Exposure to Hg2+ and Pb2+ changes NTPDase and ecto-5'-nucleotidase activities in central nervous system of zebrafish (Danio rerio)

Effect of sulfate on the osmoregulatory and physio-biochemical responses of GIFT (Oreochromis niloticus) juveniles reared in potassium-deficient medium saline waters

The inland saline waters were continuously observed to have low potassium concentrations compared to their seawater counterpart of the same salinity. We hypothesize that the toxic effect of sulfate may manifest in low potassium saline (LPSW) waters compared to brackish water of the same salinity. Thus, LC50 trials were performed in GIFT (genetically improved farmed tilapia) fry (0.5 ± 0.02 g) to determine the acute sulfate toxicity in freshwater (FW, 0.5 g L-1), artificial seawater (ASW, 10 g L-1), and LPSW (10 g L-1). The median lethal concentrations (96h LC50) of sulfate ion in FW, LPSW, and ASW for the GIFT were 5.30 g L-1, 2.56 g L-1, and 2.98 g L-1, respectively. A second experiment was conducted for 21 days, exposing fish to a sub-lethal level of sulfate ion (SO42-) concentration (1000 mg L-1, one-fifth of FW LC50) with different types of waters (FW, freshwater, 0.5 g L-1; ASW, artificial seawater, 10 g L-1; LPSW, low potassium saline water, 10 g L-1) with and without sulfate inclusion to constitute the treatments as follows, (FW, FW + SO4, ASW, ASW + SO4, LPSW, LPSW + SO4). The effect of sulfate on GIFT reared in sulfate-rich potassium-deficient medium saline water was evaluated by focusing on the hematological adjustments, stress-induced oxidative damage, and osmoregulatory imbalances. The survival was not altered due to the sulfate concentration and K+ deficiency; however, there were significant changes in branchial NKA (Na+/K+-ATPase) activity and osmolality. The increase in NKA was highest in LPSW treatment, suggesting that internal ionic imbalance was triggered due to an interactive effect of sulfate and K+ deficiency. The cortisol levels showed a pronounced increase due to sulfate inclusion irrespective of K+ deficiency. The antioxidant enzymes, i.e., SOD (superoxide dismutase), catalase, GST (glutathione-S-transferase), and GPX (glutathione peroxidase), reflected a similar pattern of increment in the gills and liver of the LPSW + SO4 groups, suggesting a poor antioxidant status of the exposed group. The hepatic peroxidation status, i.e. TBARS (thiobarbituric acid reactive substances), and the peroxide values were enhanced due to both K+ deficiency and sulfate inclusion, suggesting a possible lipid peroxidation in the liver due to handling the excess sulfate anion concentration. The hematological parameters, including haemoglobin, total erythrocyte count, and hematocrit level, reduced significantly in the LPSW + SO4 group, indicating a reduced blood oxygen capacity due to the sulfate exposure and water potassium deficiency. The hepatic acetylcholine esterase activity was suppressed in all the treatments with sulfate inclusion, while the highest suppression was observed in the LPSW + SO4 group. Thus, it is concluded that sulfate-induced physiological imbalances manifest more in potassium-deficient water, indicating that environmental sulfate is more detrimental to inland saline water than freshwater or brackish water of the same salinity.

Unveiling the molecular mechanisms and developmental consequences of mercury (Hg) toxicity in zebrafish embryo-larvae: A comprehensive approach

Mercury (Hg) is a global contaminant affecting aquatic ecosystems' health. Chronic exposure to Hg has shown that the normal development of zebrafish embryo-larvae is affected. However, the molecular mechanisms behind the toxicity of Hg on fish embryonic development are still poorly understood. This work aimed to investigate the effects of Hg exposure on zebrafish embryo-larvae using a combined approach at individual (mortality, embryo development and locomotor behavior) and biochemical (neurotoxicity and oxidative stress enzymatic activities and protein phosphatase expression) levels. The Fish Embryo Toxicity assay followed the Organization for Economic Cooperation and Development Guideline 236 and used a concentration range between 13 and 401 μg Hg/L. Lethal and developmental endpoints were examined at 24, 48, 72 and 96 hpf. Biochemical markers, including Acetylcholinesterase (AChE), Catalase (CAT), Glutathione Reductase (GR), and Glutathione-S-Transferase (GST) activities and, for the first time, the expression of the protein phosphatase 1 gamma (PP1γ) was assessed after 24, 48, 72 and 96 h of exposure to 10 and 100 μg Hg/L. The behavioral effects of a sublethal range of Hg (from 0.8 to 13 μg Hg/L) were assessed using an automated video tracking system at 120 hpf. Several developmental abnormalities on zebrafish embryos and larvae, including pericardial edema, spin and tail deformities and reduced rate of consumption of the yolk sac, were found after exposure to Hg (LC50 at 96 hpf of 139 μg Hg/L) with EC50 values for total malformations ranging from 22 to 264 μg Hg/L. After 96 hpf, no significant effects were observed in the CAT and GR activities. However, an increase in the GST activity in a concentration and time-dependent manner was found, denoting possible stress-related adaptation of zebrafish embryos to deleterious effects of Hg exposure. The AchE activity showed a response pattern in line with the behavioral responses. At the lowest concentration tested, no significant effects were found for the AChE activity, whereas a decrease in AChE activity was observed at 100 μg Hg/L, suggesting that exposure to Hg induced neurotoxic effects in zebrafish embryos which in turn may explain the lack of equilibrium found in this study (EC50 at 96 hpf of 83 μg Hg/L). Moreover, a decrease in the PP1γ expression was found after 96 h of exposure to 10 and 100 μg Hg/L. Thus, we suggest that Hg may be an inhibitor of PP1γ in zebrafish embryos-larvae and thus, along with the alterations in the enzymatic activity of GST, explain some of the developmental malformations observed, as well as the lack of equilibrium. Hence, in this study, we propose the use of PP1 expression, in combination with apical and biochemical endpoints, as a precursor for assessing Hg's toxic mechanism on embryonic development.

Zebrafish as a Potential Model for Neurodegenerative Diseases: A Focus on Toxic Metals Implications

In the last century, industrial activities increased and caused multiple health problems for humans and animals. At this moment, heavy metals are considered the most harmful substances for their effects on organisms and humans. The impact of these toxic metals, which have no biological role, poses a considerable threat and is associated with several health problems. Heavy metals can interfere with metabolic processes and can sometimes act as pseudo-elements. The zebrafish is an animal model progressively used to expose the toxic effects of diverse compounds and to find treatments for different devastating diseases that human beings are currently facing. This review aims to analyse and discuss the value of zebrafish as animal models used in neurological conditions, such as Alzheimer's disease (AD), and Parkinson's disease (PD), particularly in terms of the benefits of animal models and the limitations that exist.

Evaluation of the hair cell regeneration and claudin b and phoenix gene expression during exposure to low concentrations of cadmium and zinc in early developing zebrafish larvae

Zebrafish possess hair cells on the body surface similar to that of mammals inner hear, in particular in the neuromasts, and due to its ability in regenerating damaged hair cells, is regularly used as a powerful animal model to study in vivo cytotoxicity. Among the factors leading to hair cell disruption, metal ions are of particular concern since they are important environmental pollutants. To date, several studies on zebrafish hair cell regeneration after metal exposure exist, while no data on regeneration during continuous metal exposure are available. In the present study, neuromast hair cell disruption and regeneration were assessed in zebrafish larvae for the first time during zinc (Zn) and cadmium (Cd) continuous exposure and a visual and molecular approach was adopted. Fluorescent vital dye DASPEI was used to assess hair cell regeneration and the gene expression of claudin b (cldnb) and phoenix (pho), was analyzed. Metallotionein-2 (mt2) gene expression was used as standard molecular marker of metal toxicity and confirmed the higher toxicity of Cd compared to Zn. In addition, Cd caused a delay in hair cell regeneration compared to Zn. Molecular analysis showed cldnb gene expression increased in relation to the metal concentrations used, confirming the involvement of this gene in hair cell regeneration. On the contrary, a dramatic decrease of pho gene expression was observed in Cd exposed groups, suggesting a negative impact of Cd on pho expression, thus negatively interfering with hair cell regeneration in zebrafish larvae exposed to this metal.

Zebrafish as an Emerging Model System in the Global South: Two Decades of Research in Brazil

The zebrafish (Danio rerio) is an emerging model system in several research areas worldwide, especially in the Global South. In this context, the present study revised the historical use and trends of zebrafish as experimental models in Brazil. The data concerning the bibliometric parameters, research areas, geographic distribution, experimental design, zebrafish strain, and reporter lines, as well as recent advances were revised. In addition, the comparative trends of Brazilian and global research were discussed. Revised data showed the rapid growth of Brazilian scientific production using zebrafish as a model, especially in three main research areas (Neuroscience &and Behavior, Pharmacology and Toxicology, and Environment/Ecology). Studies were conducted in 19 Brazilian states (70.37%), confirming the wide geographic distribution and importance of zebrafish research. Results indicated that research related to toxicological approaches are widespread in Global South countries such as Brazil. Studies were performed mainly using in vivo tests (89.58%) with adult fish (59.75%) and embryos (30.67%). Moreover, significant research gaps and recommendations for future research are presented. The present study shows that the zebrafish is a suitable vertebrate model system in the Global South.

Soyuretox, an Intrinsically Disordered Polypeptide Derived from Soybean (Glycine Max) Ubiquitous Urease with Potential Use as a Biopesticide

Ureases from different biological sources display non-ureolytic properties that contribute to plant defense, in addition to their classical enzymatic urea hydrolysis. Antifungal and entomotoxic effects were demonstrated for Jaburetox, an intrinsically disordered polypeptide derived from jack bean (Canavalia ensiformis) urease. Here we describe the properties of Soyuretox, a polypeptide derived from soybean (Glycine max) ubiquitous urease. Soyuretox was fungitoxic to Candida albicans, leading to the production of reactive oxygen species. Soyuretox further induced aggregation of Rhodnius prolixus hemocytes, indicating an interference on the insect immune response. No relevant toxicity of Soyuretox to zebrafish larvae was observed. These data suggest the presence of antifungal and entomotoxic portions of the amino acid sequences encompassing both Soyuretox and Jaburetox, despite their small sequence identity. Nuclear Magnetic Resonance (NMR) and circular dichroism (CD) spectroscopic data revealed that Soyuretox, in analogy with Jaburetox, possesses an intrinsic and largely disordered nature. Some folding is observed upon interaction of Soyuretox with sodium dodecyl sulfate (SDS) micelles, taken here as models for membranes. This observation suggests the possibility for this protein to modify its secondary structure upon interaction with the cells of the affected organisms, leading to alterations of membrane integrity. Altogether, Soyuretox can be considered a promising biopesticide for use in plant protection.

Metabolite tracking to elucidate the effects of environmental pollutants

The purpose of this study was to determine whether behavioral tests and metabolic profiling of organisms can be promising alternatives for assessing the health of aquatic systems. Water samples from four potential pollution sources in South Korea were collected for toxicity evaluation. First, conventional acute toxicity test in Daphnia magna and behavioral test in zebrafish was conducted to assess water quality. Second, metabolomic analysis was performed on zebrafish exposed to water samples and on environmental fish collected from the same source. Acute toxicity test in D. magna showed that none of the water samples exerted significant adverse effects. However, activity of zebrafish larvae exposed to samples from the zinc smelter (ZS) and industrial complex (IND) sites decreased compared to those exposed to samples from the reference site (RS). Metabolomic analysis using the Manhattan plot and Partial Least Square (PLS)/Orthogonal PLS Discriminant Analysis (OPLS-DA) showed differences in metabolic profiles between RS and ZS, and between IND and abandoned mine site (M). Interestingly, applying the same metabolomic analysis to environmental fish revealed patterns similar to those for zebrafish, despite the uncontrollable variables involved in environmental sampling. This study shows that metabolomics is a promising tool in assessing the health of aquatic environments.

Diphenyl diselenide dietary supplementation protects against methylmercury-chloride-induced immunotoxicity in the head kidney and spleen of grass carp (Ctenopharyngodon idella) via regulation of purinergic signaling and the NLRP3 inflammasome

This study aimed to evaluate whether dietary supplementation with diphenyl diselenide (Ph₂Se₂) would prevent the impaired immune and inflammatory responses elicited by methylmercury chloride (CH₃HgCl) via protective effects on purinergic signaling in fish immune organs. Tissue and lymphocytic nucleoside triphosphate diphosphohydrolase (NTPDase) activity for adenosine triphosphate (ATP) and adenosine diphosphate (ADP) was downregulated in the head kidney and spleen of grass carp (Ctenopharyngodon idella) exposed to CH₃HgCl. Concomitantly, adenosine deaminase (ADA) activity was upregulated. Further, nucleotide-binding oligomerization domain-like receptor (NLRP3) inflammasome gene expression was upregulated in the spleen and head kidney of CH₃HgCl-exposed grass carp. Dietary supplementation with Ph₂Se₂ ameliorated these CH₃HgCl-mediated alterations on purinergic enzymes, and their activities returned to baseline levels (except NTPDase activity for ADP). Based on these results, purinergic signaling in immune organs and lymphocytes can be considered a pathway linked to pro-inflammatory effects during exposure to environmental CH₃HgCl concentrations, which may contribute to mortality of the affected fish. Since dietary supplementation with 3 mg Ph₂Se₂/kg in the feed prevented the CH₃HgCl-induced alterations, it can be considered a potential suitable treatment to prevent impaired immune and inflammatory responses caused by Hg.

Toxic effects of lead exposure on bioaccumulation, oxidative stress, neurotoxicity, and immune responses in fish: A review

Lead (Pb) is a highly toxic metal in aquatic environments. Fish are at the top of the food chain in most aquatic environments, and are the most susceptible to the toxic effects of Pb exposure. In addition, fish are one of the most abundant vertebrates, and they can directly affect humans through food intake; therefore, fish can be used to assess the extent of environmental pollution in an aquatic environment. Pb-induced toxicity in fish exposed to toxicants is primarily induced by bioaccumulation in specific tissues, and the accumulation mechanisms vary depending on water habitat (freshwater or seawater) and pathway (waterborne or dietary exposure). Pb accumulation in fish tissues causes oxidative stress due to excessive ROS production. Oxidative stress by Pb exposure induces synaptic damage and neurotransmitter malfunction in fish as neurotoxicity. Moreover, Pb exposure influences immune responses in fish as an immune-toxicant. Therefore, the purpose of this review was to examine the various toxic effects of Pb exposure, including bioaccumulation, oxidative stress, neurotoxicity, and immune responses, and to identify indicators to evaluate the extent of Pb toxicity by based on the level of Pb exposure.

Bioaccumulation, cytotoxicity and oxidative stress of the acute exposure selenium in Oreochromis mossambicus

Selenium (Se) is an essential trace-element that becomes toxic when present at high concentrations for aquatic organisms. The knowledge about the mechanism of Se toxicity in freshwater ecosystem is still poorly studied. Thus the aim of the present study was to assess the impact of environmentally relevant concentrations of Se toxicity: 5, 10, 25, 50 and 100 µg/L or water only (control) for periods of 96 hour (h) to test for Se accumulation (gill, liver and brain), its effects on enzymatic and non-enzymatic antioxidant defenses (gill and liver), oxidative stress effects on lipid, protein (gill and liver), DNA (liver) and inhibition of AchE (brain) activity were measured in Mozambique tilapia, Oreochromis mossambicus. Our result showed that Se accumulation was observed in the gill, liver and brain tissues of fish exposed to different concentrations and accumulation varied upon different tissues. Enzymatic (SOD, CAT, GPx and GST) and non-enzymatic (GSH and MT) antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione-s-transferase (GST) were significantly increased after 96 h exposure of higher concentrations Se in the gill and liver tissue with the exception of GST activity was significantly inhibited in liver after 96 h exposure of higher concentrations of Se. In contrast, catalase (CAT) activities were inhibited for both tissues of Se exposure at 96 h. Reduced glutathione (GSH) and Metallothionein (MT) levels were increased in the gill and liver tissues after exposure to Se for 96 h. We also observed that Se affected antioxidant defense, increasing oxidative stress indicator of lipid peroxidation (LPO) and protein carbonyl (PCO) in gill and liver tissues of fish exposed to Se for 96 h at the concentration dependent manner. Increased DNA damage scores observed in liver tissue of fish exposed to Se for concentrations dependent manner, indicating potential of Se on fish. We also observed inhibition of acetylcholine esterase (AchE) activity in brain tissue of fish exposed to Se for higher concentrations. The changes in these parameters can be used as suitable biomarkers for monitoring the toxicity of Se in the aquatic environment.

Zinc Chloride Exposure Inhibits Brain Acetylcholine Levels, Produces Neurotoxic Signatures, and Diminishes Memory and Motor Activities in Adult Zebrafish

In this study, we evaluated the acute (24, 48, 72, and 96 h) and chronic (21 days) adverse effects induced by low doses (0.1, 0.5, 1, and 1.5 mg/L) of zinc chloride (ZnCl₂) exposure in adult zebrafish by using behavioral endpoints like three-dimensional (3D) locomotion, passive avoidance, aggression, circadian rhythm, and predator avoidance tests. Also, brain tissues were dissected and subjected to analysis of multiple parameters related to oxidative stress, antioxidant responses, superoxide dismutase (SOD), neurotoxicity, and neurotransmitters. The results showed that ZnCl₂-exposed fishes displayed decreased locomotor behavior and impaired short-term memory, which caused an Alzheimer’s Disease (AD)-like syndrome. In addition, low concentrations of ZnCl₂ induced amyloid beta (amyloid β) and phosphorylated Tau (p-Tau) protein levels in brains. In addition, significant induction in oxidative stress indices (reactive oxygen species (ROS) and malondialdehyde (MDA)), reduction in antioxidant defense system (glutathione (GSH), GSH peroxidase (GSH-Px) and SOD) and changes in neurotransmitters were observed at low concentrations of ZnCl₂. Neurotoxic effects of ZnCl₂ were observed with significant inhibition of acetylcholine (ACh) activity when the exposure dose was higher than 1 ppm. Furthermore, we found that zinc, metallothionein (MT), and cortisol levels in brain were elevated compared to the control group. A significantly negative correlation was observed between memory and acetylcholinesterase (AChE) activity. In summary, these findings revealed that exposure to ZnCl₂ affected the behavior profile of zebrafish, and induced neurotoxicity which may be associated with damaged brain areas related to memory. Moreover, our ZnCl₂-induced zebrafish model may have potential for AD-associated research in the future.

Fabrication of Composite Beads Based on Calcium Alginate and Tetraethylenepentamine-Functionalized MIL-101 for Adsorption of Pb(II) from Aqueous Solutions

In this work, a tetraethylenepentamine (TEPA)-grafted metal-organic framework material (MIL-101) was synthesized. The introduction of TEPA increased the abundance of functional groups on the MIL-101. As a powdery adsorbent, MIL-101-TEPA can be difficult to separate. In order to solve this problem, we combined MIL-101-TEPA with sodium alginate (SA) and injected the mixture into a CaCl₂ solution to solidify the powder into beads with a particle size of 3 mm. The easily recovered adsorbent was applied to the adsorption of Pb(II) from water. The structure and characterization of the adsorbent were investigated through scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). We also optimized the adsorption conditions. The results of the study showed that the adsorption process was chemisorptive and endothermic in nature. The maximum adsorption capacity of the composite beads was 558.6 mg/g. Meanwhile MIL-101-TEPA@CA showed good repeatable utilization.

Effects of short term lead exposure on gut microbiota and hepatic metabolism in adult zebrafish

Lead (Pb) is one of the most prevalent toxic, nonessential heavy metals that has been associated with a wide range of toxic effects in humans and environmental animals. Here, effects of short time exposure to 10 and 30 μg/L Pb on gut microbiota and hepatic metabolism were analyzed in adult male zebrafish. We observed that both 10 and 30 μg/L Pb increased the volume of mucus in the gut. At phylum level, the abundance of α-Proteobacteria decreased significantly and the abundance of Firmicutes increased significantly in the gut when treated with 30 μg/L Pb for 7 days. In addition, the 16S rRNA gene sequencing for V3-V4 region revealed a significant change in the richness and diversity of gut microbiota in 30 μg/L Pb exposed group. A more depth analysis, at the genus level, discovered that 52 gut microbes identified by operational taxonomic unit analysis were changed significantly in 30 μg/L Pb treated group. Based on GC/MS metabolomics analysis, a total of 41 metabolites were significantly altered in 30 μg/L Pb treatment group. These changed metabolites were mainly associated with the pathways of glucose and lipid metabolism, amino acid metabolism, nucleotide metabolism. In addition, we also confirmed that the transcription of some genes related to glycolysis and lipid metabolism, including Gk, Aco, Acc1, Fas, Apo and Dgat, decreased significantly in the liver of zebrafish when exposed to 30 μg/L Pb for 7 days. Our results observed that Pb could cause gut microbiota dysbiosis and hepatic metabolic disorder in zebrafish.

Neuromast hair cells retain the capacity of regeneration during heavy metal exposure

The neuromast is the morphological unit of the lateral line of fishes and is composed of a cluster of central sensory cells (hair cells) surrounded by support and mantle cells. Heavy metals exposure leads to disruption of hair cells within the neuromast. It is well known that the zebrafish has the ability to regenerate the hair cells after damage caused by toxicants. The process of regeneration depends on proliferation, differentiation and cellular migration of sensory and non-sensory progenitor cells. Therefore, our study was made in order to identify which cellular types are involved in the complex process of regeneration during heavy metals exposure. For this purpose, adult zebrafish were exposed to various heavy metals (Arsenic, cadmium and zinc) for 72h. After acute (24h) exposure, immunohistochemical localization of S100 (a specific marker for hair cells) in the neuromasts highlighted the hair cells loss. The immunoreaction for Sox2 (a specific marker for stem cells), at the same time, was observed in the support and mantle cells, after exposure to arsenic and cadmium, while only in the support cells after exposure to zinc. After chronic (72h) exposure the hair cells were regenerated, showing an immunoreaction for S100 protein. At the same exposure time to the three metals, a Sox2 immunoreaction was expressed in support and mantle cells. Our results showed for the first time the regenerative capacity of hair cells, not only after, but also during exposure to heavy metals, demonstrated by the presence of different stem cells that can diversify in hair cells.

Maternal and embryonic exposure to the water soluble fraction of crude oil or lead induces behavioral abnormalities in zebrafish (Danio rerio), and the mechanisms involved

The water-soluble fraction (WSF) of crude oil plays an important role in the toxicity of crude oil in aquatic environments. Heavy metals, such as lead (Pb) are also important environmental contaminants, which can reach aquatic systems via the effluents of industrial, urban and mining sources. In the present study, we investigated whether maternal and embryonic exposure to the WSF (5, 50 μg/L) or Pb (10, 100 μg/L) could induce behavioral abnormalities in zebrafish. Our results showed that maternal and embryonic exposure to the WSF (5, 50 μg/L) and Pb (10, 100 μg/L) induced swimming activity alterations in larval and juvenile zebrafish. In 15 days post-fertilization (dpf) larval zebrafish, the distance moved was significantly increased in the groups treated with the WSF (5, 50 μg/L), but the angular velocity and turn angle were decreased after treatment with the WSF (5, 50 μg/L) or Pb (10, 100 μg/L). In 30 dpf juvenile zebrafish, the distance moved was markedly decreased in both groups treated with the WSF (5, 50 μg/L) and the Pb (10 μg/L) group, but the percentage of zebrafish moving up and the inter-fish distance of two juvenile fish were increased after treatment with the WSF (5, 50 μg/L) or Pb (10, 100 μg/L). Maternal and embryonic exposure to the WSF (5, 50 μg/L) or Pb (10, 100 μg/L) likely impaired the brain neurons growth and induced behavioral abnormalities in the larval and juvenile zebrafish. Furthermore, the expressions of some key genes, which were associated with calcium channels, behavioral development or the metabolism of environmental contaminants, were changed.

Chronic Dietary Selenomethionine Exposure Induces Oxidative Stress, Dopaminergic Dysfunction, and Cognitive Impairment in Adult Zebrafish (Danio rerio)

The present study was designed to investigate the effects of chronic dietary exposure to selenium (Se) on zebrafish cognition and also to elucidate possible mechanism(s) by which Se exerts its neurotoxicity. To this end, adult zebrafish were exposed to different concentrations of dietary l-selenomethionine (control, 2.3, 9.7, 32.5, or 57.7 μg Se/g dry weight) for 30 days. Cognitive performance of fish was tested using a latent learning paradigm in a complex maze. In addition, we also evaluated oxidative stress biomarkers and the expression of genes involved in dopaminergic neurotransmission in the zebrafish brain. Fish treated with higher dietary Se doses (32.5 and 57.5 μg Se/g) exhibited impaired performance in the latent learning task. The impaired learning was associated with the induction of oxidative stress and altered mRNA expression of dopamine receptors, tyrosine hydroxylase, and dopamine transporter genes in the zebrafish brain. Collectively, our results illustrate that cognitive impairment in zebrafish could be associated with Se-induced oxidative stress and altered dopaminergic neurotransmission in the brain.

Lower vertebrate and invertebrate models of Alzheimer's disease - A review

Alzheimer's disease is a common neurodegenerative disorder which is characterized by the presence of beta- amyloid protein and neurofibrillary tangles (NFTs) in the brain. Till now, various higher vertebrate models have been in use to study the pathophysiology of this disease. But, these models possess some limitations like ethical restrictions, high cost, difficult maintenance of large quantity and lesser reproducibility. Besides, various lower chordate animals like Danio rerio, Drosophila melanogaster, Caenorhabditis elegans and Ciona intestinalis have been proved to be an important model for the in vivo determination of targets of drugs with least limitations. In this article, we reviewed different studies conducted on theses models for the better understanding of the pathophysiology of AD and their subsequent application as a potential tool in the preclinical evaluation of new drugs.

Digestibility of Quinoa (Chenopodium quinoa Willd.) Protein Concentrate and Its Potential to Inhibit Lipid Peroxidation in the Zebrafish Larvae Model

Quinoa protein concentrate (QPC) was extracted and digested under in vitro gastrointestinal conditions. The protein content of QPC was in the range between 52.40 and 65.01% depending on the assay used. Quinoa proteins were almost completely hydrolyzed by pepsin at pH of 1.2, 2.0, and 3.2. At high pH, only partial hydrolysis was observed. During the duodenal phase, no intact proteins were visible, indicating their susceptibility to the in vitro simulated digestive conditions. Zebrafish larvae model was used to evaluate the in vivo ability of gastrointestinal digests to inhibit lipid peroxidation. Gastric digestion at pH 1.2 showed the highest lipid peroxidation inhibition percentage (75.15%). The lipid peroxidation activity increased after the duodenal phase. The digest obtained at the end of the digestive process showed an inhibition percentage of 82.10%, comparable to that showed when using BHT as positive control (87.13%).

Manganese(II) Chloride Alters Nucleotide and Nucleoside Catabolism in Zebrafish (Danio rerio) Adult Brain

ATP and adenosine, the main signaling molecules of purinergic system, are involved in toxicological effects induced by metals. The manganese (Mn) exposure induces several cellular changes, which could interfere with signaling pathways, such as the purinergic system. In this study, we evaluated the effects of exposure to manganese(II) chloride (MnCl₂) during 96 h on nucleoside triphosphate diphosphohydrolase (NTPDase), ecto-5'-nucleotidase, and adenosine deaminase (ADA) activities, followed by analyzing the gene expression patterns of NTPDases (entpd1, entpd2a.1, entpd2a.2, entpd2-like, entpd3) and ADA (ADA ₁ , ADA _2.1 , ADA _2.2 , ADAasi, ADAL) families in zebrafish brain. In addition, the brain metabolism of nucleotides and nucleosides was evaluated after MnCl₂ exposure. The results showed that MnCl₂ exposure during 96 h inhibited the NTPDase (1.0 and 1.5 mM) and ecto-ADA (0.5, 1.0, and 1.5 mM) activities, further decreasing ADA2.1 expression at all MnCl₂ concentrations analyzed. Purine metabolism was also altered by the action of MnCl₂. An increased amount of ADP appeared at all MnCl₂ concentrations analyzed; however, AMP and adenosine levels are decreased at the concentrations of 1.0 and 1.5 mM MnCl₂, whereas decreased inosine (INO) levels were observed at all concentrations tested. The findings of this study demonstrated that MnCl₂ may inhibit NTPDase and ecto-ADA activities, consequently modulating nucleotide and nucleoside levels, which may contribute for the toxicological effects induced by this metal.

Effects of sub-chronic exposure to lead (Pb) and ascorbic acid in juvenile rockfish: Antioxidant responses, MT gene expression, and neurotransmitters

Juvenile rockfish Sebastes schlegelii were exposed to varying levels of dietary lead (Pb²⁺) at 0, 120 and 240 mg/L, and ascorbic acid (AsA) at 100, 200 and 400 mg/L for four weeks. Antioxidant responses such as superoxide dismutase (SOD), glutathione S-transferase (GST), and glutathione (GSH) were analyzed to assess oxidative stress. SOD and GST activity in the liver and gills were considerably elevated by dietary Pb. In contrast, GSH levels in the liver and gills were significantly reduced following Pb exposure. High levels of AsA supplementation attenuated the increase in SOD and GST activity and reduction in GSH levels. The metallothionein gene (MT) in the liver was notably stimulated by Pb exposure, and AsA supplementation attenuated this increase. With respect to neurotoxicity, acetylcholinesterase (AChE) activity was substantially inhibited in the brain and muscle following Pb exposure. AsA supplementation also attenuated AChE inhibition following Pb exposure. The results of this study presented Pb exposure affected rockfish as toxicity, and AsA was effective to alleviate toxic effects of Pb.

Maternal exposure to the water soluble fraction of crude oil, lead and their mixture induces autism-like behavioral deficits in zebrafish (Danio rerio) larvae

Autism spectrum disorder (ASD) is a serious debilitating mental illness with complex symptoms and multi-factorial pathogenesis. Although the pathogenesis of ASD remains unclear, etiology is thought to involve complex, multigenic interactions and possible environmental contributions. In the present study, we used zebrafish (Danio rerio) as a model to investigate whether maternal exposure to the water soluble fraction of crude oil (WSF, 5μg/L), lead (Pb, 20μg/L) and their mixture (5 μg/L WSF+20 μg/L Pb) could induce autism-like behavior in larvae. Our results showed that isolated and combined WSF/Pb exposure altered the behavioral pattern of fish swimming. WSF significantly increased anxiety and locomotor activity, decreased repetitive behavior in the open field test, and reduced the level of serotonin. However, co-exposure to WSF/Pb decreased behavioral activity and shoaling behavior, and increased cycle swimming and edge preference. Significant changes in the expression level of the multiple genes potentially critical for regulating environmental factor induced autism-like behavior were found. A gene network regulating ASD disturbed by WSF/Pb exposure was established using computational analysis. The information from the network could provide a clue for further mechanistic studies explaining molecular events regulating WSF/Pb mediated ASD.

The immune responses and expression of metallothionein (MT) gene and heat shock protein 70 (HSP 70) in juvenile rockfish, Sebastes schlegelii, exposed to waterborne arsenic (As3+)

Juvenile rockfish, Sebastes schlegelii (mean length 16.4±1.9cm, and mean weight 71.6±6.4g) were exposed for 20days with the different levels of waterborne arsenic concentration (0, 50, 100, 200 and 400μg/L). The plasma cortisol of S. schlegelii was significantly increased by the waterborne arsenit exposure. In the immune responses, the immunoglobulin M (Ig M) and lysozyme activity of S. schlegelii were significantly increased by the waterborne arsenic exposure. The acetylcholinesterase (AChE) activity of S. schlegelii was inhibited by the waterborne arsenic exposure. The substantial increases in the gene expression such as metallothionein (MT) and heat shock protein 70 (HSP 70) were observed by the waterborne arsenic exposure. The results demonstrated that waterborne arsenic exposure can induce the significant alterations in the immune responses and specific gene expression of S. schlegelii.

Oxidative stress, neurotoxicity, and metallothionein (MT) gene expression in juvenile rock fish Sebastes schlegelii under the different levels of dietary chromium (Cr(6+)) exposure

Juvenile Sebastes schlegelii were exposed for 4 weeks with the different levels of dietary chromium (Cr(6+)) concentration (0, 30, 60, 120 and 200mg/kg). The superoxide dismutase (SOD) activity, glutathione S-transferase (GST) activity, and glutathione (GSH) level of liver and gill were evaluated after 4 weeks exposure. The SOD and GST activity of liver and gill was significantly increased in the concentration of 240mg/kg after 2 weeks and over 120mg/kg after 4 weeks, whereas a considerable decrease in the concentration of 240mg/kg after 2 weeks and over 120mg/kg after 4 weeks was observed in the GSH levels of liver and gill. In neurotoxicity, AChE activity was significatly inhibited in brain in the concentration of 240mg/kg after 2 weeks and over 60mg/kg after 4 weeks and muscle in the concentration of 240mg/kg after 2 weeks and over 120mg/kg after 4 weeks. Metallothionein (MT) gene in liver was considerably increased over 120mg/kg after 2 weeks and at 30, 120, and 240mg/kg after 4 weeks by dietary chromium exposure. The results indicate that dietary Cr exposure over 120mg/kg can induce substantial alterations in antioxidant responses, AChE activity and MT gene expression.

Genotoxic potency of mercuric chloride in gill cells of marine gastropod Planaxis sulcatus using comet assay

In vivo and in vitro exposures were used to investigate the genotoxicity of mercuric chloride (HgCl2) to the marine snail, Planaxis sulcatus. The comet assay protocol was validated on gill cells exposed in vitro to hydrogen peroxide (H2O2, 0-50 μM). Snails were exposed in vivo for 96 h to HgCl2 (10, 20, 50, and 100 μg/l). Our results showed significant concentration-dependent increase in the tail DNA (TDNA) and olive tail moment (OTM) in exposed snails for all doses compared with controls. In vitro exposure to HgCl2 (10-100 μg/l) resulted in significantly higher values for TDNA at all concentrations. Our results showed that DNA damage increased in the gill cell with increasing exposure time. This study demonstrates the usefulness of comet assay for detection of DNA damage after exposure to HgCl2 and the sensitivity of marine snail P. sulcatus as a good candidate species for metal pollution.

Methionine Exposure Alters Glutamate Uptake and Adenine Nucleotide Hydrolysis in the Zebrafish Brain

Hypermethioninemic patients may exhibit different neurological dysfunctions, and the mechanisms underlying these pathologies remain obscure. Glutamate and ATP are important excitatory neurotransmitters co-released at synaptic clefts, and whose activities are intrinsically related. Adenosine-the final product of ATP breakdown-is also an important neuromodulator. Here, we investigated the effects of long-term (7-day) exposure to 1.5 or 3 mM methionine (Met) on glutamate uptake in brain tissues (telencephalon, optic tectum, and cerebellum) and on ATP, ADP, and AMP catabolism by ecto-nucleotidases found in brain membrane samples, using a zebrafish model. Also, we evaluated the expression of ecto-nucleotidase (ntdp1, ntdp2mg, ntdp2mq, ntdp2mv, ntdp3, and nt5e) and adenosine receptor (adora1, adora2aa, adora2ab, adora2b) genes in the brain of zebrafish exposed to Met. In animals exposed to 3.0 mM Met, glutamate uptake in the telencephalon decreased significantly. Also, ATP and ADP (but not AMP) catabolism decreased significantly at both Met concentrations tested. The messenger RNA (mRNA) levels of ntpd genes and of the adenosine receptors adora1 and adora2aa increased significantly after Met exposure. In contrast, adora2ab mRNA levels decreased after Met exposure. Our data suggest that glutamate and ATP accumulate at synaptic clefts after Met exposure, with potential detrimental effects to the nervous system. This phenomenon might explain, at least in part, the increased susceptibility of hypermethioninemic patients to neurological symptoms.

Assessment of mercury chloride-induced toxicity and the relevance of P2X7 receptor activation in zebrafish larvae

Zebrafish (Danio rerio) has been adopted as a model for behavioral, immunological and toxicological studies. Mercury is a toxic heavy metal released into the environment. There is evidence indicating that heavy metals can modulate ionotropic receptors, including the purinergic receptor P2X7. Therefore, this study evaluated the in vivo effects of acute exposure to mercury chloride (HgCl2) in zebrafish larvae and to investigate the involvement of P2X7R in mercury-related toxicity. Larvae survival was evaluated for 24 h after exposure to HgCl2, ATP or A740003. The combination of ATP (1 mM) and HgCl2 (20 μg/L) decreased survival when compared to ATP 1 mM. The antagonist A740003 (300 and 500 nM) increased the survival time, and reversed the mortality caused by ATP and HgCl2 in association. Quantitative real time PCR showed a decrease of P2X7R expression in the larvae treated with HgCl2 (20 μg/L). Evaluating the oxidative stress our results showed decreased CAT (catalase) activity and increased MDA (malondialdehyde) levels. Of note, the combination of ATP with HgCl2 showed an additive effect. This study provides novel evidence on the possible mechanisms underlying the toxicity induced by mercury, indicating that it is able to modulate P2X7R in zebrafish larvae.

Long-term proline exposure alters nucleotide catabolism and ectonucleotidase gene expression in zebrafish brain

Hyperprolinemia is an inherited disorder of proline metabolism and hyperprolinemic patients can present neurological manifestations, such as seizures cognitive dysfunctions, and psychotic disorders. However, the underlying mechanisms of these symptoms are still unclear. Since adenine nucleotides play crucial roles in neurotransmission and neuromodulation, we evaluated the in vivo and in vitro effects of proline on ectonucleotidase activities and gene expression in zebrafish brain. For the in vivo studies, animals were exposed at two proline concentrations (1.5 and 3.0 mM) during 1 h or 7 days (short- or long-term treatments, respectively). For the in vitro assays, different proline concentrations (ranging from 3.0 to 1000 μM) were tested. Short-term proline exposure did not promote significant changes on the ectonucleotidase activities and gene expression. Long-term proline exposure significantly increased ATP catabolism in both concentrations tested (14 % and 22 %, respectively), whereas ADP and AMP hydrolysis were increased only at 3.0 mM proline (21 % and 17 %, respectively) when compared to control. Moreover, the relative gene expression of enpd3 increased in both treated groups after long-term proline, whereas enptd1 increased only at 3.0 mM proline. Proline in vitro did not promote significant changes on ectonucleotidase activities. Altogether, these data indicate that the enzymes responsible for the control of extracellular nucleotides levels might be altered after proline exposure in zebrafish, contributing to better understand the pathophysiology of this disease. Moreover, such findings might facilitate the use of the zebrafish as a complementary vertebrate model for studying inborn errors of amino acid metabolism.

Arsenic alters behavioral parameters and brain ectonucleotidases activities in zebrafish (Danio rerio)

Arsenic (As) exposure has been associated with serious chronic health risk to humans including cancer and neurological disturbances. However, there are limited studies about the mechanisms behind its toxicity. In this study, adult zebrafish were exposed to several concentrations of As (0.05, 5, and 15 mg As/L; Na(2)HAsO(4) as As(V)) during 96 h to evaluate the zebrafish locomotor activity, anxiety, and brain extracellular nucleotide hydrolysis. We showed that 5 mg/L As is able to promote significant decrease in the locomotor activity as evaluated by the number of line crossings. In addition, animals treated with 5mg/L As presented an increase in time spent in the lower zone of the tank test, suggesting an anxiogenic effect. Considering that behavioral parameters, such as anxiety and locomotion, might be modulated by the purinergic system, we also evaluated the ectonucleotidase activities in zebrafish brain after a 96-h As exposure. A significant decrease in ATP, ADP, and AMP hydrolysis was observed at 0.05, 5, and 15 mg/L when compared to control group. These findings demonstrated that As might affect behavioral parameters and the ectonucleotidase activities in zebrafish, suggesting this enzyme pathway is a target for neurotoxic effects induced by As.

Zebrafish neurotransmitter systems as potential pharmacological and toxicological targets

Recent advances in neurobiology have emphasized the study of brain structure and function and its association with numerous pathological and toxicological events. Neurotransmitters are substances that relay, amplify, and modulate electrical signals between neurons and other cells. Neurotransmitter signaling mediates rapid intercellular communication by interacting with cell surface receptors, activating second messenger systems and regulating the activity of ion channels. Changes in the functional balance of neurotransmitters have been implicated in the failure of central nervous system function. In addition, abnormalities in neurotransmitter production or functioning can be induced by several toxicological compounds, many of which are found in the environment. The zebrafish has been increasingly used as an animal model for biomedical research, primarily due to its genetic tractability and ease of maintenance. These features make this species a versatile tool for pre-clinical drug discovery and toxicological investigations. Here, we present a review regarding the role of different excitatory and inhibitory neurotransmitter systems in zebrafish, such as dopaminergic, serotoninergic, cholinergic, purinergic, histaminergic, nitrergic, glutamatergic, glycinergic, and GABAergic systems, and emphasizing their features as pharmacological and toxicological targets. The increase in the global knowledge of neurotransmitter systems in zebrafish and the elucidation of their pharmacological and toxicological aspects may lead to new strategies and appropriate research priorities to offer insights for biomedical and environmental research.

Chronic ethanol treatment alters purine nucleotide hydrolysis and nucleotidase gene expression pattern in zebrafish brain

Ethanol is a widely consumed drug that acts on the central nervous system (CNS), modifying several signal transduction pathways activated by hormones and neurotransmitters. The zebrafish is an experimental model for the study of human diseases and the use of this species in biochemical and behavioral studies on alcoholism and alcohol-dependence has increased recently. However, there are no data concerning the effects of chronic ethanol exposure on the purinergic system, where extracellular nucleotides act as signaling molecules. Purinergic signaling is controlled by a group of enzymes named ectonucleotidases, which include NTPDases and ecto-5'-nucleotidase already characterized in zebrafish brain. The aim of this study was to evaluate nucleotide hydrolysis by NTPDases and ecto-5'-nucleotidase after long-term ethanol exposure. Additionally, the gene expression patterns of NTPDases1-3 and 5'-nucleotidase were determined. Animals were exposed to 0.5% ethanol for 7, 14, and 28 days. There were no significant changes in ATP and GTP hydrolysis after all treatments. However, a decrease in ADP (46% and 34%) and GDP (48% and 36%) hydrolysis was verified after 7 and 14 days, respectively. After 7 and 14 days of ethanol exposure, a significant decrease in AMP hydrolysis (48% and 36%) was also observed, whereas GMP hydrolysis was inhibited only after 7 days (46%). NTPDase2_mv and NTPDase3 mRNA transcript levels decreased after 7 and 14 days, respectively. In contrast, ethanol increased NTPDase1, NTPDase2_mq, and NTPDase3 transcript levels after 28 days of exposure. NTPDase2_mg and 5'-nucleotidase gene expression was not altered. Therefore, the ectonucleotidase pathway may be a target of chronic ethanol toxicity and the regulation of purinergic system could play a key role in the neurochemical mechanisms underlying the effects of ethanol on the CNS.

Influence of mercury chloride on adenosine deaminase activity and gene expression in zebrafish (Danio rerio) brain

Mercury is a widespread environmental contaminant that is neurotoxic even at very low concentrations. In this study we investigated the effects of mercury chloride on soluble and membrane adenosine deaminase (ADA) activity and gene expression in zebrafish brain. Inhibition of ADA activity was observed in the soluble fraction at 5-250 microM HgCl(2) (84.6-92.6%, respectively), whereas inhibition occurred at 50-250 microM in membrane fractions (20.9-26%, respectively). We performed in vitro experiments with chelants (EDTA and DTT) to test if these compounds prevented or reversed the inhibition caused by HgCl(2) and found that the inhibition was partially or fully abolished. The effect on ADA activity in soluble and membrane fractions was evaluated after acute (24h) and subchronic (96h) in vivo exposure of zebrafish to 20 microg/l HgCl(2). ADA activity in the soluble fraction was decreased after both acute (24.5%) and subchronic (40.8%) exposures, whereas in brain membranes the enzyme was inhibited only after subchronic exposure (21.9%). Semiquantitative RT-PCR analysis showed that HgCl(2) did not alter ADA gene expression. This study demonstrated that ADA activity was inhibited by mercury and this effect might be related to the neurotoxicity of this heavy metal.

Evolutionary origins of the purinergic signalling system

Purines appear to be the most primitive and widespread chemical messengers in the animal and plant kingdoms. The evidence for purinergic signalling in plants, invertebrates and lower vertebrates is reviewed. Much is based on pharmacological studies, but important recent studies have utilized the techniques of molecular biology and receptors have been cloned and characterized in primitive invertebrates, including the social amoeba Dictyostelium and the platyhelminth Schistosoma, as well as the green algae Ostreococcus, which resemble P2X receptors identified in mammals. This suggests that contrary to earlier speculations, P2X ion channel receptors appeared early in evolution, while G protein-coupled P1 and P2Y receptors were introduced either at the same time or perhaps even later. The absence of gene coding for P2X receptors in some animal groups [e.g. in some insects, roundworms (Caenorhabditis elegans) and the plant Arabidopsis] in contrast to the potent pharmacological actions of nucleotides in the same species, suggests that novel receptors are still to be discovered.

IL-6 downregulates transcription of NTPDase2 via specific promoter elements

Bile ductular proliferation is markedly upregulated in biliary fibrosis and cirrhosis. However, the mechanisms regulating this upregulation in bile ductular proliferation have not been defined. Recently, we demonstrated that expression of the ectonucleotidase nucleoside triphosphate diphosphohydrolase-2 (NTPDase2/Entpd2) by portal fibroblasts (PF) is a critical regulator of bile ductular proliferation. Since interleukin 6 (IL-6) is markedly upregulated in biliary cirrhosis, our aims were to determine the role and mechanism of IL-6 in the regulation of NTPDase2 by PF. We found that IL-6 downregulated NTPDase2 protein expression in a concentration-dependent and time-dependent fashion but did not alter PF alpha-smooth muscle actin expression. IL-6 markedly downregulated NTPDase2 mRNA expression. Expression of the IL-6 receptor gp130 but not the IL-6 receptor gp80 was detected in PF. Two transcription start sites were identified in rat Entpd2 by the method of RNA ligase-mediated rapid amplification of 5' cDNA ends. The minimal promoter construct, but not shorter constructs, was downregulated by IL-6. Three putative IL-6 response elements were identified in silico and mutated. Mutation of all three response elements, but not fewer elements, completely abolished the IL-6 response. Thus IL-6 transcriptionally downregulates NTPDase2 expression by PF via actions at specific promoter elements independently of myofibroblastic differentiation. This effect may represent a novel signaling pathway by which bile ductular proliferation is dysregulated in biliary cirrhosis and thus provides a potential therapeutic approach for the regulation of bile ductular growth.

Comparative expression of p2x receptors and ecto-nucleoside triphosphate diphosphohydrolase 3 in hypocretin and sensory neurons in zebrafish

The hypocretin/orexin (HCRT/ORX) excitatory neuropeptides are expressed in a small population of lateral hypothalamic cells in mammals and fish. In humans, loss of these cells causes the sleep disorder narcolepsy. Identification of genes expressed in HCRT-producing cells may be revealing as to the regulation of sleep and the pathophysiology of narcolepsy. In this study, in situ hybridization analyses were performed to characterize the expression pattern of receptors and enzyme, which regulate ATP-mediated transmission in hypocretin cells of zebrafish larvae. The zebrafish cDNA encoding the ecto-nucleoside triphosphate diphosphohydrolase 3 (ENTPD3/NTPDase3) was isolated. This transcript was found to be expressed in zebrafish HCRT cells as previously reported in mammals. It was also expressed in the cranial nerves (gV, gVII, gIV and gX) and in primary sensory neurons (i.e., Rohon-Beard neurons) in the spinal cord. The expression of known zebrafish p2rx purinergic receptor family members was next studied and found to overlap with the entpd3 expression pattern. Specifically, p2rx2, p2rx3.1, p2rx3.2 and p2rx8 were expressed in the trigeminal ganglia and subsets of Rohon-Beard neurons. In contrast to mammals, p2rx2 was not expressed in HCRT cells; rather, p2rx8 was expressed with entpd3 in this hypothalamic region. The conservation of expression of these genes in HCRT cells and sensory neurons across vertebrates suggests an important role for ATP mediated transmission in the regulation of sleep and the processing of sensory inputs.

Acute and subchronic copper treatments alter extracellular nucleotide hydrolysis in zebrafish brain membranes

Copper is a divalent cation with physiological importance since deficiency of copper homeostasis can cause serious neurological diseases. ATP is an important signalling molecule stored at nerve endings and its inactivation is promoted by ecto-nucleotidases. In this study, we verified the effect of acute and subchronic copper treatments on ecto-nucleotidase activities in zebrafish brain membranes. Treatment with copper sulfate (15 microg/L) during 24h inhibited ATP hydrolysis (16%), whereas ADP and AMP hydrolysis were not altered. Nevertheless, a 96-h exposure with the copper concentration mentioned above inhibited NTPDase (31% and 42% for ATP and ADP hydrolysis, respectively) and ecto-5'-nucleotidase (40%) activities. NTPDase1, NTPDase2_mg and NTPDase2_mv transcripts were decreased after copper exposures during 24 and 96 h. Subchronic copper treatment also reduced the NTPDase2_mq and ecto-5'-nucleotidase expression. In vitro assays demonstrated that NTPDase activities were reduced after copper exposure during 40 min. ATP hydrolysis was inhibited at 0.25, 0.5 and 1mM (13%, 31% and 48%, respectively) and ADP hydrolysis also had a significant decrease at these same copper concentrations (41%, 63% and 68%, respectively). In contrast to the subchronic exposure, no significant changes on ecto-5'-nucleotidase were observed after in vitro assays. Lineweaver-Burk plots suggested that both inhibitory effects on nucleotide hydrolysis may occur in a non-competitive manner. Altogether, these findings indicate that copper is able to promote distinct changes on ecto-nucleotidases after in vivo and in vitro treatments and, consequently, it could control the nucleotide and nucleoside levels, modulating the purinergic signalling.