Metallothionein: an intracellular protein to protect against cadmium toxicity

Effects of the methanol root extract of Carpolobia lutea on sperm indices, acrosome reaction, and sperm DNA integrity in cadmium-induced reproductive toxicity in male Wistar rats

OBJECTIVE

Oxidative stress is a mechanism of cadmium-induced reproductive dysfunction. Carpolobia lutea is a free radical scavenger. Our study investigated the potential protective effects of Carpolobia lutea root methanol extract against cadmium-induced reproductive toxicity.

METHODS

We obtained the Carpolobia lutea root in Akure, and it was authenticated at the Forestry Research Institute of Nigeria (FRIN) herbarium, Ibadan, Nigeria, with FHI number 109784. We used Soxhlet extraction to obtain its methanol extract. We used thirty male Wistar rats (150-170g) in this study, (n=5 per group), and treated them as follows: Control (1 ml/kg normal saline), Cd (2 mg/kg), Cd+MCL (2 mg/kg+100 mg/kg), Cd+MCL (2 mg/kg+200 mg/kg), MCL (100 mg/kg), MCL (200 mg/kg). We administered Carpolobia lutea orally for 8 weeks. We administered a single dose of 2 mg/kg of cadmium intraperitoneally. We assessed the sperm profile using a computer-aided sperm analyzer. Under microscopy, we determined the sperm acrosome reaction and the DNA damage. We measured the seminal fructose level using spectrophotometry, and the data were analyzed using ANOVA at p<0.05.

RESULTS

Cd+MCL (2mg/kg+200 mg/kg) significantly increased sperm count (339.0±25.0 vs. 29.0±4.5 million/mL), motility (80.0±0.2 vs. 55.0±4.9%), viability (68.7±2.7 vs. 31.3±2.9%) and decreased abnormal sperm (28.3±1.7 vs. 43.3±2.5%), relative to the cadmium group. Cd+MCL (2mg/kg+200 mg/kg) significantly increased acrosome reaction (68.0±7.5 vs. 15.2±2.4%) and seminal fructose level (0.49±0.06 vs. 0.28±0.06 mmol/L) relative to the cadmium group. Cd+MCL (2mg/kg+200 mg/kg) significantly decreased sperm DNA damage (14.1±1.6 vs. 35.9±5.3%) in relation to the cadmium group.

CONCLUSIONS

Carpolobia lutea root extract improves the sperm variables of rats exposed to cadmium.

Back to Nucleus: Combating with Cadmium Toxicity Using Nrf2 Signaling Pathway as a Promising Therapeutic Target

There are concerns about the spread of heavy metals in the environment, and human activities are one of the most important factors in their spread. These agents have the high half-life resulting in their persistence in the environment. So, prevention of their spread is the first step. However, heavy metals are an inevitable part of modern and industrial life and they are applied in different fields. Cadmium is one of the heavy metals which has high carcinogenesis ability. Industrial waste, vehicle emissions, paints, and fertilizers are ways of exposing human to cadmium. This potentially toxic agent harmfully affects the various organs and systems of body such as the liver, kidney, brain, and cardiovascular system. Oxidative stress is one of the most important pathways of cadmium toxicity. So, improving the antioxidant defense system can be considered as a potential target. On the other hand, the Nrf2 signaling pathway involves improving the antioxidant capacity by promoting the activity of antioxidant enzymes such as catalase and superoxide dismutase. At the present review, we demonstrate how Nrf2 signaling pathway can be modulated to diminish the cadmium toxicity.

Copper-induced oxidative stress and biomarkers in the postlarvae of Penaeus indicus

The objective of the present research is to study the levels of reactive oxygen species (ROS) and protein carbonyl (PC) and the functional protein levels of metallothioneins (MT) in Penaeus indicus postlarvae (PL) upon sublethal copper exposure and to determine the biomarkers. The PL were exposed to sublethal copper of 0.164 ppm. The experiments were carried out in the laboratory over a period of 30 days with sampling intervals of 24, 48, and 96 h and 10, 20, and 30 days. The present study confirms that high oxidative stress can be induced from 24 h onwards upon sublethal exposure to copper in P. indicus PL. This is evident from the increasing levels of ROS in the exposed PL during both short-term and long-term exposures to sublethal copper. Since variability in metallothionein levels from 24 h through 30 days of experimental period was observed, metallothioneins cannot be regarded as a good biomarker as far as copper toxicity with respect to P. indicus PL is concerned. The effect of copper on protein carbonyl seems to be very rapid and consistent. The results suggest that protein carbonyl in P. indicus PL is significantly induced in a time-dependent manner upon copper exposure even at sublethal dose, and it seems reasonable to support that protein carbonyl could be used as a biomarker to copper toxicity.

Upregulation of epithelial metallothioneins by metal-rich ultrafine particulate matter from an underground railway

Airborne particulate matter (PM) is a leading cause of mortality and morbidity. However, understanding of the range and mechanisms of effects of PM components is poor. PM generated in underground railways is rich in metals, especially iron. In the ultrafine (UFPM; <0.1 μm diameter) fraction, the combination of small size and metal enrichment poses an unknown health risk. This study aimed to analyse transcriptomic responses to underground UFPM in primary bronchial epithelial cells (PBECs), a key site of PM deposition. The oxidation state of iron in UFPM from an underground station was determined by X-ray absorption near edge structure (XANES) spectroscopy. Antioxidant response was assayed using a reporter cell line transfected with an antioxidant response element (ARE)-luciferase construct. Differentiated PBECs were exposed to UFPM for 6 h or 24 h for RNA-Seq and RT-qPCR analysis. XANES showed predominance of redox-active Fe3O4, with ROS generation confirmed by induction of ARE-luciferase expression. 6 h exposure of PBECs to UFPM identified 52 differentially expressed genes (DEGs), especially associated with epithelial maintenance, whereas 24 h exposure yielded 23 DEGs, particularly involved with redox homeostasis and metal binding. At both timepoints, there was upregulation of members of the metallothionein family, low molecular weight proteins with antioxidant activity whose main function is binding and homeostasis of zinc and copper ions, but not iron ions. This upregulation was partially inhibited by metal chelation or ROS scavenging. These data suggest differential regulation of responses to metal-rich UFPM depending on exposure period, and highlight novel pathways and markers of PM exposure, with the role of metallothioneins warranting further investigation.

Chemical imaging and assessment of cadmium distribution in the human body

The scientific interest in cadmium (Cd) as a human health damaging agent has significantly increased over the past decades. However, particularly the histological distribution of Cd in human tissues is still scarcely defined. Using inductively coupled plasma-mass spectrometry (ICP-MS), we determined the concentration of Cd in 40 different human tissues of four body donors and provided spatial information by elemental imaging on the microscopic distribution of Cd in 8 selected tissues by laser ablation (LA)-ICP-MS. ICP-MS results show that Cd concentrations differ by a factor of 20 000 between different tissues. Apart from the well know deposits in kidney, bone, and liver, our study provides evidence that muscle and adipose tissue are underestimated Cd pools. For the first time, we present spatially resolved Cd distributions in a broad panel of human soft tissues. The defined histological structures are mirrored by sharp cut differences in Cd concentrations between neighboring tissue types, particularly in the rectum, testis, and kidneys. The spatial resolution of the Cd distribution at microscopic level visualized intratissue hot spots of Cd accumulation and is suggested as a powerful tool to elucidate metal based toxicity at histological level.

Chronic Manganese Administration with Longer Intervals Between Injections Produced Neurotoxicity and Hepatotoxicity in Rats

Abstract

Subacute exposure to manganese (Mn) produced Parkinson’s disease-like syndrome called Manganism. Chronic onset and progression are characteristics of Manganism, therefore, this study aimed to examine Mn toxicity following chronic exposures. Male Sprague-Dawley rats were injected Mn²⁺ 1 and 5 mg/kg, every 10 days for 150 days (15 injections). Animal body weight and behavioral activities were recorded. At the end of experiments, the brain and liver were collected for morphological and molecular analysis. Chronic Mn exposure did not affect animal body weight gain, but the high dose of Mn treatment caused 20% mortality after 140 days of administration. Motor activity deficits were observed in a dose-dependent manner at 148 days of Mn administration. Immunofluorescence double staining of substantia nigra pars compacta (SNpc) revealed the activation of microglia and loss of dopaminergic neurons. The chronic neuroinflammation mediators TNFα, inflammasome Nlrp3, Fc fragment of IgG receptor IIb, and formyl peptide receptor-1 were increased, implicating chronic Mn-induced neuroinflammation. Chronic Mn exposure also produced liver injury, as evidenced by hepatocyte degeneration with pink, condensed nuclei, indicative of apoptotic lesions. The inflammatory cytokines TNFα, IL-1β, and IL-6 were increased, alone with stress-related genes heme oxygenase-1, NAD(P)H:quinone oxidoreductase-1 and metallothionein. Hepatic transporters, such as multidrug resistant proteins (Abcc1, Abcc2, and Abcc3) and solute carrier family proteins (Slc30a1, Slc39a8 and Slc39a14) were increased in attempt to eliminate Mn from the liver. In summary, chronic Mn exposure produced neuroinflammation and dopaminergic neuron loss in the brain, but also produced inflammation to the liver, with upregulation of hepatic transporters.

Graphic Abstract

Electronic supplementary material

The online version of this article (10.1007/s11064-020-03059-2) contains supplementary material, which is available to authorized users.

Protective effect of polaprezinc on cadmium-induced injury of lung epithelium

Cadmium is a toxic metal contained in food, water and the atmosphere, and exposure to cadmium can cause respiratory diseases in humans. Various health problems caused by cadmium result from oxidative stress-dependent cellular injury. Metallothioneins are intracellular, cysteine-rich, metal-binding proteins that have a detoxifying action on heavy metals such as cadmium in various organs. In addition, expression of metallothioneins is induced by metals with low biological toxicity, such as zinc. Therefore, in this study we examined whether polaprezinc, a chelate compound consisting of carnosine and zinc, can suppress cadmium-induced lung epithelial cell death. We found that cell viability markers (intracellular ATP levels and mitochondrial activity) and cytotoxicity (lactate dehydrogenase release) were decreased and increased, respectively by cadmium treatment; however, polaprezinc significantly reversed these changes. Moreover, cadmium-dependent endoplasmic reticulum stress responses were suppressed by polaprezinc treatment. We then examined the protective mechanisms of polaprezinc, focusing on oxidative stress. Cadmium induced the production of reactive oxygen species (ROS) in A549 cells in a dose-dependent manner and polaprezinc significantly suppressed this cadmium-induced ROS production. Finally, we examined whether polaprezinc exerts an antioxidative action by inducing metallothioneins. We found that polaprezinc dose-dependently induced metallothioneins using real-time RT-PCR, ELISA, and western blotting analyses. These results indicate that polaprezinc can suppress cadmium-induced lung epithelial cell death and oxidative stress by inducing metallothioneins. We therefore suggest that polaprezinc may have therapeutic effects against respiratory diseases, such as chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis.

Exposure of earthworm (Eisenia fetida) to bauxite residue: Implications for future rehabilitation programmes

Bauxite residue is typically alkaline, has high sodium content and elevated concentrations of trace elements. Effective rehabilitation strategies are needed to mitigate potential environmental risks from its disposal and storage. Increasingly, the importance of viable soil faunal populations as well as establishment of vegetation covers is recognized as key components of successful rehabilitation. Inoculation with earthworms is a strategy for accelerating mine site rehabilitation, but little is known on the effects of bauxite residue properties on earthworm survival and viability. In the current study, earthworms (Eisenia fetida) were exposed for 28 days to a series of bauxite residue/soil treatments (0, 10, 25, 35, 50, 75 and 100% residue) to evaluate possible toxic effects on earthworms, investigate the bioavailability of relevant elements (e.g. As, Cr, V), and assess the risk of element transfer. Results showed that soil containing ≥25% residue (pH ≥ 9.8; ESP ≥ 18.5%; extractable Na ≥ 1122 mg/kg) significantly impacted survival (mortality ≥28%) and reproduction (cocoon production inhibition ≥76%) of the exposed earthworms. Alkalinity, sodicity and bioavailable Na were identified as major factors causing toxicity and some earthworms were observed to adopt compensative response (i.e. swollen body) to cope with osmotic stress. Conversely, soil containing 10% residue (pH = 9.1; ESP = 9.2%; extractable Na = 472 mg/kg) did not elicit significant toxicity at the organism level, but biomarker analysis (i.e. superoxide dismutase and catalase) in earthworm coelomocytes showed an oxidative stress. Furthermore, earthworms exposed to soil containing ≥10% residue took up and accumulated elevated concentrations of Al, As, Cr and V in comparison to the control earthworms. We concluded that earthworm inoculation could be used in future rehabilitation programmes once the key parameters responsible for toxicity are lowered below specific target values (i.e. pH = 9.1, ESP = 18.5%, extractable Na = 1122 mg/kg for Eisenia fetida). Nonetheless, trace element uptake in earthworms should be regularly monitored and the risk to the food chain further investigated.

Cadmium in plants: uptake, toxicity, and its interactions with selenium fertilizers

Cd is the third major contaminant of greatest hazard to the environment after mercury and lead and is considered as the only metal that poses health risks to both humans and animals at plant tissue concentrations that are generally not phytotoxic. Cd accumulation in plant shoots depends on Cd entry through the roots, sequestration within root vacuoles, translocation in the xylem and phloem, and Cd dilution within the plant shoot throughout its growth. Several metal transporters, processes, and channels are involved from the first step of Cd reaching the root cells and until its final accumulation in the edible parts of the plant. It is hard to demonstrate one step as the pivotal factor to decide the Cd tolerance or accumulation ability of plants since the role of a specific transporter/process varies among plant species and even cultivars. In this review, we discuss the sources of Cd pollutants, Cd toxicity to plants, and mechanisms of Cd uptake and redistribution in plant tissues. The metal transporters involved in Cd transport within plant tissues are also discussed and how their manipulation can control Cd uptake and/or translocation. Finally, we discuss the beneficial effects of Se on plants under Cd stress, and how it can minimize or mitigate Cd toxicity in plants.

Zinc protects against cadmium-induced toxicity in neonatal murine engineered cardiac tissues via metallothionein-dependent and independent mechanisms

Cadmium (Cd) is a nonessential heavy metal and a prevalent environmental toxin that has been shown to induce significant cardiomyocyte apoptosis in neonatal murine engineered cardiac tissues (ECTs). In contrast, zinc (Zn) is a potent metallothionein (MT) inducer, which plays an important role in protection against Cd toxicity. In this study, we investigated the protective effects of Zn against Cd toxicity in ECTs and explore the underlying mechanisms. ECTs were constructed from neonatal ventricular cells of wild-type (WT) mice and mice with global MT gene deletion (MT-KO). In WT-ECTs, Cd (5-20 μM) caused a dose-dependent toxicity that was detected within 8 h evidenced by suppressed beating, apoptosis, and LDH release; Zn (50-200 μM) dose-dependently induced MT expression in ECTs without causing ECT toxicity; co-treatment of ECT with Zn (50 µM) prevented Cd-induced toxicity. In MT-KO ECTs, Cd toxicity was enhanced; but unexpectedly, cotreatment with Zn provided partial protection against Cd toxicity. Furthermore, Cd, but not Zn, significantly activated Nrf2 and its downstream targets, including HO-1; inhibition of HO-1 by a specific HO-1 inhibitor, ZnPP (10 µM), significantly increased Cd-induced toxicity, but did not inhibit Zn protection against Cd injury, suggesting that Nrf2-mediated HO-1 activation was not required for Zn protective effect. Finally, the ability of Zn to reduce Cd uptake provided an additional MT-independent mechanism for reducing Cd toxicity. Thus, Zn exerts protective effects against Cd toxicity for murine ECTs that are partially MT-mediated. Further studies are required to translate these findings towards clinical trials.

Constitutive overexpression of rice metallothionein-like gene OsMT-3a enhances growth and tolerance of Arabidopsis plants to a combination of various abiotic stresses

Metallothioneins (MT) are primarily involved in metal chelation. Recent studies have shown that MT proteins are also involved in the responses of plants to various environmental stresses. The rice metallothionein-like gene OsMT-3a is upregulated by salinity and various abiotic stressors. A DNA construct containing the complete OsMT-3a coding sequence cloned downstream to the CaMV35S promoter was transformed into Arabidopsis and homozygous single-copy transgenic lines were produced. Compared to wild-type plants, transgenic plants showed substantially increased salinity tolerance (NaCl), drought tolerance (PEG), and heavy metal tolerance (CdCl₂) as individual stresses, as well as different combinations of these stresses. Relevantly, under unstressed control conditions, vegetative growth of transgenic plants was also improved. The shoot Na⁺ concentration and hydrogen peroxide in transgenic plants were lower than those in wild-type plants. OsMT-3a-overexpressing Arabidopsis lines accumulated higher levels of Cd²⁺ in both shoots and roots following CdCl₂ treatment. In the transgenic MT-3a lines, increased activity of two major antioxidant enzymes, catalase and ascorbate peroxidase, was observed. Thus, rice OsMT-3a is a valuable target gene for plant genetic improvement against multiple abiotic stresses.

Interspecific Variation in Nematode Responses to Metals

Performing toxicity testing on multiple species with differing degrees of evolutionary relatedness can provide important information on how chemical sensitivity varies among species and can help pinpoint the biological drivers of species sensitivity. Such knowledge could ultimately be used to design better multispecies predictive ecological risk assessment models and identify particularly sensitive species. However, laboratory toxicity tests involving multiple species can also be resource intensive, especially when each species has unique husbandry conditions. We performed lethality tests with 2 metals, copper chloride and zinc chloride, on 5 different nematode species, which are nested in their degree of evolutionary relatedness: Caenorhabditis briggsae, Caenorhabditis elegans, Oscheius myriophila, Oscheius tipulae, and Pristionchus pacificus. All species were successfully cultured and tested concurrently with limited resources, demonstrating that inexpensive, multispecies nematode toxicity testing systems are achievable. The results indicate that P. pacificus is the most sensitive to both metals. Conversely, C. elegans is the least sensitive species to copper, but the second most sensitive to zinc, indicating that species relationships do not necessarily predict species sensitivity. Toxicity testing with additional nematode species and types of chemicals is feasible and will help form more generalizable conclusions about relative species sensitivity. Environ Toxicol Chem 2020;39:1006-1016. © 2020 SETAC.

Environmental behavior of and gastropod biomarker response to trace metals from a backwater area of Xian'nv lake

Combined with sediment pollutant analysis, the gastropod Cipangopaludina cahayensis was chosen as an indicator organism to evaluate the environmental behavior of trace metals and the aquatic ecological risk that they present in a backwater area of Xian'nv Lake. Based on hydrological characteristics, 24 sampling sites representing the main stream (MS), tributaries (TR), lake area (LA) and lake tributaries (LT) were collected. The results revealed that cadmium (Cd) was the main pollutant and that it significantly accumulated in sediments of the research area. Based on the pollutant concentrations, the degree of Cd pollution was ranked in the following order: LA > MS > TR > LT. Several intersections between the rivers and Xian'nv Lake, including LA1, LA7 and LA 10, were observed to have higher Cd deposition. There was a significant difference in the spatial distribution of pollutants, which resulted in a higher accumulation of trace metals in the backwater area and its tributary. The Cd content in the visceral sac of C. cahayensis was positively correlated with the concentration of heavy metals in the sediment. The response of multiple antioxidant biomarkers, including superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST), as well as the glutathione (GSH) content and the level of by-products of lipid peroxidation (TBARS), in C. cahayensis revealed a potential relationship to the environmental behavior of the pollutants. By combining the different biomarkers responses, the integrated biomarker response index (IBR) corresponded well with the pollution distribution characteristics in different areas.

Metal(loid) exposure assessment and biomarker responses in captive and free-ranging European brown bear (Ursus arctos)

We investigated the level of five non-essential metal(loid)s (As, Cd, Hg, Tl, Pb) and nine essential metals (Mg, Ca, Mn, Fe, Co, Cu, Zn, Se, Mo) in hair and blood components of captive and free-ranging European brown bear populations in Croatia and Poland. Metal(loid) associations with biomarkers of oxidative stress (superoxide dismutase, SOD; glutathione-peroxidase, GSH-Px; malondialdehyde, MDA) and metal exposure (metallothionein, MT) were estimated in this top predatory mammal. Lead was the most abundant non-essential metal(loid) in both blood and hair, with 4 of 35 individuals having blood levels over 100 μg/L. A positive association was found between Pb level and SOD activity in blood. Free-ranging bears had higher blood SOD activity, Mn, Zn and Cd levels, hair Co, Cd, Tl and Pb compared to captive individuals, while the opposite was true for Mg and hair Ca thereby reflecting habitat and diet differences. With increasing age, animals showed lower levels of SOD activity and certain essential metals. Females had higher SOD activity and blood levels of some essential metals than males. Hair showed a higher Fe and Co level when sampled during the growth phase and was not predictive of non-essential metal(loid) blood levels. The established metal(loid) baseline values will enable future risk assessment in both captive and wild European brown bear populations.

GOLD: human exposure and update on toxic risks

Gold is ubiquitous in the human environment and most people are in contact with it through wearing jewelry, dental devices, implants or therapies for rheumatoid arthritis. Gold is not a nutrient but people are exposed to it as a food colorant and in food chains. The present review discusses the hazards faced in personal and domestic use of gold and the far greater risks presented through occupational exposure to the metal in mining and processing gold ores. In the last situation, regular manual contact or inhalation of toxic or carcinogenic materials like mercury or arsenic, respectively, presents far greater hazard and greatly complicates the evaluation of gold toxicity. The uses and risks presented by new technology and use of nanoparticulate gold in anti-cancer therapies and diagnostic medicine forms a major consideration in gold toxicity, where tissue uptake and distribution are determined largely by particle size and surface characteristics. Many human problems arise through the ability of metallic gold to induce allergic contact hypersensitivity. While gold in jewelry can evoke allergic reactions, other metals such as nickel, chromium and copper present in white gold or alloys exhibit more serious clinical problems. It is concluded that toxic risks associated with gold are low in relation to the vast range of potential routes of exposure to the metal in everyday life.

Metallothionein isoforms as double agents - Their roles in carcinogenesis, cancer progression and chemoresistance

Metallothioneins (MTs) are small cysteine-rich intracellular proteins with four major isoforms identified in mammals, designated MT-1 through MT-4. The best known biological functions of MTs are their ability to bind and sequester metal ions as well as their active role in redox homeostasis. Despite these protective roles, numerous studies have demonstrated that changes in MT expression could be associated with the process of carcinogenesis and participation in cell differentiation, proliferation, migration, and angiogenesis. Hence, MTs have the role of double agents, i.e., working with and against cancer. In view of their rich biochemical properties, it is not surprising that MTs participate in the emergence of chemoresistance in tumor cells. Many studies have demonstrated that MT overexpression is involved in the acquisition of resistance to anticancer drugs including cisplatin, anthracyclines, tyrosine kinase inhibitors and mitomycin. The evidence is gradually increasing for a cellular switch in MT functions, showing that they indeed have two faces: protector and saboteur. Initially, MTs display anti-oncogenic and protective roles; however, once the oncogenic process was launched, MTs are utilized by cancer cells for progression, survival, and contribution to chemoresistance. The duality of MTs can serve as a potential prognostic/diagnostic biomarker and can therefore pave the way towards the development of new cancer treatment strategies. Herein, we review and discuss MTs as tumor disease markers and describe their role in chemoresistance to distinct anticancer drugs.

The Role of Natural Antioxidants Against Reactive Oxygen Species Produced by Cadmium Toxicity: A Review

Cadmium (Cd) is a significant ecotoxic heavy metal that adversely affects all biological processes of humans, animals and plants. Exposure to acute and chronic Cd damages many organs in humans and animals (e.g. lung, liver, brain, kidney, and testes). In humans, the Cd concentration at birth is zero, but because the biological half-life is long (about 30 years in humans), the concentration increases with age. The industrial developments of the last century have significantly increased the use of this metal. Especially in developing countries, this consumption is higher. Oxidative stress is the imbalance between antioxidants and oxidants. Cd increases reactive oxygen species (ROS) production and causes oxidative stress. Excess cellular levels of ROS cause damage to proteins, nucleic acids, lipids, membranes and organelles. This damage has been associated with various diseases. These include cancer, hypertension, ischemia/perfusion, cardiovascular diseases, chronic obstructive pulmonary disease, diabetes, insulin resistance, acute respiratory distress syndrome, idiopathic pulmonary fibrosis, asthma, skin diseases, chronic kidney disease, eye diseases, neurodegenerative diseases (amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, and Huntington disease). Natural antioxidants are popular drugs that are used by the majority of people and have few side effects. Natural antioxidants play an important role in reducing free radicals caused by Cd toxicity. Our goal in this review is to establish the relationship between Cd and oxidative stress and to discuss the role of natural antioxidants in reducing Cd toxicity.

Segment-specific and direction-dependent transport of cadmium and manganese in immortalized S1, S2, and S3 cells derived from mouse kidney proximal tubules

The kidney proximal tubule is a target of many renal toxicants, including cadmium (Cd), and also a place of reabsorption of essential metals in glomerular filtrate to systemic circulation. Although the mechanisms of metal transport in the convoluted proximal tubule (S1 and S2 segments) and the straight proximal tubule (S3 segment) may differ, little is known about the segment-specific modes of metal transport. Here, we utilized immortalized cell lines derived from the S1, S2, and S3 segments of mouse kidney proximal tubules, and examined the segment-specific and direction-dependent transport of Cd and manganese (Mn) using a trans-well culture system. The results showed that the uptakes of Cd²⁺ and Mn²⁺ from apical sides were the highest in S3 cells, and Cd²⁺, Mn²⁺, and Zn²⁺ mutually inhibited the apical uptake of each metal. As the expression of ZIP8, a zinc transporter having affinities for Cd²⁺ and Mn²⁺, was the highest in S3 cells, ZIP8 may contribute largely to the apical uptakes of these metals. The efficient uptake of Mn²⁺ from apical side of S3 cells may suggest an important role of ZIP8 in proximal tubule in reabsorption of Mn, an essential metal. Our study demonstrated that S1, S2, and S3 cells provide a useful tool for studying the segment-specific and direction-dependent transport of both toxic and essential metals in the kidney's proximal tubules.

Metallomics reveals a persisting impact of cadmium on the evolution of metal-selective snail metallothioneins

The tiny contribution of cadmium (Cd) to the composition of the earth's crust contrasts with its high biological significance. We suggest that in gastropod clades, the protein family of metallothioneins (MTs) has evolved to specifically detoxify Cd.

Essential and nonessential metal effects on extracellular Leishmania amazonensis in vitro

Protozoan parasites like Leishmania amazonensis are excellent models to test the effects of new drugs against a functional molecular arsenal used to establish successfully an infection in the vertebrate host, where they invade the cells of the monocytic system. However, little is known about the influence of metal ions on the cellular functionality of the infective forms of L. amazonensis. In the present work, we show that ZnCl₂ (an essential metal to cellular metabolism) did not induce drastic effects on the survival of the promastigote under the conditions tested. However, incubation of ZnCl₂ prior to subsequent treatment with CdCl₂ and HgCl₂ led to a drastic toxic effect on parasite survival in vitro. Nonessential metals such as CdCl₂ and HgCl₂ promoted a drastic effect on parasite survival progressively with increasing dose and time of exposure. Notably, HgCl₂ produced an effective elimination of the parasite in doses/time smaller than the CdCl₂. This toxic action induced in the parasite a high condensation of the nuclear heterochromatin, besides the absence or de-structuring of functional organelles such as glycosomes, acidocalcisomes, and mitochondria in the cytoplasm. Our results suggest that promastigotes of L. amazonensis are sensitive to the toxic activity of nonessential metals, and that this activity increases when parasites are previously exposed to Zn. To summarize, toxic effects of the tested metals are dose and time dependent and can be used as a study model to better understand the functionality of the molecular arsenal responsible for the parasitism.

Dynamics of Cadmium Acclimation in Daphnia pulex: Linking Fitness Costs, Cross-Tolerance, and Hyper-Induction of Metallothionein

Acclimation increases tolerance to stress in individuals but is assumed to contribute fitness costs when the stressor is absent, though data supporting this widely held claim are sparse. Therefore, using clonal (i.e., genetically identical) cultures of Daphnia pulex, we isolated the contributions of acclimation to the regulation of the metal response gene, metallothionein 1 (MT1), and defined the reproductive benefits and costs of cadmium (Cd)-acclimation. Daphnia pulex were exposed for 50 parthenogenetic generations to environmentally realistic levels (1 μg Cd/L), and tolerance to Cd and other metals assessed during this period via standard toxicity tests. These tests revealed (1) increased tolerance to Cd compared to genetically identical nonacclimated cultures, (2) fitness costs in Cd-acclimated Daphnia when Cd was removed, and (3) cross-tolerance of Cd-acclimated Daphnia to zinc and silver, but not arsenic, thereby defining a functional role for metallothionein. Indeed, Cd-acclimated clones had significantly higher expression of MT1 mRNA than nonacclimated clones, when Cd exposed. Both the enhanced induction of MT1 and tolerant phenotype were rapidly lost when Cd was removed (1-2 generations), which is further evidence of acclimation costs. These findings provide evidence for the widely held view that acclimation is costly and are important for investigating evolutionary principles of genetic assimilation and the survival mechanisms of natural populations that face changing environments.

Barium chloride dose-dependently induced heart and lung injury in Wistar rats

Barium (Ba) is one of the environmental pollutant metals that incite deleterious effects on human health. The present study investigated the effects of exposure to different doses of barium chloride (BaCl₂ ) on heart and lung of Wistar rats. Rats were exposed to BaCl₂ at 150, 300, and 600 mg/L for seven consecutive days. Results indicated that exposure to Ba caused heart and lung damage evidenced by significant increase in plasma lactate dehydrogenase and creatine kinase activities, total cholesterol, triglyceride, and low-density lipoprotein-cholesterol levels, while high-density lipoprotein-cholesterol level decreased when compared with control. Moreover, BaCl₂ significantly decreased superoxide dismutase, catalase, and acetylcholinesterase activities as well as glutathione level in heart and lung of the treated rats. Furthermore, the dose-dependent increase in cardiac and lung lipid peroxidation, advanced oxidative protein product and nitric oxide levels were accompanied by marked increase in metallothionein in the BaCl₂ -treated rats. Administration of BaCl₂ altered hematological parameters and significantly increased concentrations of interleukin-6 in the treated rats. Histology analysis showed significant alteration in the heart and lung tissues of Ba-treated rats. In conclusion, BaCl₂ -induced heart and lung damages via disruption of antioxidant defense systems, and activation of inflammatory mediators and alteration in hematological parameters in rats.

The freshwater isopod Asellus aquaticus as a model biomonitor of environmental pollution: A review

Anthropogenic substances pollute freshwater systems worldwide, with serious, long-lasting effects to aquatic biota. Present methods of detecting elevated levels of trace metal pollutants are typically accurate but expensive, and therefore not suitable for applications requiring high spatial resolution. Additionally, these methods are not efficient solutions for the determination of long-term averages of pollution concentration. This is the rationale for the implementation of a biomonitoring programme as an alternative means of pollutant detection. This review summarises recent literature concerning the past and potential uses of the benthic isopod Asellus aquaticus as a biomonitor for pollution in freshwater systems. Recent studies indicate that A. aquaticus is well suited for this purpose. However, the mechanisms by which it bioaccumulates toxins have yet to be fully understood. In particular, the interactions between coexisting trace metal pollutants in the aquatic environment have only recently been considered, and it remains unclear how a biomonitoring programme should adapt to the effects of these interactions. It is evident that failing to account for these additional stressors will result in an ineffective biomonitoring programme; for this reason, a comprehensive understanding of the bioaccumulation mechanisms is required in order to reliably anticipate the effects of any interferences on the outcome.

Metal binding characterization of heterologously expressed metallothionein of the freshwater crab Sinopotamon henanense

We characterized the metal tolerance of recombinant strains harboring metallothionein from the freshwater crab Sinopotamon henanense (ShMT) in vivo and metal binding properties of ShMT purified in vitro. The recombinant strains harboring ShMT were exposed to 0.1 mM Cd²⁺, 0.3 mM Cu²⁺, 0.5 mM Pb²⁺, and 0.8 mM Zn²⁺. The growth curves and spot assays of recombinant strains and the contents of heavy metal ions were analysed in the media supplemented with above metal ions provided to recombinant E. coli synthesis. The structural characteristics of the Cd-, Cu-, Pb-, and Zn-ShMT were determined through ultraviolet spectroscopy (UV-vis), circular dichroism (CD), and isothermal titration calorimetry (ITC). The in vivo results showed that, compared to control strains, recombinant strains tolerated Cd²⁺, Cu²⁺, Pb²⁺, and Zn²⁺. Furthermore, the contents of Cd²⁺ and Pb²⁺ in media decreased substantially. In vitro and the Cd-ShMT had a higher degree of folding compactness in solution. 5,5'-Dithiobis-(2-nitrobenzoic) acid (DTNB) reaction and ITC results demonstrated that ShMT yielded Cd₆-, Cu₇-, and Pb₆-ShMT. The binding stability order was Cu-ShMT > Cd-ShMT > Pb-ShMT > Zn-ShMT. Overall, ShMT is a canonical crustacean MT and is defined as a Cd-specific MT isoform that functions mainly in a detoxifying Cd²⁺ and Pb²⁺ and in regulating Zn²⁺ homeostasis in S. henanense. This research on the metal binding properties of ShMT provides a better understanding of the physiological function of ShMT reducing heavy metal bioavailability and by regulating essential trace metals.

Transgelin-2 as a therapeutic target for asthmatic pulmonary resistance

There is a clinical need for new bronchodilator drugs in asthma, because more than half of asthmatic patients do not receive adequate control with current available treatments. We report that inhibition of metallothionein-2 protein expression in lung tissues causes the increase of pulmonary resistance. Conversely, metallothionein-2 protein is more effective than β₂-agonists in reducing pulmonary resistance in rodent asthma models, alleviating tension in tracheal spirals, and relaxing airway smooth muscle cells (ASMCs). Metallothionein-2 relaxes ASMCs via transgelin-2 (TG2) and induces dephosphorylation of myosin phosphatase target subunit 1 (MYPT1). We identify TSG12 as a nontoxic, specific TG2-agonist that relaxes ASMCs and reduces asthmatic pulmonary resistance. In vivo, TSG12 reduces pulmonary resistance in both ovalbumin- and house dust mite-induced asthma in mice. TSG12 induces RhoA phosphorylation, thereby inactivating the RhoA-ROCK-MYPT1-MLC pathway and causing ASMCs relaxation. TSG12 is more effective than β₂-agonists in relaxing human ASMCs and pulmonary resistance with potential clinical advantages. These results suggest that TSG12 could be a promising therapeutic approach for treating asthma.

Selective cadmium regulation mediated by a cooperative binding mechanism in CadR

The highly toxic cadmium ion can cause destructive hazards to living systems by nonspecific and tight binding on functional macromolecules. However, most of the developed cadmium detoxification systems are not sufficient to recognize or detoxify cadmium ions, specifically due to the similar coordination behavior of heavy metal ions in thiolate-rich sites. Here we report that the ultraspecific cadmium regulator CadR has evolved 2 distinct types of functional recognition sites rather than a mono-type thiolate-rich site to achieve outstanding selectivity. The thiolate-rich site I and the adjacent histidine-rich recognition site II are highly associated with transcription activation. This cooperative binding mechanism could improve our understanding of the relationship between the structural dynamics and biological function of metalloregulators.

Detoxification of the highly toxic cadmium element is essential for the survival of living organisms. Pseudomonas putida CadR, a MerR family transcriptional regulator, has been reported to exhibit an ultraspecific response to the cadmium ion. Our crystallographic and spectroscopic studies reveal that the extra cadmium selectivity of CadR is mediated by the unexpected cooperation of thiolate-rich site I and histidine-rich site II. Cadmium binding in site I mediates the reorientation of protein domains and facilitates the assembly of site II. Subsequently, site II bridge-links 2 DNA binding domains through ligands His140/His145 in the C-terminal histidine-rich tail. With dynamic transit between 2 conformational states, this bridge could stabilize the regulator into an optimal conformation that is critical for enhancing the transcriptional activity of the cadmium detoxification system. Our results provide dynamic insight into how nature utilizes the unique cooperative binding mechanism in multisite proteins to recognize cadmium ions specifically.

Subcellular metal distributions and metallothionein associations in rough-toothed dolphins (Steno bredanensis) from Southeastern Brazil

Metals are subject to internal subcellular compartmentalization, altering their bioavailability. Thus, subcellular metal assessments are crucial in biomonitoring efforts. Metal distribution in three subcellular fractions (insoluble - ISF, thermolabile - TLF and thermostable - TSF) were determined by ICP-MS in Steno bredanensis specimens from Southeastern Brazil. Associations between metals, metallothionein (MT) and reduced glutathione (GSH) were also investigated. Differential metal-detoxification mechanisms were observed. MT detoxification was mostly noted for As, Cd, and Pb, while Cu, Cr, Hg, Ni, Se and Ti displayed lower MT-associations. Fe, Zn and Se, on the other hand, were poorly associated to MT, and mostly present in the ISF, indicating low bioavailability. This is the first report on subcellular Sn and Ti distribution in cetaceans and the first in this species in Brazil. Potential protective roles of essential metals against toxic elements are postulated. This study indicates that important biochemical detoxification information is obtained through subcellular fraction analyses in marine mammals.

Elemental Metabolomics: Modulation of Egg Metallome with Flavonoids, an Exploratory Study

The basic principles of elemental metabolomics were applied to investigate whether alteration of egg metallome could be achieved after two flavonoids addition, namely hesperidin and naringin in diets of laying hens. A total of 72 hens were divided into six groups: Control (C) (basal diet), E1 (750 mg hesperidin/kg diet), E2 (1500 mg hesperidin/kg diet), N1 (750 mg naringin/kg diet), N2 (1500 mg naringin/kg diet), and VE (200 mg vitamin E/kg diet). The same diet was provided to birds of all treatments, with the exception of added supplements. The diets had the same vitamin and mineral premix; thus, all birds received the same number of elements because no differences on feed intake existed. The egg elemental profile consisted of As, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sr, V, Zn, and was determined using ICP-MS. Flavonoid supplementation altered the elemental profile. Most notably, in both albumen and yolk, hesperidin increased Ni, Pb, and Sr concentration while it decreased that of Co and Sb. Naringin increased Cd, Cr, Cu, Ni, and V and lowered the concentration of Co and Sb in both yolk and albumen. Vitamin E supplementation, in comparison to the control, decreased Co in both albumen and yolk and also raised Sb in albumen. Flavonoid presence led to the differences in deposition of certain trace minerals in egg compared to that of hens fed a basal diet or a diet with vitamin E supplementation.

Diallyl disulfide attenuation effect on transcriptome in rat liver cells against cadmium chloride toxicity

In this report, liver cells were treated with cadmium chloride (CdCl₂ ) and diallyl disulfide (DADS), a major compound from garlic to attenuate the toxic effect of Cd on transcriptome. The viability of Cd treated cells was reduced to 19.9% ± 2.4% in comparison to the untreated cells, whereas the viability of DADS pretreated cells was increased to 48.6% ± 2%. The attenuation effect of DADS was studied at shorter period (6 hours). Transcriptome analysis of CdCl₂ alone treated cells resulted in 2119 and 982 (up and down) regulated genes (≥ 2 or ≤ 2-fold), whereas pretreated cells with DADS resulted in 2597 and 1784 genes. These genes were known to function in many important biological processes. Affymetrix array analysis was validated by the pathway specific PCR array that exhibited the same trend of expression. The current study clearly shows the DADS attenuation effect on transcriptome in CdCl₂ -treated rat liver cells.

Overexpression of a Metallothionein 2A Gene from Date Palm Confers Abiotic Stress Tolerance to Yeast and Arabidopsis thaliana

Although the date palm tree is an extremophile with tolerance to drought and certain levels of salinity, the damage caused by extreme salt concentrations in the soil, has created a need to explore stress-responsive traits and decode their mechanisms. Metallothioneins (MTs) are low-molecular-weight cysteine-rich proteins that are known to play a role in decreasing oxidative damage during abiotic stress conditions. Our previous study identified date palm metallothionein 2A (PdMT2A) as a salt-responsive gene, which has been functionally characterized in yeast and Arabidopsis in this study. The recombinant PdMT2A protein produced in Escherichia coli showed high reactivity against the substrate 5′-dithiobis-2-nitrobenzoic acid (DTNB), implying that the protein has the property of scavenging reactive oxygen species (ROS). Heterologous overexpression of PdMT2A in yeast (Saccharomyces cerevisiae) conferred tolerance to drought, salinity and oxidative stresses. The PdMT2A gene was also overexpressed in Arabidopsis, to assess its stress protective function in planta. Compared to the wild-type control, the transgenic plants accumulated less Na⁺ and maintained a high K⁺/Na⁺ ratio, which could be attributed to the regulatory role of the transgene on transporters such as HKT, as demonstrated by qPCR assay. In addition, transgenic lines exhibited higher chlorophyll content, higher superoxide dismutase (SOD) activity and improved scavenging ability for reactive oxygen species (ROS), coupled with a better survival rate during salt stress conditions. Similarly, the transgenic plants also displayed better drought and oxidative stress tolerance. Collectively, both in vitro and in planta studies revealed a role for PdMT2A in salt, drought, and oxidative stress tolerance.

Chlorogenic acid relieves lead-induced cognitive impairments and hepato-renal damage via regulating the dysbiosis of the gut microbiota in mice

Lead (Pb), a heavy metal which is widely recognized as an environmental toxicant, is transported from the earth's crust into the human body to a significant extent. To control and reduce the hazard of Pb burdens in the human body, chlorogenic acid (CGA) has been used to antagonize Pb-induced cognitive impairments, and hepatic and renal toxicity in the present study. Seven-week-old male Kunming mice were treated with PbCl2 (1.34 g L-1 in drinking water) and/or CGA (30 mg per kg mouse per day) by gavage administration for 8 weeks. In this study, we evaluated behavior tests, serum biochemical parameters, biomarkers of oxidative stress, and community structure of gut microbiota in mice to explore the potential mechanism of the protective effect. Based on our results, CGA appreciably prevented memory impairment, the release of serum biomarkers, and oxidative stress caused by Pb intake. CGA significantly inhibited Pb-induced increase of cytoplasmic NF-κB, Bax, cytochrome C, and caspase-9 protein expressions. Furthermore, Pb + CGA treatment had a remarkable reversion effect of the gut microbiota composition change induced by Pb, for example increasing the ratio of Helicobacter from 2.95% (Pb) to 11.24% (Pb + CGA) and decreasing the ratio of the Lachnospiraceae_NK4A136_ group from 7.09% (Pb) to 2.68% (Pb + CGA), which suggests that CGA is a superior natural product to eliminate Pb-induced nephrotoxicity and hepatotoxicity.

Assessment of the heavy metal accumulation in the Blue Swimmer Crab (Portunus pelagicus), northern Bay of Bengal: Role of salinity

This is the first report to assay the heavy metal accumulation in Blue Swimmer Crab in the northern Bay of Bengal. The present study finds that copper (Cu) concentration though has been the highest compared to the other metals, particularly in the gill. Cadmium (Cd) and lead (Pb) have high affinity to be concentrated in Hepatopancreas all through the year. All the metal concentrations were higher during monsoon season (comparatively low salinity) than non-monsoon (high salinity) in the different body parts of Blue swimmer crab i.e. the inverse relationship between accumulation of heavy metals and sea water salinity has been shown. Present study revealed that salinity having the role to accumulate metal in different body parts of Blue Swimmer Crab. In future, microcosm experiments should be done to test the effect of frequent fluctuations of ambient salinity, such as is usual in different seasons in the present study area.

Occurrence of heavy metals in sediment and their bioaccumulation in sentinel crab (Macrophthalmus depressus) from highly impacted coastal zone

The current study aimed to investigate the eight heavy metals (Fe, Cu, Zn, Cr, Ni, Co, Pb, and Cd) occurrence and risk assessment in the sediment and sentinel crab (Macrophthalmus depressus) from the mangrove and coastal environment of industrialized and mega city Karachi, Pakistan. The sediment analyzed for physiochemical properties (grain size composition, organic matter, and heavy metals), that presented significant variability (p < 0.05) among the selected sites. The environmental health and eco-toxicological profile of the habitat determined through the enrichment factor (EF), adverse effect index (AEI) and potential ecological risk index (RI) that revealed high anthropogenic influences along the Karachi coast. All heavy metals in crab showed significant spatial differences (p < 0.001) and the strong correlation between the essential and non-essential metals. Sediment-biota accumulation factor (SBAF) suggested active bio-accumulation (>1.0) in crabs for all metals, except Cr. Pb accumulation in crabs showed a significant increase (p < 0.05) with the exposure Pb levels in sediment, which indicated the potential of crab as a bioindicator of Pb contamination. Principal component analysis (PCA) concluded that environmental factors like seawater temperature, salinity, sediment grain size and organic matter had a significant association with different metal accumulation in crabs. The current study revealed the ecological significance of sentinel crab, M. depressus, as they endure with wide range (low to serious RI) of metal contaminated environment.

RNA-Seq provides new insights on the relative mRNA abundance of antioxidant components during mouse liver development

Mammals have developed a variety of antioxidant systems to protect them from the oxygen environment and toxic stimuli. Little is known about the mRNA abundance of antioxidant components during postnatal development of the liver. Therefore, the purpose of this study was to compare the mRNA abundance of antioxidant components during liver development. Livers from male C57BL/6J mice were collected at 12 ages from prenatal to adulthood. The transcriptome was determined by RNA-Seq with transcript abundance estimated by Cufflinks. RNA-Seq provided a complete, more accurate, and unbiased quantification of the transcriptome. Among 33 known antioxidant components examined, three ontogeny patterns of liver antioxidant components were observed: (1) Prenatal-enriched, in which the mRNAs decreased from fetal livers to adulthood, such as metallothionein and heme oxygenase-1; (2) adolescent-rich and relatively stable expression, such as peroxiredoxins; and (3) adult-rich, in which the mRNA increased with age, such as catalase and superoxide dismutase. Alternative splicing of several antioxidant genes, such as Keap1, Glrx2, Gpx3, and Txnrd1, were also detected by RNA-Seq. In summary, RNA-Seq revealed the relative abundance of hepatic antioxidant enzymes, which are important in protecting against the deleterious effects of oxidative stress.

Heavy metals in food crops: Health risks, fate, mechanisms, and management

Food security is a high-priority issue for sustainable global development both quantitatively and qualitatively. In recent decades, adverse effects of unexpected contaminants on crop quality have threatened both food security and human health. Heavy metals and metalloids (e.g., Hg, As, Pb, Cd, and Cr) can disturb human metabolomics, contributing to morbidity and even mortality. Therefore, this review focuses on and describes heavy metal contamination in soil-food crop subsystems with respect to human health risks. It also explores the possible geographical pathways of heavy metals in such subsystems. In-depth discussion is further offered on physiological/molecular translocation mechanisms involved in the uptake of metallic contaminants inside food crops. Finally, management strategies are proposed to regain sustainability in soil-food subsystems.

Cadmium-induced hepatocellular injury: Modulatory effects of γ-glutamyl cysteine on the biomarkers of inflammation, DNA damage, and apoptotic cell death

Cadmium is an extremely toxic pollutant that reaches human body through intake of the industrially polluted food and water as well as through cigarette smoking and exposure to polluted air. Cadmium accumulates in different body organs especially the liver. It induces tissue injury largely through inflammation and oxidative stress-based mechanisms. The aim of the current study was to investigate the ability of γ glutamyl cysteine (γGC) to protect against cadmium-induced hepatocellular injury employing Wistar rats as a mammalian model. The results of the current work indicated that γGC upregulated the level of the anti-inflammatory cytokine IL-10 and downregulated the levels of the pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) in the cadmium-exposed rats. In addition, γGC reduced the liver tissues cadmium content in the cadmium-treated rats, suppressed the cadmium-induced hepatocellular apoptosis and oxidative modifications of cellular DNA, lipids, and proteins. Additionally, γGC enhanced the antioxidant potential of the liver tissues in the cadmium-treated rats as evidenced by a remarkable increase in the activity of the antioxidant enzymes superoxide dismutase and glutathione peroxidase and significant increase in the levels of the total antioxidant capacity and reduced glutathione as well as a significant reduction in oxidized to reduced glutathione (GSSG/GSH) ratio. Moreover, it effectively improved liver cell integrity in the cadmium-treated rats as demonstrated by a significant reduction in the serum activity of the liver enzymes (ALT and AST) and amelioration of the cadmium-evoked histopathological alterations. Together, these findings underscore, for the first time, the alleviating effects of γGC against cadmium-induced hepatocellular injury that is potentially mediated through reduction of liver tissue cadmium content along with modulation of both hepatocellular redox status and inflammatory cytokines.

Site-specific regulation of transcriptional responses to cadmium stress in the hyperaccumulator, Sedum alfredii: based on stem parenchymal and vascular cells

We compared the transcriptomes of parenchymal and vascular cells of Sedum alfredii stem under Cd stress to reveal gene regulatory networks underlying Cd hyperaccumulation. Cadmium (Cd) hyperaccumulation in plants is a complex biological process controlled by gene regulatory networks. Efficient transport through vascular systems and storage by parenchymal cells are vital for Cd hyperaccumulation in the Cd hyperaccumulator Sedum alfredii, but the genes involved are poorly understood. We investigated the spatial gene expression profiles of transport and storage sites in S. alfredii stem using laser-capture microdissection coupled with RNA sequencing. Gene expression patterns in response to Cd were distinct in vascular and parenchymal cells, indicating functional divisions that corresponded to Cd transportation and storage, respectively. In vascular cells, plasma membrane-related terms enriched a large number of differentially-expressed genes (DEGs) for foundational roles in Cd transportation. Parenchymal cells contained considerable DEGs specifically concentrated on vacuole-related terms associated with Cd sequestration and detoxification. In both cell types, DEGs were classified into different metabolic pathways in a similar way, indicating the role of Cd in activating a systemic stress signalling network where ATP-binding cassette transporters and Ca²⁺ signal pathways were probably involved. This study identified site-specific regulation of transcriptional responses to Cd stress in S. alfredii and analysed a collection of genes that possibly function in Cd transportation and detoxification, thus providing systemic information and direction for further investigation of Cd hyperaccumulation molecular mechanisms.

Metallothionein expression on oysters ( Crassostrea cuculata and Crassostrea glomerata) from the southern coastal region of East Java

Background: This study aimed to analyse levels of heavy metals (Pb, Hg and Cd) in the aquatic body, gills and stomach of the oysters Crassostrea cuculata and Crassostrea glomerata, the metallothionein (MT) level in the gills and stomach of both oysters, and relationships between heavy metals level (Pb, Hg and Cd) in the gills and stomach to MT level in both species of oysters. Methods: The research method utilized was a descriptive method. The oyster samples were taken from three stations: Sendang Biru, Popoh and Prigi beaches. MT values were assessed using confocal laser scanning microscopy. The heavy metal levels were assessed using atomic absorption spectrophotometry method. Results: Both oyster heavy metal content obtained in the southern coastal waters exceeded the safe limit set by the State Minister of Environment No. 51 of 2004. In general, the expression of MT was found to be higher in stomach tissue compared to gill tissue. Conclusions: The levels of the heavy metals Pb, Hg, and has a strong relationship with MT levels in the gills and stomach in both types of oysters.

Metallothionein expression on oysters ( Crassostrea cuculata and Crassostrea glomerata) from the southern coastal region of East Java

Background: This study aimed to analyse levels of heavy metals (Pb, Hg and Cd) in the aquatic body, gills and stomach of the oysters Crassostrea cuculata and Crassostrea glomerata, the metallothionein (MT) level in the gills and stomach of both oysters, and relationships between heavy metals level (Pb, Hg and Cd) in the gills and stomach to MT level in both types of oysters. Methods: The research method utilized was a descriptive method. The oyster samples were taken from three stations: Sendang Biru, Popoh and Prigi beaches. MT values were assessed using confocal laser scanning microscopy. The heavy metal levels were assessed using atomic absorption spectrophotometry method. Results: Both oyster heavy metal content obtained in the southern coastal waters exceeded the safe limit set by the State Minister of Environment No. 51 of 2004. In general, the expression of MT was found to be higher in gastric tissue compared to gill tissue. Conclusions: The relationship between levels of the heavy metals Pb, Hg, and Cd in oyster gills and stomach has a strong relationship with MT levels in the gills and stomach in both types of oysters.

Selection of biochemical and physiological parameters in the croaker Micropogonias furnieri as biomarkers of chemical contamination in estuaries using a generalized additive model (GAM)

Biochemical and physiological parameters in the croaker Micropogonias furnieri were evaluated as biomarkers of chemical contaminants in estuaries. Juvenile croakers (10-20 cm total body length) were collected in summer and winter (2011 and 2012), in two sites at the Lagoa dos Patos estuary (southern Brazil). Fish were also collected in summer (2011 and 2012) in one site at the Barra do Chui estuary (southern Brazil). Tissue (gills, muscle or liver) samples were dissected and analyzed for contaminants [metals, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs)] and selected biochemical and physiological parameters [metallothionein-like proteins (MTLP), acetylcholinesterase (AChE) activity, ethoxyresorufin-O-deethylase (EROD) activity, and lipid peroxidation (LPO)]. Additionally, water samples were collected for water chemical analyses (salinity, pH, temperature, dissolved oxygen, total alkalinity, and sulfate concentration). Data obtained were integrated and analyzed, using Principal Component Analysis (PCA) and Generalized Additive Model (GAM) approaches. Results showed that changes in concentrations of chemical contaminants and responses of biochemical and physiological parameters did not show any pattern according to the site, season and year of fish collection. However, they were influenced by fish body length and water temperature and salinity. Liver LPO and EROD activity were not responsive to PAHs. However, liver LPO was responsive to HCB, p,p-DDD, p,p-DDT and endosulfan sulfate. In turn, gill MTLP concentration, muscle AChE activity and liver EROD activity were responsive to non-essential metals (Pb, Cd and Ag). Considering that the ecotoxicological modeling approach adopted (GAM) accounted for biological, spatial and temporal variability of data associated with fish body size and site, season and year of fish collection, gill MTLP concentration, muscle AChE activity, as well as liver LPO and EROD activity can be considered as reliable biomarkers of fish exposure to chemical contaminants in estuaries.

Mercury (Hg), Lead (Pb), Cadmium (Cd), Selenium (Se), and Arsenic (As) in Liver, Kidney, and Feathers of Gulls: A Review

Mercury (Hg), lead (Pb), cadmium (Cd), selenium (Se), and arsenic (As) are metals or metalloids of high concern because of their effects on the environment and, specially, their potential toxicity on the animals inhabiting there. Due to their relevance, these elements have been object of several biomonitoring studies in different animal species around the world. Birds are widespread and, as species, are able to supply specific and relevant information about the regions where they live, being useful as bioindicators, as long as they are not birds with a strong migratory character. The main goal of this review is to summarize data collected from different studies using seabirds, paying special attention to gulls, in order to be helpful for coming studies and regulatory affairs.Several tissues have been used to evaluate Hg, Cd, Pb, Se, and As concentrations in seabirds, being focused the present review in those analyzing the liver, kidneys, and feathers. The most frequently analyzed tissue for Hg was the liver, followed by feathers, and finally kidney. For Cd levels, most of the studies were carried out in the liver, followed by feathers and kidneys. Pb, Se, and As levels were determined to a lesser extent. Feathers should be taken carefully as indicator of accumulation of pollutants, since procedure during analysis may lead to controversial results.Some authors reported that interspecific differences in the exposure of elements are determined by multiple factors, including properties of the contaminant, species, feeding habits, migratory status, sex, and age.The present review provides a comprehensive overview of the analyzed elements' occurrence in different species of seabirds, including gulls. Therefore, it can be a useful database providing for Hg, Pb, Cd, Se, and As levels in different tissues of seabirds.

Cadmium-induced ultrastructural changes in primary target organs of developing chicken embryos (Gallus domesticus)

The aim of this study was to evaluate ultrastructural changes in kidney and liver tissue of chicken embryos exposed in ovo to cadmium. Embryonated eggs were injected on the 4^th day of incubation with cadmium at the dose of 0, 2, 4 and 8 μg/egg (80 eggs/group). The samples of kidney and liver tissues were collected from embryos at the 14th and 18th day of incubation (E14 and E18) and at hatching day (D1). The tissue structure was evaluated by transmission electron microscopy (Tecnai G2 Spirit). The results indicate that hepatocytes responded to damage caused by toxic cadmium activity with a significant disturbance in the structure of mitochondria and a considerable expansion of the lysososmal system, while glomerular cells additionally reacted with an increased proliferation of peroxisomes. The range of changes observed on the subcellular level was dependent on the dose of cadmium, embryogenesis stage and cell type.

Combined toxicity of organophosphate flame retardants and cadmium to Corbicula fluminea in aquatic sediments

Organophosphate flame retardants (OPFRs), as alternatives to polybrominated biphenyl ethers (PBDEs), are frequently detected in various environmental matrices. Owing to urbanization and industrial pollution, co-contamination of OPFRs and heavy metals is ubiquitous in the environment. The toxicity of OPFRs in aqueous phase is a significant concern, but uncertainty still exists regarding the co-toxicity to benthic organisms of OPFRs and metals in sediments. Hence, we explored the physiological response of Corbicula fluminea to OPFRs and Cd in sediments. The results indicated that the antioxidant system in the clams was stimulated in the presence of OPFRs and Cd, and the oxidative stress increased with increasing concentrations of OPFRs. In contrast, the cytochrome P450 (CYP450) content and acetylcholinesterase (AChE) activity were reduced by exposure to both OPFRs and Cd. The cytochrome P450 4 family (CYP4) mRNA expression and OPFR toxicity were lower than those in previously reported experiments conducted in the water phase. Moreover, the expression levels of metallothionein (MT) and AChE mRNA decreased when OPFRs and Cd were present together. The highest integrated biomarker response (IBR) index (IBR = 15.41) was observed in the presence of 45 mg kg^-1 Cd + 200 mg kg^-1 OPFRs, rather than the 45 mg kg^-1 Cd + 400 mg kg^-1 OPFRs treatment (IBR = 9.48). In addition, CYP450 and AChE in the digestive glands of C. fluminea exhibited significant correlations with the concentration of the OPFR/Cd mixture (p < 0.01) and could be effective biomarkers for OPFR and Cd co-contamination. The results potentially contribute to more realistic predictions and evaluations of the environmental risks posed by OPFRs in aquatic sediments contaminated with heavy metals, particularly with respect to the risk to benthic organisms.

Trace elements influence the hatching success and emergence of Caretta caretta and Chelonia mydas

Trace elements from industrial, domestic and agricultural activities can be transferred into marine environments, affecting the survival of sea species. Due to their global distribution, sea turtles are recognized as indicators of ocean pollution. The aim of this work was to quantify Ba, Cd, Cr, Cu, Fe, Mn, Pb, Sr and Zn using inductively coupled plasma optical emission spectrometry (ICP-OES) in the eggs and offspring of Caretta caretta and Chelonia mydas from two important nesting beaches, Guanabara Beach, Anchieta, and Trindade/Martim Vaz Island, Espírito Santo, Brazil. C. mydas pups and eggs collected on Trindade/Martim Vaz Island presented significant differences in Ba, Cr, Cu, Mn and Sr (p < 0.001). Higher concentrations of Ba, Pb, and Sr were detected in eggs of this species in comparison to those of C. caretta on Guanabara Beach, Anchieta. Ba and Cd presented higher concentrations in pups than in eggs of C. caretta, which could indicate nesting pollution. Positive correlations between trace element concentrations and hatching success in C. caretta nests from Guanabara Beach, Anchieta, could be identified for Cu and Zn (r² = 0.86, F2.7 = 21, p < 0.001). Emergence success was influenced by Cu and Cd (r² = 0.84, F2.7 = 18.9, p = 0.002). In addition, Ba and Cd also influenced the emergence sucess (r² = 0.56, F2, 10 = 6.29, p = 0.017). The hatching success of C. mydas was influenced by the concentration of Cu (r² = 0.53, F2.14 = 7.82, p = 0.005). Further studies including the analyzed areas and migratory routes should be performed to promote conservation management at these beaches.

Evaluation of the potential nephrotoxicity and mechanism in rats after long-term exposure to the traditional Tibetan medicine tsothel

CONTEXT

Tsothel, a traditional Tibetan medicine, is regarded as 'the king of essences'. Nevertheless, tsothel has aroused serious concern regarding its biosafety because its main component is HgS. Unfortunately, toxicological studies on tsothel are scarce.

OBJECTIVE

As inorganic mercury has high affinity for the kidney, the present investigation was designed to determine the potential nephrotoxicity and mechanism of tsothel.

MATERIALS AND METHODS

Sprague-Dawley rats were orally administered different doses of tsothel (0, 66.70, 33.35 and 16.68 mg/kg) daily for 180 days, followed by the withdrawal of tsothel for 120 days. Then, the related nephrotoxicity was examined by the ICP-MS, ELISA, colorimetric, RT-PCR, HE staining, immunohistochemical staining and flow cytometry methods.

RESULTS

Although tsothel administration led to a large accumulation of Hg (794.25 ± 464.30 ng/g in the 66.70 mg/kg group, 775.75 ± 307.89 ng/g in the 33.35 mg/kg group and 532.60 ± 356.77 ng/g in the 16.68 mg/kg group) in the kidney after 120 days of tsothel withdrawal, the blood CREA and BUN, urinary Kim-1, NAG, RBP and β2-MG, renal SOD, MDA, pathology, proliferation, apoptosis and cell cycle had no significant changes compared with the control group. Additionally, the high GSH content (318.87 ± 44.19 nmol/mL in the 33.35 mg/kg group) and the relative expression levels of Kim-1 (1.08 ± 0.11 in the 33.35 mg/kg group), MT-1 (1.46 ± 0.10 in the 66.70 mg/kg group, 1.61 ± 0.19 in the 33.35 mg/kg group and 1.57 ± 0.14 in the 16.68 mg/kg group) and GST-Pi (1.76 ± 0.89 in the 33.35 mg/kg group) mRNA recovered to normal after tsothel withdrawal. Interestingly, the change trend of GST-Pi gene expression was consistent with the change trend of GSH activity.

CONCLUSIONS

Overall, our study shows that tsothel administration did not induce overt nephrotoxicity but did have reversible stress-related effects. These results suggest that tsothel affects stress response mechanisms with the involvement of detoxifying enzyme systems. The formulation method and chemotype could play a role in the reduced toxicity potential of tsothel compared to common mercurials.

The role of GST omega in metabolism and detoxification of arsenic in clam Ruditapes philippinarum

The major hazard of arsenic in living organisms is increasingly being recognized. Marine mollusks are apt to accumulate high levels of arsenic, but knowledge related to arsenic detoxification in marine mollusks is still less than sufficient. In this study, arsenic bioaccumulation as well as the role of glutathione S-transferase omega (GSTΩ) in the process of detoxification were investigated in the Ruditapes philippinarum clam after waterborne exposure to As(III) or As(V) for 30 days. The results showed that the gills accumulated significantly higher arsenic levels than the digestive glands. Arsenobetaine (AsB) and dimethylarsenate (DMA) accounted for most of the arsenic found, and monomethylarsonate (MMA) can be quickly metabolized. A subcellular distribution analysis showed that most arsenic was in biologically detoxified metal fractions (including metal-rich granules and metallothionein-like proteins), indicating their important roles in protecting cells from arsenic toxicity. The relative mRNA expressions of two genes encoding GSTΩ were up-regulated after arsenic exposure, and the transcriptional responses were more sensitive to As(III) than As(V). The recombinant GSTΩs exhibited high activities at optimal conditions, especially at 37 °C and pH 4-5, with an As(V) concentration of 60 mM. Furthermore, the genes encoding GSTΩ significantly enhance the arsenite tolerance but not the arsenate tolerance of E. coli AW3110 (DE3) (ΔarsRBC). It can be deduced from these results that GSTΩs play an important role in arsenic detoxification in R. philippinarum.

Characterization analysis and heavy metal-binding properties of CsMTL3 in Escherichia coli

Members of the metallothionein (MT) superfamily are involved in coordinating transition metal ions. In plants, MT family members are characterized by their arrangement of Cys residues. In this study, one member of the MT superfamily, CsMTL3, was characterized from a complementary DNA (cDNA) library from young cucumber fruit; CsMTL3 is predicted to encode a 64 amino acid protein with a predicted molecular mass of 6.751 kDa. Phylogenetic analysis identified it as a type 3 family member as the arrangement of N-terminal Cys residues was different from that of MT-like 2. Heterologous expression of CsMTL3 in Escherichia coli improved their heavy metal tolerance, particularly to Cd2+ and Cu2+, and led to increased uptake of Cd2+ and Cu2+; increased uptake was also observed for cells expressing Arabidopsis thaliana metallothionein 3 (AtMT3) and phytochelatin-like (PCL), with greatest uptake in PCL-expressing cells. These findings demonstrate that CsMTL3 can improve metal tolerance, especially for Cd2+ ions, when heterologously expressed in E. coli, and suggest that the composition and arrangement of N-terminal Cys residues are associated with binding capacity and preference for different metal ions.