Antioxidant activity and protective ability of seeds of milk thistle (Silybum marianum L. Gaertner) against oxidative DNA damage and protein oxidation

Silybum marianum L. Gaertner is a member of the Asteraceae family and its seed extract contains large numbers of chemical constituents including several flavonolignans collectively known as silymarin. Silymarin has powerful antioxidant properties and has a beneficial effect on various hepatic disorders, including hepatotoxicity secondary to acute and chronic viral hepatitis and mushroom poisoning.In this study, we have evaluated the antioxidant activity and DNA oxidative damage and protein oxidation protection effect of seed of cultivated milk thistle (Silybum marianum L. Gaertner), harvested from the field (University of Dicle, Faculty of Agriculture, Department of Field Crops, Diyarbakır, Turkey).The ethanol extract of seeds of cultivated milk thistle were prepared and total phenolics and total flavanoids contents were determined. The amount of total phenolic and total flavonoid in ethanol extract seeds (0.5 mg) were found to be 310±4.93 ?g GAE/mg extract and 19±0.11 ?g QUE/mg extract respectively.The antioxidant potency of ethanol extract of seeds were investigated employing various established in vitro systems, such as lipid peroxidation in rat brain homogenate, 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydrogen peroxide scavenging activity, reducing power, and inhibitory effect on protein oxidation.In conclusion, ethanol extract of seeds showed strong inhibitory activity toward lipid peroxidation of rat brain homogenate induced by the FeCl2-H2O2 system. The extract was able to reduce the stable free radical DPPH with % 91.95±5.20 at the 150 ?g/ml concentration. Reducing power activity of ethanol extract of seeds were found to be lower than BHT and BHA. However H2O2 scavenging activity of ethanol extract of Silybum marianum seeds were found to be % 57±0.04 at the 2.5 mg/ml concentration. The protect effect of ethanol extract of Silybum marianum seeds, on oxidative damage of Bovin serum albumin (BSA) induced by H2O2/ Fe3+/ ascorbic acid system were found to be %92.9±3.3 at he 1000 ?g/ml concentration. Besides, the protect effect of ethanol extract of seeds on DNA aganist to OH radical generated by H2O2-UV photolysis were found to be % 82.80 at 1000 ?g/ml concentration.Key Words: Free radicals, Milk thistle (Silybum marianum L. Gaertner) seeds, Antioxidant activity, Oxidative DNA damage, Protein oxidation, Lipid peroxidation.