Glutathione and its dependent enzymes' modulatory responses to toxic metals and metalloids in fish--a review

Toxicity of microplastics and copper, alone or combined, in blackspot seabream (Pagellus bogaraveo) larvae

Plastics pose serious risks for fish productivity and a potential constraint for food security. Newly hatched blackspot seabream larvae were exposed to microplastics (MPs), copper (Cu, 10-810 µg/L) and their mixtures (Cu+MPs), during 3 and 9 days. Biochemical biomarkers and the expression of antioxidant and neurotoxicity-related genes were evaluated. In the 3-day exposure, catalase and glutathione-S-transferase activities decreased in MPs, Cu and Cu+MPs groups, followed by an increase of lipid peroxidation in the Cu270 and Cu270 +MPs exposed larvae. In the 9-day exposure, ROS levels increased in MPs and Cu30 groups, but no significant oxidative damage was observed, suggesting that the antioxidant system overcome the induced oxidative stress. However, the acetylcholinesterase transcript was downregulated in MPs, Cu and Cu10+MPs groups, indicating that MPs effects in cholinergic neurotransmission may arise after longer exposures. Overall, MPs and Cu can reduce survival, induce oxidative stress, lipid peroxidation, neurotoxicity, and impact negatively fish larvae fitness.

Dietary Inclusion of Hydrolyzed Debaryomyces hansenii Yeasts Modulates Physiological Responses in Plasma and Immune Organs of Atlantic Salmon (Salmo salar) Parr Exposed to Acute Hypoxia Stress

Stress related to salmon aquaculture practices (handling, sub-optimal nutrition, diseases, and environmental problems) may compromise fish welfare. This study describes the effects of two hydrolyzed Debaryomyces hansenii yeast-based products (LAN4 and LAN6) on physiological and immune responses of Atlantic salmon (Salmo salar) parr exposed to short hypoxia stress. A commercial-like diet (control diet: CD) and two experimental diets (CD supplemented with 0.1% of either component LAN4 or LAN6) were fed to fish for 8 weeks. At the end of the feeding experiment, fish were exposed to 1-min hypoxia and samples were collected at 0, 1, 3, 6, 12, and 24 h post-stress. Results showed that plasma cortisol reached a peak at 1 h post-stress in CD and LAN6 groups, whereas no significant increase in cortisol levels was detected in the LAN4 group. Moreover, the LAN6 group enhanced IL-10 responses to hypoxia, when compared to the control and LAN4 group. This suggests a regulation of immunosuppressive profiles in fish fed LAN4. Hypoxia stress increased TNFα in all groups, which indicates that fish may compensate for the short-term stress response, by modulating innate immune molecules. The apparent suppression of hypoxia responses in the LAN4 group coincided with the detection of differences in goblet cells size and Muc-like proteins production in DI; and upregulation (1 h post-stress) of pathways related to oxygen transport, hemoglobin complex, and glutathione transferase activity and the downregulation of fatty acid metabolism (6 h post-stress) in gills. To conclude, a 1-min hypoxia stress exposure affects the response to stress and immunity; and D. hansenii-based yeast products are promising components in functional aquafeeds for salmon due to their ability to counteract possible consequences of hypoxic stress.

Dietary inclusion of rambutan (Nephelium lappaceum L.) seed to Nile tilapia (Oreochromis niloticus) reared in biofloc system: Impacts on growth, immunity, and immune-antioxidant gene expression

An eight-week feeding trial was carried out to determine the effects of rambutan seed (RS) as a feed additive on the growth, skin mucus, serum immune parameters, and gene expression of Nile tilapia (Oreochromis niloticus) raised under a biofloc system. Nile tilapia fingerlings (14.77 ± 0.80 g fish^-1) were fed five experimental diets containing 0, 5, 10, 20, and 40 g kg^-1 of RS, corresponding to five treatments (RS0, RS5, RS10, RS20, and RS40) with three replications per treatment. The results showed that fish consuming the RS10 and RS20 diets presented a substantial (P < 0.05) improvement in specific growth rate (SGR), weight gain (WG), and feed conversion ratio (FCR) after eight weeks. The highest values were recorded in the RS10 diet; however, there were no significant (P > 0.05) differences exhibited in the fish survival rates between treatments. The RS supplementation diets demonstrated greater immunological parameters, particularly skin mucus and serum immune responses (P < 0.05), than that of the control after eight the eight-week feeding trial. The highest level was seen in fish fed the RS10; followed by the RS20, RS40 (P > 0.05), and RS5 diets. Regarding gene expressions, IL1, IL8, LBP, GSTa, and GSR genes were significantly up-regulated in fish provided the RS10 diet in comparison to the control and other supplemented diets (P < 0.05). However, no significant up-regulation was found in these genes among the RS0, RS5, RS20, and RS40 diets, with the exception of the GPX gene. Similarly, up-regulation of IL-8, LBP, GSTa, GPX, and GSR were noted in fish fed the RS10 diet (P < 0.05). Notably, no significant differences were evident in these genes among the RS5, RS20, and RS40 diets. In conclusion, fish fed RS10 (10 g kg^-1) significantly enhanced growth, skin mucus, serum immunities, and immune-antioxidants related gene expressions of Nile tilapia raised under biofloc system.

Anoxia-reoxygenation modulates cadmium-induced liver mitochondrial reactive oxygen species emission during oxidation of glycerol 3-phosphate

Aquatic organisms are frequently exposed to multiple stressors including low dissolved oxygen (O₂) and metals such as cadmium (Cd). Reduced O₂ concentration and Cd exposure alter cellular function in part by impairing energy metabolism and dysregulating reactive oxygen species (ROS) homeostasis. However, little is known about the role of mitochondrial glycerol 3-phosphate dehydrogenase (mGPDH) in ROS homeostasis in fish and its response to environmental stress. In this study, mGPDH activity and the effects of anoxia-reoxygenation (A-RO) and Cd on ROS (as hydrogen peroxide, H₂O₂) emission in rainbow trout liver mitochondria during oxidation of glycerol 3-phosphate (G3P) were probed. Trout liver mitochondria exhibited low mGPDH activity that supported a low respiratory rate but substantial H₂O₂ emission rate. Cd evoked a low concentration stimulatory-high concentration inhibitory H₂O₂ emission pattern that was blunted by A-RO. At specific redox centers, Cd suppressed H₂O₂ emission from site I_Q, but stimulated emission from sites III_Qo and G_Q. In contrast, A-RO stimulated H₂O₂ emission from site I_Q following 15 min exposure and augmented Cd-stimulated emission from site II_F after 30 min exposure but did not alter the rate of H₂O₂ emission from sites III_Qo and G_Q. Additionally, Cd neither altered the activities of catalase, glutathione peroxidase, or thioredoxin reductase nor the concentrations of total glutathione, reduced glutathione, or oxidized glutathione. Overall, this study indicates that oxidation of G3P drives ROS production from mGPDH and complexes I, II and III, whereas Cd directly modulates redox sites but not antioxidant defense systems to alter mitochondrial H₂O₂ emission.

Updating the use of biochemical biomarkers in fish for the evaluation of alterations produced by pharmaceutical products

The evaluation of toxic effects in stressful environmental conditions can be determined through the imbalance between exogenous factors (environmental contaminants) and enzymatic and non-enzymatic defenses in biological systems. The use of fish for the identification of alterations in biochemical biomarkers provides a comprehensive vision of the effects that pharmaceutical products cause in the aquatic ecosystem, as they are organisms with high sensitivity to contaminants, filtering capacity, and potential for environmental toxicology studies. A wide range of pharmaceuticals can stimulate or alter a variety of biochemical mechanisms, such as oxidative damage to membrane lipids, proteins, and changes in antioxidant enzymes. This review includes a summary of knowledge of the last 20 years, in the understanding of the different biochemical biomarkers generated by exposure to pharmaceuticals in fish, which include different categories of pharmaceutical products: NSAIDs, analgesics, antibiotics, anticonvulsants, antidepressants, hormones, lipid regulators and mixtures. This review serves as a tool in the design of studies for the evaluation of the effects of pharmaceutical products, taking into account the most useful biomarkers, type of matrix, enzyme alterations, all taking the pharmaceutical group of interest.

Impacts of wildfires in aquatic organisms: biomarker responses and erythrocyte nuclear abnormalities in Gambusia holbrooki exposed in situ

Wildfires are an environmental concern due to the loss of forest area and biodiversity, but also because their role as drivers of freshwater systems contamination by metals. In this context, the fish Gambusia holbrooki was used as a model, deployed for in situ exposure in watercourses standing within a recently burnt area and further assessment of toxic effects. The fish were exposed during 4 days at four different sites: one upstream and another downstream the burnt area and two within the burnt area. Biochemical biomarkers for oxidative stress and damage were assessed. The extent of lipoperoxidative damage was monitored by quantifying malondialdehyde and DNA damage evaluated through erythrocyte nuclear abnormalities observation. Chemical analysis revealed higher metal levels within the burnt area, and exposed fish consistently showed pro-oxidative responses therein, particularly an increase of gill glutathione peroxidase and glutathione reductase activity, the records doubling compared to samples from sites in the unburnt area; also the activity of glutathione-S-transferases comparatively increased (by 2-fold in the liver) in samples from the burnt area, and malondialdehyde was produced twice as much therein and in samples downstream the burnt area reflecting oxidative damage. Consistently, the frequency of erythrocyte nuclear abnormalities was higher at sites within and downstream the burnt area. This study supports the use of sensitive oxidative stress and genotoxicity biomarkers for an early detection of potentially noxious ecological effects of wildfires runoff.

Ecotoxicological effects of dietary titanium dioxide nanoparticles on metabolic and biochemical parameters of model organism Galleria mellonella (Lepidoptera: Pyralidae)

Nanoparticles (NPs) are now being used in many industrial activities, such as mining, paint and glass industries. The frequent industrial use of NPs contributes to environmental pollution and may cause cellular and oxidative damage in native organisms. In this study, the toxic effects of titanium dioxide nanoparticles (TiO₂ NPs) were investigated using Galleria mellonella larvae as a model insect species. Alterations in cell damage indicators, such as alanine transferase, aspartate transferase, lactate dehydrogenase, non-enzymatic antioxidants and biochemical parameters, were determined in the hemolymph of G. mellonella larvae exposed to TiO₂ NPs at different concentrations (5, 50, 250 and 1250 μg/mL) in their diets. TiO₂ NPs caused concentration-dependent cellular damage in the hemolymph of G. mellonella larvae and increased the levels of the non-enzymatic antioxidants uric acid and bilirubin. In addition, total protein in hemolymph significantly decreased at the highest concentration (1250 μg/mL) of TiO₂ NPs. Level of the urea increased at the highest concentration (1250 μg/mL) of TiO₂ NPs, whereas the amount of glucose was not affected. These findings demonstrated that TiO₂ NPs caused concentration-dependent toxic effects on G. mellonella larvae.

Sublethal diclofenac induced oxidative stress, neurotoxicity, molecular responses and alters energy metabolism proteins in Nile tilapia, Oreochromis niloticus

Reports have shown that residues of pharmaceuticals and their metabolites can pose toxicological threats to organisms living in aquatic ecosystem. Nile tilapia, Oreochromis niloticus, was exposed at 0.17, 0.34, and 0.68 mg L^-1 of diclofenac up to 60 days in a renewal static bioassay system. Antioxidant enzymes reactions, molecular responses, activities of energy metabolism proteins, and the neurotoxic potentials of the drug in the brain and fish muscle were evaluated. Antioxidant enzyme activities such as superoxide dismutase, glutathione-S-transferase, and also fructose 1, 6 bisphosphatase and glucose-6-phosphate dehydrogenase as well as the levels of lipid peroxidation and protein carbonyl were elevated, while glutathione peroxidase, total reduced glutathione, and acetylcholinesterase in the brain and muscles of the treated groups were significantly inhibited in a dose-dependent association. Expression of superoxide dismutase (sod), catalase (cat), and heat shock proteins (hsp 70) genes in brain and muscle tissues was up-regulated. Continuous treatment with sublethal diclofenac for a long time can induce oxidative imbalance, cause neurotoxicity, and alter the expression of genes related to stress in Nile tilapia, suggesting the use of these biomarkers in monitoring the adverse effects the pharmaceuticals could cause to organisms in aquatic ecosystem for possible mitigation.

Ecotoxicological effect of ketoconazole on the antioxidant system of Daphnia similis

The occurrence of emerging pharmaceutical pollutants (i.e. small drugs, antibiotics) present in aquatic environments shown to be a current environmental problem still without apparent solution. In this regard, the use of ecotoxicological techniques has been shown fundamental for the appraisal of damage to affected living organisms. Herein, ecotoxicological tests were conducted, focusing on the evaluation of the effects of ketoconazole (KTZ) on the antioxidant system of the model body Daphnia similis. In order to study the biochemical changes caused by KTZ in the antioxidant system, the enzymatic biomarkers glutathione S-transferase (GST), catalase (CAT), and ascorbate peroxidase (APX) were monitored. Toxicological tests were conducted using KTZ concentrations (0-10 μg·L^-1). Prolonged exposure to KTZ (336 h) caused changes upon the expression of antioxidant enzymes and simultaneously affected the reproductive system in those organisms. Moreover, a decrease in GST and APX activity was observed caused by KTZ exposure, respectively 79.2% (3.53 μmol min^-1 mg^-1 protein) and 24.4% (0.88 μmol min^-1 mg^-1 protein). On the other hand, it was observed an increase of 27% (0.17 μmol min^-1 mg^-1 protein) in CAT activity. Through this study, it was possible to observe the toxicological effects of KTZ, which proves its action as an oxidative stress-inducing agent and endocrine modifier in daphnids organisms.

Does acidification lead to impairments on oxidative status and survival of orange clownfish Amphiprion percula juveniles?

The nitrification process in recirculating aquaculture systems can reduce water pH. Fish can also be exposed to water acidification during transport, an important feature in the aquarium industry, as live fish can be kept in a closed environment for more than 24 h during overseas aerial transportation. Therefore, it is important to study the responses of fish to acidic environments. We investigated the impacts of acute exposure to decreasing pH levels in orange clownfish Amphiprion percula juveniles on their survival and oxidative stress status. Fish were exposed to pH 5, 6, 7, and 8 for 96 h. We observed a significant reduction in survival (85%) and protein damage as measured by P-SH (protein thiol) for fish maintained at pH 5. Despite no effects on survival or oxidative damage, fish exposed to pH 6 showed an increase in their antioxidant defense systems, demonstrating this pH level could not be suitable for them as well. Furthermore, there were no negative effects for fish kept at pH 7, compared to those maintained at pH 8 during this short-term evaluation.

Developmental toxicity, antioxidant, and marker enzyme assessment of swertiamarin in zebrafish (Danio rerio)

A secoiridoid glycoside called swertiamarin has been widely used as a herbal medicine for many decades. In particular, swertiamarin from the Enicostema axillare herb has been used as a multipurpose drug to treat innumerable health problems. As this medicine is consumed orally, its toxicity level should be determined. To examine the safety of this compound, toxicology work was done in zebrafish, and this is the first report to describe swertiamarin toxicity in zebrafish. Zebrafish embryos were used in this swertiamarin toxicity study, and morphological changes were observed. Further, the compound was also studied in adult zebrafish to determine the impact of the compound on the fish liver. Enzyme profiling with superoxide dismutase, glutathione peroxidase, catalase, reduced glutathione levels, glutathione S-transferase, lactate dehydrogenase, glutamic oxaloacetic transaminases, lipid peroxidation, Na⁺ /K⁺ -ATPase, and glutamic pyruvic transaminases) was evaluated (p ≤ 0.05). Results suggest that swertiamarin is a safe drug only at a low concentration (40 µM). This study also shows that even herbal medicinal compounds may be toxic to humans at higher dosages. Hence, irrespective of whether a drug is synthetic or natural, it needs to be tested for its toxicity before use in humans.

Domestication affected stress and immune response markers in Perca fluviatilis in the early larval stage

It is already known that domestication modifies stress and immune responses in juveniles and adults of several fish species. However, there is a lack of information on whether these modulations result from adaptability along the life cycle or if they are pre-determined in very early developmental stages. To shed light on mechanisms that help to explain the process of domestication, a study was conducted to analyze comparatively Eurasian perch larval performance, stress, and immune status between wild and domesticated specimens. Eurasian perch larvae obtained from wild and domesticated (generation F5 reared in recirculating aquaculture systems) spawners were reared in the same conditions during the main rearing trial (MRT) and also subjected to a thermal challenge (TC). During the study, larval performance (including survival, growth performance, swim bladder inflation effectiveness, deformity rate), the expression of genes involved in immune and stress response, and the specific activity of oxidative stress enzymes (during MRT only) were analyzed. No significant differences in hatching rate, deformity rate, or swim bladder inflation effectiveness between wild and domesticated larvae were found, whereas specific growth rate, final total length, and wet body weight were significantly lower in wild larvae. Higher mortality was also observed in wild larvae during both MRT and TC. The data obtained in this study clearly indicated that during domestication, significant modifications in stress and immune response, such as complement component c3, were noted as early as just after hatching. Generally, domesticated fish were characterized by a lower stress response and improved immune response in comparison to the wild fish. This probably resulted from the domesticated larvae being better adapted to the conditions of artificial aquaculture. The data obtained provided information on how domestication affects fish in aquaculture, and they contribute to the development of efficient selective breeding programs of Eurasian perch and other freshwater teleosts.

Garlic (Allium sativum) and Fu-ling (Poria cocos) mitigate lead toxicity by improving antioxidant defense mechanisms and chelating ability in the liver of grass carp (Ctenopharyngodon idella)

The heavy metal lead (Pb) is a contaminant widely distributed in the food chain. In this study, eight weeks of feeding containing Garlic (Allium sativum) or Fu-ling (Poria cocos) or both, markedly increased the growth index, enzyme activity, and serum index and significantly decreased muscle Pb level in grass carp (Ctenopharyngodon idella). Upon Pb exposure, the feeding Garlic or Fu-ling or both possessed the similar effects on improving the function of the antioxidant system and chelating ability. Further, the gene expressions of metal binding proteins (TF and MT-2) in the liver of the three experimental groups were significantly higher than those of the control group, which were all highly up-regulated after Pb exposure. At the same time, the activities of antioxidant enzymes (SOD and CAT) and the content of non-enzymatic substance (GSH) in the liver of the Garlic group, Fu-ling group and mixed group were stable compared to the control group after Pb exposure. Moreover, the reduction of Pb toxicity was manifested by the decrease of Pb content in the muscle, and the stable expression of heat stress proteins (HSP30 and HSP60) and immune-related genes (TNF-α and IL-1β). Taken together, the study preliminarily shows that the Garlic and Fu-ling play a role in mitigating the toxicity of Pb in grass carp.

Inhibition of Glutathione Reductase Activity from Baker's Yeast (Saccharomyces cerevisiae) By Copper(II) Oxide Nanoparticles and Copper(II) Chloride

In this study, glutathione reductase (GR) from baker's yeast (Saccharomyces cerevisiae) was exposed to 0, 25, 50, 100, 250 and 500 mg/L copper(II) oxide nanoparticles (CuO NPs) and copper(II) chloride (CuCl₂). Changes in GR% activity upon exposure to 25, 50, 100, 250 and 500 mg/L CuO NPs and CuCl₂ were found to be + 0.3, - 3.4, - 8.1, - 25.7 and - 37.4 and - 60.7, - 72.7, - 77.8, - 85.3 and - 90.6, respectively. The 50% inhibition concentration (IC50) was 625 ppm (78.6 × 10^-4 M) for CuO NPs and 21 ppm (1.56 × 10^-4 M) for CuCl₂. Moreover, CuO NPs and CuCl₂ inhibited GR competitively and noncompetitively, respectively.

Effects of bromate on life history parameters, swimming speed and antioxidant biomarkers in Brachionus calyciflorus

The baking industries and disinfection of tap water released a considerable amount of bromate into surface water, which has been reported as a carcinogenic compound to mammals. Rotifers play an important role in freshwater ecosystems and are model organisms to assess environmental contamination. In the present study, the effects of different concentrations (0.001, 0.01, 0.1, 1, 10, 100 and 200 mg/L) of bromate on the life-table and population growth parameters were investigated in the rotifer Brachionus calyciflorus. The results showed that the 24-h LC₅₀ of bromate to B. calyciflorus was 365.29 mg/L (95%Cl: 290.37-480.24). Treatments with 0.01, 10 and 200 mg/L bromate shorten the reproductive period. High levels of bromate (100 and 200 mg/L) significantly decreased net reproductive rate, intrinsic rate of population increase, life span, mictic rate of B. calyciflorus. To investigate the underlying mechanisms, swimming speed and antioxidative biomarkers were compared between bromate treatments and the control. The results showed that glutathione (GSH) and malondialdehyde (MDA) contents, total superoxide dismutase (T-SOD) and peroxidase (POD) activities decreased significantly in response to bromate exposure and the reasons required further investigation. Treatments with 0.001-200 mg/L bromate all significantly reduced swimming linear speed to rotifer larvae and treatments with 100-200 mg/L bromate significantly suppressed the swimming linear speed of adult rotifer. These changes would reduce filtration of algal food and could explain the decreased survival and reproduction. Overall, bromate may not show acute toxicity to rotifers, but still have potential adverse effects on rotifer behavior, which may then influence the community structure in aquatic ecosystems.

Comparative transcriptome analysis uncovers roles of hydrogen sulfide for alleviating cadmium toxicity in Tetrahymena thermophila

Background

Cadmium (Cd) is a nonessential heavy metal with potentially deleterious effects on different organisms. The organisms have evolved sophisticated defense system to alleviate heavy metal toxicity. Hydrogen sulfide (H₂S) effectively alleviates heavy metal toxicity in plants and reduces oxidative stress in mammals. However, the function of H₂S for alleviating heavy metal toxicity in aquatic organisms remains less clear. Tetrahymena thermophila is an important model organism to evaluate toxic contaminants in an aquatic environment. In this study, the molecular roles of exogenously H₂S application were explored by RNA sequencing under Cd stress in T. thermophila.

Results

The exposure of 30 μM Cd resulted in T. thermophila growth inhibition, cell nigrescence, and malondialdehyde (MDA) content considerably increase. However, exogenous NaHS (donor of H₂S, 70 μM) significantly alleviated the Cd-induced toxicity by inhibiting Cd absorbtion, promoting CdS nanoparticles formation and improving antioxidant system. Comparative transcriptome analysis showed that the expression levels of 9152 genes changed under Cd stress (4658 upregulated and 4494 downregulated). However, only 1359 genes were differentially expressed with NaHS treatment under Cd stress (1087 upregulated and 272 downregulated). The functional categories of the differentially expressed genes (DEGs) by gene ontology (GO) revealed that the transcripts involved in the oxidation–reduction process, oxidoreductase activity, glutathione peroxidase activity, and cell redox homeostasis were the considerable enrichments between Cd stress and NaHS treatment under Cd stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) indicated that the carbon metabolism, glutathione metabolism, metabolism of xenobiotics by cytochrome P450, and ABC transporters were significantly differentially expressed components between Cd stress and NaHS treatment under Cd stress in T. thermophila. The relative expression levels of six DEGs were further confirmed through quantitative real-time polymerase chain reaction (qRT-PCR).

Conclusion

NaHS alleviated Cd stress mainly through inhibiting Cd absorbtion, promoting CdS nanoparticles formation, increasing oxidation resistance, and regulation of transport in free-living unicellular T. thermophila. These findings will expand our understanding for H₂S functions in the freshwater protozoa.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07337-9.

Molecular and functional characterization of a mitochondrial glutathione reductase homolog from redlip mullet (Liza haematocheila): Disclosing its antioxidant properties in the fish immune response mechanism

Glutathione reductase (GSHR) is a biologically important enzyme involved in the conversion of oxidized glutathione (GSSG) into its reduced form, reduced glutathione (GSH), with the catalytic activity of NADPH. Most animals and aquatic organisms, including fish, possess high levels of this enzyme system to neutralize oxidative stress in cells. The current study was conducted to broaden our knowledge of GSHR in fish by identifying a mitochondrial isoform of this enzyme (LhGSHRm) in redlip mullet, Liza haematocheila, and clarifying its structure and function. The complete open reading frame of LhGSHRm consists of 1527 base pairs, encoding 508 amino acids, with a predicted molecular weight of 55.43 kDa. Multiple sequence alignment revealed the conservation of important amino acids in this fish. Phylogenetic analysis demonstrated the closest evolutionary relationship between LhGSHRm and other fish GSHRm counterparts. In tissue distribution analysis, the highest mRNA expression of LhGSHRm was observed in the gill tissue under normal physiological conditions. Following pathogenic challenges, the LhGSHRm transcription level was upregulated in a time-dependent manner in the gill and liver tissues, which may modulate the immune reaction against pathogens. rLhGSHRm showed considerable glutathione reductase activity in an enzyme assay. Further, the biological activity of rLhGSHRm in balancing cellular oxidative stress was observed in both disk diffusion and DPPH assays. Collectively, these results support that LhGSHRm has profound effects on modulating the immune reaction in fish to sustain precise redox homeostasis.

Biochemical and functional responses of stream invertebrate shredders to post-wildfire contamination

Forests in Mediterranean Europe including Portugal are highly susceptible to wildfires. Freshwaters are often exposed to post-wildfire contamination that contains several toxic substances, which may impose risk to freshwater organisms and ecosystem functions. However, knowledge on the impacts of post-wildfire runoffs from different origins on freshwater biota is scarce. In forest streams, invertebrate shredders have a major contribution to aquatic detrital-based food webs, by translocating energy and nutrients from plant-litter to higher trophic levels. We investigated the leaf consumption behaviour and the responses of oxidative and neuronal stress enzymatic biomarkers in the freshwater invertebrate shredder Allogamus ligonifer after short-term exposure (96 h) to post-wildfire runoff samples from Pinus and Eucalyptus plantation forests and stream water from a burnt catchment in Portugal. Chemical analyses indicated the presence of various metals and PAHs at considerable concentrations in all samples, although the levels were higher in the runoff samples from forests than in the stream water. The shredding activity was severely inhibited by exposure to increased concentrations of post-wildfire runoff samples from both forests. The dose-response patterns of enzymatic biomarkers suggest oxidative and neuronal stress in the shredders upon exposure to increasing concentrations of post-wildfire runoffs. The impacts were more pronounced for the runoffs from the burnt forests. Moreover, the response patterns suggest that the energy from the feeding activity of shredders might have contributed to alleviate the stress in A. ligonifer. Overall, the outcomes suggest that the post-wildfire contamination can induce sublethal effects on invertebrate shredders with impacts on key ecological processes in streams.

Properties of Carotenoids in Fish Fitness: A Review

Carotenoids, one of the most common types of natural pigments, can influence the colors of living organisms. More than 750 kinds of carotenoids have been identified. Generally, carotenoids occur in organisms at low levels. However, the total amount of carotenoids in nature has been estimated to be more than 100 million tons. There are two major types of carotenoids: carotene (solely hydrocarbons that contain no oxygen) and xanthophyll (contains oxygen). Carotenoids are lipid-soluble pigments with conjugated double bonds that exhibit robust antioxidant activity. Many carotenoids, particularly astaxanthin (ASX), are known to improve the antioxidative state and immune system, resulting in providing disease resistance, growth performance, survival, and improved egg quality in farmed fish without exhibiting any cytotoxicity or side effects. ASX cooperatively and synergistically interacts with other antioxidants such as α-tocopherol, ascorbic acid, and glutathione located in the lipophilic hydrophobic compartments of fish tissue. Moreover, ASX can modulate gene expression accompanying alterations in signal transduction by regulating reactive oxygen species (ROS) production. Hence, carotenoids could be used as chemotherapeutic supplements for farmed fish. Carotenoids are regarded as ecologically friendly functional feed additives in the aquaculture industry.

Isatidis Folium alleviates acetaminophen-induced liver injury in mice by enhancing the endogenous antioxidant system

Isatidis Folium (IF) has been clinically combined with acetaminophen (APAP), but the rationality of combinational therapy is still ambiguous. In the present study, the protective effect and related mechanism of IF on APAP-induced hepatotoxicity were evaluated. Hepatic histopathology and blood biochemistry investigations clearly demonstrated that IF could restore APAP-induced hepatotoxicity. Liver distribution study indicated that the hepatoprotective effect of IF on APAP is attributed to the reduction of N-acetyl-p-benzoquinone imine (NAPQI) in liver, which is a known hepatotoxic metabolite of APAP. Further study suggested the reduction is not via decreasing the generation of NAPQI through inhibiting the enzyme activities of CYP 1A2, 2E1, and 3A4 but via accelerating the transformation of NAPQI to NAPQI-GSH by promoting GSH and decreasing GSSG contents in liver. Furthermore, IF significantly enhanced the hepatic activities of GSH-associated enzymes in APAP-treated mice. In summary, IF could alleviate APAP-induced hepatotoxicity by reducing the content of NAPQI via enhancing the level of GSH and the followed generation of NAPQI-GSH which might be ascribed to the upregulation of GSH-associated enzymes.

Oxidative stress ecology on Pacific oyster Crassostrea gigas from lagoon and offshore Italian sites

Crassostrea gigas is a sentinel species along the Italian coast. In mussels, the levels of oxidative stress biomarkers can be modulated by several environmental pollutants or pathogens and also fluctuate in response to reproductive stages and seasonal changes. In this study, adult Crassostrea gigas were sampled during summer and autumn from two lagoon and two offshore sites along the Adriatic coast of Italy in order to investigate the influence of seasonality on oxidative stress biomarkers. Trace elements load of Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Se and Zn suggests low contamination for lagoon and offshore sites. Levels of total glutathione, superoxide dismutase, catalase, glutathione peroxidases, glutathione reductase and glutathione S-transferase were analyzed in digestive gland and gills of the Pacific oysters in June, July, September and October. OsHV-1 and Vibrio aestuarianus were detected in lagoon sites, but both pathogens did not affect the biomarkers levels in both tissues. Although several biological responses were found different among the four sites in the same month, principal component analysis revealed similar trend in biomarkers levels between sites during the whole sampling period. On the other hand, a different biochemical pattern through the months emerged, suggesting that the level of oxidative stress biomarkers in both tissues may be related to seasonal progress and biological cycle of oysters sampled from the two lagoons and offshore sites along the Italian coasts of the Mediterranean Sea.

Antioxidant system status in threatened native fish Barbus meridionalis from the Osor River (Iberian Peninsula): I. Characterization and II. In vitro Zn assays

The evaluation of antioxidant system capacity is important in aquatic toxicology. It was aimed to characterize the liver antioxidant enzymes (SOD, CAT, GPX, GR, and GST) and to test the in vitro Zn effect (200 and 400 ZnSO₄ μg/L) in native fish Barbus meridionalis obtained from the Osor River (NE, Spain) influenced by Zn contamination. The maximal enzyme activities were at pH 7.0-7.5 and 100 mM phosphate buffer. Barbel showed high catalytic activity (high Vmax and low Km) indicating the efficient antioxidant detoxification ability. Direct Zn effect caused an antioxidant system imbalance. Mostly upon lower Zn concentration, GPX activity decreased (95-100 %) though CAT, GR, and GST increased (36-1543 %). GSH values either stimulated (290 %) or inhibited (85-93 %) due to tissue differences. The first record of barbel antioxidant enzyme characterization and in vitro data presenting an unbalanced antioxidant pattern could be significant to evaluate the metal pollution in the Osor River for further in vivo studies.

The Nrf2 molecule trigger antioxidant defense against acute benzo(a)pyrene exposure in the thick shell mussel Mytilus coruscus

The NF-E2-related factor 2 (Nrf2), an ubiquitous, evolutionarily conserved transcription factor, acts as a major sensor of oxidative stress in cells. In the present study, a Nrf2 homolog was newly identified in the thick shell mussel Mytilus coruscus. Accordingly, its functional role in antioxidant defense in response to acute benzo(a)pyrene (Bap) exposure was assessed. The newly identified McNrf2 affiliated to traditional Nrf2 family through Blast, multiple alignment and phylogenetic analysis. After acute exposure to Bap, antioxidants including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathine reductase (GR) were significantly induced in gills and digestive glands at both mRNA and enzymatic levels, and the expression of McNrf2 mRNA was also up-regulated. The analysis of correlating the expression of McNrf2 and the mRNA levels of these antioxidant genes showed positive ties, indicating that Nrf2 was needed for protracted induction of such genes. Further, the recombinant McNrf2 was produced through pET-32a prokaryotic system. After 50 μg/L Bap exposure, ROS generation and LPO level in gills of Nrf2 over-expressed mussels significantly decreased compared to Nrf2 wild-type mussels, as well as reduced ROS production in digestive glands. Collectively, these results show that Nrf2 pathway can provide protection from oxidative stress triggered by Bap in the thick shell mussel.

Potential of environmental concentrations of the musks galaxolide and tonalide to induce oxidative stress and genotoxicity in the marine environment

Polycyclic musk compounds have been identified in environmental matrices (water, sediment and air) and in biological tissues in the last decade, yet only minimal attention has been paid to their chronic toxicity in the marine environment. In the present research, the clams Ruditapes philippinarum were exposed to 0.005, 0.05, 0.5, 5 and 50 μg/L of the fragrances Galaxolide® (HHCB) and Tonalide® (AHTN) for 21 days. A battery of biomarkers related with xenobiotics biotransformation (EROD and GST), oxidative stress (GPx, GR and LPO) and genotoxicity (DNA damage) were measured in digestive gland tissues. HHCB and AHTN significantly (p < 0.05) induced EROD and GST enzymatic activities at environmental concentrations. Both fragrances also induced GPx activity. All concentrations of both compounds induced an increase of LPO and DNA damage on day 21. Although these substances have been reported as not acutely toxic, this study shows that they might induce oxidative stress and genotoxicity in marine organisms.

Ziziphus mauritiana supplementation of Nile tilapia (Oreochromis niloticus) diet for improvement of immune response to Aeromonas hydrophila infection

This study evaluated the effectiveness of dietary Ziziphus mauritiana leaf powder (ZLP) to control Aeromonas hydrophila infection in Nile tilapia and reduce damage to vital immune organs. Four experimental groups were fed a diet supplemented with ZLP at concentrations of 0, 5, 10, and 20 g/kg (w/w) for 6 weeks. At the end of the feeding trial, all groups were intraperitoneally injected with pathogenic A. hydrophila. It was found that Z. mauritiana significantly (P < 0.05) upregulated (lysozyme, interleukin 1 beta) and superoxide dismutase gene expressions as well as improved the activity of serum lysozyme and liver antioxidant enzymes. The fish that were fed a ZLP-supplemented diet also exhibited significantly higher survival rates after A. hydrophila challenge than those that were fed a ZLP-free diet (P < 0.05). Supplementation of 10 g/kg ZLP most effectively reduced the histopathological alterations caused by A. hydrophila challenge in the liver, spleen, kidney, and muscle of the fish. In conclusion, ZLP can be effective in controlling A. hydrophila infection in Nile tilapia (particularly at a concentration of 10 g/kg) through enhancement of its immune and antioxidant status.

Antioxidative and immunoprotective potential of Chlorella vulgaris dietary supplementation against chlorpyrifos-induced toxicity in Nile tilapia

This study highlighted the effects of chronic chlorpyrifos (CPF) exposure on Nile tilapia (Oreochromis niloticus) and the benefits of using dietary Chlorella vulgaris (Ch) to ameliorate CPF-induced toxicity. Genes encoding antioxidant enzymes and stress-responsive proteins in the liver as well as cytokine expression in the spleen and head kidney were evaluated in O. niloticus fed with a basal diet or diets containing 1, 2, and 3% of supplementary Ch against 15 mg/L CPF at 4 and 8 weeks. CPF-exposed groups displayed a notable induction in the hepatic expression of heat shock protein 70/hsp70, glutathione peroxidase/GPx, and glutathione synthase/GSS, while glutathione reductase/GSR was markedly decreased. The mRNA levels of interleukin 1β/IL-1β, TNF-α, transforming growth factor β1/TGFβ1, and interleukin 8/ IL-8 in the spleen and head kidney increased significantly after CPF exposure. Interestingly, Ch supplementation, particularly at levels 2 and 3%, was able to modulate the stress and immune-related genes of Nile tilapia sub-chronically exposed to CPF. These outcomes provide valuable insights regarding the toxic impact of chronic exposure to CPF in fish at the molecular level and a better understanding of the Ch dietary vital roles. Besides, our findings encourage adequate monitoring of pesticide levels owing to its impacts on fish health and human as a final consumer.

Integrative transcriptome analysis and discovery of signaling pathways involved in the protective effects of curcumin against oxidative stress in tilapia hepatocytes

Summer outbreaks of the hepatobiliary syndrome in fish impose a heavy burden on aquaculture in China. Curcumin is a polyphenol with antioxidant activity that has been used to protect the health of fish livers, but the mechanism underlying its protective effect is unclear. In this study, an in vitro model of hepatocyte oxidative damage in Oreochromis niloticus was established using H₂O₂. Treatment with 5 mM H₂O₂ for 2.5 h markedly reduced cell viability and antioxidant activity and elevated lactate dehydrogenase (LDH) activity, indicating conditions that can be used to establish an oxidative stress model. Under H₂O₂ stress, curcumin pretreatment significantly maintained cell viability, reduced malondialdehyde (MDA) levels, and increased superoxide dismutase (SOD) activity. RNA-seq results showed that acute H₂O₂ treatment resulted in minor changes in gene expression, whereas curcumin changed the expression profile and affected cytochrome P450 (Cyp 450), glutathione (GSH) metabolism, and the peroxisome proliferator-activated receptor (PPAR) signaling pathway. Several critical antioxidant defense signaling pathways were identified, and altered expression was confirmed by q-PCR. These results indicate that curcumin might upregulate PPAR expression by increasing Cyp2J2 expression. Further experiments showed that curcumin can upregulate the Nrf2-Keap1 signaling pathway at the transcriptional level, and this upregulation can induce downstream defense genes, including glutamate cysteine ligase catalytic subunit(GCLC) and glutamate cysteine ligase modifier subunit (GCLM), and thereby promote GSH synthesis and the expression of related antioxidases. This study might shed light on the effects of curcumin on the prevention and alleviation of liver diseases in fish.

Ecotoxicological effects of microplastics and cadmium on the earthworm Eisenia foetida

As microplastics (MPs) have become ubiquitous in both aquatic and terrestrial environments, there has been a growing concern about these new anthropogenic stressors. However, comparatively little is known about the negative effects of MPs, co-contamination of MPs and heavy metals on terrestrial organisms. The objective of this study was performed to understand the adverse effects of exposure to MPs and co-exposure to MPs and cadmium (Cd) on the earthworm Eisenia foetida (E. foetida). Results showed that exposure to MPs only or to a combination of MPs + Cd decreased growth rate and increased the mortality (>300 mg kg^-1) after exposure for 42 d, with MPs + Cd (>3000 mg kg^-1) posing higher negative influence on the growth of E. foetida. Exposure to MPs might induce oxidative damage in E. foetida, and the presence of Cd accelerates the adverse effects of MPs. Furthermore, the MPs particles can be retained within E. foetida, with values of 4.3-67.2 particles·g^-1 earthworm, and can increase the accumulation of Cd in earthworm from 9.7%-161.3%. Collectively, the results of this study demonstrate that combined exposure to MPs and Cd poses higher negative effects on E. foetida, and that MPs have the potential to increase the bioaccessibility of heavy metal ions in the soil environment.

Effects of seawater acidification and cadmium on the antioxidant defense of flounder Paralichthys olivaceus larvae

Increasing atmospheric carbon dioxide has led to a decrease in the pH of the ocean, which influences the speciation of heavy metals and consequently affects metal toxicity in marine organisms. To investigate the effects of seawater acidification and metals on the antioxidant defenses of marine fishes, the flounder Paralichthys olivaceus, was continuously exposed to cadmium (Cd; control, 0.01 and 0.15 mg L^-1) and acidified seawater (control (pH 8.10), 7.70 and 7.30) for 49 days from embryogenesis to settlement. The results demonstrated that both Cd and acidified seawater could induce oxidative stress and consequently cause lipid peroxidation (LPO) in the larvae. Antioxidants (i.e., superoxide dismutase, SOD; catalase, CAT; reduced glutathione, GSH; glutathione S-transferase, GST; glutathione peroxidase, GPx; and glutathione reductase, GR) functioned to defend the larvae against oxidative damage. Overall, Cd induced (SOD, GST and GSH) or inhibited (CAT and GPx) the enzymatic activities or contents of all the selected antioxidants except for GR. The antioxidants responded differently to seawater acidification, depending on their interaction with the metal. Similarly, the mRNA expressions of the antioxidant-related genes were upregulated (sod, gr and gst) or downregulated (cat and gpx) in response to increasing Cd exposure. Seawater acidification did not necessarily affect all of the biomarkers; in some cases (e.g., SOD and sod, GR and gr), Cd stress may have exceeded and masked the stress from seawater acidification in regulating the antioxidant defense of the larvae. The integrated biomarker response (IBR) was enhanced with increasing levels of the stressors. These findings support the hypothesis that seawater acidification not only directly affects the antioxidant defense in flounder larvae but also interacts with Cd to further regulate this defense. This study has ecological significance for assessing the long-term impacts of ocean acidification and metal pollution on the recruitment of fish populations in the wild.

Selenomethionine exposure affects chondrogenic differentiation and bone formation in Japanese medaka (Oryzias latipes)

Excess selenium entering the aquatic environment from anthropogenic activities has been associated with developmental abnormalities in fish including skeletal deformities of the head and spine. However, mechanisms of this developmental toxicity have not been well-characterized. In this study, Japanese medaka (Oryzias latipes) embryos were exposed to seleno-l-methionine (Se-Met) in a range of concentrations. Gene expression was evaluated for sex-determining region Y (SRY)-related box (Sox9a and Sox9b), runt-related transcription factor 2 (Runx2), and melatonin receptor (Mtr). Alterations in the length of Meckel's cartilage, tail curvature, and decreased calcification were observed in skeletal stains at 10- and 22-days post-fertilization (dpf). Embryonic exposure of Osterix-mCherry transgenic medaka resulted in fewer teeth. Sox9a and Sox9b were up-regulated, while Runx2 and Mtr were down-regulated by Se-Met prior to hatch. Whole mount in situ hybridization (WISH) localized gene expression to areas observed to be affected in vivo. In addition, Se-Met exposures of a Mtr morpholino (Mtr-MO) as well as Luzindole exposed embryos developed similar skeletal malformations, supporting involvement of Mtr. These findings demonstrate that Se-Met modulates expression of key genes involved in chondrogenic differentiation and bone formation during development.

Evolution of cellular stress response mechanisms

The cellular stress response (CSR) is pervasive to all domains of life. It has shaped the interaction between organisms and their environment since the origin of the first cell. Although the CSR has been subject to a myriad of nuanced modifications in the various branches of life present today, its core features remain preserved. The scientific literature covering the CSR is enormous and the broad scope of this brief overview was challenging. However, it is critical to conceptually understand how cells respond to stress in a holistic sense and to point out how fundamental aspects of the CSR framework are integrated. It was necessary to be extremely selective and not feasible to even mention many interesting and important developments in this expansive field. The purpose of this overview is to sketch out general and emerging CSR concepts with an emphasis on the initial cellular strain resulting from stress (macromolecular damage) and the evolutionarily most highly conserved elements of the CSR. Examples emphasize fish and aquatic invertebrates to highlight what is known in organisms beyond mammals, yeast, and other common models. Nonetheless, select pioneering studies using canonical models are also considered and the concepts discussed are applicable to all cells. More detail on important aspects of the CSR in aquatic animals is provided in the accompanying articles of this special issue.

Effect of dietary threonine on growth performance and muscle growth, protein synthesis and antioxidant-related signalling pathways of hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂

The experiment was conducted to investigate the effects of dietary threonine (Thr) on growth performance and muscle growth, protein synthesis and antioxidant-related signalling pathways of hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂. A total of 1200 fish (14·19 (se 0·13) g) were randomly distributed into six groups with four replicates each, fed six diets with graded level of Thr (9·5, 11·5, 13·5, 15·4, 17·4 and 19·3 g/kg diets) for 56 d. Results showed (P < 0·05) that dietary Thr (1) increased percentage weight gain, specific growth rate, feed efficiency and protein efficiency ratio; (2) up-regulated growth hormone (GH), insulin-like growth factor 1 (IGF-1), proliferating cell nuclear antigen, myogenic regulation factors (MyoD, Myf5, MyoG and Mrf4) and myosin heavy chain (MyHC) mRNA levels; (3) increased muscle protein content via regulating the protein kinase B/target of rapamycin signalling pathway and (4) decreased malondialdehyde and protein carbonyl contents, increased catalase, glutathione-S-transferase, glutathione reductase and GSH activities, up-regulated mRNA levels of antioxidant enzymes related to NFE2-related factor 2 and γ-glutamylcysteine ligase catalytic subunit. These results suggest that Thr has a potential role to improve muscle growth and protein synthesis, which might be due to the regulation of GH-IGF system, muscle growth-related gene, antioxidative capacity and protein synthesis-related signalling pathways. Based on the quadratic regression analysis of specific growth rate, the Thr requirement of hybrid catfish (14·19-25·77 g) was estimated to be 13·77 g/kg of the diet (33·40 g/kg of dietary protein).

Toxic effects of ornamental stone processing waste effluents on Geophagus brasiliensis (Teleostei: Cichlidae)

The ornamental stone industry generates considerable amounts of waste (OSPW), which may eventually reach natural environments and impact the local ecosystem. The aim of this study was to compare the toxic effects of two OSPW effluents in Geophagus brasiliensis: i) leachate effluent from a lagoon in an OSPW landfill (LE) and ii) decanted effluent from an ornamental stone processing industry (DE). G. brasiliensis were submitted to acute contamination with both OSPW effluents. After contamination, the gills were extracted for evaluation of histopathological alterations and ion concentration, while the liver underwent catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD) and glutathione s-transferase (GST) enzyme activity analysis. An induced biomarker response (IBRv2) index was determined to correlate the multi-biomarker response in G. brasiliensis. Fish gills exposed to DE showed increased concentration of Ca²⁺, Mg²⁺, Na⁺, and K⁺ when compared to those treated with LE. Histopathological lesions were observed in gills of animals exposed to both effluents. Micronucleus and comet assay were significantly greater in fish exposed to DE, when compared to those contaminated with LE. The evaluation of the enzymatic activity of CAT, GPx and SOD indicate greater oxidative stress in DE and LE-exposed fish, while GST activity was not altered. DE showed an IBRv2 value almost two-times higher in relation to LE, indicating that this waste may present higher toxic potential. The results demonstrate that both contaminants led to substantial toxic effects in G. brasiliensis, although the decanted waste induced the most remarkable responses in G. brasiliensis.

Dietary tryptophan affects growth performance, digestive and absorptive enzyme activities, intestinal antioxidant capacity, and appetite and GH-IGF axis-related gene expression of hybrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂)

The 56-day feeding trial was carried out to investigate the effects of dietary tryptophan (Trp) on growth performance, digestive and absorptive enzyme activities, intestinal antioxidant capacity, and appetite and GH-IGF axis-related genes expression of hybrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂). A total of 864 hybrid catfish (21.82 ± 0.14 g) were fed six different experimental diets containing graded levels of Trp at 2.6, 3.1, 3.7, 4.2, 4.7, and 5.6 g kg^-1 diet. The results indicated that dietary Trp increased (P < 0.05) (1) final body weight, percent weight gain, specific growth rate, feed intake, feed efficiency, and protein efficiency ratio; (2) fish body protein, lipid and ash contents, protein, and ash production values; (3) stomach weight, stomach somatic index, liver weight, intestinal weight, length and somatic index, and relative gut length; and (4) activities of pepsin in the stomach; trypsin, chymotrypsin, lipase, and amylase in the pancreas and intestine; and γ-glutamyl transpeptidase, Na⁺, K⁺-ATPase, and alkaline phosphatase in the intestine. Dietary Trp decreased malondialdehyde content, increased antioxidant enzyme activities and glutathione content, but downregulated Keap1 mRNA expression, and upregulated the expression of NPY, ghrelin, GH, GHR, IGF1, IGF2, IGF1R, PIK3Ca, AKT1, TOR, 4EBP1, and S6K1 genes. These results indicated that Trp improved hybrid catfish growth performance, digestive and absorptive ability, antioxidant status, and appetite and GH-IGF axis-related gene expression. Based on the quadratic regression analysis of PWG, SGR, and FI, the dietary Trp requirement of hybrid catfish (21.82-39.64 g) was recommended between 3.96 and 4.08 g kg^-1 diet (9.4-9.7 g kg^-1 of dietary protein).

Subcellular metal distributions and metallothionein associations in rough-toothed dolphins (Steno bredanensis) from Southeastern Brazil

Metals are subject to internal subcellular compartmentalization, altering their bioavailability. Thus, subcellular metal assessments are crucial in biomonitoring efforts. Metal distribution in three subcellular fractions (insoluble - ISF, thermolabile - TLF and thermostable - TSF) were determined by ICP-MS in Steno bredanensis specimens from Southeastern Brazil. Associations between metals, metallothionein (MT) and reduced glutathione (GSH) were also investigated. Differential metal-detoxification mechanisms were observed. MT detoxification was mostly noted for As, Cd, and Pb, while Cu, Cr, Hg, Ni, Se and Ti displayed lower MT-associations. Fe, Zn and Se, on the other hand, were poorly associated to MT, and mostly present in the ISF, indicating low bioavailability. This is the first report on subcellular Sn and Ti distribution in cetaceans and the first in this species in Brazil. Potential protective roles of essential metals against toxic elements are postulated. This study indicates that important biochemical detoxification information is obtained through subcellular fraction analyses in marine mammals.

Effect of acute ammonia exposure on the glutathione redox system in FFRC strain common carp (Cyprinus carpio L.)

Ammonia is one of the most common aquatic pollutants. To analyze the effect of ammonia exposure on the glutathione redox system, we investigated the levels of hydrogen peroxide (H₂O₂) and glutathione, and transcription and activities of glutathione-related enzymes in liver and gills of FFRC strain common carp (Cyprinus carpio L.) exposed to 0, 10, 20, and 30 mg/L of ammonia. The results showed that H₂O₂ content reached a maximum level at 48 h of exposure in the liver of fish. In gills, H₂O₂ increased rapidly at 6 h and reached to maximum levels at 24 h of exposure, indicating that gills experienced oxidative stress earlier than the liver of fish exposed to ammonia. Reduced glutathione (GSH) content and reduced glutathione/oxidized glutathione (GSH/GSSG) ratio increased significantly within 24 h of exposure. Meanwhile, the transcription and activities of glutathione S-transferase (GST) and glutathione reductase (GR) increased significantly in the liver, and glutathione peroxidase (GSH-Px) and GST increased in the gills of fish exposed to ammonia. Malondialdehyde (MDA) content kept at a low level after exposure to low concentration of ammonia, but increased significantly after exposure to 30 mg/L ammonia for 48 h along with a decrease in GSH content and GSH/GSSG ratio. These data showed that the glutathione redox system played an important role in protection against ammonia-induced oxidative stress in the liver and gills of FFRC strain common carp, though the defense capacity was not able to completely prevent oxidative damage occurring after exposure to higher concentration of ammonia. This research systematically studied the response of the glutathione redox system to ammonia stress and would provide novel information for a better understanding of the adaptive mechanisms of fish to environmental stress.

Bioaccumulation of Copper and Zinc and the Effects on Antioxidant Enzyme Activities in the Liver of Acipenser stellatus (Pallas, 1771)

Although water pollution by metals in the Danube River is considered high, little is known about its impact on sturgeons. In this regard, the aim of this study was to investigate the bioaccumulation of copper and zinc as well as their effects on antioxidant enzymes activities in the liver of Acipenser stellatus. The fish were exposed for 7 and 14 days, to two concentrations of copper and zinc (10% and 25% of LC50 96 h), previously determined as 0.54 mg/L Cu²⁺ and, 34.22 mg/L Zn²⁺ respectively. The enzymatic responses of A. stellatus varied greatly depending on metal type, concentration and time. Significant bioaccumulation of the two metals was recorded. Even though the water hardness used in the experiment is known to offer a clear protection against metal contamination, stellate sturgeon remains a sensitive species in the face of metal toxicity.

Toxic Effects and Depuration on the Antioxidant and Neurotransmitter Responses after Dietary Lead Exposure in Starry Flounder

Starry Flounder Platichthys stellatus were exposed to dietary lead (Pb) at concentrations of 0, 30, 60, 120, and 240 mg/kg for 4 weeks. Recover period was conducted for 2 weeks after the exposure. Exposure to Pb concentrations over 60 mg/kg induced significant changes in the antioxidant responses in the liver, kidney, and gill and continued even after the depuration period in the liver (over 120 mg/kg for superoxide dismutase [SOD] activity) and kidney (at 240 mg/kg for glutathione [GSH] levels). Glutathione S-transferase (GST) activity in liver, kidney, and gill were increased by dietary Pb exposure, and recovery was observed in all groups during the recovery period. Acetylcholinesterase (AChE) activity was significantly inhibited in the brain and muscle of flounder at Pb exposure over 120 mg/kg, and no restoration was observed after the depuration period. Lysozyme activity in the plasma was significantly increased at Pb exposures greater than 60 mg kg but was restored after the depuration period. The results of this study indicate that dietary Pb exposure induces toxic effects on antioxidant responses, neurotransmitter, and immune responses of Starry Flounder.

Developmental toxicity and biological responses of zebrafish (Danio rerio) exposed to anti-inflammatory drug ketoprofen

Ketoprofen a nonsteroidal anti-inflammatory drug (NSAID) is widely used in over-the-counter to treat pain, swelling and inflammation. Due to extensive application these drugs has been detected in surface waters which may create a risk to aquatic organisms. The aim of the present study is to assess the ecotoxicity of ketoprofen at different concentrations (1, 10 and 100 μg/ml) on embryos and adult zebrafish (1, 10 and 100 μg L^-1) under laboratory conditions. In embryos, concentration dependent developmental changes such as edema, spinal curvature, slow heartbeat, delayed hatching, and mortality rate were observed. In adult zebrafish, biochemical enzymes such as AST, ALT and LDH activities were significantly (P < 0.05) increased whereas a decrease in Na⁺/K⁺-ATPase activity was noticed in all the tested concentrations of the drug ketoprofen. Similarly, exposure of ketoprofen caused a significant decrease in antioxidant levels in liver tissue (SOD, CAT, GSH, GPx, and GST). However, lipid peroxidation (LPO) level in liver tissue was found to be increased. The histopathological studies further evidenced the impact of ketoprofen in the liver tissue of zebrafish. The present result concludes that ketoprofen could have an impact on the development and biological endpoints of the zebra fish at above concentrations. The malformation in the development of the embryo and changes in the biological end points may provide integrated evaluation of the toxic effect of ketoprofen on zebrafish in a new perspective.

Redox Challenge in a Cultured Temperate Marine Species During Low Temperature and Temperature Recovery

Aquaculture is a growing industry that is increasingly providing a sizable proportion of fishery products for human consumption. Dietary energy and temperature fluctuations affect fish health and may even trigger mortality, causing great losses in fish production during winter. To better understand this unproductive winter period in aquaculture, the redox status in a cultured marine species, the gilthead sea bream, was analyzed for the first time by inducing controlled temperature fluctuations and reducing dietary lipid content. Two groups of fish (by triplicate), differing in their dietary lipid content (18% vs. 14%), were subjected to 30 days at 22°C (Pre-Cold), 50 days at 14°C (Cold) and then 35 days at 22°C (Recovery). Plasma and liver redox metabolites (oxidized lipid, oxidized protein and thiol groups), liver glutathione forms (total, oxidized and reduced) and liver antioxidant enzyme activities were measured. Reducing dietary lipid content did not affect gilthead sea bream growth, glutathione levels or enzyme activities, but did reduce the amount of oxidized lipids. A sustained low temperature of 14°C showed a lack of adaptation of antioxidant enzyme activities, mainly catalase and glutathione reductase, which subsequently affected the glutathione redox cycle and caused an acute reduction in total hepatic glutathione levels, irrespective of diet. Antioxidant enzyme activities were gradually restored to their pre-cold levels, but the glutathione redox cycle was not restored to its pre-cold values during the recovery period used. Moreover, the lower lipid diet was associated with transiently increased liver oxidized protein levels. Thus, we propose that fish should be fed a low lipid diet during pre-cold and cold periods, which would reduce oxidized lipid levels without affecting fish growth, and a higher energy diet during the recovery period. Moreover, diets supplemented with antioxidants should be considered, especially during temperature recovery.

Variation of Metallothionein I and II Gene Expression in the Bank Vole (Clethrionomys glareolus) Under Environmental Zinc and Cadmium Exposure

The main idea of the study was to assess how environmental metal pollution activates defence responses at transcription levels in the tissues of bank voles (Clethrionomys glareolus). For this purpose, the metallothioneine (MT) genes expression (a well known biomarker of exposure and response to various metals) was measured. The real-time PCR method was used for relative quantification of metallothionein I and metallothionein II expressions in the livers, kidneys and testes of bank voles from six populations exposed to different contaminants, mainly zinc, cadmium and iron. The assessment of Zn, Cu and Fe concentrations in the tissues allowed to study the MTs gene expression responses to these metals. ANOVA analysis showed differences between populations in terms of metal concentration in tissues, livers and kidneys. Student T test showed significant differences in metal concentration between unpolluted and polluted sites only for the liver tissue: significantly lower Zn levels and significantly higher Fe levels in the unpolluted sites. Kruskal-Wallis test performed on C T data shows differences in the gene expressions between populations for both MT genes for liver and testes. In the liver metallothionein I gene expression was upregulated in populations considered as more polluted (up to 7.5 higher expression in Miasteczko Śląskie comparing to Mikołajki). Expression of metallothionein II revealed a similar pattern. In kidneys, differences in expression of both MT genes were not that evident. In testes, MT upregulation in polluted sites was noted for metallothionein II. For metallothionein however, we found downregulation in populations from more contaminated sites. The expressions of both MTs were positively influenced by cadmium in kidney (concentration data from the previous study) and zinc and copper in liver, while cadmium had effects only on the liver MT II gene expression. Positive relationship was obtained for lead and metallothionein II expression in the liver.

Toxicological responses on cytochrome P450 and metabolic transferases in liver of goldfish (Carassius auratus) exposed to lead and paraquat

As the producer of reactive oxygen species (ROS), both lead (Pb) and paraquat (PQ) can generate serious oxidative stress in target organs which result in irreversible toxic effects on organisms. They can disturb the normal catalytic activities of many enzymes by means of different toxicity mechanism. The changed responses of enzymes are frequently used as the biomarkers for indicating the relationship between toxicological effects and exposure levels. In this work, goldfish was exposed to a series of test groups containing lead and paraquat in the range of 0.05-10mg/L, respectively. Four hepatic enzyme activities, including 7-ethoxyresorufinO-deethylase (EROD), 7-benzyloxy-4-trifluoromethyl-coumarin-O-debenzyloxylase (BFCOD), glutathione S-transferase (GST) and UDP-glucuronosyltransferase (UGT) were determined after 1, 7, 14, 28 days exposure. The results showed that the activities of EROD and BFCOD in fish were significantly inhibited in response to paraquat at all exposure levels during the whole experiment. Similarly, the inhibitory effects of lead exposure on BFCOD activity were found in our study, while different responses of lead on EROD were observed. There were no significant differences on EROD activity under lower concentrations of lead (less than 0.1mg/L) before 14 days until an obvious increase was occurred for the 0.5mg/L lead treatment group at day 14. Furthermore, lead showed stronger inhibition on GST activity than paraquat when the concentrations of the two toxicants were more than 0.5mg/L. However, the similar dose and time-dependent manners of UGT activity were found under lead and paraquat exposure. Our results indicated that higher exposure levels and longer accumulations caused inhibitory effects on the four enzymes regardless of lead or paraquat stress. In addition, the responses of phase I enzymes were more sensitive than that of phase II enzymes and they may be served as the acceptable biomarkers for evaluating the toxicity effects of both lead and paraquat.

Effect of excessive doses of oxytetracycline on stress-related biomarker expression in coho salmon

Fish are exposed to a wide variety of environmental stressors, such as chemicals and acute changes in temperature. Oxytetracycline (OTC) has been used as an antibiotic for many kinds of bacterial diseases in cultured fish, but excessive doses of OTC are known to cause side effects in fish and can have negative effects on their environment. In the present study, we examined stress-related biomarker expression in response to excessive doses of dietary OTC in coho salmon (Oncorhynchus kisutch). Fish received OTC (100 mg/kg body weight/day) orally for 2 weeks. The percentage of liver to body weight (hepatosomatic index; HSI) and plasma biochemical parameter, alanine aminotransferase (ALT) activity, of the group fed a diet containing OTC were observed to be significantly higher than those of the control group. The total glutathione (tGSH) levels in the liver of OTC-fed fish were four fold higher than those in control fish and double the control levels in muscle and stomach. Plasma tGSH levels in OTC-fed fish were also higher than those in control fish. Expression levels of heat shock protein 70 in the liver, muscle, and stomach decreased by OTC administration. Accordingly, OTC-induced stress might increase the metabolic turnover of GSH due to consumption by scavenging oxidants generated by stress. These results concerning the changing patterns of stress-related biomarkers indicate that excessive doses of OTC fed to coho salmon induce oxidative stress, which might enhance oxidation in the body and result in damage to tissues, especially in the liver. The present results also suggest that tissue-specific damage caused by OTC might already exist in fish.

Lysine and methionine supplementation ameliorates high inclusion of soybean meal inducing intestinal oxidative injury and digestive and antioxidant capacity decrease of yellow catfish

The yellow catfish Pelteobagrus fulvidraco with initial average weight 16.6 ± 0.17 g were fed three extruded diets for 56 days. Fish meal (FM) diet was formulated as the normal control with 380 g FM and 200 g soybean meal (SBM) kg-1 diet. The SBM diet was prepared with 220 g FM and 360 g SBM kg-1 diet without Lys or Met supplementation. The SBM supplement (SBMS) diet was similar to SBM diet and supplemented with Lys and Met to ensure their levels similar to FM diet. The results showed fish fed SBM diet had lower percent weight gain and specific growth rate than the other two groups (P < 0.05). Whole body protein content of fish fed FM and SBMS diets were higher than that of fish fed SBM diet (P < 0.05). The hepatosomatic and intestosomatic indexes of fish fed SBM diet were significantly lower than that of fish fed FM and SBMS diets (P < 0.05). The activities of pepsin in stomach, trypsin, and chymotrypsin in intestine, alkaline phosphatase and creatine kinase in proximal intestine, Na+, K+-ATPase, and gamma-glutamyl transpeptidase in distal intestine were significantly higher in fish fed FM and SBMS diets compared to SBM diet. The activities of catalase, glutathione-S-transferase, reduced glutathione, superoxide anion scavenging, and hydroxyl radical scavenging in the intestine showed the same changes (P < 0.05). Malondialdehyde and protein carbonyl contents in intestine were significantly decreased in fish fed SBMS diet compared to SBM diet. These results indicated high inclusion of SBM induced intestinal oxidative injury and digestive and antioxidant capacity decrease. The Lys and Met supplementation could ameliorate these adverse effects on yellow catfish.

Effect on oxidative stress, hepatic chemical metabolizing parameters, and genotoxic damage of mad honey intake in rats

A total of 66 male Wistar rats were used and six groups (control: 10 animals and experimental: 12 animals) were formed. While a separate control group was established for each study period, mad honey application to the animals in the experimental group was carried out with a single dose (12.5 g kg−1 body weight (b.w.); acute stage), at a dose of 7.5 g kg−1 b.w. for 21 days (subacute stage), and at a dose of 5 g kg−1 b.w. for 60 days (chronic stage). Tissue and blood oxidative stress markers (malondialdehyde (MDA), nitric oxide (NO), 4-hydroxynonenal (HNE), superoxide dismutase, catalase, glutathione (GSH) peroxidase, and glucose-6-phosphate dehydrogenase), hepatic chemical metabolizing parameters in the liver (cytochrome P450 2E1, nicotinamide adenine dinucleotide (NADH)-cytochrome b5 reductase, nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome c reductase (CYTC), GSH S-transferase (GST), and GSH), and micronucleus and comet test in some samples were examined. Findings from the study showed that single and repeated doses given over the period increased MDA, NO, and HNE levels while decreasing/increasing tissue and blood antioxidant enzyme activities. From hepatic chemical metabolizing parameters, GST activity increased in the subacute and chronic stages and CYTC activity increased in the acute period, whereas GSH level decreased in the subacute stage. Changes in tail and head intensities were found in most of the comet results. Mad honey caused oxidative stresses for each exposure period and made some significant changes on the comet test in certain periods for some samples obtained. In other words, according to the available research results obtained, careless consumption of mad honey for different medical purposes is not appropriate.

Identification and characterization of two selenium-dependent glutathione peroxidase 1 isoforms from Larimichthys crocea

Glutathione peroxidases, a vital family of antioxidant enzymes in oxybiotic organisms, are involved in anti-pathogen immune response. In this study, two complete selenium-dependent glutathione peroxidase 1 cDNAs (designated as LcGPx1a and LcGPx1b) were obtained from the large yellow croaker Larimichthys crocea by rapid amplification of cDNA ends. The full-length sequence of LcGPx1a was 917 bp with a 5'-untranslated region (UTR) of 52 bp, a 3'-UTR of 289 bp, and an open reading frame of 576 bp encoding 191 amino acid (aa) polypeptides. The cDNA of LcGPx1b was composed of 884 bp with a 5'-UTR of 59 bp, a 3'-UTR of 258 bp, and an open reading frame of 567 bp encoding 188 aa polypeptides. The conserved selenocysteine insertion sequence was detected in the 3'-UTR of both isoforms, which can classify types I and II. Protein sequence analysis revealed that both isoforms included a selenocysteine encoded by an opal codon (TGA) and formed the functioning tetrad site with glutamine, tryptophan, and asparagine. Three conservative motifs, including one active site motif ("GKVVLIENVASLUGTT") and two signature site motifs ("LVILGVPCNQFGHQENC" and "V(A/S)WNFEKFLI"), were conserved both in sequence and location. Multiple alignments revealed that they exhibited a high level of identities with GPx1 from other organisms, especially in the abovementioned conserved amino acid sequence motifs. Tissue expression analysis indicated that LcGPx1a and LcGPx1b had a wide distribution in nine tissues with various abundances. The transcript level of LcGPx1a was not significantly different among the nine tissues, whereas that of LcGPx1b was higher in the kidney and head kidney than in the other tissues. After Vibrio parahaemolyticus stimulation, the expression levels of LcGPx1a and LcGPx1b were unanimously altered in the liver, spleen, kidney, and head kidney but with different magnitudes and response time. LcGPx1a and LcGPx1b showed distinct expression trends in the liver, where LcGPx1b was induced and LcGPx1a was depressed in response to pathogen infection. These results indicate that LcGPx1a and LcGPx1b display functional diversities and play crucial roles in mediating the immune response of fish.

Genotoxic and mutagenic assessment of iron oxide (maghemite-γ-Fe2O3) nanoparticle in the guppy Poecilia reticulata

The environmental risk of nanomaterials (NMs) designed and used in nanoremediation process is of emerging concern, but their ecotoxic effects to aquatic organism remains unclear. In this study, the citrate-coated (maghemite) nanoparticles (IONPs) were synthesized and its genotoxic and mutagenic effects were investigated in the female guppy Poecilia reticulata. Fish were exposed to IONPs at environmentally relevant iron concentration (0.3 mg L^-1) during 21 days and the animals were collected at the beginning of the experiment and after 3, 7, 14 and 21 days of exposure. The genotoxicity and mutagenicity were evaluated in terms of DNA damage (comet assay), micronucleus (MN) test and erythrocyte nuclear abnormalities (ENA) frequency. Results showed differential genotoxic and mutagenic effects of IONPs in the P. reticulata according to exposure time. The IONP induced DNA damage in P. reticulata after acute (3 and 7 days) and long-term exposure (14 and 21 days), while the mutagenic effects were observed only after long-term exposure. The DNA damage and the total ENA frequency increase linearly over the exposure time, indicating a higher induction rate of clastogenic and aneugenic effects in P. reticulata erythrocytes after long-term exposure to IONPs. Results indicated that the P. reticulata erythrocytes are target of ecotoxicity of IONPs.