Natural plant extract tubeimoside I promotes apoptosis-mediated cell death in cultured human hepatoma (HepG2) cells.

Tubeimoside I (TBMS I), an extract from Chinese herbal medicine Bolbostemma paniculatum (MAXIM.) FRANQUET (Cucurbitaceae) has been shown as a potent anti-tumor agent for a variety of human cancers, but yet to be evaluated for hepatoma that is highly prevalent in Eastern Asian countries including China. Here, we examined in vitro the cytotoxic effects of TBMS I on human hepatoma (HepG2) and normal liver (L-02) cell lines. We also investigated TBMS I-induced molecular events related to apoptosis in HepG2 cells. The results show that TBMS I inhibited the proliferation of both HepG2 and L-02 cells in a dose- and time-dependent manner, but HepG2 cells appeared more sensitive to the agent. When exposed to TBMS I for 24, 48 and 72 h, IC50 for HepG2 cells versus L-02 cells were 15.5 vs. 23.1, 11.7 vs. 16.2, 9.2 vs. 13.1 (µM, p<0.01), respectively. TBMS I induced cell shrinkage, nuclear condensation and fragmentation, cell cycle arrest at the G2/M phase, mitochondrial membrane disruption, release of cytochrome c from the mitochondria, activation of caspase 3 and 9, and shifting Bax/Bcl-2 ratio from being anti-apoptotic to pro-apoptotic, all indicative of initiation and progression of apoptosis involving mitochondrial dysfunction. Taken together, these results indicate for the first time that TBMS I potently inhibited growth in HepG2 cells by mediating a cascade of apoptosis signaling pathways. Considering its sensitivity of HepG2 cells, preferential distribution in the liver and natural product origin, TBMS I therefore may have a great potential as a chemotherapeutic drug candidate for hepatoma.

Natural plant extract tubeimoside I induces cytotoxicity via the mitochondrial pathway in human normal liver cells.

Tubeimoside I (TBMS I) is a natural compound extracted from Bolbostemma paniculatum (Maxim.) Franquet (Cucurbitaceae), a traditional Chinese herbal medicine widely used for the treatment of inflammation. Recently, it has been suggested that TBMS I may be a potent anticancer agent for a variety of human cancers. However, TBMS I is known to distribute preferentially in the liver, and thus may harm normal liver cells if it is delivered systemically for cancer treatment. This safety concern warrants careful evaluation of the hepatotoxicity of TBMS I to normal liver cells, which to date has not been carried out. Here, we report the cytotoxic effects of TBMS I on one type of normal liver cells (L-02 cells), and the associated molecular events as underlying mechanisms. Cultured human normal liver L-02 cells were treated with TBMS I at concentrations of 0, 15 and 30 µM for 24, 48 and 72 h, respectively. Subsequently, the cell survival rate was evaluated by the MTT dye method, and several key molecular events associated with apoptosis were assayed, including mitochondrial depolarization, release of cytochrome c (cyt-c), activation of caspases, and the balance between Bax and Bcl-2 protein expression. Our results indicate that TBMS I inhibited the proliferation of L-02 cells in a dose- and time-dependent manner. The TBMS I-induced growth inhibition of L-02 cells was accompanied by the collapse of mitochondrial membrane potential, release of cyt-c from the mitochondria to the cytosol, activation of caspase-9 and -3, decrease of anti-apoptotic protein Bcl-2 levels and increase of the pro-apoptotic protein Bax levels, all indicative of apoptosis through the mitochondrial pathway. Taken together, these results confirm that TBMS I has a significant apoptotic effect on normal liver L-02 cells, which may be significant to its clinical applications.