OxyFile #233

Exposure of cells to nonlethal concentrations of hydrogen 
peroxide induces degeneration-repair mechanisms involving 
lysosomal destabilization.


Author:  Brunk UT; Zhang H; Dalen H; Ollinger K

Source:  Free Radic Biol Med 1995 Dec; 19(6):813-22

Abstract:

The cytotoxicity of hydrogen peroxide is, at least partly, 
mediated by the induction of intralysosomal iron-catalyzed 
oxidative reactions with damage to lysosomal membranes 
and leakage of destructive contents. We hypothesize that 
minor such leakage may be nonlethal, and the ensuing cellular 
degeneration repairable. Consequently, we investigated, 
using a model system of cultured J-774 cells, the effects 
of hydrogen peroxide in moderate concentrations on cellular 
viability, lysosomal membrane integrity, morphology, and 
ATP and reduced glutathione concentrations. These parameters 
were initially estimated directly after a 30 min 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 cells survived an exposure to 250 microM 
hydrogen peroxide for 30 min, whereas 350 and 500 microM 
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 the lysosomal compartment to the cytosol. This 
phenomenon is known to parallel leakage of damaging lysosomal 
contents such as hydrolytic enzymes. There were also signs 
of cellular damage in the form of surface blebbing and 
increased autophagocytosis, more marked with the higher 
doses of hydrogen peroxide. Also found was a rapid depletion 
of ATP and GSH. These alterations were all reversible, 
as long as cells were exposed to nonlethal amounts of hydrogen 
peroxide. Based on these and previous findings, we suggest 
that lysosomes are less stable organelles than 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 autophagocytosis.