Bitter orange peel extract induces endoplasmic reticulum-mediated autophagy in human hepatoma cells

This study was aimed at investigating the anti-cancer effect of bitter orange peel extract (BOPE) on Hep3B, a human hepatoma cell line. Upon treatment of Hep3B cells with 6.25–100 μg/mL of BOPE for 72 h, its antiproliferative effect was shown to increase in a concentration- and time-dependent manner. The observations, such as concentration-dependent elevation of LC3 fluorescent puncta, increased conversion of LC3-I to LC3-II, no characteristic apoptotic nuclear fragmentation, and no significant effect on percentages of annexin V-positive apoptotic cells, confirmed the autophagy triggered by BOPE in Hep3B cells. Moreover, BOPE promoted ROS generation and induced endoplasmic reticulum stress through calcium ion-related AMPK/TSC2/mTOR and DAPK/Beclin-1 pathways, leading to autophagic cell death. Furthermore, our analysis showed that the major components of BOPE, tangeretin and nobiletin, exhibited a synergistic effect on the growth inhibition of Hep3B cells. Thus, these results suggest that BOPE may be used as a functional food against liver cancer.