Involvement of apoptosis in neurological injury after hypothermic circulatory arrest: A new target for therapeutic intervention?

Background. This study was undertaken to evaluate the role of apoptosis in neurological injury after hypothermic circulatory arrest (HCA). Methods. Twenty-one pigs (27 to 31 kg) underwent 90 minutes of HCA at 20 degreesC and were electively sacrificed at 6, 24, 48, and 72 hours, and at 7, 10, and 12 days after HCA, and compared with unoperated controls. In addition, 3 animals that had HCA at 10 degreesC, and 3 treated with cyclosporine A (CsA) in conjunction with HCA at 20 degreesC, were examined 72 hours after HCA. After selective perfusion and cryopreservation, all brains were examined to visualize apoptotic DNA fragmentation and chromatin condensation on the same cryosection of the hippocampus: fluorescent in situ end labeling (ISEL) was combined with staining with a nucleic acid-binding cyanine dye (YOYO). Results. In addition to apoptosis, which was seen at a significantly higher level (p = 0.05) after HCA than in controls, two other characteristic degenerative morphological cell types (not seen in controls) were characterized after HCA. Cell death began 6 hours after HCA and reached its peak at 72 hours, but continued for at least 7 days. Compared with the standard protocol at 20 degreesC, HCA at 10 degreesC and CsA treatment both significantly reduced overall cell death after HCA, but not apoptosis. Conclusions. The data establish that significant neuronal apoptosis occurs as a consequence of HCA, but at 20 degreesC, other pathways of cell death, probably including necrosis, predominate. Although preliminary results suggest that the neuroprotective effects of lower temperature and of CsA are not a consequence of blockade of apoptotic pathways, inhibition of apoptosis nevertheless seems promising as a strategy to protect the brain from the subtle neurological injury that is associated with prolonged HCA at clinically relevant temperatures. (C) 2001 by The Society of Thoracic Surgeons.