Update on cardiac stem cell therapy in heart failure

SERS monitoring of local pH in encapsulated therapeutic cells

Microencapsulation of therapeutic cells has widely advanced toward the development of treatments for various diseases, in particular seeking the protection of cell transplants from immune rejection. However, several challenges in cell therapy remain due to the lack of suitable methods to monitor in vivo microcapsule tracking, microcapsule stability and/or altered cell viability and proliferation upon transplantation. We propose in this work the incorporation of contrast agents in microcapsules, which can be easily visualized by SERS imaging. By placing SERS probes in the alginate extracellular layer, a high contrast can be obtained with negligible toxicity. Specifically, we used a pH-sensitive SERS tracking probe consisting of gold nanostars encoded with a pH-sensitive Raman-active molecule, and protected by a layer of biocompatible polymer coating, grafted on the nanoparticles via electrostatic interactions. This nanomaterial is highly sensitive within the biologically relevant pH range, 5.5-7.8. We demonstrate that this SERS-based pH sensor can provide information about cell death of microencapsulated cells, in a non-invasive manner. As a result, we expect that this approach should provide a general strategy to study biological interactions at the microcapsule level.

Hyaluronate supports hESC-cardiomyocyte cell therapy for cardiac regeneration after acute myocardial infarction

Introduction

Enormous progress has been made in cardiac regeneration using human embryonic stem cell‐derived cardiomyocyte (hESC‐CM) grafts in pre‐clinical trials. However, the rate of cell survival has remained very low due to anoikis after transplantation into the heart as single cells. Numerous solutions have been proposed to improve cell survival, and one of these strategies is to co‐transplant biocompatible materials or hydrogels with the hESC‐CMs.

Methods

In our study, we screened various combinations of biomaterials that could promote anoikis resistance and improve hESC‐CM survival upon co‐transplantation and promote cardiac functional recovery. We injected different combinations of Matrigel, alginate and hyaluronate with hESC‐CM suspensions into the myocardium of rat models with myocardial infarction (MI).

Results

Our results showed that the group treated with a combination of hyaluronate and hESC‐CMs had the lowest arrhythmia rates when stimulated with programmed electrical stimulation. While all three combinations of hydrogel‐hESC‐CM treatments improved rat cardiac function compared with the saline control group, the combination with hyaluronate most significantly reduced pathological changes from left ventricular remodelling and improved both left ventricular function and left ventricular ejection fraction by 28 days post‐infarction.

Conclusion

Hence, we concluded that hyaluronate‐hESC‐CM is a superior combination therapy for promoting cardiac regeneration after myocardial infarction.

Is Stem Cell Therapy an Answer to Heart Failure: A Literature Search

The heart is one of the most industrious organs in the human body. It starts beating in the first few weeks of embryonic life and keeps pumping blood till death. This organ can host a range of diseases as well. Some can hamper the vasculature, while others can affect its electrical activity, the heart valves, etc. All these conditions can lead to end-stage failure where it can no longer meet the requirements of the body’s milieu. This imbalance between supply and demand leads to an array of symptoms. Medical management can reduce these clinical effects and possibly prolong the life expectancy in such patients. However, prescription medications can also have their own adverse effects. This necessitates that each line of treatment should be assessed on a risk vs benefit basis. The conventional approach has been to try and slow down the progression of heart failure (HF). However, the inception of stem cells in the management of HF has the potential for reversal of this pathology. Keeping this in view, many studies and trials are under process. To turn the clock back on the HF, before complications set in or get out of control, is the main focus of the time. This article attempts to evaluate various studies about stem cell therapy (SCT) and highlight the important aspects of this novel modality in changing patients' lives.

Mesenchymal Stem Cell Deformability and Implications for Microvascular Sequestration

Mesenchymal stem cells (MSCs) have received considerable attention in regenerative medicine, particularly in light of prospects for targeted delivery by intra-arterial injection. However, little is known about the mechanics of MSC sequestration in the microvasculature and the yield pressure (PY), above which MSCs will pass through microvessels of a given diameter. The objectives of the current study were to delineate the dependency of PY on cell size and the heterogeneity of cell mechanical properties and diameters (DCELL) of cultured MSCs. To this end the transient filtration test was employed to elucidate the mean filtration pressure (〈PY〉) for an ensemble of pores of a given size (DPORE) similar to in vivo microvessels. Cultured MSCs had a log-normal distribution of cell diameters (DCELL) with a mean of 15.8 ± 0.73 SD μm. MSC clearance from track-etched polycarbonate filters was studied for pore diameters of 7.3-15.4 μm. The pressure required to clear cells from filters with 30-85 × 103 pores rose exponentially with the ratio λ = DCELL/DPORE for 1.1 ≤ λ ≤ 2.2. The clearance of cells from each filter was characterized by a log-normal distribution in PY, with a mean filtration pressure of 0.02 ≤ 〈PY〉 ≤ 6.7 cmH2O. For λ ≤ 1.56, the yield pressure (PY) was well represented by the cortical shell model of a cell with a viscous interior encapsulated by a shell under cortical tension τ0 = 0.99 ± 0.42 SD dyn/cm. For λ > 1.56, the 〈PY〉 characteristic of the cell population rose exponentially with λ. Analysis of the mean filtration pressure (〈PY〉) of each sample suggested that the larger diameter cells that skewed the distribution of DCELL contributed to about 20% of the mean filtration pressure. Further, if all cells had the same deformability (i.e., PY as a function of λ) as the average cell population, then 〈PY〉 would have risen an order of magnitude above the average from fivefold at λ = 1.56 to 200-fold at λ = 2.1. Comparison of 〈PY〉 to published microvascular pressures suggested that 〈PY〉 may exceed microvessel pressure drops for λ exceeding 2.1, and rise 14-fold above capillary pressure drop at λ = 3 leading to 100% sequestration. However, due to the large variance of in vivo microvascular pressures entrapment of MSCs may be mitigated. Thus it is suggested that selecting fractions of the MSC population according to cell deformability may permit optimization of entrapment at sites targeted for tissue regeneration.

Epicardial delivery of autologous atrial appendage micrografts during coronary artery bypass surgery-safety and feasibility study

Background

The atrial appendages are a tissue reservoir for cardiac stem cells. During on-pump coronary artery bypass graft (CABG) surgery, part of the right atrial appendage can be excised upon insertion of the right atrial cannula of the heart-lung machine. In the operating room, the removed tissue can be easily cut into micrografts for transplantation. This trial aims to assess the safety and feasibility of epicardial transplantation of atrial appendage micrografts in patients undergoing CABG surgery.

Methods/design

Autologous cardiac micrografts are made from leftover right atrial appendage during CABG of 6 patients. Atrial appendage is mechanically processed to micrografts consisting of atrial appendage-derived cells (AADCs) and their extracellular matrix (ECM). The micrografts are epicardially transplanted in a fibrin gel and covered with a tissue-engineered ECM sheet. Parameters including echocardiography—reflecting cardiac insufficiency—are studied pre- and post-operatively as well as at 3 and 6 months of the follow-up. Cardiac functional magnetic resonance imaging is performed preoperatively and at 6-month follow-up. The primary outcome measures are patient safety in terms of hemodynamic and cardiac function over time and feasibility of therapy administration in a clinical setting. Secondary outcome measures are left ventricular wall thickness, change in the amount of myocardial scar tissue, changes in left ventricular ejection fraction, plasma concentrations of N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels, New York Heart Association class, days in hospital, and changes in the quality of life. Twenty patients undergoing routine CAGB surgery will be recruited to serve as a control group.

Discussion

This study aims to address the surgical feasibility and patient safety of epicardially delivered atrial appendage micrografts during CABG surgery. Delivery of autologous micrografts and AADCs has potential applications for cell and cell-based gene therapies.

Trial registration

ClinicalTrials.gov Identifier: NCT02672163. Date of registration: 02.02.2016

Wound repair and regeneration: mechanisms, signaling, and translation

The cellular and molecular mechanisms underpinning tissue repair and its failure to heal are still poorly understood, and current therapies are limited. Poor wound healing after trauma, surgery, acute illness, or chronic disease conditions affects millions of people worldwide each year and is the consequence of poorly regulated elements of the healthy tissue repair response, including inflammation, angiogenesis, matrix deposition, and cell recruitment. Failure of one or several of these cellular processes is generally linked to an underlying clinical condition, such as vascular disease, diabetes, or aging, which are all frequently associated with healing pathologies. The search for clinical strategies that might improve the body's natural repair mechanisms will need to be based on a thorough understanding of the basic biology of repair and regeneration. In this review, we highlight emerging concepts in tissue regeneration and repair, and provide some perspectives on how to translate current knowledge into viable clinical approaches for treating patients with wound-healing pathologies.

Leptin signaling is required for augmented therapeutic properties of mesenchymal stem cells conferred by hypoxia preconditioning

Hypoxia preconditioning enhances the therapeutic effect of mesenchymal stem cells (MSCs). However, the mechanism underlying hypoxia-induced augmentation of the protective effect of MSCs on myocardial infarction (MI) is poorly understood. We show that hypoxia-enhanced survival, mobility, and protection of cocultured cardiomyocytes were paralleled by increased expression of leptin and cell surface receptor CXCR4. The enhanced activities were abolished by either knockdown of leptin with a selective shRNA or by genetic deficiency of leptin or its receptor in MSCs derived, respectively, from ob/ob or db/db mice. To characterize the role of leptin in the regulation of MSC functions by hypoxia and its possible contribution to enhanced therapeutic efficacy, cell therapy using MSCs derived from wild-type, ob/ob, or db/db mice was implemented in mouse models of acute MI. Augmented protection by hypoxia pretreatment was only seen with MSCs from wild-type mice. Parameters that were differentially affected by hypoxia pretreatment included MSC engraftment, c-Kit(+) cell recruitment to the infarct, vascular density, infarct size, and long-term contractile function. These data show that leptin signaling is an early and essential step for the enhanced survival, chemotaxis, and therapeutic properties of MSCs conferred by preculture under hypoxia. Leptin may play a physiological role in priming MSCs resident in the bone marrow endosteum for optimal response to systemic signaling molecules and subsequent tissue repair.

Cardiac stem cells and their roles in myocardial infarction

Myocardial infarction leads to loss of cardiomyocytes, scar formation, ventricular remodeling and eventually deterioration of heart function. Over the past decade, stem cell therapy has emerged as a novel strategy for patients with ischemic heart disease and its beneficial effects have been demonstrated by substantial preclinical and clinical studies. Efficacy of several types of stem cells in the therapy of cardiovascular diseases has already been evaluated. However, repair of injured myocardium through stem cell transplantation is restricted by critical safety issues and ethic concerns. Recently, the discovery of cardiac stem cells (CSCs) that reside in the heart itself brings new prospects for myocardial regeneration and reconstitution of cardiac tissues. CSCs are positive for various stem cell markers and have the potential of self-renewal and multilineage differentiation. They play a pivotal role in the maintenance of heart homeostasis and cardiac repair. Elucidation of their biological characteristics and functions they exert in myocardial infarction are very crucial to further investigations on them. This review will focus on the field of cardiac stem cells and discuss technical and practical issues that may involve in their clinical applications in myocardial infarction.

Autologous bone marrow-derived stem cell therapy in heart disease: discrepancies and contradictions

BACKGROUND

Autologous bone marrow stem cell therapy is the greatest advance in the treatment of heart disease for a generation according to pioneering reports. In response to an unanswered letter regarding one of the largest and most promising trials, we attempted to summarise the findings from the most innovative and prolific laboratory.

METHOD AND RESULTS

Amongst 48 reports from the group, there appeared to be 5 actual clinical studies ("families" of reports). Duplicate or overlapping reports were common, with contradictory experimental design, recruitment and results. Readers cannot always tell whether a study is randomised versus not, open-controlled or blinded placebo-controlled, or lacking a control group. There were conflicts in recruitment dates, criteria, sample sizes, million-fold differences in cell counts, sex reclassification, fractional numbers of patients and conflation of competitors' studies with authors' own. Contradictory results were also common. These included arithmetical miscalculations, statistical errors, suppression of significant changes, exaggerated description of own findings, possible silent patient deletions, fractional numbers of coronary arteries, identical results with contradictory sample sizes, contradictory results with identical sample sizes, misrepresented survival graphs and a patient with a negative NYHA class. We tabulate over 200 discrepancies amongst the reports. The 5 family-flagship papers (Strauer 2002, STAR, IACT, ABCD, BALANCE) have had 2665 citations. Of these, 291 citations were to the pivotal STAR or IACT-JACC papers, but 97% of their eligible citing papers did not mention any discrepancies. Five meta-analyses or systematic reviews covered these studies, but none described any discrepancies and all resolved uncertainties by undisclosed methods, in mutually contradictory ways. Meta-analysts disagreed whether some studies were randomised or "accepter-versus-rejecter". Our experience of presenting the discrepancies to journals is that readers may remain unaware of such problems.

CONCLUSIONS

Modern reporting of clinical research can still be imperfect. The scientific literature absorbs such reports largely uncritically. Even meta-analyses seem to resolve contradictions haphazardly. Discrepancies communicated to journals are not guaranteed to reach the scientific community. Journals could consider prioritising systematic reporting of queries even if seemingly minor, and establishing a policy of "habeas data".

Microencapsulated cell tracking

Microencapsulation of therapeutic cells has been widely pursued to achieve cellular immunoprotection following transplantation. Initial clinical studies have shown the potential of microencapsulation using semi-permeable alginate layers, but much needs to be learned about the optimal delivery route, in vivo pattern of engraftment, and microcapsule stability over time. In parallel with noninvasive imaging techniques for 'naked' (i.e. unencapsulated) cell tracking, microcapsules have now been endowed with contrast agents that can be visualized by (1) H MRI, (19) F MRI, X-ray/computed tomography and ultrasound imaging. By placing the contrast agent formulation in the extracellular space of the hydrogel, large amounts of contrast agents can be incorporated with negligible toxicity. This has led to a new generation of imaging biomaterials that can render cells visible with multiple imaging modalities.

Stem cell transplantation in cardiovascular disease: an update

Despite the development of novel therapeutic strategies, cardiovascular diseases remain the main cause of morbidity and mortality worldwide. Many phase 1 and 2 clinical trials have reported the safety, feasibility and promising potential of stem cell transplantation, however, the optimal cell types, timing of infusion, cell dosage and routes of administration remain to be determined. This paper reviews the findings of various clinical studies and discusses the challenges facing the delivery of stem cell therapy in cardiovascular diseases.

The renin–angiotensin system, bone marrow and progenitor cells

Modulation of the RAS (renin–angiotensin system), in particular of the function of the hormones AngII (angiotensin II) and Ang-(1–7) [angiotensin-(1–7)], is an important target for pharmacotherapy in the cardiovascular system. In the classical view, such modulation affects cardiovascular cells to decrease hypertrophy, fibrosis and endothelial dysfunction, and improves diuresis. In this view, excessive stimulation of AT1 receptors (AngII type 1 receptors) fulfils a detrimental role, as it promotes cardiovascular pathogenesis, and this is opposed by stimulation of the AT2 receptor (angiotensin II type 2 receptor) and the Ang-(1–7) receptor encoded by the Mas proto-oncogene. In recent years, this view has been broadened with the observation that the RAS regulates bone marrow stromal cells and stem cells, thus involving haematopoiesis and tissue regeneration by progenitor cells. This change of paradigm has enlarged the field of perspectives for therapeutic application of existing as well as newly developed medicines that alter angiotensin signalling, which now stretches beyond cardiovascular therapy. In the present article, we review the role of AngII and Ang-(1–7) and their respective receptors in haematopoietic and mesenchymal stem cells, and discuss possible pharmacotherapeutical implications.