RYR2 Channel Inhibition Is the Principal Mechanism of Flecainide Action in CPVT

Abstract

Rationale: The class Ic antiarrhythmic drug flecainide prevents ventricular tachyarrhythmia in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), a disease caused by hyperactive RyR2 (cardiac ryanodine receptor) mediated calcium (Ca) release. Although flecainide inhibits single RyR2 channels in vitro, reports have claimed that RyR2 inhibition by flecainide is not relevant for its mechanism of antiarrhythmic action and concluded that sodium channel block alone is responsible for flecainide’s efficacy in CPVT. Objective: To determine whether RyR2 block independently contributes to flecainide’s efficacy for suppressing spontaneous sarcoplasmic reticulum Ca release and for preventing ventricular tachycardia in vivo. Methods and Results: We synthesized N-methylated flecainide analogues (QX-flecainide and N -methyl flecainide) and showed that N -methylation reduces flecainide’s inhibitory potency on RyR2 channels incorporated into artificial lipid bilayers. N -methylation did not alter flecainide’s inhibitory activity on human cardiac sodium channels expressed in HEK293T cells. Antiarrhythmic efficacy was tested utilizing a Casq2 (cardiac calsequestrin) knockout (Casq2−/−) CPVT mouse model. In membrane-permeabilized Casq2−/− cardiomyocytes—lacking intact sarcolemma and devoid of sodium channel contribution—flecainide, but not its analogues, suppressed RyR2-mediated Ca release at clinically relevant concentrations. In voltage-clamped, intact Casq2−/− cardiomyocytes pretreated with tetrodotoxin to inhibit sodium channels and isolate the effect of flecainide on RyR2, flecainide significantly reduced the frequency of spontaneous sarcoplasmic reticulum Ca release, while QX-flecainide and N -methyl flecainide did not. In vivo, flecainide effectively suppressed catecholamine-induced ventricular tachyarrhythmias in Casq2−/− mice, whereas N -methyl flecainide had no significant effect on arrhythmia burden, despite comparable sodium channel block. Conclusions: Flecainide remains an effective inhibitor of RyR2-mediated arrhythmogenic Ca release even when cardiac sodium channels are blocked. In mice with CPVT, sodium channel block alone did not prevent ventricular tachycardia. Hence, RyR2 channel inhibition likely constitutes the principal mechanism of antiarrhythmic action of flecainide in CPVT.

Flecainide Paradoxically Activates Cardiac Ryanodine Receptor Channels under Low Activity Conditions: A Potential Pro-Arrhythmic Action

“…At the cellular level, this could be reflected in differing reports of its in vivo actions in both suppressing Ca 2+ waves in intact and permeabilized myocytes, while increasing Ca 2+ spark frequency [28]. In contrast, in intact hearts from a homozygotic CPVT mouse model exhibiting compromised Nav1.5 function, flecainide, despite being a Nav1.5 blocker, mediated anti-arrhythmic effects likely via the inhibition of RyR2-mediated Ca 2+ release [6,7,16,33]. This indirect, RyR2-mediated effect may be the basis for the recent use of flecainide monotherapy in human CPVT, although here individuals are usually heterozygotic and thus flecainide could be acting on both WT and mutant RyR2 [34][35][36].…”

Molecular Mechanism and Current Therapies for Catecholaminergic Polymorphic Ventricular Tachycardia

“…Evidence has been provided that flecainide is effective in reducing DCR in cells harboring the RyR2 R4496C +/− mutation, but this effect could be masked by experimental conditions such as Ca overload [93]. On the other hand, more convincing evidence comes from a recent study that employed a synthesized analog of flecainide with reduced inhibition on RyR2 activity but unaltered inhibition on Na channel [94]. This analog failed to reduce DCR at cellular level and arrhythmia burden in vivo, indicating that flecainide acts through inhibition of RyR2 activity.…”

Mitochondrial and Sarcoplasmic Reticulum Interconnection in Cardiac Arrhythmia

“…Up until now, classic antiarrhythmic drugs' main mechanism known to prevent arrhythmias does not include the mitochondrial-SR interconnection. However, they have effects on either of these organelles (Sugiyama et al, 1985;Sano et al, 1990;Deng and Zhang, 1993;Tsutsumi et al, 2001;Afanas'ev et al, 2002;Ugdyzhekova et al, 2005;Wang et al, 2007;Bannister et al, 2015;Kryshtal et al, 2020). Flecainide can inhibit RyR2 opening, although its relevance in preventing arrhythmias is still controversial (Bannister et al, 2015;Kryshtal et al, 2020).…”

“…However, they have effects on either of these organelles (Sugiyama et al, 1985;Sano et al, 1990;Deng and Zhang, 1993;Tsutsumi et al, 2001;Afanas'ev et al, 2002;Ugdyzhekova et al, 2005;Wang et al, 2007;Bannister et al, 2015;Kryshtal et al, 2020). Flecainide can inhibit RyR2 opening, although its relevance in preventing arrhythmias is still controversial (Bannister et al, 2015;Kryshtal et al, 2020). Lidocaine might inhibit mitoK ATP channels, as shown in isolated cardiomyocytes utilizing a mitochondrial redox state reporter as a surrogate for mitoK ATP opening (Tsutsumi et al, 2001), and prevents mitochondrial Ca 2+ overload in a model of closed-chest VF and resuscitation (Wang et al, 2007), but the widely reported mechanism of action of Lidocaine is prolonging the inactivation of the fast voltage-gated Na + channels, inhibiting spontaneous depolarization (Sheu and Lederer, 1985).…”