Tocopherols and tocotrienols are food ingredients that are believed to have a positive effect on health. The most studied property of both groups of compounds is their antioxidant action. Previously, we found that tocopherols and diverse tocopherol derivatives can inhibit the activity of human glutathione S-transferase P1-1 (GST P1-1). In this study we found that GST P1-1 is also inhibited, in a concentration-dependent manner, by alpha- and gamma-tocotrienol. The concentration giving 50% inhibition of GST P1-1 is 1.8 +/- 0.1 microM for alpha-tocotrienol and 0.7 +/- 0.1 microM for gamma-tocotrienol. This inhibition of GST P1-1 is noncompetitive with respect to both substrates CDNB and GSH. We also examined the 3D structure of GST P1-1 for a possible tocopherol/tocotrienol binding site. The enzyme contains a very hydrophobic pit-like structure where the phytyl tail of tocopherols and tocotrienols could fit in. Binding of tocopherol and tocotrienol to this hydrophobic region might lead to bending of the 3D structure. In this way tocopherols and tocotrienols can inhibit the activity of the enzyme; this inhibition can have far-reaching implications for humans.
A tocotrienol (T3) mixture was intragastricaly administered to Sprague-Dawley rats, and the T3 levels in various tissues were measured 0, 4, 8 and 24 hr after the administration. In blood clots, brain, thymus, testes, vice-testes and muscles, T3 homologues were not detected at all. In epididymal adipose, renal adipose, subcutaneous adipose and brown adipose tissues and in the heart, the T3 levels were maintained or increased for 24 hr after the administration. In the serum, liver, mesenteric lymph node, spleen and lungs, the T3 levels were highest 8 hr after the T3 administration. These results suggest that the distribution and metabolism of T3 in the rat vary considerably among different tissues.