The therapeutic effect of controlled reoxygenation on chronic hypoxia-associated brain injury.

Cardiopulmonary bypass (CPB) is the most general technique applied in congenital heart disease (CHD). However, standard CPB poses a specific pathologic condition for patients during surgery: exposure to reoxygenation. When surgery is performed on cyanotic infants, standard CPB is usually initiated at a high concentration of oxygen without consideration of cytotoxic effects. Controlled reoxygenation is defined as using normoxic CPB with a pump primed to the PO2 (oxygen tension in the blood), which is matched to the patient's preoperative saturation. The aim of this study was to determine whether controlled reoxygenation could avoid standard reoxygenation injury and also to clarify the molecular signaling pathways during hypoxia. We successfully reproduced the abnormal brain observed in mice with chronic hypoxia during early postnatal development - equivalent to the third trimester in human. Mice were treated with standard reoxygenation and controlled reoxygenation after hypoxia for 24 h. We then assessed the brain tissue of these mice. In standard reoxygenation-treated hypoxia mice, the caspase-3-dependent neuronal apoptosis was enhanced by increasing concentration of oxygen. Interestingly, controlled reoxygenation inhibited neuron and glial cell apoptosis through suppressing cleavage of caspase-3 and PARP. We also found that controlled reoxygenation suppressed LCN2 expression and inflammatory cytokine (including TNF-α, IL-6, and CXCL10) production, in which the JAK2/STAT3 signaling pathway might participate. In conclusion, our findings propose the novel therapeutic potential of controlled reoxygenation on CPB during CHD.