Coupling Data Mining and Laboratory Experiments to Discover Drug Interactions Causing QT Prolongation.

BACKGROUND: QT interval-prolonging drug-drug interactions (QT-DDIs) may increase the risk of life-threatening arrhythmia. Despite guidelines for testing from regulatory agencies, these interactions are usually discovered after drugs are marketed and may go undiscovered for years. OBJECTIVES: Using a combination of adverse event reports, electronic health records (EHR), and laboratory experiments, the goal of this study was to develop a data-driven pipeline for discovering QT-DDIs. METHODS: 1.8 million adverse event reports were mined for signals indicating a QT-DDI. Using 1.6 million electrocardiogram results from 380,000 patients in our institutional EHR, these putative interactions were either refuted or corroborated. In the laboratory, we used patch-clamp electrophysiology to measure the human ether-à-go-go-related gene (hERG) channel block (the primary mechanism by which drugs prolong the QT interval) to evaluate our top candidate. RESULTS: Both direct and indirect signals in the adverse event reports provided evidence that the combination of ceftriaxone (a cephalosporin antibiotic) and lansoprazole (a proton-pump inhibitor) will prolong the QT interval. In the EHR, we found that patients taking both ceftriaxone and lansoprazole had significantly longer QTc intervals (up to 12 ms in white men) and were 1.4 times more likely to have a QTc interval above 500 ms. In the laboratory, we found that, in combination and at clinically relevant concentrations, these drugs blocked the hERG channel. As a negative control, we evaluated the combination of lansoprazole and cefuroxime (another cephalosporin), which lacked evidence of an interaction in the adverse event reports. We found no significant effect of this pair in either the EHR or in the electrophysiology experiments. Class effect analyses suggested this interaction was specific to lansoprazole combined with ceftriaxone but not with other cephalosporins. CONCLUSIONS: Coupling data mining and laboratory experiments is an efficient method for identifying QT-DDIs. Combination therapy of ceftriaxone and lansoprazole is associated with increased risk of acquired long QT syndrome.

KCNE1 alters the voltage sensor movements necessary to open the KCNQ1 channel gate.

The delayed rectifier I(Ks) potassium channel, formed by coassembly of α- (KCNQ1) and ß- (KCNE1) subunits, is essential for cardiac function. Although KCNE1 is necessary to reproduce the functional properties of the native I(Ks) channel, the mechanism(s) through which KCNE1 modulates KCNQ1 is unknown. Here we report measurements of voltage sensor movements in KCNQ1 and KCNQ1/KCNE1 channels using voltage clamp fluorometry. KCNQ1 channels exhibit indistinguishable voltage dependence of fluorescence and current signals, suggesting a one-to-one relationship between voltage sensor movement and channel opening. KCNE1 coexpression dramatically separates the voltage dependence of KCNQ1/KCNE1 current and fluorescence, suggesting an imposed requirement for movements of multiple voltage sensors before KCNQ1/KCNE1 channel opening. This work provides insight into the mechanism by which KCNE1 modulates the I(Ks) channel and presents a mechanism for distinct ß-subunit regulation of ion channel proteins.

Autonomic control of cardiac action potentials: role of potassium channel kinetics in response to sympathetic stimulation.

I(Ks), the slowly activating component of the delayed rectifier current, plays a major role in repolarization of the cardiac action potential (AP). Genetic mutations in the alpha- (KCNQ1) and beta- (KCNE1) subunits of I(Ks) underlie Long QT Syndrome type 1 and 5 (LQT-1 and LQT-5), respectively, and predispose carriers to the development of polymorphic ventricular arrhythmias and sudden cardiac death. beta-adrenergic stimulation increases I(Ks) and results in rate dependent AP shortening, a control system that can be disrupted by some mutations linked to LQT-1 and LQT-5. The mechanisms by which I(Ks) regulates action potential duration (APD) during beta-adrenergic stimulation at different heart rates are not known, nor are the consequences of mutation induced disruption of this regulation. Here we develop a complementary experimental and theoretical approach to address these questions. We reconstituted I(Ks) in CHO cells (ie, KCNQ1 coexpressed with KCNE1 and the adaptator protein Yotiao) and quantitatively examined the effects of beta-adrenergic stimulation on channel kinetics. We then developed theoretical models of I(Ks) in the absence and presence of beta-adrenergic stimulation. We simulated the effects of sympathetic stimulation on channel activation (speeding) and deactivation (slowing) kinetics on the whole cell action potential under different pacing conditions. The model suggests these kinetic effects are critically important in rate-dependent control of action potential duration. We also investigate the effects of two LQT-5 mutations that alter kinetics and impair sympathetic stimulation of I(Ks) and show the likely mechanism by which they lead to tachyarrhythmias and indicate a distinct role of I(KS) kinetics in this electrical dysfunction. The full text of this article is available online at http://circres.ahajournals.org.