Platelet Glutathione Peroxidase Activity Research Articles

Generation of superoxide anion radicals and platelet glutathione peroxidase activity in patients with schizophrenia.

Blood platelets are considered to be a peripheral marker in schizophrenia and other psychiatric disorders. Oxidative stress in schizophrenia may be responsible for changes in platelet metabolism and function; therefore, the aim of this study was to examine and compare the generation of superoxide anions and activity of an antioxidant enzyme (glutathione peroxidase [GPx]) in blood platelets in patients with schizophrenia and healthy subjects. The level of superoxide anions generated in platelets after thrombin and platelet-activating factor stimulation and activity of GPx in patients with schizophrenia and healthy volunteers was estimated. The results obtained from the study indicate that the generation of superoxide anions in platelets as a response of platelets in patients with schizophrenia to such activating factors as thrombin or platelet-activating factor is higher than in the response of platelets of healthy subjects. In platelets from schizophrenic patients, suppressed GPx activity of about 67% was observed.

Establishing optimal selenium status: results of a randomized, double-blind, placebo-controlled trial

Dietary recommendations for selenium differ between countries, mainly because of uncertainties over the definition of optimal selenium status. The objective was to examine the dose-response relations for different forms of selenium. A randomized, double-blind, placebo-controlled dietary intervention was carried out in 119 healthy men and women aged 50-64 y living in the United Kingdom. Daily placebo or selenium-enriched yeast tablets containing 50, 100, or 200 microg Se ( approximately 60% selenomethionine), selenium-enriched onion meals ( approximately 66% gamma-glutamyl-methylselenocysteine, providing the equivalent of 50 microg Se/d), or unenriched onion meals were consumed for 12 wk. Changes in platelet glutathione peroxidase activity and in plasma selenium and selenoprotein P concentrations were measured. The mean baseline plasma selenium concentration for all subjects was 95.7 +/- 11.5 ng/mL, which increased significantly by 10 wk to steady state concentrations of 118.3 +/- 13.1, 152.0 +/- 24.3, and 177.4 +/- 26.3 ng/mL in those who consumed 50, 100, or 200 microg Se-yeast/d, respectively. Platelet glutathione peroxidase activity did not change significantly in response to either dose or form of selenium. Selenoprotein P increased significantly in all selenium intervention groups from an overall baseline mean of 4.99 +/- 0.80 microg/mL to 6.17 +/- 0.85, 6.73 +/- 1.01, 6.59 +/- 0.64, and 5.72 +/- 0.75 microg/mL in those who consumed 50, 100, or 200 microg Se-yeast/d and 50 microg Se-enriched onions/d, respectively. Plasma selenoprotein P is a useful biomarker of status in populations with relatively low selenium intakes because it responds to different dietary forms of selenium. To optimize the plasma selenoprotein P concentration in this study, 50 microg Se/d was required in addition to the habitual intake of approximately 55 microg/d. In the context of established relations between plasma selenium and risk of cancer and mortality, and recognizing the important functions of selenoprotein P, these results provide important evidence for deriving estimated average requirements for selenium in adults. This trial was registered at clinicaltrials.gov as NCT00279812.

The Effect of Consumption of Selenium Enriched Rye/Wheat Sourdough Bread on the Body’s Selenium Status

The potential of selenium-enriched rye/wheat sourdough bread as a route for supplementing dietary selenium intakes is reported. In addition to their normal diets, 24 female volunteers (24 to 25 years old) were fed either selenium-enriched bread or non-enriched bread each day (68.02 and 0.84 microg selenium day(-1) respectively) for 4 weeks. The chemical form of the selenium in the bread had been characterised using HPLC-ICP-MS, which showed that 42% of the extractable selenium was present as selenomethionine. Plasma selenium levels and plasma platelet glutathione peroxidase (GPx1) activity were measured in the volunteers' blood over a 6-week period. A statistically significant difference (p = 0.001) was observed in the mean percentage change data, calculated from the plasma selenium level measurements for the enriched and control group, over the duration of the study. A comparable difference was not observed for the platelet GPx1 activity (p = 0.756), over the same period. Two weeks after cessation of the feeding stage, i.e., at t = 6 weeks, the mean percentage change value for the selenium plasma levels in the enriched group was still significantly elevated, suggesting that the absorbed selenium had been incorporated into the body's selenium reserves, and was then being slowly released back into the volunteers' blood.

Evidence for in situ ethanolamine phospholipid adducts with hydroxy-alkenals

Hydroxy-alkenals, such as 4-hydroxy-2(E)-nonenal (4-HNE; from n-6 fatty acids), are degradation products of fatty acid hydroperoxides, including those generated by free radical attack of membrane polyunsaturated fatty acyl moieties. The cytotoxic effects of hydroxy-alkenals are well known and are mainly attributable to their interaction with different molecules to form covalent adducts. Indeed, ethanolamine phospholipids (PEs) can be covalently modified in a cellular system by hydroxy-alkenals, such as 4-HNE, 4-hydroxy-2(E)-hexenal (4-HHE; from n-3 fatty acids), and 4-hydroxy-dodecadienal (4-HDDE; from the 12-lipoxygenase product of arachidonic acid), to form mainly Michael adducts. In this study, we describe the formation of PE Michael adducts in human blood platelets in response to oxidative stress and in retinas of streptozotocin-induced diabetic rats. We have successfully characterized and evaluated, for the first time, PEs coupled with 4-HHE, 4-HNE, and 4-HDDE by gas chromatography-mass spectrometry measurement of their ethanolamine moieties. We also report that aggregation of isolated human blood platelets enriched with PE-4-hydroxy-alkenal Michael adducts was altered. These data suggest that these adducts could be used as specific markers of membrane disorders occurring in pathophysiological states with associated oxidative stress and might affect cell function.

Glutathione peroxidase activity in blood cells from aspirin-induced asthma patients.

Aspirin and other inhibitors of cyclo-oxygenase precipitate acute bronchospasm in about 10% of adult asthmatics. It has been assumed that cyclo-oxygenase is involved in the pathogenesis of bronchospasm, but the precise mechanism remains poorly understood. The oxygenation products of arachidonic acid include hydroperoxyeicosatetraenoic acid and cyclic endoperoxides. Glutathione peroxidase (GPX) reduces semi-stable hydroperoxides to less reactive alcohols and removes H(2)O(2) involved in inflammation. GPX could, therefore, modulate oxidation of arachidonic acid in the cyclo-oxygenase and lipoxygenase pathways, but the involvement of GPX in the pathogenesis of asthma has received little attention. We measured GPX activity in platelets, peripheral blood lymphocytes (PBL), red blood cells (RBC) and plasma from 13 patients with aspirin-induced asthma (AIA). Age- and sex-matched healthy individuals served as the comparison group. The patients had significantly higher GPX activity in platelets (P = 0.05) and tended to have high GPX activity (P = 0.08) in plasma but not in RBC or PBL. The results suggest that the increased GPX activity may be an adaptive advantage in AIA to protect against increased free radical production by inflammatory cells. That the higher GPX activity was not evident in all cell types studied may indicate a differential role played by them as effector cells in the pathogenesis of AIA.

Pathophysiologic role of redox status in blood platelet activation. Influence of docosahexaenoic acid.

Decrease of platelet glutathione peroxidase activity results in increased life span of lipid hydroperoxides, especially the 12-lipoxygenase product of arachidonic acid, 12-HpETE. Phospholipase A2 activity is subsequently enhanced with the release of arachidonic acid, which results in higher thromboxane formation and platelet function. Docosahexaenoic acid may either potentiate platelet lipid peroxidation or lower it when used at high or low concentrations, respectively. In the case of slowing down lipid peroxidation, docosahexaenoic acid was specifically incorporated in plasmalogen ethanolamine phospholipids. This could have a relevant pathophysiologic role in atherothrombosis.

Adequacy or deprivation of dietary selenium in healthy men: Clinical and psychological findings

Thirty healthy young men were fed diets that provided either 32.6 or 226.5 μg of selenium (Se)/d for 105 d. The high Se diet significantly elevated plasma Se and platelet glutathione peroxidase activity. Selenium balance of subjects consuming the high Se diet was >100 μg/d, whereas subjects on the low Se diet were in approximately zero balance. High dietary Se significantly improved mood; specifically, subjects on the high Se diet improved in the clearheaded/confused, elated/depressed, composed/anxious, and confident/unsure subscores, and total mood disturbance was less in men consuming the high Se diet. These data show that North American men are able to stay in zero Se balance on as little as 24 μg/d. Additionally, they show that psychological function, specifically mood, can be influenced by increasing or decreasing the amount of Se in the diet. J. Trace Elem. Exp. Med. 11:11–27, 1998. Published 1998 Wiley-Liss, Inc.1 This article is a US Government work and, as such, is in the public domain in the United States of America.

Adequacy or deprivation of dietary selenium in healthy men: Clinical and psychological findings

Thirty healthy young men were fed diets that provided either 32.6 or 226.5 μg of selenium (Se)/d for 105 d. The high Se diet significantly elevated plasma Se and platelet glutathione peroxidase activity. Selenium balance of subjects consuming the high Se diet was >100 μg/d, whereas subjects on the low Se diet were in approximately zero balance. High dietary Se significantly improved mood; specifically, subjects on the high Se diet improved in the clearheaded/confused, elated/depressed, composed/anxious, and confident/unsure subscores, and total mood disturbance was less in men consuming the high Se diet. These data show that North American men are able to stay in zero Se balance on as little as 24 μg/d. Additionally, they show that psychological function, specifically mood, can be influenced by increasing or decreasing the amount of Se in the diet. J. Trace Elem. Exp. Med. 11:11–27, 1998. Published 1998 Wiley-Liss, Inc.1

Involvement of lipid peroxidation in platelet signalling

A well-known signalling pathway in blood platelets consists in the release of arachidonic acid (AA) from membrane phospholipids and its specific oxygenation into bioactive derivatives. In particular, cyclic prostaglandin endoperoxides and thromboxane A 2 are potent inducers of platelet functions and are produced in greater amounts when the level of lipid hydroperoxides is higher than normal, as ‘physiological concentrations’ of such peroxides activate the cyclooxygenation of AA. In this context, a lower activity of platelet glutathione peroxidase (GPx), the key-enzyme for the degradation of lipid hydroperoxides, has been reported in aging, which will ensure a longer life span to those peroxides. Accordingly, the biosynthesis of pro-aggregatory prostanoids is elevated in platelets from the elderly. On the other hand, fatty acids from marine origin have been recognized as inhibitors of platelet functions, and they may alter the redox status of cells. They may for instance increase the platelet GPx activity, an effect that can be prevented by antioxidants. Overall, these data point out the relevance of the redox status in platelet functions.

Selenium level and glutathione peroxidase activity in plasma, erythrocytes and platelets of healthy Japanese volunteers.

The purpose of this study was to determine both the selenium (Se) level and glutathione peroxidase (GSH-Px) activity in plasma, erythrocytes and platelets from 51 healthy Japanese individuals. The Se levels (mean +/- SD) of plasma, erythrocytes and platelets were 117.4 +/- 15.7 micrograms/L, 0.954 +/- 0.159 microgram/g hemoglobin, and 4.93 +/- 1.52 ng/mg protein, respectively, and GSH-Px activity was 318 +/- 50 U/L, 18.0 +/- 5.0 U/g hemoglobin, and 0.142 +/- 0.035 U/mg protein, respectively. There was a negative correlation between age and the platelet Se level in men (r = -0.761, p < 0.001), and a positive correlation between the plasma and platelet GSH-Px activities in women (r = 0.663, p < 0.001).

Reduced platelet glutathione peroxidase activity and serum selenium concentration in atopic asthmatic patients

Reduced platelet glutathione peroxidase activity and serum selenium concentration in atopic asthmatic patients

Reduced platelet glutathione peroxidase activity and serum selenium concentration in atopic asthmatic patients

Asthmatic inflammation results in increased oxygen free radical generation and assessment of the activity of the selenium (Se) dependent anti-oxidant enzyme, glutathione peroxidase (GSH-Px) in asthma may therefore be important. To test the hypothesis that reduced GSH-Px activity and Se intake contribute to asthmatic inflammation, platelet and whole blood GSH-Px activities and serum and whole blood Se concentrations were measured and compared in atopic and non-atopic asthmatic patients and non-asthmatic control subjects. GSH-Px activities of whole blood and isolated platelets were assessed in 41 asthmatic patients (33 atopic) and 41 age- and sex-matched non-asthmatic subjects (15 atopic) by spectrophotometric assay based on the oxidation of NADPH. Se concentrations were determined by semi-automated fluorimetric assay. Mean (+/-SD) platelet GSH-Px activity was lower in asthmatic (89.5 +/- 45.7 mumol NADPH oxidized min-1 g-1 of protein) than in non-asthmatic subjects (109.9 +/- 41.9; P = 0.038) and in atopic (89.7 +/- 45.1, n = 48) compared with non-atopic subjects (113.7 +/- 40.9, n = 34; P = 0.016). Mean whole blood GSH-Px activity was also lower in atopic (12.2 +/- 5.2 mumol NADPH oxidized min-1 g-1 of Hb) than in non-atopic subjects (14.5 +/- 4.2; P = 0.038). In non-asthmatic subjects, the mean whole blood GSH-Px activity was lower in men (9.9 +/- 3.5) than in women (14.5 +/- 3.7; P = 0.0004) and was positively correlated with age (r = 0.51; P = 0.0006). Mean serum Se was lower in asthmatic (1.07 +/- 0.12 mumol/L) than in non-asthmatic subjects (1.16 +/- 0.31; P = 0.036). Using multiple linear regression, asthma was an independent predictor of decreased platelet GSH-Px after gender, age and serum Se were taken into account (P = 0.048) while atopy was a significant predictor of low whole blood GSH-Px independent of asthma, gender, age and whole blood Se (P = 0.033). In addition to Se status, atopy, gender and age all appear to influence GSH-Px activity, although the relative importance of these factors may differ in asthmatic and non-asthmatic populations. It seems likely that the reduced activity of this enzyme in platelets and blood may reflect mechanisms associated with the pathogenesis and severity of asthma.

Purification and characterization of glutathione peroxidase from human blood platelets. Age-related changes in the enzyme

Platelet glutathione peroxidase (GPx) is known to play a pivotal role in controlling the level of lipid hydroperoxides, especially those resulting from the 12-lipoxygenase activity. GPx was purified fromm the cell cytosol by more than 700-fold using an exchange chromatography, FPLP, gel filtration and covalent fixation. Isoelectric focusing revealed a peak activity at pH 5.1. The molecular mass of enzyme was found between 90 and 100 kDa by gel filtration, and was approximating at 23kDa by SDS-PAGE. A polyclonal antibody raised against commercial bovine erthrocyte GPx recognized the human platelet enzyme. It is concluded that human platelet GPx is likely a homotetramer of 92 kDa as described for most sources. We have also found that the decreased platelet GPx activity observed in platelets from elederly people is associated with a lower content of the immunoreactive enzyme.

Low platelet glutathione peroxidase activity and serum selenium concentration in patients with chronic renal failure: relations to dialysis treatments, diet and cardiovascular complications.

1. Selenium status was investigated in patients with chronic renal failure, with special regard to its relations to the dialysis treatments, dietary habits and clinical signs of atherosclerosis. 2. Serum selenium concentration and platelet glutathione peroxidase activity were measured in 45 patients with chronic renal failure subdivided into three groups according to the type of treatment: 15 non-dialysed, 15 on haemodialysis, 15 on continuous ambulatory peritoneal dialysis. A 7-day diet history was carried out in all patients. Seventeen of the patients with chronic renal failure had clinically overt cardiovascular disease. Forty-five age-matched healthy subjects were considered as controls. 3. Both serum selenium concentration and platelet glutathione peroxidase were significantly reduced in all patients with chronic renal failure compared with control subjects; a direct and significant correlation was found between the two parameters. No differences in selenium status were observed among the non-dialysed, haemodialysis and continuous ambulatory peritoneal dialysis groups. No correlation between total calorie or protein intakes and selenium indices were observed. The chronic renal failure patients with cardiovascular complications showed a further significant reduction in both serum selenium concentration and platelet glutathione peroxidase activity as compared with the patients without cardiovascular complications; these two groups were similar with respect to the other well-known cardiovascular risk factors (age, smoking, plasma lipids, hypertension, body mass index). 4. It is concluded that a low selenium concentration is present in chronic renal failure, which is independent of dialysis and is accompanied by biological repercussion in terms of reduced platelet glutathione peroxidase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in antioxidant enzymes activities, aggregability and malonyldialdehyde concentration in blood platelets from patients with coronary heart disease

In 41 patients with coronary heart disease (CHD) the concentrations of total blood platelet malonyldialdehyde (MDA: 2.11 ± 0.25 nmol/10 9 platelets) and MDA corresponding to thromboxane A 2 (TXA 2 0.84 ± 0.13 nmol/10 9 platelets) were increased in comparison with values in blood platelets of healthy subjects (1.19 ± 0.09 and 0.71 ± 0.05 nmol/10 9 platelets), respectively. The increased aggregability with ADP and thrombin of patient platelets was also observed. In relation to the blood platelets of healthy subjects, the antioxidant enzymes activities of patient blood platelets were significantly ( P < 0.001) decreased. Platelet glutathione peroxidase (GSH-Px) activity of the patients (11.3 ± 0.85 U/g protein) was significantly lower than controls (18.3 ± 1.12 U/g protein). In patients with CHD the activities of the other antioxidative platelet enzymes: catalase (Cat, 7.37 ± 1.38 U/g protein) and superoxide dismutase (SOD, 1529.4 ± 167 U/g protein) were also significantly decreased in comparison with values for healthy subjects (Cat: 9.06 ± 1.30 U/g protein and SOD: 1987 ± 230 U/g protein, respectively). It is suggested that antioxidative defense in blood platelets may affect the haemostatic processes and lipid peroxidation in patients with CHD.

Different bioavailability in humans of wheat and fish selenium as measured by blood platelet response to increased dietary Se

The bioavailabilities of selenium (Se) from Se-rich fish species and Se-rich wheat were compared in a study involving 32 healthy volunteers. Initial serum Se values were 109±16 μg/L (mean±SD). For 6 wk, one group (n=11) included Se-rich bread in their diet, bringing daily average intake of Se up to 135±25 μg/d. Another group (n=11) consumed Se-rich fish daily (average Se intake: 115±31 μg/d), whereas the control group (n=10) ate their normal diet, providing 77±25 μg Se/d. Serum Se increased by 17% (P<0.01), and platelet Se increased by 30% (P<0.01) in the wheat group. Although platelet Se decreased by 11% in the fish group, no changes in serum and platelet Se in the fish or control group reached statistical significance. Glutathione peroxidase (EC 1.11.1.9; GSH-Px) activity in serum and platelets did not change during the study, nor did platelet mercury (Hg) content. Since the dietary intake of Hg, arsenium (As), and fatty acids could not satisfactorily explain the lack of response in the fish group, the results are indicative of low bioavailability of fish Se in humans. At present, wheat Se seems to be the most important factor contributing to the body stores of Se in this study population.

Thromboxane Production in Copper-Deficient and Marginal Platelets: Influence of Superoxide Dismutase and Lipid Hydroperoxides

Platelet thromboxane (TX) production was examined in response to dietary copper. Groups of eight rats were fed copper-deficient, -marginal, and -adequate diets providing 0.5, 1.7, and 7.5 micrograms Cu/g, respectively, with controlled dietary Se and vitamin E. Platelets were purified and washed by centrifugation. Separate platelet samples from each rat were challenged with 10 micrograms/ml of collagen and 1 unit/ml (27.3 nM) of thrombin in Tyrode's buffer, 2.0 mM Ca2+. Platelet copper-dependent superoxide dismutase (CuSOD) activity showed a significant depression with reduced diet copper, but platelet glutathione peroxidase activity was unaffected. Challenged platelet TX production showed a significant 1.5- to 2.5-fold increase in response to both dietary copper deficiency and marginality, with highly significant negative correlations between challenged platelet TX production and platelet CuSOD activity and between TX production and copper status (liver copper). Endogenous (unchallenged) platelet lipid hydroperoxide concentrations, measured as free fatty acid hydroperoxides by a glutathione-disulfide-specific glutathione reductase recycling assay, showed a nonsignificant 47-67% increase in copper deficiency. Pooled data showed a significant 71% increase in platelet lipid hydroperoxides in copper deficiency. Platelet TX production showed a significant correlation with endogenous lipid hydroperoxides. The results suggest that dietary copper insufficiency increases platelet TX synthesis through changes in CuSOD in a dose-responsive (diet copper and platelet CuSOD activity) manner, and that platelet TX synthesis is influenced by lipid hydroperoxides (peroxide tone).

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.

Selenium status in relation to reduced glutathione peroxidase activity in aspirin‐sensitive asthma

Selenium status and its relationship to lowered platelet glutathione peroxidase activity was investigated in 18 subjects with aspirin (ASA)-induced asthma and in asthmatic and non-asthmatic ASA-tolerant subjects. Mean serum selenium concentration in ASA-tolerant asthmatics (1.25 microns/l; 98.5 micrograms/l) was significantly higher than that in ASA-induced asthma subjects (1.14 microns/l; 89.7 micrograms/l) and than that in healthy controls (1.15 microns/l; 91 micrograms/l). Although there was a correlation between serum selenium concentration and platelet glutathione peroxidase activity, enzyme activity was significantly lower in the ASA-induced asthma group compared to other groups even after correcting for selenium status. These results indicate that lowered platelet glutathione peroxidase activity in ASA-induced asthma is a product of both selenium availability and an unidentified syndrome-specific (possibly genetic) factor.

Selenium metabolism and platelet glutathione peroxidase activity in healthy Finnish men: effects of selenium yeast, selenite, and selenate

The mean dietary selenium intake in Finland increased from 40 to 100 micrograms/d in 1987 because of the addition in 1985 of selenium to fertilizers. A selenium-supplementation study was performed in 1987 on the same men as were followed in a 1981 study that had a similar design (200 micrograms Se/d). Selenite and selenate, but not selenium yeast increased platelet glutathione peroxidase (GSHPx) activity by 30% compared with placebo, much less than the 70% found in the previous study. Selenium yeast and selenite increased plasma selenium after 11 wk from 1.39 mumol/L to peak values of 2.15 and 1.58 mumol/L, respectively. Only yeast selenium was incorporated into red cells. From a regression plot based on present and literature data, it was estimated that the plasma selenium concentration needed to achieve maximal platelet GSHPx activity was 1.25-1.45 mumol/L. At the present selenium intake in Finland, 100 micrograms/d, GSHPx activity is saturated in plasma and red cells and almost saturated in platelets.