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

AIMS: Late phase ischemic preconditioning (LPC) 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 I/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 mmHg, p<0.01). This hyperoxygenation was attenuated by LPC in the LPC+I/R mice (11.9 ± 2.0 mmHg, 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.