Intro: Reactive oxygen species (ROS) are central to SCD pathophysiology, but their effects depend on where and how ROS are generated. Insight into this has been limited by the lack of adequate experimental methods. Employing innovative approaches, we tested the hypothesis that elevated mitochondrial ROS (mROS) is a principal source of oxidative stress and in vivo reduction of mROS mitigates SCD in non-ischemic heart failure (HF).
Methods: In a unique guinea pig model that mimics human non-ischemic HF with a high incidence of SCD, we performed a randomized 2x2 crossover study of vehicle (v) and MitoTEMPO therapies (vM/Mv). In the untreated HF model, we performed in vivo gene transfer with novel, genetically encoded ratiometric redox sensors targeted to the cytosol (cROS) or mitochondria of cardiomyocytes. In isolated left ventricular (LV) myocytes, we quantified ROS dynamics during field stimulation (1 Hz, 37°C) in the presence or absence of MitoTEMPO.
Results: Over 4 weeks, 65% of the HF animals experienced SCD. MitoTEMPO therapy abolished SCD and LV dysfunction. Crossover to MitoTEMPO (vM) prevented SCD and improved LV function; the converse (Mv) worsened HF without increasing SCD for up to 5 weeks of follow up, suggesting distinct underlying mechanisms. EKG analysis revealed that MitoTEMPO therapy decreased PVC burden, reduced dispersion of repolarization and decreased QT variability in arrhythmogenic failing hearts. MitoTEMPO therapy also prevented many of the changes in expression proteome and phosphoproteome leading to contractile dysfunction, arrhythmia and SCD. In subcellular studies of LV myocytes, acute MitoTEMPO exposure strongly suppressed both mROS and cROS. Exogenous H2O2 increased ROS in all intracellular compartments, but mROS scavenging was impaired more than cROS, consistent with downregulation of mitochondrial antioxidant enzymes.
Conclusions: Mitochondria are a principal source of cellular oxidative stress in failing arrhythmogenic hearts, but also are the major sink of ROS. Impaired mROS scavenging cause failing hearts to become more vulnerable to demand-induced oxidative stress and promote arrhythmic SCD. Maintaining global redox balance by enhanced mROS scavenging may be an effective strategy for SCD therapy in HF.