Atrial fibrillation is associated with the fibrotic remodelling of adipose tissue in the subepicardium of human and sheep atria.

AIMS: Accumulation of atrial adipose tissue is associated with atrial fibrillation (AF). However, the underlying mechanisms remain poorly understood. We examined the relationship between the characteristics of fatty infiltrates of the atrial myocardium and the history of AF. METHODS AND RESULTS: Atrial samples, collected in 92 patients during cardiac surgery and in a sheep model of persistent AF, were subjected to a detailed histological analysis. In sections of human right atrial samples, subepicardial fatty infiltrations were commonly observed in the majority of patients. A clear difference in the appearance and fibrotic content of these fatty infiltrations was observed. Fibro-fatty infiltrates predominated in patients with permanent AF (no AF: 37 ± 24% vs. paroxysmal AF: 50 ± 21% vs. permanent AF: 64 ± 23%, P < 0.001). An inverse correlation between fibrotic remodelling and the amount of subepicardial adipose tissue suggested the progressive fibrosis of fatty infiltrates with permanent AF. This hypothesis was tested in a sheep model of AF. In AF sheep, an increased accumulation of peri-atrial fat depot was observed on cardiac magnetic resonance imaging and dense fibro-fatty infiltrations predominated in the left atria of AF sheep. Cellular inflammation, mainly consisting of functional cytotoxic T lymphocytes, was observed together with adipocyte cell death in human atria. CONCLUSION: Atrial fibrillation is associated with the fibrosis of subepicardial fatty infiltrates, a process in which cytotoxic lymphocytes might be involved. This remodelling of the atrial subepicardium could contribute to structural remodelling forming a substrate for AF.

Long-term functional benefits of epicardial patches as cell carriers.

Both enzymatic dissociation of cells prior to needle-based injections and poor vascularization of myocardial infarct areas are two important contributors to cell death and impede the efficacy of cardiac cell therapy. Because these limitations could be overcome by scaffolds ensuring cell cohesiveness and codelivery of angiogenic cells, we used a chronic rat model of myocardial infarction to assess the long-term (6 months) effects of the epicardial delivery of a composite collagen-based patch harboring both cardiomyogenesis-targeted human embryonic SSEA-1(+) (stem cell-derived stage-specific embryonic antigen-1 positive) cardiovascular progenitors and autologous (rat) adipose tissue-derived angiogenesis-targeted stromal cells (n = 27). Cell-free patches served as controls (n = 28). Serial follow-up echocardiographic measurements of left ventricular ejection fraction (LVEF) showed that the composite patch group yielded a significantly better preservation of left ventricular function that was sustained over time as compared with controls, and this pattern persisted when the assessment was restricted to the subgroup of rats with initial LVEFs below 50%. The composite patch group was also associated with significantly less fibrosis and more vessels in the infarct area. However, although human progenitors expressing cardiac markers were present in the patches before implantation, none of them could be subsequently identified in the grafted tissue. These data confirm the efficacy of epicardial scaffolds as cell carriers for ensuring long-term functional benefits and suggest that these effects are likely related to paracrine effects and call for optimizing cross-talks between codelivered cell populations to achieve the ultimate goal of myocardial regeneration.

Efficacy of epicardially delivered adipose stroma cell sheets in dilated cardiomyopathy.

AIMS: Few studies have assessed the effects of cell therapy in non-ischaemic cardiomyopathies which, however, contribute to a large number of cardiac failures. Assuming that such conditions are best suited for a global delivery of cells, we assessed the effects of epicardially delivered adipose tissue-derived stroma cell (ADSC) sheets in a mouse model of dilated cardiomyopathy based on cardiac-specific and tamoxifen-inducible invalidation of serum response factor. METHODS AND RESULTS: Three weeks after tamoxifen administration, the function of the left ventricle (LV) was assessed by echocardiography. Twenty-nine mice were then allocated to control (n = 9, non-transgenic), sham (n = 10, transgenic non-treated), and treated (n = 10, transgenic) groups. In the treated group, 3 × 10(6) allogeneic ADSCs were cultured for 2 days onto temperature-responsive polymers and the generated sheets were then transplanted over the surface of the heart. In 10 additional mice, the sheet was made of green fluorescent protein (GFP)-labelled ADSCs to track cell fate. Function, engraftment, and fibrosis were blindly assessed after 3 weeks. In the non-treated group, fractional shortening declined compared with baseline, whereas the sheet application resulted in its stabilization. This correlated with a lesser degree of LV remodelling, as LV end-diastolic and end-systolic diameters did not differ from baseline values. Many GFP(+) cells were identified in the epicardial graft and in the myocardium. Treated animals also displayed a reduced expression of the stress-induced atrial natriuretic factor and beta-myosin heavy chain genes. These protective effects were also accompanied by a reduction of myocardial fibrosis. CONCLUSION: These results strongly suggest the functional relevance of epicardially delivered cell-seeded biomaterials to non-ischaemic heart failure.

Epicardial adipose stem cell sheets results in greater post-infarction survival than intramyocardial injections.

AIMS: Intramyocardial injections of cells can damage tissue and enhance dissociation-induced cell death. We assessed whether epicardial delivery of cell sheets could overcome these issues in a rat model of chronic myocardial infarction. METHODS AND RESULTS: Eighty-two rats that had undergone coronary ligation and simultaneous harvest of fat tissue to yield the adipose-derived stromal cell (ADSC) fraction were randomized 1 month after infarction to receive injections of either control medium (n= 24) or 10 × 10(6) autologous ADSC (n= 37) or the epicardial deposit, onto the infarcted area, of a trilayered ADSC sheet (10 × 10(6), n= 21) prepared by culturing cells on temperature-sensitive dishes. Some treated rats received green fluorescent protein labelled ADSC. Survival, function, and cell engraftment were blindly assessed after 2 months. Prior to implantation, cell sheets and suspended cells were assessed for the expression of extracellular matrix constituents and molecules involved in angiogenesis and cardiac remodelling. The survival rate of rats receiving the cell sheets was significantly higher than after cell injections (73 vs. 41%, P = 0.01). This correlated with the absence of left ventricular (LV) remodelling in the cell sheet group, as end-diastolic volume only increased by 2.8% compared with baseline [95% confidence interval (CI): -18.7%; +30.0%, P = 0.81] vs. increases of 25.9% (-0.4%; +59.2%, P = 0.05) and 51.2% (+18.6%; +92.8, P = 0.001) in the cell and medium injection groups, respectively. Sheets also resulted in a greater cell engraftment possibly related to the greater expression of extracellular matrix constituents. CONCLUSION: The better preservation of LV geometry afforded by ADSC sheets is associated with increased survival and engraftment, which supports the concept of an epicardial delivery of cell-seeded biomaterials.

Cell delivery: intramyocardial injections or epicardial deposition? A head-to-head comparison.

BACKGROUND: Multiple needle-based injections of cells in the myocardium are associated with a low engraftment rate, which may limit the benefits of the procedure. This study used skeletal myoblasts to perform a head-to-head comparison of conventional injections with epicardial deposition of scaffold-embedded cells. METHODS: Four weeks after ligation-induced myocardial infarction, 40 rats were randomly allocated to receive intramyocardial injections of 5 million human skeletal myoblasts or control medium or to have the infarcted area covered with either a bilayer myoblast cell sheet prepared from a fibrin-coated culture plate or a myoblast-seeded collagen sponge (Gelfoam; Pharmacia & Upjohn, Kalamazoo, MI). End points, assessed after 1 month, included left ventricular function blindly measured by echocardiography, quantification of cell engraftment by quantitative real-time polymerase chain reaction and immunostaining, histologic assessment of fibrosis and angiogenesis, and tissue levels of host-specific angiogenic and antifibrotic cytokines. RESULTS: Compared with control medium- or myoblast-injected hearts, those receiving the two cell constructs demonstrated the highest recoveries of left ventricular function (p = 0.004 versus controls). Both myoblast cell sheets and myoblast-seeded Gelfoam sponges also resulted in significantly greater angiogenesis compared with controls. The Gelfoam group was associated with the best outcome with regard to the number of engrafted donor cells (p = 0.03 versus myoblasts) and the reduction of fibrosis (p = 0.02 and p = 0.04 versus the control and myoblast groups, respectively). CONCLUSIONS: Compared with injections, delivery of myoblasts in a construct overlaying the infarcted area is associated with better graft functionality, possibly because of maintenance of improved cell patterning. The cell-seeded Gelfoam construct was found to feature a user-friendly, reproducible, and atraumatic technique.