The caspase inhibitor IDN-6556 prevents caspase activation and apoptosis in sinusoidal endothelial cells during liver preservation injury

Cold ischemia (CI) followed by warm reperfusion (WR) remains a significant issue in liver transplantation, leading to liver injury. CI-WR primarily causes apoptosis of sinusoidal endothelial cells (SECs) through a caspase-dependent mechanism. We previously demonstrated that the caspase inhibitor IDN-1965 prevents CI-WR-induced SEC apoptosis; however, it required administration to the donor, preservation solution, and recipient for effectiveness. In this study, we show that a second-generation caspase inhibitor, IDN-6556, effectively prevents CI-WR-induced SEC injury when added solely to University of Wisconsin (UW) cold storage media. Rat livers were stored in UW solution at 4°C for 24 hours and then reperfused at 37°C for 1 hour. Apoptosis was measured using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, and caspase 3 activation was assessed by biochemical and immunohistochemical analysis. Pan-caspase inhibitors (IDN-8066, IDN-7503, IDN-7436, IDN-1965, and IDN-6556) were administered at preischemic, cold preservation, or reperfusion stages. CI-WR increased TUNEL-positive SECs and caspase 3-like activity in the liver. Three inhibitors—IDN-8066, IDN-1965, and IDN-6556—effectively reduced SEC apoptosis and caspase 3 activation. IDN-6556 was the most potent, reducing SEC apoptosis and caspase 3 activity by 55% and 94%, respectively. Notably, the prevention of SEC apoptosis by IDN-6556 was still effective when the inhibitor was only administered during the cold preservation phase. These findings suggest that the caspase inhibitor IDN-6556, when added to the preservation solution, is a promising therapeutic agent for ischemia-reperfusion injury in liver transplantation.