Developmental Toxicity In Zebrafish Research Articles

Diverse PFAS produce unique transcriptomic changes linked to developmental toxicity in zebrafish.

Per- and polyfluoroalkyl substances (PFAS) are a widespread and persistent class of contaminants posing significant environmental and human health concerns. Comprehensive understanding of the modes of action underlying toxicity among structurally diverse PFAS is mostly lacking. To address this need, we recently reported on our application of developing zebrafish to evaluate a large library of PFAS for developmental toxicity. In the present study, we prioritized 15 bioactive PFAS that induced significant morphological effects and performed RNA-sequencing to characterize early transcriptional responses at a single timepoint (48h post fertilization) after early developmental exposures (8h post fertilization). Internal concentrations of 5 of the 15 PFAS were measured from pooled whole fish samples across multiple timepoints between 24-120h post fertilization, and additional temporal transcriptomics at several timepoints (48-96h post fertilization) were conducted for Nafion byproduct 2. A broad range of differentially expressed gene counts were identified across the PFAS exposures. Most PFAS that elicited robust transcriptomic changes affected biological processes of the brain and nervous system development. While PFAS disrupted unique processes, we also found that similarities in some functional head groups of PFAS were associated with the disruption in expression of similar gene sets. Body burdens after early developmental exposures to select sulfonic acid PFAS, including Nafion byproduct 2, increased from the 24-96h post fertilization sampling timepoints and were greater than those of sulfonamide PFAS of similar chain lengths. In parallel, the Nafion byproduct 2-induced transcriptional responses increased between 48 and 96h post fertilization. PFAS characteristics based on toxicity, transcriptomic effects, and modes of action will contribute to further prioritization of PFAS structures for testing and informed hazard assessment.

Using Zebrafish to Screen Developmental Toxicity of Per- and Polyfluoroalkyl Substances (PFAS).

Per- and polyfluoroalkyl substances (PFAS) are found in many consumer and industrial products. While some PFAS, notably perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), are developmentally toxic in mammals, the vast majority of PFAS have not been evaluated for developmental toxicity potential. A concentration-response study of 182 unique PFAS chemicals using the zebrafish medium-throughput, developmental vertebrate toxicity assay was conducted to investigate chemical structural identifiers for toxicity. Embryos were exposed to each PFAS compound (≤100 μM) beginning on the day of fertilization. At 6 days post-fertilization (dpf), two independent observers graded developmental landmarks for each larva (e.g., mortality, hatching, swim bladder inflation, edema, abnormal spine/tail, or craniofacial structure). Thirty percent of the PFAS were developmentally toxic, but there was no enrichment of any OECD structural category. PFOS was developmentally toxic (benchmark concentration [BMC] = 7.48 μM); however, other chemicals were more potent: perfluorooctanesulfonamide (PFOSA), N-methylperfluorooctane sulfonamide (N-MeFOSA), ((perfluorooctyl)ethyl)phosphonic acid, perfluoro-3,6,9-trioxatridecanoic acid, and perfluorohexane sulfonamide. The developmental toxicity profile for these more potent PFAS is largely unexplored in mammals and other species. Based on these zebrafish developmental toxicity results, additional screening may be warranted to understand the toxicity profile of these chemicals in other species.

Co-exposure to microplastic and plastic additives causes development impairment in zebrafish embryos

Since the run off of microplastic and plastic additives into the aquatic environment through the disposal of plastic products, we investigated the adverse effects of co-exposure to microplastics and plastic additives on zebrafish embryonic development. To elucidate the combined effects between microplastic mixtures composed of microplastics and plastic additives in zebrafish embryonic development, polystyrene (PS), bisphenol S (BPS), and mono-(2-ethylhexyl) phthalate (MEHP) were chosen as a target contaminant. Based on non-toxic concentration of each contaminant in zebrafish embryos, microplastic mixtures which is consisted of binary and ternary mixed forms were prepared. A strong phenotypic toxicity to zebrafish embryos was observed in the mixtures composed with non-toxic concentration of each contaminant. In particular, the mixture combination with ≤ EC10 values for BPS and MEHP showed a with a strong synergistic effect. Based on phenotypic toxicity to zebrafish embryos, change of transcription levels for target genes related to cell damage and thyroid hormone synthesis were analyzed in the ternary mixtures with low concentrations that were observed non-toxicity. Compared with the control group, cell damage genes linked to the oxidative stress response and thyroid hormone transcription factors were remarkably down-regulated in the ternary mixture-exposed groups, whereas the transcriptional levels of cyp1a1 and p53 were significantly up-regulated in the ternary mixture-exposed groups (P < 0.05). These results demonstrate that even at low concentrations, exposure to microplastic mixtures can cause embryonic damage and developmental malformations in zebrafish, depending on the mixed concentration-combination. Consequently, our findings will provide data to examine the action mode of zebrafish developmental toxicity caused by microplastic mixtures exposure composed with microplastics and plastic additives.

Metabolic perturbations in zebrafish (Danio rerio) larvae exposed to sulfentrazone and imidacloprid

The intensive and widespread application of pesticides in agroecosystems can lead to the simultaneous exposure of non-target aquatic organisms to insecticides and herbicides. However, the underlying mechanisms through which aquatic organisms undergo metabolic reprogramming to withstand the combined effects of the insecticide imidacloprid (IMI) and herbicide sulfentrazone (SUL) remain poorly elucidated. This study employs metabolomics to investigate the effects of individual and combined exposures to IMI and SUL on zebrafish (Danio rerio), aiming to simulate complex environmental conditions. Metabolomics analysis revealed extensive metabolic reprogramming in larvae induced by the selected agrochemicals. Both individual and combined exposures disrupted nucleotide metabolism, inhibited glycolysis, and led to the accumulation of acetylcholine through the shared modulation of differential metabolites. Notably, individual exposure exhibited a unique mode of action. Larvae exposed to IMI alone showed mitochondrial dysfunction, potentially stemming from interference with the electron transport chain, while SUL-induced disruptions were associated with glycerophospholipid accumulation, marking it as a critical target. Additionally, calculations of the metabolic effect level index indicated antagonistic interactions between SUL and IMI mixtures at an overall metabolic level. The results obtained through investigating the lethal and sub-lethal effects also revealed that the simultaneous application of SUL and IMI may have the potential to diminish acute and developmental toxicity in zebrafish. This study underscores the significance of metabolomics as a valuable and effective strategy for deciphering the toxicity and interactions of agrochemical mixtures.

Ensemble multiclassification model for predicting developmental toxicity in zebrafish

In recent years, with the rapid development of society, organic compounds have been released into aquatic environments in various forms, posing a significant threat to the survival of aquatic organisms. The assessment of developmental toxicity is an important part of environmental safety risk systems, helping to identify the potential impacts of organic compounds on the embryonic development of aquatic organisms and enabling early detection and warning of potential ecological risks. Additionally, binary classification models cannot accurately classify organic compounds. Therefore, it is crucial to construct a multiclassification model for predicting the developmental toxicity of organic compounds. In this study, binary and multiclassification models were developed based on the ToxCast™ Phase I chemical library and literature data. The random forest, support vector machine, extreme gradient boosting, adaptive gradient boosting, and C5.0 decision tree algorithms, as well as 8 types of molecular fingerprint were used to establish a multiclassification base model for predicting developmental toxicity through 5-fold cross-validation and external validation. Ultimately, a multiclassification ensemble model was derived through a voting method. The performance of the binary ensemble model, as measured by the balanced accuracy, was 0.918, while that of the multiclassification model was 0.819. The developmental toxicity voting ensemble model (DT-VEM) achieved accuracies of 0.804, 0.834, and 0.855. Furthermore, by utilizing the XGBoost machine learning algorithm to construct separate models for molecular descriptors and substructure molecular fingerprints, we identified several substructures and physical properties related to developmental toxicity. Our research contributes to a more detailed classification of developmental toxicity, providing a new and valuable tool for predicting the developmental toxicity effects of unknown compounds. This supplement addresses the limitations of previous tools, as it offers an enhanced ability to predict potential developmental toxicity in novel compounds.

Reproductive and Developmental Effects of Sex-Specific Chronic Exposure to Dietary Arsenic in Zebrafish (Danio rerio).

The present study investigated the reproductive and developmental effects of sex-specific chronic exposure to dietary arsenic in zebrafish. Adult zebrafish (Danio rerio) were exposed to environmentally realistic doses of arsenic via diet [0 (control; no added arsenic), 30 (low), 60 (medium), and 100 (high) μg/g dry weight, as arsenite] for 90 days. Following exposure, arsenic-exposed females from each dietary treatment were mated with control males, and similarly, arsenic-exposed males from each dietary treatment were mated with control females. In females, arsenic exposure resulted in a dose-dependent decrease in reproductive performance (fecundity, fertilization success, and hatching success). Moreover, a dose-dependent increase in developmental toxicity (larval deformities and larval mortality) was observed with maternal exposure to arsenic. In contrast, in males, arsenic exposure also induced similar reproductive and developmental toxicity; however, the adverse effects were mainly evident only in the medium and high dietary arsenic treatment groups. We also examined the sex-specific effects of dietary arsenic exposure on the expression of genes that regulate the hypothalamus-pituitary-gonadal-liver (HPG-L) axis in fish. The gene expression results indicated the downregulation of HPG-L axis genes in females irrespective of the arsenic treatment dose; however, the reduced expression of HPG-L axis genes in males was recorded only in the medium and high arsenic treatment groups. These observations suggest that chronic arsenic exposure in either females or males causes reproductive and developmental toxicity in zebrafish. However, these toxic effects are markedly higher in females than in males. Our results also suggest that arsenic can act as an endocrine disruptor and mediate reproductive and developmental toxicity by disrupting the HPG-L axis in zebrafish.

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.

Dimethyl fumarate induces cardiac developmental toxicity in zebrafish via down-regulation of oxidative stress

Dimethyl fumarate (DMF) is an immunosuppressant commonly used to treat multiple sclerosis and other autoimmune diseases. Despite known side effects such as lymphopenia, the effect of DMF on cardiac development remains unclear. To assess this, we used zebrafish to evaluate the cardiac developmental toxicity of DMF. Our study showed that DMF reduced the survival rate of zebrafish embryos, with those exposed to 1, 1.3, and 1.6 mg/L exhibiting heart rate reduction, shortened body length, delayed yolk sac absorption, pericardial edema, increased distance from sinus venous to bulbus arteriosus, and separation of cardiomyocytes and endocardial cells at 72 hpf. Heart development-related genes showed disorder, apoptosis-related genes were up-regulated, and the oxidative stress response was down-regulated. Treatment with cysteamine ameliorated the heart development defects. Our study demonstrates that DMF induces cardiac developmental toxicity in zebrafish, possibly by down-regulating oxidative stress responses. This study provides a certain research basis for further study of DMF-induced cardiac developmental toxicity, and provides some experimental evidence for future clinical application and study of DMF.

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 (R2: 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)

Crosstalk between aryl hydrocarbon receptor and Wnt/β-catenin signaling pathway: Possible culprit of di (2-ethylhexyl) phthalate-mediated cardiotoxicity in zebrafish larvae

Typical plasticizer di (2-ethylhexyl) phthalate (DEHP) has been demonstrated to induce cardiotoxicity in zebrafish, but the potential molecular mechanisms involved have not been fully elucidated. Aryl hydrocarbon receptor (AhR), an essential protein for inducing developmental abnormalities, has been demonstrated to be activated by DEHP in other species, but whether the AhR signaling pathway also contributes to DEHP-mediated cardiac developmental toxicity in zebrafish remains unclear. Firstly, molecular docking simulations initially confirmed the possibility that DEHP has AhR agonistic activity. To further confirm this conjecture, this work analyzed the changes of cardiac-related indexes in zebrafish stressed by DEHP at individual, protein, and gene levels. The results showed that DEHP mediated cardiac phenotypic developmental defects, increased CYP1A1 activity, and oxidative stress as well as significant changes in the expression levels of key proteins and genes of AhR, Wnt/β-catenin, and Nrf2-Keap1 signaling pathways. Notably, the addition of AhR inhibitors effectively alleviated the above negative effects, indicating that the AhR signaling pathway and its crosstalk with the Wnt/β-catenin signaling pathway is an essential pathway for DEHP-mediated cardiac developmental toxicity. Overall, this work enriches the molecular mechanism of DEHP-mediated cardiac developmental defects in zebrafish and provides a reliable biomarker for future environmental risk assessment of DEHP.

The effects of Spinosad on zebrafish larvae and THP-1 cells: Associated with immune cell damage and NF-kappa B signaling pathway activation

Spinosad is a highly effective macrolide insecticide with a wide range of applications. However, few studies have been reported on the effects of Spinosad on immune cells. The immune system is an important line of defense in the human body and plays an important role in maintaining the normal functioning of the organism. Meanwhile, macrophages, neutrophils and Thymic T cells are an important component of the immune system. We studied the immunotoxicity of Spinosad using zebrafish and THP-1 cells. In vivo, Spinosad (0–20 μM) did not cause developmental toxicity in zebrafish, but induced damage to immune cells. In vitro, Spinosad (0–20 μM) inhibited THP-1 cells viability and induced mitochondrial damage and oxidative stress production. In further studies, it impaired phagocytosis of THP-1 cells and interfered with lipid metabolism. In addition, we found that Spinosad can promote the formation of the inflammatory body NLRP3 (NLR family, pyrin domain-containing 3) and activate the NF-kappa B (NF-κB) signaling pathway. These results suggest that Spinosad has a potential risk for inducing immunotoxicity. This study has drawn attention to Spinosad-induced immunotoxicity.

Developmental toxicity induced by chelerythrine in zebrafish embryos via activating oxidative stress and apoptosis pathways

Chelerythrine (CHE), a natural benzophenanthridine alkaloid, possesses various biological and pharmacological activities, such as antimicrobial, antitumor and anti-inflammatory effects. However, its adverse side effect has not been fully elucidated. Therefore, this study was designed to investigate the developmental toxicity of CHE in zebrafish. We found that CHE could lead to a notably increase of the mortality and malformation rate, while lead to reduction of the hatching rate and body length. CHE also could affect the normal developing processes of the heart, liver and phagocytes in zebrafish. Furthermore, the reactive oxygen species (ROS) and apoptosis levels were notably increased. In addition, the mRNA expressions of genes (bax, caspase-9, p53, SOD1, KEAP1, TNF-α, STAT3 and NF-κB) were significantly increased, while the bcl2 and nrf2 were notably inhibited by CHE. These results indicated that the elevation of ROS and apoptosis were involved in the developmental toxicity induced by CHE. In conclusion, CHE exhibits a developmental toxicity in zebrafish, which helps to understand the potential toxic effect of CHE.

Tralomethrin causes cardiovascular toxicity in zebrafish (Danio rerio) embryos.

Tralomethrin, a synthetic pyrethroid insecticide used to control a wide range of pests in agriculture and public health, is highly toxic to aquatic organisms. However, data regarding the toxicity and underlying mechanisms of tralomethrin in aquatic organisms are limited. Thus, this study aimed to investigate the toxicity of tralomethrin in zebrafish. Zebrafish embryos were exposed to tralomethrin at different concentrations (16.63, 33.25, and 49.88 μg/L). Results showed that tralomethrin exposure caused cardiovascular dysplasia and dysfunction, including developmental abnormalities (pericardial edema, delayed yolk absorption, and uninflated swim bladder), elevated heart rate, and erythrogenesis disorders. Moreover, the expression patterns of crucial genes responsible for cardiovascular development (alas2, gata1a, hbbe2, nkx2.5, myl7, and myh6) also exhibited dysregulation in response to tralomethrin exposure. Oxidative stress occurred in embryos after exposure to tralomethrin. Collectively, our data suggest that exposure to tralomethrin induces cardiovascular and developmental toxicity in zebrafish. These findings are instrumental for evaluations of the environmental risk of tralomethrin in aquatic ecosystems in the future.

Terbutryn causes developmental toxicity in zebrafish (Danio rerio) via apoptosis and major organ malformation in the early stages of embryogenesis

Terbutryn (2-(ethylamino)-4-(tert-butylamino)-6-(methylthio)-1,3,5-triazine) is a substituted symmetrical triazine herbicide used in agricultural fields to prevent undesired vegetation growth by inhibiting photosynthesis in target weeds. Although terbutryn has various benefits, long-term exposure, misuse, or abuse of terbutryn may cause non-target toxicity and severe ecosystem pollution. To provide a detailed description of the embryonic developmental toxicity of terbutryn, zebrafish (Danio rerio) were exposed to 2, 4, and 6 mg/L of terbutryn and the morphological changes, pathological abnormalities, and developmental endpoints were assessed relative to that of a solvent control. The results showed that terbutryn induces a loss of survivability, reduction in body and eye size, and edema in the yolk sac. Through fluorescence microscopy, blood vessels, motor neurons, and liver development were investigated using transgenic zebrafish models based on fluorescently tagged genes (fllk1:eGFP, olig2:dsRed, and L-fabp:dsRed). Furthermore, cell death by apoptosis in zebrafish caused by terbutryn exposure was evaluated via acridine orange staining, which is a selective fluorescent staining agent. To support the preceding results, gene expression alterations caused by terbutryn exposure in zebrafish larvae were assessed. The overall results indicate that exposure to terbutryn induces apoptosis and disrupts organ development. These embryonic developmental toxicity results suggest that terbutryn should be applied in the right areas at the appropriate rates, concentrations, and quantities.

TiO2 nanoparticles: green synthesis, characterization, and investigation of antimicrobial properties, and developmental toxicity in zebrafish (Danio rerio) embryos

The present study was designed to green synthesize titanium dioxide nanoparticles (G-TiO2 NPs) using Salacia reticulata leaf extract as a reducing and capping agent to assess antidiabetic, anti-inflammatory, and antibacterial effects as well as toxicity evaluation in zebrafish. Besides, zebrafish embryos were employed to study the effect of G-TiO2 NPs on embryonic development. Zebrafish embryos were treated with TiO2 as well as G-TiO2 NPs at four different concentrations, i.e., 25, 50, 100, and 200 µg/ml for 24–96-hour post-fertilization (hpf). The SEM analysis of G-TiO2 NPs confirmed that the size was in the range of 32–46 nm and characterized by EDX, X-ray diffraction (XRD), FTIR, UV–vis spectra. During 24–96-hour post-fertilization (hpf), the results showed that 25–100 µg/ml of TiO2 and G-TiO2 NP instigated developmental acute toxicity in these embryos, causing mortality, hatching delay, and malformation. TiO2 and G-TiO2 NPs exposure induced axis bent, tail bent, spinal cord curvature, yolk-sac, and pericardial edema. Exposure of larvae to the highest concentrations of 200 μg/ml TiO2 and G-TiO2 NPs caused maximum mortality at all time points and reached 70% and 50%, respectively, at 96 hpf. Besides, both TiO2 and G-TiO2 NP revealed antidiabetic and anti-inflammatory effects in vitro. In addition, G-TiO2 NPs exhibited antibacterial effects. Taken together, this study provided a valuable insight into the synthesis of TiO2 NPs using green methods and the synthesized G-TiO2 NPs possess moderate toxicity and potent antidiabetic, anti-inflammatory and antibacterial activities.

Green Synthesis Iron Oxide Nanoparticles (Fe@AV NPs) Induce Developmental Toxicity and Anxiety-Like Behavior in Zebrafish Embryo-Larvae

The synthesis of nanoparticles and the usage areas of these nanoparticles show a rapid increase. In addition to the beneficial use of nanoparticles, their toxic effects cannot be ignored. In our study, iron oxide nanoparticle (Fe@AV NPs) (mean size: 20.852 nm) was synthesized from Aloe vera plant and the developmental toxicity of zebrafish was investigated. Zebrafish embryo-larvae were treated with different concentrations of Fe@AV NPs (1, 10, and 50 mg/L) starting at 4 hours after fertilization and continuing until 96 hours, and different developmental parameters (such as survival rate, hatchability rates, malformations, and behavior) were examined. In our study, it was determined that Fe@AV NPs caused developmental toxicity in zebrafish embryos depending on the dose increase. More than 60% died at 96 hours, especially in the highest (50 mg/L) application group. It was observed that Fe@AV NPs decreased and delayed the success of exiting the chorion depending on the dose increase, and caused various morphological abnormalities (like pericardial edema, tail deformation, and scoliosis) in all application groups except the lowest application group (1 mg/L). While 10 mg/L Fe@AV NPs caused sleep-like behaviors during the daytime by decreasing the daytime motility of the larvae, it caused hyperactivity by increasing their nocturnal motility. The results of thigmotaxis, which is an anxiety parameter, were found to increase anxiety at 10 mg/L Fe@AV NPs exposure.Our findings showed that Fe@AV NPs synthesized from Aloe vera plant have in vivo toxicity and their use at concentrations lower than 1 mg/L can be safe in environmental and medical applications.

The toxicity of 4-tert-butylphenol in early development of zebrafish: morphological abnormality, cardiotoxicity, and hypopigmentation.

Endocrine disrupting effects of 4-tert-butylphenol (4-t-BP) are well described in literature. However, the evidence regarding developmental toxic effect of 4-t-BP is still vague. The present study used zebrafish as a model organism to investigate the toxic effect of 4-t-BP. The results showed that 4-t-BP exposure at 3, 6, and 12 μM induced developmental toxicity in zebrafish, such as reduced embryo hatchability and abnormality morphological. Flow cytometry analysis showed that 4-t-BP also induced intracellular ROS production. 4-t-BP induced changes in the expression of genes related to cardiac development and melanin synthesis, resulting in cardiotoxicity and hypopigmentation. 4-t-BP also caused oxidative stress, and initiated apoptosis through p53-bcl-2/bax-capase3 pathway. Integrative biomarker response analysis showed time- and dose-dependent effects of 4-t-BP on oxidative damage and developmental toxicity in zebrafish embryos. Overall, this study contributed to a comprehensive evaluation of the toxicity of 4-t-BP, and the findings provided new evidence for early warning of residues in aquatic environments.

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.

Impacts of PFOAC8, GenXC6, and their mixtures on zebrafish developmental toxicity and gene expression provide insight about tumor-related disease

Concerns about per- and polyfluoroalkyl substances (PFASs) have grown in importance in the fields of ecotoxicology and public health. This study aims to compare the potential effects of long-chain (carbon atoms ≥ 7) and short-chain derivatives and their mixtures' exposure according to PFASs-exposed (1, 2, 5, 10, and 20 mg/L) zebrafish's (Danio rerio) toxic effects and their differential gene expression. Here, PFOAC8, GenXC6, and their mixtures (v/v, 1:1) could reduce embryo hatchability and increase teratogenicity and mortality. The toxicity of PFOAC8 was higher than that of GenXC6, and the toxicity of their mixtures was irregular. Their exposure (2 mg/L) caused zebrafish ventricular edema, malformation of the spine, blood accumulation, or developmental delay. In addition, all of them had significant differences in gene expression. PFOAC8 exposure causes overall genetic changes, and the pathways of this transformation were autophagy and apoptosis. More importantly, in order to protect cells from PFOAC8, GenXC6, and their mixtures' influences, zebrafish inhibited the expression of ATPase and Ca2+ transport gene (atp1b2b), mitochondrial function-related regulatory genes (mt-co2, mt-co3, and mt-cyb), and tumor or carcinogenic cell proliferation genes (laptm4b and ctsbb). Overall, PFOAC8, GenXC6, and their mixtures' exposures will affect the gene expression effects of zebrafish embryos, indicating that PFASs may pose a potential threat to aquatic biological safety. These results showed that the relevant genes in zebrafish that were inhibited by PFASs exposure were related to tumorigenesis. Therefore, the effect of PFASs on zebrafish can be further used to study the pathogenesis of tumors.

Sex-specific thyroid disruption caused by phenanthrene in adult zebrafish (Danio rerio)

Polycyclic aromatic hydrocarbons (PAHs) are well-known contaminants with widespread distribution in environment and food. Phenanthrene is one of the most abundant PAHs in food and aquatic environment and generates reproductive and developmental toxicity in zebrafish. Nonetheless, whether phenanthrene caused sex-specific thyroid disruption in adult zebrafish is unclear. To determine this, adult zebrafish (male and female) were treated with phenanthrene (0, 0.85, 8.5, and 85 μg/L) for 60 days. After the treatment period, we assessed the concentrations of thyroid hormones (THs) and expression levels of genes in the hypothalamic-pituitary-thyroid (HPT) axis. The results showed that phenanthrene exposure can lead to thyroid disruption in both male and female zebrafish. Exposure to phenanthrene dramatically reduced the levels of L-thyroxine (T4) and L-triiodothyronine (T3) in both male and female zebrafish, with a similar trend in both. However, the genes expression profiles of hypothalamic-pituitary-thyroid (HPT) axis were sex-specific. In all, the present study demonstrated that phenanthrene exposure could result in sex-specific thyroid disruption in adult zebrafish.