Relaxin induces mast cell inhibition and reduces ventricular arrhythmias in a swine model of acute myocardial infarction

doi:10.1016/j.phrs.2007.11.001

Pharmacological Research

Volume 57, Issue 1, January 2008, Pages 43-48

https://doi.org/10.1016/j.phrs.2007.11.001 Get rights and content

Abstract

Resident cardiac mast cells, located mainly around coronary vessels and in the right atrium close to the sinoatrial node, are the main repository of cardiac histamine. Inflammatory activation of cardiac mast cells, as occurs upon acute myocardial infarction, causes the release of histamine and prostanoids. These substances lead to severe tachyarrhythmias, cardiodepressive effects and coronary spasm, thus contributing to myocardial damage and early, lethal outcome.

Relaxin, known to inhibit mast cell activation, has been recently validated as a cardiotropic hormone, being produced by the heart and acting on specific heart receptors. In this study, we report on a swine model of heart ischemia/reperfusion, currently used to test cardiotropic drugs, in which human recombinant relaxin (2.5 and 5 μg/kg b.w.), given at reperfusion upon a 30-min ischemia, markedly reduced cardiac injury as compared with the vehicle-treated animals. Evidence is provided that relaxin, at both the assayed doses, causes a clear-cut, significant reduction of plasma histamine, increase in cardiac histamine content and decrease in cardiac mast cell degranulation. This is accompanied by a reduction of oxidative cardiac tissue injury (assessed as tissue malondialdehyde) and of the occurrence of severe ventricular arrhythmias. In conclusion, this study provides further insight into the cardioprotective effects of relaxin, which also involve mast cell inhibition, and confirms the relevance of histamine in the pathophysiology of ischemia-reperfusion-induced cardiac injury and dysfunction. It also offers additional evidence for the potential therapeutic effects of relaxin in animal models of disease involving mast cell activation.

Introduction

Resident cardiac mast cells, located mainly around coronary vessels and in the right atrium close to the sinoatrial node, are the main repository of cardiac histamine [1]. Inflammatory activation of cardiac mast cells, as occurs upon acute myocardial infarction, causes the release of histamine, leukotrienes and cytokines. These substances may immediately affect coronary vascular resistance and permeability and precipitate reoxygenation damage by increasing tissue edema and no-reflow, thus giving a substantial contribution to myocardial injury [2], [3]. Histamine, acting through cardiac H₁ and H₂ receptors, have prominent functional effects on heart contractility, causing negative dromotropic and positive chronotropic and inotropic effects [4]. When released in high amounts, as occurs during reperfusion-induced myocardial inflammation, histamine can contribute to cardiodepression and severe tachyarrhythmias [5], which are a major cause of early, lethal outcome.

Relaxin (RLX) belongs to a newly defined hormone family, termed the relaxin peptide family which includes three RLX and four insulin-like peptide isoforms [6]. Best known for its effects on reproduction [7], [8], RLX has been recently validated as a cardiotropic hormone [9], [10], [11], [12], being produced by the heart [13], [14] and acting on specific heart receptors [15]. Our previous studies on animal models of myocardial ischemia/reperfusion (IR) have provided evidence that RLX can protect the heart from IR-induced injury when administered either preventatively before ischemia [16], [17] or therapeutically at reperfusion [18]. RLX appears to protect the heart by multiple mechanisms, including up-regulation of endogenous nitric oxide production, coronary vasodilatation and reduction of inflammatory infiltrate and tissue oxidative stress [11]. In other studies, RLX has been shown to inhibit mast cell and basophil activation [19], [20], thereby having beneficial effects in animal models of allergic inflammation, such as asthma-like reaction [21] and cardiac anaphylaxis [22]. The present study was therefore designed to evaluate whether the cardioprotective effect of RLX on myocardial IR-induced damage also involves the inhibition of cardiac mast cell activation.

Section snippets

Surgical induction of cardiac IR

The experimental protocol, designed in compliance with the recommendations of the European Economic Community (86/609/CEE) for the care and use of laboratory animals and with the Good Laboratory Practice, was approved by the animal care committee of the University of Florence, Italy. Male swine, 30–40 kg, were anesthesized by ketamine (0.2 ml/kg b.w.) intubated orotracheally and ventilated mechanically with O₂ and 1.5% isoflurane. Electrocardiogram and arterial blood pressure were monitored

Results

In the vehicle-treated swine undergoing IR serum histamine levels increased markedly as compared with the basal, pre-ischemic values (40.5 ± 1.1 ng/ml), peaking at 30-min reperfusion and declining to the basal levels at 120-min reperfusion. Treatment with recombinant human RLX caused a dose-dependent, statistically significant reduction of the plasma histamine levels (Fig. 1). Measurement of tissue histamine content in cardiac samples taken at end reperfusion showed that in the vehicle-treated, IR

Discussion

In this study, we used a swine model of cardiac IR suited to test cardiotropic drugs due to its similarities with acute myocardial infarction in humans [27]. The present findings provide further evidence for the cardioprotective effects of RLX against IR-induced myocardial injury and demonstrate that these effects also involve the inhibition of cardiac mast cell activation and histamine release, an adverse phenomenon typically occurring during IR [2], [3]. Human recombinant RLX (2.5 and 5 μg/kg

Acknowledgment

The authors are grateful to Professor Mario Bigazzi, Prosperius Institute, Florence, Italy, who kindly provided human recombinant relaxin as a gift.

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ROS such as superoxide, a main mediator of I/R injury is detoxified by superoxide dismutase (SOD) which is one of antioxidant enzymes that is highly expressed in cardiac tissue and plays an important role ischemic injury defense (Bhargava, 2019). Furthermore, malondialdehyde (MDA) is an index of oxidative myocardial damage, especially at reperfusion (Nistri et al., 2008). One of the most significant factors that increase the susceptibility of arrhythmia development during I/R is the activation of RAAS (Van der Weg et al., 2018).
Ventricular arrhythmias are considered as a major risk of sudden cardiac death. This study was designed to investigate the potential effects of angiotensin receptor neprilysin inhibitor; thiorphan/irbesartan (TH/IRB) combination therapy on myocardial ischemic-reperfusion (I/R)-induced arrhythmia. Fifty male Wistar rats were divided into 5 groups; (I, II): Sham, I/R both received DMSO intraperitoneally before the procedure. (III, IV, V): TH/IRB + IR (0.1/5 mg/kg, 0.1/10 mg/kg and 0.1/15 mg/kg). The drugs were injected intraperitoneally 15 min before I/R induction. Electrocardiograms changes, mean arterial blood pressure, incidence of ventricular tachycardia (VT), incidence of ventricular fibrillation (VF) and arrhythmia score were assessed. Cardiac levels of creatinine kinase–MB (CK-MB), Malondialdehyde (MDA), superoxide dismutase (SOD), endothelin-1 (ET-1), ATP content, and Na⁺/K⁺-ATPase pump activity were measured. TH (0.1 mg/kg) in combination with IRB (5, 10 and 15 mg/kg) produced significant decrease in QTc interval duration, ST height, incidence of VT and VF, duration of VT + VF, and arrhythmia score compared to I/R group. All treated groups showed significant decrease in the cardiac levels of: CK-MB, MDA and ET-1 and significant increase in SOD, ATP content, and Na⁺/K⁺-ATPase pump activity compared to I/R. TH/IRB + IR (0.1/10 mg/kg) group produced significant decrease in CK-MB, MDA and ET-1 and a significant increase in SOD, ATP content, and Na⁺/K⁺-ATPase pump activity compared to other treated groups. In conclusion, angiotensin receptor neprilysin inhibitor (thiorphan/irbesartan) decreased arrhythmia score and decreased cardiac damage. These could be explained in part by its ability to decrease oxidative stress and ET-1, increase ATP, and Na⁺/K⁺-ATPase pump activity in this rat model of I/R-induced arrhythmia.
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Relaxin is a hormone of pregnancy first discovered for its ability to induce ligament relaxation in nonpregnant guinea pig and is important for softening of the birth canal during parturition, decidualization, implantation, nipple development and increased maternal renal perfusion, glomerular filtration, and cardiac output. Subsequently, relaxin has been shown to exert multiple beneficial cardiovascular effects during pathological events such as hypertension, atrial fibrillation, heart failure and myocardial infarction, including suppression of arrhythmia and inflammation, and reversal of fibrosis. Despite extensive studies, the mechanisms underlying relaxin's effects are not well understood. Relaxin signals primarily through its G protein coupled receptor, the relaxin family peptide receptor-1, to activate multiple signaling pathways and this review summarizes our understanding of these pathways as they relate to the cardioprotective actions of relaxin, focusing on relaxin's anti-fibrotic, anti-arrhythmic and anti-inflammatory properties. Further, this review includes a brief overview of relaxin in clinical trials for heart failure and progress in the development of relaxin mimetics.
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Finally, we report to our knowledge for the first time sustained protection of cardiac function and electrical stability by chronic lower-dose RLX treatment, the latter having been assessed also by programmed stimulation as mainly used in clinical EP studies. The use of RLX during myocardial ischemia has already been investigated in porcine models with superior translational perspective to human cardiovascular disease [15,41,45], but diverging approaches. While two studies were performed as acute ischemia-reperfusion experiments ending after 3 h of reperfusion [15,41], Formigli and co-workers transplanted genetically engineered myoblasts expressing RLX after MI instead of direct RLX application [45].
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Relaxin-2 (RLX) is a peptide hormone that exerts beneficial anti-fibrotic and anti-inflammatory effects in diverse models of cardiovascular disease. The goal of this study was to determine the effects of RLX treatment on the susceptibility to atrial fibrillation (AF) after myocardial infarction (MI).
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Relaxin is safe and efficient to use for treating acute heart failure. However, the electrophysiological and arrhythmogenic effects of relaxin in an experimental healing infarction model remain unknown. In this study, a rat model with myocardial infarction (MI) received relaxin (0.5 mg/kg per day) or vehicle (sodium acetate) infusion via implantable mini-pumps for 2 weeks. Thereafter, hemodynamic measurement, electrophysiological study, histological examination, and immunofluorescence labeling were performed. Relaxin treatment significantly attenuated tachyarrhythmia inducibility and cardiac dysfunction in healing infarcted heart. Epicardial monophasic action potentials showed that relaxin significantly reduced the dispersion of action potential duration in postinfarcted hearts. Histological study revealed that relaxin significantly reduced myocardial apoptosis and cardiac fibrotic collagen deposition. Western blot revealed that relaxin treatment significantly suppressed the protein expression levels of TGFβ1, α-SMA, and type I collagen. Furthermore, abnormal alterations of Connexin 43, including reduction and lateralization, were significantly attenuated by relaxin treatment at the infarcted border zone. This study provides strong evidence that continuous relaxin intervention ameliorates cardiac fibrosis and apoptosis, attenuates remodeling of gap junction and focal heterogeneity of repolarization, and reduces vulnerability to tachyarrhythmias.

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Relaxin induces mast cell inhibition and reduces ventricular arrhythmias in a swine model of acute myocardial infarction

Abstract

Introduction

Section snippets

Surgical induction of cardiac IR

Results

Discussion

Acknowledgment

Trends Endocrinol Metab

Gen Pharmacol

Pharm Ther

Int Immunopharmacol

J Mol Cell Cardiol

Lancet

J Am Coll Cardiol

J Mol Cell Cardiol

Free Radic Biol Med

The influences of adrenotropic drugs and noradrenaline on the histamine release in cardiac anaphylaxis in vitro

J Physiol

Resident cardiac mast cells degranulate and release preformed TNF-alpha, initiating the cytokine cascade in experimental canine myocardial ischemia/reperfusion

Circulation

Acute reoxygenation injury in the isolated rat heart: role of resident cardiac mast cells

Circ Res

Histamine H1 and H2 receptor gene and protein levels are differentially expressed in the hearts of rodents and humans

J Pharmacol Exp Ther

Histamine and cardiac arrhythmias

Circ Res

Relaxin's physiological roles and other diverse actions

Endocr Rev

Emering role of relaxin in renal and cardiovascular function

Am J Physiol Integr Comp Physiol

Relaxin: a pregnancy hormone as a central player of body fluid and circulation homeostasis

Cell Mol Life Sci

Relaxin as a cardiovascular hormone. Physiology, pathophysiology and therapeutic promises

Cardiovasc Hematol Agents Med Chem (CHA-MC)