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Ultrastructural analysis of garlic roots treated for 24 h with sodium selenate or sodium selenite at the concentrations 80, 160, 320 microM revealed the presence of selenium deposits in meristematic cells. They appeared as small and large granules or aggregates of electron-dense material. Many small granules were localised in plastids but some in mitochondria, endoplasmic reticulum as well as in Golgi apparatus, nucleus and cytoplasm. Sometimes the large granules were seen in cytoplasm but aggregates of electron-dense material only in vacuoles. It seems possible that these deposits represent a non-dissolved form of selenium, i.e. elemental selenium or its complexes with other ions.

The main goal of this study was to investigate the role of cadmium in the promotion of lipid peroxidation in the homogenates of rat testes and the effect of selenium on lipid peroxidation in testes of rats after cadmium injection. Treatment of rats with cadmium resulted in a time- and dose-related accumulation of the metal ions in testes. The concentrations of cadmium, copper, zinc, selenium and iron in the tissues were determined by an atomic absorption spectrophotometer and lipid peroxidation in testes was measured by a spectrophotometer. Cadmium produced enhanced lipid peroxidation in testes. These cadmium-induced changes were accompanied by a significant increase of iron and copper, and a decrease of zinc in testes. Concurrent treatment with selenium and cadmium reduced the cadmium-induced alterations in lipid peroxidation and essential metal levels. Data suggest that lipid peroxidation was associated with cadmium toxicity in testes and that the addition of selenium was found to be effective in attenuation of this effect.

Antioxidant properties of selenium producing a protective barrier against free radicals play an important role in numerous metabolic and immunologic processes associated with oxidation-reduction reactions which take place during intracellular digestion of phagocyted bacteria. The aim of our study was to examine the properties of an organic compound of selenium, 4-(o-tolilo)-selenosemicarbazide of p-chlorobenzoic acid in terms of its retention in organs, effect on erythropoesis and phagocytic abilities of neutrophiles as well as antioxidant properties in neutrophiles tested with NBT test. This compound as well as inorganic sodium selenate was given to Swiss mice at the dose of 10(-3) g Se/kg for the period of 10 days. The concentrations of selenium in livers of mice treated with sodium selenate and selenosemicarbazide were found to be higher than in controls (18.7 micrograms lg-1 and 23.2 micrograms lg-1 vs. 12 micrograms lg-1, respectively). Analysis of blood cells count has shown a significant decrease in neutrophile levels in both groups treated with selenium. The influence of selenium compounds on phagocytosis and especially NBT test has been determined (3.8% of positive cells in the controls vs. 2.2% and 0.9% in the groups treated with sodium selenate and selenosemicarbazide, respectively). Our preliminary investigations suggest that selenosemicarbazides are biologically active compounds and can modify neutrophile functions.

The main aim of this trial was to define the possible differences between selenite and selenate in their ability to increase the selenium (Se) concentration of milk, in comparison with organic Se. Dairy cows (n = 42) were fed a basal diet containing .10 to .12 mg Se/kg DM for 5 mo and were then divided into four groups of 10 or 11, as similar as possible in age and stage of lactation. During the next 84 d, the cows in three of the groups were supplemented with 3 mg of Se daily, whereas the cows in one control group remained unsupplemented. The Se supplement was given as sodium selenite, sodium selenate, or a Se yeast product. The total Se concentration of the diets varied with the cows' stage of lactation and was for the supplemented groups .24 to .31 mg/kg DM, but remained between .10 and .12 mg/kg in the control group. At the end of the trial, the mean whole blood Se concentrations in the selenite, selenate, yeast, and control groups were 138, 141, 165, and 104 microg/L, respectively. The Se concentration in plasma apparently reached a plateau level within 4 wk, at approximately 75 microg/L in the selenite group, 80 microg/L in the selenate group, and 90 microg/L in the yeast group. In the control group the mean concentration in plasma remained at approximately 50 microg/L. The increase of the activity of glutathione peroxidase (GSH-Px) in the erythrocytes was significantly higher in the supplemented groups than in the control group. The mean concentrations of Se in milk in the selenite, selenate, and yeast groups were 16.4, 16.4, and 31.2 microg/L, respectively, whereas the concentration remained at approximately 14 microg/L in the control group. The milk Se concentration reached a plateau within 1 wk after the start of Se supplementation. Dietary supplementation with selenite and selenate, thus, had only a limited effect on the Se concentration in milk, and there was no significant difference between the two inorganic compounds in any variable measured. Organic Se was much more effective than inorganic Se in increasing the concentration of Se in milk.

We investigated the relationship between active oxygen species (AOS) generation and cultured vascular endothelial cellular damage caused by simultaneous exposure to selenium compounds and sulfhydryl compounds such as cysteine (Cys) or reduced glutathione (GSH). Selenium compounds, selenite, selenate or selenomethionine (SeMet), are added to total parenteral nutrition (TPN) and intravenously administered. We confirmed by luminol dependent chemiluminescence, an indicator of AOS generation, that selenite generates AOS in the presence of clinical concentrations of sulfhydryl compounds, 0.5 mM Cys or 0.5 mM GSH, and that the amount of AOS generated reaches the maximum when their mole ratio is 1:50. However, AOS generation was not observed after simultaneous administration of various concentrations of selenate or SeMet with sulfhydryl compounds. Moreover, simultaneous exposure to 10 microM selenite and sulfhydryl compounds was found to result in significant increases in the [3H]-adenine and lactate dehydrogenase (LDH) release rates from cells, a significant decrease in the amount of cellular protein, and enhancement of cellular damage as compared with after exposure to selenite alone. However, simultaneous exposure to 10 microM selenate or 10 microM SeMet together with sulfhydryl compounds did not induce cellular damage. These findings revealed that selenite generates AOS and causes cellular damage in the presence of sulfhydryl compounds. Accordingly, it seems better to choose selenate or SeMet instead of selenite when a selenium compound is to be added to TPN.

The thioredoxin (TRX) system, composed of nicotinamide adenine dinucleotide phosphate (reduced form), TRX, and TRX reductase (TRXR), has multiple biologic functions via thiol-mediated redox control. In this study, we investigated the relationship between intracellular TRXR levels and cellular sensitivity to cis-diamminedichloroplatinum (II) (CDDP). HeLa, a human cervical carcinoma cell line, cultured with CDDP showed a time- and dose-dependent reduction of intracellular TRXR activity, which was well correlated with the decrease in cell viability after exposure to CDDP. In a cell-free system, CDDP was found to directly inactivate the reduced form of purified human TRXR. The CDDP-resistant variants of HeLa cells, established by continuous exposure to CDDP, exhibited an increased expression and activity of TRXR as well as TRX compared with the parental cells. In addition, sodium selenate, an inhibitor of TRXR, was found to increase the susceptibility to CDDP in the CDDP-resistant cells. Moreover, the HeLa cells transfected with an antisense TRXR RNA expression vector to reduce the intracellular enzyme activity displayed an enhanced sensitivity to CDDP. Taken together with previous reports on TRX, these results indicate the possible involvement of TRXR as well as TRX in the cellular sensitivity and resistance to CDDP.

There is increasing evidence that selenium can protect against tumorigenesis or preneoplastic lesion development induced by chemical carcinogens. This study examined whether selenite, selenate or selenomethionine would be protective against 3, 2'-dimethyl-4-aminobiphenyl (DMABP)-DNA adduct formation in the liver and colon of rats and sought to delineate the mechanism for the protective effects of the different chemical forms of selenium against aberrant crypt formation, a preneoplastic lesion for colon cancer. After injection of DMABP, two DNA adducts were identified in the liver and colon of rats. Supplementation with either 0.1 or 2.0 mg selenium/kg diet as either selenite or selenate but not selenomethionine resulted in significantly fewer (53-70%; P < 0.05) N-(deoxyguanosin-8-yl)-(deoxyguanosin-8-yl)-3, 2'-dimethyl-4-aminobiphenyl (C8-DMABP)-DNA adducts in the colon but not the liver than in rats fed a selenium-deficient diet. Rats supplemented with selenomethionine had greater (P < 0.05) plasma and liver selenium concentrations and glutathione peroxidase activity than those supplemented with selenite or selenate; however, they also had more DMABP-DNA adducts. The protective effect of selenite and selenate against DMABP-DNA adduct formation apparently is not a result of alterations in plasma or liver selenium concentrations or altered glutathione peroxidase or glutathione transferase activities but may be related to differences in the metabolism of the different forms of selenium.

Based on the assumption that glutathione peroxidase (GPx) activity might be limiting in preventing peroxide-induced impairment of endothelial regulatory functions, we studied the effect of a series of new selenium-containing GPx mimics on endothelial cells exposed to an inflammatory stress. The two compounds that have the highest GPx activity, BXT-51072 and BXT-51077, were shown to be the most efficient inhibitors of leukocyte recruitment by human umbilical vein endothelial cells (HUVEC), upon incubation with neutrophils (10-fold excess over HUVEC) and with 1 ng/ml TNF-alpha for 1 or 3.5 h. When HUVEC were pre- and cotreated with 10 microM of either compound, neutrophil adhesion and endothelial alteration were markedly inhibited, as assessed by immunoassays of myeloperoxidase and von Willebrand factor, respectively. These two GPx mimics were also found to be the most efficient inhibitors of the TNFalpha-induced endothelial expression of P- and E-selectin and of the TNFalpha- or interleukin1-induced endothelial release of interleukin-8. Our results demonstrate that GPx mimics such as BXT-51072 behave as potent antagonists of TNF-alpha and interleukin-1 through the downregulation of endothelial proinflammatory responses.

Four selenium derivatives (sodium selenate, sodium selenite, selenourea and selenomethionine) and the sulphur analogues (sodium sulfate, sodium sulfite, thiourea and methionine), together with urea, were examined by means of polarography to study their reactivity towards superoxide ion O2. In order that experimental results could be applied to physiological conditions and to control the electroreduction of oxygen, most reactions were carried out in model systems (in the presence and in the absence of triphenyl phosphine oxide and at increasing pH) which are briefly described and discussed. Sodium sulfite and thiourea react with molecular oxygen; selenourea originates an anodic wave, although under other pH conditions. Other compounds (selenate, selenite, seleno-methionine and methionine) display an interesting antioxidant capacity because they catalyse the disproportion of the superoxide ion, as documented by the increase in the limiting current. Methionine appears to be particularly efficient in this respect, since it retains its catalytic ability in a poorly protic environment. Experimental results support the view that exogenous compounds, administered for particular purposes, can display unanticipated, and sometimes positive, side effects.

The aim of this study was to determine the effect of selenium (Se) supplementation to lactating women on Se concentrations and glutathione peroxidase (GSH-Px) activities in blood components of mothers and breast-fed infants and on milk Se levels and Se intake by breast-fed infants. Lactating mothers were supplied for 3 months with 200 micrograms Se/day in the form of yeast-Se (Y-Se) and sodium selenite. Initial blood and plasma Se levels of all women (n = 67) were 76.6 and 53.2 micrograms/L, respectively. After 3 months Se concentrations both in whole blood and in plasma from mothers and infants were significantly higher than the initial values. Y-Se exerts a stronger effects than selenite on blood and plasma Se levels. Initial milk Se concentration was 8.9 micrograms/L and after 1 month in both groups in reached a plateau at 14-16 micrograms/L. This resulted in an increase of Se intake in breast-fed infants from 6.1 to a plateau of 11-13 micrograms Se/day. GSH-Px activities in plasma and red cells of Y-Se group increased significantly and reached a plateau after 1 and 2 months, respectively, while in the selenite group the enzyme activities increased steadily throughout the entire period of the study. Selenite exerts a stronger effect on GSH-Px both in maternal and in infant blood components as compared with Y-Se. In milk the GSH-Px activity in the Y-Se group did not change during the study, while in the selenite group after 3 months it increased almost 2-fold compared to the initial value. In conclusion, this study shows that organic Se causes higher Se deposition than did the inorganic form.

Ninety white rats were treated with liquid lead acetate. When the concentration of lead in urine was more than (0.81 +/- 0.26) mg/L and blood lead was more than (4.8 +/- 0.33) mg/L, the rats were divided into three groups randomly. The oxygenic damage indicators in serum showed SOD activity decreased and MDA content increased. In one group of lead rats fed with an organic selenium compound (code FCQY) the SOD activities were high and the lipid peroxidation was inhibited compared with controls without selenium supplementation. The lead contents of bone, kidney and liver were measured. The results suggested that the organic selenium compound could interfere with the absorption and accumulation of lead.

Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) are respectively involved in the endothelial recruitment of neutrophils, and in that of lymphocytes or tumor cells, in response to specific signals. We have used the glutathione peroxidase (GPx) mimic BXT-51072 to assess the possibility that endogenous hydroperoxides play a role in the tumor necrosis factor-alpha (TNFalpha)-induced expression of ICAM-1 and VCAM-1 by monolayers of human endothelial cells. The GPx mimic BXT-51072 strongly inhibits the TNFalpha-induced and cycloheximide-sensitive expression of ICAM-1 and VCAM-1. It also inhibits the TNFalpha-induced reorganization of the actin network and the associated formation of stress fibers. Actin reorganization induced by cytochalasin D treatment did not inhibit ICAM-1 expression. Our results are compatible with specific and synergistic effects of endogenous hydroperoxides on the biosynthesis and processing of cell adhesion molecules and cytoskeleton components.

The organoselenium compounds benzyl selenocyanate (BSC) and 1,4-phenylenebis(methylene)selenocyanate (p-XSC), as well as sodium selenite, are effective chemopreventive agents for various chemically induced tumors in animal models at both the initiation and postinitiation stages. The mechanisms involved at the postinitiation stage are not clear. Because several lines of evidence indicate that inhibition of excess DNA (cytosine-5)-methyltransferase (Mtase) may be a sufficient factor for the suppression or reversion of carcinogenesis, we examined the effects of sodium selenite, BSC, p-XSC and benzyl thiocyanate (BTC), the sulfur analog of BSC, on Mtase activity in nuclear extracts of human colon carcinomas, and of p-XSC on the Mtase activity of HCT116 human colon carcinoma cells in culture. For this purpose, we developed an improved Mtase assay, in which the incorporation of the methyl-[3H] group from S-adenosyl[methyl-3H]methionine into deoxycytidine of poly(dI-dC)-poly(dI-dC), is specifically determined by HPLC with radioflow detection after enzymatic hydrolysis, enhancing specificity and reliability. In a variation, using SssI methyltransferase and labeled S-adenosylmethionine, the overall methylation status of DNA in various tissues can also be compared. Selenite, BSC and p-XSC inhibited Mtase extracted from a human colon carcinoma with IC50s of 3.8, 8.1 and 5.2 microM, respectively; BTC had no effect. p-XSC also inhibited the Mtase activity and growth of human colon carcinoma HCT116 cells, with an IC50 of approximately 20 microM. The improved Mtase assay should prove to be a reliable method for screening potential Mtase inhibitors, especially using cells in culture. We suggest that inhibition of Mtase may be a major mechanism of chemoprevention by selenium compounds at the postinitiation stage of carcinogenesis.

The present study was undertaken to investigate the effects of selenite (SeIV) and selenate (SeVI) on the all-trans retinoic acid (RA)-nuclear retinoic acid receptor (RAR) complex formation in rat liver. We also present the data on the in vitro effects of SeIV on the RARalpha and the type I iodothyronine 5'-deiodinase gene expression in the GH4C1 rat pituitary tumor cells. SeIV at 1.0 micromol/L was found to reduce (p < 0.05) the RA specific binding to RAR in rat liver. Dithiothreitol (DTT), a protective agent for sulfhydryl groups, was found to be slightly effective in protecting the RAR binding properties when affected by SeIV. SeVI at 0.1 micromol/L reduced (p < 0.05) the RA specific binding to RAR in liver, as well. Seleno-L-methionine (Se-II) when compared to L-methionine did not exert any inhibitory effect on the formation of the RA-RAR complex. SeIV (up to 2.5 micromol/L) has no inhibitory effect on GH4C1 cell proliferation as well as the prolactin secretion. SeIV at 1.0 micromol/L significantly decreases the rate of mRNA synthesis and/or degradation of the alpha form of the RAR and causes the enhancement of the type I iodothyronine 5'-deiodinase gene expression in GH4C1 cells. The results based on in vitro experiments suggest that inorganic selenium may affect the RA specific binding to their cognate receptor molecules, and it may reduce expression of the gene encoding the RARalpha, with the cell vitality and the cell growth remaining unchanged.

Sodium selenate, administered intraperitoneally (i.p.), resulted in an improvement in glucose tolerance in treated diabetic rats. Fed rat plasma glucose levels were reduced by selenate treatment in streptozotocin diabetic rats. The lowest values of blood glucose were reached within 3 weeks of beginning the treatment. Food and fluid consumption was reduced in treated compared to untreated diabetic rats. Diabetic treated rats did not release insulin in response to a glucose challenge and insulin release in response to a challenge was markedly reduced in control treated rats. Assessment of heart function using a working heart apparatus showed that treated diabetic rats with improved blood glucose levels had normal heart function at 8 weeks of diabetes in contrast to hearts from non-treated diabetics. This study extends previous observations on the in vivo insulin-like effects of sodium selenate.

The effects of selenium polysaccharide and sodium selenite administered by single or repetitive intraperitoneal injection (i.p.) on blood selenium concentration, the activities of liver cytochrome P450, b5 as well as NAD(P)H cytochrome C reductase, glutathione S-transferase and glutathione were studied in rats. The biological effects of selenium polysaccharide and sodium selenite were also compared. The results indicated that the blood selenium concentration was increased rapidly and reached the peak in 2 hours followed by gradual decline after selenium polysaccharide and sodium selenite were i.p. injected at a dose of Se 0.6 mg/kg. The absorption and eliminating rates of Se from sodium selenite were faster than that from selenium polysaccharide. Administration of selenium polysaccharide and sodium selenite at a dose of 0.2 mg/kg by i.p. increased the blood selenium concentration to 2.6 and 2.1 times of those of control group, respectively, and the blood selenium concentration of selenium polysaccharide group was significantly higher than that of sodium selenite group (P < 0.05). The activities of liver cytochrome P450, b5 and GST were inhibited by selenium polysaccharide and sodium selenium in vivo and in vitro experiments. Those proteins were decreased to 57%, 70% and 62% of the control, respectively, by selenium polysaccharide which has particularly stronger effects on cytochrome P-450 monooxygenase system (P < 0.05). The two selenium compounds did not appear to affect the activity of NAD(P)H cytochrome C reductase. Both of the selenium polysaccharide and sodium selenite could enhance the activity of glutathion peroxidase significantly (P < 0.05).

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., (Copyright 1997 Academic Press Limited.)

The effects of inorganic selenium (Se) compounds (sodium selenite and selenate) on the activities of glutathione-related enzymes (glutathione peroxidase, glutathione-S-transferase [GST] and glutathione reductase [GR]) in pig blood platelets were investigated in vitro. GST activity in blood platelets treated with 10(-4)M of selenite was reduced to 50%, whereas no decrease GST activity was observed after the treatment of platelets with the same dose of selenate. In platelets incubated with physiological doses (10(-7) and 10(-6)M) of Se compounds, the activity of glutathione peroxidase (GSH-Px) was enhanced (about 20%). GR activity after the exposure of platelets to tested Se compounds was unaffected.

The influence of the combined use of selenious acid and SH compounds (glutathione (GSH) and cysteine (Cys), or ascorbic acid (Asc)) on cultured venous vascular cells was investigated experimentally. When cultured human umbilical venous vascular endothelial cells were exposed to 10 microM of selenious acid combined with 0.5 mM-GSH or 0.5 mM-Cys, the release rates of [3H]-adenine and lactate dehydrogenase (LDH) from cells into the medium increased significantly as compared with after exposure to selenious acid alone, and damage to the vascular endothelial cells was found to be intensified. Addition of 1 microM of selenious acid simultaneously with 0.5 mM-GSH or 0.5 mM-Cys showed no differences in toxicity for the vascular endothelial cells as compared with the addition of selenious acid alone. On the other hand, simultaneous exposure to 10 microM of selenious acid and 1 mM-Asc induced no significant differences in the release rates of [3H]-adenine and LDH, and no damage was observed to the vascular endothelial cells. These results suggest that simultaneous addition of selenious acid together with GSH or Cys, which have the SH-group, may cause damage to the vascular endothelial cells. Therefore careful attention is warranted in total parenteral nutrition (TPN).

Arsenic is a human carcinogen. On the other hand, selenium supplementation can inhibit induction of carcinogenesis by chemical carcinogens. The effect of selenium compounds on the cytotoxicity of dimethylarsinic acid (DMA) and on the induction of tetraploidy by DMA were studied using Chinese hamster V79 cells. Two selenium compounds were tested, sodium selenite and trimethylselenonium iodide (TMSeI). Trimethylselenonium is a major excretory product of selenite metabolism. The cytotoxicity of sodium selenite was 1000-fold greater than that of TMSeI. The cytotoxicity of DMA was about the same as that of TMSeI. The mitotic index for DMA administration was increased by these selenium compounds at low concentrations and decreased by them at high concentrations. The tetraploid index for DMA decreased with increasing concentrations of these selenium compounds. Tetraploidy is a form of aneuploidy, and aneuploidy is known to induce carcinogenesis. The finding that selenium inhibited induction of tetraploidy by DMA may yield clues to the role of selenium in the chemoprevention of carcinogenesis by chemical carcinogens.

The effects of two types of selenium compounds on the expression levels of growth arrest and DNA damage-inducible (gadd) genes and on selected cell death genes were examined in mouse mammary MOD cells to test the hypothesis that the diversity of selenium-induced cellular responses to these compounds could be distinguished by unique gene expression patterns. Whereas the expression patterns of known cell death-related genes (bcl-2 and bax) were not informative with respect to the cellular response patterns upon exposure to selenium compounds, time-dependent and selenium species-specific induction patterns were observed for gadd34, gadd45 and gadd153 genes. It was also observed that the MOD cells expressed a truncated p53 transcript but no detectable immunoreactive P53 protein, indicating a null p53 phenotype. The fact that selenium compounds induced growth arrest and death of these cells and that these compounds induced specific patterns of expression of gadd genes indicates that these genes may mediate some selenium-induced cellular responses. The findings further imply that selenium compounds may be effective chemopreventive agents for human breast carcinogenesis, in which p53 mutations are frequent.

This study describes that the affinity for specific L-tryptophan binding to hepatic nuclei in vitro is markedly decreased in NZBWF1 mice in comparison to that in Swiss mice. Also, the hepatic nuclei of NZBWF1 mice have a significantly decreased binding response in vitro to Showa Denko L-tryptophan (implicated in the eosinophilia-myalgia syndrome) or to its contaminants, 1,1'-ethylidenebis(tryptophan) or 3-phenylamino-L-alanine, when each is added to control, non-implicated L-tryptophan compared with hepatic nuclei of Swiss mice. Enhanced hepatic protein synthesis induced by tube-feeding control L-tryptophan is much less in NZBWF1 mice than in Swiss mice. Tube-feeding of Showa Denko L-tryptophan induced less stimulation of hepatic protein synthesis than did control L-tryptophan in Swiss mice but essentially none in NZBWF1 mice. NZBWF1 mice have a genetically altered response to L-tryptophan which may prove to be useful is studying the role of L-tryptophan in health and in disease.

The effect of selenium (Se) supplementation of ewes with blood Se concentrations ranging between 100-200 ng/ml on embryonic survival during the early post-mating period (days 15-35) was studied in 4 trials. In the 1st 2 trials 137 ewes were used in 1991 and 118 in 1992. After being mated as a single flock, these ewes were stratified randomly into 3 groups. One group served as a control, the 2nd was injected with 1 ml Deposel (containing 50 mg Se as Ba selenate) and the 3rd group injected with 1 ml containing 1 mg Se as Na selenite. During 1991, supplementation was administered immediately after the mating period. It was postponed by 14 days in 1992. Parenteral Se supplementation reduced (p < 0.10) the number of ewes that lambed by > 19% during 1991 but not during 1992. The number of ewes producing twins was unaffected. In Trials 3 and 4 there was a consistent indication that parenteral Se supplementation of pregnant ewes between 15-35 days after mating resulted in a reduced (22-40%) embryonic survival rate, although significant (p < or = 0.10) differences were only observed after the pooling of treatments receiving parenteral Se supplementation. Drenching of ewes with 50 mg Se as Na selenite resulted in a similar tendency. Biochemical appraisal of the blood, kidney and liver Se status of ewes failed to reveal toxic levels. The possible mechanisms involved in impaired embryonic survival are unclear. Supplementation of ewes during the 1st month of pregnancy with parenteral Se preparations is not recommended.

The purpose of this study was to determine whether selenate fortification of infant formula would improve the selenium status of relatively well, growing, preterm infants during the first 12 wk of enteral feeding. A high-selenium group (n = 7, mean body weight = 1312 g) received selenate-fortified preterm and full-term infant formulas containing 0.36 and 0.22 mumol Se/L, respectively, and a low-selenium group (n = 10, mean body weight = 1262 g) received non-selenium-fortified preterm and full-term infant formulas containing 0.12 and 0.11 mumol Se/L, respectively. There were no significant differences in growth between the two groups throughout the study. The high-selenium group had significantly greater mean selenium intakes than did the low-selenium group from weeks 2 to 12. Plasma selenium concentrations decreased over the study period in the low-selenium group. Plasma selenium-dependent glutathione peroxidase activity was greater in the high-selenium group at week 12 only. Red blood cell selenium concentrations decreased over time in both groups and were significantly greater in the high-selenium group at weeks 4, 8, and 12. Plasma selenium concentrations were significantly correlated with plasma glutathione peroxidase activity for all infants on study day 1 and at weeks 4 and 12. Selenium intake of all infants was significantly correlated with plasma glutathione peroxidase activity at 12 wk. Selenate fortification of infant formulas can improve the selenium status of preterm infants. Current selenium contents of infant formulas and recommendations for dietary intakes of selenium for some preterm infants may be inadequate.

Selenium compounds like selenite and selenate have strong inhibitory effects, particularly on mammalian tumor cell growth by unknown mechanisms. We found that the addition of sodium selenite and sodium selenate inhibited the growth of human 3B6 and BL41 lymphocytes. Selenite was more potent because 10 microM selenite produced a growth inhibitory effect similar to that of 250 microM selenate. The mechanism of action of selenite and selenate appears to be different. 3B6 and BL41 cells treated with selenite accumulated in the S-phase; however, selenate caused an accumulation of cells in G2. Selenite-mediated growth inhibition was irreversible, although the effects of selenate could be reversed. Selenite, in contrast to selenate, is efficiently reduced by the thioredoxin system (thioredoxin, thioredoxin reductase, and NADPH). At concentrations required to observe a similar effect on cell growth, the activity of thioredoxin reductase, recently shown to be a selenoprotein, increased in selenite-treated cells and decreased in selenate-treated cells. Ribonucleotide reductase activity was inhibited in an in vitro assay by selenite and selenodiglutathione but not by selenate. These results show that selenite and selenate use different mechanisms to inhibit cell growth.

Pot culture experiments were conducted to study the effects of selenite and selenate treatment (0.5-6.0 microg/ml) on the uptake and translocation of root-absorbed mercury (Hg) in radish plants irrigated with 2 and 5 microg/ml Hg in sand and soil culture. Statistically significant reductions in mercury uptake with increasing concentrations of selenium (Se) were observed. Both forms of selenium (selenite and selenate) were equally effective in reducing the mercury burden of the plant. The observed reduction in plant uptake of mercury is explained by the formation of an HgSe insoluble complex in the soil-root environment. No significant difference (P > 0.05) in dry matter yields with the various selenium treatments was found, suggesting that no selenium toxicity or salt injury occurred in the plants.

Selenite and selenodiglutathione (GS-Se-SG) efficiently inhibited 5-lipoxygenase activity in sonicates of human monoclonal B-lymphocytes. The apparent IC50 of GS-Se-SG was 0.5 microM. The inhibitory effect of these compounds was observed within 10 min of incubation. In order to elucidate if the mechanism of inhibition by these compounds was result of direct interference with lipoxygenase or indirectly mediated by cellular factors, pure 15-lipoxygenase from soybeans was used as a model system for enzyme assays and electron spin resonance (ESR) measurements. Incubation of 15-lipoxygenase with a mixture of human placenta thioredoxin reductase (TR) or calf-thymus TR, selenite, and NADPH blocked the activity of the enzyme. Neither TR and NADPH nor selenite inhibited soybean lipoxygenase when incubated separately. These results suggest that selenite must be reduced to selenide in order to inhibit 5- and 15-lipoxygenase activities. Preincubation anaerobically of 15-lipoxygenase with chemically generated selenide (6 microM) resulted in a strong inhibition of activity, in assays with arachidonic acid in the presence of oxygen. In contrast, selenide exposed to air prior to preincubation did not inhibit the enzyme. Since selenide is known to be efficiently oxidized by oxygen and to form elemental selenium the results evidence that selenide was the inhibitor of lipoxygenase activity in the anaerobic preincubations. After incubation with TR, NADPH, and selenite or with chemically generated selenide, the ESR spectrum of 15-lipoxygenase changed: the dominant axial component with a peak at g = 6.1 decreased, and a rhombic form with a feature at g = 4.28 grew. The results suggest that selenide produced by the reduction of selenite reduces the active site iron to the ESR invisible state and changes the ligation geometry of the oxidized form.

Selenium-dependent glutathione peroxidase (GPx) plays a protective role in oxidative stress-induced apoptosis. In this study, we demonstrated that MDBK cells, a bovine renal epithelial cell line, exhibited internucleosomal DNA fragmentation characteristic of apoptotic cell death under selenium-deficient conditions with lower doses of hydrogen peroxide (H2O2) than under selenium-supplemented ones. This was due to a decreased amount of GPx in the cells under selenium-deficient conditions, because other antioxidative enzyme activities were not affected by the selenium supplementation. Cumene hydroperoxide also induced DNA fragmentation in selenium-deficient cells but no ladder formation was observed. Flow cytometric analysis showed that selenium-deficient cells were less capable of scavenging intracellular peroxides after exposure to exogenous H2O2 than selenium-supplemented ones. In contrast, there was no difference in viability between selenium-supplemented and non-supplemented cells in cell survival after exposure to menadione, which activates the electron transport system and increases intracellular superoxide radicals. Clofibrate, a peroxisomal proliferator and an inducer of catalase (CAT), partially protected both Se-deficient and Se-supplemented cells from exogenous H202. We concluded that selenium-deficient cells were more easily brought to apoptotic cell death by peroxides, but not by superoxide radicals, than selenium-supplemented ones and that CAT could compensate for the depletion of GPx to a certain degree by scavenging H2O2.

The differences in the effects of inorganic Se (IV and VI) compounds and seleno-cystine [(CySe)2] on the Te (as Na2TeO3) uptake by the yeast, Saccharomyces cerevisiae, has been studied. Se, Te, Ag, Zn, Fe and Co contents of the cells were measured by instrumental neutron activation analysis. For the determination of the Ag content, the monostandard method was applied as the analytical method. The contents of other elements were determined by comparison with standards having similar amounts of the determined element as the sample. Results obtained show that an antagonist interaction occurs between SeO2 and Te. There was a significant increase in the concentrations of Se and Te when the yeast was incubated in the medium containing (CySe)2 and Te. (CySe)2 markedly increased the Ag content of cells, especially within the first 8 h of incubation. The low level of SeO2 in the medium are the exterior factor which produce an observable increase of the Ag concentration in the cells. The higher level of SeO2 in the medium causes a long-term marked increase in the Ag content of the cells. The uptake yield of Ag also increased in the presence of (NH4)2SeO4 in the medium. The Te supply produced a significant enhancement in the Ag content of the cells during the initial 8 h of incubation. The presence of Se and/or Te in the medium causes change in the intracellular Zn, Fe and Co levels.

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.

The direct impact of vanadate, tungstate, selenate, and selenite on glucose metabolism of isolated rat soleus muscle was investigated. All compounds stimulated glucose transport, but only vanadate exerted an insulin-like effect on glycogen synthesis (mumol glucose into glycogen*g-1*h-1: control 1.43 +/- 0.11 vs. 1 mmol/l vanadate, 2.08 +/- 0.11, p < 0.0001), which was more distinct in the presence of 1 mmol/l H2O2 (control, 1.44 +/- 0.13 vs. 1 mmol/l vanadate, 3.49 +/- 0.12, p < 0.001). Glucose handling of muscles exposed to tungstate, selenate, or selenite resembled that of hypoxic muscle, i.e. the induced rise in glucose uptake was inhibited by dantrolene and associated with high rates of glycolysis and rapid glycogen depletion (glycogen content after incubation, mumol glucosyl units/g: control, 16.2 +/- 0.7 vs. hypoxia, 2.7 +/- 0.5, p < 0.0001; control, 17.0 +/- 0.5 vs. 100 mmol/l tungstate, 5.5 +/- 0.4, p < 0.001; control, 16.2 +/- 0.7 vs. 100 mmol/l selenate, 1.5 +/- 0.3, and vs. 300 mumol/l selenite, 1.7 +/- 0.3, p < 0.0001 each). The results suggest that vanadate (and more pronounced it's peroxides) exerts true insulin-like action on isolated muscle glucose metabolism, whereas tungsten and selenium salts trigger glucose transport in association with a catabolic response, which may represent an unspecific response to toxic/osmotic stress.

Selenium not only has an important role in controlling lipid hydroperoxides through glutathione peroxidase (GPX) activity, but also can produce oxidative stress through exposure to selenite. Because levels of lipid hydroperoxides affect the production of thromboxane A2 (TxA2) and prostacyclin (PGI2), selenium compounds may be able to influence the production of these two vasoactive substances. Late-gestation pregnancy reduces the half-life of PGI2; therefore, pregnancy itself may enhance susceptibility to changes in the production of TxA2 and PGI2. The objective of this investigation was to determine if different selenium compounds, selenite, selenate, and ebselen, can influence the human term placental production of thromboxane B2 (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), the inactive hydrolysis products of TxA2 and PGI2. Although selenate exposure (40 microM 24 hr) increased TxB2 production, and ebselen (an organic selenium compound with GPX activity) exposure (40 microM, 24 hr) decreased both TxB2 and 6-keto-PGF1 alpha production, only selenite had a significant effect on the TxB2/6-keto-PGF1 alpha ratio. Three exposures to selenite at 6 microM (32 hr) significantly decreased 6-keto-PGF1 alpha production with no effect on TxB2 production or tissue GPX activity. Following two exposures to selenite at 20 and 40 microM (24 hr), TxB2 production was significantly increased, while tissue 6-keto-PGF1 alpha production and tissue GPX activity were significantly decreased. These results indicate that selenite, but not selenate or ebselen, can directly affect the human placenta by producing changes in the TxB2/6-keto-PGF1 alpha ratio, which may be related to increased vasoconstriction and blood coagulation.

The effects of forms of selenium compounds that enter the cellular selenium metabolic pathway at different points were investigated in a mouse mammary carcinoma cell line. The goal of these experiments was to determine if the genotoxicity of selenium, defined as its ability to induce DNA single-strand breaks, could be dissociated from activities proposed to account for its cancer inhibitory activity. The results demonstrated that growth inhibition, measured as inhibition of cell proliferation and induction of cell death, was induced by all the forms of selenium evaluated. However, sodium selenite and sodium selenide, which are metabolized predominantly to hydrogen selenide, caused the rapid induction of DNA single-strand breaks as an early event that preceded growth inhibition. Interestingly methylselenocyanate and Se-methylselenocysteine, which are initially metabolized predominantly to methylselenol, induced growth inhibition in the absence of DNA single-strand breakage. Differences in the time course of selenium retention, in the occurrence of membrane damage, and in the induction of morphological changes by selenite versus methylselenocyanate were noted. Collectively, these data indicate that different pathways affecting cell proliferation and cell death are induced depending on whether selenium undergoes metabolism predominantly to hydrogen selenide or to methylselenol.

Objective: To describe the impact of acute vanadate and selenate exposure on glucose tolerance of obese Zucker rats (fa/fa)., Design: Intravenous glucose tolerance tests (2.4 mmol/kg, continuously from 0 to 30 min) were performed in conscious Zucker rats exposed to a bolus-continuous infusion of sodium vanadate (2.45 mumol/h) or sodium selenate (0.90 and 2.45 mumol/h) and were compared to intraindividual control experiments with saline infusion., Results: Vanadate infusion improved glucose tolerance and decreased insulin release, as shown by total areas under the curves (0-120 min: Glucose, min.mmol/l: control, 983 +/- 59 vs vanadate, 915 +/- 54, P < 0.02; Insulin min.nmol/l: control, 117.5 +/- 19.9 vs vanadate, 88.5 +/- 26.2, P < 0.01). In contrast, infusion of selenate increased glucose induced insulin release during the first phase of the IVGTT (0-60 min, incremental area under the insulin curve: by 57% and 110% for low and high selenate infusion rate, respectively) and transiently improved glucose tolerance (0-60 min, decrease of incremental area under the glucose curve: 31% and 28%, respectively). That effect of selenate was lost with progression of the experiment during the second hour of the IVGTT, when plasma glucose continued to decline slowly in control experiments, but increased in selenate exposed rats without any adequate insulin secretory response to hyperglycemia., Conclusion: The results demonstrate improved glucose tolerance and decreased plasma insulin concentration during acute vanadate exposure. Only a transient insulinotropic effect with improved glucose tolerance is induced during acute selenate exposure, and is followed by progressive development of hyperglycemia indicating selenate toxicity.

The metabolic significance of Se in plants is not well documented, though the presence of many selenoenzymes in bacteria and the essentiality of Se in higher animals is established. Since germination is an active process in plant growth and metabolism, the effect of Se was investigated in germinating Vigna radiata L, a nonaccumulating Se-deficient legume. Growth and protein were enhanced in seedlings supplemented with selenium (Se) as sodium selenite in the medium up to 1 microgram/mL. The pattern of uptake of 75Se in the differentiating tissues and the subcellular distribution were investigated. The percentage of incorporation of 75Se was greater in the mitochondria at the lowest level (0.5 micrograms/mL) of Se supplementation compared to higher levels of Se exposure. Proteins precipitated from the postmitochondrial supernatant fractions, when separated by means of polyacrylamide gel electrophoresis (PAGE), indicated a major selenoprotein in the seedlings germinated at 2.0 micrograms/mL Se. In seedlings grown with supplemented Se, enhanced respiratory control ratio and succinate dehydrogenase activity were observed in the mitochondria of tissues, indicative of a role for Se in mitochondrial membrane functions.

Triphenylselenonium chloride, a novel synthetic organic selenium compound in which selenium is bonded to three unsubstituted benzene rings, possesses significant chemopreventive activity against chemically-induced mammary carcinogenesis. The effects of triphenylselenonium chloride on a mammary tumor cell line (MOD) were compared to selenite, a reference compound in selenium chemoprevention research. It was observed that triphenylselenonium chloride treatment exerted a cytostatic effect in the absence of membrane damage or DNA strand breaks. The observed cytostasis was associated with a selenium concentration-dependent inhibition of cell proliferation, measured by [3H]thymidine incorporation into DNA, and delayed cell cycle progression. In contrast, selenite treatment rapidly induced DNA damage and cell death. These marked differences were observed across the same levels of cellular selenium. In addition, triphenylselenonium chloride treatment increased glucose consumption and lactate production, indicating an effect of the compound on cellular energy metabolism. Collectively these observations demonstrate that the toxic activities associated with selenite treatment do not occur when cells are treated with triphenylselenonium chloride. This compound represents a new type of selenium compound that exerts significant cellular effects through mechanisms distinct from those induced by selenite.

The effects of selenium and silver salts was studied by scanning ionic microscopy during experimental argyria mapping of the different basement membrane elements. The ionic microscope (IMS 4F) was equipped with a high resolution spectrometer giving high spatial resolution on the image obtained. After long-term treatment with silver salt alone, silver and sulphur deposits were observed in the membranes. After administration of selenium and silver salt, it was possible to map nitrogen, sulphur, selenium and silver to the glomerular basement membrane as well as to the wall of the kidney arterioles. In the latter, sulphur, selenium and silver were localized only in the elastic laminae of the walls. This process of precipitation of silver deposits in the membrane can be interpreted as process of selenium "detoxification" of the organism.

Liver and kidney copper (Cu) and selenium (Se) concentrations were studied over a 7-month period after parenteral supplementation using Cu heptonate and barium (Ba) selenate in 44 8-month-old South African (SA) Mutton Merino wethers. Responses in plasma Cu and blood Se concentrations, as well as fecundity were also measured in a breeding flock of SA Mutton Merino ewes for 3 consecutive years. The effect of maternal supplementation with Cu and Se was assessed in terms of biochemical parameters and production responses in 654 lambs produced by these ewes. Parenteral treatments with Cu and Se raised liver and kidney concentrations (P < or = 0.05) for up to 7 months in wethers under conditions where liver Cu and Se respectively declined to concentrations below 30 mg/kg DM and 300 micrograms/kg dry matter (DM) in spring. Plasma Cu concentrations of breeding ewes which received Cu heptonate were increased (P < or = 0.05) by 18% relative to the control group in which concentrations declined to 91 micrograms/dl during late pregnancy. Blood Se concentrations of control ewes exceeded 200 ng/ml, and were unaffected by parenteral Se supplementation. Survival of progeny of Cu heptonate treated ewes tended (P < or = 0.10) to be improved by 13% (0.68 vs 0.60). This tendency was accompanied by generally higher (P < or = 0.10) plasma Cu concentrations of these lambs relative to control lambs at 10 - 20 and 45 - 55 d of age. Lambs of Cu supplemented ewes that died prior to weaning, had higher (P < or = 0.05) liver Cu concentrations than control group contemporaries.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium selenide was used as a retrograde tracer to assess the callosal origin of zinc-rich boutons in the neocortex of the rat. Selenide injections were placed in the lateral end of area Oc1 (area 17). Zinc present in synaptic boutons precipitated as zinc selenide and was transported retrogradely to the parent cell bodies. In addition to the ipsilateral labelling, contralateral retrogradely labelled somata were mainly observed along the border between areas Oc1 and Oc2L (area 18a). Labelled neurones were present in layer 2-3 and layer 6. In contrast to tracing studies with peroxidase, no labelled neurone was observed in layers 4 and 5 except at the inner border of layer 5. This study reveals the chemical heterogeneity of callosal projections, which may be divided into zinc-rich and zinc-poor systems.

The present study compared the effects of naturally occurring extracts or compound in combination with synthetic selenium compounds on the colony formation and nucleic acid synthesis of cultured human cervical epitheloid carcinoma cells (Hela). Crude extract of bean (Phaseolus vulgaris) or purified lectin from red kidney bean (Phaseolus vulgaris) in combination with selenomethionine were more effective in inhibiting the colony formation of Hela cells than when these cells were treated with these agents alone. Extracts of saffron (Crocus sativus) and selenite have previously been shown to inhibit the colony formation and nucleic acid synthesis by Hela cells in vitro. In the present study we examined the effects of saffron extract in combination with selenite on the colony formation and DNA and RNA synthesis in Hela cells. We found that the treatment of tumor Hela cells with saffron extract in combination with selenite increased the level of inhibition of the colony formation and nucleic acid synthesis in comparison with cells that were treated with only one of these agents. The inhibitory effect of saffron extract in combination with selenite was modified by intracellular sulfhydryl compounds.

Insulin is capable of regulating cellular and metabolic processes as well as gene expression. In recent years, enthusiasm has surfaced for using insulin-mimetics to study the mechanism of action of insulin. Vanadate and selenate are two compounds that have been found to mimic the action of insulin on control of blood glucose levels in vivo. Vanadate has also been shown to regulate the expression of several enzymes both in vivo and in vitro, however, studies concerning selenate's ability to regulate expression have not been reported. In this study we show that administration of vanadate or selenate to streptozotocin-induced diabetic rats not only normalizes blood glucose levels similarly to insulin but also positively affects the expression of two key metabolic enzymes, glucose-6-phosphate dehydrogenase (G6PDH) and fatty acid synthase (FAS). Both G6PDH and FAS activity are significantly decreased in diabetic animals compared to non-diabetic control. Treatment of the diabetic animals with either insulin, vanadate or selenate restored both activities to about 80-90% of control. All treatment conditions exhibited activities significantly higher than those determined for the diabetic group but did not differ significantly from each other. Increases in G6PDH or FAS activity are due to increases in mRNA level. Increase in both G6PDH and FAS mRNA was comparable to the observed increase in activity suggesting that regulation of expression by the mimetics occurs pretranslationally.

Thirty-three healthy term infants were fed either soy formula (SF, 0.028 mumol Se/L; n = 17) or soy formula with added selenate (SF+Se, 0.17 mumol Se/L; n = 16) from birth (+4 d) to 16 wk. Selenium intakes of infants fed SF+Se were similar to the recommended dietary allowance and significantly greater than those of SF-fed infants. The SF group had significantly lower plasma, erythrocyte, and urine selenium, and lower plasma and erythrocyte glutathione peroxidase (GPx) activities at 16 wk compared to those of infants fed SF+Se. A decrease in plasma selenium was observed in SF-fed infants, whereas no differences in plasma selenium were found in infants fed SF+Se. These results indicate that selenate added to soy formula is highly available and effective at maintaining infant plasma and erythrocyte selenium concentrations and GPx activities that are greater than those of infants fed soy formula not fortified with selenium.

Insulin regulates the expression of genes involved in a variety of metabolic processes. In chick-embryo hepatocytes in culture, insulin amplifies the tri-iodothyronine (T3)-induced enzyme activity, and the level and rate of transcription of mRNA for both fatty acid synthase (FAS) and malic enzyme (ME). Insulin alone, however, has little or no effect on the expression of these genes. In chick-embryo hepatocytes, the mechanism by which insulin regulates the expression of these or other genes is not known. Several recent studies have compared the effects of zinc, vanadate and selenate on insulin-sensitive processes in an attempt to probe the mechanism of insulin action. Because zinc, vanadate and selenate mimic the effects of insulin on several processes, they have been termed insulin-mimetics. We have studied the effect of zinc, vanadate and selenate on the T3-induced expression of both FAS and ME. Like insulin, these agents had little or no effect on the basal activities for FAS and ME in chick-embryo hepatocytes in culture for 48 h. Unlike insulin, however, zinc, vanadate and selenate inhibited the T3-induced activities and mRNA levels of both FAS and ME. Maximal inhibition was achieved at concentrations of 50 microM zinc or vanadate, or 20 microM selenate. Zinc and vanadate also inhibited the T3-induced transcription of the FAS and ME genes. Although the mechanism of this inhibition is unknown, our results indicate that it is not mediated through inhibition of binding of T3 to its nuclear receptor nor through a general toxic effect. Thus zinc, vanadate and selenate are not insulin-mimetics under all conditions, and their effects on other insulin-sensitive processes may be fortuitous and unrelated to actions or components of the insulin signalling pathway.

The present study was undertaken to investigate the effects of selenite (SeIV) or selenate (SeVI) on nuclear T3 receptors of rat liver. Selenite at 0.1 microM (p < 0.01) inhibited the T3 specific binding to rat liver nuclear receptors. The specific binding of the T3 receptor was fully restored when even 1.0 microM selenite was separated from the T3 receptor by gel filtration. No inhibitory effect of selenite (up to 100 microM) on the T3 binding to nuclear receptor was found in the presence of 1.0 mM dithiothreitol. The rate of dissociation of the T3-nuclear receptor complex was effectively increased by 0.1 microM selenite. Selenate up to 1 mM as well as sulfite or sulfate up to 0.1 mM did not exert an inhibitory effect on T3 receptors. The results based on the in vitro experiments suggest that the selenium in the form of selenite may reversibly affect the T3 binding on the receptor molecule.

The selenoorganic compounds di(4-aminophenyl)selenide (10) and 4-nitro-4'-amino-diphenylselenide (36) were shown to inhibit lipid peroxidation in ADP/Fe2+/ascorbate-treated microsomes and tert-butylhydroperoxide-treated hepatocytes with IC50s of 3 and 10 microM, and 14 and 10 microM, respectively. In the former system, these inhibition constants compare favourably with those of Ebselen and classical antioxidants such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA). In the cell system, these selenium compounds were equipotent with BHA but more potent than Ebselen and its analogues. The diamino compound (10) was also an effective inhibitor of lipid peroxidation initiated by diquat redox cycling in hepatocytes, again being equipotent with BHA but more potent than Ebselen and its analogues, which actually stimulated lipid peroxidation in this test system. Manipulation of the amino functions of (10) and (36) by alkylation or acylation altered the antioxidant capacity. Optimal activity in this series was achieved by N-ethylation or N-isobutylation of (10). This produced antioxidants having IC50s below 1 microM in the microsome system, 3-13 microM in the tert-butylhydroperoxide system, and being 100% effective in the diquat model at 50 microM. On the other hand, acylation or alkylation of the amino groups with long chain acyl or alkyl groups reduced the efficacy of the structures below that of the parent diamine. As with other antioxidant compounds, several of the chalcogenides were relatively selective inhibitors of monocyte 5'-lipoxygenase-dependent secretion of LTB4 as compared to their effect on cyclooxygenase-dependent secretion of PGE2 (for example compound 42 had IC50s of 0.6 microM and 10 microM, respectively). No correlation was observed between the redox-properties of the chalcogenides and their respective abilities to inhibit these enzymes.

The synthesis of a series of 2-arylamido and 2-alkylamido derivatives of 2-amino-4-(isothiocyanatomethyl)thiazole and 2-amino-4-(isothiocyanatomethyl)selenazole is described. In vitro antiproliferative evaluations were carried out using L1210 cells. The 2-(alkylamido)thiazole derivatives were moderately antiproliferative, with IC50's of 4-8 microM. A significant increase in activity was obtained for the arylamido derivatives, with IC50's of 0.2-1 microM. The results obtained for the selenazoles were similar to those for the thiazoles. 2-Benzamido-4-(isothiocyanatomethyl)-thiazole (19) was found to be a potent inhibitor of GMP synthetase. None of the compounds prepared in this study demonstrated antifilarial activity.

Bis(2-bromo-4,5-dimethoxyphenyl)sulfide (5) and bis(2-bromo-4,5-dimethoxyphenyl) selenide (7) have been shown to block cells in the G2/M phase of the cell cycle, whereas the debromo (4,6) equivalents do not. The biobromoselenide (7) is cytotoxic to tumour cells in vitro and has been shown to increase the mitotic index of treated cells. These biological effects are consistent with disruption of the mitotic apparatus. This agent does not inhibit microtubule assembly in vitro, but does bind to tubulin. Molecular modelling of these structures indicates that their spatial and electronic structures may make an important contribution to the biological activity.