Metallothionein Expression as a Physiological Response against Metal Toxicity in the Striped Rockcod Trematomus hansoni

Characterisation of the prdx4 gene in Squalius cephalus and its role in freshwater environments with varying impact of perfluoroalkyl substances (PFAS)

Given the pervasive detection of perfluoroalkyl substances (PFAS) in several environmental matrices and their known toxicological effects, it is imperative to investigate their impact on the physiological responses of freshwater organisms. This research is crucial for developing effective strategies to protect aquatic ecosystems by directly addressing how PFAS influences aquatic species' health and survival. In this study, we conducted a biomonitoring analysis to evaluate the effects of naturally occurring PFAS, specifically perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), on the physiology of common chub (Squalius cephalus), a freshwater fish native to the Veneto region. We measured oxidative damage in the kidney and skeletal muscle, with results showing that low PFAS contamination is sufficient to increase protein oxidation in both tissues. Conversely, even high PFAS levels did not induce lipid peroxidation in either tissue. We also examined the expression of peroxiredoxin isoform 4 (prdx4) in the kidney, finding its down-regulation with increasing PFAS pollution, which demonstrates the minor function of Prdx4 against oxidative stress. Instead, its down-regulation plays an important role in increasing lipid accumulation in the cell, creating a hydrophobic environment that limits PFAS bioaccumulation and their capacity to bind proteins, thus preserving them from further damage.

Effects of metallic dust on Nile tilapia: Exploring the relationship between metal bioaccumulation, metallothionein levels, and oxidative stress responses

Settleable atmospheric particulate matter (SePM), from steelmaking processes, contains a complex mixture of metals, metalloids, and metallic nanoparticles. The SePM is released airborne and disperses in water, representing a significant threat to aquatic life, particularly fish. This study investigated the effects of a sublethal and environmentally relevant concentration of SePM (1 g·L-1) for 96 h in the gill, liver, kidney, and white muscle of Nile tilapia (Oreochromis niloticus), employing exposure and effect biomarkers to test causality between metal accumulation and biochemical responses. The gills and liver showed the highest bioaccumulation of metals and integrated response index value, indicating susceptibility to metal accumulation. However, the gills produce a protective mucus layer that may mitigate metal toxicity. The kidneys and muscle tissue also showed bioaccumulation of metals, although to a lesser extent. The liver and kidneys experienced oxidative stress, characterized by reduced metallothionein and glutathione levels, as well as damage to lipids, proteins, and DNA. The accumulation of less-studied metals, particularly Rare Earth Elements (REEs), compromised the integrity of biomolecules in these tissues. In conclusion, the complex dynamics of metal bioaccumulation in Nile tilapia exposed to SePM reveal varied tissue responses and primary effects like oxidative damage. They also highlight the need for further research and regulation of other metals and their potential impacts on aquatic ecosystems and human health.

Ecotoxicological risk of asphalt pavements to aquatic animals associated with pollutant leaching

Contaminants such as heavy metals and polycyclic aromatic hydrocarbons (PAHs) can be released from asphalt pavement and transported through stormwater runoff to nearby water bodies, leading to water pollution and potential harm to living aquatic animals. This study characterizes the heavy metal and PAH leaching from various asphalt paving materials and their potential ecotoxicological effects on zebrafish Danio rerio. Artificial runoffs were prepared in the laboratory concerning the effects of water, temperature, and traffic. The concentrations of heavy metals and PAHs in the leachates were quantified, while the toxicity assessment encompassed mortality, metal stress, PAH toxicity, inflammation, carcinogenicity, and oxidative damage. Gene expressions of related proteins or transcription factors were assessed, including metallothionines, aryl hydrocarbon receptors, interleukin-1β, interleukin-10, nuclear factor-κB, tumor necrosis factor-α, tumor suppressor p53, heat shock protein 70, and reactive oxygen species (ROS). The findings demonstrate that leachates from asphalt pavements containing waste bottom ash, crumb rubber, or specific chemicals could induce notable stress and inflammation responses in zebrafish. In addition, potential carcinogenic effects and the elevation of ROS were identified within certain treatment groups. This study represents the first attempt to assess the ecotoxicity of pavement leachates employing a live fish model, thereby improving the current understanding of the environmental impact of asphalt pavements.

Expression and Functional Analysis of the Metallothionein and Metal-Responsive Transcription Factor 1 in Phascolosoma esculenta under Zn Stress

Metallothioneins (MTs) are non-enzymatic metal-binding proteins widely found in animals, plants, and microorganisms and are regulated by metal-responsive transcription factor 1 (MTF1). MT and MTF1 play crucial roles in detoxification, antioxidation, and anti-apoptosis. Therefore, they are key factors allowing organisms to endure the toxicity of heavy metal pollution. Phascolosoma esculenta is a marine invertebrate that inhabits intertidal zones and has a high tolerance to heavy metal stress. In this study, we cloned and identified MT and MTF1 genes from P. esculenta (designated as PeMT and PeMTF1). PeMT and PeMTF1 were widely expressed in all tissues and highly expressed in the intestine. When exposed to 16.8, 33.6, and 84 mg/L of zinc ions, the expression levels of PeMT and PeMTF1 in the intestine increased first and then decreased, peaking at 12 and 6 h, respectively, indicating that both PeMT and PeMTF1 rapidly responded to Zn stress. The recombinant pGEX-6p-1-MT protein enhanced the Zn tolerance of Escherichia coli and showed a dose-dependent ABTS free radical scavenging ability. After RNA interference (RNAi) with PeMT and 24 h of Zn stress, the oxidative stress indices (MDA content, SOD activity, and GSH content) and the apoptosis indices (Caspase 3, Caspase 8, and Caspase 9 activities) were significantly increased, implying that PeMT plays an important role in Zn detoxification, antioxidation, and anti-apoptosis. Moreover, the expression level of PeMT in the intestine was significantly decreased after RNAi with PeMTF1 and 24 h of Zn stress, which preliminarily proved that PeMTF1 has a regulatory effect on PeMT. Our data suggest that PeMT and PeMTF1 play important roles in the resistance of P. esculenta to Zn stress and are the key factors allowing P. esculenta to endure the toxicity of Zn.

A metallothionein from disk abalone (Haliotis discus discus): Insights into its functional roles in immune response, metal tolerance, and oxidative stress

Metallothioneins (MTs) are cysteine-rich metal-binding proteins whose expression is induced by exposure to essential and non-essential metals, making them potential biological markers for assessing metal pollution in various biomonitoring programs. However, the functional properties of these proteins are yet to be comprehensively characterized in most marine invertebrates. In this study, we identified and characterized an MT homolog from the disk abalone (Haliotis discus discus), referred to as disk abalone MT (AbMT). AbMT exhibited the same primary structural features as MTs from other mollusks containing two β-domains (β2β1-form). AbMT protein demonstrated metal-binding and detoxification abilities against Zn, Cu, and Cd, as evidenced by Escherichia coli growth kinetics, metal tolerance analysis, and UV absorption spectrum. Transcriptional analysis revealed that AbMT was ubiquitously expressed in all analyzed tissues and upregulated in gill tissue following challenge with Vibrio parahaemolyticus, Listeria monocytogenes, and viral hemorrhagic septicemia virus (VHSV). Additionally, overexpression of AbMT suppressed LPS-induced NO production in RAW264.7 macrophages, protected cells against H2O2-induced oxidative stress, and promoted macrophage polarization toward the M1 phase. Conclusively, these findings suggest an important role for AbMT in environmental stress protection and immune regulation in disk abalone.

A metallothionein gene from hard clam Meretrix meretrix: Sequence features, expression patterns, and metal tolerance activities

Metallothioneins (MTs) are low-molecular weight cytoplasmic heavy metal binding proteins. MTs can regulate the concentration of essential or non-essential metals in organisms, and have many important biological functions, including detoxification, trace element metabolism, and anti-oxidation. In the present study, we cloned and characterized a metallothionein gene (designated as MmMT) from the hard clam Meretrix meretrix. The complete cDNA sequence of MmMT contained an open reading frame (ORF) of 629 bp, which encoded a protein of 76 amino acids with a predicted molecular mass of 7.66 kDa and a calculated theoretical isoelectric point of 7.24. MmMT is highly similar to previously identified MTs from other species, with typical metallothionein features such as a high cysteine residue content and the absence of histidine and aromatic residues. The mRNA transcripts of MmMT were prevalent in all the tested tissues, and the expression levels of MmMT were highest in the hepatopancreas and hemocytes. During the stimulation of Vibrio splendidus, the mRNA transcripts of MmMT in the hepatopancreas and hemocytes were significantly increased. The Escherichia coli overexpressing MmMT performed strong growth in the media supplemented with CdCl2 and CuSO4 compared to the control strains. These results provide useful information for further investigation of the functions of MmMT in metal detoxification and the innate immune system.

Toxicological effects of copper on bioaccumulation and mRNA expression of antioxidant, immune, and apoptosis-related genes in Chinese striped-necked turtle (Mauremys sinensis)

Heavy metals are among the most ubiquitous environmental pollutants of recent decades. Copper is commonly used to control algal blooms or macrophyte and waste infestations, its ambient concentration has increased significantly, indicating possible environmental risk. To investigate the effects of copper exposure on bioaccumulation, antioxidant defense, immune response, and apoptosis in the Chinese Striped-necked Turtle Mauremys sinensis, three experimental groups, control (0.0 mg/L), Cu2 (2 mg/L) and Cu4 (4 mg/L) were designed, and sampled at 14 and 28 days. Results showed that copper accumulates in different organs depending on the concentration and exposure time, Liver > Kidney > Gut > Heart > Brain > Muscle and the time order was 28 days > 14 days. The liver enzymes AST, ALT, and ALP decreased when the turtles were exposed to copper stress, while the contents of bilirubin TBIL, DBIL, IBIL, and LDH showed a significant upward trend. Similarly, the mRNA expression level of acetylcholinesterase AChE in the brain was significantly downregulated upon copper exposure. An upward trend was noticed in the liver Metallothionein MT mRNA expression levels compared to the control group. The mRNA expression levels of antioxidant enzymes CAT, SOD, MnSOD, and GSH-PX1 in the liver increased initially and then significantly decreased. Furthermore, the relative mRNA expression levels of inflammatory cytokines IL-1β, IL-8, TNF-α, and IFN-γ involved in inflammatory response significantly upregulated. Copper significantly increased the hepatic mRNA transcription of heat shock proteins HSP70 and HSP90 at different exposure durations. In addition, the relative mRNA levels of caspase3, caspase8, and caspase9 related to the caspase-dependent apoptotic pathway significantly increased under copper stress. These results explain that copper toxicity causes bioaccumulation, promotes oxidative stress, obstructs immunity, and induces inflammation and apoptosis by altering their gene expression levels in M. sinensis.

Examining the subchronic (28-day) effects of aqueous Cd-BaP co-exposure on detoxification capacity and cardiac function in adult zebrafish (Danio rerio)

The present study aimed to examine the effects of environmentally relevant concentrations of cadmium (Cd) and Benzo[a]Pyrene (BaP) in the adult zebrafish (Danio rerio). To this end, fish were exposed to either 1 or 10 μg/L Cd or 0.1 or 1 μg/L BaP in isolation, or a co-exposure containing a mixture of the two toxicants. Our results showed extensive modulation of the expression of key antioxidant genes (GPx, SOD1, catalase), detoxifying genes (MT1, MT2, CYP1A1) and a stress biomarker (HSP70) differing between control, single toxicant groups and co-exposure groups. We additionally carried out histopathological analysis of the gills, liver, and hearts of exposed animals, noting no differences in tissue necrosis or apoptosis. Finally, we carried out ultrasonographic analysis of cardiac function, noting a significant decrease of E-wave peak velocity and end diastolic volume in exposed fish. This in turn was accompanied by a decrease in stroke volume and ejection fraction, but not cardiac output in co-exposed fish. The present study is the first to demonstrate that a subchronic aqueous exposure to a Cd-BaP mixture can extensively modulate detoxification capacity and cardiac function in adult zebrafish in a tissue-specific manner.

Earlier biomarkers in fish evidencing stress responses to metal and organic pollution along the Doce River Basin

The Doce River Basin (DRB) represents a well-described watershed in terms of contamination by metals, especially after a major environmental disaster of a mining tailing dam failure. Despite the massive mortality of the ichthyofauna, very few studies addressed the risks to the health of wild fish exposed to complex mixtures of pollutants from multiple sources. The present study proposed to investigate earlier responses of fish for assessing the impacts of multiple sources of pollution, considering: different niches of fish and target organs; and the influence of seasonality, associated with their probable sources of pollution. To achieve that, fish were collected along the DRB, and biomarkers responses were assessed in target organs and correlated with the levels of inorganic and organic contaminants. As one of the most prominent responses, fishes from the Upper DRB showed the highest expression of the metallothionein and oxidative stress parameters which were related to the higher levels of metals in this region due to the proximity of mining activities. On the other hand, higher levels of DNA damage and increased AChE activity from fish sampled in the Mid and Lower DRB were more associated with organic contaminants, from other sources of pollution than mining residues. The integrated biomarker responses also revealed seasonal variations, with higher values in fishes from the dry season, and pelagic fish showing greater variation within the seasons. The multivariate analysis integrating suitable biomarkers with chemical data represented an adequate strategy for assessing the ecological risks in the DRB, allowing the identification of distinct spatio-temporal impacts from multiple sources of contaminants. The continued exposure of the ichthyofauna representing future risks reinforces the need for ecological restoration and the protection of the fauna from the Doce River.

Evaluation of metal exposure through the composition of essential and toxic micro-minerals in freshwater turtles (Phrynops geoffroanus) from a Brazilian river

This study aimed to evaluate metal exposure through the concentration of essential and toxic micro-minerals in biological samples of Phrynops geoffroanus from an anthropized river. The work was carried out in four areas with different flow characteristics and uses of the river, where individuals of both sexes were captured during the dry and rainy seasons. The elements Al, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, and Zn were quantified in samples of serum (168), muscle (62), liver (61), and kidney (61) by inductively coupled plasma optical emission spectrometry. The concentration of the elements varied according to the sample type, being higher in the liver and the kidney. In the serum, many elements were below the limit of quantification, but it was possible to determine Al, Cu, Fe, Mn, Pb, and Zn. The liver showed high levels of Cu, Fe, Pb, and Zn, and muscle for Fe, Ni, Pb, and Zn, with most of the elements accumulated in the kidney (Al, Cd, Co, Cr, Mn, Mo, and Ni) relative to other tissues. There was no significant difference between the sexes in the accumulation of elements. Between seasons, Cu was higher in serum and Mn in muscle and liver in the dry period, while in the kidney, almost all the elements were higher in the rainy period. The concentrations of the elements in the samples indicated a high degree of environmental contamination, representing risk in the use of the river and consumption of food from local fisheries.

Zinc Chloride Can Mitigate the Alterations in Metallothionein and Some Apoptotic Proteins Induced by Cadmium Chloride in Mice Hepatocytes: A Histological and Immunohistochemical Study

The heavy metal cadmium is extremely harmful to both humans and animals. Zinc supplementation protects the biological system and reduces cadmium-induced toxicity. This study aimed to determine whether zinc chloride (ZnCl₂) could protect male mice with the damaged liver induced by cadmium chloride (CdCl₂). The protective role of zinc chloride and expression of the metallothionein (MT), Ki-67, and Bcl-2 apoptotic proteins in hepatocytes were studied after subchronic exposure of mice to cadmium chloride for 21 days. Thirty male mice were randomly categorized into 6 groups (5 mice/group) as follows: a control group that did not receive any treatment, a group given ZnCl₂ at 10 mg/kg alone, and two groups received ZnCl₂ (10 mg/kg) in combination with CdCl₂ at two concentrations (1.5 and 3 mg/kg), while the last two groups received CdCl₂ alone at 1.5 and 3 mg/kg, respectively. Immunohistochemical examination revealed a decrease in Ki-67 expression in Kupffer and endothelial cells, which reflected cell proliferation downregulation accompanied by MT increased expression. However, the Bcl-2 was ameliorated and reduced to demonstrate an enhanced rate of necrosis rather than apoptosis. Furthermore, histopathological results showed significant alteration such as hepatocytes with a pyknotic nucleus, infiltration of inflammatory cells around the central vein, and the presence of many binucleated hepatocytes. Zinc chloride treatment resulted in histological and morphological improvements that were average in the expression of apoptosis proteins modifications induced by cadmium. Our findings revealed that the positive effects of zinc might be linked to the high metallothionein expression and enhanced cell proliferation. Furthermore, at low-dose exposure, cadmium-induced damage to cells could be more closely related to necrosis rather than apoptosis.