Hepatoprotective effect of selenium and vitamin E in rabbits fed a high-fat diet.

The high-fat diet consisted of cholesterol, hydrogenated coconut oil, and cholic acid. In the blood serum and in liver homogenate lipid content, cholesterol, and triglycerides were assayed. Cytochrome P-450 concentration in liver microsomes was also estimated. In animals receiving selenium and vitamin E, the content of lipid fractions in the blood serum and liver homogenate fell, while the cytochrome P-450 content in the liver microsomes was markedly elevated. The intensified protective effect of vitamin E and selenium applied in combination against changes induced in the liver of animals receiving a HFD was confirmed by macroscopic and microscopic examination of the organ.     

Effect of selenium deficiency and vitamin E deficiency on glutathione metabolism in isolated rat hepatocytes

Selenium deficiency and vitamin E deficiency both affect xenobiotic metabolism and toxicity. In addition, selenium deficiency causes changes in the activity of some glutathione-requiring enzymes. We have studied glutathione metabolism in isolated hepatocytes from selenium-deficient, vitamin E-deficient, and control rats. Cell viability, as measured by trypan blue exclusion, was comparable for all groups during the 5-h incubation. Freshly isolated hepatocytes had the same glutathione concentration regardless of diet group. During the incubation, however, the glutathione concentration in selenium-deficient hepatocytes rose to 1.4 times that in control hepatocytes. The selenium-deficient cells also released twice as much glutathione into the incubation medium as did the control cells. Total glutathione (intracellular plus extracellular) in the incubation flask increased from 47.7 +/- 8.9 to 152 +/- 16.5 nmol/10(6) selenium-deficient cells over 5 h compared with an increase from 46.7 +/- 7.1 to 92.0 +/- 17.4 nmol/10(6) control cells and from 47.7 +/- 11.7 to 79.5 +/- 24.9 nmol/10(6) vitamin E-deficient cells. This overall increase in glutathione concentration suggested that glutathione synthesis was accelerated by selenium deficiency. The activity of gamma-glutamylcysteine synthetase was twice as great in selenium-deficient liver supernatant (105,000 X g) as in vitamin E-deficient or control liver supernatant (105,000 X g). Hemoglobin-free perfused livers were used to determine the form of glutathione released and its route. Selenium-deficient livers released 4 times as much GSH into the caval perfusate as did control livers. Plasma glutathione concentration in selenium-deficient rats was found to be 2-fold that in control rats, suggesting that increased GSH synthesis and release is an in vivo phenomenon associated with selenium deficiency.     

Effect of selenium and vitamin E dietary deficiencies on chick lymphoid organ development

Diets specifically deficient in selenium (Se) and/or vitamin E or adequate in both nutrients were fed to chicks from the time of hatching. Lymphoid organs (bursa, thymus, and in some instances, spleen) were collected from chicks 7-35 days of age. Growth of the chicks fed these diets was monitored over the experimental period as was lymphoid organ growth. The development of the primary lymphoid organs was further assessed by histological techniques and the organ contents of vitamin E (alpha-tocopherol) and Se were determined. Specific deficiencies of either Se or vitamin E were found to significantly impair bursal growth as did a combined deficiency. Thymic growth was impaired only by the combined deficiency diet. Severe histopathological changes in the bursa resulted from the combined deficiency and these were detectable by 10-14 days after hatching. These changes were characterized by a gradual degeneration of the epithelium and an accompanying depletion of lymphocytes. Similar changes, although slower to develop and less severe, were observed in the thymus as a result of the combined deficiency. When both serum and tissue levels of vitamin E and Se were monitored, it was observed that these were rapidly and independently depleted by the specific deficiency diets. These data suggest that the primary lymphoid organs are major targets of Se and vitamin E dietary deficiencies and provide a possible mechanism by which immune function may be impaired.     

Oxidative status of plasma and muscle in rabbits supplemented with dietary vitamin E

Thirty New Zealand white rabbits, mean weight 2 kg, were divided into three equal groups balanced for body weight and randomly assigned to a diet containing 60 (C), 150 (T1) or 375 (T2) mg/kg of all-rac-alpha-tocopheryl acetate. After 29 days, the animals were slaughtered. alpha-Tocopherol was assayed in muscle (longissimus dorsi) and plasma; triglycerides and cholesterol (total, high density lipoprotein, low density lipoprotein) were analysed in plasma; reactive oxygen metabolites (ROMs) were analysed in serum; and thiobarbituric acid-reactive substances (TBARS) were analysed in muscle. There were no body weight and food intake differences between the groups. The plasma vitamin E and vitamin E:lipid ratio were significantly higher in groups T1 and T2 than in C, but increases were not linearly related to dietary levels. Muscle alpha-tocopherol concentrations in the treated groups were significantly higher than in C, and linearly related (R =.67) to the vitamin E:lipid ratio. ROM and vitamin E levels in blood were inversely related (R =.74), with ROMs significantly lower in the treated groups than in C. The 60-mg/kg dose of C recommended by the National Research Council was unable to control ROM production. Lipid oxidation in muscle was significantly lower in T2 than in the other groups, and TBARS correlated significantly with muscle vitamin E (R =.61) and serum ROM (R =.73). These data suggest that vitamin E supplemented at 375 mg/kg diet can effectively control ROM production and improve muscle lipostability. ROM assay provides a useful indirect estimate of the oxidative status of muscle in vivo.     

Exercise-induced oxidant stress in the lung tissue: role of dietary supplementation of vitamin E and selenium.

Strenuous physical exercise in the form of swimming in female albino rats increased the oxidative reactions, probably leading to the generation of oxy-free radicals in the lung tissue. Free radical-mediated lipid peroxidation measured in the form of lipid peroxides increased in the pulmonary tissue in response to exhaustive exercise, indicating such a possibility. Dietary supplementation of vitamin E (Vit.E) and selenium (Se) for a period of 12 weeks reduced the oxidative reactions and the ensuing lipid peroxidation in the pulmonary tissue. Physical exercise in control animals induced the activity of superoxide dismutase (SOD), the superoxide anion radical (O2-.) quencher. However, the SOD levels in nutrient-fed animals at rest and after exercise remained well below the control levels, indicating the decreased generation of oxy-free radicals in them. Similarly, selenium-dependent glutathione peroxidase (Se-GSH Px), the enzyme involved in the reduction of organic and inorganic peroxides, and glutathione S- transferase (GST), the multifunctional protein involved in the detoxification of a number of xenobiotics, were increased in response to exercise in control animals, but were significantly decreased in nutrient-fed animals upon exercise. The induction of GST seems to be more towards the peroxidase activity of GST, i.e., non-selenium glutathione peroxidase (Non-Se-GSH Px), which is primarily involved in the reduction of endoperoxides. The studies thus indicate the induction of oxidative stress in the pulmonary tissue upon exhaustive physical exercise and the effectiveness of vit.E and Se independently and more so in combination in combating the exercise-induced oxidant stress.     

Effects of vitamin E and selenium deficiency on the fatty acid composition of rat retinal tissues.

The fatty acid composition of retinal tissues was measured in rats maintained for 26--32 weeks on each of the following diets: a purified basal diet deficient in alpha-tocopherol and selenium, an identical control diet supplemented with alpha-tocopherol and selenium, and a commerical laboratory rat chow. Dietary deficiencies of antioxidant nutrients were found to cause a large decrease in total polyunsaturated fatty acids in the retinal pigment epithelium, a small decrease in the retinal rod outer segments, but no change in the whole retina or liver when compared to tissues from animals fed the vitamin E- and selenium-supplemented control diet. The polyunsaturated fatty acid content which we have observed for the retinal pigment epithelium from rats fed commerical lab chow is similar to that which we observed for bovine retinal pigment epithelium. Our results indicate that changes in fatty acid composition are not generalized to all tissues in severely antioxidant-deficient animals, but that changes do occur in some tissues, such as the retinal pigment epithelium, which appears to be particularly sensitive to in vivo lipid peroxidation.     

Impact of vitamin E or selenium deficiency on nematode-induced alterations in murine intestinal function

The effects of deficiencies in the antioxidant nutrients, vitamin E and selenium, on the host response to gastrointestinal nematode infection are unknown. The aim of the study was to determine the effect of antioxidant deficiencies on nematode-induced alterations in intestinal function in mice. BALB/c mice were fed control diets or diets deficient in selenium or vitamin E and the response to a secondary challenge inoculation with Heligmosomoides polygyrus was determined. Egg and worm counts were assessed to determine host resistance. Sections of jejunum were mounted in Ussing chambers to measure changes in permeability, absorption, and secretion, or suspended in organ baths to determine smooth muscle contraction. Both selenium and vitamin E deficient diets reduced resistance to helminth infection. Vitamin E, but not selenium, deficiency prevented nematode-induced decreases in glucose absorption and hyper-contractility of smooth muscle. Thus, vitamin E status is an important factor in the physiological response to intestinal nematode infection and may contribute to antioxidant-dependent protective mechanisms in the small intestine.     

The influence of dietary selenium and vitamin E on glutathione peroxidase and glutathione in the rat

The effect of dietary selenium (Se) and vitamin E supplementation on tissue reduced glutathione (GSH) and glutathione peroxidase activity has been studied in the rat. Increasing Se intake by 0.4 ppm gave significantly higher enzyme levels in all tissues studied, an effect not influenced by vitamin E intake. Further increasing Se to 4 ppm gave higher enzyme levels in red blood cells only, while in liver was there was a significant decrease in enzyme activity probably reflecting Se hepatotoxicity. In the absence of Se supplements increasing dietary vitamin E to 100 mg/kg diet significantly increased enzyme activity but this effect was modified by simultaneous Se supplementation.Se intake had no effect on GSH levels. Rats on high vitamin E intake 500 mg/kg had a significantly higher tissue GSH level. Dietary Se had a sparing effect on vitamin E, rats supplemented with Se having significantly raised plasma vitamin E levels.These results confirm the role of selenium in glutathione peroxidase and also show that vitamin E influences the activity of the enzyme.     

Investigations into combined dietary deficiencies of copper,selenium, and vitamin E in the rat

Interactions between dietary Cu, Se, and vitamin E in ascorbate-induced hemolysis of erythrocytes obtained from rats fed diets deficient or adequate in these elements were investigated. Hemolysis was affected by all three dietary factors, through closely interrelated but distinct mechanisms. In vitamin E-deficient cells, hemolysis was increased and the amount of hemolysis was directly related to the amount of hemoglobin breakdown. Deficiency of Cu or Se decreased hemolysis, but only in vitamin E-deficient cells. Vitamin E did not affect the breakdown of hemoglobin, but Cu and Se did. Hemolysis and hemoglobin breakdown were decreased by the addition of glucose, through mechanisms independent of that involving reduced glutathione metabolism. These results suggest that vitamin E acts within erythrocyte membranes to prevent products of hemoglobin breakdown from initiating peroxidation and subsequent hemolysis. Effects of Cu and Se are linked with that of vitamin E by the involvement of glutathione peroxidase and Cu superoxide dismutase in the cytoplasmic breakdown of hemoglobin, rather than by a direct effect of these enzymes on lipid peroxidation. It is concluded that the erythrocyte, because of its high heme content, probably represents a special system in terms of peroxidative pathways, and these findings may not be directly applicable to other tissues.     

Erythrocyte membrane-bound acetylcholinesterase in vitamin E deficient rabbits.

1. The specific activities of erythrocyte membrane-bound acetylcholinesterase (EC 3.1.1.7.) and soluble hexokinase (EC 2.7.1.1.) in vitamin E deficient and vitamin E sufficient rabbits were investigated. 2. Acetylcholinesterase specific activities values of 43.4 in deficient and 57.4 in sufficient vitamin E rabbits were obtained. Hexokinase specific activity was not modified, and values of 3.31 in deficient and 3.6 in controls were found. 3. No peroxidation process was detected by us on vitamin E deficient diets. 4. These observations would suggest that the membrane stabilizing effect of vitamin E may be accomplished by a mode of action not necessarily related to its ability to prevent lipid peroxidation.     

Influence of vitamin E and selenium on immune response mechanisms.

Vitamin E and selenium have both been shown to have immunostimulatory effects in a variety of species when administered in quantities in excess of established deitary requirements. Responses to each nutrient appeared to be independent of the nutrition of the other. Deficiencies of vitamin E and selenium conversely caused suppression of the immune response system, particularly, cell mediated mechanisms. Suppression was shown to be associated with serum factors coating lymphocytes from dogs deficient in vitamin E and selenium. Oral supplementation with vitamin E transformed or removed the suppressive factors, dietary selenium had no effect. In vitro peripheral lymphocyte blast transformation tests corroborated observations of in vivo studies. Reducing agents and synthetic anti-oxidants eliminated suppressive effects in vitro. Suppression was most marked in dogs fed diets highest in polyunsaturated fatty acid (PUFA) content, providing conditions most conductive to lipid peroxidation in vivo. The essential fatty acids linoleic and arachidonic have been shown to similarly influence immunoregulatory mechanisms in vivo. The effect may be a direct one since plasma membrane fluidity of lymphoid cells increases the probability of modification of cell--antigen interactions by PUFA. However, their effect may also be an indirect one. PUFA are known precursor substances of E anf F type prostaglandins which have been shown to affect immediate and delayed hypersensitivity by stimulating synthesis of cyclic AMP. More definitive studies are needed to resolve this question.     

Effects of vitamin E and selenium deficiency on the fatty acid composition of rat retinal tissues

The fatty acid composition of retinal tissues was measured in rats maintained for 26–32 weeks on each of the following diets: a purified basal diet deficient in α-tocopherol and selenium, an identical control diet supplemented with α-tocopherol and selenium, and a commercial laboratory rat chow. Dietary deficiencies of antioxidant nutrients were found to cause a large decrease in total polyunsaturated fatty acids in the retinal pigment epithelium, a small decrease in the retinal rod outer segments, but no change in the whole retina or liver when compared to tissues from animals fed the vitamin E- and selenium-supplemented control diet. The polyunsaturated fatty acid content which we have observed for the retinal pigment epithelium from rats fed commercial lab chow is similar to that which we observed for bovine retinal pigment epithelium.Our results indicate that changes in fatty acid composition are not generalized to all tissues in severely antioxidant-deficient animals, but that changes do occur in some tissues, such as the retinal pigment epithelium, which appears to be particularly sensitive to in vivo lipid peroxidation.