Selenium and myocardial infarction: glutathione peroxidase in platelets

Determination of Essential and Toxic Elements in Cattle Blood: Serum vs Plasma

Simple Summary

Knowledge of type of blood sample (serum or plasma) for determination of essential and toxic elements is essential for assessing the health and nutritional status of the animals and the herd. We demonstrate that both plasma and serum samples are suitable and interchangeable for the determination of most of the essential and toxic elements in blood in cattle. Nevertheless, we must take into account that the concentrations of Cu and Se are lower in the serum than in plasma.

Abstract

This study was designed to evaluate the influence of type of blood sample (serum or plasma) on essential and toxic element analysis in cattle. Paired plasma and serum samples (n = 20) were acid digested, and the concentrations of As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, Li, Mg, Mn. Mo, Ni, P, Pb, Sb, Se, Sr and Zn were determined by inductively coupled plasma mass spectrometry (ICP-MS). The study findings indicate that plasma and serum samples appear suitable and interchangeable for the determination of most of the essential and toxic elements in blood in cattle. The only exceptions are Cu and Se, the concentrations of which were significantly lower (40.9 and 29.9% respectively) in serum than in plasma. Some of the Cu in blood samples from bovine ruminants is known to be sequestered during clotting. However, further research on Se in ruminants and other animal species is warranted. Finally, the significantly higher Mn (9.9%) concentrations in serum than in plasma may have been caused by haemolysis of some samples. Special attention should be paid to preventing haemolysis of samples during collection and processing, in order to prevent overestimation of elements present at high concentrations inside erythrocytes (i.e., Fe, Mn and Zn).

Oxidants downstream from superoxide inhibit nitric oxide production by vascular endothelium--a key role for selenium-dependent enzymes in vascular health

Although superoxide can directly quench endothelium-generated nitric oxide (NO), there is considerable evidence that oxidants derived from superoxide--notably peroxides and their further derivatives--can also impair NO bioactivity. In part, this reflects inhibition of NO synthase activity, perhaps mediated by the oxidation of labile sulfhydryl groups, as well as the activation of protein kinase C. Selenium deficiency exacerbates these effects, presumably owing to the crucial role of selenium-dependent thioredoxin reductase and glutathione peroxidases in preventing and reversing oxidant damage to proteins. High-normal homocyst(e)ine levels may induce an 'effective selenium deficiency' by suppressing glutathione peroxidase transcription in endothelial cells. Considerable epidemiology, primarily of European origin, points to mediocre selenium nutrition as a significant vascular risk factor; the risk associated with elevated plasma homocyst(e)ine levels is now well established. In addition to preventing LDL oxidation, vitamin E can be expected to minimize the contribution of lipid peroxides to endothelial dysfunction. Lipoic acid, which can function in vivo as a versatile antioxidant and sulfhydryl reductant, may have particular value for protecting endothelium from oxidants; its clinical utility in diabetic neuropathy may reflect this benefit. Good selenium status, as well as supra-nutritional intakes of lipoic acid, may down-regulate cytokine-mediated endothelial activation by helping to maintain the proper structure of oxidant-labile proteins--such as tyrosine phosphatases--that modulate this signaling. It can be concluded that a number of supplemental nutrients--including selenium, vitamin E, lipoic acid, and the vitamins that promote catabolism of homocysteine--have the potential to promote vascular health by mitigating the adverse impact of superoxide-derived oxidants on endothelial function.

Biological chemistry of thiols in the vasculature and in vascular-related disease

For all their similarities in structure and common chemistry, the functions of the amino thiols in vascular biology are remarkably different. This review details the basic chemistry of sulfhydryls that dictates their functions in health and disease. In addition, the biochemistry and metabolism of each thiol are outlined, in an effort to highlight its specific contributions to the normal biology and physiology of blood vessels and to the pathogenesis of vascular-related disease.

Natural antioxidants for the prevention of atherosclerosis

Hypercholesterolemia, cigarette smoking, hypertension, and obesity are known contributing risk factors for the development of atherosclerotic coronary artery disease (CAD). However, they account for only half of all cases of CAD, and the complete pathologic process underlying atherosclerosis remains unknown. Growing evidence suggests that oxidative modification of low-density lipoprotein (LDL) may be of particular importance in the pathogenesis. Oxidized LDL exhibits proatherogenic effects. Therefore, current research has focused on inhibiting the oxidation of LDL as a means of inhibiting the atherosclerotic process. One such approach is to enhance the endogenous antioxidant defense systems within the LDL particle with lipophilic antioxidants such as alpha-tocopherol and beta-carotene, or by supplementing the aqueous-phase antioxidant capacity with ascorbic acid. Observational data suggest a protective effect of antioxidant supplementation on the incidence of CAD; however, specific doses cannot be recommended since the data are inconclusive.

Selenium enhances glutathione peroxidase activity and prostacyclin release in cultured human endothelial cells. Concurrent effects on mRNA levels

Selenium (Se) is an essential component of glutathione peroxidase (GSH-Px), an enzyme that protects cells by reducing intracellular peroxides. Impaired Se status and GSH-Px activity seem associated with increased risk of atherosclerotic vascular diseases. This study reports the effects of Se supplementation on GSH-Px activity, on prostacyclin (PGI2) production, on 12-hydroxy-eicosatetraenoic acid (12-HETE) levels, and on GSH-Px mRNA expression in cultured human umbilical vein endothelial cells (HUVEC). Se-enriched HUVEC showed significant increase of both GSH-Px activity and thrombin-stimulated production of PGI2 in the presence of stable concentrations of 12-HETE. On the other hand, an inverse correlation between Se concentrations in culture media and GSH-Px mRNA levels in Northern blot analysis was shown; this suggests that a major degree of regulation for GSH-Px expression by Se is most likely exerted at the posttranscriptional level. These observations may help to explain the increased incidence of atherosclerosis described in Se-deficient individuals.

Can anti-oxidants prevent ischaemic heart disease?

Ischaemic heart disease remains a major cause of mortality in developed countries. A number of important risk factors for the development of coronary atherosclerosis have been identified including hypertension, hypercholesterolaemia, insulin resistance and smoking. However, these factors can only partly explain variations in the incidence of ischaemic heart disease either between populations or within populations over time. In addition, population interventions based upon these factors have had little impact in the primary prevention of heart disease. Recent evidence suggests that one of the important mechanisms predisposing to the development of atherosclerosis is oxidation of the cholesterol-rich low-density lipoprotein particle. This modification accelerates its uptake into macrophages, thereby leading to the formation of the cholesterol-laden 'foam cell'. In vitro, low-density lipoprotein oxidation can be prevented by naturally occurring anti-oxidants such as vitamin C, vitamin E and beta-carotene. This article explores the evidence that these dietary anti-oxidants may influence the rate of progression of coronary atherosclerosis in vivo and discusses the need for formal clinical trials of anti-oxidant therapy.

Selenium and glutathione peroxidase variations induced by polyunsaturated fatty acids oral supplementation in humans

Serum and erythrocyte selenium, erythrocyte and platelet glutathione-peroxidase (GSH-Px) activities, and erythrocyte reduced glutathione (GSH) content were measured in 25 healthy adult individuals before and after daily supplementation with 20 ml of fish oil for 10 weeks. Serum-Se decreased from 0.83 +/- 0.01 mumol/l to 0.75 +/- 0.02 mumol/l (mean +/- S.E.M.) (P less than 0.01); erythrocyte-Se decreased from 4.39 +/- 0.17 nmol/g hemoglobin (Hb) to 2.83 +/- 0.15 nmol/g (P less than 0.001). GSH-Px activities increased both in erythrocytes (6.93 +/- 0.24 iu/g vs 8.18 +/- 0.27 iu/g Hb, P less than 0.01) and in platelets (69.2 +/- 2.8 iu/g vs 90.9 +/- 3.6 iu/g protein, P less than 0.001). The concentration of GSH in erythrocytes fell from 9.56 +/- 0.29 mumol/g Hb to 5.90 +/- 0.30 mumol/g Hb (P less than 0.001). The effects on plasma lipids were evident only for triglycerides (before 1.96 +/- 0.16 mmol/l, after 1.75 +/- 0.14 mmol/l, P less than 0.001). We hypothesise the enrichment of erythrocyte and platelet membranes with polyunsaturated fatty acids (PUFAs), following fish oil intake, can generate increased amounts of lipid peroxides and thus allosterically activate GSH-Px: with time this is harmful for the integrity of the enzyme molecule and Se release may result. We suggest that the Se status of individuals given PUFAs is assessed before and during intake; Se supplements should only be given when serum and/or erythrocyte Se are reduced.

Selenium and Behçet's disease

Behçet's disease is an inflammatory disorder of unknown etiology, characterized by recurrent oral and genital aphthous ulcers, ocular inflammation, and skin lesions of erythema nodosum and acneiform eruptions. Selenium (Se) affects all components of the immune system, i.e., the development and expression of nonspecific, humoral, and cell-mediated responses. In general, a deficiency in Se appears to result in immunosuppression, whereas supplementation with low doses of Se appears to result in augmentation and/or restoration of immunologic functions. In this study, the distribution of Se and IgG, IgM in serum were compared in samples from healthy adult control and Behçet's disease patients. The serum Se levels were measured by AA-30-40 Varian Spectra, and immunoglobulins were measured by immunodiffusion technique. The mean (SD) serum Se level of 54.24 +/- 8.06 ng/mL among Behçet's disease subjects was significantly different (P less than 0.01) from that in the control subjects (90.01 +/- 9.94 ng/mL). We also measured IgG and IgM as 10.01 +/- 2.74 mg/mL and 1.26 +/- 0.29 mg/mL, respectively for patients, and 15.08 +/- 4.73 mg/mL and 1.58 +/- 0.43 mg/mL for controls. The mean values of IgG and IgM for patients were significantly (P less than 0.05) different from the values of controls. It seems, therefore, that a deficiency in selenium impedes the humoral immune response.

Selenium and cardiovascular disease

For humans, ecological and epidemiological results are reported that show a relationship between the serum selenium concentration and cardiovascular disease in populations where low serum selenium concentrations are found, e.g., in Eastern Finland. From clinical studies done in Germany (FRG and GDR), Finland, and Sweden, subnormal serum selenium and partially whole blood selenium concentrations are reported in patients with acute myocardial infarction. For patients with coronary arteriosclerosis, subnormal serum selenium concentrations are reported from the USA and Germany and subnormal whole blood selenium concentrations from Germany. Subnormal serum and subnormal whole blood selenium concentrations of patients with cardiomyopathy are reported from non Keshan disease affected areas in Germany, France, and China. In selenium deficiency, an accumulation of lipid peroxides in the heart may occur, especially under ischemic conditions and if ischemic tissue is reperfused. Lipid peroxides in the heart may damage the cell membrane and may lead to an impaired calcium transport with an uncontrolled calcium accumulation in the cell. This may result in an activation of phospholipids, and, in consequence, to an enhanced formation of arachidonic acid. An increased concentration of lipid peroxides owing to selenium deficiency may shift the prostaglandin synthesis from prostacyclin to thromboxane, causing enhanced blood pressure and platelet aggregability. From animal experiments, it is known that selenium protects against cardiotoxic elements, cardiotoxic xenobiotics, and viral infections that affect the heart. Selenium deficiency may also be a secondary factor in the causation of hypertension and myocardial ischemia.

Relationship of serum selenium and antioxidants to plasma lipoproteins, platelet aggregability and prevalent ischaemic heart disease in Eastern Finnish men

In a cross-sectional population study of 1132 unselected Eastern Finnish men aged 54 years, serum selenium concentration had a weak positive association with plasma HDL cholesterol (standardised partial regression coefficient, beta = 0.061, P = 0.019) and a fairly strong inverse relationship (beta = -0.223, P less than 0.001) with the extent of ADP-induced platelet aggregation. Neither plasma ascorbate concentration nor alpha-tocopherol to total cholesterol ratio had any association with plasma lipoproteins, platelet aggregability or prevalent ischaemic heart disease (IHD). When a covariance-correction was applied, men with ischaemic ECG findings at exercise had a lower mean serum selenium than others (81.5 micrograms/l vs. 85.9 micrograms/l, P less than 0.01 for difference). This difference was equally large for men with neither symptoms nor previous diagnosis of IHD.

Clinical aspects of selenium metabolism

Whereas defined selenium deficiency diseases are well characterized in animals, analogous syndromes in humans are unknown or occur only rarely under conditions of extreme selenium depletion. However, selenium deficiency has since been recognized to play important secondary roles in a variety of human diseases, and several of these can be prevented or treated by means of selenium supplementation. In clinical practice, the selenium status of patients should be monitored routinely, and corrective measures should be instituted to replete the Se body stores of patients where necessary. Interactions of Se with other elements are also of potentially great clinical significance. The importance of such interactions is exemplified by the effects of cadmium on selenium metabolism in spontaneously hypertensive rats.

Effect of selenium supplementation on platelet selenium, glutathione peroxidase, and aggregation

The selenium content of platelets is extremely high. About half of this selenium originates from irreversible incorporation by bone marrow precursor cells, which satisfy their need for selenium even under conditions of marked selenium deficiency. In order to study the effect of increased dietary selenium supply on the concentration of selenium, glutathione peroxidase (GSH-Px-) activity, and aggregability of platelets, normal healthy subjects were supplemented with 300 micrograms of selenium as Se-rich yeast/d for 3 mo. No significant effect of Se supplementation on platelet Se and GSH-Px were observed, whereas erythrocytes accumulated Se without reaching saturation. Although platelet aggregability was variable during the period of observation, this was traced back to factors other than selenium, including environmental temperature. This study demonstrates that the selenium concentration of platelets is subject to tight physiological control also at high dietary selenium intakes.

The Tromsø Heart Study: serum selenium and risk of myocardial infarction a nested case-control study

The association between serum selenium concentration and the risk of myocardial infarction was studied in a nested case-control study. Altogether 59 men, initially free of disease, aged 28-54 at the time of blood sampling, died suddenly or experienced a fatal or non-fatal myocardial infarction during a six year follow-up period. Case-control pairs came from a population of 9364 persons examined in 1979-80 in the second Tromsø Heart Study. No significant difference was observed between serum selenium in cases and controls (p = 0.34). The major determinants of myocardial infarction and sudden death were raised levels of serum cholesterol and triglycerides (p less than or equal to 0.001) and high systolic blood pressure (p less than 0.05). Thus, in this population with intermediate selenium intake, low serum selenium is not associated with an excess risk of myocardial infarction.

Platelet glutathione peroxidase activity is impaired in patients with coronary heart disease

Platelet glutathione peroxidase (GSH-Px) activity was measured in 25 healthy individuals and in 25 patients affected with well-documented coronary artery stenosis. In parallel, malondialdehyde (MDA) production was assayed on platelets following stimulation with sodium arachidonate. Mean platelet GSH-Px activity was significantly reduced and mean platelet MDA production was significantly increased in the patient group. The difference observed in the GSH-Px activity might be a consequence of different nutritional habits, suggesting an impaired intake of selenium, the inorganic moiety of GSH-Px. As low GSH-Px activities in human platelets may be associated with increased MDA and thromboxane production, we hypothesize that a low enzyme activity may be a risk factor for the development of coronary artery disease.

An antithrombotic role for nutritional antioxidants: implications for tumor metastasis and other pathologies

Nutritional antioxidants support prostacyclin synthesis by preventing lipid hydroperoxide-mediated inhibition of prostacyclin synthetase. Recent preliminary clinical studies indicate that supplementary antioxidants exert antithrombotic effects in vivo that are most likely attributable to enhanced prostacyclin production. Optimal antioxidant nutrition may thus have preventive and therapeutic value for disorders in which inappropriate platelet aggregation plays an etiologic role, including MI, stroke, atherogenesis, pre-eclampsia, and the vascular complications of diabetes. In light of evidence that platelet aggregation encourages the implantation of hematogenous tumor metastases, supplemental antioxidants should also impede tumor dissemination--an effect which will be complemented by the immunostimulant actions of these nutrients. By exerting anticarcinogenic, immunostimulant and anti-metastatic effects, nutritional antioxidants should act to inhibit neoplasia at each stage of its development.

Selenium status in patients with liver cirrhosis and alcoholism

1. Selenium status and blood levels of other nutrients related to lipid peroxidation were studied in patients with advanced alcoholic liver cirrhosis, in male alcoholics who had been abstinent for at least 1 month and in healthy control subjects. 2. Plasma Se was decreased in alcoholic cirrhosis but not among alcoholics in abstinence. Platelet glutathione peroxidase (EC 1.11.1.9; GSH-Px) activity was decreased in cirrhotic patients, whereas GSH-Px in blood and plasma was the same as in controls for both groups of patients. 3. Plasma retinol and plasma alpha-tocopherol were decreased in alcoholic cirrhosis, whereas plasma ascorbic acid was the same in all groups. 4. The decreases in platelet GSH-Px, plasma Se and alpha-tocopherol indicate a deranged antioxidant defence in patients with advanced alcoholic cirrhosis, but the levels of these and other nutrients were generally not correlated to common clinical chemical indicators of liver disease.

Serum selenium, glutathione peroxidase, lipids, and human liver microsomal enzyme activity : A double-blind controlled trial of selenium supplementation

This study evaluated selenium status in relation to lipid peroxidation, liver microsomal function, and serum lipids in humans. Serum selenium concentration, glutathione peroxidase (GSH-Px) activity, liver microsomal enzyme activity, assessed by plasma antipyrine clearance (AP-CL) rate, and serum lipids were determined in 23 healthy subjects in a double-blind placebo-controlled trial of selenium supplementation. The low selenium concentration (74.0±14.2 μg/L, mean±SD) is attributable to the low selenium content of the diet. Subjects with the lowest selenium levels (n=11) had reduced serum GSH-Px activity, AP-CL rate, high-density lipoprotein cholesterol (HDL-C), and total cholesterol (T-C) as compared with subjects with higher selenium concentrations (n=12). Low AP-CL rates were associated with low HDL-C: T-C ratios. Selenium supplementation, 96 μg/d for 2 wk, increased serum selenium, GSH-Px activity, and the HDL-C: T-C ratio. The results suggest that a low serum selenium level is associated with a decrease in liver microsomal enzyme activity and serum HDL-C and T-C concentrations. Selenium supplementation in subjects with low serum selenium may favorably influence relations between serum lipoproteins connected with the development of atherosclerotic vascular disease.

Selenium deficiency

Selenium is undoubtedly an essential trace element: its involvement in GPx structure, the presence of deleterious effects of selenium deficiency in animals, and the recognition of deficiency states in man attest to its importance. However, if the consequences of selenium deficiency in man are now widely recognized, the mechanisms underlying these conditions are poorly understood. The definition of the exact role of selenium in human homeostasis has been hampered by the lack of a sensitive parameter, usable in routine investigation, to assess selenium status. Measurements of plasma and urinary levels, although useful in clinical practice, are inadequate indicators. The only true evidence of selenium deficiency lies in a positive response to selenium therapy. Deficiency states have been demonstrated for inhabitants of regions where selenium supply is limited, in protein-energy malnutrition, and in patients maintained on total parenteral nutrition without selenium supplementation. The benefit of selenium supplementation, together with other antioxidant drugs, in non-deficient subjects is still a matter of debate; its protective effect in neoplastic, cardiovascular and neurological degenerative diseases is not yet proven.

Potential clinical applications for high-dose nutritional antioxidants

High but well-tolerated doses of the nutritional antioxidants selenium and vitamins E and C have significant immunostimulant, anti-inflammatory, and anti-carcinogenic effects which are well documented in the existing biomedical literature. In addition, these antioxidants help to protect the structural integrity of ischemic or hypoxic tissues, and may have useful anti-thrombotic actions as well. Supplementation with high-dose nutritional antioxidants may eventually gain a broad role in the prevention, treatment, or palliation of cancer, cardiovascular disease, infection, inflammatory disorders, and certain diabetic complications.

The incorporation of selenium and alterations of macro- and trace element levels in individual blood cells following supplementation with sodium selenite and vitamin E : A nuclear microprobe application

Significant alterations in the selenium content of erythrocytes, thrombocytes, and neutrophil granulocytes were observed following a daily supplementation of 200 μg Se + 100 mg vitamin E during a period of 2 months. The neutrophil granulocytes incorporated more selenium than the thrombocytes. The iron content of the thrombocytes decreased on selenium supplementation, while the opposite was noted for the neutrophil granulocytes. The glutathione peroxidase activity was not significantly changed during the period of observation.

Glutathione peroxidase and glutathione S-transferase activity of platelets

A low Se intake in dietetically treated patients with phenylketonuria (PKU) or maple syrup urine disease (MSUD) leads to a marked reduction of the platelet glutathione peroxidase activity (GSHPx). The mean value amounted to 2.0 U/10(11) platelets with t-butyl hydroperoxidase (t-BOOH) (2.2 U/10(11) with H2O2) in patients and 5.8 U/10(11) with t-BOOH (5.4 U/10(11) with H2O2) in the control children. After Se supplementation with yeast rich in Se (dose: 135 micrograms Se/m2) the GSHPx activities rapidly increased. They reached a plateau after 2-3 weeks and remained there during the following 15-20 weeks of supplementation. After the cessation of supplementation there was a slow decrease, the values reached a low plateau after 24 weeks. In addition platelet glutathione S-transferase (GSHTf) was estimated with 1-chloro-2,4-dinitrobenzene. No significant difference between the values in healthy and dietetically treated patients in a low or normal Se state was observed. GSHTf did not exhibit peroxidase activity and did not show a compensatory increase when Se dependent GSHPx activity was low. The patients do not reveal clinical signs of disturbed platelet function. GSHPx may act in platelets via lipoxygenase on the prostaglandin pathway. The physiologic consequence of altered arachidonate metabolism, when GSHPx is deficient in platelets, remains to be elucidated.

Clinical consequences of low selenium intake and its relationship to vitamin E

Great differences in dietary selenium intake have resulted in naturally occurring human selenium deficiencies and toxicities in certain parts of the world. Most North American diets, however, provide levels of selenium that fall within the estimated safe and adequate range of intake (50 to 200 microgram/day for adults) as established by the U.S. National Research Council. Low selenium status may develop in individuals fed certain therapeutic diets or given total parenteral nutrition. Attempts have been made to link low selenium intake with cancer and heart disease, but additional research is needed in this area. Selenium, as a constituent of glutathione peroxidase, plays a role in the antioxidant defense systems of the body, but other metabolic roles for selenium may yet be discovered.