Search

Objectives This study sought to investigate the hypothesis that the favorable effects of mesenchymal stromal cells (MSCs) on infarct repair are mediated by macrophages. Background The favorable effects of MSC therapy in myocardial infarction (MI) are complex and not fully understood. Methods We induced MI in mice and allocated them to bone marrow MSCs, mononuclear cells, or saline injection into the infarct, with and without early (4 h before MI) and late (3 days after MI) macrophage depletion. We then analyzed macrophage phenotype in the infarcted heart by flow cytometry and macrophage secretome in vitro. Left ventricular remodeling and global and regional function were assessed by echocardiography and speckle-tracking based strain imaging. Results The MSC therapy significantly increased the percentage of reparative M2 macrophages (F4/80+CD206+) in the infarcted myocardium, compared with mononuclear- and saline-treated hearts, 3 and 4 days after MI. Macrophage cytokine secretion, relevant to infarct healing and repair, was significantly increased after MSC therapy, or incubation with MSCs or MSC supernatant. Significantly, with and without MSC therapy, transient macrophage depletion increased mortality 30 days after MI. Furthermore, early macrophage depletion produced the greatest negative effect on infarct size and left ventricular remodeling and function, as well as a significant incidence of left ventricular thrombus formation. These deleterious effects were attenuated with macrophage restoration and MSC therapy. Conclusions Some of the protective effects of MSCs on infarct repair are mediated by macrophages, which are essential for early healing and repair. Thus, targeting macrophages could be a novel strategy to improve infarct healing and repair.

Uncontrolled activation of pro-inflammatory macrophages after myocardial infarction (MI) accelerates adverse left ventricular (LV) remodeling and dysfunction. Hemin, an iron-containing porphyrin, activates heme oxygenase-1 (HO-1), an enzyme with anti-inflammatory and cytoprotective properties. We sought to determine the effects of hemin formulated in a macrophage-targeted lipid-based carrier (denoted HA-LP) on LV remodeling and function after MI. Hemin encapsulation efficiency was ~ 100% at therapeutic dose levels. In vitro, hemin/HA-LP abolished TNF-α secretion from macrophages, whereas the same doses of free hemin and drug free HA-LP had no effect. Hemin/HA-LP polarized peritoneal and splenic macrophages toward M2 anti-inflammatory phenotype. We next induced MI in mice and allocated them to IV treatment with hemin/HA-LP (10 mg/kg), drug free HA-LP, free hemin (10 mg/kg) or saline, one day after MI. Active in vivo targeting to infarct macrophages was confirmed with HA-LP doped with PE-rhodamine. LV remodeling and function were assessed by echocardiography before, 7, and 30 days after treatment. Significantly, hemin/HA-LP effectively and specifically targets infarct macrophages, switches infarct macrophages toward M2 anti-inflammatory phenotype, improves angiogenesis, reduces scar expansion and improves infarct-related regional function. In conclusion, macrophage-targeted lipid-based drug carriers with hemin switch macrophages into an anti-inflammatory phenotype, and improve infarct healing and repair. Our approach presents a novel strategy to modulate inflammation and improve infarct repair.

Background— The identification and isolation of human cardiac progenitor cells (hCPCs) offer new approaches for myocardial regeneration and repair. Still, the optimal source of human cardiac progenitor cells and the influence of patient characteristics on their number remain unclear. Using a novel method to isolate human cardiac progenitor cells, we aimed to define the optimal source and association between their number and patient characteristics. Methods and Results— We developed a novel isolation method that produced viable cells (7×10 6 ±6.53×10 5 /g) from various tissue samples obtained during heart surgery or endomyocardial biopsies (113 samples from 94 patients 23 to 80 years of age). The isolated cardiac cells were grown in culture with a stem cell expansion medium. According to fluorescence-activated cell sorting analysis, cultured cells derived from the right atrium generated higher amounts of c-kit + (24±2.5%) and Islet-1 + cells (7%) in culture (mean of passages 1, 2, and 3) than did cultured cells from the left atrium (7.3±3.5%), right ventricle (4.1±1.6%), and left ventricle (9.7±3%; P =0.001). According to multivariable analysis, the right atrium as the cell source and female sex were associated with a higher number of c-kit + cells. There was no overlap between c-kit + and Islet-1 expression. In vitro assays of differentiation into osteoblasts, adipocytes, and myogenic lineage showed that the isolated human cardiac progenitor cells were multipotent. Finally, the cells were transplanted into infarcted myocardium of rats and generated myocardial grafts. Conclusion— Our results show that the right atrium is the best source for c-kit + and Islet-1 progenitors, with higher percentages of c-kit + cells being produced by women.

Previous studies have shown that pre-exposure of the heart to weak magnetic field reduces infarct size shortly after induction of myocardial ischemia. To investigate the role of AC magnetic field with a frequency of 15.95-16 Hz and 80 mT on left ventricular (LV) remodeling following chronic coronary occlusion and a short episode of ischemia followed by reperfusion (I/R). LV dimension and function were measured using echocardiography. Femur bone marrow was isolated and cells were phenotyped for endothelial linage and immuno stained for endothelial cells. The area at risk was measured using triphenyltetrazolium chloride staining. A significant reduction of 27% in shortening fraction (SF) was measured following acute myocardial infarction (AMI) compared with a 7% decrease in animals exposed to magnetic field (p < 0.04). A significantly higher number of colony forming units and endothelial progenitor cells were counted within the treated groups subjected to magnetic field (p < 0.02). Exposing the heart to magnetic field prior to reperfusion did not show any preservation either on SF or on infarct size. Magnetic field was protective in the AMI but not in the I/R model. The mechanisms underlying cardiac protection induced by AC magnetic field following chronic injury deserves further investigation.

Tissue engineering holds the promise of providing new solutions for heart transplant shortages and pediatric heart transplantation. The aim of this study was to evaluate the ability of a peritoneal-generated, tissue-engineered cardiac patch to replace damaged myocardium in a heterotopic heart transplant model. Fetal cardiac cells (1 × 106/scaffold) from syngeneic Lewis rats were seeded into highly porous alginate scaffolds. The cell constructs were cultured in vitro for 4 days and then they were implanted into the rat peritoneal cavity for 1 week. During this time the peritoneal-implanted patches were vascularized and populated with myofibroblasts. They were harvested and their performance in an infrarenal heterotopic abdominal heart transplantation model was examined ( n = 15). After transplantation and before reperfusion of the donor heart, a 5-mm left ( n = 6) or right ( n = 9) ventriculotomy was performed and the patch was sutured onto the donor heart to repair the defect. Echocardiographical studies carried out 1–2 weeks after transplantation showed normal LV function in seven of the eight hearts studied. After 1 month, visual examination of the grafted patch revealed no aneurysmal dilatation. Microscopic examination revealed, in most of the cardiac patches, a complete disappearance of the scaffold and its replacement by a consistent tissue composed of myofibroblasts embedded in collagen bundles. The cardiac patch was enriched with a relatively large number of infiltrating blood vessels. In conclusion, cardiac patches generated in the peritoneum were developed into consistent tissue patches with properties to seal and correct myocardial defects. Our study also offers a viable rat model for screening and evaluating new concepts in cardiac reconstruction and engineering.

Background— Adverse cardiac remodeling and progression of heart failure after myocardial infarction are associated with excessive and continuous damage to the extracellular matrix. We hypothesized that injection of in situ–forming alginate hydrogel into recent and old infarcts would provide a temporary scaffold and attenuate adverse cardiac remodeling and dysfunction. Methods and Results— We developed a novel absorbable biomaterial composed of calcium-crosslinked alginate solution, which displays low viscosity and, after injection into the infarct, undergoes phase transition into hydrogel. To determine the outcome of the biomaterial after injection, calcium-crosslinked biotin-labeled alginate was injected into the infarct 7 days after anterior myocardial infarction in rat. Serial histology studies showed in situ formation of alginate hydrogel implant, which occupied up to 50% of the scar area. The biomaterial was replaced by connective tissue within 6 weeks. Serial echocardiography studies before and 60 days after injection showed that injection of alginate biomaterial into recent (7 days) infarct increased scar thickness and attenuated left ventricular systolic and diastolic dilatation and dysfunction. These beneficial effects were comparable and sometimes superior to those achieved by neonatal cardiomyocyte transplantation. Moreover, injection of alginate biomaterial into old myocardial infarction (60 days) increased scar thickness and improved systolic and diastolic dysfunction. Conclusions— We show for the first time that injection of in situ–forming, bioabsorbable alginate hydrogel is an effective acellular strategy that prevents adverse cardiac remodeling and dysfunction in recent and old myocardial infarctions in rat.

Objective: To test the hypothesis that human embryonic stem cells (hESCs) can be guided to form new myocardium by transplantation into the normal or infarcted heart, and to assess the influence of hESC-derived cardiomyocytes (hESCMs) on cardiac function in a rat model of myocardial infarction (MI). Methods: Undifferentiated hESCs (0.5–1×10 6 ), human embryoid bodies (hEBs) (4–8 days; 0.5–1×10 6 ), 0.1 mm pieces of embryonic stem-derived beating myocardial tissue, and phosphate-buffered saline (control) were injected into the normal or infarcted myocardium of athymic nude rats (n = 58) by direct injection into the muscle or into preimplanted three-dimensional alginate scaffold. By 2–4 weeks after transplantation, heart sections were examined to detect the human cells and differentiation with fluorescent in situ hybridisation, using DNA probes specific for human sex chromosomes and HLA-DR or HLA-ABC immunostaining. Results: Microscopic examination showed transplanted human cells in the normal, and to a lesser extent in the infarcted myocardium (7/7 vs 2/6; p Conclusions: Undifferentiated hESCs and hEBs are not directed to form new myocardium after transplantation into normal or infarcted heart and may create teratoma. Nevertheless, this study shows that hESC-derived cardiomyocyte transplantation can attenuate post-MI scar thinning and left ventricular dysfunction.

Introduction and Hypothesis: Mesenchymal stem/stromal cells (MSCs) are appealing candidates for cardiac cell therapy due to their ease of preparation, immunoprivilege properties, reparative potential and safety. We aimed to test the hypothesis that the inflammatory environment following myocardial infarction (MI) and left ventricular (LV) dysfunction could modulate the reparative properties of resident and transplanted MSCs. Methods and Results: To test this hypothesis, we isolated and cultured resident cardiac and subcutaneous (SC) fat tissue MSCs from mice, 28 days after MI (LVEF: 27.9%±3.8) or sham operation (LVEF: 54.9%±3.8). Proliferation rate was highest in cardiac MSCs after MI, compared with other groups (pTLR4 ) deficient and wild-type mice, with the secretome of LPS-activated macrophages. Significantly, there was less inflammatory cytokine secretion in TLR4-deficient MSCs, compared with control suggesting that cardiac MSC polarization is mediated by TLR4 activation. Conclusions: Post MI inflammatory environment switches resident cardiac and implanted MSCs toward a pro-inflammatory phenotype and impair their reparative properties. This effect is mediated by TLR4 . Our findings are relevant to the pathogenesis and progression of LV remodeling, and could guide the selection and engineering of MSCs for heart repair.

Background Human mesenchymal stromal cells ( hMSC s) from adipose cardiac tissue have attracted considerable interest in regard to cell‐based therapies. We aimed to test the hypothesis that hMSC s from the heart and epicardial fat would be better cells for infarct repair. Methods and Results We isolated and grew hMSC s from patients with ischemic heart disease from 4 locations: epicardial fat, pericardial fat, subcutaneous fat, and the right atrium. Significantly, hMSC s from the right atrium and epicardial fat secreted the highest amounts of trophic and inflammatory cytokines, while hMSC s from pericardial and subcutaneous fat secreted the lowest. Relative expression of inflammation‐ and fibrosis‐related genes was considerably higher in hMSC s from the right atrium and epicardial fat than in subcutaneous fat hMSC s. To determine the functional effects of hMSC s, we allocated rats to hMSC transplantation 7 days after myocardial infarction. Atrial hMSC s induced greatest infarct vascularization as well as highest inflammation score 27 days after transplantation. Surprisingly, cardiac dysfunction was worst after transplantation of hMSC s from atrium and epicardial fat and minimal after transplantation of hMSC s from subcutaneous fat. These findings were confirmed by using hMSC transplantation in immunocompromised mice after myocardial infarction. Notably, there was a correlation between tumor necrosis factor‐α secretion from hMSC s and posttransplantation left ventricular remodeling and dysfunction. Conclusions Because of their proinflammatory properties, hMSC s from the right atrium and epicardial fat of cardiac patients could impair heart function after myocardial infarction. Our findings might be relevant to autologous mesenchymal stromal cell therapy and development and progression of ischemic heart disease.

The recent progress made in the bioengineering of cardiac patches offers a new therapeutic modality for regenerating the myocardium after myocardial infarction (MI). We present here a strategy for the engineering of a cardiac patch with mature vasculature by heterotopic transplantation onto the omentum. The patch was constructed by seeding neonatal cardiac cells with a mixture of prosurvival and angiogenic factors into an alginate scaffold capable of factor binding and sustained release. After 48 h in culture, the patch was vascularized for 7 days on the omentum, then explanted and transplanted onto infarcted rat hearts, 7 days after MI induction. When evaluated 28 days later, the vascularized cardiac patch showed structural and electrical integration into host myocardium. Moreover, the vascularized patch induced thicker scars, prevented further dilatation of the chamber and ventricular dysfunction. Thus, our study provides evidence that grafting prevascularized cardiac patch into infarct can improve cardiac function after MI.

Adverse cardiac remodeling and dysfunction after myocardial infarction (MI) is associated with excessive damage to the extracellular matrix. Biomaterials, such as the in situ-forming alginate hydrogel (BioLineRx, BL-1040 myocardial implant), provide temporary support and attenuate these processes. Here, we tested the effects of decorating alginate biomaterial with cell adhesion peptides, containing the sequences RGD and YIGSR, or a non-specific peptide (RGE), in terms of therapeutic outcome soon after MI. The biomaterial (i.e., both unmodified and peptide-modified alginate) solutions retained the ability to flow after cross-linking with calcium ions, and could be injected into 7-day infarcts, where they underwent phase transition into hydrogels. Serial echocardiography studies performed before and 60 days after treatment showed that alginate modification with the peptides reduced the therapeutical effects of the hydrogel, as revealed by the extent of scar thickness, left ventricle dilatation and function. Histology and immunohistochemistry revealed no significant differences in blood vessel density, scar thickness, myofibroblast or macrophage infiltration or cell proliferation between the experimental groups BioLineRx BL-1040 myocardial implant. Our studies thus reveal that the chemical and physical traits of the biomaterial can affect its therapeutical efficacy in attenuating left ventricle remodeling and function, post-MI.

Background— Cell labeling with superparamagnetic iron oxide (SPIO) nanoparticles enables noninvasive MRI and tracking of transplanted stem cells. We sought to determine whether mesenchymal stem cell (MSC) outcome is affected by SPIO labeling in a rat model of myocardial infarction. Methods and Results— Rat MSCs were labeled with SPIO (ferumoxides; Endorem; Guerbet, Villepinte, France). By trypan-blue exclusion assay, almost 100% of the cells remained viable after labeling. Seven days after MI, rats were randomized to injections of 2×10 6 SPIO-labeled MSCs, 2×10 6 unlabeled MSCs, or saline. Labeled cells were visualized in the infarcted myocardium as large black spots by serial MRI studies throughout the 4-week follow-up. The presence of labeled cells was confirmed by iron staining and real-time polymerase chain reaction on postmortem specimens. At 4 weeks after transplantation, the site of cell injection was infiltrated by inflammatory cells. Costaining for iron and ED1 (resident macrophage marker) showed that the iron-positive cells were cardiac macrophages. By real-time polymerase chain reaction, the Y-chromosome-specific SRY DNA of MSCs from male donors was not detected in infarcted hearts of female recipients. Serial echocardiography studies at baseline and 4 weeks after cell transplantation showed that both unlabeled and labeled MSCs attenuated progressive left ventricular dilatation and dysfunction compared with controls. Conclusions— At 4 weeks after transplantation of SPIO-labeled MSCs, the transplanted cells are not present in the scar and the enhanced MRI signals arise from cardiac macrophages that engulfed the SPIO nanoparticles. However, both labeled and unlabeled cells attenuate left ventricular dilatation and dysfunction after myocardial infarction.

Background— Activated macrophages have a significant role in wound healing and damaged tissue repair. We sought to explore the ability of ex vivo activated macrophages to promote healing and repair of the infarcted myocardium. Methods and Results— Human activated macrophage suspension (AMS) was prepared from a whole blood unit obtained from young donors in a closed sterile system and was activated by a novel method of hypo-osmotic shock. The AMS (&4×10 5 cells) included up to 43% CD14-positive cells and was injected into the ischemic myocardium of rats (n=8) immediately after coronary artery ligation. The control group (n=9) was treated with saline injection. The human cells existed in the infarcted heart 4 to 7 days after injection, as indicated by histology, human growth hormone-specific polymerase chain reaction, and magnetic resonance imaging (MRI) tracking of iron oxide–nanoparticle-labeled cells. After 5 weeks, scar vessel density (±SE) (25±4 versus 10±1 per mm 2 ; P P P P Conclusions— Early after myocardial infarction, injection of AMS accelerates vascularization, tissue repair, and improves cardiac remodeling and function. Our work suggests a novel clinically relevant option to promote the repair of ischemic tissue.

The aim of conducting this study was to assess the clinical relevance of matrix metalloproteinase (MMP) inhibition by doxycycline, an effective MMP inhibitor, in a rat model of extensive myocardial infarction (MI) and left ventricular (LV) dysfunction. Rats (n = 22) were subjected to extensive anterior MI. Doxycycline (25 mg SC, daily) or saline (control) injections were started for nine days thereafter. The effect of doxycycline on MMP activity in the infarcted and remote myocardium was measured by zymography, in another subgroup (n = 8), nine days after MI. Echocardiography and magnetic resonance imaging (MRI) studies were performed at one and thirty days after MI to assess LV remodeling and function. After 4 weeks, hearts were fixed, and subjected to morphometric and histological analysis. Compared with control, doxycycline treatment attenuated MMP-9 and -2 activity in both infarcted and remote myocardium. Serial echocardiography studies showed that doxycycline failed to attenuate scar thinning, LV dilatation and dysfunction. MRI study showed that doxycycline impaired LV compensatory hypertrophy. Furthermore, compared with control, doxycycline reduced vessel density (/mm(2) +/- SEM) in the infarcted myocardium (84 +/- 16 vs. 46 +/- 9/mm(2), respectively; p < 0.05). Our work suggest that effective MMPs' inhibition in the infarcted and remote myocardium by doxycycline does not prevent LV remodeling and dysfunction but impairs angiogenesis and compensatory LV hypertrophy. Our findings caution against aggressive, non-selective inhibition of MMPs in the early healing phase after MI.

The use of adult stem cells for myocardial tissue repair might be limited in elderly and sick people because their cells are depleted and exhausted. The present study was conducted to explore the potential of human umbilical cord blood (UCB) CD133+ progenitor cells for myocardial tissue repair in a model of extensive myocardial infarction (MI). CD133+ progenitor cells were isolated from newborn UCB. Cells (1.2–2 × 106) or saline (control) was infused intravenously 7 days after permanent coronary artery ligation in athymic nude rats. Left ventricular (LV) function was assessed before and 1 month after infusion by echocardiography. Tracking of human cells was performed by fluorescent in situ hybridization for human X and Y chromosomes or by immunostaining for HLA-DR or HLA-ABC. One month after delivery, LV fractional shortening improved by 42 ± 17% in cell-treated hearts and decreased by 39 ± 10% in controls (p = .001). Anterior wall thickness decreased significantly in controls but not in treated hearts. Microscopic examination revealed that the UCB cells were able to migrate, colonize, and survive in the infarcted myocardium. Human cells were identified near vessel walls and LV cavity and were occasionally incorporated into endothelial cells in six of nine cell-treated animals but not in controls. Scar tissue from cell-treated animals was significantly populated with autologous myofibroblasts as indicated by colocalization of HLA-DR and α-smooth muscle actin staining. In conclusion, the present work suggests that, after MI, intravenous delivery of human UCB-derived CD133+ cells can produce functional recovery by preventing scar thinning and LV systolic dilatation.

We review an experimental protocol for investigating concepts and methods for myocardial repair using fetal cardiomyocyte transplantation. We describe methods of cell isolation, culture, labeling, and assessment of the influence of the engrafted cells on left ventricular remodeling and function.

We review an experimental protocol for investigating concepts and methods for myocardial repair using fetal cardiomyocyte transplantation. We describe methods of cell isolation, culture, labeling, and assessment of the influence of the engrafted cells on left ventricular remodeling and function.

Background The muscle-specific MyoD family of transcription factors function as master genes that are able to prompt myogenesis in a variety of cells. The purpose of our study was to determine whether MyoD could induce primary cardiac fibroblasts, isolated from infarcted myocardium or pericardium, to undergo myogenic conversion in a clinically relevant approach. Methods and Results Primary rat fibroblasts from 7-day-old infarcted myocardium or normal pericardium were transfected by an E1/E3-deleted adenoviral vector carrying both a human MyoD cDNA driven by a CMV promoter and a green fluorescent protein (GFP) reporter gene driven by a second CMV promoter. Expression of MyoD caused myogenic differentiation of cultured fibroblasts, as defined by elongation and fusion into multinucleated myotubes, typical cross striation as identified by electron microscopy, and positive immunostaining for sarcomeric actin, fast myosin heavy chain (MHC), and actinin. The myogenic cells (1.5×10 6 ) were transplanted into the infarcted myocardium 7 days after coronary artery occlusion. By 1 month after transplantation, the converted fibroblasts gave rise to a cluster of myogenic cells that in a few hearts occupied a large part of the scar with positive immunostaining for the myogenic proteins fast-MHC and sarcomeric actin. A few cells expressed the gap junction protein connexin 43 in a disorganized manner. There was no positive staining in the control hearts treated with injections of untreated fibroblasts or culture medium. Conclusions Our work shows that it is possible to exploit the unique capacity of MyoD to activate myogenesis in fibroblasts ex vivo and to create a vast source of autologous myogenic cells for transplantation.

Purpose: Ischemic cardiac damage is associated with upregulation of cardiac pro-inflammatory cytokines, as well as invasion of leukocytes and lymphocytes into the heart and to injured muscle. Regulatory T cells (Tregs) exert suppressive effects on several immune and non-immune cellular elements. We aimed hypothesized that Tregs improve cardiac function after myocardial infarction (MI) with potential alteration of postischemic vessel growth. Methods and results: The number and functional suppressive activity of Tregs were assayed in mice subjected to experimental MI (n=40), and to hindlimb ischemia (n=24). The numbers of splenocyte-derived Tregs were significantly higher after the injury, both in MI mice (16±0.6% vs. 12±0.7%, p

The limited ability of cardiac muscle to regenerate after an extensive myocardial infarction (MI) and the scarcity of cardiac donors have fueled the field of cardiac tissue engineering as a potential therapeutic approach to enhance cardiac function in post-MI patients. We are exploring the ex vivo bioengineering of cardiac muscle tissue by seeding isolated cardiac cells within alginate scaffolds and supplementing the culture with "smart" media. The hypothesis investigated herein is that sera derived from autospecies and from post-MI animals contain agents that might induce cell proliferation, survival, and maturation in vitro. The results of the metabolic activity of the neonatal cardiac cell constructs (6.4-51x10(6) cells/cm(3)), as measured by MTT viability assay, indicated a significant advantage (p < 0.05) to the constructs supplemented with serum from normal and post-MI adult rats compared to fetal calf serum (FCS) supplementation. H&E staining and alpha-sarcomeric actin immunofluorescence staining revealed thick viable cardiac cell clusters (150-300 microm), with abundant 3D architecture in the cardiac cell constructs supplemented with post-MI and normal adult rat serum. The number of cells positively immunostained with Ki-67, a cell proliferation marker, was significantly higher in post-MI adult rat serum-supplemented cultures compared to negative results in the FCS-supplemented culture. The results presented in this study indicate that media supplemented with post-MI adult rat serum and normal adult rat serum compared to FCS have a significant advantage in the regeneration of injured cardiac tissue.