Pub Date : 2019-02-04DOI: 10.1039/9781788016216-00001
E. Niki, K. Abe
Vitamin E is the collective name for lipophilic, naturally occurring compounds whose molecular structure is comprised of a chromanol ring with a side chain located at the C2 position and includes four tocopherols and four tocotrienols. Vitamin E, discovered as a dietary factor essential for normal reproduction, is now accepted as a major free radical scavenging antioxidant in humans and protects biological molecules from detrimental oxidative modifications. The structures and properties of vitamin E homologues and their sources, functions, and applications are summarized.
{"title":"CHAPTER 1. Vitamin E: Structure, Properties and Functions","authors":"E. Niki, K. Abe","doi":"10.1039/9781788016216-00001","DOIUrl":"https://doi.org/10.1039/9781788016216-00001","url":null,"abstract":"Vitamin E is the collective name for lipophilic, naturally occurring compounds whose molecular structure is comprised of a chromanol ring with a side chain located at the C2 position and includes four tocopherols and four tocotrienols. Vitamin E, discovered as a dietary factor essential for normal reproduction, is now accepted as a major free radical scavenging antioxidant in humans and protects biological molecules from detrimental oxidative modifications. The structures and properties of vitamin E homologues and their sources, functions, and applications are summarized.","PeriodicalId":23674,"journal":{"name":"Vitamin E","volume":"19 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83045629","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-02-04DOI: 10.1039/9781788016216-00051
Yoshiro Saito, Y. Yoshida
It is well known that both tocopherols (T) and tocotrienols (T3) act as radical-scavenging antioxidants. The reactivities of α, β, γ, and δT and the corresponding T3 isoforms toward free radicals are the same, and the corresponding T and T3 inhibit lipid peroxidation in solution similarly. T3 has a higher mobility between membranes and a higher rate of incorporation into membranes than does T. The initial rate of cellular uptake of T3 is higher than that of T, which confers an apparently higher cytoprotective capacity to T3 compared with T. The incorporated T and T3 are distributed proportionally to the lipids in the cells and function as radical scavengers to prevent lipid peroxidation and cell death. Oxidized products of vitamin E, such as tocopheryl quinone, have unique chemical and biological properties as arylating or non-arylating quinone. In this chapter, the chemical reactivity and cytoprotective effects of T and T3 are comparatively described.
{"title":"CHAPTER 4. Chemical Reactivity and Cellular Uptake of Tocopherols and Tocotrienols","authors":"Yoshiro Saito, Y. Yoshida","doi":"10.1039/9781788016216-00051","DOIUrl":"https://doi.org/10.1039/9781788016216-00051","url":null,"abstract":"It is well known that both tocopherols (T) and tocotrienols (T3) act as radical-scavenging antioxidants. The reactivities of α, β, γ, and δT and the corresponding T3 isoforms toward free radicals are the same, and the corresponding T and T3 inhibit lipid peroxidation in solution similarly. T3 has a higher mobility between membranes and a higher rate of incorporation into membranes than does T. The initial rate of cellular uptake of T3 is higher than that of T, which confers an apparently higher cytoprotective capacity to T3 compared with T. The incorporated T and T3 are distributed proportionally to the lipids in the cells and function as radical scavengers to prevent lipid peroxidation and cell death. Oxidized products of vitamin E, such as tocopheryl quinone, have unique chemical and biological properties as arylating or non-arylating quinone. In this chapter, the chemical reactivity and cytoprotective effects of T and T3 are comparatively described.","PeriodicalId":23674,"journal":{"name":"Vitamin E","volume":"116 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87880725","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-02-04DOI: 10.1039/9781788016216-00189
R. Brigelius-Flohé
Almost 100 years after the detection of vitamin E, its biological function is still waiting to be identified. The postulated function of an antioxidant is obviously not the only one. All forms of vitamin E have a chromanol structure and a 13-carbon-long side chain. The first degradation products to be found pointed to an oxidative opening of the chromanol structure, which supported the antioxidant theory. However, in all more recently analyzed metabolites, the chromanol ring is intact, which does not point to an oxidative action. The start of degradation is catalyzed by enzymes of the CYP system with two preferential ones: CYP3A4 and CYP4F2. CYP3A4 obviously acts preferentially on α-tocopherol, whereas CYP4F2 appears to preferentially degrade non-α-forms. Non-α-forms are metabolized fast, α-tocopherol only if present in excess. Both CYPs can be up-regulated, but differ in the response to different vitamin E forms. Detailed studies of the functions of individual metabolites are needed since they are appearing to turn out to be a new class of regulatory signaling molecules.
{"title":"CHAPTER 14. Metabolism of Vitamin E","authors":"R. Brigelius-Flohé","doi":"10.1039/9781788016216-00189","DOIUrl":"https://doi.org/10.1039/9781788016216-00189","url":null,"abstract":"Almost 100 years after the detection of vitamin E, its biological function is still waiting to be identified. The postulated function of an antioxidant is obviously not the only one. All forms of vitamin E have a chromanol structure and a 13-carbon-long side chain. The first degradation products to be found pointed to an oxidative opening of the chromanol structure, which supported the antioxidant theory. However, in all more recently analyzed metabolites, the chromanol ring is intact, which does not point to an oxidative action. The start of degradation is catalyzed by enzymes of the CYP system with two preferential ones: CYP3A4 and CYP4F2. CYP3A4 obviously acts preferentially on α-tocopherol, whereas CYP4F2 appears to preferentially degrade non-α-forms. Non-α-forms are metabolized fast, α-tocopherol only if present in excess. Both CYPs can be up-regulated, but differ in the response to different vitamin E forms. Detailed studies of the functions of individual metabolites are needed since they are appearing to turn out to be a new class of regulatory signaling molecules.","PeriodicalId":23674,"journal":{"name":"Vitamin E","volume":"40 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78868756","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-02-04DOI: 10.1039/9781788016216-00075
A. Azzi
Older studies of the phosphoric acid ester of α-tocopherol (TP) in enzymes and animal models have given no conclusive results. More recently, the molecule has been the object of new scientific attention as an extension to the renewed popularity of vitamin E (α-tocopherol). α-Tocopherol is a micronutrient that is needed to prevent a form of cerebellar ataxia, but several alleged functions have been attributed to it, including protection against neurodegeneration, atherosclerosis, cancer and aging. Initially, the biological function of TP was seen as a pro-vitamin E capable of releasing α-tocopherol in the body. Subsequent studies have indicated that the nanomolar amount of TP in the body is not compatible with functioning as a reserve of vitamin E, whose concentration in plasma is in the micromolar order. On the other hand, its existence in humans, animals and plants has prompted studies on TP's molecular functions, and these have revealed that it can be synthesized and hydrolyzed in cells and in animals. The enzymes responsible for α-tocopherol kinase and tocopheryl phosphate phosphatase cellular activities have not been purified. TP inhibits cell proliferation and regulates gene expression more potently than α-tocopherol; furthermore, some genes are exclusively regulated by TP. These signaling effects of TP are in connection with phosphatidyl inositol kinase. In animal models, TP has shown more potency than α-tocopherol against atherosclerosis and inflammation. TP has been proposed to be an activated form of α-tocopherol.
{"title":"CHAPTER 6. Tocopheryl Phosphate","authors":"A. Azzi","doi":"10.1039/9781788016216-00075","DOIUrl":"https://doi.org/10.1039/9781788016216-00075","url":null,"abstract":"Older studies of the phosphoric acid ester of α-tocopherol (TP) in enzymes and animal models have given no conclusive results. More recently, the molecule has been the object of new scientific attention as an extension to the renewed popularity of vitamin E (α-tocopherol). α-Tocopherol is a micronutrient that is needed to prevent a form of cerebellar ataxia, but several alleged functions have been attributed to it, including protection against neurodegeneration, atherosclerosis, cancer and aging. Initially, the biological function of TP was seen as a pro-vitamin E capable of releasing α-tocopherol in the body. Subsequent studies have indicated that the nanomolar amount of TP in the body is not compatible with functioning as a reserve of vitamin E, whose concentration in plasma is in the micromolar order. On the other hand, its existence in humans, animals and plants has prompted studies on TP's molecular functions, and these have revealed that it can be synthesized and hydrolyzed in cells and in animals. The enzymes responsible for α-tocopherol kinase and tocopheryl phosphate phosphatase cellular activities have not been purified. TP inhibits cell proliferation and regulates gene expression more potently than α-tocopherol; furthermore, some genes are exclusively regulated by TP. These signaling effects of TP are in connection with phosphatidyl inositol kinase. In animal models, TP has shown more potency than α-tocopherol against atherosclerosis and inflammation. TP has been proposed to be an activated form of α-tocopherol.","PeriodicalId":23674,"journal":{"name":"Vitamin E","volume":"42 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88239177","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-02-04DOI: 10.1039/9781788016216-00064
N. Kono, H. Arai
α-Tocopherol transfer protein (α-TTP) is an α-tocopherol-selective vitamin E-binding protein expressed predominantly in hepatocytes. By stimulating the secretion of endocytosed α-tocopherol to the systemic circulation in hepatocytes, α-TTP plays a critical role in maintaining the α-tocopherol level in the body. Heritable mutations in the α-TTP gene are the cause of familial vitamin E deficiency, termed ataxia with vitamin E deficiency (AVED). Recent studies on missense mutations found in AVED patients highlight the molecular mechanism underlying the intracellular α-tocopherol transport by α-TTP. In this review, we will discuss the molecular mechanism and physiological roles of α-TTP-mediated α-tocopherol transport in the hepatocytes.
{"title":"CHAPTER 5. α-Tocopherol Transfer Protein","authors":"N. Kono, H. Arai","doi":"10.1039/9781788016216-00064","DOIUrl":"https://doi.org/10.1039/9781788016216-00064","url":null,"abstract":"α-Tocopherol transfer protein (α-TTP) is an α-tocopherol-selective vitamin E-binding protein expressed predominantly in hepatocytes. By stimulating the secretion of endocytosed α-tocopherol to the systemic circulation in hepatocytes, α-TTP plays a critical role in maintaining the α-tocopherol level in the body. Heritable mutations in the α-TTP gene are the cause of familial vitamin E deficiency, termed ataxia with vitamin E deficiency (AVED). Recent studies on missense mutations found in AVED patients highlight the molecular mechanism underlying the intracellular α-tocopherol transport by α-TTP. In this review, we will discuss the molecular mechanism and physiological roles of α-TTP-mediated α-tocopherol transport in the hepatocytes.","PeriodicalId":23674,"journal":{"name":"Vitamin E","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79300941","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-02-04DOI: 10.1039/9781788016216-00165
N. Noguchi
It has been known that a major role of vitamin E is to inhibit lipid peroxidation by scavenging a lipid peroxyl radical by donating an electron and hydrogen from the phenol group on the chroman ring. The radical scavenging activity of tocopherols in solution is dependent on the methyl substituents on the chroman ring but not on the side chain at the C-2 position. Therefore, tocopherol (Toc) and tocotrienol (Toc3) show almost the same efficacy in the inhibition of lipid peroxidation in solution. However, the action of vitamin E in the cell is more complicated and is dependent on the efficacy of its incorporation, retention, and mobility, which in turn are affected by the nature of the side chains. Toc3 shows an advantage in the inhibition of oxidative-stress-involved alteration of a cell's function due to its higher uptake by the cell. The critical effect of the side chain of vitamin E has been implicated in the inhibition of cell death, depending on what causes the cell death. For example, the cell death induced by 24S-hydroxycholesterol was inhibited by Toc but not by Toc3. In this chapter, the efficacy of vitamin E homologues in the inhibition of lipid peroxidation under different conditions and against cell death caused by different stimuli is described.
{"title":"CHAPTER 12. Action of Vitamin E Against Lipid Peroxidation and Cell Death","authors":"N. Noguchi","doi":"10.1039/9781788016216-00165","DOIUrl":"https://doi.org/10.1039/9781788016216-00165","url":null,"abstract":"It has been known that a major role of vitamin E is to inhibit lipid peroxidation by scavenging a lipid peroxyl radical by donating an electron and hydrogen from the phenol group on the chroman ring. The radical scavenging activity of tocopherols in solution is dependent on the methyl substituents on the chroman ring but not on the side chain at the C-2 position. Therefore, tocopherol (Toc) and tocotrienol (Toc3) show almost the same efficacy in the inhibition of lipid peroxidation in solution. However, the action of vitamin E in the cell is more complicated and is dependent on the efficacy of its incorporation, retention, and mobility, which in turn are affected by the nature of the side chains. Toc3 shows an advantage in the inhibition of oxidative-stress-involved alteration of a cell's function due to its higher uptake by the cell. The critical effect of the side chain of vitamin E has been implicated in the inhibition of cell death, depending on what causes the cell death. For example, the cell death induced by 24S-hydroxycholesterol was inhibited by Toc but not by Toc3. In this chapter, the efficacy of vitamin E homologues in the inhibition of lipid peroxidation under different conditions and against cell death caused by different stimuli is described.","PeriodicalId":23674,"journal":{"name":"Vitamin E","volume":"87 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78067001","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-02-04DOI: 10.1039/9781788016216-00032
J. Atkinson, D. Marquardt, T. Harroun
The neutral lipids of the vitamin E family (tocopherols and tocotrienols) are well known antioxidants with α-tocopherol (α-Toc) being the sole tocopherol retained in mammalian tissues after absorption from the diet. Because of their high hydrophobicity, tocopherols partition easily into biological membranes. The location and dynamic behavior of tocopherols and tocotrienols in phospholipid membranes is essential information for describing the mechanism(s) of action of these molecules. The bilayer orientation and dynamics are central to our comprehension of their action as antioxidants, protecting free radical-induced peroxidation of polyunsaturated phospholipids. Tocopherols and tocotrienols may also affect sub-membrane domains such as lipid rafts, and the unusual biological activities for non-α-tocopherols is potentially explainable by their oxidative conversion to arylating quinones. In this review we describe recent work on the location and behavior of mainly α-Toc in model bilayers.
{"title":"CHAPTER 3. The Behaviour of Vitamin E in Membranes","authors":"J. Atkinson, D. Marquardt, T. Harroun","doi":"10.1039/9781788016216-00032","DOIUrl":"https://doi.org/10.1039/9781788016216-00032","url":null,"abstract":"The neutral lipids of the vitamin E family (tocopherols and tocotrienols) are well known antioxidants with α-tocopherol (α-Toc) being the sole tocopherol retained in mammalian tissues after absorption from the diet. Because of their high hydrophobicity, tocopherols partition easily into biological membranes. The location and dynamic behavior of tocopherols and tocotrienols in phospholipid membranes is essential information for describing the mechanism(s) of action of these molecules. The bilayer orientation and dynamics are central to our comprehension of their action as antioxidants, protecting free radical-induced peroxidation of polyunsaturated phospholipids. Tocopherols and tocotrienols may also affect sub-membrane domains such as lipid rafts, and the unusual biological activities for non-α-tocopherols is potentially explainable by their oxidative conversion to arylating quinones. In this review we describe recent work on the location and behavior of mainly α-Toc in model bilayers.","PeriodicalId":23674,"journal":{"name":"Vitamin E","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82007350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-02-04DOI: 10.1039/9781788016216-00175
R. Yamauchi
Vitamin E is the most important lipophilic antioxidant in vivo and in vitro, which scavenges lipid-derived free radicals. This chapter has reviewed the oxidation products of two vitamin E compounds, α- and γ-tocopherols (αTH and γTH), during the degradation process of lipid hydroperoxides. Lipid hydroperoxides, the primary products of lipid peroxidation, are decomposed by transition metal ions or heme compounds to produce a wide range of secondary products, such as some toxic aldehydes. Since this process takes place via free radical reactions in lipophilic circumstances, THs can suppress the formation of such secondary products by trapping free-radical intermediates in micellar and liposomal systems. The oxidation products of αTH during the degradation process of lipid hydroperoxides are α-tocopherylquinone, 8a-(epoxylipid-dioxy)-α-tocopherones, 6-O-epoxylipid-αTHs, and αTH dimer. The products of γTH with lipid hydroperoxide-derived free radicals are tocored, γ-tocopherylquinone, 8a-(epoxylipid-dioxy)-γ-tocopherones, 6-O-epoxylipid-γTHs, and two γTH dimers. The produced γTH dimers are still effective in trapping lipid hydroperoxide-derived free radicals and form some addition products.
维生素E是体内体外最重要的亲脂抗氧化剂，具有清除脂源性自由基的作用。本章综述了两种维生素E化合物α-和γ-生育酚(α th和γTH)在脂质氢过氧化物降解过程中的氧化产物。脂质氢过氧化物是脂质过氧化反应的初级产物，它被过渡金属离子或血红素化合物分解，产生多种次级产物，如某些有毒的醛类。由于这一过程是在亲脂性环境下通过自由基反应发生的，因此三萜类化合物可以通过在胶束和脂质体系统中捕获自由基中间体来抑制这类二次产物的形成。脂类氢过氧化物降解过程中αTH的氧化产物为α-生育酚基醌、8a-(环氧脂-二氧基)-α-生育酚酮、6- o -环氧脂-α ths和αTH二聚体。γ- th与脂质氢过氧化物自由基的产物为γ-生育酚基醌、8a-(环氧脂-二氧基)-γ-生育酚酮、6- o -环氧脂-γ- ths和两种γ- th二聚体。生成的γ - th二聚体仍然有效地捕获脂质氢过氧化氢自由基并形成一些加成产物。
{"title":"CHAPTER 13. Oxidation Products of Vitamin E with Lipid-derived Free Radicals","authors":"R. Yamauchi","doi":"10.1039/9781788016216-00175","DOIUrl":"https://doi.org/10.1039/9781788016216-00175","url":null,"abstract":"Vitamin E is the most important lipophilic antioxidant in vivo and in vitro, which scavenges lipid-derived free radicals. This chapter has reviewed the oxidation products of two vitamin E compounds, α- and γ-tocopherols (αTH and γTH), during the degradation process of lipid hydroperoxides. Lipid hydroperoxides, the primary products of lipid peroxidation, are decomposed by transition metal ions or heme compounds to produce a wide range of secondary products, such as some toxic aldehydes. Since this process takes place via free radical reactions in lipophilic circumstances, THs can suppress the formation of such secondary products by trapping free-radical intermediates in micellar and liposomal systems. The oxidation products of αTH during the degradation process of lipid hydroperoxides are α-tocopherylquinone, 8a-(epoxylipid-dioxy)-α-tocopherones, 6-O-epoxylipid-αTHs, and αTH dimer. The products of γTH with lipid hydroperoxide-derived free radicals are tocored, γ-tocopherylquinone, 8a-(epoxylipid-dioxy)-γ-tocopherones, 6-O-epoxylipid-γTHs, and two γTH dimers. The produced γTH dimers are still effective in trapping lipid hydroperoxide-derived free radicals and form some addition products.","PeriodicalId":23674,"journal":{"name":"Vitamin E","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78955283","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-02-04DOI: 10.1039/9781788016216-00098
C. Winterbourn
Living organisms are continually exposed to free radicals and other reactive oxygen species as a result of metabolising oxygen and other redox-active compounds. Excessive production can result in biological damage whereas in other situations, specific oxidants are generated as a host defence mechanism or as a cell signal that activates gene expression and metabolic responses. This chapter provides an overview of the different reactive oxygen species generated in biological systems and the reactions they undergo with biological molecules.
{"title":"CHAPTER 8. Reactive Oxygen Species in Biological Systems","authors":"C. Winterbourn","doi":"10.1039/9781788016216-00098","DOIUrl":"https://doi.org/10.1039/9781788016216-00098","url":null,"abstract":"Living organisms are continually exposed to free radicals and other reactive oxygen species as a result of metabolising oxygen and other redox-active compounds. Excessive production can result in biological damage whereas in other situations, specific oxidants are generated as a host defence mechanism or as a cell signal that activates gene expression and metabolic responses. This chapter provides an overview of the different reactive oxygen species generated in biological systems and the reactions they undergo with biological molecules.","PeriodicalId":23674,"journal":{"name":"Vitamin E","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84318275","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-02-04DOI: 10.1039/9781788016216-00228
R. Bruno
Vitamin E is the term that describes eight structurally-related vitamers, specifically four tocopherols (α-, β-, γ-, and δ-) and four tocotrienols (α-, β-, γ-, and δ-). Although each vitamer has antioxidant activity that prevents the cyclic progression of lipid peroxidation, α-tocopherol is the only form that is essential for humans because it prevents and reverses clinical deficiency of vitamin E. These vitamers also differ substantially in their bioavailability, which results in α-tocopherol accumulating to the greatest extent in the circulation and tissues in humans. In nature, α-tocopherol exists as a single stereoisomer (2R, 4′R, 8′R- or RRR-α-tocopherol) whereas most dietary supplements and fortified foods contain an all racemic mixture of eight α-tocopherol stereoisomers. Importantly, only 50% of these stereoisomers are appreciably bioavailable, and therefore capable of contributing to dietary α-tocopherol requirements in humans. This chapter will therefore focus on the bioavailability, metabolism, and trafficking of vitamin E forms along the gut–liver axis. It will also discuss their structure–function aspects concerning their ability to contribute to dietary vitamin E requirements and associated health benefits.
{"title":"CHAPTER 16. Essentiality, Bioavailability, and Health Benefits of α-Tocopherol Stereoisomers","authors":"R. Bruno","doi":"10.1039/9781788016216-00228","DOIUrl":"https://doi.org/10.1039/9781788016216-00228","url":null,"abstract":"Vitamin E is the term that describes eight structurally-related vitamers, specifically four tocopherols (α-, β-, γ-, and δ-) and four tocotrienols (α-, β-, γ-, and δ-). Although each vitamer has antioxidant activity that prevents the cyclic progression of lipid peroxidation, α-tocopherol is the only form that is essential for humans because it prevents and reverses clinical deficiency of vitamin E. These vitamers also differ substantially in their bioavailability, which results in α-tocopherol accumulating to the greatest extent in the circulation and tissues in humans. In nature, α-tocopherol exists as a single stereoisomer (2R, 4′R, 8′R- or RRR-α-tocopherol) whereas most dietary supplements and fortified foods contain an all racemic mixture of eight α-tocopherol stereoisomers. Importantly, only 50% of these stereoisomers are appreciably bioavailable, and therefore capable of contributing to dietary α-tocopherol requirements in humans. This chapter will therefore focus on the bioavailability, metabolism, and trafficking of vitamin E forms along the gut–liver axis. It will also discuss their structure–function aspects concerning their ability to contribute to dietary vitamin E requirements and associated health benefits.","PeriodicalId":23674,"journal":{"name":"Vitamin E","volume":"21 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91005478","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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