Modeling of an SCN5A founder mutation in iPSC-derived cardiomyocytes

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation - Flanders (FWO)

Introduction

SCN5A encodes the α-subunit of voltage-gated cardiac sodium channel Nav1.5. Mutations in SCN5A are identified in about 20% of patients with Brugada syndrome (BrS), an inherited cardiac arrhythmia. We have identified an SCN5A founder mutation (c.4813+3_4813+6dupGGGT), leading to a loss-of-function of Nav1.5 in 25 different families. Mutation carriers show variable expression of the phenotype: from asymptomatic to syncopes and sudden cardiac death. We used induced pluripotent stem cell derived cardiomyocytes (iPSC-CM) to investigate the underlying pathophysiology.

Material & Methods

Dermal fibroblasts of six patients with different disease severity, and two unrelated healthy control individuals were reprogrammed using a commercially available reprogramming kit. iPSC-CMs were differentiated following a published protocol. We performed several differentiation rounds and investigated expression of cardiac markers using qPCR and immunocytochemistry and electrophysiological properties using patch-clamping.

Results

All iPSC-CMs expressed the tested markers. We observed reduction in sodium current density in patient iPSC-CMs compared to the control cells. However, our data display variability in AP characteristics between the differentiation batches, as well as between clones generated from one donor.

Conclusions

We established iPSC-CM models for a unique Belgian SCN5A founder mutation. Despite the observed variability, we could detect expected differences in electrophysiological properties of patient cells compared to controls.

Drug block of I(kr): model systems and relevance to human arrhythmias

The long QT-related arrhythmia torsades de pointes (TdP) can arise with mutations in HERG and during treatment with drugs that block cardiac I Kr, the current encoded by HERG. Multiple test systems have been used to assess drug block of I Kr. This study evaluated the I Kr blocking potency of a series of antiarrhythmics associated with a range of clinical risks of TdP in two such systems: mouse AT-1 cells (in which I Kr is the major repolarizing current) and Ltk cells transiently transfected with HERG (n = 4-10 cells per drug). For each compound, the concentration required to produce 50% block of I Kr or HERG tail currents (IC 50 ) was determined. There was an excellent correlation ( r = 0.98, p < 10 -5 ) between values obtained in the two systems. However, the relation between the liability of a drug to cause TdP appeared dissociated from I Kr blocking potency. Quinidine, dofetilide, ibutilide, procainamide, and disopyramide are all associated with TdP, but only the first three were potent blockers (IC 50 < or = 1 microM ), whereas procainamide and disopyramide were not (IC 50 > 50 microM ). Conversely, verapamil and amiodarone, drugs not associated with TdP, were also blockers (IC 50 < or = 1 microM ). We conclude that I Kr blocking potency can be readily assessed in either AT-1 cells or systems in which HERG is heterologously expressed. However, not all drugs causing TdP are potent I Kr blockers, and I Kr block is not necessarily associated with TdP. Other properties of these drugs, therefore, contribute to their propensity to cause TdP.

Benzocaine enhances and inhibits the K+ current through a human cardiac cloned channel (Kv1.5)

OBJECTIVE

The aim of this study was to analyze the effects of a neutral local anaesthetic, benzocaine, on a cardiac K+ channel cloned from human ventricle.

METHODS

Experiments were performed on hKv1.5 channels stably expressed on mouse cells using the whole-cell configuration of the patch clamp technique.

RESULTS

At 10 nM, benzocaine increased the current amplitude ("agonist effect") by shifting the activation curve 8.4 +/- 2.7 mV in the negative direction, and slowed the time course of tail current decline. In contrast, benzocaine (100-700 microM) inhibited hKv1.5 currents (KD = 901 +/- 81 microM), modified the voltage-dependence of channel activation, which became biphasic, and accelerated the channel deactivation. Extracellular K+ concentration ([K+]o) also affected the channel gating. At 140 mM [K+]o, the time course of tail currents deactivation was significantly accelerated, whereas at 0 mM [K+]o, it was slowed. At both [K+]o the activation curve became biphasic. Benzocaine accelerated the tail current decay at 0 mM but not at 140 mM [K+]o. The reduction in the permeation of K+ through the pore did not modify the blocking effects of micromolar concentrations of benzocaine, but suppressed the agonist effect observed at nanomolar concentrations.

CONCLUSIONS

All these results suggest that benzocaine blocks and modifies the voltage- and time-dependent properties of hKv1.5 channels, binding to an extracellular and to an intracellular site at the channel level. Moreover, both sites are related to each other and can also interact with K+.

Anthropometric and calorimetric evidence for the protein sparing effects of a new protein supplemented low calorie preparation

A commercial protein sparing modified fast (PSMF) preparation has been evaluated for the protein sparing effects in 15 morbidly obese patients. During a 500 kcal preparation, given during a 6-week period, mean body weight and BMI decreased significantly. Total body fat decreased from 55.8 to 41.4 kg and lean body mass and arm muscle circumference (AMC) remained unchanged. Using indirect calorimetry and under the same degree of energy expenditure, carbohydrate metabolic consumption was significantly diminished (166 to 61 g/24 hr; p less than 0.001) but fat consumption was increased (116 to 155 g/24 hr; p less than 0.05) while the metabolic turn-over of protein was unchanged. This new presented PSMF preparation seems to present the typical properties of a protein sparing modified fast.