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 radiation. Very little is known of the molecular mechanisms by which radiation induces apoptosis. Morphology changes and chromatin cleavage at internucleosomal sites accompany apoptosis in these cells. We found that trolox, a water-soluble derivative of vitamin E that penetrates biomembranes 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 radiation dose and time postirradiation. Preincubation of cells with trolox or incubation with trolox only during irradiation did not protect cells. A 4 h postirradiation incubation with trolox was sufficient to completely block fragmentation measured at 24 h, indicating the processes triggered by radiation to induce DNA fragmentation occur early after irradiation. Removal of cells from trolox earlier than 4 h resulted in progressively less inhibition. Trolox preserves the integrity of irradiated cells as judged by increased viability and thymidine incorporation. Radiation induces an uptake of extracellular Ca2+ into MOLT-4 cells that was blocked by a postirradiation incubation with trolox. These results suggest that membrane-associated oxidations triggered by radiation are responsible for radiation-induced apoptosis in MOLT-4 cells.