Relaxin antagonizes hypertrophy and apoptosis in neonatal rat cardiomyocytes

Relaxin agonists under preclinical and early clinical investigation for the treatment of heart failure

INTRODUCTION

Acute failure is a critical condition, encompassed by the sudden or progressive onset of symptoms or signs of congestion. The treatment strategies available are mainly supportive and do not improve mortality or long-term outcomes. Therefore, there is a need for alternative novel treatment strategies. In this narrative review, we explore the role of relaxin agonist as a potential therapeutic strategy in acute heart failure.

AREAS COVERED

We aim to provide an overview of the evidence of preclinical and clinical studies on relaxin as a treatment strategy for acute heart failure. Papers collected in this review are from original research and systematic reviews which have been filtered following Medline and Cochrane Library searches.

EXPERT OPINION

Relaxin has shown great potential in both preclinical and clinical studies due to its antifibrotic, anti-inflammatory, and vasodilatory effect on the heart. However, there has been mixed evidence from clinical trials involving relaxin which could be due to patient groups, investigation sites, trial design, and chance. Further studies should focus on developing biomarkers to identify specific population groups who are most likely to benefit from relaxin.

Therapeutic potential of relaxin or relaxin mimetics in managing cardiovascular complications of diabetes

Diabetes mellitus is a metabolic disease with an escalating global prevalence. Despite the abundance and relative efficacies of current therapeutic approaches, they primarily focus on attaining the intended glycaemic targets, but patients ultimately still suffer from various diabetes-associated complications such as retinopathy, nephropathy, cardiomyopathy, and atherosclerosis. There is a need to explore innovative and effective diabetic treatment strategies that not only address the condition itself but also combat its complications. One promising option is the reproductive hormone relaxin, an endogenous ligand of the RXFP1 receptor. Relaxin is known to exert beneficial actions on the cardiovascular system through its vasoprotective, anti-inflammatory and anti-fibrotic effects. Nevertheless, the native relaxin peptide exhibits a short biological half-life, limiting its therapeutic potential. Recently, several relaxin mimetics and innovative delivery technologies have been developed to extend its biological half-life and efficacy. The current review provides a comprehensive landscape of the cardiovascular effects of relaxin, focusing on its potential therapeutic applications in managing complications associated with diabetes. The latest advancements in the development of relaxin mimetics and delivery methods for the treatment of cardiometabolic disorders are also discussed.

Translational pharmacokinetic/pharmacodynamic model for mRNA-0184, an investigational therapeutic for the treatment of heart failure

Heart failure (HF) is a complex, progressive disorder that is associated with substantial morbidity and mortality on a global scale. Relaxin-2 is a naturally occurring hormone that may have potential therapeutic benefit for patients with HF. To investigate the therapeutic potential of relaxin in the treatment of patients with HF, mRNA-0184, a novel, investigational, lipid nanoparticle (LNP)-encapsulated mRNA therapy that encodes for human relaxin-2 fused to variable light chain kappa (Rel2-vlk) was developed. A translational semi-mechanistic population pharmacokinetic (PK)/pharmacodynamic (PD) model was developed using data from non-human primates at dose levels ranging from 0.15 to 1 mg/kg. The PK/PD model was able to describe the PK of Rel2-vlk mRNA and translated Rel2-vlk protein in non-human primates adequately with relatively precise estimates. The preclinical PK/PD model was then scaled allometrically to determine the human mRNA-0184 dose that would achieve therapeutic levels of Rel2-vlk protein expression in patients with stable HF with reduced ejection fraction. Model-based simulations derived from the scaled PK/PD model support the selection of 0.025 mg/kg as an appropriate starting human dose of mRNA-0184 to achieve average trough relaxin levels between 1 and 2.5 ng/mL, which is the potential exposure for cardioprotective action of relaxin.

Targeting G protein-coupled receptors for heart failure treatment

Heart failure remains a leading cause of morbidity and mortality worldwide. Current treatment for patients with heart failure include drugs targeting G protein-coupled receptors such as β-adrenoceptor antagonists (β-blockers) and angiotensin II type 1 receptor antagonists (or angiotensin II receptor blockers). However, many patients progress to advanced heart failure with persistent symptoms, despite treatment with available therapeutics that have been shown to reduce mortality and mortality. GPCR targets currently being explored for the development of novel heart failure therapeutics include adenosine receptor, formyl peptide receptor, relaxin/insulin-like family peptide receptor, vasopressin receptor, endothelin receptor and the glucagon-like peptide 1 receptor. Many GPCR drug candidates are limited by insufficient efficacy and/or dose-limiting unwanted effects. Understanding the current challenges hindering successful clinical translation and the potential to overcome existing limitations will facilitate the future development of novel heart failure therapeutics. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Cardiomyocyte-specific RXFP1 overexpression protects against pressure overload-induced cardiac dysfunction independently of relaxin

Heart failure (HF) prevalence is rising due to reduced early mortality and demographic change. Relaxin (RLN) mediates protective effects in the cardiovascular system through Relaxin-receptor 1 (RXFP1). Cardiac overexpression of RXFP1 with additional RLN supplementation attenuated HF in the pressure-overload transverse aortic constriction (TAC) model. Here, we hypothesized that robust transgenic RXFP1 overexpression in cardiomyocytes (CM) protects from TAC-induced HF even in the absence of RLN. Hence, transgenic mice with a CM-specific overexpression of human RXFP1 (hRXFP1tg) were generated. Receptor functionality was demonstrated by in vivo hemodynamics, where the administration of RLN induced positive inotropy strictly in hRXFP1tg. An increase in phospholamban-phosphorylation at serine 16 was identified as a molecular correlate. hRXFP1tg were protected from TAC without additional RLN administration, presenting not only less decline in systolic left ventricular (LV) function but also abrogated LV dilation and pulmonary congestion compared to WT mice. Molecularly, transgenic hearts exhibited not only a significantly attenuated fetal and fibrotic gene activation but also demonstrated less fibrotic tissue and CM hypertrophy in histological sections. These protective effects were evident in both sexes. Similar cardioprotective effects of hRXFP1tg were detectable in a RLN-knockout model, suggesting an alternative mechanism of receptor activation through intrinsic activity, alternative endogenous ligands or crosstalk with other receptors. In summary, CM-specific RXFP1 overexpression provides protection against TAC even in the absence of endogenous RLN. This suggests RXFP1 overexpression as a potential therapeutic approach for HF, offering baseline protection with optional RLN supplementation for specific activation.

Simultaneous late-gadolinium enhancement and T1 mapping of fibrosis and a novel cell-based combination therapy in hypertensive mice

Fibrosis is a hallmark of chronic hypertension and disrupts the viability of human bone marrow-derived mesenchymal stromal cells (BM-MSCs) post-transplantation. This study thus, determined whether the anti-fibrotic drug, serelaxin (RLX), could enhance the therapeutic effects of BM-MSCs or BM-MSC-derived exosomes (BM-MSC-EXO) in hypertensive mice. Left ventricular (LV) fibrosis in particular was assessed using conventional histological staining and non-invasive cardiac magnetic resonance imaging (CMRI). CMRI was employed using a novel magnetisation prepared 2 rapid acquisition gradient echo (MP2RAGE) sequence to simultaneously perform late gadolinium enhancement imaging and T1 mapping. Adult male C57BL/6 mice were uninephrectomised, received deoxycorticosterone acetate and saline to drink (1 K/DOCA/salt) for 21 days, whilst control mice were given normal drinking water for the same time-period. On day 14 post-injury, subgroups of 1 K/DOCA/salt-hypertensive mice were treated with RLX alone or in combination with BM-MSCs or BM-MSC-EXO; or the mineralocorticoid receptor antagonist, spironolactone. At day 21 post-injury, LV and kidney histopathology was assessed, whilst LV fibrosis and function were additionally analysed by CMRI and echocardiography. 1 K/DOCA/salt-hypertensive mice developed kidney tubular injury, inflammation, fibrosis, and more moderate LV hypertrophy, fibrosis and diastolic dysfunction. RLX and BM-MSCs combined provided optimal protection against these pathologies and significantly reduced picrosirius red-stained organ fibrosis and MP2RAGE analysis of LV fibrosis. A significant correlation between MP2RAGE analysis and histologically-stained interstitial LV fibrosis was detected. It was concluded that the MP2RAGE sequence enhanced the non-invasive CMRI detection of LV fibrosis. Furthermore, combining RLX and BM-MSCs may represent a promising treatment option for hypertensive cardiorenal syndrome.

Minimally invasive, sustained-release relaxin-2 microparticles reverse arthrofibrosis

Substantial advances in biotherapeutics are distinctly lacking for musculoskeletal diseases. Musculoskeletal diseases are biomechanically complex and localized, highlighting the need for novel therapies capable of addressing these issues. All frontline treatment options for arthrofibrosis, a debilitating musculoskeletal disease, fail to treat the disease etiology-the accumulation of fibrotic tissue within the joint space. For millions of patients each year, the lack of modern and effective treatment options necessitates surgery in an attempt to regain joint range of motion (ROM) and escape prolonged pain. Human relaxin-2 (RLX), an endogenous peptide hormone with antifibrotic and antifibrogenic activity, is a promising biotherapeutic candidate for musculoskeletal fibrosis. However, RLX has previously faltered through multiple clinical programs because of pharmacokinetic barriers. Here, we describe the design and in vitro characterization of a tailored drug delivery system for the sustained release of RLX. Drug-loaded, polymeric microparticles released RLX over a multiweek time frame without altering peptide structure or bioactivity. In vivo, intraarticular administration of microparticles in rats resulted in prolonged, localized concentrations of RLX with reduced systemic drug exposure. Furthermore, a single injection of RLX-loaded microparticles restored joint ROM and architecture in an atraumatic rat model of arthrofibrosis with clinically derived end points. Finally, confirmation of RLX receptor expression, RXFP1, in multiple human tissues relevant to arthrofibrosis suggests the clinical translational potential of RLX when administered in a sustained and targeted manner.

Mesenchymal Stem Cells May Alleviate the Intervertebral Disc Degeneration by Reducing the Oxidative Stress in Nucleus Pulposus Cells

Background

Stem cell therapy is a promising therapeutic modality for intervertebral disc degeneration (IDD). Oxidative stress is a vital contributor to the IDD; however, the definite role of oxidative stress in stem cell therapy for IDD remains obscure. The aim of this study was to determine the vital role of oxidative stress-related differentially expressed genes (OSRDEGs) in degenerative NPCs cocultured with mesenchymal stem cells (MSCs).

Methods

A series of bioinformatic methods were used to calculate the oxidative stress score and autophagy score, identify the OSRDEGs, conduct the function enrichment analysis and protein-protein interaction (PPI) analysis, build the relevant competing endogenous RNA (ceRNA) regulatory networks, and explore the potential association between oxidative stress and autophagy in degenerative NPCs cocultured with MSCs.

Results

There was a significantly different oxidative stress score between NPC/MSC samples and NPC samples (p < 0.05). Forty-one OSRDEGs were selected for the function enrichment and PPI analyses. Ten hub OSRDEGs were obtained according to the PPI score, including JUN, CAT, PTGS2, TLR4, FOS, APOE, EDN1, TXNRD1, LRRK2, and KLF2. The ceRNA regulatory network, which contained 17 DElncRNAs, 240 miRNAs, and 10 hub OSRDEGs, was constructed. Moreover, a significant relationship between the oxidative stress score and autophagy score was observed (p < 0.05), and 125 significantly related gene pairs were obtained (|r| > 0.90, p < 0.05).

Conclusion

Stem cell therapy might repair the degenerative IVD via reducing the oxidative stress through the ceRNA regulatory work and restoration of autophagy in degenerative NPCs. This research could provide new insights into the mechanism research of stem cell therapy for IDD and potential therapeutic targets in the IDD treatment.

Relaxin does not prevent development of hypoxia-induced pulmonary edema in rats

Acute hypoxia impairs left ventricular (LV) inotropic function and induces development of pulmonary edema (PE). Enhanced and uneven hypoxic pulmonary vasoconstriction is an important pathogenic factor of hypoxic PE. We hypothesized that the potent vasodilator relaxin might reduce hypoxic pulmonary vasoconstriction and prevent PE formation. Furthermore, as relaxin has shown beneficial effects in acute heart failure, we expected that relaxin might also improve LV inotropic function in hypoxia. Forty-two rats were exposed over 24 h to normoxia or hypoxia (10% N₂ in O₂). They were infused with either 0.9% NaCl solution (normoxic/hypoxic controls) or relaxin at two doses (15 and 75 μg kg⁻¹ day⁻¹). After 24 h, hemodynamic measurements and bronchoalveolar lavage were performed. Lung tissue was obtained for histological and immunohistochemical analyses. Hypoxic control rats presented significant depression of LV systolic pressure by 19% and of left and right ventricular contractility by about 40%. Relaxin did not prevent the hypoxic decrease in LV inotropic function, but re-increased right ventricular contractility. Moreover, hypoxia induced moderate interstitial PE and inflammation in the lung. Contrasting to our hypothesis, relaxin did not prevent hypoxia-induced pulmonary edema and inflammation. In hypoxic control rats, PE was similarly distributed in the apical and basal lung lobes. In relaxin-treated rats, PE index was 35–40% higher in the apical than in the basal lobe, which is probably due to gravity effects. We suggest that relaxin induced exaggerated vasodilation, and hence pulmonary overperfusion. In conclusion, the results show that relaxin does not prevent but rather may aggravate PE formation.

Relaxin-2 as a Potential Biomarker in Cardiovascular Diseases

The pleiotropic hormone relaxin-2 plays a pivotal role in the physiology and pathology of the cardiovascular system. Relaxin-2 exerts relevant regulatory functions in cardiovascular tissues through the specific receptor relaxin family peptide receptor 1 (RXFP1) in the regulation of cardiac metabolism; the induction of vasodilatation; the reversion of fibrosis and hypertrophy; the reduction of inflammation, oxidative stress, and apoptosis; and the stimulation of angiogenesis, with inotropic and chronotropic effects as well. Recent preclinical and clinical outcomes have encouraged the potential use of relaxin-2 (or its recombinant form, known as serelaxin) as a therapeutic strategy during cardiac injury and/or in patients suffering from different cardiovascular disarrangements, especially heart failure. Furthermore, relaxin-2 has been proposed as a promising biomarker of cardiovascular health and disease. In this review, we emphasize the relevance of the endogenous hormone relaxin-2 as a useful diagnostic biomarker in different backgrounds of cardiovascular pathology, such as heart failure, atrial fibrillation, myocardial infarction, ischemic heart disease, aortic valve disease, hypertension, and atherosclerosis, which could be relevant in daily clinical practice and could contribute to comprehending the specific role of relaxin-2 in cardiovascular diseases.

Relaxin/serelaxin for cardiac dysfunction and heart failure in hypertension

The pregnancy related hormone relaxin is produced throughout the reproductive system. However, relaxin also has important cardiovascular effects as part of the adaptation that the cardiovascular system undergoes in response to the extra demands of pregnancy. These effects are primarily mediated by the relaxin family peptide receptor 1, which is one of four known relaxin receptors. The effects of relaxin on the cardiovascular system during pregnancy, as well as its anti-fibrotic and anti-inflammatory properties, have led to extensive studies into the potential of relaxin therapy as an approach to treat heart failure. Cardiomyocytes, cardiac fibroblasts, and endothelial cells all possess relaxin family peptide receptor 1, allowing for direct effects of therapeutic relaxin on the heart. Many pre-clinical animal studies have demonstrated a beneficial effect of exogenous relaxin on adverse cardiac remodeling including inflammation, fibrosis, cardiomyocyte hypertrophy and apoptosis, as well as effects on cardiac contractile function. Despite this, clinical studies have yielded disappointing results for the synthetic seralaxin, even though seralaxin was well tolerated. This article will provide background on relaxin in the context of normal physiology, as well as the role of relaxin in pregnancy-related adaptations of the cardiovascular system. We will also present evidence from pre-clinical animal studies that demonstrate the potential benefits of relaxin therapy, as well as discussing the results from clinical trials. Finally, we will discuss possible reasons for the failure of these clinical trials as well as steps being taken to potentially improve relaxin therapy for heart failure.

Relaxin as an anti-fibrotic treatment: Perspectives, challenges and future directions

Fibrosis refers to the scarring and hardening of tissues, which results from a failed immune system-coordinated wound healing response to chronic organ injury and which manifests from the aberrant accumulation of various extracellular matrix components (ECM), primarily collagen. Despite being a hallmark of prolonged tissue damage and related dysfunction, and commonly associated with high morbidity and mortality, there are currently no effective cures for its regression. An emerging therapy that meets several criteria of an effective anti-fibrotic treatment, is the recombinant drug-based form of the human hormone, relaxin (also referred to as serelaxin, which is bioactive in several other species). This review outlines the broad anti-fibrotic and related organ-protective roles of relaxin, mainly from studies conducted in preclinical models of ageing and fibrotic disease, including its ability to ameliorate several aspects of fibrosis progression and maturation, from immune cell infiltration, pro-inflammatory and pro-fibrotic cytokine secretion, oxidative stress, organ hypertrophy, cell apoptosis, myofibroblast differentiation and ECM production, to its ability to facilitate established ECM degradation. Studies that have compared and/or combined these therapeutic effects of relaxin with current standard of care medication have also been discussed, along with the main challenges that have hindered the translation of the anti-fibrotic efficacy of relaxin to the clinic. The review then outlines the future directions as to where scientists and several pharmaceutical companies that have recognized the therapeutic potential of relaxin are working towards, to progress its development as a treatment for human patients suffering from various fibrotic diseases.

Anti-apoptotic and Matrix Remodeling Actions of a Small Molecule Agonist of the Human Relaxin Receptor, ML290 in Mice With Unilateral Ureteral Obstruction

Diseases, such as diabetes and hypertension, often lead to chronic kidney failure. The peptide hormone relaxin has been shown to have therapeutic effects in various organs. In the present study, we tested the hypothesis that ML290, a small molecule agonist of the human relaxin receptor (RXFP1), is able to target the kidney to remodel the extracellular matrix and reduce apoptosis induced by unilateral ureteral obstruction (UUO). UUO was performed on the left kidney of humanized RXFP1 mice, where the right kidneys served as contralateral controls. Mice were randomly allocated to receive either vehicle or ML290 (30 mg/kg) via daily intraperitoneal injection, and kidneys were collected for apoptosis, RNA, and protein analyses. UUO significantly increased expression of pro-apoptotic markers in both vehicle- and ML290-treated mice when compared to their contralateral control kidneys. Specifically, Bax expression and Erk1/2 activity were upregulated, accompanied by an increase of TUNEL-positive cells in the UUO kidneys. Additionally, UUO induced marked increase in myofibroblast differentiation and aberrant remodeling on the extracellular matrix. ML290 suppressed these processes by promoting a reduction of pro-apoptotic, fibroblastic, and inflammatory markers in the UUO kidneys. Finally, the potent effects of ML290 to remodel the extracellular matrix were demonstrated by its ability to reduce collagen gene expression in the UUO kidneys. Our data indicate that daily administration of ML290 has renal protective effects in the UUO mouse model, specifically through its anti-apoptotic and extracellular matrix remodeling properties.

Relaxin peptides reduce cellular damage in cultured brain slices exposed to transient oxygen–glucose deprivation: an effect mediated by nitric oxide

The effect of treatment with human relaxins on cell death was studied in oxygen- and glucose-deprived brain slices. In addition, involvement of nitric oxide and the relaxin receptor, RXFP3, was studied. Brain slices ( n = 12–18/group) were cultured under standard conditions for two weeks and then exposed to: ( i) an oxygenated balanced salt solution, ( ii) a deoxygenated, glucose-free balanced salt solution (OGD media), or ( iii) OGD media containing 10−7 mol/L H2 relaxin, 10−7 mol/L H2 relaxin with 50 μmol/L L-NIL, 10−7 mol/L H3 relaxin, or 10−7 mol/L H3 relaxin with 50 μmol/L L-NIL. Cell death was assessed using propidium iodide fluorescence. In a separate experiment, 10−5 mol/L R3 B1-22R (an antagonist of RXFP3) was added to both H2 and H3 relaxin treatments. H2 and H3 relaxin treatment reduced cell damage or death in OGD slices and L-NIL partially attenuated the effect of H3 relaxin. Antagonism of RXFP3 blocked the effect of H3 but not H2 relaxin. These data increase our understanding of the role of relaxin ligands and their receptors in protecting tissues throughout the body from ischemia and reperfusion injury.

Human Relaxin-2 (Serelaxin) Attenuates Oxidative Stress in Cardiac Muscle Cells Exposed In Vitro to Hypoxia-Reoxygenation. Evidence for the Involvement of Reduced Glutathione Up-Regulation

Serelaxin (RLX) designates the pharmaceutical form of the human natural hormone relaxin-2 that has been shown to markedly reduce tissue and cell damage induced by hypoxia and reoxygenation (HR). The evidence that RLX exerts similar protective effects on different organs and cells at relatively low, nanomolar concentrations suggests that it specifically targets a common pathogenic mechanism of HR-induced damage, namely oxidative stress. In this study we offer experimental evidence that RLX (17 nmol L-1), added to the medium of HR-exposed H9c2 rat cardiac muscle cells, significantly reduces cell oxidative damage, mitochondrial dysfunction and apoptosis. These effects appear to rely on the up-regulation of the cellular availability of reduced glutathione (GSH), a ubiquitous endogenous antioxidant metabolite. Conversely, superoxide dismutase activity was not influenced by RLX, which, however, was not endowed with chemical antioxidant properties. Taken together, these findings verify the major pharmacological role of RLX in the protection against HR-induced oxidative stress, and shed first light on its mechanisms of action.

The effect of nutraceuticals on multiple signaling pathways in cardiac fibrosis injury and repair

Cardiac fibrosis is one of the most common pathological conditions caused by different heart diseases, including myocardial infarction and diabetic cardiomyopathy. Cardiovascular disease is one of the major causes of mortality worldwide. Cardiac fibrosis is caused by different processes, including inflammatory reactions and oxidative stress. The process of fibrosis begins by changing the balance between production and destruction of extracellular matrix components and stimulating the proliferation and differentiation of cardiac fibroblasts. Many studies have focused on finding drugs with less adverse effects for the treatment of cardiovascular disease. Some studies show that nutraceuticals are effective in preventing and treating diseases, including cardiovascular disease, and that they can reduce the risk. However, big clinical studies to prove the therapeutic properties of all these substances and their adverse effects are lacking so far. Therefore, in this review, we tried to summarize the knowledge on pathways and mechanisms of several nutraceuticals which have shown their usefulness in the prevention of cardiac fibrosis.

Serelaxin activates eNOS, suppresses inflammation, attenuates developmental delay and improves cognitive functions of neonatal rats after germinal matrix hemorrhage

Germinal matrix hemorrhage (GMH) is a detrimental form of neonatal CNS injury. Following GMH-mediated eNOS inhibition, inflammation arises, contributing to GMH-induced brain injury. We investigated the beneficial effects of Serelaxin, a clinical tested recombinant Relaxin-2 protein, on brain injury after GMH in rats. We investigated whether effects of Serelaxin are mediated by its ability to activate the GMH-suppressed eNOS pathway resulting in attenuation of inflammatory marker overproduction. GMH was induced by intraparenchymal injection of bacterial collagenase (0.3U). Seven day old Sprague–Dawley rat pups (P7) were used (n = 63). GMH animals were divided in vehicle or serelaxin treated (3 µg once, 30 µg once, 30 µg multiple, i.p., starting 30 after GMH and then daily). Sham operated animals were used. We monitored the developmental profile working memory and spatial function (T-maze and open field test respectively). At day 28, all rats underwent MRI-scans for assessment of changes in cortical thickness and white matter loss. Effects of Serelaxin on eNOS pathway activation and post-GMH inflammation were evaluated. We demonstrated that Serelaxin dose-dependently attenuated GMH-induced developmental delay, protected brain and improved cognitive functions of rats after GMH. That was associated with the decreased post-GMH inflammation, mediated at least partly by amelioration of GMH-induced eNOS inhibition.

Understanding relaxin signalling at the cellular level

The peptide hormone relaxin mediates many biological actions including anti-fibrotic, vasodilatory, angiogenic, anti-inflammatory, anti-apoptotic, and organ protective effects across a range of tissues. At the cellular level, relaxin binds to the G protein-coupled receptor relaxin family peptide receptor 1 (RXFP1) to activate a variety of downstream signal transduction pathways. This signalling cascade is complex and also varies in diverse cellular backgrounds. Moreover, RXFP1 signalling shows crosstalk with other receptors to mediate some of its physiological functions. This review summarises known signalling pathways induced by acute versus chronic treatment with relaxin across a range of cell types, it describes RXFP1 crosstalk with other receptors, signalling pathways activated by other ligands targeting RXFP1, and it also outlines physiological relevance of RXFP1 signalling outputs. Comprehensive understanding of the mechanism of relaxin actions in fibrosis, vasodilation, as well as organ protection, will further support relaxin's clinical potential.

Relaxin-2 for heart failure with preserved ejection fraction (HFpEF): Rationale for future clinical trials

Heart Failure with preserved Ejection Fraction (HFpEF), a distinct sub-entity of chronic heart failure characterized by generalized inflammatory non-compliance of the cardio-vascular system, is associated with high mortality and still an unmet medical need. Many novel and promising therapeutic approaches have failed in large studies. This review focuses on basic research, pre-clinical and clinical findings that may account for the potential benefit of relaxin-2 in HFpEF. The peptide combines short-term hemodynamic advantages, such as moderate blood pressure decline and functional endothelin-1 antagonism, with a wealth of protective effects harboring long-term benefits, such as anti-inflammatory, anti-fibrotic, and anti-oxidative actions. These pleiotropic effects are exerted through a complex and intricate signaling cascade involving the relaxin-family peptide receptor-1, the glucocorticoid receptor, the nitric oxide system, and a cell type-dependent variety of down-stream mediators.

Relaxin as a Therapeutic Target for the Cardiovascular Complications of Diabetes

Cardiovascular complications are the major cause of mortality in patients with diabetes. This is closely associated with both macrovascular and microvascular complications of diabetes, which lead to organ injuries in diabetic patients. Previous studies have consistently demonstrated the beneficial effects of relaxin treatment for protection of the vasculature, with evidence of antioxidant and anti-remodeling actions. Relaxin enhances nitric oxide, prostacyclin and endothelium-derived hyperpolarization (EDH)-type-mediated relaxation in various vascular beds. These effects of relaxin on the systemic vasculature, coupled with its cardiac actions, reduce pulmonary capillary wedge pressure and pulmonary artery pressure. This results in an overall decrease in systemic and pulmonary vascular resistance in heart failure patients. The anti-fibrotic actions of relaxin are well established, a desirable property in the context of diabetes. Further, relaxin ameliorates diabetic wound healing, with accelerated angiogenesis and vasculogenesis. Relaxin-mediated stimulation of vascular endothelial growth factor (VEGF) and stromal cell-derived factor 1-α, as well as regulation of metalloproteinase expression, ameliorates cardiovascular fibrosis in diabetic mice. In the heart, relaxin is a cardioprotective molecule in several experimental animal models, exerting anti-fibrotic, anti-hypertrophy and anti-apoptotic effects in diabetic pathologies. Collectively, these studies provide a foundation to propose the therapeutic potential for relaxin as an adjunctive agent in the prevention or treatment of diabetes-induced cardiovascular complications. This review provides a comprehensive overview of the beneficial effects of relaxin, and identifies its therapeutic possibilities for alleviating diabetes-related cardiovascular injury.

Relaxin activates AMPK-AKT signaling and increases glucose uptake by cultured cardiomyocytes

PURPOSE

Many evidences show that the hormone relaxin plays a pivotal role in the physiology and pathology of the cardiovascular system. This pleiotropic hormone exerts regulatory functions through specific receptors in cardiovascular tissues: in experimental animal models it was shown to induce coronary vasodilation, prevent cardiac damage induced by ischemia/reperfusion and revert cardiac hypertrophy and fibrosis. A tight relationship between this hormone and important metabolic pathways has been suggested, but it is at present unknown if relaxin could regulate cardiac metabolism. Our aim was to study the possible effects of relaxin on cardiomyocyte metabolism.

METHODS

Neonatal rat cardiomyocytes were treated with relaxin and (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assays (MTT) were performed to assess metabolic activity; while 2-deoxy-D-[³H] glucose and BODIPY-labelled fatty acid incorporations were analyzed to measure glucose and fatty acid uptakes, and western blot was utilized to study the intracellular signaling pathways activated by the hormone.

RESULTS

We observed that relaxin at 10 ng/ml was able to increase the level of metabolic activity of cultured neonatal rat cardiomyocytes; the rate of 2-deoxy-D-[³H]glucose incorporation demonstrated that relaxin also induced an increase in glucose uptake. First evidence is also offered that relaxin can activate the master energy sensor and regulator AMPK in cardiomyocytes. Moreover, the treatment of cardiomyocytes with relaxin also induced dose-dependent increases in ERK1/2, AKT, and AS160 phosphorylation. That raise in AS160 phosphorylation induced by relaxin was prevented by the pretreatment with AMPK and AKT pathways inhibitors, indicating that both molecules play important roles in the relaxin effects reported.

CONCLUSION

Relaxin can regulate cardiomyocyte metabolism and activate AMPK, the central sensor of energy status that maintains cellular energy homeostasis, and also ERK and AKT, two molecular sensing nodes that coordinate dynamic responses of the cell's metabolic responses.

Relaxin ameliorates high glucose-induced cardiomyocyte hypertrophy and apoptosis via the Notch1 pathway

The present study aimed to investigate the role of relaxin (RLX) on high glucose (HG)-induced cardiomyocyte hypertrophy and apoptosis, as well as the possible molecular mechanism. H9c2 cells were exposed to 33 mmol/l HG with or without RLX (100 nmol/ml). Cell viability, apoptosis, oxidative stress, cell hypertrophy and the levels of Notch1, hairy and enhancer of split 1 (hes1), atrial natriuretic polypeptide (ANP), brain natriuretic peptide (BNP), manganese superoxide dismutase (MnSOD), cytochrome C and caspase-3 were assessed in cardiomyocytes. Compared with the HG group, the viability of H9c2 cells was increased by RLX in a time- and dose-dependent manner, and was accompanied with a significant reduction in apoptosis. Furthermore, RLX significantly suppressed the formation of reactive oxygen species and malondialdehyde, and enhanced the activity of SOD. In addition, the levels of ANP, BNP, cytochrome C and caspase-3 were increased and Notch1, hes1 and MnSOD were inhibited in the HG group compared with those in the normal group. However, the Notch inhibitor DAPT almost abolished the protective effects of RLX. These results suggested that RLX protected cardiomyocytes from HG-induced hypertrophy and apoptosis partly through a Notch1-dependent pathway, which may be associated with reducing oxidative stress.

Relaxin-2 in Cardiometabolic Diseases: Mechanisms of Action and Future Perspectives

Despite the great effort of the medical community during the last decades, cardiovascular diseases remain the leading cause of death worldwide, increasing their prevalence every year mainly due to our new way of life. In the last years, the study of new hormones implicated in the regulation of energy metabolism and inflammation has raised a great interest among the scientific community regarding their implications in the development of cardiometabolic diseases. In this review, we will summarize the main actions of relaxin, a pleiotropic hormone that was previously suggested to improve acute heart failure and that participates in both metabolism and inflammation regulation at cardiovascular level, and will discuss its potential as future therapeutic target to prevent/reduce cardiovascular diseases.

Alterations of relaxin and its receptor system components in experimental diabetic cardiomyopathy rats

High glucose induces apoptosis of cardiomyocytes and fibrosis of cardiac fibroblasts, contributing to diabetic cardiomyopathy. In this work, we explore the production of relaxin alterations and the significance of their receptor system components in the hearts of experimental diabetic cardiomyopathy rats. We measured rat relaxin-1 (equivalent to human relaxin-2), relaxin-3, RXFP1 and RXFP3 mRNA expression in the hearts of experimental diabetic cardiomyopathy rats. Neonatal rat ventricular myocytes (NRVMs) and cardiac fibroblasts were treated with 5.5 mmol/l normal glucose (NG) and 33 mmol/l high glucose (HG) for 0, 6, 12, 24, 48 and 72 h. Rat relaxin-1, relaxin-3, RXFP1 and RXFP3 mRNA expression were determined by real-time PCR. In the present study, we offer the first evidence that Relaxin-1 mRNA significantly increased and Relaxin-3 mRNA expression decreased at 4 and 8 weeks after STZ in the hearts of diabetic rats. In addition, significant down regulation of the mRNA expression of RXFP1 and RXFP3 was observed at 4 w after STZ; however, the mRNA expression levels of RXFP1 and RXFP3 were increased at 8 weeks after STZ. Apoptotic NRVMs induced by high glucose generate a decreased level of relaxin-1 and RXFP1. In HG-administered cardiac fibroblasts, Relaxin-1 mRNA was significantly increased and relaxin-3 mRNA was significantly decreased. Additionally, the mRNA expression of RXFP1 was decreased, and the mRNA expression of RXFP3 was increased. This results showed that an important role of relaxin-2, relaxin-3 and their receptors system in the regulation of diabetic cardiomyopathy.

Anti-fibrotic actions of relaxin

Fibrosis refers to the hardening or scarring of tissues that usually results from aberrant wound healing in response to organ injury, and its manifestations in various organs have collectively been estimated to contribute to around 45-50% of deaths in the Western world. Despite this, there is currently no effective cure for the tissue structural and functional damage induced by fibrosis-related disorders. Relaxin meets several criteria of an effective anti-fibrotic based on its specific ability to inhibit pro-fibrotic cytokine and/or growth factor-mediated, but not normal/unstimulated, fibroblast proliferation, differentiation and matrix production. Furthermore, relaxin augments matrix degradation through its ability to up-regulate the release and activation of various matrix-degrading matrix metalloproteinases and/or being able to down-regulate tissue inhibitor of metalloproteinase activity. Relaxin can also indirectly suppress fibrosis through its other well-known (anti-inflammatory, antioxidant, anti-hypertrophic, anti-apoptotic, angiogenic, wound healing and vasodilator) properties. This review will outline the organ-specific and general anti-fibrotic significance of exogenously administered relaxin and its mechanisms of action that have been documented in various non-reproductive organs such as the cardiovascular system, kidney, lung, liver, skin and tendons. In addition, it will outline the influence of sex on relaxin's anti-fibrotic actions, highlighting its potential as an emerging anti-fibrotic therapeutic.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Relaxin Attenuates Contrast-Induced Human Proximal Tubular Epithelial Cell Apoptosis by Activation of the PI3K/Akt Signaling Pathway In Vitro

Background. Contrast-induced acute kidney injury (CI-AKI) is one of the main causes of iatrogenic acute kidney injury (AKI); however, therapeutic strategies for AKI remain limited. This study aims to explore the effect of relaxin (RLX) on contrast-induced HK-2 apoptosis and its underlying mechanisms. Methods. Renal tubular epithelial cells (HK-2) were incubated either with or without ioversol, human H2 relaxin, and LY294002 (the inhibitor of the PI3K/Akt signal pathway). Cell viability was evaluated with a CCK-8 assay. Apoptotic morphologic alterations were observed using the Hoechst 33342 staining method. Apoptosis was detected with Annexin V staining. Western blot analysis was employed to measure the expression of pAkt (S473), Akt, cleaved caspase-3, Bcl-2, Bax, and actin proteins. Results. Ioversol reduced the viability of HK-2 cells. Western blotting results revealed decreased expression of phosphorylated Akt in cells treated with ioversol. The activities of caspase-3 and Bax protein increased, while the expression of Bcl-2 protein decreased. As a result, the Bax/Bcl-2 ratio increased after treatment with ioversol. These effects were reversed when HK-2 cells were cotreated with RLX. However, with preadministration of PI3K/Akt pathway inhibitor LY294002, the effect of RLX was blocked. Conclusion. Our study demonstrates that relaxin attenuates ioversol induced cell apoptosis via activation of the PI3K/Akt signaling pathway, suggesting that RLX might play a protective role in the treatment of CI-AKI.

Relaxin confers cytotrophoblast protection from hypoxia-reoxygenation injury through the phosphatidylinositol 3-kinase-Akt/protein kinase B cell survival pathway

Preeclampsia is a hypertensive syndrome that manifests after 20 wk of gestation. Contemporary understanding of the maternal-fetal interface in preeclampsia suggests a major role for placental oxidative stress resulting from ischemia-reperfusion injury. We hypothesized that the pregnancy hormone relaxin would reduce cytotrophoblast apoptosis and necrosis (aponecrosis) and, hence, the export of placental debris into the maternal circulation. If so, then relaxin might be employed as a therapeutic intervention to diminish the activation of the maternal systemic inflammatory response central to the development of clinical disease. HTR-8/SVneo cells, a model for first trimester extravillous trophoblast, were subjected to serum deprivation and hypoxia or hypoxia-reoxygenation. The cells were treated with recombinant human relaxin or vehicle and apoptosis and/or necrosis evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), CellEvent Caspase-3/7 and SYTOX AADvanced kit, and propidium iodide staining as determined by fluorescence microscopy or flow cytometry. To interrogate mechanisms of relaxin cytoprotection, HTR-8/SVneo cells were pretreated with pharmacological inhibitors of PI3-kinase LY294004, Akt/PKB MK-2206, or DMSO vehicle. HTR-8/SVneo cell identity was first confirmed by RT-PCR. The cells expressed placental alkaline phosphatase, aromatase, and human leukocyte antigen G. In addition, the cells expressed the relaxin receptor RXFP1 as well as H1 and H2 relaxins. Serum deprivation and hypoxia increased apoptotic cell death in HTR-8/SVneo cells, which was significantly ameliorated by concurrent treatment with relaxin. Serum deprivation and hypoxia-reoxygenation increased necrotic cell death in HTR-8/SVneo cells, which was also significantly rescued by concurrent treatment with relaxin. Pretreatment with LY294002 or MK-2206, to inhibit the phosphatidylinositol 3-kinase-Akt/protein kinase B cell survival pathway, significantly blunted the cytoprotective effect of relaxin. We demonstrated trophoblast cytoprotection by intervention with supraphysiological concentrations of relaxin, a process in part mediated through the PI3-kinase-Akt/PKB cell survival pathway. These results provide further rationale for clinical investigation of relaxin as a potential therapeutic in preeclampsia.

Serelaxin treatment reverses vascular dysfunction and left ventricular hypertrophy in a mouse model of Type 1 diabetes

Serelaxin prevents endothelial dysfunction in the mouse aorta ex vivo and inhibits apoptosis in cardiomyocytes under acute hyperglycaemia. Less is known about the effects of serelaxin in an in vivo mouse model of diabetes. Therefore, we tested the hypothesis in streptozotocin (STZ)-treated mice that serelaxin is able to reverse diabetes-induced vascular dysfunction and cardiac remodelling. Mice were divided into citrate buffer + placebo, STZ + placebo and STZ + serelaxin (0.5 mg/kg/d, 2 weeks) groups. After 12 weeks of diabetes, sensitivity to the endothelium-dependent agonist acetylcholine (ACh) was reduced in the mesenteric artery. This was accompanied by an enhanced vasoconstrictor prostanoid contribution and a decrease in endothelium-derived hyperpolarisation (EDH)-mediated relaxation. Serelaxin restored endothelial function by increasing nitric oxide (NO)-mediated relaxation but not EDH. It also normalised the contribution of vasoconstrictor prostanoids to endothelial dysfunction and suppressed diabetes-induced hyper-responsiveness of the mesenteric artery to angiotensin II. Similarly, diabetes reduced ACh-evoked NO-mediated relaxation in the aorta which was reversed by serelaxin. In the left ventricle, diabetes promoted apoptosis, hypertrophy and fibrosis; serelaxin treatment reversed this ventricular apoptosis and hypertrophy, but had no effect on fibrosis. In summary, serelaxin reversed diabetes-induced endothelial dysfunction by enhancing NO-mediated relaxation in the mouse vasculature and attenuating left ventricular hypertrophy and apoptosis.

Effects of relaxin on cardiac fibrosis, apoptosis, and tachyarrhythmia in rats with myocardial infarction

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 (0.5mg/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.

The actions of relaxin on the human cardiovascular system

The insulin-like peptide relaxin, originally identified as a hormone of pregnancy, is now known to exert a range of pleiotropic effects including vasodilatory, anti-fibrotic, angiogenic, anti-apoptotic and anti-inflammatory effects in both males and females. Relaxin produces these effects by binding to a cognate receptor RXFP1 and activating a variety of signalling pathways including cAMP, cGMP and MAPKs as well as by altering gene expression of TGF-β, MMPs, angiogenic growth factors and endothelin receptors. The peptide has been shown to be effective in halting or reversing many of the adverse effects including fibrosis in animal models of cardiovascular disease including ischaemia/reperfusion injury, myocardial infarction, hypertensive heart disease and cardiomyopathy. Relaxin given to humans is safe and produces favourable haemodynamic changes. Serelaxin, the recombinant form of relaxin, is now in extended phase III clinical trials for the treatment of acute heart failure. Previous clinical studies indicated that a 48 h infusion of relaxin improved 180 day mortality, yet the mechanism underlying this effect is not clear. This article provides an overview of the cellular mechanism of effects of relaxin and summarizes its beneficial actions in animal models and in the clinic. We also hypothesize potential mechanisms for the clinical efficacy of relaxin, identify current knowledge gaps and suggest new ways in which relaxin could be useful therapeutically.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

G-Protein-coupled receptors as potential drug candidates in preeclampsia: targeting the relaxin/insulin-like family peptide receptor 1 for treatment and prevention

BACKGROUND

Important roles for G-protein-coupled receptors (GPCRs) have been identified in the maternal physiological adaptations to pregnancy and in the pathogenesis of preeclampsia. On this basis, GPCRs are potential therapeutic targets for preeclampsia.

OBJECTIVES AND RATIONALE

In this review, vasopressin and apelin are initially considered in this context before the focus on the hormone relaxin and its cognate receptor, the relaxin/insulin-like family peptide receptor 1 (RXFP1). Based on both compelling scientific rationale and a promising safety profile, the relaxin ligand-receptor system is comprehensively evaluated as a potential therapeutic endpoint in preeclampsia.

SEARCH METHODS

The published literature relating to the topic was searched through January 2016 using PubMed.

OUTCOMES

Relaxin is a peptide hormone secreted by the corpus luteum; it circulates in the luteal phase and during pregnancy. Activation of RXFP1 is vasodilatory; thus, relaxin supplementation is expected to at least partly restore the fundamental vasodilatory changes of normal pregnancy, thereby alleviating maternal organ hypoperfusion, which is a major pathogenic manifestation of severe preeclampsia. Specifically, by exploiting its pleiotropic hemodynamic attributes in preeclampsia, relaxin administration is predicted to (i) reverse robust arterial myogenic constriction; (ii) blunt systemic and renal vasoconstriction in response to activation of the angiotensin II receptor, type 1; (iii) mollify the action of endogenous vasoconstrictors on uterine spiral arteries with failed remodeling and retained smooth muscle; (iv) increase arterial compliance; (v) enhance insulin-mediated glucose disposal by promoting skeletal muscle vasodilation and (vi) mobilize and activate bone marrow-derived angiogenic progenitor cells, thereby repairing injured endothelium and improving maternal vascularity in organs such as breast, uterus, pancreas, skin and fat. By exploiting its pleiotropic molecular attributes in preeclampsia, relaxin supplementation is expected to (i) enhance endothelial nitric oxide synthesis and bioactivity, as well as directly reduce vascular smooth muscle cytosolic calcium, thus promoting vasodilation; (ii) improve the local angiogenic balance by augmenting arterial vascular endothelial and placental growth factor (VEGF and PLGF) activities; (iii) ameliorate vascular inflammation; (iv) enhance placental peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PCG1α) expression, and hence, peroxisome proliferator-activated receptor gamma (PPAR-γ) activity and (v) confer cytotrophoblast and endothelial cytoprotection. Insofar as impaired endometrial maturation (decidualization) predisposes to the development of preeclampsia, relaxin administration in the late secretory phase and during early pregnancy would be anticipated to improve decidualization, and hence trophoblast invasion and spiral artery remodeling, thereby reducing the risk of preeclampsia. Relaxin has a favorable safety profile both in the non-pregnant condition and during pregnancy.

WIDER IMPLICATIONS

There is a strong scientific rationale for RXFP1 activation in severe preeclampsia by administration of relaxin, relaxin analogs or small molecule mimetics, in order to mollify the disease pathogenesis for safe prolongation of pregnancy, thus allowing time for more complete fetal maturation, which is a primary therapeutic endpoint in treating the disease. In light of recent data implicating deficient or defective decidualization as a potential etiological factor in preeclampsia and the capacity of relaxin to promote endometrial maturation, the prophylactic application of relaxin to reduce the risk of preeclampsia is a plausible therapeutic approach to consider. Finally, given its pleiotropic and beneficial attributes particularly in the cardiovascular system, relaxin, although traditionally considered as a 'pregnancy' hormone, is likely to prove salutary for several disease indications in the non-pregnant population.

Combining an epithelial repair factor and anti-fibrotic with a corticosteroid offers optimal treatment for allergic airways disease

BACKGROUND AND PURPOSE

We evaluated the extent to which individual versus combination treatments that specifically target airway epithelial damage [trefoil factor-2 (TFF2)], airway fibrosis [serelaxin (RLX)] or airway inflammation [dexamethasone (DEX)] reversed the pathogenesis of chronic allergic airways disease (AAD).

EXPERIMENTAL APPROACH

Following induction of ovalbumin (OVA)-induced chronic AAD in 6–8 week female Balb/c mice, animals were i.p. administered naphthalene (NA) on day 64 to induce epithelial damage, then received daily intranasal administration of RLX (0.8 mg·mL(−1)), TFF2 (0.5 mg·mL(−1)), DEX (0.5 mg·mL(−1)), RLX + TFF2 or RLX + TFF2 + DEX from days 67–74. On day 75, lung function was assessed by invasive plethysmography, before lung tissue was isolated for analyses of various measures. The control group was treated with saline + corn oil (vehicle for NA).

KEY RESULTS

OVA + NA-injured mice demonstrated significantly increased airway inflammation, airway remodelling (AWR) (epithelial damage/thickness; subepithelial myofibroblast differentiation, extracellular matrix accumulation and fibronectin deposition; total lung collagen concentration), and significantly reduced airway dynamic compliance (cDyn). RLX + TFF2 markedly reversed several measures of OVA + NA-induced AWR and normalized the reduction in cDyn. The combined effects of RLX + TFF2 + DEX significantly reversed peribronchial inflammation score, airway epithelial damage, subepithelial extracellular matrix accumulation/fibronectin deposition and total lung collagen concentration (by 50–90%) and also normalized the reduction of cDyn.

CONCLUSIONS AND IMPLICATIONS

Combining an epithelial repair factor and anti-fibrotic provides an effective means of treating the AWR and dysfunction associated with AAD/asthma and may act as an effective adjunct therapy to anti-inflammatory corticosteroids

Serelaxin for the treatment of acute heart failure: a review with a focus on end-organ protection

Acute heart failure (AHF) is a complex clinical syndrome characterized by fluid overload and haemodynamic abnormalities (short-term clinical consequences) and the development of end-organ damage (long-term consequences). Current therapies for the treatment of AHF, such as loop diuretics and vasodilators, help to relieve haemodynamic imbalance and congestion, but have not been shown to prevent (and may even contribute to) end-organ damage, or to provide long-term clinical benefit. Serelaxin is the recombinant form of human relaxin-2, a naturally occurring hormone involved in mediating haemodynamic changes during pregnancy. Preclinical and clinical studies have investigated the effects mediated by serelaxin and the suitability of this agent for the treatment of patients with AHF. Data suggest that serelaxin acts via multiple pathways to improve haemodynamics at the vascular, cardiac, and renal level and provide effective congestion relief. In addition, this novel agent may protect the heart, kidneys, and liver from damage by inhibiting inflammation, oxidative stress, cell death, and tissue fibrosis, and stimulating angiogenesis. Serelaxin may therefore improve both short- and long-term outcomes in patients with AHF. In this review, we examine the unique mechanisms underlying the potential benefits of serelaxin for the treatment of AHF, in particular, those involved in mediating end-organ protection.

Relaxin' the Heart: A Novel Therapeutic Modality

The peptide hormone relaxin has traditionally been linked to the maternal adaptation of the cardiovascular system during the first trimester of pregnancy. By promoting nitric oxide formation through different molecular signaling events, relaxin has been proposed as a pleiotropic and cardioprotective hormone in the setting of many cardiovascular diseases. In fact, preclinical studies were able to demonstrate that relaxin promotes vasodilatation and angiogenesis, ameliorates ischemia/reperfusion injury, and regulates extracellular matrix turnover and remodeling. In the RELAX-AHF phase 3 clinical trial, serelaxin (recombinant human relaxin) was shown to be safe, and it exerted survival benefits in patients with acute heart failure. RELAX-AHF-2 is currently ongoing, and it aims to address a larger population and evaluate harder clinical outcomes. Besides heart failure, acute myocardial infarction, peripheral arterial disease, and stable coronary disease could be target diseases for treatment with serelaxin in future clinical trials.

Diverse regulation of cardiac expression of relaxin receptor by α1- and β1-adrenoceptors

PURPOSE

Relaxin, a new drug for heart failure therapy, exerts its cardiac actions through relaxin family peptide receptor 1 (RXFP1). Factors regulating RXFP1 expression remain unknown. We have investigated effects of activation of adrenoceptors (AR), an important modulator in the development and prognosis of heart failure, on expression of RXFP1 in rat cardiomyocytes and mouse left ventricles (LV).

METHODS

Expression of RXFP1 at mRNA (real-time PCR) and protein levels (immunoblotting) was measured in cardiomyocytes treated with α- and β-AR agonists or antagonists. RXFP1 expression was also determined in the LV of transgenic mouse strains with cardiac-restricted overexpression of α1A-, α1B- or β2-AR. Specific inhibitors were used to explore signal pathways involved in α1-AR mediated regulation of RXFP1 in cardiomyocytes.

RESULTS

In cultured cardiomyocytes, α1-AR stimulation resulted in 2-3 fold increase in RXFP1 mRNA (P < 0.001), which was blocked by specific inhibitors for protein kinase C (PKC) or mitogen-activated protein kinases/extracellular signal-regulated kinases (MAPK/ERK). Activation of β1-, but not β2-AR, significantly inhibited RXFP1 expression (P < 0.001). Relative to respective wild-type controls, RXFP1 mRNA levels in the LV of mice overexpressing α1A- or α1B-AR were increased by 3- or 10-fold, respectively, but unchanged in β2-AR transgenic hearts. Upregulation by α1-AR stimulation RXFP1 expression was confirmed at protein levels both in vitro and in vivo.

CONCLUSIONS

Expression of RXFP1 was up-regulated by α1-AR but suppressed by β-AR, mainly β1-AR subtype, in cardiomyocytes. Future studies are warranted to characterize the functional significance of such regulation, especially in the setting of heart failure.

Relaxin peptide hormones are protective during the early stages of ischemic stroke in male rats

The pregnancy hormone relaxin protects tissue from ischemic damage. The ability of relaxin-3, a relaxin paralog, to do so has not been explored. The cerebral expression levels of these peptides and their receptors make them logical targets for study in the ischemic brain. We assessed relaxin peptide-mediated protection, relative relaxin family peptide receptor (RXFP) involvement, and protective mechanisms. Sprague-Dawley rats receiving permanent (pMCAO) or transient middle cerebral artery occlusions (tMCAO) were treated with relaxin peptides, and brains were collected for infarct analysis. Activation of the endothelial nitric oxide synthase pathway was evaluated as a potential protective mechanism. Primary cortical rat astrocytes were exposed to oxygen glucose deprivation and treated with relaxin peptides, and viability was examined. Receptor involvement was explored using RXFP3 antagonist or agonist treatment and real-time PCR. Relaxin and relaxin-3 reduced infarct size after pMCAO. Both peptides activated endothelial nitric oxide synthase. Because relaxin-3 has not previously been associated with this pathway and displays promiscuous RXFP binding, we explored the receptor contribution. Expression of rxfp1 was greater than that of rxfp3 in rat brain, although peptide binding at either receptor resulted in similar overall protection after pMCAO. Only RXFP3 activation reduced infarct size after tMCAO. In astrocytes, rxfp3 gene expression was greater than that of rxfp1. Selective activation of RXFP3 maintained astrocyte viability after oxygen glucose deprivation. Relaxin peptides are protective during the early stages of ischemic stroke. Differential responses among treatments and models suggest that RXFP1 and RXFP3 initiate different protective mechanisms. This preliminary work is a pivotal first step in identifying the clinical implications of relaxin peptides in ischemic stroke.

International Union of Basic and Clinical Pharmacology. XCV. Recent advances in the understanding of the pharmacology and biological roles of relaxin family peptide receptors 1-4, the receptors for relaxin family peptides

Relaxin, insulin-like peptide 3 (INSL3), relaxin-3, and INSL5 are the cognate ligands for the relaxin family peptide (RXFP) receptors 1-4, respectively. RXFP1 activates pleiotropic signaling pathways including the signalosome protein complex that facilitates high-sensitivity signaling; coupling to Gα(s), Gα(i), and Gα(o) proteins; interaction with glucocorticoid receptors; and the formation of hetero-oligomers with distinctive pharmacological properties. In addition to relaxin-related ligands, RXFP1 is activated by Clq-tumor necrosis factor-related protein 8 and by small-molecular-weight agonists, such as ML290 [2-isopropoxy-N-(2-(3-(trifluoromethylsulfonyl)phenylcarbamoyl)phenyl)benzamide], that act allosterically. RXFP2 activates only the Gα(s)- and Gα(o)-coupled pathways. Relaxin-3 is primarily a neuropeptide, and its cognate receptor RXFP3 is a target for the treatment of depression, anxiety, and autism. A variety of peptide agonists, antagonists, biased agonists, and an allosteric modulator target RXFP3. Both RXFP3 and the related RXFP4 couple to Gα(i)/Gα(o) proteins. INSL5 has the properties of an incretin; it is secreted from the gut and is orexigenic. The expression of RXFP4 in gut, adipose tissue, and β-islets together with compromised glucose tolerance in INSL5 or RXFP4 knockout mice suggests a metabolic role. This review focuses on the many advances in our understanding of RXFP receptors in the last 5 years, their signal transduction mechanisms, the development of novel compounds that target RXFP1-4, the challenges facing the field, and current prospects for new therapeutics.

H2 and H3 relaxin inhibit high glucose-induced apoptosis in neonatal rat ventricular myocytes

High concentrations of glucose induce cardiomyocyte apoptosis, and contribute to diabetic cardiomyopathy. Relaxin-2 and relaxin-3 are two members of the relaxin peptide family that are cardioprotective. However, it remains unknown whether relaxin-2 or relaxin-3 can regulate apoptosis in high glucose treated-neonatal rat ventricular myocytes (NRVMs). In cultured NRVMs, 33 mmol/l high glucose (HG) increased apoptosis in a time-dependent manner. HG-increased the protein expression of cleaved caspase-8 and -9, two initiators of the extrinsic and intrinsic pathways of apoptosis, Caspase-3 was attenuated by human recombinant relaxin-2 (H2 relaxin) or relaxin-3 (H3 relaxin), indicating that H2 and H3 relaxin inhibited HG-induced apoptosis. Furthermore, endoplasmic reticulum stress (ERS) markers CHOP and caspase-12 were markedly increased in HG-treated NRVMs, leading to apoptosis; this effect was also effectively attenuated by H2 relaxin or H3 relaxin. Treatment of NRVMs with HG reduced autophagy which cannot be adjusted by H2 relaxin or H3 relaxin. In conclusion, HG-induced apoptosis in NRVMs was mediated, in part, by the activation of the extrinsic and intrinsic pathways of apoptosis and ERS, all inhibited by H2 relaxin or H3 relaxin.

Protective effects of relaxin against cisplatin-induced nephrotoxicity in rats

BACKGROUND

Cisplatin (CDDP)-induced acute kidney injury (AKI) involves pro-inflammatory responses, apoptosis of renal tubular epithelial cells and vascular damage. AKI increases the risk of chronic kidney disease. Relaxin (RLX) has anti-apoptotic and anti-fibrosis properties. The aim of this study was to investigate the effects of RLX on CDDP-induced nephrotoxicity.

METHODS

We investigated the mitigating effects of RLX based on the etiopathology of AKI induced by CDDP, and also the anti-fibrotic effect of RLX on renal fibrosis after AKI. In the short-term experiments, rats were divided into the control group, CDDP group, and CDDP+RLX group. In the latter group, RLX was infused for 5 or 14 days using an implanted osmotic minipump. CDDP was injected intraperitoneally (6 mg/kg) after RLX or saline infusion. At 5 and 14 days post-CDDP, the kidneys were removed for analysis. The effect of RLX on renal fibrosis after AKI was evaluated at 6 weeks post-CDDP.

RESULTS

In short-term experiments, CDDP transiently increased plasma creatinine and blood urea nitrogen with peaks at day 5, and RLX prevented such rises. Semiquantitative analysis of the histological lesions indicated marked structural damage and apoptotic cells in the CDDP group, with the lesions being reduced by RLX treatment. Overexpression of Bax, interleukin-6 and tumor necrosis factor-α observed in the kidneys of the CDDP group was reduced in the CDDP+RLX group. In the long-term experiments, RLX significantly reduced renal fibrosis compared with the CDDP group.

CONCLUSIONS

The results suggested that RLX provided protection against CDDP-induced AKI and subsequent fibrosis by reducing apoptosis and inflammation.

Protection of cultured human hepatocytes from hydrogen peroxide‑induced apoptosis by relaxin‑3

Previous studies have suggested that hepatocyte apoptosis may be a fundamental underlying mechanism of liver injury and diseases, such as liver fibrosis. Relaxin‑3 has been reported to have anti‑fibrotic actions in the heart and to attenuate isoproterenol‑induced myocardial injury; however, the beneficial role of relaxin‑3 on hepatocyte apoptosis remains to be elucidated. The aim of the present study was to explore the role and possible mechanisms of relaxin‑3 through hydrogen peroxide (H2O2)‑induced apoptosis in primary human hepatocytes. Cells were treated with relaxin‑3 and then cell viability, morphological features, the presence of cleaved caspases as well as the levels of endoplasmic reticulum stress (ERS) protein markers and autophagy markers were evaluated. The H2O2 group showed significantly decreased cell viability, increased apoptosis as well as upregulation of caspases (cleaved caspase‑3, ‑8 and ‑9) and ERS protein markers compared with those of the control group. However, cells treated with relaxin‑3 (10 ng/ml) demonstrated improved cell viability, reduced apoptosis and decreased expression of cleaved caspases and ERS markers. However, the expression of autophagy markers remained unchanged following H2O2‑induced apoptosis and relaxin‑3 treatment. In conclusion, relaxin‑3 was shown to protect hepatocytes from H2O2‑induced apoptosis via downregulation of cleaved caspase‑8 and ‑9, as well as inhibition of the ERS pathway.

Relaxin protects cardiac muscle cells from hypoxia/reoxygenation injury: involvement of the Notch-1 pathway

In animal models, the cardiotropic hormone relaxin has been shown to protect the heart against ischemia and reperfusion-induced damage, acting by multiple mechanisms that primarily involve the coronary vessels. This in vitro study evaluates whether relaxin also has a direct protective action on cardiac muscle cells. H9c2 rat cardiomyoblasts and primary mouse cardiomyocytes were subjected to hypoxia and reoxygenation. In some experiments, relaxin was added preventatively before hypoxia; in others, at reoxygenation. To elucidate its mechanisms of action, we focused on Notch-1, which is involved in heart pre- and postconditioning to ischemia. Inactivated RLX was used as negative control. Relaxin (17 nmol/L, EC50 4.7 nmol/L), added 24 h before hypoxia or at reoxygenation, protected against cardiomyocyte injury. In fact, relaxin significantly increased cell viability (assayed by trypan blue and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide), decreased apoptosis (assayed by TUNEL and bax/bcl-2 ratio), and reduced nitroxidative damage (assayed by nitrotyrosine expression and 8-hydroxy-deoxyguanosine levels). These effects were partly attributable to the ability of relaxin to upregulate Notch-1 signaling; indeed, blockade of Notch-1 activation with the specific inhibitor DAPT reduced relaxin-induced cardioprotection during hypoxia and reoxygenation. This study adds new mechanistic insights on the cardioprotective role of relaxin on ischemic and oxidative damage.

Recombinant human relaxin-2: (how) can a pregnancy hormone save lives in acute heart failure?

Acute heart failure (AHF) syndrome, characterized by pulmonary and/or venous congestion owing to increased cardiac filling pressures with or without diminished cardiac output, is still associated with high post-discharge mortality and hospitalization rates. Many novel and promising therapeutic approaches, among them endothelin-1, vasopressin and adenosine antagonists, calcium sensitization, and recombinant B-type natriuretic hormone, have failed in large studies. Likewise, the classic drugs, vasodilators, diuretics, and inotropes, have never been shown to lower mortality.The phase III trial RELAX-AHF tested recombinant human relaxin-2 (rhRlx) and found it to improve clinical symptoms moderately, to be neutral regarding the combination of death and hospitalization at day 60, to be safe, and to lower mortality at day 180. This review focuses on basic research and pre-clinical findings that may account for the benefit of rhRlx in AHF. The drug combines short-term hemodynamic advantages, such as moderate blood pressure decline and functional endothelin-1 antagonism, with a wealth of protective effects harboring long-term benefits, such as anti-inflammatory, anti-fibrotic, and anti-oxidative actions. These pleiotropic effects are exerted through a complex and intricate signaling cascade involving the relaxin-family peptide receptor-1, the glucocorticoid receptor, nitric oxide, and a cell type-dependent variety of kinases and transcription factors.

Serelaxin: a novel therapy for acute heart failure with a range of hemodynamic and non-hemodynamic actions

Acute heart failure (AHF) is characterized by high morbidity and mortality and high costs. Although the treatment of AHF has not changed substantially in recent decades, it is becoming clear that treatment strategies for AHF need to address both the immediate hemodynamic abnormalities giving rise to congestion as well as prevent organ damage that can influence long-term prognosis. Serelaxin, the recombinant form of human relaxin-2, a naturally occurring peptide hormone, has been found to significantly improve symptoms and signs of AHF, prevent in-hospital worsening heart failure, as well as significantly improve 180-day cardiovascular and all-cause mortality after a 48-h infusion commenced within 16 h of presentation (RELAX-AHF study). Available data suggest that the clinical benefits may be attributable to a potential combination of multiple actions of serelaxin, including improving systemic, cardiac, and renal hemodynamics, and protecting cells and organs from damage via anti-inflammatory, anti-cell death, anti-fibrotic, anti-hypertrophic, and pro-angiogenic effects. This manuscript describes the short- and long-term effects of serelaxin in AHF patients, analyzing how these effects can be explained by taking into account the range of hemodynamic and non-hemodynamic actions of serelaxin. In addition, this paper also addresses several aspects related to the role of serelaxin in the therapy of AHF that remain to be clarified and warrant further investigation.

Dietary fatty acids alter left ventricular myocardial gene expression in Wistar rats

Obesity increases the risk for cardiomyopathy in the absence of comorbidities. Myocardial structure is modified by dietary fatty acids. Left ventricular hypertrophy is associated with Western (WES) diet consumption, whereas intake of n-3 polyunsaturated fatty acids is associated with antihypertrophic effects. We previously observed no attenuation of left ventricular thickening after 3 months of docosahexaenoic acid (DHA) supplementation of a WES diet, compared with WES diet intake alone, in rats that had similar weight, adiposity, and insulin sensitivity to control animals. The objective of this study was to define left ventricular gene expression in these animals to determine whether diet alone was associated with a physiologic or pathologic hypertrophic response. We hypothesized that WES diet consumption would favor a pathologic or maladaptive myocardial gene expression pattern and that DHA supplementation would favor a physiologic or adaptive response. Microarray analysis identified 64 transcripts that were differentially expressed (P ≤ .001) within one or more treatment comparisons. Using quantitative real-time polymerase chain reaction, 29 genes with fold change at least 1.74 were successfully validated; all but 3 had similar directionality to that observed using microarray, and 2 genes, connective tissue growth factor and cathepsin M, were differentially expressed according to diet. WES blot analysis was performed on 4 proteins relevant to myocardial hypertrophy and metabolism. Acyl-CoA thioesterase 1, B-cell translocation gene 2, and carbonic anhydrase III showed directional change consistent with gene expression. Retinol saturase (all-trans-retinol 13,14-reductase), although not consistent with gene expression, was different according to diet, with increased concentrations in WES-fed rats compared with control and DHA-supplemented animals. Diet did not distinguish a transcriptome reflecting physiologic or pathologic myocardial hypertrophy; furthermore, the modest changes observed suggest that obesity and associated comorbidities may play a larger role than mere dietary fatty acid composition in development of cardiomyopathy.

Therapeutic effects of serelaxin in acute heart failure

Over the past few decades, research on the peptide hormone, relaxin, has significantly improved our understanding of its biological actions under physiological and diseased conditions. This has facilitated the conducting of clinical trials to explore the use of serelaxin (human recombinant relaxin). Acute heart failure (AHF) is a very difficult to treat clinical entity, with limited success so far in developing new drugs to combat it. A recent phase-III RELAX-AHF trial using serelaxin therapy given during hospitalization revealed acute (ameliorated dyspnea) and chronic (improved 180-day survival) effects. Although these findings support a substantial improvement by serelaxin therapy over currently available therapies for AHF, they also raise key questions and stimulate new hypotheses. To facilitate the development of serelaxin as a new drug for heart disease, joint efforts of clinicians, research scientists and pharmacological industries are necessary to study these questions and hypotheses. In this review, after providing a brief summary of clinical findings and the pathophysiology of AHF, we present a working hypothesis of the mechanisms responsible for the observed efficacy of serelaxin in AHF patients. The existing clinical and preclinical data supporting our hypotheses are summarized and discussed. The development of serelaxin as a drug provides an excellent example of the bilateral nature of translational research.