Stem cell transplantation for the treatment of myocardial infarction

Dental pulp stem cells: function, isolation and applications in regenerative medicine

Dental pulp stem cells (DPSCs) are a promising source of cells for numerous and varied regenerative medicine applications. Their natural function in the production of odontoblasts to create reparative dentin support applications in dentistry in the regeneration of tooth structures. However, they are also being investigated for the repair of tissues outside of the tooth. The ease of isolation of DPSCs from discarded or removed teeth offers a promising source of autologous cells, and their similarities with bone marrow stromal cells (BMSCs) suggest applications in musculoskeletal regenerative medicine. DPSCs are derived from the neural crest and, therefore, have a different developmental origin to BMSCs. These differences from BMSCs in origin and phenotype are being exploited in neurological and other applications. This review briefly highlights the source and functions of DPSCs and then focuses on in vivo applications across the breadth of regenerative medicine.

Minimally invasive cell-seeded biomaterial systems for injectable/epicardial implantation in ischemic heart disease

Myocardial infarction (MI) is characterized by heart-wall thinning, myocyte slippage, and ventricular dilation. The injury to the heart-wall muscle after MI is permanent, as after an abundant cell loss the myocardial tissue lacks the intrinsic capability to regenerate. New therapeutics are required for functional improvement and regeneration of the infarcted myocardium, to overcome harmful diagnosis of patients with heart failure, and to overcome the shortage of heart donors. In the past few years, myocardial tissue engineering has emerged as a new and ambitious approach for treating MI. Several left ventricular assist devices and epicardial patches have been developed for MI. These devices and acellular/cellular cardiac patches are employed surgically and sutured to the epicardial surface of the heart, limiting the region of therapeutic benefit. An injectable system offers the potential benefit of minimally invasive release into the myocardium either to restore the injured extracellular matrix or to act as a scaffold for cell delivery. Furthermore, intramyocardial injection of biomaterials and cells has opened new opportunities to explore and also to augment the potentials of this technique to ease morbidity and mortality rates owing to heart failure. This review summarizes the growing body of literature in the field of myocardial tissue engineering, where biomaterial injection, with or without simultaneous cellular delivery, has been pursued to enhance functional and structural outcomes following MI. Additionally, this review also provides a complete outlook on the tissue-engineering therapies presently being used for myocardial regeneration, as well as some perceptivity into the possible issues that may hinder its progress in the future.

Experience from experimental cell transplantation therapy of myocardial infarction: what have we learned?

During the past 15 years, our research group has transplanted fetal/neonatal cardiomyocytes, mesenchymal stem cells, and embryonic stem cell-derived cardiomyocytes into infarcted myocardium in a rat myocardial infarction model. Our experimental data demonstrated that cell transplantation therapy provides a potential approach for the treatment of injured myocardium after myocardial infarction based on the reported positive effects upon histological appearance and left ventricular function. However, the underlying mechanisms of the benefits from cell transplantation therapy remain unclear and may involve replacement of scar tissue by transplanted cells, induced neoangiogenesis and paracrine effects of factors released by the transplanted cells. In this review, we summarize our experiences from experimental cell transplantation therapy in a rat myocardial infarction model and discuss the controversies and questions that need to be addressed in future studies.

Nanoparticle-based monitoring of cell therapy

Exogenous cell therapy aims to replace/repair diseased or dysfunctional cells and promises to revolutionize medicine by restoring tissue and organ function. To develop effective cell therapy, the location, distribution and long-term persistence of transplanted cells must be evaluated. Nanoparticle (NP) based imaging technologies have the potential to track transplanted cells non-invasively. Here we summarize the most recent advances in NP-based cell tracking with emphasis on (1) the design criteria for cell tracking NPs, (2) protocols for cell labeling, (3) a comparison of available imaging modalities and their corresponding contrast agents, (4) a summary of preclinical studies on NP-based cell tracking and finally (5) perspectives and future directions.

Stem cells in the treatment of patients with coronary heart disease. Part I

Heart failure (HF) is one of the leading death causes in patients with myocardial infarction (MI). The modern methods of reperfusion MI therapy, such as thrombolysis, surgery and balloon revascularization, even when performed early, could fail to prevent the development of large myocardial damage zones, followed by HF. Therefore, the researches have been searching for the methods which improve functional status of damaged myocardium. This review is focused on stem cell therapy, a method aimed at cardiac function restoration. The results of experimental and clinical studies on stem cell therapy in coronary heart disease are presented. Various types of stem cells, used for cellular cardiomyoplasty, are characterised. The methods of cell transplantation into myocardium and potential adverse effects of stem cell therapy are discussed.

Experimental cell transplantation therapy in rat myocardial infarction model including nude rat preparation

As a novel potential therapeutic strategy for cardiac disease, cell transplantation therapy has been extensively investigated in experimental studies and clinical trials. Although encouraging results have been demonstrated, a number of critical questions still remain to be answered. For example, what kind of stem cell and how many cells should be used; what is the best time for cell transplantation after acute myocardial infarction; which delivery approach is better, intravenous injection or direct intramyocardial injection? Transplantation of cells derived from human tissues into experimental animals may elicit an immune rejection. Immunodeficient nude rats provide a useful myocardial infarction model for cell transplantation therapy studies. We introduce our detailed methods of direct intramyocardial injection of immature heart cells and stem cells into the myocardial infarction region of rats and nude rats. Careful maintenance under aseptic conditions and proper surgical technique are essential to improve the survival of immunodeficient rats after surgery.

In vitro and in vivo study of human amniotic fluid-derived stem cell differentiation into myogenic lineage

Recent findings have shown that amniotic fluid (AF) could be a putative new source of multipotent stem cells (SC). We investigated whether these human SC could efficiently differentiate into myogenic lineage in vitro and integrate in vivo skeletal muscle in severe combined immunodeficiency (SCID) mice. C/kit immunomagnetic-sorted AF (AF c/kit+) SC were characterized by immunocytochemistry and Southern blotting for myogenic markers (desmin, MyoD). In vitro, AF c/kit+ SC phenotypic conversion into myogenic cells was assayed by myogenic-specific induction media. AF c/kit+ SC without ex vivo manipulation were transplanted into the tibialis anterior (TA) of (SCID) mice. Acquisition of a myogenic-like phenotype (desmin, MyoD) in AF c/kit+ SC was observed after culture in myogenic-specific induction media. In vivo, transplanted AF c/kit+ SC showed an engraftment in the skeletal muscle of SCID mice, but with unexpected tubular glandular tissue-like differentiation. Importantly, no immuno-rejection, inflammatory response or tumorigenicity of these cells was found. Within these experimental conditions, AF c/kit+ SC were able to differentiate into myogenic cells in vitro, but not in vivo after their transplantation into the skeletal muscle of SCID mice. Because AF c/kit+ SC survived and differentiated into tubular gland-like cells after their transplantation in the TA, an ex vivo engagement in myogenic pathway prior their transplantation could favor their differentiation into myogenic cells in vivo.

Intramyocardial transplantation of bone marrow-derived stem cells: ultrasonic strain rate imaging in a model of hibernating myocardium

BACKGROUND

The aim of this study was to evaluate potential cardioprotective effects of bone marrow-derived stem cells in chronic ischemic myocardium regarding strain rate parameters during dobutamine stress echocardiography.

METHODS

An ameroid constrictor was placed around the circumflex artery in 23 pigs to induce hibernating myocardium. Pigs received autologous mesenchymal stem cells (auto MSCs), allogeneic MSC (allo MSC), autologous mononuclear cells (auto MNCs), or placebo injections into the ischemic region. During dobutamine stress echocardiography, peak systolic strain rates (SR(sys)) and systolic and postsystolic strain values (epsilon(sys), epsilon(ps)) were determined. The animals were evaluated regarding myocardial fibrosis, neovascularization, apoptosis, and myocardial beta-adrenergic receptor density.

RESULTS

The median ejection fraction was reduced in the control group compared with the auto MSC-, allo MSC-, and auto MNC-treated pigs (36.5% vs 46.0% vs 46.0% vs 41.5%; P = .001, respectively). Histopathology revealed a decreased myocardial fibrosis in auto MSC- (16.3%), allo MSC- (11.3%), and auto MNC- (16.7%) treated pigs compared with controls (31.0%; P = .004). The fibrosis and echocardiographic deformation data correlated in the posterior walls: rest peak SR(sys)r = -0.92; epsilon(sys)r = -0.86; 10 microg dobutamine stimulation peak SR(sys)r = -0.88, epsilon(sys), r = -0.87 (P = .0001).

CONCLUSION

Endocardial injection of stem cells may induce cardioprotective effects in chronic ischemic myocardium and helps to keep the ischemic myocardium viable.

5-Azacytidine-treated human mesenchymal stem/progenitor cells derived from umbilical cord, cord blood and bone marrow do not generate cardiomyocytes in vitro at high frequencies

BACKGROUND AND OBJECTIVES

Mesenchymal stem/progenitor cells (MSCs) are multipotent progenitors that differentiate into such lineages as bone, fat, cartilage and stromal cells that support haemopoiesis. Bone marrow MSCs can also contribute to cardiac repair, although the mechanism for this is unclear. Here, we examine the potential of MSCs from different sources to generate cardiomyocytes in vitro, as a means for predicting their therapeutic potential after myocardial infarction.

MATERIALS AND METHODS

Mesenchymal stem/progenitor cells were isolated from the perivascular tissue and Wharton's jelly of the umbilical cord and from cord blood. Their immunophenotype and differentiation potential to generate osteoblasts, chondrocytes, adipocytes and cardiomyoxcytes in vitro was compared with those of bone marrow MSCs.

RESULTS

Mesenchymal stem/progenitor cells isolated from umbilical cord and cord blood were phenotypically similar to bone marrow MSCs, the exception being in the expression of CD106, which was absent on umbilical cord MSCs, and CD146 that was highly expressed in cord blood MSCs. They have variable abilities to give rise to osteoblasts, chondrocytes and adipocytes, with bone marrow MSCs being the most robust. While a small proportion (approximately 0.07%) of bone marrow MSCs could generate cardiomyocyte-like cells in vitro, those from umbilical cord and cord blood did not express cardiac markers either spontaneously or after treatment with 5-azacytidine.

CONCLUSION

Although MSCs may be useful for such clinical applications as bone or cartilage repair, the results presented here indicate that such cells do not generate cardiomyocytes frequently enough for cardiac repair. Their efficacy in heart repair is likely to be due to paracrine mechanisms.

Direct delivery of syngeneic and allogeneic large-scale expanded multipotent adult progenitor cells improves cardiac function after myocardial infarct

BACKGROUND

Multipotent adult progenitor cells (MAPC) comprise interesting candidates for myocardial regeneration because of a broad differentiation ability and immune privilege. We aimed to compare the improvement of cardiac function by syngeneic and allogeneic MAPC produced on a large scale using a platform optimized from MAPC research protocols.

METHODS

Myocardial infarction was induced in Lewis rats by direct left anterior descending ligation followed immediately by direct injection into the infarct border zone of either Sprague-Dawley or Lewis MAPC from large-scale expansions. Echocardiography was performed to evaluate improvement in cardiac function, and immunohistochemistry was performed to identify MAPC within the infarct zone.

RESULTS

Significant increases were observed in functional performance in animals transplanted with expanded MAPC compared with saline controls, with no significant differences between the syngeneic and allogeneic groups. Immunostaining demonstrated significant engraftment of expanded MAPC at 1 day after acute myocardial infarction, with <10% of either syngeneic or allogeneic cells remaining at 6 weeks. At this point there was no evidence of myocardial regeneration. However, a significant increase in vascular density within the infarct zone in MAPC-transplanted animals was observed, and MAPC were found to produce high levels of VEGF in culture.

DISCUSSION

These findings support a model in which delivery of expanded MAPC following acute myocardial infarction results in improvement in cardiac function because of paracrine effects resulting in vascular density increases, as well as potentially other trophic effects, supporting newly injured cardiac myocytes. Thus transplantation with MAPC may represent a promising therapeutic strategy with application in the stimulation of neovascularization in ischemic heart disease.

Role of a paracrine action of mesenchymal stem cells in the improvement of left ventricular function after coronary artery occlusion in rats

PURPOSE

We aimed to determine whether soluble factors released by cultured mesenchymal stem cells (MSCs) improved cardiac function in an experimental model of myocardial infarction.

METHODS

MSCs were cultured in fresh medium. The conditioned medium, which contained factors secreted by MSCs, was collected after 4 days of culture. Fischer rats with 1-week-old myocardial infarction were divided into four groups that received: saline (n = 12); fresh medium (n = 10); conditioned medium (n = 8); or 2 million MSCs in fresh medium (n = 10) by direct intramyocardial injection. A total of 4 weeks later, left ventricular (LV) function was assessed by LV angiogram and by LV catheterization. Hearts were processed for histology.

RESULTS

Before treatment, LV angiogram assessment demonstrated that the baseline LV function was comparable among the four groups. At 4 weeks after treatment, LV angiogram and LV catheterization showed that LV ejection fraction was better in the fresh medium (49.5 +/- 1.0%), conditioned medium (48.5 +/- 2.1%) and MSCs groups (49.9 +/- 4.2%) than in the saline group (43.7 +/- 1.2%; p < 0.05). There were no significant differences in heart rate, blood pressure, postmortem LV volume, infarct size or septum thickness among the groups. The scar thickness was similar in the saline (395 +/- 31 microm), fresh medium (404 +/- 30 microm) and conditioned medium (397 +/- 34 microm) groups, but significantly thicker in the MSCs group (560 +/- 51 microm; p < 0.05).

CONCLUSION

Fresh medium, conditioned medium and MSC injection all improved LV function at 4 weeks after treatment compared with saline treatment in a rat myocardial infarct model; only MSCs increased wall thickness. Since the culture medium contains nutrients and bovine serum, the roles of the soluble factors released by MSCs might be masked. The effect of these nutrients needs further investigation.

Survival and maturation of human embryonic stem cell-derived cardiomyocytes in rat hearts

Human embryonic stem cell (hESC)-derived cardiomyocytes are a promising cell source for cardiac repair. Whether these cells can be transported long distance, survive, and mature in hearts subjected to ischemia/reperfusion with minimal infarction is unknown. Taking advantage of a constitutively GFP-expressing hESC line we investigated whether hESC-derived cardiomyocytes could be shipped and subsequently form grafts when transplanted into the left ventricular wall of athymic nude rats subjected to ischemia/reperfusion with minimal infarction. Co-localization of GFP-epifluorescence and cardiomyocyte-specific marker staining was utilized to analyze hESC-derived cardiomyocyte fate in a rat ischemia/reperfused myocardium. Differentiated, constitutively green fluorescent protein (GFP)-expressing hESCs (hES3-GFP; Envy) containing about 13% cardiomyocytes were differentiated in Singapore, and shipped in culture medium at 4 degrees C to Los Angeles (shipping time approximately 3 days). The cells were dissociated and a cell suspension (2 x 10(6) cells for each rat, n=10) or medium (n=10) was injected directly into the myocardium within the ischemic risk area 5 min after left coronary artery occlusion in athymic nude rats. After 15 min of ischemia, the coronary artery was reperfused. The hearts were harvested at various time points later and processed for histology, immunohistochemical staining, and fluorescence microscopy. In order to assess whether the hESC-derived cardiomyocytes might evade immune surveillance, 2 x 10(6) cells were injected into immune competent Sprague-Dawley rat hearts (n=2), and the hearts were harvested at 4 weeks after cell injection and examined as in the previous procedures. Even following 3 days of shipping, the hESC-derived cardiomyocytes within embryoid bodies (EBs) showed active and rhythmic contraction after incubation in the presence of 5% CO(2) at 37 degrees C. In the nude rats, following cell implantation, H&E, immunohistochemical staining and GFP epifluorescence demonstrated grafts in 9 out of 10 hearts. Cells that demonstrated GFP epifluorescence also stained positive (co-localized) for the muscle marker alpha-actinin and exhibited cross striations (sarcomeres). Furthermore, cells that stained positive for the antibody to GFP (immunohistochemistry) also stained positive for the muscle marker sarcomeric actin and demonstrated cross striations. At 4 weeks engrafted hESCs expressed connexin 43, suggesting the presence of nascent gap junctions between donor and host cells. No evidence of rejection was observed in nude rats as determined by inspection for lymphocytic infiltrate and/or giant cells. In contrast, hESC-derived cardiomyocytes injected into immune competent Sprague-Dawley rats resulted in an overt lymphocytic infiltrate. hESCs-derived cardiomyocytes can survive several days of shipping. Grafted cells survived up to 4 weeks after transplantation in hearts of nude rats subjected to ischemia/reperfusion with minimal infarction. They continued to express cardiac muscle markers and exhibit sarcomeric structure and they were well interspersed with the endogenous myocardium. However, hESC-derived cells did not escape immune surveillance in the xenograft setting in that they elicited a rejection phenomenon in immune competent rats.

Heart repair and stem cells

Of the medical conditions currently being discussed in the context of possible treatments based on cell transplantation therapy, few have received more attention than the heart. Much focus has been on the potential application of bone marrow-derived cell preparations, which have already been introduced into double-blind, placebo-controlled clinical trials. The consensus is that bone marrow may have therapeutic benefit but that this is not based on the ability of bone marrow cells to transdifferentiate into cardiac myocytes. Are there potential stem cell sources of cardiac myocytes that may be useful in replacing those lost or dysfunctional after myocardial infarction? Here, this question is addressed with a review of the recent literature.