Reperfusion-induced mitochondrial dysfunction in the porcine heart is reduced by TRO40303 in the area at risk predominantly through preservation of outer mitochondrial membrane intactness

Abstract

Mitochondria are considered to play critical roles in cell death pathways following ischemia-reperfusion injury. The objective of the present study was to perform a functional assessment of mitochondria following ischemia-reperfusion injury of the porcine heart as well as to evaluate mitochondrial effects of hypothermia and the outer membrane translocator protein (TSPO) ligand TRO40303. Pigs were subjected to 40 min occlusion of the left anterior descending artery followed by 4 hours of reperfusion. Three groups of pigs were treated either by administration of 15 mg/kg TRO40303 or the same volume of saline (1 ml/kg) at normothermia 5 min before reperfusion, or by hypothermia (32°C) initiated prior to occlusion, n=8 for all groups. Transmural needle biopsies were taken from the non-ischemic area in the left lateral wall, from the area at risk in the midventricular anterior wall and from the ischemic core area in the apical anterior wall. Mitochondrial respiratory function was evaluated polarographically in skinned heart fibers using specific substrates and inhibitors. In the control group, heart fibers from both ischemic areas demonstrated a general reduction of respiratory states. However, respiration linked to respiratory complex I was more affected than that to complex II indicating loss of soluble matrix components such as NAD (H). Addition of exogenous cytochrome c (CytC) increased the level of respiration several fold in both ischemic areas indicating increased permeability of the outer membrane and that CytC loss contributed to the reduced levels of respiration. These changes were diminished by hypothermia in both ischemic areas. TRO40303 attenuated inhibition of respiration involving complex II and reduced the stimulatory effects of CytC in the area at risk, but did not significantly reduce the altered ratio of complex I- and II-mediated respiration, and was without effect in the ischemic core area. It is concluded that mitochondria in both the ischemic core area and the area at risk undergo significant alterations in respiratory function following ischemia-reperfusion injury consistent with both inner and outer mitochondrial membrane permeabilization which can be inhibited by hypothermia initiated prior to occlusion. Administration of TRO40303 prior to reperfusion appears to reduce reperfusion-induced mitochondrial dysfunction in the area at risk mainly by preserving outer membrane intactness and limiting CytC release.