Effect of profound hypothermia during circulatory arrest on neurologic injury and apoptotic repressor protein Bcl-2 expression in an acute porcine model

Objectives: We reported that the neocortex and hippocampus are selectively vulnerable to injury in an acute porcine model of hypothermic circulatory arrest at 18 C. We hypothesize that further cooling to 10 C could reduce neurologic injury in these regions. To further elucidate the mechanisms of neurologic injury and protection, we assessed the expression of the anti-apoptotic protein Bcl-2. Methods: Twelve piglets underwent 75 minutes of hypothermic circulatory arrest at 18 degrees C ( n= 6) and 10 degrees C ( n= 6). After gradual rewarming and reperfusion, animals were put to death and brains were perfusion-fixed and cryopreserved. Regional patterns of neuronal apoptosis after hypothermic circulatory arrest were characterized by in situ DNA fragmentation with terminal deoxynucleotidyl transferase mediated dUTP nick end labeling ( TUNEL) histochemistry. Bcl-2 protein expression was characterized with immunohistochemistry. Statistical comparisons were made by t test, analysis of variance, and Mann-Whitney U test, as appropriate. Results: Concentrations of TUNEL( +) cells were significantly lower after profound hypothermia at 10 C compared with 18 C hypothermia in the sensory and motor neocortex and hippocampus ( t test, P <.0001; P <.006; P <.006, respectively). Positive Bcl-2 immunostaining was observed only in the motor and sensory neocortex and hippocampus after 18 C hypothermic circulatory arrest. Profound cooling to 10 C resulted in a significant increase in Bcl-2 immunostaining in the motor and sensory cortex as compared with 18 C ( Mann-Whitney U test, P <.05). Conclusions: Deep hypothermia at 10 C protects the neocortex and hippocampus from insult during hypothermic circulatory arrest as suggested by significantly reduced TUNEL( +) staining in these areas. Although a concomitant increase in Bcl-2 expression was observed in the neocortex at 10 C, it remains unclear whether profound hypothermia deters from neuronal injury by activation of the anti-apoptotic protein Bcl-2.