Effects of dietary selenium on glutathione peroxidase and thioredoxin reductase activity and recovery from cardiac ischemia-reperfusion.

Glutathione peroxidase and thioredoxin reductase are selenocysteine-dependent enzymes that protect against oxidative injury. This study examined the effects of dietary selenium on the activity of these two enzymes in rats, and investigated the ability of selenium to modulate myocardial function post ischemia-reperfusion. Male wistar rats were fed diets containing 0, 50, 240 and 1000 microg/kg sodium selenite for 5 weeks. Langendorff perfused hearts isolated from these rats were subjected to 22.5 min global ischemia and 45 min reperfusion, with functional recovery assessed. Liver samples were collected at the time of sacrifice, and heart and liver tissues assayed for thioredoxin reductase and glutathione peroxidase activity. Selenium deficiency reduced the activity of both glutathione peroxidase and thioredoxin reductase systemically. Hearts from selenium deficient animals were more susceptible to ischemia-reperfusion injury when compared to normal controls (38% recovery of rate pressure product (RPP) vs. 47% recovery of RPP). Selenium supplementation increased the endogenous activity of thioredoxin reductase and glutathione peroxidase and resulted in improved recovery of cardiac function post ischemia reperfusion (57% recovery of RPP). Endogenous activity of glutathione peroxidase and thioredoxin reductase is dependent on an adequate supply of the micronutrient selenium. Reduced activity of these antioxidant enzymes is associated with significant reductions in myocardial function post ischemia-reperfusion.     

Selenium supplementation and ischemia-reperfusion injury in rats

Cardiac ischemia--reperfusion injury results in oxidative stress and poor physiological recovery. This study examined the amount of lipid and protein oxidation during ischemia-reperfusion to assess the degree of oxidative stress. Selenium supplementation was used to alter the antioxidant status of rats and the recovery of myocardial function post ischemia-reperfusion was investigated. Male Wistar rats were fed diets containing 0, 50, and 1000 microg/kg sodium selenite for 5 weeks, whilst controls received normal rat food containing 240 microg/kg selenium. Langendorff-perfused hearts were subjected to 22.5 min global ischemia and 45 min reperfusion, with functional recovery assessed. Heart tissues were assayed for the presence of lipid peroxides and protein carbonyls and correlated to cardiac recovery. Following ischemia and reperfusion there was a significant increase in both protein oxidation and lipid peroxidation. Hearts from selenium-deficient animals demonstrated higher levels of both protein carbonyls and lipid peroxides and were more susceptible to ischemia-reperfusion injury when compared to controls (38% versus 47% recovery of rate pressure product (RPP)). Selenium supplementation lowered the levels of protein carbonyls and lipid peroxides and resulted in improved recovery of cardiac function post ischemia-reperfusion (57% recovery of RPP). These data suggest that selenium supplementation may provide an effective method for reducing oxidative damage post cardiac ischemia-reperfusion.     

Oxidative damage increases and antioxidant gene expression decreases with aging in the mouse ovary

Oxidative stress has been implicated in various aspects of aging, but the role of oxidative stress in ovarian aging remains unclear. Our previous studies have shown that the initiation of apoptotic cell death in ovarian follicles and granulosa cells by various stimuli is initiated by increased reactive oxygen species. Herein, we tested the hypothesis that ovarian antioxidant defenses decrease and oxidative damage increases with age in mice. Healthy, wild-type C57BL/6 female mice aged 2, 6, 9, or 12 mo from the National Institute on Aging Aged Rodent Colony were killed on the morning of metestrus. Quantitative real-time RT-PCR was used to measure ovarian mRNA levels of antioxidant genes. Immunostaining using antibodies directed against 4-hydroxynonenal (4-HNE), nitrotyrosine (NTY), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) was used to localize oxidative lipid, protein, and DNA damage, respectively, within the ovaries. TUNEL was used to localize apoptosis. Ovarian expression of glutathione peroxidase 1 (Gpx1) increased and expression of glutaredoxin 1 (Glrx1), glutathione S-transferase mu 2 (Gstm2), peroxiredoxin 3 (Prdx3), and thioredoxin 2 (Txn2) decreased in a statistically significant manner with age. Statistically significant increases in 4-HNE, NTY, and 8-OHdG immunostaining in ovarian interstitial cells and follicles were observed with increasing age. Our data suggest that the decrease in mRNA expression of mitochondrial antioxidants Prdx3 and Txn2 as well as cytosolic antioxidants Glrx1 and Gstm2 may be involved in age-related ovarian oxidative damage to lipid, protein, DNA, and other cellular components vital for maintaining ovarian function and fertility.     

Selenium supplementation sensitizes renca cells to tert-butylhydroperoxide induced loss of viability

Mouse renal carcinoma (renca) cells growing exponentially in foetal bovine serum (1%) supplemented with selenium (1 microM, sodium selenite) were exposed to oxidative insult. It was found that glutathione peroxidase activity increased (44%), while the activities of catalase, glutathione disulfide reductase, and level of total glutathione did not change due to selenium supplementation. Selenium supplementation made renca cells susceptible to tert-butylhydroperoxide induced cell death, while it did not affect the viability when the cells were exposed to hydrogen peroxide. It suggested that the contribution of glutathione peroxidase in antioxidant defense mechanism of renca cells was possibly not crucial and the function of catalase might be important especially against hydrogen peroxide.     

Addition of docosahexaenoic acid,but not arachidonic acid,activates glutathione and thioredoxin antioxidant systems in murine hippocampal HT22 cells: potential implications in neuroprotection

Docosahexaenoic acid (DHA, 22:6n‐3) is a major constituent of nerve cell membrane phospholipids. Besides a role in membrane architecture, DHA is a pleiotropic molecule involved in multiple facets of neuronal biology and also in neuroprotection. We show here that supplementation with DHA (but not arachidonic acid) to mouse hippocampal HT22 cells modulates the expression of genes encoding for antioxidant proteins associated with thioredoxin/peroxiredoxin and glutathione/glutaredoxin systems. Thus, within the thioredoxin system, DHA increased Txn1‐2, Trxrd1‐2, Prdx3, and Srxn1 gene expression. Paralleling these changes, DHA increased thioredoxin reductase activity, the main enzyme involved in thioredoxin regeneration. For the glutathione system, the most important change triggered by DHA was the upregulation of Gpx4 gene, encoding for the nuclear, cytosolic and mitochondrial isoforms of phospholipid‐hydroperoxide glutathione peroxidase (PH‐GPx/GPx4, the main enzyme protecting cell membranes against lipid peroxidation), which was followed by a significant increase in total glutathione peroxidase and GPx4 activities. Noticeably, DHA also upregulated a new Gpx4 splicing variant that retained part of the first intronic region. Finally, we demonstrate that DHA treatment, under the same time course, protects HT22 cells from the oxitoxic exposure to amyloid beta (Aβ_25–35) peptide. Altogether, our data pinpoint to a role of DHA as Indirect Antioxidant that modulates neuronal defences in neuroprotection.

     

Cytoplasmic thioredoxin reductase is essential for embryogenesis but dispensable for cardiac development

Two distinct thioredoxin/thioredoxin reductase systems are present in the cytosol and the mitochondria of mammalian cells. Thioredoxins (Txn), the main substrates of thioredoxin reductases (Txnrd), are involved in numerous physiological processes, including cell-cell communication, redox metabolism, proliferation, and apoptosis. To investigate the individual contribution of mitochondrial (Txnrd2) and cytoplasmic (Txnrd1) thioredoxin reductases in vivo, we generated a mouse strain with a conditionally targeted deletion of Txnrd1. We show here that the ubiquitous Cre-mediated inactivation of Txnrd1 leads to early embryonic lethality. Homozygous mutant embryos display severe growth retardation and fail to turn. In accordance with the observed growth impairment in vivo, Txnrd1-deficient embryonic fibroblasts do not proliferate in vitro. In contrast, ex vivo-cultured embryonic Txnrd1-deficient cardiomyocytes are not affected, and mice with a heart-specific inactivation of Txnrd1 develop normally and appear healthy. Our results indicate that Txnrd1 plays an essential role during embryogenesis in most developing tissues except the heart.     

GPX2, encoding a phospholipid hydroperoxide glutathione peroxidase homologue, codes for an atypical 2-Cys peroxiredoxin in Saccharomyces cerevisiae

We have previously reported that Saccharomyces cerevisiae has three glutathione peroxidase homologues (GPX1, GPX2, and GPX3) (Inoue, Y., Matsuda, T., Sugiyama, K., Izawa, S., and Kimura, A. (1999) J. Biol. Chem. 274, 27002-27009). Of these, the GPX2 gene product (Gpx2) shows the greatest similarity to phospholipid hydroperoxide glutathione peroxidase. Here we show that GPX2 encodes an atypical 2-Cys peroxiredoxin which uses thioredoxin as an electron donor. Gpx2 was essentially in a reduced form even in mutants defective in glutathione reductase or glutaredoxin under oxidative stressed conditions. On the other hand, Gpx2 was partially oxidized in a mutant defective in cytosolic thioredoxin (trx1Deltatrx2Delta) under non-stressed conditions and completely oxidized in tert-butyl hydroperoxide-treated cells of trx1Deltatrx2Delta and thioredoxin reductase-deficient mutant cells. Alanine scanning of cysteine residues of Gpx2 revealed that an intramolecular disulfide bond was formed between Cys37 and Cys83 in vivo. Gpx2 was purified to determine whether it functions as a peroxidase that uses thioredoxin as an electron donor in vitro. Gpx2 reduced H2O2 and tert-butyl hydroperoxide in the presence of thioredoxin, thioredoxin reductase, and NADPH (for H2O2, Km= 20 microm, kcat = 9.57 x 10(2) s(-1); for tert-butyl hydroperoxide, Km= 62.5 microm, kcat = 3.68 x 10(2) s(-1)); however, it showed remarkably less activity toward these peroxides in the presence of glutathione, glutathione reductase, and NADPH. The sensitivity of yeast cells to tert-butyl hydroperoxide was found to be exacerbated by the co-existence of Ca2+, a tendency that was most obvious in gpx2Delta cells. Although the redox state of Gpx2 was not affected by Ca2+, the Gpx2 level was markedly increased in the presence of both tert-butyl hydroperoxide and Ca2+. Gpx2 is likely to play an important role in the protection of cells from oxidative stress in the presence of Ca2+.     

Transgenic mouse models for the vital selenoenzymes cytosolic thioredoxin reductase,mitochondrial thioredoxin reductase and glutathione peroxidase 4

Selenium, as an integral part of selenoproteins, is essential for mammals. Unequivocal evidence had been provided more than a decade ago when it was proven that mice incapable of producing any of the 24 selenoproteins failed to develop beyond the gastrulation stage (E6.5). Since then, more specific attempts have been made to unmask novel and essential functions of individual selenoproteins in mice. Genetic disruption of glutathione peroxidase 4 (GPx4; also referred to as phospholipid hydroperoxide glutathione peroxidase, PHGPx) in mice showed for the first time that a specific selenoenzyme is in fact required for early embryonic development. Later on, systemic ablation of cytosolic thioredoxin reductase (Txnrd1) or mitochondrial thioredoxin reductase (Txnrd2) yielded embryonic lethal phenotypes. Beside those three, no other selenoproteins have been found being indispensable for murine development so far. This review aims at summarizing mainly the in vivo findings on these important mammalian selenoenzymes, which have not only common attributes of being required for embryogenesis, but that they are also instrumental in the regulation of cellular redox metabolism.     

Targeted disruption of peroxiredoxin 6 gene renders the heart vulnerable to ischemia-reperfusion injury

Peroxiredoxin 6 (Prdx6) is a novel peroxidase enzyme belonging to the Prdx family, which in mammals contains five more peroxiredoxins (Prdx1-Prdx5). Like glutathione peroxidase (GSHPx) and catalase, Prdx6 possesses H(2)O(2)-scavenging activities, and, like the former, it also removes hydroperoxides. Since significant amounts of catalase and GSHPx are present in the heart contributing toward the attenuation of H(2)O(2) and hydroperoxides formed during ischemia-reperfusion injury and thereby providing cardioprotection, we asked whether Prdx6 also has any role in this process. In the present study we used Prdx6(-/-) mice to assess the role of Prdx6 in ischemic injury. Western blot analysis revealed the absence of any Prdx activity in the Prdx6(-/-) mouse heart, while the GSHPx-1 and catalase levels remained unchanged. Randomly selected hearts from Prdx6(-/-) mice and wild-type mice were subjected to 30 min of global ischemia followed by 120 min of reperfusion at normothermia. The hearts from the Prdx6(-/-) mice were more susceptible to ischemic reperfusion injury as evidenced by reduced recovery of left ventricular function, increased myocardial infarct size, and higher amount of apoptotic cardiomyocytes compared with wild-type mouse hearts. These Prdx6(-/-) hearts were also subjected to a higher amount of oxidative stress as evidenced by the presence of higher amount of malondialdehyde. The present study thus indicates a nonredundant role of Prdx6 in myocardial ischemic reperfusion injury as catalase, and GSHPx could not make up for the deficiency of Prdx6 activities.     

Selenoprotein P protects endothelial cells from oxidative damage by stimulation of glutathione peroxidase expression and activity

A major fraction of the essential trace element selenium circulating in human blood plasma is present as selenoprotein P (SeP). As SeP associates with endothelial membranes, the participation of SeP in selenium-mediated protection against oxidative damage was investigated, using the human endothelial cell line Ea.hy926 as a model system. Hepatocyte-derived SeP prevented tert-butylhydroperoxide (t-BHP)-induced oxidative cell death of Ea.hy926 cells in a similar manner as did sodium selenite, counteracting a t-BHP-induced loss of cellular membrane integrity. Protection was detected after at least 10 h of SeP supplementation and it peaked at 24 h. SeP time-dependently stimulated the expression of cytosolic glutathione peroxidase (cGPx) and increased the enzymatic activities of glutathione peroxidase (GPx) and thioredoxin reductase (TR). The cGPx inhibitor mercaptosuccinate as well as the gamma-glutamylcysteine synthetase inhibitor buthionine sulfoximine counteracted the SeP-mediated protection, while the TR inhibitors cisplatin and auranofin had no effect. The presented data suggest that selenium supplementation by SeP prevents oxidative damage of human endothelial cells by restoring expression and enzymatic activity of GPx.     

The responses of HT22 cells to the blockade of mitochondrial complexes and potential protective effect of selenium supplementation

Mitochondria are the major reactive oxygen species (ROS)--generating sites in mammalian cells. Blockade of complexes in the electron transport chain (ETC) increases the leakage of single electrons to O(2) and therefore increases ROS levels. Complexes I and III have been reported to be the major ROS-generating sites in mitochondria. In this study, using mouse hippocampal HT22 cells as in vitro model, we monitored the change of intracellular ROS level in response to the blockade of ETC at different complex, and measured changes of gene expression of antioxidant enzymes and phase II enzymes, also evaluated potential protective effect of selenium (Se) supplementation to the cells under this oxidative stress. In summary, our results showed that complex I was the major ROS-generating site in HT22 cells. Complex I blockade upregulated the mRNA levels of glutamylcysteine synthetase heavy and light chains, glutathione-S-transferases omega1 and alpha 2, hemoxygenase 1, thioredoxin reductase 1, and selenoprotein H. Unexpectedly, the expression of the enzymes that directly scavenge ROS decreased, including superoxide dismutases 1 and 2, glutathione peroxidase 1, and catalase. Se supplementation increased glutathione levels and glutathione peroxidase activity, indicating a potential protective role in oxidative stress caused by ETC blockade.     

Increased infarct size and exacerbated apoptosis in the glutathione peroxidase-1 (Gpx-1) knockout mouse brain in response to ischemia/reperfusion injury

Glutathione peroxidase is an antioxidant enzyme that is involved in the control of cellular oxidative state. Recently, unregulated oxidative state has been implicated as detrimental to neural cell viability and involved in both acute and chronic neurodegeneration. In this study we have addressed the importance of a functional glutathione peroxidase in a mouse ischemia/reperfusion model. Two hours of focal cerebral ischemia followed by 24 h of reperfusion was induced via the intraluminal suture method. Infarct volume was increased three-fold in the glutathione peroxidase-1 (Gpx-1) -/- mouse compared with the wild-type mouse; this was mirrored by an increase in the level of apoptosis found at 24 h in the Gpx-1 -/- mouse compared with the wild-type mouse. Neuronal deficit scores correlated to the histologic data. We also found that activated caspase-3 expression is present at an earlier time point in the Gpx-1 -/- mice when compared with the wild-type mice, which suggests an enhanced susceptibility to apoptosis in the Gpx-1 -/- mouse. This is the first known report of such a dramatic increase, both temporally and in level of apoptosis in a mouse stroke model. Our results suggest that Gpx-1 plays an important regulatory role in the protection of neural cells in response to the extreme oxidative stress that is released during ischemia/reperfusion injury.     

Mercury and selenium interaction in vivo: effects on thioredoxin reductase and glutathione peroxidase

Mercury compounds exert toxic effects via interaction with many vital enzymes involved in antioxidant regulation, such as selenoenzymes thioredoxin reductase (TrxR) and glutathione peroxidase (GPx). Selenium supplementation can reactivate the mercury-inhibited TrxR and recover the cell viability in vitro. To gain an insight on how selenium supplementation affects mercury toxicity in vertebrates, we investigated the effects of selenium on the mercury accumulation and TrxR and GPx activities in a fish model. Juvenile zebra-seabreams were exposed either to methylmercury (MeHg) or inorganic mercury (Hg(2+)) in the presence or absence of sodium selenite (Se) for 28 days followed by 14 days of depuration. Mercury accumulation was found to be 10-fold higher under MeHg exposure than under Hg(2+) exposure. Selenium supplementation caused a half decrease of the accumulation of MeHg but did not influence Hg(2+) accumulation. Exposure to both mercurials led to a decrease of the activity of TrxR (<50% of control) in all organs. Se supplementation coincident with Hg(2+) exposure protected the thioredoxin system in fish liver. However, supplementation of Se during the depuration phase had no effects. The activity of GPx was only affected in the brain of fishes upon the exposure to MeHg and coexposure to MeHg and Se. Selenium supplementation has a limited capacity to prevent mercury effects in brain and kidney. These results demonstrate that Se supplementation plays a protective role in a tissue-specific manner and also highlight the importance of TrxR as a main target for mercurials in vivo.     

Elemental selenium at nano size possesses lower toxicity without compromising the fundamental effect on selenoenzymes: comparison with selenomethionine in mice

Glutathione peroxidase and thioredoxin reductase are major selenoenzymes through which selenium exerts powerful antioxidant effects. Selenium also elicits pro-oxidant effects at toxic levels. The antioxidant and pro-oxidant effects, or bioavailability and toxicity, of selenium depend on its chemical form. Selenomethionine is considered to be the most appropriate supplemental form due to its excellent bioavailability and lower toxicity compared to various selenium compounds. The present studies reveal that, compared with selenomethionine, elemental selenium at nano size (Nano-Se) possesses equal efficacy in increasing the activities of glutathione peroxidase and thioredoxin reductase but has much lower toxicity as indicated by median lethal dose, acute liver injury, and short-term toxicity. Our results suggest that Nano-Se can serve as an antioxidant with reduced risk of selenium toxicity.     

Effects of thioredoxin reductase-1 deletion on embryogenesis and transcriptome

Thioredoxin reductases (Txnrd) maintain intracellular redox homeostasis in most organisms. Metazoan Txnrds also participate in signal transduction. Mouse embryos homozygous for a targeted null mutation of the txnrd1 gene, encoding the cytosolic thioredoxin reductase, were viable at embryonic day 8.5 (E8.5) but not at E9.5. Histology revealed that txnrd1-/- cells were capable of proliferation and differentiation; however, mutant embryos were smaller than wild-type littermates and failed to gastrulate. In situ marker gene analyses indicated that primitive streak mesoderm did not form. Microarray analyses on E7.5 txnrd-/- and txnrd+/+ littermates showed similar mRNA levels for peroxiredoxins, glutathione reductases, mitochondrial Txnrd2, and most markers of cell proliferation. Conversely, mRNAs encoding sulfiredoxin, IGF-binding protein 1, carbonyl reductase 3, glutamate cysteine ligase, glutathione S-transferases, and metallothioneins were more abundant in mutants. Many gene expression responses mirrored those in thioredoxin reductase 1-null yeast; however, mice exhibited a novel response within the peroxiredoxin catalytic cycle. Thus, whereas yeast induce peroxiredoxin mRNAs in response to thioredoxin reductase disruption, mice induced sulfiredoxin mRNA. In summary, Txnrd1 was required for correct patterning of the early embryo and progression to later development. Conserved responses to Txnrd1 disruption likely allowed proliferation and limited differentiation of the mutant embryo cells.     

Selenium Deficiency Inhibits the Conversion of Thyroidal Thyroxine (T4) to Triiodothyronine (T3) in Chicken Thyroids

Selenium (Se) influences the metabolism of thyroid hormones in mammals. However, the role of Se deficiency in the regulation of thyroid hormones in chickens is not well known. In the present study, we examined the levels of thyroidal triiodothyronine (T₃), thyroidal thyroxine (T₄), free triiodothyronine, free thyroxine (FT₄), and thyroid-stimulating hormone in the serum and the mRNA expression levels of 25 selenoproteins in chicken thyroids. Then, principal component analysis (PCA) was performed to analyze the relationships between the selenoproteins. The results indicated that Se deficiency influenced the conversion of T₄ to T₃ and induced the accumulation of T₄ and FT₄. In addition, the mRNA expression levels of the selenoproteins were generally decreased by Se deficiency. The PCA showed that eight selenoproteins (deiodinase 1 (Dio1), Dio2, Dio3, thioredoxin reductase 2 (Txnrd2), selenoprotein i (Seli), selenoprotein u (Selu), glutathione peroxidase 1 (Gpx1), and Gpx2) have similar trends, which indicated that they may play similar roles in the metabolism of thyroid hormones. The results showed that Se deficiency inhibited the conversion of T₄ to T₃ and decreased the levels of the crucial metabolic enzymes of the thyroid hormones, Dio1, Dio2, and Dio3, in chickens. In addition, the decreased selenoproteins (Dio1, Dio2, Dio3, Txnrd2, Seli, Selu, Gpx1, and Gpx2) induced by Se deficiency may indirectly limit the conversion of T₄ to T₃ in chicken thyroids. The information presented in this study is helpful to understand the role of Se in the thyroid function of chickens.     

Analysis of the Interactions Between Thioredoxin and 20 Selenoproteins in Chicken

Thioredoxin (Trx) is a small molecular protein with complicated functions in a number of processes, including inflammation, apoptosis, embryogenesis, cardiovascular disease, and redox regulation. Some selenoproteins, such as glutathione peroxidase (Gpx), iodothyronine deiodinase (Dio), and thioredoxin reductase (TR), are involved in redox regulation. However, whether there are interactions between Trx and selenoproteins is still not known. In the present paper, we used a Modeller, Hex 8.0.0, and the KFC2 Server to predict the interactions between Trx and selenoproteins. We used the Modeller to predict the target protein in objective format and assess the accuracy of the results. Molecular interaction studies with Trx and selenoproteins were performed using the molecular docking tools in Hex 8.0.0. Next, we used the KFC2 Server to further test the protein binding sites. In addition to the selenoprotein physiological functions, we also explored potential relationships between Trx and selenoproteins beyond all the results we got. The results demonstrate that Trx has the potential to interact with 19 selenoproteins, including iodothyronine deiodinase 1 (Dio1), iodothyronine deiodinase 3 (Dio3), glutathione peroxidase 1 (Gpx1), glutathione peroxidase 2 (Gpx2), glutathione peroxidase 3 (Gpx3), glutathione peroxidase 4 (Gpx4), selenoprotein H (SelH), selenoprotein I (SelI), selenoprotein M (SelM), selenoprotein N (SelN), selenoprotein T (SelT), selenoprotein U (SelU), selenoprotein W (SelW), selenoprotein 15 (Sep15), methionine sulfoxide reductase B (Sepx1), selenophosphate synthetase 1 (SPS1), TR1, TR2, and TR3, among which TR1, TR2, TR3, SPS1, Sep15, SelN, SelM, SelI, Gpx2, Gpx3, Gpx4, and Dio3 exhibited intense correlations with Trx. However, additional experiments are needed to verify them.     

Effect of selenium on thioredoxin reductase activity in Txnrd1 or Txnrd2 hemizygous mice

Thioredoxin reductase 1 (Txnrd1) and thioredoxin reductase 2 (Txnrd2) are selenoproteins whose expression and function depends on adequate supply of the trace element selenium (Se). As homozygous (-/-) knockout of both Txnrd1 and Txnrd2 is embryonically lethal, we investigated the effect of their hemizygosity (+/-) alone and in combination with dietary Se on enzymatic activity in various tissues. To assess the overall health of the corresponding mice, the growth, viability and fertility of the different experimental groups were also compared. Se depletion led to a marked decrease in Se organ contents. Se depletion was most prominent in lung, followed by liver, kidney, heart, muscle and brain. We found no major effect of Txnrd1 or Txnrd2 hemizygosity and/or Se on male fertility and the viability of offspring. A gene dose effect under Se-adequate conditions for Txnrd1 and Txnrd2 in all organs was observed. Haploid insufficiency decreased Txnrd activity to an extent that can be further decreased by Se deficiency, but not to levels below those observed for Se depletion alone. The only exception was Txnrd2 activity in kidney, heart and muscle, where we found an additive effect.     

The Antagonistic Effect of Selenium on Cadmium-Induced Damage and mRNA Levels of Selenoprotein Genes and Inflammatory Factors in Chicken Kidney Tissue

Selenium (Se) is a necessary trace mineral in the diet of humans and animals. Cadmium (Cd) is a toxic heavy metal that can damage animal organs, especially the kidneys. Antagonistic interactions between Se and Cd have been reported in previous studies. However, little is known about the effects of Se against Cd toxicity and on the mRNA levels of 25 selenoprotein genes and inflammatory factors in chicken kidneys. In the current study, we fed chickens with a Se-treated, Cd-treated, or Se/Cd treated diet for 90 days. We then analyzed the mRNA expression of inflammatory factors (including prostaglandin E synthase (PTGES), nuclear factor-kappa B (NF-κB), tumor necrosis factor-α (TNF-α), and cyclooxygenase-2 (COX-2)) and 25 selenoprotein genes (Gpx1, Gpx2, Gpx3, Gpx4, Txnrd1, Txnrd2, Txnrd3, Dio1, Dio2, Dio3, SPS2, Sepp1, SelPb, Sep15, Selh, Seli, Selm, Selo, Sels, Sepx1, Selu, Selk, Selw, Seln, Selt). The results demonstrated that Cd exposure increased the Cd content in the chicken kidneys, renal tubular epithelial cells underwent denaturation and necrosis, and the tubules became narrow or disappeared. However, Se supplementation reduced the Cd content in chicken kidneys and induced normal development of renal tubular epithelial cells. In addition, we also observed that Se alleviated the Cd-induced increase in the mRNA levels of inflammatory factors and ameliorated the Cd-induced downtrend in the mRNA levels of 25 selenoprotein genes in chicken kidneys.     

Regulation of selenoprotein mRNA expression by hormones and retinoic acid in bovine mammary cells

Selenium is essential for maintaining many body functions through the actions of selenoproteins. To find factors regulating selenoprotein biosynthesis in the bovine mammary cell line MAC-T, the effects of supplementation with selenite and also with retinoic acid, insulin, hydrocortisone and prolactin on the mRNA expression of a number of selenoproteins were investigated. It was found that MAC-T cells express glutathione peroxidase (GPx) 1 and 4, thioredoxin reductase 1 and selenoprotein P, but not GPx 3, which is interesting considering that GPx 3 is one of the only few selenoproteins detected in milk so far. Addition of selenite to the cell culture resulted in a large increase in GPx 1 expression and an increase in selenoprotein P expression, which is similar to the findings made in other systems investigated. Increased mRNA levels of GPx 1 were also observed in cells treated with insulin and hydrocortisone or with retinoic acid. The expression of thioredoxin reductase 1 was increased in cells treated with retinoic acid, whereas that of selenoprotein P was decreased in cells exposed to insulin. The results indicate that several hormones, selenium, and retinoic acid regulate the biosynthesis of various selenoproteins differently in the bovine mammary cell. The possible implications of the findings for processes related to milk formation and mammary carcinogenesis will need additional investigation. Further study of the detailed mechanisms involved is also necessary.