Role Of Mitochondrial Permeability Transition Pore In Human Hepatocellular Carcinoma HepG2 Cells Apoptosis Induced By Rhein

In China, liver cancer as a common cancer ranked second in males and third in females among cancer mortality. The therapies for this high mortality cancer are limited, moreover the 5-year survival rate remains only between 3-67%. An alternative therapy for liver cancer is certainly needed. Chinese traditional medicine has the advantage in improving patients symtom and quality of life, reducing adverse effects of radio-and chemo-therapy, and prolonging overall survival.Rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) is a compound found in the free state as a glucoside in the root of Rhubarb and Polygonum cuspidatum. Previous studies have shown that rhein could inhibit the growth of many cancer cells, including human breast cancer, cervical cancer, and gastric cancer, as well as human hepatocellular carcinomas. Based on the broad spectrum of anti-cancer effects, rhein was supposed to be of great clinical value. Meanwhile, based on the molecular mechanism research, it was guessed that mitochondria-dependent apoptosis pathway was involved in cells’apoptosis induced by rhein.Ca+overload, oxidative stress, hypoxia and cytotoxic drugs may all lead to the opening of mitochondrial permeability transition pore (MPTP). Furthermore, the opening of MPTP occurs along with the loss of mitochondrial transmembrane potential (MTP), which plays an important role in drug-induced necrosis and apoptosis. Although more and more reports come out about effects and mechnisms of rhein, but taking the mitochondrial function as the target to explore the mechnism of rhein on liver cancer cell apoptosis has not been reported yet. So it is of great pharmacology significance that further explorating the role of MPTP opening involved in rhein-induced HepG2 cells apoptosis.The present study was undertaken to identify the contribution of MPTP to rhein induced tumor cell apoptosis by using isolated rat liver mitochondria and the human hepatocellular carcinoma cell line, HepG2. In this study, the mitochondrial swelling, Ca2+release, MTP of HepG2 cells, and ATP levels were monitored to observe the mitochondria damage induced by rhein, and flow cytometry, western bloting, TUNEL assay were used to investigate the MPT mechanisms involved.The results showed that rhein induced mitochondrial swelling as well as the release of Ca2+ from isolated mitochondria, causing mitochondrial dysfunction in a dose-dependent way, which could be totally inhibited by CsA. These remind us that rhein could act on the mitochondia directly, induce the opening of MPTP and mitochondrial dysfunction. Moreover, the addition of CsA in the culture medium alleviated HepG2 cell apoptosis induced by rhein, which meant that MPTP played a key role in this toxic process.In conclusion, the study confirmed that rhein caused damage to HepG2 cells through a mitochondria-dependent apoptosis pathway and showed, for the first time, that MPTP played a key role in this toxic process. Thus our study improved the molecular biology theory involved in the auxiliary oncotherapy of rhein, which provided biology informations for discovering new targets for liver cancer auxiliary treatment of rhein and finding similar new drugs.