Abstract 1075: Molecular Mechanisms And Therapeutic Targeting Of Catecholaminergic Arrhythmias And Sudden Cardiac Death
INTRODUCTION: Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) is characterized by stress-induced arrhythmias and syncope caused by mutations in the ryanodine receptor (RyR2), the cardiac SR Ca2+ release channel. RyR2-R2474S knock-in mice corresponding to heterozygous human RyR2-R2474S mutation carriers were investigated for arrhythmia mechanisms. Additionally, a novel water soluble RyR2 stabilizing drug based on the 1,4-benzothiazepine structure (S107) was tested for therapeutic effects.
RESULTS: As compared to wild-type control mice (WT, n=5) which did not show sustained ventricular tachycardia (sVT) or sudden cardiac death (SCD) following standardized exercise stress testing using a previously established protocol, heterozygous R2474S/WT knock-in mice (n=7) developed sVT in 85% and SCD in 71% assessed by telemetric ECG recording. S107 treatment (10 mg/kg/h s.c. 7 d) of R2474S/WT (n=6) completely prevented both stress-induced sVT and SCD. Single channel open probability of RyR2 in lipid bilayers from the same hearts follwowing exercise stress-testing were: WT (0.057±0.021; n=6), R2474S/WT (0.635±0.146; n=7; P<0.05 vs. WT), and R2474S/WT treated with S107 (Po 0.075±0.043; n=6; P<0.05 vs. untreated). Following stress testing of R2474S/WT, the RyR2 subunit calstabin2 (also known as FKBP12.6) was significantly depleted from the cardiac RyR2 complex, which was rescued by S107 treatment (RyR2 IP followed by calstabin2 IB, each n=3). Confocal fluo-4 Ca2+ imaging of isolated R2474S/WT cardiomyocytes exposed to isoproterenol (ISO 100 nM, 5 Hz) resulted in significantly increased occurrence of diastolic Ca2+ oscillations (n=8) which were inhibited by S107 pretreatment (100 nM; n=7). Optical mapping of epicardial voltage signals in Langendorff-perfused, contracting R2474S/WT hearts with Di-4-ANEPPS during sVT (n=5) showed multiple focal arrhythmia triggers which never occurred in WT (n=3).
CONCLUSIONS: Our data suggest stress-induced intracellular Ca2+ leak through ’leaky’ RyR2 channels as a mechanism of focal arrhythmia triggers during sVT and SCD in RyR2 mutation carriers. S107 may stabilize the R2474S/WT channel closed state through increased calstabin2 binding and thereby prevent stress-induced sVT and SCD.