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Natural vitamin E contains 8 isoforms, of which four are alpha, beta, gamma and delta-tocotrienols. They differ because of the presence or absence of a methyl (-CH3) group at the 2, 4’ and 8’ positions on the chromanol ring. Natural tocotrienols have this group in the R configuration at the 2 position, which is responsible for its biological activity.
Tocotrienols are far less common in plants than tocopherols. However, vitamin E in monocot seeds and a few dicot seeds is mostly in the form of tocotrienols. The richest source of alpha-tocotrienol is the oil of the oil palm tree Elaeis guineensis, containing up to 800 mg/kg of this vitamin in the alpha and gamma isoforms. 70% of vitamin E in palm oil is in the form of tocotrienols, quite unlike other plant oils which contain exclusively tocopherols.
Tocotrienols are powerful antioxidants, and neutralize peroxyl radicals better than alpha-tocopherol. In cell research, these molecules, especially the delta isoform, show the ability to promote apoptosis and prevent cell proliferation of malignant cell lines.
The importance of alpha-tocotrienol is being reassessed today because it has biological activity that is not accounted for by its antioxidant properties.
Tocotrienol derived from palm oil appears to be capable of preventing the metabolic break down of arachidonic acid by inhibiting all the pathways. In addition, it has a separate inhibitory effect on the degeneration of the brain cells. This is achieved at concentrations of a few nanomoles, making it the most powerful biological function to be associated with natural vitamin E in any form.
Tocotrienol has a chromanol head just like alpha-tocopherol, but its hydrocarbon tail consists of an unsaturated isoprenoid chain, unlike the saturated isoprenoid structure of the tocopherol. It has three unsaturated bonds at the 3’, 7’ and 11’ positions. It manifests only less than a third of the biological activity of alpha-tocopherol.
However, its antioxidant potency is 40-60 times as high as that of alpha-tocopherol when its inhibitory effect on lipid peroxidation was studied. It was shown to protect essential liver cytochromes 6.5 times better.
This increased efficiency was thought to be due to a more uniform distribution through the bilayer because of its increased penetration into bilayers which have saturated fat, a greater capacity to recycle after being oxidized to its chromanoxyl form, and its ability to get closer to more free radicals because of its disordering of membrane lipid molecules.