Cardioplegia and Diazoxide Modulate STAT3 Activation and DNA Binding

Background Previously, we have shown that magnesium supplemented potassium (DSA) cardioplegia and DSA containing diazoxide (DSA+DZX) significantly decrease apoptosis after ischemia. The mechanism for this enhanced cardioprotection was unknown, but we believed that alterations in signal transducers and activators of transcription (STATs) may play a role. To investigate this hypothesis, we examined the effects of DSA and DSA+DZX cardioplegia on STAT1/3 phosphorylation and DNA binding in the in situ blood perfused pig heart model. Methods Pigs (32 to 42 kg) undergoing total cardiopulmonary bypass underwent left anterior descending coronary artery occlusion for 30 minutes. The aorta was crossclamped and DSA (n = 6) or DSA+DZX (n = 6) cardioplegia was administered, followed by 30 minutes of global ischemia and 120 minutes of reperfusion. Control hearts (n = 3) received cardiopulmonary bypass and sham reperfusion only. Tissue samples from regional and global ischemia zones were harvested and used for Western blot and electrophoretic mobility shift assay. Results Regional and global ischemia significantly increase proapoptotic STAT1 tyrosine phoshorylation. This increase is significantly greater in the regional as compared with the global ischemia zone. Tyrosine phosphorylation of antiapoptotic STAT3 is increased in the global ischemic zone but is significantly decreased in the regional ischemic zone and is associated with increased apoptosis. The DSA+DZX significantly increases tyrosine phosphorylation of antiapoptotic STAT3 and DNA binding in the regional ischemia zone and significantly decreases apoptosis. Conclusions The addition of diazoxide to DSA cardioplegia significantly decreases apoptosis by significantly increasing tyrosine phosphorylation of STAT3 and its DNA binding and represents an additional modality for enhancing myocardial protection.