Biological response of zebrafish embryos after short-term exposure to thifluzamide

Bioaccumulation mediated by water solubility leads to differences in the acute toxicity of organophosphorus insecticides to zebrafish (Danio rerio)

The use of some organophosphate insecticides is restricted or even banned in paddy fields due to their high toxicity to aquatic organisms. The aim of this study is to elucidate the main pathways and target organs of organophosphate insecticide toxicity to fish exposed via different routes by integrating histopathological and biochemical techniques. Using malathion as the model drug, when the dosage is 20-60 mg/L, the toxicity of whole body and head immersion drugs to zebrafish is much higher than that of trunk immersion drugs. A dose of 21.06-190.44 mg/kg of malathion feed was fed to adult zebrafish. Although the dosage was already high, no obvious toxicity was observed. Therefore, we believe that the drug mainly enters the fish body through the gills. When exposed to a drug solution of 20 mg/L and 60 mg/L, the fish showed significant neurological behavioral abnormalities, and the pathological damage to key organs and brain tissue was the most severe, showing obvious vacuolization and the highest residual amount (8.72-47.78 mg/L). The activity of acetylcholinesterase was the most inhibited (54.69-74.68%). Therefore, brain tissue is the key toxic target organ of malathion in fish. In addition, we compared the bioaccumulation effects of different water-soluble organophosphorus insecticides in fish and their toxic effects. We found that the higher the water solubility of organophosphorus insecticides, the lower their toxicity to fish.

Life cycle assessment of hepatotoxicity induced by cyhalofop-butyl in environmental concentrations on zebrafish in light of gut-liver axis

Cyhalofop-butyl (CB) poses a significant threat to aquatic organisms, but there is a discrepancy in evidence about hepatotoxicity after prolonged exposure to environmental levels. The aim of this study was to investigate long-term hepatotoxicity and its effects on the gut-liver axis through the exposure of zebrafish to environmental concentrations of CB (0.1,1,10 μg/L) throughout their life cycle. Zebrafish experienced abnormal obesity symptoms and organ index after a prolonged exposure of 120 days. The gut-liver axis was found to be damaged both morphologically and functionally through an analysis of histology, electron microscopy subcellular structure, and liver function. The disruption of the gut-liver axis inflammatory process by CB is suggested by the rise in inflammatory factors and the alteration of inflammatory genes. Furthermore, there was a noticeable alteration in the blood and gut-liver axis biochemical parameters as well as gene expression linked to lipid metabolism, which may led to an imbalance in the gut flora. In conclusion, the connection between the gut-liver axis, intestinal microbiota, and liver leads to the metabolic dysfunction of zebrafish exposed to long-term ambient concentrations of CB, and damaged immune system and liver lipid metabolism. This study gives another knowledge into the hepatotoxicity component of long haul openness to ecological centralization of CB, and might be useful to assess the potential natural and wellbeing dangers of aryloxyphenoxypropionate herbicides.

Resveratrol improves meat quality traits by activating the lncRNAs-KEAP1-NRF2 axis in pigs

This research aims at uncovering the effects and investigating the molecular mechanisms of dietary resveratrol (RES) supplementation on antioxidant capacity and meat quality of pigs. In this study, 20 μM RES could activate the KEAP1-NRF2 antioxidant defense pathway in response to oxidative stress in porcine skeletal muscle satellite cells was firstly found. Then, twenty-four healthy crossbred castrated boars were allocated to 4 treatments that were fed with a basal diet (control) and a basal diet supplemented with 200 mg, 400 mg or 600 mg RES per Kilogram (kg) of feed for 41 days, respectively. 400 and 600 mg/kg RES-supplemented diet can effectively improve the meat quality traits and activities of antioxidizing enzymes via the KEAP1-NRF2 signaling pathway of pigs. The molecular dynamic simulation further revealed that RES could directly binding to KEAP1 to reduce the tightness of KEAP1-NRF2 protein-protein interaction. More importantly, dietary supplementation of RES also improves antioxidant capacity through a series of KEAP1-NRF2 pathway-related lncRNAs were found by RNA sequencing (RNA-seq). Altogether, this study demonstrated that RES improves meat quality traits by effectively increasing antioxidant levels via the lncRNA-KEAP1-NRF2 axis in vivo and/or in vitro. These results provide new insights into the molecular mechanisms by which RES, as a nutritional agent, regulates antioxidant capacity and improves meat quality in pigs.

Comparative antioxidant and metabolomic analysis for the identification of differential response of mussel (Mytilus coruscus) to four succinate dehydrogenase inhibitor fungicides

Succinate dehydrogenase inhibitor fungicides (SDHIs) are frequently detected in the marine environment. However, studies on the toxicity of SDHIs to marine organisms, Mytilus coruscus (M. coruscus), are poorly reported. Therefore, the antioxidant activities and metabolomic response of four SDHIs, namely, boscalid (BC), thifluzamide (TF), fluopyram (FO), and bixafen (BIX), to (M. coruscus), were comprehensively investigated. The antioxidant activity of BC and TF was significantly increased (p<0.05), whereas those of FO and BIX were significantly decreased. Furthermore, metabolite discriminations among M. coruscus to four SDHIs were illustrated by an untargeted metabolomics approach. A total of 52, 50, 93, and 129 differential metabolites were obtained for BC, TF, FO, and BIX. KEGG of the different metabolites show that the four SDHIs had differential effects on the metabolic pathways of M. coruscus. The current study demonstrated four SDHIs triggered glucose metabolism, lipid metabolism, tricarboxylic acid cycle, and oxidative phosphorylation processes and caused the disruption of nutrient and energy conversion processes in mussels. Finally, five biomarkers were screened by analyzing common differential metabolites that emerged from the four SDHI exposures, which could be used for risk assessment of marine ecosystem exposure to SDHIs. Our results demonstrated the use of metabolomics to understand the potential mechanisms of toxicity of four SDHIs to mussels and to identify potential targets for future targeted risk assessment.

Characterization of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)-induced cardiotoxicity in larval zebrafish (Danio rerio)

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is a type of p-phenylenediamine (PPD), which is widely used in the manufacture of rubber tires owing to its excellent antiozonant properties. In this study, the developmental cardiotoxicity of 6PPD was evaluated in zebrafish larvae, and the LC50 was approximately 737 μg/L for the larvae at 96 h post fertilization (hpf). In the 6PPD treatment of 100 μg/L, the accumulation concentrations of 6PPD were up to 2658 ng/g in zebrafish larvae, and 6PPD induced significant oxidative stress and cell apoptosis in the early developmental stages of zebrafish. Transcriptome analysis showed that 6PPD exposure could potentially cause cardiotoxicity in larval zebrafish by affecting the transcription of the genes related to the calcium signal pathway and cardiac muscle contraction. The genes related to calcium signaling pathway (slc8a2b, cacna1ab, cacna1da, and pln) were verified by qRT-PCR, which were significantly downregulated in larval zebrafish after exposing to 100 μg/L of 6PPD. Simultaneously, the mRNA levels of the genes related to cardiac functions (myl7, sox9, bmp10, and myh71) also respond accordingly. H&E staining and heart morphology investigation indicated that cardiac malformation occurred in zebrafish larvae exposed to 100 μg/L of 6PPD. Furthermore, the phenotypic observation of transgenic Tg (myl7: EGFP) zebrafish also confirmed that 100 μg/L of 6PPD exposure could change the distance of atria and ventricles of the heart and inhibit some key genes (cacnb3a, ATP2a1l, ryr1b) related to cardiac function in larval zebrafish. These results revealed the toxic effects of 6PPD on the cardiac system of zebrafish larvae.

Developmental defects induced by thiabendazole are mediated via apoptosis, oxidative stress and alteration in PI3K/Akt and MAPK pathways in zebrafish

Thiabendazole, a benzimidazole fungicide, is widely used to prevent yield loss in agricultural land by inhibiting plant diseases derived from fungi. As thiabendazole has a stable benzimidazole ring structure, it remains in the environment for an extended period, and its toxic effects on non-target organisms have been reported, indicating the possibility that it could threaten public health. However, little research has been conducted to elucidate the comprehensive mechanisms of its developmental toxicity. Therefore, we used zebrafish, a representative toxicological model that can predict toxicity in aquatic organisms and mammals, to demonstrate the developmental toxicity of thiabendazole. Various morphological malformations were observed, including decreased body length, eye size, and increased heart and yolk sac edema. Apoptosis, reactive oxygen species (ROS) production, and inflammatory response were also triggered by thiabendazole exposure in zebrafish larvae. Furthermore, PI3K/Akt and MAPK signaling pathways important for appropriate organogenesis were significantly changed by thiabendazole. These results led to toxicity in various organs and a reduction in the expression of related genes, including cardiovascular toxicity, neurotoxicity, and hepatic and pancreatic toxicity, which were detected in flk1:eGFP, olig2:dsRED, and L-fabp:dsRed;elastase:GFP transgenic zebrafish models, respectively. Overall, this study partly determined the developmental toxicity of thiabendazole in zebrafish and provided evidence of the environmental hazards of this fungicide.

Pesticides at brain borders: Impact on the blood-brain barrier, neuroinflammation, and neurological risk trajectories

Pesticides are omnipresent, and they pose significant environmental and health risks. Translational studies indicate that acute exposure to high pesticide levels is detrimental, and prolonged contact with low concentrations of pesticides, as single and cocktail, could represent a risk factor for multi-organ pathophysiology, including the brain. Within this research template, we focus on pesticides' impact on the blood-brain barrier (BBB) and neuroinflammation, physical and immunological borders for the homeostatic control of the central nervous system (CNS) neuronal networks. We examine the evidence supporting a link between pre- and postnatal pesticide exposure, neuroinflammatory responses, and time-depend vulnerability footprints in the brain. Because of the pathological influence of BBB damage and inflammation on neuronal transmission from early development, varying exposures to pesticides could represent a danger, perhaps accelerating adverse neurological trajectories during aging. Refining our understanding of how pesticides influence brain barriers and borders could enable the implementation of pesticide-specific regulatory measures directly relevant to environmental neuroethics, the exposome, and one-health frameworks.

Transcriptome analysis reveals hepatotoxicity in zebrafish induced by cyhalofop‑butyl

Cyhalofop‑butyl is a highly effective aryloxyphenoxypropionate herbicide and widely used for weed control in paddy fields. With the increasing residue of cyhalofop‑butyl, it poses a threat to the survival of aquatic organisms. Here, we investigated the effect of cyhalofop‑butyl on zebrafish to explore its potential hepatotoxic mechanism. The results showed that cyhalofop‑butyl induced hepatocyte degeneration, vacuolation and necrosis of larvae after embryonic exposure for 4 days and caused liver atrophy after 5 days. Meanwhile, the activities of enzymes related to liver function were significantly increased by 0.2 mg/L cyhalofop‑butyl and higher, such as alanine transaminase (ALT) and aspartate transaminase (AST). And the contents of triglyceride (TG) involved in lipid metabolism were significantly decreased by 0.4 mg/L cyhalofop-buty. The expression of genes related to liver development was also significantly down-regulated. Furthermore, transcriptome results showed that the pathways involved in metabolism, immune system and endocrine system were significantly impacted, which may be related to hepatoxicity. To sum up, the present study demonstrated the hepatoxicity caused by cyhalofop-buty and its underlying mechanism. The results may provide new insights for the risk of cyhalofop‑butyl to aquatic organisms and new horizons for the pathogenesis of hepatotoxicity.

Polychlorinated biphenyl quinone induces immunotoxicity via lymphocytes apoptosis and Th1-Th2 cell imbalance in C57BL/6 mice

Polychlorinated biphenyls (PCBs) are a class of persistent organic pollutants distributed worldwide. Existing researches indicated that the immune system is one of the most sensitive indicators of adverse health effects caused by PCBs. We for the first time evaluated the immunotoxic effect of PCB29-pQ, an active quinone-type PCB metabolite. After PCB29-pQ exposure, the body weight of the mice was reduced, but increased the organ index of the spleen and lungs. The morphology and structure of the mouse spleen and lungs were changed, and partial types of lymphocyte subsets in the spleen were significantly reduced. The activation of caspase-3, the significant up-regulation of Bax and the decrease of Bcl-2 indicated occurrence of apoptosis. In addition, mRNA results showed that PCB29-pQ caused the imbalance of Th1/Th2 cytokines and promoted the Th1-type immune response. Taken together, the above results demonstrated that treatment with PCB29-pQ induced spleen immune dysfunction targeting the apoptosis pathway and Th1/Th2 cytokines imbalance in mice. Since the immune system plays a fundamental role in maintaining homeostasis and is strongly involved in the development of diseases, this study provides a new insight into the immunotoxicity mechanism of PCBs.

Residue Behavior and Risk Assessment of Pyraclostrobin and Thifluzamide in Cowpea

A rapid and sensitive analytical method for determination of pyraclostrobin and thifluzamide in cowpea was established based on QuEChERS sample preparation and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Average recoveries of pyraclostrobin and thifluzamide on cowpea were 100%-105% and 99%-105% with RSDs of 1%-5% and 2%-6%, respectively. The storage stability tests showed degradation rates of < 20% for samples stored at - 18℃ within 12 weeks. The field trials at eight locations in China showed that the residues of pyraclostrobin in cowpea at 3 and 5 days after spraying were 0.081-0.49 mg/kg and 0.029-0.48 mg/kg, and the residues of thifluzamide were 0.12-0.46 mg/kg and 0.047-0.50 mg/kg, respectively, which were all lower than the corresponding maximum residue limits in China. The dissipation of both pyraclostrobin and thifluzamide in cowpea were fast with half-lives (T_1/2) of 1.5-2.3 days and 1.7-2.4 days. This study provided risk assessment data for establishment of good agricultural practice in cowpea plant.

Microplastic-induced apoptosis and metabolism responses in marine Dinoflagellate, Karenia mikimotoi

Microplastics (MPs) occur widely in marine environments, and disturb the balance of aquatic ecosystems. In this study, programmed cell apoptosis in marine dinoflagellate, Karenia mikimotoi exposed to 10 mg L^-1 micro/nanoplastics (MPs/NPs; polystyrene and polymethyl methacrylate) for 72 h was assessed. Prior to the toxicity assay, MPs/NPs were dialyzed to remove possible additives. Cell viability, membrane integrity, cell apoptosis, and total DNA concentration were measured to assess programmed cell apoptosis in K. mikimotoi following exposure to MPs/NPs. A transcriptome analysis was used to explore the potential toxic mechanism of MPs to K. mikimotoi. Programmed cell apoptosis was related to the size of MPs/NPs, and NPs could more easily impair cell viability, and reduced cell membrane integrity and DNA concentration. NP particles caused continuous apoptosis of K. mikimotoi compared to MP particles. Size had the greatest effect on toxicity in K. mikimotoi. In conclusion, the results evidenced that both MPs and NPs have a negative impact on the marine dinoflagellate, K. mikimotoi. However, NPs were more harmful to K mikimotoi than MPs, highlighting the potential ecological problems associated with exposure to NPs.

SDHI Fungicide Toxicity and Associated Adverse Outcome Pathways: What Can Zebrafish Tell Us?

Succinate dehydrogenase inhibitor (SDHI) fungicides are increasingly used in agriculture to combat molds and fungi, two major threats to both food supply and public health. However, the essential requirement for the succinate dehydrogenase (SDH) complex—the molecular target of SDHIs—in energy metabolism for almost all extant eukaryotes and the lack of species specificity of these fungicides raise concerns about their toxicity toward off-target organisms and, more generally, toward the environment. Herein we review the current knowledge on the toxicity toward zebrafish (Brachydanio rerio) of nine commonly used SDHI fungicides: bixafen, boscalid, fluxapyroxad, flutolanil, isoflucypram, isopyrazam, penthiopyrad, sedaxane, and thifluzamide. The results indicate that these SDHIs cause multiple adverse effects in embryos, larvae/juveniles, and/or adults, sometimes at developmentally relevant concentrations. Adverse effects include developmental toxicity, cardiovascular abnormalities, liver and kidney damage, oxidative stress, energy deficits, changes in metabolism, microcephaly, axon growth defects, apoptosis, and transcriptome changes, suggesting that glycometabolism deficit, oxidative stress, and apoptosis are critical in the toxicity of most of these SDHIs. However, other adverse outcome pathways, possibly involving unsuspected molecular targets, are also suggested. Lastly, we note that because of their recent arrival on the market, the number of studies addressing the toxicity of these compounds is still scant, emphasizing the need to further investigate the toxicity of all SDHIs currently used and to identify their adverse effects and associated modes of action, both alone and in combination with other pesticides.

Behavioral and developmental toxicity assessment of the strobilurin fungicide fenamidone in zebrafish embryos/larvae (Danio rerio)

Strobilurin fungicides are among the most widely used in the world and have characteristics that include high water solubility and toxicity to aquatic organisms. While several studies report on mechanisms of toxicity of strobilurins in fish, there are no data on the sub-lethal toxicity of fish to the fungicide fenamidone. To address this gap, survival and hatch rate, deformities, mitochondrial bioenergetics, expression of oxidative stress and apoptotic genes, and behavior (locomotor activity and anxiolytic-related behaviors) were assessed in zebrafish embryos and larvae following exposure to fenamidone. Fenamidone negatively affected development of zebrafish embryos, causing a delay of hatching time at concentrations of 2.5 and 5 μM. Fenamidone caused morphological deformities in zebrafish, including pericardial edema, yolk sac edema, tail deformities, and spinal curvature. Exposure to 1.5 μM fenamidone reduced surface area of swim bladder in larvae at 6 dpf. Fenamidone significantly reduced oxygen consumption rates of embryos; 5 μM fenamidone decreased basal respiration (~85%), oligomycin induced ATP-linked respiration (~70%), FCCP-induced maximal respiration (~75%) and non-mitochondrial respiration (~90%) compared to controls. Sod2 mRNA levels were decreased by fenamidone in larval fish. Locomotor activity was significantly decreased in zebrafish larvae following exposure to 2 μM fenamidone but there was no evidence for anxiolytic nor anxiety-related behaviors (exposures of 100 nM up to 1.5 µM). This study addresses a data gap for potential risks associated with fenamidone exposure in developing fish.

Environmentally relevant concentrations of tralopyril affect carbohydrate metabolism and lipid metabolism of zebrafish (Danio rerio) by disrupting mitochondrial function

Tralopyril (TP), an antifouling biocide, is widely used to prevent heavy biofouling, and can have potential risks to aquatic organisms. However, there is little information available on the toxicity of tralopyril to aquatic organisms. In this study, the effect of TP on carbohydrate and lipid metabolism, and related mechanisms were evaluated in zebrafish (Danio rerio) larvae. Adverse modifications in carbohydrate metabolism were observed in larvae: hexokinase (HK) activity, succinate dehydrogenase (SDH) activity, and adenosine triphosphate (ATP) content were significantly decreased; and transcript expression of genes (GK, HK1, and PCK1) was also significantly changed. Changes of TG content, FAS activity and transcript expression of genes (ACO, ehhadh, and fas) indicate that TP disrupt lipid metabolism in zebrafish larvae. The change in expression of genes (ndufs4, Sdhα, and uqcrc2) involved in the mitochondrial respiratory complexes, and genes (polg1 and tk2) involved in the mitochondrial DNA replication and transcription indicates that these adverse effects on carbohydrate and lipid metabolism are caused by mitochondrial dysfunction.

Thifluzamide exposure induced neuro-endocrine disrupting effects in zebrafish (Danio rerio)

Thifluzamide is widely used fungicide and frequently detected in aquatic system. In this study, the toxicity of fungicide thifluzamide to non-targeted aquatic organisms was investigated for neuroendocrine disruption potentials. Here, zebrafish embryos were exposed to a series of concentrations of thifluzamide for 6 days. The results showed that both the development of embryos/larvae and the behavior of hatched larvae were significantly affected by thifluzamide. Importantly, the decreased activity of acetylcholinesterase (AchE) and the increased contents of neurotransmitters such as serotonin (5-HT) and norepinephrine (NE), along with transcriptional changes of nervous system related genes were observed following 4 days exposure to thifluzamide. Besides, the decreased contents of triiodothyronine (T3) and thyroxine (T4) in whole body, as well as significant expression alteration in hypothalamic-pituitary-thyroid (HPT) axis associated genes were discovered in zebrafish embryos after 4 days of exposure to thifluzamide. Our results clearly demonstrated that zebrafish embryos exposed to thifluzamide could disrupt neuroendocrine, compromise behavior and induce developmental abnormality, suggesting impact of this fungicide on developmental programming in zebrafish.

Ecotoxicological effects of pyraclostrobin on tilapia (Oreochromis niloticus) via various exposure routes

Pyraclostrobin is a widely used and highly efficient fungicide that also has high toxicity to aquatic organisms, especially fish. Although some research has reported the toxic effects of pyraclostrobin on fish, the main toxic pathways of pyraclostrobin in fish remain unclear. The present study has integrated histopathological, biochemical and hematological techniques to reveal the main toxic pathways and mechanisms of pyraclostrobin under different exposure routes. Our results indicated that pyraclostrobin entered fish mainly through the gills. The highest accumulation of pyraclostrobin was observed in the gills and heart compared with accumulation in other tissues and gill tissue showed the most severe damage. Hypoxia symptoms (water jacking, tummy turning and cartwheel formation) in fish were observed throughout the experiment. Taken together, our results suggested that the gills are important target organs. The high pyraclostrobin toxicity to gills might be associated with oxidative damage to the gills, inducing alterations in ventilation frequency, oxygen-carrying substances in blood and disorders of energy metabolism. Our research facilitates a better understanding of the toxic mechanisms of pyraclostrobin in fish, which can promote the ecotoxicological research of agrochemicals on aquatic organisms.

Toxic effects and potential mechanisms of Fluxapyroxad to zebrafish (Danio rerio) embryos

Fluxapyroxad is a broad-spectrum and high-efficiency succinate dehydrogenase inhibitor fungicide that can control plant fungal pathogens on many crops. However, fluxapyroxad can enter the aquatic environment when applied in the field, which has an impact on the aquatic environment. The potential threat and toxicological mechanisms of fluxapyroxad in aquatic organisms remain poorly understood. In this study, zebrafish embryos were exposed to fluxapyroxad to investigate the toxic effects and potential mechanisms of fluxapyroxad. In the acute toxicity test, the lethal sensitivity rank of the zebrafish during the three stages was larvae (0.699 mg/L) > adult fish (0.913 mg/L) > embryo (1.388 mg/L). Fluxapyroxad induced abnormal spontaneous movement, malformations and decreased heartbeat, hatching percentage, and body length of the embryos. In the sublethal toxicity test, succinate dehydrogenase activity was significantly increased in all treatment groups, while the activities of the electron transport chain complex II and ATPase were markedly inhibited in 0.347 and 0.694 mg/L fluxapyroxad groups compared to that of the control group. Exposure to fluxapyroxad resulted in significant increases in MDA production, and GPx activity was significantly reduced at 0.694 mg/L. Moreover, caspase-3 activity was significantly increased in the 0.694 mg/L group, and the expression of the genes related to growth (bmp4 and lox) was inhibited after fluxapyroxad exposure. These results indicated that oxidative stress, cell apoptosis and mitochondrial damage might be the potential mechanism underlying the toxic effects of fluxapyroxad on zebrafish embryos.

Effects of combined stressors to cadmium and high temperature on antioxidant defense, apoptotic cell death, and DNA methylation in zebrafish (Danio rerio) embryos

Fish are frequently affected by environmental stressors, such as temperature changes and heavy metal exposure, in aquatic ecosystems. In this study, we evaluated the combined effects of cadmium (Cd) toxicity and temperature (rearing temperature of 26 °C and heat stress at 34 °C) on zebrafish (Danio rerio) embryos. The survival and heart rates of zebrafish embryos decreased at relatively high Cd concentrations of 0.07 and 0.1 mg L^-1. Abnormal morphology was induced by exposure to a combination of Cd toxicity and heat stress. The yolk sac edema size was not significantly different between the control- and Cd-treated groups. Cd exposure induced reactive oxygen species (ROS) production and cell death in the live zebrafish. High temperature (34 °C) triggered Cd-induced cell death and intracellular ROS production to a greater extent than the rearing temperature of 26 °C. Transcriptional levels of six genes-CAT, SOD, p53, BAX, Dnmt1, and Dnmt3b-were investigated. The mRNA expression of CAT and SOD, molecular indicators of oxidative stress, was increased significantly at 34 °C after Cd exposure. The mRNA expression of CAT was more sensitive to temperature than that of SOD in Cd-treated zebrafish. p53 and BAX, apoptosis-related genes, were upregulated upon combined exposure to high temperature and Cd. In addition, at 34 °C, the expression of Dnmt1 and Dnmt3b transcripts, markers of DNA methylation, was increased upon exposure of zebrafish to all concentrations of Cd. Overall, these results suggest that high temperature facilitates the potential role of Cd toxicity in the transcriptional regulation of genes involved in the antioxidant system, apoptosis, and DNA methylation.

Toxicity testing of pesticides in zebrafish-a systematic review on chemicals and associated toxicological endpoints

The use of zebrafish (Danio rerio) has arisen as a promising biological platform for toxicity testing of pesticides such as herbicides, insecticides, and fungicides. Therefore, it is relevant to assess the use of zebrafish in models of exposure to investigate the diversity of pesticide-associated toxicity endpoints which have been reported. Thus, this review aimed to assess the recent literature on the use of zebrafish in pesticide toxicity studies to capture data on the types of pesticide used, classes of pesticides, and zebrafish life stages associated with toxicity endpoints and phenotypic observations. A total of 352 articles published between September 2012 and May 2019 were curated. The results show an increased trend in the use of zebrafish for testing the toxicity of pesticides, with a great diversity of pesticides (203) and chemical classes (58) with different applications (41) being used. Furthermore, experimental outcomes could be clustered in 13 toxicity endpoints, mainly developmental toxicity, oxidative stress, and neurotoxicity. Organophosphorus, pyrethroid, azole, and triazine were the most studied classes of pesticides and associated with various toxicity endpoints. Studies frequently opted for early life stages (embryos and larvae). Although there is an evident lack of standardization of nomenclatures and phenotypic alterations, the information gathered here highlights associations between (classes of) pesticides and endpoints, which can be used to relate mechanisms of action specific to certain classes of chemicals.

Target and Nontarget Toxicity of Cassia fistula Fruit Extract Against Culex pipiens (Diptera: Culicidae), Lung Cells (BEAS-2B) and Zebrafish (Danio rerio) Embryos

Mosquitoes transmit serious diseases, which threaten humans and severely affect livestock. The half-lethal concentration (LC50) was calculated by log probit analysis. The LC50 and LC90 values of larvicidal activity of Cassia fistula Linn. hexane-methanol soluble fraction (HMSF) after 24 h of exposure were 21.04 and 34.68 µg/ml, respectively. The LC50 values after 24 h of exposure were 84.09 µg/ml and 108.08 µg/ml for chloroform-methanol soluble fraction (CMSF) and ethyl acetate-methanol soluble fraction (EMSF) respectively. The percent hatchability of eggs exposed to the hexane extract was 90 ± 5.0, 68.33 ± 7.6, 46.6 ± 11.5, 10 ± 0.0, and 0 ± 0.0% at 10, 20, 40, 60, and 80 ppm, respectively. The pupicidal activity of the hexane extract at 40 µg/ml was 0.0%. The LC50 value of adulticidal activity of the hexane extract was 12.8 mg/test tube. The biosafety of the hexane extract was assessed in nontarget organisms, i.e., zebrafish (Danio rerio) embryos and normal lung cells (BEAS-2B). The hexane extract of C. fistula was well tolerated by zebrafish embryos, and no mortality or toxicity was found in the embryos exposed to the highest tested concentration of 300 µg/ml. Similarly, all the concentrations tested against the normal lung cells (BEAS-2B) showed more than 95% survival. The gas chromatography-mass spectroscopy analysis identified 12 compounds, and 2-methyl hexanoic acid and 2-methyl butanoic acid were the major compounds identified in the hexane extract. The larvicidal activity of C. fistula extracts will help in the development of natural substitutes for vector management of mosquito populations.

Dysregulation of circadian rhythm in zebrafish (Danio rerio) by thifluzamide: Involvement of positive and negative regulators

Thifluzamide as a fungicide is toxic to brain of zebrafish embryos. Brain can regulate biological rhythms. To clarify whether thifluzamide would influence circadian rhythms, zebrafish embryos were treated with thifluzamide (0, 0.19, 1.90 and 2.85 mg/L) for 4 days. Exposure to thifluzamide induced pronounced changes in embryo brain and melatonin levels. The mRNA levels of genes related to circadian rhythms were apparently altered. Among these, the transcripts of cry1ba and clock1 were extremely correlated with exposure concentrations. Importantly, the content of cry1 showed no apparent changes, but the clock level was dramatically increased. Moreover, consistent with the inhibition of development and behavior, the levels of GH and DA were significantly inhibited. In addition, the expression levels of genes related to development, behavior and reproduction were significantly changed by thifluzamide. Therefore, we speculated that circadian disruption due to thifluzamide exposure were primarily attributed to increases in expression of clock1a and contents of clock, which might be at least in part responsible for abnormal development and behavior of zebrafish. In addition, our research will provide important insights into the grouped assessment of SDHI pesticides in future.

Toxicity Reduction of Euphorbia kansui Stir-Fried with Vinegar Based on Conversion of 3-O-(2'E,4'Z-Decadi-enoyl)-20-O-acetylingenol

The dried roots of Euphorbia kansui S.L.Liou ex S.B.Ho have long been used to treat edema in China. However, the severe toxicity caused by Euphorbia kansui (EK) has seriously restricted its clinical application. Although EK was processed with vinegar to reduce its toxicity, the detailed mechanisms of attenuation in toxicity of EK stir-fried with vinegar (VEK) have not been well delineated. Diterpenoids are the main toxic ingredients of EK, and changes in these after processing may be the underlying mechanism of toxicity attenuation of VEK. 3-O-(2′E,4′Z-decadienoyl)-20-O-acetylingenol (3-O-EZ) is one of the diterpenoids derived from EK, and the content of 3-O-EZ was significantly reduced after processing. This study aims to explore the underlying mechanisms of toxicity reduction of VEK based on the change of 3-O-EZ after processing with vinegar. Based on the chemical structure of 3-O-EZ and the method of processing with vinegar, simulation experiments were carried out to confirm the presence of the product both in EK and VEK and to enrich the product. Then, the difference of peak area of 3-O-EZ and its hydrolysate in EK and VEK were detected by ultra-high-performance liquid chromatography (UPLC). Furthermore, the toxicity effect of 3-O-EZ and its hydrolysate, as well as the underlying mechanism, on zebrafish embryos were investigated. The findings showed that the diterpenoids (3-O-EZ) in EK can convert into less toxic ingenol in VEK after processing with vinegar; meanwhile, the content of ingenol in VEK was higher than that of EK. More interestingly, the ingenol exhibited less toxicity (acute toxicity, developmental toxicity and organic toxicity) than that of 3-O-EZ, and 3-O-EZ could increase malondialdehyde (MDA) content and reduce glutathione (GSH) content; cause embryo oxidative damage by inhibition of the succinate dehydrogenase (SDH) and superoxide dismutase (SOD) activity; and induce inflammation and apoptosis by elevation of IL-2 and IL-8 contents and activation of the caspase-3 and caspase-9 activity. Thus, this study contributes to our understanding of the mechanism of attenuation in toxicity of VEK, and provides the possibility of safe and rational use of EK in clinics.

Comparative transcriptional analysis of methylparaben and propylparaben in zebrafish

Parabens are widely used as preservatives in different commercial items including food, cosmetics and pharmaceuticals, and their wide use has resulted in accumulation in the environment. Parabens have been shown to have negative effects on animals as well as human health. In this study, we carried out a comprehensive study to determine the adverse effects associated with propylparaben (PP) and methylparaben (MP) on early developmental stages of zebrafish. Mortality, hatching, developmental abnormalities and gene expression profiles were investigated in embryos exposed to both compounds. The semi-static exposure conditions showed that both MP (≥100 μM) and PP (≥10 μM) are toxic to the embryos in a concentration-dependent manner and lead to developmental abnormality. Malformations such as spinal defects, pericardial edema, and pigmentation defects were observed following both MP and PP treatments. Hatching delay, mortality and developmental abnormality data indicate that PP is more toxic than MP. For gene expression analysis, 1 and 10 μM doses of MP and PP were analyzed. Genes from physiological pathways including stress response, cell cycle and DNA damage, inflammation, fatty acid metabolism and endocrine functions were affected by MP and PP. The gene expression profiles show that parabens cause toxicity by inducing oxidative stress, DNA double-strand breaks, apoptosis as well as by altering fatty acid metabolism. Altered expression of androgen receptor (ar) and estrogen receptor 2 alpha (esr2a) indicates an antiandrogenic and estrogenic activity of parabens in zebrafish. Overall, the present study provides considerable information on the negative effects of MP and PP using physiological endpoints and motivates further studies to explore the molecular mechanism of the toxicity associated with parabens.

Developmental neurotoxicity of maneb: Notochord defects, mitochondrial dysfunction and hypoactivity in zebrafish (Danio rerio) embryos and larvae

Broad applications and exposure to the fungicide maneb can lead to toxicity in non-target organisms. Maneb is also associated with neurogenerative diseases such as Parkinson's disease (PD). The objectives of this study were to determine the acute toxicity of maneb to zebrafish by measuring mitochondrial bioenergetics, locomotor activity, and the expression of genes related to the oxidative damage response, as well as those related to dopamine signaling due to its association with PD. Zebrafish embryos at 6 h post-fertilization (hpf) were exposed to either solvent control (0.1% DMSO, v/v), or one dose of 0.1, 0.5, 1.0 and 10.0 µM maneb for 96 h. Maneb was moderately toxic to zebrafish embryos, and had a 96-h LC₅₀ value of 4.29 μM (~ 1.14 mg/L). Maneb induced a dose-dependent increase in mortality, decreased hatching rate, and increased notochord deformity rate at both 1.0 and 10.0 µM after 72 and 96 h. Total body length was also significantly reduced with 1.0 µM maneb. A 50-60% decrease in mean basal oxygen consumption rate was also observed in embryos following a 24 hpf exposure to 10.0 µM maneb but oligomycin-induced ATP production and FCCP-induced maximum respiration remained unaffected. No change was detected in the expression levels of genes associated with oxidative stress (sod1 and sod2), nor those related to dopamine synthesis (th1), dopamine transporter (dat), dopamine receptors (drd1, drd2a, drd3, and drd4b). Thus, modifying the expression of these transcripts may not be a mechanism for maneb-induced developmental toxicity in zebrafish. To assess the potential for neurotoxicity, a dark photokinesis assay was conducted in larvae following 7 d exposure to 0.1, 0.5 and 1.0 μM maneb. Larvae exposed to 0.5 and 1.0 μM maneb showed signs related to hypoactivity, and this reduced activity is hypothesized to be associated with notochord defects as this deformity was prevalent at higher concentrations of maneb. Overall, these data demonstrate that maneb negatively affects embryonic development (i.e. notochord development), affects basal oxygen consumption rates of embryos, and induces hypoactivity in larval fish. This study improves understanding regarding the developmental neurotoxicity of the fungicide maneb to zebrafish.

Effects of penthiopyrad on the development and behaviour of zebrafish in early-life stages

The agricultural use of succinate dehydrogenase inhibitor (SDHI) fungicides has increased dramatically in the US and Europe. As the SDHI fungicides, boscalid, flutolanil and thifluzamide had been reported to induce a series of toxic effects on zebrafish. However, the toxic effects of penthiopyrad on zebrafish have not been reported yet. This study aimed to assess the acute toxicity of penthiopyrad to zebrafish in early-life stages and investigate behavioural response of larvae and the effects on lipid metabolism and pigmentation under sub-lethal exposure of penthiopyrad. Based on results of the acute toxicity tests of zebrafish embryo and larvae, penthiopyrad had an acute toxicity to early-life stages of zebrafish and induced a series of deformities during development. Based on the results of sub-lethal exposure for 8 days, penthiopyrad resulted in significant decreases in swimming velocity, acceleration speed, distance moved and inactive time of larvae at 0.3, 0.6 and 1.2 mg/L. Penthiopyrad induced the disorders of lipid metabolism via affecting fatty acid synthesis and β-oxidation, in accordance with remarkable changes in the content of triglycerides and cholesterol and the expression of key genes (hmgcrα, pparα1, srebf1, cyp51 and acca1) at 1.2 mg/L. In addition, the disorder of melanin synthesis and distribution was caused by penthiopyrad in larvae in accordance with changes in body colour and related gene expression at 8 dpe.

Mechanisms of developmental toxicity in zebrafish embryos (Danio rerio) induced by boscalid

Boscalid has been widely used for controlling various plant diseases. It is one of the most frequently detected pesticides in main coastal estuaries in California, with concentrations as high as 36μg/L, but its ecotoxicology information is scarce. To assess the aquatic risk of boscalid, acute toxicity and sub-lethal developmental toxicity toward zebrafish embryos were determined in the present study. In the acute toxicity test, a series of toxic symptoms of embryos were observed, including abnormal spontaneous movement, slow heartbeat, yolk sac oedema, pericardial oedema, spine deformation and hatching inhibition, and 96-h-LC50 (50% lethal concentration) of boscalid toward zebrafish embryos was 2.65 (2.506-2.848)mg/L. From the results of the sub-lethal developmental toxicity test, boscalid was confirmed to have a great impact on development mechanisms of zebrafish embryos. Cell apoptosis in embryos was induced by boscalid with upregulation of genes in the cell apoptosis and an increase of capspase-3 and caspase-9 activity in the present study. Lipid metabolism was affected in embryos due to changes in gene expression and the contents of total triacylglyceride and cholesterol. Melanin synthesis and deposition was caused in embryos due to alterations in related gene expression. Overall, changes in cell apoptosis, lipid metabolism and melanin synthesis and deposition might be responsible for developmental toxicity of boscalid to zebrafish embryos.

Impacts of isopyrazam exposure on the development of early-life zebrafish (Danio rerio)

Isopyrazam (IPZ) is a broad spectrum succinate dehydrogenase inhibitor fungicide. Little is known about its potential ecological risks of aquatic organisms recently. The present study examined the embryonic development effects of zebrafish exposed to IPZ under static condition using a fish embryo toxicity test. The lowest observed effect concentration of IPZ was 0.025 mg/L in 4-day exposure. Developmental abnormalities, including edema, small head deformity, body deformation and decreased pigmentation, and mortality were observed in zebrafish embryos of 0.05 mg/L and higher concentrations, which shown concentration dependency. The heart rate of zebrafish was disrupted by IPZ. Moreover, enzyme and gene experiments shown that IPZ exposure caused oxidative stress of zebrafish. Furthermore, it induced a decrease of succinate dehydrogenase (SDH) enzyme activity and gene transcription level in zebrafish larvae. It can be speculated that IPZ may have a lethal effect on zebrafish, which is accompanied by decreased SDH activity, oxidative stress, and abnormality. These results provide toxicological data about the IPZ on aquatic non-target organisms, which could be useful for further understanding potential environmental risks.

Developmental toxicity and potential mechanisms of pyraoxystrobin to zebrafish (Danio rerio)

As a newly developed, highly efficient strobilurin fungicide, pyraoxystrobin has been reported to be highly toxic to some aquatic organisms. However, the toxicity of pyraoxystrobin to different life stages of fish and the potential underlying mechanisms are still unknown. Hence, in the present study, the acute toxicity of pyraoxystrobin to different life stages of zebrafish (embryo, larva, and adult) was assessed. The developmental toxicity of pyraoxystrobin to zebrafish embryos and its effects on gene transcription in the embryo were also investigated. The results showed that the 96-h LC₅₀ values of pyraoxystrobin to embryos [2h post-fertilization (hpf)], 12h post-hatching (hph) larvae (84 hpf), 72 hph larvae (144 hpf), and adult zebrafish were 4.099, 1.069, 3.236, and 5.970µg/L, respectively. This suggests that pyraoxystrobin has very high toxicity to different life stages of zebrafish, while the newly hatched larvae constitute the most sensitive period of zebrafish to pyraoxystrobin. Decreased heart rate, hatching inhibition, growth regression, and morphological deformities were observed in zebrafish embryos after acute exposure to different concentrations of pyraoxystrobin. The rate of malformation increased in a time- and concentration-dependent manner in embryos, and the most pronounced abnormality was pericardial edema and yolk sac edema. Pyraoxystrobin (2 and 4μg/L) significantly altered the mRNA levels of genes related to mitochondrial respiratory chain and ATP synthesis (NDI, uqcrc, and ATPo6), oxidative stress (Mn-Sod, Cat, and Gpx), apoptosis (p53, Bcl2, Bax, and Cas3), and immune system (TNFα, IFN, and IL-1b) in zebrafish embryos. This result indicates that the alteration of these genes is a potential mechanism underlying the toxic effects of pyraoxystrobin on zebrafish.

Characterization of acrylamide-induced oxidative stress and cardiovascular toxicity in zebrafish embryos

Acrylamide (AA) is a high production volume chemical in industrial applications and widely found in baked or fried carbohydrate-rich foods. In this study, we unravelled that AA induced developmental toxicity associated with oxidative stress status and disordered lipid distribution in heart region of developing zebrafish. Treatment with AA caused a deficient cardiovascular system with significant heart malformation and dysfunction. We also found that AA could reduce the number of cardiomyocytes through the reduced capacity of cardiomyocyte proliferation rather than cell apoptosis. The cardiac looping and ballooning appeared abnormal though cardiac chamber-specific identity in the differentiated myocardium was maintained well after AA treatment through MF20/S46 immunofluorescence assay. Furthermore, treatment with AA disturbed the differentiation of atrioventricular canal, which was demonstrated by the disordered expressions of the atrioventricular boundary markers bmp4, tbx2b and notch1b and further confirmed by the ectopic expressions of the cardiac valve precursor markers has2, klf2a and nfatc1 through whole-mount in situ hybridization. Thus, our studies provide the evidence of cardiac developmental toxicity of AA in the cardiovascular system, and also raised health concern about the harm of trans-placental exposure to high level of AA for foetuses and the risk of high exposure to AA for the pregnant women.

The embryonic developmental effect of sedaxane on zebrafish (Danio rerio)

The succinate dehydrogenase inhibitor (SDHI) fungicides have been extensively used in agriculture, and some of their potential ecological risks to aquatic organisms have been demonstrated recently. Sedaxane (SDX) is a broad spectrum SDHI fungicide. Despite being extensively used in environment, little is known about its potential developmental effect in zebrafish embryo. This study examined the effects of which SDX triggered in zebrafish through embryonic development assessments. Results show that SDX induced mortality, hatch delay and failure in zebrafish embryos, which were concentration dependent. In addition, several developmental abnormalities were observed at 2 mg/L and higher concentrations, including edema, microcephaly, body deformation, and swim bladder not fully inflated. SDX exposure influenced reactive oxygen species, malondialdehyde, peroxidase, glutathione S-transferase, superoxide dismutase and glutathione in live larvae, which indicated that oxidative stress was caused in zebrafish. Furthermore, SDX induced decrease of succinate dehydrogenase activity in zebrafish larvae. These results provide toxicological data of SDX on developing zebrafish embryo, which could be help for further understanding the potential risk on the environment.

Modeling consequences of prolonged strong unpredictable stress in zebrafish: Complex effects on behavior and physiology

Chronic stress is the major pathogenetic factor of human anxiety and depression. Zebrafish (Danio rerio) have become a novel popular model species for neuroscience research and CNS drug discovery. The utility of zebrafish for mimicking human affective disorders is also rapidly growing. Here, we present a new zebrafish model of clinically relevant, prolonged unpredictable strong chronic stress (PUCS). The 5-week PUCS induced overt anxiety-like and motor retardation-like behaviors in adult zebrafish, also elevating whole-body cortisol and proinflammatory cytokines - interleukins IL-1β and IL-6. PUCS also elevated whole-body levels of the anti-inflammatory cytokine IL-10 and increased the density of dendritic spines in zebrafish telencephalic neurons. Chronic treatment of fish with an antidepressant fluoxetine (0.1mg/L for 8days) normalized their behavioral and endocrine phenotypes, as well as corrected stress-elevated IL-1β and IL-6 levels, similar to clinical and rodent data. The CNS expression of the bdnf gene, the two genes of its receptors (trkB, p75), and the gfap gene of glia biomarker, the glial fibrillary acidic protein, was unaltered in all three groups. However, PUCS elevated whole-body BDNF levels and the telencephalic dendritic spine density (which were corrected by fluoxetine), thereby somewhat differing from the effects of chronic stress in rodents. Together, these findings support zebrafish as a useful in-vivo model of chronic stress, also calling for further cross-species studies of both shared/overlapping and distinct neurobiological responses to chronic stress.

Time-response characteristic and potential biomarker identification of heavy metal induced toxicity in zebrafish

The present work aims to explore the time-response (from 24 h to 96 h) characteristic and identify early potential sensitive biomarkers of copper (Cu) (as copper chloride dihydrate), cadmium (Cd) (as cadmium acetate), lead (Pb) (as lead nitrate) and chromium (Cr) (as potassium dichromate) exposure in adult zebrafish, focusing on reactive oxygen species (ROS), SOD activity, lipid peroxidation and gene expression related to oxidative stress and inflammatory response. Furthermore, the survival rate decreased apparently by a concentration-dependent manner after Cu, Cr, Cd and Pb exposure, and we selected non-lethal concentrations 0.05 mg/L for Cu, 15 mg/L for Cr, 3 mg/L for Cd and 93.75μg/L for Pb to test the effect on the following biological indicators. Under non-lethal concentration, the four heavy metals have no apparent histological change in adult zebrafish gills. Similar trends in ROS production, MDA level and SOD activity were up-regulated by the four heavy metals, while MDA level responded more sensitive to Pb by time-dependent manner than the other three heavy metals. In addition, mRNA levels related to antioxidant system (SOD1, SOD2 and Nrf2) were up-regulated by non-lethal concentration Cu, Cr, Cd and Pb exposure. MDA level and SOD1 gene have a more delayed response to heavy metals. Genes related to immunotoxicity were increased significantly after heavy metals exposure at non-lethal concentrations. TNF-α and IL-1β gene have similar sensibility to the four heavy metals, while IL-8 gene was more responsive to Cr, Cd and Pb exposure at 48 h groups and IFN-γ gene showed more sensitivity to Cu at 48 h groups than the other heavy metals. In conclusion, the present works have suggested that the IFN-γ gene may applied as early sensitive biomarker to identify Cu-induced toxicity, while MDA content and IL-8 gene may use as early sensitive biomarkers for evaluating the risk of Pb exposure. Moreover, IL-8 and IFN-γ gene were more responsive to heavy metals, which may become early sensitive and potential biomarkers for evaluating inflammatory response induced by heavy metals. This work reinforces the concept of the usefulness of gene expression assays in the evaluation of chemicals effects and helps to establish a background data as well as contributes to evaluate early environmental risk for chemicals, even predicting toxicity.

Sensitive biomarkers identification for differentiating Cd and Pb induced toxicity on zebrafish embryos

Cadmium (Cd) and lead (Pb) are naturally existing heavy metals that pose significant health risks. The present study aims to identify sensitive biomarkers for differentiating the toxicities induced by Cd and Pb and for providing clues for the early prediction of toxicity and environmental risk assessment. Indicators related to oxidative stress and inflammatory responses in zebrafish treated with Cd and Pb over time (from 24hpf to 96hpf) were compared. Furthermore, endpoints such as embryo lethality and teratogenicity were detected. Then, several related genes involved in oxidative stress and inflammatory responses characterizing both Cd and Pb exposure, along with key molecules in the MAPKs pathway, were compared at the mRNA level, allowing the selection of the most sensitive and informative biomarkers. Significant increases in reactive oxygen species (ROS) production were observed in zebrafish exposed to Cd and Pb. Cd and Pb exposure induced developmental toxicity, influencing survival rate, hatching rate, larval growth, and heart rate and causing abnormal embryonic development. Similar trends in SOD1 and SOD2 gene expression were induced by Cd and Pb, while nuclear factor erythroid-2 related factor 2 (Nrf2) gene expression responded differently to each metal. In addition, Cd and Pb induced a delayed activation of the CAT and HO-1 genes, with no apparent change in the 24hpf and 48hpf groups. Genes related to immunotoxicity were activated significantly in a time-dependent manner, and these genes exhibited different sensitivities to Cd and Pb. MAPKs pathway genes were also activated in a time-dependent manner, and the expression of these genes showed different effects under Cd and Pb treatment. In summary, the present works have identified some potential sensitive biomarkers. The Nrf2 gene is a potential biomarker to differentiate Pb-induced toxicity from that of Cd, and the IFN-γ gene may be used as a sensitive biomarker for evaluating the risk of Pb contamination. We found that the timeline of MAPKs pathway activation helped to differentiate these two metals toxicities. Furthermore, Pb induced the early activation of ERK2/3 and JNK1, while p38 MAPKs showed delayed activation with no apparent change in the 24hpf group. Cd induced an early activation of ERK2 and a delayed activation of p38a, p38b, ERK3 and JNK1, indicating that the JNK1 pathway is sensitive to Pb exposure, while the p38 pathway may be susceptible to Cd. This work contributes to sensitive biomarker identification and early environmental risk evaluation for chemicals as well as toxicity prediction.