8-Tocotrienol

Tocotrienols differ from tocopherols by the presence of three isolated double bonds in the branched alkyl side chain. Oxidation of tocopherol leads to ring opening and the formation of tocoquinones that show an intense red color. This species is a significant contributor to color quaUty problems in oils that have been abused. Tocopherols function as natural antioxidants (qv). An important factor in their activity is their slow reaction rate with oxygen relative to combination with other free radicals (11). 

Vitamin E was first described ia 1922 and the name was originally applied to a material found ia vegetable oils. This material was found to be essential for fertility ia tats. It was not until the early 1980s that symptoms of vitamin E deficiency ia humans were recognized. Early work on the natural distribution, isolation, and identification can be attributed to Evans, Butt, and Emerson (University of California) and MattiU and Olcott (University of Iowa). Subsequentiy a group of substances (Eig. 1), which fall iato either the family of tocopherols or tocotrienols, were found to act like vitamin E (1 4). The stmcture of a-tocopherol was determined by degradation studies ia 1938 (5). 

Fig. 1. The four naturally occutting tocopherols (a-tocopherol, E.E.E. [59-02-9] jall-rac [2074-53-5] (1) p-tocopherol [148-03-8] (2) y-tocopherol [54-28-4] (3) 8-tocopherol [119-13-1] (4)), a-tocotrienol [1721 -51 -3] (5), and p-tocotrienol [14101-61-2] (6) where asterisks denote asymmetric centers and the...

The yield of the more active RRR-a-tocopherol can be improved by selective methylation of the other tocopherol isomers or by hydrogenation of a-tocotrienol (25,26). Methylation can be accompHshed by several processes, such as simultaneous halo alkylation and reduction with an aldehyde and a hydrogen haUde in the presence of staimous chloride (27), amino alkylation with ammonia or amines and an aldehyde such as paraformaldehyde followed by catalytic reduction (28), or via formylation with formaldehyde followed by catalytic reduction (29). 

Label claims for tocopherol levels in preparations can be based on milligrams or International Units. Only the RRR or all-rac-International Units ate also used in some reference books and compendia, eg. Food Chemicals Codex (40,53), which is of particular importance for specifications for food fortification. 

The term vitamin E describes a family of eight antioxidants, four tocopherols, alpha (a), beta ((3), gamma (y) and delta (8), and four tocotrienols (also a, (3, y, and 8). a-Tocopherol is present in nature in only one form, RRR a-tocopherol. The chemical synthesis of a-tocopherol results in eight different forms (SRR, SSR, SRS, SSS, RSR, RRS, RSS, RRR), only one of which is RRR a-tocopherol. These forms differ in that they can be right (R) or left (S) at three different places in the a-tocopherol molecule. RRR a-tocopherol is the only form of vitamin E that is actively maintained in the human body and is therefore the form of vitamin E found in the largest quantities in the blood and tissue. A protein synthesized in the liver (a-TTP alpha-tocopherol transfer protein) preferentially selects the natural form of vitamin E (RRR a-tocopherol) for distribution to the tissues. However, the mechanisms for the regulation of vitamin E in tissues are not known... 

E Tocopherols, tocotrienols Antioxidant, especially in cell membranes Extremely rare—serious neurologic dysfunction... 

No unequivocal unique function for vitamin E has been defined. However, it does act as a hpid-soluble antioxidant in cell membranes, where many of its functions can be provided by synthetic antioxidants. Vitamin E is the generic descriptor for two famihes of compounds, the tocopherols and the tocotrienols (Figure 45—5). The different vitamers (compounds having similar vitamin activity) have different biologic potencies the most active is D-a-tocopherol, and it is usual to express vitamin E intake in milhgrams of D-a-tocoph-erol equivalents. Synthetic DL-a-tocopherol does not have the same biologic potency as the namrally occurring compound. 

In inner layers, changes are much the same as during boiling. Tocopherols and tocotrienols present in wheat and rye are partially destroyed during baking. In ordinary wheat bread, losses of a-tocopherol amount to about 25%, but in the case of rye bread, prepared by traditional technology, a loss of about 50% was reported (Piironen et al, 1987). Losses of natural antioxidants in coffee brews and tomato puree were also observed (Nicoli et al, 1997). 

Tocotrienols, gamma Oryzanol Phosphatidyl chohne Antioxidants Controls liver cirrhosis and helps in effective liver detoxification (Bruni, 1988). Protectant against hver damage (Kidd, 1996). Antioxidant enzymes prevent hpid peroxidation and helps protecting the liver cells from damage. 

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... 

Tocotrienols are another group of phytochemicals of rice bran which have a chemopreventive effect and have been demonstrated to inhibit breast cancer (Nesaremam et al., 1998). The polysaccharides of rice bran contain a-glucan, the anti-tumor effect of which has been demonstrated by its inhibition of gastrointestinal carcinogenesis (Akeshita et al., 1992). Rice bran agglutinin has been shown to induce apoptosis of cancer cells by the mechanism of cell cycle dysregulation (Miyoshi et al., 2001). 

Tocotrienols present in rice bran inhibit the liver microsomal enzyme HMGCoA reductase (Qureshi and Qureshi, 1992), the key enzyme involved in the endogenous synthesis of cholesterol, and this helps to lower the circulating cholesterol. Inhibition of another enzyme, ACAT (Acyl coenzyme A acyl transferase), by y-oryzanol results in lowered LDL-C synthesis and enrichment... 

Natural products have been noted for their potential health benefits from time immemorial and are the basis of Ayurveda, an ancient Indian medical practice (Bushkin and Bushkin, 2002). However, the potential benefits of several natural products reside in one or two active ingredients. For example green tea stands for polyphenols, soy for soy estrogens, broccoli for isothiocyanates and grape seed for polyphenols. The beauty of rice bran is that there are more than 100 antioxidants, several categories of bioactive phytonutrients, such as IP6, polyphenols, phytosterols, tocotrienols, y-oryzanol, B vitamins, minerals and trace minerals in addition to fat, protein, fiber, polysaccharides and other nutrients. These phytonutrients and antioxidants of rice bran are believed to act at the cellular level, and their synergestic function is responsible for the positive health benefits. 

NESARETNAM K, STEPHEN R, OILS R, DARBRE p (1998) Tocotrienols inhibit the growth of... 

PARKER R A, PEARCE B 0, CLARK R w, GORDON D A, WRIGHT J J (1993) Tocotrienols regulate cholesterol production in mammalian cells by post-transcriptional suppression of 3-hydroxy 3-methyl-glutaryl-coenzyme A reductase. J Biol Chem, 268 11230-38. 

QURESHI A A, SAMI s A, SALSER w A, KHAN F A (2001) Syuergistic effect of tocotrienol rich fraction (TRF 25) of rice bran and lovostatin on lipid parameters in hypercholesterolemic hamnns. J Nutri Biochem, 12 318-29. 

RAEDERSTORFF D, ELSTE V, AEBiscHER c, WEBER p (2002) Effect of either gamma-tocotrienol or a tocotrienol mixture on the plasma lipid profile in hamsters. Ann Nutr Metab, 46 17-23. 

TOMEO A c, GELLER M (1995) Antioxidant effect of tocotrienols in patients with hyperlipidemia and carotid stenosis. Lipids, 30 1179-83. 

XU z, HUA N, GODBER s (2001) Antioxidant activity of tocopherols, tocotrienols, and y-oryzanol components from rice bran against cholesterol oxidation accelerated by 2, 2 -azobis(2-methylpropionamidine) dihydrochloride. J Agri Food Chem, 49 2077-81. 

Kamal-Eldin, A. Appelqvist, L. A. The chemistry and antioxidant properties of tocopher-ols and tocotrienols. Lipids 1996, 31, 671-701. 

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