Tomoharu Osada

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

INTRODUCTION Multi-electrode array (MEA) systems and human induced pluripotent stem (iPS) cell-derived cardiomyocytes are frequently used to characterize the electrophysiological effects of drug candidates for the prediction of QT prolongation and proarrhythmic potential. However, the optimal experimental conditions for obtaining reliable experimental data, such as high-pass filter (HPF) frequency and cell plating density, remain to be determined. METHODS Extracellular field potentials (FPs) were recorded from iPS cell-derived cardiomyocyte sheets by using the MED64 and MEA2100 multi-electrode array systems. Effects of HPF frequency (0.1 or 1Hz) on FP duration (FPD) were assessed in the presence and absence of moxifloxacin, terfenadine, and aspirin. The influence of cell density on FP characteristics recorded through a 0.1-Hz HPF was examined. The relationship between FP and action potential (AP) was elucidated by simultaneous recording of FP and AP using a membrane potential dye. RESULTS Many of the FP waveforms recorded through a 1-Hz HPF were markedly deformed and appeared differentiated compared with those recorded through a 0.1-Hz HPF. The concentration-response curves for FPD in the presence of terfenadine reached a steady state at concentrations of 0.1 and 0.3μM when a 0.1-Hz HPF was used. In contrast, FPD decreased at a concentration of 0.3μM with a characteristic bell-shaped concentration-response curve when a 1-Hz HPF was used. The amplitude of the first and second peaks in the FP waveform increased with increasing cell plating density. The second peak of the FP waveform roughly coincided with AP signal at 50% repolarization, and the negative deflection at the second peak of the FP waveform in the presence of E-4031 corresponded to early afterdepolarization and triggered activity. DISCUSSION FP can be used to assess the QT prolongation and proarrhythmic potential of drug candidates; however, experimental conditions such as HPF frequency are important for obtaining reliable data.

A new paradigm for drug-induced torsadogenic risk assessment using human iPS cell-derived cardiomyocytes

INTRODUCTION Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are anticipated to be a useful tool for conducting proarrhythmia risk assessments of drug candidates. However, a torsadogenic risk prediction paradigm using hiPSC-CMs has not yet been fully established. METHODS Extracellular field potentials (FPs) were recorded from hiPSC-CMs using the multi-electrode array (MEA) system. The effects on FPs were evaluated with 60 drugs, including 57 with various clinical torsadogenic risks. Actual drug concentrations in medium were measured using the equilibrium dialysis method with a Rapid Equilibrium Dialysis device. Relative torsade de pointes (TdP) scores were determined for each drug according to the degree of FP duration prolongation and early afterdepolarization occurrence. The margins were calculated from the free concentration in medium and free effective therapeutic plasma concentration. Each drugs results were plotted on a two-dimensional map of relative TdP risk scores versus margins. RESULTS Each drug was categorised as high, intermediate, or low risk based on its location within predefined areas of the two-dimensional map. We categorised 19 drugs as high risk; 18 as intermediate risk; and 17 as low risk. We examined the concordance between our categorisation of high and low risk drugs against the torsadogenic risk categorisation in CredibleMeds®. Our system demonstrated high concordance, as reflected in a sensitivity of 81%, specificity of 87%, and accuracy of 83%. DISCUSSION These results indicate that our torsadogenic risk assessment is reliable and has a potential to replace the hERG assay for torsadogenic risk prediction, however, this system needs to be improved for the accurate of prediction of clinical TdP risk. Here, we propose a novel drug induced torsadogenic risk categorising system using hiPSC-CMs and the MEA system.

Electrophysiological Characteristics of Human iPSC-Derived Cardiomyocytes for the Assessment of Drug-Induced Proarrhythmic Potential.

The aims of this study were to (1) characterize basic electrophysiological elements of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) that correspond to clinical properties such as QT-RR relationship, (2) determine the applicability of QT correction and analysis methods, and (3) determine if and how these in-vitro parameters could be used in risk assessment for adverse drug-induced effects such as Torsades de pointes (TdP). Field potential recordings were obtained from commercially available hiPSC-CMs using multi-electrode array (MEA) platform with and without ion channel antagonists in the recording solution. Under control conditions, MEA-measured interspike interval and field potential duration (FPD) ranged widely from 1049 to 1635 ms and from 334 to 527 ms, respectively and provided positive linear regression coefficients similar to native QT-RR plots obtained from human electrocardiogram (ECG) analyses in the ongoing cardiovascular-based Framingham Heart Study. Similar to minimizing the effect of heart rate on the QT interval, Fridericia’s and Bazett’s corrections reduced the influence of beat rate on hiPSC-CM FPD. In the presence of E-4031 and cisapride, inhibitors of the rapid delayed rectifier potassium current, hiPSC-CMs showed reverse use-dependent FPD prolongation. Categorical analysis, which is usually applied to clinical QT studies, was applicable to hiPSC-CMs for evaluating torsadogenic risks with FPD and/or corrected FPD. Together, this results of this study links hiPSC-CM electrophysiological endpoints to native ECG endpoints, demonstrates the appropriateness of clinical analytical practices as applied to hiPSC-CMs, and suggests that hiPSC-CMs are a reliable models for assessing the arrhythmogenic potential of drug candidates in human.

Developmental Pluripotency of the Nuclei of Neurons in the Cerebral Cortex of Juvenile Mice

Nuclei isolated from green fluorescent protein-marked neurons in the cerebral cortex of juvenile mice (14–21 d after birth) were injected into enucleated oocytes that were allowed to develop into blastocysts. Embryonic stem (ES) cell lines were established from the inner cell mass of 76 cloned blastocysts after injecting 2026 neuronal nuclei. Some ES cells were injected individually into enucleated oocytes (nuclear transfer). Other ES cells were transferred into the blastocoeles of tetraploid blastocysts (tetraploid complementation). Two-cell embryos after nuclear transfer were transferred to the oviducts of surrogate mothers. Four (1.5%) of 272 nuclear-transferred two-cell embryos developed to term, and two (0.7%) developed into fertile adults. Nineteen (1.9%) of 992 tetraploid blastocysts receiving ES cells reached term, and 10 (1.0%) developed into adults. These findings demonstrate that some of the nuclei of differentiated neurons in the cerebral cortex of juvenile mice maintain developmental pluripotency.

The importance of physiological oxygen concentrations in the sandwich cultures of rat hepatocytes on gas-permeable membranes

Oxygen supply is a critical issue in the optimization of in vitro hepatocyte microenvironments. Although several strategies have been developed to balance complex oxygen requirements, these techniques are not able to accurately meet the cellular oxygen demand. Indeed, neither the actual oxygen concentration encountered by cells nor the cellular oxygen consumption rates (OCR) was assessed. The aim of this study is to define appropriate oxygen conditions at the cell level that could accurately match the OCR and allow hepatocytes to maintain liver specific functions in a normoxic environment. Matrigel overlaid rat hepatocytes were cultured on the polydimethylsiloxane (PDMS) membranes under either atmospheric oxygen concentration [20%‐O2 (+)] or physiological oxygen concentrations [10%‐O2 (+), 5%‐O2 (+)], respectively, to investigate the effects of various oxygen concentrations on the efficient functioning of hepatocytes. In parallel, the gas‐impermeable cultures (polystyrene) with PDMS membrane inserts were used as the control groups [PS‐O2 (−)]. The results indicated that the hepatocytes under 10%‐O2 (+) exhibited improved survival and maintenance of metabolic activities and functional polarization. The dramatic elevation of cellular OCR up to the in vivo liver rate proposed a normoxic environment for hepatocytes, especially when comparing with PS‐O2 (−) cultures, in which the cells generally tolerated hypoxia. Additionally, the expression levels of 84 drug‐metabolism genes were the closest to physiological levels. In conclusion, this study clearly shows the benefit of long‐term culture of hepatocytes at physiological oxygen concentration, and indicates on an oxygen‐permeable membrane system to provide a simple method for in vitro studies.

PolyADP-Ribosylation Is Required for Pronuclear Fusion during Postfertilization in Mice

Background During fertilization, pronuclear envelope breakdown (PNEB) is followed by the mingling of male and female genomes. Dynamic chromatin and protein rearrangements require posttranslational modification (PTM) for the postfertilization development. Methodology/Principal Findings Inhibition of poly(ADP-ribose) polymerase activity (PARylation) by either PJ-34 or 5-AIQ resulted in developmental arrest of fertilized embryos at the PNEB. PARylation inhibition affects spindle bundle formation and phosphorylation of Erk molecules of metaphase II (MII) unfertilized oocytes. We found a frequent appearance of multiple pronuclei (PN) in the PARylation-inhibited embryos, suggesting defective polymerization of tubulins. Attenuated phosphorylation of lamin A/C by PARylation was detected in the PARylation-inhibited embryos at PNEB. This was associated with sustained localization of heterodomain protein 1 (HP1) at the PN of the one-cell embryos arrested by PARylation inhibition. Conclusions/Significance Our findings indicate that PARylation is required for pronuclear fusion during postfertilization processes. These data further suggest that PARylation regulates protein dynamics essential for the beginning of mouse zygotic development. PARylation and its involving signal-pathways may represent potential targets as contraceptives.

Poly(ADP-ribosylation) regulates chromatin organization through histone H3 modification and DNA methylation of the first cell cycle of mouse embryos

We examined the roles of poly(ADP-ribosylation) in chromatin remodeling during the first cell cycle of mouse embryos. Drug-based inhibition of poly(ADP-ribosylation) by a PARP inhibitor, PJ-34, revealed up-regulation of dimethylation of histone H3 at lysine 4 in male pronuclei and down-regulation of dimethylation of histone H3 at lysine 9 (H3K9) and lysine 27 (H3K27). Association of poly(ADP-ribosylation) with histone modification was suggested to be supported by the interaction of Suz12, a histone methyltransferase in the polycomb complex, with Parp1. PARP activity was suggested to be required for a proper localization and maintenance of Suz12 on chromosomes. Notably, DNA methylation level of female pronuclei in one-cell embryos was robustly decreased by PJ-34. Electron microscopic analysis showed a frequent appearance of unusual electron-dense areas within the female pronuclei, implying the disorganized and hypercondensed chromatin ultrastructure. These results show that poly(ADP-ribosylation) is important for the integrity of non-equivalent epigenetic dynamics of pronuclei during the first cell cycle of mouse embryos.

PolyADP-Ribosylation in Postfertilization and Genome Reprogramming: Implications for Carcinogenesis

© 2012 Osada and Masutani, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. PolyADP-Ribosylation in Postfertilization and Genome Reprogramming: Implications for Carcinogenesis

Parp1 deficiency confers defects in chromatin surveillance and remodeling during reprogramming by nuclear transfer.

Accumulating evidence suggests that cloned mice production by the injection of a somatic cell nucleus into an enucleated oocyte is inefficient. DNA damage and chromatin remodeling failures that occur during embryogenesis following nuclear transfer (NT) might explain the poor development of cloned embryos. To avoid these problems, it is important to elucidate somatic chromatin remodeling after NT. Because polyADP-ribosylation, which is catalyzed mainly by poly(ADP-ribose) polymerase 1 (Parp1), is a major post-translational modification that facilitates DNA repair and chromatin remodeling, we examined the effects of Parp1 deficiency in developing NT embryos. Parp1 was located within the pseudo-pronuclei (PPN) of NT eggs. We observed that NT eggs, after activation by Sr2+, formed PPN with significantly more efficiency in Parp1-null embryos than in wild-type NT embryos. However, most the Parp1-null embryos stopped developing by the four-cell stage. Immunostaining for γH2AX foci, a marker of DNA double strand breaks, showed longer retention in the PPN of Parp1-/- donor NT embryos than in wild-type NT embryos, suggesting that, in the absence of Parp1, DNA breaks are slowly repaired and consequently, entry into the S phase might be delayed. Furthermore, decreases in histone H3 acetylation, H3 monomethylation at lysine 4, and H3 trimethylation at lysine 27 after the Sr2+ activation step were observed in the PPN of Parp1-/- donor embryos. Taken together, our data suggest that Parp1 is involved in the plastic remodeling of chromatin structure after NT by supporting DNA repair and specific histone code modifications.