Tocopherol metabolism

Mardones, P and Rigotti, A, 2004. Cellular mechanisms of vitamin E uptake Relevance in alpha-tocopherol metabolism and potential implications for disease. J Nutr Biochem 15, 252-260. 

Mardones P, Strobel P, Miranda S, Leighton F, Quinones V, Amigo L, Rozowski J, Krieger M, and Rigotti A (2002) Alpha-tocopherol metabolism is abnormal in scavenger receptor class B type I (SR-BI)-deficient mice. Journal of Nutrition 132,443-9. 

Tocopherols (vitamin E) occur in many food substances that are consumed as part of the normal diet. The daily nutritional requirement has not been clearly defined but is estimated to be 3.0-20.0 mg. Absorption from the gastrointestinal tract is dependent upon normal pancreatic function and the presence of bile. Tocopherols are widely distributed throughout the body, with some ingested tocopherol metabolized in the liver excretion of metabolites is via the urine or bile. Individuals with vitamin E deficiency are usually treated by oral administration of tocopherols, although intramuscular and intravenous administration may sometimes be used. 

OCAs, therefore, may lower a-tocopherol plasma concentrations in rats receiving supplements of a-tocopherol in their diet, but an effect on human a-tocopherol metabolism has not been demonstrated. 

Himmelfarb, J., Kane, J., McMonagle, E., Zaltas, E., Bobzin, S., Boddupalli, S., Phinney, S., and Miller, G., Alpha and gamma tocopherol metabolism in healthy subjects and patients with end-stage renal disease. Kidney Int. 64 (3), 978-991,2003. 

Bieri, JG and Evarts, RP (1974) Gamma tocopherol metabolism, biological activity and significance in human vitamin E nutrition. Am. J. Cliru Nutr., 27(9), 980-986. 

A specific role for vitamin E in a required metabolic function has not been found. In addition to its direct antioxidant effects, a-tocopherol has been reported to have specific molecular functions. 

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. 

As mentioned previously, in the AMD retina iron metabolism is compromised (He et al., 2007 Wong et al., 2007). Thus, it is of interest to determine the effects of potential antioxidants in the presence of iron. In an in vitro study of ARPE-19 cells, addition of a lipophilic iron complex led to about a ninefold increase in the photosensitized yield of 7a,(3-cholesterol hydroperoxides (Wrona et al., 2004). In the presence of the iron, ascorbate exerted pro-oxidant effects, while the effects of a-tocopherol, zeaxanthin, or their combination were still protective (Wrona et al., 2004). Thus, it appears that the effects of potential antioxidants are strongly dependent on the sources of oxidative damage. The same antioxidant may be protective under certain conditions and exert deleterious effects when the conditions are changed. Therefore a detailed understanding of the sources of the oxidative damage is required in order to design an adequate antioxidant mixture. 

Another interesting feature of nutritargeting is the ability to circumvent absorption or metabolization barriers during malabsorption, maldigestion, or when there is a lack of transport proteins, for example, tocopherol-... 

Knowledge of the chemical structures of the major vitamins was acquired during the 30 years after 1920, and some were identified as known compounds. They were classified as fat-soluble and water-soluble vitamins. The only heterocyclic compounds in the former class are the tocopherols (vitamin E). They were discovered through their action in preventing sterility in rats, but they appear to play an important part in the metabolism of skeletal muscle. Vitamin E deficiency appears to occur rarely in man, but vitamin E therapy is tried in a number of clinical disorders. The tocopherols may be isolated from vegetable oils, and synthetic a-tocopherol (61) is made by condensing trimethylhydroquinone with phytol or phytyl halides (Scheme 2). For medicinal use they may be converted into their acetates or succinates. 

---