Paraquat affects mitochondrial bioenergetics, dopamine system expression, and locomotor activity in zebrafish (Danio rerio)

Chronic Exposure of Zebrafish to Iron and Aluminum: Evaluation of Reversal and Generational Transposition of Behavioral, Histopathological, and Genotoxic Changes

This study aimed to report the effects of chronic exposure of zebrafish exposed to environmentally relevant concentrations of 0.5, 2.4, and 5.0 mg L-1 iron (Fe) and 0.2, 0.4, and 2.0 mg L-1 aluminum (Al). We also evaluated the reversal and generational transposition (F1) of possible histopathological, behavioral, and genotoxic changes in the species. Locomotion changes that may have been caused by the increase in the number of apoptotic cells and in the telencephalic mitochondrial activity were observed especially after the 30 days exposure to Al and persisted after recovery (30 days). We also observed histopathological changes, such as an increase in the number of intestinal goblet cells, even after the recovery period in these animals. Our results also showed that the Fe concentrations used were insufficient to cause genotoxicity, behavioral and intestinal epithelium changes. The adult offspring (F1) of animals exposed to Al showed changes in locomotion and in the amount of goblet cells, demonstrating that even in low concentrations this pollutant can harm subsequent generations in the aquatic biota. Animals demonstrate, in general, greater tolerance to Fe which may be related to the physiological demand of this metal by the body. Even so, all concentrations of both metals that caused some change in the species represent Brazilian environmental occurrences or Brazilian legislation. It highlights the need for updating the guidelines and constant monitoring of aquatic environments, since even in the face of a hypothetical decontamination of the environment, some changes could persist and affect different trophic levels.

Genetic Evidence for Estrogenic Effects of Benzophenone-2 on Zebrafish Neurodevelopment and Its Signaling Mechanism

Estrogens play a crucial role in regulating various biological responses during the early stages of neurodevelopment. Benzophenone-2 (BP2), a widely used organic ultraviolet (UV) filter, has been proven as an estrogenic compound, whereas the estrogenic effects of BP2 on neurodevelopment remain largely unknown. Here, we investigated the neurodevelopmental toxicity of BP2 by exposing zebrafish embryos from 2 to 120 h postfertilization (hpf) at environmentally relevant concentrations. We demonstrated that early life exposure to BP2 induced multiple concentration-dependent impairments in the nervous system, including hypoactivity, abnormal brain morphology, impaired neurocyte proliferation, shortened axon, and increased neurocyte apoptosis. Moreover, metabolomic profiling revealed a decrease in dopamine (DA) and its metabolites in BP2-treated larvae. Using E2 treatment and morpholino knockdown assays, we provided strong genetic evidence that the BP2-induced behavioral disorders were associated with estrogen-dependent signaling, especially estrogen receptors 2a and 2b (esr2). Subsequently, transcriptomic profiling indicated that the activation of esr2 further inhibited the expression of LIM homeobox transcription factor 1 β a (lmx1ba), which is vital for normal neurodevelopment. Consistently, the overexpression of lmx1ba and inhibition of esr2 obviously alleviated BP2-caused neurotoxicity, uncovering a seminal role of esr2 and lmx1ba in BP2-induced neurodevelopmental toxicity. Our findings provide the first evidence in fish that BP2 can induce neurodevelopmental deficits and brain dysfunction and offer novel insights into the mechanisms of toxicity of BP2 as well as other emerging benzophenones.

Adverse Outcomes Following Exposure to Perfluorooctanesulfonamide (PFOSA) in Larval Zebrafish (Danio rerio): A Neurotoxic and Behavioral Perspective

Toxicity mechanisms of per- and polyfluoroalkyl substances (PFASs), a chemical class present in diverse ecosystems, as well as many of their precursors, have been increasingly characterized in aquatic species. Perfluorooctanesulfonamide (PFOSA, C8H2F17NO2S) is a common precursor of perfluorooctane sulfonic acid (PFOS), a long-chain PFAS. Here, we assessed sub-lethal endpoints related to development, oxidative stress, transcript levels, and distance moved in zebrafish embryos and larvae following continuous exposure to PFOSA beginning at 6 h post-fertilization (hpf). PFOSA decreased survival in fish treated with 1 µg/L PFOSA; however, the effect was modest relative to the controls (difference of 10%). Exposure up to 10 µg/L PFOSA did not affect hatch rate, nor did it induce ROS in 7-day-old larvae fish. The activity of larval fish treated with 100 µg/L PFOSA was reduced relative to the solvent control. Transcripts related to oxidative stress response and apoptosis were measured and BCL2-associated X, apoptosis regulator (bax), cytochrome c, somatic (cycs), catalase (cat), superoxide dismutase 2 (sod2) were induced with high concentrations of PFOSA. Genes related to neurotoxicity were also measured and transcript levels of acetylcholinesterase (ache), elav-like RNA binding protein 3 (elavl3), growth-associated protein 43 (gap43), synapsin II (syn2a), and tubulin 3 (tubb3) were all increased in larval fish with higher PFOSA exposure. These data improve our understanding of the potential sub-lethal toxicity of PFOSA in fish species.

Neurotoxic and behavioral deficit in Drosophila melanogaster exposed to photocatalytic products of Paraquat

The Advanced Oxidative Processes have demonstrated potential for application in the degradation of organic pollutants, such as Paraquat (PQ) from water and wastewater, due to their low price, high efficiency, and non-toxic properties. In this study, we investigated whether the photodegradation of PQ with TiO2 nanotubes reduced its toxicity in Drosophila melanogaster. However, dietary ingestion of degradation products PQ for larvae resulted in a low axial ratio (pupal volume). In the adults, products of photodegradation of PQ exposure markedly diminished climbing ability in a time-dependent manner after 10 days of feeding. In addition, exposure of D. melanogaster to photodegradation of PQ reduced acetylcholinesterase and citrate synthase activities but improved oxidative stress, as evidenced by oxide nitric, protein carbonyl, and lactate production. These results suggest that the photodegradation of PQ with TiO2 nanotubes produced PQ fragments with higher toxicity than PQ, while the precise mechanism of its action needs further investigation.

Embryonic Zebrafish as a Model for Investigating the Interaction between Environmental Pollutants and Neurodegenerative Disorders

Environmental pollutants have been linked to neurotoxicity and are proposed to contribute to neurodegenerative disorders. The zebrafish model provides a high-throughput platform for large-scale chemical screening and toxicity assessment and is widely accepted as an important animal model for the investigation of neurodegenerative disorders. Although recent studies explore the roles of environmental pollutants in neurodegenerative disorders in zebrafish models, current knowledge of the mechanisms of environmentally induced neurodegenerative disorders is relatively complex and overlapping. This review primarily discusses utilizing embryonic zebrafish as the model to investigate environmental pollutants-related neurodegenerative disease. We also review current applicable approaches and important biomarkers to unravel the underlying mechanism of environmentally related neurodegenerative disorders. We found embryonic zebrafish to be a powerful tool that provides a platform for evaluating neurotoxicity triggered by environmentally relevant concentrations of neurotoxic compounds. Additionally, using variable approaches to assess neurotoxicity in the embryonic zebrafish allows researchers to have insights into the complex interaction between environmental pollutants and neurodegenerative disorders and, ultimately, an understanding of the underlying mechanisms related to environmental toxicants.

Environmental pollution of paraben needs attention: A study of methylparaben and butylparaben co-exposure trigger neurobehavioral toxicity in zebrafish

Parabens (PBs) are commonly utilized as preservatives in various commodities. Of all the PBs, methylparaben (MeP) and butylparaben (BuP) are usually found together at similar levels in the aqueous environment. Although a few studies have demonstrated that PBs are neurotoxic when present alone, the neurobehavioral toxic effects and mechanisms of coexisting MeP and BuP at environmental levels has not been determined. Neurobehavior is a sensitive indicator for identifying neurotoxicity of environmental pollutants. Therefore, adult female zebrafish (Danio rerio) were chronic co-exposure of MeP and BuP at environmental levels (5, 50, and 500 ng/L) for 60 d to investigate the effects on neurobehavior, histopathology, oxidative stress, mitochondrial function, neurotransmitters and gene expression. The results demonstrated that chronic co-exposure of MeP and BuP interfered with several behaviors (learning-memory, anxiety, fear, aggressive and shoaling behavior) in addition to known mechanisms of producing oxidative stress and disrupting energy. More intriguingly, chronic co-exposure of MeP and BuP caused retinal vacuolization and apoptosis in the optic tectum zone. It even has further effects on the phototransduction pathway, impairing optesthesia and leading to neurotransmitters dysregulation. These are critical underlying mechanisms resulting in neurobehavioral abnormalities. This study confirms that the pollution of multiple PBs by chronic co-exposure in aquatic environments can result neurobehavioral toxicity. It also suggests that the prolonged effects of PBs on aquatic ecosystems and health require close attention.

Exposure to the antineoplastic ifosfamide alters molecular pathways related to cardiovascular function, increases heart rate, and induces hyperactivity in zebrafish (Danio rerio)

Ifosfamide is an alkylating antineoplastic drug used in chemotherapy, but it is also detected in wastewater. Here, the objectives were to (1) determine teratogenic, cardiotoxic, and mitochondrial toxicity potential of ifosfamide exposure; (2) elucidate mechanisms of toxicity; (3) characterize exposure effects on larval behavior. Survival rate, hatch rate, and morphological deformity incidence were not different amongst treatments following exposure levels up to 1000 µg/L ifosfamide over 7 days. RNA-seq reveled 231 and 93 differentially expressed transcripts in larvae exposed to 1 µg/L and 100 µg/L ifosfamide, respectively. Several gene networks related to vascular resistance, cardiovascular response, and heart rate were affected, consistent with tachycardia observed in exposed embryonic fish. Hyperactivity in larval zebrafish was observed with ifosfamide exposure, potentially associated with dopamine-related gene networks. This study improves ecological risk assessment of antineoplastics by elucidating molecular mechanisms related to ifosfamide toxicity, and to alkylating agents in general.

Developing Peripheral Biochemical Biomarkers of Brain Disorders: Insights from Zebrafish Models

High prevalence of human brain disorders necessitates development of the reliable peripheral biomarkers as diagnostic and disease-monitoring tools. In addition to clinical studies, animal models markedly advance studying of non-brain abnormalities associated with brain pathogenesis. The zebrafish (Danio rerio) is becoming increasingly popular as an animal model organism in translational neuroscience. These fish share some practical advantages over mammalian models together with high genetic homology and evolutionarily conserved biochemical and neurobehavioral phenotypes, thus enabling large-scale modeling of human brain diseases. Here, we review mounting evidence on peripheral biomarkers of brain disorders in zebrafish models, focusing on altered biochemistry (lipids, carbohydrates, proteins, and other non-signal molecules, as well as metabolic reactions and activity of enzymes). Collectively, these data strongly support the utility of zebrafish (from a systems biology standpoint) to study peripheral manifestations of brain disorders, as well as highlight potential applications of biochemical biomarkers in zebrafish models to biomarker-based drug discovery and development.

Environmental levels of azoxystrobin disturb male zebrafish behavior: Possible roles of oxidative stress, cholinergic system, and dopaminergic system

A widely applied pesticide of azoxystrobin, is increasingly detected in the water environment. Concern has been raised against its potential detriment to aquatic ecosystems. It has been shown that exposure to azoxystrobin interfere with the locomotor behavior of zebrafish larvae. This study aims to investigate whether exposure to environmental levels of azoxystrobin (2 μg/L, 20 μg/L, and 200 μg/L) changes the behavior of male adult zebrafish. Herein, we evaluated behavioral response (locomotor, anxiety-like, and exploratory behaviors), histopathology, biochemical indicators, and gene expression in male adult zebrafish upon azoxystrobin exposure. The study showed that exposure to azoxystrobin for 42 days remarkably increased the locomotor ability of male zebrafish, resulted in anxiety-like behavior, and inhibited exploratory behavior. After treatment with 200 μg/L azoxystrobin, vasodilatation, and congestion were observed in male zebrafish brains. Exposure to 200 μg/L azoxystrobin notably elevated ROS level, MDA concentration, CAT activity, and AChE activity, while inhibiting SOD activity, GPx activity, ACh concentration, and DA concentration in male zebrafish brains. Moreover, the expression levels of genes related to the antioxidant, cholinergic, and dopaminergic systems were significantly changed. This suggests that azoxystrobin may interfere with the homeostasis of neurotransmitters by causing oxidative stress in male zebrafish brains, thus affecting the behavioral response of male zebrafish.

Towards improved screening of toxins for Parkinson's risk

Parkinson's disease (PD) is a chronic, progressive and disabling neurodegenerative disorder. The prevalence of PD has risen considerably over the past decades. A growing body of evidence suggest that exposure to environmental toxins, including pesticides, solvents and heavy metals (collectively called toxins), is at least in part responsible for this rapid growth. It is worrying that the current screening procedures being applied internationally to test for possible neurotoxicity of specific compounds offer inadequate insights into the risk of developing PD in humans. Improved screening procedures are therefore urgently needed. Our review first substantiates current evidence on the relation between exposure to environmental toxins and the risk of developing PD. We subsequently propose to replace the current standard toxin screening by a well-controlled multi-tier toxin screening involving the following steps: in silico studies (tier 1) followed by in vitro tests (tier 2), aiming to prioritize agents with human relevant routes of exposure. More in depth studies can be undertaken in tier 3, with whole-organism (in)vertebrate models. Tier 4 has a dedicated focus on cell loss in the substantia nigra and on the presumed mechanisms of neurotoxicity in rodent models, which are required to confirm or refute the possible neurotoxicity of any individual compound. This improved screening procedure should not only evaluate new pesticides that seek access to the market, but also critically assess all pesticides that are being used today, acknowledging that none of these has ever been proven to be safe from a perspective of PD. Importantly, the improved screening procedures should not just assess the neurotoxic risk of isolated compounds, but should also specifically look at the cumulative risk conveyed by exposure to commonly used combinations of pesticides (cocktails). The worldwide implementation of such an improved screening procedure, would be an essential step for policy makers and governments to recognize PD-related environmental risk factors.

Neurotoxicity of the Cu(OH)2 Nanopesticide through Perturbing Multiple Neurotransmitter Pathways in Developing Zebrafish

The copper hydroxide [Cu(OH)2] nanopesticide is an emerging agricultural chemical that can negatively impact aquatic organisms. This study evaluated the behavioral changes of zebrafish larvae exposed to the Cu(OH)2 nanopesticide and assessed its potential to induce neurotoxicity. Metabolomic and transcriptomic profiling was also conducted to uncover the molecular mechanisms related to potential neurotoxicity. The Cu(OH)2 nanopesticide at 100 μg/L induced zebrafish hypoactivity, dark avoidance, and response to the light stimulus, suggestive of neurotoxic effects. Altered neurotransmitter-related pathways (serotoninergic, dopaminergic, glutamatergic, GABAergic) and reduction of serotonin (5-HT), dopamine (DA), glutamate (GLU), γ-aminobutyric acid (GABA), and several of their precursors and metabolites were noted following metabolomic and transcriptomic analyses. Differentially expressed genes (DEGs) were associated with the synthesis, transport, receptor binding, and metabolism of 5-HT, DA, GLU, and GABA. Transcripts (or protein levels) related to neurotransmitter receptors for 5-HT, DA, GLU, and GABA and enzymes for the synthesis of GLU and GABA were downregulated. Effects on both the glutamatergic and GABAergic pathways in zebrafish were specific to the nanopesticide and differed from those in fish exposed to copper ions. Taken together, the Cu(OH)2 nanopesticide induced developmental neurotoxicity in zebrafish by inhibiting several neurotransmitter-related pathways. This study presented a model for Cu(OH)2 nanopesticide-induced neurotoxicity in developing zebrafish that can inform ecological risk assessments.

Bioactive strawberry fruit (Arbutus unedo L.) extract remedies paraquat-induced neurotoxicity in the offspring prenatally exposed rats

Background

Paraquat (1,1'-dimethyl-4-4'-bipyridinium dichloride) exposure is well-established as a neurotoxic agent capable of causing neurological deficits in offspring. This study aimed to investigate therapeutic effects of Arbutus unedo L. aqueous extract (AU) against paraquat (PQ) exposure.

Methods

For that the phytoconstituents of AU was determined by LC/MS, and then its antioxidant potential was assessed by DPPH and ABTS assays. The assessment included its impact on cell viability and mitochondrial metabolism using N27 dopaminergic cells. Additionally, we evaluated the effects of prenatal PQ exposure on motor coordination, dopamine levels, trace element levels, and total antioxidant capacity (TAC) in rat progeny.

Results

The phytochemical profile of AU extract revealed the presence of 35 compounds, primarily phenolic and organic acids, and flavonoids. This accounted for its strong in vitro antioxidant activities against DPPH and ABTS radicals, surpassing the activities of vitamin C. Our findings demonstrated that AU effectively inhibited PQ-induced loss of N27 rat dopaminergic neural cells and significantly enhanced their mitochondrial respiration. Furthermore, daily post-treatment with AU during the 21 days of the rat's pregnancy alleviated PQ-induced motor deficits and akinesia in rat progeny. These effects inhibited dopamine depletion and reduced iron levels in the striatal tissues. The observed outcomes appeared to be mediated by the robust antioxidant activity of AU, effectively counteracting the PQ-induced decrease in TAC in the blood plasma of rat progeny. These effects could be attributed to the bioactive compounds present in AU, including phenolic acids such as gallic acid and flavonoids such as quercetin, rutin, apigenin, glucuronide, and kaempferol, all known for their potent antioxidant capacity.

Discussion

In conclusion, this preclinical study provided the first evidence of the therapeutic potential of AU extract against PQ-induced neurotoxicity. These findings emphasize the need for further exploration of the clinical applicability of AU in mitigating neurotoxin-induced brain damage.

Comparative Assessment of the Toxicity of Brominated and Halogen-Free Flame Retardants to Zebrafish in Terms of Tail Coiling Activity, Biomarkers, and Locomotor Activity

BDE-47, a flame retardant that is frequently detected in environmental compartments and human tissues, has been associated with various toxic effects. In turn, information about the effects of aluminum diethyl-phosphinate (ALPI), a halogen-free flame retardant from a newer generation, is limited. This study aims to assess and compare the toxicity of BDE-47 and ALPI to zebrafish by analyzing the tail coiling, locomotor, acetylcholinesterase activities, and oxidative stress biomarkers. At 3000 µg/L BDE-47, the coiling frequency increased at 26-27 h post-fertilization (hpf), but the burst activity (%) and mean burst duration (s) did not change significantly. Here, we considered that the increased coiling frequency is a slight neurotoxic effect because locomotor activity was impaired at 144 hpf and 300 µg/L BDE-47. Moreover, we hypothesized that oxidative stress could be involved in the BDE-47 toxicity mechanisms. In contrast, only at 30,000 µg/L did ALPI increase the catalase activity, while the motor behavior during different developmental stages remained unaffected. On the basis of these findings, BDE-47 is more toxic than ALPI.

Zebrafish as a Model Organism for Studying Pathologic Mechanisms of Neurodegenerative Diseases and other Neural Disorders

Zebrafish are widely considered an excellent vertebrate model for studying the pathogenesis of human diseases because of their transparency of embryonic development, easy breeding, high similarity with human genes, and easy gene manipulation. Previous studies have shown that zebrafish as a model organism provides an ideal operating platform for clarifying the pathological and molecular mechanisms of neurodegenerative diseases and related human diseases. This review mainly summarizes the achievements and prospects of zebrafish used as model organisms in the research of neurodegenerative diseases and other human diseases related to the nervous system in recent years. In the future study of human disease mechanisms, the application of the zebrafish model will continue to provide a valuable operating platform and technical support for investigating and finding better prevention and treatment of these diseases, which has broad application prospects and practical significance. Zebrafish models used in neurodegenerative diseases and other diseases related to the nervous system.

Upregulation of mitochondrial calcium uniporter contributes to paraquat-induced neuropathology linked to Parkinson's disease via imbalanced OPA1 processing

Paraquat (PQ) is the most widely used herbicide in agriculture worldwide and has been considered a high-risk environmental factor for Parkinson's disease (PD). Chronic PQ exposure selectively induces dopaminergic neuron loss, the hallmark pathologic feature of PD, resulting in Parkinson-like movement disorders. However, the underlying mechanisms remain unclear. Here, we demonstrated that repetitive PQ exposure caused dopaminergic neuron loss, dopamine deficiency and motor deficits dose-dependently in mice. Accordingly, mitochondrial calcium uniporter (MCU) was highly expressed in PQ-exposed mice and neuronal cells. Importantly, MCU knockout (KO) effectively rescued PQ-induced dopaminergic neuron loss and motor deficits in mice. Genetic and pharmacological inhibition of MCU alleviated PQ-induced mitochondrial dysfunction and neuronal death in vitro. Mechanistically, PQ exposure triggered mitochondrial fragmentation via imbalance of the optic atrophy 1 (OPA1) processing manifested by cleavage of L-OPA1 to S-OPA1, which was reversed by inhibition of MCU. Notably, the upregulation of MCU was mediated by miR-129-1-3p posttranscriptionally, and overexpression of miR-129-1-3p could rebalance OPA1 processing and attenuate mitochondrial dysfunction and neuronal death induced by PQ exposure. Consequently, our work uncovers an essential role of MCU and a novel molecular mechanism, miR-MCU-OPA1, in PQ-induced pathogenesis of PD, providing a potential target and strategy for environmental neurotoxins-induced PD treatment.

Mechanism of Bisphenol F Affecting Motor System and Motor Activity in Zebrafish

Bisphenol F (BPF; 4,4'-dihydroxydiphenylmethane) is one of the most frequently used compounds in the manufacture of plastics and epoxy resins. Previous studies have demonstrated that BPF affects locomotor behavior, oxidative stress, and neurodevelopment in zebrafish. However, its neurotoxic effects are controversial, and the underlying mechanisms are unclear. In order to determine whether BPF affects the motor system, we exposed zebrafish embryos to BPF and assessed behavioral, histological, and neurochemical changes. Spontaneous locomotor behavior and startle response were significantly decreased in BPF-treated zebrafish larvae compared with control larvae. BPF induced motor degeneration and myelination defects in zebrafish larvae. In addition, embryonic exposure to BPF resulted in altered metabolic profiles of neurochemicals, including neurotransmitters and neurosteroids, which may impact locomotion and motor function. In conclusion, exposure to BPF has the potential to affect survival, motor axon length, locomotor activity, myelination, and neurochemical levels of zebrafish larvae.

Ceftriaxone and selenium mitigate seizures and neuronal injury in pentylenetetrazole-kindled rats: Oxidative stress and inflammatory pathway

Epilepsy is one of the most serious worldwide neurological disorders that lead to the cognitive-psychosocial insults in recurrent seizures. About one third of the patients are drug-resistant, so innovative drugs are needed to manage seizures to improve the quality of life. Ceftriaxone is a cephalosporin antibiotic that increases the expression of glutamate transporters-1 and improves the neurobehavioral effects caused by increased glutamate level in the CNS. Selenium is well known antioxidant. The present study aimed to investigate ceftriaxone and selenium therapeutic effects against epilepsy in rats. Epilepsy was induced by PTZ given at a dose (50 mg/kg I.P) on alternative days for 13 days. Eighty rats were randomly divided into 8 groups: Group1-2; normal and vehicle control, Group 3; PTZ group, Group 4-8; kindled rats received selenium, ceftriaxone100, ceftriaxone200, selenium + ceftriaxone100 and selenium + ceftriaxone200 mg/kg/day respectively for a week. At the end of the study, behavioral tests were performed. Oxidative stress, inflammatory markers, neurotransmitters and GLT-1 were measured in brain tissue homogenate. Brain histopathological investigation was also done. PTZ-kindled rats exhibited increased Racine score, besides behavioral tests and histopathological changes, significant elevation in oxidative stress and inflammatory markers, with decrease in serotonin, dopamine, GABA levels and GLT-1 expressions. Selenium and Ceftriaxone alone or combined treatment decreased Racine score with remarkable improvement in behavioral and histopathological changes. The antioxidant enzymes, neurotransmitters and GLT-1 expressions were increased, along with reduced TNF-α, IL-1 levels. Current study showed that selenium + ceftriaxone100 group represents a possible approach to improve epilepsy particularly through inhibiting oxidative stress and inflammation.

A New Bioassay for the Detection of Paralytic and Amnesic Biotoxins Based on Motor Behavior Impairments of Zebrafish Larvae

The global concern about the increase of harmful algal bloom events and the possible impacts on food safety and aquatic ecosystems presents the necessity for the development of more accessible techniques for biotoxin detection for screening purposes. Considering the numerous advantages that zebrafish present as a biological model and particularly as a toxicants sentinel, we designed a sensitive and accessible test to determine the activity of paralytic and amnesic biotoxins using zebrafish larvae immersion. The ZebraBioTox bioassay is based on the automated recording of larval locomotor activity using an IR microbeam locomotion detector, and manual assessment of four complementary responses under a simple stereoscope: survival, periocular edema, body balance, and touch response. This 24 h acute static bioassay was set up in 96-well microplates using 5 dpf zebrafish larvae. For paralytic toxins, a significant decrease in locomotor activity and touch response of the larvae was detected, allowing a detection threshold of 0.1-0.2 µg/mL STXeq. In the case of the amnesic toxin the effect was reversed, detecting hyperactivity with a detection threshold of 10 µg/mL domoic acid. We propose that this assay might be used as a complementary tool for environmental safety monitoring.

Screening potential toxicity of currently used herbicides in the freshwater amphipod Gammarus fossarum based on multi-level biomarker responses to field-realistic exposures

Herbicides are widely used to control weeds and maximize crop growth. Because of agricultural runoff, these chemicals are potentially hazardous to aquatic wildlife. However, their ecotoxicity and resulting disturbance in individual performance remain scarcely documented in freshwater crustaceans. This study aimed to screen the potential toxicity of currently used herbicides in the ecosystem engineer Gammarus fossarum using multi-level biomarkers. In microcosms, gammarids were exposed for 72 h to 12 herbicides individually (quinmerac, mesotrione, bentazone, isoproturon, chlortoluron, metazachlor, chloridazone, diflufenican, flufenacet, aclonifen, prosulfocarb and metolachlor) at a field-realistic concentration (i.e. 10 μg/L). The sublethal effects were assessed by monitoring several biochemical, physiological and behavioural traits. In exposed gammarids, alterations in behavioural activities were observed, i.e. increased locomotion and respiration as a general trend. Moreover, biochemical biomarkers suggested herbicide-dependent disruptions in moulting, antioxidant responses and cell integrity. Integrating multi-metric variations through statistical analyses allowed us to identify herbicide clusters likely to trigger common sets of biological responses. Depressed antioxidant defence at the cell level and impaired respiration at the individual level were the predominant toxic effects of herbicides, related to their hydrophobic feature. Furthermore, establishing relationships between sublethal alterations in gammarids and acute lethality or chronic toxicity values defined for regulatory purposes supports the relevance of these alterations as early warnings of toxicity. Our findings demonstrate that currently used herbicides have unexpected toxicological effects in a non-target wild animal, with possible long-term alterations in population dynamics and associated ecological functions, which constitute promising diagnostic tools for risk assessment in agricultural areas.

Sulfamethoxazole (SMX) Alters Immune and Apoptotic Endpoints in Developing Zebrafish (Danio rerio)

Sulfamethoxazole (SMX) is a broad-range bacteriostatic antibiotic widely used in animal and fish farming and is also employed in human medicine. These antibiotics can ultimately end up in the aquatic ecosystem and affect non-target organisms such as fish. To discern the effect of SMX on developing zebrafish embryos and larvae, we investigated a broad range of sub-lethal toxicity endpoints. Higher concentrations of SMX affected survivability, caused hatch delay, and induced malformations including edema of the yolk sac, pericardial effusion, bent tail, and curved spine in developing embryos. Lower levels of SMX provoked an inflammatory response in larvae at seven days post fertilization (dpf), as noted by up-regulation of interferon (ifn-γ) and interleukin 1β (il-1β). SMX also increased the expression of genes related to apoptosis, including BCL2-Associated Agonist of Cell Death (bad) and BCL2 Associated X, Apoptosis Regulator (bax) at 50 µg/L and decreased caspase 3 (casp3) expression in a dose-dependent manner. SMX induced hyperactivity in larval fish at 500 and 2500 µg/L based upon the light/dark preference test. Collectively, this study revealed that exposure to SMX can disrupt the immune system by altering host defense mechanisms as well as transcripts related to apoptosis. These data improve understanding of antibiotic chemical toxicity in aquatic organisms and serves as a baseline for in-depth environmental risk assessment of SMX and antibiotics.

Fluoride exposure causes behavioral, molecular and physiological changes in adult zebrafish (Danio rerio) and their offspring

Fluoride exposure through drinking water, foods, cosmetics, and drugs causes genotoxic effects, oxidative damage, and impaired cognitive abilities. In our study, the effects of fluoride on anxiety caused by the circadian clock and circadian clock changes in a zebrafish model were investigated at the molecular level on parents and the next generations. For this purpose, adult zebrafish were exposed to 1.5 ppm, 5 ppm, and 100 ppm fluoride for 6 weeks. At the end of exposure, anxiety-like behaviors and sleep/wake behaviors of the parent fish were evaluated with the circadian rhythm test and the novel tank test. In addition, antioxidant enzyme activities and melatonin levels in brain tissues were measured. In addition, morphological, physiological, molecular and behavioral analyzes of offspring taken from zebrafish exposed to fluoride were performed. In addition, histopathological analyzes were made in the brain tissues of both adult zebrafish and offspring, and the damage caused by fluoride was determined. The levels of BMAL1, CLOCK, PER2, GNAT2, BDNF and CRH proteins were measured by immunohistochemical analysis and significant changes in their levels were determined in the F- treated groups. The data obtained as a result of behavioral and molecular analyzes showed that parental fluoride exposure disrupts the circadian rhythm, causes anxiety-like behaviors, and decreases the levels of brain antioxidant enzymes and melatonin in parents. In addition, delay in hatching, increase in death and body malformations, and decrease in blood flow velocity, and locomotor activity was observed in parallel with dose increase in offspring. On the other hand, an increase in offspring apoptosis rate, ROS level, and lipid accumulation was detected. As a result, negative effects of fluoride exposure on both parents and next generations have been identified.

Perfluorotetradecanoic Acid (PFTeDA) Induces Mitochondrial Damage and Oxidative Stress in Zebrafish (Danio rerio) Embryos/Larvae

Industrial and consumer products, such as pesticides, lubricants, and cosmetics, can contain perfluorinated compounds (PFCs). Although many short-chain PFCs have been linked to physiological and behavioral changes in fish, there are limited data on longer-chain PFCs. The objective of this study was to determine the potential impact of perfluorotetradecanoic acid (PFTeDA) exposure on zebrafish (Danio rerio) during early developmental stages. We measured several endpoints including gene expression, mitochondrial bioenergetics, and locomotor activity in zebrafish. Survival, timing of hatching, and deformity frequency were unaffected by PFTeDA at the concentrations tested (0.01, 0.1, 1, and 10 µM) over a 7-day exposure period. The expression levels of mitochondrial-related genes (cox1 and mt-nd3) and oxidative stress-related genes (cat, hsp70, and hsp90a) were increased in larval fish with exposure to 10 µM PFTeDA; however, there was no change in oxidative respiration of embryos (i.e., basal respiration and oligomycin-induced ATP-linked respiration). Reactive oxygen species were reduced in larvae treated with 10 µM PFTeDA, coinciding with the increased transcription of antioxidant defense genes. Both the visual motor response test and light-dark preference test were conducted on 7 dpf larvae and yielded no significant findings. This study improves current knowledge regarding toxicity mechanisms for longer-chain PFCs such as PFTeDA.

Dopamine Release Impairments Accompany Locomotor and Cognitive Deficiencies in Rotenone-Treated Parkinson's Disease Model Zebrafish

In this work, we carried out neurochemical and behavioral analysis of zebrafish (Danio rerio) treated with rotenone, an agent used to chemically induce a syndrome resembling Parkinson's disease (PD). Dopamine release, measured with fast-scan cyclic voltammetry (FSCV) at carbon-fiber electrodes in acutely harvested whole brains, was about 30% of that found in controls. Uptake, represented by the first order rate constant (k) and the half-life (t1/2) determined by nonlinear regression modeling of the stimulated release plots, was also diminished. Behavioral analysis revealed that rotenone treatment increased the time required for zebrafish to reach a reward within a maze by more than 50% and caused fish to select the wrong pathway, suggesting that latent learning was impaired. Additionally, zebrafish treated with rotenone suffered from diminished locomotor activity, swimming shorter distances with lower mean velocity and acceleration. Thus, the neurochemical and behavioral approaches, as applied, were able to resolve rotenone-induced differences in key parameters. This approach may be effective for screening therapies in this and other models of neurodegeneration.

Perfluorooctane sulfonic acid (PFOS) exposures interfere with behaviors and transcription of genes on nervous and muscle system in zebrafish embryos

Perfluorooctane sulfonic acid (PFOS) has been widely detected in environment and organisms. PFOS has been identified as the driving agent for the behavioral changes of zebrafish larvae, while the underlying molecular mechanism remains unclear. In this study, zebrafish embryos/larvae were exposed to 0, 0.04, 0.1, 0.4 and 1 μM PFOS for 166 h. The locomotor behaviors and the mRNA transcription of genes in neuromuscular system were detected. Exposure to PFOS did not affect the hatching/death rates and body length, but increased the heart beat rates and frequency of spontaneous tail coiling. Locomotor behavior in zebrafish larvae of 0.4 and 1 μM PFOS groups were increased in the light condition. Additionally, the levels of acetylcholine (Ach) in 0.4 μM PFOS group and dopamine (DA) in 0.1, 0.4 and 1 μM PFOS groups were found to be significantly increased. The expression of genes related to the synthesis and decomposition of ACh，the synthesis and receptor of DA, and fosab was increased in the different PFOS treatment groups, while the expression of all the other genes of the neuromuscular system were significantly reduced. The findings of this investigation demonstrated that PFOS exposure may alter the locomotor behavior of zebrafish through disrupting the expressions of genes in neuromuscular system. The disturbed process of neurotransmitter transmission and muscle contraction caused by PFOS may be the dominant mechanism of hyperactivity in zebrafish.

Zebrafish as a model organism for neurodegenerative disease

The zebrafish is increasingly recognized as a model organism for translational research into human neuropathology. The zebrafish brain exhibits fundamental resemblance with human neuroanatomical and neurochemical pathways, and hallmarks of human brain pathology such as protein aggregation, neuronal degeneration and activation of glial cells, for example, can be modeled and recapitulated in the fish central nervous system. Genetic manipulation, imaging, and drug screening are areas where zebrafish excel with the ease of introducing mutations and transgenes, the expression of fluorescent markers that can be detected in vivo in the transparent larval stages overtime, and simple treatment of large numbers of fish larvae at once followed by automated screening and imaging. In this review, we summarize how zebrafish have successfully been employed to model human neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, and Huntington’s disease. We discuss advantages and disadvantages of choosing zebrafish as a model for these neurodegenerative conditions.

Oxaloacetate acid ameliorates paraquat-induced acute lung injury by alleviating oxidative stress and mitochondrial dysfunction

Acute lung injury (ALI) is the primary cause of death among patients with acute paraquat (PQ) poisoning, whereby peroxidative damage is an important mechanism underlying PQ-induced lung injury. There is a lack of effective interventional drugs for patients with PQ poisoning. Oxaloacetic acid (OAA) participates in multiple in vivo metabolic processes, whereby it facilitates the clearance of reactive oxygen species (ROS) and improves mitochondrial function. The study aimed to assess the protective effects of OAA on PQ-induced ALI and elucidate the underlying molecular mechanism. Our data demonstrated that OAA treatment significantly alleviated PQ-induced ALI and improved the survival rate of PQ-poisoned mice, and also alleviated PQ-induced cellular oxidative stress and mitochondrial dysfunction. OAA-mediated alleviation of PQ-induced mitochondrial dysfunction depends on the following mechanisms which may explain the above findings: 1) OAA effectively cleared intracellular ROS, inhibited ROS accumulation, and mitochondrial depolarization; 2) OAA inhibited the downregulation of L-OPA1 and MFN2 caused by PQ and promoted a dynamic balance of mitochondrial fusion and fission, and 3) the expression of PGC-1α, TFAM, COX2, and COX4I1, increased significantly following OAA intervention which improved mitochondrial respiratory functions and promoted its biogenesis and energy metabolism in damaged cells. In conclusion, OAA effectively cleared ROS and improved mitochondrial dysfunction, thereby significantly improving ALI caused by PQ poisoning and the animal survival rate. Therefore, OAA may be a potential drug for the treatment of PQ poisoning.

Herbicidal characteristics and structural identification of a potential active compound produced by Streptomyces sp. KRA18-249

The KRA18-249 strain, isolated from a natural recreational forest near Jeongseon, Gangwon-do, when applied to plants induced signs of wilting within 24 h, leading to plant death. The isolated actinomycete was identified as Streptomyces gardneri based on 16S rRNA gene homogeneity analysis. The culture filtrate was solvent fractionated to obtain the active substance, and the active compound 249-Y1 was isolated from the purified fractions via a herbicide activity test using Digitaria ciliaris. NMR and ESI-MS analyses revealed that the molecular formula of 249-Y1 is C₂₀H₁₆O₆ [MW = 352.0947] and is an anthraquinone (rubiginone D2) produce by polyketide synthetase system. The active compound 249-Y1 showed strong (100%) herbicidal activity against several weeds at 500 μg mL^-1 concentration. Twisting symptoms began to appear within 24 h of treatment and intensified over time. The KRA18-249 strain produced the herbicidal compound under specific culture conditions, that is, at 200 rpm, 35 °C, for eight days at an initial pH of 10. We also found that 249-Y1 inhibited chlorophyll, but was not a radical generator. Overall, the secondary metabolite 249-Y1, produced by KRA18-249, can be used as a new biological agent for weed control.

The toxicological effects of Eryngium foetidum extracts on zebrafish embryos and larvae depend on the type of extract, dose, and exposure time

Eryngium foetidum is a herbaceous plant found in tropical and subtropical regions. In vivo pharmacological parameters show that leaf extracts of this plant have antioxidant, anti-inflammatory, antidiabetic, and antimicrobial activities due to their bioactive compounds such as flavonoids and phenols. Despite the evidence for several bioactivities of E. foetidum, information on its safety and tolerability is limited. The objective of this study was to assess the effect and concentration of different extracts of E. foetidum on the development of zebrafish (Danio rerio) embryos. To study the impact of aqueous (AE), ethanolic (EE), and methanolic (ME) extracts, the embryos were exposed to 0.625, 1.25, 2.5, 5, and 10 mg mL-1 for up to 120-h postfertilization to assess embryonic developmental toxicity and then to 0.039, 0.078, 0.156, 0.312, and 0.625 mg mL-1 to assess the antioxidant responses of the enzymes superoxide dismutase catalase, glutathione S-transferase (GST), and cell apoptosis. The results showed that, depending on the extraction solvent, concentration used, and exposure time, E. foetidum extracts caused mortality, altered the hatching time, and promoted changes in enzymatic activities. Delays in development and increased GST activity were found in all treatments. Apoptosis was not observed in any of the treatments. In conclusion, AE, EE, and ME concentrations above 0.625 mg mL-1 can cause adverse effects on the early stages of zebrafish development.

Impact of Environmental Risk Factors on Mitochondrial Dysfunction, Neuroinflammation, Protein Misfolding, and Oxidative Stress in the Etiopathogenesis of Parkinson's Disease

As a prevalent progressive neurodegenerative disorder, Parkinson's disease (PD) is characterized by the neuropathological hallmark of the loss of nigrostriatal dopaminergic (DAergic) innervation and the appearance of Lewy bodies with aggregated α-synuclein. Although several familial forms of PD have been reported to be associated with several gene variants, most cases in nature are sporadic, triggered by a complex interplay of genetic and environmental risk factors. Numerous epidemiological studies during the past two decades have shown positive associations between PD and several environmental factors, including exposure to neurotoxic pesticides/herbicides and heavy metals as well as traumatic brain injury. Other environmental factors that have been implicated as potential risk factors for PD include industrial chemicals, wood pulp mills, farming, well-water consumption, and rural residence. In this review, we summarize the environmental toxicology of PD with the focus on the elaboration of chemical toxicity and the underlying pathogenic mechanisms associated with exposure to several neurotoxic chemicals, specifically 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, paraquat (PQ), dichloro-diphenyl-trichloroethane (DDT), dieldrin, manganese (Mn), and vanadium (V). Our overview of the current findings from cellular, animal, and human studies of PD provides information for possible intervention strategies aimed at halting the initiation and exacerbation of environmentally linked PD.

Neurotoxicity of pesticides - A link to neurodegeneration

Parkinson's disease (PD) is a neurodegenerative disorder which mainly targets motor symptoms such as tremor, rigidity, bradykinesia and postural instability. The physiological changes occur due to dopamine depletion in basal ganglia region of the brain. PD aetiology is not yet elucidated clearly but genetic and environmental factors play a prominent role in disease occurrence. Despite of various environmental factors, pesticides exposure has been convicted as major candidate in PD pathogenesis. Among various pesticides 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been widely investigated in PD following with paraquat (PQ), maneb (MB), organochlorines (OC) and rotenone. Effect of these pesticides has been suggested to be involved in oxidative stress, alterations in dopamine transporters, mitochondrial dysfunction, α-synuclein (αSyn) fibrillation, and neuroinflammation in PD. The present review discusses the influence of pesticides in neurodegeneration and its related epidemiological studies conducted in PD. Furthermore, we have deliberated the common pesticides involved in PD and its associated genetic alterations and the probable mechanism of them behind PD pathogenesis. Hence, we conclude that pesticides play a prominent role in PD pathogenesis and advance research is needed to investigate the alterations in genetic and mechanistic aspects of PD.

Neurotoxicological Profiling of Paraquat in Zebrafish Model

Paraquat is a polar herbicide protecting plant products against invasive species, it requires careful manipulation and restricted usage because of its harmful potentials. Exposure to paraquat triggers oxidative damage in dopaminergic neurons and subsequently causes a behavioral defect in vivo. Thereby, persistent exposure to paraquat is known to increase Parkinson's disease risk by dysregulating dopaminergic systems in humans. Therefore, most studies have focused on the dopaminergic systems to elucidate the neurotoxicological mechanism of paraquat poisoning, and more comprehensive neurochemistry including histaminergic, serotonergic, cholinergic, and GABAergic systems has remained unclear. Therefore, in this study, we investigated the toxicological potential of paraquat poisoning using a variety of approaches such as toxicokinetic profiles, behavioral effects, neural activity, and broad-spectrum neurochemistry in zebrafish larvae after short-term exposure to paraquat and we performed the molecular modeling approach. Our results showed that paraquat was slowly absorbed in the brain of zebrafish after oral administration of paraquat. In addition, paraquat toxicity resulted in behavioral impairments, namely, reduced motor activity and led to abnormal neural activities in zebrafish larvae. This locomotor deficit came with a dysregulation of dopamine synthesis induced by the inhibition of tyrosine hydroxylase activity, which was also indirectly confirmed by molecular modeling studies. Furthermore, short-term exposure to paraquat also caused simultaneous dysregulation of other neurochemistry including cholinergic and serotonergic systems in zebrafish larvae. The present study suggests that this neurotoxicological profiling could be a useful tool for understanding the brain neurochemistry of neurotoxic agents that might be a potential risk to human and environmental health.

Enantioselective neurotoxicity and oxidative stress effects of paclobutrazol in zebrafish (Danio rerio)

Paclobutrazol is a widely used chiral plant growth regulator and its enantioselective toxicity in aquatic organisms is less explored till now. Herein, the enantioselective neurotoxicity of paclobutrazol mediated by oxidative stress in zebrafish were investigated. The oxidative stress parameters and neurotoxic biomarkers changed significantly in each exposure group, and paclobutrazol showed enantioselective toxicity in zebrafish. Firstly, (2R, 3R)-paclobutrazol exhibited a stronger oxidative stress in zebrafish than (2S, 3S)-enantiomer (P < 0.05). Then, activities of acetylcholinesterase, calcineurin, and total nitric oxide synthase in (2R, 3R)-paclobutrazol treatments were 0.61-0.89, 1.24-1.53, and 1.21-1.35-fold stronger (P < 0.05) than those in (2S, 3S)-enantiomer treatments, respectively. Next, the content variations of four neurotransmitters in zebrafish exposed to (2R, 3R)-paclobutrazol were significantly larger than those in (2S, 3S)-enantiomer treatments (P < 0.05). Moreover, (2R, 3R)-paclobutrazol had stronger binding with the receptors than (2S, 3S)-enantiomer through molecular docking. The integrated biomarker response values further demonstrated that (2R, 3R)-paclobutrazol showed stronger toxicity to zebrafish than (2S, 3S)-enantiomer. Furthermore, the neurotoxicity of paclobutrazol can be interpreted as the mediating effect of oxidative stress in zebrafish through correlation analysis, and an adverse outcome pathway for the nervous system in zebrafish induced by paclobutrazol was proposed. This work will greatly extend our understanding on the enantioselective toxic effects of paclobutrazol in aquatic organisms.

Effects of di-(2-ethylhexyl) phthalate (DEHP) on behavior and dopamine signaling in zebrafish (Danio rerio)

Di (2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer, also known as a developmental toxicant, but its neurobehavioral toxicity remains elusive. This study evaluated the neurobehavioral toxicity and its possible mechanism in larval zebrafish. Embryos at gastrula period (~6 h post fertilization, hpf) were exposure to DEHP (0, 1, 2.5, 5 and 10 mg/L) for 7 days. Spontaneous tail movement in embryos and swimming activity in larvae were monitored. Alterations in the mRNA expression of genes involved in dopamine signaling and apoptosis pathway were assessed. In situ apoptotic cells were assessed by Acridine orange staining, and oxidative damage were measured using enzymatic assay. The behavior results showed that DEHP inhibited spontaneous tail movement and decreased locomotor activities in the light/dark behavioral test. Meanwhile, behavioral changes were accompanied by increased apoptosis and malondialdehyde (MDA) content, decreased superoxide dismutase (SOD) activity and dopamine (DA) content, and perturbed the expression of genes associated with the synthesis (th), reuptake (dat) and metabolism (mao) of DA, with dopamine receptors (DRs), and with the apoptosis pathway (p53, bax, bcl2, caspase-3, caspase-8, caspase-9). The findings will help to illuminate the possible neurobehavioral toxicity mechanisms of organism exposure to DEHP.

Developmental Neurotoxicity and Behavioral Screening in Larval Zebrafish with a Comparison to Other Published Results

With the abundance of chemicals in the environment that could potentially cause neurodevelopmental deficits, there is a need for rapid testing and chemical screening assays. This study evaluated the developmental toxicity and behavioral effects of 61 chemicals in zebrafish (Danio rerio) larvae using a behavioral Light/Dark assay. Larvae (n = 16-24 per concentration) were exposed to each chemical (0.0001-120 μM) during development and locomotor activity was assessed. Approximately half of the chemicals (n = 30) did not show any gross developmental toxicity (i.e., mortality, dysmorphology or non-hatching) at the highest concentration tested. Twelve of the 31 chemicals that did elicit developmental toxicity were toxic at the highest concentration only, and thirteen chemicals were developmentally toxic at concentrations of 10 µM or lower. Eleven chemicals caused behavioral effects; four chemicals (6-aminonicotinamide, cyclophosphamide, paraquat, phenobarbital) altered behavior in the absence of developmental toxicity. In addition to screening a library of chemicals for developmental neurotoxicity, we also compared our findings with previously published results for those chemicals. Our comparison revealed a general lack of standardized reporting of experimental details, and it also helped identify some chemicals that appear to be consistent positives and negatives across multiple laboratories.

A Critical Review of Zebrafish Models of Parkinson's Disease

A wide variety of human diseases have been modelled in zebrafish, including various types of cancer, cardiovascular diseases and neurodegenerative diseases like Alzheimer’s and Parkinson’s. Recent reviews have summarized the currently available zebrafish models of Parkinson’s Disease, which include gene-based, chemically induced and chemogenetic ablation models. The present review updates the literature, critically evaluates each of the available models of Parkinson’s Disease in zebrafish and compares them with similar models in invertebrates and mammals to determine their advantages and disadvantages. We examine gene-based models, including ones linked to Early-Onset Parkinson’s Disease: PARKIN, PINK1, DJ-1, and SNCA; but we also examine LRRK2, which is linked to Late-Onset Parkinson’s Disease. We evaluate chemically induced models like MPTP, 6-OHDA, rotenone and paraquat, as well as chemogenetic ablation models like metronidazole-nitroreductase. The article also reviews the unique advantages of zebrafish, including the abundance of behavioural assays available to researchers and the efficiency of high-throughput screens. This offers a rare opportunity for assessing the potential therapeutic efficacy of pharmacological interventions. Zebrafish also are very amenable to genetic manipulation using a wide variety of techniques, which can be combined with an array of advanced microscopic imaging methods to enable in vivo visualization of cells and tissue. Taken together, these factors place zebrafish on the forefront of research as a versatile model for investigating disease states. The end goal of this review is to determine the benefits of using zebrafish in comparison to utilising other animals and to consider the limitations of zebrafish for investigating human disease.

Developmental toxicity of fenbuconazole in zebrafish: effects on mitochondrial respiration and locomotor behavior

Triazole fungicides are used to control the disease of cereal crops but may also cause adverse effects on non-target organisms. There is a lack of toxicity data for some triazoles such as fenbuconazole in aquatic organisms. This research was conducted to evaluate the toxicity of fenbuconazole at environmentally relevant concentrations with attention on the mitochondria, antioxidant system, and locomotor activity in zebrafish. Zebrafish were exposed to one concentration of 5, 50, 200 or 500ng/L fenbuconazole for 96h. There was no effect on survival nor percentage of fish hatched, but exposure to 200 and 500ng/L fenbuconazole resulted in malformation and hypoactivity in zebrafish. Oxygen consumption rates (OCR) of embryos were measured to determine if the fungicide impaired mitochondrial respiration. Exposure to 500ng/L fenbuconazole reduced basal OCR and oligomycin-induced ATP linked respiration in exposed fish. Fenbuconazole reduced mitochondrial membrane potential and reduced the activities of mitochondrial Complex II and III. Transcript levels of both sdhc and cyc1, each related to Complex II and III, were also altered in expression by fenbuconazole exposure, consistent with mitochondrial dysfunction in embryos. Fenbuconazole activated the antioxidant system, based upon both transcriptional and enzymatic data in zebrafish. Consistent with mitochondrial impairment, molecular docking confirmed a strong binding capacity of the fungicide at the Q_i site of Complex III, revealing this complex is susceptible to fenbuconazole. This study reveals potential toxicity pathways related to fenbuconazole exposure in aquatic organisms; such data can improve risk assessments for triazole fungicides.

The potential effect mechanism of high-fat and high-carbohydrate diet-induced obesity on anxiety and offspring of zebrafish

Anxiety and obesity are two current phenomena. They are among the important public health problems with increasing prevalence worldwide. Although it is claimed that there are strong relations between them, the mechanism of this relationship has not been fully clarified yet. On the other hand, the effect of this relationship on the offspring has been another research subject. In this study, obese zebrafish were obtained by feeding two different diets, one containing high amount of lipid (HF) and the other containing high amount of carbohydrate (HK), and their anxiety levels were evaluated. To establish a relationship between these two phenomena, in addition to histopathological and immunohistochemical analysis in the brain tissues of fish, the transcription levels of some genes related to lipid and carbohydrate metabolisms were determined. In addition, offspring were taken from obese zebrafish and studied to examine the effect of parental obesity on offspring. As a result, it was observed that the HC diet, causing more weight increase than the HF diet, showed an anxiolytic while the HF diet an anxiogenic effect. It was suggested that the probable cause of this situation may be the regulatory effect on the appetite-related genes depending on the upregulation severity of the PPAR gene family based on the diet content. In addition, it was also suggested that it may have contributed to this process in neuron degenerations caused by oxidative stress. Regarding effects on offspring, it can be concluded that HF diet-induced obesity has more negative effects on the next generation than the HC diet.Level of evidenceNo Level of evidence: animal study.

Molecular and behavioral assessment in larval zebrafish (Danio rerio) following exposure to environmentally relevant levels of the antineoplastic cyclophosphamide

Antineoplastics treat cancers and enter aquatic ecosystems through wastewater and hospital effluent. Risks associated with antineoplastics are not well characterized in aquatic organisms. We conducted zebrafish embryo/larvae toxicity assays to evaluate responses to cyclophosphamide (0.01-50 µM). Zebrafish survival was affected by 5 µM cyclophosphamide and deformities were noted at > 1 µM. Oxidative respiration remained unchanged in embryos with exposure up to 200 µM. Reactive oxygen species were not increased by 50 µM cyclophosphamide exposure. More than 15 oxidative stress and immune-related transcripts were measured. Superoxide dismutase 2 and heat shock protein 70 and 90a were induced in larvae by cyclophosphamide. Immune-related transcripts were assessed due to immunosuppressive properties of cyclophosphamide, and mmp9 and myd88 levels were altered in expression. Hyperactivity of larvae was noted following 5 µM cyclophosphamide exposure. There was no change in anxiety-related endpoints (light-dark preference). Risks for larval fish exposed to cyclophosphamide in the environment may be low.

Ellagic acid ameliorates paraquat-induced liver injury associated with improved gut microbial profile

Paraquat, a widely used herbicide, causes environmental pollution, and liver injury in humans and animals. As a natural compound in fruits, ellagic acid (EA) shows anti-inflammatory and antioxidant effects. This study examines the beneficial effects of dietary EA against the paraquat-induced hepatic injury and further explores the underlying molecular mechanisms using a piglet model. Post-weaning piglets are fed basal diet supplemented with 50 mg/kg, 100 mg/kg, or 200 mg/kg EA for 3 weeks. At week 2, hepatic injury is induced by 4 mg/kg paraquat followed by 7 days recovery. EA supplementation significantly mitigates paraquat-induced hepatic fibrosis, steatosis, and high apoptotic rate. In agreement, EA supplementation reduces serum pro-inflammatory levels, ameliorates inflammatory cells infiltration into hepatic tissue, which are associated with suppressed NF-κB signaling during paraquat exposure. In addition, EA supplementation significantly improves activities of antioxidative enzymes which were correlated with activated Nrf2/Keap 1 signaling during paraquat exposure. Furthermore, EA supplementation restores cecal microbial community during paraquat exposure. The protective effect of EA is strongly linked with increased relative abundance of Lactobacillus reuteri and Lactobacillus amylovorus. Taken together, EA supplementation effectively reduced the occurrence of hepatic oxidative damage and inflammation induced by paraquat through modulating cecal microbial communities, which provides a novel nutritional therapeutic strategy for hepatic injury.

Neuroprotective Effects of Resveratrol in In vivo and In vitro Experimental Models of Parkinson's Disease: a Systematic Review

Parkinson's disease (PD) is currently the second most common neurodegenerative disease, being characterized by motor and non-motor symptoms. The therapeutic options available for its treatment are limited, do not slow the progression of the disease, and have serious side effects. For this reason, many studies have sought to find compounds with neuroprotective properties that bring additional benefits to current therapy. In this context, resveratrol is a phenolic compound, found in many plant species, capable of crossing the blood-brain barrier and having multiple biological properties. Experimental studies in vitro and in vivo have shown that it can prevent or slow the progression of a variety of diseases, including PD. In this systematic review, we summarize the effects of resveratrol in experimental in vivo and in vitro models of PD and discuss the molecular mechanisms involved in its action. The bibliographic search was performed in the databases of PubMed, Web of Science, SciELO, and Google Scholar, and based on the inclusion criteria, 41 articles were selected and discussed. Most of the included studies have demonstrated neuroprotective effects of resveratrol. In general, resveratrol prevented behavioral and/or neurological disorders, improved antioxidant defenses, reduced neuroinflammatory processes, and inhibited apoptosis. In summary, this systematic review offers important scientific evidence of neuroprotective effects of resveratrol in PD and also provide valuable information about its mechanism of action that can support future clinical studies.

Naringenin alleviates paraquat-induced dopaminergic neuronal loss in SH-SY5Y cells and a rat model of Parkinson's disease

Parkinson's disease (PD), a common neurodegenerative disease is characterized by the progressive loss of dopaminergic neurons in the substantia nigra. The cause of dopaminergic loss in PD remains unknown for a long time, however, recent reports suggest oxidative stress plays a key role in the pathogenesis of PD. Paraquat (PQ), a widely used herbicide is an oxidative stress inducer that has been implicated as a potential risk factor for the development of PD. Flavonoids are naturally occurring polyphenolic compounds that display a variety of therapeutic properties against oxidative stress. Naringenin (NAR), a natural flavonoid, exhibits neuroprotection against PD-related pathology. However, studies on its neuroprotective role and the underlying mechanisms are scarce, therefore the present study explored the potential neuroprotective role of NAR in PQ-induced parkinsonism in SH-SY5Y cells and rat model. The effect of NAR on PQ-induced cellular toxicity was determined by measuring cell viability, oxidative stress, ATP levels and the same effect was determined by assessing behavioral, biochemical, immunohistochemical, qRT-PCR and Western blot in rat model. NAR treatment in SH-SY5Y cells resulted in increased cell viability, reduced oxidative stress, elevated mitochondrial membrane potential, and higher cellular ATP levels. In rats, NAR treatment resulted in significant neuroprotection against PQ-induced behavioral deficits, oxidative stress, mitochondrial dysfunction, and astrocytosis. NAR treatment significantly modulated PQ-induced mRNA expressions of DRD2, DAT, LRRK2, SNCA, β-catenin, caspase-3, BDNF genes. NAR treatment increased TH protein expression and modulated its immunoreactivity in rat striatum. Also, GFAP decreased in response to NAR treatment. So, in the present study, NAR exhibits neuroprotection against PQ-induced neurotoxicity and neurodegeneration indicating its novel therapeutic potential against PD.

ADME/T-based strategies for paraquat detoxification: Transporters and enzymes

Paraquat (PQ) is a toxic, organic herbicide for which there is no specific antidote. Although banned in some countries, it is still used as an irreplaceable weed killer in others. The lack of understanding of the precise mechanism of its toxicity has hindered the development of treatments for PQ exposure. While toxicity is thought to be related to PQ-induced oxidative stress, antioxidants are limited in their ability to ameliorate the untoward biological responses to this agent. Summarized in this review are data on the absorption, distribution, metabolism, excretion, and toxicity (ADME/T) of PQ, focusing on the essential roles of individual transporters and enzymes in these processes. Based on these findings, strategies are proposed to design and test specific and effective antidotes for the clinical management of PQ poisoning.

Temporal exposure to malathion: Biochemical changes in the Amazonian fish tambaqui, Colossoma macropomum

The main toxicity mechanism of organophosphate insecticides such as malathion is the acetylcholinesterase enzyme inhibition. However, fish responses to organophosphates may vary depending on the activation of different defense mechanisms as well as the length of exposure. As such, the evaluation of acetylcholinesterase activity, in combination with the evaluation of biotransformation and antioxidants enzymes levels, is useful for indicating damage in fish exposed to this insecticide. Moreover, evaluating mitochondrial activity might evidence how the hierarchic responses occur in relation to the length of time that the fish is exposed. Therefore, the aim of our study is to evaluate whether the length of exposure to malathion differentially affects the biochemical responses of tambaqui. Our hypothesis is that the physiological alterations due to exposure are time dependent. Fish were exposed to sublethal concentrations of the insecticide during 6, 12, 24, 36, and 48 h. Contrary to expectations, there was no acetylcholinesterase activity inhibition during the experiment, which indicates an absence of neurotoxicity. Phase II biotransformation mechanism was activated early, especially in the liver. Oxidative damage was evident in the first hours of exposure and was concurrent with the activation of antioxidant enzymes. Mitochondrial bioenergetics were differentially affected by the length of exposure. The data suggest that the tambaqui regulates mitochondrial respiration differently over time, seeking to maintain homeostasis and ATP demand, and ensures the activation of response mechanisms, thus minimizing oxidative damage and avoiding the neurotoxicity of malathion.

Assessing sub-lethal effects of the dinitroaniline herbicide pendimethalin in zebrafish embryos/larvae (Danio rerio)

Pendimethalin is a dinitroaniline herbicide used to control broadleaf weeds by inhibiting the formation of microtubules during cell division. Its use on a variety of crops leads to its potential entry into aquatic environments, but little is known about its sub-lethal toxicity to early developmental stages of aquatic vertebrates. To address this knowledge gap, we assessed the toxicity of pendimethalin to zebrafish embryos and larvae by measuring mortality, developmental abnormalities, oxidative respiration, reactive oxygen species, gene expression, and locomotor activity following exposure to the herbicide throughout early development. Embryos at ~6 h post-fertilization (hpf) were exposed to either a solvent control (0.1% DMSO, v/v), embryo rearing medium (ERM), or one dose of either 1, 2.5, 5, or 25 μM pendimethalin for up to 7-days post fertilization depending on the bioassay. Exposure to 25 μM pendimethalin resulted in high prevalence of spinal curvature, tail malformations, pericardial edema, and yolk sac edema at 4 dpf, while exposure to 5 μM pendimethalin induced pericardial edema and lordosis in the fish exposed over 7 dpf. Exposure to pendimethalin up to 5 μM did not negatively impact oxidative respiration (e.g., basal respiration, oligomycin-induced ATP production) in embryos following a 24-h exposure. Pendimethalin did not induce reactive oxygen species at concentrations of 1-5 μM. Levels of transcripts associated with oxidative respiration and damage response were altered in 7d-larvae; cox1 mRNA was increased in larvae fish exposed to 1 μM while cox5a1 and sod2 mRNA were decreased with 2.5 μM exposure. The Visual Motor Response (VMR) test for light-dark response revealed that larval activity in the dark period was reduced for zebrafish exposed to >1 μM pendimethalin compared to ERM and DMSO solvent control groups. These data inform on the sub-lethal toxicity of pendimethalin to early stages of fish embryos and larvae.

Exposure to acetochlor impairs swim bladder formation, induces heat shock protein expression, and promotes locomotor activity in zebrafish (Danio rerio) larvae

Acetochlor is one of the most widely used herbicides in the world, however, there are few data on the sub-lethal effects of acetochlor on early developmental stages of fish. To address this, we measured survival, deformity, swim bladder formation, embryo oxygen consumption rates, reactive oxygen species (ROS) levels, transcripts (related to swim bladder formation, oxidative damage response, and apoptosis) and behavior responses following exposure to acetochlor (0.001 µM up to 125 µM). Exposure to acetochlor at concentrations 50 µM and above exerted 100% mortality after 3 dpf, and significantly reduced the size of the swim bladder (25 µM). In embryos, basal respiration, oligomycin-induced ATP production, and maximal respiration were decreased 30-60% following a 24 h exposure to 125 μM acetochlor. Acetochlor did not affect ROS levels up to 25 µM in larvae with acute exposure. Acetochlor at 25 µM increased mRNA levels of bax1, hsp70, and hsp90a by ~4-fold in larval zebrafish. In both the visual motor response and light-dark preference test, 25 µM acetochlor increased locomotor activity of larval fish. At lower exposure concentrations, 100 and 1000 nM acetochlor increased the mean time spent in the dark zone, suggesting promotion of anxiolytic behavior. This study presents a comprehensive evaluation of sublethal effects of acetochlor, spanning molecular responses to behavior, which can be used to refine risk assessment decisions for aquatic environments.

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

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

Anthrahydroquinone-2-6-disulfonate is a novel, powerful antidote for paraquat poisoning

Paraquat (PQ) is a widely used fast-acting pyridine herbicide. Accidental ingestion or self-administration via various routes can cause severe organ damage. Currently, no effective antidote is available commercially, and the mortality rate of poisoned patients is exceptionally high. Here, the efficacy of anthrahydroquinone-2-6-disulfonate (AH₂QDS) was observed in treating PQ poisoning by constructing in vivo and ex vivo models. We then explored the detoxification mechanism of AH₂QDS. We demonstrated that, in a rat model, the PQ concentration in the PQ + AH₂QDS group significantly decreased compared to the PQ only group. Additionally, AH₂QDS protected the mitochondria of rats and A549 cells and decreased oxidative stress damage, thus improving animal survival and cell viability. Finally, the differentially expressed genes were analysed in the PQ + AH₂QDS group and the PQ group by NextGen sequencing, and we verified that Nrf2's expression in the PQ + AH₂QDS group was significantly higher than that in the PQ group. Our work identified that AH₂QDS can detoxify PQ by reducing PQ uptake and protecting mitochondria while enhancing the body's antioxidant activity.

Zebrafish and Medaka: Important Animal Models for Human Neurodegenerative Diseases

Animal models of human neurodegenerative disease have been investigated for several decades. In recent years, zebrafish (Danio rerio) and medaka (Oryzias latipes) have become popular in pathogenic and therapeutic studies about human neurodegenerative diseases due to their small size, the optical clarity of embryos, their fast development, and their suitability to large-scale therapeutic screening. Following the emergence of a new generation of molecular biological technologies such as reverse and forward genetics, morpholino, transgenesis, and gene knockout, many human neurodegenerative disease models, such as Parkinson's, Huntington's, and Alzheimer's, were constructed in zebrafish and medaka. These studies proved that zebrafish and medaka genes are functionally conserved in relation to their human homologues, so they exhibit similar neurodegenerative phenotypes to human beings. Therefore, fish are a suitable model for the investigation of pathologic mechanisms of neurodegenerative diseases and for the large-scale screening of drugs for potential therapy. In this review, we summarize the studies in modelling human neurodegenerative diseases in zebrafish and medaka in recent years.