Trends in selenium biochemistry

Construction of blackberry polysaccharide nano-selenium particles: Structure features and regulation effects of glucose/lipid metabolism in HepG2 cells

In this study, blackberry polysaccharide-selenium nanoparticles (BBP-24-3Se) were first prepared via Na2SeO3/Vc redox reaction, followed by coating with red blood cell membrane (RBC) to form core-shell structure polysaccharide-selenium nanoparticles (RBC@BBP-24-3Se). The particle size of BBP-24-3Se (167.1 nm) was increased to 239.8 nm (RBC@BBP-24-3Se) with an obvious core-shell structure after coating with RBC. FT-IR and XPS results indicated that the interaction between BBP-24-3 and SeNPs formed a new C-O···Se bond with valence state of Se0. Bioassays indicated that RBC coating markedly enhanced both the biocompatibility and bioabsorbability of RBC@BBP-24-3Se, and the absorption rate of RBC@BBP-24-3Se in HepG2 cells was 4.99 times higher than that of BBP-24-3Se at a concentration of 10 μg/mL. Compared with BBP-24-3Se, RBC@BBP-24-3Se possessed significantly heightened protective efficacy against oxidative damage and better regulation of glucose/lipid metabolism disorder induced by palmitic acid in HepG2 cells. Mechanistic studies demonstrated that RBC@BBP-24-3Se could effectively improve PI3K/AKT signaling pathway to promote glucose metabolism, inhibit the expression of lipid synthesis genes and up-regulate the expression of lipid-decomposing genes through AMPK signaling pathway to improve lipid metabolism. These results provided a theoretical basis for developing a new type of selenium supplement for the treatment of insulin resistance.

Interplay between diphenyl diselenide and copper: Impact on D. melanogaster survival, behavior, and biochemical parameters

Copper (Cu2+) is a biologically essential element that participates in numerous physiological processes. However, elevated concentrations of copper have been associated with cellular oxidative stress and neurodegenerative diseases. Organo‑selenium compounds such as diphenyl diselenide (DPDS) have in vitro and in vivo antioxidant properties. Hence, we hypothesized that DPDS may modulate the toxicity of Cu2+ in Drosophila melanogaster. The acute effects (4 days of exposure) caused by a high concentration of Cu2+ (3 mM) were studied using endpoints of toxicity such as survival and behavior in D. melanogaster. The potential protective effect of low concentration of DPDS (20 μM) against Cu2+ was also investigated. Adult flies aged 1-5 days post-eclosion (both sexes) were divided into four groups: Control, DPDS (20 μM), CuSO4 (3 mM), and the combined exposure of DPDS (20 μM) and CuSO4 (3 mM). Survival, biochemical, and behavioral parameters were determined. Co-exposure of DPDS and CuSO4 increased acetylcholinesterase (AChE) activity and the generation of reactive oxygen species (ROS as determined by DFCH oxidation). Contrary to our expectation, the co-exposure reduced survival, body weight, locomotion, catalase activity, and cell viability in relation to control group. Taken together, DPDS potentiated the Cu2+ toxicity.

Comparative efficacy of antioxidant therapies for sepsis and septic shock in the intensive care unit: A frequentist network meta-analysis

Background

Antioxidant therapy is gaining traction in managing sepsis and septic shock, owing to its perceived positive impact on patient outcomes. This study sought to compare the efficacy of five antioxidant therapies (melatonin, vitamin C, vitamin E, selenium, and N-acetylcysteine, both individually and in combination with other compounds such as vitamin B1, hydrocortisone, propolis, and glutamine) in treating sepsis or septic shock in the intensive care unit (ICU).

Methods

The study involved randomized and multi-arm trials with sepsis or septic shock patients using melatonin, vitamin C, vitamin E, selenium, or N-acetylcysteine. Studies were sourced from PubMed, Embase, Cochrane Library, ClinicalTrials.gov, and WHO - Clinical Trials Registry Platform for the frequentist network meta-analysis on 28-day mortality and Sequential Organ Failure Assessment (SOFA) scores. The risk of bias was assessed using the Physiotherapy Evidence Database scale. Therapies were compared directly and indirectly using R software.

Results

The study of 56 trials involving 9,366 patients was included. Bias assessment revealed that 89.3 % of trials achieved excellent or good quality. Based on treatment ranking and pairwise comparisons, melatonin with propolis (SUCRA = 93.29 %) is effective in improving SOFA scores, statistically significant, with no publication bias (p= 0.73). High-dose vitamin C (SUCRA = 83.97 %), vitamin C with vitamin B1 (SUCRA = 78.72 %), and melatonin (SUCRA = 67.03 %) are potential therapies for organ dysfunction. Melatonin (SUCRA = 88.22 %) and high-dose vitamin C (SUCRA = 80.75 %) were the most effective in reducing 28-day mortality rates. However, analysis indicated that the results for 28-day mortality rates were not statistically significant. Also, these results contained publication bias (p= 0.02).

Conclusion

The study offers fresh perspectives on antioxidant therapy treatments for sepsis or septic shock in ICU, emphasizing the combination of melatonin and propolis notably reduces SOFA scores for those patients.

Unveiling the Nature and Strength of Selenium-Centered Chalcogen Bonds in Binary Complexes of SeO2 with Oxygen-/Sulfur-Containing Lewis Bases: Insights from Theoretical Calculations

Among various non-covalent interactions, selenium-centered chalcogen bonds (SeChBs) have garnered considerable attention in recent years as a result of their important contributions to crystal engineering, organocatalysis, molecular recognition, materials science, and biological systems. Herein, we systematically investigated π-hole-type Se∙∙∙O/S ChBs in the binary complexes of SeO2 with a series of O-/S-containing Lewis bases by means of high-level ab initio computations. The results demonstrate that there exists an attractive interaction between the Se atom of SeO2 and the O/S atom of Lewis bases. The interaction energies computed at the MP2/aug-cc-pVTZ level range from -4.68 kcal/mol to -10.83 kcal/mol for the Se∙∙∙O chalcogen-bonded complexes and vary between -3.53 kcal/mol and -13.77 kcal/mol for the Se∙∙∙S chalcogen-bonded complexes. The Se∙∙∙O/S ChBs exhibit a relatively short binding distance in comparison to the sum of the van der Waals radii of two chalcogen atoms. The Se∙∙∙O/S ChBs in all of the studied complexes show significant strength and a closed-shell nature, with a partially covalent character in most cases. Furthermore, the strength of these Se∙∙∙O/S ChBs generally surpasses that of the C/O-H∙∙∙O hydrogen bonds within the same complex. It should be noted that additional C/O-H∙∙∙O interactions have a large effect on the geometric structures and strength of Se∙∙∙O/S ChBs. Two subunits are connected together mainly via the orbital interaction between the lone pair of O/S atoms in the Lewis bases and the BD*(OSe) anti-bonding orbital of SeO2, except for the SeO2∙∙∙HCSOH complex. The electrostatic component emerges as the largest attractive contributor for stabilizing the examined complexes, with significant contributions from induction and dispersion components as well.

Advancements in Understanding and Enhancing Antioxidant-Mediated Sperm Cryopreservation in Small Ruminants: Challenges and Perspectives

Cryopreservation poses significant challenges to the preservation of sperm integrity and function, particularly in small ruminants where cryodamage is pronounced. This review explores the molecular mechanisms underlying sperm cryodamage and strategies for improving cryopreservation outcomes, with a focus on the role of antioxidants. Cryopreservation-induced alterations in proteins and RNA transcripts critical for sperm function, including motility, capacitation, fertilization, and embryo development, are discussed. Proteomic, transcriptomic, and epigenomic advancements have provided valuable insights into these mechanisms, offering potential biomarkers for predicting sperm freezability and enhancing cryopreservation strategies. Combining technologies such as mass spectrometry and flow cytometry allows for a comprehensive understanding of molecular and cellular changes induced by the freezing-thawing process. However, challenges remain in optimizing cryoprotectant formulations and antioxidant supplementation to improve post-thaw sperm fertility. Further research is needed to explore a wider range of novel cryoprotectants, antioxidants, and proteins for cryopreservation media, as well as to validate their efficacy in enhancing sperm viability and function. Additionally, investigations into the effects of cryopreservation on RNA transcripts and epigenetic factors in small ruminant species are warranted to advance our understanding of sperm preservation. Overall, this review highlights the importance of antioxidants in mitigating cryodamage and underscores the need for continued research to refine cryopreservation protocols and improve reproductive outcomes in small ruminants.

Structural Characterization and Ligand-Induced Conformational Changes of SenB, a Se-Glycosyltransferase Involved in Selenoneine Biosynthesis

Selenium (Se) is an essential micronutrient that is found naturally in proteins, nucleic acids, and natural products. Unlike selenoproteins and selenonucleic acids, little is known about the structures of biosynthetic enzymes that incorporate Se into small molecules. Here, we report the X-ray crystal structure of SenB, the first known Se-glycosyltransferase that was recently found to be involved in the biosynthesis of the Se-containing metabolite selenoneine. SenB catalyzes C-Se bond formation using selenophosphate and an activated uridine diphosphate sugar as a Se and glycosyl donor, respectively, making it the first known selenosugar synthase and one of only four bona fide C-Se bond-forming enzymes discovered to date. Our crystal structure, determined to 2.25 Å resolution, reveals that SenB is a type B glycosyltransferase, displaying the prototypical fold with two globular Rossmann-like domains and a catalytic interdomain cleft. By employing complementary structural biology techniques, we find that SenB undergoes both local and global substrate-induced conformational changes, demonstrating a significant increase in α-helicity and a transition to a more compact conformation. Our results provide the first structure of SenB and set the stage for further biochemical characterization in the future.

Coupling of different antioxidative systems in rice under the simultaneous influence of selenium and cadmium

Selenium (Se) elevates the antioxidant ability of rice against cadmium (Cd) stress, but previous studies only focused on the variation in antioxidant enzymes or nonenzymatic substances induced by Se under Cd stress and ignored the relationships between different antioxidant parameters during the interaction. Here, hydroponic experiments with rice were performed by adding both Cd and Se at doses in the range of 0-50 μM to explore the physiological responses of rice and their relationships in the presence of different levels of Se and Cd. Exogenous Cd markedly promoted the activity of antioxidant enzymes with the exception of catalase (CAT) and the concentration of nonenzymatic substances in aerial parts. Se enhanced the antioxidant capacity by improving the activities of all the enzymes tested in this study and increasing the concentrations of nonenzymatic compounds. The couplings among different antioxidant substances within paddy rice were then determined based on cluster and linear fitting results and their metabolic process and physiological functions. The findings specifically highlight that couplings among the ascorbic acid (AsA)-glutathione (GSH) cycle, glutathione synthase (GS)-phytochelatin synthetase (PCS) coupling system and glutathione peroxidase (GPX)-superoxide dismutase (SOD) coupling system in aerial parts helps protect plants from Cd stress. These coupling systems form likely due to the fact that one enzyme generated a product that could be the substrate for another enzyme. Noticeably, such coupling systems do not emerge in roots because the stronger damage to roots than other organs activates the ascorbate peroxidase (APX)-GPX-CAT and PCS-GS-SOD systems with distinct functions and structures. This study provides new insights into the detoxification mechanisms of rice caused by the combined effect of Se and Cd.

Preparative Biocatalytic Synthesis of α-Ketomethylselenobutyrate-A Putative Agent for Cancer Therapy

Biomedical studies of the role of organic selenium compounds indicate that the amino acid derivative of L-selenomethionine, α-ketomethylselenobutyrate (KMSB), can be considered a potential anticancer therapeutic agent. It was noted that, in addition to a direct effect on redox signaling molecules, α-ketoacid metabolites of organoselenium compounds are able to change the status of histone acetylation and suppress the activity of histone deacetylases in cancer cells. However, the wide use of KMSB in biomedical research is hindered not only by its commercial unavailability, but also by the fact that there is no detailed information in the literature on possible methods for the synthesis of this compound. This paper describes in detail the procedure for obtaining a high-purity KMSB preparation (purity ≥ 99.3%) with a yield of the target product of more than 67%. L-amino acid oxidase obtained from C. adamanteus was used as a catalyst for the conversion of L-selenomethionine to KMSB. If necessary, this method can be used as a basis both for scaling up the synthesis of KMSB and for developing cost-effective biocatalytic technologies for obtaining other highly purified drugs.

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.

Population status of selenium in Colombia and associated factors: a cross-sectional study

OBJECTIVES

This study aims to investigate the population status of selenium in Colombia and other associated factors.

METHODS

Cross-sectional study, in population of urban or rural origin (n=412). Main outcome measures were: median serum selenium, thyrotropin, the prevalence of and positivity of anti-thyroid peroxidase, anti-thyroglobulin, and anti-TSH receptor.

RESULTS

This study found that 96.6% of the subjects had normal selenium levels, and no significant associations were found between the population median of selenium and overweight/obesity, sociodemographic variables, age, goiter, and thyroid antibody positivity.

CONCLUSIONS

In Colombia, the population status of selenium is normal, and the geological characteristics may contribute to the state of selenium in this population. However, additional studies are required to evaluate the content of selenium in plants and other foods.

Evolutionary Aspects of Selenium Binding Protein (SBP)

Selenium-binding proteins represent a ubiquitous protein family and recently SBP1 was described as a new stress response regulator in plants. SBP1 has been characterized as a methanethiol oxidase, however its exact role remains unclear. Moreover, in mammals, it is involved in the regulation of anti-carcinogenic growth and progression as well as reduction/oxidation modulation and detoxification. In this work, we delineate the functional potential of certain motifs of SBP in the context of evolutionary relationships. The phylogenetic profiling approach revealed the absence of SBP in the fungi phylum as well as in most non eukaryotic organisms. The phylogenetic tree also indicates the differentiation and evolution of characteristic SBP motifs. Main evolutionary events concern the CSSC motif for which Acidobacteria, Fungi and Archaea carry modifications. Moreover, the CC motif is harbored by some bacteria and remains conserved in Plants, while modified to CxxC in Animals. Thus, the characteristic sequence motifs of SBPs mainly appeared in Archaea and Bacteria and retained in Animals and Plants. Our results demonstrate the emergence of SBP from bacteria and most likely as a methanethiol oxidase.

Fast and Sensitive Determination of Cadmium and Selenium in Rice by Direct Sampling Electrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry

In this work, a direct solid sampling device based on modified graphite furnace electrothermal vaporization (GF-ETV) with inductively coupled plasma mass spectrometry (ICP-MS) was established for the simultaneous detection of trace selenium and cadmium in rice samples. A bypass gas was first designed in GF-ETV to improve the device’s analytical sensitivity and precision. The ashing and vaporization conditions, the flow rates of the Ar carrier and the bypass gases of ICP-MS were all investigated. Under the optimized conditions, the limits of detection (LODs) for Se and Cd were 0.5 μg kg−1 and 0.16 μg kg−1, respectively; the relative standard deviations (RSDs) of repeated measurements were within 8% (n = 6). The recoveries of Cd and Se in rice samples were in the range of 89−112% compared with the microwave digestion ICP-MS method, indicating good accuracy and precision for the simultaneous detection of Se and Cd in rice matrix. The whole analysis time is <3 min without the sample digestion process, fulfilling the fast detection of Se and Cd in rice samples to protect food safety.

Identification and Immunomodulatory Effect on Immunosuppressed Mice of Selenium-Enriched Peptides of Egg White

Selenium-enriched egg white peptides (Se-EWP) were prepared by pre-heat treatment and enzymatic hydrolysis in this study. In addition, their selenopeptide sequence identification and immunomodulatory effect were investigated. Results showed that the yield of Se-EWP obtained from alkaline-neutral protease treatment reached 76.90%, and peptides with a molecular weight of 200-1000 Da accounted for 98.33%. Four characteristic selenopeptides, including SeCys-Trp-Leu-Glu, Trp-Ser-SeCys, SeMet-Ala-Pro, and SeMet-Leu, were identified by HPLC-ESI-MS/MS, which were rich in hydrophobic and branched-chain amino acids. Se-EWP (750 mg/kg/d) could effectively retard the decrease of immune organ index in immunosuppressed mice induced by cyclophosphamide. Moreover, supplementation of Se-EWP could promote a higher content of Se in liver, the number of white blood cells, and the levels of serum cytokines (IL-6, IL-2, and TNF-α) as compared with EWP groups, indicating that Se-EWP could effectively alleviate immunosuppression induced by cyclophosphamide. These findings suggested that Se-EWP exhibited great potential as functional foods for immunomodulatory effect.

In vitro toxicological assessment of PhSeZnCl in human liver cells

Phenylselenenylzinc chloride (PhSeZnCl) is an air-stable selenolate, easily synthesizable through oxidative insertion of elemental zinc into the Se-halogen bond of the commercially available phenylselenyl chloride. PhSeZnCl was shown to possess a marked GPx-like activity both in NMR and in vitro tests, and to effectively react with cellular thiols, and was supposed for a potential use in the chemotherapy of drug-resistant cancers. However, activity of PhSeZnCl in hepatic cells has never been tested before now. In this in vitro approach, we evaluated the cytotoxic, genotoxic, and apoptotic activities, as well as the effects on cell cycle of PhSeZnCl in two preclinical hepatic models, namely HepG2 and HepaRG cells. Results showed that cell viability of HepG2 and HepaRG cells decreased in a dose-dependent manner, with a more marked effect in HepG2 tumour cells. Moreover, treatment with 50 µg/mL PhSeZnCl caused an increase of primary DNA damage (4 h) and a statistically significant increase of HepG2 cells arrested in G₂/M phase. In addition, it altered mitochondrial membrane potential and induced chromosomal DNA fragmentation (24 h). In HepaRG cells, PhSeZnCl was able to determine a cell cycle-independent induction of apoptosis. Particularly, 50 µg/mL induced mitochondrial membrane depolarization after 24 h and apoptosis after 4 h treatment. Futhermore, all PhSeZnCl concentrations tested determined a significant increase of apoptotic cells after 24 h. Apoptosis was also highlighted by the detection of active Caspase-3 by Western Blot analysis after 24 h exposure. In conclusion, this first toxicological assessment provides new insights into the biological activity of PhSeZnCl in preclinical hepatic models that will be useful in future safety assessment investigation of this compound as a potential pharmaceutical.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-022-00148-y.

Micronutrients and Renal Outcomes: A Prospective Cohort Study

Background: Micronutrients are essential in maintaining normal human physiology. Data regarding the association between micronutrients and renal outcomes in chronic kidney disease (CKD) are lacking. Methods: This prospective observational cohort study enrolled 261 patients with CKD stages 1−5 and 30 subjects with normal renal function. Baseline serum zinc (Zn), selenium (Se), chromium, manganese, and copper, and laboratory tests were performed at enrolment. The primary endpoint was the presence of end-stage renal disease (ESRD) requiring long-term renal replacement therapy. Results: The median follow-up periods of renal and non-renal survivals were 67.78 and 29.03 months, respectively. Multiple linear regression showed that Zn and Se (β ± SE: 24.298 ± 8.616, p = 0.005; 60.316 ± 21.875, p = 0.006, respectively) levels were positively correlated with renal function. Time to ESRD was significantly longer for those with Zn levels ≥1287.24 ng/g and Se levels ≥189.28 ng/g (both p < 0.001). Cox regression analysis identified a higher Zn level as an independently negative predictor of ESRD after adjusting for renal function (hazard ratio, 0.450, p = 0.019). Conclusion: Serum Se and Zn concentrations are positively associated with renal function and better renal outcomes. A higher Zn concentration could independently predict better renal survival.

The health benefits of selenium in food animals: a review

Selenium is an essential trace mineral important for the maintenance of homeostasis in animals and humans. It evinces a strong antioxidant, anti-inflammatory and potential antimicrobial capacity. Selenium biological function is primarily achieved by its presence in selenoproteins as a form of selenocysteine. Selenium deficiency may result in an array of health disorders, affecting many organs and systems; to prevent this, dietary supplementation, mainly in the forms of organic (i.e., selenomethionine and selenocysteine) inorganic (i.e., selenate and selenite) sources is used. In pigs as well as other food animals, dietary selenium supplementation has been used for improving growth performance, immune function, and meat quality. A substantial body of knowledge demonstrates that dietary selenium supplementation is positively associated with overall animal health especially due to its immunomodulatory activity and protection from oxidative damage. Selenium also possesses potential antiviral activity and this is achieved by protecting immune cells against oxidative damage and decreasing viral replication. In this review we endeavor to combine established and novel knowledge on the beneficial effects of dietary selenium supplementation, its antioxidant and immunomodulatory actions, and the putative antimicrobial effect thereof. Furthermore, our review demonstrates the gaps in knowledge pertaining to the use of selenium as an antiviral, underscoring the need for further in vivo and in vitro studies, particularly in pigs.

Amino acid pattern of rumen microorganisms in cattle fed mixed diets-An update

Rumen microorganisms turn small N-containing compounds into amino acids (AA) and contribute considerably to the supply of AA absorbed from the small intestine. Previous studies summarized the literature on microbial AA patterns, most recently in 2017 (Sok et al. Journal of Dairy Science, 100, 5241-5249). The present study intended to identify the microbial AA pattern typical when feeding Central European diets and a maximum proportion of concentrate (PCO; dry matter (DM) basis) of 0.60. Data sets were created from the literature for liquid (LAB)- and particle (PAB)-associated bacteria, total bacteria and protozoa, including 16, 9, 27 and 8 studies and 36, 21, 60 and 18 diets respectively. Because the only differences detected between LAB and PAB were slightly higher Phe and lower Thr percentages in PAB (p < 0.05), results for bacteria were pooled. A further data set evaluated AA-N (AAN) as a proportion of total N in microbial fractions and a final data set estimated protozoal contributions to total microbial N (TMN) flow to the duodenum, which were used to calculate weighted TMN AA patterns. Protozoa showed higher Lys, Asp, Glu, Ile and Phe and lower Ala, Arg, Gly, Met, Ser, Thr and Val proportions than bacteria (p < 0.05). The AAN percentage of total N in bacteria and protozoa showed large, unexplained variations, averaging 79.0% and 70.6% (p > 0.05) respectively. Estimation of protozoal contribution to TMN resulted in a cattle-specific mixed model including PCO and DM intake (DMI) per unit of metabolic body size (kg^0.75 ) as fixed effects (RMSE = 3.77). With moderate PCO and DMI between 80 and 180 g/kg^0.75 , which corresponds to a DMI of approximately 10 to 25 kg in a cow with 650 kg body weight, protozoal contribution ranged between 9% and 26% of TMN. Within this range, the estimated protozoal contribution to TMN resulted in minor effects on the total microbial AA pattern.

Radiation-Induced Oxidation Reactions of 2-Selenouracil in Aqueous Solutions: Comparison with Sulfur Analog of Uracil

One-electron oxidation of 2-selenouracil (2-SeU) by hydroxyl (^●OH) and azide (^●N₃) radicals leads to various primary reactive intermediates. Their optical absorption spectra and kinetic characteristics were studied by pulse radiolysis with UV-vis spectrophotometric and conductivity detection and by the density functional theory (DFT) method. The transient absorption spectra recorded in the reactions of ^●OH with 2-SeU are dominated by an absorption band with an λ_max = 440 nm, the intensity of which depends on the concentration of 2-SeU and pH. Based on the combination of conductometric and DFT studies, the transient absorption band observed both at low and high concentrations of 2-SeU was assigned to the dimeric 2c-3e Se-Se-bonded radical in neutral form (2^●). The dimeric radical (2^●) is formed in the reaction of a selenyl-type radical (6^●) with 2-SeU, and both radicals are in equilibrium with K_eq = 1.3 × 10⁴ M⁻¹ at pH 4 (below the pK_a of 2-SeU). Similar equilibrium with K_eq = 4.4 × 10³ M⁻¹ was determined for pH 10 (above the pK_a of 2-SeU), which admittedly involves the same radical (6^●) but with a dimeric 2c-3e Se-Se bonded radical in anionic form (2^●−). In turn, at the lowest concentration of 2-SeU (0.05 mM) and pH 10, the transient absorption spectrum is dominated by an absorption band with an λ_max = 390 nm, which was assigned to the ^●OH adduct to the double bond at C5 carbon atom (3^●) based on DFT calculations. Similar spectral and kinetic features were also observed during the ^●N₃-induced oxidation of 2-SeU. In principle, our results mostly revealed similarities in one-electron oxidation pathways of 2-SeU and 2-thiouracil (2-TU). The major difference concerns the stability of dimeric radicals with a 2c-3e chalcogen-chalcogen bond in favor of 2-SeU.

Genome-wide identification and characterization of phosphate transporter gene family members in tea plants (Camellia sinensis L. O. kuntze) under different selenite levels

Selenium (Se) is an essential element for human health and an important nutrient for plant growth. Selenite is the main form of Se available to plants in acidic soils. Previous studies have shown that phosphate transporters (PTHs) participate in selenite uptake in plants. Research on the PHT gene family is therefore vital for production of Se-rich products. Here, 23 CsPHT genes were identified in the tea (Camellia sinensis) genome and renamed based on homology with AtPHT genes in Arabidopsis thaliana. The CsPHT genes were divided into four subfamilies: PHT1, PHT3, PHT4, and PHO, containing nine, three, six, and five genes, respectively. Phylogenetic analysis indicated that fewer duplication events occurred in tea plants than in A. thaliana, rice, apple, and poplar. Genes in the same subfamily tended to share similar gene structures, conserved motifs, and potential functions. CsPHT genes were differentially expressed in various tissues and in roots under different Se levels, suggesting key roles in selenite uptake, translocation, and homeostasis. The results illuminate the contributions of CsPHT genes to selenite supply in tea plants, and lay a foundation for follow-up studies on their potential functions in this plant species.

The First Evidence of the Beneficial Effects of Se-Supplementation on In Vitro Cultivated Olive Tree Explants

Selenium is an essential micronutrient that provides important benefits to plants and humans. At proper concentrations, selenium increases plant growth, pollen vitality, the shelf life of fresh products, and seems to improve stress resistance; these effects can certainly be attributed to its direct and indirect antioxidant capacity. For these reasons, in the present work, the effects of selenium at different dosages on in vitro cultivated olive explants were investigated to observe possible positive effects (in terms of growth and vigor) on the proliferation phase. The work was carried out on four different olive cultivars: "San Felice", "Canino", "Frantoio", and "Moraiolo". The explants were cultured in aseptic conditions on olive medium (OM), with the addition of 4 mg·L^-1 of zeatin, 30 g·L^-1 of sucrose, and 7 g·L^-1 of agar. The experimental scheme included a comparison between explants grown with five different concentrations of Na₂SeO₄ (0, 10, 20, 40, and 80 mg L^-1) added to the medium during three successive subcultures. Interesting information has emerged from the results and all varieties responded to different concentrations of Selenium. The optimal Se dosages varied for each cultivar, but in general, Se concentration between 10 and 40 mg L^-1 increased fresh and dry weight of the explants and shoot lengths. Se treatment induced in all cultivars and for all dosages used an increase in total Se content in proliferated explants. Furthermore, as the subcultures proceeded, the ability of the explants to absorb Se did not diminish. The Se content ranged from 8.55 to 114.21 µg kg^-1 plant DW in 'Frantoio', from 9.83 to 94.85 µg kg^-1 plant DW in 'Moraiolo', from 19.84 to 114.21 µg kg^-1 plant DW in 'Canino', and from 20.97 to 95.54 µg kg^-1 plant DW in 'San Felice'. In general, the effect of selenium tends to decrease with the progress of subcultures and this suggests a sort of "adaptation" effect of the explants to its presence. The present study highlights for the first time the possibility of using in vitro cultures as biotechnological support to study supplementation with selenium and its effects on in vitro olive plant growth.

Selenium, as selenite, prevents adipogenesis by modulating selenoproteins gene expression and oxidative stress-related genes

OBJECTIVES

The aim of this study was to assess the effect of the micronutrient selenium, as inorganic selenite, on adipocytes differentiation, and to identify underlying molecular mechanisms to advance the understanding of basic cellular mechanisms associated with adipogenesis.

METHODS

The effect of sodium selenite (Na₂SeO₃) on cell viability (bromide 3-[4,5-dimethylthiazol-2-yl]-2,5-difeniltetrazol [MTT] assay) in preadipocytes, lipid accumulation (oil red O [ORO] assay) and intracellular reactive oxygen species (ROS, [NBT assay]) in mature adipocytes, as well as explore molecular mechanisms via gene expression analyses (real-time quantitative polymerase chain reaction), before and after differentiation, was investigated using 3T3-L1 murine preadipocytes.

RESULTS

Selenite (100, 200, and 400 nM) significantly decreased lipid accumulation during differentiation compared with untreated adipocytes (P < 0.05, 0.001, and 0.01, respectively). Preadipocytes exposure (48 h) to selenite caused an increase in glutathione peroxidase 1 (Gpx1) gene expression in a dose-dependent manner. Adipogenesis significantly increased intracellular reactive oxygen species levels (P < 0.05) while decreasing gene expression of antioxidant enzymes (Gpx1: P < 0.05) and significantly increasing gene expression of regulators of lipid catabolism (type II iodothyronine deiodinase [Dio2], P < 0.01) and markers of differentiation (eg, selenium-binding protein 1 [Selenbp1], peroxisome proliferator activated receptor gamma [Pparg], CCAAT/enhancer binding protein alpha [Cebpa], and fatty acid binding protein 4 [Fab4]) compared with preadipocytes (P < 0.01, 0.01, 0.01, and 0.001, respectively). Selenite exposure (200 nM) caused a significant increase in Gpx1, selenoprotein W (Selenow) and selenoprotein P (Selenop) gene expression, in adipocytes compared with untreated ones (P < 0.01, 0.001, and 0.05, respectively) with a significant decrease in heme oxygenase 1 (Ho-1), cyclooxygenase 2 (Cox2), Dio2, and Fabp4 gene expression (P < 0.001, 0.05, 0.05, and 0.01, respectively).

CONCLUSIONS

Selenium, as selenite, prevented adipogenesis through increasing antioxidant selenoprotein expression, leading to decreased inflammatory markers and, subsequently, to a decrease in differentiation and lipid deposition. These findings, if demonstrated in vivo, could provide valuable data for novel dietary approaches to prevent obesity.

Selenium source and level on performance, selenium retention and biochemical responses of young broiler chicks

Background

Selenium (Se) has been recognized as an essential micronutrient for nearly all forms of life. In recent decades, broiler responses to dietary Se supplemental levels and sources have received considerable attention. On environmental grounds, organic trace mineral utilization in practical broiler feeds has been defended due to its higher bioavailability. In such feeds, trace minerals are provided simultaneously in the same supplement as inorganic salts or organic chelates, a fact commonly ignored in assays conducted to validate organic trace mineral sources. The current assay aimed to investigate growth and biochemical responses, as well as Se retention of growing chicks fed diets supplemented with organic and inorganic Se levels and where the trace minerals (zinc, copper, manganese, and iron) were provided as organic chelates or inorganic salts according to Se source assessed. In so doing, a 2 × 5 factorial arrangement was used to investigate the effects of sodium selenite (SS) and selenium-yeast (SY) supplemented in feeds to provide the levels of 0, 0.08, 0.16, 0.24, and 0.32 mg Se/kg.

Results

Chicks fed selenium-yeast diets had body weight (BW), and average daily gain (ADG) maximized at 0.133 and 0.130 mg Se/kg, respectively. Both Se sources linearly increased (P < 0.05) the glutathione peroxidase (GSH-Px) activity in chick blood but higher values were observed in sodium selenite fed chicks (P < 0.05). Both Se sources influenced thyroid hormone serum concentrations (P < 0.05). Chicks fed SY exhibited greater retention of Se in the feathers (P < 0.05). Relative bioavailability of selenium yeast compared with SS for the Se content in carcass, feathers, total and Se retention were, 126, 116, 125 and 125%, respectively. SY supplementation resulted in lower liver Se concentration as Se supplementation increased (P < 0.05).

Conclusions

Based on performance traits, the supplemental level of organic Se as SY in organic trace minerals supplement to support the maximal growth of broiler chicks is 0.133 mg Se/kg.

Exploring the new dimensions of selenium research to understand the underlying mechanism of its uptake, translocation, and accumulation

Selenium (Se) is a vital mineral for both plants and animals. It is widely distributed on the earth's crust and is taken up by the plants as selenite or selenate. Plants substantially vary in their physiological response to Se. The amount of Se in edible plants is genetically controlled. Its availability can be determined by measuring its phytoavailability in soil. The low concentration of Se in plants can help them in combating stress, whereas higher concentrations can be detrimental to plant health and in most cases it is toxic. Thus, solving the double-edged sword problem of nutritional Se deficiency and its elevated concentrations in environment requires a better understanding of Se uptake and metabolism in plants. The studies on Se uptake and metabolism can help in genetic biofortification of Se in plants and also assist in phytoremediation. Moreover, Se uptake and transport, especially biochemical pathways of assimilation and incorporation into proteins, offers striking mechanisms of toxicity and tolerance. These developments have led to a revival of Se research in higher plants with significant break throughs being made in the previous years. This review explores the new dimensions of Se research with major emphasis on key research events related to Se undertaken in last few years. Further, we also discussed future possibilities in Se research for crop improvement.

Analysis of Bioavailability and Induction of Glutathione Peroxidase by Dietary Nanoelemental, Organic and Inorganic Selenium

Dietary organic selenium (Se) is commonly utilized to increase formation of selenoproteins, including the major antioxidant protein, glutathione peroxidase (GPx). Inorganic Se salts, such as sodium selenite, are also incorporated into selenoproteins, and there is evidence that nanoelemental Se added to the diet may also be effective. We conducted two trials, the first investigated inorganic Se (selenite), organic Se (L-selenomethionine) and nanoelemental Se, in conventional mice. Their bioavailability and effectiveness to increase GPx activity were examined. The second trial focused on determining the mechanism by which dietary Se is incorporated into tissue, utilising both conventional and germ-free (GF) mice. Mice were fed a diet with minimal Se, 0.018 parts per million (ppm), and diets with Se supplementation, to achieve 0.07, 0.15, 0.3 and 1.7 ppm Se, for 5 weeks (first trial). Mass spectrometry, Western blotting and enzymatic assays were used to investigate bioavailability, protein levels and GPx activity in fresh frozen tissue (liver, ileum, plasma, muscle and feces) from the Se fed animals. Inorganic, organic and nanoelemental Se were all effectively incorporated into tissues. The high Se diet (1.7 ppm) resulted in the highest Se levels in all tissues and plasma, independent of the Se source. Interestingly, despite being ~11 to ~25 times less concentrated than the high Se, the lower Se diets (0.07; 0.15) resulted in comparably high Se levels in liver, ileum and plasma for all Se sources. GPx protein levels and enzyme activity were significantly increased by each diet, relative to control. We hypothesised that bacteria may be a vector for the conversion of nanoelemental Se, perhaps in exchange for S in sulphate metabolising bacteria. We therefore investigated Se incorporation from low sulphate diets and in GF mice. All forms of selenium were bioavailable and similarly significantly increased the antioxidant capability of GPx in the intestine and liver of GF mice and mice with sulphate free diets. Se from nanoelemental Se resulted in similar tissue levels to inorganic and organic sources in germ free mice. Thus, endogenous mechanisms, not dependent on bacteria, reduce nanoelemental Se to the metabolite selenide that is then converted to selenophosphate, synthesised to selenocysteine, and incorporated into selenoproteins. In particular, the similar efficacy of nanoelemental Se in comparison to organic Se in both trials is important in the view of the currently limited cheap sources of Se.

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.

Synergetic catalysis of Se and Cu allowing diethoxylation of halomethylene ketones using O2 as the mild oxidant

Catalyzed by PhSe(O)OH/Cu(OAc)₂, sp³-C–H alkylation of bromomethylene ketones produced useful α-carbonyl acetals under mild conditions. Bromo-containing substrates could release HBr during the reaction, avoiding the use of acidic additives.

Quantitative Proteomics Reveals UGA-Independent Misincorporation of Selenocysteine throughout the Escherichia coli Proteome

Selenocysteine is cotranslationally inserted into polypeptide chains by recoding the stop codon UGA. However, selenocysteine has also been found to be misincorporated into a small number of proteins displacing cysteines in previous studies, but such misincorporation has not yet been examined at the proteome level thoroughly. We performed label-free quantitative proteomics analysis on Escherichia coli grown in a high-selenium medium to obtain a fuller picture of selenocysteine misincorporation in its proteome. We found 139 misincorporation sites, including 54 recurred in all biological replicates, suggesting that some cysteine sites are more prone to be misincorporated than others. However, sequence and evolutionary conservation analysis showed no clear pattern among these misincorporation sites. We hypothesize that misincorporations occur randomly throughout the proteome, but the degradation rate of such misincorporated proteins varies depending on the impact of the misincorporation on protein function and stability, leading to the differential detectability of misincorporated sites by proteomics. Our hypothesis is further supported by two observations: (1) cells cultured with severely limited sulfur still retained a substantial proportion of normal cysteine counterparts of all of the found misincorporated proteins and (2) proteins involved in protein folding and proteolysis were highly upregulated in high-selenium culture.

Selenium and at-risk pregnancy: challenges and controversies

Selenium (Se), an essential trace element, is inserted as selenocysteine into an array of functional proteins and forms the core of various enzymes that play a cardinal role in antioxidant defense mechanisms, in redox regulation, and in thyroid hormone metabolism. Variations in plasma Se are due to nutritional habits, geographic and ethnic differences, and probably to genetic polymorphisms, the latter still to be conclusively established. Se concentrations were reported to be low in women of reproductive age in the UK, decreasing further during pregnancy, this resulting in low plasma and placental antioxidant enzyme activities. Since low serum Se levels have been found in women with preeclampsia, it has been hypothesized that low maternal Se status during early gestation may be an indicator of preterm birth. Moreover, it is documented that Se administration during pregnancy tendentially reduced the markers of thyroid autoimmunity and the incidence of maternal hypothyroidism in the postpartum period. Importantly, low Se levels in pregnant women affect fetal growth and augment the risk of delivering a small-for-gestational age infant by reducing placental antioxidant defense, while low Se in the third trimester is thought to indicate increased demands by the placenta, an issue which requires further confirmation. There is evidently a need for double-blind, placebo-controlled studies to better determine the efficacy and safety of Se supplementation in pregnancy at high risk for complications, and for measurement of Se levels or of selenoprotein P, the most reliable parameter of Se status, particularly in selenopenic regions.

The use of biofortification for production of selenium enriched garden pea

Biofortification of crops with selenium is one of the possible manners on how to increase selenium intake by humans. The effect of selenium fertilization in relation to selenium enrichment of pea and following the phytotoxicity symptoms in garden pea plants was studied. Pot experiments were established with a control variant without selenium addition and four variants where selenium was applied as sodium selenate into the soil in four different concentrations (1 - 6 mg Se.kg-1) before seeding. Garden pea was grown in pots for 60 days and then plant material was dried and submitted to analysis. The total content of selenium was determined by the ZET-AAS method in the roots, above-ground parts of the plant (stems, leaves, extracted pods), and in seeds of a pea. Dean-Dixon´s test and paired t-test (α = 0.05) were used for statistical evaluation of the results. Transfer factors were calculated as a ratio between selenium content (mg.kg-1) in individual plant material and soil. Transfer indexes were calculated as a ratio between selenium content (mg.kg-1) in seeds and roots. The results showed that with the increasing addition of the Se to the soil, its contents in all parts of the plant proportionally increased. The content of the Se increased in the roots 43 to 173-fold, in the above-ground parts 79 to 372-fold, and in the seeds Se was accumulated 130 to 415 times more compared to control. Transfer factors and transport indexes were expressed. Transfer factors for pea varied from 11.05 to 19.25 in the case of Se transfer to the whole pea biomass. In the case of the Se transfer from soil to pea seeds, the highest transfer showed variant with addition 1 mg Se.kg-1 and the transfer factor gradually decreased with increasing addition of Se. Based on the amount of biomass produced, the experiments statistically confirmed the phytotoxicity of higher doses (4 and 6 mg Se.kg-1) of selenium to plants. The highest transport index values are shown variants with the Se addition 1 and 2 mg Se.kg-1 (2.03 and 1.77, respectively). In these variants, Se was used the most efficiently. Our results showed that the best biofortification results were obtained in experimental variants with the lower selenium additions (1 and 2 mg Se.kg-1).

Selenium Enrichment Enhances the Quality and Shelf Life of Basil Leaves

The biofortification of leafy vegetables with selenium (Se) is a good way to increase human dietary Se intake. In addition, selenium delays plant senescence by enhancing the antioxidant capacity of plant tissues, decreasing postharvest losses. We investigated the effects of selenium addition on the production and quality of sweet basil (Ocimum basilicum) leaves of two harvesting phases, hereafter referred to as cuts, during the crop cycle. Plants were hydroponically grown and treated with 0 (control), 4, 8 and 12 mg Se L⁻¹ as selenate. To evaluate the growth, nutritional value and quality of the basil leaves, selected qualitative parameters were determined at harvest and after five days of storage. Application of Se at varying rates (4, 8 and 12 mg L⁻¹) was associated with an increased leaf selenium concentration in the first, but not the second cut. The application of Se significantly affected the antioxidant capacity as well as the total phenol and rosmarinic acid contents at harvest. The reduction in ethylene production observed in the plants at 4 mg Se L⁻¹ after five days of storage suggests that this Se treatment could be used to prolong and enhance the shelf-life of basil. The daily consumption of 10 g of Se-enriched basil leaves, which, as an example, are contained in a single portion of Italian pesto sauce, would also satisfy the recommended selenium supplementation in humans.

Beneficial antioxidant status of piglets from sows fed selenomethionine compared with piglets from sows fed sodium selenite

BACKGROUND

Studies in mammals proved dietary organic selenium (Se) being superior to inorganic Se regarding effects on growth performance, antioxidative status, immune response, and Se homeostasis. However, the picture of possible effects of different Se sources and - levels can be expanded. The present field study evaluated the effects on weight gain, hematological and selected biochemical variables as well as plasma concentrations of vitamin E (vitE), total Se and selenobiomolecules in piglets throughout the suckling period.

METHODS

Piglets were monitored from birth to 38 days of age (d). The mother sows' diets were enriched with l-selenomethionine (SeMet-0.26 and -0.43 mg Se/kg feed) or sodium selenite (NaSe-0.40 and -0.60 mg Se/kg feed) from 1 month prior to farrowing until the end of lactation period. Piglets received pelleted feed supplemented with Se similarly to the sows' diets from one week of age. Selenite at 0.40 mg Se/kg (NaSe-0.40) represents a common Se source and -level in pig feed and served as control diet.

RESULTS

From 24d, piglets in SeMet-groups had higher mean body weight (BW) compared with piglets from sows fed NaSe-0.40. Furthermore, from five-d and above, piglets from sows fed NaSe-0.60 had significantly higher BW than offspring from sows fed NaSe-0.40. Neonatal piglets in group SeMet-0.43 had significantly lower red blood cell counts (RBC), hemoglobin (Hgb) and hematocrit (Hct) concentrations compared with piglets from sows fed with NaSe-0.40. Neonatal and 5d-old piglets in group SeMet-0.26 showed higher gamma-glutamyl transferase activity than piglets in group NaSe-0.40. From five d and above, group NaSe-0.60 excelled with increased specific hematological variables culminating at age 38d with increased Hct, mean corpuscular volume (MCV), and MC hemoglobin (MCH) as well as increased activities of aspartate transaminase and lactate dehydrogenase compared with the other groups. Generally, offspring in the SeMet groups had higher total Se-concentrations in plasma than those from sows fed selenite, and showed a dose-response effect on plasma Se-concentrations. Furthermore, SeMet-fed piglets had higher plasma levels of the selenoproteins (Sel) glutathione peroxidase 3 (GPx3) and SelP as well as selenoalbumin. Plasma vitE levels were significantly negatively correlated with RBC throughout trial period.

CONCLUSIONS

Maternal supplementation with SeMet during gestation influenced hematology and clinical biochemistry in neonatal piglets in a different way than in offspring from sows receiving selenite enriched diets. Growth performance was positively influenced by both dietary Se source and Se level. Higher plasma levels of GPx3 observed in piglets receiving SeMet probably improved the protection against birth or growth related oxidative stress. These might prime the piglets for demanding situations as indicated by higher weight gain in offspring from sows fed with SeMet-supplemented diets. Our results on some enzyme activities might indicate that piglets fed NaSe-0.60 had to cope with increased levels of oxidative stress compared with those originating from sows fed SeMet or lower dietary levels of selenite. We assume that combining inorganic and organic Se sources in complete feed for breeding sows might be beneficial fro reproduction and the offspring's performance.

Selenium nanovirus and its cytotoxicity in selenite-exposed higher living organisms

Selenium (Se) is an essential micronutrient in living organisms, having a narrow margin between essential and potentially toxic intake/exposure. Thus, the biochemistry of Se in living organisms must be studied in-depth to determine the underlying mechanism of Se cytotoxicity. In this study, we report the emergence of selenium nanovirus (SeNVs) in selenite-exposed fish (freshwater and saltwater) and plants (dryland) and its toxicity in them. SeNVs were found in both the abdomen and tail of Oryzias melastigma and saltwater Rhodeus ocellatus, which led to their death. The occurrence of the intracellular assembly of SeNVs was observed in the roots and leaves of corn Zea mays, but not in those of Limnobium laevigatum. SeNVs led to the death of Z. mays but caused chronic toxicity in L. laevigatum. SeNVs should be a system or structure that dissipates the intracellular redox gradients of the host cells, with simple information consisting Se-O, Se-N, or Se-S bond, that would ensure elemental Se ligand binding with nearly specific biomolecules in host cells, thereby maintaining their composition and stabilizing their structure. The multiple toxic effects of Se, therefore, could be the consequence of increase of entropy in the host cells caused by the intracellular assembly of SeNVs. This study may provide an insight into the underlying mechanism of Se in environmental toxicology and its applications in human health.

Selenocysteine as a Substrate, an Inhibitor and a Mechanistic Probe for Bacterial and Fungal Iron-Dependent Sulfoxide Synthases

Sulfoxide synthases are non-heme iron enzymes that participate in the biosynthesis of thiohistidines, such as ergothioneine and ovothiol A. The sulfoxide synthase EgtB from Chloracidobacterium thermophilum (CthEgtB) catalyzes oxidative coupling between the side chains of N-α-trimethyl histidine (TMH) and cysteine (Cys) in a reaction that entails complete reduction of molecular oxygen, carbon-sulfur (C-S) and sulfur-oxygen (S-O) bond formation as well as carbon-hydrogen (C-H) bond cleavage. In this report, we show that CthEgtB and other bacterial sulfoxide synthases cannot efficiently accept selenocysteine (SeCys) as a substrate in place of cysteine. In contrast, the sulfoxide synthase from the filamentous fungus Chaetomium thermophilum (CthEgt1) catalyzes C-S and C-Se bond formation at almost equal efficiency. We discuss evidence suggesting that this functional difference between bacterial and fungal sulfoxide synthases emerges from different modes of oxygen activation.

Fluorescence imaging of lysosomal hydrogen selenide under oxygen-controlled conditions

Hydrogen selenide (H₂Se), a central metabolite of Se supplements, displays critical biological functions in many physiological and pathological processes. To better understand its comprehensive function, especially those exerted in subcellular organelles, the development of specific assays is urgently needed. However, the methodology to detect H₂Se is poorly developed. Here, we present a concise design strategy to obtain an activatable fluorescent probe (Se-1) for H₂Se by utilizing an intramolecular photoinduced electron transfer (PET) process to switch the fluorescence. The probe is able to selectively react with H₂Se without interference from intracellular reactive species, and has been successfully used to image the H₂Se content in lysosomes. Additionally, with the aid of Se-1, we demonstrated that lysosomal H₂Se can be generated and can gradually accumulate in HepG2 cells under hypoxic conditions. These applications make Se-1 a potential new candidate for deciphering the biological effects of H₂Se on lysosomes in biology and pathology.

Selenylation Modification of Atractylodes macrocephala Polysaccharide and Evaluation of Antioxidant Activity

The Atractylodes macrocephala polysaccharide (AMP) was extracted by water extracting-alcohol precipitating method and further purified by DEAE column. After that, the polysaccharides were modified by nitric acid-sodium selenite method, and nine kinds of selenizing AMPs (sAMPs) were obtained, namely, from sAMP1 to sAMP9. AMP and sAMP were characterized using FTIR spectrometry. Then their antioxidant activities in vitro were measured by free radical-scavenging test. Among these, sAMP6 presented the strongest antioxidant effect. For the test in vivo, the chickens at day 14 vaccinated with ND vaccine were repeatedly vaccinated at day 28. The chickens in sAMP and AMP were injected respectively with 1 mg of sAMP6 and AMP and, in vaccination control (VC) and BC groups, injected with equal volume of normal saline. Respectively, after the first vaccine, on days 7, 14, 21, and 28, the serum GSH-Px and SOD activities and MDA content were determined. The results suggested that sAMP6 could significantly promote GSH-Px and SOD activities and decrease MDA content. All these results indicated that selenylation modification could significantly enhance the antioxidant activity of AMP.

Effects of sodium selenite and L-selenomethionine on feed intake, clinically relevant blood parameters and selenium species in plasma, colostrum and milk from high-yielding sows

A field study in periparturient sows fed different dietary concentrations of either sodium selenite or L-selenomethionine (SeMet) was conducted to evaluate feed intake, haematological and biochemical parameters as well as to describe some key selenium (Se) species, namely selenoprotein P (SelP), selenoalbumin (SeAlb) and selenomethionine (SeMet) as well as total Se in plasma, colostrum and milk. Thirty-two sows were allotted to four treatments from 30 days (d) prepartum throughout on average a 32 d lactation period. Sodium selenite supplemented diets contained 0.40 and 0.60 mg Se/kg feed, while SeMet supplemented feed contained 0.26 and 0.43 mg Se/kg feed. Concentrations of sodium selenite and SeMet in complete feed exceeded the upper limits for total dietary Se and added organic Se, respectively, according to the European Union legislation. Blood samples were collected at initiation of the study, at farrowing and at weaning. Colostrum samples were collected at farrowing and milk samples at weaning. Se species were subjected to liquid chromatography, and total Se and Se species were determined using inductively coupled plasma mass spectrometry. The SeMet supplemented diets resulted in higher feed intake and in higher levels of total Se, SelP, SeAlb and SeMet in colostrum compared with sows fed sodium selenite. Similar results were obtained for levels of total Se and SeMet in milk at weaning. The higher dietary sodium selenite concentration in sows' feed did not increase the Se transfer into colostrum or milk when compared with those receiving the lower level of sodium selenite. However, the increase in serum-Zn from initiation until farrowing, observed in sows fed SeMet as well as the higher glutamate dehydrogenase activity in sodium selenite supplemented sows in this period might indicate a higher requirement of antioxidant defence in sodium selenite-supplemented sows. To our knowledge, the present data on Se species in plasma, colostrum and milk of sows represent the most complete investigation of Se in sows conducted to date. A higher amount of the above-mentioned Se species in the colostrum of sows supplemented with SeMet might strengthen the piglets' antioxidative system and passive immunity as well as improve their average daily weight gain. The higher feed intake in sows fed diets supplemented with SeMet is an interesting finding that warrants further investigation.

Porous Se@SiO2 nanospheres attenuate ischemia/reperfusion (I/R)-induced acute kidney injury (AKI) and inflammation by antioxidative stress

Objectives

Acute kidney injury (AKI) is a growing global health concern, and is associated with high rates of mortality and morbidity in intensive care units. Se is a trace element with antioxidant properties. This study aimed to determine whether porous Se@SiO₂ nanospheres could relieve oxidative stress and inflammation in ischemia/reperfusion (I/R)-induced AKI.

Methods

Male 6- to 8-week-old C57bl/6 mice were divided into four groups: sham + saline, sham + Se@SiO₂, I/R + saline, and I/R + Se@SiO₂. Mice in the I/R groups experienced 30 minutes of bilateral renal I/R to induce an AKI. Porous Se@SiO₂ nanospheres (1 mg/kg) were intraperitoneally injected into mice in the I/R + Se@SiO₂ group 2 hours before I/R, and the same dose was injected every 12 hours thereafter. Hypoxia/reoxygenation (H/R) was used to mimic I/R in vitro. PBS was used as a control treatment. Human kidney 2 cells were seeded into 12-well plates (5×10⁵ cells/well) and divided into four groups: control + PBS group, control + Se@SiO₂ group, H/R + PBS group, and H/R + Se@SiO₂ group (n=3 wells). We then determined the expression levels of ROS, glutathione, inflammatory cytokines and proteins, fibrosis proteins, and carried out histological analysis upon kidney tissues.

Results

In vitro, intervention with porous Se@SiO₂ nanospheres significantly reduced levels of ROS (P<0.05), inflammatory cytokines (P<0.05), and inflammation-associated proteins (P<0.05). In vivo, tubular damage, cell apoptosis, and interstitial inflammation during AKI were reduced significantly following treatment with porous Se@SiO₂ nanospheres. Moreover, the occurrence of fibrosis and tubular atrophy after AKI was attenuated by porous Se@SiO₂ nanospheres.

Conclusion

Porous Se@SiO₂ nanospheres exhibited a protective effect in I/R-induced AKI by resisting oxidative stress and inflammation. This suggests that porous Se@SiO₂ nanospheres may represent a new therapeutic method for AKI.

Acute toxicity of selenate and selenite and their impacts on oxidative status, efflux pump activity, cellular and genetic parameters in earthworm Eisenia andrei

Selenium (Se) is an essential element for humans, animals, and certain lower plants, but can be toxic at high concentration. Even though Se is potentially toxic, little information is available about the effects of Se on soil animals. The aim of this study was to assess the impact of different concentrations of two Se forms, selenate and selenite, on earthworm Eisenia andrei. In order to obtain comprehensive overview on the Se effects, different parameters were measured. Namely, acute toxicity, apoptosis, efflux pump activity, different enzymatic and non-enzymatic biomarkers (acetylcholinesterase, carboxylesterase, glutathione S-transferase, catalase, glutathione reductase and superoxide dismutase activities, lipid peroxidation level and GSH/GSSG ratio) and expression of genes involved in oxidative and immune response have been investigated. Additionally, measurement of metallothioneins concentration and concentration of Se in exposed earthworms has been also performed. The assessment of acute toxicity showed a greater sensitivity of E. andrei to selenite exposure, whereas Se concentration measurements in earthworms showed higher accumulation of selenate form. Both Se forms caused inhibition of the efflux pump activity. Decrease in superoxide dismutase activity and increase in lipid peroxidation and glutathione reductase activity indicate that Se has a significant impact on the oxidative status of earthworms. Selenate exposure caused an apoptotic-like cell death in the coelomocytes of exposed earthworms, whereas decreased mRNA levels of stress-related genes and antimicrobial factors were observed upon the exposure to selenite. The obtained data give insight into the effects of two most common forms of Se in soil on the earthworm E. andrei.

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.

The thioredoxin system as a target for mercury compounds

BACKGROUND

Mercury interaction with selenium in vivo has been recognized for >50 years. Several researchers attempted to use selenium to mitigate the detrimental effects of mercurial compounds but the results were controversial. Selenium pools in living organisms are quite low and the high affinity of mercury to bind selenols pointed out selenoproteins as possible targets of toxicity. Such was the case of the selenoenzyme thioredoxin reductase (TrxR) which is an integrant part of the thioredoxin system. Given the important role of this redox system for cellular functioning and the high affinity of mercury for TrxR's active site, this interaction can be key to understand the mechanism by which Hg causes cell death.

SCOPE OF THE REVIEW

This review discusses the current state of knowledge concerning the interaction between mercury compounds and the thioredoxin system, its implications for the development of toxicity and the effects of selenium co-exposure.

MAJOR CONCLUSIONS

The mechanism of toxicity of mercurials is a complex chain of events starting with inhibition of the selenoenzyme, TrxR. Selenium supplementation protects TrxR from the toxicity of inorganic forms of mercury (i.e., Hg(II)) to a certain extent, but not from methylmercury. When TrxR is inhibited, thioredoxin is reduced by alternative mechanisms involving glutathione and glutaredoxin and only when this pathway is hampered does cell death occur.

GENERAL SIGNIFICANCE

Understanding the molecular mechanism of mercury toxicity and the mechanisms of enzymatic compensation allows the design of mitigation strategies and, since TxrR and Trx exist in the plasma, puts forward the possibility for future use of changes in activity/expression of these enzymes as biomarkers of mercury toxicity, thus refining the risk assessment process.

Selenium analogs of phenoxypropionic and phenoxyacetic herbicides

Selenium analogs of phenoxyacetic herbicides, namely 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP), 2-(2,4-dichlorophenoxy)acetic acid (2,4-D), 2-(4-chloro-2-methylphenoxy)propionic acid (MCPP), 2-(4-chloro-2-methylphenoxy)acetic acid (MCPA), 2-(2,4,5-trichlorophenoxy)propionic acid (2,4,5-TP), and 2-(2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), were synthesized in two steps. Iodo aryl derivatives were dimerized with elemental selenium in the presence of CuO as catalyst to the corresponding diselenides. Diselenides were reduced with NaBH4 to a selenide anion and condensed with either propionic or chloroacetic acid to achieve the selenium analogs of phenoxyacetic herbicides. These selenium analogs show moderate herbicidal and fungistatic activity.

Promoter analysis and functional implications of the selenium binding protein (SBP) gene family in Arabidopsis thaliana

Selenium Βinding Protein (SBP, originally termed SBP56) was identified in mouse liver as a cytosolic protein that could bind radioactive selenium. SBPs are highly conserved proteins present in a wide array of species across all kingdoms and are likely to be involved in selenium metabolism. In Arabidopsis, the selenium binding protein (SBP) gene family comprises three genes (AtSBP1, AtSBP2 and AtSBP3). AtSBP1 and AtSBP2 are clustered in a head-to-tail arrangement on chromosome IV, while AtSBP3 is located on chromosome III. In this work, we studied the promoter activity of the Arabidopsis SBP genes, determined their tissue specificity and showed that they are differentially regulated by sodium selenite and sodium selenate. All three SBP genes are upregulated in response to externally applied selenium compounds and the antioxidant NAC selectively downregulates SBP2. Although the effect on SBP2 levels was the most prominent, in all cases, the concurrent exposure of plants to selenite and the antioxidant supressed the expression of the SBP genes. We provide evidence that (at least) SBP1 expression is tightly linked to detoxification processes related to oxidative stress, since it is downregulated in the presence of NAC in selenium-treated plants. Furthermore, our results suggest that SBP genes may participate in the mechanisms that sense redox imbalance.