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

GABA attenuates neurotoxicity of zinc oxide nanoparticles due to oxidative stress via DAF-16/FoxO and SKN-1/Nrf2 pathways

Zinc oxide nanoparticles (ZnO-NPs) are one of the most widely used metal oxide nanomaterials. The increased use of ZnO-NPs has exacerbated environmental pollution and raised the risk of neurological disorders in organisms through food chains, and it is urgent to look for detoxification strategies. γ-Aminobutyric acid (GABA) is an inhibitory neurotransmitter that has been shown to have anxiolytic, anti-aging and inhibitory effects on nervous system excitability. However, there are few reports on the prevention and control of the toxicity of nano-metal ions by GABA. In zebrafish, ZnO-NPs exposure led to increased mortality and behavioral abnormalities of larva, which could be moderated by GABA intervention. Similar results were investigated in Caenorhabditis elegans, showing lifespan extension, abnormal locomotor frequency and behavior recovery when worms fed with GABA under ZnO-NPs exposure. Moreover, GABA enhanced antioxidant enzyme activities by upregulating the expression of antioxidant-related genes and thus scavenged excessive O2-. In the case of ZnO-NPs exposure, inhibition of nuclear translocation of DAF-16 and SKN-1 was restored by GABA. Meanwhile, the protective effect of GABA was blocked in daf-16 (-) and skn-1 (-) mutant, suggesting that DAF-16/FoxO and SKN-1/Nrf2 pathways is the key targets of GABA. This study provides a new solution for the application of GABA and mitigation of metal nanoparticle neurotoxicity.

Common and inter-specific toxic effects in three wild fish species after chronic gamma irradiation of early stages

The objective of this study was to investigate the effects of gamma irradiation on the aquatic environment. We used three wild fish species to compare phenotypic responses with a fish model such as Danio rerio. We focused on embryonic development, a sensitive life stage to stressors like ionizing radiation, to evaluate the effects of exposure to 0.5 and 5 mGy h-1 on Arctic char, trout and stickleback embryos from fertilization to free-swimming larvae. Irradiation did not cause mortality but induced an acceleration of hatching in the three species. These new data on wild species, obtained under comparable irradiation conditions, did not go against the threshold values for the protection of freshwater aquatic ecosystems. Moreover, irradiation caused inter-specific sublethal effects, such as an increase in non-eyed egg proportion in Arctic char, an increase in the incubation period in trout and an acceleration of larval mortality in stickleback. The consequences of these early effects on the adult stage remain to be studied.

Aluminum exposure alters the pedal mucous secretions of the chocolate-band snail, Eobania vermiculata (Gastropoda: Helicidae)

Aluminum (Al) is used in everyday life and present in food drugs, packaging, industry, and agriculture. Although it is the most common metal in the Earth crust, a correlation has been demonstrated between its presence and various pathologies, even serious ones, especially of a neurological type. However, there is a histological gap regarding the role Al can have in contact with the covering and secreting epithelia. The alterations of the ventral and dorsal foot mucocytes and their secretions of the snail Eobania vermiculata caused by Al were investigated in situ by histochemical and lectin-histochemical techniques. Administration to different experimental groups took place for 3 and 9 days with 50 and 200 μM of AlCl3. Several types of mucocytes were detected with a prevalent secretion of acid glycans in the foot of E. vermiculata. Sulfated glycans prevail in the dorsal region, with one type showing only fucosylated residues and another also having galactosaminylated and glycosaminylated residues. Carboxylated glycans prevail in the ventral region, with presence of galactosaminylated, glycosaminylated, and fucosylated residuals in both cells. Snails treated presented a general decrease of mucin amount in the secreting cells and affected the mucus composition. These changes could alter the rheological and functional properties of the mucus with possible implications for the health of the treated animals. RESEARCH HIGHLIGHTS: Snails were fed with Al-contaminated lettuce at different concentrations. In the foot mucocytes produced mucus with prevailing acidic glycans. In the treated resulted a reduction in the amount of mucus and an alteration of glycan composition.

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.

Insight on cytotoxic NHC gold(I) halide complexes evaluated in multifaceted culture systems

Gold complexes can be a useful system in the fight against cancer. Although many studies have been carried out on in vitro 2D cell culture models embryotoxic assays are particularly lacking. Embryotoxicity and DNA damage are critical concerns in drug development. In this study, the effects of a new N-Heterocyclic carbene (NHC)-Au compound (Bromo[1,3-di-4-methoxybenzyl-4,5-bis(4-methoxyphenyl)imidazol-2-ylidene]gold(I)) at different concentrations were explored using multifaceted approach, encompassing 2D cancer cell cultures, in vivo zebrafish and in vitro bovine models, and compared with a consolidated similar complex (Bromo[1,3-diethyl-4,5-bis(4-methoxyphenyl)imidazol-2-ylidene]gold(I)). The results obtained from 2D cancer cell cultures revealed concentration-dependent effects of the gold compounds by estimating the cytotoxicity with MTT assay and cellular damage as indicated by LDH release. Selected concentrations of gold complexes demonstrated no adverse effects on zebrafish embryo development. However, in bovine embryos, these same concentrations led to significant impairments in the early developmental stages, triggering cell apoptosis and reducing blastocyst competence. These findings underscore the importance of evaluating drug effects across different model systems to comprehensively assess their safety and potential impact on embryonic development.

Combined effects of copper and cadmium exposure on ovarian function and structure in Nile Tilapia (Oreochromis niloticus)

With the rapid development of industrialization and urbanization, the issue of copper (Cu) and cadmium (Cd) pollution in aquatic ecosystems has become increasingly severe, posing threats to the ovarian tissue and reproductive capacity of aquatic organisms. However, the combined effects of Cu and Cd on the ovarian development of fish and other aquatic species remain unclear. In this study, female Nile tilapia (Oreochromis niloticus) were individually or co-exposed to Cu and/or Cd in water. Ovarian and serum samples were collected at 15, 30, 60, 90, and 120 days, and the bioaccumulation, ovarian development, and hormone secretion were analyzed. Results showed that both single and combined exposure significantly reduced the gonadosomatic index and serum hormone levels, upregulated estrogen receptor (er) and progesterone receptor (pr) gene transcription levels, and markedly affected ovarian metabolite levels. Combined exposure led to more adverse effects than single exposure. The data demonstrate that the Cu and Cd exposure can impair ovarian function and structure, with more pronounced adverse effects under Cu and Cd co-exposure. The Cu and Cd affect the metabolic pathways of nucleotides and amino acids, leading to ovarian damage. This study highlights the importance of considering combined toxicant exposure in aquatic toxicology research and provides insights into the potential mechanisms underlying heavy metal-induced reproductive toxicity in fish.

The effects of plastic additives on swimming activity and startle response in marine amphipod Echinogammarus marinus

Plastic additives are widely used in plastic production and are found in the environment owing to their widespread applications. Among these additives, N-butyl benzenesulfonamide (NBBS) and triphenyl phosphate (TPHP) are under international watchlist for evaluation, with limited studies on amphipods. Di-ethylhexyl phthalate (DEHP) and dibutyl phthalate (DBP) are banned in some countries and categorised as substances of very high concern. This study aimed to investigate the effects of NBBS, TPHP, DEHP and DBP on the swimming activity of a coastal intertidal marine amphipod, Echinogammarus marinus. Furthermore, this study is the first to quantify startle response in E. marinus in response to light stimuli. Amphipods were exposed to 0, 0.5, 5, 50 and 500 μg/l concentrations of all test compounds. Swimming activity and startle responses were assessed by video tracking and analysis using an 8-min alternating dark and light protocol after exposure on days 7 and 14. We observed an overall compound and light effect on the swimming activity of E. marinus. A significant decrease in swimming distance was found in 500 μg/l NBBS and TPHP. We observed that the startle response in E. marinus had a latency period of >2 s and animals were assessed at 1 s and the sum of the first 5 s. There was a clear startle response in E. marinus during dark to light transition, evident with increased swimming distance. NBBS exposure significantly increased startle response at environmental concentrations, while significant effects were only seen in 500 μg/l TPHP at 5 s. We found no significant effects of DEHP and DBP on swimming behaviour at the concentrations assessed. The findings of this study affirm the necessity for a continuous review of plastic additives to combat adverse behavioural effects that may be transferable to the population levels.

Chronic cadmium exposure impairs flight behavior by dampening flight muscle carbon metabolism in bumblebees

Cadmium pollution affects the global ecosystem because cadmium can be transferred up the food chain. The bumblebee, Bombus terrestris, is an important insect pollinator. Their foraging activity on flowers exposes them to harmful heavy metals, which damages their health and leads to massive population declines. However, the effects of chronic exposure to heavy metals on the flight performance of bumblebees have not yet been characterized. Here, we studied variation in the flight capacity of bumblebees induced by chronic cadmium exposure at field-realistic concentrations using behavioral, physiological, and molecular approaches. Chronic cadmium exposure caused a significant reduction in the duration, distance, and mean velocity of bumblebee flight. Transcriptome analysis showed that the impairment of carbon metabolism and mitochondrial dysfunction in the flight muscle were the primary causes. Physiological, biochemical, and metabolomic analyses validated disruptions in energy metabolism, and impairments in mitochondrial respiratory chain complexes activities. Histological analysis revealed muscle fiber damage and mitochondrial loss. Exogenous decanoic acid or citric acid partially restored sustained flight ability of bumblebees by mitigating muscle fiber damage and increasing energy generation. These findings provide insights into how long-term cadmium stress affects the flight ability of insects and will aid human muscle or exercise-related disease research.

Polystyrene microplastics effects on zebrafish embryological development: Comparison of two different sizes

Microplastics have become a great worldwide problem and it's therefore important to study their possible effects on human and environmental health. In this study, zebrafish embryos were used to compare two different sizes of polystyrene microplastics (PS-MPs), 1 µm and 3 µm respectively, at 0.01, 0.1, 1.0 and 10.0 mgL-1, and were monitored up to 72 h. Toxicity tests demonstrated that neither of the PS-MPs altered the embryos' survival and the normal hatching process. Instead, higher concentrations of both sizes caused an increase of the heart rate and phenotypic changes. The PS-MPs of both sizes entered and accumulated in the larvae at the concentration of 10.0 mgL-1 and the same concentration caused an increase of apoptotic processes correlated to redox homeostasis changes. The reported results give a realistic view of the negative effects of exposure to PS-MPs and provide new information on their toxicity, also considering their sizes.

Astilbin antagonizes developmental cardiotoxicity after cadmium exposure in chicken embryos by inhibiting endoplasmic reticulum stress and maintaining calcium homeostasis

Cadmium (Cd) is a dangerous heavy metal with high toxicity that is known to impair development. Astilbin (ASB) is a protective flavonoid compound. We aimed to explore whether ASB can antagonize the myocardial developmental toxicity of Cd exposure. Cd (2 µg) and/or ASB (0.002 µg) were injected into embryonized eggs that were 1 day old. Histological examinations revealed Cd-induced ventricular dilation, reduced wall thickness, and disrupted myocardial fiber connections, while co-administration of ASB mitigated these effects. Electron microscopy confirmed ASB's ability to counteract Cd-induced myocardial cell myofibril damage. Real-time quantitative PCR (QRT-PCR) and western blot (WB) molecular investigations revealed that Cd increased endoplasmic reticulum stress in myocardial tissue and primary cardiomyocytes, as shown by raised expression of stress-related genes (GRP78, XBP1, GRP94, ATF4, ATF6, IRE1, and CHOP). Moreover, Cd disrupted calcium homeostasis, affecting important genes linked to Ca2+ channels and causing an excess of Ca2+ in the cytoplasm. In addition, we detected genes related to development and differentiation-related genes in myocardial tissue and primary cardiomyocytes. The results showed that the downregulation of transcription factors in the IrxA cluster, Mefs, and Tbxs families after Cd exposure indicated that cardiac transcription was hindered and cardiac markers (TnnT2, TnnC1, Gata4, Gata6, and Nkx2-5) were abnormally expressed. ASB successfully mitigated these disturbances. During the cell cycle, primary cardiomyocytes undergo growth arrest in flow cytometry. These results suggest that the maturation and differentiation of cardiomyocytes are inhibited after Cd exposure, and ASB has an antagonistic effect on Cd. The present study indicated that Cd could trigger developmental cardiotoxicity in chicken embryos and primary cardiomyocytes by endoplasmic reticulum stress and Ca2+ overload, respectively, while ASB has an antagonistic effect.

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.

Toxicity and teratogenicity effects of valproic acid on zebrafish (Danio rerio) embryos in relation to autism spectrum disorder

Valproic acid (VPA) is a widely prescribed antiepileptic drug with various medicinal efficacies. Accumulated evidence implied that prenatal exposure to VPA is highly associated with autism spectrum disorder (ASD). In this study, the zebrafish were exposed to a set of VPA concentrations (0, 5, 10, 20, 40, 80, 160, 320, 640, 1280, and 2560 μM) at 5 h post fertilization (hpf) to 120 hpf. The adverse effects of VPA were extensively studied through the evaluations on the mortality, heartbeats, spontaneous tail coiling, and hatching rate. Morphological observations were conducted at 120 hpf, following the exposure termination. Basic locomotor responses and anxiety-like behavioral alterations evaluated for behavioral impairments are the hallmark feature of ASD. The exposure to VPA at teratogenic concentrations reduced the aforementioned parameters in a dose-dependent manner (p ≤ .05). At the selected non-teratogenic concentrations of VPA, the treated larvae demonstrated profound alterations of basic locomotor responses. No significant changes of anxiety and thigmotactic behaviors were observed on the VPA-treated fish compared to the control (p ≥ .005). This study depicted that embryonic zebrafish exposure to VPA produced significant toxicity and teratogenicity effects as well as the alterations of basic behavioral responses. Overall, this study provides a fundamental insight of the toxicity effects at morphological and behavioral levels to facilitate the understanding of ASD mechanisms at different molecular levels.

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.

2,4-Dinitrotoluene (2,4-DNT) exposure induces liver developmental damage and perturbs lipid metabolism and oxygen transport gene expression in zebrafish (Danio rerio)

2,4-Dinitrotoluene (2, 4-DNT) is a common environmental pollutant. The toxic effect on mammals of 2,4-DNT has been well studied, but its toxicity on aquatic organisms is little known. In this study, 126 healthy female zebrafish (Danio rerio) were exposed to different concentrations of 2,4-DNT (0, 2, 4, 8, 12 and 16 mg/L) to determine 96-h semi-lethal concentrations (LC₅₀). And then, 90 female zebrafish were exposed to 0, 2, 4 and 8 mg/L 2,4-DNT for 5 days to study liver toxicity. Exposed zebrafish developed hypoxia features, such as floating head and breathing rapidly, and then died. 96-h LC₅₀ of 2,4-DNT in zebrafish was 9.36 mg/L. Histological data revealed that 2,4-DNT severely damaged the liver tissues, following with the round nucleus, dense interstitial tissue, dense arranged hepatocyte cords and more inflammatory cells. Additionally, the further result showed that the lower levels of lipid transport and metabolism (apoα2, mtp, ppar-α and acox) were noticed. But, exposed to 2,4-DNT for 5 days significantly upregulated the expression levels of genes involved in respiration (hif1a, tfa and ho1, p < 0.05). These results indicated that 2,4-DNT exposure disturbed lipid transport and metabolism and oxygen supply in zebrafish, which could contribute to severe damage in liver and death.

Cadmium effects on the freshwater teleost Prochilodus lineatus: Accumulation and biochemical, genotoxic, and behavioural biomarkers

In order to evaluate the effects of Cd, juveniles of the Neotropical fish Prochilodus lineatus were exposed to 1 and 10 μg L^-1 Cd, for 24 and 96 h. Fish exposed to Cd showed metal accumulation in the gills, kidney, and liver, an increase in DNA damage in erythrocytes, and an increase in lipid peroxidation (LPO) in the kidney. Cd exposure also caused a reduction in catalase activity, metallothionein induction, and LPO in the liver. Cd stimulated the swimming activity of exposed fish, resulting in longer swimming times and distances travelled, especially for the shortest exposure time. Changes in acetylcholinesterase activity (AChE) in the muscle and brain are probably related to these behavioural responses. These results show that Cd affects the functioning of several organs in P. lineatus, which is indicated by the genotoxic damage and changes in the AChE and swimming pattern of the exposed fish.

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

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

Impact of aluminum exposure on oxidative stress, intestinal changes and immune responses in red swamp crayfish (Procambarus clarkii)

Aluminum (Al) is an abundant metal that has been classified as a threatening pollutant due to indiscriminate use and anthropogenic activities. This study aimed to evaluate the impacts of Al on crayfish (Procambarus clarkii), including biochemical change, histological alteration, gut microbial community diversification, and immune changes. The bioaccumulation of Al was detected in the hemolymph and intestine of crayfish after Al exposure at different time points. Results showed that Al exposure significantly induced oxidative stress and caused pathohistological changes on intestinal barrier structures in crayfish. It was found that the intestinal microbiota was affected by retained Al and the intestinal community diversity was changed after Al treated in the crayfish. Furthermore, Al exposure affected the immunity in crayfish, by altering the expression of a set of immune-related genes, as well as reducing the phenoloxidase and lysozyme activities. Moreover, Al exposure promoted hemocytes apoptosis and impaired hemophagocytic capacity against Vibro parahamolyticus, resulting in higher mortality of crayfish upon bacterial infection. Taken these results together, we conclude that excessive Al exposure caused adverse effects on multiple biological processes of crayfish and Al pollution is a potential threat to crayfish culture.

Characterization of Orange Peel Extract and Its Potential Protective Effect against Aluminum Chloride-Induced Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder without a cure. Hence, developing an effective treatment or protective agent is crucial for public health. The present study aims to characterize orange peel extract (OPE) through in vitro and in silico studies. Furthermore, it examines the protective effect of OPE against experimentally-induced Alzheimer's disease in rats. The total phenolic and flavonoid content of OPE was 255.86 ± 1.77 and 52.06 ± 1.74 (mg/100 g), respectively. Gallic acid, the common polyphenol in OPE detected by HPLC was 3388.60 μg/100 g. OPE antioxidant IC₅₀ was 67.90 ± 1.05, 60.48 ± 0.91, and 63.70 ± 0.30 by DPPH, ABTS and Hydroxyl radical scavenging activity methods, respectively. In vitro anti-acetylcholinesterase (AChE) IC₅₀ was 0.87 ± 0.025 mg/mL for OPE and 2.45 ± 0.001 mg/mL for gallic acid. Molecular docking analysis for human AChE (4EY7) with donepezil, gallic acid, and acetylcholine showed binding energy ΔG values of -9.47, -3.72, and -5.69 Kcal/mol, respectively. Aluminum chloride injection (70 mg/Kg/day for 6 weeks) induced Alzheimer's-like disease in male rats. OPE (100 and 200 mg/kg/d) and gallic acid (50 mg/kg/d) were administered orally to experimental animals for 6 weeks in addition to aluminum chloride injection (as protective). OPE was found to protect against aluminum chloride-induced neuronal damage by decreasing both gene expression and activity of acetylcholinesterase (AChE) and a decrease in amyloid beta (Aβ42) protein level, thiobarbituric acid-reactive substances (TBARS), and nitric oxide (NO), and increased reduced glutathione (GSH) level and activity of the antioxidant enzymes in the brain tissues. Additionally, gene expressions for amyloid precursor protein (APP) and beta secretase enzyme (BACE1) were downregulated, whereas those for presinilin-2 (PSEN2) and beta cell lymphoma-2 (BCL2) were upregulated. Furthermore, the reverse of mitochondrial alternation and restored brain ultrastructure might underlie neuronal dysfunction in AD. In conclusion, our exploration of the neuroprotective effect of OPE in vivo reveals that OPE may be helpful in ameliorating brain oxidative stress, hence protecting from Alzheimer's disease progression.

Visualization of Mitochondria During Embryogenesis in Zebrafish by Aggregation-Induced Emission Molecules

PURPOSE

Aggregation-induced emission (AIE) molecules have been widely utilized for fluorescence imaging in many biomedical applications, benefited from large Stokes shift, high quantum yield, good biocompatibility, and resistance to photobleaching. And visualization of mitochondria is almost investigated in vitro and ex vivo, but in vivo study of mitochondria is more essential for systematic biological research, especially during embryogenesis. Therefore, suitable and time-saving alternatives with simple operation based on AIE molecules are urgently needed compared with traditional transgenic approach.

PROCEDURES

Five tetraphenylethylene isoquinolinium (TPE-IQ)-based molecules with AIE characteristics and their ability of mitochondrial visualization in vitro and in vivo and mitochondrial tracking during embryogenesis on zebrafish model were investigated. The biosafety of these AIE molecules was also evaluated systematically in vitro and in vivo.

RESULTS

All these five AIE molecules could image mitochondria in vitro with good biocompatibility. In them, TPE-IQ1 exhibited excellent imaging quality for in vivo visualization and tracking of mitochondria during the 4-day embryogenesis in zebrafish, in comparison with the conventional transgenic fluorescent protein. Furthermore, TPE-IQ1 could visualize mitochondrial damage induced by chemicals in real time on 24-h post fertilization (hpf) embryos.

CONCLUSIONS

This study indicated TPE-IQ-based AIE molecules had the potential for mitochondrial imaging and tracking during embryogenesis and mitochondrial damage visualization in vivo.

Aluminium exposure leads to neurodegeneration and alters the expression of marker genes involved to parkinsonism in zebrafish brain

Aluminium, despite being extremely widespread in the world, is a non-essential metal to human metabolism. This metal is known to have toxic effects on a variety of organs including the brain and is considered an etiological factor in neurodegenerative diseases. However, the molecular mechanisms by which aluminium exerts neurotoxic effects are not yet completely understood. Zebrafish is an animal model also used to study neurodegenerative diseases since the overall anatomical organization of the central nervous system is relatively conserved and similar to mammals. Adult zebrafish were exposed to 11 mg/L of Al for 10, 15, and 20 days and the neurotoxic effects of aluminium were analysed by histological, biochemical, and molecular evaluations. Histological stainings allowed to evaluation of the morphology of the brain parenchyma, the alteration of myelin and the activation of neurodegenerative processes. The expression of the Glial Fibrillary Acidic Protein, a marker of glial cells, was evaluated to observe the quantitative alteration of this important protein for the nervous system. In addition, the poly(ADP-ribose) polymerase activity was measured to verify a possible oxidative DNA damage caused by exposure to this metal. Finally, the evaluation of the markers involved in Parkinsonism was assessed by Real-Time PCR to better understand the role of aluminium in the regulation of genes related to Parkinson's neurodegenerative disease. Data showed that aluminium significantly affected the histology of cerebral tissue especially in the first periods of exposure, 10 and 15 days. This trend was also followed by the expression of GFAP. At longer exposure times, there was an improvement/stabilization of the overall neurological conditions and decrease in PARP activity. In addition, aluminium is involved in the deregulation of the expression of genes closely related to Parkinsonism. Overall, the data confirm the neurotoxicity induced by aluminium and shed a light on its involvement in neurodegenerative processes.

Multiview behavior and neurotransmitter analysis of zebrafish dyskinesia induced by 6PPD and its metabolites

The typical tire manufacturing additive 6PPD, its metabolites 6PPDQ and 4-Hydroxy should be monitored because of their ubiquitous presence in the environment and the high toxicity of 6PPDQ to coho salmon. The toxic effect of 6PPD and its metabolites have been revealed superficially, especially on behavioral characteristics. However, the behavioral indicators explored so far are relatively simple and the toxic causes are poorly understood. With this in mind, our work investigated the toxic effects of 6PPD, 6PPDQ and 4-Hydroxy on adult zebrafish penetratingly through machine vision, and the meandering, body angle, top time and 3D trajectory are used for the first time to show the abnormal behaviors induced by 6PPD and its metabolites. Moreover, neurotransmitter changes in the zebrafish brain were measured to explore the causes of abnormal behavior. The results showed that high-dose treatment of 6PPD reduced the velocity by 42.4% and decreased the time at the top of the tank by 91.0%, suggesting significant activity inhibition and anxiety. In addition, γ-aminobutyric acid and acetylcholine were significantly impacted by 6PPD, while dopamine exhibited a slight variation, which can explain the bradykinesia, unbalance and anxiety of zebrafish and presented similar symptoms as Huntingdon's disease. Our study explored new abnormal behaviors of zebrafish induced by 6PPD and its metabolites in detail, and the toxic causes were revealed for the first time by studying the changes of neurotransmitters, thus providing an important reference for further studies of the biological toxicity of 6PPD and its metabolites.

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.

Transgenerational effects of zinc in zebrafish following early life stage exposure

Although toxic effects of zinc (Zn) have been well established in the different developmental stages in fish, long-lasting effects of Zn exposure during embryonic development have not been explored. Exposure to an environmentally relevant Zn concentration of 10 μM (650 μg/L) during the first five days after fertilization did not affect survival, body weight, malformations or overall hatching success of F0 and F1 larvae. Zn exposure did, however, result in delayed hatching in both the F0 and F1 generations and caused significant changes in homeostasis of Zn and selenium (Se) in F0 and F1 fish. This was especially pronounced when F1 embryos from Zn-exposed parents were treated with 30 μM (2000 μg/L) Zn. In the F0 generation, skewed sex ratio towards males and changes in homeostasis of Zn, Se and manganese (Mn) in the brain, gill, liver and gonad of adult fish were also observed. These changes were associated with altered expression of Zn- and Mn-regulatory genes and sex differentiation genes in F0 and F1 fish. The present study suggests that fish may carry memory from embryo-larval Zn exposure into adulthood and further to the next generation. The present study shows that ecotoxicological risk of an exposure to Zn during embryo-larval development may persist long after recovery and may also manifest in the F1 generation.

EFFECTS OF DIFFERENT FORMS OF PRACTICING A SPORT ON ATHLETES’ NERVE FUNCTION

ABSTRACT Introduction: Poor reaction time can cause irritability, easier distractions, and interfere with normal activities that require concentration. Objective: To study the impact of simulated hypoxic training on the immune system of female middle- and long-distance runners. Methods: Observation of 50 female middle- and long-distance runners living high and training low (HiHiLo) in regard to changes in CD3+, CD4+, CD8+, NK cells and NKT cells during the process of living low and training high (LoHi). Research indicates: HiHiLo training does have a significant effect on these indicators to enhance the antioxidant capacity of the brain and nervous system. Results: Living high and training low (HiHiLo) can improve the excitability of the nervous system of long-distance endurance athletes and has a very significant impact on the stability of the nervous system. This improves cardiopulmonary function under hypoxic conditions and has a role in promoting the ability to mobilize the skeletal muscles. Conclusions: It has been proved that different forms of exercise can effectively improve the athlete’s nervous response. Level of evidence II; Therapeutic studies - investigation of treatment results.

The zebrafish (Danio rerio) embryo-larval contact assay combined with biochemical biomarkers and swimming performance in sewage sludge and hydrochar hazard assessment

Hydrothermal carbonization is considered a powerful technology to convert sewage sludge (SS) into a valuable carbonaceous solid known as hydrochar (HC). Up to now criteria for landfill application of SS and HC are based only on physicochemical properties and levels of pollutant residues. Nevertheless, to ensure their safe environmental applications it is mandatory to develop biosensors which can provide relevant information on their toxic potential for natural ecosystems. Therefore, this study aimed to assess the suitability of a contact assay using zebrafish embryo/larvae combined with sub-lethal end-points to evaluate the hazard associated with SS and related HC exposure. A suite of biomarkers was also applied on larvae, related to detoxification and oxidative stress as the activity of Ethoxyresorufin-O-deethylase, glutathione-S-transferase, and catalase, the content of reactive oxygen species and the behavioral assay using the DanioVision™ chamber. Legacy priority pollutants were also measured either in SS and HC tested samples and in contact waters. The exposure to SS caused higher lethality compared to HC. No significant changes in the activity of oxidative stress markers was observed upon exposure to both matrices. The behavioral test showed a hypoactivity condition in larvae exposed to both SS and HC with the effects of SS stronger than HC. Chemical analysis revealed the presence of trace elements and halogenated compounds in either SS, HC. Heavy metals were also released in contact waters, while volatile hydrocarbons (C6-C10) and halogenated compounds resulted below LOD (<0.05 μ L^-1). Our study highlights the suitability of zebrafish embryotoxicity test, coupled with behavioral traits, as screening tool for assessing potential risks, associated with the landfill application of both SS and HC, for aquatic wildlife.

Commercial Red Food Dyes Preparations Modulate the Oxidative State in Three Model Organisms (Cucumis sativus, Artemia salina, and Danio rerio)

The growing environmental spreading of food synthetic dyes and bio-colors have the potential for altering organisms’ redox states. Here, three model species for aquatic pollution trials, Cucumis sativus seeds, Artemia salina cysts, and Danio rerio embryos, were short-term exposed to a fixed concentration of the artificial red E124, and two red bio-colors, cochineal E120, and vegan red (VEGR). In the animal models, we evaluated the total reactive oxygen species (ROS) and the susceptibility to in vitro oxidative stress, and in C. sativus, H2O2 production and antioxidant capacity. We also measured organismal performance indices (routine oxygen consumption in the animal models, dark oxygen consumption, and photosynthetic efficiency in C. sativus). In C. sativus, only E124 increased ROS and affected dark oxygen consumption and photosynthetic efficiency, while all dyes enhanced the antioxidant defenses. In the A. salina nauplii, all dyes increased ROS, while E120 and E124 reduced the susceptibility to oxidative stress. In D. rerio, treatments did not affect ROS content, and reduced oxidative stress susceptibility. Our data show that red food dyes affect the redox state of the developing organisms, in which ROS plays a significant role. We suggest a potentially toxic role for red food dyes with environmentally relevant consequences.

Environmental Co-Exposure to Potassium Perchlorate and Cd Caused Toxicity and Thyroid Endocrine Disruption in Zebrafish Embryos and Larvae (Danio rerio)

The increasing pollution of aquatic habitats with anthropogenic compounds has led to various test strategies to detect hazardous chemicals. However, information on the effects of pollutants on the thyroid system in fish, which is essential for growth, development, and parts of reproduction, is still scarce. Modified early life-stage tests were carried out with zebrafish exposed to the known thyroid inhibitor potassium perchlorate (0.1, 1, 1.5, 2, 2.5, and 5 mM) to identify adverse effects on embryo development. The endogenous antioxidant defense mechanism is one of the key functions of the thyroid gland; in this regard, we examined the co-exposure to potassium perchlorate (KClO₄), which could disrupt thyroid function, with cadmium (Cd), a known pro-oxidant compound. Zebrafish embryos were exposed to control KClO₄ 1 mM and Cd 0.5 μM for 96 h after fertilization (hpf) individually and in combination. The morphological alteration, body length, and messenger RNA (mRNA) expression related to thyroid function and oxidative stress, thyroid hormone levels, and malondialdehyde were measured. Significant down-regulation of mRNAs related to thyroid function (thyroid hormone receptor-alpha (THRα), thyroid hormone receptor-beta (THRβ), haematopoietically expressed homeobox (hhex)) and decreased thyroxin (T4) levels were observed after co-exposure to KClO₄ and Cd, but this was not observed in the individually treated groups. These results suggest that co-exposure to KClO₄ and Cd could affect antioxidant defense mechanisms and potentially normally increase Cd toxicity on mRNA expression, altering the thyroid functions important in zebrafish embryonic developmental stages.

Dopamine Homeostasis Imbalance and Dopamine Receptors-Mediated AC/cAMP/PKA Pathway Activation are Involved in Aconitine-Induced Neurological Impairment in Zebrafish and SH-SY5Y Cells

Aconitine is one of the main bioactive and toxic ingredients of Aconitum species. Increasingly, aconitine has been reported to induce neurotoxicity. However, whether aconitine has effects on the dopaminergic nervous system remains unclear. In this study, zebrafish embryos at 6-days postfertilization were exposed to aconitine at doses of 0.5, 1, and 2 μM for 24 h, and SH-SY5Y cells were treated with 50, 100, and 200 μM of aconitine for 24 h. Results demonstrated that aconitine treatment induced deformities and enhanced the swimming behavior of zebrafish larvaes. Aconitine exposure suppressed cell proliferation and increased the number of reactive oxygen species and apoptosis in zebrafish larvaes and SH-SY5Y cells. Aconitine altered the levels of dopamine and its metabolites by regulating the expression of genes and proteins related to dopamine synthesis, storage, degradation, and reuptake in vivo and in vitro. Moreover, aconitine activated the AC/cAMP/PKA pathway by activating the dopamine D1 receptor (D1R) and inhibiting the dopamine D2 receptor (D2R) to disturb intracellular calcium homeostasis, eventually leading to the damage of nerve cells. Furthermore, the D1R antagonist SCH23390 and D2R agonist sumanirole pretreatment effectively attenuated the excitatory state of larvaes. Sumanirole and PKA antagonist H-89 pretreatment effectively decreased intracellular Ca²⁺ accumulation induced by aconitine in vivo. SCH23390 and sumanirole also reduced aconitine-induced cytotoxicity by inhibiting the AC/cAMP/PKA pathway in vitro. These results suggested that dopamine homeostasis imbalance and dopamine receptors (DRs)-mediated AC/cAMP/PKA pathway activation might be vital mechanisms underlying aconitine-induced neurological injury.

Developmental exposure to environmental levels of cadmium induces neurotoxicity and activates microglia in zebrafish larvae: From the perspectives of neurobehavior and neuroimaging

Cadmium (Cd) is a worldwide environmental pollutant that postures serious threats to humans and ecosystems. Over the years, its adverse effects on the central nervous system (CNS) have been concerned, whereas the underlying cellular/molecular mechanisms remain unclear. In this study, taking advantages of zebrafish model in high-throughput imaging and behavioral tests, we have explored the potential developmental neurotoxicity of Cd at environmentally relevant levels, from the perspectives of neurobehavior and neuroimaging. Briefly, Cd²⁺ exposure resulted in a general impairment of zebrafish early development. Zebrafish neurobehavioral patterns including locomotion and reactivity to environmental signals were significantly perturbed upon Cd²⁺ exposure. Importantly, a combination of in vivo two-photon neuroimaging, flow cytometry and gene expression analyses revealed notable neurodevelopmental disorders as well as neuroimmune responses induced by Cd²⁺ exposure. Both cell-cycle arrest and apoptosis contributed jointly to a significant decrease of neuronal density in zebrafish larvae exposed to Cd²⁺. The dramatic morphological alterations of microglia from multi-branched to amoeboid, the microgliosis, as well as the modulation of gene expression profiles demonstrated a strong activation of microglia and neuroinflammation triggered by environmental levels of Cd²⁺. Together, our study points to the developmental toxicity of Cd in inducing CNS impairment and neuroinflammation thereby providing visualized etiological evidence of this heavy metal induced neurodevelopmental disorders. It's tempting to speculate that this research model might represent a promising tool not only for understanding the molecular mechanisms of Cd-induced neurotoxicity, but also for developing pharmacotherapies to mitigate the neurological damage resulting from exposure to Cd, and other neurotoxicants.

Toxicological effects of 6PPD and 6PPD quinone in zebrafish larvae

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is the most widely used antioxidant in automobile tyres and many rubber products. We investigated the impact of 6PPD and 6PPD quinone on acute toxicity, morphology, swimming behaviour, heart rate, and oxygen consumption in zebrafish larvae. Zebrafish embryos were exposed to 6PPD and 6PPD quinone at concentrations of 1, 10, and 25 µg/L during the development period of 1-96 hpf. In the present study, 6PPD quinone was found to be toxic to zebrafish larvae with a 24 h LC₅₀ of 308.67 µg/L. No significant mortality was observed at any of the tested concentrations. A dose-dependent reduction in swimming performance was observed in the exposed larvae at 116 hpf for both toxicants. Overall, our study shows that exposure of zebrafish embryos to 6PPD and 6PPD quinone at environmentally relevant concentrations (1 µg/L) does not affect its behaviour. However, exposure to higher but still sublethal concentrations of 6PPD and 6PPD quinone (10 and 25 µg/L) can affect behavioural endpoints. These findings reveal the toxicity of 6PPD and 6PPD quinone to early life stages of fish.

Effects of Cadmium Exposure on Gut Villi in Danio rerio

In aquatic organisms, cadmium exposure occurs from ovum to death and the route of absorption is particularly wide, being represented by skin, gills and gastrointestinal tract, through which contaminated water and/or preys are ingested. It is known that cadmium interferes with the gut; however, less information is available on cadmium effects on an important component of the gut, namely goblet cells, specialized in mucus synthesis. In the present work, we studied the effects of two sublethal cadmium concentrations on the gut mucosa of Danio rerio. Particular attention was paid to changes in the distribution of glycan residues, and in metallothionein expression in intestinal cells. The results show that cadmium interferes with gut mucosa and goblet cells features. The effects are dose- and site-dependent, the anterior gut being more markedly affected than the midgut. Cadmium modifies the presence and/or distribution of glycans in the brush border and cytoplasm of enterocytes and in the goblet cells’ cytoplasm and alters the metallothionein expression and localization. The results suggest a significant interference of cadmium with mucosal efficiency, representing a health risk for the organism in direct contact with contamination and indirectly for the trophic chain.

Cadmium induced oxidative stress, endoplasmic reticulum (ER) stress and apoptosis with compensative responses towards the up-regulation of ribosome, protein processing in the ER, and protein export pathways in the liver of zebrafish

The present study identified that exposure to 5, 10, and 20 µg/L Cd for 48 days reduced growth, increased Cd accumulation and levels of reactive oxygen species (ROS) and lipid peroxidation, and induced ER stress and cellular apoptosis in the liver in a dose-dependent manner. However, the survival rate was not affected by Cd. The increased production of ROS might result from reduced catalase (CAT) and copper/zinc-superoxide dismutase (Cu/Zn-SOD) activities, which might trigger ER stress pathways and subsequently induce apoptotic responses, ultimately leading to growth inhibition. Transcriptomic analyses indicated that the differentially expressed genes (DEGs) involved in metabolic pathways were significantly enriched and dysregulated by Cd, suggesting that metabolic disturbances may contribute to Cd toxicity. However, there were increases in glutathione peroxidase (GPX) activity, protein levels of metallothioneins (MTs) and heat shock protein 70 (HSP70), and mRNA levels of sod1, cat, gpx, mt2, and hsp70. Furthermore, DEGs related to ribosome, protein processing in the ER, and protein export pathways were significantly enriched and up-regulated by Cd. These increases may be compensatory responses following oxidative stress, ER stress, and apoptosis to resist negative effects. Taken together, we demonstrated that environmentally relevant levels of Cd induced adaptive responses with compensatory mechanisms in fish, which may help to maintain fish survival at the cost of growth.

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.

Cadmium-induced oxidative stress in Meretrix meretrix gills leads to mitochondria-mediated apoptosis

Cadmium (Cd) is one of the most important marine environmental pollutants that can cause oxidative damage and apoptosis in living organisms, and mitochondria are the key cell organelles affected by Cd toxicity. In this study, we investigated the effect of Cd on the mitochondria in the gill cells of the clam Meretrix meretrix and the underlying mechanism of mitochondria-mediated apoptosis following exposure to the metal. Exposure of the clams to artificial seawater containing 1.5, 3, 6 and 12 mg L^-1 Cd²⁺ led to swollen mitochondria compared with the untreated clams. The mitochondria also became vacuolated at the higher Cd²⁺ concentrations. Biochemical assays showed that monoamine oxidase (MAO) activity and mitochondrial membrane potential (Δψm) increased at 1.5 mg L^-1 Cd²⁺, but decreased at higher Cd²⁺ concentrations, while the activities of malate dehydrogenase (MDH) and cytochrome oxidase (CCO) and the scavenging capacities of anti-superoxide anion (ASA) and anti-hydroxy radical (AHR) all decreased with increasing Cd²⁺ concentrations. Significant increases in the levels of malondialdehyde (MDA) and H₂O₂ as well as in the activity levels of caspase-3, -8, and -9 were also observed in the Cd²⁺-treated clams. The results implied that Cd might induce apoptosis in M. meretrix via the mitochondrial caspase-dependent pathway.

Synchronous Fluorescence Determination of Al3+ Using 3-Hydroxy-2-(4-Methoxy Phenyl)-4H-Chromen-4-One as a Fluorescent Probe

A simple synchronous fluorescent chemosensor 3-hydroxy-2-(4-methoxyphenyl)-4H-chromen-4-one (3-HC) has been synthesized for the selective analysis of Al³⁺. On the addition of Al³⁺, 3-HC displayed a redshift with a change in wavelength of emission maximum from 436 to 465 nm along with enhancement in fluorescence intensity, which formed the basis for its sensitive detection. Under optimized conditions, 3-HC was applied for the determination of Al³⁺ in the concentration range of 1 × 10^-7-1 × 10^-6 M. The limit of detection (LOD) and limit of quantification (LOQ) values were found out to be 1.69 × 10^-8 and 5.07 × 10^-8 M respectively. Further, the developed method was applied for the analysis of Al³⁺ in real water samples (tap water, bottled water, and tube well water) which showed good recovery values in the range of 95-99.7% with RSD less than 4%.

Endocrine disruption caused by the aquatic exposure to aluminum and manganese in Astyanax altiparanae (Teleostei: Characidae) females during the final ovarian maturation

Aluminum (Al) and manganese (Mn) can be toxic to aquatic biota and cause endocrine disruption in fish, affecting reproduction. This study evaluates the physiological responses of the ray-finned teleost fish Astyanax altiparanae vitellogenic females after acute exposure (96 h) to Al and Mn (alone and combined) in acid pH followed by the same period of exposure to metal-free water in neutral pH. The aim of this second period of exposure was to assess the recovery capacity from the toxic effects these metals. Five experimental groups were established: a control in neutral pH (Ctrl), and acidic pH (Ac), aluminum (Al), manganese (Mn), and Al + Mn groups, maintaining the acidic pH in the groups to which metals were added. The following biological parameters were evaluated: metal tissue concentration, relative fecundity (RF: absolute fecundity/body mass). Plasma levels of cortisol (proxy for stress) and 17α hydroxyprogesterone (17α-OHP), and gene expression of pituitary lhβ mRNA (proxies for final maturation) were measured to evaluate endocrine disruption. In the synchronic exposure, the presence of Mn potentiated the accumulation of Al in gills. The females from acidic pH and Al groups showed a reduced RF. Exposure to Al and Mn triggered an endocrine disruption response, evidenced by a decrease in the plasma concentration of 17α-OHP and cortisol. Despite this anti-steroidogenic effect, no changes occurred in the pituitary gene expression of lhβ. The endocrine changes and the metal accumulation were temporary, while the impacts on RF under the experimental conditions suggest permanent impairment in the reproduction of this species.

Effects of continuous and intermittent cadmium exposure on HPGL axis, GH/IGF axis and circadian rhythm signaling and their consequences on reproduction in female zebrafish: Biomarkers independent of exposure regimes

Typical biomarkers of cadmium (Cd) pollution have well been confirmed in fish from continuous exposure pattern. However, in a natural environment, fish may be exposed to Cd intermittently. In this study, juvenile female zebrafish were exposed for 48 days to 10 μg/L Cd continuously, 20 μg/L for 1 day in every 2 days or 30 μg/L for 1 day in every 3 days. The toxic effects were evaluated using 8 various physiological and biochemical endpoints like specific growth rate (SGR), 17β-estradiol (E2) and vitellogenin (VTG) concentrations in plasma, reproductive parameters (gonadosomatic index (GSI), egg-laying amount, spawning percentage, and hatching and mortality rate of embryos). Transcription of 59 genes related to hypothalamic-pituitary-gonadal-liver (HPGL) axis, circadian rhythm signaling and insulin-like growth factor (IGF) system was examined. SGR, spawning percentage, E2 and VTG levels declined in fish exposed to 10 and 20 μg/L Cd but remained relatively stable in fish exposed to 30 μg/L Cd. Exposure to 10, 20 and 30 μg/L Cd significantly reduced GSI, hatching rate and mortality rate. Similarly, mRNA expression of 27 genes were sensitive to both continuous and intermittent Cd exposure. Among these genes, expression levels of 10 genes had more than 5-fold increase or decrease, including mRNA levels of vtg1, vtg2, vtg3, esr1, igf2a, igf2b, igfbp5b, nr1d1, gnrh3 and gnrhr4. The most sensitive molecular biomarker was vtg3 expression with 1500-3100 fold increase in the liver. The present study, for the first time, provides effective candidate biomarkers for Cd, which are independent of exposure regimes.

Cadmium significantly changes major morphometrical points and cardiovascular functional parameters during early development of zebrafish

Living organisms are commonly exposed to cadmium and other toxic metals. A vast body of research has shown the significant effects of these toxic metals on developmental processes. In order to study the role of toxic metals on early developmental stages of eukaryotes, we explored the effect of cadmium (Cd²⁺) contaminant on zebrafish. Thus, zebrafish embryos were exposed to 3 mg/L (16.7 μM) Cd²⁺ for 96 h and imaged every 24 h from the exposure onwards. Hatching rates of the eggs were determined at 72 h, followed by analyses at 96 h for: survival rate, morphometrical factors, and functional parameters of the cardiovascular system. Interestingly enough, significant hatching delays along with smaller cephalic region and some morphological abnormalities were observed in the treatment group. Moreover, substantial changes were noticed in the length of notochord and embryo, absorption of yolk sac with shorter extension, area of swimming bladder, as well as pericardium sac after Cd²⁺ treatment. Cadmium also caused significant abnormalities in heart physiology which could be the leading cause of mentioned morphological deformities. Herein, our results shine light on systematic acute embryological effects of cadmium in the early development of zebrafish for the first time.

Single and combined acute and subchronic toxic effects of microplastics and copper in zebrafish (Danio rerio) early life stages

The evaluation of the interaction between microplastics (MPs) and heavy metals is of special importance for risk assessment. In this study, zebrafish (Danio rerio) were exposed to MPs (2 mg/L), two sub-lethal concentrations of copper (Cu, 60 and 125 μg/L) and their mixtures (Cu60 + MPs, Cu125 + MPs), from 2-h post-fertilization (hpf) until 14-days post-fertilization (dpf). Lethal and sublethal endpoints were evaluated, along with a set of biochemical and genetic biomarkers between 2 and 14 dpf. Exposure to MPs and Cu, single or combined, induced high mortality and oxidative stress in zebrafish larvae, with data showing that the antioxidant enzymes were inhibited at 6 dpf, increasing thereafter until 14 dpf, due to the accumulation of reactive oxygen species. MPs and Cu, single or combined, caused neurotoxicity in larvae by inhibiting acetylcholinesterase activity. There was an increased and significant effect of Cu + MPs groups on the evaluated biomarkers, concerning the corresponding Cu groups, suggesting that MPs may have a synergistic effect in relation to Cu. The Integrated Biomarker Response (IBR) evidenced that a higher degree of stress occurred at the larval period. Our findings highlight that MPs can act as a vector for heavy metals, therefore, influencing their bioavailability and toxicity in the organisms.

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.

Fluorescence resonance energy transfer-based sensor zebrafish for detecting toxic agents with single-cell sensitivity

Zebrafish are widely used for detecting toxic agents because of their unique advantages. The conventional zebrafish-based tests use lethal rates and morphological changes as criteria to evaluate the toxicity. To increase the sensitivity of using zebrafish to detect toxic agents, a fluorescence resonance energy transfer-based apoptotic biosensor was introduced into zebrafish genome to generate transgenic sensor zebrafish. Seven chemicals including heavy metals, nanomaterials and DNA-damaging agents were used to treat the sensor zebrafish to determine the sensitivity of the sensor zebrafish. The results showed that sensor zebrafish can detect the toxicity of the tested agents with single-cell sensitivity. Using the sensor zebrafish, we found that, at 100 nM, heavy metal cadmium (Cd) induced apoptosis of zebrafish cells, while no obvious morphological or behavioral changes were observed from the sensor zebrafish. Even at 44.5 nM (the maximum allowable concentration in drinking water), Cd induced a significant increase of apoptosis in sensor zebrafish. ZnO nanoparticles caused apoptosis in sensor zebrafish at a very low concentration of 100 ng/mL. DNA-damaging agents induced the apoptosis of many cells in sensor zebrafish. The sensor zebrafish are much more sensitive than the conventional zebrafish-based tests and can serve as a powerful tool for detecting toxic agents.

Endocrine disrupting effects of copper and cadmium in the oocytes of the Antarctic Emerald rockcod Trematomus bernacchii

Antarctica has long been considered a continent free from anthropic interference. Unfortunately, recent evidence indicate that metal contamination has gone so far and that its effects are still unknown. For this reason, in the present work, the potential endocrine disrupting effect of two highly polluting metals, copper and cadmium, were examined in the Antarctic teleost Trematomus bernacchii. After a 10 days waterborne exposure, ovarian metal uptake was determined by atomic absorption; in parallel, classical histological approaches were adopted to determine the effects on oocyte morphology, carbohydrate composition and presence and localization of progesterone and estrogen receptors. Results show that both metals induce oocyte degeneration in about one third of the previtellogenic oocytes, no matter the stage of development. In apparently healthy oocytes, changes in cytoplasm, cortical alveoli and/or chorion carbohydrates composition are observed. Cadmium but not copper also induces significant changes in the localization of progesterone and beta-estrogen receptors, a result that well correlates with the observed increase in ovarian metals concentrations. In conclusion, the acute modifications detected are suggestive of a significantly impaired fecundity and of a marked endocrine disrupting effects of copper and cadmium in this teleost species.

Sodium dehydroacetate exposure decreases locomotor persistence and hypoxia tolerance in zebrafish

Environmental exposure to sodium dehydroacetate (DHA-S) is inevitable as DHA-S is a high-volume preservative widely used in cosmetics, processed foods and personal care products. DHA-S is absorbed rapidly when administered orally or on the skin and generally considered to be safe and well tolerated. However, DHA-S has recently been reported to induce weight loss and allergic contact dermatitis, yet little is known about how DHA-S affect the related biological processes. Here, we characterize the biological effects of DHA-S on zebrafish model by directly waterborne exposure. Zebrafish is susceptible to DHA-S exposure at early developmental stage. DHA-S decreased the hatch rate and locomotor persistence of zebrafish, and eventually induced lethality during the continuous exposure at relatively low concentrations of commonly addition. Acute DHA-S exposure decreased respiration capacity in larval zebrafish, promoted the expression of HIF-1α (hypoxia-inducible factor-1α) and caused rapid adult zebrafish death in 30 h. We further demonstrated that DHA-S inhibited the activity of succinate dehydrogenase (SDH) inducing respiratory chain interruption, energy deficiency and organic acids accumulation. These results suggest that the approved DHA-S may pose serious environmental/ecological pressures on the aquatic animal's migration.

Aluminum bioconcentration in female Nile tilapia Oreochromis niloticus (Perciformes: Cichlidae) and the effects on pituitary gonadotropins

In this study, we measured aluminum (Al) bioconcentration in the brain, ovaries, and liver of Oreochromis niloticus females, and analyzed the effects of exposure to Al and acidic pH on the gene expression of follicle-stimulating hormone (βfsh) and luteinizing hormone (βlh) in these animals. Mature females were divided into 4 groups, thus being maintained for 96 h in one of the following conditions: control at neutral pH (Ctr); Al at neutral pH (Al); acidic pH (Ac), and Al at acidic pH (Al-Ac). pH alone did not influence Al bioconcentration in the brain. The animals from the Al-Ac group bioconcentrated more Al in the ovaries than those from the Al group, while no differences were observed in the liver. Aluminum bioconcentration was higher in the brain than in the liver and ovaries in Al-exposed animals (Al and Al-Ac), and higher in the brain than in the ovaries in the Ctr and Ac groups. The liver bioconcentrates more Al than the ovaries in the females from the Ctr and Ac groups. Aluminum and/or acidic pH did not alter βfsh gene expression, while βlh gene expression decreased in females from the Al group. Aluminum acted as an endocrine disruptor, suggesting deleterious effects in reproduction that could result in ovulation failure. Aluminum can act directly and/or indirectly in the pituitary, affecting ovarian steroidogenesis and altering the reproductive endocrine axis of mature O. niloticus females in an acute period of exposure.

Low-dose methylmercury exposure impairs the locomotor activity of zebrafish: Role of intestinal inositol metabolism

Methylmercury (MeHg) is a ubiquitous environmental toxicant with neurotoxic effects. Although its neurotoxicity had been more studied, the role of gut microbiota remains unclear. In this study, adult zebrafish and larvae were exposed to MeHgCl at the dose of 0, 1 and 10 ng/mL. MeHgCl exposure impaired the locomotor activity via upregulation of apoptosis and autophagy related genes in the brain. Intestinal and cerebral metabolome indicated that phosphatidylinositol signaling system and inositol phosphate metabolism pathways were significantly impacted in adult zebrafish upon MeHgCl exposure. The levels of myo-inositol (MI) in the intestine and brain were decreased and positively correlated. 16 S rRNA sequencing data from adult zebrafish showed that MeHgCl exposure also shifted the structure of gut microbiota and reduced the relative abundance of Bacteroidetes and Proteobacteria, which were further identified at genus level as Aeromonas and Cetobacterium. Further functional analysis indicated that MeHgCl disrupted inositol phosphate metabolism of gut microbiota. Notably, MI supplementation restored the impairment of locomotor activity and inhibited the upregulation of apoptosis and autophagy related genes, such as bcl-2 and atg5. Thus, this study not only revealed the key role of gut microbiota in MeHgCl-mediated neurotoxicity but also gave new insights into antagonizing its toxicity.

Eobania vermiculata as a potential indicator of nitrate contamination in soil

The effects of nitrates were analysed on the land snail Eobania vermiculata, a good bioindicator to assess the effects of certain pollutants in soil. It is known that the molluscs are very sensitive to contamination substances and can be used as sentinel organism for environmental pollution assessment. The nitrates are present in fertilizers and in food additives and their excess can not only be harmful to the environment but also dangerous for the humans. Indeed, in the mammals the nitrates are converted into nitrites and can cause a series of complications as the formation of methaemoglobin and cancers. In this study, adult organisms of E. vermiculata were exposed to soil containing 2000 mg/L of nitrates for 30 days to evaluate the stool microbiome and the histological changes at the level of the foot. Eggs of these snails were similarly treated to observe their hatching, survival and development. Histological changes were observed at level of the foot of adult snails exposed to nitrate and in their stools was evident an increase of bacteria, especially those that have a high ability to exploit nitrates and nitrogen as nutrients. Instead, the treated eggs showed changes in hatching, hypopigmentation of newborn snails and a decrease of their survival in time. The overall information obtained from these endpoints can provide important information regarding the quality of the environment. In addition, they also showed that the invertebrate organism E. vermiculata despite being a simple organism is very useful and efficient for ecotoxicological studies.