Background. Cold ischemia/warm reperfusion (CI/WR) liver injury remains a problem in liver transplants. Sinusoidal endothelial cells (SEC) are a target of CI/WR injury, during which they undergo apoptosis. Because caspase proteases have been implicated in apoptosis, our aim was to determine whether liver CI/WR injury induces a caspase-dependent apoptosis of SEC. Methods. Rat livers were stored in the University of Wisconsin (UW) solution for 24 hr at 4°C and reperfused for 1 hr at 37°C in vitro. Apoptosis was quantitated using the TUNEL assay, and caspase 3 activation determined by immunohistochemical analysis. Rat liver orthotopic liver transplants (OLT) were also performed using livers stored for 30 hr. Results. Terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL) positive hepatocytes were rare and did not increase during CI/WR injury. In contrast, TUNEL positive SEC increased 6-fold after reperfusion of livers stored under cold ischemic conditions, compared with controls or livers stored but not reperfused. Immunohistochemical analysis demonstrated active caspase 3 only in endothelial cells after CI/WR injury. When IDN-1965, a caspase inhibitor, was given i.v. to the donor animal and added to UW solution and the reperfusion media, TUNEL positive endothelial cells were reduced 63±11% (P<0.05). Similarly, the duration of survival after OLT was significantly increased in the presence of the inhibitor. Conclusion. During liver CI/WR injury: 1) selective apoptosis of endothelial cells occurs; 2) caspase 3 is activated only in endothelial cells; and 3) a caspase inhibitor reduces endothelial cell apoptosis and prolongs animal survival after OLT. The pharmacologic use of caspase inhibitors could prove useful in clinical transplantation.
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