Regulation of glutathione peroxidase mRNA level by dietary selenium manipulation

The Effects of In Ovo Feeding of Selenized Glucose on Selenium Concentration and Antioxidant Capacity of Breast Muscle in Neonatal Broilers

This study aims to investigate the impacts of in ovo feeding (IOF) of selenized glucose (SeGlu) on selenium (Se) level and antioxidant capacity of breast muscle in newborn broilers. After candling on 16 day of incubation, a total of 450 eggs were randomly divided into three treatments. On the 17.5th day of incubation, eggs in a control treatment were injected with 0.1 mL of physiological saline (0.75%), while the 2nd group and 3rd group were supplied with 0.1 mL of physiological saline containing 10 μg Se from SeGlu (SeGlu10 group) and 20 μg Se from SeGlu (SeGlu20 group). The results showed that in ovo injection in both SeGlu10 and SeGlu20 increased the Se level and reduced glutathione concentration (GSH) in pectoral muscle of hatchlings (P < 0.05). Compared with the control group, the SeGlu20-treated chicks significantly enhanced the activity of the superoxide dismutase (SOD) and mRNA expression of NAD(P)H quinone dehydrogenase 1 (NQO1) in breast muscle, while there was upregulation in mRNA expressions of glutathione peroxidase 1 (GPX-1) and thioredoxin reductase 1 (TrxR1) and higher total antioxidant capacity (T-AOC) in SeGlu10 treatment (P < 0.05). However, no significant difference on enzyme activities of glutathione peroxidase (GR), glutathione reductase, thioredoxin reductase, concentration of malondialdehyde, and free radical scavenging ability (FRSA) of superoxide radical (O2-•) and hydroxyl radical (OH•) was observed among the three treatments (P > 0.05). Therefore, IOF of SeGlu enhanced Se deposition in breast muscle of neonatal broilers. In addition, in ovo injection of SeGlu could increase the antioxidant capacity of newborn chicks possibly through upregulating the mRNA expression of GPX1, TrxR1, and NQO1, as well as the SOD activity.

Integrated insight into the molecular mechanisms of selenium-modulated, MPP+-induced cytotoxicity in a Parkinson's disease model

OBJECTIVE

Parkinson's disease (PD) is a neurodegenerative disease that is associated with oxidative stress. Due to the anti-inflammatory and antioxidant functions of Selenium (Se), this molecule may have neuroprotective functions in PD; however, the involvement of Se in such a protective function is unclear.

METHODS

1-methyl-4-phenylpyridinium (MPP⁺), which inhibits mitochondrial respiration, is generally used to produce a reliable cellular model of PD. In this study, a MPP⁺-induced PD model was used to test if Se could modulate cytotoxicity, and we further capture gene expression profiles following PC12 cell treatment with MPP⁺ with or without Se by genome wide high-throughput sequencing.

RESULTS

We identified 351 differentially expressed genes (DEGs) and 14 differentially expressed long non-coding RNAs (DELs) in MPP⁺-treated cells when compared to controls. We further document 244 DEGs and 27 DELs in cells treated with MPP⁺ and Se vs. cells treated with MPP⁺ only. Functional annotation analysis of DEGs and DELs revealed that these groups were enriched in genes that respond to reactive oxygen species (ROS), metabolic processes, and mitochondrial control of apoptosis. Thioredoxin reductase 1 (Txnrd1) was also identified as a biomarker of Se treatment.

CONCLUSIONS

Our data suggests that the DEGs Txnrd1, Siglec1 and Klf2, and the DEL AABR07044454.1 which we hypothesize to function in cis on the target gene Cdkn1a, may modulate the underlying neurodegenerative process, and act a protective function in the PC12 cell PD model. This study further systematically demonstrated that mRNAs and lncRNAs induced by Se are involved in neuroprotection in PD, and provides novel insight into how Se modulates cytotoxicity in the MPP⁺-induced PD model.

Changes in performance, egg quality and blood parameters of laying hens fed selenium and oregano oil

Context Organic and herbal additives in feed may lead to more healthy animal products. For this study, we hypothesised that an organic form of selenium and/or a herbal additive (oregano, Origanum vulgare L.) may improve performance of laying hens. Aims The study was designed to determine the effects of selenium source (SS, sodium selenite; or selenium yeast, SY), oregano essential oil (OEO) and a combination of Se and OEO on performance, egg quality and blood parameters of laying hens. Methods In total, 216 Lohmann LSL-Lite laying hens, 66 weeks of age, were assigned to feed on one of six diets: control group, receiving basal diet (BD); BD + 0.3 mg SS/kg; BD + 0.3 mg SY/kg; BD + 250 mg OEO/kg; BD + 250 mg OEO + 0.3 mg SS/kg; BD + 250 mg OEO + 0.3 mg SY/kg. For each treatment, there were six replicates of six hens each for 12 weeks. Key results Feed conversion ratio was higher (P &lt; 0.05) with the OEO diet than in the control. The SY diet decreased egg production and the OEO diet decreased egg mass (P &lt; 0.05), although this effect was reversed with the SY + OEO diet. This would illustrate a synergistic effect of OEO with SY. Highest and lowest yolk colour values were found with the SY and SS diets, respectively (P &lt; 0.05). Serum uric acid was lower with diets containing Se than the control diet (P &lt; 0.05). Glutathione peroxidase activity was highest with SY and SY + OEO diets and lowest with the OEO diet (P &lt; 0.05). Birds fed the SS + OEO diet showed the highest total antioxidant capacity and those fed SY showed the lowest total antioxidant capacity (P &lt; 0.05). Conclusions Based on the results of the current study, it can be concluded that SY diet have increasing effect on egg weight in laying hens. In addition, novel synergistic effects between OEO and SY diets on improving egg production, egg mass and feed conversion ratio have been found. In terms of oxidative status, the detected synergistic effects between OEO and SS diets on total antioxidant capacity and between OEO and SY diets on glutathione peroxidase (GPx) have not been reported before, that appreciate more clarifying investigations in future. Although, dietary supplemental SY individually and also with OEO increased GPx, adding SS to diet together with OEO showed more improving effect on GPx compared to the separate usage. Implications Dietary supplemental SY can improve egg weight in laying hens. In addition, adding SY to diet of laying hens individually and with OEO have beneficial effects on oxidative status of bird in terms of GPs activity, which in turn can ameliorate the unfavourable impressions of probable environmentally oxidative stress on productive performance.

Modeling and gene knockdown to assess the contribution of nonsense-mediated decay, premature termination, and selenocysteine insertion to the selenoprotein hierarchy

The expression of selenoproteins, a specific group of proteins that incorporates selenocysteine, is hierarchically regulated by the availability of Se, with some, but not all selenoprotein mRNA transcripts decreasing in abundance with decreasing Se. Selenocysteine insertion into the peptide chain occurs during translation following recoding of an internal UGA stop codon. There is increasing evidence that this UGA recoding competes with premature translation termination, which is followed by nonsense-mediated decay (NMD) of the transcript. In this study, we tested the hypothesis that the susceptibility of different selenoprotein mRNAs to premature termination during translation and differential sensitivity of selenoprotein transcripts to NMD are major factors in the selenoprotein hierarchy. Selenoprotein transcript abundance was measured in Caco-2 cells using real-time PCR under different Se conditions and the data obtained fitted to mathematical models of selenoprotein translation. A calibrated model that included a combination of differential sensitivity of selenoprotein transcripts to NMD and different frequency of non-NMD related premature translation termination was able to fit all the measurements. The model predictions were tested using SiRNA to knock down expression of the crucial NMD factor UPF1 (up-frameshift protein 1) and selenoprotein mRNA expression. The calibrated model was able to predict the effect of UPF1 knockdown on gene expression for all tested selenoproteins, except SPS2 (selenophosphate synthetase), which itself is essential for selenoprotein synthesis. These results indicate an important role for NMD in the hierarchical regulation of selenoprotein mRNAs, with the exception of SPS2 whose expression is likely regulated by a different mechanism.

Comparative study of DL-selenomethionine vs sodium selenite and seleno-yeast on antioxidant activity and selenium status in laying hens

The aim of this study was to compare the effect of DL-selenomethionine (SM) with 2 routinely used Se sources, sodium selenite (SS) and seleno-yeast (SY), on relative bioavailability based on antioxidant activity and tissue Se content. Six hundred thirty 131-day-old brown laying hens were randomly assigned to 7 treatments for 168 d (24 wks) with 6 replicates of 15 hens per replicate. The SS and SY animals were supplemented a cornmeal and soybean diet that supplied a total Se 0.3 mg/kg whereas SM was added at 4 different levels to the total Se at 0.1, 0.3, 0.5 and 0.7 mg/kg. All hens fed the Se-supplemented diet showed higher glutathione peroxidase (GSH-Px) activity (P < 0.01), higher superoxide dismutase (SOD) activity (P < 0.05), lower malondialdehyde (MDA) content (P < 0.05) in plasma, and greater Se contents in egg yolks, albumen, leg muscle, breast muscle, liver, and plasma compared with those fed the control diet (P < 0.01). The organic sources (SY and SM) exhibited a greater ability to increase the GSH-Px activity (P < 0.01) and Se content in albumen (P < 0.01), leg, and breast muscles (P = 0.0099 and P = 0.0014, respectively) than the SS that was added at 0.3 mg Se/kg. The higher SM added levels increased the GSH-Px activity until the dose of 0.5mg Se/kg (P < 0.01).The greater Se concentrations in albumen, muscle and liver appeared in the higher SM-added level, as well as above the dose of 0.1 mg Se/kg (P < 0.01). In addition, hens fed the diet with SM accumulated more Se in albumen, leg, and breast muscle than those fed diets with SY (P < 0.05). These results confirmed the higher ability of organic Se sources to increase the antioxidant activity and Se deposition in egg albumen, leg, and breast muscles compared with SS, and demonstrated a significantly better efficiency of SM compared with SY for albumen and muscle Se enrichment.

Chromatographic behavior of selenoproteins in rat serum detected by inductively coupled plasma mass spectrometry

Two major selenoproteins are present in mammalian serum: extracellular glutathione peroxidase (eGPx) and selenoprotein P (Sel P). The chromatographic behaviors of the two serum selenoproteins were compared in four rodent species, and the selenoproteins in rat serum were identified by measuring enzyme activity and Western blotting. The selenoproteins in rat serum showed a specific chromatographic behavior. In particular, rat eGPx was eluted faster than eGPxs of the other rodent species, although the amino-acid sequences of the rodent species were identical. The elution profiles of Se in rat serum obtained by inductively coupled plasma tandem mass spectrometry (ICP-MS-MS) and ICP-MS were compared. The tandem quadrupoles and the O₂ reaction/collision gas completely removed severe interferences with the Se speciation originating from the plasma source and the biological sample matrix. ICP-MS-MS under the O₂ mass shift mode gave us more accurate abundance ratios of Se than ICP-MS.

Selenium regulation of the selenoprotein and nonselenoprotein transcriptomes in rodents

This review discusses progress in understanding the hierarchy of selenoprotein expression at the transcriptome level from selenium (Se) deficiency to Se toxicity. Microarray studies of the full selenoproteome have found that 5 of 24 rodent selenoprotein mRNA decrease to <40% of Se adequate levels in Se deficient liver but that the majority of selenoprotein mRNA are not regulated by Se deficiency. These differences match with the hierarchy of selenoprotein expression, helping to explain these differences and also showing that selenoprotein transcripts can be used as molecular biomarkers for assessing Se status. The similarity of the response curves for regulated selenoproteins suggests one underlying mechanism is responsible for the downregulation of selenoprotein mRNA in Se deficiency, but the heterogeneity of the UGA position in regulated and nonregulated selenoprotein transcripts now indicates that current nonsense mediated decay models cannot explain which transcripts are susceptible to mRNA decay. Microarray studies on the full liver transcriptome in rats found only <10 transcripts/treatment were significantly down- or upregulated by Se deficiency or by supernutritional Se up to 2.0 μg Se/g diet (20× requirement), suggesting that cancer prevention associated with supernutritional Se may not be mediated by transcriptional changes. Toxic dietary Se at 50× requirement (5 μg Se/g diet), however, significantly altered ∼4% of the transcriptome, suggesting number of transcriptional changes itself as a biomarker of Se toxicity. Finally, panels of Se regulated selenoprotein plus nonselenoprotein transcripts predict Se status from deficient to toxic better than conventional biomarkers, illustrating potential roles for molecular biomarkers in nutrition.

Zebrafish (Danio rerio) vary by strain and sex in their behavioral and transcriptional responses to selenium supplementation

We used the Nadia, Gaighatta, Scientific Hatcheries, and TM1 zebrafish (Danio rerio) strains to test the hypothesis that variation among populations influences the behavioral and transcriptional responses to selenium supplementation. When fed a diet with control levels of selenium, zebrafish strains differed significantly in behavior, characterized as their mean horizontal and vertical swimming positions within the tank. The four strains also differed in brain expression of selenoprotein P1a (sepp1a), glutathione peroxidase 3 (gpx3), thioredoxin reductase 1 (txnrd1), and tRNA selenocysteine associated protein 1 (secp43). Iodothyronine deiodinase 2 (dio2) did not differ among strains but showed a sex-specific expression pattern. When supplemented with selenium, all strains spent a greater proportion of time near the front of the tank, but the response of vertical swimming depth varied by strain. Selenium supplementation also caused changes in selenoprotein expression in the brain that varied by strain for sepp1a, secp43, and dio2, and varied by strain and sex for txnrd1. Expression of gpx3 was unaffected by selenium. Our data indicate that selenium homeostasis in the brain may be a regulator of behavior in zebrafish, and the strain-specific effects of selenium supplementation suggest that genetic heterogeneity among populations can influence the results of selenium supplementation studies.

Methionine and selenium yeast supplementation of the maternal diets affects antioxidant activity of breeding eggs

Four hundred fifty 52-wk-old Langshan layer hens (dual-purpose type, an indigenous poultry breed of China) were randomly divided into 9 treatments with 5 replicates in each treatment. Birds were fed corn-soybean diets (0.13 mg of Se/kg) supplemented with 0, 0.30, and 0.60 mg/kg of Se from Se yeast and 3.2, 4.0, and 5.4 g of dl-Met/kg, respectively. Increasing Se yeast supplementation significantly increased Se concentration in the egg yolk (P < 0.01) and the Se concentration of the 3.2 g of Met/kg treatment was higher than those of the 4.0 and 5.4 g of Met/kg treatments. Adding 0.3 mg of Se/kg to the diet significantly increased glutathione peroxidase (GSH-Px) activity in the egg yolk compared with 0 and 0.6 mg of Se/kg (P < 0.01) and increasing Se yeast supplementation significantly increased the GSH-Px activity in the egg albumen (P < 0.01). Increasing Met supplementation significantly decreased the GSH-Px activity in both the yolk and the albumen of the eggs (P < 0.01). Methionine supplemented at 3.2 and 4.0 g/kg significantly increased glutathione concentration in the egg yolk compared with 5.4 g of Met/kg (P < 0.01) and increasing Met supplementation increased the glutathione concentration in the egg albumen. Increasing Met supplementation significantly decreased malondialdehyde concentration in the egg yolk (P < 0.01) and Se supplemented at 0 and 0.6 mg/kg increased the malondialdehyde concentrations in the egg yolk compared with 0.3 mg of Se/kg (P < 0.01). Methionine supplemented at 4.0 and 5.4 g/kg significantly decreased carbonyl concentration compared with 3.2 g of Met/kg. The conclusion was drawn that Se yeast and Met supplementation of the maternal diets could enhance antioxidant activity of breeding eggs.

Role of Oxidative Stress in Peroxisome Proliferator-Mediated Carcinogenesis

In this review, the evidence about the role of oxidative stress in the induction of hepatocellular carcinomas by peroxisome proliferators is examined. The activation of PPAR-alpha by peroxisome proliferators in rats and mice may produce oxidative stress, due to the induction of enzymes like fatty acyl coenzyme A (CoA) oxidase (AOX) and cytochrome P-450 4A1. The effect of peroxisome proliferators on the antioxidant defense system is reviewed, as is the effect on endpoints resulting from oxidative stress that may be important in carcinogenesis, such as lipid peroxidation, oxidative DNA damage, and transcription factor activation. Peroxisome proliferators clearly inhibit several enzymes in the antioxidant defense system, but studies examining effects on lipid peroxidation and oxidative DNA damage are conflicting. There is a profound species difference in the induction of hepatocellular carcinomas by peroxisome proliferators, with rats and mice being sensitive, whereas species such as nonhuman primates and guinea pigs are not susceptible to the effects of peroxisome proliferators. The possible role of oxidative stress in these species differences is also reviewed. Overall, peroxisome proliferators produce changes in oxidative stress, but whether these changes are important in the carcinogenic process is not clear at this time.

Glucocorticosteroids as antioxidants in treatment of asthma and COPD. New application for an old medication?

Inhaled corticosteroids (ICS) are the standard of care in asthma and are widely used in the treatment of patients with COPD. The influence of steroids on inflammatory processes has long been established since glucocorticoids and their receptor belong to the regulatory network involved in inhibition of several inflammatory pathways. Inflammatory processes are usually accompanied by an increased oxidative burden followed by a depletion of antioxidants. Therefore, the effects of steroids on antioxidant status have been investigated revealing possible positive effects on the reduced antioxidant enzyme activity. Nevertheless, the mechanisms of this modulation have not been fully elucidated yet. It is possible that antioxidant enzyme activity is regulated at the level of transcription. Additionally, because of the fact that antioxidant enzymes are trace element dependent, steroids may affect their activity through influence on trace element accumulation. This review summarizes the effects of steroids on the antioxidant enzymes activity in vitro and in vivo in relation to asthma and COPD.

Retinoid X receptor alpha regulates glutathione homeostasis and xenobiotic detoxification processes in mouse liver

Retinoid X receptor alpha (RXRalpha) plays a pivotal role in regulating liver metabolism. RXRalpha-mediated gene expression involved in amino acid metabolism was examined using the NIA Mouse 15K cDNA microarray containing 15,000 different expressed sequence tags. Seven amino acid metabolic genes, three of which encode enzymes involved in phase II detoxification process, were identified as RXRalpha target genes in mouse liver. Glutamate-cysteine ligase catalytic subunit (GCLC), glutathione S-transferasemu, and glutathione peroxidase 1 were down-regulated in the liver of hepatocyte RXRalpha-deficient mice. The down-regulation of GCLC in RXRalpha-deficient mice led to 40% and 45% reductions in the rate of glutathione (GSH) synthesis and level of hepatic GSH, respectively. Primary hepatocytes from RXRalpha-deficient mice were more sensitive to t-butylhydroperoxide-induced oxidative stress. However, GSH diminished RXRalpha-deficient mice were resistant to acetaminophen (APAP)-induced hepatotoxicity. Analysis of phase I detoxification genes revealed that CYP1A2 and CYP3A11 were up-regulated in wild-type mice but down-regulated in RXRalpha-deficient mice after APAP administration. Taken together, the data indicate that RXRalpha centrally regulates both phase I and phase II drug metabolism and detoxification. Regulation of hepatic GSH levels by RXRalpha is essential to protect hepatocytes from oxidative stress, whereas up-regulation of phase I drug metabolism genes by RXRalpha may render the liver more sensitive to APAP-induced toxicity.

Nonsense-mediated decay: assaying for effects on selenoprotein mRNAs

If the abundance of a particular selenoprotein mRNA is reduced during selenium deprivation, then the mRNA is likely to be a natural substrate for NMD. One assay for NMD involves changing the TGA Sec codon(s) to either a TGC cysteine codon or a TAA nonsense codon. If selenium deprivation elicits NMD and has no other effect on selenoprotein gene expression, then, regardless of selenium concentration, the level of UGC-containing mRNA should be most abundant, the level of UGA-containing mRNA should be intermediate in abundance, and the level of UAA-containing mRNA should be least abundant. Furthermore, the level of UGA-containing mRNA should be decreased by a decrease in selenium concentration, while the levels of UGC- and UAA-containing mRNAs should be unaffected by selenium concentration. A different assay for NMD involves coexpression of the particular selenoprotein gene and a vector expressing a dominant-negative version of hUpf1p. This assay is simpler and more versatile than the first assay because it can be used to assay any cellular gene in situ provided the cells can be stably transfected with the hUpf1p expression vector.

A selenoprotein in the plant kingdom. Mass spectrometry confirms that an opal codon (UGA) encodes selenocysteine in Chlamydomonas reinhardtii gluththione peroxidase

Selenoproteins that contain the rare amino acid selenocysteine in their primary structure have been identified in diverse organisms such as viruses, bacteria, archea, and mammals, but so far not in yeast or plants. Among the most thoroughly investigated families of selenoenzymes are the animal glutathione peroxidases (GPXs). In the last few years, genes encoding GPX-like homologues from Chlamydomonas and higher plants have been isolated, but, unlike the animal ones, all of them have cysteine (rather than selenocysteine) residues in their catalytic site. In all organisms investigated that contain selenoproteins, selenocysteine is encoded by a UGA opal codon, which is usually a stop codon. We report here that, in Chlamydomonas reinhardtii, the cDNA-cloned sequence of a GPX homologue contains an internal TGA codon in frame to the ATG. Specific mRNA expression, protein production, and enzyme activity are selenium-dependent. Sequence analysis of the peptides produced by proteolytic digestion, performed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), confirmed the presence of a selenocysteine residue at the predicted site and suggest its location in the mitochondria. Thus, our data present the first direct proof that a UGA opal codon is decoded in the plant kingdom to incorporate selenocysteine.

Effect of selenium and vitamin E content of the maternal diet on the antioxidant system of the yolk and the developing chick

1. The effects of selenium and vitamin E supplementation of the maternal diet on their transfer to the egg yolk and tissues of the newly hatched chick and on the development of the antioxidant system in the chick liver in early postnatal life were investigated. 2. One hundred Cobb broiler breeder hens were divided into 10 equal groups and housed in pens at 25 weeks of age. Each hen received 1 of the treatment diets which included 0.2 or 0.4 mg/kg selenium, 40, 100, 200 mg/kg vitamin E or their combination. After 6 weeks, the hens were artificially inseminated once per week. From week 8, eggs were collected and placed in an incubator. After hatching, chicks from each group were reared (under standard commercial conditions) to 10 d of age. The chicks were fed on a standard starter commercial broiler diet. At the time of hatching, and at 5 and 10 days old, 4 chicks from each group were sacrificed and blood, liver and brain were collected for the subsequent biochemical analyses. 3. The inclusion of organic selenium or vitamin E in the commercial diet significantly increased their concentration in the egg and in the liver of 1-d-old chicks obtained from the eggs enriched with these substances. A positive effect of such dietary supplementation was seen at d 5 and d 10 of postnatal development. 4. There was a positive effect of selenium supplementation of the maternal diet on glutathione concentration in the liver of 1-d-old and 5-d-old chicks. A combination of a dietary selenium supplementation with high vitamin E doses further increased glutathione concentration in the liver. Dietary selenium supplementation significantly increased selenium-dependent glutathione peroxidase (Se-GSH-Px) activity in the liver of the 1-d-old and 5-d-old chicks and decreased liver susceptibility to peroxidation. 6. It is concluded that the nutritional status of the laying hen determines the efficiency of the antioxidant system throughout embryonic and early postnatal development of the offspring.

Oxidative stress during selenium deficiency in seedlings of Trigonella foenum-graecum and mitigation by mimosine. Part I. Hydroperoxide metabolism

Oxidative stress during selenium (Se) deficiency in the seedlings of Trigonella foenum-graecum grown for 72 h was investigated and the response to supplemented levels of Se (0.5-1 ppm) and mimosine (0.05-1 mM) was evaluated. Beneficial effects of Se was maximal at 0.75 ppm. Mimosine, a toxic amino acid, was also found to be beneficial to the growth of the seedlings exposed up to 0.2 mM. When compared to the stressed seedlings, mitochondrial oxygen uptake from seedlings of Se (0.75 ppm) group and mimosine (0.2 mM) group exhibited threefold enhancement in state 3 respiration rate and a controlled state 4 rate, with respiratory control ratios of 5-8. Upon supplementation at the optimal levels, superoxide dismutase (SOD) activities were enhanced fourfold with Se and eightfold with mimosine in the mitochondria. The soluble activity in mimosine groups increased twofold, but only by 75% in Se groups. Peroxidase activity registered a significant increase by threefold in mitochondria and fourfold in soluble fraction in both Se and mimosine groups. Exposure to Se or mimosine exhibited a differential response in the mitochondrial catalase and ascorbate peroxidase (Asc-Px) activities. In the Se groups, both catalase and Asc-Px in mitochondria decreased by 50-60%, which was contrasted by 60% increase in Asc-Px activity and 40% in catalase activity in mimosine groups. Supplementation with either Se or mimosine evoked similar responses of increases with respect to soluble catalase by twofold to threefold and Asc-Px by 90%. The results of the present study reveal (1) the prevalence of oxidative stress in T. foenum-graecum during Se deficiency, (2) enhanced mitochondrial functional efficiency mediated by Se and mimosine independently, and (3) an antioxidative role for mimosine during Se deficiency. The study demonstrates for the first time that mimosine, a naturally occurring toxic amino acid, could be a beneficial growth factor in concentrations between 0.1 and 0.2 mM.

Orphan selenoproteins

Selenoproteins contain selenium in stoichiometric amounts. Most are synthesized by a process that decodes UGA codons as selenocysteine. Twelve animal selenoproteins have been characterized, and biochemical functions have been described for all but three. Two of these "orphan" selenoproteins are discussed in this paper. Selenoprotein P is an extracellular glycoprotein that contains multiple selenocysteines. It binds heparin and associates with endothelial cells. Two isoforms have been identified. Plasma concentration of selenoprotein P correlates with protection against diquat liver injury, suggesting that the protein protects against oxidant injury. Selenoprotein W is a small intracellular protein that contains one selenocysteine. It binds glutathione and has been suggested to function in oxidant defense. The postulated oxidant defense properties of these selenoproteins are consistent with the facile thiol-redox properties of selenocysteine. It can be predicted that more proteins will be discovered that take advantage of the chemical properties of selenium.

Effects of pancreatic enzyme preparations on erythrocyte glutathione peroxidase activities and plasma selenium concentrations in cystic fibrosis

To substitute for exocrine pancreatic insufficiency, patients with cystic fibrosis (CF) take pancreatic enzymes (PE) originating from porcine pancreas. Five different pancreatic enzyme preparations used by our patients contained 0.5-1.4 microg selenium per g tablet. In patients taking PE in doses that were gradually increased to improve fat absorption during a 48-month period, the effects of PE dose on erythrocyte selenium-dependent glutathione peroxidase (SeGSH-Px) activities and plasma selenium concentrations were studied. At baseline, erythrocyte SeGSH-Px activities were significantly lower in patients (p=.01), while plasma selenium concentrations did not differ between patients and healthy subjects. When PE dose and, consequently, selenium intake from PE was increased, erythrocyte SeGSH-Px activities (p < .001) and plasma selenium concentrations (p=.02) increased. Changes in SeGSH-Px activities during the initial 8 months correlated with those in selenium intake from PE (r=0.67, p < .001). Plasma selenium concentrations plateaued at 12 months and erythrocyte SeGSH-Px activities did so at 36 months, when patients had reached SeGSH-Px activities similar to those of healthy subjects. At 48 months, patients took an average lipase dose of 17400 U x kg(-1) x d(-1) and selenium dose from PE of 0.53 microg x kg(-1) x d(-1). We conclude that selenium content of PE preparations has a significant effect on SeGSH-Px activity in patients with CF. This form of selenium supply needs to be taken into account when selenium supplements are given to patients with CF.

Effects of mild chronic heat exposure on the concentrations of thiobarbituric acid reactive substances, glutathione, and selenium, and glutathione peroxidase activity in the mouse liver

To determine whether mild and chronic heat stress leads to oxidative stress and to differentiate such effects of different exposure periods, we kept male ICR-mice at an ambient temperature of either 35 degrees C or 25 degrees C for 6 hours, 3 days, or 7 days and measured the concentrations of thiobarbituric acid reactive substances (TBARS), glutathione (GSH), selenium (Se), and glutathione peroxidase (GSH-Px) activities in the liver. Since the food consumption of the heat-exposed group was only half that of the control, we prepared pair-fed groups, which were kept at 25 degrees C and whose food consumption were limited to those of the heat-exposed group for the 3-day and the 7-day exposure. TBARS concentrations of the liver was significantly higher in the heat group than the control after the 3-day exposure, while there was no significant difference among the groups after the 7-day exposure. There was no significant difference in GSH concentrations between the heat-exposed group and the control after the 7-day exposure, when the GSH concentration of the pair-fed group was significantly lower than that of the control. Hepatic cytosolic Se GSH-Px activity in the heat group was significantly less than that in the control group after the 6-hour exposure and it tended to be lower in the heat group than that of the control group after the 7-day exposure, while there was no difference in the total GSH-Px activity among the three groups. Our results showed that mild and chronic heat exposure may cause oxidative damage to organisms and that GSH-related anti-oxidative systems would play an important role to defensive reaction.

Selenium deficiency reduces the abundance of mRNA for Se-dependent glutathione peroxidase 1 by a UGA-dependent mechanism likely to be nonsense codon-mediated decay of cytoplasmic mRNA

The mammalian mRNA for selenium-dependent glutathione peroxidase 1 (Se-GPx1) contains a UGA codon that is recognized as a codon for the nonstandard amino acid selenocysteine (Sec). Inadequate concentrations of selenium (Se) result in a decrease in Se-GPx1 mRNA abundance by an uncharacterized mechanism that may be dependent on translation, independent of translation, or both. In this study, we have begun to elucidate this mechanism. We demonstrate using hepatocytes from rats fed either a Se-supplemented or Se-deficient diet for 9 to 13 weeks that Se deprivation results in an approximately 50-fold reduction in Se-GPx1 activity and an approximately 20-fold reduction in Se-GPx1 mRNA abundance. Reverse transcription-PCR analyses of nuclear and cytoplasmic fractions revealed that Se deprivation has no effect on the levels of either nuclear pre-mRNA or nuclear mRNA but reduces the level of cytoplasmic mRNA. The regulation of Se-GPx1 gene expression by Se was recapitulated in transient transfections of NIH 3T3 cells, and experiments were extended to examine the consequences of converting the Sec codon (TGA) to either a termination codon (TAA) or a cysteine codon (TGC). Regardless of the type of codon, an alteration in the Se concentration was of no consequence to the ratio of nuclear Se-GPx1 mRNA to nuclear Se-GPx1 pre-mRNA. The ratio of cytoplasmic Se-GPx1 mRNA to nuclear Se-GPx1 mRNA from the wild-type (TGA-containing) allele was reduced twofold when cells were deprived of Se for 48 h after transfection, which has been shown to be the extent of the reduction for the endogenous Se-GPx1 mRNA of cultured cells incubated as long as 20 days in Se-deficient medium. In contrast to the TGA allele, Se had no effect on expression of either the TAA allele or the TGC allele. Under Se-deficient conditions, the TAA and TGC alleles generated, respectively, 1.7-fold-less and 3-fold-more cytoplasmic Se-GPx1 mRNA relative to the amount of nuclear Se-GPx1 mRNA than the TGA allele. These results indicate that (i) under conditions of Se deprivation, the Sec codon reduces the abundance of cytoplasmic Se-GPx1 mRNA by a translation-dependent mechanism and (ii) there is no additional mechanism by which Se regulates Se-GPx1 mRNA production. These data suggest that the inefficient incorporation of Sec at the UGA codon during mRNA translation augments the nonsense-codon-mediated decay of cytoplasmic Se-GPx1 mRNA.

Elevated reactive oxygen species and antioxidant enzyme activities in animal and cellular models of Parkinson's disease

The dopaminergic neurotoxin N-methyl,4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) causes a syndrome in primates and humans which mimics Parkinson's disease (PD) in clinical, pathological, and biochemical findings, including diminished activity of complex I in the mitochondrial electron transport chain. Reduced complex I activity is found in sporadic PD and can be transferred through mitochondrial DNA, suggesting a mitochondrial genetic etiology. We now show that MPTP treatment of mice and N-methylpyridinium (MPP+) exposure of human SH-SY5Y neuroblastoma cells increases oxygen free radical production and antioxidant enzyme activities. Cybrid cells created by transfer of PD mitochondria exhibit similar characteristics; however, PD cybrids' antioxidant enzyme activities are not further increased by MPP+ exposure, as are the activities in control cybrids. PD mitochondrial cybrids are subject to metabolic and oxidative stresses similar to MPTP parkinsonism and provide a model to determine mechanisms of oxidative damage and cell death in PD.

Dietary selenium increases selenoprotein W levels in rat tissues

Two experiments were conducted to evaluate the influence of dietary selenium (Se) on tissue levels of selenoprotein W (Se-W) in rats. Se dependent glutathione peroxidase (GPX) activity and Se levels were also determined for comparative measurements. In the first experiment, rats were fed a basal diet deficient in Se or supplemented with either 0.1 or 4.0 mg Se (as selenite) per kg diet for 6 wk. Se-W levels were significantly higher in muscle, spleen and testes of rats fed 0.1 mg Se per kg diet compared to those fed the deficient diet (controls), and those fed 4.0 mg Se per kg diet had significantly higher levels in muscle, brain and spleen (P < 0. 05) than those fed 0.1 mg Se per kg diet. No further increases, however, occurred in the tests. There was a significant increase (P < 0.05) of mRNA encoding Se-W in muscle with each increase of dietary Se. In the second experiment rats were fed the basal diet or this diet plus 0.01, 0.03, 0.06, 0.1, 1.0, 2.0 or 4.0 mg Se per kg diet. The levels of Se-W in muscle did not increase (P < 0.05) until 0.06 mg Se per kg diet were fed to rats. A very marked increase (P < 0.05) occurred when 1.0 mg Se per kg diet was fed with no further increases with higher levels. There was a linear increase of Se-W in brain (r = 0.89) and spleen (r = 0.98) with the Se concentration in the diet up to 0.1 mg Se per kg where a plateau was reached. The testes showed a different pattern in that a very marked increase (P < 0.01) occurred when only 0.01 mg Se per kg diet was fed where an inflection was reached. Except for muscle, GPX activities reached a plateau in all tissues when diets containing 0.06 to 0.1 mg supplemental Se per kg were fed. The Se concentration in these tissues increased at a linear rate with the Se concentration in the diets up to 0.1 mg Se per kg where it continued to rise at a different rate. The results indicate that in rats, the regulation of Se-W by Se is different for various tissues and differs from that for GPX.

Selenium regulation of classical glutathione peroxidase expression requires the 3' untranslated region in Chinese hamster ovary cells

Classical glutathione peroxidase (GPX) mRNA levels fall dramatically in selenium (Se)-deficient animals, but it is not known whether this mechanism is related to the mRNA 3' untranslated region (3'UTR) sequences that have been shown to direct Se incorporation. In this study, we used recombinant GPX constructs to investigate the role of the GPX 3'UTR in Se regulation of GPX mRNA levels in Chinese hamster ovary (CHO) cells. The CHO cells were transfected with GPX (pRc/GPX), GPX lacking the 3'UTR (pRc/Delta3'UTR) or the pRc/CMV vector alone, and GPX activity and GPX mRNA levels were determined in stable transfectants grown in low Se basal medium with a range of added Se concentrations. We identified two pRc/GPX transfectants with significantly elevated GPX activity levels compared with pRc/CMV transfectants. The elevated GPX expression did not dramatically shift the amount of Se that was sufficient for GPX activity to reach the Se-adequate plateau level (100 nmol/L added Se). As expected, GPX activity was not significantly different when pRc/Delta3'UTR transfectants were compared with pRc/CMV control transfectants. Among the wild type and transfected CHO cells, Se-deficient GPX activity levels averaged 35 +/- 5% of Se-adequate levels. Selenium-deficient levels of endogenous GPX mRNA as well as recombinant pRc/GPX mRNA averaged 54-58% of Se-adequate levels; 3-4 nmol/L added Se was sufficient for maximal GPX mRNA levels. In contrast, pRc/Delta3'UTR mRNA levels in the unsupplemented cells remained at Se-adequate levels and showed no distinct Se regulation. These studies demonstrate that the GPX 3'UTR is necessary for Se regulation of GPX mRNA levels in addition to its role in Se incorporation.

Dietary selenium increases cellular glutathione peroxidase activity and reduces the enhanced susceptibility to lipid peroxidation of plasma and low-density lipoprotein in kidney transplant recipients

The glutathione system plays a major role in the protection of cells against oxidative stress in humans. The aim of the present study was to find out the relationship between the glutathione system and plasma lipid peroxidation in six renal transplant recipients (who are under oxidative stress and thus at high risk for atherosclerosis), by using dietary selenium to activate the glutathione system. 2,2'-Azobis-2-amidinopropane hydrochloride (AAPH)-induced plasma lipid peroxidation was increased (by 60%) in all six patients in comparison to normal subjects. A similar pattern of increased plasma lipid peroxidation was found even in the basal state (in the absence of added AAPH). CuSO4-induced low-density lipoprotein (LDL) oxidation measured by peroxide formation was also significantly increased by 2.3-fold in the patients' LDL in comparison to normal LDL. Even in the absence of CuSO4, the LDL oxidation state was also increased in the patients' LDL in comparison to normal LDL. We thus analyzed the effect of dietary selenium (0.2 mg/day for a period of 3 months, followed by an additional 3 months on placebo) on plasma and on LDL lipid peroxidation. Selenium treatment resulted in a 50% reduction in AAPH-induced plasma lipid peroxidation. The susceptibility of the patients' plasma to lipid peroxidation returned toward baseline values 3 months after termination of the selenium treatment. Similar results, although less pronounced (only 15% reduction), were obtained for CuSO4-induced LDL oxidation. Analyses of the patients' red blood cell (RBC) glutathione system revealed low levels of reduced glutathione and decreased activities of RBC glutathione peroxidase and glutathione reductase by 23%, 18%, and 20%, respectively, in comparison to normal RBC. Selenium treatment resulted in a significant elevation of RBC glutathione peroxidase and glutathione reductase activities and in reduced glutathione content by 64%, 57%, and 11%, respectively; this effect was also paralleled by a 39% reduction in the RBC oxidized glutathione content. On termination of the selenium treatment, and after 3 months on placebo, all of these values of the glutathione system elements returned toward baseline levels. We thus conclude that dietary selenium, which activates the glutathione system, is a potent antioxidant against plasma and LDL lipid peroxidation in renal transplant recipients, and may thus be considered antiatherogenic.

Selenium status and plasma glutathione peroxidase in patients with IgA nephropathy

The abnormal proliferation of mesangial cells with IgA deposition in the glomeruli characterizes primitive mesangial glomerulonephritis (IgA nephropathy, IgAN); this disease reduces the normal renal parenchyma while renal function becomes progressively impaired. The possible role of selenium has never been considered in evaluating factors involved in the pathogenesis of IgAN. In this work we compared the Se status of 14 IgAN patients (8 with normal renal function, IgAN NRF; 6 with impaired renal function, IgAN IRF) to that of 14 normal individuals (CG NRF) before and after an oral supplementation with selenite (0.13 mol Se/kg b.w./day for 60 days). The following indices of Se status were measured: Se in plasma and urine samples by PIXE; glutathione peroxidase activity in the cytosol of platelets (PLTs-GSH-Px) and of erythrocytes (RBCs-GSH-Px). Both concentrations and activities of plasma glutathione peroxidase (pl-GPx), a selenoenzyme mainly synthesized in and secreted by the kidney, were measured in plasma samples and results compared among groups. IgAN patients showed lower pl-Se and lower activities of selenoenzymes than normal controls before Se supplementation (p < 0.001). These findings suggest that an impaired Se status coexisted with the proliferation of mesangial cells in patients. Selenite induced PLTs-GSH-Px activity in all individuals (p < 0.001), but no variation was observed in RBCs-GSH-Px activity or in the concentration of pl-GPx in the plasma. On the other hand, selenium induced pl-GPx activity in CG NRF (p < 0.001) and in IgAN NRF (p < 0.01), but poorly stimulated pl-GPx activity in IgAN IRF (p = n.s.). However, only 17% and 25% of the pl-GPx activity of normal controls was measured in the plasma of IgAN IRF and IgAN NRF patients, respectively (p < 0.001). In conclusion, selenite only partially restored a normal Se status in patients whose low pl-GPx activity probably reflects an impaired synthesis of this protein as a consequence of reduced normal functioning of the parenchyma in kidneys affected by IgA nephropathy.

Tissue-specific regulation of selenoenzyme gene expression during selenium deficiency in rats

Regulation of synthesis of the selenoenzymes cytosolic glutathione peroxidase (GSH-Px), phospholipid hydroperoxide glutathione peroxidase (PHGSH-Px) and type-1 iodothyronine 5'-deiodinase (5'IDI) was investigated in liver, thyroid and heart of rats fed on diets containing 0.405, 0.104 (Se-adequate), 0.052, 0.024 or 0.003 mg of Se/kg. Severe Se deficiency (0.003 mg of Se/kg) caused almost total loss of GSH-Px activity and mRNA in liver and heart. 5'IDI activity decreased by 95% in liver and its mRNA by 50%; in the thyroid, activity increased by 15% and mRNA by 95%. PHGSH-Px activity was reduced by 75% in the liver and 60% in the heart but mRNA levels were unchanged; in the thyroid, PHGSH-Px activity was unaffected by Se depletion but its mRNA increased by 52%. Thus there is differential regulation of the three mRNAs and subsequent protein synthesis within and between organs, suggesting both that mechanisms exist to channel Se for synthesis of a particular enzyme and that there is tissue-specific regulation of selenoenzyme mRNAs. During Se depletion, the levels of selenoenzyme mRNA did not necessarily parallel the changes in enzyme activity, suggesting a distinct mechanism for regulating mRNA levels. Nuclear run-off assays with isolated liver nuclei showed severe Se deficiency to have no effect on transcription of the three genes, suggesting that there is post-transcriptional control of the three selenoenzymes, probably involving regulation of mRNA stability.

Hydrogen peroxide degradation and glutathione peroxidase activity in cultures of thyroid cells

The degradation rate of H2O2, added to the incubation medium, and glutathione (GSH) peroxidase activity were measured in cultures of FRTL-5 cells and porcine thyroid cells. The H2O2 degradation rate increased proportionally to the H2O2 concentration and was in FRTL-5 cells, cultured with TSH, approximately 50 nmol/min and mg DNA at 0.01 mM H2O2 and approximately 3 x 10(4) nmol/min and mg DNA at 10 mM H2O2. The GSH peroxidase activity in the same cells was equivalent to an H2O2 degradation of approximately 400 nmol/min and mg DNA. The involvement of enzymes in H2O2 degradation was studied by inhibiting catalase with aminotriazole (ATZ) and reducing GSH peroxidase by omitting glucose in the incubation medium. At 0.1 mM H2O2, ATZ or glucose omission alone did not measurably reduce H2O2 degradation but did so when combined. At 10 mM H2O2 ATZ caused a clear inhibition whereas glucose omission had no additive effect. These observations indicate that GSH peroxidase was involved in H2O2 degradation only at low H2O2 concentrations. The GSH peroxidase activity decreased by reduction of the selenite supply and increased after replenishment. The recovery of the enzyme activity required the presence of TSH in FRTL-5 cells but not in porcine thyrocytes.

Differential selenium-dependent expression of type I 5'-deiodinase and glutathione peroxidase in the porcine epithelial kidney cell line LLC-PK1

The Se-dependent expression of two selenoproteins, cytosolic glutathione peroxidase (cGPx) and type I iodothyronine-5'-deiodinase (5'DI), was investigated in the porcine epithelial kidney cell line LLC-PK1 in serum-free medium. The selenite-dependent expression of cGPx and 5'DI was revealed by enzyme-activity measurements, affinity labelling of 5'DI, metabolic labelling of proteins with 75Se and steady-state mRNA analysis. The expression of the two enzymes strongly depended on selenite concentrations of the culture medium. cGPx required 2-fold higher selenite levels than 5'DI to reach half-maximal activity. The Se-dependent enzyme activities were approximately paralleled by the corresponding steady-state mRNA levels. The response of the two enzymes to Se supply was further characterized by kinetic Se-depletion and -repletion experiments. Upon removal of medium selenite, cGPx activity decreased exponentially, whereas after an initial decrease over 1-2 days, 5'DI levels completely recovered during a further 2 days. These data indicate a differential Se-dependent regulation of the two selenoproteins, with 5'DI being preferentially supplied with the trace element Se, thus ensuring a continuous cellular capacity for thyroid-hormone activation, even under Se-deficient conditions. The abundant cGPx in cells with sufficient Se supply might serve as a cellular Se store which can be mobilized for the synthesis of more vital selenoproteins such as 5'DI under shortage conditions. Thus, a cellular hierarchy of selenoprotein expression, reflected by different individual regulation mechanisms at the transcriptional and post-transcriptional level, adds to the previously recognized tissue-specific hierarchy of Se retention.

Differential regulation of glutathione peroxidase by selenomethionine and hyperoxia in endothelial cells

We have studied the effect of selenomethionine (SeMet) and hyperoxia on the expression of glutathione peroxidase (GP) in human umbilical vein endothelial cells. Incubation of HUVEC with 1 x 10(-6) M SeMet for 24 h and 48 h caused a 65% and 86% increase in GP activity respectively. The same treatment did not result in significant changes in GP gene transcription and mRNA levels. Pactamycin, a specific inhibitor of the initiation step of translation, prevented the rise in GP activity induced by SeMet and caused an increase in GP mRNA in both cells grown in normal and SeMet-supplemented medium. Interestingly, SeMet supplementation stimulated the recruitment of GP mRNA from an untranslatable pool on to polyribosomes, so that the concentration of GP mRNA in polyribosomal translatable pools was 50% higher in cells grown in SeMet-supplemented medium than in cells grown in normal medium. On the other hand, cells exposed to 95% O2 for 3 days in normal medium showed a 60%, 394% and 81% increase in GP gene transcription rate, mRNA levels and activity respectively. Hyperoxia also stabilized GP mRNA. Hyperoxic cells grown in SeMet-supplemented medium did not show any change in GP gene transcription and mRNA levels, but expressed an 81% and 100% increase in GP activity and amount of GP mRNA associated with polyribosomes respectively, when compared with hyperoxic cells maintained in normal medium. Thus, GP appeared to be regulated post-transcriptionally, most probably co-translationally, in response to selenium availability, and transcriptionally and post-transcriptionally in response to oxygen.

Selenium enhances glutathione peroxidase activity and prostacyclin release in cultured human endothelial cells. Concurrent effects on mRNA levels

Selenium (Se) is an essential component of glutathione peroxidase (GSH-Px), an enzyme that protects cells by reducing intracellular peroxides. Impaired Se status and GSH-Px activity seem associated with increased risk of atherosclerotic vascular diseases. This study reports the effects of Se supplementation on GSH-Px activity, on prostacyclin (PGI2) production, on 12-hydroxy-eicosatetraenoic acid (12-HETE) levels, and on GSH-Px mRNA expression in cultured human umbilical vein endothelial cells (HUVEC). Se-enriched HUVEC showed significant increase of both GSH-Px activity and thrombin-stimulated production of PGI2 in the presence of stable concentrations of 12-HETE. On the other hand, an inverse correlation between Se concentrations in culture media and GSH-Px mRNA levels in Northern blot analysis was shown; this suggests that a major degree of regulation for GSH-Px expression by Se is most likely exerted at the posttranscriptional level. These observations may help to explain the increased incidence of atherosclerosis described in Se-deficient individuals.

Tissue-specific expression of glutathione peroxidase gene in guinea pigs

Glutathione peroxidase (GSH-Px), a selenocysteine-containing enzyme, is generally considered to be important in protecting animals from oxidative injury. However, guinea pigs have very low GSH-Px activity in major tissues such as liver and kidney, while the activity in the erythrocytes is as high as that of mice or rats. The present study attempted to clarify which step in the gene expression of GSH-Px is responsible for the tissue specific regulation of GSH-Px activity in guinea pigs. Northern blot analysis showed clear signals of GSH-Px mRNA in the reticulocytes and erythroblast-enriched bone marrow cells of guinea pigs, while it was barely detectable in the liver, kidney and heart. Using the nuclear run-on assay, we confirmed that the difference in GSH-Px mRNA levels among tissues of guinea pigs results primarily from the difference in the transcription rate of the GSH-Px gene. Thus, the guinea pig may be a good model for studying the factors regulating the tissue-specific gene expression of this selenoenzyme as well as its essential role.

Oxidative stress in a clonal cell line of neuronal origin: effects of antioxidant enzyme modulation

The effects of intracellularly generated H2O2 on cell viability, morphology, and biochemical markers of injury have been investigated in a clonal cell line of neuronal origin (140-3, mouse neuroblastoma X rat glioma) as a cell culture model for the role of oxidative stress in the long-term loss of neurons in the brain. The H2O2 was generated from the redox cycling of menadione, or by the oxidation of serotonin catalyzed by monoamine oxidase, to simulate the effect of amine neurotransmitter turnover. Incubation with menadione at concentrations as low as 10 microM for several hours resulted in significant losses of cell viability and altered morphology. Similar effects were evident in the presence of serotonin only after incubation overnight with concentrations > 1 mM. The cytotoxicity of either agent was potentiated by preincubation with specific inhibitors of two enzymes important to cellular antioxidant defenses, 3-amino-1,2,4-triazole for catalase and 1,3-bis(chloromethyl)-1-nitrosourea for glutathione reductase. Activity of another antioxidant enzyme of particular importance to antioxidant defenses in brain, the selenoprotein glutathione peroxidase, was stimulated fourfold by growth of cultures in the presence of sodium selenite as a source of active-site Se for the enzyme. The only effect of the selenite on other functionally coupled antioxidant enzymes was a decrease in activity of superoxide dismutase at concentrations > 200 nM. The selenite substantially protected cells against oxidative stress induced by combinations of menadione, 3-amino-1,2,4-triazole, and 1,3-bis(chloromethyl)-1-nitrosourea, but was only marginally effective with serotonin as a source of oxidative stress. The monoamine oxidase inhibitor pargyline increased cell survival in the presence of serotonin, demonstrating the role of this enzyme in its cytotoxicity. DNA damage (single strand breaks), but not lipid peroxidation, correlated with the cytotoxic effects of menadione.

Differential regulation of rat liver selenoprotein mRNAs in selenium deficiency

Selenium deficiency causes a fall in the concentrations of selenoproteins but selenoprotein P and type I iodothyronine 5'-deiodinase (5'-deiodinase) are more resistant to this effect than is glutathione peroxidase. To investigate the differential regulation of these selenoproteins, a selenium-deficient diet was fed to weanling rats for 14.5 weeks and their hepatic mRNAs were measured by Northern analysis. Levels of all 3 mRNAs fell progressively with time. Selenoprotein P and 5'-deiodinase mRNAs remained higher at all time points relative to control than glutathione peroxidase mRNA. mRNA decreases were mirrored by decreases in glutathione peroxidase activity and selenoprotein P concentration. However, the decreases in the protein levels were greater than the decreases in their mRNAs, suggesting that synthesis of both proteins was limited to a similar extent at the translational level by the availability of selenium. In addition to this apparently unregulated translational effect, these results point to a pretranslational regulation, affecting mRNA levels, which could account for the differential effect of selenium deficiency on glutathione peroxidase and the other selenoproteins. This regulation might serve to direct selenium to selenoprotein P and 5'-deiodinase when limited amounts of the element are available.

Active transcription of the selenium-dependent glutathione peroxidase gene in selenium-deficient rats

Selenium-dependent glutathione peroxidase (Se-GSH-Px, Ec.1.11.1.9) is the best characterized selenoenzyme in higher animals. However, neither the mechanism whereby selenium (Se) becomes incorporated into the enzyme nor the level at which the expression of Se-GSH-Px gene is regulated by Se is fully understood. In the current investigation, we have determined the relative rates of the transcription of the Se-GSH-Px gene in purified liver nuclei isolated from rats fed on Se-supplemented or Se-deficient diets. No significant difference in the transcription rates appeared in these two groups. These results are consistent with the previous observations that active message for Se-GSH-Px- that is, translatable mRNA for Se-GSH-Px- is present in Se-deficient tissues (Li et al., J. Biol. Chem., 265, 108-113, 1990). The data also suggest that the alteration of Se-GSH-Px activity and the corresponding protein and mRNA levels in rats subjected to dietary Se manipulation can be attributed only to post-transcriptional regulation.