A Multiwell Cardiac μGMEA Platform for Action Potential Recordings from Human iPSC-Derived Cardiomyocyte Constructs

Micronano Synergetic Three-Dimensional Bioelectronics: A Revolutionary Breakthrough Platform for Cardiac Electrophysiology

Cardiovascular diseases (CVDs) are the leading cause of mortality and therefore pose a significant threat to human health. Cardiac electrophysiology plays a crucial role in the investigation and treatment of CVDs, including arrhythmia. The long-term and accurate detection of electrophysiological activity in cardiomyocytes is essential for advancing cardiology and pharmacology. Regarding the electrophysiological study of cardiac cells, many micronano bioelectric devices and systems have been developed. Such bioelectronic devices possess unique geometric structures of electrodes that enhance quality of electrophysiological signal recording. Though planar multielectrode/multitransistors are widely used for simultaneous multichannel measurement of cell electrophysiological signals, their use for extracellular electrophysiological recording exhibits low signal strength and quality. However, the integration of three-dimensional (3D) multielectrode/multitransistor arrays that use advanced penetration strategies can achieve high-quality intracellular signal recording. This review provides an overview of the manufacturing, geometric structure, and penetration paradigms of 3D micronano devices, as well as their applications for precise drug screening and biomimetic disease modeling. Furthermore, this review also summarizes the current challenges and outlines future directions for the preparation and application of micronano bioelectronic devices, with an aim to promote the development of intracellular electrophysiological platforms and thereby meet the demands of emerging clinical applications.

Statins affect human iPSC-derived cardiomyocytes by interfering with mitochondrial function and intracellular acidification

Statins are effective drugs in reducing cardiovascular morbidity and mortality by inhibiting cholesterol synthesis. These effects are primarily beneficial for the patient's vascular system. A significant number of statin users suffer from muscle complaints probably due to mitochondrial dysfunction, a mechanism that has recently been elucidated. This has raised our interest in exploring the effects of statins on cardiac muscle cells in an era where the elderly and patients with poorer functioning hearts and less metabolic spare capacity start dominating our patient population. Here, we investigated the effects of statins on human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-derived CMs). hiPSC-derived CMs were exposed to simvastatin, atorvastatin, rosuvastatin, and cerivastatin at increasing concentrations. Metabolic assays and fluorescent microscopy were employed to evaluate cellular viability, metabolic capacity, respiration, intracellular acidity, and mitochondrial membrane potential and morphology. Over a concentration range of 0.3-100 µM, simvastatin lactone and atorvastatin acid showed a significant reduction in cellular viability by 42-64%. Simvastatin lactone was the most potent inhibitor of basal and maximal respiration by 56% and 73%, respectively, whereas simvastatin acid and cerivastatin acid only reduced maximal respiration by 50% and 42%, respectively. Simvastatin acid and lactone and atorvastatin acid significantly decreased mitochondrial membrane potential by 20%, 6% and 3%, respectively. The more hydrophilic atorvastatin acid did not seem to affect cardiomyocyte metabolism. This calls for further research on the translatability to the clinical setting, in which a more conscientious approach to statin prescribing might be considered, especially regarding the current shift in population toward older patients with poor cardiac function.

Interpretation of field and LEAP potentials recorded from cardiomyocyte monolayers

Multielectrode arrays (MEAs) are the method of choice for electrophysiological characterization of cardiomyocyte monolayers. The field potentials recorded using an MEA are like extracellular electrograms recorded from the myocardium using conventional electrodes. Nevertheless, different criteria are used to interpret field potentials and extracellular electrograms, which hamper correct interpretation and translation to the patient. To validate the criteria for interpretation of field potentials, we used neonatal rat cardiomyocytes to generate monolayers. We recorded field potentials using an MEA and simultaneously recorded action potentials using sharp microelectrodes. In parallel, we recreated our experimental setting in silico and performed simulations. We show that the amplitude of the local RS complex of a field potential correlated with conduction velocity in silico but not in vitro. The peak time of the T wave in field potentials exhibited a strong correlation with APD90 while the steepest upslope correlated well with APD50. However, this relationship only holds when the T wave displayed a biphasic pattern. Next, we simulated local extracellular action potentials (LEAPs). The shape of the LEAP differed markedly from the shape of the local action potential, but the final duration of the LEAP coincided with APD90. Criteria for interpretation of extracellular electrograms should be applied to field potentials. This will provide a strong basis for the analysis of heterogeneity in conduction velocity and repolarization in cultured monolayers of cardiomyocytes. Finally, a LEAP is not a recording of the local action potential but is generated by intracellular current provided by neighboring cardiomyocytes and is superior to field potential duration in estimating APD90.NEW & NOTEWORTHY We present a physiological basis for the interpretation of multielectrode array-derived, extracellular, electrical signals.

Cardiotoxicity drug screening based on whole-panel intracellular recording

Unintended binding of small-molecule drugs to ion channels affects electrophysiological properties of cardiomyocytes and potentially leads to arrhythmia and heart failure. The waveforms of intracellular action potentials reflect the coordinated activities of cardiac ion channels and serve as a reliable means for assessing drug toxicity, but the implementation is limited by the low throughput of patch clamp for intracellular recording measurements. In the last decade, several new technologies are being developed to address this challenge. We recently developed the nanocrown electrode array (NcEA) technology that allows robust, parallel, and long-duration recording of intracellular action potentials (iAPs). Here, we demonstrate that NcEAs allow comparison of iAP waveforms before and after drug treatment from the same cell. This self-referencing comparison not only shows distinct drug effects of sodium, potassium, and calcium blockers, but also reveals subtle differences among three subclasses of sodium channel blockers with sub-millisecond accuracy. Furthermore, self-referencing comparison unveils heterogeneous drug responses among different cells. In our study, whole-panel simultaneous intracellular recording can be reliably achieved with ∼94% success rate. The average duration of intracellular recording is ∼30 min and some last longer than 2 h. With its high reliability, long recording duration, and easy-to-use nature, NcEA would be useful for iAP-based preclinical drug screening.

Repeated and On-Demand Intracellular Recordings of Cardiomyocytes Derived from Human-Induced Pluripotent Stem Cells

Pharmaceutical compounds may have cardiotoxic properties, triggering potentially life-threatening arrhythmias. To investigate proarrhythmic effects of drugs, the patch clamp technique has been used as the gold standard for characterizing the electrophysiology of cardiomyocytes in vitro. However, the applicability of this technology for drug screening is limited, as it is complex to use and features low throughput. Recent studies have demonstrated that 3D-nanostructured electrodes enable to obtain intracellular signals from many cardiomyocytes in parallel; however, the tedious electrode fabrication and limited measurement duration still remain major issues for cardiotoxicity testing. Here, we demonstrate how porous Pt-black electrodes, arranged in high-density microelectrode arrays, can be used to record intracellular-like signals of cardiomyocytes at large scale repeatedly over an extended period of time. The developed technique, which yields highly parallelized electroporations using stimulation voltages around 1 V peak-to-peak amplitude, enabled intracellular-like recordings at high success rates without causing significant alteration in key electrophysiological features. In a proof-of-concept study, we investigated electrophysiological modulations induced by two clinically applied drugs, nifedipine and quinidine. As the obtained results were in good agreement with previously published data, we are confident that the developed technique has the potential to be routinely used in in vitro platforms for cardiotoxicity screening.

Nanocrown electrodes for parallel and robust intracellular recording of cardiomyocytes

Drug-induced cardiotoxicity arises primarily when a compound alters the electrophysiological properties of cardiomyocytes. Features of intracellular action potentials (iAPs) are powerful biomarkers that predict proarrhythmic risks. In the last decade, a number of vertical nanoelectrodes have been demonstrated to achieve parallel and minimally-invasive iAP recordings. However, the large variability in success rate and signal strength have hindered nanoelectrodes from being broadly adopted for proarrhythmia drug assessment. In this work, we develop vertically-aligned nanocrown electrodes that are mechanically robust and achieve > 99% success rates in obtaining intracellular access through electroporation. We validate the accuracy of nanocrown electrode recordings by simultaneous patch clamp recording from the same cell. Finally, we demonstrate that nanocrown electrodes enable prolonged iAP recording for continual monitoring of the same cells upon the sequential addition of four incremental drug doses. Our technology development provides an advancement towards establishing an iAP screening assay for preclinical evaluation of drug-induced arrhythmogenicity.

Systems for the functional evaluation of human heart tissues derived from pluripotent stem cells

Human pluripotent stem cells (hPSCs) are expected to be a promising cell source in regenerative medicine and drug discovery for the treatment of various intractable diseases. An approach for creating a three-dimensional (3D) structure from hPSCs that mimics human cardiac tissue functions has made it theoretically possible to conduct drug discovery and cardiotoxicity tests by assessing pharmacological responses in human cardiac tissues by a screening system using a compound library. The myocardium functions as a tissue composed of organized vascular networks, supporting stromal cells and cardiac muscle cells. Considering this, the reconstruction of tissue structure by various cells of cardiovascular lineages, such as vascular cells and cardiac muscle cells, is desirable for the ideal conformation of hPSC-derived cardiac tissues. Heart-on-a-chip, an organ-on-a-chip system to evaluate the physiological pump function of 3D cardiac tissues might hold promise in medical researches such as drug discovery and regenerative medicine. Here, we review various modalities to evaluate the function of human stem cell-derived cardiac tissues and introduce heart-on-a-chip systems that can recapitulate physiological parameters of hPSC-derived cardiac tissues.

Intracellular Recording of Cardiomyocytes by Integrated Electrical Signal Recording and Electrical Pulse Regulating System

The electrophysiological signal can reflect the basic activity of cardiomyocytes, which is often used to study the working mechanism of heart. Intracellular recording is a powerful technique for studying transmembrane potential, proving a favorable strategy for electrophysiological research. To obtain high-quality and high-throughput intracellular electrical signals, an integrated electrical signal recording and electrical pulse regulating system based on nanopatterned microelectrode array (NPMEA) is developed in this work. Due to the large impedance of the electrode, a high-input impedance preamplifier is required. The high-frequency noise of the circuit and the baseline drift of the sensor are suppressed by a band-pass filter. After amplifying the signal, the data acquisition card (DAQ) is used to collect the signal. Meanwhile, the DAQ is utilized to generate pulses, achieving the electroporation of cells by NPMEA. Each channel uses a voltage follower to improve the pulse driving ability and isolates each electrode. The corresponding recording control software based on LabVIEW is developed to control the DAQ to collect, display and record electrical signals, and generate pulses. This integrated system can achieve high-throughput detection of intracellular electrical signals and provide a reliable recording tool for cell electro-physiological investigation.

Automated feature extraction from large cardiac electrophysiological data sets

RATIONALE

A new multi-electrode array-based application for the long-term recording of action potentials from electrogenic cells makes possible exciting cardiac electrophysiology studies in health and disease. With hundreds of simultaneous electrode recordings being acquired over a period of days, the main challenge becomes achieving reliable signal identification and quantification.

OBJECTIVE

We set out to develop an algorithm capable of automatically extracting regions of high-quality action potentials from terabyte size experimental results and to map the trains of action potentials into a low-dimensional feature space for analysis.

METHODS AND RESULTS

Our automatic segmentation algorithm finds regions of acceptable action potentials in large data sets of electrophysiological readings. We use spectral methods and support vector machines to classify our readings and to extract relevant features. We are able to show that action potentials from the same cell site can be recorded over days without detrimental effects to the cell membrane. The variability between measurements 24 h apart is comparable to the natural variability of the features at a single time point.

CONCLUSIONS

Our work contributes towards a non-invasive approach for cardiomyocyte functional maturation, as well as developmental, pathological and pharmacological studies. As the human-derived cardiac model tissue has the genetic makeup of its donor, a powerful tool for individual drug toxicity screening emerges.

Polycystin 2 is increased in disease to protect against stress-induced cell death

Polycystin 2 (PC2 or TRPP1, formerly TRPP2) is a calcium-permeant Transient Receptor Potential (TRP) cation channel expressed primarily on the endoplasmic reticulum (ER) membrane and primary cilia of all cell and tissue types. Despite its ubiquitous expression throughout the body, studies of PC2 have focused primarily on its role in the kidney, as mutations in PC2 lead to the development of autosomal dominant polycystic kidney disease (ADPKD), a debilitating condition for which there is no cure. However, the endogenous role that PC2 plays in the regulation of general cellular homeostasis remains unclear. In this study, we measure how PC2 expression changes in different pathological states, determine that its abundance is increased under conditions of cellular stress in multiple tissues including human disease, and conclude that PC2-deficient cells have increased susceptibility to cell death induced by stress. Our results offer new insight into the normal function of PC2 as a ubiquitous stress-sensitive protein whose expression is up-regulated in response to cell stress to protect against pathological cell death in multiple diseases.

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.

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.