Neovascularization of ischemic myocardium by newly isolated tannins prevents cardiomyocyte apoptosis and improves cardiac function

During remodeling progress post myocardial infarction, the contribution of neoangiogenesis to the infarct-bed capillary is insufficient to support the greater demands of the hypertrophied but viable myocardium resulting in further ischemic injury to the viable cardiomyocytes at risk. Here we reported the bio-assay-guided identification and isolation of angiogenic tannins (angio-T) from Geum japonicum that induced rapid revascularization of infarcted myocardium and promoted survival potential of the viable cardiomyocytes at risk after myocardial infarction. Our results demonstrated that angio-T displayed potent dual effects on up-regulating expression of angiogenic factors, which would contribute to the early revascularization and protection of the cardiomyocytes against further ischemic injury, and inducing antiapoptotic protein expression, which inhibited apoptotic death of cardiomyocytes in the infarcted hearts and limited infarct size. Echocardiographic studies demonstrated that angio-T-induced therapeutic effects on acute infarcted myocardium were accompanied by significant functional improvement by 2 days after infarction. This improvement was sustained for 14 days. These therapeutic properties of angio-T to induce early reconstitution of a blood supply network, prevent apoptotic death of cardiomyocytes at risk, and improve heart function post infarction appear entirely novel and may provide a new dimension for therapeutic angiogenesis medicine for the treatment of ischemic heart diseases.     

Dynamic induction of ADAMTS1 gene in the early phase of acute myocardial infarction

Extracellular matrix (ECM)-degrading enzymes such as matrix metalloproteases (MMPs) play an essential role in the repair of infarcted tissue, which affects ventricular remodeling after myocardial infarction. ADAMTS1 (A disintegrin and metalloprotease with thrombospondin motifs), a newly discovered metalloprotease, was originally cloned from a cancer cell line, but little is known about its contribution to disease. To test the hypothesis that ADAMTS1 appears in infarcted myocardial tissue, we examined ADAMTS1 mRNA expression in a rat myocardial infarction model by Northern blotting, real-time RT-PCR and in situ hybridization. Normal endothelium expressed little ADAMTS1 mRNA, while normal myocardium expressed no detectable ADAMTS1 mRNA. Up-regulation of ADAMTS1 was demonstrated by Northern blot analysis and real-time RT-PCR at 3 h after coronary artery ligation. In situ hybridization revealed strong ADAMTS1 mRNA signals in the endothelium and myocardium in the infarcted heart, mainly in the infarct zone, at 3 h after myocardial infarction. The rapid and transient up-regulation of the ADAMTS1 gene in the ischemic heart was distinct from the regulatory patterns of other MMPs. Our study demonstrated that the ADAMTS1 gene is a new early immediate gene expressed in the ischemic endothelium and myocardium.     

Augmentation of autophagy by mTOR-inhibition in myocardial infarction: When size matters

The extent of adverse myocardial remodeling contributes essentially to the prognosis after myocardial infarction (MI). Currently, therapeutic strategies that inhibit remodeling are limited to inhibition of neurohumoral activation. mTOR-dependent signaling mechanisms are centrally involved in the myocardial remodeling process. There exists a controversy as to whether autophagy is beneficial in the setting of myocardial infarction. We now provide evidence that induction of autophagy by inhibition of mTOR with everolimus (RAD) prevents adverse left ventricular remodeling and limits infarct size following myocardial infarction. mTOR inhibition increases autophagy and concomitantly decreases proteasome activity especially in the border zone of the infarcted myocardium. The induction of autophagy via mTOR inhibition is a novel potential therapeutic approach to limit infarct size and to attenuate adverse left ventricular remodeling following MI.     

Repair of Ischemic Heart Disease with Novel Bone Marrow-Derived Multipotent Stem Cells

Congestive heart failure is a growing, worldwide epidemic. The major causes of heart failure are related to irreversible damage resulting from myocardial infarction (heart attack). The long-standing axiom has been that the myocardium has a limited capacity for self-repair or regeneration; and the irreversible loss of cardiac muscle and accompanying contraction and fibrosis of myocardial scar tissue, sets into play a series of events, namely, progressive ventricular remodeling of nonischemic myocardium that ultimately leads to progressive heart failure. The loss of cardiomyocyte survival cues is associated with diverse pathways for heart failure, underscoring the importance of maintaining the number of viable cardiomyocytes during heart failure progression. Currently, no medication or procedure used clinically has shown efficacy in replacing the myocardial scar with functioning contractile tissue. Therefore, given the major morbidity and mortality associated with myocardial infarction and heart failure, new approaches have been sought to address the principal pathophysiologic deficits responsible for these conditions, resulting from the loss of cardiomyocytes and viable blood vessels. Recently, the identification of stem cells from bone marrow capable of contributing to tissue regeneration has ignited significant interest in the possibility that cell therapy could be employed therapeutically for the repair of damaged myocardium. In this review, we will discuss the currently available bone marrow-derived stem progenitor cells for myocardial repair and focus on the advantages of using recently identified novel bone marrow-derived multipotent stem cells (BMSC)     

Mesenchymal stem cells modified with angiopoietin-1 improve remodeling in a rat model of acute myocardial infarction

We used human angiopoietin-1 (hAng1)-modified mesenchymal stem cells (MSCs) to treat acute myocardial infarction (AMI) in rats. The hAng1 gene was transfected into cultured rat MSCs using an adenoviral vector. Five million hAng-transfected MSCs (MSC(Ang1)) or green fluorescent protein transfected MSCs (MSC(GFP)) or PBS only (PBS group) were injected intramyocardially into the inbred Lewis rat hearts immediately after myocardial infarction. MSC(Ang1) survived in the infarcted myocardium, and expressed hAng1 at both mRNA and protein levels. The vascular density was higher in the MSC(Ang1) and MSC(GFP) groups than in the PBS group. The measurements of infarcted ventricular wall thickness, infarction area, and left ventricular diameter indicated that heart remodeling was inhibited and heart function was improved in both the MSC(Ang1) and MSC(GFP) groups. However, in contrast to the MSC(GFP) group, the MSC(Ang1) group showed enhanced angiogenesis and arteriogenesis (by 11-35%), infarction area was reduced by 30% and the left ventricular wall was 46% thicker (P<0.05). The results indicated that hAng1-modified MSCs improved heart function, followed by angiogenic effects in salvaging ischemic myocardium and reduced cardiac remodeling.     

Implanted bone marrow-derived mesenchymal stem cells fail to metabolically stabilize or recover electromechanical function in infarcted hearts

Mesenchymal stem cells (MSCs) have been used with success in several clinical applications for clinical treatment of ischemic hearts. However, the reported effects of MSC-based therapy on myocardial infarction (MI) are inconsistent. In particular, the preventive effects of MSC-based therapy on arrhythmic sudden death and metabolic disorders after infarction remain controversial. Here, we investigated the effects of MSCs on reverse remodeling in an infarcted myocardium, and found that MSC-therapy failed to achieve the complete regeneration of infarcted myocardium. Histological analyses showed that although infarct size and interstitial fibrosis induced by MI recovered significantly after MSC treatment, these improvements were marginal, indicating that a significant amount of damaged tissue was still present. Furthermore, transplanted MSCs had slight anti-apoptotic and anti-inflammatory effects in MSC-implanted regions and no significant improvements in cardiac function were observed, suggesting that naïve MSCs might not be the right cell type to treat myocardial infarction. Furthermore, small ion profiling using ToF-SIMS revealed that the metabolic stabilization provided by the MSCs implantation was not significant compared to the sham group. Together, these results indicate that pretreatment of MSCs is needed to enhance the benefits of MSCs, particularly when MSCs are used to treat arrhythmogenicity and metabolically stabilize infarcted myocardium.     

Progressive left ventricular remodeling and apoptosis late after myocardial infarction in mouse heart

We tested the hypothesis that left ventricular (LV) remodeling late after myocardial infarction (MI) is associated with myocyte apoptosis in myocardium remote from the infarcted area and is related temporally to LV dilation and contractile dysfunction. One, four, and six months after MI caused by coronary artery ligation, LV volume and contractile function were determined using an isovolumic balloon-in-LV Langendorff technique. Apoptosis and nuclear morphology were determined by terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) and Hoechst 33258 staining. Progressive LV dilation 1-6 mo post-MI was associated with reduced peak LV developed pressure (LVDP). In myocardium remote from the infarct, there was increased wall thickness and expression of atrial natriuretic peptide mRNA consistent with reactive hypertrophy. There was a progressive increase in the number of TUNEL-positive myocytes from 1 to 6 mo post-MI (2.9-fold increase at 6 mo; P < 0. 001 vs. sham). Thus LV remodeling late post-MI is associated with increased apoptosis in myocardium remote from the area of ischemic injury. The frequency of apoptosis is related to the severity of LV dysfunction.     

Intracoronary delivery of autologous bone marrow mononuclear cells radiolabeled by 18F-fluoro-deoxy-glucose: tissue distribution and impact on post-infarct swine hearts

Intracoronary injection of the bone marrow-derived mononuclear cells (MNCs) is emerging as a potentially novel therapy for ischemic heart failure. This study was aimed at assessing the efficacy of intracoronary MNC delivery in the myocardium. The in vivo distribution and myocardial homing of intracoronarily delivered MNCs in experimental Chinese swine with acute myocardial infarction (AMI) created by occlusion of left anterior descending (LAD) coronary artery for 90 min. MNCs radiolabeled with 18F-fluoro-deoxy-glucose (18F-FDG) were delivered using a coronary catheter into the infarct-related coronary artery 1 week after AMI. Dual-nuclide single photon emission computed tomography (SPECT) revealed that 1 h after cell infusion, 6.8 +/- 1.8% of 18F-FDG-labeled MNCs occurred in the infarcted myocardium with the remaining activity found primarily in the liver and spleen. In the heart, MNCs were detected predominantly in the under-perfused myocardium. The infused cells retained in the hearts at a rate highly correlated with the under-perfused lesional sizes. Pathological examination further demonstrated that 6 weeks after infusion, compared to controls, the hearts receiving MNCs exhibited less fibrosis and inflammatory infiltrate, more viable tissue, and higher vascular density. Cardiac function was significantly improved in the MNC-infused hearts. Thus, 18F-FDG labeling and dual-nuclide SPECT imaging is capable of monitoring in vivo distribution and homing of MNCs after intracoronary infusion. MNC coronary delivery may improve cardiac function and positive ventricular remodeling in the heart with AMI.     

Influence of gender on the response to hemodynamic overload after myocardial infarction

After myocardial infarction (MI), the left ventricle (LV) undergoes ventricular remodeling characterized by progressive global dilation, infarct expansion, and compensatory hypertrophy of the noninfarcted myocardium. Little attention has been given to the response of remodeling myocardium to additional hemodynamic overload. Studies have indicated that gender may influence remodeling and the response to both MI and hemodynamic overload. We therefore determined 1) structural and function consequences of superimposing hemodynamic overload (systemic hypertension) on remodeling myocardium after a MI and 2) the potential influence of gender on this remodeling response. Male and female Dahl salt-sensitive and salt-resistant rats underwent coronary ligation, resulting in similar degrees of MI. One week post-MI, all rats were placed on a high-salt diet. Four groups were then studied 4 wk after initiation of high-salt feeding: MI female, MI female + hypertension, MI male, and MI male + hypertension. Hypertension-induced pressure overload resulted in additional comparable degrees of myocardial hypertrophy in both females and males. In females, hypertension post-MI resulted in concentric hypertrophy with no additional cavity dilation and no measurable scar thinning. In contrast, in males, hypertension post-MI resulted in eccentric hypertrophy, further LV cavity dilation, and scar thinning. Physiologically, concentric hypertrophy in post-MI hypertensive females resulted in elevated contractile function, whereas eccentrically hypertrophied males had no such increase. Female gender influences favorably the remodeling and physiological response to hemodynamic overload after large MI.     

Apoptosis at a distance: remote activation of caspase-3 occurs early after myocardial infarction

Objective: After an acute myocardial infarction, the viable myocardium remote from the infarct zone is subjected to ventricular remodeling. Besides hypertrophy, processes of apoptosis may contribute to these remodeling processes. Reports on apoptosis in this area have been doubted because they were mainly based on in-situ nick-end DNA labeling (TUNEL) measurements, with questionable specifity. Moreover, the time course of initiation of these processes has not been characterized. Therefore the goals of this study were to (1) reliably determine if in the remote area of the infarcted heart apoptosis may be initiated using highly specific biochemical markers and (2) evaluate the time course of such an activation. Methods: A well-defined model, regional myocardial infarction induced by ligation of the left anterior coronary artery in rats in vivo, was used. Heart and lung wet weights, the left ventricular end-diastolic pressure (LVEDP), and the serum level of the atrial natriuretic propeptide (proANP) were determined from 1 day up to 4 weeks as indicators of developing heart failure. In transmural biopsies from the non-ischemic left ventricular wall of the infarcted heart, the activation of caspase-3, the bcl-2/bax ratio (Western blot analysis), and the DNA laddering (LM-PCR) were determined. Results: Although heart- and lung weights did not increase before 1 week after infarction, proANP levels were elevated already 1 day after myocardial infarction suggesting early sub-clinical heart failure. The activity of caspase-3 increased significantly to 160± 20% compared to sham operated controls as early as 1 day after ligation and remained elevated over the entire time course. In parallel, the bcl-2/bax ratio shifted toward the pro-apoptotic bax. Moreover, these clear and specific biochemical indicators of apoptosis in the remote area of the infarcted heart were paralleled by the fragmentation of genomic DNA. Conclusion: These data demonstrate that apoptotic markers are activated in the surviving zone of the heart remote from the infarct area as early as 1 day after myocardial infarction with persistence for up to 4 weeks. This activation coincides with early markers of heart failure. The exact regulation of this apoptotic process remains to be elucidated. Parts of this study were presented at the Annual Meetings of the American College of Cardiology 2002.     

Temporal and spatial characteristics of apoptosis in the infarcted rat heart

Following myocardial infarction (MI), tissue repair/remodeling occurs in both the infarcted and noninfarcted myocardium. Apoptosis has been demonstrated to play an important role in these processes. In the present study, we sought to determine the temporal and spatial characteristics of apoptosis in the infarcted heart as well as to identify cells undergoing programmed cell death at different stages of repair/remodeling and their relationship to the expression of anti-/pro-apoptotic genes following MI. Our study has shown that apoptosis appears in both infarcted and noninfarcted myocardium, and cells undergoing apoptosis depend on the stage of healing. In the infarcted myocardium, apoptosis contributes to the loss of cardiomyocytes during the early stage of healing, elimination of inflammatory cells during the inflammatory phase of healing, and reduction of myofibroblasts with the fibrogenic phase of repair in the infarcted myocardium. In noninfarcted myocardium, cardiomyocyte apoptosis was observed from day 3 to 28 postMI. Cardiac apoptosis following MI is correlated with the increase of Bax expression.     

Stable benefit of embryonic stem cell therapy in myocardial infarction

Conventional therapies for myocardial infarction attenuate disease progression without contributing significantly to repair. Because of the capacity for de novo cardiogenesis, embryonic stem cells are considered a potential source for myocardial regeneration, yet limited information is available on their ultimate therapeutic value. We treated infarcted rat hearts with CGR8 embryonic stem cells preexamined for cardiogenicity, serially probed left ventricular function, and determined final pathological outcome. Stem cell delivery generated new cardiomyocytes of embryonic stem cell origin that integrated with host myocardium within infarct regions. This resulted in a functional benefit within 3 wk that remained sustained over 12 wk of continuous follow-up and included a vigorous inotropic response to beta-adrenergic challenge. Integration of stem cell-derived cardiomyocytes was associated with normalized ventricular architecture, little scar, and a decrease in signs of myocardial necrosis. In contrast, sham-treated infarcted hearts exhibited ventricular cavity dilation and aneurysm formation, poor ventricular function, and a lack of response to beta-adrenergic stimulation. No evidence of graft rejection, ectopy, sudden cardiac death, or tumor formation was observed after therapy. These findings indicate that embryonic stem cells, through differentiation within the host myocardium, can contribute to a stable beneficial outcome on contractile function and ventricular remodeling in the infarcted heart.     

Remodeling in myocardium adjacent to an infarction in the pig left ventricle

Changes in the structure of the "normal" ventricular wall adjacent to an infarcted area involve all components of the myocardium (myocytes, fibroblasts and the extracellular matrix, and the coronary vasculature) and their three-dimensional structural relationship. Assessing changes in these components requires tracking material markers in the remodeling tissue over long periods of time with a three-dimensional approach as well as a detailed histological evaluation of the remodeled structure. The purpose of the present study was to examine the hypotheses that changes in the tissue adjacent to an infarct are related to myocyte elongation, myofiber rearrangement, and changes in the laminar architecture of the adjacent tissue. Three weeks after myocardial infarction, noninfarcted tissue adjacent to the infarct remodeled by expansion along the direction of the fibers and in the cross fiber direction. These changes are consistent with myocyte elongation and myofiber rearrangement (slippage), as well as a change in cell shape to a more elliptical cross section with the major axis in the epicardial tangent plane, and indicate that reorientation of fibers either via "cell slippage" or changes in orientation of the laminar structure of the ventricular wall are quantitatively important aspects of the remodeling of the normally perfused myocardium.     

Quantitative MR measurements of regional and global left ventricular function and strain after intramyocardial transfer of VM202 into infarcted swine myocardium

Previous studies have shown the beneficial effects of the hepatocyte growth factor (HGF) gene on myocardial perfusion and infarction size but not on the regional strain in relationship to global left ventricular function. A noninvasive magnetic resonance (MR) study was performed to determine the effect of a new HGF gene, VM202, expressing two isoforms of HGF, on regional and global left ventricular function. Pigs (8/group) were divided into three groups: 1) controls without infarction; 2) reperfused, infarcted controls; and 3) infarcted, treated (1 h after reperfusion) with VM202 injected at eight sites. Cine, tagging, and delayed enhancement MR images were acquired at 3 and 50 +/- 3 days after infarction. At 50 days, ejection fraction in infarcted, treated animals increased (38 +/- 1% to 47 +/- 2%, P < 0.01) to the level of controls without infarction (52 +/- 1%, P = 0.16) but decreased in infarcted controls (41 +/- 1% to 37 +/- 1%, P < 0.05). Two-dimensional strain improved in remote, peri-infarcted, and infarcted myocardium. Furthermore, the infarction size was smaller in infarcted, treated animals (7.0 +/- 0.5%) compared with infarcted controls (13.2 +/- 1.6%, P < 0.05). Histopathology showed a lack of hypertrophy in myocytes in peri-infarcted and remote myocardium and the formation of islands/peninsulas of myocytes in infarcted, treated animals but not in infarcted controls. In conclusion, the plasmid HGF gene caused a near complete recovery of ejection fraction and improved the radial and circumferential strain of remote, peri-infarcted, and infarcted regions within 50 days. These beneficial effects may be explained by the combined effects of a speedy and significant infarct resorption and island/peninsulas of hypertrophied myocytes within the infarcted territory but not by compensatory hypertrophy. The combined use of cine and tagging MR imaging provides valuable information on the efficacy of gene therapy.     

Granulocyte colony-stimulating factor treatment enhances the efficacy of cellular cardiomyoplasty with transplantation of embryonic stem cell-derived cardiomyocytes in infarcted myocardium

We tested the hypothesis that granulocyte colony-stimulating factor (G-CSF) administration would enhance the efficacy of cellular cardiomyoplasty with embryonic stem (ES) cell-derived cardiomyocytes in infarcted myocardium. Three weeks after myocardial infarction by cryoinjury, Sprague-Dawley rats were randomized to receive either an injection of medium, ES cell-derived cardiomyocyte transplantation, G-CSF administration, or a combination of G-CSF administration and ES cell-derived cardiomyocyte transplantation. Eight weeks after treatment, the cardiac tissue formation, neovascularization, and apoptotic activity in the infarct regions were evaluated by histology and immunohistochemistry. The left ventricular (LV) dimensions and function of the treated heart were evaluated by echocardiography. Transplanted ES cell-derived cardiomyocytes survived and participated in the myocardial regeneration in the infarcted heart. A combination of G-CSF treatment and ES cell-derived cardiomyocyte transplantation significantly promoted angiogenesis and reduced the infarct area and cell apoptosis in the infarcted myocardium compared with ES cell-derived cardiomyocyte transplantation alone. The combination therapy also attenuated LV dilation, as compared with ES cell-derived cardiomyocyte transplantation alone. G-CSF treatment can enhance the efficacy of cellular cardiomyoplasty by ES cell-derived cardiomyocyte transplantation to treat myocardial infarction.     

DITPA stimulates arteriolar growth and modifies myocardial postinfarction remodeling

Myocardial infarction (MI) is characterized by ventricular remodeling, hypertrophy of the surviving myocardium, and an insufficient angiogenic response. Thyroxine is a powerful stimulus for myocardial angiogenesis. Male rats that underwent coronary artery ligation and subsequent MI were given 3,5-diiodothyropropionic acid (DITPA; MI+DITPA group) during a 3-wk period. We evaluated ventricular remodeling using echocardiography and histology and myocardial vessel growth using image analysis. Protein expression was assessed using Western blotting and immunohistochemistry. This study tested the hypothesis that the thyroxine analog DITPA facilitates angiogenesis and influences postinfarction remodeling in the surviving hypertrophic myocardium. The increase in the region of akinesis (infarct expansion) was blunted in the MI+DITPA rats compared with the MI group (3 vs. 21%); the treated rats had smaller percent increases in the left ventricular (LV) volume (64 +/- 14 vs. 95 +/- 12) and the LV volume-to-mass ratio (47 +/- 13 vs. 84 +/- 10) as well as a blunted decrease in ejection fraction (-9 +/- 8 vs. -30 +/- 7%). Arteriolar length density was higher after treatment in the largest (>50% of the free wall) infarcts (64 +/- 3 vs. 43 +/- 7). Angiogenic growth factors [vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF)] and the angiopoietin receptor tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (Tie-2) values were elevated during the first week after infarction. DITPA did not cause additional increases in VEGF or Tie-2 values but did induce an increase in bFGF value after 3 days of treatment. This study provides the first evidence for an anatomical basis, i.e., attenuated ventricular remodeling and arteriolar growth, for improved function attributed to DITPA therapy of the infarcted heart. The favorable influences of DITPA on LV remodeling after large infarction are principally due to border zone preservation.     

Electrotonic remodeling following myocardial infarction in dogs susceptible and resistant to sudden cardiac death.

Passive electrical remodeling following myocardial infarction (MI) is well established. These changes can alter electrotonic loading and trigger the remodeling of repolarization currents, a potential mechanism for ventricular fibrillation (VF). However, little is known about the role of passive electrical markers as tools to identify VF susceptibility post-MI. This study investigated electrotonic remodeling in the post-MI ventricle, as measured by myocardial electrical impedance (MEI), in animals prone to and resistant to VF. MI was induced in dogs by a two-stage left anterior descending (LAD) coronary artery ligation. Before infarction, MEI electrodes were placed in remote (left circumflex, LCX) and infarcted (LAD) myocardium. MEI was measured in awake animals 1, 2, 7, and 21 days post-MI. Subsequently, VF susceptibility was tested by a 2-min LCX occlusion during exercise; 12 animals developed VF (susceptible, S) and 12 did not (resistant, R). The healing infarct had lower MEI than the normal myocardium. This difference was stable by day 2 post-MI (287 +/- 32 Omega vs. 425 +/- 62 Omega, P < 0.05). Significant differences were observed between resistant and susceptible animals 7 days post-MI; susceptible dogs had a wider electrotonic gradient between remote and infarcted myocardium (R: 89 +/- 60 Omega vs. S: 180 +/- 37 Omega). This difference increased over time in susceptible animals (252 +/- 53 Omega at 21 days) due to post-MI impedance changes on the remote myocardium. These data suggest that early electrotonic changes post-MI could be used to assess later arrhythmia susceptibility. In addition, passive-electrical changes could be a mechanism driving active-electrical remodeling post-MI, thereby facilitating the induction of arrhythmias.     

Mesenchymal stem cell injection after myocardial infarction improves myocardial compliance

Cellular therapy for myocardial injury has improved ventricular function in both animal and clinical studies, though the mechanism of benefit is unclear. This study was undertaken to examine the effects of cellular injection after infarction on myocardial elasticity. Coronary artery ligation of Lewis rats was followed by direct injection of human mesenchymal stem cells (MSCs) into the acutely ischemic myocardium. Two weeks postinfarct, myocardial elasticity was mapped by atomic force microscopy. MSC-injected hearts near the infarct region were twofold stiffer than myocardium from noninfarcted animals but softer than myocardium from vehicle-treated infarcted animals. After 8 wk, the following variables were evaluated: MSC engraftment and left ventricular geometry by histological methods, cardiac function with a pressure-volume conductance catheter, myocardial fibrosis by Masson Trichrome staining, vascularity by immunohistochemistry, and apoptosis by TdT-mediated dUTP nick-end labeling assay. The human cells engrafted and expressed a cardiomyocyte protein but stopped short of full differentiation and did not stimulate significant angiogenesis. MSC-injected hearts showed significantly less fibrosis than controls, as well as less left ventricular dilation, reduced apoptosis, increased myocardial thickness, and preservation of systolic and diastolic cardiac function. In summary, MSC injection after myocardial infarction did not regenerate contracting cardiomyocytes but reduced the stiffness of the subsequent scar and attenuated postinfarction remodeling, preserving some cardiac function. Improving scarred heart muscle compliance could be a functional benefit of cellular cardiomyoplasty.     

Impact of elevated uric acid on ventricular remodeling in infarcted rats with experimental hyperuricemia

Hyperuricemia is associated with cardiovascular disease, but it is usually considered a marker rather than a risk factor. Previous studies using uric acid-lowering drugs in normouricemic animals are not suitable to answer the effect of hyperuricemia on ventricular remodeling after myocardial infarction. The purpose of this study was to determine whether hyperuricemia adversely affects ventricular remodeling in infarcted rats with elevated uric acid. Male Wistar rats aged 8 wk were randomly assigned into either vehicle, oxonic acid, oxonic acid + allopurinol, oxonic acid + benzbromarone, oxonic acid + ABT-627, or oxonic acid + tempol for 4 wk starting 24 h after ligation. Postinfarction was associated with increased oxidant production, as measured by myocardial superoxide, isoprostane, xanthine oxidase activity, and dihydroethidium staining. Compared with normouricemic infarcted rats, hyperuricemic infarcted rats had a significant increase of superoxide production (1.7×) and endothelin-1 protein (1.2×) and mRNA (1.4×) expression, which was associated with increased left ventricular dysfunction and enhanced myocardial hypertrophy and fibrosis. These changes were all prevented by treatment with allopurinol. For similar levels of urate lowering, the uricosuric agent benzbromarone had no effect on ventricular remodeling. In spite of equivalent hyperuricemia, the ability of both ABT-627 and tempol to attenuate ventricular remodeling suggested involvement of endothelin-1 and redox pathways. Hyperuricemia is associated with unfavorable ventricular remodeling probably through a superoxide and endothelin-1-dependent pathway. Uric acid lowering without inhibition of superoxide and endothelin-1 may not have an effect on remodeling. Chronic administration of allopurinol, ABT-627, and tempol is associated with attenuated ventricular remodeling.     

Differential effect of myocardial matrix and integrins on cardiac differentiation of human mesenchymal stem cells

Dysregulation of matrix synthesis during myocardial fibrosis in post-infarct ventricular remodeling contributes to ventricular dysfunction. Bone marrow stem cell transplantation prevents functional deterioration following myocardial infarction. However, effect of myocardial extracellular matrix (ECM) on stem cell differentiation is poorly understood. We investigate the role of collagen matrices and integrin system in cardiac differentiation and engraftment of stem cells in infarcted myocardium. Sternum-derived bone marrow mesenchymal stem cells (MSCs) were differentiated into cardiomyocyte-like cells (CLCs). They were characterized using RT-PCR, immunofluorescence, flow cytometry and functional integrin neutralization assays. CLCs were injected into peri-infarct borders of injured myocardium of Wistar rats one week following left anterior descending (LAD) artery ligation. Cardiac function was analyzed via pressure-volume relationships. Cardiac differentiated CLCs displayed collagen V specificity, which was absent in undifferentiated MSCs. Collagen V, but not collagen I matrix, promoted attachment, proliferation and cardiac differentiation of CLCs. In contrast to β₁, α_v integrin contributed minimally in the attachment of CLCs on collagen matrices. However, inhibition of α_vβ_3, but not α₂β₁ integrin, selectively attenuated troponin T, sarcomeric α-actin and ryanodine 2 receptor gene expression in CLCs. Both MSC and CLC transplantation prevented chamber dilatation and improved contractile function. However, systolic activity in MSC transplanted animals was accompanied by heightened wall stress as demonstrated by elevated myocardial end-diastolic pressure and prolonged tissue relaxation time. Localization of CLCs in the vicinity of collagen V-expressing myofibers promoted their integration into cardiac syncytium. CLCs may facilitate hemodynamic recovery by preserving tissue elasticity in the peri-infarct borders that sustains contractile efficiency for functional recovery in an actively remodeling infarcted myocardium.