Development of a screening assay to identify teratogenic and embryotoxic chemicals using the zebrafish embryo

Effects of 5α-reductase inhibition by dutasteride on reproductive gene expression and hormonal responses in zebrafish embryos

Steroid 5α-reductase (SRD5A) is a crucial enzyme involved in steroid metabolism, primarily converting testosterone to dihydrotestosterone (DHT). Dutasteride, an inhibitor of SRD5A types 1 and 2, is widely used for treating benign prostatic hyperplasia. An adverse outcome pathway (AOP) has been documented wherein SRD5A inhibition decreases DHT synthesis, leading to reduced levels of 17β-estradiol (E2) and vitellogenin (VTG), subsequently impairing fecundity in fish (AOP 289). However, the molecular and cellular mechanisms underlying these effects remain poorly understood. In this study, we assessed the impact of SRD5A inhibition on zebrafish embryos (Danio rerio). Exposure to dutasteride resulted in decreased DHT, E2, and VTG levels, showing a positive correlation. Dutasteride also downregulated the expression of reproduction-related genes (srd5a2, cyp19a1, esr1, esr2a, esr2b, and vtg), with interrelated reductions observed across these levels. Docking studies suggested that dutasteride's effects may operate independently of androgen receptor (AR) and estrogen receptor (ER) interactions. Furthermore, co-exposure of dutasteride (0.5 or 2 μM) with 0.5 μM DHT revealed gene expression levels comparable to the control group. These findings underscore DHT's pivotal role in modulating estrogenic function and the interplay between estrogenic and androgenic responses in vertebrates. Our proposed AOP model offers insights into mechanistic gaps, thereby enhancing current understanding and bridging knowledge disparities.

Assessment of receptor-mediated activity (AhR and ERα), mutagenicity, and teratogenicity of metal shredder wastes in Wallonia, Belgium

In this study, hazardous wastes including fluff, dust, and scrubbing sludge were sampled in 2019 from two metal shredding facilities located in Wallonia, Belgium. To assess the extent of the contamination, a global approach combining chemical and biological techniques was used, to better reflect the risks to health and the environment. The samples investigated induced significant in vitro aryl hydrocarbon receptor (AhR) agonistic bioactivities and estrogenic receptor (ERα) (ant)agonistic bioactivities in the respective CALUX (chemical activated luciferase gene expression) bioassays. The mutagenicity of the samples was investigated with the bacterial reverse gene mutation test using the Salmonella typhimurium TA98 and TA100 strains. Except for the sludge sample (site 3), all samples induced a mutagenic response in the TA98 strain (± S9 metabolic fraction) whereas in the TA100 strain (+ S9 metabolic fraction), only the sludge sample (site 2) showed a clear mutagenic effect. The in vivo toxicity/teratogenicity of the shredder wastes was further evaluated with zebrafish embryos. Except for the dust sample (site 2), all samples were found to be teratogenic as they returned teratogenic indexes (TIs) > 1. The high levels of contamination, the mutagenicity, and the teratogenicity of these shredder wastes raise significant concerns about their potential negative impacts on both human health and environment.

Toxicokinetics of a developmental toxicity test in zebrafish embryos and larvae: Relationship with drug exposure in humans and other mammals

To study the effects of drugs on embryo/fetal development (EFD), developmental and reproductive toxicity studies in zebrafish (Danio rerio) embryos is expected to be an accepted alternative method to animal studies using mammals. However, there is a lack of clarity in the relationship between the concentration of developmental toxicity agents in whole embryos or larvae (Ce) and that in aqueous solution (Cw), and also between the amount of drug exposure required to cause developmental toxicity in zebrafish embryos or larvae and that required in mammals. Here, we measured Ce for developmental toxicity agents every 24 h starting at 24 h post fertilization (hpf). We found a high correlation (R 2: 0.87-0.96) between log [Ce/Cw] and the n-octanol-water distribution coefficient at pH 7 (logD) of each drug at all time points up to 120 hpf. We used this relationship to estimate the Ce values of the 21 positive-control reference drugs listed in ICH guidelines on reproductive and developmental toxicity studies (ICH S5). We then calculated the area under the Ce-time curve in zebrafish (zAUC) for each drug from the regression equation between log [Ce/Cw] and logD and compared it with the AUC at the no-observed-adverse-effect level in rats and rabbits and at the effective dose in humans described in ICH S5. The log of the calculated zAUC for the 14 drugs identified as positive in the zebrafish developmental toxicity test was relatively highly positively correlated with the log [AUC] for rats, rabbits, and humans. These findings provide important and positive information on the applicability of the zebrafish embryo developmental toxicity test as an alternative method of EFD testing. (267 words).

Polystyrene nanoplastics synergistically exacerbate diclofenac toxicity in embryonic development and the health of adult zebrafish

In this study, we investigated the possible ecotoxicological effect of co-exposure to polystyrene nanoplastics (PS-NPs) and diclofenac (DCF) in zebrafish (Danio rerio). After six days of exposure, we noticed that the co-exposure to PS-NP (100 μg/L) and DCF (at 50 and 500 μg/L) decreased the hatching rate and increased the mortality rate compared to the control group. Furthermore, we noted that larvae exposed to combined pollutants showed a higher frequency of morphological abnormalities and increased oxidative stress, apoptosis, and lipid peroxidation. In adults, superoxide dismutase and catalase activities were also impaired in the intestine, and the co-exposure groups showed more histopathological alterations. Furthermore, the TNF-α, COX-2, and IL-1β expressions were significantly upregulated in the adult zebrafish co-exposed to pollutants. Based on these findings, the co-exposure to PS-NPs and DCF has shown an adverse effect on the intestinal region, supporting the notion that PS-NPs synergistically exacerbate DCF toxicity in zebrafish.

Exposure to the pesticide tefluthrin causes developmental neurotoxicity in zebrafish

BACKGROUND

The insecticide tefluthrin is widely used in agriculture, resulting in widespread pollution. Tefluthrin is a type I pyrethroid characterized by its high persistence in the environment. Understanding the mechanisms of toxicity of tefluthrin will improve its risk assessment.

OBJECTIVES

We aimed to decipher the molecular modes of action of tefluthrin.

METHODS

Phenotypic developmental toxicity was assessed by exposing zebrafish embryos and larvae to increasing concentrations of tefluthrin. Tg(mnx:mGFP) line was used to assess neurotoxicity. Multi-omics approaches including transcriptomics and lipidomics were applied to analyze RNA and lipid contents, respectively. Finally, an in-silico ligand-protein docking computational method was used to study a possible interaction between tefluthrin and a protein target.

RESULTS

Tefluthrin exposure caused severe morphological malformations in zebrafish larvae, including motor neuron abnormalities. The differentially expressed genes were associated with neurotoxicity and metabolic disruption. Lipidomics analysis revealed a disruption in fatty acid, phospholipid, and lysophospholipid recycling. Protein docking modeling suggested that the LPCAT3 enzyme, which recycles lysophospholipids in the Land's cycle, directly interacts with tefluthrin.

CONCLUSIONS

Tefluthrin exposure causes morphological and neuronal malformations in zebrafish larvae at nanomolar concentrations. Multi-omics results revealed a potential molecular initiating event i.e., inhibition of LPCAT3, and key events i.e., an altered lysophospholipid to phospholipid ratio, leading to the adverse outcomes of neurotoxicity and metabolic disruption.

From Pipeline to Plant Protection Products: Using New Approach Methodologies (NAMs) in Agrochemical Safety Assessment

The human population will be approximately 9.7 billion by 2050, and food security has been identified as one of the key issues facing the global population. Agrochemicals are an important tool available to farmers that enable high crop yields and continued access to healthy foods, but the average new agrochemical active ingredient takes more than ten years, 350 million dollars, and 20,000 animals to develop and register. The time, monetary, and animal costs incentivize the use of New Approach Methodologies (NAMs) in early-stage screening to prioritize chemical candidates. This review outlines NAMs that are currently available or can be adapted for use in early-stage screening agrochemical programs. It covers new in vitro screens that are on the horizon in key areas of regulatory concern. Overall, early-stage screening with NAMs enables the prioritization of development for agrochemicals without human and environmental health concerns through a more directed, agile, and iterative development program before animal-based regulatory testing is even considered.

Burn pit-related smoke causes developmental and behavioral toxicity in zebrafish: Influence of material type and emissions chemistry

Combustion of mixed materials during open air burning of refuse or structural fires in the wildland urban interface produces emissions that worsen air quality, contaminate rivers and streams, and cause poor health outcomes including developmental effects. The zebrafish, a freshwater fish, is a useful model for quickly screening the toxicological and developmental effects of agents in such species and elicits biological responses that are often analogous and predictive of responses in mammals. The purpose of this study was to compare the developmental toxicity of smoke derived from the burning of 5 different burn pit-related material types (plywood, cardboard, plastic, a mixture of the three, and the mixture plus diesel fuel as an accelerant) in zebrafish larvae. Larvae were exposed to organic extracts of increasing concentrations of each smoke 6-to-8-hr post fertilization and assessed for morphological and behavioral toxicity at 5 days post fertilization. To examine chemical and biological determinants of toxicity, responses were related to emissions concentrations of polycyclic hydrocarbons (PAH). Emissions from plastic and the mixture containing plastic caused the most pronounced developmental effects, including mortality, impaired swim bladder inflation, pericardial edema, spinal curvature, tail kinks, and/or craniofacial deformities, although all extracts caused concentration-dependent effects. Plywood, by contrast, altered locomotor responsiveness to light changes to the greatest extent. Some morphological and behavioral responses correlated strongly with smoke extract levels of PAHs including 9-fluorenone. Overall, the findings suggest that material type and emissions chemistry impact the severity of zebrafish developmental toxicity responses to burn pit-related smoke.

Toxicological and Sedative Effects of Chipilin (Crotalaria longirostrata) Leaf Extracts Obtained by Maceration and Supercritical Fluid Extraction

Chipilin (Crotalaria longirostrata) is consumed as a vegetable in the preparation of traditional dishes. As a folk medicine, Chipilin extracts are used as a hypnotic and sedative agent; however, there are few reports that support these uses. This study aimed to characterize the compounds present in Chipilin leaf extracts and to investigate their sedative effect using zebrafish as an in vivo model. Extracts were obtained by maceration with water (H2O), ethanol (EtOH), and EtOH-H2O, while oleoresin was obtained by supercritical fluid extraction (SFE). Total phenolic and flavonoid contents were quantified by colorimetric methods. Phytochemical constituents were identified by gas chromatography-mass spectrometry (GC-MS) analysis. The chronic and acute toxicities of Chipilin extracts were tested in zebrafish embryos and larvae, respectively. Chipilin sedative effect was tested by the larvae response to dark-light-dark transitions. EtOH-H2O extracts had the highest value of total phenolics (5345 ± 5.1 μg GAE/g), followed by water and oleoresin (1815 ± 5.1 and 394 ± 5.1 μg GAE/g, respectively). In water extracts were identified the alkaloid trachelanthamidine, 1,2β-epoxy- and the alkyl ketone 7,9-di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione, while oleamide, α-monostearin, and erucamide were detected in all samples except in water extracts. Oleoresin extract had the lowest embryotoxicity (LC50 = 4.99 μg/mL) and the highest sedative effects. SFE is a green alternative to obtain Chipilin extracts rich in erucamide, an endocannabinoid analogue, which plays an important role in the development of the central nervous system and in modulating neurotransmitter release.

Polystyrene nanoplastics induce developmental impairments and vasotoxicity in zebrafish (Danio rerio)

The exponential use of plastics has significantly increased environmental pollution by nanoplastics (NPs). In the aquatic environment, NPs interact and bioaccumulate in the biota, posing a potential ecotoxicological risk. The present study investigated the developmental toxicity, vasotoxicity, cytotoxicity, ROS induction, and behavioral impairments in zebrafish (Danio rerio) exposed to environmentally relevant polystyrene NPs (PS-NPs) concentrations (0.04, 34 ng L-1, and 34 μg L-1) for 144 h through multiple biomarkers response (mortality, frequency of spontaneous contractions, heart rate, and morphological changes). Furthermore, vasotoxicity (head, yolk sac, tail, and branchial vessels) was evaluated using the transgenic zebrafish tg(Fli1:eGFP). Results showed that PS-NPs interacted mainly with zebrafish chorion, gills, tail, and larvae head. PS-NPs at 34 ng L-1 and 34 μg L-1 induced neurotoxicity (decreased frequency of spontaneous contractions), cardiotoxicity (bradycardia), and morphological changes in the eyes and head, indicating that PS-NPs induce developmental impairments in zebrafish. In addition, cytotoxicity in the caudal region (34 ng L-1), ROS production, decreased mean swimming speed, and distance covered were observed in all tested concentrations. PS-NPs also induced vasotoxicity (yolk sac region) in transgenic zebrafish. Overall, the present study demonstrates the harmful effects of PS-NPs on the early developmental stages of freshwater fish, indicating their environmental risk.

Guidelines on Developmental Toxicity Tests: Brief Insights

Developmental toxicology is a constantly evolving research field which needs to attend to a complex underlying regulatory network. In order to ensure human health and environmental safety, new substances have to be tested for toxic effects on reproduction and development, before being commercialized. Traditional in vivo mammalian models represent the intricacy of human development and provide more adequately an assessment of the interaction of chemical compounds with the reproductive system. However, in the last years, the directives are to reduce the use of vertebrate animals, promoting their use only as a last resort. Consequently, the interest on the development and validation of alternative tests, able to cover the various aspects of the reproductive cycle, has significantly increased. Reproductive toxicity is probably the most difficult endpoint to be replaced by alternative assays, since it should provide information on mechanism interactions essential for female and male fertility and also knowledge on the animal development during the first phases of its life cycle. This complexity explains the slow progress in implementing alternative models for reproductive toxicity safety assays. Alternative test models may be based on in vitro systems and nonmammalian animal models. Many biological processes have been successfully addressed using in vitro models, opening the possibility to study the interference of teratogenic compounds. Their validation and implementation have lagged behind, in part because of difficulties in establishing their predictability. Nevertheless, the advance toward the process of validation is crucial to replace and reduce the use of living animals. Based on the present state of the art, it is not probable that such testing strategies will completely replace the need to assess reproductive toxicity in vivo in the near future, but they will contribute to reduce animal tests and will provide important information. In this chapter, the approved guidelines for standard methods and alternative methods, according to their regulatory and scientific status, are enumerated and briefly described.

Biocompatible nanoscale silica particles fabricated from aminopropyltriethoxysilane functionalized brick ash induced versatile pesticidal activity

The present study is aimed to evaluate pesticidal activity and biocompatibility including ecotoxicity of functionalized silica nanoparticles that synthesized by simple, in vitro, green technology principles. Sol-gel method was adopted for the synthesis of silica nanoparticles and was functionalized by Aminopropyltriethoxysilane (APS), characterized and confirmed the uniform, monodispersive, highly stable particles with the size range of 10-200 nm. The synthesized Nano silica was screened against the developmental stages of Spodoptera litura. Pesticidal study revealed that the functionalized nanoparticles were effective against all the life stages of the insect by recording high mortality and the drastic reduction in the larval, pupae, adult emergence, and adult longevity stages. The ecotoxic effect of synthesized nano-silica was tested on soil parameters, growth parameters of Arachis hypogaea, and compatibility with Trichoderma viride. This study revealed there was no toxic effect on soil, growth parameters of Arachis hypogaea, and most significantly the growth of Trichoderma viride was not inhibited. A biocompatibility study was done by using Zebrafish and Rabbit model. The study divulges there was no toxic effect on all the developmental stages of the Embryo. Further, the nanoparticles did not exhibit any dermatotoxicological effect which confirmed no signs and symptoms of inflammation. Nano-silica emerges as a promising eco-friendly and non-toxic substitute for conventional insecticides. Its utilization has the potential to augment both environmental preservation and economic prosperity on a national scale. Furthermore, the integration of silica-based nanoparticles with biocidal agents demonstrates notable biocompatibility and the capacity to hinder bacterial adhesion.

Dimethenamid promotes oxidative stress and apoptosis leading to cardiovascular, hepatic, and pancreatic toxicities in zebrafish embryo

Dimethenamid, one of the acetamide herbicides, is widely used on soybeans and corns to inhibit weed growth. Although other acetamide herbicides have been reported to have several toxicities in non-target organisms including developmental toxicity, the toxicity of dimethenamid has not yet been studied. In this research, we utilized the zebrafish animal model to verify the developmental toxicity of dimethenamid. It not only led to morphological abnormalities in zebrafish larvae but also reduced their viability. ROS production and inflammation responses were promoted in zebrafish larvae. Also, uncontrolled apoptosis occurred when the gene expression level related to the cell cycle and apoptosis was altered by dimethenamid. These changes resulted in toxicities in the cardiovascular system, liver, and pancreas are observed in transgenic zebrafish models including fli1a:EGFP and L-fabp:dsRed;elastase:GFP. Dimethenamid triggered morphological defects in the heart and vasculature by altering the mRNA levels related to cardiovascular development. The liver and pancreas were also damaged through not only the changes of their morphology but also through the dysregulation in their function related to metabolic activity. This study shows the developmental defects induced by dimethenamid in zebrafish larvae and the possibility of toxicity in other non-target organisms.

Reimagining safe lithium applications in the living environment and its impacts on human, animal, and plant system

Lithium's (Li) ubiquitous distribution in the environment is a rising concern due to its rapid proliferation in the modern electronic industry. Li enigmatic entry into the terrestrial food chain raises many questions and uncertainties that may pose a grave threat to living biota. We examined the leverage existing published articles regarding advances in global Li resources, interplay with plants, and possible involvement with living organisms, especially humans and animals. Globally, Li concentration (<10-300 mg kg-1) is detected in agricultural soil, and their pollutant levels vary with space and time. High mobility of Li results in higher accumulation in plants, but the clear mechanisms and specific functions remain unknown. Our assessment reveals the causal relationship between Li level and biota health. For example, lower Li intake (<0.6 mM in serum) leads to mental disorders, while higher intake (>1.5 mM in serum) induces thyroid, stomach, kidney, and reproductive system dysfunctions in humans and animals. However, there is a serious knowledge gap regarding Li regulatory standards in environmental compartments, and mechanistic approaches to unveil its consequences are needed. Furthermore, aggressive efforts are required to define optimum levels of Li for the normal functioning of animals, plants, and humans. This review is designed to revitalize the current status of Li research and identify the key knowledge gaps to fight back against the mountainous challenges of Li during the recent digital revolution. Additionally, we propose pathways to overcome Li problems and develop a strategy for effective, safe, and acceptable applications.

Optimizing assays of zebrafish larvae swimming performance for drug discovery

INTRODUCTION

Zebrafish larvae are one of the few vertebrates amenable to large-scale drug discovery screens. Larval swimming behavior is often used as an outcome variable and many fields of study have developed assays for evaluating swimming performance. An unintended consequence of this wide interest is that details related to assay methodology and interpretation become scattered across the literature. The aim of this review is to consolidate this information, particularly as it relates to high-throughput approaches.

AREAS COVERED

The authors describe larval swimming behaviors as this forms the basis for understanding their experimentally evoked swimming or spontaneous activity. Next, they detail how swimming activity can serve as an outcome variable, particularly in the multi-well formats used in large-scale screening studies. They also highlight biological and technical factors that can impact the sensitivity and variability of these measurements.

EXPERT OPINION

Careful attention to animal husbandry, experimental design, data acquisition, and interpretation of results can improve screen outcomes by maximizing swimming activity while minimizing intra- and inter-larval variability. The development of more sensitive, quantitative methods of assessing swimming performance that can be incorporated into high-throughput workflows will be important in order to take full advantage of the zebrafish model.

Experimental arena size alters larval zebrafish photolocomotor behaviors and influences bioactivity responses to a model neurostimulant

Zebrafish behavior is increasingly common in biomedical and environmental studies of chemical bioactivity. Multiple experimental arena sizes have been used to measure photolocomotion in zebrafish depending on age, endpoints observed, and instrumentation, among other factors. However, the extent to which methodological parameters may influence naïve behavioral performance and detection of behavioral changes is poorly understood. Here we measured photolocomotion and behavioral profiles of naïve larval zebrafish across arena sizes. We then performed concentration response studies with the model neurostimulant caffeine, again across various arena dimensions. We found total swimming distance of unexposed fish to increase logarithmically with arena size, which as related to circumference, area, and volume. Photomotor response during light/dark transitions also increased with arena size. Following caffeine exposure, total distance travelled was significantly (p < 0.001) affected by well size, caffeine treatment (p < 0.001), and the interaction of these two experimental factors (p < 0.001). In addition, behavioral response profiles showed differences between 96 well plates and larger well sizes. Biphasic response, with stimulation at lower concentrations and refraction at the highest concentration, was observed in dark conditions for the 96 well size only, though almost no effects were identified in the light. However, swimming behavior was significantly (p < 0.1) altered in the highest studied caffeine treatment level in larger well sizes during both light and dark periods. Our results indicate zebrafish swim more in larger arenas and arena size influences behavioral response profiles to caffeine, though differences were mostly observed between very small and large arenas. Further, careful consideration should be given when choosing arena size, because small wells may lead to restriction, while larger wells may differentially reflect biologically relevant effects. These findings can improve comparability among experimental designs and demonstrates the importance of understanding confounding methodological variables.

Interaction of Fumonisin B1, N-Palmitoyl-Fumonisin B1, 5-O-Palmitoyl-Fumonisin B1, and Fumonisin B4 Mycotoxins with Human Serum Albumin and Their Toxic Impacts on Zebrafish Embryos

Fumonisins are frequent food contaminants. The high exposure to fumonisins can cause harmful effects in humans and animals. Fumonisin B1 (FB1) is the most typical member of this group; however, the occurrence of several other derivatives has been reported. Acylated metabolites of FB1 have also been described as possible food contaminants, and the very limited data available suggest their significantly higher toxicity compared to FB1. Furthermore, the physicochemical and toxicokinetic properties (e.g., albumin binding) of acyl-FB1 derivatives may show large differences compared to the parent mycotoxin. Therefore, we tested the interactions of FB1, N-palmitoyl-FB1 (N-pal-FB1), 5-O-palmitoyl-FB1 (5-O-pal-FB1), and fumonisin B4 (FB4) with human serum albumin as well as the toxic effects of these mycotoxins on zebrafish embryos were examined. Based on our results, the most important observations and conclusions are the following: (1) FB1 and FB4 bind to albumin with low affinity, while palmitoyl-FB1 derivatives form highly stable complexes with the protein. (2) N-pal-FB1 and 5-O-pal-FB1 likely occupy more high-affinity binding sites on albumin. (3) Among the mycotoxins tested, N-pal-FB1 showed the most toxic effects on zebrafish, followed by 5-O-pal-FB1, FB4, and FB1. (4) Our study provides the first in vivo toxicity data regarding N-pal-FB1, 5-O-pal-FB1, and FB4.

Prediction of zebrafish embryonic developmental toxicity by integrating omics with adverse outcome pathway

New approach methodologies (NAMs), especially omics-based high-throughput bioassays have been developed rapidly, providing rich mechanistic information such as molecular initiation events (MIEs) and (sub)cellular key events (KEs) in adverse outcome pathways (AOPs). However, how to apply the knowledge of MIEs/KEs to predict adverse outcomes (AOs) induced by chemicals represents a new challenge for computational toxicology. Here, an integrated method named ScoreAOP was developed and evaluated to predict chemicals' developmental toxicity for zebrafish embryos by integrating four related AOPs and dose-dependent reduced zebrafish transcriptome (RZT). The rules of ScoreAOP included 1) sensitivity of responsive KEs demonstrated by point of departure of KEs (POD_KE), 2) evidence reliability and 3) distance between KEs and AOs. Moreover, eleven chemicals with different modes of action (MoAs) were tested to evaluate ScoreAOP. Results showed that eight of the eleven chemicals caused developmental toxicity at tested concentration in apical tests. All the tested chemicals' developmental defects were predicted using ScoreAOP, whereas eight out of the eleven chemicals predicted by ScoreMIE which was developed to score MIEs disturbed by chemicals based on in vitro bioassays data. Finally, in terms of mechanism explanation, ScoreAOP clustered chemicals with different MoAs while ScoreMIE failed, and ScoreAOP revealed the activation of aryl hydrocarbon receptor (AhR) plays a significant role in dysfunction of cardiovascular system, resulting in zebrafish developmental defects and mortality. In conclusion, ScoreAOP represents a promising approach to apply mechanism information obtained from omics to predict AOs induced by chemicals.

A continuous in silico learning strategy to identify safety liabilities in compounds used in the leather and textile industry

There is a widely recognized need to reduce human activity's impact on the environment. Many industries of the leather and textile sector (LTI), being aware of producing a significant amount of residues (Keßler et al. 2021; Liu et al. 2021), are adopting measures to reduce the impact of their processes on the environment, starting with a more comprehensive characterization of the chemical risk associated with the substances commonly used in LTI. The present work contributes to these efforts by compiling and toxicologically annotating the substances used in LTI, supporting a continuous learning strategy for characterizing their chemical safety. This strategy combines data collection from public sources, experimental methods and in silico predictions for characterizing four different endpoints: CMR, ED, PBT, and vPvB. We present the results of a prospective validation exercise in which we confirm that in silico methods can produce reasonably good hazard estimations and fill knowledge gaps in the LTI chemical space. The proposed protocol can speed the process and optimize the use of resources including the lives of experimental animals, contributing to identifying potentially harmful substances and their possible replacement by safer alternatives, thus reducing the environmental footprint and impact on human health.

Triadimenol promotes the production of reactive oxygen species and apoptosis with cardiotoxicity and developmental abnormalities in zebrafish

Various types of fungicides, especially triazole fungicides, are used to prevent fungal diseases on farmlands. However, the developmental toxicity of one of the triazole fungicides, triadimenol, remains unclear. Therefore, we used the zebrafish animal model, a representative toxicological model, to investigate it. Triadimenol induced morphological alterations in the eyes and body length along with yolk sac and heart edema. It also stimulated the production of reactive oxygen species and expression of inflammation-related genes and caused apoptosis in the anterior regions of zebrafish, especially in the heart. The phosphorylation levels of Akt, ERK, JNK, and p38 proteins involved in the PI3K and MAPK pathways, which are important for the development process, were also reduced by triadimenol. These changes led to malformation of the heart and vascular structures, as observed in the flk1:eGFP transgenic zebrafish models and a reduction in the heart rate. In addition, the expression of genes associated with cardiac and vascular development was also reduced. Therefore, we elucidated the mechanisms associated with triadimenol toxicity that leads to various abnormalities and developmental toxicity in zebrafish.

Morphological Alterations in the Early Developmental Stages of Zebrafish (Danio rerio; Hamilton 1822) Induced by Exposure to Polystyrene Microparticles

Microplastics (MPs) are emerging pollutants of widespread concern in aquatic environments. The aim of this study was to evaluate the negative impact of pristine MPs of polystyrene of 100 μm on embryo and larvae of Danio rerio exposed to three environmentally relevant concentrations of polystyrene (3.84 × 10^- 6, 3.84 × 10^- 7, and 3.84 × 10^- 8 g/mL). The exposure effect was evaluated through the general morphology score, biometrics, and integrated biomarker response version 2 index. No mortality was observed but the anatomical structure of fishes was affected showing pigmentation deficiency and alterations in the head region as the main affected endpoints. The general morphology score and the integrated biomarker response values were highly sensitive to address the effect of the three concentrations of MPs used here. Our results provide solid evidence of the negative impact of 100 μm pristine polystyrene MPs exposure on early stages of zebrafish.

Synthetic approaches to potent heterocyclic inhibitors of tuberculosis: A decade review

Tuberculosis (TB) continues to be a significant global health concern with about 1.5 million deaths annually. Despite efforts to develop more efficient vaccines, reliable diagnostics, and chemotherapeutics, tuberculosis has become a concern to world health due to HIV, the rapid growth of bacteria that are resistant to treatment, and the recently introduced COVID-19 pandemic. As is well known, advances in synthetic organic chemistry have historically enabled the production of important life-saving medications that have had a tremendous impact on patients' lives and health all over the world. Small-molecule research as a novel chemical entity for a specific disease target offers in-depth knowledge and potential therapeutic targets. In this viewpoint, we concentrated on the synthesis of a number of heterocycles reported in the previous decade and the screening of their inhibitory action against diverse strains of Mycobacterium tuberculosis. These findings offer specific details on the structure-based activity of several heterocyclic scaffolds backed by their in vitro tests as a promising class of antitubercular medicines, which will be further useful to build effective treatments to prevent this terrible illness.

Disruptions of circadian rhythms, sleep, and stress responses in zebrafish: New infrared-based activity monitoring assays for toxicity assessment

Behavioural disruptions are sensitive indicators of alterations to normal animal physiology and can be used for toxicity assessment. The small vertebrate zebrafish is a leading model organism for toxicological studies. The ability to continuously monitor the toxicity of drugs, pollutants, or environmental changes over several days in zebrafish can have high practical application. Although video-recordings can be used to monitor short-term zebrafish behaviour, it is challenging to videorecord prolonged experiments (e.g. circadian behaviour over several days) because of the darkness periods (nights) and the heavy data storage and image processing requirements. Alternatively, infrared-based activity monitors, widely used in invertebrate models such as drosophila, generate simple and low-storage data and could optimize large-scale prolonged behavioural experiments in zebrafish, thus favouring the implementation of high-throughput testing strategies. Here, we validate the use of a Locomotor Activity Monitor (LAM) to study the behaviour of zebrafish larvae, and we characterize the behavioural phenotypes induced by abnormal light conditions and by the Parkinsonian toxin MPP⁺. When zebrafish were deprived from daily light-cycle synchronization, the LAM detected various circadian disruptions, such as increased activity period, phase shifts, and decreased inter-daily stability. Zebrafish exposed to MPP⁺ (10, 100, 500 μM) showed a concentration-dependent decrease in activity, sleep disruptions, impaired habituation to repetitive startles (visual-motor responses), and a slower recovery to normal activity after the startle-associated stress. These phenotypes evidence the feasibility of using infrared-based LAM to assess multi-parameter behavioural disruptions in zebrafish. The procedures in this study have wide applicability and may yield standard methods for toxicity testing.

Protection against Paraquat-Induced Oxidative Stress by Curcuma longa Extract-Loaded Polymeric Nanoparticles in Zebrafish Embryos

The link between oxidative stress and environmental factors plays an important role in chronic degenerative diseases; therefore, exogenous antioxidants could be an effective alternative to combat disease progression and/or most significant symptoms. Curcuma longa L. (CL), commonly known as turmeric, is mostly composed of curcumin, a multivalent molecule described as having antioxidant, anti-inflammatory and neuroprotective properties. Poor chemical stability and low oral bioavailability and, consequently, poor absorption, rapid metabolism, and limited tissue distribution are major restrictions to its applicability. The advent of nanotechnology, by combining nanosacale with multi-functionality and bioavailability improvement, offers an opportunity to overcome these limitations. Therefore, in this work, poly-Ɛ-caprolactone (PCL) nanoparticles were developed to incorporate the methanolic extract of CL, and their bioactivity was assessed in comparison to free or encapsulated curcumin. Their toxicity was evaluated using zebrafish embryos by applying the Fish Embryo Acute Toxicity test, following recommended OECD guidelines. The protective effect against paraquat-induced oxidative damage of CL extract, free or encapsulated in PCL nanoparticles, was evaluated. This herbicide is known to cause oxidative damage and greatly affect neuromotor functions. The overall results indicate that CL-loaded PCL nanoparticles have an interesting protective capacity against paraquat-induced damage, particularly in neuromuscular development that goes well beyond that of CL extract itself and other known antioxidants.

Review of the state of science and evaluation of currently available in silico prediction models for reproductive and developmental toxicity: A case study on pesticides

BACKGROUND

In silico methods for toxicity prediction have increased significantly in recent years due to the 3Rs principle. This also applies to predicting reproductive toxicology, which is one of the most critical factors in pesticide approval. The widely used quantitative structure-activity relationship (QSAR) models use experimental toxicity data to create a model that relates experimentally observed toxicity to molecular structures to predict toxicity. Aim of the study was to evaluate the available prediction models for developmental and reproductive toxicity regarding their strengths and weaknesses in a pesticide database.

METHODS

The reproductive toxicity of 315 pesticides, which have a GHS classification by ECHA, was compared with the prediction of different in silico models: VEGA, OECD (Q)SAR Toolbox, Leadscope Model Applier, and CASE Ultra by MultiCASE.

RESULTS

In all models, a large proportion (up to 77%) of all pesticides were outside the chemical space of the model. Analysis of the prediction of remaining pesticides revealed a balanced accuracy of the models between 0.48 and 0.66.

CONCLUSION

Overall, predictions were only meaningful in rare cases and therefore always require evaluation by an expert. The critical factors were the underlying data and determination of molecular similarity, which offer great potential for improvement.

Toxicological and Teratogenic Effect of Various Food Additives: An Updated Review

Scientific evidence is mounting that synthetic chemicals used as food additives may have harmful impacts on health. Food additives are chemicals that are added to food to keep it from spoiling, as well as to improve its colour and taste. Some are linked to negative health impacts, while others are healthy and can be ingested with little danger. According to several studies, health issues such as asthma, attention deficit hyperactivity disorder (ADHD), heart difficulties, cancer, obesity, and others are caused by harmful additives and preservatives. Some food additives may interfere with hormones and influences growth and development. It is one of the reasons why so many children are overweight. Children are more likely than adults to be exposed to these types of dietary intakes. Several food additives are used by women during pregnancy and breast feeding that are not fully safe. We must take specific precaution to avoid consuming dangerous compounds before they begin to wreak havoc on our health. This study is intended to understand how the preservatives induce different health problem in the body once it is consumed. This review focuses on some specific food additives such as sodium benzoate, aspartame, tartrazine, carrageenan, and potassium benzoate, as well as vitamin A. Long-term use of food treated with the above-mentioned food preservatives resulted in teratogenicity and other allergens, according to the study. Other health issues can be avoided in the future by using natural food additives derived from plants and other natural sources.

Novel Quorum Quenching YtnP Lactonase From Bacillus paralicheniformis Reduces Pseudomonas aeruginosa Virulence and Increases Antibiotic Efficacy in vivo

Bacterial infections have become increasingly difficult to treat due to the occurrence of antibiotic-resistant strains. A promising strategy to increase the efficacy of therapy is to combine antibacterials with agents that decrease pathogen virulence via the modulation of the quorum sensing (QS). Lactonases inhibit acylated homoserine lactone (AHL)-mediated QS in Gram-negative bacteria, including the leading nosocomial pathogen Pseudomonas aeruginosa. Here we describe the characteristics of heterologously expressed YtnP lactonase from Bacillus paralicheniformis ZP1 (YtnP-ZP1) isolated from agricultural soil using the culture enrichment method. Purified YtnP-ZP1 hydrolyzed different AHLs with preference to substrates with long acyl residues as evaluated in assays with biosensors and HPLC. The enzyme showed good thermostability and activity in a wide temperature range. YtnP-ZP1 in 50 μg mL^-1 concentration reduced the amount of P. aeruginosa-produced long-chain AHLs by 85%, while it hydrolyzed 50% of short-chain AHLs. Incubation of P. aeruginosa PAO1 with YtnP-ZP1 reduced its swarming motility and elastolytic activity without bactericidal effect. YtnP-ZP1 caused the inhibition of biofilm formation and disintegration of mature biofilms in P. aeruginosa PAO1 and multiresistant clinical strain BR5H that was visualized by crystal violet staining. The treatment with YtnP-ZP1 in concentrations higher than 25 μg mL^-1 improved the survival of P. aeruginosa PAO1-infected zebrafish (Danio rerio), rescuing 80% of embryos, while in combination with tobramycin or gentamicin survival rate increased to 100%. The treatment of P. aeruginosa PAO1 biofilms on infected zebrafish tail wounds with 50 μg mL^-1 YtnP-ZP1 and 2 × MIC tobramycin led to infection clearing in 2 days. The extensive toxicity studies proved YtnP-ZP1 was non-toxic to human cells and zebrafish. In conclusion, novel YtnP-ZP1 lactonase with its effective anti-virulence activity could be used to increase the efficacy of clinically approved antibiotics in clearing both systemic and biofilm-associated P. aeruginosa infections.

Teratogenicity of retinoids detected in surface waters in zebrafish embryos and its predictability by in vitro assays

Retinoids are newly detected compounds in aquatic ecosystems associated with cyanobacterial water blooms. Their potential health risks are only scarcely described despite numerous detections of all-trans retinoic acid (ATRA) and its derivatives in the environment. Besides the known teratogen ATRA there is only little or no information about their potency and namely their effects in vivo. We characterize ATRA and 8 other retinoids reported to occur in the environment for their bioactivity and teratogenicity using four in vitro reporter gene assays and zebrafish (Danio rerio) embryotoxicity assay. Our results document the ability of these compounds to interfere with retinoid signalling and cause teratogenicity at environmentally relevant levels with EC₅₀ values at nM (hundreds of ng/L) levels and teratogenic indexes ranging from 2.8 (9cis retinoic acid) to 15.8 (retinal). The relative potency of individual compounds for teratogenicity ranged from 0.059 (retinal) to 0.96 (5,6-epoxy ATRA) when compared to ATRA. An environmentally relevant mixture of retinoids was tested showing good predictability of teratogenicity from the in vitro activities and additive toxicity of the mixture. The high teratogenicity of the newly described compounds associated with cyanobacteria presents a concern for developmental stages due to high conservation of the retinoid signalling across vertebrates.

Comparison Evaluation of the Biological Effects of Sterigmatocystin and Aflatoxin B1 Utilizing SOS-Chromotest and a Novel Zebrafish (Danio rerio) Embryo Microinjection Method

Aflatoxin B1 (AFB1) is a potent mycotoxin and natural carcinogen. The primary producers of AFB1 are Aspergillus flavus and A. parasiticus. Sterigmatocystin (STC), another mycotoxin, shares its biosynthetic pathway with aflatoxins. While there are abundant data on the biological effects of AFB1, STC is not well characterised. According to published data, AFB1 is more harmful to biological systems than STC. It has been suggested that STC is about one-tenth as potent a mutagen as AFB1 as measured by the Ames test. In this research, the biological effects of S9 rat liver homogenate-activated and non-activated STC and AFB1 were compared using two different biomonitoring systems, SOS-Chromotest and a recently developed microinjection zebrafish embryo method. When comparing the treatments, activated STC caused the highest mortality and number of DNA strand breaks across all injected volumes. Based on the E. coli SOS-Chromotest, the two toxins exerted the same genotoxicities. Moreover, according to the newly developed zebrafish microinjection method, STC appeared more toxic than AFB1. The scarce information correlating AFB1 and STC toxicity suggests that AFB1 is a more potent genotoxin than STC. Our findings contradict this assumption and illustrate the need for more complex biomonitoring systems for mycotoxin risk assessment.

Grouping of chemicals into mode of action classes by automated effect pattern analysis using the zebrafish embryo toxicity test

A central element of high throughput screens for chemical effect assessment using zebrafish is the assessment and quantification of phenotypic changes. By application of an automated and more unbiased analysis of these changes using image analysis, patterns of phenotypes may be associated with the mode of action (MoA) of the exposure chemical. The aim of our study was to explore to what extent compounds can be grouped according to their anticipated toxicological or pharmacological mode of action using an automated quantitative multi-endpoint zebrafish test. Chemical-response signatures for 30 endpoints, covering phenotypic and functional features, were generated for 25 chemicals assigned to 8 broad MoA classes. Unsupervised clustering of the profiling data demonstrated that chemicals were partially grouped by their main MoA. Analysis with a supervised clustering technique such as a partial least squares discriminant analysis (PLS-DA) allowed to identify markers with a strong potential to discriminate between MoAs such as mandibular arch malformation observed for compounds interfering with retinoic acid signaling. The capacity for discriminating MoAs was also benchmarked to an available battery of in vitro toxicity data obtained from ToxCast library indicating a partially similar performance. Further, we discussed to which extent the collected dataset indicated indeed differences for compounds with presumably similar MoA or whether other factors such as toxicokinetic differences could have an important impact on the determined response patterns.

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.

Carbonic Anhydrases in Metazoan Model Organisms: Molecules, Mechanisms, and Physiology

During the past three decades, mice, zebrafish, fruit flies, and Caenorhabditis elegans have been the primary model organisms used for the study of various biological phenomena. These models have also been adopted and developed to investigate the physiological roles of carbonic anhydrases (CAs) and carbonic anhydrase-related proteins (CARPs). These proteins belong to eight CA families and are identified by Greek letters: α, β, γ, δ, ζ, η, θ, and ι. Studies using model organisms have focused on two CA families, α-CAs and β-CAs, which are expressed in both prokaryotic and eukaryotic organisms with species-specific distribution patterns and unique functions. This review covers the biological roles of CAs and CARPs in light of investigations performed in model organisms. Functional studies demonstrate that CAs are not only linked to the regulation of pH homeostasis, the classical role of CAs but also contribute to a plethora of previously undescribed functions.

Evaluation of the Toxicity of Bisphenol A in Reproduction and Its Effect on Fertility and Embryonic Development in the Zebrafish (Danio rerio)

Bisphenol A (BPA) is a chemical substance commonly used in the manufacture of plastic products. Its inhalation or ingestion from particles in suspension, water, and/or polluted foods can trigger toxic effects related to endocrine disruption, resulting in hormonal, reproduction, and immunological alterations in humans and animals. The zebrafish (Danio rerio) is an ideal experimental model frequently used in toxicity studies. In order to assess the toxic effects of BPA on reproduction and embryonic development in one generation after parental exposure to it, a total of 80 zebrafish, males and females, divided into four groups in duplicate (n = 20) were exposed to BPA concentrations of 500, 50, and 5 µg L^-1, along with a control group. The fish were kept in reproduction aquariums for 21 days. The embryos obtained in the crosses were incubated in a BPA-free medium and observed for signs of embryotoxicity. A histopathological study (under optical and electron microscopes) was performed of adult fish gonads. The embryos of reproducers exposed to BPA were those most frequently presenting signs of embryotoxicity, such as mortality and cardiac and musculoskeletal malformations. In the histopathological studies of adult individuals, alterations were found in ovocyte maturation and in spermatazoid formation in the groups exposed to the chemical. Those alterations were directly related to BPA action, affecting fertility in both sexes, as well as the viability of their offspring, proportionally to the BPA levels to which they were exposed, so that our results provide more information by associating toxic effects on the offspring and on the next generation.

The crucial role of model systems in understanding the complexity of cell signaling in human neurocristopathies

Animal models are useful to study the molecular, cellular, and morphogenetic mechanisms underlying normal and pathological development. Cell-based study models have emerged as an alternative approach to study many aspects of human embryonic development and disease. The neural crest (NC) is a transient, multipotent, and migratory embryonic cell population that generates a diverse group of cell types that arises during vertebrate development. The abnormal formation or development of the NC results in neurocristopathies (NCPs), which are characterized by a broad spectrum of functional and morphological alterations. The impaired molecular mechanisms that give rise to these multiphenotypic diseases are not entirely clear yet. This fact, added to the high incidence of these disorders in the newborn population, has led to the development of systematic approaches for their understanding. In this article, we have systematically reviewed the ways in which experimentation with different animal and cell model systems has improved our knowledge of NCPs, and how these advances might contribute to the development of better diagnostic and therapeutic tools for the treatment of these pathologies. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Stem Cells and Development Congenital Diseases > Molecular and Cellular Physiology Neurological Diseases > Genetics/Genomics/Epigenetics.

Developmental toxicity testing of unsubstituted and methylated 4- and 5-ring polycyclic aromatic hydrocarbons using the zebrafish embryotoxicity test

The present study evaluates the in vitro developmental toxicity of 4- and 5-ring PAHs including benz[a]anthracene and benzo[a]pyrene and six of their monomethylated congeners, and dibenz[a,h]anthracene using the zebrafish embryotoxicity test (ZET). In general, the tested PAHs induced various developmental effects in the zebrafish embryos including unhatched embryos, no movement and circulation, yolk sac and pericardial edemas, deformed body shape, and cumulative mortality at 96 h post fertilization (hpf). The alkyl substituent on different positions of the aromatic ring of the PAHs appeared to change their in vitro developmental toxicity. Comparison to a previously reported molecular docking study showed that the methyl substituents may affect the interaction of the PAHs with the aryl hydrocarbon receptor (AhR) which is known to play a role in the developmental toxicity of some PAHs. Taken together, our results show that methylation can either increase or decrease the developmental toxicity of PAHs and suggest this may relate to effects on the molecular dimensions and resulting consequences for interactions with the AhR.

The fish early-life stage sublethal toxicity syndrome - A high-dose baseline toxicity response

A large number of toxicity studies report abnormalities in early life-stage (ELS) fish that are described here as a sublethal toxicity syndrome (TxSn_FELS) and generally include a reduced heart rate, edemas (yolk sac and cardiac), and a variety of morphological abnormalities. The TxSn_FELS is very common and not diagnostic for any chemical or class of chemicals. This sublethal toxicity syndrome is mostly observed at high exposure concentrations and appears to be a baseline, non-specific toxicity response; however, it can also occur at low doses by specific action. Toxicity metrics for this syndrome generally occur at concentrations just below those causing mortality and have been reported for a large number of diverse chemicals. Predictions based on tissue concentrations or quantitative-structure activity relationship (QSAR) models support the designation of baseline toxicity for many of the tested chemicals, which is confirmed by observed values. Given the sheer number of disparate chemicals causing the TxSn_FELS and correlation with QSAR derived partitioning; the only logical conclusion for these high-dose responses is baseline toxicity by nonspecific action and not a lock and key type receptor response. It is important to recognize that many chemicals can act both as baseline toxicants and specific acting toxicants likely via receptor interaction and it is not possible to predict those threshold doses from baseline toxicity. We should search out these specific low-dose responses for ecological risk assessment and not rely on high-concentration toxicity responses to guide environmental protection. The goal for toxicity assessment should not be to characterize toxic responses at baseline toxicity concentrations, but to evaluate chemicals for their most toxic potential. Additional aspects of this review evaluated the fish ELS teratogenic responses in relation to mammalian oral LD50s and explored potential key events responsible for baseline toxicity.

24-Epibrassinolide modulates the neurodevelopmental outcomes of high caffeine exposure in zebrafish (Danio rerio) embryos

Previous embryonic fish data have shown caffeine to induce potential teratogenic and long-term neurodevelopmental outcomes through oxidative stress-mediated apoptosis. In this context, antioxidants may have the potential to counteract the caffeine-induced effects. Therefore, the present study aimed to investigate the potential protective role of 24-epibrassinolide (24-EPI), a natural brassinosteroid with proven antioxidant properties, against caffeine-induced teratogenic effects during early zebrafish development. Embryos (~2 h post-fertilization - hpf) were exposed to 0.5 mM caffeine, co-exposed to 24-EPI (0.01, 0.1 and 1 μM) and to 24-EPI alone (1 μM) for 96 h. During exposure, lethal and sublethal developmental parameters were evaluated. At the end of the exposure, biochemical evaluations were made, and 24 h after, different behavioural paradigms were assessed. An increased number of animals showing oedema and malformations were observed after caffeine exposure, while these were reduced after co-exposure to 24-EPI concentration, namely the tail curvature. The results showed oxidative stress and related parameters similar among treatments. Yet, caffeine exposure resulted in locomotor deficits (decreased speed and distance) and disrupted anxiety-like and avoidance responses. The co-exposure to caffeine and to the highest 24-EPI concentrations resulted in less pronounced behavioural deficits. Overall, there was an absence of effects in the embryo/larvae exposed solely to 24-EPI, while caffeine caused developmental and neurotoxic effects. Although further studies are needed, the results showed promising protective effects of the highest 24-EPI concentration tested against the toxicity induced by caffeine in zebrafish.

Human Drug Pollution in the Aquatic System: The Biochemical Responses of Danio rerio Adults

Simple Summary

The release of medicinal products for human use in the aquatic environment is now a serious problem, and can be fatal for the organisms that live there. Danio rerio is a freshwater fish that provides the possibility to study the effects of these pollutants on the health of aquatic organisms. The results of the various existing scientific studies are scarce and conflicting. Here, we review the scientific studies that have analyzed these effects, highlighting that the impacts of drugs are evident in the biochemical responses of these animals.

Abstract

To date, drug pollution in aquatic systems is an urgent issue, and Danio rerio is a model organism to study the toxicological effects of environmental pollutants. The scientific literature has analyzed the effect of human drug pollution on the biochemical responses in the tissues of D. rerio adults. However, the information is still scarce and conflicting, making it difficult to understand its real impact. The scientific studies are not consistent with each other and, until now, no one has grouped their results to create a baseline of knowledge of the possible impacts. In this review, the analysis of literature data highlights that the effects of drugs on adult zebrafishes depend on various factors, such as the tissue analyzed, the drug concentration and the sex of the individuals. Furthermore, the most influenced biochemical responses concern enzymes (e.g., antioxidants and hydrolase enzymes) and total protein and hormonal levels. Pinpointing the situation to date would improve the understanding of the chronic effects of human drug pollution, helping both to reduce it in the aquatic systems and then to draw up regulations to control this type of pollution.

Neuromotor activity inhibition in zebrafish early-life stages after exposure to environmental relevant concentrations of caffeine

Caffeine (CAF), a neuroactive compound, has been found in surface waters at concentrations ranging from few nanograms up to micrograms and may induce adverse effects in aquatic vertebrates. Thus, the aim of this study was to evaluate the potential of CAF in affecting fish early-life stages in a wide concentration range, including occurring levels in surface waters. Specimens of zebrafish in early-life stages were exposed to CAF for 168 h and survival, developmental alterations, locomotor activity and acetylcholinesterase activity were evaluated. CAF induced mortality in embryos unable to hatch or in larvae after hatching (LC₅₀ - 168 h = 283.2 mg/L). Tail deformities were observed in organisms exposed to concentrations ≥ 40 mg/L, while edemas were found at concentrations of 100 mg/L. CAF also decreased the total swimming time and distance moved of exposed organisms (LOEC = 0.0006 mg/L). Locomotor inhibition may be associated with an acetylcholinesterase inhibition observed at concentration ≥ 0.0088 mg/L. Therefore, the hazard of CAF for fish populations deserves further attention since unexpected effects on neuro-behavioral parameters occurs at concentrations often detected in natural aquatic ecosystems.

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.

A Systematic Review to Compare Chemical Hazard Predictions of the Zebrafish Embryotoxicity Test With Mammalian Prenatal Developmental Toxicity

Originally developed to inform the acute toxicity of chemicals on fish, the zebrafish embryotoxicity test (ZET) has also been proposed for assessing the prenatal developmental toxicity of chemicals, potentially replacing mammalian studies. Although extensively evaluated in primary studies, a comprehensive review summarizing the available evidence for the ZET's capacity is lacking. Therefore, we conducted a systematic review of how well the presence or absence of exposure-related findings in the ZET predicts prenatal development toxicity in studies with rats and rabbits. A two-tiered systematic review of the developmental toxicity literature was performed, a review of the ZET literature was followed by one of the mammalian literature. Data were extracted using DistillerSR, and study validity was assessed with an amended SYRCLE's risk-of-bias tool. Extracted data were analyzed for each species and substance, which provided the basis for comparing the 2 test methods. Although limited by the number of 24 included chemicals, our results suggest that the ZET has potential to identify chemicals that are mammalian prenatal developmental toxicants, with a tendency for overprediction. Furthermore, our analysis confirmed the need for further standardization of the ZET. In addition, we identified contextual and methodological challenges in the application of systematic review approaches to toxicological questions. One key to overcoming these challenges is a transition to more comprehensive and transparent planning, conduct and reporting of toxicological studies. The first step toward bringing about this change is to create broad awareness in the toxicological community of the need for and benefits of more evidence-based approaches.

Variability in retinoid-like activity of extracellular compound mixtures produced by wide spectra of phytoplankton species and contributing metabolites

Some phytoplankton species were shown to produce teratogenic retinoids. This study assessed the variability in the extracellular production of compounds with retinoid-like activity for 50 independent cultivations of wide spectra of species including 12 cyanobacteria (15 strains) and 4 algae of different orders. Extracellular retinoid-like activity was detected for repeated cultivations of six cyanobacteria. The results were consistent for some species including Microcystis aeruginosa and Aphanizomenon gracile. The detected retinoid-like activities ranged from below the limit of quantification of 16 ng/L to over 6 µg all-trans retinoic acid (ATRA) equivalent/L. Nontargeted virtual fractionation together with suspect screening approach enabled to identify some retinoid-like compounds in exudates, including ATRA, 9/13-cis retinoic acid, all-trans 5,6-epoxy retinoic acid, 4keto-ATRA, 4keto-retinal, 4hydroxy-ATRA, and retinal. Most of them were for the first time repeatedly detected in exudates of all studied algae (at ng/L levels) and cyanobacteria. Their relative potencies ranged from 0.018 (retinal) to 1 compared to ATRA. They accounted for less than 0.1-50% of total detected retinoid-like activity. The high detected activities and concentrations of retinoids in some samples and their direct accessibility from exudates document potential risk of developmental toxicity for organisms in proximity of massive water blooms.

Toxicogenomic fin(ger)prints for thyroid disruption AOP refinement and biomarker identification in zebrafish embryos

Endocrine disruption (ED) can trigger far-reaching effects on environmental populations, justifying a refusal of market approval for chemicals with ED properties. For the hazard assessment of ED effects on the thyroid system, regulatory decisions mostly rely on amphibian studies. Here, we used transcriptomics and proteomics for identifying molecular signatures of interference with thyroid hormone signaling preceding physiological effects in zebrafish embryos. For this, we analyzed the thyroid hormone 3,3',5-triiodothyronine (T3) and the thyroid peroxidase inhibitor 6-propyl-2-thiouracil (6-PTU) as model substances for increased and repressed thyroid hormone signaling in a modified zebrafish embryo toxicity test. We identified consistent gene expression fingerprints for both modes-of-action (MoA) at sublethal test concentrations. T3 and 6-PTU both significantly target the expression of genes involved in muscle contraction and functioning in an opposing fashion, allowing for a mechanistic refinement of key event relationships in thyroid-related adverse outcome pathways in fish. Furthermore, our fingerprints identify biomarker candidates for thyroid disruption hazard screening approaches. Perspectively, our findings will promote the AOP-based development of in vitro assays for thyroidal ED assessment, which in the long term will contribute to a reduction of regulatory animal tests.

Zebrafish early life stages as alternative model to study 'designer drugs': Concordance with mammals in response to opioids

The number of new psychoactive substances (NPS) on the illicit drug market increases fast, posing a need to urgently understand their toxicity and behavioural effects. However, with currently available rodent models, NPS assessment is limited to a few substances per year. Therefore, zebrafish (Danio rerio) embryos and larvae have been suggested as an alternative model that would require less time and resources to perform an initial assessment and could help to prioritize substances for subsequent evaluation in rodents. To validate this model, more information on the concordance of zebrafish larvae and mammalian responses to specific classes of NPS is needed. Here, we studied toxicity and behavioural effects of opioids in zebrafish early life stages. Synthetic opioids are a class of NPS that are often used in pain medication but also frequently abused, having caused multiple intoxications and fatalities recently. Our data shows that fentanyl derivatives were the most toxic among the tested opioids, with toxicity in the zebrafish embryo toxicity test decreasing in the following order: butyrfentanyl>3-methylfentanyl>fentanyl>tramadol> O-desmethyltramadol>morphine. Similar to rodents, tramadol as well as fentanyl and its derivatives led to hypoactive behaviour in zebrafish larvae, with 3-methylfentanyl being the most potent. Physico-chemical properties-based predictions of chemicals' uptake into zebrafish embryos and larvae correlated well with the effects observed. Further, the biotransformation pattern of butyrfentanyl in zebrafish larvae was reminiscent of that in humans. Comparison of toxicity and behavioural responses to opioids in zebrafish and rodents supports zebrafish as a suitable alternative model for rapidly testing synthetic opioids.

Embryotoxicity evaluation of atractylodin and β-eudesmol using the zebrafish model

Atractylodin and β-eudesmol are the major active ingredients of Atractylodes lancea (Thunb) DC. (AL). Both compounds exhibit various pharmacological activities, including anticancer activity against cholangiocarcinoma. Despite the widespread use of this plant in traditional medicine in China, Japan, Korea, and Thailand, studies of their toxicological profiles are limited. The present study aimed to evaluate the embryotoxicity of atractylodin and β-eudesmol using the zebrafish model. Zebrafish embryos were exposed to a series of concentrations (6.3, 12.5, 25, 50, and 100 μM) of each compound up to 72 h post-fertilization (hpf). The results showed that atractylodin and β-eudesmol induced mortality of zebrafish embryos with the 50% lethal concentration (LC₅₀) of 36.8 and 53.0 μM, respectively. Both compounds also caused embryonic deformities, including pericardial edema, malformed head, yolk sac edema, and truncated body. Only β-eudesmol decreased the hatching rates, while atractylodin reduced the heart rates of the zebrafish embryos. Additionally, both compounds increased reactive oxygen species (ROS) production and altered the transcriptional expression levels of superoxide dismutase 1 (sod1), catalase (cat), and glutathione S-transferase pi 2 (gstp2) genes. In conclusion, atractylodin and β-eudesmol induce mortality, developmental toxicity, and oxidative stress in zebrafish embryos. These findings may imply similar toxicity of both compounds in humans.

Chemical-Induced Cleft Palate Is Caused and Rescued by Pharmacological Modulation of the Canonical Wnt Signaling Pathway in a Zebrafish Model

Cleft palate is one of the most frequent birth defects worldwide. It causes severe problems regarding eating and speaking and requires long-term treatment. Effective prenatal treatment would contribute to reducing the risk of cleft palate. The canonical Wnt signaling pathway is critically involved in palatogenesis, and genetic or chemical disturbance of this signaling pathway leads to cleft palate. Presently, preventative treatment for cleft palate during prenatal development has limited efficacy, but we expect that zebrafish will provide a useful high-throughput chemical screening model for effective prevention. To achieve this, the zebrafish model should recapitulate cleft palate development and its rescue by chemical modulation of the Wnt pathway. Here, we provide proof of concept for a zebrafish chemical screening model. Zebrafish embryos were treated with 12 chemical reagents known to induce cleft palate in mammals, and all 12 chemicals induced cleft palate characterized by decreased proliferation and increased apoptosis of palatal cells. The cleft phenotype was enhanced by combinatorial treatment with Wnt inhibitor and teratogens. Furthermore, the expression of tcf7 and lef1 as a readout of the pathway was decreased. Conversely, cleft palate was prevented by Wnt agonist and the cellular defects were also prevented. In conclusion, we provide evidence that chemical-induced cleft palate is caused by inhibition of the canonical Wnt pathway. Our results indicate that this zebrafish model is promising for chemical screening for prevention of cleft palate as well as modulation of the Wnt pathway as a therapeutic target.

Cytochrome P450 Expression and Chemical Metabolic Activity before Full Liver Development in Zebrafish

Zebrafish are used widely in biomedical, toxicological, and developmental research, but information on their xenobiotic metabolism is limited. Here, we characterized the expression of 14 xenobiotic cytochrome P450 (CYP) subtypes in whole embryos and larvae of zebrafish (4 to 144 h post-fertilization (hpf)) and the metabolic activities of several representative human CYP substrates. The 14 CYPs showed various changes in expression patterns during development. Many CYP transcripts abruptly increased at about 96 hpf, when the hepatic outgrowth progresses; however, the expression of some cyp1s (1b1, 1c1, 1c2, 1d1) and cyp2r1 peaked at 48 or 72 hpf, before full liver development. Whole-mount in situ hybridization revealed cyp2y3, 2r1, and 3a65 transcripts in larvae at 55 hpf after exposure to rifampicin, phenobarbital, or 2,3,7,8-tetrachlorodibenzo-p-dioxin from 30 hpf onward. Marked conversions of diclofenac to 4′-hydroxydiclofenac and 5-hydroxydiclofenac, and of caffeine to 1,7-dimethylxanthine, were detected as early as 24 or 50 hpf. The rate of metabolism to 4’-hydroxydiclofenac was more marked at 48 and 72 hpf than at 120 hpf, after the liver had become almost fully developed. These findings reveal the expression of various CYPs involved in chemical metabolism in developing zebrafish, even before full liver development.

Methyl Palmitate-A suitable adjuvant for Sorafenib therapy to reduce in vivo toxicity and to enhance anti-cancer effects on hepatocellular carcinoma cells

This study focused on evaluating the potency of Methyl Palmitate in reducing in vivo toxicity with enhancement of anti-cancer effects of Sorafenib. In vitro anti-cancer effects on human Hep-G2 cell line were analysed by MTT, Trypan blue, clonogenic, wound scratch migration and TUNEL assays. An in vivo study for anti-angiogenesis effect, toxicity and teratogenicity was analysed in Zebrafish embryos. The combination of Sorafenib (4.5 µmol/L) with Methyl Palmitate (3 mmol/L) significantly enhanced anti-cancer effects on Hep-G2 cell line by increasing cytotoxicity (P ≤ .05 in MTT assay; P ≤ .01 in Trypan blue assay), apoptosis (P ≤ .05) and decreasing the metastatic migration (P ≤ .01) than Sorafenib alone treatment. A prominent inhibition of angiogenesis in vivo was observed for combination treatment. At 5 dpf, only <20% toxicity was observed for 3 mmol/L Methyl palmitate while it was 65.75% for Sorafenib treatment which implies that it is a safer dose for in vivo treatments. A highly significant (P ≤ .001) reduction (43.20%) in toxicity was observed in combination treatment. Thus, the Sorafenib-Methyl Palmitate combination showed a promising treatment effect with significantly reduced in vivo toxicity when compared with Sorafenib alone treatment, and hence the Methyl Palmitate may serve as a good adjuvant for Sorafenib therapy.

Neurobehavioral effects of cyanobacterial biomass field extracts on zebrafish embryos and potential role of retinoids

Cyanobacteria are known for their ability to produce and release mixtures of up to thousands of compounds into the environment. Recently, the production of novel metabolites, retinoids, was reported for some cyanobacterial species along with teratogenic effects of samples containing these compounds. Retinoids are natural endogenous substances derived from vitamin A that play a crucial role in early vertebrate development. Disruption of retinoid signalling- especially during the early development of the nervous system- might lead to major malfunctions and malformations. In this study, the toxicity of cyanobacterial biomass samples from the field containing retinoids was characterized by in vivo and in vitro bioassays with a focus on the potential hazards towards nervous system development and function. Additionally, in order to identify the compounds responsible for the observed in vitro and in vivo effects the complex cyanobacterial extracts were fractionated (C18 column, water-methanol gradient) and the twelve obtained fractions were tested in bioassays. In all bioassays, all-trans retinoic acid (ATRA) was tested along with the environmental samples as a positive control. Retinoid-like activity (mediated via the retinoic acid receptor, RAR) was measured in the transgenic cell line p19/A15. The in vitro assay showed retinoid-like activity by specific interaction with RAR for the biomass samples. Neurotoxic effects of selected samples were studied on zebrafish (Danio rerio) embryos using the light/dark transition test (Viewpoint, ZebraLab system) with 120 hpf larvae. In the behavioural assay, the cyanobacterial extracts caused significant hyperactivity in zebrafish at 120 hpf after acute exposure (3 h prior to the measurement) at concentrations below the teratogenicity LOEC (0.2 g dw L^-1). Similar effect was observed after exposure to fractions of the extracts with detected retinoid-like activity and additive effect was observed after combining the fractions. However, the effect on behaviour was not observed after exposure to ATRA only. To provide additional insight into the behavioural effects and describe the underlying mechanism gene expression of selected biomarkers was measured. We evaluated an array of 28 genes related to general toxicity, neurodevelopment, retinoid and thyroid signalling. We detected several affected genes, most notably, the Cyp26 enzymes that control endogenous ATRA concentration, which documents an effect on retinoid signalling.

Terminalia chebula and Ficus racemosa principles mediated repression of novel drug target Las R - the transcriptional regulator and its controlled virulence factors produced by multiple drug resistant Pseudomonas aeruginosa - Biocompatible formulation against drug resistant bacteria

Pseudomonas aeruginosa- major group of an aerobic bacteria associated with nosocomial and other life threatening infections. Diverse virulence factors produced by P. aeruginosa is due to distinct molecular cell signaling mechanism termed as quorum sensing (QS). Interfering with normal QS mechanism by active biomolecules is an effective strategy for attenuating its virulence. With this objective, the present study is undertaken to evaluate the inhibition of quorum sensing of clinical isolate of P. aeruginosa by repression of Las R-a transcriptional regulator for QS by ethanol extract of Terminalia chebula and Ficus racemosa. Las R repression by the plant extracts was measured in inhibition of various virulence factors like biofilm, pyocyanin production, total proteolytic activity, swarming and twisting motility. Fabrication of the extracted metabolites on the wound dressing and its effect on anti bacterial activity was also investigated. Compatibility of plant extracts on zebra fish development and blood cells was further studied. P. aeruginosa was isolated from the post operative patient and the isolated pure culture was identified by cultural, biochemical, molecular characteristics. Active principles of both the plants were readily extracted in ethanol and effectively repressed the expression of Las R. Both the tested plant extracts effectively repressed Las R expression which in turn affect the production of various virulence factors like biofilm formation, pyocyanin production, swarming motility, twisting motility, total proteolytic activity, cell adhesion and signaling molecule acyl honoserine lactone (AHL) production. Plant extract treatment brought about drastic reduction of all the tested virulence factors and AHL production. Extracted metabolites were fabricated on the wound dressing material adopting simple dip or immersion method reveals uniform coating, effective embedding of phytochemicals with the fibers and retained the anti bacterial activity against P. aeruginosa. Biocompatibility studies with zebra fish model shows both the tested plant extracts treatment was not exhibited any sign of toxicity on the developmental stages of Zebra fish. Hemolysis and changes in anti oxidative enzymes were not recorded in the plant extracts treated blood which demonstrated the best biocompatibility of the tested plant extracts. These results shows that the presence of potential phytochemicals in the ethanolic extract of Terminalia chebula and Ficus racemosa effectively represses the Las R followed by inhibition of quorum sensing mediated virulence factors production may be useful in the lead of anti bacterial drugs.