Tebuconazole alters morphological, behavioral and neurochemical parameters in larvae and adult zebrafish (Danio rerio)

Behavioral changes occur earlier than redox alterations in developing zebrafish exposed to Mancozeb

As agriculture expands to provide food and wellbeing to the world's growing population, there is a simultaneous increasing concern about the use of agrochemicals, which can harm non-target organisms, mainly in the aquatic environment. The fungicide Mancozeb (MZ) has been used on a large-scale and is a potent inducer of oxidative stress. Therefore, there is an urgent need for the development of more sensitive biomarkers designed to earlier biomonitoring of this compound. Here we tested the hypothesis that behavioral changes induced by sublethal MZ concentrations would occur first as compared to biochemical oxidative stress markers. Embryos at 4 h post-fertilization (hpf) were exposed to Mancozeb at 5, 10 and 20 μg/L. Controls were kept in embryo water only. Behavioral and biochemical parameters were evaluated at 24, 28, 72, and 168 hpf after MZ exposure. The results showed that MZ significantly altered spontaneous movement, escape responses, swimming capacity, and exploratory behavior at all exposure times. However, changes in ROS steady-stead levels and the activity of antioxidant enzymes were observable only at 72 and 168 hpf. In conclusion, behavioral changes occurred earlier than biochemical alterations in zebrafish embryos exposed to MZ, highlighting the potential of behavioral biomarkers as sensitive tools for biomonitoring programs.

Effects of pyriproxyfen on zebrafish brain mitochondria and acetylcholinesterase

Pyriproxyfen is an insecticide used worldwide that acts as a biomimetic of juvenile hormone. This study investigated metabolic and synaptic impairments triggered by pyriproxyfen using zebrafish acetylcholinesterase (zbAChE) and mitochondria as markers. A brain zbAChE assay was performed in vitro and in vivo covering a range of pyriproxyfen concentrations (0.001-10 μmol/L) to assess inhibition kinetics. Docking simulations were performed to characterize inhibitory interactions. Zebrafish male adults were acutely exposed to 0.001, 0.01 and 0.1 μg/mL pyriproxyfen for 16 h. Mitochondrial respiration of brain tissues was assessed. ROS generation was estimated using H₂DCF-DA and MitoSOX. Calcium transport was monitored by Calcium Green™ 5 N. NO synthesis activity was estimated using DAF-FM-DA. Brain acetylcholinesterase showed an in vivo IC₂₀ of 0.30 μmol/L pyriproxyfen, and an IC₅₀ of 92.5 μmol/L. The inhibitory effect on zbAChE activity was competitive-like. Respiratory control of Complex I/II decreased significantly after insecticide exposure. The MitoSOX test showed that O₂^- generation had a pyriproxyfen dose-dependent effect. Brain tissue lost 50% of Ca²⁺ uptake capacity at 0.1 μg/mL pyriproxyfen. Ca²⁺ release showed a clear mitochondrial impairment at lower pyriproxyfen exposures. Thus, Ca²⁺ transport imbalance caused by pyriproxyfen may be a novel deleterious mechanism of action. Overall, the results showed that pyriproxyfen can compromise multiple and interconnected pathways: (1) zbAChE impairment and (2) the functioning of the electron transport chain, ROS generation and calcium homeostasis in zebrafish brain mitochondria. Considering the many similarities between zebrafish and human, more caution is needed when pyriproxyfen is used in both urban and agricultural pest control.

Butyrate alleviates PTZ-induced mitochondrial dysfunction, oxidative stress and neuron apoptosis in mice via Keap1/Nrf2/HO-1 pathway

This study aims to evaluate the neuroprotective effect of sodium butyrate against the pentylenetetrazol (PTZ)-induced kindling epilepsy. Sodium butyrate (SB) (5, 10 and 20 mg/kg) and sodium valproate for 40 days and PTZ (37 mg/kg) injection every day were conducted for Kunming mice, to investigate seizure intensity and latency, oxidative stress parameters, mitochondrial structure and function, histopathology, and Keap1/Nrf2/HO-1 expressions. It is shown that seizure latency was effectively increased and the intensity of seizures decreased by treatment with sodium butyrate. It was also found to reverse the structural disruption of the mitochondria, reduce the ROS level and improve the levels of NAD + and ATP in the brains of epileptic mice. Furthermore, pretreatment with SB led to an increase in antioxidant enzyme activity (CAT, SOD and GSH-PX) in the brain as well as conferred a neuroprotective effect against neuron loss and apoptosis. The activation of Keap1/Nrf2/HO-1 signals was also identified, in which the antiepileptic effect of SB may be partially due to its anti-mitochondrial injury and neuroprotective activities. Accordingly, the results of a series of functional tests indicate a significant improvement of neurological function following SB treatment. In a mouse model of seizures, brain injury and neurological deficits can be attenuated by treatment with butyrate through the activation of Nrf2 pathway and the improvement of mitochondrial function.

Tissues injury and pathological changes in Hyla intermedia juveniles after chronic larval exposure to tebuconazole

Tebuconazole (TBZ), an azole pesticide, is one of the most frequently detected fungicides in surface water. Despite its harmful effects, mainly related to endocrine disturbance, the consequences of TBZ exposure in amphibians remain poorly understood. Here, we investigated the adverse and delayed effects of TBZ chronic exposure on a native anuran species, often inhabiting cultivated areas, the Italian tree frog (Hyla intermedia). To disclose the multiple mechanisms of action through which TBZ exerts its toxicity we exposed tadpoles over the whole larval period to two sublethal TBZ concentrations (5 and 50 μg/L), and we evaluated histological alterations in three target organs highly susceptible to xenobiotics: liver, kidney, and gonads. We also assessed morphometric and gravimetric parameters: snout-vent length (SVL), body mass (BM), liver somatic index (LSI), and gonad-mesonephros complex index (GMCI) and determined sex ratio, gonadal development, and differentiation. Our results show that TBZ induces irreversible effects on multiple target organs in H. intermedia, exerting its harmful effects through several pathological pathways, including a massive inflammatory response. Moreover, TBZ markedly affects sexual differentiation also by inducing the appearance of sexually undetermined individuals and a general delay of germ cell maturation. Given the paucity of data on the effects of TBZ in amphibians, our results will contribute to a better understanding of the environmental risk posed by this fungicide to the most endangered group of vertebrates.

Stereoselective uptake and metabolism of prothioconazole caused oxidative stress in zebrafish (Danio rerio)

Prothioconazole (PTA) is a novel, broad-spectrum, chiral triazole fungicide that is mainly used to prevent and control the disease of cereal crops. However, the adverse effects of PTA and its major metabolite on nontarget organisms have aroused wide concern. In the present work, the acute toxic of the metabolite prothioconazole-desthio (PTA-desthio), with an LC₅₀ of 1.31 mg L^-1, was 3.5-fold more toxic than the parent compound, indicating that the metabolism of PTA in zebrafish was toxic. The stereoselective uptake and metabolism of PTA and PTA-desthio in zebrafish was firstly investigated using LC-MS/MS. Remarkable enantioselectivity was observed: S-PTA and S-PTA-desthio were preferentially uptake with the uptake rate constants of 8.22 and 8.15 d^-1 at exposure concentration of 0.5 mg L^-1, respectively, and the R-PTA-desthio were preferentially metabolized. PTA-desthio was rapidly formed during the uptake processes. The antioxidant enzyme activities in the zebrafish changed significantly, and these effects were reversible. A metabolic pathway including 13 phase I metabolites and 2 phase II metabolites was firstly proposed. A glucuronic acid conjugate and sulfate conjugate were observed in zebrafish. The results of this work provide information that highlights and can help mitigate the potential toxicity of PTA to the ecological environment and humans health.

Folic acid reduces the ethanol-induced morphological and behavioral defects in embryonic and larval zebrafish (Danio rerio) as a model for fetal alcohol spectrum disorder (FASD)

The objective of this work was to determine whether folic acid (FA) reduces the embryonic ethanol (EtOH) exposure induced behavioral and morphological defects in our zebrafish fetal alcohol spectrum disorder (FASD) model. Teratogenic effects, mortality, the excitatory light-dark locomotion (ELD), sleep (SL), thigmotaxis (TH), touch sensitivity (TS), and optomotor response (OMR) tests were evaluated in larvae (6-7 days post-fertilization) using four treatment conditions: Untreated, FA, EtOH and EtOH + FA. FA reduced morphological defects on heart, eyes and swim bladder inflation seen in EtOH exposed fish. The larvae were more active in the dark than in light conditions, and EtOH reduced the swimming activity in the ELD test. EtOH affected the sleep pattern, inducing several arousal periods and increasing inactivity in zebrafish. FA reduces these toxic effects and produced more consistent inactivity during the night, reducing the arousal periods. FA also prevented the EtOH-induced defects in thigmotaxis and optomotor response of the larvae. We conclude that in this FASD model, EtOH exposure produced several teratogenic and behavioral defects, FA reduced, but did not totally prevent, these defects. Understanding of EtOH-induced behavioral defects could help to identify new therapeutic or prevention strategies for FASD.

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.

Pyriproxyfen Exposure Impairs Cognitive Parameters and Alters Cortisol Levels in Zebrafish

Pyriproxyfen is one of the most used larvicides and insecticides; it acts as an analog of juvenile insect hormone (a growth regulator). It is highly toxic during all stages of mosquito development, suppresses metamorphosis, and interferes in insect reproduction and proliferation. Pyriproxyfen and its main metabolite have been shown to affect brain development in rodents. This compound is employed mainly to eliminate outbreaks of the genus Aedes, even in potable water. Despite the increasing number of toxicological studies about larvicides and insecticides-with an indication of continuous use-there have been few studies about the effects of pyriproxyfen in non-target species such as fish. This study evaluated the effects of pyriproxyfen on behavioral, cognitive, and endocrine parameters in zebrafish. We exposed adult zebrafish to different pyriproxyfen (Pestanal®) concentrations (0.125, 0.675, and 1.75 mg/l) for 96 h. We analyzed behavioral parameters, memory, cortisol levels, and gene expression of glucocorticoid receptor (gr) and corticotrophin-releasing factor (crf) after pyriproxyfen exposure. This exposure did not alter locomotion (distance or mean speed), anxiety-like behavior (latency to enter to the top zone of the tank or time in the top zone of the tank), and social or aggressive behavior. However, there was impaired inhibitory avoidance memory at all tested pyriproxyfen concentrations. Cortisol levels were reduced in exposed groups when compared to control or vehicle. However, gr and crf gene expression in pyriproxyfen-treated animals were unaltered when compared to control or vehicle groups. Taken together, these findings indicate that pyriproxyfen may induce cognitive impairment and altered cortisol levels in zebrafish, a non-target species.

Withdrawal Effects Following Methionine Exposure in Adult Zebrafish

Methionine (Met) has important functions for homeostasis of various species, including zebrafish. However, the increased levels of this amino acid in plasma, a condition known as hypermethioninemia, can lead to cell alterations. Met is crucial for the methylation process and its excesses interfere with the cell cycle, an effect that persists even after the removal of this amino acid. Some conditions may lead to a transient increase of this amino acid with unexplored persistent effects of Met exposure. In the present study, we investigated the behavioral and neurochemical effects after the withdrawal of Met exposure. Zebrafish were divided into two groups: control and Met-treated group (3 mM) for 7 days and after maintained for 8 days in tanks containing only water. In the eighth day post-exposure, we evaluated locomotion, anxiety, aggression, social interaction, and memory, as well as oxidative stress parameters, amino acid, and neurotransmitter levels in the zebrafish brain. Our results showed that 8 days after Met exposure, the treated group showed decreased locomotion and aggressive responses, as well as impaired aversive memory. The Met withdrawal did not change thiobarbituric acid reactive substances, reactive oxygen species, and nitrite levels; however, we observed a decrease in antioxidant enzymes superoxide dismutase, catalase, and total thiols. Epinephrine and cysteine levels were decreased after the Met withdrawal whereas carnitine and creatine levels were elevated. Our findings indicate that a transient increase in Met causes persistent neurotoxicity, observed by behavioral and cognitive changes after Met withdrawal and that the mechanisms underlying these effects are related to changes in antioxidant system, amino acid, and neurotransmitter levels.

Understanding the neurobiological effects of drug abuse: Lessons from zebrafish models

Drug abuse and brain disorders related to drug comsumption are public health problems with harmful individual and social consequences. The identification of therapeutic targets and precise pharmacological treatments to these neuropsychiatric conditions associated with drug abuse are urgently needed. Understanding the link between neurobiological mechanisms and behavior is a key aspect of elucidating drug abuse-related targets. Due to various molecular, biochemical, pharmacological, and physiological features, the zebrafish (Danio rerio) has been considered a suitable vertebrate for modeling complex processes involved in drug abuse responses. In this review, we discuss how the zebrafish has been successfully used for modeling neurobehavioral phenotypes related to drug abuse and review the effects of opioids, cannabinoids, alcohol, nicotine, and psychedelic drugs on the central nervous system (CNS). Moreover, we summarize recent advances in zebrafish-based studies and outline potential advantages and limitations of the existing zebrafish models to explore the neurochemical bases of drug abuse and addiction. Finally, we discuss how the use of zebrafish models may present fruitful approaches to provide valuable clinically translatable data.

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

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

Interaction of tebuconazole with bovine serum albumin: determination of the binding mechanism and binding site by spectroscopic methods

This study investigates the interaction between tebuconazole and bovine serum albumin (BSA) in a physiological buffer (pH = 7.4) using the fluorescence quenching method to obtain the apparent binding constants (K) and number of binding sites (n) in the interaction between tebuconazole and BSA. The results revealed that tebuconazole can quench the intrinsic fluorescence of BSA through a static quenching procedure. It also shows that the thermodynamic parameters of enthalpy change (ΔH) and entropy change (ΔS) are negative, indicating that the interaction of tebuconazole with BSA is mainly driven by van der Waals forces and hydrogen bonds. The process of binding was a spontaneous process in which Gibbs free energy change was negative. The distance of r between the donor (BSA) and acceptor (tebuconazole) was calculated to be 0.68 nm based on Forster's non-radiative energy transfer theory. Analysis of synchronous fluorescence, three-dimensional fluorescence and circular dichroism (CD) spectra demonstrates that tebuconazole can induce conformational changes of BSA.

Investigation into the sub-lethal effects of the triazole fungicide triticonazole in zebrafish (Danio rerio) embryos/larvae

Global use of azole fungicides is expected to increase over the next several years. Triticonazole is a triazole fungicide that is used for turf protection, residential, and other commercial applications. As such, it can enter local rural and urban water systems via run-off and rain events. Early life stages of aquatic organisms can be susceptible to pesticides that enter the water, but in the case of triticonazole, data on the potential for subacute toxicity are lacking. Here, we determined the effects of triticonazole on development, oxygen consumption rates, and locomotor activity in zebrafish to address this knowledge gap. Wild-type zebrafish (ABTu strain) embryos and larvae were exposed to triticonazole (1-100 μM) in early development for different lengths of time depending on the assay conducted. Triticonazole did not affect survival nor induce significant deformity (pericardial edema, skeletal defects) in zebrafish at doses up to 100 μM. Oxygen consumption rate was measured in embryos after 24 and 48 hour exposure to triticonazole beginning at ∼6 hpf using the XF_e flux analyzer. Triticonazole did not affect basal respiration, oligomycin-induced ATP linked respiration, FCCP-induced maximum respiration, proton leak, spare capacity, nor non-mitochondrial respiration at doses up to 100 μM for 24 hours, even for exposure up to 250 μM for 48 hours. To determine whether the fungicide affected larval swimming activity, the visual motor response test was conducted following triticonazole exposure for 6 days. Larval zebrafish exposed to triticonazole showed hypoactivity in the dark following a 100 μM treatment, suggesting that the fungicide can affect the locomotor activity of zebrafish, albeit at relatively high levels. Given the fact that sublethal biological responses were absent at lower environmentally relevant concentrations, we conclude that triticonazole, relative to other triazole fungicides and types of pesticides, exhibits a relatively low risk of toxicity to the early life stages of fish.

Tebuconazole induced oxidative stress related hepatotoxicity in adult and larval zebrafish (Danio rerio)

Tebuconazole is widely used as fungicide and has frequently been detected at elevated concentrations in environmental media. To characterize the potential toxicity of tebuconazole on vertebrate and humans. Using zebrafish as a vertebrate model, the toxic effects in liver that produced by low-toxic concentrations of tebuconazole were assessed in adult zebrafish. We further focused on tebuconazole-induced toxicity and its possible mechanism in larval zebrafish using a hepatotoxicity assay. The induction of oxidative stress in adult fish was evaluated by superoxide dismutase (T-SOD), catalase (CAT), peroxidase (POD), glutathione S-transferase (GST) activity, and the increased aspartate aminotransferase (AST)/alanine aminotransferase (ALT) ratio. Significantly increased enzyme activity was observed in the liver of male and female fish at both exposure and depuration stage. Exposure to maximum non-lethal (MNLC) concentration of tebuconazole from 72 to 120 h post-fertilization (hpf) affected the liver size and yolk retention in larval zebrafish. Decreased fluorescence intensity was observed in larval Tg(Apo14:GFP) zebrafish, indicating liver degeneration after tebuconazole treated. Histopathological examination confirmed the alterations in liver histoarchitecture in exposed zebrafish. Significant 1.28-fold and 1.65-fold increases in reactive oxygen species levels were observed in juveniles exposed to MNLC and lethal concentration 10 (LC₁₀) group, respectively. The acridine orange staining assay showed that apoptotic cells occurred in the liver regions. These results indicated that tebuconazole exposure resulted in impacts on the ecological risk in fish and vertebrate. Overall, the present study suggested further research in needed to better understand the tebuconazole-induced toxicity mechanism that associated with oxidative stress.

Exploring the mechanisms of graphene oxide behavioral and morphological changes in zebrafish

The presence of natural organic matter such as humic acid (HA) can influence the behavior of graphene oxide (GO) in the aquatic environment. In this study, zebrafish embryos were analyzed after 5 and 7 days of exposure to GO (100 mg L^-1) and HA (20 mg L^-1) alone or together. The results indicated that, regardless of the presence of HA, larvae exposed to GO for 5 days showed an increase in locomotor activity, reduction in the yolk sac size, and total length and inhibition of AChE activity, but there was no difference in enzyme expression. The statistical analysis indicated that the reductions in total larval length, yolk sac size, and AChE activity in larvae exposed to GO persisted in relation to the control group, but there was a recovery of these parameters in groups also exposed to HA. Larvae exposed to GO for 7 days did not show significant differences in locomotor activity, but the RT-PCR gene expression analysis evidenced an increase in the AChE expression. Since the embryos exposed to GO showed a reduction in overall length, they were submitted to confocal microscopy and their muscle tissue configuration investigated. No changes were observed in the muscle tissue. The results indicated that HA is associated with the toxicity risk modulation by GO and that some compensatory homeostasis mechanisms may be involved in the developmental effects observed in zebrafish.

Characterization of the adenosinergic system in a zebrafish embryo radiotherapy model

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

Propiconazole induces abnormal behavior and oxidative stress in zebrafish

The use of pesticides has been growing along with the demand for agricultural products. These compounds, however, are not restricted to the field, spreading easily through the soil, contaminating groundwater and reaching urban centers. Propiconazole is a triazole fungicide that has been increasingly used in agriculture. However, there are few data about its effects on non-target organisms. This study aimed to evaluate the effects of propiconazole in zebrafish. The animals were exposed for 96 h to different concentrations of propiconazole (425, 850, 1700, 8500 ng/L), then submitted to the novel tank test for behavioral analyses. The brains were collected for evaluation of oxidative stress parameters. Exposure to propiconazole (1700 and 8500 ng/L) decreased the number of crossings, entries, and time spent in the top, and increased the time spent in the bottom area of the tank. We also observed an increase in the activities of superoxide dismutase and catalase in zebrafish brain exposed to propiconazole at 425, 850, and 1700 ng/L. We conclude that propiconazole alters normal fish behavior and disrupts oxidative status. More studies are necessary to elucidate the exact mechanism underlying the effects of propiconazole on non-target-organisms.

Mitochondrial dysfunction-based cardiotoxicity and neurotoxicity induced by pyraclostrobin in zebrafish larvae

Pyraclostrobin is widely used to control crop diseases, and was reported to be highly toxic to aquatic organisms. The molecular target of pyraclostrobin to fungus is the mitochondrion, but its effect on mitochondria of aquatic organisms has rarely been investigated. In this study, zebrafish larvae at 4 days post fertilization (dpf) were exposed to a range of pyraclostrobin for 96 h to assess its acute toxicity and effects on mitochondria. Pyraclostrobin at 36 μg/L or higher concentrations caused significant influences on larval heart and brain including pericardial edema, brain damage malformations, histological and mitochondrial structural damage of the two organs. The results of RNA-Seq revealed that the transcripts of genes related to oxidative phosphorylation, cardiac muscle contraction, mitochondrion, nervous system development and glutamate receptor activity were significantly influenced by 36 μg/L pyraclostrobin. Further tests showed that pyraclostrobin at 18 and 36 μg/L reduced the concentrations of proteins related to cardiac muscle contraction, impaired cardiac function, inhibited glutamate receptors activities and suppressed locomotor behavior of zebrafish larvae. Negative changes in mitochondrial complex activities, as well as reduced ATP content were also observed in larvae treated with 18 and 36 μg/L pyraclostrobin. These results suggested that pyraclostrobin exposure caused cardiotoxicity and neurotoxicity in zebrafish larvae and mitochondrial dysfunction might be the underlying mechanism of pyraclostrobin toxicity.

Comparative Lipid Peroxidation and Apoptosis in Embryo-Larval Zebrafish Exposed to 3 Azole Fungicides, Tebuconazole, Propiconazole, and Myclobutanil, at Environmentally Relevant Concentrations

Azole fungicides have entered the aquatic environment through agricultural and residential runoff. In the present study, we compared the off-target toxicity of tebuconazole, propiconazole, and myclobutanil using embryo-larval zebrafish as a model. The aim of the present study was to investigate the relative toxicity of tebuconazole, propiconazole, and myclobutanil using multiple-level endpoints such as behavioral endpoints and enzymatic and molecular biomarkers associated with their mode of action. Zebrafish embryos were exposed to azoles at environmentally relevant and high concentrations, 0.3, 1.0, and 1000 µg/L, starting at 5 h postfertilization (hpf) up to 48 hpf, as well as 5 d postfertilization (dpf). Relative mRNA expressions of cytochrome P450 family 51 lanosterol-14α-demethylase, glutathione S-transferase, caspase 9, phosphoprotein p53, and BCL2-associated X protein were measured to assess toxicity attributable to fungicides at the mRNA level, whereas caspase 3/7 (apoptosis) and 3,4-methylene​dioxy​amphetamine (lipid peroxidation) levels were measured at the enzymatic level. Furthermore, mitochondrial dysfunction was measure through the Mito Stress test using the Seahorse XFe24 at 48 hpf. In addition, light to dark movement behavior was monitored at 5 dpf using Danio Vision® to understand adverse effects at the organismal level. There was no significant difference in the light to dark behavior with exposure to azoles compared to controls. The molecular biomarkers indicated that propiconazole and myclobutanil induced lipid peroxidation, oxidative stress, and potentially apoptosis at environmentally relevant concentrations (0.3 and 1 µg/L). The results from the mitochondrial respiration assay indicated a slight decrease in spare respiratory capacity with an acute exposure (48 hpf) to all 3 azoles at 1000 µg/L. Based on the present results, propiconazole and myclobutanil are acutely toxic compared to tebuconazole in aquatic organisms at environmentally relevant concentrations. Environ Toxicol Chem 2019;38:1455-1466. © 2019 SETAC.

Sub-lethal effects of the triazole fungicide propiconazole on zebrafish (Danio rerio) development, oxidative respiration, and larval locomotor activity

Propiconazole is a triazole fungicide used in agriculture. Via run-off, it can enter the aquatic environment, and can adversely affect organisms. However, data are scarce on how propiconazole may affect early developmental life stages of fish. The objectives of this study were to evaluate the potential sub-lethal effects of propiconazole during zebrafish development. Wildtype zebrafish (ABTu strain) embryos and larvae were exposed to propiconazole (0.1-100 μM) for up to 150 hours post fertilization (hpf) depending upon the endpoint measured. Propiconazole decreased survival and induced hypopigmentation in fish at 100 μM compared to the water and solvent controls. Pericardial edema was also noted in embryos and larvae (beginning at 2-3 dpf) exposed to 100 μM propiconazole. To visualize the effects of propiconazole on the circulatory system in more detail, we exposed transgenic zebrafish (globin-LCR:eGFP) to the fungicide. Hematopoietic changes were observed within 48 h of exposure to 100 μM, and localization of blood cells in the cardic region became diffuse, indicating pooling of blood in the pericardial region. We measured oxidative respiration in embryos as sufficient ATP is needed for development. Exposure to 100 μM propiconazole (~6-30 hpf) reduced basal respiration (~50%), oligomycin-induced ATP linked respiration (~70%), proton leak (~30%), and non-mitochondrial respiration (~50%), indicating compromised mitochondrial bioenergetics. A Visual Motor Response (VMR) test was used to measure dark photokinesis behavior in larval fish exposed to propiconazole for a 6-day period. Larval fish exposed to the highest concentration in the assay (10 μM) showed evidence of hypoactivity. This study demonstrates that propiconazole can induce hypopigmentation in zebrafish, disrupt mitochondrial bioenergetics, and can alter locomotor activity. However, these sub-lethal responses were observed at concentrations above what is typically detected in the environment.

Tebuconazole reduces basal oxidative respiration and promotes anxiolytic responses and hypoactivity in early-staged zebrafish (Danio rerio)

Triazole fungicides are increasingly used in North America to combat mold and fungi, in order to protect vegetables, citrus, ornamental plants and field crops. To determine the biological impacts of tebuconazole in non-target aquatic organisms, early life stage zebrafish were exposed to 0.1-100 μM tebuconazole for 120 h (5 dpf). There was a significant increase in mortality over time and at 100 μM, only 50% of the animals survived 96 h compared to >95% for all other experimental groups. There was evidence for increased hatching time with 10 μM tebuconazole compared to the control group (~7 h longer at 50% total hatch) or a lack of hatch observed with 100 μM. Oxidative respiration and behavior were evaluated to assess whether the fungicide impaired energy-associated processes. Oxygen consumption rates in embryos (exposed from ~6 hpf) were determined with exposure to 2.5, 25, 50, 100 μM tebuconazole for 24 h using the XFe24 Extracellular Flux Analyzer. Embryos treated with 100 μM showed a ~60% reduction in basal respiration, indicating impaired oxygen consumption and/or changes in resource allocation (e.g. anti-oxidant production, metabolite synthesis). Environmentally-relevant concentrations of tebuconazole did not affect oxidative phosphorylation. As behavior is a sensitive endpoint for toxicity, we measured the dark photokinesis response and conducted a light-dark preference test in 6 dpf larvae following a sub-chronic exposure to 0.1, 1 and 10 μM tebuconazole beginning with 6 hpf embryos. It was observed in two independent experiments for dark photokinesis that 10 μM tebuconazole reduced total distance moved (i.e. hypoactivity) in the dark period by ~25-35%. In the light-dark preference test, there was an increase for mean time in dark zone (~100% increase in the average time/visits per second) and frequency in dark zone (increase of ~35% in average number of visits) with tebuconazole, suggestive of anxiolytic behavior at environmentally-relevant doses. This study demonstrates that exposure to tebuconazole can affect survival, hatch time, oxidative phosphorylation, and behavioral activity of early-staged zebrafish. While survival, hatch time, and mitochondrial bioenergetics were not different than control fish at environmentally-relevant levels of tebuconazole, behavioral responses were detected at concentrations reported in some aquatic environments.

Dichlorvos alters morphology and behavior in zebrafish (Danio rerio) larvae

Dichlorvos (2,2-dichlorovinyl-dimethylphosphate), an organophosphorus pesticide used for indoor insect and livestock parasite control, is among the most common commercially available pesticides. However, there are significant concerns over its toxicity, especially due to its relative stability in water, soil, and air. Zebrafish, an important developmental model, has been used for studying the effects of toxic compounds. The aim of this study was to evaluate the exposure to dichlorvos at early life stages (1 h postfertilization - 7 days postfertilization) in the zebrafish and its toxicological effects during the development, through morphological (7 days postfertilization), locomotor and social behavior analysis (7, 14, 30, 70, and 120 days postfertilization). Dichlorvos (1, 5, and 10 mg/L) exposure reduced the body length and heartbeat rate at 7 days postfertilization (dpf), as well as the surface area of the eyes (5 and 10 mg/L). The avoidance behavior test showed a significant decrease in escape responses at 7 (1, 5, and 10 mg/L) and 14 (5 and 10 mg/L) dpf zebrafish. The evaluation of larval exploratory behavior showed a reduction in distance traveled, mean speed (1, 5, and 10 mg/L) and time mobile (10 mg/L) between control and dichlorvos groups. In addition, the analysis performed on adult animals showed that the changes in distance traveled and mean speed remained reduced in 30 (1, 5, and 10 mg/L) and 70 dpf (5 and 10 mg/L), recovering values similar to the control at 120 dpf. The social behavior of zebrafish was not altered by exposure to dichlorvos in the early stages of development. Thus, the exposure to organophosphorus compounds at early stages of development induces an increased susceptibility to behavioral and neuronal changes that could be associated with several neurodegenerative diseases.

Anxiety-associated behavior and genotoxicity found in adult Danio rerio exposed to tebuconazole-based commercial product

The effects of different concentrations of commercial product based on tebuconazole, on adults of Danio rerio, were evaluated through novel tank diving test and micronucleus and comet assay tests. A total of 320 adult D. rerio were divided into eight tanks and exposed to concentrations of 0; 100; 200 and 300 μg/L the commercial product based on tebuconazole, with their respective replicates at 24, 72 and 96 h. The results showed a behavioral deviation of zebrafish and a significant (p < 0.05) increase in DNA damage as a function of exposed time and different concentrations of the commercial product in relation to the negative control. The results obtained in this study allow to conclude that tebuconazole has effects on adults of Danio rerio, inducing genotoxicity and mutagenicity, as well as altering neurological functions related to the change in the behavior of adults.

N-acetylcysteine protects against motor, optomotor and morphological deficits induced by 6-OHDA in zebrafish larvae

Background

Parkinson's disease (PD) is the second most common neurodegenerative disorder. In addition to its highly debilitating motor symptoms, non-motor symptoms may precede their motor counterparts by many years, which may characterize a prodromal phase of PD. A potential pharmacological strategy is to introduce neuroprotective agents at an earlier stage in order to prevent further neuronal death. N-acetylcysteine (NAC) has been used against paracetamol overdose hepatotoxicity by restoring hepatic concentrations of glutathione (GSH), and as a mucolytic in chronic obstructive pulmonary disease by reducing disulfide bonds in mucoproteins. It has been shown to be safe for humans at high doses. More recently, several studies have evidenced that NAC has a multifaceted mechanism of action, presenting indirect antioxidant effect by acting as a GSH precursor, besides its anti-inflammatory and neurotrophic effects. Moreover, NAC modulates glutamate release through activation of the cystine-glutamate antiporter in extra-synaptic astrocytes. Its therapeutic benefits have been demonstrated in clinical trials for several neuropsychiatric conditions but has not been tested in PD models yet.

Methods

In this study, we evaluated the potential of NAC to prevent the damage induced by 6-hydroxydopamine (6-OHDA) on motor, optomotor and morphological parameters in a PD model in larval zebrafish.

Results

NAC was able to prevent the motor deficits (total distance, mean speed, maximum acceleration, absolute turn angle and immobility time), optomotor response impairment and morphological alterations (total length and head length) caused by exposure to 6-OHDA, which reinforce and broaden the relevance of its neuroprotective effects.

Discussion

NAC acts in different targets relevant to PD pathophysiology. Further studies and clinical trials are needed to assess this agent as a candidate for prevention and adjunctive treatment of PD.

Bioaccumulation and oxidative stress caused by pesticides in Cyprinus carpio reared in a rice-fish system

Nowadays, many irrigated rice producers have adopted the rice-fish farming systems, in which fish are reared in the same environment as rice is grown. These animals can biologically control many pests that disturb the crop, as well as increase the income of producers when they are reared in the same area as rice. However, a large variety of pesticides is often used for pest control in conventional irrigated rice crops, and fish are exposed to different pesticide concentrations and active ingredients. Thus, the aim of the current study is to assess the potential risks of these pesticides to freshwater fish (Cyprinus carpio) cultured in integrated rice-fish farming systems. We assessed five pesticides widely used in rice culture. This is the first report on the bioaccumulation of the insecticides lambda-cyhalothrin + thiamethoxam and clorantraniliprole and of the fungicide tebuconazole + trifloxystrobin associated with oxidative stress and with enzymatic and non-enzymatic parameters in edible fish samples reared in integrated in rice-fish farming systems. After 100 days of exposure, lambda-cyhalothrin and tebuconazole bioaccumulated in carp muscles. Acethylcholinesterase activity in the brain was lower in the experimental group than in the control group. Overall, the biochemical analyses showed increased responses in the experimental groups in comparison to the controls. Lipid peroxidation levels increased in the liver, gills and muscles. Protein oxidation increased in the liver and muscles. Catalase activity increased in the liver, and glutathione S-transferase increased in the liver, gills and muscles. Results demonstrate that these pesticides have severe adverse consequences in fish and indicate their potential risk to human health due to their bioaccumulation in farmed fish.

Nickel exposure alters behavioral parameters in larval and adult zebrafish

Nickel is a heavy metal that, at high concentrations, leads to environmental contamination and causes health problems. We evaluated the effects of NiCl₂ exposure on cognition and behavior in larval and adult zebrafish. Larval and adult zebrafish were exposed to NiCl₂ concentrations (0.025, 2.0, 5.0, and 15.0mg/L) or water (control) in two treatment regimens: acute and subchronic. Larvae were exposed to NiCl₂ for 2h (acute treatment: 5-day-old larvae treated for 2h, tested after treatment) or 11days (subchronic treatment: 11-day-old larvae treated since fertilization, tested at 5, 8 and 11days post-fertilization, dpf). Adults were exposed for 12h (acute treatment) or 96h (subchronic treatment) and were tested after the treatment period. In both regimens, exposed zebrafish showed concentration-dependent increases in body nickel levels compared with controls. For larvae, delayed hatching, decreased heart rate and morphological alterations were observed in subchronically treated zebrafish. Larvae from subchronic treatment tested at 5dpf decrease distance and mean speed at a low concentration (0.025mg/L) and increased at higher concentrations (5.0 and 15.0mg/L). Subchronic treated larvae decrease locomotion at 15.0mg/L at 8 and 11dpf, whereas decreased escape responses to an aversive stimulus was observed at 2.0, 5.0 and 15.0mg/L in all developmental stages. For adults, the exploratory behavior test showed that subchronic nickel exposure induced anxiogenic-like behavior and decrease aggression, whereas impaired memory was observed in both treatments. These results indicate that exposure to nickel in early life stages of zebrafish leads to morphological alterations, avoidance response impairment and locomotor deficits whereas acute and subchronic exposure in adults resulst in anxiogenic effects, impaired memory and decreased aggressive behavior. These effects may be associated to neurotoxic actions of nickel and suggest this metal may influence animals' physiology in doses that do not necessarily impact their survival.

Effect of 1-methyl-3-hexylimidazolium bromide on zebrafish (Danio rerio)

Room-temperature ionic liquids, generally referred to ionic liquids (ILs), are "green solvents". Antioxidant responses and DNA damage in zebrafish livers exposed to 1-methyl-3-hexylimidazolium bromide ([C₆mim]Br) were evaluated at various doses (5-40 mg/L) for a 28-day IL-exposure. A significant decrease of superoxide dismutase (SOD) activity was exhibited, and catalase (CAT) was inhibited at the highest dose (40 mg/L). Reactive oxygen species (ROS) levels were significantly promoted at most exposure interval times except for the dose of 5 mg/L on day 21 in male and days 21 and 28 in female. Malonaldehyde (MDA) contents remarkable increased exposed to [C₆mim]Br. Besides, a notable increase was exhibited, which indicated an inducement of DNA damage with respect to control groups. Thus, we believed that [C₆mim]Br causes oxidative stress and DNA damage in zebrafish. Gender differences were insignificant in almost all the tested biomarkers, thus, male and female zebrafish could be mixed at a ratio of 1:1 in the future evaluation. The present study may also provide basic toxicology information for IL evaluation to aquatic organisms.

Adsorption-desorption and hysteresis phenomenon of tebuconazole in Colombian agricultural soils: Experimental assays and mathematical approaches

The adsorption-desorption, hysteresis phenomenon, and leachability of tebuconazole were studied for Inceptisol and Histosol soils at the surface (0-10 cm) and in the subsurface (40-50 cm) of an agricultural region from Colombia by the batch-equilibrium method and mathematical approaches. The experimental K_fa and K_d (L kg^-1) values (7.9-289.2) decreased with depth for the two Inceptisols and increased with depth for the Histosol due to the organic carbon content, aryl and carbonyl carbon types. Single-point and desorption isotherms depended on adsorption reversibility and suggested that tebuconazole showed hysteresis; which can be adequately evaluated with the single-point desorption isotherm and the linear model using the hysteresis index HI. The most suitable mathematical approach to estimate the adsorption isotherms of tebuconazole at the surface and in the subsurface was that considering the combination of the n-octanol-water partition coefficient, pesticide solubility, and the mass-balance concept. Tebuconazole had similar moderate mobility potential as compared with the values of other studies conducted in temperate amended and unamended soils, but the risk of the fungicide to pollute groundwater sources increased when the pesticide reached subsurface soil layers, particularly in the Inceptisols.

Acute and subchronic toxicity of pyraclostrobin in zebrafish (Danio rerio)

The aim of the present study was to assess the toxic effects of pyraclostrobin on DNA damage and antioxidant enzymatic activities in the zebrafish (Danio rerio) liver. Based on the 96-h median lethal concentration (96 h LC₅₀, 0.056 mg/L) of this chemical, fish were exposed to three doses (0.001, 0.01, and 0.02 mg/L) and sampled on days 7, 14, 21 and 28 after the initiation of a subchronic toxicity test. The levels of superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), glutathione S-transferase (GST), reactive oxygen species (ROS) and DNA damage were determined. The amount of pyraclostrobin residue in the water was also measured. The concentrations in the three treatment groups varied no more than 5% during the exposure periods, indicating that pyraclostrobin is relatively stable during this time in an aquatic environment. ROS and MDA levels significantly changed in a dose dependent manner during the experiment. Enzymatic activities were inhibited to a certain extent. DNA damage was significantly enhanced. These results collectively indicate that pyraclostrobin induces oxidative stress and DNA damage in zebrafish.

Glyphosate and Roundup® alter morphology and behavior in zebrafish

Glyphosate has become the most widely used herbicide in the world, due to the wide scale adoption of transgenic glyphosate resistant crops after its introduction in 1996. Glyphosate may be used alone, but it is commonly applied as an active ingredient of the herbicide Roundup®. This pesticide contains several adjuvants, which may promote an unknown toxicity. The indiscriminate application poses numerous problems, both for the health of the applicators and consumers, and for the environment, contaminating the soil, water and leading to the death of plants and animals. Zebrafish (Danio rerio) is quickly gaining popularity in behavioral research, because of physiological similarity to mammals, sensitivity to pharmacological factors, robust performance, low cost, short spawning intervals, external fertilization, transparency of embryos through larval stages, and rapid development. The aim of this study was evaluate the effects of glyphosate and Roundup® on behavioral and morphological parameters in zebrafish larvae and adults. Zebrafish larvae at 3days post-fertilization and adults were exposed to glyphosate (0.01, 0.065, and 0.5mg/L) or Roundup® (0.01, 0.065, and 0.5mg/L) for 96h. Immediately after the exposure, we performed the analysis of locomotor activity, aversive behavior, and morphology for the larvae and exploratory behavior, aggression and inhibitory avoidance memory for adult zebrafish. In zebrafish larvae, there were significant differences in the locomotor activity and aversive behavior after glyphosate or Roundup® exposure when compared to the control group. Our findings demonstrated that exposure to glyphosate at the concentration of 0.5mg/L, Roundup® at 0.065 or 0.5mg/L reduced the distance traveled, the mean speed and the line crossings in adult zebrafish. A decreased ocular distance was observed for larvae exposed at 0.5mg/L of glyphosate. We verified that at 0.5mg/L of Roundup®-treated adult zebrafish demonstrated a significant impairment in memory. Both glyphosate and Roundup® reduced aggressive behavior. Our data suggest that there are small differences between the effects induced by glyphosate and Roundup®, altering morphological and behavioral parameters in zebrafish, suggesting common mechanisms of toxicity and cellular response.

Ecotoxicity of water-soluble lectin from Moringa oleifera seeds to zebrafish (Danio rerio) embryos and larvae

The evaluation of ecotoxicity of mosquito larvicidal agents (such as the water-soluble lectin from Moringa oleifera seeds, WSMoL) is an essential step to establish the guidelines for their use. In this sense, this work evaluated the toxicity of WSMoL to Danio rerio embryos and larvae. Embryos were exposed to waterborne WSMoL (0.0125-0.2 mg mL^-1) for 96 h and lethal and sub-lethal effects were observed every 24 h. In the bioassays with larvae, the individuals were exposed to the WSMoL (0.025-0.2 mg mL^-1), mortality was recorded daily, and larval swimming velocities were analyzed after 72 h and 168 h of exposure. Additionally, acetylcholinesterase (AChE) activity of larvae was determined after 168 h of exposure. WSMoL LC₅₀ values to embryos were 0.190, 0.133 and 0.049 mg mL^-1 after 48, 72 and 96 h, respectively. No toxic endpoint was observed after exposure for 24 h. In addition, hatching was delayed and larval length at 96 h was reduced compared to the control. WSMoL LC₅₀ to larvae were 0.21 and 0.135 mg mL^-1, after 24 h and 96 h, respectively. Larvae exposed to 0.1 and 0.2 mg mL^-1 showed a decrease in swimming speed and a significant reduction in AChE activity. In conclusion, WSMoL at waterborne concentrations needed for its use as a larvicide to A. aegypti causes lethal and sublethal effects to zebrafish embryos and larvae. Therefore, its use in waterbodies where there are non-target organisms is not recommended.