Se Accumulation In Tissues Research Articles

Effects of dietary selenium on growth performance, antioxidative status and tissue selenium deposition of juvenile Chu's croaker (Nibea coibor)

Selenium (Se) is an essential antioxidative trace element for animals. Proper dietary Se supplementation could promote growth and antioxidative ability of fish species, especially for those under oxidative stress caused by high-density aquaculture model. However, the narrow safety rage between deficiency and toxicity doses of Se complicates its use for supplementation purpose. Here, we reported the effects of dietary Se supplementation with sodium selenite (0.21, 0.53, 0.79, 1.11, 1.45 and 1.72 mg Se/kg diet, P1–P6) on the growth performance, antioxidative status and tissue Se deposition of an important marine economic fish, Chu's croaker (Nibea coibor). After an 8-week feeding trial, it was demonstrated that the dietary Se supplementation (P1–P3) significantly improved the weight gain of the fish, while a decreased trend of weight gain was observed at higher Se supplementation levels (P4–P6). The activities of glutathione peroxidase (GPx) in serum and liver significantly increased with the increasing Se levels. While, the activities of superoxide dismutase (SOD) and catalase (CAT) firstly increased and then decreased with the increasing Se levels, with highest value presented in P4 and P3 group, respectively. The trends of malondialdehyde (MDA) content in serum and liver were opposite to those of CAT, with lowest value in P3 group. Similar to their enzyme activity counterparts, the mRNA expression of GPx1, SOD1 and SOD2 in liver were also significantly affected by the dietary Se levels. Furthermore, it was shown that Se contents in liver, muscle and swim bladder linearly increased with the dietary Se levels, with the Se accumulation efficiency of liver > muscle > swim bladder. It can be concluded that a dietary Se supplementation of 0.74 mg/kg is suggested for the aquaculture of juvenile N. coibor, based on the weight gain, antioxidative enzyme activities/expression and tissue Se accumulation.

High dietary inorganic selenium has minimal effects on turkeys and selenium status biomarkers.

The current NRC turkey Se requirement is 0.2μg Se/g diet. Recent studies evaluating tissue Se, glutathione peroxidase (GPX) activities, and selenoprotein transcript expression concluded that the dietary Se requirement of the turkey poult should be raised to 0.4μg Se/g when supplemented with inorganic Se. The FDA currently limits Se inclusion in premixed diets for poultry and other livestock species to 0.3μg Se/g diet. Thus, there is a need to investigate the effect of high dietary Se (>1.0μg Se/g) in turkeys. The present study fed turkey poults 2 and 5μg Se/g diet to characterize tissue Se accumulation in turkey poults fed high dietary inorganic Se and to evaluate the efficacy of selenoprotein activity and transcript expression as biomarkers of high Se status. Day-old male poults were fed 0.4, 2, or 5μg Se/g for 28 d. There was no significant effect of Se supplementation on poult growth. Supplementation with 5μg Se/g diet resulted in Se concentrations that were 5.6X, 1.7X, 1.9X, and 2.0X greater than Se-adequate levels in liver, kidney, breast, and thigh, respectively, and GPX activities in plasma, red cells, liver, kidney, and heart that were ≤2.0X Se-adequate values. In liver, kidney, heart, gizzard, breast, or thigh, no selenoprotein transcript was increased ≥2.0X, and no selenoprotein transcript was decreased ≤0.5X by 2 or 5μg Se/g diet as compared to poults fed 0.4μg Se/g diet. Of the 112 Se status biomarkers reported in this study, liver Se concentration was the only biomarker markedly altered by high Se status. This study provides evidence of no adverse effects in turkey poults fed up to 5μg Se/g diet as inorganic Se. Thus, the FDA limit for Se supplementation in turkey feed can be safely raised to 0.5μg Se/g diet. Future studies are needed to identify biomarkers for high Se status and to better understand how turkeys maintain Se homeostasis and resist Se toxicity.

Bioaccumulation, oxidative stress, immune responses and immune-related genes expression in northern snakehead fish, Channa argus, exposure to waterborne selenium.

The objective of this study was to evaluate the toxic effects on bioaccumulation, oxidative stress, immune responses and immune-related genes expression of Channa argus exposed for 28days with waterborne selenium (0, 50, 100, 200, and 400µg/L). After 28days, the order of Se accumulation in tissues was kidney > liver > spleen > intestine > gill > muscle. Antioxidant parameters in liver and spleen of C. argus evidenced an oxidative stress condition in waterborne selenium. In addition, immunological parameters and immune-related gene expression were all enhanced with an increase in Se expose levels. Our results suggest that waterborne Se exposure can induce considerable Se accumulation, oxidative stress and immunotoxic effects on C. argus.

Feed Utilisation Efficiency of Lupin Inclusion in Cobia: Role of Dietary Organic Selenium Supplementation

The dietary selenium (Se) requirement has been determined for cobia Rachycentron canadum using purified diet; however, its role in the utilisation of plant-derived ingredients has not been evaluated in the species. Therefore, a 3 x 2 factorial experimental design involving three inclusion levels (0, 210 and 315 g/kg) of lupin Lupinus angustifolius kernel meal (LKM) and two concentrations (0 and 0.8 mg/kg) of Se was used to evaluate the effects of Se supplementation in conjunction with LKM on the growth, feed utilisation and physiological responses in the cobia. Six isonitrogenous (46.5 % crude protein) and isoenergetic (21 MJ/kg gross energy) diets were formulated and fed to cobia for 7 weeks in a flow-through seawater system. The results showed significant effects of Se supplementation and its interaction with dietary lupin on the growth and feed efficiency of cobia. Se supplementation significantly improved the growth and feed utilisation efficiency in cobia fed lupin-based diets. The nutrient digestibility of fish fed supplemental Se lupin-based diets was significantly higher than that of fish fed diets without Se supplementation at each inclusion level of LKM. There were no significant effects of dietary Se supplementation on the survival, muscle composition or muscle amino acids, whereas regression analysis indicated a positive linear relationship between tissue Se accumulation and dietary Se levels. An enhancement of haematological responses was also observed in cobia fed Se-supplemented diets. In summary, cobia fed lupin-based diets required higher dietary Se supplementation for higher feed utilisation efficiency than previously quantified for the casein-based diet.

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

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

The selenium accumulation and its effect on growth, and haematological parameters in red sea bream, Pagrus major, exposed to waterborne selenium

Juvenile Pagrus major (mean length 15.8±1.6cm, and mean weight 90.4±4.7g) were exposed for 4 weeks with waterborne selenium concentration (0, 50, 100, 200, and 400µg/L). The profile of Se accumulation among tissue in P. major is dependent on the exposure periods and Se concentration. After 4 weeks, the highest accumulation of Se was observed in the kidney, and the order of Se accumulation in tissues was kidney≈liver>spleen>intestine>gill>muscle. Se decreased the growth rate, and there was an inverse proportion between growth and Se concentration. The major hematological findings were significant decrease in the RBC count, Ht value, and Hb concentration exposed to ≥100µg/L Se concentrations. Se exposure (≥100µg/L) led to significant increase in the glucose, GOT, and GPT levels, whereas the levels of calcium, magnesium, cholesterol, and total protein did not increase. The results suggest that waterborne Se exposure can induce significant Se accumulation in tissues, inhibition of growth, and hematological alterations.

Meta-analysis of selenium accumulation and expression of antioxidant enzymes in chicken tissues

A meta-analysis integrating results of 40 selenium (Se) supplementation experiments that originated from 35 different controlled randomized trials was carried out in an attempt to identify significant factors that affect tissue Se accumulation in chicken. Examined factors included: Se source (12 different sources examined), type of chicken (laying hens or broilers), age of birds at the beginning of supplementation, duration of supplementation, year during which the study was conducted, sex of birds, number of chickens per treatment, method of analysis, tissue type, concentration of Se determined and Se added to feed. A correlation analysis was also carried out between tissue Se concentration and glutathione peroxidase activity. Data analysis showed that the factors significantly affecting tissue Se concentration include type of chicken (P=0.006), type of tissue (P<0.001) and the analytical method used (P=0.014). Although Se source was not found to affect tissue Se concentration (overall P>0.05), certain inorganic (sodium selenite), calcium selenite, sodium selenate and organic sources (B-Traxim Se), Se-yeast, Se-malt, Se-enriched cabbage and Se-enriched garlic as well as background Se level from feed ingredients were found to significantly affect tissue Se concentration. The Se accumulation rate (estimated as linear regression coefficient of Se concentrations to Se added to feed) discriminated between the various tissues with highest values estimated in the leg muscle and lowest in blood plasma. Correlation analysis has also shown that tissue Se concentration (pooled data) was correlated to Se added to feed (r=0.529, P<0.01, log values) and to glutathione peroxidase activity (r=0.332, P=0.0478), with the latter not being correlated with Se added to feed. Although significant factors affecting Se concentration were reported in the present study, they do not necessarily indicate the in vivo function of the antioxidant system or the level of accumulated Se as other factors, not examined in the present study, may interact at the level of trace element absorption, distribution and retention.

Soil Sulfur Amendments Suppress Selenium Uptake by Alfalfa and Western Wheatgrass

Selenium (Se) is a potential soil contaminant in many parts of the world where it can pose a health risk to livestock and wildlife. Phosphate ore mining in Southeast Idaho has resulted in numerous waste rock dumps revegetated with forages to stabilize the dumps and support grazing. Alfalfa (Medicago sativa L.), smooth brome (Bromus inermis Leyss.), and western wheat grass [Pascopyrum smithii (Rydb.) A. Löve] are the dominant forage species on these lands. To demonstrate the feasibility of using sulfur (S) as a soil amendment to restrict plant Se uptake, 3 kg pots containing 50:50 w/w soil and waste shale were uniformly mixed with 0, 0.5, 1.0, or 2.0 Mg ha(-1) S as either elemental S or gypsum. Pots were seeded with alfalfa or western wheat grass. Dry mass and tissue Se were monitored over several clippings. Soils were sampled at the conclusion of the study and analyzed for water-soluble, oxalate-extractable, and total Se. Sulfur amendments as either elemental S or gypsum at 1.0 Mg ha(-1) or greater equally suppressed Se uptake over 60% in both forage species. Alfalfa accumulated more Se than western wheat grass. Plant removal via successive clippings resulted in lower tissue Se accumulation over time than the use of S soil amendments alone. Alfalfa-planted soils contained lower water-soluble and oxalate-extractable Se than did the non-planted controls while western wheat grass-planted soils contained lower water-soluble Se. Applying S to these shale-based soils may be an economically viable option for treating Se-impacted, revegetated lands.

Selenium from Selenium-Rich Spirulina Is Less Bioavailable than Selenium from Sodium Selenite and Selenomethionine in Selenium-Deficient Rats

The bioavailabilty of selenium (Se) from selenium-rich Spirulina (SeSp) was assessed in Se-deficient rats by measuring tissue Se accumulation and glutathione peroxidase (GSH-Px) activity. For 42 d, rats were subjected to dietary Se depletion by consumption of a Torula yeast (TY)-based diet with no Se; controls were fed the same diet supplemented with 75 microg Se/kg diet as sodium selenite. Se-deficient rats were then repleted with Se (75 microg/kg) by the addition of sodium selenite, selenomethionine (SeMet) or SeSp to the TY basal diet. Selenium speciation in SeSp emphasized the quasi-absence of selenite (2% of total Se); organic Se comprised SeMet (approximately 18%), with the majority present in the form of two selenoproteins (20-30 kDa and 80 kDa). Gross absorption of Se from SeSp was significantly lower than from free SeMet and sodium selenite. SeMet was less effective than sodium selenite in restoring Se concentration in the liver but not in kidney. SeSp was always much less effective. Similarly, Se from SeSp was less effective than the other forms of Se in restoring GSH-Px activity, except in plasma and red blood cells where no differences were noted among the three sources. This was confirmed by measuring the bioavailability of Se by slope-ratio analysis using selenite as the reference form of Se. Although Se from SeSp did not replenish Se concentration and GSH-Px activity in most tissues to the same degree as the other forms of Se, we conclude that it is biologically useful and differently metabolized due to its chemical form.

Rhizosphere bacteria enhance selenium accumulation and volatilization by indian mustard

Indian mustard (Brassica juncea L.) accumulates high tissue Se concentrations and volatilizes Se in relatively nontoxic forms, such as dimethylselenide. This study showed that the presence of bacteria in the rhizosphere of Indian mustard was necessary to achieve the best rates of plant Se accumulation and volatilization of selenate. Experiments with the antibiotic ampicillin showed that bacteria facilitated 35% of plant Se volatilization and 70% of plant tissue accumulation. These results were confirmed by inoculating axenic plants with rhizosphere bacteria. Compared with axenic controls, plants inoculated with rhizosphere bacteria had 5-fold higher Se concentrations in roots (the site of volatilization) and 4-fold higher rates of Se volatilization. Plants with bacteria contained a heat-labile compound in their root exudate; when this compound was added to the rhizosphere of axenic plants, Se accumulation in plant tissues increased. Plants with bacteria had an increased root surface area compared with axenic plants; the increased area was unlikely to have caused their increased tissue Se accumulation because they did not accumulate more Se when supplied with selenite or selenomethionine. Rhizosphere bacteria also possibly increased plant Se volatilization because they enabled plants to overcome a rate-limiting step in the Se volatilization pathway, i.e. Se accumulation in plant tissues.

Distribution of Free Seleno-amino Acids in Plant Tissue ofMelilotus indicaL. Grown in Selenium-Laden Soils

Accumulation of specific groups of seleno-amino acids in plant tissue reflects not only the Se tolerance of a plant species, but also Se toxicity to animals. The distribution of seleno-amino acids in a Se-tolerant grassland legume species (Melilotus indicaL.) grown in Se-laden soils was studied using high-resolution gas chromatography-and gas chromatography-mass spectrometry. Five seleno-amino acids including selenocystine, selenomethionine, selenocysteine, Se-methylselenocystine, andγ-glutamyl-Se-methylselenocysteine were identified and measured for their plant tissue concentrations. Se-methylselenocysteine, a nonprotein seleno-amino acid, was found in the plant tissue. Its concentration ranged from 15.3 μmol kg−1for the plants growing in soil of low Se concentration to 109.8 μmol kg−1for the plants grown in soil of high Se concentration. Accumulation of the nonprotein seleno-amino acid in this species resembles that in Se accumulator plants.γ-Glutamyl-Se-methylselenocysteine was detected in the plant. However, its concentration was very low. It might not become a toxic element in the food chain. Results of plant tissue Se accumulation analysis indicated that there was a five-fold increase in tissue selenocysteine concentration when the total tissue Se increased from 5.07 to 22.02 mg kg−1, but there was no further increase in tissue selenocysteine concentration when the tissue total Se concentration increased from 22.0 to 117.4 mg kg−1. Selenomethinone constituted more than 50% of the total seleno-amino acid in the plant. More research is needed to reveal whether the mechanisms limiting the accumulation of selenocysteine and preferential accumulation of selenomethionine found in this study play any role in Se tolerance in this species.

Subchronic effects of sodium selenite and selenomethionine on several immune-functions in mallards

The subchronic effects of selenomethionine (SeM) and sodium selenite (SeL) on several immunologic, hematologic, and serologic parameters in mallards were measured, using concentrations in drinking water of 0, 0.5, and 3.5 mg/L selenium (Se) as SeL and 2.2 mg/L (Se) as SeM. Cyclophosphamide (CP) was used as an immunosuppressive control at 20 mg/L. A battery ofin vivo andin vitro immunologic assays was performed on each bird throughout the 12 week study. The SeM-treated birds displayed a significantly impaired delayed-type hypersensitive (DTH) response to tuberculin (M. bovis), as measured by the number of positive reactions present 24 hours post PPD challenge (p ⩽ 0.05). The SeM-treated group also exhibited a significantly increased serum alanine aminotransferase (ALT) activity and an increased plasma glutathione peroxidase (GPX) activity (p ⩽ 0.05). Selenium concentration in the liver and breast muscle of SeM-treated birds was significantly elevated 4- and 14-fold, respectively, over controls (p < 0.05). Body weight and water consumption of treated birds did not differ from controls. Organ weights were not significantly affected by any Se treatment. Sodium selenite-treated birds displayed no detectable differences in immune-function or Se accumulation in tissues as compared to controls. Serum ALT activity was significantly increased in the 3.5 mg/L group, although to a lesser extent than in SeM-treated birds. Cyclophosphamide significantly depressed white blood cell number, testes weights, and also suppressed the DTH reaction. Concentrations of Se as SeL did not affect the immune system, whereas low concentrations of SeM (2.2 mg/L Se) appeared to suppress certain aspects of the mallard immune response.