Tocotrienols are members of the vitamin E family: four tocotrienols (alpha, beta, gamma, delta) and four tocopherols (alpha, beta, gamma, delta). The critical chemical structura difference between tocotrienols and tocopherols is in that tocopherols have saturated side chains, whereas tocotrienols have unsaturated isoprenoid side chains (farnesyl isoprenoid tails) with three double bonds (see Figure).
Tocotrienols are compounds naturally occurring at higher levels in select vegetable oils, including palm oil, rice bran oil wheat germ, barley, saw palmetto, anatto, and certain other types of seeds, nuts, grains, and the oils derived from them.
Chemically, different analogues of vitamin E all show some activity as a chemical antioxidant, but do not all have the same vitamin E equivalence. Alpha-Tocopherol is the form of vitamin E that has the highest biological activity and is preferentially absorbed and accumulated in humans. Like tocopherols, individual tocotrienol isomers demonstrate different bioavailability and efficacy depending on the type of antioxidant performance being measured. All tocotrienol and tocopherol isomers have some physical antioxidant activity due to an ability to donate a hydrogen atom (a proton plus electron) from the hydroxyl group on the chromanol ring, to free radical and reactive oxygen species. Historically studies of tocotrienols account for less than 1% of all research into vitamin E. A scientific compilation of tocotrienol research, Tocotrienols: Vitamin E Beyond Tocopherols, was published in 2013.
A number of health benefits have been proposed included decreased risk of heart disease and cancer. The Food and Nutrition Board of the Institute of Medicine of the United States National Academy of Sciences does not define a Recommended Dietary Allowance or Adequate Intake or Tolerable Upper Intake Level for tocotrienols, only for alpha tocopherol.
There are no human trials of tocotrienols for prevention or treatment of stroke. Use in animal models show promising results.
Tocotrienols have been linked to improved markers of heart disease.
No human trials. Following exposure to gamma radiation, hematopoietic stem cells (HSCs) in the bone marrow, which are important for producing blood cells, rapidly undergo apoptosis (cell death). There are no known treatments for this acute effect of radiation. Two studies conducted by the U.S. Armed Forces Radiobiology Research Institute (AFRRI) found that treatment with γ-tocotrienol or δ-tocotrienol enhanced survival of hematopoietic stem cells, which are essential for renewing the body's supply of blood cells. Based on these successful results of studies in mice, γ-tocotrienol is being studied for its safety and efficacy as a radioprotective measure in nonhuman primates.
Tocotrienols are generally well tolerated and without significant side effects.
The discovery of tocotrienols was first reported by Pennock and Whittle in 1964, describing the isolation of tocotrienols from rubber. The biological significance of tocotrienols was clearly delineated in the early 1980s, when its ability to lower cholesterol was first reported by Qureshi and Elson in the Journal of Medicinal Chemistry. During the 1990s, the anti-cancer properties of tocopherols and tocotrienols began to be delineated. The current commercial sources of tocotrienol are rice and palm. Other natural tocotrienol sources include rice bran oil, coconut oil, cocoa butter, barley, and wheat germ. Tocotrienols are safe and human studies show no adverse effects with consumption of 240 mg/day for 48 months. Tocotrienol rich fractions from rice, palm, or annatto, used in nutritional supplements, functional foods, and anti-aging cosmetics, are available in the market at 20%, 35%, 50%, and 70% total vitamin E content. Molecular distillation occurs at lower temperatures and reduces the problem of thermal decomposition. High vacuum also eliminates oxidation that might occur in the presence of air. Annatto tocotrienol has the highest tocotrienol concentration and is tocopherol-free.
Tocotrienols are named by analogy to tocopherols (from Greek words meaning to bear a pregnancy (see tocopherol); but with this word changed to include the chemical difference that tocotrienols are trienes, meaning that they share identical structure with the tocopherols except for the addition of the three double bonds to their side chains.
Comparison of tocotrienol and tocopherol
Tocotrienols have only a single chiral center, which exists at the 2' chromanol ring carbon, at the point where the isoprenoid tail joins the ring. The other two corresponding centers in the phytyl tail of the corresponding tocopherols do not exist due to tocotrienol's unsaturation at these sites. Tocotrienols extracted from natural sources always consist of the dextrorotatory enantiomers only. These naturally occurring, dextrorotatory stereoisomers are generally abbreviated as the "d-" forms, for example, "d-tocotrienol" or "d-alpha-tocotrienol". In theory, the unnatural "l-tocotrienol" (levorotatory) forms of tocotrienols could exist as well, which would have a 2S (rather than 2R) configuration at the molecules' single chiral center. In practice, however, tocotrienols are only produced in the d-form i.e. from natural sources. The synthetic mixed stereoisomer ("dl-tocotrienol") and its acetate are available as dietary supplements. Tocopherols and tocotrienolss have different antioxidant activities when measured in human plasma 
Tocotrienol studies confirm anti-oxidation and suggest anti-cancer effects than the common forms of tocopherol due to their chemical structure. The unsaturated side-chain in tocotrienols causes them to penetrate tissues with saturated fatty layers more efficiently.
Lipid ORAC values are highest for δ-tocotrienol. However that study also says: "Regarding α-tocopherol equivalent antioxidant capacity no significant differences in the antioxidant activity of all vitamin E isoforms were found." Scientists have suggested tocotrienols are better antioxidants than tocopherols at preventing cardiovascular diseases and cancer. From the pharmacological standpoint, current formulation of vitamin E supplements, composed mainly of alpha- tocopherol, seems questionable.
Metabolism and bioavailability
Various studies have shown that alpha-tocopherol interferes with tocotrienol benefits. High levels of α-tocopherol increase cholesterol production. α-Tocopherol interference with tocotrienol absorption was described previously by Ikeda, who showed that α-tococopherol interfered with absorption of α-tocotrienol, but not γ-tocotrienol. Finally, α-tocopherol was shown to interfere with tocotrienols by increasing catabolism.
In nature, tocotrienols are present in many plants and fruits. The palm fruit (Elaeis guineensis) is particularly high in tocotrienols, primarily gamma-tocotrienol, alpha-tocotrienol and delta-tocotrienol. Other cultivated plants high in tocotrienols includes rice, wheat, barley, rye and oat. In anatto however, tocotrienols are relatively abundant (only delta- and gamma-tocotrienol) and it contains no tocopherols.
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