Abstract 2459: Non-Pharmacologic Modulation of Mitochondrial Function: A Novel Strategy to Attenuate Lethal Reperfusion Injury in Brain and Heart
Reperfusion injury in both brain and heart has been attributed largely to reperfusion-induced mitochondrial dysfunction, resulting in production of reactive oxygen species (ROS) and subsequent cell death. Pharmacologic therapies given at reflow and aimed at scavenging ROS have, however, showed limited efficacy in attenuating reperfusion injury, possibly due to inherent difficulties in achieving adequate intracellular drug concentrations in the crucial early minutes post-reflow. Accordingly, our aim was to exploit the fact that mitochondrial cytochrome c oxidase (CcO) contains chromophores for infrared light (IRL) and, using integrated in vitro and in vivo models, develop a novel non-pharmacologic strategy to modulate mitochondrial CcO activity, attenuate ROS production, and limit reperfusion-induced neuronal and myocyte death. In Protocol 1, respiration was quantified using the polarographic method in isolated mitochondria and isolated CcO harvested from brain and heart with vs without exposure to IRL. In Protocol 2 [brain ischemia-reperfusion], rats underwent 8 min of bilateral carotid occlusion with hypotension, and, beginning 2 min before reflow, received IRL (direct cranial irradiation, maintained for 2 h) vs no intervention (control). Neuronal viability in the CA1 hippocampus was quantified by Cresyl violet staining at 7 days post-reflow while, in separate cohorts, mitochondrial ROS production was assessed at 30 min post-reflow (MitoSox assay). In Protocol 3 [cardiac ischemia-reperfusion], rats underwent 45 min coronary artery occlusion + 2 h reperfusion and received either IRL (direct cardiac irradiation, begun 10 min before reflow) vs no intervention. Infarct size was delineated by tetrazolium staining and expressed as a % of the area at risk. Exposure to IRL resulted in:
a favorable, 20% reduction in respiration in mitochondria and CcO;
attenuation of mitochondrial ROS production and preservation of neuronal viability (36±14 % vs 95±5 % loss of CA1 neurons; p<0.01); and
reduction of myocardial infarct size (20±5 % vs 59±5% of the risk region; p<0.01) in IRL vs control groups.
Thus, modulation of mitochondrial function with infrared light may provide a novel approach to attenuate reperfusion injury in brain and heart.