Induction of two major isoforms of metallothionein in crucian carp (Carassius cuvieri) by air-pumping stress, dexamethasone, and metals

Co-exposure to titanium dioxide nanoparticles (NpTiO2) and lead at environmentally relevant concentrations in the Neotropical fish species Hoplias intermedius

Growing production and utilization of titanium dioxide nanoparticles (NpTiO2) invariably lead to their accumulation in oceans, rivers and other water bodies, thus increasing the risk to the welfare of this ecosystem. The progressive launch of these nanoparticles in the environment has been accompanied by concern in understanding the dynamics and the toxic effect of these xenobiotic in different ecosystems, either on their own or in tandem with different contaminants (such as organic compounds and heavy metals), possibly altering their toxicity. Nevertheless, it remains unknown if these combined effects may induce damage in freshwater organisms. Therefore, this study aimed to analyze the consequences caused by NpTiO2, after a waterborne exposure of 96 h to a Neotropical fish species Hoplias intermedius, as well as after a co-exposure with lead, whose effects for fish have already been well described in the literature. The characterization of NpTiO2 stock suspension was carried out in order to provide additional information and revealed a stable colloidal suspension. As a result, NpTiO2 showed some genotoxic effects which were observed by comet assay in gill, kidney and brain cells. Also, the activity of brain acetylcholinesterase (AChE) has not changed, but the activity of muscle AChE decreased in the group exposed only to PbII. Regarding the hepatic antioxidant system, catalase (CAT) did not show any change in its activity, whereas that of superoxide dismutase (SOD) intensified in the groups submitted only to PbII and NpTiO2 alone. As for lipid peroxidation, there was a decrease in the group exposed to the NpTiO2 alone and to the co-exposed group (NpTiO2+PbII). As far as metallothionein is concerned, its concentration rose for the co-exposed group (NpTiO2+PbII) and for the group exposed to PbII alone. Overall, we may conclude that NpTiO2 alone caused DNA damage to vital tissues. Also, some impairment related to the antioxidant mechanism was described but it is probably not related to the DNA damage observed, suggesting that the genotoxic effect observed may be due to a different mechanism instead of ROS production.

Cloning and functional characterization of 5′-upstream region of metallothionein-I gene from crucian carp (Carassius cuvieri)

Metallothioneins are low molecular weight, cysteine-rich, metal-binding proteins, which can be induced by heavy metal ions, cytokines, stress, and hormones. To investigate the roles of the main cis-acting elements involved in the inducible expression of metallothionein gene in fish, the 5'-upstream region of crucian carp (Carassius cuvieri) metallothionein-I gene had been cloned and analyzed after our previous work on metallothionein-II. In its upstream region, several putative cis-acting elements, including nine metal regulatory elements (MREs), one antioxidant response element, one E-box, and three interleukin-6 responsive elements, etc. were found. The nine metal regulatory elements are confined in less than 1000 bp from ATG start codon and organized into two clusters with different roles to the induction of the metallothionein-I expression. Deletion mutant assays demonstrated that both the distal and proximal clusters of metal regulatory elements contributed to the basal expression of the metallothionein-I, but only the proximal cluster was the chief contributor to the metal fold induction. In transient luciferase reporter assays, Zn2+ and Cd2+ served as much stronger inducers than Cu2+ to the metallothionein-I expression. H2O2 also could activate the metallothionein-I promoter about two-fold, which was mediated by the antioxidant response element (TGACAACGC, -437/-445). In conclusion, our studies demonstrate the roles of metal regulatory element and antioxidant response element in the induction of crucian carp metallothionein-I gene, and provide the regulatory mechanism for the use of fish metallothionein as a biomarker for monitoring of metal contamination in waters.

Cloning of crucian carp (Carassius cuvieri) metallothionein-II gene and characterization of its gene promoter region

The genomic DNA of crucian carp (Carassius cuvieri) metallothionein-II (ccMT-II), with its upstream region, was obtained. The sequence analysis of its upstream region revealed several putative cis-acting elements including seven metal regulatory elements (MREs), three activator protein 1 (AP1), two glucocorticoid response elements (GREs), etc. The seven MREs locate into two clusters, a distal cluster with four MREs within -800/-600bp from the translation start site and a proximal cluster with three MREs close to TATA box. In transient luciferase gene expression assays, both of the distal and proximal cluster MREs have significantly shown synergistic effects in the transcription of ccMT-II gene; the proximal cluster of MREs serves as the major elements in metal inducing activity; Zn(2+) and Cd(2+) served as much stronger inducers than Cu(2+) shown in ccMT-II expression. The two GRE homologous sequences in ccMT-II promoter showed not to be inductive in either HepG2 or HEK293.

Cellular biomarkers of exposure and biological effect in hepatocytes of turbot (Scophthalmus maximus) exposed to Cd, Cu and Zn and after depuration

Cellular biomarkers of exposure and biological effects were measured in hepatocytes of turbot exposed to either Cd, Cu or Zn at concentrations of 1 and 10 mg/l seawater for 7 days and after depuration for 14 days. Metal content in hepatocyte lysosomes was determined by image analysis after autometallography (AMG) as volume density of autometallographed black silver deposits (Vv(BSD)). Metallothionein (MT) levels were quantified on liver sections by microdensitometry after immunohistochemical staining with a polyclonal anti cod-MT antibody (MT-OD), and in the cytosolic fraction of hepatocytes by difference pulse polarography (MT-DPP). Lysosomal structural changes (lysosomal volume, surface and numerical densities--Vv(LYS), Sv(LYS) and Nv(LYS-), and surface-to-volume ratio S/V(Lys)) were quantified by image analysis after demonstration of beta-glucuronidase activity on liver cryotome sections. Vacuolisation produced by metal-exposure in hepatocytes was quantified by stereology as volume density of vacuoles (Vv(VAC)). Exposure time and metal concentrations significantly affected Vv(BSD) in lysosomes, MT levels and the degree of vacuolisation after 1 h and 1 day exposure to the three metals. The highest Vv(BSD), MT and Vv(VAC) values were recorded after 7 days exposure in all cases. MT-OD and MT-DPP were significantly correlated with Vv(BSD). Vv(LYS) in hepatocytes increased significantly after exposure to the metals. Exposure biomarkers returned to control values after depuration with the exception of those turbots that had been exposed to 10 mg Cd/l. Alike, Vv(LYS) and Sv(lys) (Cu exposure) and Nv(LYS) (Cd and Zn exposures) returned to control values after depuration. It has been therefore demonstrated that the biomarkers used are reversible and return towards control levels once metal exposure ceases. Overall, it is concluded that Vv(BSD), MT-levels and lysosomal responses are valuable biomarkers to assess metal exposure and its effects in turbot, although in quantitative terms the biomarker response varied between metals.

Fish bioaccumulation and biomarkers in environmental risk assessment: a review

In this review, a wide array of bioaccumulation markers and biomarkers, used to demonstrate exposure to and effects of environmental contaminants, has been discussed in relation to their feasibility in environmental risk assessment (ERA). Fish bioaccumulation markers may be applied in order to elucidate the aquatic behavior of environmental contaminants, as bioconcentrators to identify certain substances with low water levels and to assess exposure of aquatic organisms. Since it is virtually impossible to predict the fate of xenobiotic substances with simple partitioning models, the complexity of bioaccumulation should be considered, including toxicokinetics, metabolism, biota-sediment accumulation factors (BSAFs), organ-specific bioaccumulation and bound residues. Since it remains hard to accurately predict bioaccumulation in fish, even with highly sophisticated models, analyses of tissue levels are required. The most promising fish bioaccumulation markers are body burdens of persistent organic pollutants, like PCBs and DDTs. Since PCDD and PCDF levels in fish tissues are very low as compared with the sediment levels, their value as bioaccumulation markers remains questionable. Easily biodegradable compounds, such as PAHs and chlorinated phenols, do not tend to accumulate in fish tissues in quantities that reflect the exposure. Semipermeable membrane devices (SPMDs) have been successfully used to mimic bioaccumulation of hydrophobic organic substances in aquatic organisms. In order to assess exposure to or effects of environmental pollutants on aquatic ecosystems, the following suite of fish biomarkers may be examined: biotransformation enzymes (phase I and II), oxidative stress parameters, biotransformation products, stress proteins, metallothioneins (MTs), MXR proteins, hematological parameters, immunological parameters, reproductive and endocrine parameters, genotoxic parameters, neuromuscular parameters, physiological, histological and morphological parameters. All fish biomarkers are evaluated for their potential use in ERA programs, based upon six criteria that have been proposed in the present paper. This evaluation demonstrates that phase I enzymes (e.g. hepatic EROD and CYP1A), biotransformation products (e.g. biliary PAH metabolites), reproductive parameters (e.g. plasma VTG) and genotoxic parameters (e.g. hepatic DNA adducts) are currently the most valuable fish biomarkers for ERA. The use of biomonitoring methods in the control strategies for chemical pollution has several advantages over chemical monitoring. Many of the biological measurements form the only way of integrating effects on a large number of individual and interactive processes in aquatic organisms. Moreover, biological and biochemical effects may link the bioavailability of the compounds of interest with their concentration at target organs and intrinsic toxicity. The limitations of biomonitoring, such as confounding factors that are not related to pollution, should be carefully considered when interpreting biomarker data. Based upon this overview there is little doubt that measurements of bioaccumulation and biomarker responses in fish from contaminated sites offer great promises for providing information that can contribute to environmental monitoring programs designed for various aspects of ERA.

Killifish metallothionein messenger RNA expression following temperature perturbation and cadmium exposure

Metallothionein (MT), a cysteine-rich metal binding protein, is considered to play an essential role in the regulation of intracellular metals. Induction of MT in mammalian and nonmammalian tissues following heavy metal exposure may serve as a defense mechanism and a biomarker of environmental exposure to chemical stressors such as toxic metals. In this study, MT messenger RNA (mRNA) expression was characterized in male and female nonspawning and spawning killifish (Fundulus heteroclitus) following an 8-day exposure to specific sublethal stressors, which included temperature perturbation (26 degrees C or 10 degrees C) and/or 6 ppb of waterborne cadmium chloride (CdCl2). Hepatic, gill, and intestinal MT mRNA, expressed as copy number per microgram of total RNA, was assessed by reverse transcriptase-polymerase chain reaction and electrochemiluminescence using winter flounder (Pleuronectes americanus) MT complementary DNA primers. Liver, gill, and intestine MT mRNA expression was significantly (P < 0.05) increased in nonspawning killifish exposed to 26 degrees C compared with those exposed to 19 degrees C (control). In addition, a significant (P < 0.05) increase in gill MT mRNA induction was observed in nonspawning killifish exposed to 6 ppb of waterborne CdCl2 compared with controls. The results of this study demonstrate significant MT mRNA induction in nonspawning killifish following short-term exposure to physiological and chemical stressors. Thus, further research may be necessary before the use of killifish MT mRNA induction as a biomarker of environmental chemical stress exposure alone.