Copper induces Cu-ATPase ATP7A mRNA in a fish cell line, SAF1

Effects of heavy metals on fish physiology - A review

The pollution by heavy metals poses a serious threat to the aquatic environment and to the organisms if the concentration of heavy metals in the environment exceeds the safe limits. Due to their non-biodegradable and long persistence nature in the environment, heavy metals cause toxicity in fish by producing oxygen reactive species through oxidizing radical production. In this review, we investigated the effects of heavy metals on fish physiology with special emphasis on hemato-biochemical properties, immunological parameters especially hormones and enzymes, histopathology of different major organs and underlying molecular mechanisms. All those parameters are significantly affected by heavy metal exposure and are found to be important bio-monitoring tools to assess heavy metal toxicity. Hematological and biochemical alterations have been documented including cellular and nuclear abnormalities in different fish species exposed to different concentrations of heavy metals. Major fish organs (gills, liver, kidneys) including intestine, muscles showed different types of pathology specific to organs in acute and chronic exposure to different heavy metals. This study also revealed the expression of different genes involved in oxidative stress and detoxification of heavy metals. In a nutshell, this article shades light on the manipulation of fish physiology by the heavy metals and sought attention in the prevention and maintenance of aquatic environments particularly from heavy metals contaminations.

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.

New Insights into Cellular Impacts of Metals in Aquatic Animals

Toxic metals remain a current important threat to aquatic ecosystems, despite regulatory efforts to reduce their release. Several toxic metals already appear in the list of priority substances polluting surface waters, while concerns arise from the increasing use of technology-critical metals such as metallic nanoparticles, rare-earth, and platinum group metals. In aquatic environments, various chemical, biological and physical processes determine the impact of metals on the biota. This review provides insights into responses to toxic metals recently reported in freshwater and marine animals. The specific emphasis is on: (i) common cellular and molecular responses; (ii) stress proteins; (iii) redox homeostasis; (iv) cytoskeleton rearrangement; (v) metabolism reshuffle; (vi) free cellular energy and mitochondrial metabolism; and (vi) immunity. These endpoints are promising, notably in multi-biomarker approaches to identify precise cellular toxicity pathways and anticipate the impact of environmental metal pollution.

Gene Expression Profiling in Fish Toxicology: A Review

In this review, we present an overview of transcriptomic responses to chemical exposures in a variety of fish species. We have discussed the use of several molecular approaches such as northern blotting, differential display reverse transcription-polymerase chain reaction (DDRT-PCR), suppression subtractive hybridization (SSH), real time quantitative PCR (RT-qPCR), microarrays, and next-generation sequencing (NGS) for measuring gene expression. These techniques have been mainly used to measure the toxic effects of single compounds or simple mixtures in laboratory conditions. In addition, only few studies have been conducted to examine the biological significance of differentially expressed gene sets following chemical exposure. Therefore, future studies should focus more under field conditions using a multidisciplinary approach (genomics, proteomics and metabolomics) to understand the synergetic effects of multiple environmental stressors and to determine the functional significance of differentially expressed genes. Nevertheless, recent developments in NGS technologies and decreasing costs of sequencing holds the promise to uncover the complexity of anthropogenic impacts and biological effects in wild fish populations.

In vitro Assessment of Hg Toxicity in Hepatocytes from Heat-Stressed Atlantic Salmon

Global warming may alter the bioavailability of contaminants in aquatic environments. In this work, mercury (Hg²⁺) toxicity was studied in cells obtained from Atlantic salmon smolt kept at 15 °C (optimal growth temperature) for 3 months or at a stepwise increase to 20 °C (temperature-stress) during 3 months prior to cell harvest to evaluate whether acclimation temperature affects Hg toxicity. To examine possible altered dietary requirements in warmer seas, one group of fish following the stepwise temperature regimes was fed a diet spiked with antioxidants. Atlantic salmon hepatocytes were exposed in vitro to 0, 1.0, or 100 μM Hg²⁺ for 48 h. Cytotoxicity, determined as electrical impedance changes with the xCELLigence system, and transcriptional responses, determined with RT-qPCR, were assessed as measures of toxicity. The results showed that inorganic Hg at a concentration up to 100 μM is not cytotoxic to Atlantic salmon hepatocytes. Significance and directional responses of the 18 evaluated target genes suggest that both Hg and temperature stress affected the transcription of genes encoding proteins involved in the protection against ROS-generated oxidative stress. Both stressors also affected the transcription of genes linked to lipid metabolism. Spiking the diet with antioxidants resulted in higher concentrations of Se and vitamin C and reduced concentration of Hg in the liver in vivo, but no interactions were seen between the dietary supplementation of antioxidants and Hg toxicity in vitro. In conclusion, no evidence was found suggesting that inorganic Hg is more toxic in cells harvested from temperature-stressed fish.

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

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

Metal-Polycyclic Aromatic Hydrocarbon Mixture Toxicity in Hyalella azteca. 2. Metal Accumulation and Oxidative Stress as Interactive Co-toxic Mechanisms

Mixtures of metals and polycyclic aromatic hydrocarbons (PAHs) are commonly found in aquatic environments. Emerging reports have identified that more-than-additive mortality is common in metal-PAH mixtures. Individual aspects of PAH toxicity suggest they may alter the accumulation of metals and enhance metal-derived reactive oxygen species (ROS). Redox-active metals (e.g., Cu and Ni) are also capable of enhancing the redox cycling of PAHs. Accordingly, we explored the mutual effects redox-active metals and PAHs have on oxidative stress, and the potential for PAHs to alter the accumulation and/or homeostasis of metals in juvenile Hyalella azteca. Amphipods were exposed to binary mixtures of Cu, Cd, Ni, or V, with either phenanthrene (PHE) or phenanthrenequinone (PHQ). Mixture of Cu with either PAH produced striking more-than-additive mortality, whereas all other mixtures amounted to strictly additive mortality following 18-h exposures. We found no evidence to suggest that interactive effects on ROS production were involved in the more-than-additive mortality of Cu-PHE and Cu-PHQ mixtures. However, PHQ increased the tissue concentration of Cu in juvenile H. azteca, providing a potential mechanism for the observed more-than-additive mortality.

Penicillamine increases free copper and enhances oxidative stress in the brain of toxic milk mice

Wilson disease (WD) is characterized by the accumulation of copper arising from a mutation in the ATP7B gene. Penicillamine (PA) makes 10–50% of the patients with neurologic symptoms neurologically worse at the early stage of administration. The aim of this study was to determine how the copper metabolism changes and whether the change impairs the brain of toxic milk (tx) mice, an animal model of WD, during the PA administration. The free copper and protein-bound copper concentrations in the serum, cortex and basal ganglia of tx mice with PA administration for 3 days, 10 days and 14 days, respectively, were investigated. The expression of copper transporters, ATP7A and CTR1,was analyzed by real-time quantitative PCR, immunofluorescence and Western blot. Then SOD, MDA and GSH/GSSG were detected to determine whether the oxidative stress changed correspondingly. The results revealed the elevated free copper concentrations in the serum and brain, and declined protein-bound copper concentrations in the brain of tx mice during PA administration. Meanwhile, transiently increased expression of ATP7A and CTR1 was observed generally in the brain parenchyma by immunofluorescence, real-time quantitative PCR and Western blot. Additionally, ATP7A and CTR1 were observed to locate mainly at Golgi apparatus and cellular membrane respectively. Intense staining of ATP7A in the choroid plexus was found in tx mice on the 3rd and 10th day of PA treatment, but rare staining of ATP7A and CTR1 in the blood-brain barrier (BBB). Decreased GSH/GSSG and increased MDA concentrations were also viewed in the cortex and basal ganglia. Our results suggested the elevated free copper concentrations in the brain might lead to the enhanced oxidative stress during PA administration. The increased free copper in the brain might come from the copper mobilized from brain parenchyma cells but not from the serum according to the ATP7A and CTR1 expression analysis.