Identification of apoptosis and macrophage migration events in paraquat-induced oxidative stress using a zebrafish model

Abnormalities of serum lipid metabolism in patients with acute paraquat poisoning caused by ferroptosis

As the mechanism of paraquat (PQ) poisoning is still not fully elucidated, and no specific treatment has been developed in medical practice, the management of PQ poisoning continues to present a medical challenge. In this study, the objective was to investigate the early metabolic changes in serum metabolism and identify the key metabolic pathways involved in patients with PQ poisoning. Quantitative analysis was conducted to determine the relevant metabolites. Additionally, experiments were carried out in both plasma and cell to elucidate the mechanisms underlying metabolic disorder and cell death in PQ poisoning. The study found that polyunsaturated fatty acids (PUFAs) and their metabolites, such as arachidonic acid (AA) and hydroxy eicosatetraenoic acids (HETEs), were significantly increased by non-enzymatic oxidative reaction. Reactive oxygen species (ROS) production increased rapidly at 2 h after PQ poisoning, followed by an increase in PUFAs at 12 h, and intracellular glutathione, cysteine (Cys), and Fe2+ at 24 h. However, at 36 h later, intracellular glutathione and Cys decreased, HETEs increased, and the expression of SLC7A11 and glutathione peroxidase 4 (GPX4) decreased. Ultrastructural examination revealed the absence of mitochondrial cristae. Deferoxamine was found to alleviate lipid oxidation, and increase the viability of PQ toxic cells in the low dose. In conclusion, unsaturated fatty acids metabolism was the key metabolic pathways in PQ poisoning. PQ caused cell death through the induction of ferroptosis. Inhibition of ferroptosis could be a novel strategy for the treatment of PQ poisoning.

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.

Transgenic zebrafish (Danio rerio) as an emerging model system in ecotoxicology and toxicology: Historical review, recent advances, and trends

Zebrafish (Danio rerio) is an alternative model system for drug screening, developing new products, and assessing ecotoxic effects of pollutants and biomonitor species in environmental risk assessment. However, the history and current use of transgenic zebrafish lines in ecotoxicology and toxicology studies remain poorly explored. Thus, the present study aimed to summarize and discuss the existing data in the literature about the applications of transgenic zebrafish lines in ecotoxicology and toxicology. The articles were analyzed according to publication year, journal, geographic distribution, and collaborations. Also, the bioassays were evaluated according to the tested chemical, transgenic lines, development stage, biomarkers, and exposure conditions (i.e., concentration, time, type, and route of exposure). Revised data showed that constitutive transgenic lines are the main type of transgenic used in the studies, besides most of uses embryos and larvae under static conditions. Tg(fli1: EGFP) was the main transgenic line, while the GFP and EGFP were the main reporter proteins. Transgenic zebrafish stands out in assessing vasotoxicity, neurotoxicity, systemic toxicity, hepatoxicity, endocrine disruption, cardiotoxicity, immunotoxicity, hematotoxicity, ototoxicity, and pancreotoxicity. This review showed that transgenic zebrafish lines are emerging as a suitable in vivo model system for assessing the mechanism of action and toxicity of chemicals and new biotechnology products, and the effects of traditional and emerging pollutants.

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.

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.

Oxidative Stress and AKT-Associated Angiogenesis in a Zebrafish Model and Its Potential Application for Withanolides

Oxidative stress and the AKT serine/threonine kinase (AKT) signaling pathway are essential regulators in cellular migration, metastasis, and angiogenesis. More than 300 withanolides were discovered from the plant family Solanaceae, exhibiting diverse functions. Notably, the relationship between oxidative stress, AKT signaling, and angiogenesis in withanolide treatments lacks comprehensive understanding. Here, we summarize connecting evidence related to oxidative stress, AKT signaling, and angiogenesis in the zebrafish model. A convenient vertebrate model monitored the in vivo effects of developmental and tumor xenograft angiogenesis using zebrafish embryos. The oxidative stress and AKT-signaling-modulating abilities of withanolides were highlighted in cancer treatments, which indicated that further assessments of their angiogenesis-modulating potential are necessary in the future. Moreover, targeting AKT for inhibiting AKT and its AKT signaling shows the potential for anti-migration and anti-angiogenesis purposes for future application to withanolides. This particularly holds for investigating the anti-angiogenetic effects mediated by the oxidative stress and AKT signaling pathways in withanolide-based cancer therapy in the future.

Bisphenol-A alters hematopoiesis through EGFR/ERK signaling to induce myeloblastic condition in zebrafish model

Experimental evidence from the etiology of cancer studies suggests that a correlation between Bisphenol-A (BPA) exposure and alterations in hematopoiesis leads to blood cancer. In our study zebrafish were used to assess the lethality, developmental effect, embryonic apoptosis and changes in transcription factor of hematopoiesis through EGFR/ERK signaling pathways in response to BPA. The in silico interaction of EGFR and BPA was analysed by molecular dynamic simulation. According to our results, BPA induced a significant lethal effect in hatching retardation, reduction in heart rate and teratogenic effects on zebrafish embryos and larvae at three different concentrations 100, 500 and 2500 μg/L. The mortality of adult zebrafish exposed to the acute toxicity of BPA from 5 to 30 mg/L concentrations was determined for 96 h. The peripheral blood cells and vital organs such as kidney, liver and spleen from BPA exposed fish showed predominantly abnormal myeloid blast cells along with severe morphological changes in erythrocytes at sublethal concentration 245 μg/L. The BPA showed the highest binding affinity to zebrafish EGFR with a docking score of -7.5 kcal/mol with an RMSD of 3.0 nm during MD simulation. We found that EGFR/ERK overexpression leads to induce hematopoietic cell proliferation and impaired differentiation, which enhances the myeloid repopulating activity and the accumulation of immature myeloblast cells. BPA also caused a corresponding increase in expression of hematopoietic transcription factor c-MYB and RUNX-1 leading to polychromasia, poikilocytosis, acanthocytes and anisocytosis and promoted myeloblastosis by inhibiting GATA-1 expression. These morphological changes often resulted in the prior condition of acute myeloid leukemia (AML). Comprehensively, our data suggest that BPA can trigger the malignancy of AML cells by alteration of respective hematopoietic transcription factors via EGFR/ERK signaling in the zebrafish model.

Bacopaside-I Alleviates the Detrimental Effects of Acute Paraquat Intoxication in the Adult Zebrafish Brain

Paraquat (PQ), an environmental neurotoxicant, causes acute fatal poisoning upon accidental or intentional ingestion (suicidal cases) worldwide. To date, an effective remedy for PQ toxicity is not available. In this study, we have evaluated the therapeutic efficacy of Bacopaside-I (BS-I), an active compound found in the plant extract of Bacopa monnieri (Brahmi), against acute PQ intoxication using zebrafish as a model organism. Adult zebrafish were injected with a dose of either 30 mg/kg or 50 mg/kg PQ. PQ-intoxicated zebrafish showed an increased rate of mortality and oxidative imbalance in their brain. Also, the proliferation of neural cells in the adult zebrafish brain was inhibited. However, when BS-I pretreated zebrafish were intoxicated with PQ, the toxic effects of PQ were ameliorated. PQ treatment also affected the expression of particular genes concerned with the apoptosis and dopamine signaling, which was not altered by BS-I administration. Our results highlight the efficiency of BS-I as a novel therapeutic agent for PQ intoxication. It further compels us to search and evaluate the molecular mechanisms targeted by BS-I to develop a potent therapy for acute PQ intoxication.

Bixafen causes cardiac toxicity in zebrafish (Danio rerio) embryos

Bixafen (BIX) is a succinate dehydrogenase inhibitor (SDHI)-class fungicide that is used to control crop diseases. However, data on the toxicity of BIX to zebrafish are limited. Here, zebrafish embryos were exposed to 0.1, 0.3, and 0.9 μM BIX. After BIX exposure, zebrafish embryos exhibited cardiac dysplasia and dysfunction, including pericardial edema, reduced heart rate, and drastically decreased erythrocytes in the cardiac area; the severity of these negative effects increased with BIX concentration and the duration of BIX exposure. In addition, the transcription levels of erythropoiesis-related genes decreased significantly in BIX-treated embryos, as compared to untreated control embryos. Similarly, compared with the control, key genes responsible for cardiac development (myh6, nkx2.5, and myh7) also exhibited dysregulated expression patterns in response to BIX treatment, suggesting that BIX might specifically affect cardiac development. Finally, cell apoptosis was induced in embryos after BIX treatment. In combination, our results suggested that exposure to BIX induced cardiac toxicity in zebrafish. These data will be valuable for future evaluations of the environmental risks of BIX.

Strategies of cellular energy allocation to cope with paraquat-induced oxidative stress: Chironomids vs Planarians and the importance of using different species

Paraquat (PQ) is still used in several countries worldwide as an herbicide for weed control in agricultural production, ponds, reservoirs and irrigation canals. Thus, PQ is frequently found in surface water systems and is potentially toxic to aquatic organisms, since it can cause mitochondrial dysfunction altering in the redox state of cells. This study aimed to investigate the chronic effects of PQ to Chironomus riparius and Girardia tigrina, and compare their physiological strategies to cope with environmental stress. The mean emergence time was the most sensitive endpoint for Chironomids, with the lowest observed effect concentrations (LOEC) being 0.02 for males and 0.1 mg PQ L^-1 for females. Moreover, PQ reduced the body weight of male and female imagoes, with LOECs of 0.5 and 2.5 mg PQ L^-1, respectively. Paraquat also decreased the respiration rate (LOEC = 2.5 mg PQ L^-1) and total glutathione (tGSH) content (LOEC = 0.5 mg PQ L^-1). Thus, the aerobic production of energy was not affected and allowed chironomids to cope with oxidative stress induced by PQ, but with consequent physiological costs in terms of development rates and weight of adults. In planarians, PQ decreased the locomotion and feeding activity, and delayed photoreceptor regeneration (LOECs = 2.5 mg PQ L^-1 for all endpoints). Despite increased aerobic energy production (LOEC = 0.5 mg PQ L^-1), planarians were not able to cope with oxidative stress induced by the highest PQ concentrations, since lipid peroxidation levels were significantly increased (LOEC = 2.5 mg PQ L^-1) concomitantly with a significant decrease of tGSH (LOEC = 2.5 mg PQ L^-1). These results showed that planarians were unable to cope with oxidative stress induced by PQ with consequent impairments of behavior and regeneration despite an increased aerobic energy production.

Chemical and Genetic Zebrafish Models to Define Mechanisms of and Treatments for Dopaminergic Neurodegeneration

The zebrafish (Danio rerio) is routinely used in biological studies as a vertebrate model system that provides unique strengths allowing applications in studies of neurodevelopmental and neurodegenerative diseases. One specific advantage is that the neurotransmitter systems are highly conserved throughout vertebrate evolution, including between zebrafish and humans. Disruption of the dopaminergic signaling pathway is linked to multiple neurological disorders. One of the most common is Parkinson’s disease, a neurodegenerative disease associated with the loss of dopaminergic neurons, among other neuropathological characteristics. In this review, the development of the zebrafish’s dopaminergic system, focusing on genetic control of the dopaminergic system, is detailed. Second, neurotoxicant models used to study dopaminergic neuronal loss, including 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), the pesticides paraquat and rotenone, and 6-hydroxydopamine (6-OHDA), are described. Next, zebrafish genetic knockdown models of dj1, pink1, and prkn established for investigating mechanisms of Parkinson’s disease are discussed. Chemical modulators of the dopaminergic system are also highlighted to showcase the applicability of the zebrafish to identify mechanisms and treatments for neurodegenerative diseases such as Parkinson’s disease associated with the dopaminergic system.

Harnessing Macrophages for Controlled-Release Drug Delivery: Lessons From Microbes

With the effectiveness of therapeutic agents ever decreasing and the increased incidence of multi-drug resistant pathogens, there is a clear need for administration of more potent, potentially more toxic, drugs. Alternatively, biopharmaceuticals may hold potential but require specialized protection from premature in vivo degradation. Thus, a paralleled need for specialized drug delivery systems has arisen. Although cell-mediated drug delivery is not a completely novel concept, the few applications described to date are not yet ready for in vivo application, for various reasons such as drug-induced carrier cell death, limited control over the site and timing of drug release and/or drug degradation by the host immune system. Here, we present our hypothesis for a new drug delivery system, which aims to negate these limitations. We propose transport of nanoparticle-encapsulated drugs inside autologous macrophages polarized to M1 phenotype for high mobility and treated to induce transient phagosome maturation arrest. In addition, we propose a significant shift of existing paradigms in the study of host-microbe interactions, in order to study microbial host immune evasion and dissemination patterns for their therapeutic utilization in the context of drug delivery. We describe a system in which microbial strategies may be adopted to facilitate absolute control over drug delivery, and without sacrificing the host carrier cells. We provide a comprehensive summary of the lessons we can learn from microbes in the context of drug delivery and discuss their feasibility for in vivo therapeutic application. We then describe our proposed "synthetic microbe drug delivery system" in detail. In our opinion, this multidisciplinary approach may hold the solution to effective, controlled drug delivery.

Effects of paraquat on IL-6 and TNF-α in macrophages

Effects of paraquat (PQ) on interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in macrophages were investigated. Different concentrations of PQ were added to mouse macrophage RAW264.7 for culture. According to different concentrations of PQ, mice were divided into micro concentration (0.01 mmol/l), low concentration (0.1 mmol/l), medium concentration (1 mmol/l), high concentration (10 mmol/l), and control groups without PQ. Trypan blue solution was used for detecting cell viability, a microplate reader for detecting the fluorescence intensity of reactive oxygen species (ROS), ELISA for detecting the expression levels of IL-6 and TNF-α. The medium concentration and the high concentration groups had significantly lower cell viability than the other three groups (P<0.050). The high concentration group had significantly lower cell viability than the medium concentration group (P<0.050). At 1, 4 and 8 h, respectively, the medium and the high concentration groups had significantly higher ROS fluorescence intensity than the other three groups (P<0.050). The high concentration group had significantly higher ROS fluorescence intensity than the medium concentration group (P<0.050). There were significant differences in the expression levels of IL-6 and TNF-α at the 1st, 4th and 8th hour among the five groups (P<0.050). In the micro, the low, the medium and high concentration groups, the expression levels of IL-6 and TNF-α were the lowest at 1 h and the highest at 8 h, which were higher at 4 h than those at 1 h (P<0.050). PQ at a concentration of 1 mmol/l can produce toxicity to macrophages, and greatly increase the ROS fluorescence intensity, the expression levels of IL-6 and TNF-α. PQ poisoning is expected to be treated though IL-6 and TNF-α in the future.

An automated quantitative image analysis pipeline of in vivo oxidative stress and macrophage kinetics

Macrophage behavior is of great interest in response to tissue injury and promotion of regeneration. With increasing numbers of zebrafish reporter-based assays, new capabilities now exist to characterize macrophage migration, and their responses to biochemical cues, such as reactive oxygen species. Real time detection of macrophage behavior in response to oxidative stress using quantitative measures is currently beyond the scope of commercially available software solutions, presenting a gap in understanding macrophage behavior. To address this gap, we developed an image analysis pipeline solution to provide real time quantitative measures of cellular kinetics and reactive oxygen species content in vivo after tissue injury. This approach, termed Zirmi, differs from current software solutions that may only provide qualitative, single image analysis, or cell tracking solutions. Zirmi is equipped with user-defined algorithm parameters to customize quantitative data measures with visualization checks for an analysis pipeline of time-based changes. Moreover, this pipeline leverages open-source PhagoSight, as an automated keyhole cell tracking solution, to avoid parallel developments and build upon readily available tools. This approach demonstrated standardized space- and time-based quantitative measures of (1) fluorescent probe based oxidative stress and (2) macrophage recruitment kinetic based changes after tissue injury. Zirmi image analysis pipeline performed at execution speeds up to 10-times faster than manual image-based approaches. Automated segmentation methods were comparable to manual methods with a DICE Similarity coefficient > 0.70. Zirmi provides an open-source, quantitative, and non-generic image analysis pipeline. This strategy complements current wide-spread zebrafish strategies, for automated standardizations of analysis and data measures.

Joint toxicity on hepatic detoxication enzymes in goldfish (Carassius auratus) exposed to binary mixtures of lead and paraquat

Compared to single exposure, chemical mixtures might induce joint toxicity including additive, synergistic and antagonistic effects on both organisms and environment. Owing to the specific toxicity of oxidative stress and binding to proteins, lead (Pb) is generally recognized a non-essential and threatening heavy metal to animals and human. Paraquat (PQ) is a widely used herbicide in agriculture and can trigger oxidative stress as well as Pb. Little information was available about joint effects of the two chemicals on toxicological responses in organisms, especially in fish. In our present study, goldfish (Carassius auratus) were randomly exposed to single and combined experiments with different concentrations of Pb and PQ for 28 days. Activities of four enzyme biomarkers in liver, ethoxyresorufin-O-deethylase (EROD), 7-benzyloxy-4-trifluoromethyl-coumarin-O-debenzyloxylase (BFCOD), glutathione-S-transferase (GST) and UDP-glucuronosyltransferase (UGT) were evaluated in each experimental group on day 14 and 28. The results showed four enzyme levels were markedly reduced with the increase of concentrations in mixtures and prolonged exposure. The inhibitory EROD and BFCOD activities were not significantly changed in goldfish following PQ-treated groups with or without 0.5 mg/L Pb, which indicated PQ has more inhibitory toxicity on CYP450 enzymes than Pb in co-exposure groups. However, the reduced values of GST were observed only in the combinations containing high doses of Pb or PQ during experimental periods. Although the responses of UGT activity were similar to GST on 14th day, all combinations of Pb and PQ generated stronger inhibitions on UGT activities compared to individual Pb and PQ-treated group. These results suggested that combined exposure of Pb and PQ have more inhibitory toxicity on phase I enzymes than phase II enzymes.

High-dose acute exposure of paraquat induces injuries of swim bladder, gastrointestinal tract and liver via neutrophil-mediated ROS in zebrafish and their relevance for human health risk assessment

The exact toxicological mechanisms of paraquat (PQ) poisoning are not entirely clear, especially on the high-level acute exposure. To assess the health risk of PQ, especially to suicidal individuals, accidental ingestion eaters, occupational groups, and special multitude, firstly we explored the acute toxic effect and the possible mechanisms of high-level exposure of PQ using zebrafish. The mainly target organs of PQ were swim bladder which is the homolog of the mammalian lung, followed by gastrointestinal tract and liver. Morphological malformations which were further defined by histopathologic examination include smaller size, fibrosis and inflammatory cell invasion for swim bladder; irregularly arranged or dissolved epithelial folds, loss of villous architecture, and ecclasis of mucosal cells in a smaller lumen for gastrointestinal tract; as well as smaller size, degeneration, fibrous proliferation, atrophy for liver. In addition, PQ enhanced leukocyte recruitment (neutrophil migrated first, followed by macrophage) into swim bladder and induced ROS which can be scavenged by glutathione. Moreover, qRT-PCR results showed that PQ increased the expression level of genes involved in the inflammatory response, such as L-1β, IL-6, IL-8, TNF-α, TNF-β, IFN-1, TGF-β, and NF-kB. For the first time, our results demonstrated that acute exposure of PQ induced pulmonary toxicity which was followed by gastrointestinal and hepatic toxicity via neutrophil-mediated ROS in zebrafish. In summary, these findings generated here will contribute to our better understanding of characteristics of PQ acute poisoning and can provide valuable information on better PQ poisoning treatments, occupational disease prevention, and providing theoretical foundation for risk management measures.

Paraquat initially damages cochlear support cells leading to anoikis-like hair cell death

Paraquat (PQ), one of the most widely used herbicides, is extremely dangerous because it generates the highly toxic superoxide radical. When paraquat was applied to cochlear organotypic cultures, it not only damaged the outer hair cells (OHCs) and inner hair cells (IHCs), but also caused dislocation of the hair cell rows. We hypothesized that the dislocation arose from damage to the support cells (SCs) that anchors hair cells within the epithelium. To test this hypothesis, rat postnatal cochlear cultures were treated with PQ. Shortly after PQ treatment, the rows of OHCs separated from one another and migrated radially away from IHCs suggesting loss of cell-cell adhesion that hold the hair cells in proper alignment. Hair cells dislocation was associated with extensive loss of SCs in the organ of Corti, loss of tympanic border cells (TBCs) beneath the basilar membrane, the early appearance of superoxide staining and caspase-8 labeling in SCs below the OHCs and disintegration of E-cadherin and β-catenin in the organ of Corti. Damage to the TBCs and SCs occurred prior to loss of OHC or IHC loss suggesting a form of detachment-induced apoptosis referred to as anoikis.

Zebrafish as an Animal Model for Drug Discovery in Parkinson's Disease and Other Movement Disorders: A Systematic Review

Movement disorders can be primarily divided into hypokinetic and hyperkinetic. Most of the hypokinetic syndromes are associated with the neurodegenerative disorder Parkinson’s disease (PD). By contrast, hyperkinetic syndromes encompass a broader array of diseases, including dystonia, essential tremor, or Huntington’s disease. The discovery of effective therapies for these disorders has been challenging and has also involved the development and characterization of accurate animal models for the screening of new drugs. Zebrafish constitutes an alternative vertebrate model for the study of movement disorders. The neuronal circuitries involved in movement in zebrafish are well characterized, and most of the associated molecular mechanisms are highly conserved. Particularly, zebrafish models of PD have contributed to a better understanding of the role of several genes implicated in the disease. Furthermore, zebrafish is a vertebrate model particularly suited for large-scale drug screenings. The relatively small size of zebrafish, optical transparency, and lifecycle, are key characteristics that facilitate the study of multiple compounds at the same time. Several transgenic, knockdown, and mutant zebrafish lines have been generated and characterized. Therefore, it is central to critically analyze these zebrafish lines and understand their suitability as models of movement disorders. Here, we revise the pathogenic mechanisms, phenotypes, and responsiveness to pharmacotherapies of zebrafish lines of the most common movement disorders. A systematic review of the literature was conducted by including all studies reporting the characterization of zebrafish models of the movement disorders selected from five bibliographic databases. A total of 63 studies were analyzed, and the most relevant data within the scope of this review were gathered. The majority (62%) of the studies were focused in the characterization of zebrafish models of PD. Overall, the zebrafish models included display conserved biochemical and neurobehavioral features of the phenomenology in humans. Nevertheless, in light of what is known for all animal models available, the use of zebrafish as a model for drug discovery requires further optimization. Future technological developments alongside with a deeper understanding of the molecular bases of these disorders should enable the development of novel zebrafish lines that can prove useful for drug discovery for movement disorders.

Toxicological responses on cytochrome P450 and metabolic transferases in liver of goldfish (Carassius auratus) exposed to lead and paraquat

As the producer of reactive oxygen species (ROS), both lead (Pb) and paraquat (PQ) can generate serious oxidative stress in target organs which result in irreversible toxic effects on organisms. They can disturb the normal catalytic activities of many enzymes by means of different toxicity mechanism. The changed responses of enzymes are frequently used as the biomarkers for indicating the relationship between toxicological effects and exposure levels. In this work, goldfish was exposed to a series of test groups containing lead and paraquat in the range of 0.05-10mg/L, respectively. Four hepatic enzyme activities, including 7-ethoxyresorufinO-deethylase (EROD), 7-benzyloxy-4-trifluoromethyl-coumarin-O-debenzyloxylase (BFCOD), glutathione S-transferase (GST) and UDP-glucuronosyltransferase (UGT) were determined after 1, 7, 14, 28 days exposure. The results showed that the activities of EROD and BFCOD in fish were significantly inhibited in response to paraquat at all exposure levels during the whole experiment. Similarly, the inhibitory effects of lead exposure on BFCOD activity were found in our study, while different responses of lead on EROD were observed. There were no significant differences on EROD activity under lower concentrations of lead (less than 0.1mg/L) before 14 days until an obvious increase was occurred for the 0.5mg/L lead treatment group at day 14. Furthermore, lead showed stronger inhibition on GST activity than paraquat when the concentrations of the two toxicants were more than 0.5mg/L. However, the similar dose and time-dependent manners of UGT activity were found under lead and paraquat exposure. Our results indicated that higher exposure levels and longer accumulations caused inhibitory effects on the four enzymes regardless of lead or paraquat stress. In addition, the responses of phase I enzymes were more sensitive than that of phase II enzymes and they may be served as the acceptable biomarkers for evaluating the toxicity effects of both lead and paraquat.

Hepatotoxicity of paraquat on common carp (Cyprinus carpio L.)

Paraquat (PQ) is a nonselective herbicide that is used worldwide and has been demonstrated to be a high risk to aquatic organisms. However, relatively little is known about the mechanisms on detoxification and hepatotoxicity of PQ in fish. In the present study, a sub-acute toxicity test of PQ exposure on common carp at 1.596 and 3.192mgL^-1 for 7d was conducted under laboratory conditions. The results showed that the transcriptional levels of cytochrome P450s (CYPs), such as CYP1A, CYP2K, and CYP3A138, GSTα and GSTpi, and export pump gene MDR1, as well as the erythromycin-N-demethylase (ERND) activity were generally up-regulated by PQ exposure for 7d, indicating that these genes or enzymes are potentially involved in the detoxification of PQ in the fish liver. Further research showed that PQ exposure significantly increased the levels of HSP70, HSP90, NOS, and MDA; promoted expression of pro-inflammatory cytokines, including IL-6 and IL-8; altered the levels of anti-inflammatory cytokines IL-10 and TGF-β, and generally reduced the levels of T-AOC, SOD, CAT, and GSH. In addition, we also found that caspase-3, caspase-8, and caspase-9 were significantly activated in the fish liver following PQ exposure. In brief, the present study showed that PQ exposure induced fish liver injury by destabilizing the metabolism of fish, inhibiting antioxidant enzyme activity, elevating lipid peroxidation, and promoting an immune inflammatory response and apoptosis. The present study further enriches and perfects the mechanism theory of PQ hepatotoxicity to fish, which may be valuable for the risk assessment of PQ and human health protection.

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

The dipyridyl herbicide paraquat induces oxidative stress in cells and is implicated in adult neurodegenerative diseases. However, less is known about paraquat toxicity in early stages of vertebrate development. To address this gap, zebrafish (Danio rerio) embryos were exposed to 1, 10 and 100 μM paraquat for 96 h. Paraquat did not induce significant mortality nor deformity in embryos and larvae, but it did accelerate time to hatch. To evaluate whether mitochondrial respiration was related to earlier hatch times, oxygen consumption rate was measured in whole embryos. Maximal respiration of embryos exposed to 100 μM paraquat for 24 h was reduced by more than 70%, suggesting that paraquat negatively impacts mitochondrial bioenergetics in early development. Based upon this evidence for mitochondrial dysfunction, transcriptional responses of oxidative stress- and apoptosis-related genes were measured. Fish exposed to 1 μM paraquat showed higher expression levels of superoxide dismutase 2, heat shock protein 70, Bcl-2-associated X protein, and B-cell CLL/lymphoma 2a compared to control fish. No differences among groups were detected in larvae exposed to 10 and 100 μM paraquat, suggesting a non-monotonic response. We also measured endpoints related to larval behavior and dopaminergic signaling as paraquat is associated with degeneration of dopamine neurons. Locomotor activity was stimulated with 100 μM paraquat and dopamine transporter and dopamine receptor 3 mRNA levels were increased in larvae exposed to 1 μM paraquat, interpreted to be a compensatory response at lower concentrations. This study improves mechanistic understanding into the toxic actions of paraquat on early developmental stages.

Eukaryotic translation initiation factor 2 subunit α (eIF2α) inhibitor salubrinal attenuates paraquat-induced human lung epithelial-like A549 cell apoptosis by regulating the PERK-eIF2α signaling pathway

Paraquat (PQ), as one of the most widely used herbicides in the world, can cause severe lung damage in humans and animals. This study investigated the underlying molecular mechanism of PQ-induced lung cell damage and the protective role of salubrinal. Human lung epithelial-like A549 cells were treated with PQ for 24h and were pre-incubated with salubrinal for 2h, followed by 500μM of PQ treatment. Silencing eIF2α gene of the A549 cells with siRNA interference method was conducted. Cell morphology, cell viability, apoptosis and caspase-3 activity were assessed by different assays accordingly thereafter. The expression of PERK, p-PERK, ATF6, c-ATF6, IRE1α, p-IRE1α, CHOP, GRP78, p-eIF2α and β-actin was assayed by western blot. The data showed that PQ significantly reduced A549 cell viability, changed cell morphology, induced cell apoptosis and significantly upregulated the levels of GRP78, CHOP, p-PERK, c-ATF6 and p-IRE1α. However, 30μM salubrinal could attenuate the effects of PQ on damages to A549 cells through upregulating p-eIF2α. In contrast, knocking down eIF2α gene inhabited the effects of salubrinal. These results suggest that PQ-induced A549 cell apoptosis involved endoplasmic reticulum (ER) stress, specially the PERK-eIF2α pathway. Salubrinal attenuated A549 cells from PQ-induced damages through regulation of the PERK-eIF2α signaling.