New targets of morphine postconditioning protection of the myocardium in ischemia/ reperfusion injury: Involvement of HSP90/Akt and C5a/NF-ΚB

Background -Activation of the complement compo-nent 5a (C5a) and nuclear factor xB (NF-xB) signaling is an important feature of myocardial ischemia/reperfusion (I/R) injury and recent studies show that morphine postcon-ditioning (MP) attenuates the myocardial injury. However, the mediating cardioprotective mechanisms remain unclear. The present study explores the role and interaction of heat shock protein 90 (HSP90), Akt, C5a, and NF-xB in MP-induced cardioprotection. Methods -Male Sprague Dawley rats (n = 160) were randomized into eight groups (n = 20 per group). Rats in the sham group underwent thoracotomy, passing the ligature through the heart but without tying it (150 min), and the other seven groups were subjected to 30 min of anterior descending coronary artery occlusion followed by 2 h of reperfusion and the following treatments: I/R (30 min of ischemia and followed by 2 h of reperfusion); ischemic postconditioning (IPostC, 30 s of ischemia altered with 30 s of reperfusion, repeated for three cycles, and followed by reperfusion for 2 h); MP (0.3 mg/kg morphine administration 10 min before reperfusion); MP combined with the HSP90 inhibitor geldanamycin (GA, 1 mg/kg); MP combined with the Akt inhibitor GSK-690693 (GSK, 20 mg/kg); and MP combined with the C5a inhibitor PMX205 (PMX, 1 mg/kg/day, administration via drinking water for 28 days) and MP combined with the NF-xB inhibitor EVP4593 (QNZ, 1 mg/kg). All inhibitors were administered 10 min before morphine and followed by 2 h reperfusion. Results -MP significantly reduced the I/R-induced infarct size, the apoptosis, and the release of cardiac troponin I, lactate dehydrogenase (LDH), and creatine kinase-MB. These beneficial effects were accompanied by increased expression of HSP90 and p-Akt, and decreased expression of C5a, NF-xB, tumor necrosis factor a, interleukin-1(3, and intercellular cell adhesion molecule 1. However, HSP90 inhi-bitor GA or Akt inhibitor GSK increased the expression of C5a and NF-xB and prevented MP-induced cardioprotection. Furthermore, GA inhibited the MP-induced upregulation of p-Akt, while GSK did not affect HSP90, indicating that p-Akt acts downstream of HSP90 in MP-induced cardioprotection. In addition, C5a inhibitor PMX enhanced the MP-induced downregulation of NF-xB, while NF-xB inhibitor QNZ had no effect on C5a, indicating that the C5a/NF-KB signaling pathway is involved in MP-induced cardioprotection. Conclusion - HSP90 is critical for MP-mediated cardioprotection possibly by promoting the phosphorylation of Akt and inhibiting the activation of C5a and NF-KB signaling and the subsequent myocardial inflammation, ultimately attenuating the infarct size and cardiomyocyte apoptosis.