Human glutathione peroxidase activity in cases of high selenium exposures

Four communities with water supplies having selenium concentrations of less than 3.1, 1.7, 189, and 496 micrograms/liter were selected for study. Samples of blood, urine, and tap water were obtained from participants in each community and analyzed for selenium content. Blood samples were also analyzed for glutathione peroxidase activity. Results showed an increase in selenium concentration in the urine as the water selenium increased. Selenium concentrations in blood did not reflect the increased selenium exposure. Glutathione peroxidase activity in whole blood decreased in highly exposed participants compared to those with low exposure. We conclude that glutathione peroxidase activity in cases of possible environmental toxic exposures will not show the increased activity seen in supplementation of selenium to deficient subjects.     

Influence of maternal selenium status on human milk selenium concentration and glutathione peroxidase activity

This study assessed whether relationships existed between maternal indices of selenium (Se) nutrition and milk content of Se and activity of glutathione peroxidase (GSH-Px). Samples of milk (n = 72) collected at 4, 8, 12, and 16 wk postpartum and blood from lactating (n = 10) and control (n = 8) women were analyzed. Plasma and erythrocyte Se concentrations and plasma GSH-Px activity were significantly lower in lactating than in control women. Maternal plasma Se concentration was positively correlated with plasma GSH-Px activity (r = 0.53, p less than 0.01) and with milk Se content (r = 0.61, p less than 0.01) and GSH-Px activity (r = 0.51, p less than 0.01). Stage of lactation did not influence either milk or blood values. Milk Se concentration was positively correlated with milk GSH-Px activity (r = 0.81, p less than 0.001). Results indicate that human milk Se content and GSH-Px activity are directly influenced by maternal Se nutrition.     

Platelet glutathione peroxidase activity as an index of selenium status in rats

Glutathione peroxidase activity in platelets increased stepwise in selenium-depleted rats that were repleted with graded levels of dietary sodium selenite. In a 3-phase depletion/repletion/depletion feeding study, glutathione peroxidase activity was similar in platelets and liver, which apparently contains the largest labile pool of selenium in the body. The activity of glutathione S-transferase (selenium-independent glutathione peroxidase) in platelets was low and was not affected by selenium deficiency, even though hepatic transferase was markedly elevated in selenium-deficient rats. Vitamin E deficiency did not affect activities of glutathione peroxidase or glutathione S-transferase in platelets or liver. Determination of glutathione peroxidase activity in platelets apparently is a promising technique for assessing selenium status and, possibly, for measuring selenium bioavailability.     

硒碘对大鼠谷胱甘肽过氧化物酶活力及甲状腺激素代谢的影响──Ⅰ．硒碘营养状态对大鼠组织谷胱甘肽过氧化物酶活力的影响

用四种硒水平饲料和两种碘含量饮水饲养大鼠观察其组织硒含量和谷胱甘肽过氧化物酶（ＧＰｘ）活力。发现：硒含量和除垂体外所检组织的ＧＰｘ活力的差异硒组间均达高度显著水平；两碘组间大脑硒含量及血浆、肾脏、大脑ＧＰｘ活力差异明显；各组织硒含量及ＧＰｘ活力受硒和碘水平影响的程度和趋势有所不同。提示硒碘营养水平对各组织硒含量及ＧＰｘ活力产生不同的影响；硒的影响依赖于碘营养水平，而碘的影响又依赖于硒的营养状态。     

Brazilian nut consumption improves selenium status and glutathione peroxidase activity and reduces atherogenic risk in obese women

Studies have shown that there are inverse relationships between nut consumption and the reduction of cardiovascular risk. This study tested the hypothesis that daily consumption of Brazilian nuts would have a positive effect upon selenium (Se) status, erythrocyte glutathione peroxidase activity, lipid profile, and atherogenic risk in severely obese women. Thirty-seven severely obese women each consumed 1 Brazilian nut a day (290 μg of Se a day) for 8 weeks. Blood Se concentrations, total erythrocyte glutathione peroxidase activity, lipid profile, and Castelli I and II indexes were evaluated before and after the nuts consumption. All the patients were Se deficient at baseline; this deficiency was remedied by the consumption of the Brazilian nut (P < .0001). The intake of Brazilian nuts promoted a significant increase in high-density lipoprotein cholesterol concentrations (P < .00001), which then resulted in a significant improvement of the Castelli I (P < .0002) and II (P < .0004) indexes. This study shows that obese people who implement daily consumption of Brazilian nuts can improve both Se status and lipid profile, especially high-density lipoprotein cholesterol levels, thereby reducing cardiovascular risks.     

Distribution of selenium and glutathione peroxidase in the rat

The selenium content was determined in the adrenals, brain, erythrocytes, femur, hair, heart, kidneys, lungs, muscle, pancreas, plasma, spleen, testes, and thymus of rats, which had been fed a commercial rat diet containing 0.3 mg Se/kg diet. In the plasma, the erythrocytes, and the soluble fraction of the tissues (with the exception of femur and hair) the activity of the glutathione peroxidase (GSH-Px) was measured, using both hydrogen peroxide and t-butyl hydroperoxide as substrates. From the masses of the tissues and the values for the selenium content and the GSH-Px activity, the distribution of the element and the enzyme in the body was calculated. For selenium the main pools were the muscle and the liver, and for the GSH-Px, the liver and the erythrocytes. By comparing the selenium content and the GSH-Px activity the percentage of the tissue selenium, which was bound to the enzyme in the soluble tissue fraction, was estimated. This percentage differed considerably from tissue to tissue, the highest value being found in the erythrocytes and the smallest in the testes. According to this estimation the majority of the selenium in the rat is not contained in the GSH-Px but in other compounds.     

Low serum selenium and glutathione peroxidase activity in patients receiving short-term total parenteral nutrition

Selenium status was determined in 15 consecutive postoperative patients receiving short-term total parenteral nutrition (TPN) using both serum selenium concentration and glutathione peroxidase (GSH-Px) activity as an indicator of body selenium status. The serum selenium concentration was significantly (p less than 0.001) lower in TPN patients (0.52 +/- 0.16 mumol/l, mean +/- SD) than in age- and sex-matched controls (1.08 +/- 0.17 mumol/l). Serum selenium in TPN patients ranged from 0.28 to 0.79 mumol/l and was associated with the duration of TPN. The lowest selenium values was found in patients who had received TPN over 3 weeks (0.35 +/- 0.06 mumol/l) as compared to patients receiving TPN for 1-3 weeks (0.61 +/- 0.13 mumol/l; p less than 0.01). Serum GSH-Px activity in TPN patients was also low (116 +/- 21 U/l) and ranged from 75 to 159 U/l. A significant positive correlation was found between serum selenium and GSH-Px activity (r = 0.520; p less than 0.05) whereas serum selenium and GSH-Px activity did not correlate significantly with liver function tests and body mass index. This study suggests that also short-term TPN patients may be at risk of selenium deficiency.     

Glutathione, glutathione peroxidase, and selenium status in HIV-positive and HIV-negative adolescents and young adults

BACKGROUND: Antioxidant nutrient deficiencies may hasten the progression of HIV disease by impairing antioxidant defenses. OBJECTIVE: The objective of the study was to determine whether HIV infection is associated with poor selenium status and low antioxidant protection by glutathione and glutathione peroxidase (GPX). DESIGN: In a cross-sectional study of 365 HIV-positive and HIV-negative adolescents and young adults, we examined the relation of plasma selenium, whole-blood glutathione, and whole-blood GPX to HIV status, disease severity, immune activation, and oxidative damage. RESULTS: Selenium deficiency (plasma selenium < 0.070 microg/mL) was not seen in any subjects, and plasma selenium in 244 HIV-positive subjects (0.120 +/- 0.0013 microg/mL) did not differ significantly (P = 0.071) from that in 121 HIV-negative subjects (0.125 +/- 0.0020 microg/mL) . However, multiple regression analysis after adjustment for covariates showed a significant (P = 0.002) negative association between HIV-associated immune activation (plasma neopterin) and plasma selenium concentrations. GPX activity was highest in HIV-positive subjects taking antiretroviral therapy (median: 14.2; 25th, 75th percentiles: 11.1, 18.7 U/mL; n = 130), intermediate in HIV-positive subjects not taking antiretroviral therapy (11.8; 9.4, 15.1 U/mL; n = 114), and lowest in HIV-negative subjects (10.6; 8.6, 12.7 U/mL; n = 121; P < 0.05 for all comparisons). GPX was also positively associated with malondialdehyde, a marker of oxidative damage. CONCLUSIONS: Subjects had adequate selenium status, although HIV-related immune activation was associated with lower plasma selenium concentrations. GPX activity appears to have been induced by the oxidative stress associated with HIV infection and use of antiretroviral therapy. Thus, young, well-nourished subjects can mount a compensatory antioxidant response to HIV infection.     

妊娠期糖尿病与患者血硒水平及谷胱甘肽过氧化物酶活性的关系

目的:探讨妊娠期糖尿病(GDM)与血硒水平及谷胱甘肽过氧化物酶活性之间的关系。方法:检测GDM患者30例(GDM组)和正常妊娠者30例(对照组)血硒水平及全血谷胱甘肽过氧化物酶(GSH-PX)活性。结果:①GDM组血硒水平为(0.0620±0.0224)mg/L,GSH-PX活性为(68.20±15.91)活力单位;对照组血硒水平为(0.0783±0.0209)mg/L,GSH-PX活性为(80.36±12.68)活力单位,两组比较,差异有统计学意义(P<0.01)。②孕妇血硒水平与GSH-PX活性呈显著正相关(r=0.714,P<0.001)。结论:妊娠期糖尿病患者血硒水平与GSH-PX活性下降可能与妊娠期糖尿病的发病有关。     

Platelet glutathione peroxidase activity in long-term total parenteral nutrition with and without selenium supplementation.

Selenium (Se) is not routinely included in total parenteral nutrition (TPN) solution; thus, patients receiving long-term TPN may be at risk of Se deficiency, which may cause fatal cardiomyopathy. Platelet glutathione peroxidase (GSH-Px) activity, as well as Se levels and GSH-Px activity in plasma and erythrocytes during prolonged TPN, was measured in six patients with chronic gastrointestinal disease. During the time course of TPN, Se administration was discontinued for 12 weeks, and then resupplemented for another 12 weeks. Before the study period, all Se indices had been maintained within the normal range. After discontinuation of Se supplementation, a significant decrease in platelet GSH-Px activity was observed after 1 week (from 64 +/- 7 [mean +/- SD] to 39 +/- 5 U/g of protein). After resupplementation, it increased after 1 week (from 44 +/- 9 to 65 +/- 10 U/g of protein). Plasma Se indices significantly changed within 3 weeks after withdrawal and reintroduction of Se (Se: from 136 +/- 28 to 75 +/- 14 and from 61 +/- 22 to 125 +/- 33 micrograms/L; GSH-Px: from 236 +/- 50 to 140 +/- 36 and from 128 +/- 32 to 220 +/- 64 U/L). Erythrocyte Se indices showed no significant changes during the study period. The results demonstrate that platelet GSH-Px activity is the most sensitive index of Se status in TPN patients.     

Effect of chemical form of selenium on tissue glutathione peroxidase activity in developing rats

Two experiments were conducted to determine the effect of various forms of selenium (Se) on the activity of glutathione peroxidase (GSHPx) in liver, heart, kidney and eyes of the developing rat. In experiment 1, throughout mating, pregnancy and lactation, female rats consumed one of three diets: basal (less than 0.05 microgram Se/g); selenite (0.15 microgram Se/g) and selenomethionine (0.15 microgram Se/g). Some pups born to dams in the basal group were also given intraperitoneal doses of saline, selenite or selenomethionine. GSHPx activity was measured in tissues from fetuses, 7-d-old and 14-d-old nursing pups and the dams. In all tissues studied, GSHPx activity was highest in the 14-d-old pups whose mothers were in the selenomethionine group. Rat pups given intraperitoneal selenite (3 micrograms/kg body weight) had higher liver and kidney GSHPx activity than pups given the same amount of selenium as intraperitoneal selenomethionine. In experiment 2, all dams were fed the same basal diet, and pups were weaned to diets containing one of two levels of selenium (0.1 or 0.2 microgram/g), one of three forms of selenium (selenite, selenomethionine or selenocystine) or no added selenium. After 14 d of repletion, the highest level of hepatic GSHPx activity occurred in the selenite group and the lowest in the basal diet group. After 21 d of repletion, renal GSHPx activity was lowest in the basal group followed by the selenocystine group. The highest tissue selenium concentration was found in kidney tissues of the selenocystine group. These data support the hypothesis that these dietary forms of selenium are differentially available for GSHPx activity.     

硒碘对大鼠谷胱甘肽过氧化物酶活力及甲状腺激素代谢的影响──Ⅱ．硒碘营养状态对大鼠甲状腺激素代谢的影响

用四种硒水平饲料和两种碘含量饮水饲养大鼠观察了其甲状腺激素（ＴＨ）代谢。硒组间肝脏、肾脏Ⅰ型脱碘酶（ＩＤⅠ）活力、血清Ｔａ含量差异显著；两碘组间甲状腺重量、甲状腺过氧化物酶（ＴＰＯ）活力。甲状腺碘含量、肾脏ＩＤⅠ及大脑Ⅱ型脱碘酶（ＩＤⅡ）活力差异明显；Ⅰ－（不加碘）组中甲状腺ＩＤⅠ活力与血清三碘甲腺原氨酸（Ｔａ）含量呈显著正相关。提示硒缺乏通过ＩＤⅠ影响ＴＨ代谢继而影响大脑ＩＤⅡ活力并可加重碘缺乏的效应；低碘时甲状腺ＩＤⅠ在维持循环Ｔａ含量中起重要作用；碘缺乏有可能增加硒缺乏的效应；硒、碘对ＴＨ代谢的影响可能在一定程度上取决于自身和对方的营养状态。     

Plasma selenium and plasma and erythrocyte glutathione peroxidase activity increase with estrogen during the menstrual cycle

OBJECTIVE: This study was designed to determine the timing and magnitude of changes in selenium status in relation to the fluctuation of 17-beta-estradiol during the menstrual cycle and the effect of different phases of the menstrual cycle on dietary selenium intake. METHODS: Plasma 17-beta-estradiol and plasma and erythrocyte selenium and glutathione peroxidase (GPx) activity were measured in fasting blood samples collected in the morning at four times over three phases of the menstrual cycle: early follicular (EF: days 1-3 menstruation), periovulatory (PO; E-1: 1 day before estrogen peak and E: during estrogen peak) and mid-luteal (ML: 7-9 days after ovulation) in healthy women (n = 14) aged 21 to 39 years and with regular menstrual cycles (26 to 30 days). The estrogen peak was confirmed by measurement of the luteinizing hormone surge. Dietary records (three-day) coincided with blood collection for each phase. RESULTS: Plasma selenium and plasma and erythrocyte GPx activity were greatest during the periovulatory phase, coinciding with the estrogen peak. No differences were observed for erythrocyte selenium or dietary selenium throughout the cycle. A linear relationship existed between estradiol and plasma selenium (p < 0.0027), plasma GPx activity (p < 0.0001), and erythrocyte GPx activity (p < 0.0001). CONCLUSIONS: These results indicate that blood selenium parameters fluctuate during the menstrual cycle such that the phase of the cycle should be considered when assessing selenium status.     

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.     

The influence of atmospheric chromium on selenium content and glutathione peroxidase activity in blood of tannery workers.

The concentration of selenium and thiobarbituric acid reactive substances (TBARS) and activity of glutathione peroxidase (GSH-Px) were determined in blood of 34 workers of a tannery in Gniezno, Poland, who worked in an area containing chromium compounds. Fourteen workers were exposed to chromium compounds at concentrations of 0.11 +/- 0.07 mg Cr/m3 (mean +/- SD) and 20 at concentrations 5-10 times lower i.e., 0.022 +/- 0.009 mg Cr/m3. Excretion of Se in urine was measured in all of the investigated workers. Decreased Se concentration in whole blood and blood plasma and elevated TBARS concentration in blood plasma were found in the whole group of investigated tanners as compared to controls. Tanners working in areas with high chromium concentrations had a statistically significant decrease in Se concentration in blood and plasma and decreased urinary excretion of the microelement as compared with other tanners. TBARS concentration was 2.5 times lower in workers exposed to higher chromium concentrations (p < 0.005) than in other workers. Positive linear correlations were found between the concentration of Se in blood and the amount of the element excreted in urine (r = 0.48; p < 0.005), the concentration of Se in blood plasma and in urine (r = 0.46; p < 0.01), and the concentration of Se in blood and erythrocyte GSH-Px activity (r = 0.42; p < 0.02). The observed differences between Se concentration in blood and urine of tannery workers and people who are not employed in the industry may indicate a kind of specific adaptation of the body to the working environment containing chromium compounds.     

Effect of selenium repletion on glutathione peroxidase protein level in rat liver

We have previously reported that liver glutathione peroxidase (GSH-Px, EC 1.11.1.9) protein level and activity decrease exponentially during Se deficiency. To determine the effect of Se repletion on these parameters, Se-deficient rats were repleted with 0.1 or 0.5 mg Se/kg diet as Na2SeO3 in a 30% torula yeast-based diet and were killed 0, 1, 2, 3, 5, 7 or 14 d later. GSH-Px protein was quantitated using anti-GSH-Px antibodies. Dietary repletion with 0.5 mg Se/kg diet increased GSH-Px protein and activity significantly (P less than 0.05) after 1 d. After 5 d for GSH-Px protein and 7 d for activity the rate of increase slowed, and at d 14 neither GSH-Px protein nor activity was significantly different from that of Se-adequate rats. Repletion with 0.1 mg Se/kg diet did not significantly increase GSH-Px protein or activity until 14 d. To examine the short-term effect of Se repletion, Se-deficient rats were injected intravenously with 15 or 60 micrograms Se as Na2SeO3 and killed 1, 3, 6, 12 or 24 h later. Only rats injected with 60 micrograms Se and killed 24 h later had a significant increase in GSH-Px activity along with a marginally significant increase in GSH-Px protein. These response curves indicate that homeostatic processes control the level of GSH-Px. The lack of an increase in GSH-Px until 24 h after Se administration implies that additional metabolic events after a rise in cellular Se may be necessary prior to an increase in GSH-Px synthesis in Se-deficient rats.