Objective: Ischemic preconditioning reduces infarct size and improves hemodynamic function. Unstable angina may be a clinical analogue to ischemic preconditioning, and involve activation of gene programs. We hypothesized that preceding unstable angina and/or ischemic preconditioning activated genes regulated by nuclear factor kappa B (NFkappaB) or hypoxia-inducible factor 1 alpha in parallel to improved cardiac function.
Methods: Patients undergoing coronary artery bypass grafting with stable or unstable angina were subjected to ischemic preconditioning or sham treatment (n=10-11 in each group). Central hemodynamics were monitored. Left ventricular and atrial biopsies were harvested before cardioplegic arrest and after 25 min of reperfusion. Expression of heat shock protein 72 was evaluated by immunoblot, and activation of NFkappaB was detected by electrophoretic mobility shift assay. Real-time PCR was used to quantify expression of genes regulated by NFkappaB (inducible nitric oxide synthase, tumor necrosis factor-alpha, intercellular adhesion molecule 1) or by hypoxia-inducible factor 1 alpha (heme oxygenase-1, glucose transporter-1 and vascular endothelial growth factor-A).
Results: Ischemic preconditioning improved postoperative cardiac index and left ventricular stroke work index in both stable and unstable groups on the first postoperative day. Expression of hypoxia-inducible factor 1 alpha regulated genes was not influenced by cardioplegia and reperfusion, ischemic preconditioning or unstable angina. Expression of the NFkappaB-regulated genes increased after cardioplegia and reperfusion, but this was not influenced by ischemic preconditioning in stable patients. Inducible nitric oxide synthase and tumor necrosis factor expression were reduced after ischemic preconditioning in patients with unstable angina. There were no significant differences in gene expression between stable and unstable patients before cardioplegia and ischemic preconditioning. NFkappaB translocation at reperfusion was reduced in stable preconditioned and unstable control patients compared to stable controls. Heat shock protein 72 expression increased after preconditioning of unstable patients.
Conclusion: Cardiac function was improved by ischemic preconditioning in both stable and unstable patients. Unstable angina per se had no effect. NFkappaB-regulated genes were influenced by ischemic preconditioning, but hypoxia-inducible genes were not.