Chronic dantrolene treatment attenuates cardiac dysfunction and reduces atrial fibrillation inducibility in a rat myocardial infarction heart failure model

Background

Cardiac ryanodine receptor 2 (RyR2) dysfunction and elevated diastolic Ca²⁺ leak have been linked to arrhythmogenesis not only in inherited arrhythmia syndromes but also in acquired forms of heart disease including heart failure (HF) and atrial fibrillation (AF). Thus, stabilizing RyR2 may exert therapeutic effects in these conditions.

Objective

The purpose of this study was to investigate the effects of stabilizing RyR2 with chronic dantrolene treatment on HF development and AF inducibility in a myocardial infarction (MI)-induced HF model in rats.

Methods

MI was induced in adult Sprague-Dawley rats by ligation of the left anterior descending coronary artery. Two weeks after MI surgery, rats with large MI (≥40%) were randomly assigned to MI-vehicle (n = 14) or MI-dantrolene (10 mg/kg/d; n = 13) groups. Sham-surgery rats (n = 7) served as controls.

Results

Compared to the MI-vehicle group, 4-week dantrolene treatment significantly improved cardiac function, with increased left ventricular (LV) fractional shortening (19.48% ± 3.61% vs 15.43% ± 2.65%; P <.01), and decreased LV end-diastolic pressure (12.58 ± 8.52 mm Hg vs 21.91 ± 7.25 mm Hg; P <.01), left atrial diameter (4.97 ± 0.75 mm vs 6.09 ± 1.53 mm; P <.05), and fibrosis content (6.42% ± 0.78% vs 9.76% ± 2.25%; P <.001). Dantrolene significantly decreased AF inducibility (69% in MI-vehicle vs 23% in MI-dantrolene; P <.05). Dantrolene treatment was associated with reduced RyR2 phosphorylation and favorably altered gene expression involving ion channels, sympathetic signaling, oxidative stress, and inflammatory markers.

Conclusion

Chronic dantrolene treatment attenuated LV dysfunction and reduced AF inducibility, which was associated with decreased RyR2 phosphorylation and normalization of many adverse changes in gene expression. Thus, stabilizing RyR2 with chronic dantrolene treatment is a promising novel strategy for decreasing AF in HF.

Chronic Dantrolene Treatment Does Not Affect Hypertension, but Attenuates Sympathetic Stimulation Enhanced Atrial Fibrillation Inducibility in SHR

BACKGROUND

Ryanodine receptor (RyR) dysfunction in skeletal muscle (RyR1) leads to malignant hyperthermia, and in cardiac muscle (RyR2) triggers cardiac arrhythmias. We hypothesized that RyR dysfunction in vascular smooth muscle could increase vascular resistance and hypertension, and may contribute to increased atrial fibrillation (AF) in hypertension. Thus, stabilizing RyR function with chronic dantrolene treatment may attenuate hypertension and AF inducibility in spontaneously hypertensive rats (SHR).

METHODS

Male SHR (16 weeks old) were randomized into vehicle- (n = 10) and dantrolene-treated (10 mg/kg/day, n = 10) groups for 4 weeks. Wistar Kyoto (WKY, n = 11) rats served as controls. Blood pressures (BP) were monitored before and during the 4-week treatment. After 4-week treatment, direct BP, echocardiography, and hemodynamics were recorded. AF inducibility tests were performed in vivo at baseline and repeated under sympathetic stimulation (SS).

RESULTS

Compared with WKY, SHR had significantly higher BP throughout the experimental period. Dantrolene treatment had no effect on BP levels in SHR (final systolic BP 212 ± 9 mm Hg in vehicle group vs. 208 ± 16 mm Hg in dantrolene group, P > 0.05). AF inducibility was very low and not significantly different between 5-month-old WKY and SHR at baseline. However, under SS, AF inducibility and duration were significantly increased in SHR (20% in WKY vs. 60% in SHR-vehicle, P<0.05). Dantrolene treatment significantly attenuated AF inducibility under SS in SHR (60% in vehicle vs. 20% in dantrolene, P < 0.05).

CONCLUSIONS

Stabilizing RyR with chronic dantrolene treatment does not affect hypertension development in SHR. SHR has increased vulnerability to AF induction under SS, which can be attenuated with dantrolene treatment.

Abstract 392: Chronic Dantrolene Treatment Attenuates Cardiac Dysfunction and Reduces Atrial Fibrillation Inducibility in a Rat Myocardial Infarction Heart Failure Model

Background: Cardiac ryanodine receptor (RyR2) dysfunction and diastolic Ca 2+ leak have been linked to arrhythmogenesis not only in inherited arrhythmia syndromes but also in acquired forms of heart disease including heart failure (HF) and atrial fibrillation (AF). Thus, stabilizing RyR2 may confer therapeutic effects in these conditions.

Objective: This study is to investigate the effects of stabilizing RyR2 with chronic dantrolene treatment on HF development and AF inducibility in a myocardial infarction (MI) induced HF model in rats.

Methods: MI was induced in adult Sprague-Dawley rats by ligation of the left anterior descending coronary artery. Two weeks following MI surgery, rats with large MI ( > 40%) were randomly assigned into MI+vehicle (n=13) and MI+dantrolene (10mg/kg/d, n=13) groups. Sham-surgery rats (n=7) served as controls.

Results: Compared to vehicle-treated MI group, 4-week dantrolene treatment significantly improved cardiac function with increased left ventricle (LV) fractional shortening (19.48±3.61 vs 15.43±2.65, p<0.01), decreased LV end-diastolic pressure (12.58±8.52 vs 21.91±7.25, p<0.01), left atrial diameter (4.97±0.75 vs 6.09±1.53 p<0.05) and left atrial fibrosis content. Dantrolene significantly decreased AF inducibility (69% (9 of 13) in MI-vehicle vs 23% (3 of 13) in MI-dantrolene group, p <0.05). Dantrolene treatment was associated with reduced phosphorylation of RyR2, and favorably altered gene expressions involving ionic channels, sympathetic signaling, oxidative stress, and inflammatory markers.

Conclusion: Chronic dantrolene treatment attenuated LV dysfunction and reduced AF inducibility, which were associated with decreased phosphorylation of RyR2 and restoration of many adverse changes in gene expression. Stabilizing RyR2 with dantrolene is a promising treatment in HF and AF.