Vitamin E in immunity and reproductive performance in pigs

This review is focused on studies of vitamin E in immunity and reproductive performance in pigs. There are reports that vitamin E can have a positive effect on some parameters of the immune system in pigs. The optimal level of vitamin E needed to improve the immune system has not been determined because of several factors such as the composition of the diet, feed consumption, the rate of animal growth and living conditions or stress. Moreover, the way of action of vitamin E in enhancing immunity is still unclear but according to reports it may have antioxidant properties as well as an immunomodulator effect. In several studies, an increase in litter size and a reduction of preweaning piglet mortality have resulted from increasing dietary vitamin E intake during gestation or by intramuscular injection of vitamin E and/or selenium. However, according to reports, the positive effect of vitamin E on reproductive performance remains unclear due to the low number of animals used in most experiments.     

Clinical uses and abuses of vitamin E in children.

The major benefits arising from elevated dosages of vitamin E have been the relief of symptoms of vitamin E deficiency in humans with abetalipoproteinemia and chronic cholestasis. In addition, supplements of vitamin E prevent the isolated vitamin E deficiency that has recently been associated with spinocerebellar symptoms. In keeping with the view that newborn infants, and especially premature infants, suffer from vitamin E deficiency, elevated dosages of vitamin E have been administered to prevent the anemia of premature infants, retrolental fibroplasia, bronchopulmonary dysplasia, and intraventricular hemorrhage. However, the results have been conflicting. Furthermore, some infants treated with vitamin E die unexpectedly. The life-threatening hazard of such treatments has been attributed mainly to polysorbates that are used as detergents in preparations of vitamin E for intravenous use rather than to vitamin E itself. The possibility that vitamin E, in its action as an antioxidant, inhibits the generation of superoxide anion in leukocytes is examined in this paper.     

Vitamin E in aging, dementia, and Alzheimer's disease

Since its discovery, vitamin E has been extensively researched by a large number of investigators in an attempt to fully understand its role in a variety of pathophysiological contexts. The vast majority of published work has focused on vitamin E's antioxidant properties, which is why it is well known as a lipophilic antioxidant that protects membranes from being oxidatively damaged by free radicals. However, several lines of investigation have recently revealed that vitamin E has biological roles unrelated to its antioxidant properties. Among these roles, vitamin E has been described as: a regulator of signal transduction, gene expression, and redox sensor. In parallel with the discovery of novels cellular functions of vitamin E, the introduction of the free radical theory of brain aging has propelled a renewed interest in this vitamin. Most of the resulting work has been based on the postulate that, by preventing and/or minimizing the oxidative stress-dependent brain damage, vitamin E could be used as therapeutic approach. In this article, we will consider the existing literature regarding the biological properties of vitamin E and the potential therapeutic and/or preventative roles that this natural dietary factor plays in brain aging, cognition, and Alzheimer's dementia.     

Selenium and sulfur in antioxidant protective systems: relationships with vitamin E and malaria.

The metabolic relationships among the antioxidant nutrients selenium, sulfur, and vitamin E are particularly close. Selenium and vitamin E have long been known to spare one another in certain nutritional diseases of animals, and selenium has been considered to have a key antioxidant defense function as a component of glutathione peroxidase. However, the antioxidant role of glutathione peroxidase has been questioned and new proteins containing selenium have been identified: phospholipid hydroperoxide glutathione peroxidase, selenoprotein P, and iodothyronine deiodinase. Glutathione peroxidase activity independent of selenium resides in the glutathione S-transferases. Glutathione participates in both enzymatic and nonenzymatic antioxidant defense systems. Some low-molecular weight selenium compounds (e.g., ebselen) exhibit glutathione peroxidase-like action. Certain low molecular weight thiols decompose peroxides nonenzymatically (e.g., the ovothiols). Murine malaria appears to be a useful experimental model for investigating interrelationships of selenium and vitamin E. Vitamin E deficiency protects against the parasite, especially when the mice are concurrently fed peroxidizable fat such as fish or linseed oils. Selenium deficiency, on the other hand, has little or no protective effect against the parasite. Any practical utility of pro-oxidant diets in combating human malaria remains to be determined.     

Vitamin E: action, metabolism and perspectives

Natural vitamin E includes four tocopherols and four tocotrienols. RRR-alpha-tocopherol is the most abundant form in nature and has the highest biological activity. Although vitamin E is the main lipid-soluble antioxidant in the body, not all its properties can be assigned to this action. As antioxidant, vitamin E acts in cell membranes where prevents the propagation of free radical reactions, although it has been also shown to have pro-oxidant activity. Non-radical oxidation products are formed by the reaction between alpha-tocopheryl radical and other free radicals, which are conjugated to glucuronic acid and excreted through the bile or urine. Vitamin E is transported in plasma lipoproteins. After its intestinal absorption vitamin E is packaged into chylomicrons, which along the lymphatic pathway are secreted into the systemic circulation. By the action of lipoprotein lipase (LPL), part of the tocopherols transported in chylomicrons are taken up by extrahepatic tissues, and the remnant chylomicrons transport the remaining tocopherols to the liver. Here, by the action of the "alpha-tocopherol transfer protein", a major proportion of alpha-tocopherol is incorporated into nascent very low density lipoproteins (VLDL), whereas the excess of alpha-tocopherol plus the other forms of vitamin E are excreted in bile. Once secreted into the circulation, VLDL are converted into IDL and LDL by the action of LPL, and the excess of surface components, including alpha-tocopherol, are transferred to HDL. Besides the LPL action, the delivery of alpha-tocopherol to tissues takes place by the uptake of lipoproteins by different tissues throughout their corresponding receptors. Although we have already a substantial information on the action, effects and metabolism of vitamin E, there are still several questions open. The most intriguing is its interaction with other antioxidants that may explain how foods containing small amounts of vitamin E provide greater benefits than larger doses of vitamin E alone.     

Radiosensitive antioxidant membrane-bound factors in rat liver microsomes: I. The roles of glutathione and vitamin E

In vitro lipid peroxidation initiated by NADPH/ADP/Fe3+ reveals an alteration of rat liver microsomal antioxidant factors at day D+4 after whole-body gamma irradiation (8Gy). This alteration is partly reversed by GSH, and more efficiently by Trolox C, a water-soluble analog of vitamin E. This reversion by Trolox C, together with the observed 50% decrease in vitamin E content in microsomes of irradiated rats as compared to those of control animals, indicate that Trolox C acts as a free-radical scavenger like and in place of vitamin E. The antioxidant action of Trolox C is not improved in the presence of GSH, which suggests that the former acts earlier than the latter on the autoxidative free-radical chain reactions. Neither GSH, nor Trolox C, nor both antioxidants totally inhibit in vitro lipid peroxidation, which appeals attention on the possible role of extra-microsomal antioxidant factors, especially cytosolic ones.     

Vitamin E radical reaction with antioxidants in rat liver membranes

The Japanese herbal medicine Sho-saiko-to-go-keishi-ka-shakuyaku-to (TJ-960) has been demonstrated to have an antioxidant action by quenching free radicals. The effects of TJ-960 on the tocopheroxy radicals generated by an arachidonic acid and lipoxygenase oxidation system were compared with those of the ascorbate and glutathione in vitamin E-enriched rat liver microsomes and submitochondrial membrane particles (SMP). Using electron spin resonance spectrometry, the disappearance of the tocopheroxy radicals after addition of glutathione and ascorbate was detected in microsomes and SMP, withh ascorbate displaying a more potent action than glutathione. Addition of TJ-960 demonstrated a similar effect on the tocopheroxy radicals in microsomes and SMP. In the presence of TJ-960, ascorbate, and glutathione, the loss of vitamin E in the vitamin E-enriched microsomes of rat liver undergoing oxidation was slowed down. In this paper, we introduced TJ-960 as another replenisher of vitamin E in membrane, increasing the membrane's resistance against oxidative damage.     

Is vitamin E the only lipid-soluble,chain-breaking antioxidant in human blood plasma and erythrocyte membranes?

The concentration of lipid-soluble, chain-breaking antioxidants in human plasma and in erythrocyte ghosts have been determined for the first time by an inhibited-autoxidation method. The results are very similar to the concentrations of vitamin E measured for the same blood components by the HPLC method. It is concluded that vitamin E, which is largely present as alpha-tocopherol, is the only significant lipid-soluble, chain-breaking type of antioxidant present in human blood. The concentration of vitamin E in the plasma lipids divided by the concentration of vitamin E in the ghost membrane lipids is approximately a constant despite the large differences in vitamin E-intake and in plasma lipid concentrations in different individuals. Vitamin E/lipid ratios for plasma and ghosts were larger for subjects taking a supplement of alpha-tocopherol acetate of 100 IU per week, compared to nonsupplemented subjects (based on data from a limited number of subjects). A larger supplement of 2800 IU per week did not significantly increase the vitamin E/lipid ratios.     

Vitamin E: action, metabolism and perspectives

Natural vitamin E includes four tocopherols and four tocotrienols. RRR-α-tocopherol is the most abundant form in nature and has the highest biological activity. Although vitamin E is the main lipid-soluble antioxidant in the body, not all its properties can be assigned to this action. As antioxidant, vitamin E acts in cell membranes where prevents the propagation of free radical reactions, although it has been also shown to have pro-oxidant activity. Non-radical oxidation products are formed by the reaction between α-tocopheryl radical and other free radicals, which are conjugated to glucuronic acid and excreted through the bile or urine. Vitamin E is transported in plasma lipoproteins. After its intestinal absorption vitamin E is packaged into chylomicrons, which along the lymphatic pathway are secreted into the systemic circulation. By the action of lipoprotein lipase (LPL), part of the tocopherols transported in chylomicrons are taken up by extrahepatic tissues, and the remnant chylomicrons transport the remaining tocopherols to the liver. Here, by the action of the “α-tocopherol transfer protein”, a major proportion of α-tocopherol is incorporated into nascent very low density lipoproteins (VLDL), whereas the excess of α-tocopherol plus the other forms of vitamin E are excreted in bile. Once secreted into the circulation, VLDL are converted into IDL and LDL by the action of LPL, and the excess of surface components, including α-tocopherol, are transferred to HDL. Besides the LPL action, the delivery of α-tocopherol to tissues takes place by the uptake of lipoproteins by different tissues throughout their corresponding receptors. Although we have already a substantial information on the action, effects and metabolism of vitamin E, there are still several questions open. The most intriguing is its interaction with other antioxidants that may explain how foods containing small amounts of vitamin E provide greater benefits than larger doses of vitamin E alone.     

Anti-oxidant/pro-oxidant reactions of vitamin K

Experiments were designed to measure O2 consumption caused by the oxidation of linoleic acid. These experiments show that vitamin K has antioxidant activity and that the reduction in linoleic acid oxidation is directly dependent upon vitamin K concentration. Conversely, vitamin K hydroquinone enhances linoleic acid oxidation in the absence of iron catalyst, again in a concentration dependent manner. At equilmolar concentrations vitamin K is about 80% as effective as vitamin E as an antioxidant. Vitamin E inhibits the oxidation of linoleic acid catalyzed by vitamin K hydroquinone. Vitamin E also strongly inhibits vitamin K dependent formation of both vitamin K epoxide and gamma-carboxyglutamic acid (gla). The significance of these observations to vitamin K action in vivo is discussed.     

Protecting antioxidative effects of vitamins E and C in experimental physical stress

Like every redox-active compound vitamin E may exert pro-oxidative and antioxidative effects depending on the reaction partners present. In this work we evaluated the intensity of oxidative stress produced by a physical exercise through swimming as well as of protecting action of antioxidant vitamins E and C. Antioxidant systems include antioxidant enzymes: superoxide-dismutase (SOD), catalase (CAT), glutathion peroxidase (GSH-Px), as well as of components with an antioxidant action of the reduced glutathion type (GSH) and vitamins E and C. We determine the activities of these enzymes in the erythrocytes and heart homogenate. Our results points out a protective effect against oxidative stress produced by swimming in animals treated with vitamins E and C, which are expressed through the diminution of the malondialdehyde (MDA) quantity both in erythrocytes and in the heart, and through the conservation of GSH content in both products. CAT and GSH-Px activities decrease while that of SOD increases on both tissues, but with different intensities in accordance with the variation of protection degree performed by the vitamin couple on these tissues. The obtained data underline the necessity of intensifying the means of endogenous antiradical defence with exogenous antioxidant vitamins C and E. This study highlights the need of a proper vitamin supplement in organism under stress.     

Vitamin E and its function in membranes

Vitamin E is a fat-soluble vitamin. It is comprised of a family of hydrocarbon compounds characterised by a chromanol ring with a phytol side chain referred to as tocopherols and tocotrienols. Tocopherols possess a saturated phytol side chain whereas the side chain of tocotrienols have three unsaturated residues. Isomers of these compounds are distinguished by the number and arrangement of methyl substituents attached to the chromanol ring. The predominant isomer found in the body is alpha-tocopherol, which has three methyl groups in addition to the hydroxyl group attached to the benzene ring. The diet of animals is comprised of different proportions of tocopherol isomers and specific alpha-tocopherol-binding proteins are responsible for retention of this isomer in the cells and tissues of the body. Because of the lipophilic properties of the vitamin it partitions into lipid storage organelles and cell membranes. It is, therefore, widely distributed in throughout the body. Subcellular distribution of alpha-tocopherol is not uniform with lysosomes being particularly enriched in the vitamin compared to other subcellular membranes. Vitamin E is believed to be involved in a variety of physiological and biochemical functions. The molecular mechanism of these functions is believed to be mediated by either the antioxidant action of the vitamin or by its action as a membrane stabiliser. alpha-Tocopherol is an efficient scavenger of lipid peroxyl radicals and, hence, it is able to break peroxyl chain propagation reactions. The unpaired electron of the tocopheroxyl radical thus formed tends to be delocalised rendering the radical more stable. The radical form may be converted back to alpha-tocopherol in redox cycle reactions involving coenzyme Q. The regeneration of alpha-tocopherol from its tocopheroxyloxyl radical greatly enhances the turnover efficiency of alpha-tocopherol in its role as a lipid antioxidant. Vitamin E forms complexes with the lysophospholipids and free fatty acids liberated by the action of membrane lipid hydrolysis. Both these products form 1:1 stoichiometric complexes with vitamin E and as a consequence the overall balance of hydrophobic:hydrophillic affinity within the membrane is restored. In this way, vitamin E is thought to negate the detergent-like properties of the hydrolytic products that would otherwise disrupt membrane stability. The location and arrangement of vitamin E in biological membranes is presently unknown. There is, however, a considerable body of information available from studies of model membrane systems consisting of phospholipids dispersed in aqueous systems. From such studies using a variety of biophysical methods, it has been shown that alpha-tocopherol intercalates into phospholipid bilayers with the long axis of the molecule oriented parallel to the lipid hydrocarbon chains. The molecule is able to rotate about its long axis and diffuse laterally within fluid lipid bilayers. The vitamin does not distribute randomly throughout phospholipid bilayers but forms complexes of defined stoichiometry which coexist with bilayers of pure phospholipid. alpha-Tocopherol preferentially forms complexes with phosphatidylethanolamines rather than phosphatidylcholines, and such complexes more readily form nonlamellar structures. The fact that alpha-tocopherol does not distribute randomly throughout bilayers of phospholipid and tends to form nonbilayer complexes with phosphatidylethanolamines would be expected to reduce the efficiency of the vitamin in its action as a lipid antioxidant and to destabilise rather than stabilise membranes. The apparent disparity between putative functions of vitamin E in biological membranes and the behaviour in model membranes will need to be reconciled.     

Role of vitamin E as a lipid-soluble peroxyl radical scavenger: in vitro and in vivo evidence

Multiple reactive oxygen/nitrogen species induce oxidative stress. Mammals have evolved with an elaborate defense network against oxidative stress, in which multiple antioxidant compounds and enzymes with different functions exert their respective roles. Radical scavenging is one of the essential roles of antioxidants and vitamin E is the most abundant and important lipophilic radical-scavenging antioxidant in vivo. The kinetic data and physiological molar ratio of vitamin E to substrates show that the peroxyl radicals are the only radicals that vitamin E can scavenge to break chain propagation efficiently and that vitamin E is unable to act as a potent scavenger of hydroxyl, alkoxyl, nitrogen dioxide, and thiyl radicals in vivo. The preventive effect of vitamin E against the oxidation mediated by nonradical oxidants such as hypochlorite, singlet oxygen, ozone, and enzymes may be limited in vivo. The synergistic interaction of vitamin E and vitamin C is effective for enhancing the antioxidant capacity of vitamin E. The in vitro and in vivo evidence of the function of vitamin E as a peroxyl radical-scavenging antioxidant and inhibitor of lipid peroxidation is presented.     

Multifaceted role of tocotrienols in cardioprotection supports their structure: function relation

Tocotrienols are a class of vitamin E which modulates several mechanisms associated with cardioprotection, anti-cancer, anti-diabetic, and neuroprotection. Unlike other Vitamin E-like compounds, tocotrienols possess inimitable properties. Quite a lot of studies have determined the cardioprotective abilities of tocotrienols and have been shown to possess novel hypocholesterolemic effects together with an ability to reduce the atherogenic apolipoprotein and lipoprotein plasma levels. In addition, tocotrienol has been suggested to have an antioxidant, anti-thrombotic, and anti-tumor effect indicating that tocotrienol may serve as an effective agent in the prevention and/or treatment of cardiovascular disease and cancer. The bioactivity exhibited is due to the structural characteristics of tocotrienols. Rich sources of tocotrienols which include rice bran, palm oil, and other edible oils exhibit protective effect against cardiovascular disorders. The conclusions drawn from the early literature that vitamin E group of compounds provides an inevitable role in cardioprotection is sustained in many more recent studies.     

Vitamin E: function and metabolism.

Although vitamin E has been known as an essential nutrient for reproduction since 1922, we are far from understanding the mechanisms of its physiological functions. Vitamin E is the term for a group of tocopherols and tocotrienols, of which alpha-tocopherol has the highest biological activity. Due to the potent antioxidant properties of tocopherols, the impact of alpha-tocopherol in the prevention of chronic diseases believed to be associated with oxidative stress has often been studied, and beneficial effects have been demonstrated. Recent observations that the alpha-tocopherol transfer protein in the liver specifically sorts out RRR-alpha-tocopherol from all incoming tocopherols for incorporation into plasma lipoproteins, and that alpha-tocopherol has signaling functions in vascular smooth muscle cells that cannot be exerted by other forms of tocopherol with similar antioxidative properties, have raised interest in the roles of vitamin E beyond its antioxidative function. Also, gamma-tocopherol might have functions apart from being an antioxidant. It is a nucleophile able to trap electrophilic mutagens in lipophilic compartments and generates a metabolite that facilitates natriuresis. The metabolism of vitamin E is equally unclear. Excess alpha-tocopherol is converted into alpha-CEHC and excreted in the urine. Other tocopherols, like gamma- and delta-tocopherol, are almost quantitatively degraded and excreted in the urine as the corresponding CEHCs. All rac alpha-tocopherol compared to RRR-alpha-tocopherol is preferentially degraded to alpha-CEHC. Thus, there must be a specific, molecular role of RRR-alpha-tocopherol that is regulated by a system that sorts, distributes, and degrades the different forms of vitamin E, but has not yet been identified. In this article we try to summarize current knowledge on the function of vitamin E, with emphasis on its antioxidant vs. other properties, the preference of the organism for RRR-alpha-tocopherol, and its metabolism to CEHCs.     

Zeaxanthin in combination with ascorbic acid or alpha-tocopherol protects ARPE-19 cells against photosensitized peroxidation of lipids

The antioxidant action of carotenoids is believed to involve quenching of singlet oxygen and scavenging of reactive oxygen radicals. However, the exact mechanism by which carotenoids protect cells against oxidative damage, particularly in the presence of other antioxidants, remains to be elucidated. This study was carried out to examine the ability of exogenous zeaxanthin alone and in combination with vitamin E or C, to protect cultured human retinal pigment epithelium cells against oxidative stress. The survival of ARPE-19 cells, subjected to merocyanine 540-mediated photodynamic action, was determined by the MTT test and the content of lipid hydroperoxides in photosensitized cells was analyzed by HPLC with electrochemical detection. We found that zeaxanthin-supplemented cells, in the presence of either alpha-tocopherol or ascorbic acid, were significantly more resistant to photoinduced oxidative stress. Cells with added antioxidants exhibited increased viability and accumulated less lipid hydroperoxides than cells without the antioxidant supplementation. Such a synergistic action of zeaxanthin and vitamin E or C indicates the importance of the antioxidant interaction in efficient protection of cell membranes against oxidative damage induced by photosensitized reactions.     

The location and function of vitamin E in membranes (review)

Vitamin E is a fat-soluble vitamin that consists of a group of tocols and tocotrienols with hydrophobic character, but possessing a hydroxyl substituent that confers an amphipathic character on them. The isomers of biological importance are the tocopherols, of which alpha-tocopherol is the most potent vitamin. Vitamin E partitions into lipoproteins and cell membranes, where it represents a minor constituent of most membranes. It has a major function in its action as a lipid antioxidant to protect the polyunsaturated membrane lipids against free radical attack. Other functions are believed to be to act as membrane stabilizers by forming complexes with the products of membrane lipid hydrolysis, such as lysophospholipids and free fatty acids. The main experimental approach to explain the functions of vitamin E in membranes has been to study its effects on the structure and stability of model phospholipid membranes. This review describes the function of vitamin E in membranes and reviews the current state of knowledge of the effect of vitamin E on the structure and phase behaviour of phospholipid model membranes.     

Antioxidants and cataract

Abstract

The major causes for cataract formation are free radicals, and these free radicals are neutralized by the presence of endogenous antioxidants in the eye. Using xenobiotics, it has been confirmed that free radicals mediate the formation of cataract. Two cataract model-selenite model and the diabetic cataract model-have been developed to study the pathophysiology of cataract formation due to free radicals and the role of antioxidants during the process of cataractogenesis. This review focuses on natural compounds with antioxidant properties that could actually be applied as an interventional strategy on a large scale and are also relatively inexpensive. A brief overview of plants with antioxidant properties that in addition possess potential anti-cataract properties has been discussed. In addition to plants, three natural compounds (curcumin, vitamin C and vitamin E), on which a lot of data exist showing anti-cataract and antioxidant activities, have also been discussed. These antioxidants can be supplemented in the diet for a better defence against free radicals. Studies on vitamin C and vitamin E have proved that they are capable of preventing lipid peroxidation, thereby preventing the generation of free radicals, but their efficacy as anti-cataract agent is questionable. Unlike vitamins C and E, curcumin is well established as an anti-cataract agent, but the issue of curcumin bioavailability is yet to be addressed. Nanotechnology proves to be a promising area in increasing the curcumin bioavailability, but still a lot more research needs to be done before the use of curcumin as an effective anti-cataract agent for humans.     

The role of ascorbate in antioxidant protection of biomembranes: Interaction with vitamin E and coenzyme Q

One of the vital roles of ascorbic acid (vitamin C) is to act as an antioxidant to protect cellular components from free radical damage. Ascorbic acid has been shown to scavenge free radicals directly in the aqueous phases of cells and the circulatory system. Ascorbic acid has also been proven to protect membrane and other hydrophobic compartments from such damage by regenerating the antioxidant form of vitamin E. In addition, reduced coenzyme Q, also a resident of hydrophobic compartments, interacts with vitamin E to regenerate its antioxidant form. The mechanism of vitamin C antioxidant function, the myriad of pathologies resulting from its clinical deficiency, and the many health benefits it provides, are reviewed.