Rescue of cells from apoptosis by inhibition of active GSH extrusion.

Cells induced to apoptosis extrude glutathione in the reduced form concomitantly with (U937 cells) or before (HepG2 cells) the development of apoptosis, much earlier than plasma membrane leakage. Two specific inhibitors of carrier-mediated GSH extrusion, methionine or cystathionine, are able to decrease apoptotic GSH efflux across the intact plasma membrane, demonstrating that in these cell systems GSH extrusion occurs via a specific mechanism. While decreasing GSH efflux, cystathionine or methionine also decrease the extent of apoptosis. They fail to exert anti-apoptotic activity in cells previously deprived of GSH, indicating that the target of the protection is indeed GSH efflux. The cells rescued by methionine or cystathionine remained viable after removal of the apoptogenic inducers and were even able to replicate. This shows that a real rescue to perfect viability and not just a delay of apoptosis is achieved by forcing GSH to stay within the cells during apoptogenic treatment. All this evidence indicates that extrusion of reduced glutathione precedes and is responsible for the irreversible morphofunctional changes of apoptosis, probably by altering the intracellular redox state without intervention of reactive oxygen species, thus giving a rationale for the development of redox-dependent apoptosis under anaerobic conditions.