The importance of selenium to human health

Intracellular glutathione is a cofactor in methylseleninic acid-induced apoptotic cell death of human hepatoma HEPG(2) cells

Selenium is a widely studied dietary anticancer agent. Among various selenium compounds, the methylated forms appear to be particularly effective in cancer prevention. Intracellular glutathione (GSH) is known to be involved in the metabolism of many methylated forms of selenium. In this study, we investigated the role of intracellular GSH in methylseleninic acid (MSeA)-induced apoptosis in human hepatoma (HepG(2)) cells. MSeA was shown to deplete intracellular GSH rapidly, preceding the typical apoptotic changes such as DNA fragmentation as measured by the TUNEL assay. When the intracellular GSH concentration was enhanced using N-acetylcysteiene (NAC) (a GSH synthesis precursor) and decreased using buthionine sufoxamine (BSO) (a GSH synthesis inhibitor), NAC markedly augmented MSeA-induced apoptosis, while BSO significantly inhibited MSeA-induced apoptosis. Different from the effect of sodium selenite, there was no measurable superoxide radical level in MSeA-treated cells. These observations suggest that intracellular GSH mainly acts as a cofactor to facilitate MSeA-induced apoptosis, while its antioxidant function becomes largely irrelevant. It is thus postulated that some cancer cells, such as liver cancer cells with higher level of intracellular GSH, would be more susceptible to MSeA cytotoxicity.

Selenium deficiency increases the expression of inducible nitric oxide synthase in RAW 264.7 macrophages: role of nuclear factor-kappaB in up-regulation

The inducible isoform of nitric oxide synthase (iNOS) is implicated in atherosclerosis, malignancy, rheumatoid arthritis, tissue and reperfusion injuries. A key determinant of the pro-oxidant versus protective effects of NO is the underlying redox status of the tissue. Selenoproteins, such as glutathione peroxidases (GPxs) and thioredoxin reductases, are key components of cellular defence and promote optimal antioxidant/oxidant balance. In this study, we have investigated the relationship between Se status, iNOS expression and NO production in Se-deficient and Se-supplemented RAW 264.7 macrophage cell lines. The cellular GPx activity, a measure of Se status, was 17-fold lower in Se-deficient RAW 264.7 cells and the total cellular oxidative tone, as assessed by flow cytometry with 2',7'-dichlorodihydrofluorescein diacetate, was higher in the Se-deficient cells than the Se-supplemented cells. Upon lipopolysaccharide (LPS) stimulation of these cells in culture, we found significantly higher iNOS transcript and protein expression levels with an increase in NO production in Se-deficient RAW 264.7 cells than the Se-supplemented cells. Electrophoretic mobility-shift assays, nuclear factor-kappaB (NF-kappaB)-luciferase reporter assays and Western blot analyses indicate that the increased expression of iNOS in Se deficiency could be due to an increased activation and consequent nuclear localization of the redox-sensitive transcription factor NF-kappaB. These results suggest an inverse relationship between cellular Se status and iNOS expression in LPS-stimulated RAW 264.7 cells and provide evidence for the beneficial effects of dietary Se supplementation in the prevention and/or treatment of oxidative-stress-mediated inflammatory diseases.

Trypanosoma cruzi: host selenium deficiency leads to higher mortality but similar parasitemia in mice

Selenium is an essential trace element and its deficiency was implicated in heart diseases. We recently showed low Se levels in chronic chagasic patients with cardiomyopathy. Herein, mice were depleted in Se by feeding the mothers with chow containing only 0.005 mg Se/kg and maintaining this diet for offspring, that were further infected with Trypanosoma cruzi. Survival rate was significantly lower in Se deficient than in control mice. Parasitemia was similar in all groups. Necrotic heart lesions were found after infection (high CK-MB levels). No outbreaks of parasite growth were detected in chronic survivors submitted or not to a second Se depletion. The present results confirm our hypothesis that a nutritional deficiency in Se is associated to a higher mortality during T. cruzi infection. The potential beneficial effect of Se supplementation is a perspective. Hypothesis to explain the higher susceptibility of Se-depleted mice to T. cruzi infection are discussed.

Serum selenium and risk of large size colorectal adenomas in a geographical area with a low selenium status

OBJECTIVE

Selenium is a fundamental nutrient to human health that might have anticarcinogenic effects. Previous studies have assessed the possible relationship of selenium status to colorectal adenomas with controversial results. We primarily aimed to assess the relationship of serum selenium status with the presence of large size colorectal adenomas in subjects living in a poor selenium region. The serum selenium status in colorectal cancer was also evaluated.

METHODS

Serum selenium levels were measured in 28 patients with large size sporadic adenomatous polyps, 24 patients with colorectal adenocarcinomas, and 35 age-matched healthy individuals. A logistic regression analysis was performed to assess the relationship of serum selenium to colorectal adenomatous polyps after adjusting for confounding variables (age, sex, smoking habit, and alcohol drinking).

RESULTS

Among subjects aged < or = 60 yr, mean serum selenium levels were significantly lower in both patient groups (adenoma, 57.9 +/- 4.3 microg/L; cancer, 43.7 +/- 6.6 microg/L) than in healthy controls (88.9 +/- 8 microg/L) (p = 0.0001). There were no difference among subjects > 60 yr old. A significant inverse association between selenium status and the diagnosis of large size adenomatous polyps after adjusting for confounding variables was found (adjusted p = 0.029). Subjects with higher selenium status (> or = 75th percentile value of 82.11 microg/L) had a lower probability (OR = 0.17, 95% CI = 0.03-0.84) to be in the adenoma group than subjects with lower selenium status (< 82.11 microg/L). This association was more marked in subjects aged < or = 60 yr (adjusted p value = 0.04, OR = 0.08, 95% CI = 0.007-0.91), and was not significant in older subjects.

CONCLUSIONS

Results suggest that high selenium status may decrease the risk of large size adenomas in a low selenium region, and that this preventive effect seems to be exclusive to subjects < or = 60 yr. These results will need to be confirmed in additional epidemiological studies before recommending selenium supplementation in patients with colon adenomas.

Role of selenium depletion in the effects of dialysis on mood and behavior

Depression and behavioral problems are common in patients undergoing dialysis. Researchers have reported that serum selenium concentrations are generally lower in dialysis patients than in healthy controls. Considerable evidence suggests that selenium deprivation leads to depressed mood, and high dietary or supplementary selenium seems to improve mood. Low plasma selenium concentrations in the elderly are significantly associated with senility and cognitive decline. The author suggests that dialysis-related selenium loss may play a role in biological mechanisms of psychiatric disorders in dialysis patients.

Action of 1-(11-selenadodecyl)-glycerol and 1-(11-selenadodecyl)-3-trolox-glycerol against lipid peroxidation

The antioxidant action on lipid peroxidation of the synthesized selenium compounds 1-(11-selenadodecyl)-glycerol (SeG) and 1-(11-selenadodecyl)-3-Trolox-glycerol (SeTrG, where Trolox = 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) was investigated. We compared the reactivity of the selenium compounds toward peroxyl radicals and their inhibitory effect on lipid peroxidation, induced by several kinds of initiating species such as azo compounds, metal ions, and superoxide/nitric oxide in solution, micelles, membranes, and rat plasma. SeTrG, but not SeG, scavenged peroxyl radicals. SeG reduced methyl linoleate hydroperoxides in organic solution and in methyl linoleate micelles oxidized by ferrous ion (Fe2+)/ascorbic acid. In rat plasma SeG and SeTrG decreased the formation of lipid hydroperoxides generated by hydrophilic azo compounds. SeG and SeTrG spared alpha-tocopherol (alpha-TOH) consumption in multilamellar vesicle membranes oxidized by hydrophilic or lipophilic initiators, and only SeTrG spared alpha-TOH in superoxide/nitric oxide oxidized membranes. In rat plasma oxidized by radical initiators (either hydrophilic or lipophilic) or superoxide/nitric oxide, SeTrG suppressed alpha-TOH consumption, but SeG had no effect. The two selenium-containing compounds showed inhibitory effects on lipid peroxidation that depended on their structure, the medium where they acted, and the oxidant used.

Dysfunction of rat liver mitochondria by selenite: induction of mitochondrial permeability transition through thiol-oxidation

Selenium is an essential trace element in mammals and is thought to play a chemopreventive role in human cancer, possibly by inducing tumor cell apoptosis. Mitochondria play a pivotal role in the induction of apoptosis in many cell types. The effects of selenite on mitochondrial function were therefore investigated. Selenite induced the oxidation and cross-linking of protein thiol groups, mitochondrial permeability transition (MPT), a decrease in the mitochondrial membrane potential, and the release of cytochrome c in mitochondria isolated from rat liver. Induction of the MPT by selenite was prevented by cyclosporin A, EGTA, or N-ethylmaleimide. These results thus indicate that selenite induces the MPT as a result of direct modification of protein thiol groups, resulting in the release of cytochrome c and a loss of mitochondrial membrane potential.

Effects of 1,4-phenylenebis(methylene)selenocyanate (p-XSC) and vitamin E on 4-nitroquinoline-N-oxide (4-NQO)-induced mutagenesis in lacZ mouse upper aerodigestive tissue

The effects of dietary administration of 1,4-phenylenebis(methylene)selenocyanate (p-XSC) and Vitamin E on 4-nitroquinoline-N-oxide (4-NQO)-induced mutagenesis in lacZ mouse upper aerodigestive tissues were investigated. 4-NQO was a potent mutagen in tongue, other pooled oral tissues and esophagus when given in drinking water for 4 weeks at a concentration of 20 microg/ml [corrected]. The mutant fractions (MFs) in these tissues were: 144+/-73, 130+/-52 and 61+/-24 mutants/10(5), respectively. Background levels were 3.7+/-1.9 in tongue, 2.9+/-1.2 in esophagus and 2.4+/-1.0 in pooled oral tissue. Vitamin E at levels of 200 and 400 IU/kg diet led to no significant effects on mutagenesis although a small decrease in the MF was observed in all tissues at the higher dose. Dietary p-XSC at levels of 2.5 and 10 ppm selenium also resulted in no statistically significant effects on mutagenesis, but mutagenesis was somewhat reduced in esophagus and pooled oral tissue at the higher dose. However, the combination of the low doses of p-XSC and Vitamin E resulted in nearly a 40% decrease in mutagenesis in tongue and esophagus, and this decrease was statistically significant (P=0.008 and 0.023, respectively. No inhibition was observed using a combination of the higher doses of p-XSC and Vitamin E. These results lend support to the use of low doses of inhibitors of mutagenesis in combinations. The application of in vivo mutagenesis assays to the screening of chemopreventive agents enables investigators to evaluate potential inhibitors when given individually and in combinations on the initiation stage of carcinogenesis in a short-term in vivo bioassay.

Nutrient requirements for preterm infant formulas

Achieving appropriate growth and nutrient accretion of preterm and low birth weight (LBW) infants is often difficult during hospitalization because of metabolic and gastrointestinal immaturity and other complicating medical conditions. Advances in the care of preterm-LBW infants, including improved nutrition, have reduced mortality rates for these infants from 9.6 to 6.2% from 1983 to 1997. The Food and Drug Administration (FDA) has responsibility for ensuring the safety and nutritional quality of infant formulas based on current scientific knowledge. Consequently, under FDA contract, an ad hoc Expert Panel was convened by the Life Sciences Research Office of the American Society for Nutritional Sciences to make recommendations for the nutrient content of formulas for preterm-LBW infants based on current scientific knowledge and expert opinion. Recommendations were developed from different criteria than that used for recommendations for term infant formula. To ensure nutrient adequacy, the Panel considered intrauterine accretion rate, organ development, factorial estimates of requirements, nutrient interactions and supplemental feeding studies. Consideration was also given to long-term developmental outcome. Some recommendations were based on current use in domestic preterm formula. Included were recommendations for nutrients not required in formula for term infants such as lactose and arginine. Recommendations, examples, and sample calculations were based on a 1000 g preterm infant consuming 120 kcal/kg and 150 mL/d of an 810 kcal/L formula. A summary of recommendations for energy and 45 nutrient components of enteral formulas for preterm-LBW infants are presented. Recommendations for five nutrient:nutrient ratios are also presented. In addition, critical areas for future research on the nutritional requirements specific for preterm-LBW infants are identified.

Mitochondrial permeability transition and cytochrome c release induced by selenite

Cytochrome c release and mitochondrial permeability transition (MPT) play important roles in apoptosis. In this study, we found that selenium, an essential trace element, induced mitochondrial membrane potential (Delta psi(m)) loss, swelling, and cytochrome c release in isolated mitochondria. All of the above observations were blocked by cyclosporin A (CsA), which is a specific inhibitor to permeability transition pore (PTP), indicating selenite-induced mitochondrial changes were mediated through the opening of PTP. In physiological concentration, selenite could induce mitochondria at low-conductance PTP 'open' probability, which is correlated to regulate the physiological function, whereas in toxic concentration, induce mitochondria at high-conductance PTP 'open' probability and rapidly undergo a process of osmotic swelling following diffusion toward matrix as for inducer (Ca(2+)/P(i)). Selenite also induced other mitochondrial marker enzymes including monoamine oxidase (MAO) and mitochondria aspartate aminotransferase (mAST). Oligomycin inhibited the selenite-induced cytochrome c release and Delta psi(m) loss, showing that F(0)F(1)-ATPase was important in selenite or Ca(2+)/P(i)-induced MPT.

The argument for increasing selenium intake

The essential trace mineral, Se, is of fundamental importance to human health. As a constituent of selenoproteins it plays both structural and enzymic roles, in the latter context being best known as an antioxidant and catalyst for the production of active thyroid hormone. While Se-deficiency diseases have been recognised for some time, evidence is mounting that less-overt deficiency can also cause adverse health effects and furthermore, that supra-nutritional levels of Se may give additional protection from disease. In the context of these effects, low or diminishing Se status in some parts of the world, notably in some European countries such as the UK, is giving cause for concern. While deficiency has an adverse effect on immunocompetence, Se supplementation appears to enhance the immune response. Se appears to be a key nutrient in counteracting certain viral infections; thus, in a Se-deficient host the benign coxsackie virus becomes virulent, causing heart damage, the influenza virus causes more serious lung pathology and HIV infection progresses more rapidly to AIDS. Long recognised as essential for successful animal reproduction, Se is required for human sperm maturation and sperm motility and may reduce the risk of miscarriage. Deficiency has been linked to adverse mood states. Findings have been equivocal in linking Se to cardiovascular disease risk, although other conditions involving oxidative stress and inflammation have shown some association with Se status. There is growing evidence that higher Se intakes are associated with reduced cancer risk. While persuasive evidence already exists to suggest that additional Se would be beneficial in some health conditions, results from intervention trials underway or planned have the potential to reinforce or refute the argument for increasing Se intake.

Selenium intakes in 18-64-y-old Irish adults

OBJECTIVE

To measure the intake of selenium (Se) and the contribution of different food groups to Se intake in adults aged 18-64 y in Ireland. The adequacy of Se intake in the population is also assessed.

DESIGN

Food consumption was estimated using a 7 day food diary for a representative sample (n=1379; men=662, women=717) of 18-64-y-old Irish adults selected randomly from the electoral register. Se intake was estimated using updated tables of food composition.

RESULTS

Mean daily Se intakes (+/-s.d.) from all sources (ie food plus supplements), and from food sources alone, for the group of Irish adults aged 18-64 y were 52 (+/-23) and 50 (+/-21) microg, respectively. Mean daily Se intake (from all sources) was significantly higher in men of all ages than women of all ages at levels of 60 and 44 microg, respectively (P<0.001). Meat/meat products (30%), bread and rolls (24%), fish/fish products (approximately 11%), and milk and yoghurt (9%) were the main contributors to mean daily Se intake. Adequacy of Se intake in population groups was estimated as the percentage of the population with mean daily Se intakes that were lower than the average requirement of 40 microg. Using this measure, 45.6% of women and 17.1% of men had inadequate Se intakes.

CONCLUSION

A significant prevalence of inadequate Se intakes was observed in Irish adults. Therefore, it would seem prudent that the Se status of the Irish population be investigated at this time.

Nuclear factor-kappaB mediates over-expression of cyclooxygenase-2 during activation of RAW 264.7 macrophages in selenium deficiency

Selenium (Se) is an essential micronutrient for all mammalian species and is associated with a variety of physiological functions, notably immune system, in the form of selenoproteins. Inadequate Se nutrition has been linked to various diseases, including rheumatoid arthritis, cardiomyopathy, and cancer. Important to this discussion is that cyclooxygenase-2 (COX-2) is over-expressed in all the aforesaid pathologies; however, a casual relationship between Se status and COX-2 expression remains to be established. The present study is based on the hypothesis that oxidant stress, a consequence of Se deficiency, lowers the activation potential of the redox-sensitive transcription factor, NF-kappaB, and that the activated NF-kappaB is required for the altered expression of COX-2. To test this hypothesis, we have investigated the relationship between Se status and COX-2 expression in response to LPS stimulation in RAW 264.7, a macrophage-like cell line. In Se-deficient cells, the Se-dependent glutathione peroxidase activity (Se-GPx), a measure of Se status, was markedly reduced and the overall oxidative stress was significantly higher than Se-supplemented cells. Upon lipopolysaccharide (LPS) stimulation, we found 2-3-folds higher COX-2 protein expression as well as higher PGE2 levels in Se-deficient cells than Se-supplemented cells. In comparison, COX-1 protein expression was not affected by either LPS stimulation or Se status. Following LPS stimulation, the nuclear localization of NF-kappaB was significantly increased in Se-deficient macrophages, thereby leading to increased expression of COX-2. This is the first report demonstrating an inverse relationship between Se status and the expression of COX-2.

Selenium status of Irish adults: evidence of insufficiency

BACKGROUND

Sub-optimal selenium status may have a role in the aetiology of various pathologies. Selenium status depends on adequate selenium in the diet. A relatively high proportion of Irish adults (17% men; 46% women) have an inadequate dietary intake.

AIM

A study was designed to examine the selenium status of healthy Irish adults.

METHODS

Ninety-one healthy Irish adults, aged 18-67 years, were recruited from the Cork City area. A fasting blood sample was collected from each subject and each was assayed for serum selenium an index of serum selenium.

RESULTS

Mean (+/- SD) serum selenium concentration in healthy Irish adults was 76 (+/- 21)microg/l. There was no significant difference in values between males and females or between postmenopausal and premenopausal women or between the three main age categories.

CONCLUSION

Current serum selenium values of Irish adults would not appear to be sufficient to achieve optimal activity of glutathione peroxidase, which occurs at serum selenium concentration around 95microg/l. Sub-optimal selenium status may increase susceptibility to various chronic disorders.

Prospects for chemoprevention of cancer

The recent progress in molecular biology and pharmacology has increased the likelihood that cancer prevention will rely increasingly on interventions collectively termed 'chemoprevention'. Cancer chemoprevention is the use of agents to inhibit, delay or reverse carcinogenesis. A number of potential targets for chemoprevention have recently been identified. Many classes of agents including antioestrogens, anti-inflammatories, antioxidants and other diet-derived agents have shown a great deal of promise. In this review, we will begin by describing the general classes of chemopreventive agents and the mechanisms by which these agents act. We will then describe the opportunities that presently exist for chemoprevention of specific cancers.

Modulation of apoptosis and improved redox metabolism with the use of a new antioxidant formula

Oxidative stress is involved in the pathogenesis of a wide spectrum of diseases, implicating that strategies directed at counterbalancing oxidative processes could have a role in clinical medicine. There is also an evidence that oxidative stress acts as a major determinant of apoptotic cell death. Many studies have reported favourable effects of antioxidant formulas on several parameters of the oxidant-antioxidant balance, but none of them has focused whether antioxidant formulas could modulate apoptosis. We investigated in 20 healthy individuals the effect of supplementation with a formula containing alpha-tocopherol, alpha-lipoic acid, coenzyme Q(10), carnitines, and selenomethionine, on plasma oxidant status and peroxide levels, erythrocyte antioxidant enzymes, lymphocyte apoptosis, and generation of ROS at the mitochondrial level. Control subjects received only carnitines or an incomplete formula with alpha-tocopherol, alpha-lipoic acid, coenzyme Q(10), and selenomethionine. Supplementation with the complete formula resulted in a significant increase in the plasma antioxidant status that was mirrored by a decrease in blood peroxide levels and a reduced generation of ROS at the mitochondrial level. This was associated with a significant decrease in the frequency of peripheral blood lymphocytes, with either CD4 or CD8 phenotype, undergoing apoptosis. Less consistent results were found when either incomplete formula was used. Our study suggests that supplementation with antioxidant formulas can modulate the process of apoptosis under in vivo conditions. The clinical potential of this strategy in the treatment of diseases with an elevated commitment to apoptosis should be explored.

Selenium and the regulation of cell signaling, growth, and survival: molecular and mechanistic aspects

In the past 30 years, it has been recognized that dietary selenium (Se) is essential for the normal function of many of the systems of the body. Furthermore, low Se intake can have deleterious effects on several aspects of human and animal health. The importance of Se is characterized in its role as a constituent of several key antioxidant and redox enzyme families. Most of the effects of Se are probably mediated by selenoproteins, which have the micronutrient covalently incorporated into the protein. The purpose of this review is to examine basic mechanisms by which Se regulates cell growth, gene transcription, cell signaling, and cell death. We start with the historical background to Se. The synthesis and function of selenoproteins are described, followed by details of the dietary sources of Se and Se status in different parts of the world, together with the clinical effects of Se deficiency and toxicity. We consider some aspects of the molecular mechanisms by which Se modulates cell growth, intracellular signaling, and gene transcription.

Nutrition and disease: challenges of research design

This review discusses research methodology in the relation between diet and disease. Medical research can be divided into two types: complex research (the detailed study of disease mechanisms using such methods as biochemistry and molecular genetics) and simple research (the investigation of the factors that cause or prevent disease using methods such as epidemiology, intervention trials, and analagous studies on animals). Although complex research has received the bulk of resources, the large majority of our information of practical value has come from simple research. This general principle is illustrated in the area of diet and disease by examples from various areas: selenium, carotenoids, and cancer; vitamin E, omega-3 fatty acids, and coronary heart disease; dietary fat and obesity; dietary sodium and hypertension; and alcohol and stroke. Discussion then turns to aspects of the design of cohort (prospective) studies. Because of problems of sample size and relative lack of diversity, previous studies often failed to give clear-cut results. Suggestions are made concerning the design of cohort studies, notably the use of much larger numbers of subjects and with greater diversity in their diets. The problem of confounding also is discussed. Lifestyle factors often cluster together but cohort studies may not have fully unraveled this.

Selenium supplementation in patients with autoimmune thyroiditis decreases thyroid peroxidase antibodies concentrations

In areas with severe selenium deficiency there is a higher incidence of thyroiditis due to a decreased activity of selenium-dependent glutathione peroxidase activity within thyroid cells. Selenium-dependent enzymes also have several modifying effects on the immune system. Therefore, even mild selenium deficiency may contribute to the development and maintenance of autoimmune thyroid diseases. We performed a blinded, placebo-controlled, prospective study in female patients (n = 70; mean age, 47.5 +/- 0.7 yr) with autoimmune thyroiditis and thyroid peroxidase antibodies (TPOAb) and/or Tg antibodies (TgAb) above 350 IU/ml. The primary end point of the study was the change in TPOAb concentrations. Secondary end points were changes in TgAb, TSH, and free thyroid hormone levels as well as ultrasound pattern of the thyroid and quality of life estimation. Patients were randomized into 2 age- and antibody (TPOAb)-matched groups; 36 patients received 200 microg (2.53 micromol) sodium selenite/d, orally, for 3 months, and 34 patients received placebo. All patients were substituted with L-T(4) to maintain TSH within the normal range. TPOAb, TgAb, TSH, and free thyroid hormones were determined by commercial assays. The echogenicity of the thyroid was monitored with high resolution ultrasound. The mean TPOAb concentration decreased significantly to 63.6% (P = 0.013) in the selenium group vs. 88% (P = 0.95) in the placebo group. A subgroup analysis of those patients with TPOAb greater than 1200 IU/ml revealed a mean 40% reduction in the selenium-treated patients compared with a 10% increase in TPOAb in the placebo group. TgAb concentrations were lower in the placebo group at the beginning of the study and significantly further decreased (P = 0.018), but were unchanged in the selenium group. Nine patients in the selenium-treated group had completely normalized antibody concentrations, in contrast to two patients in the placebo group (by chi(2) test, P = 0.01). Ultrasound of the thyroid showed normalized echogenicity in these patients. The mean TSH, free T(4), and free T(3) levels were unchanged in both groups. We conclude that selenium substitution may improve the inflammatory activity in patients with autoimmune thyroiditis, especially in those with high activity. Whether this effect is specific for autoimmune thyroiditis or may also be effective in other endocrine autoimmune diseases has yet to be investigated.

[Measurement of contents in organs of selenium- or vitamin E-deficient rat using instrumental neutron activation analysis]

The contents of iron (Fe), cobalt (Co), zinc (Zn), and selenium (Se) in the organs (liver, kidney, spleen, heart, lung, and brain) and the liver cell fractions (nuclear, mitochondrial, microsomal, and cytosolic fractions) of Se- or vitamin E (VE)-deficient rats were measured using instrumental neutron activation analysis (INAA). The contents of Fe in the liver of Se-deficient rats, and in the liver and the spleen of VE-deficient rats were increased compared with those in normal rats. Fe contents increased mainly in the microsomal fraction. Contents of Co in the organs and liver cell fractions of Se- and VE-deficient rats were markedly low, reflecting the Co contents in both diets. Contents of Zn in the organs and liver cell fractions of Se- and VE-deficient rats decreased to 60-80% of the contents in normal rats. The Se contents in Se-deficient rat organs except for the kidney, spleen, and brain were below the detectable level under the present conditions. Se contents in VE-deficient rat decreased to 50-80% of those in normal rats in all organs and fractions. It is suggested that oxidative stress due to Se- or VE-deficiency affects the dynamics of Fe and Zn.

Methylseleninate is a substrate rather than an inhibitor of mammalian thioredoxin reductase. Implications for the antitumor effects of selenium

Biochemical and clinical evidence indicates that monomethylated selenium compounds are crucial for the tumor preventive effects of the trace element selenium and that methylselenol (CH(3)SeH) is a key metabolite. As suggested by Ganther (Ganther, H. E. (1999) Carcinogenesis 20, 1657-1666), methylselenol and its precursor methylseleninate might exert their effects by inhibition of the selenoenzyme thioredoxin reductase via the irreversible formation of a diselenide bridge. Here we report that methylseleninate does not act as an inhibitor of mammalian thioredoxin reductase but is in fact an excellent substrate (K(m) of 18 microm, k(cat) of 23 s(-1)), which is reduced by the enzyme according to the equation 2 NADPH + 2 H(+) + CH(3)SeO(2)H --> 2 NADP(+) + 2 H(2)O + CH(3)SeH. The selenium-containing product of this reaction was identified by mass spectrometry. Nascent methylselenol was found to efficiently reduce both H(2)O(2) and glutathione disulfide. The implications of these findings for the antitumor activity of selenium are discussed. Methylseleninate was a poor substrate not only for human glutathione reductase but also for the non-selenium thioredoxin reductases enzymes from Drosophila melanogaster and Plasmodium falciparum. This suggests that the catalytic selenocysteine residue of mammalian thioredoxin reductase is essential for methylseleninate reduction.

Malnutrition and gastrointestinal disease

The recognition of several disease processes that cause or are associated with gastrointestinal malabsorption has led to extensive investigation into their pathogenesis, diagnosis, and treatment. This review of selected articles covers a range of subjects related to some of the more common malabsorptive disease. Selected topics including celiac disease, disaccharidase deficiencies, short bowel syndrome, and Crohn disease are discussed.

Involvement of superoxide dismutases in the response of Escherichia coli to selenium oxides

Selenium can provoke contrasting effects on living organisms. It is an essential trace element, and low concentrations have beneficial effects, such as the reduction of the incidence of cancer. However, higher concentrations of selenium salts can be toxic and mutagenic. The bases for both toxicity and protection are not clearly understood. To provide insights into these mechanisms, we analyzed the proteomic response of Escherichia coli cells to selenate and selenite treatment under aerobic conditions. We identified 23 proteins induced by both oxides and ca. 20 proteins specifically induced by each oxide. A striking result was the selenite induction of 8 enzymes with antioxidant properties, particularly the manganese and iron superoxide dismutases (SodA and SodB). The selenium inductions of sodA and sodB were controlled by the transcriptional regulators SoxRS and Fur, respectively. Strains with decreased superoxide dismutase activities were severely impaired in selenium oxide tolerance. Pretreatment with a sublethal selenite concentration triggered an adaptive response dependent upon SoxRS, conferring increased selenite tolerance. Altogether, our data indicate that superoxide dismutase activity is essential for the cellular defense against selenium salts, suggesting that superoxide production is a major mechanism of selenium toxicity under aerobic conditions.

Chemoprevention of bladder cancer

The data presented herein, although highly supportive for a protective role of various nutrients against bladder cancer, are far from definitive. Many authorities question the validity of current recommendations for nutritional chemoprevention against bladder cancer. The reason for the wide variations reported in epidemiologic studies lies in the nature of observational studies. Dietary studies are limited in their conclusions because the protection afforded by the consumption of a particular nutrient may be multifactorial, with different components of the food exerting potential chemopreventive effects. Furthermore, measuring levels of nutrients in the food intake of populations is confounded by factors that might affect these levels and also the incidence of cancer. For example, vitamin A can come from animal or vegetarian sources. Because animal fat has been identified as a potential carcinogen in man, depending on the source of the vitamin, varying levels of protection might be deduced. In addition, chemoprevention studies using dietary supplements are expected to have mild effects, and large studies would be required to confirm statistical significance. Even with agents such as intravesical chemotherapy, only half the studies achieve statistical significance [29]. Prospective randomized trials with a large sample size, longer follow-up, and an extended duration of treatment are needed to clarify the association between micronutrients and cancer protection. With these caveats in mind, several recommendations can be made. Simple measures, such as drinking more fluids (especially water), can have a profound impact on the incidence of bladder cancer. Vitamins are being extensively studied in chemopreventive trials for different cancers. There is strong evidence for a chemoprotective effect of vitamin A in bladder cancer. The authors recommend 32,000 IU/day of vitamin A initially, with lower doses (24,000 IU) for persons less than 50 kg. Because liver toxicity is a possibility with long-term administration, the dose should be decreased to 16,000 IU after 3 years. High doses of beta-carotene should be avoided based on a large clinical trial reporting a 25% increase in the number of cases of prostate cancer and a statistically significant increase in the incidence of lung cancer. Vitamin B6 has been studied in several clinical trials in bladder cancer. The US-based Veterans Administration cooperative study found benefit for vitamin B6 when given as a single agent. Data for vitamins C and E are insufficient to recommend either agent as stand-alone treatment. Nonetheless, each of these vitamins is known to have beneficial effects, including improved function of the immune system. It is possible that only a small percentage of patients with bladder cancer respond to vitamins B6, C, or E, yet each is safe, nontoxic, and inexpensive. In an effort to pool the efficacy of individual agents and to increase the power of study, the authors evaluated the combination of vitamins A, B6, C, and E in a double-blind trial. The observed 50% 5-year reduction in tumor recurrence was highly significant and greater than would be expected for any of the individual ingredients and suggests that combinations of nutritional agents may be most appropriate. A large-volume study along similar lines is being conducted. Among the numerous other compounds and dietary substances purported to have chemopreventive effect, soybeans, garlic, and green tea stand out as having the greatest promise and can freely be recommended to patients. For synthetically synthesized agents such as celecoxib, piroxicam, or DFMO, recommendations must be deferred until the results of clinical trials are conclusively in favor of their use. Many of the dietary factors found to be protective against bladder cancer are being investigated in other cancers and are beneficial to general health. Although naturally occurring nutrients are ideal, especially because the delicate balance of various micronutrients might be impossible to synthesize in the laboratory, the general population finds it easier to take vitamin supplements. Unfortunately, dietary changes such as decreasing fat and increasing fruit and vegetable intake are more difficult to initiate. There is a mistaken notion that simply because an agent is naturally occurring, it cannot be as beneficial as taking a substance synthesized in the laboratory. Even in a high-risk group such as nuclear-bomb survivors in Japan, high consumption of vegetables and fruit is protective against bladder cancer [44]. Encouraging patients to follow an essentially healthy food habit lifestyle will be a significant contribution in the fight against cancer.

Rationale for clinical trials of selenium as an antioxidant for the treatment of the cardiomyopathy of Friedreich's ataxia

A pure selenium deficiency is harmful to the heart and causes a fatal dilated congestive cardiomyopathy in animals (white muscle disease) and in man (Keshan disease). Both of these syndromes are selenium-responsive. A deficiency of the micronutrient has also been reported in patients with Friedreich's ataxia and there are histological similarities between Friedreich's cardiomyopathy and Keshan disease. A low selenium status results in reduced selenium-dependent glutathione peroxidase activity. This essential antioxidant enzyme protects membrances from oxidative deterioration, a function it shares in common with vitamin E. As iron-induced mitochondrial lipid peroxidation is central to the pathology of Friedreich's ataxia, the administration of selenium supplements should normalize the antioxidant activity of myocardial glutathione peroxidase and slow the progression of the life-shortening cardiomyopathy associated with this illness.

Impact of selenium status on the pathogenesis of mycobacterial disease in HIV-1-infected drug users during the era of highly active antiretroviral therapy

The risk of mycobacterial disease is significantly increased in drug abusers as well as in immunocompromised HIV-1-infected individuals. The essential trace element selenium has an important function in maintaining immune processes and may, thus, have a critical role in clearance of mycobacteria. The impact of selenium status on the development of mycobacterial diseases in HIV-1-seropositive drug users was investigated over a 2-year period (1999-2001). Twelve cases of mycobacterial disease (tuberculosis, 9; infection due to atypical Mycobacterium species, 3) occurred; these 12 cases were compared with 32 controls with no history of respiratory infections who were matched on age, sex, and HIV status. Significant risk for development of mycobacterial disease was associated with a CD4 cell count of <200/mm 3, malnutrition, and selenium levels of <or=135 microg/L (patients with these levels were 13 times more likely to develop mycobacterial disease). Multivariate analyses controlling for antiretroviral treatment and CD4 cell count revealed that both body mass index and selenium level remained significant factors in the relative risk for developing mycobacterial disease (relative risk, 3; p =.015); these findings suggest that selenium status may have a profound impact on the pathogenesis of mycobacterial disease.

Selenite suppresses hydrogen peroxide-induced cell apoptosis through inhibition of ASK1/JNK and activation of PI3-K/Akt pathways

The relationship between selenium and signal molecules has not been well elucidated. It was found that physiological concentration of selenite, 3 microM, reduced ASK1 activity and induced PI3-kinase (PI3-K)/Akt pathways in HT1080 cells. Duration of these signal molecules by selenite was much longer than that by growth factors and other stresses. The longer duration time of these signal molecules may be important to maintain normal functions against stresses. Selenite increased cell proliferation through up-regulation of Bcl-2 expression, mitochondrial membrane potential, adenosine triphosphate (ATP) generation, and glucose uptake mediated by PI3-K pathway. High concentration of H2O2 increased an apoptotic signal molecule, ASK1, which resulted in Bcl-2 down-regulation, membrane potential disruption, decreased ATP and glucose uptake, and activation of caspases. However, an antiapoptotic signal molecule, Akt, was activated also by H2O2, but duration of its activation was much shorter. Selenite blocked apoptosis induced by H2O2, which was related to blocking ASK1 and further stimulating PI3-kinase/Akt activities. Selenite blocked mitochondrial membrane potential disruption by 400 mM H2O2. Selenite also blocked caspase-9 and -3 activities and apoptosis induced by 500 microM H2O2, even after mitochondrial membrane potential disruption. These observations demonstrate that selenite increases cell proliferation and maintains cell survival by activating the antiapoptotic signal and blocking the apoptotic signal.

Reference values of selenium in plasma in population from Barcelona. Comparison with several pathologies

Plasma selenium reference values from healthy donors in the metropolitan area of Barcelona are determined. A random sample from 156 healthy adults (control group) is analysed by using electrothermal atomic absorption spectrometry with Zeeman effect background correction. The relationship between several pathologies and Se content is also evaluated. Se content from 64 samples from subjects with chronic renal failure and 54 from subjects suffering from several malignancies are determined and the results are compared to the reference values. Moreover, Se contents are determined and compared in two groups of children, healthy (19 samples) and children of mothers infected with HIV-1 (16 samples). In the control group, Se plasma concentration ranges between 50 and 145 microg x L(-1) (82.2 +/- 17.5 microg x L(-1)). Significantly lower values are found in the two pathologies studied (malignancy and chronic renal failure), compared to the control group. However, no significant differences in Se content are found between the two groups studied regarding malignancy and chronic renal failure. In children of mothers infected with HIV-1, Se status is significantly lower than that of healthy children.

Selenium status and its correlates in a British national diet and nutrition survey: people aged 65 years and over

Plasma selenium (Se) concentrations were measured in 1134 British people aged 65 years and over, living in mainland Britain during 1994-1995. Eight hundred and eighty-three lived in the community ("free-living"), while the remainder lived in institutions (residential and nursing homes). The overall mean plasma Se concentrations was 0.90 micromol/l (inner 95% range 0.50-1.36 micromol/l). Free-living people had significantly higher values than counterparts living in institutions, and there was an overall inverse correlation with age. Plasma Se varied with season (lower from October to December than at other times of the year), while values were higher in southern Britain than in the North. Socio-economic associations also existed (lower plasma Se in people receiving state benefits or with poorer educational attainment), while smokers had lower values than non-smokers. Several indices of poor health status or of medicine use were correlated with lower plasma Se, which was also predicted by several biochemical or haematological indices of infection or inflammation. Plasma Se was strongly and directly correlated with plasma albumin, zinc, cholesterol, vitamin C, several carotenoids, alpha-tocopherol, pyridoxal phosphate, and with blood haemoglobin and several anthropometric indices. All relationships were independent of age and gender, and are consistent with the view that plasma Se levels are higher in fit and well-nourished elderly people and lower in those who are frail, poorly-nourished and unwell. Whole-blood glutathione peroxidase generally did not share these relationships, was only very weakly correlated with plasma Se, and appeared to be less useful as a status indicator in this population group.

Gene expression profiling of low selenium status in the mouse intestine: transcriptional activation of genes linked to DNA damage, cell cycle control and oxidative stress

The essential trace mineral selenium (Se) has been shown previously to inhibit intestinal, prostate, lung and liver tumor development and associated mortality in both experimental animals and humans. Although Se is likely to be one of the most powerful cancer chemopreventive agents in the human diet, its mechanism of action is unknown. To better understand the biological consequences of alterations in Se status, the gene expression profile associated with low Se status in the intestine of C57Bl/6J mice was analyzed. Mice were fed either a high fat (14%), torula yeast-based, Se-deficient diet (<0.01 mg/kg) or the same diet supplemented with a high level of dietary Se (1 mg/kg, as seleno-L-methionine) for 90 d. Use of high density oligonucleotide arrays representing 6347 genes revealed that low Se status results in a differential gene expression pattern indicative of activation of genes involved in DNA damage, oxidative stress and cell cycle control, and a decrease in the expression of genes involved in detoxification. These results suggest that suboptimal intake of a single trace mineral can have broad effects on gene expression patterns, providing a framework for understanding the multiple beneficial effects of Se in cancer chemoprevention and human health.

Malnutrition and childhood epilepsy in developing countries

A high prevalence of epilepsy in children is frequently found in developing countries. Though high rates of acquired brain injury may contribute, the possibility that malnutrition may lower seizure threshold has rarely been examined. This review suggests potential biochemical mechanisms that could adversely affect seizure threshold, particularly the effect of malnutrition on inhibitory neurotransmitters and electrolytes. Supporting evidence from animal research and epidemiological findings in children are discussed.

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

INTRODUCTION

Selenium is an essential trace element with antioxidant properties. Trials with selenium have been conducted in rheumatoid arthritis (RA) to correct impaired selenium status and increase defences against deleterious oxidant species.

AIM OF THE STUDY

To investigate in a double blind multi-centric placebo-controlled study the effects of selenium supplementation in RA.

METHODS

Fifty five patients with moderate RA received during 90 days either capsules containing selenium-enriched yeast (200 microg/d) or a placebo.

RESULTS

The visual analog scale, the Ritchie index, the number of swollen and painful joints, and morning stiffness significantly decreased with time in both groups (p<0.001), but no difference between groups could be identified. When examining the quality of life a significant (p<0.01) improvement in arm movements and health feeling was evidenced in selenium-treated patients.

CONCLUSION

Selenium treatment did not show clinical benefit on RA. Interestingly, the improval in both groups demonstrated a placebo effect of the intervention trial.

Role of thyroid hormones in the effects of selenium on mood, behavior, and cognitive function

Changes in thyroid function may affect mood, behavior, and cognitive function. Selenium is required for appropriate thyroid hormone synthesis, activation, and metabolism. Selenium status influences thyroid function. Selenium status also affects psychological condition and cognitive function. The author suggests that the effects of selenium status on mood, behavior, and cognition may be partly mediated by changes induced by selenium deficiency or selenium supplementation in thyroid function. Selenium deficiency decreases immunocompetence and promotes viral infections. The author proposes that patients who have a combination of depression, hypothyroidism, and increased susceptibility to viral infections, could reasonably be assessed for selenium deficiency, especially if they live in an area where the soil is low in selenium.

Study of preanalytical conditions for selenium determination in urine

OBJECTIVE

Assessment of preanalytical and storage conditions for selenium determination in urine.

DESIGN AND METHOD

A design is established for the study of the effect of HCl as sample preservative, and for the stability of urine samples with time and temperature of storage. The effect of sample sonication before taking aliquots is also evaluated. All measurements are performed using hydride generation atomic fluorescence spectrometry. Selenium concentrations measured from 52 urine samples of healthy population in Barcelona are used for an estimation of the selenium reference level.

RESULTS

HCl addition to urine samples has no effect on Se stability. Significant differences are due to time and temperature of storage. The Se reference level in urine samples from population in Barcelona area is estimated to be 22.8 +/- 6.7 microg Se g(CT)(-1) (CT: creatinine).

CONCLUSIONS

No significant differences are observed in selenium content when HCl is added as preservative. The Se content remains constant at room temperature for one day, for a week at 4 degrees C and for a fortnight when stored at -20 degrees C.

Nutritional aspects of nitric oxide: human health implications and therapeutic opportunities

Nitric oxide (NO), the most potent natural vasorelaxant known, has close historical ties to cardiovascular physiology, despite NO's rich physiologic chemistry as an ubiquitous, signal-transducing radical. Aspects of NO biology critical to gastrointestinal health and, consequently, nutritional status are increasingly being recognized. Attempts are underway to exploit the gastrointestinal actions of NO for therapeutic gain. Cross-talk between NO and micronutrients within and outside the gastrointestinal system affects the establishment or progression of several diseases with pressing medical needs. These concepts imply that NO biology can influence nutrition and be nutritionally modulated to affect mammalian (patho)physiology. At least four nutritional facets of NO biology are at the forefront of contemporary biomedical research: 1) NO as modulator of feeding behavior and mediator of gastrointestinal homeostasis; 2) NO supplementation as a therapeutic modality for preserving gastrointestinal health; 3) interactions among elemental micronutrients (e.g., zinc), NO, and inflammation as potential contributors to diarrheal disease; and 4) vitamin micronutrients (e.g., vitamins E and C) as protectors of NO-dependent vascular function. Discussion of extant data on these topics prompts speculation that future research will broaden NO's nutritional role as an integrative signaling molecule supporting gastrointestinal and nutritional well-being.