Immunomodulation of hepatic ischemic injury via increased Bcl-X_L and decreased Bcl-X_S

Background. Although classic ischemia-reperfusion injury is mediated by reactive oxygen intermediaries, increasing evidence implicates a role for immune-mediated apoptosis during ischemic injury in transplantation. Herein, we report the effects of polyclonal rabbit anti-thymocyte globulin (rATG) on mediators of hepatic apoptosis during cold storage. Methods. Three-month-old male Lewis rats were placed under halothane anesthesia and the portal vein cannulated. University of Wisconsin (UW) solution (35 ml) with (n = 5) and without (n = 5) 20 mg/kg anti-rat rATG was infused before hepatectomy. The liver was stored in UW solution ± rATG (143 ng/ml) at 4°C for various times up to 24 h. Specimens were terminal deoxyuridine nick end labeling-stained for apoptosis. Tissue lysates were analyzed by Western blotting and densitometry. Results. Compared to UW alone, significantly fewer apoptotic cells were present in UW + rATG perfused and stored livers. There were early and sustained significant increases in Bcl-X_L and decreases in Bcl-X_S with rATG. There was an initial, but not sustained, significant decrease in Bax with rATG. Moreover, there was a significant one-third decrease in caspase-9 production with rATG at 0, 6, 12, and 18 h. Conclusion. Decreased proapoptotic Bcl-X_S and increased antiapoptotic Bcl-X_L, as well as decreased downstream proapoptotic caspase-9 expression, during liver ischemia after treatment with rATG, all favor cell survival. Because apoptotic ischemic injury results in allograft dysfunction, preservation strategies that ameliorate such immunological effects may improve organ function.