Distinct intragraft response pattern in relation to graft size in liver transplantation

Abstract

BACKGROUND: The understanding of graft injury in relation to graft size at cellular level is important to develop new strategies to rescue marginal graft. The aim of this study was to investigate the intragraft response in relation to graft size in a rat liver transplantation model. MATERIALS AND METHODS: A rat orthotopic liver transplantation model using different sized grafts (100%, 50% and 30% of recipient rat liver) was applied. The 7-day graft survival rates were compared among the three groups. Two transcription factors, namely, NK-kB and Egr-1, were detected at different time point after reperfusion by Western blot. The apoptotic cells were detected by TUNNEL method at the same time point. Several inflammatory cytokines such as TNF-a, IL-1b and iNOS were compared by RT-PCR and immumostaining. Intragraft protein levels of Hsp-70 were also compared by enzyme immunoassay (EIA) at the early phase after reperfusion among the three groups. The microstructure were examined under light microscopy. RESULTS: According to the ratio of graft weight to recipient liver weight, the rats were grouped as: group 1 (n=6): 104% (89 - 120%); group 2 (n=8): 56% (50 - 65%); group 3 (n=27): 35% (24 - 47%). The 7-day survival rate was 100%, 62.5% and 22.2% (p=0.001 vs. group1; P=0.045 vs. group 2) in group 1, group 2 and group 3 respectively. Dilation of hepatic sinusoids was found in group 3 at 6 hours after reperfusion and became severe at 24 hours after reperfusion. The changes in the hepatic sinusoids was accompanied by the vacuolization of hepatocytes. Over-expression of Egr-1 and p65 was found at 30 minutes after reperfusion in the rats of group 3 by Western-blotting. Higher expression of intragraft mRNA level of iNOS was found in group 3 at 2 hours and 6 hours after reperfusion, consistent with their Western-blot results. Interestingly, the immunostaing results showed early over-expression of iNOS in group 3 at 30 minutes after reperfusion. At 24 hours after reperfusion, the intragraft protein level of Hsp-70 was significantly lower in group 3 rats than that in group 1 (12.4 vs. 17.0 ng/ml, p = 0.04). During the first 24 hours after reperfusion, more apoptotic cells were found in group 3 rats compared to the other groups especially at 6 hours after reperfusion. CONCLUSIONS: The graft failure after liver transplantation using small-for-size grafts is related to early over-expression of Egr-1 and NK-kB accompanied by inflammatory cytokines and reduced expression of heat shock protein that is related to intracellular homeostasis and tissue repair.