Intracardiac transplantation of a mixed population of bone marrow cells improves both regional systolic contractility and diastolic relaxation

Evaluation of Left Ventricular Regional Systolic Function Using Tissue Doppler Echocardiography After Mesenchymal Stem Cell Transplantation in Rabbits With Myocardial Infarction

OBJECTIVES

The aim of this work was to assess left ventricular (LV) regional systolic function in rabbits with myocardial infarction after allogeneic mesenchymal stem cell (MSC) transplantation using quantitative tissue velocity imaging.

METHODS

Thirty New Zealand White rabbits were assigned into 3 groups randomly: a sham-operated group (n = 10), a myocardial infarction (MI) group (n = 10), and a MSC transplantation group (n = 10). Mesenchymal stem cells (1 × 10(7) in total) were delivered into 5 spots around the left anterior descending artery (LAD) blood supply area via direct intramyocardial injections 1 hour after LAD ligation in the MSC group, whereas the MI group received the same amount of phosphate-buffered saline injections. Echocardiography was performed before LAD ligation and 1 day and 2 weeks after MSC transplantation, respectively. The peak systolic velocity (Vs) of each LV wall segment was measured. The myocardial slices were harvested for histologic staining after the last echocardiographic examination.

RESULTS

The velocity curves for the LV myocardium before LAD ligation had a trend showing that the Vs value decreased gradually from basal to apical segments. The Vs values for the LV segments around the infarcted area in the MSC group decreased significantly compared with the sham group (P < .05) 1 day after MSC transplantation, whereas they increased significantly 2 weeks after MSC transplantation compared with 1 day after LAD ligation (P < .05).

CONCLUSIONS

This study demonstrates that quantitative tissue velocity imaging may provide a promising approach to quantitatively assessing LV regional systolic function before and after MSC transplantation.

Mechanisms of bone marrow-derived cell therapy in ischemic cardiomyopathy with left ventricular assist device bridge to transplant

BACKGROUND

Clinical trials report improvements in function and perfusion with direct injection of bone marrow cells into the hearts of patients with ischemic cardiomyopathy. Preclinical data suggest these cells improve vascular density, which would be expected to decrease fibrosis and inflammation.

OBJECTIVES

The goal of this study was to test the hypothesis that bone marrow stem cells (CD34+) will improve histological measurements of vascularity, fibrosis, and inflammation in human subjects undergoing left ventricular assist device (LVAD) placement as a bridge to cardiac transplantation.

METHODS

Subjects with ischemic cardiomyopathy who were scheduled for placement of an LVAD as a bridge to transplantation underwent bone marrow aspiration the day before surgery; the bone marrow was processed into cell fractions (bone marrow mononuclear cells, CD34+, and CD34-). At LVAD implantation, all fractions and a saline control were injected epicardially into predetermined areas and each injection site marked. At the time of transplantation, injected areas were collected. Data were analyzed by paired Student t test comparing the effect of cell fractions injected within each subject.

RESULTS

Six subjects completed the study. There were no statistically significant differences in complications with the procedure versus control subjects. Histological analysis indicated that myocardium injected with CD34+ cells had decreased density of endothelial cells compared to saline-injected myocardium. There were no significant differences in fibrosis or inflammation between groups; however, density of activated fibroblasts was decreased in both CD34+ and CD34- injected areas.

CONCLUSIONS

Tissue analysis does not support the hypothesis that bone marrow-derived CD34+ cells promote increased vascular tissue in humans with ischemic cardiomyopathy via direct injection.

Angiomyogenesis for myocardial repair

The conventional therapeutic modalities for myocardial infarction have limited success in preventing the progression of left ventricular remodeling and congestive heart failure. The heart cell therapy and therapeutic angiogenesis are two promising strategies for the treatment of ischemic heart disease. After extensive assessment of safety and effectiveness in vitro and in experimental animal studies, both of these approaches have accomplished the stage of clinical utility, albeit with limited success due to the inherent limitations and problems of each approach. Neomyogenesis without restoration of regional blood flow may be less meaningful. A combined stem-cell and gene-therapy approach of angiomyogenesis is expected to yield better results as compared with either of the approaches as a monotherapy. The combined therapy approach will help to restore the mechanical contractile function of the weakened myocardium and alleviate ischemic condition by restoration of regional blood flow. In providing an overview of both stem cell therapy and gene therapy, this article is an in-depth and critical appreciation of combined cell and gene therapy approach for myocardial repair.

Injection of bone marrow cell extract into infarcted hearts results in functional improvement comparable to intact cell therapy

We compared therapeutic benefits of intramyocardial injection of unfractionated bone marrow cells (BMCs) versus BMC extract as treatments for myocardial infarction (MI), using closed-chest ultrasound-guided injection at a clinically relevant time post-MI. MI was induced in mice and the animals treated at day 3 with either: (i) BMCs from green fluorescent protein (GFP)-expressing mice (n = 14), (ii) BMC extract (n = 14), or (iii) saline control (n = 14). Six animals per group were used for histology at day 6 and the rest followed to day 28 for functional analysis. Ejection fraction was similarly improved in the BMC and extract groups versus control (40.6 +/- 3.4 and 39.1 +/- 2.9% versus 33.2 +/- 5.0%, P < 0.05) with smaller scar sizes. At day 6 but not day 28, both therapies led to significantly higher capillary area and number of arterioles versus control. At day 6, BMCs increased the number of cycling cardiomyocytes (CMs) versus control whereas extract therapy resulted in significant reduction in the number of apoptotic CMs at the border zone (BZ) versus control. Intracellular components within BMCs can enhance vascularity, reduce infarct size, improve cardiac function, and influence CM apoptosis and cycling early after therapy following MI. Intact cells are not necessary and death of implanted cells may be a major component of the benefit.

Retention of Nanoparticles-Labeled Bone Marrow Mononuclear Cells in the Isolated Ex Vivo Perfused Heart After Myocardial Infarction in Animal Model

Cell therapy of myocardial infarction (MI) is under clinical investigation, yet little is known about its underlying mechanism of function. Our aims were to induce a sub-lethal myocardial infarction in a rabbit, to evaluate the abilities of labeled bone marrow mononuclear cells to migrate from the vessel bed into extracellular space of the myocardium, and to evaluate the short-term distribution of cells in the damaged left ventricle. Sub-lethal myocardial infarction was induced in rabbits by ligation of the left coronary vessel branch ( in vivo). The Langendorff heart perfusion model ( ex vivo) was used in the next phase. The hearts subjected to MI induction were divided into 3 groups (P1–P3), and hearts without MI formed a control group (C). Nanoparticles-labeled bone marrow mononuclear cells were injected into coronary arteries via the aorta. Perfusion after application lasted 2 minutes in the P1 group, 10 minutes in the P2 and C groups, and 25 minutes in the P3 group. The myocardium of the left ventricle was examined histologically, and the numbers of labeled cells in vessels, myocardium, and combined were determined. The numbers of detected cells in the P1 and C groups were significantly lower than in the P2 and P3 groups. In the P2 and P3 groups, the numbers of cells found distally from the ligation were significantly higher than proximally from the ligation site. Bone marrow mononuclear cells labeled with iron oxide nanoparticles proved the ability to migrate in the myocardium interstitium with significantly higher affinity for the tissue damaged by infarction.

Estradiol-treated mesenchymal stem cells improve myocardial recovery after ischemia

BACKGROUND

Stem cell therapy is a promising treatment modality for injured cardiac tissue. A novel mechanism for this cardioprotection may include paracrine actions. Our lab has recently shown that gender differences exist in mesenchymal stem cell (MSC) paracrine function. Estrogen is implicated in the cardioprotection found in females. It remains unknown whether 17beta-estradiol (E2) affects MSC paracrine function and whether E2-treated MSCs may better protect injured cardiac tissue. We hypothesize that E2-exposed MSCs infused into hearts prior to ischemia may demonstrate increased vascular endothelial growth factor (VEGF) production and greater protection of myocardial function compared to untreated MSCs.

MATERIALS AND METHODS

Untreated and E2-treated MSCs were isolated, cultured, and plated and supernatants were harvested for VEGF assay (enzyme-linked immunosorbent assay). Adult male Sprague-Dawley rat hearts (n = 13) were isolated and perfused via Langendorff model and subjected to 15 min equilibration, 25 min warm global ischemia, and 40 min reperfusion. Hearts were randomly assigned to perfusate vehicle, untreated male MSC, or E2-treated male MSC. Transcoronary delivery of 1 million MSCs was performed immediately prior to ischemia in experimental hearts.

RESULTS

E2-treated MSCs provoked significantly more VEGF production than untreated MSCs (933.2 +/- 64.9 versus 595.8 +/- 10.7 pg/mL). Postischemic recovery of left ventricular developed pressure was significantly greater in hearts infused with E2-treated MSCs (66.9 +/- 3.3%) than untreated MSCs (48.7 +/- 3.7%) and vehicle (28.9 +/- 4.6%) at end reperfusion. There was also greater recovery of the end diastolic pressure with E2-treated MSCs than untreated MSCs and vehicle.

CONCLUSIONS

Preischemic infusion of MSCs protects myocardial function and viability. E2-treated MSCs may enhance this paracrine protection, which suggests that ex vivo modification of MSCs may improve therapeutic outcome.

Accuracy and reproducibility of a subpixel extended phase correlation method to determine micron level displacements in the heart

Future treatment of heart disease may involve local perturbations of mechanical function, such as intramyocardial injections of angiogenic growth factors or progenitor cells. This necessitates an accurate measurement technique to determine regional heart function. We have previously developed a method to determine regional heart function using a phase correlation algorithm. However, in determining regional function over a single heartbeat it is necessary to sum displacements between many images. We have therefore incorporated a subpixel algorithm that models the result of phase correlation as a sinc function in order to increase the accuracy of our technique. This method, which we have named high density mapping (HDM), determines the subpixel displacement of 64 x 64 pixel regions from images of the heart. To determine the accuracy and precision of the technique, a high contrast image of a heart was digitally shifted 1, 2 or 3 pixels. The original and shifted images were then downsampled four times resulting in 0.25, 0.50 or 0.75 pixel shifts between the original and shifted images. The average accuracy of HDM in the digitally shifted images was 0.06 pixels, with a precision of 0.08 pixels. Effectiveness of HDM in characterization of deformation was also assessed in digitally stretched images. Error in quantification of strain was found to be less than 3.5% of the calculated strain. In an additional set of experiments, in which accuracy was determined using physical motion instead of digital shifting and downsampling, a speckle pattern was displaced by known distances using a micromanipulator, such that the displacement between the captured images was 0.5 pixels. These data demonstrated an accuracy of 0.09 pixels and a precision of 0.02 pixels. Finally, as HDM is used to determine the regional stroke work index (RSW) in beating hearts, the repeatability of using this method to compute RSW was assessed. RSW, the integral of intraventricular pressure with respect to unitless regional area, where end diastolic area was normalized to unity, was assessed in consecutive beats from four different hearts. The average standard deviation of RSW was 0.098 mmHg. Uncertainty analysis determined the maximum error of RSW to be +/-0.41 mmHg, approximately two-thirds of the measured biologic variability. These data demonstrate the ability of HDM to accurately and reproducibly measure displacement and regional function in the beating heart.

Properties of ion channels in rabbit mesenchymal stem cells from bone marrow

The present study was designed to investigate properties of ion channels in undifferentiated rabbit mesenchymal stem cells (MSCs) from bone marrow using whole-cell patch-clamp and RT-PCR techniques. It was found that three types of outward currents were present in rabbit MSCs, including an inward rectifier K(+) current (I(Kir)), a noise-like Ca(2+)-activated K(+) current (I(KCa)) co-present with delayed rectifier K(+) current (IK(DR)). I(Kir) was inhibited by Ba(2+), while I(KCa) was inhibited by paxilline (a blocker of big conductance I(KCa) channels) and clotrimazole (an inhibitor of intermediate conductance I(KCa) channels). IK(DR) exhibited a slow inactivation, "U-shaped" voltage-dependent inactivation, and slow recovery from inactivation, and the current was inhibited by tetraethylammonium or 4-aminopyridine. RT-PCR revealed the molecular identities for the functional ionic currents, including Kir1.1 (possibly responsible for I(Kir)), KCa1.1 and KCa3.1 (possibly responsible for I(KCa)), and Kv1.2, Kv2.1, and Kv2.2 (possibly responsible for IK(DR)). These results demonstrate for the first time that three types of functional ion channel currents (i.e., I(Kir), I(KCa), and IK(DR)) are present in rabbit MSCs from bone marrow.

From cardiac repair to cardiac regeneration – ready to translate?

Cardiovascular disease is a major public health challenge in the western world. Mortality of acute events has improved, but more patients develop HF--a condition affecting up to 22 million people worldwide. Cell transplantation is the first therapy to attempt replacement of lost cardiomyocytes and vasculature to restore lost contractile function. Since the first reported functional repair after injection of autologous skeletal myoblasts into the injured heart in 1998, a variety of cell types have been proposed for transplantation in different stages of cardiovascular disease. Fifteen years of preclinical research and the rapid move into clinical studies have left us with promising results and a better understanding of cells as a potential clinical tool. Cell-based cardiac repair has been the first step, but cardiac regeneration remains the more ambitious goal. Promising new cell types and the rapidly evolving concept of adult stem and progenitor cell fate may enable us to move towards regenerating viable and functional myocardium. Meeting a multidisciplinary consensus will be required to translate these findings into safe and applicable clinical tools.

Grafting an acellular 3-dimensional collagen scaffold onto a non-transmural infarcted myocardium induces neo-angiogenesis and reduces cardiac remodeling

BACKGROUND

This study was designed to determine whether tissue engineering could be used to reduce ventricular remodeling in a rat model of non-transmural, non-ST-elevation myocardial infarction.

METHODS

We grafted an acellular 3-dimensional (3D) collagen type 1 scaffold (solid porous foam) onto infarcted myocardium in rats. Three weeks after grafting, the scaffold was integrated into the myocardium and retarded cardiac remodeling by reducing left ventricular (LV) dilation. The LV inner and outer diameters, measured at the equator at zero LV pressure, decreased (p < 0.05) from 11,040 +/- 212 to 9,144 +/- 135 microm, and 13,469 +/- 187 to 11,673 +/- 104 microm (N = 12), after scaffold transplantation onto infarcted myocardium. The scaffold also shifted the LV pressure-volume curve to the left toward control and induced neo-angiogenesis (700 +/- 25 vs 75 +/- 11 neo-vessels/cm2, N = 5, p < 0.05). These vessels (75 +/- 11%) ranged in diameter from 25 to 100 microm and connected to the native coronary vasculature. Systemic treatment with granulocyte-colony stimulating factor (G-CSF), 50 microg/kg/day for 5 days immediately after myocardial injury, increased (p < 0.05) neo-vascular density from 700 +/- 25 to 978 +/- 57 neo-vessels/cm2.

CONCLUSIONS

A 3D collagen type 1 scaffold grafted onto an injured myocardium induced neo-vessel formation and reduced LV remodeling. Treatment with G-CSF further increased the number of vessels in the myocardium, possibly due to mobilization of bone marrow cells.

Cell Therapy for Heart Failure—Muscle, Bone Marrow, Blood, and Cardiac-Derived Stem Cells

Heart failure (HF) affects a rapidly growing population of patients. Despite improvements in the understanding and therapy of many stages of cardiovascular disease, there has been little progress in treating HF. In the late-stage disease, current options are cardiac transplantation and mechanical support--options that are limited to a small patient collective. The ischemically injured failing heart lacks contractile myocardium, functional vasculature, and electrical integrity, which has made treatment of the underlying injury untenable in the past. Restoring all of these components seems an overwhelming challenge. Yet, the concept of cell therapy--tissue repair by transplantation of stem and progenitor cells--has opened new potential options for patients with heart failure. Skeletal myoblasts, bone marrow, and blood-derived stem cells have all shown considerable myogenic and angiogenic potential in vitro and have rapidly moved from bench to bedside. A number of nonrandomized, non-placebo-controlled safety and feasibility studies have been reported and now double-blinded randomized controlled trials are underway. Despite this rapid clinical pace, the exact mechanisms underlying the functional benefits of different cell types are not well understood. Instead, multiple similar mechanism have been ascribed to virtually every cell type. Thus, while the field is exciting and offers unheralded promise to treat patients with CVD, we must proceed with due diligence and caution. Only a deep understanding of the benefits versus the risks, and the mechanisms involved in cell-mediated cardiac repair, will allow us to design clinically valuable tools and fulfill the potential of this exciting 21st century approach to treating cardiovascular disease.