Selenocompounds in plants and animals and their biological significance

Major differences among chemopreventive organoselenocompounds in the sustained elevation of cytoprotective genes

Cytoprotective enzyme elevation through the nuclear erythroid 2 p45-related factor 2 (Nrf2)-Kelch-like ECH-associated protein 1/antioxidant response element pathway has been promulgated for cancer prevention. This study compares the redox insult and sustained cytoprotective enzyme elevation by organoselenocompounds and sulforaphane (SF) in lung cells. SF elicited a rise in reactive oxygen species (ROS) and drop in glutathione (GSH) at 2 h; nuclear accumulation of Nrf2 at 4 h; and a GSH rebound and elevation in NAD(P)H quinone oxidoreductase (NQO1), thioredoxin reductase (TR1), and glutamate-cysteine ligase (GCL) at 24 h. Selenocystine (SECY) elicited a similar 24 h response, despite lesser earlier time-point changes. 2-Cyclohexylselenazolidine-4-carboxylic acid effects were similar to SECY's but with a larger Nrf2 change and the largest 24 h increase in GSH, GCL, TR1, and NQO1 of any compound investigated. Selenomethionine elicited a similar acute rise in ROS, but lesser depletion of GSH, no 4 h increase in nuclear Nrf2, only minor 24 h elevations in TR1 and NQO1, and a GCL elevation insufficient to elevate GSH.

A metallomics approach discovers selenium-containing proteins in selenium-enriched soybean

Our previous study found that high-molecular-weight selenium (Se) species make up 82% of the total Se in the bean of Se-enriched soybean plants (Chan et al. 2010, Metallomics, 2(2): p. 147-153). The Se species have been commonly seen in other plants in addition to soybean, but their identities remain unresolved. The present study employs a multi-technique metallomics approach to characterize the proteins containing Se in the beans of Se-enriched soybean plants. Two main categories of proteins, maturation proteins and protease inhibitors, were found in Se-containing high-performance liquid chromatography (HPLC) fractions. The proteins were screened by two-dimensional HPLC-inductively coupled plasma mass spectrometry, size-exclusion chromatography, and anion-exchange chromatography, and the Se-containing fractions were then identified by peptide mapping using HPLC-Chip-electrospray ion trap mass spectrometry. Based on the belief that Se goes into proteins through non-specific incorporation, a new method was designed and applied for the Se-containing peptide identification. The Se-containing peptide KSDQSSSYDDDEYSKPCCDLCMCTRS, part of the sequence of protein Bowman-Birk proteinase isoinhibitor (Glycine max), was found in one of the Se-containing fractions. The nutritional value of the Se-containing proteins in Se-enriched soybeans will be an interesting topic for the future studies.

Encapsulated nanoepigallocatechin-3-gallate and elemental selenium nanoparticles as paradigms for nanochemoprevention

Chemoprevention that impedes one or more steps in carcinogenesis, via long-term administration of naturally occurring or synthetic compounds, is widely considered to be a crucial strategy for cancer control. Selenium (Se) has chemopreventive effects, but its application is limited due to a low therapeutic index as shown in numerous animal experiments. In contrast to Se, which was known for its toxicity prior to the discovery of its beneficial effects, the natural compound epigallocatechin-3-gallate (EGCG) was originally considered to be nontoxic. Due to its preventive effects on many types of cancer in various animal models, EGCG has been regarded as a prime example of a promising chemopreventive agent without major toxicity concerns. However, very recently, evidence has accumulated showing that efficacious doses of EGCG used in health promotion may not be far from its toxic dose level. Therefore, both Se and EGCG need to be modified by novel pharmaceutical technologies to attain enhanced efficacy and/or reduced toxicity. Nanotechnology may be one of these technologies. In support of this hypothesis, the characteristics of polylactic acid and polyethylene glycol-encapsulated nano-EGCG and elemental Se nanoparticles dispersed by bovine serum albumin are reviewed in this article. Encapsulation of EGCG to form nano-EGCG leads to its enhanced stability in plasma and remarkably superior chemopreventive effects, with more than tenfold dose advantages in inducing apoptosis and inhibition of both angiogenesis and tumor growth. Se at nanoparticle size (“Nano-Se”), compared with Se compounds commonly used in dietary supplements, has significantly lower toxicity, without compromising its ability to upregulate selenoenzymes at nutritional levels and induce phase II enzymes at supranutritional levels.

Designing the selenium and bladder cancer trial (SELEBLAT), a phase lll randomized chemoprevention study with selenium on recurrence of bladder cancer in Belgium

Background

In Belgium, bladder cancer is the fifth most common cancer in males (5.2%) and the sixth most frequent cause of death from cancer in males (3.8%). Previous epidemiological studies have consistently reported that selenium concentrations were inversely associated with the risk of bladder cancer. This suggests that selenium may also be suitable for chemoprevention of recurrence.

Method

The SELEBLAT study opened in September 2009 and is still recruiting all patients with non-invasive transitional cell carcinoma of the bladder on TURB operation in 15 Belgian hospitals. Recruitment progress can be monitored live at http://www.seleblat.org. Patients are randomly assigned to selenium yeast (200 μg/day) supplementation for 3 years or matching placebo, in addition to standard care. The objective is to determine the effect of selenium on the recurrence of bladder cancer. Randomization is stratified by treatment centre. A computerized algorithm randomly assigns the patients to a treatment arm. All study personnel and participants are blinded to treatment assignment for the duration of the study.

Design

The SELEnium and BLAdder cancer Trial (SELEBLAT) is a phase III randomized, placebo-controlled, academic, double-blind superior trial.

Discussion

This is the first report on a selenium randomized trial in bladder cancer patients.

Trial registration

ClinicalTrials.gov identifier: NCT00729287

Imaging translocation and transformation of bioavailable selenium by Stanleya pinnata with X-ray microscopy

Selenium hyperaccumulator Stanleya pinnata, Colorado ecotype, was supplied with water-soluble and biologically available selenate or selenite. Selenium distribution and tissue speciation were established using X-ray microscopy (micro-X-ray fluorescence and transmission X-ray microscopy) in two dimensions and three dimensions. The results indicate that S. pinnata tolerates, accumulates, and volatilizes significant concentrations of selenium when the inorganic form supplied is selenite and may possess novel metabolic capacity to differentiate, metabolize, and detoxify selenite concentrations surpassing field concentrations. The results also indicate that S. pinnata is a feasible candidate to detoxify selenium-polluted soil sites, especially locations with topsoil polluted with soluble and biologically available selenite.

Identification and characterization of selenate- and selenite-responsive genes in a Se-hyperaccumulator Astragalus racemosus

Plants with capacity to accumulate high levels of selenium (Se) are desired for phytoremediation and biofortification. Plants of genus Astragalus accumulate and tolerate high levels of Se, but their slow growth, low biomass and non-edible properties limit their direct utilization. Genetic engineering may be an alternative way to produce edible or high biomass Se-accumulating plants. The first step towards this goal is to isolate genes that are responsible for Se accumulation and tolerance. Later, these genes can be introduced into other edible and high biomass plants. In the present study, we applied fluorescent differential display to analyze the transcript profile of Se-hyperaccumulator A. racemosus treated with 20 μM selenate (K(2)SeO(4)) for 2 weeks. Among 125 identified Se-responsive candidate genes, the expression levels of nine were induced or suppressed more than twofold by selenate treatment in two independent experiments while 14 showed such changes when treated with selenite (K(2)SeO(3)). Six of them were found to respond to both selenate and selenite treatments. A novel gene CEJ367 was found to be highly induced by both selenate (1,920-fold) and selenite (579-fold). Root- or shoot-preferential expression of nine genes was further investigated. These identified genes may allow us to create Se-enriched transgenic plants.

Metallomic study of selenium biomolecules metabolized by the microalgae Chlorella sorkiniana in the biotechnological production of functional foods enriched in selenium

The optimization of culture conditions for selenium (Se) bioaccumulation in the microalgae Chlorella sorokiniana growth in a Na2SeO4-enriched medium was explored, in order to obtain a suitable approach for the biotechnological production of a Se-enriched food. Se concentration (as Na2SeO4) in the culture medium until 100 μg ml–1 allows the growth of algae colonies during long periods of time, until 300 h, but higher concentrations cause the collapse of the colony. The bioaccumulation process causes a concentration of Se in algae in the order of 3 μg g–1 in about 100 h. A metallomic analytical approach based in the coupling high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS), which uses two chromatographic switched columns (C-18 and chiral columns) with ICP-MS detection, has been applied to characterize the different Se metabolites, including chiral forms, in both the algae and culture medium. The results reveal that selenate present in the culture is biotransformed in selenocystine (SeCys2), selenomethylselenocysteine (SeMeSeCys), and mainly selenomethionine (SeMet) by the algae, although appreciable concentration of Se(VI) is also present in cells. When algae are cultured under sulfur (S) deficiency conditions, the accumulation of Se in the cell is enhanced owing to the great chemical similarity between S and Se that promotes the substitution of S by Se in the cell metabolism, therefore, SeMet concentration in the algae increases from about 7 to 15 μg g–1 and Se(VI) from 15 to 25 μg g–1, after 500 h of exposure.

Accumulation and speciation of selenium in plants as affected by arbuscular mycorrhizal fungus Glomus mosseae

Effects of arbuscular mycorrhizal fungus (Glomus mosseae) on the accumulation and speciation of selenium (Se) in alfalfa, maize, and soybean were investigated by using Se(IV)-spiked soil. Mycorrhizal inoculation decreased Se accumulation in roots and shoots of all the plants at Se spiked level of 0 or 2 mg kg(-1), while an increased Se accumulation was observed in alfalfa shoots and maize roots and shoots at the spiked level of 20 mg kg(-1). Concentration of inorganic Se (especially Se(VI)) in roots and shoots of the three plants was much higher in mycorrhizal than non-mycorrhizal treatment. Mycorrhizal inoculation decreased the portion of total organic Se in plant tissues with the exception of alfalfa and maize shoots at Se spiked level of 20 mg kg(-1), in which organic Se portion did not reduced greatly (<5%) for mycorrhizal treatment. Mycorrhizal effects on alfalfa and maize were more obvious than on soybean in terms of root colonization rate, biomass, and Se accumulation.

Glutathione peroxidase-1 in health and disease: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species, such as superoxide and hydrogen peroxide, are generated in all cells by mitochondrial and enzymatic sources. Left unchecked, these reactive species can cause oxidative damage to DNA, proteins, and membrane lipids. Glutathione peroxidase-1 (GPx-1) is an intracellular antioxidant enzyme that enzymatically reduces hydrogen peroxide to water to limit its harmful effects. Certain reactive oxygen species, such as hydrogen peroxide, are also essential for growth factor-mediated signal transduction, mitochondrial function, and maintenance of normal thiol redox-balance. Thus, by limiting hydrogen peroxide accumulation, GPx-1 also modulates these processes. This review explores the molecular mechanisms involved in regulating the expression and function of GPx-1, with an emphasis on the role of GPx-1 in modulating cellular oxidant stress and redox-mediated responses. As a selenocysteine-containing enzyme, GPx-1 expression is subject to unique forms of regulation involving the trace mineral selenium and selenocysteine incorporation during translation. In addition, GPx-1 has been implicated in the development and prevention of many common and complex diseases, including cancer and cardiovascular disease. This review discusses the role of GPx-1 in these diseases and speculates on potential future therapies to harness the beneficial effects of this ubiquitous antioxidant enzyme.

Comparison of different forms of dietary selenium supplementation on growth performance, meat quality, selenium deposition, and antioxidant property in broilers

This study was conducted to investigate the effects of different sources of dietary selenium (Se) supplementation on growth performance, meat quality, Se deposition, and antioxidant property in broilers. A total of 600 one-day-old Ross 308 broilers with an average body weight (BW) of 44.30 ± 0.49 g were randomly allotted to three treatments, each of which included five replicates of 40 birds. These three groups received the same basal diet containing 0.04 mg Se/kg, supplemented with 0.15 mg Se/kg from sodium selenite (SS) or from L-selenomethionine (L-Se-methionine (Met)) or from D-selenomethionine (D-Se-Met). The experiment lasted 42 days. Both Se source and time significantly influenced (p < 0.01) drip loss of breast muscle. Supplementation with L-Se-Met and D-Se-Met were more effective (p < 0.05) in decreasing drip loss than SS. Besides, the pH value of breast muscle was also significantly influenced (p < 0.05) by time. The SS-supplemented diet increased more (p < 0.05) liver, kidney, and pancreas glutathione peroxidase (GSH-Px) activities than the D-Se-Met-supplemented diet. In addition, L-Se-Met increased more (p < 0.01) liver and pancreas GSH-Px activities than D-Se-Met. The antioxidant status was greatly improved in broilers of L-Se-Met-treated group in comparison with the SS-treated group and was illuminated by the increased glutathione (GSH) concentration in serum, liver, and breast muscle (p < 0.05); superoxide dismutase (SOD) activity in liver (p < 0.01); total antioxidant capability (T-AOC) in kidney, pancreas, and breast muscle (p < 0.05) and decreased malondialdehyde (MDA) concentration in kidney and breast muscle (p < 0.05) of broilers. Besides, supplementation with D-Se-Met was more effective (p < 0.01) in increasing serum GSH concentration and decreasing breast muscle MDA concentration than SS. L-Selenomethionine supplementation significantly increased GSH concentration in liver and breast muscle (p < 0.05); SOD activity in liver (p < 0.01); and T-AOC in liver, pancreas, and breast muscle (p < 0.05) of broilers, compared with broilers fed D-Se-Met diet. The addition of L-Se-Met and D-Se-Met increased (p < 0.01) Se concentration in serum and different organs studied of broilers in comparision with broilers fed SS diet. Therefore, dietary L-Se-Met and D-Se-Met supplementation could improve antioxidant capability and Se deposition in serum and tissues and reduce drip loss of breast muscle in broilers compared with SS. Besides, L-Se-Met is more effective than D-Se-Met in improving antioxidant status in broilers.

Selenium Concentrations of Selected Medicinal and Aromatic Plants in Turkey

Recent scientific studies have proven the importance of trace elements on human health. The main food supplies are plants and animals, which are significant sources of these minerals. Studies on determining mineral compositions of herbs, spices and some other crops have increased all over the world. Published works revealed that spices, herbs and medicinal plants should be consumed to obtain beneficial trace elements. Selenium (Se), one of the most vital trace elements, has a significant role in human diet acting as a preventative agent against some serious illnesses. Despite numerous scientific works on mineral compositions of medicinal and aromatic plants, investigations of selenium content in these foods could not be successfully studied until recently due to the lack of suitable analytical methods for selenium analysis. Thus, publications on selenium concentrations of foods are recent. In this regard, selenium contents of some medicinal and aromatic plants commonly used as spices, herbal teas and traditional medicines in Turkey were studied in the present research. Selenium contents of the most used parts of these plants were analyzed by ICP-OES (Varian Vista-Pro, Australia). Of the analyzed 26 medicinal and aromatic plants, the highest Se concentration (1133 μg kg-1) was found in sweet basil ( Ocimum basilicum L.) and the lowest in sumac ( Rhus coriaria L.) fruits (11 μg kg-1).

Organic and inorganic selenium: I. Oral bioavailability in ewes

Although the essentiality of dietary Se for sheep has been known for decades, the chemical source and Se dosage for optimal health remain unclear. In the United States, the Food and Drug Administration (FDA) regulates Se supplementation, regardless of the source of Se, at 0.3 mg of Se/kg of diet (as fed), which is equivalent to 0.7 mg of Se/d or 4.9 mg of Se/wk per sheep. The objectives of this study were to evaluate the effects of Se source (inorganic vs. organic) and supplementation rate (FDA vs. supranutritional rates of 14.7 and 24.5 mg of Se/wk) on whole-blood (WB) and serum-Se concentrations. Mature ewes (n = 240) were randomly assigned to 8 treatment groups (n = 30 each) based on Se supplementation rate (4.9, 14.7, and 24.5 mg of Se•wk(-1)•sheep(-1)) and source [Na-selenite, Na-selenate (4.9 mg/wk only), and organic Se-yeast] with a no-Se control group (0 mg of Se/wk). Treatment groups were balanced for healthy and footrot-affected ewes. For 1 yr, ewes were individually dosed once weekly with 0, 4.9, 14.7, or 24.5 mg of Se, quantities equivalent to their summed daily supplementation rates. Serum- and WB-Se concentrations were measured every 3 mo in all ewes; additionally, WB-Se concentrations were measured once monthly in one-half of the ewes receiving 0 or 4.9 mg of Se/wk. Ewes receiving no Se showed a 78.8 and 58.8% decrease (P < 0.001) in WB- (250 to 53 ng/mL) and serum- (97 to 40 ng/mL) Se concentrations, respectively, over the duration of the study. Whole-blood Se decreased primarily during pregnancy (-57%; 258 to 111 ng/mL) and again during peak lactation (-44%; 109 to 61 ng/mL; P < 0.001). At 4.9 mg of Se/wk, Se-yeast (364 ng/mL, final Se concentration) was more effective than Na-selenite (269 ng/mL) at increasing WB-Se concentrations (P < 0.001). Supranutritional Se-yeast dosages increased WB-Se concentrations in a dose-dependent manner (563 ng/mL, 14.7 mg of Se/wk; 748 ng/mL, 24.5 mg of Se/wk; P < 0.001), whereas WB-Se concentrations were not different for the Na-selenite groups (350 ng/mL, 14.7 mg of Se/wk; 363 ng/mL, 24.5 mg of Se/wk) or the 4.9 mg of Se/wk Se-yeast group (364 ng/mL). In summary, the dose range whereby Se supplementation increased blood Se concentrations was more limited for inorganic Na-selenite than for organic Se-yeast. The smallest rate (FDA-recommended quantity) of organic Se supplementation was equally effective as supranutritional rates of Na-selenite supplementation in increasing WB-Se concentrations, demonstrating the greater oral bioavailability of organic Se.

Selenium and thyroid autoimmunity

The trace element selenium (Se) occurs in the form of the amino acid selenocysteine in selenoproteins. Selenoproteins exerts multiple physiological effects in human health, many of which are related with regulation of reduction-oxidation processes. In fact, the selenoenzyme families of glutathione peroxidase (GPx) and thioredoxin reductase (TRx) display the ability to act as antioxidants, protecting cells from oxidative damage. Furthermore, another class of selenoproteins are the iodothyronine deiodinase enzymes (DIO), which catalyze the conversion of thyroxine (T4) in triiodothyronine (T3), then exerting a fine tuned control on thyroid hormones metabolism. Several studies have investigated the potential positive effects of Se supplementation in thyroid diseases, characterized by increased levels of hydrogen peroxide and free radicals, like autoimmune chronic thyroiditis. These studies have supplied evidences indicating that Se supplementation, maximizing the antioxidant enzymes activity, may reduce the thyroid inflammatory status. Then, it may be postulated that Se could play a therapeutical role in thyroid autoimmune diseases. Despite the fact that recent studies seem to be concordant about Se beneficial effects in decreasing thyroid peroxidase antibodies (TPOAb) titers and ameliorating the ultrasound echogenicity pattern, several doubts have to be still clarified, before advising Se supplementation in chronic autoimmune thyroiditis.

Role of selenium on calcium signaling and oxidative stress-induced molecular pathways in epilepsy

Epilepsy is one of the oldest neurological conditions known to humankind. It is known that oxidative stress and generation of reactive oxygen species are a cause and consequence of epileptic seizures. Although recent years have seen tremendous progress in the molecular biology and metabolism of selenium, we still know little about the cell type-specific and temporal pattern of selenium and its derivatives in the brain of epileptic humans and experimental animals. It has been suggested that some antiepileptic drug therapies such as valproic acid, deplete the total body selenium level and selenium-dependent glutathione peroxidase (GSH-Px) activity although therapy with a new epileptic drug, topiramate, activated GSH-Px activity in epileptic animals and humans. An observation of lower blood or tissue selenium level and GSH-Px activity in epileptic patients and animals compared to controls in recent publications may support the proposed crucial role of selenium level and GSH-Px activity in the pathogenesis of epilepsy. Selenium is incorporated into an interesting class of molecules known as selenoproteins that contain the modified amino acid, selenocysteine. There are signs of selenium and selenoprotein deficiency in the pathogenesis of epilepsy. In conclusion, there is convincing evidence for the proposed crucial role of selenium and deficiency of GSH-Px enzyme activity in epilepsy pathogenesis. Blood GSH-Px activities could be a reliable indicator of selenium deficiency in patients with epilepsy.

Translocation and re-translocation of selenium taken up from nutrient solution during vegetative growth in spring wheat

BACKGROUND

Selenium (Se) is an essential micronutrient for humans, but the Se level in food plants in northern Europe is generally inadequate to meet human nutritional requirements. Commonly, food plant Se fortification is achieved by selenate fertilisation, but the effect of nitrogen (N) and sulphur (S) supply on the translocation and re-translocation of Se is unknown. Therefore the effect of N and S supply on ⁷⁵selenate/⁷⁵Se translocation and re-translocation during vegetative growth in spring wheat (Triticum aestivum) was studied.

RESULTS

The ⁷⁵Se activity in wheat varied from 148 to 549, from 277 to 1815 and from 171 to 1343 Bq ⁷⁵Se in plants exposed at Zadoks growth stages Z1.4, Z1.5 and Z1.6 respectively. Approximately 85% of the plant ⁷⁵Se was translocated into young leaves. High N supply enhanced the re-translocation of ⁷⁵Se from the stem to maturing leaves, while S inhibited this process. The relative proportion of ⁷⁵Se in L4, L5 and L6 increased with increasing N supply at low sulfate concentrations.

CONCLUSION

Selenium in the stem is more re-transportable than Se in the leaves, and the re-translocation is dependent on sulfate supply. When the sulfate supply is sufficient for plant development, less ⁷⁵Se is re-translocated from older to growing leaves.

The organochalcogen 3-methyl-1-phenyl-2-(phenylseleno)oct-2-en-1-one induces oxidative stress in heart, liver, and kidney of rats

The objective of this study was to investigate the in vitro effects of the organochalcogen 3-methyl-1-phenyl-2-(phenylseleno)oct-2-en-1-one on some parameters of oxidative stress in liver, kidney, and heart of 10-day-old rats. The homogenates of liver, kidney, and heart were incubated for 1 h in the absence (control) or in the presence of 1, 10, or 30 μM of the organoselenium and thiobarbituric acid reactive substances, carbonyl, and the activity of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) were measured. First, we tested the influence of the compound on 1,1-diphenyl-2-picrylhydrazyl (DPPH(•)) radical scavenging and verified that the organochalcogen did not have any antioxidant properties. We observed an increase of lipid peroxidation in all concentrations tested in heart and kidney, while in liver only in the concentrations of 10 and 30 μM. Moreover, we also verified an enhance of protein oxidation in the concentrations of 10 and 30 μM in kidney. On the other hand, the compound caused a reduction on the activity of CAT in heart (10 and 30 μM), liver (30 μM), and kidney (30 μM). The activity of SOD was increased in heart (10 and 30 μM), while in liver (30 μM) and in kidney (10 and 30 μM) the activity was reduced. Our findings indicate that this organoselenium compound induces oxidative stress in liver, heart, and kidney of immature rats, collaborating to the fact that these tissues are potential targets for the organochalcogen action.

Interaction of nanoparticles with edible plants and their possible implications in the food chain

The uptake, bioaccumulation, biotransformation, and risks of nanomaterials (NMs) for food crops are still not well understood. Very few NMs and plant species have been studied, mainly at the very early growth stages of the plants. Most of the studies, except one with multiwalled carbon nanotubes performed on the model plant Arabidopsis thaliana and another with ZnO nanoparticles (NPs) on ryegrass, reported the effect of NMs on seed germination or 15-day-old seedlings. Very few references describe the biotransformation of NMs in food crops, and the possible transmission of the NMs to the next generation of plants exposed to NMs is unknown. The possible biomagnification of NPs in the food chain is also unknown.

Evaluation of genotypic variation of broccoli (Brassica oleracea var. italic) in response to selenium treatment

Broccoli (Brassica oleracea var. italic) fortified with selenium (Se) has been promoted as a functional food. Here, we evaluated 38 broccoli accessions for their capacity to accumulate Se and for their responses to selenate treatment in terms of nutritional qualities and sulfur gene expresion. We found that the total Se content varied with over 2-fold difference among the leaf tissues of broccoli accessions when the plants were treated with 20 μM Na(2)SeO(4). Approximately half of total Se accumulated in leaves was Se-methylselenocysteine and selenomethionine. Transcriptional regulation of adenosine 5'-phosphosulfate sulfurylase and selenocysteine Se-methyltransferase gene expression might contribute to the different levels of Se accumulation in broccoli. Total glucosinolate contents were not affected by the concentration of selenate application for the majority of broccoli accessions. Essential micronutrients (i.e., Fe, Zn, Cu, and Mn) remained unchanged among half of the germplasm. Moreover, the total antioxidant capacity was greatly stimulated by selenate in over half of the accessions. The diverse genotypic variation in Se, glucosinolate, and antioxidant contents among accessions provides the opportunity to breed broccoli cultivars that simultaneously accumulate Se and other health benefit compounds.

Selenium in human health and disease

This review covers current knowledge of selenium in the environment, dietary intakes, metabolism and status, functions in the body, thyroid hormone metabolism, antioxidant defense systems and oxidative metabolism, and the immune system. Selenium toxicity and links between deficiency and Keshan disease and Kashin-Beck disease are described. The relationships between selenium intake/status and various health outcomes, in particular gastrointestinal and prostate cancer, cardiovascular disease, diabetes, and male fertility, are reviewed, and recent developments in genetics of selenoproteins are outlined. The rationale behind current dietary reference intakes of selenium is explained, and examples of differences between countries and/or expert bodies are given. Throughout the review, gaps in knowledge and research requirements are identified. More research is needed to improve our understanding of selenium metabolism and requirements for optimal health. Functions of the majority of the selenoproteins await characterization, the mechanism of absorption has yet to be identified, measures of status need to be developed, and effects of genotype on metabolism require further investigation. The relationships between selenium intake/status and health, or risk of disease, are complex but require elucidation to inform clinical practice, to refine dietary recommendations, and to develop effective public health policies.

A human model of selenium that integrates metabolism from selenite and selenomethionine

Selenium (Se) metabolism is affected by its chemical form in foods and by its incorporation (specific vs. nonspecific) into multiple proteins. Modeling Se kinetics may clarify the impact of form on metabolism. Although the kinetics of Se forms have been compared in different participants, or the same participants at different times, direct comparisons of their respective metabolism in the same participants have not been made. The aim of this study was to simultaneously compare kinetics of absorbed Se from inorganic selenite (Sel) and organic selenomethionine (SeMet) in healthy participants (n = 31). After oral administration of stable isotopic tracers of each form, urine and feces were collected for 12 d and blood was sampled over 4 mo. Tracer enrichment was determined by isotope-dilution-GC-MS. Using WinSAAM, a compartmental model was fitted to the data. Within 30 min of ingestion, Se from both forms entered a common pool, and metabolism was similar for several days before diverging. Slowly turning-over pools were required in tissues and plasma for Se derived from SeMet to account for its 3-times-higher incorporation into RBC compared with Se from Sel; these presumably represent nonspecific incorporation of SeMet into proteins. Pool sizes and transport rates were determined and compared by form and gender. The final model consisted of 11 plasma pools, 2 pools and a delay in RBC, and extravascular pools for recycling of Se back into plasma. This model will be used to evaluate changes in Se metabolism following long-term (2 y) Se supplementation.

Selenium accumulation in lettuce germplasm

Selenium (Se) is an essential micronutrient for animals and humans. Increasing Se content in food crops offers an effective approach to reduce the widespread selenium deficiency problem in many parts of the world. In this study, we evaluated 30 diverse accessions of lettuce (Lactuca sativa L.) for their capacity to accumulate Se and their responses to different forms of Se in terms of plant growth, nutritional characteristics, and gene expression. Lettuce accessions responded differently to selenate and selenite treatment, and selenate is superior to selenite in inducing total Se accumulation. At least over twofold change in total Se levels between cultivars with high and low Se content was found. Synergistic relationship between Se and sulfur accumulation was observed in nearly all accessions at the selenate dosage applied. The change in shoot biomass varied between lettuce accessions and the forms of Se used. The growth-stimulated effect by selenate and the growth-inhibited effect by selenite were found to be correlated with the alteration of antioxidant enzyme activities. The different ability of lettuce accessions to accumulate Se following selenate treatment appeared to be associated with an altered expression of genes involved in Se/S uptake and assimilation. Our results provide important information for the effects of different forms of Se on plant growth and metabolism. They will also be of help in selecting and developing better cultivars for Se biofortification in lettuce.

Effect of organic and inorganic forms of selenium in diets on turkey semen quality

The effects of Se supplementation and its organic or inorganic form on semen quantitative parameters (ejaculate volume, sperm concentration, and total number of sperm) and biochemical parameters of seminal plasma (protein concentration, acid phosphatase activity, superoxide dismutase activity, and total antioxidant capacity) were investigated over a 25-wk reproductive season. Additionally, DNA fragmentation and motility characteristics of turkey spermatozoa were measured. The parameters of turkey semen in relation to yellow semen syndrome were also determined. Twenty-four males (Big 6) were divided into 3 experimental groups differing in form of Se supplementation (no Se supplementation, 0.3 mg/kg of inorganic Se from sodium selenite and 0.3 mg/kg of organic Se from Sel-Plex, Alltech Inc., Nicholasville, KY). Dietary Se supplementation enhanced the sperm concentration and total number of sperm and did not influence the antioxidative properties of turkey seminal plasma and most biochemical parameters. Only seminal plasma acid phosphatase activity was increased in turkeys fed inorganic Se. The main sperm DNA fragmentation parameters were not affected by dietary Se. The highest percentage of motile spermatozoa (85%) was recorded for the semen of turkeys fed organic Se. Values of the biochemical parameters (acid phosphatase, superoxide dismutase, total antioxidant capacity) of seminal plasma increased during the reproductive season. Yellow semen was characterized by increased biochemical parameters and decreased spermatozoa motility characteristics. However, the percentage of motile spermatozoa did not differ between white and yellow semen. Organic Se seemed to be the preferred form of diet supplementation in comparison with inorganic Se. Biochemical parameters of semen and spermatozoa motility parameters appear to be useful for evaluating the effect of age on semen quality. Monitoring the DNA fragmentation of spermatozoa at the end of the reproductive season could be a useful tool for monitoring turkey semen quality. Increased superoxide dismutase activity can be used as an indicator of yellow semen. A decline in the quality of yellow semen can be related to a decrease in the spermatozoa motility parameters of turkeys.

An in vitro comparison of a new vinyl chalcogenide and sodium selenate on adenosine deaminase activity of human leukocytes

Selenium (Se) is a dietary essential trace element with important biological roles. Sodium selenate (Na(2)SeO(4)) is an inorganic Se compound used in human and animal nutrition that acts as precursor for selenoprotein synthesis. The organoselenium 3-methyl-1-phenyl-2-(phenylseleno)oct-2-en-1-one (C(21)H(2)HOSe) is an α,β-unsaturated ketone functionalized vinyl chalcogenide that has been found as a potential tool in organic synthesis. Adenosine deaminase (ADA) is an important enzyme in the degradation of adenine nucleotides. In this study, we investigated the in vitro effects of both Se compounds on ADA activity and cell viability in leukocyte suspension (LS) of healthy donors (n=12). We first observed an inhibition of ADA activity using 0.1 μM of 3-methyl-1-phenyl-2-(phenylseleno)oct-2-en-1-one, and an increase in cellular viability when 30 μM were used. However, we did not observe alterations in the presence of sodium selenate. Moreover, both Se compounds did not alter lactate dehydrogenase activity and thiobarbituric acid reactive substance levels. These results suggest that the inhibition of ADA activity caused by α,β-unsaturated ketone may affect the adenosine levels in LS and modulate cell viability, attenuating conditions that involve the activation of the immune system.

Selenium speciation in soil and rice: influence of water management and Se fertilization

Rice (Oryza sativa) is the staple food for half of the world's population, but the selenium (Se) concentrations in rice grain are low in many rice-growing regions. This study investigated the effects of water management on the Se speciation dynamics in the soil solution and Se uptake and speciation in rice in a pot experiment. A control containing no Se or 0.5 mg kg(-1) of soil of selenite or selenate was added to the soil, and plants were grown under aerobic or flooded conditions. Flooding soil increased soluble Se concentration when no Se or selenite was added to the soil, but decreased it markedly when selenate was added. Selenate was the main species in the +selenate treatment, whereas selenite and selenomethionine selenium oxide were detected in the flooded soil solutions of the control and +selenite treatments. Grain Se concentration was 49% higher in the flooded than in the aerobic treatments without Se addition. In contrast, when selenate or selenite was added, the aerobically grown rice contained 25- and 2-fold, respectively, more Se in grain than the anaerobically grown rice. Analysis of Se in rice grain using enzymatic hydrolysis followed by HPLC-ICP-MS and in situ X-ray absorption near-edge structure (XANES) showed selenomethionine to be the predominant Se species. The study showed that selenate addition to aerobic soil was the most effective way to increase Se concentration in rice grain.

Dietary broccoli sprouts protect against myocardial oxidative damage and cell death during ischemia-reperfusion

Cruciferous vegetables are known for antioxidant and anti-carcinogenic effects. In the current study we asked whether dietary broccoli sprouts can protect the heart from ischemia-reperfusion. Rats were fed either control diet (sham and control groups) or a diet mixed with 2% dried broccoli sprouts for 10 days. After 10 days the isolated hearts were subjected to ischemia for 20 min and reperfusion for 2 h, and evaluated for cell death, oxidative damage, and Nrf2-regulated phase 2 enzyme activities. Broccoli sprouts feeding inhibited markers of necrosis (lactate dehydrogenase release) and apoptosis (caspase-3 activity) by 78-86%, and decreased indices of oxidative stress (thiobarbituric acid reactive substances and aconitase inactivation) by 82-116%. While broccoli sprouts increased total glutathione and activities of the phase 2 enzymes glutamate cysteine ligase and quinone reductase in liver, they did not affect these in ischemic-reperfused heart. While the mechanism is not clear, the results show that a relatively short dietary treatment with broccoli sprouts can strongly protect the heart against oxidative stress and cell death caused by ischemia-reperfusion.

Cadmium and Selenium Interaction in Mammals

Izloženost kadmiju neizbježna je zbog njegove sveprisutnosti u okolišu kao prirodne sastavnice Zemljine kore i kao onečišćenja. Kadmij može izazvati toksične učinke u gotovo cijelom organizmu vezanjem za biološke strukture i nakupljanjem u tkivima, poticanjem stvaranja slobodnih radikala, kao i međudjelovanjem s esencijalnim elementima, često u obliku antagonizma. S druge strane, dodatnim unosom esencijalnih elemenata može se utjecati na raspodjelu i štetne učinke kadmija. Selenij je esencijalan mikroelement i antioksidans, a zbog svojstva vezanja za kadmij (kao i živu, arsen i druge toksične elemente) te uloge u detoksifikaciji, detaljnije se počelo istraživati međudjelovanje kadmija i selenija. U radu je dan pregled dosadašnjih saznanja o toksikokinetici i toksikodinamici kadmija, biokinetici i biodinamici selenija i mehanizmima njihova međudjelovanja proizašlih uglavnom iz istraživanja na životinjama i ograničenu broju istraživanja u ljudima. Različite doze i odnos doza, način i dužina izloženosti kadmiju i seleniju u pokusima na životinjama uzrok su često vrlo oprečnih rezultata istraživanja opisanih u literaturi. Buduća istraživanja međudjelovanja kadmija i selenija treba usmjeriti na osjetljive skupine stanovništva i na istraživanje mehanizama tog međudjelovanja. Doze i izloženost u pokusima na životinjama treba prilagoditi dugotrajnim i niskim razinama izloženosti koje su najčešće u ljudi.

Elevated levels of selenium in the typical diet of Amazonian riverside populations

Selenium (Se) intake is generally from food, whose Se content depends on soil Se and plant accumulation. For humans, adequate Se intake is essential for several selenoenzymes. In the Lower Tapajós region of the Brazilian Amazon, Se status is elevated with large inter-community variability. Se intake in this region, where Hg exposure is among the highest in the world, may be important to counteract mercury (Hg) toxicity. The present study was conducted in 2006 with 155 persons from four communities of the Lower Tapajós. The objectives were: i) to evaluate Se content in their typical diet and drinking water; ii) to compare food Se concentrations with respect to geographic location; and iii) to examine the contribution of consumption of different food items to blood Se. More than 400 local foods and 40 drinking water samples were collected. Participants responded to an interview-administered food frequency questionnaire and provided blood samples. Food, water and blood Se levels were assessed by ICP-MS. Since Brazil nuts may also contain significant levels of barium (Ba) and strontium (Sr), these elements were likewise analyzed in nuts. The highest Se concentrations were found in Brazil nuts, but concentrations were highly variable (median: 13.9 microg/g; range: 0.4-158.4 microg/g). Chicken, game meat, eggs and beef also contained considerable levels of Se, with median concentrations from 0.3 to 1.4 microg/g. There was no particular geographic distribution of food Se. Se concentration in drinking water was very low (< 1.4 microg/L). Blood Se covered a (103-1500 microg/L), and was positively related to regular consumption of Brazil nuts, domestic chicken and game meat. Brazil nuts were found to contain highly variable and often very high concentrations of Ba (88.0 microg/g, 1.9-1437 microg/g) and Sr (38.7 microg/g, 3.3-173 microg/g).

Selenium bioavailability: current knowledge and future research requirements

Information on selenium bioavailability is required to derive dietary recommendations and to evaluate and improve the quality of food products. The need for robust data is particularly important in light of recent suggestions of potential health benefits associated with different intakes of selenium. The issue is not straightforward, however, because of large variations in the selenium content of foods (determined by a combination of geologic/environmental factors and selenium supplementation of fertilizers and animal feedstuffs) and the chemical forms of the element, which are absorbed and metabolized differently. Although most dietary selenium is absorbed efficiently, the retention of organic forms is higher than that of inorganic forms. There are also complications in the assessment and quantification of selenium species within foodstuffs. Often, extraction is only partial, and the process can alter the form or forms present in the food. Efforts to improve, standardize, and make more widely available techniques for species quantification are required. Similarly, reliable and sensitive functional biomarkers of selenium status are required, together with improvements in current biomarker methods. This requirement is particularly important for the assessment of bioavailability, because some functional biomarkers respond differently to the various selenium species. The effect of genotype adds a potential further dimension to the process of deriving bioavailability estimates and underlines the need for further research to facilitate the process of deriving dietary recommendations in the future.

Selenium and its species distribution in above-ground plant parts of selenium enriched buckwheat (Fagopyrum esculentum Moench)

Common buckwheat (Fagopyrum esculentum Moench) was foliarly sprayed with a water solution containing 10 mg Se(VI) L(-1) at the beginning of flowering. The total Se content in plant parts in the untreated group was low, whereas in the Se-sprayed group it was approximately 50- to 500-fold higher, depending on the plant part (708-4231 ng Se g(-1) DM(-1) (DM: dry matter)). We observed a similar distribution of Se in plant parts in both control and treated groups, with the highest difference in Se content being in ripe seeds. Water-soluble Se compounds were extracted by enzymatic hydrolysis with protease XIV, resulting in above 63% of soluble Se from seeds, approximately 14% from stems, leaves and inflorescences and less than 1% from husks. Se-species were determined in enzymatic extracts using HPLC-UV-HG-AFS (HPLC-hydride generation-atomic fluorescence spectrometry with UV treatment). The main Se species found in seeds was SeMet ( approximately 60% according to total Se content), while in stems, leaves and inflorescences the only form of soluble Se present was Se(VI) (up to 10% of total Se). In husks no Se-species were detected. We observed an instability of Se(IV) in seed extracts as a possible consequence of binding to the matrix components. Therefore, special care concerning sample extraction and the storage time of the extracts should be taken.

Selenium speciation profiles in selenite-enriched soybean (Glycine Max) by HPLC-ICPMS and ESI-ITMS

Soybean (Glycine Max) plants were grown in soil supplemented with sodium selenite. A comprehensive selenium profile, including total selenium concentration, distribution of high molecular weight selenium and characterization of low molecular weight selenium compounds, is reported for each plant compartment: bean, pod, leaf and root of the Se-enriched soybean plants. Two chromatographic techniques, coupled with inductively coupled plasma mass spectrometry (ICPMS) for specific selenium detection, were employed in this work to analyze extract solutions from the plant compartments. Size-exclusion chromatography revealed that the bean compartment, well-known for its strong ability to make proteins, produced high amounts (82% of total Se) of high molecular weight selenospecies, which may offer additional nutritional value and suggest high potential for studying proteins containing selenium in plants. The pod, leaf and root compartments primarily accumulate low molecular weight selenium species. For each compartment, low molecular weight selenium species (lower than 5 kDa) were characterized by ion-pairing reversed phase HPLC-ICPMS and confirmed by electrospray ionization ion trap mass spectrometry (ESI-ITMS). Selenomethionine and selenocystine are the predominant low molecular weight selenium compounds found in the bean, while inorganic selenium was the major species detected in other plant compartments.

NanoSIMS analysis of arsenic and selenium in cereal grain

*Cereals are an important source of selenium (Se) to humans and many people have inadequate intakes of this essential trace element. Conversely, arsenic (As) is toxic and may accumulate in rice grain at levels that pose a health risk. Knowledge of the localization of selenium and arsenic within the cereal grain will aid understanding of their deposition patterns and the impact of processes such as milling. *High-resolution secondary ion mass spectrometry (NanoSIMS) was used to determine the localization of Se in wheat (Triticum aestivum) and As in rice (Oryza sativa). Combined synchrotron X-ray fluorescence (S-XRF) and NanoSIMS analysis utilized the strengths of both techniques. *Selenium was concentrated in the protein surrounding the starch granules in the starchy endosperm cells and more homogeneously distributed in the aleurone cells but with Se-rich hotspots. Arsenic was concentrated in the subaleurone endosperm cells in association with the protein matrix rather than in the aleurone cells. NanoSIMS indicated that the high intensity of As identified in the S-XRF image was localized in micron-sized hotspots near the ovular vascular trace and nucellar projection. *This is the first study showing subcellular localization in grain samples containing parts per million concentrations of Se and As. There is good quantitative agreement between NanoSIMS and S-XRF.

Involvement of a broccoli COQ5 methyltransferase in the production of volatile selenium compounds

Selenium (Se) is an essential micronutrient for animals and humans but becomes toxic at high dosage. Biologically based Se volatilization, which converts Se into volatile compounds, provides an important means for cleanup of Se-polluted environments. To identify novel genes whose products are involved in Se volatilization from plants, a broccoli (Brassica oleracea var italica) cDNA encoding COQ5 methyltransferase (BoCOQ5-2) in the ubiquinone biosynthetic pathway was isolated. Its function was authenticated by complementing a yeast coq5 mutant and by detecting increased cellular ubiquinone levels in the BoCOQ5-2-transformed bacteria. BoCOQ5-2 was found to promote Se volatilization in both bacteria and transgenic Arabidopsis (Arabidopsis thaliana) plants. Bacteria expressing BoCOQ5-2 produced an over 160-fold increase in volatile Se compounds when they were exposed to selenate. Consequently, the BoCOQ5-2-transformed bacteria had dramatically enhanced tolerance to selenate and a reduced level of Se accumulation. Transgenic Arabidopsis expressing BoCOQ5-2 volatilized three times more Se than the vector-only control plants when treated with selenite and exhibited an increased tolerance to Se. In addition, the BoCOQ5-2 transgenic plants suppressed the generation of reactive oxygen species induced by selenite. BoCOQ5-2 represents, to our knowledge, the first plant enzyme that is not known to be directly involved in sulfur/Se metabolism yet was found to mediate Se volatilization. This discovery opens up new prospects regarding our understanding of the complete metabolism of Se and may lead to ways to modify Se-accumulator plants with increased efficiency for phytoremediation of Se-contaminated environments.

Selenium in human and animal nutrition: resolved and unresolved issues. A partly historical treatise in commemoration of the fiftieth anniversary of the discovery of the biological essentiality of selenium, dedicated to the memory of Klaus Schwarz (1914-1978) on the occasion of the thirtieth anniversary of his death

Selenium (Se) is an essential trace element unevenly distributed on the Earth's crust with low selenium regions predominating. To prevent selenium-deficiency diseases in livestock, additions of selenium to animal feed are required and were approved for all species, but the chemical form of the element to be added was not specified. Presently, sodium selenite is still widely employed, although it is not a natural nutritional form of selenium. Its use creates ecological problems and affects human selenium nutriture in as much as the meat, milk, and eggs from animals maintained on selenite contain less selenium than from animals receiving it as selenomethionine, the chief natural nutritional form of the element present in grain crops grown in selenium-adequate regions, or from high-selenium yeast added to feedstock. Human dietary selenium intakes are sub-optimal in many countries but are considered to be adequate if they reach the currently adopted Recommended Dietary Allowances (RDAs). Their upward revision will be required if the health benefits of selenium are to be fully utilized.

Novel reactions of one-electron oxidized radicals of selenomethionine in comparison with methionine

Pulse radiolysis studies on hydroxyl (*OH) radical reactions of selenomethionine (SeM), a selenium analogue of methionine, were carried out, and the resultant transient radical cations and their subsequent reactions have been reported. At pH<3, the >Se*-OH radical adducts produced on reaction of SeM with *OH radical were converted to selenium centered radical cations (Se*+M), which react with another molecule of SeM to form dimer radical cation M(Se therefore Se)M+. At pH 7, the >Se*-OH radical adducts were converted to a monomer radical of the type (Se therefore N)M+ that acquires intramolecular stability through interaction with the lone pair of the N atom and this radical is denoted as SeM*+. SeM*+ decayed by first order kinetics, and the reduction potential of the couple SeM*+/SeM was determined to be 1.21+/-0.05 V vs NHE at pH 7. SeM*+ oxidized ABTS2- and TMPD with rate constants of (2.5+/-0.1)x10(8) and (6.1+/-0.2)x10(8) M(-1) s(-1), respectively, and reacted with hydroxide ion with a rate constant of (3.8+/-0.9)x10(5) M(-1) s(-1). SeM*+ reacts with molecular oxygen, and the rate constant for this reaction was determined to be (4.3+/-0.2)x10(8) M(-1) s(-1); similar reaction with methionine could not be observed experimentally. Like methionine radical cations, SeM*+ undergoes decarboxylation, although with lesser yield, to produce reducing 3-methyl-selenopropyl amino radicals (referred as alpha-amino radicals). The formation of these radicals was confirmed both by the estimation of the liberated CO2 and by one-electron reduction of MV2+, thionine, and PNAP. These results have been supported by quantum chemical calculations. Implications of these results in the biological role of SeM have also been briefly discussed.