Different effects of dronedarone and amiodarone on pulmonary vein electrophysiology, mechanical properties and H2O2-induced arrhythmogenicity

Relaxin-2 plasma levels in atrial fibrillation are linked to inflammation and oxidative stress markers

Relaxin-2 exerts many favourable cardiovascular effects in pathological circumstances such as atrial fibrillation (AF) and heart failure, but the mechanisms underlying its actions are not completely understood. Since inflammation and fibrosis are pivotal processes in the pathogenesis of AF, our aim was to study the relationship between relaxin-2 plasma levels in left atrium (LA) and peripheral vein with molecules implicated in fibrosis, inflammation and oxidative stress in AF patients, and to evaluate the anti-fibrotic ability of relaxin-2 in normal human atrial cardiac fibroblasts (NHCF-A). Peripheral vein relaxin-2 plasma levels were higher than LA relaxin-2 plasma levels in men while, in women, peripheral vein relaxin-2 levels were increased compared to men. AF patients with higher levels of relaxin-2 exhibited a reduction in H2O2 plasma levels and in mRNA levels of alpha-defensin 3 (DEFA3) and IL-6 in leucocytes from LA plasma. Relaxin-2-in-vitro treatment inhibited NHCF-A migration and decreased mRNA and protein levels of the pro-fibrotic molecule transforming growth factor-β1 (TGF-β1). Our results support an association between relaxin-2 and molecules involved in fibrosis, inflammation and oxidative stress in AF patients, and reinforce an anti-fibrotic protective role of this hormone in NHCF-A; strengthening the relevance of relaxin-2 in AF physiopathology, diagnosis and treatment.

Fibroblast Growth Factor 1 Reduces Pulmonary Vein and Atrium Arrhythmogenesis via Modification of Oxidative Stress and Sodium/Calcium Homeostasis

Rationale

Atrial fibrillation is a critical health burden. Targeting calcium (Ca²⁺) dysregulation and oxidative stress are potential upstream therapeutic strategies. Fibroblast growth factor (FGF) 1 can modulate Ca²⁺ homeostasis and has antioxidant activity. The aim of this study was to investigate whether FGF1 has anti-arrhythmic potential through modulating Ca²⁺ homeostasis and antioxidant activity of pulmonary vein (PV) and left atrium (LA) myocytes.

Methods

Patch clamp, western blotting, confocal microscopy, cellular and mitochondrial oxidative stress studies were performed in isolated rabbit PV and LA myocytes treated with or without FGF1 (1 and 10 ng/mL). Conventional microelectrodes were used to record electrical activity in isolated rabbit PV and LA tissue preparations with and without FGF1 (3 μg/kg, i.v.).

Results

FGF1-treated rabbits had a slower heart rate than that observed in controls. PV and LA tissues in FGF1-treated rabbits had slower beating rates and longer action potential duration than those observed in controls. Isoproterenol (1 μM)-treated PV and LA tissues in the FGF1-treated rabbits showed less changes in the increased beating rate and a lower incidence of tachypacing (20 Hz)-induced burst firing than those observed in controls. FGF1 (10 ng/mL)-treated PV and LA myocytes had less oxidative stress and Ca²⁺ transient than those observed in controls. Compared to controls, FGF1 (10 ng/mL) decreased I_Na−L in PV myocytes and lowered I_to, I_Kr−tail in LA myocytes. Protein kinase C (PKC)ε inhibition abolished the effects of FGF1 on the ionic currents of LA and PV myocytes.

Conclusion

FGF1 changes PV and LA electrophysiological characteristics possibly via modulating oxidative stress, Na⁺/Ca²⁺ homeostasis, and the PKCε pathway.

Atrial Fibrillation Initiated by Early Afterdepolarization-Mediated Triggered Activity during Acute Oxidative Stress: Efficacy of Late Sodium Current Blockade

Background

The mechanism of Atrial Fibrillation (AF) that emerges spontaneously during acute oxidative stress is poorly defined and its drug therapy remains suboptimal. We hypothesized that oxidative activation of Ca-calmodulin dependent protein kinase (CaMKII) promotes Early Afterdepolarization-(EAD)-mediated triggered AF in aged fibrotic atria that is sensitive to late Na current (I_Na-L) blockade.

Method and Results

High-resolution voltage optical mapping of the Left and Right Atrial (LA & RA) epicardial surfaces along with microelectrode recordings were performed in isolated-perfused male Fisher 344 rat hearts in Langendorff setting. Aged atria (23-24 months) manifested 10-fold increase in atrial tissue fibrosis compared to young/adult (2-4 months) atria (P<0001. Spontaneous AF arose in 39 out of 41 of the aged atria but in 0 out of 12 young/adult hearts (P<001) during arterial perfusion of with 0.1 mm of hydrogen peroxide (H₂O₂). Optical Action Potential (AP) activation maps showed that the AF was initiated by a focal mechanism in the LA suggestive of EAD-mediated triggered activity. Cellular AP recordings with glass microelectrodes from the LA epicardial sites showing focal activity confirmed optical AP recordings that the spontaneous AF was initiated by late phase 3 EAD-mediated triggered activity. Inhibition of CaMKII activity with KN-93 (1 μM) (N=6) or its downstream target, the enhanced I_Na-L with GS-967 (1 μM), a specific blocker of I_Na-L (N=6), potently suppressed the AF and prevented its initiation when perfused 15 min prior to H₂O₂ (n=6).

Conclusions

Increased atrial tissue fibrosis combined with acute oxidative activation of CaMK II Initiate AF by EAD-mediated triggered activity. Specific block of the I_Na-L with GS-967 effectively suppresses the AF. Drug therapy of oxidative AF in humans with traditional antiarrhythmic drugs remains suboptimal; suppressing I_Na-L offers a potential new strategy for effective suppression of oxidative human AF that remains suboptimal.

Synthesis and 2D-QSAR Study of Active Benzofuran-Based Vasodilators

A new series of 2-alkyloxy-pyridine-3-carbonitrile-benzofuran hybrids (4a–x) was synthesized. All the new derivatives were examined via the standard technique for their vasodilation activity. Some of the investigated compounds exhibited a remarkable activity, with compounds 4w, 4e, 4r, 4s, 4f and 4g believed to be the most active hits in this study with IC₅₀ values 0.223, 0.253, 0.254, 0.268, 0.267 and 0.275 mM, respectively, compared with amiodarone hydrochloride, the reference standard used (IC50 = 0.300 mM). CODESSA PRO was employed to obtain a statistically significant 2-Dimensional Quantitative Structure Activity Relationship (2D-QSAR) model describing the bioactivity of the newly synthesized analogs (N = 24, n = 4, R² = 0.816, R²_cvOO = 0.731, R²_cvMO = 0.772, F = 21.103, s² = 6.191 × 10⁻⁸).

Dronedarone: Basic Pharmacology and Clinical Use

Dronedarone is the newest antiarrhythmic drug approved for the maintenance of sinus rhythm in patients with nonpermanent atrial fibrillation (AF). It is a multi-channel blocker with diverse electrophysiologic properties. Dronedarone decreases the incidence of AF recurrence and the ventricular rate during recurrence. Dronedarone decreases rates of cardiovascular hospitalizations in patients with paroxysmal and persistent AF. Dronedarone increases mortality in patients with permanent AF and those with moderate-severe heart failure, and should thus be avoided in these populations. Dronedarone is less effective than amiodarone but also has less toxicity. Direct comparison with other antiarrhythmic drugs is not available.