Hyaluronic acid-based hydrogel induces neovascularization and improves cardiac function in a rat model of myocardial infarction.

OBJECTIVES: The use of stem cells in cardiac regeneration is still limited due to low cellular integration and engraftment rates. Consequently, there has been a spurt in research on developing alternative regenerative therapies. Hyaluronic acid (HA) is a major component of the extracellular matrix that is non-immunogenic, and has been implicated in various wound-healing functions such as angiogenesis and inflammation modulation, making it an ideal candidate for regenerative biomaterials. In this study, we examine the potential of acellular hyaluronic acid-based hydrogel in improving cardiac function post-myocardial infarction in a rat model. METHODS: Hyaluronic acid-based hydrogel was injected into the peri-infarct region post-myocardial infarction induction in Lewis rats. Cardiac function in control (n = 10) and gel-injected groups (n = 10) was evaluated up to 4 weeks post-myocardial infarction. Evaluation of cardiac function was conducted using transthoracic echocardiography. Histological analysis of scar area was evaluated via haematoxylin and eosin (H & E), and Sirius red staining. Neovascularization was detected using vascular endothelial growth factor (VEGF) staining. RESULTS: Evaluation of cardiac function using transthoracic echocardiography revealed a 18.2% (P < 0.01) increase in ejection fraction in gel-injected groups when compared with the control group, almost returning the ejection fraction to baseline levels (preop). Histological analysis of scar area by haematoxylin and eosin (H&E), and Sirius red staining demonstrated decreased scarring, and a 22.6% (P < 0.01) decrease in collagen deposition in the gel-injected group compared with the control group. VEGF staining indicated a significant increase in novel vasculature formation in hydrogel-injected groups when compared with control. CONCLUSIONS: Due to its regenerative potential, hyaluronic acid-based hydrogel provides a promising novel therapy to be used alone, or as a scaffold delivering a variety of drugs or cells to combat heart disease in a multifaceted approach.

Bone marrow stem cells.

The "mesenchymal stem cells (MSCs)" are cells adherent in the bone marrow, which can be isolated to induce differentiation. In contrast to the "embryonic stem cells" whose goal is to develop a new organism, the "MSC adult stem cells" can participate in tissue growth and repair throughout postnatal life. Addition of 5-azacytidine to MSCs in vitro induces the gradual increase in cellular size and begins spontaneous beatings, thereafter differentiating into cardiomyocytes. The "Methods" and "Protocols" to induce structural and functional maturations of MSCs, thus to achieve "Cellular Cardiomyoplasty," are described. With appropriate media, differentiations of MSCs to various kinds of cells such as chondrocytes, osteocytes, and adipocytes are also achievable.

Immune responses after mesenchymal stem cell implantation.

Stem cell transplantation is a promising approach for improving cardiac function after severe myocardial damage for which use of autologous cells have been preferred to avoid immune rejection. Recently, however, rodent as well as human mesenchymal stromal cells (MSCs) have been reported to be uniquely immune tolerant, both in in vitro as well as in vivo transplant models. In this chapter, we summarize the current understanding of the underlying immunologic mechanisms, which can facilitate the use of such cells as "universal donor cells."

Placental mesenchymal stem cells: a unique source for cellular cardiomyoplasty.

In coronary heart disease, the use of stem cells for regeneration purposes has been broadly studied. Whereas bone marrow mesenchymal stem cells remain the most extensively investigated, other cell sources have been reported. Here we discuss and compare the characteristics of placenta-derived mesenchymal stem cells as a novel alternative cell source for cellular cardiomyoplasty. These cells are isolated from the human term placenta, which is normally discarded post partum. With their lack of ethical conflicts and young age, the readily available placenta-derived mesenchymal stem cells could be more suitable for myocardial regenerative therapy.

Concise review: immunomodulatory properties of mesenchymal stem cells in cellular transplantation: update, controversies, and unknowns.

Stem cell transplantation is a promising approach for improving cardiac function after severe myocardial damage, for which the use of autologous donor cells has been preferred to avoid immune rejection. Recently, however, rodent as well as human mesenchymal stem cells have been reported to be uniquely immune-tolerant, in both in vitro and in vivo transplant models. In this review, we explore in detail the current understanding of the underlying immunologic mechanisms, which can facilitate the use of such cells as "universal donor cells" with fascinating clinical implications.

Mesenchymal stromal cells as universal donor cells.

Stem cell transplantation is a promising approach for improving cardiac function after severe myocardial damage for which use of autologous cells have been preferred to avoid immune rejection. Recently, however, rodent as well as human mesenchymal stromal cells (MSCs) have been reported to be uniquely immune tolerant, both in in vitro as well as in vivo transplant models. In this editorial, we briefly summarize the current understanding of the underlying immunologic mechanisms, which can facilitate the use of such cells as "Universal Donor Cells."

Superior therapeutic potential of young bone marrow mesenchymal stem cells by direct intramyocardial delivery in aged recipients with acute myocardial infarction: in vitro and in vivo investigation.

Introduction. Bone-marrow-derived mesenchymal stem cells (MSCs) have been studied for treatment of myocardial infarction (MI). Since MSCs from older donors show quantitative and qualitative senescent changes, we hypothesized that a better outcome may be achieved if aged recipients are given MSCs obtained from young donors, rather than using their own autologous MSCs. Methods. In vitro studies compared properties of young and old MSCs. Aged rats randomized into 3 groups underwent coronary artery ligations and were then injected with either old (O) or young (Y) MSCs, or ligation alone. Echocardiography evaluated ejection fractions (EF). At 16 weeks, scar deposition was analyzed. Results. Old MSCs exhibited decreased cell viability, proliferation, and differentiation potentials. EF significantly improved early in both cell therapy groups (P < .05). However, at later stages of the study, group Y showed significantly better function which correlated with decreased scar deposition. Conclusions. The significant difference between young and old cells indicates the possible advantage for allotransplanting MSCs from young donors to elderly patients with MI.

Microencapsulation to reduce mechanical loss of microspheres: implications in myocardial cell therapy.

OBJECTIVE: Previous regenerative studies have demonstrated massive cell losses after intramyocardial cellular delivery. Therefore, efforts at reducing mechanical losses may prove more successful in optimising cellular therapy. In this study, we hypothesized that escalating mesenchymal stem cells (MSCs) dose will not produce corresponding improvement in cardiac function due to washout of the small cells in microcirculation. Using microspheres similar in size to MSCs, that are encapsulated in alginate-poly-l-lysine-alginate (APA), we tested the hypothesis that size is an important factor in early losses. METHODS: In experiment I, five groups of rats (n=9 each) underwent coronary ligation; group I had no treatment; the other groups received escalating 0.5 × 10(6), 1.5 × 10(6), 3 × 10(6) and 5 × 10(6) of MSCs each. Echocardiogram was performed at baseline, 2 days and 7 weeks after surgery. In experiment II, cell-sized microspheres (10 µm) were encapsulated in APA microcapsules. In group I (n=16), rats received bare microspheres, group II (n=16) microspheres within 200 µm microcapsules and in group III (n=16), microspheres within 400 µm microcapsules. After 20 min, hearts were quantified for the amount retained. RESULTS: Myocardial function did not improve further with escalating cell doses beyond an initial response at 1.5 × 10(6) cells. Encapsulated microspheres in 200 µm and 400 µm microcapsules demonstrated a fourfold increase in retention rate compared with 10 µm microspheres. CONCLUSION: We concluded that suboptimal functional improvement in this animal model starts at 1.5 × 10(6) cells and does not respond to escalating cell doses. Improving mechanical retention is possible by increasing the size of the injectate. Microencapsulation could be used to encapsulate donor cells and facilitate functional improvement in cellular heart failure therapy.

Marrow stromal cells for cell-based therapy: the role of antiinflammatory cytokines in cellular cardiomyoplasty.

BACKGROUND: The mechanism by which marrow stromal cells (MSCs) improve cardiac function after myocardial infarction (MI) is still unclear. Because MI patients with lower circulating proinflammatory/antiinflammatory cytokine ratios have been reported to have a better prognosis and in vitro studies showed that MSCs express antiinflammatory cytokines, we hypothesized that changes in cytokine ratios in the infarct microenvironment after MSC therapy may play a role in improving early cardiac function after MI. METHODS: Sixty-three rats that survived left coronary artery ligations were injected with culture media (group M) or MSCs (group C). Cardiac functional changes were assessed with echocardiography. Cytokine gene expressions of interleukin (IL)-1beta, IL-6, IL-8, (proinflammatory) and IL-10 (antiinflammatory) were quantified by real-time polymerase chain reaction. Extracellular matrix deposition, injury score, and the matrix metallopeptidase 2/tissue inhibitor of metallopeptidase 1 ratio were also analyzed. RESULTS: The ratio of proinflammatory/antiinflammatory cytokine gene expression was decreased in group C at various times, particularly in the early postoperative period. In group C, the matrix metallopeptidase 2/tissue inhibitor of metallopeptidase 1 gene expression ratio was significantly lower than group M at the early phase (12 hours), which in group C was translated into significantly lower extracellular matrix deposition at 24 hours, 1, and 2 weeks. Functional recovery was also significantly better in cell therapy group C. CONCLUSIONS: Our data demonstrate that MSC therapy decreases the proinflammatory/antiinflammatory cytokine ratio in the microenvironment early after MI. This is associated with subsequent less scar formation and improved cardiac function.

Myocardial regenerative therapy: immunologic basis for the potential "universal donor cells".

Stem cell transplantation is a promising approach for improving cardiac function after severe myocardial damage for which use of autologous donor cells have been preferred to avoid immune rejection. Recently however, rodent, porcine, and even human bone marrow stromal cells have been reported to be uniquely immune tolerant, both in the in vitro mixed lymphocyte co-culture studies and in the in vivo allo-transplant and xeno-transplant models. In this review, we explore the current understanding of the underlying immunologic mechanisms, which can facilitate the use of such cells as "universal donor cells" with fascinating therapeutic implications.

Marrow stromal cells as universal donor cells for myocardial regenerative therapy: their unique immune tolerance.

BACKGROUND: Recently rodent and porcine bone marrow stromal cells (MSCs) have been reported to be uniquely immune tolerant. To confirm these findings in human cells, we tested whether human MSCs are also immune tolerant, such that they can be used as universal donor cells for myocardial regenerative therapy. METHODS: Immunocompetent female rats underwent coronary ligations (n = 90). In group I, lacZ-labeled male human MSCs were implanted into the peri-infarcted area. In groups II, III, and IV, isogeneic rat MSCs, culture medium, or human fibroblasts were injected, respectively. Echocardiography was carried out to assess cardiac function, and the specimens were examined serially for up to 8 weeks with immunohistochemistry, fluorescent in situ hybridization, and polymerase chain reaction to examine MSCs survival and differentiation. RESULTS: Human MSCs survived within the rat myocardium for more than 8 weeks without immunosuppression. Furthermore, the implanted MSCs significantly contributed to the improvement in ventricular function and attenuated left ventricular remodeling. No cellular infiltration characteristic of immune rejection was noted in contrast to group IV. CONCLUSIONS: Human MSCs survived within this xenogeneic environment, and contributed to the improvement in cardiac function. Our findings support the feasibility of using these cells as universal donor cells for xenogeneic or allogeneic cell therapy, as they can be prepared and stored well in advance for urgent use. Allogeneic MSCs from healthy donors may be particularly useful for severely ill or elderly patients whose own MSCs could be dysfunctional.

Cellular cardiomyoplasty: routes of cell delivery and retention.

Experimental and clinical studies have proven the feasibility of cellular cardiomyoplasty in treating the damaged myocardium following ischemic injury. Over the years, this field has exploded with different investigators trying different routes of cell delivery ranging from direct cell injection into the heart to peripheral intravenous delivery utilizing the various signaling mechanisms known. These different routes have resulted in a wide range of retention and engraftment of cells in the target tissues. In this review, we will explore the different modalities of cell delivery, the pros and cons of each route and the cellular retention and therapeutic efficacy of these routes. We will then look into the different theories that try to explain the observed retention and engraftment of cells in the target tissues. Finally, we will discuss various methods that can improve cellular retention and engraftment and hence better improvement in myocardial function.

From "spongy" and "cold" hearts to cellular cardiomyoplasty: tales of Canadian contribution to global cardiac surgery.

Despite the small size of its population and the number of its cardiac surgeons, Canadians have participated actively in the birth and development of cardiac surgery during the past half century, with pioneers such as Arthur Vineberg and Wilfred Bigelow leading the way. New and innovative cardiac surgical techniques and their scientific bases were developed and shared globally over the years. Canadian surgeons continue to be productive and are contributing to advances in this field at the dawn of the twenty-first century. Some of these efforts and achievements are illustrated in this review.

Massive mechanical loss of microspheres with direct intramyocardial injection in the beating heart: implications for cellular cardiomyoplasty.

OBJECTIVE: Direct intramyocardial injection is a common route of donor cell administration for myocardial cell therapy. Studies have demonstrated a significant and rapid loss of implanted cells, which is thought to be biologically caused. We hypothesized that mechanical loss of cells from the contracting myocardium might actually be the main culprit. METHODS: Intramyocardial injections of fluorescent microspheres (10 microm) were carried out in both small and large animal models. The hearts of Lewis rats (250-350 g) received 3 x 10(6) microspheres injected into the left ventricular myocardium. Rats were divided evenly between two experienced operators. The nonbeating (n = 2) and beating (n = 5) hearts of piglets (7.5-7.8 kg) received 3 x 10(6) microspheres. The hearts were excised within 10 minutes, and the microspheres retained in the myocardium were quantified with fluorescent flow cytometry. RESULTS: In the beating-heart rat model, the microsphere retention rates after a single injection were similar with and without purse-string occlusion of needle puncture sites and slightly lower than after multiple site injections (6.19% +/- 4.05% vs 5.44% +/- 5.66% vs 8.83% +/- 3.29%). There were no significant operator-dependent differences. The retention rates in beating porcine hearts were higher than those in the rats (P < .05) but markedly lower than those in nonbeating porcine hearts (11.1% vs 67.4%). CONCLUSION: Mechanical leakage and washout may account for a major portion of cell loss after cell implantation, and efforts aimed at reducing mechanical loss in the beating heart may yield a greater benefit than those targeting biologic loss alone.

Persistence of marrow stromal cells implanted into acutely infarcted myocardium: observations in a xenotransplant model.

OBJECTIVE: It has been reported that unmatched adult bone marrow stromal cells could be tolerated by immune-competent allotransplant or xenotransplant recipients under various conditions. This study examined whether xenogeneic bone marrow stromal cells implanted immediately after myocardial infarction can survive and differentiate, attenuating deterioration in left ventricular function. METHODS: In groups I and II (n = 34), myocardial infarctions were created in immunocompetent adult Lewis rats by proximal left coronary artery ligation. In group I, 3 x 10(6)lacZ-labeled mouse bone marrow stromal cells were immediately injected into the peri-infarct area of the left ventricle, whereas in group II, only culture medium was injected. There were 10 early and 4 late deaths. At 4 weeks after injection, hearts were stained for beta-galactosidase and troponin IC. In groups IIIA and IIIB, lacZ-labeled mouse skin fibroblasts were implanted into rat myocardium (n = 10 each) with and without left coronary artery ligation, respectively, and the rats were killed serially. In group IV, animals underwent sham surgery (n = 5, no deaths). At 4 weeks, surviving rats in groups I, II, and IV (n = 10, n = 10, and n = 5, respectively) underwent blinded transthoracic echocardiography for ventricular function studies. RESULTS: In group I, labeled mouse-derived bone marrow stromal cells were found within rat myocardium that stained positively for troponin IC 4 weeks after implantation. Functionally, mean left ventricular ejection fraction (P = .007), stroke volume (P = .03), and fractional shortening (P = .02) were all significantly higher in group I than in group II. In groups IIIA and IIIB, mouse fibroblasts induced cellular infiltration with rapid loss of donor cells. No labeled cells were found after 4 days. In group IV, there was no change in cardiac function. CONCLUSION: Xenogeneic bone marrow stromal cells implanted into acutely ischemic myocardium induced by coronary artery ligation were immunologically tolerated, survived and differentiated, resulting in a cardiac chimera which improved left ventricular function. This unique immunologic tolerance may suggest the feasibility of using bone marrow stromal cells as universal donor cells.