Aluminum exposure alters behavioral parameters and increases acetylcholinesterase activity in zebrafish (Danio rerio) brain

Prolonged exposure to the synthetic glucocorticoid dexamethasone induces brain damage via oxidative stress and apoptotic response in adult Daniorerio

Due to its extensive use as a painkiller, anti-inflammatory, and immune modulatory agent, as well as its effectiveness in treating severe COVID-19, dexamethasone, a synthetic glucocorticoid, has gained attention not only for its impact on public health but also for its environmental implications. Various studies have reported its presence in aquatic environments, including urban waters, surface samples, sediments, drinking water, and wastewater effluents. However, limited information is available regarding its toxic effects on nontarget aquatic organisms. Therefore, this study aimed to investigate the mechanism of toxicity underlying dexamethasone-induced brain damage in the bioindicator Danio rerio following long-term exposure. Adult zebrafish were treated with environmentally relevant concentrations of dexamethasone (20, 40, and 60 ng L-1) for 28 days. To elucidate the possible mechanisms involved in the toxicity of the pharmaceutical compound, we conducted a behavioral test battery (Novel Tank and Light and Dark tests), oxidative stress biomarkers, acetylcholinesterase enzyme activity quantification, histopathological analysis, and gene expression analysis using qRT-PCR (p53, bcl-2, bax, caspase-3, nrf1, and nrf2).The results revealed that the pharmaceutical compound could produce anxiety-like symptoms, increase the oxidative-induced stress response, decrease the activity of acetylcholinesterase enzyme, and cause histopathological alterations, including perineuronal vacuolization, granular and molecular layers deterioration, cell swallowing and intracellular spaces. The expression of genes involved in the apoptotic process (p53, bax, and casp-3) and antioxidant defense (nrf1 and nrf2) was upregulated in response to oxidative damage, while the expression of the anti-apoptotic gene bcl-2 was down-regulated indicating that the environmental presence of dexamethasone may pose a threat to wildlife and human health.

Exploring the Combined Effect of Exercise and Apigenin on Aluminium-Induced Neurotoxicity in Zebrafish

Aluminium (AL) is a strong environmental neurotoxin linked to neurodegenerative disorders. Widespread industrial use leads to its presence in water systems, causing bioaccumulation in organisms. This, in turn, results in the bioaccumulation of AL in various organisms. Several studies have highlighted the benefits of enhanced physical activity in combating neurodegenerative diseases. Meanwhile widespread presence of apigenin in aquatic environment has been largely overlooked, in terms of its potential to counter AL-induced neurotoxicity. The combined impact of exercise and apigenin in mitigating the effects of AL-induced neurotoxicity in aquatic animals remains unexplored. Hence, the objective of this study is to determine whether the combined treatment of exercise and apigenin can effectively alleviate the chronic neurotoxicity induced by AL. Zebrafish that were exposed to AL showed behaviours resembling anxiety, increased aggression, unusual swimming pattern, and memory impairment, which are typical features observed in Alzheimer's disease (AD)-like syndrome. Combined treatment of exercise and apigenin protects zebrafish from AL-induced neurotoxicity, which was measured by improvements in memory, reduced anxiety and aggression, and increased levels of antioxidant enzymes and acetylcholinesterase (AChE) activity. Furthermore, AL exposure is associated with increased expression of genes related to neuroinflammation and AD. However, synergistic effect of exercise and apigenin counteract this effect in AL-treated zebrafish. These findings suggest that AL is involved in neurodegenerative diseases in fish, which could affect the integrity of aquatic ecosystem. Hence, there is a strong correlation between enhanced physical activity, apigenin, and the well-being of the ecosystem.

Biochemistry biomarkers and metal levels as indicators of environmental pollution in Danio rerio exposed to the Sorocaba River (S.P.), Brazil

Metal contamination of the environment poses a significant threat to human health and can cause significant damage to aquatic ecosystems. Danio rerio was exposed to Sorocaba River water for 96 h from two different sites in summer (S) and winter (W). Concentrations of Al, Cd, Cu, Mn and Zn were determined in the exposure water and in sediment. At the end of the exposure, the concentrations of Al, Cu and Mn at the Ibiúna point (P1) and Mn at the Itupararanga point (P2) decreased compared to the initial concentrations in the water. In summer and winter, the highest concentrations of Cu and Mn were found in the sediment. Exposure to the Sorocaba River water caused various responses both in summer and winter. For example, GPx decreased in winter, Glutathione S-Transferase (GST) increased in summer, and Nitric Oxide Synthase (NOS) decreased in both seasons in the viscera. In winter, SOD Superoxide Dismutase (SOD) increased, while GPx and GST (winter) decreased in muscle; regarding viscera carbonyl proteins, there was an increase in the summer at P2. Acetylcholinesterase activity decreased in the brain in winter at P2 and NOS decreased in the summer-exposed groups and increased in the winter P2-exposed group. Lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) decreased in viscera (S, P1) and increased in muscle (S, P1 and P2). The glucose and triglycerides increased in muscle, both in summer and winter. Correlation analysis revealed associations between biomarkers from different organs. These alterations suggest that the fish experienced oxidative stress in response to exposure to the Sorocaba River, contaminated with metals, highlighting their vulnerability to environmental pollutants.

Metal-contaminated sediment toxicity in a highly impacted Neotropical river: Insights from zebrafish embryo toxicity assays

The Fundão dam collapse was one of the largest mining-related disasters globally. It resulted in the release of mining tailings containing heavy metals, which contaminated the Doce River in southeastern Brazil. This study assessed the effects of acute exposure of Danio rerio embryos to sediments contaminated by mine tailings six years after the Fundão dam collapse. The study sites included P2, P3, and P4 in the upper Doce River, as well as site P1 on the Piranga River, an uncontaminated river. Sediment samples were analyzed for 10 metals/metalloid by atomic absorption spectrometry. In the assays, embryos were exposed to sediment from P1-P4 sites, and uncontaminated quartz was used as control sediment. Various biomarkers were applied to assess biological responses, and the integrated biomarker response (IBR) index was calculated for each site. Sediment samples revealed elevated levels of As, Cr, Cu, Hg, and Ni beyond Brazilian legislation limits. At 96-h exposure, embryo mortality rates exceeded 20% in P1, P2, and P3, higher than the control and P4 (p < 0.0001). Hatching rates ranged from 60 to 80% in P1, P2, and P3, lower than the control and P4 (p < 0.001). Larvae exposed to P2 sediment (closest to the Fundão dam) exhibited skeletal, physiological, and sensory malformations. Neurotoxicity was indicated by increased acetylcholinesterase activity and reduced spontaneous movements in embryos exposed to Doce River sediment. Contamination also increased metallothionein and heat shock protein 70 levels, along with changes in cell proliferation and apoptosis. Principal component analysis showed a good correlation between metals/metalloid in the sediment and larval morphometric endpoints. The IBR index highlighted suitable biomarkers for monitoring metal contamination in fish embryos. Overall, our findings suggest that sediment toxicity following the Fundão dam failure may compromise the sustainability of fish communities in the Doce River.

Neuroprotective effects of Shenghui decoction via inhibition of the JNK/p38 MAPK signaling pathway in an AlCl3-induced zebrafish (Danio rerio) model of Alzheimer's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Alzheimer's disease (AD) is a multi-factorial degenerative disease, and multi-targeted therapies targeting multiple pathogenic mechanisms should be explored. Shenghui decoction (SHD) is an ancient traditional Chinese medicine (TCM) formula used clinically to alleviate AD. However, the precise mechanism of action of SHD as a therapeutic agent for AD remains unclear.

AIM OF THE STUDY

This study investigated the neuroprotective properties and potential mechanisms of action of SHD in mitigating AD-like symptoms induced by AlCl3 in a zebrafish model.

MATERIALS AND METHODS

Active components of SHD were detected using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Zebrafish were exposed to AlCl3 (200 μg/L) for 30 days to establish an AD zebrafish model. AlCl3-exposed zebrafish were treated with SHD or donepezil. Behavioral tests were used to assess learning and memory, locomotor activity, and AD-related anxiety and aggression in AlCl3-exposed zebrafish. Nissl staining and transmission electron microscopy were used to evaluate histological alterations in brain neurons. The concentrations of pro-inflammatory cytokines (tumor necrosis factor-α, TNF-α; interleukin-1β, IL-1β) were quantified using Enzyme-linked immunosorbent assay (ELISA). Markers of oxidative stress and cholinergic activity (acetylcholinesterase, AChE) were detected using biochemical assays. Western blotting and immunofluorescence were used to detect the protein expression levels of Aβ, p-tau, PSD-95, synaptophysin, TLR4, phosphorylation of NF-κB p65, p38, and JNK.

RESULTS

Fifteen SHD compounds were identified by UPLC-MS/MS analysis. SHD improved AlCl3-induced dyskinesia, learning and memory impairment, anxiety-like behavior, and aggressive behavior in zebrafish. AlCl3-exposed zebrafish showed AD-like pathology, overexpression of Aβ, hyperphosphorylated tau protein, marked neuronal damage, decreased expression of synaptic proteins, synaptophysin, and PSD-95, and impairment of synaptic structural plasticity. These effects were reversed by the SHD treatment. We also observed that SHD ameliorated oxidative stress and decreased AChE activity and inflammatory cytokine levels. These effects are similar to those observed for donepezil. Meanwhile, SHD could decrease the protein expression of TLR4 and inhibit phosphorylation of NF-κB, JNK, and p38 MAPK. These results demonstrate that SHD has the potential to exert neuroprotective effects, which may be partly mediated via inhibition of the JNK/p38 MAPK signaling pathway.

CONCLUSIONS

Our findings revealed the therapeutic mechanism of SHD in mitigating AD progression and suggested that SHD is a potent neuroprotectant that contributes to the future development of TCM modernization and broader clinical applications.

Polluted water from a storage dam (Villa Victoria, méxico) induces oxidative damage, AChE activity, embryotoxicity, and behavioral changes in Cyprinus carpio larvae

The Villa Victoria dam is one of the most important storage reservoirs in Mexico since it distributes water to more than 20 million inhabitants in the Metropolitan Zone of Mexico City. In this dam, the common carp (Cyprinus carpio) is an important food resource for the inhabitants, so the aim of this work was to evaluate the oxidative damage (lipoperoxidation, oxidized proteins, antioxidant enzymes activity and gene expression), AChE, embryotoxicity and behavioral changes in C. carpio embryos and larvae exposed to water from Villa Victoria dam for 24, 48, 72 and 96 h. The embryotoxicity was evaluated trough the General Morphology Score (GMS) and the teratogenic index. Behavioral changes in basal locomotor activity and thigmotaxis were evaluated in a DanioVision, Noldus ™. An increase in lipid and protein oxidation as well as modification of CAT, SOD and GPx enzymatic activity was observed during the exposure times. The GMS indicated a low development in the embryos, the teratogenic index was less than 1, however teratogenic effects as yolk edema, fin malformation, head malformation and scoliosis were observed. In parallel, an increase in AChE activity and gene expression was observed reflecting changes in distance traveled of the basal locomotor activity and thigmotaxis at the sampling points. In conclusion, pollutants in water from Villa Victoria dam caused oxidative damage, changes in SOD, CAT, GPx and AChE activity as well as embryotoxicity and modifications in the behavior of C. carpio larvae. This study demonstrates the need to implement restoration programs for this reservoir since, contamination in the Villa Victoria dam could eventually endanger aquatic life and human health.

Petrosamine isolated from marine sponge Petrosia sp. demonstrates protection against neurotoxicity in vitro and in vivo

According to The World Alzheimer Report 2023 by Alzheimer's Disease International (ADI) estimates that 33 to 38.5 million people worldwide suffer from Alzheimer's Disease (AD). A crucial hallmark associated with this disease is associated with the deficiency of the brain neurotransmitter acetylcholine, due to an affected acetylcholinesterase (AChE) activity. Marine organisms synthesize several classes of compounds, some of which exhibit significant AChE inhibition, such as petrosamine, a coloured pyridoacridine alkaloid. The aim of this work was to characterize the activity of petrosamine isolated for the first time from a Brazilian marine sponge, using two neurotoxicity models with aluminium chloride, as exposure to aluminium is associated with the development of neurodegenerative diseases. The in vitro model was based in a neuroblastoma cell line and the in vivo model exploited the potential of zebrafish (Danio rerio) embryos in mimicking hallmarks of AD. To our knowledge, this is the first report on petrosamine's activity over these parameters, either in vitro or in vivo, in order to characterize its full potential for tackling neurotoxicity.

Ecotoxicological assessment of Cu-rich acid mine drainage of Sulitjelma mine using zebrafish larvae as an animal model

Acid mine drainage (AMD) is widely acknowledged as a substantial threat to the biodiversity of aquatic ecosystems. The present study aimed to study the toxicological effects of Cu-rich AMD from the Sulitjelma mine in zebrafish larvae. The AMD from this mine was found to contain elevated levels of dissolved metals including Mg (46.7 mg/L), Al (20.2 mg/L), Cu (18.3 mg/L), Fe (19.8 mg/L) and Zn (10.6 mg/L). To investigate the toxicological effects, the study commenced by exposing zebrafish embryos to various concentrations of AMD (ranging from 0.75% to 9%) to determine the median lethal concentration (LC50). Results showed that 96 h LC50 for zebrafish larvae following AMD exposure was 2.86% (95% CI: 2.32-3.52%). Based on acute toxicity results, zebrafish embryos (<2 hpf) were exposed to 0.1% AMD (Cu: 21.7 µg/L) and 0.45% AMD (Cu: 85.7 µg/L) for 96 h to assess development, swimming behaviour, heart rate, respiration and transcriptional responses at 116 hpf. Light microscopy results showed that both 0.1% and 0.45% AMD reduced the body length, eye size and swim bladder area of zebrafish larvae and caused phenotypic abnormalities. Swimming behaviour results showed that 0.45% AMD significantly decreased the locomotion of zebrafish larvae. Heart rate was not affected by AMD exposure. Furthermore, exposure caused a significant increase in oxygen consumption indicating vascular stress in developing larvae. Taken altogether, the study shows that even heavily diluted AMD with environmentally relevant levels of Cu caused toxicity in zebrafish larvae.

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.

Effect of an environmental microplastic mixture from the Seine River and one of the main associated plasticizers, dibutylphthalate, on the sentinel species Hediste diversicolor

The aim of this study was to explore the adverse effects of a microplastic (MP) mixture obtained from litter accumulated in the Seine River (France) compared to those of their major co-plasticizer, dibutylphthalate (DBP), on the sentinel species Hediste diversicolor. A suite of biomarkers has been investigated to study the impacts of MPs (100 mg kg-1 sediment), DBP (38 μg kg-1 sediment) on worms compared to non-exposed individuals after 4 and 21 days. The antioxidant response, immunity, neurotoxicity and energy and respiratory metabolism were investigated using biomarkers. After 21 days, worms exposed to MPs showed an increasing aerobic metabolism, an enhancement of both antioxidant and neuroimmune responses. Energy-related biomarkers demonstrated that the energy reallocated to the defence system may come from proteins. A similar impact was depicted after DBP exposure, except for neurotoxicity. Our results provide a better understanding of the ecotoxicological effects of environmental MPs and their associated-contaminants on H. diversicolor.

Synthesis and biological evaluation of thieno[3,2-c]pyrazol-3-amine derivatives as potent glycogen synthase kinase 3β inhibitors for Alzheimer's disease

Glycogen synthase kinase 3β (GSK-3β) is a potential target for anti-Alzheimer's disease (AD) drug development. In this study, a series of novel thieno[3,2-c]pyrazol-3-amine derivatives was synthesized and evaluated as potential GSK-3β inhibitors by structure-based drug design. The thieno[3,2-c]pyrazol-3-amine derivative 54 with a 4-methylpyrazole moiety which interacted with Arg141 by π-cation interaction was identified as a potent GSK-3β inhibitor with an IC50 of 3.4 nM and an acceptable kinase selectivity profile. In the rat primary cortical neurons, compound 54 showed neuroprotective effects on Aβ-induced neurotoxicity. Western blot analysis indicated that 54 inhibited GSK-3β by up-regulating the expression of phosphorylated GSK-3β at Ser9 and down-regulating the expression of phosphorylated GSK-3β at Tyr216. Meanwhile, 54 decreased tau phosphorylation at Ser396 in a dose-dependent way. In astrocytes and microglia cells, 54 inhibited the expression of inducible nitric oxide synthase (iNOS), indicating that 54 showed an anti-neuroinflammatory effect. In the AlCl3-induced zebrafish AD model, 54 significantly ameliorated the AlCl3-induced dyskinesia, demonstrating its anti-AD activity in vivo.

Cannabis sativa-based oils against aluminum-induced neurotoxicity

The use of terpenoid compounds in different neural-related conditions is becoming useful for several illnesses. Another possible activity of these compounds is the reduction of nervous impairment. Cannabis sativa plants are known for their concentration of two important terpenoids, the delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). CBD and THC have central peripheral activities already described and their usage in different brain diseases, such as Alzheimer's and multiple sclerosis. Aluminum (Al) is known as an important neurotoxic compound, the physiological action of Al is not known already, and in high concentrations can lead to intoxication and cause neurotoxicity. Here we evaluated the potential effect of two different doses of CBD- and THC-rich based oils against Al-induced toxicity, in the zebrafish model. We evaluated behavioral biomarkers of the novel tank test (NTT) and social preference test (SPT), and biochemical markers: the activity of the enzyme acetylcholinesterase (AChE) and the antioxidant enzymes-catalase, superoxide dismutase, and glutathione-S-transferase. CBD- and THC-based oils were able to increase the AChE activity helping the cholinergic nervous system actuate against Al toxicity which was reflected by the behavioral biomarkers changes. We concluded that the oils have a protective effect and might be used with proposals for neurological and antioxidant impairment avoidance caused by Al intoxications.

Improvement in Zebrafish with Diabetes and Alzheimer's Disease Treated with Pasteurized Akkermansia muciniphila

Diabetes and Alzheimer's disease (AD) are associated with specific changes in the composition of the intestinal flora. Studies have shown that the supplementation with pasteurized Akkermansia muciniphila has therapeutic and preventive effects on diabetes. However, it is not clear whether there is any association with improvement in and prevention of Alzheimer's disease and diabetes with Alzheimer's disease. Here, we found that pasteurized Akkermansia muciniphila can significantly improve the blood glucose, body mass index, and diabetes indexes of zebrafish with diabetes mellitus complicated with Alzheimer's disease and also alleviate the related indexes of Alzheimer's disease. The memory, anxiety, aggression, and social preference behavior of zebrafish with combined type 2 diabetes mellitus (T2DM) and Alzheimer's disease (TA zebrafish) were significantly improved after pasteurized Akkermansia muciniphila treatment. Moreover, we examined the preventive effect of pasteurized Akkermansia muciniphila on diabetes mellitus complicated with Alzheimer's disease. The results showed that the zebrafish in the prevention group were better in terms of biochemical index and behavior than the zebrafish in the treatment group. These findings provide new ideas for the prevention and treatment of diabetes mellitus complicated with Alzheimer's disease. IMPORTANCE The interaction between intestinal microflora and host affects the progression of diabetes and Alzheimer's disease. As a recognized next-generation probiotic, Akkermansia muciniphila has been shown to play a key role in the progression of diabetes and Alzheimer's disease, but whether A. muciniphila can improve diabetes complicated with Alzheimer's disease and its potential mechanism are unclear. In this study, a new zebrafish model of diabetes mellitus complicated with Alzheimer's disease was established, and the effect of Akkermansia muciniphila on diabetes mellitus complicated with Alzheimer's disease is discussed. The results showed that Akkermansia muciniphila after pasteurization significantly improved and prevented diabetes mellitus complicated with Alzheimer's disease. Treatment with pasteurized Akkermansia muciniphila improved the memory, social preference, and aggressive and anxiety behavior of TA zebrafish and alleviated the pathological characteristics of T2DM and AD. These results provide a new prospect for probiotics in the treatment of diabetes and Alzheimer's disease.

Trihydroxy piperlongumine protects aluminium induced neurotoxicity in zebrafish: Behavioral and biochemical approach

Aluminium (Al) is proven to be a potent environmental neurotoxin involved in progressive neurodegeneration. Al primarily induces oxidative stress by free radical generation in the brain, followed by neuronal apoptosis. Antioxidants are promising therapeutic options for Al toxicity. Piperlongumine is traditionally long known for its medicinal properties. Therefore, the present study has been designed to explore the antioxidant role of trihydroxy piperlongumine (THPL) against Al-induced neurotoxicity in the zebrafish model. Zebrafish exposed to AlCl₃ exhibited higher oxidative stress and altered locomotion. Adult fish displayed anxiety comorbid with depression phenotype. THPL increases antioxidant enzyme activity by quenching Al-induced free radicals and lipid peroxidation, thus minimizing oxidative damage in the brain. THPL rescues behavior deficits and improves anxiety-like phenotype in adult fish. Histological alterations caused by Al were also attenuated on administration with THPL. Results of the study demonstrate the neuroprotective role of THPL against Al-induced oxidative damage and anxiety, which could be exploited as a psychopharmacological drug.

Ameliorative Effect of Palm Oil in Aluminum Lactate Induced Biochemical and Histological Implications in Rat Brain

α-Tocotrienol is one of the major constituents of palm oil. It is a well-known antioxidant and cholesterol-lowering neuroprotectant. To prevent the initiation of Alzheimer's like symptoms, much attention has been shifted to the major role played by antioxidants. Previous epidemiological reports correlate the increasing incidence of developing Alzheimer's disease (AD), to the aluminum (Al) content in drinking water. Al, being a ubiquitous element, has a long history of being particularly reactive towards multiple aspects of neurobiology. So, the current study examines the effect of Al-induced behavioral, biochemical, and histopathological changes in rat brain; and the ameliorative effect of palm oil in reducing the resulting neurotoxicity. The experimental design consisted of 4 groups: control group which received rodent chow diet and water ad libitum; Al group received aluminum lactate (50 mg/kg bw); Al + palm oil group was administered with Al (50 mg/kg bw) and palm oil (60 mg/kg bw); and palm oil group received palm oil (60 mg/kg bw). Al was given by oral gavage once daily for 6 weeks and palm oil was administered intraperitoneally. After 6 weeks of supplementation, Al + palm oil group showed significantly lower malondialdehyde (MDA) content, but higher superoxide dismutase (SOD), catalase (CAT), GST, and GPx activity as compared to Al group. Al group has significantly higher level of MDA content, but lower SOD, CAT, GST, and GPx activity as compared to control group. In conclusion, this study suggested that palm oil was effective in preventing the Al-induced brain damage in rats.

Changes in blood parameters and metabolism in bullfrog tadpoles, Lithobates catesbeianus, (Shaw, 1802) after exposure to the Sorocaba River (São Paulo, Brazil) water

This study evaluated the genetic damage, oxidative stress, neurotoxicity, and energy metabolism in bullfrog tadpoles (Lithobates catesbeianus) exposed to water from two sites of the Sorocaba River, Ibiúna (PI), and Itupararanga reservoir (PIR), in summer and winter. After 96-h exposure, the erythrocyte number decreased in PI and increase in PIR in summer. Bullfrogs show oxidative unbalance (liver, kidney, and muscle), with alterations in the nitric oxide synthase and glucose 6-phosphate dehydrogenase. Cholinesterase increased in the brain in PI and PIR in the summer and decreased in PI in the winter. It also increased in the muscle in both PI and PIR in the winter. Tadpoles show alterations in the activity of the metabolic enzymes (liver, kidney, and muscle), such as phosphofructokinase, pyruvatokinase, malate dehydrogenase, and lactate dehydrogenase; and in the amount of glucose and triglycerides metabolites. Exposure to the Sorocaba River reflected a stressful situation for L. catesbeianus as the changes caused to their metabolism associated with oxidative stress and neurotoxicity may have effects on the development of tadpoles.

Nutrient combinations exhibit universal antianxiety, antioxidant, neuro-protecting, and memory-improving activities

Anxiety disorders are the most common mental disorders and, without proper treatment, may lead to severe conditions: e.g., somatic disorders or permanent damage to central nervous system. Although there are drugs in clinical trials, this study focuses on exploring the efficacy of nutrients in treating these diseases. We built different zebrafish models and screened several nutrient combinations for their antianxiety, antioxidant, neuro-protecting, and memory-improving activities. Our results showed that the combinations of nutrients (e.g., Walnut Peptides + Theanine at 14.2 + 33.3 μg/ml) have similar or better activities than the positive control drugs. In addition, we discovered that the effects of the nutrients in the above four aspects were universal and highly related. This study is noteworthy as it suggested that nutrients could be healthier and greener drug alternatives and provide similar or better universal treatments for anxiety and related conditions.

Single and joint effects of cadmium and selenium on bioaccumulation, oxidative stress and metabolomic responses in the clam Scrobicularia plana

Selenium (Se) is a vital trace element for many living organisms inclusive of aquatic species. Although the antagonistic action of this element against other pollutants has been previously described for mammals and birds, limited information on the join effects in bivalves is available. To this end, bivalves of the species Scrobicularia plana were exposed to Se and Cd individually and jointly. Digestive glands were analysed to determine dose-dependent effects, the potential influence of Se on Cd bioaccumulationas well as the possible recover of the oxidative stress and metabolic alterations induced by Cd. Selenium co-exposure decreased the accumulation of Cd at low concentrations. Cd exposure significantly altered the metabolome of clams such as aminoacyltRNA biosynthesis, glycerophospholipid and amino acid metabolism, while Se co-exposure ameliorated several altered metabolites such asLysoPC (14:0), LysoPE (20:4), LysoPE (22:6), PE (14:0/18:0), PE (20:3/18:4) andpropionyl-l-carnitine.Additionally, Se seems to be able to regulate the redox status of the digestive gland of clams preventing the induction of oxidativedamage in this organ. This study shows the potential Se antagonism against Cd toxicity in S. plana and the importance to study join effects of pollutants to understand the mechanism underlined the effects.

Hizikia fusiforme functional oil (HFFO) prevents neuroinflammation and memory deficits evoked by lipopolysaccharide/aluminum trichloride in zebrafish

Background

Oxidative stress, cholinergic deficiency, and neuroinflammation are hallmarks of most neurodegenerative disorders (NDs). Lipids play an important role in brain development and proper functioning. Marine-derived lipids have shown good memory-improving potentials, especially those from fish and microalgae. The cultivated macroalga Hizikia fusiforme is healthy food and shows benefits to memory, but the study is rare on the brain healthy value of its oil. Previously, we had reported that the Hizikia fusiforme functional oil (HFFO) contains arachidonic acid, 11,14,17-eicosatrienoic acid, phytol, and other molecules displaying in vitro acetylcholinesterase inhibitory and nitroxide scavenging activity; however, the in vivo effect remains unclear. In this study, we further investigated its potential effects against lipopolysaccharides (LPS)- or aluminum trichloride (AlCl3)-induced memory deficiency in zebrafish and its drug-related properties in silica.

Methods

We established memory deficit models in zebrafish by intraperitoneal (i.p.) injection of lipopolysaccharides (LPS) (75 ng) or aluminum trichloride (AlCl3) (21 μg), and assessed their behaviors in the T-maze test. The interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), acetylcholine (ACh), and malondialdehyde (MDA) levels were measured 24 h after the LPS/AlCl3 injection as markers of inflammation, cholinergic activity, and oxidative stress. Furthermore, the interaction of two main components, 11,14,17-eicosatrienoic acid and phytol, was investigated by molecular docking, with the important anti-inflammatory targets nuclear factor kappa B (NF-κB) and cyclooxygenase 2 (COX-2). Specifically, the absorption, distribution, metabolism, excretion, and toxicity (ADMET) and drug-likeness properties of HFFO were studied by ADMETlab.

Results

The results showed that HFFO reduced cognitive deficits in zebrafish T-maze induced by LPS/AlCl3. While the LPS/AlCl3 treatment increased MDA content, lowered ACh levels in the zebrafish brain, and elevated levels of central and peripheral proinflammatory cytokines, these effects were reversed by 100 mg/kg HFFO except for MDA. Moreover, 11,14,17-eicosatrienoic acid and phytol showed a good affinity with NF-κB, COX-2, and HFFO exhibited acceptable drug-likeness and ADMET profiles in general.

Conclusion

Collectively, this study's findings suggest HFFO as a potent neuroprotectant, potentially valuable for the prevention of memory impairment caused by cholinergic deficiency and neuroinflammation.

Multi-biomarker approach to evaluate the neurotoxic effects of environmentally relevant concentrations of phenytoin on adult zebrafish Danio rerio

Several studies have reported the presence of phenytoin (PHE) in wastewater treatment plant effluents, hospital effluents, surface water, and even drinking water. However, published studies on the toxic effects of PHE at environmentally relevant concentrations in aquatic organisms are scarce. The present study aimed to determine the effect of three environmentally relevant concentrations of PHE (25, 282, and 1500 ng L^-1) on behavioral parameters using the novel tank test. Moreover, we also aimed to determine whether or not these concentrations of PHE may impair acetylcholinesterase (AChE) activity and oxidative status in the brain of Danio rerio adults. Behavioral responses suggested an anxiolytic effect in PHE-exposed organisms, mainly observed in organisms exposed to 1500 ng L^-1, with a significant decrease in fish mobility and a significant increase in activity at the top of the tank. Besides the behavioral impairment, PHE-exposed fish also showed a significant increase in the levels of lipid peroxidation, hydroperoxides, and protein carbonyl content compared to the control group. Moreover, a significant increase in brain AChE levels was observed in fish exposed to 282 and 1500 ng L^-1. The results obtained in the present study show that PHE triggers a harmful response in the brain of fish, which in turn generates fish have an anxiety-like behavior.

Histological alterations and oxidative stress in adult zebrafish muscle after aluminium exposure

Aluminium (Al) is among the most abundant metals in nature, and its presence in the environment is further increasing by anthropogenic activities. In water bodies, the Al concentrations ranged between 0.001 and 50 mg/L, raising concerns about the health of aquatic organisms. For this reason, zebrafish was chosen as the model, since it is well suited for ecotoxicological studies. Adult specimens were exposed to 11 mg/L of Al for 10, 15 and 20 days to assess both the morphology and the oxidative state of muscle tissue. Considering the involvement of ROS, the activity of the main antioxidant enzymes, metallothioneins contents, but also oxidative damage and enzymes involved in energy consumption and neuromuscular transmission were assessed. Collected data showed an increase in the thickness of the endomysium and resorbed myofibrils in the organisms exposed to Al for 10 days, and an increase of myotomes' size in the organisms exposed to Al for 15 days. Moreover, the organisms exposed for less time to Al, it was evident an activation of anaerobic metabolism and the increased activity of antioxidant enzymes such as superoxide dismutase, glutathione peroxidase and glutathione S-transferases. However, these effects stabilized with increasing exposure time. In addition, only after 20 days of treatment did the oxidative damage to the proteins and the activity of acetylcholinesterase increase while the levels of metallothioneins and the lipid peroxidation were lower for all treated animals when compared to the control group. Overall, the biochemical and histological changes induced by aluminium exposure in the muscular tissue represent a relevant contribution to understanding the environmental risk due to the diffusion of this metal within the aquatic compartment.

AlCl3 induced learning and memory deficit in zebrafish

Aluminium is a metal known to cause neurotoxicity in the brain, by promoting neurodegeneration and affecting memory and cognitive ability. AlCl₃ has been reported to enhance reactive oxygen species (ROS) and inflammatory markers which are further responsible for the degeneration of neurons. AlCl₃ exposure to zebrafish causes behavioral, biochemical, and neurochemical changes in the brain. In our study, Zebrafish were exposed to AlCl₃ at three different doses (50 µg/L, 100 µg/L, and 200 µg/L) for four consecutive days. On days 1st and 4th, a novel diving test was performed to check anxiety in zebrafish. T - maze and novel object recognition test were used to check the memory on days 3rd and 4th with the help of ANY-maze software. On the last day (4th day), zebrafishes were sacrificed and whole brains were used to perform the biochemical, neurotransmitters, histopathological, and immunohistochemistry analysis. Our study revealed that AlCl₃ exposure significantly decreased the total distance traveled, and the number of entries in the top zone and increased the time spent in the bottom zone, checked through the novel diving test. In the T maze test, AlCl₃ treated zebrafish showed significantly increased transfer latency to the favorable zone and time spent, and the number of entries to the unfavorable zone. The exploration time with the novel object was reduced significantly after AlCl₃ treatment. Moreover, reduced glutathione (GSH) and superoxide dismutase (SOD) levels were significantly reduced in AlCl₃ treated zebrafish whereas malondialdehyde (MDA) level was found to be increased, indicating high oxidative stress. The neurotransmitters level was also disturbed indicated by the significantly decreased GABA, dopamine, noradrenaline, and Serotonin levels and increased glutamate level in the brain of zebrafish treated with AlCl₃. Moreover, histopathological and immunohistochemistry study shows a markedly increased number of pyknotic neurons and reduced the expression of Nrf2 in the zebrafish brain after AlCl₃ exposure. These findings suggest that AlCl₃ significantly causes behavioral, biochemical, neurotransmitters, morphological, and molecular changes in zebrafish, ultimately causing AD.

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.

Modeling neurodegenerative disorders in zebrafish

Neurodegeneration is a major cause of Alzheimer's, Parkinson's, Huntington's, multiple and amyotrophic lateral sclerosis, pontocerebellar hypoplasia, dementia and other related brain disorders. Their complex pathogenesis commonly includes genetic and neurochemical deficits, misfolded protein toxicity, demyelination, apoptosis and mitochondrial dysfunctions. Albeit differing in specific underlying mechanisms, neurodegenerative disorders typically display evolutionarily conserved mechanisms across taxa. Here, we review the role of zebrafish models in recapitulating major human and rodent neurodegenerative conditions, demonstrating this species as a highly relevant experimental model for research on neurodegenerative diseases, and discussing how these fish models can further clarify the underlying genetic, neurochemical, neuroanatomical and behavioral pathogenic mechanisms.

Induction of aggression and anxiety-like responses by perfluorooctanoic acid is accompanied by modulation of cholinergic- and purinergic signaling-related parameters in adult zebrafish

Perfluorooctanoic acid (PFOA) is a contaminant of global concern owing to its prevalent occurrence in aquatic and terrestrial environments with potential hazardous impact on living organisms. Here, we investigated the influence of realistic environmental concentrations of PFOA (0, 0.25, 0.5, or 1.0 mg/L) on relevant behaviors of adult zebrafish (Danio rerio) (e.g., exploration to novelty, social preference, and aggression) and the possible role of PFOA in modulating cholinergic and purinergic signaling in the brain after exposure for 7 consecutive days. PFOA significantly increased geotaxis as well as reduced vertical exploration (a behavioral endpoint for anxiety), and increased the frequency and duration of aggressive episodes without affecting their social preference. Exposure to PFOA did not affect ADP hydrolysis, whereas ATP and AMP hydrolysis were significantly increased at the highest concentration tested. However, AChE activity was markedly decreased in all PFOA-exposed groups when compared with control. In conclusion, PFOA induces aggression and anxiety-like behavior in adult zebrafish and modulates both cholinergic and purinergic signaling biomarkers. These novel data can provide valuable insights into possible health threats related to human activities, demonstrating the utility of adult zebrafish to elucidate how PFOA affects neurobehavioral responses in aquatic organisms.

Role of Environmental Toxicants on Neurodegenerative Disorders

Neurodegeneration leads to the loss of structural and functioning components of neurons over time. Various studies have related neurodegeneration to a number of degenerative disorders. Neurological repercussions of neurodegeneration can have severe impacts on the physical and mental health of patients. In the recent past, various neurodegenerative ailments such as Alzheimer’s and Parkinson’s illnesses have received global consideration owing to their global occurrence. Environmental attributes have been regarded as the main contributors to neural dysfunction-related disorders. The majority of neurological diseases are mainly related to prenatal and postnatal exposure to industrially produced environmental toxins. Some neurotoxic metals, like lead (Pb), aluminium (Al), Mercury (Hg), manganese (Mn), cadmium (Cd), and arsenic (As), and also pesticides and metal-based nanoparticles, have been implicated in Parkinson’s and Alzheimer’s disease. The contaminants are known for their ability to produce senile or amyloid plaques and neurofibrillary tangles (NFTs), which are the key features of these neurological dysfunctions. Besides, solvent exposure is also a significant contributor to neurological diseases. This study recapitulates the role of environmental neurotoxins on neurodegeneration with special emphasis on major neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease.

Marine fungal metabolite butyrolactone I prevents cognitive deficits by relieving inflammation and intestinal microbiota imbalance on aluminum trichloride-injured zebrafish

Background

Mounting evidences indicate that oxidative stress, neuroinflammation, and dysregulation of gut microbiota are related to neurodegenerative disorders (NDs). Butyrolactone I (BTL-I), a marine fungal metabolite, was previously reported as an in vitro neuroprotectant and inflammation inhibitor. However, little is known regarding its in vivo effects, whereas zebrafish (Danio rerio) could be used as a convenient in vivo model of toxicology and central nervous system (CNS) diseases.

Methods

Here, we employed in vivo and in silico methods to investigate the anti-NDs potential of BTL-I. Specifically, we established a cognitive deficit model in zebrafish by intraperitoneal (i.p.) injection of aluminum trichloride (AlCl₃) (21 μg) and assessed their behaviors in the T-maze test. The proinflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) as well as acetylcholinesterase (AChE) activity or glutathione (GSH) levels were assayed 24 h after AlCl₃ injection. The intestinal flora variation of the zebrafish was investigated by 16S rDNA high-throughput analysis. The marine fungal metabolite, butyrolactone I (BTL-I), was used to modulate zebrafish cognitive deficits evoked by AlCl₃ and evaluated about its effects on the above inflammatory, cholinergic, oxidative stress, and gut floral indicators. Furthermore, the absorption, distribution, metabolism, excretion, and toxicity (ADMET) and drug-likeness properties of BTL-I were studied by the in silico tool ADMETlab.

Results

BTL-I dose-dependently ameliorated AlCl₃-induced cognitive deficits in zebrafish. While AlCl₃ treatment elevated the levels of central and peripheral proinflammatory cytokines, increased AChE activity, and lowered GSH in the brains of zebrafish, these effects, except GSH reduction, were reversed by 25–100 mg/kg BTL-I administration. Besides, 16S rDNA high-throughput sequencing of the intestinal flora of zebrafish showed that AlCl₃ decreased Gram-positive bacteria and increased proinflammatory Gram-negative bacteria, while BTL-I contributed to maintaining the predominance of beneficial Gram-positive bacteria. Moreover, the in silico analysis indicated that BTL-I exhibits acceptable drug-likeness and ADMET profiles.

Conclusions

The present findings suggest that BTL-I is a potential therapeutic agent for preventing CNS deficits caused by inflammation, neurotoxicity, and gut flora imbalance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02403-3.

Effects of Aluminium Contamination on the Nervous System of Freshwater Aquatic Vertebrates: A Review

Aluminium (Al) is the most common natural metallic element in the Earth’s crust. It is released into the environment through natural processes and human activities and accumulates in aquatic environments. This review compiles scientific data on the neurotoxicity of aluminium contamination on the nervous system of aquatic organisms. More precisely, it helps identify biomarkers of aluminium exposure for aquatic environment biomonitoring in freshwater aquatic vertebrates. Al is neurotoxic and accumulates in the nervous system of aquatic vertebrates, which is why it could be responsible for oxidative stress. In addition, it activates and inhibits antioxidant enzymes and leads to changes in acetylcholinesterase activity, neurotransmitter levels, and in the expression of several neural genes and nerve cell components. It also causes histological changes in nerve tissue, modifications of organism behaviour, and cognitive deficit. However, impacts of aluminium exposure on the early stages of aquatic vertebrate development are poorly described. Lastly, this review also poses the question of how accurate aquatic vertebrates (fishes and amphibians) could be used as model organisms to complement biological data relating to the developmental aspect. This “challenge” is very relevant since freshwater pollution with heavy metals has increased in the last few decades.

Developmental alterations, teratogenic effects, and oxidative disruption induced by ibuprofen, aluminum, and their binary mixture on Danio rerio

Several studies highlighted the ubiquitous presence of ibuprofen and aluminum in the aquatic environment around the world and demonstrated their potential to induce embryotoxic and teratogenic defects on aquatic species individually. Although studies that evaluate developmental alterations induced by mixtures of these pollutants are scarce; and, since environmental contamination presented in the form of a mixture of toxicants with different chemical properties and toxicity mechanisms capable of generating interactions; the objective of this study was to evaluate the developmental defects, teratogenic alterations, and oxidative stress induced by individual forms and the mixture of ibuprofen (IBU) and aluminum (Al) on zebrafish embryos. Oocytes exposed to environmentally relevant concentrations of IBU (0.1-20 μg L-1) and Al (0.01-8 mg L-1) and one binary mixture. The LC50 and EC50 were obtained to calculate the teratogenic index (TI). The IBU LC50, EC50, and TI were 8.06 μg L-1, 2.85 μg L-1 and 2.82. In contrast, Al LC50 was 5.0 mg L-1with an EC50 of 3.58 mg L-1 and TI of 1.39. The main alterations observed for individual compounds were hatching alterations, head malformation, skeletal deformities, hypopigmentation, pericardial edema, and heart rate impairment. The mixture also showed significant delays to embryonic development. Moreover, oxidative stress biomarkers of cellular oxidation and antioxidant defenses at 72 and 96 hpf significantly increased. Results show that environmentally relevant concentrations of ibuprofen (IBU), aluminum (Al), and their mixture promote a series of developmental defects, teratogenic effects, and oxidative disruption on D. rerio embryos, and the interaction of both substances altered the response. In conclusion, morphological and biochemical tests are suitable tools for assessing the health risk of aquatic wildlife by exposure to individual and mixed pollutants in freshwater bodies.

Essential Oils from Spices Inhibit Cholinesterase Activity and Improve Behavioral Disorder in AlCl3 Induced Dementia

The chemical compositions of essential oils (EOs) prepared from six spices including cinnamon, amomum tsao-ko, cardamom, amomum, black pepper and white pepper were analyzed by gas chromatography-mass spectrometry (GC/MS), which led to identify almost 200 volatile compounds. All EOs of spices showed cholinesterase inhibitory activity. Among them, pepper EO showed most potent acetylcholinesterase (AChE) inhibitory activity with IC₅₀ values of 8.54 μg/mL (black pepper EO) and 5.02 μg/mL (white pepper EO). Molecular docking and in vitro validation suggested that 3-carene, α-pinene and β-pinene with IC₅₀ value of 1.73, 2.66, and 14.75 μg/mL, respectively, might be active constituents of spices oil in inhibiting AChE. Furthermore, amomum tsao-ko EO and amomum EO can improve behavioral disorder in dementia zebrafish induced by aluminum trichloride (AlCl₃ ).

Environmental impacts of COVID-19 treatment: Toxicological evaluation of azithromycin and hydroxychloroquine in adult zebrafish

One of the most impact issues in recent years refers to the COVID-19 pandemic, the consequences of which thousands of deaths recorded worldwide, are still inferior understood. Its impacts on the environment and aquatic biota constitute a fertile field of investigation. Thus, to predict the impact of the indiscriminate use of azithromycin (AZT) and hydroxychloroquine (HCQ) in this pandemic context, we aim to assess their toxicological risks when isolated or in combination, using zebrafish (Danio rerio) as a model system. In summary, we observed that 72 h of exposure to AZT and HCQ (alone or in binary combination, both at 2.5 μg/L) induced the reduction of total protein levels, accompanied by increased levels of thiobarbituric acid reactive substances, hydrogen peroxide, reactive oxygen species and nitrite, suggesting a REDOX imbalance and possible oxidative stress. Molecular docking analysis further supported this data by demonstrating a strong affinity of AZT and HCQ with their potential antioxidant targets (catalase and superoxide dismutase). In the protein-protein interaction network analysis, AZT showed a putative interaction with different cytochrome P450 molecules, while HCQ demonstrated interaction with caspase-3. The functional enrichment analysis also demonstrated diverse biological processes and molecular mechanisms related to the maintenance of REDOX homeostasis. Moreover, we also demonstrated an increase in the AChE activity followed by a reduction in the neuromasts of the head when zebrafish were exposed to the mixture AZT + HCQ. These data suggest a neurotoxic effect of the drugs. Altogether, our study demonstrated that short exposure to AZT, HCQ or their mixture induced physiological alterations in adult zebrafish. These effects can compromise the health of these animals, suggesting that the increase of AZT and HCQ due to COVID-19 pandemic can negatively impact freshwater ecosystems.

Long-term exposure to environmentally relevant concentrations of ibuprofen and aluminum alters oxidative stress status on Danio rerio

Despite the ubiquitous presence of multiple pollutants in aqueous environments have been extensively demonstrated, the ecological impact of chemical cocktails has not been studied in depth. In recent years, environmental studies have mainly focused on the risk assessment of individual chemical substances neglecting the effects of complex mixtures even though it has been demonstrated that combined effects exerted by pollutants might represent a greater hazard to the biocenosis. The current study evaluates the effects on the oxidative stress status induced by individual forms and binary mixtures of ibuprofen (IBU) and aluminum (Al) on brain, gills, liver and gut tissues of Danio rerio after long-term exposure to environmentally relevant concentrations (0.1-11 μg L^-1 and 0.05 mg L^-1- 6 mg L^-1, respectively). Lipid peroxidation (LPO), Protein carbonyl content (PCC) and activity of Superoxide Dismutase (SOD), Catalase (CAT), and Glutathione Peroxidase (GPX) were evaluated. Moreover, concentrations of both toxicants and the metabolite 2-OH-IBU were quantified on test water and tissues. Results show that ibuprofen (IBU) and aluminum (Al) singly promote the production of radical species and alters the oxidative stress status in all evaluated tissues of zebrafish, nevertheless, higher effects were elicited by mixtures as different interactions take place.

Advances of Zebrafish in Neurodegenerative Disease: From Models to Drug Discovery

Neurodegenerative disease (NDD), including Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis, are characterized by the progressive loss of neurons which leads to the decline of motor and/or cognitive function. Currently, the prevalence of NDD is rapidly increasing in the aging population. However, valid drugs or treatment for NDD are still lacking. The clinical heterogeneity and complex pathogenesis of NDD pose a great challenge for the development of disease-modifying therapies. Numerous animal models have been generated to mimic the pathological conditions of these diseases for drug discovery. Among them, zebrafish (Danio rerio) models are progressively emerging and becoming a powerful tool for in vivo study of NDD. Extensive use of zebrafish in pharmacology research or drug screening is due to the high conserved evolution and 87% homology to humans. In this review, we summarize the zebrafish models used in NDD studies, and highlight the recent findings on pharmacological targets for NDD treatment. As high-throughput platforms in zebrafish research have rapidly developed in recent years, we also discuss the application prospects of these new technologies in future NDD research.

A Systematic Analysis of Metal and Metalloid Concentrations in Eight Zebrafish Recirculating Water Systems

Metals and metalloids are integral to biological processes and play key roles in physiology and metabolism. Nonetheless, overexposure to some metals or lack of others can lead to serious health consequences. In this study, eight zebrafish facilities collaborated to generate a multielement analysis of their centralized recirculating water systems. We report a first set of average concentrations for 46 elements detected in zebrafish facilities. Our results help to establish an initial baseline for trouble-shooting purposes, and in general for safe ranges of metal concentrations in recirculating water systems, supporting reproducible scientific research outcomes with zebrafish.

Exposure to aluminium causes behavioural alterations and oxidative stress in the brain of adult zebrafish

Aluminium (Al) water pollution is an increasing environmental problem. Accordingly, this study aimed to find out more about its toxic effects on aquatic organisms. Adult zebrafish were exposed to 11 mg/L of Al and the behavioural responses and its correlation with brain oxidative stress, antioxidant-defences, changes in metabolism and neurotransmission were assessed at 10, 15 and 20 days of exposure. The behavioural and locomotory responses, suggest an increase in the anxiety state, especially observed in animals exposed to Al for 15 days. The reactive oxygen species increased in a time-dependent trend, while the oxidative damage varied over exposure time. The activity of antioxidant enzymes, as superoxide dismutase, glutathione peroxidase and glutathione S-transferases, and the metallothioneins levels increased after short-term exposures and tended to decrease or stabilize at longer times. The results contribute to understand the toxic mechanisms activated by Al highlighting correlations like behavioural disorders and oxidative state.

Apoptosis, oxidative stress and genotoxicity in developing zebrafish after aluminium exposure

Aluminium is a non-essential metal and potentially toxic to organisms whose environmental concentration increases due to pollution. In our previous studies, the behavioral changes induced by aluminium were already shown on zebrafish, a model organism widely used for ecotoxicology screening. To examine in depth the knowledge about the toxicity mechanism induced by this metal, zebrafish embryos, at 6 hpf, have been exposed to 50, 100 and 200 µM of AlCl₃ for 72 h. Phenotypic alterations, apoptosis and oxidative stress responses have been assessed by evaluations of antioxidant defence and changes in metabolism at the end of treatment. The mRNA expression level of c-fos, appa and appb as marker genes of neural development and function were analyzed by qPCR for the highest used concentration. The data showed that aluminium significantly affected the development of zebrafish inducing morphological alterations and cell death. The oxidative state of larvae was altered, although the formation of reactive oxygen species and the levels of metallothioneins, and the activity of some antioxidant enzymes, decreased at the maximum concentration tested. In addition, at this concentration, the expression of the evaluated genes increased. The comprehensive information obtained gives a realistic snapshot of the aluminium toxicity and provides new information on the mechanism of action of this metal.

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.

Sublethal effects of microcystin-LR in the exposure and depuration time in a neotropical fish: Multibiomarker approach

Eutrophication is an ecological process that results in cyanobacterial blooms. Microcystin-LR is the most toxic variant of microcystins and may cause toxic effects in the organisms, mainly in hepatic tissues. The aims of this study were to use multiple biomarkers in order to evaluate the sublethal effects of a low concentration of MC-LR (1 μg/L) in fish Geophagus brasiliensis by waterborne exposure; and evaluate the depuration of this toxin during 15 days. A group of 30 fish was exposed to 1 μg/L of MC-LR solution for 96 h in a static bioassay. After this time, blood, brain, muscle, liver, gonad and gills were collected from half of the exposed fish group in order to evaluate chemical, biochemical, histological and genotoxic biomarkers. The rest of the fish group was submitted to the depuration experiment with free MC-LR water for 15 days. After this time the same tissues were collected and evaluated using biomarkers analysis. Toxic effects were found mostly in the fish liver from depuration time as alterations on the antioxidant system and histopathologies. The results showed that even low concentrations can cause sublethal effects to aquatic organisms, and cyanotoxins monitoring and regulation tools are required.

Synthesis and biological evaluation of 3-(4-aminophenyl)-coumarin derivatives as potential anti-Alzheimer's disease agents

The work is focused on the design of drugs that prevent and treat Alzheimer’s disease (AD) and its complications. A series of 3–(4-aminophenyl)-coumarin derivatives designed, synthesised, fully characterised and evaluated in vitro/vivo. The biological assay experiments showed that some compounds displayed a clearly selective inhibition for acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Among all compounds, compound 4m exhibited the highest AChE inhibition with an IC₅₀ value of 0.091 ± 0.011 µM and compound 4k exhibited the highest BuChE inhibition with an IC₅₀ value of 0.559 ± 0.017 µM. A zebrafish behaviour analyser (Zebrobox) was used to determine the behavioural effects of the active compound on the movement distance of the aluminium chloride-induced zebrafish. Compound 4m offered a potential drug design concept for the development of therapeutic or preventive agents for AD and its complications.

Effects of aluminium and cadmium on hatching and swimming ability in developing zebrafish

Aluminium and cadmium are biologically non-essential metals with a role in neurodegenerative and neuromuscular diseases. As an attractive model for neurobehavioural studies, zebrafish at 6 h post fertilization were exposed to 9, 18, 36 and 72 μM CdCl₂ and 50, 100 and 200 μM AlCl₃, respectively, for 72 h, and motility such as distance moved, mean velocity, cumulative movement, meander and heading were measured by DanioVision equipment. The hatching time was also analysed. A delay in the exit from the chorion was observed in all treated larvae with respect to the controls. CdCl₂ acted on the exit from the chorion of larvae with a dose-dependent delay. By contrast, the delay caused by AlCl₃ was greater at low concentrations. A dose-dependent reduction in swimming performance was observed in the larvae exposed to CdCl₂. Instead, for those exposed to AlCl₃, swimming performance improved at higher concentrations although values were in general lower than those of control. All the parameters had a similar trend except the meander parameter which showed a dose-dependent reduction. These data show that cadmium and aluminium can delay hatching and alter swimming ability in the early developmental stages of zebrafish, albeit with different effects, suggesting that exposure to sublethal concentrations of both metals can change behavioural parameters.

Effects of acetochlor on neurogenesis and behaviour in zebrafish at early developmental stages

The herbicide acetochlor is used in most parts of the world and is frequently detected in agricultural land and surface water; however, knowledge on the neurotoxicity of acetochlor is limited. Here, to test the effects of acetochlor on zebrafish development and behaviour, zebrafish embryos were exposed to acetochlor from 6 h post-fertilization (hpf) to 24 hpf, and larvae at 6 days post-fertilization (dpf) were exposed to acetochlor for 24 h. Both were exposed to 5, 10, or 20 mg/L acetochlor. We found that acetochlor induced developmental abnormalities, locomotion variations and changes in the physiology and gene expression in the embryos and larvae. The abnormalities included spinal curvature, brain abnormalities, and the decreased formation of newborn neurons. Larval locomotion was decreased with increases in the absolute turn angle and sinuosity. Acetylcholinesterase activity reduced in both embryos and larvae, and the expression of genes that are involved in neurodevelopment and the neurotransmitter system altered. Acetochlor increased the production of ROS and the accumulation of MDA but decreased CAT activity in the embryonic brain. Additionally, acetochlor induced cell death in the brain and tail spinal cord, and the expression of the apoptosis-related genes Bcl2 and caspase 3 were significantly upregulated. Collectively, this is the first study to examine the molecular and physiological effects of acetochlor on neuronal development, and the potential mechanisms appear to be associated with oxidative stress and decreased AChE activity, which disrupt the expression of nervous system genes and apoptosis-related genes and finally lead to apoptosis and morphological malformations.

Evaluation of the Effects of Carbon 60 Nanoparticle Exposure to Adult Zebrafish: A Behavioral and Biochemical Approach to Elucidate the Mechanism of Toxicity

There is a growing concern for the potential toxicity of engineered nanomaterials that have made their way into virtually all novel applications in the electronics, healthcare, cosmetics, technology, and engineering industries, and in particular, biomedical products. However, the potential toxicity of carbon 60 (C₆₀) at the behavioral level has not been properly evaluated. In this study, we used idTracker, a multitracking algorithm to quantitatively assess behavioral toxicity induced by C₆₀ nanoparticles (C₆₀ NPs) in adult zebrafish. We demonstrated that locomotion, novel tank exploration, aggression, shoaling, and color preference activities of the C₆₀ NPs-treated fish was significantly reduced. In addition, the C₆₀ NPs-treated fish also displayed dysregulation of the circadian rhythm by showing lower locomotion activities in both day and night cycles. The biochemical results showed that C₆₀ NPs exposure at low concentration induced oxidative stress and DNA damage, reduced anti-oxidative capacity and ATP (adenosine triphosphate) levels, and induced stress-associated hormones, hypoxia, as well as inflammation marker upregulation in muscle and gill tissues. Together, this work, for the first time, provide direct evidence showing that the chronic exposure of C₆₀ NPs induced multiple behavioral abnormalities in adult zebrafish. Our findings suggest that the ecotoxicity of C₆₀ NPs towards aquatic vertebrates should be carefully evaluated.

Environmental pollution and toxic substances: Cellular apoptosis as a key parameter in a sensible model like fish

The industrial wastes, sewage effluents, agricultural run-off and decomposition of biological waste may cause high environmental concentration of chemicals that can interfere with the cell cycle activating the programmed process of cells death (apoptosis). In order to provide a detailed understanding of environmental pollutants-induced apoptosis, here we reviewed the current knowledge on the interactions of environmental chemicals and programmed cell death. Metals (aluminum, arsenic, cadmium, chromium, cobalt, zinc, copper, mercury and silver) as well as other chemicals including bleached kraft pulp mill effluent (BKME), persistent organic pollutants (POPs), and pesticides (organo-phosphated, organo-chlorinated, carbamates, phyretroids and biopesticides) were evaluated in relation to apoptotic pathways, heat shock proteins and metallothioneins. Although research performed over the past decades has improved our understanding of processes involved in apoptosis in fish, yet there is lack of knowledge on associations between environmental pollutants and apoptosis. Thus, this review could be useful tool to study the cytotoxic/apoptotic effects of different pollutants in fish species.

Assessment and monitoring of water quality of the gulf of Morbihan, a littoral ecosystem under high anthropic pressure

This field study is intended to propose a global methodology to assess and monitor the water quality of the gulf of Morbihan, a littoral ecosystem under increasing anthropic pressure. To this end, the Locmariaquer site, where Crassostrea gigas is extensively cultivated, was selected to perform a one-year follow-up of tissular glutathione S-transferase and acetylcholinesterase specific activities in this filter feeder organism. Calculation of an integrated index, corresponding to the ratio of the two enzymes activities, allowed to discriminate from the environmental noise, several clusters which could be representative environmental stress, potentially latent pollution. Moreover, the estrogenic activity was assessed in water samples collected at Locmariaquer and other strategic sites of the gulf. The results evidenced a low estrogenic-disrupting compound contamination of waters. Overall, this methodology produced an accurate outlook of a basal state for the gulf and could be developed in the context of a chronic monitoring of this site.

Former uranium mine-induced effects in caged roach: a multiparametric approach for the evaluation of in situ metal toxicity

To characterize environmental risks linked to former uranium mines in the Limousin region of France, a study was conducted on fish health effects from uranium releases. Two private ponds were compared in this study, one with uranium contamination and one background site, upstream of the mining zone. Roach, Rutilus rutilus, were caged for 28 days in both ponds. Physico-chemical parameters of water and sediments and bioaccumulation of metals in several organs were determined. After 14 and 28 days of caging, immune, oxidative stress, biotransformation, neurotoxicity and physiological parameters were measured. Iron and aluminium were quantified in the water of both sites; however, barium and manganese were only present in the water of the uranium contaminated site. Uranium was present in both sites but at very different concentrations. The sediments from the uranium contaminated site contained high levels of radioactive elements coming from the disintegration chain of uranium. Results of biological parameters indicated stimulation of immune parameters and of oxidative stress and a decrease of AChE in fish caged in the uranium contaminated pond compared to the uranium-free pond. Overall, the results determined roach health status in the context of pollution from poly-metallic mining. The data strengthen our knowledge of the environmental risk assessment associated with radioactive substances in the environment.

Transient modulation of acetylcholinesterase activity caused by exposure to dextran-coated iron oxide nanoparticles in brain of adult zebrafish

Superparamagnetic iron oxide nanoparticles (SPIONs) are of great interest in nanomedicine due to their capability to act simultaneously as a contrast agent and as a targeted drug delivery system. At present, one of the biggest concerns about the use of SPIONs remains around its toxicity and, for this reason, it is important to establish the safe upper limit for each use. In the present study, SPION coated with cross-linked aminated dextran (CLIO-NH₂) were synthesized and their toxicity to zebrafish brain was investigated. We have evaluated the effect of different CLIO-NH₂ doses (20, 50, 100, 140 and 200 mg/kg) as a function of time after exposure (one, 16, 24 and 48 h) on AChE activity and ache expression in zebrafish brain. The animals exposed to 200 mg/kg and tested 24 h after administration of the nanoparticles have shown decreased AChE activity, reduction in the exploratory performance, significantly higher level of ferric iron in the brains and induction of casp8, casp 9 and jun genes. Taken together, these findings suggest acute brain toxicity by the inhibition of acetylcholinesterase and induction of apoptosis.

Drosophila melanogaster as a model system of aluminum toxicity and aging

The aim of this study was to investigate the toxic effects of aluminum (Al) on the model organism-Drosophila melanogaster. The study is especially concerned with the effects of aluminum on the fruit fly's development, life span, and circadian rhythm in rest and activity. Flies were exposed to aluminum in concentrations from 40 to 280 mg/kg in rearing media or the flies were raised on control medium. Moreover, the life span of insects exposed to aluminum containing 40, 120, or 240 mg/kg of Al in the medium, only during their larval development, during the whole life cycle and only in their adult life was tested. To check if aluminum and aging cause changes in D. melanogaster behavior, the locomotor activity of flies at different ages was recorded. Results showed that aluminum is toxic in concentrations above 160 mg/kg in the rearing medium. Depending on Al concentration and time of exposure, the life span of the flies was shortened. At intermediate concentrations (120 mg/kg), however, Al had a stimulating effect on males increasing their life span and level of locomotor activity. At higher concentration the aluminum exposure increased or decreased the level of locomotor activity of D. melanogaster depending on age of flies. In addition, in the oldest insects reared on aluminum supplemented media and in mid-aged flies reared on the highest concentration of Al the daily rhythm of activity was disrupted.