Organic Selenium Compounds Research Articles

Retention Behavior of Inorganic and Organic Selenium Compounds on a Polymer-Based Cation Exchange Column

The retention behavior of selenous acid, selenic acid, selenomethionine, selenoethionine, selenocystine, selenohomocystine, trimethyl-selenonium iodide, and (3-amino-3-carboxy-1-propyl)-dimethylselenonium iodide was studied on the polymer-based PRP-X200 cation exchange column with an aqueous solution of pyridine (20 to 100 mM) in the pH range 1.1-6.0 adjusted with formic acid as the mobile phase. An inductively coupled plasma mass spectrometer equipped with a hydraulic high pressure nebulizer served as selenium specific detector. The retention behavior was rationalized in terms of the pH-dependent deprotonation of the selenium compounds and of the pyridinium cation and of the formation of ion-pairs between hydrogen selenite, selenate, or the zwitterionic groups of the selenoamino acids with the pyridinium cation. A good separation of seven selenium compounds was achieved within 5.0 min at 40°C with 20 mM pyridine (pH 3.70). Selenoethionine eluted 15 min after injection. Peak areas and peak heights of the chromatographic signals provided linear calibration curves (r2 > 0.990). Detection limits obtained were 1 μg/L with the exception of selenoethionine (5 μg/L).

Optimization of microwave digestion for determination of selenium in human urine by flow injection-hydride generation-atomic absorption spectrometry

A microwave digestion program, which completely decomposes and oxidizes selenium compounds in urine to selenate, was developed by monitoring the pressure and the temperature during microwave digestion. The efficient decomposition and quantitative recovery of trimethylselenonium iodide spiked into urine was achieved in 18 min using the optimized microwave program reaching 200 °C and 8 bar. The selenate in the digest was reduced to selenite by hydrochloric acid with the aid of microwave energy. Urea was found useful to eliminate NOx fumes, which might be absorbed in the digest and interfere in the determination of selenium by flow injection-hydride generation-atomic absorption spectrometry (FI-HG-AAS). The recovery of trimethylselenonium iodide, selenomethionine, and selenoethionine added to urine was 96.5–105%. The whole procedure, FI-HG-AAS determination following microwave digestion of urine sample and microwave reduction of selenate in the digests into selenite, was checked with two Standard Reference Materials 2670 (toxic metals in human urine). The results showed good agreement with the certified values (normal level 30 ± 8 µg Se l–1 and elevated level 460 ± 30 µg Se l–1. The detection limit of the whole procedure was 3 µg Se l–1 urine. Selenomethionine and selenoethionine were found unstable during the microwave heating used to reduce selenate to selenite. Such a microwave reduction procedure should be cautioulsy used to distinguish selenate from selenite in the matrices which might contain organic selenium compounds.

Determination of selenium in solid samples by continuous subcritical water extraction, flow injection derivatisation and atomic fluorescence detection

A method for the determination of selenium in solid samples is proposed. The method involves two main steps: (a) continuous leaching of the analyte by subcritical water (250 °C, 200 bar, 0.7 ml min–1), which is complete in 15 min and (b) continuous derivatisation (hydride formation) and detection by atomic fluorescence. The design of the derivatisation manifold, based on flow injection, enables speciation analysis of inorganic selenium (as SeIV/SeVI) and organo-selenium compounds by appropriate selection of the reagent streams. Both conversions of organic into inorganic Se by oxidation and reduction of the SeVI formed as well as that of SeVI initially present in the samples to SeIV is accelerated by irradiation with focused microwaves using 1 m reactors and a flow-rate of 4.4 ml min–1. The linear range of the calibration curves is between 10–50 000 ng ml–1 with RSD values lower than 4.5%. The method has been applied successfully to sludge samples from an interlaboratory study. The drastic conditions of extraction convert organic Se into inorganic, so the method does not enable inorganic-Se/organic-Se speciation in solid samples.

Brassica Plants to Provide Enhanced Human Mineral Nutrition: Selenium Phytoenrichment and Metabolic Transformation

It is widely recognized that plants contain nutrients and chemicals that are beneficial beyond general nutrient needs. In fact, research has shown that of the more than 4,000 chemical compounds found in plants, some help prevent the development of disease by interfering with the destructive oxidation of cellular components, and others prevent the development of certain cancers. Moreover, plants can also provide for enhanced mineral nutrition. The same mechanisms that allow plants to extract heavy metals such as lead and uranium can also be applied to the phytoextraction of desirable, beneficial micronutrients, such as selenium, under controlled growing conditions. This process provides for hyperenrichment of the desired micronutrient. Plants containing targeted micronutrients can provide the minimum daily adult requirements in a single tablet or capsule. We describe in this report selected cultivars of Brassica juncea, or Indian mustard, a member of the Brassicaceae (formerly the Cruciferae) containing 2,000 ppm selenium under hydroponic cultivation. The supplied selenium is converted by the plants to organic selenium compounds following the sulfur assimilatory scheme. We present data that confirms the usefulness of Indian mustard and the potential of Astragalus bisulcatus as a source of genetic material for enhancement of selenium biotransformation in the mustard plant.

Speciation of organic selenium compounds by reversed-phase liquid chromatography and inductively coupled plasma mass spectrometry. Part I. Sector field instrument with low mass resolution

The speciation of selenocystine, selenocystamine, selenomethionine and selenoethionine was studied by on-line coupling of high performance liquid chromatography with inductively coupled plasma mass spectrometry with hydraulic high pressure nebulization (HHPN) for sample introduction employing a double-focusing magnetic sector field mass spectrometer in order to achieve the utmost sensitivity. Reversed-phase chromatography was applied to separate the organic Se compounds. The eluent was 30 mm ammonium buffer adjusted to pH 3.0 in methanol-water (5+95 v/v). The operating conditions for chromatographic separation (pH of the mobile phase, methanol content of the mobile phase, pH of the sample and sample uptake rate) were carefully optimized. With the developed procedure, detection limits below 0.02 ng ml –1 were achieved, so that even low pg levels could be detected when applying sample volume of 200 μl.

ChemInform Abstract: Synthesis and Stereochemistry of Optically Active Organic Selenium and Tellurium Compounds

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Determination of trace inorganic selenium in organoselenium (selenosugar) oral nutrition liquids by graphite furnace atomic absorption spectrometry with hydride generation

A method has been proposed for the determination of trace levels of inorganic selenium in organoselenium (selenosugar) oral nutrition liquids using hydride generation-graphite furnace atomic absorption spectrometry (HG-GFAAS), taking advantage of the fact that this organic selenium compound did not generate volatile hydride upon reduction. K2S2O8 was selected for the decomposition of the compound in a boiling water bath. Selenium was found to give a sharp analytical signal upon reduction with NaBH4 in 1.0 mol L-1HCl medium. The characteristic mass giving an integrated absorbance of 0.0044 s was 21 pg. An absolute detection limit (3s) of 36 pg was obtained. The recovery was in the range of 94.2–102.1%. Less than parts per million levels of inorganic Se in the presence of organic selenium can be determined.

Retention behavior of inorganic and organic selenium compounds on a silica-based strong-cation-exchange column with an inductively coupled plasma mass spectrometer as selenium-specific detector

The retention behavior of eight selenium compounds (selenous acid, selenic acid, selenocystine, selenohomocystine, selenomethionine, selenoethionine, trimethylselenonium iodide, and dimethyl(3-amino-3-carboxy-1-propyl)selenonium iodide) with aqueous solutions of pyridine (20 mmol/l) in the pH range 2.0–5.7 on a Supelcosil LC-SCX cation-exchange column was investigated. An inductively coupled plasma mass spectrometer was employed as the selenium-specific detector. To increase the nebulization efficiency, the Meinhard concentric glass nebulizer was replaced by a hydraulic high-pressure nebulizer. At pH 5.0, seven selenium compounds could be separated within 400 s, but selenohomocystine and selenomethionine had the same retention time. Selenomethionine can be separated from selenohomocystine with an aqueous solution of pyridine (20 mmol/l) adjusted with formic acid to pH 2.0. At 1 ng Se ml −1, the relative standard deviations ( n=5) of the signal area for the eight selenium compounds ranged from 7 to 11%, and at 50 ng Se ml −1 from 0.6 to 2.6%.

Inhibition of cdk2 kinase activity by methylselenocysteine in synchronized mouse mammary epithelial tumor cells.

Methylselenocysteine (MSC), an organic selenium compound has significant anticarcinogenic activity against mammary tumorigenesis. Previous experiments have demonstrated that MSC and inorganic selenite inhibit mammary cell (TM6 cell line) growth through different pathways. The present investigation demonstrated that MSC arrested cells in S phase during the TM6 cell cycle, which was followed by cells entering apoptosis at 48 h. Methylselenocysteine specifically affected the cdk2 kinase activity of the TM6 cells (54% reduction) at 16 h after release from growth arrest. The cdk4 kinase activity did not change during the cell cycle, confirming that cells had passed the G1 checkpoint and had entered S phase. The amount of cyclin E associated with cdk2 was increased by MSC by the 12 h time point, thereby facilitating entry of cells into S phase. Afterwards, cyclin E and cyclin A associated with cdk2 did not change for the remainder of the cell cycle. The data demonstrate that inhibition of mammary cell growth by MSC is mediated by alterations in progression of cells through S phase. The decrease in cdk2 kinase activity is coincident with prolonged arrest in S phase. One consequence of prolonged arrest may be apoptosis.

Comparative effects of selenite and selenite on the glutathione-related enzymes activity in pig blood platelets

The effects of inorganic selenium (Se) compounds (sodium selenite and selenate) on the activities of glutathione-related enzymes (glutathione peroxidase, glutathione-S-transferase [GST] and glutathione reductase [GR]) in pig blood platelets were investigated in vitro. GST activity in blood platelets treated with 10(-4)M of selenite was reduced to 50%, whereas no decrease GST activity was observed after the treatment of platelets with the same dose of selenate. In platelets incubated with physiological doses (10(-7) and 10(-6)M) of Se compounds, the activity of glutathione peroxidase (GSH-Px) was enhanced (about 20%). GR activity after the exposure of platelets to tested Se compounds was unaffected.

Selenium methylation and toxicity mechanism of selenocystine

Selenium is an essential trace element and a toxicant for animals. Selenocystine, a selenium-containing amino acid, is one of the chemical forms in which selenium exists in food. This review summarized recent studies on the toxicity mechanism of selenocystine in experimental animals. Hepatotoxicity is caused by repeated oral administration of selenocystine. Selenocystine is metabolized by reduced glutathione and/or glutathione reductase to hydrogen selenide via selenocysteine-glutathione selenenyl sulfide. The hydrogen selenide is a key intermediate in the selenium methylation metabolism of inorganic and organic selenium compounds. Accumulation of the hydrogen selenide resulting from inhibition of the selenium methylation metabolism, detoxification metabolic pathway of selenium, is found in animals following repeated administration of a toxic dose of selenocystine. The excess of the hydrogen selenide produced by inhibition of the selenium methylation metabolism contributes to the hepatotoxicity caused by selenocystine.

Studies on the Pharmacokinetics of Ebselen in Rats (3): Absorption, Distribution and Excretion after Administration of 75Se-labelled Compound.

In order to clarify whether ebselen, 2-phenyl-1, 2-benzisoselenazol-3(2H)-one is metabolized to liberate its selenium atom as an inorganic compound(s) or not in vivo, blood level of radioactivity and excretion of radioactivity in urine and feces were determined, and whole body autoradiograms were prepared after oral administration of 75Se-ebselen (50 mg/kg) or intravenous injection of Na275SeO3, an inorganic selenium compound, as a control (1 mg/kg) to male rats. Following results were obtained: 1. For 75Se-ebselen dosing group, the mean blood levels of radioactivity reached the Cmax of 29.17 nmol eq. to ebselen/ml (8.00 μg eq./ml) at 1 hr and declined with a half-life, t1/2 of 7.6 hr from 2 to 24 hr after dosing. For Na275SeO3 dosing group, the blood level of radioactivity was 57.75 nmol eq. to Na275SeO3/ml (9.99 μgeq./ml) at the first sampling time and thereafter declined slowly with a half-life, t1/2 of 190 hr from 24 to 168 hr after dosing. 2. For 75Se-ebselen dosing group, the highest levels of radioactivity were observed in the gastric and intestinal contents, followed by fat, brown fat and liver, showing higher radioactivity than that in blood. The overall distribution of radioactivity decreased with time and the radioactivity was not detected at 168 hr after dosing. For Na275SeO3 dosing group, high levels of radioactivity remained in liver, kidney and blood even at 168 hr after dosing. 3. For 75Se-ebselen dosing group, within 168 hr after dosing, 53.8% of the dosed radioactivity was excreted in urine, and 45.8% of that in feces. The residual radioactivity in the carcass was not detected. For Na275SeO3 dosing group, within 168 hr after dosing, 44.8% of the dosed radioactivity was excreted in urine, and 8.0% of that in feces. The radioactivity remained in the carcass, being 41.1% of the dose. From the results above, the extent of inorganic selenium release from ebselen was estimated to be 0.0% of the dose.

Synthesis and Stereochemistry of Optically Active Organic Selenium and Tellurium Compounds

Some optically active tricoordinate selenium and tellurium compounds, such as selenonium ylide, telluronium ylide, selenonium imide, selenonium salt, telluronium salt, and telluroxide, were isolated by means of optical resolution of corresponding diastereomeric mixtures or asymmetric syntheses. Absolute configurations of the optically active isomers obtained were determined by their X-ray crystallographic analyses, specific rotations, and circular dichroism spectra. Racemization of the isomers by pyramidal inversion or via achiral hydrate were also examined, and activation energies for the pyramidal inversion were estimated based on ab initio MO calculations.

Speciation analysis of arsenic and selenium compounds by capillary electrophoresis.

High-performance capillary electrophoresis is applied to the separation of different inorganic and organic arsenic and selenium compounds. In comparison with UV-detection, an approach with conductivity detection is described expecting higher sensitivity and universality. In this case the capillary was statically modified with CTAB before the electromigration procedure. The separation was performed with an electrolyte system consisting of CHES and Triton X-100. Detection limits of 0.06 mg/L or lower were obtained for As(V) and Se(VI). Water samples of an arsenic-polluted tailing of tin mining processes were analysed for anions as well as arsenic and selenium species.

Selenium status in infants and children with phenylketonuria and in maternal phenylketonuria.

The selenium status was investigated in 87 patients of the German Collaborative Study of Phenylketonuria (PKU) (mean age 9.7 years). The selenium values and glutathione peroxidase activity in plasma and erythrocytes were negatively correlated to the quality of dietary management (mean plasma phenylalanine value). Despite a low selenium state, the children showed no clinical sign of deficiency and almost all biochemical parameters checked were normal. In the low selenium state thyroxine values are increased and decline during selenium supplementation, whereas tri-iodothyronine and thyroid stimulating hormone levels remain unchanged. The reduction in glutathione peroxidase activity in plasma was more pronounced than in the erythrocytes pointing to a different availability of both enzymes for selenium. In addition we estimated the selenium status in 29 women with PKU during pregnancy. In 32 healthy pregnant women we observed a decrease in plasma selenium values and the glutathione peroxidase activity in the third trimester, whereas the erythrocyte glutathione peroxidase activity remained stable. In contrast to the healthy women we found in the PKU group a steady decrease of all selenium parameters tested during the whole pregnancy. During the long-term low-dose selenium supplementation in PKU children the glutathione peroxidase activity of plasma and erythrocytes increased. They reached a similar plateau after the application of inorganic or organic selenium compounds. In contrast the selenium values of plasma and whole blood showed only a plateau after the application of sodium selenite. The supplementation with low doses of selenium in the form of selenomethionine increased the plasma and whole blood selenium values constantly within the first 9 months. Therefore selenomethionine supplementation cannot be recommended.

Speciation of organic selenium compounds by high-performance liquid chromatography–inductively coupled plasma mass spectrometry in natural samples

The importance of selenium in the environment and in biological systems is now well recognized. Its biochemical functions, e.g., its anti-oxidant role and therefore cell protecting function, as an essential constituent of the enzyme glutathione peroxidase, has provoked a growing interest in the determination of this element. Selenoamino acids are essential for the understanding of the biogeochemical cycle of Se and TMSe+ is a known urinary metabolite present at high levels when Se is taken in excess. In this work we present a hyphenated technique (HPLC–ICP-MS) available for the separation of the organic Se compounds (selenocystine, selenomethionine and trimethylselenonium ion). The choice of column and solvents has been a critical parameter. Good repeatability and excellent detection limits (less than 1 µg l–1 for each species) have been reached for standard solutions and the application to some natural samples (enriched yeast, human serum and urine) has shown quite promising results.

Speciation analysis of some organic selenium compounds. A review

The first page of this article is displayed as the abstract.

Effects of organic and inorganic selenium compounds on rat mammary tumor cells.

To explore cellular effects of potent organoselenium chemopreventive agents we have used a rat mammary tumor cell line. We demonstrate that 1,4-phenylenebis(methylene) selenocyanate (p-XSC) at a dose of 5 microM is a more potent inhibitor of DNA, RNA and protein synthesis as well as of mitochondrial transmembrane potential than its chemopreventive counterparts benzyl selenocyanate (BSC) and sodium selenite. These differences were also reflected in reduced growth rate by 24 and 48 hr. Cell-cycle and cell-morphology analysis revealed that higher doses of p-XSC (10 microM) caused DNA fragmentation which was accompanied with partial loss of nuclear stainability, whereas BSC caused a noticeable change in cell-cycle distribution and extensive micronucleation. Overall, our results point to cellular targets of selenium compounds which may mediate their chemopreventive activities in mammary tissues.

The Effect of Selenium Compounds (Selenite, Selenate, Ebselen) on the Production of Thromboxane and Prostacyclin by the Human Term Placenta in Vitro

Selenium not only has an important role in controlling lipid hydroperoxides through glutathione peroxidase (GPX) activity, but also can produce oxidative stress through exposure to selenite. Because levels of lipid hydroperoxides affect the production of thromboxane A2 (TxA2) and prostacyclin (PGI2), selenium compounds may be able to influence the production of these two vasoactive substances. Late-gestation pregnancy reduces the half-life of PGI2; therefore, pregnancy itself may enhance susceptibility to changes in the production of TxA2 and PGI2. The objective of this investigation was to determine if different selenium compounds, selenite, selenate, and ebselen, can influence the human term placental production of thromboxane B2 (TxB2) and 6-keto-prostaglandin F1α (6-keto-PGF1α), the inactive hydrolysis products of TxA2 and PGI2. Although selenate exposure (40 μM 24 hr) increased TxB2 production, and ebselen (an organic selenium compound with GPX activity) exposure (40 μM, 24 hr) decreased both TxB2 and 6-keto-PGF1α production, only selenite had a significant effect on the TxB2/6-keto-PGF1α, ratio. Three exposures to selenite at 6 μM (32 hr) significantly decreased 6-keto-PGF1α production with no effect on TxB2 production or tissue GPX activity. Following two exposures to selenite at 20 and 40 μM (24 hr), TxB2 production was significantly increased, while tissue 6-keto-PGF1α production and tissue GPX activity were significantly decreased. These results indicate that selenite, but not selenate or ebselen, can directly affect the human placenta by producing changes in the TxB2/6-keto-PGF1α ratio, which may be related to increased vasoconstriction and blood coagulation.

Chalcogen-Centered Radicals

Abstract The main types of radicals formed in initiated reactions of organic compounds of selenium and tellurium, detection methods, and their physico-chemical properties and reactivity are presented in this review.