Do Nanoparticles of Calcium Disodium EDTA Minimize the Toxic Effects of Cadmium in Female Rats?

The present study aims to investigate the ability of CaNa2EDTA (ethylenediaminetetraacetic acid) macroparticles and nanoparticles to treat cadmium-induced toxicity in female rats and to compare their efficacies. Forty rats were divided into 4 equal groups: control, cadmium, cadmium + CaNa2EDTA macroparticles and Cd + CaNa2EDTA nanoparticles. Cadmium was added to the drinking water in a concentration of 30 ppm for 10 weeks. CaNa2EDTA macroparticles and nanoparticles (50 mg/kg) were intraperitoneally injected during the last 4 weeks of the exposure period. Every two weeks, blood and urine samples were collected for determination of urea, creatinine, metallothionein and cadmium concentrations. At the end of the experiment, the skeleton of rats was examined by X-ray and tissue samples from the kidney and femur bone were collected and subjected to histopathological examination. Exposure to cadmium increased the concentrations of urea and creatinine in the serum and the concentrations of metallothionein and cadmium in serum and urine of rats. A decrease in bone mineralization by X-ray examination in addition to various histopathological alterations in the kidney and femur bone of Cd-intoxicated rats were also observed. Treatment with both CaNa2EDTA macroparticles and nanoparticles ameliorated the toxic effects induced by cadmium on the kidney and bone. However, CaNa2EDTA nanoparticles showed a superior efficacy compared to the macroparticles and therefore can be used as an effective chelating antidote for treatment of cadmium toxicity.

Blockage of metallothionein synthesis via adrenaline β receptor activation invalidates dehydroeffusol-mediated prevention of amyloid β1-42 toxicity

Dehydroeffusol, a major phenanthrene in Juncus effusus, protects neurodegeneration induced by intracellular Zn2+ ferried by extracellular amyloid β1-42 (Aβ1-42). Here we focused on adrenaline β receptor activation and the induction of metallothioneins (MTs), intracellular Zn2+-binding proteins to test the protective mechanism of dehydroeffusol. Isoproterenol, an agonist of adrenergic β receptors elevated the level of MTs in the dentate granule cell layer 1 day after intracerebroventricular (ICV) injection. When Aβ1-42 was injected 1 day after isoproterenol injection, pre-injection of isoproterenol protected Aβ1-42 toxicity via reducing the increase in intracellular Zn2+ after ICV injection of Aβ1-42. On the basis of the effect of increased MTs by isoproterenol, dehydroeffusol (15 mg/kg body weight) was orally administered to mice once a day for 2 days. On day later, dehydroeffusol elevated the level of MTs and prevented Aβ1-42 toxicity via reducing Aβ1-42-mediated increase in intracellular Zn2+. In contrast, propranolol, an antagonist of adrenergic β receptors reduced the level of MTs increased by dehydroeffusol, resulting in invalidating the preventive effect of dehydroeffusol on Aβ1-42 toxicity. The present study indicates that blockage of MT synthesis via adrenaline β receptor activation invalidates dehydroeffusol-mediated prevention of Aβ1-42 toxicity. It is likely that MT synthesis via adrenaline β receptor activation is beneficial to neuroprotection and that oral intake of dehydroeffusol preventively serves against the Aβ1-42 toxicity.

MT1G, an emerging ferroptosis-related gene: A novel prognostic biomarker and indicator of immunotherapy sensitivity in prostate cancer

BACKGROUND

Prostate cancer is a leading cause of cancer-related deaths in men worldwide. Despite advances in treatment strategies, there is still a need for novel therapeutic targets and approaches. Ferroptosis has emerged as a critical process in the development and progression of several cancers, including prostate cancer (PCA). In this study, we investigate the role of MT1G, a gene implicated in immune responses and ferroptosis, in the pathogenesis of PCA. Our objective is to elucidate its prognostic significance and its impact on the tumor microenvironment, while exploring its potential in enhancing the sensitivity to immune checkpoint inhibitor (ICI) therapy.

METHODS

We utilized a combination of in silico analysis and experimental techniques to investigate the role of MT1G in PCA. First, we analyzed large-scale genomic datasets to assess the expression pattern and prognostic significance of MT1G in PCA patients. Subsequently, we performed functional assays to explore the impact of MT1G in PCA and its potential involvement in modulating immune responses. In addition, we conducted in vivo experiments to evaluate the effect of MT1G on tumor growth and response to ICI therapy.

RESULTS

Our analysis revealed that MT1G expression is significantly downregulated in PCA tissues compared to normal prostate tissues and is associated with poor prognosis. Furthermore, MT1G overexpression inhibited the growth of PCA cells in vitro and in vivo. Importantly, we found that MT1G regulates the tumor microenvironment by modulating immune cell infiltration and inhibiting immunosuppressive factors. Furthermore, our study reveals a significant correlation between MT1G expression levels and the response to immune checkpoint inhibitor (ICI) therapy in prostate cancer (PCA) patients, as MT1G upregulation leads to an increase in PDL-1 expression. These findings underscore the potential of MT1G as a promising predictive biomarker for ICI therapy response in PCA patients.

CONCLUSION

Our study elucidates the pivotal role played by MT1G in the pathogenesis of prostate cancer (PCA) and its profound implications for prognosis. Moreover, it raises the intriguing possibility that MT1G could pave the way for novel therapeutic approaches in PCA treatment. This potential arises from its ability to orchestrate immune infiltration within the tumor microenvironment, consequently enhancing sensitivity to immune checkpoint inhibitor (ICI) therapy. Therefore, our findings hold substantial promise for advancing our comprehension of PCA and exploring innovative therapeutic strategies.

Heavy Metal Scavenger Metallothionein Rescues Against Cold Stress-Evoked Myocardial Contractile Anomalies Through Regulation of Mitophagy

Cold stress prompts an increased prevalence of cardiovascular morbidity yet the underneath machinery remains unclear. Oxidative stress and autophagy appear to contribute to cold stress-induced cardiac anomalies. Our present study evaluated the effect of heavy metal antioxidant metallothionein on cold stress (4 °C)-induced in cardiac remodeling and contractile anomalies and cell signaling involved including regulation of autophagy and mitophagy. Cold stress (3 weeks) prompted interstitial fibrosis, mitochondrial damage (mitochondrial membrane potential and TEM ultrastructure), oxidative stress (glutathione, reactive oxygen species and superoxide), lipid peroxidation, protein injury, elevated left ventricular (LV) end systolic and diastolic diameters, decreased fractional shortening, ejection fraction, Langendorff heart function, cardiomyocyte shortening, maximal velocities of shortening/relengthening, and electrically stimulated intracellular Ca2+ rise along with elongated relaxation duration and intracellular Ca2+ clearance, the responses of which were overtly attenuated or mitigated by metallothionein. Levels of apoptosis, cell death (Bax and loss of Bcl2, IL-18), and autophagy (LC3BII-to-LC3BI ratio, Atg7 and Beclin-1) were overtly upregulated with comparable p62 under cold stress. Cold stress also evoked elevated mitophagy (decreased TOM20, increased Parkin and FUNDC1 with unaltered BNIP3). Cold stress overtly dampened phosphorylation of autophagy/mitophagy inhibitory molecules Akt and mTOR, stimulated and suppressed phosphorylation of ULK1 and eNOS, respectively, in the absence of altered pan protein levels. Cold stress-evoked responses in cell death, autophagy, mitophagy and their regulatory domains were overtly attenuated or ablated by metallothionein. Suppression of autophagy and mitophagy with 3-methyladenine, bafilomycin A1, cyclosporine A, and liensinine rescued hypothermia-instigated cardiomyocyte LC3B puncta formation and mechanical anomalies. Our findings support a protective nature for metallothionein in deep hypothermia-evoked cardiac abnormalities associated with regulation of autophagy and mitophagy.

Pollutant bioaccumulation in sentinel fish chronically exposed in Iguaçu river reservoirs (Southern Brazil) and human health risk of fish consumption

Bioaccumulation studies in fish mark the initial phase of assessing the risk of chemical exposure to biota and human populations. The Iguaçu River boasting a diverse endemic ichthyofauna, is grappling with the repercussions of human activities. This study delved into the bioaccumulation of micropollutants, the early-warning effects on Rhamdia quelen and Oreochomis niloticus in the Segredo Reservoir (HRS) and the potential risk of human exposure. Two groups of caged fish in three sites of the reservoir were exposed during the autumn-winter and spring-summer, while a third group (O. niloticus) underwent a twelve-month exposure, and inorganic and organic chemicals analysis in water, sediment, and biota. Additionally, metallothionein expression and genotoxicity were employed as biomarkers. PAHs, PCBs, Al, Cu, Fe, and As in water and DDTs, Cu, Zn, and As in sediment surpassed the thresholds set by Brazilian regulations, where DDT exhibited bioaccumulation in muscle, alongside metals in liver, kidney, gills, and muscle tissues. R. quelen showed metallothionein expression whereas DNA damage and NMA frequencies were elevated in target organs and in brain and erythrocytes of O. niloticus during summer. In this species the DNA damage in liver was remarkable after twelve months. Target Hazard Quotients and Cancer Risk values shedding light on the vulnerability of both children and adults. The reservoir's conditions led to heightened sensitivity to micropollutants for R. quelen species. The data presented herein provides decision-makers with pertinent insights to facilitate effective management and conservation initiatives within the Iguaçu Basin.

Beneficial impact of cardiac heavy metal scavenger metallothionein in sepsis-provoked cardiac anomalies dependent upon regulation of endoplasmic reticulum stress and ferroptosis but not autophagy

AIMS

Sepsis represents a profound proinflammatory response with a major contribution from oxidative injury. Here we evaluated possible impact of heavy metal scavenger metallothionein (MT) on endotoxin lipopolysaccharide (LPS)-induced oxidative stress, endoplasmic reticulum (ER) stress, autophagy, and ferroptosis enroute to myocardial injury along with interplay among these stress domains.

MATERIALS AND METHODS

Echocardiographic, cardiomyocyte mechanical and intracellular Ca2+ responses were monitored in myocardia from WT and transgenic mice with cardiac-selective MT overexpression challenged with LPS. Oxidative stress, stress signaling (p38, ERK, JNK), ER stress, autophagy, and ferroptosis were scrutinized.

KEY FINDINGS

RNAseq analysis revealed discrepant patterns in ferroptosis between LPS-exposed and normal murine hearts. LPS insult enlarged LV end systolic dimension, suppressed fractional shortening, ejection fraction, maximal velocity of shortening/relengthening and peak shortening, as well as elongated relengthening along with dampened intracellular Ca2+ release and reuptake. In addition, LPS triggered oxidative stress (lowered glutathione/glutathione disulfide ratio and O2- production), activation of stress cascades (p38, ERK, JNK), ER stress (GRP78, PERK, Gadd153, and IRE1α), inflammation (TNFα and iNOS), unchecked autophagy (LCB3, Beclin-1 and Atg7), ferroptosis (GPx4 and SLC7A11) and interstitial fibrosis. Although MT overexpression itself did not reveal response on cardiac function, it attenuated or mitigated LPS-evoked alterations in echocardiographic, cardiomyocyte contractile and intracellular Ca2+ characteristics, O2- production, TNFα level, ER stress and ferroptosis (without affecting autophagy, elevated AMP/ATP ratio, and iNOS). In vitro evidence revealed beneficial effects of suppression of oxidative stress, ER stress and ferroptosis against LPS-elicited myocardial anomalies.

SIGNIFICANCE

These data strongly support the therapeutic promises of MT and ferroptosis in septic cardiomyopathy.

Employing molecular, chemical and physiological techniques using Crassostrea virginica to assess ecosystem health along coastal South Carolina and North Carolina, United States

Natural and anthropogenic environmental impacts can introduce contaminants into sensitive habitats, threatening ecosystems and human health. Consistent monitoring of coastal areas provides critical environmental assessment data. Sediments and Eastern Oyster (Crassostrea virginica) tissues were collected at fourteen South Carolina (SC) and four North Carolina (NC) sites as part of the National Oceanic and Atmospheric Administration's Mussel Watch environmental monitoring program. Cellular and molecular techniques were employed to measure C. virginica stress response, specifically, Lipid Peroxidation (LPx), Glutathione (GSH), and qPCR techniques. Gene specific primers targeted for detecting oxidative stress and cellular death were developed in C. virginica to gauge response to current environmental conditions using gill and hepatopancreas (HP) tissue. In order to validate gene specific markers as additional assessment tools, a 96 h zinc (Zn) laboratory exposure was performed. Cellular biomarker data revealed tissue specific responses. Hepatopancreas data showed C. virginica exhibited stress through the lipid peroxidation assay amongst sampling sites, however, response was managed through glutathione detoxification. Gill tissue data had significantly lower levels of cellular biomarker response compared to hepatopancreas. Molecular biomarkers targeting these cellular stress pathways through qPCR analysis show upregulation of Metallothionein in hepatopancreas and gill tissue with a concurrent > 2-fold upregulation in the detoxification marker Superoxide Dismutase (SOD) at three NC sites. SC sites displayed higher stress levels through LPx assays and down-regulation in GPx gene activity. Laboratory zinc exposure revealed no significance in cellular biomarker results, however, molecular data showed gills responding to zinc treatment through upregulation of Metallothionein, SOD and Cathepsin L, indicating an acute response in gills. Collectively, chemical, cellular and molecular methods clarify sentinel stress response of biological impacts and aid in evaluating environmental health in coastal ecosystems. This combined methodological approach provides a detailed analysis of environmental conditions and improves land-use management decisions.

Metallothionein expression in the central nervous system in response to chronic heavy metal exposure: possible neuroprotective mechanism

It has been reported that volcanoes release several tonnes of mercury per year among other heavy metals through eruptions, fumaroles, or diffuse soil degassing. Since a high percentage of the world's population lives in the vicinity of an active volcano, the aim of this study is to evaluate the accumulation of these metals in the central nervous system and the presence of cellular mechanisms of heavy metal detoxification such as metallothioneins. To carry out this study, wild mice (Mus musculus) chronically exposed to an active volcanic environment were captured in Furnas village (Azores, Portugal) and compared with those trapped in a reference area (Rabo de Peixe, Azores, Portugal). On the one hand, the heavy metal load has been evaluated by analyzing brain and cerebellum using ICP-MS and a mercury analyzer and on the other hand, the presence of metallothionein 2A has been studied by immunofluorescence assays. Our results show a higher load of metals such as mercury, cadmium and lead in the central nervous system of exposed mice compared to non-exposed individuals and, in addition, a higher immunoreactivity for metallothionein 2A in different areas of the cerebrum and cerebellum indicating a possible neuroprotection process.

Ultrasonic treatment alleviated cadmium stress in sugarcane via improving antioxidant activity and physiological and biochemical status

Cadmium (Cd) is a toxic element that endangers crop growth and affects food safety and human health. Therefore, the study of Cd mitigation technology is important. Ultrasonic treatment can improve crop growth and enhance their ability to resist various abiotic stresses. In this study, the effect of ultrasonic treatment on alleviating sugarcane Cd stress was studied in a barrel experiment using sugarcane varieties 'ROC22' and 'LC05-136' as test materials. Sugarcane buds without ultrasonic treatment and with ultrasonic treatment (20-40 kHz mixed frequency ultrasound for 2 min, dry treatment) were planted in soil with Cd contents of 0, 50, 100, 250, and 500 mg·kg-1. Compared with non-ultrasonic treatment, Ultrasonic treatment significantly increased the activities of antioxidant enzymes in sugarcane, significantly increased the content of osmoregulation substances, significantly reduced the content of superoxide anion (the highest decreases reached 11.55%) and malondialdehyde (the highest decreases reached 20.59%), and significantly increased the expression level of metallothionein (MT)-related genes, with the expression of ScMT1 increased by 8.80-37.49% and the expression of ScMT2-1-5 increased by 1.55-69.33%. In addition, ultrasonic treatment significantly reduced the Cd contents in sugarcane roots, stems, leaves, bagasse, and juice (the highest reduction in Cd content was 49.18%). In general, ultrasonic treatment regulated the metabolism of reactive oxygen species and MT-related gene expression in sugarcane, increased the Cd tolerance of sugarcane, promoted photosynthesis in sugarcane leaves, improved root morphology, enhanced sugarcane growth, and increased cane and sugar yield.

Single-cell transcriptome analysis revealing the intratumoral heterogeneity of ccRCC and validation of MT2A in pathogenesis

Clear-cell renal cell carcinoma (ccRCC) appears as the most common type of kidney cancer, the carcinogenesis of which has not been fully elucidated. Tumor heterogeneity plays a crucial role in cancer progression, which could be largely deciphered by the implement of scRNA-seq. The bulk and single-cell RNA expression profile is obtained from TCGA and study conducted by Young et al. We utilized UMAP, TSNE, and clustering algorithm Louvain for dimensionality reduction and FindAllMarkers function for determining the DEGs. Monocle2 was utilized to perform pseudo-time series analysis. SCENIC was implemented for transcription factor analysis of each cell subgroup. A series of WB, CFA, CCK-8, and EDU analysis was utilized for the validation of the role of MT2A in ccRCC carcinogenesis. We observed higher infiltration of T/NK and B cells in tumorous tissues, indicating the role of immune cells in ccRCC carcinogenesis. Transcription factor analysis revealed the activation of EOMES and ETS1 in CD8 + T cells, while CAFs were divided into myo-CAFs and i-CAFs, with i-CAFs showing distinct enrichment of ATF3, JUND, JUNB, EGR1, and XBP1. Through cell trajectory analysis, we discerned three distinct stages of cellular evolution, where State2 symbolizes normal renal tubular cells that underwent transitions into State1 and State3 as the CNV score ascended. Functional enrichment examination revealed an amplification of interferon gamma and inflammatory response pathways within tumor cells. The consensus clustering algorithm yielded two molecular subtypes, with cluster 2 being associated with advanced tumor stages and an abundance of infiltrated immune cells. We identified 17 prognostic genes through Cox and LASSO regression models and used them to construct a prognostic model, the efficacy of which was verified in multiple cohorts. Furthermore, we investigated the role of MT2A, one of our hub genes, in ccRCC carcinogenesis, and found it to regulate proliferation and migration of malignant cells. We depicted a detailed single-cell landscape of ccRCC, with special focus on CAFs, endothelial cells, and renal tubular cells. A prognostic model of high stability and accuracy was constructed based on the DEGs. MT2A was found to be actively implicated in ccRCC carcinogenesis, regulating proliferation and migration of the malignant cells.

Assessment of toxic metal pollution in Yueqing Bay and the extent of metal-induced oxidative stress in Tegillarca granosa raised in this water

Yueqing Bay is an important economic shellfish culture zone in Zhejiang Province, China. However, increased pollution in the water caused by toxic metals has led to the bioaccumulation of toxic metals in cockles such as Tegillarca granosa, and the consequence of toxic metal-associated toxicity in these animals. This study aimed to assess the concentration of toxic metals in the water and sediment in four different sites (Baisha, Qingjiang, Nanyue, and Wengyang) within Yueqing Bay and to evaluate the extent of metal bioaccumulation in T. granosa raised in the aquaculture farms located within the four sites, as well as the changes in biomarkers in T. granosa in response to the metals. The assessment was carried out at two different times of the year, January and July. The water and sediment samples taken from the aquaculture farms in Baisha (S1), Qingjiang (S2) and Nanyue (S3) were found to have a comprehensive toxic metal pollution index (Pc) <1, indicating that these farms were not polluted. However, the water and sediment samples taken from the aquaculture farm in Wengyang (S4) had a Pc between 1 and 2, indicating mild toxic metal pollution. The edible risk assessments (HQ) of T. granosa in all four farms were <1, and therefore, these cockles could be considered safe for human consumption. The toxic metal enrichment in T. granosa exhibited a strong correlation with the toxic metal content in the sediment. In all four farms, CAT and SOD activity levels in the visceral mass of T. granosa were higher than those found in the foot, and a significantly higher level of CAT activity was detected in July compared with January. Similarly, MDA and H2O2 contents in the visceral mass were also higher in July than in January. Tegillarca granosa individuals taken from S4 and S3 farms exhibited significantly higher levels of metallothionein (MT) mRNA and MDA compared with individuals from S1 and S2 farms. Furthermore, the levels of MDA and MT mRNA showed significant positive correlations with Cd, Cr, Hg, and Cu. Elevation of lipid peroxidation in these cockles coincided with increasing levels of endogenous antioxidants. The visceral mass of T. granosa and its MDA level could be used as a tissue indicator and a biochemical marker, respectively, for detecting toxic metal pollution. MT mRNA might also be used as a molecular marker of toxic metal pollution. The integrated biomarker response version 2 (IBRv2) values of the four aquaculture farms in Yueqing Bay showed the order S4 > S3 > S2 > S1, indicating that S4 had the most serious metal-induced stress. Furthermore, the IBRv2 values correlated with the Nemerow composite index (Pc) for all the cockles examined. Thus, as far as the contamination of aquaculture farms in Yueqing Bay by toxic metals is concerned, the aquaculture farm in Wengyang (S4) was mildly contaminated by toxic metals. However, the contamination was relatively low, presenting a low risk for the local population of T. granosa.

Metal and metallothionein concentrations in mesozooplankton from an oligotrophic offshore area in the eastern Mediterranean Sea (Cretan Passage/Levantine Sea)

Spatial variability of Cd, Cu, Cr, Ni, Zn, Fe, Mn, Pb and metallothionein (MT) concentrations were determined in mesozooplankton samples along the west-east axis of the Cretan Passage in the western Levantine Sea (Eastern Mediterranean). Metal and MT values from the present study are proposed as background levels, due to the lack of substantial anthropogenic activities in the area, where only maritime traffic and atmospheric deposition could be potential sources. Higher concentrations, of both metals and MTs, were recorded mainly at the western stations indicating higher metal bioavailability than in the eastern part. An inverse relationship of the metal zooplankton levels with zooplankton biomass, abundance and vital rates (production, respiration and ingestion rates), as well as salinity, was evident. We discuss the hypothesis that physical and biological characteristics of the marine environment, affecting growth dynamics of phytoplankton and zooplankton communities, may also act on metal uptake in oligotrophic marine systems.

Vermi-cyanobacterial remediation of cadmium-contaminated soil with rice husk biochar: An eco-friendly approach

Present study is aimed to evaluate the influence of earthworm (Eisenia fetida), Cyanobacteria (Cylindrospermum stagnale), and rice husk biochar (BC) on cadmium (Cd) detoxification in artificially contaminated soil. The Cd content was kept at 10 mg/kg in factorial design I, coupled with 2% and 0% BC. E. fetida and C. stagnale un-inoculated and inoculated experiments were maintained respectively as negative and positive controls. In factorial design II, E. fetida and C. stagnale were inoculated, along with BC (0% and 2%, denoted as B), without BC (WB), along with four different Cd concentrations (Cd-0, Cd-5, Cd-10, and Cd-20 mg/kg). Results suggest a substantial amount of Cd removal in BC-assisted treatments when compared to negative control-1. Cd (mg/g) in E. fetida tissue ranged from 0.019 (WB2) to 0.0985 (B4). C. stagnale of WB4 (0.036) bioaccumulated the most Cd (mg/g), while B2 showed the least (0.018). The maximum quantity of metallothionein (5.34 μM/mg) was detected in E. fetida of B4 (factorial design - II) and the minimum was claimed in WB1 (0.48 μM/mg) at the end. Earthworm metallothionein protein is a key component in Cd removal from soil by playing an important role in detoxification process. Microbial communities and humic substances were observed in BC-assisted treatments, which aided in Cd-contaminated soil remediation. The present findings suggest that BC (2%) + earthworms + algae could be a suitable remediation strategy for Cd contaminated soil. BC + earthworm + algal-based investigation on heavy metal remediation will be a valuable platform for detoxifying harmful metals in soils.

Characteristics of Zn Content and Localization, Cu-Zn SOD, and MT Levels in the Tissues of Marginally Zn-Deficient Mice

Zinc (Zn) is an important trace element in the human body, and Zn deficiency affects the Zn content of major tissues. Marginal Zn deficiency is more common than severe Zn deficiency in humans. The objective of the present study was to compare the content and distribution of Zn and the change in the copper (Cu)-Zn superoxide dismutase (SOD) and metallothionein (MT) levels of soft tissues. Mice were fed with 30 mg/kg (control) or 10 mg/kg (marginally Zn-deficient, MZD) Zn diet for 35 days. We observed that only the Zn contents of serum, bones, and muscles in the control group were higher than those in the MZD group. Autometallography (AMG) was used as a method for staining Zn ions, and the semi-quantitative result indicated that the AMG products of the liver, duodenum, heart, lung, testes, and epididymis in the control group were higher than those in the MZD group. Furthermore, the contents of MT and the activities of Cu-Zn SOD in the testes, brain, duodenum, and liver were higher in the control group than those in the MZD group. However, the AMG products and the activities of Cu-Zn SOD of the kidney in the MZD group were more/higher than those in the control group. These results indicated that a change in the total Zn content of soft tissues may be not obvious and insensitive, and thus, more attention should be given to the distribution and localization of Zn ions. The functional indicators, MT and Cu-Zn SOD, are suitable biomarkers for evaluating zinc nutritional status. The brain, testes, duodenum, and liver are susceptive organs to Zn deficiency.

Multibiomarker approach in fish to assess a heavily polluted Brazilian estuary, Guanabara Bay

Brazil's Guanabara Bay (GB), located in Rio De Janeiro, is a deeply contaminated, eutrophic waterbody that challenges the understanding of the effects of pollutants on the biota. This paper presents a strategy to evaluate the impact of contamination utilizing a multibiomarker approach in two fish species: corvine (Micropogonias furnieri) and burrfish (Chilomycterus spinosus). The strategy is comprised of a general biomarker of fish' physical condition, the condition factor (CF), and specific biomarkers of pollutant exposure such as acetylcholinesterase (AChE), metallothionein (MT) activity and biliary polycyclic aromatic hydrocarbons (PAH) metabolites. Our results indicate that fish from GB are greatly affected by environmental pollution. CF values were lower in fishes from GB than in the reference site indicating that these fishes were under higher environmental stress. Lower AChE activity level in both species showed vulnerability to the presence of pesticide residues. Higher levels of MT in both species in GB reflect the consequences of heavy metal exposure in the bay, in spite of their bioavailability being restricted specially by the high organic matter content of GB. The levels of PAHs were higher in GB for both fish species, indicating exposure to these substances. However, the fish species showed different behavior regarding the origin of the PAHs. The multibiomarker approach used in this study evidently depicted effects on the health of fish in a waterbody with a complex polluted situation and further categorized the effects of anthropogenic activities in this aquatic system.

Intake of mother's milk by very-low-birth-weight infants and variation in DNA methylation of genes involved in neurodevelopment at 5.5 years of age

BACKGROUND

Mechanisms responsible for associations between intake of mother's milk in very-low-birth-weight (VLBW, <1500 g) infants and later neurodevelopment are poorly understood. It is proposed that early nutrition may affect neurodevelopmental pathways by altering gene expression through epigenetic modification. Variation in DNA methylation (DNAm) at cytosine-guanine dinucleotides (CpGs) is a commonly studied epigenetic modification.

OBJECTIVES

We aimed to assess whether early mother's milk intake by VLBW infants is associated with variations in DNAm at 5.5 y, and whether these variations correlate with neurodevelopmental phenotypes.

METHODS

This cohort study was a 5.5-y follow-up (2016-2018) of VLBW infants born in Ontario, Canada who participated in the Donor Milk for Improved Neurodevelopmental Outcomes trial. We performed an epigenome-wide association study (EWAS) to test whether percentage mother's milk (not including supplemental donor milk) during hospitalization was associated with DNAm in buccal cells during early childhood (n = 143; mean ± SD age: 5.7 ± 0.2 y; birth weight: 1008 ± 517 g). DNAm was assessed with the Illumina Infinium MethylationEPIC array at 814,583 CpGs. In secondary analyses, we tested associations between top-ranked CpGs and measures of early childhood neurodevelopment, e.g., total surface area of the cerebral cortex (n = 41, MRI) and Full-Scale IQ (n = 133, Wechsler Preschool and Primary Scale of Intelligence-IV).

RESULTS

EWAS analysis demonstrated percentage mother's milk intake by VLBW infants during hospitalization was associated with DNAm at 2 CpGs, cg03744440 [myosin XVB (MYO15B)] and cg00851389 [metallothionein 1A (MT1A)], at 5.5 y (P < 9E-08). Gene set enrichment analysis indicated that top-ranked CpGs (P < 0.001) were annotated to genes enriched in neurodevelopmental biological processes. Corroborating these findings, DNAm at several top identified CpGs from the EWAS was associated with cortical surface area and IQ at 5.5 y (P < 0.05).

CONCLUSIONS

In-hospital percentage mother's milk intake by VLBW infants was associated with variations in DNAm of neurodevelopmental genes at 5.5 y; some of these DNAm variations are associated with brain structure and IQ.This trial was registered at isrctn.com as ISRCTN35317141 and at clinicaltrials.gov as NCT02759809.

Clay Types Modulate the Toxicity of Low Concentrated Copper Oxide Nanoparticles Toward Springtails in Artificial Test Soils

Copper oxide nanoparticles (CuO-NPs) can be applied as an efficient alternative to conventional Cu in agriculture. Negative effects of CuO-NPs on soil organisms were found, but only in clay-rich loamy soils. It is hypothesized that clay-NP interactions are the origin of the observed toxic effects. In the present study, artificial Organisation for Economic Co-operation and Development soils containing 30% of kaolin or montmorillonite as clay type were spiked with 1-32 mg Cu/kg of uncoated CuO-NPs or CuCl₂ . We performed 28-day reproduction tests with springtails of the species Folsomia candida and recorded the survival, reproduction, dry weight, and Cu content of adults. In a second experiment, molting frequency and the Cu content of exuviae, as well as the biochemical endpoints metallothionein and catalase (CAT) in springtails, were investigated. In the reproduction assay, negative effects on all endpoints were observed, but only in soils containing montmorillonite and mostly for CuO-NPs. For the biochemical endpoints and Cu content of exuviae, effects were clearly distinct between Cu forms in montmorillonite soil, but a significant reduction compared to the control was only found for CAT activity. Therefore, the reduced CAT activity in CuO-NP-montmorillonite soil might be responsible for the observed toxicity, potentially resulting from reactive oxygen species formation overloading the antioxidant system. This process seems to be highly concentration-dependent, because all endpoints investigated in reproduction and biochemical assays of CuO-NP-montmorillonite treatments showed a nonlinear dose-response relationship and were constantly reduced by approximately 40% at a field-realistic concentration of 3 mg/kg, but not at 32 mg/kg. The results underline that clay-CuO-NP interactions are crucial for their toxic behavior, especially at low, field-realistic concentrations, which should be considered for risk assessment of CuO-NPs. Environ Toxicol Chem 2022;41:2454-2465. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Transcriptional Responses of Stress-Related Genes in Pale Chub (Zacco platypus) Inhabiting Different Aquatic Environments: Application for Biomonitoring Aquatic Ecosystems

Pale chub (Zacco platypus) is a dominant species in urban rivers and reservoirs, and it is used as an indicator to monitor the effects of environmental contaminants. Gene responses at the molecular level can reflect the health of fish challenged with environmental stressors. The objective of this study was to identify correlations between water quality factors and the expression of stress-related genes in Z. platypus from different lake environments (Singal and Juam Lakes). To do so, transcriptional responses of genes involving cellular homeostasis (heat-shock protein 70, HSP70; heat-shock protein 90, HSP90), metal detoxification (metallothionein, MT), and antioxidation (superoxide dismutase, SOD; catalase, CAT) were analyzed in the gill and liver tissues of Z. platypus. HSP70, HSP90, and MT genes were overall upregulated in Z. platypus from Singal Lake, which suffered from poorer water quality than Juam Lake. In addition, gene responses were significantly higher in Singal Lake outflow. Upregulation of HSP70, HSP90, and MT was significantly higher in Z. platypus gills than in the liver tissue. In addition, integrated biomarker response and heatmap analysis determined correlations between expression of biomarker genes or water quality factors and sampling sites of both lakes. These results suggest that stress-related genes used as multiple biomarkers may reflect spatial characteristics and water quality of different lake environments, and they can be used for biomonitoring and ecological risk assessment.

The impact of co-treatment with graphene oxide and metal mixture on Salmo trutta at early development stages: The sorption capacity and potential toxicity

Graphene oxide (GO) are novel nanomaterials with a wide range of applications due to their high absorption capacity. This study was undertaken with a view to assess the bioaccumulation and acute toxicity of GO used in combination with the heavy metal mixture (Cr, Cu, Ni and Zn) to fish embryos and larvae. For this purpose, Salmo trutta embryos and larvae were subjected to the 4-day long treatment with three different concentrations of GO, the metal mixture, which was prepared of four metals at the concentrations corresponding to the maximum-permissible-concentrations for EU inland waters (Cr-0.01, Cu-0.01, Ni-0.034, and Zn-0.1 mg/L), and with GO in combination with MIX (GO+MIX). When used in combination with the metal mixture, GO exhibited a high metal sorption capacity. The obtained confocal fluorescence microscopy results showed that GO located in the embryo chorion causing its damage; in larvae, however, GO were found only in the gill region. Results of these experiments confirmed the hypothesis that GO affects the accumulation of metals and mitigates their toxic effects on organism. In embryos, the acute toxicity of exposure to GO and co-exposure to MIX+GO was found to manifest itself through the decreased heart rate (HR) and malondialdehyde (MDA) level and through the increased metallothionein (MT) concentration. Meanwhile, in larvae, GO and MIX+GO were found to induce genotoxicity effects. However, changes in HR, MDA, MT, gill ventilation frequency, yolk sack absorption and cytotoxicity compared with those of the control group were not recorded in larvae. The obtained results confirmed our hypothesis: the combined effect of MIX and GO was less toxic to larvae (especially survival) than individual effects of MIX components. However, our results emphasize that fish exposure to GO alone and in combination with heavy metal contaminants (MIX+GO) even at environmentally relevant concentrations causes health risks that cannot be ignored.

Arsenate and arsenite differential toxicity in Tetrahymena thermophila

A comparative analysis of toxicities of both arsenic forms (arsenite and arsenate) in the model eukaryotic microorganism Tetrahymena thermophila (ciliate protozoa) has shown the presence of various detoxification mechanisms and cellular effects comparable to those of animal cells under arsenic stress. In the wild type strain SB1969 arsenate is almost 2.5 times more toxic than arsenite. According to the concentration addition model used in binary metallic mixtures their toxicities show an additive effect. Using fluorescent assays and flow cytometry, it has been detected that As(V) generates elevated levels of ROS/RNS compared to As(III). Both produce the same levels of superoxide anion, but As(V) also causes greater increases in hydrogen peroxide and peroxynitrite. The mitochondrial membrane potential is affected by both As(V) and As(III), and electron microscopy has also revealed that mitochondria are the main target of both arsenic ionic forms. Fusion/fission and swelling mitochondrial and mitophagy, together with macroautophagy, vacuolization and mucocyst extruction are mainly associated to As(V) toxicity, while As(III) induces an extensive lipid metabolism dysfunction (adipotropic effect). Quantitative RT-PCR analysis of some genes encoding antioxidant proteins or enzymes has shown that glutathione and thioredoxin metabolisms are involved in the response to arsenic stress. Likewise, the function of metallothioneins seems to be crucial in arsenic detoxification processes, after using both metallothionein knockout and knockdown strains and cells overexpressing metallothionein genes from this ciliate. The analysis of the differential toxicity of As(III) and As(V) shown in this study provides cytological and molecular tools to be used as biomarkers for each of the two arsenic ionic forms.

Metal Contamination of Oman Sea Seaweed and Its Associated Public Health Risks

Oman Sea region is a major gateway for international and local shipping. Metal pollution of aquatic environment is primarily caused by such shipping and industrial activities. Agricultural runoffs are also of concern. Seaweed contamination with heavy metals in this area is therefore a distinct possibility. We examined seaweed of Oman Sea for heavy metal content and potential risk of its consumption to the public. During winter of 2019, water, sediment, and seaweed were collected along twelve stations on the coast of Oman Sea. Triplicates of each sample were analyzed for metal content by atomic absorption spectroscopy. Biomarkers of metals in seaweed (metallothionein and phytochelatin) were also analyzed. A significant positive correlation exists among levels of Zn, Ni, Pb, Cr, Cu, and Fe in water, sediment, and seaweed (P < 0.05). Cadmium correlations were weak. The highest levels of metallothionein and phytochelatin were found in brown and red seaweed (118.6 µg/g wet weight, 16.4 amol/cell; 111.4 µg/g ww, 12.1 amol/cell), respectively. For nickel and lead, human consumption of red, brown, and green seaweed was associated with "some health hazard," with a target hazard quotient of > 1. We conclude that concerns over heavy metal contamination of some parts of Oman Sea are valid, and we invite policy makers to implement measures for protection of public and environment from metal toxic effects in the region.

Effects of pile driving sound playbacks and cadmium co-exposure on the early life stage development of the Norway lobster, Nephrops norvegicus

There is an urgent need to understand how organisms respond to multiple, potentially interacting drivers in today's world. The effects of the pollutants anthropogenic sound (pile driving sound playbacks) and waterborne cadmium were investigated across multiple levels of biology in larval and juvenile Norway lobster, Nephrops norvegicus under controlled laboratory conditions. The combination of pile driving playbacks (170 dB_pk-pk re 1 μPa) and cadmium combined synergistically at concentrations >9.62 μg_[Cd] L^-1 resulting in increased larval mortality, with sound playbacks otherwise being antagonistic to cadmium toxicity. Exposure to 63.52 μg_[Cd] L^-1 caused significant delays in larval development, dropping to 6.48 μg_[Cd] L^-1 in the presence of piling playbacks. Pre-exposure to the combination of piling playbacks and 6.48 μg_[Cd] L^-1 led to significant differences in the swimming behaviour of the first juvenile stage. Biomarker analysis suggested oxidative stress as the mechanism resultant deleterious effects, with cellular metallothionein (MT) being the predominant protective mechanism.

Assessment of the heavy metal levels and biomarker responses in the smooth scallop Flexopecten glaber from a heavily urbanized Mediterranean lagoon (Bizerte lagoon)

Marine heavy metal pollution is a worldwide serious issue. Like almost all Mediterranean lagoons, the Bizerte lagoon is highly urbanized and suffers from intensive anthropogenic pressure. In the present study, we screened the metal contamination and biomarker responses in the smooth scallop Flexopecten glaber inhabiting this vulnerable ecosystem. To this end, the concentrations of six heavy metals (HM) (i.e., Cu, Pb, Zn, Cd, Hg, and Fe) and a panel of biochemical endpoints including malondialdehyde (MDA), metallothioneins (MT), reduced glutathione (GSH), glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) were determined in the gills and digestive gland across seasons (warm and cold) and sites (S1 and S2). The distribution of almost all analyzed metals in F. glaber tissues varied significantly between sites, seasons, and organs. The highest levels were recorded at S2 during the warm period. Moreover, the digestive gland was found to accumulate greater concentrations of HM than the gills. Marked spatio-temporal variations were also observed for oxidative stress biomarkers, mainly in the gills, while the digestive gland seems to be rather sensitive to seasonal variability. Particularly, we noticed that among the used biomarkers, MT did not show significant variations in the two tested organs across seasons and sites. From the obtained results, F. glaber appears as a sensitive organism to anthropogenic metal contamination and can be proposed as a promising bioindicator species for marine pollution.

Does roundup affect zinc functions in a bivalve mollusk in ex vivo exposure?

Roundup (Rn), a glyphosate-based formulation, is one of the most commonly used herbicides in the world. It affects non-targeted organisms in several ways, including adhesive activity towards metal ions. Zinc (Zn) plays a crucial role in a number of biochemical processes. In this study, we aim to elucidate the direct impact of Rn on Zn accumulation and Zn-dependent activities in the ex vivo system. To this end, we exposed the samples of the digestive gland of a bivalve mollusk Unio tumidus to 3 µM of Rn (calculated as 3 µM of glyphosate), Zn, Zn chelator (N,N,N',N'-Tetrakis(2-pyridylmethyl)ethylenediamine) (TPEN, Tp), and their combinations ZnTp and ZnRn for 17 h. We determined the levels of Zn in the tissue (Zn t) and metallothioneins (Zn-MT), metallothioneins (MTSH), and glutathione (GSH & GSSG), total antioxidant capacity (TAC), lysosomal membrane integrity, and caspase-3 activity. Our study demonstrated that Rn and Tp had different effects on the accumulation and functionality of Zn. Rn did not affect the accumulation of Zn (Zn t, Zn-MT) in the Zn- and ZnRn-groups. On the contrary, Tp produced effects antagonistic to Zn on caspase-3 activity, lysosomal stability, and MTSH concentration. Rn caused particular pro-oxidative effect that decreased GSH level (Rn- and ZnRn-groups) and lysosomal stability (Rn-group). The shared affected index was the GSH/GSSG ratio, which decreased by 2-8 times in each exposure. As the first experience with the application of Tp to indicate Zn activity in mollusks, the study concluded that the ex vivo approach could be useful in the study of numeral aquatic pollutants.

Metallothionein and Cadmium Toxicology—Historical Review and Commentary

More than one and a half centuries ago, adverse human health effects were reported after use of a cadmium-containing silver polishing agent. Long-term cadmium exposure gives rise to kidney or bone disease, reproductive toxicity and cancer in animals and humans. At present, high human exposures to cadmium occur in small-scale mining, underlining the need for preventive measures. This is particularly urgent in view of the growing demand for minerals and metals in global climate change mitigation. This review deals with a specific part of cadmium toxicology that is important for understanding when toxic effects appear and, thus, is crucial for risk assessment. The discovery of the low-molecular-weight protein metallothionein (MT) in 1957 was an important milestone because, when this protein binds cadmium, it modifies cellular cadmium toxicity. The present authors contributed evidence in the 1970s concerning cadmium binding to MT and synthesis of the protein in tissues. We showed that binding of cadmium to metallothionein in tissues prevented some toxic effects, but that metallothionein can increase the transport of cadmium to the kidneys. Special studies showed the importance of the Cd/Zn ratio in MT for expression of toxicity in the kidneys. We also developed models of cadmium toxicokinetics based on our MT-related findings. This model combined with estimates of tissue levels giving rise to toxicity, made it possible to calculate expected risks in relation to exposure. Other scientists developed these models further and international organizations have successfully used these amended models in recent publications. Our contributions in recent decades included studies in humans of MT-related biomarkers showing the importance of MT gene expression in lymphocytes and MT autoantibodies for risks of Cd-related adverse effects in cadmium-exposed population groups. In a study of the impact of zinc status on the risk of kidney dysfunction in a cadmium-exposed group, the risks were low when zinc status was good and high when zinc status was poor. The present review summarizes this evidence in a risk assessment context and calls for its application in order to improve preventive measures against adverse effects of cadmium exposures in humans and animals.

Assessing integrated biomarkers of triplefin fish Forsterygion capito inhabiting contaminated marine water - A multivariate approach

The presence of multiple chemicals in aquatic ecosystems makes evaluation of their real impact on the biota difficult. Integrated biomarkers are therefore needed to evaluate how these chemicals contribute to environmental degradation. The aims of the present study were to evaluate responses to and effects of marine pollution using a series of biomarkers through multivariate analyses. Transcriptional responses of cyp1a (cytochrome P450), mt (metallothionein), vtg (vitellogenin) and cyp19b (cytochrome P450 aromatase); branchial and hepatic histological alterations; and Fulton condition factors (CF) were evaluated, as well as the metals and polycyclic aromatic hydrocarbons present in Forsterygion capito in Auckland, New Zealand. Sites were selected along a contamination gradient: four highly contaminated sites and four less contaminated. Molecular responses with a higher relative expression of the mt and cyp1a genes were detected at a highly contaminated site (Panmure). Several histological lesion types were found in the livers of fish inhabiting both types of sites, but gill lesions were present primarily at highly contaminated sites. In terms of general health status, the lowest CF values were overwhelmingly found in fish from the same site (Panmure). The multivariate approach revealed that telangiectasia and hyperplasia were associated with the presence of chemicals, and these showed negative associations with the CF values, with fish from three highly contaminated sites being most affected. In conclusion, the multivariate approach helped to integrate these biological markers in this blennioid fish, thus providing a more holistic view of the complex chemical mixtures involved. Future studies should implement these analyses.

A Comprehensive Review on the Heavy Metal Toxicity and Sequestration in Plants

Heavy metal (HM) toxicity has become a global concern in recent years and is imposing a severe threat to the environment and human health. In the case of plants, a higher concentration of HMs, above a threshold, adversely affects cellular metabolism because of the generation of reactive oxygen species (ROS) which target the key biological molecules. Moreover, some of the HMs such as mercury and arsenic, among others, can directly alter the protein/enzyme activities by targeting their –SH group to further impede the cellular metabolism. Particularly, inhibition of photosynthesis has been reported under HM toxicity because HMs trigger the degradation of chlorophyll molecules by enhancing the chlorophyllase activity and by replacing the central Mg ion in the porphyrin ring which affects overall plant growth and yield. Consequently, plants utilize various strategies to mitigate the negative impact of HM toxicity by limiting the uptake of these HMs and their sequestration into the vacuoles with the help of various molecules including proteins such as phytochelatins, metallothionein, compatible solutes, and secondary metabolites. In this comprehensive review, we provided insights towards a wider aspect of HM toxicity, ranging from their negative impact on plant growth to the mechanisms employed by the plants to alleviate the HM toxicity and presented the molecular mechanism of HMs toxicity and sequestration in plants.

from the Western North Atlantic Ocean

BACKGROUND

Elasmobranchs are particularly vulnerable to environmental metal contamination, accumulating these contaminants at high rates and excreting them slowly. The blue shark Prionace glauca L. is one of the most heavily fished elasmobranchs, although information regarding metal contamination and detoxification in this species is notably lacking.

METHODS

Blue sharks were sampled in the western North Atlantic Ocean, in offshore waters adjacent to Cape Cod, Massachusetts. Total and metallothionein-bound liver and muscle metal concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS), metallothionein detoxification and oxidative stress endpoints were determined by UV-vis spectrophotometry.

RESULTS

Metallothionein detoxification occurred for As, Cd, Cs, Cu, Hg, Pb, Se, Ti and Zn in liver, and for As, Cd, Cs, Pb, Se, and Zn in muscle, while reduced glutathione defenses seem to be related to Co and Zn exposure.

CONCLUSION

This is the first report for several metals (Ag, Co, non-radioactive Cs, Sb, Ti and V) for this species, which will aid in establishing baseline elemental data for biomonitoring efforts, health metrics, and conservation measures.

An Integrated Mass Spectrometry and Molecular Dynamics Simulations Approach Reveals the Spatial Organization Impact of Metal-Binding Sites on the Stability of Metal-Depleted Metallothionein-2 Species

Mammalian metallothioneins (MTs) are a group of cysteine-rich proteins that bind metal ions in two α- and β-domains and represent a major cellular Zn(II)/Cu(I) buffering system in the cell. At cellular free Zn(II) concentrations (10-11-10-9 M), MTs do not exist in fully loaded forms with seven Zn(II)-bound ions (Zn7MTs). Instead, MTs exist as partially metal-depleted species (Zn4-6MT) because their Zn(II) binding affinities are on the nano- to picomolar range comparable to the concentrations of cellular Zn(II). The mode of action of MTs remains poorly understood, and thus, the aim of this study is to characterize the mechanism of Zn(II) (un)binding to MTs, the thermodynamic properties of the Zn1-6MT2 species, and their mechanostability properties. To this end, native mass spectrometry (MS) and label-free quantitative bottom-up and top-down MS in combination with steered molecular dynamics simulations, well-tempered metadynamics (WT-MetaD), and parallel-bias WT-MetaD (amounting to 3.5 μs) were integrated to unravel the chemical coordination of Zn(II) in all Zn1-6MT2 species and to explain the differences in binding affinities of Zn(II) ions to MTs. Differences are found to be the result of the degree of water participation in MT (un)folding and the hyper-reactive character of Cys21 and Cys29 residues. The thermodynamics properties of Zn(II) (un)binding to MT2 are found to differ from those of Cd(II), justifying their distinctive roles. The potential of this integrated strategy in the investigation of numerous unexplored metalloproteins is attested by the results highlighted in the present study.

Metal removal by metallothionein and an acid phosphatase PhoN, surface-displayed on the cells of the extremophile, Deinococcus radiodurans

The utility of surface layer proteins (Hpi and SlpA) of the radiation resistant bacterium, Deinococcus radiodurans, was investigated for surface display and bioremediation of cadmium and uranium. The smtA gene, from Synechococcus elongatus (encoding the metal binding metallothionein protein), was cloned and over-expressed in D. radiodurans, either as such or as a chimeric gene fused with hpi ORF (Hpi-SmtA), or fused to the nucleotide sequence encoding the SLH domain of the SlpA protein (SLH-SmtA). The expressed fusion proteins localized to the deinococcal cell surface, while the SmtA protein localized to the cytoplasm. Recombinant cells surface-displaying the SLH-SmtA or Hpi-SmtA fusion proteins respectively removed 1.5-3 times more cadmium than those expressing only cytosolic SmtA. The deinococcal Hpi protein layer per se also contributed to U binding, by conferring substantial negative charge to deinococcal cell surface. The ORF of an acid phosphatase, PhoN was fused with the hpi or SLH domain DNA sequence and purified. Isolated Hpi-PhoN and SLH-PhoN, immobilized on deinococcal peptidoglycan showed efficient uranium precipitation (446 and 160 mg U/g biomass used respectively). The study demonstrates effective exploitation of the deinococcal S layer protein components for (a) cell surface-based sequestration of cadmium, and (b) cell-free preparations for uranium remediation.

Are long-term exposure studies needed? Short-term toxicokinetic model predicts the uptake of metal nanoparticles in earthworms after nine months

Uptake of most metal nanoparticles (NPs) in organisms is assumed to be mainly driven by the bioavailability of the released ions, as has been verified in controlled and short-term exposure tests. However, the changeability of NPs and the dynamic processes which NPs undergo in the soil environment, bring uncertainty regarding their interactions with soil organisms over a long period of time. To assess the potential impacts of long-term exposure scenarios on the toxicokinetic of metal NPs, earthworms Eisenia fetida were exposed to soils spiked with pristine Ag-NP, aged Ag-NP (Ag₂S-NP) and ionic Ag for nine months, and results were compared to those from a similar short-term (28 days) experiment, conducted under similar conditions. Overall, there were no statistical differences between long-term accumulation patterns in earthworms exposed to pristine Ag-NP and AgNO₃, while for Ag₂S-NP, the amount of Ag internalized after 9 months was five times lower than for the other treatments. Average Ag concentrations in soil pore water in all treatments did not change over time, however the soil pH decreased and electrical conductivity increased in all treatments. Metallothionein concentrations in exposed earthworms were not statistically different from levels in untreated earthworms. Finally, the short-term toxicokinetic models predicted the bioaccumulation in earthworms exposed to Ag-NP, AgNO₃ after nine months on the whole. Although the bioaccumulation for Ag₂S-NPs was somewhat under-predicted, the rate of accumulation of Ag₂S-NPs is much lower than that of Ag-NPs or AgNO₃ and thus potentially of lower concern. Nevertheless, better understanding about the exposure kinetics of Ag₂S-NP would help to address potential nano-specific toxicokinetic and toxicodynamics, also of other sulfidized metal NPs.

Metallothionein expression in Aspergillus exposed to environmentally relevant concentrations of heavy metals at different pH levels

Heavy metal pollution represents a health threat. Many fungal species are capable of tolerating various heavy metals, especially if they are isolated from a contaminated watercourse. One of the mechanisms by which fungi can sequester certain heavy metals is synthesizing stress proteins. The aim of this study is to investigate the production of metallothioneins in Aspergillus oryzae and Aspergillus clavatus exposed to environmentally relevant concentrations of Cd, Cu, Fe, and Zn at neutral, alkaline, and acidic pH conditions within 10 days. We determined the concentrations of these heavy metals in certain watercourses representing Behira and Giza governorates; also, we identified the most prevalent fungal species. We carried out a statistical correlation between different heavy metals and the isolated fungi. Then, in the laboratory, we exposed two of the most prevalent fungal species to the environmentally detected concentrations of the heavy metals and their doubles. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated that in A. oryzae, the metallothionein bands appeared in neutral medium containing Cd and Cu and in alkaline medium containing Cd and Zn, while in A. clavatus, no metallothionein bands appeared at all. In conclusion, metallothionein is a good indicator of pollution with Cd, Cu, and Zn in Aspergillus oryzae, and pH plays a central role in metallothionein production.

Serum metallothionein - a potential oncomarker?

INTRODUCTION

Metallothionein's (MT) overexpression has been demonstrated immunohistochemically in neoplastic cells of many tumour types. Its elevation above the physiological level has been confirmed in circulation of their hosts. The results of studies dealing with the topic have been summarized to verify if this marker can be applied in the current oncologic practise.

METHODS

The Pubmed and Google Scholar medical databases were reviewed for full-text articles focused on MT blood (plasma / serum) levels in patients with malignant tumours.

RESULTS

In our review, after a precise selection, we included 8 prospective randomized trials encompassing 561 blood samples taken from patients with a large histopathological spectrum of malignancies. In general, significant differences in blood MT levels between oncological patients and healthy subjects were confirmed. No particular value of the MT level has been demonstrated to be unequivocally predictive of oncologic diseaseCONCLUSION: The results of our review suggest that although the elevation of MT in blood serum in patients with solid malignancy can be regarded as a promising tumour marker, the recommendations of its applicability in clinical practice require to be derived from further research on extended cohorts of patients (Tab. 1, Fig. 1, Ref. 49).

Modulation of endogenous antioxidants by zinc and copper in signal crayfish (Pacifastacus leniusculus)

Metal pollution is a long-standing concern and bioindicators are commonly used in ecotoxicological studies to monitor impacted wildlife populations for evidence of sublethal effects. Significant variation in the response of common biomarkers to metals is reported across taxa, thus necessitating careful characterization in model organisms. In this study, we describe the regulation of glutathione S-transferase (GST), glutathione (GSH), and metallothionein (MT) by zinc chloride (0.6, 0.9, 1.2, 2.4, 4.8, 9.6 μg g^-1) and copper chloride (0.6, 0.9, 1.2 μg g^-1) in signal crayfish (Pacifastacus leniusculus). Zinc chloride did not alter GST activity relative to controls in the hepatopancreas. Crayfish exposed to copper chloride exhibited decreased GST activity at the lowest dose tested (0.6 μg g^-1) with no change observed at the higher doses. GSH did not change in response to either metal when sexes were grouped together. MT concentrations increased in response to zinc (2.4, 4.6, and 9.6 μg g^-1 doses) and copper (0.6, 0.9, and 1.2 μg g^-1 doses) in gill tissue. In tail tissue, MT increased at the 2.4 and 4.8 μg g^-1 zinc chloride doses and all the concentrations of copper tested. Sex-specific differences in endogenous antioxidant expression were also analyzed with no clear patterns emerging. We concluded that these endpoints are sensitive to zinc and copper in signal crayfish, although careful interpretation is needed when applying them in field studies given the variation in responses, non-monotonic dose responses, and differences in biotic and abiotic factors that inevitably exist in different aquatic ecosystems.

Comparative responses of Sinopotamon henanense to acute and sub-chronic Cd exposure

Studies on the freshwater crab Sinopotamon henanense have shown that acute and sub-chronic Cd²⁺ exposure induced differential alterations in the respiratory physiology and gill morphology. To elucidate Cd²⁺ toxicity under these two exposure conditions, crabs were acutely exposed to 7.14, 14.28, and 28.55 mg/L Cd²⁺ for 96 h and sub-chronically exposed to 0.71, 1.43, and 2.86 mg/L Cd²⁺ for 3 weeks. The Cd²⁺ accumulation, total metallothionein (MT), superoxide dismutase, and malondialdehyde (MDA) contents in the gill tissues were detected. Moreover, the glucose-6-phosphate dehydrogenase (G6PDH) activity, NADPH content, reduced glutathione (GSH), oxidized glutathione (GSSG), and GSH/GSSG ratio in the hepatopancreas were determined. The morphology of the X-organ-sinus gland complex was also observed. The results showed that sub-chronical Cd²⁺ exposure induced lower MT content and higher MDA level in the gills than in the acute exposure. In the hepatopancreas, acute Cd²⁺ exposure decreased the pentose phosphate pathway activity and NADPH content; however, an increased G6PDH activity and NADPH content were detected in sub-chronic Cd²⁺ exposure (2.86 mg/L). Morphological changes occurred in the sinus gland in crabs exposed to 2.86 mg/L Cd²⁺ for 3 weeks. The tightly packed structure composed by the axons, enlarged terminals, and glial cells, became loose and porous. Ultra-structurally, a large number of vacuoles and few neurosecretory granules were observed in the axon terminal. These effects added to our understanding of the toxic effects of Cd²⁺ and provide biochemical and histopathological evidence for S. henanense as a biomarker of acute or long-term waterborne Cd²⁺ pollution.

Effect of short-term dietary exposure on metal assimilation and metallothionein induction in the estuarine fish Pseudogobius sp

Metals introduced into the urban aquatic environment through anthropogenic activities have the potential to accumulate in organisms via multiple uptake routes. Understanding the impact different routes have on metal accumulation is important for the continued management of these ecosystems, where current water quality guidelines (WQGs) tend to be derived from aqueous metal exposure tests. In this study, the estuarine fish Pseudogobius sp. was exposed to a mixture of cadmium (Cd) and zinc (Zn) radiotracers dissolved in water or present in experimental food. Metal-spiked food was presented to fish as a single 'pulse-chase' feed or as three consecutive feeds, where the cumulative metal dose provided by both treatments was equal. Fish did not accumulate either metal from water, even after the length of exposure was increased from 12 h to 36 h. Fish did accumulate metals from diet and the assimilation efficiency (AE) was low following a single feed (12% for both Cd and Zn). Following multiple feeds fish displayed a significantly higher AE for zinc only, suggesting that fish are susceptible to retention of dietary Zn over an extended time period albeit at lower daily loadings. The final body burden and efflux rate did not differ between feeding regimes. Tissue accumulation of Cd and Zn indicated metal specific distribution. The gastro-intestinal (GI) tract contained >90% of total Cd body burden, whilst the carcass accounted for the majority (70-88%) of Zn body burden. There was significant induction of the biomarker metallothionein (MT) in the GI tract. These results demonstrate the differences in Cd and Zn metal uptake characteristics in this estuarine fish species, and how feeding frequency and metal loading of food may influence assimilation. This study highlights the importance of considering the inclusion of dietary exposures in WQG frameworks.

Metal and metallothionein levels in zooplankton in relation to environmental exposure: spatial and temporal variability (Saronikos Gulf, Greece)

Metal and metallothionein (MT) in mixed zooplankton were investigated as means of monitoring metal availability regarding environmental exposure. Spatial and temporal variability of Cd, Cu, Ni, Zn, Fe, Mn and Pb in zooplankton and seawater were studied in Saronikos Gulf (Aegean Sea, Eastern Mediterranean), once every second month during an annual cycle (2011-2012). Particulate organic carbon and chlorophyll α were also measured in seawater samples. Median zooplankton metal concentrations were 0.65, 32.4, 7.1, 864, 1420, 40.2 and 26.8 μg g^-1 dw for Cd, Cu, Ni, Zn, Fe, Mn and Pb, respectively, and 109 μg g^-1 ww for MTs. Metal levels in zooplankton and MTs were higher at sites influenced by human-derived pressures. Additionally, metal concentrations in pelagic fish flesh from the Greek MED-POL data base were used for bioconcentration and biomagnification factors calculation. Bioconcentration from water to zooplankton was higher than metal transfer from either seston to zooplankton or zooplankton to fish.

The role of the cadmium-binding protein response of the digestive gland of the Yesso scallop Mizuhopecten yessoensis (Jay, 1857) for marine environmental assessments

The ability of Pectinidae to accumulate heavy metals and store them in their tissues allows the use of scallops for biomonitoring marine pollution. High molecular weight metallothionein (MT)-like proteins (MTlps) play a central role in this process. Two major MTlps (72 and 43 kDa) have been identified in the digestive glands of Mizuhopecten yessoensis (Yesso scallop). These proteins have a very high affinity for the heavy metals cadmium, cobalt, and caesium. Additionally, these proteins can be deposited in large quantities in the digestive glands of this mollusc. It has been shown that 72 kDa MTlp is the main stress-response protein in areas polluted with cadmium or radioactive metals. Monitoring the amounts of MTlps in the digestive glands of the scallop M. yessoensis in areas with different anthropogenic pollutants has shown that these proteins are reliable biological markers of heavy-metal pollution in the marine environment.

Consequences of a short-term exposure to a sub lethal concentration of CdO nanoparticles on key life history traits in the fruit fly (Drosophila melanogaster)

Nanoparticles of cadmium oxide (CdO NPs) are among the most common industrial metal oxide nanoparticles. Early adulthood (P1) fruit flies (D. melanogaster) were exposed for 7 days to a sub lethal concentration (0.03 mg CdO NPs/mL, which was 20% of the LC₅₀), spiked into food media to test whether short episodes of CdO NPs exposures early in adult life have long-lasting effects on life history traits such as fecundity well beyond exposure times. All studied life history traits, as well as climbing behavior were adversely affected by exposure to CdO NPs. A blistered wing phenotype was also observed in the non-exposed progeny (F1) of adult flies (P1) and their fecundity was significantly decreased (-50%) compared to the fecundity of non-exposed (control) F1 flies. Expressions of antioxidant enzymes encoding genes; catalase and superoxide dismutase (SOD2) were significantly up regulated in P1 flies compared to control. Expression of metallothionein encoding genes (MTn A-D) were significantly up-regulated in both parent flies (P1) and their progeny (F1) after exposure of P1 flies to CdO NPs compared to non-exposed control flies, suggesting long-term potential effects. Taken together, these findings indicate that short-term exposure to a sub-lethal CdO NP concentration is sufficient to have long-lasting, adverse effects on fruit flies.

Combined forms of Pb and its detoxification and absorption in Cladophora rupestris subcells

This study aims to analyze the combined form, detoxification, and adsorption mechanism of Pb in Cladophora rupestris subcells. The chemical form analysis at different concentrations (0, 0.5, 1.0, 2.5, 5.0, 7.5, and 10 mg/L) indicated that most of the Pb (37%-76%) were integrated with oxalate and undissolved phosphate, which were important to the detoxification of C. rupestris. The characterization of Pb (0, 0.5, and 5.0 mg/L) at the subcellular was conducted via Fourier-transform infrared spectroscopy (FTIR), Three-dimensional excitation-emission matrix spectroscopy (3D-EEM), and protein secondary structure fitting. Results revealed that Pb-polysaccharides ((C₆H₅)-OO-Pb-OH, C-O-Pb, and symmetric Pb-O-Pb), Pb-functional-groups ((C₆H₅)-COO-Pb and (C₆H₅)-P = O-Pb), and Pb-protein complexes (OH-C₇H₆-CN-Pb-COOH, C₉H₁₀-NH-CN-C = O-Pb, Pb-S-C, and Pb-S) were formed. The cell wall produced transport proteins, such as metallothionein and glutathione, which bound and helped Pb²⁺ enter the cell. After entering the soluble fraction, the Pb-organic acid ((C₆H₅)-COO-Pb, (C₆H₅)-O-Pb, and (C₆H₅)-P = O-Pb) and Pb-sulfhydryl compound (Pb-S-C/Pb-S) assumed the most important role in resisting the toxicity of Pb²⁺. Pb²⁺ was absorbed in the organelle and formed (C₆H₅)-C-O-Pb and (C₆H₅)-P = O-Pb, and complexed with protein (Pb-C-N) when treated with 5.0 mg/L Pb. Results could help understand the role of subcellular fraction in the algal adaptation to stressful heavy metal conditions.

Metallothionein dependent-detoxification of heavy metals in the agricultural field soil of industrial area: Earthworm as field experimental model system

Earthworms are known to reclaim soil contamination and maintain soil health. In the present study, the concentration of DTPA extractable heavy metals, Cd, Cu, Cr, Pb, and Zn in vermicasts and tissues of the earthworms (anecic: Lampito mauritii; epigeic: Drawida sulcata) collected from the soils of four different industrial sites, Site-I (Sago industry), Site-II (Chemplast industry), Site-III (Dairy industry) and Site-IV (Dye industry) have been studied. The heavy metals in industrial soils recorded were 0.01-326.42 mg kg^-1 with higher Cu, Cr, and Zn contents while the vermicasts showed lower heavy metal loads with improved physicochemical properties and elevated humic substances. The higher humic substances dramatically decreased the heavy metals in the soil. The bioaccumulation factors of heavy metals (mg kg^-1) are in the order: Zn (54.50) > Cu (17.43) > Cr (4.54) > Pb (2.24) > Cd (2.12). The greatest amount of metallothionein protein (nmol g^-1) was recorded in earthworms from Site-IV (386.76) followed by Site-III (322.14), Site-II (245.82), and Site-I (232.21). Drawida sulcata can produce a considerable amount of metallothionein protein than Lampito mauritii as the metallothionein production is dependent upon the presence of pollutants. The molecular docking analysis indicates a binding score of 980 for Cd, Cr and Cu, and 372 for Zn. Pb may bind with a non-metallothionein protein of earthworms and bio-accumulated in the internal chloragogenous tissues. Metallothionein neutralizes the metal toxicity and controls the ingestion of essential elements.

Cytosolic and Metallothionein-Bound Hepatic Metals and Detoxification in a Sentinel Teleost, Dules auriga, from Southern Rio de Janeiro, Brazil

Dules auriga, a native Brazilian teleost, was applied as a sentinel species regarding metal contamination at Ilha Grande Bay, previously considered a reference site in Southeastern Brazil. Cytosolic (S50) and metallothionein-bound (HTS50) hepatic iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), cadmium (Cd), and silver (Ag) were determined by inductively coupled plasma optical emission spectrometry (ICP-OES), while metallothionein (MT) concentrations were determined by polarography. Ag concentrations in both cytosolic fractions were below the limit of detection. All other HTS50 metal contents were significantly lower than S50 contents. No significant associations were found for MT. Fe and Mn S50 were positively and moderately correlated to total length, as well as HTS50 Mn, while total weight was correlated to both Mn fractions, suggesting that environmental Mn and Fe concentrations may influence fish growth. A moderate correlation between the condition factor and the S50 Cu fraction was observed, also indicating that Cu may affect fish growth. Inter-element correlations were observed, including between Cd, a toxic element, and Mn and Zn, both essential elements. Calculated molar ratios indicate that both Mn and Zn are in molar excesses compared with Cd, corroborating literature assessments regarding protective Mn and Zn effects against Cd. Lack of MT correlations suggests that metal concentrations may not be high enough to reach an MT induction threshold and that MT variability is probably linked to environmental metal concentrations. Therefore, the increased environmental contaminant levels observed in the study area indicate the need for biomonitoring efforts aiming at the application of efficient mitigation measures.

Comparison of Thymulin Activity with Other Measures of Marginal Zinc Deficiency

Activity of the immunoregulatory peptide thymulin reflects differences in zinc status. This study compared thymulin activity with four other zinc status measures in rats fed zinc at either 5 or 25 ppm. Rats fed the lower zinc showed the following results compared with rats with adequate zinc intake: serum thymulin activity 61% lower, serum zinc 31% lower, serum extracellular superoxide dismutase 18% lower, serum 5'-nucleotidase activity 26% lower, and liver metallothionein 28% lower. Thus, thymulin activities showed more sensitivity to restricted zinc intake than did four other parameters.

Cadmium exposure alters expression of protective enzymes and protein processing genes in venom glands of the wolf spider Pardosa pseudoannulata

Cadmium (Cd) pollution is currently the most serious type of heavy metal pollution throughout the world. Previous studies have shown that Cd elevates the mortality of paddy field spiders, but the lethal mechanism remains to be explored profoundly. In the present study, we measured the activities of protective enzymes (acetylcholinesterase, glutathione peroxidase, phenol oxidase) and a heavy metal chelating protein (metallothionein) in the pond wolf spider Pardosa pseudoannulata after Cd exposure. The results indicated that Cd initially increased the enzyme activities and protein concentration of the spider after 10- and 20-day exposure before inhibiting them at 30-day exposure. Further analysis showed that the enzyme activities in the cephalothorax were inhibited to some extent. Since the cephalothorax region contains important venom glands, we performed transcriptome sequencing (RNA-seq) analysis of the venom glands collected from the spiders after long-term Cd exposure. RNA-seq yielded a total of 2826 differentially expressed genes (DEGs), and most of the DEGs were annotated into the process of protein synthesis, processing and degradation. Furthermore, a mass of genes involved in protein recognition and endoplasmic reticulum (ER) -associated protein degradation were down-regulated. The reduction of protease activities supports the view that protein synthesis and degradation in organelles and cytoplasm were dramatically inhibited. Collectively, our outcomes illustrate that Cd poses adverse effects on the expression of protective enzymes and protein, which potentially down-regulates the immune function in the venom glands of the spiders via the alteration of protein processing and degradation in the ER.

Subcellular metal distribution in two deep-sea mollusks: Insight of metal adaptation and detoxification near hydrothermal vents

In this study, we determined the concentrations of Cu, Zn, Ni, Cd, Pb and As and their subcellular distributions within the tissues of mussels (Bathymodiolus marisindicus) and snails (Gigantopelta aegis) from two hydrothermal vent regions, i.e., Tiancheng and Longqi, at Southwest Indian Ridge. Mussels collected from the two venting regions showed comparable concentrations for Ni and Pb, but Cu, Zn, Cd and As concentrations were significantly different in mussel gills between the two vent regions. Similar ranges of metal concentrations were found in the snails as those in the mussels, but most of the metals were mainly accumulated in the viscera, except for Ni. Similar subcellular partitioning of Cu, Zn and Cd was documented in different mussel tissues, with cellular debris (50%) being the predominant fraction, followed by equivalent values in other fractions. Lead was distributed in both cellular debris and metal-rich granules (MRG) fraction, whereas Ni was predominantly distributed in MRG (90%). Arsenic was mainly partitioned in cellular debris and metallothionein-like protein. However, deep-sea snails displayed elevated subcellular partitioning of Cu in the organelles (up to 60%) and may be more susceptible to Cu stress than the mussels. Our results demonstrated the metal-specificity of detoxification strategies in these deep-sea hydrothermal vent mollusks, and the mussels may be more adaptable to high metal exposures than the snails at hydrothermal vent.

Membrane insertion exacerbates the α-Synuclein-Cu(II) dopamine oxidase activity: Metallothionein-3 targets and silences all α-synuclein-Cu(II) complexes

Copper binding to α-synuclein (α-Syn), the major component of intracellular Lewy body inclusions in substantia nigra dopaminergic neurons, potentiate its toxic redox-reactivity and plays a detrimental role in the etiology of Parkinson disease (PD). Soluble α-synuclein-Cu(II) complexes possess dopamine oxidase activity and catalyze ROS production in the presence of biological reducing agents via Cu(II)/Cu(I) redox cycling. These metal-centered redox reactivities harmfully promote the oxidation and oligomerization of α-Syn. While this chemistry has been investigated on recombinantly expressed soluble α-Syn, in vivo, α-Syn is acetylated at its N-terminus and is present in equilibrium between soluble and membrane-bound forms. This post-translational modification and membrane-binding alter the Cu(II) coordination environment and binding modes and are expected to affect the α-Syn-Cu(II) reactivity. In this work, we first investigated the reactivity of acetylated and membrane-bound complexes, and subsequently addressed whether the brain metalloprotein Zn₇-metallothionein-3 (Zn₇MT-3) possesses a multifaceted-role in targeting these aberrant copper interactions and consequent reactivity. Through biochemical characterization of the reactivity of the non-acetylated/N-terminally acetylated soluble or membrane-bound α-Syn-Cu(II) complexes towards dopamine, oxygen, and ascorbate, we reveal that membrane insertion dramatically exacerbates the catechol oxidase-like reactivity of α-Syn-Cu(II) as a result of a change in the Cu(II) coordination environment, thereby potentiating its toxicity. Moreover, we show that Zn₇MT-3 can efficiently target all α-Syn-Cu(II) complexes through Cu(II) removal, preventing their deleterious redox activities. We demonstrate that the Cu(II) reduction by the thiolate ligands of Zn₇MT-3 and the formation of Cu(I)₄Zn₄MT-3 featuring an unusual redox-inert Cu(I)₄-thiolate cluster is the molecular mechanism responsible for the protective effect exerted by MT-3 towards α-Syn-Cu(II). This work provides the molecular basis for new therapeutic interventions to control the deleterious bioinorganic chemistry of α-Syn-Cu(II).

Uptake and detoxification of trace metals in estuarine crabs: insights into the role of metallothioneins

The detoxification process of trace metals in the estuarine burrowing crab Neohelice granulata, after previously being exposed to anthropogenic pressures in the field, is described for the first time. The objectives of this study were (a) to assess the metal content (Cd, Cu, Pb, Zn, Mn, Ni, Cr, Fe) in the sediments and the uptake of these elements in the hepatopancreas of N. granulata; (b) to quantify trace metal concentrations in the hepatopancreas before and after the detoxification experiment; and (c) to relate this information to metallothionein (MT) induction or reversibility. The detoxification assay was performed for 25 days with artificial seawater under controlled conditions in a culture chamber. The results showed higher uptake and bioaccumulation of Zn and Cu from the sediments, and the hepatopancreas exhibited increased levels of Zn and lower concentrations of the rest of the metals and MTs after the assay, mainly Fe and Mn that were significantly lower. We conclude that trace metals could be translocated to and accumulated in the hepatopancreas, the main metabolic organ, and then eliminated under controlled conditions with corresponding reversibility of MTs. Graphical abstract.

Biochemical profile and gene expression of Clarias gariepinus as a signature of heavy metal stress

Heavy metals have been found in increasing concentrations in the aquatic environment. Fishes exposed to such metals have altered gene expression, serum profiles, tissue histology and bioindices that serve as overall health biomarkers. The heavy metals (Ni, Cd, and Cr) accumulated in water and fish tissues, were beyond the permissible limits defined by the Central Pollution Control Board/World Health Organization. Metallothionein (MT) and glutathione peroxidase (GPX) genes expression patterns highlighted the metal-specific exposure of fish. An increased fold change of genes against beta-actin serves as a potential feature for toxicity. Metal toxicity is also reflected by an increased level of digestive enzymes (amylase and lipase) in the serum and alterations in values of reproductive hormones (11-Ketotestosterone and progesterone). Total serum bilirubin attribute to the liver and biliary tract disease in fishes. Histopathological studies show cellular degeneration, breakage, vacuolization signifying the chronic stress.

A metallothionein type 2 from Avicennia marina binds to iron and mediates hydrogen peroxide balance by activation of enzyme catalase

Metallothioneins (MTs) are low molecular weight, cysteine-rich, metal-binding proteins that are important for essential metal homeostasis, protection against oxidative stress, and buffering against toxic heavy metals. In this work the gene encoding an MT type 2 from Avicennia marina (Forssk.) Vierh. (AmMT2) was cloned into pET41a and transformed into the Escherichia coli strain Rosetta (DE3). Following the induction with isopropyl β-_D-1-thiogalactopyranoside, AmMT2 was expressed as glutathione-S-transferase (GST)-tagged fusion protein. The accumulation of Zn²⁺, Cu²⁺, Fe²⁺, Ni²⁺ and Cd²⁺ for strain R-AmMT2 was 4, 8, 5.4, 2 and 1.6 fold of control strain suggesting the role of AmMT2 in accumulation of metals. Particularly the strain R-AmMT2 was able to accumulate 30.7 mg per g dry weight. The cells expressing AmMT2 was more tolerant to hydrogen peroxide and had higher catalase (CAT) activity. To understand the mechanistic action of AmMT2 hydrogen peroxide tolerance, the activity of CAT in the E. coli protein extract was assayed after addition of pure Fe²⁺/GST-AmMT complex and Apo/GST-AmMT2 in vitro. Whereas, the activity of CAT did not change by the addition of Apo/GST-AmMT2, the activity of CAT significantly increased after addition of Fe²⁺/GST-AmMT2. These results show that AmMT2 activates CAT through Fe²⁺ transfer which subsequently causes the oxidative stress tolerance.