EXPOSURE OF CELLS TO NONLETHAL CONCENTRATIONS OF HYDROGEN-PEROXIDE INDUCES DEGENERATION-REPAIR MECHANISMS INVOLVING LYSOSOMAL DESTABILIZATION

The cytotoxicity of hydrogen peroxide is, at least partly, mediated by the induction of intralysosomal iron-catalyzed oxidative reactions wi th damage to lysosomal membranes and leakage of destructive contents. We hypothesize that minor such leakage may be nonlethal, and the ensui ng cellular degeneration repairable. Consequently, we investigated, us ing a model system of cultured J-774 cells, the effects of hydrogen pe roxide in moderate concentrations on cellular viability, lysosomal mem brane integrity, morphology, and ATP and reduced glutathione concentra tions. These parameters were initially estimated directly after a 30 m in exposure to a bolus dose of hydrogen peroxide in phosphate buffered saline at 37 degrees C, and then again following subsequent recovery periods of different lengths under ordinary culture conditions. All ce lls survived an exposure to 250 mu M hydrogen peroxide for 30 min, whe reas 350 and 500 mu M exposure was lethal to a small fraction of cells . The oxidative stress caused early, time- and dose-dependent, partial relocalization of the lysosomotropic weak base acridine orange from t he lysosomal compartment to the cytosol. This phenomenon is known to p arallel leakage of damaging lysosomal contents such as hydrolytic enzy mes. There were also signs of cellular damage in the form of surface b lebbing and increased autophagocytosis, more marked with the higher do ses of hydrogen peroxide. Also found was a rapid depletion of ATP and GSH. These alterations were all reversible, as long as cells were expo sed to nonlethal amounts of hydrogen peroxide. Based on these and prev ious findings, we suggest that lysosomes are less stable organelles th an has hitherto been assumed. Restricted lysosomal leakage might be a common event, for example, during sublethal oxidative Stress, causing reversible, degenerative alterations, which are repaired by autophagoc ytosis.