Infarcted Rat Hearts Research Articles

PROTECTIVE EFFECTS OF LEONURINE IN NEONATAL RAT HYPOXIC CARDIOMYOCYTES AND RAT INFARCTED HEART

1. Previous studies have shown that extracts of Herba leonuri, predominantly containing the phytochemical components leonurine and stachydrine, provide protective effects in the ischaemic myocardium by acting as free radical scavengers and inhibiting the formation of reactive oxygen species. 2. The present study was designed to investigate the cardioprotective effects of 10(-6) mol/L leonurine on neonatal rat cardiomyocytes treated with hypoxia plus serum deprivation, a component of ischaemia, and to determine the mechanisms underlying the protective effects with regard to cardiac anti-oxidant enzymes and apoptosis genes. Cardiomyocytes were treated with leonurine 8 h prior to exposure to hypoxia. In addition, we investigated the effects of 7.5 and 15 mg/kg leonurine, administered to rats i.p. for 7 days prior to left coronary artery ligation, on subsequent infarct size of the ischaemic heart. 3. Leonurine significantly increased the viability of cardiomyocytes injured by hypoxia. In the leonurine-treated group, gene expression levels of pro-apoptotic genes, namely Bax and Fas, were significantly downregulated (by 0.95- and 0.72-fold, respectively; P < 0.001) compared with the hypoxic control group, whereas the expression of Bcl-2 and Bcl-xl was upregulated following leonurine treatment (by 1.03- and 1.07-fold, respectively; P < 0.05). Correspondingly, leonurine treatment increased Bcl-2 protein levels and decreased Bax protein levels. Assays investigating cardiac anti-oxidant enzymes provided further evidence for a protective effect of leonurine, as indicated by the induction of the anti-oxidant enzymes superoxide dismutase and catalase. Furthermore, leonurine decreased infarct size in ischaemic rat heart. 4. The results of the present study suggest that the mechanisms of action of leonurine in hypoxic neonatal rat cardiomyocytes and infarcted rat heart may be related to its anti-oxidant and anti-apoptotic properties.

Cardiac Renin Levels Are Not Influenced by the Amount of Resident Mast Cells

To investigate whether mast cells release renin in the heart, we studied renin and prorenin synthesis by such cells, using the human mast cell lines human mastocytoma 1 and LAD2, as well as fresh mast cells from mastocytosis patients. We also quantified the contribution of mast cells to cardiac renin levels in control and infarcted rat hearts. Human mastocytoma 1 cells contained and released angiotensin I-generating activity, and the inhibition of this activity by the renin inhibitor aliskiren was comparable to that of recombinant human renin. Prorenin activation with trypsin increased angiotensin I-generating activity in the medium only, suggesting release but not storage of prorenin. The adenylyl cyclase activator forskolin, the cAMP analogue 8-db-cAMP, and the degranulator compound 48/80 increased renin release without affecting prorenin. Angiotensin II blocked the forskolin-induced renin release. Angiotensin I-generating activity was undetectable in LAD2 cells and fresh mast cells. Nonperfused rat hearts contained angiotensin I-generating activity, and aliskiren blocked approximately 70% of this activity. A 30-minute buffer perfusion washed away >70% of the aliskiren-inhibitable angiotensin I-generating activity. Prolonged buffer perfusion or compound 48/80 did not decrease cardiac angiotensin I-generating activity further or induce angiotensin I-generating activity release in the perfusion buffer. Results in infarcted hearts were identical, despite the increased mast cell number in such hearts. In conclusion, human mastocytoma 1 cells release renin and prorenin, and the regulation of this release resembles that of renal renin. However, this is not a uniform property of all mast cells. Mast cells appear an unlikely source of renin in the heart, both under normal and pathophysiological conditions.

Myocardial Infarct Size-Limiting and Anti-Arrhythmic Effects of Mildronate Orotate in the Rat Heart

Mildronate and orotic acid act as modulators of energy metabolism and are considered as cardioprotective agents. This study was performed to compare the cardioprotective effects of mildronate, orotic acid and mildronate orotate. Male Wistar rats received mildronate, orotic acid or mildronate orotate for 14 days. The isolated rat heart infarction and isoproterenol-induced ischemia models were used to test the cardioprotective effects of compounds studied. Experimental arrhythmias were induced by the ligation of the left anterior descending coronary artery for 10 min with subsequent reperfusion or by administration of calcium chloride or aconitine at arrhythmogenic doses. The data obtained showed a statistically significant decrease of necrotic area in 25% of infarcted rat hearts after 14 days of treatment with mildronate and orotic acid, whereas mildronate orotate decreased the infarct size by 50%. Moreover, we found that the administration of mildronate and its orotate salt decreased the duration and incidence of arrhythmias in experimental arrhythmia models. The study provides experimental evidence that the combination of orotic acid and mildronate possesses additive pharmacological effects and that mildronate orotate might be considered as a powerful therapeutic agent facilitating recovery from ischemia-reperfusion injury.

A redox-metabolic-electrical remodeling in the diseased left and right ventricle: direct clinical implications in heart disease and beyond. Focus on “Role of γ-glutamyl transpeptidase in redox regulation of K+ channel remodeling in postmyocardial infarction rat hearts”

“Birth and death are not two different states, but they are different aspects of the same state …” — Mahatma Gandhi both our first and our last breath are associated with inhibition of voltage-gated K+ channels (Kv). Upon our first breath, the transition from the fetal to the adult

Antioxidative Effect Of Exercise Training Combined With Losartan Treatment In The Infarcted Rat Hearts

Antioxidative Effect Of Exercise Training Combined With Losartan Treatment In The Infarcted Rat Hearts

Proteome analysis of differential protein expression in infarcted rat heart after verapamil treatment

To explore the protein-level mechanism of action verapamil in acute myocardial infarcted rats, the myocardial proteome was analyzed by two-dimensional electrophoresis (2-DE). Compared with the sham-operated group and the infarcted group, the result shows that 8 protein expressions in the verapamil treated group were up-regulated, and 7 protein expressions in this group were down-regulated significantly. Using MALDI-TOF-MS, 15 proteins with significant changes were identified through a database search. These proteins can be divided into 4 groups by their biological function: (1) Energy metabolism and mitochondrial function related proteins; (2) oxidative stress-induced proteins; (3) cytoskeletal Proteins; (4) other proteins. The findings show that the myocardial protective effects of verapamil in the myocardial damage process are related to the recovery of energy supply as well as anti-oxidative stress property.

Hyperbaric oxygenation enhances transplanted cell graft and functional recovery in the infarct heart

A major limitation to the application of stem-cell therapy to repair ischemic heart damage is the low survival of transplanted cells in the heart, possibly due to poor oxygenation. We hypothesized that hyperbaric oxygenation (HBO) can be used as an adjuvant treatment to augment stem-cell therapy. Therefore, the goal of this study was to evaluate the effect of HBO on the engraftment of rat bone marrow-derived mesenchymal stem cells (MSCs) transplanted in infarct rat hearts. Myocardial infarction (MI) was induced in Fisher-344 rats by permanently ligating the left-anterior-descending coronary artery. MSCs, labeled with fluorescent superparamagnetic iron oxide (SPIO) particles, were transplanted in the infarct and peri-infarct regions of the MI hearts. HBO (100% oxygen at 2 ATA for 90 min) was administered daily for 2 weeks. Four MI groups were used: untreated (MI); HBO; MSC; MSC + HBO. Echocardiography, electro-vectorcardiography, and magnetic resonance imaging were used for functional evaluations. The engraftment of transplanted MSCs in the heart was confirmed by SPIO fluorescence and Prussian-blue staining. Immunohistochemical staining was used to identify key cellular and molecular markers including CD29, troponin-T, connexin-43, VEGF, α-smooth-muscle actin, and von Willebrand factor in the tissue. Compared to MI and MSC groups, the MSC + HBO group showed a significantly increased recovery of cardiac function including left-ventricular (LV) ejection fraction, fraction shortening, LV wall thickness, and QRS vector. Further, HBO treatment significantly increased the engraftment of CD29-positive cells, expression of connexin-43, troponin-T and VEGF, and angiogenesis in the infarct tissue. Thus, HBO appears to be a potential and clinically-viable adjuvant treatment for myocardial stem-cell therapy.

The basic helix–loop–helix transcription factor scleraxis regulates fibroblast collagen synthesis

The transcription factor scleraxis has been implicated in regulating the development of collagen-rich tissues such as tendons and cardiac valves, but its role in general collagen synthesis in the heart is unknown. Scleraxis expression in cardiac fibroblasts was examined, and its ability to regulate gene expression of collagen Iα2, the predominant cardiac collagen isoform, was assayed. Using real-time PCR, we demonstrate here that scleraxis mRNA is up-regulated by the profibrotic agonist TGF-β 1 in rat cardiac myofibroblasts, and that phenoconversion of fibroblasts to myofibroblasts similarly increases scleraxis expression. Over-expression of scleraxis in NIH-3T3 or primary rat cardiac fibroblasts by adenoviral gene delivery is sufficient to significantly increase collagen Iα2 gene expression. Using luciferase reporter assays, we demonstrate that scleraxis transactivates the human collagen Iα2 promoter in a DNA- and protein-binding dependent manner. Intriguingly, examination of infarcted rat hearts reveals a nearly four-fold increase in scleraxis expression in the infarct scar, but not in non-infarcted tissue. These data support a novel and previously unknown role for scleraxis in the regulation of collagen gene expression in the heart, including in post-infarct scar formation.

Implantation of Low-Level Laser Irradiated Mesenchymal Stem Cells into the Infarcted Rat Heart Is Associated with Reduction In Infarct Size and Enhanced Angiogenesis

The aim of the present study was to evaluate the possible beneficial effects of implantation of laser-irradiated mesenchymal stem cells (MSCs) into the infarcted rat heart. It was demonstrated that low-level laser therapy (LLLT) upregulates cytoprotective factors in ischemic tissues. MSCs were isolated from rat bone marrow and grown in culture. The cells were laser irradiated with a Ga-Al-As laser (810 nm wavelength), labeled with 5-bromo-2'deoxyuridine (BrdU), and then implanted into infarcted rat hearts. Non-irradiated cells were similarly labeled and acted as controls. Hearts were excised 3 wk later and cells were stained for BrdU and c-kit immunoreactivity. Infarcted hearts that were implanted with laser-treated cells showed a significant reduction of 53% in infarct size compared to hearts that were implanted with non-laser-treated cells. The hearts implanted with laser-treated cells prior to implantation demonstrated a 5- and 6.3-fold significant increase in cell density that positively immunoreacted to BrdU and c-kit, respectively, as compared to hearts implanted with non-laser-treated cells. A significantly 1.4- and 2-fold higher level of angiogenesis and vascular endothelial growth factor, respectively, were observed in infarcted hearts that were implanted with laser-treated cells compared to non-laser-treated implanted cells. The findings of the present study provide the first evidence that LLLT can significantly increase survival and/or proliferation of MSCs post-implantation into the ischemic/infarcted heart, followed by a marked reduction of scarring and enhanced angiogenesis. The mechanisms associated with this phenomenon remain to be elucidated in further studies.

Alterations in energy substrate utilization associated with high dietary fat in the infarcted rat heart

Lipid accumulation in non‐adipose tissues, such as the heart, causes toxicity suggesting excess lipid is pathological. However, our work suggests high dietary fat subsequent to myocardial infarct results in less contractile dysfunction &amp; increased β‐oxidation enzyme activity than a standard diet. This study aimed to define the impact of high fat (SAT) on cardiac energy metabolism after infarction. Rats underwent coronary ligation (HF) or sham (SH) surgery &amp; were fed SAT (60% kcal fat) or normal chow (NC) for 8 weeks with echocardiographic evaluation. Hearts were perfused in working mode with 14C glucose and 3H oleate for metabolic analysis in coronary effluent. Hearts were also monitored for output, heart rate, &amp; oxygen uptake. Results show function was similar across groups, but oxygen consumption decreased 20% with HF. Glucose oxidation was increased in HF, but increased less in HF‐SAT. Fatty acid oxidation was increased in both SAT groups. Lower oxygen consumption &amp; increased glucose utilization suggests less aerobic metabolism, in agreement with literature on HF. Lower elevations of glucose oxidation in the HF‐SAT group suggests altered metabolism is less pronounced with high fat, further supported by the elevated rates of fatty acid oxidation in the HF‐SAT group. Results suggest high fat is protective of function by maintaining fatty acid metabolism in the heart. (Supported by NHBLI HL‐081857 &amp; AHA‐0535361N).

Reactive Oxygen Species Promote Angiogenesis in the Infarcted Rat Heart

Cardiac reactive oxygen species (ROS) production is significantly increased following infarction (MI), particularly at early stage. Herein we sought to determine whether ROS play a role on angiogenesis in the infarcted heart. Experimental MI rats were treated with combined antioxidants, tempol and apocynin, each 120mg/kg/day. Non‐treated MI rats served as controls. Hearts were collected at day 1, 3, 7, 14, 28 and 42. We examined effect of antioxidants on angiogenesis in the infarcted myocardium. Following MI, NADPH oxidase (gp91phox subunit) was significantly increased in the infarcted myocardium at day 3, reached peak at day 7, and gradually declined thereafter. In the infarcted region, existing vessels were lost at day 1 postMI. Newly formed vessels appeared in the border zone as early as day 3, followed by the infarcted myocardium. Vascular density peaked at day 7 and 14, and progressively reduced thereafter. Antioxidants significantly reduced cardiac vascular density at day 7 and 14, but not in the later time points. Thus, angiogenesis is activated in the infarcted myocardium in the first two weeks and becomes quiescent in the late stage of MI, which is temporally and spatially coincident with increased ROS production. Our study also indicates that ROS promote angiogenesis in the infarcted myocardium. Further studies are required to determine the mechanisms responsible for ROS mediated cardiac angiogenesis.

Estrogen receptor α supports cardiomyocytes indirectly through post-infarct cardiac c-kit+ cells

Despite previous studies demonstrating a cardioprotective role of estradiol via its estrogen receptor (ER)α, the underlying mechanisms remain unclear. Here we aimed to define ERα-involved mechanisms against cardiac injury. Seven days after myocardial infarction in male rats, cardiac ERα was upregulated in post-infarct cardiac c-kit+ cells accumulating in periinfarct myocardium as shown by Western blotting and immunofluorescence staining. Further, we isolated post-infarct cardiac c-kit+ cell population by modified magnetic activated cell sorting (MACS) and fluorescence activated cell sorting (FACS), and confirmed predominant ERα expression in this post-infarct cardiac c-kit+ cell population by real-time PCR. These post-infarct cardiac c-kit+ cells, characterized by upregulated transcription factors implicated in cardiogenic differentiation (GATA-4, Notch-2) and genes required for self-renewal (Tbx3, Akt), maintained a stable phenotype in vitro for more than 3 months. ERα stimulation supported proliferation but prevented differentiation of undifferentiated myoblast cells. When adult myocytes isolated from infarcted rat hearts were co-cultured with post-infarct cardiac c-kit+ cells, ERα stimulation inhibited apoptosis and enhanced survival of these myocytes. These findings suggest that cardiac ERα supports survival of cardiomyocytes through post-infarct cardiac c-kit+ cells, which may contribute to cardioprotection against cardiac injury.

Myocardial oxygenation and functional recovery in infarct rat hearts transplanted with mesenchymal stem cells

Stem cell therapy for myocardial tissue repair is limited by the poor survival of transplanted cells, possibly because of inadequate supply of oxygen and nutrients. The purpose of this study was to assess the oxygenation level and functional recovery after allogenic transplantation of mesenchymal stem cells (MSC) in a rat model of myocardial infarction (MI). Myocardial oxygen tension (Po(2)) was measured by electron paramagnetic resonance oximetry using an implantable oxygen-sensing spin probe (OxySpin). MSCs incubated with OxySpins showed substantial uptake of the probe without affecting its oxygen sensitivity or calibration. The cells internalized with OxySpins were able to differentiate into osteogenic, adipogenic, cardiomyocyte, and endothelial cell lineages. The labeled cells tested positive for CD44 and CD29 markers and negative for the hematopoietic markers CD14 and CD45. For the in vivo studies, MI was induced in rats by permanently ligating the left anterior descending coronary artery. MSCs with OxySpins were transplanted in the infarct region of hearts. A significant increase in Po(2) was observed in the MSC group compared with the untreated MI group (18.1 +/- 2.6 vs. 13.0 +/- 1.8 mmHg, n = 4, P < 0.05) at 4 wk after transplantation. Echocardiography showed a significant improvement in ejection fraction and fraction shortening, which inversely correlated with the magnitude of fibrosis in the treated hearts. The cell-transplanted hearts also showed an increase in vascular endothelial growth factor level and capillary density in the infarct region. The study established our ability to measure and correlate changes in myocardial tissue oxygenation with cardiac function in infarcted rat hearts treated with MSCs.

Fate of undifferentiated mouse embryonic stem cells within the rat heart: role of myocardial infarction and immune suppression

It has recently been suggested that the infarcted rat heart microenvironment could direct pluripotent mouse embryonic stem cells to differentiate into cardiomyocytes through an in situ paracrine action. To investigate whether the heart can function as a cardiogenic niche and confer an immune privilege to embryonic stem cells, we assessed the cardiac differentiation potential of undifferentiated mouse embryonic stem cells (mESC) injected into normal, acutely or chronically infarcted rat hearts. We found that mESC survival depended on immunosuppression both in normal and infarcted hearts. However, upon Cyclosporin A treatment, both normal and infarcted rat hearts failed to induce selective cardiac differentiation of implanted mESC. Instead, teratomas developed in normal and infarcted rat hearts 1 week and 4 weeks (50% and 100%, respectively) after cell injection. Tight control of ESC commitment into a specific cardiac lineage is mandatory to avoid the risk of uncontrolled growth and tumourigenesis following transplantation of highly plastic cells into a diseased myocardium.

Erythropoietin Enhances Arterioles More Significantly Than it Does Capillaries in an Infarcted Rat Heart Model

Erythropoietin (Epo) is a hormone which regulates erythrocyte production. It has recently become known that Epo enhances angiogenesis. However, since shear stress is an initiator of arteriogenesis, this increase with Epo may be due to increased shear stress from erythrocytosis. To clarify this, we compared the effects of Epo on both angiogenesis and arteriogenesis. Myocardial infarction was induced by LAD ligation in Wistar rats (Epo, G-CSF and control). Epo (1,000 IU/kg) was administered immediately after ligation of the LAD. G-CSF was administered at 100 microg/kg/day for 5 days after the coronary ligation. Four weeks later, coronary angiography was performed using synchrotron radiation coronary micro-angiography with a Langendorff apparatus. The number of vessels was investigated by microscopy. The numbers of capillaries and arterioles (> 100 microm in diameter) were measured. Microscopical examination: Capillary density in the twilight zone was 95 +/- 19 in the control group, 126 +/- 24 in the G-CSF group, and 142 +/- 32 in the EPO group (control versus Epo: P < 0.005, control versus G-CSF: P < 0.05). Arteriole numbers were 4.3 +/- 0.2 in the control group, 6.9 +/- 1.0 in the G-CSF, and 11.8 +/- 0.6 in the Epo group (control versus Epo: P < 0.00001, G-CSF versus Epo: P < 0.00001, control versus G-CSF: P < 0.00001). The ratios of arterioles and capillaries were 0.048 +/- 0.013 in the control group, 0.057 +/- 0.016 in the G-CSF group, and 0.088 +/- 0.019 in the Epo group (control versus Epo: P < 0.0005, G-CSF versus Epo: P < 0.05). Angiography: The number of crossing arterioles in the 2 mm lattice was 5.4 +/- 1.7 in the Epo group and 3.8 +/-0.4 in the control group (P < 0.05). The gray scale values for the evaluation of capillaries was 128 +/- 3.7 and 119 +/- 2.1 in the Epo and control groups, respectively (P < 0.00005). Epo enhanced arterioles more significantly than it did capillaries in this infarcted rat heart model.

Dietary (n-3) Long-Chain Polyunsaturated Fatty Acids Inhibit Ischemia and Reperfusion Arrhythmias and Infarction in Rat Heart Not Enhanced by Ischemic Preconditioning

Ischemic preconditioning (IPC) and (n-3) PUFA are both cardioprotective. This study compared effects of dietary fish oil, IPC, and their interactions on heart function and injury during myocardial ischemia and reperfusion. Male Wistar rats were fed diets containing 10% wt:wt fat comprising either 7% high-docosahexaenoic acid (DHA) [22:6(n-3)] tuna fish oil + 3% olive oil [(n-3) PUFA]; 5% sunflower seed oil + 5% olive oil [(n-6) PUFA]; or 7% beef tallow + 3% olive oil [saturated fat (SF)] for 6 wk. In control experiments, isolated perfused hearts were subjected to 30-min regional ischemia and reperfused for 120 min. The IPC hearts were subjected to 3 cycles of 5-min global ischemia before the ischemia and reperfusion. Control (n-3) PUFA hearts had significantly lower heart rate, coronary flow, end diastolic pressure, maximum relaxation rate, and ischemic and reperfusion arrhythmias. In reperfusion, they had greater developed pressure and maximum relaxation rate and smaller infarct (10.9 ± 0.6% ischemic zone, n = 6) than (n-6) PUFA (47.4 ± 0.3%, n = 6) or SF (50.3 ± 0.3%, n = 6). Compared with control, IPC significantly improved heart function and reduced infarct in (n-6) PUFA (11.8 ± 0.4%, n = 6) and SF hearts (13.1 ± 0.1%, n = 6). Heart function and infarct [(n-3) PUFA 9.6 ± 0.1%, n = 6] did not differ among dietary IPC groups. Arrhythmias, significantly reduced by IPC in (n-6) PUFA and SF hearts, were significantly lower in (n-3) PUFA IPC hearts. Dietary fish oil induces a form of preconditioning, nutritional preconditioning, limiting ischemic cardiac injury, and myocardial infarction and endows cardioprotection as powerful as IPC, which provides no additional protection in (n-3) PUFA hearts.

Endothelial Cell Coculture Within Tissue-Engineered Cardiomyocyte Sheets Enhances Neovascularization and Improves Cardiac Function of Ischemic Hearts

Regenerative therapies, including myocardial tissue engineering, have been pursued as a new possibility to repair the damaged myocardium, and previously the transplantation of layered cardiomyocyte sheets has been shown to be able to improve cardiac function after myocardial infarction. We examined the effects of promoting neovascularization by controlling the densities of cocultured endothelial cells (ECs) within engineered myocardial tissues created using our cell sheet-based tissue engineering approach. Neonatal rat cardiomyocytes were cocultured with GFP-positive rat-derived ECs on temperature-responsive culture dishes. Cocultured ECs formed cell networks within the cardiomyocyte sheets, which were preserved during cell harvest from the dishes using simple temperature reduction. We also observed significantly increased in vitro production of vessel-forming cytokines by the EC-positive cardiac cell sheets. After layering of 3 cardiac cell sheets to create 3-dimensional myocardial tissues, these patch-like tissue grafts were transplanted onto infarcted rat hearts. Four weeks after transplantation, recovery of cardiac function could be significantly improved by increasing the EC densities within the engineered myocardial tissues. Additionally, when the EC-positive cardiac tissues were transplanted to myocardial infarction models, we observed significantly greater numbers of capillaries in the grafts as compared with the EC-negative cell sheets. Finally, blood vessels originating from the engineered EC-positive cardiac tissues bridged into the infarcted myocardium to connect with capillaries of the host heart. In vitro engineering of 3-dimensional cardiac tissues with preformed EC networks that can be easily connected to host vessels can contribute to the reconstruction of myocardial tissue grafts with a high potential for cardiac function repair. These results indicate that neovascularization can contribute to improved cardiac function after the transplantation of engineered cardiac tissues.

Novel MRI method to detect altered left ventricular ejection and filling patterns in rodent models of disease.

The aim of this study was to determine whether high-temporal-resolution (HTR) cardiac cine-MRI could be used to identify subtle alterations in contractility and diastolic function in rodent models of disease. Following standard 45-min in vivo MRI measurements of left ventricular (LV) volumes, a single mid-ventricular slice was selected for 3-min HTR imaging. Cavity volume was measured every 2.4 ms, yielding approximately 60 images through the cardiac cycle. From these images, peak ejection and filling rates were calculated and two separate filling phases (comparable with the early (E) and late (A) phases of a Doppler echocardiogram) were identified during diastole. Repeated HTR imaging of the same animals on sequential days indicated reproducibility of E'/A' ratios of 11%. In chronically infarcted rat hearts, HTR imaging revealed lower peak ejection rates (PERs), peak early filling rates (E') and E'/A' ratios, and higher peak late filling rates (A') than in sham-operated rats. Diabetic db/db mouse hearts had the same function as controls when using standard cine-MRI, yet HTR imaging identified significantly lower PERs, early filling rates and E'/A' ratios in diabetic mouse hearts. In conclusion, the HTR MRI technique revealed changes in function that were below the limits of detection of standard cine-MRI.

Bone marrow-derived stromal cells home to and remain in the infarcted rat heart but fail to improve function: an in vivo cine-MRI study

Basic and clinical studies have shown that bone marrow cell therapy can improve cardiac function following infarction. In experimental animals, reported stem cell-mediated changes range from no measurable improvement to the complete restoration of function. In the clinic, however, the average improvement in left ventricular ejection fraction is around 2% to 3%. A possible explanation for the discrepancy between basic and clinical results is that few basic studies have used the magnetic resonance (MR) imaging (MRI) methods that were used in clinical trials for measuring cardiac function. Consequently, we employed cine-MR to determine the effect of bone marrow stromal cells (BMSCs) on cardiac function in rats. Cultured rat BMSCs were characterized using flow cytometry and labeled with iron oxide particles and a fluorescent marker to allow in vivo cell tracking and ex vivo cell identification, respectively. Neither label affected in vitro cell proliferation or differentiation. Rat hearts were infarcted, and BMSCs or control media were injected into the infarct periphery (n = 34) or infused systemically (n = 30). MRI was used to measure cardiac morphology and function and to determine cell distribution for 10 wk after infarction and cell therapy. In vivo MRI, histology, and cell reisolation confirmed successful BMSC delivery and retention within the myocardium throughout the experiment. However, no significant improvement in any measure of cardiac function was observed at any time. We conclude that cultured BMSCs are not the optimal cell population to treat the infarcted heart.

Mechanisms by Which Late Coronary Reperfusion Mitigates Postinfarction Cardiac Remodeling

Although recanalization of the infarct-related artery late after myocardial infarction (MI) is known to reduce both cardiac remodeling and mortality, the mechanisms responsible are not yet fully understood. We compared infarcted rat hearts in which the infarct-related coronary artery was opened 24 hours after infarction (late reperfusion [LR] group) with those having a permanently occluded artery. Left ventricular dilatation and dysfunction were significantly mitigated in the LR group 1, 2, and 4 weeks post-MI. Attributable, in large part, to the greater number of cells present, the infarcted wall was significantly thicker in the LR group, which likely reduced wall stress and mitigated cardiac dysfunction. Granulation tissue cell proliferation was increased to a greater degree in the LR group 4 days post-MI, whereas the incidence of apoptosis was significantly lower throughout the subacute stage (4 days, 1 week, and 2 weeks post-MI), further suggesting preservation of granulation tissue cells contributes to the thick, cell-rich scar. Functionally, myocardial debris was more rapidly removed from the infarcted areas in the LR group during subacute stages, and stouter collagen was more rapidly synthesized in those areas. Direct acceleration of Fas-mediated apoptosis by hypoxia was confirmed in vitro using infarct tissue-derived myofibroblasts. In salvaged cardiomyocytes, degenerative changes, but not apoptosis, were mitigated in the LR group, accompanied by restoration of GATA-4 and sarcomeric protein expression. Along with various mechanisms proposed earlier, the present findings appear to provide an additional pathophysiological basis for the benefits of late reperfusion.