Combined Effects of Fluoride and Dietary Seleno-L-Methionine at Environmentally Relevant Concentrations on Female Zebrafish (Danio rerio) Liver: Histopathological Damages, Oxidative Stress and Inflammation

Fluoride, a global environmental pollutant, is ubiquitous in aquatic environments and coexists with selenium, which can cause complex effects on exposed organisms. However, data on the interaction of fluoride and selenium remain scarce. In this study, female zebrafish (Danio rerio) were exposed to fluoride (80 mg/L sodium fluoride) and/or dietary selenomethionine (Se-Met) for 30, 60 and 90 days, the effects on the liver of zebrafish were investigated. The results indicated that an increase in fluoride burden, inhibited growth and impaired liver morphology were recorded after fluoride exposure. Furthermore, fluoride alone caused oxidative stress and inflammation in the liver, as reflected by the increase in ROS and MDA contents, the reduction of anti-oxidative enzymes, the altered immune related enzymes (ACP, AKP, LZM and MPO) and the expression of IL-6, IL-1β, TNF-α, IL-10 and TGF-β. In contrast, co-exposure to fluoride and Se-Met decreased fluoride burden and restored growth. Furthermore, dietary Se-Met alleviated oxidative stress, inflammation and impaired morphology in liver trigger by fluoride. However, dietary Se-Met alone increased the activities of SOD and CAT. These results demonstrate that the protective effect of dietary Se-Met against chronic fluoride toxicity at a certain level.

Genome-wide identification of HMT gene family explores BpHMT2 enhancing selenium accumulation and tolerance in Broussonetia papyrifera

Broussonetia papyrifera, a valuable feed resource, is known for its fast growth, wide adaptability, high protein content and strong selenium enrichment capacity. Selenomethionine (SeMet), the main selenium form in selenium fortification B. papyrifera, is safe for animals and this enhances its nutritional value as a feed resource. However, the molecular mechanisms underlying SeMet synthesis remain unclear. This study identified three homocysteine S-methyltransferase genes from the B. papyrifera genome. The phylogenetic tree demonstrated that BpHMTs were divided into two classes, and BpHMT2 in the Class 2-D subfamily evolved earlier and possesses more fundamental functions. On the basis of the correlation between gene expression levels and selenium content, BpHMT2 was identified as a key candidate gene associated with selenium tolerance. Subcellular localization experiments confirmed the targeting of BpHMT2 in nucleus, cell membrane and chloroplasts. Moreover, three BpHMT2 overexpression Arabidopsis thaliana lines were confirmed to enhance plant selenium tolerance and SeMet accumulation. Overall, our finding provides insights into the molecular mechanisms of selenium metabolism in B. papyrifera, highlighting the potential role of BpHMT2 in SeMet synthesis. This research contributes to our understanding of selenium-enriched feed resources, with increased SeMet content contributing to the improved nutritional value of B. papyrifera as a feed resource.

Selenomethionine modulates the JAK2 / STAT3 / A20 pathway through oxidative stress to alleviate LPS-induced pyroptosis and inflammation in chicken hearts

Selenium (Se) is involved in many physiopathologic processes in humans and animals and is strongly associated with the development of heart disease. Lipopolysaccharides (LPS) are cell wall components of gram-negative bacteria that are present in large quantities during environmental pollution. To investigate the mechanism of LPS-induced cardiac injury and the efficacy of the therapeutic effect of SeMet on LPS, a chicken model supplemented with selenomethionine (SeMet) and/or LPS treatment, as well as a primary chicken embryo cardiomyocyte model with the combined effect of SeMet / JAK2 inhibitor (INCB018424) and/or LPS were established in this experiment. CCK8 kit, Trypan blue staining, DCFH-DA staining, oxidative stress kits, immunofluorescence staining, LDH kit, real-time fluorescence quantitative PCR, and western blot were used. The results proved that LPS exposure led to ROS explosion, hindered the antioxidant system, promoted the expression of the JAK2 pathway, and increased the expression of genes involved in the pyroptosis pathway, inflammatory factors, and heat shock proteins (HSPs). Upon co-treatment with SeMet and LPS, SeMet reduced LPS-induced pyroptosis and inflammation and restored the expression of HSPs by inhibiting the ROS burst and modulating the antioxidant capacity. Co-treatment with INCB018424 and LPS resulted in inhibited of the JAK2 pathway, attenuating pyroptosis, inflammation, and high expression of HSPs. Thus, LPS induced pyroptosis, inflammation, and changes in HSPs activity by activating of the JAK2 / STAT3 / A20 signaling axis in chicken hearts. Moreover, SeMet has a positive effect on LPS-induced injury. This work further provides a theoretical basis for treating cardiac injury by SeMet.

Selenomethionine Inhibits NF-κB-mediated Inflammatory Responses of Bovine Mammary Epithelial Cells Caused by Klebsiella pneumoniae by Increasing Autophagic Flux

Klebsiella pneumoniae (K. pneumoniae) is one of the major pathogens causing bovine clinical mastitis. Autophagy maintains cellular homeostasis and resists excessive inflammation in eukaryotic organisms. Selenomethionine (Se-Met) is commonly used as a source of selenium supplementation for dairy cows. This study aimed to investigate the effects of Se-Met on inflammatory responses mediated by nuclear factor-kappa B (NF-κB) through autophagy. We infected bovine mammary epithelial cell line (MAC-T) with K. pneumoniae and examined the expression of autophagy-related proteins and changes in autophagic vesicles, LC3 puncta, and autophagic flux at various intervals. The results showed that K. pneumoniae activated the early-stage autophagy of MAC-T cells. The levels of LC3-II, Beclin1, and ATG5, as well as the number of LC3 puncta and autophagic vesicles, increased after 2 h post-treatment. However, the late-stage autophagic flux was blocked. Furthermore, the effect of autophagy on NF-κB-mediated inflammation was investigated with different autophagy levels. The findings showed that enhanced autophagy inhibited the K. pneumoniae-induced inflammatory responses of MAC-T cells. The opposite results were found with the inhibition of autophagy. Finally, we examined the effect of Se-Met on NF-κB-mediated inflammation based on autophagy. The results indicated that Se-Met alleviated K. pneumoniae-induced autophagic flux blockage, inhibited NF-κB-mediated inflammation, and decreased the adhesion of K. pneumoniae to MAC-T cells. The inhibitory effect of Se-Met on NF-κB-mediated inflammation could be partially blocked by the autophagy inhibitor chloroquine (CQ). Overall, Se-Met attenuated K. pneumoniae-induced NF-κB-mediated inflammatory responses by enhancing autophagic flux.

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.

Selenomethionine protects the liver from dietary deoxynivalenol exposure via Nrf2/PPARγ-GPX4-ferroptosis pathway in mice

Deoxynivalenol (DON) is a significant Fusarium toxin that has gained global attention due to its high frequency of contamination in food and feed. It was reported to have hepatotoxicity, immunotoxicity, and reproduction toxicity in organs. On the other hand, Selenomethionine (SeMet) was proven to have anti-oxidation, tissue repairing, immunity improvement, and antifungal mycotoxin infection functions. However, the molecular mechanism by which SeMet alleviates DON damage is not yet clear. C57BL/6 mice were randomly divided into three groups, Se-A and Se-A+DON were fed with a diet containing 0.2 mg/kg Se whereas Se-S+DON were fed with a diet of 1.0 mg/kg Se. After feeding for four weeks, the mice were gavaged for 21 days with DON (2.0 mg/kg BW) or ultrapure water once per day. In the present study, we showed that SeMet significantly decreased the lipid peroxidation product malondialdehyde, and increased activities of antioxidant enzymes superoxide dismutase and total antioxidant capacity after DON exposure. In addition, our investigation revealed that SeMet regulated pathways related to lipid synthesis and metabolisms, and effectively mitigated DON-induced liver damage. Moreover, we have discovered that SeMet downregulation of N-acylethanolamine and HexCer accumulation induced hepatic lipotoxicity. Further study showed that SeMet supplementation increased protein levels of glutathione peroxidase 4 (GPX4), peroxisome proliferator-activated receptor γ (PPARγ), nuclear erythroid 2-related factor 2 (Nrf2), and upregulated target proteins, indicating suppression of oxidative stress in the liver. Meanwhile, we found that SeMet significantly reduced the DON-induced protein abundances of Bcl2, Beclin1, LC3B and proteins related to ferroptosis (Lpcat3, and Slc3a2), and downregulation of Slc7a11. In conclusion, SeMet protected the liver from damage by enhancing the Nrf2/PPARγ-GPX4-ferroptosis pathway, inhibiting lipid accumulation and hepatic lipotoxicity. The findings of this study indicated that SeMet has a positive impact on liver health by improving antioxidant capacity and relieving lipotoxicity in toxin pollution.

Comparison of different organic selenium supplementations on selenium status and serum biomarkers in dairy cows

The objective of this study was to investigate the effects of two different organic selenium (Se) supplements, selenomethionine (Se-Met) and selenohomolanthionine (Se-Hlan), on the serum biochemical parameters and Se status of dairy cows. Different dietary Se supplementation treatments were set as follows: a control group (CON, adding sodium selenite at 0.3 mg Se/kg dry matter [DM]), 0.3 and 0.5 Se-Met (adding Se-Met at 0.3 and 0.5 mg Se/kg DM, respectively), as well as 0.3 and 0.5 Se-Hlan (adding Se-Hlan at 0.3 and 0.5 mg Se/kg DM, respectively). The experiment lasted 8 weeks. The serum measurements showed that both organic Se treatments resulted in higher uric acid than CON. Se-Met produced higher aspartate aminotransferase, glucose, urea, low-density lipoprotein cholesterol, and lactate dehydrogenase than Se-Hlan. Regarding the Se status, the highest milk Se values appeared in 0.5 Se-Met, with intermediate values in 0.3 Se-Met and 0.5 Se-Hlan, whereas the highest and lowest serum Se levels were presented in 0.5 Se-Met and 0.3 Se-Hlan, respectively. Our results suggest that Se-Hlan was not as efficient in boosting serum or milk Se as Se-Met and differences in serum biomarkers between Se-Met and Se-Hlan may be associated with distinct metabolic pathways for different forms of organic Se.

SeMet alleviates LPS-induced eggshell gland necroptosis mediated inflammation by regulating the Keap1/Nrf2/HO-1 pathway

Exposure to lipopolysaccharide (LPS) can lead to inflammation in a variety of tissues and organs. Selenium (Se) plays a crucial role in mitigating inflammatory damage. Compared with inorganic selenium, organic selenium, such as selenomethionine (SeMet), has the advantages of a higher absorption rate and lower toxicity in animals. This study examined the protective effects of SeMet on eggshell gland tissue damage caused by LPS. Hy-Line Brown laying hens were chosen as the experimental animals and were randomly assigned to four groups: control group (C), lipopolysaccharide group (LPS), SeMet group (Se), and SeMet + lipopolysaccharide group (Se + LPS). H&E staining and transmission electron microscope were performed to observe the pathological changes of eggshell glands, oxidative stress related indicators were measured using relevant kits, qRT‒PCR and western blotting were used to evaluate the mRNA and protein levels of the Nrf2 pathway, necroptosis, and inflammation related indicators. The results showed that LPS treatment increased the content of malondialdehyde (MDA), decreased the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX), and decreased the content of glutathione (GSH). LPS increased the levels of Keap1, RIPK1, RIPK3, MLKL, TNF-α, COX-2, and NF-κB, while decreasing the levels of HO-1, NQO1, Nrf2, and Caspase-8. However, SeMet treatment effectively reversed the changes of the above indicators, indicating that SeMet alleviates eggshell gland cell necroptosis-mediated inflammation induced by LPS via regulating the Keap1/Nrf2/HO-1 pathway. This study elucidated the mechanism by which SeMet alleviates LPS-induced eggshell gland tissue damage in Hy-Line Brown laying hens and provided a new direction for expanding the application of SeMet in the feeding and production of laying hens.

Selenomethionine supplementation and expression of selenosugars, selenocysteine, and other selenometabolites in rat liver

Selenomethionine (SeMet) as a methionine analog can be incorporated into protein. In turkeys, we recently found that selenium (Se) as selenite is not metabolized to SeMet but rather to selenosugars (seleno-N-acetyl galactosamine) bound to protein as well as to selenocysteine (Sec) in selenoproteins. To characterize the metabolism of SeMet, we fed rats graded levels of SeMet from 0 to 5 µg Se/g in a Se-deficient diet for 4 wk, and investigated the fate and accumulation of liver Se using high pressure liquid chromatography (HPLC) coupled with Se-specific inductively coupled plasma mass spectrometry (ICP-MS) and molecule specific (Orbitrap MS/MS) detection. Up to 0.24 µg Se/g (Se requirement for maximal glutathione peroxidase activity), Sec accounted for ∼40% of total liver Se whereas SeMet only accounted for 3-11%. Analysis of water-soluble extracts found negligible low molecular weight (LMW) Se species in rats fed 0 and 0.08 µg Se/g, including no SeMet. At 0.24 µg Se/g and above, SeMet accounted for only 10% of LMW Se species, whereas methyl- and glutathionyl-selenosugars accounted for 70% of LMW Se species. Above the Se requirement, SeMet was ∼30% of the proteinaceous amino acids, whereas Sec levels fell to 5% in rats fed 5 µg Se/g as SeMet. Last, considerably less inorganic Se was bound to liver protein with high SeMet as compared to selenite in a parallel study. SeMet is efficiently metabolized and mixes with the common Se metabolite pool, where Se is preferentially incorporated into Sec and Sec-selenoproteins until selenoproteins plateau; with high SeMet intake, Se is increasingly accumulated as LMW selenosugars and as selenosugar-decorated proteins.

Effects of feeding diets with zinc-l-selenomethionine on growth performance of broilers subjected to cyclic heat stress

Limited information exists on the use of zinc-l-selenomethionine (Zn-L-SeMet) in broiler diets and its effects on the growth performance, body temperature, mortality rates, blood profile, and gene expression, especially when animals are reared under cyclic heat stress conditions. This study aimed to investigate the impact of Zn-L-SeMet in broiler diets from 1 to 42 days of age reared under cyclic heat stress and its effects on growth performance, cloacal temperatures, mortality rate, blood parameters, and insulin-like growth factor 1 (IGF-1) and growth hormone receptor (GHR) gene expression in the breast muscle. A total of 1000 male Cobb 500® broiler chicks were randomly assigned to five treatments: 0, 0.15, 0.23, 0.47, and 1.30 mg/kg of Zn-L-SeMet. Each treatment consisted of 10 replicates with 20 birds each. No statistically significant differences in growth performance were observed from 1 to 21 days of age (P > 0.05). However, from 1 to 42 days, feed intake (FI) and feed conversion ratio (FCR) decreased linearly (P < 0.05). Cloacal temperatures showed no significant effects (P > 0.05), while overall mortality rate exhibited a quadratic response (P < 0.05), with the optimal inclusion level predicted to reduce broiler mortality at 0.71 mg/kg. Triglyceride (TRG) levels increased with 0.97 mg/kg (P < 0.05), and gama-glutamil transferase (GGT) levels decreased with the inclusion of 1.19 mg/kg (P < 0.05). No significant effects on IGF-1 and GHR gene expression were found (P > 0.05). In conclusion, the inclusion of 1.30 mg/kg of Zn-L-SeMet in diets of heat-stressed broilers improved growth performance from 1 to 42 days of age. An inclusion of 0.71 mg/kg reduced mortality rate, while 0.97 mg and 1.19 mg increased and reduced TRG and GGT levels, respectively.

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.

Selenomethionine against titanium particle-induced osteolysis by regulating the ROS-dependent NLRP3 inflammasome activation via the β-catenin signaling pathway

Wear debris-induced osteolysis, especially titanium (Ti) particles-induced osteolysis, is the most common cause of arthroplasty failure with no effective therapy. Previous studies have suggested that inflammation and impaired osteogenesis are associated with Ti particles -induced osteolysis. Selenium (Se) is an essential trace element in the human body, which forms selenomethionine (Se-Met) in nature, and selenoproteins has strong anti-inflammatory and antioxidant stress effects. In this study, the effects of Se-Met on Ti particles-induced osteolysis were observed and the potential mechanism was explored. We found that exogenous Se-Met relieved osteolysis induced by Ti particles in two animal models and MC3T3-E1 cells. We found that the addition of Se-Met effectively inhibited Ti particle-induced inflammation by regulating reactive oxygen species-dependent (ROS-dependent) NOD-like receptor protein 3 (NLRP3) inflammasome activation. These therapeutic effects were abrogated in MC3T3-E1 cells that had received a β-catenin antagonist, suggesting that Se-Met alleviates inflammatory osteolysis via the β-catenin signaling pathway. Collectively, these findings indicated that Se-Met may serve as a potential therapeutic agent for treating Ti particle-induced osteolysis.

Adaptive Laboratory Evolution Reveals the Selenium Efflux Process To Improve Selenium Tolerance Mediated by the Membrane Sulfite Pump in Saccharomyces cerevisiae

Selenium (Se) is a micronutrient in most eukaryotes, and Se-enriched yeast is the most common selenium supplement. However, selenium metabolism and transport in yeast have remained unclear, greatly hindering the application of this element. To explore the latent selenium transport and metabolism mechanisms, we performed adaptive laboratory evolution under the selective pressure of sodium selenite and successfully obtained selenium-tolerant yeast strains. Mutations in the sulfite transporter gene ssu1 and its transcription factor gene fzf1 were found to be responsible for the tolerance generated in the evolved strains, and the selenium efflux process mediated by ssu1 was identified in this study. Moreover, we found that selenite is a competitive substrate for sulfite during the efflux process mediated by ssu1, and the expression of ssu1 is induced by selenite rather than sulfite. Based on the deletion of ssu1, we increased the intracellular selenomethionine content in Se-enriched yeast. This work confirms the existence of the selenium efflux process, and our findings may benefit the optimization of Se-enriched yeast production in the future. IMPORTANCE Selenium is an essential micronutrient for mammals, and its deficiency severely threatens human health. Yeast is the model organism for studying the biological role of selenium, and Se-enriched yeast is the most popular selenium supplement to solve Se deficiency. The cognition of selenium accumulation in yeast always focuses on the reduction process. Little is known about selenium transport, especially selenium efflux, which may play a crucial part in selenium metabolism. The significance of our research is in determining the selenium efflux process in Saccharomyces cerevisiae, which will greatly enhance our knowledge of selenium tolerance and transport, facilitating the production of Se-enriched yeast. Moreover, our research further advances the understanding of the relationship between selenium and sulfur in transport.

Selenium Alleviates Ammonia-Induced Splenic Cell Apoptosis and Inflammation by Regulating the Interleukin Family/Death Receptor Axis and Nrf2 Signaling Pathway

Ammonia (NH₃) is a harmful gas in livestock houses. So far, many researchers have demonstrated that NH₃ is detrimental to animal and human organs. Selenium (Se) is one of the essential trace elements in the body and has a good antioxidant effect. However, there was little conclusive evidence that Se alleviated NH₃ poisoning. To investigate the toxic mechanism of NH₃ on pig spleen and the antagonistic effect of L-selenomethionine, a porcine NH₃-poisoning model and an L-selenomethionine intervention model were established in this study. Our results showed that NH₃ exposure increased the apoptosis rate, while L-selenomethionine supplementation alleviated the process of excessive apoptosis. Immunofluorescence staining, real-time quantitative polymerase chain reaction (qRT-PCR), and western blot results confirmed that exposure to NH₃ changed the expression levels of interleukin family factors, apoptosis, death receptor, and oxidative stress factors. Our study further confirmed that excessive NH₃ induced inflammatory response and mediated necroptosis leading to cell apoptosis by activating the Nrf2 signaling pathway. Excessive NH₃ could mediate spleen injury through oxidative stress-induced mitochondrial dynamics disorder. L-Selenomethionine could alleviate inflammation and abnormal apoptosis by inhibiting the IL-17/TNF-α/FADD axis. Our study would pave the way for comparative medicine and environmental toxicology.

Photocatalytic treatment of organoselenium in synthetic mine-impacted effluents

Biological selenium reduction processes are commonly employed as the best available technology (BAT) for selenium removal; however, as a by-product they produce trace amounts of organoselenium compounds with orders of magnitude greater bioaccumulation potential and toxicity. Here, we assessed buoyant photocatalysts (BPCs) as a potential passive advanced oxidation process (P-AOP) for organoselenium treatment. Using a synthetic mine-impacted water solution, spiked with selenomethionine (96 μg/L) as a representative organoselenium compound, photocatalysis with BPCs fully eliminated selenomethionine to <0.01 μg/L with conversion to selenite and selenate. A theoretical reaction pathway was inferred, and a kinetics model developed to describe the treatment trends and intermediates. Given the known toxic responses of Lepomis macrochirus and Daphnia magna to organoselenium, it was estimated that photocatalysis could effectively eliminate organoselenium acute toxicity within a UV dose of 8 kJ/L (1-2 days solar equivalent exposure), by transformation of selenomethionine to less hazardous oxidized Se species. Solar photocatalysis may therefore be a promising passive treatment technology for selenium-impacted mine water management.

Protective effect of selenomethionine on kidney injury induced by ochratoxin A in rabbits

The purpose of this study was to investigate the protective effect and mechanism of selenomethionine (SeMet) on ochratoxin A (OTA)-induced nephrotoxicity in rabbits. In total, sixty Ira rabbits were randomly divided into 5 groups (the control group, OTA group, 0. 2 mg/kg SeMet + OTA group, 0. 4 mg/kg SeMet + OTA group, and 0. 6 mg/kg SeMet + OTA group). The rabbits were fed diets supplemented with different doses of SeMet for 21 days and given 0. 2 mg/kg OTA starting on day 15 for a week. The results showed that the SeMet supplementation could improve the changes in blood physiological indices and renal function decline caused by OTA poisoning, and alleviate pathological kidney injury in the rabbits. SeMet also increased the activities of total antioxidant capacity, superoxide dismutase, and glutathione peroxidase, and decreased the contents of malondialdehyde and reactive oxygen species and the expression of interleukin-1β, interleukin-6, and tumor necrosis factor-α in the damaged kidneys of the rabbits. In addition, the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream gene heme oxygenase 1 (HO-1) was also inhibited after OTA poisoning, while SeMet activated the Nrf2 signaling pathway and enhanced the expression of Nrf2 and the downstream gene HO-1. In conclusion, SeMet protected against kidney injury caused by OTA in rabbits, and the mechanism may be the activation of the Nrf2 signaling pathway.

Influence of exogenous selenomethionine and selenocystine on uptake and accumulation of Se in winter wheat (Triticum aestivum L. cv. Xinong 979)

Soil selenium (Se) is mainly inorganic including selenate and selenite but organic forms such as selenomethionine (SeMet) and selenocystine (SeCys₂) are commonly present. Although organic Se is bioavailable or potentially bioavailable to plants, whether the effects of the organic Se on uptake and accumulation of Se in winter wheat differ in forms is still not clear. Both hydroponic experiments and a pot trial of whole plant growth stage were conducted to investigate the effects of SeMet and L-selenocystine (SeCys₂) on uptake and accumulation of Se in winter wheat (Triticum aestivum L. cv. Xinong 979). Not only metabolic inhibitor (carbonyl cyanide m-chlorophenylhydrazone (CCCP)) inhibited SeMet (44%) influx into wheat roots but also aquaporin inhibitor (AgNO₃) or putative inhibitor (H₂SiO₄ and H₃BO₃) suppressed 83%, 62%, or 64% SeMet influx into the roots. However, these inhibitors had insignificant effects on SeCys₂ influx into the roots. Wheat grain possessed more effective Se accumulation under SeCys₂ treatments than under SeMet treatments, which was contributed to more efficiently translocation of Se from husk to grain, more remobilization of tissue Se to grain, and significantly higher concentration of soluble Se (SOL-Se) and exchangeable and carbonate-bound Se (EXC-Se) in the rhizosphere of winter wheat. The present study indicated that the effects of organic Se on uptake and accumulation of Se in winter wheat differed in forms and that SeCys₂ exhibited the potential to increase grain Se concentration in winter wheat. The results from the present study will replenish information about the effects and related mechanisms of SeMet or SeCys₂ on uptake and accumulation of Se in winter wheat and provide insights of effects of organic Se on wheat grain Se accumulation.

Direct and indirect selenium speciation in biofortified wheat: A tale of two techniques

Wheat can be biofortified with different inorganic selenium (Se) forms, selenite or selenate. The choice of Se source influences the physiological response of the plant and the Se metabolites produced. We looked at selenium uptake, distribution and metabolization in wheat exposed to selenite, selenate and a 1:1 molar mixture of both to determine the impact of each treatment on the Se speciation in roots, shoots, and grains. To achieve a comprehensive quantification of the Se species, the complementarity of high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry and X-ray absorption spectroscopy was exploited. This approach allowed the identification of the six main selenium species: selenomethionine, selenocysteine, selenocystine, selenite, selenate, and elemental selenium. The three treatments resulted in similar total selenium concentration in grains, 90-150 mg Se kg^-1 , but produced different effects in the plant. Selenite enhanced root accumulation (66% of selenium) and induced the maximum toxicity, whereas selenate favored shoot translocation (46%). With the 1:1 mixture, selenium was distributed along the plant generating lower toxicity. Although all conditions resulted in >92% of organic selenium in the grain, selenate produced mainly C-Se-C forms, such as selenomethionine, while selenite (alone or in the mixture) enhanced the production of C-Se-Se-C forms, such as selenocystine, modifying the selenoamino acid composition. These results provide a better understanding of the metabolization of selenium species which is key to minimize plant toxicity and any concomitant effect that may arise due to Se-biofortification.

Selenomethionine incorporation in proteins of individual mammalian cells determined with a genetically encoded fluorescent sensor

Selenomethionine (SeMet) randomly replaces methionine (Met) in protein translation. Because of strongly differing redox properties of SeMet and Met, SeMet mis-incorporation may have detrimental effects on protein function, possibly compromising the use of nutritional SeMet supplementation as an anti-oxidant. Studying the functional impact of SeMet in proteins on a cellular level is hampered by the lack of accurate and efficient methods for estimating the SeMet incorporation level in individual viable cells. Here we introduce and apply a method to measure the extent of SeMet incorporation in cellular proteins by utilizing a genetically encoded fluorescent methionine oxidation probe. Supplementation of SeMet in mammalian culture medium resulted in >84% incorporation of SeMet, and SeMet labeling as low as 5% was readily measured. Kinetics and extent of SeMet incorporation on the single-cell level under live-cell imaging conditions provided direct access to protein turn-over kinetics and SeMet redox properties in a cellular context. The method is furthermore suited for experiments utilizing high-throughput fluorescence microplate readers or fluorescence-activated cell sorting (FACS) analysis.

Evaluation of L-Selenomethionine on Ameliorating Cardiac Injury Induced by Environmental Ammonia

L-Selenomethionine is one of the important organic selenium sources. The supplementation of L-selenomethionine in diets is significant to improve the health of pigs. Ammonia is a major pollutant in the atmosphere and piggery, posing a threat to human and animal health. Although ammonia exposure can damage the heart, the mechanism of cardiac toxicity by ammonia is still unknown. In this study, we investigated the mechanism of cardiac injury induced by ammonia exposure in pigs and the protective effect of L-selenomethionine on its cardiotoxicity. The results showed that the blood ammonia content of pig increased significantly in ammonia group, the expressions of energy metabolism-related genes (LDHA, PDK4, HK2, and CPTIB) and the oxidative stress indexes were significantly changed (P < 0.05), the AMPK/PPAR-γ/NF-κB signaling pathways were activated, the chromatin edge aggregation and nuclear pyknosis were observed in ultrastructure, the apoptotic cells were significantly increased (P < 0.05), and the mRNA and protein expressions of apoptosis-related genes (Bcl-2, Bax, Cyt-c, caspase-3, and caspase-9) were significantly affected (P < 0.05). The above changes were significantly alleviated in ammonia + L-selenomethionine group, but there were still significant differences compared with the C group (P < 0.05). Our results indicated that ammonia exposure could cause energy metabolism disorder and oxidative stress and induce apoptosis of cardiomyocytes through AMPK/PPAR-γ/NF-κB pathways, which could lead to cardiac injury and affect cardiac function. L-Selenomethionine could effectively alleviate the cardiac damage caused by ammonia and antagonize the cardiotoxicity of ammonia.

Interactive effects of fluoride and seleno-l-methionine at environmental related concentrations on zebrafish (Danio rerio) liver via the gut-liver axis

Fluoride (F) is a ubiquitous aquatic environmental pollutant and co-exists with other pollutants to form combined pollution. Selenium (Se) is beneficial at low levels yet toxic at high levels and can interact with some metals. However, the interactive effects of F and Se on the liver in fish remains enigmatic. In this study, zebrafish (Danio rerio) were exposed to F (80 mg/L) and dietary seleno-l-methionine (Se-Met, 0.25, 0.5 and 1.0 μg/g dry weight) alone or in combination for 90 d. The results indicated that co-treatment to F and Se-Met attenuated the histopathological damage, oxidative stress, and inflammatory in the liver, compared with the F treatment alone. Meanwhile, dietary Se-Met treatment improved F-induced intestinal barrier dysfunction, increased the transcripts of tight junction proteins (ZO-1, Claudin-1 and Occludin), and restored the homeostasis of intestinal microbiota. Moreover, dietary Se-Met ameliorated F-induced intestinal and liver inflammation by inhibiting lipopolysaccharide (LPS) levels and transcripts of TLR4 and p65 in the intestine and liver. This study manifested that Se-Met alleviates F-induced liver and intestinal injury when both co-occur at specific concentrations, and that the gut-liver axis pathway may serve as a mechanistic base for these alleviative effects.

Identification of γ-Glutamyl-Selenomethionine as the Principal Selenium Metabolite in a Selenium-Enriched Probiotic, Bifidobacterium longum, by Two-Dimensional HPLC-ICP MS and HPLC-ESI Orbitrap MS

Selenium (Se)-enriched probiotics are potential sources of organic Se in the human diet, but their application in food is debated because most selenized probiotics and their metabolites are not well-characterized. We analyzed a Se-enriched probiotic, Bifidobacterium longum DD98, to unveil its Se metabolite profiles by two-dimensional high-performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP MS) and HPLC-electrospray ionization Orbitrap MS. A major Se metabolite was identified as gamma-glutamyl-selenomethionine (γ-Glu-SeMet), which accounted for 42.5 ± 3.4% of water-soluble Se. Most of the remaining Se was present as SeMet (35.2 ± 0.6%) in a free or protein-bound form. In addition, 11 minor Se metabolites were identified, eight of which had not been reported before in probiotics. Six of the identified compounds contained γ-Glu-SeMet as the core structure, constituting a γ-Glu-SeMet family. This study demonstrates the presence of γ-Glu-SeMet in a probiotic, showing a different selenite metabolite pathway from that of Se-enriched yeast, and it offers an alternative and potentially attractive source of organic Se for food and feed supplementation.

77Se-13C based dipolar correlation experiments to map selenium sites in microcrystalline proteins

Sulfur-containing sites in proteins are of great importance for both protein structure and function, including enzymatic catalysis, signaling pathways, and recognition of ligands and protein partners. Selenium-77 is an NMR active spin-1/2 nucleus that shares many physiochemical properties with sulfur and can be readily introduced into proteins at sulfur sites without significant perturbations to the protein structure. The sulfur-containing amino acid methionine is commonly found at protein-protein or protein-ligand binding sites. Its selenium-containing counterpart, selenomethionine, has a broad chemical shift dispersion useful for NMR-based studies of complex systems. Methods such as (¹H)-⁷⁷Se-¹³C double cross polarization or {⁷⁷Se}-¹³C REDOR could be valuable to map the local environment around selenium sites in proteins but have not been demonstrated to date. In this work, we explore these dipolar transfer mechanisms for structural characterization of the GB1 V39SeM variant of the model protein GB1 and demonstrate that ⁷⁷Se-¹³C based correlations can be used to map the local environment around selenium sites in proteins. We have found that the general detection limit is ~ 5 Å, but longer range distances up to ~ 7 Å can be observed as well. This study establishes a framework for the future characterization of selenium sites at protein-protein or protein-ligand binding interfaces.

Protective Effect of Selenomethionine on T-2 Toxin-Induced Rabbit Immunotoxicity

T-2 toxin is a trichothecene mycotoxin produced by fusarium species, which is mainly prevalent in grain and livestock feed. One of the main effects of this toxin is immunodepression. Previous studies have shown that T-2 toxin can cause damage to immune organs and impaired immune function in animals. However, selenomethionine (SeMet) as an organic selenium source can not only promote the growth and development of the body but also effectively improve the body's immune function. In this study, rabbits were exposed to 0.4-mg/kg T-2 toxin, and abnormal blood routine indicators were found in the rabbits. HE staining also showed obvious lesions in the spleen and thymus tissue structures, accompanied by a large number of bleeding points. In addition, rabbits showed strong oxidative stress and inflammatory response after T-2 toxin action. 0.2 mg/kg, 0.4 mg/kg, and 0.6 mg/kg organic selenium were added to the feed. However, it was found that 0.2 mg/kg selenium can effectively improve the abnormal changes of blood routine and spleen and thymus tissue of rabbits. On the other hand, it can significantly increase the expression of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and total antioxidant capacity (T-AOC) in the spleen and thymus, and downregulate the expression of reactive oxygen species (ROS) and malondialdehyde (MDA). In addition, inflammatory factors interleukin-1 beta (IL-1β) and interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) in blood were also significantly inhibited; the expression of proliferating cell nuclear antigen (PCNA) in the spleen and thymus was also significantly increased after low-dose selenium treatment. Surprisingly, 0.4 mg/kg and 0.6 mg/kg of selenium did not effectively alleviate the immunotoxic effects caused by T-2 toxin, and cause damage to a certain extent. In summary, our results show that 0.2 mg/kg of SeMet can effectively alleviate the immunotoxicity caused by T-2 toxin. Selenium may protect rabbits from T-2 toxin by improving its antioxidant and anti-inflammatory capabilities.

Protective Effect of Organic Selenium on Oxidative Damage and Inflammatory Reaction of Rabbit Kidney Induced by T-2 Toxin

T-2 toxin is a member of a class of mycotoxins produced by a variety of Fusarium species under appropriate temperature and humidity conditions and is a common contaminant in food and feedstuffs of cereal origin. Selenium is an indispensable element in animals, regulates a variety of biological functions of the body, and can antagonize metal and mycotoxin poisoning to a certain extent. However, the effect of selenium on kidney injury induced by T-2 toxin has not been reported. In this study, 50 New Zealand rabbits were divided into 5 groups (the control group, T-2 toxin group, low-dose Se + T-2 toxin group, medium-dose Se + T-2 toxin group, and high-dose Se + T-2 toxin group). Rabbits were examined after oral administration of different doses of selenomethionine (SeMet) for 21 days and after perfusion with 0.4 mg/kg T-2 toxin (or the same dose of olive oil in the control group) for 5 days. We found that T-2 toxin induced kidney function damage and increased the levels of ROS and the contents of inflammatory factors. Renal structure was pathologically damaged. However, we found that after pretreatment with 0.2 mg/kg SeMet, oxidative stress, the inflammatory response, and pathological damage induced by T-2 toxin were attenuated. The results indicate that a low dose (0.2 mg/kg) of SeMet effectively reversed T-2 toxin-induced kidney injury in rabbits.

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.

Chronic exposure to dietary selenomethionine dysregulates the genes involved in serotonergic neurotransmission and alters social and antipredator behaviours in zebrafish (Danio rerio)

Selenium (Se) is a metalloid of potential interest from both a toxicological and nutritional perspective, having a range of safe intake. The adverse neuro-behavioural effects of Se have been investigated in both humans and fishes, but little is known about its effects on social behaviours or the serotonergic signaling pathway in the brain. In the present study, we investigated the effects of chorionic dietary exposure to Se (as selenomethionine) at different concentrations (control, 2.1, 11.6 or 31.5 μg/g dry wt.) on antipredator avoidance, shoaling behaviour, and social group preferences in adult zebrafish (Danio rerio). In addition, we also measured the expression of important genes in the serotonergic pathway that influence social behaviours. After 60 days of exposure, the highest dose (31.5 μg/g dry wt.) caused the highest level of baseline fear behaviour, with fish swimming lower in the water column and in tighter shoals compared to fish in the other treatments. With high levels of baseline fear, these fish did not significantly intensify fear behaviours in response to predation risk in the form of exposure to chemical alarm cues. When individual fish were given an opportunity to shoal with groups of differing sizes (3 vs. 4 individuals), fish exposed to the high dose spent less time with groups in general, and only control fish showed a significant preference for the larger group. In the zebrafish brain, we found significant upregulation in the mRNA expression of serotonin receptors (htr1aa and htr1b), a transporter (slc6a4a), and tryptophan hydroxylase-2 (tph2), whereas there was a downregulation of the monoamine oxidase (mao) gene. The results of this study suggest that disruption of serotonergic neurotransmission might have been responsible for Se-induced impairment of antipredator and social behaviour in zebrafish.

A practical method for efficient and optimal production of Seleno-methionine-labeled recombinant protein complexes in the insect cells

The use of Seleno-methionine (SeMet) incorporated protein crystals for single or multi-wavelength anomalous diffraction (SAD or MAD) to facilitate phasing has become almost synonymous with modern X-ray crystallography. The anomalous signals from SeMets can be used for phasing as well as sequence markers for subsequent model building. The production of large quantities of SeMet incorporated recombinant proteins is relatively straightforward when expressed in Escherichia coli. In contrast, production of SeMet substituted recombinant proteins expressed in the insect cells is not as robust due to the toxicity of SeMet in eukaryotic systems. Previous protocols for SeMet-incorporation in the insect cells are laborious, and more suited for secreted proteins. In addition, these protocols have generally not addressed the SeMet toxicity issue, and typically result in low recovery of the labeled proteins. Here we report that SeMet toxicity can be circumvented by fully infecting insect cells with baculovirus. Quantitatively controlling infection levels using our Titer Estimation of Quality Control (TEQC) method allow for the incorporation of substantial amounts of SeMet, resulting in an efficient and optimal production of labeled recombinant protein complexes. With the method described here, we were able to consistently reach incorporation levels of about 75% and protein yield of 60-90% compared with native protein expression.

Selenium Biofortification and Antioxidant Activity in Cordyceps militaris Supplied with Selenate, Selenite, or Selenomethionine

Selenium (Se) is an essential trace element with multiple functions that may help mitigate adverse health conditions. Cordyceps militaris is an edible mushroom with medicinal properties. The experiment was conducted under artificial cultivation, with five Se concentrations (0, 5, 10, 20, and 40 μg g^-1) and three forms of Se (selenate, selenite, and selenomethionine). C. militaris can absorb inorganic from the substrate and convert it to organic Se compounds (selenocystine, selenomethionine, and an unknown species) in fruiting bodies. Compared with the control treatment, Se applications (40 μg g^-1 selenate and selenite) significantly increased the Se concentration in fruiting bodies by 130.9 and 128.1 μg g^-1, respectively. The biofortification with selenate and selenite did not affect fruiting body production, in some case, but did enhance the biological efficiency. Moreover, the abundance of cordycepin and adenosine increased, while the amino acid contents remained relatively stable. Meanwhile, Se-biofortified C. militaris showed effective antioxidant activities. These results suggest that Se-biofortified C. militaris fruiting bodies may enhance human and animal health when it was included as part of a healthy diet or used as Se supplements.

Effects of dietary sodium selenite and organic selenium sources on immune and inflammatory responses and selenium deposition in growing pigs

The study was conducted to compare effects of different dietary Se sources (sodium selenite [NaSe], Se-enriched yeast [Se yeast] or L-selenomethionine [SeMet]) and one Se-deficient control diet on the expression of selected genes, hematological and clinical biochemical parameters, and muscle morphology in two parallel trials with finisher pigs. Se concentrations in blood plasma and tissues were also monitored. From the pigs in one of the parallel groups, muscle samples obtained from Musculus longissimus dorsi (LD) before and during the trial were examined. The pigs in the other parallel group were challenged once with lipopolysaccharide (LPS) intravenously. Transcriptional analyses of LD showed that selenogenes SelenoW and H were higher expressed in pigs fed Se-supplemented diets compared with control. Furthermore, the expression of interferon gamma and cyclooxygenase 2 was lower in the Se-supplemented pigs versus control. In whole blood samples prior to LPS, SelenoN, SelenoS and thioredoxin reductase 1 were higher expressed in pigs fed NaSe supplemented feed compared with the other groups, possibly indicating a higher level of oxidative stress. After LPS exposure glutathione peroxidase 1 and SelenoN were more reduced in pigs fed NaSe compared with pigs fed organic Se. Products of most above-mentioned genes are intertwined with the oxidant-antioxidant system. No significant effects of Se-source were found on hematologic parameters or microscopic anatomy. The Se-concentrations in various skeletal muscles and heart muscle were significantly different between the groups, with highest concentrations in pigs fed SeMet, followed by those fed Se yeast, NaSe, and control diet. Consistent with previous reports our results indicate that dietary Se at adequate levels can support the body's antioxidant system. Our results indicate that muscle fibers of pigs fed organic Se are less vulnerable to oxidative stress compared with the other groups.

Crystallization and X-ray diffraction analysis of native and selenomethionine-substituted PhyH-DI from Bacillus sp. HJB17

Phytases are phosphatases that hydrolyze phytates to less phosphorylated myo-inositol derivatives and inorganic phosphate. β-Propeller phytases, which are very diverse phytases with improved thermostability that are active at neutral and alkaline pH and have absolute substrate specificity, are ideal substitutes for other commercial phytases. PhyH-DI, a β-propeller phytase from Bacillus sp. HJB17, was found to act synergistically with other single-domain phytases and can increase their efficiency in the hydrolysis of phytate. Crystals of native and selenomethionine-substituted PhyH-DI were obtained using the vapour-diffusion method in a condition consisting of 0.2 M sodium chloride, 0.1 M Tris pH 8.5, 25%(w/v) PEG 3350 at 289 K. X-ray diffraction data were collected to 3.00 and 2.70 Å resolution, respectively, at 100 K. Native PhyH-DI crystals belonged to space group C121, with unit-cell parameters a = 156.84, b = 45.54, c = 97.64 Å, α = 90.00, β = 125.86, γ = 90.00°. The asymmetric unit contained two molecules of PhyH-DI, with a corresponding Matthews coefficient of 2.17 Å3 Da-1 and a solvent content of 43.26%. Crystals of selenomethionine-substituted PhyH-DI belonged to space group C2221, with unit-cell parameters a = 94.71, b = 97.03, c = 69.16 Å, α = β = γ = 90.00°. The asymmetric unit contained one molecule of the protein, with a corresponding Matthews coefficient of 2.44 Å3 Da-1 and a solvent content of 49.64%. Initial phases for PhyH-DI were obtained from SeMet SAD data sets. These data will be useful for further studies of the structure-function relationship of PhyH-DI.

Selenomethionine as a Safer Substitute for Barium Selenate in Long-Acting Injectable Se Supplements for Food-Producing Animals

Nutritional supplementation with selenium (Se) can prevent Se deficiency in food-producing animals. Injection with slow-release formulations is a preferred method for free-range grazing sheep and cattle, and barium selenate (BaSeO₄) provides optimal efficacy. This chemical can become a health risk to humans if the concentrated depot of an injection site is consumed, and consequently such use is recently banned in the EU. A possible replacement is selenomethionine (SeMet), a naturally occurring form of Se supplementation hitherto only administered orally. In four animal studies we found that injection with SeMet maintained nutritionally adequate concentrations of Se in blood and tissues of lambs for at least 191 days and in blood and milk of dairy cows for at least 95 days. Stereoisomer forms L- and DL-SeMet were functionally equivalent. This is the first demonstration that injectable SeMet can deliver efficacy similar to BaSeO₄ but with less risk of undesirable residues in edible tissues.

Selenium accumulation and metabolism in algae

Selenium (Se) is an intriguing element because it is metabolically required by a variety of organisms, but it may induce toxicity at high doses. Algae primarily absorb selenium in the form of selenate or selenite using mechanisms similar to those reported in plants. However, while Se is needed by several species of microalgae, the essentiality of this element for plants has not been established yet. The study of Se uptake and accumulation strategies in micro- and macro-algae is of pivotal importance, as they represent potential vectors for Se movement in aquatic environments and Se at high levels may affect their growth causing a reduction in primary production. Some microalgae exhibit the capacity of efficiently converting Se to less harmful volatile compounds as a strategy to cope with Se toxicity. Therefore, they play a crucial role in Se-cycling through the ecosystem. On the other side, micro- or macro-algae enriched in Se may be used in Se biofortification programs aimed to improve Se content in human diet via supplementation of valuable food. Indeed, some organic forms of selenium (selenomethionine and methylselenocysteine) are known to act as anticarcinogenic compounds and exert a broad spectrum of beneficial effects in humans and other mammals. Here, we want to give an overview of the developments in the current understanding of Se uptake, accumulation and metabolism in algae, discussing potential ecotoxicological implications and nutritional aspects.

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.

Dietary Selenomethionine Administration in the American Alligator (Alligator mississippiensis): Hepatic and Renal Se Accumulation and Its Effects on Growth and Body Condition

Selenium (Se) is an essential trace nutrient, but in excess, it can induce toxicity. Incomplete combustion of coal produces coal combustion wastes, which are enriched in Se and often disposed of in aquatic basins. While a multitude of studies have investigated Se accumulation in vertebrates, few studies have examined its effects on longer-lived top trophic carnivores, such as the American alligator (Alligator mississippiensis). In this study, alligators were fed one of three Dietary Treatments: mice injected with water (controls) or water supplemented with 1000 or 2000 ppm selenomethionine (SeMet). Dietary Treatment significantly affected Se levels in both the liver (p < 0.0001; raw mean ± SE: 1000 ppm group, 35.20 ± 6.32 ppm; 2000 ppm group, 49.97 ± 4.00 ppm) and kidney (p < 0.0001; raw mean ± SE: 1000 ppm group, 101.60 ± 8.64 ppm; 2000 ppm, 96.38 ± 5.81 ppm), which were significantly higher in alligators fed SeMet than in controls. Post-treatment head length, used to control for size variation, was negatively related to both kidney (p = 0.0142) and liver (p = 0.0010) Se concentrations. Dietary treatment with SeMet significantly reduced body condition (1000 ppm, p < 0.0029; 2000 ppm, p = 0.0075), but it significantly increased growth (1000 ppm, p < 0.0001; 2000 ppm, p = 0.0316). Body condition and growth remained unchanged in control alligators (p > 0.05). Our results demonstrate alligators are capable of accumulating high levels of Se through trophic transfer. The positive effects of accumulation on growth may demonstrate Se essentiality, whereas the negative effects on condition may demonstrate toxicity. Accumulation also was associated with mortality, further demonstrating toxicity. Future studies should further investigate the physiological effects of Se accumulation in long-lived, top-trophic carnivores.

Binding and Conversion of Selenium in Candida utilis ATCC 9950 Yeasts in Bioreactor Culture

Selenium is considered an essential component of all living organisms. The use of yeasts as a selenium supplement in human nutrition has gained much interest over the last decade. The accumulation and biochemical transformation of selenium in yeast cells is particularly interesting to many researchers. In this article, we present the results of the determination of selenium and selenomethionine content in the biomass of feed yeast Candida utilis ATCC 9950 obtained from the culture grown in a bioreactor. The results indicated that C. utilis cells performed the biotransformation of inorganic selenium(IV) to organic derivatives (e.g., selenomethionine). Selenium introduced (20–30 mg Se⁴⁺∙L⁻¹) to the experimental media in the form of sodium(IV) selenite (Na₂SeO₃) salt caused a significant increase in selenium content in the biomass of C. utilis, irrespective of the concentration. The highest amount of selenium (1841 μg∙g_d.w.⁻¹) was obtained after a 48-h culture in media containing 30 mg Se⁴⁺∙L⁻¹. The highest content of selenomethionine (238.8 μg∙g_d.w.⁻¹) was found after 48-h culture from the experimental medium that was supplemented with selenium at a concentration of 20 mg Se⁴⁺∙L⁻¹. Biomass cell in the cultures supplemented with selenium ranged from 1.5 to 14.1 g∙L⁻¹. The results of this study indicate that yeast cell biomass of C. utilis enriched mainly with the organic forms of selenium can be a valuable source of protein. It creates the possibility of obtaining selenium biocomplexes that can be used in the production of protein-selenium dietary supplements for animals and humans

Effects of Different Forms of Selenium Fertilizers on Se Accumulation, Distribution, and Residual Effect in Winter Wheat-Summer Maize Rotation System

Foliar Se fertilizers were applied to investigate the effects of Se forms on Se accumulation and distribution in the wheat-maize rotation system and residual concentration of Se in subsequent crops. Sodium selenite, sodium selenate, selenomethionine, chemical nano-Se, humic acid + sodium selenite, and compound fertilizer + sodium selenite were applied once at the flowering stage of wheat (30 g ha^-1) and at the bell stage of maize (60 g ha^-1). Compared with the control treatment, foliar Se applications significant increased the grain Se concentration of wheat and maize by 0.02-0.31 and 0.07-1.09 mg kg^-1, respectively. Wheat and maize grain Se recoveries were 3.0-10.4 and 4.1-18.5%, respectively. However, Se concentrations in the grain of subsequent wheat and maize significantly decreased by 77.9 and 91.2%, respectively. The change of Se concentration in soil was a dynamic process with Se depletion after harvest of maize.

Structural Snapshots of an Engineered Cystathionine-γ-lyase Reveal the Critical Role of Electrostatic Interactions in the Active Site

Enzyme therapeutics that can degrade l-methionine (l-Met) are of great interest as numerous malignancies are exquisitely sensitive to l-Met depletion. To exhaust the pool of methionine in human serum, we previously engineered an l-Met-degrading enzyme based on the human cystathionine-γ-lyase scaffold (hCGL-NLV) to circumvent immunogenicity and stability issues observed in the preclinical application of bacterially derived methionine-γ-lyases. To gain further insights into the structure-activity relationships governing the chemistry of the hCGL-NLV lead molecule, we undertook a biophysical characterization campaign that captured crystal structures (2.2 Å) of hCGL-NLV with distinct reaction intermediates, including internal aldimine, substrate-bound, gem-diamine, and external aldimine forms. Curiously, an alternate form of hCGL-NLV that crystallized under higher-salt conditions revealed a locally unfolded active site, correlating with inhibition of activity as a function of ionic strength. Subsequent mutational and kinetic experiments pinpointed that a salt bridge between the phosphate of the essential cofactor pyridoxal 5'-phosphate (PLP) and residue R62 plays an important role in catalyzing β- and γ-eliminations. Our study suggests that solvent ions such as NaCl disrupt electrostatic interactions between R62 and PLP, decreasing catalytic efficiency.

Molecular mechanisms of selenium-Induced spinal deformities in fish

Selenium toxicity to oviparous vertebrates is often attributed to selenomethionine (SeMet), which can biomagnify through maternal transfer. Although oxidative stress is implicated in SeMet toxicity, knowledge gaps remain in how SeMet causes characteristic spinal deformities. In the present study, we use the Japanese medaka (Oryzias latipes) model to investigate the role of oxidative stress, cell death, and the unfolded protein response (UPR) on skeletal gene expression and SeMet toxicity, linking localization of cellular effects to observed abnormalities. Medaka embryos were treated with 2.5μM or 5μM SeMet for 24h at stage 25 (48h post fertilization). Post treatment, embryos were separated into normal, deformed (mild, moderate or severe), or dead categories. Dichlorofluorescein staining demonstrated oxidative stress in tails of embryos with observable spinal malformations. Furthermore, acridine orange staining for apoptosis identified significantly more dead cells in tails of treated embryos. Gene expression studies for the UPR suggest a potential role for CHOP (c/ebp homologous protein) induced apoptosis deformed embryos after 5μM SeMet, accompanied by a significant decrease in PDIA4 (protein disulfide isomerase A4) and no change in Dnajb9 (ER DNA J Domain-Containing Protein 4). This expression was distinct from the UPR induced by well-studied ER stress inducer, tunicamycin, which robustly activated CHOP, PDIA4 and Dnajb9. Finally, SeMet treatment significantly decreased transcripts of cartilage development, Sox9 (SRY box 9), while increasing Runx2 in deformed embryos, without altering Twist or Collagen 2a1. Results suggest that oxidative stress, the UPR and cell death play key roles in SeMet induced deformities and altered skeletal development factors.

The bioaccumulation and effects of selenium in the oligochaete Lumbriculus variegatus via dissolved and dietary exposure routes

Aquatic organisms take up selenium from solution and from their diets. Many questions remain regarding the relative importance of selenium accumulation from these sources and resulting effects in benthic invertebrates. The present study addressed the toxicity and accumulation of Se via dissolved and dietary exposures to three different Se species, in the freshwater oligochaete Lumbriculus variegatus. Worms were exposed to 20μg/g dry weight of selenite (Se(IV)), selenate (Se(VI)), or seleno-l-methionine (Se-Met) in their diet (sediment) or to 15μg/L dissolved Se in water-only exposures. While the dissolved and sediment Se levels differed greatly, such levels may co-occur at a Se-contaminated site. Se accumulation, worm population growth, lipid peroxidation (as TBARS), and Na(+)/K(+)-ATPase activity were quantified at the end of the 2-week exposure. The sediment Se-Met exposure caused 100% mortality, while worm densities were reduced by the other exposures except the Se(VI) one. Se bioaccumulation was generally higher for the sediment-Se exposure than the dissolved-Se ones, and was higher for Se(IV) than Se(VI) in the dissolved-Se exposure but not the sediment-Se one. The Se accumulation was highest for Se-Met. The oligochaetes that accumulated Se had higher levels of lipid peroxidation and reduced Na(+)/K(+)-ATPase activity. The present study's findings of differences in Se accumulation and toxicity for the three Se species, with effects generally but not exclusively a function of Se body burdens, underscore the need for research on these issues in invertebrates. Moreover, the results imply that the dietary uptake route is the predominant one for Se accumulation in L. variegatus.

Characterization of the NTPR and BD1 interacting domains of the human PICH-BEND3 complex

Chromosome integrity depends on DNA structure-specific processing complexes that resolve DNA entanglement between sister chromatids. If left unresolved, these entanglements can generate either chromatin bridging or ultrafine DNA bridging in the anaphase of mitosis. These bridge structures are defined by the presence of the PICH protein, which interacts with the BEND3 protein in mitosis. To obtain structural insights into PICH-BEND3 complex formation at the atomic level, their respective NTPR and BD1 domains were cloned, overexpressed and crystallized using 1.56 M ammonium sulfate as a precipitant at pH 7.0. The protein complex readily formed large hexagonal crystals belonging to space group P6122, with unit-cell parameters a = b = 47.28, c = 431.58 Å and with one heterodimer in the asymmetric unit. A complete multiwavelength anomalous dispersion (MAD) data set extending to 2.2 Å resolution was collected from a selenomethionine-labelled crystal at the Swiss Light Source.

Envelope protein VP24 from White spot syndrome virus: expression, purification and crystallization

White spot syndrome virus (WSSV) is a major shrimp pathogen known to infect penaeid shrimp and other crustaceans. VP24 is one of the major envelope proteins of WSSV. In order to facilitate purification, crystallization and structure determination, the predicted N-terminal transmembrane region of approximately 26 amino acids was truncated from VP24 and several mutants were prepared to increase the proportion of selenomethionine (SeMet) residues for subsequent structural determination using the SAD method. Truncated VP24, its mutants and the corresponding SeMet-labelled proteins were purified, and the native and SeMet proteins were crystallized by the hanging-drop vapour-diffusion method. Crystals of VP24 were obtained using a reservoir consisting of 0.1 M Tris-HCl pH 8.5, 2.75 M ammonium acetate with a drop volume ratio of two parts protein solution to one part reservoir solution. Notably, ATP was added as a critical additive to the drop with a final concentration of 10 mM. Crystals of SeMet-labelled VP24 mutant diffracted to 3.0 Å resolution and those of the native diffracted to 2.4 Å resolution; the crystals belonged to space group I213, with unit-cell parameters a = b = c = 140 Å.

Adverse health effects and histological changes in white sturgeon (Acipenser transmontanus) exposed to dietary selenomethionine

It has been shown that selenium (Se) released to the aquatic environment can have devastating effects on local wildlife. White sturgeon (Acipenser transmontanus) have a life history particularly susceptible to contaminants, and their protection is of interest as they are culturally and economically important, and many populations are classified as endangered. During the present 72-d dietary study, multiple signs of decreased health and Se lethality were observed. Juvenile white sturgeon were given diets containing 1.4 μg, 5.6 μg, 22.4 μg, or 104.4 μg selenomethionine/g food (dry mass). Selenium accumulated in muscle and liver tissue in a dose-dependent manner. Edema causing exophthalmos developed within 15 d and 23 d, and lethal effects occurred in 54% and 22% of fish in the high- and medium-dose groups, respectively. Growth and hepatosomatic index were significantly lower in the high-dose group, which also had a high incidence of food avoidance. Histology of the liver revealed a dose-dependent increase in melanomacrophage aggregates and decrease of energy stores, which indicated toxicity. These results indicate that white sturgeon are susceptible to the effects of Se accumulation over relatively short time periods. This stresses the need for continued sturgeon research and studies looking into the environmental fate and regulation of released Se. Environ Toxicol Chem 2016;35:1741-1750. © 2015 SETAC.

Atomic resolution experimental phase information reveals extensive disorder and bound 2-methyl-2,4-pentanediol in Ca(2+)-calmodulin

Calmodulin (CaM) is the primary calcium signaling protein in eukaryotes and has been extensively studied using various biophysical techniques. Prior crystal structures have noted the presence of ambiguous electron density in both hydrophobic binding pockets of Ca(2+)-CaM, but no assignment of these features has been made. In addition, Ca(2+)-CaM samples many conformational substates in the crystal and accurately modeling the full range of this functionally important disorder is challenging. In order to characterize these features in a minimally biased manner, a 1.0 Å resolution single-wavelength anomalous diffraction data set was measured for selenomethionine-substituted Ca(2+)-CaM. Density-modified electron-density maps enabled the accurate assignment of Ca(2+)-CaM main-chain and side-chain disorder. These experimental maps also substantiate complex disorder models that were automatically built using low-contour features of model-phased electron density. Furthermore, experimental electron-density maps reveal that 2-methyl-2,4-pentanediol (MPD) is present in the C-terminal domain, mediates a lattice contact between N-terminal domains and may occupy the N-terminal binding pocket. The majority of the crystal structures of target-free Ca(2+)-CaM have been derived from crystals grown using MPD as a precipitant, and thus MPD is likely to be bound in functionally critical regions of Ca(2+)-CaM in most of these structures. The adventitious binding of MPD helps to explain differences between the Ca(2+)-CaM crystal and solution structures and is likely to favor more open conformations of the EF-hands in the crystal.

Selenium bioaccessibility in stomach, small intestine and colon: Comparison between pure Se compounds, Se-enriched food crops and food supplements

Selenium (Se) is an essential nutrient for humans as it plays an important role in glutathione peroxidase (GPx) activity. Moreover, it may reduce cancer risks. The objective of this work was to examine in vitro the bioaccessibility of Se in three different Se-enriched food supplements and two different Se-enriched food crops, with reference to two pure Se standards, and changes in its speciation during intestinal digestion. Selenate was found to be stable throughout the entire digestion, whereas incubation of selenomethionine resulted in the chemical and microbial production of minor metabolites. The bioaccessibility of Se in Se-enriched food supplements and food crops was found to be highest in the small intestine. Compared to SelenoPrecise and Se-ACE tablets, a yoghurt-based supplement exhibited a much lower Se bioaccessibility, possibly due to the presence of nano- or microparticles of elemental Se. Colon microbiota were found to primarily affect Se bioaccessibility in the colon environment, with the presence of inactivated microbiota resulting in a higher bioaccessibility. A higher potential of Se to reach the colon and become accessible in this phase may result in beneficial effects on the colon health.

Selenomethionine metabolism and its toxicity in yeast

The importance of selenium for organisms can be explained by its existence as selenocysteine in the catalytic centers of glutathione peroxidase and thioredoxin reductase. Another selenoamino acid, selenomethionine, is the major form of selenium in foods, and organisms that require selenium as a nutrient directly metabolize selenomethionine to a reactive form of selenium or store it in general proteins. Selenium is recognized as an essential nutrient for human and animal health; however, its excessive uptake harms mammals and the cytotoxic mechanism of selenium remains unclear. Recent progress in the development of selenium-enriched yeast and selenomethionine-resistant mutant to produce selenomethionine-containing proteins for X-ray crystallography has provided new insights into the molecular mechanism of selenomethionine toxicity. In this review, we describe the metabolism of seleno-compounds in yeast and discuss the cytotoxicity caused by selenomethionine against yeast from a metabolic viewpoint.

Maintaining tissue selenium species distribution as a potential defense mechanism against methylmercury toxicity in juvenile white sturgeon (Acipenser transmontanus)

Selenium (Se) has been shown to antagonize mercury (Hg) toxicity. We have previously demonstrated that orally intubated selenomethionine (SeMet) and methylmercury (MeHg) reduced tissue Se accumulation, as well as blood and kidney Hg concentrations in juvenile white sturgeon (Acipenser transmontanus). However, the form of Se accumulated is not known. In this study, three organoseleniums: selenocysteine (Sec), Se-methyl-selenocysteine (MSeCys), and SeMet and two inorganic Se species: selenate and selenite were determined and quantified in the blood at different post-intubation periods (12, 24, 48h) and in the muscle, liver, and kidneys at 48h in white sturgeon orally intubated with a single dose of control (carrier), SeMet (500μg Se/kg body weight; BW), MeHg (850μg Hg/kg BW), and both (Se+Hg; at 500μg Se/kg and 850μg Hg/kg BW). When only SeMet was intubated, the accumulative/unmodified pathway took precedent in the blood, white muscle, liver, and kidneys. In the presence of MeHg, however, active metabolic transformation and de novo synthesis of biologically active Se forms are seen in the liver and kidneys, as indicated by a gradual increase in blood Sec:SeMet ratios and Se metabolites. In the white muscle, mobilization of endogenous Se storage by MeHg is supported by the absence of tissue SeMet and detectable levels of blood SeMet. In contrast, co-intubation with SeMet increased muscle SeMet. The high levels of unknown Se metabolites and detectable levels of selenite in the kidney reflect its role as the major excretory organ for Se. Selenium metabolism is highly regulated in the kidneys, as Se speciation was not affected by MeHg or by its co-intubation with SeMet. In the Se+Hg group, the proportion of SeMet in the liver has decreased to nearly 1/8th of that of the SeMet only group, resulting in a more similar selenocompound distribution profile to that of the MeHg only group. This is likely due to the increased need for Se metabolites necessary for MeHg demethylation in the liver. Our study demonstrated that in the presence of MeHg, regulating tissue Se speciation, hence, Se bioavailability, is more an important strategy than maintaining total Se levels in major organs of juvenile white sturgeon.

Selenoglycoproteins attenuate adhesion of tumor cells to the brain microvascular endothelium via a process involving NF-κB activation

Selenium-containing compounds and selenized yeast have anticancer properties. In order to address possible mechanisms involved in these effects, selenoglycoproteins (SGPs) were extracted from selenium-enriched yeast at pH 4.0 and 6.5 (the fractions are called SGP40 and SGP65, respectively), followed by evaluation of their impact on the interactions of lung and breast tumor cells with human brain microvascular endothelial cells (HBMECs). Extracted SGPs, especially SGP40, significantly inhibited adhesion of tumor cells to HBMECs and their transendothelial migration. Because the active components of SGPs are unknown, small selenium-containing compounds [leucyl-valyl-selenomethionyl-arginine (LVSe-MR) and methylselenoadenosine (M-Se-A)], which are normally present in selenized yeast, were introduced as additional treatment groups. Treatment of HBMECs with SGP40, LVSe-MR and M-Se-A induced changes in gene signatures, which suggested a central involvement of nuclear factor (NF)-κB-dependent pathway. These observations were confirmed in the subsequent analysis of NF-κB DNA binding activity, quantitative measurements of the expression of selected genes and proteins, and tumor cell adhesion assay with a specific NF-κB inhibitor as the additional treatment factor. These findings indicate that specific organic selenium-containing compounds have the ability to inhibit tumor cell adhesion to brain endothelial cells via down-regulation of NF-κB. SGPs appear to be more effective than small selenium-containing compounds, suggesting the role of not only selenium but also the glycoprotein component in the observed protective impact.

Structural characterization of a novel autonomous cohesin from Ruminococcus flavefaciens

Ruminococcus flavefaciens is a cellulolytic bacterium found in the rumen of herbivores and produces one of the most elaborate and variable cellulosome systems. The structure of an R. flavefaciens protein (RfCohG, ZP_06142108), representing a freestanding (non-cellulosomal) type III cohesin module, has been determined. A selenomethionine derivative with a C-terminal histidine tag was crystallized and diffraction data were measured to 2.44 Å resolution. Its structure was determined by single-wavelength anomalous dispersion, revealing eight molecules in the asymmetric unit. RfCohG exhibits the most complex among all known cohesin structures, possessing four α-helical elements and a topographical protuberance on the putative dockerin-binding surface.

Effect of dietary selenomethionine on growth performance, tissue burden, and histopathology in green and white sturgeon

A comparative examination of potential differences in selenium (Se) sensitivity was conducted on two sturgeon species indigenous to the San Francisco Bay-Delta. Juvenile green (Acipenser medirostris), recently given a federally threatened status, and white sturgeon (Acipenser transmontanus) were exposed to one of four nominal concentrations of dietary l-selenomethionine (SeMet) (0 (control), 50, 100, or 200 mg SeMet/kg diet) for 8 weeks. Mortality, growth performance, whole body composition, histopathology, and Se burdens of the whole body, liver, kidneys, gills, heart, and white muscle were determined every 2 to 4 weeks. Significant (p<0.05) mortality was observed in green sturgeon fed the highest SeMet diet after 2 weeks, whereas no mortality was observed in white sturgeon. Growth rates were significantly reduced in both species; however, green sturgeon was more adversely affected by the treatment. Dietary SeMet significantly affected whole body composition and most noticeably, in the decline of lipid contents in green sturgeon. Selenium accumulated significantly in all tissues relative to the control groups. After 4 and 8 weeks of exposure, marked abnormalities were observed in the kidneys and liver of both sturgeon species; however, green sturgeon was more susceptible to SeMet than white sturgeon at all dietary SeMet levels. Our results showed that a dietary Se concentration at 19.7 ± 0.6 mg Se/kg, which is in range with the reported Se concentrations of the benthic macro-vertebrate community of the San Francisco Bay, had adverse effects on both sturgeon species. However, the exposure had a more severe pathological effect on green sturgeon, suggesting that when implementing conservation measures, this federally listed threatened species should be monitored and managed independently from white sturgeon.