Background—: Despite rapid clinical translation and widespread enthusiasm, the therapeutic benefits of adult bone marrow cell (BMC) transplantation in patients with ischemic heart disease continue to remain controversial. A synthesis of the available data is critical to appreciate and underscore the true impact of this promising approach. Methods and Results—: A total of 50 studies (enrolling 2625 patients) identified by database searches through January 2012 were included. Weighted mean differences for changes in left ventricular (LV) ejection fraction, infarct size, LV end-systolic volume, and LV end-diastolic volume were estimated with random-effects meta-analysis. Compared with control subjects, BMC-treated patients exhibited greater LV ejection fraction (3.96%; 95% confidence interval, 2.90–5.02; P <0.00001) and smaller infarct size (−4.03%, 95% confidence interval, −5.47 to −2.59; P <0.00001), LV end-systolic volume (−8.91 mL; 95% confidence interval, −11.57 to −6.25; P <0.00001), and LV end-diastolic volume (−5.23 mL; 95% confidence interval, −7.60 to −2.86; P <0.0001). These benefits were noted regardless of the study design (randomized controlled study versus cohort study) and the type of ischemic heart disease (acute myocardial infarction versus chronic ischemic heart disease) and persisted during long-term follow-up. Importantly, all-cause mortality, cardiac mortality, and the incidence of recurrent myocardial infarction and stent thrombosis were significantly lower in BMC-treated patients compared with control subjects. Conclusions—: Transplantation of adult BMCs improves LV function, infarct size, and remodeling in patients with ischemic heart disease compared with standard therapy, and these benefits persist during long-term follow-up. BMC transplantation also reduces the incidence of death, recurrent myocardial infarction, and stent thrombosis in patients with ischemic heart disease.

Rationale:: Extracellular vesicles (EVs) are tiny membrane-enclosed droplets released by cells through membrane budding or exocytosis. The myocardial reparative abilities of EVs derived from induced pluripotent stem cells (iPSCs) have not been directly compared with the source iPSCs. Objective:: To examine whether iPSC-derived EVs can influence the biological functions of cardiac cells in vitro and to compare the safety and efficacy of iPSC-derived EVs (iPSC-EVs) and iPSCs for cardiac repair in vivo. Methods and Results:: Murine iPSCs were generated, and EVs isolated from culture supernatants by sequential centrifugation. Atomic force microscopy, high-resolution flow cytometry, real-time quantitative RT-PCR, and mass spectrometry were used to characterize EV morphology and contents. iPSC-EVs were enriched in miRNAs and proteins with proangiogenic and cytoprotective properties. iPSC-EVs enhanced angiogenic, migratory, and antiapoptotic properties of murine cardiac endothelial cells in vitro. To compare the cardiac reparative capacities in vivo, vehicle, iPSCs, and iPSC-EVs were injected intramyocardially at 48 hours after a reperfused myocardial infarction in mice. Compared with vehicle-injected mice, both iPSC- and iPSC-EV–treated mice exhibited improved left ventricular function at 35 d after myocardial infarction, albeit iPSC-EVs rendered greater improvement. iPSC-EV injection also resulted in reduction in left ventricular mass and superior perfusion in the infarct zone. Both iPSCs and iPSC-EVs preserved viable myocardium in the infarct zone, whereas reduction in apoptosis was significant with iPSC-EVs. iPSC injection resulted in teratoma formation, whereas iPSC-EV injection was safe. Conclusions:: iPSC-derived EVs impart cytoprotective properties to cardiac cells in vitro and induce superior cardiac repair in vivo with regard to left ventricular function, vascularization, and amelioration of apoptosis and hypertrophy. Because of their acellular nature, iPSC-EVs represent a safer alternative for potential therapeutic applications in patients with ischemic myocardial damage.

Rationale:: The role of interleukin (IL)-6 in the pathogenesis of cardiac myocyte hypertrophy remains controversial. Objective:: To conclusively determine whether IL-6 signaling is essential for the development of pressure overload–induced left ventricular (LV) hypertrophy and to elucidate the underlying molecular pathways. Methods and Results:: Wild-type and IL-6 knockout ( IL-6 ^−/− ) mice underwent sham surgery or transverse aortic constriction (TAC) to induce pressure overload. Serial echocardiograms and terminal hemodynamic studies revealed attenuated LV hypertrophy and superior preservation of LV function in IL-6 ^−/− mice after TAC. The extents of LV remodeling, fibrosis, and apoptosis were reduced in IL-6 ^−/− hearts after TAC. Transcriptional and protein assays of myocardial tissue identified Ca ²⁺ /calmodulin-dependent protein kinase II (CaMKII) and signal transducer and activator of transcription 3 (STAT3) activation as important underlying mechanisms during cardiac hypertrophy induced by TAC. The involvement of these pathways in myocyte hypertrophy was verified in isolated cardiac myocytes from wild-type and IL-6 ^−/− mice exposed to prohypertrophy agents. Furthermore, overexpression of CaMKII in H9c2 cells increased STAT3 phosphorylation, and exposure of H9c2 cells to IL-6 resulted in STAT3 activation that was attenuated by CaMKII inhibition. Together, these results identify the importance of CaMKII-dependent activation of STAT3 during cardiac myocyte hypertrophy via IL-6 signaling. Conclusions:: Genetic deletion of IL-6 attenuates TAC-induced LV hypertrophy and dysfunction, indicating a critical role played by IL-6 in the pathogenesis of LV hypertrophy in response to pressure overload. CaMKII plays an important role in IL-6–induced STAT3 activation and consequent cardiac myocyte hypertrophy. These findings may have significant therapeutic implications for LV hypertrophy and failure in patients with hypertension.

Rationale:: Notwithstanding the uncertainties about the outcomes of bone marrow cell (BMC) therapy for heart repair, further insights are critically needed to improve this promising approach. Objective:: To delineate the true effect of BMC therapy for cardiac repair and gain insights for future trials through systematic review and meta-analysis of data from eligible randomized controlled trials. Methods and Results:: Database searches through August 2014 identified 48 eligible randomized controlled trials (enrolling 2602 patients). Weighted mean differences for changes in left ventricular (LV) ejection fraction, infarct size, LV end-systolic volume, and LV end-diastolic volume were analyzed with random-effects meta-analysis. Compared with standard therapy, BMC transplantation improved LV ejection fraction (2.92%; 95% confidence interval, 1.91–3.92; P <0.00001), reduced infarct size (−2.25%; 95% confidence interval, −3.55 to −0.95; P =0.0007) and LV end-systolic volume (−6.37 mL; 95% confidence interval, −8.95 to −3.80; P <0.00001), and tended to reduce LV end-diastolic volume (−2.26 mL; 95% confidence interval, −4.59 to 0.07; P =0.06). Similar effects were noted when data were analyzed after excluding studies with discrepancies in reporting of outcomes. The benefits also persisted when cardiac catheterization was performed in control patients as well. Although imaging modalities partly influenced the outcomes, LV ejection fraction improved in BMC-treated patients when assessed by magnetic resonance imaging. Early (<48 hours) BMC injection after myocardial Infarction was more effective in reducing infarct size, whereas BMC injection between 3 and 10 days proved superior toward improving systolic function. A minimum of 50 million BMCs seemed to be necessary, with limited additional benefits seen with increasing cell numbers. BMC therapy was safe and improved clinical outcomes, including all-cause mortality, recurrent myocardial Infarction, ventricular arrhythmia, and cerebrovascular accident during follow-up, albeit with differences between acute myocardial Infarction and chronic ischemic heart disease subgroups. Conclusions:: Transplantation of adult BMCs improves LV ejection fraction, reduces infarct size, and ameliorates remodeling in patients with ischemic heart disease. These effects are upheld in the analyses of studies using magnetic resonance imaging and also after excluding studies with discrepant reporting of outcomes. BMC transplantation may also reduce the incidence of death, recurrent myocardial Infarction, ventricular arrhythmia, and cerebrovascular accident during follow-up.

Adult bone marrow‐derived very small embryonic‐like stem cells (VSEL‐SCs) exhibit a Sca‐1⁺/Lin^–/CD45^– phenotype and can differentiate into various cell types, including cardiomyocytes and endothelial cells. We have previously reported that transplantation of a small number (1 × 10⁶) of freshly isolated, non‐expanded VSEL‐SCs into infarcted mouse hearts resulted in improved left ventricular (LV) function and anatomy. Clinical translation, however, will require large numbers of cells. Because the frequency of VSEL‐SCs in the marrow is very low, we examined whether VSEL‐SCs can be expanded in culture without loss of therapeutic efficacy. Mice underwent a 30 min. coronary occlusion followed by reperfusion and, 48 hrs later, received an intramyocardial injection of vehicle (group I, n= 11), 1 × 10⁵ enhanced green fluorescent protein (EGFP)‐labelled expanded untreated VSEL‐SCs (group II, n= 7), or 1 × 10⁵ EGFP‐labelled expanded VSEL‐SCs pre‐incubated in a cardiogenic medium (group III, n= 8). At 35 days after myocardial infarction (MI), mice treated with pre‐incubated VSEL‐SCs exhibited better global and regional LV systolic function and less LV hypertrophy compared with vehicle‐treated controls. In contrast, transplantation of expanded but untreated VSEL‐SCs did not produce appreciable reparative benefits. Scattered EGFP⁺ cells expressing α‐sarcomeric actin, platelet endothelial cell adhesion molecule (PECAM)‐1, or von Willebrand factor were present in VSEL‐SC‐treated mice, but their numbers were very small. No tumour formation was observed. We conclude that VSEL‐SCs expanded in culture retain the ability to alleviate LV dysfunction and remodelling after a reperfused MI provided that they are exposed to a combination of cardiomyogenic growth factors and cytokines prior to transplantation. Counter intuitively, the mechanism whereby such pre‐incubation confers therapeutic efficacy does not involve differentiation into new cardiac cells. These results support the potential therapeutic utility of VSEL‐SCs for cardiac repair.

Background—: The use of cardiac resynchronization therapy (CRT) has increased significantly since its initial approval in 2001 for use in patients with advanced heart failure. However, trends in utilization of CRT have not been systematically characterized. Methods and Results—: We used the Nationwide Inpatient Sample database to identify all patients with CRT implantation during 2002 to 2010. The overall trends in CRT device implantation, patient characteristics, and outcomes were examined in detail and compared among demographic subgroups. During 2002 to 2010, a total of 374 202 CRT procedures were recorded. Significant and persistent gender and racial disparities favoring men (71.4%) and white (79.6%), respectively, were noted in all years. The highest number of CRT devices were implanted in the 65- to 84-year age group (64.6%), with significant increase in number of CRT implants in older patients ≥85 years over the years ( P =0.02). The CRT-associated in-hospital mortality improved from 1.08% in 2003 to 0.70% in 2010 ( P =0.03). The correlates of higher mortality included males (0.93% versus 0.71% in females; P =0.04) and older age (age ≥85 years had 1.5% mortality versus 0.8% for age <85 year; P females), older age, and greater comorbidities. Conclusions—: CRT implantation is a relatively safe procedure that has become safer in higher risk patients. However, significant disparities in CRT utilization exist in certain demographic subgroups, and these disparities have persisted across the years.