Late phase ischemic preconditioning preserves mitochondrial oxygen metabolism and attenuates post-ischemic myocardial tissue hyperoxygenation

Aims: Late phase ischemic preconditioning ([PC) protects the heart against ischemia-reperfusion (I/R) injury. However, its effect on myocardial tissue oxygenation and related mechanism(s) is unknown. The aim of the current study is to determine whether LPC attenuates post-ischemic myocardial tissue hyperoxygenation through preserving mitochondrial oxygen metabolism. Main methods: C57BL/6 mice were subjected to 30 min coronary ligation followed by 60 min or 24 h reperfusion with or without LPC (3 cycles of 5 min 1/5 min R): Sham, LPC, I/R, and LPC + I/R group. Myocardial tissue Po-2 and redox status were measured with electron paramagnetic resonance (EPR) spectroscopy. Key findings: Upon reperfusion, tissue Po-2 rose significantly above the pre-ischemic level in the I/R mice (23.1 +/- 2.2 vs. 12.6 +/- 1.3 mm Hg, p<0.01). This hyperoxygenation was attenuated by LPC in the LPC + I/R mice (11.9 +/- 2.0 mm Hg, p <0.01). Activities of NADH dehydrogenase (NADH-DH), succinate-cytochrome c reductase (SCR) and cytochrome c oxidase (CcO) were preserved or increased in the LPC group, significantly reduced in the I/R group, and conserved in the LPC +I/R group. Manganese superoxide dismutase (Mn-SOD) protein expression was increased by LPC in the LPC and LPC + I/R mice compared to that in the Sham control (1.24 +/- 0.01 and 1.23 +/- 0.01, p<0.05). Tissue redox status was shifted to the oxidizing state with I/R (0.0268 +/- 0.0016/min) and was corrected by LPC in the LPC + I/R mice (0.0379 +/- 0.0023/min). Finally, LPC reduced the infarct size in the LPC + I/R mice (10.5 +/- 0.4% vs. 33.3 +/- 0.6%, p<0.05). Significance: Thus, LPC preserved mitochondrial oxygen metabolism, attenuated post-ischemic myocardial tissue hyperoxygenation, and reduced I/R injury. (C) 2010 Elsevier Inc. All rights reserved.