Zoran B. Popović

Effect of stromal-cell-derived factor 1 on stem-cell homing and tissue regeneration in ischaemic cardiomyopathy

BACKGROUND Myocardial regeneration via stem-cell mobilisation at the time of myocardial infarction is known to occur, although the mechanism for stem-cell homing to infarcted tissue subsequently and whether this approach can be used for treatment of ischaemic cardiomyopathy are unknown. We investigated these issues in a Lewis rat model (ligation of the left anterior descending artery) of ischaemic cardiomyopathy. METHODS We studied the effects of stem-cell mobilisation by use of granulocyte colony-stimulating factor (filgrastim) with or without transplantation of syngeneic cells. Shortening fraction and myocardial strain by tissue doppler imaging were quantified by echocardiography. FINDINGS Stem-cell mobilisation with filgrastim alone did not lead to engraftment of bone-marrow-derived cells. Stromal-cell-derived factor 1 (SDF-1), required for stem-cell homing to bone marrow, was upregulated immediately after myocardial infarction and downregulated within 7 days. 8 weeks after myocardial infarction, transplantation into the peri-infarct zone of syngeneic cardiac fibroblasts stably transfected to express SDF-1 induced homing of CD117-positive stem cells to injured myocardium after filgrastim administration (control vs SDF-1-expressing cardiac fibroblasts mean 7.2 [SD 3.4] vs 33.2 [6.0] cells/mm2, n=4 per group, p<0.02) resulting in greater left-ventricular mass (1.24 [0.29] vs 1.57 [0.27] g) and better cardiac function (shortening fraction 9.2 [4.9] vs 17.2 [4.2]%, n=8 per group, p<0.05). INTERPRETATION These findings show that SDF-1 is sufficient to induce therapeutic stem-cell homing to injured myocardium and suggest a strategy for directed stem-cell engraftment into injured tissues. Our findings also indicate that therapeutic strategies focused on stem-cell mobilisation for regeneration of myocardial tissue must be initiated within days of myocardial infarction unless signalling for stem-cell homing is re-established.

SDF-1 expression by mesenchymal stem cells results in trophic support of cardiac myocytes after myocardial infarction

Stem cell transplantation at the time of acute myocardial infarction (AMI) improves cardiac function. Whether the improved cardiac function results from regeneration of cardiac myocytes, modulation of remodeling, or preservation of injured tissue through paracrine mechanisms is actively debated. Because no specific stem cell population has been shown to be optimal, we investigated whether the benefit of stem cell transplantation could be attributed to a trophic effect on injured myocardium. Mesenchymal stem cells secrete SDF‐1 and the interaction of SDF‐1 with its receptor, CXCR4, increases survival of progenitor cells. Therefore, we compared the effects of MSC and MSC engineered to overexpress SDF‐1 on cardiac function after AMI. Tail vein infusion of syngeneic MSC and MSC:SDF‐1 1 day after AMI in the Lewis rat led to improved cardiac function by echocardiography by 70.7% and 238.8%, respectively, compared with saline controls 5 wk later. The beneficial effects of MSC and MSC:SDF‐1 transplantation were mediated primarily through preservation, not regeneration of cardiac myocytes within the infarct zone. The direct effect of SDF‐1 on cardiac myocytes was due to the observation that’ between 24 and 48 h after AMI, SDF‐1‐expressing MSC increased cardiac myocyte surviva, vascular density (18.2±4.0 vs. 7.6±2.3 vessels/mm2, P<0.01; SDF‐1:MSC vs. MSC), and cardiac myosin‐positive area (MSC: 49.5%;mSC:SDF‐1: 162.1%) within the infarct zone. There was no evidence of cardiac regeneration by the infused MSC or endogenous cardiac stem cells based on lack of evidence for cardiac myocytes being derived from replicating cells. These results indicate that stem cell transplantation may have significant beneficial effects on injured organ function independent of tissue regeneration and identify SDF‐1:CXCR4 binding as a novel target for myocardial preservation.—Zhang, M., Mal, N., Kiedrowski, M., Chacko, M., Askari, A. T., Popovic, Z. B., Koc, O. N., Penn, M. S. SDF‐1 expression by mesenchymal stem cells results in trophic support of cardiac myocytes after myocardial infarction. FASEB J. 21, 3197–3207 (2007)

Enhanced Ventricular Untwisting During Exercise A Mechanistic Manifestation of Elastic Recoil Described by Doppler Tissue Imaging

Background— The cascade of events by which early diastolic left ventricular (LV) filling increases with exercise is not fully elucidated. Doppler tissue imaging (DTI) can detect myocardial motion, including torsion, whereas color M-mode Doppler (CMM) can quantify LV intraventricular pressure gradients (IVPGs). Methods and Results— Twenty healthy volunteers underwent echocardiographic examination with DTI at rest and during submaximal supine bicycle exercise. We assessed LV long-/short-axis function, torsion, volume, inflow dynamics, and early diastolic IVPG derived from CMM data. LV torsion and untwisting velocity increased with exercise (torsion, 11±4° to 24±8°; untwisting velocity, −2.0±0.7 to −5.6±2.3 rad/s) that was associated with an increase in IVPG (1.4±0.5 to 3.7±1.2 mm Hg). Untwisting in normal subjects occurred during isovolumic relaxation and early filling, significantly before long-axis lengthening or radial expansion. The clinical feasibility of this method was tested in 7 patients with hypertrophic cardiomyopathy (HCM); torsion was higher at rest but did not increase with exercise (16±4° to 14±6°), whereas untwisting was delayed and unenhanced (−1.6±0.8 to −2.3±1.2 rad/s). In concert, IVPG was similar at rest (1.2±0.3 mm Hg), but the exercise response was blunted (1.6±0.8 mm Hg). In normal subjects and HCM patients, there was a similar linear relation between IVPG and untwisting rate, with an overall correlation coefficient of r=0.75 (P<0.0001). Conclusions— LV untwisting appears to be linked temporally with early diastolic base-to-apex pressure gradients, enhanced by exercise, which may assist efficient LV filling, an effect that appears blunted in HCM. Thus, LV torsion and subsequent rapid untwisting appear to be manifestations of elastic recoil, critically linking systolic contraction to diastolic filling.

Geometric differences of the mitral apparatus between ischemic and dilated cardiomyopathy with significant mitral regurgitation: real-time three-dimensional echocardiography study

Background—This study was conducted to elucidate the geometric differences of the mitral apparatus in patients with significant mitral regurgitation caused by ischemic cardiomyopathy (ICM-MR) and by idiopathic dilated cardiomyopathy (DCM-MR) by use of real-time 3D echocardiography (RT3DE). Methods and Results—Twenty-six patients with ICM-MR caused by posterior infarction, 18 patients with DCM-MR, and 8 control subjects were studied. With the 3D software, commissure-commissure plane and 3 perpendicular anteroposterior (AP) planes were generated for imaging the medial, central, and lateral sides of the mitral valve (MV) during mid systole. In 3 AP planes, the angles between the annular plane and each leaflet (anterior, A&agr;; posterior, P&agr;) were measured. In ICM-MR, A&agr; measured in the medial and central planes was significantly larger than that in the lateral plane (39±5°, 34±6°, and 27±5°, respectively;P <0.01), whereas P&agr; showed no significant difference in any of the 3 AP planes (61±7°, 57±7°, and 56±7°, P >0.05). In DCM-MR, both A&agr; (38±8°, 37±9°, and 36±7°, P >0.05) and P&agr; (59±6°, 58±5°, and 57±6°, P >0.05) revealed no significant differences in the 3 planes. Conclusions—The pattern of MV deformation from the medial to the lateral side was asymmetrical in ICM-MR, whereas it was symmetrical in DCM-MR. RT3DE is a helpful tool for differentiating the geometry of the mitral apparatus between these 2 different types of functional mitral regurgitation.

Reproducibility of Echocardiographic Techniques for Sequential Assessment of Left Ventricular Ejection Fraction and Volumes Application to Patients Undergoing Cancer Chemotherapy

OBJECTIVES The aim of this study was to identify the best echocardiographic method for sequential quantification of left ventricular (LV) ejection fraction (EF) and volumes in patients undergoing cancer chemotherapy. BACKGROUND Decisions regarding cancer therapy are based on temporal changes of EF. However the method for EF measurement with the lowest temporal variability is unknown. METHODS We selected patients in whom stable function in the face of chemotherapy for breast cancer was defined by stability of global longitudinal strain (GLS) at up to 5 time points (baseline, 3, 6, 9, and 12 months). In this way, changes in EF were considered to reflect temporal variability of measurements rather than cardiotoxicity. A comprehensive echocardiogram consisting of 2-dimensional (2D) and 3-dimensional (3D) acquisitions with and without contrast administration was performed at each time point. Stable LV function was defined as normal GLS (≤-16.0%) at each examination. The EF and volumes were measured with 2D-biplane Simpsons method, 2D-triplane, and 3-dimensional echocardiography (3DE) by 2 investigators blinded to any clinical data. Inter-, intra-, and test-retest variability were assessed in a subgroup. Variability was assessed by analysis of variance and compared with Levenes or t test. RESULTS Among 56 patients (all female, 54 ± 13 years of age), noncontrast 3D EF, end-diastolic volume, and end-systolic volume had significantly lower temporal variability than all other methods. Contrast only decreased the temporal variability of LV end-diastolic volume measurements by the 2D biplane method. Our data suggest that a temporal variability in EF of 0.06 might occur with noncontrast 3DE due to physiological differences and measurement variability, whereas this might be >0.10 with 2D methods. Overall, 3DE also had the best intra- and inter-observer as well as test-retest variability. CONCLUSIONS Noncontrast 3DE was the most reproducible technique for LVEF and LV volume measurements over 1 year of follow-up.

Assessment of left ventricular torsional deformation by Doppler tissue imaging: Validation study with tagged magnetic resonance imaging

Background—Left ventricular (LV) torsional deformation is a sensitive index for LV performance but difficult to measure. The present study tested the accuracy of a novel method that uses Doppler tissue imaging (DTI) for quantifying LV torsion in humans with tagged magnetic resonance imaging (MRI) as a reference. Methods and Results—Twenty patients underwent DTI and tagged MRI studies. Images of the LV were acquired at apical and basal short-axis levels to assess LV torsion. We calculated LV rotation by integrating the rotational velocity, determined from DTI velocities of the septal and lateral regions, and correcting for the LV radius over time. LV torsion was defined as the difference in LV rotation between the 2 levels. DTI rotational and torsional profiles throughout systole and diastole were compared with those by tagged MRI at isochronal points. Rotation and torsion by DTI were closely correlated with tagged MRI results during systole and early diastole (apical and basal rotation, r=0.87 and 0.90, respectively; for torsion, 0.84; P<0.0001, by repeated-measures regression models). Maximal torsion showed even better correlation (r=0.95, P<0.0001). Conclusions—The present study has shown that DTI can quantify LV torsional deformation over time. This novel method may facilitate noninvasive quantification of LV torsion in clinical and research settings.

Monocyte Chemotactic Protein‐3 Is a Myocardial Mesenchymal Stem Cell Homing Factor

MSCs have received attention for their therapeutic potential in a number of disease states, including bone formation, diabetes, stem cell engraftment after marrow transplantation, graft‐versus‐host disease, and heart failure. Despite this diverse interest, the molecular signals regulating MSC trafficking to sites of injury are unclear. MSCs are known to transiently home to the freshly infarcted myocardium. To identify MSC homing factors, we determined chemokine expression pattern as a function of time after myocardial infarction (MI). We merged these profiles with chemokine receptors expressed on MSCs but not cardiac fibroblasts, which do not home after MI. This analysis identified monocyte chemotactic protein‐3 (MCP‐3) as a potential MSC homing factor. Overexpression of MCP‐3 1 month after MI restored MSC homing to the heart. After serial infusions of MSCs, cardiac function improved in MCP‐3‐expressing hearts (88.7%, p < .001) but not in control hearts (8.6%, p = .47). MSC engraftment was not associated with differentiation into cardiac myocytes. Rather, MSC engraftment appeared to result in recruitment of myofibroblasts and remodeling of the collagen matrix. These data indicate that MCP‐3 is an MSC homing factor; local overexpression of MCP‐3 recruits MSCs to sites of injured tissue and improves cardiac remodeling independent of cardiac myocyte regeneration.

Clinical ResearchCardiac ImagingReproducibility of Echocardiographic Techniques for Sequential Assessment of Left Ventricular Ejection Fraction and Volumes: Application to Patients Undergoing Cancer Chemotherapy

OBJECTIVES The aim of this study was to identify the best echocardiographic method for sequential quantification of left ventricular (LV) ejection fraction (EF) and volumes in patients undergoing cancer chemotherapy. BACKGROUND Decisions regarding cancer therapy are based on temporal changes of EF. However the method for EF measurement with the lowest temporal variability is unknown. METHODS We selected patients in whom stable function in the face of chemotherapy for breast cancer was defined by stability of global longitudinal strain (GLS) at up to 5 time points (baseline, 3, 6, 9, and 12 months). In this way, changes in EF were considered to reflect temporal variability of measurements rather than cardiotoxicity. A comprehensive echocardiogram consisting of 2-dimensional (2D) and 3-dimensional (3D) acquisitions with and without contrast administration was performed at each time point. Stable LV function was defined as normal GLS (≤-16.0%) at each examination. The EF and volumes were measured with 2D-biplane Simpsons method, 2D-triplane, and 3-dimensional echocardiography (3DE) by 2 investigators blinded to any clinical data. Inter-, intra-, and test-retest variability were assessed in a subgroup. Variability was assessed by analysis of variance and compared with Levenes or t test. RESULTS Among 56 patients (all female, 54 ± 13 years of age), noncontrast 3D EF, end-diastolic volume, and end-systolic volume had significantly lower temporal variability than all other methods. Contrast only decreased the temporal variability of LV end-diastolic volume measurements by the 2D biplane method. Our data suggest that a temporal variability in EF of 0.06 might occur with noncontrast 3DE due to physiological differences and measurement variability, whereas this might be >0.10 with 2D methods. Overall, 3DE also had the best intra- and inter-observer as well as test-retest variability. CONCLUSIONS Noncontrast 3DE was the most reproducible technique for LVEF and LV volume measurements over 1 year of follow-up.

Left Atrial Strain Measured by Two-Dimensional Speckle Tracking Represents a New Tool to Evaluate Left Atrial Function

BACKGROUND Left atrial (LA) strain (epsilon) and epsilon rate (SR) analysis by two-dimensional speckle tracking can represent a new tool to evaluate LA function. To assess its potential value, the authors addressed whether LA epsilon and SR measured in normal subjects correlates with other Doppler echocardiographic parameters that evaluate LA function and left ventricular function. METHODS Sixty-four healthy subjects were studied. LA epsilon and SR were calculated with the reference point set at the P wave, which enabled the recognition of peak negative epsilon (epsilon(neg peak)), peak positive epsilon (epsilon(pos peak)), and the sum of those values, total LA epsilon (epsilon(tot)), corresponding to LA contractile, conduit, and reservoir function, respectively. Similarly, peak negative SR (LA SR(late neg peak)) during LA contraction, peak positive SR (LA SR(pos peak)) at the beginning of LV systole, and peak negative SR (LA SR(early neg peak)) at the beginning of LV diastole were identified. RESULTS Global LA epsilon(pos peak), epsilon(neg peak), and epsilon(tot) were 23.2 +/- 6.7%, -14.6 +/- 3.5%, and 37.9 +/- 7.6%, respectively. Global LA SR(pos peak), SR(early neg peak) , and SR(late neg peak) were 2.0 +/- 0.6 s(-1), -2.0 +/- 0.6 s(-1), and -2.3 +/- 0.5 s(-1), respectively. The above-described variables derived from analysis of global LA epsilon and LA SR correlated significantly with Doppler echocardiographic indexes that evaluated the same phase of the cardiac cycle or the same component of the LA function, including indexes derived from mitral inflow, pulmonary vein velocities, tissue Doppler, and LA volumes. Global LA epsilon(pos peak), LA epsilon(tot), and LA SR(early neg peak) also correlated significantly with age or body mass index. Global LA SR(late neg peak) also correlated significantly with age. CONCLUSIONS LA epsilon analysis is a new tool that can be used to evaluate LA function. Further studies are warranted to determine the utility of LA epsilon in disease states.

Relative apical sparing of longitudinal strain using two-dimensional speckle-tracking echocardiography is both sensitive and specific for the diagnosis of cardiac amyloidosis

Background The diagnosis of cardiac amyloidosis (CA) is challenging owing to vague symptomatology and non-specific echocardiographic findings. Objective To describe regional patterns in longitudinal strain (LS) using two-dimensional speckle-tracking echocardiography in CA and to test the hypothesis that regional differences would help differentiate CA from other causes of increased left ventricular (LV) wall thickness. Methods and results 55 consecutive patients with CA were compared with 30 control patients with LV hypertrophy (n=15 with hypertrophic cardiomyopathy, n=15 with aortic stenosis). A relative apical LS of 1.0, defined using the equation (average apical LS/(average basal LS + mid-LS)), was sensitive (93%) and specific (82%) in differentiating CA from controls (area under the curve 0.94). In a logistic regression multivariate analysis, relative apical LS was the only parameter predictive of CA (p=0.004). Conclusions CA is characterised by regional variations in LS from base to apex. A relative ‘apical sparing’ pattern of LS is an easily recognisable, accurate and reproducible method of differentiating CA from other causes of LV hypertrophy.