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Vitamin E is a generic name that consists of two subgroups of four each tocopherols and tocotrienols. Accumulated experimental results indicate that tocotrienols are more potent antioxidants than tocopherols. Since the chromanol ring of Vitamin E is involved in free radical reactions and is shared by both tocopherols and tocotrienols, it is clear that other mechanism must be involved to explain this difference. Recently, we found that the unsaturated phytol side chain of tocotrienols played an important role in the prevention of the formation of 17β-estradiol (E2 ) epoxide, and suggested that distinct from the chromanol ring, the unsaturated phytol side chain in tocotrienols should be considered as a separate antioxidant site where oxygen atom transfer is involved [Cancer Detection and Prevention 29 (2005) 383-388]. Since epoxidation is required for the activation of many chemical carcinogens including aflatoxin B1 , this report is to compare the preventive effect of α- tocopherol, α-, γ-, and δ- tocotrienols on AFB1 epoxidation. Using the versatile epoxide-forming oxidant dimethyldioxirane (DMDO) to activate [3H-AFB1] (40 µg), we found that the binding of AFB1 to calf thymus DNA(400 µg) was 11,123 pmoles AFB1 /mg DNA (100%). Under identical conditions, when 40 µg [3H-AFB1] was mixed with 400 µg α- tocopherol before DMDO activation, the binding was 10,901 pmoles AFB1 /mg DNA (98 %), and bindings were 8,453 (76%), 4004 (36%), and 5117 (46%) for α-tocotrienol, δ-tocotrienol, and γ-tocotrienol, respectively. Similar conclusion was obtained when liver microsome activation system was used. In support to our earlier studies on the formation of E2 epoxide, we conclude that tocotrienols are more potent in the prevention of AFB1 epoxidation. As a dietary supplement, the tocotrienols may have the potential to prevent AFB1 induced liver carcinogenesis at the initiation. [This work was partially supported by a grant from Malaysian Palm Oil Board].

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA