Sodium-dependent copper uptake across epithelia: a review of rationale with experimental evidence from gill and intestine

Trace metals in the teleost fish gill: biological roles, uptake regulation, and detoxification mechanisms

In fish, the gill plays a vital role in regulating the absorption of trace metals and is also highly susceptible to metal toxicity. Trace metals such as iron (Fe), copper (Cu), zinc (Zn), and manganese (Mn) are involved in various catalytic activities and molecular binding within the gill, thereby supporting a range of physiological processes in this organ. While beneficial at normal levels, these metals can become toxic when present in excess. Conversely, nonessential metals like cadmium (Cd) and lead (Pb) can gain entry into gill cells through similar metal transport pathways, potentially interfering with various cellular processes. The transepithelial transport of these metals across the gill epithelium is governed by a variety of metal transport and metal binding proteins. These include the Cu transporter 1 (CTR1), divalent metal transporter 1 (DMT1), and members of the Zrt-/Irt-like protein (ZIP) and zinc transport (ZnT) families. Additionally, some of these metals can compete with major ions (e.g., calcium, sodium) for absorption sites in the gill. This complex crosstalk suggests an interdependent mechanism that balances metal uptake to meet physiological needs while preventing excessive accumulation. In this article, I review the roles of trace metals in proteins/enzymes that support the different functions in the gill of teleost fish. I also discuss current understanding of the pathways involved in regulating the branchial uptake of metals and their influence on ionic regulation, and the potential detoxification mechanisms in the gill. Finally, I summarize knowledge gaps and potential areas for further investigation.

Interactive Effects of Copper-Silver Mixtures at the Intestinal Epithelium of Rainbow Trout: An In Vitro Approach

While metals are present in mixture in the environment, metal toxicity studies are usually conducted on an individual metal basis. There is a paucity of data in the existing literature regarding specific metal-metal interactions and their effect on metal toxicity and bioavailability. We studied interactions of a silver (Ag)-copper (Cu) mixture at the intestinal epithelium using an intestinal cell line derived from rainbow trout (Oncorhynchus mykiss), the RTgutGC. Exposures were conducted in media containing different chloride concentrations (low chloride, 1 mM; high chloride, 146 mM), thus resulting in different metal speciation. Cytotoxicity was evaluated based on two endpoints, cell metabolic activity and cell membrane integrity. The Ag-Cu mixture toxicity was assessed using two designs: independent action and concentration addition. Metal mixture bioavailability was studied by exposing cells to 500 nM of Ag or Cu as a single metal or a mixture (i.e., 500 nM of Cu plus 500 nM of Ag). We found an antagonistic effect in the low-chloride medium and an additive/synergistic effect in the high-chloride medium. We found that Cu dominates over Ag toxicity and bioavailability, indicating a competitive inhibition when both metals are present as free metal ions in the exposure media, which supports our hypothesis. Our study also suggests different mechanisms of uptake of free metal ions and metal complexes. The study adds valuable information to our understanding of the role of metal speciation on metal mixture toxicity and bioavailability. Environ Toxicol Chem 2024;43:105-114. © 2023 SETAC.

Influences of chronic copper exposure on intestinal histology, antioxidative and immune status, and transcriptomic response in freshwater grouper (Acrossocheilus fasciatus)

Copper (Cu) contamination is commonly found in both natural water environments and fish farms, and it can cause severe damage to different fish organs, but Cu-induced intestinal damage has been rarely studied. This study subjected three groups of freshwater grouper (Acrossocheilus fasciatus) (initial weight: 1.56 ± 0.10 g) to 0 mg/L, 0.01 mg/L, and 0.04 mg/L Cu2+ for 30 days, named Con, Cu0.01, and Cu0.04 groups, respectively. The histological observation indicated that the Cu0.04 group caused a significant decrease in villus length, lamina propria width, and muscular thickness compared to the Con group (P < 0.05). Additionally, the Cu0.04 group significantly increased intestinal superoxide dismutase (SOD), glutathione peroxidase (GPx), lysozyme (LZM) activities, as well as malondialdehyde (MDA) content than the Con group (P < 0.05). Meanwhile, the Cu0.01 and Cu0.04 groups showed significantly increased immunoglobulin M (IgM), complement 3 (C3), and glutathione (GSH) contents than the Con group (P < 0.05). Transcriptomic analysis revealed a total of 101 differentially expressed genes (DEGs), including 47 up-regulated and 54 down-regulated DEGs, were identified between the Cu0.04 and Con groups. Notably, the DEGs were mainly related to intestinal structure construction, immune functions, apoptosis, and resistance to DNA damage and pathogen infection. The findings suggest that chronic Cu exposure caused intestinal histological alterations, activated the antioxidative and immune systems, and induced systematic adaptation to cope with the physical barrier injury, DNA damage, and potential pathogen growth.

Differences in toxicity and accumulation of metal from copper oxide nanomaterials compared to copper sulphate in zebrafish embryos: Delayed hatching, the chorion barrier and physiological effects

The mechanisms of toxicity of engineered nanomaterials (ENMs) to the early life stages of freshwater fish, and the relative hazard compared to dissolved metals, is only partially understood. In the present study, zebrafish embryos were exposed to lethal concentrations of copper sulphate (CuSO₄) or copper oxide (CuO) ENMs (primary size ∼15 nm), and then the sub-lethal effects investigated at the LC₁₀ concentrations over 96 h. The 96 h-LC₅₀ (mean ± 95% CI) for CuSO₄ was 303 ± 14 µg Cu L^-1 compared to 53 ± 9.9 mg L^-1 of the whole material for CuO ENMs; with the ENMs being orders of magnitude less toxic than the metal salt. The EC₅₀ for hatching success was 76 ± 11 µg Cu L^-1 and 0.34 ± 0.78 mg L^-1 for CuSO₄ and CuO ENMs respectively. Failure to hatch was associated with bubbles and foam-looking perivitelline fluid (CuSO₄), or particulate material smothering the chorion (CuO ENMs). In the sub-lethal exposures, about 42% of the total Cu as CuSO₄ was internalised, as measured by Cu accumulation in the de-chorionated embryos, but for the ENMs exposures, nearly all (94%) of the total Cu was associated with chorion; indicating the chorion as an effective barrier to protect the embryo from the ENMs in the short term. Both forms of Cu exposure caused sodium (Na⁺) and calcium (Ca²⁺), but not magnesium (Mg²⁺), depletion from the embryos; and CuSO₄ caused some inhibition of the sodium pump (Na⁺/K⁺-ATPase) activity. Both forms of Cu exposure caused some loss of total glutathione (tGSH) in the embryos, but without induction of superoxide dismutase (SOD) activity. In conclusion, CuSO₄ was much more toxic than CuO ENMs to early life stage zebrafish, but there are subtle differences in the exposure and toxic mechanisms for each substance.

Role of the luminal composition on intestinal metal toxicity, bioavailability and bioreactivity: An in vitro approach based on the cell line RTgutGC

The bioavailability of metal complexes is poorly understood. To evaluate bioavailability and toxicity of neutral and charged complexes as well as free metal ions, Visual Minteq, a chemical equilibrium model, was used to design media containing different metal species. Two non-essential (silver and cadmium) and two essential (copper and zinc) metals were selected. The rainbow trout (Oncorhynchus mykiss) gut cell line (RTgutGC) was used to investigate bioavailability, bioreactivity and toxicity of the different metal species. Toxicity was measured using a multiple endpoint cytotoxicity assay, bioavailability by measuring intracellular metal concentration, and bioreactivity by quantification of mRNA level of the metal responsive genes, metallothionein (MT), glutathione reductase (GR) and zinc transporter 1 (ZnT1). Speciation calculations showed that silver and cadmium preferentially bind chloride, copper phosphate and bicarbonate, and zinc remained primarily as a free ion. Cysteine avidly complexed with all metals reducing toxicity, bioavailability and bioreactivity. Silver and copper toxicity was not affected by inorganic metal speciation, whereas cadmium and zinc toxicity was decreased by chloride complexation. Moreover, reduction of calcium concentration in the medium increased toxicity and bioavailability of cadmium and zinc. Bioavailability of silver and zinc was reduced by low chloride while cadmium bioavailability was increased by low chloride and in presence of bicarbonate. Copper bioavailability was not affected by the medium composition. Cadmium and silver were more bioreactive, independently from the medium composition, in comparison to copper and zinc (i.e., higher induction of MT and GR). Cadmium was the only metal able to induce MT in presence of cysteine. ZnT1 was induced by cadmium in low-chloride, by zinc in low-chloride low-calcium and by cadmium and copper in the bicarbonate media. Overall, this study demonstrates that metal complexation alone is not sufficient to explain metal toxicity, and that anion exchange mechanisms play a role in metal uptake and bioreactivity.

Effects of waterborne Pb/Cu mixture on Chinese toad, Bufo gargarizans tadpoles: morphological, histological, and intestinal microbiota assessment

Coexistence of heavy metals in aquatic environments exert complex effects on amphibians. Here, the adverse effects of Pb (0.14 μM) combined with Cu at concentrations of 0, 0.25, and 1.0 μM were investigated in Bufo gargarizans tadpoles. Tadpoles were chronically exposed from Gosner stage (Gs) 26 to Gs 38, and morphology of tadpoles as well as intestinal histology and bacterial community were assessed. Our results indicated that Pb+Cu1.0 exposure induced significant retardation of somatic mass, total length, intestine mass, and intestine length as well as intestinal histological alterations. Pb+Cu0.25 and Pb+Cu1.0 exposure were associated with the loss of gut bacterial diversity. Proteobacteria and Bacteroidetes were two dominant phyla in tadpoles independently of heavy metal exposure, but the abundance of Proteobacteria increased significantly in Pb+Cu1.0 group and Bacteroidetes decreased significantly in all treatment groups. Furthermore, functional prediction indicated that metabolic disorders were associated with Pb+Cu0.25 and Pb+Cu1.0 exposure. Overall, relative limited shifts in intestinal bacterial diversity, composition, and functionality caused by Pb+Cu0 exposure, while coexistence of Pb and Cu induced gut dysbiosis and might further cause disturbance of metabolic homeostasis. The findings of this study provide insights into the effects of Pb and Cu coexistence on the health of amphibians.

Real-time determination of water status upon simultaneous zebrafish exposure to sublethal concentrations of CuSO4

Water pollution from commonly occurring contaminants (metals, xenobiotics, etc.) is a serious global problem. Copper is a commonly occurring water contaminant. A variety of physiological and biological methods have been developed to monitor water quality. The assessment of biological responses is an effective method for identifying the harmful effects of contaminants on ecosystems. Fish is a highly recommended animal model in water quality monitoring. Swimming consistency (firmness) and respiratory metabolism (oxygen consumption rate, carbon dioxide excretion rate and respiratory quotient) are essential for fish to maintain body homeostasis toward coping with environmental stress. We exposed zebrafish to different concentrations (Treatment I-0.1 mg/L and Treatment II-1.58 mg/L) of CuSO₄. We have continuously quantified the strength of behavior (swimming consistency) and physiological (respiratory rates) biomarkers for ten days using an online monitoring system of swimming behavior and external respiration. Swimming consistency and respiratory rates of zebrafish (p<0.05) decreased in the CuSO₄-treated groups compared to the control group. Avoidance behavior has led to an endpoint behavior at copperiedus. The time-delayed toxic effect has resulted in CuSO₄ treatment groups. We checked for swimming consistency aberration on the artificial neural array, Self-organizing map (SOM). Circadian rhythms were influenced by prolonged exposure to CuSO₄ toxicity. A concentration- and duration-dependent behavior anomaly was noted in this study. Swimming behavior and respiratory metabolism patterns are sensitive non-invasive stress biomarkers for water quality monitoring studies.

Univariate or multivariate approaches for histopathological biomarkers in the context of environmental quality assessments?

Although the simplification of multivariate histopathological data into univariate indices can be useful for the assessment of environmental quality, this implies a great loss of information. The objective of the present study was to evaluate the effectiveness, in the context of environmental quality assessment, of an approach that integrates individual histopathological responses in a discriminated manner with the results of contaminants by means of multivariate analyses. This analysis was compared to the diagnosis of environmental quality provided by the use of the univariate Bernet histopathological index. Contaminant loads (sediments and fish) and the liver histopathology of Cathorops spixii were integrated through multivariate analysis. Integrated individual histopathological responses allowed classifying environmental quality from more to less impacted sites, while the univariate index showed some inconsistencies with chemical loads and allowed identifying only the most impacted site.

Delineation of the exposure-response causality chain of chronic copper toxicity to the zebra mussel, Dreissena polymorpha, with a TK-TD model based on concepts of biotic ligand model and subcellular metal partitioning model

A toxicokinetic-toxicodynamic model was constructed to delineate the exposure-response causality. The model could be used: to predict metal accumulation considering the influence of water chemistry and biotic ligand characteristics; to simulate the dynamics of subcellular partitioning considering metabolism, detoxification, and elimination; and to predict chronic toxicity as represented by biomarker responses from the concentration of metals in the fraction of potentially toxic metal. The model was calibrated with data generated from an experiment in which the Zebra mussel Dreissena polymorpha was exposed to Cu at nominal concentrations of 25 and 50 μg/L and with varied Na⁺ concentrations in water up to 4.0 mmol/L for 24 days. Data used in the calibration included physicochemical conditions of the exposure environment, Cu concentrations in subcellular fractions, and oxidative stress-induced responses, i.e. glutathione-S-transferase activity and lipid peroxidation. The model explained the dynamics of subcellular Cu partitioning and the effect mechanism reasonably well. With a low affinity constant for Na ⁺ binding to Cu²⁺ uptake sites, Na ⁺ had limited influence on Cu²⁺ uptake at low Na⁺ concentrations in water. Copper was taken up into the metabolically available pool (MAP) at a largely higher rate than into the cellular debris. Similar Cu concentrations were found in these two fractions at low exposure levels, which could be attributed to sequestration pathways (metabolism, detoxification, and elimination) in the MAP. However, such sequestration was inefficient as shown by similar Cu concentrations in detoxified fractions with increasing exposure level accompanied by the increasing Cu concentration in the MAP.

Functional significance and physiological regulation of essential trace metals in fish

Trace metals such as iron, copper, zinc and manganese play essential roles in various biological processes in fish, including development, energy metabolism and immune response. At embryonic stages, fish obtain essential metals primarily from the yolk, whereas in later life stages (i.e. juvenile and adult), the gastrointestine and the gill are the major sites for the acquisition of trace metals. On a molecular level, the absorption of metals is thought to occur at least in part via specific metal ion transporters, including the divalent metal transporter-1 (DMT1), copper transporter-1 (CTR1), and Zrt- and Irt-like proteins (ZIP). A variety of other proteins are also involved in maintaining cellular and systemic metal homeostasis. Interestingly, the expression and function of these metal transport- and metabolism-related proteins can be influenced by a range of trace metals and major ions. Increasing evidence also demonstrates an interplay between the gastrointestine and the gill for the regulation of trace metal absorption. Therefore, there is a complex network of regulatory and compensatory mechanisms involved in maintaining trace metal balance. Yet, an array of factors is known to influence metal metabolism in fish, such as hormonal status and environmental changes. In this Review, we summarize the physiological significance of iron, copper, zinc and manganese, and discuss the current state of knowledge on the mechanisms underlying transepithelial metal ion transport, metal-metal interactions, and cellular and systemic handling of these metals in fish. Finally, we identify knowledge gaps in the regulation of metal homeostasis and discuss potential future research directions.

Development of a toxicokinetic-toxicodynamic model simulating chronic copper toxicity to the Zebra mussel based on subcellular fractionation

A toxicokinetic-toxicodynamic model based on subcellular metal partitioning is presented for simulating chronic toxicity of copper (Cu) from the estimated concentration in the fraction of potentially toxic metal (PTM). As such, the model allows for considering the significance of different pathways of metal sequestration in predicting metal toxicity. In the metabolically available pool (MAP), excess metals above the metabolic requirements and the detoxification and elimination capacity form the PTM fraction. The reversibly and irreversibly detoxified fractions were distinguished in the biologically detoxified compartment, while responses of organisms were related to Cu accumulation in the PTM fraction. The model was calibrated using the data on Cu concentrations in subcellular fractions and physiological responses measured by the glutathione S-transferase activity and the lipid peroxidation level during 24-day exposure of the Zebra mussel to Cu at concentrations of 25 and 50 µg/L and varying Na⁺ concentrations up to 4.0 mmol/L. The model was capable of explaining dynamics in the subcellular Cu partitioning, e.g. the trade-off between elimination and detoxification as well as the dependence of net accumulation, elimination, detoxification, and metabolism on the exposure level. Increases in the net accumulation rate in the MAP contributed to increased concentrations of Cu in this fraction. Moreover, these results are indicative of ineffective detoxification at high exposure levels and spill-over effects of detoxification.

Intestinal response characteristic and potential microbial dysbiosis in digestive tract of Bufo gargarizans after exposure to cadmium and lead, alone or combined

The gastrointestinal tract is the largest immune organ in the body and meanwhile, accommodates a large number of microorganisms. Heavy metals could disturb the intestinal homeostasis and change the gut microbial composition. However, the information regarding the links between dysbiosis of gut microbiota and imbalance of host intestinal homeostasis induced by the mixture of heavy metals is insufficient. The present study investigates the effects of Cd/Pb, both single and combination exposure, on the growth performance, intestinal histology, digestive enzymes activity, oxidative stress and immune parameters, and intestinal microbiota in Bufo gargarizans tadpoles. Our results revealed that co-exposure of Cd-Pb induced more severe impacts not only on the host, but the intestinal microbiota. On the one hand, co-exposure of Cd-Pb significantly induced growth retardation, intestinal histological injury, decreased activities of digestive enzymes. On the other hand, Cd and Pb exposure, especially in mixed form, changed the diversity and richness, structure of microbiota. Also, the intestinal microbial composition was altered by Cd/Pb exposure (alone and combination) both at the different levels. Proteobacteria, act as front-line responder, was significantly increased in tadpoles under the exposure of metals. Finally, the functional prediction revealed that the disorders of metabolism and immune responses of intestinal microbiota was increased in tadpoles exposed to Cd/Pb (especially the mixture of Cd and Pb). Our research complements the understanding of links between changes in host fitness loss and intestinal microbiota and will add a new dimension of knowledge to the ecological risks of mixed heavy metals in amphibian.

Copper-induced sublethal effects in Bufo gargarizans tadpoles: growth, intestinal histology and microbial alternations

Copper (Cu) is one of the environmental contaminations which can pose significant risks for organisms. The current study explores the effects of Cu exposure on the growth, intestinal histology and microbial ecology in Bufo gargarizans. The results revealed that 0.5-1 μM Cu exposure induced growth retardation (including reduction of total body length and wet weight) and intestinal histological injury (including disordered enterocyte, changes in the villi and vacuoles) of tadpoles. Also, high-throughput sequencing analysis showed that Cu exposure caused changes in richness, diversity and structure of intestinal microbiota. Moreover, the composition of intestinal microbiota was altered in tadpoles exposed to different concentrations of Cu. At the phylum level, we observed the abundance of proteobacteria was increased, while the abundance of fusobacteria was decreased in the intestinal microbiota of tadpoles exposed to 1 μM Cu. At the genus level, a reduced abundance of kluyvera and aeromonas was observed in the intestinal microbiota of tadpoles under the exposure of 0-0.5 μM Cu. Finally, functional predictions revealed that tadpoles exposed to copper may be at a higher risk of developing metabolic disorders or diseases. Above all, our results will develop a comprehensive view of the Cu exposure in amphibians and will yield a new consideration for sublethal effects of Cu on aquatic organisms.

Applications of the RTgill-W1 Cell Line for Acute Whole-Effluent Toxicity Testing: In Vitro-In Vivo Correlation and Optimization of Exposure Conditions

The cell line RTgill-W1 was evaluated as an in vitro alternative model for acute fish whole-effluent toxicity (WET) testing. We determined the 50% effective concentration (EC50) that reduces the viability of RTgill-W1 cells for selected toxicants commonly found in effluent samples and correlated those values with the respective 50% lethal concentration (LC50) of freshwater (fathead minnow, Pimephales promelas) and marine (sheepshead minnow, Cyprinodon variegatus) fish species obtained from the literature. Excluding low water-soluble organics and the volatile sodium hypochlorite, significant correlations were measured for metal, metalloids, ammonia, and higher water-soluble organics between in vitro EC50 values and in vivo LC50 values for both species. Typically, toxicity studies with RTgill-W1 cells are conducted by adding salts to the exposure medium, which may affect the bioavailability of toxicants. Osmotic tolerance of RTgill-W1 cells was found between 150 and 450 mOsm/kg, which were set as the hypoosmotic and hyperosmotic limits. A subset of the toxicants were then reexamined in hypoosmotic and hyperosmotic media. Copper toxicity decreased in hyperosmotic medium, and nickel toxicity increased in hypoosmotic and hyperosmotic media. Linear alkylbenzene sulfonate toxicity was not affected by the medium osmolality. Overall, RTgill-W1 cells have shown potential for applications in measuring metal, metalloids, ammonia, and water-soluble organic chemicals in acute WET tests, as well as complementing current toxicity identification and reduction evaluation strategies. In the present study, RTgill-W1 cells have been established as a valid animal alternative for WET testing, and we show that through manipulation of medium osmotic ranges, sensitivity to nickel was enhanced. Environ Toxicol Chem 2021;40:1050-1061. © 2020 SETAC.

Modelling copper toxicokinetics in the zebra mussel, Dreissena polymorpha, under chronic exposures at various pH and sodium concentrations

The stenohaline zebra mussel, Dreissena polymorpha, is uniquely sensitive to the ionic composition of its aquatic environment. Waterborne copper (Cu) uptake and accumulation in zebra mussels were examined at various conditions in an environmentally relevant range in freshwater, i.e. Cu exposure levels (nominal concentrations of 25 and 50 μg/L), pH (5.8-8.3), and sodium (Na⁺) concentrations (up to 4.0 mM). Copper accumulation was simulated by a kinetic model covering two compartments, the gills and the remaining tissues. The Cu uptake rate constant decreased with decreasing pH from 8.3 down to 6.5, indicating interactions between H⁺ and Cu at uptake sites. The kinetic simulation showed dose-dependent effects of Na⁺ on Cu uptake. At 25 μg/L Cu, addition of Na⁺ at 0.5 mM significantly inhibited the Cu uptake rate, while no significant differences were found in the uptake rate upon further addition of Na⁺ up to a concentration of 4.0 mM. At 50 μg/L Cu, the Cu uptake rate was not influenced by Na⁺ addition. Calibration results exhibited dose-dependent elimination rates with more profound elimination with increasing exposure levels. With kinetic parameters calibrated at environmentally relevant conditions, in terms of pH and Na⁺ concentrations, the model performed well in predicting Cu accumulation based on independent data sets. Estimates of the Cu concentration in mussels were within a factor of 2 of the measurements. This demonstrates potential application of kinetic models that are calibrated in environmentally relevant freshwater conditions.

Role of metal speciation in the exposure medium on the toxicity, bioavailability and bio-reactivity of copper, silver, cadmium and zinc in the rainbow trout gut cell line (RTgutGC)

The role of metal speciation on metal bioavailability, bio-reactivity and toxicity at the fish intestine is poorly understood. To investigate these processes, we used an in vitro model of the rainbow trout (Oncorhynchus mykiss) intestine, the RTgutGC cell line. Cells were exposed to two essential metals (copper and zinc) and two non-essential metals (cadmium and silver) in a medium of well-defined composition, which allowed the determination of metal speciation in solution. Concentrations resulting in a 50% cell viability reduction (EC₅₀) were measured using a viability assay based on two endpoints: metabolic activity and membrane integrity. Metal bioavailability and bio-reactivity was studied at non-toxic (300 nM all metals) and toxic (EC₁₀; Ag-0.6, Cu-0.9, Cd-3, and Zn-9 μM) concentrations. Bioavailability (i.e. intracellular metal accumulation) was determined by ICP-MS, while bio-reactivity (i.e. induction of a metal specific transcriptional response) was determined by measuring the mRNA levels of a known biomarker of metal exposure (i.e. metallothionein) and of copper and zinc transporters (i.e. ATP7A and ZnT1). Dominant metal species in the exposure medium were Zn²⁺, CuHPO₄, CdCl⁺, and AgCl₂^- respectively for Zn, Cu, Cd, and Ag. The EC_50s showed the metal toxicity hierarchy: Ag > Cu > Cd > Zn. In RTgutGC cells, essential metal homeostasis was tightly regulated while non-essential metals accumulated more readily. Non-essential metals were also more bio-reactive inducing higher MT and ZnT1 mRNA levels. Taken together these findings indicate that metal toxicity in RTgutGC cannot solely be explained by extracellular metal speciation but requires the evaluation of metal bioavailability and bio-reactivity.

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.

Tissue Accumulation and the Effects of Long-Term Dietary Copper Contamination on Osmoregulation in the Mudflat Fiddler Crab Minuca rapax (Crustacea, Ocypodidae)

We examined copper accumulation in the hemolymph, gills and hepatopancreas, and hemolymph osmolality, Na⁺ and Cl^- concentrations, together with gill Na⁺/K⁺-ATPase and carbonic anhydrase activities, after dietary copper delivery (0, 100 or 500 Cu µg g^-1) for 12 days in a fiddler crab, Minuca rapax. In contaminated crabs, copper concentration decreased in the hemolymph and hepatopancreas, but increased in the gills. Hemolymph osmolality and gill Na⁺/K⁺-ATPase activity increased while hemolymph [Na⁺] and [Cl^-] and gill carbonic anhydrase activity decreased. Excretion likely accounts for the decreased hemolymph and hepatopancreas copper titers. Dietary copper clearly affected osmoregulatory ability and hemolymph Na⁺ and Cl^- regulation in M. rapax. Gill copper accumulation decreased carbonic anhydrase activity, suggesting that dietary copper affects acid-base balance. Elevated gill Na⁺/K⁺-ATPase activity appears to compensate for the ion-regulatory disturbance. These effects of dietary copper illustrate likely impacts on semi-terrestrial species that feed on metal-contaminated sediments.

Effects of copper on a reconstructed freshwater rainbow trout gill epithelium: Paracellular and intracellular aspects

The barrier properties and intracellular responses of a primary cultured trout gill epithelium (containing both mitochondria-rich and pavement cells) were examined over 24 h of copper (Cu) exposure (0, 200 and 1000 μg/L) in apical fresh water. Transepithelial resistance (TER) and mRNA abundance of tight junction proteins zonula occludens-1, occludin, cingulin, claudin-8d and -28b were examined as endpoints of barrier function and the paracellular pathway. Intracellular endpoints analyzed were Cu accumulation, Na⁺ content, carbonic anhydrase activity and mRNA abundance of carbonic anhydrase (ca-II) and Na⁺/K⁺ ATPase (nka α1a and nka α1b isoforms). After a brief initial drop in TER in the 1000 μg Cu/L treatment, Cu at both levels increased TER over the first 6 h of exposure but there were no differences among groups from 12 h onwards. After 24 h of Cu exposure, there were no differences in mRNA abundance of any of the tight junction proteins examined. Cu accumulation occurred at 1000 μg Cu/L (5.5-fold increase), but no depletion of Na⁺ content. Carbonic anhydrase activity decreased significantly (by 76%), however Cu exposure did not alter the transcript abundance of ca-II, nka α1a, or nka α1b. This study provides a first report of carbonic anhydrase sensitivity to Cu exposure in a cultured model gill epithelium. We conclude that Cu impacts the permeability of this model during the early stages of exposure and that the use of carbonic anhydrase inhibition as an endpoint of metal toxicity in this model preparation may be useful for future mechanistic investigations and environmental monitoring.

Comparative Proteomics on Deep-Sea Amphipods after in Situ Copper Exposure

The interest in deep-sea mining increased along with the environmental concerns of these activities to the deep-sea fauna. The discovery of optimal biomarkers of deep-sea mining activities in deep-sea species is a crucial step toward the supply of important ecological information for environmental impact assessment. In this study, an in situ copper exposure experiment was performed on deep-sea scavenging amphipods. Abyssorchomene distinctus individuals were selected among all the exposed amphipods for molecular characterization. Copper concentration within the gut was assessed, followed by a tandem mass tag-based coupled with two-dimensional liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) applied to identify and quantify the protein expression changes after 48 h of exposure. 2937 proteins were identified and annotated, and 1918 proteins among all identified proteins were assigned by at least two nonambiguous peptides. The screening process was performed based on the differences in protein abundance and the specific correlation between the proteins and copper in previous studies. These differentially produced proteins include Na⁺/K⁺ ATPase, cuticle, chitinase, and proteins with unknown function. Their abundances showed correlation with copper and had high sensitivity to indicate the copper level, being here proposed as biomarker candidates for deep-sea mining activities in the future. This is a key step in the development of environmental impact assessment of deep-sea mining activities integrating ecotoxicological data.

Inhibitory effect of cadmium exposure on digestive activity, antioxidant capacity and immune defense in the intestine of yellow catfish (Pelteobagrus fulvidraco)

Cadmium (Cd) is a toxic heavy metal that can pose a serious threat to aquatic organisms. To evaluate the physiological response and defense mechanism of fish intestine to Cd toxicity, yellow catfish (Pelteobagrus fulvidraco) were exposed to 0 (control), 50 μg/L and 200 μg/L Cd²⁺ for a period of 8 weeks, and then histological changes, digestive activity, antioxidant status and immune responses in the anterior intestine were assessed. After exposure, significant growth retardation and Cd accumulation were observed, and obvious histopathological lesions in the intestine such as increased goblet cells, excessive mucus, vacuolization and thickened lamina propria were detected. Intestinal digestive enzymes activities and related gene expression were inhibited markedly in Cd²⁺ treatments. Furthermore, Cd exposure induced oxidative stress inhibiting antioxidant activity, characterized by an increase in malondialdehyde level as well as the decrease in the activity and transcription level of antioxidant enzymes. In addition, exposure to Cd²⁺ down-regulated the expression of key genes involved in the immune response (lys, c3, tor, tgf-β, il-10, tnf-α and il-8), suggesting immune defense was inhibited. Taken together, the decreased digestive enzyme activity and Cd-induced toxicity stress for antioxidant and immune systems in the intestine might be account for individual growth retardation.

The Chronic Effects of Copper and Cadmium on Life History Traits Across Cladocera Species: A Meta-analysis

The effect of sublethal concentrations of heavy metals on cladoceran growth and reproduction is a cornerstone of modern ecotoxicology. However, the literature contains assays across numerous concentrations, on numerous species and genotypes, and conditions are far from consistent. We undertook a systematic review of the sublethal effects of copper and cadmium concentrations on Cladocera spp. life history (reproduction, maturation age, and somatic growth rate). Using meta-analysis, we tested the hypothesis that the effects of increasing Cu and Cd concentrations on traits may vary by species. We also evaluated where possible whether the effect of metal concentrations on traits vary by water hardness, exposure duration, or whether the metals were delivered in aqueous solution or via food. We surveyed > 200 papers, resulting in a set of 32 experimental studies representing 446 trials where the results were presented compared with Daphnia magna-the most commonly assayed species. We found qualitatively similar effects of Cu and Cd on life history traits that included reduction in reproduction and somatic growth rate and delay of maturation. Cladocera species showed marked variations in their susceptibility to metals, and D. magna was found to be the least sensitive species to sublethal changes in reproduction. The effects were largely consistent for aqueous vs. dietary food. Water hardness, where data were available, had no detectable effect. Available data indicate that exposure duration had no effect on the toxicity of Cu but did for D. magna reproductive response to Cd. Our study highlights the importance of including species identity when considering toxicological testing and regulation development.

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

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

Disturbance in Na+ regulation in cells rich in mitochondria isolated from gills of the yellow clam Mesodesma mactroides exposed to copper under different osmotic conditions

Cells rich in mitochondria were isolated from gills of the seawater clam Mesodesma mactroides, incubated in isosmotic saline solution (840 mOsmol/kg H₂O), and exposed (3 h) to environmentally realistic Cu concentrations (nominally: 0, 5, 9 and 20 μg/L). In cells exposed to 20 μg Cu/L, Cu accumulation, Na⁺ content reduction and carbonic anhydrase (CA) activity inhibition were observed, without significant changes in cell viability and Na⁺,K⁺-ATPase (NKA) activity. In the absence of Cu, cell viability and Cu content were reduced in hyposmotic media respect with the control, without changes in Na⁺ content and enzyme (CA and NKA) activities. In the presence of 5 or 9 μg/L Cu, cell Cu content was increased, especially at 670 mOsmol/kg H₂O. Cell Na⁺ content and NKA activity were reduced after exposure to 20 μg/L Cu at 670 mOsmol/kg H₂O. In turn, CA activity was dependent on Cu concentration, being significantly reduced in cells exposed to 9 and 20 μg/L Cu in both hyposmotic conditions. These findings indicate that Cu also negatively affects Na⁺ regulation in gill cells of the seawater clam M. mactroides, with Cu toxicity increasing at hyposmotic conditions. Also, they indicate that physiology is more important than water chemistry in predicting Cu toxicity in environments of changing salinity, pointing out CA activity as a potential biomarker of Cu exposure.

Complex role of titanium dioxide nanoparticles in the trophic transfer of arsenic from Nannochloropsis maritima to Artemia salina nauplii

Increasing concern has been focused on the potential risks associated with the trophic transfer to aquatic organisms of ambient contaminants in the presence of titanium dioxide nanoparticles (nano-TiO₂). This study investigated the influence of nano-TiO₂ on the trophic transfer of arsenic (As) from the microalgae Nannochloropsis maritima to the brine shrimp Artemia salina nauplii. We found that nano-TiO₂ could significantly facilitate As sorption on N. maritima within an exposure period of 24 h, and this sorption subsequently led to higher As trophic transfer from the algae to A. salina according to trophic transfer factors (TTF_As+nano-TiO2 > TTF_As). However, after 48 h of depuration, the retention of As in A. salina fed As-nano-TiO₂-contaminated algae was even lower than that in A. salina fed As-contaminated algae at the same exposure concentrations. This result indicates that the increased food chain transfer of As in the presence of nano-TiO₂ can be explained by adsorption of As onto nano-TiO₂ in contaminated food (algae), but the bioavailability of As in A. salina is reduced after the introduction of nanoparticles. Although the stress enzyme activities of superoxide dismutase (SOD) and acetylcholinesterase (AChE) in A. salina at a lower As concentration treatment in the presence of nano-TiO₂ were not significantly changed, they increased with higher exposure concentrations of As with or without nano-TiO₂. Our study highlighted the complex role of nanomaterials in the transfer of ambient contaminants via trophic chains and the potential of nano-TiO₂ to reduce the bioavailability of As via trophic transfer to saltwater zooplankton.

Transcriptomic approach: A promising tool for rapid screening nanomaterial-mediated toxicity in the marine bivalve Mytilus edulis-Application to copper oxide nanoparticles

The extensive development of nanotechnologies will inevitably lead to the release of nanomaterials (NMs) in the environment. As the aquatic environments represent the ultimate sink for various contaminants, it is highly probable that they also constitute a reservoir for NMs and hence aquatic animals represent potential targets. In a regulatory perspective, it is necessary to develop tools to rapidly screen the impact of NMs on model organisms, given that the number of NMs on the market will be increasing. In this context High Throughput Screening approaches represent relevant tools for the investigation of NM-mediated toxicity. The objective of this work was to study the effects of copper oxide nanoparticles (CuONPs) in the marine bivalve Mytilus edulis, using a transcriptomic approach. Mussels were exposed in vivo to CuONPs (10 μg·L^-1CuO NPs) for 24 h and analysis of mRNA expression levels of genes implicated in immune response, antioxidant activities, cell metabolism, cell transport and cytoskeleton was investigated by qPCR on hemocytes and gills. Results showed common effects of CuONPs and its ionic counterpart. However, greater effects of CuONPs on GST, SOD, MT, Actin, ATP synthase gene expressions were observed compared to ionic form indicating that toxicity of CuONPs is not solely due to the release of Cu²⁺. Even though M. edulis genome is not fully characterized, this study provides additional knowledge on the signaling pathways implicated in CuONP-mediated toxicity and demonstrates the reliability of using a qPCR approach to go further in the cellular aspects implicated in response to NPs in marine bivalves.

Alterations of larval photo-dependent swimming responses (PDR): New endpoints for rapid and diagnostic screening of aquatic contamination

Detection and toxicity assessment of waterborne contaminants are crucial for protecting human health and the environment. Development of easy-to-implement, rapid and cost-effective tools to measure anthropogenic effects on watersheds are critical for responsible management, particularly in times of increasing development and urbanization. Traditionally, environmental toxicology has focused on limited endpoints, such as lethality and fertility, which are directly affecting population levels. However, more sensitive readings are needed to assess sub-lethal effects. Monitoring of contaminant-induced behavior alterations was proposed before, but is difficult to implement in the wild and performing it in aquatic laboratory models seem more suited. For this purpose, we adapted a photo-dependent swimming response (PDR) that was previously described in zebrafish larva. We first asked if PDR was present in other aquatic animals. We measured PDR in larvae from two freshwater prawn species (Macrobrachium rosenbergii, MR, and Macrobrachium carcinus, MC) and from another fish the fathead minnow (FHM, Pimephales promelas). In all, we found a strong and reproducible species-specific PDR, which is arguing that this behavior is important, therefore an environmental relevant endpoint. Next, we measured PDR in fish larvae after acute exposure to copper, a common waterborne contaminant. FHM larvae were hyperactive at all tested concentrations in contrast to ZF larvae, which exhibited a concentration-dependent hyperactivity. In addition to this well-accepted anxiety-like behavior, we examined two more: photo-stimulated startle response (PSSR) and center avoidance (CA). Both were significantly increased. Therefore, PDR measures after acute exposure to this waterborne contaminant provided as sensitive readout for its detection and toxicity assessment. This approach represents an opportunity to diagnostically examine any substance, even when present in complex mixtures like ambient surface waters. Mechanistic studies of toxicity using the extensive molecular tool kit of ZF could be a direct extension of such approaches.

Biochemical, Histopathological and Molecular Responses in Gills of Leuciscus cephalus Exposed to Metals

Gills are major targets for acute metal toxicity in fish, due to their permanent contact with aquatic pollutants. To assess the effects of metals on gills of the Leuciscus cephalus (chub), fish individuals were collected from two sites in the Tur River, Romania, in upstream (site 1) and downstream (site 2) of a metal pollution source. Quantitative and hyperspectral analyses showed that Zn, Sr, and Fe concentrations were significantly higher in gills from site 2 compared with site 1. Malondialdehyde and advanced oxidation protein products levels increased 17 and 28%, respectively, whereas reduced glutathione level diminished significantly in the gills of fish collected from site 2 compared to site 1. The activities of superoxide dismutase, catalase, and glutathione-S-transferase increased significantly at 41, 21, and 28%, respectively. Proliferating cell nuclear antigen (PCNA) protein levels, as well as the amount of DNA damage, were significantly increased for site 2 compared with site 1. The induced oxidative stress generated hyperplasia, hypertrophy, and inflammation in the epithelial cells and apoptosis. Hence, this could suggest that gill cells have tried to counteract the oxidative stress-induced DNA fragmentation by PCNA up-regulation, but the PCNA expression decreased on longer time due to the low level of GSH, resulting in apoptosis.

Sub-lethal effects of waterborne exposure to copper nanoparticles compared to copper sulphate on the shore crab (Carcinus maenas)

The toxicity of soluble copper (Cu) to marine organisms is reasonably well described. However, the hazard of Cu engineered nanomaterial (ENMs) is poorly understood. The aim of the present study was to compare the toxicity of Cu ENMs to Cu as CuSO₄ in the shore crab, Carcinus maenas. The crabs were exposed via the water using a semi-static approach to 0.2 or 1mgL^-1 of Cu ENMs or 1mgL^-1 of Cu as CuSO₄. Gills, hepatopancreas, chela muscle and haemolymph were collected at days 0, 4 and 7 for the body burden of Cu, histology and biochemical analysis [thiobarbituric acid reactive substances (TBARS) and total glutathione (GSH)]. Nominal exposure concentrations of both the ENMs and the metal salt were maintained at over 80% in each treatment throughout the experiment. By day 7, 54% mortality was recorded in the 1mgL^-1 CuSO₄ treatment, compared to just 21% in the 1mgL^-1 Cu ENM-exposed crabs. The target organs for Cu accumulation were similar for both forms of Cu with highest concentrations in the gills, particularly the posterior gills; followed by the hepatopancreas, and with the lowest concentrations in the chela muscle. No changes were observed in the osmolarity of the haemolymph (ANOVA, P>0.05). TBARS were measured as an indicator of lipid peroxidation and showed the greatest change in the anterior and posterior gills and hepatopancreas of animals exposed to 1mgL^-1 Cu ENMs (ANOVA or Kruskal-Wallis, P<0.05). No statistically significant changes in total GSH were observed (ANOVA, P>0.05; n=6 crabs per treatment). Histological analysis revealed organ injuries in all treatments. The types of pathologies observed in the Cu ENM treatments were broadly similar to those of the Cu as CuSO₄ treatment. Overall, the target organs and Cu accumulation from Cu ENMs were comparable to that following exposure to Cu as CuSO₄, and although there were some differences in the sub-lethal effects, the metal salt was more acutely toxic.

Kidney activity increases in copper exposed goldfish (Carassius auratus auratus)

In the present study, the effect of copper was examined in the common goldfish (Carassius auratus auratus). Fish were fasted and exposed to either a high (0.84μM), a low (0.34μM) or a control copper concentration (0.05μM) for 1 and 7days. Swimming performance was not affected by either fasting or copper exposure. Food deprivation alone had no effect on ionoregulation, but low plasma osmolality levels and plasma Na⁺ were noticed in fasted fish exposed to Cu for 7days. Both gill Na⁺/K⁺-ATPase and H⁺-ATPase activities were undisturbed, while both kidney ATPase activities were up-regulated when challenged with the high Cu levels. Up-regulated kidney ATPase activities likely acted as compensatory strategy to enhance Na⁺ reabsorption. However, this up-regulation was not sufficient to restore Na⁺ to control levels in the highest exposure group.

Copper Bioaccumulation and Depuration in Common Carp (Cyprinus carpio) Following Co-exposure to TiO2 and CuO Nanoparticles

Metal oxide nanoparticles (NPs), such as TiO₂ and CuO, are widely applied in an increasing number of products and applications, and therefore their release to the aquatic ecosystems is unavoidable. However, little is known about joint toxicity of different NPs on tissues of aquatic organisms, such as fish. This study was conducted to assess the uptake and depuration of Cu following exposure to CuO NPs in the presence of TiO₂ NPs in the liver, intestine, muscle, and gill of common carp, Cyprinus carpio. Carps with a mean total length of 23 ± 1.5 cm and mean weight of 13 ± 1.3 g were divided into 6 groups of 15 each (1 control group) and exposed to TiO₂ NPs, CuO NPs, and a mixture of TiO₂ and CuO NPs for periods of 20 days for uptake and 10 days for depuration. The determination of total Cu concentration was carried out by an ICP-OES. The order of Cu uptake in different tissues of the carps was liver > gill > muscle > intestine in both levels of CuO NPs alone; results showed that the total Cu concentrations in the presence of TiO₂ nanoparticles were increased and were in the sequence of liver > gill > intestine > muscle. In depuration period, Cu concentrations were decreased in all treatments in the sequence of gill > intestine > muscle > liver. Uptake of Cu in different tissues of common carp increased with increasing concentration and time and was tissues- and time-dependent. In conclusion, this study suggested that the uptake of Cu in the tissues of common carp increased in the joint presence of TiO₂ NPs.

Effects of metal contamination in situ on osmoregulation and oxygen consumption in the mudflat fiddler crab Uca rapax (Ocypodidae, Brachyura)

The contamination of estuaries by metals can impose additional stresses on estuarine species, which may exhibit a limited capability to adjust their regulatory processes and maintain physiological homeostasis. The mudflat fiddler crab Uca rapax is a typical estuarine crab, abundant in both pristine and contaminated areas along the Atlantic coast of Brazil. This study evaluates osmotic and ionic regulatory ability and gill Na(+)/K(+)-ATPase activity in different salinities (<0.5, 25 and 60‰ S) and oxygen consumption rates at different temperatures (15, 25 and 35°C) in U. rapax collected from localities along the coast of São Paulo State showing different histories of metal contamination (most contaminated Ilha Diana, Santos>Rio Itapanhaú, Bertioga>Picinguaba, Ubatuba [pristine reference site]). Our findings show that the contamination of U. rapax by metals in situ leads to bioaccumulation and induces biochemical and physiological changes compared to crabs from the pristine locality. U. rapax from the contaminated sites exhibit stronger hyper- and hypo-osmotic regulatory abilities and show greater gill Na(+)/K(+)-ATPase activities than crabs from the pristine site, revealing that the underlying biochemical machinery can maintain systemic physiological processes functioning well. However, oxygen consumption, particularly at elevated temperatures, decreases in crabs showing high bioaccumulation titers but increases in crabs with low/moderate bioaccumulation levels. These data show that U. rapax chronically contaminated in situ exhibits compensatory biochemical and physiological adjustments, and reveal the importance of studies on organisms exposed to metals in situ, particularly estuarine invertebrates subject to frequent changes in natural environmental parameters like salinity and temperature.

Prediction of acute toxicity of cadmium and lead to zebrafish larvae by using a refined toxicokinetic-toxicodynamic model

The biotic ligand model (BLM) and the toxicokinetic-toxicodynamic (TK-TD) model are essential in predicting the acute toxicity of metals in various species and exposure conditions; however, these models are usually separately utilized. In this study, a mechanistic TK-TD model was developed to predict the acute toxicity of 10(-6)M Cd and 10(-6)M Pb to zebrafish (Danio rerio) larvae. The novel approach links the BLM with relevant TK processes to simulate the bioaccumulation processes of Cd or Pb as a function of the maximum uptake rate of each metal, the affinity constants, and the concentrations of free metal ions and H(+) in test solutions. Results showed that the refined TK-TD model can accurately predict the accumulation and acute toxicity of Cd and Pb to zebrafish larvae at pH 5.5, 6.5, and 7.0.

Effects of Waterborne Lead Exposure in Mozambique Tilapia: Oxidative Stress, Osmoregulatory Responses, and Tissue Accumulation

We studied the oxidative stress and osmoregulatory damage as well as the accumulation of lead in Mozambique Tilapia Oreochromis mossambicus exposed to different sublethal concentrations-low, medium, and high (0.5, 2.5, and 5.0 mg/L)-of waterborne lead for 14 d in a semistatic condition. The accumulated levels of Na⁺, K⁺-ATPase, glutathione (GSH), and thiobarbituric acid reactive substances (TBARS) were determined from samples of gill, liver, intestine, brain, kidney, and muscle tissues. At the end of the experiment, the GSH levels of most tissues were higher in the treated group than in the control group (especially in the liver and kidney) but lower in the intestine. The levels of TBARS in the gill and brain tissues of the fish exposed to high lead doses were significantly higher than those of fish in the control group. Na⁺, K⁺-ATPase activity seemed to be significantly inhibited in the gill, intestine, and brain tissues across all treatment groups. At the end of the study, the total amount of lead that had accumulated within the various tissues ranked as follows: intestines > kidney > brain > gill > liver > muscle. Our findings suggest that sublethal concentrations of lead can disrupt the health of Mozambique Tilapia and cause oxidative stress and osmoregulatory damage.

Analyzing the effectiveness of using branchial NKA activity as a biomarker for assessing waterborne copper toxicity in tilapia (Oreochromis mossambicus): A damage-based modeling approach

Branchial Na(＋)-K(＋)-ATPase (NKA) activity has been suggested as a promising biomarker for assessing metal stress in aquatic organisms. However, studies that systematically show the effectiveness of using NKA activity to detect metal exposure and toxicity at the individual level are limited. In this study, we aimed to determine whether branchial NKA activity mechanistically responds to the accumulation of waterborne copper (Cu) and accounts for observed toxicity over time under environmentally-relevant and aquafarming Cu exposure levels (0.2, 1 and 2 mg L(-1)). Temporal trends in Cu accumulation and the corresponding responses of branchial NKA activity resulting from Cu exposure were investigated in laboratory experiments conducted on juvenile tilapia (Oreochromis mossambicus), a freshwater teleost that shows potential as a bioindicator of real-time and historical metal pollution. We used the process-based damage assessment model (DAM) to inspect the time course of Cu toxicity by integrating the compensation process between Cu-induced inhibition and repair of branchial NKA activity. NKA activity acted as a sensitive biomarker for Cu exposure and accumulation in tilapia, which showed induced impairment of osmoregulation and lethality when they were exposed to environmentally relevant levels (0.2 mg L(-1)), but not to higher exposure levels (1 and 2 mg L(-1)) in aquaculture farms or contaminated aquatic ecosystems. This study highlights the benefits and limitations of using branchial NKA activity as a sensitive biomarker to assess the health status of a fish population and its ecosystem.

Toxicokinetic toxicodynamic (TKTD) modeling of Ag toxicity in freshwater organisms: whole-body sodium loss predicts acute mortality across aquatic species

ToxicoKinetic ToxicoDynamic (TKTD) models are considered essential tools to further advance acute toxicity prediction of metals for a range of species and exposure conditions, but they are currently underutilized. We present a mechanistic TKTD model for acute toxicity prediction of silver (Ag) in freshwater organisms. In this new approach, we explicitly link relevant TKTD processes to species (physiological) characteristics, which facilitates model application to other untested freshwater organisms. The model quantifies the reduction in whole-body sodium concentration over time as a function of the target site inhibition over time, the target site density and the species-specific sodium turnover rate. Freshwater species are assumed to die instantly when they have lost a critical amount of their initial whole-body sodium concentration. Results show that mortality is significantly related to sodium loss (r(2) = 0.86) for various aquatic organisms and exposure durations. The model accurately predicts lethal effect concentrations for different freshwater organisms, including Daphnia magna, rainbow trout and juvenile crayfish, and is able to capture the observed size-specific variation of nearly 2 orders of magnitude in empirical LC50s.

Evidence of maternal copper and cadmium transfer in two live-bearing fish species

We studied maternal transfer of an essential metal (copper) and a non-essential one (cadmium) in the live-bearing fishes Heterandria formosa and Gambusia affinis. The goals of this study were: (1) to determine whether metals are transferred from exposed females to their developing offspring; (2) to determine if this transfer differs between two fish species that differ in their degree of maternal provisioning during development; (3) to determine the duration of maternal metal transfer once females are no longer exposed; and (4) to determine whether copper and cadmium are transferred equivalently. We exposed gravid females to background levels (control) or 0.15 µM of metal for 10 days, and then transferred them to clean water. We allowed females to give birth to up to three broods, and then quantified metal levels in offspring born at least 3 days after the transfer. We detected maternal metal transfer for both metals and in both species. Offspring metal levels decreased as females spent more time in clean water. Similarly, metal levels were lower in later broods than in earlier ones. Maternal metal transfer was higher in H. formosa than in G. affinis. Our results constitute the first report of maternal metal transfer in live-bearing fishes, and show that developing embryos acquire both essential and non-essential metals from their mothers in both species. This shows that metal toxicity may be an issue for live-bearing fish in clean environments when the previous generation has encountered metal pollution.

Low bioavailability of silver nanoparticles presents trophic toxicity to marine medaka (Oryzias melastigma)

Concerns for the potential risks of silver nanoparticles (AgNPs) to aquatic organisms have increased. The present study investigated the trophic transfer of AgNPs from brine shrimp (Artemia salina) nauplii to marine medaka. We found that the aggregated AgNPs (20 and 80 nm) and well dispersed 80-nm AgNPs (stabilized by 20 μM Tween 20) could be readily accumulated by brine shrimp, while far less well-dispersed 20-nm AgNPs were accumulated. The assimilation efficiency (AE) of AgNPs in medaka fed AgNPs-contaminated brine shrimp was low (<6%), resulting in a low trophic transfer efficiency (0.01-0.04) after 28 days of chronic dietary exposure. However, such low bioavailability of dietary AgNPs could inhibit the whole-body Na+/K+-ATPase and superoxide dismutase (SOD) activity in the fish within the first 2 weeks of exposure. Significant (p<0.05, two-way ANOVA) inhibition occurred in the high AgNPs-contaminated brine shrimp treatment over 28 days of chronic exposure. Furthermore, reduced growth and water content percentage were also observed in fish fed high dosages of AgNPs-contaminated brine shrimp. Our study highlighted the potential of trophically available AgNPs in bringing toxicity to the marine fish.

Common genes underlying asthma and COPD? Genome-wide analysis on the Dutch hypothesis

Asthma and chronic obstructive pulmonary disease (COPD) are thought to share a genetic background ("Dutch hypothesis"). We investigated whether asthma and COPD have common underlying genetic factors, performing genome-wide association studies for both asthma and COPD and combining the results in meta-analyses. Three loci showed potential involvement in both diseases: chr2p24.3, chr5q23.1 and chr13q14.2, containing DDX1, COMMD10 (both participating in the nuclear factor (NF) κβ pathway) and GNG5P5, respectively. Single nucleotide polymorphisms (SNPs) rs9534578 in GNG5P5 reached genome-wide significance after first replication phase (p=9.96×10(-9)). The second replication phase, in seven independent cohorts, provided no significant replication. Expression quantitative trait loci (eQTL) analysis in blood cells and lung tissue on the top 20 associated SNPs identified two SNPs in COMMD10 that influenced gene expression. Inflammatory processes differ in asthma and COPD and are mediated by NF-κβ, which could be driven by the same underlying genes, COMMD10 and DDX1. None of the SNPs reached genome-wide significance. Our eQTL studies support a functional role for two COMMD10 SNPs, since they influence gene expression in both blood cells and lung tissue. Our findings suggest that there is either no common genetic component in asthma and COPD or, alternatively, different environmental factors, e.g. lifestyle and occupation in different countries and continents, which may have obscured the genetic common contribution.

The potential toxicity of copper nanoparticles and copper sulphate on juvenile Epinephelus coioides

Copper nanoparticles (Cu-NPs) were widely used in various industrial and commercial applications. In this study the effects of Cu-NPs and soluble Cu were investigated on juvenile Epinephelus coioides. The fish were exposed in triplicate to control, 20 or 100μgCuL(-1) as either copper sulphate (CuSO4) or Cu-NPs in a semi-static aqueous culture for 25 days. The growth parameters were significantly lower at 100μgCuL(-1) as CuSO4 or Cu-NPs treatment compared to control. Time-dependent Cu accumulation in all tissues increased with increasing the Cu dose. The percentage of total Cu found in remaining tissues (head, bones, fins, etc.) decreased more in the CuSO4 than Cu-NPs treatment after 25 days, but increased in all other tissues (especially in liver). Compared with the control, either Cu-NPs or CuSO4 induced higher malonaldehyde concentration in tissues by overwhelming total superoxide dismutase activity, total glutathione concentration and Na(+)/K(+)-ATPase activity, but the opposite results were recorded for the brain. With increasing the CuSO4 or Cu-NPs dose, apoptosis was exacerbated in the liver and gills, more so by CuSO4 than Cu-NPs. Overall, these findings showed that Cu-NPs had the toxic effects similar to dissolved Cu; hence, Cu-NPs need to be included in the assessment of toxicological impacts in the aquatic environment.

Exposure to waterborne Cu inhibits cutaneous Na⁺ uptake in post-hatch larval rainbow trout (Oncorhynchus mykiss)

In freshwater rainbow trout (Oncorhynchus mykiss), two common responses to acute waterborne copper (Cu) exposure are reductions in ammonia excretion and Na(+) uptake at the gills, with the latter representing the likely lethal mechanism of action for Cu in adult fish. Larval fish, however, lack a functional gill following hatch and rely predominantly on cutaneous exchange, yet represent the most Cu-sensitive life stage. It is not known if Cu toxicity in larval fish occurs via the skin or gills. The present study utilized divided chambers to assess cutaneous and branchial Cu toxicity over larval development, using disruptions in ammonia excretion (Jamm) and Na(+) uptake (Jin(Na)) as toxicological endpoints. Early in development (early; 3 days post-hatch; dph), approximately 95% of Jamm and 78% of Jin(Na) occurred cutaneously, while in the late developmental stage (late; 25 dph), the gills were the dominant site of exchange (83 and 87% of Jamm and Jin(Na), respectively). Exposure to 50 μg/l Cu led to a 49% inhibition of Jamm in the late developmental stage only, while in the early and middle developmental (mid; 17 dph) stages, Cu had no effect on Jamm. Jin(Na), however, was significantly inhibited by Cu exposure at the early (53% reduction) and late (47% reduction) stages. Inhibition at the early stage of development was mediated by a reduction in cutaneous uptake, representing the first evidence of cutaneous metal toxicity in an intact aquatic organism. The inhibitions of both Jamm and Jin(Na) in the late developmental stage occurred via a reduction in branchial exchange only. The differential responses of the skin and gills to Cu exposure suggest that the mechanisms of Jamm and Jin(Na) and/or Cu toxicity differ between these tissues. Exposure to 20μg/l Cu revealed that Jamm is the more Cu-sensitive process. The results presented here have important implications in predicting metal toxicity in larval fish. The Biotic Ligand Model (BLM) is currently used to predict metal toxicity in aquatic organisms. However, for rainbow trout this is based on gill binding constants from juvenile fish. This may not be appropriate for post-hatch larval fish where the skin is the site of toxic action of Cu. Determining Cu binding constants and lethal accumulation concentrations for both skin and gills in larval fish may aid in developing a larval fish-specific BLM. Overall, the changing site of toxic action and physiology of developing larval fish present an interesting and exciting avenue for future research.

Involvement of CTR1 and ATP7A in lead (Pb)-induced copper (Cu) accumulation in choroidal epithelial cells

The blood-cerebrospinal fluid barrier (BCB) plays a key role in maintaining copper (Cu) homeostasis in the brain. Cumulative evidences indicate that lead (Pb) exposure alters cerebral Cu homeostasis, which may underlie the development of neurodegenerative diseases. This study investigated the roles of Cu transporter 1 (CTR1) and ATP7A, two Cu transporters, in Pb-induced Cu accumulation in the choroidal epithelial cells. Pb exposure resulted in increased intracellular (64)Cu retention, accompanying with up-regulated CTR1 level. Knockdown of CTR1 using siRNA before Pb exposure diminished the Pb-induced increase of (64)Cu uptake. The expression level of ATP7A was down-regulated following the Pb exposure. ATP7A siRNA knockdown, or PCMB treatment, inhibited the (64)Cu efflux from the cells, while the following additional incubation with Pb failed to further increase the intracellular (64)Cu retention. Cu exposure, or intracellular Cu accumulation following the tetracycline (Tet)-induced overexpression of CTR1, did not result in significant change in ATP7A expression. Taken together, these data indicate that CTR1 and ATP7A play important roles in Cu transport in choroidal epithelial cells, and the Pb-induced intracellular Cu accumulation appears to be mediated, at least in part, via the alteration of CTR1 and ATP7A expression levels following Pb exposure.

Bioavailability of silver nanoparticles and ions: from a chemical and biochemical perspective

Owing to their antimicrobial properties, silver nanoparticles (NPs) are the most commonly used engineered nanomaterial for use in a wide array of consumer and medical applications. Many discussions are currently ongoing as to whether or not exposure of silver NPs to the ecosystem (i.e. plants and animals) may be conceived as harmful or not. Metallic silver, if released into the environment, can undergo chemical and biochemical conversion which strongly influence its availability towards any biological system. During this process, in the presence of moisture, silver can be oxidized resulting in the release of silver ions. To date, it is still debatable as to whether any biological impact of nanosized silver is relative to either its size, or to its ionic constitution. The aim of this review therefore is to provide a comprehensive, interdisciplinary overview--for biologists, chemists, toxicologists as well as physicists--regarding the production of silver NPs, its (as well as in their ionic form) chemical and biochemical behaviours towards/within a multitude of relative and realistic biological environments and also how such interactions may be correlated across a plethora of different biological organisms.

Individual and combined effects of copper and parasitism on osmoregulation in the European eel Anguilla anguilla

The European eel (Anguilla anguilla), a catadromous species, breeds in the sea and migrates to estuarine, lagoon or freshwater habitats for growth and development. Yellow eels, exposed to low or fluctuating salinities, are also exposed to multiple other stressors as pollution, over-fishing and parasitism, which contribute to the dramatic decrease of eel populations in several European countries. The objective of this study was to evaluate the single and combined effects of waterborne copper and experimental infestation of eels with the nematode Anguillicoloides crassus after a salinity challenge from nearly isotonic (18ppt) to hypo- (5ppt) and hypertonic (29ppt) conditions, in order to investigate the osmoregulatory capacity of eels exposed to these stressors. In a nearly isotonic condition (18ppt), blood osmolality remained constant over the 6 weeks contamination to Cu(2+) and Anguillicoloides crassus. In fish exposed to a salinity challenge of 29ppt for 2 weeks, no significant effect was recorded in blood osmolality, Na(+)/K(+)-ATPase (NKA) activity, Na(+) and Cl(-) concentrations. After 2 weeks at 5ppt however, a significant blood osmolality decrease was detected in fish exposed to Anguillicoloides crassus infestation with or without Cu(2+) addition. This decrease may originate from lower Cl(-) levels measured in eels exposed to both stressors. Blood Na(+) levels remained relatively stable in all tested animals, but gill NKA activities were lower in eels exposed to combined stress. No apparent branchial lesions were detected following the different treatments and immunolocalization of NKA revealed well-differentiated ionocytes. Thus, the 5ppt challenge in eels exposed to copper and Anguillicoloides crassus seems to clearly enhance iono/osmoregulatory disturbances. Funded by ANR CES/CIEL 2008-12.

Occurrence of copper acclimation in the least killifish Heterandria formosa, and associated biochemical and physiological mechanisms

We investigated the occurrence of copper acclimation in the least killifish, Heterandria formosa using both lethal and sublethal endpoints. We also investigated potential mechanisms underlying the observed acclimation. To assess the occurrence of acclimation, fish were exposed to either a background Cu level or to 15 μg/L Cu for seven days and subsequently exposed to a lethal Cu level (150 μg/L Cu). During the latter exposure, fish were monitored for survival till all fish had died, and (during the first 8h of this exposure) for changes in whole-body Na levels and lipid peroxidation (LPO). During the high-level Cu exposure, fish pre-exposed to copper had a significantly longer time-to-death than did the control fish. Similarly, neither whole-body Na nor LPO changed in the Cu-pre-exposed fish during the 8h of the exposure to 150 μg/L Cu - while both decreased significantly in the control fish. Thus, acclimation was evident for both time-to-death and the sublethal endpoints. These results also indicate that Cu toxicity may involve both Na loss and LPO, and that Cu-acclimation may be brought about by prevention of these effects. Our follow-up study on potential mechanisms underlying this copper acclimation used a similar pre-exposure/exposure design. Fish were subsampled at the end of the 7-day acclimation period - just before the commencement of high-level Cu exposure (T), after 4h of this Cu exposure (T), and again after 8h of this Cu exposure (T). Whole-body Cu accumulation, Na/K-ATPase activity, metallothionein levels, and catalase activity were quantified for these time points. While Cu levels were higher in the Cu-pre-exposed fish than in the control fish at T, net Cu accumulation was faster in the control fish than in the Cu-pre-exposed fish during the subsequent high-level Cu exposure. Consequently, changes in Cu accumulation dynamics may play a role in the resistance. Metallothionein induction may also play a role in the observed acclimation, as Cu-acclimated fish had a significantly higher metallothionein concentration compared to the control fish. There was no evidence of involvement of Na/K-ATPase in the acclimation, as the activity of this enzyme remained lower in the pre-exposed fish than in the control fish throughout both Cu exposure periods. There was limited evidence that a reduced loss of catalase activity plays a role in the acclimation; catalase activity did not differ after the pre-exposure period but was significantly higher in Cu-acclimated fish than in the control fish at T.

The effects of copper on Na(+)/K (+)-ATPase and aquaporin expression in two euryhaline invertebrates

We used immunocytochemical and fluorometric techniques to show that gill cells of two marine invertebrates, the crab Neohelice granulata (osmoregulator) and the clam Mesodesma mactroides (osmoconformer), increase the expression of membrane transporters [Na(+)/K(+)-ATPase and aquaporin (AQP1)] after whole-animals exposure (96 h) to sublethal concentrations of copper in water of salinity 30 ppt, when both clams and crabs are isosmotic with respect to the environmental medium. A plausible interpretation of our findings is that this increased expression in membrane transporters may serve as an attempt to ameliorate the deleterious effects of copper on the mechanisms involved in ion and volume regulation in gill cells.

Ingestion of metal-nanoparticle contaminated food disrupts endogenous microbiota in zebrafish (Danio rerio)

Nanoparticles (NPs) can be ingested by organisms, and NPs with antimicrobial properties may disrupt beneficial endogenous microbial communities and affect organism health. Zebrafish were fed diets containing Cu-NPs or Ag-NPs (500 mg kg(-1) food), or an appropriate control for 14 d. Intestinal epithelium integrity was examined by transmission electron microscopy, and microbial community structure within the intestine was assessed by denaturing gradient gel electrophoresis (DGGE) of partial 16S rRNA. No lesions were observed in intestinal epithelia; however, presence of NPs in diets changed intestinal microbial community structure. In particular, some beneficial bacterial strains (e.g., Cetobacterium somerae) were suppressed to non-detectable levels by Cu-NP exposure, and two unidentified bacterial clones from the Firmicutes phylum were sensitive (not detected) to Cu, but were present in Ag and control fish. Unique changes in zebrafish microbiome caused by exposure to Ag-NP and Cu-NP indicate that NP ingestion could affect digestive system function and organism health.

Adrenaline and triiodothyronine modify the iron handling in the freshwater air-breathing fish Anabas testudineus Bloch: role of ferric reductase in iron acquisition

The effects of in vivo adrenaline and triiodothyronine (T(3)) on ferric reductase (FR) activity, a membrane-bound enzyme that reduces Fe(III) to Fe(II) iron, were studied in the organs of climbing perch (Anabas testudineus Bloch). Adrenaline injection (10 ng g(-1)) for 30 min produced significant inhibition of FR activity in the liver and kidney and that suggests a role for this stress hormone in iron acquisition in this fish. Short-term T(3) injection (40 ng g(-1)) reduced FR activity in the gills of fed fish but not in the unfed fish. Similar reduction of FR activity was also obtained in the intestine and kidney of fed fish after T(3) injection. Feeding produced pronounced decline in FR activity in the spleen but T(3) challenge in fed and unfed fish increased its activity in this iron storing organ and that point to the sensitivity of FR system to feeding activity. The in vitro effects of Fe on FR activity in the gill explants of freshwater fish showed correlations of FR with Na(+), K(+)-ATPase and H(+)-ATPase activities. Substantial increase in the FR activity was found in the gill explants incubated with all the tested doses of Fe(II) iron (1.80, 3.59 and 7.18 μM) and Fe(III) iron (1.25, 2.51 and 5.02 μM) and this indicate that FR and Na pump activity are positively correlated. On the contrary, substantial reduction of gill H(+)-ATPase activity was found in the gill explants incubated with Fe(II) iron and Fe(III) iron indicating that perch gills may not require a high acidic microenvironment for the reduction of Fe(III) iron. Accumulation of iron in the gill explants after Fe(III) iron incubation implies a direct relationship between Fe acquisition and FR activity in this tissue. The inverse correlation between FR activity and H(+)-ATPase activity in Fe(II) or Fe(III) loaded gills and the significant positive correlations of FR activity with total [Fe] content in the Fe(III) loaded gills substantiate that FR which shows sensitivity to sodium and proton pumps, has a vital role in Fe(II) and Fe(III) iron handling in this fish. Our data also provide evidence that adrenaline, T(3) and the feeding status are the vital factors that can regulate the storage and handling of iron in fish.