Submicroscopic Changes in the Production of Hydrogen Peroxide in Necrotic and Apoptotic Cells of the Mouse Postovulatory Cumulus Oophorus

Numerous studies have recently provided evidence suggesting an association of cell injury and cell death with reactive oxygen species (ROS). In this study, the cytochemical cerium chloride procedure was used to detect in situ production of hydrogen peroxide (H2O2) in the mouse cumulus oophorus surrounding a postovulatory oocyte. Normal, active cumulus cells showed no presence of H2O2. However, H2O2 was regularly found in cells exhibiting ultrastructural signs of damage or death. The generation of H2O2 was observed in very early stages of necrotic or apoptotic processes characterised by minor ultrastructural alterations of the cell and/or cellular organelles. These events always preceded nuclear changes associated with cell death. Two different primary sites of H2O2 production were detected, i.e., the plasma membrane in necrotic cells and mitochondria in apoptotic cells. In the late phases of necrosis, H2O2 was demonstrated also on outer mitochondrial membranes and, in the late phases of apoptosis, it was also found on cell surfaces. With progression of apoptosis, multiple sites of H2O2 generation were detected in the cytoplasm, the nucleus or its fragments and in apoptotic bodies. A conspicuous finding was the presence of pairs of dying cells; in most of these, one cell was necrotic and the other apoptotic and between them a flow of H2O2 was detected. This suggests that H2O2 released by one of the cells may, like exogenous H2O2, act as a chemical signal inducing the onset of the dying process in its neighbouring cell.