Tocopherols and related compounds vitamin E

Vitamin E deficiency is normally associated with diseases of fat malabsorption and is rare in humans. Deficiency is characterized by erythrocyte haemolysis and prolonged deficiency can cause neuromuscular dysfunction. Hypervitaminosis E is not common, despite an increased intake of vitamin E supplements. Extremely high doses of the vitamin may interfere with the blood clotting process. 

The RDAs for vitamin E are 10 mg and 8 mg a-TEday for men and women, respectively. UK RNI values have not been established for vitamin E since its requirement is largely dependent on the content of polyunsaturated lipids in the diet. However, the Department of Health (1991) suggested that 4 and 3 mg a-TE day are adequate for men and women, respectively. The major food sources of vitamin E are polyunsaturated vegetable oils and products derived therefrom (e.g. maragrine, salad dressings), green and leafy 

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Vitamin E (tocopherol) and related compounds only occur in plants (e.g., wheat germ). They contain what is known as a chro-man ring. In the lipid phase, vitamin E is mainly located in biological membranes, where as an antioxidant it protects unsaturated lipids against ROS (see p. 284) and other radicals. 

Vitamin Kj was also separated on silica plates from a-tocopherol, P-carotene, and vitamins A and D2 in spinach (56). The plates were eluted with mixtures of petroleum ether-benzene (6 1, by vol) (56). For the separation of some rodenticides and related compounds (i.e. diphacinone, pindone, valone, warfarin, bromadiolon, vitamin Kj, and vitamin D3) Opong-Mensah and Porter (78) use Linear-K silica gel plates. Three mobile phases were examined (a) 1,2-dichloroethane-methanol-acetic acid (90 8 2, by vol), (b) chloroform-methanol (97 3, by vol), and (c) cyclohexane-1,2-dichloroethane-acetic acid (75 25 0.6, by vol). None of the mobile phases alone could separate all seven compounds. However, by repeating the separation in all three systems, each compound could be unequivocally identified. 

Vitamin E consists of a family of related compounds, the tocopherols. The most abundant in the American diet is 7-tocopherol and, although it is potentially superior in the detoxification of nitrogen dioxide, the biochemistry of a-tocopherol is considered more relevant to cardiovascular disease (Kayden and Traber, 1993). Vitamin E undoubtedly has several modes of action in vim. The most clearly understood of these, at the chemical level, is the role of a-tocopherol as an antioxidant. 

There are different physiological forms known as vitamins E, namely d-a-tocopherol, tocopheronolactone, and their phosphate esters. There are active analogs and related compounds knows as vitamins E, namely d/-atocopherol, /-a-tocopherol, esters (succinate, acetate, phosphate), and j8-, 1-, j-tocopherols [3]. 

Tocopherols and tocotrienols belong to the vitamin E family of compounds, which are potent antioxidants. The four isomers of tocotrienols (a-T3, P-T3, y-T3, 8-T3) are structurally related to their corresponding homologues of tocopherols (a-T, p-T, y-T, 8-T), but differ in their side-chain in that T3... 

More recently, this same group have used a combination of HPLC-NMR and HPLC-MS to identify analogues of vitamin E found in a palm oil extract rich in such tocopherol derivatives [46]. For the MS, a new technique called coordination ion spray was used in which the addition of silver ions to the HPLC eluent caused the enhanced formation of ions of such non-polar compounds. In addition, the HPLC utilised a C30 column in order to gain suitable chromatographic resolution. The compounds in the mixture comprised vitamin E itself, tocopherol, and five related compounds, some of which were isomeric. Tocopherol has the structure shown below ... 

The term Vitamin E was introduced by Evans and Bishop to describe a dietary factor important for reproduction in rats [1]. Natural vitamin E includes two groups of closely related fat-soluble compounds, the tocopherols and tocotrienols, each with the four a-, y-,... 

Since the early 1920s, it has been known that rats fed only cow s milk cannot produce offspring. The principle from wheat germ that can rectify this deficiency in both male and female rats was named vitamin E. When the compound known as vitamin E was isolated in 1936. it was named tocopherol. Since then,. several other closely related compounds have been discovered from natural sources, and thi.s family of natural products took the generic name locoph-erols. 

Of the two primary protective agents against liver necrosis, tocopherol appears more immediately related to respiratory decline and its prevention than Factor 3/selenium. Whereas in vivo application of vitamin E fully pievents respiratory failure in all systems used for its study, Factor 3-active selenium compounds afford only marginal protection in some of... 

Vitamin E is the name given to a number of structurally related compounds the most important of which is a-tocopherol. The vitamin is needed for mitochondrial electron-transport function and prevents oxidation of various compounds including polyunsaturated fatty acids and vitamin A. The dependence of vitamin E requirement on the amount of dietary polyunsaturated fatty acids has been fully discussed by Jager (1975). Traditionally, vitamin E has been known as the fertility vitamin. However, deficiency leads to serious changes in skeletal muscle, the blood system and other tissues before reproduction is impaired. The effects on different animals are described by Jager (1975). The topic of vitamin E is also covered by Scott (1978). 

Contrary to plants, higher animals can not synthesize compounds with benzenoid rings from aliphatic precursors, the very few exceptions include estrone and related phenolic steroids (Singleton, 1981). Plants are the source of nearly all the phenols found in animals. Even the phenols that are essential for animals (such as the catechol amines and phenolic indole amines involved in nerve action and associated effects), the vitamin E tocopherols, the vitamin K napthoquinones or menadiones, the ubiquinone benzoquinones, thyroxine, the tyrosine of proteins, and the tyrosine-DOPA derivatives involved in melanin pigment formation, are all drawn either directly or indirectly from plants or are modified from an essential plant precursor, usually phenylalanine (Singleton and Kratzer, 1969). 

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