Uptake, translocation and biotransformation of selenium nanoparticles in rice seedlings (Oryza sativa L.).

BACKGROUND: Selenium (Se) in soil mainly consists of selenite, selenate, and elemental Se. However, little is known about the mechanism involved in the uptake and biotransformation of elemental Se by plants. RESULTS: In this study, the uptake, translocation, subcellular distribution and biotransformation of selenium nanoparticles (SeNPs) in rice (Oryza sativa L.), and a comparison with selenite and selenate, were investigated through hydroponic experiments. The study revealed that SeNPs could be absorbed by rice plants; and aquaporin inhibitor was responsible for a 60.4% inhibition of SeNP influx, while metabolic inhibitor was ineffective. However, the SeNPs uptake rate of rice roots was approximately 1.7 times slower than that of selenite or selenate. Under the SeNPs or selenite treatment, Se was primarily accumulated in roots rather than in shoots, whereas an opposite trend was observed with selenate treatment. Additionally, most of the absorbed Se was distributed in cell wall of the SeNPs or selenite treated-rice plants, while its proportion was the highest in soluble cytosol of the selenate treated-rice plants. The absorbed SeNPs or selenite was rapidly assimilated to organic forms, with SeMet being the most predominant species in both shoots and roots of the rice plants. However, following selenate treatment, Se(VI) remained as the most predominant species, and only a small amount of it was converted to organic forms. CONCLUSION: Therefore, this study provides a deeper understanding of the mechanisms associated SeNPs uptake and biotransformation within plants.

A comparative study on the accumulation, translocation and transformation of selenite, selenate, and SeNPs in a hydroponic-plant system.

Plants can play important roles in overcoming selenium (Se) deficiency and Se toxicity in various regions of the world. Selenite (SeIV), selenate (SeVI), as well as Se nanoparticles (SeNPs) naturally formed through reduction of SeIV, are the three main Se species in the environment. The bioaccumulation and transformation of these Se species in plants still need more understanding. The aims of this study are to investigate the phytotoxicity, accumulation, and transformation of SeIV, SeVI and SeNPs in garlic, a relatively Se accumulative plant. The spatial distribution of Se in the roots were imaged using synchrotron radiation micro-focused X-ray fluorescence (SR-µXRF). The chemical forms of Se in different plant tissues were analyzed using synchrotron radiation X-ray absorption spectroscopy (SR-XAS). The results demonstrate that 1) SeNPs which has the lowest phytotoxicity is stable in water, but prone to be converted to organic Se species, such as C-Se-C (MeSeCys) upon uptake by root. 2) SeIV is prone to concentrate in the root and incorporated into C-Se-C (MeSeCys) and C-Se-R (SeCys) bonding forms; 3) SeVI with the lowest transformation probability to organic Se species has the highest phytotoxicity to plant, and is much easier to translocate from root to leaf than SeNPs and SeIV. The present work provides insights into potential impact of SeNPs, selenite and selenate on aquatic-plant ecosystems, and is beneficial for systematically understanding the Se accumulation and transformation in food chain.

Feed-to-Fillet Transfer of Selenite and Selenomethionine Additives to Plant-Based Feeds to Farmed Atlantic Salmon Fillet.

This study investigated the transfer kinetics of dietary selenite and selenomethionine (SeMet) to the fillet of farmed Atlantic salmon (Salmo salar). The uptake and elimination rate constants of the two selenium (Se) forms were determined in Atlantic salmon fed either selenite- or SeMet-supplemented diets followed by a depuration period. The fillet half-life of selenite and SeMet was 779 ± 188 and 339 ± 103 days, respectively. The elimination and uptake rates were used in a simple one-compartmental kinetic model to predict levels in fillet based on long-term (whole production cycle) feeding with given dietary Se levels. Model predictions for Atlantic salmon fed plant-based feeds low in natural Se and supplemented with either 0.2 mg of selenite or SeMet kg-1 gave a predicted fillet level of 0.042 and 0.058 mg Se kg-1 wet weight, respectively. Based on these predictions and the European Food Safety Authority risk assessment of Se feed supplementation for food-producing terrestrial farm animals, the supplementation with 0.2 mg of selenite kg-1 would likely be safe for the most sensitive group of consumers (toddlers). However, supplementing feed to farm animals, including salmon, with 0.2 mg of SeMet kg-1 would give a higher (114%) Se intake than the safe upper intake limit for toddlers.

Effect of phosphate and silicate on selenite uptake and phloem-mediated transport in tomato (Solanum lycopersicum L.).

The ambiguous mechanism that selenite seems to be absorbed by roots via phosphorus (P) and silicon (Si) transporters signifies P and Si may affect selenite uptake. However, the role of P and Si in phloem-mediated selenium (Se) transport within plant tissue is unknown. Therefore, in this work, tomato (Solanum lycopersicum L.) seedlings were exposed to selenite under different hydroponic conditions firstly. And then, split-root experiments were conducted. Results showed that Se uptake decreased as external pH increased. At pH 8, more selenite in the form of SeO32- was assimilated under P-deficient conditions than under P-normal conditions. Silicate inhibited Se uptake only at pH 3 (27.5% H2SeO3 +72.5% HSeO3-). The results of split-root experiments showed that Se concentrations in seedlings increased under heterogeneously high P or Si. Selenium transport from shoots to roots immersed in solution without selenite was also enhanced. This study illustrated that the affinity of tomato roots to assimilate selenite species followed the order of H2SeO3 >HSeO3- >SeO32-. H2SeO3 was absorbed into roots via Si transporters, whereas HSeO3- and a portion of SeO32- were absorbed via low- and high-affinity P transporters, respectively. In addition, heterogeneously high P or Si concentrations in environmental media could enhance phloem-mediated Se redistribution.

Effects of foliar application of selenate and selenite at different growth stages on Selenium accumulation and speciation in potato (Solanum tuberosum L.).

Since the potato is a new staple food in China, the production of selenium (Se)-enriched potato may be an effective approach for Se supplementation in Se-deficient populations. Herein, we biofortified potato via the foliar application of sodium selenate and sodium selenite at three growth stages and investigated the resulting Se contents and speciation. Results showed that selenate was more efficient than selenite in improving total Se, and the highest tuber Se concentration was obtained at the tuber bulking stage. However, the accumulation of inorganic Se was higher in tubers treated with selenate (31.9% of total Se) compared with the selenite treatment (1.5%). The major Se species in tubers treated with both selenite and selenate was selenomethionine, which accounted for ∼80.0% and ∼50.0% of total Se, respectively. The findings suggest that the foliar application of selenite during the tuber bulking stage is appropriate for the production of Se-rich potatoes.

Phase I trial of selenium plus chemotherapy in gynecologic cancers.

PURPOSE: Preclinical studies performed in our laboratory have shown that high-dose selenium inhibits the development of carboplatin drug resistance in an ovarian cancer mouse xenograft model. Based on these data, as well as the potential serious toxicities of supranutritional doses of selenium, a phase I trial of a combination of selenium/carboplatin/paclitaxel was designed to determine the maximum tolerated dose, safety, and effects of selenium on carboplatin pharmacokinetics in the treatment of chemo-naive women with gynecologic cancers. Correlative studies were performed to identify gene targets of selenium. METHODS: Chemo-naïve patients with gynecologic malignancy received selenious acid IV on day 1 followed by carboplatin IV and paclitaxel IV on day 3. A standard 3 + 3 dose-escalating design was used for addition of selenium to standard dose chemotherapy. Concentrations of selenium in plasma and carboplatin in plasma ultrafiltrate were analyzed. RESULTS: Forty-five patients were enrolled and 291 treatment cycles were administered. Selenium was administered as selenious acid to 9 cohorts of patients with selenium doses ranging from 50 µg to 5000 µg. Grade 3/4 toxicities included neutropenia (66.7%), febrile neutropenia (2.2%), pain (20.0%), infection (13.3%), neurologic (11.1%), and pulmonary adverse effects (11.1%). The maximum tolerated dose of selenium was not reached. Selenium had no effect on carboplatin pharmacokinetics. Correlative studies showed post-treatment downregulation of RAD51AP1, a protein involved in DNA repair, in both cancer cell lines and patient tumors. CONCLUSION: Overall, the addition of selenium to carboplatin/paclitaxel chemotherapy is safe and well tolerated, and does not alter carboplatin pharmacokinetics. A 5000 µg dose of elemental selenium as selenious acid is suggested as the dose to be evaluated in a phase II trial.

Effects of selenium application on Se content and speciation in Lentinula edodes.

Edible fungi have strong ability to transform inorganic Se into organic forms. Therefore, different concentrations of selenite, selenate and Se-yeast were injected as Se-supplements into substrates to produce Se-enriched Lentinula edodes. The Se content and its speciation distribution in the fruit bodies of L. edodes were analysed at different harvest times. Results indicate that Se concentrations of L. edodes increased first and then decreased over time. Based on Se accumulation in L. edodes, selenium use efficiency was ranked as selenite > selenate > Se-yeast. SeMet was the predominant Se speciation in the fruit bodies of L. edodes. SeMet made up the biggest proportion of total Se content and increased with application time for selenite and selenate treatments, whereas no significant change was found for Se-yeast treatment. This study demonstrates that Se-enriched L. edodes is a good source of dietary Se.

Selenium accumulation and the effects on the liver of topmouth gudgeon Pseudorasbora parva exposed to dissolved inorganic selenium.

Selenite(IV) and selenate(VI) are the major forms of Se in aquatic ecosystem. In this study, Pseudorasbora parva were exposed to 10, 200 and 1000 µg L-1 selenite and selenate for 28 days. Selenium accumulation, antioxidant enzyme levels, glutathione concentrations, lipid peroxidation and histology were evaluated in livers following exposure. Our results showed that Se(IV) and Se(VI) caused different accumulation patterns in the liver, with a more rapid accumulation of Se with Se(IV) treatment. Both Se species increased hepatic lipid peroxidation after 14 and 28 d (~ 30%). Among the antioxidants examined, the activity of SOD (except day 28) and the cellular levels of GSH were induced by 72-137% at lower concentrations, while the activity of GST was at least 24% lower than that of the control at 200 and 1000 µg L-1 for both Se species at all sampling points. Both forms of Se reduced the hepatosomatic index at 1000 µg L-1 after 28 d. In addition, marked histopathological alterations (10-31%) were observed in the liver of P. parva after exposure to both Se species, with higher frequency in the Se(IV) exposed fish. Liver local necrosis was observed only in the liver of fish exposed to 1000 µg L-1 of Se(IV) (~ 20%). Our results suggest that the ecological impacts of dissolved Se in this freshwater species may also contribute to overall toxicity.

Selenium speciation influences bioaccumulation in Limnodynastes peronii tadpoles.

Despite being essential for animal health and fitness, Se has a relatively narrow range between deficiency and toxicity, and excess Se can cause a variety of adverse effects in aquatic organisms. Amphibians are particularly vulnerable to contaminants during larval aquatic life stage, because they can accumulate toxic ions through various routes including skin, gills, lungs and digestive tract. Few attempts have been made to understand the tissue-specific accumulation of trace elements, including the impacts of chemical speciation in developing amphibian larvae. We used radiolabelled 75Se to explore the biokinetics and tissue distributions of the two dominant forms occurring in surface waters, selenite (SeIV) and selenate (SeVI). Tadpoles of the native Australian frog Limnodynastes peronii were exposed to Se in both forms, and live-animal gamma spectroscopy was used to track accumulation and retention over time. Tissue biodistributions were also quantified at the end of the uptake and depuration phases. Results showed the bioconcentration of SeIV to be 3 times greater compared to SeVI, but rates of elimination were similar for both forms. This suggests a change of Se speciation within the organism prior to excretion. Depuration kinetics were best described by a one-phase exponential decay model, and tadpoles retained approximately 19% of the accumulated Se after 12 days of depuration in clean water. Selenium bioaccumulation was greatest in digestive and excretory organs, as well as the eye, which may directly relate to previously reported Se-induced impairments. Results demonstrate how the use of radiotracing techniques can significantly improve our understanding of trace element toxicokinetics and tissue distributions in developing amphibians. From an environmental monitoring perspective, the findings highlight the importance of considering chemical speciation as this could influence the accuracy of risk assessment.

Effects of selenite on green microalga Haematococcus pluvialis: Bioaccumulation of selenium and enhancement of astaxanthin production.

Algae are at a low trophic level and play a crucial role in aquatic food webs. They can uptake and accumulate the trace element selenium (Se), which can be either essential or toxic to algal growth depending on the dosage and species. Se toxicity and algae resistance varied across different organisms. In order to investigate the effects of Se on the unicellular green alga Haematococcus pluvialis, an important industrial resource for natural astaxanthin, the algal growth rate, chlorophyll content, and fluorescence parameters were derived from experimental treatment with different concentrations of selenite. The results showed that the EC50 for the algal growth rate was 24mg/L, and that a low dosage of selenite (3mg/L) may not hinder H. pluvialis cell growth, but selenite at levels higher than 13mg/L do restrain cell growth. Bioaccumulation experiments showed that H. pluvialis accumulated up to 646µg/g total Se and 380µg/g organic Se, dry weight. However, treatment with high concentrations of selenite significantly increased intracellular hydrogen peroxide levels, antioxidant enzyme activity, and the production of astaxanthin, suggesting that Se bioaccumulation might be toxic to H. pluvialis.

Influence of Se concentrations and species in hydroponic cultures on Se uptake, translocation and assimilation in non-accumulator ryegrass.

The success of biofortification and phytoremediation practices, addressing Se deficiency and Se pollution issues, hinges crucially on the fate of selenium in the plant media in response to uptake, translocation and assimilation processes. We investigate the fate of selenium in root and shoot compartments after 3 and 6 weeks of experiment using a total of 128 plants grown in hydroponic solution supplied with 0.2, 2, 5, 20 and 100 mg L-1 of selenium in the form of selenite, selenate and a mixture of both species. Selenate-treated plants exhibited higher root-to-shoot Se translocation and total Se uptake than selenite-treated plants. Plants took advantage of the selenate mobility and presumably of the storage capacity of leaf vacuoles to circumvent selenium toxicity within the plant. Surprisingly, 28% of selenate was found in shoots of selenite-treated plants, questioning the ability of plants to oxidize selenite into selenate. Selenomethionine and methylated organo-selenium amounted to 30% and 8% respectively in shoots and 35% and 9% in roots of the identified Se, suggesting that selenium metabolization occurred concomitantly in root and shoot plant compartments and demonstrating that non-accumulator plants can synthesize notable quantities of precursor compound for volatilization. The present study demonstrated that non-accumulator plants can develop the same strategies as hyper-accumulator plants to limit selenium toxicity. When both selenate and selenite were supplied together, plants used selenate in a storage pathway and selenite in an assimilation pathway. Plants might thereby benefit from mixed supplies of selenite and selenate by saving enzymes and energy required for selenate reduction.

Differing cytotoxicity and bioavailability of selenite, methylselenocysteine, selenomethionine, selenosugar 1 and trimethylselenonium ion and their underlying metabolic transformations in human cells.

SCOPE: The trace element selenium (Se) is an integral component of our diet. However, its metabolism and toxicity following elevated uptake are not fully understood. Since the either adverse or beneficial health effects strongly depend on the ingested Se species, five low molecular weight species were investigated regarding their toxicological effects, cellular bioavailability and species-specific metabolism in human cells. METHODS AND RESULTS: For the first time, the urinary metabolites methyl-2-acetamido-2-deoxy-1-seleno-ß-D-galactopyranoside (selenosugar 1) and trimethylselenonium ion (TMSe) were toxicologically characterised in comparison to the food relevant species methylselenocysteine (MeSeCys), selenomethionine (SeMet) and selenite in human urothelial, astrocytoma and hepatoma cells. In all cell lines selenosugar 1 and TMSe showed no cytotoxicity. Selenite, MeSeCys and SeMet exerted substantial cytotoxicity, which was strongest in the urothelial cells. There was no correlation between the potencies of the respective toxic effects and the measured cellular Se concentrations. Se speciation indicated that metabolism of the respective species is likely to affect cellular toxicity. CONCLUSION: Despite being taken up, selenosugar 1 and TMSe are non-cytotoxic to urothelial cells, most likely because they are not metabolically activated. The absent cytotoxicity of selenosugar 1 and TMSe up to supra-physiological concentrations, support their importance as metabolites for Se detoxification.

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

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

[Pharmaconutrition with parenteral selenium in sepsis]. / Farmaconutrición parenteral con selenio en la sepsis.

Critical illness is characterized by oxidative stress which leads to multiple organ failure, and sepsis-related organ dysfunction remains the most common cause of death in the intensive care unit. Over the last 2 decades, different antioxidant therapies have been developed to improve outcomes in septic patients. According to recent evidence, selenium therapy should be considered the cornerstone of the antioxidant strategies. Selenium given as selenious acid or sodium selenite should be considered as a drug or pharmaconutrient with prooxidant and cytotoxic effects when a loading dose in intravenous bolus form is administered, particularly in the early stage of severe sepsis/septic shock. To date, several phase ii trials have demonstrated that selenium therapy may be able to decrease mortality, improve organ dysfunction and reduce infections in critically ill septic patients. The effect of selenium therapy in sepsis syndrome must be confirmed by large, well designed phase iii clinical trials. The purpose of this review is to discuss current evidence on selenium pharmaconutrition in sepsis syndrome.

Translocation of 125I, 75Se and 36Cl to wheat edible parts following wet foliar contamination under field conditions.

Apart from radiocaesium and radiostrontium, there have been few studies on the foliar transfer of radionuclides in plants. Consequently, specific translocation factor (ftr) values for (129)I, (79)Se and (36)Cl are still missing from the IAEA reference databases. The translocation of short - lived isotopes, (125)I and (75)Se, and of (36)Cl to wheat grain were measured under field conditions following acute and chronic wet foliar contamination at various plant growth stages in the absence of leaching caused by rain. The translocation factors ranged from 0.02% to 1.1% for (125)I (a value similar to Sr), from 0.1% to 16.5% for (75)Se, and from 1% to 14.9% for (36)Cl. Both (36)Cl and (75)Se were as mobile as Cs. The phenomenological analysis showed that each element displayed a specific behavior. Iodide showed the lowest apparent mobility because of its preferential fixation in or on the leaves and a significant amount probably volatilized. Selenite internal transfer was significant and possibly utilized the sulphur metabolic pathway. However bio - methylation of selenite may have led to increased volatilization. Chloride was very mobile and quickly diffused throughout the plant. In addition, the analysis underlined the importance of plant growth responses to annual variations in weather conditions that can affect open field experiments because plant growth stage played a major role in ftr values dispersion. The chronic contamination results suggested that a series of acute contamination events had an additive effect on translocated elements. The highest translocation value obtained for an acute contamination event was shown to be a good conservative assessment of chronic contamination if data on chronic contamination translocation are lacking. The absence of rain leaching during the experiment meant that this investigation avoided potential radionuclide transfer by the roots, which also meant that radionuclide retention on or in the leaves was maximized. This study was therefore able to obtain accurate translocation factors, which are probably among the highest that could be recorded.