Selenium Decipher: Trapping of Native Selenomethionine-Containing Peptides in Selenium-Enriched Milk and Unveiling the Deterioration after Ultrahigh-Temperature Treatment.

Selenopeptide identification relies on databases to interpret the selenopeptide spectra. A common database search strategy is to set selenium as a variable modification instead of sulfur on peptides. However, this approach generally detects only a fraction of selenopeptides. An alternative approach, termed Selenium Decipher, is proposed in the present study. It involves identifying collision-induced dissociation-cleavable selenomethionine-containing peptides by iteratively matching the masses of seleno-amino acids in selenopeptide spectra. This approach uses variable-data-independent acquisition (vDIA) for peptide detection, providing a flexible and customizable window for secondary mass spectral fragmentation. The attention mechanism was used to capture global information on peptides and determine selenomethionine-containing peptide backbones. The core structure of selenium on selenomethionine-containing peptides generates a series of fragment ions, namely, C3H7Se+, C4H10NSe+, C5H7OSe+, C5H8NOSe+, and C7H11N2O2Se+, with known mass gaps during higher-energy collisional dissociation (HCD) fragmentation. De-selenium spectra are generated by removing selenium originating from selenium replacement and then reassigning the precursors to peptides. Selenium-enriched milk is obtained by feeding selenium-rich forage fed to cattle, which leads to the formation of native selenium through biotransformation. A novel antihypertensive selenopeptide Thr-Asp-Asp-Ile-SeMet-Cys-Val-Lys TDDI(Se)MCVK was identified from selenium-enriched milk. The selenopeptide (IC50 = 60.71 µM) is bound to four active residues of the angiotensin-converting enzyme (ACE) active pocket (Ala354, Tyr523, His353, and His513) and two active residues of zinc ligand (His387 and Glu411) and exerted a competitive inhibitory effect on the spatial blocking of active sites. The integration of vDIA and the iteratively matched seleno-amino acids was applied for Selenium Decipher, which provides high validity for selenomethionine-containing peptide identification.

Determination of selenium-containing species, including nanoparticles, in selenium-enriched Lingzhi mushrooms.

Mushrooms are considered a valuable food source due to their high protein and fibre and low fat content, among the other health benefits of their consumption. Selenium is an essential nutrient and is renowned for its chemo-preventative properties. In this study, batches of selenium-enriched Lingzhi mushrooms were prepared by growing mycelium and fruit in substrates containing various concentrations of sodium selenite. The mushroom fruit accumulated low levels of selenium with selenomethionine being the most abundant form in all enriched samples. Conversely, the mycelium showed significant selenium accumulation but relatively low proportions of selenomethionine. The red colour of the selenium-enriched mycelia indicated the probable presence of selenium nanoparticles, which was confirmed by single-particle inductively coupled plasma-mass spectrometry. Mean particle diameters of 90-120 nm were observed, with size distributions of 60-250 nm. Additional analysis with transmission electron microscopy confirmed this size distribution and showed that the biogenic selenium nanoparticles were roughly spherical in shape and contained elemental selenium.

Extraction recovery and speciation of selenium in Se-enriched yeast.

The complete characterization of selenium-enriched yeast in terms of selenium species has been the goal of extensive research for the last three decades. This contribution addresses the two outstanding questions: the mass balance of the identified and reported selenium species and the possible presence of inorganic selenium. For this purpose, four procedures have been designed combining, in diverse order, the principal steps of selenium speciation analysis in Se-rich yeast: extraction of the Se-metabolome, derivatization of cysteine and Se-cysteine (SeCys) residues, proteolysis, and definitive Se recovery using SDS extraction, followed by mineralization. The recovery of selenium in each step and its speciation were controlled by ICP MS and by reversed-phase HPLC-ICP MS, respectively. The study, carried out for the SELM-1 reference material, demonstrated the presence of about 10% of inorganic selenium and a serious risk of losses of SeCys during derivatization and proteolysis. As result of our work, we postulate the following values for SELM-1: Se-metabolome fraction (SeMF) 14.8 ± 0.7%; total selenomethionine (SeMet) 66.2 ± 2.7% (including ca. 1.5% SeMet present in the SeMF); total SeCys 12.5 ± 1.5% (including 2% of SeCys present in the Se-MF); total inorganic selenium 9.7 ± 1.7%, accounting for > 99.8% of the selenium.

82Se Metabolically-Labeled Yeast as a Matrix-Matched Isotope Dilution Standard for Quantification of Selenomethionine.

Selenized yeast is commonly used as a highly bioavailable source of selenium in dietary supplements and feed additives and is used in research settings in various disciplines due to the large number of selenium-containing metabolites formed during growth. With the selenomethionine being the major form of selenium present in selenized yeasts, its accurate quantitation is essential, however, values are frequently underestimated due to the costly and time-consuming hydrolysis-based sample preparation required to release the selenoamino acid from proteins for analysis. The National Research Council Canada has developed an 82-Se-enriched selenized yeast Certified Reference Material, SEEY-1 (DOI: 10.4224/crm.2023.seey-1) intended to be used as a matrix-matched spike material for isotope dilution analysis of selenized yeasts. The total selenium and selenomethionine contents of SEEY-1 were determined to be 322.1 ± 4.8 mg/kg (k = 2) and 635.6 ± 16.8 mg/kg (k = 2), respectively. Here we present results on the preparation of the 82-Se-enriched yeast, the certification process, and provide an example of the use of SEEY-1 as a matrix-matched spike for the analysis of selenomethionine in a sample of selenized yeast. We demonstrate here that SEEY-1 is able to compensate for the partial digestion of yeast proteins and provide reliable analytical data on Se amino acid content in under an hour instead of the 16 hours required for conventional complete acid hydrolysis.

Propargylic Se-adenosyl-l-selenomethionine: A Chemical Tool for Methylome Analysis.

Devising synthetic strategies to construct a covalent bond is a common research topic among synthetic chemists. A key driver of success is the high tunability of the conditions, including catalysts, reagents, solvents, and reaction temperature. Such flexibility of synthetic operations has allowed for the rapid exploration of a myriad of artificial synthetic transformations in recent decades. However, if we turn our attention to chemical reactions controlled in living cells, the situation is quite different; the number of hit substrates for the reaction-type is relatively small, while the crowded environment is chemically complex and inflexible to control.A specific objective of this Account is to introduce our chemical methylome analysis as an example of bridging the gap between chemistry and biology. Protein methylation, catalyzed by protein methyltransferases (MTases) using S-adenosyl-l-methionine (SAM or AdoMet) as a methyl donor, is a simple but important post-translational covalent modification. We aim to efficiently identify MTase substrates and methylation sites using activity-based protein profiling (ABPP) with propargylic Se-adenosyl-l-selenomethionine (ProSeAM, also called SeAdoYn). Specifically, we draw heavily from quantitative proteomics that yields information about the differences between two samples utilizing LC-MS/MS analysis. By exploiting the use of ProSeAM, we have prepared the requisite two samples for quantitative methylome analysis. The structural difference between ProSeAM and the parent SAM is so small that the quantity of modification of the protein substrate with this artificial cofactor reflects, to a large extent, levels of activity of the MTase of interest with SAM. First, we identified that the addition of exogenous recombinant MTase (methylation accel), a natural catalyst, enhances the generation of the corresponding propargylated product even in the cell lysate. Then, we applied the principle to isotope label-free quantification with HEK293T cell lysates. By comparing the intensity of LC-MS/MS signals in the absence and presence of the MTase, we have successfully correlated the MTase substrates. We have currently applied the concept to the stable isotope label-based quantification, SILAC (stable isotope labeling by amino acids in cell culture). The strategy merging ProSeAM/MTase/SILAC (PMS) is uniquely versatile and programmable. We can choose suitable cell lines, subcellular fractions (i.e.; whole lysate or mitochondria), and genotypes as required. In particular, we would like to emphasize that the use of cell lysates derived from disease-associated MTase knockouts (KOs) holds vast potential to discover functionally unknown but biologically important methylation events. By adding ProSeAM and a recombinant MTase to the lysates derived from KO cells, we successfully characterized unprecedented nonhistone substrates of several MTases. Furthermore, this chemoproteomic procedure can be applied to explore MTase inhibitors (methylation brake). The combined strategy with ProSeAM/inhibitor/SILAC (PIS) offers intriguing opportunities to explore nonhistone methylation inhibitors.Considering that SAM is the second most widely used enzyme-substrate following ATP, the interdisciplinary research between chemistry and biology using SAM analogs has a potentially huge impact on a wide range of research fields associated with biological methylation. We hope that this Account will help to further delineate the biological function of this important class of enzymatic reaction.

Hydroxy-selenomethionine supplementation promotes the in vitro rumen fermentation of dairy cows by altering the relative abundance of rumen microorganisms.

AIMS: This study aims to investigate the effect of hydroxy-selenomethionine supplementation on the in vitro rumen fermentation characteristics and microorganisms of Holstein cows. METHODS AND RESULTS: Five fermentation substrates, including control (without selenium supplementation, CON), sodium selenite supplementation (0.3 mg kg-1 DM, SS03), and hydroxy-selenomethionine supplementation (0.3, 0.6 and 0.9 mg kg-1 DM, SM03, SM06 and SM09, respectively) were incubated with rumen fluid in vitro. The results showed that in vitro dry matter disappearance and gas production at 48 h was significantly higher in SM06 than SM03, SS03 and CON; propionate and total volatile fatty acid (VFA) production was higher in SM06 than CON. Moreover, higher species richness of rumen fluid was found in SM06 than others. Higher relative abundance of Prevotella and Prevotellaceae-UCG-003 and lower relative abundance of Ruminococcus-1 were detected in SM06 than CON. Besides, higher relative abundance of Ruminococcaceae_UCG-005 was found in CON than other treatments. CONCLUSIONS: It is observed that 0.6 mg kg-1 DM hydroxy-selenomethionine supplementation could increase cumulative gas production, propionate, and total VFAs production by altering the relative abundance of Prevotella, Prevotellaceae-UCG-003, Ruminococcaceae_UCG-005 and Ruminococcus-1, so that it can be used as a rumen fermentation regulator in Holstein cows. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides an optimal addition ratio of hydroxy-selenomethionine on rumen fermentation and bacterial composition via an in vitro test.

Systematic study of the selenium fractionation in human plasma from a cancer prevention trial using HPLC hyphenated to ICP-MS and ESI-MS/MS.

This work represents the first systematic speciation study of selenium (Se) in plasma from subjects participating in a pilot study for a cancer prevention trial (PRECISE). This involved supplementation of elderly British and Danish individuals with selenised yeast for 6 months and 5 years, respectively, at 100, 200, and 300 µg Se/day or placebo. Speciation data was obtained for male plasma using HPLC-ICP-MS and HPLC-ESI-MS/MS. With the proposed strategy, approximately 1.5 mL of plasma was needed to determine total Se concentration and the fractionation of Se in high molecular weight (HMW) and low molecular weight (LMW) pools, and for quantification and identification of small Se species. For the first time, Se-methyl-selenocysteine (MSC) and methyl-2-acetamido-2deoxy1-seleno-ß-D-galactopyranoside (Selenosugar-1) were structurally confirmed in plasma after supplementation with selenised yeast within the studied range. Determination of selenomethionine (SeMet) incorporated non-specifically into albumin (SeALB) was achieved by HPLC-ICP-MS after hydrolysis. By subtracting this SeMet concentration from the total Se in the HMW pool, the concentration of Se incorporated into selenoproteins was calculated. Results from the speciation analysis of the free Se metabolite fraction (5% of total plasma Se) suggest a significant increase in the percentage of Se (as SeMet plus Selenosugar-1) of up to 80% of the total Se in the LMW fraction after 6 months of supplementation. The Se distribution in the HMW fraction reflects a significant increase in SeALB with Se depletion from selenoproteins, which occurs most significantly at doses of over 100 µg Se/day after 5 years. The results of this work will inform future trial design. Graphical abstract.

Selenomethionine administration decreases the oxidative stress induced by post mortem ischemia in the heart, liver and kidneys of rats.

Selenium is an essential element in human and animal metabolism integrated into the catalytic site of glutathione peroxidase (GPX1), an antioxidant enzyme that protects cells from damage caused by reactive oxygen species (ROS). Oxidative stress refers the imbalance between ROS and antioxidant defense systems. It generates alterations of DNA, proteins and lipid peroxidation. The imbalance occurs particularly during ischemia and lack of postmortem perfusion. This mechanism is of relevance in transplant organs, affecting their survival. The aim of this research is to evaluate the effect of seleno-methionine (SeMet) as a protective agent against postmortem ischemia injury in transplant organs. Wistar rats were orally administered with SeMet. After sacrifice, liver, heart and kidney samples were collected at different postmortem intervals (PMIs). SeMet administration produced a significant increase of Se concentration in the liver (65%, p < 0.001), heart (40%, p < 0.01) and kidneys (45%, p < 0.05). Levels of the oxidative stress marker malondialdehyde (MDA) decreased significantly compared to control in the heart (0.21 ± 0.04 vs. 0.12 ± 0.02 mmol g-1) and kidneys (0.41 ± 0.02 vs. 0.24 ± 0.03 mmol g-1) in a PMI of 1-12 h (p < 0.01). After SeMet administration for 21 days, a significant increase in GPX1 activity was observed in the liver (80%, p < 0.001), kidneys (74%, p < 0.01) and heart (35%, p < 0.05). SeMet administration to rats significantly decreased the oxidative stress in the heart, liver and kidneys of rats generated by postmortem ischemia.

Determination of selenite and selenomethionine in kefir grains by reversed-phase high-performance liquid chromatography-inductively coupled plasma-optical emission spectrometry.

A new and efficient reversed-phase high-performance liquid chromatography-inductively coupled plasma-optical emission spectrometry method was developed for the simultaneous separation and determination of SeO3 2- and seleno-dl-methionine in kefir grains. For the system, limits of detection and quantitation values for SeO3 2- and seleno-dl-methionine were calculated as 0.52/1.73 mg/kg (as Se) and 0.26/0.87 mg/kg (as Se), respectively. After performing the system analytical performance, recovery experiment was done for kefir grains and percent recovery results for SeO3 2- and seleno-dl-methionine were calculated as 98.4 ± 0.8% and 93.6 ± 1.0%, respectively. It followed by the feeding studies that the kefir grains were exposed to three different concentrations of SeO3 2- (20, 30, and 50 mg/kg) for approximately 4 days at room temperature to investigate the conversion/non-conversion of SeO3 2- to seleno-dl-methionine. Next, the fed grains were extracted with tetramethylammonium hydroxide pentahydrate solution (20%, w/w) and then sent to the developed system. There was no detectable seleno-dl-methionine found in fed kefir grains at different concentrations of SeO3 2- while inorganic or elemental selenium in the fed kefir grains was determined between 1579.5 - 3116.0 mg/kg (as Se). Selenium species in the kefir grains samples was found in the form of SeO3 2- proved by using an anion exchange column.

A micellar electrokinetic chromatography approach using diastereomeric derivatization and a volatile surfactant for the enantioselective separation of selenomethionine.

A MEKC methodology with UV detection was developed for the enantioselective separation of selenomethionine (SeMet). The use of (+)-1-(9-fluorenyl)ethyl chloroformate (FLEC) as chiral derivatization reagent to form SeMet diastereomers enabled their subsequent separation using ammonium perfluorooctanoate (APFO) as a volatile pseudostationary phase. The effect of APFO concentration and pH, temperature, injection volume, and derivatization conditions (time and FLEC/SeMet ratio) were evaluated in order to select the best separation conditions. A chiral resolution of 4.4 for DL-SeMet was achieved in less than 6 min using 100 mM APFO at pH 8.5 as electrophoretic buffer. Satisfactory results were obtained in terms of linearity, precision (RSD from 3.4 to 5.1% for migration times and from 1.8 to 4.6% for corrected peak areas), accuracy, and LODs (3.1 × 10-6  M and 3.7 × 10-6  M for d and l enantiomers, respectively). The method was successfully applied to the determination of l-SeMet in food supplements.

Selenium-enriched Coriolus versicolor mushroom biomass: potential novel food supplement with improved selenium bioavailability.

BACKGROUND: The ability of Coriolus versicolor medicinal mushroom to accumulate and transform selenium from selenourea and sodium selenite into an organic form - l-selenomethionine - during growth in liquid medium is examined in this paper. Additionally, the impact of supplementation on biological activity of the selenated mushroom methanol extracts, as well as their chemical composition, is studied. RESULTS: Selenium accumulation was more efficient with sodium selenite application, but biomass yield was significantly lower (1.89 g DW L-1 ) compared to samples enriched with selenourea (4.48 g DW L-1 ). Mushroom sample obtained after growing in liquid medium with selenourea had significantly higher l-selenomethionine content compared to the sample grown in medium with sodium selenite. Selenium-enriched methanol extracts of C. versicolor mushroom showed improved antimicrobial and antioxidant activities compared to non-enriched extract. CONCLUSION: Our results suggest that C. versicolor mushroom cultivated in liquid culture enriched with selenourea can be used for the production of novel food supplements with improved selenium bioavailability. More than 30% of total accumulated selenium from selenourea is transformed into l-selenomethionine. Differences in biological activity of methanol extracts can be explained not only by different selenium content but also by the differences in chemical composition of extracts. © 2019 Society of Chemical Industry.

Determination of Proteinaceous Selenocysteine in Selenized Yeast.

A method for the quantitation of proteinaceous selenocysteine (SeCys) in Se-rich yeast was developed. The method is based on the reduction of the Se-Se and S-Se bridges with dithiotretiol, derivatization with iodoacetamide (carbamidomethylation), followed by HPLC-ICP MS. The chromatographic conditions were optimized for the total recovery of the proteinaceous selenocysteine, the minimum number of peaks in the chromatogram (reduction of derivatization products of other Se-species present) and the baseline separation. A typical chromatogram of a proteolytic digest of selenized yeast protein consisted of up to five peaks (including SeMet, carbamidomethylated (CAM)-SeCys, and Se(CAM)2) identified by retention time matching with available standards and electrospray MS. Inorganic selenium non-specifically attached to proteins and selenomethionine could be quantified (in the form of Se(CAM)2) along with SeCys. Selenocysteine, selenomethionine, inorganic selenium, and the water soluble-metabolite fraction accounted for the totality of selenium species in Se-rich yeast.

Deproteinization assessment using isotopically enriched compounds to trace the coprecipitation of low-molecular-weight selenium species with proteins.

Studies have shown that information related to the presence of low-molecular-weight metabolites is frequently lost after deproteinization of complex matrices, such as blood and plasma, during sample preparation. Therefore, the effect of several deproteinization reagents on low-molecular-weight selenium species has been compared by species-specific isotope labeling. Two isotopically enriched selenium tracers were used to mimic models of small inorganic anionic (77Se-selenite) and organic zwitterionic (76Se-selenomethionine) species. The results presented here show that the use of a methanol-acetonitrile-acetone (1:1:1 v/v/v) mixture provided approximately two times less tracer loss from plasma samples in comparison with the classic procedure using acetonitrile, which may not be optimal as it leads to important losses of low-molecular-weight selenium species. In addition, the possible interactions between selenium tracers and proteins were investigated, revealing that both coprecipitation phenomena and association with proteins were potentially responsible for selenite tracer losses during protein precipitation in blood samples. However, coprecipitation phenomena were found to be fully responsible for losses of both tracers observed in plasma samples and of the selenomethionine tracer in blood samples. This successfully applied strategy is anticipated to be useful for more extensive future studies in selenometabolomics.

Selenium speciation in wheat grain varies in the presence of nitrogen and sulphur fertilisers.

This study investigated whether selenium species in wheat grains could be altered by exposure to different combinations of nitrogen (N) and sulphur (S) fertilisers in an agronomic biofortification experiment. Four Australian wheat cultivars (Mace, Janz, Emu Rock and Magenta) were grown in a glasshouse experiment and exposed to 3 mg Se kg-1 soil as selenate (SeVI). Plants were also exposed to 60 mg N kg-1 soil as urea and 20 mg S kg-1 soil as gypsum in a factorial design (N + S + Se; N + Se; S + Se; Se only). Plants were grown to maturity with grain analysed for total Se concentrations via ICP-MS and Se species determined via HPLC-ICP-MS. Grain Se concentrations ranged from 22 to 70 µg Se g-1 grain (dry mass). Selenomethionine (SeMet), Se-methylselenocystine (MeSeCys), selenohomolanthionine (SeHLan), plus a large concentration of uncharacterised Se species were found in the extracts from grains. SeMet was the major Se species identified accounting for between 9 and 24 µg Se g-1 grain. Exposure to different N and S fertiliser combinations altered the SeMet content of Mace, Janz and Emu Rock grain, but not that of Magenta. MeSeCys and SeHLan were found in far lower concentrations (<4 µg Se g-1 grain). A large component of the total grain Se was uncharacterisable (>30 % of total grain Se) in all samples. When N fertiliser was applied (with or without S), the proportion of uncharacterisable Se increased between 60 and 70 % of the total grain Se. The data presented here indicate that it is possible to alter the content of individual Se species in wheat grains via biofortification combined with manipulation of N and S fertiliser regimes. This has potential significance in alleviating or combating both Se deficiency and Se toxicity effects in humans.

Selenoamino Acid-Enriched Green Pea as a Value-Added Plant Protein Source for Humans and Livestock.

Selenium deficiency in various degrees affects around 15% of the world's population, contributing to a variety of health problems. In this study, we examined the accumulation and biotransformation of soil applied Se-supplementation (sodium selenite and sodium selenate forms) at different concentrations, along with growth and yield formation of green pea, in a greenhouse experiment. Biotransformation of inorganic Se was evaluated using HPLC-ICP-MS for Se-species separation in the above ground parts of green pea. Results showed 3 mg kg-1 SeIV increased green pea growth biomarkers and also caused an increase in protein content in leaves by 17%. Selenomethionine represented 65% of the total selenium content in shoots, but was lower in pods and seeds (54 and 38%, respectively). Selenomethionine was the major species in all plant parts and the only organic selenium form in the lower SeIV concentration range. Elevating the dose of SeIV (≥30 mg kg-1) triggered detrimental effects on growth and protein content and caused higher accumulation of inorganic Se in forms of SeVI and SeIV. Selenocysteine, another organic form of proteinogenic amino acid, was determined when SeIV (≥10 mg kg-1) was applied in higher concentrations. Thus, agronomic biofortification using the appropriate chemical form and concentration of Se will have positive effects on green pea growth and its enriched shoots and seeds provide a value-added protein source for livestock and humans with significant increased selenomethionine.

Identification of trace levels of selenomethionine and related organic selenium species in high-ionic-strength waters.

A new anion-exchange chromatographic separation method was used for the simultaneous speciation analysis of selenoamino acids and the more ubiquitous inorganic selenium oxyanions, selenite and selenate. For quantification, this separation was coupled to inductively coupled plasma-mass spectrometry to achieve an instrumental detection limit of 5 ng Se L(-1) for all species. This chromatographic method was also coupled to electrospray tandem mass spectrometry to observe the negative ion mode fragmentation of selenomethionine and one of its oxidation products. Low detection limits were achieved, which were similar to those obtained using inductively coupled plasma-mass spectrometry. An extensive preconcentration and cleanup procedure using cation-exchange solid-phase extraction was developed for the identification and quantification of trace levels of selenomethionine in environmental samples. Preconcentration factors of up to five were observed for selenomethionine, which in addition to the removal of high concentrations of sulphate and chloride from industrial process waters, allowed for an unambiguous analysis that would have been impossible otherwise. Following these methods, selenomethionine was identified at an original concentration of 3.2 ng Se L(-1) in samples of effluent collected at a coal-fired power plant's biological remediation site. It is the first time that this species has been identified in the environment, outside of a biological entity. Additionally, oxidation products of selenomethionine were identified in river water and laboratory algal culture samples. High-resolution mass spectrometry was employed to postulate the chemical structures of these species.

Is hepatic oxidative stress a main driver of dietary selenium toxicity in white sturgeon (Acipenser transmontanus)?

Most species of sturgeon have experienced significant population declines and poor recruitment over the past decades, leading many, including white sturgeon (Acipenser transmontanus), to be listed as endangered. Reasons for these declines are not yet fully understood but benthic lifestyle, longevity, and delayed sexual maturation likely render sturgeon particularly susceptible to factors such as habitat alteration and contaminant exposures. One contaminant of particular concern to white sturgeon is selenium (Se), especially in its more bioavailable form selenomethionine (SeMet), as it is known to efficiently bioaccumulate in prey items of this species. Studies have shown white sturgeon to be among the most sensitive species of fish to dietary SeMet as well as other pollutants such as metals, dioxin-like chemicals and endocrine disrupters. One of the primary hypothesized mechanisms of toxicity of SeMet in fish is oxidative stress; however, little is know about the specific mode by which SeMet affects the health of white sturgeon. Therefore, the aim of this study was to characterize oxidative stress and associated antioxidant responses as a molecular event of toxicity, and to link it with the pathological effects observed previously. Specifically, three-year-old white sturgeon were exposed for 72 days via their diet to 1.4, 5.6, 22.4 or 104.4µg Se per g feed (dm). Doses were chosen to range over a necessary Se intake level, current environmentally relevant intakes and an intake representing predicted increases of Se release. Lipid hydroperoxides, which are end products of lipid oxidation, were quantified as a marker of oxidative stress. Changes in gene expression of glutathione peroxidase (GPx), superoxide dismutase, catalase, glutathione S-transferase, apoptosis inducing factor and caspase 3 were quantified as markers of the response to oxidative stress. Concentrations of lipid hydroperoxides were highly variable within dose groups and no dose response was observed. GPx expression was significantly increased in the low dose group indicating an induced antioxidant response. Expression of other genes were not significantly induced or suppressed. Overall, there was very little evidence of oxidative stress, and therefore, in contrast to previous reports on other species of teleost fishes, oxidative stress is not believed to be a main driver of toxicity in white sturgeon exposed to SeMet.

[Determination of free selenomethionine in cow milk by UPLC-MS/MS].

OBJECTIVE: To establish an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the quantification of free selenomethionine (SeMet), and be applied to the quantification of free SeMet in cow milk. METHODS: The analyte was separated on a BEH C18 column (2.1 mm x 100 mm, 1.7 µm) at 40 degrees C with a mobile phase of water: acetonitrile: formic acid (95: 5: 0.1, V/V) , a flow rate of 0.3 mL/min, and an analysis time of 2. 5 min. At positive electrospray ionization mode, multiple reaction monitoring of the precursor-product ion transitions of m/z 198.0 --> 181.1 was used for the quantification. RESULTS: The linear calibration curve was obtained in a concentration range of 0.5 - 100 ng/mL with a lower limit of quantification of 0.5 ng/mL. The value of intra- and inter-day accuracy for SeMet fell in the range of 97.6%-100.6% and 97.7%-99.2%, and value of intra- and inter-day precision 0.53%-4.49% and 1.03%-4.54%. CONCLUSION: The method is specific, sensitive, rapid, and accurate, suitable for the quantification of free SeMet in cow milk.

Dose-Dependent Early Life Stage Toxicities in Xenopus laevis Exposed In Ovo to Selenium.

Selenium (Se) is a developmental toxicant in oviparous vertebrates. The adverse reproductive effects of Se toxicity have been predominantly investigated in fishes and birds with only a few studies focusing on amphibians. The objective of this study was to determine tissue-based toxicity thresholds for early life stage Se toxicities in Xenopus laevis as a consequence of in ovo exposure through maternal transfer of dietary Se. Following a 68-day dietary exposure to food augmented with l-selenomethionine (SeMet) at measured concentrations of 0.7 (control), 10.9, 30.4, or 94.2 µg Se/g dry mass (d.m.), adult female X. laevis were bred with untreated males, and resulting embryos were incubated until 5 days postfertilization (dpf). The measured Se concentrations in eggs were 1.6, 10.8, 28.1, and 81.7 µg Se/g d.m., respectively. No biologically significant effects were observed on fertilization success, hatchability, or mortality in offspring. Frequency and severity of morphological abnormalities were significantly greater in 5 dpf tadpoles from the highest exposure group when compared to the control, with eye lens abnormalities being the most prominent of all abnormalities. The estimated EC10 value for frequency of total early life stage abnormalities was 44.9 µg Se/g egg d.m., which suggests that this amphibian species is less sensitive to in ovo Se exposure than most of the fish species studied to date.

Gamma camera imaging for studying intestinal absorption and whole-body distribution of selenomethionine.

Se metabolism in humans is not well characterised. Currently, the estimates of Se absorption, whole-body retention and excretion are being obtained from balance and tracer studies. In the present study, we used gamma camera imaging to evaluate the whole-body retention and distribution of radiolabelled selenomethionine (SeMet), the predominant form of Se present in foods. A total of eight healthy young men participated in the study. After consumption of a meal containing 4 MBq [75Se]L-SeMet ([75Se]SeMet), whole-body gamma camera scanning was performed for 45 min every hour over a 6 h period, every second hour for the next 18 h and once on each of the subsequent 6 d. Blood, urine and faecal samples were collected to determine the plasma content of [75Se]SeMet as well as its excretion in urine and faeces. Imaging showed that 87·9 (sd 3·3)% of the administered activity of [75Se]SeMet was retained within the body after 7 d. In contrast, the measured excretion in urine and faeces for the 7 d period was 8·2 (sd 1·1)% of the activity. Time-activity curves were generated for the whole body, stomach, liver, abdomen (other than the stomach and the liver), brain and femoral muscles. Gamma camera imaging allows for the assessment of the postprandial absorption of SeMet. This technique may also permit concurrent studies of organ turnover of SeMet.