Atrial Fibrillation and Obesity: Reverse Remodeling of Atrial Substrate With Weight Reduction.

OBJECTIVES: This study sought to evaluate the effect of weight loss on the atrial substrate for atrial fibrillation (AF). BACKGROUND: Whether weight loss can reverse the atrial substrate of obesity is not known. METHODS: Thirty sheep had sustained obesity induced by ad libitum calorie-dense diet over 72 weeks. Animals were randomized to 3 groups: sustained obesity and 15% and 30% weight loss. The animals randomized to weight loss underwent weight reduction by reducing the quantity of hay over 32 weeks. Eight lean animals served as controls. All were subjected to the following: dual-energy x-ray absorptiometry, echocardiogram, cardiac magnetic resonance, electrophysiological study, and histological and molecular analyses (fatty infiltration, fibrosis, transforming growth factor ß1, and connexin 43). RESULTS: Sustained obesity was associated with increased left atrium (LA) pressure (p < 0.001), inflammation (p < 0.001), atrial transforming growth factor ß1 protein (p < 0.001), endothelin-B receptor expression (p = 0.04), atrial fibrosis (p = 0.01), epicardial fat infiltration (p < 0.001), electrophysiological abnormalities, and AF burden (p = 0.04). Connexin 43 expression was decreased in the obese group (p = 0.03). In this obese ovine model, 30% weight reduction was associated with reduction in total body fat (p < 0.001), LA pressure (p = 0.007), inflammation (p < 0.001), endothelin-B receptor expression (p = 0.01), atrial fibrosis (p = 0.01), increase in atrial effective refractory period (cycle length: 400 and 300 ms; p < 0.001), improved conduction velocity (cycle length: 400 and 300 ms; p = 0.01), decreased conduction heterogeneity (p < 0.001), and decreased AF inducibility (p = 0.03). Weight loss was associated with a nonsignificant reduction in epicardial fat infiltration in posterior LA (p = 0.34). CONCLUSIONS: Weight loss in an obese ovine model is associated with structural and electrophysiological reverse remodeling and a reduced propensity for AF. This provides evidence for the direct role of obesity in AF substrate and the role of weight reduction in patients with AF.

Serelaxin enhances the therapeutic effects of human amnion epithelial cell-derived exosomes in experimental models of lung disease.

BACKGROUND AND PURPOSE: There is growing interest in stem cell-derived exosomes for their therapeutic and regenerative benefits given their manufacturing and regulatory advantages over cell-based therapies. As existing fibrosis impedes the viability and efficacy of stem cell/exosome-based strategies for treating chronic diseases, here we tested the effects of the anti-fibrotic drug, serelaxin, on the therapeutic efficacy of human amnion epithelial cell (AEC)-derived exosomes in experimental lung disease. EXPERIMENTAL APPROACH: Female Balb/c mice were subjected to either the 9.5-week model of ovalbumin and naphthalene (OVA/NA)-induced chronic allergic airway disease (AAD) or 3-week model of bleomycin (BLM)-induced pulmonary fibrosis; then administered increasing concentrations of AEC-exosomes (5 µg or 25µg), with or without serelaxin (0.5mg/kg/day) for 7-days. 1x106 AECs co-administered with serelaxin over the corresponding time-period were included for comparison in both models, as was pirfenidone-treatment of the BLM model. Control groups received saline/corn oil or saline, respectively. KEY RESULTS: Both experimental models presented with significant tissue inflammation, remodelling, fibrosis and airway/lung dysfunction at the time-points studied. While AEC-exosome (5 µg or 25µg)-administration alone demonstrated some benefits in each model, serelaxin was required for AEC-exosomes (25µg) to rapidly normalise chronic AAD-induced airway fibrosis and airway reactivity, and BLM-induced lung inflammation, epithelial damage and subepithelial/basement membrane fibrosis. Combining serelaxin with AEC-exosomes (25µg) also demonstrated broader protection compared to co-administration of serelaxin with 1x106 AECs or pirfenidone. CONCLUSIONS AND IMPLICATIONS: Serelaxin enhanced the therapeutic efficacy of AEC-exosomes in treating basement membrane-induced fibrosis and related airway dysfunction.

Serelaxin improves the therapeutic efficacy of RXFP1-expressing human amnion epithelial cells in experimental allergic airway disease.

Current asthma therapies primarily target airway inflammation (AI) and suppress episodes of airway hyperresponsiveness (AHR) but fail to treat airway remodelling (AWR), which can develop independently of AI and contribute to irreversible airway obstruction. The present study compared the anti-remodelling and therapeutic efficacy of human bone marrow-derived mesenchymal stem cells (MSCs) to that of human amnion epithelial stem cells (AECs) in the setting of chronic allergic airways disease (AAD), in the absence or presence of an anti-fibrotic (serelaxin; RLX). Female Balb/c mice subjected to the 9-week model of ovalbumin (OVA)-induced chronic AAD, were either vehicle-treated (OVA alone) or treated with MSCs or AECs alone [intranasally (i.n.)-administered with 1×106 cells once weekly], RLX alone (i.n.-administered with 0.8 mg/ml daily) or a combination of MSCs or AECs and RLX from weeks 9-11 (n=6/group). Measures of AI, AWR and AHR were then assessed. OVA alone exacerbated AI, epithelial damage/thickness, sub-epithelial extracellular matrix (ECM) and total collagen deposition, markers of collagen turnover and AHR compared with that in saline-treated counterparts (all P<0.01 compared with saline-treated controls). RLX or AECs (but not MSCs) alone normalized epithelial thickness and partially diminished the OVA-induced fibrosis and AHR by ∼40-50% (all P<0.05 compared with OVA alone). Furthermore, the combination treatments normalized epithelial thickness, measures of fibrosis and AHR to that in normal mice, and significantly decreased AI. Although AECs alone demonstrated greater protection against the AAD-induced AI, AWR and AHR, compared with that of MSCs alone, combining RLX with MSCs or AECs reversed airway fibrosis and AHR to an even greater extent.

Mesenchymal stem cells and serelaxin synergistically abrogate established airway fibrosis in an experimental model of chronic allergic airways disease.

This study determined if the anti-fibrotic drug, serelaxin (RLN), could augment human bone marrow-derived mesenchymal stem cell (MSC)-mediated reversal of airway remodeling and airway hyperresponsiveness (AHR) associated with chronic allergic airways disease (AAD/asthma). Female Balb/c mice subjected to the 9-week model of ovalbumin (OVA)-induced chronic AAD were either untreated or treated with MSCs alone, RLN alone or both combined from weeks 9-11. Changes in airway inflammation (AI), epithelial thickness, goblet cell metaplasia, transforming growth factor (TGF)-ß1 expression, myofibroblast differentiation, subepithelial and total lung collagen deposition, matrix metalloproteinase (MMP) expression, and AHR were then assessed. MSCs alone modestly reversed OVA-induced subepithelial and total collagen deposition, and increased MMP-9 levels above that induced by OVA alone (all p<0.05 vs OVA group). RLN alone more broadly reversed OVA-induced epithelial thickening, TGF-ß1 expression, myofibroblast differentiation, airway fibrosis and AHR (all p<0.05 vs OVA group). Combination treatment further reversed OVA-induced AI and airway/lung fibrosis compared to either treatment alone (all p<0.05 vs either treatment alone), and further increased MMP-9 levels. RLN appeared to enhance the therapeutic effects of MSCs in a chronic disease setting; most likely a consequence of the ability of RLN to limit TGF-ß1-induced matrix synthesis complemented by the MMP-promoting effects of MSCs.

Characterization of a novel model incorporating airway epithelial damage and related fibrosis to the pathogenesis of asthma.

Asthma develops from injury to the airways/lungs, stemming from airway inflammation (AI) and airway remodeling (AWR), both contributing to airway hyperresponsiveness (AHR). Airway epithelial damage has been identified as a new etiology of asthma but is not targeted by current treatments. Furthermore, it is poorly studied in currently used animal models of AI and AWR. Therefore, this study aimed to incorporate epithelial damage/repair with the well-established ovalbumin (OVA)-induced model of chronic allergic airway disease (AAD), which presents with AI, AWR, and AHR, mimicking several features of human asthma. A 3-day naphthalene (NA)-induced model of epithelial damage/repair was superimposed onto the 9-week OVA-induced model of chronic AAD, before 6 weeks of OVA nebulization (NA+OVA group), during the second last OVA nebulization period (OVA/NA group) or 1 day after the 6-week OVA nebulization period (OVA+NA group), using 6-8-week-old female Balb/c mice (n=6-12/group). Mice subjected to the 9-week OVA model, 3-day NA model or respective vehicle treatments (saline and corn oil) were used as appropriate controls. OVA alone significantly increased epithelial thickness and apoptosis, goblet cell metaplasia, TGF-ß1, subepithelial collagen (assessed by morphometric analyses of various histological stains), total lung collagen (hydroxyproline analysis), and AHR (invasive plethysmography) compared with that in saline-treated mice (all P<0.05 vs saline treatment). NA alone caused a significant increase in epithelial denudation and apoptosis, TGF-ß1, subepithelial, and total lung collagen compared with respective measurements from corn oil-treated controls (all P<0.01 vs corn oil treatment). All three combined models underwent varying degrees of epithelial damage and AWR, with the OVA+NA model demonstrating the greatest increase in subepithelial/total lung collagen and AHR (all P<0.05 vs OVA alone or NA alone). These combined models of airway epithelial damage/AAD demonstrated that epithelial damage is a key contributor to AWR, fibrosis and related AHR, and augments the effects of AI on these parameters.