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PubMed1993

Homocysteine-dependent demethylation of trimethylselenonium ion and selenobetaine with methionine formation.

In the presence of rat liver cytosol and homocysteine, trimethylselenonium ion (TMSe+) underwent time-dependent demethylation to dimethylselenide with the concurrent formation of methionine. Convenient methods were developed for assay of this activity using either radioactive methods based on the gamma emitting isotope 75Se or nonradioactive HPLC assay of methionine. The rate of demethylation was linear with protein concentration and dependent on homocysteine, which could not be replaced by cysteine, glutathione, or dithiothreitol. The TMSe+ demethylation rate was inhibited by the addition of betaine, sulfobetaine (dimethylthetin), or dimethylglycine. The Km for TMSe+ was 8 mM compared to 0.04 mM for betaine, but the rate of TMSe+ demethylation was approximately 50-fold that of betaine when both were assayed at 25 mM. Methionine was also produced from selenobetaine, selenobetaine methylester, and sulfobetaine. The selenium analogues of betaine inhibited the demethylation of TMSe+ with only minor decreases in methionine production, indicating substrate competition. In preliminary studies aimed at the partial purification of the TMSe+:homocysteine methyltransferase activity, the enzyme was found to have chromatographic and heat stability characteristics similar to betaine:homocysteine methyltransferase. The data indicate that betaine:homocysteine methyltransferase, or a very similar enzyme, is involved in the demethylation of TMSe+ and show that TMSe+, an in vivo urinary selenium metabolite of many selenium compounds, is not biologically inert.

Animals↗

PubMed1987

Comparison of the protection given by selenite, selenomethionine and biological selenium against the renotoxicity of mercury.

The protective effect of selenite, seleno-dl-methionine and biological selenium against the renotoxicity of mercury was tested in rats. As the source of biological selenium, the liver soluble fraction of rats given 60 mumoles/kg selenite 3 days before sacrifice was used. The aim of the experiments was to test whether protective efficiency follows the reported order of ability to form HgSe. Mercury was given subcutaneously in doses of 2.5, 5.0 and 7.5 mumoles/kg HgCl2 and selenium was given in equimolar doses at the same time as Hg2+. Liver soluble fraction, biological selenium or liver soluble fraction supplemented with selenite or seleno-dl-methionine were given orally, while in experiments without liver soluble fraction the two selenium compounds were given subcutaneously. Biological selenium was tested only at the two lower dose levels. Both biological selenium and seleno-dl-methionine decreased the urinary excretion of mercury in the first 48 h, but less so than selenite and only selenite decreased the renal content of mercury at the end of this period. Urinary alkaline phosphatase activity and plasma urea nitrogen at the 2.5 and 5.0 mumoles/kg dose levels decreased in the order of no selenium greater than biological selenium greater than seleno-dl-methionine greater than selenite. As the reported HgSe formation increases in the same order, the experiments support the role of HgSe formation in the protective effect. The degree of necrotic damage in the P2 and P3 regions of the proximal tubular cells increased in the same order as the biochemical indicators at the 5.0 and 7.5 mumoles/kg dose levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1975

X-ray photoelectron spectroscopy of some selenium containing amino acids.

X-ray photoelectron spectra of some inorganic selenium compounds, Se-methionine, Se-cystine, Se-urea and selenodicysteine were recorded and compared with the XPS data obtained from the respective sulphur containing compounds. The oxidation state of selenium could be monitored by the observed chemical shifts of the Se(3p1/2),Se(3p3/2) and Se(3d3/2,5/2) levels. Though having a formal oxidation state near zero, the binding energy of the core electrons of Se in Se-methionine, Se-cystine and selenodicysteine was shifted by 0.4, 0.7 and 0.4 eV, respectively. This phenomenon was attributed to the rather distinct polarization of Se. The reversible oxidation of Se-cystine using H2O2 and NaBH4 could be successfully demonstrated by this XPS-technique.

Amino Acids↗

PubMed1975

Modification of a selenium toxicity in chicks by dietary silver and copper.

Studies were conducted to determine the effects of high levels of dietary silver nitrate and copper sulfate on the response of chicks to toxic levels of dietary selenium. Adding 5 ppm or more selenium to a basal stock diet significantly reduced growth rate, and 40 ppm or high significantly increased mortality during the 2-week experiments. Deitary silver or copper (1,000 ppm) counteracted the growth depression and prevented mortality at the higher levels of selenium. Hepatic selenium reached a maxiumum in chicks fed the basal diet with 10 ppm dietary selenium. Hepatic selenium of chicks fed silver was less than that of the control chicks when diets containing 10 ppm or less selenium were fed. Adding copper to the diet resulted in considerable accumulation of selenium in the liver, which was evident even at the lower levels of added selenium. Rseults of an experiment to determine the effects of deitray silver and copper on the distribution of 75-Se administered either orally or in tramusculary showed that silver interfered with absorption of selenium. The results of these experiments suggest that silver modifies selenium toxity both by interfering with selenium absorption and by causing the accumulation of a nondeleterious selenium compound in the tissues. Copper modifies selenium toxicity primarily by causing the accumulation of a nondeleterious compound in the tissues.

Administration, Oral↗

PubMed1986

The metabolism of selenomethionine, Se-methylselenocysteine, their selenonium derivatives, and trimethylselenonium in the rat.

The formation of dimethylselenide (respiratory) and trimethylselenonium (urinary) metabolites from [75Se]selenomethionine, [75Se]methylselenomethionineselenonium, [75Se]methylselenocysteine, [75Se]dimethylselenocysteineselenonium, and [75Se]trimethylselenonium was determined using single sc doses of 2 or 0.064 mg Se/kg in male and female rats. The 75Se content of liver, kidney, pancreas, testis, spleen, blood, heart, brain, and skeletal muscle was determined at 0.5 and 24 h. Respiratory 75Se after 24 h was greatest from Se-dimethylselenocysteineselenonium (38 and 17% for the high and low doses, respectively). Respiratory 75Se was about 8% for the high dose of Se-methylselenocysteine and was less for all other compounds. Total 75Se excretion in the urine was highest from rats given trimethylselenonium (about 90%, both doses) and was lowest from rats given selenomethionine (4%, low dose). Urine samples were chromatographed on SP-Sephadex cation-exchange columns and 75Se was eluted with ammonium formate; trimethylselenonium was precipitated with ammonium Reineckete solution and trimethylsulfonium carrier. Urinary trimethylselenonium excretion was greatest from rats given trimethylselenonium, but rats given Se-dimethylselenocysteineselenonium (low dose) excreted 35-45% of the dose as trimethylselenonium ion. The lowest quantity of trimethylselenonium was excreted by rats given the low dose of selenomethionine (0-3%). Pancreas, kidney, and liver showed the highest uptake (% of dose/g) of the selenium compounds. Trimethylselenonium was highly concentrated by the kidney and also showed high myocardial uptake (heart/blood ratio = 5) 0.5 h after injection; the selective uptake of trimethylselenonium in heart was not observed for the other selenonium compounds.

Animals↗

PubMed1990

Subcellular distribution of selenoproteins in the liver of the rat.

After in vivo labeling with [75Se]selenite, the intracellular distribution of selenoproteins in the liver was investigated in selenium-adequate and selenium-deficient rats. In the subcellular fractions, which were obtained by differential centrifugation, the proteins were separated by means of SDS-PAGE and the selenium compounds were identified via their 75Se activity. In this way twelve selenium-containing proteins or protein subunits with molecular weights between 12,100 and 75,400 were found. Glutathione peroxidase was concentrated in the cytosol and in the mitochondria. With the newly detected selenoproteins, some were enriched in the cytosol, one was mainly found in the nuclear fraction and some, which were present mainly in the mitochondrial and microsomal fractions, are most probably membrane-bound. In the liver of selenium-depleted rats the selenium administered was used predominantly to restore the levels of some of the newly found selenoproteins, while in the liver of selenium-adequate animals most of the selenium retained was incorporated into the glutathione peroxidase. The differences in the distribution among the subcellular fractions and the specific incorporation of the element in selenium deficiency into certain compounds suggest that there are several metabolic pathways for selenium and that the selenoproteins are involved in several different processes of intracellular metabolism.

Animals↗

PubMedDate not supplied

Comparison of whole blood selenium values and erythrocyte glutathione peroxidase activities of normal individuals on supplementation with selenate, selenite, L-selenomethionine, and high selenium yeast.

The selenium levels and the glutathione peroxidase activity GSH-PX of whole blood and of erythrocytes, respectively, were determined in 139 normal Danes and related to sex and smoking habits. No differences were found in relation to sex apart from a higher GSH-PX activity of females when assayed with tertiary butyl hydroperoxide. Smokers showed significantly lower selenium values than non-smokers (p less than 0.05), but the two groups had identical GSH-PX activities. Individuals from the above-mentioned group were divided into four groups, receiving daily oral doses of 200 micrograms of selenium in the form of selenite, selenate, L-selenomethionine, and selenium as contained in yeast. Whole blood selenium values and the erythrocyte glutathione peroxidase activities were determined during three months of supplementation followed by a withdrawal period of four months. Both the inorganic selenium compounds and the organic derivatives gave rise to steady state levels of GSH-PX after one month of supplementation. However, the selenium levels in the groups receiving organic selenium showed a steady rise during the whole period, whereas those supplemented with inorganic selenium leveled off after a period of one to three months. The data for smokers and nonsmokers revealed identical results when organic selenium was supplemented. However, selenite gave rise to significantly higher selenium levels and GSH-PX activities in smokers than in non-smokers. Less significant (p less than 0.08) elevations of both parameters were also observed among the smokers in the selenate group. By taking both the selenium level and the GSH-PX activity into consideration, organic selenium (i.e., L-(+) selenomethionine) was judged to be more bioavailable than selenite and selenate.

Adult↗

PubMed1985

Antitumor effect of 6-phenyl-7(6H)-isoselenazolo[4,3-d]pyrimidone on the growth of Ehrlich ascites tumor.

Two selenium compounds have a strong antitumor effect on Ehrlich ascites tumor; 6-phenyl-7(6H)-isoselenazolo[4,3-d]pyrimidone (ISP) especially, markedly inhibited the growth of tumor inoculated i.p. in mice, inducing almost complete regression of tumors at doses of 100 micrograms/mouse per day X 10 with no sign of toxicity. The antitumor activity of 4,5-dihydro-4-methyl-6-oxo-5-phenyl-6H-pyrazolo [4,5-c]isoselenazole(PIS) was weaker than that of ISP. The total lipid and phospholipid contents in the tumor cells treated with ISP were significantly decreased. In addition, the fatty acid pattern of cholesterol esters, phosphatidyl choline and phosphatidyl ethanolamine from the ISP-treated Ehrlich ascites tumor cells differed markedly from that of the corresponding lipids from the control tumor cells.

Animals↗

PubMed1995

Inhibition of aflatoxin B1-induced cell injury by selenium: an in vitro study.

Dietary selenium is an essential trace element in human nutrition. Selenium has been shown in animal studies to inhibit aflatoxin hepatocarcinogenesis. However, the cellular mechanism responsible for the inhibition has not been thoroughly studied. This study examines the effect of two selenium compounds, namely, sodium selenite and selenium-enriched yeast extract (SeY), on the cytotoxicity, DNA-binding and mutagenicity of aflatoxin B1 (AFB1) in cultured Chinese hamster ovary (CHO) cells. CHO cells, after treatment with 2 micrograms ml-1 selenite or 80 micrograms ml-1 SeY, exhibited increased resistance to AFB1-induced cell killing. At a concentration of 50 micrograms ml-1 AFB1, cell survival, measured by the clonogenicity assay, was increased by 21- and 10-fold in selenite- and SeY-treated cells, respectively. However, selenium treatment did not appear to affect AFB1-DNA binding. Similarly, no effect was observed on AFB1 mutagenicity, as determined by the hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene mutation assay. The results showed that selenium could effectively protect cells from AFB1 cytotoxicity in cultured cells but had no effect on AFB1-DNA adduct formation or mutagenesis. It is suggested that there are multiple pathways of AFB1 toxicity and that selenium can modulate AFB1-induced cell killing independent of its genotoxicity.

Aflatoxin B1↗

PubMed1990

Chromosome aberrations, sister-chromatid exchanges and cell-cycle kinetics in human peripheral blood lymphocytes exposed to organoselenium in vitro.

The ability of 2 synthetic organoselenium compounds, a dimer of p-methoxybenzeneselenol (DPMBS) and benzylselenocyanate (BSC), to induce sister-chromatid exchanges (SCE) and chromosome aberrations (CA) as well as to alter the progression of the cell through mitosis has been investigated in cultured human lymphocytes. Cultures treated with the highest concentration (2.27 x 10(-5) M) of the 2 compounds exhibited about a 3-fold increase in the level of SCE and about 2-3-fold increase in the incidence of CA. In addition, the 2 selenium compounds led to an inhibition of cell proliferation as was evidenced by the depression of the proliferation rate index (PRI).

Adult↗

PubMed1995

Studies on the distribution and characteristics of new mammalian selenium-containing proteins.

It has now been established that the essential effects of selenium in mammals are owing to the presence of several biologically active selenium compounds. Seleno-enzymes identified so far include several glutathione peroxidases and the type 1 iodothyronine de-iodinase. Some other selenoproteins have been sequenced and characterized. After in vivo labelling of rats with 75Se and protein separation using gel electrophoretic methods, more than 25 selenium-containing proteins or protein sub-units were detected. Some of the results of the investigations on these compounds are summarized and discussed here. By determining the pattern in a large number of tissues information on the distribution of the selenium-containing proteins was obtained. Their biological significance is not yet known but several findings indicate that some of these proteins may have important functions, especially in the brain and the endocrine and reproductive organs. More detailed information is already available on a 34 kDa-protein found in the testis and spermatozoa. Studies on the effects of dosage and chemical form of dietary selenium indicated that the tissue levels of the seleno-enzymes are homeostatically controlled and cannot be increased by additional supply. The increase in the tissue selenium observed with high selenium intake was found to be mainly caused by the non-specific incorporation of the element into a large number or proteins. The formation of most of the other selenium-containing proteins has priority over that of the cytosolic and plasma glutathione peroxidases. Thus the selenium requirement, which was calculated for optimum plasma glutathione peroxidase activity, also covers the amounts needed for normal levels of the other biologically important selenium compounds.

Animals↗

PubMed1987

The effects of humic acid on the chemical and biological properties of selenium in the environment.

To shed light on the causes of Kaschin-Beck disease, which can be prevented by supplementation of the diet with sodium selenite, the interactions between inorganic selenium compounds (selenite and selenate) and humic/fulvic acid were investigated. Selenate was found to be slowly reduced to selenite by humic acid in acidic solution. Selenite was adsorbed on manganese dioxide and iron(III) oxide from solution to a much greater degree than on kaolin, humic acid, Yongshu soil, or silicon dioxide. Feeding mice a diet supplemented with sodium selenite increased the selenium concentration in the kidney, liver, spleen, lung, heart and blood. A diet containing sodium selenite and fulvic acid caused the selenium concentrations in the organs, with the exception of the spleen, to be lower than observed with the selenite-only diet. Selenium and fulvic acid increase the activity of glutathione peroxidase. Sodium selenite and fulvic acid injected in combination into the abdominal cavity of mice and rats were less toxic than either substance alone. Selenite and fulvic acid applied separately enhanced the luminosity of photobacterium phosphoreum T-3 at low concentrations but depressed the luminosity at higher concentrations. Selenite and fulvic acid in combination caused a larger enhancement and a smaller depression of the luminosity than observed with either substance alone. The hypothesis is formulated that Kaschin-Beck disease is caused by selenium levels insufficient to prevent the toxic effects of the organic compounds present in the drinking water of the regions in which the disease is endemic.

Animals↗

PubMed1994

Antioxidant activity of some diarylselenides in biological systems.

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.

Adenosine Diphosphate↗

PubMed1982

Serum selenium levels in liver diseases.

A possible pathogenetic role of selenium deficiency in alcoholic cirrhosis of the liver has previously been discussed. In the present study serum selenium was analyzed in 5 groups of liver diseases. The method used for selenium determination was electrothermal atomic absorption, after thermal stabilization of selenium compounds by addition of nickel nitrate. The selenium level of a reference group of healthy Norwegian adults (n = 40) was 1.53 +/- 0.25 mumol/l. The serum concentrations of selenium in patients suffering from alcoholic cirrhosis, chronic active hepatitis and chronic persistent hepatitis were lowered to 40-80 per cent of those of the reference group. In alcoholic cirrhosis and chronic active hepatitis the decreased serum selenium concentrations were significantly correlated to decreased levels of albumin and prealbumin.

Hepatitis, Chronic↗

PubMed1981

Metal interactions in carcinogenesis: enhancement, inhibition.

Metals constitute a fundamentally important part of the total human environment. Since human exposure often involves complex mixtures of metal compounds and, possibly, organic compounds which may be carcinogenic per se, interactions between these compounds may add significantly to human cancer risk. Our present knowledge about these kinds of interactions is very limited. The best investigated area is benzo(a)pyrene (BP)-metal oxide particle interactions in respiratory carcinogenesis in the hamster. Metal oxide particles were also shown to modify the carcinogenic effect of nitrosamines. Several reports describe experiments in which selenium compounds exerted a generally anticarcinogenic and antimutagenic activity. Inorganic arsenic compounds, which are accepted to be carcinogenic in man, have so far been negative in animal experiments except for one recent suggested report. Several authors have, however, suggested that these compounds may act as cocarcinogens due to their inhibition of DNA repair, although animal experiments to demonstrate a cocarcinogenic effect of arsenic compounds have been negative so far, except for one preliminary report. The concentration of zinc in the diet seemed to influence both transplanted tumor growth and the carcinogenicity of several organic compounds, and the possibility of a correlation between dietary zinc and certain cancer forms in man has been suggested. Protection against development of Leydigiomas usually induced by cadmium injection was afforded by simultaneous injection of zinc salts. Nickel carcinogenesis has been reported to be antagonized by manganese, and synergism between Ni and organic carcinogens, e.g. BP, has been demonstrated. There is no firm evidence that lead may be a cocarcinogen, although some limited experimental evidence is available. Oxidizing agents have been demonstrated to increase, and reducing agents to antagonize, the mutagenic effect of chromium compounds in vitro. The content of carcinogenic and other metals in asbestos has been suggested to modify the carcinogenic properties of asbestos. Since much of the information available at present is suggestive, further research on these interactions as well as other possible interactions in metal carcinogenesis is needed. Studies should be made both in well defined in vitro systems and in relevant animal models.

Animals↗

PubMed1989

Mercury-selenium interaction: distribution and excretion of 203Hg2+ in rats after simultaneous administration of selenite or selenate.

In female rats intravenously injected with 203HgCl2 (0.6 mg Hg2+ per kg body wt.) the effect of intraperitoneal administration of selenite or selenate (0.525 mg Se per kg body wt.) on distribution and excretion of 203Hg was studied. The content of 203Hg was lower in kidney and higher in liver and blood in the groups treated with selenate or selenite when compared with rats which received only mercury. The brain content of 203Hg was significantly increased in rats injected with selenite. Both selenium compounds injected immediately after mercury significantly decreased urinary as well as biliary excretion of 203Hg. A transient increase in the rate of biliary excretion of 203Hg during the first 2 h after administration was observed in rats treated with selenate. This finding seems to support the idea that the reduction of selenate to selenite in the body is not rapid but takes at least several hours.

Animals↗

PubMed1986

A novel biologically active seleno-organic compound--VI. Protection by ebselen (PZ 51) against galactosamine/endotoxin-induced hepatitis in mice.

Male albino NMRI mice were given 700 mg/kg galactosamine and 33 micrograms/kg salmonella endotoxin intraperitoneally. After 9 hr, serum sorbitol dehydrogenase activity had risen from 60 to 7320 U/l, SGOT from 90 to 5580, and SGPT from 70 to 10,440. When a similar dose of galactosamine alone or endotoxin alone was given, no significant liver injury was found. Animals pre-treated with an oral dose of ebselen (600 mg/kg 1-3 hr before galactosamine/endotoxin administration) were fully protected against this type of hepatitis. When pretreated 1 hr before intoxication with different doses of ebselen, significant dose-dependent reduction of serum enzyme activities was observed at doses higher than 1 mg/kg. After pre-treatment with 6 mg/kg ebselen, no biochemical or histological signs of liver lesions were detectable 36 hr after intoxication. In order to comparatively evaluate the model used, several established anti-inflammatory drugs were administered at doses which showed 50% effectiveness in preventing carageenan paw edema. A dose of 200 micrograms/kg dexamethasone, or 9 mg/kg indomethacin abolished galactosamine/endotoxin-induced enzyme release in our animals, as did the lipoxygenase pathway inhibitor diethylcarbamazine (78 mg/kg). In contrast, administration of cyclooxygenase pathway inhibitors such as aspirin (220 mg/kg) or ibuprofen (45 mg/kg) failed to prevent hepatitis. The effect of ebselen was also investigated in four different models of acute drug-induced liver damage. A dose of 600 mg/kg of the organic selenium compound was ineffective or weakly active in benzo(alpha)pyrene- or phenobarbital-treated mice which were intoxicated by intraperitoneal administration of 350 or 400 mg/kg body weight of paracetamol. Similarly negative results were obtained against bromobenzene-induced hepatotoxicity (520 mg/kg bromobenzene i.p.), carbon tetrachloride intoxication (3.2 g/kg), or allyl alcohol-induced liver damage (60 mg/kg). The selective efficacy of ebselen against galactosamine/endotoxin induced liver damage is interpreted in terms of its recently recognized ability to inhibit the formation of leukotrienes.

Alanine Transaminase↗

PubMed1985

Selenium absorption by canine jejunum.

Deficiency of the trace element selenium causes disease in domestic animals and may also be implicated in the pathogenesis of some human illness. In this study, the triple-lumen perfusion method was used to measure the rate of absorption of trace quantities of selenium (50 micrograms/liter in a physiological electrolyte solution) from the jejunum when given as D,L-selenomethione, D,L-selenocystine, or sodium selenite to healthy dogs in vivo. Selenium absorption from the test segment (expressed as percent administered dose per centimeter +/- SEM) was 1.97 +/- 0.04 from D,L-selenomethionine, 1.15 +/- 0.06 from D,L-selenocystine, and 0.51 +/- 0.07 from sodium selenite (P less than 0.01, N = 5). In separate studies in four anesthetized dogs, the jejunum was perfused with L-[75Se] selenomethionine while concentrations of 75Se were measured in the portal venous blood; these studies established that [75Se]selenomethionine disappearing from the gut lumen corresponded quantitatively to 75Se appearing in the portal venous effluent (74 +/- 6%) and incorporated into intestinal tissue (24 +/- 5%). These results are consistent with the hypothesis that the absorption of amino acid-bound selenium is accelerated by the specific amino acid active transport mechanisms in the gut mucosa. Sodium selenite is absorbed more slowly, possibly by simple diffusion through the intestinal mucosa, than the amino acid-bound selenium compounds.

Animals↗