Chemical Forms Of Se Research Articles

Selenium Compounds, Apoptosis and Other Types of Cell Death: An Overview for Cancer Therapy

Selenium (Se) is an essential trace element involved in different physiological functions of the human body and plays a role in cancer prevention and treatment. Induction of apoptosis is considered an important cellular event that can account for the cancer preventive effects of Se. The mechanisms of Se-induced apoptosis are associated with the chemical forms of Se and their metabolism as well as the type of cancer studied. So, some selenocompounds, such as SeO2 involve the activation of caspase-3 while sodium selenite induces apoptosis in the absence of the activation of caspases. Modulation of mitochondrial functions has been reported to play a key role in the regulation of apoptosis and also to be one of the targets of Se compounds. Other mechanisms for apoptosis induction are the modulation of glutathione and reactive oxygen species levels, which may function as intracellular messengers to regulate signaling pathways, or the regulation of kinase, among others. Emerging evidence indicates the overlaps between the apoptosis and other types of cell death such as autophagy. In this review we report different processes of cell death induced by Se compounds in cancer treatment and prevention.

Influence of mycorrhizal inoculation on the accumulation and speciation of selenium in maize growing in selenite and selenate spiked soils

Abstract Effects of inoculation with arbuscular mycorrhizal (AM) fungus Glomus mosseae on the accumulation and speciation of selenium (Se) in maize were systematically investigated using soil spiked with selenite (Se(IV)) and selenate (Se(VI)). Selenium speciation was analyzed by HPLC–ICP-MS. The results indicated that accumulation and speciation of Se in plants and the influence of mycorrhizal inoculation depend on the chemical form of Se that the soil was spiked with. There was no obvious influence of inoculation on Se species distribution, plant uptake and translocation for the experimental treatment that was supplied with Se(VI). When Se(IV) was supplied to the soil, mycorrhizal inoculation promoted oxidation of Se(IV) to Se(VI) in the soil, inhibited Se accumulation by maize, enhanced the accumulation of Se(VI) but reduced the accumulation of organic Se in maize. Microbeam X-ray fluorescence (μ-XRF) mapping confirmed that mycorrhizal inoculation inhibited the translocation of Se from the surface to the inner of roots when Se(IV) was added to soil. This study elucidates, for the first time, the speciation-dependent influence of mycorrhizal inoculation on the behavior of Se in the soil–plant system.

Agronomic biofortification with selenium: Effects on whole blood selenium and humoral immunity in beef cattle

The purpose of this study was to evaluate Se supplementation strategies in mature beef cattle by measuring changes in whole-blood Se (WB-Se) status and humoral immune response to vaccination. Mature beef cows ( n = 45) were balanced by age and randomly assigned to 1 of 3 supplementation groups that received different chemical forms of Se or Se dosages compared to a standard (control) Se treatment. Supplementation treatment groups were provided limited access (6 weeks) to either sodium selenite (200 mg/kg Se; LSe) or Se-fertilized forage (FSe) and subsequently had no additional Se in their mineral supplement for the study duration. The LSe group cows grazed non-Se-fertilized forage. The control group grazed non-Se-fertilized forage and received continuous Se supplementation (CSe) from a free-choice mineral supplement (120 mg/kg Se from sodium selenite). Cows were bled pre and post grazing and then every 4 weeks thereafter for approximately 5 months to assess WB-Se concentration. All cows were immunized with J-5 Escherichia coli bacterin at the end of the 6-week supplementation period, and serum was collected for antibody titers 2 and 4 weeks after the third immunization. Covariate adjusted WB-Se concentrations were influenced (P<0.0001) by group, time and their interaction. Cows in the FSe group had higher (P<0.0001) WB-Se concentration (186 ± 5 ng/mL) immediately post-grazing (42 days) compared to LSe (117 ± 5 ng/mL) and CSe cows (130 ± 5 ng/mL). WB-Se concentration in FSe cows remained higher (P=0.02 to P<0.0001) over the next 4 (CSe) and 5 (LSe) months. Higher (P<0.05) WB-Se concentrations were observed in CSe compared to LSe cows over the last 4 months of the study. Treatment group (P=0.036) and time post vaccination (P<0.0001) influenced J-5 E. coli antibody titers, with FSe cows having higher titers than LSe cows (P=0.01), although FSe and CSe cows were not different. Short-term exposure of cattle to Se-fertilized forage elevates WB-Se concentrations within several weeks and this exposure is sufficient to maintain adequate concentrations throughout grazing periods when there is limited access to Se supplements. Short term exposure to higher levels of inorganic Se supplementation is not equivalent to ongoing inorganic Se supplementation at lower rates.

Chemical Form of Selenium Affects Its Uptake, Transport, and Glutathione Peroxidase Activity in the Human Intestinal Caco-2 Cell Model

Determining the effect of selenium (Se) chemical form on uptake, transport, and glutathione peroxidase activity in human intestinal cells is critical to assess Se bioavailability at nutritional doses. In this study, we found that two sources of L-selenomethionine (SeMet) and Se-enriched yeast each increased intracellular Se content more effectively than selenite or methylselenocysteine (SeMSC) in the human intestinal Caco-2 cell model. Interestingly, SeMSC, SeMet, and digested Se-enriched yeast were transported at comparable efficacy from the apical to basolateral sides, each being about 3-fold that of selenite. In addition, these forms of Se, whether before or after traversing from apical side to basolateral side, did not change the potential to support glutathione peroxidase (GPx) activity. Although selenoprotein P has been postulated to be a key Se transport protein, its intracellular expression did not differ when selenite, SeMSC, SeMet, or digested Se-enriched yeast was added to serum-contained media. Taken together, our data show, for the first time, that the chemical form of Se at nutritional doses can affect the absorptive (apical to basolateral side) efficacy and retention of Se by intestinal cells; but that, these effects are not directly correlated to the potential to support GPx activity.

Application of XANES spectroscopy in understanding the metabolism of selenium in isolated rainbow trout hepatocytes: insights into selenium toxicity

Selenium (Se) is an essential element, but causes toxic effects in fish at a slightly elevated level beyond the threshold. However, the degree of Se toxicity differs depending on the chemical forms of Se (e.g., organic vs. inorganic) to which fish are exposed to. The mechanisms of Se metabolism and toxicity in fish, particularly at cellular level, are poorly understood. The present study was designed to examine the metabolic fate of different seleno-compounds, both inorganic and organic, in isolated hepatocytes of rainbow trout (Oncorhynchus mykiss) in primary culture using XANES spectroscopy. In cells exposed to 100 μM of selenate and selenite for 6-24 h, elemental Se was found to be the primary metabolite. Whereas, selenocystine appeared to be the major metabolite in cells exposed to 100 μM seleno-L-methionine for 6-24 h. Interestingly, we recorded L-methionine-γ-lyase activity in S9 fraction of cell lysate-an enzyme that directly catalyzes selenomethionine into methylselenol. We also found concurrent reduction of glutathione (GSH) concentration following reaction of seleno-L-methionine with cellular S9 fraction. Moreover, we observed a rapid increase in cellular reactive oxygen species (ROS) generation with increasing seleno-L-methionine exposure dose (100-1000 μM). These findings indicated the rapid cellular metabolism of seleno-L-methionine into methylselenol at higher exposure dose (≥100 μM), and the occurrence of GSH mediated redox cycling of methylselenol--a process that is known to produce reactive oxygen species (ROS). Overall, our results suggest that inorganic and organic selenium are metabolized through different metabolic pathways in rainbow trout hepatocytes. The findings of our study have important implications for understanding the chemical species-specific differences in Se toxicity to fish.

A method for measurement of ultratrace 79Se with accelerator mass spectrometry

79Se is a long-lived fission product with chemical and radiological toxicity. It is one of the radionuclides of interest in nuclear waste disposal due to its potential migration capacity to the surface environment. Furthermore, 79Se is an ideal tracer in biomedicine. One of the major obstacles in the measurement of ultratrace 79Se with AMS is the strong interference from the isobaric nuclide 79Br. This paper presents a new ultra-sensitive method for 79Se measurements with AMS. The novel aspects of our procedures include the extraction of SeO 2 - molecular ions, that results in a suppression of 79Br background by as much as about five orders of magnitude; the selection of Ag 2SeO 3 as the chemical form of Se in the target sample, that brings about a relatively large and stable SeO 2 - beam current; and the renovation of the multi-anode detector, that makes 79Se better identified from the interfering nuclide 79Br. By using these procedures, a sensitivity of better than 1.0 × 10 −12 has been achieved for 79Se/Se measurement with the CIAE-AMS system. It is then possible to quantify the tracer 79Se in biological samples. Recently, we are prepared to develop the 79Se-AMS biological tracer methodology.

Bioaccumulation and toxicity of selenium compounds in the green alga Scenedesmus quadricauda

BackgroundSelenium is a trace element performing important biological functions in many organisms including humans. It usually affects organisms in a strictly dosage-dependent manner being essential at low and toxic at higher concentrations. The impact of selenium on mammalian and land plant cells has been quite extensively studied. Information about algal cells is rare despite of the fact that they could produce selenium enriched biomass for biotechnology purposes.ResultsWe studied the impact of selenium compounds on the green chlorococcal alga Scenedesmus quadricauda. Both the dose and chemical forms of Se were critical factors in the cellular response. Se toxicity increased in cultures grown under sulfur deficient conditions. We selected three strains of Scenedesmus quadricauda specifically resistant to high concentrations of inorganic selenium added as selenite (Na2SeO3) – strain SeIV, selenate (Na2SeO4) – strain SeVI or both – strain SeIV+VI. The total amount of Se and selenomethionine in biomass increased with increasing concentration of Se in the culturing media. The selenomethionine made up 30–40% of the total Se in biomass. In both the wild type and Se-resistant strains, the activity of thioredoxin reductase, increased rapidly in the presence of the form of selenium for which the given algal strain was not resistant.ConclusionThe selenium effect on the green alga Scenedesmus quadricauda was not only dose dependent, but the chemical form of the element was also crucial. With sulfur deficiency, the selenium toxicity increases, indicating interference of Se with sulfur metabolism. The amount of selenium and SeMet in algal biomass was dependent on both the type of compound and its dose. The activity of thioredoxin reductase was affected by selenium treatment in dose-dependent and toxic-dependent manner. The findings implied that the increase in TR activity in algal cells was a stress response to selenium cytotoxicity. Our study provides a new insight into the impact of selenium on green algae, especially with regard to its toxicity and bioaccumulation.

Differences in uptake and translocation of selenate and selenite by the weeping willow and hybrid willow

Due to its essentiality, deficiency, and toxicity to living organisms and the extensive use in industrial activities, selenium (Se) has become an element of global environmental and health concern. Se removal from contaminated sites using physical, chemical, and engineering techniques is quite complicated and expensive. The goal of this study was to investigate uptake and translocation of Se in willows and to provide quantitative information for field application whether Se phytoremediation is feasible and ecologically safe. Intact pre-rooted plants of hybrid willows (Salix matsudana Koidz x alba L.) and weeping willows (Salix babylonica L.) were grown hydroponically and treated with selenite or selenate at 24.0 +/- 1 degrees C for 144 h. Removal of leaves was also performed as a treatment to quantify the effect of transpiration on translocation and volatilization of Se. At the end of the study, total Se in the hydroponic solution and in different parts of plant tissues was analyzed quantitatively by hydride generation-atomic fluorescence spectrometry. The capacity of willows to assimilate both chemical forms of Se was also evaluated using detached leaves and roots in sealed glass vessels in vivo. Translocation efficiency of Se in both plants was estimated. Significant amounts of the applied selenite and selenate were eliminated from plant growth media by willows during the period of incubation. Both willows showed a significantly higher removal rate for selenate than for selenite (p < 0.05). Substantial differences existed in the distribution of both chemical forms of Se in plant materials: lower stems and roots were the major sites for accumulation of selenite and selenate, respectively. Translocation efficiency for selenite was significantly higher than that for selenate in both willow species (p < 0.01). Compared to the intact trees, remarkable decrease in the removal rate of both chemical forms of Se was found for willows without any leaves (p < 0.01). Volatilization of Se by plant leaves was estimated to be approximately 10% of the total applied selenite or selenate. Significant reduction (>20%) of selenate was observed in the sealed vessel with excised roots of willows, whereas trace amounts of selenite were eliminated from the hydroponic solution in the presence of roots. Detached leaves from neither of them reduced the concentration of selenite or selenate in the solution. Due to the significant difference in the removal rate and the distribution of the two chemical forms of Se in plant materials, the conversion of selenate to selenite in hydroponic solution prior to uptake and within plant tissues is unlikely. An independent uptake and translocation mechanisms are likely to exist for each Se chemical species. Uptake of selenate is mediated possibly through an active transport mechanism, whereas that of selenite may possibly depend on plant transpiration. Uptake velocities of selenite are linear (zero-order kinetics), while selenate removal processes obey first-order kinetics. In experiments with detached leaves in closed bottles, the cuticle of leaves was the major obstacle to extract both chemical forms of Se from the hydroponic solution. Phytovolatilization is a biological process playing an important role in Se removal. Although faster removal rates of selenate than selenite from plant growth media were observed by both willow species, selenite in plant materials was more mobile than selenate. Significant decrease in removal rates of both chemical forms of Se was detected for willows without any leaves. Significant differences in extraction, assimilation and transport pathways for selenite and selenate exist in willow trees. Phytoremediation of Se is an attractive approach of cleaning up Se contaminated environmental sites. More detailed investigation on the assimilation of Se in plant roots and transport in tissues will provide further biochemical evidence to explain the differences in uptake and translocation mechanisms between selenite and selenate in willows. A relevant phytoremediation scheme can then be designed to clean up Se contaminated sites. Willows show a great potential for uptake, assimilation and translocation of both selenite and selenate. Phytotreatment of Se is potentially an efficient and practical technology for cleaning up contaminated environmental sites.

Study of Selenium Speciation in Selenized Rice Using High-Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometer

On the basis of Osborne fractionation, albumin, globulin, protamine and glutelin in selenium (Se)-rich rice were extracted with water, 2% NaCl solution, 70% alcohol and 0.5% alkaline solution subsequently. The content of Se in these protein extracts was determined by inductively coupled plasma mass spectrometer (ICP-MS). The chemical forms of Se in albumin extract and enzymatic digests of rice were analyzed with a hyphenated technique of high-performance liquid chromatography and ICP-MS. The Se content in four types of extracts shows an order of glutelin > protamine > albumin > globulin. The protein with molecular weight of 12.6 kDa is the primary Se-containing protein in extracts of albumin, and selenocysteine is the predominant selenoamino acid in the enzymatic digests of rice.

Metabolic responses of weeping willows to selenate and selenite

Selenium (Se) is one of the most widely distributed elements of the earth's crust at low concentrations. The extensive use of Se-containing chemicals due to anthropogenic activities has increased the ecological risk to environmental compartments. Plants, under unfavorable environmental conditions, often increase the formation of reactive oxygen species (ROS), and consequently plant antioxidant enzymatic systems have been proposed to be important in plant stress tolerance. The goal of this study was to find out the metabolic responses of plants to Se, to provide quantitative information whether exogenous Se has a beneficial role in plants, and to investigate the potential of vegetation management of Se for potential phytoremediation. Pre-rooted plants of weeping willows (Salix babylonica L.) were grown hydroponically in growth chambers and treated with Na2SeO4 or Na2SeO3 at 24.0 +/- 1 degrees C for 168 h. Five different treatment concentrations were used, ranging from 0.44 to 8.72 mg Se/L for the treatments exposed to SeO4(2-) and from 0.50 to 10.0 mg Se/L for the treatments exposed to SeO3(2-), respectively. Transpiration rates, soluble protein contents and antioxidative enzyme activities of the plants were monitored to evaluate toxicity from exogenous Se exposure. At the end of the study, total Se in the hydroponic solution was analyzed by hydride generation-atomic fluorescence spectrometry (HG-AFS). Both chemical forms of Se at low concentrations showed growth-promoting effects on plants. A significant decrease of transpiration rates and of soluble protein contents of plants was observed at higher Se concentrations after 168 h of exposure. Measurable change of superoxide dismutases (SOD) activity in leaves was only detected under high Se treatments. Catalase (CAT) activity was significantly affected by the Se application. Slight change of peroxidase (POD) activity was measured in all treatments, whereas significant inhibition of POD activity was detected for the plants exposed to SeO3(2-) of 10.0 mg Se/L. Se-induced stress appeared in all treatments, thus resulting in measurable increase of glutathione peroxidase (GSH-Px) activity of the plants. Although both chemical forms of Se were taken up by weeping willows efficiently, their uptake rates were different. Of all measured parameters, POD and CAT activities in leaves were noted the most sensitive indicator for the plants exposed to SeO4(2-) and SeO3(2-), respectively. Deleterious effects on plant physiological functions due to Se application were not observed over 168 h of exposure. This is largely due to the fact that well-established antioxidant enzymatic systems in plants and higher activities of GSH-Px largely reduced the negative effects on plants; SeO3(2-) caused much more severe stress to plants than SeO4(2-) at higher Se application rates. The uptake mechanisms between the two chemical species were quite different. Neither visible toxic symptoms nor metabolic lesions were observed at low concentrations of Se, probably due to the effective established enzymatic systems in weeping willows. All selected parameters for toxicity determination were significantly correlated to Se application, but metabolic responses of plants to SeO4(2-) and SeO3(2-) were quite different. GSH-Px in leaves was probably the principle enzyme responsible for stress reduction from Se exposure. Due to their different chemical properties, weeping willows showed a faster uptake rate for SeO4(2-) than for SeO3(2-). Exogenous Se has a beneficial role in plants and vegetation management of Se is a potential remediation strategy in cleaning up Se-contaminated sites. Further investigation on the biochemical mechanism of Se metabolism will provide insight to the specific interactions between Se and plants on the molecular level. Weeping willow has a sound potential for phytoremediation of Se-contaminated sediment and groundwater because the tree is not only tolerant to Se but also uptakes chemical species from the environment.

Dietary Selenium for the counteraction of oxidative damage: fortified foods or supplements?

Since any significant modification in the Se status, leading to changes in the activity of the seleno-enzymes, may have important consequences on the susceptibility of tissues to oxidative stress, considerable efforts have been made upon increasing Se dietary intake. In this respect, an important debate is still open about the bioavailability and the effectiveness of Se, and more generally nutrients, in supplements compared with foods. Using male Wistar rats, we have compared the effectiveness of two different diets in which an adequate Se content (0.1 mg/kg) was achieved by adding the element as sodium selenite or as component of a lyophilized Se-enriched food, in the counteraction of an oxidative stress induced by intraperitoneal administration of adriamycin. Both Se-enriched diets were able to reduce the consequences of the oxidative stress in liver, mainly by increasing glutathione peroxidase activity. This increase was more evident in rats fed on the diet enriched with the lyophilized food, probably due to the different chemical forms of Se, or to other components of the food itself. Although further studies are needed, data herein presented may contribute to the characterization of the effectiveness of Se from different sources, foods or supplements, in the light of dietary advice to the population concerning improvement of Se intake.

Increased intakes of selenium‐enriched foods may benefit human health

AbstractSelenium is an essential nutrient and deficient intakes compromise health in domestic animals and humans. A recommended dietary allowance (RDA) of 55 µg d−1 has been set for adult males and females in the United States; most North Americans consume more than this amount, but many residents of Europe, Asia and Africa consume less. While there are very few reports of outright Se deficiency in people consuming mixed Western diets that have Se intakes below the RDA, there is evidence that dietary intakes of selenium greater than the requirement may help reduce the risk of cancer, especially prostate cancer, to men. Selenium metabolism depends on the chemical form of Se in the diet, and some forms are better for some actions (e.g., cancer reduction) than other forms. Foods may contain different amounts and chemical forms of Se; consequently the benefits of Se may depend on the particular foods consumed. There are many reports of the chemistry and health benefits of Se from plant foods; animal foods also contain Se, but there are fewer reported studies. Fully understanding the health benefits of Se that may be gained by consumption of Se‐enriched foods will require multidisciplinary approaches by teams of medical researchers, chemists, nutritionists, and agricultural scientists. Copyright © 2007 Society of Chemical Industry

Selenium Speciation in Kerogen from Two Chinese Selenium Deposits: Environmental Implications

Selenium is an essential trace element for humans, animals, and vegetation. Its occurrence in the environment is characterized by specific chemical and biochemical properties that control its elemental solubility, toxicity, and environmental behavior. The Laerma Se-Au deposit and Yutangba Se deposit are two important Se-bearing deposits found recently in China. In one of these areas (Yutangba), a serious environmental impact happened involving Se poisoning. Previous studies have shown that Se in both deposits is closely related to organic matter, especially kerogen fractions, but detailed relationships between Se and kerogen and Se chemical forms were not reported. In this study, the different speciation of Se is identified by transmission electron microscopy (TEM) and other geochemical techniques (infrared spectra (IS) and X-ray diffraction (XRD)) from kerogen samples extracted from ore rocks of both deposits. The occurrence of organically bound Se in the Laerma deposit and elemental Se nanograins in the Yutangba deposit is observed, indicating the diversity of formation mechanisms and possible chemical forms of Se in Se-rich rocks. The formation of elemental Se associated with organic matter is likely related to redox conditions, whereas organic species are related to the higher sulfur content of kerogen and possibly result from S-Se substitutions. This discovery provides new evidence with which to assess potential Se mobility during weathering of ore-bearing rocks. In an altered rock, the elemental Se in kerogen is more steadily mobilized and is potentially accumulated by vegetation, which may explain the sudden prevalence of Se poisoning in the Yutangba area. In contrast, organically bound Se seems more resistant to chemical alteration compared to other Se species so that its bioavailability may be very restricted.

Proposed criteria for assessing the efficacy of cancer reduction by plant foods enriched in carotenoids, glucosinolates, polyphenols and selenocompounds.

The cancer-protective properties of vegetable consumption are most likely mediated through 'bioactive compounds' that induce a variety of physiologic functions including acting as direct or indirect antioxidants, regulating enzymes and controlling apoptosis and the cell cycle. The 'functional food' industry has produced and marketed foods enriched with bioactive compounds, but there are no universally accepted criteria for judging efficacy of the compounds or enriched foods. Carotenoids, glucosinolates, polyphenols and selenocompounds are families of bioactive compounds common to vegetables. Although numerous studies have investigated the agricultural and human health implications of enriching foods with one or more of these compounds, inadequate chemical identification of compounds, lack of relevant endpoints and inconsistencies in mechanistic hypotheses and experimental methodologies leave many critical gaps in our understanding of the benefits of such compounds. This review proposes a decision-making process for determining whether there is reasonable evidence of efficacy for the both the compound and the enriched food. These criteria have been used to judge the evidence of efficacy for cancer prevention by carotenoids, polyphenols, glucosinolates and selenocompounds. The evidence of efficacy is weak for carotenoids and polyphenols; the evidence is stronger for glucosinolates and lycopene, but production of enriched foods still is premature. Additionally there is unacceptable variability in the amount and chemical form of these compounds in plants. The evidence of efficacy for selenocompounds is strong, but the clinical study that is potentially the most convincing is still in progress; also the variability in amount and chemical form of Se in plants is a problem. These gaps in understanding bioactive compounds and their health benefits should not serve to reduce research interest but should, instead, encourage plant and nutritional scientists to work together to develop strategies for improvement of health through food.

Distribution coefficient of selenium in Japanese agricultural soils

In order to evaluate the selenium (Se) sorption level in Japanese soils, soil/soil solution distribution coefficients ( K ds) were obtained for 58 agricultural soil samples (seven soil classification groups) using 75Se as a tracer. Although several chemical forms of Se are present in agricultural fields, selenite was used, because it is the major inorganic Se form in acid soils such as found in Japan. The K d values obtained covered a wide range, from 12 to 1060 l/kg, and their arithmetic mean was 315 l/kg. Among the soil groups, Andosols had higher K d values. The K d values for all samples were highly correlated with soil active-aluminum (Al) and active-iron (Fe) contents. Thus, active-Al and active-Fe were considered to be the major adsorbents of Se. Then, a new sequential extraction procedure was applied to 12 soil samples in order to quantify the effect of soil components on Se adsorption. The sequential extraction results showed that 80–100% of the adsorbed Se was recovered as Al-bound Se and Fe-bound Se. The amount of Al-bound Se was the highest in the soils that showed high K d values, though the relative contribution of Fe-bound Se tended to increase with decreasing K d values. The high values of K d seemed to be caused mainly by the adsorption of Se onto active-Al in Japanese soils.

Bioavailability of selenium from meat and broccoli as determined by retention and distribution of 75Se.

The concentration of selenium (Se), an essential nutrient, is variable in foods, depending, in part, on how and where foods are produced; some foods accumulate substantial amounts of Se when produced on high-Se soils. The chemical form of Se also differs among foods. Broccoli is a Se-accumulating plant that contains many methylated forms of Se, and Se bioavailability from broccoli has been reported to be low. Red meats such as pork or beef could accumulate Se when the animal is fed high-Se diets, and Se from such meats has been reported to be highly bioavailable for selenoprotein synthesis. In a further attempt to characterize the utilization of Se from broccoli and meats such as pork or beef, we have fed rats diets adequate (0.1 microg Se/g diet) in Se or high in Se (1.5 microg S/g diet), with the Se source being either high-Se broccoli or beef. Rats were then given test meals of broccoli or pork intrinsically labeled with 75Se. When dietary Se was nutritionally adequate (0.1 microg/g diet), more 75Se from pork than broccoli was retained in tissues; however, there were no significant differences in whole-body retention when dietary Se was high (1.5 microg/g diet). A significantly greater percentage of 75Se from broccoli than pork was excreted in the urine and dietary Se did not affect urinary excretion of broccoli 75Se, but the amount excreted from pork varied directly with dietary Se intake. Radiolabeled 75Se derived from pork effectively labeled selenoproteins in all tissues examined, but 75Se from broccoli was undetectable in selenoproteins. These differences in retention and distribution of Se from broccoli or pork are consistent with reported differences in bioavailability of Se from beef and broccoli. They also suggest that there are fewer differences in bioavailability when Se is consumed in supranutritional amounts.

Metabolism of subtoxic level of selenite by double-perfused small intestine in rats.

Intestinal metabolism of the subtoxic level of selenite in rats was investigated using a double-perfusion system, which is an in situ, in vitro preparation in which the intestinal lumen and its vasculature are perfused simultaneously. The toxicity of sodium selenite was determined by inhibition of 3-O-methyl glucose (3MG) absorption and by histological examination. Levels of 1.2 mM selenite were required to significantly (p<0.05) reduce 3MG intestinal absorption (58+/-11%, mean+/-SD). Cation-exchange chromatography was used to determine the chemical forms of Se from selenite after using luminal concentrations of 1-200 microM in vascular perfusates. The chemical forms were selenite, selenodiglutathione (GS-Se-SG), mixed selenoglutathione plus cysteine (GS-Se-CYS), selenodicysteine (CYS-Se-CYS), protein-bound Se, and unidentified selenocompounds. Selenite was the predominant selenocompound found in vascular perfusate, but protein-bound Se was the predominant metabolite from selenite present in the vascular effluents. There was a corresponding increase of all metabolites with increased levels of selenite with time of absorption, but not with increased concentration of luminal selenite.

The antioxidant role of selenium and seleno-compounds

Selenium (Se) is an essential trace element for animals and humans that is obtained from dietary sources including cereals, grains and vegetables. The Se content of plants varies considerably according to its concentration in soil. Plants convert Se mainly into Se-methionine (Se-Met) and incorporate it into protein in place of methionine (Met). Selenocystine (Se-Cys), methyl-Se-Cys and γ-glutamyl-Se-methyl-Cys are not significantly incorporated into plant protein and are at relatively low levels irrespective of soil Se content. Higher animals are unable to synthesize Se-Met and only Se-Cys was detected in rats supplemented with Se as selenite. Renal regulation is the mode by which whole body Se is controlled. Se is concentrated in hair and nail and it occurs almost exclusively in organic compounds. The potentiating effect of Se deficiency on lipid peroxidation is enhanced in some tissues by concurrent deficiency of copper or manganese. In the in vitro system, the chemical form of Se is an important factor in eliciting cellular responses. Although the cytotoxic mechanisms of selenite and other redoxing Se compounds are still unclear, it has been suggested that they derive from their ability to catalyze the oxidation of thiols and to produce superoxide simultaneously. Selenite-induced cytotoxicity and apoptosis in human carcinoma cells can be inhibited with copper (CuSO 4) as an antioxidant. High doses of selenite result in induction of 8-hydroxydeoxyguanosine (8-OHdG) in mouse skin cell DNA and in primary human keratinocytes. It may cause DNA fragmentation and decreased DNA synthesis, cell growth inhibition, DNA synthesis, blockade of the cell cycle at the S/G 2-M phase and cell death by necrosis. In contrast, in cells treated with methylselenocyanate or Se methylselenocysteine, the cell cycle progression was blocked at the G 1 phase and cell death was predominantly induced by apoptosis.

Reduction of cancer risk by consumption of selenium-enriched plants: enrichment of broccoli with selenium increases the anticarcinogenic properties of broccoli.

Plant-based diets and phytochemicals present in plants are associated with decreased risk of cancer. Brassica species, and broccoli in particular, are associated with reduced risk of several important cancers. Selenium (Se) is an essential nutrient that is covalently bound in a number of different chemical forms found in plants. Broccoli accumulates Se many-fold beyond the concentration of Se in the soil, and the chemical form of Se in broccoli is similar to the chemical form in high-Se garlic, a food with unique chemoprotective properties. Se from broccoli grown to accumulate more than 500 micro g Se/g did not accumulate in rat tissues or increase glutathione peroxidase enzyme activity to the same extent as Se salts or seleno-amino acids. Se from high-Se broccoli decreased the incidence of aberrant crypts in rats with chemically induced colon cancer by more than 50%, compared with controls. Se from high-Se broccoli also decreased the incidence of mammary tumors in rats treated with 7,12-dimethylbenz(a)anthracene (DMBA) and tumor number and volume in APC(min) mice. These results suggest that development of methods to increase the natural accumulation of Se in broccoli may greatly enhance its health-promoting properties.

Physiological function of Se‐enriched tea fertilised with sodium selenite and naturally high‐Se tea in rats

In order to increase food selenium (Se) content, Se-enriched tea was produced by fertilising with sodium selenite in low-Se soil. Five groups of rats were fed a low-Se diet supplemented with either water (Se-deficient), sodium selenite or an aqueous extraction of low-Se tea, Se-enriched tea or naturally high-Se tea. The chemical form of Se in Se-enriched tea and the physiological function in rats fed the different Se sources were determined after 8 weeks. The results showed that organic Se accounted for 80% or more of the Se in Se-enriched tea fertilised with sodium selenite and naturally high-Se tea, but no significant differences in the proportion of organic Se and protein Se were found between Se-enriched tea and naturally high-Se tea. The Se biological utilisation rates were 65.41, 68.05 and 70.49% for sodium selenite, Se-enriched tea and naturally high-Se tea respectively. The Se content of blood and liver and the glutathione peroxidase (GSH-Px) activity were significantly increased by feeding Se-enriched tea and sodium selenite compared with low-Se tea, but a more efficient increase in liver GSH-Px activity was obtained with Se-enriched tea than with sodium selenite. No significant differences were found between Se-enriched tea fertilised with sodium selenite and naturally high-Se tea, which proved that the biological effectiveness of Se in Se-enriched tea was higher than that of sodium selenite in increasing liver GSH-Px activity. Se-enriched tea fertilised with sodium selenite in low-Se soil gave the same biological function as naturally high-Se tea. Therefore Se-enriched tea is a safe and effective means of increasing the Se intake of both humans and animals in low-Se areas. © 2000 Society of Chemical Industry