Mechanism of Action of Mesenchymal Stem Cells (MSCs): impact of delivery method.

INTRODUCTION: Mesenchymal stromal cells (MSCs; AKA mesenchymal stem cells) stimulate healing and reduce inflammation. Promising therapeutic responses are seen in many late-phase clinical trials, but others have not satisfied their primary endpoints, making translation of MSCs into clinical practice difficult. These inconsistencies may be related to the route of MSC delivery, lack of product optimization, or varying background therapies received in clinical trials over time. AREAS COVERED: Here we discuss the different routes of MSC delivery, highlighting the proposed mechanism(s) of therapeutic action as well as potential safety concerns. PubMed search criteria used: MSC plus: local administration; routes of administration; delivery methods; mechanism of action; therapy in different diseases. EXPERT OPINION: Direct injection of MSCs using a controlled local delivery approach appears to have benefits in certain disease states, but further studies are required to make definitive conclusions regarding the superiority of one delivery method over another.

Growth hormone-releasing hormone agonists ameliorate chronic kidney disease-induced heart failure with preserved ejection fraction.

Therapies for heart failure with preserved ejection fraction (HFpEF) are lacking. Growth hormone-releasing hormone agonists (GHRH-As) have salutary effects in ischemic and nonischemic heart failure animal models. Accordingly, we hypothesized that GHRH-A treatment ameliorates chronic kidney disease (CKD)-induced HFpEF in a large-animal model. Female Yorkshire pigs (n = 16) underwent 5/6 nephrectomy via renal artery embolization and 12 wk later were randomized to receive daily subcutaneous injections of GHRH-A (MR-409; n = 8; 30 µg/kg) or placebo (n = 8) for 4 to 6 wk. Renal and cardiac structure and function were serially assessed postembolization. Animals with 5/6 nephrectomy exhibited CKD (elevated blood urea nitrogen [BUN] and creatinine) and faithfully recapitulated the hemodynamic features of HFpEF. HFpEF was demonstrated at 12 wk by maintenance of ejection fraction associated with increased left ventricular mass, relative wall thickness, end-diastolic pressure (EDP), end-diastolic pressure/end-diastolic volume (EDP/EDV) ratio, and tau, the time constant of isovolumic diastolic relaxation. After 4 to 6 wk of treatment, the GHRH-A group exhibited normalization of EDP (P = 0.03), reduced EDP/EDV ratio (P = 0.018), and a reduction in myocardial pro-brain natriuretic peptide protein abundance. GHRH-A increased cardiomyocyte [Ca2+] transient amplitude (P = 0.009). Improvement of the diastolic function was also evidenced by increased abundance of titin isoforms and their ratio (P = 0.0022). GHRH-A exerted a beneficial effect on diastolic function in a CKD large-animal model as demonstrated by improving hemodynamic, structural, and molecular characteristics of HFpEF. These findings have important therapeutic implications for the HFpEF syndrome.

Sustained IGF-1 Secretion by Adipose-Derived Stem Cells Improves Infarcted Heart Function.

The mechanism by which stem cell-based therapy improves heart function is still unknown, but paracrine mechanisms seem to be involved. Adipose-derived stem cells (ADSCs) secrete several factors, including insulin-like growth factor-1 (IGF-1), which may contribute to myocardial regeneration. Our aim was to investigate whether the overexpression of IGF-1 in ADSCs (IGF-1-ADSCs) improves treatment of chronically infarcted rat hearts. ADSCs were transduced with a lentiviral vector to induce IGF-1 overexpression. IGF-1-ADSCs transcribe100- to 200-fold more IGF-1 mRNA levels compared to nontransduced ADSCs. IGF-1 transduction did not alter ADSC immunophenotypic characteristics even under hypoxic conditions. However, IGF-1-ADSCs proliferate at higher rates and release greater amounts of growth factors such as IGF-1, vascular endothelial growth factor (VEGF), and hepatocyte growth factor (HGF) under normoxic and hypoxic conditions. Importantly, IGF-1 secreted by IGF-1-ADSCs is functional given that Akt-1 phosphorylation was remarkably induced in neonatal cardiomyocytes cocultured with IGF-1-ADSCs, and this increase was prevented with phosphatidylinositol 3-kinase (PI3K) inhibitor treatment. Next, we tested IGF-1-ADSCs in a rat myocardial infarction (MI) model. MI was performed by coronary ligation, and 4 weeks after MI, animals received intramyocardial injections of either ADSCs (n = 7), IGF-1-ADSCs (n = 7), or vehicle (n = 7) into the infarcted border zone. Left ventricular function was evaluated by echocardiography before and after 6 weeks of treatment, and left ventricular hemodynamics were assessed 7 weeks after cell injection. Notably, IGF-1-ADSCs improved left ventricular ejection fraction and cardiac contractility index, but did not reduce scar size when compared to the ADSC-treated group. In summary, transplantation of ADSCs transduced with IGF-1 is a superior therapeutic approach to treat MI compared to nontransduced ADSCs, suggesting that gene and cell therapy may bring additional benefits to the treatment of MI.

Growth hormone-releasing hormone agonists reduce myocardial infarct scar in swine with subacute ischemic cardiomyopathy.

BACKGROUND: Growth hormone-releasing hormone agonists (GHRH-As) stimulate cardiac repair following myocardial infarction (MI) in rats through the activation of the GHRH signaling pathway within the heart. We tested the hypothesis that the administration of GHRH-As prevents ventricular remodeling in a swine subacute MI model. METHODS AND RESULTS: Twelve female Yorkshire swine (25 to 30 kg) underwent transient occlusion of the left anterior descending coronary artery (MI). Two weeks post MI, swine were randomized to receive injections of either 30 µg/kg GHRH-A (MR-409) (GHRH-A group; n=6) or vehicle (placebo group; n=6). Cardiac magnetic resonance imaging and pressure-volume loops were obtained at multiple time points. Infarct, border, and remote (noninfarcted) zones were assessed for GHRH receptor by immunohistochemistry. Four weeks of GHRH-A treatment resulted in reduced scar mass (GHRH-A: -21.9 ± 6.42%; P=0.02; placebo: 10.9 ± 5.88%; P=0.25; 2-way ANOVA; P=0.003), and scar size (percentage of left ventricular mass) (GHRH-A: -38.38 ± 4.63; P=0.0002; placebo: -14.56 ± 6.92; P=0.16; 2-way ANOVA; P=0.02). This was accompanied by improved diastolic strain. Unlike in rats, this reduced infarct size in swine was not accompanied by improved cardiac function as measured by serial hemodynamic pressure-volume analysis. GHRH receptors were abundant in cardiac tissue, with a greater density in the border zone of the GHRH-A group compared with the placebo group. CONCLUSIONS: Daily subcutaneous administration of GHRH-A is feasible and safe in a large animal model of subacute ischemic cardiomyopathy. Furthermore, GHRH-A therapy significantly reduced infarct size and improved diastolic strain, suggesting a local activation of the GHRH pathway leading to the reparative process.

Adipose-derived stromal cell therapy improves cardiac function after coronary occlusion in rats.

Recent studies have identified adipose tissue as a new source of mesenchymal stem cells for therapy. The purpose of this study was to investigate the therapy with adipose-derived stromal cells (ASCs) in a rat model of healed myocardial infarction (MI). ASCs from inguinal subcutaneous adipose tissue of male Wistar rats were isolated by enzymatic digestion and filtration. Cells were then cultured until passage 3. Four weeks after ligation of the left coronary artery of female rats, a suspension of either 100 µl with phosphate-buffered saline (PBS) + Matrigel + 2 × 10(6) ASCs labeled with Hoechst (n = 11) or 100 µl of PBS + Matrigel (n = 10) was injected along the borders of the ventricular wall scar tissue. A sham-operated group (n = 5) was submitted to the same surgical procedure except permanent ligation of left coronary artery. Cardiac performance was assessed by electro- and echocardiogram. Echo was performed prior to injections (baseline, BL) and 6 weeks after injections (follow-up, FU), and values after treatment were normalized by values obtained before treatment. Hemodynamic measurements were performed 6 weeks after injections. All infarcted animals exhibited cardiac function impairment. Ejection fraction (EF), shortening fractional area (SFA), and left ventricular akinesia (LVA) were similar between infarcted groups before treatment. Six weeks after therapy, ASC group showed significant improvement in all three ECHO indices in comparison to vehicle group. In anesthetized animals dp/dt(+) was also significantly higher in ASCs when compared to vehicle. In agreement with functional improvement, scar area was diminished in the ASC group. We conclude that ASCs improve cardiac function in infarcted rats when administered directly to the myocardium.