Abstract
[Introduction]
The cancer therapy with ascorbic acid (AsA) is expected as a therapy with little effects, thus its use alone or combined with chemotherapy. However, little information has so far been reported regarding the combination of AsA with radiation. It is known that AsA shows cytotoxic effects to tumor cells which less content of intracellular catalase neutralizing H 2O2, therefore, the generation of reactive oxygen species (ROS) derived from H 2O2 is thought to be involved. While, most of cell death induced by X-irradiation depend on the intracellular ROS production. In the present study, the action of AsA combined with radiation and the role of ROS was studied by using human promyelocytic leukemia HL60 cells.
[Material and Methods]
HL60 cells were cultured in RPMI-1640 supplemented with 10% fetal bovine serum. A final concentration 0.01 mM - 2.5 mM AsA was added to the culture and the number of a viable cell was counted after 24 h. Catalase (1,300 U/mL ) was added to the culture, then the cells were treated with AsA, 2 Gy X-irradiation and a combination of them. The viable cells were counted after 24 h. The intracellular ROS production was measured by a flow cytometer using ROS-sensitive fluorescent probe CM-H 2DCFDA.
[Result and Discussion]
AsA showed cytotoxic effects on the growth of HL60 cells with a dose-dependent manner. When X-irradiation was performed after AsA treatment, the additive cytotoxic effects were observed. When catalase was added to the culture with AsA alone, the cytotoxic effects of AsA were disappeared. In addition, the additive cytotoxic effects were decreased to the same level obtained by X-irradiation alone. The intracellular ROS production reached to the peak at 12 h after X-irradiation, but AsA resulted in the decrease of ROS. These results suggest that the action pathway of hydroxyl radical derived from H 2O2 was different from between AsA and X-irradiation.
