Kamunde 2018 Free Radic Biol Med
|Kamunde C, Sharaf M, MacDonald N (2018) H2O2 metabolism in liver and heart mitochondria: Low emitting-high scavenging and high emitting-low scavenging systems. Free Radic Biol Med 124:135-48.|
Abstract: Although mitochondria are presumed to emit and consume reactive oxygen species (ROS), the quantitative interplay between the two processes in ROS regulation is not well understood. Here, we probed the role of mitochondrial bioenergetics in H2O2 metabolism using rainbow trout liver and heart mitochondria. Both liver and heart mitochondria emitted H2O2 at rates that depended on their metabolic state, with the emission rates (free radical leak) constituting 0.8-2.9% and 0.2-2.5% of the respiration rate in liver and heart mitochondria, respectively. When presented with exogenous H2O2, liver and heart mitochondria consumed it by first order reactions with half-lives (s) of 117 and 210, and rate constants of 5.96 and 3.37 (× 10-3 s-1), respectively. The mitochondrial bioenergetic status greatly affected the rate of H2O2 consumption in heart but not liver mitochondria. Moreover, the activities and contribution of H2O2 scavenging systems varied between liver and heart mitochondria. The significance of the scavenging systems ranked by the magnitude (%) of inhibition of H2O2 removal after correcting for emission were, liver (un-energized and energized): catalase > glutathione (GSH) ≥ thioredoxin reductase (TrxR); un-energized heart mitochondria: catalase > TrxR > GSH and energized heart mitochondria: GSH > TrxR > catalase. Notably, depletion of GSH evoked a massive surge in H2O2 emission that grossly masked the contribution of this pathway to H2O2 scavenging in heart mitochondria. Irrespective of the organ of their origin, mitochondria behaved as H2O2 regulators that emitted or consumed it depending on the ambient H2O2 concentration, mitochondrial bioenergetic state and activity of the scavenging enzyme systems. Indeed, manipulation of mitochondrial bioenergetics and H2O2 scavenging systems caused mitochondria to switch from being net consumers to net emitters of H2O2. Overall, our data suggest that the low levels of H2O2 typically present in cells would favor emission of this metabolite but the scavenging systems would prevent its accumulation.
Labels: MiParea: Respiration, Comparative MiP;environmental MiP
Stress:Oxidative stress;RONS Organism: Fishes Tissue;cell: Heart, Liver Preparation: Isolated mitochondria
Coupling state: LEAK Pathway: N, ROX HRR: Oxygraph-2k, O2k-Fluorometer