Toona sinensis (T. sinensis), well known in Taiwan as a traditional Chinese medicine, has been shown to exhibit antioxidant effects. In this study, therefore, the ability of T. sinensis to induce apoptosis was studied in cultured human premyelocytic leukemia HL-60 cells. Treatment of the HL-60 cells with a variety of concentrations of the aqueous extracts of T. sinensis (TS extracts) and gallic acid, the natural phenolic components purified from TS extracts, resulted in dose- and time-dependent sequences of events marked by apoptosis, as shown by loss of cell viability and internucleosomal DNA fragmentation. Furthermore, apoptosis in the HL-60 cells was accompanied by the release of cytochrome c, caspase 3 activation and specific proteolytic cleavage of poly (ADP-ribose) polymerase (PARP). This increase in TS extracts- and gallic acid-induced apoptosis was also associated with a reduction in the levels of Bcl-2, a potent cell-death inhibitor, and an increase in those of the Bax protein, which heterodimerizes with and thereby inhibits Bcl-2. Interestingly, TS extracts and gallic acid induced dose-dependent reactive oxygen species (ROS) generation in HL-60 cells. The data suggest that T. sinensis exerts antiproliferative action and growth inhibition on HL-60 cells through apoptosis induction, and, therefore, that it may have anticancer properties valuable for application in food and drug products.
