Structure and macromolecular composition of the zebrafish egg chorion

Preparation and extraction of chorion proteins from Salmo salar embryos at the pigmented eye stage for electrophoresis with SDS-polyacrylamide gel

The chorion fulfills important functions in fish embryos, including protecting the embryo during development. The characterization of the protein profile of this envelope could be used as a bioindicator in the evaluation of the quality of embryonic development. The object of this work was to validate a standardized protocol for protein extraction from chorion of Salmo salar embryos at 280 accumulated thermal units (ATU) by comparing and combining existing methods. The protocol consists of consecutive washing of the chorion samples followed by protein extraction with the solution that was named SDS solution (Tris-HCl 100 mM (pH 8), Urea 8 M, 1% SDS, β-mercaptoethanol 300 mM and EGTA 10 Mm, and 1% protease inhibitor cocktail) and mechanical methods. Protein extraction is enhanced by a working temperature of 75 °C and use of a disperser. The protein concentration was quantified by Bradford Assay. After extraction, the samples were diluted (dilution factor 10) before reading against the calibration curve. After gel electrophoresis with a load of 3 µg of protein, staining showed more than 4 bands, with molecular weights between 25 kDa and 180 kDa.•The protein profile of fish chorion was between 25 kDa and 180 kDa.•Solution containing 1% SDS allows a higher extraction of proteins from the chorion of Atlantic salmon embryos with 280 ATU.•Chorion protein identification is a valuable tool in determining gamete and embryo quality in fish.

Structural Characterization and Anti-Osteoporosis Effects of a Novel Sialoglycopeptide from Tuna Eggs

Several sialoglycopeptides were isolated from several fish eggs and exerted anti-osteoporosis effects. However, few papers have explored sialoglycopeptide from tuna eggs (T-ES). Here, a novel T-ES was prepared through extraction with KCl solution and subsequent enzymolysis. Pure T-ES was obtained through DEAE-Sepharose ion exchange chromatography and sephacryl S-300 gel filtration chromatography. The T-ES was composed of 14.07% protein, 73.54% hexose, and 8.28% Neu5Ac, with a molecular weight of 9481 Da. The backbone carbohydrate in the T-ES was →4)-β-D-GlcN-(1→3)-α-D-GalN-(1→3)-β-D-Glc-(1→2)-α-D-Gal-(1→2)-α-D-Gal-(1→3)-α-D-Man-(1→, with two branches of β-D-GlcN-(1→ and α-D-GalN-(1→ linking at o-4 in →2,4)-α-D-Gal-(1→. Neu5Ac in the T-ES was linked to the branch of α-D-GlcN-(1→. A peptide chain, Ala-Asp-Asn-Lys-Ser*-Met-Ile that was connected to the carbohydrate chain through O-glycosylation at the -OH of serine. Furthermore, in vitro data revealed that T-ES could remarkably enhance bone density, bone biomechanical properties, and bone microstructure in SAMP mice. The T-ES elevated serum osteogenesis-related markers and reduced bone resorption-related markers in serum and urine. The present study's results demonstrated that T-ES, a novel sialoglycopeptide, showed significant anti-osteoporosis effects, which will accelerate the utilization of T-ES as an alternative marine drug or functional food for anti-osteoporosis.

Investigation of Zebrafish Embryo Membranes at Epiboly Stage through Electrorotation Technique

A preliminary exploration of the physiology and morphology of the zebrafish embryo (ZFE) during the late-blastula and early-gastrula stages through its electrical properties was performed, applying the electrorotation (ROT) technique. This method, based on induced polarizability at the interfaces, was combined with an analytical spherical shell model to obtain the best fit of empirical data and the desired information, providing a means of understanding the role of different membranes. Suspended in two solutions of low conductivity, the major compartments of the ZFE were electrically characterized, considering morphological data from both observed records and data from the literature. Membrane integrity was also analyzed for dead embryos. The low permeability and relatively high permittivity obtained for the chorion probably reflected both its structural characteristics and external conditions. Reasonable values were derived for perivitelline fluid according to the influx of water that occurs after the fertilization of the oocyte. The so-called yolk membrane, which comprises three different and contiguous layers at the epiboly stage, showed atypical electrical values of the membrane, as did the yolk core with a relatively low permittivity. The internal morphological complexity of the embryo itself could be addressed in future studies by developing an accurate geometric model.

The sensitivity of the zebrafish embryo coiling assay for the detection of neurotoxicity by compounds with diverse modes of action

In the aim to determine neurotoxicity, new methods are being validated, including tests and test batteries comprising in vitro and in vivo approaches. Alternative test models such as the zebrafish (Danio rerio) embryo have received increasing attention, with minor modifications of the fish embryo toxicity test (FET; OECD TG 236) as a tool to assess behavioral endpoints related to neurotoxicity during early developmental stages. The spontaneous tail movement assay, also known as coiling assay, assesses the development of random movement into complex behavioral patterns and has proven sensitive to acetylcholine esterase inhibitors at sublethal concentrations. The present study explored the sensitivity of the assay to neurotoxicants with other modes of action (MoAs). Here, five compounds with diverse MoAs were tested at sublethal concentrations: acrylamide, carbaryl, hexachlorophene, ibuprofen, and rotenone. While carbaryl, hexachlorophene, and rotenone consistently induced severe behavioral alterations by ~ 30 h post fertilization (hpf), acrylamide and ibuprofen expressed time- and/or concentration-dependent effects. At 37-38 hpf, additional observations revealed behavioral changes during dark phases with a strict concentration-dependency. The study documented the applicability of the coiling assay to MoA-dependent behavioral alterations at sublethal concentrations, underlining its potential as a component of a neurotoxicity test battery.

Comparison of Pronase versus Manual Dechorionation of Zebrafish Embryos for Small Molecule Treatments

Zebrafish are a powerful animal model for small molecule screening. Small molecule treatments of zebrafish embryos usually require that the chorion, an acellular envelope enclosing the embryo, is removed in order for chemical compounds to access the embryo from the bath medium. For large-scale studies requiring hundreds of embryos, manual dechorionation, using forceps, can be a time-consuming and limiting process. Pronase is a non-specific protease that is widely used as an enzymatic alternative for dechorionating zebrafish embryos. However, whether pronase treatments alter the effects of subsequent small molecule treatments has not been addressed. Here, we provide a detailed protocol for large-scale pronase dechorionation of zebrafish embryos. We tested whether pronase treatment can influence the efficacy of drug treatments in zebrafish embryos. We used a zebrafish model for Duchenne muscular dystrophy (DMD) to investigate whether the efficacies of trichostatin-A (TSA) or salermide + oxamflatin, small molecule inhibitors known to ameliorate the zebrafish dmd muscle degeneration phenotype, are significantly altered when embryos are treated with pronase versus manual dechorionation. We also tested the effects of pronase on the ability of the anthracycline cancer drug doxorubicin to induce cardiotoxicity in zebrafish embryos. When comparing pronase- versus forceps-dechorionated embryos used in these small molecule treatments, we found no appreciable effects of pronase on animal survival or on the effects of the small molecules. The significant difference that was detected was a small improvement in the ability of salermide + oxamflatin to ameliorate the dmd phenotype in pronase-treated embryos when compared with manual dechorionation. Our study supports the use of pronase treatment as a dechorionation method for zebrafish drug screening experiments.

PBTK modeled perfluoroalkyl acid kinetics in zebrafish eleutheroembryos suggests impacts on bioconcentrations by chorion porosity dynamics

The zebrafish eleutheroembryo (zfe) is widely used as a model to characterize the toxicity of chemicals. However, analytical methods are still missing to measure organ concentrations. Therefore, physiologically-based toxicokinetic (PBTK) modeling may overcome current limitations to help understand the relationship between toxic effects and internal exposure in various organs. A previous PBTK model has been updated to include the chorionic transport barrier and its permeabilization, hatching dynamics within a zfe population over development, and active mediated transport mechanisms. The zfe PBTK model has been calibrated using measured time-dependent internal concentrations of PFBA, PFHxS, PFOA, and PFOS in a zfe population and evaluated using external datasets from the literature. Calibration was successful with 96% of the predictions falling within a 2-fold range of the observed concentrations. The external dataset was correctly estimated with about 50% of the predictions falling within a factor of 3 of the observed data and 10% of the predictions are out of the 10-fold error. The calibrated model suggested that active mediated transport differs between PFAS with a sulfonic and carboxylic acid functional end groups. This PBTK model predicts well the fate of PFAS with various physicochemical properties in zfe. Therefore, this model may improve the use of zfe as an alternative model in toxicokinetic-toxicodynamic studies and help to refine and reduce zfe-based experiments, while giving insights into the internal kinetics of chemicals.

Anti-Melanogenic Potential of Natural and Synthetic Substances: Application in Zebrafish Model

Melanogenesis is a biosynthetic pathway for the formation of the pigment melanin in human skin. A key enzyme in the process of pigmentation through melanin is tyrosinase, which catalyzes the first and only limiting step in melanogenesis. Since the discovery of its methanogenic properties, tyrosinase has been the focus of research related to the anti-melanogenesis. In addition to developing more effective and commercially safe inhibitors, more studies are required to better understand the mechanisms involved in the skin depigmentation process. However, in vivo assays are necessary to develop and validate new drugs or molecules for this purpose, and to accomplish this, zebrafish has been identified as a model organism for in vivo application. In addition, such model would allow tracking and studying the depigmenting activity of many bioactive compounds, important to genetics, medicinal chemistry and even the cosmetic industry. Studies have shown the similarity between human and zebrafish genomes, encouraging their use as a model to understand the mechanism of action of a tested compound. Interestingly, zebrafish skin shares many similarities with human skin, suggesting that this model organism is suitable for studying melanogenesis inhibitors. Accordingly, several bioactive compounds reported herein for this model are compared in terms of their molecular structure and possible mode of action in zebrafish embryos. In particular, this article described the main metabolites of Trichoderma fungi, in addition to substances from natural and synthetic sources.

Effects of glyphosate on zebrafish: a systematic review and meta-analysis

Glyphosate herbicide is widely used in worldwide crop production. Consequently, its active ingredient, surfactants, and adjuvants commonly reach the aquatic ecosystem, thereby harming the biota. An investigation into how this herbicide affects aquatic species is important, especially in fish, as they have the ability to absorb and concentrate toxins. We aimed to evaluate the effects of glyphosate on the embryonic, larval and adult stages of zebrafish (Danio rerio), an appreciable organismal model. In this sense, we performed a meta-analysis using published articles from online databases (PubMed and ScienceDirect), which covered studies published until 2022. From a massive compilation of studies evaluating the effects of active substance glyphosate and Glyphosate-Based Herbicides (GBH) on zebrafish, we selected 36 studies used in downstream analyses. Overall, we report that glyphosate affects developmental stages and demonstrates toxicity and damage in zebrafish. We observed that embryos exposed to glyphosate exhibit increased mortality. There was also an increase in the number of morphological abnormalities related to yolk sac oedema, pericardial oedema, spinal curvature and body malformations, and a decrease in body size was observed. Furthermore, there was a decrease in the number of beats. The biochemical results demonstrated an increase in reactive oxygen species and antioxidant capacity against peroxyl radicals in the gills. The literature shows that glyphosate decreased the distance covered and the mean speed of the animals and increased the number of rotations. We concluded that glyphosate causes damage in the embryonic, larval and adult stages of this species. These results are valid for zebrafish and can be applied to other freshwater fish species. Graphical abstract.

Self-recovery study of fluoride-induced ferroptosis in the liver of zebrafish (Danio rerio)

Ferroptosis plays a key role in fluorosis in aquatic organisms, but whether it is involved in fluoride-induced liver damage remains unclear. Previous studies have indicated that fluoride toxicity has the reversible tendency, but the mechanism of self-recovery after fluorosis in aquatic animals has not been elucidated. In this study, adult zebrafish and embryos were exposed to 0, 20, 40, 80 mg/L of fluoride for 30, 60 and 90 d and 3, 4 and 5 d post-fertilization (dpf), respectively. After 90 d, adult zebrafish were transferred to clean water for self-recovery of 30 d. The results showed that fluoride induced the prominent histopathologial changes in liver of adults, and the developmental delay and dark liver area in larvae. Fluoride significantly increased the iron overload, while decreased the expression levels of transferrin (tf), transferrin receptor (tfr), ferroportin (fpn), membrane iron transporter (fpn), and ferritin heavy chain (fth) in adults and larvae. Fluoride also induced the oxidative stress in adults and larvae by increasing the levels of reactive oxygen species (ROS) and malondialdehyde (MDA), while decreasing the glutathione (GSH) content and the levels of glutathione peroxidase 4 (gpx4) and solute carrier family 7 member 11 (slc7a11). Self-recovery relieved fluoride-induced ferroptosis by reducing the histopathological damage and oxidative stress, reversing the expression levels of fth and slc7a11, Fe²⁺ metabolism and GSH synthesis. Lipid peroxidation and Fe²⁺ metabolism may be the key factor in alleviating effects of self-recovery on fluoride toxicity. Moreover, males are more sensitive than females. Our results provide a theoretical basis for studying the alleviating effects of self-recovery on fluoride toxicity and the underlying mechanism of its protective effect.

Potency matters: Impacts of embryonic exposure to nAChR agonists thiamethoxam and nicotine on hatching success, growth, and neurobehavior in larval zebrafish

Thiamethoxam (TM) is a neonicotinoid insecticide that acts as a nicotinic acetylcholine receptor (nAChR) agonist. While designed to specifically target invertebrate nAChRs, recent studies have reported adverse effects of neonicotinoid exposure in early life-stage fish. This study examined the health and neurobehavioral impacts of chronic exposure to various concentrations of TM or nicotine (NIC) in early life zebrafish (Danio rerio) in conjunction with in-silico molecular docking to compare their ligand-receptor interactions with vertebrate nAChR. Chronic exposure to both reduced survival by approximately 20% (163 µg TM/l) and 25-100% (≥0.49 µg NIC/l). Hatching and growth were impaired following exposure to ≥0.21 µg TM/l or 4.9 µg NIC/l. Both TM and NIC produced morphological and behavioral indicators of neurotoxicity, with more potent effects following NIC exposure. NIC impaired embryonic motor activity by 40% (49 µg NIC/l), while both TM and NIC significantly altered predator escape response in larvae, specifically the latency and the initial burst movement of the response were impacted. Molecular docking predicted variations in the type and strength of interactions that occur between NIC or TM and vertebrate nAChR. These findings demonstrate that chronic exposure to TM might impact general health and neurobehavior of early-stage zebrafish. Our data support hypotheses that TM presents low affinity for vertebrate nAChR but may still pose an adverse risk to larval fish growth and neurobehavior.

Toxicity of oleate-based amino protic ionic liquids towards Escherichia coli, Danio rerio embryos and human skin cells

Protic ionic liquids (PILs) have been widely employed with the label of "green solvents'' in different sectors of technology and industry. The studied PILs are promising for corrosion inhibition and lubrication applications in industry. Industrial use of the PILs can transform them in wastes, due to accidental spill or drag in water due to washing, that can reach water bodies. In addition, the handling of the product by the workers can expose them to accidental contact. Thus, the aim of this work is to evaluate the toxicity of PILs 2-hydroxyethylammonium oleate (2-HEAOl), N-methyl-2-hydroxyethylammonium oleate (m-2HEAOl) and bis-2-hydroxyethylammonium oleate (BHEAOl) towards Escherichia coli, zebrafish embryos, model organisms that can be present in water, and human skin cells. This is the first work reporting toxicity results for these PILs, which constitutes its novelty. Results showed that the studied PILs did not inhibit E. coli bacterial growth but could cause human skin cells death at the concentrations of use. LC₅₀ values for zebrafish eggs were 40.21 mg/L for 2HEAOl, 12.92 mg/L for BHEAOl and 32.74 mg/L for m-2HEAOl, with sublethal effects at lower concentrations, such as hatching retarding, low heart rate and absence of free swimming.

Zebrafish models of fetal alcohol spectrum disorders

Fetal alcohol spectrum disorder (FASD) describes a wide range of structural deficits and cognitive impairments. FASD impacts up to 5% of children born in the United States each year, making ethanol one of the most common teratogens. Due to limitations and ethical concerns, studies in humans are limited in their ability to study FASD. Animal models have proven critical in identifying and characterizing the mechanisms underlying FASD. In this review, we will focus on the attributes of zebrafish that make it a strong model in which to study ethanol-induced developmental defects. Zebrafish have several attributes that make it an ideal model in which to study FASD. Zebrafish produced large numbers of externally fertilized, translucent embryos. With a high degree of genetic amenability, zebrafish are at the forefront of identifying and characterizing the gene-ethanol interactions that underlie FASD. Work from multiple labs has shown that embryonic ethanol exposures result in defects in craniofacial, cardiac, ocular, and neural development. In addition to structural defects, ethanol-induced cognitive and behavioral impairments have been studied in zebrafish. Building upon these studies, work has identified ethanol-sensitive loci that underlie the developmental defects. However, analyses show there is still much to be learned of these gene-ethanol interactions. The zebrafish is ideally suited to expand our understanding of gene-ethanol interactions and their impact on FASD. Because of the conservation of gene function between zebrafish and humans, these studies will directly translate to studies of candidate genes in human populations and allow for better diagnosis and treatment of FASD.

Toxicity in vitro and in Zebrafish Embryonic Development of Gold Nanoparticles Biosynthesized Using Cystoseira Macroalgae Extracts

INTRODUCTION

Research on gold nanoparticles (AuNPs) occupies a prominent place in the field of biomedicine nowadays, being their putative toxicity and bioactivity areas of major concern. The green synthesis of metallic nanoparticles using extracts from marine organisms allows the avoidance of hazardous production steps while maintaining features of interest, thus enabling the exploitation of their promising bioactivity.

OBJECTIVE

To synthesize and characterize AuNPs using, for the first time, macroalga Cystoseira tamariscifolia aqueous extract (Au@CT).

METHODS

Algal aqueous extracts were used for the synthesis of AuNPs, which were characterized using a wide panel of physicochemical techniques and biological assays.

RESULTS

The characterization by UV-Vis spectroscopy, transmission electron microscopy, Z-potential and infrared spectroscopy confirmed that Au@CT were stable, spherical and polycrystalline, with a mean diameter of 7.6 ± 2.2 nm. The antioxidant capacity of the extract, prior to and after synthesis, was analyzed in vitro, showing that the high antioxidant potential was not lost during the synthesis. Subsequently, in vitro and in vivo toxicity was screened, by comparing two species of the genus Cystoseira (C. tamariscifolia and C. baccata) and the corresponding biosynthesized gold nanoparticles (Au@CT and Au@CB). Cytotoxicity was tested in mouse (L929) and human (BJ5ta) fibroblast cell lines. In both cases, only the highest (nominal) test concentration of both extracts (31.25 mg/mL) or Au@CB (12.5 mM) significantly affected cell viability, as measured by the MTT assay. These results were corroborated by a Fish Embryo Acute Toxicity (FET) test. Briefly, it was shown that, at the highest (nominal) tested concentration (31.25 mg/mL), CT extract induced significantly higher cytotoxicity and embryotoxicity than CB extract. However, it was demonstrated that Au@CT, but not Au@CB, were generally non-toxic. At sub-lethal (nominal) test concentrations (1.25 and 2.5 mM), Au@CT affected zebrafish embryonic development to a much lesser extent than Au@CB. In vitro wound healing assays also revealed that, while other experimental conditions did not impact cell migration, CT and Au@CT displayed a moderate positive effect.

CONCLUSION

Au@CT and Au@CB display promising features, desirable for biomedical applications, as wound healing.

The Role of Polymeric Coatings for a Safe-by-Design Development of Biomedical Gold Nanoparticles Assessed in Zebrafish Embryo

In the biomedical field, gold nanoparticles (GNPs) have attracted the attention of the scientific community thanks to their high potential in both diagnostic and therapeutic applications. The extensive use of GNPs led researchers to investigate their toxicity, identifying stability, size, shape, and surface charge as key properties determining their impact on biological systems, with possible strategies defined to reduce it according to a Safe-by-Design (SbD) approach. The purpose of the present work was to analyze the toxicity of GNPs of various sizes and with different coating polymers on the developing vertebrate model, zebrafish. In particular, increasing concentrations (from 0.001 to 1 nM) of 6 or 15 nm poly-(isobutylene-alt-maleic anhydride)-graft-dodecyl polymer (PMA)- or polyethylene glycol (PEG)-coated GNPs were tested on zebrafish embryos using the fish embryo test (FET). While GNP@PMA did not exert significant toxicity on zebrafish embryos, GNP@PEG induced a significant inhibition of embryo viability, a delay of hatching (with the smaller size NPs), and a higher incidence of malformations, in terms of tail morphology and eye development. Transmission electron microscope analysis evidenced that the more negatively charged GNP@PMA was sequestered by the positive charges of chorion proteins, with a consequent reduction in the amount of NPs able to reach the developing embryo and exert toxicological activity. The mild toxic response observed on embryos directly exposed to GNP@PMA suggest that these NPs are promising in terms of SbD development of gold-based biomedical nanodevices. On the other hand, the almost neutral GNP@PEG, which did not interact with the chorion surface and was free to cross chorion pores, significantly impacted the developing zebrafish. The present study raises concerns about the safety of PEGylated gold nanoparticles and contributes to the debated issue of the free use of this nanotool in medicine and nano-biotechnologies.

On the effects of iron ore tailings micro/nanoparticles in embryonic and larval zebrafish (Danio rerio)

Iron ore tailings (IOT) represent a major problem in the mining industry worldwide due to large volumes of waste disposed in mine sites. IOT are exposed to the environment and subjected to wind and water dispersion, even under non-catastrophic scenarios as dam collapses, and the effects of these particles to the biota are still mostly unknown. This work aimed to prepare and to characterize a suspension containing the finest (micro/nano range) particles of IOT and to evaluate its effects on development and behavior of zebrafish (Danio rerio), at both embryonic and larval stages. IOT suspension comprised 37 mg L^-1 of a multi-mineral material mainly composed by hematite and quartz, in a size-range of 33-1400 nm. Regarding in vivo toxicological assays, no robust alterations were recorded in functional, morphological and behavioral end-points analyzed, although a significant adhesion of IOT particles on zebrafish chorion was observed, without a prejudice of embryo hatching. Under applied conditions, iron ore particles did not present harmful effects to the initial stages of zebrafish development, and the particle size range and potential interactions with SiO₂ content might be behind such effect.

Developmental toxicity in zebrafish (Danio rerio) exposed to uranium: A comparison with lead, cadmium, and iron

Populations of plants and animals, including humans, living in close proximity to abandoned uranium mine sites are vulnerable to uranium exposure through drainage into nearby waterways, soil accumulation, and blowing dust from surface soils. Little is known about how the environmental impact of uranium exposure alters the health of human populations in proximity to mine sites, so we used developmental zebrafish (Danio rerio) to investigate uranium toxicity. Fish are a sensitive target for modeling uranium toxicity, and previous studies report altered reproductive capacity, enhanced DNA damage, and gene expression changes in fish exposed to uranium. In our study, dechorionated zebrafish embryos were exposed to a concentration range of uranyl acetate (UA) from 0 to 3000 μg/L for body burden measurements and developmental toxicity assessments. Uranium was taken up in a concentration-dependent manner by 48 and 120 h post fertilization (hpf)-zebrafish without evidence of bioaccumulation. Exposure to UA was not associated with teratogenic outcomes or 24 hpf behavioral effects, but larvae at 120 hpf exhibited a significant hypoactive photomotor response associated with exposure to 3 μg/L UA which suggested potential neurotoxicity. To our knowledge, this is the first time that uranium has been associated with behavioral effects in an aquatic organism. These results were compared to potential metal co-contaminants using the same exposure paradigm. Similar to uranium exposure, lead, cadmium, and iron significantly altered neurobehavioral outcomes in 120-hpf zebrafish without inducing significant teratogenicity. Our study informs concerns about the potential impacts of developmental exposure to uranium on childhood neurobehavioral outcomes. This work also sets the stage for future, environmentally relevant metal mixture studies. Summary Uranium exposure to developing zebrafish causes hypoactive larval swimming behavior similar to the effect of other commonly occurring metals in uranium mine sites. This is the first time that uranium exposure has been associated with altered neurobehavioral effects in any aquatic organism.

Impacts of subchronic exposure to a commercial 2,4-D herbicide on developmental stages of multiple freshwater fish species

Invasive, nuisance aquatic species such as Eurasian watermilfoil (Myriophyllum spicatum) are rapidly spreading across the United States. One common active ingredient used to control this invasive species is 2,4-Dichlorophenoxyacetic acid (2,4-D). Application of 2,4-D to aquatic environments typically occurs while many freshwater fish are spawning and due to 2,4-D stability in aquatic environments, many non-target species experience prolonged exposure throughout embryogenesis and larval development. The impacts of 2,4-D exposure on phylogenetically distant fish species is poorly understood. Herein, we investigated the impacts of the 2,4-D commercial herbicide DMA4®IVM on nine freshwater fish species from six different families (four orders) at different points during ontogeny. Each species was exposed to ecologically relevant concentrations of a commercial 2,4-D herbicide (0.05, 0.50, and 2.00 ppm or mg/L 2,4-D a. e.), and effects on morphology, survival, and growth were evaluated. Our results demonstrate that exposure of embryonic and larval fish to ecologically relevant concentrations of a commercial 2,4-D herbicide reduced survival in early developmental stages of six freshwater species that spanned five phylogenetic families and three phylogenetic orders; however, sensitivity to 2,4-D exposure did not show correlation with phylogenetic proximity. Altogether, our results indicate that the use of 2,4-D herbicides in aquatic ecosystems at current recommended concentrations (≤2 ppm whole-lake treatment) could present risk to multiple freshwater fish species survival during early development.

Cellular and molecular modification of egg envelope hardening in fertilization

Fertilization is an essential process that fundamentally impacts fitness. An egg changes dramatically after fertilization mediating the beginning of life, which mainly includes the transformation of the egg envelope via hardening, which is thought to be due to complex reactions involved in the conversion of cellular and molecular. This review highlights the mechanisms of egg envelope hardening in teleost fish. We conclude that the egg envelope hardening might be carried out in two steps. (a) A metalloprotease (alveolin) hydrolyzes the N-terminal proline-glutamine (Pro-Gln) region of zona pellucida (ZP) 1 and (b) triggers intermolecular cross-linking to ZP3 catalyzed by transglutaminase (TGase). The post-fertilization hardening of the egg envelope is an evolutionarily conserved phenomenon across species. We discuss the biochemical function and interaction of some factors reported to be essential to egg envelope hardening in mammalian and nonmammalian species, including metalloprotease, TGase, peroxidase/ovoperoxidase, and other factors (carbohydrate moieties, zinc and Larp6 proteins), and the relevant data suggest that egg envelope hardening is crucial to block polyspermy in internal fertilization, in addition to protecting the developing embryo from mechanical shock and preventing bacterial infection in external fertilization. Increased knowledge of the processes of egg envelope hardening and fertilization is likely to make a remarkable contribution to reproduction and aquaculture.

Cisplatin alkylating activity in zebrafish causes resistance to chorionic degradation and inhibition of osteogenesis

Zebrafish have gained popularity as a model organism due to their rapid, external, and transparent development, high fecundity, and gene homology with higher vertebrate models and humans. Specifically, drug discovery has had high success in the implementation of zebrafish in studies for target discovery, efficacy, and toxicity. However, a major limitation of the zebrafish model is a dependence on waterborne exposure in order to maintain high throughput capabilities. Dose delivery can be impeded by a matrix of N-linked glycoproteins and other polypeptides called the chorion. This acelluar barrier is protective of the developing embryo, and thus new approaches for assessment have involved their removal. In these studies, we explored the chorionic interference of a well-characterized alkylating chemotherapeutic, cisplatin, known to accumulate in the chorion of zebrafish and cause delayed hatching. Our results indicated that increased exposure of cisplatin due to dechorionation did not alter morphological endpoints, although retained confinement reduced total body length and yolk utilization. Additionally, inhibition of osteogenesis visualized with Alizarian Red staining, was observable in dechorionated and non-dechorionated treatment groups. The chorions of cisplatin-treated embryos showed resistance to degradation unless treated with a pronase solution. This may be may be due to cisplatin covalently crosslinking which reinforces the structure. As such, the chorion may play an advantageous role in studies to determine alkylating activity of novel compounds. Furthermore, the expression of zebrafish hatching enzyme was not affected by cisplatin exposure. These studies demonstrate that not only was recapitulation of mechanistic activity supported in zebrafish, but highly relevant off-target toxicities observed in higher vertebrates were identified in zebrafish, regardless of chorionation. Experimental design in drug discovery should consider preliminary studies without dechorionation in order to determine dose impediment or off-target adducting.

Are TiO2 nanoparticles safe for photocatalysis in aqueous media?

Although environmental and toxicity concerns are inherently linked, catalysis using photoactive nanoparticles and their hazardous potential are usually addressed independently. A toxicological assessment under the application framework is particularly important, given the pristine nanoparticles tend to change characteristics during several processes used to incorporate them into products. Herein, an efficient TiO₂-functionalized macroporous structure was developed using widely adopted immobilization procedures. The relationships between photocatalysis, catalyst release and associated potential environmental hazards were assessed using zebrafish embryonic development as a proxy. Immobilized nanoparticles demonstrated the safest approach to the environment, as the process eliminates remnant additives while preventing the release of nanoparticles. However, as acute sublethal effects were recorded in zebrafish embryos at different stages of development, a completely safe release of TiO₂ nanoparticles into the aquatic environment cannot be advocated.

Evaluation of potential environmental toxicity of polymeric nanomaterials and surfactants

Nanomaterials have gained huge importance in various fields including nanomedicine. Nanoformulations of drugs and nanocarriers are used to increase pharmaceutical potency. However, it was seen that polymeric nanomaterials can cause negative effects. Thus, it is essential to identify nanomaterials with the least adverse effects on aquatic organisms. To determine the toxicity of polymeric nanomaterials, we investigated the effects of poly(lactic-co-glycolid) acid (PLGA), Eudragit® E 100 and hydroxylpropyl methylcellulose phthalate (HPMCP) on zebrafish embryos using the fish embryo toxicity test (FET). Furthermore, we studied Cremophor® RH40, Cremophor® A25, Pluronic® F127 and Pluronic® F68 applied in the generation of nanoformulations to identify the surfactant with minimal toxic impact. The order of ecotoxicty was HPMCP < PLGA < Eudragit® E100 and Pluronic® F68 < Pluronic® F127 < Cremophor® RH40 < Cremophor® A25. In summary, HPMCP and Pluronic® F68 displayed the least toxic impact, thus suggesting adequate environmental compatibility for the generation of nanomedicines.

Study of mastoparan analog peptides against Candida albicans and safety in zebrafish embryos (Danio rerio)

Aim: In this work, mastoparan analog peptides from wasp venom were tested against Candida albicans and safety assays were performed using cell culture and model zebrafish. Materials & methods: Minimal inhibitory concentration was determined and toxicity was performed using human skin keratinocyte and embryo zebrafish. Also, permeation of peptides through embryo chorion was performed. Results: The peptides demonstrated anti-C. albicans activity, with low cytotoxicity and nonteratogenicity in Danio rerio. The compounds had different permeation through chorion, suggesting that this occurs due to modifications in their amino acid sequence. Conclusion: The results showed that the studied peptides can be used as structural study models for novel potential antifungal agents.

The Use of Complementary Luminescent and Fluorescent Techniques for Imaging Ca2+ Signaling Events During the Early Development of Zebrafish (Danio rerio)

We have visualized many of the Ca²⁺ signaling events that occur during the early stages of zebrafish development using complementary luminescent and fluorescent imaging techniques. We initially microinject embryos with the luminescent Ca²⁺ reporter, f-holo-aequorin, and using a custom-designed luminescent imaging system, we can obtain pan-embryonic visual information continually for up to the first ~24 h postfertilization (hpf). Once we know approximately when and where to look for these Ca²⁺ signaling events within a complex developing embryo, we then repeat the experiment using a fluorescent Ca²⁺ reporter such as calcium green-1 dextran and use confocal laser scanning microscopy to provide time-lapse series of higher-resolution images. These protocols allow us to identify the specific cell types and even the particular subcellular domain (e.g., nucleus or cytoplasm) generating the Ca²⁺ signal. Here, we outline the techniques we use to precisely microinject f-holo-aequorin or calcium green-1 dextran into embryos without affecting their viability or development. We also describe how to inject specific regions of early embryos in order to load localized embryonic domains with a particular Ca²⁺ reporter. These same techniques can also be used to introduce other membrane-impermeable reagents into embryos, including Ca²⁺ channel antagonists, Ca²⁺ chelators, fluorescent dyes, RNA, and DNA.

Imidacloprid induces adverse effects on fish early life stages that are more severe in Japanese medaka (Oryzias latipes) than in zebrafish (Danio rerio)

Neonicotinoids are widely used insecticides that have frequently been found in freshwater with concentrations ranging from ng to μg/L. It is known that these compounds impact non-target invertebrates, such as bees and gammaridae, in terms of toxicity and behavior, but impacts and species differences on vertebrates such as fish are little explored. The aim of this study was to investigate and compare the effects of one widely used neonicotinoid, imidacloprid, on development and behavior of two fish model species: Zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). Fish were exposed for 5 (zebrafish) and 14 (medaka) days from 0.2 to 2000 μg/L imidacloprid by aqueous exposure. Survival, development, behavior and histological features were monitored and organism-internal concentrations and biotransformation products measured. Imidacloprid caused sublethal effects in both species but the effects were much stronger in medaka with deformities, lesions and reduced growth being the most prominent impacts. Due to the overall longer time of development, time-integrated exposure of medaka was about 2-fold higher compared to zebrafish, potentially accounting for parts of the sensitivity differences. Our results underline the importance of taking species sensitivity differences into account especially when considering that medaka responded at imidacloprid concentrations that have been measured in the environment.

Toxicokinetics of Perfluorinated Alkyl Acids Influences Their Toxic Potency in the Zebrafish Embryo ( Danio rerio)

Perfluorinated alkyl acids (PFAA) are highly persistent and bioaccumulative and have been associated with several adverse health effects. The chemical structure mainly differs in two ways: the length of the hydrophobic alkyl chain and the type of hydrophilic end group. Little is known how the chemical structure affects the toxicokinetics (TK) in different organisms. We studied the TK of four PFAA (PFOS, PFHxS, PFOA, and PFBA) with different chain lengths (4-8 carbons) and functional groups (sulfonic and carboxylic acid) in zebrafish ( Danio rerio) embryo. The time courses of the external (ambient water) and internal concentrations were determined at three exposure concentrations from 2 up to 120 h postfertilization (hpf). Three of the four PFAA showed a biphasic uptake pattern with slow uptake before hatching (around 48 hpf) and faster uptake thereafter. A two-compartment TK model adequately described the biphasic uptake pattern, suggesting that the chorion functions as an uptake barrier until 48 hpf. The bioconcentration factors (BCF) determined at 120 hpf varied widely between PFAA with averages of approximately 4000 (PFOS), 200 (PFHxS), 50 (PFOA), and 0.8 (PFBA) L kg dry weight^-1, suggesting that both the alkyl chain length and the functional group influence the TK. The differences in toxic potency were reduced by 3 orders of magnitude when comparing internal effect concentrations instead of effective external concentrations.

Construction of a Quantitative Structure Activity Relationship (QSAR) Model to Predict the Absorption of Cephalosporins in Zebrafish for Toxicity Study

Cephalosporins are beta-lactam antibiotics that are widely used in China. Five generations of cephalosporins have been introduced in clinical practice to date; moreover, some new candidates are also undergoing clinical evaluations. To improve the success rates of new drug development, we need to have a comprehensive understanding about the relationship between the structure of cephalosporins and the toxicity that it induces at an early stage. In the cephalosporins toxicity study using zebrafish, the drug absorption is a key point. In this study, we determined the absorption of cephalosporins in zebrafish during toxicity test. The internal concentrations of 19 cephalosporins in zebrafish were determined using a developed liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Furthermore, a quantitative structure-activity relationship (QSAR) model was established by multilinear regression; moreover, it was used to predict the absorption of cephalosporins in zebrafish. During leave-one-out cross-validation, a satisfactory performance was obtained with a predictive ability (q ²) of 0.839. The prediction ability of the model was further confirmed when the predictive ability (q ²) was 0.859 in external prediction. The best QSAR model, which was based on five molecular descriptors, exhibited a promising predictive performance and robustness. In experiments involving drug toxicity, the developed QSAR model was used to estimate internal concentrations of cephalosporins. Thus, the toxicity results were correlated with the internal concentration of the drug within the larvae. The developed model served as a new powerful tool in zebrafish toxicity tests.

Graphene-Based Nanomaterials Toxicity in Fish

Due to their unique physicochemical properties, graphene-based nanoparticles (GPNs) constitute one of the most promising types of nanomaterials used in biomedical research. GPNs have been used as polymeric conduits for nerve regeneration and carriers for targeted drug delivery and in the treatment of cancer via photothermal therapy. Moreover, they have been used as tracers to study the distribution of bioactive compounds used in healthcare. Due to their extensive use, GPN released into the environment would probably pose a threat to living organisms and ultimately to human health. Their accumulation in the aquatic environment creates problems to aquatic habitats as well as to food chains. Until now the potential toxic effects of GPN are not properly understood. Despite agglomeration and long persistence in the environment, GPNs are able to cross the cellular barriers successfully, entered into the cells, and are able to interact with almost all the cellular sites including the plasma membrane, cytoplasmic organelles, and nucleus. Their interaction with DNA creates more potential threats to both the genome and epigenome. In this brief review, we focused on fish, mainly zebrafish (Danio rerio), as a potential target animal of GPN toxicity in the aquatic ecosystem.

Quantification of Estradiol Uptake in Zebrafish Embryos and Larvae

Zebrafish are a powerful model system to assess the molecular and cellular effects of exposure to toxic chemicals during embryonic development. To study the effects of environmental endocrine disruptors, embryos and larvae are commonly exposed to supraphysiologic concentrations of these compounds in the water, but their bioavailability in zebrafish is largely unknown. One hypothesis is that supraphysiologic concentrations of estrogens in the water are required to achieve physiologic levels in vivo; however, this has not been directly tested. To test this hypothesis, we developed an assay using radiolabeled estradiol ([3H]E2) to measure uptake from water at multiple concentrations and exposure durations in developing zebrafish from 0 to 5 days postfertilization (dpf). We found that [3H]E2 uptake increased with increasing concentration, duration, and developmental stage. Percent uptake from the total volume of treatment solution increased with increasing exposure duration and developmental stage, but remained constant with increasing concentration. We also found that the chorion, an acellular envelope surrounding embryos through 3 dpf, did not substantially affect [3H]E2 uptake. Finally, we found that at 1 dpf, E2 was preferentially taken up by the yolk at multiple exposure durations, while at 2 dpf E2 was preferentially taken up into the embryonic body. Our results support the hypothesis that exposing zebrafish embryos and larvae to supraphysiologic concentrations of estrogens is required to achieve physiologically relevant doses in vivo. The isotopic assay reported here will provide a foundation for determining the uptake of other compounds for teratogenicity, toxicology and drug discovery studies.

A Zebrafish Embryo as an Animal Model for the Treatment of Hyperpigmentation in Cosmetic Dermatology Medicine

For years, clinical studies involving human volunteers and several known pre-clinical in vivo models (i.e., mice, guinea pigs) have demonstrated their reliability in evaluating the effectiveness of a number of depigmenting agents. Although these models have great advantages, they also suffer from several drawbacks, especially involving ethical issues regarding experimentation. At present, a new depigmenting model using zebrafish has been proposed and demonstrated. The application of this model for screening and studying the depigmenting activity of many bioactive compounds has been given great attention in genetics, medicinal chemistry and even the cosmetic industry. Depigmenting studies using this model have been recognized as noteworthy approaches to investigating the antimelanogenic activity of bioactive compounds in vivo. This article details the current knowledge of zebrafish pigmentation and its reliability as a model for the screening and development of depigmenting agents. Several methods to quantify the antimelanogenic activity of bioactive compounds in this model, such as phenotype-based screening, melanin content, tyrosinase inhibitory activity, other related proteins and transcription genes, are reviewed. Depigmenting activity of several bioactive compounds which have been reported towards this model are compared in terms of their molecular structure and possible mode of actions. This includes patented materials with regard to the application of zebrafish as a depigmenting model, in order to give an insight of its intellectual value. At the end of this article, some limitations are highlighted and several recommendations are suggested for improvement of future studies.

Differential uptake of and sensitivity to diphenhydramine in embryonic and larval zebrafish

The zebrafish fish embryo toxicity (FET) test is increasingly employed for alternative toxicity studies, yet our previous research identified increased sensitivity of zebrafish slightly older than embryos employed in FET methods (0-4 d postfertilization [dpf]). We identified rapid steady-state accumulation of diphenhydramine across zebrafish embryo and larval stages. However, significantly (p < 0.05) lower accumulation was observed at 48 h compared to 96 h in chorionated and dechorionated embryos (0-4 dpf), but not in zebrafish at 7 to 11 and 14 to 18 dpf. Increased uptake and toxicity of diphenhydramine was further observed in zebrafish at 7 to 11 and 14 to 18 dpf compared with 0-4 dpf embryos with chorion or dechorionated, which indicates that differential zebrafish sensitivity with age is associated with accumulation resulting from gill and other toxicokinetic and toxicodynamic changes during development. Environ Toxicol Chem 2018;37:1175-1181. © 2017 SETAC.

Assessment of the permeability and toxicity of polymeric nanocapsules using the zebrafish model

Aim: To assess the capacity of a new drug delivery nanocapsule (NC) with a double shell of hyaluronic acid and protamine to overcome biological barriers using the zebrafish model. Materials & methods: NCs were prepared by the solvent displacement method, tagged with fluorescent makers and physicochemically characterized. Toxicity was evaluated according to the Fish Embryo Acute Toxicity test, and permeability was tested by exposing zebrafish, with and without chorion, to the fluorescent NCs. Results: Toxicity of NCs was very low as compared with that of a control nanoemulsion. Double-shell NCs were able to cross chorion and skin. Conclusion: Beyond the potential value of hyaluronic acid:protamine NCs for overcoming epithelial barriers, this works highlights the utility of zebrafish for fast screening of nanocarriers.

Kinetics of glucocorticoid exposure in developing zebrafish: A tracer study

In the current study the dynamics of glucocorticoid uptake by zebrafish chorionated embryos from the surrounding medium were studied, using 2.5 μM cortisol or dexamethasone solutions complemented with their tritiated variant. We measured the uptake of radioactive cortisol by embryos during a 1 h submersion. Interestingly, the signal in chorionated embryos was 85% (exposure: 1-2 hpf) or 78% (exposure: 48-49 hpf) of the signal present in an equal volume medium. By comparing embryos measured without chorion, we found that 18-20% of the radioactivity present in chorionated embryos is actually bound to the chorion or located in the perivitelline space. Consequently, embryonic tissue contains radioactivity levels of 60% of a similar volume of medium after 1 h incubation. During early developmental stages (1-48 hpf) exposure of more than 24 h in cortisol was needed to achieve radioactivity levels similar to an equal volume of medium within the embryonic tissue and more than 48 h for dexamethasone. In glucocorticoid-free medium, radioactivity dropped rapidly below 10% for both glucocorticoids, suggesting that the major portion of the embryonic radioactivity was a result of simple diffusion. During later developmental stages (48-96 hpf) initial uptake dynamics were similar, but showed a decrease of tissue radioactivity to 20% of an equal volume of medium after hatching, probably due to development and activation of the hypothalamic pituitary interrenal axis. Uptake is dependent on the developmental stage of the embryo. Furthermore, the presence of the chorion during exposure should be taken into account even when small lipophilic molecules are being tested.

A versatile and low-cost open source pipetting robot for automation of toxicological and ecotoxicological bioassays

In the past decades, bioassays and whole-organism bioassay have become important tools not only in compliance testing of industrial chemicals and plant protection products, but also in the monitoring of environmental quality. With few exceptions, such test systems are discontinuous. They require exposure of the biological test material in small units, such as multiwell plates, during prolonged incubation periods, and do not allow online read-outs. It is mostly due to these shortcomings that applications in continuous monitoring of, e.g., drinking or surface water quality are largely missing. We propose the use of pipetting robots that can be used to automatically exchange samples in multiwell plates with fresh samples in a semi-static manner, as a potential solution to overcome these limitations. In this study, we developed a simple and low-cost, versatile pipetting robot constructed partly using open-source hardware that has a small footprint and can be used for online monitoring of water quality by means of an automated whole-organism bioassay. We tested its precision in automated 2-fold dilution series and used it for exposure of zebrafish embryos (Danio rerio)-a common model species in ecotoxicology-to cadmium chloride and permethrin. We found that, compared to conventional static or semi-static exposure scenarios, effects of the two chemicals in zebrafish embryos generally occurred at lower concentrations, and analytically verified that the increased frequency of media exchange resulted in a greater availability of the chemical. In combination with advanced detection systems this custom-made pipetting robot has the potential to become a valuable tool in future monitoring strategies for drinking and surface water.

Size does matter - Determination of the critical molecular size for the uptake of chemicals across the chorion of zebrafish (Danio rerio) embryos

In order to identify the upper limits of the molecular size of chemicals to cross the chorion of zebrafish, Danio rerio, differently sized, non-toxic and chemically inert polyethylene glycols (PEGs; 2000-12,000Da) were applied at concentrations (9.76mM) high enough to provoke osmotic pressure. Whereas small PEGs were expected to be able to cross the chorion, restricted uptake of large PEGs was hypothesized to result in shrinkage of the chorion. Due to a slow, but gradual uptake of PEGs over time, molecular size-dependent equilibration in conjunction with a regain of the spherical chorion shape was observed. Thus, the size of molecules able to cross the chorion could be narrowed down precisely to ≤4000Da, and the time-dependency of the movement across the chorion could be described. To account for associated alterations in embryonic development, fish embryo toxicity tests (FETs) according to OECD test guideline 236 (OECD, 2013) were performed with special emphasis to changes in chorion shape. FETs revealed clear-cut size-effects: the higher the actual molecular weight (=size) of the PEG, the more effects (both acutely toxic and sublethal) were found. No effects were seen with PEGs of 2000 and 3000Da. In contrast, PEG 8000 and PEG 12,000 were found to be most toxic with LC₅₀ values of 16.05 and 16.40g/L, respectively. Likewise, the extent of chorion shrinkage due to increased osmotic pressure strictly depended on PEG molecular weight and duration of exposure. A reflux of water and PEG molecules into the chorion and a resulting re-shaping of the chorion could only be observed for eggs exposed to PEGs ≤4000Da. Results clearly indicate a barrier function of the zebrafish chorion for molecules larger than 3000 to 4,000Da.

Basagran® induces developmental malformations and changes the bacterial community of zebrafish embryos

This study aimed to assess the effects of Basagran^® on zebrafish (Danio rerio) embryos. The embryos were exposed to Basagran^® at concentrations ranging from 120.0 to 480.6 mg/L, and the effects on embryo development (up to 96 h) and bacterial communities of 96 h-larvae were assessed. The embryo development response was time-dependent and concentration-dependent (106.35 < EC₅₀ < 421.58 mg/L). The sensitivity of embryo-related endpoints decreased as follows: blood clotting in the head and/or around the yolk sac > delay or anomaly in yolk sac absorption > change in swimming equilibrium > development of pericardial and/or yolk sac oedema > scoliosis. A PCR-DGGE analysis was used to evaluate changes in the structure, richness, evenness and diversity of bacterial communities after herbicide exposure. A herbicide-induced structural adjustment of bacterial community was observed. In this study, it was successfully demonstrated that Basagran^® affected zebrafish embryos and associated bacterial communities, showing time-dependent and concentration-dependent embryos' developmental response and structural changes in bacterial community. Thus, this work provides for the first time a complementary approach, which is useful to derive robust toxicity thresholds considering the embryo-microbiota system as a whole. The aquatic hazard assessment will be strengthened by combining current ecotoxicological tests with molecular microbiology tools.

Differential Lectin Binding Patterns Identify Distinct Heart Regions in Giant Danio ( Devario aequipinnatus) and Zebrafish ( Danio rerio) Hearts

Lectins are carbohydrate-binding proteins commonly used as biochemical and histochemical tools to study glycoconjugate (glycoproteins, glycolipids) expression patterns in cells, tissues, including mammalian hearts. However, lectins have received little attention in zebrafish ( Danio rerio) and giant danio ( Devario aequipinnatus) heart studies. Here, we sought to determine the binding patterns of six commonly used lectins-wheat germ agglutinin (WGA), Ulex europaeus agglutinin, Bandeiraea simplicifolia lectin (BS lectin), concanavalin A (Con A), Ricinus communis agglutinin I (RCA I), and Lycopersicon esculentum agglutinin (tomato lectin)-in these hearts. Con A showed broad staining in the myocardium. WGA stained cardiac myocyte borders, with binding markedly stronger in the compact heart and bulbus. BS lectin, which stained giant danio coronaries, was used to measure vascular reconstruction during regeneration. However, BS lectin reacted poorly in zebrafish. RCA I stained the compact heart of both fish. Tomato lectin stained the giant danio, and while low reactivity was seen in the zebrafish ventricle, staining was observed in their transitional cardiac myocytes. In addition, we observed unique staining patterns in the developing zebrafish heart. Lectins' ability to reveal differential glycoconjugate expression in giant danio and zebrafish hearts suggests they can serve as simple but important tools in studies of developing, adult, and regenerating fish hearts.

Body Mass Parameters, Lipid Profiles and Protein Contents of Zebrafish Embryos and Effects of 2,4-Dinitrophenol Exposure

Morphology and physiology of fish embryos undergo dramatic changes during their development until the onset of feeding, supplied only by endogenous yolk reserves. For obtaining an insight how these restructuring processes are reflected by body mass related parameters, dry weights (dw), contents of the elements carbon and nitrogen and lipid and protein levels were quantified in different stages within the first four days of embryo development of the zebrafish (Danio rerio). The data show age dependent changes in tissue composition. Dry weights decreased significantly from 79μgdw/egg at 0hours post fertilization (hpf) to 61 μgdw/egg after 96 hpf. The amounts of total carbon fluctuated between 460 mg g^-1 and 540 mg g^-1 dw, nitrogen was at about 100 mg g^-1 dw and total fatty acids were between 48–73 mg g^-1 dw. In contrast to these parameters that remained relatively constant, the protein content, which was 240 mg g^-1 at 0 hpf, showed an overall increase of about 40%. Comparisons of intact eggs and dechorionated embryos at stages prior to hatching (24, 30, 48 hpf) showed that the differences seen for dry weight and for carbon and nitrogen contents became smaller at more advanced stages, consistent with transition of material from the chorion to embryo tissue. Further, we determined the effect of 2,4-dinitrophenol at a subacutely toxic concentration (14 μM, LC10) as a model chemical challenge on the examined body mass related parameters. The compound caused significant decreases in phospholipid and glycolipid fatty acid contents along with a decrease in the phospholipid fatty acid unsaturation index. No major changes were observed for the other examined parameters. Lipidomic studies as performed here may thus be useful for determining subacute effects of lipophilic organic compounds on lipid metabolism and on cellular membranes of zebrafish embryos.

Mortality Caused by Bath Exposure of Zebrafish (Danio rerio) Larvae to Nervous Necrosis Virus Is Limited to the Fourth Day Postfertilization

Nervous necrosis virus (NNV) is a member of the Betanodavirus genus that causes fatal diseases in over 40 species of fish worldwide. Mortality among NNV-infected fish larvae is almost 100%. In order to elucidate the mechanisms responsible for the susceptibility of fish larvae to NNV, we exposed zebrafish larvae to NNV by bath immersion at 2, 4, 6, and 8 days postfertilization (dpf). Here, we demonstrate that developing zebrafish embryos are resistant to NNV at 2 dpf due to the protection afforded by the egg chorion and, to a lesser extent, by the perivitelline fluid. The zebrafish larvae succumbed to NNV infection during a narrow time window around the 4th dpf, while 6- and 8-day-old larvae were much less sensitive, with mortalities of 24% and 28%, respectively.

Influence of the perivitelline space on the quantification of internal concentrations of chemicals in eggs of zebrafish embryos (Danio rerio)

The chorion and the perivitelline space which surround unhatched zebrafish embryos (ZFE, Danio rerio) may affect the determination of internal concentrations of study compounds taken up in early life-stages of ZFE. Internal concentration-time profiles were gathered for benzocaine, caffeine, clofibric acid, metribuzin and phenacetin as study compounds over 96 h of exposure starting with ZFE at 4h post-fertilization. Liquid chromatography coupled to tandem-mass spectrometry (LC-MS/MS) was used to determine the concentration of the study compounds from intact (i.e. unhatched), dechorionated and from hatched ZFE. The mass of the study compounds per ZFE was 5-30 ng higher for intact ZFE compared to dechorionated ones. Thus, internal concentrations were overestimated if only intact ZFE were analyzed. Dechorionation of unhatched ZFE after their exposure is proposed to determine the true internal concentration in the embryo. For the compounds studied here the mass of the study compounds determined in unhatched ZFE after a short term (5 min) exposure provided a reasonable estimate of the mass taken up by the chorion and the PVS. This mass can be subtracted from the total mass found in unhatched ZFE to calculate the true internal mass. Estimating the mass in the chorion and the PVS from the concentration of the study compound in the external exposure medium and the volume of the PVS provided no reasonable results.

Zebrafish (Danio rerio) as a possible bioindicator of epigenetic factors present in drinking water that may affect reproductive function: is chorion an issue?

Emerging organic contaminants have been monitored in stream waters, raw and finished waters and wastewater effluents. Most of these contaminants, such as epigenetic substances, have been detected at very low levels. Unfortunately, their complete monitoring and/or removal are very difficult, given the increasing presence of new contaminants and due to analytical and economic considerations. For this reason, bioindicators are used as an alternative to monitor their presence. To this end, zebrafish is being used to assess certain contaminants in water quality studies. As our long-term aim is to determine if zebrafish (Danio rerio) can be used to detect environmental epigenetic factors in drinking waters with effects on human reproduction, an initial question is whether the chorion could interfere with the possible action of epigenetic factors in two reproductive events: genital ridge formation and migration of the primordial germ cells (PGCs) to these genital ridges. In the first experiment, we attempted to partially degrade the chorion of mid blastula transition (MBT) embryos with pronase, with acceptable survival rates at 5 days post fertilisation (dpf), with the group exposed for 15 min giving the best survival results. As denuded early embryos require a specific culture medium, in the next experiment embryo survival was evaluated when they were cultured up to 5 dpf in drinking waters from six different sources. Results showed a negative effect on embryo survival at 5 dpf from several waters but not in others, thus distorting the survival outcomes. These results suggest using embryos with the chorion intact from the outset when drinking waters from different sources are to be tested.

DMSO modifies the permeability of the zebrafish (Danio rerio) chorion-implications for the fish embryo test (FET)

Since 2007, when REACH came into force, the fish embryo test has received increasing attention as a potential alternative for the acute fish test. Due to its low toxicity and the ability to permeate biological membranes without significant damage to their structural integrity, dimethyl sulfoxide (DMSO) is a commonly used solvent in the fish embryo test. Little is known, however, about the membrane penetration properties of DMSO, the impact of different concentrations of DMSO on the potential barrier function of the zebrafish chorion and on changes in the uptake of chemicals into the embryo. Therefore, in the present study, the fluorescent dyes fluorescein (mol wt 332; Pow 3.4) and 2,7-dichlorofluorescein (mol wt 401; Pow 4.7), both substances with limited water solubility, were used to visualize the uptake into the egg as well as the accumulation in the embryo of the zebrafish depending on different concentrations of DMSO. The distribution of fluorescein within the egg compartments varied with DMSO concentration: When dissolved in 0.01% DMSO, fluorescein did not pass the chorion. In contrast, concentrations ≥ 0.1% DMSO increasingly facilitated the uptake into the perivitelline space. In contrast, the uptake of 2,7-dichlorofluorescein was not substantially increased with rising DMSO concentrations, indicating the importance of factors other than the solvent (e.g. mol wt). With respect to the fish embryo test, results indicate that DMSO may be used without complications as a solvent, however, only at a maximum concentration of 0.01% (0.1 mL/L) as already indicated in the OECD difficult substances paper (OECD, 2000).

Development and characterization of nanostructured mists with potential for actively targeting poorly water-soluble compounds into the lungs

PURPOSE

To formulate nanoemulsions (NE) with potential for delivering poorly water-soluble drugs to the lungs.

METHOD

A self nanoemulsifying composition consisting of cremophor RH 40, PEG 400 and labrafil M 2125 CS was selected after screening potential excipients. The solubility of carbamazepine, a poorly water-soluble drug, was tested in the formulation components. Oil-in-water (o/w) NEs were characterized using dynamic light scattering, electrophoretic light scattering, transmission electron microscopy (TEM) and differential scanning calorimetry. NEs were nebulized into a mist using a commercial nebulizer and characterized using laser diffraction and TEM. An aseptic method was developed for preparing sterile NEs. Biocompatibility of the formulation was evaluated on NIH3T3 cells using MTT assay. In vitro permeability of the formulation was tested in zebra fish eggs, HeLa cells, and porcine lung tissue.

RESULTS

NEs had neutrally charged droplets of less than 20 nm size. Nebulized NEs demonstrated an o/w nanostructure. The mist droplets were of size less than 5 μm. Sterility testing and cytotoxicity results validated that the NE was biocompatible and sterile. In vitro tests indicated oil nanodroplets penetrating intracellularly through biological membranes.

CONCLUSION

The nanoemulsion mist has the potential for use as a pulmonary delivery system for poorly water-soluble drugs.

Microinjecting holo-aequorin into dechorionated and intact zebrafish embryos

The injection of holo-aequorin into embryos at the one-cell stage, along with the use of a simple photomultiplier tube or luminescence imaging system, allows transient localized elevations of free cytosolic Ca(2+) to be recorded and observed during the first 24 h of zebrafish development. The technique for loading dechorionated or intact one-cell stage zebrafish embryos with holo-aequorin is described here.

Effects of nanotoxicity on female reproductivity and fetal development in animal models

The extensive application of nanomaterials in industry, medicine and consumer products has raised concerns about their potential toxicity. The female population is particularly vulnerable and deserves special attention because toxicity in this group may impact both female reproductivity and fetal development. Mouse and zebrafish models each have their own unique features and studies using these models to examine the potential toxicity of various nanoparticles are compared and summarized in this review. Several nanoparticles exhibit detrimental effects on female reproductivity as well as fetal development, and these adverse effects are related to nanoparticle composition, surface modification, dose, exposure route and animal species. Limited studies on the mechanisms of nanotoxicity are also documented and reviewed herein.

Evaluation of nephrotoxic effects of mycotoxins, citrinin and patulin, on zebrafish (Danio rerio) embryos

Citrinin (CTN) and patulin (PAT) are fungal secondary metabolites which are found in food and feed and showed organotoxicity in mature animals. In this study zebrafish embryos were applied to investigate the developmental toxicity of CTN and PAT on embryonic kidney. In the presence of CTN and PAT, the gross morphology of kidneys from embryos with green fluorescent kidney (wt1b:GFP) was not apparently altered. Histological analysis of CTN-treated embryos indicated cystic glomerular and tubular lesions; a disorganized arrangement of renal cells was also found in the PAT-treated group. From the view point of renal function, dextran clearance abilities of embryos exposed to CTN and PAT were significantly reduced. The damaged renal function caused by CTN could be partially rescued by the administration of pentoxifylline, suggesting the reduction of glomerular blood flow contributes to CTN-induced renal dysfunction. Additionally, CTN induced the expression of proinflammation genes, including COX2a, TNF-α and IL-1β, but failed to modify the levels and distribution of wt1a transcript and Na(+)/K(+)-ATPase protein. In summary, CTN and PAT caused profound nephrotoxicity in histological structure and biological function of zebrafish embryos; the inflammatory pathway and blood rheology may involve in CTN-induced renal impairment.

High content screening in zebrafish speeds up hazard ranking of transition metal oxide nanoparticles

Zebrafish is an aquatic organism that can be used for high content safety screening of engineered nanomaterials (ENMs). We demonstrate, for the first time, the use of high content bright-field and fluorescence-based imaging to compare the toxicological effect of transition metal oxide (CuO, ZnO, NiO, and Co(3)O(4)) nanoparticles in zebrafish embryos and larvae. High content bright-field imaging demonstrated potent and dose-dependent hatching interference in the embryos, with the exception of Co(3)O(4) which was relatively inert. We propose that the hatching interference was due to the shedding of Cu and Ni ions, compromising the activity of the hatching enzyme, ZHE1, similar to what we previously proposed for Zn(2+). This hypothesis is based on the presence of metal-sensitive histidines in the catalytic center of this enzyme. Co-introduction of a metal ion chelator, diethylene triamine pentaacetic acid (DTPA), reversed the hatching interference of Cu, Zn, and Ni. While neither the embryos nor larvae demonstrated morphological abnormalities, high content fluorescence-based imaging demonstrated that CuO, ZnO, and NiO could induce increased expression of the heat shock protein 70:enhanced green fluorescence protein (hsp70:eGFP) in transgenic zebrafish larvae. Induction of this response by CuO required a higher nanoparticle dose than the amount leading to hatching interference. This response was also DTPA-sensitive. We demonstrate that high content imaging of embryo development, morphological abnormalities, and HSP70 expression can be used for hazard ranking and determining the dose-response relationships leading to ENM effects on the development of the zebrafish embryo.