A metabolomic study of fipronil for the anxiety-like behavior in zebrafish larvae at environmentally relevant levels

Insecticide-Induced Metabolic Dysregulation in Model Microbe E. coli Discovered by Comprehensive Metabolic Profiling

Fipronil, malathion, and permethrin are widely used insecticides in agriculture, public areas, and residential spaces. The globally abused application of these chemicals results in residues surpassing established maximum residue levels, giving rise to potential toxicity in unintended organisms. Long-term exposure and the persistent accumulation of these insecticides in animals and humans pose threats such as neurotoxicity, liver and kidney damage, and microbiota dysbiosis. Despite the known risks, the specific impact of these insecticides on gut microbiota and their metabolic processes, as well as the subsequent effects on host health, remain largely unknown. This study aimed to address this gap by utilizing nonpathogenic Escherichia coli as a representative of human gut bacteria and examining its growth and metabolic perturbations induced by exposure to fipronil, malathion, and permethrin. Our research showed that exposure of E. coli to fipronil, malathion, and permethrin at physiologically relevant concentrations resulted in significant growth inhibition. Furthermore, we have observed the biodegradation of fipronil and permethrin by E. coli, while no biodegradation was found for malathion. Thus, E. coli is capable of degrading fipronil and permethrin, thereby enabling the removal of those substances. Next, we studied how insecticides affect bacterial metabolism to understand their influence on the functions of the microbes. Our metabolomics analysis revealed chemical-dependent alterations in metabolic profiles and metabolite compositions following insecticide exposure. These changes encompassed shifts in carboxylic acids and derivatives, organooxygen compounds, as well as indoles and their derivatives. To gain a deeper insight into the systematic changes induced by these insecticides, we conducted a metabolic pathway analysis. Our data indicated that fipronil, compared with malathion and permethrin, exhibited opposite regulation in glycine, serine, and threonine metabolism and valine, leucine, and isoleucine biosynthesis. In summary, our study demonstrates the capability of E. coli to degrade fipronil and permethrin, leading to their removal, while malathion remains unaffected. Additionally, we reveal chemical-dependent alterations in bacterial metabolism induced by insecticide exposure, with specific impacts on metabolic pathways, particularly in pathways related to amino acid metabolism.

Hazardous fipronil insecticide effects on aquatic animals' health: Historical review and trends

Fipronil (FIP) is a broad-spectrum and highly efficient insecticide used against several arthropod pests, such as parasitic mites and insect pests affecting both animals and plants. Given its several benefits, FIP is widely used in the agricultural and veterinary medicine fields, but its indiscriminate use can have ecotoxic effects on non-target species. Thus, the current study aimed to summarise and critically analyse FIP's ecotoxicity in aquatic animals. Data referring to bibliometric parameters (publication year and geographical distribution), experimental conditions (field and laboratory, FIP type, animal class, species, habitat, and exposure conditions), and biomarkers (oxidative stress, DNA damage, neurotoxicity, and morphological changes) were summarised and critically analysed. Ecotoxicological studies were mainly conducted with insects, crustaceans, molluscs, and fish. Exposure to pure FIP or FIP-based commercial formulation can induce mortality and have sublethal effects on non-target organisms, such as increased reactive oxygen species (ROS), oxidative damage, genotoxicity (DNA damage), neurotoxicity, and morphological changes. The herein reviewed data have evidenced high median lethal FIP concentration (LC50) in vertebrates in comparison to invertebrates. The current findings confirmed that FIP can have several effects on aquatic organisms, besides suggesting potential ecotoxicological risks posed by this insecticide.

Environmentally relevant exposure to cotinine induces neurobehavioral toxicity in zebrafish (Danio rerio): A study using neurobehavioral and metabolomic approaches

As an important psychoactive substance, cotinine is ubiquitous in aquatic environment and poses a threat to aquatic organisms. However, the mechanism of its adverse health impacts remains unclear. We evaluated the effects of cotinine exposure at environmentally relevant concentrations on the development and locomotor behavior of zebrafish (Danio rerio) larvae using neurotransmitters and whole endogenous metabolism. Mild developmental toxicity and significant neurobehavior disorder, such as spontaneous movement (1-1000 μg/L), 48 hpf tactile response (50, 100, and 1000 μg/L), and 144 hpf swimming speed (1, 10, 100, 500, and 1000 μg/L), were observed in zebrafish. Exposure to cotinine led to significant alterations in 11 neurotransmitters, including homogentisic acid, serotonin, glutamic acid and aspartic acid, etc. 298 metabolites were identified and two pathways - linoleic acid metabolism and taurine and hypotaurine metabolism - were delineated. In addition, amino acid neurotransmitters were significantly correlated with metabolites such as arachidonic acid as well as its derivatives, steroidal compounds, and amino acids. Serotonin demonstrates a noteworthy correlation with 31 out of 40 differentially expressed neurotransmitters, encompassing lipids, amino acids, and other compounds. These novel findings contribute to a comprehensive understanding of the ecological risks associated with cotinine contamination in surface waters.

N-nitrosamines induced gender-dimorphic effects on infant rats at environmental levels

The safety of drinking water has always been a concern for people all over the world. N-nitrosamines (NAs), a kind of nitrogenous disinfection by-products (N-DBPs), are generally detected as a mixture in drinking water at home and abroad. Studies have shown that individual NAs posed strong carcinogenicity at high concentrations. However, health risks of NAs at environmental levels (concentrations in drinking water) are still unclear. Therefore, the potential health risks of environmentally relevant NAs exposure in drinking water needs to be conducted. In this study, blood biochemical analysis and metabolomics based on nuclear magnetic resonance (NMR) were performed to comprehensively investigate NAs induced metabolic disturbance in infant rats at environmental levels. Results of blood biochemical indices analysis indicated that AST in the serum of male rats in NAs-treated group exhibited a significant gender-specific difference. Multivariate statistics showed that two and eight significantly disturbed metabolic pathways were identified in the serum samples of NAs-treated male and female rats, respectively. In the urine samples of NAs-treated female rats, glycine, serine, and threonine metabolism pathway was significantly disturbed; while three significantly disturbed metabolic pathways were found in the urine of NAs-treated male rats. Finally, results of spearman correlation coefficients suggested that the disturbances of metabolism profile in serum and urine were correlated with changes in the gut microbiota (data derived from our published paper). Data presented here aimed to generate new health risk data of NAs mixture exposure at environmental levels and provide theoretical support for drinking water safety management. ENVIRONMENTAL IMPLICATION: N-nitrosamines (NAs) are a kind of nitrogenous disinfection by-products (N-DBPs) generated during drinking water disinfection processes. Herein, health risks of NAs at environmental levels (concentrations in drinking water) are investigated using blood biochemical analysis and nuclear magnetic resonance (NMR)-based metabolomics. Results confirmed NAs induced gender-specific on the metabolism in rat and the disturbances of metabolism profile in serum and urine were correlated with changes in the gut microbiota. Data presented here aimed to generate new health risk data of NAs mixture exposure at environmental levels and provide theoretical support for drinking water safety management.

Vitamin B12 Ameliorates Pesticide-Induced Sociability Impairment in Zebrafish (Danio rerio): A Prospective Controlled Intervention Study

Constant exposure to a variety of environmental factors has become increasingly problematic. A variety of illnesses are initiated or aided by the presence of certain perturbing factors. In the case of autism spectrum disorder, the environmental component plays an important part in determining the overall picture. Moreover, the lack of therapies to relieve existing symptoms complicates the fight against this condition. As a result, animal models have been used to make biomedical research easier and more suited for disease investigations. The current study used zebrafish as an animal model to mimic a real-life scenario: acute exposure to an increased dose of pesticides, followed by prospective intervention-based therapy with vitamin B12 (vit. B12). It is known that vit. B12 is involved in brain function nerve tissue, and red blood cell formation. Aside from this, the role of vit. B12 in the redox processes is recognized for its help against free radicals. To investigate the effect of vit. B12, fish were divided into four different groups and exposed to a pesticide mixture (600 μg L-1 fipronil + 600 μg L-1 pyriproxyfen) and 0.24 μg L-1 vit. B12 for 14 days. The impact of the compounds was assessed daily with EthoVision XT 11.5 software for behavioral observations, especially for sociability, quantified by the social interaction test. In addition, at the end of the study, the activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and malondialdehyde (MDA) were measured. The results showed significant improvements in locomotor activity parameters and a positive influence of the vitamin on sociability. Regarding the state of oxidative stress, high activity was found for SOD and GPx in the case of vit. B12, while fish exposed to the mixture of pesticides and vit. B12 had a lower level of MDA. In conclusion, the study provides new data about the effect of vit. B12 in zebrafish, highlighting the potential use of vitamin supplementation to maintain and support the function of the organism.

Review on typical organophosphate diesters (di-OPEs) requiring priority attention: Formation, occurrence, toxicological, and epidemiological studies

The impact of primary metabolites of organophosphate triesters (tri-OPEs), namely, organophosphate diesters (di-OPEs), on the ecology, environment, and humans cannot be ignored. While extensive studies have been conducted on tri-OPEs, research on the environmental occurrence, toxicity, and health risks of di-OPEs is still in the preliminary stage. Understanding the current research status of di-OPEs is crucial for directing future investigations on the production, distribution, and risks associated with environmental organophosphate esters (OPEs). This paper specifically reviews the metabolization process from tri-OPEs to di-OPEs and the occurrence of di-OPEs in environmental media and organisms, proposes typical di-OPEs in different media, and classifies their toxicological and epidemiological findings. Through a comprehensive analysis, six di-OPEs were identified as typical di-OPEs that require prioritized research. These include di-n-butyl phosphate (DNBP), bis(2-butoxyethyl) phosphate (BBOEP), bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), bis(2-chloroethyl) phosphate (BCEP), bis(1-chloro-2-propyl) phosphate (BCIPP), and diphenyl phosphate (DPHP). This review provides new insights for subsequent toxicological studies on these typical di-OPEs, aiming to improve our understanding of their current status and provide guidance and ideas for research on the toxicity and health risks of di-OPEs. Ultimately, this review aims to enhance the risk warning system of environmental OPEs.

Histopathological and Behavioral Impairments in Zebrafish (Danio rerio) Chronically Exposed to a Cocktail of Fipronil and Pyriproxyfen

BACKGROUND

Lately, the high incidence of pesticide usage has attracted everyone's interest due to the serious effects produced. Fipronil (FIP) is a phenylpyrazole compound that acts on the insect's GABA neurotransmitter by inhibiting its activity. Moreover, the literature reports highlight its implication in neurodevelopmental abnormalities and oxidative stress production in different organisms. Similarly, pyriproxyfen (PYR) is known to affect insect activity by mimicking the natural hormones involved in the maturation of the young insects. The aim of the present study was to investigate the impact of the mixture of these pesticides on the tissues and behavior of zebrafish.

METHODS

To assess the influence of this cocktail on zebrafish, three groups of animals were randomly selected and exposed to 0, 0.05, and 0.1 mg L-1 FIP and PYR mixture for five days. The fish were evaluated daily by the T-maze tests for locomotor activity and the light-dark test and recordings lasted four min. The data were quantified using the EthoVision software.

RESULTS

Our results indicated significant changes in locomotor activity parameters that showed increased levels following exposure to the mixture of FIP and PYR. On the other hand, the mixture also triggered anxiety in the zebrafish, which spent more time in the light area than in the dark area. In addition, mixture-induced histological changes were observed in the form of numerous hemosiderin deposits found in various zebrafish tissues.

CONCLUSIONS

The current findings indicate that the mixture of FIP and PYR can have considerable consequences on adult zebrafish and may promote or cause functional neurological changes in addition to histological ones.

Polyhalogenated carbazoles induce hepatic metabolic disorders in mice via alteration in gut microbiota

Polyhalogenated carbazoles (PHCZs) have been widely accepted as emerging pollutants, whereas their ecological and health risks remain uncertain. Herein, female and male Sprague-Dawley (SD) mice were treated with four typical PHCZs to investigate their negative consequences, along with alternations in gut microbiota to indicate underlying mechanisms. In female mice, the relative liver weight ratio increased after four PHCZs exposure; 2-bromocarbazole (2-BCZ) increased urine glucose level; 3-bromocarbazole (3-BCZ) decreased the glucose and total cholesterol levels; 3,6-dichlorocarbazole (3,6-DCCZ) decreased glucose level. The only disturbed biochemical index in male mice was the promoted alkaline phosphatase (ALP) level by 3,6-DCCZ. We also found that the differential blood biochemical indices were correlated with gut microbiota. 3-BCZ and 3,6-DCCZ altered Bacteroidetes and Proteobacteria phyla in female and male mice, which were correlated with metabolic disorders. Our findings demonstrated the correlation between PHCZs induced potential hepatotoxicity and metabolic disorders may be due to their dioxin-like potentials and endocrine disrupting activities, and the gender differences might result from their estrogenic activities. Overall, data presented here can help to evaluate the ecological and health risks of PHCZs and reveal the underlying mechanisms.

Enrofloxacin exposure induces anxiety-like behavioral responses in zebrafish by affecting the microbiota-gut-brain axis

The ubiquitous presence of antibiotic residues in aqueous environments poses a great potential threat to aquatic organisms. Nevertheless, the behavioral effects of environmentally realistic levels of antibiotics remain poorly understood in fish species. In this study, the behavioral impacts of enrofloxacin, one of typical fluoroquinolone antibiotics that is frequently detected in aquatic environments, were evaluated by the classic light-dark test (LDT) and novel tank task (NTT) in zebrafish. Furthermore, the effects of enrofloxacin exposure on the microbiota-gut-brain axis were also assessed to reveal potential affecting mechanisms underlying the behavioral abnormality observed. Our results demonstrated that zebrafish exposed to 60 μg/L enrofloxacin for 28 days took significantly longer to enter the stressful area of the testing tank and spent significantly less time there in both the LDT and NTT, indicating abnormal anxiety-like behaviors induced by the exposure. In addition, exposure to enrofloxacin at 6 and 60 μg/L resulted in a significant elevation in Bacteroidetes and a marked decline in the Firmicutes/Bacteroidetes ratio of the gut microbiota. Moreover, the intestinal contents of interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-α), glucagon-like peptide 1 (GLP-1), and 5-hydroxytryptamine (5-HT) in zebrafish were significantly upregulated, whereas those of plasma adrenocorticotropic hormone (ACTH) and cortisol (COR) were markedly downregulated upon enrofloxacin exposure. Incubation of zebrafish with a high dose of enrofloxacin (60 μg/L) also resulted in evident increases in the contents of corticotropin-releasing hormone (CRH), brain-derived neurotrophic factor (BDNF), and neuropeptide Y (NPY) in the brain. Fortunately, no significant alteration in the expression of glial fibrillary acidic protein (GFAP) was detected in the brain after enrofloxacin exposure. Our findings suggest that the disruption of the microbiota-gut-brain axis may account for enrofloxacin-induced anxiety-like behaviors in zebrafish. Since the disruption of microbiota-gut-brain axis may give rise to various clinical symptoms, the health risk of antibiotic exposure deserves more attention.

Enantioselectivity in the toxicological effects of chiral pesticides: A review

As a special category of pesticides, chiral pesticides have increased the difficulty in investigating pesticide toxicity. Based on their usage, chiral pesticides can be divided into insecticides, herbicides, and fungicides. Over the past decades, great efforts have been made on elucidating their toxicological effects. However, no literature has reviewed the enantioselective toxicity of chiral pesticides since 2014. In recent years, more chiral pesticides have been registered for application. As such, huge research progresses have been achieved in enantioselective toxicity of chiral pesticides. Generally, more researches have remedied the knowledge gap in toxicological effects of old and new chiral pesticides. And the toxicological endpoints being evaluated have become more specific rather than centering on basic toxicity and target organisms. Besides, the underlying mechanisms accounting for the enantioselectivity in toxicological effects of chiral pesticides have been discussed as well. All in all, this review provides the critical knowledge for risk assessments, and help to drive the green-technology of single- or enriched-enantiomer pesticides and formulation of relevant laws and regulations.

Perinatal exposure to low-level PBDE-47 programs gut microbiota, host metabolism and neurobehavior in adult rats: An integrated analysis

Polybrominated diphenyl ethers (PBDEs), a major class of flame retardants, have been extensively applied in plastics, electrical equipment, textile fabrics, and so on. Early-life exposure to PBDEs is correlated to neurobehavioral deficits in adulthood, yet the underlying mechanism has not been fully understood. Increasing evidence has demonstrated that gut microbiota dysbiosis and serum metabolites alterations play a role in behavioral abnormalities. However, whether their perturbation is implicated in PBDEs-induced neurotoxicity remains unclear. Here, we sought to explore the effects of developmental exposure to environmentally relevant levels of 2, 2', 4, 4'-tetrabromodiphenyl ether (PBDE-47), a major congener in human samples, on gut microbiota and serum metabolic profile as well as their link to neurobehavioral parameters in adult rats. The open field test showed that gestational and lactational exposure to PBDE-47 caused hyperactivity and anxiety-like behavior. Moreover, 16S rRNA sequencing of fecal samples identified a distinct community composition in gut microbiota following PBDE-47 exposure, manifested as decreased genera Ruminococcaceae and Moraxella, increased families Streptococcaceae and Deferribacteraceae as well as genera Escherichia-Shigella, Pseudomonas and Peptococcus. Additionally, the metabolomics of the blood samples based on liquid chromatography-mass spectrometry revealed a significant shift after PBDE-47 treatment. Notably, these differential serum metabolites were mainly involved in amino acid, carbohydrate, nucleotide, xenobiotics, and lipid metabolisms, which were further validated by pathway analysis. Importantly, the disturbed gut microbiota and the altered serum metabolites were associated with each other and with neurobehavioral disorders, respectively. Collectively, these results suggest that gut microbiota dysbiosis and serum metabolites alterations potentially mediated early-life low-dose PBDE-47 exposure-induced neurobehavioral impairments, which provides a novel perspective on understanding the mechanisms of PBDE-47 neurotoxicity.

Metabonomic and transcriptomic modulations of HepG2 cells induced by the CuO-catalyzed formation of disinfection byproducts from biofilm extracellular polymeric substances in copper pipes

Cupric oxide (CuO) is able to catalyze the reactions among disinfectant, extracellular polymeric substances (EPS) and bromide (Br^-) in copper pipes, which may deteriorate the water quality. This study aimed to investigate the metabonomic and transcriptomic modulations of HepG2 cells caused by the CuO-catalyzed formation of disinfection byproducts (DBPs) from EPS. The presence of CuO favored the substitution reactions of chlorine and bromine with EPS, inducing a higher content of total organic halogen (TOX). In addition, DBPs were shifted from chlorinated species to brominated species. A total of 182 differential metabolites (DMs) and 437 differentially expressed genes (DEGs) were identified, which were jointly involved in 38 KEGG pathways. Topology analysis indicates that glycerophospholipid and purine metabolism were disturbed most obviously. During glycerophospholipid metabolism, the differential expression of genes GPATs, AGPATs, LPINs and DGKs impacted the conversion of glycerol-3-phosphate to 2-diacyl-sn-glycerol, which further affected the conversion among phosphatidylcholine, phosphatidylserine and phosphocholines. During purine metabolism, it was mainly the differential expression of genes POLRs, RPAs, RPBs, RPCs, ENTPDs and CDs that impacted the transformation of RNA into guanine-, xanthosine-, inosine- and adenosine monophosphate, which were further successively transformed into their corresponding nucleosides and purines. The study provides an omics perspective to assess the potential adverse effects of overall DBPs formed in copper pipes on human.

Bioconcentration and toxicological impacts of fipronil and 2,4-D commercial formulations (single and in mixture) in the tropical fish, Danio rerio

The insecticide fipronil and the herbicide 2,4-D are the most applied pesticides in sugarcane crops leading to aquatic contamination. The whole-body bioconcentration of fipronil and 2,4-D, single and in mixture, was evaluated in Danio rerio after 96-h exposure. The activities of catalase (CAT) and glutathione S-transferase(GST) in whole body and in the gills and the acetylcholinesterase (AChE) in muscle were determined. The gill histopathology and the morphology of the pavement (PVC) and the mitochondria-rich(MRC) cells at gill surface were analyzed. Bioconcentration occurred after exposure to fipronil (2.69 L kg^-1) and 2,4-D (1.73 L kg^-1) single and in mixture of fipronil (3.10 L kg^-1) and 2,4-D (1.27 L kg^-1). Whole-body CAT activity was unchanged, and its activity decreased in the gills after exposure to fipronil and increased after exposure to 2,4-D and mixture. GST and AChE increased after single exposure to each pesticide and mixture of both. Fish exposed to mixture increased the MRC fractional area (MRCFA) which suggested possible ionic regulation disturbance and reduced the microridge of the PVC surface. Synergistic interactions occurred in the CAT activity and MRCFA after exposure to mixture of pesticides. The results indicate that the recommended application dose of fipronil and 2,4-D, single or in mixture, for sugarcane crops affects this fish species altering its homeostasis.

Excessive ammonia inhalation causes liver damage and dysfunction by altering gene networks associated with oxidative stress and immune function

Ammonia (NH₃) is a major gaseous pollutant in livestock production and has adverse effects on production, health and welfare of animals. The liver is one of the target organs of NH₃, and excessive NH₃ inhalation can induce liver damage. However, the toxicity assessment of NH₃ on pig liver and its mechanism have not been reported yet. Recently, transcriptome analysis has become a major method to study the toxic mechanism of pollutants in environmental toxicology. Therefore, in the present study, we examined the effects of excessive NH₃ inhalation on the liver of fattening pig through chemical analysis, ELISA, transcriptome analysis and real-time quantitative PCR (qRT-PCR). Our results showed that the transcriptome analysis database of fattening pig liver under excessive NH₃ exposure, and 449 differentially expressed genes (DEGs) (including 181 up-regulated DEGs and 168 down-regulated DEGs) were found. Some genes associated with the 3 Gene Ontology (GO) terms (liver function, immune, antioxidant defense) were validated by quantitative real-time PCR. In addition, the activities of GPT and GOT in NH₃ group were significantly increased by 63.5% and 37.4% (P < 0.05), respectively. Our results indicated that NH₃ exposure could cause changes in transcriptional profiles and liver function, and induce liver damage in fattening pigs through oxidative stress and immune dysfunction. Our study results not only provide a new perspective for the toxicity assessment of NH₃, but also enrich the toxicological mechanism of NH₃.

Direct analysis of metabolites in the liver tissue of zebrafish exposed to fiproles by internal extractive electrospray ionization mass spectrometry

Exploring the metabolic disturbance of fipronil and its derivatives in aquatic organisms may provide a more comprehensive understanding of the impact of fipronil on the ecological environment. In this work, internal extractive electrospray ionization mass spectrometry (iEESI-MS) was used to directly analyze metabolites in the liver tissue of zebrafish exposed to fipronil and its three derivatives. Partial least squares-discriminant analysis (PLS-DA) revealed that 32 signals were considered as differential signals in zebrafish after the exposure treatment of fipronil and its derivatives, including phosphatidylcholines (PCs), lysophosphatidylcholines (LPCs), phosphatidylethanolamines (PEs), fatty acids and so on. The pathway analysis result showed that both fipronil and its derivatives have a significant impact on the glycerophospholipid metabolism of zebrafish. Besides, the intensities of PC signals in the liver samples of each group showed such a trend: mixed fiprole exposed group > fipronil sulfone exposed group ≈ fipronil sulfide exposed group > fipronil exposed group > fipronil desulfinyl exposed group > control group, indicating that mixed exposure of fipronil and its derivatives exhibited more significant metabolic disturbance in zebrafish. Taken together, iEESI-MS is applied to environmental toxicology and investigating the metabolic disturbance induced by fipronil and its derivatives in aquatic organisms, providing a new analytical method for this field.

Effects of Dufulin on Oxidative Stress and Metabolomic Profile of Tubifex

Dufulin is a highly effective antiviral pesticide used in plants. In this study, a seven-day experiment was conducted to evaluate the effects of Dufulin at five different concentrations (1 × 10⁻⁴, 1 × 10⁻³, 1 × 10⁻², 0.1, and 1 mg/L) on Tubifex. LC-MS-based metabolome analysis detected a total of 5356 features in positive and 9110 features in negative, of which 41 showed significant changes and were identified as differential metabolites. Four metabolic pathways were selected for further study. Detailed analysis revealed that Dufulin exposure affected the urea cycle of Tubifex, probably via argininosuccinate lyase (ASL) inhibition. It also affected the fatty acid metabolism, leading to changes in the concentration of free fatty acids in Tubifex. Furthermore, the changes in metabolites after exposure to Dufulin at 1 × 10⁻² mg/L were different from those at the other concentrations.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 2: impacts on organisms and ecosystems

New information on the lethal and sublethal effects of neonicotinoids and fipronil on organisms is presented in this review, complementing the previous Worldwide Integrated Assessment (WIA) in 2015. The high toxicity of these systemic insecticides to invertebrates has been confirmed and expanded to include more species and compounds. Most of the recent research has focused on bees and the sublethal and ecological impacts these insecticides have on pollinators. Toxic effects on other invertebrate taxa also covered predatory and parasitoid natural enemies and aquatic arthropods. Little new information has been gathered on soil organisms. The impact on marine and coastal ecosystems is still largely uncharted. The chronic lethality of neonicotinoids to insects and crustaceans, and the strengthened evidence that these chemicals also impair the immune system and reproduction, highlights the dangers of this particular insecticidal class (neonicotinoids and fipronil), with the potential to greatly decrease populations of arthropods in both terrestrial and aquatic environments. Sublethal effects on fish, reptiles, frogs, birds, and mammals are also reported, showing a better understanding of the mechanisms of toxicity of these insecticides in vertebrates and their deleterious impacts on growth, reproduction, and neurobehaviour of most of the species tested. This review concludes with a summary of impacts on the ecosystem services and functioning, particularly on pollination, soil biota, and aquatic invertebrate communities, thus reinforcing the previous WIA conclusions (van der Sluijs et al. 2015).

Short-term effects of pesticide fipronil on behavioral and physiological endpoints of Daphnia magna

Fipronil (FIP) is an organic pesticide with many practical uses. Although some results indicated toxic effects in some terrestrial and aquatic animal species, little is known on its influence on behavioral and physiological endpoints of cladocerans. The aim of our study was to determine the short-term effects of FIP at concentrations of 0.1 μg/L, 1 μg/L, 10 μg/L, and 100 μg/L on Daphnia magna sublethal indices: behavioral (swimming speed, distance traveled) and physiological endpoints (heart rate, post-abdominal claw activity and thoracic limb movements). The results showed that FIP induced reduction of swimming speed and distance traveled in a concentration- and time-dependent manner at all the concentrations used. The lowest concentration of the insecticide temporarily stimulated post-abdominal claw activity after 24 h and thoracic limb activity after 48 h; however, the highest concentrations reduced all the studied physiological endpoints. IC50 values showed that thoracic limb activity, swimming speed, and distance traveled were most sensitive to FIP after 24-h exposure. The most sensitive parameter after 48 h and 72 h was swimming speed and post-abdominal claw activity, respectively. The study indicated that (i) behavioral and physiological endpoints of Daphnia magna are reliable and valuable sublethal indicators of toxic alterations induced by FIP; however, they respond with different sensitivity at various times of exposure, (ii) FIP may alter cladoceran behavior and physiological processes at concentrations detected in the aquatic environment; therefore, it should be considered as an ecotoxicological hazard to freshwater cladocerans.

Fipronil and 2,4-D effects on tropical fish: Could avoidance response be explained by changes in swimming behavior and neurotransmission impairments?

Brazil is the largest producer of sugarcane, a crop largely dependent on chemical control for its maintenance. The insecticide fipronil and herbicide 2,4-D stand out among the most commonly used pesticides and, therefore, environmental consequences are a matter of concern. The present study aimed to investigate the toxicity mechanisms of Regent® 800 WG (a.i. fipronil) and DMA® 806 BR (a.i. 2,4-D) pesticides using forced and non-forced exposures through an integrative approach: firstly, to assess whether contamination by fipronil and 2,4-D can trigger the avoidance behavior of the fish Danio rerio (zebrafish) and Hyphessobrycon eques (serpae tetra or mato-grosso). Additionally, the effects on fish were analyzed considering the swimming behavior together with a biomarker of neurotoxicity, the activity of acetylcholinesterase (AChE). In avoidance tests with pesticide gradients, D. rerio avoided the highest concentrations of the two compounds and H. eques avoided only the highest concentration of 2,4-D. The swimming behavior (distance moved) was reduced and AChE was inhibited when D. rerio was exposed to fipronil. The 2,4-D affected the swimming (maximum speed) of H. eques, but AChE was not altered. Avoidance response seemed not to have been affected by possible effects of contaminants on swimming behavior and Ache activity. This study showed the importance of knowing the avoidance capacity, swimming behavior and neurotoxic effects of pesticides on fish in an integrated and realistic context of exposure in environments contaminated with pesticides and can be useful as ecologically relevant tools for ecological risk assessment.

Ecological and toxicological assessments of anthropogenic contaminants based on environmental metabolomics

There has long been a great concern with growing anthropogenic contaminants and their ecological and toxicological effects on living organisms and the surrounding environment for decades. Metabolomics, a functional readout of cellular activity, can capture organismal responses to various contaminant-related stressors, acquiring direct signatures to illustrate the environmental behaviours of anthropogenic contaminants better. This review entails the application of metabolomics to profile metabolic responses of environmental organisms, e.g. animals (rodents, fish, crustacean and earthworms) and microorganisms (bacteria, yeast and microalgae) to different anthropogenic contaminants, including heavy metals, nanomaterials, pesticides, pharmaceutical and personal products, persistent organic pollutants, and assesses their ecotoxicological impacts with regard to literature published in the recent five years. Contaminant-induced metabolism alteration and up/down-regulation of metabolic pathways are revealed in typical organisms. The obtained insights of variations in global metabolism provide a distinct understanding of how anthropogenic contaminants exert influences on specific metabolic pathways on living organisms. Thus with a novel ecotechnique of environmental metabolomics, risk assessments of anthropogenic contaminants are profoundly demonstrated.

Vitamin C Attenuates Oxidative Stress and Behavioral Abnormalities Triggered by Fipronil and Pyriproxyfen Insecticide Chronic Exposure on Zebrafish Juvenile

Chronic exposure to synthetic insecticides in the early life of a child can lead to a series of disorders. Several causes as parental age, maternal smoking, birth complications, and exposure to toxins such as insecticides on childhood can lead to Autism spectrum disorder (ASD) occurrence. The aim of this study was to evaluate the potential protective role of vitamin C (Vit. C) from children's supplements after 14 days chronic exposure to insecticide mixture fipronil (Fip) + pyriproxyfen (Pyr) on juvenile zebrafish for swimming performances, social behavior and oxidative stress associated with ASD model. Juvenile (14-17 mm) wild-type AB zebrafish (Danio rerio) (45 days) were exposed to relevant concentrations: vit. C (25 µg L-1), Fip (600 µg L-1/1.372 μM) + Pyr (600 µg L-1/1.89 μM), and [Fip (600 µg L-1/1.372 μM) + Pyr (600 µg L-1 /1.89 μM)] + vit. C (25 µg L-1). Our results showed that insecticides can disturb the social behavior of zebrafish during 14 days of the administration, decreased the swimming performances, and elevated the oxidative stress biomarkers of SOD (superoxide dismutase), GPx (glutathione peroxidase), and MDA (malondialdehyde). The vitamin C supplement significantly attenuated the neurotoxicity of insecticide mixture and oxidative stress. This study provides possible in vivo evidence to show that vitamin C supplements could attenuate oxidative stress and brain damage of fipronil and pyriproxyfen insecticide chronic exposure on zebrafish juvenile.

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.

Carbofuran induces increased anxiety-like behaviors in female zebrafish (Danio rerio) through disturbing dopaminergic/norepinephrinergic system

Carbofuran, a carbamate pesticide, is widely used in developing countries to manage insect pests. Studies have found that carbofuran posed potential risks for the neurotransmitter systems of non-target species, we speculated that these disruptive effects on the neurotransmitter systems could trigger anxiety-like behaviors. In this study, female zebrafish were exposed to environmental levels (5, 50, and 500 μg/L) of carbofuran for 48 h to evaluate the effects of carbofuran on anxiety-like behaviors. Results showed that zebrafish exhibited more anxiety-like behaviors which proved by the observed higher bottom trend and more erratic movements in the novel tank after carbofuran treatment. In order to elucidate the underlying molecular mechanisms of carbofuran-induced anxiety-promoting effects, we measured the levels of neurotransmitters, precursors, and major metabolites, along with the level of gene expression and the enzyme activities involved in neurotransmitter synthesis and metabolism. The results demonstrated that acute carbofuran exposure stimulated the mRNA expression and enzyme activity of tyrosine hydroxylase, which sequentially induced the increased levels of dopamine and norepinephrine. Tyrosine hydroxylase inhibitor relieved the anxiety-related changes induced by carbofuran, confirming the overactive tyrosine hydroxylase-mediated accumulation of dopamine and norepinephrine in the brain was one of the main reasons for carbofuran-induced anxiety-like behaviors in the female zebrafish. Overall, our study indicated the environmental health risks of carbamate pesticide in inducing neurobehavioral disorders and provided novel insights into the investigation of the relevant underlying mechanisms.

Evaluation of toxicological responses and promising biomarkers of topmouth gudgeon (Pseudorasbora parva) exposed to fipronil at environmentally relevant levels

Fipronil is an insecticide commonly used in agriculture. We report here on the sublethal and sub-chronic effects of fipronil on non-target topmouth gudgeon (Pseudorasbora parva) at environmentally relevant levels. The results showed that fipronil did not cause significant changes in brain acetylcholinesterase activities, glutathione S-transferase (GST) activities in the intestine, and GST, glutamic pyruvic transaminase (GPT), and glutamic oxaloacetic transaminase (GOT) activities in the liver tissues at environmentally relevant levels for 96-h exposure. In the further test for a 12-day exposure, dose-dependent responses of the serum GPT and GOT activities were observed in all treated groups with sublethal concentrations of fipronil. Furthermore, fipronil could reduce the liver mitochondrial membrane fluidity of P. parva, especially with high concentration of fipronil at high temperature. The results suggest that serum GPT and GOT in P. parva might be useful biomarkers for effects of fipronil exposure at environmentally relevant level, and reducing fluidity of liver mitochondrial membrane may be one toxic mechanism of fipronil.

Four cypermethrin isomers induced stereoselective metabolism in H295R cells

Cypermethrin (CP) is widely used for controlling agricultural and indoor vermin. Previous studies have reported the stereoselective difference of CP in biological activities. However, little is known about their potential mechanisms between metabolic phenotypes and endocrine-disrupting effects. Herein, nuclear magnetic resonance (NMR)-based metabolomics combining metabolite identification and pathway analysis were applied to evaluate the stereoselective metabolic cdisorders induced by CP isomers in human adrenocortical carcinoma cells (H295R) culture medium. Then, gene expression levels related to disturbed metabolic pathways were assessed to verify according to metabolic phenotypes. Metabolomics profiles showed that [(S)-cyano(3-phenoxyphenyl)methyl](1R,3R)-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropane-1-carboxylate [(1R,3R,αS)-CP] induced the most significant changes in metabolic phenotypes than did the other stereoisomers. There are 10 differential metabolites (isoleucine, valine, leucine, ethanol, alanine, acetate, aspartate, arginine, lactate, and glucose) as well as two significantly disturbed pathways, including "pyruvate metabolism" and "alanine, aspartate, and glutamate metabolism," that were confirmed in H295R cells culture medium of (1R,3R,αS)-CP compared with other stereoisomers. Polymerase chain reaction (PCR) array also confirmed the results of metabolomics. Our results can help to understand the potential mechanisms between the isomer selectivity in metabolic phenotypes and endocrine-disrupting effects. Data provided here not only lend authenticity to the cautions issued by the scientists and researchers but also offer a solution for the balance between environment and political regulations.

Targeted toxicometabolomics of endosulfan sulfate in adult zebrafish (Danio rerio) using GC-MS/MS in multiple reaction monitoring mode

Endosulfan sulfate is a major oxidative metabolite of the chlorinated insecticide endosulfan. In this study, a targeted metabolomics approach was used to investigate the toxic mechanisms of endosulfan sulfate in adult zebrafish using the multiple reaction monitoring mode of a GC-MS/MS. The LC₅₀ of endosulfan sulfate in adult zebrafish was determined and then zebrafish were exposed to endosulfan sulfate at one-tenth the LC₅₀ (0.1LC₅₀) or the LC₅₀ for 24 and 48 h. After exposure, the fish were extracted, derivatized and analyzed by GC-MS/MS for 379 metabolites to identify 170 metabolites. Three experimental groups (control, 0.1LC₅₀ and LC₅₀) were clearly separated in PLS-DA score plots. Based on the VIP, ANOVA, and fold change results, 40 metabolites were selected as biomarkers. Metabolic pathways associated with those metabolites were identified using MetaboAnalyst 4.0 as follows: aminoacyl-tRNA biosynthesis, valine/leucine/isoleucine biosynthesis, citrate cycle, glycerolipid metabolism, and arginine/proline metabolism. Gene expression studies confirmed the activation of citrate cycle and glycerolipids metabolism. MDA levels of the exposed group significantly increased in oxidative toxicity assay tests. Such significant perturbations of important metabolites within key biochemical pathways must result in biologically hazardous effects in zebrafish.

New Insights in the Endocrine Disrupting Effects of Three Primary Metabolites of Organophosphate Flame Retardants

Despite the ubiquity of organophosphate flame retardants (OPFRs) metabolites in the biota, the endocrine disrupting potency has not been well examined. Herein, we chose three primary metabolites of OPFRs (BCIPP, BDCIPP, and DPHP) to investigate their potential endocrine disrupting effects by in vitro, in vivo, and in silico assays. Three metabolites were agonistic to rat estrogenic receptor alpha (ERα) and antagonists to human mineralocorticoid receptor (MR). BCIPP exerted endocrine disrupting effect contrasting to the negative response of its parental compound. It also poses the strongest binding capacity to ERα among the tested compounds. Both BCIPP and BDCIPP upregulated the genes encoded for estrogenic synthesis enzymes in H295R cells, including 17βHSD and CYP19. All three compounds stimulated the transcription of CYP11B1, whereas BCIPP and DPHP also triggered CYP11B2, encoding for corticoid production. BDCIPP inhibits genes for progesterone synthesis including CYP11A1, STAR, and 3-βHSD. The induction of mortality and low hatchability of zebrafish embryo were ranked as BCIPP ≥ BDCIPP > DPHP. All compounds lead to malformation of zebrafish larvae. Both of the hypothalamic-pituitary-adrenocortical and hypothalamic-pituitary-gonadal axes were disrupted, with the highest impact by BCIPP. Altogether, the data clarified OPFRs metabolites may produce comparable or even higher endocrine disrupting effects than OPFRs.

Effects of prednisolone on behavior and hypothalamic-pituitary-interrenal axis activity in zebrafish

Prednisolone is a synthetic glucocorticoid used clinically for treating allergies, inflammation, and autoimmune diseases. Long-term prednisolone use has been shown to have negative effects on physiology and mood. We aimed to study the pharmacology and toxicology of glucocorticoid-like drugs by investigating behavioral and hypothalamic-pituitary-interrenal (HPI) axis effects in a zebrafish model. Zebrafish embryos 24 h post fertilization were exposed to 25 μM prednisolone. Their behavior was investigated 5 days post fertilization (dpf), and their HPI axis-related activity and related neurotransmitter levels were investigated 3, 4, 5, and 6 dpf. The behavior results showed that exposure to prednisolone resulted in decreased autonomic activity and low sensitivity to light. qRT-PCR and ELISA results showed decreased activity of the HPI axis and increased secretion of dopamine and serotonin after exposure to prednisolone. This study provides us with new insights into understanding the effects of glucocorticoids on the HPI axis.

The comparative metabolic response of Bactrocera dorsalis larvae to azadirachtin, pyriproxyfen and tebufenozide

Azadirachtin, as the most promising and effective botanical insecticide, exhibits significant growth inhibition activity against agricultural and forestry pests. However, its biochemical effects at the metabolic level compared with those of other insect growth regulators have not been studied. Therefore, in this study, a GC-MS based untargeted metabolomics approach was applied to compare azadirachtin with pyriproxyfen (a juvenile hormone analog) and tebufenozide (a molting hormone analog) in terms of their metabolic effects on Bactrocera dorsalis larvae. The bioactivity of azadirachtin against B. dorsalis larvae was significantly different than those of pyriproxyfen and tebufenozide. A total of 693 mass features were recognized, and 112 metabolites were identified in this study. The results showed that a total of 16, 13 and 10 differentially regulated metabolites corresponding to 12, 5 and 8 pathways occur in Aza versus CK, Pyr versus CK and Teb versus CK group, respectively. Further analysis showed that 6 differentially regulated metabolites corresponding to 5 key pathways could be the primary differential metabolic response of B. dorsalis larvae to the three insect growth regulators. The pathways were myo-inositol corresponding to ascorbate and aldarate metabolism as the specific response of B. dorsalis larvae to azadirachtin; xylitol, xylulose and 3-aminopropionitrile corresponding to pentose and glucuronate interconversions, and cyanoamino acid metabolism as the common responses to azadirachtin and pyriproxyfen; and 3-hydroxypropionic acid and beta-alanine corresponding to propanoate metabolism and beta-alanine metabolism as the specific responses to tebufenozide. The results showed that the metabolic response of B. dorsalis larvae to azadirachitin is closer to that of pyriproxyfen than tebufenozide. The differentially regulated metabolites and pathways responsible for this difference are discussed.

Glyphosate- and Fipronil-Based Agrochemicals and Their Mixtures Change Zebrafish Behavior

Environmental contamination caused by the human occupancy and economic activities that generate a wide range of contaminated effluents that reach natural water resources, is a current reality. Residues of agrichemicals used in plant production were detected in different environments and in different countries. Among these agrochemicals, we studied a glyphosate-based herbicide (GBH), a fipronil-based insecticide (FBI), and their mixtures (GBH + FBI). Zebrafish exposed to 3 and 5 mg/L of GBH spend more time in the top zone and less time in the bottom zone. Fish exposed to 0.009 and 0.018 mg/L of FBI spent less time in the bottom zone, whereas zebrafish exposed to the three GBH + FBI mixtures spend more time in the top zone compared with unexposed control fish. This clear anxiolytic pattern, in an environmental context, can directly impair the ability of fish to avoid or evade predators. We concluded that both glyphosate-based herbicide and fipronil-based insecticide and their mixtures alter zebrafish behavior, which may result in significant repercussions on the maintenance of the species as well as on the food chain and the ecosystem.

Evaluation and optimization of sample pretreatment for GC/MS-based metabolomics in embryonic zebrafish

Metabolomics tactics have been applied in the research associated with embryonic zebrafish. However, the report regarding the evaluation of impacts of sample pretreatment on metabolomics results from zebrafish embryos is limited. In the present study, different data normalization approaches, extraction solvents, and extraction strategies for off-line derivatization gas chromatography coupled with mass spectrometry-based metabolomics analysis of zebrafish eleutheroembryos were evaluated and optimized. The results showed that, when 4-chlorophenylalanine normalization, sample homogenization and pure methanol combined with ultrasonic extraction were conducted, better repeatabilities, higher signals and broader coverages of detected metabolites can be achieved. The recovery and standard deviation of most standards were in the range of 82%-121% and 6.6%-12%, respectively, while the relative standard deviation of major detected metabolites ranged from 5.4% to 19%, indicating good extraction efficiencies and method precision. Under the developed method, 87 important endogenous metabolites such as citric acid and hypoxanthine were identified by universal databases or standards among 270 extracted metabolites, which consisted of sugars, amines, amino acids, nucleotides, fatty acids, and sterols. Therefore, the results could provide a proper pretreatment protocol for the analysis of wide-coverage metabolome in embryonic zebrafish. In addition, this study highlights the impact of normalization and extraction methods on the data quality of metabolomics analysis.

Metabolomic modulations of HepG2 cells exposed to bisphenol analogues

Bisphenol analogues including bisphenol A (BPA), bisphenol AF (BPAF), bisphenol F (BPF), and bisphenol S (BPS) share similar chemical structures and endocrine disrupting effects. Their effects on metabolisms, however, are so far only marginally understood. In this study, NMR-based metabonomic profiles of HepG2 cell culture media and PCR array were used to assess the metabolomics disturbances and gene expression levels of HepG2 in response to four BPs (BPA, BPAF, BPF, and BPS). The results indicated that BP analogues resulted in disturbances in 7-15 metabolites that were classified as amino acid (alanine, glutamine, glutamate), intermediates and end-products in the glycolysis (pyruvate) and the tricarboxylic acid cycle (acetate, lactate). Their rank in order according to the number of metabolites and pathways was BPF > BPA > BPAF > BPS. The common disrupted pathways (pyruvate metabolism; alanine, aspartate, and glutamate metabolism) indicated enhanced glycolysis. The following glucometabolic PCR array analysis suggested that although four BPs shared the capability of disrupting glucose metabolism, they may act through different mechanisms: BPAF has increased the pyruvate kinase (PKLR) expression level, which implied enhanced glycolysis that was agreed with NMR results. The other three BP analogues, however, decreased the expression level of glucokinase (GCK) that indicated glucose sensing impairment. Our results demonstrated the potential for using metabolomic and PCR array to understand the underlying action of mechanisms and identify the potential targets for future targeted risk assessment.

Exposure of low-dose fipronil enantioselectively induced anxiety-like behavior associated with DNA methylation changes in embryonic and larval zebrafish

Fipronil, a broad-spectrum chiral insecticide, has been documented to induce significant neurotoxicity to nontarget aquatic species; however, whether its neurotoxicity behaves enantioselectively and what molecular mechanisms correspond to the neurotoxicity remain unanswered. To date, few investigations have focused on the genomic mechanisms responsible for the enantioselective toxicity of chiral pesticides. The epigenetic modifications, especially DNA methylation, caused by the pesticides are also blind spot of the research works. Video tracking showed that R-fipronil exhibited more intense neurotoxicity, as well as the induction of more severe anxiety-like behavior, such as boosted swimming speed and dysregulated photoperiodic locomotion, to embryonic and larval zebrafish compared with S-fipronil. The MeDIP-Seq analysis, combined with Gene Ontology and KEGG, revealed that R-fipronil disrupted five signaling pathways (MAPK, Calcium signaling, Neuroactive ligand-receptor interaction, Purine metabolism, and Endocytosis) to a greater extent than S-fipronil through the hypermethylation of several important neuro-related genes, whereas no significant alterations of global DNA methylation were observed on the two enantiomers. To summarize, our data indicated that the fipronil-conducted enantioselective neurotoxicity likely applied its enantioselectivity by the dysregulation of DNA methylation. Our study also provided novel epigenetic insights into the study of enantioselective biological effects and the relevant underlying mechanisms of chiral insecticide.

Maternal exposure to fipronil results in sulfone metabolite enrichment and transgenerational toxicity in zebrafish offspring: Indication for an overlooked risk in maternal transfer?

Ecotoxicological studies show the association between pesticide pollution and transgenerational toxicity in aquatic organisms. However, a less considered risk is that many pesticides can be metabolized and transferred to offspring as new toxicants. In this study, we used zebrafish to evaluate the maternal transfer risk of fipronil (FIP), which is a great threat to aquatic organisms with toxic metabolite formation. After 28-day exposure to environmentally relevant concentrations (1.0, 5.0 and 10.0 μg/L) of FIP in adult female zebrafish (F0), the toxicants off-loading and transgenerational toxicity in offspring were studied. High burdens of FIP and its sulfone metabolite were found in both F0 and the embryos (F1), resulting in increased CYP450 activity. The residual levels of the metabolite were higher than those of the parent compound. Chiral analysis further showed a preferential accumulation of S-enantiomer of FIP in both F0 and F1. Maternal exposure to FIP increased the malformation rate and decreased the swim speed in larvae. Additionally, after exposure, the levels of thyroid hormones (THs), including triiodothyronine (T3) and thyroxine (T4), decreased in both generations, particularly in the F1. Gene transcription expression along the hypothalamic-pituitary-thyroid (HPT) axis was also significantly affected. Maternal exposure to FIP increased sulfone metabolite enrichment and cause multiple toxic effects in F1. Findings from this study highlight the key role of biologically active product formation in the maternal transfer of pollutants and associated risk assessment.

Lethal Toxicity and Sublethal Metabolic Interference Effects of Sulfoxaflor on the Earthworm ( Eisenia fetida)

Testing for effects of pesticides on nontarget organisms is an integral part of ecological risk assessment. In the present study, the acute toxicity of sulfoxaflor to earthworms was evaluated using an artificial soil toxicity test, and sublethal effects were assessed through oxidative stress and metabolomics. Sulfoxaflor is a supertoxic pollutant to earthworms that easily bioaccumulates in earthworms, and contains LC₂, LC₁₀, and LC₅₀ values of 0.08 (0.04-0.13), 0.19 (0.11-0.25), and 0.54 (0.45-0.65) mg/kg, respectively. Sublethal doses of sulfoxaflor resulted in oxidative damage to earthworms in which antioxidant enzymatic activities including SOD, CAT, and GST were significantly inhibited and MDA content accumulated. Metabolomics analysis suggested that the energy metabolism and the urea cycle in earthworms were significantly activated, while nucleotide metabolism was depressed, which could cause DNA damage. The results suggest earthworms have the potential to be a new entry point for sulfoxaflor into the wildlife food chain. Since earthworms significantly contribute to soil function and ecosystems, the high safety risks of sulfoxaflor to the earthworm could extend to the environment. In view of these findings, more attention should be given to the risks sulfoxaflor poses to the environment through its effects on earthworms.

Fipronil (Phenylpyrazole) induces hemato-biochemical, histological and genetic damage at low doses in common carp, Cyprinus carpio (Linnaeus, 1758)

This study was conducted to investigate the toxic effects of fipronil on common carp (Cyprinus carpio). The trial was performed in laboratory of Department of Life Sciences at the Islamia University of Bahawalpur, Punjab, Pakistan. Total of 72 fishes, with apparently no clinical signs were purchased from local fish hatchery near Bahawalpur, Punjab, Pakistan. After 2 weeks of acclimatization fish were divided into six groups in glass aquaria (each having 100 liters of water capacity) and treated with different concentrations of fipronil for 12 days: 0 mg/L-control group (A),0.02 mg/L (B),0.04 mg/L (C),0.06 mg/L (D),0.08 mg/L (E) and 0.10 mg/L (F). Blood samples were taken every 4 days for evaluation of hemato-biochemical parameters. Fish in high doses treated groups show severe abnormalities in clinical-hematological and biochemical parameters. At high dose in group E and F fish show clinical ailments such as convulsions, jerking, faintness, increase in operculum movement, body curvature and breathing difficulty. Erythrocyte count, hemoglobin, hematocrit were decreased significantly (P < 0.05) and mean corpuscular volume, total leukocyte count, neutrophils, monocytes, and lymphocytes were significantly increased. Biochemical parameters including urea, creatinine, cholesterol, triglyceride, glucose were significantly increased but albumin was significantly decreased. Nuclear and cellular abnormalities were also increased in high dose treated groups. Hence fipronil induces clinico-hematological and serum biochemical changes in common carp C. carpio.

Fipronil-induced toxic effects in zebrafish (Danio rerio) larvae by using digital gene expression profiling

Fipronil residue has caused widespread concern around the world, especially after the recent "toxic eggs" event in seven European countries. To evaluate the effects of fipronil on vertebrates, zebrafish larvae were used as an animal model to examine the lethal effect, developmental phenotypes at high doses, and possible mechanisms of toxicity by employing digital gene expression (DGE) profiling at environmentally relevant doses. The results of acute toxicity test indicated that treatment with fipronil from 75 h post-fertilization (hpf) led to the death of larvae with a 96-h LC50 value of 459 μg/L, as well as abnormal development including bent spine and shortened body length. Besides, we obtained high-quality-sequencing DGE profilings at fipronil concentrations of 0.5, 5, and 50 μg/L, respectively. The results revealed that 44 differentially expressed genes, 10 GO terms, and 3 KEGG pathways were overlapped among the three concentrations. MIDN, one of the 44 differentially expressed genes, showed dose-dependent responses at the transcriptional level, indicating that it was possibly a potential biomarker to reflect fipronil toxicity in zebrafish. Furthermore, we presumed that the changing transcriptional level of AP-1 family was possibly a reason for bent spine and shortened body length in larvae exposed to fipronil. Concurrently, altered abundance of transcripts of the ELOVL family in a key step of fatty acid elongation could possibly lead to the accumulation of long-chain fatty acids. Collectively, our results suggested that exposure to fipronil caused lethal and developmental toxicity in zebrafish larvae, and demonstrated the need for a comprehensive understanding of the potential mechanisms of fipronil toxicity due to fipronil's frequent presence in the environment and its potential threat to human health.

Adverse effects of the insecticides chlordecone and fipronil on population growth and expression of the entire cytochrome P450 (CYP) genes in the freshwater rotifer Brachionus calyciflorus and the marine rotifer Brachionus plicatilis

Chlordecone and fipronil are used as an insecticide and have been widely detected in the aquatic environments. However, their toxicity is still poorly investigated in aquatic invertebrates. In this study, we examined effects of chlordecone and fipronil on population growth and transcriptional regulation of the entire cytochrome P450 (CYP) genes in the freshwater rotifer Brachionus calyciflorus and the marine rotifer B. plicatilis. In B. calyciflorus, a 24 h-no observed effect concentration (NOEC-24 h) and a 24 h-median lethal concentration (LC50-24 h) of chlordecone were determined as 100 μg/L and 193.8 μg/L, respectively, while NOEC-24 h and LC50-24 h of fipronil were determined as 1000 μg/L and 2033.0 μg/L, respectively. In B. plicatilis, NOEC-24 h and LC50-24 h of chlordecone were 100 μg/L and 291.0 μg/L, respectively, while NOEC-24 h and LC50-24 h of fipronil were determined as 1000 μg/L and 5735.0 μg/L, respectively. Moreover, retardation in the population growth were observed in response to chlordecone and fipronil in both rotifer species, suggesting that chlordecone and fipronil have a potential adverse effects on life cycle parameters of two rotifer species. Additionally, modulation in the expressions of the entire CYP genes were demonstrated in response to chlordecone and fipronil at 24 h period. These results provide the better understanding on how chlordecone and fipronil can affect in population growth of two rotifers and CYP gene expressions in chlordecone- and fipronil-exposed rotifers.

Metabolomic analysis of short-term sulfamethazine exposure on marine medaka (Oryzias melastigma) by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

Toxicological effects of sulfamethazine (SM₂) have garnered increasing concern due to its wide applications in aquaculture and persistence in the aquatic environment. Most studies have main focused on freshwater fish (i.e. zebrafish), while information regarding effects of SM₂ on marine species is still scarce. Here, the hepatotoxicities in marine medaka (Oryzias melastigma) with an increasing SM2 concentration exposures (0.01 mg/L, 0.1 mg/L and 1 mg/L) were assessed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOF/MS) based metabolomics. Significant metabolites belonging to different metabolites classes were identified by multivariate statistical analysis. The increases levels of amino acids including alanine, asparagine, ornithine, proline, threonine, glutamic acid, lysine, tyrosine and phenylalanine were found in at least two exposure levels. Pathway analysis revealed that amino acids played important biological roles during SM₂ exposure: up-regulation of high energy-related amino acids for energy alteration; immune function disorder, oxidative stress and corresponding toxicities defenses. The down regulations of sugar and fatty acid metabolism were observed with an increasing level of SM2 exposure, suggesting that extra energy for cellular defense and detoxification was demanded in terms of different stress request. This study provided an innovative perspective to explore possible SM2 induced hepatic damages at three exposure levels on a nontarget aquatic specie.

Enantioselective Effects of Metalaxyl Enantiomers in Adolescent Rat Metabolic Profiles Using NMR-Based Metabolomics

More than 30% of the registered pesticides are chiral with one or more chiral centers and exist as two or more enantiomers. The frequency of chiral chemicals and their environmental safety has been considered in their risk assessment in recent decades. Despite the fact that metabolic disturbance is an important sensitive molecular initiating event of toxicology effects, the potential mechanisms of how chiral compounds affect metabolism phenotypes in organisms remain unclear. As a typical chiral pesticide, metalaxyl is an acylalanine fungicide with systemic function. Although the fungicidal activity almost comes from the R-enantiomer, the toxicity of both enantiomers in animals and human beings is not yet clear. In this study, a nuclear magnetic resonance (NMR)-based metabolomics approach was adopted to evaluate the enantioselectivity in metabolic perturbations in adolescent rats. On the basis of multivariate statistical results, stable and evident metabolic profiles of the enantiomers were obtained. When rats were exposed to R-metalaxyl, the significantly perturbed metabolic pathways were biosynthesis of valine, leucine, and isoleucine, synthesis and degradation of ketone bodies, and metabolism of glycerolipid. In contrast, more significantly perturbed metabolic pathways were obtained when the rats were exposed to S-metalaxyl, including glycolysis, biosynthesis of valine, leucine, and isoleucine, metabolism of glycine, serine, and threonine, synthesis and degradation of ketone bodies, metabolism of glycerophospholipid and glycerolipid. These abnormal metabolic pathways were closely related to liver metabolism. These results offer more detailed information about the enantioselective metabolic effects of metalaxyl in adolescent development and provide data for the health risk assessment of metalaxyl at molecular level.

Assessing biological effects of fluoxetine in developing zebrafish embryos using gas chromatography-mass spectrometry based metabolomics

Continuous low-dose exposure of pharmaceutically active compounds (PhACs) in aquatic ecosystems is a concern worldwide. In this study, we utilized a gas chromatography mass spectrometry (GC-MS) based metabolomics approach to assess endogenous metabolite changes in developing zebrafish embryos exposed to different concentrations of the widely used antidepressant, fluoxetine. Embryos were exposed from 2 h post fertilization (hpf) until 96 hpf. Using the Fiehn GC-MS library, a total of 31 metabolites were positively identified in embryos. Statistical analyses revealed significant dysregulation of 11 metabolites in fluoxetine exposed embryos. Metabolite classes that were significantly altered included, amino acids, monosaccharides, glycerophosphates, fatty acids, carboxylic acid derivatives and sugars. Concentrations of amino acids, maltose, d-malic acid, 3-phosphoglycerate and d-glucose were significantly reduced in exposed embryos. Conversely, concentrations of citric acid were in some cases significantly elevated in exposed embryos. Metabolic pathway analysis revealed perturbation of five main pathways, including (i) alanine, aspartate and glutamate metabolism, (ii) phenylalanine, tyrosine and tryptophan biosynthesis, (iii) phenylalanine metabolism. (iv) tyrosine metabolism and (v) starch and sucrose metabolism. The results indicate fluoxetine exposure causes perturbation of energy and amino acid metabolism, which may adversely impact embryogenesis due to depletion of energy reserves during this period. Also, the observed alterations in aspartic acid, phenylalanine and tyrosine in fluoxetine exposed embryos suggests potential disruption of normal neurobehavioral and liver function. The results further demonstrate that GC-MS based metabolomics is an effective approach for assessing toxicodynamics and threshold effect levels of environmental pollutants in aquatic organisms.

Environmentally relevant levels of λ-cyhalothrin, fenvalerate, and permethrin cause developmental toxicity and disrupt endocrine system in zebrafish (Danio rerio) embryo

Synthetic pyrethroids (SPs) are one of the most widely used pesticides and frequently detected in the aquatic environment. Previous studies have shown that SPs posed high aquatic toxicity, but information on the developmental toxicity and endocrine disruption on zebrafish (Danio rerio) at environmentally relevant concentrations is limited. In this study, zebrafish embryos were employed to examine the adverse effects of λ-cyhalothrin (LCT), fenvalerate (FEN), and permethrin (PM) at 2.5, 10, 25, 125, 500 nM for 96 h. The results showed these 3 SPs caused dose-dependent mortality, malformation rate, and hatching rate. Thyroid hormone triiodothyronine (T₃) levels were significantly decreased after exposure to LCT and FEN. Quantitative real-time PCR analysis was then performed on a series of nuclear receptors (NRs) genes involved in the hypothalamic-pituitary-gonadal (HPG), hypothalamic-pituitary-thyroid (HPT), hypothalamic-pituitary-adrenocortical (HPA) axes, and oxidative-stress-related system. Our results showed that LCT, FEN, and PM downregulated AR expression while upregulated ER1 expression, and caused alteration to ER2a and ER2b expression. As for the expression of TRα and TRβ, they were both decreased following exposure to the 3 SPs. LCT and PM downregulated the MR expression and FEN induced MR expression. In addition, the expression of GR was increased after treating with LCT, while it was suppressed after exposure to FEN and PM. The 3 SPs also caused various alterations to the expression of genes including AhRs, PPARα, and PXR. These findings suggest that these 3 SPs may cause developmental toxicity to zebrafish larvae by disrupting endocrine signaling at environmentally relevant concentrations.

Diuron and diazinon alter the behavior of zebrafish embryos and larvae in the absence of acute toxicity

The use of zebrafish for aquatic vertebrate (eco)toxicity testing allows the assessment of effects on a wide range of biological levels - from enzymes to sensory organs and behavioral endpoints. The present study investigated the effects of the insecticide diazinon and the herbicide diuron regarding the acute toxicity and behavior of zebrafish embryos and larvae. After conducting the fish embryo toxicity test, three concentrations (1, 2 and 3.5 mg L^-1 for diazinon and 1, 2 and 3.8 mg L^-1 for diuron) were evaluated for effects on embryonic spontaneous movement and heartbeat, larval light-dark transition response, and thigmotaxis. Although the modes-of-action are different, both pesticides proved to be moderately toxic to early life stages of zebrafish with 96 h LC₅₀ of approximately 6.5 mg L^-1 and similar EC₅₀ values of approximately 4 mg L^-1. Changes in behavioral endpoints were detected 24 h of exposure, suggesting that behavioral measurements can serve as sensitive and early indicators of pesticide exposure. Changes in behavior, such as decrease in spontaneous coiling movements of embryos and reduction of thigmotaxis in larvae, were pronounced for diuron, indicating the usefulness of the application of behavioral endpoints to assess the effects of other herbicides. In the case of diazinon, the effects were less prominent, but the detected changes in ratios between activity in light and darkness also point to the possibility of using behavioral changes for evaluation of insecticide effects. The obtained results support the usage of behavioral endpoints in zebrafish embryos and larvae for the detection of early effects of pesticides.

Fipronil-induced enantioselective developmental toxicity to zebrafish embryo-larvae involves changes in DNA methylation

Enantioselectivity in the aquatic toxicity of chiral pesticides has been widely investigated, while the molecular mechanisms remain unclear. Thus far, few studies has focused on genomic expression related to selective toxicity in chiral pesticide, nor on epigenetic changes, such as DNA methylation. Here, we used fipronil, a broad-spectrum insecticide, as a model chemical to probe its enantioselective toxicity in embryo development. Our results showed that S-(+)-fipronil caused severer developmental toxicity in embryos. The MeDIP-Seq analysis demonstrated that S-(+)-fipronil dysregulated a higher level of genomic DNA methylation than R-(−)-fipronil. Gene Ontology analysis revealed that S-(+)-fipronil caused more differentially methylated genes that are involved in developmental processes. Compared with R-(−)-fipronil, S-(+)-fipronil significantly disrupted 7 signaling pathways (i.e., mitogen-activated protein kinases, tight junctions, focal adhesion, transforming growth factor-β, vascular smooth muscle contraction, and the hedgehog and Wnt signaling pathways) by hyper-methylation of developmentally related genes, which further induced the downregulation of those genes. Together, these data suggest that differences in DNA methylation may partly explain the enantioselectivity of fipronil to zebrafish embryos. The application of epigenetics to investigate the enantioselective toxicity mechanism of chiral chemicals would provide a further understanding of their stereoselectivity biological effects.

Untargeted metabolomics approach for unraveling robust biomarkers of nutritional status in fasted gilthead sea bream (Sparus aurata)

A metabolomic study has been performed to identify sensitive and robust biomarkers of malnutrition in farmed fish, using gilthead sea bream (Sparus aurata) as a model. The metabolomic fingerprinting of serum from fasted fish was assessed by means of ultra-high performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. More than 15,000 different m/z ions were detected and Partial Least Squares–Discriminant analysis allowed a clear differentiation between the two experimental groups (fed and 10-day fasted fish) with more than 90% of total variance explained by the two first components. The most significant metabolites (up to 45) were elucidated on the basis of their tandem mass spectra with a broad representation of amino acids, oligopeptides, urea cycle metabolites, L-carnitine-related metabolites, glutathione-related metabolites, fatty acids, lysophosphatidic acids, phosphatidylcholines as well as biotin- and noradrenaline-related metabolites. This untargeted approach highlighted important adaptive responses in energy and oxidative metabolism, contributing to identify robust and nutritionally-regulated biomarkers of health and metabolic condition that will serve to assess the welfare status of farmed fish.

Perturbation of metabonome of embryo/larvae zebrafish after exposure to fipronil

The escalating demand for fipronil by the increasing insects' resistance to synthetic pyrethroids placed a burden on aquatic vertebrates. Although awareness regarding the toxicity of fipronil to fish is arising, the integral alteration caused by fipronil remains unexplored. Here, we investigated on the development toxicity of fipronil and the metabolic physiology perturbation at 120h post fertilization through GC-MS metabolomics on zebrafish embryo. We observed that fipronil dose-dependently induced malformations including uninflated swim bladder and bent spine. Further, the "omic" technique hit 26 differential metabolites after exposure to fipronil and five significant signaling pathways. We speculated that changes in primary bile acid synthesis pathway and the content of saturated fatty acid in the chemical-related group indicated the liver toxicity. Pathway of Aminoacyl-tRNA biosynthesis changed by fipronil may relate to the macromolecular synthesis. Concurrently, methane metabolism pathway was also identified while the role in zebrafish needs further determination. Overall, this study revealed several new signaling pathways in fipronil-treated zebrafish embryo/larval.