Selenoneine Is Methylated in the Bodies of Mice and then Excreted in Urine as Se-Methylselenoneine

Oral intake of purified selenoneine and seafoods has been reported to result in selenoneine accumulation in erythrocytes in mice and human. In addition, Se-methylselenoneine was suggested to be produced as a metabolite of selenoneine in the urine and whole blood of humans. In order to confirm the molecular mechanism of production of Se-methylselenoneine, a stable isotope (Se-76) labeled selenoneine was biosynthesized using genetically modified fission yeast and administered to mice. The Se-76-labeled Se-methylselenoneine was detected in urine but Se-78 and Se-80-labeled Se-methylselenoneine arising from natural isotopes of Se was hardly detected. These results suggest that Se-methylselenoneine was a metabolite and the excreted form of selenoneine. The methylation of selenoneine in mice administered selenoneine continuously was evaluated by the analyses of organs using an online liquid chromatograph system with an inductively coupled plasma mass spectrometer (LC-ICP-MS). These experiments indicate that selenoneine is methylated in the liver and (or) kidneys.

Assessment of dietary Selenium and its role in Mercury fate in cultured fish rainbow trout with two sustainable aquafeeds

This study enhances the current limited understanding of the interaction between mercury (Hg) and selenium (Se) species in fish. Rainbow trout (Oncorhynchus mykiss), a model aquaculture fish, was exposed to Hg and Se species through controlled dietary conditions. Over a 6-month feeding trial, the impact of dietary Se on Hg bioaccumulation in fish, including flesh, brain, and liver, was tracked. Twelve dietary conditions were tested, including plant-based diets (0.25 µgSe g-1) and tuna byproduct diets (0.25 µgHg g-1, 8.0 µgSe g-1) enriched with methylmercury and/or Se as selenite or selenomethionine. The tuna byproduct diet resulted in lower Hg levels than the plant-based diets, with muscle Hg content below the European Commission's safe threshold. This study highlights the significant impact of specific Se compounds in the diet, particularly from tuna-based aquafeed, on Hg bioaccumulation. These promising results provide a strong recommendation for future use of fisheries byproducts in sustainable aquafeeds.

Simultaneous determination of ergothioneine, selenoneine, and their methylated metabolites in human blood using ID-LC-MS/MS

Ergothioneine and selenoneine are structurally related dietary antioxidants and cytoprotectants that may help prevent several chronic diseases associated with inflammation and aging. Both compounds share pharmacokinetic characteristics such as cellular uptake through the ergothioneine transporter, accumulation in red blood cells, and biotransformation to methylated metabolites. A rapid, sensitive, specific, precise, and cost-effective analytical method is required to further investigate the potential health benefits of these compounds, individually or combined, in large epidemiological studies. We developed and validated an isotope-dilution liquid chromatography tandem mass spectrometry (ID-LC-MS/MS) method for the simultaneous specific quantification of these analytes in human blood following a simple sample preparation consisting of dilution in aqueous dithiothreitol followed by centrifugal filtration. Chromatographic separation of the analytes is achieved using a reversed-phase chromatography within an 8-min run. Analyte detection is performed using triple quadrupole mass spectrometry in multiple reaction monitoring mode. Each analyte is quantified against its corresponding isotopically labeled internal standard either commercially available or synthesized in-house (77Se-labeled selenoneine compounds). The validated method demonstrates excellent linearity and very good precision (all CV < 10%). Matrix effects are minimal, suggesting that this method could easily be adapted to other matrices. Freeze/thaw cycles have little effect on methylated metabolites but significantly reduced concentrations of the parent compounds. The method was successfully applied to a small set of volunteer blood samples containing low levels of the analytes. The developed ID-LC-MS/MS method opens new avenues for exploring the roles of these bioactive compounds and their metabolites in human health and disease.

Isotopologue pattern based data mining for selenium species from HILIC-ESI-Orbitrap-MS-derived spectra

Automated and specific picking of selenium-containing molecular entities has not been an obvious option for software tools associated with electrospray high-resolution mass spectrometry (MS). In our study, a comprehensive pattern matching approach based on intra-isotopologue distance and isotopologue ratio data was critically evaluated in terms of reproducibility and selenium isotope selection on three samples, including selenized Torula yeast and the selenium hyperaccumulator plant Cardamine violifolia. Hydrophilic interaction liquid chromatography was applied to provide a one-step separation for water soluble metabolites to put an end to the need for either orthogonal setups or poor retention on reversed phase chromatography. Assistance from inductively coupled plasma-MS was taken only for chromatographic verification purposes, and the involvement of absolute mass defect (MD) data in selenometabolite-specific screening was assessed by multivariate statistical tools. High focus was placed on screening efficiency and on the validation of discovered selenized molecules to avoid reporting of artefacts. From the >1000 molecular entries detected, selenium-containing molecules were picked up with a recovery rate of >88% and a false positive rate of <10%. Isotop(ologu)e pairs of 78Se-80Se and 80Se-82Se proved to be the most performant in the detection. On the basis of accurate mass information and hypothetical deamination processes, elemental composition could be proposed for 72 species out of the 75 selenium species encountered without taking into account selenocompound databases. Absolute MD data were used to significantly differentiate a potentially sample-specific subgroup of false positive molecular entities from non-selenized and selenized entities.

Diet and Blood Concentrations of Essential and Non-Essential Elements among Rural Residents in Arctic Russia

Nutrition is an essential factor for human health. Earlier research has suggested that Arctic residents are vulnerable to environmental toxic exposures through traditional foods. Although Russia is the largest Arctic country, the evidence on the topic from the Russian part of the Arctic is scarce. We studied associations between blood concentrations of essential and non-essential elements and traditional food consumption in 297 adults from seven rural settlements in the Nenets Autonomous Area, Northwest Russia. Blood arsenic concentration was positively associated with consumption of rainbow smelt, pink salmon, Arctic char and navaga fish. Frequent consumption of northern pike was associated with increased concentration of blood mercury. Blood mercury and arsenic concentrations were significantly associated with blood selenium. We also observed positive associations between blood lead levels and the frequency of goose consumption. Moreover, subjects who reported to be hunters had higher blood levels of lead, suggesting contamination of goose meat with fragments of shotgun shells. Blood cobalt and manganese concentrations were inversely associated with serum ferritin levels. Positive associations between blood levels of manganese and lead were observed. Moreover, blood lead concentrations were significantly associated with cadmium, mercury, copper, and zinc. Our results corroborate earlier findings on the traditional foods as source of non-essential elements for the Arctic residents. Observed correlations between the levels of lead and other elements warrant further research and may have potential implications for the studies on the associations between essential elements and health outcomes.

First Time Identification of Selenoneine in Seabirds and Its Potential Role in Mercury Detoxification

Birds are principally exposed to selenium (Se) through their diet. In long-lived and top predator seabirds, such as the giant petrel, extremely high concentrations of Se are found. Selenium speciation in biota has aroused great interest in recent years; however, there is a lack of information about the chemical form of Se in (sea)birds. The majority of publications focus on the growth performance and antioxidant status in broilers in relation to Se dietary supplementation. The present work combines elemental and molecular mass spectrometry for the characterization of Se species in wild (sea)birds. A set of eight giant petrels (Macronectes sp.) with a broad age range from the Southern Ocean were studied. Selenoneine, a Se-analogue of ergothioneine, was identified for the first time in wild avian species. This novel Se-compound, previously reported in fish, constitutes the major Se species in the water-soluble fraction of all of the internal tissues and blood samples analyzed. The levels of selenoneine found in giant petrels are the highest reported in animal tissues until now, supporting the trophic transfer in the marine food web. The characterization of selenoneine in the brain, representing between 78 and 88% of the total Se, suggests a crucial role in the nervous system. The dramatic decrease of selenoneine (from 68 to 3%) with an increase of Hg concentrations in the liver strongly supports the hypothesis of its key role in Hg detoxification.

Determination of the Intracellular Complexation of Inorganic and Methylmercury in Cyanobacterium Synechocystis sp. PCC 6803

Understanding of mercury (Hg) complexation with low molecular weight (LMW) bioligands will help elucidate its speciation. In natural waters, the rate of this complexation is governed by physicochemical, geochemical, and biochemical parameters. However, the role of bioligands involved in Hg intracellular handling by aquatic microorganisms is not well documented. Here, we combine the use of isotopically labeled Hg species (inorganic and monomethylmercury, iHg and MeHg) with gas or liquid chromatography coupling to elemental and molecular mass spectrometry to explore the role of intracellular biogenic ligands involved in iHg and MeHg speciation in cyanobacterium Synechocystis sp. PCC 6803, a representative phytoplankton species. This approach allowed to track resulting metabolic and newly found intracellular Hg biocomplexes (e.g., organic thiols) in Synechocystis sp. PCC 6803 finding different intracellular Hg species binding affinities with both high and low molecular weight (HMW and LMW) bioligands in the exponential and stationary phase. Furthermore, the parallel detection with both elemental and molecular ionization sources allowed the sensitive detection and molecular identification of glutathione (GSH) as the main low molecular weight binding ligand to iHg ((GS)₂-Hg) and MeHg (GS-MeHg) in the cytosolic fraction. Such a novel experimental approach expands our knowledge on the role of biogenic ligands involved in iHg and MeHg intracellular handling in cyanobacteria.

Absorption, distribution, metabolism and excretion (ADME) of oral selenium from organic and inorganic sources: A review

BACKGROUND

Selenium is a trace element traditionally ingested either in its organic form via food or in its inorganic form through nutritional supplements, while selenium formulated as nanoparticles is a putative long-acting alternative. To understand the physiology and toxicology of the different selenium formulations, it is important to determine how their selenium content is absorbed, distributed, metabolised and excreted; therefore, we reviewed their biokinetics following oral exposure.

METHODS

We retrieved and reviewed the literature on the absorption, distribution, metabolism, and excretion of oral exposure to different forms of selenium.

RESULTS

Selenium in both the organic form (containing carbon to selenium chemical bonds) and the inorganic form is absorbed into the blood in humans. The mean normal blood level of many studies was 139 μg/L. There are indications that selenium from organic sources is more bioavailable than selenium from inorganic sources. Selenium is distributed throughout the body, including in breast milk. The elimination of selenium mainly involves the faecal and urinary pathways, whereas breath, saliva and hair are minor contributors. Urinary metabolites include trimethylselenium ions, selenosugars and Se-methylselenoneine.

CONCLUSION

Selenium is absorbed to a high extent, and selenium from organic sources is more bioavailable than from inorganic sources. Selenium, as expected as an essential trace element, is distributed throughout the body. Selenium is extensively metabolised, and various excretion metabolites have been identified in both urine and breath, while some selenium is also excreted via faeces.

Identification and determination of selenocysteine, selenosugar, and other selenometabolites in turkey liver

Liver and other tissues accumulate selenium (Se) when animals are supplemented with high dietary Se as inorganic Se. To further study selenometabolites in Se-deficient, Se-adequate, and high-Se liver, turkey poults were fed 0, 0.4, and 5 μg Se g-1 diet as Na2SeO3 (Se(iv)) in a Se-deficient (0.005 μg Se g-1) diet for 28 days, and the effects of Se status determined using HPLC-ICP-MS and HPLC-ESI-MS/MS. No selenomethionine (SeMet) was detected in liver in turkeys fed either this true Se-deficient diet or supplemented with inorganic Se, showing that turkeys cannot synthesize SeMet de novo from inorganic Se. Selenocysteine (Sec) was also below the level of detection in Se-deficient liver, as expected in animals with negligible selenoprotein levels. Sec content in high Se liver only doubled as compared to Se-adequate liver, indicating that the 6-fold increase in liver Se was not due to increases in selenoproteins. What increased dramatically in high Se liver were low molecular weight (MW) selenometabolites: glutathione-, cysteine- and methyl-conjugates of the selenosugar, seleno-N-acetyl galactosamine (SeGalNac). Substantial Se in Se-adequate liver was present as selenosugars decorating general proteins via mixed-disulfide bonds. In high-Se liver, these "selenosugar-decorated" proteins comprised ∼50% of the Se in the water-soluble fraction, in addition to low MW selenometabolites. In summary, more Se is present as the selenosugar moiety in Se-adequate liver, mostly decorating general proteins, than is present as Sec in selenoproteins. With high Se supplementation, increased selenosugar formation occurs, further increasing selenosugar-decorated proteins, but also increasing selenosugar linked to low MW thiols.

Implications for an imidazol-2-yl carbene intermediate in the rhodanase-catalyzed C-S bond formation reaction of anaerobic ergothioneine biosynthesis

In the anaerobic ergothioneine biosynthetic pathway, a rhodanese domain containing enzyme (EanB) activates tne hercynine's sp² ε-C-H Dona ana replaces it with a C-S bond to produce ergothioneine. The key intermediate for this trans-sulfuration reaction is the Cys412 persulfide. Substitution of the EanB-Cys412 persulfide with a Cys412 perselenide does not yield the selenium analog of ergothioneine, selenoneine. However, in deuterated buffer, the perselenide-modified EanB catalyzes the deuterium exchange between hercynine's sp² ε-C-H bond and D₂O. Results from QM/MM calculations suggest that the reaction involves a carbene intermediate and that Tyr353 plays a key role. We hypothesize that modulating the pK_a of Tyr353 will affect the deuterium-exchange rate. Indeed, the 3,5-difluoro tyrosine containing EanB catalyzes the deuterium exchange reaction with k _ex of ~10-fold greater than the wild-type EanB (EanB_WT). With regards to potential mechanisms, these results support the involvement of a carbene intermediate in EanB-catalysis, rendering EanB as one of the few carbene-intermediate involving enzymatic systems.

Capabilities of selenoneine to cross the in vitro blood-brain barrier model

The naturally occurring selenoneine (SeN), the selenium analogue of the sulfur-containing antioxidant ergothioneine, can be found in high abundance in several marine fish species. However, data on biological properties of SeN and its relevance for human health are still scarce. This study aims to investigate the transfer and presystemic metabolism of SeN in a well-established in vitro model of the blood-brain barrier (BBB). Therefore, SeN and the reference Se species selenite and Se-methylselenocysteine (MeSeCys) were applied to primary porcine brain capillary endothelial cells (PBCECs). Se content of culture media and cell lysates was measured via ICP-MS/MS. Speciation analysis was conducted by HPLC-ICP-MS. Barrier integrity was shown to be unaffected during transfer experiments. SeN demonstrated the lowest transfer rates and permeability coefficient (6.7 × 10-7 cm s-1) in comparison to selenite and MeSeCys. No side-directed accumulation was observed after both-sided application of SeN. However, concentration-dependent transfer of SeN indicated possible presence of transporters on both sides of the barrier. Speciation analysis demonstrated no methylation of SeN by the PBCECs. Several derivatives of SeN detected in the media of the BBB model were also found in cell-free media containing SeN and hence not considered to be true metabolites of the PBCECs. In concluding, SeN is likely to have a slow transfer rate to the brain and not being metabolized by the brain endothelial cells. Since this study demonstrates that SeN may reach the brain tissue, further studies are needed to investigate possible health-promoting effects of SeN in humans.

The biology of ergothioneine, an antioxidant nutraceutical

Ergothioneine (ERG) is an unusual thio-histidine betaine amino acid that has potent antioxidant activities. It is synthesised by a variety of microbes, especially fungi (including in mushroom fruiting bodies) and actinobacteria, but is not synthesised by plants and animals who acquire it via the soil and their diet, respectively. Animals have evolved a highly selective transporter for it, known as solute carrier family 22, member 4 (SLC22A4) in humans, signifying its importance, and ERG may even have the status of a vitamin. ERG accumulates differentially in various tissues, according to their expression of SLC22A4, favouring those such as erythrocytes that may be subject to oxidative stress. Mushroom or ERG consumption seems to provide significant prevention against oxidative stress in a large variety of systems. ERG seems to have strong cytoprotective status, and its concentration is lowered in a number of chronic inflammatory diseases. It has been passed as safe by regulatory agencies, and may have value as a nutraceutical and antioxidant more generally.

Expanding beyond ICP-MS to better understand selenium biochemistry

Selenium is an essential trace element in human health and therefore its concentration in biological samples (biofluids and tissues) is used as an indicator of health and nutritional status. In humans, selenium's biological activity occurs through the 25 identified selenoproteins. As total selenium concentration encompasses both functional selenoproteins, small selenocompounds and other selenium-binding proteins, selenium speciation, rather than total concentration, is critical in order to assess functional selenium. Previously, quantitative analysis of selenoproteins required laborious techniques that were often slow and costly. However, more recent advancements in tandem mass spectrometry have facilitated the qualitative and quantitative identification of these proteins. In light of the current alternatives for understanding selenium biochemistry, we aim to provide a review of the modern applications of electrospray ionisation mass spectrometry (ESI-MS) as an alternative to inductively coupled plasma mass spectrometry (ICP-MS) for qualitative and quantitative selenium speciation.

Determination of eleven small selenium species in human urine by chromatographic-coupled ICP-MS methods

BACKGROUND

The determination of various selenium species in urine enables a specific biomonitoring of the exposure to different selenium compounds.

METHODS

For this task a coupling of three chromatographic techniques with ICP-MS was developed for the separate quantification of eleven species in urine. The first procedure was based on reverse phase chromatography and was designed for the separate determination of methyl-2-acetamido-2-deoxy-1-seleno-b-d-galactopyranoside (SeSug1), methyl-2-acetamido-2-deoxy-1-seleno-b-d-glucopyranoside (SeSug2), selenomethionine (SeMet), methylselenocysteine (MeSeC), seleno-D,L-ethionine (SeEt), methylselenic acid (MeSeA) and methylselenoglutathione (MeSeG); the second procedure was based on anion exchange chromatography and measured selenate (Se (VI)) and selenite (Se (IV)); the third procedure was based on cationic exchange chromatography and determined methyl-2-amino-2-deoxy-1-seleno-b-d-galactopyranoside (SeSug3) and the trimethylselenium ion (TMSe). A fourth method for the more sensitive determination of TMSe was upgraded by an on-line after-column reaction process.

RESULTS

The validation of the methods yielded sensitive detection limits of the species between 0.03 and 0.10 μg Se/L. For TMSe a detection limit of 0.02 μg Se/L resulted by the fourth method. An intra-day precision of 2.7-10.6% and a relative recovery between 87 % and 108 % confirm the robustness of the methods.

CONCLUSION

The developed procedures enable a separate and sensitive determination of eleven selenium species in urine and thus permit the exploring of metabolic factors in the general population and particularly exposed individuals.

Knockout of Selenoprotein V Affects Regulation of Selenoprotein Expression by Dietary Selenium and Fat Intakes in Mice

BACKGROUND

The metabolic function of selenoprotein V (SELENOV) remains unknown.

OBJECTIVES

Two experiments were conducted to determine effects of the Selenov knockout (KO) on selenium concentration and mRNA, protein, and/or activity of 4 major selenoproteins [glutathione peroxidase (GPX) 1, GPX4, thioredoxin reductase-1 (TXNRD1), and selenoprotein P (SELENOP)] in the serum, liver, testis, and/or white adipose tissue (WAT) of mice fed different dietary selenium and fat concentrations.

METHODS

In Experiment (Expt) 1, 40 KO and 40 wild-type (WT) mice (males, 8 wk old) were fed (n = 10/genotype) a casein-sucrose basal diet plus 0, 0.3, 1, or 3 mg Se/kg (as sodium selenite) for 32 wk . In Expt 2, 20 KO and 20 WT mice (males, 8 wk old) were fed (n  = 10/genotype) a normal-fat diet (NF; 10% calories from fat) or a high-fat diet (HF; 60% calories from fat) for 19 wk.

RESULTS

In Expt 1, the KO caused consistent or substantial decreases (P < 0.05) of mRNA amounts of Gpx1, Txnrd1, and Selenop in the testis (≤52%), but selenium concentrations (19-29%) and GPX activities (≤ 50%) were decreased in the liver across different dietary selenium concentrations . Hepatic and testis GPX1 protein was elevated (≤31%) and decreased (≤45%) by the KO, respectively. In Expt 2, the genotype and dietary fat intake exerted interaction effects ( P < 0.05) on Gpx1 mRNA amounts in the WAT; Gpx1, Txnrd1, and Selenop mRNA amounts and TXNRD activities in the testis; and selenium concentrations in the serum and liver. However, these 2 treatments produced largely independent or additive effects (P < 0.05) on the GPX1 and SELENOP protein amounts in the liver and testis (up to ± 50% changes).

CONCLUSIONS

The KO-mediated changes in the tissue selenium concentrations and functional expression of 3 major selenoproteins implied potential for SELENOV in regulating body selenium metabolism in the mouse.

Se deficiency induces renal pathological changes by regulating selenoprotein expression, disrupting redox balance, and activating inflammation

Selenium (Se) is closely associated with kidney disease, and renal injury often occurs together with hyposelenemia. This study was designed to reveal the mechanism underlying renal injury induced by Se deficiency in pigs. Twenty-four castrated male Yorkshire pigs were divided into two groups fed either a Se-deficient diet (0.007 mg Se per kg) or a Se-adequate diet (0.3 mg Se per kg). Serum and kidney samples were collected at the 16th week of the trial, processed, and analyzed for serum biochemistry, Se concentration, kidney index markers, histology, selenoprotein mRNA expression, redox status, and inflammatory cytokines. Dietary Se deficiency induced kidney injury, decreased (P < 0.05) Se concentrations, and increased (P < 0.05) kidney index and serum blood urea nitrogen, creatinine, and carbon dioxide values. Histological analysis indicated that Se deficiency induced inflammatory lesions and renal tubular atrophy in the renal medulla. Se deficiency downregulated (P < 0.05) nine selenoprotein genes (GPX1, SELENOW, SELENOH, SELENOP, GPX3, TXNRD2, SELENOI, SELENON, and SELENOM) and upregulated (P < 0.05) SEPHS2 in the kidneys. Se deficiency decreased (P < 0.05) the activity of glutathione peroxidase, thioredoxin reductase, and catalase, as well as the hydroxyl radical inhibition capacity, and increased (P < 0.05) the content of malondialdehyde and nitric oxide. Se deficiency increased (P < 0.05) the expression of the transcription factors NF-κB and HIF-1α, and regulated inflammatory cytokines. Se deficiency increased (P < 0.05) the expression of IL-6, IL-8, IL-12, IL-17, and cyclooxygenase-2, and decreased (P < 0.05) the expression of IL-10, IL-13, and TGF-β. These results indicated that Se deficiency induces kidney injury through the regulation of selenoproteins, oxidative stress, and inflammation.

Selenoneine ameliorates peroxide-induced oxidative stress in C. elegans

SCOPE

Selenoneine (2-selenyl-N_α, N_α, N_α-trimethyl-L-histidine), the selenium (Se) analogue of the ubiquitous thiol compound and putative antioxidant ergothioneine, is the major organic selenium species in several marine fish species. Although its antioxidant efficacy has been proposed, selenoneine has been poorly characterized, preventing conclusions on its possible beneficial health effects.

METHODS AND RESULTS

Treatment of Caenorhabditis elegans (C. elegans) with selenoneine for 18 h attenuated the induction of reactive oxygen and nitrogen species (RONS). However, the effect was not immediate, occurring 48 h post-treatment. Total Se and Se speciation analysis revealed that selenoneine was efficiently taken up and present in its original form directly after treatment, with no metabolic transformations observed. 48 h post-treatment, total Se in worms was slightly higher compared to controls and no selenoneine could be detected.

CONCLUSION

The protective effect of selenoneine may not be attributed to the presence of the compound itself, but rather to the activation of molecular mechanisms with consequences at more protracted time points.

Selenoneine is a major selenium species in beluga skin and red blood cells of Inuit from Nunavik

Nunavimmiut (Inuit of Nunavik, Northern Quebec, Canada) exhibit a high selenium (Se) status because of their frequent consumption of marine mammal foods. Indirect evidence from our previous studies had suggested that selenoneine - a novel selenocompound - may be accumulating in the blood of Nunavimmiut. We used a liquid-chromatography/inductively coupled tandem mass spectrometry (LC-ICP-MS/MS) method to measure concentrations of selenoneine and its methylated metabolite Se-methylselenoneine in archived red blood cells (RBC) obtained from 210 Nunavimmiut living in communities along the Hudson Strait, where marine mammal hunting and consumption are most frequent in Nunavik. This method was adapted to quantify selenoneine and its methylated metabolite in beluga mattaaq, an Inuit delicacy consisting of the skin with the underlying layer of fat and the major dietary source of Se for Nunavimmiut. Total selenium concentration was also measured in RBC and beluga mattaaq samples by isotope dilution ICP-MS/MS. The median selenoneine concentration in RBC was 413 μg Se/L (range = 3.20-3230 μg Se/L), representing 54% (median) of total Se content (range = 1.6-91%). Quantification of selenoneine in five beluga mattaaq samples (skin layer) from Nunavik revealed a median concentration of 1.8 μg Se/g wet wt (range = 1.2-7.4 μg Se/g), constituting 54% (median) of the total Se content (range = 44-74%). Se-methylselenoneine was also detected in Inuit RBC but not in beluga mattaaq, suggesting that selenoneine undergoes methylation in humans. Selenoneine may protect Nunavimmiut from methylmecury toxicity by increasing its demethylation in RBC and in turn decreasing its distribution to target organs.

Coordination of 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone to zinc and cadmium: Monotonic and non-monotonic bond length variations for [H(sebenzimMe)]2MCl2 complexes (M = Zn, Cd, Hg)

The reactions of 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone, H(sebenzimMe), towards the zinc and cadmium halides, MX2 (M = Zn, Cd; X = Cl, Br, I), afford the adducts, [H(sebenzimMe)]2MX2, which have been structurally characterized by X-ray diffraction. The halide ligands of each of these complexes participate in hydrogen bonding interactions with the imidazole N-H moieties, although the nature of the interactions depends on the halide. Specifically, the chloride and bromide derivatives, [H(sebenzimMe)]2ZnX2 and [H(sebenzimMe)]2CdX2 (X = Cl, Br), exhibit two intramolecular N-H•••X interactions, whereas the iodide derivatives, [H(sebenzimMe)]2ZnI2 and [H(sebenzimMe)]2CdI2, exhibit only one intramolecular N-H•••I interaction. Comparison of the M-Se and M-Cl bond lengths of the chloride series, [H(sebenzimMe)]2MCl2 (M = Zn, Cd, Hg), indicates that while the average M-Cl bond lengths progressively increase as the metal becomes heavier, the variation in M-Se bond length exhibits a non-monotonic trend, with the Cd-Se bond being the longest. These different trends provide an interesting subtlety concerned with use of covalent radii in predicting bond length differences. In addition to tetrahedral [H(sebenzimMe)]2CdCl2, [H(sebenzimMe)]3,CdCl2•[H(sebenzim)Me]4CdCl2, which features both five-coordinate and six-coordinate coordinate centers, has also been structurally characterized. Finally, the reaction between CdI2 and H(sebenzimMe) at elevated temperatures affords the 1-methylbenzimidazole complex, [H(sebenzimMe)]-[H(benzimMe)]CdI2, a transformation that is associated with cleavage of the C-Se bond.

Hydrophilic interaction liquid chromatography in the speciation analysis of selenium

The hydrophilic interaction liquid chromatography (HILIC) coupled to mass spectrometry was employed to study retention behavior of selected selenium compounds using two different HILIC stationary phases: silica and zwitterionic. Two organic solvents - acetonitrile and methanol - were compared as a component of mobile phase. Separation parameters such as a content of organic modifier, the eluent pH and inorganic buffer concentration were investigated. Based on all observations, methanol seems to be beneficial for the separation of studied compounds. The optimal HILIC separation method involved silica column and eluent composed of 85% MeOH and CH₃COONH₄ (8 mM, pH 7) was compared to RP method in terms of time of the single run, the separation efficiency and limit of detection.

Biosynthesis and isolation of selenoneine from genetically modified fission yeast

Selenoneine was successfully purified from genetically modifiedSchizosaccharomyces pombegrown in selenate containing culture medium.

Dietary and blood selenium are inversely associated with the prevalence of stroke among Inuit in Canada

Inuit in Canada have high selenium intake from the consumption of country food such as fish and marine mammals. The health consequence is not known. This study examines the association between blood selenium concentration and prevalence of stroke among Canadian Inuit. The International Polar Year Inuit Health Survey was conducted in 2007-2008. Among the 2077 adults participants (≥18years old) who completed a questionnaire and gave blood samples, 49 stroke cases were reported, 31 of which were from women. The crude prevalence of stroke was 2.4% in the participants. Participants with stroke had lower blood selenium (geometric mean: 260μg/L vs. 319μg/L) and dietary selenium (144μg/day vs. 190μg/day) compared to individuals without stroke. Participants with high blood/dietary selenium exposure (quartiles 3 and 4) had a lower prevalence of stroke compared to those with low selenium exposure (quartile 1). The adjusted odds ratio ranged from 0.09 to 0.25 among subgroups (e.g. age, sex, and blood mercury). An L-shaped relationship between prevalence of stroke with blood and dietary selenium was observed, based on the cubic restricted spline and segmented regression analyses. The estimated turning points of the L-shaped curve for blood selenium and dietary selenium were 450μg/L and 350μg/day, respectively. Below the turning points, it was estimated that each 50-μg/L increase in blood selenium was associated with a 38% reduction in the prevalence of stroke, and each 50-μg/day increase in dietary selenium was associated with a 30% reduction in the prevalence of stroke. In conclusion, blood and dietary selenium are reversely associated with the prevalence of stroke in Inuit, which follows an L-shaped relationship. Whether this relationship applies to other population needs further investigation.

Exploring the urinary selenometabolome following a multi-phase selenite administration regimen in humans

To gain more insight into the human metabolism of the essential trace element selenium, we investigate the response of the urinary selenium metabolites to changing selenium intake by applying a stepwise selenium administration regimen based on repeated dosaging. Sodium selenite was administered orally to healthy volunteers at an incrementally increasing dosage. The supplementation regimen extended over 20 days for each volunteer, and daily morning urine samples were collected prior to, during, and following the supplementation phases. A total of 160 urine samples were analyzed for total urinary selenium and a panel of selenometabolites by using ICPMS and HPLC/ICPMS. Selenosugar 1 gave the strongest response followed by TMSe and then selenosugar 3. Se-methylselenoneine excretion was not stimulated by increased selenium intake, suggesting that it is not in equilibrium with selenium body pools. Selenate was detected in all urine samples; it showed a clear and consistent response to supplementation and an abrupt return to baseline levels upon cessation of supplementation, indicating that it arose from the oxidation of the administered selenite rather than from the oxidation of endogenous hydrogen selenide. The gap between total urinary selenium and the sum of Se species markedly increased in response to selenium administration, which highlights the presence of unknown Se species that respond to selenite supplementation. The characterization of these unknown species and their possible biological activities might be essential before considering selenium supplementation in clinical trials. We discuss the implications of the responses of the selenium metabolites and their inter-relationships for selenium metabolism.

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.

High selenium exposure lowers the odds ratios for hypertension, stroke, and myocardial infarction associated with mercury exposure among Inuit in Canada

BACKGROUND

Selenium (Se) has been reported to protect against the neurotoxicity of mercury (Hg). However, the effect of Se against Hg on cardiovascular diseases remains unclear. Inuit living in the Arctic have high exposure to both Se and Hg through their marine mammal and fish rich traditional diet.

OBJECTIVE

To characterize the co-exposure of Hg and Se among Inuit in Canada and to assess the associations between Hg, Se and cardiovascular health outcomes, including stroke, hypertension, and myocardial infarction (MI).

METHODS

Data was collected from the International Polar Year Inuit Health Survey (IHS) conducted in 2007 and 2008. Blood Se and Hg were measured, and self-report cardiovascular health outcomes were collected through a questionnaire interview from 2169 adults aged 18 and above.

RESULTS

The mean age was 42.4years, and 38.7% of the participants were male. The geometric means (GM) of blood Se and total Hg were 319.5μg/L and 7.0μg/L, respectively. The crude prevalence of heart attack, stroke and hypertension were 3.55%, 2.36%, and 24.47% respectively. Participants were categorized into 4 exposure groups according to blood Hg (high: ≥7.8μg/L; low: <7.8μg/L), and Se (high: ≥280μg/L; low: <280μg/L). The odds ratio (OR) of cardiovascular outcomes were estimated using general linearized models. Results showed the low Se and high Hg group had a higher prevalence of cardiovascular disease (OR=1.76 for hypertension, 1.57 for stroke, and 1.26 for MI. However, the prevalence was decreased in both the high Se and low Hg group (OR=0.57 for hypertension, 0.44 for stroke, and 0.27 for MI) and the high Se and high Hg group (OR=1.14 for hypertension, 0.31 for stroke, and 0.80 for MI).

CONCLUSIONS

The high Se and low Hg group had the lowest prevalence of cardiovascular outcomes, except for stroke. These results provide evidence that Se may exhibit a protective effect against Hg on cardiovascular disease.

Investigating the intra-individual variability in the human metabolic profile of urinary selenium

Selenium is an essential micronutrient widely present in our diet. It plays its role through the selenoproteins. Previous reports have shown marked variation between individuals in the excretion of this trace element, but the intra-individual variability in selenium excretion has not been specifically investigated. The present study investigates the intra-individual variation in the urinary excretion of selenium in a group of healthy volunteers. We also discuss inter-individual variability trends. Urine samples were collected from healthy volunteers without selenium supplementation twice a day for 7 days and then once a week for an additional 7 weeks. A total of 168 urine samples were collected and analyzed for total selenium and individual selenium species using elemental mass spectrometry and HPLC/mass spectrometry, respectively. We found only modest day-to-day and week-to-week intra-individual variation of selenium excretion. Two commonly reported urine metabolites, selenosugar 1 and selenosugar 3, were detected in all urine samples, and our data suggest that selenosugar 3 is a deacetylated product of selenosugar 1 produced in a manner dependent on selenium intake. Trimethylselenonium displayed no intra-individual variability but considerable inter-individual variability in agreement with the involvement of genetic polymorphisms, as recently reported. Se-methylselenoneine was consistently detected in the urine of all volunteers and was a significant metabolite in one volunteer contributing up to 24% of total urinary selenium. Our data indicate that selenium urinary excretion is consistent within an individual, and that intra-individual variation in selenium excretion is unlikely to complicate future inter-individual variation studies.

Why Nature Chose Selenium

The authors were asked by the Editors of ACS Chemical Biology to write an article titled "Why Nature Chose Selenium" for the occasion of the upcoming bicentennial of the discovery of selenium by the Swedish chemist Jöns Jacob Berzelius in 1817 and styled after the famous work of Frank Westheimer on the biological chemistry of phosphate [Westheimer, F. H. (1987) Why Nature Chose Phosphates, Science 235, 1173-1178]. This work gives a history of the important discoveries of the biological processes that selenium participates in, and a point-by-point comparison of the chemistry of selenium with the atom it replaces in biology, sulfur. This analysis shows that redox chemistry is the largest chemical difference between the two chalcogens. This difference is very large for both one-electron and two-electron redox reactions. Much of this difference is due to the inability of selenium to form π bonds of all types. The outer valence electrons of selenium are also more loosely held than those of sulfur. As a result, selenium is a better nucleophile and will react with reactive oxygen species faster than sulfur, but the resulting lack of π-bond character in the Se-O bond means that the Se-oxide can be much more readily reduced in comparison to S-oxides. The combination of these properties means that replacement of sulfur with selenium in nature results in a selenium-containing biomolecule that resists permanent oxidation. Multiple examples of this gain of function behavior from the literature are discussed.

Phenylselenolate Mercury Alkyl Compounds, PhSeHgMe and PhSeHgEt: Molecular Structures, Protolytic Hg-C Bond Cleavage and Phenylselenolate Exchange

The phenylselenolate mercury alkyl compounds, PhSeHgMe and PhSeHgEt, have been structurally characterized by X-ray diffraction, thereby demonstrating that both compounds are monomeric with approximately linear coordination geometries; the mercury centers do, nevertheless, exhibit secondary Hg•••Se intermolecular interactions that serve to increase the coordination number in the solid state. The ethyl derivative, PhSeHgEt, undergoes facile protolytic cleavage of the Hg-C bond to release ethane at room temperature, whereas PhSeHgMe exhibits little reactivity under similar conditions. Interestingly, the cleavage of the Hg-C bond of PhSeHgEt is also more facile than that of the thiolate analogue, PhSHgEt, which demonstrates that coordination by selenium promotes protolytic cleavage of the mercury-carbon bond. The phenylselenolate compounds PhSeHgR (R = Me, Et) also undergo degenerate exchange reactions with, for example, PhSHgR and RHgCl. In each case, the alkyl groups preserve coupling to the 199Hg nuclei, thereby indicating that the exchange process involves metathesis of the Hg-SePh/Hg-X groups rather than metathesis of the Hg-R/Hg-R groups.

Synthesis, characterization, DFT calculations, and electrochemical comparison of novel iron(ii) complexes with thione and selone ligands

Characterization of Fe(ii)–thone and –selone complexes revealed that these ligands oxidize before Fe(ii), suggesting an iron-binding mechanism for similar antioxidants.

Protolytic cleavage of Hg-C bonds induced by 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone: synthesis and structural characterization of mercury complexes

Multinuclear ((1)H, (77)Se, and (199)Hg) NMR spectroscopy demonstrates that 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone, H(sebenzim(Me)), a structural analogue of the selenoamino acid, selenoneine, binds rapidly and reversibly to the mercury centers of HgX2 (X = Cl, Br, I), while X-ray diffraction studies provide evidence for the existence of adducts of composition [H(sebenzim(Me))]xHgX2 (X = Cl, x = 2, 3, 4; X = I, x = 2) in the solid state. H(sebenzim(Me)) also reacts with methylmercury halides, but the reaction is accompanied by elimination of methane resulting from protolytic cleavage of the Hg-C bond, an observation that is of relevance to the report that selenoneine demethylates CysHgMe, thereby providing a mechanism for mercury detoxification. Interestingly, the structures of [H(sebenzim(Me))]xHgX2 exhibit a variety of different hydrogen bonding patterns resulting from the ability of the N-H groups to form hydrogen bonds with chlorine, iodine, and selenium.

Selenium and selenium-dependent antioxidants in chronic kidney disease

Oxidative stress plays a key role in numerous disease processes including chronic kidney disease (CKD). In general, oxygen metabolism leads to the formation of reactive oxygen species (ROS) dangerous to cells. Although enzymes and low-molecular-weight antioxidants protect against ROS, chronic imbalances of formation and elimination can eventually overwhelm endogenous defenses leading to deleterious consequences. In CKD, glutathione peroxidases (GSH-Px) play an important role in ROS metabolism. Plasma GSH-Px is synthesized in the kidney and requires selenium (Se) as a cofactor. Interestingly, Se and plasma GSH-Px are both significantly reduced in CKD, especially for those patients on hemodialysis. Supplementation of Se in these patients results in modest increases of GSH-Px, presumably from residual renal tissue. Kidney transplantation rapidly restores plasma GSH-Px. In this chapter, the relevance of these findings to CKD is explored with emphasis on renal disease processes and impact on attendant disorders including cancer and cardiovascular disease.

Simple separation and characterization of lanthanide–polyaminocarboxylic acid complexes by HILIC ESI-MS

Lanthanide complexes with EDTA and DTPA ligands were separated and characterized by HILIC ESI-MS for the first time.

Sulfur and selenium antioxidants: challenging radical scavenging mechanisms and developing structure-activity relationships based on metal binding

Because sulfur and selenium antioxidants can prevent oxidative damage, numerous animal and clinical trials have investigated the ability of these compounds to prevent the oxidative stress that is an underlying cause of cardiovascular disease, Alzheimer's disease, and cancer, among others. One of the most common sources of oxidative damage is metal-generated hydroxyl radical; however, very little research has focused on determining the metal-binding abilities and structural attributes that affect oxidative damage prevention by sulfur and selenium compounds. In this review, we describe our ongoing investigations into sulfur and selenium antioxidant prevention of iron- and copper-mediated oxidative DNA damage. We determined that many sulfur and selenium compounds inhibit Cu(I)-mediated DNA damage and that DNA damage prevention varies dramatically when Fe(II) is used in place of Cu(I) to generate hydroxyl radical. Oxidation potentials of the sulfur or selenium compounds do not correlate with their ability to prevent DNA damage, highlighting the importance of metal coordination rather than reactive oxygen species scavenging as an antioxidant mechanism. Additional gel electrophoresis, mass spectrometry, and UV-visible studies confirmed sulfur and selenium antioxidant binding to Cu(I) and Fe(II). Ultimately, our studies established that both the hydroxyl-radical-generating metal ion and the chemical environment of the sulfur or selenium significantly affect DNA damage prevention and that metal coordination is an essential mechanism for these antioxidants.

Shotgun metabolomic profiles in maternal urine identify potential mass spectral markers of abnormal fetal biochemistry - dihydrouracil and progesterone in the metabolism of Down syndrome

In Down syndrome (DS) in particular, the precise cellular mechanisms linking genotype to phenotype is not straightforward despite a clear mapping of the genetic cause. Metabolomic profiling might be more revealing in understanding molecular-cellular mechanisms of inborn errors of metabolism/syndromes than genomics alone and also result in new prenatal screening approaches. The urinary metabolome of 122 maternal urine from women with and without an aneuploid pregnancy (predominantly Down syndrome) were compared by both zwitterionic hydrophilic interaction chromatography (ZIC-HILIC) and reversed-phase liquid chromatography (RPLC) coupled to hybrid ion trap time of flight mass spectral analysis. ZIC-HILIC mass spectrometry resolved 10-fold more unique molecular ions than RPLC mass spectrometry, of which molecules corresponding to ions of m/z 114.07 and m/z 314.20 showed maternal urinary level changes that significantly coincided with the presence of a DS fetus. The ion of m/z 314.20 was identified as progesterone and m/z 114.07 as dihydrouracil. A metabolomics profiling-based maternal urinary screening test modelled from this separation data would detect approximately 87 and 60.87% (using HILIC-MS and RPLC-MS, respectively) of all DS pregnancies between 9 and 23 weeks of gestation with no false positives.

EURRECA-Estimating selenium requirements for deriving dietary reference values

Current reference values for selenium, an essential micronutrient, are based on the intake of selenium that is required to achieve maximal glutathione peroxidase activity in plasma or erythrocytes. In order to assess the evidence of relevance to setting dietary reference values for selenium, the EURRECA Network of Excellence focused on systematic searches, review, and evaluation of (i) selenium status biomarkers and evidence for relationships between intake and status biomarkers, (ii) selenium and health (including the effect of intake and/or status biomarkers on cancer risk, immune function, HIV, cognition, and fertility), (iii) bioavailability of selenium from the diet, and (iv) impact of genotype/single nucleotide polymorphisms on status or health outcomes associated with selenium. The main research outputs for selenium and future research priorities are discussed further in this review.

Metabolomics and systems pharmacology: why and how to model the human metabolic network for drug discovery

Metabolism represents the 'sharp end' of systems biology, because changes in metabolite concentrations are necessarily amplified relative to changes in the transcriptome, proteome and enzyme activities, which can be modulated by drugs. To understand such behaviour, we therefore need (and increasingly have) reliable consensus (community) models of the human metabolic network that include the important transporters. Small molecule 'drug' transporters are in fact metabolite transporters, because drugs bear structural similarities to metabolites known from the network reconstructions and from measurements of the metabolome. Recon2 represents the present state-of-the-art human metabolic network reconstruction; it can predict inter alia: (i) the effects of inborn errors of metabolism; (ii) which metabolites are exometabolites, and (iii) how metabolism varies between tissues and cellular compartments. However, even these qualitative network models are not yet complete. As our understanding improves so do we recognise more clearly the need for a systems (poly)pharmacology.

Identification and determination of selenoneine, 2-selenyl-N α , N α , N α -trimethyl-L-histidine, as the major organic selenium in blood cells in a fish-eating population on remote Japanese Islands

Selenoneine is the major selenium compound in fish muscles, and fish appears to be an important source of selenium in the fish-eating population. Selenoneine has strong antioxidant activity and a detoxifying function against methylmercury (MeHg) toxicity. Dietary intake, bioaccumulation, and metabolism of selenoneine have not been characterized in humans. A nutritional survey was conducted in remote islands of the Kagoshima Prefecture in Japan. To evaluate the potential risks and benefits of fish consumption for health, we measured concentrations of selenoneine, total selenium, MeHg, inorganic mercury, and polyunsaturated fatty acid (LC-PUFA) in the blood of a fish-eating human population. The erythrocyte, leukocyte, and platelet residues following removal of serum (cellular fraction) contained 0.510 μg Se/g, 0.212 μg selenoneine Se/g, and 0.262 μg Se-containing proteins Se/g, whereas the serum contained 0.174 μg total Se/g. Selenoneine was highly concentrated in the cellular fraction in a manner that was dependent on subjects' frequency of fish consumption. Concentrations of selenoneine were closely correlated with concentrations of MeHg in the cellular fraction. Selenoneine is the major chemical form of selenium in the blood cells of this fish-eating human population and may be an important biomarker for selenium redox status.