Cytoprotective effect of 20S-Rg3 on benzo[a]pyrene-induced DNA damage

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon ubiquitously existing in the environment. Its metabolites have been shown to cause DNA damage and cellular dysfunction in humans. Panax ginseng C.A. Meyer is a Chinese medicinal herb, and ginsenosides are the main active constituent of ginseng. Accumulating evidence had indicated that ginseng extract and ginsenosides possess cytoprotective effects. In this study, the protective effect of ginsenosides on BaP-induced DNA damage in human dermal fibroblasts (HDFs) and HepG2 cells was investigated. The genotoxic effect of BaP was measured by the comet assay. Results showed that tail moment was increased in BaP-treated cells, but cotreatment of ginsenoside 20(S)-Rg3 can significantly decrease BaP-induced DNA damage. A downstream mechanistic study revealed that 20(S)-Rg3 increased the gene expression of an important phase II detoxifying enzyme NAD(P)H:quinine oxidoreductase 1. The effect was also associated with the activation of protein kinase B (Akt) and nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2). These results indicated that 20(S)-Rg3 might protect HDFs from BaP-induced DNA damage through the activation of the phosphatidylinositol 3-kinase/Akt/Nrf2 pathway. Our results also demonstrated that 20(S)-Rg3 is a functional ligand of pregnane X receptor (PXR), a nuclear receptor that mediates the induction of drug clearance pathways. Subsequent knockdown of PXR expression by small interfering RNA confirmed the involvement of PXR on the protective effects of 20(S)-Rg3 against BaP-induced DNA damage. In summary, ginsenoside 20(S)-Rg3 can protect against BaP-induced genotoxicity in human cells, suggesting that ginseng may serve as a natural cytoprotective agent against environmental carcinogens.