Urinary selenium and iodine during pregnancy and lactation.

The New Zealand environment is low in selenium and iodine, and is therefore ideally suited for the study of these anionic trace elements. The aim of this study was to determine urinary excretion of selenium and iodine during pregnancy and postpartum as part of an investigation of the influence of pregnancy and lactation on selenium metabolism in women of low selenium status. In a double-blind placebo-controlled study, 35 women in the earliest stages of pregnancy and 17 non-pregnant women were recruited in Dunedin, New Zealand. Eighteen pregnant women received 50 microg selenium as L-selenomethionine, while the others received a placebo daily during pregnancy and 12 months postpartum. The non-pregnant women received the supplement, serving as a positive control. Blood samples and twenty-four hour urine samples were collected monthly during pregnancy and at 3, 6, and 12 months postpartum for analysis of selenium and iodine. Selenium content in plasma and urinary excretion of selenium fell during pregnancy; however, total excretion of selenium was greater during pregnancy than postpartum. Urinary iodine excretion was much lower than reported previously in New Zealand. Due to large intra- and inter-subject variability, no trends in iodide excretion were observed. Factors which influence urinary excretion of selenium include dietary intake, but more closely, plasma concentrations of selenium (which is probably related to total selenium pool), creatinine excretion and therefore lean body mass, and glomerular filtration rate. The exact mechanism and sequence of events remains unclear and future studies incorporating new speciation techniques are necessary.

Glutathione peroxidase activity and selenoprotein W levels in different brain regions of selenium-depleted rats(1).

Previous studies in selenium (Se)-depleted sheep and rats showed that selenoprotein W (SeW) levels decreased in all tissues except brain. To further investigate this depletion in different parts of the brain, second generation Se-depleted rats were used. Dams consumed a Se-deficient basal diet during gestation and lactation, and deficient rats were obtained by continuation on the same diet. Control rats were fed a diet with 0.1-mg Se/kg diet after weaning. Glutathione peroxidase (GPX) activities were measured for comparative purposes to SeW levels. GPX activity in muscle, skin, spleen, and testis increased about 4-fold with Se repletion and reached a plateau after 6 or 10 weeks, but GPX activity decreased to almost one tenth of the original activity with continuous Se depletion. In contrast, GPX activities increased, rather than declined, in various brain regions (cortex, cerebellum, and thalamus) with time of feeding the deficient diet. An experiment with first generation rats, however, indicated that GPX activity was significantly lower in these three brain regions from rats fed the deficient diet as compared to rats fed the supplemented diet. SeW levels in skin, spleen, muscle, and testis were undetectable in weanling rats, but became detectable after 6 weeks of Se repletion. In contrast, the expression of SeW in cortex, cerebellum, and thalamus was not significantly affected by Se depletion, but increased SeW levels occurred only in thalamus with Se supplementation. The results with GPX using first and second generation rats suggest that there are "mobile" and "immobile" GPX fractions in the brain.

Selenium supplementation of Chinese women with habitually low selenium intake increases plasma selenium, plasma glutathione peroxidase activity, and milk selenium, but not milk glutathione peroxidase activity.

Twenty-one pregnant women living in Xichang County, China, a selenium-deficient area, were divided into two groups and given either a placebo (n = 10) as yeast or selenium-enriched yeast tablets (n = 11) to provide 100 microg selenium per day. This supplementation was begun the last trimester of pregnancy and continued for 3 months after parturition. Plasma selenium levels and glutathione peroxidase (GPX) activity steadily declined in supplemented women, but a curvilinear response occurred in milk selenium and GPX activity in both supplemented and deficient women and in plasma selenium and GPX activity in deficient women. The milk selenium levels were higher in supplemented women but there were no differences in the milk GPX activity between the two groups of women. The plasma alpha-tocopherol concentrations declined after parturition in both groups but no differences were found between the two groups of women. Plasma thiobarbituric acid reactive substances declined in supplemented women but showed a curvilinear response in unsupplemented women, suggesting peroxidative stress in these women. GPX, selenium, and peroxidative responses in plasma and milk following parturition is advocated as a new method to assess selenium status of lactating women.

Metabolism of selenite in men with widely varying selenium status.

OBJECTIVE: This study was undertaken to investigate the metabolism of selenite in men with life-long intakes of deficient, adequate and excess selenium. METHODS: Stable isotopes of selenium were infused for five hours into Chinese men living in deficient, adequate or excessive selenium areas, and 24-hour urine and blood samples were collected daily for the next seven days. Stable isotopic selenium excretion was determined in urine and in whole plasma and plasma fractions. RESULTS: Even though there was a positive correlation of selenium intake with the urinary excretion of this element, this relationship was not linear over the entire range (deficient, adequate, excessive) of selenium intake. When the urine excretion was normalized internally within each group, a sharp increase in the slope of this relationship was found when long-term intake increased to adequate amounts, but the slope reached a plateau when the daily intake exceeded the adequate group. The plasma selenoprotein P fraction was labeled initially, but the incorporation in the glutathione peroxidase fraction subsequently increased by a small amount. A two-month dietary restriction of selenium of the subjects from the excess area did not result in a reduction of urinary excretion of infused selenite. CONCLUSION: A complex relationship exists between long-term intake of selenium and selenium status, and subjects living in the excess area are more saturated with selenium than anticipated. More than two months of depletion are required to affect urinary excretion of selenium.

Glutathione peroxidase activity modulates fatty acid profiles of plasma and breast milk in Chinese women.

Since little is known about the effect of selenium on the fatty acid profiles (FAP) of human breast milk, the purpose of this study was to measure the effect of habitual dietary selenium (Se) intake on this profile in plasma and breast milk. Subjects were lactating women from three locations in China where habitual selenium intakes are extremely low (Xichang), adequate (Beijing), or extremely high (Enshi). Plasma and milk samples were obtained within seven days of parturition (early samples) or within eighteen months postpartum (mature samples) and analyzed for selenium concentration, glutathione peroxidase (Gpx) activity and FAP. Plasma and milk selenium concentrations were significantly lower in the samples from women from Xichang and significantly higher in those from Enshi when compared to those from Beijing. Plasma Gpx activity, however, was higher in samples from Beijing than Xichang or Enshi. In contrast, the early breast milk samples had similar Gpx activity regardless of location. The mature samples, however, followed the same trend as plasma with the samples obtained from the women in Beijing having the highest activity. Of the unsaturated fatty acids examined, the concentration of linoleic acid, 18:2(n-6), in both plasma and milk was greater in the samples from Beijing when compared to those from Xichang or Enshi. Thus dietary selenium appears to influence the fatty acid composition in human breast milk, but influences Gpx activity only in mature milk samples.

Quantitative significance of measuring trimethylselenonium in urine for assessing chronically high intakes of selenium in human subjects.

The purpose of the present study was to investigate the effects of Se restriction on the excretion of Se in men who had consumed high levels of this element during their entire lives. With the use of stable isotopes of Se as selenite, the excretion of methylated Se in urine was investigated in Chinese men (n 10) who had habitual chronic high intakes of this element. The relationship between either urine Se or trimethylselenonium (TMSe) to the estimated long-term Se intake was not linear over the entire range of intake, which was also true for the infusion of labelled selenite. A non-linear relationship was also found between urine TMSe and urine Se both for TMSe arising from catabolism of endogenous body Se and that from infused selenite. The data suggest a close precursor-product relationship of urine Se and its TMSe component based on the nearly identical specific activities for these two selenocompounds. Although dimethylselenide in breath was not measured in the present study, combining urinary TMSe with this breath test may be more useful in the assessment of long-term Se status.

Organic and inorganic selenium supplementation to lactating mothers increase the blood and milk Se concentrations and Se intake by breast-fed infants.

The aim of this study was to determine the effect of selenium (Se) supplementation to lactating women on Se concentrations and glutathione peroxidase (GSH-Px) activities in blood components of mothers and breast-fed infants and on milk Se levels and Se intake by breast-fed infants. Lactating mothers were supplied for 3 months with 200 micrograms Se/day in the form of yeast-Se (Y-Se) and sodium selenite. Initial blood and plasma Se levels of all women (n = 67) were 76.6 and 53.2 micrograms/L, respectively. After 3 months Se concentrations both in whole blood and in plasma from mothers and infants were significantly higher than the initial values. Y-Se exerts a stronger effects than selenite on blood and plasma Se levels. Initial milk Se concentration was 8.9 micrograms/L and after 1 month in both groups in reached a plateau at 14-16 micrograms/L. This resulted in an increase of Se intake in breast-fed infants from 6.1 to a plateau of 11-13 micrograms Se/day. GSH-Px activities in plasma and red cells of Y-Se group increased significantly and reached a plateau after 1 and 2 months, respectively, while in the selenite group the enzyme activities increased steadily throughout the entire period of the study. Selenite exerts a stronger effect on GSH-Px both in maternal and in infant blood components as compared with Y-Se. In milk the GSH-Px activity in the Y-Se group did not change during the study, while in the selenite group after 3 months it increased almost 2-fold compared to the initial value. In conclusion, this study shows that organic Se causes higher Se deposition than did the inorganic form.

Distribution of selenium between plasma fractions in guinea pigs and humans with various intakes of dietary selenium.

The distribution of selenium between the plasma fractions was investigated in guinea pigs fed various levels (basal, 0.5, 1.0, 2.0, 4.0, 6.0 and 8.0 mg Se/kg) of dietary selenomethionine (Semet) and in humans living in different areas of China with different selenium status. There was a corresponding increase of selenium concentration in liver, kidney, brain, testis, spleen, heart and muscle with each increase of dietary selenium, but there were no increases of glutathione peroxidase (GPX) activity in liver, brain, testis, heart or muscle in pigs fed any of the selenium levels as compared to controls fed a basal commercial diet. On a percentage distribution basis, the selenium in selenoprotein P decreased and that in the albumin fraction increased with increased dietary intakes of selenium as Semet. The ratios of selenium to albumin in either the plasma or the albumin fractions increased with each increase in dietary selenium. The greatest percentage of selenium was in the albumin fraction of Chinese living in the high selenium areas whereas the greatest amount was in the selenoprotein P fraction in subjects living in deficient and adequate areas of China. Increases in the ratios of selenium to albumin in either the plasma or the albumin fraction also occurred with increases of selenium intake of these subjects. The results indicate that the distribution of selenium in plasma fractions reflect the levels of dietary intakes of Semet.

Dietary selenium increases selenoprotein W levels in rat tissues.

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

Uptake of selenite, selenomethionine and selenate by brush border membrane vesicles isolated from rat small intestine.

The uptake of selenite, selenate and selenomethionine (SeMet) was performed with brush border membrane vesicles (BBMV) prepared from rats fed selenium-deficient and supplemented diets. At equilibrium (60 min), the uptake of 75Se from [75Se]selenite ranged from 16.5 to 18.9 nmol mg-1 protein. There was a curvilinear relationship in the uptake of selenite over a concentration range of 10-1000 microM. About 2 nmol mg-1 protein was obtained with selenomethionine (SeMet) which occurred between 90 and 180 s. In contrast to selenite, there was a linear relationship in the initial uptake of SeMet over a concentration range of 10-1000 microM. The uptake of selenate was approximately 50-fold lower than selenite, reaching 350 pmol mg-1 protein. Dietary selenium level had no effect on the rate of 75Se accumulation by BBMV. Dramatic differences are found in the uptake and binding of selenium by BBMV incubated with different selenocompounds.

Long-term supplementation with selenate and selenomethionine: selenium and glutathione peroxidase (EC 1.11.1.9) in blood components of New Zealand women.

Thirty-three New Zealand women aged 18-23 years received daily for 32 weeks, 200 micrograms Se as Se-enriched yeast (selenomethionine), or brewer's yeast mixed with selenate, or no added Se (placebo) in a double-blind trial. Se supplementation raised (P = 0.001) platelet glutathione peroxidase (EC 1.11.1.9; GSHPx) activity, and also Se and GSHPx in whole blood, erythrocytes and plasma. Selenomethionine was more effective in raising blood Se concentrations than selenate, but both were equally effective in raising GSHPx activities in whole blood, erythrocytes and plasma, indicating a similar bioavailability for the two forms. These observations and those of gel filtration studies of erythrocytes and plasma proteins reported elsewhere (Butler et al. 1991) are consistent with the incorporation of Se from selenomethionine into a general tissue protein pool while selenate is directly available for GSHPx synthesis, and explain the poorer correlation between Se and GSHPx in individuals with higher Se status. However, selenate raised platelet GSHPx activities to a greater extent than did selenomethionine suggesting some other effect of selenate on platelets which needs further investigation. A response of GSHPx activity in these New Zealand subjects indicates that their dietary Se intake is insufficient to meet recommended intakes based on the criterion of saturation of GSHPx activity, and could reflect a marginal Se status. The level of blood Se necessary for saturation of GSHPx of about 100 ng Se/ml whole blood confirms observations in earlier studies.

Determination of the distribution of selenium between glutathione peroxidase, selenoprotein P, and albumin in plasma.

A chromatographic method is described to determine the distribution of selenium between selenoprotein P, glutathione peroxidase (GSH-Px), and albumin in plasma, using two small columns of heparin-Sepharose and reactive blue 2-Sepharose linked together in tandem. One milliliter of plasma was diluted to 12 ml with 0.02 M sodium phosphate buffer, pH 7.0 (the equilibration buffer), applied to the heparin-Sepharose column, and eluted at a flow rate of 30 ml per hour. GSH-Px was not retained by either of these columns but selenoprotein P was retained by heparin-Sepharose and albumin by reactive blue. After the two columns were separated, selenoprotein P was eluted with heparin from heparin-Sepharose and albumin eluted from reactive blue with high salt. Analytical work confirmed the presence of selenoprotein P, GSH-Px, and albumin in the respective fractions. When rats were injected with 75Se as either selenite or selenomethionine most of the radioactivity was incorporated into the selenoprotein P fraction, with the next greatest amount into GSH-Px, and the least amount into albumin. Slab gel electrophoresis was used to determine that most of the selenium in each of the three fractions was associated with each of these selenium containing proteins. This method indicated that the majority of the selenium in plasma is associated with selenoprotein P, and the only time this was found not to be true was with high levels of dietary selenomethionine.

Influence of arsenic on selenium metabolism and glutathione peroxidase activity in rats.

Arsenic accumulated to the greatest extent in blood followed in decreasing order by kidney, hair and liver in rats fed with various levels of arsenic. Within the intracellular fractions of the liver, arsenic accumulated to the greatest extent in the nuclear fraction, followed by cytosol, mitochondria and microsomes in decreasing order. Increasing arsenic significantly increased the deposition of 75Se-selenite in heart and testis but had no effect in blood, liver, spleen or kidney and significantly increased the excretion of 75Se in feces with a concomitant decrease in urinary excretion. Within the hepatic intracellular fractions, arsenic significantly altered only the 75Se content of the microsomes. Arsenic had no effect upon the glutathione peroxidase activities in blood, kidney or testes, but depressed this activity and the stable selenium content in liver.

Presence of an SH2 domain in the actin-binding protein tensin.

The molecular cloning of the complementary DNA coding for a 90-kilodalton fragment of tensin, an actin-binding component of focal contacts and other submembraneous cytoskeletal structures, is reported. The derived amino acid sequence revealed the presence of a Src homology 2 (SH2) domain. This domain is shared by a number of signal transduction proteins including nonreceptor tyrosine kinases such as Abl, Fps, Src, and Src family members, the transforming protein Crk, phospholipase C-gamma 1, PI-3 (phosphatidylinositol) kinase, and guanosine triphosphatase-activating protein (GAP). Like the SH2 domain found in Src, Crk, and Abl, the SH2 domain of tensin bound specifically to a number of phosphotyrosine-containing proteins from v-src-transformed cells. Tensin was also found to be phosphorylated on tyrosine residues. These findings suggest that by possessing both actin-binding and phosphotyrosine-binding activities and being itself a target for tyrosine kinases, tensin may link signal transduction pathways with the cytoskeleton.

Selenium distribution in blood fractions of New Zealand women taking organic or inorganic selenium.

Three groups of 11 New Zealand women each received, for 32 wk, yeast tablets with no added selenium (placebo) or 200 micrograms Se/d in tablets either as selenate or as selenium-enriched yeast (SeMet) in a double-blind selenium trial. Plasma and erythrocyte (RBC) samples were collected bimonthly. Gel filtration of plasma from women taking SeMet revealed two major selenium-containing peaks with most of the selenium in the second peak. In contrast, the first peak contained most of the selenium in plasma from women taking selenate. Chromatography of RBC lysates indicated that the majority of the selenium was with hemoglobin (Hb) in women taking SeMet but was about equally distributed between glutathione peroxidase (GSH-Px) and Hb in women taking selenate. The percentage of selenium associated with GSH-Px was found to be greater in RBCs and plasma of women taking selenate than of those taking SeMet.

Metabolism of selenite and selenomethionine in the rhesus monkey.

Female rhesus monkeys were fed a commercial monkey diet and given selenium (Se) as either selenite or selenomethionine (SeMet) in the drinking water for 11 mo. Muscle and liver biopsies were taken initially and at the end of the experiment for determination of Se levels and glutathione peroxidase (GPX) activity. Blood was collected at monthly to bimonthly intervals, and the plasma and erythrocytes were subjected to gel filtration to determine the distribution of Se among proteins of various molecular weights. At the end of the experiment, there was significantly more Se in liver, muscle and hair from the monkeys given SeMet than in tissues from those given selenite, but there were no differences in liver or muscle GPX activity between the two treatment groups. The erythrocyte and plasma Se levels were significantly higher in the monkeys given SeMet than in those receiving selenite, but there were no differences in the GPX levels between these groups. About 68% of erythrocyte Se was associated with GPX in monkeys given selenite whereas only 34% was associated with GPX in those administered SeMet. The correlation coefficient for blood Se level and erythrocyte GPX activity was 0.92 in monkeys given selenite but only 0.37 in those given SeMet. Gel filtration of plasma revealed only one Se peak for plasma from the monkeys given selenite but at least two major Se peaks for plasma from monkeys receiving SeMet. The possible implications of these results for humans are discussed, including the reasons for poor correlations of GPX activity and blood Se levels.

Influence of dietary methionine on the metabolism of selenomethionine in rats.

To determine the influence of methionine on selenomethionine (SeMet) metabolism, weanling male rats were fed for 8 wk a basal diet marginally deficient in sulfur amino acids, containing 2.0 micrograms selenium (Se)/g as DL-SeMet and supplemented with 0, 0.3, 0.6 or 1.2% DL-methionine. Increased dietary methionine caused decreased selenium deposition in all tissues examined but increased glutathione peroxidase (GSHPx, EC 1.11.1.9) activity in testes, liver and lungs. A positive correlation was found between dietary methionine and the calculated percentage of selenium associated with GSHPx. In a second experiment, 75SeMet was injected into weanling male rats which had been fed the basal diet containing 2.0 micrograms selenium as DL-SeMet with or without the addition of 1.0% methionine. The selenoamino acid content of tissues and the distribution of 75Se in erythrocyte proteins were determined. In comparison to the rats fed the basal diet without added methionine, significantly more 75Se-selenocysteine was found in liver and muscle, more 75Se was found in erythrocyte GSHPx and less 75Se was found in erythrocyte hemoglobin of rats fed 1.0% methionine. These data suggest that methionine diverts SeMet from incorporation into general proteins and enhances its conversion to selenocysteine for specific selenium-requiring proteins, such as GSHPx.

Effects of various dietary levels of selenium as selenite or selenomethionine on tissue selenium levels and glutathione peroxidase activity in rats.

Weanling rats were fed a basal diet or this diet plus 0.2, 1.0, 2.0 or 4.0 mg/kg selenium (Se) as either selenite or selenomethionine (SeM). Except at the 0.2 mg/kg Se level, Se accumulated in all tissues at higher levels when SeM was fed than when selenite was given, and the magnitude of difference became more pronounced with increasing levels of dietary Se. This was particularly true for muscle and brain. Se levels in whole blood, testes, kidney and lungs were not significantly different between rats fed 0.2 mg/kg Se as selenite or as SeM, but the Se levels in liver, muscle and brain were higher in rats fed SeM. Although the tissue Se concentrations differed markedly, there were no differences in the glutathione peroxidase (GPX) activity in tissues of rats fed SeM rather than selenite. The percentage of Se associated with GPX was lower in all tissues from rats fed SeM than in those from rats fed selenite. These results indicate that the chemical forms of dietary Se can have a marked influence on biological responses, including bioavailability of dietary Se.

Effects of feeding selenium deficient diets to rhesus monkeys (Macaca Mulatta).

Pregnant rhesus monkeys (Macaca mulatta) were fed either selenium (Se) deficient or Se supplemented diets with adequate vitamin E. Except for some cardiac irregularities in the first babies born to these females, no physiological disorders due to Se deficiency were seen in a subsequent offspring. Plasma and erythrocyte glutathione peroxidase activities and blood Se levels increased in the Se supplemented monkeys but decreased in the deficient ones. The data indicated that hair Se levels reflect long term exposure to this element. In a very preliminary experiment, evidence was obtained to indicate that dietary protein deficiency along with Se deficiency will generate cardiomyopathic lesions characteristic of Se deficiency. It is hypothesized that, in addition to Se deficiency, another dietary deficiency (or abnormality) is necessary to produce Se deficiency lesions in higher primates. Higher glutathione transferase (or non-Se glutathione peroxidase) activity in tissues of rhesus monkeys may account for this resistance.

Effects of dietary selenite, selenocystine and selenomethionine on selenocysteine lyase and glutathione peroxidase activities and on selenium levels in rat tissues.

Weanling male rats were fed a basal selenium (Se)-deficient diet or this diet plus 2 ppm Se as either selenite, selenocystine (SeCys) or selenomethionine (SeMet) for 9 wk. The rats were killed by decapitation while anesthetized with ether, and tissues were assayed for glutathione peroxidase (GPx) and selenocysteine lyase activities, and for Se content. Dietary Se had no effect upon the activity of tissue selenocysteine lyase. This activity was highest in the liver, followed by kidney, muscle and testis in decreasing order. Although the GPx activity was lower in tissues of the Se-deficient rats, there were no significant differences in its activity between animals given the different chemical forms of dietary Se. Except for the kidney, the tissue Se concentrations were similar in rats fed selenite or SeCys, but the Se content in testis, muscle, pancreas, heart, spleen, whole blood, erythrocytes and plasma was significantly higher in rats fed SeMet than in those fed either selenite or SeCys. The greatest increase due to SeMet compared with the selenite and SeCys treatments was about 10-fold in the muscle compared with 1.3- to 3.6-fold for the other tissues.