Metabolism of L-selenomethionine and selenite by probiotic bacteria: in vitro and in vivo studies

Since selenium supplements have been shown to undergo biotransformation in the gut, probiotic treatment in combination with selenium supplements may change selenium disposition. We investigated the metabolism of L-selenomethionine (SeMet) and selenite by probiotic bacteria in vitro and the disposition of selenium after probiotic treatment followed by oral dosing with SeMet and selenite in rats. When SeMet was incubated anaerobically with individual antibiotic-resistant probiotic strains (Streptococcus salivarius K12, Lactobacillus rhamnosus 67B, Lactobacillus acidophilus L10, and Bifidobacterium lactis LAFTI® B94) at 37°C for 24 h, 11-18% was metabolized with 44-80% of SeMet lost being converted to dimethyldiselenide (DMDSe) and dimethylselenide (DMSe). In similar incubations with selenite, metabolism was more extensive (26-100%) particularly by the lactobacilli with 0-4.8% of selenite lost being converted to DMSe and DMDSe accompanied by the formation of elemental selenium. Four groups of rats (n = 5/group) received a single oral dose of either SeMet or selenite (2 mg selenium/kg) at the time of the last dose of a probiotic mixture or its vehicle (lyoprotectant mixture used to maintain cell viability) administered every 12 h for 3 days. Another three groups of rats (n = 3/group) received a single oral dose of saline or SeMet or selenite at the same dose (untreated rats). Serum selenium concentrations over the subsequent 24 h were not significantly different between probiotic and vehicle treated rats but appeared to be more sustained (SeMet) or higher (selenite) than in the corresponding groups of untreated rats. Probiotic treated rats given SeMet also had selenium concentrations at 24 h that were significantly higher in liver and lower in kidney than untreated rats given SeMet. Thus, treatment with probiotics followed by SeMet significantly affects tissue levels of selenium.

Selenomethionine incorporation into amyloid sequences regulates fibrillogenesis and toxicity

Background

The capacity of a polypeptide chain to engage in an amyloid formation process and cause a conformational disease is contained in its sequence. Some of the sequences undergoing fibrillation contain critical methionine (Met) residues which in vivo can be synthetically substituted by selenomethionine (SeM) and alter their properties.

Methodology/Principal Findings

Using peptide synthesis, biophysical techniques and cell viability determinations we have studied the effect of the substitution of methionine (Met) by selenomethionine (SeM) on the fibrillogenesis and toxic properties of Aβ40 and HuPrP(106–140). We have found that the effects display site-specificity and vary from inhibition of fibrillation and decreased toxicity ([SeM³⁵]Aβ40, [SeM¹²⁹]HuPrP(106–140) and [SeM¹³⁴]HuPrP(106–140)), retarded assembly, modulation of polymer shape and retention of toxicity ([SeM¹¹²]HuPrP(106–140) to absence of effects ([SeM¹⁰⁹]HuPrP(106–140)).

Conclusions/Significance

This work provides direct evidence that the substitution of Met by SeM in proamyloid sequences has a major impact on their self-assembly and toxic properties, suggesting that the SeM pool can play a major role in dictating the allowance and efficiency of a polypeptide chain to undergo toxic polymerization.

Evaluating the trophic transfer of selenium in aquatic ecosystems using caged fish, X-ray absorption spectroscopy and stable isotope analysis

This research evaluated the dominant exposure pathways with regard to the bioaccumulation and trophic transfer of selenium (Se) in caged small-bodied fish inhabiting the receiving waters of a uranium-processing mill in northern Saskatchewan, Canada. A 21-day cage study was conducted using wild naïve lake chub (Couesius plumbeus) collected from a reference lake and caged in a reference and an exposure lake downstream of the mill discharge. Caged fish were fed commercially produced Chironomus spp. diets of 1.5 (basal - commercial food) and 5.5 (lab reared in Se-spiked water) μgSe/g (dry weight) at a feeding ration of 10 percent percent body weight/day. Lake chub fed the Se-spiked diet and caged in the reference lake showed increased whole-body Se concentrations compared to chub fed the basal diet after 21 days. Lake chub caged in the exposure lake from both the elevated Se and basal diet groups had significantly greater whole-body Se concentrations compared to the reference lake, and were not significantly different from each other. The use of stable carbon (C), nitrogen (N), and sulphur (S) isotope analyses indicated that alternate benthic food sources native to the exposure lake were likely consumed in conjunction with the controlled diets. Stable isotope analysis of both wild and caged lake chub indicated that the N and S isotopic signatures decreased with increasing Se exposure, which was reflective of the differences in isotopic signatures of the food sources. Dose-dependent substitution of Se for S in methionine as a consequence of dietary Se exposure was illustrated by a decreasing whole-body S isotope signature and an increasing proportion of selenomethionine-like compounds (as measured by synchrotron-based X-ray absorption spectroscopy) with increasing Se exposure. Speciation results from caged lake chub indicated that Se substituted for S in methionine was the dominant Se species found in caged lake chub exposed to dietary sources of Se.

Selenium uptake and speciation in wild and caged fish downstream of a metal mining and milling discharge

The aim of this research was to evaluate the dominance of the feeding pathway with respect to selenium (Se) uptake and speciation in fish inhabiting the receiving waters downstream of a uranium processing mill in northern Saskatchewan, Canada. The experimental design included analysis of Se in the predominant fish species located in the study area, a caging validation study using wild, naïve (i.e., collected from a reference lake) lake chub (Couesius plumbeus) and spottail shiner (Notropis hudsonius), and a 21-day feeding cage study using wild naïve lake chub. Three exposure lakes located downstream of the uranium mill and one reference lake situated in an adjacent watershed were studied to investigate a gradient of Se exposure. Lake chub were identified as more suitable candidates for caging due to higher survival and condition factor at the completion of the 21-day trial. Analytical results indicated that lake chub caged in the exposure lakes had significantly greater whole-body Se concentrations after 21 days compared to fish caged in the reference lake. Selenium speciation results (obtained using X-ray absorption spectroscopy) from wild and caged lake chub indicated that organic Se modeled as selenomethionine was the dominant form of Se found in both wild and caged lake chub from the exposure lakes, and that selenomethionine (R-Se-R) acts as a marker of bioavailable Se exposure.

Anti-hemolytic and peroxyl radical scavenging activity of organoselenium compounds: an in vitro study

Selenium-containing amino acids, selenocystine (CysSeSeCys), methylselenocysteine (MeSeCys), and selenomethionine (SeMet) have been examined for anti-hemolytic and peroxyl radical scavenging ability. Effect of these compounds on membrane lipid peroxidation, release of hemoglobin, and loss of intracellular K(+) ion as a consequence of peroxyl radicals-induced oxidation of human red blood cells were used to evaluate their anti-hemolytic ability. The peroxyl radicals were generated from thermal degradation of 2,2'-azobis(2-methylpropionamidine) dihydrochloride. Significant delay (t(eff)) was observed in oxidative damage in the presence of the selenium compounds. From the IC(50) values for the inhibition of hemolysis, lipid peroxidation, and K(+) ion leakage, the relative anti-hemolytic ability of the compounds were found to be in the order of CysSeSeCys > MeSeCys > SeMet. The anti-hemolytic abilities of the compounds, when compared with sodium selenite (Na(2)SeO(3)) under identical experimental conditions, were found to be better than Na(2)SeO(3). Relative rate constants estimated for the reaction of MeSeCys and SeMet with peroxyl radicals by competition kinetics using ABTS(2-) as a reference confirmed that all the compounds are efficient peroxyl radical scavengers. Comparison of the GPx-like activity of these compounds, by NADPH-GSH reductase coupled assay, indicated that CysSeSeCys exhibits the highest activity. Based on these results, it is concluded that among the compounds examined, CysSeSeCys, possessing the ability to reduce peroxyl radicals and hydroperoxides showed efficient anti-hemolytic activity.

[Effects of organic selenium substance, selenomethionine, in acute alcohol intoxication]

The effect of the preliminary saturation of rats with selenomethionine (50 g/kg, intragastrically, daily, 10 days) prior to acute alcohol intoxication (5 g/kg, 20% ethanol solution, intragastrically, singly on the 11th day with the exposure for 2 hours) was investigated. The activities of glutathione peroxidases (gastrointestinal mucosa, blood plasma, erythrocytes, liver), the levels of oxidized and reduced glutathione, LPO intensity and blood corticosterone level were studied.

Biotransformation of L-selenomethionine and selenite in rat gut contents

L-selenomethionine (SeMet) and sodium selenite are widely used selenium nutritional supplements with potential benefit in preventing cancer. However, supplementation is not without risks of toxicity if intake is too high. The aim of the present study was to investigate SeMet and selenite metabolism in the gastrointestinal tract with particular focus on the formation of the volatile selenium excretion products, dimethylselenide (DMSe) and dimethyldiselenide (DMDSe). Adult male Wistar rats (n = 5) were euthanized, their intestinal tracts removed and the contents of jejunum, ileum, caecum and colon used to prepare 10% suspensions in saline. SeMet and selenite (0.5-0.6 mM) were then incubated with these suspensions at 37°C for 3 h. Caecum and colon contents were the most metabolically active towards SeMet with 30% and 15% metabolized over 3 h. DMDSe was the only volatile selenium metabolite detected accounting for 8.7 ± 1.3% of the selenium lost in caecum contents. Selenite was completely metabolized by caecum contents and 73% by colon contents under the same conditions forming DMSe (5.7 ± 0.9% of the selenium lost in caecum) and a precipitate of red amorphous elemental selenium. Based on previous literature and these results, we conclude that the gut microbiota contributes to the excretion of excess selenium through the production of methylated selenium compounds and elemental selenium.

Sites and extent of selenomethionine incorporation into recombinant Cas6 protein by top-down and bottom-up proteomics with 14.5 T Fourier transform ion cyclotron resonance mass spectrometry

Selenomethionine-modified proteins can improve X-ray crystallographic structural resolution by multi-wavelength anomalous diffraction (MAD) phasing. However, the specificity and extent of selenomethionine incorporation must first be assessed. Bottom-up and top-down proteomics with a modified 14.5 T LTQ Fourier transform ion cyclotron resonance mass spectrometer offer a quick, accurate, and robust method to locate and quantify selenomethionine incorporation after auxotrophic expression. Selenomethionine (methionine with sulfur replaced by selenium) has a different natural-abundance isotopic distribution and a mass increase of 47.94 Da relative to wild-type methionine. Here, both wild-type and selenomethionine-substituted forms of the Cas6 protein containing 'clustered regularly interspaced short palindromic repeats' (CRISPRs) were expressed and purified. Comparative bottom-up and top-down proteomics confirmed that all six methionines were fully replaced by selenomethionines in Se-Cas6.

Competition between selenomethionine and methionine absorption in the intestinal tract of green sturgeon (Acipenser medirostris)

l-Selenomethionine (SeMet) is a dominant form of selenium (Se) found in organisms at all levels of aquatic food chains and a key source of Se bioaccumulation and ecotoxicity. In mammals, intestinal absorption of SeMet is at least partly via the Na(+)-dependent neutral amino acid transporter. The mechanism of SeMet absorption and competitive effects of other dietary components on SeMet absorption in fish are unknown. Thus the in vitro uptake rates of l-methionine (Met) and the competitive effect of SeMet on Met absorption, an indicator that SeMet uses the same nutrient transporter(s) for absorption, in the various regions of the green sturgeon (Acipenser medirostris) intestine were investigated using intact tissues (a modified everted sleeve method). Intestinal tissue was incubated in Ringer's solution containing 0-10mmolL(-1) Met or SeMet (n=5 for each substrate's concentration and intestinal region), respectively, as well as constant tracer levels of isotope-labeled Met. The data indicate that SeMet uptake was mediated by the same transporter(s) as Met and that the absorption kinetics were similar for both substrates. When there were differences in absorption they appeared to be mostly due to higher permeability (passive uptake) of the tissue for Met than for SeMet, particularly in the pyloric caeca (PC) and distal intestine (DI). Maximum rates of absorption, on the other hand, tended to be higher for SeMet than Met in the mid intestine and DI, whereas differences in affinity for the transporters varied between these tissues but were very similar in the PC. These differences may be due to differences in regional intestinal characteristics such as amount of mucus secreted and degree of tissue contraction, and/or substrate differences regarding solubility in and movement through the mucus, influence on tissue contraction, permeability through membranes or between cells, intracellular metabolism, as well as basolateral transport. Interestingly, an increasing proximal-to-distal gradient for rates of methionine and putative SeMet absorption was observed in green sturgeon which differs from the declining gradient usually observed for substrate absorption in other fish species and mammals.

Structural studies of MAP Kinase cascade components

MAPK cascade components have been the subject of structural analysis, advancing our understanding of how these enzymes are activated and how they interact. A surprising finding has been that unique inactive conformers are adopted by many of these kinases. These inactive conformers are interesting and often require experimental phases to determine their crystal structures because molecular replacement techniques are not successful. Here, we describe the preparation of MAP2K MEK6 and MAP3K TAO2 substituted with selenomethionine (SeMet) for de novo phasing. TAO2 and SeMet TAO2 were expressed in insect cells.

Cloning, expression, purification, crystallization and preliminary crystallographic studies of UgdG, an UDP-glucose dehydrogenase from Sphingomonas elodea ATCC 31461

Gellan gum, a commercial gelling agent produced by Sphingomonas elodea ATCC 31461, is a high-value microbial exopolysaccharide. UDP-glucose dehydrogenase (UGD; EC 1.1.1.22) is responsible for the NAD-dependent twofold oxidation of UDP-glucose to UDP-glucuronic acid, one of the key components for gellan biosynthesis. S. elodea ATCC 31461 UGD, termed UgdG, was cloned, expressed, purified and crystallized in native and SeMet-derivatized forms in hexagonal and tetragonal space groups, respectively; the crystals diffracted X-rays to 2.40 and 3.40 A resolution, respectively. Experimental phases were obtained for the tetragonal SeMet-derivatized crystal form by a single-wavelength anomalous dispersion experiment. This structure was successfully used as a molecular-replacement probe for the hexagonal crystal form of the native protein.

Effects of dietary selenomethionine supplementation on growth performance, meat quality and antioxidant property in yellow broilers

This study was conducted to investigate the effects of dietary selenomethionine (Se-Met) supplementation on growth performance, meat quality and antioxidant property in male broilers. A total of 800 43-day-old Lingnan yellow male broilers were randomly allotted to 5 dietary treatments with four replicates of 40 birds for a period of 3 weeks ad libitum. Final BW and weight gain of birds significantly increased by Se-Met supplementation at the 0.225 mg/kg level (P < 0.05). The addition of Se-Met significantly decreased drip loss, lightness value, and elevated pH value of meat (p < 0.05). Adding sodium selenite (SS) only increased pH value of meat (p < 0.05). In plasma, supplemental Se-Met at 0.225 mg/kg level increased total antioxidant capability (T-AOC), glutathione peroxidase (GPX), total superoxide dismutase (T-SOD), catalase (CAT) activities, glutathione (GSH) concentration (p < 0.05), and decreased malondialdehyde production (p < 0.05), compared with the control and broilers fed SS diet. In breast muscle, the addition of Se-Met significantly elevated T-AOC, GPX, T-SOD, CAT activities, contents of metallothionein and GSH (p < 0.05), and reduced carbonyl protein content (p < 0.05). While compared with broilers fed SS diet, supplemental 0.225 mg/kg Se-Met increased T-AOC, GPX, CAT activities, and GSH content (p < 0.05). Therefore, dietary Se-Met supplementation could improve growth performance and meat quality by enhancing antioxidative capacity in broilers compared with SS.

Lactosylceramide causes endothelial dysfunction in porcine coronary arteries and human coronary artery endothelial cells

BACKGROUND

Lactosylceramide (LacCer) is a member of the glycosphingolipid family, which has been implicated in the atherogenic process. The goal of this study was to determine the effects and molecular mechanisms of LacCer on endothelial functions in porcine coronary arteries and human coronary endothelial cells (HCAECs).

MATERIAL/METHODS

The vessel rings and HCAECs were treated with different concentrations of LacCer for 24 hours. Vasomotor function was studied using a myograph tension system in response to thromboxane A2 analog U46619, bradykinin and sodium nitroprusside (SNP). Superoxide anion production was determined using lucigenin-enhanced chemiluminescence. The expression of endothelial nitric oxide synthase (eNOS), NADPH oxidase subunit NOX4 and catalase was determined by real-time PCR.

RESULTS

LacCer (0.1, 1 and 10 microM) significantly decreased endothelium-dependent vasorelaxation (bradykinin) in porcine coronary artery rings in a concentration-dependent manner compared with untreated controls (P<0.05). High concentration of LacCer (10 microM) also reduced endothelium-independent vasorelaxation (SNP). However, LacCer did not affect vessel contraction (U46619). Antioxidant selenomethionine (SeMet) effectively reversed LacCer-induced endothelial dysfunction in the vessel rings. Furthermore, LacCer significantly increased superoxide anion production in the vessel rings in a concentration-dependent manner compared with untreated controls (P<0.05). In response to LacCer treatment, NOX4 mRNA levels were significantly increased, while the expression of catalase and eNOS was significantly decreased in HCAECs compared with controls (P<0.05).

CONCLUSIONS

LacCer causes endothelial dysfunction with potential mechanisms of the down-regulation of eNOS and increase of oxidative stress due to the activation of NADPH oxidase and inhibition of internal antioxidant catalase. This study suggests that LacCer may represent a risk factor to the vascular system and antioxidant SeMet may have clinical applications for prevention of vascular disease.

A description of the structural determination procedures of a gap junction channel at 3.5 A resolution

Intercellular signalling is an essential characteristic of multicellular organisms. Gap junctions, which consist of arrays of intercellular channels, permit the exchange of ions and small molecules between adjacent cells. Here, the structural determination of a gap junction channel composed of connexin 26 (Cx26) at 3.5 A resolution is described. During each step of the purification process, the protein was examined using electron microscopy and/or dynamic light scattering. Dehydration of the crystals improved the resolution limits. Phase refinement using multi-crystal averaging in conjunction with noncrystallographic symmetry averaging based on strictly determined noncrystallographic symmetry operators resulted in an electron-density map for model building. The amino-acid sequence of a protomer structure consisting of the amino-terminal helix, four transmembrane helices and two extracellular loops was assigned to the electron-density map. The amino-acid assignment was confirmed using six selenomethionine (SeMet) sites in the difference Fourier map of the SeMet derivative and three intramolecular disulfide bonds in the anomalous difference Fourier map of the native crystal.

Structure of the sporulation histidine kinase inhibitor Sda from Bacillus subtilis and insights into its solution state

The crystal structure of the DNA-damage checkpoint inhibitor of sporulation, Sda, from Bacillus subtilis, has been solved by the MAD technique using selenomethionine-substituted protein. The structure closely resembles that previously solved by NMR, as well as the structure of a homologue from Geobacillus stearothermophilus solved in complex with the histidine kinase KinB. The structure contains three molecules in the asymmetric unit. The unusual trimeric arrangement, which lacks simple internal symmetry, appears to be preserved in solution based on an essentially ideal fit to previously acquired scattering data for Sda in solution. This interpretation contradicts previous findings that Sda was monomeric or dimeric in solution. This study demonstrates the difficulties that can be associated with the characterization of small proteins and the value of combining multiple biophysical techniques. It also emphasizes the importance of understanding the physical principles behind these techniques and therefore their limitations.

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

BACKGROUND

Selenium 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.

RESULTS

We 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.

CONCLUSION

The 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.

Expression, purification and crystallization of the cofactor-independent monooxygenase SnoaB from the nogalamycin biosynthetic pathway

12-deoxy-nogalonic acid oxygenase (SnoaB) catalyzes the oxygenation of 12-deoxy-nogalonic acid at position 12 to yield nogalonic acid, which is one of the steps in the biosynthesis of the polyketide nogalamycin in Streptomyces nogalater. SnoaB belongs to a family of small cofactor-free oxygenases which carry out oxygenation reactions without the aid of any prosthetic group, cofactor or metal ion. Recombinant SnoaB was crystallized in space group P2(1)2(1)2, with unit-cell parameters a = 58.8, b = 114.1, c = 49.5 A, and these crystals diffracted to 2.4 A resolution. Recombinant SnoaB does not contain any methionine residues and three double mutants were designed and produced for the preparation of selenomethionine-substituted samples. The selenomethionine-substituted mutant F40M/L89M crystallized in the same space group as the native enzyme.

Production and characterization of fully selenomethionine-labeled Saccharomyces cerevisiae

This paper reports, for the first time, a quantitative replacement of methionine (Met) by selenomethionine (SeMet) at >98% substitution, with up to 4940 microg of SeMet/g of yeast obtained for the entire protein pool of a wild-type yeast grown on a SeMet-containing medium. The incorporation of selenium in yeast proteins, in the form of selenomethionine, and the influence of various organic and inorganic Se and S sources present in the media were monitored during the growth of a wild-type Saccharomyces cerevisiae , which allowed the optimization of the composition of a fully defined synthetic growth medium that ensured maximum SeMet incorporation. Quantitation of SeMet and Met was performed by species-specific isotope dilution GC-MS. The use of ascorbic acid and a minimum concentration of cysteine (5 microg/L) was found to be beneficial to achieve incorporation by limiting the oxidative stress due to the presence of selenium. Except for small amounts of cysteine, no other sources of sulfur were necessary to achieve yeast growth. In a medium containing Se(VI), the maximum replacement of Met with SeMet was 50%, which is considerably higher than that obtained with the current commercial Se yeast formulations. For yeast grown in a Met-free defined medium, which was supplemented with SeMet, nearly total replacement of Met with SeMet could be achieved. The fully Se-labeled yeast could be an important tool for the study of eukaryotic protein structures both by mass spectrometry and by X-ray crystallography through selenomethionine single- and multiple-wavelength anomalous dispersion (SAD and MAD) phasing. In addition, a particular yeast strain, BY4741, that cannot synthesize Met using inorganic sulfur (met15Delta0) was shown to produce SeMet in the presence of inorganic selenium. This might indicate that the incorporation of inorganic selenium salts [Se(VI) and Se(IV)] is obviously not occurring exclusively through the same biological pathways as for sulfur. The reduction of inorganic Se to hydrogen selenide (H(2)Se), its reactions with organic compounds present in the yeast or in the media, and the possible metabolization through unspecific enzymatic pathways (such as transsulfuration) could also be of considerable importance in the production of selenoamino acids during yeast growth.

Expression, purification, crystallization and preliminary X-ray studies of histamine dehydrogenase from Nocardioides simplex

Histamine dehydrogenase (HADH) from Nocardioides simplex catalyzes the oxidative deamination of histamine to produce imidazole acetaldehyde and an ammonium ion. HADH is functionally related to trimethylamine dehydrogenase (TMADH), but HADH has strict substrate specificity towards histamine. HADH is a homodimer, with each 76 kDa subunit containing two redox cofactors: a [4Fe-4S] cluster and an unusual covalently bound flavin mononucleotide, 6-S-cysteinyl-FMN. In order to understand the substrate specificity of HADH, it was sought to determine its structure by X-ray crystallography. This enzyme has been expressed recombinantly in Escherichia coli and successfully crystallized in two forms. Diffraction data were collected to 2.7 A resolution at the SSRL synchrotron with 99.7% completeness. The crystals belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 101.14, b = 107.03, c = 153.35 A.

Selenium speciation and bioavailability in biofortified products using species-unspecific isotope dilution and reverse phase ion pairing-inductively coupled plasma-mass spectrometry

In some regions of the world, where the bioavailability of selenium (Se) in soil is low and/or declining (e.g., due to use of high-sulfur fertilizers), there is increased risk of adverse affects on animals and human health. In recent years, increased research attention has focused on understanding the relationships between Se contents in foods and supplements and their nutritional benefits for animal and humans. The objective of this study was to use a species-unspecific isotope dilution and reverse phase ion pairing-inductively coupled plasma-mass spectrometry techniques for the identification and quantification of Se species in biofortified grains (i.e., wheat and triticale), flour, and wheat biscuits. The information on Se species was used to gain an understanding of the bioavailability of Se in biofortified and process-fortified wheat biscuits used in a clinical trail. The major Se species identified in biofortified and process-fortified samples were selenomethionine (76-85%) and selenomethionine selenoxide (51-60%), respectively. Total plasma Se concentrations in the biofortified Se exposure group were found to increase throughout the 6 month trial period (mean=122 microg L(-1) at 0 months to 194 microg L(-1) at 6 months). In contrast, the trial group exposed to process-fortified Se biscuits showed little increase in mean total Se plasma concentrations until 4 months of exposure (mean=122 microg L(-1) at 0 months to 140 microg L(-1) at 4 months) that remained constant until the end of the trial period (mean=140 microg L(-1) at 4 months to 138 microg L(-1) at 6 months). The difference in total Se plasma concentrations may be due to the presence and bioavailability of different Se species in biofortified and process-fortified biscuits. An understanding of Se speciation in foods enables better understanding of pathways and their potential benefits for animals and humans.

Monitoring of changes in selenium concentration in goat milk during short-term supplementation of various forms of selenium

The goal of the experiment was to monitor the changes in the selenium concentration in goat milk during short-term oral supplementation of three different forms of selenium. The experiment involved 24 lactating goats of white shorthaired breed. Group C was the control; group S received selenium in the form of selenium-enriched yeast, group L in the form of lactate, and group B in the form of proteinate. Individual selenium preparations were administered individually orally in 250 microg Se dose per animal for 20 days. After the beginning of selenium supplementation, the selenium concentration in milk during the first 5 days grew gradually in group S. Between days 7 and 20 of Se supplementation, the mean Se concentrations in milk in groups were 12.53 +/- 3.69 microg l(-1) (C), 25.90 +/- 6.30 microg l(-1) (S), 13.14 +/- 3.54 microg l(-1) (L), 11.70 +/- 3.69 microg l(-1) (B). Differences between group S and other groups (C, B, L) were highly significant (p < 0.0001). Based on our results, selenium in the form of lactate and proteinate was excreted into the milk similarly, but selenium in the form of yeast, which contains high amount of selenomethionine, was excreted by milk in the highest amounts.

Expression, purification, crystallization and preliminary X-ray diffraction analysis of Thermotoga neapolitana beta-glucosidase B

Beta-glucosidases belong to families 1, 3 and 9 of the glycoside hydrolases and act on cello-oligosaccharides. Family 1 and 3 enzymes are retaining and are reported to have transglycosylation activity, which can be used to produce oligosaccharides and glycoconjugates. Family 3 enzymes are less well characterized than their family 1 homologues and to date only two crystal structures have been solved. Here, the expression, purification, crystallization and X-ray diffraction data of a family 3 beta-glucosidase from the hyperthermophilic bacterium Thermotoga neapolitana are reported. Crystals of selenomethionine-substituted protein have also been grown. The crystals belong to space group C222(1), with unit-cell parameters a = 74.9, b = 127.0, c = 175.2 A. Native data have been collected to 2.4 A resolution and the structure has been solved to 2.7 A using the selenomethionine MAD method. Model building and refinement of the structure are under way.

Selenomethionine induces polyamine biosynthesis in regenerating rat liver tissue

Our study was undertaken to elucidate the effects of selenomethionine (SeMet) on polyamine metabolism in regenerating rat liver tissue, as useful model of rapidly growing normal tissue. We have examined the levels of spermine, spermidine and putrescine in liver tissue. At the same time we have evaluated the activities of polyamine oxidase (PAO) and diamine oxidase (DAO), the catabolic enzymes of polyamine metabolism. The obtained results suggest that polyamine levels in regenerating liver tissue, at 7(th) day after two-thirds partial hepatectomy, were higher in comparison with control group. The administration of selenomethionine to hepatectomized animals during seven days, in a single daily dose of 2.5 microg/100 g body weight, increases the amount of spermine and spermidine; the level of putrescine does not change under the influence of SeMet in regenerating rat liver tissue.PAO activity is lower in regenerating hepatic tissue than in control group. Supplementation of hepatectomized animals with SeMet significantly decreases the activity of this enzyme. DAO activity was significantly higher in hepatectomized and in operated animals treated with SeMet compared to the sham-operated and control ones. The differential sensitivity observed in our model of highly proliferating normal tissue to SeMet, compared with the reported anticancer activity of this molecule is discussed.

Methylselenol generated from selenomethionine by methioninase downregulates integrin expression and induces caspase-mediated apoptosis of B16F10 melanoma cells

Melanoma is a highly metastatic cancer resistant to current chemotherapeutic and radiotherapeutic approaches. Several studies have shown that interactions between cancer cells and the extracellular matrix (ECM) are critical for the survival and invasion of metastatic cancer cells. In this study, we examine the effects of methylselenol generated from selenomethionine (SeMet) by methioninase (METase) on cell proliferation, adhesion, and expression of integrins in murine melanoma B16F10 cells, which are metastatic in the lungs of syngeneic C57BL/6J mice. Combined treatment with SeMet-METase decreased the expression of integrins alpha(4), beta(1), alpha(nu), and beta(3), and inhibited melanoma-ECM adhesion. Caspase-mediated apoptosis was induced following loss of cell adherence. Phosphorylation of focal adhesion kinase (FAK) and Akt, related to integrin-mediated survival, were decreased upon treatment with SeMet-METase while phosphorylation of p38, PKC-delta, and IkappaBalpha increased. In the presence of specific inhibitors of p38, PKC-delta, and NF-kappaB, expression of integrins and cell adhesion to ECM were maintained and cell apoptosis was prevented in SeMet-METase-treated melanoma cells. Treatment with caspase inhibitors restored cell viability and blocked poly (ADP-ribose) polymerase (PARP) cleavage, but did not restore integrin expression and cell adhesion to ECMs reduced by SeMet-METase. Based on these results, we propose that combined treatment with SeMet-METase induces caspase-mediated apoptosis in melanoma cells by altering integrin expression and adhesion. Furthermore, activation of p38, PKC-delta, and NF-kappaB is a prerequisite for the down-regulation of integrin expression, followed by detachment-mediated apoptosis.