Tocopherols Vitamin E as Antioxidants

Some sprays include vitamins such as tocopherols (vitamin E) or panthenol, which is metabolized in the skin to become pantothenic acid, a B vitamin. Since hair does not metabolize ( It s dead, Jim ), these sprays perform the functions of antioxidants (tocopherols). In other words, they add shine and moisture (panthenol) rather than perform their normal vitamin roles. Moisture helps prevent damage during combing. 

The major lipid-soluble antioxidant primarily associated with lipid membranes is a-tocopherol (vitamin E). Circulating a-tocopherol is carried by chylomicrons, LDL and HDL and also has extracellular antioxidant capacities. As a chain-breaking antioxidant, it short circuits the propagation phase of lipid peroxidation because the peroxyl radical will react with a-tocopherol more rapidly than a polyunsaturated ffitty acid (Burton and Traber, 1990). The resulting a-tocopheryl radical reacts with a second peroxyl radical to form an inactive, nonradical complex. In vitro, ascorbate regenerates the tocopheryl radical into its native non-radical form (Burton and Traber, 1990). 

The mechanism of prooxidant effect of a-tocopherol in aqueous lipid dispersions such as LDLs has been studied [22], This so-called tocopherol-mediated peroxidation is considered in detail in Chapter 25, however, in this chapter we should like to return once more to the question of possible prooxidant activity of vitamin E. The antioxidant effect of a-tocopherol on lipid peroxidation including LDL oxidation is well established in both in vitro and in vivo systems (see, for example, Refs. [3,4] and many other references throughout this book). However, Ingold et al. [22] suggested that despite its undoubted high antioxidant efficiency in homogenous solution a-tocopherol can become a chain transfer agent in aqueous LDL... 

Vitamin E, a natural antioxidant, is essential for growth, disease prevention, tissue integrity and reproduction in all fauna. Natural vitamin E, as it occurs in plants, consists mainly of a-tocopherol (III, R = H) with minor amounts of y-tocopherol (IV), although this ratio can vary as for example in the vegetable oil composition shown in Fig. 5a. In animal husbandry, such as dairy farms or cattle feed lots, the stock diets are commonly supplemented with vitamin E, because processed grain-based cereal fodder, hay, and silage are deficient in vitamin This results in higher levels of a-tocopherol... 

Tobacco mosaic virus 247, 334s, 336s Tocopherols 392,815 — 822,818 as antioxidants 822 a-Tocopherol (vitamin E) 819s Tocopherolquinone 818, 819, 819s Tocotrienols 818 Togavirus 247... 

Oxidation of chromans has been extensively studied, especially of those which resemble the tocopherols which act as antioxidants in nature and in food. The behaviour of a-tocopherol (vitamin E, 547) and many simpler model compounds under oxidizing conditions varies with the oxidizing agent. Among the many products formed are the o- and p-quinones (609) and (610), the spiran (611) and dimer (612). A detailed account is available (81HC(36)59). 

The same is true of antioxidants like BHT (butylhydroxytoluene). Although it is used in purified form in human and animal food, its more common use is as a stabilizer for polymers and lubricants. Only BHA (butylhydrox-yanisole), a-tocopherol (vitamin E), TBHQ (tertiary-butylhydroquinone) and propylgal-late, which are marketed by Eastman Kodak, can be considered as purely food antioxidants for the two reasons that they are not toxic and that they are high priced. In fact, Eastman Kodak is the only chemical leader to produce an extended range of food additives mono-and diglycerides and vitamins. 

Reduction of the Vitamin E Radical by Ascorbate Asdiscussed in Section 4.3.1, one of the major roles of vitamin E is as a radical-trapping antioxidant in membranes and lipoproteins. a-Tocopherol reacts with lipid peroxides forming the a-tocopheroxyl radical, which reacts with ascorbate in the aqueous phase, regenerating a-tocopherol, and forming monodehydroascorbate. Vitamin C may have a vitamin E-sparing antioxidant action, coupling lipophilic and hydrophilic reactions. 

It is known that a cooperative effect between LA and other natural antioxidants, such as tocopherol (vitamin E) or ascorbic acid, affords the possibility to reduce the formation of reactive oxygen species (ROS), associated with various pathological disorders. Thus triamine spacer as backbone was used to attach Trolox , a water-soluble analogue of vitamin E, and LA, to obtain new analogues 356 which were tested as inhibitors of the microsomal lipid peroxidation. Attachment of LA to the chroman moiety, as in compound 357, is a useful extension of this study <2001JME4300, 2004BMC4835>. 

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