Methylselenol Formed by Spontaneous Methylation of Selenide Is a Superior Selenium Substrate to the Thioredoxin and Glutaredoxin Systems

Naturally occurring selenium compounds like selenite and selenodiglutathione are metabolized to selenide in plants and animals. This highly reactive form of selenium can undergo methylation and form monomethylated and multimethylated species. These redox active selenium metabolites are of particular biological and pharmacological interest since they are potent inducers of apoptosis in cancer cells. The mammalian thioredoxin and glutaredoxin systems efficiently reduce selenite and selenodiglutathione to selenide. The reactions are non-stoichiometric aerobically due to redox cycling of selenide with oxygen and thiols. Using LDI-MS, we identified that the addition of S-adenosylmethionine (SAM) to the reactions formed methylselenol. This metabolite was a superior substrate to both the thioredoxin and glutaredoxin systems increasing the velocities of the nonstoichiometric redox cycles three-fold. In vitro cell experiments demonstrated that the presence of SAM increased the cytotoxicity of selenite and selenodiglutathione, which could neither be explained by altered selenium uptake nor impaired extra-cellular redox environment, previously shown to be highly important to selenite uptake and cytotoxicity. Our data suggest that selenide and SAM react spontaneously forming methylselenol, a highly nucleophilic and cytotoxic agent, with important physiological and pharmacological implications for the highly interesting anticancer effects of selenium.     

Selenium induces a multi‐targeted cell death process in addition to ROS formation

Selenium compounds inhibit neoplastic growth. Redox active selenium compounds are evolving as promising chemotherapeutic agents through tumour selectivity and multi‐target response, which are of great benefit in preventing development of drug resistance. Generation of reactive oxygen species is implicated in selenium‐mediated cytotoxic effects on cancer cells. Recent findings indicate that activation of diverse intracellular signalling leading to cell death depends on the chemical form of selenium applied and/or cell line investigated. In the present study, we aimed at deciphering different modes of cell death in a single cell line (HeLa) upon treatment with three redox active selenium compounds (selenite, selenodiglutathione and seleno‐DL‐cystine). Both selenite and selenodiglutathione exhibited equipotent toxicity (IC₅₀ 5 μM) in these cells with striking differences in toxicity mechanisms. Morphological and molecular alterations provided evidence of necroptosis‐like cell death in selenite treatment, whereas selenodiglutathione induced apoptosis‐like cell death. We demonstrate that selenodiglutathione efficiently glutathionylated free protein thiols, which might explain the early differences in cytotoxic effects induced by selenite and selenodiglutathione. In contrast, seleno‐DL‐cystine treatment at an IC₅₀ concentration of 100 μM induced morphologically two distinct different types of cell death, one with apoptosis‐like phenotype, while the other was reminiscent of paraptosis‐like cell death, characterized by induction of unfolded protein response, ER‐stress and occurrence of large cytoplasmic vacuoles. Collectively, the current results underline the diverse cytotoxic effects and variable potential of redox active selenium compounds on the survival of HeLa cells and thereby substantiate the potential of chemical species‐specific usage of selenium in the treatment of cancers.     

Uptake of selenotrisulfides of glutathione and cysteine by brush border membranes from rat intestines.

The uptake of selenodiglutathione and selenodicysteine was compared to that of selenite by brush border membrane vesicles (BBMV) prepared from rat intestinal tracts. It was found that it is critical to maintain a pH of 6.0 or below to prevent the spontaneous breakdown of these compounds. When conducted at pH 6.0, the uptake of selenodiglutathione and selenodicysteine was more than ten times faster than for selenite selenium. Ligated intestinal loop studies were conducted to determine if similar results would be obtained in vivo. In comparison to selenite, selenium absorption was enhanced 68% and the transfer to the body increased 2.4-fold when selenium as selenodiglutathione was placed in the ileum. The absorption of selenium as selenodicysteine was increased by 57% and the transfer doubled in comparison to selenite when placed in the ileum. Thus, the stimulated absorption of selenite by glutathione or cysteine appears to be through the formation of complexes with these compounds.     

Extracellular production of hydrogen selenide accounts for thiol-assisted toxicity of selenite against Saccharomyces cerevisiae

Administration of selenium in humans has anticarcinogenic effects. However, the boundary between cancer-protecting and toxic levels of selenium is extremely narrow. The mechanisms of selenium toxicity need to be fully understood. In Saccharomyces cerevisiae, selenite in the millimolar range is well tolerated by cells. Here we show that the lethal dose of selenite is reduced to the micromolar range by the presence of thiols in the growth medium. Glutathione and selenite spontaneously react to produce several selenium-containing compounds (selenodiglutathione, glutathioselenol, hydrogen selenide, and elemental selenium) as well as reactive oxygen species. We studied which compounds in the reaction pathway between glutathione and sodium selenite are responsible for this toxicity. Involvement of selenodiglutathione, elemental selenium, or reactive oxygen species could be ruled out. In contrast, extracellular formation of hydrogen selenide can fully explain the exacerbation of selenite toxicity by thiols. Indeed, direct production of hydrogen selenide with D-cysteine desulfhydrase induces high mortality. Selenium uptake by S. cerevisiae is considerably enhanced in the presence of external thiols, most likely through internalization of hydrogen selenide. Finally, we discuss the possibility that selenium exerts its toxicity through consumption of intracellular reduced glutathione, thus leading to severe oxidative stress.     

Glutathione contributes to the efflux of selenium from hepatoma cells

Selenite is a selenium source for selenoprotein biosynthesis in mammalian cells. Although previous studies have suggested the involvement of glutathione (GSH) and/or thioredoxin reductase in selenite metabolism, intracellular selenite metabolism remains largely unknown. Here, we report that GSH depletion did not affect the amount of selenoprotein in Hepa 1–6 cells, suggesting that GSH does not play a central role in the reduction of selenite in selenoprotein biosynthesis. On the other hand, we found that GSH is involved in the efflux of low-molecular-weight selenium compounds from cells, presumably via the formation of selenodiglutathione. Moreover, selenite inhibited the efflux of a fluorescent bimane-GS conjugate that is mediated by ATP-dependent multidrug-resistant proteins, implying the existence of an active transporter for selenodiglutathione. This is the first report demonstrating that GSH plays a role in selenium excretion from cells by forming a GSH-conjugate, which may contribute to the distribution, detoxification, and homeostasis of selenium in the body.     

Copper may interact with selenite extracellularly in cultured HT-29 cells

Previous studies have demonstrated that copper (15.7 micromol/L) can inhibit selenite (12.6 micromol/L)-induced cytotoxicity and apoptosis in HT-29 cells. However, the exact nature of the interactions between selenium and copper is not fully understood. In this study, the effect of copper on the cell cycle arrest induced by selenite or selenocystine was examined. Both selenite and selenocystine were effective in inhibition of cell growth and cell cycle progression. Cell cycle analysis revealed that selenite (3-5 micromol/L) caused a decrease in G1 phase cells that corresponded with an increase in S and G2 phase cells, and that 0.625 or 1.25 micromol/L copper sufficiently inhibited selenite-induced cell cycle arrest. In contrast, selenocystine caused an increase in G1 phase cells that corresponded with a decrease in S and G2 phase cells. Interestingly, 0.625 or 1.25 micromol/L copper did not inhibit selenocystine-induced cell cycle arrest. In addition, cell free gel shift assay demonstrated that selenite suppressed the inhibitory effect of copper on SP-1 DNA binding. Furthermore, although 5 micromol/L selenite in culture media significantly increased the intracellular selenium content, 1.25 micromol/L copper sulfate blocked this increase of the intracellular selenium content. Collectively, these data demonstrate that selenite and selenocystine cause cell cycle arrest via distinct mechanisms, and suggest that copper may interact with selenite extracellularly, which represents the basis of antagonism between copper sulfate and selenite.     

Selenium metabolism in Escherichia coli

Escherichia coli will reduce selenite (SeO 3 2- ) andselenate (SeO 4 2- ) to elemental selenium Se 0 . Seleniumwill also become incorporated intoproteins as part of the amino acids selenocysteine or selenomethionine.The reaction of selenitewith glutathione produces selenodiglutathione (GS-Se-GS). Selenodiglutathioneand itssubsequent reduction to glutathioselenol (GS-SeH) are likely the key intermediatesin the possiblemetabolic fates of selenium. This review presents the possible pathwaysinvolving selenium in E. coli. Identification of intermediates and potentialprocesses from uptake of the toxic oxyanions through to theirdetoxification will assist us inunderstanding the complexities of metalloid oxyanion metabolism in thesebacteria.     

Reduction of selenium-binding protein 1 sensitizes cancer cells to selenite via elevating extracellular glutathione: A novel mechanism of cancer-specific cytotoxicity of selenite

Selenium is an essential trace element and has been extensively studied for preventive effects on cancers. Recent emerging evidence has also shown that selenium at supranutritional dosage has a preferential cytotoxicity in cancer cells and chemotherapeutic drug-resistant cells, but the underlying mechanisms remain largely unknown. This study was to investigate the roles of two distinct representatives of selenium-containing proteins, selenium-binding protein 1 (SBP1) and glutathione peroxidase 1 (GPX1), in selenite-mediated cancer-specific cytotoxicity. We found that there was a significantly inverse correlation between SBP1 and GPX1 protein level in human breast cancers and adjacent matched nontumor tissues (Pearson r=–0.4347, P=0.0338). Ectopic expression of GPX1 enhanced selenite cytotoxicity through down-regulation of SBP1, and SBP1 was likely to be a crucial determinant for selenite-mediated cytotoxicity. Reduction of SBP1 in cancer cells and epirubicin-resistant cells on selenite exposure resulted in a dramatic increase in the generation of hydrogen peroxide and superoxide anion, which in turn caused oxidative stress and triggered apoptosis. Furthermore, knockdown SBP1 by small interfering RNA increased selenite sensitivity by elevating extracellular glutathione (GSH), which spontaneously reacted with selenite and led to the rapid depletion of selenium (IV) in growth medium and the high-affinity uptake of selenite. In conclusion, these findings would improve our understanding of the roles of selenium-containing proteins in selenite-mediated cytotoxicity, and revealed a potent mechanism of the selective cytotoxicity of selenite in cancer cells and drug-resistant cells, in which SBP1 was likely to play an important role in modulating the extracellular microenvironment by regulating the levels of extracellular GSH.     

Similarities between the abiotic reduction of selenite with glutathione and the dissimilatory reaction mediated by Rhodospirillum rubrum and Escherichia coli

Various mechanisms have been proposed to explain the biological dissimilatory reduction of selenite (SeO3(2-)) to elemental selenium (Se(o)), although none is without controversy. Glutathione, the most abundant thiol in the eukaryotic cells, the cyanobacteria, and the alpha, beta, and gamma groups of the proteobacteria, has long been suspected to be involved in selenium metabolism. Experiments with the phototrophic alpha proteobacterium Rhodospirillum rubrum showed that the rate of selenite reduction was decreased when bacteria synthesized lower than normal levels of glutathione, and in Rhodobacter sphaeroides and Escherichia coli the reaction was reported to induce glutathione reductase. In the latter organism superoxide dismutase was also induced in cells grown in the presence of selenite, indicating that superoxide anions (O2-) were produced. These observations led us to investigate the abiotic (chemical) reduction of selenite by glutathione and to compare the features of this reaction with those of the reaction mediated by R. rubrum and E. coli. Our findings imply that selenite was first reduced to selenodiglutathione, which reached its maximum concentration within the 1st min of the reaction. Formation of selenodiglutathione was paralleled by a rapid reduction of cytochrome c, a known oxidant for superoxide anions. Cytochrome c reduction was inhibited by superoxide dismutase, indicating that O2- was the source of electrons for the reduction. These results demonstrated that superoxide was produced in the abiotic reduction of selenite with glutathione, thus lending support to the hypothesis that glutathione may be involved in the reaction mediated by R. rubrum and E. coli. The second phase of the reaction, which led to the formation of elemental selenium (Se(o)), developed more slowly. Se(o) precipitation reached a maximum within 2 h after the beginning of the reaction. Secondary reactions leading to the degradation of the superoxide significantly decreased the yield of Se(o) in the abiotic reaction compared with that of the bacterially mediated selenite reduction. Abiotically formed selenium particles showed the same characteristic orange-red color, spherical structure, and size as particles produced by R. rubrum, again providing support for the hypothesis that glutathione is involved in the reduction of selenite to elemental selenium in this organism.     

Interaction of glutathione and sodium selenite in vitro investigated by electrospray ionization tandem mass spectrometry

Selenite has been found to be an active catalyst for the oxidation of sulphhydryl compounds, such as glutathione (GSH). Considering the biological importance of GSH oxidation and the implication of sulphhydryl compounds in selenium poisoning and other biological activities, more information on selenite oxidation of GSH in enzyme-free conditions is desirable. Herein, we describe glutathione and sodium selenite simply mixed in aqueous solutions. The interaction products and transient intermediate are identified and characterized using electrospray ionization (ESI) tandem mass spectrometry. In the first step, GSH directly reacts to form diglutathione (GSSG) and unstable selenodiglutathione (GS-Se-SG). Then selenodiglutathione further reacted with remaining GSH to form diglutathione and elemental selenium, Se(0). As the amount of GSSG significantly increased or acidity of the solution increased, the redox potential of glutathione [E(0')(GSSG/2GSH) approximately -250 mV (NHE)] significantly shifted to the positive direction. This makes the GSSG react with elemental selenium formed in the solution, which can be demonstrated by another unstable intermediate ion identified at m/z 418 by mass spectrometry with the elemental composition of [GSS-Se](-). The reaction mechanism between GSH and sodium selenite has been proposed according to the ESI-MS, NMR and UV-vis spectrometric measurements.     

Characterization of the selenite uptake mechanism in the coccolithophore Emiliania huxleyi (Haptophyta)

The marine coccolithophore Emiliania huxleyi (Haptophyta) requires selenium as an essential element for growth, and the active species absorbed is selenite, not selenate. This study characterized the selenite uptake mechanism using ??Se as a tracer. Kinetic analysis of selenite uptake showed the involvement of both active and passive transport processes. The active transport was suppressed by 0.5 mM vanadate, a membrane-permeable inhibitor of H?-ATPase, at pH 8.3. When the pH was lowered from 8.3 to 5.3, the selenite uptake activity greatly increased, even in the presence of vanadate, suggesting that the H? concentration gradient may be a motive force for selenite transport. [??Se]Selenite uptake at selenite-limiting concentrations was hardly affected by selenate, sulfate and sulfite, even at 100 μM. In contrast, 3 μM orthophosphate increased the K(m) 5-fold. These data showed that HSeO??, a dominant selenite species at acidic pH, is the active species for transport through the plasma membrane and transport is driven by ΔpH energized by H?-ATPase. Kinetic analysis showed that the selenite uptake activity was competitively inhibited by orthophosphate. Furthermore, the active selenite transport mechanism was shown to be induced de novo under Se-deficient conditions and induction was suppressed by the addition of either sufficient selenite or cycloheximide, an inhibitor of de novo protein synthesis. These results indicate that E. huxleyi cells developed an active selenite uptake mechanism to overcome the disadvantages of Se limitation in ecosystems, maintaining selenium metabolism and selenoproteins for high viability.     

Arsenic suppresses necrosis induced by selenite in human leukemia HL-60 cells

Selenium, an essential trace element for humans, has been shown to have anticancer effects. Arsenic, a possibly essential ultratrace element for humans, has been used in the treatment of leukemia. Anticancer effects of selenium and arsenic have been related to their ability to induce apoptosis. Because humans are exposed to diverse trace elements simultaneously, it is important to learn their interrelationship. In this study, we demonstrate that sodium selenite (Na₂SeO₃) causes apoptosis at 3 μM and necrosis at high concentrations (>3 μM) in HL-60 cells. Similarly, both sodium arsenite (NaAsO₂) at 50 μM and sodium arsenate (Na₂HAsO₄) induce apoptosis at 500 μM and necrosis at higher concentrations (>50 μM and >500 μM, respectively) in HL-60 cells. Arsenite/arsenate, but not selenite, enhances AP-1 DNA-binding activity. This finding indicates different mechanisms through which apoptosis is induced by these two elements. Interestingly, we observed that HL-60 cell necrosis induced by a high concentration (>3 μM) of selenite was essentially inhibited by arsenic (50 μM of NaAsO₂ or 500 μM of Na₂HAsO₄), which resulted in a net effect of apoptosis. Because AP-1 DNA-binding activity was not induced in the presence of a combination of necrotic amount of selenite and apoptotic amount of arsenite/arsenate, the observed apoptosis apparently was through the mechanism used by selenite. Our results suggest, for the first time, that the toxic necrotic effect of selenite can be neutralized by arsenite/arsenate at the cellular level. The U.S. Department of Agriculture, Agricultural Research Service, Northern Plains Area, is an equal opportunity/affirmative action employer and all agency services are available without discrimination. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Selenium compounds have disparate abilities to impose oxidative stress and induce apoptosis

The cancer chemopreventive effect of selenium cannot be fully accounted for by the role of selenium as a component of the antioxidant enzyme glutathione peroxidase, which suggests that chemoprevention occurs by another mechanism. Several studies have shown that thiol oxidation and free radical generation occur as a consequence of selenium catalysis and toxicity. In the present study, we evaluated three different selenium compounds; selenite, selenocystamine, and selenomethionine to determine the relative importance of the prooxidative effects of these compounds with regard to their ability to induce apoptosis. The experimental results suggest that, in addition to supporting an increased activity of glutathione peroxidase, an antioxidant function that the three selenium compounds did with equal efficacy, catalytic selenite, and selenocystamine generated 8-hydroxydeoxyguanosine DNA adducts, induced apoptosis and were found to be cytotoxic in mouse keratinocytes. The noncatalytic selenomethionine was not cytotoxic, did not generate 8-hydroxydeoxyguanosine adducts and did not induce cellular apoptosis at any of the selenium concentrations studied. In keratinocytes, apoptosis may be initiated by superoxide (O₂^•−) and oxidative free radicals that are generated by selenite and selenocystamine, but not by selenomethionine.     

Selenium homeostasis and induction of thioredoxin reductase during long term selenite supplementation in the rat

Selenium is a candidate treatment for liver tumour prevention in chronic liver disease. In this study, we have studied selenium uptake, distribution and accumulation in rats provided with water containing tumour-preventive doses of sodium selenite for 10 weeks. Male Fischer 344 rats were given drinking water containing 1 μg/mL or 5 μg/mL sodium selenite. Selenium levels were monitored in serum and liver tissue over the 10-week period, and the kinetics of induction of the redox-active cytosolic selenoenzyme thioredoxin reductase were followed. Selenite exposure via drinking water caused a dose-dependent increase in blood and liver selenium levels, with plateaus at 6 and 8 weeks, respectively. These plateaus were reached at the same level of selenium regardless of dose, and no further accumulation was observed. A selenium-dependent increase in the activity of TrxR1 in parallel with the increase in liver selenium levels was also seen, and the induction of TrxR1 mRNA was seen only during the first three days of treatment, when the levels of selenium in the liver were increasing. Sodium selenite at 1 and 5 μg/mL did not affect body weight or relative liver mass. We concluded that long-term treatment with selenite did not cause accumulation of selenium and that the activity of TrxR1 in the liver rose with the selenium levels. We therefore suggest that sodium selenite at doses up to 5 μg/mL could be used for long-term tumour prevention.     

Intracellular glutathione is a cofactor in methylseleninic acid-induced apoptotic cell death of human hepatoma HEPG(2) cells

Selenium is a widely studied dietary anticancer agent. Among various selenium compounds, the methylated forms appear to be particularly effective in cancer prevention. Intracellular glutathione (GSH) is known to be involved in the metabolism of many methylated forms of selenium. In this study, we investigated the role of intracellular GSH in methylseleninic acid (MSeA)-induced apoptosis in human hepatoma (HepG(2)) cells. MSeA was shown to deplete intracellular GSH rapidly, preceding the typical apoptotic changes such as DNA fragmentation as measured by the TUNEL assay. When the intracellular GSH concentration was enhanced using N-acetylcysteiene (NAC) (a GSH synthesis precursor) and decreased using buthionine sufoxamine (BSO) (a GSH synthesis inhibitor), NAC markedly augmented MSeA-induced apoptosis, while BSO significantly inhibited MSeA-induced apoptosis. Different from the effect of sodium selenite, there was no measurable superoxide radical level in MSeA-treated cells. These observations suggest that intracellular GSH mainly acts as a cofactor to facilitate MSeA-induced apoptosis, while its antioxidant function becomes largely irrelevant. It is thus postulated that some cancer cells, such as liver cancer cells with higher level of intracellular GSH, would be more susceptible to MSeA cytotoxicity.     

Effects of selenium compounds on proliferation and epigenetic marks of breast cancer cells

Breast cancer is a global public health problem and the most frequent cause of cancer death among women. Mammary carcinogenesis is driven not only by genetic alterations but also by epigenetic disturbances. Because epigenetic marks are potentially reversible they represent promising molecular targets for breast cancer prevention interventions. Selenium is a promising anti-breast cancer trace element that has shown the modulation of DNA methylation and histone post-translational modifications in other malignancies. This study aimed to evaluate the effects of selenium compounds [methylseleninic acid (MSA) and selenite] on cell proliferation and death, expression of the tumor suppressor gene RASSF1A and epigenetic marks in MCF-7 human breast adenocarcinoma cells. Treatment with MSA or selenite markedly inhibited (P < 0.05) in a dose-dependent manner the proliferation of MCF-7 cells. MSA induced (P < 0.05) G2/M cell arrest while selenite presented the opposite effect. Regarding cell death induction, MSA acted mainly by inducing apoptosis (P < 0.05), while selenite only induced necrosis (P < 0.05). Furthermore selenite, but not MSA, markedly induced (P < 0.05) cytotoxicity and increased (P < 0.05) RASSF1A expression. Both selenium compounds inhibited (P < 0.05) DNMT1 expression. MSA decreased (P < 0.05) H3K9me3 and increased (P < 0.05) H4K16ac, while selenite decreased (P < 0.05) this latter histone mark. To the best of our knowledge this is the first report showing that selenite and MSA modulate epigenetic marks specifically in breast cancer cells. Our data reinforce the anti-breast cancer potential of selenium that is dependent on its chemical form. Furthermore the data show that epigenetic mechanisms represent relevant molecular targets involved in selenium inhibitory effects in breast cancer cells.     

Effects of metal ions and selenoamino acids on induction of glutathione peroxidase in mouse neuroblastoma

The induction of glutathione peroxidase in mouse neuroblastoma cells by selenite is enhanced by equimolar amounts of arsenate, arsenite, molybdate, chromic or dichromate ions. At equimolar selenium concentration, selenite, selenocystine and selenomethionine induced glutathione peroxidase activities having the ratios 4:4:1. Protein synthesis inhibitors prevented the induction of glutathione peroxidase by selenite indicating that de novo protein synthesis is required.     

Selenoprotein expression is regulated at multiple levels in prostate cells

Selenium supplementation in a population with low basal blood selenium levels has been reported to decrease the incidence of several cancers including prostate cancer. Based on the clinical findings, it is likely that the antioxidant function of one or more selenoproteins is responsible for the chemopreventive effect, although low molecular weight seleno-compounds have also been posited to selectively induce apoptosis in transformed cells. To address the effects of selenium supplementation on selenoprotein expression in prostate cells, we have undertaken an analysis of antioxidant selenoprotein expression as well as selenium toxicity in non-tumorigenic prostate epithelial cells （RWPE- 1 ） and prostate cancer cells （LNCaP and PC-3）. Our results show that two of the glutathione peroxidase family members （GPX1 and GPX4） are highly induced by supplemental selenium in prostate cancer cells but only slightly induced in RWPE-1 cells. In addition, GPX 1 levels are dramatically lower in PC-3 cells as compared to RWPE- 1 or LNCaP cells. GPX2 protein and mRNA, however, are only detectable in RWPE-1 cells. Of the three selenium compounds tested （sodium selenite, sodium selenate and selenomethionine）, only sodium selenite shows toxicity in a physiological range of selenium concentrations. Notably and in contrast to previous studies, RWPE-1 cells were significantly more sensitive to selenite than either of the prostate cancer cell lines. These results demonstrate that selenoproteins and selenium metabolism are regulated at multiple levels in prostate cells.     

Inhibiting effect of selenium on oxysterols-induced apoptosis of rat vascular smooth muscle cells

To evaluate the cytoprotection mechanism of selenium against cholestane-3beta,5alpha,6beta-triol (3-triol)-induced vascular smooth muscle cells (VSMCs) damage, cell viability was analyzed by 3-(4,5-dimethylthiazol-2 -yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cell count, the percentage release of lactate dehydrogenase (LDH) from the cell was assessed, and apoptosis was detected by DNA laddering and flow cytometric analysis. Meanwhile, the activity of glutathione peroxidase (GPx) of VSMCs was measured. The results showed that 3-triol could inhibit proliferation of VSMCs time-dependently and dose-dependently, increase the percentage release of LDH and induce VSMCs apoptosis. While the cytotoxicity and cells apoptosis induced by 3-triol was attenuated by pretreatment of cells with low concentration of sodium selenite, and the longer the pretreated time was, the stronger the inhibition was. Preincubation of cells with sodium selenite (50 nM) for 12 or 24 h before 1, 5, 10, 25, or 50 microM 3-triol exposure, the cell viabilities increased 28.5% (P<0.05), 18.3%, 197.6% (P<0.01), 66.7%, 50.0% or 35.1% (P<0.05), 62.3% (P<0.05), 329.6% (P<0.01), 221.3% (P<0.05), 74.0% compared with the control cells, respectively. When the cells were preincubated with sodium selenite (50 nM) for 12 or 24 h before exposure to 3-triol (10 microM), the percent of apoptotic cells reduced from 30.47+/-15.34% to 26.88+/-17.32% or 7.41+/-5.46% (P<0.05). With preincubation of sodium selenite (50 nM) for 24 h, the GPx activity of VSMCs increased 18.5% compared with control (P<0.05). In conclusion, the results suggested that incubated VSMCs could absorb and transfer selenite as selenoprotrein, such as GPx, if the time is long enough and VSMCs selenoproteins can protect markedly against apoptosis and damage induced by 3-triol in VSMCs.     

Selenium antagonizes the induction of human heme oxygenase by arsenite and cadmium ions.

Effects of selenium compounds on the induction of heme oxygenase in human cells exposed to sodium arsenite or cadmium chloride have been investigated by an immunoblotting technique. Exposure of HeLa cells to arsenite or cadmium ions caused a marked increase in the synthesis of heme oxygenase, and the presence of sodium selenite suppressed the induction. DL-Selenocystine was an effective suppressor, and sodium selenate was less effective. DL-Selenomethionine had no effect. Northern blot analysis showed that selenite abolished the induction of heme oxygenase mRNA in the cells exposed to arsenite or cadmium ions. These results indicated that selenium antagonizes the induction of heme oxygenase by heavy metals ions.