Effect And Mechanism Of Emodin On Apoptosis In Human Hepatoblastoma Cells

As a natural anthraquinone derivative, emodin recently had been reported to possess potential bioactivities, especially anti-proliferative and apoptotic induction activities on malignant human cancer cells.Prior studies reported that emodin could cause G2/M arrest and occurrence of apoptosis via activations of p53, p21, Fas, caspase-3 and caspase-9 as well as disruption of mitochondrial membrane potential in human hepatoblastoma cells. However, the underlying molecular mechanism of its hepatocyte toxicity remains poorly clarified.Therefore, the objective of current study was to ascertain the cytotoxicities of emodin, chrysophanol and rhein to HepG2 and HL-7702 cells, the underlying signal transduction pathways and inter-relationship among these pathways in the cytotoxicity of emodin. The study provides more evidences to support that emodin holds a promise for developing safer alternative to the chemically synthesized medicine.The main results are as follows:(1) Trough examining cytotoxicities of emodin, chrysophanol and rhein to HepG2 and HL-7702 cells, the study demonstrated that emodin targeted HepG2 cells without being cytotoxic to primary human hepatocyte cells in comparison with chrysophanol and rhein.(2) Trough measuring apoptotic induction abilities of emodin, chrysophanol and rhein by AO/EB, DAPI and protein expressions of caspase-3 and PARP, the study indicated that rhein and emodin induced HepG2 cells apoptosis, but chrysophanol could not induce HepG2 cells apoptosis. Moreover, emodin induced HepG2 cells apoptosis in a concentration-dependent fashion.(3) Explore molecular mechanism of emodin-induced HepG2 cells apoptosis. The results manifested that emodin generated reactive oxygen species(ROS), triggered intracellular oxidative stress and mitochondrial dysfunction. Afterwards, emodin effectively attenuated phosphorylations of Akt and ERK and promoted phosphorylation of p38. phosphatidylinositol 3 kinase/protein kinase B(PI3K/Akt), ERK and p38 signaling pathways mediated emodin-induced apoptosis through modulating downstream mitochondrial pathway and/or death receptor pathway. Emodin increased Bax/Bcl-2 ratio, evoked disruption of mitochondrial membrane potential and promoted efflux of cytochrome c to cytosol, indicative of features of mitochondrial apoptotic signals. Emodin concurrently led to activations of Fas, Fas-L, caspase-8 and tBid, which provoked death receptor apoptotic signal. Activated tBid relayed the Fas apoptotic signal to the mitochondrial pathway. Besides, there was a cross-talk between PI3K/Akt and mitogen-activated protein kinases(MAPK) pathways in emodin-induced apoptosis and this cross-talkstrengthened the apoptotic induction ability of emodin through keeping maintenance of signaling.