Improved left ventricular function after transplantation of microspheres and fibroblasts in a rat model of myocardial infarction

Endogenous Modulation of Extracellular Matrix Collagen during Scar Formation after Myocardial Infarction

Myocardial infarction is remains the leading cause of death in developed countries. Recent data show that the composition of the extracellular matrix might differ despite similar heart function and infarction sizes. Because collagen is the main component of the extracellular matrix, we hypothesized that changes in inflammatory cell recruitment influence the synthesis of different collagen subtypes in myofibroblasts, thus changing the composition of the scar. We found that neutrophils sustain the proliferation of fibroblasts, remodeling, differentiation, migration and inflammation, predominantly by IL-1 and PPARγ pathways (n = 3). They also significantly inhibit the mRNA expression of fibrillar collagen, maintaining a reduced stiffness in isolated myofibroblasts (n = 4-5). Reducing the neutrophil infiltration in CCR1^-/- resulted in increased mRNA expression of collagen 11, moderate expression of collagen 19 and low expression of collagen 13 and 26 in the scar 4 weeks post infarction compared with other groups (n = 3). Mononuclear cells increased the synthesis of all collagen subtypes and upregulated the NF-kB, angiotensin II and PPARδ pathways (n = 3). They increased the synthesis of collagen subtypes 1, 3, 5, 16 and 23 but reduced the expression of collagens 5 and 16 (n = 3). CCR2^-/- scar tissue showed higher levels of collagen 13 (n = 3), in association with a significant reduction in stiffness (n = 4-5). Upregulation of the inflammation-related genes in myofibroblasts mostly modulated the fibrillar collagen subtypes, with less effect on the FACIT, network-forming and globular subtypes (n = 3). The upregulation of proliferation and differentiation genes in myofibroblasts seemed to be associated only with the fibrillar collagen subtype, whereas angiogenesis-related genes are associated with fibrillar, network-forming and multiplexin subtypes. In conclusion, although we intend for our findings to deepen the understanding of the mechanism of healing after myocardial infarction and scar formation, the process of collagen synthesis is highly complex, and further intensive investigation is needed to put together all the missing puzzle pieces in this still incipient knowledge process.

Cytoglobin Promotes Cardiac Progenitor Cell Survival against Oxidative Stress via the Upregulation of the NFκB/iNOS Signal Pathway and Nitric Oxide Production

Human cardiac stem/progenitor cells (hCPCs) may serve in regenerative medicine to repair the infarcted heart. However, this approach is severely limited by the poor survival of donor cells. Recent studies suggest that the mammalian globin cytoglobin (CYGB) regulates nitric oxide (NO) metabolism and cell death. In the present study, we found that CYGB is expressed in hCPCs. Through molecular approaches aimed at increasing or decreasing CYGB expression in hCPCs, we found that CYGB functions as a pro-survival factor in response to oxidative stress. This was associated with the upregulation of primary antioxidant systems such as peroxiredoxins-1, heme oxygenase-1, and anti-apoptotic factors, including BCL2, BCL-XL, and MCL1. Most significantly, we established that CYGB increased the expression of NFкB-dependent genes including iNOS, and that iNOS-dependent NO production was required for a feedforward loop that maintains CYGB expression. Our study delineates for the first time a role for a globin in regulating hCPC survival and establishes mechanistic insights in the function of CYGB. It provides a rationale for the exploration of the CYGB pathway as a molecular target that can be used to enhance the effectiveness of cardiac stem/progenitor cell therapy for ischemic heart disease.

Hypoxia training attenuates left ventricular remodeling in rabbit with myocardial infarction

Objective

Previous studies showed that hypoxia preconditioning could protect cardiac function against subsequent myocardial infarction injury. However, the effect of hypoxia on left ventricular after myocardial infarction is still unclear. This study therefore aims to investigate the effects of hypoxia training on left ventricular remodeling in rabbits post myocardial infarction.

Methods

Adult male rabbits were randomly divided into three groups: group SO (sham operated), group MI (myocardial infarction only) and group MI-HT (myocardial infarction plus hypoxia training). Myocardial infarction was induced by left ventricular branch ligation. Hypoxia training was performed in a hypobaric chamber (having equivalent condition at an altitude of 4000 m, F_iO₂14.9%) for 1 h/day, 5 days/week for four weeks. At the endpoints, vascular endothelial growth factor (VEGF) in the plasma was measured. Infarct size and capillary density were detected by histology. Left ventricular remodeling and function were assessed by echocardiography.

Results

After the 4-week experiment, compared with the group SO, plasma VEGF levels in groups MI (130.27 ± 18.58 pg/mL, P < 0.01) and MI-HT (181.93 ± 20.29 pg/mL, P < 0.01) were significantly increased. Infarct size in Group MI-HT (29.67% ± 7.73%) was deceased remarkably, while its capillary density (816.0 ± 122.2/mm²) was significantly increased. For both groups MI and MI-HT, left ventricular end-diastolic and end-systolic dimensions were increased whereas left ventricular ejection fraction was decreased. However, compared with group MI, group MI-HT diminished left ventricular end-diastolic (15.86 ± 1.09 mm, P < 0.05) and end-systolic dimensions (12.10 ± 1.20 mm, P < 0.01) significantly and improved left ventricular ejection fraction (54.39 ± 12.74 mm, P < 0.05).

Conclusion

Hypoxia training may improve left ventricular function and reduce remodeling via angiogenesis in rabbits with MI.

Intramyocardial injection of hypoxia-preconditioned adipose-derived stromal cells treats acute myocardial infarction: an in vivo study in swine

Hypoxic preconditioning is a promising method for improving the anti-apoptotic and paracrine signaling capabilities of adipose-derived stromal cells (ADSCs). The purpose of this study was to analyze the influence of different hypoxic conditions on ADSCs and the therapeutic effects of hypoxia-preconditioned ADSCs (HPADSCs) on an animal model of myocardial infarction (MI). For the in vitro studies, ADSCs were divided into five groups and cultured in different oxygen concentrations (1, 3, 5, 10, and 21 %). After 24 h, RT-PCR and western blots showed that 3 % oxygen preconditioning could improve the viability and cytokine secretion of the ADSCs. A Matrigel assay indicated that the HPADSC-conditioned medium could stimulate endothelial cells to form capillary-like tubes. For the in vivo studies, MI was induced by coronary occlusion in 24 mature Chinese minipigs. The animals were divided into three groups and treated by intramyocardial injection with vehicle alone (saline group), with 1 × 10(8) ADSCs cultured in normoxic conditions (ADSCs group) or with 1 × 10(8) ADSCs precultured in 3 % oxygen (HPADSCs group). SPECT and echocardiography demonstrated that cardiac function was improved significantly in the HPADSC transplant group compared with the vehicle control group (P < 0.05). Immunofluorescence showed fewer apoptotic cells and more small- to medium-sized vessels in the HPADSC transplantation group (P < 0.05). Three percent oxygen is the optimum preconditioning treatment for ADSCs. HPADSC transplantation can prevent ventricular remodeling and reduce the infarct size.

Survival, integration, and differentiation of unrestricted somatic stem cells in the heart

Unrestricted somatic stem cells (USSCs) derived from human umbilical cord blood represent an attractive cell source to reconstitute the damaged heart. We have analyzed the cardiomyogenic potential and investigated the fate of USSCs after transplantation into rat heart in vivo. USSCs demonstrated cardiomyogenic differentiation properties characterized by the spontaneously beating activity and the robust expression of cardiac α-actinin and troponin T (cTnT) at protein and mRNA level after cocultivation with neonatal rat cardiomyocytes. To study the fate in vivo, eGFP⁺ USSCs were injected transcoronarily into immunosuppressed rats via a catheter-based technique. Nearly 80% USSCs were retained within the myocardium without altering cardiac hemodynamics. After 7 days, 20% of the transplanted cells survived in the host myocardium and showed elongated morphology with weak expression of cardiac-specific markers, while some eGFP⁺ USSCs were found to integrate into the vascular wall. After 21 days, only a small fraction of USSCs were found in the myocardium (0.13%); however, the remaining cells clearly exhibited a sarcomeric structure similar to mature cardiomyocytes. Identical results were also obtained in nude rats. In addition, we found some cells stained positively for activated caspase 3 paralleled by the massive infiltration of CD11b⁺ cells into the myocardium. In summary, USSCs can differentiate into beating cardiomyocytes by cocultivation in vitro. After coronary transplantation in vivo, however, long-term survival of differentiated USSCs was rather low despite a high initial fraction of trapped cells.

Controlled intramyocardial release of engineered chemokines by biodegradable hydrogels as a treatment approach of myocardial infarction

Myocardial infarction (MI) induces a complex inflammatory immune response, followed by the remodelling of the heart muscle and scar formation. The rapid regeneration of the blood vessel network system by the attraction of hematopoietic stem cells is beneficial for heart function. Despite the important role of chemokines in these processes, their use in clinical practice has so far been limited by their limited availability over a long time-span in vivo. Here, a method is presented to increase physiological availability of chemokines at the site of injury over a defined time-span and simultaneously control their release using biodegradable hydrogels. Two different biodegradable hydrogels were implemented, a fast degradable hydrogel (FDH) for delivering Met-CCL5 over 24 hrs and a slow degradable hydrogel (SDH) for a gradual release of protease-resistant CXCL12 (S4V) over 4 weeks. We demonstrate that the time-controlled release using Met-CCL5-FDH and CXCL12 (S4V)-SDH suppressed initial neutrophil infiltration, promoted neovascularization and reduced apoptosis in the infarcted myocardium. Thus, we were able to significantly preserve the cardiac function after MI. This study demonstrates that time-controlled, biopolymer-mediated delivery of chemokines represents a novel and feasible strategy to support the endogenous reparatory mechanisms after MI and may compliment cell-based therapies.

Novel insights into the mechanism of cell-based therapy after chronic myocardial infarction

Cell transplantation therapy is considered a novel and promising strategy in regenerative medicine. Recent studies point out that paracrine effects and inflammation induced by transplanted cells are key factors for the improvement of myocardial function. The present study aims at differentiating paracrine effects from inflammatory reactions after cell transplantation. Therefore, in vitro induced apoptotic bodies were transplanted after myocardial infarction in a rat model. Eight weeks after transplantation, the functional results showed no improvement in left ventricular function. Histological analysis revealed no significant differences in the amount of infiltrated cells and collagen content did not differ among the four groups, which sustains the functional data. Surprisingly, angiogenesis increased in groups with apoptotic bodies derived from HUVEC and endothelial progenitor cells, but not from fibroblasts. A complex genetic analysis of apoptotic bodies indicated that miRNAs could be responsible for these changes. Our study demonstrates that inflammatory reaction is critical for scar remodelling and improvement of the heart function after late cell therapy, while neoangiogenesis alone is not sufficient to improve heart function.

Myocardial regeneration by transplantation of modified endothelial progenitor cells expressing SDF-1 in a rat model

Cell based therapy has been shown to attenuate myocardial dysfunction after myocardial infarction (MI) in different acute and chronic animal models. It has been further shown that stromal-cell derived factor-1α (SDF-1α) facilitates proliferation and migration of endogenous progenitor cells into injured tissue. The aim of the present study was to investigate the role of exogenously applied and endogenously mobilized cells in a regenerative strategy for MI therapy. Lentivirally SDF-1α-infected endothelial progenitor cells (EPCs) were injected after 90 min. of ligation and reperfusion of the left anterior descending artery (LAD) intramyocardial and intracoronary using a new rodent catheter system. Eight weeks after transplantation, echocardiography and isolated heart studies revealed a significant improvement of LV function after intramyocardial application of lentiviral with SDF-1 infected EPCs compared to medium control. Intracoronary application of cells did not lead to significant differences compared to medium injected control hearts. Histology showed a significantly elevated rate of apoptotic cells and augmented proliferation after transplantation of EPCs and EPCs + SDF-1α in infarcted myocardium. In addition, a significant increased density of CD31⁺ vessel structures, a lower collagen content and higher numbers of inflammatory cells after transplantation of SDF-1 transgenic cells were detectable. Intramyocardial application of lentiviral-infected EPCs is associated with a significant improvement of myocardial function after infarction, in contrast to an intracoronary application. Histological results revealed a significant augmentation of neovascularization, lower collagen content, higher numbers of inflammatory cells and remarkable alterations of apoptotic/proliferative processes in infarcted areas after cell transplantation.

Application of peripheral-blood-derived endothelial progenitor cell for treating ischemia-reperfusion injury and infarction: a preclinical study in rat models

Background

Our aim was to explore the therapeutic effects of peripheral blood-derived endothelial progenitor cells (PB-EPC) in cardiac ischemia-reperfusion infarction models in rats and in in vitro culture systems.

Methods

Rat models of ischemia reperfusion and myocardial infarction were developed using male, Sprague–Dawley rats. Cardiomyocyte and endothelial cell cultures were also established. Therapeutic effects of PB-EPCs were examined in vivo and in vitro in both models. Rats underwent either cardiac ischemia-reperfusion (n = 40) or infarction (n = 56) surgeries and were transplanted with genetically modified EPCs. Treatment efficacy in the ischemia-reperfusion group was measured by infarct size, myocardial contraction velocity, and myeloperoxidase activity after transplantation. Cardiomyocyte survival and endothelial cell apoptosis were investigated in vitro. Vascular growth-associated protein expression and cardiac function were evaluated in the myocardial infarction group by western blot and echocardiography, respectively.

Results

Infarct size and myeloperoxidase activity were significantly decreased in the ischemia-reperfusion group, whereas myocardial contractility was significantly increased in the EPC and Tβ4 groups compared with that in the control group. In contrast, no differences were found between EPC + shRNA Tβ4 and control groups. Rates of cardiomyocyte survival and endothelial cell apoptosis were significantly higher and lower, respectively, in the EPC and Tβ4 groups than in the control group, whereas no differences were found between the EPC + shRNA Tβ4 and control group. Four weeks after myocardial infarction, cardiac function was significantly better in the EPC group than in the control group. Expressions of PDGF, VEGF, and Flk-1 were significantly higher in EPC group than in control group.

Conclusions

Study findings suggest that PB-EPCs are able to protect cardiomyocytes from ischemia-reperfusion or infarction-induced damage via a Tβ4-mediated mechanism. EPCs may also provide protection through increased expression of proteins involved in mediating vascular growth. Autologous peripheral-blood-derived EPCs are readily available for efficient therapeutic use without the concerns of graft rejection.

Anti-thymocyte globulin induces neoangiogenesis and preserves cardiac function after experimental myocardial infarction

Rationale

Acute myocardial infarction (AMI) followed by ventricular remodeling is the major cause of congestive heart failure and death in western world countries.

Objective

Of relevance are reports showing that infusion of apoptotic leucocytes or anti-lymphocyte serum after AMI reduces myocardial necrosis and preserves cardiac function. In order to corroborate this therapeutic mechanism, the utilization of an immunosuppressive agent with a comparable mechanism, such as anti-thymocyte globulin (ATG) was evaluated in this study.

Methods and Results

AMI was induced in rats by ligation of the left anterior descending artery. Initially after the onset of ischemia, rabbit ATG (10 mg/rat) was injected intravenously. In vitro and in vivo experiments showed that ATG induced a pronounced release of pro-angiogenic and chemotactic factors. Moreover, paracrine factors released from ATG co-incubated cell cultures conferred a down-regulation of p53 in cardiac myocytes. Rats that were injected with ATG evidenced higher numbers of CD68+ macrophages in the ischemic myocardium. Animals injected with ATG evidenced less myocardial necrosis, showed a significant reduction of infarct dimension and an improvement of post-AMI remodeling after six weeks (infarct dimension 24.9% vs. 11.4%, p<0.01). Moreover, a higher vessel density in the peri-infarct region indicated a better collateralization in rats that were injected with ATG.

Conclusions

These data indicate that ATG, a therapeutic agent successfully applied in clinical transplant immunology, triggered cardioprotective effects after AMI that salvaged ischemic myocardium by down-regulation of p53. This might have raised the resistance against apoptotic cell death during ischemia. The combination of these mechanisms seems to be causative for improved cardiac function and less ventricular remodeling after experimental AMI.

Repetitive transplantation of different cell types sequentially improves heart function after infarction

Cell-based therapy is considered a novel and potentially new strategy in regenerative medicine. But the efficacy of cell-based therapy has been limited by the poor survival of the transplanted cells in an ischaemic environment. The goal of the present study is to present a possibility to increase survival of the transplanted cardiomyocytes, by increasing the vascularization of the infarcted area. First, we injected endothelial progenitor cells (EPCs) to augment the vascular density in infarcted areas and to improve the benefit of a subsequent Tx of foetal cardiomyocytes. Serial echocardiography indeed showed significant improvement of the left ventricular function after application of EPC and a significant additive improvement after Tx of foetal cardiomyocytes. In contrast, repetitive EPC transplantation as a control group did not show an additional improvement after the second transplantation. Histologically, cells could be readily detected after Tx by BrdU-staining for EPC and by carboxy-fluorescein diacetate succinimidyl ester (CFSE)-staining for foetal cardiomyocytes. Staining for CD31 revealed a significant increase in vessel density in the infarction area compared with medium controls, possibly contributing to the benefit of transplanted foetal cardiomyocytes. Notably, a significant increase in the number of apoptotic cells was observed in cell-transplanted hearts accompanied by an increase in proliferation, collagen content and neutrophil infiltration, suggesting an active remodelling concomitant with sustained inflammatory processes. In conclusion, repetitive Tx of different cell types after myocardial infarction in rat hearts significantly improved left ventricular function and could represent a feasible option to enhance the benefit of cell therapy.

The heme oxygenase 1 inducer (CoPP) protects human cardiac stem cells against apoptosis through activation of the extracellular signal-regulated kinase (ERK)/NRF2 signaling pathway and cytokine release

Intracoronary delivery of c-kit-positive human cardiac stem cells (hCSCs) is a promising approach to repair the infarcted heart, but it is severely limited by the poor survival of donor cells. Cobalt protoporphyrin (CoPP), a well known heme oxygenase 1 inducer, has been used to promote endogenous CO generation and protect against ischemia/reperfusion injury. Therefore, we determined whether preconditioning hCSCs with CoPP promotes CSC survival. c-kit-positive, lineage-negative hCSCs were isolated from human heart biopsies. Lactate dehydrogenase release assays demonstrated that preconditioning CSCs with CoPP markedly enhanced cell survival after oxidative stress induced by H(2)O(2), concomitant with up-regulation of heme oxygenase 1, COX-2, and anti-apoptotic proteins (BCL2, BCL2-A1, and MCL-1) and increased phosphorylation of NRF2. Apoptotic cytometric assays showed that pretreatment of CSCs with CoPP enhanced the cells' resistance to apoptosis induced by oxidative stress. Conversely, knocking down HO-1, COX-2, or NRF2 by shRNA gene silencing abrogated the cytoprotective effects of CoPP. Further, preconditioning CSCs with CoPP led to a global increase in release of cytokines, such as EGF, FGFs, colony-stimulating factors, and chemokine ligand. Conditioned medium from cells pretreated with CoPP conferred naive CSCs remarkable resistance to apoptosis, demonstrating that cytokines released by preconditioned cells play a key role in the anti-apoptotic effects of CoPP. Preconditioning CSCs with CoPP also induced an increase in the phosphorylation of Erk1/2, which are known to modulate multiple pro-survival genes. These results potentially provide a simple and effective strategy to enhance survival of CSCs after transplantation and, therefore, their efficacy in repairing infarcted myocardium.

Repair after myocardial infarction, between fantasy and reality: the role of chemokines

Despite considerable progress over the last decades, acute myocardial infarction continues to remain the major cause of morbidity and mortality worldwide. The present therapies include only cause-dependent interventions, which are not able to reduce myocardial necrosis and optimize cardiac repair following infarction. This review highlights the cellular and molecular processes after myocardial injury and focuses on chemokines, the main modulators of the inflammatory and reparatory events, as the most valuable drug targets.

Mesenchymal stromal cells mediate a switch to alternatively activated monocytes/macrophages after acute myocardial infarction

Given the established anti-inflammatory properties of mesenchymal stromal cells (MSCs), we investigated their effect on inflammatory cell infiltration of ischemic cardiac tissue and cardiac function. We employed two types of MSCs, human bone marrow-derived (BM) MSCs and human umbilical cord perivascular cells in an experimental acute myocardial infarction (MI) model with the immune-deficient NOD/SCID gamma null mouse. Cells were infused 48 h after induction of MI and mice assessed 24 h later (72 h after MI) for bone marrow (BM), circulating and cardiac tissue-infiltrating monocytes/macrophages. We showed that in the presence of either MSC type, overall macrophage/monocyte levels were reduced, including pro-inflammatory M1-type macrophages, while the proportion of alternatively activated M2-type macrophages was significantly increased in the circulation and heart but not the BM. Moreover, we found decreased expression of IL-1β and IL-6, increased IL-10 expression and fewer apoptotic cardiomyocytes without changes in angiogenesis in the infarct area. Fractional shortening was enhanced 2 weeks after cell infusion but was similar to medium controls 16 weeks after MI. In vitro studies showed that BM MSCs increased the frequency of alternatively activated monocytes/macrophages, in part by MSC-mediated secretion of IL-10. Our data suggest a new mechanism for MSC-mediated enhancement of cardiac function, possibly via an IL-10 mediated switch from infiltration of pro-inflammatory to anti-inflammatory macrophages at the infarct site. Additional studies are warranted confirming the role of IL-10 and augmenting the anti-inflammatory effects of MSCs in cardiac regeneration.

Impact of elevated uric acid on ventricular remodeling in infarcted rats with experimental hyperuricemia

Hyperuricemia is associated with cardiovascular disease, but it is usually considered a marker rather than a risk factor. Previous studies using uric acid-lowering drugs in normouricemic animals are not suitable to answer the effect of hyperuricemia on ventricular remodeling after myocardial infarction. The purpose of this study was to determine whether hyperuricemia adversely affects ventricular remodeling in infarcted rats with elevated uric acid. Male Wistar rats aged 8 wk were randomly assigned into either vehicle, oxonic acid, oxonic acid + allopurinol, oxonic acid + benzbromarone, oxonic acid + ABT-627, or oxonic acid + tempol for 4 wk starting 24 h after ligation. Postinfarction was associated with increased oxidant production, as measured by myocardial superoxide, isoprostane, xanthine oxidase activity, and dihydroethidium staining. Compared with normouricemic infarcted rats, hyperuricemic infarcted rats had a significant increase of superoxide production (1.7×) and endothelin-1 protein (1.2×) and mRNA (1.4×) expression, which was associated with increased left ventricular dysfunction and enhanced myocardial hypertrophy and fibrosis. These changes were all prevented by treatment with allopurinol. For similar levels of urate lowering, the uricosuric agent benzbromarone had no effect on ventricular remodeling. In spite of equivalent hyperuricemia, the ability of both ABT-627 and tempol to attenuate ventricular remodeling suggested involvement of endothelin-1 and redox pathways. Hyperuricemia is associated with unfavorable ventricular remodeling probably through a superoxide and endothelin-1-dependent pathway. Uric acid lowering without inhibition of superoxide and endothelin-1 may not have an effect on remodeling. Chronic administration of allopurinol, ABT-627, and tempol is associated with attenuated ventricular remodeling.

Intracoronary administration of cardiac stem cells in mice: a new, improved technique for cell therapy in murine models

A model of intracoronary stem cell delivery that enables transgenesis/gene targeting would be a powerful tool but is still lacking. To address this gap, we compared intracoronary and intramyocardial delivery of lin(-)/c-kit(+)/GFP(+) cardiac stem cells (CSCs) in a murine model of reperfused myocardial infarction (MI). Lin(-)/c-kit(+)/GFP(+) CSCs were successfully expanded from GFP transgenic hearts and cultured with no detectable phenotypic change for up to ten passages. Intracoronary delivery of CSCs 2 days post-MI resulted in significant alleviation of adverse LV remodeling and dysfunction, which was at least equivalent, if not superior, to that achieved with intramyocardial delivery. Compared with intramyocardial injection, intracoronary infusion was associated with a more homogeneous distribution of CSCs in the infarcted region and a greater increase in viable tissue in this region, suggesting greater formation of new cardiomyocytes. Intracoronary CSC delivery resulted in improved function in the infarcted region, as well as in improved global LV systolic and diastolic function, and in decreased LV dilation and LV expansion index; the magnitude of these effects was similar to that observed after intramyocardial injection. We conclude that, in the murine model of reperfused MI, intracoronary CSC infusion is at least as effective as intramyocardial injection in limiting LV remodeling and improving both regional and global LV function. The intracoronary route appears to be superior in terms of uniformity of cell distribution, myocyte regeneration, and amount of viable tissue in the risk region. To our knowledge, this is the first study to report that intracoronary infusion of stem cells in mice is feasible and effective.

Intravenous and intramyocardial injection of apoptotic white blood cell suspensions prevents ventricular remodelling by increasing elastin expression in cardiac scar tissue after myocardial infarction

Congestive heart failure developing after acute myocardial infarction (AMI) is a major cause of morbidity and mortality. Clinical trials of cell-based therapy after AMI evidenced only a moderate benefit. We could show previously that suspensions of apoptotic peripheral blood mononuclear cells (PBMC) are able to reduce myocardial damage in a rat model of AMI. Here we experimentally examined the biochemical mechanisms involved in preventing ventricular remodelling and preserving cardiac function after AMI. Cell suspensions of apoptotic cells were injected intravenously or intramyocardially after experimental AMI induced by coronary artery ligation in rats. Administration of cell culture medium or viable PBMC served as controls. Immunohistological analysis was performed to analyse the cellular infiltrate in the ischaemic myocardium. Cardiac function was quantified by echocardiography. Planimetry of the infarcted hearts showed a significant reduction of infarction size and an improvement of post AMI remodelling in rats treated with suspensions of apoptotic PBMC (injected either intravenously or intramoycardially). Moreover, these hearts evidenced enhanced homing of macrophages and cells staining positive for c-kit, FLK-1, IGF-I and FGF-2 as compared to controls. A major finding in this study further was that the ratio of elastic and collagenous fibres within the scar tissue was altered in a favourable fashion in rats injected with apoptotic cells. Intravenous or intramyocardial injection of apoptotic cell suspensions results in attenuation of myocardial remodelling after experimental AMI, preserves left ventricular function, increases homing of regenerative cells and alters the composition of cardiac scar tissue. The higher expression of elastic fibres provides passive energy to the cardiac scar tissue and results in prevention of ventricular remodelling.

Therapeutic effect of intermittent hypobaric hypoxia on myocardial infarction in rats

Intermittent hypobaric hypoxia (IHH) preconditioning protects the heart against ischemic injuries. However, little is known about the therapeutic effect of IHH on myocardial infarction (MI). The aim of this study was to test whether IHH treatment influences infarct size and cardiac performance after MI. Seven days after sham operation or left anterior descending coronary artery ligation, male Sprague-Dawley rats were randomly exposed to normoxia or one 6-h period each day of IHH (5,000 m) for 14 and 28 days. Echocardiography analysis showed that IHH significantly reduced left ventricular (LV) dilation and improved cardiac performance after 14- or 28-day treatment compared with MI-normoxic groups. The improvement of LV function was further confirmed in isolated perfused MI-IHH hearts. Such protection was associated with attenuated infarct size, myocardial fibrosis, and apoptotic cardiomyocytes. IHH treatment also enhanced coronary flow and phosphorylation of heat shock protein 27 in both sham and MI groups compared with the control groups. In addition, IHH increased the capillary density and vascular endothelial growth factor expression in peri-infarcted zones compared with sham-IHH and MI-normoxic groups. Our data demonstrated for the first time that IHH treatment exerts a therapeutic effect on MI by attenuating progressive myocardial remodeling and improving myocardial contractility. IHH treatment might provide a unique and promising therapeutic approach for ischemic heart diseases.