Micro-Electrode Arrays in Cardiac Safety Pharmacology

Nanoelectronics meets biology: from new nanoscale devices for live-cell recording to 3D innervated tissues

High spatiotemporal resolution interfaces between electrical sensors and biological systems, from single live cells to tissues, is crucial for many areas, including fundamental biophysical studies as well as medical monitoring and intervention. Herein, we summarize recent progress in the development and application of novel nanoscale devices for intracellular electrical recording of action potentials and the effort of merging electronic and biological systems seamlessly in three dimensions by using macroporous nanoelectronic scaffolds. The uniqueness of these nanoscale devices for minimally invasive, large-scale, high spatial resolution, and three-dimensional neural activity mapping are highlighted.

Cardiomyocyte MEA data analysis (CardioMDA)--a novel field potential data analysis software for pluripotent stem cell derived cardiomyocytes

Cardiac safety pharmacology requires in-vitro testing of all drug candidates before clinical trials in order to ensure they are screened for cardio-toxic effects which may result in severe arrhythmias. Micro-electrode arrays (MEA) serve as a complement to current in-vitro methods for drug safety testing. However, MEA recordings produce huge volumes of data and manual analysis forms a bottleneck for high-throughput screening. To overcome this issue, we have developed an offline, semi-automatic data analysis software, ‘Cardiomyocyte MEA Data Analysis (CardioMDA)’, equipped with correlation analysis and ensemble averaging techniques to improve the accuracy, reliability and throughput rate of analysing human pluripotent stem cell derived cardiomyocyte (CM) field potentials. With the program, true field potential and arrhythmogenic complexes can be distinguished from one another. The averaged field potential complexes, analysed using our software to determine the field potential duration, were compared with the analogous values obtained from manual analysis. The reliability of the correlation analysis algorithm, evaluated using various arrhythmogenic and morphology changing signals, revealed a mean sensitivity and specificity of 99.27% and 94.49% respectively, in determining true field potential complexes. The field potential duration of the averaged waveforms corresponded well to the manually analysed data, thus demonstrating the reliability of the software. The software has also the capability to create overlay plots for signals recorded under different drug concentrations in order to visualize and compare the magnitude of response on different ion channels as a result of drug treatment. Our novel field potential analysis platform will facilitate the analysis of CM MEA signals in semi-automated way and provide a reliable means of efficient and swift analysis for cardiomyocyte drug or disease model studies.

Nanoelectronics-biology frontier: From nanoscopic probes for action potential recording in live cells to three-dimensional cyborg tissues

Semiconductor nanowires configured as the active channels of field-effect transistors (FETs) have been used as detectors for high-resolution electrical recording from single live cells, cell networks, tissues and organs. Extracellular measurements with substrate supported silicon nanowire (SiNW) FETs, which have projected active areas orders of magnitude smaller than conventional microfabricated multielectrode arrays (MEAs) and planar FETs, recorded action potential and field potential signals with high signal-to-noise ratio and temporal resolution from cultured neurons, cultured cardiomyocytes, acute brain slices and whole animal hearts. Measurements made with modulation-doped nanoscale active channel SiNW FETs demonstrate that signals recorded from cardiomyocytes are highly localized and have improved time resolution compared to larger planar detectors. In addition, several novel three-dimensional (3D) transistor probes, which were realized using advanced nanowire synthesis methods, have been implemented for intracellular recording. These novel probes include (i) flexible 3D kinked nanowire FETs, (ii) branched intracellular nanotube SiNW FETs, and (iii) active silicon nanotube FETs. Following phospholipid modification of the probes to mimic the cell membrane, the kinked nanowire, branched intracellular nanotube and active silicon nanotube FET probes recorded full-amplitude intracellular action potentials from spontaneously firing cardiomyocytes. Moreover, these probes demonstrated the capability of reversible, stable, and long-term intracellular recording, thus indicating the minimal invasiveness of the new nanoscale structures and suggesting biomimetic internalization via the phospholipid modification. Simultaneous, multi-site intracellular recording from both single cells and cell networks were also readily achieved by interfacing independently addressable nanoprobe devices with cells. Finally, electronic and biological systems have been seamlessly merged in 3D for the first time using macroporous nanoelectronic scaffolds that are analogous to synthetic tissue scaffold and the extracellular matrix in tissue. Free-standing 3D nanoelectronic scaffolds were cultured with neurons, cardiomyocytes and smooth muscle cells to yield electronically-innervated synthetic or 'cyborg' tissues. Measurements demonstrate that innervated tissues exhibit similar cell viability as with conventional tissue scaffolds, and importantly, demonstrate that the real-time response to drugs and pH changes can be mapped in 3D through the tissues. These results open up a new field of research, wherein nanoelectronics are merged with biological systems in 3D thereby providing broad opportunities, ranging from a nanoelectronic/tissue platform for real-time pharmacological screening in 3D to implantable 'cyborg' tissues enabling closed-loop monitoring and treatment of diseases. Furthermore, the capability of high density scale-up of the above extra- and intracellular nanoscopic probes for action potential recording provide important tools for large-scale high spatio-temporal resolution electrical neural activity mapping in both 2D and 3D, which promises to have a profound impact on many research areas, including the mapping of activity within the brain.

Synthetically encoded ultrashort-channel nanowire transistors for fast, pointlike cellular signal detection

Nanostructures, which have sizes comparable to biological functional units involved in cellular communication, offer the potential for enhanced sensitivity and spatial resolution compared to planar metal and semiconductor structures. Silicon nanowire (SiNW) field-effect transistors (FETs) have been used as a platform for biomolecular sensors, which maintain excellent signal-to-noise ratios while operating on lengths scales that enable efficient extra- and intracellular integration with living cells. Although the NWs are tens of nanometers in diameter, the active region of the NW FET devices typically spans micrometers, limiting both the length and time scales of detection achievable with these nanodevices. Here, we report a new synthetic method that combines gold-nanocluster-catalyzed vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) NW growth modes to produce synthetically encoded NW devices with ultrasharp (<5 nm) n-type highly doped (n(++)) to lightly doped (n) transitions along the NW growth direction, where n(++) regions serve as source/drain (S/D) electrodes and the n-region functions as an active FET channel. Using this method, we synthesized short-channel n(++)/n/n(++) SiNW FET devices with independently controllable diameters and channel lengths. SiNW devices with channel lengths of 50, 80, and 150 nm interfaced with spontaneously beating cardiomyocytes exhibited well-defined extracellular field potential signals with signal-to-noise values of ca. 4 independent of device size. Significantly, these "pointlike" devices yield peak widths of ∼500 μs, which is comparable to the reported time constant for individual sodium ion channels. Multiple FET devices with device separations smaller than 2 μm were also encoded on single SiNWs, thus enabling multiplexed recording from single cells and cell networks with device-to-device time resolution on the order of a few microseconds. These short-channel SiNW FET devices provide a new opportunity to create nanoscale biomolecular sensors that operate on the length and time scales previously inaccessible by other techniques but necessary to investigate fundamental, subcellular biological processes.

Averaging in vitro cardiac field potential recordings obtained with microelectrode arrays

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

Design, synthesis, and characterization of novel nanowire structures for photovoltaics and intracellular probes

Semiconductor nanowires (NWs) represent a unique system for exploring phenomena at the nanoscale and are expected to play a critical role in future electronic, optoelectronic, and miniaturized biomedical devices. Modulation of the composition and geometry of nanostructures during growth could encode information or function, and realize novel applications beyond the conventional lithographical limits. This review focuses on the fundamental science aspects of the bottom-up paradigm, which are synthesis and physical property characterization of semiconductor NWs and NW heterostructures, as well as proof-of-concept device concept demonstrations, including solar energy conversion and intracellular probes. A new NW materials synthesis is discussed and, in particular, a new "nanotectonic" approach is introduced that provides iterative control over the NW nucleation and growth for constructing 2D kinked NW superstructures. The use of radial and axial p-type/intrinsic/n-type (p-i-n) silicon NW (Si-NW) building blocks for solar cells and nanoscale power source applications is then discussed. The critical benefits of such structures and recent results are described and critically analyzed, together with some of the diverse challenges and opportunities in the near future. Finally, results are presented on several new directions, which have recently been exploited in interfacing biological systems with NW devices.

Patterned cardiomyocytes on microelectrode arrays as a functional, high information content drug screening platform

Cardiac side effects are one of the major causes of drug candidate failures in preclinical drug development or in clinical trials and are responsible for the retraction of several already marketed therapeutics. Thus, the development of a relatively high-throughput, high information content tool to screen drugs and toxins would be important in the field of cardiac research and drug development. In this study, recordings from commercial multielectrode arrays were combined with surface patterning of cardiac myocyte monolayers to enhance the information content of the method; specifically, to enable the measurement of conduction velocity, refractory period after action potentials and to create a functional re-entry model. Two drugs, 1-Heptanol, a gap junction blocker, and Sparfloxacin, a fluoroquinone antibiotic, were tested in this system. 1-Heptanol administration resulted in a marked reduction in conduction velocity, whereas Sparfloxacin caused rapid, irregular and unsynchronized activity, indicating fibrillation. As shown in these experiments, patterning of cardiac myocyte monolayers solved several inherent problems of multielectrode recordings, increased the temporal resolution of conduction velocity measurements, and made the synchronization of external stimulation with action potential propagation possible for refractory period measurements. This method could be further developed as a cardiac side effect screening platform after combination with human cardiomyocytes.

Electromagnetic exposure of scaffold-free three-dimensional cell culture systems

In recent years, a number of in vitro studies have reported on the possible athermal effects of electromagnetic exposure on biological tissue. Typically, this kind of study is performed on monolayers of primary cells or cell lines. However, two-dimensional cell layer systems lack physiological relevance since cells in vivo are organized in a three-dimensional (3D) architecture. In monolayer studies, cell-cell and cell-ECM interactions obviously differ from live tissue and scale-ups of experimental results to in vivo systems should be considered carefully. To overcome this problem, we used a scaffold-free 3D cell culture system, suitable for the exploration of electrophysiological effects due to electromagnetic fields (EMF) at 900 MHz. Dissociated cardiac myocytes were reaggregated into cellular spheres by constant rotation, and non-invasive extracellular recordings of these so-called spheroids were performed with microelectrode arrays (MEA). In this study, 3D cell culture systems were exposed to pulsed EMFs in a stripline setup. We found that inhomogeneities in the EMF due to electrodes and conducting lines of the MEA chip had only a minor influence on the field distribution in the spheroid if the exposure parameters were chosen carefully.

Evaluation of doxorubicin toxicity on cardiomyocytes using a dual functional extracellular biochip

Nowadays, cardiotoxicity induced by clinical drugs presents a high prevalence and has aroused great attention onto the effective and reliable drug evaluation before clinical treatment. Doxorubicin (Adriamycin), as a type of anthracycline chemotherapy agent for cancer treatment, was restricted in the clinical use because of its cardiotoxicity. In the present work, a dual functional biochip ExCell integrated with microelectrode arrays and interdigitated electrodes was designed to study the electrophysiological function and physical state of cardiomyocytes under the treatment of doxorubicin. Extracellular field potentials and cell-substrate impedance were measured to respectively express these two functions simultaneously in the same culture. The result detected by ExCell presented a portrait of cardiotoxicity induced by doxorubicin. The amplitude of extracellular field potentials decreased to 93%, 82% and 50% at 50 min treatment of doxorubicin with concentrations of 20 μM, 100 μM and 200 μM, respectively. Successively, beating rate decrease, beat-to-beat variation and Ca(2+) flux manifested severe abnormality. The cell-substrate impedance declined continuously in the depressing process of electrophysiological function and cell death was induced in high concentration treatment. All these result indicate that the biochip ExCell has the potential to be a fast-response and subtle tool for high-throughput drug evaluation assays.

Design and Implementation of Functional Nanoelectronic Interfaces With Biomolecules, Cells, and Tissue Using Nanowire Device Arrays

Nanowire FETs (NWFETs) are promising building blocks for nanoscale bioelectronic interfaces with cells and tissue since they are known to exhibit exquisite sensitivity in the context of chemical and biological detection, and have the potential to form strongly coupled interfaces with cell membranes. We present a general scheme that can be used to assemble NWs with rationally designed composition and geometry on either planar inorganic or biocompatible flexible plastic surfaces. We demonstrate that these devices can be used to measure signals from neurons, cardiomyocytes, and heart tissue. Reported signals are in millivolts range, which are equal to or substantially greater than those recorded with either planar FETs or multielectrode arrays, and demonstrate one unique advantage of NW-based devices. Basic studies showing the effect of device sensitivity and cell/substrate junction quality on signal magnitude are presented. Finally, our demonstrated ability to design high-density arrays of NWFETs enables us to map signal at the subcellular level, a functionality not enabled by conventional microfabricated devices. These advances could have broad applications in high-throughput drug assays, fundamental biophysical studies of cellular function, and development of powerful prosthetics.

Graphene and nanowire transistors for cellular interfaces and electrical recording

Nanowire field-effect transistors (NW-FETs) have been shown to be powerful building blocks for nanoscale bioelectronic interfaces with cells and tissue due to their excellent sensitivity and their capability to form strongly coupled interfaces with cell membranes. Graphene has also been shown to be an attractive building block for nanoscale electronic devices, although little is known about its interfaces with cells and tissue. Here we report the first studies of graphene field effect transistors (Gra-FETs) as well as combined Gra- and NW-FETs interfaced to electrogenic cells. Gra-FET conductance signals recorded from spontaneously beating embryonic chicken cardiomyocytes yield well-defined extracellular signals with signal-to-noise ratio routinely >4. The conductance signal amplitude was tuned by varying the Gra-FET working region through changes in water gate potential, V(wg). Signals recorded from cardiomyocytes for different V(wg) result in constant calibrated extracellular voltage, indicating a robust graphene/cell interface. Significantly, variations in V(wg) across the Dirac point demonstrate the expected signal polarity flip, thus allowing, for the first time, both n- and p-type recording to be achieved from the same Gra-FET simply by offsetting V(wg). In addition, comparisons of peak-to-peak recorded signal widths made as a function of Gra-FET device sizes and versus NW-FETs allowed an assessment of relative resolution in extracellular recording. Specifically, peak-to-peak widths increased with the area of Gra-FET devices, indicating an averaged signal from different points across the outer membrane of the beating cells. One-dimensional silicon NW- FETs incorporated side by side with the two-dimensional Gra-FET devices further highlighted limits in both temporal resolution and multiplexed measurements from the same cell for the different types of devices. The distinct and complementary capabilities of Gra- and NW-FETs could open up unique opportunities in the field of bioelectronics in the future.

A new target for amyloid beta toxicity validated by standard and high-throughput electrophysiology

Background

Soluble oligomers of amyloid beta (Aβ) are considered to be one of the major contributing factors to the development of Alzheimer's disease. Most therapeutic development studies have focused on toxicity directly at the synapse.

Methodology/Principal Findings

Patch clamp studies detailed here have demonstrated that soluble Aβ can also cause functional toxicity, namely it inhibits spontaneous firing of hippocampal neurons without significant cell death at low concentrations. This toxicity will eventually lead to the loss of the synapse as well, but may precede this loss by a considerable amount of time. In a key technological advance we have reproduced these results utilizing a fast and simple method based on extracellular electrophysiological recording of the temporal electrical activity of cultured hippocampal neurons using multielectrode arrays (MEAs) at low concentrations of Aβ (1–42). We have also shown that this functional deficit can be reversed through use of curcumin, an inhibitor of Aβ oligomerization, using both analysis methods.

Conclusions/Significance

The MEA recording method utilized here is non-invasive, thus long term chronic measurements are possible and it does not require precise positioning of electrodes, thus it is ideal for functional screens. Even more significantly, we believe we have now identified a new target for drug development for AD based on functional toxicity of hippocampal neurons that could treat neurodegenerative diseases prior to the development of mild cognitive impairment.

In vitro electrophysiological mapping of stem cells

The use of stem cells for cardiac regeneration is a revolutionary, emerging research area. For proper function as replacement tissue, stem cell-derived cardiomyocytes (SC-CMs) must electrically couple with the host cardiac tissue. Electrophysiological mapping techniques, including microelectrode array (MEA) and optical mapping, have been developed to study cardiomyocytes and cardiac cell monolayers, and these can be applied to study stem cells and SC-CMs. MEA recordings take extracellular measurements at numerous points across a small area of cell cultures and are used to assess electrical propagation during cell culture. Optical mapping uses fluorescent dyes to monitor electrophysiological changes in cells, most commonly transmembrane potential and intracellular calcium, and can be easily scaled to areas of different sizes. The materials and methods for MEA and optical mapping are presented here, together with detailed notes on their use, design, and fabrication. We also provide examples of voltage and calcium maps of mouse embryonic stem cell-derived cardiomyocytes (mESC-CMs), obtained in our laboratory using optical mapping techniques.

Global expression profile of highly enriched cardiomyocytes derived from human embryonic stem cells

Human embryonic stem cells (hESC), with their ability to differentiate into cardiomyocytes in culture, hold great potential for cell replacement therapies and provide an in vitro model of human heart development. A genomewide characterization of the molecular phenotype of hESC-derived cardiomyocytes is important for their envisioned applications. We have employed a lineage selection strategy to generate a pure population of cardiomyocytes (>99%) from transgenic hESC lines. Global gene expression profiling showed that these cardiomyocytes are distinct from pluripotent and differentiated hESC cultures. Pure cardiomyocytes displayed similarities with heart tissue, but in many aspects presented an individual transcriptome pattern. A subset of 1,311 cardiac-enriched transcripts was identified, which were significantly overpresented (p < .01) in the Gene Ontology (GO) categories of heart function and heart development. Focused analysis of the GO categories ion transport, sarcomere, and heart development uncovered a unique molecular signature of hESC cardiomyocytes. Pathway analysis revealed an extensive cardiac transcription factor network and novel peroxisome proliferator-activated receptor signaling components within the cardiac-enriched genes. Notably, approximately 80% of these genes were previously uncharacterized. We have evaluated the biological relevance of four candidates-Rbm24, Tcea3, Fhod3, and C15orf52-by in situ hybridization during early mouse development and report that all were prominently expressed in cardiac structures. Our results provide the fundamental basis for a comprehensive understanding of gene expression patterns of hESC cardiomyocytes and will greatly help define biological processes and signaling pathways involved in hESC cardiomyogenic differentiation and in human heart development.

Flexible electrical recording from cells using nanowire transistor arrays

Semiconductor nanowires (NWs) have unique electronic properties and sizes comparable with biological structures involved in cellular communication, thus making them promising nanostructures for establishing active interfaces with biological systems. We report a flexible approach to interface NW field-effect transistors (NWFETs) with cells and demonstrate this for silicon NWFET arrays coupled to embryonic chicken cardiomyocytes. Cardiomyocyte cells were cultured on thin, optically transparent polydimethylsiloxane (PDMS) sheets and then brought into contact with Si-NWFET arrays fabricated on standard substrates. NWFET conductance signals recorded from cardiomyocytes exhibited excellent signal-to-noise ratios with values routinely >5 and signal amplitudes that were tuned by varying device sensitivity through changes in water gate-voltage potential, V(g). Signals recorded from cardiomyocytes for V(g) from -0.5 to +0.1 V exhibited amplitude variations from 31 to 7 nS whereas the calibrated voltage remained constant, indicating a robust NWFET/cell interface. In addition, signals recorded as a function of increasing/decreasing displacement of the PDMS/cell support to the device chip showed a reversible >2x increase in signal amplitude (calibrated voltage) from 31 nS (1.0 mV) to 72 nS (2.3 mV). Studies with the displacement close to but below the point of cell disruption yielded calibrated signal amplitudes as large as 10.5 +/- 0.2 mV. Last, multiplexed recording of signals from NWFET arrays interfaced to cardiomyocyte monolayers enabled temporal shifts and signal propagation to be determined with good spatial and temporal resolution. Our modular approach simplifies the process of interfacing cardiomyocytes and other cells to high-performance Si-NWFETs, thus increasing the experimental versatility of NWFET arrays and enabling device registration at the subcellular level.

A composite model for HERG blockade

hERG blockade is one of the major toxicological problems in lead structure optimization. Reliable ligand-based in silico models for predicting hERG blockade therefore have considerable potential for saving time and money, as patch-clamp measurements are very expensive and no crystal structures of the hERG-encoded channel are available. Herein we present a predictive QSAR model for hERG blockade that differentiates between specific and nonspecific binding. Specific binders are identified by preliminary pharmacophore scanning. In addition to descriptor-based models for the compounds selected as hitting one of two different pharmacophores, we also use a model for nonspecific binding that reproduces blocking properties of molecules that do not fit either of the two pharmacophores. PLS and SVR models based on interpretable quantum mechanically derived descriptors on a literature dataset of 113 molecules reach overall R(2) values between 0.60 and 0.70 for independent validation sets and R(2) values between 0.39 and 0.76 after partitioning according to the pharmacophore search for the test sets. Our findings suggest that hERG blockade may occur through different types of binding, so that several different models may be necessary to assess hERG toxicity.

Human cardiovascular progenitor cells develop from a KDR+ embryonic-stem-cell-derived population

The functional heart is comprised of distinct mesoderm-derived lineages including cardiomyocytes, endothelial cells and vascular smooth muscle cells. Studies in the mouse embryo and the mouse embryonic stem cell differentiation model have provided evidence indicating that these three lineages develop from a common Flk-1(+) (kinase insert domain protein receptor, also known as Kdr) cardiovascular progenitor that represents one of the earliest stages in mesoderm specification to the cardiovascular lineages. To determine whether a comparable progenitor is present during human cardiogenesis, we analysed the development of the cardiovascular lineages in human embryonic stem cell differentiation cultures. Here we show that after induction with combinations of activin A, bone morphogenetic protein 4 (BMP4), basic fibroblast growth factor (bFGF, also known as FGF2), vascular endothelial growth factor (VEGF, also known as VEGFA) and dickkopf homolog 1 (DKK1) in serum-free media, human embryonic-stem-cell-derived embryoid bodies generate a KDR(low)/C-KIT(CD117)(neg) population that displays cardiac, endothelial and vascular smooth muscle potential in vitro and, after transplantation, in vivo. When plated in monolayer cultures, these KDR(low)/C-KIT(neg) cells differentiate to generate populations consisting of greater than 50% contracting cardiomyocytes. Populations derived from the KDR(low)/C-KIT(neg) fraction give rise to colonies that contain all three lineages when plated in methylcellulose cultures. Results from limiting dilution studies and cell-mixing experiments support the interpretation that these colonies are clones, indicating that they develop from a cardiovascular colony-forming cell. Together, these findings identify a human cardiovascular progenitor that defines one of the earliest stages of human cardiac development.

High-throughput electrophysiology: an emerging paradigm for ion-channel screening and physiology

Ion channels represent highly attractive targets for drug discovery and are implicated in a diverse range of disorders, in particular in the central nervous and cardiovascular systems. Moreover, assessment of cardiac ion-channel activity of new chemical entities is now an integral component of drug discovery programmes to assess potential for cardiovascular side effects. Despite their attractiveness as drug discovery targets ion channels remain an under-exploited target class, which is in large part due to the labour-intensive and low-throughput nature of patch-clamp electrophysiology. This Review provides an update on the current state-of-the-art for the various automated electrophysiology platforms that are now available and critically evaluates their impact in terms of ion-channel screening, lead optimization and the assessment of cardiac ion-channel safety liability.

The application of human embryonic stem cell technologies to drug discovery

The isolation of human embryonic stem cells about a decade ago marked the birth of a new era in biomedical research. These pluripotent stem cells possess unique properties that make them exceptionally useful in a range of applications. Discussions about human stem cells are most often focused around the area of regenerative medicine and indeed, the possibility to apply these cells in cell replacement therapies is highly attractive. More imminent, however, is the employment of stem cell technologies for drug discovery and development. Novel improved in vitro models based on physiologically relevant human cells will result in better precision and more cost-effective assays ultimately leading to lower attrition rates and safe new drugs.

Human embryonic stem cells: current technologies and emerging industrial applications

The efficiency and accuracy of the drug development process is severely restricted by the lack of functional human cell systems. However, the successful derivation of pluripotent human embryonic stem (hES) cell lines in the late 1990s is expected to revolutionize biomedical research in many areas. Due to their growth capacity and unique developmental potential to differentiate into almost any cell type of the human body, hES cells have opened novel avenues both in basic and applied research as well as for therapeutic applications. In this review we describe, from an industrial perspective, the basic science that underlies the hES cell technology and discuss the current and future prospects for hES cells in novel and improved stem cell based applications for drug discovery, toxicity testing as well as regenerative medicine.

A possible mechanism of halocarbon-induced cardiac sensitization arrhythmias

Cardiac sensitization is the term used for malignant ventricular arrhythmias associated with exposure to inhaled halocarbons in the presence of catecholamines. We investigated the electrophysiological changes associated with cardiomyocyte exposure to epinephrine and a halocarbon known to be associated with cardiac sensitization (halon 1301, CF3Br). Cardiomyocytes (CMs) were isolated from neonatal rats and grown on multielectrode arrays (MEAs). Upon exposure to epinephrine, the CM inter-spike interval (ISI) was decreased 14% at 10 microg/L (P<0.05) and 27% at 100 microg/L (P<0.05) as compared to baseline. Halon alone (50 mg/L) mildly prolonged the field potential (FP) duration (7%). CMs exposed to combinations of epinephrine (100 microg/L) and halon (50 mg/L) for 15 min showed a blunted increase in the ISI (35+/-12%) and a 38% decrease in conduction velocity (P<0.05) when compared to epinephrine alone. There was no change in field potential properties, but dephosphorylated connexin 43 (Cx43) was increased 60+/-16% with the combination as compared to epinephrine alone (P<0.05). Treatment with okadaic acid, a phosphatase inhibitor, prevented the Cx43 dephosphorylation and the reduction in conduction velocity upon exposure to halon and epinephrine. Moreover, the electrophysiological changes induced by epinephrine and halon were indistinguishable from those seen with the gap junction inhibitor heptanol. In conclusion, the combination of a halocarbon and epinephrine results in a unique electrophysiological signature including slow conduction that may explain, in part, the basis for cardiac sensitization. The slowing of conduction is most likely related to changes in the phosphorylation state of Cx43.

Extracellular recordings of field potentials from single cardiomyocytes

Open microfluidic channels were used to separate the extracellular space around a cardiomyocyte into three compartments: the cell ends and a central partition (insulating gap). The microchannels were filled with buffer solution and overlaid with paraffin oil, thus forming the cavities for the cell ends. The central part of the cardiomyocyte rested on the partition between two adjacent microchannels and was entirely surrounded by the paraffin oil. This arrangement increased the extracellular electrical resistance to > 20 MOmega and facilitated the recording of the time course of the change in extracellular voltage and current during subthreshold and suprathreshold stimuli. The waveform of the extracellular current and voltage in response to an extracellular depolarizing stimulus comprised an initial monophasic signal followed by a biphasic signal with a delay of 2-15 ms. The latter was associated with a transient contraction and therefore caused by an action potential. The biphasic signal became monophasic after the depolarization of one cell end by raised extracellular [K+]. This form of differential recording revealed the repolarization phase of the action potential. At rest, the sarcomere length within the gap was 12% +/- 4.8% longer than outside the gap, but intracellular Ca2+ transients occurred to the same extent as that observed in the outer pools. This data demonstrate the feasibility of the use of a microfluidic bath design to limit the extracellular resistance between two ends of an isolated cardiomyocyte.

A novel hypothesis for the binding mode of HERG channel blockers

We present a new docking model for HERG channel blockade. Our new model suggests three key interactions such that (1) a protonated nitrogen of the channel blocker forms a hydrogen bond with the carbonyl oxygen of HERG residue T623; (2) an aromatic moiety of the channel blocker makes a pi-pi interaction with the aromatic ring of HERG residue Y652; and (3) a hydrophobic group of the channel blocker forms a hydrophobic interaction with the benzene ring of HERG residue F656. The previous model assumes two interactions such that (1) a protonated nitrogen of the channel blocker forms a cation-pi interaction with the aromatic ring of HERG residue Y652; and (2) a hydrophobic group of the channel blocker forms a hydrophobic interaction with the benzene ring of HERG residue F656. To test these models, we classified 69 known HERG channel blockers into eight binding types based on their plausible binding modes, and further categorized them into two groups based on the number of interactions our model would predict with the HERG channel (two or three). We then compared the pIC(50) value distributions between these two groups. If the old hypothesis is correct, the distributions should not differ between the two groups (i.e., both groups show only two binding interactions). If our novel hypothesis is correct, the distributions should differ between Groups 1 and 2. Consistent with our hypothesis, the two groups differed with regard to pIC(50), and the group having more predicted interactions with the HERG channel had a higher mean pIC(50) value. Although additional work will be required to further validate our hypothesis, this improved understanding of the HERG channel blocker binding mode may help promote the development of in silico predictions methods for identifying potential HERG channel blockers.

The electrocardiogram of human embryonic stem cell-derived cardiomyocytes

Microelectrode arrays enable to map extracellular field potentials of excitable organs (eg, cardiac tissue) in an electrocardiogram-like manner: They allow to detect (a) rhythmicity, (b) the origin and route of excitation, (c) repolarization, and (d) conduction in heart tissue in short- and long-term experimental approaches. Using it as a screening tool for potential side effects of drugs, we here provide evidence for d-sotalol-induced delayed repolarization in human embryonic stem (hES) cell-derived cardiomyocytes. Thus, the combination of the microelectrode array system with cardiac clusters derived from hES cells heralds a paradigm shift toward improved pharmaceutical drug safety. However, the mixture of various cell types in hES cell cardiac clusters (eg, atrial, immature and mature ventricular cardiomyocytes) indicates the strong need for improved selectivity of cardiac differentiation protocols using hES cells.

Generation and Characterization of Functional Cardiomyocytes from Rhesus Monkey Embryonic Stem Cells

Embryonic stem cells (ESCs) from mice and humans (hESCs) have been shown to be able to efficiently differentiate toward cardiomyocytes (CMs). Because murine ESCs and hESCs do not allow for establishment of pre-clinical allogeneic transplantation models, the aim of our study was to generate functional CMs from rhesus monkey ESCs (rESCs). Although formation of ectodermal and neuronal/glial cells appears to be the default pathway of the rESC line R366.4, we were able to change this commitment and to direct generation of endodermal/mesodermal cells and further differentiation toward CMs. Differentiation of rESCs resulted in an average of 18% of spontaneously contracting embryoid bodies (EBs) from rESCs. Semiquantitative reverse transcription-polymerase chain reaction analyses demonstrated expression of marker genes typical for endoderm, mesoderm, cardiac mesoderm, and CMs, including brachyury, goosecoid, Tbx-5, Tbx-20, Mesp1, Nkx2.5, GATA-4, FOG-2, Mlc2a, MLC2v, ANF, and alpha-MHC in rESC-derived CMs. Immunohistological and ultrastructural studies showed expression of CM-typical proteins, including sarcomeric actinin, troponin T, titin, connexin 43, and cross-striated muscle fibrils. Electrophysiological studies by means of multielectrode arrays revealed evidence of functionality, electrical coupling, and beta-adrenergic signaling of the generated CMs. This is the first study demonstrating generation of functional CMs derived from rESCs. In contrast to hESCs, rESCs allow for establishment of pre-clinical allogeneic transplantation models. Moreover, rESC-derived CMs represent a cell source for the development of high-throughput assays for cardiac safety pharmacology.

In vitro models to evaluate acute and chronic injury to the heart and vascular systems

Multiple in vitro model systems are currently available to evaluate structure and function relationships in the cardiovascular system as well as the system's response to injury. As the level of molecular sophistication continues to advance, so does the level of complexity of the analysis. One of the most daunting tasks faced by researchers interested in studying cardiovascular function and injury is the selection of the system or systems best suited to answer the particular question at hand. In order to successfully apply any given model system, the researcher must recognize the advantages and limitations in the system of choice. This review provides a listing of the historical and modern techniques used to study cardiovascular function and chemically-induced toxicity. With the growing number of new pharmaceuticals discovered each year, it is imperative to use experimental model systems that allow for identification of targets that participate in or mediate adverse outcomes. Clearly, in vitro analysis cannot replace in vivo experimentation, but the methods currently available allow for a reduction in the number of animals used for experimentation and a better understanding of the complexity associated with the injury response.

QT-screen: high-throughput cardiac safety pharmacology by extracellular electrophysiology on primary cardiac myocytes

Cardiac safety pharmacology focuses mostly on the drug-induced prolongation of the QT interval in the electrocardiogram. A prolonged QT interval is an important indicator for an increased risk of severe ventricular arrhythmia. Guidelines demand safety tests addressing QT prolongation in vitro and in vivo before a drug enters clinical trials. If safety risks will be detected not until an advanced stage of preclinical drug development, a considerable sum of money has already been invested into the drug development process. To prevent this, high-throughput systems have been developed to obtain information on the potential toxicity of a substance earlier. We will discuss in this publication that the QT-Screen system, which is based on primary cardiac myocytes, is able to provide a sufficient throughput for secondary screening. With this system, extracellular field potentials can be recorded from spontaneously beating cultures of mammalian or avian ventricular cardiac myocytes simultaneously on 96 channels. The system includes software-controlled and automated eight-channel liquid handling, data acquisition, and analysis. These features allow a user-friendly and unsupervised operation. The throughput is over 100 compounds in six replicates and with full dose-response relationships per day. This equals a maximum of approximately 6,000 data points per day at an average cost for consumables of 0.20 US pennies (U.S.) per data point. The system is intended for a non-good laboratory practice-compliant screening; however, it can be adapted to be used in a good laboratory practice environment.