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PubMed1994

Metabolic relevance of selenium in the insect Corcyra cephalonica. Uptake of 75Se and subcellular distribution.

Requirement, uptake, and subcellular distribution of Na2(75)SeO3 in the larvae of the insect C. cephalonica was investigated. That Se is well tolerated by C. cephalonica upto an added level of 2 ppm in the diet is suggested by the observed increase in body weight, total protein, and succinate dehydrogenase levels. Significant increases in the State 3 respiration ensued with Se supplementation up to 2 ppm in the mitochondrial oxidation of D-glycerol 1-phosphate, succinate and NADH, along with concomitant unaltered State 4 respiration, leading to enhanced RCR values. Maximal uptake of 75Se was registered in the larvae maintained on basal diet when subjected to short-term exposure to 0.5 ppm 75Se level. When exposure level was further increased up to 20 ppm, the observed decrease in the uptake of 75Se suggested that Se status of larvae itself controlled the tissue uptake. Subcellular distribution pattern revealed maximal incorporation of 75Se (cpm/g tissue) in the supernatant fraction, whereas, maximal specific 75Se activity (cpm/mg protein) was associated with the mitochondrial fraction. Autoradiography of the soluble fractions indicated the presence of single selenoprotein in the larval group with short term 2 ppm 75Se exposure. Inherent Se controls both the extent and the nature of distribution of mitochondrial 75Se incorporation. Uptake of 45Ca by the insect mitochondria was enhanced by dietary Se up to 2 ppm but was unaffected by addition of in vitro 75Se in the medium. A more fundamental role for Se in the mitochondrial energy metabolism emerges from these studies.

Animals↗
PubMedDate not supplied

The incorporation of Na2 75SeO3 into sheep erythrocytes.

Injection of Na2 75SeO3 into untreated, phlebotomized, and phenylhydrazine treated sheet has shown that the rate of 75SeO3-incorporation into erythrocytes is dependent on the degree of stimulation. Analysis of labeled erythrocytes by gel filtration and two-dimensional electrophoresis has indicated that the transient labeling of a hemoglobin-like peptide is the only protein labeled in addition to glutathione peroxidase.

Animals↗
PubMedDate not supplied

Role of glutathione in selenite binding by human plasma.

The erythrocyte-mediated reduction of selenite has been reproduced by the addition of reduced glutathione to plasma at levels comparable to those present in the erythrocyte. The reaction has been followed by chromatography and ultraviolet (UV) absorption spectroscopy (in the absence of plasma). The first detectable compound, selenium diglutathione, is very unstable in physiological conditions. The product of the reaction does not contain glutathione and is able to react and incorporate selenium into plasma proteins without the participation of hemoglobin or glutathione reductase. A saturable low molecular weight compound is also able to bind selenium, which may be relevant in the initial distribution and excretion of selenium after selenite administration.

Blood Proteins↗
PubMedDate not supplied

Cellular selenoproteins and the effects of selenite on cell proliferation.

The incorporation of radioactive selenium into cellular proteins and the effect of selenite on proliferation were examined in human (HeLa, HT-29, and IMR-90) and mouse (3T3 and CMT-93) cell lines. Proteins incorporating selenium were detected by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Major polypeptide subunits at 60, 23, 21, 19, and 16 kD were detected in the two tumorigenic and one normal human cell lines. The 23 kD polypeptide migrated to the same position on the gel as the major subunit of human erythrocyte glutathione peroxidase. In the mouse cells, the 60 kD polypeptide was almost entirely absent; four other major selenoproteins were detected, with molecular weights similar to those in the human cells. In both mouse and human cells, the same pattern of selenoproteins was observed irrespective of whether the cells were grown in medium containing 10% fetal bovine serum or in defined medium supplemented with 0.1 or 1 microM selenite, or with 1% serum. The effect of selenite on proliferation of HeLa, HT-29, and CMT-93 cells in medium supplemented with 10% fetal bovine serum and in serum-free medium was examined. At concentrations up to about 1 microM, selenite stimulated proliferation of the human cells slightly in serum-free medium but not in serum-supplemented medium. At concentrations of about 5 microM and higher selenite significantly inhibited proliferation of all cells in both types of media. In CMT-93 cells, this inhibition was greater in serum-free medium, but there were no significant differences in this regard in the human cells. These results demonstrate that selenium is stably incorporated into several polypeptides in human and mouse cells, that there are no significant differences in this regard among several cell lines, and slight differences between human and mouse cells. They further confirm that selenium can have a slight stimulatory effect on cell growth, and a much larger inhibitory effect, depending on its concentration.

Animals↗
PubMedDate not supplied

Effect of dietary selenium and tumor status on the retention of 75Se by tissues and mammary tumors of DMBA-treated rats.

The effects of the presence of mammary tumors on 75Se retention was examined in DMBA-treated rats. Tumor bearing rats fed varying amounts of Se exhibited an inverse linear dose response between dietary Se intake and tissue retention of 75Se in whole body, heart, lungs, ovaries, adrenals, spleen, and muscle. Tumor 75Se retention, however, was independent of the dietary intake of Se. Tumor bearing rats excreted more 75 Se label in the urine compared to both control rats fed the same amount of Se and DMBA-treated animals that remained tumor free. In the short term, no significant differences were seen in tissue retention of 75Se. By 7 d, the increased urinary excretion of the label resulted in significantly decreased retention of 75Se in blood, spleen, liver, lungs, and kidneys of tumor-bearing rats compared to tumor-free animals. The presence of tumors, however, did not affect the liver distribution of the label among cytosolic proteins. These results suggest that tumor bearing animals have an accelerated urinary excretion of Se compared to animals without tumors and that tumors either have a very slow turnover of Se or a low priority for the element.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1994

Uptake, distribution, and turnover rates of selenium in barley.

The present communication elucidates initially the topographic distribution of selenium in barley grains. Then by the fluorimetric method the uptake of selenium (selenite) in 8-16 d old germinating barley was estimated. Finally by means of 75Se the anabolic and catabolic rates (turnover) of 75Se (selenite) was compared. The distribution of selenium in barley was evaluated after micro-dissection of barley grains. In dried grains the highest concentration was found in husk and pericarp with about 0.6 ppm Se. Then followed Scutellum with 0.4 and 0.3 ppm in embryon. The aleurone layer, embryonic leaves, and initial root did only have 0.2 ppm Se. In order to know more about the uptake and distribution of selenium in 8-d-old barley, the plants were cultivated for a further 8 d in the culture medium with variation in selenite concentration. In roots and leaves, the uptake did not arrive at saturation during the period studied since the dose-response curve increased up to 0.34 mM selenite in the medium, whereas the selenium levels were about 200 ppm in roots and 30 ppm in leaves. However, the uptake was linear, with concentration during 8 d of cultivation up to 0.84 microM selenite for grain and stem. At higher concentrations the dose-response curve diminished its slope. At 0.34 mM selenite the concentration in grain increased to 6.87 ppm and in the stem to 8.13 ppm. The uptake, distribution, and catabolic rate of selenium components in germinating barley were further evaluated by exposing the plants to 0.0492 microCi 75Se (12.6 microM selenite) for up to 4 d. Then the plants were moved to a selenium deficient medium for further 4 d. Then finally the medium was supplemented with high doses of cold selenite (0.126 mM selenite) for further 4 d. The first third period made it possible to estimate the rate of uptake. It was highest in roots (313 fmol/h/mg dw), i.e., about 10 times those of grains, stems, and leaves. The intermediate period where the barley was transferred to a selenium deficient medium made it possible to estimate the kinetics and eventual sparing mechanisms. The selenium losses were highest for leaves (39%), then followed by roots and stems (22 and 25%, respectively). The losses were lowest in grain with 9% Se losses. The losses were three times more pronounced during the first day than in the following 3 d. These data may argue that the selenium is distributed into different pools and that sparing mechanisms may be in function.(ABSTRACT TRUNCATED AT 400 WORDS)

Hordeum↗
PubMedDate not supplied

Selenite metabolism in rat and human blood.

The binding of selenite, the form of selenium used in the treatment of Keshan disease, to plasma proteins and the role of erythrocytes in this process have been studied. The experiments were carried out by incubating 75Se as selenite with plasma and whole blood in vitro (human and rat) and in vivo (rat) and subsequent fractionation by Sephadex G-150 gel filtration. Human and rat plasma proteins were unable to incorporate selenium from selenite, as shown by the negligible amount present in proteins after incubation of plasma with selenite. The incorporation can be carried out after internalization of selenite by the erythrocytes in a fast, temperature dependent process. Hemoglobin, being the major binding protein for the newly reduced selenium in the erythrocyte, might have a role in the uptake of selenite by erythrocytes. The greater affinity of plasma proteins for the final selenium compound resulting from reduction could be the cause of the efflux. However, this is minimal in the absence of plasma, as is evident from the results obtained from blood reconstituted with saline solution instead of plasma. At least two proteins, one albumin like, probably albumin itself and the other of molecular weight close to or greater than 200,000 in the plasma, are involved in the binding and efflux processes.

Animals↗
PubMedDate not supplied

Zinc-selenium interaction in the rat.

Retention, dynamics of 75Se and 65Zn distribution, and elimination were studied in rats after separate or joint single doses of these metals. White female Wistar rats were divided into four groups (fifteen rats each). Group I received Na2(75)SeO3 (0.1 mg Se/kg i.g.), group II received Na2(75)SeO3 + ZnCl2 (5 mg Zn/kg s.c.), group III received 65ZnCl2, and group IV received 65ZnCl2 + Na2SeO3. The zinc and selenium contents in the tissues were estimated during 120 h after administration; excretion in urine and feces of animals was determined throughout the experiment. Combined administration of zinc and selenium resulted in an enhanced selenium retention in the brain, spleen, kidneys, blood, lungs, and heart. A selenium-induced increase in the concentration of zinc was noted in the bowels, blood, liver, kidneys, spleen, brain, and lungs. The effects of the zinc/selenium interaction were visible especially in the lowered level of excretion of these elements. Zinc induced a decrease in the excretion of selenium in urine, with no concomitant changes in the excretion in feces. However, a visible decrease in the excretion of zinc in the feces was observed in the presence of selenium. The present results indicate an occurrence of clear-cut interaction effects between zinc and selenium administered simultaneously in the rat.

Animals↗
PubMedDate not supplied

Selenium in the anterior pituitary of the rat after a single injection of 75Se sodium selenite.

In order to investigate the selenite metabolism in the anterior pituitary and compare it with other endocrine organs, rats were injected intraperitoneally with 75Se sodium selenite (5 mg/kg). The rats were whole body counted shortly after injection and recounted just before sacrifice, which was performed 2, 24, 48 h, and 4, 10, 20, 30, 40, 60, and 80 d after injection. Besides the anterior pituitary, the selenium content was also estimated in the thyroid gland, testis, adrenals, liver, kidney, and blood. The maximum selenium content was observed in all organs 2 h after injection, at which time the anterior pituitary contained 2.9 micrograms/g wet wt, compared to 13.5 micrograms/g wet wt in liver and .6 micrograms/mg wet wt in testis. The excretion of selenite from the anterior pituitary resembled that seen in most other organs investigated, i.e., an initial rapid excretion and a slower secondary phase resembling a first order reaction. Practically all selenium was excreted by 60 d after injection. The selenium content in pituitaries from untreated rats was estimated by PIXE analysis to be 2.2 +/- .1 micrograms dry wt and .48 +/- .03 micrograms/g wet wt. From the present study it can be concluded that selenium in the form of selenite accumulates in the anterior pituitary after a single intraperitoneal injection; selenite is excreted from the gland in a biphasic manner; practically all selenium is excreted within 60 d; and pituitaries from normal rats contain .48 micrograms selenium/g wet wt.

Adrenal Glands↗
PubMed1991

Products of the reaction of selenite with intracellular sulfhydryl compounds.

The usual first step in the intracellular metabolism of exogenous selenite is its chemical reaction with glutathione to form selenodiglutathione (1). We have investigated whether selenite also reacts intracellularly with other SH compounds. HeLa cells were exposed to [75Se]selenite and lysed with SDS. Cellular proteins and nucleic acids were precipitated with trichloroacetic acid, and the acid-soluble fraction was analyzed by ion-exchange thin-layer chromatography (ion-exchange TLC) and autoradiography. In control cells, the major [75Se]-containing species detected can be identified by its mobility as selenodiglutathione. Two other species were detected, which can be identified as selenodimercaptoethylamine and the mixed selenotrisulfide of mercaptoethylamine and glutathione. In contrast, in cells that were depleted of glutathione (by treatment with buthionine sulfoximine), very little, if any, selenodiglutathione was detected. However, new [75Se]-containing species were detected, which can be identified as selenodicysteine and the mixed selenotrisulfide of cysteine and glutathione. The same species were detected when [75Se]selenite was added to the acid-soluble fraction of a cell extract (as opposed to living cells), confirming that these compounds can be formed by nonenzymatic reactions.

Antimetabolites↗
PubMedDate not supplied

Combination of neutron activation analysis, tracer techniques, and biochemical methods in the investigation of selenium metabolism.

In several studies on rats, the metabolism of selenium was investigated. The quantitative determination of the element was carried out by instrumental neutron activation analysis. For in vivo tracer experiments, 75Se-labeled selenium compounds were used. In addition to these methods, procedures for the measurement of the selenoenzyme glutathione peroxidase, and for the investigation of other selenoproteins, were applied. In this way, information on the specific pools and sites of action of the element, on biologically important selenoproteins and the regulation of the selenium metabolism, was obtained.

Animals↗
PubMed1994

Effect of selenium compounds on murine B16 melanoma cells and pigmented cloned pB16 cells.

The effects of selenium compounds such as sodium selenite, sodium selenate, seleno-DL-cystine and seleno-DL-methionine (100 microM and 10 microM) on B16 and pigmented cloned pB16 murine melanoma cells were investigated in vitro. At the tested concentrations, B16 cells showed a greater sensitivity to the toxic effects of sodium selenite and seleno-DL-cystine than pB16 cells, whereas no decrease of B16 and pB16 cell number was observed after incubation with sodium selenate or seleno-DL-methionine. Glutathione (GSH) percentages were strongly decreased only by selenite and seleno-DL-cystine; it was marked more in B16 than in pB16 cells. The pretreatment of B16 cells with a GSH depleting agent (10 microM buthionine-[S,R]-sulfoximine) did not significantly influence the cytotoxic effects of selenite and seleno-DL-cystine. On both cell populations, GSH preincubation (50 microM) enhanced the cytotoxicity of selenite whereas the survival of seleno-DL-cystine treated cells was increased. Glutathione peroxidase (GSH-Px) activity in B16 cells was more sensitive than in pB16 cells to the activating effect of selenite, and particularly of seleno-DL-cystine: however, cell-free controls indicated that activation was mainly due to glutathione reductase. The rate of 75Se (as sodium selenite) uptake in both cell populations was maximal within the first hour of incubation, with a preferential accumulation in the cytosol; after 24 h of incubation, the amount of 75Se in cytosol and pellet was approximately the same.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Characterisation of selenium compounds in rye seedling biomass using 75Se-labelling/SDS-PAGE separation/gamma-scintillation counting, and HPLC-ICP-MS analysis of a range of enzymatic digests.

In the present study, selenium-enriched plant biomass was investigated to evaluate the ability of rye seedlings to take up, and assimilate, inorganic selenium. Two different analytical approaches were used. Electrophoretic separation (SDS-PAGE) of proteins extracted from 75Se-labelled biomass was used to investigate the biotransformation of selenite into organic forms of the element. Ion-pair chromatography coupled with ICP-MS detection was chosen for the analysis of selenium species, enzymatically extracted from the plant biomass. The results of three enzymatic hydrolysis procedures and three sequential enzymatic extractions procedures are compared. The most effective single extraction was proteolysis (using protease type XIV), giving an overall extraction efficiency of 48%. However, for combinations of enzymes, the most effective was cellulase (Trichoderma viride) followed by sequential extraction of the solid pellet using protease type XIV, giving an extraction efficiency of 70%. The complementary data from the electrophoretic fractionation of proteins, and the HPLC separation of Se-species in the proteolytic digests, reveal the existence of large number of selenium-containing compounds in the rye seedling plant biomass. The results showed the complete biotransformation of inorganic selenium into organic forms during germination of the rye seedlings. HPLC-ICP-MS analysis of extracts from the plant biomass did not show the presence of selenate or selenite. At the time of this study, the lack of suitable organic-MS facilities meant that it was not possible to characterise them fully. However, the data does show that a combination of different enzymes, rather than just the commonly-used protease, should be considered when developing an extraction strategy for selenium in different food types to those already reported in the literature.

Biomass↗
PubMed2001

ICP-MS with hexapole collision cell for isotope ratio measurements of Ca, Fe, and Se.

To avoid mass interferences on analyte ions caused by argon ions and argon molecular ions via reactions with collision gases, an rf hexapole filled with helium and hydrogen has been used in inductively coupled plasma mass spectrometry (ICP-MS), and its performance has been studied. Up to tenfold improvement in sensitivity was observed for heavy elements (m > 100 u), because of better ion transmission through the hexapole ion guide. A reduction of argon ions Ar+ and the molecular ions of argon ArX+ (X = O, Ar) by up to three orders of magnitude was achieved in a hexapole collision cell of an ICP-MS ("Platform ICP", Micromass, Manchester, UK) as a result of gas-phase reactions with hydrogen when the hexapole bias (HB) was set to 0 V; at an HB of 1.6 V argon, and argon-based ions of masses 40 u, 56 u, and 80 u, were reduced by approximately four, two, and five orders of magnitude, respectively. The signal-to-noise ratio 80Se/ 40Ar2+ was improved by more than five orders of magnitude under optimized experimental conditions. Dependence of mass discrimination on collision-cell properties was studied in the mass range 10 u (boron) to 238 u (uranium). Isotopic analysis of the elements affected by mass-spectrometric interference, Ca, Fe, and Se, was performed using a Meinhard nebulizer and an ultrasonic nebulizer (USN). The measured isotope ratios were comparable with tabulated values from IUPAC. Precision of 0.26%, 0.19%, and 0.12%, respectively, and accuracy of 0.13% 0.25%, and 0.92%, respectively, was achieved for isotope ratios 44Ca/ 40Ca and 56Fe/57Fe in 10 microg L(-1) solution nebulized by means of a USN and for 78Se/80Se in 100 microg L(-1) solution nebulized by means of a Meinhard nebulizer.

Calcium↗
PubMed2005

A new method for evaluation of radioactive label transport intensity in the predominant direction between blood and liver.

The intensity of (75)Se transport in the predominant direction after intraperitoneal injection of [(75)Se]selenate was compared in 1- and 3-month-old rats receiving common vivarium ration or sucrose diet. The incorporation percent, blood/liver relative radioactivity, and relative radioactivity difference coefficient were evaluated in the blood and liver. The dynamics of label incorporation in the blood of rats fed common diets has two peaks (at 1-3 h and 12-24 h) and a drop at 6 h. Coefficient of difference in 1-month-old rats was characterized by a greater amplitude of fluctuations than in 3-month-old animals.

Age Factors↗