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PubMedDate not supplied

Selenium concentration and glutathione peroxidase activity in selenium and magnesium deficient rats.

To clarify the effects of selenium (Se) and magnesium (Mg) deficiencies on Se and glutathione peroxidase (GSHPx) status, weanling male Wistar rats weighing 50-60 g were placed on four kinds of diets divided by two levels of Se (0.5 or 0.019 mg/kg) and Mg (500 or 50 mg/kg) for 8 wk. Magnesium deficiency had an influence on distribution of Se, which was increased in muscle and decreased in other tissues. The changes in GSHPx matched those in Se. The levels of Se and GSHPx in most tissues were lower in Se-Mg-deficient rats than in Se-deficient rats. Thus, selenium and Mg deficiencies would make oxidant lesion more serious than Se deficiency.

Animals↗
PubMed1998

Enhancement of selenium excretion in bile by sulfobromophthalein: elucidation of the mechanism.

This work was intended to explore the mechanism whereby sulfobromophthalein (BSP), an electrophilic and cholephilic organic acid, increases the biliary excretion of selenium in rats injected with sodium [75Se]selenite. In such animals, neither BSP-glutathione conjugate nor dibromosulfophthalein, nonelectrophilic congeners of BSP, enhanced the hepatobiliary transport of selenium, suggesting that reaction of nucleophilic selenite metabolites formed in vivo with the injected BSP may be involved. Indeed, HPLC analysis of bile from rats receiving [75Se]selenite and BSP revealed two peaks (X and Y) that were simultaneously detected both by absorbance as BSP metabolites and by radioactivity as [75Se] metabolites, indicating that these represent selenium-containing BSP metabolites. Pretreatment of rats with inhibitors of selenium methylation, such as periodate-oxidized adenosine (PAD) and ethionine, drastically diminished the size of peak X, while increasing (PAD) or not influencing (ethionine) the size of peak Y. This finding indicates that production of metabolite X, but not Y, is dependent on formation of methylated selenium metabolites. A compound chromatographically indistinguishable from that in peak X was formed in vitro during incubation of BSP with methylselenol, suggesting that biliary metabolite X is identical to the reaction product of BSP and selenite-derived methylselenol. Incubation of BSP with selenite in the presence of a thiol, namely glutathione, cysteine or N-acetylcysteine (which convert selenite into nucleophilic products, i.e. the respective selenopersulfides and hydrogen selenide) resulted in product(s) chromatographically identical to the biliary selenium-containing BSP metabolite(s) of peak Y, irrespective of the nature of the thiol used. Thus, biliary metabolite(s) Y may be reaction products of BSP and hydrogen selenide. Finally, BSP significantly diminished exhalation of dimethyl selenide in selenite-injected rats, purportedly because it reacted with precursors of dimethyl selenide, that include hydrogen selenide and methylselenol. In summary, BSP increases biliary excretion of selenium in rats receiving selenite because it forms selenium-containing BSP metabolites that are readily transported into bile. It is suggested that the in vivo reaction of nucleophilic selenite metabolites with electrophilic compounds may influence the fate of selenium and may contribute to some of the effects of this essential and anticarcinogenic metalloid.

Animals↗
PubMed1983

In vitro hemolysis of rat erythrocytes by selenium compounds.

Rat erythrocytes were incubated in vitro with various selenium compounds at 37 degrees. Hemolysis occurred with some selenium compounds but not with corresponding sulfur analogues. Selenite induced more rapid loss of intracellular glutathione (GSH) than did selenocystine but was less hemolytic. Cystine caused neither loss of intracellular GSH nor hemolysis. Addition of GSH to the incubation medium enhanced hemolysis by selenite and selenium dioxide but inhibited hemolysis by selenocystine. Inclusion of glucose in the incubation medium also inhibited selenocystine-induced lysis of erythrocytes from both selenium-supplemented rats and selenium-deficient rats. The results suggest a relationship between the oxidation of intracellular GSH and the hemolysis by selenocystine, selenite and selenium dioxide.

Animals↗
PubMed2005

Anti-thyroid drugs and thyroid hormone synthesis: effect of methimazole derivatives on peroxidase-catalyzed reactions.

Syntheses and characterization of the selenium analogue (MSeI) of anti-thyroid drug methimazole and a series of organoselenium compounds bearing N-methylimidazole pharmacophore are described. In contrast to the sulfur compound that exists predominantly in its thione form, the selenium analogue exists in a selenol form, which spontaneously oxidizes in air to produce the corresponding diselenide. The reduction of the diselenide by GSH or NaBH(4) affords the biologically active selenol, which effectively inhibits the lactoperoxidase (LPO) activity in vitro. The monoselenides having N-methylimidazole moiety are found to be much less active than the selenol, suggesting that the presence of a selenol moiety is important for the LPO inhibition. The kinetic and mechanistic studies reveal that MSeI inhibits the LPO activity by reducing the H(2)O(2), providing a novel method to reversibly inhibit the enzyme. Although MSeI strongly inhibits LPO, the enzyme's activity can be completely recovered by increasing the H(2)O(2) concentration. On the other hand, the inhibition by methimazole (MMI), the sulfur analogue, cannot be reversed by increasing the H(2)O(2) concentration, leading to a complete inactivation of the enzyme. The reversible inhibition of LPO by some of the selenium derivatives is correlated with their glutathione peroxidase (GPx) activity, and the high GPx activity of the selenium compounds as compared with their sulfur analogues suggests that the selenium derivatives may protect the thyroid gland from oxidative damage.

Antithyroid Agents↗
PubMedDate not supplied

Dietary supplementation with antioxidants improves functions and decreases oxidative stress of leukocytes from prematurely aging mice.

OBJECTIVES: Aging is accompanied by chronic inflammation and oxidative stress, which lead to a marked impairment of immune function and therefore increased mortality. This study assessed the effect of dietary supplementation, for 15 wk, with 5% and 20% (w/w) of biscuits enriched with nutritional doses of vitamins C and E, zinc, selenium, and beta-carotenes on function and oxidative stress parameters of peritoneal leukocytes from middle-aged, prematurely aging mice (PAM) and non-prematurely aging mice (NPAM). METHODS: After supplementation we measured leukocyte functions (adherence, chemotaxis, phagocytosis, intracellular reactive oxygen species levels, lymphoproliferation, natural killer activity, and interleukin-2 release), antioxidant defenses (superoxide dismutase, glutathione peroxidase, and reduced glutathione), oxidant compounds (extracellular O(2)(-), glutathione disulfide, glutathione disulfide/reduced glutathione ratio, tumor necrosis factor-alpha, nitric oxide, and prostaglandin E(2)), and lipid and DNA oxidative damage, measured by malondialdehyde and 8-oxo,7,8-dihydro-2'-deoxyguanosine levels, respectively. RESULTS: In general, leukocyte functions were improved and redox homeostasis was restored after intake of antioxidants. In consequence, malondialdehyde and 8-oxo,7,8-dihydro-2'-deoxyguanosine in PAM and NPAM were strikingly decreased after 5% and 20% supplementation (malondialdehyde, P < 0.001 in PAM; P < 0.01 in NPAM after both treatments; 8-oxo,7,8-dihydro-2'-deoxyguanosine, P < 0.01 after 5% supplementation and P < 0.001 after 20% supplementation in PAM and NPAM). Moreover, the effect of the antioxidants was stronger in PAM than in NPAM, and 20% supplementation was more effective than 5%. CONCLUSION: Our data suggest that improvement of leukocyte function and restoration of redox balance after consumption of adequate levels of antioxidants from adulthood may be useful to attain healthy aging, especially in animals with premature aging.

Aging↗
PubMed2001

Plasma fatty acid status in Moroccan children: increased lipid peroxidation and impaired polyunsaturated fatty acid metabolism in protein-calorie malnutrition.

In previous studies on plasma fatty acid and antioxidant status in 29 malnourished Moroccan children (12 with mild protein-calorie malnutrition, 17 with severe protein-calorie malnutrition) compared to 15 healthy control children from the same area, we pointed out that these populations were heterogeneous in terms of their essential fatty acid and antioxidant status. The aim of the present study was to classify the children using the Waterlow classification and their essential fatty acid status. The discrepancies in lipid parameters, nutritional and inflammatory markers, blood oxidative indexes, antioxidant micronutrients or trace elements (selenium, zinc, vitamin E) related to polyunsaturated fatty acids were checked in these populations. Eight of the control subjects and nine of the severe protein-calorie malnutrition children were essential fatty acid-deficient, compared to only one of the mild protein-calorie malnutrition group. Examination of the essential fatty acid-sufficient subjects with mild protein-calorie malnutrition, compared to the essential fatty acid-sufficient control subjects, showed only a decrease in Z scores and a non-significant decrease in selenium and vitamin E. In severely malnourished children, albumin, cholesterol and low density lipoprotein (LDL) cholesterol, plasma selenium, vitamin E and zinc were low, whereas inflammatory proteins and triglycerides were high. These features worsened with essential fatty acid deficiency. In all protein-calorie malnutrition subjects, there was oxidative stress (increase in thiobarbituric-acid reactants, imbalance between plasma polyunsaturated fatty acid, vitamin E and selenium levels), even in the absence of essential fatty acid deficiency. Monounsaturated fatty acids, oleic acid/stearic acid (C18:1 n-9/C18:0) delta9 desaturase and n-3 and n-6 elongase activity indexes increased. The C18:1/C18:0 delta9 desaturase activity index was negatively correlated to Z scores (r = -0.44, P< 0.01 for Z score weight, r = -0.39, P < 0.01 for Z score height), albumin (r = -0.82, P < 0.01) and zinc (r = -0.51, P< 0.01) levels. In essential fatty acid-deficient, severe protein-calorie malnutrition subjects, delta6 desaturase activity was impaired, and there was a non-significant decrease in arachidonic acid. Essential fatty acid deficiency is a type of malnutrition, and is associated with an aggravation of all parameters in severe protein-calorie malnutrition. The increase in the C18:1/C18:0 delta9 desaturase activity and enhanced lipid peroxidation without any essential fatty acid deficiency could be early markers of protein-calorie malnutrition.

Antioxidants↗
PubMed2001

Selenium supplementation in rheumatoid arthritis investigated in a double blind, placebo-controlled trial.

INTRODUCTION: Selenium is an essential trace element with antioxidant properties. Trials with selenium have been conducted in rheumatoid arthritis (RA) to correct impaired selenium status and increase defences against deleterious oxidant species. AIM OF THE STUDY: To investigate in a double blind multi-centric placebo-controlled study the effects of selenium supplementation in RA. METHODS: Fifty five patients with moderate RA received during 90 days either capsules containing selenium-enriched yeast (200 microg/d) or a placebo. RESULTS: The visual analog scale, the Ritchie index, the number of swollen and painful joints, and morning stiffness significantly decreased with time in both groups (p<0.001), but no difference between groups could be identified. When examining the quality of life a significant (p<0.01) improvement in arm movements and health feeling was evidenced in selenium-treated patients. CONCLUSION: Selenium treatment did not show clinical benefit on RA. Interestingly, the improval in both groups demonstrated a placebo effect of the intervention trial.

Adolescent↗
PubMed1998

Cellular glutathione peroxidase is the mediator of body selenium to protect against paraquat lethality in transgenic mice.

The antioxidative role of Se-dependent cellular glutathione peroxidase (EC 1.11.1.9, GPX1) in vivo has not been established. Our objective was to determine the effects of GPX1 knockout or overexpression on the susceptibility of mice to paraquat toxicity and the contributions of GPX1, compared with other selenoproteins and vitamin E, to body defenses against such acute oxidative stress. Four experiments were conducted using 111 GPX1 knockout or overexpressing mice and the respective controls. Mice were fed diets supplemented with Se (as sodium selenite) at 0-0.4 mg/kg and/or all-rac-alpha-tocopheryl acetate at 0-75 mg/kg before intraperitoneal injections of 12.5, 50 or 125 mg paraquat/kg body weight. All mice that received 50 or 125 mg paraquat/kg died spontaneously, and the survival time of mice was (independent of dietary levels of Se per se or alpha-tocopheryl acetate) solely a function of tissue GPX1 activity (P < 0.001). Severe acute pulmonary interstitial necrosis was found only in the GPX1 overexpressing mice and the controls that had extended survival time. Thiobarbituric acid reacting substances in postmortem liver inversely correlated with the tissue GPX1 activity and dietary levels of Se and/or alpha-tocopheryl acetate. In contrast, all mice that received 12.5 mg paraquat/kg survived and were killed 2 wk after the injection for tissue collection. Compared with the saline injection, this low dose of paraquat resulted in greater (P < 0.001) liver and lung F2-isoprostanes in both the GPX1 knockout mice and the controls. However, there was no difference in plasma alanine transaminase (EC 2.6.1.2) activity or overt injuries in liver, lung and kidney in either group. Our data indicate that GPX1 is the major, if not the only, metabolic form of body Se that protects mice against the lethal oxidative stress caused by high levels of paraquat; it seems less important, however, in protecting mice against the moderate oxidative stress by the low level of paraquat.

Animals↗
PubMed2005

Methanococcus vannielii selenium-binding protein (SeBP): chemical reactivity of recombinant SeBP produced in Escherichia coli.

A selenium-binding protein (SeBP) from Methanococcus vannielii was recently identified, and its gene was isolated and overexpressed in Escherichia coli [Self, W. T., Pierce, R. & Stadtman, T. C. (2004) IUBMB Life 56, 501-507]. SeBP and recombinant SeBP (rSeBP) migrated as approximately 42-kDa species on native gels and as approximately 33-kDa species on SDS gels. rSeBP consists of identical 8.8-kDa subunits, each containing a single cysteine residue. rSeBP isolated in the absence of reducing agents contained oxidized cysteine (89%) and very little bound selenium (0.05 eq or less per subunit). Complete reduction of the oxidized cysteine residues in rSeBP with Tris(2-carboxyethyl)phosphine required addition of a denaturant, such as 1 M guanidine-hydrochloride. With selenite as the selenium source and the isolated reduced protein as sole reductant, binding of one selenium per tetramer under anaerobic conditions required four cysteine thiol groups, one on each subunit. In the corresponding reaction, with reduced glutathione (GSH), equimolar amounts of selenodiglutathione (GSSeSG) and glutathione disulfide are formed from selenite and 4 GSH. At GSH-to-selenite ratios >4:1, conversion of GSSeSG to a perselenide derivative, GSSe(-), occurs. However, with the reduced rSeBP as sole electron donor in the reaction with selenite, further conversion of the R-SSeS-R product apparently did not occur. Prior alkylation of the cysteine thiol groups in reduced rSeBP prevented selenite reduction and selenium binding under comparable conditions.

Calorimetry, Differential Scanning↗
PubMed1994

Emerging awareness of the critical roles of S-phosphocysteine and selenophosphate in biological systems.

S-Phosphocysteine residues in proteins are formed as key intermediates in certain enzyme-catalyzed reactions. In phosphoenolpyruvate (PEP)-dependent carbohydrate transport processes, the phosphoryl group of PEP is transferred sequentially to histidine residues of two cytoplasmic proteins, Enzyme I and HPr, common to all of the PEP-dependent carbohydrate transport systems. The phosphoryl group of HPr then is transferred to an essential histidine and an essential cysteine residue located in the cytoplasmic domains of certain substrate-specific, membrane-bound proteins, the actual transporters. Both the N-phosphohistidine and the S-phosphocysteine residues in these Enzyme II domains are transient catalytic intermediates in the final steps that lead to phosphorylation of the bound carbohydrate substrate. In a different type of biological system, numerous proteins involved in signal transduction pathways are phosphorylated on specific tyrosine residues by various kinases and the effects of these modifications are modulated by a family of protein tyrosine phosphate-specific phosphatases. The mechanism of action of these phosphatases involves the transfer of the phosphoryl group from a phosphotyrosine residue in the protein substrate to an essential ionized cysteine residue in the phosphatase polypeptide forming an S-phosphocysteine residue. Reaction of the latter with water and release of orthophosphate complete the phosphatase-catalyzed reaction. Selenophosphate, formed by phosphorylation of a selenol, is a key selenium donor compound in prokaryotes. This extremely oxygen-labile compound is synthesized from ATP and selenide by selenophosphate synthetase. This novel reactive selenium compound is the selenium donor for selenocysteyl-tRNA biosynthesis and for conversion of 2-thiouridine residues in tRNAs to 2-selenouridine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1994

Selenoprotein P. A selenium-rich extracellular glycoprotein.

Selenoprotein P is a glycoprotein that has been purified from rat and human plasma. In selenium-replete rats it contains 65% of the plasma selenium and its concentration is 25-30 mg protein/L. In selenium-deficient rats its concentration is < 3 mg protein/L. The plasma half life of 75Se in selenoprotein P is 3 to 4 h, indicating a rapid turnover. Purified rat selenoprotein P contains 7.5 +/- 1 selenium atoms per molecule as selenocysteine. The sequence of the cloned cDNA predicts 10 selenocysteine residues, which suggests that the protein in plasma is a modification of the predicted one. Deduced amino acid sequence identity between rats and humans is 72%. The 3' untranslated region of selenoprotein P cDNA contains two predicted stem loops of the type essential for selenocysteine incorporation. Northern analysis indicates that selenoprotein P is expressed by many tissues. Hepatic selenoprotein P mRNA level, but not its transcription, decreases during selenium deficiency. The decrease is less than the decrease of glutathione peroxidase mRNA, however. Selenoprotein P is postulated to serve as an extracellular oxidant defense because its presence correlates with selenium protection of selenium-deficient rats against diquat-induced lipid peroxidation and liver necrosis. More research will be required to test this hypothesis and to establish the biochemical function of selenoprotein P.

Amino Acid Sequence↗
PubMed1996

Synthesis and biological activity of 3- and 5-amino derivatives of pyridine-2-carboxaldehyde thiosemicarbazone.

A series of 3- and 5-alkylamino derivatives, as well as other structurally modified analogues of pyridine-2-carboxaldehyde thiosemicarbazone, have been synthesized and evaluated as inhibitors of CDP reductase activity and for their cytotoxicity in vitro and antineoplastic activity in vivo against the L1210 leukemia. Alkylation of 3- and 5-amino-2-(1,3-dioxolan-2-yl)pyridines (1, 2) resulted in corresponding 3-methylamino, 5-methylamino, 3-allylamino, 5-ethylamino, 5-allylamino, 5-propylamino, and 5-butylamino derivatives (5, 6, and 11-15), which were then condensed with thiosemicarbazide to yield the respective thiosemicarbazones (7, 8, and 16-20). Oxidation of 3,5-dinitro-2-methylpyridine (21) with selenium dioxide, followed by treatment with ethylene glycol and p-toluenesulfonic acid, produced the cyclic ethylene acetal, 23. Oxidation of 2-(1,3-dioxolan-2-yl)-4-methyl-5-nitropyridine (26) with selenium dioxide, followed by sequential treatment with sodium borohydride, methanesulfonyl chloride, and morpholine afforded the morpholinomethyl derivative 30. Catalytic hydrogenation of 23 and 30 with Pd/C yielded the corresponding amino derivatives 24 and 31. Catalytic hydrogenation of 5-cyano-2-methylpyridine (33) with Raney nickel, followed by treatment with acetic anhydride, gave the amide derivative 35. N-Oxidation of 35, followed by rearrangement with acetic anhydride, produced the acetate derivative, 5-[(acetylamino)methyl]-2-(acetoxymethyl)pyridine (37). Repetition of the N-oxidation and rearrangement procedures with compound 37 yielded the diacetate derivative 39. Condensation of compounds 24, 31, and 39 with thiosemicarbazide afforded the respective 3,5-diaminopyridine-, 4-(4-morpholinylmethyl)-5-aminopyridine-, and 5-(aminomethyl)pyridine-2-carboxaldehyde thiosemicarbazones (25, 32, and 40). The most biologically active compounds synthesized were the 5-(methylamino)-, 5-(ethylamino)-, and 5-(allylamino)pyridine-2-carboxaldehyde thiosemicarbazones (8, 17, and 18), which were potent inhibitors of ribonucleotide reductase activity with corresponding IC50 values of 1.3, 1.0, and 1.4 microM and which produced significant prolongation of the survival time of L1210 leukemia-bearing mice, with corresponding optimum % T/C values of 223, 204, and 215 being obtained when administered twice daily for six consecutive days at dosages of 60, 80, and 80 mg/kg, respectively.

Animals↗
PubMed2006

Proposed reaction mechanisms for selenium UV photolysis vapor generation by computational methods.

The production of volatile analyte species by UV photolysis in the presence of low-molecular-weight organic acids as an alternative to chemical vapor generation has been of recent interest. The mechanism of this process is not well understood. Proposed mechanisms often involve photolytic cleavage of the organic acid as the initial step. Evidence suggests that this may not be the dominant route for UV photolysis vapor generation. In this work computational methods were applied to determine a possible alternative mechanism in the absence of free-radical production. The proposed mechanism specifically focused on selenium vapor generation. An energetically favored mechanism was found for UV photolysis of inorganic selenium in the presence of formic and acetic acids which is consistent with previously reported experimental results.

Acetic Acid↗
PubMed1986

Selenium effects on human neutrophilic granulocyte function in vitro.

The effects of an inorganic selenium salt on phagocytic functions of human neutrophilic granulocytes from donors with a low activity of glutathione peroxidase have been investigated. Granulocytes were exposed for 60 min in vitro to sodium selenite in two physiological concentrations (100 and 200 ng Se/ml) and one unphysiologically high concentration (2000 ng/ml). The spontaneous and chemotactic migration, the nitroblue tetrazolium reduction, the phagocytosis of fluorescein-labeled yeast particles and the intracellular killing of staphylococci were then studied in such granulocytes and compared to control cells, which had not been exposed to selenium. The migration and nitroblue tetrazolium reduction abilities of granulocytes were not affected by selenium exposure. The phagocytic and bactericidal activities were significantly increased in granulocytes exposed to selenium in physiological concentrations. However, at 2000 ng Se/ml these activities were found to be equal to or lower than control levels. Thus selenium supplementation might enhance phagocytic and bactericidal functions of human granulocytes, thereby improving the host defense against bacterial infections.

Bacteriolysis↗
PubMed2002

Comparison of the chemopreventive potentials of melatonin and vitamin E plus selenium on 7,12-dimethylbenz[a]anthracene-induced inhibition of mouse liver antioxidant enzymes.

Chemoprevention is a rapidly growing area of oncology that is identifying agents with a potentially preventive role in cancer. In this study, it was our goal to compare the chemopreventive effects of vitamin E plus selenium, and melatonin. Forty female mice were divided into four equal groups. The first group served as control. The second group had i.p. injections of 7,12-dimethylbenz[a]anthracene (DMBA) (20 mg/kg body weight) in corn oil for 21 days. The third group had the same procedure of DMBA injections as the second group and received vitamin E + selenium (90 microg + 1.8 microg/day), simultaneously. The fourth group had DMBA injections and melatonin (4.2 mg/kg body weight), simultaneously. DMBA alone caused significant inhibition of hepatic glutathione peroxidase (GSHPx), catalase (CAT), and superoxide dismutase (SOD) in the second group. In the third group, vitamin E + selenium restored DMBA-induced GSHPx inhibition significantly whereas CAT and SOD inhibition remained essentially unchanged. In the fourth group, melatonin not only significantly decreased DMBA-induced GSHPx inhibition but also fully reversed CAT and SOD inhibitions caused by DMBA. We speculate that melatonin alone provides better chemoprevention against DMBA-induced oxidative stress than the vitamin E+selenium combination.

9,10-Dimethyl-1,2-benzanthracene↗