Induction and activity of oxidative stress-related proteins during waterborne Cd/Zn-exposure in brown trout (Salmo trutta)

Context-dependent antioxidant defense system (ADS)-based stress memory in response to recurrent environmental challenges in congeneric invasive species

Marine ecosystems are facing escalating environmental fluctuations owing to climate change and human activities, imposing pressures on marine species. To withstand recurring environmental challenges, marine organisms, especially benthic species lacking behavioral choices to select optimal habitats, have to utilize well-established strategies such as the antioxidant defense system (ADS) to ensure their survival. Therefore, understanding of the mechanisms governing the ADS-based response is essential for gaining insights into adaptive strategies for managing environmental challenges. Here we conducted a comparative analysis of the physiological and transcriptional responses based on the ADS during two rounds of 'hypersalinity-recovery' challenges in two model congeneric invasive ascidians, Ciona robusta and C. savignyi. Our results demonstrated that C. savignyi exhibited higher tolerance and resistance to salinity stresses at the physiological level, while C. robusta demonstrated heightened responses at the transcriptional level. We observed distinct transcriptional responses, particularly in the utilization of two superoxide dismutase (SOD) isoforms. Both Ciona species developed physiological stress memory with elevated total SOD (T-SOD) and glutathione (GSH) responses, while only C. robusta demonstrated transcriptional stress memory. The regulatory distinctions within the Nrf2-Keap1 signalling pathway likely explain the formation disparity of transcriptional stress memory between both Ciona species. These findings support the 'context-dependent stress memory hypothesis', emphasizing the emergence of species-specific stress memory at diverse regulatory levels in response to recurrent environmental challenges. Our results enhance our understanding of the mechanisms of environmental challenge management in marine species, particularly those related to the ADS.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00228-y.

Transgenerational effects of microplastics on Nrf2 signaling, GH/IGF, and HPI axis in marine medaka Oryzias melastigma under different salinities

Little information is available on the toxicity of microplastics (MPs) under different salinities in aquatic organisms. Consequently, the effects of larvae exposure to 180 μg/L MPs with 5.0 μm diameter on growth, antioxidant capacity and stress response were investigated in exposed F1 larvae and unexposed F2 larvae in marine medaka Oryzias melastigma at 5 ‰ and 25 ‰ salinities. Poor growth performance of F1 and F2 larvae and F1 adult fish was merely found under high salinity, as well as changes in the growth hormone/insulin-like growth factor-I (GH/IGF). Although malondialdehyde (MDA) content and antioxidant capacity remained constant in F1 larvae under high salinity, MPs increased MDA content and reduced antioxidant capacity in F2 larvae. Contrarily, MDA and antioxidant capacity increased in F1 and F2 larvae under low salinity. The mRNA expression levels of genes in the NF-E2-related factor 2 (Nrf2) pathway were dysregulated. Cortisol levels in the whole body increased in F1 larvae and recovered to the control level under low salinity while cortisol levels declined in F1 larvae and increased in F2 larvae under high salinity, which was related to the transcriptional regulation of the hypothalamus-pituitary-interrenal (HPI) axis genes. To summary, the present study determined the toxic effects of MPs on growth, antioxidant capacity, and stress response by disturbing Nrf2, HPI, and GH/IGF signaling in exposed larvae and unexposed offspring of marine medaka in a salinity-dependent manner. For the first time, our results highlight the interference effects of salinity on MPs toxicity in fish.

Integrated biomarker responses and metal contamination survey in the wedge clam Donax trunculus from the Atlantic coast of Morocco

In Morocco, the marine environment has always been a major occupation for socioeconomic activities (industry, tourism, urbanization, etc.). Thus, this work displays a case study of Taghazout coast in the central Atlantic part of the country, which becomes the center of several development projects, such as the touristic resort Taghazout Bay. In the aim to assess the health status of this coastal ecosystem, a multi-indicator approach based on the response of biomarkers in the wedge clam Donax trunculus was adopted during two years (2016/2017). The undertaken investigations on the response of biomarkers (AChE, GST, MDA, and CAT) in the sentinel species D. trunculus showed an activation of defense mechanisms in this bivalve, which would imply exposure to chemical stress in this ecosystem. The monitoring of seasonal bioaccumulation of cadmium (Cd), lead (Pb), and copper (Cu) by D. trunculus indicates that the bivalves collected have been exposed to these metal sources in the study area. In addition, the correlation study has reported a significant effect of environmental parameters on biomarker response. Overall, the multi-indicator approach has clearly revealed the health status of Taghazout coast registered in a coastal urbanization.

Alterations in Daphnia magna exposed to enniatin B and beauvericin provide additional value as environmental indicators

Mycotoxins beauvericin (BEA) and enniatin B (ENN B) affect negatively several systems and demand more studies as the mechanisms are still unclear. The simultaneous presence of contaminants in the environment manifests consequences of exposure for both animals and flora. Daphnia magna is considered an ideal invertebrate to detect effects of toxic compounds and environmental alterations. In this study, the potential toxicity and the basic mechanism of BEA and ENN B individually and combined were studied in D. magna. Acute and delayed toxicity were evaluated, and transcript levels of genes involved in xenobiotic metabolism (mox, gst, abcb1, and abcc5), reproduction, and oxidative stress (vtg-SOD) were analyzed by qPCR. Though no acute toxicity was found, results revealed a spinning around and circular profile of swimming, a strong decrease of survival after 72 h for BEA and ENN B at 16 µM and 6.25 µM, respectively, while for BEA + ENN B [8 + 1.6] µM after 96 h. The amount of mycotoxin remaining in the media revealed that the higher the concentration assayed the higher the amount remaining in the media. Differential regulation of genes suggests that xenobiotic metabolism is affected denoting different effects on transcription for tested mycotoxins. The results provide new insights into the underlying risk assessment of BEA and ENN B not only through food for consumers but also for the environment.

Molecular cloning, the characterization of metallothionein and catalase, and the evaluation of testicular toxicity of Cd in the Chinese fire-bellied newt (Cynops orientalis)

Cadmium (Cd) is an environmental toxicant and a nonessential metal. Cd can attack a wide range of organs, such as the liver, kidney, lung, ovary, testis, brain, and muscle in vertebrates. Among these organs, the testis might be the most sensitive organ to Cd toxicity. Metallothionein (MT) is a cysteine-rich protein with a low molecular weight, that can bind with Cd and eliminate reactive oxygen species (ROSs). Hydrogen peroxide, which as a crucial type of ROS that is induced by Cd, can be eliminated by catalase (CAT) in the self-protection of cells and to realize Cd toxicity resistance. To investigate the functions of MT and CAT in the testis of Cynops orientalis, we cloned the full-length MT and CAT genes of C. orientalis for the first time. Immunofluorescence results demonstrated that MT and CAT were expressed in Sertoli cells and all spermatogenic cells in the testis of C. orientalis. The results of the ultrastructural damage assay demonstrated that there were various impairments, which included organelle vacuolization, abnormal chromatin distribution, and apoptotic bodies, in somatic cells that were exposed to Cd. However, the anomalies of spermatozoa were located mainly in the mid-piece and head, many of which showed severely impaired structures. The results demonstrated that MT and CAT expression had distinct patterns in response to various Cd concentrations: an increase in MT mRNA levels with elevated Cd levels and a persistent increase in CAT mRNA levels with elevated Cd levels. These results suggested that MT and CAT play roles in Cd toxicity resistance in the testis and that the expression of CAT may be a better biomarker than the expression of MT for assessing Cd pollution.

The Duckweed, Lemna minor Modulates Heavy Metal-Induced Oxidative Stress in the Nile Tilapia, Oreochromis niloticus

A two-fold integrated research study was conducted; firstly, to understand the effects of copper (Cu) and zinc (Zn) on the growth and oxidative stress in Nile tilapia, Oreochromis niloticus; secondly, to study the beneficial effects of the duckweed Lemna minor L. as a heavy metal remover in wastewater. Experiments were conducted in mesocosms with and without duckweed. Tilapia fingerlings were exposed to Cu (0.004 and 0.02 mg L−1) and Zn (0.5 and 1.5 mg L−1) and fish fed for four weeks. We evaluated the fish growth performance, the hepatic DNA structure using comet assay, the expression of antioxidative genes (superoxide dismutase, SOD; catalase, CAT; glutathione peroxidase, GPx and glutathione-S-transferase, GST) and GPx and GST enzymatic activity. The results showed that Zn exhibited more pronounced toxic effects than Cu. A low dose of Cu did not influence the growth whereas higher doses of Cu and Zn significantly reduced the growth rate of tilapia compared to the control, but the addition of duckweed prevented weight loss. Furthermore, in the presence of a high dose of Cu and Zn, DNA damage decreased, antioxidant gene expressions and enzymatic activities increased. In conclusion, the results suggest that duckweed and Nile tilapia can be suitable candidates in metal remediation wastewater assessment programs.

Biomarkers of the oxidative stress and neurotoxicity in tissues of the bullfrog, Lithobates catesbeianus to assess exposure to metals

Lithobates catesbeianus tadpoles were exposed to 1 μg L^-1 of zinc (Zn), copper (Cu) and cadmium (Cd) alone or combined (1:1 and 1:1:1) for 2 and 16 days. Results showed a significant increase in the superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities in the liver, kidney and muscle (except for GPx) in the groups exposed to metal either alone or co-exposed after 2 days compared to the control. After 16 days, SOD, CAT and GST activities decreased significantly in the liver and kidney and GPx activity increased in the liver. Reduced glutathione (GSH) increased in the liver and kidney following combined exposure and decreased after 2 days of metal exposure in the muscle. There were significant increases in lipid hydroperoxide (LPO) levels in the liver, kidney and muscle (2 and 16 days), with the highest levels after metal co-exposure. Cholinesterase (ChE) activity increased significantly in the brain after 2 days of exposure but decreased in the brain (16 days) and muscle (2 days) after exposure to metals, alone and combined. The current study highlighted that the antioxidant system of L. catesbeianus was sensitive to metals and specially to the co-exposure of the three metals, despite presenting differences in the response among tissues. In addition, tadpoles were sensitive at both periods of exposure, but in different modes with stress response (activation, up-regulation) at 2 days and oppression (down-regulation) at 16 days.

Comparative assessment of biomarker response to tissue metal concentrations in urban populations of the land snail Helix pomatia (Pulmonata: Helicidae)

The traffic pressure is increasing, resulting in the emission of atmospheric pollution. Soil organisms will need to respond to pollution stressors. Among them, land snails are valuable indicators of ecosystem disturbance. In this study, land snails Helix pomatia were sampled from three city localities with different traffic intensity. Oxidative stress biomarkers catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-S-transferase (GST) in the foot muscle (FM) and hepatopancreas (HP) tissue were determined. Also, five heavy metal (Cd, Cu, Ni, Pb, and Zn) concentrations were quantified in soil and tissue samples. According to the results, the highway induces the strongest contamination on the surrounding environment, with the highest metal concentrations measured in soil and snails. At the most polluted locality, only Cd exceeded some soil guidelines authorities that we referred to in this study. In addition, tissue Cd concentrations exceeded the United States Environmental Protection Agency (USEPA) value (1 mg kg^-1) for soil invertebrate toxicity at all localities making it likely responsible for generating adverse effects in snails. Regarding HP, the CAT and GST are the most sensitive parameters that could be useful as oxidative stress biomarkers in snails exposed to the actual metals in the environment. On the other hand, in FM tissue, the most pronounced changes were recorded for GPX and GR. Based on tissue-specific enzyme responses, three urban populations were clearly separated. Therefore land snails are the promising candidates for quick field-based biomarker studies after showing a tissue-specific concentration-dependent induction of certain enzymes to heavy metals.

Toxic effect of chronic waterborne copper exposure on growth, immunity, anti-oxidative capacity and gut microbiota of Pacific white shrimp Litopenaeus vannamei

Copper can be accumulated in water through excessive sewage discharge or residual algaecide to generate toxic effect to aquatic animals. In this study, the juvenile of Pacific white shrimp, Litopenaeus vannamei was exposed to 0 (control), 0.05, 0.1, 0.2, 0.5 or 1 mg Cu²⁺ L^-1 for 30 days. Growth, immune function, anti-oxidative status and gut microbiota were evaluated. Weight gain and specific growth rate of L. vannamei were significantly decreased with the increase of ambient Cu²⁺. Enlarged lumen and ruptured cells were found in the hepatopancreas of shrimp in the 0.5 or 1 mg Cu²⁺ L^-1 treatment. Total hemocyte counts of shrimp in 0.5 or 1 mg Cu²⁺ L^-1 were significantly lower than in the control. The hemocyanin concentration was also significantly increased in 0.2 or 0.5 mg Cu²⁺ L^-1. Lysozyme contents were reduced in shrimp when Cu²⁺ exceeded 0.2 mg L^-1. Meanwhile, activities of superoxide dismutase and glutathione peroxidase were increased in the hepatopancreas and the activity of Na⁺-K⁺ ATPase was decreased in the gills with increasing Cu²⁺. The mRNA expressions of immune deficiency, toll-like receptor and caspase-3 were all significantly higher in the hepatopancreas in 0.05 mg Cu²⁺ L^-1 than in the control. For the diversity of intestinal microbes, Bacteroidetes significantly decreased in 1 mg Cu²⁺ L^-1 at the phylum level. KEGG pathway analysis demonstrates that 1 mg L^-1 Cu²⁺ can significantly alter metabolism, cellular processes and environmental information processing. This study indicates that the concentration of 1 mg L^-1 Cu can negatively impact growth, hemolymph immunity, anti-oxidative capacity and gut microbiota composition of L. vannamei.

Waterborne zinc induced lobe-dependent effect on oxidative stress and energy metabolism in hepatopancreas of Larimichthys crocea

The study aimed to compare differences in oxidative stress and energy metabolism between the left and right lobe of hepatopancreas in large yellow croaker Larimichthys crocea exposed to 0 (control), 20, and 100 μM Zn for 96 h. Tipical biomarkers were examined including the proportion of white hepatopancreas, lipid content, malondialdehyde (MDA) level, glutathione (GSH) content, activity levels of enzymes (Cu/Zn-superoxide dismutase, Cu/Zn-SOD; catalase, CAT; glutathione peroxidase, GPx; glutathione reductase, GR; mitochondrial ATP synthase, F-ATPase; malate dehydrogenase, MDH; succinate dehydrogenase, SDH; hepatic lipase, HTGL; lipoprotein lipase, LPL), mRNA levels of genes encoding these enzymes (sod1, cat, gpx1a, gr, atp5b, mdh, sdh, htgl, and lpl), and gene expression of signaling molecules the NF-E2-related nuclear factor 2 (nrf2) and Kelch-like ECH-associated protein 1 (keap1). A whitish color in the left lobe of hepatopancreas was observed in the control and Zn-exposed fish. Contrarily, the right lobe of hepatopancreas tended towards red with increasing Zn levels. The phenomenon was further confirmed by that lipid content was reduced in the right lobe and was not significantly affected in the left lobe by Zn. The right lobe showed higher energy consumption than the left lobe as reflected by the up-regulation of activity levels of HTGL, LPL, F-ATPase, MDH, and SDH. Lipid peroxidation declined by 20 μM Zn and was unchanged by 100 μM Zn in both lobes, which could be explained by increased activity levels of Cu/Zn-SOD and GPx. However, the magnitude of increase in Cu/Zn-SOD activity was greater in the right lobe than that in the left one. The difference in enzyme activity between two lobes may be involved in changes in mRNA levels of sod1, gr, atp5b, sdh, htgl, lpl, and nrf2, which was further confirmed by positive relationships between enzyme activity and gene expression. Our data also showed positive correlations between nrf2 expression and mRNA levels of its target genes, suggesting that Nrf2 was required for the protracted induction of these genes. Our results demonstrated the potential molecular mechanism of Zn-induced differences between lobes of hepatopancreas, suggesting that the sampling part of hepatopancreas should be considered with caution when assessing metal contamination.

Mixture toxicity effects and uptake of titanium dioxide (TiO2) nanoparticles and 3,3',4,4'-tetrachlorobiphenyl (PCB77) in juvenile brown trout following co-exposure via the diet

Titanium dioxide nanoparticles (n-TiO₂) are among the man-made nanomaterials that are predicted to be found at high concentrations in the aquatic environment. There, they likely co-exist with other chemical pollutants. Thus, n-TiO₂ and other chemical pollutants can be taken up together or accumulate independently from each other in prey organisms of fish. This can lead to dietary exposure of fish to n-TiO₂-chemical pollutant mixtures. In this study, we examine if simultaneous dietary exposure to n-TiO₂ and 3,3',4,4'-Tetrachlorobiphenyl (PCB77) -used as a model compound for persistent organic pollutants with dioxin-like properties- can influence the uptake and toxicological response elicited by the respective other substance. Juvenile brown trout (Salmo trutta) were fed custom-made food pellets containing n-TiO_2, PCB77 or n-TiO₂+PCB77 mixtures for 15 days. Ti and PCB77 concentrations in the liver were measured by ICP-MS and GC-MS, respectively. Besides, n-TiO₂ uptake was assessed using TEM. Combination effects on endpoints specific for PCB77 (i.e., cytochrome P450 1A (CYP1A) induction) and endpoints shared by both PCB77 and n-TiO₂ (i.e., oxidative stress-related parameters) were measured in intestine and liver using RT-qPCR and enzyme activity assays. The results show that genes encoding for proteins/enzymes essential for tight junction function (zo-1) and ROS elimination (sod-1) were significantly upregulated in the intestine of fish exposed to n-TiO₂ and PCB77 mixtures, but not in the single-substance treatments. Besides, n-TiO₂ had a potentiating effect on PCB77-induced CYP1A and glutathione reductase (GR) expression/enzyme activity in the liver. This study shows that simultaneous dietary exposure to nanomaterials and traditional environmental pollutants might result in effects that are larger than observed for the substances alone, but that understanding the mechanistic basis of such effects remains challenging.

Genotoxicity assessment of polluted urban streams using a native fish Astyanax altiparanae

Water quality has declined globally due to increased contamination of aquatic ecosystems. The use of fish genotoxicity biomarkers may improve and complement parameters for environmental risk assessment. The aim of this study was to assess the genotoxicity of samples collected from streams of the Jordão River, a tributary of the Paranaíba River, Brazil with different levels of metal contamination, utilizing a native fish species to determine the sensitivity and viability of implementing a useful, reliable technique for routine biomonitoring programs. Chemical analysis of water and sediments collected from different sites indicated that a gradient of contamination existed as evidenced by different concentrations of metals detected. After chronic exposure to contaminated samples, micronucleus (MN) frequencies in fish erythrocytes were measured and correlation with environmental parameters determined. Sites where the water concentrations of the metals aluminum (Al), iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) were high indicating a greater genotoxic potential of these elements. At the samples collected from the urban zone, a gradual increase was found for chromium (Cr), cadmium (Cd) and nickel (Ni) indicative of adverse impacts of discharge of urban effluents. Data demonstrated that Astyanax altiparanae, used in the test, exhibited a reliable sensitivity for detection of genotoxic consequences attributed to exposure to water samples collected near the discharge of industrial and domestic waste.

Toxicity Assessment of Impacted Sediments from Southeast Coast of Tunisia Using a Biomarker Approach with the Polychaete Hediste diversicolor

Toxicity caused by exposure to pollutants from marine sediments is a consequence of the interaction between biota and xenobiotics most frequently released by anthropogenic activities. The present work intended to characterize the toxicity of natural sediments putatively impacted by distinct human activities, collected at several sites located in the south of the Gulf of Gabes, Zarzis area, Tunisia. The selected toxicity criteria were analysed following ecologically relevant test conditions. Organisms of the polychaete species Hediste diversicolor were chronically exposed (28 days) to the mentioned sediments. Toxicity endpoints were biomarkers involved in the toxic response to common anthropogenic chemicals, namely neurotoxic (acetylcholinesterase), anti-oxidant (catalase, glutathione peroxidase), metabolic (glutathione S-transferases) enzymatic activities, and oxidative damage (lipid peroxidation, TBARS assay). The chemical characterization of sediments showed that the samples collected from the site near an aquaculture facility were highly contaminated by heavy metals (Cd, Cu, Cr, Hg, Pb, and Zn) and polycyclic aromatic hydrocarbons (fluorene, phenanthrene, anthracene, fluoranthene and pyrene). H. diversicolor individuals exposed to the sediments from this specific site showed the highest values among all tested biomarkers, suggesting that these organisms were possibly under a pro-oxidative stress condition potentially promoted by anthropogenic pollution. Moreover, it was possible to conclude that individuals of the polychaete species H. diversicolor responded to the chronic exposure to potentially contaminated sediments from the southeast coast of Tunisia, eliciting adaptive responses of significant biological meaning.

Limited oxidative stress in common carp (Cyprinus carpio, L., 1758) exposed to a sublethal tertiary (Cu, Cd and Zn) metal mixture

Analyzing effects of metal mixtures is important to obtain a realistic understanding of the impact of mixed stress in natural ecosystems. The impact of a one-week exposure to a sublethal metal mixture containing copper (4.8 μg/L), cadmium (2.9 μg/L) and zinc (206.8 μg/L) was evaluated in the common carp (Cyprinus carpio). To explore whether this exposure induced oxidative stress or whether defense mechanisms were sufficiently fitting to prevent oxidative stress, indicators of apoptosis (expression of caspase 9 [CASP] gene) and of oxidative stress (malondialdehyde [MDA] level and xanthine oxidase [XO] activity) were measured in liver and gills, as well as activities and gene expression of enzymes involved in antioxidant defense (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx], glutathione reductase [GR] and glutathione-S-transferase [GST]). The total antioxidative capacity (T-AOC) was also quantified. No proof of oxidative stress was found in either tissue but there was indication of apoptosis in the liver. CAT, GPx, GR and GST total activities were reduced after 7 days, suggesting a potential decrease of glutathione levels and risk of increased free radicals if the exposure would have lasted longer. There were no major changes in the total activities of antioxidant enzymes in the gills, but the relative expression of the genes coding for CAT and GR were triggered, suggesting a response at the transcription level. These results indicate that C. carpio is well equipped to handle these levels of metal pollution, at least during short term exposure.

Molecular cloning, characterization, expression and enzyme activity of catalase from planarian Dugesia japonica in response to environmental pollutants

Catalase (CAT) is an important antioxidant enzyme that protects aerobic organisms against oxidative damage by degrading hydrogen peroxide to oxygen and water. CAT mRNAs have been cloned from many species and employed as useful biomarkers of oxidative stress. In the present study, we cloned the cDNA sequence of CAT gene from freshwater planarian Dugesia japonica (designated as DjCAT) by means of RACE method. Sequence analysis and multiple alignment jointly showed that the full-length cDNA sequence consists of 1734 nucleotides, encoding 506 amino acids. Three catalytic amino acid residues of His71, Asn144 and Tyr354, two CAT family signature sequences of a proximal active site signature (60FDRERIPERVVHAKGGGA77) and a heme-ligand signature motif (350RLFSYRDTQ358) are highly conserved, suggesting that the DjCAT belongs to the NADPH and heme-binding CAT family and has similar functions. In addition, the transcriptional level of CAT gene and activity of CAT enzyme upon acute exposure of environmental pollutants glyphosate and 1-decyl-3-methylimidazolium bromide ([C10mim]Br) were investigated systematically. The variation of CAT mRNA expression in D. japonica was quantified by real-time PCR and the results indicated that it was up-regulated after exposure to glyphosate or [C10mim]Br with a dose-dependent manner but not linearly. Even though the variation trend of CAT activity upon glyphosate stress was not monotonously increased and inconsistent with that after [C10mim]Br exposure on day 1 and 3 sampling time, with the duration prolonged to day 5 they both presented a dose-dependent increase and the differences achieved extreme significance in all treated groups compared to the control. These findings suggested that DjCAT plays an important role in antioxidant defense in D. japonica, and the mRNA expression of CAT would also be used as an effective biomarker to monitor the pollution in aquatic environment just like its corresponding enzyme.

Zn Stimulates the Phospholipids Biosynthesis via the Pathways of Oxidative and Endoplasmic Reticulum Stress in the Intestine of Freshwater Teleost Yellow Catfish

The hypothesis of our study was that waterborne Zn exposure evoked phospholipids (PL) biosynthesis to compensate for the loss of membrane integrity, and the pathways of oxidative stress and endoplasmic reticulum (ER) stress mediated the Zn-evoked changes of PL biosynthesis. Thus, we conducted RNA sequencing to analyze the differences in the intestinal transcriptomes between the control and Zn-treated P. fulvidraco. The 56-day Zn exposure increased the intestinal Zn accumulation, and mRNA levels of 816 genes were markedly up-regulated, while that of 263 genes were down-regulated. Many differentially expressed genes in the pathways of PL biosynthesis and protein processing in ER were identified. Their expression profiles indicated that waterborne Zn exposure injured protein metabolism, induced PL biosynthesis caused oxidative stress and ER stress, and activated the unfolded protein response. Then, using the primary enterocytes, we identified the mechanism of oxidative and ER stress mediating Zn-induced PL biosynthesis, and indicated that the activation of these pathways constituted adaptive mechanisms to reduce Zn toxicity. Our study demonstrated that Zn exposure via the water increased Zn accumulation and PL biosynthesis, and that oxidative stress and ER stress were interdependent and mediated the Zn-induced PL biosynthesis of the intestine in the freshwater teleost.

Acute exposure to copper induces variable intensity of oxidative stress in goldfish tissues

Copper is an essential element, but at high concentrations, it is toxic for living organisms. The present study investigated the responses of goldfish, Carassius auratus, to 96 h exposure to 30, 300, or 700 μg L^-1 of copper II chloride (Cu²⁺). The content of protein carbonyls was higher in kidney (by 158%) after exposure to 700 mg L^-1 copper, whereas in gills, liver, and brain, we observed lower content of protein carbonyls after exposure to copper compared with control values. Exposure to copper resulted in increased levels of lipid peroxides in gills (76%) and liver (95-110%) after exposure to 300 and 700 μg L^-1 Cu²⁺. Low molecular mass thiols were depleted by 23-40% in liver and by 29-67% in kidney in response to copper treatment and can be used as biomarkers toxicity of copper. The activities of primary antioxidant enzymes, superoxide dismutase and catalase, were increased in liver as a result of Cu²⁺ exposure, whereas in kidney catalase activity was decreased. The activities of glutathione-related enzymes, glutathione peroxidase, glutathione-S-transferase, and glutathione reductase were decreased as a result of copper exposure, but glutathione reductase activity increased by 25-40% in liver. Taken together, these data show that exposure of fish to Cu²⁺ ions results in the development of low/high intensity oxidative stress reflected in enhanced activities of antioxidant and associated enzymes in different goldfish tissues.

Zn2+ induced molecular responses associated with oxidative stress, DNA damage and histopathological lesions in liver and kidney of the fish, Channa punctatus (Bloch, 1793)

Zn²⁺ is essential for normal physiological functioning of all organisms in small quantities, but when its concentration enhances in surrounding environment it acts as a toxicant to organisms. Common sources of Zn²⁺ pollution are electroplating, alloying, mining, and allied industrial operations. The present study aims to assess the biochemical, histopathological and genotoxicological implications under Zn²⁺ intoxication along with its accumulation patterns in prime biotransformation sites-liver and kidney, of a bottom feeder fish, Channa punctatus. Fish were chronically exposed to two different concentrations of Zn²⁺i.e., 5mg/L (permissible limit, T1) and 10mg/L (twice the permissible limit, T2). Simultaneous control was maintained. A significant (p<0.05) increment in Zn²⁺ bioaccumulation, antioxidant enzymes activities of SOD, CAT and GR and induction in micronuclei frequencies along with the significant (p<0.05) decrement in total protein and GSH were observed in all the exposed groups after 28 d. Altered biochemical parameters coupled with enhanced induction in micronuclei and accumulation of Zn²⁺ in liver and kidney of fish can be regarded as sensitive biomarkers of Zn²⁺ induced toxicological manifestations and thus, they may be effectively utilized for reliable ecotoxicological biomonitoring of aquatic regimes polluted with Zn²⁺.

Nfu1 Mediated ROS Removal Caused by Cd Stress in Tegillarca granosa

The blood clam Tegillarca granosa, a eukaryotic bottom-dwelling bivalve species has a strong ability to tolerate and accumulate cadmium. In our previous study, Nfu1 (iron-sulfur cluster scaffold protein), which is involved in Fe-S cluster biogenesis, was shown to be significantly up-regulated under Cd stress, as determined by proteomic analysis. To investigate the function of Nfu1 in cadmium (Cd) detoxification, the function of blood clam Nfu1 (designated as Tg-Nfu1) was investigated by integrated molecular and protein approaches. The full-length cDNA of Tg-Nfu1 is 1167 bp and encodes a protein of 272 amino acid residues. The deduced Tg-Nfu1 protein is 30 kDa contains a conserved Nfu-N domain and a Fe-S cluster binding motif (C-X-X-C). qRT-PCR analysis revealed that Tg-Nfu1 was ubiquitously expressed in all examined tissues; it was up-regulated in the hepatopancreas and gill, and kept a high level from 9 to 24 h after Cd exposure (250 μg/L). Western blot analysis further revealed that the Tg-Nfu1 protein was also highly expressed in the hepatopancreas and gill after 24 h of Cd stress. Further functional analysis showed that the production of ROS was increased and Cu/ZnSOD activity was inhibited in blood clam, treated with the specific Nfu1 siRNA and Cd stress, respectively. These results suggest that Tg-Nfu1 could protect blood clam from oxidative damage caused by Cd stress.

Overexpressing the Sedum alfredii Cu/Zn Superoxide Dismutase Increased Resistance to Oxidative Stress in Transgenic Arabidopsis

Superoxide dismutase (SOD) is a very important reactive oxygen species (ROS)-scavenging enzyme. In this study, the functions of a Cu/Zn SOD gene (SaCu/Zn SOD), from Sedum alfredii, a cadmium (Cd)/zinc/lead co-hyperaccumulator of the Crassulaceae, was characterized. The expression of SaCu/Zn SOD was induced by Cd stress. Compared with wild-type (WT) plants, overexpression of SaCu/Zn SOD gene in transgenic Arabidopsis plants enhanced the antioxidative defense capacity, including SOD and peroxidase activities. Additionally, it reduced the damage associated with the overproduction of hydrogen peroxide (H2O2) and superoxide radicals (O2•-). The influence of Cd stress on ion flux across the root surface showed that overexpressing SaCu/Zn SOD in transgenic Arabidopsis plants has greater Cd uptake capacity existed in roots. A co-expression network based on microarray data showed possible oxidative regulation in Arabidopsis after Cd-induced oxidative stress, suggesting that SaCu/Zn SOD may participate in this network and enhance ROS-scavenging capability under Cd stress. Taken together, these results suggest that overexpressing SaCu/Zn SOD increased oxidative stress resistance in transgenic Arabidopsis and provide useful information for understanding the role of SaCu/Zn SOD in response to abiotic stress.

Tolerance of whitefish (Coregonus lavaretus) early life stages to manganese sulfate is affected by the parents

European whitefish (Coregonus lavaretus) embryos and larvae were exposed to 6 different manganese sulfate (MnSO₄ ) concentrations from fertilization to the 3-d-old larvae. The fertilization success, offspring survival, larval growth, yolk consumption, embryonic and larval Mn tissue concentrations, and transcript levels of detoxification-related genes were measured in the long-term incubation. A full factorial breeding design (4 females × 2 males) allowed examination of the significance of both female and male effects, as well as female-male interactions in conjunction with the MnSO₄ exposure in terms of the observed endpoints. The MnSO₄ exposure reduced the survival of the whitefish early life stages. The offspring MnSO₄ tolerance also was affected by the female parent, and the female-specific mean lethal concentrations (LC50s) varied from 42.0 mg MnSO₄ /L to 84.6 mg MnSO₄ /L. The larval yolk consumption seemed slightly inhibited at the exposure concentration of 41.8 mg MnSO₄ /L. The MnSO₄ exposure caused a significant induction of metallothionein-A (mt-a) and metallothionein-B (mt-b) in the 3-d-old larvae, and at the exposure concentration of 41.8 mg MnSO₄ /L the mean larval mt-a and mt-b expressions were 47.5% and 56.6% higher, respectively, than at the control treatment. These results illustrate that whitefish reproduction can be impaired in waterbodies that receive Mn and SO₄ in concentrations substantially above the typical levels in boreal freshwaters, but the offspring tolerance can be significantly affected by the parents and in particular the female parent. Environ Toxicol Chem 2017;36:1343-1353. © 2016 SETAC.

Chronic waterborne zinc and cadmium exposures induced different responses towards oxidative stress in the liver of zebrafish

Based on the same toxic level of 0.6% LC50 for 96-h and the severe situation of water pollution, we compared effects of chronic Zn (180μgL(-1)) and Cd exposures (30μgL(-1)) on growth, survival, histology, ultrastructure, and oxidative stress in the liver of zebrafish for 5 weeks. Growth performance and survival rate remained relatively constant under Zn stress, but was reduced under Cd exposure. Cd exposure also induced severe pyknotic nuclei, evident ultrastructure damage, and considerable lipid inclusions in the hepatocytes. However, these phenomena were not pronounced under Zn exposure. The negative effects caused by Cd may be explained by an increase in hepatic oxidative damage, as reflected by the enhanced levels of lipid peroxidation (LPO) and protein carbonylation (PC). The reduced activity of Cu/Zn-superoxide dismutase (Cu/Zn-SOD) and catalase (CAT) may result in the enhanced hepatic oxidative damage, though the mRNA and protein levels of both genes increased and remained unchanged respectively. On the contrary, Zn up-regulated the levels of mRNA, protein and activity of Cu/Zn-SOD, which may contribute to the decreased LPO levels. Nonetheless, the sharply up-regulated mRNA levels of CAT did not induce an increase in the protein and activity levels of CAT under Zn stress. Furthermore, transcription factor NF-E2-related factor 2 (Nrf2) expression parelleled with its target genes, suggesting that Nrf2 is required for the protracted induction of antioxidant genes. In conclusion, our data demonstrated that essential and non-essential metals induced some differences in oxidative damage in fish. The differences were not caused by the transcriptional level of related genes but depended on post-transcriptional modifications.

Effects of dietary cadmium on growth, antioxidants and bioaccumulation of sea cucumber (Apostichopus japonicus) and influence of dietary vitamin C supplementation

The effects of dietary cadmium (Cd) supplementation on growth, antioxidant capacity and accumulation of Cd in tissues (body wall, digestive tracts, and respiratory tree) of sea cucumber, Apostichopus japonicus, exposed to sub-chronic concentrations (0, 10, 50, 100, and 500mg Cd/kg dry weight) of Cd were investigated. In addition, the potential protective effects of vitamin C (L-ascorbic acid, AsA) against the effects of Cd on sea cucumbers were investigated. Sea cucumbers were exposed to dietary Cd for 30 days, after which another group of healthy sea cucumbers was supplied diet supplemented with mixed Cd and AsA for another 30 days. Cd exposure for 30 days resulted in increased Cd accumulation in tissues of sea cucumbers with exposure time and concentration. The order of Cd accumulation in organs was digestive tracts>respiratory tree>body wall. On day 30, the body weight gain (BWG) and specific growth rate (SGR) decreased significantly (P<0.05) in the 500mg Cd/kg treatment. Superoxide dismutase (SOD) activity, glutathione peroxidase (GSH-Px) activity and catalase (CAT) activity in the coelomic fluid of sea cucumbers decreased with increasing dietary Cd concentration, but malondialdehyde (MDA) content in the coelomic fluid increased. Providing diet supplemented with Cd and AsA indicated that although sea cucumbers exhibited signs of Cd toxicity, no death occurred in response to 50mg Cd/kg for 30 days. Based on these findings, five treatments were provided: 50mg Cd/kg+0mg AsA/kg, 50mg Cd/kg+ 3000mg AsA/kg, 50mg Cd/kg+ 5000mg AsA/kg, 50mg Cd/kg+10,000mg AsA/kg, and 50mg Cd/kg+15,000mg AsA/kg. The BWG and SGR of sea cucumbers fed the AsA supplemented diet mixed with Cd increased. Additionally, MDA levels in coelomic fluid were negatively correlated with dietary AsA levels, while antioxidant capacities (SOD, GSH-Px and CAT) were positively correlated with dietary AsA levels. Moreover, Cd accumulation in tissues decreased in response to dietary AsA supplementation of treatments. Overall, antioxidant capacity and bioaccumulation in sea cucumber was found to decrease and be induced in response to Cd, but vitamin C mitigated these effects, with 5000mg AsA/kg providing the optimum protection against 50mg/kg Cd.

Antioxidant defenses at transcriptional and enzymatic levels and gene expression of Nrf2-Keap1 signaling molecules in response to acute zinc exposure in the spleen of the large yellow croaker Pseudosciaena crocea

We evaluated the effects of acute Zn exposure (4 and 8 mg L(-1) Zn) on lipid peroxidation, and activities and mRNA levels of antioxidant enzyme genes (Cu/Zn-SOD, CAT, GPx, and GR), and gene expression of the Nrf2-Keap1 signaling molecule at different exposure times (0, 6, 12, 24, 48, and 96 h) in the spleen of large yellow croaker. Lipid peroxidation remained relatively constant during 6-48 h and 6-24 h and sharply increased at 96 h and during 48-96 h in fish exposed to 4 and 8 mg L(-1) Zn, respectively. Activities of all tested enzymes increased during the early stage of exposure and decreased towards the end of the exposure in both groups. However, mRNA levels of antioxidant enzyme genes were dramatically up-regulated by 4 and 8 mg L(-1) Zn during the late stage of exposure. During the early stage of exposure for 6 h, the 8 mg L(-1) Zn exposure sharply increased mRNA levels of Cu/Zn-SOD, CAT, GPx1b, Nrf2, and Keap1, whereas, the 4 mg L(-1) Zn exposure did not significantly affect the expression of these genes. Our data also showed positive relationships between Nrf2 expression and mRNA levels of its target genes, suggesting that Nrf2 was required for the protracted induction of these genes. Furthermore, a sharp increase in Keap1 expression levels was observed in fish exposed to 4 mg L(-1) at 96 h, and 8 mg L(-1) at 6, 48, and 96 h. In conclusion, the present study demonstrated that Zn-induced antioxidant defenses were involved in modifications at enzymatic and transcriptional levels and the transcriptional regulation of the Nrf2-Keap1 signaling molecule; these results may contribute to the understanding of mechanisms that maintain the correct redox balance in the immune organ of the large yellow croaker.

Antioxidant defenses and histological changes in Carassius auratus after combined exposure to zinc and three multi-walled carbon nanotubes

With the increasing applications of carbon nanotubes (CNTs) worldwide, considerable concerns have been raised regarding their inevitable releases into natural waters and ecotoxicity. It was supposed that CNTs may interact with some existing pollutants like zinc in aquatic systems and exhibit different effects when compared with their single treatments. However, data on their possible combined toxicity on aquatic species are still lacking. Moreover, the interactions of Zn with different functionalized CNTs may be distinct and thereby lead to diverse results. It is like that functional groups play a vital role in illustrating the differences in toxicity among various CNTs. In this study, the single and joint effects of multi-walled carbon nanotubes (MWCNTs) and two MWCNTs functionalized with carboxylation (COOH-MWCNTs) or hydroxylation (OH-MWCNTs) in the absence or presence of zinc (Zn) on antioxidant status and histopathological changes in Carassius auratus were evaluated. Synergistic effect was tentatively proposed for joint-toxicity action, which was supported by apparently observed oxidative stress and histopathological changes in joint exposure groups. The integrated biomarker response index was calculated to rank the toxicity order, from which the conclusion of synergistic effect was strengthened. Regarding differences among various CNTs, our data showed that OH-MWCNTs and COOH-MWCNTs were more stressful to fish than raw MWCNTs. This finding sustained that functionalization is an important factor in nanotoxicity, which may serve as clues for future design and application of CNTs. Overall, these results provided some valuable toxicological data on the joint effects of CNTs and heavy metals on aquatic species, which can facilitate further understanding on the potential impacts of other coexisting pollutants in the culture of freshwater fish.

Fish pre-acclimation temperature only modestly affects cadmium toxicity in Atlantic salmon hepatocytes

An emerging focus in environmental toxicology is how climate change will alter bioavailability and uptake of contaminants in organisms. Ectothermic animals unable to adjust their temperature by local migration, such as farmed fish kept in net pens, may become more vulnerable to contaminants in warmer seas. The aim of this work was to study cadmium (Cd) toxicity in cells obtained from fish acclimated to sub-optimal growth temperature. Atlantic salmon hepatocytes, harvested from fish pre-acclimated either at 15°C (optimal growth temperature) or 20°C (heat-stressed), were exposed in vitro to two concentrations of Cd (control, 1 and 100µM Cd) for 48h. Cd-induced cytotoxicity, determined with the xCELLigence system, was more pronounced in cells from fish pre-acclimated to a high temperature than in cells from fish grown at optimal temperature. A feed spiked with antioxidants could not ameliorate the Cd-induced cytotoxicity in cells from temperature-stressed fish. At the transcriptional level, Cd exposure affected 11 out of 20 examined genes, of which most are linked to oxidative stress. The transcriptional levels of a majority of the altered genes were changed in cells harvested from fish grown at sub-optimal temperature. Interaction effects between Cd exposure and fish pre-acclimation temperature were seen for four transcripts, hmox1, mapk1, fth1 and mmp13. Overall, this study shows that cells from temperature-stressed fish are modestly more vulnerable to Cd stress, and indicate that mechanisms linked to oxidative stress may be differentially affected in temperature-stressed cells.

Gene response of CYP360A, CYP314, and GST and whole-organism changes in Daphnia magna exposed to ibuprofen

The fate and ecological impact of non-steroidal anti-inflammatory drugs (NSAIDs) in aquatic environments has gained increasingly concern recently. However, limited information is provided about the toxicity mechanism of NSAIDs to aquatic invertebrates. In the present study, we investigated the expression of CYP360A, CYP314, and GST genes involved in the detoxification process and the responses of their associated enzymes activity, as well as whole-organism changes in Daphnia magna exposed to environmentally relevant concentrations of ibuprofen (IBU). Results showed that the total amount of eggs produced per female, total number of brood per female, and body length were significantly decreased under IBU exposure, suggesting the effects of chronic IBU exposure on growth and reproduction of D. magna cannot be ignored. In gene expression level, the CYP360A gene, homologue to CYP3A in mammalian, showed inhibition at low concentration of IBU (0.5μg·L(-1)) and induction at high concentration of IBU (50μg·L(-1)). GST gene also exhibited a similar performance to CYP3A. CYP314 displayed inhibition for short time exposure (6h) and induced with prolonged exposure time (48h) at low concentration of IBU (0.5μg·L(-1)). Erythromycin N-demethylase (ERND) and aminopyrine N-demethylase (APND) related to cytochrome oxidase P450 (CYPs) were inhibited for short time exposure (6h) to IBU and then activated with prolonged exposure time (48h) at low concentration of IBU (0.5μg·L(-1)), while EROD showed a dose-dependent pattern under IBU exposure. As for antioxidative system, induction of glutathione S-transferase (GST), superoxide dismutase (SOD), and catalase (CAT) was observed in short-term exposure to IBU. Meanwhile, methane dicarboxylic aldehyde (MDA) content increased with the increasing IBU concentration and the delayed exposure time, displaying obvious dose- and time-dependent pattern. In summary, IBU significantly altered some physiological and biochemical parameters and genes expressions associated with detoxification metabolism in D. magna, the integrated approach combining the response in molecule levels with the performance of the whole organism can help elucidate the toxic effects of IBU and provide more insight into the exact mechanism of toxicity in aquatic organisms.

Evaluation of the estrogenic and oxidative stress effects of the UV filter 3-benzophenone in zebrafish (Danio rerio) eleuthero-embryos

Personal care products have been detected in superficial waters, representing an environmental risk to the biota. Some studies indicated that 3-benzophenone (3BP) alters hormones, inducing vitellogenesis and having adverse effects on fish reproduction. Other studies have reported generation of free radicals and changes in antioxidant enzymes. Therefore, the aim of the present study was to test acute exposure to 3BP at concentrations within and beyond that found environmentally to provide important toxicological information regarding this chemical. We evaluated the effect of 3BP on vitellogenin 1 (VTG1) gene expression and the transcription of the enzymes catalase (CAT), superoxide dismutase (SOD) or glutathione peroxidase (GPx), which are involved in cellular redox balance. Zebrafish eluthero-embryos (168hpf) were exposed to 1,10, 100, 1000µg/L 3BP, in addition to a negative control and a 0.1% ethanol control for 48h. The results of our study indicated a positive significant correlation between exposure concentrations and VTG1 expression (r=0.986, p=0.0028) but only 1000µg/L 3BP produced a significant increase from control. Acute exposure showed no significant differences in transcription levels of CAT, SOD or GPx at the tested conditions. Nevertheless, a trend toward increase in GPx expression was observed as a positive significant correlation (r=0.928, p=0.017) was noted.

Waterborne cadmium and nickel impact oxidative stress responses and retinoid metabolism in yellow perch

In this experiment, we studied the transcriptional and functional (enzymatic) responses of yellow perch (Perca flavescens) to metal stress, with a focus on oxidative stress and vitamin A metabolism. Juvenile yellow perch were exposed to two environmentally relevant concentrations of waterborne cadmium (Cd) and nickel (Ni) for a period of 6 weeks. Kidney Cd and Ni bioaccumulation significantly increased with increasing metal exposure. The major retinoid metabolites analyzed in liver and muscle decreased with metal exposure except at high Cd exposure where no variation was reported in liver. A decrease in free plasma dehydroretinol was also observed with metal exposure. In the liver of Cd-exposed fish, both epidermal retinol dehydrogenase 2 transcription level and corresponding enzyme activities retinyl ester hydrolase and lecithin dehydroretinyl acyl transferase increased. In contrast, muscle epidermal retinol dehydrogenase 2 transcription level decreased with Cd exposure. Among antioxidant defences, liver transcription levels of catalase, microsomal glutathione-S-transferase-3 and glucose-6-phosphate dehydrogenase were generally enhanced in Cd-exposed fish and this up-regulation was accompanied by an increase in the activities of corresponding enzymes, except for microsomal glutathione-S-transferase. No consistent pattern in antioxidant defence responses was observed between molecular and biochemical response when fish were exposed to Ni, suggesting a non-synchronous response of antioxidant defence in fish exposed to waterborne Ni. There was a general lack of consistency between muscle transcription level and enzyme activities analyzed. The overall findings from this investigation highlight the usefulness of transcriptional and biochemical endpoints in the identification of oxidative stress and vitamin A metabolism impairment biomarkers and the potential use of multi-level biological approaches when assessing environmental risk in fish.

Development of a non-lethal method for evaluating transcriptomic endpoints in Arctic grayling (Thymallus arcticus)

With increases in active mining and continued discharge associated with former mine operations, evaluating the health of watersheds in the Canadian Yukon Territory is warranted. Current environmental assessment approaches often employ guidelines established using sentinel species not relevant to Arctic monitoring programs. The present study focused on the successful development of a quantitative real-time polymerase chain reaction (qPCR) assay directed towards the indigenous Arctic grayling (Thymallus arcticus) and examines the feasibility of using non-lethal sampling from the caudal fin as a means for evaluation of mRNA abundance profiles reflective of environmental conditions. In a proof of concept study performed blind, qPCR results from animals in an area with elevated water concentrations of cadmium (Cd) and zinc (Zn) and higher body burdens of Cd, Zn, and lead (Pb) were compared to a reference location in the Yukon Territory. Lower condition factor and a higher abundance of hepatic and caudal fin gene transcripts encoding the metallothionein isoforms (mta/mtb), in addition to elevated heat shock protein 70 (hsp70) and catalase (cat) mRNAs in liver, were observed in fish from the test site. The strong positive correlation between metal body burden and caudal fin mta/mtb mRNA abundance demonstrates a high potential for use of the Arctic grayling assay in non-lethal environmental monitoring programs.

Metal accumulation and oxidative stress biomarkers in liver of freshwater fish Carassius auratus following in vivo exposure to waterborne zinc under different pH values

In this study, laboratory experiments were conducted to investigate the combined effect of zinc and pH on metal accumulation and oxidative stress biomarkers in Carassius auratus. Fish were exposed to 0.1 and 1.0mg Zn/L at three pH values (5.0, 7.25, 9.0) for 3, 12, and 30 d. After each exposure, the contents of three trace elements (Zn, Fe and Cu) were determined in liver. Generally, longer exposure to zinc (12d and 30 d) increased hepatic Zn and Cu deposition, but decreased Fe content. Increasing accumulation of Zn in the tissue was also observed with increasing zinc concentration in the exposure medium. Moreover, hepatic antioxidant enzyme activities including superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), together with the level of glutathione (GSH) were measured to evaluate the oxidative stress status. The decreases in the four measured biochemical parameters after 3d exposure might reflect the failure of the antioxidant defense system in neutralizing the ROS generated during the metabolic process, while the recovery of the antioxidants at days 12 and 30 suggested a possible shift toward a detoxification mechanism. With regard to the influence of pH on zinc toxicity, the general observation was that the living environment became more stressful when the water conditions changed from an acidic state toward a near-neutral or alkaline state.

Oxidative pathways of chemical toxicity and oxidative stress biomarkers in marine organisms

The antioxidant system of marine organisms consists of low molecular weight scavengers and antioxidant enzymes which interact in a sophisticated network. Environmental pollutants can unbalance this system through closely related mechanisms, indirect relationships and cascade effects acting from pre-transcriptional to catalytic levels. Chemically-mediated pathways have the potential to greatly enhance intracellular formation of reactive oxygen species (ROS); at the same time, excessive levels of oxyradicals down-regulate xenobiotics metabolism, with important environmental implications for organisms exposed to chemical mixtures. Interactions between different classes of chemicals, generation of ROS and onset of oxidative stress conditions are partly modulated by changes in levels and functions of redox-sensitive signaling proteins and transcription factors. The Nrf2-Keap1 pathway still remains largely unexplored in marine organisms, despite the elevated degree of identity and similarity with homolog transcripts and proteins from different species. Recent evidences on transcriptional up-regulation of this system are consistent with the capability to provide a prolonged expression of ARE-regulated cytoprotective genes, and to efficiently switch off this mechanism when oxidative pressure decreases. Although gene expression and catalytic activities of antioxidants are often measured as alternative biomarkers in monitoring biological effects of contaminants, conflicting results between molecular and biochemical responses are quite frequent. The links between effects occurring at various intracellular levels can be masked by non-genomic processes affecting mRNA stability and protein turnover, different timing for transcriptional and translational mechanisms, metabolic capability of tissues, post-transcriptional modifications of proteins, bi-phasic responses of antioxidant enzymes and interactions occurring in chemical mixtures. In this respect, caution should be taken in monitoring studies where mRNA levels of antioxidants could represent a snapshot of cell activity at a given time, not an effective endpoint of environmental pollutants.

Oxidative stress parameters induced by exposure to either cadmium or 17β-estradiol on Mytilus galloprovincialis hemocytes. The role of signaling molecules

The aim of the present study was to determine and compare the possible effects of exposure to an estrogen, 17β-estradiol and to a metal, cadmium on oxidative parameters of Mytilus galloprovincialis hemocytes and to elucidate the signaling pathways that probably mediate the studied effects exerted by these two chemicals. In addition, it was of interest to investigate if the studied parameters could constitute biomarkers for aquatic pollution monitoring. Our results suggest that micromolar concentrations of either cadmium or 17β-estradiol affected the redox status of mussels by modulating oxidative parameters and antioxidant enzymes gene expression in mussel M. galloprovincialis hemocytes. In particular, our results showed that treatment of hemocytes with either 5 μM of cadmium chloride or with 25 nM of 17β-estradiol for 30 min caused significant increased ROS production; this led to oxidative damage exemplified by significant increased DNA damage, protein carbonylation and lipid peroxidation, as well as increased mRNA levels of the antioxidant enzymes catalase (CAT), superoxide dismoutase (SOD) and glutathione S-transferase (GST). Furthermore, our results suggest that either cadmium or 17β-estradiol signal is mediated either through one of the already known pathways initiated by photatidyl-inositol 3-kinase (PI3K) and reaching Na(+)/H(+) exchanger (NHE) probably through protein kinase C (PKC) or a kinase-mediated signaling pathway that involves in most of the cases NHE, PKC, Ca(2+)-dependent PKC isoforms, PI3-K, NADPH oxidase, nitric oxide (NO) synthase, c-Jun N-terminal kinase (JNK) and cyclic adenosine-3'-5'-monophosphate (cAMP). Our results also attribute a protective role to cAMP, since pre-elevated intracellular cAMP levels inhibited the signal induced by each exposure. Finally, since aquatic invertebrates have been the most widely used monitoring organisms for pollution impact evaluation in marine environments and taking under consideration the positive correlation obtained between the studied parameters, we can suggest the simultaneous use of these oxidative stress parameters offering an effective early warning system in biomonitoring of aquatic environments.

Heavy-metal levels in feathers of cattle egret and their surrounding environment: a case of the Punjab Province, Pakistan

Levels of 10 heavy metals in cattle egret chick feathers, prey, and surrounding soils from three heronries in Punjab Province, Pakistan, were assessed by atomic absorption spectrophotometry. Mean levels of cadmium (Cd), iron (Fe), chromium (Cr), and lithium (Li) in feathers, manganese (Mn), cobalt (Co), and nickel (Ni) in prey, and lead (Pb), iron (Fe), chromium (Cr), zinc (Zn), cobalt (Co), and lithium (Li) in soils were significantly different among Trimun Headworks, Shorkot, and Mailsi heroneries. Mean levels of Pb (43.10 μg/g), Cr (35.77 μg/g), Co (18.34 μg/g), Cu (0.20 μg/g), and Ni (0.22 μg/g) in feathers were significantly greater at Mailsi, and Mn (3.07 μg/g), Zn (18.83 μg/g), and Li (1.5 μg/g) levels were significantly greater at Shorkot. Multivariate analysis identified that some metals, such as Fe, Zn, and Li, in feathers were either associated with natural sources or with human-related activities, whereas Ni, Cr, Pb, Cd, Cu, Co, and Mn were correlated mainly with anthropogenic processes. Alarming levels were recorded for Cr, Pb, and Cd in feathers that were above threshold levels that may affect cattle egret flighting capacity and reproduction, thus leading to their population decline in Punjab Province. The results of this study provide evidence for the potential of feathers of cattle egret to be used as a biomonitor for the local heavy-metal contamination.

Copper/zinc superoxide dismutase from the Cladoceran Daphnia magna: molecular cloning and expression in response to different acute environmental stressors

The copper/zinc superoxide dismutase (Cu/Zn-SOD) is a representative antioxidant enzyme that is responsible for the conversion of superoxide to oxygen and hydrogen peroxide in aerobic organisms. Cu/Zn-SOD mRNAs have been cloned from many species and employed as useful biomarkers of oxidative stresses. In the present study, we cloned Cu/Zn-SOD cDNA from the cladoceran Daphnia magna, analyzed its catalytic properties, and investigated mRNA expression patterns after exposure to known oxidative stressors. The full-length Cu/Zn-SOD of the D. magna (Dm-Cu/Zn-SOD) sequence consisted of 703 bp nucleotides, encoding 178 amino acids, showing well-conserved domains that were required for metal binding and several common characteristics. The deduced amino acid sequence of Dm-Cu/Zn-SOD showed that it shared high identity with Daphnia pulex (88%), Alvinella pompejana (56%), and Cristaria plicata (56%). The phylogenetic analysis indicated that Dm-Cu/Zn-SOD was highly homologous to D. pulex. The variation of Dm-Cu/Zn-SOD mRNA expression was quantified by real-time PCR, and the results indicated that the expression was up-regulated after 48-h exposure to copper, un-ionized ammonia, and low dissolved oxygen. This study shows that the Dm-Cu/Zn-SOD mRNA could be successfully employed as a biomarker of oxidative stress, which is a common mode of toxicity for many other aquatic hazardous materials.

Contamination by metals and pharmaceuticals in northern Taihu Lake (China) and its relation to integrated biomarker response in fish

Taihu Lake is the largest shallow freshwater lake in eastern China and is suffering not only from an increasingly serious threat of eutrophication but also potential ecological risk due to the input of emerging contaminants. Active biomonitoring was conducted in Taihu Lake using transplanted goldfish (Carassius auratus) to determine the contamination by pharmaceuticals and metals and to assess the potential ecological risk. A suite of biomarkers including acetylcholinesterase, ethoxyresorufin O-deethylase, glutathione S-transferase, glutathione peroxidase and superoxide dismutase activities in fish after 7, 14, 21 and 28 days of exposure in situ, as well as pharmaceuticals and metals in water, were determined during the field exposure period. The results indicate that pharmaceuticals exist mainly in Zhushan Bay and Meiliang Bay, while metals are present mainly in Gong Bay. An integrated biomarker response (IBR) was calculated and used to evaluate the ecological risk of the polluted area of Taihu Lake. It was found that Zhushan Bay might present higher risk to fish, followed by Meiliang Bay. IBR values were in good agreement with copper and caffeine concentrations.

The yellow catfish, Pelteobagrus fulvidraco (Siluriformes) metallothionein cDNA: molecular cloning and transcript expression level in response to exposure to the heavy metals Cd, Cu, and Zn

Metallothionein (MT) has been used extensively as a potential molecular biomarker to detect heavy metal pollution in aquatic organisms. In order to investigate the modulation effect of heavy metals and to establish suitable biomarkers for the monitoring of heavy metal pollution, Pelteobagrus fulvidraco metallothionein gene was characterized as the first report in the family Bagridae. Pf-MT transcript was detected at high levels in liver, gonad, kidney, and brain compared to other tissues. A time-course study in response to waterborne Cd (5 ppm) revealed that a significant increase in the Pf-MT transcript abundance was observed at 6 h in gill, kidney, and liver. These elevated levels were kept for 96 h, implying that Cd distributed fast into different organs and was involved in the tissue-specific induction pattern. We observed a significant Pf-MT transcript increase in liver tissues at 48 h, followed by gill at 12 h and intestine at 48 h after Cd exposure. This indicates hepatic MT expression as a potential biomarker of acute Cd exposure in this species. Cd-binding ability of recombinant Pf-MT protein provided evidence for sensitivity to Cd and other heavy metal exposure. In the case of Zn exposure (1 ppm), a significant increase in Pf-MT transcript abundance was observed at 12 h, and a peak induction level reaching sixfold at 24 h was kept until 48 h, showing similar transcript induction patterns with Cd. A high level of Pf-MT mRNA after exposure to Cu (1 ppm) was observed at 12 h that gradually increased until 96 h with a 12-fold induction, revealing a long-lasting induction and somewhat dissimilar pattern compared to other metals in liver. Our results demonstrate that Pf-MT can be induced by heavy metals in a tissue-specific and metal-specific manner and plays probably a conserved role in metal detoxification. This study provides new information on P. fulvidraco metallothionein gene for the use of biomarkers indicating metal pollution in fish.

Oxidative stress indicators and trace elements in the blue shark (Prionace glauca) off the east coast of the Mexican Pacific Ocean

Trace element concentrations and oxidative stress indicators (including production of reactive oxygen species (ROS), antioxidant enzyme activities and oxidative damage) were measured in muscle of blue sharks collected along the west coast of Baja California Sur to determine potential differences by sex and maturity cohorts. Mercury (Hg) concentration in muscle samples from larger sharks (>200 cm LT) exceeded the permissible limit (>1 ppm wet weight) for human consumption set by numerous international agencies. Significant differences were found in Hg concentrations (mature>immature; males>females), and in protein carbonyl concentrations (male>female); however, except for carbonyl protein levels, no significant differences by sex or maturity stage were found in the oxidative stress indicators. Differences between sexes and maturity stages in trace element concentration and carbonyl protein levels in blue shark muscle may be related to variations in diet within different cohorts.

Tissue-specific accumulation of cadmium and its effects on antioxidative responses in Japanese flounder juveniles

This study investigated the accumulation of cadmium (0-8 mg Cd L⁻¹) and its toxicological effects on oxidative stress biomarkers in different tissues of Japanese flounder juveniles. Following Cd exposure for 28 d, accumulation of Cd in fish was dose-dependent and tissue-specific, with the greatest accumulation in the liver, followed by the kidney, gill, and muscle. Although the gill and liver mounted active antioxidant responses at ≥ 4 mg L⁻¹ Cd including a decrease in glutathione level and GST and GPx activities, the antioxidant response failed to prevent lipid peroxidation induction in these organs. In the kidney, increased GPx and GST activities and decreased SOD activity were observed in fish exposed to high Cd concentrations, but LPO levels did not significantly differ among the exposure concentrations. The gill was most sensitive to oxidative damage, followed by the liver; the kidney was the least affected tissue.

Transcriptomic analyses in a benthic fish exposed to contaminated estuarine sediments through laboratory and in situ bioassays

The transcription of contaminant response-related genes was investigated in juvenile Senegalese soles exposed to sediments from three distinct sites (a reference plus two contaminated) of a Portuguese estuary (the Sado, W Portugal) through simultaneous 28-day laboratory and in situ bioassays. Transcription of cytochrome P450 1A (CYP1A), metallothionein 1 (MT1), glutathione peroxidase (GPx), catalase (CAT), caspase 3 (CASP3) and 90 kDa heat-shock protein alpha (HSP90AA) was surveyed in the liver by real-time PCR. CASP3 transcription analysis was complemented by surveying apoptosis through the TUNEL reaction. After 14 days of exposure, relative transcription was either reduced or decreased in fish exposed to the contaminated sediments, revealing a disturbance stress phase during which animals failed to respond to insult. After 28 days of exposure all genes' transcription responded to contamination but laboratory and in situ assays depicted distinct patterns of regulation. Although sediments revealed a combination of organic and inorganic toxicants, transcription of the CYP1A gene was consistently correlated to organic contaminants. Metallothionein regulation was found correlated to metallic and organic xenobiotic contamination in the laboratory and in situ, respectively. The transcription of oxidative stress-related genes can be a good indicator of general stress but caution is mandatory when interpreting the results since regulation may be influenced by multiple factors. As for MT1, HSP90 up-regulation has potential to be a good indicator for total contamination, as well as the CASP3 gene, even though hepatocyte apoptosis depicted values inconsistent with sediment contamination, showing that programmed cell death did not directly depend on caspase transcription alone.

Expression of catalase and glutathione S-transferase genes in Chironomus riparius on exposure to cadmium and nonylphenol

Antioxidant enzymes play important roles in the protection against oxidative damage caused by environmental pollutants by scavenging high levels of reactive oxygen species and have been quantified as oxidative stress markers. However, combining mRNA expressions of genes coding for detoxification enzymes along with enzyme activities will be more useful biomarkers of stress. Therefore, in this study the cDNA of the catalase gene from the aquatic midge, Chironomus riparius (CrCAT) was sequenced using 454 pyrosequencing. The 2139 bp CrCAT cDNA included an open reading frame of 1503 bp encoding a putative protein of 500 amino acids with a predicted molecular mass of 56.72 kDa. There was an 18 bp 5' and a long 618 bp 3' untranslated region with a polyadenylation signal site (AATAAA). The deduced amino acid sequence of CrCAT contained several highly conserved motifs including the proximal heme-ligand signature sequence RLFSYNDTX and the proximal active site signature FXRERIPERVVHAKGXGA. A comparative analysis showed the presence of conserved amino acid residues and all of the catalytic amino acids (His(70), Asn(143), and Tyr(353)) were conserved in all species. The CrCAT contained three potential glycosylation sites and a peroxisome targeting signal of 'AKM'. The mRNA was detected using RT-PCR at all developmental stages. The time-course expression of CrCAT was measured using quantitative real-time PCR after exposure to different concentration and durations of Paraquat (PQ), cadmium chloride (Cd) and nonylphenol (NP). The expression of CrCAT was significantly up regulated on exposure to 50 and 100mg/L PQ for 12 and 24h. Among the different concentrations and durations of Cd tested, significantly highest level of expression for CrCAT mRNA and catalase enzyme activity was observed on exposure to 10mg/L for 24h. In the case of NP, the highest level of CrCAT expression was observed after exposure to 100 μg/L for 24h. The expression profiles of three selected C. riparius glutathione S-transferase genes (CrGSTs) viz. CrGSTdelta3, CrGSTsigma4 and CrGSTepsilon1 was also studied on exposure to NP and were up or down regulated at different time points and concentrations. Significantly highest level of expression for CrGSTdelta3 was observed after 48 h and for CrGSTsigma4 and CrGSTepsilon1 after 24h exposure to 100 μg/L of NP. The results show that CrGSTs and CrCAT could be used as potential biomarkers in C. riparius for aquatic ecotoxicological studies.

Molecular and biochemical biomarkers in environmental monitoring: a comparison of biotransformation and antioxidant defense systems in multiple tissues

The cytochrome P450 pathway and antioxidant responses are known for their responsiveness to environmental pollutants and are frequently used as biomarkers at the transcriptional, translational and catalytic levels. Although molecular responses are often assumed to reflect similar changes in enzyme function, several factors can influence intracellular effects, including mRNA stability and protein turnover, signal sensing and transduction, post-translational modifications of proteins, and multiple mode of action of chemicals in complex mixtures. The aim of this study was to use experimental data for a general discussion on the importance of mechanisms modulating transcriptional and catalytic responses of these pathways, and the resulting implications for environmental monitoring. The European eel Anguilla anguilla was selected as fish model to compare the effects of polluted sediments on gene expression and functional levels of cytochrome P450, glutathione S-transferases, UDP-glucoronosyl transferases, catalase, glutathione peroxidases, superoxide dismutase, glutathione, glutathione reductase, glucose 6-phosphate dehydrogenase and γ-glutamylcysteine ligase in the liver and gills. The overall results confirmed significant changes in gene transcription related to biotransformation and oxyradical metabolism, but also supported the evidence of a frequent dissociation between mRNA expression and protein activity. More similar trends of variations and exposure-dependent relationships was observed in the liver for transcriptional and catalytic responses of those pathways closely regulated by specific interactions between substrate, transcription factors, gene and metabolizing protein (i.e. phase I and phase II). On the other hand, the lower metabolism and the cellular machinery of gill cells may prevent elevated transcriptional responsiveness to be translated to an adequate functional response of a protein. Relationships between transcriptional and catalytic effects were often inconsistent for antioxidant responses confirming the complexity of interactions between exposure to chemical pollutants and regulation of oxidative stress responses. Oxidative stress responses may not necessarily be associated with transcriptional variations of genes, but rather with post-translational modifications of proteins. These mechanisms are just beginning to be revealed in marine organisms, but their characterization will be fundamental for better understanding of the implications of variations in gene expressions according to system, tissue, intensity and duration of exposure.

Metallothionein as potential biomarker of cadmium exposure in Persian sturgeon (Acipenser persicus)

Metallothionein (MT) concentration in gills, liver, and kidney tissues of Persian sturgeon (Acipenser persicus) were determined following exposure to sublethal levels of waterborne cadmium (Cd) (50, 400, and 1,000 μg l(-1)) after 1, 2, 4, and 14 days. The increases of MT from background levels were 4.6-, 3-, and 2.8-fold for kidney, liver, and gills, respectively. The results showed that MT level change in the kidney is time and concentration dependent. Also, cortisol measurement revealed elevation at the day 1 of exposure and followed by MT increase in the liver. Cd concentrations in the cytosol of experimental tissues were measured, and the results indicated that Cd levels in the cytosol of liver, kidney, and gills increased 240.71-, 32.05-, and 40.16-fold, respectively, 14 days after exposure to 1,000 μg l(-1) Cd. The accumulation of Cd in cytosol of tissues is in the order of liver > gills > kidney. Pearson correlation coefficients showed that the MT content in kidney is correlated with Cd concentration, the value of which is more than in liver and gills. Thus, kidney can be considered as a tissue indicator in A. persicus for waterborne Cd contamination.

Chemoprotection of lipoic acid against microcystin-induced toxicosis in common carp (Cyprinus carpio, Cyprinidae)

This paper evaluated the chemoprotective effect of lipoic acid (LA) against microcystin (MC) toxicity in carp Cyprinus carpio. To determine the LA dose and the time necessary for the induction of three different classes (alpha, mu and pi) of glutathione S-transferase (GST) gene transcription, carp were i.p. injected with 40mg/kg lipoic acid solution. A group was killed 24h after the first i.p. injection (condition 1); another group received two i.p. injections with a 24h of interval between each one and was killed 48h after the first injection (condition 2) and a third group received one i.p. injection and was killed 48h latter (condition 3). Results showed that LA was effective in promoting an increase in GSTs gene transcription in liver only in the condition 2. A second experiment was done, where carp pre-treated with LA (condition 2) were gavaged twice with a 24h interval with 50μg MC/kg. Ninety-six hours after experiment beginning, carp were killed, and organs were dissected. Results of GST activity in liver and brain suggest that LA can be a useful chemoprotection agent against MC induced toxicity, stimulating detoxification through the increment of GST activity (brain) or through reversion of GST inhibition (liver).

Response of Cyprinus carpio to copper exposure: alterations in reduced glutathione, catalase and proteins electrophoretic patterns

This study was conducted to characterize the alterations in reduced glutathione (GSH) level, catalase (CAT) activity and proteins electrophoretic patterns in response to sublethal copper (Cu) exposure in Cyprinus carpio and to determine whether these responses are related to Cu accumulation in gills, chosen as target tissue. Fish were exposed to 0.1 and 1.0 mg/l Cu for 10 and 20 days. There were increasing level of Cu in the gill with increasing concentrations of metal in the exposure medium, and with increasing duration of exposure. GSH level and CAT activity increased in fish exposed to 1.0 mg/l Cu for both exposure periods, while no change was detected at the lower Cu concentration. Electrophoretic patterns of gill proteins by sodium dodecyl sulphate gel electrophoresis (SDS-PAGE) consist of 25-, 26-, 30-, 44- and 48-kDA medium molecular weight proteins (MMP) for five bands and 64-, 72-, 90- and 101-kDA high molecular weight proteins (HMP) for four bands in both control and treatment groups. The levels of 25-, 26- and 30-kDA MMP and 72- and 90-kDA HMP increased in response to Cu exposure. The present study demonstrated that Cu caused stress in fish gills and an acclimation with induction of GSH, CAT, MMP and HMP, which were important in the protection against metal damage, was observed.

Metallothionein biosynthesis as a detoxification mechanism in mercury exposure in fish, spotted scat (Scatophagus argus)

It is of crucial importance to study on the biomarkers types to assess the specification of the pollutants and health status of marine ecosystems in environmental evaluation projects. In this respect, total metallothionein biosynthesis and mercury bioaccumulation in the liver and gills under acute mercury exposure were investigated in fish, Scat (Scatophagus argus). Spotted scat was exposed to different mercury concentrations (0, 10, 20, 30) for 24, 48, 72 h. Total MT levels were determined by enzyme-linked immunosorbent assay (ELISA) method. Mercury contents were determined through cold vapor atomic absorption spectrometry (CVAAS). Induction of MT during exposure was tissue specific, displaying different response pattern in gills and liver. Mercury accumulated in liver much higher than in gills and the latter also showed lower MT level (P<0.05). MT biosynthesis in liver showed a significant (P<0.05) increase after exposure to different mercury concentration with increase in exposure time, whereas total MT content did not significantly (P>0.05) change in gills except for 72 h exposure at 30 μg l(-1). Nonetheless, the relationship between MT biosynthesis and Mercury bioaccumulation in both tissues was significant (P<0.05). The results suggest that this form of MT in S. argus was Hg inducible and could be extended as a biomarker of mercury pollution in marine ecosystems.