Inhibition of myocardial apoptosis by postconditioning is associated with attenuation of oxidative stress-mediated nuclear factor-kappaB translocation and TNFalpha release

ABSTRACT: Oxidative stress-stimulated nuclear factor-I?B (NF-I?B) activation has been associated with rapid transcription of TNF-I? and induction of apoptosis. This study tested the hypothesis that postconditioning (Postcon) reduces myocardial apoptosis and inhibits translocation of NF-I?B and release of TNF-I? secondary to an attenuation of oxidant generation during reperfusion. Anesthetized rats were subjected to 30 min of ischemia and 3 h of reperfusion and divided randomly to Control or Postcon (three cycles of 10-s reperfusion and 10-s reocclusion applied at the onset of reperfusion) group, respectively. Relative to Control, Postcon reduced the plasma malondialdehyde (1.21 A? 0.08 vs. 0.8 A? 0.06* I?M/mL) and decreased the generation of superoxide radical in area at risk myocardium (dihydroethidium staining). Compared with Control, Postcon also inhibited translocation of NF-I?B to nuclei (167 A? 21 vs. 142 A? 18 *), decreased the level of plasma TNF-I? (1,994 A? 447 vs. 667 A? 130* pg/mL), and inhibited caspase-3 activity (0.57 A? 0.1 vs. 0.21 A? 0.1 *). The number of apoptotic cells (percent total nuclei) in ischemic myocardium was reduced (20 A? 1 vs. 11 A? 2 *), consistent with reduced appearance of DNA fragmentation. To support whether oxidant generation is important in the triggering of cytokine release and apoptosis, N-acetylcysteine (NAC), a potent antioxidant agent, was administered before ischemia and at reperfusion. Treatment with NAC inhibited superoxide radical generation and decreased plasma malondialdehyde to a comparable level to that in Postcon, concomitant with an inhibition of NF-I?B expression (42 A? 8 *) and reduction of release of TNF-I? (231 A? 72* pg/mL). Caspase-3 activity (0.33 A? 0.1 *) and apoptotic cells (12 A? 1 *) were also comparably reduced by NAC. These data suggest that Postcon attenuates myocardial apoptosis, reduces caspase-3 activity, and is potentially mediated by inhibiting oxidant-activated NF-I?B-TNF-I? signaling pathway. *P <0.05 Postcon and NAC vs. Contro