Abstract
Roles of intracellular oxidative stress in apoptosis induced by radiation and hyperthermia were studied. Various endpoints of apoptosis, DNA fragmentation, morphological changes, and phosphatidylserine externalization, etc. were examined. Enhancement of radiation-induced apoptosis in human lymphoma U937 cells by sanazole was found. Our results revealed that, compared with 10 mM sanazole or radiation alone, the combination of both resulted in a significant enhancement of apoptosis after 6 h, which was evaluated on the basis of DNA fragmentation, morphological changes, and phosphatidylserine externalization. Sanazole alone enhanced intracellular superoxide and hydrogen peroxide formation, which further increased when the cells were irradiated. Significant enhancement of Fas externalization, loss of mitochondrial membrane potential, and activation of caspase-3 and caspase-8 were observed after the combined treatment. Moreover, this combination could also enhance Bid activation, reduction of Hsp70 expression level and release of cytochrome c from the mitochondria to the cytosol. An immediate increase in the intracellular Ca2+ concentration ([Ca2+]i) was observed after the combined treatment. These results suggest that the intracellular superoxide and peroxide generated by sanazole might be involved in the enhancement of radiation-induced apoptosis. Here roles of intracellular oxidative stress in radiation as well as hyperthermia-induced apoptosis will be discussed.
