Repolarisation of human induced pluripotent stem cell cardiomyocytes in engineered heart tissue: A systematic comparison to human adult cardiac tissue

Abstract

Cardiac ventricular tachyarrhythmias are possibly lethal occurrences in patients when they cause too fast myocardial excitation and contraction of the ventricular muscle. A prolongation of action potential (AP) duration and QT interval leads to a substantial risk for Torsade-de-Pointes tachycardias (long QT syndrome, LQTS). Causes for AP prolongation can be ion channel mutations or drug induced channel dysfunction. In safety pharmacology, substances are screened for potential proarrhythmic blocking effect of repolarising potassium channels. The effect on a single ion channel can be monitored in expression systems, but AP measurements are necessary to estimate the net effect of drugs on repolarisation. Since human cardiac tissue is only available to a limited extent, measurements are performed in animal models with notable interspecies differences in AP regulation by different potassium channels. Are human induced pluripotent stem cell cardiomyocytes (hiPSC-CM) able to close the gap to animal models? Thus far, the exact contribution of individual potassium channels to repolarisation of mature hiPSC-CM in engineered heart tissue (EHT) is not fully characterised yet. This work will investigate how closely EHT resembles human ventricular tissue with respect to repolarisation. The final goal is to investigate whether EHT may lead to a superior test system compared to established animal tissue models. Methods: Engineered heart tissue (EHT) was created from hiPSC-CM. Human left ventricular (LV) tissue was collected from patients undergoing heart surgery. For action potential measurements, the sharp microelectrode technique was used. Action potentials could be measured and remained stable over hours, allowing application of stimulation protocols as well as pharmacologic interventions with ion channel altering drugs. Results: In contrast to LV, EHT showed spontaneous diastolic depolarisation, excitation and contraction, which could be mostly abolished by ivabradine-induced block of the funny current If. AP shape in EHT resembled that in human left ventricle, but AP duration in EHT was shorter. IKr block by E-4031 induced a larger AP prolongation and showed a stronger reverse use dependency than LV. A possible cause for this may be the higher channel density and gene expression of hERG-channels. IKs block prolonged APD only when beta adrenoceptors were stimulated; the increase in APD was much smaller than with IKr block. Upon IKr block half of the EHTs developed early afterdepolarisations (EAD), associated with arrhythmia. In contrast, several proarrhythmic factors were necessary to evoke EADs in LV. Conclusion: Overall, LV and EHT share common features in repolarisation, but repolarisation reserve is much smaller in EHT, in which IKr dominates repolarisation. Contribution of IKs is rather small in both preparations and depends on beta adrenoceptor stimulation. The data suggest that EHT is a promising model in safety pharmacology as it provides a complete model of human electrophysiology compared to animal models.