Abstract 13383: The Vascular Endothelial Barrier: A Novel Therapeutic Target for Preventing Atrial Fibrillation

Abstract

Atrial fibrillation (AF), the most common arrhythmia, is associated with inflammation and vascular dysfunction. AF patients have elevated levels of vascular endothelial growth factor (VEGF; 90-580 pg/ml), which promotes vascular leak and edema. We have previously identified edema-induced disruption of sodium channel (Na V 1.5) -rich intercalated disk (ID) nanodomains as a novel arrhythmia mechanism. We hypothesized that (i) elevated VEGF levels promote AF by disrupting ID nanodomains, and slowing atrial conduction, and (ii) protection of the vascular barrier can prevent these arrhythmias. Clinically-relevant VEGF levels (500 pg/ml, 60 minutes) increased FITC-dextran extravasation (99.3% vs. 24.3% in vehicle controls) in WT mouse hearts, consistent with increased vascular leak. Electron microscopy revealed ID nanodomain swelling, near both gap junctions (perinexi; 64±9nm vs 17±1nm) and mechanical junctions (63±4nm vs 27±2nm) in VEGF-treated hearts relative to controls. Super-resolution STORM microscopy revealed Na V 1.5 enrichment at perinexi (9±2 fold) and N-cadherin-rich sites (7±1 fold) relative to non-junctional ID sites in control hearts. VEGF reduced Na V 1.5 enrichment at both sites (6±1 and 4±1 fold, respectively), consistent with Na V 1.5 translocation from ID nanodomains. Atrial conduction, assessed by optical mapping, was slowed by VEGF (10±0.4 cm/s vs 21.3±1.3 cm/s at baseline). VEGF increased atrial arrhythmia burden both ex vivo (80% vs 0% in vehicle controls) and in vivo (70% vs 20% in vehicle controls). Next, we tested two strategies shown to prevent vascular barrier breakdown. Blocking connexin43 hemichannels (αCT11 peptide) decreased both incidence (40%) and duration (1.45±3.42s) of VEGF-induced arrhythmias. Likewise, blocking pannexin1 channels (Panx1-IL2 peptide) shortened VEGF-induced arrhythmias (2.48±0.83s). Mefloquine and spironolactone, which are small molecules that respectively inhibit Cx43 hemichannels and pannexin channels, were also found to effectively prevent VEGF-induced atrial arrhythmias. These results highlight VEGF-induced vascular leak as a novel mechanism for AF, and suggest vascular barrier protection as an anti-arrhythmic strategy.