Skeletal myoblasts transplanted in the ischemic myocardium enhance in situ oxygenation and recovery of contractile function

tRNA-derived small RNA changes in bone marrow stem cells under hypoxia and osteogenic conduction

BACKGROUND

Tissue engineering using bone mesenchymal stem cells (BMSCs) transplantation is a promising therapeutic for bone regeneration. However, the effect of bone regeneration remains unsatisfactory due to the BMSCs' functional abnormality influenced by hypoxia. In this study, we attempt to explore the mechanism of osteogenic differentiation of BMSCs under hypoxic conditions from the perspective of non-coding RNA regulation.

METHODS

The study employed BMSCs obtained from healthy donors and simulated hypoxia using CoCl2 stimulation. High-throughput sequencing technique was used to identify differential expression profiles of tRNA-derived small RNA (tsRNA) in three experimental groups: BMSCs-0d, BMSCs-7d and BMSCs-0d-CoCl2 . TargetScan and miRanda algorithms were used to determine tsRNA target genes, while Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis were employed for the prediction of biological functions. Real-time reverse transcriptase-polymerase chain reaction (Real-time RT-PCR) was carried out on four selected differentially expressed tsRNAs.

RESULTS

After the osteogenic induction and CoCl2 stimulated separately, there were 19 tsRNAs differentially expressed in BMSCs, including 14 upregulated and five downregulated. According to the analysis of biological information, these tsRNAs may regulate 311 potential target genes and mainly enrich the pathways such as metabolic pathways, Wnt signalling pathway, osteoclast differentiation, cellular senescence and mTOR signalling pathway. The results of Real-time RT-PCR for 3'tiRNA-41-GlnTTG-6, 3'tiRNA-42-LysTTT-8, 5'tiRNA-35-CysACA-1 and tRF3a-AsnGTT-9 were consistent with small RNA sequencing data.

CONCLUSION

We discovered the tsRNA that changes the process of osteogenesis and hypoxia, which provides new targets for promoting survival and regeneration functions after BMSCs transplantation.

Cell augmentation strategies for cardiac stem cell therapies

Myocardial infarction (MI) has been the primary cause of death in developed countries, resulting in a major psychological and financial burden for society. Current treatments for acute MI are directed toward rapid restoration of perfusion to limit damage to the myocardium, rather than promoting tissue regeneration and subsequent contractile function recovery. Regenerative cell therapies (CTs), in particular those using multipotent stem cells (SCs), are in the spotlight for treatment post‐MI. Unfortunately, the efficacy of CTs is somewhat limited by their poor long‐term viability, homing, and engraftment to the myocardium. In response, a range of novel SC‐based technologies are in development to provide additional cellular modalities, bringing CTs a step closer to the clinic. In this review, the current landscape of emerging CTs and their augmentation strategies for the treatment post‐MI are discussed. In doing so, we highlight recent advances in cell membrane reengineering via genetic modifications, recombinant protein immobilization, and the utilization of soft biomimetic scaffold interfaces.

Application of Cell, Tissue, and Biomaterial Delivery in Cardiac Regenerative Therapy

Cardiovascular diseases (CVD) are the leading cause of death around the world, being responsible for 31.8% of all deaths in 2017 (Roth, G. A. et al. The Lancet 2018, 392, 1736-1788). The leading cause of CVD is ischemic heart disease (IHD), which caused 8.1 million deaths in 2013 (Benjamin, E. J. et al. Circulation 2017, 135, e146-e603). IHD occurs when coronary arteries in the heart are narrowed or blocked, preventing the flow of oxygen and blood into the cardiac muscle, which could provoke acute myocardial infarction (AMI) and ultimately lead to heart failure and death. Cardiac regenerative therapy aims to repair and refunctionalize damaged heart tissue through the application of (1) intramyocardial cell delivery, (2) epicardial cardiac patch, and (3) acellular biomaterials. In this review, we aim to examine these current approaches and challenges in the cardiac regenerative therapy field.

Stem cell therapy in the heart: Biomaterials as a key route

Cardiovascular diseases are one of the main concerns, nowadays causing a high rate of mortality in the world. The majority of conventional treatment protects the heart from failure progression. As a novel therapeutic way, Regenerative medicine in the heart includes cellular and noncellular approaches. Despite the irrefutable privileges of noncellular aspects such as administration of exosomes, utilizing of miRNAs, and growth factors, they cannot reverse necrotic or ischemic myocardium, hence recruiting of stem cells to help regenerative therapy in the heart seems indispensable. Stem cell lineages are varied and divided into two main groups namely pluripotent and adult stem cells. Not only has each of which own regenerative capacity, benefits, and drawbacks, but their turnover also close correlates with the target organ and/or tissue as well as the stage and level of failure. In addition to inefficient tissue integration due to the defects in delivering methods and poor retention of transplanted cells, the complexity of the heart and its movement also make more rigorous the repair process. Hence, utilizing biomaterials can make a key route to tackle such obstacles. In this review, we evaluate some natural products which can help stem cells in regenerative medicine of the cardiovascular system.

Cardiomyocyte Induction and Regeneration for Myocardial Infarction Treatment: Cell Sources and Administration Strategies

Occlusion of coronary artery and subsequent damage or death of myocardium can lead to myocardial infarction (MI) and even heart failure-one of the leading causes of deaths world wide. Notably, myocardium has extremely limited regeneration potential due to the loss or death of cardiomyocytes (i.e., the cells of which the myocardium is comprised) upon MI. A variety of stem cells and stem cell-derived cardiovascular cells, in situ cardiac fibroblasts and endogenous proliferative epicardium, have been exploited to provide renewable cellular sources to treat injured myocardium. Also, different strategies, including direct injection of cell suspensions, bioactive molecules, or cell-incorporated biomaterials, and implantation of artificial cardiac scaffolds (e.g., cell sheets and cardiac patches), have been developed to deliver renewable cells and/or bioactive molecules to the MI site for the myocardium regeneration. This article briefly surveys cell sources and delivery strategies, along with biomaterials and their processing techniques, developed for MI treatment. Key issues and challenges, as well as recommendations for future research, are also discussed.

Biocompatibility of Oxygen-Sensing Paramagnetic Implants

Oxygen-sensing implants, composed of paramagnetic microcrystals embedded in a biocompatible polymer, are increasingly being used for electron paramagnetic resonance (EPR) oximetry in animal models and human subjects. The implants are stable and designed to stay in the tissues for indefinite periods. However, it is not known whether the crystals that may be exposed on the surface of the implants or leached out from the implants will induce cytotoxicity thereby compromising their biocompatibility over the long term. The goal of the current study was to evaluate the cytotoxicity of the implants and crystalline particulates under in vitro conditions. Apoptosis and cell viability studies were performed using L6, a rat muscle cell line and AsPC-1, a cancer cell line derived from human pancreatic adenocarcinoma. The results indicated that neither the intact implants nor their components elicit cytotoxicity, thus establishing their biocompatibility for use in human subjects.

Transcutaneous oxygen measurement in humans using a paramagnetic skin adhesive film

PURPOSE

Transcutaneous oxygen tension (TcpO₂ ) provides information about blood perfusion in the tissue immediately below the skin. These data are valuable in assessing wound healing problems, diagnosing peripheral vascular/arterial insufficiency, and predicting disease progression or the response to therapy. Currently, TcpO₂ is primarily measured using electrochemical skin sensors, which consume oxygen and are prone to calibration errors. The goal of the present study was to develop a reliable method for TcpO₂ measurement in human subjects.

METHODS

We have developed a novel TcpO₂ oximetry method based on electron paramagnetic resonance (EPR) principles with an oxygen-sensing skin adhesive film, named the superficial perfusion oxygen tension (SPOT) chip. The SPOT chip is a 3-mm diameter, 60-μm thick circular film composed of a stable paramagnetic oxygen sensor. The chip is covered with an oxygen-barrier material on one side and secured on the skin by a medical adhesive transfer tape to ensure that only the oxygen that diffuses through the skin surface is measured. The method quantifies TcpO₂ through the linewidth of the EPR spectrum.

RESULTS

Repeated measurements using a cohort of 10 healthy human subjects showed that the TcpO₂ measurements were robust, reliable, and reproducible. The TcpO₂ values ranged from 7.8 ± 0.8 to 22.0 ± 1.0 mmHg in the volar forearm skin (N = 29) and 8.1 ± 0.3 to 23.4 ± 1.3 mmHg in the foot (N = 86).

CONCLUSIONS

The results demonstrated that the SPOT chip can measure TcpO₂ reliably and repeatedly under ambient conditions. The SPOT chip method could potentially be used to monitor TcpO₂ in the clinic.

Contribution of Harold M. Swartz to In Vivo EPR and EPR Dosimetry

In 2015, we are celebrating half a century of research in the application of Electron Paramagnetic Resonance (EPR) as a biodosimetry tool to evaluate the dose received by irradiated people. During the EPR Biodose 2015 meeting, a special session was organized to acknowledge the pioneering contribution of Harold M. (Hal) Swartz in the field. The article summarizes his main contribution in physiology and medicine. Four emerging themes have been pursued continuously along his career since its beginning: (1) radiation biology; (2) oxygen and oxidation; (3) measuring physiology in vivo; and (4) application of these measurements in clinical medicine. The common feature among all these different subjects has been the use of magnetic resonance techniques, especially EPR. In this article, you will find an impressionist portrait of Hal Swartz with the description of the 'making of' this pioneer, a time-line perspective on his career with the creation of three National Institutes of Health-funded EPR centers, a topic-oriented perspective on his career with a description of his major contributions to Science, his role as a mentor and his influence on his academic children, his active role as founder of scientific societies and organizer of scientific meetings, and the well-deserved international recognition received so far.

Non-invasive technology that improves cardiac function after experimental myocardial infarction: Whole Body Periodic Acceleration (pGz)

Myocardial infarction (MI) may produce significant inflammatory changes and adverse ventricular remodeling leading to heart failure and premature death. Pharmacologic, stem cell transplantation, and exercise have not halted the inexorable rise in the prevalence and great economic costs of heart failure despite extensive investigations of such treatments. New therapeutic modalities are needed. Whole Body Periodic Acceleration (pGz) is a non-invasive technology that increases pulsatile shear stress to the endothelium thereby producing several beneficial cardiovascular effects as demonstrated in animal models, normal humans and patients with heart disease. pGz upregulates endothelial derived nitric oxide synthase (eNOS) and its phosphorylation (p-eNOS) to improve myocardial function in models of myocardial stunning and preconditioning. Here we test whether pGz applied chronically after focal myocardial infarction in rats improves functional outcomes from MI. Focal MI was produced by left coronary artery ligation. One day after ligation animals were randomized to receive daily treatments of pGz for four weeks (MI-pGz) or serve as controls (MI-CONT), with an additional group as non-infarction controls (Sham). Echocardiograms and invasive pressure volume loop analysis were carried out. Infarct transmurality, myocardial fibrosis, and markers of inflammatory and anti-inflammatory cytokines were determined along with protein analysis of eNOS, p-eNOS and inducible nitric oxide synthase (iNOS).At four weeks, survival was 80% in MI-pGz vs 50% in MI-CONT (p< 0.01). Ejection fraction and fractional shortening and invasive pressure volume relation indices of afterload and contractility were significantly better in MI-pGz. The latter where associated with decreased infarct transmurality and decreased fibrosis along with increased eNOS, p-eNOS. Additionally, MI-pGz had significantly lower levels of iNOS, inflammatory cytokines (IL-6, TNF-α), and higher level of anti-inflammatory cytokine (IL-10). pGz improved survival and contractile performance, associated with improved myocardial remodeling. pGz may serve as a simple, safe, non-invasive therapeutic modality to improve myocardial function after MI.

Effect of serum and oxygen concentration on gene expression and secretion of paracrine factors by mesenchymal stem cells

Mesenchymal stem cells (MSC) secrete paracrine factors that may exert a protective effect on the heart after coronary artery occlusion. This study was done to determine the effect of hypoxia and serum levels on the mRNA expression and secretion of paracrine factors. Mouse bone marrow MSC were cultured with 5% or 20% serum and in either normoxic (21% O₂) or hypoxic (1% O₂) conditions. Expression of mRNA for vascular endothelial growth factor (VEGF), monocyte chemotactic protein-1 (MCP-1), macrophage inflammatory protein-1α (MIP-1α), MIP-1β, and matrix metalloproteinase-2 (MMP-2) was determined by RT-qPCR. Secretion into the culture media was determined by ELISA. Hypoxia caused a reduction in gene expression for MCP-1 and an increase for VEGF (5% serum), MIP-1α, MIP-1β, and MMP-2. Serum reduction lowered gene expression for VEGF (normoxia), MCP-1 (hypoxia), MIP-1α (hypoxia), MIP-1β (hypoxia), and MMP-2 (hypoxia) and increased gene expression for MMP-2 (normoxia). The level of secretion of these factors into the media generally paralleled gene expression with some exceptions. These data demonstrate that serum and oxygen levels have a significant effect on the gene expression and secretion of paracrine factors by MSC which will affect how MSC interact in vivo during myocardial ischemia.

Noninvasive monitoring of small intestinal oxygen in a rat model of chronic mesenteric ischemia

We noninvasively monitored the partial pressure of oxygen (pO2) in rat's small intestine using a model of chronic mesenteric ischemia by electron paramagnetic resonance oximetry over a 7-day period. The particulate probe lithium octa-n-butoxynaphthalocyanine (LiNc-BuO) was embedded into the oxygen permeable material polydimethyl siloxane by cast-molding and polymerization (Oxy-Chip). A one-time surgical procedure was performed to place the Oxy-Chip on the outer wall of the small intestine (SI). The superior mesenteric artery (SMA) was banded to ~30% of blood flow for experimental rats. Noninvasive measurement of pO2 was performed at the baseline for control rats or immediate post-banding and on days 1, 3, and 7. The SI pO2 for control rats remained stable over the 7-day period. The pO2 on day-7 was 54.5 ± 0.9 mmHg (mean ± SE). SMA-banded rats were significantly different from controls with a noted reduction in pO2 post banding with a progressive decline to a final pO2 of 20.9 ± 4.5 mmHg (mean ± SE; p = 0.02). All SMA-banded rats developed adhesions around the Oxy-Chip, yet remained asymptomatic. The hypoxia marker Hypoxyprobe™ was used to validate the low tissue pO2. Brown cytoplasmic staining was consistent with hypoxia. Mild brown staining was noted predominantly on the villus tips in control animals. SMA-banded rats had an extended region of hypoxic involvement in the villus with a higher intensity of cytoplasmic staining. Deep brown stainings of the enteric nervous system neurons and connective tissue both within layers and in the mesentery were noted. SMA-banded rats with lower pO2 values had a higher intensity of staining. Thus, monitoring SI pO2 using the probe Oxy-Chip provides a valid measure of tissue oxygenation. Tracking pO2 in conditions that produce chronic mesenteric ischemia will contribute to our understanding of intestinal tissue oxygenation and how changes impact symptom evolution and the trajectory of chronic disease.

The stem cell adjuvant with Exendin-4 repairs the heart after myocardial infarction via STAT3 activation

The poor survival of cells in ischaemic myocardium is a major obstacle for stem cell therapy. Exendin-4 holds the potential of cardioprotective effect based on its pleiotropic activity. This study investigated whether Exendin-4 in conjunction with adipose-derived stem cells (ADSCs) could improve the stem cell survival and contribute to myocardial repairs after infarction. Myocardial infarction (MI) was induced by the left anterior descending artery ligation in adult male Sprague-Dawley rats. ADSCs carrying double-fusion reporter gene [firefly luciferase and monomeric red fluorescent protein (fluc-mRFP)] were quickly injected into border zone of MI in rats treated with or without Exendin-4. Exendin-4 enhanced the survival of transplanted ADSCs, as demonstrated by the longitudinal in vivo bioluminescence imaging. Moreover, ADSCs adjuvant with Exendin-4 decreased oxidative stress, apoptosis and fibrosis. They also improved myocardial viability and cardiac function and increased the differentiation rates of ADSCs into cardiomyocytes and vascular smooth muscle cells in vivo. Then, ADSCs were exposed to hydrogen peroxide/serum deprivation (H₂O₂/SD) to mimic the ischaemic environment in vitro. Results showed that Exendin-4 decreased the apoptosis and enhanced the paracrine effect of ADSCs. In addition, Exendin-4 activated signal transducers and activators of transcription 3 (STAT3) through the phosphorylation of Akt and ERK1/2. Furthermore, Exendin-4 increased the anti-apoptotic protein Bcl-2, but decreased the pro-apoptotic protein Bax of ADSCs. In conclusion, Exendin-4 could improve the survival and therapeutic efficacy of transplanted ADSCs through STAT3 activation via the phosphorylation of Akt and ERK1/2. This study suggests the potential application of Exendin-4 for stem cell–based heart regeneration.

Advances in probes and methods for clinical EPR oximetry

EPR oximetry, which enables reliable, accurate, and repeated measurements of the partial pressure of oxygen in tissues, provides a unique opportunity to investigate the role of oxygen in the pathogenesis and treatment of several diseases including cancer, stroke, and heart failure. Building on significant advances in the in vivo application of EPR oximetry for small animal models of disease, we are developing suitable probes and instrumentation required for use in human subjects. Our laboratory has established the feasibility of clinical EPR oximetry in cancer patients using India ink, the only material presently approved for clinical use. We now are developing the next generation of probes, which are both superior in terms of oxygen sensitivity and biocompatibility including an excellent safety profile for use in humans. Further advances include the development of implantable oxygen sensors linked to an external coupling loop for measurements of deep-tissue oxygenations at any depth, overcoming the current limitation of 10 mm. This paper presents an overview of recent developments in our ability to make meaningful measurements of oxygen partial pressures in human subjects under clinical settings.

Recent advancements in tissue engineering for stem cell-based cardiac therapies

Advances in cardiac tissue engineering have recently focused on utilizing stem cells to regenerate infarcted and scarred myocardium. Due to their proliferative nature and tremendous potential for differentiation, stem cells are presently being investigated for clinical applications. Unfortunately, limiting factors such as massive cell death and poor retention have hampered clinical outcomes. Consequently, the development of an efficient delivery system for stem cells to the target site is essential. The use of innovative tissue engineering techniques has opened up new horizons within the field of cellular cardiomyoplasty. This paper will present a comprehensive overview of the recent advancements in stem cell technology destined for myocardial tissue repair. In addition, the multidisciplinary approach to tissue engineering presented here will provide the reader with insight into the clinical realization of cellular cardiomyoplasty.

Stem cell transplantation as a therapy for cardiac fibrosis

Cardiac fibrosis is a fundamental constituent of most cardiac pathologies and represents the upshot of nearly all types of cardiac injury. Generally, fibrosis is a scarring process, characterized by accumulation of fibroblasts and deposition of increasing amounts of extracellular matrix (ECM) proteins in the myocardium. Therapeutic approaches that control fibroblast activity and evade maladaptive processes could represent a potential strategy to attenuate progression towards heart failure. Currently, cell therapy is actively perceived as an alternative to traditional pharmacological management of myocardial infarction (MI). The majority of the studies applying stem cell therapy following MI have demonstrated a decline in fibrosis. However, it was not clearly recognized whether the decline in cardiac fibrosis was due to replacement of dead cardiomyocytes or because of the direct effects of paracrine factors released from the transplanted stem cells on the ECM. Therefore, the main focus of this review is to discuss the impact of different types of stem cells on cardiac fibrosis and associated cardiac remodelling in a variety of experimental models of heart failure, particularly MI.

Carvedilol enhances mesenchymal stem cell therapy for myocardial infarction via inhibition of caspase-3 expression

Adult stem cells have shown great promise toward repairing infarcted heart and restoring cardiac function. Mesenchymal stem cells (MSCs), because of their inherent multipotent nature and their ability to secrete a multitude of growth factors and cytokines, have been used for cardiac repair with encouraging results. Preclinical studies showed that MSCs injected into infarcted hearts improve cardiac function and attenuate fibrosis. Although stem cell transplantation is a promising therapeutic option to repair the infarcted heart, it is faced with a number of challenges, including the survival of the transplanted cells in the ischemic region, due to excessive oxidative stress present in the ischemic region. The objective of this study was to determine the effect of Carvedilol (Carv), a nonselective β-blocker with antioxidant properties, on the survival and engraftment of MSCs in the infarcted heart. MSCs were subjected to a simulated host-tissue environment, similar to the one present in the infarcted myocardium, by culturing them in the presence of hydrogen peroxide (H(2)O(2)) to induce oxidative stress. MSCs were treated with 2.5 μM Carv for 1 h in serum-free medium, followed by treatment with H(2)O(2) for 2 h. The treated cells exhibited significant protection against H(2)O(2)-induced cell death versus untreated controls as determined by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assays. Likewise, transplantation of MSCs after permanent left coronary artery ligation and treatment of animals after myocardial infarction (MI) with Carv (5 mg/kg b.wt.) led to significant improvement in cardiac function, decreased fibrosis, and caspase-3 expression compared with the MI or MSC-alone groups.

Effect of oxygenation on stem-cell therapy for myocardial infarction

Stem-cell transplantation to treat acute myocardial infarction (MI) is gaining importance as a minimally invasive and potent therapy to replace akinetic scar tissue by viable myocardium. Our recent studies have shown that stem-cell transplantation marginally improves myocardial oxygenation in the infarct tissue leading to improvement in cardiac function. The aim of the present study was to determine the effect of hyperbaric oxygen (HBO) treatment on myocardial oxygenation and recovery of function in MI hearts. Fisher-344 rats were subjected to MI by permanently ligating the left-anterior-descending (LAD) coronary artery. The rats were then exposed to 100% O(2) at a pressure of 2 atmospheres for 90 minutes, and the exposure was repeated for 5 days a week for 2 weeks. Adult bone-marrow-derived rat mesenchymal stem cells (MSC, 5x10⁵ cells) were mixed with OxySpin (LiNc- BuO, oxygen sensor) and implanted in the infarct and peri-infarct regions of the heart. M-mode ultrasound echocardiography was performed at baseline and at 2 weeks post-transplantation. The myocardial pO(2) in the MSC+HBO group (16.2±2.2 mmHg) was significantly higher when compared to untreated MI (3.8±1.9 mmHg) or MSC (9.8±2.3 mmHg) groups. In addition, there was a significant improvement in cardiac function, increased vessel density, and VEGF expression in MSC+HBO group compared to MSC group (p < 0.05). In conclusion, the results suggested a beneficial effect of HBO administration on stem-cell therapy for MI.

Skeletal myoblasts for cardiac repair

Stem cells provide an alternative curative intervention for the infarcted heart by compensating for the cardiomyocyte loss subsequent to myocardial injury. The presence of resident stem and progenitor cell populations in the heart, and nuclear reprogramming of somatic cells with genetic induction of pluripotency markers are the emerging new developments in stem cell-based regenerative medicine. However, until safety and feasibility of these cells are established by extensive experimentation in in vitro and in vivo experimental models, skeletal muscle-derived myoblasts, and bone marrow cells remain the most well-studied donor cell types for myocardial regeneration and repair. This article provides a critical review of skeletal myoblasts as donor cells for transplantation in the light of published experimental and clinical data, and indepth discussion of the advantages and disadvantages of skeletal myoblast-based therapeutic intervention for augmentation of myocardial function in the infarcted heart. Furthermore, strategies to overcome the problems of arrhythmogenicity and failure of the transplanted skeletal myoblasts to integrate with the host cardiomyocytes are discussed.

De novo myocardial regeneration: advances and pitfalls

The capability of adult tissue-derived stem cells for cardiogenesis has been extensively studied in experimental animals and clinical studies for treatment of postischemic cardiomyopathy. The less-than-anticipated improvement in the heart function in most clinical studies with skeletal myoblasts and bone marrow cells has warranted a search for alternative sources of stem cells. Despite their multilineage differentiation potential, ethical issues, teratogenicity, and tissue rejection are main obstacles in developing clinically feasible methods for embryonic stem cell transplantation into patients. A decade-long research on embryonic stem cells has paved the way for discovery of alternative approaches for generating pluripotent stem cells. Genetic manipulation of somatic cells for pluripotency genes reprograms the cells to pluripotent status. Efforts are currently focused to make reprogramming protocols safer for clinical applications of the reprogrammed cells. We summarize the advancements and complicating features of stem cell therapy and discuss the decade-and-a-half-long efforts made by stem cell researchers for moving the field from bench to the bedside as an adjunct therapy or as an alternative to the contemporary therapeutic modalities for routine clinical application. The review also provides a special focus on the advancements made in the field of somatic cell reprogramming.

Hypoxic preconditioning induces the expression of prosurvival and proangiogenic markers in mesenchymal stem cells

Stem cells transplanted to the ischemic myocardium usually encounter massive cell death within a few days of therapy. Hypoxic preconditioning (HPC) is currently employed as a strategy to prepare stem cells for increased survival and engraftment in the heart. However, HPC of stem cells has provided varying results, supposedly due to the differences in the oxygen concentration, duration of exposure, and passage conditions. In the present study, we determined the effect of HPC on rat mesenchymal stem cells (MSCs) exposed to 0.5% oxygen concentration for 24, 48, or 72 h. We evaluated the expression of prosurvival, proangiogenic, and functional markers such as hypoxia-inducible factor-1α, VEGF, phosphorylated Akt, survivin, p21, cytochrome c, caspase-3, caspase-7, CXCR4, and c-Met. MSCs exposed to 24-h hypoxia showed reduced apoptosis on being subjected to severe hypoxic conditions. They also had significantly higher levels of prosurvival, proangiogenic, and prodifferentiation proteins when compared with longer exposure (72 h). Cells taken directly from the cryopreserved state did not respond effectively to the 24-h HPC as those that were cultured under normoxia before HPC. Cells cultured under normoxia before HPC showed decreased apoptosis, enhanced expression of connexin-43, cardiac myosin heavy chain, and CD31. The preconditioned cells were able to differentiate into the cardiovascular lineage. The results suggest that MSCs cultured under normoxia before 24-h HPC are in a state of optimal expression of prosurvival, proangiogenic, and functional proteins that may increase the survival and engraftment in the infarct heart. These results could provide further insights into optimal preparation of MSCs which would greatly influence the effectiveness of cell therapy in vivo.

Oxygen and oxygenation in stem-cell therapy for myocardial infarction

Myocardial infarction (MI) is caused by deprivation of oxygen and nutrients to the cardiac tissue due to blockade of coronary artery. It is a major contributor to chronic heart disease, a leading cause of mortality in the modern world. Oxygen is required to meet the constant energy demands for heart contractility, and also plays an important role in the regulation of heart function. However, reoxygenation of the ischemic myocardium upon restoration of blood flow may lead to further injury. Controlled oxygen delivery during reperfusion has been advocated to prevent this consequence. Monitoring the myocardial oxygen concentration would play a vital role in understanding the pathological changes in the ischemic heart following myocardial infarction. During the last two decades, several new techniques have become available to monitor myocardial oxygen concentration in vivo. Electron paramagnetic resonance (EPR) oximetry would appear to be the most promising and reliable of these techniques. EPR utilizes crystalline probes which yield a single sharp line, the width of which is highly sensitive to oxygen tension. Decreased oxygen tension results in a sharpening of the EPR spectrum, while an increase results in widening. In our recent studies, we have used EPR oximetry as a valuable tool to monitor myocardial oxygenation for several applications like ischemia-reperfusion injury, stem-cell therapy and hyperbaric oxygen therapy. The results obtained from these studies have demonstrated the importance of tissue oxygen in the application of stem-cell therapy to treat ischemic heart tissues. These results have been summarized in this review article.

A molecular paramagnetic spin-doped biopolymeric oxygen sensor

Electron paramagnetic resonance (EPR) oximetry is a powerful technique capable of providing accurate, reliable, and repeated measurements of tissue oxygenation, which is crucial to the diagnosis and treatment of several pathophysiological conditions. Measurement of tissue pO(2) by EPR involves the use of paramagnetic, oxygen-sensitive probes, which can be either soluble (molecular) in nature or insoluble paramagnetic materials. Development of innovative strategies to enhance the biocompatibility and in vivo application of these oxygen-sensing probes is crucial to the growth and clinical applicability of EPR oximetry. Recent research efforts have aimed at encapsulating particulate probes in bioinert polymers for the development of biocompatible EPR probes. In this study, we have developed novel EPR oximetry probes, called perchlorotriphenylmethyl triester (PTM-TE):polydimethyl siloxane (PDMS) chips, by dissolving and incorporating the soluble (molecular) EPR probe, PTM-TE, in an oxygen-permeable polymer matrix, PDMS. We demonstrate that such incorporation (doping) of PTM-TE in PDMS enhanced its oxygen sensitivity several fold. The cast-molding method of fabricating chips enabled them to be made with increasing amounts of PTM-TE (spin density). Characterization of the spin distribution within the PDMS matrix, using EPR micro-imaging, revealed potential inhomogeneties, albeit with no adverse effect on the oxygen-sensing characteristics of PTM-TE:PDMS. The chips were resistant to autoclaving or in vitro oxidoreductant treatment, thus exhibiting excellent in vitro biostability. Our results establish PTM-TE:PDMS as a viable probe for biological oxygen-sensing, and also validate the incorporation of soluble probes in polymer matrices as an innovative approach to the development of novel probes for EPR oximetry.

Injectable, rapid gelling and highly flexible hydrogel composites as growth factor and cell carriers

A family of injectable, rapid gelling and highly flexible hydrogel composites capable of releasing insulin-like growth factor (IGF-1) and delivering mesenchymal stromal cell (MSC) were developed. Hydrogel composites were fabricated from Type I collagen, chondroitin sulfate (CS) and a thermosensitive and degradable hydrogel copolymer based on N-isopropylacrylamide, acrylic acid, N-acryloxysuccinimide and a macromer poly(trimethylene carbonate)-hydroxyethyl methacrylate. The hydrogel copolymer was gellable at body temperature before degradation and soluble at body temperature after degradation. Hydrogel composites exhibited LCSTs around room temperature. They could easily be injected through a 26-gauge needle at 4 degrees C, and were capable of gelling within 6s at 37 degrees C to form highly flexible gels with moduli matching those of the rat and human myocardium. The hydrogel composites showed good oxygen permeability; the oxygen pressure within the hydrogel composites was similar to that in the air. The effects of collagen and CS contents on LCST, gelation time, injectability, mechanical properties and degradation properties were investigated. IGF-1 was loaded into the hydrogel composites for enhanced cell survival/growth. The released IGF-1 remained bioactive during a 2-week release period. Small fraction of CS in the hydrogel composites significantly decreased IGF-1 release rate. The release kinetics appeared to be controlled mainly by hydrogel composite water content, degradation and interaction with IGF-1. Human MSC adhesion on the hydrogel composites was comparable to that on the tissue culture plate. MSCs were encapsulated in the hydrogel composites and were found to grow inside during a 7-day culture period. IGF-1 loading significantly accelerated MSC growth. RT-PCR analysis demonstrated that MSCs maintained their multipotent differentiation potential in hydrogel composites with and without IGF-1. These injectable and rapid gelling hydrogel composites demonstrated attractive properties for serving as growth factor and cell carriers for cardiovascular tissue engineering applications.

Trimetazidine, administered at the onset of reperfusion, ameliorates myocardial dysfunction and injury by activation of p38 mitogen-activated protein kinase and Akt signaling

Trimetazidine [1-(2,3,4-trimethoxybenzyl)piperazine; TMZ] is an anti-ischemic cardiac drug; however, its efficacy and mechanism of cardioprotection upon reperfusion are largely unknown. The objective of this study was to determine whether TMZ, given before reperfusion, could attenuate myocardial reperfusion injury. Ischemia/reperfusion (I/R) was induced in rat hearts by ligating the left anterior descending (LAD) coronary artery for 30 min followed by 48 h of reperfusion. TMZ (5 mg/kg b.wt.) was administered 5 min before reperfusion. The study used three experimental groups: control (-I/R; -TMZ), I/R (+I/R; -TMZ), and TMZ (+I/R; +TMZ). Echocardiography and EPR oximetry were used to assess cardiac function and oxygenation, respectively. The ejection fraction, which was significantly depressed in the I/R group (62 +/- 5 versus 84 +/- 3% in control), was restored to 72 +/- 3% in the TMZ group. Myocardial pO2 in the TMZ group returned to baseline levels (approximately 20 mm Hg) within 1 h of reperfusion, whereas the I/R group showed a significant hyperoxygenation even after 48 h of reperfusion. The infarct size was significantly reduced in the TMZ group (26 +/- 3 versus 47 +/- 5% in I/R). TMZ treatment significantly attenuated superoxide levels in the tissue. Tissue homogenates showed a significant increase in p38 and p-Akt and decrease in caspase-3 levels in the TMZ group. In summary, the results demonstrated that TMZ is cardioprotective when administered before reperfusion and that this protection appears to be mediated by activation of p38 mitogen-activated protein kinase and Akt signaling. The study emphasizes the importance of administering TMZ before reflow to prevent reperfusion-mediated cardiac injury and dysfunction.

Application of in vivo EPR for tissue pO2 and redox measurements

The technique of electron paramagnetic resonance (EPR) spectroscopy is more than 50 years old, but only recently it has been used for in vivo studies. Its limited application in the past was due to the problem of high nonresonant dielectric loss of the exciting frequency because of high water content in biological samples. However, with the development of spectrometers working at lower frequencies (1,200 MHz and below) during the last 15 years, it is now possible to conduct in vivo measurements on a variety of animals and isolated organs. This is further facilitated by the development of new resonators with high sensitivity and appropriate stability for in vivo applications. It now has become feasible to obtain new insights into the complex aspects of physiology and pathophysiology using in vivo EPR. Among several important applications of this technique, the in vivo tissue pO(2) (partial pressure of oxygen) and redox measurements seem to be the most extensive use of this technique. In this chapter, we describe the procedure for in vivo pO(2) and redox measurements in animal models.

Oxygen sensitivity and biocompatibility of an implantable paramagnetic probe for repeated measurements of tissue oxygenation

The use of oxygen-sensing water-insoluble paramagnetic probes, such as lithium octa-n-butoxynaphthalocyanine (LiNc-BuO), enables repeated measurements of pO(2) from the same location in tissue by electron paramagnetic resonance (EPR) spectroscopy. In order to facilitate direct in vivo application, and hence eventual clinical applicability, of LiNc-BuO, we encapsulated LiNc-BuO microcrystals in polydimethylsiloxane (PDMS), an oxygen-permeable and bioinert polymer, and developed an implantable chip. In vitro evaluation of the chip, performed under conditions of sterilization, high-energy irradiation, and exposure to cultured cells, revealed that it is biostable and biocompatible. Implantation of the chip in the gastrocnemius muscle tissue of mice showed that it is capable of repeated and real-time measurements of tissue oxygenation for an extended period. Functional evaluation using a murine tumor model established the suitability and applicability of the chip for monitoring tumor oxygenation. This study establishes PDMS-encapsulated LiNc-BuO as a promising choice of probe for clinical EPR oximetry.

Angiomyogenesis for myocardial repair

The conventional therapeutic modalities for myocardial infarction have limited success in preventing the progression of left ventricular remodeling and congestive heart failure. The heart cell therapy and therapeutic angiogenesis are two promising strategies for the treatment of ischemic heart disease. After extensive assessment of safety and effectiveness in vitro and in experimental animal studies, both of these approaches have accomplished the stage of clinical utility, albeit with limited success due to the inherent limitations and problems of each approach. Neomyogenesis without restoration of regional blood flow may be less meaningful. A combined stem-cell and gene-therapy approach of angiomyogenesis is expected to yield better results as compared with either of the approaches as a monotherapy. The combined therapy approach will help to restore the mechanical contractile function of the weakened myocardium and alleviate ischemic condition by restoration of regional blood flow. In providing an overview of both stem cell therapy and gene therapy, this article is an in-depth and critical appreciation of combined cell and gene therapy approach for myocardial repair.

Hyperbaric oxygenation enhances transplanted cell graft and functional recovery in the infarct heart

A major limitation to the application of stem-cell therapy to repair ischemic heart damage is the low survival of transplanted cells in the heart, possibly due to poor oxygenation. We hypothesized that hyperbaric oxygenation (HBO) can be used as an adjuvant treatment to augment stem-cell therapy. Therefore, the goal of this study was to evaluate the effect of HBO on the engraftment of rat bone marrow-derived mesenchymal stem cells (MSCs) transplanted in infarct rat hearts. Myocardial infarction (MI) was induced in Fisher-344 rats by permanently ligating the left-anterior-descending coronary artery. MSCs, labeled with fluorescent superparamagnetic iron oxide (SPIO) particles, were transplanted in the infarct and peri-infarct regions of the MI hearts. HBO (100% oxygen at 2 ATA for 90 min) was administered daily for 2 weeks. Four MI groups were used: untreated (MI); HBO; MSC; MSC+HBO. Echocardiography, electro-vectorcardiography, and magnetic resonance imaging were used for functional evaluations. The engraftment of transplanted MSCs in the heart was confirmed by SPIO fluorescence and Prussian-blue staining. Immunohistochemical staining was used to identify key cellular and molecular markers including CD29, troponin-T, connexin-43, VEGF, alpha-smooth-muscle actin, and von Willebrand factor in the tissue. Compared to MI and MSC groups, the MSC+HBO group showed a significantly increased recovery of cardiac function including left-ventricular (LV) ejection fraction, fraction shortening, LV wall thickness, and QRS vector. Further, HBO treatment significantly increased the engraftment of CD29-positive cells, expression of connexin-43, troponin-T and VEGF, and angiogenesis in the infarct tissue. Thus, HBO appears to be a potential and clinically-viable adjuvant treatment for myocardial stem-cell therapy.

Sulfaphenazole protects heart against ischemia-reperfusion injury and cardiac dysfunction by overexpression of iNOS, leading to enhancement of nitric oxide bioavailability and tissue oxygenation

The objective of this study was to establish the cardioprotective effect of sulfaphenazole (SPZ), a selective inhibitor of cytochrome P450 2C9 enzyme, in an in vivo rat model of acute myocardial infarction (MI). MI was induced by 30 min ligation of left anterior descending coronary artery, followed by 24 h reperfusion (I/R). The study used 6 groups: I/R (control); SPZ; L-NAME; L-NAME + SPZ; 1400W (an inhibitor of iNOS); 1400W + SPZ. The agents were administered orally through drinking water for 3 days prior to induction of I/R. Myocardial oxygenation (pO(2)) at the I/R site was measured using EPR oximetry. The preischemic pO(2) value was 18 +/- 2 mm Hg in all groups. At 1 h of reperfusion, the SPZ group showed a significantly higher hyperoxygenation when compared to control (45 +/- 1 vs. 34 +/- 2 mm Hg). The SPZ group showed a significant improvement in the contractile functions and reduction in infarct size. Histochemical staining of SPZ-treated hearts exhibited significantly lower levels of superoxide and peroxynitrite, and markedly increased levels of iNOS activity and nitric oxide. Western blot analysis indicated upregulation of Akt and attenuation of p38MAPK activities in the reperfused myocardium. The study established that SPZ attenuated myocardial I/R injury through overexpression of iNOS, leading to enhancement of nitric oxide bioavailability and tissue oxygenation.

Myocardial oxygenation and functional recovery in infarct rat hearts transplanted with mesenchymal stem cells

Stem cell therapy for myocardial tissue repair is limited by the poor survival of transplanted cells, possibly because of inadequate supply of oxygen and nutrients. The purpose of this study was to assess the oxygenation level and functional recovery after allogenic transplantation of mesenchymal stem cells (MSC) in a rat model of myocardial infarction (MI). Myocardial oxygen tension (Po(2)) was measured by electron paramagnetic resonance oximetry using an implantable oxygen-sensing spin probe (OxySpin). MSCs incubated with OxySpins showed substantial uptake of the probe without affecting its oxygen sensitivity or calibration. The cells internalized with OxySpins were able to differentiate into osteogenic, adipogenic, cardiomyocyte, and endothelial cell lineages. The labeled cells tested positive for CD44 and CD29 markers and negative for the hematopoietic markers CD14 and CD45. For the in vivo studies, MI was induced in rats by permanently ligating the left anterior descending coronary artery. MSCs with OxySpins were transplanted in the infarct region of hearts. A significant increase in Po(2) was observed in the MSC group compared with the untreated MI group (18.1 +/- 2.6 vs. 13.0 +/- 1.8 mmHg, n = 4, P < 0.05) at 4 wk after transplantation. Echocardiography showed a significant improvement in ejection fraction and fraction shortening, which inversely correlated with the magnitude of fibrosis in the treated hearts. The cell-transplanted hearts also showed an increase in vascular endothelial growth factor level and capillary density in the infarct region. The study established our ability to measure and correlate changes in myocardial tissue oxygenation with cardiac function in infarcted rat hearts treated with MSCs.

Pharmacological preconditioning of mesenchymal stem cells with trimetazidine (1-[2,3,4-trimethoxybenzyl]piperazine) protects hypoxic cells against oxidative stress and enhances recovery of myocardial function in infarcted heart through Bcl-2 expression

Stem cell transplantation is a possible therapeutic option to repair ischemic damage to the heart. However, it is faced with a number of challenges including the survival of the transplanted cells in the ischemic region. The present study was designed to use stem cells preconditioned with trimetazidine (1-[2,3,4-trimethoxybenzyl]piperazine; TMZ), a widely used anti-ischemic drug for treating angina in cardiac patients, to increase the rate of their survival after transplantation. Bone marrow-derived rat mesenchymal stem cells (MSCs) were subjected to a simulated host tissue environment by culturing them under hypoxia (2% O(2)) and using hydrogen peroxide (H(2)O(2)) to induce oxidative stress. MSCs were preconditioned with 10 microM TMZ for 6 h followed by treatment with 100 microM H(2)O(2) for 1 h and characterized for their cellular viability and metabolic activity. The preconditioned cells showed a significant protection against H(2)O(2)-induced loss of cellular viability, membrane damage, and oxygen metabolism accompanied by a significant increase in HIF-1alpha, survivin, phosphorylated Akt (pAkt), and Bcl-2 protein levels and Bcl-2 gene expression. The therapeutic efficacy of the TMZ-preconditioned MSCs was evaluated in an in vivo rat model of myocardial infarction induced by permanent ligation of left anterior descending coronary artery. A significant increase in the recovery of myocardial function and up-regulation of pAkt and Bcl-2 levels were observed in hearts transplanted with TMZ-preconditioned cells. This study clearly demonstrated the potential benefits of pharmacological preconditioning of MSCs with TMZ for stem cell therapy for repairing myocardial ischemic damage.

Molecular packing and magnetic properties of lithium naphthalocyanine crystals: hollow channels enabling permeability and paramagnetic sensitivity to molecular oxygen

The synthesis, structural framework, magnetic and oxygen-sensing properties of a lithium naphthalocyanine (LiNc) radical probe are presented. LiNc was synthesized in the form of a microcrystalline powder using a chemical method and characterized by electron paramagnetic resonance (EPR) spectroscopy, magnetic susceptibility, powder X-ray diffraction analysis, and mass spectrometry. X-Ray powder diffraction studies revealed a structural framework that possesses long, hollow channels running parallel to the packing direction. The channels measured approximately 5.0 × 5.4 Å(2) in the two-dimensional plane perpendicular to the length of the channel, enabling diffusion of oxygen molecules (2.9 × 3.9 Å(2)) through the channel. The powdered LiNc exhibited a single, sharp EPR line under anoxic conditions, with a peak-to-peak linewidth of 630 mG at room temperature. The linewidth was sensitive to surrounding molecular oxygen, showing a linear increase in pO(2) with an oxygen sensitivity of 31.2 mG per mmHg. The LiNc microcrystals can be further prepared as nano-sized crystals without the loss of its high oxygen-sensing properties. The thermal variation of the magnetic properties of LiNc, such as the EPR linewidth, EPR intensity and magnetic susceptibility revealed the existence of two different temperature regimes of magnetic coupling and hence differing columnar packing, both being one-dimensional antiferromagnetic chains but with differing magnitudes of exchange coupling constants. At a temperature of ∼50 K, LiNc crystals undergo a reversible phase transition. The high degree of oxygen-sensitivity of micro- and nano-sized crystals of LiNc, combined with excellent stability, should enable precise and accurate measurements of oxygen concentration in biological systems using EPR spectroscopy.

Cardioprotection by HO-4038, a novel verapamil derivative, targeted against ischemia and reperfusion-mediated acute myocardial infarction

Many cardiac interventional procedures, such as coronary angioplasty, stenting, and thrombolysis, attempt to reintroduce blood flow (reperfusion) to an ischemic region of myocardium. However, the reperfusion is accompanied by a complex cascade of cellular and molecular events resulting in oxidative damage, termed myocardial ischemia-reperfusion (I/R) injury. In this study, we evaluated the ability of HO-4038, an N-hydroxypiperidine derivative of verapamil, on the modulation of myocardial tissue oxygenation (Po(2)), I/R injury, and key signaling molecules involved in cardioprotection in an in vivo rat model of acute myocardial infarction (MI). MI was created in rats by ligating the left anterior descending coronary artery (LAD) for 30 min followed by 24 h of reperfusion. Verapamil or HO-4038 was infused through the jugular vein 10 min before the induction of ischemia. Myocardial Po(2) and the free-radical scavenging ability of HO-4038 were measured using electron paramagnetic resonance spectroscopy. HO-4038 showed a significantly better scavenging ability of reactive oxygen radicals compared with verapamil. The cardiac contractile functions in the I/R hearts were significantly higher recovery in HO-4038 compared with the verapamil group. A significant decrease in the plasma levels of creatine kinase and lactate dehydrogenase was observed in the HO-4038 group compared with the verapamil or untreated I/R groups. The left ventricular infarct size was significantly less in the HO-4038 (23 +/- 2%) compared with the untreated I/R (36 +/- 4%) group. HO-4038 significantly attenuated the hyperoxygenation (36 +/- 1 mmHg) during reperfusion compared with the untreated I/R group (44 +/- 2 mmHg). The HO-4038-treated group also markedly attenuated superoxide production, increased nitric oxide generation, and enhanced Akt and Bcl-2 levels in the reperfused myocardium. Overall, the results demonstrated that HO-4038 significantly protected hearts against I/R-induced cardiac dysfunction and damage through the combined beneficial actions of calcium-channel blocking, antioxidant, and prosurvival signaling activities.

Strategies to promote donor cell survival: combining preconditioning approach with stem cell transplantation

Stem cell transplantation has emerged as a potential modality in cardiovascular therapeutics due to their inherent characteristics of self-renewal, unlimited capacity for proliferation and ability to cross lineage restrictions and adopt different phenotypes. Constrained by extensive death in the unfriendly milieu of ischemic myocardium, the results of heart cell therapy in experimental animal models as well as clinical studies have been less than optimal. Several factors which play a role in early cell death after engraftment in the ischemic myocardium include: absence of survival factors in the transplanted heart, disruption of cell-cell interaction coupled with loss of survival signals from matrix attachments, insufficient vascular supply and elaboration of inflammatory cytokines resulting from ischemia and/or cell death. This article reviews various signaling pathways involved in triggering highly complex forms of cell death and provides critical appreciation of different novel anti-death strategies developed from the knowledge gained from using an ischemic preconditioning approach. The use of pharmacological preconditioning for up-regulation of pro-survival proteins and cardiogenic markers in the transplanted stem cells will be discussed.

Stem cells and cardiac repair: a critical analysis

Utilizing stem cells to repair the damaged heart has seen an intense amount of activity over the last 5 years or so. There are currently multiple clinical studies in progress to test the efficacy of various different cell therapy approaches for the repair of damaged myocardium that were only just beginning to be tested in preclinical animal studies a few years earlier. This rapid transition from preclinical to clinical testing is striking and is not typical of the customary timeframe for the progress of a therapy from bench-to-bedside. Doubtless, there will be many more trials to follow in the upcoming years. With the plethora of trials and cell alternatives, there has come not only great enthusiasm for the potential of the therapy, but also great confusion about what has been achieved. Cell therapy has the potential to do what no drug can: regenerate and replace damaged tissue with healthy tissue. Drugs may be effective at slowing the progression of heart failure, but none can stop or reverse the process. However, tissue repair is not a simple process, although the idea on its surface is quite simple. Understanding cells, the signals that they respond to, and the keys to appropriate survival and tissue formation are orders of magnitude more complicated than understanding the pathways targeted by most drugs. Drugs and their metabolites can be monitored, quantified, and their effects correlated to circulating levels in the body. Not so for most cell therapies. It is quite difficult to measure cell survival except through ex vivo techniques like histological analysis of the target organ. This makes the emphasis on preclinical research all the more important because it is only in the animal studies that research has the opportunity to readily harvest the target tissues and perform the detailed analyses of what has happened with the cells. This need for detailed and usually time-intensive research in animal studies stands in contrast to the rapidity with which therapies have progressed to the clinic. It is now becoming clear through a number of notable examples that progress to the clinic may have occurred too quickly, before adequate testing and independent verification of results could be completed (Check, Nature 446:485-486, 2007; Chien, J Clin Investig 116:1838-1840, 2006; Giles, Nature 442:344-347, 2006). Broad reproducibility and transfer of results from one lab to another has been and always will be essential for the successful application of any cell therapy. So, what is the prognosis for cell therapy to repair heart damage? Will there be an approved cell therapy, or multiple ones, or will it require combinations of more than one cell type to be successful? These are questions often asked. The answers are difficult to know and even more difficult to predict because there are so many variables associated with cell-based therapies. There is much about the biology of cell systems that we still do not understand. Much of the pluripotency or transdifferentiation phenomena (see below) being observed go against accepted and well-tested principles for cell development and fate choice, and has caused a reevaluation of long-accepted theories. Clearly, new pathways for tissue repair and regeneration have been uncovered, but will these new pathways be sufficient to effect significant tissue repair and regeneration? Despite the false starts so far, there is the strong likelihood one or possibly multiple cell therapies will succeed. Clearly, important information has been gained, which should better guide the field to achieving success. When there is the successful verification in patients of a cell therapy, there will be an explosion of technological advances around the approach(es) that succeed. Whatever cells get approved accompanying them will be: more effective delivery methods; growth and storage methods; combination therapies, mixes of cells or cells + gene therapies; combinations with biomaterials and technologies for immune protection, allowing allografting. There are many parallel paths of technology development waiting to be brought together once there is an effective cellular approach. The coming years will no doubt bring some exciting developments.