Abstract

Hydroclathrus clathratus is a well-known endemic alga in Korea having antiviral effects. In this study, its ability to induce cytotoxicity and apoptosis in cultured HL-60 human promyelocytic leukaemia cells was investigated. Treatment of the human promyelocytic leukaemia cell line (HL-60), cells with various concentrations of H. clathratus ethyl acetate extract (HCE) resulted in growth inhibition and induction of apoptosis in a dose-dependent manner, as determined by the cell viability, chromatin condensation, DNA fragmentation and sub-G1 phase accumulation. The HCE-induced apoptotic cell-death was associated with caspase-3 and caspase-9 activation, and poly ADP-ribose polymerase (PARP) degradation in the HL-60 cells. This increase in the HCE-induced apoptosis was also associated with a reduction in the levels of Bcl-xL, a potent cell-death inhibitor, and an increase in the levels of the Bax protein, which heterodimerises with and thereby inhibits Bcl-2. Finally, the intracellular reactive oxygen species (ROS), especially hydrogen peroxide (H₂O₂) and superoxide anion (O₂⁻), were found to be elevated after HCE treatment of these cells. In addition, antioxidant N-acetyl cysteine (NAC) pretreatment almost completely inhibited the HCE-induced apoptosis, suggesting that ROS are the key mediators of HCE-induced apoptosis. In conclusion, HCE induces apoptosis of human leukaemia cells through caspase activation, upregulation of the pro-apoptotic Bax/Bcl-2 ratio and ROS generation. Therefore, it may have anticancer properties valuable for application in food and drug products.

Key words: Apoptosis, Bcl-2, Hydroclathrus clathratus, reactive oxygen species.