Remote Ischemic Postconditioning Increases HIF-1α Plasma Levels and Improves Cardiac Markers After Cardiac Surgery

Cardiac surgery with cardiopulmonary bypass (CPB) is associated with ischemia-reperfusion (I-R) injury. Acute myocardial injury after cardiac surgery is associated with increased mortality and morbidity. In 1993, reported that brief circumflex artery occlusion reduces myocardial infarct size induced by a definitive occlusion of the left anterior descending artery, a phenomenon which has been named remote ischemic preconditioning (RIPC). This approach confers resistance to subsequent ischemic episodes in remote organs, possibly by transferring protective mediators through humoral, neuronal, and systemic mechanisms, however the mechanisms involved are not yet fully known. A recent study has found that cardioprotection induced by RIPC the mitochondria appear to be an important subcellular effector organelle. It has been reported that RIPC could be a potential protective approach for perioperative complications. Therefore, the effects on myocardial injury and clinical outcome in patients undergoing on-pump cardiac surgery (OPCS) are inconclusive. In the present study, we conducted a randomized clinical trial on patients undergoing OPCS by application of remote ischemic postconditioning (RIP), an alternative to remote ischemic preconditioning. RIP can be applied in different clinical situations, medical or surgical, when reperfusion is initiated and associated to acidosis, nitric oxide formation, mitochondrial permeability transition pore inhibition and reactive oxygen species generation. In the present study we have opted for remote postconditioning because we speculate a possible losses of plasmatic effectors during CPB procedures using polyvinylchloride (PVC) tubing. Since, when blood is exposed to the PVC surface the plasma proteins may be adsorbed. Also to minimize the bleeding or hemodilution effects on the potential protective plasmatic effectors levels during CPB.

Tissue exposure to low O2 concentration starts a hypoxic response of the hypoxia-inducible factor 1 (HIF-1), a transcription factor heterodimer, consisting of an O2 regulated HIF-1α subunit and a constitutively expressed HIF-1β subunit that binds to the consensus sequence 5'-RCGTG-3', which is present near HIF-1-regulated genes. HIF-1α protein stability is upregulated in response to hypoxia. HIF-1α protein stability is negatively regulated by O2-dependent prolyl hydroxylation and is degraded under normoxia by prolyl hydroxylase. HIF-1α plays a critical role in the mammalian cells activating genes associate with angiogenesis, ischemia, energy metabolism and cell cycle.

The aim of this study carried out in patients undergoing OPCS was the determination of the time course of HIF-1α plasma levels in response to RIP and the possible correlation between aortic cross-clamping time and HIF-1α plasma levels in both groups. HIF-1α role in remote ischemic conditioning (pre or post) is very little known. Therefore, we tested the hypothesis that RIP induces cardiac protection after OPCS and that this is associated to an increase of HIF-1α plasma levels.

Inclusion criteria

• elective cardiac surgery (coronary arteries and/or valve replacement)
• ASA physical status III or less

Exclusion criteria

• pregnancy
• previous cardiac surgery
• myocardial infarction (< 6 weeks)
• renal failure
• severe chronic pulmonary disease.