Biological Chemistry - Berezov, T. T., Korovkin, B. F. 1998

Vitamins
Fat-Soluble Vitamins
Vitamin E Group

In the early 1920s, H. Evans demonstrated that mixed diets contain a substance that is strictly essential for normal animal reproduction. For instance, rats fed a synthetic diet consisting of milk, iron supplements, and Yeast (as a source of B-group Vitamins) developed Infertility. Supplementing this diet with lettuce leaves completely cured the animals of infertility. The active anti-sterility substance was isolated from wheat germ oil and cottonseed oil and named vitamin E, or tocopherol (from the Greek tokos meaning offspring, and phero meaning to bear). Chemical synthesis was soon accomplished as well. Currently, five natural compounds exhibiting the biological activity of vitamin E are known. All of them have been isolated in pure form from vegetable oils or obtained synthetically, and are designated as a-, ß-, y-, δ-tocopherols and 8-methyltocotrienol, respectively.

From a chemical standpoint, tocopherols are derivatives of 2-methyl-2(4', 8', 12'-trimethyltridecyl)-chroman-6-ol, or tocol*.

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* Tocotrienols and tocols share an almost identical Structure, differing in that the former contain an unsaturated isoprenoid side chain instead of a fully hydrogenated one.

The various tocopherols differ from one another in the number and arrangement of methyl groups on the benzene ring. They are colorless, oily liquids that are highly soluble in fats (oils) and fat Solvents, quite stable against heat, but rapidly destroyed by UV radiation.

Changes in The Human Body due to vitamin E deficiency have not been sufficiently studied, as humans obtain adequate amounts of vitamin E from vegetable oils. Deficiency has been noted in certain tropical countries where CARBOHYDRATES serve as the primary dietary source while fats are consumed in negligible amounts. Vitamin E preparations have found application in medical practice, sometimes preventing spontaneous (or habitual) abortions in women. In experimental animals, particularly rats, vitamin E deficiency disrupts Embryogenesis and causes degenerative changes in reproductive Organs, leading to sterility. In females, the Placenta is affected to a greater extent than the Ovaries; the Fertilization process of the ovum remains unimpaired, but the fetus is resorbed very shortly thereafter. In males, Atrophy of the Gonads occurs, resulting in complete or partial sterility. Specific manifestations of vitamin E deficiency also include muscular dystrophy, fatty Liver infiltration, and Spinal Cord degeneration. The degenerative and dystrophic changes in Muscles result in a sharp restriction of animal mobility; the levels of Myosin, Glycogen, potassium, magnesium, phosphorus, and creatinine sharply decrease in muscles, whereas the content of Lipids and sodium chloride increases.

Biological Role. There is a direct relationship between vitamin E and tissue Respiration, and an inverse relationship between this vitamin and the degree of lipid oxidation.

It is known that tocopherols perform two main metabolic Functions in the body. First, they are the most active and perhaps the principal natural fat-soluble antioxidants: they scavenge the most reactive oxygen species and consequently protect polyunsaturated Fatty acids from oxidation. Second, tocopherols play a specific, yet not fully elucidated role in selenium METABOLISM. Selenium is known to be an integral part of Glutathione peroxidase, an enzyme that ensures the protection of membranes against the damaging action of peroxide radicals. Thus, the Biological Role of vitamin E boils down to preventing the auto-oxidation of biomembrane lipids and potentially reducing the demand for glutathione peroxidase required to destroy peroxides generated within The Cell. The involvement of tocopherols in electron and proton transport mechanisms, as well as in the Introduction/30.html">Regulation of Gene Transcription and their role in ubiquinone metabolism, remains insufficiently clarified.

Occurrence in Nature and Daily Requirement. Vitamin E Group compounds are quite widespread in nature. The most important sources of vitamin E for humans are vegetable oils (sunflower, cottonseed, soybean, corn, etc.), as well as lettuce, cabbage, and cereal seeds; among animal products, vitamin E is found in meat, butter, egg yolk, etc. Vitamin E is stored in many Tissues throughout the body (muscles, Pancreas, adipose tissue), which is why The Development of vitamin E deficiency or hypovitaminosis is rarely observed, even when this vitamin is excluded from the diet for several months. Similarly, this explains the difficulties in determining the daily requirement for vitamin E, which, according to rough estimates, is about 5 mg.