Can bone marrow-derived multipotent adult progenitor cells regenerate infarcted myocardium?

OBJECTIVES: To assess the functional effects of multipotent adult progenitor cells (MAPCs) transplanted in a rat model of chronic myocardial infarction. METHODS: Forty-four rats underwent coronary ligation and, 14 days later, were randomly allocated to receive in-scar injections (5 x 10(6) cells/150 microL) of green fluorescent protein (eGFP)-transduced allogeneic MAPCs (n = 25) or culture medium (controls, n = 19). Nine of the MAPC-treated hearts were employed for functional studies while the remaining 16 received cells co-labeled with Resovist and were only used for serial histological assessments. Left ventricular (LV) function was assessed echocardiographically before transplantation and 1 month thereafter in a blinded manner. Immunohistochemistry, electron microscopy and PCR were used to detect grafted cells. All data were compared by nonparametric tests. RESULTS: Baseline ejection fractions (EF, median;[interquartile range]) did not differ significantly among the groups: 30% [0.23;0.37] and 37% [0.32;0.38] in control and rMAPC-transplanted hearts, respectively. One month later, LV function of control hearts was found to have deteriorated, as reflected by a decline in EF to 24% [0.21;0.30], and although EF tended to remain more stable after cell transplantation (37% [0.27;0.41]), the difference between the two groups failed to achieve statistical significance (p = 0.06). While MAPCs could be identified early post-transplant, no evidence of engraftment was further observed at 1 month by immunohistochemistry, electron microscopy or PCR. CONCLUSIONS: In this model, MAPCs did not improve global pump function, and although some of these cells expressed endothelial markers during the early post-transplant period, we could not detect any evidence for differentiation into cardiomyocytes and no engraftment was further identified beyond 2 weeks after cell injections.

Transplantation of autologous fresh bone marrow into infarcted myocardium: a word of caution.

BACKGROUND: As the benefits of extemporaneous transplantation (Tx) of fresh (unfractionated) autologous bone marrow (BM) have been primarily studied in the setting of acute myocardial infarction, we assessed whether this approach could be effective for regenerating chronically infarcted myocardium. METHODS AND RESULTS: Myocardial infarction was created in 18 sheep by ligation of circumflex arterial branches. Three weeks later, BM was aspirated from the iliac crest, washed, labeled with the fluorescent dye Dil and reinjected (mean: 422 x 10(6) cells in 3 mL) in 10 sites across the infarcted area through the reopened thoracotomy (n=9). Nine controls received culture medium. Left ventricular (LV) function was assessed before and 2 months after Tx by two-dimensional echocardiography whereas transmural velocity gradients were measured using M-mode tissue Doppler imaging at the center of the infarcted/grafted area. Formalin-fixed hearts were processed for the detection of grafted cells and angiogenesis. LV ejection fraction deteriorated similarly in the Tx and control groups (from 42+/-5% to 30+/-4% and from 40+/-4% to 31+/-1%, respectively; P=0.86). Likewise, BM Tx failed to prevent LV dilatation and impairment of the global wall motion score. The decrease in regional systolic velocity gradients (s(-1)) featured a similar pattern (Tx group: from 0.77+/-0.11 to 0.31+/-0.07; control group: from 0.73+/-0.10 to 0.50+/-0.07; P=0.06). Histologically, there was neither BM tissue engraftment, except for a few scattered Dil-positive macrophages in the infarcted fibrotic areas nor transdifferentiation of BM cells into endothelial cells. CONCLUSIONS: These data caution against the functional efficacy of extemporaneous Tx of fresh unfractionated BM into postinfarction scars.

Comparison of human skeletal myoblasts and bone marrow-derived CD133+ progenitors for the repair of infarcted myocardium.

OBJECTIVES: The present study was designed as a face-to-face functional comparison of human skeletal myoblasts (SMs) and CD133(+) bone marrow-derived hematopoietic progenitors in an animal model of semichronic myocardial infarction. BACKGROUND: Compared with SMs, bone marrow-derived cells have the advantage of plasticity and might more effectively regenerate ischemic cardiac tissue. However, few data exist on the comparative efficacy of these two cell types in semichronic infarcts. METHODS: A myocardial infarction was created by coronary ligation in 32 nude rats. Ten days later, rats received in-scar injections of human SMs, CD133(+) progenitors, or culture medium. Left ventricular function was assessed before and one month after transplantation by echocardiography and pressure-volume loops. Immunofluorescence, polymerase chain reaction, and in situ hybridization were used to detect cells grafted in the hearts. RESULTS: One month after transplantation, left ventricular ejection fraction decreased by 8 +/- 4% in controls, whereas it increased by 7 +/- 3% in CD133(+)-grafted hearts (p = 0.0015 vs. controls) and further by 15 +/- 5% in SM-treated hearts (p = 0.008 vs. controls). Systolic indices yielded by pressure-volume loops paralleled these data. Engrafted myotubes were identified in all SM-treated hearts by immunofluorescence, whereas in CD133(+)-grafted hearts, few human cells were only detected by polymerase chain reaction. CONCLUSIONS: In the setting of postinfarction scars, the transplantation of bone marrow-derived CD133(+) progenitors improves cardiac function, but this benefit is not superior to that afforded by myogenic cells.

Temporal patterns of bone marrow cell differentiation following transplantation in doxorubicin-induced cardiomyopathy.

OBJECTIVE: Recent studies have suggested benefits of bone marrow cell transplantation for the regeneration of ischemic cardiac tissue. To extend the potential of cell transplantation, we assessed this treatment in a mouse model of acute nonischemic doxorubicin-induced cardiomyopathy. METHODS: To allow detection of engrafted cells, we used transgenic mice expressing the nuclear-located LacZ under the control of either desmin or vimentin promoters, which identify muscle lineage and mesenchymal cells, respectively. All transplanted cells were also labeled with the fluorescent dye DIL. One week after the administration of doxorubicin (15 mg/kg), mice were intramyocardially injected with either allogeneic unpurified bone marrow cells (6 x 10(6) in 30 microl, n=59) or purified sca-1(pos) cells (4 x 10(5) in 30 microl, n=22). In parallel, control normal mice received only unpurified bone marrow cells (n=28). Hearts were harvested at serial intervals until 2 weeks after transplantation and analyzed by immunohistochemistry to assess the degree of engraftment and transplanted cell differentiation. RESULTS: In control mice, no differentiation of bone marrow cells was detected. In contrast, unpurified bone marrow cells grafted into diseased myocardium featured two successive phases of cell differentiation. The first yielded cells with a mesenchymal phenotype (44.1+/-10.1 cells/3 x 10(-2) mm(3) at 2 days), was transient and lasted 1 week. The second phase was characterized by cells with a muscular phenotype detected in a small number of cells (5.6+/-2.3 cells/3 x 10(-2) mm(3) at 7 days). Two weeks after transplantation, some of these cells appeared phenotypically close to cardiomyocytes, as evidenced by morphology and positive staining for myosin binding protein C, vinculin and myosin heavy chain. In sca-1(pos) hematopoietic progenitor grafted mice hearts, no transdifferentiation into cardiac cells was detected at any time point. CONCLUSION: These data support the hypothesis of the potential for a myogenic differentiation of bone marrow cells following engraftment in a nonischemic model of global cardiomyopathy. Bone marrow-derived cells amenable to cardiac differentiation are present in total unpurified bone marrow but not in the sca-1(pos) hematopoietic progenitor cell population. However, the very small number of transdifferentiated cells raises concerns over their functional efficacy.

Molecular mechanisms in evolutionary cardiology failure.

Integration of the relevant evolutionary paradigm in cardiology has not yet been fully achieved: In the past, heart failure (HF) was mainly ascribed to infections, and the origins of cardiac hypertrophy (CH) were regarded as mechanical. Recent changes in lifestyle have both reduced the incidence of infections and increased lifespan, and HF is now seen as a complex disease--one that is still caused by mechanical disorder, but also associated with ischemia and senescence. The long-held view that CH serves to restore myocardial economy back to normal is still valid. The adaptive process is characterized by a quantitative and a qualitative fetal gene reprogramming, which is now being confirmed by recent advances in microRNA research. It underscores the fact CH is the physiologic reaction of the heart to a pathologic stimulus. The goal for therapy is economic, not inotropic. Another major issue is myocardial fibrosis, a major determinant of diastolic function and arrhythmias. Recent changes in lifestyle have crucially modified the context in which HF occurs.

Role of oxidative stress in cardiac dysfunction of PPARalpha-/- mice.

This study was designed to determine the effects of PPARalpha lack on cardiac mechanical performance and to identify potential intracellular mechanisms linking PPARalpha pathway deficiency to cardiac contractile dysfunction. Echocardiography, ex vivo papillary muscle assays, and in vitro motility assays were used to assess global, intrinsic ventricular muscle performance and myosin mechanical properties, respectively, in PPARalpha(-/-) and age-matched wild-type mice. Three-nitrotyrosine formation and 4-hydroxy-2-nonenal protein-adducts, both markers of oxidative damage, were analyzed by Western blot analysis and immunolabeling. Radical scavenging capacity was analyzed by measuring protein levels and/or activities of the main antioxidant enzymes, including catalase, glutathione peroxidase, and manganese and copper-zinc superoxide dismutases. Echocardiographic left ventricular fractional shortening in PPARalpha(-/-) was 16% lower than that in wild-type. Ex vivo left ventricular papillary muscle exhibited reduced shortening velocity and isometric tension (three- and twofold, respectively). In vitro myosin-based velocity was approximately 20% slower in PPARalpha(-/-), indicating that myosin itself was involved in the contractile dysfunction. Staining of 3-nitrotyrosine was more pronounced in PPARalpha(-/-), and myosin heavy chain was the main nitrated protein. Formation of 3-nitrotyrosine myosin heavy chain was twofold higher in PPARalpha(-/-) and 4-hydroxy-2-nonenal protein-adducts were threefold higher. The expression and activity of manganese superoxide dismutase were respectively 33% and 50% lower in PPARalpha(-/-), with no changes in copper-zinc superoxide dismutase, catalase, or glutathione peroxidase. These findings demonstrate that PPARalpha pathway deficiency impairs cardiac function and also identify oxidative damage to myosin as a link between PPARalpha deficiency and contractile dysfunction.