In vitro studies on radioprotective efficacy of silymarin against γ-irradiation

Purpose : Silymarin has been widely exploited for its hepatoprotective activities. This study aimed to evaluate the protective efficacy of silymarin against gamma-radiation. Materials and methods: The radioprotective properties of silymarin were studied using different assays. Cytotoxicity of silymarin on Human embryonic kidney (HEK) cells was evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Protective efficacy against gamma-radiation was assessed by studying reduction in micronuclei frequency and free radical generation using 2',7'-dichlorodihydroflurescin diacetate (H(2)DCFDA). Radiation-induced apoptosis was estimated by Annexin V-PI (propidium iodide) analysis and cell cycle analysis. gamma-radiation induced changes in mitochondrial membrane potential (MMP) and DNA damage was estimated employing flow-cytometry and comet assay respectively. Results : MTT assay and Annexin V-PI studies showed that pre-incubation of HEK cells with silymarin protected them from gamma-irradiation. Significant reduction in apoptosis (76.36%) was observed. Silymarin also decreased the percentage of radiation-induced micronuclei (>69%) (p < 0.05). Measurement of intracellular reactive oxygen species (ROS) by H(2)DCFDA revealed a reduction in ROS (21%) at 0.5 h. Cell cycle analysis revealed G(1) block in the unirradiated control, which declined in the silymarin pretreated irradiated group (0.5 h). Silymarin treatment resulted in a significant increase in MMP (2 h) against the radiation control. Moreover, the presence of silymarin during irradiation significantly decreased the DNA damage (as measured by comet assay). Conclusions : Protection against radiation-induced cell-death and DNA damage by silymarin could be attributed to a reduction in ROS induced by gamma-radiation. In vitro experiments on HEK cells explicitly prove that silymarin is a promising, effective and safe radiation countermeasure agent.