Effects of mRg2, a mixture of ginsenosides containing 60% Rg2, on the ultraviolet B-induced DNA repair synthesis and apoptosis in NIH3T3 cells

Ginseng has been used worldwidely as a traditional medicine of Asian countries for treatment of various diseases including cancer. The purpose of this study was to determine the effect of ginseng saponin mRg2, a mixture of ginsenosides containing 60% Rg2, on the repair and apoptosis of ultraviolet B (UVB)-exposed NIH3T3 cells. When cells were exposed to UVB and then incubated with normal growth medium for 48 h, cell viability, as determined by trypan blue exclusion assay decreased to about 25%. However, when mRg2 was included in the postincubation medium, the UVB induced loss of cell viability was significantly reduced as compared with that postincubated in normal growth medium. 4,6-diamidino-2-phenylindole (DAPI) staining showed that postincubation of the UVB-exposed cells in medium containing mRg2 significantly reduced the apoptotic nuclear fragmentation. Interestingly, when cells were preincubated with mRg2 for 24 h and then exposed to various doses of UV, the amount of repair synthesis significantly increased as compared with those in cells exposed to UVB alone. Western blot analysis indicated that the mRg2 postincubation after UVB exposure potentiated the level of p53 and p21. The level of Triton nonextractable proliferating cell nuclear antigen (PCNA) also remained elevated by mRg2 postincubation. All these results suggest that mRg2 protects cells against UVB-induced genotoxicity by increasing DNA repair and decreasing apoptosis, in possible association with the modulation of protein levels involved in cell cycle arrest or progression.