Oxidative Stress Assessment in Zebrafish Larvae

Effects of non-ionizing radio frequency electromagnetic radiation on the development and behavior of early embryos of Danio rerio

Biological effects of radio frequency electromagnetic radiation (RF-EMR) in the range of 900-1800 MHz emerging from the mobile phone were investigated and were found to influence the locomotor pattern when exposure was initiated from 1 hour post fertilization (hpf) in zebrafish embryos (ZE), Danio rerio. Mobile phones and other wireless devices offer tremendous advantages. However, on the flipside they are leading to an increased electromagnetic energy in the environment, an excess of which could be termed as electromagnetic pollution. Herein, we tried to understand the effects of RF-EMR emerging from the mobile phone, on the development and behavior of ZE, exposed to RF-EMR (specific absorption rate of 1.13 W/kg and 1800 MHz frequency) 1 hr daily, for 5 days. To understand if there could be any developmental stage-specific vulnerability to RF-EMR, the exposure was initiated at three different time points: 1hpf, 6hpf and 24hpf of ZE development. Observations revealed no significant changes in the survival rate, morphology, oxidative stress or cortisol levels. However, statistically significant variations were observed in the batch where exposure started at 1hpf, with respect to locomotion patterns (distance travelled: 659.1 ± 173.1 mm Vs 963.5 ± 200.4 mm), which could be correlated to anxiety-like behavior; along with a corresponding increase in yolk consumption (yolk sac area: 0.251 ± 0.019 mm2 Vs 0.225 ± 0.018 mm2). Therefore, we conclude that RF-EMR exposure influences the organism maximally during the earliest stage of development, and we also believe that an increase in the time of exposure (corresponding to the patterns of current usage of mobile phones) might reveal added afflictions.

Immunomodulatory effects of single and combined exposure to ZnO and TiO2 nanoparticles on rainbow trout challenged with Aeromonas salmonicida achromogenes

The increasing release of engineered nanoparticles (ENPs) in aquatic ecosystems stresses the need for stringent investigations of nanoparticle mixture toxicity towards aquatic organisms. Here, the individual and combined immunotoxicity of two of the most consumed ENPs, the ZnO and the TiO2 ones, was investigated on rainbow trout juveniles (Oncorhynchus mykiss). Fish were exposed to environmentally realistic concentrations (21 and 210 µg L-1 for the ZnO and 210 µg L-1 for the TiO2) for 28 days, and then challenged with the pathogenic bacterium, Aeromonas salmonicida achromogenes. Antioxidant and innate immune markers were assessed before and after the bacterial infection. None of the experimental conditions affected the basal activity of the studied innate immune markers and the redox balance. However, following the bacterial infection, the expression of genes coding for pro and anti-inflammatory cytokines (il1β and il10), as well as innate immune compounds (mpo) were significantly reduced in fish exposed to the mixture. Conversely, exposure to ZnO NPs alone seemed to stimulate the immune response by enhancing the expression of the IgM and c3 genes for instance. Overall, our results suggest that even though the tested ENPs at their environmental concentration do not strongly affect basal immune functions, their mixture may alter the development of the immune response when the organism is exposed to a pathogen by interfering with the inflammatory response.

Long-term effects of embryonic exposure to benzophenone-3 on neurotoxicity and behavior of adult zebrafish

Benzophenone-3 (BP-3) is the most widely used ultraviolet filter (UV filter) in industries to avoid UV radiation damage. BP-3 is added to most sunscreens to protect the skin, hair, and lips from sun rays. It results in continuous discharge into aquatic environments, leading to aquatic biota and human's continuous exposure. Consequences of BP-3 exposure on the physiology and behavior of aquatic animals, mainly zebrafish, have been investigated, including their neurotoxic effects. However, little is known about its consequences in long-term developmental endpoints. This study aimed to investigate the long-term effects of embryonic BP-3 exposure on biomarkers of neurotoxicity in zebrafish. For this, we exposed embryos to 5, 10, and 20 μg∙L-1 BP-3 concentration and let fish grow to adulthood (5mpf). We evaluated anxiety-like behavior, social preference, aggressiveness, and enzymatic activity of the antioxidant defenses system and neurotoxic biomarkers (Glutathione S-transferase -GST, catalase -CAT, and acetylcholinesterase -AChE) in adult zebrafish. Enzymatic activities were also investigated in larvae immediately after BP-3 exposure. Animals early exposed to BP-3 presented anxiety-like behaviors and decreased social preference, but aggressiveness was not altered. In general, exposure to BP-3 leads to altered enzymatic activity, which persists into adulthood. GST activity increased in embryos and adults, while CAT activity decreased in both life stages. AChE activity enhanced only at the larval stage (96 hpf). The long-term behavioral and biochemical effects of BP-3 highlight the need for abolishing or restricting the compound from personal care products, which are continually disposed into the environment and threaten the biota and human health.

Responses of Mytilus galloprovincialis in a Multi-Stressor Scenario: Effects of an Invasive Seaweed Exudate and Microplastic Pollution under Ocean Warming

Microplastic pollution, global warming, and invasive species are known threats to marine biota, but the impact of their simultaneous exposure is still not well understood. This study investigated whether the toxic effects posed by the invasive red seaweed Asparagopsis armata exudate (2%) to the mussel Mytilus galloprovincialis are amplified by a 96 h exposure to increased temperature (24 °C) and polyethylene microplastics (PE-MPs, 1 mg/L). Biochemical (neurotoxicity, energy metabolism, oxidative stress, and damage) and physiological (byssal thread production) responses were evaluated. The number of produced byssus greatly decreased under concomitant exposure to all stressors. The antioxidant defences were depleted in the gills of mussels exposed to temperature rises and PE-MPs, regardless of exudate exposure, preventing oxidative damage. Moreover, the heat shock protein content tended to decrease in all treatments relative to the control. The increased total glutathione in the mussels' digestive gland exposed to 24 °C, exudate, and PE-MPs avoided oxidative damage. Neurotoxicity was observed in the same treatment. In contrast, the energy metabolism remained unaltered. In conclusion, depending on the endpoint, simultaneous exposure to A. armata exudate, PE-MPs, and warming does not necessarily mean an amplification of their single effects. Studies focusing on the impact of multiple stressors are imperative to better understand the underlying mechanisms of this chronic exposure.

Effects of cyanobacterial metabolites: Aeruginosin 98A, microginin-FR1, anabaenopeptin-A, cylindrospermopsin in binary and quadruple mixtures on the survival and oxidative stress biomarkers of Daphnia magna

The aim of our study was to determine the effects of aeruginosin 98 A (ARE-A), microginin-FR1 (MG-FR1), anabaenopeptin-A (ANA-A) cylindrospermopsin (CYL) and their binary and quadruple mixtures on the survival and the levels of oxidative stress biomarkers in Daphnia magna: total glutathione (GSH), catalase (CAT), dismutase (SOD) and malondialdehyde (MDA). The biochemical indicators were measured with ELISA kits and the interactive effects were determined by isobole and polygonal analysis with Compusyn® computer software. The study revealed that oligopeptides did not decrease daphnid survival, only CYL inhibited this parameter, with synergistic effects when it was used as a component. The single metabolites at the two highest concentrations and all the binary and quadruple mixtures at all concentrations diminished GSH level, however both in the binary and in the quadruple mixtures most of the interactions between the metabolites were antagonistic. Nearly additive effects were found only in AER-A + CYL and MG-FR1+CYL. On the other hand, CAT activity was slightly increased in daphnids exposed to the binary mixtures with antagonistic interactions, however nearly addivive effects were found in animals exposed to the mixture of AER-A + ANA-A and synergistic in the quadruple mixture. SOD was elevated in daphnids exposed to single AER-A and MG-FR1, however it was diminished in the animals exposed to ANA-A and CYL. Binary mixtures in which CYL was present as a component decreased the level of this enzyme with nearly additive interactions in ANA-A + CYL. The quadruple mixture increased SOD level, with antagonistic interactions. Both single cyanobacterial metabolites, their binary and quadruple mixtures induced lipid peroxidation measured by MDA level and most of interactions in the binary mixtures were synergistic. The study suggested that antioxidative system of Daphnia magna responded to the tested metabolites and the real exposure to mixtures of these products may lead to various interactive effects with varied total toxicity.

Neuroprotective effect of Biochanin a against Bisphenol A-induced prenatal neurotoxicity in zebrafish by modulating oxidative stress and locomotory defects

Exogenous toxicants cause oxidative stress and damage to brain cells, resulting in inflammation. Neuroinflammation is important in the pathobiology of various neurological illnesses, including Alzheimer's disease (AD). In this context, Bisphenol A (BPA), a common toxin, causes oxidative damage and has been linked to neurological problems. An O-methylated isoflavone known as Biochanin A (5,7-dihydroxy-4'-methoxy-isoflavone, BCA) is considered to be a phytoestrogen, which is abundant in some legume plants and soy which have preventive effects against cancer, osteoporosis, menopausal symptoms and oxidative stress. However, the mechanism by which BCA protected the prenatal neurological stress are not known. So that, in this study we investigated the BCA neuroprotective effect against BPA-induced neuroinflammation in zebrafish embryo models. For this study, fertilized zebrafish embryos are exposed to BPA (1 µM) with or without BCA. Our finding suggested that BCA co-exposure prevented the depletion of antioxidant defense enzymes by BPA and reduced the production of intracellular ROS production, superoxide anion (O₂^-), lipid peroxidation (LPO), lactate dehydrogenase (LDH) and nitric oxide (NO) levels in the head that aided in safeguarding neuronal development. Baseline locomotion was rendered and a total distance was calculated to assess the motor function. Exposure to BCA increased acetylcholinestrase (AChE) and improved motor neuron functions. It also reduced the pro-inflammatory response expression and prevented neuroinflammation. Our study suggests that BCA has a positive role in the attenuation or amelioration of neuronal oxidative damage and locomotory behaviour induced by BPA.

Co-Exposure with an Invasive Seaweed Exudate Increases Toxicity of Polyamide Microplastics in the Marine Mussel Mytilus galloprovincialis

Plastic pollution and invasive species are recognised as pervasive threats to marine biodiversity. However, despite the extensive on-going research on microplastics’ effects in the biota, knowledge on their combination with additional stressors is still limited. This study investigates the effects of polyamide microplastics (PA-MPs, 1 mg/L), alone and in combination with the toxic exudate from the invasive red seaweed Asparagopsis armata (2%), after a 96 h exposure, in the mussel Mytilus galloprovincialis. Biochemical responses associated with oxidative stress and damage, neurotoxicity, and energy metabolism were evaluated in different tissues (gills, digestive gland, and muscle). Byssus production and PA-MP accumulation were also assessed. Results demonstrated that PA-MPs accumulated the most in the digestive gland of mussels under PA-MP and exudate co-exposure. Furthermore, the combination of stressors also resulted in oxidative damage at the protein level in the gills as well as in a significant reduction in byssus production. Metabolic capacity increased in both PA-MP treatments, consequently affecting the energy balance in mussels under combined stress. Overall, results show a potential increase of PA-MPs toxicity in the presence of A. armata exudate, highlighting the importance of assessing the impact of microplastics in realistic scenarios, specifically in combination with co-occurring stressors, such as invasive species.

Exposure to 2,4-D herbicide induces hepatotoxicity in zebrafish larvae

2,4-Dichlorophenoxyacetic acid (2,4-D) herbicide is the main ingredient in over 1500 commercially available products such as Weedestroy® AM40 and DMA® 4 IVM. Although the liver has been identified as one of the organs that are affected by this herbicide, reports on its hepatotoxic effects available in the literature are restricted to rats. Thus, there is a gap in information on other organisms that may be vulnerable to 2,4-D exposure, such as fish. Therefore, the present work aimed to assess the hepatotoxic potential of 2,4-D in fish using zebrafish (Danio rerio) larvae as a model system. For this purpose, its acute toxicity to zebrafish embryos was assessed, as well as its sublethal effects (< LC₅₀) on the activity of enzymes related to oxidative (GST, CAT and GPX) and metabolic (LDH) stress and liver parameters (AST, ALT and ALP) after 48 h of exposure. Morphological analyses of the liver were also assessed in zebrafish larvae. As a result, 2,4-D reduced larvae survival (LC₅₀ 15.010 mg/L in 96 h of exposure), induced malformations, altered the activity of LDH, GST and CAT enzymes and significantly increased the activity of all biomarkers for liver damage. Although no changes in the color or size of larval liver were observed, histopathological analysis revealed that treatment with 2,4-D caused severe changes in liver tissue, such as vacuolization of the cytosol, eccentric cell nucleus, loss of tissue architecture and cellular boundaries. Thus, the results showed that 2,4-D altered the enzymatic profile related to oxidative stress, and induces liver damage.

In vitro antibacterial and anti-inflammatory effects of Anacardium occidentale L. extracts and their toxicity on PBMCs and zebrafish embryos

This study evaluated the in vitro antimicrobial and immunomodulatory action of crude extracts from Anacardium occidentale L. (cashew tree) leaves and bark, and to determine their toxicity to peripheral-blood mononuclear cells (PBMCs) and to zebrafish embryos and larvae. Chemical analysis of extracts was performed by proton nuclear magnetic resonance (¹H-NMR). The antibacterial activity was evaluated against selected bacteria strains by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Cytotoxicity of the extracts was assessed using resazurin method, while the effect on production of ROS by PMN leukocytes was measured by luminol. Embryotoxicity to zebrafish was assessed using the fish embryo acute toxicity test (FET) and quantification of toxicity marker enzymes (AChE, LDH, and GST). ¹H-NMR results showed anacardic acid as the main component of the extracts. All bacterial species tested were sensitive to the extracts, with MICs ranging from 312.5 to 10,000 μg/mL. Streptococcus mutans and Escherichia coli were the most susceptible species. The extracts promoted cell viability above 75% at concentrations from 1.25 to 80 μg/mL. Both extracts reduced zymosan-induced ROS (p < 0.05) at concentrations of 1, 8, and 80 μg/mL compared to the control. In vivo, there were embryotoxic effects in zebrafish embryos exposed to both extracts through the presence of lethal and sublethal endpoints. The samples also acted by inhibiting the activities of biomarker enzymes. The A. occidentale L. bark and leaf extracts showed antimicrobial potential and modulated ROS production in vitro, but these also showed embryotoxic effects to zebrafish.

How Does Mytilus galloprovincialis Respond When Exposed to the Gametophyte Phase of the Invasive Red Macroalga Asparagopsis armata Exudate?

Asparagopsis armata is classified as an invasive species in Europe. Through the exudation of secondary metabolites, this macroalga holds a chemical defence against consumers, with potential toxic effects to native rocky shore communities. This study aims to evaluate the potential impact of A. armata (gametophyte) exudate in a native species, the mussel Mytilus galloprovincialis, in terms of biochemical and organismal effects. The 96 h-LC50 was 3.667% and based on it, exudate concentrations (0.25; 0.5; 1; 2%) were determined to further sublethal experiments. These sublethal concentrations caused no oxidative damage in the digestive gland since lipid peroxidation and protein carbonylation were not affected. Nevertheless, there was a significant rise in the electron transport system activity and total glutathione content in muscle, suggesting an increased non-enzymatic antioxidant capacity and consequent energy consumption to cope with potential pro-oxidant compounds. This might have contributed to the observed decline in cellular energy allocation of the exposed mussels. At the organismal level, clearance capacity declined along the concentration gradient. Moreover, the number of functional byssuses decreased with increasing concentrations and a significant reduction in their attachment strength was observed. These findings suggest that the presence of A. armata may compromise M. galloprovincialis integrity in the invaded coastal areas.

Assessing the effects of an acute exposure to worst-case concentration of Cry proteins on zebrafish using the embryotoxicity test and proteomics analysis

Cry1C, Cry1F and Cry1Ab are insecticidal proteins from Bacillus thuringiensis (Bt) which are expressed in transgenic crops. Given the entry of these proteins into aquatic environments, it is relevant to evaluate their impacts on aquatic organisms. In this work, we sought to evaluate the effects of Cry1C, Cry1F and Cry1Ab on zebrafish embryos and larvae of a predicted worst-case scenario concentration of these proteins (set to 1.1 mg/L). For that, we coupled a traditional toxicity approach (the zebrafish embryotoxicity test and dosage of enzymatic biomarkers) to gel free proteomics analysis. At the concentration tested, these proteins did not cause adverse effects in the zebrafish early life stages, either by verifying phenotypic endpoints of toxicity or alterations in representative enzymatic biomarkers (catalase, glutathione-S-tranferase and lactate-dehydrogenase). At the molecular level, the Cry proteins tested lead to very small changes in the proteome of zebrafish larvae. In a global way, these proteins upregulated the expression of vitellogenins. Besides that, Cry1C e Cry1F deregulated heterogeneous nuclear ribonucleoproteins (Hnrnpa0l and Hnrnpaba, respectively), implicated in mRNA processing and gene regulation. Overall, these data lead to the conclusion that Cry1C, Cry1F and Cry1Ab proteins, even at a very high concentration, have limited effects in the early stages of zebrafish life.

Embryotoxicity evaluation of atractylodin and β-eudesmol using the zebrafish model

Atractylodin and β-eudesmol are the major active ingredients of Atractylodes lancea (Thunb) DC. (AL). Both compounds exhibit various pharmacological activities, including anticancer activity against cholangiocarcinoma. Despite the widespread use of this plant in traditional medicine in China, Japan, Korea, and Thailand, studies of their toxicological profiles are limited. The present study aimed to evaluate the embryotoxicity of atractylodin and β-eudesmol using the zebrafish model. Zebrafish embryos were exposed to a series of concentrations (6.3, 12.5, 25, 50, and 100 μM) of each compound up to 72 h post-fertilization (hpf). The results showed that atractylodin and β-eudesmol induced mortality of zebrafish embryos with the 50% lethal concentration (LC₅₀) of 36.8 and 53.0 μM, respectively. Both compounds also caused embryonic deformities, including pericardial edema, malformed head, yolk sac edema, and truncated body. Only β-eudesmol decreased the hatching rates, while atractylodin reduced the heart rates of the zebrafish embryos. Additionally, both compounds increased reactive oxygen species (ROS) production and altered the transcriptional expression levels of superoxide dismutase 1 (sod1), catalase (cat), and glutathione S-transferase pi 2 (gstp2) genes. In conclusion, atractylodin and β-eudesmol induce mortality, developmental toxicity, and oxidative stress in zebrafish embryos. These findings may imply similar toxicity of both compounds in humans.