Toxicity of seleno-L-methionine, seleno-DL-methionine, high selenium wheat, and selenized yeast to mallard ducklings

Environmental and occupational exposure of metals and female reproductive health

Untainted environment promotes health, but the last few decades experienced steep upsurge in environmental contaminants posing detrimental physiological impact. The responsible factors mainly include the exponential growth of human population, havoc rise in industrialization, poorly planned urbanization, and slapdash environment management. Environmental degradation can increase the likelihood of human exposure to heavy metals, resulting in health consequences such as reproductive problems. As a result, research into metal-induced causes of reproductive impairment at the genetic, epigenetic, and biochemical levels must be strengthened further. These metals impact upon the female reproduction at all strata of its regulation and functions, be it development, maturation, or endocrine functions, and are linked to an increase in the causes of infertility in women. Chronic exposures to the heavy metals may lead to breast cancer, endometriosis, endometrial cancer, menstrual disorders, and spontaneous abortions, as well as pre-term deliveries, stillbirths. For example, endometriosis, endometrial cancer, and spontaneous abortions are all caused by the metalloestrogen cadmium (Cd); lead (Pb) levels over a certain threshold can cause spontaneous abortion and have a teratogenic impact; toxic amounts of mercury (Hg) have an influence on the menstrual cycle, which can lead to infertility. Impact of environmental exposure to heavy metals on female fertility is therefore a well-known fact. Thus, the underlying mechanisms must be explained and periodically updated, given the growing evidence on the influence of increasing environmental heavy metal load on female fertility. The purpose of this review is to give a concise overview of how heavy metal affects female reproductive health.

Voyage of selenium from environment to life: Beneficial or toxic?

Selenium (Se), a naturally occurring metalloid, is an essential micronutrient for life as it is incorporated as selenocysteine in proteins. Although beneficial at low doses, Se is hazardous at high concentrations and poses a serious threat to various ecosystems. Due to this contrasting 'dual' nature, Se has garnered the attention of researchers wishing to unravel its puzzling properties. In this review, we describe the impact of selenium's journey from environment to diverse biological systems, with an emphasis on its chemical advantage. We describe the uneven distribution of Se and how this affects the bioavailability of this element, which, in turn, profoundly affects the habitat of a region. Once taken up, the subsequent incorporation of Se into proteins as selenocysteine and its antioxidant functions are detailed here. The causes of improved protein function due to the incorporation of redox-active Se atom (instead of S) are examined. Subsequently, the reasons for the deleterious effects of Se, which depend on its chemical form (organo-selenium or the inorganic forms) in different organisms are elaborated. Although Se is vital for the function of many antioxidant enzymes, how the pro-oxidant nature of Se can be potentially exploited in different therapies is highlighted. Furthermore, we succinctly explain how the presence of Se in biological systems offsets the toxic effects of heavy metal mercury. Finally, the different avenues of research that are fundamental to expand our understanding of selenium biology are suggested.

Adult dragonflies are indicators of environmental metallic elements

Adult dragonflies (Insecta; Odonata) are aerial predatory arthropods that occur globally except in the polar regions. However, we know of no research on adult dragonflies as potential indicators of metallic elements in the environment or metallic element concentrations and relative contribution patterns between sites, species, size classes, habitat types, and relation to possible pollution sources. There is also no information available about adult dragonflies and their responses to toxic metals. However, metallic elements are toxic in elevated concentrations to all organisms. We predict that adult dragonflies would be suitable indicators of elemental concentrations. We analysed 105 adult male dragonflies from 21 sites in South Africa for 33 metallic elements including Hg, As, Pb, Cr, Cu, Cd, Ni, Se, Al, and Au. The results indicated that all species of dragonflies, regardless of body size, are suitable indicators. Furthermore, different aquatic habitat types did not affect the metallic element concentrations at the scale of this study. Dragonflies collected near wastewater treatment plants showed concentrations of certain elements such as Au higher than from elsewhere. Elements such as As and Pb were found at elevated concentrations (relative to the other sites) in dragonflies collected near mines. Dragonflies from sampling sites near potential pollution sources, but had seemingly isolated water sources, showed lower metallic element concentrations when compared with other sites. We conclude that adult dragonflies would be good indicators of environmental metallic elements.

Organic selenium in animal nutrition – utilisation, metabolism, storage and comparison with other selenium sources

The importance of selenium as a key component of antioxidant systems in animals is well recognised due to much research about this mineral in many species. Selenium is required as part of the antioxidant enzyme structure and plays a major role in various protective systems in animal physiology, including immunity, cellular stability and DNA protection. The following review is the first in a series of three which details the importance of selenium in animal nutrition, and how the chemically organic form, which is akin to the form of the mineral in natural feed materials, can provide increased benefits in utilisation, storage and metabolism compared to inorganic sources.

Evaluation of the toxicity of selenium from hydroponically produced selenium-enriched kale sprout in laying hens

Hydroponically produced Se-enriched kale sprouts (HPSeKS) are studied for their use as an alternative dietary Se supplement for poultry. The study experimented with different levels and sources of Se to determine toxicity and how the toxicity may affect productive performance, Se concentration in egg and tissues, and physiological responses of laying hens. One-hundred and twenty hens, 59 weeks of age, were divided into 5 groups. Each group consisted of 4 replicates and each replicate had 6 birds according to a 2 × 2 + 1 Augmented Factorial Experiment in a Completely Randomized Design. The experiment was conducted over a 4 week period, and 5 dietary treatments (T) were used: T1 basal diet, T2 and T3 basal diet plus 5 and 10mg Se/kg from sodium selenite (SS), T4 and T5 basal diet plus 5 and 10mg Se/kg from HPSeKS, respectively. The results make clear that Se from HPSeKS, at 5-10mg/kg, did not affect (P>0.05) feed intake and egg production; however, Se bioavailability decreased (P<0.05). Egg, tissue and plasma Se concentrations, and GSH-Px activity in red blood cells increased (P<0.05) compared to those in T1. Final body weight, feed intake, Se bioavailability, concentration of Se in breast muscle and plasma of hens fed Se from SS were lower (P<0.05) than those of hens fed Se from HPSeKS. The findings demonstrate that dietary Se from HPSeKS at 5-10mg/kg is not considered a toxic level for laying hens. The toxicity of Se from HPSeKS was less than the toxicity of Se from SS.

Fish toxicity testing with selenomethionine spiked feed--what's the real question being asked?

The US Environmental Protection Agency and several U.S. states and Canadian provinces are currently developing national water quality criteria for selenium that are based in part on toxicity tests performed by feeding freshwater fish a selenomethionine-spiked diet. Using only selenomethionine to examine the toxicity of selenium is based in part on the limitations of the analytical chemistry methods commonly used in the 1990s and 2000s to speciate selenium in freshwater biota. While these methods provided a good starting point, recent improvements in analytical chemistry methodology have demonstrated that selenium speciation in biota is far more complex than originally thought. Here, we review the recent literature that suggests that there are numerous additional selenium species present in freshwater food chains and that the toxicities of these other selenium species, both individually and in combination, have not been evaluated in freshwater fishes. Evidence from studies on birds and mammals suggests that the other selenium forms differ in their metabolic pathways and toxicity from selenomethionine. Therefore, we conclude that toxicity testing using selenomethionine-spiked feed is only partly addressing the question "what is the toxicity of selenium to freshwater fishes?" and that using the results of these experiments to derive freshwater quality criteria may lead to biased water quality criteria. We also discuss additional studies that are needed in order to derive a more ecologically relevant freshwater quality criterion for selenium.

Dietary selenomethionine exposure induces physical malformations and decreases growth and survival to metamorphosis in an amphibian (Hyla chrysoscelis)

Selenium (Se) is an essential micronutrient with a narrow therapeutic concentration range. The relative toxicity of Se increases as it is biotransformed into organic compounds, primarily selenomethionine (SeMet), within the aquatic food chain. Effects of aquatic Se contamination are well quantified for many freshwater fish and aquatic bird species, but impacts on amphibians are not well known. This study investigated the responses of larval Cope's gray tree frogs (Hyla chrysoscelis) fed a diet enriched with one of two concentrations of SeMet (50.1 and 489.9 μg Se g(-1) dw [low and high groups, respectively]) by way of a food-limited (ration) or ad libitum (ad lib) feeding regimen. The high dose caused 100 % mortality during the larval period independent of resource provision levels. Regardless of feeding regimen, the low dose decreased larval survival and successful metamorphosis relative to control treatments. The low dose also induced rear limb deformities in ≤73 % of individuals initiating metamorphosis. Providing low-dose food by way of a rationed feeding regimen decreased observed toxicity, likely because of decreased dietary exposure to SeMet relative to the low ad lib treatment. Individuals from the low ration treatment had decreased wet mass at initiation and completion of metamorphic climax (Gosner stages 42 through 46) compared with those from the control ad lib treatment, indicating that resource limitation combined with Se exposure might negatively affect energy stores after metamorphosis. However, lipid content analyses of recently metamorphosed individuals did not reveal any influence of treatment or resource provision on energy stored as lipids. The mean tissue Se concentration of individuals that received the low dose and completed metamorphosis was significantly greater than that of control ad lib or ration individuals at the same developmental stage. This study demonstrates that larval exposure to dietary SeMet can decrease growth and survival and induce deformities in a developing amphibian. Furthermore, retention of Se body burdens through metamorphosis suggests that surviving individuals can transport Se accumulated from contaminated aquatic environments into terrestrial food webs.

Interactions between methylmercury and selenomethionine injected into mallard eggs

Methylmercury chloride and seleno-L-methionine were injected separately or in combinations into mallard eggs (Anas platyrhynchos), and embryo mortality and teratogenic effects (deformities) were modeled using a logistic regression model. Methylmercury was injected at doses that resulted in concentrations of 0, 0.2, 0.4, 0.8, and 1.6 µg/g Hg in the egg on a wet weight basis and selenomethionine at doses that resulted in concentrations of 0, 0.1, 0.2, 0.4, and 0.6 µg/g Se in the egg, also on a wet weight basis. When selenomethionine and methylmercury were injected separately, hatching probability decreased in both cases. However, when methylmercury was injected at 1.6 µg/g in combination with selenomethionine at 0.2 µg/g, the presence of the methylmercury resulted in less embryo mortality than had been seen with 0.2 µg/g Se by itself, but it increased the number of deformed embryos and hatchlings. Selenomethionine appeared to be more embryotoxic than equivalent doses of methylmercury when injected into eggs, and both injected methylmercury and selenomethionine were more toxic to mallard embryos than when deposited naturally in the egg by the mother. The underlying mechanisms behind the interactions between methylmercury and selenomethionine and why methylmercury appeared to improve hatching probability of Se-dosed eggs yet increased deformities when the two compounds were combined are unclear. These findings warrant further studies to understand these mechanisms in both laboratory and field settings.

Effect of different selemethionine forms and levels on performance of breeder hens and se distribution of tissue and egg inclusion

A 2×2 factorial arrangement of treatments in randomized design was conducted to investigate the effect of different selenomethionine (SM) sources and levels on the productive performance of breeder hens and the Se distribution in the inclusion of eggs and serum and tissues of breeder hens and its offspring. A total of 480 Ling-Nan-Huang breeder hens, 48 weeks of age, were allocated to four treatments, each of which included three replicates of 40 hens. Pretreatment period was 2 weeks, and the experiment lasted 8 weeks. Two SM forms of DL-SM and L-SM were supplemented at 0.15 or 0.30 mg Se/kg into the basal diet. Results showed that the Se level of 0.15 mg/kg supplemented in the diet, compared to 0.30 mg/kg, significantly elevated the percentage of egg production (p<0.05), hatchability (p<0.01), and birthrate (p<0.01), whereas the Se level of 0.30 mg/kg led to a higher Se content in egg contents, serum, and all tissues (p<0.01). In addition, the form of DL-SM showed a significant increase in Se content of egg inclusion (p<0.01), serum (p<0.01), and all tissues (p<0.01, except breeder hens' pancreas and its offspring's liver and breast muscle). The birthrate and yolk Se content were markedly influenced by the interaction between Se source and Se level (p<0.01). The above results suggested that DL-SM, compared to L-SM, had a similar equal effect on the performance of breeder hens, but DL-SM was superior to L-SM with respect to selenium distribution in egg inclusion, serum, and tissues.

Comparison of different forms of dietary selenium supplementation on growth performance, meat quality, selenium deposition, and antioxidant property in broilers

This study was conducted to investigate the effects of different sources of dietary selenium (Se) supplementation on growth performance, meat quality, Se deposition, and antioxidant property in broilers. A total of 600 one-day-old Ross 308 broilers with an average body weight (BW) of 44.30 ± 0.49 g were randomly allotted to three treatments, each of which included five replicates of 40 birds. These three groups received the same basal diet containing 0.04 mg Se/kg, supplemented with 0.15 mg Se/kg from sodium selenite (SS) or from L-selenomethionine (L-Se-methionine (Met)) or from D-selenomethionine (D-Se-Met). The experiment lasted 42 days. Both Se source and time significantly influenced (p < 0.01) drip loss of breast muscle. Supplementation with L-Se-Met and D-Se-Met were more effective (p < 0.05) in decreasing drip loss than SS. Besides, the pH value of breast muscle was also significantly influenced (p < 0.05) by time. The SS-supplemented diet increased more (p < 0.05) liver, kidney, and pancreas glutathione peroxidase (GSH-Px) activities than the D-Se-Met-supplemented diet. In addition, L-Se-Met increased more (p < 0.01) liver and pancreas GSH-Px activities than D-Se-Met. The antioxidant status was greatly improved in broilers of L-Se-Met-treated group in comparison with the SS-treated group and was illuminated by the increased glutathione (GSH) concentration in serum, liver, and breast muscle (p < 0.05); superoxide dismutase (SOD) activity in liver (p < 0.01); total antioxidant capability (T-AOC) in kidney, pancreas, and breast muscle (p < 0.05) and decreased malondialdehyde (MDA) concentration in kidney and breast muscle (p < 0.05) of broilers. Besides, supplementation with D-Se-Met was more effective (p < 0.01) in increasing serum GSH concentration and decreasing breast muscle MDA concentration than SS. L-Selenomethionine supplementation significantly increased GSH concentration in liver and breast muscle (p < 0.05); SOD activity in liver (p < 0.01); and T-AOC in liver, pancreas, and breast muscle (p < 0.05) of broilers, compared with broilers fed D-Se-Met diet. The addition of L-Se-Met and D-Se-Met increased (p < 0.01) Se concentration in serum and different organs studied of broilers in comparision with broilers fed SS diet. Therefore, dietary L-Se-Met and D-Se-Met supplementation could improve antioxidant capability and Se deposition in serum and tissues and reduce drip loss of breast muscle in broilers compared with SS. Besides, L-Se-Met is more effective than D-Se-Met in improving antioxidant status in broilers.

Examining the effects of metal mining mixtures on fathead minnow (Pimephales promelas) using field-based multi-trophic artificial streams

This study illustrates the use of a mesocosm approach for assessing the independent effects of three treated metal mine effluents (MME) discharging into a common receiving environment and regulated under the same regulation. A field-based, multi-trophic artificial stream study was conducted in August 2008 to assess the effects of three metal mining effluents on fathead minnow (Pimephales promelas) in a 21-day reproduction bioassay. The nature of the approach allowed for assessment of both dietary and waterborne exposure pathways. Elements (e.g. Se, Co, Cl, Cu, Fe) were analyzed in several media (water, sediments) and tissues (biofilm, Chironomus dilutus, female fathead minnow (FHM) body, ovary, liver, gills). Significant increases in metal and micronutrient concentrations were observed in the water and biofilm tissues in all MME treatments [20% surface water effluent (SWE), 30% mine water effluent (MWE), and 45% process water effluent (PWE)], compared to reference. However, copper was the only element to significantly increase in the sediments when exposed to PWE. Co and Ni increased significantly in C. dilutus tissues in SWE (1.4- and 1.5-fold, respectively), Cu and Se also increased in chironomid tissues in PWE (5.2- and 3.3-fold, respectively); however, no significant increases in metals or micronutrients occurred in chironomid tissues when exposed to MWE compared to reference. There were no significant increases in metal concentrations in female FHM tissues (body, liver, gonads, gills) in any of the treatments suggesting that metals were either not bioavailable, lost from the females via the eggs, or naturally regulated through homeostatic mechanisms. Cumulative number of eggs per female per day increased significantly (∼127%) after exposure to SWE and decreased significantly (∼33%) after exposure to PWE when compared to reference. Mean total number of days to hatch was reduced in PWE compared to reference. This study shows the importance of isolating treatment streams in cumulative discharge environments to assess aquatic effects due to the different nature of the effluents.

Nutritional and medicinal aspects of D-amino acids

This paper reviews and interprets a method for determining the nutritional value of D-amino acids, D-peptides, and amino acid derivatives using a growth assay in mice fed a synthetic all-amino acid diet. A large number of experiments were carried out in which a molar equivalent of the test compound replaced a nutritionally essential amino acid such as L-lysine (L-Lys), L-methionine (L-Met), L-phenylalanine (L-Phe), and L-tryptophan (L-Trp) as well as the semi-essential amino acids L-cysteine (L-Cys) and L-tyrosine (L-Tyr). The results show wide-ranging variations in the biological utilization of test substances. The method is generally applicable to the determination of the biological utilization and safety of any amino acid derivative as a potential nutritional source of the corresponding L-amino acid. Because the organism is forced to use the D-amino acid or amino acid derivative as the sole source of the essential or semi-essential amino acid being replaced, and because a free amino acid diet allows better control of composition, the use of all-amino-acid diets for such determinations may be preferable to protein-based diets. Also covered are brief summaries of the widely scattered literature on dietary and pharmacological aspects of 27 individual D-amino acids, D-peptides, and isomeric amino acid derivatives and suggested research needs in each of these areas. The described results provide a valuable record and resource for further progress on the multifaceted aspects of D-amino acids in food and biological samples.

Food-chain selenium and human health: spotlight on speciation

There is a growing appreciation that it is not just the total intake of dietary Se that is important to health but that the species of Se ingested may also be important. The present review attempts to catalogue what is known about Se species in foods and supplements and the health effects in which they are implicated. The biosynthetic pathways involved in Se assimilation by plants and the way in which Se species are metabolised in animals are presented in order to give an insight into the species likely to be present in plant and animal foods. Known data on the species of Se in the food chain and in food supplements are tabulated along with their concentrations and the analytical methodology used. The latter is important, since identification that is only based on retention-time matching with authentic standards must be considered as tentative: for evidence of structural confirmation, fragmentation of the molecular ion in addition to MS data is required. Bioavailability, as normally defined, is higher for organic Se species. Health effects, both beneficial and toxic, thought to be associated with specific Se species are described. Potent anti-tumour effects have been attributed to the low-molecular-weight species,Se-methyl-selenocysteine and its γ-glutamyl-derivative, found in a number of edible plants of theAlliumandBrassicafamilies. There remain considerable gaps in our knowledge of the forms of Se that naturally occur in foods. Without adequate knowledge of Se speciation, false conclusions may be drawn when assessing Se requirements for optimal health.

Developmental responses of a terrestrial insect detritivore, Megaselia scalaris (Loew) to four selenium species

Megaselia scalaris (Loew) (Diptera: Phoridae) is an important and ubiquitous terrestrial detritivore that consumes both animal and plant material. Because both plants and animals convert selenium pollutants into various forms, the relative toxicities of ecologically relevant concentrations of sodium selenate, sodium selenite, seleno-L-methionine, and Se-(methyl) selenocysteine hydrochloride to larvae were assessed in diet bioassays. In addition, ovipositional preferences of adults and developmental effects on the eggs and larvae were measured. With chronic exposure selenocysteine was the most toxic of the selenium species to the larvae (LC50: 83 microg/g wet weight), followed by seleno-L-methionine (LC50: 130 microg/g), selenate (LC50: 258 microg/g), and selenite (LC50: 392 microg/g). Ovipositing females did not discriminate between the highest treatment concentrations of any of the pollutants as compared to the controls, indicating a lack of avoidance behavior. Larval development time was significantly increased with exposure to selenate at 100 microg/g wet weight and above, selenite at 300 microg/g and above, and at 50 microg/g and 25 microg/g and above for seleno-L-methionine and selenocysteine respectively. Pupal development was not affected by any of the selenium treatments. Significant differences between male and female adult eclosion times were observed, with females eclosing later than males as selenium concentrations increased. Significant decreases in larval survival relative to controls occurred at the lowest treatment tested (100 microg/g) for both selenate and selenite and at 100 microg/g for seleno-L-methionine, and 50 microg/g for selenocysteine. The population level implications of lack of avoidance of contaminated food, and the effects of increased development times, reduced survivorship, and non-synchronized male and female emergence are discussed.

Review of selenium toxicity in the aquatic food chain

In many environmental contaminant situations selenium has become the primary element of concern because of its bioaccumulative nature in food webs. Initial concerns about selenium were related to fish kills at Belews Lake, NC, Martin Lake, TX, and Kesterson Reservoir, CA, and to bird deformities at Kesterson Reservoir. Additional concerns were identified under the National Irrigation Water Quality Program at Salton Sea, CA, Kendrick, WY, Stewart Lake, UT, and Grand Valley and Uncompahgre Valley, CO. Recent studies have raised concerns about selenium impacts on aquatic resources in Southeastern Idaho and British Columbia. The growing discomfort among the scientific community with a waterborne criterion has lead the US Environment Protection Agency to consider a tissue-based criterion for selenium. Some aquatic ecosystems have been slow to recover from selenium contamination episodes. In recent years, non-governmental researchers have been proposing relatively high selenium thresholds in diet and tissue relative to those proposed by governmental researchers. This difference in opinions is due in part to the selection of datasets and caveats in selecting scientific literature. In spite of the growing selenium literature, there are needs for additional research on neglected organisms. This review also discusses the interaction of selenium with other elements, inconsistent effects of selenium on survival and growth of fish, and differences in depuration rates and sensitivity among species.

The nutritional significance, metabolism and toxicology of selenomethionine

SeMet is a naturally occurring toxic amino acid but at the same time represents the major nutritional source of selenium for higher animals and humans. The ability of SeMet to be incorporated into the body proteins in place of Met furthermore provides a means of reversible Se storage in organs and tissues. This property is not shared by any other naturally occurring selenoamino acid and thus could be associated with a specific physiological function of SeMet. Since higher animals cannot synthesize SeMet, yet from it all needed forms of Se are produced, SeMet meets the criteria of an essential amino acid. Accordingly, SeMet, or enriched food sources thereof, are appropriate forms of Se for human nutritional Se supplementation. However, while SeMet or Se yeast are already widely used in over-the-counter nutritional supplements, infant formulas and parenteral feeding mixtures still contain Se in the form of sodium selenate or sodium selenite, even though these are not the normal nutritional forms of Se. In animal nutrition, these inorganic selenium salts are increasingly replaced by food sources of SeMet such as Se yeast. Synthetic SeMet could also be employed as a feed additive, but its regulatory status is as yet undetermined. The optimal nutritional levels of SeMet for different animal species still need to be determined. The expectation is that lower additions to feedstock of equivalent levels of SeMet will suffice to achieve adequacy than currently approved maximum levels of Se in the form of inorganic Se salts.

Role of selenium toxicity and oxidative stress in aquatic birds

Adverse effects of selenium (Se) in wild aquatic birds have been documented as a consequence of pollution of the aquatic environment by subsurface agricultural drainwater and other sources. These effects include mortality, impaired reproduction with teratogenesis, reduced growth, histopathological lesions and alterations in hepatic glutathione metabolism. A review is provided, relating adverse biological effects of Se in aquatic birds to altered glutathione metabolism and oxidative stress. Laboratory studies, mainly with an organic form of Se, selenomethionine, have revealed oxidative stress in different stages of the mallard (Anas platyrhynchos) life cycle. As dietary and tissue concentrations of Se increase, increases in plasma and hepatic GSH peroxidase activities occur, followed by dose-dependent increases in the ratio of hepatic oxidized to reduced glutathione (GSSG:GSH) and ultimately hepatic lipid peroxidation measured as an increase in thiobarbituric acid reactive substances (TBARS). One or more of these oxidative effects were associated with teratogenesis (4.6 ppm wet weight Se in eggs), reduced growth in ducklings (15 ppm Se in liver), diminished immune function (5 ppm Se in liver) and histopathological lesions (29 ppm Se in liver) in adults. Manifestations of Se-related effects on glutathione metabolism were also apparent in field studies in seven species of aquatic birds. Reduced growth and possibly immune function but increased liver:body weight and hepatic GSSG:GSH ratios were apparent in american avocet (Recurvirostra americana) hatchlings from eggs containing 9 ppm Se. In black-necked stilts (Himantopus mexicanus), which contained somewhat lower Se concentrations, a decrease in hepatic GSH was apparent with few other effects. In adult American coots (Fulica americana), signs of Se toxicosis included emaciation, abnormal feather loss and histopathological lesions. Mean liver concentrations of 28 ppm Se (ww) in the coots were associated with elevated hepatic GSH peroxidase, depletion of hepatic protein bound thiols and total thiols, but a small increase in GSH. Diving ducks in the San Francisco Bay area exhibited a positive correlation between hepatic Se concentration and GSH peroxidase activity (r=0.63, P<0.05), but a negative correlation between hepatic Se and GSH concentration (r=-0.740, P<0.05). In willets (Catoptrophorus semipalmatus) from the San Diego area, positive correlations occurred between hepatic Se concentration and GSSG (r=0.70, P<0.001), GSSG:GSH ratio, and TBARS. In emperor geese (Chen canagica) from western Alaska, blood levels of up to 9.4 ppm occurred and were associated with increased plasma GSH peroxidase activity (r=0.62, P<0.001), but with decreased plasma GSSG reductase activity. When evaluating Se toxicity, interactive nutritional factors, including other elements and dietary protein, should also be taken into consideration. Further studies are needed to examine the relationship between different forms of environmentally occurring selenium, arsenic and mercury on reproduction, hepatotoxicity and immune function of aquatic birds. Further selenium nutritional interaction studies may also help to illucidate the mechanism of selenium induced teratogenesis, by optimizing GSH and other antioxidant defense mechanisms in a manner that would stabilize or raise the cell's threshold for susceptibility to toxic attack from excess selenium. It is concluded that Se-related manifestations of oxidative stress may serve as useful bioindicators of Se exposure and toxicity in wild aquatic birds.

Selenium toxicity: cause and effects in aquatic birds

There are several manners in which selenium may express its toxicity: (1) an important mechanism appears to involve the formation of CH(3)Se(minus sign) which either enters a redox cycle and generates superoxide and oxidative stress, or forms free radicals that bind to and inhibit important enzymes and proteins. (2) Excess selenium as selenocysteine results in inhibition of selenium methylation metabolism. As a consequence, concentrations of hydrogen selenide, an intermediate metabolite, accumulate in animals and are hepatotoxic, possibly causing other selenium-related adverse effects. (3) It is also possible that the presence of excess selenium analogs of sulfur-containing enzymes and structural proteins play a role in avian teratogenesis. L-selenomethionine is the most likely major dietary form of selenium encountered by aquatic birds, with lesser amounts of L-selenocysteine ingested from aquatic animal foods. The literature is suggestive that L-selenomethionine is not any more toxic to adult birds than other animals. L-Selenomethionine accumulates in tissue protein of adult birds and in the protein of egg white as would be expected to occur in animals. There is no suggestion from the literature that the levels of L-selenomethionine that would be expected to accumulate in eggs in the absence of environmental concentration of selenium pose harm to the developing embryo. For several species of aquatic birds, levels of Se as selenomethionine in the egg above 3 ppm on a wet weight basis result in reduced hatchability and deformed embryos. The toxicity of L-selenomethionine injected directly into eggs is greater than that found from the entry of L-selenomethionine into the egg from the normal adult diet. This suggests that there is unusual if not abnormal metabolism of L-selenomethionine in the embryo not seen when L-selenomethionine is present in egg white protein where it likely serves as a source of selenium for glutathione peroxidase synthesis in the developing aquatic chick.

Capillary gas chromatography inductively coupled plasma mass spectrometry (CGC-ICPMS) for the enantiomeric analysis of D,L-selenomethionine in food supplements and urine

Capillary gas chromatography inductively coupled plasma mass spectrometry (CGC-ICPMS) was applied to the determination of D- and L-selenomethionine in food supplements and in urine. Derivatization was performed with ethylchloroformate (ECF) offering the advantage that the reaction can be carried out in aqueous medium i.e. urine. The derivatives were separated on the chiral stationary phase (CSP) Chiralsil-L-Val. The method was validated with D- and L-seleno-ethionine as internal standard (IS) and the linearity for a seven point calibration from 12.5 pg to 2.5 ng per enantiomer was excellent (R(2) 0.9997). Repeatability of injection (n=3) was <1.8%. The limit of detection (LOD) and quantification (LOQ) were 4 and 12 pg, respectively. Food supplements presently on the market contain L-selenomethionine for at least 90%. Repeatability of the whole procedure (n=6) was tested on one L-selenomethionine formulation and was 3.8 (R.S.D.%). Data for urine samples after a daily intake of L-selenomethionine or the racemate D,L-selenomethionine corresponding to 100 microg selenium indicate that the D-enantiomer is not metabolized.

Effect of moisture and casein on demethylation of trimethylselenonium in soil

Trimethylselenonium ion (TMSe+) is a major urinary selenium (Se) metabolite of animals. The effect of soil moisture and casein on the demethylation of TMSe+ were examined in three California soils [Tulare Basin (TL), Losthill (LH) and Five Points (FP) upland areas] treated with 20 microg/g TMSe+. Results showed that soil moisture positively affected the demethylation of TMSe+ to volatile dimethylselenide (DMSe). In the non-saline TL and FP soils, the highest demethylation rates were 0.169-0.454, 0.646-2.71, and 3.15-6.01 microg/g per day from a 10, 20, and 100% moisture soil, respectively. During 51 days of the experiment, approximately 75.4-80.2% of added TMSe+ was demethylated to volatile DMSe. In contrast, in a saline LH soil, the demethylation rate was < 0.2 microg/g per day, and only 7% of the added TMSe+ was demethylated to volatile DMSe. Addition of casein stimulated the demethylation of TMSe+ in a 10% moisture TL soil. Dissolved DMSe, dimethylselenoxide (DMSeO) and TMSe+, and adsorbed TMSe+ were found in the three experimental soils. Concentrations of dissolved and adsorbed TMSe+ were much higher in the LH soil than in the TL and FP soils. This study showed that demethylation of TMSe+ dominates in the FP and TL soils, and adsorption of TMSe+ is a more important process in the LH soil.

Selenomethionine: a review of its nutritional significance, metabolism and toxicity

Although the need for selenium in human and animal nutrition is well recognized, the question concerning the proper form of selenium for supplemental use is still being debated. Ideally, selenium should be supplemented in the form in which it occurs naturally in foods. Because the L-isomer of selenomethionine (Se-met) is a major natural food-form of selenium, synthetic L-Se-met or enriched food sources thereof such as selenium yeast are appropriate supplemental forms of Se for humans; for animals, DL-Se-met is acceptable. Ingested Se-met is either metabolized directly to reactive forms of selenium or stored in place of methionine in body proteins. Se-met metabolism is closely linked to protein turnover. At constant intakes in the nutritional range, tissue Se levels increase until a steady state is established, preventing the build-up to toxic levels.

Chemistry, nutrition, and microbiology of D-amino acids

Exposure of food proteins to certain processing conditions induces two major chemical changes: racemization of all L-amino acids to D-isomers and concurrent formation of cross-linked amino acids such as lysinoalanine. Racemization of L-amino acids residues to their D-isomers in food and other proteins is pH-, time-, and temperature-dependent. Although racemization rates of the 18 different L-amino acid residues in a protein vary, the relative rates in different proteins are similar. The diet contains both processing-induced and naturally formed D-amino acids. The latter include those found in microorganisms, plants, and marine invertebrates. Racemization impairs digestibility and nutritional quality. The nutritional utilization of different D-amino acids varies widely in animals and humans. In addition, some D-amino acids may be both beneficial and deleterious. Thus, although D-phenylalanine in an all-amino-acid diet is utilized as a nutritional source of L-phenylalanine, high concentrations of D-tyrosine in such diets inhibit the growth of mice. Both D-serine and lysinoalanine induce histological changes in the rat kidney. The wide variation in the utilization of D-amino acids is illustrated by the fact that whereas D-methionine is largely utilized as a nutritional source of the L-isomer, D-lysine is totally devoid of any nutritional value. Similarly, although L-cysteine has a sparing effect on L-methionine when fed to mice, D-cysteine does not. Because D-amino acids are consumed by animals and humans as part of their normal diets, a need exists to develop a better understanding of their roles in nutrition, food safety, microbiology, physiology, and medicine. To contribute to this effort, this multidiscipline-oriented overview surveys our present knowledge of the chemistry, nutrition, safety, microbiology, and pharmacology of D-amino acids. Also covered are the origin and distribution of D-amino acids in the food chain and in body fluids and tissues and recommendations for future research in each of these areas. Understanding of the integrated, beneficial effects of D-amino acids against cancer, schizophrenia, and infection, and overlapping aspects of the formation, occurrence, and biological functions of D-amino should lead to better foods and improved human health.

Determination of inorganic ions in food and beverages by capillary electrophoresis

A review of the applications of electrophoresis to the determination of inorganic anions (sulphate, sulphite, phosphate, nitrate, nitrite and halides) and inorganic cations (ammonium, alkali and alkaline metals and trace elements) in food and beverages is presented.

High-performance liquid chromatography of selenoamino acids and organo selenium compounds. Speciation by inductively coupled plasma mass spectrometry

As part of an ongoing study to identify selenium compounds with cancer chemopreventive activity, extracts of selenium-enriched samples were analyzed by HPLC-inductively coupled plasma (ICP)-MS. Ion-exchange, ion pair and derivatization methods for reversed-phase HPLC were considered and advantages and disadvantages for each compared. Anion exchange allows separation of selenite and selenate, but otherwise provides poor separation. Pre-column derivatization and reversed-phase chromatography provides separation of compounds with terminal amine functionalities, but many other species elute in the void volume. The ion pair method gave optimal separation and was compatible with standard ICP-MS operating conditions.

Kinetics of selenium incorporation into tissues of female mallard ducks

Selenium is essential for both mammalian and avian species, although its metabolism in birds has been less thoroughly studied. Little information has been available on the kinetics of selenium in birds, especially as it relates to the teratogenicity seen in waterfowl consuming excessive amounts. This study describes the pharmacokinetics of small amounts of 75Se as selenious acid injected into female mallard ducks. Labeled selenium was injected into a wing vein of restrained animals and tissues taken at five different time points up to 24 h post-injection. Selenium levels as percent of injected dose were determined in liver, kidney, heart, lung, adrenals, thyroid, spleen, pancreas, ovaries, intestine, muscle and plasma. Estimates of kinetic parameters (uptake and elimination rates, time of maximum concentration and maximum concentration) were obtained with a non-linear kinetics computer program (PCNONLIN, SCI Software, Lexington, KY). Results showed four basic patterns of distribution, uptake and elimination. Visceral tissues exhibited a triphasic pattern with a rapid rise, a decline followed by a distinctive increase in levels between the last two time points. Brain uptake was continuous over the 24 h. Plasma rose rapidly and then declined to a constant level. The ovaries as a tissue of interest relating to the teratogenic effects of selenium showed the greatest relative increase at 24 h, suggesting kinetic mechanisms consistent with a pathway that might lead to accumulation of toxic levels and teratogenic effects during embryo development.

Experimentally induced selenosis of adult mallard ducks: clinical signs, lesions, and toxicology

Selenosis is thought to be a significant problem among waterfowl populations in selenium-contaminated wetlands in the western United States. Chemical analysis of avian tissues is currently the principal basis for diagnosis. The purpose of these two 150-day studies was to establish whether morphological criteria for selenosis could be developed to supplement chemical analysis. Forty-eight flightling male mallard ducks were fed either a proprietary waterfowl ration (< 1 ppm selenium) or the same ration amended to contain 10, 25, and 60 ppm selenium supplied as seleno-L-methionine (n = 12/group). In a separate study, 12 birds fed twice daily were offered either a proprietary ration or a selenium-supplemented ration (120 microg/g) for one of two daily feedings. Selenium in whole blood increased from baseline concentrations (< 0.4 microg/ml) to means of 4.5, 8.9, and 16.0 microg/ml in the 10-, 25-, and 60-ppm groups, respectively. All birds in the 60-ppm-dose group rapidly lost weight and were killed (11/12) or died (1/12) between 22 and 50 days of dietary exposure. In addition to emaciation, six of 12 birds (50%) fed the 60-microg/g diet developed mild to moderate generalized hepatopathy with single-cell necrosis, karyomegaly of hepatocytes, hyperplastic bile duct epithelium, and/or iron accumulation in Kupffer cells. The principal lesions in birds exposed to other dietary concentrations of selenium involved integumentary structures containing hard keratin. Gross lesions developed after 76 days of dietary exposure and consisted of bilaterally symmetrical alopecia of the scalp and dorsal cervical midline, broken or lost digital nails, and necrosis of the tip of the beak (maxillary nail). One or more of these three lesions were present in 0/12 birds (0%) fed 10 ppm selenium, 5/12 birds (42%) fed 25 ppm selenium, and 4/9 (44%) birds fed a split-feed diet containing 120 ppm selenium. Controls were unaffected. Histologic lesions in digital and maxillary nails consisted of single-cell to full-thickness necrosis of keratinocytes and multifocal parakeratosis in stratum corneum. Histologic lesions in alopecic skin (necrosis of the epidermal collar, inflammation of the feather pulp, and follicular keratosis) were mild. Some birds with alopecia had no detectable lesions in feather follicles from affected areas of skin. The highest tissue concentrations of selenium were in liver, kidney, and feathers, respectively. Mean hepatic tissue concentrations were 14.5 microg/g (10 ppm group), 29.6 microg/g (25 ppm group), 60.6 microg/g (60 ppm group), 13.0 microg/g (120 ppm split-feed group), and 2.0 microg/g (controls). Integumentary and hepatic lesions may be of value in corroborating a diagnosis of selenosis based on chemical analysis of tissues from naturally intoxicated waterfowl. Some birds with fatal selenosis may have no morphologic lesions other than emaciation.

Comparison of the effects of seleno-L-methionine, seleno-DL-methionine, and selenized yeast on reproduction of mallards

The toxicities of seleno-L-methionine, seleno-DL-methionine, and selenized yeast were compared. Ten pairs of mallards were fed a control diet and 15 pairs were fed diets containing 10 ppm selenium as seleno-DL-methionine, seleno-L-methionine, or selenized yeast. Hatching of fertile eggs was significantly lower for females fed 10 ppm selenium as seleno-DL-methionine (7.6%) and seleno-L-methionine (6.4%) than for controls (41.3%). Survival of ducklings was lower when their parents had been fed 10 ppm selenium as seleno-L-methionine (20.0%) than for controls (98.4%). The number of 6-day-old ducklings produced per female was significantly lower for mallards fed 10 ppm selenium as seleno-DL-methionine (0.47) or selenized yeast (2.67) than for controls (6.10), and was significantly lower for mallards fed seleno-L-methionine (0.13) than for mallards fed selenized yeast. The eighth eggs of females fed the DL or L forms of selenomethionine contained means of 9.2 and 8.9 ppm selenium, wet weight; these means were higher than the mean (6.6 ppm) for females fed selenized yeast. Among embryos that died at 7 days of age or older, the percentage of embryos that were deformed was 1.3% for controls, 24.6% for seleno-DL-methionine, 28.2% for seleno-L-methionine, and 11.0% for selenized yeast. The results suggested that seleno-DL-methionine and seleno-L-methionine were of similar toxicity and were both more toxic than selenium from selenized yeast.