Autometallography and metallothionein immunohistochemistry in hepatocytes of turbot (Scophthalmus maximus L.) after exposure to cadmium and depuration treatment

Biomarkers of Exposure to Chemical Contamination in the Commercial Fish Species Lepidopus caudatus (Euphrasen, 1788): A Particular Focus on Plastic Additives

In recent years, the Mediterranean Sea has become an accumulation zone for waste generated by the 22 countries bordering its shores. Although the effects of plastic litter on the marine environment and on organisms have recently been studied in other areas, further information is needed for the Mediterranean Sea and, in particular, about plastics additives inputs and interactions with the biota and the trophic network, such as phthalates and bisphenol A. Plastic material production, use and disposal contribute also to the release of heavy metals into the environment, such as mercury (Hg), often used during the production of chlorine, the primary ingredient in PVC, lead (Pb) and cadmium (Cd), which are used as stabilizers in PVC and leach out of products during use and disposal. Our research aims to evaluate phthalates, bisphenol A and heavy metals contamination in Lepidopus caudatus (Pisces, Trichiuridae), which could be considered as a potential sentinel species. For the evaluation of toxicological effects, we evaluated the expression of vitellogenin and metallothioneins 1. In all samples analyzed, we have not found microplastics in the gastrointestinal tract but chemical analysis revealed the presence of high content of phthalates, and in particular high quantities of DIDP, DEHP, bis-benzylester phthalate, bis-butyl ester phthalate and mono-N-butyl ester phthalate in different organs. Instead, trace elements detected in tissue revealed a trend of concentrations generally higher in liver and intestine than gill and muscle tissues. Immunohistochemical analysis for anti-metallothionein 1 antibody showed a strong positivity of liver cells, both in females and males. Analysis for the anti-vitellogenin antibody showed in females a strong positivity both in the liver cells and in the gonads, in male specimens was found to be always negative except for a specimen, in which it was highlighted a positivity in some areas of the liver and of the gonad.

Molecular cloning, characterization and expression analysis of metallothionein in the liver of the teleost Acrossocheilus fasciatus exposed to cadmium chloride

Metallothionein (MT) has a characteristic molecular structure with a cysteine-rich content. This unique structure provides metal-binding and redox capabilities and promoting metal homeostasis and detoxification in living animals. In order to evaluate the effects of cadmium (Cd) on hepatic MT expression in the liver of Acrossocheilus fasciatus, we obtained the complete cDNA of the A. fasciatus liver MT for the first time. The MT cDNA contains a 605-bp sequence, which codes for 60 amino acids. Protein alignment showed that the similarity between MT protein sequences of A. fasciatus and those of other vertebrates (especially teleosts) was very high and a cysteine residue structure was also conserved. MT was detected in the liver, kidney, gill, testis, muscle, spleen, heart and brain tissues of A. fasciatus by tissue-specific expression analysis. After Cd exposure, Cd/hemoglobin saturation assay, immunohistochemistry and reverse-transcription quantitative PCR (RT-qPCR) were used to describe MT expression in liver tissue. These techniques indicate a sensitive response by liver MT to Cd exposure. The results suggest that A. fasciatus MT may play an important role in the detoxification processes in the liver, and also would be a useful biomarker for monitoring metal pollution in aquatic environments. In addition, A. fasciatus could be regarded as one candidate for a model species for bony fishes in ecotoxicology.

Immunolocalization of metallothionein in hepatocytes of guppy fish (Poecilia reticulata) exposed to tannery effluent: A biomarker study

Composite tannery effluent (TE) contaminated with a load of metals, especially chromium, is used in East Calcutta Wetland Ecosystem (ECW; a Ramsar site of West Bengal; No 1208) after natural stabilization for pisciculture and agriculture. Quantity and synergistic and antagonistic activities of both essential and nonessential metals in the effluents can induce a variety of complex changes in animal physiology. High fish yield and no apparent adverse influence on the fish biosystems thriving under pollutant stress at ECW allowed the practice to thrive sustainably over the last nearly 100 years. Thus, the present study was conducted to investigate the role of metallothionein (MT) as a potential biomarker in a fish biosystem following acute and chronic exposure to sublethal concentrations of tannery wastewater. MT localization in the liver tissue of guppy fish (Poecilia reticulata) was studied by the immuno gold-labeled electron microscopic technique. The data demonstrated increased metal content in fish body upon exposure to TE. Electron micrographs showed significant induction of hepatic MT in exposed P. reticulata over control specimens. Liver, being the detoxification site of an organism, plays a crucial role in the synthesis of MT and arrest of excess metal. The method employed in the present study for demonstrating the induction and localization of MT is innovative and could be used as a biomarker in fish exposed to metal stress. Our study also indicated that the metalloprotein complexes in fish tissue sequestered excess load of metals and thereby arrested unwanted interferences of excess metal loads in metabolic processes.

Bioaccumulation of mercury, cadmium, zinc, chromium, and lead in muscle, liver, and spleen tissues of a large commercially valuable catfish species from Brazil

The increasing amounts of heavy metals entering aquatic environments can result in high accumulation levels of these contaminants in fish and their consumers, which pose a serious risk to ecosystems and human health. We investigated the concentrations of mercury (Hg), cadmium (Cd), zinc (Zn), chromium (Cr), and lead (Pb) in muscle, liver, and spleen tissues of Pseudoplatystoma corruscans specimens collected from two sites on the Paraopeba River, Brazil. The level of heavy metals concentrations in the tissues was often higher in viscera (i.e. liver and spleen) than in muscle, and thus, the viscera should not be considered for human consumption. Correlations between metal concentrations and fish size were not significant. Although the levels of muscle bioaccumulation of Hg, Cd, Zn, Cr, and Pb, generally do not exceed the safe levels for human consumption, the constant presence of heavy metals in concentrations near those limits considered safe for human consumption, is a reason for concern, and populations who constantly consume fish from polluted rivers should be warned. Our findings also indicate that in a river network where certain areas are connected to other areas with high rates of environmental pollutants, people should be cautious about the regular consumption of fish, even when the fish consumed are caught in stretches of the basin where contamination levels are considered low, since many of the freshwater fish with high commercial value, such as the catfish surubim, are migratory.

A Comparison Effect of Copper Nanoparticles versus Copper Sulphate on Juvenile Epinephelus coioides: Growth Parameters, Digestive Enzymes, Body Composition, and Histology as Biomarkers

Copper nanoparticles (Cu-NPs) are components in numerous commercial products, but little is known about their potential hazard in the marine environments. In this study the effects of Cu-NPs and soluble Cu on juvenile Epinephelus coioides were investigated. The fish were exposed in triplicate to control, 20 or 100 µg Cu L(-1) as either copper sulphate (CuSO4) or Cu-NPs for 25 days. The growth performance decreased with increasing CuSO4 or Cu-NPs dose, more so in the CuSO4 than Cu-NPs treatment. Both forms of Cu exposure inhibited activities of digestive enzymes (protease, amylase, and lipase) found in liver, stomach, and intestine. With an increase in CuSO4 and Cu-NPs dose, crude protein and crude lipid decreased, but ash and moisture increased, more so in the CuSO4 than Cu-NPs treatment. The Cu-NPs treatment caused pathologies in liver and gills, and the kinds of pathologies were broadly of the same type as with CuSO4. With an increase in CuSO4 or Cu-NPs dose, the total polyunsaturated fatty acids decreased, but total monounsaturated fatty acids and total saturated fatty acids increased compared to control. Overall, these data showed that Cu-NPs had a similar type of toxic effects as CuSO4, but soluble Cu was more toxic than Cu-NPs.

Assessment of growth rate, chlorophyll a fluorescence, lipid peroxidation and antioxidant enzyme activity in Aphanizomenon flos-aquae, Pediastrum simplex and Synedra acus exposed to cadmium

In this study, the effects of cadmium on the cyanobacterium Aphanizomenon flos-aquae, the green alga Pediastrum simplex and the diatom Synedra acus was evaluated on the basis of growth rate, chlorophyll a fluorescence, lipid peroxidation and antioxidant enzyme activity. The EC50 values (effective concentration inducing 50 % of growth inhibition) of cadmium in A. flos-aquae, P. simplex and S. acus were 1.18 ± 0.044, 4.32 ± 0.068 and 3.7 ± 0.055 mg/L, respectively. The results suggested that cadmium stress decreases growth rate and chlorophyll a concentration. The normalized chlorophyll a fluorescence transients significantly increased at cadmium concentrations of 5.0, 10.0 and 20.0 mg/L, but slightly decreased at concentrations of 0.2, 0.5 and 1.0 mg/L. The chlorophyll fluorescence parameters showed considerable variation among the three species, while lipid peroxidation and antioxidant enzyme activities showed a significant increase. Our results demonstrated that blockage of electron transport on the acceptor side of photosystem II is the mechanism responsible for cadmium toxicity in freshwater microalgae, and that the tolerance of the three species to cadmium was in the order green alga P. simplex > diatom S. acus > cyanobacterium A. flos-aquae.

Assessment of the health status of wild fish inhabiting a cotton basin heavily impacted by pesticides in Benin (West Africa)

To determine the impact of agricultural pesticides used in cotton cultivation on the health status of fish living in a Beninese cotton basin, we compared the reproductive and hepatic systems of fish sampled from rivers located in both contaminated and pristine conditions. Different types of biomarkers, including biometric indices (a condition factor K, a gonadosomatic index GSI, and a hepatosomatic index HSI), plasma levels of sex steroids (11-ketotestosterone 11-KT, testosterone T and estradiol-17β E2) and the histopathology of the gonads and liver, were investigated for two different trophic levels of the following two fish species: the Guinean tilapia Tilapia guineensis and the African catfish Clarias gariepinus. The fish were captured during both the rainy season (when there is heavy use of pesticides on cotton fields) and the dry season from one site, in Pendjari River (reference site), which is located outside the cotton-producing basin, and from three other sites on the Alibori River within the cotton-producing basin. Comparing fish that were sampled from contaminated (high levels of endosulfan, heptachlor and DDT and metabolites) and reference sites, the results clearly indicated that agricultural pesticides significantly decreased K and GSI while they increased HSI, regardless of the season, species and sex of the fish. These pesticides also induced a decrease in the plasma levels of 11-KT and T and increased those of E2. The histopathology of the testes revealed, in both species, a high rate of testicular oocytes, up to 50% in the African catfish, downstream of the Alibori River, which indicated estrogenic effects from the pesticides. The disruption of male spermatogenesis primarily included necrosis, fibrosis and the presence of foam cells in the lobular lumen. The histopathology of the ovaries revealed high levels of pre-ovulatory follicular atresia, impaired oogenesis, a decrease in the oocyte vitellogenic diameter and other lesions, such as fibrosis, vacuolation and melano-macrophagic centers. The histopathology of the liver revealed the presence of necrosis, hypertrophic hepatocytes, foci of vacuolation, glycogen depletion and hemosiderin. An assessment of the general health of the fish indicated that all of the sampled fish from the polluted sites were in poorer health compared with those from the reference site but that the African catfish appeared much more affected than the Guinean tilapia, regardless of the sex and season. In conclusion, the overall results indicated that agricultural pesticides significantly impair the endocrine regulation of fish living in the Beninese cotton basin and that this would most likely be one of the causes of the severe damage observed in the liver and gonads and the reduced health condition.

Histopathological effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in the gills, intestine and liver of turbot (Psetta maxima)

Polybrominated diphenyl ethers (PBDEs) have become ubiquitous environmental pollutants because of their widespread use as flame retardants in various consumer products (plastics, textiles, electronic appliances and building materials) and their long half-life. BDE-47 (2,2',4,4'-tetrabromodiphenyl ether) is the major PBDE congener detected in the environment and in animal tissues. In the present study, the histopathological effects are examined of BDE-47 on the gills, intestine and liver tissues of juvenile turbot (Psetta maxima).The specimens were exposed to two concentrations of BDE-47 (0.03 and 0.3 µg/L) for a period of 15 days. The histological changes were detected microscopically and evaluated with quantitative or semi-quantitative analyses. At the doses of BDE-47 assayed, the most common gill injuries were lamellar fusion, blood congestion and hyperplasia and hypertrophy of the epithelial and mucous cells. In the intestine of fish exposed to BDE-47, the alterations detected were hyperplasia and hypertrophy of mucous cells. Hepatic lesions in the liver of fish exposed to BDE-47 were characterized by circulatory disturbances, irregular morphology of hepatocytes, cellular and nuclear hypertrophy, and nuclear vacuolation and pyknosis. As BDE-47 is present in food and other material related to aquaculture systems, our results indicate that exposure to this pollutant could have serious consequences on health in turbot and other cultured fish.

Trace metals and over-expression of metallothioneins in bladder tumoral lesions: a case-control study

BACKGROUND

Previous studies have provided some evidence of a possible association between cancer and metallothioneins. Whether this relates to an exposure to carcinogenic metals remains unclear.

METHODS

In order to examine the association between the expression of metallothioneins and bladder tumors, and to compare the levels of arsenic, cadmium, chromium, lead and nickel in animals with bladder tumors and animals without bladder tumors, 37 cases of bovine bladder tumors and 17 controls were collected. The detection and quantification of metallothioneins in bladder tissue of both cases and controls was performed by immunohistochemistry. And the quantification of metals in tissue and hair was assessed by inductively coupled plasma - mass spectrometry.

RESULTS

Increased expression of metallothioneins was associated with bladder tumors when compared with non-tumoral bladder tissue (OR = 9.3, 95% CI: 1.0 - 480). The concentrations of cadmium, chromium, lead and nickel in hair of cases were significantly higher than those of controls. However, as for the concentration of metals in bladder tissue, the differences were not significant.

CONCLUSION

Though the sample size was small, the present study shows an association between bladder tumors and metallothioneins. Moreover, it shows that concentrations of metals such as cadmium, chromium, lead and nickel in hair may be used as a biomarker of exposure.

The dynamics of protein and metal metabolism in acclimated and Cd-exposed freshwater crabs (Potamonautes warreni)

Climatic and man-made impacts induced dynamic molecular responses in the South African freshwater crab, Potamonautes warreni. Adult crabs exhibited MT-like protein, binding Cd (0.02micromolg(-1) wet mass+/-0.02), Cu (0.326micromolg(-1) wet mass+/-0.15), and Zn (0.534micromolg(-1) wet mass+/-0.20). The native protein binding Cd, Cu, and Zn showed a respective molecular mass (M) of 9.10kDa+/-1.74, 8.95kDa+/-1.66, and 9.32kDa+/-0.93. With exposure to 0.2mgCd(2+)l(-1) for up to 21 days in 50% of these crabs approximately 90% of Cd was bound to the MT-like protein component (8.54kDa+/-1.64), coinciding with a Zn-bound MT-like component (8.2kDa+/-1.54). Less than 10% were bound in the high M protein component, suggesting a protective function of the protein. In the remaining crabs metals were bound to protein (6.8kDa) with a predominant Cu-binding component.

Metallothionein-2 gene from the mandarin fish Siniperca chuatsi: cDNA cloning, tissue expression, and immunohistochemical localization

The metallothionein-2 (MT-2) gene was isolated from the mandarin fish, one of the most important industrial aquatic animals in China, by using rapid amplification of cDNA ends (RACE). The deduced amino acid sequence of MT-2 comprised 60 amino acids and showed approximately 62.3% identity to human metallothionein. Its promoter region was amplified by thermal asymmetric interlaced polymerase chain reaction (TAIL-PCR). The MT-2 gene consists of 3 exons and 2 introns, extending approximately 900 bp of genomic sequence. Phylogenetic analysis clearly demonstrated that MT-2 formed a clade with fish metallothionein. The promoter region contained 5 putative metal-regulatory elements (MREs) and 1 TATA box. Real-time quantitative RT-PCR analysis revealed that MT-2 transcripts were significantly increased in the brain and gills and were stable in the muscles, liver, and trunk kidney in Cd(2+)-stimulated fish. Western blotting analysis demonstrated that the protein of the MT-2 gene was expressed mainly in the gills, liver, heart, trunk kidney, muscle, and intestine; it was weakly detected in the brain and head kidney. Moreover, the MT-2 protein was immunohistochemically detected in the cytoplasm in the liver and trunk kidney. All the above results revealed that the mandarin fish MT-2 would be a useful biomarker for metal pollution.

Identification of Wap65, a human homologue of hemopexin as a copper-inducible gene in swordtail fish, Xiphophorus helleri

Copper is one of the major heavy metal pollutants found in the aquatic environment. Therefore, it is important for determining the genes that play a key role in copper metabolism in aquatic organisms. This study, thus, aimed to identify a new copper-inducible gene in swordtail fish, Xiphophorus helleri. Using ACP-based RT-PCR coupled with RLM-RACE, we cloned Wap65, a mammalian homologue of hemopexin gene. The gene exhibits high identity at amino acid levels with the Wap65 gene of other fish species (42-68%) and mammalian hemopexin gene (35-37%). In addition, ten cysteine and two histidine residues are conserved in the swordtail fish Wap65 gene. These cysteine residues are vital for structural integrity, and histidine residues provide high binding affinity towards heme. As revealed by RT-PCR, the gene was upregulated in swordtail fish that were exposed to copper in a dose- and time-dependent manner. Therefore, the identification of Wap65, a mammalian homologue of hemopexin, as a new copper-inducible gene will provide greater insight into the role of this gene in copper metabolism.

Apoptosis, metallothionein, and bioavailable metals in domestic mice (Mus musculus L.) from a human-inhabited volcanic area

The influence of extreme environments of volcanic origin over vertebrates and the cellular responses that these may give are almost unknown. The main objectives were to evaluate the exposure of mice to metals in the interior of houses of a small village settled inside a volcanic crater (Furnas, Azores), and the levels of apoptosis and metallothionein in the organs (lung, liver, and kidney) of those animals. Adult mice (Mus musculus) were captured in two areas, one with volcanic activity and the other without it over the last three centuries. In the excised organs, analysis of metals (Al, Cd, Pb, Zn), TUNEL assay for apoptosis, and immunohistochemistry for metallothionein were undertook. Mice from the area with volcanic activity presented higher levels of apoptosis and metallothionein than those from the area without volcanic activity. Such results were in agreement with the differences in metal burdens of the three organs, and interestingly these concentrations were similar to or higher than others found in heavily polluted areas outside the Azores. Thus, there may be a high risk of harmful effects for organisms, including humans, inhabiting areas with volcanism, where hazardous gases and metals in the air are very common during the entire day or even all year round.

Quantitative changes in metallothionein expression in target cell-types in the gills of turbot (Scophthalmus maximus) exposed to Cd, Cu, Zn and after a depuration treatment

Turbot (Scophthalmus maximus) were exposed to two sublethal concentrations (1 and 10 mg metal/l) of cadmium (8.9 and 89 microM Cd), copper (15.26 and 152.6 microM Cu) and zinc (15.3 and 153 microM Zn) for 7 days, and afterwards were maintained depurating for 14 days. Immunoreactive metallothioneins (irMTs) and metal ions were localized in the branchial epithelium by immunohistochemistry (using an anti-Cod MT antibody) and autometallography (AMG), respectively. Metal ions were demonstrated by AMG as black silver deposits (BSD), mainly in mucocytes (MC) and to a lesser extent in the other branchial cell-types (respiratory cells (RC), chloride cells (CC) and basal layer cells (BLC)). Irrespective of the metal supplied, BSD were rapidly visualized in MC after 1 h of exposure. This accumulation did not increase with increasing exposure time and concentration. Metallothionein expression was mainly observed in mature CC in the interlamellar space for all exposure conditions and it was shown that all mature cells express the same amount of irMT. The number of CC exhibiting irMT in metal-exposed turbots increased following short exposure times (1 h-1 day) in the filament epithelium and following longer exposure times (1-7 days) in the secondary lamellae. Total levels of irMT in the gills (quantified by image analysis and densitometry) increased significantly in metal-exposed turbot and were related to increased exposure times. It can be concluded that the total content of irMT in the gills of metal-exposed turbot is governed by changes in the number of mature CC expressing the protein. The quantification of total irMT in branchial CC can be considered as a reliable biomarker of metal exposure since reflects changes in metal bioavailability. This approach based on cell-selective immunohistochemistry can be simplified by only quantifying the number of mature CC. In addition, the dramatic increase of CC in the gills that produces epithelial thickening of the FE enhances migration of CC up to the edge of the SL and provokes the hypertrophy and fusion of secondary lamellae can be considered as unspecific biomarkers of effect indicating disturbed health in turbot.

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.