Apoptosis induced by ischemia and reperfusion in experimental lung transplantation

Background. Apoptosis is a distinct form of single-cell death in response t o injury. Time course of apoptosis in lung parenchymal cells during posttra nsplant reperfusion and the influence of oxygen content during preservation on apoptosis of parenchymal cells are studied. Methods. Orthotopic syngenic single left lung transplantation was performed in male Fischer (F344) rats after 18 hours of cold ischemia (n = 5 in all groups). Apoptotic cells were stained by the terminal deoxynucleotidyl tran sferase-mediated dUTP nick-end labeling (TUNEL) technique. Strictly TUNEL-p ositive pneumocytes were counted on anonymized slides by a pathologist on 1 00 fields (x400) per specimen (mean +/- SEM). Results. The peak of apoptotic pneumocytes occurred 2 hours after reperfusi on (16.8 +/- 2.2 pneumocytes/100 fields [p/100f]; p = 0.000012 vs controls, lungs fixed after 18 hours of ischemia), whereas the lowest level of apopt otic pneumocytes was seen in lungs fixed after harvest (1.4 +/- 0.51 p/100f ) and lungs not undergoing reperfusion (2.8 +/- 0.49 p/100f). Four hours af ter reperfusion, the number of apoptotic pneumocytes was lower than 2 hours after reperfusion (13.6 +/- 3.1 p/100f; p = 0.00032 vs controls), with a f urther decline at 8 hours (6.4 +/- 1.5 p/100f) and 12 hours after reperfusi on (4.0 +/- 1.2 p/100f). Interestingly, lungs inflated with N-2 before stor age revealed a significantly lower level of TUNEL-positive pneumocytes 2 ho urs after reperfusion (8.8 +/- 2.0 p/100f) compared with lungs inflated wit h 100% O-2 (p = 0.0052). Conclusions. Apoptosis of pneumocytes after posttransplant lung reperfusion is a very early event. Prolonged hypothermic preservation without reperfus ion, however, does not lead to an elevated rate of apoptotic pneumocytes in lung grafts. (C) 2000 by The Society of Thoracic Surgeons.