Effect of selenium deficiency on the disposition of plasma glutathione

Selenium deficiency causes increased hepatic synthesis and release of GSH into the blood. The purpose of this study was to examine the effect of selenium deficiency on the disposition of plasma glutathione. Plasma glutathione concentration was 40 +/- 3.4 nmol GSH equivalents/ml in selenium-deficient rats and 17 +/- 5.4 nmol GSH equivalents/ml in control rats. The half-life and systemic clearance of plasma glutathione were found to be the same in selenium-deficient and control rats (t1/2 = 3.4 +/- 0.7 min). Because selenium-deficient plasma glutathione concentration was twice that of control, the determination that selenium deficiency did not affect glutathione plasma systemic clearance indicated that the flux of glutathione through the plasma was doubled by selenium deficiency. It has been proposed that the kidney is responsible for the removal of a major fraction of plasma glutathione. In these studies, renal clearance accounted for 24% of plasma systemic glutathione clearance in controls and 44% in selenium-deficient rats. This indicates that a significant amount of glutathione is metabolized at extrarenal sites, especially in control animals. More than half of the increased plasma glutathione produced in selenium deficiency was removed by the kidney. Thus, selenium deficiency results in a doubling of cysteine transport in the form of glutathione from the liver to the periphery as well as a doubling of plasma glutathione concentration.     

Increased sister-chromatid exchange in bone-marrow cells of mice exposed to whole cigarette smoke

Male Wistar rats were fed diets of varying selenium content in order to obtain selenium-deficient and selenium-supplemented rats. After 5-6 weeks on the respective diet, the rats were used to investigate how selenium influences the effect of dimethylnitrosamine (DMN) on some liver enzymes and related reactions. The selenium-dependent glutathione peroxidase activity in postmicrosomal supernatant from liver was about 1% in selenium-deficient rats as compared to selenium-supplemented rats or rats fed a standard diet. The highest DMN-demethylase activity was observed in postmitochondrial supernatant from selenium-deficient rat liver, and the lowest in selenium-supplemented rats. No dietary effect was observed on hepatic microsomal cytochrome P450 levels. C-Oxygenation of N,N-dimethylaniline (DMA) was not affected by the selenium level. On the other hand, selenium deficiency seemed to reduce N-oxygenation of DMA. The mutagenicity of DMN in Chinese hamster V79 cells after metabolic activation by the isolated perfused rat liver, was approximately doubled when selenium-deficient livers were used as compared to selenium-supplemented livers and livers from rats fed a standard diet. A negative correlation between DMA-N-oxygenation and mutagenicity from DMN was observed, whereas no correlation between DMA-C-oxygenation and mutagenicity from DMN was found.     

Selenium deficiency potentiates paraquat-induced lipid peroxidation in isolated perfused rat lung

Glutathione peroxidase (GSHPx), a seleno-enzyme, reduces lipid hydroperoxides while producing oxidized glutathione (GSSG), which can efflux from cells. To study the role of GSHPx in antioxidant defense, isolated lungs from selenium-deficient rats were perfused for 2 h with or without 1 mM paraquat. Perfusate GSSG was measured as an index of GSHPx activity, and malondialdehyde (MDA) as an index of lipid peroxidation. Selenium deficiency decreased lung GSHPx activity 75-80%. During perfusion control lungs showed GSSG efflux of 8.5 +/- 4.5 nmol/h and with paraquat 49.1 +/- 12.1 nmol/h. Selenium-deficient lungs with or without paraquat showed GSSG efflux of 16.4 +/- 5.3 and 13.7 +/- 8.9 nmol/h, respectively. MDA efflux occurred only in paraquat-perfused selenium-deficient lungs (7.8 +/- 2.7 nmol/h). Lung homogenates from this group had lower GSH + GSSG than the other three groups. These results indicate an inverse correlation between GSSG efflux and MDA accumulation from paraquat-perfused lungs and suggest that increased turnover of the GSHPx reaction protects paraquat-perfused lungs from lipid peroxidation.     

Influence of selenium deficiency on glutathione disulfide metabolism in isolated perfused rat heart

Selenium deficiency causes a fall in rat cardiac glutathione peroxidase activity. As a consequence, isolated perfused selenium-deficient heart does not release increased amounts of GSSG when hydroperoxide is infused. However, the total amount of glutathione measured as intracellular GSH, intracellular GSSG and GSSG released from the heart when hydroperoxide is infused does not equal the total glutathione measured in these pools in untreated hearts (Xia, Y., Hill, K.E. and Burk, R.F. (1985) J. Nutr. 115, 733-742). GSSG can react with protein sulfhydryl groups to form glutathione-protein mixed disulfides (PrS-SG). PrS-SG were measured in perfused selenium-deficient and control hearts infused with t-butylhydroperoxide and were found to account for the previously unmeasured glutathione. The ability of the selenium-deficient heart to transport GSSG was also examined. GSSG was produced non-enzymatically by infusing diamide. The diamide-treated selenium-deficient heart formed GSSG and released it at the same rate as similarly-treated control heart. Thus although selenium deficiency decreases GSSG formation by glutathione peroxidase, it does not affect cardiac GSSG transport.     

Effect of selenium deficiency on tissue taurine concentration and urinary taurine excretion in the rat

The purpose of this study was to determine the effect of selenium deficiency on tissue taurine levels and urinary taurine excretion. Weanling male Sprague-Dawley rats were fed selenium-deficient or selenium-adequate diets for 20 weeks. As selenium deficiency developed, urinary taurine excretion increased in selenium-deficient rats compared to controls. At 12 weeks, the selenium-deficient rats excreted 1.7-fold more taurine than control rats. At the same time plasma glutathione peroxidase was 1.2% of control and plasma glutathione was 226% of control. At 20 weeks, renal taurine was decreased but renal glutathione was increased in selenium-deficient rats compared to controls. Feeding the experimental diet for 6 weeks without methionine supplementation caused a fall in urinary taurine excretion. However, there was no difference between selenium-deficient and control rats. These results indicate that selenium deficiency affects renal handling of taurine in the rat when dietary sulfur amino acids are not restricted.     

Selenium deficiency, endurance exercise capacity, and antioxidant status in rats

Increased O2 metabolism imposed by physical exercise is likely to augment the production of active O2 species that have been shown to react with lipids, proteins, and DNA. Antioxidants and antioxidant enzymes, such as the selenium enzyme glutathione peroxidase, minimize or prevent such potentially toxic reactions. This study shows that selenium deficiency decreases glutathione peroxidase activity in liver and muscle (less than 80%, P less than 0.001), increases total glutathione in liver, muscle, and plasma (P less than 0.05) and increases muscle cytochrome oxidase activity, and ubiquinone content (P less than 0.05) but has no effect on endurance capacity. Exercise to exhaustion resulted in a significant (P less than 0.001) elevation of total and oxidized glutathione (GSSG) and a significant (P less than 0.05) decrease of vitamin E in plasma of control and selenium-deficient rats. Acute exercise also increased tissue GSSG levels in both control and selenium-deficient groups of rats. Hence, despite a large depletion of selenium-deficient glutathione peroxidase, pronounced oxidation of glutathione to GSSG can be produced by the increased oxidative metabolism during physical exercise. The results suggest that the residual glutathione peroxidase activity is sufficient to detoxify hydroperoxides in exercising selenium-deficient animals and to prevent the impairment of endurance capacity.     

Elevation of rat liver mRNA for selenium-dependent glutathione peroxidase by selenium deficiency.

Selenium-dependent glutathione peroxidase (Se-GSH-Px, GSH-H2O2 oxidoreductase EC 1.11.1.9) is the best characterized selenoprotein in higher animals, but the mechanism whereby selenium becomes incorporated into the enzyme protein remains under investigation. To elucidate the mechanism of insertion of selenium into Ge-GSH-Px further, we have systematically analyzed and compared the results of Western blot, in vitro translation immunoprecipitation, and Northern blot experiments conducted with liver proteins and RNAs obtained from rats fed on selenium-deficient and selenium-supplemented diets. The anti-serum employed in this study was raised against an electrophoretically pure Se-GSH-Px preparation obtained from rat livers by a simplified purification procedure involving separation by high performance liquid chromatography on a hydrophobic interaction column. Different forms of Se-GSH-Px, including apo-protein, cross-reacted with this antiserum and Western blot analysis found no Se-GSH-Px protein present in livers from rats fed on selenium-deficient diets. By contrast, a distinct protein band corresponding to purified Se-GSH-Px was detected in livers from selenium-supplemented animals, a result consistent with the finding that the Se-GSH-Px activity was reduced to undetectable levels in livers of selenium-deficient rats. The in vitro translation experiments, however, indicated not only that mRNA for Se-GSH-Px was present during selenium deficiency but also that its translation products contained 2-3-fold as much immunoprecipitable protein as the products of poly(A) RNA from livers of selenium-supplemented rats. This result suggests that the Se-GSH-Px mRNA may be increased in the selenium-deficient state. Elevated levels of Se-GSH-Px mRNA were directly demonstrated in Northern blot experiments employing cDNA clone pGPX1211 as a probe. A similar increase in Se-GSH-Px mRNA was observed in such other tissues as kidney, testis, brain, and lung tissue, in selenium-deficient states. The present data support the co-translational mechanism for the incorporation of selenium into Se-GSH-Px in rat liver.     

A comparative study on effect of dietary selenium and vitamin E on some antioxidant enzyme activities of liver and brain tissues

Since selenium and vitamin E have been increasingly recognized as an essential element in biology and medicine, current research activities in the field of human medicine and nutrition are devoted to the possibilities of using these antioxidants for the prevention or treatment of many diseases. The present study was aimed at investigating and comparing the effects of dietary antioxidants on glutathione reductase and glutathione peroxidase activities as well as free and protein-bound sulfhydryl contents of rat liver and brain tissues. For 12–14 wk, both sex of weanling rats were fed a standardized selenium-deficient and vitamin E-deficient diet, a selenium-excess diet, or a control diet. It is observed that glutathione reductase and glutathione peroxidase activities of both tissues of the rats fed with a selenium-deficient or excess diet were significantly lower than the values of the control group. It is also shown that free and bound sulfhydryl concentrations of these tissues of both experimental groups were significantly lower than the control group. The percentage of glutathione reductase and glutathione peroxidase activities of the deficient group with respect to the control were 50% and 47% in liver and 66% and 61% in the brain, respectively; while these values in excess group were 51% and 69% in liver and 55% and 80% in brain, respectively. Free sulfhydryl contents of the tissues in both experimental groups showed a parallel decrease. Furthermore, the decrease in protein-bound sulfhydryl values of brain tissues were more pronounced than the values found for liver. It seems that not only liver but also the brain is an important target organ to the alteration in antioxidant system through either a deficiency of both selenium and vitamin E or an excess of selenium alone in the diet.     

Rat lung glutathione release: response to oxidative stress and selenium deficiency

We performed experiments to characterize the glutathione-dependent metabolism occurring during tert-butyl hydroperoxide infusion in isolated perfused rat lungs and to examine the effect of selenium deficiency on this metabolism. Selenium deficiency resulted in decreased lung glutathione peroxidase activity but normal glutathione reductase activity and glutathione content. Infusion of the hydroperoxide into control lungs caused a proportional increase in tissue glutathione disulfide (GSSG) concentration and release of GSSG into the perfusate up to an infusion rate of 250 nmol of tert-butyl hydroperoxide X min-1 X 100 g body wt-1. Infusion rates greater than this resulted in continued rise of tissue GSSG concentrations but GSSG release into the perfusate plateaued. Infusion of tert-butyl hydroperoxide into selenium-deficient rat lungs resulted in much lower concentrations of tissue GSSG and GSSG release into the perfusate; however, release in the selenium-deficient rat lung was also found to be saturable at infusion rates of 450 nmol of tert-butyl hydroperoxide X min-1 X 100 g of body wt-1. Selenium deficiency in the rat decreases the rate of reduction of infused tert-butyl hydroperoxide by glutathione and may predispose the lung to free radical damage.     

Purification and quantitation of a rat plasma selenoprotein distinct from glutathione peroxidase using monoclonal antibodies

Studies with 75Se have shown the existence of a rat plasma selenoprotein in addition to glutathione peroxidase. Because the function of the protein is not known, it has been referred to as selenoprotein P. A partially purified preparation was used to produce a monoclonal antibody to selenoprotein P. The antibody did not bind glutathione peroxidase as evidenced by its failure to remove glutathione peroxidase activity from rat plasma by immunoprecipitation. An immunoaffinity column was prepared with the monoclonal antibody, and selenoprotein P was purified 1270-fold from rat plasma in a two-step procedure. The purified selenoprotein P migrated in a single band with an Mr of 57,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Autoradiography demonstrated that this band contained 75Se when the protein was purified from rats which had received 75SeO2-(3). A competitive radioimmunoassay for selenoprotein P was developed. The selenoprotein P concentration in plasma of selenium-replete rats was determined with this assay to be 51 +/- 3.7 micrograms/ml. It was less than 5 micrograms/ml in plasma from selenium-deficient rats. Injection of 50 micrograms of selenium into selenium-deficient rats caused an increase in selenoprotein P from less than 10% of control to 52% of control in 6 h. Plasma glutathione peroxidase activity increased only from 2.2 to 3.1% of control. These experiments demonstrate that rat plasma contains a selenoprotein distinct from glutathione peroxidase. The concentration of this selenoprotein is depressed in selenium deficiency, as is glutathione peroxidase activity, but selenoprotein P increases more rapidly when selenium is supplied than does glutathione peroxidase activity.     

Plasma glutathione turnover in the rat: effect of fasting and buthionine sulfoximine

Hepatic glutathione (GSH) plays an important role in the detoxification of reactive molecular intermediates. Because of evidence that the intrahepatic turnover of glutathione in the rat may be largely accounted for by efflux from hepatocytes into the general circulation, the quantitation of plasma GSH turnover in vivo could provide a noninvasive index of hepatic glutathione metabolism. We developed a method to estimate plasma glutathione turnover and clearance in the intact, anesthetized rat using a 30-min unprimed, continuous infusion of 35S-labelled GSH. A steady state of free plasma glutathione specific radioactivity was achieved within 10 min, as determined by high-pressure liquid chromatography with fluorometric detection after precolumn derivatization of the plasma samples with monobromobimane. The method was tested after two treatments known to alter hepatic GSH metabolism: 90 min after intraperitoneal injection of 4 mmol/kg buthionine sulfoximine (BSO), an inhibitor of glutathione synthesis, and after a 48-h fast. Liver glutathione concentration (mean +/- SEM) was 5.00 +/- 0.53 mumol/g wet weight in control rats. It decreased to 3.10 +/- 0.35 mumol/g wet weight after BSO injection and to 3.36 +/- 0.14 mumol/g wet weight after fasting (both p less than 0.05). Plasma glutathione turnover was 63.0 +/- 7.46 nmol.min-1.100 g-1 body weight in control rats, 35.0 +/- 2.92 nmol.min-1.g-1 body weight in BSO-treated rats, and 41.7 +/- 2.28 nmol.min-1.g-1 body weight after fasting (both p less than 0.05), thus reflecting the hepatic alterations. This approach might prove useful in the noninvasive assessment of liver glutathione status.     

Impairment of iodothyronine 5'-deiodinase activity in brown adipose tissue and its acute stimulation by cold in selenium deficiency

The activity of the type II iodothyronine 5'-deiodinase enzyme in brown adipose tissue has been examined in rats-fed a selenium-deficient diet. Iodothyronine 5'-deiodinase activity was threefold lower in brown adipose tissue of deficient rats than in control animals. The activity of glutathione peroxidase, a biochemical index of selenium deficiency, was also greatly decreased in deficient animals. Cytochrome oxidase activity in brown fat was, however, unaltered by selenium deficiency. Acute exposure to cold (4 degrees C for 18 h) resulted in a substantial increase in iodothyronine 5'-deiodinase activity in brown adipose tissue of control rats, but the stimulatory effect of cold was attenuated in selenium-deficient animals. These results support the concept that the iodothyronine 5'-deiodinases are selenium-dependent enzymes, and indicate that the thermogenic response to cold may be impaired in selenium deficiency.     

The effect of vitamin E on the intracellular distribution of the different oxidation states of selenium in rat liver

1. The liver intracellular distribution of (75)Se, (75)Se(2-) and (75)SeO(3) (2-) formed from orally administered Na(2) (75)SeO(3) was studied in rats given four different dietary treatments. 2. Subcellular fractionation was done by using sucrose density gradients in a B XIV zonal centrifuge rotor, and conditions were established so that separation of lysosomal, mitochondrial, smooth- and rough-surfaced endoplasmic reticulum, and soluble fractions was achieved. 3. Marker enzymes acid phosphatase, succinate-2 - p - iodophenyl - 3 - p -nitrophenyl - 5 - phenyltetrazolium reductase and glucose 6-phosphatase were used, together with electron microscopy, to establish the identity of the fractions. 4. The dietary treatments investigated were: (a) vitamin E-deficient diet for 3 months, re-fed with vitamin E during the terminal 5 days; (b) vitamin E-deficient diet; (c) adequate diet; (d) vitamin E- and selenium-deficient diet, re-fed with vitamin E during the terminal 5 days. 5. In adequately fed rats, selenide was particularly associated with the mitochondrial fractions; in vitamin E-deficient rats, little selenide was found and the buoyant density of the mitochondria was increased, whereas re-feeding with vitamin E showed a restoration of the normal pattern. In vitamin E- and selenium-deficient rats, re-fed with vitamin E, there was no tendency for selenide to be localized in the mitochondria. 6. In the microsomal regions of the gradients, adequately fed rats showed a concentration of selenide, particularly in the smooth endoplasmic reticulum fractions, and to a lesser extent in the rough endoplasmic reticulum fractions. This was not observed in vitamin E-deficient rats, and the normal pattern was restored on re-feeding with vitamin E, both in rats given the vitamin E-deficient diet and the vitamin E- and selenium-deficient diet. 7. Some selenide was also found in the soluble fractions, when vitamin E was present, and a substantial proportion of this selenide was found to pass through a dialysis membrane. 8. These results are taken to support our hypothesis that the active form of selenium may be selenide located in non-haem iron-containing proteins, and that the function of vitamin E may be to protect the selenide from oxidation.     

Inhibition of type I and type II iodothyronine deiodinase activity in rat liver, kidney and brain produced by selenium deficiency.

Selenium deficiency for periods of 5 or 6 weeks in rats produced an inhibition of tri-iodothyronine (T3) production from added thyroxine (T4) in brain, liver and kidney homogenate. This inhibition was reflected in plasma T4 and T3 concentrations, which were respectively increased and decreased in selenium-deficient animals. Although plasma T4 levels increased in selenium-deficient animals, this did not produce the normal feedback inhibition on thyrotropin release from the pituitary. Selenium deficiency was confirmed in the animals by decreased selenium-dependent glutathione peroxidase (Se-GSH-Px) activity in all of these tissues. Administration of selenium, as a single intraperitoneal injection of 200 micrograms of selenium (as Na2SeO3)/kg body weight completely reversed the effects of selenium deficiency on thyroid-hormone metabolism and partly restored the activity of Se-GSH-Px. Selenium administration at 10 micrograms/kg body weight had no significant effect on thyroid-hormone metabolism or on Se-GSH-Px activity in any of the tissues studied. The characteristic changes in plasma thyroid-hormone levels that occurred in selenium deficiency appeared not to be due to non-specific stress factors, since food restriction to 75% of normal intake or vitamin E deficiency produced no significant changes in plasma T4 or T3 concentration. These data are consistent with the view that the Type I and Type II iodothyronine deiodinase enzymes are seleno-enzymes or require selenium-containing cofactors for activity.     

Cell death caused by selenium deficiency and protective effect of antioxidants

Selenium is an essential trace element and it is well known that selenium is necessary for cell culture. However, the mechanism underlying the role of selenium in cellular proliferation and survival is still unknown. The present study using Jurkat cells showed that selenium deficiency in a serum-free medium decreased the selenium-dependent enzyme activity (glutathione peroxidases and thioredoxin reductase) within cells and cell viability. To understand the mechanism of this effect of selenium, we examined the effect of other antioxidants, which act by different mechanisms. Vitamin E, a lipid-soluble radical-scavenging antioxidant, completely blocked selenium deficiency-induced cell death, although alpha-tocopherol (biologically the most active form of vitamin E) could not preserve selenium-dependent enzyme activity. Other antioxidants, such as different isoforms and derivatives of vitamin E, BO-653 and deferoxamine mesylate, also exerted an inhibitory effect. However, the water-soluble antioxidants, such as ascorbic acid, N-acetyl cysteine, and glutathione, displayed no such effect. Dichlorodihydrofluorescein (DCF) assay revealed that cellular reactive oxygen species (ROS) increased before cell death, and sodium selenite and alpha-tocopherol inhibited ROS increase in a dose-dependent manner. The generation of lipid hydroperoxides was observed by fluorescence probe diphenyl-1-pyrenylphosphine (DPPP) and HPLC chemiluminescence only in selenium-deficient cells. These results suggest that the ROS, especially lipid hydroperoxides, are involved in the cell death caused by selenium deficiency and that selenium and vitamin E cooperate in the defense against oxidative stress upon cells by detoxifying and inhibiting the formation of lipid hydroperoxides.     

Variation of glutathione level and synthesis activity in chick liver due to selenium and vitamin E deficiencies

Chicks were fed an amino acid mixture-based diet (basal diet) or one supplemented with selenium (Se, 0.2 micrograms/g as Na2SeO3) and/or vitamin E (100 micrograms/g as alpha-tocopherol). The group receiving the basal diet devoid of Se and vitamin E showed a tendency to grow slowly, but not significantly so, compared to the non-deficient control and manifested a symptom of exudative diathesis after the feeding period of 4 weeks. Supplementation of the basal diet with Se or vitamin E prevented the deficiency symptoms in the chicks. The hepatic GSH level and GSH synthesis activity were about three times as much in the Se- and vitamin E-deficient group as in the control. This was also the case for in vivo sulfur incorporation into hepatic GSH for 10 h post-injection with [35S]methionine. The increased level of GSH may partly compensate the hepatocytes for peroxidative damage.     

The effects of selenium depletion and repletion on the metabolism of thyroid hormones in the rat

Rats were fed selenium-deficient (less than 0.005 mg selenium/kg) or selenium-supplemented diets (0.1 mg selenium/kg, as Na2SeO2) for up to five wks from weaning to assess the effects of developing selenium deficiency on the metabolism of thyroid hormones. Within two wks 3:5,3'-triiodothyronine (T3) production from thyroxine (T4) in liver homogenates from selenium-deficient rats was significantly lower compared with the activity in liver homogenates from selenium-supplemented rats. This decreased activity was probably responsible, in part, for the higher T4 and lower T3 concentrations in plasma from the selenium-deficient rats after 3, 4, and 5 weeks of experiment. Repletion of selenium-deficient rats with single intra-peritoneal injections of 200 micrograms selenium/kg body wt. (as Na2SeO3) 5 days before sampling reversed the effects of the deficiency on thyroid hormone metabolism and significantly increased liver and plasma glutathione peroxidase activities. However a dose of 10 micrograms selenium/kg body wt given to rats of similar low selenium status had no effect on thyroid hormone metabolism or glutathione peroxidase activity but did reverse the increase in hepatic glutathione S-transferase activity characteristic of severe selenium deficiency. Imbalances in thyroid hormone metabolism are an early consequence of selenium deficiency and are probably not related to changes in hepatic xenobiotic metabolizing enzymes associated with severe deficiency.     

Relationship between selenium, immunity and resistance against infection

1. Food selenium content, selenium supply and selenium needs are presented, along with methods of evaluation of selenium status. Glutathione peroxidase, a selenium-containing enzyme, is ubiquitous in the organism. 2. Some experimental studies on animal models reported a positive relationship between selenium status and resistance against infections. 3. Only one study in humans concerned the mechanisms of immune functions in selenium deficiency. Several experimental works suggest that severe selenium deficiency compromises T-cell dependent immune functions such as the blastogenic response to mitogens, but selenium deficiency was concomitant with vitamin E deficiency in most of them. Delayed hypersensitivity response is controversial in selenium-supplemented rats and guinea-pigs. 4. Selenium deficiency in animals decreases the antibody response, especially if associated with vitamin E deficiency. Low dietary selenium supplementation of healthy animals has a positive effect upon humoral responses. 5. Despite some controversies, most experimental studies on selenium-deficient animals report normal phagocytosis and an altered bactericidal capacity of neutrophils. The decrease in glutathione peroxidase activity of polymorphonuclear cells following selenium deficiency could explain some of these alterations. 6. Splenic Natural Killer cells activity is enhanced in selenium-supplemented, healthy animals.     

Selenium deficiency inhibits prostacyclin release and enhances production of platelet activating factor by human endothelial cells

Selenium is an essential component of glutathione peroxidase, an enzyme which protects cells against peroxidation and controls concentrations of intracellular peroxides. Since selenium deficiency is clinically associated with an increased degree of atherosclerosis, the effects of selenium deficiency on prostacyclin (PGI2) and platelet activating factor (PAF) production by cultured human umbilical vein endothelial cells (HUVEC) were investigated. In selenium-deficient HUVEC, histamine-induced PGI2 synthesis was significantly decreased when compared to selenium-supplemented HUVEC; in contrast, histamine-induced PAF production was increased by selenium deficiency. Histamine-induced inositol trisphosphate and [Ca2+]i responses and the conversion of PGG2 and PGH2 to PGI2 were not altered by selenium deficiency. However, selenium deficiency decreased the conversion of exogenous arachidonate to PGI2 and markedly suppressed glutathione peroxidase activity. These results suggest that selenium deficiency, by decreasing glutathione peroxidase activity, makes HUVEC susceptible to peroxide-induced inhibition of the cyclooxygenase activity of PGH2 synthase, resulting in decreased PGI2 production. These changes may alter platelet function in vivo and thus play a role in the increased incidence of atherosclerosis reported in selenium-deficient individuals.     

Effect of increasing selenite concentrations, vitamin E supplementation and different fetal calf serum content on GPx1 activity in primary cultured rabbit hepatocytes

Primary rabbit hepatocytes from 6 week old female New Zealand White rabbits (3.0 x 10(6) viable hepatocytes per treatment) were incubated for 24 h or 48 h with two basic variants of the selenium and vitamin E free DMEM/F12-HAM nutrition medium containing 2.5% or 10% fetal calf serum (FCS). Selenium and vitamin E concentrations of the media were varied by the addition of 0, 10, 50 and 100 ng Se/mL medium as sodium selenite and 100 microg alpha-tocopheryl acetate/mL. Lactic dehydrogenase (LDH) leakage of the hepatocytes was not influenced by the various selenium concentrations of the media, whereas vitamin E addition significantly inhibited LDH release. The activity of cellular glutathione peroxidase (GPx1) was markedly induced by increasing the selenium supplementation of the culture media. Vitamin E supply further enhanced GPx1 induction. In hepatocytes cultivated at the lower serum concentration (2.5% FCS), increasing the selenite concentration of the media raised GPx1 and reduced the intracellular levels of the reduced tripeptide glutathione (GSH). No vectored relation between the selenium concentration of the media and the activity of superoxide dismutase (SOD) could be observed. After both incubation periods (24 h and 48 h) SOD activity was significantly higher in the cytosol of hepatocytes grown in media containing 10% FCS as compared to cells incubated at the 2.5% FCS level. Furthermore, SOD activity was reduced by the addition of vitamin E to the media. In conclusion the results indicate an effective metabolism of rabbit hepatocytes for selenite even in amounts as low as nanograms. A general cytoprotective role for vitamin E can be shown by its ability to decrease LDH leakage and by the reduction of SOD activity.