The Inhibitory Effect And Mechanism Of Sesamin On Human Hepatoma Cell Line HepG2

Cancer is a broad group of diseases involving unregulated cell growth. In cancer, cells divide and grow uncontrollably and invade nearby parts of the body. Cancer cell may also spread to more distant parts of the body through the lymphatic system or bloodstream. Death rates caused by cancer are rising as more people live to an old age and as mass lifestyle changes occur in the developing world. Liver cancers are malignant tumors that grow on the surface or inside the liver. Hepatocellular carcinoma (HCC) is the most common type of liver cancer. Liver cancer ranks the sixth in incidence and the third in mortality rate among common human tumors.Although there are several treatments for HCC, including surgical resection, chemotherapy, and radiation therapy etc, the recurrence and metastasis rate is still very high compared to other major tumours. Therefore, there is an urgent need for the development of high efficient and low toxicity anti-cancer drugs.Sesame (Sesamum indicum) seed is an important traditional Chinese medicine and health food, which is rich in nutrients. Sesamin is the most abundant lignan in sesame seed and has been found to have various pharmaceutical functions, including anti-oxidation, anti-hypertension, anti-hyperlipidemia, anti-inflammation and anti-cancer. Previous studies have demonstrated that the proliferation of several kinds of tumour cells was suppressed by sesamin treatment, such as cancers of the prostate, colon, pancreas, breast, and lung. However, the effect of sesamin on liver cancer cells has not been reported and the underlying mechanism on sesamin-induced inhibition of the proliferation of tumour cells remains to be clarified. The aim of present study is to elucidate whether sesamin inhibits the survival and proliferation of human hepatocellular carcinoma cell line HepG2and further to explore the underlying molecular mechanisms. The main results are as follows:1) Sesamin displayed selectively inhibitory effects against HepG2cell proliferation. The effects of sesamin on the proliferation of hepatocellular carcinoma cell line HepG2and human normal liver cell line L02were investigated using the MTT assay. Our results showed that48h treatment of sesamin inhibited the proliferation of HepG2cells in a concentration-dependent manner and the IC50value for sesamin was98μM, whereas sesamin was less cytotoxic to the hepatocyte L02cells when compared with HepG2cells. 2) Sesamin significantly induced G2/M phase arrest and apoptosis of HepG2cells. The effect of sesamin on cell cycle distribution was examined by flow cytometry using PI staining. The results showed that sesamin treatment resulted in a concentration-dependent increase in the G2/M phase cell population. To determine whether sesamin-induced HepG2cell death involves apoptosis, Hoechst33258staining and flow cytometry using Annexin V-PI staining were performed. The results showed that sesamin induced early apoptosis of HepG2cells.3) Sesamin inhibited the STAT3and NF-κB signaling in HepG2cells. Results of STAT3inhibitor AG490and STAT3activator IL-6treatment suggested that STAT3played an important role in HepG2cell survival and proliferation. Western blotting analysis with specific antibodies against JAK2, p-JAK2, STAT3, and p-STAT3revealed that48h-sesamin treatment resulted in a strong concentration-dependent decrease in the phosphorylation level of JAK2and STAT3and nuclear translocation of STAT3in HepG2cells. Furthermore, sesamin inhibited the IL-6-induced gp130phosphorylation and STAT3activation. As there was a synergistic effect between NF-κB an STAT3signaling, we investigated the activation of NF-κB in sesamin treated HepG2cells and found that sesamin inhibited the activation and nuclear translocation of NF-κB as well.4) Sesamin regulated the expression of STAT3and NF-κB downstream genes related to the HepG2cell cycle and apoptosis at transcriptional and translational levels. The expression of STAT3and NF-κB downstream genes involved in cell cycle and apoptosis, including cyclin A, cyclin B1, Cdc2, p53, p21, Bcl-2, Bcl-xL, Bax and COX-2, were investigated at transcriptional and translational levels by RT-PCR and Western blotting in HepG2cells treated with sesamin, AG490and IL-6. These results demonstrated that sesamin could regulate the expression of genes involved in cell cycle and apoptosis in HepG2cells, which was caused by the STAT3and NF-κB inhibition.In conclusion, our results demonstrate that sesamin can become a candidate drug for liver cancer treatment, which functions through arresting cell cycle progression at G2/M phase and inducing apoptosis through the inhibition of the STAT3and NF-κB signaling.