Transplanted human cord blood-derived unrestricted somatic stem cells preserve high-energy reserves at the site of acute myocardial infarction

Background aimsIt has been demonstrated that transplantation of human cord blood-derived unrestricted somatic stem cells (USSC) in a porcine model of acute myocardial infarction (MI) significantly improved left ventricular (LV) function and prevented scar formation as well as LV dilation. Differentiation, apoptosis and macrophage mobilization at the infarct site could be excluded as the underlying mechanisms. The paracrine effect of the cells is most likely to be observed as the cause for the USSC treatment. The aim of our study was to examine the cardiomyocyte metabolism and the role of high-energy phosphates at the marginal infarct.MethodsUSSC were transplanted into the myocardium of the LV, which was supplied by a ligated circumflex artery. Forty-eight hours later, the hearts were harvested and biopsies were performed from the marginal infarct zone surrounding the site of the cell injection. The concentrations of creatinine phosphate (CP), adenosine monophosphate (AMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP) were determined by chromatography.ResultsThe concentration of ADP, ATP and CP in the marginal zone of the infarction was significantly higher in the USSC group. The mean global left ventricular ejection fraction (LVEF) (SD) was 64% (8%) before MI; post-MI, LVEF decreased to 35% (9%).ConclusionsPreservation of high-energy phosphates in the marginal infarct zone suggests that the preservation of energy reserves of surviving cardiomyocytes is a possible mechanism of action of transplanted stem cells in acutely ischemic myocardium.     

Granulocyte colony-stimulating factor treatment enhances the efficacy of cellular cardiomyoplasty with transplantation of embryonic stem cell-derived cardiomyocytes in infarcted myocardium

We tested the hypothesis that granulocyte colony-stimulating factor (G-CSF) administration would enhance the efficacy of cellular cardiomyoplasty with embryonic stem (ES) cell-derived cardiomyocytes in infarcted myocardium. Three weeks after myocardial infarction by cryoinjury, Sprague-Dawley rats were randomized to receive either an injection of medium, ES cell-derived cardiomyocyte transplantation, G-CSF administration, or a combination of G-CSF administration and ES cell-derived cardiomyocyte transplantation. Eight weeks after treatment, the cardiac tissue formation, neovascularization, and apoptotic activity in the infarct regions were evaluated by histology and immunohistochemistry. The left ventricular (LV) dimensions and function of the treated heart were evaluated by echocardiography. Transplanted ES cell-derived cardiomyocytes survived and participated in the myocardial regeneration in the infarcted heart. A combination of G-CSF treatment and ES cell-derived cardiomyocyte transplantation significantly promoted angiogenesis and reduced the infarct area and cell apoptosis in the infarcted myocardium compared with ES cell-derived cardiomyocyte transplantation alone. The combination therapy also attenuated LV dilation, as compared with ES cell-derived cardiomyocyte transplantation alone. G-CSF treatment can enhance the efficacy of cellular cardiomyoplasty by ES cell-derived cardiomyocyte transplantation to treat myocardial infarction.     

Bone Marrow Progenitor Cell Therapy-Mediated Paracrine Regulation of Cardiac miRNA-155 Modulates Fibrotic Response in Diabetic Hearts

Diabetes is associated with a higher incidence of myocardial infarction (MI) and increased risk for adverse vascular and fibrogenic events post-MI. Bone marrow-derived progenitor cell (BMPC) therapy has been shown to promote neovascularization, decrease infarct area and attenuate left ventricular (LV) dysfunction after MI. Unlike vascular effects, the anti-fibrosis mechanisms of BMPC, specifically under diabetic conditions, are poorly understood. We demonstrated that intramyocardial delivery of BMPCs in infarcted diabetic db/db mice significantly down-regulates profibrotic miRNA-155 in the myocardium and improves LV remodeling and function. Furthermore, inhibition of paracrine factor hepatocyte growth factor (HGF) signaling in vivo suppressed the BMPC-mediated inhibition of miR-155 expression and the associated protective effect on cardiac fibrosis and function. In vitro studies confirmed that the conditioned media of BMPC inhibited miR-155 expression and profibrotic signaling in mouse cardiac fibroblasts under diabetic conditions. However, neutralizing antibodies directed against HGF blocked these effects. Furthermore, miR-155 over-expression in mouse cardiac fibroblasts inhibited antifibrotic Sloan-Kettering Institute proto-oncogene (Ski) and Ski-related novel gene, non-Alu-containing (SnoN) signaling and abrogated antifibrogenic response of HGF. Together, our data demonstrates that paracrine regulation of cardiac miRNAs by transplanted BMPCs contributes to the antifibrotic effects of BMPC therapy. BMPCs release HGF, which inhibits miR-155-mediated profibrosis signaling, thereby preventing cardiac fibrosis. These data suggest that targeting miR-155 might serve as a potential therapy against cardiac fibrosis in the diabetic heart.     

Intramyocardial transplantation of cardiac telocytes decreases myocardial infarction and improves post‐infarcted cardiac function in rats

The midterm effects of cardiac telocytes (CTs) transplantation on myocardial infarction (MI) and the cellular mechanisms involved in the beneficial effects of CTs transplantation are not understood. In the present study, we have revealed that transplantation of CTs was able to significantly decrease the infarct size and improved cardiac function 14 weeks after MI. It has established that CT transplantation exerted a protective effect on the myocardium and this was maintained for at least 14 weeks. The cellular mechanism behind this beneficial effect on MI was partially attributed to increased cardiac angiogenesis, improved reconstruction of the CT network and decreased myocardial fibrosis. These combined effects decreased the infarct size, improved the reconstruction of the LV and enhanced myocardial function in MI. Our findings suggest that CTs could be considered as a potential cell source for therapeutic use to improve cardiac repair and function following MI, used either alone or in tandem with stem cells.     

Elastin overexpression by cell-based gene therapy preserves matrix and prevents cardiac dilation

After a myocardial infarction, thinning and expansion of the fibrotic scar contribute to progressive heart failure. The loss of elastin is a major contributor to adverse extracellular matrix remodelling of the infarcted heart, and restoration of the elastic properties of the infarct region can prevent ventricular dysfunction. We implanted cells genetically modified to overexpress elastin to re‐establish the elastic properties of the infarcted myocardium and prevent cardiac failure. A full‐length human elastin cDNA was cloned, subcloned into an adenoviral vector and then transduced into rat bone marrow stromal cells (BMSCs). In vitro studies showed that BMSCs expressed the elastin protein, which was deposited into the extracellular matrix. Transduced BMSCs were injected into the infarcted myocardium of adult rats. Control groups received either BMSCs transduced with the green fluorescent protein gene or medium alone. Elastin deposition in the infarcted myocardium was associated with preservation of myocardial tissue structural integrity (by birefringence of polarized light; P < 0.05 versus controls). As a result, infarct scar thickness and diastolic compliance were maintained and infarct expansion was prevented (P < 0.05 versus controls). Over a 9‐week period, rats implanted with BMSCs demonstrated better cardiac function than medium controls; however, rats receiving BMSCs overexpressing elastin showed the greatest functional improvement (P < 0.01). Overexpression of elastin in the infarcted heart preserved the elastic structure of the extracellular matrix, which, in turn, preserved diastolic function, prevented ventricular dilation and preserved cardiac function. This cell‐based gene therapy provides a new approach to cardiac regeneration.     

Mesenchymal stem cells from ischemic heart disease patients improve left ventricular function after acute myocardial infarction

Mesenchymal stem cells (MSCs) from healthy donors improve cardiac function in experimental acute myocardial infarction (AMI) models. However, little is known about the therapeutic capacity of human MSCs (hMSCs) from patients with ischemic heart disease (IHD). Therefore, the behavior of hMSCs from IHD patients in an immune-compromised mouse AMI model was studied. Enhanced green fluorescent protein-labeled hMSCs from IHD patients (hMSC group: 2 x 10(5) cells in 20 microl, n = 12) or vehicle only (medium group: n = 14) were injected into infarcted myocardium of NOD/scid mice. Sham-operated mice were used as the control (n = 10). Cardiac anatomy and function were serially assessed using 9.4-T magnetic resonance imaging (MRI); 2 wk after cell transplantation, immunohistological analysis was performed. At day 2, delayed-enhancement MRI showed no difference in myocardial infarction (MI) size between the hMSC and medium groups (33 +/- 2% vs. 36 +/- 2%; P = not significant). A comparable increase in left ventricular (LV) volume and decrease in ejection fraction (EF) was observed in both MI groups. However, at day 14, EF was higher in the hMSC than in the medium group (24 +/- 3% vs. 16 +/- 2%; P < 0.05). This was accompanied by increased vascularity and reduced thinning of the infarct scar. Engrafted hMSCs (4.1 +/- 0.3% of injected cells) expressed von Willebrand factor (16.9 +/- 2.7%) but no stringent cardiac or smooth muscle markers. hMSCs from patients with IHD engraft in infarcted mouse myocardium and preserve LV function 2 wk after AMI, potentially through an enhancement of scar vascularity and a reduction of wall thinning.     

Inhibiting Extracellular Vesicle Release from Human Cardiosphere Derived Cells with Lentiviral Knockdown of nSMase2 Differentially Effects Proliferation and Apoptosis in Cardiomyocytes,Fibroblasts and Endothelial Cells In Vitro

Numerous studies have shown a beneficial effect of cardiosphere-derived cell (CDC) therapy on regeneration of injured myocardium. Paracrine signaling by CDC secreted exosomes may contribute to improved cardiac function. However, it has not yet been demonstrated by a genetic approach that exosome release contributes to the therapeutic effect of transplanted CDCs. By employing a lentiviral knockdown (KD) strategy against neutral spingomyelinase 2 (nSMase2), a crucial gene in exosome secretion, we have defined the role of physiologically secreted human CDC-derived exosomes on cardiac fibroblast, endothelial cell and primary cardiomyocyte proliferation, cell death, migration and angiogenesis using a series of in vitro coculture assays. We found that secretion of hCDC-derived exosomes was effectively inhibited by nSMase2 lentiviral KD and shRNAi expression was stable and constitutive. hCDC exosome release contributed to the angiogenic and pro-migratory effects of hCDCs on HUVECs, decreased proliferation of fibroblasts, and decreased apoptosis of cardiomyocytes. These in vitro reactions support a role for exosome secretion as a paracrine mechanism of stem cell-mediated cardiac repair in vivo. Importantly, we have established a novel tool to test constitutive inhibition of exosome secretion in stem cell populations in animal models of cardiac disease.     

Total Mechanical Unloading Minimizes Metabolic Demand of Left Ventricle and Dramatically Reduces Infarct Size in Myocardial Infarction

BackgroundLeft ventricular assist device (LVAD) mechanically unloads the left ventricle (LV). Theoretical analysis indicates that partial LVAD support (p-LVAD), where LV remains ejecting, reduces LV preload while increases afterload resulting from the elevation of total cardiac output and mean aortic pressure, and consequently does not markedly decrease myocardial oxygen consumption (MVO₂). In contrast, total LVAD support (t-LVAD), where LV no longer ejects, markedly decreases LV preload volume and afterload pressure, thereby strikingly reduces MVO₂. Since an imbalance in oxygen supply and demand is the fundamental pathophysiology of myocardial infarction (MI), we hypothesized that t-LVAD minimizes MVO₂ and reduces infarct size in MI. The purpose of this study was to evaluate the differential impact of the support level of LVAD on MVO₂ and infarct size in a canine model of ischemia-reperfusion.MethodsIn 5 normal mongrel dogs, we examined the impact of LVAD on MVO₂ at 3 support levels: Control (no LVAD support), p-LVAD and t-LVAD. In another 16 dogs, ischemia was induced by occluding major branches of the left anterior descending coronary artery (90 min) followed by reperfusion (300 min). We activated LVAD from the beginning of ischemia until 300 min of reperfusion, and compared the infarct size among 3 different levels of LVAD support.Resultst-LVAD markedly reduced MVO₂ (% reduction against Control: -56 ± 9%, p<0.01) whereas p-LVAD did less (-21 ± 14%, p<0.05). t-LVAD markedly reduced infarct size compared to p-LVAD (infarct area/area at risk: Control; 41.8 ± 6.4, p-LVAD; 29.1 ± 5.6 and t-LVAD; 5.0 ± 3.1%, p<0.01). Changes in creatine kinase-MB paralleled those in infarct size.ConclusionsTotal LVAD support that minimizes metabolic demand maximizes the benefit of LVAD in the treatment of acute myocardial infarction.     

Human endometrial stem cells confer enhanced myocardial salvage and regeneration by paracrine mechanisms

Human endometrial stem cells (EnSCs) have the potential to be ‘off the shelf’ clinical reagents for the treatment of heart failure. Here, using an immunocompetent rat model of myocardial infarction (MI), we provide evidence that the functional benefits of EnSC transplantation are principally and possibly exclusively through a paracrine effect. Human EnSCs were delivered by intramyocardial injection into rats 30 min. after coronary ligation. EnSC therapy significantly preserved viable myocardium in the infarct zone and improved cardiac function at 28 days. Despite increased viable myocardium and vascular density, there was scant evidence of differentiation of EnSCs into any cardiovascular cell type. Cultured human EnSCs expressed a distinctive profile of cytokines that enhanced the survival, proliferation and function of endothelial cells in vitro. When injected into the peri‐infarct zone, human EnSCs activated AKT, ERK1/2 and STAT3 and inhibited the p38 signalling pathway. EnSC therapy decreased apoptosis and promoted cell proliferation and c‐kit+ cell recruitment in vivo. Myocardial protection and enhanced post‐infarction regeneration by EnSCs is mediated primarily by paracrine effects conferred by secreted cytokines that activate survival pathways and recruit endogenous progenitor stem cells. Menstrual blood provides a potentially limitless source of biologically competent ‘off the shelf’ EnSCs for allogeneic myocardial regenerative medicine.     

Cardiac Restricted Overexpression of Membrane Type-1 Matrix Metalloproteinase Causes Adverse Myocardial Remodeling following Myocardial Infarction

The membrane type-1 matrix metalloproteinase (MT1-MMP) is a unique member of the MMP family, but induction patterns and consequences of MT1-MMP overexpression (MT1-MMPexp), in a left ventricular (LV) remodeling process such as myocardial infarction (MI), have not been explored. MT1-MMP promoter activity (murine luciferase reporter) increased 20-fold at 3 days and 50-fold at 14 days post-MI. MI was then induced in mice with cardiac restricted MT1-MMPexp (n = 58) and wild type (WT, n = 60). Post-MI survival was reduced (67% versus 46%, p < 0.05), and LV ejection fraction was lower in the post-MI MT1-MMPexp mice compared with WT (41 ± 2 versus 32 ± 2%,p < 0.05). In the post-MI MT1-MMPexp mice, LV myocardial MMP activity, as assessed by radiotracer uptake, and MT1-MMP-specific proteolytic activity using a specific fluorogenic assay were both increased by 2-fold. LV collagen content was increased by nearly 2-fold in the post-MI MT1-MMPexp compared with WT. Using a validated fluorogenic construct, it was discovered that MT1-MMP proteolytically processed the pro-fibrotic molecule, latency-associated transforming growth factor-1 binding protein (LTBP-1), and MT1-MMP-specific LTBP-1 proteolytic activity was increased by 4-fold in the post-MI MT1-MMPexp group. Early and persistent MT1-MMP promoter activity occurred post-MI, and increased myocardial MT1-MMP levels resulted in poor survival, worsening of LV function, and significant fibrosis. A molecular mechanism for the adverse LV matrix remodeling with MT1-MMP induction is increased processing of pro-fibrotic signaling molecules. Thus, a proteolytically diverse portfolio exists for MT1-MMP within the myocardium and likely plays a mechanistic role in adverse LV remodeling.     

Transmyocardial drilling revascularization combined with heparinized bFGF-incorporating stent activates resident cardiac stem cells via SDF-1/CXCR4 axis

ObjectiveTo investigate whether transmyocardial drilling revascularization combined with heparinized basic fibroblast growth factor (bFGF)-incorporating degradable stent implantation (TMDRSI) can promote myocardial regeneration after acute myocardial infarction (AMI).MethodsA model of AMI was generated by ligating the mid-third of left anterior descending artery (LAD) of miniswine. After 6 h, the animals were divided into none-treatment (control) group (n = 6) and TMDRSI group (n = 6). For TMDRSI group, two channels with 3.5 mm in diameter were established by a self-made drill in the AMI region, into which a stent was implanted. Expression of stromal cell-derived factor-1_α (SDF-1_α) and CXC chemokine receptor 4 (CXCR4), cardiac stem cell (CSC)-mediated myocardial regeneration, myocardial apoptosis, myocardial viability, and cardiac function were assessed at various time-points.ResultsSix weeks after the operation, CSCs were found to have differentiated into cardiomyocytes to repair the infarcted myocardium, and all above indices showed much improvement in the TMDRSI group compared with the control group (P < 0.001).ConclusionsThe new method has shown to be capable of promoting CSCs proliferation and differentiation into cardiomyocytes through activating the SDF-1/CXCR4 axis, while inhibiting myocardial apoptosis, thereby enhancing myocardial regeneration following AMI and improving cardiac function. This may provide a new strategy for myocardial regeneration following AMI.     

Cardiomyocyte progenitor cell‐derived exosomes stimulate migration of endothelial cells

Patients suffering from heart failure as a result of myocardial infarction are in need of heart transplantation. Unfortunately the number of donor hearts is very low and therefore new therapies are subject of investigation. Cell transplantation therapy upon myocardial infarction is a very promising strategy to replace the dead myocardium with viable cardiomyocytes, smooth muscle cells and endothelial cells, thereby reducing scarring and improving cardiac performance. Despite promising results, resulting in reduced infarct size and improved cardiac function on short term, only a few cells survive the ischemic milieu and are retained in the heart, thereby minimizing long-term effects. Although new capillaries and cardiomyocytes are formed around the infarcted area, only a small percentage of the transplanted cells can be detected months after myocardial infarction. This suggests the stimulation of an endogenous regenerative capacity of the heart upon cell transplantation, resulting from release of growth factor, cytokine and other paracrine molecules by the progenitor cells – the so-called paracrine hypothesis. Here, we focus on a relative new component of paracrine signalling, i.e. exosomes. We are interested in the release and function of exosomes derived from cardiac progenitor cells and studied their effects on the migratory capacity of endothelial cells.     

Paracrine effect of CXCR4‐overexpressing mesenchymal stem cells on ischemic heart injury

It has been reported that CXCR4‐overexpressing mesenchymal stem cells (MSC^CX4) can repair heart tissue post myocardial infarction. This study aims to investigate the MSCCX4‐derived paracrine cardio‐protective signaling in the presence of myocardial infarction. Mesenchymal stem cells (MSCs) were divided into 3 groups: MSC only, MSC^CX4, and CXCR4 gene‐specific siRNA‐transduced MSC. Mesenchymal stem cells were exposed to hypoxia, and then MSCs‐conditioned culture medium was incubated with neonatal and adult cardiomyocytes, respectively. Cell proliferation–regulating genes were assessed by real‐time polymerase chain reaction (RT‐PCR). In vitro: The number of cardiomyocytes undergoing DNA synthesis, cytokinesis, and mitosis was increased to a greater extent in MSC^CX4 medium‐treated group than control group, while this proproliferative effect was reduced in CXCR4 gene‐specific siRNA‐transduced MSC–treated cells. Accordingly, the maximal enhancement of vascular endothelial growth factor, cyclin 2, and transforming growth factor‐β2 was observed in hypoxia‐exposed MSC^CX4. In vivo: MSCs were labeled with enhanced green fluorescent protein (EGFP) and engrafted into injured myocardium in rats. The number of EGFP and CD31 positive cells in the MSC^CX4 group was significantly increased than other 2 groups, associated with the reduced left ventricular (LV) fibrosis, the increased LV free wall thickness, the enhanced angiogenesis, and the improved contractile function. CXCR4 overexpression can mobilize MSCs into ischemic area, whereby these cells can promoted angiogenesis and alleviate LV remodeling via paracrine signaling mechanism.     

Incremental benefits of repeated mesenchymal stromal cell administration compared with solitary intervention after myocardial infarction

Background aimsTraditionally, stem cell therapy for myocardial infarction (MI) has been administered as a single treatment in the acute or subacute period after MI. These time intervals coincide with marked differences in the post-infarct myocardial environment, raising the prospect that repeat cell dosing could provide incremental benefit beyond a solitary intervention. This prospect was evaluated with the use of mesenchymal stromal cells (MSCs).MethodsThree groups of rats were studied. Single-therapy and dual-therapy groups received allogeneic, prospectively isolated MSCs (1 × 10⁶ cells) by trans-epicardial injection immediately after MI, with additional dosing 1 week later in the dual-therapy cohort. Control animals received cryopreservant solution only. Left ventricular (LV) dimensions and ejection fraction (EF) were assessed by cardiac magnetic resonance immediately before MI and at 1, 2 and 4 weeks after MI.ResultsImmediate MSC treatment attenuated early myocardial damage with EF of 35.3 ± 3.1% (dual group, n = 12) and 35.2 ± 2.2% (single group, n = 15) at 1 week after MI compared with 22.1 ± 1.9% in controls (n = 17, P < 0.01). In animals receiving a second dose of MSCs, EF increased to 40.7 ± 3.1% by week 4, which was significantly higher than in the single-therapy group (EF 35.9 ± 1.8%, P < 0.05). Dual MSC treatment was also associated with greater myocardial mass and arteriolar density, with trends toward reduced myocardial fibrosis. These incremental benefits were especially observed in remote (non-infarct) segments of LV myocardium.ConclusionsRepeated stem cell intervention in both the acute and the sub-acute period after MI provides additional improvement in ventricular function beyond solitary cell dosing, largely owing to beneficial changes remote to the area of infarction.     

Pluripotent stem cell-derived mesenchymal stromal cells improve cardiac function and vascularity after myocardial infarction

Background aimsMesenchymal stromal cells (MSCs) have been shown to improve cardiac function after injury and are the subject of ongoing clinical trials. In this study, the authors tested the cardiac regenerative potential of an induced pluripotent stem cell-derived MSC (iPSC-MSC) population (Cymerus MSCs) in a rat model of myocardial ischemia-reperfusion (I/R). Furthermore, the authors compared this efficacy with bone marrow-derived MSCs (BM-MSCs), which are the predominant cell type in clinical trials.MethodsFour days after myocardial I/R injury, rats were randomly assigned to (i) a Cymerus MSC group (n = 15), (ii) a BM-MSC group (n = 15) or (iii) a vehicle control group (n = 14). For cell-treated animals, a total of 5 × 10⁶ cells were injected at three sites within the infarcted left ventricular (LV) wall.ResultsOne month after cell transplantation, Cymerus MSCs improved LV function (assessed by echocardiography) compared with vehicle and BM-MSCs. Interestingly, Cymerus MSCs enhanced angiogenesis without sustained engraftment or significant impact on infarct scar size. Suggesting safety, Cymerus MSCs had no effect on inducible tachycardia or the ventricular scar heterogeneity that provides a substrate for cardiac re-entrant circuits.ConclusionsThe authors here demonstrate that intra-myocardial administration of iPSC-MSCs (Cymerus MSCs) provide better therapeutic effects compared with conventional BM-MSCs in a rodent model of myocardial I/R. Because of its manufacturing scalability, iPSC-MSC therapy offers an exciting opportunity for an “off-the-shelf” stem cell therapy for cardiac repair.     

Mesenchymal stem cell-derived exosomes increase ATP levels,decrease oxidative stress and activate PI3K/Akt pathway to enhance myocardial viability and prevent adverse remodeling after myocardial ischemia/reperfusion injury

We have previously identified exosomes as the paracrine factor secreted by mesenchymal stem cells. Recently, we found that the key features of reperfusion injury, namely loss of ATP/NADH, increased oxidative stress and cell death were underpinned by proteomic deficiencies in ischemic/reperfused myocardium, and could be ameliorated by proteins in exosomes. To test this hypothesis in vivo, mice (C57Bl6/J) underwent 30 min ischemia, followed by reperfusion (I/R injury). Purified exosomes or saline was administered 5 min before reperfusion. Exosomes reduced infarct size by 45% compared to saline treatment. Langendorff experiments revealed that intact but not lysed exosomes enhanced viability of the ischemic/reperfused myocardium. Exosome treated animals exhibited significant preservation of left ventricular geometry and contractile performance during 28 days follow-up. Within an hour after reperfusion, exosome treatment increased levels of ATP and NADH, decreased oxidative stress, increased phosphorylated-Akt and phosphorylated-GSK-3β, and reduced phosphorylated-c-JNK in ischemic/reperfused hearts. Subsequently, both local and systemic inflammation were significantly reduced 24 h after reperfusion. In conclusion, our study shows that intact exosomes restore bioenergetics, reduce oxidative stress and activate pro-survival signaling, thereby enhancing cardiac function and geometry after myocardial I/R injury. Hence, mesenchymal stem cell-derived exosomes are a potential adjuvant to reperfusion therapy for myocardial infarction.     

Cell transplantation for myocardial injury: a preliminary comparative study

Background aimsCell transplantation may restore viable muscle after myocardial infarction. Because many studies have focused on one cell type, we compared the characteristics of skeletal myoblasts (SKM), bone marrow stromal/stem cells (BMSC) and smooth muscle cells (SMC) and their effects on cardiac function after myocardial injury.MethodsIn vitro cell characteristics, including proliferation, hypoxic survival and vascular endothelial cell growth factor (VEGF) expression, of SKM, BMSC and SMC were compared. An in vivo left anterior descending artery ligation rat model was used, and cells were implanted into the infarct (n = 16 per cell type). Cell survival was determined by PKH26 staining and real-time polymerase chain reaction (PCR). Cardiac function, tissue VEGF and stem cell factor (SCF) expression and vasculogenesis were evaluated.ResultsAlthough cell morphologies were distinct, in vitro proliferation was similar. In vitro studies showed that SKM had the highest hypoxic survival, whereas BMSC had the lowest hypoxic survival but the highest VEGF expression. After implantation, SKM showed the highest overall survival and in vivo SCF expression, and both SMC and SKM expressed the highest VEGF levels. Vasculogenesis was significantly (P < 0.001) improved after transplantation of each cell type. Overall, BMSC and SKM promoted the greatest improvement in cardiac function.ConclusionsSKM, BMSC and SMC expressed VEGF and SCF and promoted vasculogenesis. Although BMSC showed the greatest regenerative potential relative to cell survival and growth factor expression, the greatest improvement in cardiac function was observed with BMSC and SKM.     

Cardioprotection of electroacupuncture against myocardial ischemia-reperfusion injury by modulation of cardiac norepinephrine release

Augmentation of cardiac sympathetic tone during myocardial ischemia has been shown to increase myocardial O(2) demand and infarct size as well as induce arrhythmias. We have previously demonstrated that electroacupuncture (EA) inhibits the visceral sympathoexcitatory cardiovascular reflex. The purpose of this study was to determine the effects of EA on left ventricular (LV) function, O(2) demand, infarct size, arrhythmogenesis, and in vivo cardiac norepinephrine (NE) release in a myocardial ischemia-reperfusion model. Anesthetized rabbits (n = 36) underwent 30 min of left anterior descending coronary artery occlusion followed by 90 min of reperfusion. We evaluated myocardial O(2) demand, infarct size, ventricular arrhythmias, and myocardial NE release using microdialysis under the following experimental conditions: 1) untreated, 2) EA at P5-6 acupoints, 3) sham acupuncture, 4) EA with pretreatment with naloxone (a nonselective opioid receptor antagonist), 5) EA with pretreatment with chelerythrine (a nonselective PKC inhibitor), and 6) EA with pretreatment with both naloxone and chelerythrine. Compared with the untreated and sham acupuncture groups, EA resulted in decreased O(2) demand, myocardial NE concentration, and infarct size. Furthermore, the degree of ST segment elevation and severity of LV dysfunction and ventricular arrhythmias were all significantly decreased (P < 0.05). The cardioprotective effects of EA were partially blocked by pretreatment with naloxone or chelerythrine alone and completely blocked by pretreatment with both naloxone and chelerythrine. These results suggest that the cardioprotective effects of EA against myocardial ischemia-reperfusion are mediated through inhibition of the cardiac sympathetic nervous system as well as opioid and PKC-dependent pathways.     

Functional and bioenergetic modulations in the infarct border zone following autologous mesenchymal stem cell transplantation

Preclinical and clinical studies have demonstrated that stem cell transplantation can improve the left ventricular (LV) contractile performance, yet the underlying mechanisms remain unknown. We examined whether mesenchymal stem cell (MSC) transplantation-induced beneficial effects are secondary to paracrine-associated improvements in LV contractile performance, wall stress, and myocardial bioenergetics in hearts with postinfarction LV remodeling. Myocardial contractile function and bioenergetics were compared 4 wk after acute myocardial infarction in normal pigs (n = 6), untreated pigs with myocardial infarction (MI group; n = 6), and pigs receiving autologous MSC transplantation (MI + MSC group; n = 5). A distal occlusion of the left anterior descending coronary artery instigated significant myocardial hypertrophy. Ejection fraction decreased from 55.3 +/- 3.1% (normal) to 30.4 +/- 2.3% (MI group; P < 0.01) and to 45.4 +/- 3.1% (MI + MSC group; P < 0.01 vs. MI). Hearts in the MI group developed severe contractile dyskinesis in the infarct zone and border zone (BZ). MSC transplantation significantly improved contractile performance from dyskinesis to active contraction (P < 0.01 vs. MI). BZ systolic wall stress was severely increased in MI hearts but significantly improved after MSC transplantation (P < 0.01 vs. MI). The BZ demonstrated profound bioenergetic abnormalities in MI pigs; this was significantly improved after MSC transplantation (P < 0.01 vs. MI). Patchy spared myocytes were found in the infarct zone of hearts receiving MSC transplantation but not in control hearts. These data demonstrate that MSC transplantation into the BZ causes significant improvements in myocardial contractile performance and reduction in wall stress, which ultimately results in significant bioenergetic improvements. Low cell engraftment indicates that MSCs did not provide a structural contribution to the damaged heart and that the observed beneficial effects likely resulted from paracrine repair mechanisms.