Selenium nanoparticles inhibit the formation of atherosclerosis in apolipoprotein E deficient mice by alleviating hyperlipidemia and oxidative stress.

Atherosclerosis can cause severe cardiovascular diseases, which is the most common cause of death in the world. It's of great significance to study the prevention and treatment of atherosclerosis. Selenium nanoparticles (SeNPs) has drawn more and more attention due to high biological activity, high bioavailability, strong antioxidant capacity and low toxicity, exhibiting great potential in biomedical application. Thus, this study aimed at explore the anti-atherosclerotic effect of two kinds of SeNPs, bovine serum albumin (BSA) surface-decorated SeNPs and chitosan (CS) surface-decorated SeNPs (CS-SeNPs), in apolipoprotein E deficient (ApoE-/-) mice fed with a high-cholesterol and high-fat diet, and the possible mechanisms. The results demonstrated that both BSA-SeNPs (25, 50 and 100 µg Se/kg body weight/day) and CS-SeNPs (50 µg Se/kg body weight/day) could reduce atherosclerotic lesions in ApoE-/- mice after oral administration for 12 weeks. And these effects might mainly attributed to the ability of BSA-SeNPs and CS-SeNPs to inhibit hyperlipidemia by suppressing hepatic cholesterol and fatty acid metabolism, and alleviate oxidative stress by enhancing antioxidant activity. Moreover, the benefits of BSA-SeNPs were dose-dependent and the medium dose of BSA-SeNPs (50 µg Se/kg body weight/day) was optimal. Generally, BSA-SeNPs with mean size 38.5 nm and negative surface charge showed better anti-atherosclerotic effect than CS-SeNPs with mean size 65.8 nm and positive surface charge. These results suggested that SeNPs could significantly alleviate the formation of atherosclerosis in ApoE-/- mice, possibly by inhibiting hyperlipidemia and oxidative stress, exhibiting a potential to serve as an anti-atherosclerotic agent.

Development of Formulation Methods and Physical Characterization of Injectable Sodium Selenite Nanoparticles for the Delivery of Sorafenib tosylate.

BACKGROUND: Sorafenib is the first oral therapeutic agent to show the activity against human hepatocellular carcinoma. Sorafenib leads to severe toxicity due to the multiple-dose regimen. Reducing the overall dose of sorafenib through injectable dosage form to release sustainably is of therapeutically more important to combat drug-induced toxicity. OBJECTIVE: The purpose of this study was to formulate and evaluate the physical parameters of sorafenib- loaded Sodium Selenite Nanoparticles (SSSNP). METHODS: Two different methods: chemical crosslinking and solvent evaporation were applied for the formulation of nanoparticles using various crosslinkers such as formaldehyde, magnesium sulfate, tripolyphosphate, dextran sulfate, and aluminum hydroxide. Physical characterization was performed with zeta potential analysis, polydispersity index, particle size and scanning electron microscopic studies for morphological analysis for all the formulated nanoparticles developed using the chemical crosslinking technique based ionic interaction. RESULTS: Tripolyphosphate was selected as an ideal crosslinker and used for nanoparticle formulation with the solvent evaporation technique. Based on the physical characterization, SSSNP was formulated successfully with the solvent evaporation technique using tripolyphosphate as a cross-linker. The zeta potential of SSSNP was -37.5 mV, PDI was approximately 0.3 to 0.4, and the observed size (diameter) was in the range of 208 nm to 0.2 µm. Furthermore, the particles were smooth in morphology and appeared as crystals. CONCLUSION: The novel injectable sorafenib loaded sodium selenite nanoparticle dosage form will serve better than conventional oral dosage form to elicit a safe therapeutic effect.

Extracellular Synthesis of Selenium Nanoparticles from an Actinomycetes Streptomyces griseoruber and Evaluation of its Cytotoxicity on HT-29 Cell Line.

BACKGROUND: Selenium nanoparticles (SeNPs) have gained significant importance because of its bioavailability, least toxicity, its interaction with proteins and its biocompatibility. OBJECTIVE: In the present study, the extracellular synthesis of SeNPs was carried out by using culture supernatant of Streptomyces griseoruber, an Actinomycetes member isolated from the soil and cytotoxicity was tested on HT-29 cell line. METHODS: Culture supernatant was mixed with 1mM sodium selenite for the biosynthesis of SeNPs. Characterisation of the synthesised SeNPs was done by UV-Visible spectrophotometer, FTIR, XRD, DLS and HR-TEM. The cytotoxicity of nanoparticles on HT-29 cell line was studied by MTT assay and with different staining procedure. RESULTS: Bioreduction of SeNPs was confirmed by UV-Visible spectrophotometer that showed the peak at 575 nm. Size and distribution of the biosynthesised SeNPs were analysed by HR-TEM that showed the formation of particle size in the range of 100-250nm. The synthesised SeNPs showed good cytotoxic activity against HT-29 cell line with 40.5%, 33% and 23.7% of cell viability at 2µg/ ml, 4µg/ml and 30µg/ml concentration respectively. CONCLUSION: The present study reports the simple and eco-friendly synthesis of SeNPs that showed good cytotoxic activity against HT-29 cell line suggesting that biogenic SeNPs could be a potential chemotherapeutic agent.

Green synthesis of selenium nanoparticles using Acinetobacter sp. SW30: optimization, characterization and its anticancer activity in breast cancer cells.

The aim of this study was to synthesize selenium nanoparticles (SeNPs) using cell suspension and total cell protein of Acinetobacter sp. SW30 and optimize its synthesis by studying the influence of physiological and physicochemical parameters. Also, we aimed to compare its anticancer activity with that of chemically synthesized SeNPs in breast cancer cells. Cell suspension of Acinetobacter sp. SW30 was exposed to various physiological and physicochemical conditions in the presence of sodium selenite to study their effects on the synthesis and morphology of SeNPs. Breast cancer cells (4T1, MCF-7) and noncancer cells (NIH/3T3, HEK293) were exposed to different concentrations of SeNPs. The 18 h grown culture with 2.7×109 cfu/mL could synthesize amorphous nanospheres of size 78 nm at 1.5 mM and crystalline nanorods at above 2.0 mM Na2SeO3 concentration. Polygonal-shaped SeNPs of average size 79 nm were obtained in the supernatant of 4 mg/mL of total cell protein of Acinetobacter sp. SW30. Chemical SeNPs showed more anticancer activity than SeNPs synthesized by Acinetobacter sp. SW30 (BSeNPs), but they were found to be toxic to noncancer cells also. However, BSeNPs were selective against breast cancer cells than chemical ones. Results suggest that BSeNPs are a good choice of selection as anticancer agents.

Synergism between thioredoxin reductase inhibitor ethaselen and sodium selenite in inhibiting proliferation and inducing death of human non-small cell lung cancer cells.

New effective treatment for human non-small cell lung cancer (NSCLC) is needed. The thioredoxin (Trx) system composes of thioredoxin reductase (TrxR), Trx and NADPH. In this study, we combined an organic selenium compound--TrxR inhibitor ethaselen (BBSKE) with low dosage sodium selenite to inhibit proliferation and induce death of NSCLC cells, and identified underlying mechanisms. Synergistic anti-proliferation effect of BBSKE and selenite was found in human NSCLC cell lines, A549, NCI-H1299 and NCI-1266. A significant increase of apoptosis, necrosis and autophagy were observed in the group of BBSKE plus selenite in A549 cells. The autophagy induced by BBSKE and selenite inhibited apoptosis and necrosis. In addition, BBSKE plus selenite induced G2/M arrest, which was verified by the alteration of gene and protein expression of cell cycle regulatory complexes. The intracellular enzyme activity of TrxR was remarkably decreased by cotreatment of BBSKE and selenite. Besides, the mRNA and protein level of TrxR1 and Trx1 were significantly inhibited by cotreatment of BBSKE and selenite. HEK 293 cells overexpressing TrxR1 were more sensitive to BBSKE plus selenite. The nuclear translocation of Trx1 and Ref-1, as well as expression of Ref-1 and AP-1 were inhibited by combination treatment. In short, BBSKE synergizes selenite in inhibiting proliferation and inducing death of NSCLC cells; BBSKE combined with selenite may be a treatment strategy for NSCLC.

In vitro study on antagonism mechanism of glutathione, sodium selenite and mercuric chloride.

It has been broadly recognized that the antagonism between selenium (Se) and mercury (Hg) can reduce the toxicity of mercury in organism. Glutathione (GSH) can participate in the metabolism of Se and Hg in vivo and promote the formation of low-toxic Hg-Se complexes, which is a vital way of detoxification for Hg. In this paper, the reaction mechanism of GSH-Se(IV) binary system, GSH-Hg(II) binary system and GSH-Se(IV)-Hg(II) ternary system were systematically studied from the aspects of stoichiometry, thermodynamics and kinetics, via hyphenated techniques including high performance liquid chromatography (HPLC)-ultraviolet (UV) detection, HPLC-inductively coupled plasma mass spectrometry (ICP-MS) and HPLC-electrospray ionization mass spectrometry (ESI-MS). For GSH-Se(IV) binary system, selenodiglutathione (GSSeSG) was the crucial intermediate; the reaction was exothermic and irreversible at constant pressure; it followed second-order kinetics with a fast kinetics (rate constant (k)=4534.2mol-1Ls-1). For GSH-Se(IV)-Hg(II) ternary system, GSSeSeSG would form by the extremely weak dissociation of two molecules of GSSeSG; Hg(II) would rapidly coordinate with GSSeSeSG to generate (HgxSey)n(GS)m precipitates. The mechanism of GSH-Se(IV)-Hg(II) antagonism system involves two processes, the competitive combination of Hg and Se with GSH and the formation of (HgxSey)n(GS)m complexes.

Sodium Selenite as an Anticancer Agent.

Selenium (Se) is a ubiquitous, albeit not uniformly distributed metalloid present in earth crust. Consequently, its human intake with food products, particularly grains and vegetables, is also very uneven, and in certain cases can result in a severe Se deficiency. It was also documented that Se deficiency observed in some countries and/or geographic regions (e.g. Keshan region in China), is associated with an increased morbidity and mortality of neoplastic diseases. To correct this problem a number of organic and inorganic selenium compounds were developed and tested. However, it is now firmly established that only an inorganic sodium selenite with four-valent Se, and not that with six-valent (selenate) cation shows anticancer activity. This difference in their biological activities is due to their physicochemical properties. Thus selenite (Se+4) can undergo redox reaction, for example with protein's sulfhydryl groups expressed on the surface of tumor cells. In this way selenite prevents non-enzymatic formation of parafibrin that coats tumors cells and hence presents them as 'self' to the innate cellular immune system. Consequently, macrophages of the lymphatic system do not recognize neoplastic cells as 'foreign' bodies and spare them from the immune destruction. This mechanism can explain the failure of various immunotherapies to completely eliminate tumors from human bodies. Another contributing factor to carcinogenesis is the excessive consumption of red meat containing redox-active iron (Fe+3) that initiates parafibrin formation from blood fibrinogen. In conclusion, sodium selenite is a readily available and inexpensive drug of choice in the cancer treatment and prevention.

Sodium selenite and cancer related lymphedema: Biological and pharmacological effects.

A significant percentage of cancer patients develop secondary lymphedema after surgery or radiotherapy. The preferred treatment of secondary lymphedema is complex physical therapy. Pharmacotherapy, for example with diuretics, has received little attention, because they were not effective and only offered short-term solutions. Sodium selenite showed promise as a cost-effective, nontoxic anti-inflammatory agent. Treatment with sodium selenite lowers reactive oxygen species (ROS) production, causes a spontaneous reduction in lymphedema volume, increases the efficacy of physical therapy for lymphedema, and reduces the incidence of erysipelas infections in patients with chronic lymphedema. Besides biological effects in reducing excessive production of ROS, sodium selenite also displays various pharmacological effects. So far the exact mechanisms of these pharmacological effects are mostly unknown, but probably include inhibition of adhesion protein expression.

Combined Effect of Sodium Selenite and Ginsenoside Rh2 on HCT116 Human Colorectal Carcinoma Cells.

BACKGROUND: Sodium selenite and ginsenoside Rh2 (G-Rh2) are well known for their anticancer properties and have been exploited as a new therapeutic approach. In this study, we are interested to evaluate if sodium selenite and G-Rh2 combination results in a synergistic anticancer effect that could contribute to lower systemic toxicity. METHODS: We observed the synergistic antitumor effect by combination of sodium selenite and G-Rh2 on HCT-116 human colorectal carcinoma cells in vitro. Cell growth, viability, cell cycle progression and cell apoptosis, Bax/Bcl2 ratio, caspase-3 expression, reactive oxygen species (ROS) production and autophagy were evaluated. RESULTS: The results showed that sodium selenite and G-Rh2 combination have a synergistic effect on cell growth inhibition (57%) compared with sodium selenite (25%) and G-Rh2 alone (28%) after 24 hours of treatment. This combination also induced G1 and S phase arrest simultaneously and increased apoptosis rate. The results also indicated that Bax/Bcl2 ratio and caspase-3 expression, known as proapoptotic factors, were increased in the presence of sodium selenite and G-Rh2 alone. However, combined drug treatment results in a more significant increase in Bax/Bcl2 ratio and caspase-3 expression (P < 0.05). In addition, this combination significantly induces a depletion of ROS production and autophagy, compared to control, sodium selenite and G-Rh2 alone (P < 0.05). CONCLUSION: Sodium selenite and ginsenoside Rh2 combination may be a more effective treatment for human colorectal carcinoma and is a promising chemotherapeutic approach for malignant tumors.

Chokeberry (Aronia melanocarpa (Michx.) Elliot) concentrate inhibits NF-κB and synergizes with selenium to inhibit the release of pro-inflammatory mediators in macrophages.

Black chokeberry has been known to play a protective role in human health due to its high polyphenolic content including anthocyanins and caffeic acid derivatives. In the present study, we first characterized the polyphenolic content of a commercial chokeberry concentrate and investigated its effect on LPS-induced NF-κB activation and release of pro-inflammatory mediators in macrophages in the presence or the absence of sodium selenite. Examination of the phytochemical profile of the juice concentrate revealed high content of polyphenols (3.3%), including anthocyanins, proanthocyanidins, phenolic acids, and flavonoids. Among them, cyanidin-3-O-galactoside and caffeoylquinic acids were identified as the major compounds. Data indicated that chokeberry concentrate inhibited both the release of TNFα, IL-6 and IL-8 in human peripheral monocytes and the activation of the NF-κB pathway in RAW 264.7 macrophage cells. Furthermore, chokeberry synergizes with sodium selenite to inhibit NF-κB activation, cytokine release and PGE2 synthesis. These findings suggest that selenium added to chokeberry juice enhances significantly its anti-inflammatory activity, thus revealing a sound approach in order to tune the use of traditional herbals by combining them with micronutrients.

Selenylation modification can enhance immune-enhancing activity of Chinese angelica polysaccharide.

On the basis of previous test that selenizing Chinese angelica polysaccharides (sCAPs) with stronger immune-enhancing activity in vitro were picked out, the immune-enhancing activity in vivo of three sCAPs, sCAP2, sCAP6 and sCAP8, at high and low dosage were compared taking the unmodified Chinese angelica polysaccharide (CAP) as control by determination of peripheral lymphocyte proliferation, serum antibody titer, IFN-γ and IL-6 contents in chicken vaccinated with Newcastle Disease vaccine. The results showed that three sCAPs at suitable dosage could significantly promote lymphocyte proliferation, enhance serum antibody titer, IFN-γ and IL-6 contents as compared with unmodified CAP, sCAP2 at low dosage possessed the strongest action. These results indicated that selenylation modification could significantly enhance the immune-enhancing activity of CAP, sCAP2 possessed the best efficacy and would be as a component drug of new-type immunoenhancer.

Selenium toxicity toward yeast as assessed by microarray analysis and deletion mutant library screen: a role for DNA repair.

Selenium (Se) is a trace element that is essential for human health as it takes part in many cellular processes. The cellular response to this compound elicits very diverse processes including DNA damage response and repair. Because an inorganic form of Se, sodium selenite (SeL), has often been a part of numerous studies and because this form of Se is used as a dietary supplement by the public, here, we elucidated mechanisms of SeL-induced toxicity in yeast Saccharomyces cerevisiae using a combination of systematic genetic and transcriptome analysis. First, we screened the yeast haploid deletion mutant library for growth in the presence of this Se compound. We identified 39 highly SeL sensitive mutants. The corresponding deleted genes encoded mostly proteins involved in DNA damage response and repair, vacuole function, glutathione (GSH) metabolism, transcription, and chromatin metabolism. DNA damage response and repair mutants were examined in more detail: a synergistic interaction between postreplication (PRR) and homologous recombination (HRR) repair pathways was revealed. In addition, the effect of combined defects in HRR and GSH metabolism was analyzed, and again, the synergistic interaction was found. Second, microarray analysis was used to reveal expression profile changes after SeL exposure. The gene process categories "amino acid metabolism" and "generation of precursor metabolites and energy" comprised the greatest number of induced and repressed genes, respectively. We propose that SeL-induced toxicity markedly results from DNA injury, thereby highlighting the importance of DNA damage response and repair pathways in protecting cells against toxic effects of this Se compound. In addition, we suggest that SeL toxicity also originates from damage to cellular proteins, including those acting in DNA damage response and repair.

Transport of selenium across the plasma membrane of primary hepatocytes and enterocytes of rainbow trout.

Transport of essential solutes across biological membranes is one of the fundamental characteristics of living cells. Although selenium is an essential micronutrient, little is known about the cellular mechanisms of chemical species-specific selenium transport in fish. We report here the kinetic and pharmacological transport characteristics of selenite and its thiol (glutathione and l-cysteine) derivatives in primary cultures of hepatocytes and isolated enterocytes of rainbow trout. Findings from the current study suggest an apparent low-affinity linear transport system for selenite in both cell types. However, we recorded high-affinity Hill kinetics (K(d)=3.61±0.28 µmol l(-1)) in enterocytes exposed to selenite in the presence of glutathione. The uptake of selenite in the presence of thiols was severalfold higher than uptake of selenite alone (at equimolar concentration) in both hepatocytes and enterocytes. Cellular accumulation of selenium was found to be energy independent. Interestingly, we observed a decrease in selenite transport with increasing pH, whereas selenite uptake increased with increasing pH in the presence glutathione in both cell types. The cellular uptake of selenite demonstrated a pronounced competitive interaction with a structurally similar compound, sulfite. The uptake of selenite as well as its thiol derivatives was found to be sensitive to the anion transport blocker DIDS, irrespective of the cell type. Inorganic mercury (Hg(2+)) elicited an inhibition of selenite transport in both cell types, but augmented the transport of reduced forms of selenite in hepatocytes. Based on the substrate choice and comparable pharmacological properties, we advocate that multiple anion transport systems are probably involved in the cellular transport of selenite in fish.

Effect of two selenium sources on hepatocarcinogenesis and several angiogenic cytokines in diethylnitrosamine-induced hepatocarcinoma rats.

This experiment was designed to compare the effect of two selenium sources at the dosage of therapeutic level on hepatocarcinogenesis and angiogenic cytokines in DEN-induced hepatocarcinoma rats to further approach their possible anticancer's mechanism. One hundred and seventy-eight Sprague-Dawley (SD) rats (average weight being 100-120g) were randomly divided into 5 groups (I-V). Animals in group I, group II and group III served as the negative control, sodium selenite control (SS) and positive controls respectively, and received 0.1, 3.0, and 0.1mg/kg selenium from sodium selenite supplemented diets during the whole experimental time. Rats in group IV and group V were fed with selenium from selenium-enriched malt (SEM) and sodium selenite (SS) supplemented diets (3mg/kg respectively). To balance the nutritional content among each group, normal malt which was not treated with selenium was added into the diets of the challenge groups. The nutrition contents, except the selenium of the diet in each group, were similar and in accordance with NRC standards. Rats in groups III-V were treated by aqueous diethylnitrosamine solution (100mg/L) at the dosage of 10mg/kg body weight every day for 16 weeks to induce hepatocarcinoma, and drank sterilized water for an additional two weeks. Rats in group I and group II drank sterilized water throughout the experiment. At 4th, 8th, 12th, 16th week, five rats in each group were then sacrificed by cervical decapitation. At the termination of the study, at 18th week, the surplus rats were sacrificed by cervical decapitation. Feed was withheld from the rats for 12h before sampling. The number of hepatoma nodules in liver and mortality of rats were calculated. The values of the following items, including α-fetoprotein (AFP), gamma-glutamyltranspeptidase (GGT), tumor necrosis factor-α (TNF-α), insulin-like growth factors-II (IGF-II), nitric oxide (NO) and total nitric oxide synthase (T-NOS) in plasma were determined. At the same time, the positive numbers of vascular endothelial growth factor (VEGF) and protein kinase C-α (PKCα) staining cells in tumor tissue were analyzed by immunohistochemistry using the Envision two step methods with a kit. The results indicated that SEM could significantly decrease the mortality of rats and the number of hepatoma nodules, values of GGT and AFP, and the levels of IGF-II, NO and NOS and lessen the positive numbers of VEGF and PKCα staining cells in tumor tissue. Moreover, SEM could increase the levels of TNF-α in the initiated time of hepatocarcinogenesis, whereas, decrease the levels of TNF-α in the progressive time of hepatocarcinogenesis. SS could only significantly inhibit the positive numbers of PKCα staining cells in tumor tissue, decrease the levels of GGT, AFP and TNF-α at minority sampling times, and increase the levels of NO. In conclusion, SEM could reduce the mortality. It might be related to deaden significantly the lesion of liver, delay the cause of hepatocarcinogenesis, and inhibit the progress of angiogenesis to increase the livability of DEN-induced hepatocarcinoma rats. SS at the same therapeutic dosage had less effect on the hepatocarcinogenesis by inhibiting angiogenesis and relative cytokines to some extent.

Sorption kinetic study of selenite and selenate onto a high and low pressure aged iron oxide nanomaterial.

The sorption of selenite (SeO(3)(2-)) and selenate (SeO(4)(2-)) onto Fe(3)O(4) nanomaterials produced by non microwave-assisted or microwave-assisted synthetic techniques was investigated through use of the batch technique. The phase of both synthetic nanomaterials was determined to be magnetite by X-ray diffraction. The average grain sizes of non microwave-assisted and microwave-assisted synthetic Fe(3)O(4) were determined to be 27 and 25 nm, respectively through use of the Scherrer's equation. Sorption of selenite was pH independent in the pH range of 2-6, while sorption of selenate decreased at pH 5 and 6. The addition of Cl(-) had no significant effect on selenite or selenate binding, while the addition of NO(3)(-) only affected selenate binding to the microwave assisted Fe(3)O(4). A decrease of selenate binding to both synthetic particles was observed after the addition of SO(4)(2-) while selenite binding was not affected. The addition of PO(4)(3-) beginning at concentrations of 0.1 ppm had the most prominent effect on the binding of both selenite and selenate. The capacities of binding, determined through the use of Langmuir isotherm, were found to be 1923 and 1428 mg Se/kg of non microwave-assisted Fe(3)O(4) and 2380 and 2369 mg Se/kg of microwave-assisted Fe(3)O(4) for selenite and selenate, respectively.

Metabolism of selenite in human lung cancer cells: X-ray absorption and fluorescence studies.

Selenite is an inorganic form of selenium that has a cytotoxic effect against several human cancer cell lines: one or more selenite metabolites are considered to be responsible for its toxicity. X-ray absorption spectroscopy was used to monitor Se speciation in A549 human lung cancer cells incubated with selenite over 72 h. As anticipated, selenodiglutathione and elemental Se both comprised a large proportion of Se in the cells between 4 and 72 h after treatment, which is in accordance with the reductive metabolism of selenite in the presence of glutathione and glutathione reductase/NADPH system. Selenocystine was also present in the cells but was only detected as a significant component between 24 and 48 h concomitant with a decrease in the proportion of selenocysteine and the viability of the cells. The change in speciation from the selenol, selenocysteine, to the diselenide, selenocystine, is indicative of a change in the redox status of the cells to a more oxidizing environment, likely brought about by metabolites of selenite. X-ray fluorescence microscopy of single cells treated with selenite for 24 h revealed a punctate distribution of Se in the cytoplasm. The accumulation of Se was associated with a greater than 2-fold increase in Cu, which was colocalized with Se. Selenium K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy revealed Se-Se and Se-S bonding, but not Se-Cu bonding, despite the spatial association of Se and Cu. Microprobe X-ray absorption near-edge structure spectroscopy (µ-XANES) showed that the highly localized Se species was mostly elemental Se.

Interaction of selenite and tellurite with thiol-dependent redox enzymes: Kinetics and mitochondrial implications.

The interactions of selenite and tellurite with cytosolic and mitochondrial thioredoxin reductases (TrxR1 and TrxR2) and glutathione reductases (GR) from yeast and mammalian sources were explored. Both TrxR1 and TrxR2 act as selenite and tellurite reductases. Kinetic treatment shows that selenite has a greater affinity than tellurite with both TrxR1 and TrxR2. Considering both k(cat) and K(m), selenite shows a better catalytic efficiency than tellurite with TrxR1, whereas with TrxR2, the catalytic efficiency is similar for both chalcogens. Tellurite is a good substrate for GR, whereas selenite is almost completely ineffective. Selenite or tellurite determine a large mitochondrial permeability transition associated with thiol group oxidation. However, with increasing concentrations of both chalcogens, only about 25% of total thiols are oxidized. In isolated mitochondria, selenite or tellurite per se does not stimulate H2O2 production, which, however, is increased by the presence of auranofin. They also determine a large oxidation of mitochondrial pyridine nucleotides. In ovarian cancer cells both chalcogens decrease the mitochondrial membrane potential. These results indicate that selenite and tellurite, interacting with the thiol-dependent enzymes, alter the balance connecting pyridine nucleotides and thiol redox state, consequently leading to mitochondrial and cellular alterations essentially referable to a disulfide stress.

Encapsulation of selenium in chitosan nanoparticles improves selenium availability and protects cells from selenium-induced DNA damage response.

Selenium, an essential mineral, plays important roles in optimizing human health. Chitosan (CS) is an effective, naturally oriented material for synthesizing nanoparticles with preferable properties such as biocompatibility, biodegradation and resistance to certain enzymes. We have recently shown that cellular exposure to selenium compounds activates ataxia-telangiectasia mutated (ATM)-dependent DNA damage responses, a tumorigenesis barrier. To test whether nanoencapsulation of selenium modulates the cellular response to selenium compounds, the HCT 116 cancerous and the MRC-5 normal cells were treated with Na(2)SeO(3) and methylseleninic acid (MSeA) encapsulated in CS/polyphosphate nanoparticles. Analyses of cellular selenium levels demonstrate that (1) the nanoencapsulation enhances selenium levels in cells after exposure to Na(2)SeO(3) and MSeA (1-10 µM); (2) cells retained more selenium when treated with Na(2)SeO(3) than with MSeA; (3) selenium levels are greater in HCT 116 than in MRC-5 cells after Na(2)SeO(3), but not MSeA, exposure. Survival analysis shows that CS encapsulation desensitizes HCT 116 and MRC-5 cells to Na(2)SeO(3) or MSeA exposure. Immunofluorescent analysis demonstrates that CS encapsulation attenuates the selenium-induced ATM phosphorylation on Ser-1981, and the extent is greater in HCT 116 than in MRC-5 cells. Our results reveal features of selenium nanoencapsulation in CS, including increased selenium retention in cells and decreased cellular sensitivity and DNA damage response to selenium exposure.

Site-specific effects of diselenide bridges on the oxidative folding of a cystine knot peptide, omega-selenoconotoxin GVIA.

Structural and functional studies of small, disulfide-rich peptides depend on their efficient chemical synthesis and folding. A large group of peptides derived from animals and plants contains the Cys pattern C-C-CC-C-C that forms the inhibitory cystine knot (ICK) or knottin motif. Here we report the effect of site-specific incorporation of pairs of selenocysteine residues on oxidative folding and the functional activity of omega-conotoxin GVIA, a well-characterized ICK-motif peptidic antagonist of voltage-gated calcium channels. Three selenoconotoxin GVIA analogues were chemically synthesized; all three folded significantly faster in the glutathione-based buffer compared to wild-type GVIA. One analogue, GVIA[C8U,C19U], exhibited significantly higher folding yields. A recently described NMR-based method was used for mapping the disulfide connectivities in the three selenoconotoxin analogues. The diselenide-directed oxidative folding of selenoconotoxins was predominantly driven by amino acid residue loop sizes formed by the resulting diselenide and disulfide cross-links. Both in vivo and in vitro activities of the analogues were assessed; the block of N-type calcium channels was comparable among the analogues and wild-type GVIA, suggesting that the diselenide replacement did not affect the bioactive conformation. Thus, diselenide substitution may facilitate oxidative folding of pharmacologically diverse ICK peptides. The diselenide replacement has been successfully applied to a growing number of bioactive peptides, including alpha-, mu-, and omega-conotoxins, suggesting that the integrated oxidative folding of selenopeptides described here may prove to be a general approach for efficient synthesis of diverse classes of disulfide-rich peptides.

Transition metal ions and selenite modulate the methylation of arsenite by the recombinant human arsenic (+3 oxidation state) methyltransferase (hAS3MT).

This report demonstrates that transition metal ions and selenite affect the arsenite methylation by the recombinant human arsenic (+3 oxidation state) methyltransferase (hAS3MT) in vitro. Co(2+), Mn(2+), and Zn(2+) inhibited the arsenite methylation by hAS3MT in a concentration-dependent manner and the kinetics indicated Co(2+) and Mn(2+) to be mixed (competitive and non-competitive) inhibitors while Zn(2+) to be a competitive inhibitor. However, only a high concentration of Fe(2+) could restrain the methylation. UV-visible, CD and fluorescence spectroscopy were used to study the interactions between the metal ions above and hAS3MT. Further studies showed that neither superoxide anion nor hydrogen peroxide was involved in the transition metal ion or selenite inhibition of hAS3MT activity. The inhibition of arsenite methylating activity of hAS3MT by selenite was reversed by 2mM DTT (dithiothreitol) but neither by cysteine nor by beta-mercaptoethanol. Whereas, besides DTT, cysteine can also prevent the inhibition of hAS3MT activity by Co(2+), Mn(2+), and Zn(2+). Free Cys residues were involved in the interactions of transition metal ions or selenite with hAS3MT. It is proposed that the inhibitory effect of the ions (Co(2+), Mn(2+), and Zn(2+)) or selenite on hAS3MT activity might be via the interactions of them with free Cys residues in hAS3MT to form inactive protein adducts.