Biomarker responses of Cu-induced toxicity in European seabass Dicentrarchus labrax: Assessing oxidative stress and histopathological alterations

Effects of cadmium exposure on metabolism, antioxidant defense, immune function, and the hepatopancreas transcriptome of Cipangopaludina cathayensis

Cadmium (Cd) is a common contaminant in aquatic environments. However, little is known about the mechanisms underlying Cd toxicity in the freshwater snail Cipangopaludina cathayensis (Heude, 1890). This study to investigate the toxic effects of Cd on the standard metabolism, antioxidant activities, immune function, and hepatopancreas transcriptome profiles of C. cathayensis. C. cathayensis was exposed to 0.25, 0.5, 1.0, or 1.5 mg/L Cd for 3 h, with results showing that Cd significantly inhibited oxygen consumption and ammonia excretion and disrupted the respiratory metabolism of C. cathayensis. In addition, the O:N ratio dropped below 7, indicating that C. cathayensis may rely exclusively on proteins as an energy source under Cd stress. To understand how Cd impacts the antioxidant activities, immune function, and transcriptional profiles, C. cathayensis were exposed to 0.5 (low exposure, L14) or 1.5 (high exposure, H14) mg/L Cd for 14 days. Our results indicate that Cd exposure leads to oxidative stress and immunosuppression, with the latter effect being larger for exposure to higher Cd concentrations. A total of 2172 differentially expressed genes (DEGs) were identified by transcriptome analysis of the hepatopancreas, of which 885 were upregulated and 1287 were downregulated. Gene ontology and KEGG analyses revealed that the DEGs in the H14 group are enriched for energy generation terms and the "oxidative phosphorylation" pathway, respectively. Therefore, up-regulation of energy metabolism may be an adaptive strategy under Cd stress. Moreover, several genes involved in antioxidant activity were downregulated, whereas genes related to reactive oxygen species generation were upregulated. In addition, many immunity-related genes were identified within the DEGs, indicating that Cd toxicity may affect immune defense. Further, DEGs in the H14 group were enriched for disease-associated pathways. Taken together, our results indicate that Cd exposure leads to metabolic disorders, oxidative stress, and immunosuppression and thus may potentially contribute to disease outbreaks.

Histological alterations, oxidative stress, and inflammatory response in the liver of swamp eel (Monopterus albus) acutely exposed to copper

Copper (Cu) is widely used as an essential trace element in diets as well as a therapeutic chemical. However, excessive Cu has deleterious effects on organisms, including teleosts. Although numerous toxic effects of Cu have been reported, the effects of Cu exposure on the swamp eel (Monopterus albus) as well as the underlying mechanisms have not yet been elucidated. In this study, swamp eels were acutely exposed to 100, 200, and 400 μg/L of Cu for 96 h to evaluate liver histopathology, oxidative stress, and inflammation. Dissolution of hepatocyte membrane, vacuolar degeneration, and inflammatory cell infiltration were detected in the livers of the Cu-treated swamp eels, especially in the 400 μg Cu/L group. Cu-induced hepatic dysfunction was further verified by the elevated activities of glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT) and transcript levels of GOT and GPT genes. In addition, Cu exposure decreased the activities of total superoxide dismutase T-SOD and catalase (CAT) and the contents of glutathione (GSH) and total antioxidant capacity (T-AOC) and increased the levels of malondialdehyde (MDA). Cu exposure also significantly decreased the transcript levels of glutathione synthetase (GSS) and increased the transcript levels of SOD1, SOD2, CAT, and heme oxygenase-1 (HO-1) genes. Furthermore, pro-inflammatory genes such as interleukin (IL)-1β, tumor necrosis factor-α (TNF-α), and IL-8 were significantly upregulated. These results indicate that Cu induces oxidative stress and inflammatory response and causes pathological changes in the liver of the swamp eel.

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.

Physiological performance of common carp (Cyprinus carpio, L., 1758) exposed to a sublethal copper/zinc/cadmium mixture

In a natural ecosystem, fish are subjected to a multitude of variable environmental factors. It is important to analyze the impact of combined factors to obtain a realistic understanding of the mixed stress occurring in nature. In this study, the physiological performance of juvenile common carp (Cyprinus carpio) exposed for one week to an environmentally relevant metal mixture (4.8 μg/L of copper; 2.9 μg/L of cadmium and 206.8 μg/L of zinc) and to two temperatures (10 °C and 20 °C), were evaluated. After 1, 3 and 7 days, standard (SMR) and maximum metabolic rate (MMR) were measured and aerobic scope (AS) was calculated. In addition, hematocrit, muscle lactate, histology of the gills and metal accumulation in gills were measured. While SMR, MMR and AS were elevated at the higher temperature, the metal mixture did not have a strong effect on these parameters. At 20 °C, SMR transiently increased, but no significant changes were observed for MMR and AS. During metal exposure, hematocrit levels were elevated in the 20 °C group. The bioaccumulation of Cd in the gills reflected the increased metabolic rate at the higher temperature, with more accumulation at 20 °C than at 10 °C. Anaerobic metabolism was not increased, which corresponds with the lack of significant histopathological damage in the gill tissue. These results show that common carp handled these metal exposures well, although increased temperature led to higher Cd accumulation and necessitated increased hematocrit levels to maintain aerobic performance.

Ecotoxicity assessment of a molybdenum mining effluent using acute lethal, oxidative stress, and osmoregulatory endpoints in zebrafish (Danio rerio)

The present study investigated the ecotoxicity of raw mining effluent from the largest molybdenum (Mo) open-pit mine in the Qinling mountains, China, and the treated effluent with neutralization and coagulation/adsorption processes, using zebrafish (Danio rerio). The results showed the following: (1) the mining effluent is acid mine drainage (AMD) and is highly toxic to zebrafish with a 96-h median lethal concentration (LC₅₀) of 3.80% (volume percentage) of the raw effluent; (2) sublethal concentrations of the raw effluent (1/50, 1/10, and 1/2 96-h LC₅₀) induced oxidative stress and osmoregulatory impairment, as reflected by the alterations in activities of superoxide dismutase and catalase and contents of malondialdehyde, and inhibition of Na⁺, K⁺-ATPase activity in gills and muscle after 28 days of sub-chronic exposure when compared with the unexposed group; and (3) the treatment of the raw effluent with neutralizer (NaOH) and adsorbent activated carbon reduced the acute lethal effect of raw effluent. The used endpoints including acute lethal and biochemical parameters related to oxidative stress and osmoregulatory impairment in zebrafish are cost-effective for toxicity assessment of AMD like the studied Mo mining effluent. Mining effluent management strategies extended by these results, i.e., the restriction of discharging raw and diluted effluent to adjacent waterways and the introduction of bio-monitoring system across all mining drainages in this area, were also proposed and discussed.

Consequences of oxidative damage on the fatty acid profile in muscle of Cichlasoma amazonarum acutely exposed to copper

Rapid industrialization results in the production of large quantities of waste that are commonly discharged into water bodies, leading to the damage of the aquatic ecosystem and freshwater organisms. Copper (Cu) can induce oxidative damage in fish muscle, the main fish portion that is consumed by humans. However, the responses of the Amazon fish Cichlasoma amazonarum and its capacity to withstand acute Cu concentrations found in Amazon water around mines remain unknown. Thus, the aim of this study was to evaluate whether exposure to Cu causes muscle oxidative stress and/or oxidative damage and impairs the fillet fatty acid profile of C. amazonarum acutely exposed to Cu found in Amazon waters around mines. Muscle reactive oxygen species and protein carbonylation levels were significantly higher in fish exposed to 1500 μg/L Cu compared with the control group, while muscle lipid peroxidation levels were significantly higher in fish exposed to 500, 750, and 1500 μg/L Cu compared with control group. Muscle antioxidant capacity against peroxyl radical's levels and glutathione peroxidase activity were significantly lower in fish exposed to 1500 μg/L Cu compared with the control group, while muscle superoxide dismutase activity was significantly lower in fish exposed to 750 and 1500 μg/L Cu compared with control group. The total content of saturated fatty acids was significantly higher in fish exposed to 1500 μg/L Cu compared with the control group, while the total content of monounsaturated fatty acids and sum of n3 fatty acids were significantly lower in fish exposed to 1500 μg/L Cu compared with control group. No significant difference was observed regarding muscle catalase, glutathione S-transferase, and glutathione reductase activities. Based on these lines of evidence, the results of this comprehensive study agree with the initial hypothesis that the exposure to Cu found in Amazon water around mines induces oxidative damage and inhibits enzymatic and non-enzymatic antioxidant response in the muscle of C. amazonarum exposed to high Cu levels. Moreover, the impairment of the fillet fatty acid profile appears to be mediated by oxidative damage, representing a negative impact on fish health.

Antagonistic bioaccumulation of waterborne Cu(II) and Cd(II) in common carp (Cyprinus carpio) and effects on ion-homeostasis and defensive mechanisms

In the aquatic environment, metals are present as mixtures, therefore studies on mixture toxicity are crucial to thoroughly understand their toxic effects on aquatic organisms. Common carp (Cyprinus carpio) were used to assess the effects of short-term Cu(II) and Cd(II) mixtures, using a fixed concentration of one of the metals, representing 25 % of its individual 96h-LC₅₀ (concentration lethal for 50 % of the population) combined with a variable concentration of the other metal corresponding to 10, 25 or 50 % of its 96h-LC₅₀, and vice versa. Our results showed a fast Cu and Cd bioaccumulation, with the percentage of increase in the order gill > liver > carcass. An inhibitory effect of Cu on Cd uptake was observed; higher Cu concentrations at fixed Cd levels resulted in a decreased accumulation of Cd. The presence of the two metal ions resulted in losses of total Na, K and Ca. Fish tried to compensate for the Na loss through the induction of the genes coding for Na⁺/K⁺-ATPase and H⁺-ATPase. Additionally, a counterintuitive induction of the gene encoding the high affinity copper transporter (CTR1) occurred, while a downregulation was expected to prevent further metal ion uptake. An induction of defensive mechanisms, both metal ion binding protein and anti-oxidant defences, was observed. Despite the metal accumulation and electrolyte loss, the low mortality suggest that common carp is able to cope with these metal levels, at least during a one-week exposure.

Effect of sublethal gradient concentrations of nickel on postlarvae of Penaeus monodon, Perna viridis and Terapon jarbua: Enzyme activities and histopathological changes

The present study evaluates the enzyme activities and histopathological changes in the post larvae (PL) of shrimp (Penaeus monodon), green mussel (Perna viridis) and fingerlings of crescent perch (Terapon jarbua) exposed to sublethal gradient concentrations of Nickel (Ni). The median lethal concentration (LC₅₀) values were 2.49, 66.03 and 43.92 mg Ni L^-1 derived for the PL of shrimp, green mussel and fish fingerlings respectively. No Observed Effect Concentration (NOEC), Lowest Observed Effect Concentration (LOEC) and chronic values of the PL of shrimp were 46.5, 73.0 and 58.3 μg Ni L^-1 derived for the 21-d survival endpoint. The NOEC, LOEC and chronic values for the 30-d survival endpoint of the green mussels and fish fingerlings were 4.6, 6.32, 5.4 and 1.95, 2.6, 2.25 mg Ni L^-1 respectively. The isoforms of esterase, superoxide dismutase and malate dehydrogenase activities in the whole body tissues of test organisms were studied by native polyacrylamide gel electrophoresis after exposure to Ni. Histological examination of compound eye sections of shrimp revealed deformation, compression, fusion and detachement in the corneal cells from the corneal facet of the ommatidia indicating cellular anomalies due to Ni toxicity. Gill sections of the green mussel witnessed reduced haemolymph in sinuses of gill filaments, degenerative changes in interfilamentous junction and necrosis of frontal ciliated epithelial cells with vacuoles after exposure to Ni. Nickel affects the vision of shrimp and fish fingerlings, gills and byssus of green mussels.

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.

Essential element Cu and non-essential element Hg exposures have different toxicological effects in the liver of large yellow croaker

The objective was to compare the different effects of essential element Cu and non-essential element Hg on antioxidant and inflammatory responses in the liver of large yellow croaker Larimichthys crocea. Fish were exposed to Cu stresses (72 and 288 μg L^-1) and Hg stresses (14 and 56 μg L^-1) for 96 h. High-dose Cu increased metallothioneins (MTs) levels and immune defenses in response to elevated reactive oxygen species (ROS), but low-dose Cu had no effect on ROS. High-dose Hg reduced antioxidant and inflammatory responses, which contributed to the increment of ROS. MTs may be a suitable biomarker to assess Cu contamination, but no relationship was observed between MTs levels and Hg content. Furthermore, NFE2-related nuclear factor 2 (Nrf2) and nuclear transcription factor κB (NF-κB) were positively related to their respective target genes in the Cu-exposed groups. In conclusion, Cu and Hg induced some differences in antioxidant and inflammatory responses, which providing some novel insights into toxicological effects of Cu and Hg stresses.

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.