Disruption of NOX2-dependent Oxidative Injury with a Targeted Gene-Therapy Approach Prevents Atrial Fibrillation in a Canine Model

Abstract

Atrial fibrillation is the most common heart rhythm disorder in adults and a major cause of stroke. Unfortunately, current treatments of AF are suboptimal as they are not targeted to the molecular mechanisms underlying AF. In this study, we demonstrated using a novel gene-based strategy in a clinically relevant large animal of AF that oxidative injury is a key mechanism underlying the onset and perpetuation of AF. First, we demonstrated that generation of oxidative injury in atrial myocytes is a frequency-dependent process, with rapid pacing in canine atrial myocytes inducing oxidative injury through induction of NADPH oxidase 2 (NOX2) and generation of mitochondrial reactive oxygen species. We show that oxidative injury likely contributes to electrical remodeling in AF by upregulating a constitutively active form of acetylcholine-dependent K+ current (IKACh) - called IKH - by a mechanism involving frequency-dependent activation of protein kinase C epsilon (PKC{varepsilon}). To understand the mechanism by which oxidative injury promotes the genesis and/or maintenance of AF, we performed targeted injection of NOX2 shRNA in atria of normal dogs followed by rapid atrial pacing. The time to onset of non-sustained AF increased by more than 5-fold in NOX2 shRNA treated dogs. Furthermore, animals treated with NOX2 shRNA did not develop sustained AF for up to 12 weeks. The electrophysiological mechanism underlying AF prevention was prolongation of atrial effective refractory periods, with attenuated activation of PKC{varepsilon}, a likely molecular mechanism underlying this beneficial electrophysiological remodeling. Future optimization of this approach may lead to a novel, mechanism-guided therapy for AF.\n\nOne Sentence SummaryTargeted disruption of NOX2-dependent oxidative injury with a novel gene therapy approach prevents onset as well as perpetuation of atrial fibrillation.