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Apoptosis of sinusoidal endothelial cells is a critical mechanism of preservation injury in rat liver transplantation

In livers excised for transplantation, sinusoidal endothelium appears especially vulnerable to injury during organ preservation in the cold and subsequent reperfusion. The degree of endothelial cell injury correlates with functional impairment of the graft following transplantation. The mechanism of injury remains obscure, but endothelial cell damage has been described as coagulative necrosis secondary to irreversible physico‐chemical damage. We investigated whether endothelial cell death is caused by apoptosis rather than by necrosis. Tissue from rat livers stored for varying periods in cold (1°C) Euro‐Collins solution and then reperfused for 1 hour at 37°C were studied for evidence of apoptosis by detection of DNA fragmentation using the in situ terminal deoxynucleotidyl transferase d‐uridine triphosphate nick end labeling (TUNEL) assay, DNA gel electrophoresis, and by transmission electron microscopy (EM). DNA fragmentation of the type characteristic of apoptosis was identified in 49.7% ± 2.2% of sinusoidal lining cells after 8 hours of ischemia + reperfusion (viable graft) vs. 70.7% ± 4.3% after 16 hours + reperfusion (nonviable graft) (P < .001). No such fragmentation was observed after cold preservation without reperfusion or in unpreserved, reperfused livers. EM demonstrated changes characteristic of apoptosis exclusively in endothelial cells. The study suggests that the apoptosis of sinusoidal endothelial cells is a pivotal mechanism of preservation injury in liver transplantation.