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

Newly synthesized derivatives with a thiosemicarbazide group reduce the viability of cancer cell lines. Acute toxicity assessment in Zebrafish (Danio rerio) early life stages

Due to the variability and ability of tumor to mutate, as well as the heterogeneity of tumor tissue, such drugs are sought that would act selectively and multidirectionally on the cancer cell. Therefore, two newly synthesized semicarbazide structured substances were evaluated for anticancer properties in our study: 1a and 1b. In order to evaluate the cytotoxicity and selectivity of the tested compounds, MTT and Neutral Red uptake assay on cell lines (HEK293, LN229, 769-P, HepG2 and NCI-H1563) and cell cycle analysis were performed. Acute toxicity and cardiotoxicity were also evaluated in the zebrafish model. The tested compounds (1a, 1b) showed cytotoxic activity, with the greatest selectivity noted against the glioblastoma multiforme cell line (LN229). However, compound 1b showed stronger selective activity than 1a. Both of compounds were shown to significantly affect the M phase of the cell cycle. Whereas, the conducted toxicological examination of newly synthesized thiosemicarbazide derivates showed, that direct exposition of Danio rerio embryos to compound 1a, but not 1b, causes a concentration-dependent increase in developmental malformations, indicating possible teratogenic effects.

Integrated histopathology and transcriptome metabolome profiling reveal the toxicity mechanism of phenazine-1-carboxylic acid in zebrafish

Phenazine-1-carboxylic acid (PCA) is a new type of agrochemical used to prevent plant diseases, but its effects on aquatic organisms are unclear. To comprehensively assess the impacts of PCA for aquatic organisms and its associated environmental risks, this study investigated, taking zebrafish as the research object, the toxicological mechanism of PCA by means of optical microscopy, hematoxylin and eosin (HE) staining, ultrastructural observation, physiological and biochemical testing, transcriptome sequencing, metabolome analysis, fluorescence quantitative PCR and molecular simulation. The results indicated that PCA was detrimental to zebrafish embryos, larvae and adults, with LC50 values at 96 h of 3.9093 mg/L, 8.5075 mg/L, and 13.6388 mg/L, respectively. PCA caused abnormal spontaneous movement, slowed the heart rate, delayed hatching, shortened the body length, slowed growth, and caused malformations. PCA mainly affected the brain, liver, heart, and ovaries. PCA distorted cell morphology, damaged mitochondrial membranes, disintegrated mitochondrial ridges, and dissociated nuclear membranes. PCA inhibited the enzyme activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-PX), decreased the malondialdehyde (MDA) content and disrupted antioxidant effects. The results of omics studies confirmed that PCA interfered with the transcriptional and metabolic network of zebrafish, downregulating most genes and metabolites. PCA mainly affected functions related to mitochondrial steroids, lipids, sterols, oxidoreductase activity and pathways involving cofactors, steroids, porphyrin, cytochromes, which specifically bound to targets such as panx3, agmat, and ace2. PCA was moderately toxic to zebrafish, and its usage should be strictly controlled to reduce toxic effects on aquatic organisms. The results of this study provide a new insights for ecotoxicology research.

Impact of exposure to glyphosate-based herbicide on morphological and physiological parameters in embryonic and larval development of zebrafish

Glyphosate-based herbicides (GBH) have been commonly used in agriculture to inhibit weed growth and increase yields. However, due to the high solubility of these herbicides in water, they can reach aquatic environments, by infiltration, erosion, and/or lixiviation, affecting non target organisms. Thus, this study aimed to characterize the toxicity of GBH Roundup WG® (RWG®) during the embryonic and larval development of Danio rerio. Embryos (3 hours post fertilization, hpf-until hatching) and larvae (3 days post fertilization, dpf to 6 dpf) were exposed to concentrations of 0.065 and 6.5 mg L-1 . They were evaluated for survival, hatching, spontaneous movements, heartbeat, morphology, and morphometry by in vivo photographs in microscope, cell proliferation and apoptosis by immunohistochemistry, and exploratory behavior and phototropism by video recording. Our results showed an increase in embryo and larvae mortality in those exposed to 0.065 mg L-1 , as well as a reduction in spontaneous embryo movements. The larval heartbeats showed a decrease at 4 dpf in the group exposed to 0.065 mg L-1 and an increase at 5 and 6 dpf in both exposed groups. Cell proliferation was reduced in both groups exposed in embryos and only in the 0.065 mg L-1 group in larvae, while cell death increased in embryos exposed to 6.5 mg L-1 . These results demonstrated the toxic effect of low concentrations of the herbicide RWG® during embryonic and larval development of non target organisms, as well as the importance of constantly reviewing acceptable limits for exposure in natural environments.

Neurobehavioral effects of fungicides in zebrafish: a systematic review and meta-analysis

Pesticides are widely used in global agriculture to achieve high productivity levels. Among them, fungicides are specifically designed to inhibit fungal growth in crops and seeds. However, their application often results in environmental contamination, as these chemicals can persistently be detected in surface waters. This poses a potential threat to non-target organisms, including humans, that inhabit the affected ecosystems. In toxicologic research, the zebrafish (Danio rerio) is the most commonly used fish species to assess the potential effects of fungicide exposure, and numerous and sometimes conflicting findings have been reported. To address this, we conducted a systematic review and meta-analysis focusing on the neurobehavioral effects of fungicides in zebrafish. Our search encompassed three databases (PubMed, Scopus, and Web of Science), and the screening process followed predefined inclusion/exclusion criteria. We extracted qualitative and quantitative data, as well as assessed reporting quality, from 60 included studies. Meta-analyses were performed for the outcomes of distance traveled in larvae and adults and spontaneous movements in embryos. The results revealed a significant overall effect of fungicide exposure on distance, with a lower distance traveled in the exposed versus control group. No significant effect was observed for spontaneous movements. The overall heterogeneity was high for distance and moderate for spontaneous movements. The poor reporting practices in the field hindered a critical evaluation of the studies. Nevertheless, a sensitivity analysis did not identify any studies skewing the meta-analyses. This review underscores the necessity for better-designed and reported experiments in this field.

Yeast vacuolar enzymes as novel hatching inhibitors for aquatic organisms, Daphnia magna and Danio rerio eggs

Concerns over the spread of non-native species in aquatic environments have led to the need for effective methods to prevent and control their spread while protecting native species. This study investigated the potential of yeast vacuolar enzymes as a natural hatching inhibitor for controlling aquatic organisms. Hatching experiments with Daphnia magna eggs demonstrated that exposure to yeast vacuole enzymes inhibited hatching in a concentration-dependent manner, suggesting their potential as an effective inhibitor of egg hatching in aquatic organisms. Interestingly, the protease used for comparative purposes did not inhibit hatching, but instead increased the mortality of hatched D. magna. Additionally, chorionic changes were observed in non-hatched D. magna eggs and zebrafish eggs exposed to yeast vacuole enzymes, suggesting that the enzyme can alter the chorion and interfere with hatching. These findings suggest that yeast vacuolar enzymes may be a promising and natural management tool for controlling the spread of harmful aquatic organisms, and further research is warranted to explore their potential for species-specific control.

Toxic Effects of Copper Fungicides on the Development and Behavior of Zebrafish in Early-Life Stages

Copper-based fungicides have been used to control various plant diseases for more than one hundred years and play very important roles in agriculture. Accumulation of copper in freshwater and environment pose severe threats to human health and the environment. The current study evaluated the developmental and behavioral toxicity of PEG@Cu NCs (copper nanoclusters), Kocide® 3000 (copper hydroxide), and Cu(CH3COO)2 (copper acetate) to zebrafish in early-life stages. The developmental toxicity was evaluated according to the parameters of mortality, hatching rate, autonomous movement and heartbeat of embryos, and body length of larvae. The 9 dpf (days postfertilization)-LC50 (50% lethal concentration) of embryonic mortality was 0.077, 0.174 or 0.088 mg/L, and the 9 dpf-EC50 (effective concentration of 50% embryos hatching) of hatching rate was 0.079 mg/L, 0.21 mg/L and 0.092 mg/L when the embryos were exposed to PEG@Cu NCs, Kocide® 3000 or Cu(CH3COO)2, respectively. Kocide® 3000 and Cu(CH3COO)2 obviously decreased the spontaneous movements, while PEG@Cu NCs had no adverse effects on that of embryos. The reduced heartbeat can return to normal after exposure to PEG@Cu NCs for 96 h, while it cannot recover from Kocide® 3000. In addition, Kocide® 3000 (≥0.2 mg/L), PEG@Cu NCs and Cu(CH3COO)2 with 0.05 mg/L or higher concentration exhibited obvious behavioral toxicity to zebrafish larvae according to the parameters of movement distance, average velocity, absolute sinuosity, absolute turn angle and absolute angular velocity.

Comparison of Efavirenz and Doravirine Developmental Toxicity in an Embryo Animal Model

In the past, one of the most widely used non-nucleoside reverse transcriptase inhibitors (NNRTI) in first-line antiretroviral therapy (ART) of HIV infection was efavirenz (EFV), which is already used as a cost-effective treatment in developing countries due to its efficacy, tolerability, and availability. However, EFV also demonstrates several adverse effects, like hepatotoxicity, altered lipid profile, neuropsychological symptoms, and behavioral effects in children after in utero exposure. In 2018, another NNRTI, doravirine (DOR), was approved due to its similar efficacy but better safety profile. Preclinical safety studies demonstrated that DOR is not genotoxic and exhibits no developmental toxicity or effects on fertility in rats. Zebrafish (Danio rerio) embryos have been widely accepted as a vertebrate model for pharmacological and developmental studies. We used zebrafish embryos as an in vivo model to investigate the developmental toxicity of DOR compared to EFV. After exposure of the embryos to the drugs from the gastrula stage up to different developmental stages (30 embryos for each arm, in three independent experiments), we assessed their survival, morphology, hatching rate, apoptosis in the developing head, locomotion behavior, vasculature development, and neutral lipid distribution. Overall, DOR showed a better safety profile than EFV in our model. Therapeutic and supra-therapeutic doses of DOR induced very low mortality [survival rates: 92, 90, 88, 88, and 81% at 1, 5, 10, 25, and 50 μM, respectively, at 24 h post fecundation (hpf), and 88, 85, 88, 89, and 75% at the same doses, respectively, at 48 hpf] and mild morphological alterations compared to EFV exposure also in the sub-therapeutic ranges (survival rates: 80, 77, 69, 63, and 44% at 1, 5, 10, 25, and 50 μM, respectively, at 24 hpf and 72, 70, 63, 52, and 0% at the same doses, respectively, at 48 hpf). Further, DOR only slightly affected the hatching rate at supra-therapeutic doses (97, 98, 96, 87, and 83% at 1, 5, 10, 25, and 50 μM, respectively, at 72 hpf), while EFV already strongly reduced hatching at sub-therapeutic doses (83, 49, 11, 0, and 0% at 1, 5, 10, 25, and 50 μM, respectively, at the same time endpoint). Both DOR at therapeutic doses and most severely EFV at sub-therapeutic doses enhanced apoptosis in the developing head during crucial phases of embryo neurodevelopment and perturbed the locomotor behavior. Furthermore, EFV strongly affected angiogenesis and disturbed neutral lipid homeostasis even at sub-therapeutic doses compared to DOR at therapeutic concentrations. Our findings in zebrafish embryos add further data confirming the higher safety of DOR with respect to EFV regarding embryo development, neurogenesis, angiogenesis, and lipid metabolism. Further studies are needed to explore the molecular mechanisms underlying the better pharmacological safety profile of DOR, and further human studies are required to confirm these results in the zebrafish animal model.

Triazole fungicides induce adipogenesis and repress osteoblastogenesis in zebrafish

Triazoles are a major group of azole fungicides commonly used in agriculture, and veterinary and human medicine. Maternal exposure to certain triazole antifungal medication causes congenital malformations, including skeletal malformations. We hypothesized that triazoles used as pesticides in agriculture also pose a risk of causing skeletal malformations in developing embryos. In this study, teratogenic effects of three commonly used triazoles, cyproconazole, paclobutrazol, and triadimenol, were investigated in zebrafish, Danio rerio. Exposure to the triazole fungicides caused bone and cartilage malformations in developing zebrafish larvae. Data from whole-embryo transcriptomics with cyproconazole suggested that exposure to this compound induces adipogenesis while repressing skeletal development. Confirming this finding, the expression of selected bone and cartilage marker genes were significantly downregulated with triazoles exposure as determined by quantitative PCR. The expression of selected adipogenic genes was upregulated by the triazoles. Furthermore, exposure to each of the three triazoles induced adipogenesis and lipid droplet formation in vitro in 3T3-L1 pre-adipocyte cells. In vivo in zebrafish larvae, cyproconazole exposure caused lipid accumulation. These results suggest that exposure to triazoles promotes adipogenesis at the expense of skeletal development, and thus they expand the chemical group of bona fide bone to fat switchers.

A study on the mechanism of Indium phosphide/zinc sulfide core/shell quantum dots influencing embryo incubation of rare minnow (Gobiocypris rarus)

Quantum dots (QDs) inhibit fish hatching, but the mechanism is still unclear. In this study, the effect of Indium phosphide/zinc sulfide quantum dots (InP/ZnS QDs) on the embryo incubation of rare minnow was investigated. Five experimental concentration groups were set up according to the preliminary experimental results, which were 0, 50, 100, 200 and 400 nM. A direct exposure method was adopted to expose embryos to InP/ZnS QDs solution. The results showed that InP/ZnS QDs significantly inhibited the embryo hatching rate, delayed embryo emergence, affected the expression of genes associated with hatching gland cells and hatching enzymes. InP/ZnS QDs also destroy the structure of the embryo chorion. In addition, QDs can cause oxidative stress in embryos. Transcriptional sequencing analysis showed that InP/ZnS QDs InP/ZnS QDs may have induced the production of a hypoxic environment and triggered induce abnormal cardiac muscle contraction, inflammatory response and apoptosis process in embryos. In conclusion, QDs influences embryo hatchability largely through egg chorion mediation.

Dimeric polyphenols to pave the way for new antimalarial drugs

Because of the threat of resistant Plasmodium sp., new orally active antimalarials are urgently needed. Inspired by the structure of ellagic acid, exhibiting potent in vivo and in vitro antiplasmodial effects, polyphenolic structures possessing a similar activity-safety profile were synthesized. Indeed, most exhibited a marked in vitro effect (IC50 < 4 μM) on resistant P. falciparum, without any detrimental effects reported during the toxicity assays (hemolysis, cytotoxicity, in vivo). In addition, they possessed a greater hydrosolubility (from 7 μM to 2.7 mM) compared to ellagic acid. Among them, 30 is the most promising for antimalarial purposes since it displayed a significant parasitaemia reduction after oral administration in mice (50 mg kg-1) compared to the orally ineffective ellagic acid. In conclusion, our investigations led to the identification of a promising scaffold, which could bring new insights for malaria treatment.

A New Bioassay for the Detection of Paralytic and Amnesic Biotoxins Based on Motor Behavior Impairments of Zebrafish Larvae

The global concern about the increase of harmful algal bloom events and the possible impacts on food safety and aquatic ecosystems presents the necessity for the development of more accessible techniques for biotoxin detection for screening purposes. Considering the numerous advantages that zebrafish present as a biological model and particularly as a toxicants sentinel, we designed a sensitive and accessible test to determine the activity of paralytic and amnesic biotoxins using zebrafish larvae immersion. The ZebraBioTox bioassay is based on the automated recording of larval locomotor activity using an IR microbeam locomotion detector, and manual assessment of four complementary responses under a simple stereoscope: survival, periocular edema, body balance, and touch response. This 24 h acute static bioassay was set up in 96-well microplates using 5 dpf zebrafish larvae. For paralytic toxins, a significant decrease in locomotor activity and touch response of the larvae was detected, allowing a detection threshold of 0.1-0.2 µg/mL STXeq. In the case of the amnesic toxin the effect was reversed, detecting hyperactivity with a detection threshold of 10 µg/mL domoic acid. We propose that this assay might be used as a complementary tool for environmental safety monitoring.

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

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

QNZ exposure induces development toxicity and mechanisms of hatching inhibition in large-scale loach (Paramisgurnus dabryanus) embryos

QNZ is a quinazoline-type NF-κB inhibitor and is one of the hot anti-inflammatory drug candidates in recent years. With its development and application, QNZ will inevitably enter the aquatic environment posing a threat to aquatic organisms. To investigate the potential toxicity of QNZ in the early life stages of the organism, this study exposed embryos of large-scale loach (Paramisgurnus dabryanus) to 0, 20, 40, 60, and 80 nM of QNZ. The hatching of embryos was significantly inhibited and hatching time was delayed. We explored the mechanism of hatching delay and failure. The results suggested that QNZ exposure reduced the number of hatching gland cells (HGCs) and hatching enzyme activity. Also, the frequency of spontaneous movements was inhibited by interfering with the expression of genes related to the cholinergic system and skeletal muscle development. Further, QNZ exposure induces a series of morphological changes (spine deformation, pericardial edema, tail deformation, and yolk sac edema) in embryos and newly-hatched larvae, and finally increased the deformity rate and mortality rate of newly-hatched larvae. The information presented in this study will provide a scientific basis for further studies into the potential toxicity of QNZ on aquatic organisms.

Environmental exposure to triazole fungicide causes left-right asymmetry defects and contributes to abnormal heart development in zebrafish embryos by activating PPARγ-coupled Wnt/β-catenin signaling pathway

Triazole fungicides have been widely used all over the world. However, their potential ecological safety and health risks remain unclear, especially their cardiac developmental toxicity. This study systematically investigated whether and how triazole fungicides could activate peroxisome proliferative activity receptor γ (PPARγ) to cause abnormal heart development. Among ten triazole fungicides, difenoconazole (DIF) exhibited the strongest agonistic activity and caused severe pericardial edema in zebrafish embryos, accompanied by a reduction in heart rate, blood flow and cardiac function. In vitro transcriptomic profile implicated that DIF inhibited the Wnt signaling pathway, and in vivo DIF exposure significantly increased the phosphorylation of β-catenin (p = 0.0002) and altered the expression of related genes in zebrafish embryos. Importantly, exposure to DIF could activate PPARγ and inhibit the Wnt/β-catenin signaling pathway, which changed the size of Kupffer's vesicle (KV) (p = 0.02), altered the expression of left-right (LR) asymmetry-related genes, caused cardiac LR asymmetry defect, and eventually led to abnormal heart development. These findings provide evidence for potential developmental toxicity of triazole fungicides and highlight the necessity of assessing their ecological safety and human health risks.

Evaluation of developmental toxicity in zebrafish embryos and antiproliferative potential against human tumor cell lines of new derivatives containing 4-nitrophenyl group

The aim of the studies was to evaluate the antiproliferative potential against human tumor cell lines of newly synthetized derivatives containing 4-nitrophenyl group, as well as its impact on developmental toxicity in zebrafish model. We selected 1-(4-nitrobenzoyl)-4-ethylsemicarbazide (APS-1) and 1-[(4-nitrophenyl)acetyl]-4-hexyl-thiosemicarbazide (APS-18) for research. The antiproliferative properties of semicarbazide derivatives were assessed against human cancer cell lines derived from hepatocellular adenocarcinoma (HepG2), renal cell carcinoma (769-P), non-small cell lung cancer (NCI-H1563) and glioblastoma multiforme (LN229) in comparison to the physiological human embryonic kidney (HEK-293) cell line. The influence of the tested substances on the cell cycle and apoptosis was also evaluated. Fish embryo acute toxicity test (FET) was performed based on OECD Guidelines (Test No. 236), and was carried out for the first 5 days post fertilization. The following concentrations of APS-1 and APS-18 were tested: 125-2000 μM and 0.125-1000 μM, respectively. The presented studies on the antiproliferative properties of the new semicarbazide derivatives showed that the compounds APS-1 and APS-18 reduce the viability of human tumor lines. Particularly noteworthy is the strong and selective antiproliferative activity of APS-18 against all neoplastic cell lines, in particular against glioblastoma. Against this tumor line, the compound APS-1 showed an effective inhibitory effect. In the FET we noted that the direct exposure of zebrafish embryos to APS-1 and APS-18 in used range of concentration did not cause morphological abnormalities, including cardiotoxicity. On basis of obtained outcomes it could be concluded that APS-1 and APS-18 may constitute models for further research, design and synthesis of new, safer drugs with more favorable anticancer properties.

Toxic effects of four cardiovascular drugs on the development and epigenetics of zebrafish (Danio rerio)

Due to the prevalence of cardiovascular diseases, therapeutic drugs such as atenolol (ATE), metoprolol (MET), atorvastatin (ATO), and bezafibrate (BZB) have been widely used and thus frequently detected in surface water at ng·L^-1-μg·L^-1 level. In this study, the developmental toxicity of these drugs (0.5 μg·L^-1-500 μg·L^-1) to zebrafish, an aquatic model organism, was investigated; and the epigenetic toxicity of BZB was also explored. For all four drugs, the results showed that the drugs exposure could cause sublethal toxic effects on zebrafish larvae, such as decreases in hatching rate, body length, and heart rate. ATO also induced the swelling of the eyes of larvae by 5 %-15 %. Yolk sac edema, pericardial edema, bent spine, and tail malformation were observed in larvae exposed to the drugs, and yolk sac edema was the most common malformation. In addition, the spontaneous movement and free-swimming activity could be inhibited by the drugs. Combined with RNA-seq results, the adverse development of larvae in exposure groups may be caused by the disruption of lipid and carbohydrate metabolism, and the development and function of eye and nervous system. After a 30-day uptake period, the accumulation of BZB and the decrease of global DNA methylation level were observed in the liver, kidneys, gut, gills, and brain of adult zebrafish (4-month-old) exposed to 0.5 μg·L^-1 to 500 μg·L^-1 BZB. The liver was the main organ for BZB accumulation and the occurrence of DNA hypomethylation. In the liver, overexpression (1.5-7.6 times) of genes related to lipid metabolism (PPARα), DNA methylation (Dnmt1), and apoptosis (p53) was also observed. The results of the current study suggest that long-term exposure to low-concentrations of cardiovascular drugs may pose significant threats to aquatic ecosystems.

The toxicological effects of Eryngium foetidum extracts on zebrafish embryos and larvae depend on the type of extract, dose, and exposure time

Eryngium foetidum is a herbaceous plant found in tropical and subtropical regions. In vivo pharmacological parameters show that leaf extracts of this plant have antioxidant, anti-inflammatory, antidiabetic, and antimicrobial activities due to their bioactive compounds such as flavonoids and phenols. Despite the evidence for several bioactivities of E. foetidum, information on its safety and tolerability is limited. The objective of this study was to assess the effect and concentration of different extracts of E. foetidum on the development of zebrafish (Danio rerio) embryos. To study the impact of aqueous (AE), ethanolic (EE), and methanolic (ME) extracts, the embryos were exposed to 0.625, 1.25, 2.5, 5, and 10 mg mL-1 for up to 120-h postfertilization to assess embryonic developmental toxicity and then to 0.039, 0.078, 0.156, 0.312, and 0.625 mg mL-1 to assess the antioxidant responses of the enzymes superoxide dismutase catalase, glutathione S-transferase (GST), and cell apoptosis. The results showed that, depending on the extraction solvent, concentration used, and exposure time, E. foetidum extracts caused mortality, altered the hatching time, and promoted changes in enzymatic activities. Delays in development and increased GST activity were found in all treatments. Apoptosis was not observed in any of the treatments. In conclusion, AE, EE, and ME concentrations above 0.625 mg mL-1 can cause adverse effects on the early stages of zebrafish development.

Embryonic exposure to butylparaben and propylparaben induced developmental toxicity and triggered anxiety-like neurobehavioral response associated with oxidative stress and apoptosis in the head of zebrafish larvae

Parabens are synthetic antimicrobial compounds used as a preservative for extending the shelf life of food, pharmaceutical and cosmetic products. The alkyl chain length of the paraben esters positively correlates with their antimicrobial property. Hence, long-chain paraben esters, namely butylparaben and propylparaben, are used in combination as they have better solubility and antimicrobial efficacy. Extensive use of parabens has now resulted in the ubiquitous presence of these compounds in various human and environmental matrices. During early life, exposure to environmental contaminants is known to cause oxidative-stress mediated apoptosis in developing organs. The brain being one of the high oxygen-consuming, metabolically active and lipid-rich organ, it is primarily susceptible to reactive oxygen species (ROS) and lipid peroxidation (LP) induced neuronal cell death. The primary cause for the impairment in cognitive and emotional neurobehvioural outcomes in neurodegenerative disease was found to be associated with neuronal apoptosis. The present study aimed to study butylparaben and propylparaben's effect on zebrafish during early embryonic stages. Besides this, the association between alteration in anxiety-like neurobehavioral response with oxidative stress and antioxidant status in head region was also studied. The study results showed variation in the toxic signature left by butylparaben and propylparaben on developmental parameters such as hatching rate, survival and non-lethal malformations in a time-dependent manner. Data from the light-dark preference test showed embryonic exposure to butylparaben and propylparaben to trigger anxiety-like behavior in zebrafish larvae. In addition, a significant increase in intracellular ROS and LP levels correlated with suppressed antioxidant enzymes: superoxide dismutases (SOD), catalases (CAT), Glutathione peroxidase (GPx), glutathione S-transferase (GST), and Glutathione (GSH) activity in the head region of the zebrafish larvae. Acetylcholinesterase (AChE) activity was also suppressed in the exposed groups, along with increased nitric oxide production. The overall observations show increased oxidative stress indices correlating with upregulated expression of apoptotic cells in a dose-dependent manner. Collectively, our findings reveal butylparaben and propylparaben as an anxiogenic neuroactive compound capable of inducing anxiety-like behavior through a mechanism involving oxidative-stress-induced apoptosis in the head of zebrafish larvae, which suggests a potential hazard to the early life of zebrafish and this can be extrapolated to human health as well.

A comprehensive review of 1,2,4-triazole fungicide toxicity in zebrafish (Danio rerio): A mitochondrial and metabolic perspective

In this critical review, we synthesize data from peer-reviewed literature reporting on triazole fungicide exposures in the zebrafish model. Based on their mode of action in plants (potent inhibitors of ergosterol synthesis), we focused attention on mechanisms related to cellular, lipid, and steroid metabolism. Evidence from several studies reveals that zebrafish exposed to triazoles present with impaired mitochondrial oxidative phosphorylation and oxidative stress, as well as dysregulation of lipid metabolism. Such metabolic disruptions are expected to underscore developmental delays, deformity, and aberrant locomotor activity and behaviors often observed following exposure. We begin by summarizing physiological and behavioral effects observed with triazole fungicide exposure in zebrafish. We then discuss mechanisms that may underlie adverse apical effects, focusing on mitochondrial bioenergetics and metabolism. Using computational approaches, we also identify novel biomarkers of triazole fungicide exposure. Extracting and analyzing data contained in the Comparative Toxicogenomics Database (CTD) revealed that transcriptional signatures responsive to different triazoles are related to metabolism of lipids and lipoproteins, biological oxidations, and fatty acid, triacylglycerol, and ketone body metabolism among other processes. Pathway and sub-network analysis identified several transcripts that are responsive in organisms exposed to triazole fungicides, several of which include lipid-related genes. Knowledge gaps and recommendations for future investigations include; (1) targeted metabolomics for metabolites in glycolysis, Krebs cycle, and the electron transport chain; (2) additional studies conducted at environmentally relevant concentrations to characterize the potential for endocrine disruption, given that studies point to altered cholesterol (precursor for steroid hormones), as well as altered estrogen receptor alpha and thyroid hormone expression; (3) studies into the potential role for lipid peroxidation and oxidation of lipid biomolecules as a mechanism of triazole-induced toxicity, given the strong evidence for oxidative damage in zebrafish following exposure to triazole fungicides.

Effects of the food colorant carmoisine on zebrafish embryos at a wide range of concentrations

Since the middle of the twentieth century, the use of dyes has become more common in every food group as well as in the pharmaceutical, textile and cosmetic industries. Azo dyes, including carmoisine, are the most important of the dye classes with the widest color range. In this study, the effects of carmoisine exposure on the embryonic development of zebrafish at a wide dose scale, including recommended and overexposure doses (from 4 to 2000 ppm), were investigated in detail. For this purpose, many morphological and physiological parameters were examined in zebrafish exposed to carmoisine at determined doses for 96 h, and the mechanisms of action of the changes in these parameters were tried to be clarified with the metabolite levels determined. The no observed effect concentration (NOEC) and median lethal concentration (LC₅₀) were recorded at 5 ppm and 1230.53 ppm dose at 96 hpf, respectively. As a result, it was determined that the applied carmoisine caused serious malformations, reduction in height and eye diameter, increase in the number of free oxygen radicals, in apoptotic cells and in lipid accumulation, decrease in locomotor activity depending on the dose and at the highest dose, decrease in blood flow rate. In the metabolome analysis performed to elucidate the metabolism underlying all these changes, 45 annotated metabolites were detected.

Oxidative stress as a potential mechanism by which guanylurea disrupts the embryogenesis of Danio rerio

Metformin is one the most prescribed drug to treat type 2 diabetes. In wastewater treatment plants, this drug is bacterially transformed to guanylurea, which occurs at higher concentrations in the aquatic environments than its parent compound. Since there is a huge knowledge gap about the toxicity of this metabolite on aquatic organisms, we aimed to investigate the impact of guanylurea on the embryonic development and oxidative stress biomarkers of zebrafish (Danio rerio). For this effect, zebrafish embryos (4 h post fertilization) were exposed to 25, 50, 100, 200, 250, 25,000, 50,000, 75,000 μg/L guanylurea until 96 h post fertilization. Guanylurea led to a significant delay in the hatching process in all exposure groups. Furthermore, this transformation product affected the embryonic development of fish, inducing severe body alterations and consequently leading to their death. The most pronounced malformations were malformation of tail, scoliosis, pericardial edema, yolk deformation and craniofacial malformation. Concerning oxidative stress response, we demonstrated that guanylurea induced the antioxidant activity of superoxide dismutase, catalase, and glutathione peroxidase in zebrafish embryos. In addition, the levels of lipid peroxidation, protein carbonyl and hydroperoxide content were also increased in the embryos exposed to this transformation product. However, the integrated biomarker response (IBR) analysis carried out in this study demonstrated that oxidative damage biomarkers got more influence over the embryos than antioxidant enzymes. Thus, we can conclude that guanylurea induces oxidative stress in zebrafish embryos, and that this transformation product impair the normal development of this freshwater organism.

Antidiabetic drug metformin disrupts the embryogenesis in zebrafish through an oxidative stress mechanism

In recent years, the consumption of metformin has increased not only due to the higher prevalence of type 2 diabetes, but also due to their usage for other indications such as cancer and polycystic ovary syndrome. Consequently, metformin is currently among the highest drug by weight released into the aquatic environments. Since the toxic effects of this drug on aquatic species has been scarcely explored, the aim of this work was to investigate the influence of metformin on the development and redox balance of zebrafish (Danio rerio) embryos. For this purpose, zebrafish embryos (4 hpf) were exposed to 1, 10, 20, 30, 40, 50, 75 and 100 μg/L metformin until 96 hpf. Metformin significantly accelerated the hatching process in all exposure groups. Moreover, this drug induced several morphological alterations on the embryos, affecting their integrity and consequently leading to their death. The most frequent malformations found on the embryos included malformation of tail, scoliosis, pericardial edema and yolk deformation. Regarding oxidative balance, metformin significantly induced the activity of antioxidant enzymes and the levels of oxidative damage biomarkers. However, our IBR analisis demonstrated that oxidative damage biomarkers got more influence over the embryos. Together these results demonstrated that metformin may affect the embryonic development of zebrafish and that oxidative stress may be involved in the generation of this embryotoxic process.

Influence of salinity on the toxicity of copper and cadmium to Zebrafish embryos

Salinization has become a serious worldwide environmental perturbation in freshwater ecosystems. Concomitantly, many of such ecosystems are already impacted by other toxicants, which together with increased salinity may result in synergistic, antagonistic or additive toxic effects to biota. This work intended to assess the influence of increasing salinity (by using NaCl) on the lethal and sublethal toxicity of two metallic elements (copper and cadmium) in embryos of the fish species Danio rerio. This goal was achieved by exposing zebrafish embryos to seven concentrations of NaCl, individually or combined with each metal, using a full factorial design. The following endpoints were monitored in the test organisms: mortality, hatching, malformations and the enzymatic activity of glutathione S-transferase (GST) and cholinesterase (ChE). Overall, moderate salinity levels alleviated the lethal toxicity of both copper and cadmium although this effect was stronger in the copper assay. This effect was also influenced, as expected, by the concentrations of the metals indicating that the protective effect of salt only reaches some levels, after what is overwhelmed by the high metal toxicity, especially with the non-essential metal cadmium. At sub-lethal concentrations, the interactive effect resulting from NaCl and metals was not consistent and varied with the endpoint analyzed and the metal tested. Overall, the interactions between the salt and metals seem complex and with more drastic effects (positive or negative) on lethal endpoints than sub-lethal.

Comparative Toxicity Assessment of Kratom Decoction, Mitragynine and Speciociliatine Versus Morphine on Zebrafish (Danio rerio) Embryos

Background: Kratom (Mitragyna speciosa Korth), a popular opioid-like plant holds its therapeutic potential in pain management and opioid dependence. However, there are growing concerns about the safety or potential toxicity risk of kratom after prolonged use.

Aim of the study: The study aimed to assess the possible toxic effects of kratom decoction and its major alkaloids, mitragynine, and speciociliatine in comparison to morphine in an embryonic zebrafish model.

Methods: The zebrafish embryos were exposed to kratom decoction (1,000–62.5 μg/ml), mitragynine, speciociliatine, and morphine (100–3.125 μg/ml) for 96 h post-fertilization (hpf). The toxicity parameters, namely mortality, hatching rate, heart rate, and morphological malformations were examined at 24, 48, 72, and 96 hpf, respectively.

Results: Kratom decoction at a concentration range of ≥500 μg/ml caused 100% mortality of zebrafish embryos and decreased the hatching rate in a concentration-dependent manner. Meanwhile, mitragynine and speciociliatine exposure resulted in 100% mortality of zebrafish embryos at 100 μg/ml. Both alkaloids caused significant alterations in the morphological development of zebrafish embryos including hatching inhibition and spinal curvature (scoliosis) at the highest concentration. While exposure to morphine induced significant morphological malformations such as pericardial oedema, spinal curvature (lordosis), and yolk edema in zebrafish embryos.

Conclusion: Our findings provide evidence for embryonic developmental toxicity of kratom decoction and its alkaloids both mitragynine and speciociliatine at the highest concentration, hence suggesting that kratom consumption may have potential teratogenicity risk during pregnancy and thereby warrants further investigations.

Is the Synthetic Fungicide Fosetyl-Al Safe for the Ecotoxicological Models Danio rerio and Enchytraeus crypticus?

Worldwide, pesticides have contaminated the environment, affecting non-target species. The aim of this work was to evaluate the effects of fosetyl-Al (FOS) on model organisms. Based on the 3 Rs for animal research and described guidelines, the OECD 236 and 220 were applied with some modifications. The FOS test concentrations were 0.02–0.2–2–20–200 mg/L for Danio rerio and 250–500–750–1000–1250 mg/kg for Enchytraeus crypticus. Besides the standard endpoints, additional endpoints were evaluated (D. rerio: behavior and biochemical responses; E. crypticus: extension of exposure duration (28 d (days) + 28 d) and organisms’ sizes). For D. rerio, after 96 h (h), hatching was inhibited (200 mg/L), proteins’ content increased (2 and 20 mg/L), lipids’ content decreased (2 mg/L), glutathione S-transferase activity increased (2 mg/L), and, after 120 h, larvae distance swam increased (20 mg/L). For E. crypticus, after 28 d, almost all the tested concentrations enlarged the organisms’ sizes and, after 56 d, 1250 mg/kg decreased the reproduction. In general, alterations in the organisms’ biochemical responses, behavior, and growth occurred at lower concentrations than the effects observed at the standard endpoints. This ecotoxicological assessment showed that FOS may not be considered safe for the tested species, only at higher concentrations than the predicted environmental concentrations (PECs). This research highlighted the importance of a multi-endpoint approach to assess the (eco)toxic effects of the contaminants.

Seasonal variation in oestrogenic potency and biological effects of wastewater treatment works effluents assessed using ERE-GFP transgenic zebrafish embryo-larvae

Effluents from wastewater treatment works (WwTW) exhibit both temporal and spatial variation in oestrogenicity, however few studies have attempted to quantify how this variation affects biological responses in fish. Here we used an oestrogen-responsive green fluorescent protein (ERE-GFP) transgenic zebrafish (Danio rerio) to quantify oestrogenic activity and health effects for exposure to three different WwTW effluents. Endpoints measured included survival/hatching rate, GFP induction (measured in target tissues or gfp mRNA induction in whole embryos) and vtg mRNA induction in whole embryos. Exposure to one of the study effluents (at 100%), resulted in some mortality, and exposure to all three effluents (at 50% and 100%) caused decreases in hatching rates. Higher levels of vtg mRNA corresponded with higher levels of steroidal oestrogens in the different effluents, with lowest-observed-effect concentrations (LOECs) between 31 ng/L and 39 ng/L oestradiol equivalents (EEQs). Tissue patterns of GFP expression for all three WwTWs effluents reflected the known targets for steroidal oestrogens and for some other oestrogenic chemicals likely present in those effluents (i.e. nonylphenol or bisphenolic compounds). GFP induction was similarly responsive to vtg mRNA induction (a well-established biomarker for oestrogen exposure). We thus demonstrate the ERE-GFP transgenic zebrafish as an effective model for monitoring the oestrogenic potency and health effects for exposure to complex mixtures of chemicals contained within WwTW effluents.

Mechanisms of parental co-exposure to polystyrene nanoplastics and microcystin-LR aggravated hatching inhibition of zebrafish offspring

The combined toxicity effects of microcystins-LR (MCLR) and polystyrene nanoplastics (PSNPs) on the hatching of F1 zebrafish (Danio rerio) embryos were investigated in this study due to the increasing concerns of both plastic pollution and eutrophication in aquatic environments. Three-month-old zebrafish were used to explore the molecular mechanisms underlying the combined effect of MCLR (0, 0.9, 4.5, and 22.5 μg/L) on egg hatching in the existence of PSNPs (100 μg/L). The results demonstrated the existence of PSNPs further increased the accumulation of MCLR in F1 embryos. The hatching rates of F1 embryos were inhibited after exposure to 22.5 μg/L MCLR, and the presence of PSNPs aggravated the hatching inhibition induced by MCLR. The decrease of hatching enzyme activity and the abnormality of spontaneous movement were observed. We examined the altered expression levels of the genes associated with the hatching enzyme (tox16, foxp1, ctslb, xpb1, klf4, cap1, bmp4, cd63, He1.2, zhe1, and prl), cholinergic system (ache and chrnα7), and muscle development (Wnt, MyoD, Myf5, Myogenin, and MRF4). The results suggested the existence of PSNPs exacerbated the hatching inhibition of F1 embryos through decreasing the activity of enzyme, interfering with the cholinergic system, and affecting the muscle development.

Teratogenic and Neurotoxic Effects of n-Butanol on Zebrafish Development

In recent years, n-butanol, a type of alcohol, has been widely used from the chemical industry to the food industry. In this study, toxic effects of n-butanol's different concentrations (10, 50, 250, 500, 750, 1,000, and 1,250 mg/L) in Zebrafish Danio rerio embryos and larvae were investigated. For this purpose, Zebrafish embryos were exposed to n-butanol in acute semistatic applications. Teratogenic effects such as cardiac edema, scoliosis, lordosis, head development abnormality, yolk sac edema, and tail abnormality were determined at different time intervals (24, 48, 72, 96, and 120 h). Additionally, histopathological abnormalities such as vacuole formation in brain tissue and necrosis in liver tissue were observed at high doses (500, 750, and 1,000 mg/L) in all treatment groups at 96 h. It was determined that heart rate decreased at 48, 72, and 96 h due to an increase in concentration. In addition, alcohol-induced eye size reduction (microphthalmia) and single eye formation (cyclopia) are also among the effects observed in our research findings. In conclusion, n-butanol has been observed to cause intense neurotoxic, teratogenic, and cardiotoxic effects in Zebrafish embryos and larvae.

The Kunitz-type serine protease inhibitor Spint2 is required for cellular cohesion, coordinated cell migration and cell survival during zebrafish hatching gland development

We have previously shown that the Kunitz-type serine protease inhibitor Spint1a, also named Hai1a, is required in the zebrafish embryonic epidermis to restrict the activity of the type II transmembrane serine protease (TTSP) Matriptase1a/St14a, thereby ensuring epidermal homeostasis. A closely related Kunitz-type inhibitor is Spint2/Hai2, which in mammals plays multiple developmental roles that are either redundant or non-redundant with those of Spint1. However, the molecular bases for these non-redundancies are not fully understood. Here, we study spint2 during zebrafish development. It is co-expressed with spint1a in multiple embryonic epithelia, including the outer/peridermal layer of the epidermis. However, unlike spint1a, spint2 expression is absent from the basal epidermal layer but present in hatching gland cells. Hatching gland cells derive from the mesendodermal prechordal plate, from where they undergo a thus far undescribed transit into, and coordinated sheet migration within, the interspace between the outer and basal layer of the epidermis to reach their final destination on the yolk sac. Hatching gland cells usually survive their degranulation that drives embryo hatching but die several days later. In spint2 mutants, cohesion among hatching gland cells and their collective intra-epidermal migration are disturbed, leading to a discontinuous organization of the gland. In addition, cells undergo precocious cell death before degranulation, so that embryos fail to hatch. Chimera analyses show that Spint2 is required in hatching gland cells, but not in the overlying periderm, their potential migration and adhesion substrate. Spint2 acts independently of all tested Matriptases, Prostasins and other described Spint1 and Spint2 mediators. However, it displays a tight genetic interaction with and acts at least partly via the cell-cell adhesion protein E-cadherin, promoting both hatching gland cell cohesiveness and survival, in line with formerly reported effects of E-cadherin during morphogenesis and cell death suppression. In contrast, no such genetic interaction was observed between Spint2 and the cell-cell adhesion molecule EpCAM, which instead interacts with Spint1a. Our data shed new light onto the mechanisms of hatching gland morphogenesis and hatching gland cell survival. In addition, they reveal developmental roles of Spint2 that are strikingly different from those of Spint1, most likely due to differences in the expression patterns and relevant target proteins.

Embryonic zebrafish response to a commercial formulation of azoxystrobin at environmental concentrations

Azoxystrobin is a broad-spectrum strobilurin fungicide for use on a wide range of crops available to end-users as formulated products. Due to its extensive application, it has been detected in aquatic ecosystems, raising concerns about its environmental impact, which is still poorly explored. The objective of this work was to study the effects of a commercial formulation of azoxystrobin in the zebrafish embryo model. Sublethal and lethal effects were monitored during the exposure period from 2 h post fertilisation (hpf) to 96 hpf after exposure to azoxystrobin concentrations (1, 10 and 100 μg L^-1). The responses of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR)) as well as detoxifying enzymes (glutathione-s-transferase (GST) and carboxylesterase (CarE)) were evaluated at 96 hpf. Similarly, glutathione levels (reduced (GSH) and oxidised (GSSG) glutathione), neurotransmission (acetylcholinesterase (AChE)) and anaerobic respiration (lactate dehydrogenase (LDH)) -related enzymes were assayed. At 120 hpf, larvae from each group were used for behaviour analysis. Results from this study showed concentration-dependent teratogenic effects, particularly by increasing the number of malformations (yolk and eye), with a higher prevalence at the highest concentration. However, it was found that the lowest concentration induced a high generation of reactive oxygen species (ROS) and increased activity of SOD, GST, and CarE. In addition, GR and GSSG levels were decreased by the lowest concentration, suggesting an adaptive response to oxidative stress, which is also supported by the increased AChE activity and absence of behavioural changes. These findings advance the knowledge of the azoxystrobin developmental and environmental impacts, which may impose ecotoxicological risks to non-target species.

Comparison of in situ sediment remediation amendments: Risk perspectives from species sensitivity distribution

Contaminated sediment is a major issue for aquatic environments, but attention must be kept even during remediation activities that can negatively affect resident biota especially when applied in situ. For the first time, the species sensitivity distribution (SSD) approach was applied to amendments used for in situ sediment remediation considering 39 papers including both freshwater (F) and saltwater (S) effect data (i.e. n = 17 only F, n = 19 only S, and n = 3 both F and S). Toxicity data related to the application of activated carbon (AC), nano-Zero-Valent-Iron (nZVI), apatite (A), organoclay (OC) and zeolite (Z) were collected and analyzed. SSD curves were constructed by lognormal model providing comprehensive comparisons of the sensitivities of different species to the relative testing methods. Results indicated that Bacteria were the most sensitive group of testing organisms, while Crustaceans were the less sensitive. The hazardous concentration for 5% of the affected species (HC5) were derived to determine the concentration protecting 95% of the species. OC, A and Z presented both acute and chronic toxicity. The HC5 values in descending order are: AC (4.79 g/L) > nZVI (0.02 g/L) > OC, A and Z (1.77E-04 g/L). AC and nZVI can be considered safer than OC, A and Z in sediment remediation activities, even if in situ long-term effects remained still underexplored.

Embryonic exposure to prothioconazole induces oxidative stress and apoptosis in zebrafish (Danio rerio) early life stage

Triazole fungicides are extensively applied in general agriculture for fungal control and have negative impacts on aquatic organisms. Prothioconazole, a widely used triazole fungicide, is toxic to zebrafish, but systematic research on the negative effects caused by prothioconazole in zebrafish embryos is limited. In this study, we studied the developmental toxicology, oxidative stress and apoptosis caused by prothioconazole in zebrafish embryos. Exposure to 0.850 mg/L prothioconazole impacts embryo survival and hatching. Prothioconazole exposure caused embryo malformation, especially yolk-sac and pericardial edemas, and prothioconazole-induced apoptosis was observed. Additionally, exposure to a high prothioconazole concentration up-regulated the expression levels of oxidative stress defense-related genes and p53. The bax to bcl2 ratio increased along with exposure time and prothioconazole concentration. Prothioconazole induced apoptosis during the early life stages of zebrafish and may trigger oxidative-stress and p53-dependent pathway responses. Our findings increase our understanding of the molecular mechanisms of oxidative stress and cell death caused by prothioconazole.

Acute effects of acetaminophen on the developmental, swimming performance and cardiovascular activities of the African catfish embryos/larvae (Clarias gariepinus)

Acetaminophen is a widely used analgesic that has been detected in many water bodies with few reports concerning its potential toxicity to fish. This study sought to assess the developmental, swimming performance and cardiovascular activities of embryo/larvae catfish (Clarias gariepinus) exposed to acetaminophen. The Organization for Economic Development (OECD) Fish Embryo Acute Toxicity Test (OECD 236) was employed. Fertilized embryo were exposed to different concentrations of acetaminophen (0, 0.5, 1, 10 µg/L) for 96 h. Hatching rates of the embryo were observed to decrease with increasing concentrations of acetaminophen. Fish embryo exposed to acetaminophen displayed varying levels of teratogenic effects at different levels of development in a dose-dependent manner. The results also showed a significant (p < 0.05) dose-dependent increase in swimming speed and movement patterns in fish larvae exposed to acetaminophen, with distance travelled in larvae exposed to the highest concentration of acetaminophen (10 µg/L) about eight (8) times the distance travelled by the control larvae, indicating that acetaminophen-induced erratic swimming behaviour in the catfish species. Cardiotoxicity was evident, with a significant reduction in heartbeat rate with increasing concentrations of acetaminophen. The results showed that exposure to acetaminophen resulted in teratogenic, neurotoxic and cardiotoxic effects in embryo/larvae of Clarias gariepinus. The findings suggest that acetaminophen which has recently been detected in many water bodies could potentially impact on survival of aquatic life, especially catfish.

Health Effects and Life Stage Sensitivities in Zebrafish Exposed to an Estrogenic Wastewater Treatment Works Effluent

A wide range of health effects in fish have been reported for exposure to wastewater treatment work (WwTW) effluents including feminized responses in males. Most of these exposure studies, however, have assessed acute health effects and chronic exposure effects are less well established. Using an Estrogen Responsive Element-Green Fluorescent Protein (ERE-GFP)-Casper transgenic zebrafish, we investigated chronic health effects and life stage sensitivities for exposure to an estrogenic WwTW effluent and the synthetic estrogen 17α-ethinylestradiol (EE2). Exposure to the WwTW effluent (at full strength;100%) and to 10 ng/L (nominal) EE2 delayed testis maturation in male fish but accelerated ovary development in females. Exposure to 50% and 100% effluent, and to 10 ng/L EE2, also resulted in skewed sex ratios in favor of females. Differing patterns of green fluorescent protein (GFP) expression, in terms of target tissues and developmental life stages occurred in the ERE-GFP- zebrafish chronically exposed to 100% effluent and reflected the estrogenic content of the effluent. gfp and vitellogenin (vtg) mRNA induction were positively correlated with measured levels of steroidal estrogens in the effluent throughout the study. Our findings illustrate the importance of a fish's developmental stage for estrogen exposure effects and demonstrate the utility of the ERE-GFP zebrafish for integrative health analysis for exposure to estrogenic chemical mixtures.

Zebrafish (Danio rerio) as an excellent vertebrate model for the development, reproductive, cardiovascular, and neural and ocular development toxicity study of hazardous chemicals

In the past decades, the type of chemicals has gradually increased all over the world, and many of these chemicals may have a potentially toxic effect on human health. The zebrafish, as an excellent vertebrate model, is increasingly used for assessing chemical toxicity and safety. This review summarizes the efficacy of zebrafish as a model for the study of developmental toxicity, reproductive toxicity, cardiovascular toxicity, neurodevelopmental toxicity, and ocular developmental toxicity of hazardous chemicals, and the transgenic zebrafish as biosensors are used to detect the environmental pollutants.

Exposure to prothioconazole induces developmental toxicity and cardiovascular effects on zebrafish embryo

Prothioconazole is a fungicide that has been widely used in general agriculture and livestock husbandry. This study evaluated the acute toxicity of prothioconazole to zebrafish embryos by assessing their hatching rate and malformation when exposed to different concentrations of prothioconazole. The 96 h-LC₅₀ value of zebrafish embryos was 1.70 mg/L. Upon exposure to 0.85 mg/L, the mortality rate of the embryos significantly increased while their hatching rate decreased significantly. At prothioconazole concentrations higher than 0.43 mg/L, developmental morphologic abnormalities such as heart and yolk-sac edema, spine curvature, tail deformity, shortened body length and decreased eye area were observed. The heart rate of embryos decreased in a dose-dependent fashion during the exposure time. Prothioconazole exposure also resulted in increased rates of cardiac malformation detected by significant increase in the distance between the sinus venosus and bulbus arteriosus and the pericardium area. Moreover, the expression levels of genes related to cardiac development (amhc, vmhc, fli1, hand2, gata4, nkx2.5, tbx5 and atp2a2a) were significantly altered after exposure to prothioconazole. Indeed, this study revealed the adverse effects on the developmental and cardiovascular system of zebrafish embryo caused by prothioconazole. It further elucidated the risk of prothioconazole exposure to vertebrate cardiovascular toxicity. As such, it provides a theoretical foundation for pesticide risk management measures.

A Phenotypic and Genotypic Evaluation of Developmental Toxicity of Polyhexamethylene Guanidine Phosphate Using Zebrafish Embryo/Larvae

Polyhexamethylene guanidine-phosphate (PHMG-P), a guanidine-based cationic antimicrobial polymer, is an effective antimicrobial biocide, potent even at low concentrations. Due to its resilient bactericidal properties, it has been used extensively in consumer products. It was safely used until its use in humidifiers led to a catastrophic event in South Korea. Epidemiological studies have linked the use of PHMG-P as a humidifier disinfectant to pulmonary fibrosis. However, little is known about its harmful impacts other than pulmonary fibrosis. Thus, we applied a zebrafish embryo/larvae model to evaluate developmental and cardiotoxic effects and transcriptome changes using RNA-sequencing. Zebrafish embryos were exposed to 0.1, 0.2, 0.3, 0.4, 0.5, 1, and 2 mg/L of PHMG-P from 3 h to 96 h post fertilization. 2 mg/L of PHMG-P resulted in total mortality and an LC₅₀ value at 96 h was determined at 1.18 mg/L. Significant developmental changes were not observed but the heart rate of zebrafish larvae was significantly altered. In transcriptome analysis, immune and inflammatory responses were significantly affected similarly to those in epidemiological studies. Our qPCR analysis (Itgb1b, TNC, Arg1, Arg2, IL-1β, Serpine-1, and Ptgs2b) also confirmed this following a 96 h exposure to 0.4 mg/L of PHMG-P. Based on our results, PHMG-P might induce lethal and cardiotoxic effects in zebrafish, and crucial transcriptome changes were linked to immune and inflammatory response.

Toxicity Assessment of 4 Azo Dyes in Zebrafish Embryos

Azo dyes are used widely as color additives in food, drugs, and cosmetics; hence, there is an increasing concern about their safety and possible health hazards. In the present study, we chose 4 azo dyes tartrazine, Sunset Yellow, amaranth, and Allura red and evaluated their developmental toxicity on zebrafish embryos. At concentration levels of 5 to 50 mM, we found that azo dyes can induce hatching difficulty and developmental abnormalities such as cardiac edema, decreased heart rate, yolk sac edema, and spinal defects including spinal curvature and tail distortion. Exposure to 100 mM of each azo dye was completely embryolethal. The median lethal concentration (LC50), median effective concentration (EC50), and teratogenic index (TI) were calculated for each azo dye at 72 hours postfertilization. For tartrazine, the LC50 was 47.10 mM and EC50 value was at 42.66 mM with TI ratio of 1.10. For Sunset Yellow, the LC50 was 38.93 mM and EC50 value was at 29.81 mM with TI ratio of 1.31. For amaranth, the LC50 was 39.86 mM and EC50 value was at 31.94 mM with TI ratio of 1.25. For Allura red, the LC50 was 47.42 mM and EC50 value was 40.05 mM with TI ratio of 1.18. This study reports the developmental toxicity of azo dyes in zebrafish embryos at concentrations higher than the expected human exposures from consuming food and drugs containing azo dyes.

Novel pectin isolated from Spirulina maxima enhances the disease resistance and immune responses in zebrafish against Edwardsiella piscicida and Aeromonas hydrophila

In this study, we demonstrate the enhanced disease resistance and positive immunomodulation of novel pectin isolated from Spirulina maxima (SmP) in zebrafish model. Zebrafish larvae exposed to SmP had significantly (p < 0.05) higher cumulative percent survival (CPS) at 25 (44.0%) and 50 μg/mL (67.0%) against Edwardsiella piscicida compared to the control. However, upon Aeromonas hydrophila challenge, SmP exposed larvae at 50 μg/mL had slightly higher CPS (33.3%) compared to control group (26.7%). SmP supplemented zebrafish exhibited the higher CPS against E. piscicida (93.3%) and A. hydrophila (60.0%) during the early stage of post-infection (<18 hpi). qRT-PCR results demonstrated that exposing (larvae) and feeding (adults) of SmP, drive the modulation of a wide array of immune response genes. In SmP exposed larvae, up-regulation of the antimicrobial enzyme (lyz: 3.5-fold), mucin (muc5.1: 2.84, muc5.2: 2.11 and muc5.3: 2.40-fold), pro-inflammatory cytokines (il1β: 1.79-fold) and anti-oxidants (cat: 2.87 and sod1: 1.82-fold) were identified. In SmP fed adult zebrafish (gut) showed >2-fold induced pro-inflammatory cytokine (il1β) and chemokines (cxcl18b, ccl34a.4 and ccl34b.4). Overall results confirmed the positive modulation of innate immune responses in larval stage and it could be the main reason for developing disease resistance against E. piscicida and A. hydrophila. Thus, non-toxic, natural and biodegradable SmP could be considered as the potential immunomodulatory agent for sustainable aquaculture.

Effects of four food dyes on development of three model species, Cucumis sativus, Artemia salina and Danio rerio: Assessment of potential risk for the environment

Food dyes, or color additives, are chemicals added to industrial food products and in domestic cooking to improve the perceived flavor and attractiveness. Of natural and synthetic origin, their safety has been long discussed, and concern for human safety is now clearly manifested by warnings added on products labels. Limited attention, however, has been dedicated to the effects of these compounds on aquatic flora and fauna. For this reason, the toxicity of four different commercially available food dyes (cochineal red E120, Ponceau red E124, tartrazine yellow E102 and blue Patent E131) was assessed on three different model organisms, namely Cucumis sativus, Artemia salina and Danio rerio that occupy diverse positions in the trophic pyramid. The evidence collected indicates that food dyes may target several organs and functions, depending on the species. C. sativus rate of germination was increased by E102, while root/shoot ratio was ∼20% reduced by E102, E120 and E124, seed total chlorophylls and carotenoids were 15-20% increased by E120 and 131, and total antioxidant activity was ∼25% reduced by all dyes. Mortality and low mobility of A. salina nauplii were increased by up to 50% in presence of E124, E102 and E131, while the nauplii phototactic response was significantly altered by E102, E120 and E124. Two to four-fold increases in the hatching percentages at 48 h were induced by E124, E102 and E131 on D. rerio, associated with the occurrence of 20% of embryos showing developmental defects. These results demonstrated that the food dyes examined are far from being safe for the aquatic organisms as well as land organisms exposed during watering with contaminated water. The overall information obtained gives a realistic snapshot of the potential pollution risk exerted by food dyes and of the different organism' ability to overcome the stress induced by contamination.

Characterization of the adenosinergic system in a zebrafish embryo radiotherapy model

Adenosine is a nucleoside that acts as a signaling molecule by activating P1 purinergic receptors (A₁, A_2A, A_2B and A₃). This activation is involved in immune responses, inflammation, and tissue remodeling and tumor progression. Gamma rays are a type of ionizing radiation widely adopted in radiotherapy of tumors. Although it brings benefits to the success of the therapeutic scheme, it can trigger cellular damages, inducing a perpetual inflammatory response that culminates in adverse effects and severe toxicity. Our study aims to characterize the adenosinergic system in a zebrafish embryo radiotherapy model, relating the adenosine signaling to the changes elicited by radiation exposure. To standardize the radiotherapy procedure, we established a toxicological profile after exposure. Zebrafish were irradiated with different doses of gamma rays (2, 5, 10, 15 and 20 Gy) at 24 hpf. Survival, hatching rate, heartbeats, locomotor activity and morphological changes were determined during embryos development. Although without significant difference in survival, gamma-irradiated embryos had their heartbeats increased and presented decreased hatching time, changes in locomotor activity and important morphological alterations. The exposure to 10 Gy disrupted the ecto-5'-nucleotidase/CD73 and adenosine deaminase/ADA enzymatic activity, impairing adenosine metabolism. We also demonstrated that radiation decreased A_2B receptor gene expression, suggesting the involvement of extracellular adenosine in the changes prompted by radiotherapy. Our results indicate that the components of the adenosinergic system may be potential targets to improve radiotherapy and manage the tissue damage and toxicity of ionizing radiation.

Characterization of biklf/klf17-deficient zebrafish in posterior lateral line neuromast and hatching gland development

Krüpple-like factors (Klfs) are highly conserved zinc-finger transcription factors that regulate various developmental processes, such as haematopoiesis and cardiovascular development. In zebrafish, transient knockdown analysis of biklf/klf17 using antisense morpholino suggests the involvement of biklf/klf17 in primitive erythropoiesis and hatching gland development; however, the continuous physiological importance of klf17 remains uncharacterized under the genetic ablation of the klf17 gene among vertebrates. We established the klf17-disrupted zebrafish lines using the CRISPR/Cas9 technology and performed phenotypic analysis throughout early embryogenesis. We found that the klf17-deficient embryos exhibited abnormal lateral line neuromast deposition, whereas the production of primitive erythrocytes and haemoglobin production were observed in the klf17-deficient embryos. The expression of lateral line neuromast genes, klf17 and s100t, in the klf17-deficient embryos was detected in posterior lateral line neuromasts abnormally positioned at short intervals. Furthermore, the klf17-deficient embryos failed to hatch and died without hatching around 15 days post-fertilization (dpf), whereas the dechorionated klf17-deficient embryos and wild-type embryos were alive at 15 dpf. The klf17-deficient embryos abolished hatching gland cells and Ctsl1b protein expression, and eliminated the expression of polster and hatching gland marker genes, he1.1, ctsl1b and cd63. Thus, the klf17 gene plays important roles in posterior lateral line neuromast and hatching gland development.

Impact of copper oxide nanoparticles (CuO NPs) exposure on embryo development and expression of genes related to the innate immune system of zebrafish (Danio rerio)

CuO NPs are nanomaterials with catalytic activity and unique thermo-physical properties used in different fields such as sensors, catalysts, surfactants, batteries, antimicrobials and solar energy transformations. Because of its wide field of use, these nanoparticles accumulate in the aquatic environment and thus lead to toxic effects on aquatic organisms. The toxicological findings about CuO NPs are controversial and these effects of CuO NPs on aquatic organisms have not been elucidated in detail. Therefore, the aim of this study was to investigate the toxic effect of CuO NPs on zebrafish embryos using different parameters including molecular and morphologic. For this purpose, zebrafish embryos at 4 h after post fertilization (hpf) were exposed to different concentrations of CuO NPs (0.5, 1, 1.5 mg/L) until 96 hpf. Mortality, hatching, heartbeat, malformation rates were examined during the exposure period. In addition, Raman spectroscopy was used to determine whether CuO NPs entered into the tissues of zebrafish larvae or not. Moreover, the alterations in the expression of genes related to the antioxidant system and innate immune system were examined in the embryos exposed to CuO NPs during 96 h. The results showed that CuO NPs was not able to enter into the zebrafish embryos/larvae tissues but caused an increased the mortality rate, a delayed hatching, and a decreased heartbeat rate. Moreover, CuO NPs caused several types of abnormalities such as head and tail malformations, vertebral deformities, yolk sac edema, and pericardial edema. RT-PCR results showed that the transcription of mtf-1, hsp70, nfkb and il-1β, tlr-4, tlr-22, trf, cebp was changed by the application of CuO NPs. In conclusion, short-term exposure to CuO NPs has toxic effects on the development of zebrafish embryos.

Behavioral effects of triadimefon in zebrafish are associated with alterations of the dopaminergic and serotonergic pathways

Triadimefon (TDF) is a triazole fungicide extensively used in agriculture that has been found as a pollutant in numerous water sources. In mammals, it inhibits monoamine uptake through binding to the dopamine transporter, with a mechanism of action similar to cocaine, resulting in higher levels of dopamine at the synapse. Dopamine is a neurotransmitter involved in a broad spectrum of processes such as locomotion, cognition, reward, and mental disorders. In this work we have studied, for the first time, the effects of TDF on behavior of both larval and adult zebrafish and its connection with changes in the dopaminergic and serotonergic systems. We evaluated the acute exposure of 5 dpf larvae to different concentrations of TDF, ranging from 5 mg/L to 35 mg/L. The lowest concentration does not alter neither locomotor activity nor dopamine levels but produced changes in the expression of two genes, tyrosine hydroxylase 1 (th1) and dopamine transporter (dat). Besides, it induced a reduction in extracellular serotonin and had an anxiolytic-like effect, supported by a decrease in cortisol production. On the other hand, a high concentration of TDF produced a dose-dependent reduction in locomotion, which was reversed or enhanced by D1 (SCH-23390) or D2 (Haloperidol) dopamine receptor antagonists, respectively. Using in vivo electrochemistry, we show that these changes could be associated with higher levels of dopamine in the brain. Thus, in adult zebrafish, though not in larvae, TDF exposure increases locomotor activity, anxiety and aggressiveness, which coincides with the behaviors observed in mammals.

A holistic study on potential toxic effects of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) on zebrafish (Danio rerio) embryos/larvae

Multi-walled carbon nanotubes (MWCNTs) have widespread use in industrial and consumer products and great potential in biomedical applications. This leads to inevitably their release into the environment and the formation of their toxic effects on organisms. These effects can change depending on their physicochemical characteristics. Therefore, the toxicological findings of MWCNTs are inconsistent. Their toxicities related to surface modification have not been elucidated in a holistic manner. Hence, this study was conducted to clarify their potential toxic effects on zebrafish embryos/larvae in a comprehensive approach using morphologic, biochemical and molecular parameters. Zebrafish embryos were exposed to 5, 10, 20 mg/L doses of MWCNTs-COOH at 4 h after fertilization and grown until 96 hpf. Physiological findings demonstrated that they induced a concentration-dependent increase in the mortality rate, delayed hatching and decrease in the heartbeat rate. Moreover, it caused abnormalities including yolk sac edema, pericardial edema, head, tail malformations, and vertebral deformities. These effects may be due to the alterations in antioxidant and immune system related gene expressions after their entry into zebrafish embryo/larvae. The entry was confirmed from the evaluation of Raman spectra collected from the head, yolk sac, and tail of control and the nanotube treated groups. The gene expression analysis indicated the changes in the expression of oxidative stress (mtf-1, hsp70, and nfkb) and innate immune system (il-1β, tlr-4, tlr-22, trf, and cebp) related genes, especially an increased in the expression of the hsp70 and il-1β. These findings proved the developmental toxicities of MWCNTs-COOH on the zebrafish embryos/larvae.

Effects of aluminium and cadmium on hatching and swimming ability in developing zebrafish

Aluminium and cadmium are biologically non-essential metals with a role in neurodegenerative and neuromuscular diseases. As an attractive model for neurobehavioural studies, zebrafish at 6 h post fertilization were exposed to 9, 18, 36 and 72 μM CdCl₂ and 50, 100 and 200 μM AlCl₃, respectively, for 72 h, and motility such as distance moved, mean velocity, cumulative movement, meander and heading were measured by DanioVision equipment. The hatching time was also analysed. A delay in the exit from the chorion was observed in all treated larvae with respect to the controls. CdCl₂ acted on the exit from the chorion of larvae with a dose-dependent delay. By contrast, the delay caused by AlCl₃ was greater at low concentrations. A dose-dependent reduction in swimming performance was observed in the larvae exposed to CdCl₂. Instead, for those exposed to AlCl₃, swimming performance improved at higher concentrations although values were in general lower than those of control. All the parameters had a similar trend except the meander parameter which showed a dose-dependent reduction. These data show that cadmium and aluminium can delay hatching and alter swimming ability in the early developmental stages of zebrafish, albeit with different effects, suggesting that exposure to sublethal concentrations of both metals can change behavioural parameters.

Exposure to DBP induces the toxicity in early development and adverse effects on cardiac development in zebrafish (Danio rerio)

Dibutyl phthalate (DBP) is one of the most ubiquitous plasticizers used worldwide and has been frequently detected in soil, water, atmosphere, and other environmental media. DBP has become a ubiquitous environment contaminant and causes serious pollution. However, much attention has been paid to the toxicity of DBP, with only limited attention paid to its detrimental effects on the heart. In the present study, we investigated the toxicity of DBP in zebrafish embryo development, especially adverse effects on cardiac development. Embryos at 4-h post-fertilization (hpf) were exposed to different concentrations of DBP (0, 0.36, 1.8 and 3.6 μM) until 72 hpf. Exposure to DBP resulted in morphological abnormalities in zebrafish embryos. Exposure to 1.8 μM DBP significantly affected the growth, malformation rate, cardiac malformation rate and cardiac looping. Exposure to 3.6 μM DBP significantly affected all endpoints. To preliminarily understand the underlying mechanisms of toxic effects of DBP on the embryo heart, we examined the expression of master cardiac transcription factors such as NKX2.5 and TBX5. The expression of this two transcription factors was significantly reduced with DBP treatment in a dose-dependent manner. Our results demonstrate that exposure to DBP resulted in zebrafish developmental toxicity, pericardial edema, cardiac structure deformities and function alteration, and changed the expression of master cardiac transcription factors such as NKX2.5 and TBX5.

Developmental toxicity of the triazole fungicide cyproconazole in embryo-larval stages of zebrafish (Danio rerio)

Cyproconazole is a triazole fungicide used to protect a diverse range of fruits, vegetables, and grain crops. As such, it has the potential to enter aquatic environments and affect non-target organisms. The objective of this study was to assess the acute toxicity of the triazole fungicide cyproconazole to zebrafish embryos by assessing mortality, developmental defects, morphological abnormality, oxidative respiration, and locomotor activity following a 96-h exposure. Zebrafish embryos at 6-h post-fertilization (hpf) were exposed to either a solvent control (0.1% DMSO, v/v), or one dose of 10, 25, 50, 100, 250, and 500 μM cyproconazole for 96 h. Data indicated that cyproconazole exhibited low toxicity to zebrafish embryos, with a 96-h LC₅₀ value of 90.6 μM (~ 26.4 mg/L). Zebrafish embryos/larvae displayed a significant decrease in spontaneous movement, hatching rate, and heartbeats/20 s with 50, 100, and 250 μM cyproconazole exposure. Malformations (i.e., pericardial edema, yolk sac edema, tail deformation, and spine deformation) were also detected in zebrafish exposed to ≥ 50 μM cyproconazole, with significant increases in cumulative deformity rate at 48, 72, and 96 hpf. In addition, a 20-30% decrease in basal and oligomycin-induced ATP respiration was observed after 24-h exposure to 500 μM cyproconazole in embryos. To determine if cyproconazole affected locomotor activity, a dark photokinesis assay was conducted in larvae following 7-day exposure to 1, 10, and 25 μM cyproconazole in two independent trials. Activity in the dark period was decreased for zebrafish exposed to 25 μM cyproconazole in the first trial, and hypoactivity was also observed in zebrafish exposed to 1 μM cyproconazole in a second trial, suggesting that cyproconazole can affect locomotor activity. These data improve understanding of the toxicity of cyproconazole in developing zebrafish and contribute to environmental risk assessments for the triazole fungicides on aquatic organisms. We report that, based on the overall endpoints assessed, cyproconazole exhibits low risk for developing fish embryos, as many effects were observed above environmentally-relevant levels.