Systemic Delivery of Extracellular Vesicles Attenuates Atrial Fibrillation in Heart Failure With Preserved Ejection Fraction.

BACKGROUND: Atrial fibrillation (AF) is a common comorbidity in heart failure with preserved ejection fraction (HFpEF) patients. To date, treatments for HFpEF-related AF have been limited to anti-arrhythmic drugs and ablation. Here we examined the effects of immortalized cardiosphere-derived extracellular vesicles (imCDCevs) in rats with HFpEF. OBJECTIVES: This study sought to investigate the mechanisms of AF in HFpEF and probe the potential therapeutic efficacy of imCDCevs in HFpEF-related AF. METHODS: Dahl salt-sensitive rats were fed a high-salt diet for 7 weeks to induce HFpEF and randomized to receive imCDCevs (n = 18) or vehicle intravenously (n = 14). Rats fed a normal-salt diet were used as control animals (n = 26). A comprehensive characterization of atrial remodeling was conducted using functional and molecular techniques. RESULTS: HFpEF-verified animals showed significantly higher AF inducibility (84%) compared with control animals (15%). These changes were associated with prolonged action potential duration, slowed conduction velocity (connexin 43 lateralization), and fibrotic remodeling in the left atrium of HFpEF compared with control animals. ImCDCevs reversed adverse electrical remodeling (restoration of action potential duration to control levels and reorganization of connexin 43) and reduced AF inducibility (33%). In addition, fibrosis, inflammation, and oxidative stress, which are major pathological AF drivers, were markedly attenuated in imCDCevs-treated animals. Importantly, these effects occurred without changes in blood pressure and diastolic function. CONCLUSIONS: Thus, imCDCevs attenuated adverse remodeling, and prevented AF in a rat model of HFpEF.

MicroRNA-dependent suppression of biological pacemaker activity induced by TBX18.

Chemically modified mRNA (CMmRNA) with selectively altered nucleotides are used to deliver transgenes, but translation efficiency is variable. We have transfected CMmRNA encoding human T-box transcription factor 18 (CMmTBX18) into heart cells or the left ventricle of rats with atrioventricular block. TBX18 protein expression from CMmTBX18 is weak and transient, but Acriflavine, an Argonaute 2 inhibitor, boosts TBX18 levels. Small RNA sequencing identified two upregulated microRNAs (miRs) in CMmTBX18-transfected cells. Co-administration of miR-1-3p and miR-1b antagomiRs with CMmTBX18 prolongs TBX18 expression in vitro and in vivo and is sufficient to generate electrical stimuli capable of pacing the heart. Different suppressive miRs likewise limit the expression of VEGF-A CMmRNA. Cells therefore resist translation of CMmRNA therapeutic transgenes by upregulating suppressive miRs. Blockade of suppressive miRs enhances CMmRNA expression of genes driving biological pacing or angiogenesis. Such counterstrategies constitute an approach to boost the efficacy and efficiency of CMmRNA therapies.

Biological substrate modification suppresses ventricular arrhythmias in a porcine model of chronic ischaemic cardiomyopathy.

AIMS: Cardiomyopathy patients are prone to ventricular arrhythmias (VA) and sudden cardiac death. Current therapies to prevent VA include radiofrequency ablation to destroy slowly conducting pathways of viable myocardium which support re-entry. Here, we tested the reverse concept, namely that boosting local tissue viability in zones of slow conduction might eliminate slow conduction and suppress VA in ischaemic cardiomyopathy. METHODS AND RESULTS: Exosomes are extracellular vesicles laden with bioactive cargo. Exosomes secreted by cardiosphere-derived cells (CDCEXO) reduce scar and improve heart function after intramyocardial delivery. In a VA-prone porcine model of ischaemic cardiomyopathy, we injected CDCEXO or vehicle into zones of delayed conduction defined by electroanatomic mapping. Up to 1-month post-injection, CDCEXO, but not the vehicle, decreased myocardial scar, suppressed slowly conducting electrical pathways, and inhibited VA induction by programmed electrical stimulation. In silico reconstruction of electrical activity based on magnetic resonance images accurately reproduced the suppression of VA inducibility by CDCEXO. Strong anti-fibrotic effects of CDCEXO, evident histologically and by proteomic analysis from pig hearts, were confirmed in a co-culture assay of cardiomyocytes and fibroblasts. CONCLUSION: Biological substrate modification by exosome injection may be worth developing as a non-destructive alternative to conventional ablation for the prevention of recurrent ventricular tachyarrhythmias.

Mechanisms of atrial fibrillation in aged rats with heart failure with preserved ejection fraction.

BACKGROUND: Although ∼20% of the elderly population develops atrial fibrillation (AF), little is known about the mechanisms. Heart failure with preserved ejection fraction (HFpEF), which is associated with AF, is more common in aged women than in men. OBJECTIVE: The purpose of this study was to identify potential mechanisms of AF in an age-related HFpEF model. METHODS: In aged female Fischer F344 rats (21- to 24-month-old), which are prone to HFpEF, we induced AF by atrial pacing. Young Fischer F344 female rats (3- to 4-month-old) and age-matched Sprague Dawley female rats (27-month-old) served as controls. Phenotyping included echocardiography to assess left ventricular structure/function; in vivo electrophysiology and ex vivo high-resolution optical mapping to assess AF vulnerability; systemic and atrial inflammatory profiling; atrial histology; and expression of inflammasome signaling proteins. RESULTS: Aged rats developed left ventricular hypertrophy, left atrial enlargement, diastolic dysfunction, and pulmonary congestion, without ejection fraction impairment, thus meeting the criteria for HFpEF. Increased serum inflammatory markers, hypertension, and obesity further characterize aged females. Sinoatrial and atrioventricular node dysfunction was associated with the high inducibility of AF in aged rats. Ex vivo electrical activation mapping revealed abnormal ß-adrenergic responsiveness and slowed conduction velocity. Atrial inflammasome signaling was enhanced in aged rats, which may contribute to fibrotic remodeling and high AF susceptibility. CONCLUSION: Together, our data demonstrate that aging-related atrial remodeling and HFpEF are associated with atrial enlargement, fibrosis, conduction abnormalities, and nodal dysfunction, favoring a substrate conducive to AF.

Ventricular Arrhythmias Underlie Sudden Death in Rats With Heart Failure and Preserved Ejection Fraction.

BACKGROUND: Heart failure (HF) with preserved ejection fraction (HFpEF) is increasingly common clinically, now rivaling or exceeding HF with reduced ejection fraction . Sudden death is the leading mode of exodus in patients with HFpEF, but the underlying causes are largely unknown. Using ambulatory recordings in a rat model, we test the hypothesis that ventricular arrhythmias (VA) underlie sudden death in HFpEF. METHODS: Dahl salt-sensitive rats (7 weeks of age) were fed a high-salt diet to induce HFpEF (n=13) or a normal-salt diet (controls, n=9). Transthoracic echocardiography was performed to check systolic and diastolic function at 14 to 18 weeks of age. Telemetric electrocardiographic recordings were analyzed for QT interval duration, burden of premature ventricular contractions, spontaneous VA, and heart rate variability. Survival was monitored twice daily. RESULTS: High-salt-fed rats with clear diastolic dysfunction, preserved ejection fraction, and HF signs were diagnosed with HFpEF at 14 to 15 weeks of age. QT and QTc intervals were prolonged in HFpEF rats compared with controls. Heart rate variability was reduced in HFpEF rats compared with controls. Spontaneous VA were more prevalent in HFpEF rats (6/13=46.1% versus 0/9=0% in controls; P<0.05), and sudden death was observed in 4 of 13 HFpEF rats. Three of the 4 sudden deaths were associated with VA as the terminal rhythm. CONCLUSIONS: In this rat model with phenotypically verified HFpEF, sudden death was common and generally associated with VA. Further clinical studies are warranted to determine whether these insights translate to sudden death in HFpEF patients.