TROLOX INHIBITS APOPTOSIS IN IRRADIATED MOLT-4 LYMPHOCYTES

MOLT-4 cells, a human lymphocytic leukemia line, undergo apoptosis in response to a variety of stimuli, including exposure to ionizing radia tion. Very little is known of the molecular mechanisms by which radiat ion induces apoptosis, Morphology changes and chromatin cleavage at in ternucleosomal sites accompany apoptosis in these cells. We found that trolox, a water-soluble derivative of vitamin E that penetrates biome mbranes and protects mammalian cells from oxidative damage, blocks DNA fragmentation in irradiated MOLT-4 cells. Levels of DNA fragmentation in cells not treated with trolox were directly related to both radiat ion dose and time postirradiation. Preincubation of cells with trolox or incubation with trolox only during irradiation did not protect cell s. A 4 h postirradiation incubation with trolox was sufficient to comp letely block fragmentation measured at 24 h, indicating the processes triggered by radiation to induce DNA fragmentation occur early after i rradiation. Removal of cells from trolox earlier than 4 h resulted in progressively less inhibition, Trolox preserves the integrity of irrad iated cells as judged by increased viability and thymidine incorporati on. Radiation induces an uptake of extracellular Ca2+ into MOLT-4 cell s that was blocked by a postirradiation incubation with trolox. These results suggest that membrane-associated oxidations triggered by radia tion are responsible for radiation-induced apoptosis in MOLT-4 cells.