The properties, functions, and use of selenium compounds in living organisms

Arsenic bioaccumulation and biotransformation in different tissues of Nile tilapia (Oreochromis niloticus): A comparative study between As(III) and As(V) exposure and evaluation of antagonistic effects of selenium

The speciation of arsenic in fish has been widely investigated, but bioaccumulation and biotransformation of inorganic As in different tissues of Nile tilapia (Oreochromis niloticus) are not fully understood. The present study aimed to investigate the bioaccumulation of As in Nile tilapia, as well as to evaluate the distribution of the main arsenic species (As(III), As(V), MMA, DMA, and AsB) in liver, stomach, gill, and muscle, after controlled exposures to As(III) and As(V) at concentrations of 5.0 and 10.0 mg L-1 during periods of 1 and 7 days. Total As was determined by inductively coupled plasma mass spectroscopy (ICP-MS). For both exposures (As(III) and As(V)), the total As levels after 7-day exposure were highest in the liver and lowest in the muscle. Overall, the Nile tilapia exposed to As(III) showed higher tissue levels of As after the treatments, compared to As(V) exposure. Speciation of arsenic present in the tissues employed liquid chromatography coupled to ICP-MS (LC-ICP-MS), revealing that the biotransformation of As included As(V) reduction to As(III), methylation to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), and subsequent conversion to nontoxic arsenobetaine (AsB), which was the predominant arsenic form. Finally, the interactions and antagonistic effects of selenium in the bioaccumulation processes were tested by the combined exposure to As(III), the most toxic species of As, together with tetravalent selenium (Se(IV)). The results indicated a 4-6 times reduction of arsenic toxicity in the tilapia.

Effects of selenium enrichment on fermentation characteristics, selenium content and microbial community of alfalfa silage

BACKGROUND

Selenium is essential for livestock and human health. The traditional way of adding selenium to livestock diets has limitations, and there is a growing trend to provide livestock with a safe and efficient source of selenium through selenium-enriched pasture. Therefore, this study was conducted to investigate the effects of selenium enrichment on fermentation characteristics, selenium content, selenium morphology, microbial community and in vitro digestion of silage alfalfa by using unenriched (CK) and selenium-enriched (Se) alfalfa as raw material for silage.

RESULTS

In this study, selenium enrichment significantly increased crude protein, soluble carbohydrate, total selenium, and organic selenium contents of alfalfa silage fresh and post-silage samples, and it significantly decreased neutral detergent fiber and acid detergent fiber contents (p < 0.05). Selenium enrichment altered the form of selenium in plants, mainly in the form of SeMet and SeMeCys, which were significantly higher than that of CK (p < 0.05). Selenium enrichment could significantly increase the lactic acid content, reduce the pH value, change the diversity of bacterial community, promote the growth of beneficial bacteria such as Lactiplantibacillus and inhibit the growth of harmful bacteria such as Pantoea, so as to improve the fermentation quality of silage. The in vitro digestibility of dry matter (IVDMD), in vitro digestibility of acid detergent fibers (IVADFD) and in vitro digestibility of acid detergent fibers (IVNDFD) of silage after selenium enrichment were significantly higher than those of CK (p < 0.05).

CONCLUSION

This study showed that the presence of selenium could regulate the structure of the alfalfa silage bacterial community and improve alfalfa silage fermentation quality. Selenium enrichment measures can change the morphology of selenium in alfalfa silage products, thus promoting the conversion of organic selenium.

Selenium as a Modulator of Redox Reactions in the Prevention and Treatment of Cardiovascular Diseases

Cardiovascular diseases stand as the predominant global cause of mortality, exerting a profound impact on both life expectancy and its quality. Given their immense public health burden, extensive efforts have been dedicated to comprehending the underlying mechanisms and developing strategies for prevention and treatment. Selenium, a crucial participant in redox reactions, emerges as a notable factor in maintaining myocardial cell homeostasis and influencing the progression of cardiovascular disorders. Some disorders, such as Keshan disease, are directly linked with its environmental deficiency. Nevertheless, the precise extent of its impact on the cardiovascular system remains unclear, marked by contradictory findings in the existing literature. High selenium levels have been associated with an increased risk of developing hypertension, while lower concentrations have been linked to heart failure and atrial fibrillation. Although some trials have shown its potential effectiveness in specific groups of patients, large cohort supplementation attempts have generally yielded unsatisfactory outcomes. Consequently, there persists a significant need for further research aimed at delineating specific patient cohorts and groups of diseases that would benefit from selenium supplementation.

Modulation of oxidative stress machinery determines the contrasting ability of cyanobacteria to adapt to Se(VI) or Se(IV)

Excess of selenium (Se) in aquatic ecosystems has necessitated thorough investigations into the effects/consequences of this metalloid on the autochthonous organisms exposed to it. The molecular details of Se-mediated adaptive response remain unknown in cyanobacteria. This study aims to uncover the molecular mechanisms driving the divergent physiological responses of cyanobacteria on exposure to selenate [Se(VI)] or selenite [Se(IV)], the two major water-soluble oxyanions of Se. The cyanobacterium, Anabaena PCC 7120, withstood 0.4 mM of Se(VI), whereas even 0.1 mM of Se(IV) was detrimental, affecting photosynthesis and enhancing endogenous ROS. Surprisingly, Anabaena pre-treated with Se(VI), but not Se(IV), showed increased tolerance to oxidative stress mediated by H2O2/methyl viologen. RNA-Seq analysis showed Se(VI) to elevate transcription of genes encoding anti-oxidant proteins and Fe-S cluster biogenesis, whereas the photosynthesis-associated genes, which were mainly downregulated by Se(IV), remained unaffected. Specifically, the content of typical 2-Cys-Prx (Alr4641), a redox-maintaining protein in Anabaena, was elevated with Se(VI). In comparison to the wild-type, the Anabaena strain over-expressing the Alr4641 protein (An4641+) showed enhanced tolerance to Se(VI) stress, whereas the corresponding knockdown-strain (KD4641) was sensitive to this stressor. Incidentally, among these strains, only An4641+ was better protected from the ROS-mediated damage caused by high dose of Se(VI). These results suggest that altering the content of the antioxidant protein 2-Cys-Prx, could be a potential strategy for modulating resistance to selenate. Thus, involvement of oxidative stress machinery appears to be the major determinant, responsible for the contrasting physiological differences observed in response to selenate/selenite in cyanobacteria.

One-step novel synthesis of alginate-based SeNPs of cluster beans by reduction of Se(IV) by vitamin C in aqueous media

Alginate powder was applied as stabilizer and capping agent surfactant in green synthesis of SeNPs of cluster shapes for the first time by reduction of Se (IV) with vitamin C. The naked eyes observations noticed a rapid change in color of Se (IV) solution from colorless to bright crimson aggregates as just the solution gets in contact with added mixture of vitamin C and alginate of powder natures then is rapidly turned to a reddish-pink aggregate. The formed aggregate was converted into violet crystals by aging or heating. In absence of vitamin C, addition of alginate powder to Se (IV) electrolyte whilst stirring the mixture leads to the formation of a precipitate of granule grains nature. The FTIR, XRD and SEM and TEM investigations indicated the formation of SeNPs of cluster beans for the crystals and alginate-based Se (IV) complex for the granule grains, respectively. The complex was invested for evaluation the alginate capacity for removal of Se (IV) ions from aqueous solutions and was found to be 63.66 mg/g at 25 °C. Some kinetic runs were performed to gain some information on growth rates of SeNPs formation in terms of electron-transfer pathway in the rate-determining step.

Tomato lipidic extract plus selenium decrease prostatic hyperplasia, dihydrotestosterone and androgen receptor expression versus finasteride in rats

PURPOSE

Evaluate the therapeutic effect of a tomato lipidic extract (STE) in combination with selenium (Se) on rats with prostatic hyperplasia (PH) and to observe its possible mechanisms of action and synergism versus finasteride.

MATERIALS AND METHODS

54 male Wistar rats of nine weeks old were divided in Control (C), PH, Finasteride (F), STE, Se, F + STE, F + Se, STE + Se and F + STE + Se with testosterone enanthate (except C). After 4 weeks of treatment administration, prostate weight, bladder weight, diuresis, prooxidant and antioxidant activity, dihydrotestosterone (DHT), androgen receptor (AR) expression and anatomopathological analysis were determined.

RESULTS

STE + Se decreased prostate weight 53.8% versus 28% in F group, also STE + Se decreased significatively glandular hyperplasia, prooxidant activity, DHT and AR expression and increased diuresis and antioxidant activity versus finasteride which increased MDA in prostate.

CONCLUSIONS

These results demonstrate a greater therapeutic and beneficial effect of tomato lipidic extract in combination with Se in young rats with PH with respect to finasteride without increase prooxidant activity.

Selenium in combination with a tomato lipid extract as a therapy for benign prostatic hyperplasia and its alterations in rats with induced BPH

Benign prostatic hyperplasia (BPH) is the most common adenoma in old men. Tomatoes are a rich source of bioactive compounds that, as well as selenium (Se), possess antioxidant and antiproliferative activity. The aim was to evaluate the therapeutic effect of Se in combination with a tomato extract in aged rats with BPH. Aged male Wistar rats were divided in the following groups (n = 10 rats/group): Control (C), BPH, BPH + Finasteride (BPH + F), BPH + Tomato Lipidic Extract (BPH + E), BPH + Selenium (BPH + S) and BPH plus E plus S (BPH + E + S). After 4 weeks of treatment, prostate weight, diuresis, antioxidants enzymes, prooxidants and inflammatory markers, growth factors and androgens were determined. BPH + E + S reduced prostate weight by 59.29% and inhibited growth by 99.35% compared to BPH + F which only decreased weight and inhibited growth by 15.31% and 57.54%, respectively. Prooxidant markers were higher with BPH + F (49.4% higher vs. BPH), but BPH + E + S decreased these markers (94.27% vs. BPH) and increased antioxidant activity. Finally, diuresis was higher with the BPH + E + S combination and markers of inflammation and growth factors were significantly lower with respect to BPH + F. Our findings provide a beneficial and protective therapeutic option of E + S directed against androgens, oxidative stress and inflammation that regulates cell proliferation in the prostate gland.

Next generation of selenocyanate and diselenides with upgraded leishmanicidal activity

Nowadays, leishmaniasis is still treated with outdated drugs that present several obstacles related to their high toxicity, long duration, parenteral administration, high costs and drug resistance. Therefore, there is an urgent demand for safer and more effective novel drugs. Previous studies indicated that selenium compounds are promising derivatives for innovative therapy in leishmaniasis treatment. With this background, a new library of 20 selenocyanate and diselenide derivatives were designed based on structural features present in the leishmanicidal drug miltefosine. Compounds were initially screened against promastigotes of L. major and L. infantum and their cytotoxicity was evaluated in THP-1 cells. Compounds B8 and B9 were the most potent and less cytotoxic and were further screened for the intracellular back transformation assay. The results obtained revealed that B8 and B9 showed EC50 values of 7.7 µM and 5.7 µM, respectively, in L. major amastigotes, while they presented values of 6.0 µM and 7.4 µM, respectively, against L. infantum amastigotes. Furthermore, they exerted high selectivity (60 < SI > 70) towards bone marrow-derived macrophages. Finally, these compounds exhibited higher TryR inhibitory activity than mepacrine (IC50 7.6 and 9.2 µM, respectively), and induced nitric oxide (NO) and reactive oxygen species (ROS) production in macrophages. These results suggest that the compounds B8 and B9 could not only exert a direct leishmanicidal activity against the parasite but also present an indirect action by activating the microbicidal arsenal of the macrophage. Overall, these new generation of diselenides could constitute promising leishmanicidal drug candidates for further studies.

Selenium in soil-plant system: Transport, detoxification and bioremediation

Selenium (Se) is an essential micronutrient for humans and a beneficial element for plants. However, high Se doses always exhibit hazardous effects. Recently, Se toxicity in plant-soil system has received increasing attention. This review will summarize (1) Se concentration in soils and its sources, (2) Se bioavailability in soils and influencing factors, (3) mechanisms on Se uptake and translocation in plants, (4) toxicity and detoxification of Se in plants and (5) strategies to remediate Se pollution. High Se concentration mainly results from wastewater discharge and industrial waste dumping. Selenate (Se [VI]) and selenite (Se [IV]) are the two primary forms absorbed by plants. Soil conditions such as pH, redox potential, organic matter and microorganisms will influence Se bioavailability. In plants, excessive Se will interfere with element uptake, depress photosynthetic pigment biosynthesis, generate oxidative damages and cause genotoxicity. Plants employ a series of strategies to detoxify Se, such as activating antioxidant defense systems and sequestrating excessive Se in the vacuole. In order to alleviate Se toxicity to plants, some strategies can be applied, including phytoremediation, OM remediation, microbial remediation, adsorption technique, chemical reduction technology and exogenous substances (such as Methyl jasmonate, Nitric oxide and Melatonin). This review is expected to expand the knowledge of Se toxicity/detoxicity in soil-plant system and offer valuable insights into soils Se pollution remediation strategies.

The accessibility, necessity, and significance of certified reference materials for total selenium content and its species to improve food laboratories' performance

Micronutrients are one of the most important groups of nutrients that our body needs daily in trace amounts to tackle deficiencies. Selenium (Se) is a mineral that occurs naturally in foods and is an essential component of selenoproteins that support the healthy functioning of the human body. Therefore, monitoring dietary Se concentrations must be a higher priority to meet daily intakes. Fulfillment can be addressed through applying various analytical techniques, and the certified reference materials (CRMs) tool plays a crucial role in quality assurance/quality control (QA/QC). The availability of certified CRMs for total Se content with addition to their species is presented. The review emphasizes the necessity of incorporating more food matrix CRMs certifying Se species, apart from total Se content, to meet method validation requirements for food analysis laboratories. This would help CRM producers bridge the gap between available food matrix materials that are not certified for Se species.

The use of selenium for controlling plant fungal diseases and insect pests

The selenium (Se) applications in biomedicine, agriculture, and environmental health have become great research interest in recent decades. As an essential nutrient for humans and animals, beneficial effects of Se on human health have been well documented. Although Se is not an essential element for plants, it does play important roles in improving plants' resistances to a broad of biotic and abiotic stresses. This review is focused on recent findings from studies on effects and mechanisms of Se on plant fungal diseases and insect pests. Se affects the plant resistance to fungal diseases by preventing the invasion of fungal pathogen through positively affecting plant defense to pathogens; and through negative effects on pathogen by destroying the cell membrane and cellular extensions of pathogen inside plant tissues after invasion; and changing the soil microbial community to safeguard plant cells against invading fungi. Plants, grown under Se enriched soils or treated with Se through foliar and soil applications, can metabolize Se into dimethyl selenide or dimethyl diselenide, which acts as an insect repellent compound to deter foraging and landing pests, thus providing plant mediated resistance to insect pests; moreover, Se can also lead to poisoning to some pests if toxic amounts of Se are fed, resulting in steady pest mortality, lower reproduction rate, negative effects on growth and development, thus shortening the life span of many insect pests. In present manuscript, reports are reviewed on Se-mediated plant resistance to fungal pathogens and insect pests. The future perspective of Se is also discussed on preventing the disease and pest control to protect plants from economic injuries and damages.

Predictive modelling and optimization of an airlift bioreactor for selenite removal from wastewater using artificial neural networks and particle swarm optimization

Selenite (Se⁴⁺) is the most toxic of all the oxyanion forms of selenium. In this study, a feed forward back propagation (BP) based artificial neural network (ANN) model was developed for a fungal pelleted airlift bioreactor (ALR) system treating selenite-laden wastewater. The performance of the bioreactor, i.e., selenite removal efficiency (RE_selenite) (%) was predicted through two input parameters, namely, the influent selenite concentration (IC_selenite) (10 mg/L - 60 mg/L) and hydraulic retention time (HRT) (24 h - 72 h). After training and testing with 96 sets of data points using the Levenberg-Marquardt algorithm, a multi-layer perceptron model (2-10-1) was established. High values of the correlation coefficient (0.96 ≤ R ≤ 0.98), along with low root mean square error (1.72 ≤ RMSE ≤ 2.81) and mean absolute percentage error (1.67 ≤ MAPE ≤ 2.67), clearly demonstrate the accuracy of the ANN model (> 96%) when compared to the experimental data. To ensure an efficient and economically feasible operation of the ALR, the process parameters were optimized using the particle swarm optimization (PSO) algorithm coupled with the neural model. The RE_selenite was maximized while minimizing the HRT for a preferably higher range of IC_selenite. Thus, the most favourable optimum conditions were suggested as: IC_selenite - 50.45 mg/L and HRT - 24 h, resulting in RE_selenite of 69.4%. Overall, it can be inferred that ANN models can successfully substitute knowledge-based models to predict the RE_selenite in an ALR, and the process parameters can be effectively optimized using PSO.

Reversal of Multidrug Resistance by Symmetrical Selenoesters in Colon Adenocarcinoma Cells

Recently, selenium containing derivatives have attracted more attention in medicinal chemistry. In the present work, the anticancer activity of symmetrical selenoesters was investigated by studying the reversal of efflux pump-related and apoptosis resistance in sensitive and resistant human colon adenocarcinoma cells expressing the ABCB1 protein. The combined effect of the compounds with doxorubicin was demonstrated with a checkerboard assay. The ABCB1 inhibitory and the apoptosis-inducing effects of the derivatives were measured with flow cytometry. Whole transcriptome sequencing was carried out on Illumina platform upon the treatment of resistant cells with the most potent derivatives. One ketone and three methyl ester selenoesters showed synergistic or weak synergistic interaction with doxorubicin, respectively. Ketone selenoesters were the most potent ABCB1 inhibitors and apoptosis inducers. Nitrile selenoesters could induce moderate early and late apoptotic processes that could be explained by their ABCB1 modulating properties. The transcriptome analysis revealed that symmetrical selenoesters may influence the redox state of the cells and interfere with metastasis formation. It can be assumed that these symmetrical selenocompounds possess toxic, DNA-damaging effects due to the presence of two selenium atoms in the molecule, which may be augmented by the presence of symmetrical groups.

Small molecules containing chalcogen elements (S, Se, Te) as new warhead to fight neglected tropical diseases

Neglected tropical diseases (NTDs) encompass a group of infectious diseases with a protozoan etiology, high incidence, and prevalence in developing countries. As a result, economic factors constitute one of the main obstacles to their management. Endemic countries have high levels of poverty, deprivation and marginalization which affect patients and limit their access to proper medical care. As a matter of fact, statistics remain uncollected in some affected areas due to non-reporting cases. World Health Organization and other organizations proposed a plan for the eradication and control of the vector, although many of these plans were halted by the COVID-19 pandemic. Despite of the available drugs to treat these pathologies, it exists a lack of effectiveness against several parasite strains. Treatment protocols for diseases such as American trypanosomiasis (Chagas disease), leishmaniasis, and human African trypanosomiasis (HAT) have not achieved the desired results. Unfortunately, these drugs present limitations such as side effects, toxicity, teratogenicity, renal, and hepatic impairment, as well as high costs that have hindered the control and eradication of these diseases. This review focuses on the analysis of a collection of scientific shreds of evidence with the aim of identifying novel chalcogen-derived molecules with biological activity against Chagas disease, leishmaniasis and HAT. Compounds illustrated in each figure share the distinction of containing at least one chalcogen element. Sulfur (S), selenium (Se), and tellurium (Te) have been grouped and analyzed in accordance with their design strategy, chemical synthesis process and biological activity. After an exhaustive revision of the related literature on S, Se, and Te compounds, 183 compounds presenting excellent biological performance were gathered against the different causative agents of CD, leishmaniasis and HAT.

Applied Selenium as a Powerful Antioxidant to Mitigate the Harmful Effects of Salinity Stress in Snap Bean Seedlings

Selenium (Se) plays several significant roles in regulating growth, development and plant responses to various abiotic stresses. However, its influence on sulfate transporters (SULTRS) and achieving the harmony with other salt-tolerance features is still limited in the previous literatures. This study elucidated the effect of Se supplementation (5, 10 and 20 µM) on salt-stressed (50 mM NaCl) snap bean seedlings. Generally, the results indicated that Se had dual effects on the salt stressed seedlings according to its concentration. At a low level (5 µM), plants demonstrated a significant improvement in shoot (13.8%) and root (22.8%) fresh weight, chlorophyll a (7.4%), chlorophyll b (14.7%), carotenoids (23.2%), leaf relative water content (RWC; 8.5%), proline (17.2%), total soluble sugars (34.3%), free amino acids (FAA; 18.4%), K (36.7%), Ca (33.4%), K/Na ratio (77.9%), superoxide dismutase (SOD; 18%), ascorbate peroxidase (APX;12.8%) and guaiacol peroxidase (G-POX; 27.1%) compared to the untreated plants. Meanwhile, most of these responses as well as sulfur (S), Se and catalase (CAT) were obviously decreased in parallel with increasing the applied Se up to 20 µM. The molecular study revealed that three membrane sulfate transporters (SULTR1, SULTR2 and SULTR 3) in the root and leaves and salinity responsive genes (SOS1, NHX1 and Osmotin) in leaves displayed different expression patterns under various Se treatments. Conclusively, Se at low doses can be beneficial in mitigating salinity-mediated damage and achieving the functioning homeostasis to tolerance features.

Selenate and selenite transporters in proso millet: Genome extensive detection and expression studies under salt stress and selenium

Crops are susceptible to a variety of stresses and amongst them salinity of soil is a global agronomic challenge that has a detrimental influence on crop yields, thus posing a severe danger to our food security. Therefore, it becomes imperative to examine how plants respond to salt stress, develop a tolerance that allows them to live through higher salt concentrations and choose species that can endure salt stress. From the perspective of food, security millets can be substituted to avoid hardships because of their efficiency in dealing with salt stress. Besides, this problem can also be tackled by using beneficial exogenous elements. Selenium (Se) which exists as selenate or selenite is one such cardinal element that has been reported to alleviate salt stress. The present study aimed for identification of selenate and selenite transporters in proso millet (Panicum miliaceum L.), their expression under NaCl (salt stress) and Na₂SeO₃ (sodium selenite)treatments. This study identified eight transporters (RLM65282.1, RLN42222.1, RLN18407.1, RLM74477.1, RLN41904.1, RLN17428.1, RLN17268.1, RLM65753.1) that have a potential role in Se uptake in proso millet. We analyzed physicochemical properties, conserved structures, sub-cellular locations, chromosome location, molecular phylogenetic analysis, promoter regions prediction, protein-protein interactions, three-dimensional structure modeling and evaluation of these transporters. The analysis revealed the chromosome location and the number of amino acids present in these transporters as RLM65282.1 (16/646); RLN42222.1 (1/543); RLN18407.1 (2/483); RLM74477.1 (15/474); RLN41904.1 (1/521); RLN17428.1 (2/522); RLN17268.1(2/537);RLM65753.1 (16/539). The sub-cellular locations revealed that all the selenite transporters are located in plasma membrane whereas among selenate transporters RLM65282.1 and RLM74477.1 are located in mitochondria and RLN42222.1 and RLN18407.1 in chloroplast. The transcriptomic studies revealed that NaCl stress decreased the expression of both selenate and selenite transporters in proso millet and the applications of exogenous 1µM Se (Na₂SeO₃) increased the expression of these Se transporter genes. It was also revealed that selenate shows similar behavior as sulfate, while selenite transport resembles phosphate. Thus, it can be concluded that phosphate and sulphate transporters in millets are responsible for Se uptake.

Selenium: a potent regulator of ferroptosis and biomass production

Emerging evidence supports the notion that selenium (Se) plays a beneficial role in plant development for modern crop production and is considered an essential micronutrient and the predominant source of plants. However, the essential role of selenium in plant metabolism remains unclear. When used in moderate concentrations, selenium promotes plant physiological processes such as enhancing plant growth, increasing antioxidant capacity, reducing reactive oxygen species and lipid peroxidation and offering stress resistance by preventing ferroptosis cell death. Ferroptosis, a recently discovered mechanism of regulated cell death (RCD) with unique features such as iron-dependant accumulation of lipid peroxides, is distinctly different from other known forms of cell death. Glutathione peroxidase (GPX) activity plays a significant role in scavenging the toxic by-products of lipid peroxidation in plants. A low level of GPX activity in plants causes high oxidative stress, which leads to ferroptosis. An integrated view of ferroptosis and selenium in plants and the selenium-mediated nanofertilizers (SeNPs) have been discussed in more recent studies. For instance, selenium supplementation enhanced GPX4 expression and increased TFH cell (Follicular helper T) numbers and the gene transcriptional program, which prevent lipid peroxidase and protect cells from ferroptosis. However, though ferroptosis in plants is similar to that in animals, only few studies have focused on plant-specific ferroptosis; the research on ferroptosis in plants is still in its infancy. Understanding the implication of selenium with relevance to ferroptosis is indispensable for plant bioresource technology. In this review, we hypothesize that blocking ferroptosis cell death improves plant immunity and protects plants from abiotic and biotic stresses. We also examine how SeNPs can be the basis for emerging unconventional and advanced technologies for algae/bamboo biomass production. For instance, algae treated with SeNPs accumulate high lipid profile in algal cells that could thence be used for biodiesel production. We also suggest that further studies in the field of SeNPs are essential for the successful application of this technology for the large-scale production of plant biomass.

Dietary selenium intake and the risk of kidney stones in adults, an analysis of 2007-2018 National Health and Nutrition Examination Survey, a cross-sectional study

Purpose

To evaluate the association between dietary selenium intake and the risk of kidney stones in adults.

Materials and methods

We performed a cross-sectional analysis using data from 2007 to 2018 National Health and Nutrition Examination Survey (NHANES). Dietary intake information of 30,184 participants was obtained using first 24-h dietary recall interview, and kidney stones were presented by a standard questionnaire. The quartile analysis, stratified analysis and non-linearity analysis were used to estimate the association between dietary selenium intake and kidney stones after an adjustment for potential confounders.

Results

The multiple logistic regression indicated that the fourth quantile (Q4) of dietary selenium intake had a lower risk of kidney stones than the first quantile (Q1) in Model 3 (OR 0.82, P < 0.05). The stratified analyses indicated there were statistical differences between dietary selenium intake and kidney stones among younger (age < 50) (OR 0.65, P < 0.01), male (OR 0.73, P < 0.01) and overweight/obese (BMI ≥ 25.0) (OR 0.80, P < 0.05) individuals in Model 3. The non-linear relationship was founded between dietary selenium intake and kidney stones in all participants, younger, male and overweight/obese individuals after adjusting for confounding factors.

Conclusion

Our study revealed an inverse relation between the level of dietary selenium intake and the risk of kidney stones for the United States population, especially for younger (age < 50), male and overweight/obese (BMI ≥ 25.0) individuals. The study provides preliminary guidance on dietary selenium intake for the prevention of kidney stones in different populations. Further studies are required to confirm our findings and clarified the biological mechanisms.

The Role of Selenium Nanoparticles in Agriculture and Food Technology

Selenium (Se) is an essential micronutrient for diverse organisms such as mammals, bacteria, some insects and nematodes, archaea, and algae, as it is involved in a large number of physiological and metabolic processes and is part of approximately 25 selenoproteins in mammals. In plants, Se has no essential metabolic role, high concentrations of inorganic Se can lead to the formation of Se-amino acids, and its incorporation into selenoproteins can generate toxicity. Conversely, low doses of Se can trigger a variety of beneficial effects as an antioxidant, antimicrobial, or stress-modulating agent without being an essential element. Therefore, Se can generate toxicity depending on the dose and the chemical form in which it is supplied. Selenium nanoparticles (SeNPs) have emerged as an approach to reduce this negative effect and improve its biological properties. In turn, SeNPs have a wide range of potential advantages, making them an alternative for areas such as agriculture and food technology. This review focuses on the use of SeNPs and their different applications as antimicrobial agents, growth promoters, crop biofortification, and nutraceuticals in agriculture. In addition, the utilization of SeNPs in the generation of packaging with antioxidant and antimicrobial traits and Se enrichment of animal source foods for human consumption as part of food technology is addressed. Additionally, possible action mechanisms and potential adverse effects are discussed. The concentration, size, and synthesis method of SeNPs are determining factors of their biological properties.

Radiolytic synthesis and characterization of selenium nanoparticles: comparative biosafety evaluation with selenite and ionizing radiation

The goal of this work is use a green chemistry route to synthesize selenium nanoparticles (SeNPs) that do not trigger oxidative stress, typical of metallic, oxide metallic and carbonaceous nanostructures, and supply the same beneficial effects as selenium nanostructures. SeNPs were synthesized using a radiolytic method involving irradiating a solution containing sodium selenite (Se⁴⁺) as the precursor in 1% Yeast extract, 2% Peptone, 2% Glucose (YPG) liquid medium with gamma-rays (⁶⁰Cobalt). The method did not employ any hazardous reducing agents. Saccharomyces cerevisiae cells were incubated with 1 mM SeNPs for 24 h and/or then challenged with 400 Gy of ionizing radiation were assessed for viability and biomarkers of oxidative stress: lipid peroxidation, protein carbonylation, free radical generation, and total sulfhydryl content. Spherical SeNPs with variable diameters (from 100 to 200 nm) were formed after reactions of sodium selenite with hydrated electrons (e_aq^-) and hydrogen radicals (H·). Subsequent structural characterizations indicated an amorphous structure composed of elemental selenium (Se⁰). Compared to 1 mM selenite, SeNPs were considered safe and less toxic to Saccharomyces cerevisiae cells as did not elicit significant modifications in cell viability or oxidative stress parameters except for increased protein carbonylation. Furthermore, SeNPs treatment afforded some protection against ionizing radiation exposure. SeNPs produced using green chemistry attenuated the reactive oxygen species generation after in vitro ionizing radiation exposure opens up tremendous possibilities for radiosensitizer development.

Mercury and selenium in squids from the Pacific Ocean and Indian Ocean: The distribution and human health implications

Squids are globally distributed. Hg-contaminated squids may have high risks on humans. With abundant Se (antagonistic effect on Hg), the risks can be reduced. We collected squids around the world (Northwest Pacific Ocean, Southeast Pacific Ocean and Indian Ocean). Concentrations of Hg and Se were region-based and tissue-based. The higher content of Se were, the lower relative Hg levels were. The correlation between Se:Hg and Se was the strongest in the digestive gland. The values of Se:Hg and THQ all confirm that the health risk was lower in samples with higher concentrations of Se. Despite the risk assessment by Se:Hg, BRV and THQ analysis showed no risk when consumed in moderation, the maximum daily intake is provided based on Monte Carlo simulation. In future, when evaluating the risks cause by Hg exposure and providing the recommended daily amount, it may need to concurrent consideration of Se levels.

Selenomethionine Improves Mitochondrial Function by Upregulating Mitochondrial Selenoprotein in a Model of Alzheimer's Disease

Alzheimer’s disease (AD), the most common neurodegenerative disease in elderly humans, is pathologically characterized by amyloid plaques and neurofibrillary tangles. Mitochondrial dysfunction that occurs in the early stages of AD, which includes dysfunction in mitochondrial generation and energy metabolism, is considered to be closely associated with AD pathology. Selenomethionine (Se-Met) has been reported to improve cognitive impairment and reduce amyloid plaques and neurofibrillary tangles in 3xTg-AD mice. Whether Se-Met can regulate mitochondrial dysfunction in an AD model during this process remains unknown.In this study, the N2a-APP695-Swedish (N2aSW) cell and 8-month-old 3xTg-AD mice were treated with Se-Met in vitro and in vivo. Our study showed that the numbers of mitochondria were increased after treatment with Se-Met. Se-Met treatment also significantly increased the levels of NRF1 and Mfn2, and decreased those of OPA1 and Drp1. In addition, the mitochondrial membrane potential was significantly increased, while the ROS levels and apoptosis rate were significantly decreased, in cells after treatment with Se-Met. The levels of ATP, complex IV, and Cyt c and the activity of complex V were all significantly increased. Furthermore, the expression level of SELENO O was increased after Se-Met treatment. Thus, Se-Met can maintain mitochondrial dynamic balance, promote mitochondrial fusion or division, restore mitochondrial membrane potential, promote mitochondrial energy metabolism, inhibit intracellular ROS generation, and reduce apoptosis. These effects are most likely mediated via upregulation of SELENO O. In summary, Se-Met improves mitochondrial function by upregulating mitochondrial selenoprotein in these AD models.

Microbes: a potential tool for selenium biofortification

Selenium (Se) is a component of many enzymes and indispensable for human health due to its characteristics of reducing oxidative stress and enhancing immunity. Human beings take Se mainly from Se-containing crops. Taking measures to biofortify crops with Se may lead to improved public health. Se accumulation in plants mainly depends on the content and bioavailability of Se in soil. Beneficial microbes may change the chemical form and bioavailability of Se. This review highlights the potential role of microbes in promoting Se uptake and accumulation in crops and the related mechanisms. The potential approaches of microbial enhancement of Se biofortification can be summarized in the following four aspects: (1) microbes alter soil properties and impact the redox chemistry of Se to improve the bioavailability of Se in soil; (2) beneficial microbes regulate root morphology and stimulate the development of plants through the release of certain secretions, facilitating Se uptake in plants; (3) microbes upregulate the expression of certain genes and proteins that are related to Se metabolism in plants; and (4) the inoculation of microbes give rise to the generation of certain metabolites in plants contributing to Se absorption. Considering the ecological safety and economic feasibility, microbial enhancement is a potential tool for Se biofortification. For further study, the recombination and establishment of synthesis microbes is of potential benefit in Se-enrichment agriculture.

Comparative proteomics analysis of the responses to selenium in selenium-enriched alfalfa (Medicago sativa L.) leaves

The mass of leaves and the chlorophyll and selenium content of alfalfa can be increased by the foliar spraying of selenite. To better understand the relationship between changes in the expression of specific proteins and the various metabolic and regulatory pathways affected by selenium treatment, labeling with Tandem Mass Tags (TMT) was used as a proteomics technique to compare control leaves with those enriched with Se. A total of 8,411 proteins were identified, the expression levels of 195 of which were significantly modified, 67 significantly up-regulated and 128 significantly down-regulated. Using gene functional classification and metabolic pathway annotation, selenium treatment was found to have a significant impact on metabolic processes. The energy and substances produced by the metabolic processes of a variety of carbohydrates, lipids, and amino acids, and the metabolism of carbon may be responsible for increasing the yield of alfalfa leaves. Administration of selenium substantially influenced Se-responsive proteins, including ABC transporter G family member 36, Probable glutathione S-transferase and cysteine tRNA ligase. Selenium treatment may also enhance photosynthesis and the defense response of cells. Furthermore, protein ubiquitination also played an important role in the selenium response of alfalfa leaves. In summary, a basic analysis of the selenium response pathway in alfalfa leaves at the proteomics level was conducted, which may assist in a more detailed elucidation of selenium enrichment in alfalfa in the future.

Effect of Selenium Nanoparticles on Germination of Hordéum Vulgáre Barley Seeds

Within the framework of this study, the effect of nanoparticles of the essential trace element selenium stabilized by Polyvinylpirrolidone (PVP) C15 (8 ± 2 kDa) and ascorbic acid on the germination of barley seeds has been studied. Selenium nanoparticles stabilized by PVP C15 (8 ± 2 kDa) and ascorbic acid, characterized by a spherical shape, monodisperse size distribution, and a diameter of about 70 ± 5 nm, were obtained by the chemical reduction method. The experiment compared the effect of selenium nanoparticles and selenous acid on seed germination. The positive effect of preparation of selenium nanoparticles stabilized by PVP C15 (8 ± 2 kDa) and ascorbic acid on the length of roots and shoots, the number of roots, and the percentage of seed germination has been revealed. It was determined that the highest percentage of Hordeum vulgare L. culture seed germination was achieved using a preparation of selenium nanoparticles stabilized by PVP C15 (8 ± 2 kDa) and ascorbic acid at a concentration of of 4.65 µg/mL. Analysis of the results showed that selenium in the form of nanoparticles has an order of magnitude that is less toxic than in the form of selenous acid. The study of morphological and functional parameters during the germination of Hordeum vulgare L. seeds allowed us to conclude that selenium nanoparticles can be successfully used in agronomy and agriculture to provide plants with the essential microelement selenium, which is necessary for the normal growth and development of crops.

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.

Selenium Biofortification: Roles, Mechanisms, Responses and Prospects

The trace element selenium (Se) is a crucial element for many living organisms, including soil microorganisms, plants and animals, including humans. Generally, in Nature Se is taken up in the living cells of microorganisms, plants, animals and humans in several inorganic forms such as selenate, selenite, elemental Se and selenide. These forms are converted to organic forms by biological process, mostly as the two selenoamino acids selenocysteine (SeCys) and selenomethionine (SeMet). The biological systems of plants, animals and humans can fix these amino acids into Se-containing proteins by a modest replacement of methionine with SeMet. While the form SeCys is usually present in the active site of enzymes, which is essential for catalytic activity. Within human cells, organic forms of Se are significant for the accurate functioning of the immune and reproductive systems, the thyroid and the brain, and to enzyme activity within cells. Humans ingest Se through plant and animal foods rich in the element. The concentration of Se in foodstuffs depends on the presence of available forms of Se in soils and its uptake and accumulation by plants and herbivorous animals. Therefore, improving the availability of Se to plants is, therefore, a potential pathway to overcoming human Se deficiencies. Among these prospective pathways, the Se-biofortification of plants has already been established as a pioneering approach for producing Se-enriched agricultural products. To achieve this desirable aim of Se-biofortification, molecular breeding and genetic engineering in combination with novel agronomic and edaphic management approaches should be combined. This current review summarizes the roles, responses, prospects and mechanisms of Se in human nutrition. It also elaborates how biofortification is a plausible approach to resolving Se-deficiency in humans and other animals.

Effects of Sub-Lethal Doses of Selenium Nanoparticles on the Health Status of Rats

Selenium nanoparticles (SeNPs) are fast becoming a key instrument in several applications such as medicine or nutrition. Questions have been raised about the safety of their use. Male rats were fed for 28 days on a monodiet containing 0.5, 1.5, 3.0 and 5.0 mg Se/kg. Se content in blood and liver, liver panel tests, blood glucose, total antioxidant capacity (TAC), the activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx) were analysed. Liver and duodenum were subjected to histopathology examination. The weight gain of rats showed no differences between tested groups. Se content in blood was higher in all treated groups compared to the control group. The liver concentration of Se in the treated groups varied in the range from 222 to 238 ng/g. No differences were observed in the activity of AST (aspartate aminotransferase), ALP (alkaline phosphatase) and TAS (total antioxidant status). A significant decrease in ALT activity compared to the control group was observed in the treated groups. GPx activity varied from 80 to 88 U/mL through tested groups. SOD activity in liver was decreased in the SeNP-treated group with 5 mg Se/kg (929 ± 103 U/mL). Histopathological examination showed damage to the liver parenchyma and intestinal epithelium in a dose-dependent manner. This study suggests that short-term SeNP supplementation can be safe and beneficial in Se deficiency or specific treatment.

Transcriptomic Characterization of the Effects of Selenium on Maize Seedling Growth

Selenium (Se) is a trace mineral element in soils that can be beneficial to plants in small amounts. Although maize is among the most economically important crops, there are few reports on the effects of Se on maize seedling growth at the molecular level. In this study, the growth of maize seedlings treated with different concentrations of Na₂SeO₃ was investigated, and the physiological characteristics were measured. Compared with the control, a low Se concentration promoted seedling growth, whereas a high Se concentration inhibited it. To illustrate the transcriptional effects of Se on maize seedling growth, samples from control plants and those treated with low or high concentrations of Se were subjected to RNA sequencing. The differentially expressed gene (DEG) analysis revealed that there were 239 upregulated and 106 downregulated genes in the low Se treatment groups, while there were 845 upregulated and 1,686 downregulated DEGs in the high Se treatment groups. Both the Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation analyses showed a low concentration of the Se-stimulated expression of "DNA replication" and "glutathione (GSH) metabolism"-related genes. A high concentration of Se repressed the expression of auxin signal transduction and lignin biosynthesis-related genes. The real-time quantitative reverse transcription PCR (qRT-PCR) results showed that in the low Se treatment, "auxin signal transduction," "DNA replication," and lignin biosynthesis-related genes were upregulated 1.4- to 57.68-fold compared to the control, while, in the high Se concentration treatment, auxin signal transduction and lignin biosynthesis-related genes were downregulated 1.6- to 16.23-fold compared to the control. Based on these transcriptional differences and qRT-PCR validation, it was found that a low dosage of Se may promote maize seedling growth but becomes inhibitory to growth at higher concentrations. This study lays a foundation for the mechanisms underlying the effects of Se on maize seedling growth.

Selenium Toxicity in Plants and Environment: Biogeochemistry and Remediation Possibilities

Selenium (Se) is a widely distributed trace element with dual (beneficial or toxic) effects for humans, animals, and plants. The availability of Se in the soil is reliant on the structure of the parental material and the procedures succeeding to soil formation. Anthropogenic activities affect the content of Se in the environment. Although plants are the core source of Se in animal and human diet, the role of Se in plants is still debatable. A low concentration of Se can be beneficial for plant growth, development, and ecophysiology both under optimum and unfavorable environmental conditions. However, excess Se results in toxic effects, especially in Se sensitive plants, due to changing structure and function of proteins and induce oxidative/nitrosative stress, which disrupts several metabolic processes. Contrary, Se hyperaccumulators absorb and tolerate exceedingly large amounts of Se, could be potentially used to remediate, i.e., remove, transfer, stabilize, and/or detoxify Se-contaminants in the soil and groundwater. Thereby, Se-hyperaccumulators can play a dynamic role in overcoming global problem Se-inadequacy and toxicity. However, the knowledge of Se uptake and metabolism is essential for the effective phytoremediation to remove this element. Moreover, selecting the most efficient species accumulating Se is crucial for successful phytoremediation of a particular Se-contaminated area. This review emphasizes Se toxicity in plants and the environment with regards to Se biogeochemistry and phytoremediation aspects. This review follows a critical approach and stimulates thought for future research avenues.

Selenium Toxicity in Plants and Environment: Biogeochemistry and Remediation Possibilities

Selenium (Se) is a widely distributed trace element with dual (beneficial or toxic) effects for humans, animals, and plants. The availability of Se in the soil is reliant on the structure of the parental material and the procedures succeeding to soil formation. Anthropogenic activities affect the content of Se in the environment. Although plants are the core source of Se in animal and human diet, the role of Se in plants is still debatable. A low concentration of Se can be beneficial for plant growth, development, and ecophysiology both under optimum and unfavorable environmental conditions. However, excess Se results in toxic effects, especially in Se sensitive plants, due to changing structure and function of proteins and induce oxidative/nitrosative stress, which disrupts several metabolic processes. Contrary, Se hyperaccumulators absorb and tolerate exceedingly large amounts of Se, could be potentially used to remediate, i.e., remove, transfer, stabilize, and/or detoxify Se-contaminants in the soil and groundwater. Thereby, Se-hyperaccumulators can play a dynamic role in overcoming global problem Se-inadequacy and toxicity. However, the knowledge of Se uptake and metabolism is essential for the effective phytoremediation to remove this element. Moreover, selecting the most efficient species accumulating Se is crucial for successful phytoremediation of a particular Se-contaminated area. This review emphasizes Se toxicity in plants and the environment with regards to Se biogeochemistry and phytoremediation aspects. This review follows a critical approach and stimulates thought for future research avenues.

The Relevance of Selenium Status in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune and inflammatory disease that can cause joint damage. Among the environmental risk factors, diet plays an important role because it can aggravate or attenuate inflammation. Selenium (Se) is considered an essential trace element since it is a structural component of antioxidant enzymes; however, its concentration can be affected by diet, drugs and genetic polymorphisms. Studies have reported that RA patients have a deficient diet in some food groups that is associated with parameters of disease activity. Furthermore, it has been shown that there is an alteration in serum Se levels in this population. Although some clinical trials have been conducted in the past to analyze the effect of Se supplementation in RA, no significant results were obtained. Contrastingly, experimental studies that have evaluated the effect of novel Se nanoparticles in RA-induced models have shown promising results on the restoration of antioxidant enzyme levels. In particular, glutathione peroxidase (GPx) is an important selenoprotein that could have a modulating effect on inflammation in RA. Considering that RA patients present an inflammatory and oxidative state, the aim of this review is to give an overview of the current knowledge about the relevance of Se status in RA.

Selenosis in Ruminants

Selenium (Se) is a metalloid that exists as a red amorphous powder, reddish crystal, silver-gray crystal, or brown-black solid. Its potency as a nutrient and a toxicant is such that few people have seen the pure element. It is easy to lose sight of the narrow margin between too little and too much. The most common cause of selenosis is accidental or intentional overuse of supplements. Many target organs and effects of Se toxicity are similar to those of Se deficiency, so laboratory confirmation is necessary. Prevention consists of minimizing exposure to seleniferous feedstuffs and optimizing dietary factors that might aggravate selenosis.

Selenium in plant foods: speciation analysis, bioavailability, and factors affecting composition

Interest in selenium has been increasing over the past few decades with growing knowledge of its importance to overall health. The ability of several plants to accumulate and transform inorganic selenium forms into its bioactive organic compounds has important implications for human nutrition and health. In this review, we present the studies carried out during the last decade to characterize selenium species produced by different plant foods. Attention is also paid to the effect of selenium treatment on chemical composition and antioxidant properties of plants.

Biofortification with selenium and iodine changes morphological properties of Brassica oleracea L. var. gongylodes) and increases their contents in tubers

Kohlrabi (Brassica oleracea L. var. gongylodes L.) was biofortified with selenium (Se), as selenite and selenate, and iodine (I), as iodide and iodate, and their combinations through foliar spraying, to study absorption of these elements by the plants, separately and in combination. The effects on selected physiological and morphological traits and optical characteristics were monitored. Treatments with Se positively affected total chlorophylls and carotenoids, and leaf stomata dimensions. Addition of I decreased total chlorophylls and increased anthocyanins. In reflectance spectra of the leaves, specific colour regions differed significantly due to the different treatments. Reflectance in the UV correlated positively with Se and I contents of the leaves, which indicated lower demand for production of phenolic compounds. Differences in reflectance in UV part of the spectra could be a consequence of changes in the cuticle. The Se and I levels increased markedly in leaves and tubers, without loss of biomass or yield. Se had antagonistic effects on accumulation of I in leaves. The similar levels of Se and I in the leaves and tubers suggest that the transport of both elements in these plants occurs from the leaves to the tubers through the phloem. According to the Se and I contents in the kohlrabi tubers, biofortification with both elements simultaneously is feasible for human nutrition.

Selenium Interactions with Algae: Chemical Processes at Biological Uptake Sites, Bioaccumulation, and Intracellular Metabolism

Selenium (Se) uptake by primary producers is the most variable and important step in determining Se concentrations at higher trophic levels in aquatic food webs. We gathered data available about the Se bioaccumulation at the base of aquatic food webs and analyzed its relationship with Se concentrations in water. This important dataset was separated into lotic and lentic systems to provide a reliable model to estimate Se in primary producers from aqueous exposure. We observed that lentic systems had higher organic selenium and selenite concentrations than in lotic systems and selenate concentrations were higher in lotic environments. Selenium uptake by algae is mostly driven by Se concentrations, speciation and competition with other anions, and is as well influenced by pH. Based on Se species uptake by algae in the laboratory, we proposed an accurate mechanistic model of competition between sulfate and inorganic Se species at algal uptake sites. Intracellular Se transformations and incorporation into selenoproteins as well as the mechanisms through which Se can induce toxicity in algae has also been reviewed. We provided a new tool for risk assessment strategies to better predict accumulation in primary consumers and consequently to higher trophic levels, and we identified some research needs that could fill knowledge gaps.

Selenium protection against mercury toxicity on the male reproductive system of Clarias gariepinus

The present study aimed to evaluate the protective role of Selenium (Se) (0.1 ppm) on the male reproductive system of the catfish Clarias gariepinus exposed to sublethal doses of Mercury (Hg) (0.04 and 0.12 ppm) for 30 days. Indicators of seminal and gonadal hormone disruption (testosterone, estradiol and 11 keto testosterone), antioxidants (total antioxidant capacity (TAO), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx)), oxidative stress biomarkers (lipid peroxidation (LPO), percentage of DNA fragmentation, carbonylated proteins (CP) and nitric oxide (NO)) and histopathological alterations in testicles of Clarias gariepinus were determined. The exposure to Hg resulted in a high accumulation of residues of this metal in testicular tissues. The results showed a significant decrease in sperm count, activity and motility and in all gonadal hormones in Hg exposed groups. Hg exposure also induced a decline in TAO, SOD, CAT and GPx, whereas LPO, DNA fragmentation, CP and NO significantly increased in testicles of C. gariepinus respect to the control group. Although exposure to Se did not reduce the degree of mercury bioconcentration in the testicles, the sperm quality parameters were recovered. Moreover, TAO levels and GPx activity significantly increased after fish exposure to Se, whereas CP levels decreased. LPO, NO, CAT and SOD were also partially normalized when compared with the groups exposed to only Hg. In conclusion, the results showed that Hg, even in the small doses is capable to induce reproductive toxicity in the male catfish. Se exposure partially restored the values of biochemical parameters and sperm quality in Hg-treated fish suggesting protective effects against Hg reproductive toxicity.

Selenium Accumulation, Speciation and Localization in Brazil Nuts (Bertholletia excelsa H.B.K.)

More than a billion people worldwide may be selenium (Se) deficient, and supplementation with Se-rich Brazil nuts may be a good strategy to prevent deficiency. Since different forms of Se have different nutritional value, and Se is toxic at elevated levels, careful seed characterization is important. Variation in Se concentration and correlations of this element with other nutrients were found in two batches of commercially available nuts. Selenium tissue localization and speciation were further determined. Mean Se levels were between 28 and 49 mg kg⁻¹, with up to 8-fold seed-to-seed variation (n = 13) within batches. Brazil nut Se was mainly in organic form. While present throughout the seed, Se was most concentrated in a ring 1 to 2 mm below the surface. While healthy, Brazil nuts should be consumed in moderation. Consumption of one seed (5 g) from a high-Se area meets its recommended daily allowance; the recommended serving size of 30 g may exceed the allowable daily intake (400 μg) or even its toxicity threshold (1200 μg). Based on these findings, the recommended serving size may be re-evaluated, consumers should be warned not to exceed the serving size and the seed may be sold as part of mixed nuts, to avoid excess Se intake.