Minute oxidative stress is sufficient to induce apoptotic death of NIT-1 insulinoma cells

When cultured NIT-1 cells were subjected to a low level of oxidative stress (30 mu M hydrogen peroxide for 15 min at 37 degrees C) several of their ly sosomes ruptured, as demonstrated by intravital staining with the lysosomot ropic weak base acridine orange. Such rupture is due to intralysosomal, iro n-catalyzed oxidative reactions, since it was largely prevented by previous endocytotic uptake of desferrioxamine. The resultant limited leakage of ly sosomal hydrolytic enzymes into the cytosol could be important for an apopt otic-type degradation/fragmentation process within initially intact plasma membranes. In contrast, extensive lysosomal rupture leads to necrosis. The development of the damage process was followed by light- and electron micro scopy; and by the TUNEL-reaction. As a result of the applied oxidative stre ss, which is comparable to that expected to occur within the microenvironme nt surrounding activated macrophages under oxidative burst (e.g. during aut oimmune insulitis), about 90% of the cells eventually died due to post-apop totic secondary necrosis. The few surviving cells phagocytosed the debris f rom their fragmented neighbours and began to divide about 24 h after the in sult. Thus the sensitivity to oxidative stress varies, perhaps as a consequ ence of varying amounts of intralysosomal redox-active iron, as we have fou nd to be the case in several other cellular systems. Since the NIT-1 cells are highly differentiated, and in many ways like beta cells, we consider ou r result to be of value for the understanding of beta-cell death during the development of insulin-dependent (Type I) diabetes mellitus (IDDM).