Human embryonic stem cell-derived cardiomyocytes: demonstration of a portion of cardiac cells with fairly mature electrical phenotype

Advances in Manufacturing Cardiomyocytes from Human Pluripotent Stem Cells

The emergence of human pluripotent stem cell (hPSC) technology over the past two decades has provided a source of normal and diseased human cells for a wide variety of in vitro and in vivo applications. Notably, hPSC-derived cardiomyocytes (hPSC-CMs) are widely used to model human heart development and disease and are in clinical trials for treating heart disease. The success of hPSC-CMs in these applications requires robust, scalable approaches to manufacture large numbers of safe and potent cells. Although significant advances have been made over the past decade in improving the purity and yield of hPSC-CMs and scaling the differentiation process from 2D to 3D, efforts to induce maturation phenotypes during manufacturing have been slow. Process monitoring and closed-loop manufacturing strategies are just being developed. We discuss recent advances in hPSC-CM manufacturing, including differentiation process development and scaling and downstream processes as well as separation and stabilization. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Cell surface markers for immunophenotyping human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cells (hPSC) self-renew and represent a potentially unlimited source for the production of cardiomyocytes (CMs) suitable for studies of human cardiac development, drug discovery, cardiotoxicity testing, and disease modelling and for cell-based therapies. However, most cardiac differentiation protocols yield mixed cultures of atrial-, ventricular-, and pacemaker-like cells at various stages of development, as well as non-CMs. The proportions and maturation states of these cell types result from disparities among differentiation protocols and time of cultivation, as well as hPSC reprogramming inconsistencies and genetic background variations. The reproducible use of hPSC-CMs for research and therapy is therefore limited by issues of cell population heterogeneity and functional states of maturation. A validated method that overcomes issues of cell heterogeneity is immunophenotyping coupled with live cell sorting, an approach that relies on accessible surface markers restricted to the desired cell type(s). Here we review current progress in unravelling heterogeneity in hPSC-cardiac cultures and in the identification of surface markers suitable for defining cardiac identity, subtype specificity, and maturation states.

Dynamic Clamp in Electrophysiological Studies on Stem Cell-Derived Cardiomyocytes-Why and How?

ABSTRACT

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are supposed to be a good human-based model, with virtually unlimited cell source, for studies on mechanisms underlying cardiac development and cardiac diseases, and for identification of drug targets. However, a major drawback of hPSC-CMs as a model system, especially for electrophysiological studies, is their depolarized state and associated spontaneous electrical activity. Various approaches are used to overcome this drawback, including the injection of "synthetic" inward rectifier potassium current (IK1), which is computed in real time, based on the recorded membrane potential ("dynamic clamp"). Such injection of an IK1-like current results in quiescent hPSC-CMs with a nondepolarized resting potential that show "adult-like" action potentials on stimulation, with functional availability of the most important ion channels involved in cardiac electrophysiology. These days, dynamic clamp has become a widely appreciated electrophysiological tool. However, setting up a dynamic clamp system can still be laborious and difficult, both because of the required hardware and the implementation of the dedicated software. In the present review, we first summarize the potential mechanisms underlying the depolarized state of hPSC-CMs and the functional consequences of this depolarized state. Next, we explain how an existing manual patch clamp setup can be extended with dynamic clamp. Finally, we shortly validate the extended setup with atrial-like and ventricular-like hPSC-CMs. We feel that dynamic clamp is a highly valuable tool in the field of cellular electrophysiological studies on hPSC-CMs and hope that our directions for setting up such dynamic clamp system may prove helpful.

Electrophysiological evaluation of human induced pluripotent stem cell-derived cardiomyocytes obtained by different methods

The human induced pluripotent stem cells (hiPSCs) derived cardiomyocytes (CMs) (hiPSC-CMs) retain the same genetic information as the donor, and they have been shown to faithfully recapitulate the disease phenotypes of various genetic cardiac diseases. The hiPSC-CMs can be utilized in multiple types of studies and in most cases, the functionality of hiPSC-CMs is of interest. For the functional analyses, the hiPSC-CMs need to be manipulated after differentiation, e.g. enriched or dissociated into single-cell stage. For the functional assessments to be reliable and reproducible, the cell culture environment should support the cells in an optimal manner. The aim of the present study was to evaluate the effect of various differentiation methods, as well as coating materials used for the dissociated cells on the functionality of the differentiated hiPSC-CMs. The different protocols not only had different differentiation efficiencies, but they also yielded functionally different hiPSC-CMs. Additionally, the coating material had a major effect on the functionality of the hiPSC-CMs. The results of the present study emphasize that the cardiac differentiation method and the coating material have a major effect on hiPS-CMs' characteristics. Thus, when different hiPSC lines and results obtained in different labs are compared, extra care should be taken to check the conditions when results are compared.

Arrhythmia Mechanisms in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

ABSTRACT

Despite major efforts by clinicians and researchers, cardiac arrhythmia remains a leading cause of morbidity and mortality in the world. Experimental work has relied on combining high-throughput strategies with standard molecular and electrophysiological studies, which are, to a great extent, based on the use of animal models. Because this poses major challenges for translation, the progress in the development of novel antiarrhythmic agents and clinical care has been mostly disappointing. Recently, the advent of human induced pluripotent stem cell-derived cardiomyocytes has opened new avenues for both basic cardiac research and drug discovery; now, there is an unlimited source of cardiomyocytes of human origin, both from healthy individuals and patients with cardiac diseases. Understanding arrhythmic mechanisms is one of the main use cases of human induced pluripotent stem cell-derived cardiomyocytes, in addition to pharmacological cardiotoxicity and efficacy testing, in vitro disease modeling, developing patient-specific models and personalized drugs, and regenerative medicine. Here, we review the advances that the human induced pluripotent stem cell-derived-based modeling systems have brought so far regarding the understanding of both arrhythmogenic triggers and substrates, while also briefly speculating about the possibilities in the future.

Specific induction and long-term maintenance of high purity ventricular cardiomyocytes from human induced pluripotent stem cells

Currently, cardiomyocyte (CM) differentiation methods require a purification step after CM induction to ensure the high purity of the cell population. Here we show an improved human CM differentiation protocol with which high-purity ventricular-type CMs can be obtained and maintained without any CM purification process. We induced and collected a mesodermal cell population (platelet-derived growth factor receptor-α (PDGFRα)-positive cells) that can respond to CM differentiation cues, and then stimulated CM differentiation by means of Wnt inhibition. This method reproducibly generated CMs with purities above 95% in several human pluripotent stem cell lines. Furthermore, these CM populations were maintained in culture at such high purity without any further CM purification step for over 200 days. The majority of these CMs (>95%) exhibited a ventricular-like phenotype with a tendency to structural and electrophysiological maturation, including T-tubule-like structure formation and the ability to respond to QT prolongation drugs. This is a simple and valuable method to stably generate CM populations suitable for cardiac toxicology testing, disease modeling and regenerative medicine.

Coculture of Endothelial Cells with Human Pluripotent Stem Cell-Derived Cardiac Progenitors Reveals a Differentiation Stage-Specific Enhancement of Cardiomyocyte Maturation

Cardiomyocytes (CMs) generated from human pluripotent stem cells (hPSCs) are immature in their structure and function, limiting their potential in disease modeling, drug screening, and cardiac cellular therapies. Prior studies have demonstrated that coculture of hPSC-derived CMs with other cardiac cell types, including endothelial cells (ECs), can accelerate CM maturation. To address whether the CM differentiation stage at which ECs are introduced affects CM maturation, the authors coculture hPSC-derived ECs with hPSC-derived cardiac progenitor cells (CPCs) and CMs and analyze the molecular and functional attributes of maturation. ECs have a more significant effect on acceleration of maturation when cocultured with CPCs than with CMs. EC coculture with CPCs increases CM size, expression of sarcomere, and ion channel genes and proteins, the presence of intracellular membranous extensions, and chronotropic response compared to monoculture. Maturation is accelerated with an increasing EC:CPC ratio. This study demonstrates that EC incorporation at the CPC stage of CM differentiation expedites CM maturation, leading to cells that may be better suited for in vitro and in vivo applications of hPSC-derived CMs.

Representation of Multiple Cellular Phenotypes Within Tissue-Level Simulations of Cardiac Electrophysiology

Distinct electrophysiological phenotypes are exhibited by biological cells that have differentiated into particular cell types. The usual approach when simulating the cardiac electrophysiology of tissue that includes different cell types is to model the different cell types as occupying spatially distinct yet coupled regions. Instead, we model the electrophysiology of well-mixed cells by using homogenisation to derive an extension to the commonly used monodomain or bidomain equations. These new equations permit spatial variations in the distribution of the different subtypes of cells and will reduce the computational demands of solving the governing equations. We validate the homogenisation computationally, and then use the new model to explain some experimental observations from stem cell-derived cardiomyocyte monolayers.

TBX18 transcription factor overexpression in human-induced pluripotent stem cells increases their differentiation into pacemaker-like cells

BACKGROUND

The discovery of gene- and cell-based strategies has opened a new area to investigate novel approaches for the treatment of many conditions caused by cardiac cell failure. The TBX18 (T-box 18) transcription factor is considered as a prominent factor in the sinoatrial node (SAN) formation during the embryonic development. In this in vitro study, the effect of TBX18 gene expression on human-induced pluripotent-stem-cell-derived cardiomyocytes (hiPS-CMs) to induce pacemaker-like cells was examined.

METHODS

The human-dermal-fibroblast-derived iPSCs were transfected using chemical, physical, and Lentiviral methods of TBX18 gene delivery during differentiation into cardiomyocytes (CMs). After the differentiation process through small-molecule-based temporal modulation of the Wnt signaling pathway, the hiPSC-CMs were analyzed using the real-time polymerase chain reaction, immunocytochemistry, immunofluorescence, whole-cell patch-clamp recording, and western blotting to investigate the accuracy of differentiation and identify the effect exerted by TBX18.

RESULTS

The hiPS-CMs showed spontaneous beating and expressed specific markers of cardiac cells. The lentiviral-mediated TBX18 delivery was the most efficient method for transfection. The results showed the increment in Connexin 43 expression among untransfected hiPS-CMs, whereas this protein was significantly downregulated followed by TBX18 overexpression. TBX18-hiPSCMs were detected with pacemaker cell features.

CONCLUSIONS

It was demonstrated that the TBX18 gene is able to conduct hiPSCs to differentiate into pacemaker-like cells. The TBX18 gene delivery seems to have the potential for the development of biological pacemakers; however, more investigations are still needed to assess its usefulness to fix arrhythmic conditions with SAN failure basis.

The march of pluripotent stem cells in cardiovascular regenerative medicine

Cardiovascular disease (CVD) continues to be the leading cause of global morbidity and mortality. Heart failure remains a major contributor to this mortality. Despite major therapeutic advances over the past decades, a better understanding of molecular and cellular mechanisms of CVD as well as improved therapeutic strategies for the management or treatment of heart failure are increasingly needed. Loss of myocardium is a major driver of heart failure. An attractive approach that appears to provide promising results in reducing cardiac degeneration is stem cell therapy (SCT). In this review, we describe different types of stem cells, including embryonic and adult stem cells, and we provide a detailed discussion of the properties of induced pluripotent stem cells (iPSCs). We also present and critically discuss the key methods used for converting somatic cells to pluripotent cells and iPSCs to cardiomyocytes (CMs), along with their advantages and limitations. Integrating and non-integrating reprogramming methods as well as characterization of iPSCs and iPSC-derived CMs are discussed. Furthermore, we critically present various methods of differentiating iPSCs to CMs. The value of iPSC-CMs in regenerative medicine as well as myocardial disease modeling and cardiac regeneration are emphasized.

Engineering Scalable Manufacturing of High-Quality Stem Cell-Derived Cardiomyocytes for Cardiac Tissue Repair

Recent advances in the differentiation and production of human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs) have stimulated development of strategies to use these cells in human cardiac regenerative therapies. A prerequisite for clinical trials and translational implementation of hPSC-derived CMs is the ability to manufacture safe and potent cells on the scale needed to replace cells lost during heart disease. Current differentiation protocols generate fetal-like CMs that exhibit proarrhythmogenic potential. Sufficient maturation of these hPSC-derived CMs has yet to be achieved to allow these cells to be used as a regenerative medicine therapy. Insights into the native cardiac environment during heart development may enable engineering of strategies that guide hPSC-derived CMs to mature. Specifically, considerations must be made in regard to developing methods to incorporate the native intercellular interactions and biomechanical cues into hPSC-derived CM production that are conducive to scale-up.

Electrophysiological mechanisms of vandetanib-induced cardiotoxicity: Comparison of action potentials in rabbit Purkinje fibers and pluripotent stem cell-derived cardiomyocytes

Vandetanib, a multi-kinase inhibitor used for the treatment of various cancers, has been reported to induce several adverse cardiac effects. However, the underlying mechanisms of vandetanib-induced cardiotoxicity are unclear. This study aimed to investigate the mechanism of vandetanib-induced cardiotoxicity using intracellular electrophysiological recordings on human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), rabbit Purkinje fibers, and HEK293 cells transiently expressing human ether-a-go-go-related gene (hERG; the rapidly activating delayed rectifier K⁺ channel, I_Kr), KCNQ1/KCNE1 (the slowly activating delayed rectifier K⁺ current, I_Ks), KCNJ2 (the inwardly rectifying K⁺ current, I_K1) or SCN5A (the inward Na⁺ current, I_Na). Purkinje fiber assays and ion channel studies showed that vandetanib at concentrations of 1 and 3 μM inhibited the hERG currents and prolonged the action potential duration. Alanine scanning and in silico hERG docking studies demonstrated that Y652 and F656 in the hERG S6 domain play critical roles in vandetanib binding. In hiPSC-CMs, vandetanib markedly reduced the maximum rate of depolarization during the AP upstroke. Ion channel studies revealed that hiPSC-CMs were more sensitive to inhibition of the I_Na by vandetanib than in a heterogeneously expressed HEK293 cell model, consistent with the changes in the AP parameters of hiPSC-CMs. The subclasses of Class I antiarrhythmic drugs inhibited I_Na currents in a dose-dependent manner in hiPSC-CMs and SCN5A-encoded HEK293 cells. The inhibitory potency of vandetanib for I_Na was much higher in hiPSC-CMs (IC₅₀: 2.72 μM) than in HEK293 cells (IC₅₀: 36.63 μM). These data suggest that AP and I_Na assays using hiPSC-CMs are useful electrophysiological models for prediction of drug-induced cardiotoxicity.

Human embryonic stem cell-derived cardiomyocytes as an in vitro model to study cardiac insulin resistance

Patients with type 2 diabetes (T2D) and/or insulin resistance (IR) have an increased risk for the development of heart failure (HF). Evidence indicates that this increased risk is linked to an altered cardiac substrate preference of the insulin resistant heart, which shifts from a balanced utilization of glucose and long-chain fatty acids (FAs) towards an almost complete reliance on FAs as main fuel source. This shift leads to a loss of endosomal proton pump activity and increased cardiac fat accumulation, which eventually triggers cardiac dysfunction. In this review, we describe the advantages and disadvantages of currently used in vitro models to study the underlying mechanism of IR-induced HF and provide insight into a human in vitro model: human embryonic stem cell-derived cardiomyocytes (hESC-CMs). Using functional metabolic assays we demonstrate that, similar to rodent studies, hESC-CMs subjected to 16h of high palmitate (HP) treatment develop the main features of IR, i.e., decreased insulin-stimulated glucose and FA uptake, as well as loss of endosomal acidification and insulin signaling. Taken together, these data propose that HP-treated hESC-CMs are a promising in vitro model of lipid overload-induced IR for further research into the underlying mechanism of cardiac IR and for identifying new pharmacological agents and therapeutic strategies. This article is part of a Special issue entitled Cardiac adaptations to obesity, diabetes and insulin resistance, edited by Professors Jan F.C. Glatz, Jason R.B. Dyck and Christine Des Rosiers.

In silico assessment of the effects of various compounds in MEA/hiPSC-CM assays: Modeling and numerical simulations

We propose a mathematical approach for the analysis of drugs effects on the electrical activity of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) based on multi-electrode array (MEA) experiments. Our goal is to produce an in silico tool able to simulate drugs action in MEA/hiPSC-CM assays. The mathematical model takes into account the geometry of the MEA and the electrodes' properties. The electrical activity of the stem cells at the ion-channel level is governed by a system of ordinary differential equations (ODEs). The ODEs are coupled to the bidomain equations, describing the propagation of the electrical wave in the stem cells preparation. The field potential (FP) measured by the MEA is modeled by the extracellular potential of the bidomain equations. First, we propose a strategy allowing us to generate a field potential in good agreement with the experimental data. We show that we are able to reproduce realistic field potentials by introducing different scenarios of heterogeneity in the action potential. This heterogeneity reflects the differentiation atria/ventricles and the age of the cells. Second, we introduce a drug/ion channels interaction based on a pore block model. We conduct different simulations for five drugs (mexiletine, dofetilide, bepridil, ivabradine and BayK). We compare the simulation results with the field potential collected from experimental measurements. Different biomarkers computed on the FP are considered, including depolarization amplitude, repolarization delay, repolarization amplitude and depolarization-repolarization segment. The simulation results show that the model reflect properly the main effects of these drugs on the FP.

Phenotypic assays for analyses of pluripotent stem cell-derived cardiomyocytes

Stem cell-derived cardiomyocytes (CMs) hold great hopes for myocardium regeneration because of their ability to produce functional cardiac cells in large quantities. They also hold promise in dissecting the molecular principles involved in heart diseases and also in drug development, owing to their ability to model the diseases using patient-specific human pluripotent stem cell (hPSC)-derived CMs. The CM properties essential for the desired applications are frequently evaluated through morphologic and genotypic screenings. Even though these characterizations are necessary, they cannot in principle guarantee the CM functionality and their drug response. The CM functional characteristics can be quantified by phenotype assays, including electrophysiological, optical, and/or mechanical approaches implemented in the past decades, especially when used to investigate responses of the CMs to known stimuli (eg, adrenergic stimulation). Such methods can be used to indirectly determine the electrochemomechanics of the cardiac excitation-contraction coupling, which determines important functional properties of the hPSC-derived CMs, such as their differentiation efficacy, their maturation level, and their functionality. In this work, we aim to systematically review the techniques and methodologies implemented in the phenotype characterization of hPSC-derived CMs. Further, we introduce a novel approach combining atomic force microscopy, fluorescent microscopy, and external electrophysiology through microelectrode arrays. We demonstrate that this novel method can be used to gain unique information on the complex excitation-contraction coupling dynamics of the hPSC-derived CMs.

Maturation of pluripotent stem cell derived cardiomyocytes: The new challenge

Stem cell therapy appears to be a promising area of research for cardiac regeneration following ischemic heart failure. However, in vitro differentiation of cardiomyocytes from pluripotent stem cells, or directly from somatic cells, leads to generation of "immature" cardiomyocytes that differ from their adult counterparts in various ways. This immaturity triggers some challenges for their potential clinical use, and multiple techniques reviewed here have been developed for in vitro maturation of those cells. Nevertheless, full maturity of cardiomyocytes remains elusive and will remain the main challenge for stem cell therapy in the near future.

The electrophysiological development of cardiomyocytes

The generation of human cardiomyocytes (CMs) from human pluripotent stem cells (hPSCs) has become an important resource for modeling human cardiac disease and for drug screening, and also holds significant potential for cardiac regeneration. Many challenges remain to be overcome however, before innovation in this field can translate into a change in the morbidity and mortality associated with heart disease. Of particular importance for the future application of this technology is an improved understanding of the electrophysiologic characteristics of CMs, so that better protocols can be developed and optimized for generating hPSC-CMs. Many different cell culture protocols are currently utilized to generate CMs from hPSCs and all appear to yield relatively “developmentally” immature CMs with highly heterogeneous electrical properties. These hPSC-CMs are characterized by spontaneous beating at highly variable rates with a broad range of depolarization-repolarization patterns, suggestive of mixed populations containing atrial, ventricular and nodal cells. Many recent studies have attempted to introduce approaches to promote maturation and to create cells with specific functional properties. In this review, we summarize the studies in which the electrical properties of CMs derived from stem cells have been examined. In order to place this information in a useful context, we also review the electrical properties of CMs as they transition from the developing embryo to the adult human heart. The signal pathways involved in the regulation of ion channel expression during development are also briefly considered.

Tissue-Mimicking Geometrical Constraints Stimulate Tissue-Like Constitution and Activity of Mouse Neonatal and Human-Induced Pluripotent Stem Cell-Derived Cardiac Myocytes

The present work addresses the question of to what extent a geometrical support acts as a physiological determining template in the setup of artificial cardiac tissue. Surface patterns with alternating concave to convex transitions of cell size dimensions were used to organize and orientate human-induced pluripotent stem cell (hIPSC)-derived cardiac myocytes and mouse neonatal cardiac myocytes. The shape of the cells, as well as the organization of the contractile apparatus recapitulates the anisotropic line pattern geometry being derived from tissue geometry motives. The intracellular organization of the contractile apparatus and the cell coupling via gap junctions of cell assemblies growing in a random or organized pattern were examined. Cell spatial and temporal coordinated excitation and contraction has been compared on plain and patterned substrates. While the α-actinin cytoskeletal organization is comparable to terminally-developed native ventricular tissue, connexin-43 expression does not recapitulate gap junction distribution of heart muscle tissue. However, coordinated contractions could be observed. The results of tissue-like cell ensemble organization open new insights into geometry-dependent cell organization, the cultivation of artificial heart tissue from stem cells and the anisotropy-dependent activity of therapeutic compounds.

Physical developmental cues for the maturation of human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are the most promising source of cardiomyocytes (CMs) for experimental and clinical applications, but their use is largely limited by a structurally and functionally immature phenotype that most closely resembles embryonic or fetal heart cells. The application of physical stimuli to influence hPSC-CMs through mechanical and bioelectrical transduction offers a powerful strategy for promoting more developmentally mature CMs. Here we summarize the major events associated with in vivo heart maturation and structural development. We then review the developmental state of in vitro derived hPSC-CMs, while focusing on physical (electrical and mechanical) stimuli and contributory (metabolic and hypertrophic) factors that are actively involved in structural and functional adaptations of hPSC-CMs. Finally, we highlight areas for possible future investigation that should provide a better understanding of how physical stimuli may promote in vitro development and lead to mechanistic insights. Advances in the use of physical stimuli to promote developmental maturation will be required to overcome current limitations and significantly advance research of hPSC-CMs for cardiac disease modeling, in vitro drug screening, cardiotoxicity analysis and therapeutic applications.

The case for induced pluripotent stem cell-derived cardiomyocytes in pharmacological screening

The current drug screening models are deficient, particularly in detecting cardiac side effects. Human stem cell-derived cardiomyocytes could aid both early cardiotoxicity detection and novel drug discovery. Work over the last decade has generated human embryonic stem cells as potentially accurate sources of human cardiomyocytes, but ethical constraints and poor efficacy in establishing cell lines limit their use. Induced pluripotent stem cells do not require the use of human embryos and have the added advantage of producing patient-specific cardiomyocytes, allowing both generic and disease- and patient-specific pharmacological screening, as well as drug development through disease modelling. A critical question is whether sufficient standards have been achieved in the reliable and reproducible generation of 'adult-like' cardiomyocytes from human fibroblast tissue to progress from validation to safe use in practice and drug discovery. This review will highlight the need for a new experimental system, assess the validity of human induced pluripotent stem cell-derived cardiomyocytes and explore what the future may hold for their use in pharmacology.

Developmental cues for the maturation of metabolic, electrophysiological and calcium handling properties of human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cells (hPSCs), including embryonic and induced pluripotent stem cells, are abundant sources of cardiomyocytes (CMs) for cell replacement therapy and other applications such as disease modeling, drug discovery and cardiotoxicity screening. However, hPSC-derived CMs display immature structural, electrophysiological, calcium-handling and metabolic properties. Here, we review various biological as well as physical and topographical cues that are known to associate with the development of native CMs in vivo to gain insights into the development of strategies for facilitated maturation of hPSC-CMs.

Preclinical stem cell therapy in Chagas Disease: Perspectives for future research

Chagas cardiomyopathy still remains a challenging problem that is responsible for high morbidity and mortality in Central and Latin America. Chagas disease disrupts blood microcirculation via various autoimmune mechanisms, causing loss of cardiomyocytes and severe impairment of heart function. Different cell types and delivery approaches in Chagas Disease have been studied in both preclinical models and clinical trials. The main objective of this article is to clarify the reasons why the benefits that have been seen with cell therapy in preclinical models fail to translate to the clinical setting. This can be explained by crucial differences between the cellular types and pathophysiological mechanisms of the disease, as well as the differences between human patients and animal models. We discuss examples that demonstrate how the results from preclinical trials might have overestimated the efficacy of myocardial regeneration therapies. Future research should focus, not only on studying the best cell type to use but, very importantly, understanding the levels of safety and cellular interaction that can elicit efficient therapeutic effects in human tissue. Addressing the challenges associated with future research may ensure the success of stem cell therapy in improving preclinical models and the treatment of Chagas disease.

Induced pluripotent stem cells as cardiac arrhythmic in vitro models and the impact for drug discovery

INTRODUCTION

The development of new antiarrhythmic agents is challenging and is hampered by high attrition rate of novel drug candidates. One of the reasons for this is limited predictability of existing preclinical models for drug assessment. Cardiomyocytes (CMs) derived from disease-specific induced pluripotent stem cells (iPSC) represent a novel in vitro cellular model of cardiac arrhythmias with an unprecedented potential for generating new mechanistic insight into disease pathophysiology and improving the process of drug development.

AREAS COVERED

This review outlines recent studies demonstrating the suitability and limitations of iPSC-derived CMs (iPS-CMs) for in vitro modeling inherited arrhythmias and drug testing. The authors focus on channelopathies and outline the properties of iPS-CMs, highlighting their utility and limitations for investigating the mechanism of cardiac arrhythmias and drug discovery.

EXPERT OPINION

The iPS-CMs represent a valuable addition to the already existing armamentarium of cardiac arrhythmic models. However, the superiority of iPS-CMs over other arrhythmia models has not yet been rigorously established and the limitations of the model must be overcome before its full potential for antiarrhythmic drug discovery can be realized. Nevertheless, iPS cell-based platforms hold a great potential for increasing our knowledge about cellular arrhythmia mechanisms and improving the drug discovery process.

Concise review: maturation phases of human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cell-derived cardiomyocytes (hPS-CM) may offer a number of advantages over previous cardiac models, however, questions of their immaturity complicate their adoption as a new in vitro model. hPS-CM differ from adult cardiomyocytes with respect to structure, proliferation, metabolism and electrophysiology, better approximating fetal cardiomyocytes. Time in culture appears to significantly impact phenotype, leading to what can be referred to as early and late hPS-CM. This work surveys the phenotype of hPS-CM, including structure, bioenergetics, sensitivity to damage, gene expression, and electrophysiology, including action potential, ion channels, and intracellular calcium stores, while contrasting fetal and adult CM with hPS-CM at early and late time points after onset of differentiation.

SK4 Ca2+ activated K+ channel is a critical player in cardiac pacemaker derived from human embryonic stem cells

Proper expression and function of the cardiac pacemaker is a critical feature of heart physiology. Two main mechanisms have been proposed: (i) the "voltage-clock," where the hyperpolarization-activated funny current If causes diastolic depolarization that triggers action potential cycling; and (ii) the "Ca(2+) clock," where cyclical release of Ca(2+) from Ca(2+) stores depolarizes the membrane during diastole via activation of the Na(+)-Ca(2+) exchanger. Nonetheless, these mechanisms remain controversial. Here, we used human embryonic stem cell-derived cardiomyocytes (hESC-CMs) to study their autonomous beating mechanisms. Combined current- and voltage-clamp recordings from the same cell showed the so-called "voltage and Ca(2+) clock" pacemaker mechanisms to operate in a mutually exclusive fashion in different cell populations, but also to coexist in other cells. Blocking the "voltage or Ca(2+) clock" produced a similar depolarization of the maximal diastolic potential (MDP) that culminated by cessation of action potentials, suggesting that they converge to a common pacemaker component. Using patch-clamp recording, real-time PCR, Western blotting, and immunocytochemistry, we identified a previously unrecognized Ca(2+)-activated intermediate K(+) conductance (IK(Ca), KCa3.1, or SK4) in young and old stage-derived hESC-CMs. IK(Ca) inhibition produced MDP depolarization and pacemaker suppression. By shaping the MDP driving force and exquisitely balancing inward currents during diastolic depolarization, IK(Ca) appears to play a crucial role in human embryonic cardiac automaticity.

Stem cell therapy in heart diseases: a review of selected new perspectives, practical considerations and clinical applications

Degeneration of cardiac tissues is considered a major cause of mortality in the western world and is expected to be a greater problem in the forthcoming decades. Cardiac damage is associated with dysfunction and irreversible loss of cardiomyocytes. Stem cell therapy for ischemic heart failure is very promising approach in cardiovascular medicine. Initial trials have indicated the ability of cardiomyocytes to regenerate after myocardial injury. These preliminary trials aim to translate cardiac regeneration strategies into clinical practice. In spite of advances, current therapeutic strategies to ischemic heart failure remain very limited. Moreover, major obstacles still need to be solved before stem cell therapy can be fully applied. This review addresses the current state of research and experimental data regarding embryonic stem cells (ESCs), myoblast transplantation, histological and functional analysis of transplantation of co-cultured myoblasts and mesenchymal stem cells, as well as comparison between mononuclear and mesenchymal stem cells in a model of myocardium infarction. We also discuss how research with stem cell transplantation could translate to improvement of cardiac function.

Label-free electrophysiological cytometry for stem cell-derived cardiomyocyte clusters

Stem cell therapies hold great promise for repairing tissues damaged due to disease or injury. However, a major obstacle facing this field is the difficulty in identifying cells of a desired phenotype from the heterogeneous population that arises during stem cell differentiation. Conventional fluorescence flow cytometry and magnetic cell purification require exogenous labeling of cell surface markers which can interfere with the performance of the cells of interest. Here, we describe a non-genetic, label-free cell cytometry method based on electrophysiological response to stimulus. As many of the cell types relevant for regenerative medicine are electrically-excitable (e.g. cardiomyocytes, neurons, smooth muscle cells), this technology is well-suited for identifying cells from heterogeneous stem cell progeny without the risk and expense associated with molecular labeling or genetic modification. Our label-free cell cytometer is capable of distinguishing clusters of undifferentiated human induced pluripotent stem cells (iPSC) from iPSC-derived cardiomyocyte (iPSC-CM) clusters. The system utilizes a microfluidic device with integrated electrodes for both electrical stimulation and recording of extracellular field potential (FP) signals from suspended cells in flow. The unique electrode configuration provides excellent rejection of field stimulus artifact while enabling sensitive detection of FPs with a noise floor of 2 μV(rms). Cells are self-aligned to the recording electrodes via hydrodynamic flow focusing. Based on automated analysis of these extracellular signals, the system distinguishes cardiomyocytes from non-cardiomyocytes. This is an entirely new approach to cell cytometry, in which a cell's functionality is assessed rather than its expression profile or physical characteristics.

Engineered human pluripotent stem cell-derived cardiac cells and tissues for electrophysiological studies

Human cardiomyocytes (CMs) do not proliferate in culture and are difficult to obtain for practical reasons. As such, our understanding of the mechanisms that underlie the physiological and pathophysiological development of the human heart is mostly extrapolated from studies of the mouse and other animal models or heterologus expression of defective gene product(s) in non-human cells. Although these studies provided numerous important insights, much of the exact behavior in human cells remains unexplored given that significant species differences exist. With the derivation of human embryonic stem cells (hESC) and induced pluripotent stem cells (iPSCs) from patients with underlying heart disease, a source of human CMs for disease modeling, cardiotoxicity screening and drug discovery is now available. In this review, we focus our discussion on the use of hESC/ iPSC-derived cardiac cells and tissues for studying various heart rhythm disorders and the associated pro-arrhythmogenic properties in relation to advancements in electrophysiology and tissue engineering.

Cardiac repair and restoration using human embryonic stem cells

Advances in directed differentiation of human embryonic stem cells (hESCs) toward cardiac lineages have generated much interest within the myocardial therapy field. Beyond the promise that hESCs would provide a supply of new cardiomyocytes to the damaged heart, recent studies have also shown that paracrine effects of stem cell therapy may facilitate myocardial healing. This review describes the advantages of hESCs for these purposes, current methods for directing differentiation of hESCs toward cardiac fates, approaches to purification and engineered selection of hESC-derived cardiomyocytes and cardiac precursors, as well as animal studies that have shed light on the therapeutic uses of hESCs in cardiac regenerative medicine.

Current status of drug screening and disease modelling in human pluripotent stem cells

The emphasis in human pluripotent stem cell (hPSC) technologies has shifted from cell therapy to in vitro disease modelling and drug screening. This review examines why this shift has occurred, and how current technological limitations might be overcome to fully realise the potential of hPSCs. Details are provided for all disease-specific human induced pluripotent stem cell lines spanning a dozen dysfunctional organ systems. Phenotype and pharmacology have been examined in only 17 of 63 lines, primarily those that model neurological and cardiac conditions. Drug screening is most advanced in hPSC-cardiomyocytes. Responses for almost 60 agents include examples of how careful tests in hPSC-cardiomyocytes have improved on existing in vitro assays, and how these cells have been integrated into high throughput imaging and electrophysiology industrial platforms. Such successes will provide an incentive to overcome bottlenecks in hPSC technology such as improving cell maturity and industrial scalability whilst reducing cost.

Electrophysiological and contractile function of cardiomyocytes derived from human embryonic stem cells

Human embryonic stem cells have emerged as the prototypical source from which cardiomyocytes can be derived for use in drug discovery and cell therapy. However, such applications require that these cardiomyocytes (hESC-CMs) faithfully recapitulate the physiology of adult cells, especially in relation to their electrophysiological and contractile function. We review what is known about the electrophysiology of hESC-CMs in terms of beating rate, action potential characteristics, ionic currents, and cellular coupling as well as their contractility in terms of calcium cycling and contraction. We also discuss the heterogeneity in cellular phenotypes that arises from variability in cardiac differentiation, maturation, and culture conditions, and summarize present strategies that have been implemented to reduce this heterogeneity. Finally, we present original electrophysiological data from optical maps of hESC-CM clusters.

Maximum diastolic potential of human induced pluripotent stem cell-derived cardiomyocytes depends critically on I(Kr)

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) hold promise for therapeutic applications. To serve these functions, the hiPSC-CM must recapitulate the electrophysiologic properties of native adult cardiomyocytes. This study examines the electrophysiologic characteristics of hiPSC-CM between 11 and 121 days of maturity. Embryoid bodies (EBs) were generated from hiPS cell line reprogrammed with Oct4, Nanog, Lin28 and Sox2. Sharp microelectrodes were used to record action potentials (AP) from spontaneously beating clusters (BC) micro-dissected from the EBs (n = 103; 37°C) and to examine the response to 5 µM E-4031 (n = 21) or BaCl(2) (n = 22). Patch-clamp techniques were used to record I(Kr) and I(K1) from cells enzymatically dissociated from BC (n = 49; 36°C). Spontaneous cycle length (CL) and AP characteristics varied widely among the 103 preparations. E-4031 (5 µM; n = 21) increased Bazett-corrected AP duration from 291.8±81.2 to 426.4±120.2 msec (p<0.001) and generated early afterdepolarizations in 8/21 preparations. In 13/21 BC, E-4031 rapidly depolarized the clusters leading to inexcitability. BaCl(2), at concentrations that selectively block I(K1) (50-100 µM), failed to depolarize the majority of clusters (13/22). Patch-clamp experiments revealed very low or negligible I(K1) in 53% (20/38) of the cells studied, but presence of I(Kr) in all (11/11). Consistent with the electrophysiological data, RT-PCR and immunohistochemistry studies showed relatively poor mRNA and protein expression of I(K1) in the majority of cells, but robust expression of I(Kr.) In contrast to recently reported studies, our data point to major deficiencies of hiPSC-CM, with remarkable diversity of electrophysiologic phenotypes as well as pharmacologic responsiveness among beating clusters and cells up to 121 days post-differentiation (dpd). The vast majority have a maximum diastolic potential that depends critically on I(Kr) due to the absence of I(K1). Thus, efforts should be directed at producing more specialized and mature hiPSC-CM for future therapeutic applications.

Current Applications of Human Pluripotent Stem Cells: Possibilities and Challenges

Stem cells are self-renewable cells with the differentiation capacity to develop into somatic cells with biological functions. This ability to sustain a renewable source of multi- and/or pluripotential differentiation has brought new hope to the field of regenerative medicine in terms of cell therapy and tissue engineering. Moreover, stem cells are invaluable tools as in vitro models for studying diverse fields, from basic scientific questions such as developmental processes and lineage commitment, to practical application including drug screening and testing. The stem cells with widest differentiation potential are pluripotent stem cells (PSCs), which are rare cells with the ability to generate somatic cells from all three germ layers. PSCs are considered the most optimal choice for therapeutic potential of stem cells, bringing new impetus to the field of regenerative medicine. In this article, we discuss the therapeutic potential of human PSCs (hPSCs) including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), reviewing the current preclinical and clinical data using these stem cells. We describe the classification of different sources of hPSCs, ongoing research, and currently encountered clinical obstacles of these novel and versatile human stem cells.

Comparison of the IKr blockers moxifloxacin, dofetilide and E-4031 in five screening models of pro-arrhythmia reveals lack of specificity of isolated cardiomyocytes

BACKGROUND AND PURPOSE

Drug development requires the testing of new chemical entities for adverse effects. For cardiac safety screening, improved assays are urgently needed. Isolated adult cardiomyocytes (CM) and human embryonic stem cell-derived cardiomyocytes (hESC-CM) could be used to identify pro-arrhythmic compounds. In the present study, five assays were employed to investigate their sensitivity and specificity for evaluating the pro-arrhythmic properties of I(Kr) blockers, using moxifloxacin (safe compound) and dofetilide or E-4031 (unsafe compounds).

EXPERIMENTAL APPROACH

Assays included the anaesthetized remodelled chronic complete AV block (CAVB) dog, the anaesthetized methoxamine-sensitized unremodelled rabbit, multi-cellular hESC-CM clusters, isolated CM obtained from CAVB dogs and isolated CM obtained from the normal rabbit. Arrhythmic outcome was defined as Torsade de Pointes (TdP) in the animal models and early afterdepolarizations (EADs) in the cell models.

KEY RESULTS

At clinically relevant concentrations (5-12 µM), moxifloxacin was free of pro-arrhythmic properties in all assays with the exception of the isolated CM, in which 10 µM induced EADs in 35% of the CAVB CM and in 23% of the rabbit CM. At supra-therapeutic concentrations (≥100 µM), moxifloxacin was pro-arrhythmic in the isolated rabbit CM (33%), in the hESC-CM clusters (18%), and in the methoxamine rabbit (17%). Dofetilide and E-4031 induced EADs or TdP in all assays (50-83%), and the induction correlated with a significant increase in beat-to-beat variability of repolarization.

CONCLUSION AND IMPLICATIONS

Isolated cardiomyocytes lack specificity to discriminate between TdP liability of the I(Kr) blocking drugs moxifloxacin and dofetilide or E4031.

Stem cell therapy for cardiac disease

Congenital heart disease occurs in 1% of liveborn infants, making it the most common birth defect worldwide. Many of these children develop heart failure. In addition, both genetic and acquired forms of dilated cardiomyopathy are a significant source of heart failure in the pediatric population. Heart failure occurs when the myocardium is unable to meet the body's metabolic demands. Unlike some organs, the heart has limited, if any, capacity for repair after injury. Heart transplantation remains the ultimate approach to treating heart failure, but this is costly and excludes patients who are poor candidates for transplantation given their comorbidities, or for whom a donor organ is unavailable. Stem cell therapy represents the first realistic strategy for reversing the effects of what has until now been considered terminal heart damage. We will discuss potential sources of cardiac-specific stem cells, including mesenchymal, resident cardiac, embryonic, and induced pluripotent stem cells. We will consider efforts to enhance cardiac stem cell engraftment and survival in damaged myocardium, the incorporation of cardiac stem cells into tissue patches, and techniques for creating bioartificial myocardial tissue as well as whole organs. Finally, we will review progress being made in assessing functional improvement in animals and humans after cellular transplant.

Engraftment of human embryonic stem cell derived cardiomyocytes improves conduction in an arrhythmogenic in vitro model

In this study, we characterized the electrophysiological benefits of engrafting human embryonic stem cell-derived cardiomyocytes (hESC-CMs) in a model of arrhythmogenic cardiac tissue. Using transforming growth factor-β treated monolayers of neonatal rat ventricular cells (NRVCs), which retain several key aspects of the healing infarct such as an excess of contractile myofibroblasts and slowed, heterogeneous conduction, we assessed the ability of hESC-CMs to improve conduction and prevent arrhythmias. Cells from beating embryoid bodies (hESC-CMs) can form functional monolayers which beat spontaneously and can be electrically stimulated, with mean action potential duration of 275 ± 36 ms and conduction velocity (CV) of 10.6 ± 4.2 cm/s (n = 3). These cells, or cells from non-beating embryoid bodies (hEBCs) were added to anisotropic, NRVC monolayers. Immunostaining demonstrated hESC-CM survival and engraftment, and dye transfer assays confirmed functional coupling between hESC-CMs and NRVCs. Conduction velocities significantly increased in anisotropic NRVC monolayers after engraftment of hESC-CMs (13.4 ± 0.9 cm/s, n = 35 vs. 30.1 ± 3.2 cm/s, n = 20 in the longitudinal direction and 4.3 ± 0.3 cm/s vs. 9.3 ± 0.9 cm/s in the transverse direction), but decreased to even lower values after engraftment of non-cardiac hEBCs (to 10.6 ± 1.3 cm/s and 3.1 ± 0.5 cm/s, n = 11, respectively). Furthermore, reentrant wave vulnerability in NRVC monolayers decreased by 20% after engraftment of hESC-CMs, but did not change with engraftment of hEBCs. Finally, the culture of hESC-CMs in transwell inserts, which prevents juxtacrine interactions, or engraftment with connexin43-silenced hESC-CMs provided no functional improvement to NRVC monolayers. These results demonstrate that hESC-CMs can reverse the slowing of conduction velocity, reduce the incidence of reentry, and augment impaired electrical propagation via gap junction coupling to host cardiomyocytes in this arrhythmogenic in vitro model.

The effect of human and mouse fibroblast feeder cells on cardiac differentiation of human pluripotent stem cells

Mouse embryonic fibroblasts (MEFs) and human foreskin fibroblasts (hFFs) are commonly used as feeder cells to maintain the pluripotent state of stem cells. The aim of the present study was to evaluate the effect of MEF and hFF feeders on the cardiac differentiation. Two human embryonic and two induced pluripotent stem cell lines were cultured on MEF and hFF before cardiac differentiation. The expression of Brachyury T was higher in cell lines cultured on MEF, than if cultured on hFF, suggesting enhanced mesoderm formation. However, significant positive influence of MEF feeders on cardiac differentiation was only seen with one cell line. Further, the ability of hFF to maintain pluripotency of stem cells originally cultured on MEF was quite poor. In conclusion, the cells behaved differently whether cultured on hFF or MEF feeders. However, the influence of the feeder cells on differentiation was less than the difference observed between the cell lines.

Impedance-based detection of beating rhythm and proarrhythmic effects of compounds on stem cell-derived cardiomyocytes

The xCELLigence real time cell analyzer Cardio system offers a new system for real-time cell analysis that measures impedance-based signals in a label-free noninvasive manner. The aim of this study was to test whether impedance readings are a useful tool to detect compound effects on beating frequency (beats per minute, bpm) and arrhythmias of human induced pluripotent stem cell- and a mouse embryonic stem cell-derived cardiomyocyte line (hiPSC-CM and mESC-CM, respectively). Baseline values for control wells were 45±3 and 179±6 bpm, respectively (n=6). Correspondingly, isoproterenol increased beating frequency by 77% and 71%, whereas carbachol decreased frequency by 11% and 100% (stopped in 5/6 mESC-CM wells). E-4031 decreased beating rate and caused arrhythmias in both cell types, however, more pronounced in the human iPSC-CMs. Amlodipine inhibited contractions in both models, and T-type calcium channel block strongly reduced beating rate and eventually stopped beating in mESC-CM but caused a smaller effect in hiPSC-CM. The results of this initial study show that, under the right conditions, the beating frequency of a monolayer of cells can be stably recorded over several days. Additionally, the system detects changes in beating frequency and amplitude caused by added reference compounds. This assay system has the potential to enable medium-throughput screening, but for implementation into routine daily work, extended validation, testing of additional batches of cardiomyocytes, and further assay optimization (e.g., frequency of media exchange, growth matrix, seeding density, age of cells after plating, and temperature control) will be needed.

Averaging in vitro cardiac field potential recordings obtained with microelectrode arrays

Extracellular field potential (FP) recordings with microelectrode arrays (MEAs) from cardiomyocyte cultures offer a non-invasive way of studying the electrophysiological properties of these cells at the population level. Several studies have examined the FP properties of cardiomyocytes of various origins, including stem cell-derived cardiomyocytes. This focus reflects growing importance and interest in the field of MEA. High-quality cardiac FP signals are often difficult to obtain, especially from stem cell-derived cardiomyocyte cultures, which represent an important new field in cardiac electrophysiology. One way to improve the quality of these recordings is to average the cardiac FP signals. To date, however, no studies have examined the effect of averaging on cardiac FP signals. We report here that cardiac FP averaging can yield higher-quality signals than original individual FPs, and therefore promise more accurate detection of different phases and analysis of the cardiac FP signal. Averaged signals improved the signal-to-noise ratio (SNR), and obtaining reliable averages required approximately 50 cardiac cycles. We therefore propose that routine cardiac FP averaging can serve as a tool to compare the effects of different experimental conditions or stimuli on the properties of cardiac FPs.

High purity human-induced pluripotent stem cell-derived cardiomyocytes: electrophysiological properties of action potentials and ionic currents

Human-induced pluripotent stem cells (hiPSCs) can differentiate into functional cardiomyocytes; however, the electrophysiological properties of hiPSC-derived cardiomyocytes have yet to be fully characterized. We performed detailed electrophysiological characterization of highly pure hiPSC-derived cardiomyocytes. Action potentials (APs) were recorded from spontaneously beating cardiomyocytes using a perforated patch method and had atrial-, nodal-, and ventricular-like properties. Ventricular-like APs were more common and had maximum diastolic potentials close to those of human cardiac myocytes, AP durations were within the range of the normal human electrocardiographic QT interval, and APs showed expected sensitivity to multiple drugs (tetrodotoxin, nifedipine, and E4031). Early afterdepolarizations (EADs) were induced with E4031 and were bradycardia dependent, and EAD peak voltage varied inversely with the EAD take-off potential. Gating properties of seven ionic currents were studied including sodium (I(Na)), L-type calcium (I(Ca)), hyperpolarization-activated pacemaker (I(f)), transient outward potassium (I(to)), inward rectifier potassium (I(K1)), and the rapidly and slowly activating components of delayed rectifier potassium (I(Kr) and I(Ks), respectively) current. The high purity and large cell numbers also enabled automated patch-clamp analysis. We conclude that these hiPSC-derived cardiomyocytes have ionic currents and channel gating properties underlying their APs and EADs that are quantitatively similar to those reported for human cardiac myocytes. These hiPSC-derived cardiomyocytes have the added advantage that they can be used in high-throughput assays, and they have the potential to impact multiple areas of cardiovascular research and therapeutic applications.

Present state and future perspectives of using pluripotent stem cells in toxicology research

The use of novel drugs and chemicals requires reliable data on their potential toxic effects on humans. Current test systems are mainly based on animals or in vitro–cultured animal-derived cells and do not or not sufficiently mirror the situation in humans. Therefore, in vitro models based on human pluripotent stem cells (hPSCs) have become an attractive alternative. The article summarizes the characteristics of pluripotent stem cells, including embryonic carcinoma and embryonic germ cells, and discusses the potential of pluripotent stem cells for safety pharmacology and toxicology. Special attention is directed to the potential application of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) for the assessment of developmental toxicology as well as cardio- and hepatotoxicology. With respect to embryotoxicology, recent achievements of the embryonic stem cell test (EST) are described and current limitations as well as prospects of embryotoxicity studies using pluripotent stem cells are discussed. Furthermore, recent efforts to establish hPSC-based cell models for testing cardio- and hepatotoxicity are presented. In this context, methods for differentiation and selection of cardiac and hepatic cells from hPSCs are summarized, requirements and implications with respect to the use of these cells in safety pharmacology and toxicology are presented, and future challenges and perspectives of using hPSCs are discussed.

Very small embryonic-like stem cells (VSELs)-a new promising candidate for use in cardiac regeneration

In recent years, stem cell-based therapy has been given increased attention in terms of its potential contribution to cardiac regeneration and repair, after acute myocardial infarction (AMI). The published studies have identified many kinds of stem cells with the ability to regenerate and repair damaged myocardium after AMI. These include embryonic stem cells (ESCs), mesenchymal stem cells (MSCs), multipotent adult progenitor cells, unrestricted somatic stem cells, etc. More recently, very small embryonic-like stem cells (VSELs) were identified from murine, as a population of very small CXCR4(+) Lin(-) CD45(-) cells and from human, as a population of very small CD34(+) CD133(+) CXCR4(+) Lin(-) CD45(-) cells. These cells exhibit beneficial effects on improving cardiac function and attenuating cardiac remodeling after AMI. However, the mechanisms underlying the benefits associated with VSELs therapy, in cardiac regeneration and repair, remain poorly understood. This review summarizes the current studies on cardiac repair with VSELs after AMI, and discusses the potential mechanisms and implications of these cells in cardiac repair.

Cardiac slices as a predictive tool for arrhythmogenic potential of drugs and chemicals

IMPORTANCE OF THE FIELD

cardiac arrhythmia represents one of the primary safety pharmacological concerns in drug development. The most prominent example is drug induced ventricular tachycardia of the Torsade des Pointes type. The mechanism how this type of arrhythmia develops is a complex multi-cellular phenomenon. It can only be insufficiently reflected by cellular or molecular assays. However, organ models - such as Langendorff hearts - or in vivo experiments are expensive and time consuming and not suitable for assays requiring an increased throughput.

AREAS COVERED IN THIS REVIEW

here, we describe and review an assay bridging the gap between cardiomyocyte based assays and organ based systems - cardiac slices. This assay is reviewed in direct comparison with established safety pharmacological assays.

WHAT THE READER WILL GAIN

while slices have played an important role in brain research for > 2 decades, cardiac slices are experiencing a renaissance due to the novel challenges in safety pharmacology just in the last few years. Cardiac slices can be cultured and recorded over several days. It is possible to access electrophysiological data with a high number of electrodes - up to 256 electrodes - embedded in the surface of a microelectrode array.

TAKE HOME MESSAGE

cardiac slices close the gap between cellular and organ based assays in cardiac safety pharmacology. The tissue properties of a functional cardiac syncytium are more accurately reflected by a slice rather than a single cell.