Transcriptome analysis of zebrafish embryos exposed to deltamethrin

Toxicity effects of pesticides based on zebrafish (Danio rerio) models: Advances and perspectives

Pesticides inevitably enter aquatic environments, posing potential risks to organisms. The common aquatic model organism, zebrafish (Danio rerio), are widely used to evaluate the toxicity of pesticides. In this review, we searched the Web of Science database for articles published between 2012 and 2022, using the keywords "pesticide", "zebrafish", and "toxicity", retrieving 618 publications. Furthermore, we described the main pathways by which pesticides enter aquatic environments and the fate of their residues in these environments. We systematically reviewed the toxicity effects of pesticides on zebrafish, including developmental toxicity, endocrine-disrupting effects, reproductive toxicity, neurotoxicity, immunotoxicity, and genotoxicity. Importantly, we summarized the latest research progress on the toxicity mechanism of pesticides to zebrafish based on omics technologies, including transcriptomics, metabolomics, and microbiomics. Finally, we discussed future research prospects, focusing on the combined exposure of multiple pollutants including pesticides, the risk of multigenerational exposure to pesticides, and the chronic toxicity of aquatic nanopesticides. This review provides essential data support for ecological risk assessments of pesticides in aquatic environments, and has implications for water management in the context of pesticide pollution.

Neurotoxicity of nanoparticles: Insight from studies in zebrafish

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

Developmental pyrethroid exposure and age influence phenotypes in a Chd8 haploinsufficient autism mouse model

Hundreds of genes have been associated with autism spectrum disorder (ASD), including loss-of-function mutations in chromodomain helicase DNA binding protein 8 (Chd8). Environmental factors also are implicated in autism risk and have the potential to exacerbate phenotypes in genetically sensitized backgrounds. Here we investigate transcriptional and behavioral phenotypes in a Chd8 haploinsufficient (Chd8^V986*/+) mouse line exposed to the pesticide deltamethrin (DM) from conception to postnatal day 22. Vehicle-exposed Chd8^V986*/+ mice displayed ASD-associated phenotypes, including anxiety-like behavior and altered sociability, replicating a previous study with this mouse line. A core set of genes was altered in Chd8^V986*/+ mice at multiple ages, including Usp11, Wars2, Crlf2, and Eglf6, and proximity ligation data indicated direct binding of CHD8 to the 5’ region of these genes. Moreover, oligodendrocyte and neurodegenerative transcriptional phenotypes were apparent in 12 and 18 month old Chd8^V986*/+ mice. Following DM exposure, the mutant mice displayed an exacerbated phenotype in the elevated plus maze, and genes associated with vascular endothelial cells were downregulated in the cerebral cortex of older Chd8^V986*/+ animals. Our study reveals a gene x environment interaction with a Chd8 haploinsufficient mouse line and points to the importance of investigating phenotypes in ASD animal models across the lifespan.

Embryonic toxicity of epoxiconazole exposure to the early life stage of zebrafish

Epoxiconazole (EPX), as a broad-spectrum triazole fungicide, is widely used in agriculture to resist pests and diseases, while it may have potential toxicity to non-target organisms. In the present study, early developmental stage zebrafish were used as the subject organisms to assess the toxicity of EPX, and the possible mechanism of toxicity was also discussed by biochemical and transcriptomic analysis. Through embryo toxicity test, we had made it clear that the 96 h LC₅₀ of embryo was 7.204 mg/L, and acute exposure to EPX effected hatching rate, heartbeats, body length and even morphological defects. Then, by being exposed to EPX for 7 days at concentrations of 175 (1/40 LC₅₀), 350 (1/20 LC₅₀) and 700 (1/10 LC₅₀), biochemical parameters were affected, mainly manifested as increase of the triglyceride (TG) level and decrease of glucose content. Correspondingly, the transcription of genes related of glucose metabolism, lipid metabolism and cholesterol metabolism were also affected significantly in larval zebrafish. Moreover, some pathways, including lipid metabolism, glucose metabolism and amino acid metabolism were affected through transcriptome sequencing analysis in the larval zebrafish. Further data analysis based on the sequencing, EPX exposure also affected the expression of genes related to cell apoptosis. We further conformed that the bright fluorescence on the liver and bright spots near the liver by acridine orange staining. In addition, the mRNA levels of apoptosis related genes were also significantly affected in the EPX exposed larval zebrafish. Taken together, the work could provide an insight into toxic effects of EPX on the zebrafish larvae at embryo toxicity and transcriptional levels, providing some evidences for the toxic effects of triazole fungicides on non-target organisms.

Effects of microplastics on head kidney gene expression and enzymatic biomarkers in adult zebrafish

Due to massive production, improper use, and disposal of plastics, microplastics have become global environmental pollutants affecting both freshwater and marine ecosystems. Several studies have documented the uptake of microplastics in wild species and the correlated biological effects, such as epithelial damage, inflammation, metabolic alterations, and neurotoxicity. However, the effects of microplastics are not fully understood yet. In this study, adult zebrafish have been exposed for twenty days to two concentrations of a mix of polystyrene and high-density polyethylene microplastics. The biological effects were investigated through the expression levels of a set of selected genes in head kidney samples and two enzymatic biomarkers, acetylcholinesterase and lactate dehydrogenase, in head and body homogenates respectively. The lowest microplastic concentration up-regulated genes involved in xenobiotics catabolic processes (cyp2p8), and adaptive immunity (tcra). Acetylcholinesterase activity was inhibited by the highest microplastics exposure, while a weaker and no significant inhibition was induced by the lowest concentration. No significant effects on lactate dehydrogenase activity were observed. The results presented in this study support the hypothesis that MPs exposure could induce the activation of an immune response and the xenobiotic metabolism, suggesting also that the cytochrome P450 enzyme cyp2p8 and acetylcholinesterase may be sensitive to MPs contamination.

Transcriptomic and Histopathological Effects of Bifenthrin to the Brain of Juvenile Rainbow Trout (Oncorhynchus mykiss)

The increased global use of pyrethroids raises concern for non-target aquatic species. Bifenthrin, among the most predominantly detected pyrethroids in the environment, is frequently measured in water samples above concentrations reported to induce neuroendocrine and neurotoxic effects to several threatened and endangered fish species, such as the Chinook salmon and steelhead trout. To better characterize the neurotoxic effect of bifenthrin to salmonids, rainbow trout were treated with environmentally relevant concentrations of bifenthrin (15 and 30 ng/L) for two weeks and assessed for changes in transcriptomic profiles and histopathological alterations. The top bioinformatic pathways predicted to be impaired in bifenthrin-exposed trout were involved in gonadotropin releasing hormone signaling, the dysregulation of iron homeostasis, reduced extracellular matrix stability and adhesion, and cell death. Subsequent histopathological analysis showed a significant increase in TUNEL positive cells in the cerebellum and optic tectum of bifenthrin-treated trout, relative to controls (p < 0.05). These findings suggest that low, ng/L concentrations of bifenthrin are capable of dysregulating proper neuroendocrine function, impair the structural integrity of the extracellular matrix and cell signaling pathways in the brain, and induce apoptosis in neurons of juvenile salmonids following bifenthrin treatment, which is consistent with metabolomic profiles demonstrating a common target and mechanism.

Effect of long-term treatment with a mixture of pyrethroids on the expression of genes that govern male germ cell production in rats

Humans are exposed to pyrethroid-based pesticides through agricultural produce. In this study, male Wistar rats were orally treated for 9 to 12 months with a mixture of pyrethroids that is equivalent to one-fifth (high dose; HD) or one-twenty fifth (low dose; LD) of the amount of pyrethroids present in the cereals and rice consumed by an average Indian. In rats treated for 9 months, the spermatogenesis-associated genes Abp, Ar, Cd9, Dax1, Dazap1, Ddx3y, Gdnf, Gfra1, Grth, Inhb, Ovol1, P1, Plzf, Pygo2, Scf, Tgfb1, Tp1, Tp2, and Vim1 were downregulated in both LD and HD groups. In rats treated for 12 months Gdnf, Hsf2, Inhb, Tgfb1, Thy1, and Ybx2 expression was downregulated in both LD and HD groups. Steroidogenesis-associated genes 17-β-Hsd, Gata4, Hmgcr, Hmgcs1, Pde4b, and Tspo gene expression were reduced in both LD- and HD-treated groups treated for 9 months. In 12-month-treated rats, Creb1 expression decreased in both LD and HD groups. The epigenetic reprogramming-associated genes, Dnmt1, Dnmt3a, Dnmt3b, Hdac10, Hp1bp3, Kat3a Kat3b, Mch2ta, Ncoa7, and Sirt1 were downregulated in both HD and LD groups of 9-months-treated rats. In rats treated for 12 months, Hdac10, Mch2ta, Ncoa7, and Sirt1 messenger RNA levels decreased in both the HD and LD groups. Thus, we demonstrate that long-term exposure to a mixture of pyrethroids caused aberrations in the transcriptome of factors involved in sperm production and development.

Zebrafish as a Successful Animal Model for Screening Toxicity of Medicinal Plants

The zebrafish (Danio rerio) is used as an embryonic and larval model to perform in vitro experiments and developmental toxicity studies. Zebrafish may be used to determine the toxicity of samples in early screening assays, often in a high-throughput manner. The zebrafish embryotoxicity model is at the leading edge of toxicology research due to the short time required for analyses, transparency of embryos, short life cycle, high fertility, and genetic data similarity. Zebrafish toxicity studies range from assessing the toxicity of bioactive compounds or crude extracts from plants to determining the optimal process. Most of the studied extracts were polar, such as ethanol, methanol, and aqueous solutions, which were used to detect the toxicity and bioactivity. This review examines the latest research using zebrafish as a study model and highlights its power as a tool for detecting toxicity of medicinal plants and its effectiveness at enhancing the understanding of new drug generation. The goal of this review was to develop a link to ethnopharmacological zebrafish studies that can be used by other researchers to conduct future research.

Pyrethroid pesticide exposure during early pregnancy and birth outcomes in southwest China: a birth cohort study

Despite the developmental toxicity reported in animals, few epidemiologic studies have investigated the potential effects of prenatal exposure to pyrethroid pesticides (PYRs) on fetal growth. A birth cohort study was conducted to examine the association between prenatal exposure to PYRs and birth outcomes, and a nested case-control study was conducted in this cohort to evaluate the effects of PYR on congenital defects. The assessment of PYR exposure was based on self-reported household pesticide use and urinary PYR metabolite levels. We found that pregnant women in this region were ubiquitously exposed to low-level PYRs, although few reported household pesticide use. Women who often ate bananas or cantaloupes had a higher level of urinary 3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (DBCA), and the number of fruit types consumed by pregnant women was positively related to the concentrations of 3-phenoxybenzoic acid (3PBA) and total PYR metabolites (P < 0.05). Increased urinary 4-fluoro-3-phenoxybenzoic acid (4F3PBA), DBCA, and total PYR metabolites were associated with increased birth weight, length, and gestational age, and with decreased risk of small for gestational age (SGA) and/or premature birth. However, maternal household pesticides use was related to congenital anomalies. Thus, although prenatal exposure to low-dose PYRs promoted the fetal growth, the beneficial effects of fruit intake may outweigh the adverse effects of pesticide exposure. This study provided us an insight into the biological mechanisms for the effect of prenatal PYR exposure on fetal development, and suggested that further investigations in a larger study population with low-dose PYR exposure is needed.

Residual molecular and behavioral effects of the phenylpyrazole pesticide fipronil in larval zebrafish (Danio rerio) following a pulse embryonic exposure

Pesticides are typically applied to crops as acute applications, and residual effects of such intermittent exposures are not often characterized in developing fish. Fipronil is an agricultural pesticide that inhibits γ-amino-butyric acid (GABA) gated chloride channels. In this study, zebrafish (Danio rerio) embryos were exposed for 48 h (starting at ~3 h post fertilization, hpf) to various concentrations of fipronil (0.02 μg/L up to 4000 μg/L). Following this acute exposure, a subset of fish was transferred to clean water for a 7-day depuration phase. We hypothesized that a pulse exposure to fipronil during critical periods of central nervous system development would adversely affect fish later in life. After a 48 hour pulse exposure, survival was reduced in embryos exposed to 2 μg fipronil/L or greater. However, there was no further mortality during the depuration phase, nor were there changes in body length nor notochord length in larvae 9 dpf (days post-fertilization) compared to controls. Additional experiments were carried out at higher concentrations over 96 h (up to 4 dpf) to also elucidate developmental effects and teratogenicity of fipronil (43.7 μg/L up to 4370 μg/L). Fipronil at these higher concentrations significantly impacted the development of zebrafish, and the following morphometric and teratogenic effects were observed in 4 dpf fish; reduced body length, yolk sac and pericardial edema, reduced midbrain length, reduced optic and otic diameter, and truncation of the lower jaw. In depurated fish, we hypothesized that there would exist residual effects of exposure at the molecular level. Transcriptome profiling was therefore conducted on 9 dpf depurated larvae exposed initially for 48 h to one dose of either 0.2 μg/L, 200 μg/L or 2000 μg/L fipronil. The expression of gene networks associated with glycogen and omega-3-fatty acid metabolism were decreased in larvae exposed to each of the three concentrations of fipronil, suggesting metabolic disruption. Moreover, transcriptomics revealed that fipronil suppressed gene networks related to light-dark adaptation, photoperiod sensing, and circadian rhythm. Based on these data, we tested fish for altered behavioral responses in a Light-Dark preference test. Larvae exposed to >200 μg fipronil/L as embryos showed fewer number of visits (20-30% less) to the dark zone compared to controls. Larvae also spent a lower amount of time in the dark zone compared to controls, suggesting that fipronil strengthened dark avoidance behavior which is indicative of anxiety. This study demonstrates that a short pulse exposure to fipronil can affect transcriptome networks for metabolism, circadian rhythm, and response to light in fish after depuration, and these molecular responses are hypothesized to be related to aberrant behavioral effects observed in the light-dark preference test.

Protective Effects of Spermidine and Melatonin on Deltamethrin-Induced Cardiotoxicity and Neurotoxicity in Zebrafish

Increased application of the pyrethroid insecticide deltamethrin has adverse effects on the cardiac system and neurobehavior on the non-target organisms, which has raised the public's attention. Because of spermidine and melatonin considered to have cardioprotective and neuroprotective characteristics, zebrafish were utilized as the model organism to explore the protective effects of spermidine and melatonin against deltamethrin-induced toxicity. We tested the neurobehavior of zebrafish larvae through a rest/wake behavior assay, and evaluated the levels of the expression of Scn5lab, gata4, nkx2.5, hcrt, hcrtr, and aanat2 by qRT-PCR. Besides that cmlc2 was evaluated by whole-mount in situ hybridization. Results have shown that compared with control group, 0.025 mg/L deltamethrin could significantly disturb the cardiac development, downregulating the expression of Scn5lab and transcriptional factors gata4 and nkx2.5, disturbing cardiac looping, resulting in defects in cardiac morphology and function. Moreover, deltamethrin could alter the expression levels of rest/wake genes and cause hyperactivity in zebrafish larvae. Besides, compared with deltamethrin group, the exogenous 0.01 mg/L spermidine and 0.232 mg/L melatonin could significantly rescue the adverse effects of deltamethrin on the cardiac system and neurobehavior in zebrafish. This indicated that spermidine and melatonin have neuroprotective and cardioprotective effects against deltamethrin-induced adverse effects in zebrafish.

Immunotoxicity and transcriptome analysis of zebrafish embryos in response to glufosinate-ammonium exposure

Glufosinate-ammonium (Gla) is a broad-spectrum and non-selective herbicide that widely used in many countries worldwide, but the biological safety including potentially negative effects on aquatic organisms remains largely unknown. In this study, we investigated the immunotoxic effects of Gla exposure on zebrafish embryos. Firstly, Gla markedly decreased the survival rate and caused a series of morphological malformations in a dose-dependent manner. Meanwhile, the number of macrophages and neutrophils was substantially reduced upon Gla exposure. In addition, the levels of oxidative stress were changed and the antioxidant enzyme activities such as CAT and SOD were elevated with the increase of Gla concentrations. Secondly, comparative transcriptome analysis identified 1, 366 differentially expressed genes (DEGs) including 789 up-regulated and 577 down-regulated in zebrafish embryos after Gla exposure. KEGG pathway analysis revealed that metabolic pathways such as drug metabolism-cytochrome P450 was markedly regulated and proteolysis, oxidation-reduction process, and peptidase activity were significantly enriched by the GO analysis. Besides, 55 immunity-related genes were identified in the DEGs, and we found that the genes in the metabolism, redox and immunity display an unique expression profilings by clustering analysis. Finally, 8 inflammatory cytokines and chemokines were further confirmed and they were differentially regulated after Gla exposure. In summary, a global survey of zebrafish defense against glufosinate was performed, and a large number of gene expression levels regarding metabolism, redox, and immunity-related genes were acquired from RNA-Seq. This study provides valuable informations for future elucidating the molecular mechanism of herbicide induced immunotoxicity in aquatic ecosystems.

Transcriptome analysis reveals global gene expression changes of Chilo suppressalis in response to sublethal dose of chlorantraniliprole

The anthranilic diamide insecticide chlorantraniliprole was widely used for the controlling of Chilo suppressalis in China. Previous studies have revealed sublethal effects of chlorantraniliprole on the development and reproduction of C. suppressalis. In the present study, a comparative transcriptome analysis was performed to investigate the global gene expression changes in third-instar larvae of C. suppressalis after exposure to LC₃₀ of chlorantraniliprole. A total of 908 differentially expressed genes (DEGs) were identified including 441 up-regulated and 467 down-regulated unigenes. Gene enrichment analysis revealed that the down-regulated DEGs were mainly linked to carbohydrate, energy, lipid and amino acid metabolisms as well as posttranslational modification, while most of the DEGs involved in signal transduction were up-regulated. Specifically, the DEGs encoding detoxification related genes were identified and validated by RT-qPCR. Our results provide a basis for understanding the molecular mechanisms of chlorantraniliprole action and detoxification in C. suppressalis and other insect pests.

Toxicity of diuron in HepG2 cells and zebrafish embryos

Diuron is an herbicide, which is used to control a wide variety of annual and perennial broadleaf, grassy weeds, and mosses. However, the toxicity of diuron in HepG2 cells and zebrafish embryos was unclear. In this study, HpeG2 cells and zebrafish embryos were exposed to different concentrations of diuron for 24 h and 48 h, respectively. Results reveal the diuron caused cytotoxicity and the generation of reactive oxygen species (ROS) in the treated HepG2 cells. The effects of diuron on the expression of catalase and superoxide dismutase (SOD1 and SOD2), an antioxidant enzyme, were investigated. Results showed that only SOD1 was significantly induced after treated diuron 48 h, but the expression of catalase and SOD2 was unaffected. Additionally, the cytotoxicity of diuron was not attenuated in cells pretreated with of N-acetyl-cysteine (NAC), a well-known antioxidant, indicating that oxidative stress could not contribute to cellular death in the treated HepG2 cells. In zebrafish embryos, results from proteomic analysis show that 332 differentially upregulated proteins and 199 down-regulated proteins were detected in the treated embryos (P < 0.05). In addition to the up-regulated antioxidant proteins (prdx3, cat, prdx4, txnrd1, prdx1, sod1, prdx2, and sod2), some decreased proteins were related to cytoskeleton formation, tight junction, and gap junction, which could be related to the malformation of the treated zebrafish embryos. In summary, diuron caused cytotoxicity in HepG2 cells, and the mechanisms of toxicity in zebrafish were addressed using the proteomic analysis.

The Utility of Zebrafish as a Model for Screening Developmental Neurotoxicity

The developing central nervous system and the blood brain barrier are especially vulnerable and sensitive to different chemicals, including environmental contaminants and drugs. Developmental exposure to these compounds has been involved in several neurological disorders, such as autism spectrum disorders as well as Alzheimer's and Parkinson's diseases. Zebrafish (Danio Rerio) have emerged as powerful toxicological model systems that can speed up chemical hazard assessment and can be used to extrapolate neurotoxic effects that chemicals have on humans. Zebrafish embryos and larvae are convenient for high-throughput screening of chemicals, due to their small size, low-cost, easy husbandry, and transparency. Additionally, zebrafish are homologous to other higher order vertebrates in terms of molecular signaling processes, genetic compositions, and tissue/organ structures as well as neurodevelopment. This mini review underlines the potential of the zebrafish as complementary models for developmental neurotoxicity screening of chemicals and describes the different endpoints utilized for such screening with some studies illustrating their use.

Opportunities and challenges for using the zebrafish to study neuronal connectivity as an endpoint of developmental neurotoxicity

Chemical exposures have been implicated as environmental risk factors that interact with genetic susceptibilities to influence individual risk for complex neurodevelopmental disorders, including autism spectrum disorder, schizophrenia, attention deficit hyperactivity disorder and intellectual disabilities. Altered patterns of neuronal connectivity represent a convergent mechanism of pathogenesis for these and other neurodevelopmental disorders, and growing evidence suggests that chemicals can interfere with specific signaling pathways that regulate the development of neuronal connections. There is, therefore, a growing interest in developing screening platforms to identify chemicals that alter neuronal connectivity. Cell-cell, cell-matrix interactions and systemic influences are known to be important in defining neuronal connectivity in the developing brain, thus, a systems-based model offers significant advantages over cell-based models for screening chemicals for effects on neuronal connectivity. The embryonic zebrafish represents a vertebrate model amenable to higher throughput chemical screening that has proven useful in characterizing conserved mechanisms of neurodevelopment. Moreover, the zebrafish is readily amenable to gene editing to integrate genetic susceptibilities. Although use of the zebrafish model in toxicity testing has increased in recent years, the diverse tools available for imaging structural differences in the developing zebrafish brain have not been widely applied to studies of the influence of gene by environment interactions on neuronal connectivity in the developing zebrafish brain. Here, we discuss tools available for imaging of neuronal connectivity in the developing zebrafish, review what has been published in this regard, and suggest a path forward for applying this information to developmental neurotoxicity testing.

High-throughput assessment of oxidative respiration in fish embryos: Advancing adverse outcome pathways for mitochondrial dysfunction

Mitochondrial dysfunction is a prevalent molecular event that can result in multiple adverse outcomes. Recently, a novel high throughput method to assess metabolic capacity in fish embryos following exposure to chemicals has been adapted for environmental toxicology. Assessments of oxygen consumption rates using the Seahorse XF(e) 24/96 Extracellular Flux Analyzer (Agilent Technologies) can be used to garner insight into toxicant effects at early stages of development. Here we synthesize the current state of the science using high throughput metabolic profiling in zebrafish embryos, and present considerations for those wishing to adopt high throughput methods for mitochondrial bioenergetics into their research. Chemicals that have been investigated in zebrafish using this metabolic platform include herbicides (e.g. paraquat, diquat), industrial compounds (e.g. benzo-[a]-pyrene, tributyltin), natural products (e.g. quercetin), and anti-bacterial chemicals (i.e. triclosan). Some of these chemicals inhibit mitochondrial endpoints in the μM-mM range, and reduce basal respiration, maximum respiration, and spare capacity. We present a theoretical framework for how one can use mitochondrial performance data in zebrafish to categorize chemicals of concern and prioritize mitochondrial toxicants. Noteworthy is that our studies demonstrate that there can be considerable variation in basal respiration of untreated zebrafish embryos due to clutch-specific effects as well as individual variability, and basal oxygen consumption rates (OCR) can vary on average between 100 and 300 pmol/min/embryo. We also compare OCR between chorionated and dechorionated embryos, as both models are employed to test chemicals. After 24 h, dechorionated embryos remain responsive to mitochondrial toxicants, although they show a blunted response to the uncoupling agent carbonylcyanide-4-trifluoromethoxyphenylhydrazone (FCCP); dechorionated embryos are therefore a viable option for investigations into mitochondrial bioenergetics. We present an adverse outcome pathway framework that incorporates endpoints related to mitochondrial bioenergetics. High throughput bioenergetics assays conducted using whole embryos are expected to support adverse outcome pathways for mitochondrial dysfunction.