerous fields of study. While methods for collecting DNA from early stage larvae have been published, a non-lethal, non-invasive genotyping protocol for hatchlings that is amenable to high-throughput approaches is desirable. Here, we describe a method to individually genotype live, free-swimming, early fish larvae by characterizing their environmental DNA (eDNA). We demonstrate the utility of the method by assigning parentage to a sample (n = 50) of 3-5-day-old sheepshead minnow (Cyprinodon variegatus) larvae hatchlings, with very high rates of genotyping success (98%) and survival (92%) using mitochondrial and microsatellite DNA data. This method could be easily adapted to characterize early fish larvae from other model and non-model fish species, such as Danio rerio (zebrafish) and Medaka medaka.

Effects of the soya isoflavone genistein in early life stages of the Senegalese sole, Solea senegalensis: Thyroid, estrogenic and metabolic biomarkers

This study examines the effects induced by environmentally relevant concentrations of the isoflavone genistein (3mg/L and 10mg/L) during early life stages of the Senegalese sole. Throughout the hypothalamus-pituitary-thyroid (HPT) axis, several neurohormonal regulatory thyroid signalling patterns (thyroglobulin/Tg, thyroid peroxidase/TPO, transthyretin/TTR, thyroid receptors/TRβ, and iodothrynonine deiodinases, Dio2 and Dio3) were analysed. Furthermore, the expression patterns of estrogen receptor ERβ and haemoprotein Cyp1a were also evaluated. In the control larvae, progressive increases of constitutive hormonal signalling pathways have been evidenced from the pre-metamorphosis phase onwards, reaching the highest expression basal levels at the metamorphosis (Tg, TPO, Dio2) and/or during post-metamorphosis (TTR, TRβ, ERβ). When the early larvae were exposed to both genistein concentrations (3mg/L and 10mg/L), a statistically significant down-regulation of TPO, TTR and Tg mRNA levels was clearly detected at the metamorphic stages. In addition, the Dio2 and Dio3 transcript expression levels were also down and up-regulated when exposed to both genistein concentrations. In the larvae exposed to genistein, no statistically significant responses were recorded for the TRβ expression patterns. Nevertheless, the ERβ and Cyp1a transcript levels were up-regulated at the middle metamorphic stage (S2, at 16 dph) in the larvae exposed to high genistein concentrations and, only the ERβ was down-regulated (S1, at 12dph) at the lower doses. Finally, all these pointed out imbalances were only temporarily disrupted by exposure to genistein, since most of the modulated transcriptional signals (i.e. up or down-regulation) were quickly restored to the baseline levels. Additionally, the control and genistein-exposed Senegalese sole specimens showed characteristic ontogenetic patterns and completely suitable for an optimal development, metamorphosis, and growth.

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.

Phytoestrogens and sterols in waters with cyanobacterial blooms - Analytical methods and estrogenic potencies

Compounds with estrogenic potencies and their adverse effects in surface waters have received much attention. Both anthropogenic and natural compounds contribute to overall estrogenic activity in freshwaters. Recently, estrogenic potencies were also found to be associated with cyanobacteria and their blooms in surface waters. The present study developed and compared the solid phase extraction and LC-MS/MS analytical approaches for determination of phytoestrogens (8 flavonoids - biochanin A, coumestrol, daidzein, equol, formononetin, genistein, naringenin, apigenin - and 5 sterols - ergosterol, β-sitosterol, stigmasterol, campesterol, brassicasterol) and cholesterol in water. The method was used for analyses of samples collected in stagnant water bodies dominated by different cyanobacterial species. Concentrations of individual flavonoids ranged from below the limit of detection to 3.58 ng/L. Sterols were present in higher amounts up to 2.25 μg/L. Biological potencies of these phytoestrogens in vitro were characterized using the hERα-HeLa-9903 cell line. The relative estrogenic potencies (compared to model estrogen - 17β-estradiol) of flavonoids ranged from 2.25E-05 to 1.26E-03 with coumestrol being the most potent. None of the sterols elicited estrogenic response in the used bioassay. Estrogenic activity was detected in collected field water samples (maximum effect corresponding to 2.07 ng/L of 17β-estradiol equivalents, transcriptional assay). At maximum phytoestrogens accounted for only 1.56 pg/L of 17β-estradiol equivalents, contributing maximally 8.5% of the total estrogenicity of the water samples. Other compounds therefore, most likely of anthropogenic origin such as steroid estrogens, are probably the major drivers of total estrogenic effects in these surface waters.

Gene Expression Profiling in Fish Toxicology: A Review

In this review, we present an overview of transcriptomic responses to chemical exposures in a variety of fish species. We have discussed the use of several molecular approaches such as northern blotting, differential display reverse transcription-polymerase chain reaction (DDRT-PCR), suppression subtractive hybridization (SSH), real time quantitative PCR (RT-qPCR), microarrays, and next-generation sequencing (NGS) for measuring gene expression. These techniques have been mainly used to measure the toxic effects of single compounds or simple mixtures in laboratory conditions. In addition, only few studies have been conducted to examine the biological significance of differentially expressed gene sets following chemical exposure. Therefore, future studies should focus more under field conditions using a multidisciplinary approach (genomics, proteomics and metabolomics) to understand the synergetic effects of multiple environmental stressors and to determine the functional significance of differentially expressed genes. Nevertheless, recent developments in NGS technologies and decreasing costs of sequencing holds the promise to uncover the complexity of anthropogenic impacts and biological effects in wild fish populations.

Toxicogenomics to Evaluate Endocrine Disrupting Effects of Environmental Chemicals Using the Zebrafish Model

The extent of our knowledge on the number of chemical compounds related to anthropogenic activities that can cause damage to the environment and to organisms is increasing. Endocrine disrupting chemicals (EDCs) are one group of potentially hazardous substances that include natural and synthetic chemicals and have the ability to mimic endogenous hormones, interfering with their biosynthesis, metabolism, and normal functions. Adverse effects associated with EDC exposure have been documented in aquatic biota and there is widespread interest in the characterization and understanding of their modes of action. Fish are considered one of the primary risk organisms for EDCs. Zebrafish (Danio rerio) are increasingly used as an animal model to study the effects of endocrine disruptors, due to their advantages compared to other model organisms. One approach to assess the toxicity of a compound is to identify those patterns of gene expression found in a tissue or organ exposed to particular classes of chemicals, through new technologies in genomics (toxicogenomics), such as microarrays or whole-genome sequencing. Application of these technologies permit the quantitative analysis of thousands of gene expression changes simultaneously in a single experiment and offer the opportunity to use transcript profiling as a tool to predict toxic outcomes of exposure to particular compounds. The application of toxicogenomic tools for identification of chemicals with endocrine disrupting capacity using the zebrafish model system is reviewed.

Reproductive toxicity of azoxystrobin to adult zebrafish (Danio rerio)

In the past few decades, extensive application of azoxystrobin has led to great concern regarding its adverse effects on aquatic organisms. The objective of the present study was to evaluate the reproductive toxicity of azoxystrobin to zebrafish. After adult zebrafish of both sexes were exposed to 2, 20 and 200 μg/L azoxystrobin for 21 days, egg production, the fertilization rate, the gonadosomatic index (GSI) and hepatosomatic index (HSI), 17β-estradiol (E2), testosterone (T) and vitellogenin (Vtg) concentrations, and histological alterations in the gonads and livers were measured. Meanwhile, expression alterations of genes encoding gonadotropins and gonadotropin receptors (fshb, lhb, fshr and lhr), steroid hormone receptors (era, er2b and ar), steroidogenic enzymes (cyp11a, cyp11b, cyp17, cyp19a, cyp19b, hsd3b and hsd17b) in the hypothalamic-pituitary-gonad (HPG) axis and vitellogenin (vtg1 and vtg2) in the livers were also investigated. The results showed that reduced egg production and fertilization rates were observed at 200 μg/L azoxystrobin. In female zebrafish, reduced E2 and Vtg concentrations, decreased GSI, increased T concentrations, and histological alterations in the ovaries and livers were observed at 200 μg/L azoxystrobin, along with significant down-regulation of lhb, cyp19b, lhr, cyp19a, vtg1 and vtg2, and up-regulation of cyp17, hsd3b and hsd17b. In male zebrafish, increased E2 and Vtg concentrations, reduced T concentration and GSI, and histological alterations in the testes and livers were observed after exposure to 20 and 200 μg/L azoxystrobin, along with significant up-regulations of cyp19b, cyp11a, cyp17, cyp19a, hsd3b and hsd17b, vtg1 and vtg2. Moreover, cyp11a, hsd3b, cyp19a, vtg1 and vtg2 in male zebrafish were significantly up-regulated after treatment with 2 μg/L azoxystrobin. The results of the present study indicate that azoxystrobin led to reproductive toxicity in zebrafish and male zebrafish were more sensitive to azoxystrobin than female zebrafish.

Mechanistic Evaluation of Benzo[a]pyrene's Developmental Toxicities Mediated by Reduced Cyp19a1b Activity

Benzo[a]pyrene (BaP) is a ubiquitous environmental contaminant that is both an endocrine disruptor and a carcinogen. Aromatase (CYP19) is a key enzyme in steroidogenesis that is responsible for conversion of androgens to estrogens and thus plays a key role in steroid homeostasis. We hypothesized that some of the adverse outcomes of early developmental exposure to BaP are the result of reduced Cyp19a1b activity. Our goal was to investigate the role of estrogen homeostasis during early development and determine the role of aromatase inhibition as a relevant mechanism in BaP's developmental toxicities. One-cell zebrafish embryos were injected with a Cyp19a1b-morpholino (MO) or control-MO. Other non-injected embryos were exposed to waterborne BaP, fadrozole (a Cyp19 inhibitor), estradiol (E2), BaP + E2, Cyp19a1b MO + E2, or fadrozole + E2 for 96 hours post-fertilization (hpf). Adverse outcomes were compared between treatments, and the ability of E2 co-exposure to rescue each observed dysmorphology was assessed. BaP significantly decreased cyp19a1b gene expression in 96 hpf zebrafish larvae homogenates. Concentrations of E2 in 48 hpf larvae were significantly decreased by BaP, fadrozole and Cyp19a1b-MO. Cumulative mortality of zebrafish larvae was significantly increased following BaP or fadrozole exposure or Cyp19a1b knockdown compared to controls. E2 co-treatment rescued mortality caused by 10 μg/L BaP, 10 μg/L fadrozole, or Cyp19a1b-MO. In a treatment-blinded morphological assessment of larvae at 96 hpf, several phenotypes were negatively impacted by BaP, fadrozole, or Cyp19a1b knockdown and rescued by exogenous E2 co-treatment; these included body length, optic vesicle size, swim bladder inflation, pericardial and abdominal edema, and incidence of normal larval tail shape. Abnormal pectoral fins were caused by BaP exposure only. Uninflated swim bladders were caused by all treatments including E2 alone. Our results indicate that certain BaP-mediated adverse developmental outcomes were mechanistically in accordance with BaP-mediated Cyp19a1b inhibition.

Protective Effects of Otophylloside N on Pentylenetetrazol-Induced Neuronal Injury In vitro and In vivo

Approximately 30% of epileptic patients worldwide are medically unable to control their seizures. In addition, repeated epileptic seizures generally lead to neural damage. Pentylenetetrazol (PTZ) is a clinical circulatory and respiratory stimulant that is experimentally used to mimic epileptic convulsion in epilepsy research. Here, we systematically explore the neuroprotective effects of a pure compound isolated from Cynanchum otophyllum Schneid (Qingyangshen), Otophylloside N (OtoN), against PTZ-induced neuronal injury. We used three models: in vitro primary cortical neurons, in vivo mice, and in vivo zebrafish. Our results revealed that OtoN treatment may attenuate PTZ-induced morphology changes, cell death, LDH efflux in embryonic neuronal cells of C57BL/6J mice, and convulsive behavior in zebrafish. Additionally, our Western blot and RT-PCR results demonstrated that OtoN may attenuate PTZ-induced apoptosis and neuronal activation in neuronal cells, mice, and zebrafish. OtoN may reduce PTZ-induced cleavage of poly ADP-ribose polymerase and upregulation of the Bax/Bcl-2 ratio and decrease the expression level of c-Fos. This study is the first investigation of the neuroprotective effects of OtoN, which might be developed as a novel antiepileptic drug.

Steroid androgen 17α-methyltestosterone induces malformations and biochemical alterations in zebrafish embryos

The synthetic androgen 17α-methyltestosterone is widely used in fish aquaculture for sex reversion of female individuals. Little is known about the amount of MT residues reaching the aquatic environment and further impacts in non-target organisms, including fish early-life stages. Thus, in this work, zebrafish embryos were exposed to two forms of 17α-methyltestosterone: the pure compound (MT) and a formulation commonly used in Brazil (cMT). For MT, a 96h-LC50 of 10.09mg/l was calculated. MT also affected embryo development inducing tail malformations, edemas, abnormal development of the head, and hatching delay. At biochemical level MT inhibited vitellogenin (VTG) and inhibited cholinesterase and lactate dehydrogenase. cMT elicited similar patterns of toxicity as the pure compound (MT). Effects reported in this study suggest a potential environmental risk of MT, especially since the VTG effects occurred at environmental relevant concentrations (0.004mg/l).

Severe malformations of eelpout (Zoarces viviparus) fry are induced by maternal estrogenic exposure during early embryogenesis

Pregnant eelpout were exposed via the water to known endocrine disrupting compounds (EDCs) to clarify if EDCs could be causing the increased eelpout fry malformation frequencies observed in coastal areas receiving high anthropogenic input. The presence of a teratogenic window for estrogen-induced malformations was also investigated by starting the exposure at different times during eelpout pregnancy. Both 17α-ethinylestradiol (EE2) (17.8 ng/L) and pyrene (0.5 μg/L) significantly increased fry malformation frequency whereas 4-t-octylphenol (4-t-OP) up to 14.3 μg/L did not. Vitellogenin was significantly induced by EE2 (5.7 and 17.8 ng/L) but not by 4-t-OP and pyrene. A critical period for estrogen-induced fry malformations was identified and closed between 14 and 22 days post fertilization (dpf). Exposure to 17β-estradiol (E2) between 0 and 14 dpf caused severe malformations and severity increased the closer exposure start was to fertilization, whereas malformations were absent by exposure starting later than 14 dpf. Data on ovarian fluid volume and larval length supported the suggested teratogenic window. Larval mortality also increased when exposure started right after fertilization.

Textile dyes induce toxicity on zebrafish early life stages

Textile manufacturing is one of the most polluting industrial sectors because of the release of potentially toxic compounds, such as synthetic dyes, into the environment. Depending on the class of the dyes, their loss in wastewaters can range from 2% to 50% of the original dye concentration. Consequently, uncontrolled use of such dyes can negatively affect human health and the ecological balance. The present study assessed the toxicity of the textile dyes Direct Black 38 (DB38), Reactive Blue 15 (RB15), Reactive Orange 16 (RO16), and Vat Green 3 (VG3) using zebrafish (Danio rerio) embryos for 144 h postfertilization (hpf). At the tested conditions, none of the dyes caused significant mortality. The highest RO16 dose significantly delayed or inhibited the ability of zebrafish embryos to hatch from the chorion after 96 hpf. From 120 hpf to 144 hpf, all the dyes impaired the gas bladder inflation of zebrafish larvae, DB38 also induced curved tail, and VG3 led to yolk sac edema in zebrafish larvae. Based on these data, DB38, RB15, RO16, and VG3 can induce malformations during embryonic and larval development of zebrafish. Therefore, it is essential to remove these compounds from wastewater or reduce their concentrations to safe levels before discharging textile industry effluents into the aquatic environment.

Ketamine-induced oxidative stress at different developmental stages of zebrafish (Danio rerio) embryos

The changes induced by ketamine exposure were developmental stage-dependent, and related with the gradual development of the antioxidant defense system of the embryo, which is dependent on changes in energy-sensing pathways.