Neutralization by metal ions of the toxicity of sodium selenide

Emerging evidence on selenoneine and its public health relevance in coastal populations: a review and case study of dietary Se among Inuit populations in the Canadian Arctic

Selenium is an essential mineral yet both deficiency and excess are associated with adverse health effects. Dietary intake of Se in humans varies greatly between populations due to food availability, dietary preferences, and local geological and ecosystem processes impacting Se accumulation into agricultural products and animal populations. We argue there is a need to evaluate and reconsider the relevance of public health recommendations on Se given recent evidence, including the metabolic pathways and health implications of Se. This argument is particularly pertinent for Inuit populations in Northern Canada, who often exceed dietary tolerable upper intake levels and exhibit very high whole blood Se concentrations due to their dependence on local country foods high in the newly discovered Se compound, selenoneine. Since selenoneine appears to have lower toxicity compared to other Se species and does not contribute to the circulating pools of Se for selenoprotein synthesis, we argue that total dietary Se or total Se in plasma or whole blood are poor indicators of Se adequacy for human health in these populations. Overall, this review provides an overview of the current evidence of Se speciation, deficiency, adequacy, and excess and implications for human health and dietary recommendations, with particular reference to Inuit populations in the Canadian Arctic and other coastal populations consuming marine foods.

A combination of selenium and Bacillus subtilis improves the quality and flavor of meat and slaughter performance of broilers

This study aimed to investigate the effects of the combination of selenium and Bacillus subtilis (Se-BS) on the quality and flavor of meat and slaughter performance of broilers. A total of 240 one-day-old Arbor Acres broilers were randomly allotted to four treatments of a basal diet supplemented with no selenium (control), sodium selenite (SS), BS, or Se-BS and raised for 42 days. Compared with the control group, Se-BS significantly increased the carcass weight, the half-eviscerated weight, the completely eviscerated weight, the carcass rate, and redness in broiler muscles; improved the antioxidant state by increasing glutathione peroxidase (GPx) and glutathione S-transferase activities, the total antioxidant capacity, and GPx-1 and thioredoxin reductase 1 messenger RNA (mRNA) levels; promoted biological activity by increasing the contents of glutamate, phenylalanine, lysine, and tyrosine; and increased Se and five types of nitrogenous volatile substances in muscles. On the other hand, Se-BS treatment decreased the shear force, drip loss, and the malondialdehyde, glutathione, and lead contents in muscles. Se-BS exerted a better effect on slaughter performance, the physicochemical quality of meat, the redox status, the amino acid contents, the trace element contents, and volatile substances compared with SS and BS. In conclusion, Se-BS had a positive effect on the quality and flavor of meat and slaughter performance of broilers, suggesting that Se-BS may be a beneficial feed additive.

Body burdens and distribution of mercury and selenium in bottlenose, striped and Risso's dolphins along the Adriatic coast: A 20-year retrospective

Top marine predators present high mercury concentrations in their tissues due to biomagnification in the marine food chain. This study reports mercury (Hg) and selenium (Se) status, and the Hg:Se molar ratio assessment in bottlenose (Tursiops truncatus), striped (Stenella coeruleoalba) and Risso's dolphins (Grampus griseus). Total Hg and Se concentrations were determined in muscle, liver, kidney, lung, spleen, adipose tissue and skin collected from 186 specimens stranded in the Croatian part of Adriatic Sea from 1995 to 2014. Total Hg concentrations in tissue samples ranged from 0.001 in the spleen to 2238 mg/kg wet weight in liver. Se concentrations in dolphin samples ranged from 0.010 to 2916 mg/kg ww. Minimum Se concentration was found in muscle and maximum Se concentration were found in liver of bottlenose dolphin. Hg and Se levels in Risso's dolphins showed higher concentrations in all tissues in comparison to bottlenose and striped dolphins. Significant and positive correlations were observed between age and Hg concentrations (P < 0.05). In 66.6 % of Risso's, 15.3 % of bottlenose dolphins and one stranded striped dolphin in this study, the hepatic concentration of Hg exceeded the higher toxic thresholds (400 mg/kg w.w.) previously defined as evidence of liver damage in marine mammals. The Hg:Se molar ratio in the liver of Risso's dolphin was 0.670. The liver of adult bottlenose dolphins showed expected values (0.870), while the liver of young dolphins had a high ratio (0.750), non-specific for the age group. The Hg:Se molar ratio in the liver of striped dolphins was 0.390, which is lower than the literature values.

Protective Role of the Essential Trace Elements in the Obviation of Cadmium Toxicity: Glimpses of Mechanisms

Cadmium (Cd) is toxic non-essential heavy metal that precipitates adverse health effects in humans and animals. Chelation therapy, the typical treatment for cadmium toxicity, has certain safety and efficacy issues to treat long term cadmium toxicity, in particular. Recent studies have shown that essential trace elements can play important roles in obviating experimental Cd toxicity. This study organizes and reviews the prototypical evidences of the protective effects of essential trace elements against Cd toxicity in animals and attempts to point out the underlying mechanisms. Zinc, selenium, iron, and combinations thereof are reported to be active. The major mechanisms elucidated inter alia are-induction of metallothionein (MT) synthesis and Cd-MT binding (for zinc), modulation of oxidative stress and apoptosis, interference in cadmium absorption and accumulation from body-thereby maintenance of essential metal homeostasis and cytoprotection. Based on the findings, essential trace elements can be recommended for the susceptible population. The application of these trace elements appears beneficial for both the prevention and remediation of long-term Cd toxicity operative via multiple mechanisms with no or minimal adverse effects as compared to the conventional chelation therapy.

Associations between Metal Exposures and Cognitive Function in American Older Adults

Cognitive function frequently declines with older age, independently of the development of neurodegenerative diseases, and few interventions are known to counter this decline. Exposure to neurotoxic metals may contribute to this decline in cognitive function in older adults. Using the National Health and Nutrition Examination Survey (NHANES) data, the performance of 3042 adults aged 60 years and older on three cognitive tests for immediate, delayed, and working memory were examined in relation to blood concentrations of seven metals and metalloids and urinary concentrations of nineteen metals and metabolites. Using linear regression models, associations between cognitive tests and logarithms of metal exposures were adjusted for age, sex, ethnicity, education level, depression, diabetes, alcohol consumption, and cigarette use. Increased selenium was strongly associated with better performance on all three cognitive tests. Cadmium and lead were negatively associated with performance on all three cognitive tests. Some urinary metabolites of arsenic, urinary lead, cadmium, and tungsten were significantly associated with poor performance on some tests. In older adults, higher selenium levels were strongly associated with better cognitive performance.

The Effects of Selenium on Bone Health: From Element to Therapeutics

Osteoporosis, characterized by low bone mass and a disruption of bone microarchitecture, is traditionally treated using drugs or lifestyle modifications. Recently, several preclinical and clinical studies have investigated the effects of selenium on bone health, although the results are controversial. Selenium, an important trace element, is required for selenoprotein synthesis and acts crucially for proper growth and skeletal development. However, the intake of an optimum amount of selenium is critical, as both selenium deficiency and toxicity are hazardous for health. In this review, we have systematically analyzed the existing literature in this field to determine whether dietary or serum selenium concentrations are associated with bone health. In addition, the mode of administration of selenium as a supplement for treating bone disease is important. We have also highlighted the importance of using green-synthesized selenium nanoparticles as therapeutics for bone disease. Novel nanobiotechnology will be a bridgehead for clinical applications of trace elements and natural products.

Molecular Biology of Cadmium Toxicity in Saccharomyces cerevisiae

Cadmium (Cd) is a toxic heavy metal mainly originating from industrial activities and causes environmental pollution. To better understand its toxicity and pollution remediation, we must understand the effects of Cd on living beings. Saccharomyces cerevisiae (budding yeast) is an eukaryotic unicellular model organism. It has provided much scientific knowledge about cellular and molecular biology in addition to its economic benefits. Effects associated with copper and zinc, sulfur and selenium metabolism, calcium (Ca²⁺) balance/signaling, and structure of phospholipids as a result of exposure to cadmium have been evaluated. In yeast as a result of cadmium stress, "mitogen-activated protein kinase," "high osmolarity glycerol," and "cell wall integrity" pathways have been reported to activate different signaling pathways. In addition, abnormalities and changes in protein structure, ribosomes, cell cycle disruption, and reactive oxygen species (ROS) following cadmium cytotoxicity have also been detailed. Moreover, the key OLE1 gene that encodes for delta-9 FA desaturase in relation to cadmium toxicity has been discussed in more detail. Keeping all these studies in mind, an attempt has been made to evaluate published cellular and molecular toxicity data related to Cd stress, and specifically published on S. cerevisiae.

Mercury interactions with selenium and sulfur and the relevance of the Se:Hg molar ratio to fish consumption advice

Eating fish is often recommended as part of a healthful diet. However, fish, particularly large predatory fish, can contain significant levels of the highly toxic methylmercury (MeHg). Ocean fish in general also contain high levels of selenium (Se), which is reported to confer protection against toxicity of various metals including mercury (Hg). Se and Hg have a high mutual binding affinity, and each can reduce the toxicity of the other. This is an evolving area of extensive research and controversy with variable results in the animal and epidemiologic literature. MeHg is toxic to many organ systems through high affinity for -SH (thiol) ligands on enzymes and microtubules. Hg toxicity also causes oxidative damage particularly to neurons in the brain. Hg is a potent and apparently irreversible inhibitor of the selenoenzymes, glutathione peroxidases (GPX), and thioredoxin reductases (TXNRD) that are important antioxidants, each with a selenocysteine (SeCys) at the active site. Hg binding to the SeCys inhibits these enzymes, accounting in part for the oxidative damage that is an important manifestation of Hg toxicity, particularly if there is not a pool of excess Se to synthesize new enzymes. A molar excess of Se reflected in an Se:Hg molar ratio > 1 is often invoked as evidence that the Hg content can be discounted. Some recent papers now suggest that if the Se:Hg molar ratio exceeds 1:1, the fish is safe and the mercury concentration can be ignored. Such papers suggested that the molar ratio rather than the Hg concentration should be emphasized in fish advisories. This paper examines some of the limitations of current understanding of the Se:Hg molar ratio in guiding fish consumption advice; Se is certainly an important part of the Hg toxicity story, but it is not the whole story. We examine how Hg toxicity relates also to thiol binding. We suggest that a 1:1 molar ratio cannot be relied on because not all of the Se in fish or in the fish eater is available to interact with Hg. Moreover, in some fish, Se levels are sufficiently high to warrant concern about Se toxicity.

In Vivo Formation of HgSe Nanoparticles and Hg-Tetraselenolate Complex from Methylmercury in Seabirds-Implications for the Hg-Se Antagonism

In vivo and in vitro evidence for detoxification of methylmercury (MeHg) as insoluble mercury selenide (HgSe) underlies the central paradigm that mercury exposure is not or little hazardous when tissue Se is in molar excess (Se:Hg > 1). However, this hypothesis overlooks the binding of Hg to selenoproteins, which lowers the amount of bioavailable Se that acts as a detoxification reservoir for MeHg, thereby underestimating the toxicity of mercury. This question was addressed by determining the chemical forms of Hg in various tissues of giant petrels Macronectes spp. using a combination of high energy-resolution X-ray absorption near edge structure and extended X-ray absorption fine structure spectroscopy, and transmission electron microscopy coupled to elemental mapping. Three main Hg species were identified, a MeHg-cysteinate complex, a four-coordinate selenocysteinate complex (Hg(Sec)₄), and a HgSe precipitate, together with a minor dicysteinate complex Hg(Cys)₂. The amount of HgSe decreases in the order liver > kidneys > brain = muscle, and the amount of Hg(Sec)₄ in the order muscle > kidneys > brain > liver. On the basis of biochemical considerations and structural modeling, we hypothesize that Hg(Sec)₄ is bound to the carboxy-terminus domain of selenoprotein P (SelP) which contains 12 Sec residues. Structural flexibility allows SelP to form multinuclear Hg_x(Se,Sec)_y complexes, which can be biomineralized to HgSe by protein self-assembly. Because Hg(Sec)₄ has a Se:Hg molar ratio of 4:1, this species severely depletes the stock of bioavailable Se for selenoprotein synthesis and activity to one μg Se/g dry wet in the muscle of several birds. This concentration is still relatively high because selenium is naturally abundant in seawater, therefore it probably does not fall below the metabolic need for essential selenium. However, this study shows that this may not be the case for terrestrial animals, and that muscle may be the first tissue potentially injured by Hg toxicity.

Nearly Monodisperse Copper Selenide Nanoparticles for Recognition, Enrichment, and Sensing of Mercury Ions

In the current work, Cu(I)_1.28Cu(II)_0.36Se nanoparticles were synthesized via a simple procedure and were applied for the first time for recognition, adsorption, enrichment, and detection of Hg(II) ions. The experimental results show that 99.9% Hg(II) could be adsorbed by Cu(I)_1.28Cu(II)_0.36Se nanoparticles within just 30 s, and the Hg(II) concentration could be lowered down to a super-low level of 0.01 ppb. Cu(I)_1.28Cu(II)_0.36Se nanoparticles also demonstrate high selectivity to Hg(II) and Ag(I) among nine representative metal ions. The enrichment experiments show that Hg(II) of ultratrace concentration could be enriched significantly by Cu(I)_1.28Cu(II)_0.36Se nanoparticles, and thus, the detection limit of Hg(II) based on inductively coupled plasma emission spectroscopy-mass spectrometry would be pushed down by 2 orders of magnitude. These outstanding features of Cu(I)_1.28Cu(II)_0.36Se nanoparticles could be well accounted for in terms of the solubility product principle and the high affinity between selenium and mercury. Cu(I)_1.28Cu(II)_0.36Se nanoparticles were also found to have peroxidase-like activity, which could be inhibited by Hg(II) but not by Ag(I). This unique characteristic coupled with the solubility product principle successfully allows recognition and detection of Hg(II) even in the presence of Ag(I), which has a similar pK_sp to Hg(II). As a result, the qualitative and quantitative analyses of Hg(II) could be performed by the naked eye and UV-visible spectroscopy, respectively. The current results indicate that Cu(I)_1.28Cu(II)_0.36Se nanoparticles not only have great potential in various aspects of dealing with Hg(II) pollution but would also shed light on discovering new nanomaterials to address other heavy metal ions.

Selenium detoxification is required for cancer-cell survival

The micronutrient selenium is incorporated via the selenocysteine biosynthesis pathway into the rare amino acid selenocysteine, which is required in selenoproteins such as glutathione peroxidases and thioredoxin reductases^1,2. Here, we show that selenophosphate synthetase 2 (SEPHS2), an enzyme in the selenocysteine biosynthesis pathway, is essential for survival of cancer, but not normal, cells. SEPHS2 is required in cancer cells to detoxify selenide, an intermediate that is formed during selenocysteine biosynthesis. Breast and other cancer cells are selenophilic, owing to a secondary function of the cystine/glutamate antiporter SLC7A11 that promotes selenium uptake and selenocysteine biosynthesis, which, by allowing production of selenoproteins such as GPX4, protects cells against ferroptosis. However, this activity also becomes a liability for cancer cells because selenide is poisonous and must be processed by SEPHS2. Accordingly, we find that SEPHS2 protein levels are elevated in samples from people with breast cancer, and that loss of SEPHS2 impairs growth of orthotopic mammary-tumour xenografts in mice. Collectively, our results identify a vulnerability of cancer cells and define the role of selenium metabolism in cancer.

The Role of Selenium in Arsenic and Cadmium Toxicity: an Updated Review of Scientific Literature

Arsenic (As) and cadmium (Cd) are elements arousing major public health concerns associated with environmental pollution, high toxicity potential, and carcinogenic nature. However, selenium (Se) at low doses and incorporated into enzymes and proteins has antioxidant properties and protects animals and humans from the risk of various diseases. It also has an exceptionally narrow range between necessary and toxic concentrations, which is a well-known hindrance in its use as a dietary supplement. The present article aims to update and expand the role of Se in As and Cd toxicity discussed in our earlier paper. In general, recent reports show that Se, regardless of its form (as selenite, selenomethionine, nanoSe, or Se from lentils), can reduce As- or Cd-mediated toxicity in the liver, kidney, spleen, brain, or heart in animal models and in cell culture studies. As was suggested in our earlier review, Se antagonizes the toxicity of As and Cd mainly through sequestration of these elements into biologically inert complexes and/or through the action of Se-dependent antioxidant enzymes. An increase in the As methylation efficiency is proposed as a possible mechanism by which Se can reduce As toxicity. However, new studies indicate that Se may also diminish As or Cd toxicity by activation of the Nrf2 pathway. In addition, this paper discusses possible signs of Se toxic effects, which may be a challenge for its future use in the therapy of As and Cd poisoning and provide future directions to address this issue.

Copper-Driven Deselenization: A Strategy for Selective Conversion of Copper Ion to Nanozyme and Its Implication for Copper-Related Disorders

Synthetic organic molecules, which can selectively convert excess intracellular copper (Cu) ions to nanozymes with an ability to protect cells from oxidative stress, are highly significant in developing therapeutic agents against Cu-related disorder like Wilson's disease. Here, we report 1,3-bis(2-hydroxyethyl)-1 H-benzoimidazole-2-selenone (1), which shows a remarkable ability to remove Cu ion from glutathione, a major cytosolic Cu-binding ligand, and thereafter converts it into copper selenide (CuSe) nanozyme that exhibits remarkable glutathione peroxidase-like activity, at cellular level of H₂O₂ concentration, with excellent cytoprotective effect against oxidative stress in hepatocyte. Cu-driven deselenization of 1, under physiologically relevant conditions, occurred in two steps. The activation of C═Se bond by metal ion is the crucial first step, followed by cleavage of the metal-activated C═Se bond, initiated by the OH group of N-(CH₂)₂OH substituent through neighboring group participation (deselenization step), resulted in the controlled synthesis of various types of Cu_2-xSe nanocrystals (NCs) (nanodisks, nanocubes, and nanosheets) and tetragonal Cu₃Se₂ NCs, depending upon the oxidation state of the Cu ion used to activate the C═Se bond. Deselenization of 1 is highly metal-selective. Except Cu, other essential metal ions, including Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, or Zn²⁺, failed to produce metal selenide under identical reaction conditions. Moreover, no significant change in the expression level of Cu-metabolism-related genes, including metallothioneines MT1A, is observed in liver cells co-treated with Cu and 1, as opposed to the large increase in the concentrations of these genes observed in cells treated with Cu alone, suggesting the participation of 1 in Cu homeostasis in hepatocyte.

Functional comparision between truncated MTT1 and truncated MTT2 from Tetrahyemna thermophila

Metallothioneins (MTs) are low-molecular-weight proteins with high Cys content and high metal-chelating ability. CdMT and CuMT subfamilies present different characteristics in Tetrahymena. To explore the effect of the cysteine arrangement and sequence length of MTs for binding different metal ions, MTT1, truncated MTT1 (TM1), MTT2, and truncated MTT2 (TM2) were expressed in E. coli. The half-maximal inhibiting concentrations (IC50) of Cd2+ and Cu+ for the recombinant strains were different. Furthermore, E. coli cells expressing MTT1 and TM1 exhibited higher accumulating ability for Cd2+ than cells expressing MTT2 and TM2. However, the opposite is true for Cu+. The binding ability of the different recombinant proteins to Cd2+ and Cu+ were also different. MTT1 and truncated mutant TM1 were the preference for Cd2+, whereas MTT2 and truncated mutant TM2 were the preference for Cu+ coordination. These results showed that metal ion tolerance and accumulation ability not only depended on cysteine arrangement pattern but also on sequence length of MT in Tetrahymena.

Bioleaching of electronic waste using bacteria isolated from the marine sponge Hymeniacidon heliophila (Porifera)

The bacteria isolated from Hymeniacidon heliophila sponge cells showed bioleaching activity. The most active strain, Hyhel-1, identified as Bacillus sp., was selected for bioleaching tests under two different temperatures, 30°C and 40°C, showing rod-shaped cells and filamentous growth, respectively. At 30°C, the bacteria secreted substances which linked to the leached copper, and at 40°C metallic nanoparticles were produced inside the cells. In addition, infrared analysis detected COOH groups and linear peptides in the tested bacteria at both temperatures. The Hyhel-1 strain in presence of electronic waste (e-waste) induced the formation of crust, which could be observed due to bacteria growing on the e-waste fragment. SEM-EDS measurements showed that the bacterial net surface was composed mostly of iron (16.1% w/w), while a higher concentration of copper was observed in the supernatant (1.7% w/w) and in the precipitated (49.8% w/w). The substances linked to copper in the supernatant were sequenced by MALDI-TOF-ms/ms and identified as macrocyclic surfactin-like peptides, similar to the basic sequence of Iturin, a lipopeptide from Bacillus subtilis. Finally, the results showed that Hyhel-1 is a bioleaching bacteria and cooper nanoparticles producer and that this bacteria could be used as a copper recovery tool from electronic waste.

Quantitative Probing of Cu(2+) Ions Naturally Present in Single Living Cells

Quantitative probing of Cu(2+) ions naturally present in single living cells is realized by developing a quantum-dot-embedded nanowire-waveguide probe. The intracellular Cu(2+) ion concentration is quantified by direct monitoring of photoluminescence quenching during the insertion of the nanowire in a living neuron. The measured intracellular Cu(2+) ion concentration is 3.34 ± 1.04 × 10(-6) m (mean ± s.e.m.) in single hippocampal neurons.

Importance of selenium and selenoprotein for brain function: From antioxidant protection to neuronal signalling

Multiple biological functions of selenium manifest themselves mainly via 25 selenoproteins that have selenocysteine at their active centre. Selenium is vital for the brain and seems to participate in the pathology of disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and epilepsy. Since selenium was shown to be involved in diverse functions of the central nervous system, such as motor performance, coordination, memory and cognition, a possible role of selenium and selenoproteins in brain signalling pathways may be assumed. The aim of the present review is to analyse possible relations between selenium and neurotransmission. Selenoproteins seem to be of special importance in the development and functioning of GABAergic (GABA, γ-aminobutyric acid) parvalbumin positive interneurons of the cerebral cortex and hippocampus. Dopamine pathway might be also selenium dependent as selenium shows neuroprotection in the nigrostriatal pathway and also exerts toxicity towards dopaminergic neurons under higher concentrations. Recent findings also point to acetylcholine neurotransmission involvement. The role of selenium and selenoproteins in neurotransmission might not only be limited to their antioxidant properties but also to inflammation, influencing protein phosphorylation and ion channels, alteration of calcium homeostasis and brain cholesterol metabolism. Moreover, a direct signalling function was proposed for selenoprotein P through interaction with post-synaptic apoliprotein E receptors 2 (ApoER2).

Yeast as a model system to study metabolic impact of selenium compounds

Inorganic Se forms such as selenate or selenite (the two more abundant forms in nature) can be toxic in Saccharomyces cerevisiae cells, which constitute an adequate model to study such toxicity at the molecular level and the functions participating in protection against Se compounds. Those Se forms enter the yeast cell through other oxyanion transporters. Once inside the cell, inorganic Se forms may be converted into selenide through a reductive pathway that in physiological conditions involves reduced glutathione with its consequent oxidation into diglutathione and alteration of the cellular redox buffering capacity. Selenide can subsequently be converted by molecular oxygen into elemental Se, with production of superoxide anions and other reactive oxygen species. Overall, these events result in DNA damage and dose-dependent reversible or irreversible protein oxidation, although additional oxidation of other cellular macromolecules cannot be discarded. Stress-adaptation pathways are essential for efficient Se detoxification, while activation of DNA damage checkpoint and repair pathways protects against Se-mediated genotoxicity. We propose that yeast may be used to improve our knowledge on the impact of Se on metal homeostasis, the identification of Se-targets at the DNA and protein levels, and to gain more insights into the mechanism of Se-mediated apoptosis.

Selenite-mediated production of superoxide radical anions in A549 cancer cells is accompanied by a selective increase in SOD1 concentration, enhanced apoptosis and Se-Cu bonding

Selenite may exert its cytotoxic effects against cancer cells via the generation of reactive oxygen species (ROS). We investigated sources of, and the cellular response to, superoxide radical anion (O2 (·-)) generated in human A549 lung cancer cells after treatment with selenite. A temporal delay was observed between selenite treatment and increases in O2 (·-) production and biomarkers of apoptosis/necrosis, indicating that the reduction of selenite by the glutathione reductase/NADPH system (yielding O2 (·-)) is a minor contributor to ROS production under these conditions. By contrast, mitochondrial and NADPH oxidase O2 (·-) generation were the major contributors. Treatment with a ROS scavenger [poly(ethylene glycol)-conjugated superoxide dismutase (SOD) or sodium 4,5-dihydroxybenzene-1,3-disulfonate] 20 h after the initial selenite treatment inhibited both ROS generation and apoptosis determined at 24 h. In addition, SOD1 was selectively upregulated and its perinuclear cytoplasmic distribution was colocalised with the cellular distribution of selenium. Interestingly, messenger RNA for manganese superoxide dismutase, catalase, inducible haem oxygenase 1 and glutathione peroxidase either remained unchanged or showed a delayed response to selenite treatment. Colocalisation of Cu and Se in these cells (Weekley et al. in J. Am. Chem. Soc. 133:18272-18279, 2011) potentially results from the formation of a Cu-Se species, as indicated by Cu K-edge extended X-ray absorption fine structure spectra. Overall, SOD1 is upregulated in response to selenite-mediated ROS generation, and this likely leads to an accumulation of toxic hydrogen peroxide that is temporally related to decreased cancer cell viability. Increased expression of SOD1 gene/protein coupled with formation of a Cu-Se species may explain the colocalisation of Cu and Se observed in these cells.

XAS and XFM studies of selenium and copper speciation and distribution in the kidneys of selenite-supplemented rats

Se and Cu were colocalised in the kidneys of selenite-fed rats, but there was no evidence of Se–Cu bonding.