Improvement of acquisition and analysis methods in multi-electrode array experiments with iPS cell-derived cardiomyocytes

hiPSC-CM electrophysiology: impact of temporal changes and study parameters on experimental reproducibility

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are frequently used for preclinical cardiotoxicity testing and remain an important tool for confirming model-based predictions of drug effects in accordance with the comprehensive in vitro proarrhythmia assay (CiPA). Despite the considerable benefits hiPSC-CMs provide, concerns surrounding experimental reproducibility have emerged. We investigated the effects of temporal changes and experimental parameters on hiPSC-CM electrophysiology. iCell cardiomyocytes2 were cultured and biosignals were acquired using a microelectrode array (MEA) system (2-14 days). Continuous recordings revealed a 22.6% increase in the beating rate and 7.7% decrease in the field potential duration (FPD) during a 20-min equilibration period. Location-specific differences across a multiwell plate were also observed, with iCell cardiomyocytes2 in the outer rows beating 8.8 beats/min faster than the inner rows. Cardiac endpoints were also impacted by cell culture duration; from 2 to 14 days, the beating rate decreased (-12.7 beats/min), FPD lengthened (+257 ms), and spike amplitude increased (+3.3 mV). Cell culture duration (4-10 days) also impacted cardiomyocyte drug responsiveness (E-4031, nifedipine, isoproterenol). qRT-PCR results suggest that daily variations in cardiac metrics may be linked to the continued maturation of hiPSC-CMs in culture (2-30 days). Daily experiments were also repeated using a second cell line (Cor.4U). Collectively, our study highlights multiple sources of variability to consider and address when performing hiPSC-CM MEA studies. To improve reproducibility and data interpretation, MEA-based studies should establish a standardized protocol and report key experimental conditions (e.g., cell line, culture time, equilibration time, electrical stimulation settings, and raw data values).NEW & NOTEWORTHY We demonstrate that iCell cardiomyocytes2 electrophysiology measurements are impacted by deviations in experimental techniques including electrical stimulation protocols, equilibration time, well-to-well variability, and length of hiPSC-CM culture. Furthermore, our results indicate that hiPSC-CM drug responsiveness changes within the first 2 wk following defrost.

Low-adhesion culture selection for human iPS cell-derived cardiomyocytes

Despite progress in generating cardiomyocytes from pluripotent stem cells, these populations often include non-contractile cells, necessitating cardiomyocyte selection for experimental purpose. This study explores a novel cardiomyocyte enrichment mechanism: low-adhesion culture selection. The cardiac cells derived from human induced pluripotent stem cells were subjected to a coating-free low-adhesion culture using bovine serum albumin and high molecular weight dextran sulfate. This approach effectively increased the population of cardiac troponin T-positive cardiomyocytes. Similar results were obtained with commercially available low-adhesion culture dishes. Subsequently, we accessed the practicality of selection of cardiomyocytes using this phenomenon by comparing it with established methods such as glucose-free culture and selection based on puromycin resistance genes. The cardiomyocytes enriched through low-adhesion culture selection maintained autonomous pulsation and responsiveness to beta-stimuli. Moreover, no significant differences were observed in the expression of genes related to subtype commitment and maturation when compared to other selection methods. In conclusion, cardiomyocytes derived from pluripotent stem cells were more low-adhesion culture resistant than their accompanying non-contractile cells, and low-adhesion culture is an alternative method for selection of pluripotent stem cell-derived cardiomyocytes.

Multifunctional cardiac microphysiological system based on transparent ITO electrodes for simultaneous optical measurement and electrical signal monitoring

Drug-induced cardiotoxicity is a significant contributor to drug recalls, primarily attributed to limitations in existing drug screening platforms. Traditional heart-on-a-chip platforms often employ metallic electrodes to record cardiomyocyte electrical signals. However, this approach hinders direct cardiomyocyte morphology observation and typically yields limited functionality. Consequently, this limitation may lead to an incomplete understanding of cardiomyocyte characteristics. To address these challenges, we introduce a multifunctional cardiac microphysiological system featuring transparent indium tin oxide electrodes. This innovative design aims to overcome the limitations of conventional heart-on-a-chip systems where metal electrodes interfere with the observation of cells and increase the difficulty of subsequent image processing of cell images. In addition to facilitating optical measurement combined with image processing capabilities, this system integrates a range of electrodes with diverse functionalities. These electrodes can realize cellular electrical stimulation, field potential monitoring, and impedance change tracking, enabling a comprehensive investigation of various cardiomyocyte traits. To demonstrate its versatility, we investigate the effects of four cardiac drugs with distinct pharmacological profiles on cardiomyocytes using this system. This platform provides a means for quantitatively and predictively assessing cardiac toxicity, which could be applied to conduct a comprehensive evaluation during the drug discovery process.

hiPSC-CM Electrophysiology: Impact of Temporal Changes and Study Parameters on Experimental Reproducibility

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are frequently used for preclinical cardiotoxicity testing and remain an important tool for confirming model-based predictions of drug effects in accordance with the Comprehensive in Vitro Proarrhythmia Assay (CiPA) initiative. Despite the considerable benefits hiPSC-CMs provide, concerns surrounding experimental reproducibility have emerged. Our study aimed to investigate the effects of temporal changes and experimental parameters on hiPSC-CM electrophysiology. hiPSC-CMs (iCell cardiomyocyte 2 ) were cultured for 14 days and biosignals were acquired using a microelectrode array (MEA) system. Continuous recordings revealed a 22.6% increase in the beating rate and 7.7% decrease in the field potential duration (FPD) during a 20-minute equilibration period. Location specific differences across a multiwell plate were also observed, with hiPSC-CMs in the outer rows beating 8.8 beats per minute (BPM) faster than the inner rows. Cardiac endpoints were also impacted by cell culture duration; from 2-14 days the beating rate decreased (-12.7 BPM), FPD lengthened (+257 ms), and spike amplitude increased (+3.3 mV). Cell culture duration (4-10 days) also impacted hiPSC-CM drug responsiveness (E-4031, nifedipine, isoproterenol). Our study highlights multiple sources of variability that should be considered and addressed when performing hiPSC-CM MEA studies. To improve reproducibility and data interpretation, MEA-based studies should establish a standardized protocol and report key experimental conditions (e.g., culture time, equilibration time, electrical stimulation settings, report raw data values).

New & Noteworthy

We demonstrate that hiPSC-CM electrophysiology measurements are significantly impacted by slight deviations in experimental techniques including electrical stimulation protocols, equilibration time, well-to-well variability, and length of hiPSC-CM culture. Furthermore, our results indicate that hiPSC-CM drug responsiveness changes within the first two weeks following defrost.

The evolving role of investigative toxicology in the pharmaceutical industry

For decades, preclinical toxicology was essentially a descriptive discipline in which treatment-related effects were carefully reported and used as a basis to calculate safety margins for drug candidates. In recent years, however, technological advances have increasingly enabled researchers to gain insights into toxicity mechanisms, supporting greater understanding of species relevance and translatability to humans, prediction of safety events, mitigation of side effects and development of safety biomarkers. Consequently, investigative (or mechanistic) toxicology has been gaining momentum and is now a key capability in the pharmaceutical industry. Here, we provide an overview of the current status of the field using case studies and discuss the potential impact of ongoing technological developments, based on a survey of investigative toxicologists from 14 European-based medium-sized to large pharmaceutical companies.

[Toward Regulatory Acceptance of MPS-Cardiac Safety Assessment as an Example]

Microphysiological system (MPS) are "Cell/tissue culture systems that reproduce in vivo organ functions in vitro by placing organ compartments that mimic the physiological environment of various organs such as the liver, small intestine, and lungs in micro-spaces." The MPS are attracting attention around the world as tools to improve human predictability in drug discovery research. In the U.S., in 2012, the NIH (National Institutes of Health) allocated a large budget to academia for research development of MPS. In Japan, the National Institute of Advanced Industrial Science and Technology and the NIHS (National Institute of Health Sciences) have been playing a central role in commercialization, performance evaluation, and standardization of MPS devices developed by academia for the liver, small intestine, kidney, and BBB as target organs/tissues in the AMED-MPS project that started in 2017. Pharmaceutical companies are beginning to utilize MPS in drug discovery research. However, MPS have only just been raised as a topic of discussion between regulatory authorities and pharmaceutical companies, and it will be necessary to overcome many barriers before data obtained by MPS can be included in drug approval documents and be widely accepted administratively. In this review, I would like to introduce cardiac safety evaluation as a concrete example to show what paths MPS should take to gain regulatory approval. In addition, I would like also to introduce human 3D heart tissue, which was developed in NIHS, as a cardiac MPS.

A functional neuron maturation device provides convenient application on microelectrode array for neural network measurement

BACKGROUND

Microelectrode array (MEA) systems are valuable for in vitro assessment of neurotoxicity and drug efficiency. However, several difficulties such as protracted functional maturation and high experimental costs hinder the use of MEA analysis requiring human induced pluripotent stem cells (hiPSCs). Neural network functional parameters are also needed for in vitro to in vivo extrapolation.

METHODS

In the present study, we produced a cost effective nanofiber culture platform, the SCAD device, for long-term culture of hiPSC-derived neurons and primary peripheral neurons. The notable advantage of SCAD device is convenient application on multiple MEA systems for neuron functional analysis.

RESULTS

We showed that the SCAD device could promote functional maturation of cultured hiPSC-derived neurons, and neurons responded appropriately to convulsant agents. Furthermore, we successfully analyzed parameters for in vitro to in vivo extrapolation, i.e., low-frequency components and synaptic propagation velocity of the signal, potentially reflecting neural network functions from neurons cultured on SCAD device. Finally, we measured the axonal conduction velocity of peripheral neurons.

CONCLUSIONS

Neurons cultured on SCAD devices might constitute a reliable in vitro platform to investigate neuron functions, drug efficacy and toxicity, and neuropathological mechanisms by MEA.

Establishment and validation of a torsade de pointes prediction model based on human iPSC‑derived cardiomyocytes

Drug-induced cardiotoxicity is one of the main causes of drug failure, which leads to subsequent withdrawal from pharmaceutical development. Therefore, identifying the potential toxic candidate in the early stages of drug development is important. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are a useful tool for assessing candidate compounds for arrhythmias. However, a suitable model using hiPSC-CMs to predict the risk of torsade de pointes (TdP) has not been fully established. The present study aimed to establish a predictive TdP model based on hiPSC-CMs. In the current study, 28 compounds recommended by the Comprehensive in vitro Proarrhythmia Assay (CiPA) were used as training set and models were established in different risk groups, high- and intermediate-risk versus low-risk groups. Subsequently, six endpoints of electrophysiological responses were used as potential model predictors. Accuracy, sensitivity and area under the curve (AUC) were used as evaluation indices of the models and seven compounds with known TdP risk were used to verify model differentiation and calibration. The results showed that among the seven models, the AUC of logistic regression and AdaBoost model was higher and had little difference in both training and test sets, which indicated that the discriminative ability and model stability was good and excellent, respectively. Therefore, these two models were taken as submodels, similar weight was configured and a new TdP risk prediction model was constructed using a soft voting strategy. The classification accuracy, sensitivity and AUC of the new model were 0.93, 0.95 and 0.92 on the training set, respectively and all 1.00 on the test set, which indicated good discrimination ability on both training and test sets. The risk threshold was defined as 0.50 and the consistency between the predicted and observed results were 92.8 and 100% on the training and test sets, respectively. Overall, the present study established a risk prediction model for TdP based on hiPSC-CMs which could be an effective predictive tool for compound-induced arrhythmias.

High-throughput optical action potential recordings in hiPSC-derived cardiomyocytes with a genetically encoded voltage indicator in the AAVS1 locus

Cardiomyocytes (CMs) derived from human induced pluripotent stem cells (hiPSCs) represent an excellent in vitro model in cardiovascular research. Changes in their action potential (AP) dynamics convey information that is essential for disease modeling, drug screening and toxicity evaluation. High-throughput optical AP recordings utilizing intramolecular Förster resonance energy transfer (FRET) of the voltage-sensitive fluorescent protein (VSFP) have emerged as a substitute or complement to the resource-intensive patch clamp technique. Here, we functionally validated our recently generated voltage indicator hiPSC lines stably expressing CAG-promoter-driven VSFP in the AAVS1 safe harbor locus. By combining subtype-specific cardiomyocyte differentiation protocols, we established optical AP recordings in ventricular, atrial, and nodal CMs in 2D monolayers using fluorescence microscopy. Moreover, we achieved high-throughput optical AP measurements in single hiPSC-derived CMs in a 3D context. Overall, this system greatly expands the spectrum of possibilities for high-throughput, non-invasive and long-term AP analyses in cardiovascular research and drug discovery.

A Carbon-Based Biosensing Platform for Simultaneously Measuring the Contraction and Electrophysiology of iPSC-Cardiomyocyte Monolayers

Heart beating is triggered by the generation and propagation of action potentials through the myocardium, resulting in the synchronous contraction of cardiomyocytes. This process highlights the importance of electrical and mechanical coordination in organ function. Investigating the pathogenesis of heart diseases and potential therapeutic actions in vitro requires biosensing technologies which allow for long-term and simultaneous measurement of the contractility and electrophysiology of cardiomyocytes. However, the adoption of current biosensing approaches for functional measurement of in vitro cardiac models is hampered by low sensitivity, difficulties in achieving multifunctional detection, and costly manufacturing processes. Leveraging carbon-based nanomaterials, we developed a biosensing platform that is capable of performing on-chip and simultaneous measurement of contractility and electrophysiology of human induced pluripotent stem-cell-derived cardiomyocyte (iPSC-CM) monolayers. This platform integrates with a flexible thin-film cantilever embedded with a carbon black (CB)-PDMS strain sensor for high-sensitivity contraction measurement and four pure carbon nanotube (CNT) electrodes for the detection of extracellular field potentials with low electrode impedance. Cardiac functional properties including contractile stress, beating rate, beating rhythm, and extracellular field potential were evaluated to quantify iPSC-CM responses to common cardiotropic agents. In addition, an in vitro model of drug-induced cardiac arrhythmia was established to further validate the platform for disease modeling and drug testing.

In vitro circulation model driven by tissue-engineered dome-shaped cardiac tissue

The heart is an essential organ for animals and humans. With the increased availability of pluripotent stem cells, the use of three-dimensional cardiac tissues consisting of cultured cardiomyocytes in in vitro drug evaluation has been widely studied. Several models have been proposed for the realization of the pump function, which is the original function of the heart. However, there are no models that simulate the human circulatory system using cultured cardiac tissue. This study shows that a dome-shaped cardiac tissue fabricated using the cell sheet stacking technique can achieve a heart-like pump function and circulate culture medium, there by mimicking the human circulatory system. Firstly, human induced pluripotent stem cells were differentiated into autonomously beating cardiomyocytes, and cardiomyocyte cell sheets were created using temperature-responsive culture dishes. A cardiomyocyte sheet and a human dermal fibroblast sheet were stacked using a cell sheet manipulator. This two-layered cell sheet was then inflated to create a dome-shaped cardiac tissue with a base diameter of 8 mm. The volume of the dome-shaped cardiac tissue changed according to the autonomous beating. The stroke volume increased with the culture period and reached 21 ± 8.9 μL (n = 6) on day 21. It also responded to β-stimulant and extracellular calcium concentrations. Internal pressure fluctuations were also recorded under isovolumetric conditions by dedicated culture devices. The peak heights of pulsatile pressure were 0.33 ± 0.048 mmHg (n = 3) under a basal pressure of 0.5 mmHg on day 19. When the tissue was connected to a flow path that had check valves applied, it drove a directional flow with an average flow rate of approximately 1 μL/s. Furthermore, pressure-volume (P-V) diagrams were created from the simultaneous measurement of changes in pressure and volume under three conditions of fluidic resistance. In conclusion, this cardiac model can potentially be used for biological pumps that drive multi-organ chips and for more accurate in vitro drug evaluation using P-V diagrams.

Electrospun piezoelectric scaffolds for cardiac tissue engineering

The use of smart materials in tissue engineering is becoming increasingly appealing to provide additional functionalities and control over cell fate. The stages of tissue development and regeneration often require various electrical and electromechanical cues supported by the extracellular matrix, which is often neglected in most tissue engineering approaches. Particularly, in cardiac cells, electrical signals modulate cell activity and are responsible for the maintenance of the excitation-contraction coupling. Addition of electroconductive and topographical cues improves the biomimicry of cardiac tissues and plays an important role in driving cells towards the desired phenotype. Current platforms used to apply electrical stimulation to cells in vitro often require large external equipment and wires and electrodes immersed in the culture media, limiting the scalability and applicability of this process. Piezoelectric materials represent a shift in paradigm in materials and methods aimed at providing electrical stimulation to cardiac cells since they can produce and deliver electrical signals to cells and tissues by mechanoelectrical transduction. Despite the ability of piezoelectric materials to mimic the mechanoelectrical transduction of the heart, the use of these materials is limited in cardiac tissue engineering and methods to characterise piezoelectricity are often built in-house, which poses an additional difficulty when comparing results from the literature. In this work, we aim at providing an overview of the main challenges in cardiac tissue engineering and how piezoelectric materials could offer a solution to them. A revision on the existing literature in electrospun piezoelectric materials applied to cardiac tissue engineering is performed for the first time, as electrospinning plays an important role in the manufacturing of scaffolds with enhanced piezoelectricity and extracellular matrix native-like morphology. Finally, an overview of the current techniques used to evaluate piezoelectricity and their limitations is provided.

OUP accepted manuscript

The content of this article derives from a Health and Environmental Sciences Institute (HESI) consortium with a focus to improve cardiac safety during drug development. A detailed literature review was conducted to evaluate the concordance between nonclinical repolarization assays and the clinical thorough QT (TQT) study. Food and Drug Administration and HESI developed a joint database of nonclinical and clinical data, and a retrospective analysis of 150 anonymized drug candidates was reviewed to compare the performance of 3 standard nonclinical assays with clinical TQT study findings as well as investigate mechanism(s) potentially responsible for apparent discrepancies identified. The nonclinical assays were functional (I_Kr) current block (Human ether-a-go-go related gene), action potential duration, and corrected QT interval in animals (in vivo corrected QT). Although these nonclinical assays demonstrated good specificity for predicting negative clinical QT prolongation, they had relatively poor sensitivity for predicting positive clinical QT prolongation. After review, 28 discordant TQT-positive drugs were identified. This article provides an overview of direct and indirect mechanisms responsible for QT prolongation and theoretical reasons for lack of concordance between clinical TQT studies and nonclinical assays. We examine 6 specific and discordant TQT-positive drugs as case examples. These were derived from the unique HESI/Food and Drug Administration database. We would like to emphasize some reasons for discordant data including, insufficient or inadequate nonclinical data, effects of the drug on other cardiac ion channels, and indirect and/or nonelectrophysiological effects of drugs, including altered heart rate. We also outline best practices that were developed based upon our evaluation.

Phenotypic Variability in iPSC-Induced Cardiomyocytes and Cardiac Fibroblasts Carrying Diverse LMNA Mutations

Mutations in the LMNA gene (encoding lamin A/C) are a significant cause of familial arrhythmogenic cardiomyopathy. Although the penetrance is high, there is considerable phenotypic variability in disease onset, rate of progression, arrhythmias, and severity of myopathy. To begin to address whether this variability stems from specific LMNA mutation sites and types, we generated seven patient-specific induced pluripotent stem cell (iPSC) lines with various LMNA mutations. IPSC-derived cardiomyocytes (iCMs) and cardiac fibroblasts (iCFs) were differentiated from each line for phenotypic analyses. LMNA expression and extracellular signal-regulated kinase pathway activation were perturbed to differing degrees in both iCMs and iCFs from the different lines. Enhanced apoptosis was observed in iCMs but not in iCFs. Markedly diverse irregularities of nuclear membrane morphology were present in iCFs but not iCMs, while iCMs demonstrated variable sarcomere disarray. Heterogenous electrophysiological aberrations assayed by calcium indicator imaging and multi-electrode array suggest differing substrates for arrhythmia that were accompanied by variable ion channel gene expression in the iCMs. Coculture studies suggest enhancement of the LMNA mutation effects on electrophysiological function exerted by iCFs. This study supports the utility of patient-specific iPSC experimental platform in the exploration of mechanistic and phenotypic heterogeneity of different mutations within a cardiac disease-associated gene. The addition of genetically defined coculture of cardiac-constituent non-myocytes further expands the capabilities of this approach.

Gain-of-function cardiomyopathic mutations in RBM20 rewire splicing regulation and re-distribute ribonucleoprotein granules within processing bodies

Mutations in the cardiac splicing factor RBM20 lead to malignant dilated cardiomyopathy (DCM). To understand the mechanism of RBM20-associated DCM, we engineered isogenic iPSCs with DCM-associated missense mutations in RBM20 as well as RBM20 knockout (KO) iPSCs. iPSC-derived engineered heart tissues made from these cell lines recapitulate contractile dysfunction of RBM20-associated DCM and reveal greater dysfunction with missense mutations than KO. Analysis of RBM20 RNA binding by eCLIP reveals a gain-of-function preference of mutant RBM20 for 3' UTR sequences that are shared with amyotrophic lateral sclerosis (ALS) and processing-body associated RNA binding proteins (FUS, DDX6). Deep RNA sequencing reveals that the RBM20 R636S mutant has unique gene, splicing, polyadenylation and circular RNA defects that differ from RBM20 KO. Super-resolution microscopy verifies that mutant RBM20 maintains very limited nuclear localization potential; rather, the mutant protein associates with cytoplasmic processing bodies (DDX6) under basal conditions, and with stress granules (G3BP1) following acute stress. Taken together, our results highlight a pathogenic mechanism in cardiac disease through splicing-dependent and -independent pathways.

Simultaneous measurement of contractile force and field potential of dynamically beating human iPS cell-derived cardiac cell sheet-tissue with flexible electronics

Human induced pluripotent stem (iPS) cell-derived cardiomyocytes are used for in vitro pharmacological and pathological studies worldwide. In particular, the functional assessment of cardiac tissues created from iPS cell-derived cardiomyocytes is expected to provide precise prediction of drug effects and thus streamline the process of drug development. However, the current format of electrophysiological and contractile assessment of cardiomyocytes on a rigid substrate is not appropriate for cardiac tissues that beat dynamically. Here, we show a novel simultaneous measurement system for contractile force and extracellular field potential of iPS cell-derived cardiac cell sheet-tissues using 500 nm-thick flexible electronic sheets. It was confirmed that the developed system is applicable for pharmacological studies and assessments of excitation-contraction coupling-related parameters, such as the electro-mechanical window. Our results indicate that flexible electronics with cardiac tissue engineering provide an advanced platform for drug development. This system will contribute to gaining new insight in pharmacological study of human cardiac function.

Scaffold-based and scaffold-free cardiac constructs for drug testing

The safety and therapeutic efficacy of new drugs are tested in experimental animals. However, besides being a laborious, costly process, differences in drug responses between humans and other animals and potential cardiac adverse effects lead to the discontinued development of new drugs. Thus, alternative approaches to animal tests are needed. Cardiotoxicity and responses of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to drugs are conventionally evaluated by cell seeding and two-dimensional (2D) culture, which allows measurements of field potential duration and the action potentials of CMs using multielectrode arrays. However, 2D-cultured hiPSC-CMs lack 3D spatial adhesion, and have fewer intercellular and extracellular matrix interactions, as well as different contractile behavior from CMsin vivo. This issue has been addressed using tissue engineering to fabricate three-dimensional (3D) cardiac constructs from hiPSC-CMs culturedin vitro. Tissue engineering can be categorized as scaffold-based and scaffold-free. In scaffold-based tissue engineering, collagen and fibrin gel scaffolds comprise a 3D culture environment in which seeded cells exhibit cardiac-specific functions and drug responses, whereas 3D cardiac constructs fabricated by tissue engineering without a scaffold have high cell density and form intercellular interactions. This review summarizes the characteristics of scaffold-based and scaffold-free cardiac tissue engineering and discusses the applications of fabricated cardiac constructs to drug screening.

Bisphenol S and bisphenol F are less disruptive to cardiac electrophysiology, as compared to bisphenol A

Bisphenol A (BPA) is a high-production volume chemical used to manufacture consumer and medical-grade plastic products. Due to its ubiquity, the general population can incur daily environmental exposure to BPA, while heightened exposure has been reported in intensive care patients and industrial workers. Due to health concerns, structural analogues are being explored as replacements for BPA. This study aimed to examine the direct effects of BPA on cardiac electrophysiology compared with recently developed alternatives, including BPS (bisphenol S) and BPF (bisphenol F). Whole-cell voltage-clamp recordings were performed on cell lines transfected to express the voltage-gated sodium channel (Nav1.5), L-type voltage-gated calcium channel (Cav1.2), or the rapidly activating delayed rectifier potassium channel (hERG). Cardiac electrophysiology parameters were measured using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) and intact, whole rat heart preparations. BPA was the most potent inhibitor of fast/peak (INa-P) and late (INa-L) sodium channel (IC50= 55.3, 23.6 µM, respectively), L-type calcium channel (IC50= 30.8 µM) and hERG channel current (IC50= 127 µM). Inhibitory effects on L-type calcium channels were supported by microelectrode array recordings, which revealed a shortening of the extracellular field potential (akin to QT interval). BPA and BPF exposures slowed atrioventricular (AV) conduction and increased AV node refractoriness in isolated rat heart preparations, in a dose-dependent manner (BPA: +9.2% 0.001 µM, +95.7% 100 µM; BPF: +20.7% 100 µM). BPS did not alter any of the cardiac electrophysiology parameters tested. Results of this study demonstrate that BPA and BPF exert an immediate inhibitory effect on cardiac ion channels, while BPS is markedly less potent. Additional studies are necessary to fully elucidate the safety profile of bisphenol analogues on the heart.

Investigating inherited arrhythmias using hiPSC-derived cardiomyocytes

Fundamental to the functional behavior of cardiac muscle is that the cardiomyocytes are integrated as a functional syncytium. Disrupted electrical activity in the cardiac tissue can lead to serious complications including cardiac arrhythmias. Therefore, it is important to study electrophysiological properties of the cardiac tissue. With advancements in stem cell research, protocols for the production of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been established, providing great potential in modelling cardiac arrhythmias and drug testing. The hiPSC-CM model can be used in conjunction with electrophysiology-based platforms to examine the electrical activity of the cardiac tissue. Techniques for determining the myocardial electrical activity include multielectrode arrays (MEAs), optical mapping (OM), and patch clamping. These techniques provide critical approaches to investigate cardiac electrical abnormalities that underlie arrhythmias.

Comprehensive Cardiotoxicity Assessment of COVID-19 Treatments Using Human Induced Pluripotent Stem Cell-derived Cardiomyocytes

Coronavirus disease 2019 (COVID-19) continues to spread across the globe, with numerous clinical trials underway seeking to develop and test effective COVID-19 therapies, including remdesivir. Several ongoing studies have reported hydroxychloroquine-induced cardiotoxicity, including development of torsade de pointes (TdP). Meanwhile, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are expected to serve as a tool for assessing drug-induced cardiotoxicity, such as TdP and contraction impairment. However, the cardiotoxicity of COVID-19 treatments has not been fully assessed using hiPSC-CMs. In the present study, we focused on drug repurposing with various modes of actions and examined the TdP risk associated with COVID-19 treatments using field potential using multi-electrode array (MEA) system and motion analysis with hiPSC-CMs. Hydroxychloroquine induced early after depolarization, while remdesivir, favipiravir, camostat and ivermectin had little effect on field potentials. We then analyzed electromechanical window (EMw), which is defined as the difference between field potential and contraction-relaxation durations. Hydroxychloroquine decreased EMw of hiPSC-CMs in a concentration-dependent manner. In contrast, other drugs have little effect. Our data suggest that hydroxychloroquine has proarrhythmic risk and other drugs have low proarrhythmic risk. Thus, hiPSC-CMs represent a useful tool for assessing the comprehensive cardiotoxicity caused by COVID-19 treatments in non-clinical settings.

An Optical-Flow-Based Method to Quantify Dynamic Behavior of Human Pluripotent Stem Cell-Derived Cardiomyocytes in Disease Modeling Platforms

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) hold great promise for cardiovascular disease modeling, drug screening and personalized medicine. A crucial requirement to establish an hPSC-CM-based disease model is the availability of a reliable differentiation protocol and a functional assessment of phenotypic properties of CMs in a disease context. Characterization of relative changes in contractile behavior of CMs can provide insight not only about drug effects but into the pathogenesis of cardiovascular diseases. Image-based optical-flow analysis, which applies a speckle tracking algorithm to videomicroscopy of hPSC-CMs, is a noninvasive method to quantitatively assess the dynamics of mechanical contraction of the CMs. This method offers an efficient characterization of contractile cycles. It quantifies contraction velocity field, beat rate, contractile strain and contraction-relaxation strain rate profile, which are important phenotypic characteristics of CMs.

Improving reliability and reducing costs of cardiotoxicity assessments using laser-induced cell poration on microelectrode arrays

Drug-induced cardiotoxicity is a major barrier to drug development and a main cause of withdrawal of marketed drugs. Drugs can strongly alter the spontaneous functioning of the heart by interacting with the cardiac membrane ion channels. If these effects only surface during in vivo preclinical tests, clinical trials or worse after commercialization, the societal and economic burden will be significant and seriously hinder the efficient drug development process. Hence, cardiac safety pharmacology requires in vitro electrophysiological screening assays of all drug candidates to predict cardiotoxic effects before clinical trials. In the past 10 years, microelectrode array (MEA) technology began to be considered a valuable approach in pharmaceutical applications. However, an effective tool for high-throughput intracellular measurements, compatible with pharmaceutical standards, is not yet available. Here, we propose laser-induced optoacoustic poration combined with CMOS-MEA technology as a reliable and effective platform to detect cardiotoxicity. This approach enables the acquisition of high-quality action potential recordings from large numbers of cardiomyocytes within the same culture well, providing reliable data using single-well MEA devices and single cardiac syncytia per each drug. Thus, this technology could be applied in drug safety screening platforms reducing times and costs of cardiotoxicity assessments, while simultaneously improving the data reliability.

Identifying Drug Response by Combining Measurements of the Membrane Potential, the Cytosolic Calcium Concentration, and the Extracellular Potential in Microphysiological Systems

Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) offer a new means to study and understand the human cardiac action potential, and can give key insight into how compounds may interact with important molecular pathways to destabilize the electrical function of the heart. Important features of the action potential can be readily measured using standard experimental techniques, such as the use of voltage sensitive dyes and fluorescent genetic reporters to estimate transmembrane potentials and cytosolic calcium concentrations. Using previously introduced computational procedures, such measurements can be used to estimate the current density of major ion channels present in hiPSC-CMs, and how compounds may alter their behavior. However, due to the limitations of optical recordings, resolving the sodium current remains difficult from these data. Here we show that if these optical measurements are complemented with observations of the extracellular potential using multi electrode arrays (MEAs), we can accurately estimate the current density of the sodium channels. This inversion of the sodium current relies on observation of the conduction velocity which turns out to be straightforwardly computed using measurements of extracellular waves across the electrodes. The combined data including the membrane potential, the cytosolic calcium concentration and the extracellular potential further opens up for the possibility of accurately estimating the effect of novel drugs applied to hiPSC-CMs.

Cardiotoxicity Assessment of Drugs Using Human iPS Cell-Derived Cardiomyocytes: Toward Proarrhythmic Risk and Cardio-Oncology

Growing evidence suggests that Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes (hiPSC-CMs) can be used as a new human cell-based platform to assess cardiac toxicity/safety during drug development. Cardiotoxicity assessment is highly challenging due to species differences and various toxicities, such as electrophysiological and contractile toxicities, which can result in proarrhythmia and heart failure. To explore proarrhythmic risk, the Multi-Electrode Array (MEA) platform is widely used to assess QT-interval prolongation and the proarrhythmic potential of drug candidates using hiPSC-CMs. Several consortiums, including the Comprehensive in vitro Proarrhythmia Assay (CiPA) and the Japanese iPS Cardiac Safety Assessment (JiCSA), have demonstrated the applicability of hiPSC-CMs/MEA for assessing the torsadogenic potential of drug candidates. Additionally, contractility is a key safety issue in drug development, and efforts have been undertaken to measure contractility by a variety of imaging-based methods using iPS-CMs. Therefore, hiPSC-CMs might represent a standard testing tool for evaluating the proarrhythmic and contractile potentials. This review provides new insights into the practical application of hiPSC-CMs in early or late-stage nonclinical testing during drug development.

Modeling Cardiac Disease Mechanisms Using Induced Pluripotent Stem Cell-Derived Cardiomyocytes: Progress, Promises and Challenges

Cardiovascular diseases (CVDs) are a class of disorders affecting the heart or blood vessels. Despite progress in clinical research and therapy, CVDs still represent the leading cause of mortality and morbidity worldwide. The hallmarks of cardiac diseases include heart dysfunction and cardiomyocyte death, inflammation, fibrosis, scar tissue, hyperplasia, hypertrophy, and abnormal ventricular remodeling. The loss of cardiomyocytes is an irreversible process that leads to fibrosis and scar formation, which, in turn, induce heart failure with progressive and dramatic consequences. Both genetic and environmental factors pathologically contribute to the development of CVDs, but the precise causes that trigger cardiac diseases and their progression are still largely unknown. The lack of reliable human model systems for such diseases has hampered the unraveling of the underlying molecular mechanisms and cellular processes involved in heart diseases at their initial stage and during their progression. Over the past decade, significant scientific advances in the field of stem cell biology have literally revolutionized the study of human disease in vitro. Remarkably, the possibility to generate disease-relevant cell types from induced pluripotent stem cells (iPSCs) has developed into an unprecedented and powerful opportunity to achieve the long-standing ambition to investigate human diseases at a cellular level, uncovering their molecular mechanisms, and finally to translate bench discoveries into potential new therapeutic strategies. This review provides an update on previous and current research in the field of iPSC-driven cardiovascular disease modeling, with the aim of underlining the potential of stem-cell biology-based approaches in the elucidation of the pathophysiology of these life-threatening diseases.

Drug response analysis for scaffold-free cardiac constructs fabricated using bio-3D printer

Cardiac constructs fabricated using human induced pluripotent stem cells-derived cardiomyocytes (iPSCs-CMs) are useful for evaluating the cardiotoxicity of and cardiac response to new drugs. Previously, we fabricated scaffold-free three-dimensional (3D) tubular cardiac constructs using a bio-3D printer, which can load cardiac spheroids onto a needle array. In this study, we developed a method to measure the contractile force and to evaluate the drug response in cardiac constructs. Specifically, we measured the movement of the needle tip upon contraction of the cardiac constructs on the needle array. The contractile force and beating rate of the cardiac constructs were evaluated by analysing changes in the movement of the needle tip. To evaluate the drug response, contractile properties were measured following treatment with isoproterenol, propranolol, or blebbistatin, in which the movement of the needle tip was increased following isoproterenol treatment, but was decreased following propranolol or blebbistain, treatments. To evaluate cardiotoxicity, contraction and cell viability of the cardiac constructs were measured following doxorubicin treatment. Cell viability was found to decrease with decreasing movement of the needle tip following doxorubicin treatment. Collectively, our results show that this method can aid in evaluating the contractile force of cardiac constructs.

Integrating in vitro data and physiologically based kinetic modeling-facilitated reverse dosimetry to predict human cardiotoxicity of methadone

Development of novel testing strategies to detect adverse human health effects is of interest to replace in vivo-based drug and chemical safety testing. The aim of the present study was to investigate whether physiologically based kinetic (PBK) modeling-facilitated conversion of in vitro toxicity data is an adequate approach to predict in vivo cardiotoxicity in humans. To enable evaluation of predictions made, methadone was selected as the model compound, being a compound for which data on both kinetics and cardiotoxicity in humans are available. A PBK model for methadone in humans was developed and evaluated against available kinetic data presenting an adequate match. Use of the developed PBK model to convert concentration–response curves for the effect of methadone on human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) in the so-called multi electrode array (MEA) assay resulted in predictions for in vivo dose–response curves for methadone-induced cardiotoxicity that matched the available in vivo data. The results also revealed differences in protein plasma binding of methadone to be a potential factor underlying variation between individuals with respect to sensitivity towards the cardiotoxic effects of methadone. The present study provides a proof-of-principle of using PBK modeling-based reverse dosimetry of in vitro data for the prediction of cardiotoxicity in humans, providing a novel testing strategy in cardiac safety studies.

Direct investigation of current transport in cells by conductive atomic force microscopy

Currents play critical roles in neurons. Direct observation of current flows in cells at nanometre dimensions and picoampere current resolution is still a daunting task. In this study, we investigated the current flows in hippocampal neurons, PC12 cells and astrocytes in response to voltages applied to the cell membranes using conductive atomic force microscopy (CAFM). The spines in the hippocampal neurons play crucial roles in nerve signal transfer. When the applied voltage was greater than 7.2 V, PC12 cells even show metallic nanowire-like characteristics. Both the cell body and glial filaments of astrocytes yielded CAFM test results that reflect different electrical conductance. To our best knowledge, the electrical characteristics and current transport through components of cells (especially neurons) in response to an applied external voltage have been revealed for the first time at nanometre dimensions and picoampere current levels. We believe that such studies will pave new ways to study and model the electrical characteristics and physiological behaviours in cells and other biological samples.

Human Heart Cardiomyocytes in Drug Discovery and Research: New Opportunities in Translational Sciences

In preclinical drug development, accurate prediction of drug effects on the human heart is critically important, whether in the context of cardiovascular safety or for the purpose of modulating cardiac function to treat heart disease. Current strategies have significant limitations, whereby, cardiotoxic drugs can escape detection or potential life-saving therapies are abandoned due to false positive toxicity signals. Thus, new and more reliable translational approaches are urgently needed to help accelerate the rate of new therapy development. Renewed efforts in the recovery of human donor hearts for research and in cardiomyocyte isolation methods, are providing new opportunities for preclinical studies in adult primary cardiomyocytes. These cells exhibit the native physiological and pharmacological properties, overcoming the limitations presented by artificial cellular models, animal models and have great potential for providing an excellent tool for preclinical drug testing. Adult human primary cardiomyocytes have already shown utility in assessing drug-induced cardiotoxicity risk and helping in the identification of new treatments for cardiac diseases, such as heart failure and atrial fibrillation. Finally, strategies with actionable decision-making trees that rely on data derived from adult human primary cardiomyocytes will provide the holistic insights necessary to accurately predict human heart effects of drugs.

Comprehensive Cardiac Safety Assessment using hiPS-cardiomyocytes (Consortium for Safety Assessment using Human iPS Cells: CSAHi)

Current cardiac safety assessment platforms (in vitro hERG-centric, APD, and/or in vivo animal QT assays) are not fully predictive of drug-induced Torsades de Pointes (TdP) and do not address other mechanism-based arrhythmia, including ventricular tachycardia or ventricular fibrillation, or cardiac safety liabilities such as contractile and structural cardiotoxicity which are another growing safety concerns. We organized the Consortium for Safety Assessment using Human iPS cells (CSAHi; http://csahi.org/en/) in 2013, based on the Japan Pharmaceutical Manufacturers Association (JPMA), to verify the application of human iPS/ES cell-derived cardiomyocytes for drug safety evaluation. The CSAHi HEART team focused on comprehensive screening strategies to predict a diverse range of cardiotoxicities using recently introduced platforms such as the Multi-Electrode Array (MEA), cellular impedance, Motion Field Imaging (MFI), and optical imaging of Ca transient to identify strengths and weaknesses of each platform. Our study showed that hiPS-CMs used in these platforms could detect pharmacological responses that were more relevant to humans compared to existing hERG, APD, or Langendorff (MAPD/contraction) assays. Further, MEA and other methods such as impedance, MFI, and Ca transient assays provided paradigm changes of platforms for predicting drug-induced QT risk and/or arrhythmia or contractile dysfunctions. In contrast, since discordances such as overestimation (false positive) of arrhythmogenicity, oversight, or opposite conclusions in positive inotropic and negative chronotropic activities to some compounds were also confirmed, possibly due to their functional immaturity of hiPS-CMs, hiPS-CMs should be used in these platforms for cardiac safety assessment based upon their advantages and disadvantages.

hiPSCs Derived Cardiac Cells for Drug and Toxicity Screening and Disease Modeling: What Micro- Electrode-Array Analyses Can Tell Us

Human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CM) have been intensively used in drug development and disease modeling. Since iPSC-cardiomyocyte (CM) was first generated, their characterization has become a major focus of research. Multi-/micro-electrode array (MEA) systems provide a non-invasive user-friendly platform for detailed electrophysiological analysis of iPSC cardiomyocytes including drug testing to identify potential targets and the assessment of proarrhythmic risk. Here, we provide a systematical overview about the physiological and technical background of micro-electrode array measurements of iPSC-CM. We introduce the similarities and differences between action- and field potential and the advantages and drawbacks of MEA technology. In addition, we present current studies focusing on proarrhythmic side effects of novel and established compounds combining MEA systems and iPSC-CM. MEA technology will help to open a new gateway for novel therapies in cardiovascular diseases while reducing animal experiments at the same time.

Human induced pluripotent stem cell line with genetically encoded fluorescent voltage indicator generated via CRISPR for action potential assessment post-cardiogenesis

Genetically encoded fluorescent voltage indicators, such as ArcLight, have been used to report action potentials (APs) in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). However, the ArcLight expression, in all cases, relied on a high number of lentiviral vector-mediated random genome integrations (8-12 copy/cell), raising concerns such as gene disruption and alteration of global and local gene expression, as well as loss or silencing of reporter genes after differentiation. Here, we report the use of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 nuclease technique to develop a hiPSC line stably expressing ArcLight from the AAVS1 safe harbor locus. The hiPSC line retained proliferative ability with a growth rate similar to its parental strain. Optical recording with conventional epifluorescence microscopy allowed the detection of APs as early as 21 days postdifferentiation, and could be repeatedly monitored for at least 5 months. Moreover, quantification and analysis of the APs of ArcLight-CMs identified two distinctive subtypes: a group with high frequency of spontaneous APs of small amplitudes that were pacemaker-like CMs and a group with low frequency of automaticity and large amplitudes that resembled the working CMs. Compared with FluoVolt voltage-sensitive dye, although dimmer, the ArcLight reporter exhibited better optical performance in terms of phototoxicity and photostability with comparable sensitivities and signal-to-noise ratios. The hiPSC line with targeted ArcLight engineering design represents a useful tool for studying cardiac development or hiPSC-derived cardiac disease models and drug testing.

Cardiotoxicity screening of illicit drugs and new psychoactive substances (NPS) in human iPSC-derived cardiomyocytes using microelectrode array (MEA) recordings

The use of recreational drugs, including new psychoactive substances (NPS), is paralleled by emergency department visits of drug users with severe cardiotoxicity. Drug-induced cardiotoxicity can be the (secondary) result of increased norepinephrine blood concentrations, but data on potential drug-induced direct effects on cardiomyocyte function are scarce. The presence of hundreds of NPS therefore calls for efficient screening models to assess direct cardiotoxicity. We investigated effects of four reference compounds (3-30 nM dofetilide, nifedipine and isoproterenol, and 1-10 μM mexiletine) and six recreational drugs (0.01-100 μM cocaine, 0.01-1000 μM amphetamine, MDMA, 4-fluoroamphetamine, α-PVP and MDPV) on cardiomyocyte function (beat rate, spike amplitude and field potential duration (FPD ≈ QT interval in ECGs)), using Pluricyte® human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes cultured on ready-to-use CardioPlate™ multi-well microelectrode arrays (mwMEAs). Moreover, the effects of exposure to recreational drugs on cell viability were assessed. Effects of reference compounds were in accordance with the literature, indicating the presence of hERG potassium (dofetilide), sodium (mexiletine) and calcium (nifedipine) channels and α-adrenergic receptors (isoproterenol). All recreational drugs decreased the spike amplitude at 10-100 μM. All amphetamine-type stimulants and α-PVP decreased the beat rate at 300 μM, while cocaine and MDPV did so at 10 μM and 30 μM, respectively. All drugs increased the FPD, however at varying concentrations. MDMA, MDPV and amphetamine affected cardiomyocyte function at concentrations relevant for human exposure, while other drugs affected cardiomyocyte function only at higher concentrations (≥ 10 μM). Cell viability was only mildly affected at concentrations well above the lowest concentrations affecting cardiomyocyte function. We demonstrate that MEA recordings of hiPSC-derived cardiomyocytes enable screening for acute, direct effects on cardiomyocyte function. Our data further indicate that tachycardia in patients exposed to recreational drugs is likely due to indirect drug effects, while prolonged repolarization periods (prolonged QT_c interval) could (partly) result from direct drug effects on cardiomyocyte function.

Chromatin compartment dynamics in a haploinsufficient model of cardiac laminopathy

Mutations in A-type nuclear lamins cause dilated cardiomyopathy, which is postulated to result from dysregulated gene expression due to changes in chromatin organization into active and inactive compartments. To test this, we performed genome-wide chromosome conformation analyses in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) with a haploinsufficient mutation for lamin A/C. Compared with gene-corrected cells, mutant hiPSC-CMs have marked electrophysiological and contractile alterations, with modest gene expression changes. While large-scale changes in chromosomal topology are evident, differences in chromatin compartmentalization are limited to a few hotspots that escape segregation to the nuclear lamina and inactivation during cardiogenesis. These regions exhibit up-regulation of multiple noncardiac genes including CACNA1A, encoding for neuronal P/Q-type calcium channels. Pharmacological inhibition of the resulting current partially mitigates the electrical alterations. However, chromatin compartment changes do not explain most gene expression alterations in mutant hiPSC-CMs. Thus, global errors in chromosomal compartmentation are not the primary pathogenic mechanism in heart failure due to lamin A/C haploinsufficiency.

Considerations for an In Vitro, Cell-Based Testing Platform for Detection of Drug-Induced Inotropic Effects in Early Drug Development. Part 2: Designing and Fabricating Microsystems for Assaying Cardiac Contractility With Physiological Relevance Using Human iPSC-Cardiomyocytes

Contractility of the myocardium engines the pumping function of the heart and is enabled by the collective contractile activity of its muscle cells: cardiomyocytes. The effects of drugs on the contractility of human cardiomyocytes in vitro can provide mechanistic insight that can support the prediction of clinical cardiac drug effects early in drug development. Cardiomyocytes differentiated from human-induced pluripotent stem cells have high potential for overcoming the current limitations of contractility assays because they attach easily to extracellular materials and last long in culture, while having human- and patient-specific properties. Under these conditions, contractility measurements can be non-destructive and minimally invasive, which allow assaying sub-chronic effects of drugs. For this purpose, the function of cardiomyocytes in vitro must reflect physiological settings, which is not observed in cultured cardiomyocytes derived from induced pluripotent stem cells because of the fetal-like properties of their contractile machinery. Primary cardiomyocytes or tissues of human origin fully represent physiological cellular properties, but are not easily available, do not last long in culture, and do not attach easily to force sensors or mechanical actuators. Microengineered cellular systems with a more mature contractile function have been developed in the last 5 years to overcome this limitation of stem cell-derived cardiomyocytes, while simultaneously measuring contractile endpoints with integrated force sensors/actuators and image-based techniques. Known effects of engineered microenvironments on the maturity of cardiomyocyte contractility have also been discovered in the development of these systems. Based on these discoveries, we review here design criteria of microengineered platforms of cardiomyocytes derived from pluripotent stem cells for measuring contractility with higher physiological relevance. These criteria involve the use of electromechanical, chemical and morphological cues, co-culture of different cell types, and three-dimensional cellular microenvironments. We further discuss the use and the current challenges for developing and improving these novel technologies for predicting clinical effects of drugs based on contractility measurements with cardiomyocytes differentiated from induced pluripotent stem cells. Future research should establish contexts of use in drug development for novel contractility assays with stem cell-derived cardiomyocytes.

Novel method for action potential measurements from intact cardiac monolayers with multiwell microelectrode array technology

The cardiac action potential (AP) is vital for understanding healthy and diseased cardiac biology and drug safety testing. However, techniques for high throughput cardiac AP measurements have been limited. Here, we introduce a novel technique for reliably increasing the coupling of cardiomyocyte syncytium to planar multiwell microelectrode arrays, resulting in a stable, label-free local extracellular action potential (LEAP). We characterized the reliability and stability of LEAP, its relationship to the field potential, and its efficacy for quantifying AP morphology of human induced pluripotent stem cell derived and primary rodent cardiomyocytes. Rise time, action potential duration, beat period, and triangulation were used to quantify compound responses and AP morphology changes induced by genetic modification. LEAP is the first high throughput, non-invasive, label-free, stable method to capture AP morphology from an intact cardiomyocyte syncytium. LEAP can accelerate our understanding of stem cell models, while improving the automation and accuracy of drug testing.

Cyborg Organoids: Implantation of Nanoelectronics via Organogenesis for Tissue-Wide Electrophysiology

Tissue-wide electrophysiology with single-cell and millisecond spatiotemporal resolution is critical for heart and brain studies. Issues arise, however, from the invasive, localized implantation of electronics that destroys well-connected cellular networks within matured organs. Here, we report the creation of cyborg organoids: the three-dimensional (3D) assembly of soft, stretchable mesh nanoelectronics across the entire organoid by the cell-cell attraction forces from 2D-to-3D tissue reconfiguration during organogenesis. We demonstrate that stretchable mesh nanoelectronics can migrate with and grow into the initial 2D cell layers to form the 3D organoid structure with minimal impact on tissue growth and differentiation. The intimate contact between the dispersed nanoelectronics and cells enables us to chronically and systematically observe the evolution, propagation, and synchronization of the bursting dynamics in human cardiac organoids through their entire organogenesis.

Phenotype-Based High-Throughput Classification of Long QT Syndrome Subtypes Using Human Induced Pluripotent Stem Cells

For long QT syndrome (LQTS), recent progress in genome-sequencing technologies enabled the identification of rare genomic variants with diagnostic, prognostic, and therapeutic implications. However, pathogenic stratification of the identified variants remains challenging, especially in variants of uncertain significance. This study aimed to propose a phenotypic cell-based diagnostic assay for identifying LQTS to recognize pathogenic variants in a high-throughput manner suitable for screening. We investigated the response of LQT2-induced pluripotent stem cell (iPSC)-derived cardiomyocytes (iPSC-CMs) following I_Kr blockade using a multi-electrode array, finding that the response to I_Kr blockade was significantly smaller than in Control-iPSC-CMs. Furthermore, we found that LQT1-iPSC-CMs and LQT3-iPSC-CMs could be distinguished from Control-iPSC-CMs by I_Ks blockade and I_Na blockade, respectively. This strategy might be helpful in compensating for the shortcomings of genetic testing of LQTS patients.

Cross-Site Reliability of Human Induced Pluripotent stem cell-derived Cardiomyocyte Based Safety Assays Using Microelectrode Arrays: Results from a Blinded CiPA Pilot Study

Recent in vitro cardiac safety studies demonstrate the ability of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to detect electrophysiologic effects of drugs. However, variability contributed by unique approaches, procedures, cell lines, and reagents across laboratories makes comparisons of results difficult, leading to uncertainty about the role of hiPSC-CMs in defining proarrhythmic risk in drug discovery and regulatory submissions. A blinded pilot study was conducted to evaluate the electrophysiologic effects of 8 well-characterized drugs on 4 cardiomyocyte lines using a standardized protocol across 3 microelectrode array platforms (18 individual studies). Drugs were selected to define assay sensitivity of prominent repolarizing currents (E-4031 for IKr, JNJ303 for IKs) and depolarizing currents (nifedipine for ICaL, mexiletine for INa) as well as drugs affecting multichannel block (flecainide, moxifloxacin, quinidine, and ranolazine). Inclusion criteria for final analysis was based on demonstrated sensitivity to IKr block (20% prolongation with E-4031) and L-type calcium current block (20% shortening with nifedipine). Despite differences in baseline characteristics across cardiomyocyte lines, multiple sites, and instrument platforms, 10 of 18 studies demonstrated adequate sensitivity to IKr block with E-4031 and ICaL block with nifedipine for inclusion in the final analysis. Concentration-dependent effects on repolarization were observed with this qualified data set consistent with known ionic mechanisms of single and multichannel blocking drugs. hiPSC-CMs can detect repolarization effects elicited by single and multichannel blocking drugs after defining pharmacologic sensitivity to IKr and ICaL block, supporting further validation efforts using hiPSC-CMs for cardiac safety studies.

Electrophysiological characterization of drug response in hSC-derived cardiomyocytes using voltage-sensitive optical platforms

INTRODUCTION

Voltage-sensitive optical (VSO) sensors offer a minimally invasive method to study the time course of repolarization of the cardiac action potential (AP). This Comprehensive in vitro Proarrhythmia Assay (CiPA) cross-platform study investigates protocol design and measurement variability of VSO sensors for preclinical cardiac electrophysiology assays.

METHODS

Three commercial and one academic laboratory completed a limited study of the effects of 8 blinded compounds on the electrophysiology of 2 commercial lines of human induced pluripotent stem-cell derived cardiomyocytes (hSC-CMs). Acquisition technologies included CMOS camera and photometry; fluorescent voltage sensors included di-4-ANEPPS, FluoVolt and genetically encoded QuasAr2. The experimental protocol was standardized with respect to cell lines, plating and maintenance media, blinded compounds, and action potential parameters measured. Serum-free media was used to study the action of drugs, but the exact composition and the protocols for cell preparation and drug additions varied among sites.

RESULTS

Baseline AP waveforms differed across platforms and between cell types. Despite these differences, the relative responses to four selective ion channel blockers (E-4031, nifedipine, mexiletine, and JNJ 303 blocking I_Kr, I_CaL, I_Na, and I_Ks, respectively) were similar across all platforms and cell lines although the absolute changes differed. Similarly, four mixed ion channel blockers (flecainide, moxifloxacin, quinidine, and ranolazine) had comparable effects in all platforms. Differences in repolarisation time course and response to drugs could be attributed to cell type and experimental method differences such as composition of the assay media, stimulated versus spontaneous activity, and single versus cumulative compound addition.

DISCUSSION

In conclusion, VSOs represent a powerful and appropriate method to assess the electrophysiological effects of drugs on iPSC-CMs for the evaluation of proarrhythmic risk. Protocol considerations and recommendations are provided toward standardizing conditions to reduce variability of baseline AP waveform characteristics and drug responses.

Cell-based biosensors: Recent trends, challenges and future perspectives

Existing at the interface of biology and electronics, living cells have been in use as biorecognition elements (bioreceptors) in biosensors since the early 1970s. They are an interesting choice of bioreceptors as they allow flexibility in determining the sensing strategy, are cheaper than purified enzymes and antibodies and make the fabrication relatively simple and cost-effective. And with advances in the field of synthetic biology, microfluidics and lithography, many exciting developments have been made in the design of cell-based biosensors in the last about five years. 3D cell culture systems integrated with electrodes are now providing new insights into disease pathogenesis and physiology, while cardiomyocyte-integrated microelectrode array (MEA) technology is set to be standardized for the assessment of drug-induced cardiac toxicity. From cell microarrays for high-throughput applications to plasmonic devices for anti-microbial susceptibility testing and advent of microbial fuel cell biosensors, cell-based biosensors have evolved from being mere tools for detection of specific analytes to multi-parametric devices for real time monitoring and assessment. However, despite these advancements, challenges such as regeneration and storage life, heterogeneity in cell populations, high interference and high costs due to accessory instrumentation need to be addressed before the full potential of cell-based biosensors can be realized at a larger scale. This review summarizes results of the studies that have been conducted in the last five years toward the fabrication of cell-based biosensors for different applications with a comprehensive discussion on the challenges, future trends, and potential inputs needed for improving them.

Scaling and correlation properties of RR and QT intervals at the cellular level

We study complex scaling properties of RR and QT intervals of electrocardiograms (ECGs) with their equivalences at the cellular level, that is, inter-beat intervals (IBI) and field potential durations (FPD) of spontaneously beating human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) aggregates. Our detrended fluctuation analysis and Poincaré plots reveal remarkable similarities between the ECG and hiPSC-CM data. In particular, no statistically significant difference was found in the short- and long-term scaling exponents α₁ and α₂ of RR and QT intervals and their cellular equivalences. Previously unknown scaling properties of FPDs of hiPSC-CM aggregates reveal that the increasing scaling exponent of QT intervals as a function of the time scale, is an intrinsic feature at the cellular level.

Optical Recording of Action Potentials in Human Induced Pluripotent Stem Cell-Derived Cardiac Single Cells and Monolayers Generated from Long QT Syndrome Type 1 Patients

Induced pluripotent stem cells (iPSCs) from type 1 long QT (LQT1) patients can differentiate into cardiomyocytes (CMs) including ventricular cells to recapitulate the disease phenotype. Although optical recordings using membrane potential dyes to monitor action potentials (APs) were reported, no study has investigated the disease phenotypes of cardiac channelopathy in association with the cardiac subtype at the single-cell level. We induced iPSC-CMs from three control and three LQT1 patients. Single-cell analysis using a fast-responding dye confirmed that ventricular cells were the dominant subtype (control-iPSC-CMs: 98%, 88%, 91%; LQT1-iPSC-CMs: 95%, 79%, 92%). In addition, LQT1-iPSC-ventricular cells displayed an increased frequency of early afterdepolarizations (pvalue = 0.031). Cardiomyocyte monolayers constituted mostly of ventricular cells derived from LQT1-iPSCs showed prolonged AP duration (APD) (pvalue = 0.000096). High-throughput assays using cardiomyocyte monolayers in 96-well plates demonstrated that I_Kr inhibitors prolonged APDs in both control- and LQT1-iPSC-CM monolayers. We confirmed that the optical recordings of APs in single cells and monolayers derived from control- and LQT1-iPSC-CMs can be used to assess arrhythmogenicity, supporting the feasibility of membrane potential dye-based high-throughput screening to study ventricular arrhythmias caused by genetic channelopathy or cardiotoxic drugs.

High-speed mechano-active multielectrode array for investigating rapid stretch effects on cardiac tissue

Systematic investigations of the effects of mechano-electric coupling (MEC) on cellular cardiac electrophysiology lack experimental systems suitable to subject tissues to in-vivo like strain patterns while simultaneously reporting changes in electrical activation. Here, we describe a self-contained motor-less device (mechano-active multielectrode-array, MaMEA) that permits the assessment of impulse conduction along bioengineered strands of cardiac tissue in response to dynamic strain cycles. The device is based on polydimethylsiloxane (PDMS) cell culture substrates patterned with dielectric actuators (DEAs) and compliant gold ion-implanted extracellular electrodes. The DEAs induce uniaxial stretch and compression in defined regions of the PDMS substrate at selectable amplitudes and with rates up to 18 s⁻¹. Conduction along cardiomyocyte strands was found to depend linearly on static strain according to cable theory while, unexpectedly, being completely independent on strain rates. Parallel operation of multiple MaMEAs provides for systematic high-throughput investigations of MEC during spatially patterned mechanical perturbations mimicking in-vivo conditions.

While strain is known to affect cardiac electrophysiology, experimental systems to interrogate the effect of rapid strain cycles on cardiac tissue are lacking. Here the authors introduce a multielectrode array that can induce rapid dynamic strain cycles on cardiomyocyte strands and see effects of strain amplitude but not strain rate on impulse conduction.

Ultrasoft electronics to monitor dynamically pulsing cardiomyocytes

In biointegrated electronics, the facile control of mechanical properties such as softness and stretchability in electronic devices is necessary to minimize the perturbation of motions inherent in biological systems^1-5. For in vitro studies, multielectrode-embedded dishes^6-8 and other rigid devices^9-12 have been widely used. Soft or flexible electronics on plastic or elastomeric substrates^13-15 offer promising new advantages such as decreasing physical stress^16-18 and/or applying mechanical stimuli^19,20. Recently, owing to the introduction of macroporous plastic substrates with nanofibre scaffolds^21,22, three-dimensional electrophysiological mapping of cardiomyocytes has been demonstrated. However, quantitatively monitoring cells that exhibit significant dynamical motions via electric probes over a long period without affecting their natural motion remains a challenge. Here, we present ultrasoft electronics with nanomeshes that monitor the field potential of human induced pluripotent stem cell-derived cardiomyocytes on a hydrogel, while enabling them to move dynamically without interference. Owing to the extraordinary softness of the nanomeshes, nanomesh-attached cardiomyocytes exhibit contraction and relaxation motions comparable to that of cardiomyocytes without attached nanomeshes. Our multilayered nanomesh devices maintain reliable operations in a liquid environment, enabling the recording of field potentials of the cardiomyocytes over a period of 96 h without significant degradation of the nanomesh devices or damage of the cardiomyocytes.

Inversion and computational maturation of drug response using human stem cell derived cardiomyocytes in microphysiological systems

While cardiomyocytes differentiated from human induced pluripotent stems cells (hiPSCs) hold great promise for drug screening, the electrophysiological properties of these cells can be variable and immature, producing results that are significantly different from their human adult counterparts. Here, we describe a computational framework to address this limitation, and show how in silico methods, applied to measurements on immature cardiomyocytes, can be used to both identify drug action and to predict its effect in mature cells. Our synthetic and experimental results indicate that optically obtained waveforms of voltage and calcium from microphysiological systems can be inverted into information on drug ion channel blockage, and then, through assuming functional invariance of proteins during maturation, this data can be used to predict drug induced changes in mature ventricular cells. Together, this pipeline of measurements and computational analysis could significantly improve the ability of hiPSC derived cardiomycocytes to predict dangerous drug side effects.