Evaluation of 14 organic solvents and carriers for screening applications in zebrafish embryos and larvae

Toxicity of water-soluble polymers polyethylene glycol and polyvinyl alcohol for fish and frog embryos

Personal Care Products (PCPs) have been one of the most studied chemicals in the last twenty years since they were identified as pseudo-persistent pollutants by the European Union in the early 2000s. The accumulation of PCPs in the aquatic environment and their effects on non-target species make it necessary to find new, less harmful, substances. Polyethylene glycol (PEGs) and polyvinyl alcohol (PVAs) are two polymers that have increased their presence in the composition of PCPs in recent years, but little is known about the effect of their accumulation in the environment on non-target species. Through embryotoxicity tests on two common models of aquatic organisms (Danio rerio and Xenopus laevis), this work aims to increase the knowledge of PEGs and PVAs' effects on non-target species. Animals were exposed to the pollutant for 96 h. The main embryotoxicity endpoint (mortality, hatching, malformations, heartbeat rate) was recorded every 24 h. The most significant results were hatching delay in Danio rerio exposed to both chemicals, in malformations (oedema, body malformations, changes in pigmentation and deformations of spine and tail) in D. rerio and X. laevis and significant change in the heartbeat rate (decrease or increase in the rate) in both animals for all chemicals tested.

The influence of copper-doped mesoporous bioactive nanospheres on the temperature rise during polymerization, polymer cross-linking density, monomer release and embryotoxicity of dental composites

OBJECTIVES

Composites with copper-doped mesoporous bioactive nanospheres (Cu-MBGN) were developed to prevent secondary caries by imparting antimicrobial and ion-releasing/remineralizing properties.

METHODS

Seven experimental composites containing 1, 5 or 10 wt% Cu-MBGN, the corresponding inert controls (silica) and bioactive controls (bioactive glass 45S5) were prepared. The temperature rise during light curing, cross-linking density by ethanol softening test, monomer elution and their potential adverse effects on the early development of zebrafish Danio rerio was investigated.

RESULTS

Materials combining Cu-MBGN and silica showed the highest resistance to ethanol softening, as did the bioactive controls. Cu-MBGN composites showed significant temperature rise and reached maximum temperature in the shortest time. Bisphenol A was not detected, while bis-GMA was found only in the control materials and TEGDMA in the eluates of all materials. There was no increase in zebrafish mortality and abnormality rates during exposure to the eluates of any of the materials.

CONCLUSIONS

The composite with 5 wt% Cu-MBGN combined with nanosilica fillers showed the lowest ethanol softening, indicating the polymer's highest durability and cross-linking density. Despite the TEGDMA released from all tested materials, no embryotoxic effect was observed.

The potential of zebrafish as drug discovery research tool in immune-mediated inflammatory disease

Immune-mediated inflammatory disease (IMID) prevalence is estimated at 3-7% for Westernised populations, with annual incidence reported at almost 1 in 100 people globally. More recently, drug discovery approaches have been evolving towards more targeted therapies with an improved long-term safety profile, while the requirement for individualisation of medicine in complex conditions such as IMIDs, is acknowledged. However, existing preclinical models-such as cellular and in vivo mammalian models-are not ideal for modern drug discovery model requirements, such as real-time in vivo visualisation of drug effects, logistically feasible safety assessment over the course of a lifetime, or dynamic assessment of physiological changes during disease development. Zebrafish share high homology with humans in terms of proteins and disease-causing genes, with high conservation of physiological processes at organ, tissue, cellular and molecular level. These and other unique attributes, such as high fecundity, relative transparency and ease of genetic manipulation, positions zebrafish as the next major role player in IMID drug discovery. This review provides a brief overview of the suitability of this organism as model for human inflammatory disease and summarises the range of approaches used in zebrafish-based drug discovery research. Strengths and limitations of zebrafish as model organism, as well as important considerations in research study design, are discussed. Finally, under-utilised avenues for investigation in the IMID context are highlighted.

Impact of Mycotoxin Metabolites Deepoxy-Deoxynivalenol and Beta-Zearalenol on Bovine Preimplantation Embryo Development in the Presence of Acetonitrile

The quality of animal feed is increasingly affected by weather conditions, high humidity, and damage to grains, which have led to various mycotoxin-producing moulds. The aim of this study was to determine the effects of the combination of deepoxy-deoxynivalenol and beta-zearalenol on the development of preimplantation bovine embryos, the extent to which the presence of both mycotoxin metabolites affects the development of in vitro cultured bovine embryos, or whether the effect of both toxins enhances embryotoxicity. Ovaries were transported from the abattoir to the laboratory and, after maturation and fertilisation, zygotes were placed in an embryo culture medium (IVC) with different mycotoxin metabolite concentrations diluted in acetonitrile. It was found that the blastocyst rate of cleaved embryos was affected by 1 μL acetonitrile in 400 μL medium (0.25%) compared to the group without acetonitrile. For this reason, it was decided to use acetonitrile as a control group, and the desired mycotoxin metabolite concentrations were diluted in the lowest possible amount of acetonitrile (0.5 μL) that could be accurately added to the study groups. There was no statistical difference when the higher mycotoxin metabolite concentrations were added.

UV filter benzophenone-2: Effects on zebrafish (Danio rerio) cytochrome P450

Benzophenone-2 (2,2', 4,4'- Tetrahydroxybenzophenone; BP-2) is widely used as a sunscreen in Personal and Care Products (PCPs) for protection against ultraviolet (UV) radiation. The effects of BP-2 on random-sex adult zebrafish (Danio rerio) cytochrome P450 (CYP450) were studied. The main goal was to investigate the detoxification mechanisms underlying the adverse consequences of exposure to xenobiotic chemicals such as BP-2. Total protein content, CYP450 content, and erythromycin N-demethylase (ERND) activity were evaluated as indicators of protein CYP3A expression. Five sets of pooled random-sex adult zebrafish were exposed to 0.0, 0.1, 5.0, and 10.0 mg/L of BP-2 to evaluate their acute and chronic toxicity (4 and 15 days, respectively). ERND activity was significantly increased in the chronic toxicity group compared to that in the control group, whereas CYP450 remained unchanged. The results suggest a sufficiently fast catalytic process that does not alter the total CYP450 content. It implies a mediation of CYP450 3A induction by BP-2 and the pregnane X receptor ligand-binding domain (PXR LBD) interaction. Ligand-protein interactions were confirmed via in silico docking with AutoDock Vina. Further computational studies indicate BP-2 potential binding affinity for the Estrogen receptor alpha ligand binding domain (ERα LBD). These results suggest that CYPs effects may result in significant toxicity in the zebrafish. Our study highlights the importance of studying biomarkers in aquatic organisms to assess xenobiotic exposure and the potential toxicity of UV filters to humans.

Toxicity of UV Filter Benzophenone-3 in Brine Shrimp Nauplii (Artemia salina) and Zebrafish (Danio rerio) Embryos

The benzophenone (BP) family, including oxybenzone (BP-3), a prevalent sunscreen ingredient and environmental contaminant, has raised concerns since the year 2005. This study investigated oxybenzone toxicity in zebrafish (Danio rerio) eleutheroembryos and brine shrimp (Artemia salina) nauplii, focusing on the LC50 and developmental impacts. Zebrafish embryos (0.100-1.50 mg/L BP-3, 96 h) and A. salina (0.100-5.00 mg/L BP-3, 48 h) were tested with ultrasound-assisted emulsified liquid-phase microextraction (UA-ELPME) used for zebrafish tissue analysis. HPLC-DAD determined BP-3 concentrations (highest: 0.74 ± 0.13 mg/L). Although no significant zebrafish embryo mortality or hatching changes occurred, developmental effects were evident. Lethal concentrations were determined (A. salina LC50 at 24 h = 3.19 ± 2.02 mg/L; D. rerio embryos LC50 at 24 h = 4.19 ± 3.60 mg/L), with malformations indicating potential teratogenic effects. A. salina displayed intestinal tract alterations and D. rerio embryos exhibited pericardial edema and spinal deformities. These findings highlight oxybenzone's environmental risks, posing threats to species and ecosystem health.

Cardiac and neurobehavioral impairments in three phylogenetically distant aquatic model organisms exposed to environmentally relevant concentrations of boscalid

Boscalid (2-Chloro-N-(4'-chlorobiphenyl-2-yl) nicotinamide), a pyridine carboxamide fungicide, is an inhibitor of the complex II of the respiration chain in fungal mitochondria. As boscalid is only moderately toxic for aquatic organisms (LC50 > 1-10 mg/L), current environmental levels of this compound in aquatic ecosystems, in the range of ng/L-μg/L, are considered safe for aquatic organisms. In this study, we have exposed zebrafish (Danio rerio), Japanese medaka (Oryzias latipes) and Daphnia magna to a range of concentrations of boscalid (1-1000 μg/L) for 24 h, and the effects on heart rate (HR), basal locomotor activity (BLA), visual motor response (VMR), startle response (SR), and habituation (HB) to a series of vibrational or light stimuli have been evaluated. Moreover, changes in the profile of the main neurotransmitters have been determined. Boscalid altered HR in a concentration-dependent manner, leading to a positive or negative chronotropic effect in fish and D. magna, respectively. While boscalid decreased BLA and increased VMR in Daphnia, these behaviors were not altered in fish. For SR and HB, the response was more species- and concentration-specific, with Daphnia exhibiting the highest sensitivity. At the neurotransmission level, boscalid exposure decreased the levels of L-aspartic acid in fish larvae and increased the levels of dopaminergic metabolites in D. magna. Our study demonstrates that exposure to environmental levels of boscalid alters cardiac activity, impairs ecologically relevant behaviors, and leads to changes in different neurotransmitter systems in phylogenetically distinct vertebrate and invertebrate models. Thus, the results presented emphasize the need to review the current regulation of this fungicide.

Toxicity of organic solvents and surfactants to the sea urchin embryos

A comparative toxicity of widely applied organic solvents (methanol, ethanol, n-propanol, i-propanol, n-butanol, 2-butanol, i-butanol, t-butanol, 3-methoxy-3-methylbutanol-1 (MMB), ethylene glycol, diethylene glycol, 2-methoxyethanol, 2-ethoxyethanol, glycerol, ethyl acetate, acetonitrile, benzene, dioxane, dimethylformamide, dimethylacetamide, dimethylsulfoxide, 2-pyrrolidone, and N-methyl-2-pyrrolidone) and surfactants (PEG 300, PEG 6000, Tween 20, Tween 80, miramistin, and Cremophor EL) was studied using a sea urchin embryo model. Sea urchin embryo morphological alterations caused by the tested chemicals were described. The tested molecules affected P. lividus embryo development in a concentration-dependent manner. The observed phenotypic anomalies ranged from developmental delay and retardation of plutei growth to formation of aberrant blastules and gastrules, cleavage alteration/arrest, and embryo mortality. Discernible morphological defects were found after embryo exposure with common pharmaceutical ingredients, such as glycerol, Tween 80, and Cremophor EL. In general, solvents were less toxic than surfactants. PEG 6000 PEG 300, DMSO, ethanol, and methanol were identified as the most tolerable compounds with minimum effective concentration (MEC) values of 3.0-7.92 mg/mL. Previously reported MEC value of Pluronic F127 (4.0 mg/mL) fell within the same concentration range. Toxic effects of methanol, ethanol, DMSO, 2-methoxyethanol, 2-ethoxyethanol, Tween 20, and Tween 80 on P. lividus embryos correlated well with their toxicity obtained using other cell and animal models. The sea urchin embryos could be considered as an appropriate test system for toxicity assessment of solvents and surfactants for their further application as solubilizers of hydrophobic molecules in conventional in vitro cell-based assays and in vivo mammalian models. Nevertheless, to avoid adverse effect of a solubilizing agent in ecotoxicological and biological experiments, the preliminary assessment of its toxicity on a chosen test model would be beneficial.

The tunicamycin derivative TunR2 exhibits potent antibiotic properties with low toxicity in an in vivo Mycobacterium marinum-zebrafish TB infection model

Tunicamycins (TUN) are well-defined, Streptomyces-derived natural products that inhibit protein N-glycosylation in eukaryotes, and by a conserved mechanism also block bacterial cell wall biosynthesis. TUN inhibits the polyprenylphosphate-N-acetyl-hexosamine-1-phospho-transferases (PNPT), an essential family of enzymes found in both bacteria and eukaryotes. We have previously published the development of chemically modified TUN, called TunR1 and TunR2, that have considerably reduced activity on eukaryotes but that retain the potent antibacterial properties. A mechanism for this reduced toxicity has also been reported. TunR1 and TunR2 have been tested against mammalian cell lines in culture and against live insect cells but, until now, no in vivo evaluation has been undertaken for vertebrates. In the current work, TUN, TunR1, and TunR2 are investigated for their relative toxicity and antimycobacterial activity in zebrafish using a well-established Mycobacterium marinum (M. marinum) infection system, a model for studying human Mycobacterium tuberculosis infections. We also report the relative ability to activate the unfolded protein response (UPR), the known mechanism for the eukaryotic toxicity observed with TUN treatment. Importantly, TunR1 and TunR2 retained their antimicrobial properties, as evidenced by a reduction in M. marinum bacterial burden, compared to DMSO-treated zebrafish. In summary, findings from this study highlight the characteristics of recently developed TUN derivatives, mainly TunR2, and its potential for use as a novel anti-bacterial agent for veterinary and potential medical purposes.

Polystyrene microplastics effects on zebrafish embryological development: Comparison of two different sizes

Microplastics have become a great worldwide problem and it's therefore important to study their possible effects on human and environmental health. In this study, zebrafish embryos were used to compare two different sizes of polystyrene microplastics (PS-MPs), 1 µm and 3 µm respectively, at 0.01, 0.1, 1.0 and 10.0 mgL-1, and were monitored up to 72 h. Toxicity tests demonstrated that neither of the PS-MPs altered the embryos' survival and the normal hatching process. Instead, higher concentrations of both sizes caused an increase of the heart rate and phenotypic changes. The PS-MPs of both sizes entered and accumulated in the larvae at the concentration of 10.0 mgL-1 and the same concentration caused an increase of apoptotic processes correlated to redox homeostasis changes. The reported results give a realistic view of the negative effects of exposure to PS-MPs and provide new information on their toxicity, also considering their sizes.

1H NMR metabolomics insights into comparative diabesity in male and female zebrafish and the antidiabetic activity of DL-limonene

Zebrafish have been utilized for many years as a model animal for pharmacological studies on diabetes and obesity. High-fat diet (HFD), streptozotocin and alloxan injection, and glucose immersion have all been used to induce diabetes and obesity in zebrafish. Currently, studies commonly used both male and female zebrafish, which may influence the outcomes since male and female zebrafish are biologically different. This study was designed to investigate the difference between the metabolites of male and female diabetic zebrafish, using limonene - a natural product which has shown several promising results in vitro and in vivo in treating diabetes and obesity-and provide new insights into how endogenous metabolites change following limonene treatment. Using HFD-fed male and female zebrafish, we were able to develop an animal model of T2D and identify several endogenous metabolites that might be used as diagnostic biomarkers for diabetes. The endogenous metabolites in males and females were different, even though both genders had high blood glucose levels and a high BMI. Treatment with limonene prevented high blood glucose levels and improved in diabesity zebrafish by limonene, through reversal of the metabolic changes caused by HFD in both genders. In addition, limonene was able to reverse the elevated expression of AKT during HFD.

Preclinical toxicological assessment of polydatin in zebrafish model

Polydatin (3,4',5-trihydroxystilbene-3-β-D-glucoside, piceid), a natural stilbenoid found in different plant sources, has gained increasing attention for its potential health benefits. However, prior to its widespread adoption in human therapeutics and consumer products, a comprehensive investigation of its toxicological effects is crucial. In this study, the toxicity of polydatin was investigated in a developmental toxicity test using zebrafish (Danio rerio) as a valuable model for preclinical assessments. We employed the Fish Embryo Test (FET test - OECD n°236) to investigate the effects of polydatin on survival, hatchability, development, and behavior of zebrafish embryo-larval stage. Remarkably, the results demonstrated that polydatin up to 435 μM showed no toxicity. Throughout the exposure period, zebrafish embryos exposed to polydatin exhibited normal development, with no significant mortality observed. Furthermore, hatching success and heartbeat rate were unaffected, and no morphological abnormalities were identified, signifying a lack of teratogenic effects and cardiotoxicity. Locomotion activity assessment revealed normal swimming patterns and response to stimuli, indicating no neurotoxic effects. Our study provides valuable insights into the toxicological profile of polydatin, suggesting that it may offer potential therapeutic benefits under a considerable concentration range. In addition, zebrafish model proves to be an efficient system for early-stage toxicological screening, guiding further investigations into the secure utilization of polydatin for human health and wellness.

Identification and pretreatment analysis of endogenous degradation products of patulin in zebrafish

Identification and pretreatment analysis of endogenous metabolites of patulin (PAT) in zebrafish were successfully carried out using UHPLC-Q-Orbitrap-HRMS. Three major metabolites, namely hydroascladiol, E-ascladiol, and Z-ascladiol, were identified. They exhibited similar fragmentation pathways to PAT, with the structurally significant ions *b' and *c' generated through the cleavage of the side chains of *b and *c, respectively. These ions were crucial for confirming the modification site and have been confirmed as characteristic fragments for the identification of PAT metabolites. Furthermore, a pretreatment method for analyzing PAT and the three metabolites in zebrafish was proposed, using solid-phase-assisted liquid/liquid extraction (SLLE) and matrix solid-phase dispersion (MSPD) techniques. The initial purification process involved loading the aqueous phase onto a macroporous diatomaceous column, followed by elution with acetonitrile. Following this, neutral alumina powder was added to the organic phase, effectively eliminating interference from hydrophilic and lipid-soluble compounds through the optimization of this step. Due to their structural similarity, the three metabolites were semi-quantitatively analyzed using a PAT standard curve. The results demonstrated a good linear relationship in the concentration range of 0.001-0.02 μg/mL (r2 ≥ 0.999). The limit of detection for PAT and the three metabolites ranged from 0.01 to 0.03 mg/kg.

Lipidomic profiling study on neurobehavior toxicity in zebrafish treated with aflatoxin B1

Mycotoxin aflatoxin B1 (AFB1) has been proven to cause neurotoxicity, but its potential interference with the normal function of brain tissue is not fully defined. As the indispensable role of lipids in maintaining the normal function of brain tissue, the aim of this study is to clarify the effect of AFB1 short-term (7 days) exposure on brain tissue from the perspective of lipid metabolism. In this study, zebrafish were exposed to two concentrations (5, 20 μg/L). Through quantitative analysis of AFB1, the detection of AFB1 in zebrafish brain tissue was discovered for the first time, combined with the changes in zebrafish neurobehavior, the occurrence of brain injury was deduced. Subsequently, 1734 lipids in zebrafish brain tissue were mapped using ion mobility time-of-flight mass spectrometry (UPLC-QTOF-IMS-MS), which has great advantages in lipid detection. Comparative analysis of the abnormal lipid metabolism in zebrafish brain revealed 114 significantly changed lipids, mainly involving two pathways of sphingolipid metabolism and fatty acid degradation. This study discovered the detection of AFB1 in the brain and revealed a potential link between AFB1-induced behavioral abnormalities and lipid metabolism disorders in brain tissue, providing reliable evidence for elucidating the neurotoxicity of AFB1.

Clomiphene Citrate and Enclomiphene Hydrochloride Exposure Is Associated With Interfrontal Suture Fusion in Zebrafish

Background: The last several decades have witnessed an increase in metopic craniosynostosis incidence. Population-based studies suggest that pharmacological exposure in utero may be responsible. This study examined effects of the fertility drug clomiphene citrate (CC) on calvarial development in an established model for craniofacial development, the zebrafish Danio rerio. Results: Zebrafish larvae were exposed to clomiphene citrate or its isomer enclomiphene for five days at key points during calvarial development. Larvae were then raised to adulthood in normal rearing water. Zebrafish were analyzed using whole-mount skeletal staining. We observed differential effects on survivability, growth and suture formation depending on the treatment. Treatments with CC or enclomiphene at 5.5 mm SL led to increased fusion of the interfrontal suture (p < .01) compared to controls. Conclusions: Exposure to fertility drugs appears to affect development of the cranial vault, specifically the interfrontal suture, in zebrafish. Further research is required to identify the signaling mechanisms at play. This work suggests that fertility drug treatment may contribute to the increased incidence of metopic craniosynostosis observed globally.

Comparative analysis between zebrafish and an automated live-cell assay to classify developmental neurotoxicant chemicals

Modern toxicology's throughput has dramatically increased due to alternative models, laboratory automation, and machine learning. This has enabled comparative studies across species and assays to prioritize chemical hazard potential and to understand how different model systems might complement one another. However, such comparative studies of high-throughput data are still in their infancy, with more groundwork needed to firmly establish the approach. Therefore, this study aimed to compare the bioactivity of the NIEHS Division of Translational Toxicology's (DTT) 87-compound developmental neurotoxicant (DNT) library in zebrafish and an in vitro high-throughput cell culture system. The early life-stage zebrafish provided a whole animal approach to developmental toxicity assessment. Chemical hits for abnormalities in embryonic zebrafish morphology, mortality, and behavior (ZBEscreen™) were compared with chemicals classified as high-risk by the Cell Health Index (CHI™), which is an outcome class probability from a machine learning classifier using 12 parameters from the SYSTEMETRIC® Cell Health Screen (CHS). The CHS was developed to assess human toxicity risk using supervised machine learning to classify acute cell stress phenotypes in a human leukemia cell line (HL60 cells) following a 4-h exposure to a chemical of interest. Due to the design of the screen, the zebrafish assays were more exhaustive, yielding 86 total bioactive hits, whereas the SYSTEMETRIC® CHS focusing on acute toxicity identified 20 chemicals as potentially toxic. The zebrafish embryonic and larval photomotor response assays (EPR and LPR, respectively) detected 40 of the 47 chemicals not found by the zebrafish morphological screen and CHS. Collectively, these results illustrate the advantages of using two alternative models in tandem for rapid hazard assessment and chemical prioritization and the effectiveness of CHI™ in identifying toxicity within a single multiparametric assay.

Metastable Amorphous Dispersions of Hydrophobic Naphthalene Compounds Can Be Formed in Water without Stabilizing Agents via the "Ouzo Effect"

Hydrophobic molecules dissolved in water-miscible organic solvents are used in vitro for biological membrane studies and for testing of potential pharmaceuticals in high-throughput screenings. When these solutions are introduced into an aqueous environment, it is possible that metastable "ouzo-like" dispersions form from liquid-liquid phase separation. It is therefore hypothesized that when solutions of naphthalene compounds in water-miscible solvents are added to water, metastable dispersions will form. Millimolar solutions of naphthalene, N-phenyl-1-naphthylamine (NPN), 1-aminonaphthalene, 1-iodonaphthalene (INAP), 1,4-dimethoxynaphthalene, and 1-naphthol were prepared in either dimethyl sulfoxide, ethanol, or acetone at concentrations similar to those used in biological membrane studies. Each solution was diluted 10-fold in water. Particle formation was characterized by qualitative observations, dynamic light-scattering, nephelometry, and optical microscopy. It was discovered that two of the compounds tested made metastable dispersions: INAP and NPN. The initial particle sizes were ∼400 nm (radius), with turbidity ranging from 1,000 to 20,000 NTU, depending on the initial concentrations used. Fluorescence microscopy imaging showed spherical particles that do not aggregate while under observation. Slow-nucleating crystallization occurs over days, presumably from a heterogeneous nucleation process. The formation of these dispersions has implications for in vitro delivery of hydrophobic molecules to biological membranes.

A Short Review of the Toxicity of Dentifrices-Zebrafish Model as a Useful Tool in Ecotoxicological Studies

This review aims to summarize the literature data regarding the effects of different toothpaste compounds in the zebrafish model. Danio rerio provides an insight into the mechanisms of the ecotoxicity of chemicals as well as an assessment of their fate in the environment to determine long-term environmental impact. The regular use of adequate toothpaste with safe active ingredients possessing anti-bacterial, anti-inflammatory, anti-oxidant, and regenerative properties is one of the most effective strategies for oral healthcare. In addition to water, a typical toothpaste consists of a variety of components, among which three are of predominant importance, i.e., abrasive substances, fluoride, and detergents. These ingredients provide healthy teeth, but their environmental impact on living organisms are often not well-known. Each of them can influence a higher level of organization: subcellular, cellular, tissue, organ, individual, and population. Therefore, it is very important that the properties of a chemical are detected before it is released into the environment to minimize damage. An important part of a chemical risk assessment is the estimation of the ecotoxicity of a compound. The zebrafish model has unique advantages in environmental ecotoxicity research and has been used to study vertebrate developmental biology. Among others, the advantages of this model include its external, visually accessible development, which allows for providing many experimental manipulations. The zebrafish has a significant genetic similarity with other vertebrates. Nevertheless, translating findings from zebrafish studies to human risk assessment requires careful consideration of these differences.

A fish perspective on SARS-CoV-2: Toxicity of benzalkonium chloride on Danio rerio

SARS-CoV-2 outbreak led to an increased marketing of disinfectants, creating a potential environmental problem. For instance, pre-pandemic environmental levels of the disinfectant benzalkonium chloride (BAC) ranging from 0.5 to 5 mgL-1 in effluents were expected to further increase threatening aquatic life. Our aim was to characterize potential adverse effects after an acute exposure of zebrafish to different concentrations of BAC. An increase in the overall swimming activity, thigmotaxis behavior, and erratic movements were observed. An increase in CYP1A1 and catalase activities, but inhibitions of CY1A2, GSTs and GPx activities were also noticed. BAC is metabolized by CYP1A1, increasing the production of H2O2, thereby activating the antioxidant enzyme CAT. Data also showed an increase of AChE activity. Our study highlights adverse embryonic, behavioral, and metabolic effects of noteworthy environmental significance, especially considering that the use and release of BAC is most likely to increase in a near future.

Zebrafish as a robust preclinical platform for screening plant-derived drugs with anticonvulsant properties-a review

Traditionally, selected plant sources have been explored for medicines to treat convulsions. This continues today, especially in countries with low-income rates and poor medical systems. However, in the low-income countries, plant extracts and isolated drugs are in high demand due to their good safety profiles. Preclinical studies on animal models of seizures/epilepsy have revealed the anticonvulsant and/or antiepileptogenic properties of, at least some, herb preparations or plant metabolites. Still, there is a significant number of plants known in traditional medicine that exert anticonvulsant activity but have not been evaluated on animal models. Zebrafish is recognized as a suitable in vivo model of epilepsy research and is increasingly used as a screening platform. In this review, the results of selected preclinical studies are summarized to provide credible information for the future development of effective screening methods for plant-derived antiseizure/antiepileptic therapeutics using zebrafish models. We compared zebrafish vs. rodent data to show the translational value of the former in epilepsy research. We also surveyed caveats in methodology. Finally, we proposed a pipeline for screening new anticonvulsant plant-derived drugs in zebrafish ("from tank to bedside and back again").

Influence of Methylene Blue or Dimethyl Sulfoxide on Larval Zebrafish Development and Behavior

The use of larval zebrafish developmental testing and assessment, specifically larval zebrafish locomotor activity, has been recognized as a higher throughput testing strategy to identify developmentally toxic and neurotoxic chemicals. There are, however, no standardized protocols for this type of assay, which could result in confounding variables being overlooked. Two chemicals commonly employed during early-life stage zebrafish assays, methylene blue (antifungal agent) and dimethyl sulfoxide (DMSO, a commonly used vehicle) have been reported to affect the morphology and behavior of freshwater fish. In this study, we conducted developmental toxicity (morphology) and neurotoxicity (behavior) assessments of commonly employed concentrations for both chemicals (0.6-10.0 μM methylene blue; 0.3%-1.0% v/v DMSO). A light-dark transition behavioral testing paradigm was applied to morphologically normal, 6 days postfertilization (dpf) zebrafish larvae kept at 26°C. Additionally, an acute DMSO challenge was administered based on early-life stage zebrafish assays typically used in this research area. Results from developmental toxicity screens were similar between both chemicals with no morphological abnormalities detected at any of the concentrations tested. However, neurodevelopmental results were mixed between the two chemicals of interest. Methylene blue resulted in no behavioral changes up to the highest concentration tested, 10.0 μM. By contrast, DMSO altered larval behavior following developmental exposure at concentrations as low as 0.5% (v/v) and exhibited differential concentration-response patterns in the light and dark photoperiods. These results indicate that developmental DMSO exposure can affect larval zebrafish locomotor activity at routinely used concentrations in developmental neurotoxicity assessments, whereas methylene blue does not appear to be developmentally or neurodevelopmentally toxic to larval zebrafish at routinely used concentrations. These results also highlight the importance of understanding the influence of experimental conditions on larval zebrafish locomotor activity that may ultimately confound the interpretation of results.

Optimization and calibration of behavioural tests on different species of planaria for ecotoxicological studies

Freshwater planarian are emerging as a valuable in vivo model for (eco) toxicological studies, but the lack of harmonization of procedures between laboratories remains a challenge. This study aimed to optimize, automate and select the best behavioural tests and analyse the potential of different planarian species as models for toxicological assessment. We implemented four tests: exploration, photomotor response, Tapping and Planarian Light Dark Test, on different planaria species using the DanioVision system. We conclude that the exploration assay performed in 24 wellplate at 10 000 lux is the one that is robust and reliable for toxicological studies with planaria. Dugesia japonica and Schmidtea mediterranea have proved to be sensitive models for toxicological screening of organophosphorus pesticides through behavioural analysis. Under necessary experimental conditions, the motility baseline in controls, for both species allowed the detection of behavioural changes, making both good models for behavioural testing in (eco) toxicological context.

Metabolomics to study the sublethal effects of diazepam and irbesartan on glass eels (Anguilla anguilla)

Since glass eels are continuously exposed to contamination throughout their migratory journey in estuaries, to a certain extent the fall in the population of this endangered species might be attributed to this exposure, which is especially acute in estuaries under high urban pressure. In this work, metabolomics was used to address the main objective of this study, to evaluate the effects of two pharmaceuticals previously identified as potential concerning chemicals for fish (diazepam and irbesartan) on glass eels. An exposure experiment to diazepam, irbesartan and their mixture was carried out over 7 days followed by 7 days of depuration phase. After exposure, glass eels were individually sacrificed using a lethal bath of anesthesia, and then an unbiased sample extraction method was used to extract separately the polar metabolome and the lipidome. The polar metabolome was submitted to targeted and non-targeted analysis, whereas for the lipidome only the non-targeted analysis was carried out. A combined strategy using partial least squares discriminant analysis and univariate and multivariate statistical analysis (ANOVA, ASCA, t-test, and fold-change analysis) was used to identify the metabolites altered in the exposed groups with respect to the control group. The results of the polar metabolome analysis revealed that glass eels exposed to the diazepam-irbesartan mixture were the most impacted ones, with altered levels for 11 metabolites, some of them belonging to the energetic metabolism, which was confirmed to be sensitive to these contaminants. Additionally, the dysregulation of the levels of twelve lipids, most of them with energetic and structural functions, was also found after exposure to the mixture, which might be related to oxidative stress, inflammation, or alteration of the energetic metabolism.

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.

Refined high-content imaging-based phenotypic drug screening in zebrafish xenografts

Zebrafish xenotransplantation models are increasingly applied for phenotypic drug screening to identify small compounds for precision oncology. Larval zebrafish xenografts offer the opportunity to perform drug screens at high-throughput in a complex in vivo environment. However, the full potential of the larval zebrafish xenograft model has not yet been realized and several steps of the drug screening workflow still await automation to increase throughput. Here, we present a robust workflow for drug screening in zebrafish xenografts using high-content imaging. We established embedding methods for high-content imaging of xenografts in 96-well format over consecutive days. In addition, we provide strategies for automated imaging and analysis of zebrafish xenografts including automated tumor cell detection and tumor size analysis over time. We also compared commonly used injection sites and cell labeling dyes and show specific site requirements for tumor cells from different entities. We demonstrate that our setup allows us to investigate proliferation and response to small compounds in several zebrafish xenografts ranging from pediatric sarcomas and neuroblastoma to glioblastoma and leukemia. This fast and cost-efficient assay enables the quantification of anti-tumor efficacy of small compounds in large cohorts of a vertebrate model system in vivo. Our assay may aid in prioritizing compounds or compound combinations for further preclinical and clinical investigations.

Heart rate and behavioral responses in three phylogenetically distant aquatic model organisms exposed to environmental concentrations of carbaryl and fenitrothion

Carbaryl and fenitrothion are two insecticides sharing a common mode of action, the inhibition of the acetylcholinesterase (AChE) activity. Their use is now regulated or banned in different countries, and the environmental levels of both compounds in aquatic ecosystems have decreased to the range of pg/L to ng/L. As these concentrations are below the non-observed-adverse-effect-concentrations (NOAEC) for AChE inhibition reported for both compounds in aquatic organisms, there is a general agreement that the current levels of these two chemicals are safe for aquatic organisms. In this study we have exposed zebrafish, Japanese medaka and Daphnia magna to concentrations of carbaryl and fenitrothion under their NOAECs for 24-h, and the effects on heart rate (HR), basal locomotor activity (BLA), visual motor response (VMR), startle response (SR) and its habituation have been evaluated. Both pesticides increased the HR in the three selected model organisms, although the intensity of this effect was chemical-, concentration- and organism-dependent. The exposure to both pesticides also led to a decrease in BLA and an increase in VMR in all three species, although this effect was only significant in zebrafish larvae. For SR and its habituation, the response profile was more species- and concentration-specific. The results presented in this manuscript demonstrate that concentrations of carbaryl and fenitrothion well below their respective NOAECs induce tachycardia and the impairment of ecologically relevant behaviors in phylogenetically distinct aquatic model organisms, both vertebrates and invertebrates, emphasizing the need to include this range of concentrations in the environmental risk assessment.

Mass Spectroscopy as an Analytical Tool to Harness the Production of Secondary Plant Metabolites: The Way Forward for Drug Discovery

The molecular map of diverse biological molecules linked with structure, function, signaling, and regulation within a cell can be elucidated using an analytically demanding omic approach. The latest trend of using "metabolomics" technologies has explained the natural phenomenon of opening a new avenue to understand and enhance bioactive compounds' production. Examination of sequenced plant genomes has revealed that a considerable portion of these encodes genes of secondary metabolism. In addition to genetic and molecular tools developed in the current era, the ever-increasing knowledge about plant metabolism's biochemistry has initiated an approach for wisely designed, more productive genetic engineering of plant secondary metabolism for improved defense systems and enhanced biosynthesis of beneficial metabolites. Secondary plant metabolites are natural products synthesized by plants that are not directly involved with their average growth and development but play a vital role in plant defense mechanisms. Plant secondary metabolites are classified into four major classes: terpenoids, phenolic compounds, alkaloids, and sulfur-containing compounds. More than 200,000 secondary metabolites are synthesized by plants having a unique and complex structure. Secondary plant metabolites are well characterized and quantified by omics approaches and therefore used by humans in different sectors such as agriculture, pharmaceuticals, chemical industries, and biofuel. The aim is to establish metabolomics as a comprehensive and dynamic model of diverse biological molecules for biomarkers and drug discovery. In this chapter, we aim to illustrate the role of metabolomic technology, precisely liquid chromatography-mass spectrometry, capillary electrophoresis mass spectrometry, gas chromatography-mass spectrometry, and nuclear magnetic resonance spectroscopy, specifically as a research tool in the production and identification of novel bioactive compounds for drug discovery and to obtain a unified insight of secondary metabolism in plants.

Endogenous AhR agonist FICZ accumulates in rainbow trout (Oncorhynchus mykiss) alevins exposed to a mixture of two PAHs, retene and fluoranthene

Multiple studies have reported synergized toxicity of PAH mixtures in developing fish larvae relative to the additive effect of the components. From a toxicological perspective, multiple mechanisms are known to contribute to synergism, such as altered toxicodynamics and kinetics, as well as increased oxidative stress. An understudied contributor to synergism is the accumulation of endogenous metabolites, for example: the aryl hydrocarbon receptor 2 (AhR2) agonist and tryptophan metabolite 6-Formylindolo(3,2-b)carbazole (FICZ). Fish larvae exposed to FICZ, alongside knock-down of cytochrome p450 (cyp1a), has been reported to induced symptoms of toxicity similar to those observed following exposure to PAHs or the dioxin 2,3,7,8-tetrachlorodibenzo-p-dioxin. Here, we explored if FICZ accumulates in newly hatched rainbow trout alevins (Oncorhynchus mykiss) exposed to two PAHs with different properties: retene (potent AhR2 agonist) and fluoranthene (weak AhR2 agonist and Cyp1a inhibitor), either alone or as a binary mixture for 3 and 7 days. We found that exposure to the mixture resulted in accumulation of endogenous FICZ, synergized the blue sac disease index (BSD), and altered the body burden profiles of the PAHs, when compared to the alevins exposed to the individual components. It is thus very plausible that accumulation of endogenously derived FICZ contributed to the synergized BSD index and toxicity in exposed alevins. Accumulation of endogenously derived FICZ is a novel finding that extends our general understanding on PAHs toxicity in developing fish larvae, while at the same time highlighting why environmental risk assessment of PAHs should not be based solely results from the assessment of individual compounds.

Prioritization based on risk assessment to study the bioconcentration and biotransformation of pharmaceuticals in glass eels (Anguilla anguilla) from the Adour estuary (Basque Country, France)

The presence of contaminants of emerging concern in the aquatic environment directly impacts water-living organisms and can alter their living functions. These compounds are often metabolized and excreted, but they can also be accumulated and spread through the food chain. The metabolized contaminants can also lead to the formation of new compounds with unknown toxicity and bioaccumulation potential. In this work, we have studied the occurrence, bioconcentration, and biotransformation of CECs in glass eels (Anguilla anguilla) using UHPLC-HRMS. To select the target CECs, we first carried out an environmental risk assessment of the WWTP effluent that releases directly into the Adour estuary (Bayonne, Basque Country, France). The risk quotients of every detected contaminant were calculated and three ecotoxicologically relevant contaminants were chosen to perform the exposure experiment: propranolol, diazepam, and irbesartan. An experiment of 14 days consisting of 7 days of exposure and 7 days of depuration was carried out to measure the bioconcentration of the chosen compounds. The quantitative results of the concentrations in glass eel showed that diazepam and irbesartan reached BCF ≈10 on day 7, but both compounds were eliminated after 7 days of depuration. On the other hand, propranolol's concentration remains constant all along with the experiment, and its presence can be detected even in the non-exposed control group, which might suggest environmental contamination. Two additional suspect screening strategies were used to identify metabolization products of the target compounds and other xenobiotics already present in wild glass eels. Only one metabolite was identified, nordiazepam, a well-known diazepam metabolite, probably due to the low metabolic rate of glass eels at this stage. The xenobiotic screening confirmed the presence of more xenobiotics in wild glass eels, prominent among them, the pharmaceuticals exemestane, primidone, iloprost, and norethandrolone.

Neurotoxicity of nanoparticles: Insight from studies in zebrafish

Nanoparticles are widely used in industry and personal care, and they inevitably end up in people's bodies and the environment. The widespread use of nanoparticles has raised new concerns about their neurotoxicity, as nanoparticles can enter the nervous system by blood-brain barrier. In neurotoxicity testing, the zebrafish provides powerful tools to overcome the limitations of other models. This paper will provide a comprehensive review of the power of zebrafish in neurotoxicity tests and the neurotoxic effects of nanoparticles, including inorganic, organic, and metal-based nanoparticles, on zebrafish from different perspectives. Such information can be used to predict not only the effects of nanoparticles on other species exposed to the aquatic environment but also the neurotoxicity of nanoparticles in humans.

Collagen-Sealed Polyester Vascular Prostheses Functionalized by Polycatecholamine Coatings

Collagen-sealed polyester (PET) prostheses are commonly used in reconstructive vascular surgery due to their self-sealing properties. To prevent post-surgical infection, different modification methods have been tested but so far none have showed long-term satisfactory efficiency. For this reason, in the present study, a commercial collagen-sealed PET prosthesis was coated by a highly adhesive poly (L-DOPA) layer maintaining the sealing protein without losing the original properties and functionality. This modified (as proven by SEM, FTIR, XPS and contact angle) graft exhibited comparable wettability and elasticity as pristine commercial graft, as well as reduced hemolysis-inducing effect, lowered toxicity against human endothelial cells and reduced toxicity in Danio rerio model. Poly (L-DOPA)-coated grafts were shown to bind six times more aminoglycoside antibiotic (gentamicin) than pristine graft. Poly (L-DOPA)-coated antibiotic-bound prostheses exhibited an improved antibacterial activity (bacterial growth inhibition and anti-adhesive capacity) in comparison with pristine antibiotic-bound graft. Overall, poly (L-DOPA)-coatings deposited on PET vascular grafts can effectively functionalize collagen-sealed prostheses without the loss of protein sealing layer and allow for antibiotics incorporation to provide higher safety in biomedical applications.

Multi-biomarker approach to evaluate the neurotoxic effects of environmentally relevant concentrations of phenytoin on adult zebrafish Danio rerio

Several studies have reported the presence of phenytoin (PHE) in wastewater treatment plant effluents, hospital effluents, surface water, and even drinking water. However, published studies on the toxic effects of PHE at environmentally relevant concentrations in aquatic organisms are scarce. The present study aimed to determine the effect of three environmentally relevant concentrations of PHE (25, 282, and 1500 ng L^-1) on behavioral parameters using the novel tank test. Moreover, we also aimed to determine whether or not these concentrations of PHE may impair acetylcholinesterase (AChE) activity and oxidative status in the brain of Danio rerio adults. Behavioral responses suggested an anxiolytic effect in PHE-exposed organisms, mainly observed in organisms exposed to 1500 ng L^-1, with a significant decrease in fish mobility and a significant increase in activity at the top of the tank. Besides the behavioral impairment, PHE-exposed fish also showed a significant increase in the levels of lipid peroxidation, hydroperoxides, and protein carbonyl content compared to the control group. Moreover, a significant increase in brain AChE levels was observed in fish exposed to 282 and 1500 ng L^-1. The results obtained in the present study show that PHE triggers a harmful response in the brain of fish, which in turn generates fish have an anxiety-like behavior.

Is Mixtures' Additivity Supported by Empirical Data? A Case Study of Developmental Toxicity of PFOS and 6:2 FTS in Wildtype Zebrafish Embryos

Per- and polyfluoroalkyl substances (PFASs) are a major priority for many federal and state regulatory agencies charged with monitoring levels of emerging contaminants in environmental media and setting health-protective benchmarks to guide risk assessments. While screening levels and toxicity reference values have been developed for numerous individual PFAS compounds, there remain important data gaps regarding the mode of action for toxicity of PFAS mixtures. The present study aims to contribute whole-mixture toxicity data and advance the methods for evaluating mixtures of two key components of aqueous film-forming foams: perfluorooctanesulfonic acid (PFOS), and 6:2 fluorotelomer sulfonic acid (6:2 FTS). Wildtype (AB) zebrafish embryos were exposed to PFOS and 6:2 FTS, both as individual components and as binary mixtures, from 2 to 122 h post-fertilization. Five treatment levels were selected to encompass environmentally relevant exposure levels. Experimental endpoints consisted of mortality, hatching, and developmental endpoints, including swim bladder inflation, yolk sac area, and larval body length. Results from dose-response analysis indicate that the assumption of additivity using conventional points of departure (e.g., NOAEL, LOAEL) is not supported for critical effect endpoints with these PFAS mixtures, and that the interactions vary as a function of the dose range. Alternative methods for quantifying relative potency are proposed, and recommendations for additional investigations are provided to further advance assessments of the toxicity of PFAS mixtures to aquatic organisms.

Environmental levels of carbaryl impair zebrafish larvae behaviour: The potential role of ADRA2B and HTR2B

The insecticide carbaryl is commonly found in indirectly exposed freshwater ecosystems at low concentrations considered safe for fish communities. In this study, we showed that after only 24 h of exposure to environmental concentrations of carbaryl (0.066-660 ng/L), zebrafish larvae exhibit impairments in essential behaviours. Interestingly, the observed behavioural effects induced by carbaryl were acetylcholinesterase-independent. To elucidate the molecular initiating event that resulted in the observed behavioural effects, in silico predictions were followed by in vitro validation. We identified two target proteins that potentially interacted with carbaryl, the α2B adrenoceptor (ADRA2B) and the serotonin 2B receptor (HTR2B). Using a pharmacological approach, we then tested the hypothesis that carbaryl had antagonistic interactions with both receptors. Similar to yohimbine and SB204741, which are prototypic antagonists of ADRA2B and HTR2B, respectively, carbaryl increased the heart rate of zebrafish larvae. When we compared the behavioural effects of a 24-h exposure to these pharmacological antagonists with those of carbaryl, a high degree of similarity was found. These results strongly suggest that antagonism of both ADRA2B and HTR2B is the molecular initiating event that leads to adverse outcomes in zebrafish larvae that have undergone 24 h of exposure to environmentally relevant levels of carbaryl.

Efficacy of Tricaine (MS-222) and Hypothermia as Anesthetic Agents for Blocking Sensorimotor Responses in Larval Zebrafish

Tricaine, or MS-222, is the most commonly used chemical anesthetic in zebrafish research. It is thought to act via blocking voltage-gated sodium channels, though its mechanism of action, particularly at the neuronal level, is not yet fully understood. Here, we first characterized the effects of tricaine on both body balance and touch responses in freely swimming animals, before determining its effect on the neural activity underlying the optokinetic response at the level of motion perception, sensorimotor signaling and the generation of behavior in immobilized animals. We found that the standard dose for larvae (168 mg/L) induced loss of righting reflex within 30 seconds, which then recovered within 3 minutes. Optokinetic behavior recovered within 15 minutes. Calcium imaging showed that tricaine interferes with optokinetic behavior by interruption of the signals between the pretectum and hindbrain. The motion sensitivity indices of identified sensory neurons were unchanged in larvae exposed to tricaine, though fewer such neurons were detected, leaving a small population of active sensory neurons. We then compared tricaine with gradual cooling, a potential non-chemical alternative method of anesthesia. While neuronal tuning appeared to be affected in a similar manner during gradual cooling, gradual cooling induced a surge in calcium levels in both the pretectum and hindbrain. This calcium surge, alongside a drop in heartrate, is potentially associated with harmful changes in physiology and suggests that tricaine is a better anesthetic agent than gradual cooling for zebrafish laboratory research.

Optimization of a locomotion-based zebrafish seizure model

BACKGROUND

Locomotor assays in zebrafish have emerged as a screening test in early drug discovery for antiseizure compounds. However, parameters differ considerably between published studies, which may explain some discrepant results with (candidate) antiseizure medications.

NEW METHOD

We optimized a locomotor-based seizure assay in zebrafish with pentylenetetrazol (PTZ) as the pharmacological proconvulsant to generate a therapeutic window in which proconvulsant-treated zebrafish larvae could be discriminated from a non-treated control. To generate a reliable control, exposure time and concentration of valproate (VPA, anticonvulsant) was optimized.

RESULTS

Wells with one or three larvae show a similar PTZ dose-dependent increase in locomotion with less variability in motility for the latter. Zebrafish immersed in 10 mM PTZ showed a significant increase in movement with a sustained effect, without any indication of toxicity. Animals treated with 3 mM VPA showed the strongest reduction of PTZ-induced movement without toxicity. The decrease in PTZ-induced locomotion was greater after 18 h versus 2 h.

COMPARISON WITH EXISTING METHOD(S)

For the larval zebrafish PTZ-induced seizure model, varying experimental parameters have been reported in literature. Our results show that PTZ is often used at toxic concentrations, and we provide instead reliable conditions to quantify convulsant behaviour using an infrared-beam motility assay.

CONCLUSIONS

We recommend using three zebrafish larvae per well to quantify locomotion in 96-multiwell plates. Larvae should preferably be exposed to 10 mM PTZ for 1 h, consisting of 30 min acclimation and 30 min subsequent recording. As positive control for anticonvulsant activity, we recommend exposure to 3 mM VPA for 18 h before administration of PTZ.

Rethinking the relevance of microplastics as vector for anthropogenic contaminants: Adsorption of toxicants to microplastics during exposure in a highly polluted stream - Analytical quantification and assessment of toxic effects in zebrafish (Danio rerio)

Given the increasing amounts of plastic debris entering marine and freshwater ecosystems, there is a growing demand for environmentally relevant exposure scenarios to improve the risk assessment of microplastic particles (MPs) in aquatic environments. So far, data on adverse effects in aquatic organisms induced by naturally exposed MPs are scarce and controversially discussed. As a consequence, we investigated the potential role of MPs regarding the sorption and transfer of environmental contaminants under natural conditions. For this end, a mixture of four common polymer types (polyethylene, polypropylene, polystyrene, polyvinyl chloride) was exposed to natural surface water in a polluted stream for three weeks. Samples of water, MP mixture, sediment, and suspended matter were target-screened for the presence of pollutants using GC/LC-MS, resulting in up to 94 different compounds. Possible adverse effects were investigated using several biomarkers in early developmental stages of zebrafish (Danio rerio). Exposure to natural stream water samples significantly inhibited acetylcholinesterase activity, altered CYP450 induction and modified behavioral patterns of zebrafish. In contrast, effects by samples of both non-exposed MPs and exposed MPs in zebrafish were less prominent than effects by water samples. In fact, the analytical target screening documented only few compounds sorbed to natural particles and MPs. Regarding acute toxic effects, no clear differentiation between different MPs and natural particles could be made, suggesting that - upon exposure in natural water bodies - MPs seem to approximate the sorption behavior of natural particles, presumably to a large extent due to biofilm formation. Thus, if compared to natural inorganic particles, MPs most likely do not transfer elevated amounts of environmental pollutants to biota and, therefore, do not pose a specific additional threat to aquatic organisms.

A Critical Review of Zebrafish Models of Parkinson's Disease

A wide variety of human diseases have been modelled in zebrafish, including various types of cancer, cardiovascular diseases and neurodegenerative diseases like Alzheimer’s and Parkinson’s. Recent reviews have summarized the currently available zebrafish models of Parkinson’s Disease, which include gene-based, chemically induced and chemogenetic ablation models. The present review updates the literature, critically evaluates each of the available models of Parkinson’s Disease in zebrafish and compares them with similar models in invertebrates and mammals to determine their advantages and disadvantages. We examine gene-based models, including ones linked to Early-Onset Parkinson’s Disease: PARKIN, PINK1, DJ-1, and SNCA; but we also examine LRRK2, which is linked to Late-Onset Parkinson’s Disease. We evaluate chemically induced models like MPTP, 6-OHDA, rotenone and paraquat, as well as chemogenetic ablation models like metronidazole-nitroreductase. The article also reviews the unique advantages of zebrafish, including the abundance of behavioural assays available to researchers and the efficiency of high-throughput screens. This offers a rare opportunity for assessing the potential therapeutic efficacy of pharmacological interventions. Zebrafish also are very amenable to genetic manipulation using a wide variety of techniques, which can be combined with an array of advanced microscopic imaging methods to enable in vivo visualization of cells and tissue. Taken together, these factors place zebrafish on the forefront of research as a versatile model for investigating disease states. The end goal of this review is to determine the benefits of using zebrafish in comparison to utilising other animals and to consider the limitations of zebrafish for investigating human disease.

Evaluation of the wound healing properties of South African medicinal plants using zebrafish and in vitro bioassays

ETHNOPHARMACOLOGICAL RELEVANCE

In South Africa, medicinal plants have a history of traditional use, with many species used for treating wounds. The scientific basis of such uses remains largely unexplored.

AIM OF THE STUDY

To screen South African plants used ethnomedicinally for wound healing based on their pro-angiogenic and wound healing activity, using transgenic zebrafish larvae and cell culture assays.

MATERIALS AND METHODS

South African medicinal plants used for wound healing were chosen according to literature. Dried plant material was extracted using six solvents of varying polarities. Pro-angiogenesis was assessed in vivo by observing morphological changes in sub-intestinal vessels after crude extract treatment of transgenic zebrafish larvae with vasculature-specific expression of a green fluorescent protein. Subsequently, the in vitro anti-inflammatory, fibroblast proliferation and collagen production effects of the plant extracts that were active in the zebrafish angiogenesis assay were investigated using murine macrophage (RAW 264.7) and human fibroblast (MRHF) cell lines.

RESULTS

Fourteen plants were extracted using six different solvents to yield 84 extracts and the non-toxic (n=72) were initially screened for pro-angiogenic activity in the zebrafish assay. Of these plant species, extracts of Lobostemon fruticosus, Scabiosa columbaria and Cotyledon orbiculata exhibited good activity in a concentration-dependent manner. All active extracts showed negligible in vitro toxicity using the MTT assay. Lobostemon fruticosus and Scabiosa columbaria extracts showed noteworthy anti-inflammatory activity in RAW 264.7 macrophages. The acetone extract of Lobostemon fruticosus stimulated the most collagen production at 122% above control values using the MRHF cell line, while all four of the selected extracts significantly stimulated cellular proliferation in vitro in the MRHF cell line.

CONCLUSIONS

The screening of the selected plant species provided valuable preliminary information validating the use of some of the plants in traditional medicine used for wound healing in South Africa. This study is the first to discover through an evidence-based pharmacology approach the wound healing properties of such plant species using the zebrafish as an in vivo model.

DMSO Concentrations up to 1% are Safe to be Used in the Zebrafish Embryo Developmental Toxicity Assay

Dimethyl sulfoxide (DMSO) is a popular solvent for developmental toxicity testing of chemicals and pharmaceuticals in zebrafish embryos. In general, it is recommended to keep the final DMSO concentration as low as possible for zebrafish embryos, preferably not exceeding 100 μL/L (0.01%). However, higher concentrations of DMSO are often required to dissolve compounds in an aqueous medium. The aim of this study was to determine the highest concentration of DMSO that can be safely used in our standardized Zebrafish Embryo Developmental Toxicity Assay (ZEDTA). In the first part of this study, zebrafish embryos were exposed to different concentrations (0–2%) of DMSO. No increase in lethality or malformations was observed when using DMSO concentrations up to 1%. In a follow-up experiment, we assessed whether compounds that cause no developmental toxicity in the ZEDTA remain negative when dissolved in 1% DMSO, as false positive results due to physiological disturbances by DMSO should be avoided. To this end, zebrafish embryos were exposed to ascorbic acid and hydrochlorothiazide dissolved in 1% DMSO. Negative control groups were also included. No significant increase in malformations or lethality was observed in any of the groups. In conclusion, DMSO concentrations up to 1% can be safely used to dissolve compounds in the ZEDTA.

Estrogenic mixtures induce alterations in lipidomic profiles in the gonads of female oysters

This study aimed to reveal possible alterations to lipidomic profiles in Sydney rock oysters, Saccostrea glomerata, exposed to estrogenic mixtures (i.e., estrone, E1; 17β-estradiol, E2; estriol, E3; 17α-ethinylestradiol, EE2; bisphenol A, BPA; 4-t-octylphenol, 4-t-OP; and 4-nonylphenol, 4-NP) at "low" and "high" concentrations, typical of those detected in Australian and global receiving waters. A seven-day acute exposure window exhibited significantly lower abundances of many non-polar metabolites in digestive gland, gills, and gonads. Overall, there was a strong effect of the carrier solvent ethanol (despite a low exposure of 0.0002%), with all solvent containing treatments exhibiting lower abundances of lipidic metabolites, especially in the gill and digestive gland. No significant changes of the lipidome were exhibited in the male gonad by estrogenic exposure. However, in the female gonad, significant reductions of phospholipids and phosphatidylcholine were associated with exposure to high estrogenic mixtures. We hypothesise that the decreases in these phospholipids in the female gonad may be attributable to 1) lower algal consumption and thus lower uptake of lipidic building blocks; 2) a reduction of available substrates for phospholipid and phosphatidylcholine synthesis; and/or 3) induction of reactive oxygen species via estrogen metabolism, which may cause lipid peroxidation and lower abundance of phospholipids.

Specificity of time- and dose-dependent morphological endpoints in the fish embryo acute toxicity (FET) test for substances with diverse modes of action: the search for a "fingerprint"

The fish embryo acute toxicity (FET) test with the zebrafish (Danio rerio) embryo according to OECD TG 236 was originally developed as an alternative test method for acute fish toxicity testing according to, e.g., OECD TG 203. Given the versatility of the protocol, however, the FET test has found application beyond acute toxicity testing as a common tool in environmental hazard and risk assessment. Whereas the standard OECD guideline is restricted to four core endpoints (coagulation as well as lack of somite formation, heartbeat, and tail detachment) for simple, rapid assessment of acute toxicity, further endpoints can easily be integrated into the FET test protocol. This has led to the hypothesis that an extended FET test might allow for the identification of different classes of toxicants via a "fingerprint" of morphological observations. To test this hypothesis, the present study investigated a set of 18 compounds with highly diverse modes of action with respect to acute and sublethal endpoints. Especially at higher concentrations, most observations proved toxicant-unspecific. With decreasing concentrations, however, observations declined in number, but gained in specificity. Specific observations may at best be made at test concentrations ≤ EC10. The existence of a "fingerprint" based on morphological observations in the FET is, therefore, highly unlikely in the range of acute toxicity, but cannot be excluded for experiments at sublethal concentrations.

N-Aryl Mercaptopropionamides as Broad-Spectrum Inhibitors of Metallo-β-Lactamases

Drug-resistant pathogens pose a global challenge to public health as they cause diseases that are extremely difficult to cure. Metallo-β-lactamases (MBLs) are a diverse set of zinc-containing enzymes that catalyze the hydrolysis of β-lactam drugs, including carbapenems, which are considered as the last resort to fight severe infections. To restore the activity of current β-lactam antibiotics and to offer an orthogonal strategy to the discovery of new antibiotics, we have identified a series of polar N-aryl mercaptopropionamide derivatives as potent inhibitors of several class B1 MBLs. We have identified a hit structure with high selectivity restoring the effect of imipenem and reducing minimum inhibitory concentration (MIC) values up to 256-fold in resistant isolates from Escherichia coli. Furthermore, the combination of imipenem with our inhibitor showed in vivo efficacy in a Galleria mellonella model, increasing the survival rate of infected larvae by up to 31%.

Bioprospecting of Less-Polar Fractions of Ericaria crinita and Ericaria amentacea: Developmental Toxicity and Antioxidant Activity

Ericaria crinita and Ericaria amentacea from the Adriatic Sea (Croatia) were investigated with respect to the presence of less-polar compounds for the first time after fractionation by solid-phase extraction (SPE). The composition of less-polar fractions of freeze-dried E. crinita (FdEc) and E. amentacea (FdEa) were analyzed by high-performance liquid chromatography-high-resolution mass spectrometry with electrospray ionization (UHPLC-ESI-HRMS). The major identified compounds were: amides of higher aliphatic acids (palmitoleamide, linoleamide, palmitamide, oleamide and erucamide) and related compounds, carotenoid (fucoxanthin), chlorophyll derivatives (pheophytin a and b and their derivatives) and higher terpenes (loliolide, isoamijiol with its oxidation product), β-stigmasterol and (3β,6α)-14-methylergosta-8,24(28)-diene-3,6-diol). The toxic effects observed on the less-polar fractions obtained from Ericaria species on zebrafish Danio rerio embryos could be associated with the high abundance of all five detected amides. The antioxidant activity of the fractions was evaluated by means of five independent assays, including the reduction of the radical cation (ABTS), the oxygen radical absorbance capacity (ORAC), ferric-reducing antioxidant power (FRAP), the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) assay and the Folin-Ciocalteu method. A higher antioxidant activity of E. amentacea in comparison to that of the E. crinita fractions was found with IC50 concentrations of 0.072 and 1.177 mg/mL, respectively. The correlation between the activity and the chemical composition revealed that the synergistic effect of different compounds impacted their antioxidant response.

Designed Peptide Inhibitors of STEP Phosphatase-GluA2 AMPA Receptor Interaction Enhance the Cognitive Performance in Rats

Cognitive impairment and learning ability of the brain are directly linked to synaptic plasticity as measured in changes of long-term potentiation (LTP) and long-term depression (LTD) in animal models of brain diseases. LTD reflects a sustained reduction of the synaptic AMPA receptor content based on targeted clathrin-mediated endocytosis. AMPA receptor endocytosis is initiated by dephosphorylation of Tyr⁸⁷⁶ on the C-terminus of the AMPAR subunit GluA2. The brain-specific striatal-enriched protein tyrosine phosphatase (STEP) is responsible for this process. To identify new, highly effective inhibitors of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) internalization, we performed structure-based design of peptides able to inhibit STEP-GluA2-CT complex formation. Two short peptide derivatives were found as efficient in vitro inhibitors. Our in vivo experiments evidenced that both peptides restore the memory deficits and display anxiolytic and antidepressant effects in a scopolamine-treated rat model. The interference peptides identified and characterized here represent promising lead compounds for novel cognitive enhancers and/or behavioral modulators.

Solketal Removal from Aqueous Solutions Using Activated Carbon and a Metal-Organic Framework as Adsorbents

The worldwide rise in biodiesel production has generated an excess of glycerol, a byproduct of the process. One of the most interesting alternative uses of glycerol is the production of solketal, a bioadditive that can improve the properties of both diesel and gasoline fuels. Even with its promising future, not much research has been performed on its toxicity in aqueous environments. In this work, solketal adsorption has been tested with two different commercial adsorbents: an activated carbon (Hydrodarco 3000) and a metal-organic framework (MIL-53). Diclofenac and caffeine were also chosen as emerging contaminants for comparison purposes. The effect of various parameters, such as the adsorbent mass or initial concentration of pollutants, has been studied. Adsorption kinetics with a better fit to a pseudo-second-order model, intraparticle diffusion, and effective diffusion coefficient were studied as well. Various isotherm equation models were employed to study the equilibrium process. The results obtained indicate that activated carbon is more effective in removing solketal from aqueous solutions than the metal-organic framework.

Zinc oxide-induced changes to sunscreen ingredient efficacy and toxicity under UV irradiation

Sunscreen safety and efficacy is generally evaluated based upon the properties of the individual chemicals in a formulation. However, the photostability of sunscreens has been shown to be highly dependent on the mixture of chemicals present. To better understand how sunscreen formulation influences stability, and to establish a foundation for probing the influence of zinc oxide additives, we formulated five different small-molecule based ultraviolet-filter (UV-filter) mixtures with a Sun Protection Factor (SPF) of 15. These mixtures contained active ingredients approved in either the United States or European Union and were designed to represent formulations of actual products on the market. We evaluated the photostability and toxicity of these mixtures in the absence and presence of zinc oxide after UV exposure for two hours. Changes in UV absorbance were minimal for all five small-molecule-based mixtures without zinc oxide. The presence of either micro- or nano-sized zinc oxide caused significant small-molecule photodegradation and the degraded mixtures exhibited higher levels of toxicity in embryonic zebrafish assays. This study suggests that caution must be taken when formulating sunscreens containing both zinc oxide and small-molecule UV-filters to avoid unintended consequences during use.

Minimum reporting standards based on a comprehensive review of the zebrafish embryo teratogenicity assay

Reproductive toxicity chemical safety assessment involves extensive use of vertebrate animals for regulatory testing purposes. Although alternative methods such as the zebrafish embryo teratogenicity assay (identified in the present manuscript by the acronym ZETA) are promising for replacing tests with mammals, challenges to regulatory application involve lack of standardization and incomplete validation. To identify key protocol aspects and ultimately support improving this situation, a comprehensive review of the literature on the level of harmonization/standardization and validation status of the ZETA has been conducted. The gaps and needed advances of the available ZETA protocols were evaluated and discussed with respect to its applicability as an alternative approach for teratogenicity assessment. Based on the review outcomes, a set of minimum reporting standards for the experimental protocol is proposed. Together with other initiatives towards implementation of alternative approaches at the screening and regulatory levels, the application of minimum reporting requirements is anticipated to support future method standardization and validation, as well as identifying potential improvement aspects. Present findings are expected to ultimately support advancing the ongoing validation initiatives towards the regulatory acceptance of the ZETA.

Developmental phenotypic and transcriptomic effects of exposure to nanomolar levels of metformin in zebrafish

Metformin is found in the majority of lakes and streams in the United States, leading to widespread environmental exposure. Results of the present study indicate that extended duration metformin exposure at critical developmental periods leads to decreased survival rates in zebrafish (danio rerio), an NIH approved human model. Significant abnormalities are seen with extended duration metformin exposure from 4 h post fertilization up to 5 days post fertilization, although short term metformin exposure for 24 h at 4-5 days post fertilization did not lead to any significant abnormalities. Both extended and short term duration did however have an impact on locomotor activity of zebrafish, and several genes involved in neurological and cardiovascular development were differentially expressed after exposure to metformin. The changes seen in behavior, gene expression and morphological abnormalities caused by metformin exposure should be examined further in future studies in order to assess their potential human health implications as metformin prescriptions continue to increase worldwide.