Copper acutely impairs behavioral function and muscle acetylcholinesterase activity in zebrafish (Danio rerio)

Biochemical changes and bioaccumulation of manganese in Astyanax lacustris (Teleostei: Characidae)

Major tailings dam failures have occurred recently around the world and resulted in severe environmental impacts, such as metal contamination. Manganese is a metal highly associated with mining activities, largely detected in mining dam collapses. This metal is considered necessary for different organisms, but it can be toxic and cause oxidative stress and genetic damage in fishes. In this study, we investigated the toxic effects of manganese on Astyanax lacustris, by exposing the fish individually to different concentrations of this metal (2.11, 5.00, and 10.43 mg/L) for 96 h. To assess the effects of manganese, we used biochemical biomarkers (glutathione S-transferase, catalase, and acetylcholinesterase enzyme activity) and the manganese bioaccumulation in different tissues (liver and gills). The obtained data showed that only at concentrations of 5.00 mg/L and 10.43 mg/L the activity of glutathione S-transferase differed significantly. Additionally, the acetylcholinesterase activity in the brain tissue was inhibited. The highest level of manganese bioaccumulation was observed in the liver and branchial tissue. Overall, we concluded that high concentrations of manganese may cause physiological changes in Astyanax lacustris.

Microbial Polysaccharides Extracted from Different Mature Muds of the Euganean Thermal District Show Similar Anti-Inflammatory Activity In Vivo

The Euganean Thermal District, situated in North-East Italy, is one of Europe's largest and oldest thermal centres. The topical application of its therapeutic thermal muds is recognised by the Italian Health System as a beneficial treatment for patients suffering from arthro-rheumatic diseases. Polysaccharides produced by the mud microbiota have been recently identified as anti-inflammatory bioactive molecules. In this paper we analysed the efficacy of Microbial-Polysaccharides (M-PS) derived from mature muds obtained at different maturation temperatures, both within and outside the codified traditional mud maturation range. M-PSs were extracted from six mature muds produced by five spas of the Euganean Thermal District and investigated for their chemical properties, monosaccharide composition and in vivo anti-inflammatory potential, using the zebrafish model organism. Additionally, mature muds were characterized for their microbiota composition using Next-Generation Sequencing. The results showed that all M-PSs exhibit similar anti-inflammatory potential, referable to their comparable chemical composition. This consistency was observed despite changes in cyanobacteria populations, suggesting a possible role of the entire microbial community in shaping the properties of these biomolecules. These findings highlight the importance of scientific research in untangling the origins of the therapeutic efficacy of Euganean Thermal muds in the treatment of chronic inflammatory conditions.

Co-exposure to sodium hypochlorite and cadmium induced locomotor behavior disorder by influencing neurotransmitter secretion and cardiac function in larval zebrafish

Sodium hypochlorite (NaClO) and cadmium (Cd) are widely co-occurring in natural aquatic environment; however, no study has been conducted on effects of their combined exposure on aquatic organisms. To assess effects of exposure to NaClO and Cd in zebrafish larvae, we designed six treatment groups, as follows: control group, NaClO group (300 μg/L), 1/100 Cd group (48 μg/L), 1/30 Cd group (160 μg/L), NaClO+1/100 Cd group, and NaClO+1/30 Cd group analyzed behavior, neurological function and cardiac function. Results revealed that exposure to 1/30 Cd and NaClO+1/30 Cd caused abnormal embryonic development in larvae by altering body morphology and physiological indicators. Combined exposure to NaClO and 1/30 Cd affected the free-swimming activity and behavior of larvae in response to light-dark transition stimuli. Moreover, exposure to 1/30 Cd or NaClO+1/30 Cd resulted in a significant increase in tyrosine hydroxylase and acetylcholinesterase activities, as well as significant changes of various neurotransmitters. Lastly, exposure to 1/30 Cd or NaClO+1/30 Cd influenced the transcription of cardiac myosin-related genes and disturbed the myocardial contractile function. Altogether, our results suggested that combined exposure to NaClO and Cd induced oxidative damage in larvae, resulting in detrimental effects on nervous system and cardiac function, thus altering their swimming behavior.

Zebrafish Experimental Animal Models for AD: A Comprehensive Review

AD disease (AD) is a multifaceted and intricate neurodegenerative disorder characterized by intracellular neurofibrillary tangle (NFT) formation and the excessive production and deposition of Aβ senile plaques. While transgenic AD models have been found instrumental in unravelling AD pathogenesis, they involve cost and time constraints during the preclinical phase. Zebrafish, owing to their simplicity, well-defined behavioural patterns, and relevance to neurodegenerative research, have emerged as a promising complementary model. Zebrafish possess glutaminergic and cholinergic pathways implicated in learning and memory, actively contributing to our understanding of neural transmission processes. This review sheds light on the molecular mechanisms by which various neurotoxic agents, including okadaic acid (OKA), cigarette smoke extract, metals, and transgenic zebrafish models with genetic similarities to AD patients, induce cognitive impairments and neuronal degeneration in mammalian systems. These insights may facilitate the identification of effective neurotoxic agents for replicating AD pathogenesis in the zebrafish brain. In this comprehensive review, the pivotal role of zebrafish models in advancing our comprehension of AD is emphasized. These models hold immense potential for shaping future research directions and clinical interventions, ultimately contributing to the development of novel AD therapies.

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

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

High dietary copper intake induces perturbations in the gut microbiota and affects host ovarian follicle development

Increasing evidence has shown that gut microbes play an important role in the reproductive endocrine system and the development of polycystic ovary syndrome (PCOS). However, whether environmental factors are involved in these gut microbiota alterations has seldom been studied. In this study, we aimed to explore the crucial role of an imbalanced gut microbiota on abnormal ovarian follicle development induced by Cu. A 1:1 matched case-control study with 181 PCOS patients and 181 controls was conducted using a propensity score matching protocol. Information regarding dietary Cu intake was obtained from a face-to-face dietary intake interview. Alterations in the gut microbiota were detected by high-throughput 16 S rDNA sequencing. The results showed that dietary Cu intake was positively correlated with the risk of PCOS, and the risk threshold was approximately 1.992 mg/d. Compared with those with dietary Cu intakes lower than 1.992 mg/d, those who had a higher dietary Cu intake had a 1.813-fold increased risk of PCOS (OR=1.813, 95% CI: 1.150-2.857). PCOS patients had a lower relative abundance of Bacteroides than controls (P = 0.003), and Bacteroides played a partial mediating role between dietary Cu exposure and PCOS (P_{indirect effect}=0.026, 95% CI: 0.002-0.072). In addition, an animal model of Cu exposure through the diet showed that Cu can induce gut microbiota disorder; increase serum levels of LPS, MDA, and IL-6; and alter host ovarian steroidogenesis to affect ovarian follicle development. Staphylococcus played a partial mediating role between Cu exposure and CYP17A1 (P_{g_Staphylococcus}=0.083, 95% CI: 0.001-0.228). Overall, this study shows that long-term exposure to high dietary Cu levels can affect the composition of the gut microbiota, cause inflammation and oxidative stress, and then interfere with hormone signaling, ultimately affecting ovarian follicle development.

Oxidative Stress in a Wild Population of the Freshwater Fish Hyphessobrycon Luetkenii Chronically Exposed to a Copper Mining Area: New Insights into Copper Toxicology

In this study, we examine markers of oxidative stress in the tetra Hyphessobrycon luetkenii collected from two locations in the copper contaminated João Dias creek (southern Brazil). Also, specimens were translocated from a clean reference section of the creek to a polluted stretch and vice-versa. Fish were held at in submerged cages for 96 h and then sacrificed. Nuclear abnormalities in erythrocytes and total antioxidant capacity, lipid peroxidation and protein carbonylation in gills, brain, liver and muscle displayed similar trends in both groups. Lipid peroxidation increased in all tissues of individuals translocated to the polluted site but only in liver and muscle of those translocated to the reference site. Increased protein carbonylation was also observed in gills of individuals translocated to the reference location. These results suggest similar oxidative stress among fish from the reference and polluted locations and that long-term metals exposure may require adaptations toward oxidative stress responses.

Flumequine-mediated fluorescent zeolitic imidazolate framework functionalized by Eu3+ for sensitive and selective detection of UO22+, Ni2+ and Cu2+ in nuclear wastewater

Currently, antibiotics and heavy metal contaminants have posed a great threat for ecological security and human health. Herein, the lanthanide functionalized ZIF (named ZIF-90-PABA-Eu) is constructed by coordinating with Eu³⁺ via p-aminobenzoic acid intermediate. Due to the excellent fluorescence properties, the novel fluorescent probe can selectively monitor flumequine based on "turn on" mode. Furthermore, the obtained new material (named ZIF-90-PABA-Eu-Flu) can be used as "turn off" sensor for selective detection of both radioactive and nonradioactive heavy metal ions (UO₂²⁺, Ni²⁺ and Cu²⁺) which are the main component of nuclear industrial wastewater. ZIF-90-PABA-Eu-Flu shows ultra-short fluorescence response time (3 s) and ultra-low limit of detection (9.0 × 10^-3, 1.3 × 10^-2 and 6.1 × 10^-4 ppm) for three metal ions, which may be attributed to its good affinity with UO₂²⁺, Ni²⁺ and Cu²⁺. Moreover, principal component analysis (PCA) is applied to distinguish the three metal ions. Additionally, the possible sensing mechanism is investigated by the UV-vis spectra, luminescence lifetimes and theoretical calculation analysis. Based on these results, ZIF-90-PABA-Eu possesses promising potential in practical application and provides insight for the design of novel probes to continuously monitor flumequine, radioactive and nonradioactive heavy metal ions.

Mitigation of nicotine-induced developmental effects by 24-epibrassinolide in zebrafish

Nicotine is a highly addictive substance that can cause teratogenic impacts in the embryo through redox-dependent pathways. As antioxidants, naturally occurring chemicals can protect cells from redox imbalance. The purpose of this study was to evaluate the effectiveness of 24-epibrassinolide (24-EPI), a natural brassinosteroid with well-known antioxidant properties, in protecting zebrafish embryos against nicotine's teratogenic effects. For 96 h, embryos (2 h post-fertilization - hpf) were exposed to 100 μM nicotine, co-exposed with 24-EPI (0.01, 0.1, and 1 μM), and 24-EPI alone (1 μM). Lethal and sublethal developmental characteristics were evaluated during exposure. Biochemical tests were performed at the conclusion of the exposure, and distinct behavioural paradigms were analysed 24 h later. Nicotine exposure resulted in a higher proportion of larvae with deformities, which were decreased following co-exposure to 24-EPI. Nicotine exposure also caused an increase in oxidative stress as observed by the increased activity of superoxide dismutase and catalase accompanied by an increase in the malondialdehyde levels. Besides, metabolic changes were noticed as observed by the increased lactate dehydrogenase activity that were hypothesised to be associated to nicotine-induced hypoxia which may be responsible for the increased oxidative damage. In addition, locomotor deficits were observed as well as a decrease in the acetylcholinesterase activity denoting nicotine-induced cognitive dysfunction. However, co-exposure to 24-EPI alleviated behavioural deficits and improved nicotine-induced emotional states. Overall, and although further studies are required to clarify these effects, 24-EPI showed promising ameliorative properties against the teratogenic effects induced by nicotine.

Neurotoxicity of singular and combined exposure of Oreochromis niloticus to methomyl and copper sulphate at environmentally relevant levels: Assessment of neurotransmitters, neural stress, oxidative injury and histopathological changes

Aquatic organisms are concomitantly exposed to multiple noxious chemicals that can be discharged into water bodies. We aimed to investigate the single and simultaneous sub-acute exposure to copper and methomyl on juvenile Oreochromis niloticus. Compared to the controls, the outcomes revealed that brain of methomyl-exposed fish displayed significant declines in the activities of SOD, CAT, and GST in addition to higher MDA and lower GSH levels. Methomyl induced notable declines in levels of GABA and acetylcholine esterase in brain and muscle of exposed fish. Noteworthy downregulated gene expression levels of TNF-α, HSP-70 together with upregulated c-fos were evident in brain of fish expose to either of tested compounds. Marked apoptotic changes were observed in fish brain exposed to copper and methomyl indicated by augmented immune expression of caspase-3. Conclusively, the results indicated the possible interaction between both compounds with subsequent toxic effects that differ from their single exposure.

Beyond the behavioural phenotype: Uncovering mechanistic foundations in aquatic eco-neurotoxicology

During the last decade, there has been an increase in awareness of how anthropogenic pollution can alter behavioural traits of diverse aquatic organisms. Apart from understanding profound ecological implications, alterations in neuro-behavioural indices have emerged as sensitive and physiologically integrative endpoints in chemical risk assessment. Accordingly, behavioural ecotoxicology and broader eco-neurotoxicology are becoming increasingly popular fields of research that span a plethora of fundamental laboratory experimentations as well as applied field-based studies. Despite mounting interest in aquatic behavioural ecotoxicology studies, there is, however, a considerable paucity in deciphering the mechanistic foundations underlying behavioural alterations upon exposure to pollutants. The behavioural phenotype is indeed the highest-level integrative neurobiological phenomenon, but at its core lie myriads of intertwined biochemical, cellular, and physiological processes. Therefore, the mechanisms that underlie changes in behavioural phenotypes can stem among others from dysregulation of neurotransmitter pathways, electrical signalling, and cell death of discrete cell populations in the central and peripheral nervous systems. They can, however, also be a result of toxicity to sensory organs and even metabolic dysfunctions. In this critical review, we outline why behavioural phenotyping should be the starting point that leads to actual discovery of fundamental mechanisms underlying actions of neurotoxic and neuromodulating contaminants. We highlight potential applications of the currently existing and emerging neurobiology and neurophysiology analytical strategies that should be embraced and more broadly adopted in behavioural ecotoxicology. Such strategies can provide new mechanistic discoveries instead of only observing the end sum phenotypic effects.

In vivo anti-inflammatory and antioxidant effects of microbial polysaccharides extracted from Euganean therapeutic muds

Therapeutic thermal mud produced by spas of the Euganean Thermal District (Italy) is used as a treatment for arthro-rheumatic diseases. Its production involves the growth of a specific microbiota embedded in a polysaccharidic matrix. Polysaccharides (Microbial-PolySaccharides, M-PS) released in the mud by the resident microorganisms were extracted and analyzed. The monosaccharidic composition analysis showed the presence of galacturonic acid, mannose, xylose, ribose and glucose and a high percentage of sulfated groups in the polymers. To assess their involvement in the therapeutic efficacy of the mud, the M-PS were tested using the model organism zebrafish (Danio rerio). The anti-inflammatory and antioxidant activities were evaluated after confirming the lack of toxic effects during development. Inflammatory state was induced chemically with copper sulfate, or through tail fin amputation procedure and UVB exposure. Recovery from inflammatory condition after exposure to M-PS was always observed with specific morphometric analyses, and further supported by qPCR. Genes linked with the inflammatory and oxidative stress response were investigated confirming the M-PS treatment's efficacy.

Copper leaching from recreational vessel antifouling paints in freshwater: A Berlin case study

Copper leached from recreational vessel antifouling paints can pose a threat to aquatic organisms. To date, leaching rates have mainly been studied in seawater and brackish water. The aim of this study was to investigate the copper input from antifouling paints to freshwater using field and laboratory studies. Therefore, a large sailing area in Berlin was sampled. According to a risk assessment, the use of copper containing antifouling paints in Berlins is predicted to have no significant impact on aquatic organisms. An exception was found in sport boat marinas where, in dependence on the boat number, the sediment copper concentrations were up to 2 times higher than the German environmental quality standard for sediments. The most important result revealed by the laboratory batch tests is that the copper leaching rate in freshwater is much lower compared to seawater and brackish water. The dissolution of copper from antifouling paints into freshwater is overestimated up to now. Nevertheless, the leached copper from antifouling paints is the second largest anthropogenic copper source in the urban area of Berlin and the third largest anthropogenic copper source in German freshwaters.

Microplastics alone or co-exposed with copper induce neurotoxicity and behavioral alterations on zebrafish larvae after a subchronic exposure

Microplastics (MPs, <5 mm) have been frequently detected in aquatic ecosystems, representing both health and ecological concerns. However data about the combined effects of MPs and other contaminants is still limited. This study aimed to evaluate the impact of MPs and the heavy metal copper (Cu) on zebrafish (Danio rerio) larvae development and behavior. Zebrafish embryos were subchronically exposed to MPs (2 mg/L), two sub-lethal concentrations of Cu (60 and 125 µg/L) and binary mixtures of MPs and Cu using the same concentrations, from 2-h post fertilization until 14 days post fertilization. Lethal and sub-lethal responses (mortality, hatching, body length) were evaluated during the embryogenesis period, and locomotor, avoidance, anxiety and shoaling behaviors, and acetylcholinesterase (AChE) activity were measured at 14 dpf. The results showed that survival of larvae was reduced in groups exposed to MPs, Cu and Cu+MPs. Regarding the behavioral patterns, the higher Cu concentration and mixtures decreased significantly the mean speed, the total distance traveled and the absolute turn angle, demonstrating an adverse effect on swimming competence of zebrafish larvae. Exposure to MPs and Cu, alone or combined, also affected avoidance behavior of zebrafish, with larvae not reacting to the aversive stimulus. There was a significant inhibition of AChE activity in larvae exposed to all experimental groups, compared to the control group. Moreover, a higher inhibition of AChE was noticed in larvae exposed to MPs and both Cu+MPs groups, comparatively to the Cu alone groups. Our findings demonstrate the adverse effects of MPs, alone or co-exposed with Cu, on fish early life stages behavior. This study highlights that MPs and heavy metals may have significant impacts on fish population fitness by disrupting locomotor and avoidance behaviors.

Comparative toxicity assessment of in situ burn residues to initial and dispersed heavy fuel oil using zebrafish embryos as test organisms

In situ burning (ISB) is discussed to be one of the most suitable response strategies to combat oil spills in extreme conditions. After burning, a highly viscous and sticky residue is left and may over time pose a risk of exposing aquatic biota to toxic oil compounds. Scientific information about the impact of burn residues on the environment is scarce. In this context, a comprehensive ISB field experiment with approx. 1000L IFO 180 was conducted in a fjord in Greenland. The present study investigated the toxicity of collected ISB residues to early life stages of zebrafish (Danio rerio) as a model for potentially exposed pelagic organisms. The toxicity of ISB residues on zebrafish embryos was compared with the toxicity of the initial (unweathered) IFO 180 and chemically dispersed IFO 180. Morphological malformations, hatching success, swimming behavior, and biomarkers for exposure (CYP1A activity, AChE inhibition) were evaluated in order to cover the toxic response on different biological organization levels. Across all endpoints, ISB residues did not induce greater toxicity in zebrafish embryos compared with the initial oil. The application of a chemical dispersant increased the acute toxicity most likely due to a higher bioavailability of dissolved and particulate oil components. The results provide insight into the adverse effects of ISB residues on sensitive life stages of fish in comparison with chemical dispersant application.

Zebrafish as a Promising Tool for Modeling Neurotoxin-Induced Alzheimer's Disease

Drug discovery and development for Alzheimer's disease (AD) are complex and challenging due to the higher failure rate in the drug development process. The overproduction and deposition of Aβ senile plaque and intracellular neurofibrillary tangle (NFT) formation are well-recognized diagnostic hallmarks of AD. Numerous transgenic models of Alzheimer's disease have restrictions on cost-effectiveness and time in the preclinical setup. Zebrafish has emerged as an excellent complementary model for neurodegenerative research due to simpler organisms with robust, clearly visible behavior forms. Glutaminergic and cholinergic pathways responsible for learning and memory are present in zebrafish and actively participate in the transmission process. Therefore, it is imperative to study neurotoxic agents' mechanisms that induce dysfunction of memory, learning, and neurons in the zebrafish. This review illustrates the in-depth molecular mechanism of several neurotoxic agents such as okadaic acid, cigarette smoke extract, and metals to produce cognitive deficits or neurodegeneration similar to mammals. These updates would determine an ideal and effective neurotoxic agent for producing AD pathophysiology in the zebrafish brain for preclinical screening.

Water and suspended sediment runoff from vineyard watersheds affecting the behavior and physiology of zebrafish

Viticulture plays an important role in generating income for small farms globally. Historically, vineyards use large quantities of phytosanitary products, such as Bordeaux mixture [Ca(OH)₂ + CuSO₄], to control plant diseases. These products result in the accumulation of copper (Cu) in the soil and increases the risk of transfer to water bodies. Thus, it is important to evaluate whether the presence of Cu-bearing particles in water is toxic to aquatic fauna. This study conducted chemical, mineralogical, and particle size evaluations on water samples and sediments collected from a watershed predominantly cultivated with old vineyards. The proportion of Cu-rich nanoparticles (<10 nm) in the sediment was ~27%. We exposed zebrafish to different dilutions of water and sediment samples that collected directly from the study site (downstream river) under laboratory conditions. Then, we evaluated their exploratory behavior and the stress-related endocrine parameter, whole-body cortisol. We also carried out two experiments in which zebrafish were exposed to Cu. First, we determined the median lethal concentration (LC_{50-96 h}) of Cu and then assessed whether Cu exposure results in effects similar to those associated with exposure to the water and sediment samples collected from the study site. The water and sediment samples directly impacted the exploratory behavior of zebrafish, showing clear anxiety-like behavioral phenotype and stress in terms of cortisol increase (during the second rain event). The Cu exposure did not mimic the same behavioral changes triggered by the water and sediment samples, although it had caused similar stress in the fish. Our results highlight that even at low concentrations, the water and sediment samples from vineyard watershed runoff were able to induce behavioral and endocrine changes that may harm the ecological balance of an aquatic environment.

Toxicological effects induced on early life stages of zebrafish (Danio rerio) after an acute exposure to microplastics alone or co-exposed with copper

Data about the toxicological interactions of MPs and heavy metals in biota is limited, particularly in fish early life stages. This study aimed to evaluate the toxicological effects of MPs and copper (Cu), alone or combined, in zebrafish early life stages. Embryos were exposed from 2 until 96-h post-fertilization (hpf) to MPs (2 mg/L), three sub-lethal concentrations of Cu (15, 60 and 125 μg/L) and binary mixtures containing Cu and MPs (Cu15+MPs, Cu60+MPs, Cu125+MPs). Lethal and sub-lethal parameters, histopathological changes, biochemical biomarkers, gene expression and behavior were assessed. Our findings showed that Cu and Cu + MPs decreased embryos survival and hatching rate. Increased ROS levels were observed in larvae exposed to the two lowest Cu and Cu + MPs groups, suggesting an induction of oxidative stress. An increased CAT and GPx activities were observed in Cu and Cu + MPs, implying a response of the antioxidant defense system to overcome the metal and MPs stress. The sod1 expression was downregulated in all Cu groups and in the two highest Cu + MPs exposed groups. AChE was significantly inhibited in Cu and Cu + MPs groups, indicating neurotoxicity. A disruption of avoidance and social behaviors were also noticed in the Cu125 and Cu125+MPs exposed larvae. Evidences of Cu-toxicity modulation by MPs were observed in some endpoints. Overall, the findings of this study highlight that Cu alone or co-exposed with MPs lead to oxidative stress, neurotoxicity and ultimately behavioral alterations in early life stages of zebrafish, while MPs alone do not produce significant effects on zebrafish larvae.

An acetylcholinesterase inhibitor, donepezil, increases anxiety and cortisol levels in adult zebrafish

BACKGROUND

A potent acetylcholinesterase inhibitor, donepezil is a cognitive enhancer clinically used to treat neurodegenerative diseases. However, its complete pharmacological profile beyond cognition remains unclear. The zebrafish (Danio rerio) is rapidly becoming a powerful novel model organism in neuroscience and central nervous system drug screening.

AIM

Here, we characterize the effects of 24-h donepezil administration on anxiety-like behavioral and endocrine responses in adult zebrafish.

METHODS

We evaluated zebrafish anxiety-like behaviors in the novel tank, the light-dark and the shoaling tests, paralleled by assessing brain acetylcholinesterase activity and whole-body cortisol levels.

RESULTS

Overall, donepezil dose-dependently decreased zebrafish locomotor activity in the novel tank test and reduced time in light in the light-dark test, likely representing hypolocomotion and anxiety-like behaviors. Donepezil predictably decreased brain acetylcholinesterase activity, also increasing whole-body cortisol levels, thus further linking acetylcholinesterase inhibition to anxiety-like behavioral and endocrine responses.

CONCLUSION

Collectively, these findings suggest negative modulation of zebrafish affective behavior by donepezil, support the key role of cholinergic mechanisms in behavioral regulation in zebrafish, and reinforce the growing utility of zebrafish models for studying complex behavioral processess and their neuroendocrine and neurochemical regulation.

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.

The Single and Combined Effects of Wildfire Runoff and Sediment-Bound Copper on the Freshwater Amphipod Hyalella azteca

The frequency of wildfire is expected to increase with time as a function of climate change. Recent studies in our laboratory have demonstrated that pyrogenic polycyclic aromatic hydrocarbons can cause greater-than-additive effects in Hyalella azteca in the presence of low concentrations of Cu. We hypothesized that freshwater animals inhabiting Cu-contaminated sites, such as those in the vicinity of Cu mines, may be vulnerable to nonadditive toxicity from contaminants released by wildfires. To investigate the interaction between Cu and water conditioned by burnt wood ash (fire extract), we exposed H. azteca for 14 d to binary mixtures of 225 mg/kg Cu-enriched artificial sediment (225 mg Cu/kg) and a fire extract dilution series (12.5, 25, 50, 75, and 100%). All binary mixtures of Cu-enriched sediment and fire extract resulted in complete mortality with the exception of Cu-enriched sediment + 12.5% fire extract. The combination of Cu-enriched sediment with 12.5% fire extract had a more-than-additive effect on survival and tissue Cu concentration, but there was no reduction in growth or acetylcholinesterase activity compared to the 225 mg/kg Cu-contaminated sediment or fire extract control, respectively. Acetylcholinesterase activity was significantly reduced in amphipods exposed to fire extract, but the presence of Cu did not exacerbate this effect. The results suggest that Cu-contaminated water bodies that receive runoff from wildfires are at risk of enhanced toxicity. Environ Toxicol Chem 2020;39:1988-1997. © 2020 SETAC.

D-Penicillamine prolongs survival and lessens copper-induced toxicity in Drosophila melanogaster

D-penicillamine (DPA) is an amino-thiol that has been established as a copper chelating agent for the treatment of Wilson's disease. DPA reacts with metals to form complexes and/or chelates. Here, we investigated the survival rate extension capacity and modulatory role of DPA on Cu²⁺-induced toxicity in Drosophila melanogaster. Adult Wild type (Harwich strain) flies were exposed to Cu²⁺ (1 mM) and/or DPA (50 μM) in the diet for 7 days. Additionally, flies were exposed to acute Cu²⁺ (10 mM) for 24 h, followed by DPA (50 μM) treatment for 4 days. Thereafter, the antioxidant status [total thiol (T-SH) and glutathione (GSH) levels and glutathione S-transferase and catalase activities] as well as hydrogen peroxide (H₂O₂) level and acetylcholinesterase activity were evaluated. The results showed that DPA treatment prolongs the survival rate of D. melanogaster by protecting against Cu²⁺-induced lethality. Further, DPA restored Cu²⁺-induced depletion of T-SH level compared to the control (P < 0.05). DPA also protected against Cu²⁺ (1 mM)-induced inhibition of catalase activity. In addition, DPA ameliorated Cu²⁺-induced elevation of acetylcholinesterase activity in the flies. The study may therefore have health implications in neurodegenerative diseases involving oxidative stress such as Alzheimer's disease.

Zebrafish Models in Neural and Behavioral Toxicology across the Life Stages

The industry is increasingly relying on fish for toxicity assessment. However, current guidelines for toxicity assessment focus on teratogenicity and mortality. From an ecotoxicological point of view, however, these endpoints may not reflect the “full picture” of possible deleterious effects that can nonetheless result in decreased fitness and/or inability to adapt to a changing environment, affecting whole populations. Therefore, assessing sublethal effects add relevant data covering different aspects of toxicity at different levels of analysis. The impacts of toxicants on neurobehavioral function have the potential to affect many different life-history traits, and are easier to assess in the laboratory than in the wild. We propose that carefully-controlled laboratory experiments on different behavioral domains—including anxiety, aggression, and exploration—can increase our understanding of the ecotoxicological impacts of contaminants, since these domains are related to traits such as defense, sociality, and reproduction, directly impacting life-history traits. The effects of selected contaminants on these tests are reviewed, focusing on larval and adult zebrafish, showing that these behavioral domains are highly sensitive to small concentrations of these substances. These strategies suggest a way forward on ecotoxicological research using fish.

The synergistic toxicity of Cd(II) and Cu(II) to zebrafish (Danio rerio): Effect of water hardness

We have evaluated the interactive toxicity of Cu(II) and Cd(II) in water with different hardness levels using adult zebrafish (Danio rerio). Zebrafish were exposed to Cd(II) (0.2-22 μM) or Cu(II) (0.1-8 μM) in single or binary exposures in very soft, moderately hard or very hard water. The whole body burdens of Cd(II) and Cu(II) reflect the net effect of biouptake and elimination, mortality was the indicator of toxicity, and whole body major ion content was measured to assess ion regulatory functions. Cu(II) was found to be more toxic than Cd(II) for zebrafish, and Cu(II) and Cd(II) exhibited a significant synergistic effect. The toxicity of metal ions increased upon decreasing the ionic strength of the exposure medium, probably due to elevated competition between metal ions with other cations in hard water and increased activity of Ca²⁺ pathways in soft water treatments. Whole body metal accumulation and the accumulation rate of both Cu and Cd increased as the metal ion concentration in the exposure medium increased. Nevertheless, neither parameter explained the observed synergistic effect on mortality. Finally, we observed a significant loss of whole body Na⁺ in fish which died during the metal exposure compared to surviving fish, irrespective of exposure conditions. Such an effect was not observed for other major cations (K⁺, Ca²⁺ and Mg²⁺). This observation suggests that, under the applied exposure conditions, survival was correlated to the capacity of the organism to maintain Na⁺ homeostasis.

Triclosan alters adult zebrafish behavior and targets acetylcholinesterase activity and expression

Triclosan is widely used in consumer products as an antimicrobial agent. Epidemiological studies have reported the association of triclosan with adverse birth outcomes. The toxic effects of triclosan on the developing stages of zebrafish are reported, however, its role as behavioral modifier is limited. In the present study, adult zebrafish were exposed to triclosan (0.3 and 0.6 mg/L) for 48 h and the exploratory behavior was analyzed using ZebraTrack. Triclosan exposed group showed significantly reduced locomotion concomitant with increased freezing duration. They also showed erratic movements suggesting that triclosan induced anxiety-like behavior in adult zebrafish. Next, we tested the hypothesis that the anxiety-like behavior is linked to altered acetylcholinesterase activity. We found that the triclosan exposure decreased acetylcholinesterase activity in the brain and skeletal muscle but acetylcholinesterase (ache) gene was significantly down-regulated only in the skeletal muscle of the adult zebrafish exposed to triclosan. In addition, we also observed a down-regulation of myelin basic protein (mbp) gene in the skeletal muscle of adult zebrafish treated with triclosan. Thus, our data indicates that even short exposure of triclosan is potent enough to induce behavioral anomalies in adult zebrafish that appear to involve acetylcholinesterase and other structural proteins especially in the skeletal muscle.

The effect of copper on behaviour, memory, and associative learning ability of zebrafish (Danio rerio)

Copper is an essential element in many biological processes, but may exert toxic effects at levels surplus to metabolic requirements. Herein we assess the effect of copper on zebrafish behaviour using two assays, namely the novel tank diving test and a T-maze test with food reward. Novel tank diving tests were conducted on days 0, 4, and 10 of a 10 day Cu exposure (at concentrations of 0.77 μM (25% of the 240 h LC50) and 1.52 μM (50% of the 240 h LC50) to assess the alterations of behavioural responses in repeating novel tank diving assays and the effect of Cu on these patterns. Results demonstrate habituation to novelty, which is an indicator of spatial memory. Copper exposure had no effect on the latency of entry into the upper zones of the tank, nor on the total time spent therein, but did cause a greater number of freezing bouts in comparison to the control group. Additionally, Cu exposure had no effect on the habituation responses of zebrafish. Using the T-maze assay, we tested the effect of prior exposure to Cu for 10 days on subsequent behavioural trainings. The T-maze protocol was based on associative learning, where a visual stimulus (colour) was linked with a natural stimulus (food). Results of the control group showed that zebrafish are able to perform associative learning tasks. Moreover, Cu was found to negatively affect the associative learning capabilities. Specifically, while zebrafish in the control group achieved a significant number of correct choices (leading to food reward) throughout the T-maze training, such a trend was not observed for Cu exposed fish. Thus at the exposure concentrations and exposure times considered herein, Cu has no determinative impact on instinctual behavioural responses of zebrafish in repeated novel tank diving assays but does limit the associative learning capabilities.

The interactive effect of copper(II) and conspecific alarm substances on behavioural responses of zebrafish (Danio rerio)

Environmental contaminants such as metal ions can have detrimental effects on aquatic organisms at the molecular, organismal and population levels. In the present work, we examined the interactive effect of Cu(II) and conspecific alarm substance on zebrafish behavioural responses utilizing the novel tank diving assay. To this end, 3 novel tank diving tests (on day 0, 3 and 10 of the experimental phase) were conducted on zebrafish in 4 experimental groups: (1) control: no Cu(II) and no alarm substance, (2) Cu(II) only: exposed to 0.78 μM Cu(II) (25 % of the 240 h LC50) in the home tank for 10 days, (3) alarm substance only: exposed to alarm substance for 6 min concomitant with behavioural testing, and (4) Cu(II) + alarm substance: exposed to 0.78 μM Cu(II) in the home tank for 10 days and treated with alarm substance for 6 min during the behavioural testing. Results showed robust habituation response of zebrafish. Exposure to Cu(II) did not affect the behavioural phenotypes of zebrafish in the novel tank diving test or habituation responses. Alarm substance treatment evoked strong anxiety-like behaviour. Finally, zebrafish in the Cu(II) + alarm substance group lost their sensitivity to alarm substance in repeated novel tank assays throughout the concomitant Cu(II) exposure; this observation is tentatively ascribed to Cu(II)-induced olfactory impairment.

Effects of oral administration of copper capsules on helminth control in lactating dairy sheep: An effective alternative to replace conventional antiparasitics during lactation

Two experiments were performed to determine whether oral administration of copper oxide capsules controlled helminthic infections in Lacaune sheep without acute collateral effects on animal health. In experiment 1, 48 multiparous lactating sheep (60.1 ± 8.5 kg) were stratified according to initial number of eggs (Haemonchus contortus) per gram of feces (EPG) and were assigned randomly to 1 of two treatments (24 sheep/treatment): no oral administration (control) or oral administration of two copper capsules (treated; approximately 58 mg copper/kg body weight). Blood and fecal samples were collected on days 0, 15 and 45. Animals treated with copper capsules showed lower of EPG, eosinophils, acetylcholinesterase (AChE) in whole blood, and lower butyrylcholinesterase (BChE) activity in serum. Treated sheep had higher erythrocyte numbers, hemoglobin concentrations, hematocrit, and lymphocyte numbers. In experiment 2, 12 male lambs negative for helminths and coccidia were assigned randomly to one of two treatments (six lambs/treatment): control or treated (one copper capsule; approximately 58 mg copper/kg body weight); the experiment was designed to determine whether the results of experiment 1 were due to treatment or parasitism. Blood samples were collected on days 0, 5, 10 and 15 and fecal samples were collected on days 0, 7 and 15. Treated animals showed greater concentrations of lymphocytes; however, treatment had no effect on other hemogram variables, AChE and BChE activities, or levels of alanine aminotransferase, aspartate aminotransferase, gamma-glutamyl transferase, creatinine, urea, albumin, total protein, and reactive oxygen species. These data suggest that copper capsules in dairy sheep efficiently controlled H. contortus infections. Treatment was not harmful to lambs during the first 15 days, i.e. there were no signs of acute toxicity.

Iron and manganese present in underground water promote biochemical, genotoxic, and behavioral alterations in zebrafish (Danio rerio)

Iron (Fe) and manganese (Mn) are metals commonly found at high concentrations in underground water. These metals are essential for the good functioning of living organisms, but high concentrations lead to imbalance, potentiating the appearance of pathologies. This study aimed to evaluate the effect of exposure to naturally occurring metals in groundwater, using zebrafish (Danio rerio) as an experimental model. Thus, zebrafish were exposed to Fe (0.8 and 1.3 mg/L), Mn (0.2 and 0.4 mg/L), and groundwater collected from deep tube wells with Fe and Mn (Fe 0.8/Mn 0.2 mg/L and Fe 1.3/Mn 0.4 mg/L) for 30 days. Bioaccumulation of these metals has been demonstrated in the livers and muscles of zebrafish. Acetylcholinesterase activity changed only in zebrafish muscles in all groups. Sulfhydryl levels changed mainly in the group Mn 0.4. SOD/CAT ratio decreased in the groups Fe 0.8 and 1.3, Mn 0.4, and Fe 0.8/Mn 0.4. An increase in the frequency of micronucleus in all groups was shown as a consequence of these changes. Behavioral parameters (time and distance traveled, mean speed, turn angle, latency, and number of crossings between compartments) have also changed, mainly in the groups Fe 1.3, Mn 0.4, and Fe 1.3/Mn 0.4. Therefore, long-term exposure to Fe and Mn, even at not so high concentrations, may cause biochemical, genotoxic, and behavioral changes in zebrafish.

Is there a link between acetylcholinesterase, behaviour and density populations of the ragworm Hediste diversicolor?

The main objective of the present study was to explore the potential link between acetylcholinesterase (AChE) activity and burrowing behaviour of the ragworm Hediste diversicolor, which may have consequences at higher levels of biological organisation. Two complementary studies were conducted. AChE activity, at the sub-individual level, and behavioural responses, at the individual level, were evaluated in worms from the Loire estuary (France), whereas density and biomass of H. diversicolor were determined at the population level. A Spearman positive correlation between both biomarkers (AChE and burrowing) suggested that inhibition of AChE activity was linked to behaviour impairments. At the population level, lower AChE and behaviour activities were detected in worms corresponding to lower population density and biomass. These results provide direct empirical field evidence demonstrating the sensitivity of behaviour of H. diversicolor as a biomonitor of estuarine health status assessment.

Sub-lethal effects of waterborne copper in early developmental stages of rainbow trout (Oncorhynchus mykiss)

The aim of this work was to study the impact of copper during a sub-chronic exposure to environmental concentrations in the early life stages of rainbow trout (Oncorhynchus mykiss). Eyed-stage embryos of rainbow trout, at 265 °D, were exposed in semi-static conditions to sub-lethal concentrations of CuSO₄ up to the larval stage (528 °D) under laboratory-controlled conditions. During 3 weeks, they were exposed to the environmentally-realistic concentration of 2 µg/L Cu and to a 10-fold higher concentration, 20 µg/L Cu. Several biological (survival, hatching success, malformation, growth) and behavioral (swimming activity) and molecular endpoints (genotoxicity and gene transcription) were studied. Exposure to 20 µg/L Cu had an inhibitory effect on hatching and increased half-hatched embryos (25%). At the end of the exposure, no significant differences were observed in growth of the larvae exposed to the highest Cu concentration. However, larvae exposed to 2 µg/L Cu exhibited increased growth in comparison with non-exposed larvae. The percentage of malformed larvae was significantly higher for both copper conditions, with skeletal malformations being the most observed. Expression of several genes was evaluated in whole larvae using quantitative real-time PCR. Genes involved in detoxification (gst, mt1 and mt2) and in cell cycle arrest (p53) were significantly repressed in both copper conditions when compared to control. In addition, potential genotoxic effects on larvae were investigated by the comet assay on blood cells, but this test did not demonstrate any significant DNA damage on larvae exposed to copper. This study confirms the adverse effects of copper on early life stages of rainbow trout even at the lowest environmentally relevant tested concentration.

Spatial avoidance, inhibition of recolonization and population isolation in zebrafish (Danio rerio) caused by copper exposure under a non-forced approach

Aquatic ecosystems receive run-off and discharges from different sources that lead to the accumulation of contaminants such as copper. Besides producing lethal and sub-lethal effects, copper has shown to be aversive to zebrafish (Danio rerio) by triggering avoidance response. The primary aim of the present study was to evaluate how a copper gradient could affect the spatial distribution of D. rerio by triggering avoidance, preventing recolonization and isolating populations. Secondly, to what extent the food availability in a previously avoided environment could make it a less aversive environment was assessed. A non-forced, multi-compartmented exposure system with a copper gradient (0-300 μg·L^-1), through which fish could move, was used for the avoidance and recolonization assays. To test the effect of copper on population isolation, two uncontaminated connected zones were separated by a chemical barrier with a copper concentration of 90 μg·L^-1 (a concentration producing an avoidance of 50% - AC₅₀). Zebrafish avoided copper and the 2 h-AC₅₀ was 90.8 μg·L^-1. The recolonization was in accordance with avoidance and the relationship AC_x/RC_100-x (RC: recolonization concentration) was around 2.5. When food was provided in the highest copper concentration, the recolonization pattern was altered, although the distribution of the fish was not statistically different from the scenario without food. The chemical barrier formed by copper (90 μg·L^-1) impaired the migratory potential of the fish population by 41.3%; when food was provided in the last compartment, no statistically significant trend of fish moving towards that concentration was observed. Copper might act as an environmental disruptor by triggering spatial avoidance, preventing recolonization and isolating populations in zebrafish. The present study allows simultaneously including three ecological concepts to ecotoxicological studies that have received little attention: habitat selection, recolonization and habitat chemical fragmentation.

Stress-driven emigration in complex field scenarios of habitat disturbance: The heterogeneous multi-habitat assay system (HeMHAS)

Lines of evidence used in ecological risk assessment (ERA) are essentially three: chemistry, biology and ecotoxicology. Until now, the fundamental assumption made when measuring ecological risks is that organisms are forcedly exposed to stressors. However, when organisms can avoid disturbed habitats by escaping to less stressful areas, the assumption that exposure is mandatory to pose risk may not match field disturbance scenarios. A non-forced exposure approach using a linear free-choice multi-compartmented system has been proposed previously as a complementary tool to assess the effects on organisms' spatial avoidance/preference responses. Yet, the linearity of the latter system limits avoidance measurements to one spatial dimension. A novel, heterogeneous multi-habitat assay system (HeMHAS) consisting of 18 connected circular compartments (3 compartments on a vertical axis in each one of 6 zones on a longitudinal axis; a 2D system) is put forward here to be used in heterogeneous-habitat selection studies, as it makes it possible to assess the ability of organisms to detect contamination and other stressors and select more favorable habitats. In the present study, the avoidance to copper by zebrafish (Danio rerio) was tested after exposing organisms to a copper gradient in the HeMHAS and compared with that in the linear system. Avoidance occurred for all copper concentrations: 43% in the lowest (21 μg·L^-1) to 72% in the highest (221 μg·L^-1). Results obtained within the HeMHAS (AC₅₀: 60 μg·L^-1) were statistically (p = 0.72) similar to avoidance of copper by D. rerio in the linear non-forced system (AC₅₀: 89 μg·L^-1). In summary, the simulation of a copper gradient in the HeMHAS (2D system) allowed to assess the potential repellency of copper to zebrafish and to corroborate the ability of organisms to detect and avoid potentially toxic concentrations.

Differential copper-induced death and regeneration of olfactory sensory neuron populations and neurobehavioral function in larval zebrafish

Fish rely heavily on their sense of smell to maintain behaviors essential for survival, such as predator detection and avoidance, prey selection, social behavior, imprinting, and homing to natal streams and spawning sites. Due to its direct contact with the outside environment, the peripheral olfactory system of fish is particularly susceptible to dissolved contaminants. In particular, environmental exposures to copper (Cu) can cause a rapid loss of olfactory function. In this study, confocal imaging of double-transgenic zebrafish larvae with differentially labeled ciliated and microvillous olfactory sensory neurons (OSNs) were used to examine cell death and regeneration following Cu exposure. Changes in cell morphologies were observed at varying degrees within both ciliated and microvillous OSNs, including the presence of round dense cell bodies, cell loss and fragmentation, retraction or loss of axons, disorganized cell arrangements, and loss of cells and fluorescence signal intensity, which are all indicators of cell death after Cu exposure. A marked loss of ciliated OSNs relative to microvillous OSNs occurred after exposure to low Cu concentrations for 3 h, with some regeneration observed after 72 h. At higher Cu concentrations and 24-h exposures, ciliated and microvillous OSNs were damaged with increased severity of injury with longer Cu exposures. Interestingly, microvillous, but not ciliated OSNs, regenerated rapidly within the 72-h time period of recovery after death from Cu exposure, suggesting that microvillous OSNs may be replaced in lieu of ciliated OSNs. An increase in bromodeoxyuridine labeling was observed 24 h after Cu-induced OSN death, suggesting that increased proliferation of the olfactory stem cells replaced the damaged OSNs. Olfactory behavioral analyses supported our imaging studies and revealed both initial loss and restoration of olfactory function after Cu exposures. In summary, our studies indicate that following zebrafish OSN damage by Cu, regeneration of microvillous OSNs may occur exceeding ciliated OSNs, likely via increased proliferation of the cellular reservoir of neuronal OSC precursors. Transgenic zebrafish are a valuable tool to study metal olfactory injury and recovery and to characterize sensitive olfactory neuron populations in fish exposed to environmental pollutants.

Reactive oxygen species generation is likely a driver of copper based nanomaterial toxicity

Determining the specific nanomaterial features that elicit adverse biological responses is important to inform risk assessments, develop targeted applications, and rationally design future nanomaterials. Embryonic zebrafish are often employed to study nanomaterial-biological interactions, but few studies address the role of the chorion in nanomaterial exposure and toxicity. Here, we used chorion-intact (CI) or dechorionated (DC) embryonic zebrafish to investigate the influence of the chorion on copper-based nanoparticle toxicity. We found that despite higher dissolution and uptake, CuO NPs were less toxic than Cu NPs regardless of chorion status and did not cause 100 % mortality at even the highest exposure concentration. The presence of the chorion inhibited Cu toxicity: DC exposures to Cu NPs had an LC50 of 2.5 ± 0.3 mg/L compared to a CI LC50 of 13.7 ± 0.8 mg/L. This highlights the importance of considering zebrafish chorion status during nanotoxicological investigations, as embryo sensitivity increased by one order of magnitude or more when chorions were removed. Agglomerate size, zeta potential, and dissolved Cu did not sufficiently explain the differences in toxicity between Cu NPs and CuO NPs; however, reactive oxygen species (ROS) generation did. Cu NPs generated ROS in a concentration-dependent manner, while CuO did not and generated less than Cu NPs. We believe that the differences between the toxicities of Cu NPs and CuO NPs are due in part to their ability to generate ROS which could and should be a hazard consideration for risk assessments.

Combined effect of copper sulfate and water temperature on key freshwater trophic levels - Approaching potential climatic change scenarios

This work relied on the use microcosms to evaluate the individual and the combined effects of different levels of copper sulfate (0.0, 0.013, 0.064 and 0.318mg Cu L^-1) - a fungicide commonly exceeding allowable thresholds in agricultural areas - and a range of water temperature increase scenarios (15, 20 and 25°C) on freshwater species belonging to different functional groups. Hence, the growth inhibition of primary producers (the microalgae Raphidocelis subcapitata and the macrophyte Lemna minor), as well as the survival and feeding behavior of a shredder species (the Trichoptera Schizopelex sp.) were evaluated. The results revealed that copper was toxic to primary producers growth, as well as shredders growth and survival, being the growth of L. minor particularly affected. Higher water temperatures had generally enhanced the growth of primary producers under non-contaminated (microalgae and macrophytes) or low-contaminated (macrophytes) conditions. Despite the tendency for a more pronounced toxicity of copper under increasing water temperatures, a significant interaction between the two factors was only observed for microalgae. Since the test organisms represent relevant functional groups for sustaining freshwater systems functions, the present results may raise some concerns on the impacts caused by possible future climate change scenarios in aquatic habitats chronically exposed to the frequent or intensive use of the fungicide copper sulfate.

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.

In vivo toxic effects of 4-methoxy-5-hydroxy-canthin-6-one in zebrafish embryos via copper dyshomeostasis and oxidative stress

Dysfunction of copper homeostasis can lead to a host of disorders, which might be toxic sometimes. 4-Methoxy-5-hydroxy-canthin-6-one (CAN) is one of the major constituents from Picrasma quassioides and responsible for its therapeutic effects. In this work, we evaluated the toxic effect of CAN (7.5μM) on zebrafish embryos. CAN treatment decreased survival, delayed hatching time and induced malformations (loss of pigmentation, pericardial edema, as well as hematologic and neurologic abnormalities). Besides, exogenous copper supplementation rescued the pigmentation and cardiovascular defects in CAN-treated embryos. Further spectroscopic studies revealed a copper-chelating activity of CAN. Then its regulation on the expressions of copper homeostasis related genes also be analyzed. In addition, CAN lowered the total activity of SOD, elevated the ROS production and altered the oxidative related genes transcriptions, which led to oxidative stress. In conclusion, we demonstrated that CAN (7.5μM) might exert its toxic effects in zebrafish embryos by causing copper dyshomeostasis and oxidative stress. It will give insight into the risk assessment and prevention of CAN-mediated toxicity.

Copper at low levels impairs memory of adult zebrafish (Danio rerio) and affects swimming performance of larvae

Metal contamination at low levels is an important issue because it usually produces health and environmental effects, either positive or deleterious. Contamination of surface waters with copper (Cu) is a worldwide event, usually originated by mining, agricultural, industrial, commercial, and residential activities. Water quality criteria for Cu are variable among countries but allowed limits are generally in the μg/L range, which can disrupt several functions in the early life-stages of fish species. Behavioral and biochemical alterations after Cu exposure have also been described at concentrations close to the allowed limits. Aiming to search for the effects of Cu in the range of the allowed limits, larvae and adult zebrafish (Danio rerio) were exposed to different concentrations of dissolved Cu (nominally: 0, 5, 9, 20 and 60μg/L; measured: 0.4, 5.7, 7.2 16.6 and 42.3μg/L, respectively) for 96h. Larvae swimming and body length, and adult behavior and biochemical biomarkers (activity of glutathione-related enzymes in gills, muscle, and brain) were assessed after Cu exposure. Several effects were observed in fish exposed to 9μg/L nominal Cu, including increased larvae swimming distance and velocity, abolishment of adult inhibitory avoidance memory, and decreased glutathione S-transferase (GST) activity in gills of adult fish. At the highest Cu concentration tested (nominally: 60μg/L), body length of larvae, spatial memory of adults, and gill GST activity were decreased. Social behavior (aggressiveness and conspecific interaction), and glutathione reductase (GR) activity were not affected in adult zebrafish. Exposure to Cu, at concentrations close to the water quality criteria for this metal in fresh water, was able to alter larvae swimming performance and to induce detrimental effects on the behavior of adult zebrafish, thus indicating the need for further studies to reevaluate the currently allowed limits for Cu in fresh water.