Palm-tocotrienol rich fraction (TRF) is a more effective inhibitor of LDL oxidation and endothelial cell lipid peroxidation than alpha-tocopherol in vitro

Comparative protective effects of palm tocotrienol rich fractions (TRF) and alpha-tocopherol on the copper-induced oxidation of plasma low density lipoprotein (LDL) and indices of lipid peroxidation in human umbilical vein endothelial cells (HUVEC) were investigated. LDL (100 micrograms protein/ml) was incubated at 37 degrees C with 1 micromolar CuSO4 with or without the presence of 50 micromolar (TRF) or 50 micromolar alpha-tocopherol. Aliquots were collected at 0,1,2,3,6,9,12 and 24 h and thiobarbituric acid reactive substances (TBARS) determined. In the absence of antioxidant, TBARS increased significantly in LDL reaching a maximum after 6 h. alpha-Tocopherol and TRF delayed TBARs formation by 6 h with a maximum effect after 12 h. The rate of TBARs formation with TRF was significantly slower than with alpha-tocopherol, indicating a higher antioxidant efficacy for TRF. Low density lipoprotein isolated from volunteers consuming low or high polyunsaturated fatty acid (PUFA) diets were similarly incubated with 1 micromolar CuSO4 with or without 50 micromolar TRF or 50 micromolar alpha-tocopherol. LDL oxidation was not significantly different between low and high PUFA groups. However, LDL treated with TRF was better protected against copper-induced oxidation than that treated with alpha-tocopherol. In HUVEC pre-incubated with 100 micromolar arachidonic acid, 25 micromolar TRF treatment decreased TBARS by approximately 73% compared to approximately 50% with 25 micromolar of alpha-tocopherol. Higher concentrations of TRF did not further decrease TBARS formation in the medium. However, treatment with higher concentrations of alpha-tocopherol again increased TBARS formation. Formation of conjugated diene in HUVEC subjected to arachidonic acid (ARA)-induced oxidative stress was decreased equally with either 10 micromolar TRF or 25 micromolar alpha-tocopherol. Results suggest that TRF is a more potent antioxidant than alpha-tocopherol, at least in vitro.