Upregulation of hypoxia inducible factor is associated with attenuation of neuronal injury in neonatal piglets undergoing deep hypothermic circulatory arrest.

Abstract

Prolonged deep hypothermic circulatory arrest is known to cause neurological injury. Hypoxia inducible factor, a transcription factor that mediates adaptive changes during hypoxia, is neuroprotective in models of ischemic brain injury, in part by upregulating erythropoietin. This study tested the hypothesis that upregulation of hypoxia inducible factor and erythropoietin by preconditioning with hypoxia or the hypoxia-mimetic agents deferoxamine and cobalt chloride would be neuroprotective in a piglet model of deep hypothermic circulatory arrest. Anesthetized neonatal piglets were randomized to 4 preconditioning groups (15 per group): hypoxia, deferoxamine, cobalt chloride, or control (NaCl vehicle). Brain hypoxia inducible factor and erythropoietin contents were assessed by means of Western blotting at 3, 8, and 24 hours after treatment (n = 3 per time point). Twenty-four hours after treatment, 6 to 7 animals per group underwent cardiopulmonary bypass and 110 minutes of deep hypothermic circulatory arrest. After recovery, serial neurobehavioral examinations were conducted for 6 days, after which histopathologic brain injury and neuronal apoptosis (cleaved caspase 3) were assessed. Erythropoietin expression was not significantly increased by any of the pretreatment strategies. In contrast, there was a significant upregulation of hypoxia inducible factor by pretreatment with deferoxamine and cobalt chloride (P = .002). Neurobehavioral measures revealed no significant differences in time to recovery or extent of injury. Examination of histopathologic brain injury in the hippocampus revealed that pretreatment with deferoxamine (0.4 +/- 0.3) and cobalt chloride (0.5 +/- 0.3) were associated with significantly less neuronal loss than pretreatment with hypoxia or control (2.8 +/- 0.5, P = .004). Finally, cleaved caspase 3 (a marker of apoptotic cell death) was also shown to be diminished in the cobalt and deferoxamine groups, but the difference was not significantly different from the value in the control group. In contrast to hypoxia, deferoxamine and cobalt chloride preconditioning upregulated hypoxia inducible factor and were associated with histopathologic neuroprotection after exposure to cardiopulmonary bypass and prolonged deep hypothermic circulatory arrest.