Current Pharmaceutical Design - Volume 20, Issue 12, 2014

Myocardial infarction constitutes an important health-related problem worldwide. Despite current treatments that salvage myocardial tissue and unload the left ventricle, chronic heart failure is common and is associated with increased morbidity and mortality. During the past decade, experimental studies, using cell-based therapies and growth factor administration integrated in biomaterial scaffolds, have demonstrated the potential to reduce the infarcted area and to improve regional and global left ventricular function. Some aspects of this rapid progress are reviewed in the present ‘special issue’ and a number of novel approaches are being introduced. This series of articles, contributed by research groups with different expertise, is a small step towards the combined efforts required to address the challenges associated with regenerating the infarcted myocardium.

Loss of cardiac function following myocardial infarction (MI) remains a leading cause of morbidity in the developed world. Current percutaneous coronary intervention (PCI) practice facilitates rapid relief of acute thrombotic occlusion with follow on medical treatment of associated atherosclerotic and thrombotic risks, late ventricular remodeling and cardiac arrhythmias. The application of regenerative therapies aimed at preserving or restoring lost myocardial function post large MI is currently evolving. In the early phase of myocardial reperfusion post PCI, cardiomyocyte apoptosis occurs followed closely by pro-inflammatory cell infiltration from the circulation. At later timepoints, matrix protein deposition and scar formation become evident followed by later loss of functioning cardiomyocyte cell mass leading to a dilated failing heart. In the last decade, clinical trials have assessed the ability of therapy using progenitor cells from various tissue niches to prevent or reverse these effects in the post-reperfusion phase. Modest improvements in hemodynamic function reported in many (but not all) of these trials have tempered initial optimism for cardiac regenerative therapeutics. In addition, several issues concerning cardiac cell therapy including efficacy, quality assurance, necessary infrastructure, effective translation of preclinical studies and applicability to broader patient care, have been raised. Fortunately, a number of promising derivative therapeutic strategies have also emerged including stem cell derived paracrine factors and recent advances in tissue engineering. In this review, the ability of stem cells and/or derivative therapies to modify apoptosis and inflammation in the ischemic zone are considered along with emerging cell and tissue engineering approaches toward cardiac regeneration post-MI.

S100A6, a 20 kDa, Ca2+ - binding dimer with low basal cardiac expression, is upregulated in the rat heart following infarction and forced expression of S100A6 in rat neonatal cardiac myocyte cultures, inhibited the induction of β myosin heavy chain (MHC), skeletal α actin (skACT) and myocyte apoptosis in response to diverse stimuli including tumor necrosis factor α. To define a role for S100A6 in vivo, we generated cardiac myocyte-specific transgenic mice by placing the human S100A6 cDNA downstream of a promoter responsive to a doxycycline (DOX)-regulated transcriptional activator (tTA) and breeding this line with one harboring cardiac myocyterestricted (αMHC) expression of tTA (αMHC-tTA). We compared S100A6-αMHC-tTA mice 35 days post-myocardial infarction (MI) produced by coronary artery ligation with similar matched sham-operated controls on (S100A6 transgene overexpressed) or off (S100A6 transgene silenced) DOX. There were no differences between the sham groups on or off DOX. Thirty five days post-MI, myocardial S100A6 levels increased 12.5-fold in S100A6-α-MHC-tTA mice off DOX compared with S100A6-α-MHC-tTA mice on DOX. Hemodynamic studies, echocardiography and postmortem examination indicated that S100A6-αMHC-tTA mice on DOX 35 days post-MI mounted a hypertrophic response (20-22.5 % increase) accompanied by a program of fetal gene re-expression, fibrosis and myocardial apoptosis. Whereas the S100A6-α-MHC-tTA mice off DOX showed an attenuated myocyte hypertrophic response, less fibrosis and apoptosis which was beneficial to preservation of cardiac function. Therefore, S100A6 is a potential therapeutic target for modulation of adverse left ventricular remodeling in the early post infarct period.

This article reviews the current progresses in application of both exogenous and endogenous progenitor cells/stem cells for cardiac repair, and the current understanding of the naturally-occurring process for physiological myocyte turnover and possibly cardiac repair. In particular the development of methods for potentiating the naturally-occurring mechanism for substantial repair of pathologically damaged cardiac tissues is discussed. In the last decade, tremendous efforts to identify both exogenous and endogenous progenitor cells/stem cells possessing capacities of differentiating into cardiac lineages have been made for potential cardiac repair. Although many impressive progresses have been made in the application of differently sourced progenitor cells/stem cells, such as embryonic stem cells (ESCs), induced pluripotent stem cell (iPS), bone marrow-derived mesenchymal stem cells (MSCs), skeletal myoblasts (SMs), umbilical cord blood cells (UCBs), residential cardiac stem cells (CSCs), cardiac resident fibroblasts (CRFs), or adipose tissue-derived stem cells (ASCs) for repair of damaged heart, however, inevitable controversies exist concerning: (i) the immune compatibility of the exogenous donor progenitors/stem cells, (ii) the tumorigenicity with ESCs and iPS, and (iii) the efficiency of these exogenous or endogenous progenitors/ stem cells to acquire cardiac lineages to reconstitute the lost cardiac tissues. The recent recognition of some active small molecules that can induce myocardial regeneration to repair damaged heart tissues through enhancing the naturally-occurring cardiac-repair mechanism has offered the hope for clinical translation of the technology. Potentiating the naturally-occurring process for cardiac repair by administration of such small molecules has provided a promising strategy for reconstruction of damaged cardiac tissues after heart infarction. Therefore, this article is in favor of the notion that such small molecules with the activity of manipulating gene expressions in such a way of inducing endogenous stem cells to commit cardiac lineage differentiation and consequently myocardial regeneration may fulfill the dream of substantial repair of damaged heart.

Aim of the presented study was to investigate the role of stromal derived factor 1 (SDF-1α) in mobilizing stem cells in combination with endothelial progenitor cell (EPC) transplantation in a regenerative strategy for myocardial infarction therapy in a murine ischemia/reperfusion model. Initially bone marrow was eradicated and reconstituted with the use of green fluorescent protein (GFP) labelled allogenic cells. After reconstitution, myocardial ischemia was induced by temporary ligation of the left anterior descending coronary artery (LAD) in C57/B16 mice and maintained for 1h. After reperfusion, EPCs (1 x 106 cells) or medium were injected directly into the border zones of the infarcted areas. In addition, the animals were divided in groups treated or not with specific antibodies against SDF-1α. 4 weeks after transplantation, echocardiography revealed a significantly decreased left ventricular function after application of EPCs in anti-SDF-1α treated animals compared to untreated groups. Histology revealed that EPC transplantation and anti-SDF-1α treatment diminished the amount of intramyocardially attracted GFP positive bone marrow cells. Interestingly, no significant changes in the density of CD31+ vessel structures compared to EPC transplantation alone were detectable in anti-SDF-1α treated groups. Anti-SDF-1α treatment also increased numbers of inflammatory cells (monocytes and neutrophiles) in infarcted areas. Rate of apoptotic cells and proliferation after transplantation did not differ. In conclusion, transplanted endothelial progenitor cells as well as SDF-1α are key factors in mobilization of endogenous bone marrow cells towards infarcted myocardium. Anti-SDF-1α treatment leads to a significant decreased left ventricular function, alters the inflammatory processes, but does not lead to significant alterations in neovascularization or collagen content of infarcted areas.

Chemokines are a family of chemotactic cytokines that play an essential role in leukocyte trafficking. Upregulation of both CC and CXC chemokines is a hallmark of the inflammatory and reparative response following myocardial infarction. Release of danger signals from dying cells and damaged extracellular matrix activates innate immune pathways that stimulate chemokine synthesis. Cytokineand chemokine-driven adhesive interactions between endothelial cells and leukocytes mediate extravasation of immune cells into the infarct. CXC chemokines (such as interleukin-8) are bound to glycosaminoglycans on the endothelial surface and activate captured neutrophils, inducing expression of integrins. CC chemokines (such as monocyte chemoattractant protein (MCP)-1) mediate recruitment of proinflammatory and phagocytotic mononuclear cells into the infarct. CC Chemokines may also regulate late infiltration of the healing infarct with inhibitory leukocytes that suppress inflammation and restrain the post-infarction immune response. Non-hematopoietic cells are also targeted by chemokines; in healing infarcts, the CXC chemokine Interferon-γ inducible Protein (IP)-10 exerts antifibrotic actions, inhibiting fibroblast migration. Another member of the CXC subfamily, Stromal cell-derived Factor (SDF)-1, may protect the infarcted heart by activating pro-survival signaling in cardiomyocytes, while exerting angiogenic actions through chemotaxis of endothelial progenitors. Several members of the chemokine family may be promising therapeutic targets to attenuate adverse remodeling in patients with myocardial infarction.

It is reputed that the ideal therapeutic approaches to treatment of patients with acute coronary syndrome (ACS) and myocardium infarction (MI) should be aimed at the inflammation reaction triggers. This study investigated the effectiveness of the impact of L- 17 compound of the group of 5- phenyl substituted-6H-1,3,4-thiadiazine-2-amines upon the course of experimental MI as compared to the impact of a preparation, officially registered in Russia as an immunomodulator, Tamerit, belonging to phthalhydrazid derivative substance. Acute MI in rats was induced by left coronary artery coagulation. Histological study of the myocardium sections and biochemical analysis has been carried out at the 1st and 7th days of the experimental MI. The conducted investigations have shown that under the action of immunocorrectors the inflammation reaction character changes, exudative/destructive inflammation is replaced by a proliferativecellular one. Animals’ blood biochemical analysis at the background of L-17 and Tamerit introduction has shown a decrease of aminotransferases and lactatedehydrogenases activity in blood as compared to the reference group of animals’ indicators, which is evidently caused by epicardial injury of myocardium and lesser amount of the alternative cardiomyocytes. At the same time, no noticeable difference in biochemical characteristics in groups, having been treated to immunomodulators of different chemical composition was identified, which is the sign of the essential similarity of their impact. Thus, immunocorrectors of different chemical groups (Tamerit and compound L17) diminish the volume of initial myocardial infarction and accelerate the granulation processes in course of MI, and represent a new category of treatment agents.

Following myocardial infarction (MI), a dynamic and complex process called wound healing is initiated, aiming to produce a robust scar and limit adverse remodeling of the left ventricle (LV). Cardiac fibroblasts (CFs) - the most populous cardiac cell-type - differentiate into myofibroblasts under the influence of post-MI mechanical stress, transforming growth factor β (TGF-β) and various inflammatory signals. Myofibroblasts are contractile cells that start producing extracellular matrix (ECM) components and secrete factors that orchestrate wound healing, but also promote adverse cardiac remodeling that can progress to life-threatening heart failure (HF). Due to their vital role in the wound healing and LV remodeling after MI, (myo)fibroblasts have been receiving more and more attention lately as targets for anti-HF treatment strategies. In this review, we will summarize the current knowledge regarding the cardiac (myo)fibroblast characteristics, discuss the signaling pathways and the factors that affect their migration, proliferation and differentiation post-MI, as well as their ECM-depositing capabilities. Finally, we will provide an overview of the latest innovative research that is targeting the (myo)fibroblast, in an attempt to limit adverse remodeling and prevent HF.

In the recent years, the existence of cardiac regeneration in mammalian models and even humans has been confirmed in several, carefully designed and executed studies. However, the intrinsic rate of cardiomyocyte renewal is not sufficient to replenish the large number of cells lost after a major injury in the heart, such as myocardial infarction. Therefore, exogenously administered cells with progenitor properties have been used in order to augment this process. From the several candidate cell populations, cardiac derived progenitor cells appear particularly attractive for this purpose, based on data from many experimental studies but also preliminary clinical applications. Cardiosphere-derived cells are a mixed cell population that has shown great potential in stimulating endogenous mechanisms of cardiac repair and attenuating adverse remodeling of the heart. In the present review, we discuss in detail the existing evidence regarding the therapeutic role of cardiosphere-derived progenitor cell administration in the post-myocardial infarction setting. Proof-of-concept studies in rodents, as well as more clinically relevant experiments in large animal models, have provided consistent results regarding the potential of these cells to improve cardiac structure and function after myocardial infarction. Existing data about the underlying mechanisms that are implicated in myocardial regeneration triggered by these cells are presented, as well as preliminary data from clinical applications and future perspectives of this novel therapeutic option.

The generation of functional human cardiomyocytes carries the potential of replacing damaged, malformed, or congenitally absent cardiac tissue as a definitive cure for cardiac disease. Furthermore, patient-specific cardiomyocytes may yield useful in vitro models of heart tissue for disease investigation, drug development and personalized therapy evaluation. This field has experienced rapid advances in the past few years. Nearly pure populations of cardiomyocytes have been generated from human pluripotent stem cells and new strategies to generate cardiomyocytes from somatic cells have been introduced. Here we review the latest breakthroughs in cardiomyocyte differentiation from human pluripotent stem cells and the creation of cardiomyocytes by direct reprogramming strategies, as well as discuss their limitations.

Background: Transplantation of mesenchymal stem cells (MSCs) alters the ventricular electrophysiologic properties after myocardial infarction (MI) in rats. However, it is unclear whether MSCs transplantation enhances the secretion of nerve growth factor (NGF) and affects cardiac sympathetic remodeling. Methods: MI was induced in 35 male Sprague-Dawley rats. Two weeks later, the animals were randomized to MSCs or phosphate buffer solution (PBS) injections into the infarcted myocardium. Six weeks thereafter, the expressions of NGF, growth associated protein 43 (GAP43) and tyrosine hydroxylase (TH) were measured and the density of GAP43 and TH positive nerves was calculated in the borderzone. NGF levels were detected in different culture conditions with neonatal rat ventricular myocytes (NRVMs, 2×105/well) and MSCs (2×105/well). Results: Compared with PBS, mRNA expression and protein levels of NGF, GAP43 and TH increased in the border zone after MSCs injection. Immunohistochemistry showed more GAP43- and TH-positive nerves in the MSCs than in the PBS group. Compared to monocultured MSCs, mono-cultured NRVMs secreted more NGF in vitro. Conclusions: The expression of NGF increased after MSCs transplantation, which may affect sympathetic remodeling and the electrophysiological properties after MI. Paracrine factors secreted by MSC-CM may be involved in this process.

Cell therapy and tissue engineering attract increasing attention as a potential approach for cardiac repair. Although a plethora of interesting concepts in the emerging field of cardiac stem cell-based tissue engineering are reported, there are still challenges that this field needs to overcome to achieve therapeutic translation into the clinical praxis. Engineering biomaterial scaffolds that facilitate stem cell engraftment, survival and homing are crucial for successful cellular cardiomyoplasty after myocardial infarction (MI). In this study we investigate for the first time the cellular response of Wharton’s jelly (WJ) Mesenchymal Stem Cells (MSCs) on a copolymeric material comprising chitosan (CS) and poly(ε-caprolactone) (PCL). First we synthesize a copolymer consisting of poly(ε-caprolactone) grafted on a chemically modified chitosan-backbone (CS-g-PCL). Furthermore, we investigate the morphology, viability and proliferation of WJMSCs on material coatings and examine the cellular response from different donors. Our results show strong cell adhesion on the CS-g- PCL material surface from the first hours in culture, and a proliferation increase after 3 and 7 days. These findings support the potential use of our proposed cell-material combination in myocardium tissue engineering.

Myocardial infarction (MI) and the subsequent heart failure remain among of the leading causes of morbidity and mortality in world wide. A number of studies have demonstrated that intramyocardial biomaterials injections improve cardiac function after implantation because of their angiogenic potential. Thermoresponsive hydrogels, one member of the hydrogels family, are a kind of biomaterial whose structure is similar to that of extracellular matrix. These hydrogels have been interesting for biomedical uses as they can swell in situ under physiological conditions and provide the advantage of convenient administration. The hydrogel that our team is interested in is a novel biodegradable injectable thermoresponsive hydrogel-the copolymer dextran-poly (ε-caprolactone) -2-hydroxylethyl methacrylatepoly (N-isopropylacrylaminde) (Dex-PCL-HEMA/PNIPAAm). Thus, this review will focus on requirements and challenges of injectable synthetic material, and possible mechanism of thermoresponsive hydrogel in treating MI. The main emphases are on the work done and future interesting studies in our laboratory.

Cell therapy has been proposed to treat patients with end-stage heart failure. However, it has been suggested that the significant mechanical forces in an often ischaemic, inflamed, biochemically hostile environment may cause poor cell survival and retention. It is hypothesised that tissue engineering techniques could be used to modify the environment to improve the efficacy of cell therapy. Similarly, it has been suggested that tissue engineering technology could be used to mature the phenotype of immature cardiomyocytes in vitro, making them more useful disease models. In this review we will briefly discuss key tissue engineering techniques and principles that can be used to facilitate cell therapy, and modify the phenotype of immature cardiomyocytes and stem cells.

Cardiac tissue is composed of muscle and non-muscle cells, surrounded by extracellular matrix (ECM) and spatially organized into a complex three-dimensional (3D) architecture to allow for coordinated contraction and electrical pulse propagation. Despite emerging evidence for cardiomyocyte turnover in mammalian hearts, the regenerative capacity of human cardiac tissue is insufficient to recover from damage, e.g. resulting from myocardial infarction (MI). Instead, the heart ‘repairs’ lost or injured tissue by ongoing synthesis and remodeling of scar tissue. Conventional therapies and timely (stem) cell delivery to the injured tissue markedly improve short-term function and remodeling, but do not attenuate later stage adverse remodeling, leading to functional deterioration and eventually failure of the heart. Material-based therapies have been successfully used to mechanically support and constrain the post-MI failing heart, preventing it from further remodeling and dilation. When designed to deliver the right microenvironment for endogenous or exogenous cells, as well as the mechanical and topological cues to guide neo-tissue formation, material-based therapies may even reverse remodeling and boost cardiac regeneration. This paper reviews the up-to-date status of material-based cardiac regeneration with special emphasis on 1) the use of bare biomaterials to deliver passive constraints that unload the heart, 2) the use of materials and cells to create engineered cardiac constructs for replacement, support, or regeneration of damaged myocardium, and 3) the development of bio-inspired and bioactive materials that aim to enhance the endogenous regenerative capacity of the heart. As the therapies should function in the infarcted heart, the damaged host environment and engineered in vitro test systems that mimic this environment, are reviewed as well.