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PubMed2002

Effects of methionine on selenium embryotoxicity in cultured rat embryos.

Effects of methionine, an essential amino acid, on the embryotoxicity of selenium (Se) were examined using the rat embryo culture. Rat embryos at day 9.5 of gestation were cultured for 48 h in the presence of sodium selenite at 10 and 20 microM or sodium selenate at 30 and 100 microM with or without the addition of 1 mM DL-methionine. Selenite at 20 microM or selenate at 100 microM alone increased the incidence of embryonic malformation and inhibited the embryonic growth. The addition of methionine increased the incidence of embryonic malformation at 10 microM of selenite but decreased the incidence of embryonic malformation at 100 microM of selenate. On the other hand, the addition of methionine partially restored the inhibited embryonic growth at 20 microM of selenite or at 100 microM of selenate. It was considered from these results that the methionine availability in the embryonic environment and the oxidation state of Se are critical in Se embryotoxicity.

Abnormalities, Drug-Induced↗
PubMed2002

Inhibition of telomerase activity in endometrial cancer cells by selenium-cisplatin conjugate despite suppression of its DNA-damaging activity by sodium ascorbate.

Telomerase activation can be considered as a critical step in cell immortalization. The enzyme elongates or maintains telomere length by adding to its end tandem TTAGGG repeats by using its endogenous RNA template. Telomerase is not detectable in most somatic cells but is upregulated in germ line cells and in 85-90% of human cancers, which suggests important role of telomerase in neoplastic transformation. Consequently, telomerase has been proposed as a potentially highly selective target for the development of antiproliferative agents. Platinum complexes are widely administrated in cancer therapy. A conjugate of selenite with diammineplatinum [(NH(3))(2)Pt(SeO(3))(2)] is a novel potential anticancer drug. Using alkaline single cell gel electrophoresis (comet assay), we showed that the drug at 5-30 microM induced concentration-dependent damage to DNA of endometrial cancer cells derived from tumor samples. Sodium ascorbate at 10 and 50 microM reduced the extent of the DNA damage evoked by the drug. (NH(3))(2)Pt(SeO(3)) reduced telomerase activity in the cells in a concentration-dependent manner as measured by using the telomere repeat amplification protocol (TRAP) assay. This effect was independent of sodium ascorbate. Therefore, mutagenic effects of the conjugate can be reduced by well-recognized antimutagen, sodium ascorbate, but it can still retain ability to affect neoplastic transformation. The results obtained indicate that (NH(3))(2)Pt(SeO(3)) may specifically inhibit telomerase activity in endometrial cancer cells.

Antineoplastic Agents↗
PubMed2001

Acute toxicity of sodium selenate to two daphnids and three amphipods.

This study evaluated the acute toxicity of sodium selenate to two daphnid and three gammarid amphipod species. The daphnids, Ceriodaphnia dubia and Daphnia pulex, were evaluated in 48-hour static tests and the amphipods, Gammarus pseudolimnaeus, Gammarus lacustris, and Hyalella azteca, were evaluated in 96-hour static and flow-through tests. Tests resulted in mean LC50's of 1.92, 9.12, 1.82, 3.05, and 1.95 mg/L selenium for C. dubia, D. pulex, G. pseudolimnaeus, G. lacustris, and H. azteca, respectively. The LC50's for the G. pseudolimnaeus tests are more than 30-fold higher than previously reported LC50's for the same or similar species. The explanation for these differing results appears to be partially, but not entirely, explained by differences in ambient pH between the new studies and previous ones. Depending on how the new data are included in U.S. EPA's selenium freshwater quality criterion data set, the selenate acute water quality criterion (i.e., Criterion Maximum Concentration) increases from 12.8 to as high as 583 microg/L selenium.

Animals↗
PubMed2002

Labeling of antibodies by in situ modification of thiol groups generated from selenol-catalyzed reduction of native disulfide bonds.

A new method for labeling antibodies which involves selenol-catalyzed reduction of native disulfide bonds in antibodies to generate thiol groups, which then are labeled using thiol-reactive reagents, is described. The reduction and labeling steps of this rapid procedure are carried out in one vessel, without requiring any separation step to remove the reductant before labeling. It results in a quantitative and homogenous incorporation of about seven labeled groups per antibody molecule in less than 5 min. All reagents used are commercially available-selenocystamine (catalyst precursor), dithiothreitol or tris(2-carboxyethyl)phosphine (reductant), and thiol-reactive labeling reagents such as biotin-poly(ethylene oxide)-maleimide. This method is broadly applicable for labeling proteins such as immunoglobulins with reducible disulfide bonds, whose reduction and labeling does not result in a significant loss of activity. Biotinylated murine antibodies (anti-phosphotyrosine and anti-EGF receptor) prepared by this reduced-disulfide labeling method perform comparably or better than amino-group biotinylated antibodies in applications such as enzyme-linked immunosorbent assay, immunohistochemistry, and immunoprecipitation. This reduced-disulfide labeling method is superior to amino-group labeling methods because it is not inhibited by the presence of amines in solution, as demonstrated by the biotinylation of an antibody in a hybridoma culture supernatant containing amino acids and serum proteins.

Animals↗
PubMed1997

Selenium-induced growth reduction in Brassica land races considered for phytoremediation.

Brassica species considered for use in selenium (Se) phytoremediation need to accumulate large amounts of Se to be successful. Retarded plant growth and impaired protein synthesis are common symptoms for plants grown under seleniferous soils. Selenium accumulation by different land races of Brassica juncea (L.) Czern and Coss and one land race of Brassica carinata was investigated in Se-enriched water and soil cultures containing 2 mg Se kg-1. Effects of Se concentration in the root environment on the assimilation of Se, leaf surface area, dry matter yield, total leaf protein concentration, and free seleno-amino acid concentrations were analyzed for plants grown in Se-laden media. In water culture, shoot Se concentrations among the land races ranged from 501 to 1017 mg Se kg-1 dry matter (DM), and in plants grown in Se-laden soil, concentrations ranged from 407 to 769 mg Se kg-1 DM. Land races grown with Se exhibited decreases in dry matter yields from 12 to 23% and in leaf surface area from 5 to 26% compared to the same land races grown without Se. Protein content was significantly correlated both with shoot Se concentrations (r = 0.746, P < 0.001) and with leaf surface area (r = 0.446, P < 0.01) for all land races grown in Se-enriched water culture. There was also a significant correlation (r = 0.767, P < 0.001) between total Se assimilation and shoot protein for all land races. Free selenomethionine was detected for plants grown with Se and ranged from 92 to 958 ng g-1 DM. Other seleno-amino acids, Se-methyl-selenocysteine and selenocysteine, were not consistently detected as free amino acids in the different land races. Although visual symptoms of Se toxicity were not observed in the Brassica species, dry matter yield, leaf surface, and total shoot protein decreased, depending on the land races tested.

Amino Acids↗
PubMed2000

Expression of zinc-positive cells and terminals in fetal neocortical homografts to adult rat depends on lesion type and rearing conditions.

Zinc-positive neurons and terminals, known to be associated with the glutamatergic projections in the brain, can be demonstrated by the histochemical Timm method and later modifications thereof. The adult rat neocortex contain a uniform lamination of zinc-positive cells with specific projections to, e.g., the striatum. We have previously reported that fetal neocortical grafts implanted in the adult rat neocortex combined with rearing in an enriched environment can improve behavioral functions and reduce the secondary atrophy of thalamus after cortex infarction in adult rats. In order to examine whether the expression of zinc positivity is ontogenetically inherent to neocortical neurons we grafted fetal neocortical tissue to aspiration or ischemic lesions of the frontoparietal neocortex of adult rats, followed by histochemical visualization of the vesicular zinc pool by selenite or sulfide. One further aim of the study was to elucidate to what extent the distribution of zinc-containing neurons and terminals in the grafts depended on rearing under different environmental conditions. The foremost finding of the present study was that the overall density of zinc-containing terminals in fetal cortical transplants placed in brain infarcts of adult spontaneously hypertensive rats is higher when the rats are reared in an enriched environment. Moreover, the presence and expression of zinc-positive neurons and terminals do not seem to be ontogenetically inherent to the cortical neurons as the fetal neocortical grafts placed in aspiration lesions contained no zinc-selenide-positive neurons and few or no zinc-selenide-positive terminals. The presence or expression of zinc-positive cells may thus be induced by ingrowth of fibers and terminals from the host brain as transplants placed in the ischemic lesions expressed both zinc-positive neurons and terminals.

Animals↗
PubMed1997

SelD homolog from Drosophila lacking selenide-dependent monoselenophosphate synthetase activity.

The isolation and molecular characterization of an invertebrate gene that encodes a homolog of the human selenophosphate synthetase 1 is described. This Drosophila gene, termed selD-like, is located in the cytogenetic interval 50 D/E on the right arm of chromosome 2. It is expressed ubiquitously throughout embryogenesis and found to be highly enriched in the developing gut and in the nervous system of the embryo. The SelD-like from Drosophila was purified after expression in Escherichia coli. The purified protein does not catalyze the selenide-dependent ATP hydrolysis reaction and its gene does not complement a selD lesion in E. coli. These results and the fact that selD-like possesses an arginine residue at the position of the essential Cys17 (E. coli nomenclature) indicate that the Drosophila gene exerts a function different from that of the classical selenophosphate synthetases. Two classes of SelD proteins can therefore be differentiated. The class I proteins contain a cysteine or selenocysteine residue in the active site and display selenide-dependent selenophosphate synthetase activity. Class II proteins, including Drosophila selD-like and human selenophosphate synthetase 1 are devoid of this activity and they possess other amino acids in position 17.

Adenosine Triphosphate↗
PubMed1994

Uptake of selenite, selenomethionine and selenate by brush border membrane vesicles isolated from rat small intestine.

The uptake of selenite, selenate and selenomethionine (SeMet) was performed with brush border membrane vesicles (BBMV) prepared from rats fed selenium-deficient and supplemented diets. At equilibrium (60 min), the uptake of 75Se from [75Se]selenite ranged from 16.5 to 18.9 nmol mg-1 protein. There was a curvilinear relationship in the uptake of selenite over a concentration range of 10-1000 microM. About 2 nmol mg-1 protein was obtained with selenomethionine (SeMet) which occurred between 90 and 180 s. In contrast to selenite, there was a linear relationship in the initial uptake of SeMet over a concentration range of 10-1000 microM. The uptake of selenate was approximately 50-fold lower than selenite, reaching 350 pmol mg-1 protein. Dietary selenium level had no effect on the rate of 75Se accumulation by BBMV. Dramatic differences are found in the uptake and binding of selenium by BBMV incubated with different selenocompounds.

Animals↗
PubMed1993

Zinc-positive afferents to the rat septum originate from distinct subpopulations of zinc-containing neurons in the hippocampal areas and layers. A combined fluoro-gold tracing and histochemical study.

The purpose of the present study was to examine whether zinc-positive and zinc-negative hippocampal neurons in rats differed with respect to their projections to the septum. By combining retrograde axonal transport of the fluorescent tracer Fluoro-Gold with histochemical demonstration of zinc selenide complexes in zinc-containing neurons after intraperitoneal injection of sodium selenite, we were able to visualize the distribution of retrogradely Fluoro-Gold labeled neurons and zinc-containing neurons in the same sections. After unilateral injection of Fluoro-Gold into the rat septum a few retrogradely labeled cells were observed in layer IV of the ipsilateral medial entorhinal area, and numerous labeled cells were observed mainly in the superficial layers of the ipsilateral subicular areas and throughout the CA1 and CA3 pyramidal cell layers, as well as in the contralateral CA3 pyramidal cell layer. Zinc-containing neurons were observed in layers IV-VI of the medial entorhinal area, layers II and III of the parasubiculum, layers II, III and V of presubiculum, and in the superficial CA1 and deep CA3 pyramidal cell layers. Cells double-labeled with Fluoro-Gold and zinc selenide complexes were primarily located in distal (relative to the area dentata) parts of the superficial CA1 pyramidal cell layer and distal parts of the deep CA3 pyramidal cell layer and in layers II and III of presubiculum. Only a very few double-labeled cells were seen in the contralateral CA3. The result demonstrates that the hippocampo-septal projection of rats is a mixture of zinc-positive and zinc-negative fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1996

Oral selenate improves glucose homeostasis and partly reverses abnormal expression of liver glycolytic and gluconeogenic enzymes in diabetic rats.

Selenium is a trace element that exerts certain insulin-like actions in vitro. In this study, we evaluated its in vivo effects on the glucose homeostasis of rats made diabetic and insulin-deficient by streptozotocin. Na2SeO4 was administered ad libitum in drinking water and/or food for 10 weeks. The elevated plasma glucose levels (approximately 25 mmol/l) and glucosuria (approximately 85 mmol/day) of untreated rats were decreased by 50 and 80%, respectively, by selenate treatment. The beneficial effect of selenate was also evident during oral and intravenous glucose tolerance tests: the integrated glucose responses were decreased by 40-50% as compared to those in untreated rats. These effects were not due to an increase in plasma insulin levels. Compared to non-diabetic rats, pancreatic insulin reserves were reduced by more than 90% in treated and untreated diabetic rats. The hepatic activities and mRNA levels of two key glycolytic enzymes, glucokinase and L-type pyruvate kinase were blunted in diabetic rats. They increased approximately two- to threefold after selenate treatment, to reach 40-75% of the values in non-diabetic rats. In contrast, elevated activity and mRNA levels of the gluconeogenic enzyme, phosphoenolpyruvate carboxykinase, were reduced by 40-65% after selenate administration. Since selenate induced a moderate decrease in body weight due to an anorexigenic effect, we checked that there was no improvement of glucose homeostasis or hepatic glucose metabolism in an additional group of calorie-restricted diabetic rats, which was weight-matched with the selenate group. In addition, no obvious toxic side-effects on the kidney or liver were observed in the rats receiving selenate. In conclusion, selenate induces a sustained improvement of glucose homeostasis in streptozotocin-diabetic rats by an insulin-like action, which involves partial correction of altered pretranslational regulatory mechanisms in liver metabolism.

Administration, Oral↗
PubMed1984

Autometallography. A new technique for light and electron microscopic visualization of metals in biological tissues (gold, silver, metal sulphides and metal selenides).

The autometallographic procedure represents a new technique that can substitute for the normal methods of physical development (PD). The physical developer (a solution of reducing substance, silver salt and protection colloid) is replaced by a photographic emulsion and chemical developer. Accumulations of gold, silver, metal sulphides and metal selenides can be amplified by the present technique. Tissue sections placed on glass slides are covered by a silver bromide containing emulsion, dried and exposed to a chemical developer. After development the emulsion is either removed or cleared and the sections are counterstained and embedded. The autometallographic procedure can also be applied to ultrathin sections.

Animals↗
PubMed1982

Exogenous selenium in the brain. A histochemical technique for light and electron microscopical localization of catalytic selenium bonds.

Transcardial perfusion or intraperitoneal injections with sodium selenite result in the creation of selenium bonds that can be visualized by physical development. The present paper describes how these catalytic bonds are made visible in the tissues by surrounding them with shells of metallic silver. Based on experiments with chelating agents, the possibility that selenium-metal bonds are the catalysts is discussed. In the brain, the selenium pattern is delicate and highly laminated, the grains of silver being orderly arranged corresponding with the neuropil morphology. The precipitate is most densely packed in cortical regions. The difference in staining intensity seen in different regions of the CNS reflects the density of selenium reactive terminals. The visualized selenium bonds are predominantly located within boutons, and examination in the electron microscope reveals accumulation in the presynaptic regions. In a few places precipitates can also be found in axons, but have not been observed in perikarya or dendrites. The only non-neuronal locations of selenium were sparsely scattered, astrocyte-like neuroglia, predominantly found in the cerebellum and the hypothalamus; infrequently a few blood vessels were also stained. Sections from kidney and liver are presented as examples of localizations outside the CNS of exogenous selenium.

Animals↗