A DECREASE IN INTRACELLULAR GLUTATHIONE CONCENTRATION PRECEDES THE ONSET OF APOPTOSIS IN MURINE THYMOCYTES

Free radical damage has been implicated in the induction of apoptosis in some cells. We investigated whether the status of a cell's oxidant defence system is involved in the signalling pathways triggering apopt osis. We used three unrelated agents, dexamethasone, thapsigargin and gliotoxin to induce apoptosis in thymocytes from 10-day-old BALB/c mic e. With all stimuli there was a correlation between the percentage of cells undergoing apoptosis (as measured with propidium iodide DNA stai ning) and the percentage of cells with lowered [GSH](i). Treatment wit h either 1 mM reduced glutathione or 10 nM thapsigargin inhibited dexa methasone-induced apoptosis in thymocytes at 6h, as well as the rise i n the percentage of cells with lowered [GSH](i) that normally accompan ied the onset of apoptosis. Furthermore, following treatment of thymoc ytes with oxidized glutathione, a normal product of the action of the cell's oxidant defence system, high levels of apoptosis were observed. This suggested that the onset of apoptosis was not simply the result of a loss of GSH from the cytosol. From our evidence we suggest that a decrease in [GSH](i) or an increase in [GSSG](i) or perhaps a change in the ratio of [GSH](1) to [GSSG](i) constitutes a trigger for apopto sis.