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PubMed2001

Transport measurements across Caco-2 monolayers of different organic and inorganic selenium: influence of sulfur compounds.

The transport and uptake of the most common Se compounds, selenate (SeO42-), selenite (SeO3(2-)), selenomethionine, and selenocystine, were investigated using confluent monolayers of Caco-2 cells, a human carcinoma cell line. Comparative measurements were performed in the absorptive (apical to basolateral side) and exsorptive (basolateral to apical side) directions. Apparent permeability coefficients (Papp), calculated from transport experiments in the absorptive direction, showed increasing values in the following rank order: about 1 x 10(6) cm/s < mannitol < SeO3(2-) < or = selenocystine < selenomethionine < SeO4(2-) < or = about 16 x 10(4) cm/s. The ratios of the Papp measured in the absorptive versus exsorptive directions indicated that only the organic forms presented a net polarized transport (Papp ratio >> 1), suggesting the presence of a transcellular pathway. No significant excretion was observed. The transport of selenomethionine was inhibited by its sulfur analog, methionine, suggesting a common transport mechanism. In contrast, an inhibition of the transport of selenocystine by cysteine was not observed. From the two substrates tested, sulfate and thiosulfate, only thiosulfate inhibited the transport of SeO4(2-) . This effect was also observed for SeO32- (i.e., was unspecific), which questioned the assertion of a common transport for sulfate and SeO4(2-) and may confirm the paracellular pathway of SeO42- suggested by the Papp ratio of about 1. The addition of glutathione (GSH) in large excess had no consequence on the passage of SeO3(2-) but strongly increased the uptake (about fourfold). The liquid chromatography - mass spectrometry (LC-MS) data showed that, in the ionic condition of incubation medium, GSH promptly reduced SeO3(2-) (< or = 2 min) in its elemental form Se0, which cannot ascribe to selenodiglutathione a direct role in the effect of GSH.

Biological Transport↗
PubMed2007

Selenomethionine induced transcriptional programs in human prostate cancer cells.

PURPOSE: We determined the effects of selenomethionine, the major organic selenium containing compound found in the diet and the form of selenium being used in the Selenium and Vitamin E Cancer Prevention Trial, on prostate cancer cells. MATERIALS AND METHODS: We assessed global transcript profiles of selenomethionine treated LNCaP using cDNA microarrays and compared them to those of cells treated with methylselenic acid, a direct precursor of methylselenol, which is the active form of selenium in vivo. RESULTS: After treatment with selenomethionine 2,336 unique genes showed expression changes of at least 1.5-fold in at least 3 time points during 48 hours and 366 unique transcripts differed significantly between selenomethionine and methylselenic acid treated LNCaP. Approximately half of the 76 cell cycle regulated genes affected by selenomethionine were down-regulated and enriched for genes associated with the G2/M phase. Flow cytometry analysis showed that selenomethionine induced G2/M arrest in LNCaP at low concentrations. Selenomethionine also affected expression levels of 35 known androgen responsive genes and 18 of these transcripts showed changes that were the inverse of those seen after androgen stimulation. At high concentrations selenomethionine decreased prostate specific antigen promoter driven luciferase expression. CONCLUSIONS: Selenomethionine modulates transcript levels of genes involved in a number of biological processes, including cell cycle/apoptosis androgen signaling, signal transduction and transcriptional regulation. Although the pathways affected paralleled in many ways those that are modulated by methylselenic acid, distinct differences in transcript patterns and effects on cell cycle regulation suggest that different selenium compounds could exert unique effects in prostate cells.

Humans↗
PubMed2006

A combined experimental and quantum chemistry study of selenium chemical shift tensors.

A comprehensive investigation of selenium chemical shift tensors is presented. Experimentally determined chemical shift tensors were obtained from solid-state 77Se NMR spectra for several organic, organometallic, or inorganic selenium-containing compounds. The first reported indirect spin-spin coupling between selenium and chlorine is observed for Ph(2)SeCl(2) where 1J(77Se,35Cl)iso is 110 Hz. Selenium magnetic shielding tensors were calculated for all of the molecules investigated using zeroth-order regular approximation density functional theory, ZORA DFT. The computations provide the orientations of the chemical shift tensors, as well as a test of the theory for calculating the magnetic shielding interaction for heavier elements. The ZORA DFT calculations were performed with nonrelativistic, scalar relativistic, and scalar with spin-orbit relativistic levels of theory. Relativistic contributions to the magnetic shielding tensor were found to be significant for (NH4)2WSe4 and of less importance for organoselenium, organophosphine selenide, and inorganic selenium compounds containing lighter elements.

Journal Article↗
PubMed2005

Separation and identification of selenotrisulfides in epithelial cell homogenates by LC-ICP-MS and LC-ESI-MS after incubation with selenite.

To elucidate how selenite is metabolised in the intestine after oral intake, it was incubated with homogenized epithelial cells from pigs. When the metabolites were analysed by LC-ICP-MS, two major selenium metabolites were separated in the supernatant from the homogenate. These metabolites were formed instantly but disappeared within 15 min. No other selenium-containing compounds appeared during this time. Hence, the secondary reaction products were either volatilised or precipitated. To verify the identity of the compounds, a larger amount of selenite was incubated with epithelial cells. The presence of Cys-Se-SG and GS-Se-SG was verified by LC-ESI-MS. Selenotrisulfides were synthesized by reaction of L-cysteine and L-glutathione with sodium selenite. The reaction mixture contained three main products: selenodicysteine (Cys-Se-Cys), selenocysteine glutathione (Cys-Se-SG), and selenodiglutathione (GS-Se-SG). The two transient selenium compounds in the epithelial cell incubation mixture co-eluted with the synthesized Cys-Se-SG and GS-Se-SG, respectively. The identities of these compounds were verified by LC-ESI-MS. Hence, these selenium metabolites have now been identified by ESI-MS after isolation from epithelial cells.

Animals↗
PubMed1991

Products of the reaction of selenite with intracellular sulfhydryl compounds.

The usual first step in the intracellular metabolism of exogenous selenite is its chemical reaction with glutathione to form selenodiglutathione (1). We have investigated whether selenite also reacts intracellularly with other SH compounds. HeLa cells were exposed to [75Se]selenite and lysed with SDS. Cellular proteins and nucleic acids were precipitated with trichloroacetic acid, and the acid-soluble fraction was analyzed by ion-exchange thin-layer chromatography (ion-exchange TLC) and autoradiography. In control cells, the major [75Se]-containing species detected can be identified by its mobility as selenodiglutathione. Two other species were detected, which can be identified as selenodimercaptoethylamine and the mixed selenotrisulfide of mercaptoethylamine and glutathione. In contrast, in cells that were depleted of glutathione (by treatment with buthionine sulfoximine), very little, if any, selenodiglutathione was detected. However, new [75Se]-containing species were detected, which can be identified as selenodicysteine and the mixed selenotrisulfide of cysteine and glutathione. The same species were detected when [75Se]selenite was added to the acid-soluble fraction of a cell extract (as opposed to living cells), confirming that these compounds can be formed by nonenzymatic reactions.

Antimetabolites↗
PubMed1992

Selenium and arsenic in biology: their chemical forms and biological functions.

Based on the recent development of analytical methods, sensitive systems for the analysis and speciation of selenium and arsenic have been established. A palladium addition technique was developed for the accurate determination of selenium in biological samples using graphite furnace atomic absorption analysis. For the speciation of the elements, combined methods of HPLC either with ICP-AES or with ICP-MS were found to work well. These systems were applied to the elucidation of the chemical form of the elements in natural samples. Some chemical properties of the selenium-mercury complex in dolphin liver were elucidated: i.e., it was a cationic, water-soluble, low molecular weight compound containing selenium and mercury in a 1:1 molar ratio, and was shown to be different from a known selenium-mercury complex, bis(methylmercuric)selenide. The major selenium compound excreted in human urine was revealed to be other than any of those previously identified (TMSe, selenate, and selenite). TMSe, a suspected major metabolite in urine, was found, if at all, in low levels. The major water-soluble, and lipid-soluble arsenic compounds in a brown seaweed, U. pinnatifida (WAKAME), were rigorously identified, and the results were compared with other data on marine algae and animals. The major organic arsenic compounds (termed "arseno-sugars") in marine algae commonly contain 5-deoxy-5-dimethylarsinyl-ribofuranoside moiety. There are various kinds of arseno-sugar derivatives containing different side-chains attached to the anomeric position of the sugar, and the distribution of each arsenic species seems to be related to algal species. The arseno-sugar (A-XI) is present in every alga so far examined, is metabolized to lipids, and possibly may play some specific role in the algal cells. On the other hand, the major arsenic compound in fish, crustacea and molluscs has been identified as arsenobetaine, which is an arseno-analog of glycinebetaine, a very common osmo-regulator in living organisms. Arsenobetaine is not detected in marine algae while arseno-sugars are not present in marine animals except for some molluscs which contain both compounds in considerable amounts. Arsenobetaine is present in the urine of human beings who have eaten foods derived from marine animals.

Animals↗
PubMed1995

Use of INAA to study Se, Sb, Zn and Co levels of yeast cells.

Yeast cells, Saccharomyces cerevisiae, were exposed to Sb(V)(10-5M) and SeO2(10-4M) or seleno-cystine (CySe)2(5 x 10-5M). Se, Sb, Zn and Co levels of the yeast were measured by instrumental neutron activation analysis. The results obtained show that in the absence of Se, Sb is taken up by the cells and the highest concentration of Sb in the yeast was observed during the initial 2.5 h of incubation. Both Se-compounds resulted, in general, in a minute decrease of uptake yield of Sb by the cells. This effect can be particularly observed in the presence of SeO2. The presence of Sb in the yeast medium slightly increased the Se level only after long incubation times. Se uptake by the yeast was higher (regardless of Sb dosage) when the yeast was incubated in the medium containing (CySe)2 (in comparison with SeO2). The presence of Se-compounds and/or Sb caused decrease in the levels of Zn found in the cells. While SeO2 presence resulted in minor changes of the Co level of the yeast, the combined presence of Sb and Se-compounds produced the significant enhancement of Co abundance. The similar effect was noted in the yeast incubated in a medium containing only (CySe)2 or Sb.

Antimony↗
PubMed1999

X-ray absorption spectroscopy of selenium-containing amino acids.

The selenium K-edge X-ray absorption spectra of selenomethionine, selenocysteine, selenocystine, and sulfo-selenocystine in solution are compared with the corresponding sulfur K-edge spectra of the sulfur analogues of these compounds. The selenium and sulfur spectra follow similar trends, although the latter are significantly sharper owing to the longer core hole lifetime at the lower energies where sulfur absorbs. The spectra of the selenium compounds are sufficiently distinct that it is reasonable to expect that curve fitting will allow the speciation of the forms of selenium in complex biological samples.

Amino Acids↗
PubMed1996

Interaction between trace elements: selenium and cadmium ions.

The interaction between several inorganic and organic selenium-containing compounds (selenite, selenate, selenourea and selenomethionine) and Cd2+ ions was studied by polarography. The changes in polarographic currents and half-wave potentials of the metal ions as a function of the Se-derivative concentration were followed. Experimental results suggest a different behaviour depending on the oxidation state of selenium. Any interaction between selenate and Cd2+ ions can be excluded. In the case of selenite, the presence of complexes in the solution was demonstrated. The shift in the Cd2+ reduction half-wave potential when a relatively high concentration of selenourea is present indicates formation of complexes, while the decrease in limiting current reflects the limited solubility of the complex itself. Results concerning selenomethionine suggest a very weak interaction with Cd2+ ions. These preliminary results are discussed in comparison with previous findings in cellular systems and may prove helpful in understanding cadmium ion toxicity and the in vivo altered distribution of various metal ions following the administration of selenium compounds.

Cadmium↗
PubMed2002

Novel reactivity of SeO2 with 1,3-dienes: selenophene formation.

A novel and efficient method for the synthesis of selenophenes is disclosed. Selenophenes were synthesized in high yields in a single operation from 1,3-dienes containing a carbonyl group at the C-1 position and selenium dioxide. The bidirectional synthesis of selenophenes can also be demonstrated using this method. The selenophene is believed to form via a [4 + 2] cycloaddition between diene and selenium dioxide.

Alkenes↗