Free Radical Scavenging and Antioxidant Activities of Silymarin Components

Silymarin is an over the counter food supplement that is sold as a liver enhancement and liver protection preparation. It is a major constituent of the seeds of Silybum marianum which is composed of a mixture of seven major components and several minor compounds. The seven major components: taxifolin, silychristin, silydianin, silybin A, silybin B, iso-silybin A and iso-silybin B were isolated and purified from the crude mixture of silymarin using preparative high performance liquid chromatography to determine which were the most effective for liver protection. Free radical scavenging, hydroxyl radical antioxidant capacity, oxygen radical antioxidant capacity, trolox-equivalent antioxidant capacity and total antioxidant capacity antioxidant activities were determined for each of the individual purified components as well as the crude silymarin mixture. Taxifolin was the most effective component for scavenging free radicals in the DPPH assay with an EC(50) of 32 µM far more effective than all other components which showed EC(50) ranging from 115 to 855 µM. Taxifolin was also found to be the most effective antioxidant in the oxygen radical antioxidant capacity (ORAC) assay with a trolox equivalent of 2.43 and the second most effective in the hydroxyl radical antioxidant capacity (HORAC) assay with a gallic acid equivalent of 0.57. Other antioxidants assays did not show significant differences between samples.