Monitoring Mitochondrial Function With High-Resolution Respirometry During Ex-Situ Heart Perfusion

Due to the high adenosine-triphosphate (ATP) consumption of the myocardial tissue, cardiac function is dependent on efficient mitochondrial respiration. Ischemia and reperfusion injury (I/R) has a severe impact on the function of the mitochondrial respiratory system. Ex-situ heart perfusion (ESHP) can minimize I/R injury. We investigated mitochondrial respiration using high-resolution respirometry (HRR) in a porcine model during ESHP.

Six German domestic pigs were used as heart and blood donors. Normothermic ESHP was performed over 6 h. Tissue homogenate of porcine myocardium was assessed by HRR at baseline (starting sample), after 60, 180, and 360 min of ESHP.

The combined oxidative phosphorylation capacity with NADH, fatty acid and succinate fuel substrates remained stable during ESHP (starting sample: 198 ± 59.7, 60 min: 196.5 ± 66.7, 180 min: 207.5 ± 48.1, 360 min: 200.5 ± 27.9 pmol·s^-1·mg wet mass^-1; p = 0.707). The flux control ratio of the nicotinamide adenine dinucleotide hydrogen (NADH) pathway (starting sample: 0.43 ± 0.07, 60 min: 0.43 ± 0.05, 180 min: 0.47 ± 0.05, 360 min: 0.44 ± 0.07 pmol·s^-1·mg wet mass^-1; p = 0.549) and succinate-pathway (starting sample: 0.49 ± 0.06, 60 min: 0.49 ± 0.05, 180 min: 0.48 ± 0.01, 360 min: 0.5 ± 0.05 pmol·s^-1·mg wet mass^-1; p = 0.814) did not change during perfusion. The mitochondrial outer membrane damage was significantly decreased after 360 min of ESHP (starting sample: 0.39 ± 0.07, 60 min: 0.27 ± 0.06, 180 min: 0.18 ± 0.03, 360 min: 0.17 ± 0.02; p = 0.0124).

Our findings demonstrate that normothermic ESHP preserves mitochondrial respiratory function in a porcine model over 6 h. These results provide a mechanistic basis for the potential protective role of normothermic ESHP against ischemia-reperfusion injury. HRR represents a promising investigational tool for in-depth mitochondrial assessment during ESHP.