Relative embryotoxicity of two classes of chemicals in a modified zebrafish embryotoxicity test and comparison with their in vivo potencies

Steroidogenic factor-1 hypermethylation in maternal rat blood could serve as a biomarker for intrauterine growth retardation

Intrauterine growth retardation (IUGR) is a common obstetric complication lacking an optimal method for prenatal screening. DNA methylation profile in maternal blood holds significant promise for prenatal screening. Here, we aimed to screen out potential IUGR biomarkers in maternal blood from the perspective of DNA methylation. The IUGR rat model was established by prenatal maternal undernutrition. High-throughput bisulfite sequencing of genomic DNA methylation followed by functional clustering analysis for differentially methylated region (DMR)-associated genes demonstrated that genes regulating transcription had the most significantly changed DNA methylation status in maternal blood with IUGR. Genes about apoptosis and placental development were also changed. Besides increased placental apoptosis, IUGR rats demonstrated the same hypermethylated CpG sites of steroidogenic factor-1 (SF-1, a DMR-associated transcription factor about placenta) promoter in maternal blood and placentae. Further, ff1b, the SF-1 ortholog, was knocked out in zebrafish by CRISPR/Cas9 technology. The knock-out zebrafish demonstrated developmental inhibition and increased IUGR rates, which confirmed the role of SF-1 in IUGR development. Finally, hypermethylated SF-1 was observed in human maternal blood of IUGR. This study firstly presented distinct DNA methylation profile in maternal blood of IUGR and showed hypermethylated SF-1 could be a potential IUGR biomarker in maternal rat blood.

CuInS2/ZnS QD exposure induces developmental toxicity, oxidative stress and DNA damage in rare minnow (Gobiocypris rarus) embryos and larvae

Chinese rare minnow (Gobiocypris rarus) embryos were used as an experimental model to investigate the effects of CuInS₂/ZnS quantum dots (QDs) on the early life stages of G. rarus. Normal developmental parameters (survival rate, body length and average heart rate), biomarker genes [stress response (Hsp70), detoxification (Cyp1a), organizer function and axis formation (Wnt8α), and muscle (Mstn)], enzymatic activity and DNA damage were recorded as endpoints in the developing embryos/larvae after exposure until 96h post-fertilization (hpf). Reduced survival rate, decreased heart rate, altered body length, increased malformation rate, decreased hatching rate, advanced hatching time in response to low concentrations (50 and 100nmol/L) and delayed hatching time in response to high concentrations were observed after exposure, as were many other toxic effects, including pericardial edema and bent tails. The 72 hpf LC₅₀ (median lethal concentration) was determined to be 624.364nmol/L. Treatment with certain concentrations of CuInS₂/ZnS QDs significantly increased the superoxide dismutase (SOD) activity and malondialdehyde (MDA) levels and significantly induced DNA damage. After treatment with CuInS₂/ZnS QDs, the embryos showed highly up-regulated expression of Hsp70, Cyp1a and Wnt8a and significantly up-regulated expression of Mstn at 12 hpf. Overall, this study indicates that CuInS₂/ZnS QDs are potentially toxic to G. rarus embryos. The information presented in this study will be helpful for fully understanding the toxicity induced by CuInS₂/ZnS QDs in fish embryos.

In vitro to in vivo extrapolation of effective dosimetry in developmental toxicity testing: Application of a generic PBK modelling approach

Incorporation of kinetics to quantitative in vitro to in vivo extrapolations (QIVIVE) is a key step for the realization of a non-animal testing paradigm, in the sphere of regulatory toxicology. The use of Physiologically-Based Kinetic (PBK) modelling for determining systemic doses of chemicals at the target site is accepted to be an indispensable element for such purposes. Nonetheless, PBK models are usually designed for a single or a group of compounds and are considered demanding, with respect to experimental data needed for model parameterization. Alternatively, we evaluate here the use of a more generic approach, i.e. the so-called IndusChemFate model, which is based on incorporated QSAR model parametrization. The model was used to simulate the in vivo kinetics of three diverse classes of developmental toxicants: triazoles, glycol ethers' alkoxyacetic acid metabolites and phthalate primary metabolites. The model required specific input per each class of compounds. These compounds were previously tested in three alternative assays: the whole-embryo culture (WEC), the zebrafish embryo test (ZET), and the mouse embryonic stem cell test (EST). Thereafter, the PBK-simulated blood levels at toxic in vivo doses were compared to the respective in vitro effective concentrations. Comparisons pertaining to relative potency and potency ranking with integration of kinetics were similar to previously obtained comparisons. Additionally, all three in vitro systems produced quite comparable results, and hence, a combination of alternative tests is still preferable for predicting the endpoint of developmental toxicity in vivo. This approach is put forward as biologically more plausible since plasma concentrations, rather than external administered doses, constitute the most direct in vivo dose metric.

Toxicity of effluents from gasoline stations oil-water separators to early life stages of zebrafish Danio rerio

Used petroleum hydrocarbons and gasoline stations runoff are significant sources of polycyclic aromatic hydrocarbons (PAHs) to aquatic ecosystems. Samples of the final effluent of oil-water-separators were collected at gasoline stations in the metropolitan region of Recife, Brazil, before release to sewage or rainwater systems. Effluent soluble fractions (ESF) were prepared and bioassays were performed according to the Fish Embryo Toxicity Test. The test involved exposing zebrafish Danio rerio embryos to dilutions of the ESFs for 96 h, with daily examination of lethality and sublethal morphological effects integrated through the General Morphology Score (GMS), based on the achievement of developmental hallmarks. Frequencies of abnormalities were recorded after exposures. ESF LC50-96h (lethal concentration to 50% of exposed embryos) in the most toxic effluent achieved 8.9% (v/v), equivalent to 11 μg phenanthrene equivalents L^-1. GMS scores indicated significantly delayed embryo-larval development at ESF dilutions of 10% and 20% from effluents of all gas stations. Major abnormalities detected after the 96 h exposure included the presence of a yolk sac not fully absorbed coupled with the lack of an inflated swim bladder, lack of both pectoral fins, and the failure to develop a protruding mouth. Effective equivalent PAH concentrations that induce a 50% frequency of larvae without an inflated swim bladder (EC50) were 4.9 μg phenanthrene L^-1, 21.8 μg naphthalene L^-1, and 34.1 μg chrysene L^-1. This study shows that PAHs in ESFs from gas stations oil water separators are toxic to zebrafish, contributing to the toxicity of urban storm waters.

Toxic potential of organic constituents of submicron particulate matter (PM1) in an urban road site (Barcelona)

Atmospheric particulate matter (PM) is a recognized risk factor contributing to a number of diseases in human populations and wildlife globally. Organic matter is a major component of PM, but its contribution to overall toxicity of PM has not been thoroughly evaluated yet. In the present work, the biological activity of organic extracts from PM1 (particles with less than 1 μm of aerodynamic diameter) collected from an urban road site in the centre of Barcelona (NE Spain) was evaluated using a yeast-based assay (AhR-RYA) and different gene expression markers in zebrafish embryos. Dioxin-like activity of the extracts correlated to primary emissions from local traffic exhausts, reflecting weekday/weekend alternance. Expression levels of cyp1a and of gene markers for key cellular processes and development (ier2, fos) also correlated to vehicle emissions, whereas expression of gene markers related to antioxidant defence and endocrine effects (gstal, hao1, ttr) was strongly reduced in samples with strong contribution from regional air masses with aged secondary organic species or with strong influence of biomass burning emissions. Our data suggest that the toxic potential of PM1 organic chemical constituents strongly depends on the emission sources and on the process of ageing from primary to secondary organic aerosols.

Zebrafish as an Alternative Vertebrate Model for Investigating Developmental Toxicity-The Triadimefon Example

Triadimefon is a widely used triazole fungicide known to cause severe developmental defects in several model organisms and in humans. The present study evaluated in detail the developmental effects seen in zebrafish embryos exposed to triadimefon, confirmed and expanded upon previous phenotypic findings and compared them to those observed in other traditional animal models. In order to do this, we exposed embryos to 2 and 4 µg/mL triadimefon and evaluated growth until 120 h post-fertilization (hpf) through gross morphology examination. Our analysis revealed significant developmental defects at the highest tested concentration including somite deformities, severe craniofacial defects, a cleft phenotype along the three primary neural divisions, a rigorously hypoplastic or even absent mandible and a hypoplastic morphology of the pharyngeal arches. Interestingly, massive pericardial edemas, abnormal shaped hearts, brachycardia and inhibited or absent blood circulation were also observed. Our results revealed that the presented zebrafish phenotypes are comparable to those seen in other organism models and those derived from human observations as a result of triadimefon exposure. We therefore demonstrated that zebrafish provide an excellent system for study of compounds with toxic significance and can be used as an alternative model for developmental toxicity studies to predict effects in mammals.

Triazole Fungicides Inhibit Zebrafish Hatching by Blocking the Secretory Function of Hatching Gland Cells

In animals, hatching represents the transition point from a developing embryo to a free-living individual, the larva. This process is finely regulated by many endogenous and environmental factors and has been shown to be sensitive to a variety of chemical agents. It is commonly evaluated in bioassays in order to establish the effects of different agents on early development and reproductive capabilities in fish and other aquatic animals. In fish, the breakdown of the chorion is achieved by the secretion of choriolysin by hatching gland cells (HGCs) into the perivitelline space (PVS), coupled with spontaneous movements of the developing larva. In this work, we used zebrafish to assay the effects of a family of widely used agrochemicals-triazoles Triadimefon (FON), Triadimenol (NOL) and free triazole (1,2,4-T)-on hatching success. We found a strong inhibition of hatching by triazole exposure which was correlated with morphological changes and a reduction in the secretory function of the HGCs. As a consequence, the release of choriolytic enzymes by HGCs was reduced. We also found that HGC secretion reduction after exposure to FON can be rescued by co-incubation with a dopamine D2 receptor antagonist but not by antagonists of the D1-like receptors. This suggests a specific pathway through which this family of fungicides may be impairing a critical event in the fish life cycle.

QSAR molecular parameters calculated for US EPA ToxCast Phase 1 and 2 chemical compounds tested against embryonic zebrafish

Freshwater and marine environments are exposed to small concentrations of many different chemicals produced by industrial, agricultural, pharmaceutical, cosmetic, food, and household applications. Due to concerns regarding potential adverse events from these exposures, regulatory agencies around the world have established aquatic toxicology testing protocols that measure untoward responses in a wide variety of freshwater and marine organisms. Following a literature review of databases on the toxicity of chemicals to fish, the embryonic zebrafish ( Danio rerio) database compiled by the Tanguay Laboratory at Oregon State University was determined to be well suited for quantitative structure–activity relationship (QSAR) analysis. This database possesses a number of favorable characteristics including large size (1060 unique US Environmental Protection Agency ToxCast phase 1 and 2 chemical compounds), relatively recent data collected using state-of-the-art methods, 18 simultaneously measured toxicological end points, transparent embryos that develop externally thereby facilitating toxicological evaluation, and the vast majority of the genetic code is expressed and active during early life stages. The molecular parameters calculated for each of the chemicals in the database include the logarithm of the octanol–water partition coefficient, molar volume, and molar refractivity. For each chemical, the availability of these molecular parameter values can facilitate future QSAR studies using any of the 18 different toxicological end points measured as the biological activity of interest.

Programmed Effects in Neurobehavior and Antioxidative Physiology in Zebrafish Embryonically Exposed to Cadmium: Observations and Hypothesized Adverse Outcome Pathway Framework

Non-communicable diseases (NCDs) are a major cause of premature mortality. Recent studies show that predispositions for NCDs may arise from early-life exposure to low concentrations of environmental contaminants. This developmental origins of health and disease (DOHaD) paradigm suggests that programming of an embryo can be disrupted, changing the homeostatic set point of biological functions. Epigenetic alterations are a possible underlying mechanism. Here, we investigated the DOHaD paradigm by exposing zebrafish to subtoxic concentrations of the ubiquitous contaminant cadmium during embryogenesis, followed by growth under normal conditions. Prolonged behavioral responses to physical stress and altered antioxidative physiology were observed approximately ten weeks after termination of embryonal exposure, at concentrations that were 50–3200-fold below the direct embryotoxic concentration, and interpreted as altered developmental programming. Literature was explored for possible mechanistic pathways that link embryonic subtoxic cadmium to the observed apical phenotypes, more specifically, the probability of molecular mechanisms induced by cadmium exposure leading to altered DNA methylation and subsequently to the observed apical phenotypes. This was done using the adverse outcome pathway model framework, and assessing key event relationship plausibility by tailored Bradford-Hill analysis. Thus, cadmium interaction with thiols appeared to be the major contributor to late-life effects. Cadmium-thiol interactions may lead to depletion of the methyl donor S-adenosyl-methionine, resulting in methylome alterations, and may, additionally, result in oxidative stress, which may lead to DNA oxidation, and subsequently altered DNA methyltransferase activity. In this way, DNA methylation may be affected at a critical developmental stage, causing the observed apical phenotypes.

Zebrafish: A complete animal model to enumerate the nanoparticle toxicity

Presently, nanotechnology is a multi-trillion dollar business sector that covers a wide range of industries, such as medicine, electronics and chemistry. In the current era, the commercial transition of nanotechnology from research level to industrial level is stimulating the world’s total economic growth. However, commercialization of nanoparticles might offer possible risks once they are liberated in the environment. In recent years, the use of zebrafish (Danio rerio) as an established animal model system for nanoparticle toxicity assay is growing exponentially. In the current in-depth review, we discuss the recent research approaches employing adult zebrafish and their embryos for nanoparticle toxicity assessment. Different types of parameters are being discussed here which are used to evaluate nanoparticle toxicity such as hatching achievement rate, developmental malformation of organs, damage in gill and skin, abnormal behavior (movement impairment), immunotoxicity, genotoxicity or gene expression, neurotoxicity, endocrine system disruption, reproduction toxicity and finally mortality. Furthermore, we have also highlighted the toxic effect of different nanoparticles such as silver nanoparticle, gold nanoparticle, and metal oxide nanoparticles (TiO₂, Al2O₃, CuO, NiO and ZnO). At the end, future directions of zebrafish model and relevant assays to study nanoparticle toxicity have also been argued.

Evaluation of the Biotoxicity of Tree Wood Ashes in Zebrafish Embryos

Ashes derived from biomass combustion and used as soil fertilizers can generate negative environmental and human health risks, related to leaching of heavy metals and other putative toxic elements. Tree wood ash composition may vary depending on geographical location and surrounding industrial processes. In this study, we evaluated the biotoxicity of lixiviated tree wood ash samples from trees of the Ash (Fraxinus), Cherry (Pronus), Hazel (Corylus), and Black locust (Robinia) genus collected in an industrialized region in Northern Italy. Elemental chemical analysis of the samples was performed by total reflection X-ray fluorescence technique and their biotoxicity was assessed in zebrafish (Danio rerio) embryos. Ashes from Ash, Cherry, and Hazel trees, but not Black locust trees, had a high concentration of heavy metals and other putative toxic elements. Accordingly, a dose-dependent increase in mortality rate and morphological and teratogenic defects was observed in zebrafish embryos treated with lixiviated Ash, Cherry, and Hazel tree wood samples, whereas the toxicity of Black locust tree wood ashes was negligible. In conclusion, lixiviated wood ashes from different plants show a different content of toxic elements that correlate with their biotoxic effects on zebrafish embryos. Tree wood ashes derived from biomass combustion may represent a potential risk for the environment and human health.

COSMOS-rice technology abrogates the biotoxic effects of municipal solid waste incinerator residues

Fly ashes generated by municipal solid waste incinerator (MSWI) are classified as hazardous waste and usually landfilled. For the sustainable reuse of these materials is necessary to reduce the resulting impact on human health and environment. The COSMOS-rice technology has been recently proposed for the treatment of fly ashes mixed with rice husk ash, to obtain a low-cost composite material with significant performances. Here, aquatic biotoxicity assays, including daphnidae and zebrafish embryo-based tests, were used to assess the biosafety efficacy of this technology. Exposure to lixiviated MSWI fly ash caused dose-dependent biotoxic effects on daphnidae and zebrafish embryos with alterations of embryonic development, teratogenous defects and apoptotic events. On the contrary, no biotoxic effects were observed in daphnidae and zebrafish embryos exposed to lixiviated COSMOS-rice material. Accordingly, whole-mount in situ hybridization analysis of the expression of various tissue-specific genes in zebrafish embryos provided genetic evidence about the ability of COSMOS-rice stabilization process to minimize the biotoxic effects of MSWI fly ash. These results demonstrate at the biological level that the newly developed COSMOS-rice technology is an efficient and cost-effective method to process MSWI fly ash, producing a biologically safe and reusable material.

Toxicity of single-wall carbon nanotubes functionalized with polyethylene glycol in zebrafish (Danio rerio) embryos

Single-wall carbon nanotubes functionalized with polyethylene glycol (SWCNT-PEG) are promising materials for biomedical applications such as diagnostic devices and controlled drug-release systems. However, several questions about their toxicological profile remain unanswered. Thus, the aim of this study was to investigate the action of SWCNT-PEG in Danio rerio zebrafish embryos at the molecular, physiological and morphological levels. The SWCNT used in this study were synthesized by the high-pressure carbon monoxide process, purified and then functionalized with distearoyl phosphatidylethanolamine block copolymer-PEG (molecular weight 2 kDa). The characterization process was carried out with low-resolution transmission electron microscopy, thermogravimetric analysis and Raman spectroscopy. Individual zebrafish embryos were exposed to the SWCNT-PEG. Toxic effects occurred only at the highest concentration tested (1 ppm) and included high mortality rates, delayed hatching and decreased total larval length. For all the concentrations tested, the alkaline comet assay revealed no genotoxicity, and Raman spectroscopy measurements on the histological slices revealed no intracellular nanotubes. The results shown here demonstrate that SWCNT-PEG has low toxicity in zebrafish embryos, but more studies are needed to understand what mechanisms are involved. However, the presence of residual metals is possibly among the primary mechanisms responsible for the toxic effects observed, because the purification process was not able to remove all metal contamination, as demonstrated by the thermogravimetric analysis. More attention must be given to the toxicity of these nanomaterials before they are used in biomedical applications. Copyright © 2016 John Wiley & Sons, Ltd.

Toxicity assessment of atmospheric particulate matter in the Mediterranean and Black Seas open waters

Atmospheric deposition of particulate matter (PM) is recognized as a relevant input vector for toxic compounds, such as polycyclic aromatic hydrocarbons (PAHs), into the marine environment. In this work we aimed to analyse the biological activity and potential adverse effects of PM constituents to aquatic organisms. Organic extracts of atmospheric PM samples from different sub-basins of the Mediterranean and Black Seas were screened using different toxicological tests. A yeast-based assay (AhR-RYA) revealed that dioxin-like activity correlated with the concentration of total PAHs in the PM samples, as well as with their predicted toxic equivalent values (TEQs). Although the zebrafish embryotoxicity test (the ZET assay) showed no major phenotypical adverse effects, up-regulation of mRNA expression of cyp1a, fos and development-related genes (previously described as related to PM toxicity) was observed in exposed embryos when compared to controls. Results showed that mRNA patterns of the studied genes followed a similar geographic distribution to both PAH content and dioxin-like activity of the corresponding extracts. The analysis also showed a distinct geographical pattern of activation of pancreatic markers previously related to airborne pollution, probably indicating a different subset of uncharacterized particle-bound toxicants. We propose the combination of the bioassays tested in the present study to be applied to future research with autochthonous species to assess exposure and potential toxic effects of ambient PM. The present study emphasizes the need for more in-depth studies into the toxic burden of atmospheric PM on aquatic ecosystems, in order to improve future regulatory guidelines.

Supporting read-across using biological data

Read-across, i.e. filling toxicological data gaps by relating to similar chemicals, for which test data are available, is usually done based on chemical similarity. Besides structure and physico-chemical properties, however, biological similarity based on biological data adds extra strength to this process. In the context of developing Good Read-Across Practice guidance, a number of case studies were evaluated to demonstrate the use of biological data to enrich read-across. In the simplest case, chemically similar substances also show similar test results in relevant in vitro assays. This is a well-established method for the read-across of e.g. genotoxicity assays. Larger datasets of biological and toxicological properties of hundreds and thousands of substances become increasingly available enabling big data approaches in read-across studies. Several case studies using various big data sources are described in this paper. An example is given for the US EPA's ToxCast dataset allowing read-across for high quality uterotrophic assays for estrogenic endocrine disruption. Similarly, an example for REACH registration data enhancing read-across for acute toxicity studies is given. A different approach is taken using omics data to establish biological similarity: Examples are given for stem cell models in vitro and short-term repeated dose studies in rats in vivo to support read-across and category formation. These preliminary biological data-driven read-across studies highlight the road to the new generation of read-across approaches that can be applied in chemical safety assessment.

Enantioselective bioaccumulation of hexaconazole and its toxic effects in adult zebrafish (Danio rerio)

Little is known about the bioaccumulation and toxicity of hexaconazole (HEX) in spite of the fact that they are indispensable parts for a comprehensive assessment of its environmental behavior and toxic effects in organisms of freshwater ecosystems. In this study, adult zebrafish were used to study the enantioselective bioaccumulation of HEX and its effect endpoints in liver, including oxidative stress and the regulation of apoptosis-related gene expression. Significant enantioselective bioaccumulation was demonstrated when exposed to HEX of 100 and 200 μg L(-)(1), finding that the (-)-enantiomer tended to accumulate in zebrafish more easily than (+)-enantiomer. Activities of antioxidant enzymes (SOD, CAT and GPx) and GSH content were all significantly decreased when zebrafish were exposed to 50 and 200 μg L(-1) HEX for 21 d. A series of genes of the apoptosis pathway were examined in groups treated with 50 and 200 μg L(-)(1) HEX for 21 d using real-time PCR. Significant up-regulation of p53, Puma, Apaf-1, caspase-3 and caspase-9 expression and down-regulation of Bcl-2/Bax expression ratio were proved. The overall results indicated that waterborne HEX was able to produce oxidative stress and induce apoptosis through the involvement of caspases in adult zebrafish. The above information will play a vital role in the integrated environmental risk assessment of HEX and make its toxic mechanism in fish clear.

Genotoxic and teratogenic effect of freshwater sediment samples from the Rhine and Elbe River (Germany) in zebrafish embryo using a multi-endpoint testing strategy

The embryotoxic potential of three model sediment samples with a distinct and well-characterized pollutant burden from the main German river basins Rhine and Elbe was investigated. The Fish Embryo Contact Test (FECT) in zebrafish (Danio rerio) was applied and submitted to further development to allow for a comprehensive risk assessment of such complex environmental samples. As particulate pollutants are constructive constituents of sediments, they underlay episodic source-sink dynamics, becoming available to benthic organisms. As bioavailability of xenobiotics is a crucial factor for ecotoxicological hazard, we focused on the direct particle-exposure pathway, evaluating throughput-capable endpoints and considering toxicokinetics. Fish embryo and larvae were exposed toward reconstituted (freeze-dried) sediment samples on a microcosm-scale experimental approach. A range of different developmental embryonic stages were considered to gain knowledge of potential correlations with metabolic competence during the early embryogenesis. Morphological, physiological, and molecular endpoints were investigated to elucidate induced adverse effects, placing particular emphasis on genomic instability, assessed by the in vivo comet assay. Flow cytometry was used to investigate the extent of induced cell death, since cytotoxicity can lead to confounding effects. The implementation of relative toxicity indices further provides inter-comparability between samples and related studies. All of the investigated sediments represent a significant ecotoxicological hazard by disrupting embryogenesis in zebrafish. Beside the induction of acute toxicity, morphological and physiological embryotoxic effects could be identified in a concentration-response manner. Increased DNA strand break frequency was detected after sediment contact in characteristic non-monotonic dose-response behavior due to overlapping cytotoxic effects. The embryonic zebrafish toxicity model along with the in vivo comet assay and molecular biomarker analysis should prospectively be considered to assess the ecotoxicological potential of sediments allowing for a comprehensive hazard ranking. In order to elucidate mode of action, novel techniques such as flow cytometry have been adopted and proved to be valuable tools for advanced risk assessment and management.

Differential embryotoxicity of the organic pollutants in rural and urban air particles

Airborne particulate matter (PM) is a recognized risk factor for human populations. Here we assessed the toxic potential of the organic constituents from PM collected in urban and rural sites during warm and cold periods of 2012/2013, and fractionated into 6 size fractions. The finest PM fraction (<0.5 μm) showed the highest biological activity (dioxin-like activity and fish embryotoxicity) in all samples, and the maximal activity was observed in rural samples from the cold period. Zebrafish embryo transcriptome analysis showed a strong induction of the AhR signaling pathway correlated to PAH concentrations. Oxidative stress-related genes and pancreatic and eye-lens gene markers appeared de-regulated in embryos exposed to urban extracts, whereas exposure to rural extracts affected genes implicated in basic cellular functions. The observed effects can be directly related to air pollution-related human disorders, suggesting different potential adverse outcomes for human populations exposed to air pollution from specific sources.

Identification and Characterization of Androgen-Responsive Genes in Zebrafish Embryos

Responsive genes for fish embryos have been identified so far for some endocrine pathways but not for androgens. Using transcriptome analysis and multiple concentration-response modeling, we identified putative androgen-responsive genes in zebrafish embryos exposed to 0.05-5000 nM 11-ketotestosterone for 24 h. Four selected genes with sigmoidal concentration-dependent expression profiles (EC50 = 6.5-30.0 nM) were characterized in detail. The expression of cyp2k22 and slco1f4 was demonstrated in the pronephros; lipca was detected in the liver, and sult2st3 was found in the olfactory organs and choroid plexus. Their expression domains, the function of human orthologs, and a pathway analysis suggested a role of these genes in the metabolism of hormones. Hence, it was hypothesized that they were induced to compensate for elevated hormone levels. The induction of sult2st3 and cyp2k22 by 11-ketotestosterone was repressed by co-exposure to the androgen receptor antagonist nilutamide supporting a potential androgen receptor mediated regulation. Sensitivity (expressed as EC50 values) of sult2st3 and cyp2k22 gene expression induction after exposure to other steroidal hormones (11-ketotestosterone ∼ testosterone > progesterone > cortisol > ethinylestradiol) correlated with their known binding affinities to zebrafish androgen receptor. Hence, these genes might represent potential markers for screening of androgenic compounds in the zebrafish embryo.

Humic substances alleviate the aquatic toxicity of polyvinylpyrrolidone-coated silver nanoparticles to organisms of different trophic levels

The present study investigated how humic substances (HS) modify the aquatic toxicity of silver nanoparticles (AgNPs) as these particles agglomerate in water and interact with HS. An alga species (Raphidocelis subcapitata), a cladoceran species (Chydorus sphaericus), and a freshwater fish larva (Danio rerio), representing organisms of different trophic levels, were exposed to colloids of the polyvinylpyrrolidone-coated AgNPs in the presence and absence of HS. Results show that the presence of HS alleviated the aquatic toxicity of the AgNP colloids to all the organisms in a dose-dependent manner. The particle size distribution of the AgNPs' colloidal particles shifted to lower values due to the presence of HS, implying that the decrease in the toxicity of the AgNP colloids cannot be explained by the variation of agglomeration size. The surface charge of the AgNPs was found to be more negative in the presence of high concentrations of HS, suggesting an electrostatic barrier by which HS might limit interactions between particles and algae cells; indeed, this effect reduced the algae toxicity. Observations on silver ions (Ag(+)) release show that HS inhibit AgNP dissolution, depending on the concentrations of HS. When toxic effects were expressed as a function of each Ag-species, toxicity of the free Ag(+) was found to be much higher than that of the agglomerated particles.

Relative developmental toxicities of pentachloroanisole and pentachlorophenol in a zebrafish model (Danio rerio)

Pentachloroanisole (PCA) and pentachlorophenol (PCP) are chlorinated aromatic compounds that have been found in the environment and in human populations. The objective of this study is to characterize the effects of PCA in comparison to those of PCP on development at environmental relevant levels using a fish model. Zebrafish embryos were exposed to 0.1, 1, 10, 100, 500, 1000 μg/L PCA and PCP respectively for 96 h. Malformation observation, LC50 testing for survival rate at 96 hours post fertilization (hpf) and EC50 testing for hatching rate at 72 hpf indicated that the developmental toxicity of PCP was about 15 times higher than that of PCA. PCP exposure at 10 μg/L resulted in elevated 3, 3', 5-triiodothyronine (T3) levels and decreased thyroxine (T4) levels, whereas PCA had no effects on T3 or T4 levels. PCP and PCA exposure at 1 and 10 μg/L showed possible hyperthyroid effects similar to that of T3, due to increased relative mRNA expression of synapsin I (SYN), iodothyronine deiodinase type III (Dio3), thyroid hormone receptor alpha a (THRαa) and thyroid hormone receptor beta (THRβ), and decreased expression of iodothyronine deiodinase type II (Dio2). The results indicate that both PCA and PCP exposure can cause morphological deformities, possibly affect the timing and coordination of development in the central nervous system, and alter thyroid hormone levels by disrupting thyroid hormone regulating pathways. However, the developmental toxicity of PCA is at least ten times lower than that of PCP. Our results on the relative developmental toxicities of PCA and PCP and the possible underlying mechanisms will be useful to support interpretation of envrionmental concentrations and body burden levels observed in human populations.

Triazole-induced toxicity in developing rare minnow (Gobiocypris rarus) embryos

Using rare minnow (Gobiocypris rarus) at early-life stages as experimental models, the developmental toxicity of five widely used triazole fungicides (myclobutanil, fluconazole, flusilazole, triflumizole, and epoxiconazole) were investigated following exposure to 1-15 mg/L for 72 h. Meanwhile, morphological parameters (body length, body weight, and heart rate), enzyme activities (superoxide dismutase (SOD), glutathione S-transferase (GST), adenosine triphosphatase (ATPase), and acetyl cholinesterase (AChE)), and mRNA levels (hsp70, mstn, mt, apaf1, vezf1, and cyp1a) were also recorded following exposure to 0.2, 1.0, and 5.0 mg/L for 72 h. Results indicated that increased malformation and mortality, decreased body length, body weight, and heart rate provide a concentration-dependent pattern; values of 72 h LC50 (median lethal concentration) and EC50 (median effective concentration) ranged from 3 to 12 mg/L. Most importantly, the results of the present study suggest that even at the lowest concentration, 0.2 mg/L, five triazole fungicides also caused notable changes in enzyme activities and mRNA levels. Overall, the present study points out that those five triazole fungicides are highly toxic to the early development of G. rarus embryos. The information presented in this study will be helpful in better understanding the toxicity induced by triazole fungicides in fish embryos.

Evaluation of an alternative in vitro test battery for detecting reproductive toxicants in a grouping context

Previously we showed a battery consisting of CALUX transcriptional activation assays, the ReProGlo assay, and the embryonic stem cell test, and zebrafish embryotoxicity assay as 'apical' tests to correctly predict developmental toxicity for 11 out of 12 compounds, and to explain the one false negative [7]. Here we report on applying this battery within the context of grouping and read across, put forward as a potential tool to fill data gaps and avoid animal testing, to distinguish in vivo non- or weak developmental toxicants from potent developmental toxicants within groups of structural analogs. The battery correctly distinguished 2-methylhexanoic acid, monomethyl phthalate, and monobutyltin trichloride as non- or weak developmental toxicants from structurally related developmental toxicants valproic acid, mono-ethylhexyl phthalate, and tributyltin chloride, respectively, and, therefore, holds promise as a biological verification model in grouping and read across approaches. The relevance of toxicokinetic information is indicated.

Biosafe inertization of municipal solid waste incinerator residues by COSMOS technology

Municipal solid waste incinerator (MSWI) residues can generate negative environmental impacts when improperly handled. The COlloidal Silica Medium to Obtain Safe inert (COSMOS) technology represents a new method to stabilize MSWI residues and to produce inert safe material. Here we report the results about aquatic biotoxicity of lixiviated MSWI fly ash and the corresponding inertized COSMOS material using a zebrafish (Danio rerio) embryo toxicity test. Quantitative assessment of waste biotoxicity included evaluation of mortality rate and of different morphological and teratogenous endpoints in zebrafish embryos exposed to tested materials from 3 to 72h post-fertilization. The results demonstrate that lixiviated MSWI fly ash exerts a dose-dependent lethal effect paralleled by dramatic morphological/teratogenous alterations and apoptotic events in the whole embryo body. Similar effects were observed following MSWI fly ash stabilization in classical concrete matrices, demonstrating that the obtained materials are not biologically safe. On the contrary, no significant mortality and developmental defects were observed in zebrafish embryos exposed to COSMOS inert solution. Our results provide the first experimental in vivo evidence that, in contrast with concrete stabilization procedure, COSMOS technology provides a biologically safe inert.

Growth inhibition and coordinated physiological regulation of zebrafish (Danio rerio) embryos upon sublethal exposure to antidepressant amitriptyline

Amitriptyline is a tricyclic antidepressant used for decades. It is present at low detectable concentrations in the aquatic environment, but relative few studies have focused on its ecotoxicological effects on non-target aquatic animals. The present study conducted an acute toxicity test of waterborne amitriptyline exposure using zebrafish (Danio rerio) embryos 4 to 124 h-post-fertilization. Time-dependent lethal concentrations were firstly determined and at mg/L levels. Effects of amitriptyline on zebrafish embryos were then evaluated under amitriptyline exposure at sublethal concentrations of 1, 10, 100 ng/L, 1, 10, 100 μg/L and 1mg/L. Our results showed that amitriptyline significantly reduced the hatching time and body length of embryos after exposure in a concentration-dependent manner. Our study also revealed that the exposure evoked a coordinated modulation of physiological and biochemical parameters in exposed zebrafish embryos, including alterations of adrenocorticotropic hormone (ACTH) level, oxidative stress and antioxidant parameters, as well as nitric oxide (NO) production and total nitric oxide synthase (TNOS) activity. A U-shaped concentration-dependent response curve was observed in ACTH level in response to amitriptyline exposure. However, both U-shaped and inversed U-shaped curves were indicated in the responses of antioxidant parameters, including total antioxidant capacity, antioxidant enzyme activities (catalase, superoxide dismutase and peroxidase), glutathione content and glutathione reductase activity. Correspondingly, hydroxyl radical formation and lipid peroxidation indices changed in similar U-shaped concentration-dependent patterns, which together the results of antioxidant parameters suggested induction of oxidative stress in embryos exposed to amitriptyline at high concentrations. Moreover, NO production and TNOS activity were both significantly affected by amitriptyline exposure. Notably, significant correlations between these measured parameters were revealed, which suggested a dynamic adaptation process and coordinated regulation of multiple physiological systems in fish embryos to amitriptyline treatment. Furthermore, our study demonstrated that the effective concentrations of amitriptyline for measured parameters in zebrafish embryos were as low as 10 ng/L, and thus revealed the potential risk of amitriptyline and other antidepressants to aquatic life.

The effects of triclosan on pluripotency factors and development of mouse embryonic stem cells and zebrafish

Triclosan (TCS) poses potential risks to reproduction and development due to its endocrine-disrupting properties. However, the mechanism of TCS's effects on early embryonic development is little known. Embryonic stem cells (ESC) and zebrafish embryos provide valuable models for testing the toxic effects of environmental chemicals on early embryogenesis. In this study, mouse embryonic stem cells (mESC) were acutely exposed to TCS for 24 h, and general cytotoxicity and the effect of TCS on pluripotency were then evaluated. In addition, zebrafish embryos were exposed to TCS from 2- to 24-h post-fertilization (hpf), and their morphology was evaluated. In mESC, alkaline phosphatase staining was significantly decreased after treatment with the highest concentration of TCS (50 μM). Although the expression levels of Sox2 mRNA were not changed, the mRNA levels of Oct4 and Nanog in TCS-treated groups were significantly decreased compared to controls. In addition, the protein levels of Oct4, Sox2 and Nanog were significantly reduced in response to TCS treatment. MicroRNA (miR)-134, an expression inhibitor of pluripotency markers, was significantly increased in TCS-treated mESC. In zebrafish experiments, after 24 hpf of treatment, the controls had developed to the late stage of somitogenesis, while embryos exposed to 300 μg/L of TCS were still at the early stage of somitogenesis, and three genes (Oct4, Sox2 and Nanog) were upregulated in treated groups when compared with the controls. The two models demonstrated that TCS may affect early embryonic development by disturbing the expression of the pluripotency markers (Oct4, Sox2 and Nanog).

Developmental toxicity assay using high content screening of zebrafish embryos

Typically, time-consuming standard toxicological assays using the zebrafish (Danio rerio) embryo model evaluate mortality and teratogenicity after exposure during the first 2 days post-fertilization. Here we describe an automated image-based high content screening (HCS) assay to identify the teratogenic/embryotoxic potential of compounds in zebrafish embryos in vivo. Automated image acquisition was performed using a high content microscope system. Further automated analysis of embryo length, as a statistically quantifiable endpoint of toxicity, was performed on images post-acquisition. The biological effects of ethanol, nicotine, ketamine, caffeine, dimethyl sulfoxide and temperature on zebrafish embryos were assessed. This automated developmental toxicity assay, based on a growth-retardation endpoint should be suitable for evaluating the effects of potential teratogens and developmental toxicants in a high throughput manner. This approach can significantly expedite the screening of potential teratogens and developmental toxicants, thereby improving the current risk assessment process by decreasing analysis time and required resources.

Teratological effects of a panel of sixty water-soluble toxicants on zebrafish development

The zebrafish larva is a promising whole-animal model for safety pharmacology, environmental risk assessment, and developmental toxicity. This model has been used for the high-throughput toxicity screening of various compounds. Our aim here is to identify possible phenotypic markers of teratogenicity in zebrafish embryos that could be used for the assaying compounds for reproductive toxicity. We have screened a panel of 60 water-soluble toxicants to examine their effects on zebrafish development. A total of 22,080 wild-type zebrafish larvae were raised in 250 μL defined buffer in 96-well plates at a plating density of one embryo per well. They were exposed for a 96-h period starting at 24 h post-fertilization. A logarithmic concentration series was used for range-finding, followed by a narrower geometric series for developmental toxicity assessment. A total of 9017 survivors were analyzed at 5 days post-fertilization for nine phenotypes, namely, (1) normal, (2) pericardial oedema, (3) yolk sac oedema, (4) melanophores dispersed, (5) bent tail tip, (6) bent body axis, (7) abnormal Meckel's cartilage, (8) abnormal branchial arches, and (9) uninflated swim bladder. For each toxicant, the EC50 (concentration required to produce one or more of these abnormalities in 50% of embryos) was also calculated. For the majority of toxicants (55/60) there was, at the population level, a statistically significant, concentration-dependent increase in the incidence of abnormal phenotypes among survivors. The commonest abnormalities were pericardial oedema, yolk sac oedema, dispersed melanophores, and uninflated swim bladder. It is possible therefore that these could prove to be general indicators of reproductive toxicity in the zebrafish embryo assay.

Toxic assessment of urban atmospheric particle-bound PAHs: relevance of composition and particle size in Barcelona (Spain)

Zebrafish embryotoxicity and dioxin-like activity levels were tested for particulate air samples from an urban background site in Barcelona (Spain). Samples were collected during 14 months, and maximal values for both biological activities corresponded to samples collected during late autumn months, correlating with elevated PAH levels. Vehicle and combustion emissions appeared as the potentially most toxic sources, whereas total PM mass and mineral content appeared to be poor predictors of the biological activity of the samples. Samples simultaneously collected at different particle size cut-offs (10, 2.5, and 1 μm) did not differ significantly in dioxin-like PAH levels and biological activity, indicating that the sub-micron particle fraction (PM1) concentrated essentially all observed toxicity. Our results support the need for a tighter control on sub-micron particle emissions and show that total PM mass and, particularly, PM10, may not fully characterize the toxic potential of air samples.

Non-mammalian vertebrate embryos as models in nanomedicine

Various in vivo biological models have been proposed for studying the interactions of nano-materials in biological systems. Unfortunately, the widely used small mammalian animal models (rodents) are costly and labor intensive and generate ethical issues and antagonism from the anti-vivisectionist movement. Recently, there has been increasing interest in the scientific community in the interactions between nano-materials and non-mammalian developmental organisms, which are now being recognized as valid models for the study of human disease. This review examines and discusses the biomedical applications and the interaction of nano-materials with embryonic systems, focusing on non-mammalian vertebrate models, such as chicken, zebrafish and Xenopus.

FROM THE CLINICAL EDITOR

Animal models are critical components of preclinical biomedical research. This review discusses the feasibility and potential applications of non-mammalian vertebral animals, such as zebrafish, xenopus, and chicken as animal models in nanomedicine research.

Genotoxicity effects of Flusilazole on the somatic cells of Allium cepa

The aim of this study was to evaluate the effects of the fungicide flusilazole on somatic cells of Allium cepa. For evaluation of cytogenetic effects, root meristem cells of A. cepa were treated with 10, 20, 30 and 45 ppm (EC50 concentration) for 24, 48 and 72 h. The mitotic index and different types of chromosomal abnormalities such as bridges, stickiness and laggards were determined in both control and test groups. Acridine orange/Ethidium bromide double staining and fluorescence microscope was used to determine the stability of chromosome structure. Data obtained from staining process indicated that ratio of necrotic cells significantly increased by the flusilazole presoaking. The RAPD-PCR method was used and the higher doses treated-group (45 ppm) was more distant to the control group compare with others.

Developmental effects of aerosols and coal burning particles in zebrafish embryos

Embryo toxicity of particles generated by combustion processes is of special concern for human health. A significant part of these toxic effects is linked to the binding of some pollutants (like polycyclic aromatic hydrocarbons or PAHs) to the Aryl hydrocarbon Receptor (AhR) and the activation of target genes, like the cytochrome P4501A. This activity was analyzed for ambient air and coal-combustion particle extracts in zebrafish embryos (the cyp1aDarT assay) and in two single-cell bioassays: the yeast-based YCM-RYA and the DR-luc (rat cells) assay. Observed AhR ligand activity of samples generally correlated to the predicted toxic effect according to their PAH composition, except for one of the coal combustion samples with an anomalously high activity in the cyp1aDarT assay. This sample induced deformities in zebrafish embryos. We concluded that the combination of morphological and molecular assays may detect embryonic toxic effects that cannot be predicted from chemical analyses or single-cell bioassays.

A category approach to predicting the developmental (neuro) toxicity of organotin compounds: the value of the zebrafish (Danio rerio) embryotoxicity test (ZET)

Zebrafish embryos were exposed to different organotin compounds during very early development (<100h post fertilization). Morphology, histopathology and swimming activity (in a motor activity test) were the endpoints analyzed. DBTC was, by far, the most embryotoxic compound at all time points and endpoints studied. In fact, we observed a clear concordance between the effects observed in our zebrafish embryo model, and those observed with these compounds in full rodent in vivo studies. All organotin compounds classified as developmental (neuro) toxicants in vivo, were correctly classified in the present assay. Together, our results support the ZET model as a valuable tool for providing biological verification for a grouping and a read-across approach to developmental (neuro) toxicity.

Predictive models and computational toxicology

Understanding the potential health risks posed by environmental chemicals is a significant challenge elevated by the large number of diverse chemicals with generally uncharacterized exposures, mechanisms, and toxicities. The ToxCast computational toxicology research program was launched by EPA in 2007 and is part of the federal Tox21 consortium to develop a cost-effective approach for efficiently prioritizing the toxicity testing of thousands of chemicals and the application of this information to assessing human toxicology. ToxCast addresses this problem through an integrated workflow using high-throughput screening (HTS) of chemical libraries across more than 650 in vitro assays including biochemical assays, human cells and cell lines, and alternative models such as mouse embryonic stem cells and zebrafish embryo development. The initial phase of ToxCast profiled a library of 309 environmental chemicals, mostly pesticidal actives having rich in vivo data from guideline studies that include chronic/cancer bioassays in mice and rats, multigenerational reproductive studies in rats, and prenatal developmental toxicity endpoints in rats and rabbits. The first phase of ToxCast was used to build models that aim to determine how well in vivo animal effects can be predicted solely from the in vitro data. Phase I is now complete and both the in vitro data (ToxCast) and anchoring in vivo database (ToxRefDB) have been made available to the public (http://actor.epa.gov/). As Phase II of ToxCast is now underway, the purpose of this chapter is to review progress to date with ToxCast predictive modeling, using specific examples on developmental and reproductive effects in rats and rabbits with lessons learned during Phase I.

Evaluation of acute and developmental effects of difenoconazole via multiple stage zebrafish assays

Zebrafish, during embryo, larvae and adult stages were selected to investigate the potential environmental risk and aquatic toxicity of a widely used fungicide, difenoconazole. In addition to mortality, embryo development endpoints, teratogenic effects and behavior abnormity were measured. Finally, the developmental parameters of the adult fish were assessed after 14 days' exposure. This study concluded that the acute toxicity of difenoconazole to the three phases of zebrafish were larvae (1.17 mg/L) > adult fish (1.45 mg/L) > embryo (2.34 mg/L). A large suite of symptoms was induced in embryonic development by different dosages of difenoconazole, including hatching inhibition, abnormal spontaneous movement, slow heart rate, growth regression and morphological deformities. 0.50 mg/L of difenoconazole could cause significant body color blackening and decrease in the heart rate of zebrafish larvae over 24 h. In addition, 0.25 mg/L of difenoconazole apparently inhibited the growth weight of adult zebrafish measured after 14 days' exposure.

Evaluation of an alternative in vitro test battery for detecting reproductive toxicants

The application of alternative methods in developmental and reproductive toxicology is challenging in view of the complexity of mechanisms involved. A battery of complementary test systems may provide a better prediction of developmental and reproductive toxicity than single assays. We tested twelve compounds with varying mechanisms of toxic action in an assay battery including 24 CALUX transcriptional activation assays, mouse cardiac embryonic stem cell test, ReProGlo assay, zebrafish embryotoxicity assay, and two CYP17 and two CYP19 activity assays. The battery correctly detected 11/12 compounds tested, with one false negative occurring, which could be explained by the absence of the specific mechanism of action of this compound in the battery. Toxicokinetic modeling revealed that toxic concentrations were in the range expected from in vivo reproductive toxicity data. This study illustrates added value of combining assays that contain complementary biological processes and mechanisms, increasing predictive value of the battery over individual assays.

Experimental Assessment of the Environmental Fate and Effects of Triazoles and Benzotriazole

The environmental fate and effects of triazoles and benzotriazoles are of concern within the context of chemical regulation. As part of an intelligent testing strategy, experimental tests were performed on endpoints that are relevant for risk assessment. The experimental tests included the assessment of ecotoxicity to an alga, a daphnid and zebrafish embryos, and the assessment of ready biodegradability. Triazole and benzotriazole compounds were selected for testing, based on existing toxicity data for vertebrate and invertebrate species, as well as on the principal component analysis of molecular descriptors aimed at selecting the minimum number of test compounds in order to maximise the chemical domain spanned for both compound classes. The experimental results show that variation in the toxicities of triazoles and benzotriazole across species was relatively minor; in general, the largest factor was approximately 20. The study conducted indicated that triazoles are not readily biodegradable.

Innovations in testing strategies in reproductive toxicology

Toxicological hazard assessment currently finds itself at a crossroads where the existing classical test paradigm is challenged by a host of innovative approaches. Animal study protocols are being enhanced for additional parameters and improved for more efficient effect assessment with reduced animal numbers. Whilst existing testing paradigms have generally proven conservative for chemical safety assessment, novel alternative in silico and in vitro approaches and assays are being introduced that begin to elucidate molecular mechanisms of toxicity. Issues such as animal welfare, alternative assay validation, endocrine disruption, and the US-NAS report on toxicity testing in the twenty-first century have provided directionality to these developments. The reductionistic nature of individual alternative assays requires that they be combined in a testing strategy in order to provide a complete picture of the toxicological profile of a compound. One of the challenges of this innovative approach is the combined interpretation of assay results in terms of toxicologically relevant effects. Computational toxicology aims at providing that integration. In order to progress, we need to follow three steps: (1) Learn from past experience in animal studies and human diseases about critical end points and pathways of toxicity. (2) Design alternative assays for essential mechanisms of toxicity. (3) Build an integrative testing strategy tailored to human hazard assessment using a battery of available alternative tests for critical end points that provides optimal in silico and in vitro filters to upgrade toxicological hazard assessment to the mechanistic level.