Abstracts

This abstract is a recipient of the Young Investigator Award
This abstract has been invited to present during the Broadening Representation Inclusion and Diversity by Growing Equity (BRIDGE) poster session

Rationale: Long QT syndrome type-2 (LQT2) patients are at a high risk of cardiac arrhythmias and seizures. LQT2 is due to mutations in Kcnh2, which encodes the rapid delayed rectifier potassium current (I_Kr), a major repolarizing current in cardiac myocytes and is very susceptible to off-target drug-induced blockade. While FDA-approved antiseizure medications (ASMs) are largely safe for the general population, we showed that LQT2 patients are at an increased risk of arrhythmias when on vs. off ASMs, particularly sodium channel (Na⁺) blocking ASMs (e.g., phenytoin). Using our new CRISPR-Cas9 generated LQT2 rabbit model (Kcnh2^(+/mut)), we aim to uncover the electrophysiological mechanisms for ASM-mediated ECG changes and arrhythmias. We hypothesize that the Na⁺ channel blocking ASM, phenytoin, also exerts off-target I_Kr blockade, which leads to prolongation of the cardiac electrical activation-recovery interval (QT_c duration)._x000D_
Methods: First, we conducted single-cell voltage-clamp electrophysiology studies using HEK293 cells stably expressing WT Kcnh2 to determine the effects of a therapeutic dose (80µM) of phenytoin on I_Kr density and biophysical properties, compared to vehicle (DMSO.) Next, we evaluated the in vivo effects of therapeutic phenytoin (serum 15-25 µg/mL), through video/EEG/ECG recordings, in WT vs. Kcnh2^(+/mut) rabbits. The drug trial consisted of an oral vehicle/phenytoin crossover drug study (5 days on drug/vehicle, 7-days washout, 5-days on drug/vehicle, vehicle was carrot.)  The outcome measures were the difference in each ECG measure when on phenytoin vs. vehicle ([drug-vehicle] / vehicle).

Results: Phenytoin led to a reduction in I_Kr activation density (phenytoin 37%, n=11 vs. DMSO 8%, n=8, p=0.002) and I_Kr tail density (phenytoin 43% vs. DMSO 28%, p=0.052.) In vivo crossover drug studies suggested that phenytoin caused a larger increase in the QT_c, PR, QRS, and heart rate in the Kcnh2^(+/mut) (n=6) vs. WT (n=3) rabbits._x000D_
Conclusions: Preliminary results indicate therapeutic doses of phenytoin cause off-target I_Kr  blockade and more pronounced ECG changes in Kcnh2^(+/mut) vs. WT rabbits. Future studies will determine the phenytoin dose-dependence of I_Kr blockade, action potential changes, and alterations in ECG measures in WT vs. Kcnh2^(+/mut) rabbits. Findings will help improve risk stratification of arrhythmias for patients taking Na⁺ channel-blocking ASMs. _x000D_
Funding: AHA-CDA (18CDA34110270, PI: D.S. Auerbach), SUNY Upstate Medical University Start-up and Pilot Grant Funds