Citrus aurantium L. exhibits apoptotic effects on U937 human leukemia cells partly through inhibition of Akt

Citrus fruits have been used as edible fruits and a traditional medicine since ancient times. In particular, the peels of immature citrus fruits are frequently prescribed in concert with other support herbs for many types of disease including cancer. We investigated the anti-proliferative activity of the peels of Citrus aurantium L. along with their effects on apoptosis. We prepared crude methanol extracts of the peels of Citrus aurantium L. (CMEs) and performed experiments using U937 human leukemia cells. The growth of U937 cells was inhibited by CME treatment in a dose-dependent manner, and CME induced caspase-dependent apoptosis. CME inhibited the expression of XIAP and Bcl-xL which are anti-apoptotic proteins. CME inhibited Akt activity in a dose-dependent manner. The apoptotic activity of CME was significantly attenuated by Akt augmentation. In conclusion, this study suggested that CME should induce caspase-dependent apoptosis at least in part through Akt inhibition, providing evidence that CMEs have anticancer activity on human leukemia cells.