The importance of selenium to human health

Selenium and iodine intakes and status in New Zealand and Australia

Most New Zealand soils contain relatively low concentrations of the anionic trace elements F, I and Se. Some areas of Australia also have a history of I deficiency. In view of current interest in establishing nutrient reference intakes for Se and I in New Zealand and Australia, it is timely to review current understanding of the intakes and status of these two elements. In spite of a recent increase in Se status, the status of New Zealanders remains low compared with populations of many other countries and may still be considered marginal, although the clinical consequences of the marginal Se status are unclear. There are no recent reports of blood Se levels in Australia, but earlier reports indicate that they were generally greater than those of New Zealanders. Similarly, the consequences of decreasing I status in Australia and New Zealand are unclear. Mild I deficiency in New Zealand has resulted in enlarged thyroid glands indicating an increased risk of goitre. Currently there is little evidence, however, of any associated clinical disease. Public health recommendations to reduce salt intake, together with the reduction in I content of dairy products, are likely to result in further decreases in the I status of New Zealand and Australian residents. Some action is needed to prevent this decline and it may be necessary to consider other means of fortification than iodized salt. The consequences of possible interactions between Se and I in human nutrition are also unclear and no practical recommendations can be made.

Trends in selenium status of South Australians

OBJECTIVE

To assess trends in selenium status in South Australians from 1977 to 2002.

DESIGN

Six cross-sectional surveys.

PARTICIPANTS

117 participants in 1977, 30 in 1979, 96 and 103 (separate surveys) in 1987, 200 in 1988, and 288 volunteer blood donors in 2002. A total of 834 healthy Australian adults (mean age, 42 years [range, 17-71 years]; 445 were male).

MAIN OUTCOME MEASURES

Plasma and whole blood selenium concentrations.

RESULTS

The 2002 survey yielded a mean plasma selenium concentration of 103 micro g/L (SE, 0.65), which reached the estimated nutritional adequacy level of 100 micro g/L plasma selenium. Mean whole blood selenium declined 20% from the 1977 and 1979 surveys (mean whole blood selenium concentration, 153 micro g/L) to the 1987, 1988 and 2002 surveys (mean whole blood selenium concentration, 122 micro g/L). Plasma selenium was higher in men (P = 0.01), and increased with age in both men and women (P = 0.008).

CONCLUSIONS

In healthy South Australian adults sampled from 1977 to 2002, whole blood and plasma selenium concentrations were above those reported for most other countries and in most previous Australian studies, notwithstanding an apparent decline in selenium status from the late 1970s to the late 1980s.

Natural mechanisms protecting against cancer

Carcinogenesis is a multistage process. At each step of this process, there are natural mechanisms protecting against development of cancer. The majority of cancers in humans is induced by carcinogenic factors present in our environment including our food. However, some natural substances present in our diet or synthesized in our cells are able to block, trap or decompose reactive oxygen species (ROS) participating in carcinogenesis. Carcinogens can also be removed from our cells. If DNA damage occurs, it is repaired in most of the cases. Unrepaired DNA alterations can be fixed as mutations in proliferating cells only and mutations of very few strategic genes can induce tumor formation, the most relevant are those activating proto-oncogenes and inactivating tumor suppressor genes. A series of mutations and/or epigenetic changes is required to drive transformation of a normal cell into malignant tumor. The apparently unrestricted growth has to be accompanied by a mechanism preserving telomeres which otherwise shorten with succeeding cell divisions leading to growth arrest. Tumor can not develop beyond the size of 1-2mm in diameter without the induction of angiogenesis which is regulated by natural inhibitors. To invade the surrounding tissues epithelial tumor cells have to lose some adhesion molecules keeping them attached to each other and to produce enzymes able to dissolve the elements of the basement membrane. On the other hand, acquisition of other adhesion molecules enables interaction of circulating tumor cells with endothelial cells facilitating extravasation and metastasis. One of the last barriers protecting against cancer is the activity of the immune system. Both innate and adaptive immunity participates in anti-tumor effects including the activity of natural killer (NK) cells, natural killer T cells, macrophages, neutrophils and eosinophils, complement, various cytokines, specific antibodies, and specific T cytotoxic cells. Upon activation neutrophils and macrophages are able to kill tumor cells but they can also release ROS, angiogenic and immunosuppressive substances. Many cytokines belonging to different families display anti-tumor activity but their role in natural anti-tumor defense remains largely to be established.

Effects of 3H-1,2-dithiole-3-thione, 1,4-phenylenebis(methylene)selenocyanate, and selenium-enriched yeast individually and in combination on benzo[a]pyrene-induced mutagenesis in oral tissue and esophagus in lacZ mice

We have studied the effects of three chemopreventive agents alone or in binary combinations on benzo[a]pyrene (BaP)-induced mutagenesis in the oral cavity and esophagus of lacZ mice using galE(-) selection. The mice were fed diets supplemented with 1,4-phenylenebis(methylene)selenocyanate (p-XSC) at 2.5 and 10 ppm Se, selenium-enriched yeast (SeY) at 2.5 and 10 ppm Se, and 3H-1,2-dithiole-3-thione (D3T) at 65 and 250 ppm, for 6 weeks. Two weeks after the start of the dietary regimen, mice were gavaged with five doses of 125 mg/kg BaP over 2 weeks, and the experiment was terminated 2 weeks later. Mutagenesis was measured in tongue, other pooled oral tissues (OTs), and esophagus. In mice treated with BaP alone, mutagenesis in the above tissues was in the range of 21-32 mutants/10(5)pfu (ca. 6-10 background levels for the corresponding tissues). p-XSC modestly inhibited mutagenesis (10-33% inhibition) in all tissues, but statistical significance was only observed at the low dose in esophagus, and pooled OT. SeY was not inhibitory alone. Greater inhibitory effects were observed with D3T, and inhibition was statistically significant at the high dose in tongue and esophagus (ca. 33%). Two combinations of low doses of the inhibitors were tested, and the D3T + SeY mix was most effective, leading to statistically significant inhibition in all three tissues (ca. 30-40% inhibition). The mixture D3T + p-XSC was of similar effectiveness as the low dose of D3T alone. This study combined with those previously done in our laboratory demonstrates effectiveness of D3T and to a lesser extent, p-XSC in the inhibition of mutagenesis, and provides support for the use of certain combinations of inhibitors as a means to increase effectiveness and reduce the dose of chemopreventive agents.

The neurobiology of selenium: lessons from transgenic mice

The brain represents a privileged organ with respect to selenium (Se) supply and retention. It contains high amounts of this essential trace element, which is efficiently retained even in conditions of Se deficiency. Accordingly, no severe neurological phenotype has been reported for animals exposed to Se-depleted diets. They are, however, more susceptible to neuropathological challenges. Recently, gene disruption experiments supported a pivotal role for different selenoproteins in brain function. Using these and other transgenic models, longstanding questions concerning the preferential supply of Se to the brain and the hierarchy among the different selenoproteins are readdressed. Given that genes for at least 25 selenoproteins have been identified in the human genome, and most of these are expressed in the brain, their specific roles for normal brain function and neurological diseases remain to be elucidated.

Selenium attenuates lipopolysaccharide-induced oxidative stress responses through modulation of p38 MAPK and NF-kappaB signaling pathways

Lipopolysaccharide (LPS) produces reactive oxygen species (ROS) and nitric oxide (NO) in macrophages. These molecules are involved in inflammation associated with endotoxic shock. Selenium (Se), a biologically essential trace element, modulates the functions of many regulatory proteins involved in signal transduction and affects a variety of cellular activities, including cell growth and survival. We demonstrate that Se attenuated LPS-induced ROS and NO production in murine macrophage cultures in vitro. This Se-decreased production of NO was demonstrated by decreases in both mRNA and protein expression for inducible NO synthase (iNOS). The preventive effects of Se on iNOS were p38 mitogen-activated protein kinase- and nuclear factor-kappaB-dependent. Se specifically blocked the LPS-induced activation of p38 but not that of c-jun-N-terminal kinase and extracellular signal-regulated kinase; the p38-specific pathway was confirmed using p38 inhibitor SB 203580. These results suggest that the mechanism by which Se may act as an anti-inflammatory agent and that Se may be considered as a possible preventive intervention for endotoxemia, particularly in Se-deficient locations. However, the efficacy and safety of Se need to be further investigated, because long-term intake > 0.4 mg Se/day in adults can produce adverse effects.

DNA Stability and Serum Selenium Levels in a High-Risk Group for Prostate Cancer

The essential micronutrient, selenium, is at low levels in the New Zealand diet. Selenium is a component of a number of proteins involved in the maintenance of genomic stability, and recommended daily allowances (RDA) are set on saturation levels for glutathione peroxidase (GPx), a key enzyme in surveillance against oxidative stress. It has been assumed but not proven that this level will be adequate for other key selenoenzymes. The “Negative Biopsy Trial” identifies a group of New Zealand individuals at high risk of prostate cancer, whose serum selenium levels will be monitored and who will be supplemented with a yeast-based tablet, with or without selenium, over an extended time. Access to patients on this trial provides the opportunity to ask the more generic question as to whether selenium levels in this population are adequate to maintain genomic stability. The single cell gel electrophoresis (comet) assay was used to study DNA damage in blood leukocytes harvested from these volunteers. Average serum selenium levels before randomization was 97.8 ± 16.6 ng/ml, low by international standards. For the half of the population below this mean value, lower serum selenium levels showed a statistically significant inverse relationship (P = 0.02) with overall accumulated DNA damage. Although other interpretations cannot be excluded, the data suggest that the selenium intake in half of this population is marginal for adequate repair of DNA damage, increasing susceptibility to cancer and other degenerative diseases. It also raises the question as to whether glutathione peroxidase saturation levels are appropriate indicators of the optimal selenium levels for a given population.

Assessment of requirements for selenium and adequacy of selenium status: a review

OBJECTIVE

The intent of this review is to evaluate the scientific evidence for the assessment of adequacy of selenium status and of the requirements for selenium. From this evidence, attempts have been made to define levels of plasma selenium and dietary selenium intake, which could be used for the assessment of deficiency or adequacy of selenium status.

METHOD

The first section briefly reviews the methods for assessment of selenium status. The second section outlines the requirements for selenium based on a number of criteria, and how these have been translated into recommended intakes of selenium. In the final section, levels of plasma selenium and dietary intake based on different criteria of adequacy have been proposed.

RESULTS AND CONCLUSION

The minimum requirement for selenium is that which prevents the deficiency disease, Keshan disease. The recommended intakes of selenium have been calculated from the requirement for optimum plasma glutathione peroxidase (GPx) activity that must, because of the hierarchy of selenoproteins, also take account of the amounts needed for normal levels of other biologically necessary selenium compounds. Whether optimal health depends upon maximization of GPx or other selenoproteins, however, has yet to be resolved, and the consequences of less-than-maximal GPx activities or mRNA levels need investigation. Intakes, higher than recommended intakes, and plasma selenium concentrations that might be protective for cancer or result in other additional health benefits have been proposed. There is an urgent need for more large-scale trials to assess any such beneficial effects and to provide further data on which to base more reliable estimates for intakes and plasma selenium levels that are protective.

Selenium and its relationship to cancer: an update

Selenomethionine (Semet) is the major seleno-compound in cereal grains and enriched yeast whereas Se-methylselenocysteine (SeMCYS) is the major seleno-compound in Se-accumulator plants and some plants of economic importance such as garlic and broccoli exposed to excess Se. Animals can metabolize both Semet and SeMCYS. Epidemiological studies have indicated an inverse relationship between Se intake and the incidence of certain cancers. Blood or plasma levels of Se are usually lower in patients with cancer than those without this disorder, but inconsistent results have been found with toenail-Se values and the incidence of cancer. There have been eight trials with human subjects conducted on the influence of Se on cancer incidence or biomarkers, and except for one, all have shown a positive benefit of Se on cancer reduction or biomarkers of this disorder. This is consistent with about 100 small-animal studies where Se has been shown to reduce the incidence of tumours in most of these trials. Se-enriched yeast is the major form of Se used in trials with human subjects. In the mammary-tumour model, SeMCYS has been shown to be the most effective seleno-compound identified so far in reduction of tumours. Several mechanisms have been proposed on the mechanism whereby Se reduces tumours. Even though SeMCYS was shown to be the most effective seleno-compound in the reduction of mammary tumours, it may not be the most effective seleno-compound for reduction of colon tumours.

Methioninase and selenomethionine but not Se-methylselenocysteine generate methylselenol and superoxide in an in vitro chemiluminescent assay: implications for the nutritional carcinostatic activity of selenoamino acids

Methylselenol from selenium metabolism is postulated to be and most experimental evidence now indicates that it is the selenium metabolite responsible for the dietary chemoprevention of cancers. Using the recombinant enzyme methioninase, methylselenol-generating chemiluminesence by superoxide (O2*-) is shown to be catalytically produced from L-selenomethionine and D,L-selenoethionine, but not from methionine or L-Se-methylselenocysteine (SeMC). Methylselenol enzymaticaly generated by methioninase activity from the substrate selenomethionine arises from an initial putative selenium radical as measured by chemiluminesence in the absence of glutathione (GSH). In the presence of GSH, superoxide was generated as measured by chemiluminesence and superoxide dismutase inhibition of chemiluminescence. Ascorbic acid also quenched the chemiluminesence from the activity of methioninase with selenomethionine. Methylselenol and other redox cycling selenium compounds are almost assuredly accountable for inducing cell-cycle arrest and apoptosis in cancer cells in vitro and in vivo. Methylselenol generated from selenomethionine by methioninase is catalytic alone in oxidizing thiols, i.e. GSH, generating superoxide and inducing oxidative stress in direct proportion to its concentration. Se-methylselenocysteine in vivo is very likely carcinostatic in like manner to selenomethionine by generating methylselenol from other enzymatic activity, i.e. beta-lyase or amino acid oxidases.

Identification and characterization of Se-methyl selenomethionine in Brassica juncea roots

The present work shows the identification and characterization of Se-methyl selenomethionine (SeMMet) as an important Se species in Brassica juncea roots when grown in the presence of Se-methionine (SeMet) as the Se source. SeMMet was isolated by liquid chromatography employing two different liquid chromatographic mechanisms: reversed-phase ion-pairing using heptafluorobutyric acid as counter ion and cation exchange using a pyridinium formate gradient (pH 3). Inductively coupled plasma mass spectrometry was used for the detection of Se. SeMMet was characterized by electrospray quadrupole time-of-flight MS in both a synthesized standard and in the roots extract using collision-induced dissociation of the selected ion. Preliminary evidence suggests that Brassica juncea may also produce dimethylselenonium propionate, although to a much lesser extent.

Bioavailability of selenium from fish, yeast and selenate: a comparative study in humans using stable isotopes

OBJECTIVE

To measure the bioavailability of selenium from cooked and raw fish in humans by estimating and comparing apparent absorption and retention of selenium in biosynthetically labelled fish with labelled selenate and biosynthetically labelled selenium in brewers yeast.

DESIGN

The intervention study was a parallel, randomised, reference substance controlled design carried out at two different centres in Europe.

SETTING

The human study was carried out at the Institute of Food Research, Norwich, UK and at TNO Nutrition and Food Research, Zeist, The Netherlands.

SUBJECTS

In all, 35 male volunteers aged 18-50 y were recruited; 17 subjects were studied in Norwich (UK) and 18 in Zeist (Netherlands). All of the recruited subjects completed the study.

INTERVENTIONS

Biosynthetically labelled trout fish (processed by two different methods), biosynthetically labelled brewers yeast and isotopically labelled selenate were used to estimate selenium apparent absorption and retention by quantitative analysis of stable isotope labels recovered in faeces and urine. Subjects consumed the labelled foods in four meals over two consecutive days and absorption was measured by the luminal disappearance method over 10 days. Urinary clearance of isotopic labels was measured over 7 days to enable retention to be calculated.

RESULTS

Apparent absorption of selenium from fish was similar to selenate and there was no difference between the two processing methods used. However, retention of fish selenium was significantly higher than selenate (P<0.001). Apparent absorption and retention of yeast selenium was significantly different (P<0.001) from both fish selenium and selenate.

CONCLUSION

Fish selenium is a highly bioavailable source of dietary selenium. Cooking did not affect selenium apparent absorption or retention from fish. Selenium from yeast is less bioavailable.

Bioavailability of selenium from bovine milk as assessed in subjects with ileostomy

OBJECTIVE

To assess the absorption of dietary selenium in humans, especially of milk selenium.

DESIGN

: 1-day meal studies in subjects with ileostomy.

SETTING

Hospital outpatient clinics.

SUBJECTS

Three subjects in the pilot study and nine subjects in the main study (eight men/ four women).

INTERVENTION

Different beverages, 1 l/day, were given in addition to basal diets (soft drink, 1 week; low-fat milk, 3 weeks; fermented low-fat milk, 3 weeks and soft drink, 1 week). Ileostomy effluents were collected during the last 2 days in each of the four periods.

RESULTS

On days when the subjects were given 1 l of low-fat milk, the estimated fractional absorption of total dietary selenium was 65.5 (2.3)% (mean (s.d.), n=18), which was similar to the value when fermented low-fat milk was given (64.1 (3.2)%). However, both the calculated amount of milk selenium absorbed (10.9 (2.4) vs 9.4 (1.7) microg selenium) and its fractional absorption (73.3 (16.1) vs 64.1 (11.2)%, n=18) were significantly higher for milk than for fermented milk.

CONCLUSIONS

Selenium from milk and other sources is well absorbed in subjects with ileostomy. The real absorption may be even higher than the values shown.

Early evolution of selenium status and oxidative stress parameters in rat models of thermal injury

The objective of the present study was to measure the relationship between selenium status and oxidative stress in two rat models of thermal injury. A non-lethal third-degree burn injury involving 20% (experiment 1) or 40% (experiment 2) of total body surface area (TBSA) was applied to male Wistar rats. Selenium level, glutathione peroxidase (GPx) activity in plasma, red blood cells (RBC) and tissues (liver, kidney, muscle, and brain), and plasma selenoalbumin (Se-alb) were measured in control rats and in burned rats respectively 6 hours after injury and daily from day 1 to day 5. In parallel, lipid and protein oxidative damages, monitored by plasma and tissue thiobarbituric acid reactive species (TBARs) levels and plasma total thiol groups were assessed. We observed a decrease of plasma Se and Se-albumin 6 hours after burn injury. In parallel, plasma GPx activity rapidly decreased and remained significantly lower than in control rats. These alterations were enhanced by the burn injury severity. Plasma TBARs followed the same pattern as that of plasma cholesterol, with an initial decrease and an increase at day 3 in 40% TBSA burned rats. Plasma thiol groups decreased in the two experiments indicating plasma protein oxidation. These results confirm an early oxidative stress in burn injury, and suggest an early selenium mobilization, which might counteract this oxidative stress. These data underline the crucial need of a restored selenium status in burned patients immediately after the burn injury.

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.

Effects of nutrition and management on the production and composition of milk fat and protein: a review

The composition and functional properties of cow’s milk are of considerable importance to the dairy farmer, manufacturer, and consumer. Broadly, there are 3 options for altering the composition and/or functional properties of milk: cow nutrition and management, cow genetics, and dairy manufacturing technologies. This review considers the effects of nutrition and management on the composition and production of milk fat and protein, and the relevance of these effects to the feeding systems used in the Australian dairy industry. Dairy cows on herbage-based diets derive fatty acids for milk fat synthesis from the diet/rumen microorganisms (400–450 g/kg), from adipose tissues (<100 g/kg), and from de novo synthesis in the mammary gland (about 500 g/kg). However, the relative contributions of these sources of fatty acids to milk fat production are highly dependent upon feed intake, diet composition, and stage of lactation. Feed intake, the amount of starch relative to fibre, the amount and composition of long chain fatty acids in the diet, and energy balance are particularly important. Significant differences in these factors exist between pasture-based dairy production systems and those based on total mixed ration, leading to differences in milk fat composition between the two. High intakes of starch are associated with higher levels of de novo synthesis of fat in the mammary gland, resulting in milk fat with a higher concentration of saturated fatty acids. In contrast, higher intakes of polyunsaturated fatty acids from pasture and/or lipid supplements result in higher concentrations of unsaturated fatty acids, particularly oleate, trans-vaccenate, and conjugated linoleic acid (CLA) in milk fat. A decline in milk fat concentration associated with increased feeding with starch-based concentrates can be attributed to changes in the ratios of lipogenic to glucogenic volatile fatty acids produced in the rumen. Milk fat depression, however, is likely the result of increased rates of production of long chain fatty acids containing a trans-10 double bond in the rumen, in particular trans-10 18 : 1 and trans-10-cis-12 18 : 2 in response to diets that contain a high concentration of polyunsaturated fatty acids and/or starch. Low rumen fluid pH can also be a factor. The concentration and composition of protein in milk are largely unresponsive to variation in nutrition and management. Exceptions to this are the effects of very low intakes of metabolisable energy (ME) and/or metabolisable protein (MP) on the concentration of total protein in milk, and the effects of feeding with supplements that contain organic Se on the concentration of Se, as selenoprotein, in milk. In general, the first limitation for the synthesis of milk protein in Australian dairy production systems is availability of ME since pasture usually provides an excess of MP. However, low concentrations of protein in milk produced in Queensland and Western Australia, associated with seasonal variations in the nutritional value of herbage, may be a response to low intakes of both ME and MP. Stage of lactation is important in determining milk protein concentration, but has little influence on protein composition. The exception to this is in very late lactation where stage of lactation and low ME intake can interact to reduce the casein fraction and increase the whey fraction in milk and, consequently, reduce the yield of cheese per unit of milk. Milk and dairy products could also provide significant amounts of Se, as selenoproteins, in human diets. Feeding organic Se supplements to dairy cows grazing pastures that are low in Se may also benefit cow health. Research into targetted feeding strategies that make use of feed supplements including oil seeds, vegetable and fish oils, and organic Se supplements would increase the management options available to dairy farmers for the production of milks that differ in their composition. Given appropriate market signals, milk could be produced with lower concentrations of fat or higher levels of unsaturated fats, including CLA, and/or high concentrations of selenoproteins. This has the potential to allow the farmer to find a higher value market for milk and improve the competitiveness of the dairy manufacturer by enabling better matching of the supply of dairy products to the demands of the market.

Stable isotope-enriched selenite and selenate tracers for human metabolic studies: a fast and accurate method for their preparation from elemental selenium and their identification and quantification using hydride generation atomic absorption spectrometry

Stable isotope tracers are safe and nutritionally relevant tools for the investigation of mineral metabolism in man. Increased research into the functional role of selenium has resulted in a need for well-characterised, isotopically enriched solutions of the element in order to determine the nutritional relevance of selenium fortification of foods. A simple method for the conversion of isotopically enriched elemental selenium (2.5-10 mg) into selenite and selenate, and their accurate characterisation and quantification is described. Analysis of selenite and selenate tracers using continuous-flow hydride generation-atomic absorption spectrometry technique was based on the specificity of the selenium hydride reaction and allowed their precise (RSD<2.5%) and accurate determination in aqueous solutions. The detection and determination limits were at 0.13 and 0.36 microg Se/l, respectively. Isotopically enriched elemental selenium was converted into selenite and selenate by a nitric acid and a combined nitric acid/hydrogen peroxide oxidation, respectively. The conversion was quantitative (>95%) and specific for both inorganic selenocompounds. Selenite and selenate labels were stable in 0.1 mol/l nitric acid for at least 18 months, i.e. making them ideally suitable for use in long-term metabolic studies. An overview of data relating to the absorption and retention of selenium by humans obtained using the two, well-characterised, tracers is presented and indicates that selenite and selenate are equally well retained in adult men and infants, despite differences in their absorption and urinary excretion characteristics.

Review article: chemoprevention of colorectal cancer

Colorectal cancer is a disease with a high mortality at present, due to the late stage at which many cases present. Attention is therefore focusing on preventative strategies for colorectal cancer given that polyps appear to be identifiable and treatable precursor lesions of this disease. Endoscopic polypectomy has been shown to reduce the incidence of colorectal cancer and there is a good case for endoscopic screening of the general population. However, this will require a large amount of manpower and resources and its success will also depend on the overall compliance of the population. Epidemiological studies have shown that individuals reporting a regular intake of aspirin and other non-steroidal anti-inflammatory drugs have a reduced risk of developing colorectal polyps and cancer. Similarly, a number of natural substances, such as calcium and folate, when supplemented regularly in the diet, have also been linked to a possible decreased incidence of colorectal cancer. This has led to the concept of using such agents to reduce the number of cases of colorectal cancer. In this article, we review the current evidence for the use of these and other agents for the chemoprevention of colorectal cancer, together with theories as to their possible mechanisms of action.

No evidence for an impact of selenium supplementation on environment associated health disorders – a systematic review

In addition to vitamin C (and other vitamins/antioxidants), clinical ecologists (functional medicine) recommend selenium supplementation as a fundamental therapeutic remedy for the treatment of environment associated health disorders. This recommendation is based on the postulation that the trace element selenium inhibits oxidative stress generated during endogenous detoxification of xenobiotics (phase 1) by increasing selenium-dependent glutathione peroxidase activity, and that it counteracts heavy metal toxicity by forming inert metal complexes. The objective of this review was to investigate whether there are any valid studies providing reliable evidence of the therapeutic benefits of selenium supplementation in potentially environment associated health disorders. A systematic review was conducted based on the rigorous and well-defined methods developed by the Cochrane Collaboration. To achieve the demanding standards for systematic review set by the Cochrane Collaboration, study selection, quality assessment and data abstraction were performed independently and in duplicate using a standardized protocol. Overall, 1290 studies were identified as being eligible for inclusion. Twelve of these met the inclusion criteria and their quality was evaluated individually. None of the studies included in the analysis provided evidence of the therapeutic benefits of selenium supplementation in environment associated health disorders.

Prospective study of serum selenium concentrations and esophageal and gastric cardia cancer, heart disease, stroke, and total death

BACKGROUND

We previously reported an inverse association between prediagnostic serum selenium concentrations and the risk of esophageal squamous cell carcinoma (ESCC) and gastric cardia cancer (GCC) but not gastric noncardia cancer (GNCC) in a nested study from the Nutrition Intervention Trial in Linxian, China.

OBJECTIVE

We examined the relation between baseline serum selenium and the subsequent risk of death from ESCC, GCC, GNCC, heart disease (HD), stroke, and total death over 15 y of follow-up (1986-2001).

DESIGN

We measured baseline serum selenium concentrations in 1103 subjects randomly selected from a larger trial cohort. We identified 516 deaths during the 15-y follow up, including 75 from ESCC, 36 from GCC, 116 from HD, and 167 from stroke. Relative risks (RRs) and 95% CIs were estimated by using Cox proportional hazards regression models. Reported RRs estimated the change in risk conferred by a 25% increase in serum selenium relative to the population distribution. All estimates were adjusted for sex, age, smoking, drinking, and serum cholesterol.

RESULTS

We found significant inverse associations between baseline serum selenium and death from ESCC (RR: 0.83; 95% CI: 0.71, 0.98) and GCC (0.75; 0.59, 0.95). Trends toward inverse associations were noted for death from HD (0.89; 0.78, 1.01; P = 0.07), but no association was noted for total death (0.96; 0.90, 1.02) or stroke (0.99; 0.88, 1.11).

CONCLUSION

Population-wide selenium supplementation in the region of China with low serum selenium and high incidences of ESCC and GCC merits serious consideration.

Comparison of the serum selenium content of healthy adults living in the Antwerp region (Belgium) with recent literature data

Graphite furnace atomic absorption spectrometry, after improved matrix modification and using Zeeman background correction, was used to measure the serum selenium content of healthy adults living in the Antwerp region (Belgium). The mean serum concentration of 13 men and 13 women, sampled once a month during 1 year, was 84.3 +/- 9.4ng/ml with a broad range of 51.4-121.7 ng/ml. The intra-individual variation was remarkably high. Recent literature on selenium concentrations is reviewed and values are tabulated, with limitation to healthy adults and European countries. The mean serum selenium concentration measured corresponded well to older literature data for Belgium. The obtained values were found to be in the medium range compared with the literature data for other European countries.

Low selenium status is associated with the occurrence of the pregnancy disease preeclampsia in women from the United Kingdom

OBJECTIVE

Because the trace element selenium behaves as an antioxidant and peroxynitrite scavenger when incorporated into selenoproteins, our objective was to determine whether low selenium status was associated with a greater risk of occurrence of preeclampsia.

STUDY DESIGN

Fifty-three preeclamptic patients and 53 matched pregnant controls at the John Radcliffe Hospital, Oxford, gave clippings of their toenails (laid down from 3-12 months previously) for selenium determination by neutron activation analysis. Clinical characteristics of the women and their infants were recorded. Statistical analysis was by Wilcoxon signed rank test and odds ratios were calculated by the ratio of discordant pairs.

RESULTS

Median toenail selenium concentrations in the preeclamptic subjects were significantly lower than in their matched controls (P=.001). Being in the bottom tertile of toenail selenium was associated with a 4.4-fold (95% CI 1.6-14.9) greater incidence of the condition. Within the preeclamptic group, lower selenium status was significantly associated (P=.029) with more severe expression of disease, as measured by delivery before 32 weeks.

CONCLUSION

In the light of the reduction in selenium status in a number of European countries in recent years, this study raises the question of whether a small increase in selenium intake might help prevent preeclampsia in susceptible women.

Comparative action of 1,4-phenylenebis(methylene)selenocyanate and its metabolites against 7,12-dimethylbenz[a]anthracene-DNA adduct formation in the rat and cell proliferation in rat mammary tumor cells

1,4-phenylenebis(methylene)selenocyanate (p-XSC) inhibits 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis and DMBA-DNA binding in the rat mammary gland. Tetraselenocyclophane (TSC) was identified in rat feces as a metabolite of p-XSC. This led us to postulate the metabolic pathway: p-XSC-->glutathione conjugate (p-XSeSG)-->aromatic selenol (p-XSeH)-->TSC. Whether p-XSC or one of its metabolites is responsible for cancer prevention is the focus of this study. We utilized the DMBA-DNA binding assay with p-XSC as a positive control to evaluate the chemopreventive potential of p-XSC metabolites at dietary selenium levels of 10 ppm. Rats were fed AIN-76A diet supplemented with various selenium compounds for 1 week prior to the oral administration of a single dose of [3H]DMBA (5 mg per rat, specific activity 51.3 mCi/mmol). The rats were sacrificed 24 h later and DNA was isolated from the mammary fat pads. Relative levels of total binding were: [pmol/mg DNA, mean +/- S.D., n=6]; DMBA [7.2 +/- 1.6]; DMBA+p-XSC [3.5 +/- 2.7]; DMBA+p-XSeSG [2.2 +/- 1.1]; DMBA+TSC [5.6 +/- 2.9]. All selenium compounds, except TSC, significantly inhibited DMBA-DNA adduct formation; however, the difference between p-XSC and p-XSeSG was not statistically significant. The inhibition of total binding was attributed to a reduction in the formation of the three major adducts derived from bay-region diol epoxides of DMBA. On the basis of their chromatographic characteristics, these were identified as anti-diol-epoxide:deoxyguanosine, syn-diol-epoxide:deoxyadenosine, and anti-diol-epoxide:deoxyadenosine. Our results suggest that p-XSeSG, but not TSC, is the likely inhibitor of mammary cancer. Selenium levels measured by atomic absorption spectroscopy in the target organ (mammary fat pads) and in plasma following the dietary administration of selenium compounds were in the order of p-XSeSG congruent with p-XSC>TSC. These results appear to be consistent with their order of inhibitory effects on total DMBA-DNA binding. Further in vitro studies of the effect of selenium compounds on cell proliferation suggest that, depending on the dose and time point selected, p-XSC is comparable to or better than p-XSeSG; but both are more effective than TSC. Collectively, our in vivo and in vitro results indicate that p-XSC and its conjugate are better candidates than TSC for future studies on mammary cancer chemoprevention.

Psychological burden in the era of HAART: impact of selenium therapy

OBJECTIVE

To determine the impact of nutritional (selenium) chemoprevention on levels of psychological burden (anxiety, depression, and mood state) in HIV/AIDS.

METHOD

A randomized, double-blind, placebo-controlled selenium therapy (200 microg/day) trial was conducted in HIV+ drug users from 1998-2000. Psychosocial measures (STAI-State and Trait anxiety, BDI-depression, and POMS- mood state), clinical status (CD4 cell count, viral load), and plasma selenium levels were determined at baseline and compared with measurements obtained at the 12-month evaluation in 63 participants (32 men, 31 women).

RESULTS

The majority of the study participants reported elevated levels of both State (68%) and Trait (70%) anxiety. Approximately 25% reported overall mood distress (POMS > 60) and moderate depression (BDI > 20). Psychological burden was not influenced by current drug use, antiretroviral treatment, or viral load. At the 12-month evaluation, participants who received selenium reported increased vigor (p = 0.004) and had less anxiety (State, p = 0.05 and Trait, p = 0.02), compared to the placebo-treated individuals. No apparent selenium-related affect on depression or distress was observed. The risk for state anxiety was almost four times higher, and nearly nine times greater for trait anxiety in the placebo-treated group, controlling for antiretroviral therapy, CD4 cell decline (> 50 cells) and years of education.

CONCLUSIONS

Selenium therapy may be a beneficial treatment to decrease anxiety in HIV+ drug users who exhibit a high prevalence of psychological burden.

Prevention of liquid-diet-induced damages on submandibular glands by selenium supplementation in rats

This study was designed to explore the protective effects of selenium on submandibular glands of rats that were maintained on liquid diet. The animals kept on liquid diet for 10 days following 20 days of solid diet, had severe degeneration on both acinar and ductal cells: pycnotic nuclei, enlarged granular endoplasmic reticulum, swollen mitochondria with separated cristae, reduction of secretory granules and abundant lipid droplets were observed. Body and gland weights of these animals were found to decrease significantly compared to those of control group given solid diet for 30 days. The animals that were fed 20 days with solid diet + 10 days liquid diet and also given selenium 0.4 mg/kg for 30 days, did not have any remarkable sign of degeneration on submandibular glands, and their gland weights significantly increased when compared to the animals fed with liquid diet without selenium supplementation. Submandibular glands of the group that was maintained on solid diet for 30 days and supplemented with selenium in drinking water were found to be normal. They showed consistent gain in both body and gland weights almost equal to that of control group. As a result, we assume that adding selenium in liquid diet can prevent the detrimental effects of liquid diet consumption on submandibular glands.

Selenoprotein-deficient transgenic mice exhibit enhanced exercise-induced muscle growth

Dietary intake of selenium has been implicated in a wide range of health issues, including aging, heart disease and cancer. Selenium deficiency, which can reduce selenoprotein levels, has been associated with several striated muscle pathologies. To investigate the role of selenoproteins in skeletal muscle biology, we used a transgenic mouse (referred to as i6A-) that has reduced levels of selenoproteins due to the introduction and expression of a dominantly acting mutant form of selenocysteine transfer RNA (tRNA[Ser]Sec). As a consequence, each organ contains reduced levels of most selenoproteins, yet these mice are normal with regard to fertility, overall health, behavior and blood chemistries. In the present study, although skeletal muscles from i6A- mice were phenotypically indistinguishable from those of wild-type mice, plantaris muscles were approximately 50% heavier after synergist ablation, a model of exercise overload. Like muscle in wild-type mice, the enhanced growth in the i6A- mice was completely blocked by inhibition of the mammalian target of rapamycin (mTOR) pathway. Muscles of transgenic mice exhibited increased site-specific phosphorylation on both Akt and p70 ribosomal S6 kinase (p70S6k) (P < 0.05) before ablation, perhaps accounting for the enhanced response to synergist ablation. Thus, a single genetic alteration resulted in enhanced skeletal muscle adaptation after exercise, and this is likely through subtle changes in the resting phosphorylation state of growth-related kinases.

A randomized trial of the impact of multiple micronutrient supplementation on mortality among HIV-infected individuals living in Bangkok

OBJECTIVES

To examine the impact of high-dose multiple micronutrient supplementation on survival and disease progression among HIV-infected individuals in Thailand.

DESIGN

Randomized placebo-controlled trial.

METHODS

Four-hundred and eighty-one HIV-infected men and women living in and around Bangkok with CD4 cell counts in the range 50 x 10(6)- 550 x 10(6)/l were randomized to receive micronutrients or placebo for a period of 48 weeks. Trial participants were examined clinically 12-weekly and tested for CD4 cell count 24-weekly. A subset were tested for HIV plasma viral load at 48 weeks.

RESULTS

Seventy-nine (16%) trial participants were lost to follow-up and 23 (5%) died. The death rate was lower in the micronutrients arm with the mortality hazard ratios [95% confidence interval (CI)] of 0.53 (0.22-1.25; P = 0.1) overall and 0.37 (0.13-1.06; P = 0.052) and 0.26 (0.07-0.97; P = 0.03) among those with CD4 cell counts < 200 x 10(6)/l and < 100 x 10(6)/l respectively. There was no impact on CD4 cell count or plasma viral load.

CONCLUSIONS

Multiple micronutrient supplementation may enhance the survival of HIV-infected individuals with CD4 cell counts < 200 x 10(6)/l. This could have important public health implications in the developing world where access to antiretrovirals remains poor. The clinical findings need to be reproduced in other settings and the mechanism, which appears to be independent of change in CD4 cell count, merits further investigation.

Mechanism and regulation of selenoprotein synthesis

Selenium is an essential trace element that is incorporated into proteins as selenocysteine (Sec), the twenty-first amino acid. Sec is encoded by a UGA codon in the selenoprotein mRNA. The decoding of UGA as Sec requires the reprogramming of translation because UGA is normally read as a stop codon. The translation of selenoprotein mRNAs requires cis-acting sequences in the mRNA and novel trans-acting factors dedicated to Sec incorporation. Selenoprotein synthesis in vivo is highly selenium-dependent, and there is a hierarchy of selenoprotein expression in mammals when selenium is limiting. This review describes emerging themes from studies on the mechanism, kinetics, and efficiency of Sec insertion in prokaryotes. Recent developments that provide mechanistic insight into how the eukaryotic ribosome distinguishes between UGA/Sec and UGA/stop codons are discussed. The efficiency and regulation of mammalian selenoprotein synthesis are considered in the context of current models for Sec insertion.

Glutathione peroxidase 1 activity and cardiovascular events in patients with coronary artery disease

BACKGROUND

Cellular antioxidant enzymes such as glutathione peroxidase 1 and superoxide dismutase have a central role in the control of reactive oxygen species. In vitro data and studies in animal models suggest that these enzymes may protect against atherosclerosis, but little is known about their relevance to human disease.

METHODS

We conducted a prospective study among 636 patients with suspected coronary artery disease, with a median follow-up period of 4.7 years (maximum, 5.4) to assess the risk of cardiovascular events associated with base-line erythrocyte glutathione peroxidase 1 and superoxide dismutase activity.

RESULTS

Glutathione peroxidase 1 activity was among the strongest univariate predictors of the risk of cardiovascular events, whereas superoxide dismutase activity had no association with risk. The risk of cardiovascular events was inversely associated with increasing quartiles of glutathione peroxidase 1 activity (P for trend <0.001); patients in the highest quartile of glutathione peroxidase 1 activity had a hazard ratio of 0.29 (95 percent confidence interval, 0.15 to 0.58; P<0.001), as compared with those in the lowest quartile. Glutathione peroxidase 1 activity was affected by sex and smoking status but retained its predictive power in these subgroups. After adjustment for these and other cardiovascular risk factors, the inverse association between glutathione peroxidase 1 activity and cardiovascular events remained nearly unchanged.

CONCLUSIONS

In patients with coronary artery disease, a low level of activity of red-cell glutathione peroxidase 1 is independently associated with an increased risk of cardiovascular events. Glutathione peroxidase 1 activity may have prognostic value in addition to that of traditional risk factors. Furthermore, increasing glutathione peroxidase 1 activity might lower the risk of cardiovascular events.

Modulatory effects of selenium and zinc on the immune system

Almost all nutrients in the diet play a crucial role in maintaining an "optimal" immune response, and both insufficient and excessive intakes can have negative consequences on the immune status and susceptibility to a variety of pathogens. We summarize the evidence for the importance of two micronutrients, selenium and zinc, and describe the mechanisms through which they affect the immune status and other physiological functions. As a constituent of selenoproteins, selenium is needed for the proper functioning of neutrophils, macrophages, NK cells, T lymphocytes and some other immune mechanisms. Elevated selenium intake may be associated with reduced cancer risk and may alleviate other pathological conditions including oxidative stress and inflammation. Selenium appears to be a key nutrient in counteracting the development of virulence and inhibiting HIV progression to AIDS. It is required for sperm motility and may reduce the risk of miscarriage. Selenium deficiency has been linked to adverse mood states and some findings suggest that selenium deficiency may be a risk factor in cardiovascular diseases. Zinc is required as a catalytic, structural and regulatory ion for enzymes, proteins and transcription factors, and is thus a key trace element in many homeostatic mechanisms of the body, including immune responses. Low zinc ion bioavailability results in limited immunoresistance to infection in aging. Physiological supplementation of zinc for 1-2 months restores immune responses, reduces the incidence of infections and prolongs survival. However, in every single individual zinc supplementation of food should be adjusted to the particular zinc status in views of the great variability in habitat conditions, health status and dietary requirements.

Diphenyl diselenide protects rat hippocampal slices submitted to oxygen-glucose deprivation and diminishes inducible nitric oxide synthase immunocontent

Diphenyl diselenide (PhSe)2 is an organic selenium compound that has been little studied. In this study we investigated the effects of (PhSe)2 (0.1-3 microM) in a classical model of in vitro brain ischemia, which consists of exposing rat hippocampal slices to oxygen-glucose deprivation (OGD). Hippocampal slices were exposed for 60 min to OGD and the cellular viability (performed by MTT assay) as well as the immunocontent of nitric oxide synthase inducible (iNOS) were evaluated after 180 min of a recovery period. OGD decreased cellular viability by 50% and increased more than twice the immunocontent of iNOS of hippocampal slices. (PhSe)2 (1 and 3 microM) added during OGD and the recovery period abolished both effects. These results demonstrate for the first time the neuroprotective effects of (PhSe)2. Although the selenium analog--ebselen--has been widely used in ischemia models, our results suggest that other selenoorganic compounds could be investigated as pharmacological tools against brain disorders.

Free radical scavenging efficiency of Nano-Se in vitro

In this study, we showed that smaller size particles of Nano-Se have better scavenging effects on the following free radicals: carbon-centered free radicals (R*) generated from 2,2'-azo-bis-(2-amidinopropane) hydrochloride (AAPH), the relatively stable free radical 1,1-diphenyl-2-picryhydrazyl (DPPH), the superoxide anion (O2*-) generated from the xanthine/xanthine oxidase (X/XO) system, singlet oxygen (1O2) generated by irradiated hemoporphyrin. Furthermore, the three sizes of Nano-Se studied also show protective effects against the oxidation of DNA. The three samples all have potential size-dependent characteristics on scavenging the free radicals. Although in this study we regarded Nano-Se as a whole without considering interactions between BSA and the red selenium nano-particles, there is the possibility that the apparent free radical scavenging effects may be partially contributed by such interactions.

Soluble tumor necrosis factor-α receptor type 1 during selenium supplementation in psoriasis patients

OBJECTIVE

Tumor necrosis factor-alpha (TNF-alpha) and its receptors play important roles in the induction and maintenance of psoriatic lesions. Selenium (Se), a trace element with immunomodulatory properties, is usually decreased in psoriasis patients. We examined the influence of Se supplementation on soluble TNF-alpha receptor type 1 (sTNF-R1) and topical treatment in psoriasis patients.

METHODS

The study was conducted in between January and June 2002. Twenty-two inpatients with active plaque psoriasis received topical treatment with 5% salicylic acid ointment, 0.1% to 0.3% dithranol ointment, and 200 microg daily of Se as selenomethionine (SeMet; n = 11, group 1) or placebo (n = 11, group 2) for 4 wk. Psoriasis Area and Severity Index (PASI) score and Se and sTNF-R1 concentrations were assessed at baseline and every 2 wk. Control sera were obtained from 10 healthy subjects. For statistical analysis, parametric tests were used, and the level of significance was set at P = 0.05.

RESULTS

The baseline sTNF-R1 levels were 1.87 +/- 0.58 ng/mL (1.98 +/- 0.44 ng/mL in group 1 and 1.75 +/- 0.69 ng/mL in group 2, P = 0.34) in psoriasis patients and 1.65 +/- 0.25 ng/mL in control subjects (P = 0.17); baseline Se concentrations were 48.31 +/- 13.20 microg/L (48.31 +/- 13.20 microg/L in group 1 and 50.35 +/- 13.49 microg/L in group 2, P = 0.41) in psoriasis patients and 58.30 +/- 17.21 microg/L in control subjects (P = 0.05). A positive correlation between PASI and sTNF-R1 was noticed (r = 0.36, P = 0.04; r = 0.51 in group 1 and r = 0.18 in group 2). After 4 wk, almost complete remission of skin lesions was achieved in both groups, but the PASI score was higher in group 1 than in group 2 (4.30 +/- 3.92 and 1.67 +/- 1.17, respectively; P < 0.05). TNF-R1 levels were 1.81 +/- 0.42 ng/mL in group 1 and 1.33 +/- 0.40 ng/mL in group 2 (P = 0.01), and the correlation between PASI score and TNF-R1 level became inverse (r = -0.24 in group 1 and r = -0.59 in group 2). Se concentrations were 107.51 +/- 18.08 microg/L in group 1 and 56.83 +/- 15.32 microg/L in group 2 (P < 0.01).

CONCLUSIONS

Increased level of sTNF-R1 may be an indicator of active psoriasis. Supplementation with selenomethionine was ineffective as adjuvant treatment in plaque psoriasis and may contribute to the maintenance of elevated TNF-R1 concentration in psoriasis patients despite the remission of skin lesions.

Clinical pharmacokinetics of antioxidants and their impact on systemic oxidative stress

Dietary antioxidants play a major role in maintaining the homeostasis of the oxidative balance. They are believed to protect humans from disease and aging. Vitamin C (ascorbic acid), vitamin E (tocopherol), beta-carotene and other micronutrients such as carotenoids, polyphenols and selenium have been evaluated as antioxidant constituents in the human diet. This article addresses data provided from clinical trials, highlighting the clinical pharmacokinetics of vitamin C, vitamin E, beta-carotene, lycopene, lutein, quercetin, rutin, catechins and selenium. The bioavailability of vitamin C is dose-dependent. Saturation of transport occurs with dosages of 200-400 mg/day. Vitamin C is not protein-bound and is eliminated with an elimination half-life (t((1/2))) of 10 hours. In Western populations plasma vitamin C concentrations range from 54-91 micro mol/L. Serum alpha- and gamma-tocopherol range from 21 micro mol/L (North America) to 27 micro mol/L (Europe) and from 3.1 micro mol/L to 1.5 micro mol/L, respectively. alpha-Tocopherol is the most abundant tocopherol in human tissue. The bioavailability of all-rac-alpha-tocopherol is estimated to be 50% of R,R,R-alpha-tocopherol. The hepatic alpha-tocopherol transfer protein (alpha-TTP) together with the tocopherol-associated proteins (TAP) are responsbile for the endogenous accumulation of natural alpha-tocopherol. Elimination of alpha-tocopherol takes several days with a t((1/2)) of 81 and 73 hours for R,R,R-alpha-tocopherol and all-rac-alpha-tocopherol, respectively. The t((1/2)) of tocotrienols is short, ranging from 3.8-4.4 hours for gamma- and alpha-tocotrienol, respectively. gamma-Tocopherol is degraded to 2, 7, 8-trimethyl-2-(beta-carboxyl)-6-hyrdoxychroman by the liver prior to renal elimination. Blood serum carotenoids in Western populations range from 0.28-0.52 micro mol/L for beta-carotene, from 0.2-0.28 for lutein, and from 0.29-0.60 for lycopene. All-trans-carotenoids have a better bioavailability than the 9-cis-forms. Elimination of carotenoids takes several days with a t((1/2)) of 5-7 and 2-3 days for beta-carotene and lycopene, respectively. The bioconversion of beta-carotene to retinal is dose-dependent, and ranges between 27% and 2% for a 6 and 126mg dose, respectively. Several oxidised metabolites of carotenoids are known. Flavonols such as quercetin glycosides and rutin are predominantly absorbed as aglycones, bound to plasma proteins and subsequently conjugated to glucuronide, sulfate, and methyl moieties. The t((1/2)) ranges from 12-19 hours. The bioavailabillity of catechins is low and they are eliminated with a t((1/2)) of 2-4 hours. Catechins are degraded to several gamma-valerolactone derivatives and phase II conjugates have also been identified. Only limited clinical pharmacokinetic data for other polyphenols such as resveratrol have been reported to date.

Determination of selenium content in different types of seed oils by cathodic stripping potentiometry (CSP)

Seed oils are consumed worldwide; moreover, they are used in the alimentary, cosmetic, pharmaceutical, and chemical industries. Due to their diffusion, it is interesting to investigate the presence of important micronutrients such as selenium in seed oils. The aim of this work was to develop a rapid, precise, and sensitive cathodic stripping potentiometry (CSP) method to determine the concentration of selenium in different types of seed oils. Selenium was extracted from the oily matrix by concentrated hydrochloric acid treatment at 90 degrees C. The analysis was executed by applying an electrolysis potential of -150 mV for 60 s and a constant current of -30 microA. Under these conditions, detection limits of <0.5 ng g(-1) were obtained. The method reproducibility (expressed as total RSD %) spanned from 0.2 to 0.8%. Recoveries ranged from 92.1 to 97.5%, providing evidence that selenium quantification remained unaffected by the extraction procedure described. The results obtained with the proposed method were compared with those obtained via graphite furnace atomic absorption spectroscopy (GFAAS), a common method for determining selenium. The results of the two methods agreed within 93.5-107.7%. The mean amounts of selenium found were 313.0 +/- 2.0, 458.3 +/- 1.3, 224.6 +/- 0.9, 99.5 +/- 0.8, 332.2 +/- 0.5, 144.0 +/- 0.7, and 295.5 +/- 1.2 ng g(-1), respectively, in peanut, soybean, sunflower, rice, corn, grapestone, and seed oils.

Bioeffects of selenite on the growth of Spirulina platensis and its biotransformation

The bioeffects of selenium on the growth of Spirulina platensis and the selenium distribution were investigated. S. platensis was batch cultured in Zarrouk medium containing increasing concentrations of sodium selenite. The biotransformation characteristic of selenium was analysed by the determination of the detailed selenium distribution forms. At 35 degrees C, 315.2 microEm(-2) x s(-1), sodium selenite concentrations below 400 mg x l(-1) were found to stimulate algal growth, especially in the range of 0.5-40 mg x l(-1). However, above 500 mg x l(-1) sodium selenite was toxic to this alga with the toxicity being related to the sulfite level in the medium. S. platensis was found to resist higher selenite by reducing toxic Se(IV) to nonsoluble Se(0). Selenium was accumulated efficiently in S. platensis during cultivation with accumulated selenium increasing with selenite concentration in the medium. It was demonstrated that inorganic selenite could be transformed into organic forms through binding with protein, lipids and polysaccharides and other cell components. The organic selenium accounted for 85.1% of the total accumulated selenium and was comprised of 25.2% water-soluble protein-bound, 10.6% lipids-bound and 2.1% polysaccharides-bound selenium. Among the organic fractions lipid possessed the strongest ability to accumulate Se (6.47 mg x kg(-1)). The 14.9% inorganic selenium in S. platensis was composed of Se(IV) (13.7%) and Se(VI) (1.2%).

Element speciation definitions, analytical methodology, and some examples

This paper gives definitions related to element speciation and the reasons for the need for speciation. The problems focused on, involve sampling, sample preparation and storage, as well as changes in species information that occur during the use of various separation technologies. However, the potential and advantages of the separation methods in element speciation are also discussed. In addition, problems arising during element detection that are attributable to analytes or mobile-phase composition are outlined, as well as the pronounced advantages of detection by inductively coupled plasma-mass spectrometry (ICP-MS). The combination of the various separation systems with element- or molecule-specific detectors creates problems especially in element speciation. These difficulties are described along with recent developments for overcoming them or for improving their coupling efficiency. Finally, several elements for which the issue of speciation is important are discussed, with examples from some recent publications on arsenic, selenium and iodine speciation.

Effects of topical L-selenomethionine with topical and oral vitamin E on pigmentation and skin cancer induced by ultraviolet irradiation in Skh:2 hairless mice

BACKGROUND

The antioxidants selenium and vitamin E can be effective in reducing acute and chronic ultraviolet (UV)-induced skin damage.

OBJECTIVE

This study investigated whether topical L-selenomethionine with topical RRR-alpha-tocopherol (Eol) or oral RRR-alpha-tocopheryl acetate (Eac) can reduce the incidence of UV-induced skin damage more than treatment with each alone.

METHODS

Skh:2 hairless pigmented mice were treated with lotion vehicle, L-selenomethionine lotion, Eol lotion, oral Eac, L-selenomethionine plus Eol lotion, or L-selenomethionine lotion plus oral Eac and exposed to UVB. Skin pigmentation was scored, and the number of skin tumors per animal was counted weekly.

RESULTS

Mice treated with selenium and vitamin E had significantly less acute and chronic UV-induced skin damage.

CONCLUSION

Topical L-selenomethionine alone and combined with vitamin E gave the best protection against UV-induced blistering and pigmentation. In protecting against skin cancer, topical Eol and topical L-selenomethionine plus oral Eac were best. Significant synergy of L-selenomethionine with vitamin E was not observed.

Influence of sodium selenite on glycoprotein contents in normal and N-nitrosodiethylamine initiated and phenobarbital promoted rat liver tumors

Selenium in the form of sodium selenite is an essential micronutrient, that acts as an antioxidant/anticancer agent by its numerous macromolecules associated with them. This study emphasizes further evidence on its role as anticancer agent in experimental rats with N-nitrosodiethylamine (DEN) initiated (200 mg kg(-1) body weight) and phenobarbital (PB) promoted hepatoma. Serum, whole liver tissue (control animals, n=6), hepatoma and surrounding liver tissue samples from DEN-treated rats and rats supplemented with selenite (n=6) were collected. Total protein, albumin, globulin and albumin/globulin ratio were investigated. Hexose, hexosamine and sialic acid were also quantified. Animals treated with DEN resulted in significantly decreased levels of total protein, albumin and albumin/globulin ratio; on the other hand, globulin content was increased significantly when compared to control rats. We have also observed significant increased levels of hexose, hexosamine and sialic acid in serum, whole liver tissue (control), hepatoma and surrounding liver tissue of control and experimental animals. Supplementation of selenite (4 ppm) either before initiation, during initiation and/or during promotion stages alters the above biochemical changes significantly. Thus, supplementations of selenite in cancer bearing animals reduce the adverse changes that occur during cancer condition. However, the chemopreventive/chemotherapeutic effect of selenite is more pronounced when it was supplemented before and/or during initiation of cancer when compared to promotion stage. Our results emphasize the role of sodium selenite in cancer and strongly indicate its role as an essential micronutrient in cancer chemoprevention and therapy.

Spatial and temporal expression patterns of selenoprotein genes during embryogenesis in zebrafish

Selenium is important for embryogenesis in vertebrates but little is known about the expression patterns and biological functions of most selenoprotein genes. Taking advantage of the zebrafish model, systematic analysis of selenoprotein gene expression was performed by in situ hybridization on whole-mount embryos at different developmental stages. Twenty-one selenoprotein mRNAs were analyzed and all of them exhibited expression patterns restricted to specific tissues. Moreover, we demonstrated that highly similar selenoprotein paralogs were expressed within distinct territories. Therefore, tissue- and development-specific expression patterns provided new information for selenoproteins of unknown function.