Pleiotropic, heart rate-independent cardioprotection by ivabradine

Ivabradine ameliorates doxorubicin-induced cardiotoxicity through improving mitochondrial function and cardiac calcium homeostasis

Doxorubicin (Dox) is a potent anthracycline chemotherapeutic agent. However, its efficacy is limited by its cardiotoxicity, which is driven by excessive oxidative stress, calcium overload, and mitochondrial dysfunction. These mechanisms ultimately result in cardiomyocyte death and cardiac dysfunction. Ivabradine, a hyperpolarization-activated cyclic nucleotide-gated channel blocker, has cardioprotective effects in heart failure and coronary artery disease. However, its potential for mitigating doxorubicin-induced cardiotoxicity (DIC) has not been explored. This study hypothesized that ivabradine reduces cardiac dysfunction in DIC by improving mitochondrial function, restoring calcium homeostasis, and attenuating apoptosis. For in vitro experiments, H9C2 cells were divided into four groups: control, ivabradine (3 μM), Dox (10 μM), and ivabradine co-treated with Dox, with treatments lasting 24 h. Cell viability and mitochondrial function were assessed. For in vivo experiments, male rats (n = 6 per group) were divided into control, ivabradine (10 mg/kg/day, p.o., 30 days), Dox (3 mg/kg, i.p., 6 doses), and ivabradine co-treated with Dox. Cardiac function, mitochondrial function, calcium regulatory proteins, and apoptosis were analyzed. Dox reduced cell viability, increased oxidative stress, and decreased ATP levels in vitro. Co-treatment with ivabradine increased cell viability and reduced oxidative stress but did not restore ATP levels. In rats, Dox impaired mitochondrial function, disrupted mitochondrial dynamics and mitophagy, and altered calcium homeostasis, resulting in cardiomyocyte apoptosis and left ventricular dysfunction. Ivabradine co-treatment attenuated these pathological changes and preserved cardiac function. These findings suggest the potential of ivabradine for cardioprotection against DIC.

Chronic administration of ivabradine improves cardiac Ca handling and function in a rat model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), a severe muscle disease caused by mutations in the gene encoding for the intracellular protein dystrophin, is associated with impaired cardiac function and arrhythmias. A causative factor for complications in the dystrophic heart is abnormal calcium (Ca) handling in ventricular cardiomyocytes, and restoration of normal Ca homeostasis has emerged as therapeutic strategy. Here, we used a rodent model of DMD, the dystrophin-deficient DMDmdx rat, to test the following hypothesis: chronic administration of ivabradine (IVA), a drug clinically approved for the treatment of heart failure, improves Ca handling in dystrophic ventricular cardiomyocytes and thereby enhances contractile performance in the dystrophic heart. Intracellular Ca measurements revealed that 4-months administration of IVA to DMDmdx rats significantly improves Ca handling properties in dystrophic ventricular cardiomyocytes. In particular, IVA treatment increased electrically-evoked Ca transients and speeded their decay. This suggested enhanced sarcoplasmic reticulum Ca release and faster removal of Ca from the cytosol. Chronic IVA administration also enhanced the sarcoplasmic reticulum Ca load. Transthoracic echocardiography revealed a significant improvement of cardiac systolic function in IVA-treated DMDmdx rats. Thus, left ventricular ejection fraction and fractional shortening were enhanced, and end-systolic as well as end-diastolic diameters were diminished by the drug. Finally, chronic IVA administration neither significantly attenuated cardiac fibrosis and apoptosis, nor was vascular function improved by the drug. Collectively our findings suggest that long-term IVA administration enhances contractile function in the dystrophic heart by improvement of Ca handling in ventricular cardiomyocytes. Chronic IVA administration may be beneficial for DMD patients.

Physiological effects of ivabradine in heart failure and beyond

Ivabradine is a pharmacologic agent that inhibits the funny current responsible for determining heart rate in the sinoatrial node. Ivabradine's clinical potential has been investigated in the context of heart failure since it is associated with reduced myocardial oxygen demand, enhanced diastolic filling, stroke volume, and coronary perfusion time; however, it is yet to demonstrate definitive mortality benefit. Alternative effects of ivabradine include modulation of the renin-angiotensin-aldosterone system, sympathetic activation, and endothelial function. Here, we review key clinical trials informing the clinical use of ivabradine and explore opportunities for leveraging its potential pleiotropic effects in other diseases, including treatment of hyperadrenergic states and mitigating complications of COVID-19 infection.

Effect of the combined use of ivabradine and metoprolol in patients with acute myocardial infarction early after percutaneous coronary intervention: A randomized controlled study

Objective

To investigate the effect and safety of the combined use of ivabradine and metoprolol in patients with acute myocardial infarction (AMI) after percutaneous coronary intervention (PCI).

Methods

Eighty patients with AMI were randomly divided into the ivabradine group and the control group. The ivabradine group was treated with ivabradine combined with metoprolol after PCI, while the control group was treated with metoprolol only. Both groups were treated continuously for 1 year. Echocardiography-derived parameters, heart rate, cardiopulmonary exercise testing (CPET) data, major adverse cardiac events (MACE) and myocardial markers were analyzed. The primary endpoint was the left ventricular ejection fraction (LVEF). The safety outcomes were blood pressure, liver and kidney function.

Results

The LVEF was significantly higher in the ivabradine group than in the control group at 1 week, 3 months and 1 year after PCI. The heart rate of the ivabradine group was significantly lower than that of the control group at 1 week and 1month after PCI. The VO2max, metabolic equivalents, anaerobic threshold heart rate, peak heart rate, and heart rate recovery at 8 min of the ivabradine group were significantly higher than those of the control group at 1 year after PCI. Kaplan-Meier analysis demonstrated the one-year total incidence of MACE in the ivabradine group was significantly lower than that in the control group. The B-type natriuretic peptide of the ivabradine group was significantly lower than that of the control group on Day 2 and Day 3 after PCI. The high-sensitivity cardiac troponin I level of the ivabradine group was significantly lower than that of the control group on Day 5 after PCI.

Conclusion

Early use of ivabradine in patients with AMI after PCI can achieve effective heart rate control, reduce myocardial injury, improve cardiac function and exercise tolerance, and may reduce the incidence of major adverse cardiac events. (Clinical research registration number: ChiCTR2000032731).

Hyperpolarization-activated cyclic nucleotide-gated channel inhibitor in myocardial infarction: Potential benefits beyond heart rate modulation

Myocardial infarction (MI) and its associated complications including ventricular arrhythmias and heart failure are responsible for a significant incidence of morbidity and mortality worldwide. The ensuing cardiomyocyte loss results in neurohormone-driven cardiac remodeling, which leads to chronic heart failure in MI survivors. Ivabradine is a heart rate modulation agent currently used in treatment of chronic heart failure with reduced ejection fraction. The canonical target of ivabradine is the hyperpolarization-activated cyclic nucleotide-gated channels (HCN) in cardiac pacemaker cells. However, in post-MI hearts, HCN can also be expressed ectopically in non-pacemaker cardiomyocytes. There is an accumulation of intriguing evidence to suggest that ivabradine also possesses cardioprotective effects that are independent of heart rate reduction. This review aims to summarize and discuss the reported cardioprotective mechanisms of ivabradine beyond heart rate modulation in myocardial infarction through various molecular mechanisms including the prevention of reactive oxygen species-induced mitochondrial damage, improvement of autophagy system, modulation of intracellular calcium cycling, modification of ventricular electrophysiology, and regulation of matrix metalloproteinases.

Effects of ivabradine on myocardial autophagia and apoptosis in isoprenaline-induced heart failure in mice

Objectives

To investigate the effects and mechanisms of ivabradine (IVA) on isoprenaline-induced cardiac injury.

Materials and Methods

Forty male C57BL/6 mice were randomly divided into control group, model group, high-dose IVA group, and low-dose IVA group. The control group was given saline, other groups were given subcutaneous injections of isoproterenol (ISO) 5 mg/kg/d to make the myocardial remodeling model. A corresponding dose of IVA (high dose 50 mg/kg/d, low dose 10 mg/kg/d) was given by gavage (30 days). A transthoracic echocardiogram was obtained to detect the structure and function of the heart. An electron microscope was used to explore the cardiomyocytes' apoptosis and autophagy. HE staining and Masson's trichrome staining were performed to explore myocardial hypertrophy and fibrosis. Western blot was used to detect Bax, Bcl-2, cleaved caspase-3, Becline-1, LC3, phosphorylated p38 mitogen-activated protein kinase (p-p38MAPK), phosphorylated extracellular regulated protein kinases1/2 (p-ERK1/2), phosphorylated c-Jun N-terminal kinase (p-JNK), and α-smooth muscle actin (α-SMA) in the myocardium.

Results

Heart rate in the IVA groups was reduced, and the trend of heart rate reduction was more obvious in the high-dose group. Echocardiography showed that IVA improved the cardiac structure and function compared to the model group. IVA attenuated cardiac fibrosis, decreased cardiomyocyte apoptosis, and increased autophagy. The phosphorylated MAPK in the ISO-induced groups was increased. IVA treatment decreased the p-p38MAPK level. There were no differences in p-ERK and p-JNK levels.

Conclusion

The beneficial effects of IVA on myocardial injury are related to blocking the p38MAPK signal pathway, decreasing cardiomyocyte apoptosis, and increasing cardiomyocyte autophagy.

Heart rate reduction after genetic ablation of L-type Cav1.3 channels induces cardioprotection against ischemia-reperfusion injury

Background

Acute myocardial infarction (AMI) is the major cause of cardiovascular mortality worldwide. Most ischemic episodes are triggered by an increase in heart rate, which induces an imbalance between myocardial oxygen delivery and consumption. Developing drugs that selectively reduce heart rate by inhibiting ion channels involved in heart rate control could provide more clinical benefits. The Cav1.3-mediated L-type Ca2+ current (ICav1.3) play important roles in the generation of heart rate. Therefore, they can constitute relevant targets for selective control of heart rate and cardioprotection during AMI.

Objective

We aimed to investigate the relationship between heart rate and infarct size using mouse strains knockout for Cav1.3 (Cav1.3-/-) L-type calcium channel and of the cardiac G protein gated potassium channel (Girk4-/-) in association with the funny (f)-channel inhibitor ivabradine.

Methods

Wild-type (WT), Cav1.3+/-, Cav1.3-/- and Girk4-/- mice were used as models of respectively normal heart rate, moderate heart rate reduction, bradycardia, and mild tachycardia, respectively. Mice underwent a surgical protocol of myocardial IR (40 min ischemia and 60 min reperfusion). Heart rate was recorded by one-lead surface ECG recording, and infarct size measured by triphenyl tetrazolium chloride staining. In addition, Cav1.3-/- and WT hearts perfused on a Langendorff system were subjected to the same ischemia-reperfusion protocol ex vivo, without or with atrial pacing, and the coronary flow was recorded.

Results

Cav1.3-/- mice presented reduced infarct size (-29%), while Girk4-/- displayed increased infarct size (+30%) compared to WT mice. Consistently, heart rate reduction in Cav1.3+/- or by the f-channel blocker ivabradine was associated with significant decrease in infarct size (-27% and -32%, respectively) in comparison to WT mice.

Conclusion

Our results show that decreasing heart rate allows to protect the myocardium against IR injury in vivo and reveal a close relationship between basal heart rate and IR injury. In addition, this study suggests that targeting Cav1.3 channels could constitute a relevant target for reducing infarct size, since maximal heart rate dependent cardioprotective effect is already observed in Cav1.3+/- mice.

Topical Neck Cooling Without Systemic Hypothermia Attenuates Myocardial Ischemic Injury and Post-ischemic Reperfusion Injury

Background

Following acute myocardial infarction (MI), irreversible damage to the myocardium can only be reduced by shortening the duration between symptom onset and revascularization. While systemic hypothermia has shown promising results in slowing pre-revascularization myocardial damage, it is resource intensive and not conducive to prehospital initiation. We hypothesized that topical neck cooling (NC), an easily implemented therapy for en route transfer to definitive therapy, could similarly attenuate myocardial ischemia-reperfusion injury (IRI).

Methods

Using an in vivo mouse model of myocardial IRI, moderate systemic hypothermia or NC was applied following left coronary artery (LCA) occlusion and subsequent reperfusion, at early, late, and post-reperfusion intervals. Vagotomy was performed after late NC in an additional group. Hearts were harvested to measure infarct size.

Results

Both hypothermia treatments equally attenuated myocardial infarct size by 60% compared to control. The infarct-sparing effect of NC was temperature-dependent and timing-dependent. Vagotomy at the gastroesophageal junction abolished the infarct-sparing effect of late NC. Cardiac perfusate isolated following ischemia had significantly reduced cardiac troponin T, HMGB1, cell-free DNA, and interferon α and β levels after NC.

Conclusions

Topical neck cooling attenuates myocardial IRI in a vagus nerve-dependent manner, with an effect comparable to that of systemic hypothermia. NC attenuated infarct size when applied during ischemia, with earlier initiation resulting in superior infarct sparing. This novel therapy exerts a cardioprotective effect without requiring significant change in core temperature and may be a promising practical strategy to attenuate myocardial damage while patients await definitive revascularization.

The Bradycardic Agent Ivabradine Acts as an Atypical Inhibitor of Voltage-Gated Sodium Channels

Background and purpose: Ivabradine is clinically administered to lower the heart rate, proposedly by inhibiting hyperpolarization-activated cyclic nucleotide-gated cation channels in the sinoatrial node. Recent evidence suggests that voltage-gated sodium channels (VGSC) are inhibited within the same concentration range. VGSCs are expressed within the sinoatrial node and throughout the conduction system of the heart. A block of these channels thus likely contributes to the established and newly raised clinical indications of ivabradine. We, therefore, investigated the pharmacological action of ivabradine on VGSCs in sufficient detail in order to gain a better understanding of the pro- and anti-arrhythmic effects associated with the administration of this drug. Experimental Approach: Ivabradine was tested on VGSCs in native cardiomyocytes isolated from mouse ventricles and the His-Purkinje system and on human Nav1.5 in a heterologous expression system. We investigated the mechanism of channel inhibition by determining its voltage-, frequency-, state-, and temperature-dependence, complemented by a molecular drug docking to the recent Nav1.5 cryoEM structure. Automated patch-clamp experiments were used to investigate ivabradine-mediated changes in Nav1.5 inactivation parameters and inhibition of different VGSC isoforms. Key results: Ivabradine inhibited VGSCs in a voltage- and frequency-dependent manner, but did not alter voltage-dependence of activation and fast inactivation, nor recovery from fast inactivation. Cardiac (Nav1.5), neuronal (Nav1.2), and skeletal muscle (Nav1.4) VGSC isoforms were inhibited by ivabradine within the same concentration range, as were sodium currents in native cardiomyocytes isolated from the ventricles and the His-Purkinje system. Molecular drug docking suggested an interaction of ivabradine with the classical local anesthetic binding site. Conclusion and Implications: Ivabradine acts as an atypical inhibitor of VGSCs. Inhibition of VGSCs likely contributes to the heart rate lowering effect of ivabradine, in particular at higher stimulation frequencies and depolarized membrane potentials, and to the observed slowing of intra-cardiac conduction. Inhibition of VGSCs in native cardiomyocytes and across channel isoforms may provide a potential basis for the anti-arrhythmic potential as observed upon administration of ivabradine.

Ivabradine in the management of COVID-19-related cardiovascular complications: A perspective

Abstract:

Besides acute respiratory distress syndrome, acute cardiac injury is a major complication in severe coronavirus disease 2019 (COVID-19) and associates with a poor clinical outcome. Acute cardiac injury with COVID-19 can be of various etiologies, including myocardial ischemia or infarction and myocarditis, and may compromise cardiac function, resulting in acute heart failure or cardiogenic shock. Systemic inflammatory response increases heart rate (HR), which disrupts the myocardial oxygen supply/demand balance and worsens cardiac energy efficiency, thus further deteriorating the cardiac performance of the injured myocardium. In fact, the combination of elevated resting HR and markers of inflammation synergistically predicts adverse cardiovascular prognosis. Thus, targeted HR reduction may potentially be of benefit in cardiovascular pathologies associated with COVID-19. Ivabradine is a drug that selectively reduces HR via If current inhibition in the sinoatrial node without a negative effect on inotropy. Besides selective HR reduction, ivabradine was found to exert various beneficial pleiotropic effects, either HR-dependent or HR-independent, including anti-inflammatory, anti-atherosclerotic, anti-oxidant and antiproliferative actions and the attenuation of endothelial dysfunction and neurohumoral activation. Cardioprotection by ivabradine has already been indicated in cardiovascular pathologies that are prevalent with COVID-19, including myocarditis, acute coronary syndrome, cardiogenic shock or cardiac dysautonomia. Here, we suggest that ivabradine may be beneficial in the management of COVID-19-related cardiovascular complications.

Adaptation of Arterial Wall Viscosity to the Short-Term Reduction of Heart Rate: Impact of Aging

Background Changes in arterial wall viscosity, which dissipates the energy stored within the arterial wall, may contribute to the beneficial effect of heart rate (HR) reduction on arterial stiffness and cardiovascular coupling. However, it has never been assessed in humans and could be altered by aging. We evaluated the effect of a selective HR-lowering agent on carotid arterial wall viscosity and the impact of aging on this effect. Methods and Results This randomized, placebo-controlled, double-blind, crossover study performed in 19 healthy volunteers evaluated the effects of ivabradine (5 mg BID, 1-week) on carotid arterial wall viscosity, mechanics, hemodynamics, and cardiovascular coupling. Arterial wall viscosity was evaluated by the area of the hysteresis loop of the pressure-lumen cross-sectional area relationship, representing the energy dissipated (W_V), and by the relative viscosity (W_V/W_E), with W_E representing the elastic energy stored. HR reduction by ivabradine increased W_V and W_E whereas W_V/W_E remained stable. In middle-aged subjects (n=11), baseline arterial stiffness and cardiovascular coupling were less favorable, and W_E was similar but W_V and therefore W_V/W_E were lower than in youth (n=8). HR reduction increased W_V/W_E in middle-aged but not in young subjects, owing to a larger increase in W_V than W_E. These results were supported by the age-related linear increase in W_V/W_E after HR reduction (P=0.009), explained by a linear increase in W_V. Conclusion HR reduction increases arterial wall energy dissipation proportionally to the increase in W_E, suggesting an adaptive process to bradycardia. This mechanism is altered during aging resulting in a larger than expected energy dissipation, the impact of which should be assessed. Registration URL: https://www.clinicaltrials.gov; Unique identifier: 2015/077/HP. URL: https://www. eudract.ema.europa.eu; Unique identifier: 2015-002060-17.

Alternative Targets for Modulators of Mitochondrial Potassium Channels

Mitochondrial potassium channels control potassium influx into the mitochondrial matrix and thus regulate mitochondrial membrane potential, volume, respiration, and synthesis of reactive oxygen species (ROS). It has been found that pharmacological activation of mitochondrial potassium channels during ischemia/reperfusion (I/R) injury activates cytoprotective mechanisms resulting in increased cell survival. In cancer cells, the inhibition of these channels leads to increased cell death. Therefore, mitochondrial potassium channels are intriguing targets for the development of new pharmacological strategies. In most cases, however, the substances that modulate the mitochondrial potassium channels have a few alternative targets in the cell. This may result in unexpected or unwanted effects induced by these compounds. In our review, we briefly present the various classes of mitochondrial potassium (mitoK) channels and describe the chemical compounds that modulate their activity. We also describe examples of the multidirectional activity of the activators and inhibitors of mitochondrial potassium channels.

Ivabradine increases the high frequency gain ratio in the vagal heart rate transfer function via an interaction with muscarinic potassium channels

Muscarinic potassium channels (IK,ACh ) are thought to contribute to the high frequency (HF) dynamic heart rate (HR) response to vagal nerve stimulation (VNS) because they act faster than the pathway mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. However, the interactions between the two pathways have not yet been fully elucidated. We previously demonstrated that HCN channel blockade by ivabradine (IVA) increased the HF gain ratio of the transfer function from VNS to HR. To test the hypothesis that IVA increases the HF gain ratio via an interaction with IK,ACh , we examined the dynamic HR response to VNS under conditions of control (CNT), IK,ACh blockade by tertiapin-Q (TQ, 50 nM/kg), and TQ plus IVA (2 mg/kg) (TQ + IVA) in anesthetized rats (n = 8). In each condition, the right vagal nerve was stimulated for 10 min with binary white noise signals between 0-10, 0-20, and 0-40 Hz. On multiple regression analysis, the HF gain ratio positively correlated with the VNS rate with a coefficient of 1.691 ± 0.151 (×0.01) (p < 0.001). TQ had a negative effect on the HF gain ratio with a coefficient of -1.170 ± 0.214 (×0.01) (p < 0.001). IVA did not significantly increase the HF gain ratio in the presence of TQ. The HF gain ratio remained low under the TQ + IVA condition compared to controls. These results affirm that the IVA-induced increase in the HF gain ratio is dependent on the untethering of the hyperpolarizing effect of IK,ACh .

Extracellular Mitochondrial Components and Effects on Cardiovascular Disease

Besides being powerhouses of the cell, mitochondria released into extracellular space act as intercellular signaling. Mitochondria and their components mediate cell-to-cell communication in free form or embedded in a carrier. The pathogenesis of cardiovascular disease is complex, which shows close relationship with inflammation and metabolic abnormalities. Since mitochondria sustain optimal function of the heart, extracellular mitochondria are emerging as a key regulator in the development of cardiovascular disease. In this review, we provide recent findings in the presence and forms of mitochondria transfer between cells, as well as the effects of these mitochondria on vascular inflammation and ischemic myocardium. Mitochondrial transplantation is a novel treatment paradigm for patients suffering from acute cardiovascular accident and challenges the traditional methods of mitochondria isolation.

Noncanonical Thyroid Hormone Receptor α Action Mediates Arterial Vasodilation

CONTEXT

Hypothyroidism impairs cardiovascular health and contributes to endothelial dysfunction with reduced vasodilation. How 3,5,3'-triiodothyronine (T3) and its receptors are involved in the regulation of vasomotion is not yet fully understood. In general, thyroid hormone receptors (TRs) either influence gene expression (canonical action) or rapidly activate intracellular signaling pathways (noncanonical action).

OBJECTIVE

Here we aimed to characterize the T3 action underlying the mechanism of arterial vasodilation and blood pressure (BP) regulation.

METHODS

Mesenteric arteries were isolated from male rats, wild-type (WT) mice, TRα knockout (TRα 0) mice, and from knockin mice with a mutation in the DNA-binding domain (TRα GS). In this mutant, DNA binding and thus canonical action is abrogated while noncanonical signaling is preserved. In a wire myograph system, the isolated vessels were preconstricted with norepinephrine. The response to T3 was measured, and the resulting vasodilation (Δ force [mN]) was normalized to maximum contraction with norepinephrine and expressed as percentage vasodilation after maximal preconstriction with norepinephrine (%NE). Isolated vessels were treated with T3 (1 × 10-15 to 1 × 10-5 mol/L) alone and in combination with the endothelial nitric oxide-synthase (eNOS) inhibitor L-NG-nitroarginine methyl ester (L-NAME) or the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin. The endothelium was removed to determine the contribution of T3 to endothelium-dependent vasodilation. The physiological relevance of T3-induced vasodilation was determined by in vivo arterial BP measurements in male and female mice.

RESULTS

T3 treatment induced vasodilation of mesenteric arteries from WT mice within 2 minutes (by 21.5 ± 1.7%NE). This effect was absent in arteries from TRα 0 mice (by 5.3 ± 0.6%NE, P < .001 vs WT) but preserved in TRα GS arteries (by 17.2 ± 1.1%NE, not significant vs WT). Inhibition of either eNOS or PI3K reduced T3-mediated vasodilation from 52.7 ± 4.5%NE to 28.5 ± 4.1%NE and 22.7 ± 2.9%NE, respectively. Removal of the endothelium abolished the T3-mediated vasodilation in rat mesenteric arteries (by 36.7 ± 5.4%NE vs 3.5 ± 6.2%NE). In vivo, T3 injection led to a rapid decrease of arterial BP in WT (by 13.9 ± 1.9 mm Hg) and TRα GS mice (by 12.4 ± 1.9 mm Hg), but not in TRα 0 mice (by 4.1 ± 1.9 mm Hg).

CONCLUSION

These results demonstrate that T3 acting through noncanonical TRα action affects cardiovascular physiology by inducing endothelium-dependent vasodilation within minutes via PI3K and eNOS activation.

Ivabradine Ameliorates Cardiac Diastolic Dysfunction in Diabetic Mice Independent of Heart Rate Reduction

Cardiac fibroblast (CF) proliferation and activation play important roles in cardiac fibrosis and diastolic dysfunction (DD), which are involved in fibrosis-associated cardiovascular diseases. A previous study showed that ivabradine, a specific heart rate (HR)-lowering agent, significantly ameliorated DD in diabetic db/db mice by reducing HR. Herein, we attempted to determine whether ivabradine has antifibrotic and cardioprotective effects in diabetic mice by directly suppressing CF proliferation and activation, independent of a reduction in HR. We found that knockdown of c-Jun N-terminal kinase (JNK) or p38 mitogen-activated protein kinase (MAPK), or treatment with ivabradine, reduced JNK and p38 MAPK phosphorylation and the protein expression of proliferating cell nuclear antigen, collagen I, collagen III, tissue inhibitor of matrix metalloproteinase 2, and α-smooth muscle actin, accompanied with upregulation of matrix metalloproteinase 2 both in high glucose-treated neonatal rat CFs and left ventricular CFs isolated from db/db mice. However, zatebradine (a HR-lowering agent) did not have these effects in vitro or in vivo. In addition, cardiac fibrosis and DD were ameliorated in db/db mice that were intravenously administered lentiviruses carrying short hairpin RNAs targeting JNK and p38 MAPK or administered ivabradine. Taken together, these findings demonstrate that the ivabradine-induced amelioration of cardiac fibrosis, and DD in db/db mice may be at least in part attributable to the suppression of CF proliferation and activation, through the inhibition of JNK and p38 MAPK.

Beneficial Effects of Ivabradine on Post-Resuscitation Myocardial Dysfunction in a Porcine Model of Cardiac Arrest

Background:

Ivabradine selectively inhibits the If current, reducing the heart rate and protecting against myocardial ischemia/reperfusion injury. We investigated the effects of ivabradine on post-resuscitation myocardial function in a porcine model of cardiopulmonary resuscitation.

Methods and Results:

Ventricular fibrillation was induced and untreated for 8 min while defibrillation was attempted after 6 min of cardiopulmonary resuscitation in anesthetized domestic swine. Then the animals were randomized into ivabradine and placebo groups (n = 5 each). Ivabradine and saline were administered at the same volume 5 min after Return of Spontaneous Circulation, followed by continuous intravenous infusion at 0.5 mg/kg for 480 min. Hemodynamic parameters were continuously recorded. Myocardial function was assessed by echocardiography at baseline and at 60, 120, 240, 480 min and 24 h after resuscitation. The serum levels of N-terminal pro-brain natriuretic peptide (NT-proBNP) and cardiac troponin I (cTnI) were measured by commercial enzyme-linked immunosorbent assay kits. Animals were killed 24 h after resuscitation, and all myocardial tissue was removed for histopathological analysis. The heart rate was significantly reduced from 1 h after resuscitation in the ivabradine group (all P < 0.05). The post-resuscitation mitral E/A and E/e′ velocity ratios and left ventricular ejection fraction were significantly better in the ivabradine than placebo group (P < 0.05). The serum levels of myocardial injury biomarkers (NT-proBNP, cTnI) and the myocardial biopsy scores were significantly lower in the ivabradine than placebo group (P < 0.05). Neurological deficit scores were lower in the IVA group at PR 24 h (P < 0.05).

Conclusions:

Ivabradine improved post-resuscitation myocardial dysfunction, myocardial injury, and post-resuscitation cerebral function, and also slowed the heart rate in this porcine model.

Ivabradine augments high-frequency dynamic gain of the heart rate response to low- and moderate-intensity vagal nerve stimulation under β-blockade

Our previous study indicated that intravenously administered ivabradine (IVA) augmented the dynamic heart rate (HR) response to moderate-intensity vagal nerve stimulation (VNS). Considering an accentuated antagonism, the results were somewhat paradoxical; i.e., the accentuated antagonism indicates that an activation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels via the accumulation of intracellular cyclic adenosine monophosphate (cAMP) augments the HR response to VNS, whereas the inhibition of HCN channels by IVA also augmented the HR response to VNS. To remove the possible influence from the accentuated antagonism, we examined the effects of IVA on the dynamic vagal control of HR under β-blockade. In anesthetized rats (n = 7), the right vagal nerve was stimulated for 10 min according to binary white noise signals between 0 and 10 Hz (V_0-10), between 0 and 20 Hz (V_0-20), and between 0 and 40 Hz (V_0-40). The transfer function from VNS to HR was estimated. Under β-blockade (propranolol, 2 mg/kg iv), IVA (2 mg/kg iv) did not augment the asymptotic low-frequency gain but increased the asymptotic high-frequency gain in V_0-10 (0.53 ± 0.10 vs. 1.74 ± 0.40 beats/min/Hz, P < 0.01) and V_0-20 (0.79 ± 0.14 vs. 2.06 ± 0.47 beats/min/Hz, P < 0.001). These changes, which were observed under a minimal influence from sympathetic background tone, may reflect an increased contribution of the acetylcholine-sensitive potassium channel (I_K,ACh) pathway after IVA, because the HR control via the I_K,ACh pathway is faster and acts in the frequency range higher than the cAMP-mediated pathway.NEW & NOTEWORTHY Since ivabradine (IVA) inhibits hyperpolarization-activated cyclic nucleotide-gated channels, interactions among the sympathetic effect, vagal effect, and IVA can occur in the control of heart rate (HR). To remove the sympathetic effect, we estimated the transfer function from vagal nerve stimulation to HR under β-blockade in anesthetized rats. IVA augmented the high-frequency dynamic gain during low- and moderate-intensity vagal nerve stimulation. Untethering the hyperpolarizing effect of acetylcholine-sensitive potassium channels after IVA may be a possible underlying mechanism.

Potential Effects of Poloxamer 188 on Rat Isolated Brain Mitochondria after Oxidative Stress In Vivo and In Vitro

Outcome after cerebral ischemia is often dismal. Reperfusion adds significantly to the ischemic injury itself. Therefore, new strategies targeting ischemia/reperfusion (I/R) injury are critically needed. Poloxamer (P)188, an amphiphilic triblock copolymer, is a highly promising pharmacological therapeutic as its capability to insert into injured cell membranes has been reported to protect against I/R injury in various models. Although mitochondrial function particularly profits from P188 treatment after I/R, it remains unclear if this beneficial effect occurs directly or indirectly. Here, rat isolated brain mitochondria underwent oxidative stress in vivo by asphyxial cardiac arrest or in vitro by the addition of hydrogen peroxide (H₂O₂) after isolation. Mitochondrial function was assessed by adenosine triphosphate synthesis, oxygen consumption, and calcium retention capacity. Both asphyxia and H₂O₂ exposure significantly impaired mitochondrial function. P188 did not preserve mitochondrial function after either injury mechanism. Further research is indicated.

New Cardiomyokine Reduces Myocardial Ischemia/Reperfusion Injury by PI3K-AKT Pathway Via a Putative KDEL-Receptor Binding

Background CDNF (cerebral dopamine neurotrophic factor) belongs to a new family of neurotrophic factors that exert systemic beneficial effects beyond the brain. Little is known about the role of CDNF in the cardiac context. Herein we investigated the effects of CDNF under endoplasmic reticulum-stress conditions using cardiomyocytes (humans and mice) and isolated rat hearts, as well as in rats subjected to ischemia/reperfusion (I/R). Methods and Results We showed that CDNF is secreted by cardiomyocytes stressed by thapsigargin and by isolated hearts subjected to I/R. Recombinant CDNF (exoCDNF) protected human and mouse cardiomyocytes against endoplasmic reticulum stress and restored the calcium transient. In isolated hearts subjected to I/R, exoCDNF avoided mitochondrial impairment and reduced the infarct area to 19% when administered before ischemia and to 25% when administered at the beginning of reperfusion, compared with an infarct area of 42% in the untreated I/R group. This protection was completely abrogated by AKT (protein kinase B) inhibitor. Heptapeptides containing the KDEL sequence, which binds to the KDEL-R (KDEL receptor), abolished exoCDNF beneficial effects, suggesting the participation of KDEL-R in this cardioprotection. CDNF administered intraperitoneally to rats decreased the infarct area in an in vivo model of I/R (from an infarct area of ≈44% in the I/R group to an infarct area of ≈27%). Moreover, a shorter version of CDNF, which lacks the last 4 residues (CDNF-ΔKTEL) and thus allows CDNF binding to KDEL-R, presented no cardioprotective activity in isolated hearts. Conclusions This is the first study to propose CDNF as a new cardiomyokine that induces cardioprotection via KDEL receptor binding and PI3K/AKT activation.

Targeting myocardial ischaemic injury in the absence of reperfusion

Sudden myocardial ischaemia causes an acute coronary syndrome. In the case of ST-elevation myocardial infarction (STEMI), this is usually caused by the acute rupture of atherosclerotic plaque and obstruction of a coronary artery. Timely restoration of blood flow can reduce infarct size, but ischaemic regions of myocardium remain in up to two-thirds of patients due to microvascular obstruction (MVO). Experimentally, cardioprotective strategies can limit infarct size, but these are primarily intended to target reperfusion injury. Here, we address the question of whether it is possible to specifically prevent ischaemic injury, for example in models of chronic coronary artery occlusion. Two main types of intervention are identified: those that preserve ATP levels by reducing myocardial oxygen consumption, (e.g. hypothermia; cardiac unloading; a reduction in heart rate or contractility; or ischaemic preconditioning), and those that increase myocardial oxygen/blood supply (e.g. collateral vessel dilation). An important consideration in these studies is the method used to assess infarct size, which is not straightforward in the absence of reperfusion. After several hours, most of the ischaemic area is likely to become infarcted, unless it is supplied by pre-formed collateral vessels. Therefore, therapies that stimulate the formation of new collaterals can potentially limit injury during subsequent exposure to ischaemia. After a prolonged period of ischaemia, the heart undergoes a remodelling process. Interventions, such as those targeting inflammation, may prevent adverse remodelling. Finally, harnessing of the endogenous process of myocardial regeneration has the potential to restore cardiomyocytes lost during infarction.

The many faces of myocardial ischaemia and angina

Obstructive disease of the epicardial coronary arteries is the main cause of angina. However, a number of patients with anginal symptoms have normal coronaries or non-obstructive coronary artery disease (CAD) despite electrocardiographic evidence of ischaemia during stress testing. In addition to limited microvascular vasodilator capacity, the coronary microcirculation of these patients is particularly sensitive to vasoconstrictor stimuli, in a condition known as microvascular angina. This review briefly summarizes the determinants and control of coronary blood flow (CBF) and myocardial perfusion. It subsequently analyses the mechanisms responsible for transient myocardial ischaemia: obstructive CAD, coronary spasm and coronary microvascular dysfunction in the absence of epicardial coronary lesions, and variable combinations of structural anomalies, impaired endothelium-dependent and/or -independent vasodilation, and enhanced perception of pain. Lastly, we exemplify mechanism of angina during tachycardia. Distal to a coronary stenosis, coronary dilator reserve is already recruited and can be nearly exhausted at rest distal to a severe stenosis. Increased heart rate reduces the duration of diastole and thus CBF when metabolic vasodilation is no longer able to increase CBF. The increase in myocardial oxygen consumption and resulting metabolic vasodilation in adjacent myocardium without stenotic coronary arteries further acts to divert blood flow away from the post-stenotic coronary vascular bed through collaterals.

Five-year results of heart rate control with ivabradine or metoprolol succinate in patients after heart transplantation

Background

Cardiac graft denervation causes inadequate sinus tachycardia in patients after heart transplantation (HTX) which is associated with reduced survival. This study investigated the 5-year results of heart rate control with ivabradine or metoprolol succinate in patients after HTX.

Methods

This registry study analyzed 104 patients receiving either ivabradine (n = 50) or metoprolol succinate (n = 54) within 5 years after HTX. Analysis included patient characteristics, medication, echocardiographic features, cardiac catheterization data, cardiac biomarkers, heart rates, and post-transplant survival including causes of death.

Results

Demographics and post-transplant medication revealed no significant differences except for ivabradine and metoprolol succinate use. At 5-year follow-up, patients with ivabradine had a significantly lower heart rate (73.3 bpm) compared to baseline (88.6 bpm; P < 0.01) and to metoprolol succinate (80.4 bpm; P < 0.01), a reduced left ventricular mass (154.8 g) compared to baseline (179.5 g; P < 0.01) and to metoprolol succinate (177.3 g; P < 0.01), a lower left ventricular end-diastolic pressure (LVEDP; 12.0 mmHg) compared to baseline (15.5 mmHg; P < 0.01) and to metoprolol succinate (17.1 mmHg; P < 0.01), and a reduced NT-proBNP level (525.4 pg/ml) compared to baseline (3826.3 pg/ml; P < 0.01) and to metoprolol succinate (1038.9 pg/ml; P < 0.01). Five-year post-transplant survival was significantly better in patients with ivabradine (90.0%) versus metoprolol succinate (68.5%; P < 0.01).

Conclusion

Patients receiving ivabradine showed a superior heart rate reduction and a better left ventricular diastolic function along with an improved 5-year survival after HTX.

Novel Findings and Therapeutic Targets on Cardioprotection of Ischemia/ Reperfusion Injury in STEMI

Acute ST-segment elevation myocardial infarction (STEMI) remains a leading cause of morbidity and mortality around the world. A large number of STEMI patients after the infarction gradually develop heart failure due to the infarcted myocardium. Timely reperfusion is essential to salvage ischemic myocardium from the infarction, but the restoration of coronary blood flow in the infarct-related artery itself induces myocardial injury and cardiomyocyte death, known as ischemia/reperfusion injury (IRI). The factors contributing to IRI in STEMI are complex, and microvascular obstruction, inflammation, release of reactive oxygen species, myocardial stunning, and activation of myocardial cell death are involved. Therefore, additional cardioprotection is required to prevent the heart from IRI. Although many mechanical conditioning procedures and pharmacological agents have been identified as effective cardioprotective approaches in animal studies, their translation into the clinical practice has been relatively disappointing due to a variety of reasons. With new emerging data on cardioprotection in STEMI over the past few years, it is mandatory to reevaluate the effectiveness of "old" cardioprotective interventions and highlight the novel therapeutic targets and new treatment strategies of cardioprotection.

The role of mitochondrial reactive oxygen species, NO and H2 S in ischaemia/reperfusion injury and cardioprotection

Redox signalling in mitochondria plays an important role in myocardial ischaemia/reperfusion (I/R) injury and in cardioprotection. Reactive oxygen and nitrogen species (ROS/RNS) modify cellular structures and functions by means of covalent changes in proteins including among others S‐nitros(yl)ation by nitric oxide (NO) and its derivatives, and S‐sulphydration by hydrogen sulphide (H₂S). Many enzymes are involved in the mitochondrial formation and handling of ROS, NO and H₂S under physiological and pathological conditions. In particular, the balance between formation and removal of reactive species is impaired during I/R favouring their accumulation. Therefore, various interventions aimed at decreasing mitochondrial ROS accumulation have been developed and have shown cardioprotective effects in experimental settings. However, ROS, NO and H₂S play also a role in endogenous cardioprotection, as in the case of ischaemic pre‐conditioning, so that preventing their increase might hamper self‐defence mechanisms. The aim of the present review was to provide a critical analysis of formation and role of reactive species, NO and H₂S in mitochondria, with a special emphasis on mechanisms of injury and protection that determine the fate of hearts subjected to I/R. The elucidation of the signalling pathways of ROS, NO and H₂S is likely to reveal novel molecular targets for cardioprotection that could be modulated by pharmacological agents to prevent I/R injury.

Exogenous 10 kDa-Heat Shock Protein Preserves Mitochondrial Function After Hypoxia/Reoxygenation

Humoral factors released during ischemic preconditioning (IPC) protect the myocardium against ischemia/reperfusion (I/R) injury. We have recently identified 10 kDa-heat shock protein (HSP10) and a fraction of small 5-10 kDa peptides (5-10-sP) in the coronary effluent of IPC-treated hearts and demonstrated their cardioprotective potential. We here used our isolated mitochondria model to characterize the impact of exogenous HSP10 and 5-10-sP on mitochondria function from myocardium subjected to I/R injury. Isolated perfused rat hearts were submitted to 30-min global ischemia and 10-min reperfusion. Before ischemia, isolated hearts were infused with saline or 5-10-sP, with or without a mitochondrial ATP-sensitive-K+-channel blocker (5HD 10 μmol·L-1) or PKC inhibitor (chelerythrine 10 μmol·L-1), before I/R. HSP10 (1 µmol·L-1) was infused into isolated hearts before I/R without blockers. At 10-min reperfusion, the mitochondria were isolated and mitochondrial function was assessed. In a subset of experiments, freshly isolated mitochondria were directly incubated with HSP10 or 5-10-sP with or without 5HD or chelerythrine before in vitro hypoxia/reoxygenation. Infusion of 5-10-sP (n = 5) and HSP10 (n = 5) into isolated hearts before I/R improved mitochondrial ADP-stimulated respiration, ATP production and prevented mitochondrial ROS formation compared to the I/R group (n = 5); this effect was abrogated by 5HD and chelerythrine. In freshly isolated mitochondria with in vitro hypoxia/reoxygenation, HSP10 (n = 16) and 5-10-sP (n = 16) incubation prevented reductions of mitochondrial ADP-stimulated respiration (91.5 ± 5.1 nmol O2/min/mg PTN), ATP production (250.1 ± 9.3 μmol ATP/200μg PTN), and prevented mitochondrial ROS production (219.7 ± 9.0 nmol H2O2/200μg PTN) induced by hypoxia/reoxygenation (n = 12, 51.5 ± 5.0 nmol O2/min/mg PTN; 187 ± 21.7 μmol ATP/200 μg PTN; 339.0 ± 14.3 nmol H2O2/200 μg PTN, p < 0.001, respectively). 5HD reduced the ADP-stimulated respiration in the HSP10 group (65.84 ± 3.3 nmol O2/min/mg PTN), ATP production (193.7 ± 12.1 μmol ATP/200μg PTN) and increased ROS in the 5-10-sP group (274.4 ± 21.7 nmol H2O2/200 μg PTN). Mitochondria are a target of the cardioprotection induced by 5-10-sP and HSP10. This protection is dependent of PKC and mKATP activation. HSP10 can act directly on mitochondria and protects against hypoxia/reoxygenation injury by mKATP activation.

Does Ivabradine Decrease Cardiovascular Deaths in Heart Failure Patients?

BACKGROUND

Ivabradine, a heart rate-slowing drug used to treat heart failure and (in Europe) angina, had varying impacts upon cardiovascular events in its 3 large outcome trials. Food and Drug Administration (FDA) analyses may explain the reasons for the variability.

METHODS

An FDA reviewer analyzed the raw data from the 3 trials using logistic regressions to assess interactions between ivabradine and other drugs and forest plots to display dose responses.

RESULTS

Ivabradine in its SHIFT heart failure trial shows a significant interaction with loop diuretics with a beneficial impact upon cardiovascular deaths (odds ratio 0.61; 95% confidence interval, 0.42-0.87, P = .007). This favorable effect is supported by similar interactions in the other 2 trials (BEAUTIFUL, SIGNIFY) and by a dose response for loop diuretics interacting with ivabradine in the SHIFT and BEAUTIFUL trials. The interaction is not related to heart failure severity.

CONCLUSION

Ivabradine used concomitantly with a loop diuretic has a beneficial impact upon cardiovascular death.

Increased sarcoplasmic/endoplasmic reticulum calcium ATPase 2a activity underlies the mechanism of the positive inotropic effect of ivabradine

NEW FINDINGS

What is the central question of this study? The therapeutic effect of ivabradine on patients with chronic heart failure and chronic stable angina pectoris is mediated through a reduction in heart rate: what are the haemodynamic characteristics and the mechanism of the inotropic effect? What is the main finding and its importance? Ivabradine has a positive inotropic effect and lowers the heart rate both in vivo and in vitro. These effects are likely mediated by ivabradine's significant increase of the fast component rate constant mediated by sarcoplasmic/endoplasmic reticulum calcium ATPase 2a and decrease of the slow component rate constant that is mediated by the Na⁺ /Ca²⁺ exchanger and sarcolemmal Ca²⁺ -ATPase during the Ca²⁺ transient decay phase.

ABSTRACT

Ivabradine's therapeutic effect is mediated by a reduction of the heart rate; however, its haemodynamic characteristics and the mechanism of its inotropic effect are poorly understood. We aimed to investigate the positive inotropic effect of ivabradine and its underlying mechanism. The results demonstrated that ivabradine increased the positive inotropy of the rat heart in vivo by increasing the stroke work, cardiac output, stroke volume, end-diastolic volume, end-systolic pressure, ejection fraction, ±dP/dt_max , left ventricular end-systolic elastance and systolic blood pressure without altering the diastolic blood pressure and arterial elastance. This inotropic effect was observed in both non-paced and paced rat isolated heart. Ivabradine increased the Ca²⁺ transient amplitude and the reuptake rates of sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA2a), lowered the diastolic Ca²⁺ level and suppressed the combined extrusion rate of the Na⁺ /Ca²⁺ exchanger and the sarcolemmal Ca²⁺ -ATPase. In addition, ivabradine widened the action potential duration, hyperpolarized the resting membrane potential, increased sarcoplasmic reticulum Ca²⁺ content and reduced Ca²⁺ leak. Overall, ivabradine had a positive inotropic effect brought about by enhanced SERCA2a activity, which might be mediated by increased phospholamban phosphorylation. The positive inotropic effect along with the lowered heart rate underlies ivabradine's therapeutic effect in heart failure.

Pharmacology of Ivabradine and the Effect on Chronic Heart Failure

Chronic Heart Failure (CHF) is a complex clinical syndrome with a high incidence worldwide. Although various types of pharmacological and device therapies are available for CHF, the prognosis is not ideal, for which, the control of increased Heart Rate (HR) is critical. Recently, a bradycardic agent, ivabradine, is found to reduce HR by inhibiting the funny current (If). The underlying mechanism states that ivabradine can enter the Hyperpolarization-activated Cyclic Nucleotide-gated (HCN) channels and bind to the intracellular side, subsequently inhibiting the If. This phenomenon can prolong the slow spontaneous phase in the diastolic depolarization, and thus, reduce HR. The clinical trials demonstrated the significant effects of the drug on reducing HR and improving the symptoms of CHF with fewer adverse effects. This review primarily introduces the chemical features and pharmacological characteristics of ivabradine and the mechanism of treating CHF. Also, some expected therapeutic effects on different diseases were also concluded. However, ivabradine, as a typical If channel inhibitor, necessitates additional research to verify its pharmacological functions.

Activation of the PP2A catalytic subunit by ivabradine attenuates the development of diabetic cardiomyopathy

Hyperglycemia-induced apoptosis plays a critical role in the pathogenesis of diabetic cardiomyopathy (DCM). Our previous study demonstrated that ivabradine, a selective I_f current antagonist, significantly attenuated myocardial apoptosis in diabetic mice, but the underlying mechanisms remained unknown. This study investigated the underlying mechanisms by which ivabradine exerts anti-apoptotic effects in experimental DCM. Pretreatment with ivabradine, but not ZD7288 (an established I_f current blocker), profoundly inhibited high glucose-induced apoptosis via inactivation of nuclear factor (NF)-κB signaling in neonatal rat cardiomyocytes. The effect was abolished by transfection of an siRNA targeting protein phosphatase 2A catalytic subunit (PP2Ac). In streptozotocin-induced diabetic mice, ivabradine treatment significantly inhibited left ventricular hyperpolarization-activated cyclic nucleotide-gated channel 2 (HCN2) and HCN4 (major components of the I_f current), activated PP2Ac, and attenuated NF-κB signaling activation and apoptosis, in line with improved histological abnormalities, fibrosis, and cardiac dysfunction without affecting hyperglycemia. These effects were not observed in diabetic mice with virus-mediated knockdown of HCN2 or HCN4 after myocardial injection, but were alleviated by knockdown of PP2Acα. Molecular docking and phosphatase activity assay confirmed direct binding of ivabradine to, and activation of, PP2Ac. In conclusion, ivabradine may directly activate PP2Ac, leading to inhibition of NF-κB signaling activation, myocardial apoptosis, and fibrosis, and eventually improving cardiac function in experimental DCM. Taken together, the present findings suggest that ivabradine may be a promising drug for treatment of DCM.

Effects of Ivabradine on Residual Myocardial Ischemia after PCI Evaluated by Stress Echocardiography

Background

Residual angina after PCI is a frequently occurring disease. Ivabradine improves symptoms but its role in patients without left ventricular systolic dysfunction is still unclear. The aim was to quantify the effects of ivabradine in terms of MVO₂ indicators and diastolic function.

Methods

Twenty-eight consecutive patients with residual angina after PCI were randomized to ivabradine 5 mg twice/day (IG) or standard therapy (CG). All patients performed a stress echocardiography at the enrollment and after 30 days. MVO₂ was estimated from double product (DP) and triple product (TP) integrating DP with ejection time (ET). Diastolic function was evaluated determining E and A waves, E' measurements, and E/E' ratio both at rest and at the peak of exercise.

Results

The exercise time was longer in IG 9'49″ ± 48″ vs 8'09″ ± 59″ in CG (p=0.0001), reaching a greater workload (IG 139.3 ± 13.4 vs CG 118.7 ± 19.6 Watts; p=0.003). MVO₂ expressed with DP and TP was significantly higher in IG (DP: IG 24194 ± 2697 vs CG 20358 ± 4671.8, p=0.01; TP: IG 17239 ± 4710 vs CG 12206 ± 4413, p=0.007). At peak exercise, the ET was diminished in IG than CG. The analysis of diastolic function after the exercise revealed an increase of E and A waves, without difference in the E/A ratio. The E' wave was higher in IG than CG, and in the same group, the differences between baseline and peak exercise were greater (∆E'3.14 ± 0.7 vs 2.4 ± 1.13, p=0.047). The E/E' ratio was reduced in patients treated with ivabradine (IG 10.2 ± 2.0 vs CG 7.9 ± 1.6, p=0.002).

Conclusions

Ivabradine seems to produce a significant improvement of ischemic threshold, chronotropic reserve, and diastolic function.

Modulation of Sympathetic Activity and Innervation With Chronic Ivabradine and β-Blocker Therapies: Analysis of Hypertensive Rats With Heart Failure

BACKGROUND

Whether the reduction of heart rate with ivabradine (IVA) could affect sympathetic activation and cardiac innervation in heart failure (HF) remains unknown.

PURPOSE

The present study assessed the chronic effects of IVA and β-blocker on the systemic and local sympathetic nervous systems of hypertensive animals with HF.

METHODS AND RESULTS

The Dahl salt-sensitive rats received chronic IVA, bisoprolol (BIS), or placebo (CTL) therapy. The survival of the animal models with IVA and BIS significantly improved (median; 19.7 in IVA and 19.7 in BIS vs 17.0 weeks in CTL, P < .001). A similar decrease in 24-hour heart rate (mean; 305 in IVA and 329 in BIS vs 388 beats/min in CTL, P < .001) without effect on blood pressure, and an improvement in the left ventricular dysfunction (mean fractional shortening; 56.7% in IVA and 47.8% in BIS vs 39.0% in CTL, P < .001) were observed in the animals with IVA and BIS. However, a negative inotropic effect was only observed in the animals with BIS. Excessive urinary noradrenaline excretion in animals with CTL was only suppressed with the use of IVA (mean; 1.35 μg/d in IVA and 1.95 μg/d in BIS vs 2.27 μg/d in CTL, P = .002). In contrast, atrial noradrenaline and acetylcholine depletion in the animals with CTL improved and the tyrosine hydroxylase expression in the both atria were restored with the use of both IVA and BIS.

CONCLUSIONS

IVA therapy improved the survival of hypertensive animals with HF. Furthermore, it was associated with the amelioration of systemic sympathetic activation and cardiac sympathetic and parasympathetic nerve innervations. Chronic β-blocker therapy with negative inotropic effects had beneficial effects only on cardiac innervations.

Ivabradine does not impair anxiety-like behavior and memory in both healthy and L-NAME-induced hypertensive rats

Cardiovascular pathologies are frequently associated with anxiety and other behavioral disturbances. Ivabradine, an inhibitor of the hyperpolarization-activated cyclic nucleotide-gated channels in the sinoatrial node, decreases heart rate and provides cardiovascular protection. Although ivabradine is increasingly used in cardiovascular medicine, the data on its behavioral effects are lacking. The aim of this work was to show ivabradine's potential effect on behavior in healthy and hypertensive rats. After a four-week treatment period, systolic blood pressure was increased in the N(G)-nitro-L-arginine methyl ester (L-NAME)-group and ivabradine significantly reduced it. Furthermore, it reduced the heart rate in both the control and L-NAME-group. In the control group, ivabradine enhanced the time spent in and transition to the open arms of the elevated plus maze test (EPM). In the L-NAME-group, ivabradine does not show a significant effect on the time spent in the EPM open arms and the number of transitions into them. Furthermore, ivabradine has no impact on cognitive function in both control and L-NAME groups. We conclude that ivabradine showed no undesirable effects on anxiety, locomotion or learning; in fact, some of these parameters were even improved. For the first time it has been shown that ivabradine is a safe cardiovascular drug regarding its effect on psycho-behavioral manifestations.

Effect of Ivabradine on a Hypertensive Heart and the Renin-Angiotensin-Aldosterone System in L-NAME-Induced Hypertension

Ivabradine, the selective inhibitor of the If current in the sinoatrial node, exerts cardiovascular protection by its bradycardic effect and potentially pleiotropic actions. However, there is a shortage of data regarding ivabradine's interaction with the renin-angiotensin-aldosterone system (RAAS). This study investigated whether ivabradine is able to protect a hypertensive heart in the model of L-NAME-induced hypertension and to interfere with the RAAS. Four groups (n = 10/group) of adult male Wistar rats were treated as follows for four weeks: control, ivabradine (10 mg/kg/day), L-NAME (40 mg/kg/day), and L-NAME plus ivabradine. L-NAME administration increased systolic blood pressure (SBP) and left ventricular (LV) weight, enhanced hydroxyproline concentration in the LV, and deteriorated the systolic and diastolic LV function. Ivabradine reduced heart rate (HR) and SBP, and improved the LV function. The serum concentrations of angiotensin Ang 1⁻8 (Ang II), Ang 1⁻5, Ang 1⁻7, Ang 1⁻10, Ang 2⁻8, and Ang 3⁻8 were decreased in the L-NAME group and ivabradine did not modify them. The serum concentration of aldosterone and the aldosterone/Ang II ratio were enhanced by L-NAME and ivabradine reduced these changes. We conclude that ivabradine improved the LV function of the hypertensive heart in L-NAME-induced hypertension. The protective effect of ivabradine might have been associated with the reduction of the aldosterone level.

Inhibition of JNK and p38 MAPK-mediated inflammation and apoptosis by ivabradine improves cardiac function in streptozotocin-induced diabetic cardiomyopathy

Inflammation plays a critical role in the development of diabetic cardiomyopathy (DCM), which has been identified as a major predisposing factor for heart failure in diabetic patients. Previous studies indicated that ivabradine (a specific agent for heart rate [HR] reduction) has anti-inflammatory properties, but its role in DCM remains unknown. This study investigated whether ivabradine exerts a therapeutic effect in DCM. C57BL/6J mice were injected intraperitoneally with streptozotocin (STZ) to induce diabetes; then administered with ivabradine or saline (control). After 12 weeks, the surviving mice were analyzed to determine the cardioprotective effect of ivabradine against DCM. Although treatment with ivabradine did not affect blood glucose levels, it attenuated tumor necrosis factor-α, interleukin-1β, and interleukin-6 messenger RNA (mRNA) expression, inhibited c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK) activation, reduced histological abnormalities, myocardial apoptosis and collagen deposition, and improved cardiac function in the diabetic mice. Interestingly, the anti-inflammatory and antiapoptotic properties of ivabradine, but not its inhibitory effect on JNK and p38 MAPK, were observed in high-glucose-cultured neonatal rat ventricular cardiomyocytes. Attenuating inflammation and apoptosis via intramyocardial injection of lentiviruses carrying short hairpin RNA targeting JNK and p38 MAPK validated that the anti-inflammatory and antiapoptotic effects of ivabradine were partly attributed to JNK and p38 MAPK inactivation in diabetic mice. In summary, these data indicate that ivabradine-mediated improvement of cardiac function in STZ-induced diabetic mice may be partly attributed to inhibition of JNK/p38 MAPK-mediated inflammation and apoptosis, which is dependent on the reduction in HR.

Humoral transfer and intramyocardial signal transduction of protection by remote ischemic perconditioning in pigs, rats, and mice

Remote ischemic perconditioning (RPER) during ongoing myocardial ischemia reduces infarct size. The signal transduction of RPER's cardioprotection is still largely unknown. Anesthetized pigs were therefore subjected to RPER by 4 × 5 min/5 min of hindlimb ischemia-reperfusion during 60 min of coronary occlusion before 3 h of reperfusion. Pigs without RPER served as placebo (PLA). The phosphorylation of Akt and ERK [reperfusion injury salvage kinase (RISK) pathway] and STAT3 [survivor activating factor enhancement (SAFE) pathway] in the area at risk was determined by Western blot analysis. Wortmannin/U0126 or AG490 was used for pharmacological RISK or SAFE blockade, respectively. Pig plasma/plasma dialysate sampled after RPER or PLA, respectively, was transferred to isolated rat and mouse hearts subjected to 30 min/120 min of global ischemia-reperfusion. Mitochondria were isolated from rat hearts at early reperfusion. Isolated mouse cardiomyocytes were subjected to 1 h of hypoxia/5 min of reoxygenation without and with prior plasma dialysate incubation. RPER reduced infarct size in pigs to 21 ± 15% versus 44 ± 9% in PLA (percentage of the area at risk, mean ± SD, P < 0.05) and increased STAT3 phosphorylation at early reperfusion. AG490 but not RISK blockade abolished the protection. RPER plasma/plasma dialysate reduced infarct size in rat (22 ± 3% of ventricular mass vs. 40 ± 11% with PLA plasma, P < 0.05) and mouse (29 ± 4% vs. 63 ± 8% with PLA plasma dialysate, P < 0.05) hearts and improved mitochondrial function (e.g., increased respiration, ATP formation, and calcium retention capacity and decreased reactive oxygen species formation). RPER dialysate also improved the viability of mouse cardiomyocytes after hypoxia/reoxygenation. RISK or SAFE blockade each abrogated these beneficial effects. NEW & NOTEWORTHY Remote ischemic perconditioning salvages the myocardium in patients with acute infarction. We identified a signal transduction with humoral transfer and STAT3 activation in pigs and an involvement of reperfusion injury salvage kinases and STAT3 in rat and mouse hearts, along with better cardiomyocyte viability and mitochondrial function.

Efficacy of Ivabradine in Combination with Beta-Blockers Versus Uptitration of Beta-Blockers in Patients with Stable Angina (CONTROL-2 Study)

Introduction

Heart rate (HR) reduction is an integral part of antianginal therapy, but many patients do not reach the guideline-recommended target of less than 60 bpm despite high use of beta-blockers (BB). Failure to uptitrate BB doses may be partly to blame. To explore other options for lowering HR and improving angina control, CONTROL-2 was initiated to compare the efficacy and tolerability of the combination of BBs with ivabradine versus uptitration of BBs to maximal tolerated dose, in patients with stable angina.

Methods

This multicenter, open, randomized study included 1104 patients with Canadian Cardiovascular Society (CCS) class II or III stable angina, in sinus rhythm, and on background stable treatment with non-maximal recommended doses of BBs. Consecutive patients were allocated to ivabradine + BB or BB uptitration in a 4:1 ratio.

Results

At the end of the study (week 16), addition of ivabradine to BB treatment and BB uptitration resulted in reduction in HR (61 ± 6 vs. 63 ± 8 bpm; p = 0.001). At week 16, significantly more patients on ivabradine + BB were in CCS class I than with BB uptitration (37.1% vs. 28%; p = 0.017) and significantly more patients were angina-free (50.6% vs. 34.2%; p < 0.001). Patient health status based on the visual analogue scale (VAS) was also better in the ivabradine + BB group. Adverse events (AEs) were significantly more common with BB uptitration than with the ivabradine + BB combination (18.4% vs. 9.4%, p < 0.001).

Conclusion

In patients with stable angina, combination therapy with ivabradine + BB demonstrated good tolerability, safety, and more pronounced clinical improvement, compared to BB uptitration.

Trial Registration

ISRCTN30654443.

Funding

Servier.

Ectopic expression of S28A-mutated Histone H3 modulates longevity, stress resistance and cardiac function in Drosophila

Histone H3 serine 28 (H3S28) phosphorylation and de-repression of polycomb repressive complex (PRC)-mediated gene regulation is linked to stress conditions in mitotic and post-mitotic cells. To better understand the role of H3S28 phosphorylation in vivo, we studied a Drosophila strain with ectopic expression of constitutively-activated H3S28A, which prevents PRC2 binding at H3S28, thus mimicking H3S28 phosphorylation. H3S28A mutants showed prolonged life span and improved resistance against starvation and paraquat-induced oxidative stress. Morphological and functional analysis of heart tubes revealed smaller luminal areas and thicker walls accompanied by moderately improved cardiac function after acute stress induction. Whole-exome deep gene-sequencing from isolated heart tubes revealed phenotype-corresponding changes in longevity-promoting and myotropic genes. We also found changes in genes controlling mitochondrial biogenesis and respiration. Analysis of mitochondrial respiration from whole flies revealed improved efficacy of ATP production with reduced electron transport-chain activity. Finally, we analyzed posttranslational modification of H3S28 in an experimental heart failure model and observed increased H3S28 phosphorylation levels in HF hearts. Our data establish a critical role of H3S28 phosphorylation in vivo for life span, stress resistance, cardiac and mitochondrial function in Drosophila. These findings may pave the way for H3S28 phosphorylation as a putative target to treat stress-related disorders such as heart failure.

Ivabradine improves left ventricular twist and untwist during chronic hypertension

BACKGROUND

Left ventricular (LV) dysfunction develops during LV hypertrophy and particularly during tachycardia. Thus we investigated the effects of heart rate (HR) reduction with ivabradine, an I_f-channel blocker, on LV twist and untwist which represents myocardial deformation occurring during the overall systole and diastole and therefore provide valuable evaluation of global LV systolic and diastolic function.

METHODS

Eight chronically instrumented pigs receiving continuous angiotensin II infusion during 28days to induce chronic hypertension and LV hypertrophy. Measurements were performed at Days 0 and 28 after stopping angiotensin II infusion in the presence and absence of ivabradine.

RESULTS

At Day 0, reducing HR from 75±3 to 55±2beats/min with ivabradine did not affect LV twist but slowed LV untwist along with an increase in LV end-diastolic pressure. At Day 28, LV posterior and septal wall thickness as well as the estimated LV mass increased, indicating LV hypertrophy. LV twist and untwist were significantly reduced by 33±4% from 16±1° and 32±6% from -154±9°/s, respectively, showing global LV systolic and diastolic dysfunction. In this context, ivabradine decreased HR by 25% from 86±5beats/min and significantly improved LV twist from 11±1 to 14±1° and LV untwist from -104±8 to -146±5°/s.

CONCLUSIONS

Administration of ivabradine during chronic hypertension and LV hypertrophy improved LV twist and untwist. This further supports the beneficial effect of this drug on both LV systolic and diastolic function during the development of LV hypertrophy.

If Channel Inhibition With Ivabradine Does Not Improve Cardiac and Vascular Function in Experimental Septic Shock

OBJECTIVE

Previous studies have suggested that lowering heart rate (HR) by selective β1-blockers improves sepsis-induced cardiac and vascular dysfunction primarily by decreasing proinflammatory pathways. However, the impact of isolated heart rate reduction (HRR) on hemodynamics and inflammatory pathways remains unknown. The present study was designed to assess the effects of HRR by ivabradine, an If channel inhibitor, on cardiovascular function and inflammatory pathways in peritonitis-induced septic shock in rats.

DESIGN

Randomized animal study.

SETTING

University research laboratory.

INTERVENTIONS

Four hours after cecal ligation and puncture (CLP), Wistar rats were randomly allocated to the following groups: CLP (n = 8) and CLP + ivabradine (n = 8, administered per os 4 h after the surgery). Another eight Wistar male rats underwent sham operation. All rats received a continuous infusion of saline (10 mL kg h), analgesic (nalbuphine: 0.2 mg kg h), and antibiotics (imipenem and cilastatin sodium: 10 mg kg) 4 h after the surgery. Assessment at 18 h included hemodynamics, in vivo cardiac function by echocardiography, and ex vivo vasoreactivity by myography. Circulating cytokine levels (TNF-α, IL-6, and IL-10) were measured by ELISA, whereas cardiac and vascular protein expressions of NF-κB/IκBα/iNOS and Akt/eNOS were assessed by Western blotting.

RESULTS

Compared with sham animals, CLP induced tachycardia, hypotension, decreased cardiac output, hyperlactatemia, and vascular hyporesponsiveness to vasopressors. Compared with the CLP group, adjunction of ivabradine decreased the HR without any impact on blood pressure, lactatemia, or vascular responsiveness to vasopressors. Adjunction of ivabradine to CLP rats had no impact on TNF-α, IL-6, and IL-10 cytokines, or on the protein expression levels of phosphorylated forms of NF-κB, Akt, eNOS, and degradation of IκBα in cardiac and vascular tissues.

CONCLUSION

Isolated HRR by ivabradine in an experimental model of septic shock does not appear to be associated with any effect on the tested parameters of cardiac function or on vascular responsiveness to vasopressors. Moreover, in this setting, ivabradine does not alter the circulating levels of selected pro/anti-inflammatory cytokines or cardiac and vascular NF-κB/IκBα protein expression levels.

Cardiomyocyte mitochondria as targets of humoral factors released by remote ischemic preconditioning

INTRODUCTION

Remote ischemic preconditioning (RIPC) reduces myocardial infarct size, and protection can be transferred with plasma to other individuals, even across species. Mitochondria are the end-effectors of cardioprotection by local ischemic conditioning maneuvers. We have now analyzed mitochondrial function in response to RIPC.

MATERIAL AND METHODS

Plasma from pigs undergoing placebo or RIPC (infarct size reduction by 67% in RIPC pigs compared to placebo) was transferred to isolated perfused rat hearts subjected to 30 min global ischemia followed by 120 min reperfusion for infarct size measurement. Additional experiments were terminated at 10 min reperfusion to isolate mitochondria for functional measurements. Effects of RIPC pig plasma were compared to local ischemic preconditioning (IPC) or to infusion of tumor necrosis factor α (TNF-α).

RESULTS

Ischemia/reperfusion (I/R) induced an infarct of 41 ±2% of total ventricular mass. Placebo pig plasma did not affect infarct size (38 ±1, p = 0.13). The RIPC pig plasma reduced infarct size (27 ±2, p < 0.001), as did IPC (20 ±1, p < 0.001) and TNF-α (28 ±2, p < 0.001). Associated with cardioprotection, reductions of mitochondrial adenosine diphosphate (ADP)-stimulated respiration, adenosine triphosphate (ATP) production and calcium retention capacity (CRC) by I/R and placebo pig plasma were prevented by RIPC pig plasma, as they were by IPC and TNF-α. Mitochondrial reactive oxygen species production (nmol H₂O₂/100 µg protein) induced by I/R (272 ±34) was comparable in response to placebo pig plasma (234 ±28, p = 0.37) and was reduced by RIPC pig plasma (83 ±15, p < 0.001) as well as by IPC (78 ±21, p < 0.001) and TNF-α (125 ±42, p = 0.002).

CONCLUSIONS

In rat myocardium, mitochondria are an intracellular target of protection induced by humoral factors retrieved from pigs undergoing RIPC.

The Role of Ivabradine in the Management of Angina Pectoris

Stable angina pectoris affects 2–4 % of the population in Western countries and entails an annual risk of death and nonfatal myocardial infarction of 1–2 % and 3 %, respectively. Heart rate (HR) is linearly related to myocardial oxygen consumption and coronary blood flow, both at rest and during stress. HR reduction is a key target for the prevention of ischemia/angina and is an important mechanism of action of drugs which are recommended as first line therapy for the treatment of angina in clinical guidelines. However, many patients are often unable to tolerate the doses of beta blocker or non-dihydropyridine calcium antagonists required to achieve the desired symptom control. The selective pacemaker current inhibitor ivabradine was developed as a drug for the management of patients with angina pectoris, through its ability to reduce HR specifically. The available data suggest that ivabradine is a well-tolerated and effective anti-anginal agent and it is recommended as a second-line agent for relief of angina in guidelines. However, recent clinical trials of ivabradine have failed to show prognostic benefit and have raised potential concerns about safety. This article will review the available evidence base for the current role of ivabradine in the management of patients with symptomatic angina pectoris in the context of stable coronary artery disease.

Advances in the management of heart failure: the role of ivabradine

A high resting heart rate (≥70–75 b.p.m.) is a risk factor for patients with heart failure (HF) with reduced ejection fraction (EF), probably in the sense of accelerated atherosclerosis, with an increased morbidity and mortality. Beta-blockers not only reduce heart rate but also have negative inotropic and blood pressure-lowering effects, and therefore, in many patients, they cannot be given in the recommended dose. Ivabradine specifically inhibits the pacemaker current (funny current, I_f) of the sinoatrial node cells, resulting in therapeutic heart rate lowering without any negative inotropic and blood pressure-lowering effect. According to the European Society of Cardiology guidelines, ivabradine should be considered to reduce the risk of HF hospitalization and cardiovascular death in symptomatic patients with a reduced left ventricular EF ≤35% and sinus rhythm ≥70 b.p.m. despite treatment with an evidence-based dose of beta-blocker or a dose below the recommended dose (recommendation class “IIa” = weight of evidence/opinion is in favor of usefulness/efficacy: “should be considered”; level of evidence “B” = data derived from a single randomized clinical trial or large nonrandomized studies). Using a heart rate cutoff of ≥ 75 b.p.m., as licensed by the European Medicines Agency, treatment with ivabradine 5–7.5 mg b.i.d. reduces cardiovascular mortality by 17%, HF mortality by 39% and HF hospitalization rate by 30%. A high resting heart rate is not only a risk factor in HF with reduced EF but also at least a risk marker in HF with preserved EF, in acute HF and also in special forms of HF. In this review, we discuss the proven role of ivabradine in the validated indication “HF with reduced EF” together with interesting preliminary findings, and the potential role of ivabradine in further, specific forms of HF.

Impact of Ivabradine on Inflammatory Markers in Chronic Heart Failure

Background. Inflammation plays a crucial role in the progression of chronic heart failure (CHF). Ivabradine is known to reduce the morbidity and mortality of patients with CHF under certain conditions. Beyond the reduction of heart rate, only limited knowledge exists about potential anti-inflammatory effects of ivabradine that might contribute to its benefit in CHF. Thus, the present study aimed to investigate the effect of ivabradine on systemic inflammation. Methods. In the present study, 33 patients with CHF due to dilated, ischemic, and hypertensive cardiomyopathy were treated with ivabradine according to the guidelines of the European Society of Cardiology (ESC). A number of circulating dendritic cells as well as inflammatory mediators were investigated using FACS analysis and ELISA, respectively, before and during ivabradine therapy. Results. Treatment with ivabradine resulted in a significant improvement of CHF symptoms as well as an increase in left ventricular ejection fraction. Moreover, ivabradine treatment led to a significant reduction of TNF-alpha (TNF-α) serum levels and a reconstitution of circulating dendritic cells which are known to be reduced in patients with CHF. Conclusion. We show that treatment with ivabradine in patients with CHF resulted in an improvement of HF symptoms and ejection fraction as well as a normalization of inflammatory mediators.