Evaluation of On-Chip Quasi-In Vivo Cardiac Toxicity Assay for Direct Prediction of TdP Occurrence using Closed-Loop-Shaped Cardiomyocyte Network

Abstract

Re-entry of excitation in the heart is one of the abnormal phenomena to cause the lethal arrhythmia such as torsade de pointes (TdP) and is thought to be induced by the looped structure of excitation conduction pathway. For adaptable in vitro preclinical strategies to evaluate global cardiac safety, an on-chip quasi-in vivo cardiac toxicity assay for lethal arrhythmia measurement using circuit-shaped cardiomyocyte network model has been developed. The electrocardiogram (ECG)-like field potential data, which includes the information both of the repolarization and of the conductance abnormality, was acquired from the self-convoluted extracellular field potential (FP) profiles of a lined-up cardiomyocyte network on a ring-shaped electrode in an agarose microchamber. When E-4031 (hERG blocker) or Astemizole (TdP positive but false-negative drug traditional in vitro assay) were applied to the closed-loop cardiomyocyte network, self-convoluted FP profile of normal beating changed into an abnormal waveform, including early afterdepolarization (EAD) like or TdP-like abnormal waveform at 1 μM in either case (2 out of 8 samples in E-4031 and 8 out of 10 samples in Astemizole), and especially followed by fibrillation-like arrhythmia and arrest in Astemizole. Self-convoluted FP duration prolongation and its fluctuation increase were also observed according to the increase of E-4031 concentration (188±21% prolongation of FPD corrected with beating rate and 168±42% increase of STV at 1 μM, mean±SE, n=6). The results indicate that the self-convoluted FPs of the ring-shaped cardiomyocyte network assay could be used for quasi-ECG measurement to estimate QT prolongation and arrhythmic potential including the effects on both repolarization process and the conductance abnormality of cardiomyocyte.