Biomedical subjects

Bradley J Martin

Publications and source records attributed to Bradley J Martin.

10 recordsLinked to original sources

PubMed2005

Intravenous mesenchymal stem cell therapy early after reperfused acute myocardial infarction improves left ventricular function and alters electrophysiologic properties.

UNLABELLED: Direct intramyocardial injection of mesenchymal stem cells (MSCs) improves left ventricular ejection fraction (LVEF) and may increase ventricular arrhythmia in hearts with myocardial infarction (MI). We hypothesized that intravenous MSCs given early after acute MI would engraft in injured myocardium, improve LV function, and result in pro-arrhythmic electrical remodeling. We created an apical infarction in swine by balloon occlusion/reperfusion, administered diI-labeled allogeneic bone marrow derived MSCs intravenously 30 min post-reperfusion and measured LVEF and wall thickness at baseline, 1 month, and 3 months. Epicardial effective refractory periods (ERPs) were determined before sacrifice. At 3 months, treated pigs [n=7] had significantly higher LVEF than controls [n=8] (49+/-2% vs. 44+/-3%, P=0.015) and significantly less wall thickening of non-infarcted myocardium. ERPs were significantly shorter than controls at all pacing cycle lengths (P<or=0.002), suggesting a pro-arrhythmic potential. DiI was found in the lungs, in infarct, and peri-infarct myocardium. CONCLUSION: IV infusion of MSCs soon after acute MI in swine improves LVEF and limits wall thickening in the remote non-infarcted myocardium, consistent with a beneficial effect on post-MI ventricular remodeling. Since there is no need for immune suppression or clinical expertise, IV infusion of MSCs may expand the potential clinical application of stem cell therapy.

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PubMed2005

Altered serotonin synthesis, turnover and dynamic regulation in multiple brain regions of mice lacking the serotonin transporter.

To evaluate the consequences of inactivation of the serotonin transporter (SERT) gene on 5-HT homeostasis and function, 5-HT synthesis and turnover rates were measured using the decarboxylase inhibition method in multiple brain regions (frontal cortex, striatum, brainstem, hippocampus and hypothalamus) from mice with a genetic disruption of SERT. 5-HT synthesis rates were increased 30-60% in the different brain regions of SERT -/- mice compared to littermate +/+ control mice despite 55-70% reductions in tissue 5-HT concentrations. Brain regions that possessed a greater capacity to increase synthesis and turnover (frontal cortex, striatum) demonstrated lesser reductions in tissue 5-HT. Female SERT -/- mice had greater increases (79%) in brain 5-HT synthesis than male -/- mice did (25%), a finding associated with higher brain tryptophan concentrations in females. Despite increased 5-HT synthesis, there was no change in either TPH2 or TPH1 mRNA levels or in maximal in vitro TPH activity in the brainstem of SERT -/- mice. Catecholamine homeostasis as reflected in brain tissue concentrations and in synthesis and turnover of dopamine and norepinephrine was unchanged in SERT -/- mice. Taken together, the results demonstrate a markedly altered homeostatic situation in SERT -/- mice that lack 5-HT reuptake, resulting in markedly depleted tissue stores that are inadequately compensated for by increased 5-HT synthesis, with brain region and gender specificity observed.

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PubMed2005

Cardiac repair with intramyocardial injection of allogeneic mesenchymal stem cells after myocardial infarction.

Although clinical trials of autologous whole bone marrow for cardiac repair demonstrate promising results, many practical and mechanistic issues regarding this therapy remain highly controversial. Here, we report the results of a randomized study of bone-marrow-derived mesenchymal stem cells, administered to pigs, which offer several new insights regarding cellular cardiomyoplasty. First, cells were safely injected by using a percutaneous-injection catheter 3 d after myocardial infarction. Second, cellular transplantation resulted in long-term engraftment, profound reduction in scar formation, and near-normalization of cardiac function. Third, transplanted cells were pre-prepared from an allogeneic donor and were not rejected, a major practical advance for widespread application of this therapy. Together, these findings demonstrate that the direct injection of cellular grafts into damaged myocardium is safe and effective in the perii-nfarct period. The direct delivery of cells to necrotic myocardium offers a valuable alternative to intracoronary cell injections, and the use of allogeneic mesenchymal stem cells provides a valuable strategy for cardiac regenerative therapy that avoids the need for preparing autologous cells from the recipient.

Analysis of Variance↗

PubMed2005

Allogeneic mesenchymal stem cell transplantation in postinfarcted rat myocardium: short- and long-term effects.

BACKGROUND: Mesenchymal stem cells (MSCs) have the potential to replace infarct scar, but the long-term effects are unknown. We studied short- and long-term effects of MSC transplantation on left ventricular (LV) function in a rat myocardial infarction model. METHODS AND RESULTS: Saline (n=46) or MSCs labeled with 1,1'-dioctadecyl-3,3,3'3'-testramethylindocarbocyanine perchlorate (DiI; n=49, 2x10(6) cells each) were injected into the scar of a 1-week-old myocardial infarction in Fischer rats. The presence and differentiation of engrafted cells and their effect on LV ejection fraction was assessed. At 4 weeks, LV stroke volume was significantly greater in the MSC-treated group (145+/-9 microL) than in the saline group (122+/-3 microL, P=0.032), and LV ejection fraction was significantly greater in MSC-treated animals (43.8+/-1.0%) than in the saline group (38.8+/-1.1%, P=0.0027). However, at 6 months, these benefits of MSC treatment were lost. DiI-positive cells were observed in the MSC group at 2 weeks and at 3 and 6 months. Expression of the muscle-specific markers alpha-actinin, myosin heavy chain, phospholamban, and tropomyosin was not observed at 2 weeks in DiI-positive cells. At 3 and 6 months, the DiI-positive cells were observed to express the above muscle-specific markers, but they did not fully evolve into an adult cardiac phenotype. Some of the DiI-positive cells expressed von Willebrand factor. CONCLUSIONS: Allogeneic MSCs survive in infarcted myocardium as long as 6 months and express markers that suggest muscle and endothelium phenotypes. MSCs improved global LV function at 4 weeks; however, this benefit was transient, which suggests a possible early paracrine effect.

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PubMed2005

Mesenchymal stem cells differentiate into an endothelial phenotype, enhance vascular density, and improve heart function in a canine chronic ischemia model.

BACKGROUND: Bone marrow-derived stem cells are under investigation as a treatment for ischemic heart disease. Mesenchymal stem cells (MSCs) have been used preferentially in the acute ischemia model; data in the chronic ischemia model are lacking. METHODS AND RESULTS: Twelve dogs underwent ameroid constrictor placement. Thirty days later, they received intramyocardial injections of either MSCs (100x10(6) MSCs/10 mL saline) (n=6) or saline only (10 mL) (controls) (n=6). All were euthanized at 60 days. Resting and stress 2D echocardiography was performed at 30 and 60 days after ameroid placement. White blood cell count (WBC), C-reactive protein (CRP), creatine kinase MB (CK-MB), and troponin I levels were measured. Histopathological and immunohistochemical analyses were performed. Mean left ventricular ejection fraction was similar in both groups at baseline but significantly higher in treated dogs at 60 days. WBC and CRP levels were similar over time in both groups. CK-MB and troponin I increased from baseline to 48 hours, eventually returning to baseline. There was a trend toward reduced fibrosis and greater vascular density in the treated group. MSCs colocalized with endothelial and smooth muscle cells but not with myocytes. CONCLUSIONS: In a canine chronic ischemia model, MSCs differentiated into smooth muscle cells and endothelial cells, resulting in increased vascularity and improved cardiac function.

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PubMed2004

Mesenchymal stem cells and their potential as cardiac therapeutics.

Mesenchymal stem cells (MSCs) represent a stem cell population present in adult tissues that can be isolated, expanded in culture, and characterized in vitro and in vivo. MSCs differentiate readily into chondrocytes, adipocytes, osteocytes, and they can support hematopoietic stem cells or embryonic stem cells in culture. Evidence suggests MSCs can also express phenotypic characteristics of endothelial, neural, smooth muscle, skeletal myoblasts, and cardiac myocyte cells. When introduced into the infarcted heart, MSCs prevent deleterious remodeling and improve recovery, although further understanding of MSC differentiation in the cardiac scar tissue is still needed. MSCs have been injected directly into the infarct, or they have been administered intravenously and seen to home to the site of injury. Examination of the interaction of allogeneic MSCs with cells of the immune system indicates little rejection by T cells. Persistence of allogeneic MSCs in vivo suggests their potential "off the shelf" therapeutic use for multiple recipients. Clinical use of cultured human MSCs (hMSCs) has begun for cancer patients, and recipients have received autologous or allogeneic MSCs. Research continues to support the desirable traits of MSCs for development of cellular therapeutics for many tissues, including the cardiovascular system. In summary, hMSCs isolated from adult bone marrow provide an excellent model for development of stem cell therapeutics, and their potential use in the cardiovascular system is currently under investigation in the laboratory and clinical settings.

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PubMed2003

Serial cardiac magnetic resonance imaging of injected mesenchymal stem cells.

BACKGROUND: Delivery and tracking of endomyocardial stem cells are limited by the inability to image transplanted cells noninvasively in the beating heart. We hypothesized that mesenchymal stem cells (MSCs) could be labeled with a iron fluorophore particle (IFP) to provide MRI contrast in vivo to assess immediate and long-term localization. METHODS AND RESULTS: MSCs were isolated from swine. Short-term incubation of MSCs with IFP resulted in dose-dependent and efficient labeling. Labeled cells remained viable for multiple passages and retained in vitro proliferation and differentiation capacity. Labeled MSCs (10(4) to 10(6) cells/150 microL) were injected percutaneously into normal and freshly infarcted myocardium in swine. One, 3, and 1 animals underwent serial cardiac MRI (1.5T) for 4, 8, and 21 days, respectively. MRI contrast properties were measured both in vivo and in vitro for cells embedded in agar. Injection sites containing as few as 10(5) MSCs could be detected and contained intact IFP-bearing MSCs on histology. CONCLUSIONS: IFP labeling of MSCs imparts useful MRI contrast, enabling ready detection in the beating heart on a conventional cardiac MR scanner after transplantation into normal and infarcted myocardium. The dual-labeled MSCs can be identified at locations corresponding to injection sites, both ex vivo using fluorescence microscopy and in vivo using susceptibility contrast on MRI. This technology may permit effective in vivo study of stem cell retention, engraftment, and migration.

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PubMed2003

In vivo magnetic resonance imaging of mesenchymal stem cells in myocardial infarction.

BACKGROUND: We investigated the potential of magnetic resonance imaging (MRI) to track magnetically labeled mesenchymal stem cells (MR-MSCs) in a swine myocardial infarction (MI) model. METHODS AND RESULTS: Adult farm pigs (n=5) were subjected to closed-chest experimental MI. MR-MSCs (2.8 to 16x107 cells) were injected intramyocardially under x-ray fluoroscopy. MRIs were obtained on a 1.5T MR scanner to demonstrate the location of the MR-MSCs and were correlated with histology. Contrast-enhanced MRI demonstrated successful injection in the infarct and serial MSC tracking was demonstrated in two animals. CONCLUSIONS: MRI tracking of MSCs is feasible and represents a preferred method for studying the engraftment of MSCs in MI.

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PubMed2002

Mesenchymal stem cell implantation in a swine myocardial infarct model: engraftment and functional effects.

BACKGROUND: A novel therapeutic option for the treatment of acute myocardial infarction involves the use of mesenchymal stem cells (MSCs). The purpose of this study was to investigate whether implantation of autologous MSCs results in sustained engraftment, myogenic differentiation, and improved cardiac function in a swine myocardial infarct model. METHODS: MSCs were isolated and expanded from bone marrow aspirates of 14 domestic swine. A 60-minute left anterior descending artery occlusion was used to produce anterior wall infarction. Piezoelectric crystals were placed within the ischemic region for measurement of regional wall thickness and contractile function. Two weeks later animals autologous, Di-I-labeled MSCs (6 x 10(7)) were implanted into the infarct by direct injection. Hemodynamic and functional measurements were obtained weekly until the time of sacrifice. Immunohistochemistry was used to assess MSC engraftment and myogenic differentiation. RESULTS: Microscopic analysis showed robust engraftment of MSCs in all treated animals. Expression of muscle-specific proteins was seen as early as 2 weeks and could be identified in all animals at sacrifice. The degree of contractile dysfunction was significantly attenuated at 4 weeks in animals implanted with MSCs (5.4% +/- 2.2% versus -3.37% +/- 2.7% in control). In addition, the extent of wall thinning after myocardial infarction was markedly reduced in treated animals. CONCLUSIONS: Mesenchymal stem cells are capable of engraftment in host myocardium, demonstrate expression of muscle specific proteins, and may attenuate contractile dysfunction and pathologic thinning in this model of left ventricular wall infarction. MSC cardiomyoplasty may have significant clinical potential in attenuating the pathology associated with myocardial infarction.

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PubMedDate not supplied

Stem cell therapy for the heart.

Cellular cardiomyoplasty is an expanding field of research that involves numerous types of immature cells administered via several modes of delivery. The purpose of this review is to investigate the benefits of different types of cells used in stem cell research as well as the most efficient mode of delivery. The authors also present data showing that stem cells isolated from bone marrow are present at both 2 weeks and 3 months after engraftment in a myocardial infarction. These cells express muscle markers at both time points, which suggests that they have begun to differentiate into cardiomyocytes. Several questions must be answered, however, before stem cells can be used routinely in the clinic. Once these questions have been addressed, the use of stem cells in clinical practice can be realized.

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