Comparison of antioxidant activities of tocopherols alone and in pharmaceutical formulations

The objective of the present investigation was to compare the antioxidant effect of different forms of Vitamin E (DL-alpha-tocopherol, Mixed Tocopherols, Ronoxan MAP and alpha-tocopherol acetate) and of topical formulations containing these active pharmaceutical ingredients, using chemiluminescence and the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) assays. Inhibition of the intensity of chemiluminescence, using the H2O2-luminol-horseradish peroxidase (HRP) enzyme system, was measured for 10 min at room temperature in 10 microl samples of each vitamin at different concentrations, and of formulations containing these vitamins. H-donor ability in the DPPH assay, was measured in 10 microl samples at different concentrations of each vitamin, as well as in formulation in ethanol solution; the decrease of absorbency was read at 517 nm. DL-alpha-tocopherol, Mixed Tocopherols and Ronoxan MAP alone or in formulations, markedly inhibited chemiluminescence intensity and decreased absorbency in the DPPH assay in a concentration-dependent manner. Alpha-tocopherol acetate and formulations containing this vitamin did not show antioxidant activity in either assay. Other components of the formulations did not interfere with the measurements, indicating that the methods employed can be used to evaluate antioxidant activity in topical formulations.