ISOLATED CELLS IN THE STUDY OF THE MOLECULAR MECHANISMS OF REPERFUSION INJURY

Isolated cells make it possible to study mechanisms of cell and tissue injury under well-defined conditions, including the interaction of different cells in coculture experiments. Isolated cells, either in suspension or in monolayer cultures, have also been used to study the mechanism of reperfusion injury - in this case better termed as reoxygenation injury in view of the experimental approach taken. In hepatocytes, Kupffer, and endothelial cells, reoxygenation injury resulted in necrosis primarily mediated by reactive oxygen species released by various sources such as mitochondria (hepatocytes) and NADPH oxidase (Kupffer cells). In contrast, contracture was a characteristic feature of reoxygenation injury occurring in cardiomyocytes without loss of cytosolic enzymes. Beside reactive oxygen species, Kupffer cells were activated to release prostanoids and a decrease in endothelial cell-mediated fibrinolysis occurred upon reoxygenation. Reoxygenation injury in endothelial cells was significantly increased when neutrophils were added at the time of reoxygenation, presumably due to additional generation of reactive oxygen species and the release of proteases. As exemplified for the liver, these experiments suggest a mechanism of reperfusion injury in which the various cell types of a given tissue differ significantly in their response to hypoxia-reoxygenation but in which they interact with each other in a complex pathobiochemical network via various mediators such as cytokines, and tissue damaging effector molecules such as reactive oxygen species. Future experiments with isolated cells will allow detailed analysis of the underlying molecular mechanisms.