Induction of Human Hepatocellular Carcinoma HepG2 Cell Apoptosis by Naringin

Naringin, a bioflavonoid found in Citrus seeds, inhibits proliferation of cancer cells. The objectives of this study were to investigate the mode and mechanism(s) of hepatocellular carcinoma HepG2 cell death induced by naringin. The cytotoxicity of naringin towards HepG2 cells proved dosedependent, measured by MTT assay. Naringintreated HepG2 cells underwent apoptosis also in a concentration related manner, determined by annexin Vfluorescein isothiocyanate (FITC) and propidium iodide (PI) employing flow cytometry. Mitochondrial transmembrane potential (MTP) measured using 3,3dihexyloxacarbocyanine iodide (DiOC6) and flow cytometer was reduced concentrationdependently, which indicated influence on the mitochondrial signaling pathway. Caspase3, 8 and 9 activities were enhanced as evidenced by colorimetric detection of paranitroaniline tagged with a substrate for each caspase. Thus, the extrinsic and intrinsic pathways were linked in human naringintreated HepG2 cell apoptosis. The expression levels of proapoptotic Bax and Bak proteins were increased whereas that of the antiapoptotic BclxL protein was decreased, confirming the involvement of the mitochondrial pathway by immunoblotting. There was an increased expression of truncated Bid (tBid), which indicated caspase8 proteolysis activity in Bid cleavage as its substrate in the extrinsic pathway. In conclusion, naringin induces human hepatocellular carcinoma HepG2 cell apoptosis via mitochondriamediated activation of caspase9 and caspase8mediated proteolysis of Bid. Naringin anticancer activity warrants further investigation for application in medical treatment.