Roche Michel, Renauleaud Céline, Ballet Véronique, Doubovetzky Michel, Guillon Jean-Michel
Department of Drug Safety Evaluation, Safety Pharmacology Group, Sanofi-Aventis Recherche & Développement, 3 Digue d'Alfortville, 94140 Alfortville, France.
J Pharmacol Toxicol Methods. 2010 May-Jun;61(3):238-50. doi: 10.1016/j.vascn.2010.01.011. Epub 2010 Feb 1.
Delayed ventricular repolarization is associated with rare, but often fatal, polymorphic tachyarrhythmias named Torsades de Pointes. ICH S7B guideline recommends an integrated approach for cardiovascular preclinical evaluation of new drug candidates, including action potential assays (as a Purkinje fiber test) but also proarrhythmia models. The aim of this preliminary study was to compare the respective value of two preclinical in vitro rabbit cardiac preparations-the Purkinje fiber and the isolated perfused heart (Langendorff method)-based on effects of dofetilide, a selective IKr inhibitor.
Transmembrane action potentials from rabbit Purkinje fibers were recorded using a conventional intracellular glass microelectrode. Electrocardiograms from rabbit isolated hearts were evaluated for QRS, QT and T wave durations (Tpeak-Tend). The pacing protocol was the same for both preparations (basal rate of 80 bpm and pacing of 40, 60 and 140 bpm). Dofetilide was tested in both systems at concentrations of 1, 3 and 10 nmol/L.
In Purkinje fibers dofetilide induced a concentration- and reverse use-dependent increase in action potential durations measured at 50 and 90% of repolarization. At 10 nmol/L, only 3/10 fibers showed early after depolarizations. In the isolated heart model, dofetilide also induced a similar concentration- and reverse use-dependent increase in QT-interval. From 3 nmol/L, major changes in T wave morphology, R-on-T extrasystoles and TdP were observed, mainly at low rate. Prior to arrhythmias, T wave shape and duration were markedly altered suggesting an increase in the heterogeneity of cardiac ventricular repolarization.
The effects of dofetilide were comparable in the two models for delayed repolarization but the isolated heart appears to be a better predictor for arrhythmias and a unique in vitro model to assess arrhythmogenic potential of QT prolonging compounds at least when associated with IKr/hERG inhibition.
心室复极延迟与罕见但常致命的多形性室性心律失常——尖端扭转型室速相关。ICH S7B指南推荐了一种用于新药候选物心血管临床前评估的综合方法，包括动作电位测定（作为浦肯野纤维试验）以及致心律失常模型。这项初步研究的目的是基于选择性IKr抑制剂多非利特的作用，比较两种临床前体外兔心脏制剂——浦肯野纤维和离体灌注心脏（Langendorff法）的各自价值。
使用传统的细胞内玻璃微电极记录兔浦肯野纤维的跨膜动作电位。评估兔离体心脏的心电图的QRS、QT和T波持续时间（T峰 - T末）。两种制剂的起搏方案相同（基础心率80次/分钟，起搏频率为40、60和140次/分钟）。在两个系统中以1、3和10 nmol/L的浓度测试多非利特。
在浦肯野纤维中，多非利特在复极化50%和90%时诱导动作电位持续时间呈浓度依赖性和反向使用依赖性增加。在10 nmol/L时，仅3/10的纤维出现早期后除极。在离体心脏模型中，多非利特也诱导QT间期出现类似的浓度依赖性和反向使用依赖性增加。从3 nmol/L起，观察到T波形态、R波落在T波上的期前收缩和尖端扭转型室速的主要变化，主要发生在低心率时。在心律失常之前，T波形状和持续时间明显改变，提示心室复极异质性增加。
多非利特在两种延迟复极模型中的作用相当，但离体心脏似乎是心律失常更好的预测指标，并且是评估QT延长化合物致心律失常潜力的独特体外模型，至少在与IKr/hERG抑制相关时如此。
