Relaxin inhibits lipopolysaccharide‐induced adhesion of neutrophils to coronary endothelial cells by a nitric oxide‐mediated mechanism

Microscopic polyangiitis plasma-derived exosomal miR-1287-5p induces endothelial inflammatory injury and neutrophil adhesion by targeting CBL

Background

An inflammatory environment around the vessel wall caused by leukocyte infiltration is one of the characteristic histopathological features of microscopic polyangiitis (MPA); however, the pathogenic mechanisms are not fully understood. Studies have found that circulating microRNA (miRNA) can be used as potential biomarkers for the diagnosis and classification of anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitides (AAV), and the E3 ubiquitin ligase casitas B-lineage lymphoma (CBL) seems to be associated with inflammation. In addition, evidence indicates that miRNA can be tracked into exosomes and transferred into recipient cells to mediate the process of vascular endothelial injury. Herein, we aimed to identify the profiles of exosomal miRNA, and determine the effect of exosomal miR-1287-5p and its target gene CBL on vascular endothelial cells in MPA.

Method

We isolated plasma exosomes from patients with MPA (MPA-exo) and healthy controls (HC-exo) by ultracentrifugation and conducted exosome small-RNA sequencing to screen differential miRNA expression in MPA-exo (n = 3) compared to HC-exo (n = 3). We measured the expression levels of miR-1303, miR-1287-5p, and miR-129-1-3p using quantitative reverse transcription-polymerase chain reaction (qRT-PCR, n = 6) and performed dual luciferase reporter gene assays to confirm the downstream target gene of miR-1287-5p. In addition, we treated human umbilical vein endothelial cell (HUVEC) with MPA-exo, or transfected them with miR-1287-5p mimic/inhibitor or with CBL-siRNA/CBL-siRNA+ miR-1287-5p inhibitor. After cell culture, we evaluated the effects on vascular endothelial cells by examining the mRNA levels of IL-6, IL-8, MCP-1, ICAM-1 and E-selectin using qRT-PCR and performed neutrophil adhesion assay with haematoxylin staining.

Result

Transmission electron microscopy, Western blot and nanoparticle tracking analysis showed that we successfully purified exosomes and MPA-exo could be absorbed into HUVEC. We screened a total of 1,077 miRNA by sequencing and observed a high abundance of miR-1287-5p in the exosomes obtained from MPA plasma. The dual luciferase reporter assay identified CBL as a downstream target gene of miR-1287-5p, and the results revealed that MPA-exo decreased CBL protein expression in HUVEC. In addition, treatment with MPA-exo, up-regulating miR-1287-5p or silencing of CBL in HUVEC significantly increased the mRNA expression of inflammatory factors (including IL-6, IL-8, and MCP-1) and adhesion molecules (including ICAM-1 and E-selection) and promoted the adhesion of neutrophils to HUVEC. However, down-regulating miR-1287-5p had the opposite effect.

Conclusion

Our study revealed that MPA-exo was involved in the intercellular transfer of miR-1287-5p and subsequently promote the development of acute endothelial injury in MPA. MiR-1287-5p and CBL agonists may be promising therapeutic approach for MPA-induced vascular inflammatory injury.

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.

Chronic Exposure to Cigarette Smoke Affects the Ileum and Colon of Guinea Pigs Differently. Relaxin (RLX-2, Serelaxin) Prevents Most Local Damage

Cigarette smoking (CS) is the cause of several organ and apparatus diseases. The effects of smoke in the gut are partially known. Accumulating evidence has shown a relationship between smoking and inflammatory bowel disease, prompting us to investigate the mechanisms of action of smoking in animal models. Despite the role played by neuropeptides in gut inflammation, there are no reports on their role in animal models of smoking exposure. The hormone relaxin has shown anti-inflammatory properties in the intestine, and it might represent a putative therapy to prevent gut damage caused by smoking. Presently, we investigate the effects of chronic smoke exposure on inflammation, mucosal secretion, and vasoactive intestinal peptide (VIP) and substance P (SP) expressions in the ileum and colon of guinea pigs. We also verify the ability of relaxin to counter the smoke-induced effects. Smoke impacted plasma carbon monoxide (CO). In the ileum, it induced inflammatory infiltrates, fibrosis, and acidic mucin production; reduced the blood vessel area; decreased c-kit-positive mast cells and VIP-positive neurons; and increased the SP-positive nerve fibers. In the colon, it reduced the blood vessel area and the goblet cell area and decreased c-kit-positive mast cells, VIP-positive neurons, and SP-positive nerve fibers. Relaxin prevented most of the smoking-induced changes in the ileum, while it was less effective in the colon. This study shows the diverse sensitivity to CS between the ileum and the colon and demonstrates that both VIP and SP are affected by smoking. The efficacy of relaxin proposes this hormone as a potential anti-inflammatory therapeutic to counteract gut damage in humans affected by inflammatory bowel diseases.

Cardiac Gene Therapy With Relaxin Receptor 1 Overexpression Protects Against Acute Myocardial Infarction

•

AAV9 vectors can upregulate Rxfp1 mRNA in murine heart after intravenous injection.

•

RXFP1 upregulation sensitizes the left ventricle to relaxin-induced inotropy.

•

RXFP1 overexpression protects heart from ischemia-reperfusion injury.

Relaxin is a pleiotropic hormone shown to confer cardioprotection in several preclinical models of cardiac ischemia-reperfusion injury. In the present study, the effects of up-regulating relaxin family peptide receptor 1 (RXFP1) via adeno-associated virus serotype 9 (AAV9) vectors were investigated in a mouse model of myocardial infarction. AAV9-RXFP1 vectors were generated and injected in adult male CD1 mice. Up-regulation of Rxfp1 was confirmed via quantitative polymerase chain reaction, and overexpressing animals showed increased sensitivity to relaxin-induced ventricular inotropic response. Overexpressing animals also demonstrated reduced infarct size and preserved cardiac function 24 hours after ischemia-reperfusion. Up-regulation of RXFP1 via AAV9 vectors has potential therapeutic utility in preventing adverse remodeling after myocardial infarction.

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.

Adipokines and Inflammation: Focus on Cardiovascular Diseases

It is well established that adipose tissue, apart from its energy storage function, acts as an endocrine organ that produces and secretes a number of bioactive substances, including hormones commonly known as adipokines. Obesity is a major risk factor for the development of cardiovascular diseases, mainly due to a low grade of inflammation and the excessive fat accumulation produced in this state. The adipose tissue dysfunction in obesity leads to an aberrant release of adipokines, some of them with direct cardiovascular and inflammatory regulatory functions. Inflammation is a common link between obesity and cardiovascular diseases, so this review will summarise the role of the main adipokines implicated in the regulation of the inflammatory processes occurring under the scenario of cardiovascular diseases.

Relaxin Positively Influences Ischemia-Reperfusion Injury in Solid Organ Transplantation: A Comprehensive Review

In recent decades, solid organ transplantation (SOT) has increased the survival and quality of life for patients with end-stage organ failure by providing a potentially long-term treatment option. Although the availability of organs for transplantation has increased throughout the years, the demand greatly outweighs the supply. One possible solution for this problem is to extend the potential donor pool by using extended criteria donors. However, organs from such donors are more prone to ischemia reperfusion injury (IRI) resulting in higher rates of delayed graft function, acute and chronic graft rejection and worse overall SOT outcomes. This can be overcome by further investigating donor preconditioning strategies, graft perfusion and storage and by finding novel therapeutic agents that could reduce IRI. relaxin (RLX) is a peptide hormone with antifibrotic, antioxidant, anti-inflammatory and cytoprotective properties. The main research until now focused on heart failure; however, several preclinical studies showed its potentials for reducing IRI in SOT. The aim of this comprehensive review is to overview currently available literature on the possible role of RLX in reducing IRI and its positive impact on SOT.

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 and extracellular matrix remodeling: Mechanisms and signaling pathways

Fibrosis is associated with accumulation of excess fibrillar collagen, leading to tissue dysfunction. Numerous processes, including inflammation, myofibroblast activation, and endothelial-to-mesenchymal transition, play a role in the establishment and progression of fibrosis. Relaxin is a peptide hormone with well-known antifibrotic properties that result from its action on numerous cellular targets to reduce fibrosis. Relaxin activates multiple signal transduction pathways as a mechanism to suppress inflammation and myofibroblast activation in fibrosis. In this review, the general mechanisms underlying fibrotic diseases are described, along with the current state of knowledge regarding cellular targets of relaxin. Finally, an overview is presented summarizing the signaling pathways activated by relaxin and other relaxin family peptide receptor agonists to suppress fibrosis.

Cardioprotective actions of relaxin

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.

Hormone Replacement Therapy: Would it be Possible to Replicate a Functional Ovary?

Background: Throughout history, menopause has been regarded as a transition in a woman’s life. With the increase in life expectancy, women now spend more than a third of their lives in menopause. During these years, women may experience intolerable symptoms both physically and mentally, leading them to seek clinical advice. It is imperative for healthcare providers to improve the quality of life by reducing bothersome menopausal symptoms and preventing disorders such as osteoporosis and atherosclerosis. The current treatment in the form of hormone replacement therapy (HRT) is sometimes inadequate with several limitations and adverse effects. Objective and rationale: The current review aims to discuss the need, efficacy, and limitations of current HRT; the role of other ovarian hormones, and where we stand in comparison with ovary-in situ; and finally, explore towards the preparation of an HRT model by regeneration of ovaries tissues through stem cells which can replicate a functional ovary. Search methods: Four electronic databases (MEDLINE, Embase, Web of Science and CINAHL) were searched from database inception until 26 April 2018, using a combination of relevant controlled vocabulary terms and free-text terms related to ‘menopause’, ‘hormone replacement therapy’, ‘ovary regeneration’, ‘stem cells’ and ‘ovarian transplantation’. Outcomes: We present a synthesis of the existing data on the efficacy and limitations of HRT. HRT is far from adequate in postmenopausal women with symptoms of hormone deprivation as it fails to deliver all hormones secreted by naïve ovarian tissue. Moreover, the pharmacokinetics of synthetic hormones makes them substantially different from natural ones. Not only does the number and type of hormones given in HRT matter, but the route of delivering and their release in circulation are also imperative. The hormones are delivered either orally or topically in a non-physiological uniform manner, which brings along with it several side effects. These identify the need for a hormone delivery system which replicates, integrates and reacts as per the requirement of the female body. Wider implications: The review outlines the strengths and weaknesses of HRT and highlights the potential areas for future research. There is a tremendous potential for research in this field to understand the collective roles of the various ovarian hormones and to devise an auto-regulated hormone delivery system which replicates the normal physiology. Its clinical applications can prove to be transformative for postmenopausal women helping them to lead a healthy and productive life.

Serelaxin induces Notch1 signaling and alleviates hepatocellular damage in orthotopic liver transplantation

Liver ischemia-reperfusion injury (IRI) represents a risk factor for early graft dysfunction and an obstacle to expanding donor pool in orthotopic liver transplantation (OLT). We have reported on the crucial role of macrophage Notch1 signaling in mouse warm hepatic IRI model. However, its clinical relevance or therapeutic potential remain unknown. Here, we used Serelaxin (SER), to verify Notch1 induction and putative hepatoprotective function in ischemia-reperfusion-stressed OLT. C57BL/6 mouse livers subjected to extended (18-hour) cold storage were transplanted to syngeneic recipients. SER treatment at reperfusion ameliorated IRI, improved post-OLT survival, decreased neutrophil/macrophage infiltration, and suppressed proinflammatory cytokine programs, while simultaneously increasing Notch intracellular domain (NICD) and hairy and enhancer of split 1 (Hes1) target genes. In bone marrow-derived macrophage cultures, SER suppressed proinflammatory while enhancing antiinflammatory gene expression concomitantly with increased NICD and Hes1. Hepatic biopsies from 21 adult primary liver transplant patients (2 hours postreperfusion) were divided into low-NICD (n = 11) and high-NICD (n = 10) expression groups (western blots). Consistent with our murine findings, human livers characterized by high NICD were relatively IRI resistant, as shown by serum alanine aminotransferase (ALT) levels at day 1 post-OLT. Our study documents the efficacy of SER-Notch1 signaling in mouse OLT and highlights the protective function of Notch1 in liver transplant patients.

Recombinant relaxin protects liver transplants from ischemia damage by hepatocyte glucocorticoid receptor: From bench-to-bedside

Hepatic ischemia-reperfusion injury (IRI) represents a major risk factor of early graft dysfunction and acute/chronic rejection as well as a key obstacle to expanding the donor pool in orthotopic liver transplantation (OLT). Although glucocorticoid receptor (GR) signaling may enhance cytoprotective programs, clinical use of glucocorticoid is limited because of adverse effects, whereas clinical relevance of GR-facilitated cytoprotection in OLT remains unknown. We aimed to evaluate the significance of hepatic GR in clinical OLT and verify the impact of recombinant human relaxin (rhRLX), which may function as a GR agonist in a tissue/disease-specific manner. Fifty-one OLT patients were recruited under an institutional research board (IRB) protocol. Liver biopsies were collected after cold storage (presurgery) and 2 hours postreperfusion (before abdominal closure), followed by western blotting-assisted hepatic analyses. Forty-three percent of OLTs failed to increase GR perioperatively under surgical stress. Post-/pre-GR ratios at postoperative day 1 correlated negatively with serum aspartate aminotransferase (AST)/cleaved caspase-3 and positively with B-cell lymphoma-extra large (Bcl-xL)/B-cell lymphoma 2 (Bcl-2) levels. In a murine OLT model with extended (18-hour) cold storage, treatment with rhRLX ameliorated ischemia-reperfusion (IR) damage and improved survival while up-regulating hepatocyte GR and Bcl-xL/Bcl-2 expression in OLT. rhRLX-induced GR suppressed hepatocyte high-mobility group box 1 (HMGB1) translocation/release, accompanied by decreased Toll-like receptor 4 (TLR4)/receptor for advanced glycation end products (RAGE), suppressed interleukin 1 beta (IL1β), chemokine (C-C motif) ligand 2 (CCL2), C-X-C motif chemokine (CXCL)10, tumor necrosis factor alpha (TNFα), CXCL1, and CXCL2 levels, and attenuated neutrophil/macrophage accumulation in OLT. Inhibition of GR in hepatocyte culture and in OLT diminished rhRLX-mediated cytoprotection.

CONCLUSION

This translational study underscores the role of rhRLX-GR signaling as a regulator of hepatocellular protection against IR stress in OLT. In the context of a recent phase III clinical trial demonstrating positive outcomes of rhRLX in patients with acute heart failure, studies on rhRLX for the management of IRI in OLT recipients are warranted. (Hepatology 2018;68:258-273).

Reperfusion therapy with recombinant human relaxin-2 (Serelaxin) attenuates myocardial infarct size and NLRP3 inflammasome following ischemia/reperfusion injury via eNOS-dependent mechanism

Aims

The preconditioning-like infarct-sparing and anti-inflammatory effects of the peptide hormone relaxin following ischemic injury have been studied in the heart. Whether reperfusion therapy with recombinant human relaxin-2, serelaxin, reduces myocardial infarct size and attenuates the subsequent NLRP3 inflammasome activation leading to further loss of functional myocardium following ischemia/reperfusion (I/R) injury is unknown.

Methods and results

After baseline echocardiography, adult male wild-type C57BL or eNOS knockout mice underwent myocardial infarction (MI) by coronary artery ligation for 30 min followed by 24 h reperfusion. Mice were treated with either serelaxin (10 µg/kg; sc) or saline 1 h prior to ischemia or 5 min before reperfusion. In both pre-treatment and reperfusion therapy arms, serelaxin improved survival at 24 h post MI in wild-type mice (79% and 82%) as compared with controls (46% and 50%, P = 0.01), whereas there was no difference in survival between serelaxin- and saline-treated eNOS knockout mice. Moreover, serelaxin significantly reduced infarct size (64% and 67% reduction, P < 0.05), measured with TTC staining, and preserved LV fractional shortening (FS) and end-systolic diameter (LVESD) in wild-type mice as compared with controls (P < 0.05). Interestingly, caspase-1 activity in the heart tissue, a measure of inflammasome formation, was markedly reduced in serelaxin-treated wild-type mice compared with controls at 24 h post-MI in both treatment modalities (P < 0.05). Genetic deletion of eNOS abolished the infarct-sparing and anti-inflammatory effects of serelaxin as well as functional preservation. Serelaxin plasma levels assessed at 5 min and 1 h after treatment, using ELISA, approximated physiologic relaxin levels during pregnancy in mice and parallels that in humans.

Conclusion

Serelaxin attenuates myocardial I/R injury and the subsequent caspase-1 activation via eNOS-dependent mechanism.

Serelaxin as a novel therapeutic opposing fibrosis and contraction in lung diseases

The most common therapies for asthma and other chronic lung diseases are anti-inflammatory agents and bronchodilators. While these drugs oppose disease symptoms, they do not reverse established structural changes in the airways and their therapeutic efficacy is reduced with increasing disease severity. The peptide hormone, relaxin, is a Relaxin Family Peptide Receptor 1 (RXFP1) receptor agonist with unique combined effects in the lung that differentiates it from these existing therapies. Relaxin has previously been reported to have cardioprotective effects in acute heart failure as well anti-fibrotic actions in several organs. This review focuses on recent experimental evidence of the beneficial effects of chronic relaxin treatment in animal models of airways disease demonstrating inhibition of airway hyperresponsiveness and reversal of established fibrosis, consistent with potential therapeutic benefit. Of particular interest, accumulating evidence demonstrates that relaxin can also acutely oppose contraction by reducing the release of mast cell-derived bronchoconstrictors and by directly eliciting bronchodilation. When used in combination, chronic and acute treatment with relaxin has been shown to enhance responsiveness to both glucocorticoids and β₂-adrenoceptor agonists respectively. While the mechanisms underlying these beneficial actions remain to be fully elucidated, translation of these promising combined preclinical findings is critical in the development of relaxin as a novel alternative or adjunct therapeutic opposing multiple aspects of airway pathology in lung diseases.

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.

Protection from Cigarette Smoke-Induced Lung Dysfunction and Damage by H2 Relaxin (Serelaxin)

Cigarette smoke (CS) is the major etiologic factor of chronic obstructive pulmonary disease (COPD), which is characterized by airway remodeling, lung inflammation and fibrosis, emphysema, and respiratory failure. The current therapies can improve COPD management but cannot arrest its progression and reduce mortality. Hence, there is a major interest in identifying molecules susceptible of development into new drugs to prevent or reduce CS-induced lung injury. Serelaxin (RLX), or recombinant human relaxin-2, is a promising candidate because of its anti-inflammatory and antifibrotic properties highlighted in lung disease models. Here, we used a guinea pig model of CS-induced lung inflammation, and remodeling reproducing some of the hallmarks of COPD. Animals exposed chronically to CS (8 weeks) were treated with vehicle or RLX, delivered by osmotic pumps (1 or 10 μg/day) or aerosol (10 μg/ml/day) during CS treatment. Controls were nonsmoking animals. RLX maintained airway compliance to a control-like pattern, likely because of its capability to counteract lung inflammation and bronchial remodeling. In fact, treatment of CS-exposed animals with RLX reduced the inflammatory recruitment of leukocytes, accompanied by a significant reduction of the release of proinflammatory cytokines (tumor necrosis factor α and interleukin-1β). Moreover, RLX was able to counteract the adverse bronchial remodeling and emphysema induced by CS exposure by reducing goblet cell hyperplasia, smooth muscle thickening, and fibrosis. Of note, RLX delivered by aerosol has shown a comparable efficacy to systemic administration in reducing CS-induced lung dysfunction and damage. In conclusion, RLX emerges as a new molecule to counteract CS-induced inflammatory lung diseases.

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.

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.

Acute treatment with relaxin protects the kidney against ischaemia/reperfusion injury

Although recent preclinical and clinical studies have demonstrated that recombinant human relaxin (rhRLX) may have important therapeutic potential in acute heart failure and chronic kidney diseases, the effects of acute rhRLX administration against renal ischaemia/reperfusion (I/R) injury have never been investigated. Using a rat model of 1-hr bilateral renal artery occlusion followed by 6-hr reperfusion, we investigated the effects of rhRLX (5 μg/Kg i.v.) given both at the beginning and after 3 hrs of reperfusion. Acute rhRLX administration attenuated the functional renal injury (increase in serum urea and creatinine), glomerular dysfunction (decrease in creatinine clearance) and tubular dysfunction (increase in urinary excretion of N-acetyl-β-glucosaminidase) evoked by renal I/R. These beneficial effects were accompanied by a significant reduction in local lipid peroxidation, free radical-induced DNA damage and increase in the expression/activity of the endogenous antioxidant enzymes MnSOD and CuZnSOD superoxide dismutases (SOD). Furthermore, rhRLX administration attenuated the increase in leucocyte activation, as suggested by inhibition of myeloperoxidase activity, intercellular-adhesion-molecule-1 expression, interleukin (IL)-1β, IL-18 and tumour necrosis factor-α production as well as increase in IL-10 production. Interestingly, the reduced oxidative stress status and neutrophil activation here reported were associated with rhRLX-induced activation of endothelial nitric oxide synthase and up-regulation of inducible nitric oxide synthase, possibly secondary to activation of Akt and the extracellular signal-regulated protein kinase (ERK) 1/2, respectively. Thus, we report herein that rhRLX protects the kidney against I/R injury by a mechanism that involves changes in nitric oxide signalling pathway.

Relaxin family peptides and their receptors

There are seven relaxin family peptides that are all structurally related to insulin. Relaxin has many roles in female and male reproduction, as a neuropeptide in the central nervous system, as a vasodilator and cardiac stimulant in the cardiovascular system, and as an antifibrotic agent. Insulin-like peptide-3 (INSL3) has clearly defined specialist roles in male and female reproduction, relaxin-3 is primarily a neuropeptide involved in stress and metabolic control, and INSL5 is widely distributed particularly in the gastrointestinal tract. Although they are structurally related to insulin, the relaxin family peptides produce their physiological effects by activating a group of four G protein-coupled receptors (GPCRs), relaxin family peptide receptors 1-4 (RXFP1-4). Relaxin and INSL3 are the cognate ligands for RXFP1 and RXFP2, respectively, that are leucine-rich repeat containing GPCRs. RXFP1 activates a wide spectrum of signaling pathways to generate second messengers that include cAMP and nitric oxide, whereas RXFP2 activates a subset of these pathways. Relaxin-3 and INSL5 are the cognate ligands for RXFP3 and RXFP4 that are closely related to small peptide receptors that when activated inhibit cAMP production and activate MAP kinases. Although there are still many unanswered questions regarding the mode of action of relaxin family peptides, it is clear that they have important physiological roles that could be exploited for therapeutic benefit.

Relaxin improves TNF-α-induced endothelial dysfunction: the role of glucocorticoid receptor and phosphatidylinositol 3-kinase signalling

AIMS

Human relaxin-2 influences renal and cardiovascular functions. We investigated its effects on experimental endothelial dysfunction.

METHODS AND RESULTS

Acetylcholine-mediated vasodilation of rat aortic rings, impaired by 48 h tumour necrosis factor-α (TNF-α) treatment, was dose-dependently improved by relaxin co-incubation, an effect sensitive to phosphatidylinositol 3-kinase (PI3K) inhibition and the glucocorticoid receptor (GR) antagonist RU-486. TNF increased endothelial nitric oxide synthase (eNOS) phosphorylation at Thr495 and decreased total eNOS expression and both basal and stimulated eNOS activity. Relaxin co-incubation did not affect eNOS expression but improved its activity via PI3K-dependent Thr495 dephosphorylation and Ser1177 phosphorylation, and additional Ser633 phosphorylation. Via GR, relaxin attenuated the TNF-related stimulation of endothelin-1 expression, superoxide and nitrotyrosine formation, and arginase II expression. Relaxin restored, via GR-CCAAT/enhancer-binding protein-β (c/EBP-β)-mediated promoter stimulation, the compromised expression of superoxide dismutase-1 (SOD1). In rat aortic endothelial cells, relaxin activated protein kinase B (Akt) and repressed TNF-induced nuclear factor-κB and activator protein-1. Finally, the relevance of the different findings to the model used was proved by pharmacological interventions.

CONCLUSION

Relaxin improved endothelial dysfunction by promoting eNOS activity, suppressing endothelin-1 and arginase-II expression, and up-regulating SOD1 via GR, GR-c/EBP-β, and PI3K-Akt pathways. This corroborates the notion that it functions as an endogenous and potentially therapeutic vasoprotector.

Relaxin ameliorates hypertension and increases nitric oxide metabolite excretion in angiotensin II but not N(ω)-nitro-L-arginine methyl ester hypertensive rats

Previous findings suggest a potential therapeutic action of relaxin, the putative vasodilatory signal of normal pregnancy, in some forms of cardiovascular disease. However, the mechanisms underlying the beneficial effects of relaxin have not been fully elucidated. The purpose of this study was to determine whether the vasodilatory effects of relaxin are dependent on activation of NO synthase. We examined the effect of relaxin in male Sprague-Dawley rats given angiotensin II (Ang II; 200 ng/kg per minute SC by minipump), the NO synthase inhibitor N(ω)-nitro-l-arginine methyl ester (l-NAME; 1.5 mg/100 g IV followed by 150 mg/L in drinking water), or vehicle for 3 weeks. After 7 days of Ang II or l-NAME, mean arterial pressure was elevated compared with baseline. Relaxin was administered (4 μg/h, SC by minipump) for the next 2 weeks of Ang II, l-NAME, or vehicle treatment. Two-week relaxin treatment alone slightly reduced mean arterial pressure in normotensive rats. Three weeks of either Ang II or l-NAME treatment alone produced hypertension, albuminuria, mild glomerular sclerosis, reduced nitric oxide metabolite excretion, and increased oxidative stress (excretion of hydrogen peroxide and thiobarbituric acid reactive substances and renal cortex nitrotyrosine abundance). Relaxin reduced mean arterial pressure, albumin excretion, and oxidative stress markers and preserved glomerular structure and nitric oxide metabolite excretion in Ang II-treated rats; however, relaxin did not attenuate these changes in the rats treated with l-NAME. None of the treatments affected protein abundance of neuronal or endothelial NO synthase in the kidney cortex. These data suggest that the vasodilatory effects of relaxin are dependent on a functional NO synthase system and increased NO bioavailability possibly because of a reduction in oxidative stress.

Mast cells, peptides and cardioprotection - an unlikely marriage?

1 Mast cells have classically been regarded as the 'bad guys' in the setting of acute myocardial ischaemia, where their released contents are believed to contribute both to tissue injury and electrical disturbances resulting from ischaemia. Recent evidence suggests, however, that if mast cell degranulation occurs in advance of ischaemia onset, this may be cardioprotective by virtue of the depletion of mast cell contents that can no longer act as instruments of injury when the tissue becomes ischaemic. 2 Many peptides, such as ET-1, adrenomedullin, relaxin and atrial natriuretic peptide, have been demonstrated to be cardioprotective when given prior to the onset of myocardial ischaemia, although their physiological functions are varied and the mechanisms of their cardioprotective actions appear to be diverse and often ill defined. However, one common denominator that is emerging is the ability of these peptides to modulate mast cell degranulation, raising the possibility that peptide-induced mast cell degranulation or stabilization may hold the key to a common mechanism of their cardioprotection. 3 The aim of this review was to consolidate the evidence implying that mast cell degranulation could play both a detrimental and protective role in myocardial ischaemia, depending upon when it occurs, and that this may underlie the cardioprotective effects of a range of diverse peptides that exerts physiological effects within the cardiovascular system.

An in vitro study of the protective effect of relaxin on brain tissue under ischemic stress

Organotypic brain slice culture was used to study the direct actions of relaxin on neural cells under ischemic stress. Cortical brain slices from neonatal rats were cultured for 14 days. Experimental slices were placed in a deoxygenated, glucose-free balanced salt solution (BSS) for 1 h, one group with 10(-7) M H2 relaxin in the medium and the other without. Control slices were transferred to oxygenated BSS with glucose. Slices were returned to normal culture conditions and analyzed 1, 4, 8, and 24 h post-treatment using propidium iodide (PI) fluorescence to highlight cellular damage or death. The percentages of dead and dying cells in a slice were compared between groups. Relaxin treatment attenuated PI staining at 4 and 8 h postischemia, suggesting a direct action(s) on cells that improves their chance of survival during ischemia.

Relaxin inhibits renal myofibroblast differentiation via RXFP1, the nitric oxide pathway, and Smad2

The hormone relaxin inhibits renal myofibroblast differentiation by interfering with TGF-beta1/Smad2 signaling. However, the pathways involved in the relaxin-TGF-beta1/Smad2 interaction remain unknown. This study investigated the signaling mechanisms by which human gene-2 (H2) relaxin regulates myofibroblast differentiation in vitro by examining its effects on mixed populations of fibroblasts and myofibroblasts propagated from injured rat kidneys. Cultures containing approximately 60-70% myofibroblasts were used to determine which relaxin receptors, G-proteins, and signaling pathways were involved in the H2 relaxin-mediated regulation of alpha-smooth muscle actin (alpha-SMA; a marker of myofibroblast differentiation). H2 relaxin only inhibited alpha-SMA immunostaining and collagen concentration in the presence of relaxin family peptide receptor 1 (RXFP1). H2 relaxin also induced a transient rise in cAMP in the presence of G(i/o) inhibition, and a sustained increase in extracellular signal-regulated kinase (ERK)-1/2 phosphorylation. Furthermore, inhibition of neuronal nitric oxide synthase (nNOS), NO, and cGMP significantly blocked the inhibitory effects of relaxin on alpha-SMA and Smad2 phosphorylation, while the NO inhibitor, L-nitroarginine methyl ester (hydrochloride) (L-NAME) significantly blocked the inhibitory actions of relaxin on collagen concentration in vivo. These findings suggest that relaxin signals through RXFP1, and a nNOS-NO-cGMP-dependent pathway to inhibit Smad2 phosphorylation and interfere with TGF-beta1-mediated renal myofibroblast differentiation and collagen production.

Relaxin family peptide receptor (RXFP1) coupling to G(alpha)i3 involves the C-terminal Arg752 and localization within membrane Raft Microdomains

The relaxin family peptide receptors (RXFP) 1 and 2 are targets for the relaxin family peptides relaxin and insulin-like peptide 3 (INSL3), respectively. Although both receptors and peptides share a high degree of sequence identity, the cAMP signaling pathways activated by the two systems are quite distinct. Relaxin activation of RXFP1 initially results in accumulation of cAMP via G(alpha)(s), but this is modulated by inhibition of cAMP through G(alpha)(oB). Over time, RXFP1 recruits coupling to G(alpha)(i3), causing additional cAMP accumulation via a G(alpha)(i3)-Gbetagamma-phosphoinositide 3-kinase (PI3K)-protein kinase C (PKC)zeta pathway. In contrast, INSL3 activation of RXFP2 results in accumulation of cAMP only via G(alpha)(s), modulated by cAMP inhibition through G(alpha)(oB). Thus, the aim of this study was to identify the cause of differential G-protein coupling between these highly similar receptors. Construction of chimeric receptors revealed that G(alpha)(i3) coupling is dependent upon the transmembrane region of RXFP1 and independent of the receptor ectodomain or ligand bound. Generation of C-terminal truncated receptors identified the terminal 10 amino acids of the RXFP1 C terminus as essential for G(alpha)(i3) signaling, and point mutations revealed an obligatory role for Arg(752). RXFP1-mediated G(alpha)(i3), but not G(alpha)(s) or G(alpha)(oB), signaling was also found to be dependent upon membrane rafts, and RXFP1 coupled to G(alpha)(i3) after only 3 min of receptor stimulation. Therefore, RXFP1 coupling to the G(alpha)(i3)-Gbetagamma-PI3K-PKCzeta pathway requires the terminal 10 amino acids of the RXFP1 C terminus and membrane raft localization, and the observed delay in this pathway occurs downstream of G(alpha)(i3).

Relaxin as a natural agent for vascular health

Hypertension, atherothrombosis, myocardial infarction, stroke, peripheral vascular disease, and renal failure are the main manifestations of cardiovascular disease (CVD), the leading cause of death and disability in developed countries. Continuing insight into the pathophysiology of CVD can allow identification of effective therapeutic strategies to reduce the occurrence of death and/or severe disabilities. In this context, a healthy endothelium is deemed crucial to proper functioning and maintenance of anatomical integrity of the vascular system in many organs. Of note, epidemiologic studies indicate that the incidence of CVD in women is very low until menopause and increases sharply thereafter. The loss of protection against CVD in post-menopausal women has been chiefly attributed to ovarian steroid deficiency. However, besides steroids, the ovary also produces the peptide hormone relaxin (RLX), which provides potent vasoactive effects which render it the most likely candidate as the elusive physiological shield against CVD in fertile women. In particular, RLX has a specific relaxant effect on peripheral and coronary vasculature, exerted by the stimulation of endogenous nitric oxide (NO) generation by cells of the vascular wall, and can induce angiogenesis. Moreover, RLX inhibits the activation of inflammatory leukocytes and platelets, which play a key role in CVD. Experimental studies performed in vascular and blood cell in vitro and in animal models of vascular dysfunction, as well as pioneer clinical observations, have provided evidence that RLX can prevent and/or improve CVD, thus offering background to clinical trials aimed at exploring the broad therapeutic potential of human recombinant RLX as a new cardiovascular drug.

Relaxin antagonizes hypertrophy and apoptosis in neonatal rat cardiomyocytes

The pregnancy hormone relaxin has recently been shown to be cardio-protective. Despite its well-established antifibrotic actions in the heart, the effects of relaxin on cardiomyocytes (CM) remain to be determined. We investigated effects of isoform 2 of the human relaxin (H2-relaxin) on CM hypertrophy and apoptosis. In cultured neonatal rat CM, phenylephrine (50 microM) and cardiac fibroblast-conditioned medium were used respectively to induce CM hypertrophy. The degree of hypertrophy was indicated by increased cell size, protein synthesis and gene expression of atrial natriuretic peptide. Although H2-relaxin (16.7 nM) alone failed to suppress hypertrophy induced by phenylephrine, it repressed the cardiac fibroblast-conditioned medium-induced increase in protein synthesis by 24% (P<0.05) and reversed the increase in cell size (P<0.001) and atrial natriuretic peptide expression (P<0.01). We further studied the effect of H2-relaxin on CM apoptosis induced by H2O2 (200 microM). Studies of DNA laddering and nuclear staining demonstrated that H2-relaxin treatment reduced H2O2-induced DNA fragmentation. Real-time PCR and Western blot analysis revealed a significant increase in the Bcl2/Bax ratio in H2-relaxin-treated CM. Further analysis showed that activation of Akt (1.8-fold, P<0.001) and ERK (2.0-fold, P<0.01) were involved in the antiapoptotic action of H2-relaxin in CM, and that Gi/o coupling of relaxin receptors was associated with the H2-relaxin-induced Akt activation in CM. In conclusion, these results extend our current knowledge of the cardiac actions of relaxin by demonstrating that H2-relaxin indirectly inhibits CM hypertrophy and directly protects CM from apoptosis.

Relaxin—a pleiotropic hormone and its emerging role for experimental and clinical therapeutics

The insulin-related peptide hormone relaxin (Rlx) is known as pregnancy hormone for decades. In the 1980s, researchers began to recognize the highly intriguing fact that Rlx plays a role in a multitude of physiological processes far beyond pregnancy and reproduction. So, Rlx's contribution to the regulation of vasotonus, plasma osmolality, angiogenesis, collagen turnover, and renal function has been established. In addition, the peptide has been demonstrated to represent a mediator of cardiovascular pathology. The ongoing efforts to identify Rlx receptors eventually precipitated the discovery of the G protein-coupled receptors (GPCR) LGR7 and LGR8 as membrane receptors for human Rlx-2 in 2002. This review will summarize the current state of insight into this rapidly evolving field, which has further been expanded by the discovery of GPCR135 and GPCR142 as receptors for Rlx-3. In addition, Rlx has also been shown to activate the human glucocorticoid receptor (GR). There is evidence from Rlx and Rlx receptor knockouts suggesting that LGR7 is the only relevant receptor for mouse Rlx-1 (corresponding to human Rlx-2) in vivo and that insulin-like peptide (INSL)-3 represents the physiological ligand for LGR8. Regarding Rlx signal transduction, the cyclic adenosine monophosphate (cAMP) and nitric oxide (NO) pathways will be characterized as major cascades. Investigation of downstream signaling remains an important field for future research. Finally, the current state of therapeutical strategies using Rlx in animal models as well as in humans is summarized.

Protective effects of relaxin in ischemia/reperfusion-induced intestinal injury due to splanchnic artery occlusion

1. Splanchnic artery occlusion (SAO) followed by reperfusion causes endothelial injury and inflammation which contribute to the pathophysiology of shock. We investigated the effects of relaxin (RLX), known to afford protection against the deleterious effects of cardiac ischemia/reperfusion, given to rats subjected to splanchnic artery occlusion and reperfusion (SAO/R)-induced splanchnic injury. 2. RLX (30 ng kg(-1), 15 min. before reperfusion) significantly reduced the drop of blood pressure and high mortality rate caused by SAO/R. RLX also reduced histopathological changes, leukocyte infiltration (myeloperoxidase) and expression of endothelial cell adhesion molecules in the ileum. RLX counteracted free radical-mediated tissue injury, as judged by significant decrease in the tissue levels of peroxidation and nitration products (malondialdehyde, nitrotyrosine), DNA damage markers (8-hydroxy-2'-deoxyguanosine, poly-ADP-ribosylated DNA) and consumption of tissue antioxidant enzymes (superoxide dismutase). As a result, RLX led to a reduction of ileal cell apoptosis (caspase 3, terminal deoxynucleotidyltransferase-mediated UTP end labeling). The effects of RLX appear specific, as inactivated RLX substituted for the bioactive hormone had no effects. 3. In conclusion, these results show that RLX exerts a clear-cut protective effect in SAO/R-induced splanchnic injury, likely due to endothelial protection, decreased leukocyte recruitment and hindrance of free radical-mediated tissue injury leading to cell death, lethal complications and high mortality rate. Thus, RLX could be used therapeutically in intestinal ischemia.

'Relaxin' the stiffened heart and arteries: the therapeutic potential for relaxin in the treatment of cardiovascular disease

Although originally characterised as a reproductive hormone, relaxin has emerged as a multi-functional endocrine and paracrine factor that plays a number of important roles in several organs, including the normal and diseased cardiovascular system. The recent discovery of the H3/relaxin-3 gene, and the elusive receptors for relaxin (Relaxin family peptide receptor; RXFP1) and relaxin-3 (RXFP3/RXFP4) have led to the re-classification of a distinct relaxin peptide/receptor family. Additionally, the identification of relaxin and RXFP1 mRNA and/or relaxin binding sites in the heart and blood vessels has confirmed that the cardiovascular system is a target for relaxin peptides. While evidence for the production of relaxins within the cardiovascular system is limited, several studies have established that the relaxin genes are upregulated in the diseased human and rodent heart where they likely act as cardioprotective agents. The ability of relaxin to protect the heart is most likely mediated via its antifibrotic, anti-hypertrophic, anti-inflammatory and vasodilatory actions, but it may also directly stimulate myocardial regeneration and repair. This review describes relaxin and its primary receptor (RXFP1) in relation to the roles and effects of relaxin in the normal and pathological cardiovascular system. It is becoming increasingly clear that relaxin has a number of diverse physiological and pathological roles in the cardiovascular system that may have important therapeutic and clinical implications.

Relaxin prevents the development of severe acute pancreatitis

AIM: To investigate the severity of acute pancreatitis (AP) is associated to the intensity of leukocyte activation, inflammatory up-regulation and microcirculatory disruption associated to ischemia-reperfusion injury. Microvascular integrity and inhibition of pro-inflammatory mediators are key-factors in the evolution of AP. Relaxin is an insulin-like hormone that has been attributed vasorelaxant properties via the nitric oxide pathway while behaving as a glucocorticoid receptor agonist.

METHODS: AP was induced by the bilio-pancreatic duct-outlet-exclusion closed-duodenal-loops model. Treatment with relaxin was done at different time-points. Nitric oxide synthase inhibition by L-NAME and glucocorticoid receptor (GR) blockage by mifepristone was considered. AP severity was assessed by biochemical and histopathological analyses.

RESULTS: Treatment with relaxin reduced serum amylase, lipase, C-reactive protein, IL-6, IL-10, hsp72, LDH and 8-isoprostane as well as pancreatic and lung myeloperoxidase. Acinar and fat necrosis, hemorrhage and neutrophil infiltrate were also decreased. ATP depletion and ADP/ATP ratio were reduced while caspases 2-3-8 and 9 activities were increased. L-NAME and mifepristone decreased the efficiency of relaxin.

CONCLUSION: Relaxin resulted beneficial in the treatment of AP combining the properties of a GR agonist while preserving the microcirculation and favoring apoptosis over necrosis.

Relaxin Pretreatment Decreases Infarct Size in Male Rats after Middle Cerebral Artery Occlusion

We studied the possible neuroprotective action of relaxin in a rat stroke model. Relaxin (10 ng in 200 nL saline) or saline was injected into the secondary somatosensory cortex of anesthetized rats. Thirty minutes after treatment, the right middle cerebral artery was occluded, causing ischemic conditions. Brains were removed 4 hours after stroke, and 1-mm coronal sections were stained using 2-3-5-triphenoltetrazolium chloride. Digital photographs were taken of the sections, and the ratio of infarct area to ipsilateral hemispheric area was calculated. Relaxin treatment significantly (P < .05) reduced this ratio compared with that of saline-treated controls. Results suggest that relaxin may prevent ischemia-induced cell death.

Basic Progress and Future Therapeutic Perspectives of Relaxin in Ischemic Heart Disease

Relaxin has been validated as a cardiotropic hormone, being produced by the heart and acting on specific heart receptors. Evidence is accumulating that it could hamper the pathophysiologic mechanisms of ischemic heart disease. Time is ripe to study relaxin as a cardiotropic drug, as recombinant human relaxin (hrRLX) is now available and previous clinical trials have shown a virtual lack of toxicity and adverse side effects, even at high doses. Our recent observations suggest that relaxin, besides being a preventative agent, may also be effective in the treatment of acute myocardial infarction and may be an adjuvant for precursor cell grafting to repair postinfarct myocardium. In a swine model of myocardial infarction currently used to test cardiotropic drugs due to its similarities with human ischemic heart disease, hrRLX, given at reperfusion upon 30 min of ischemia, markedly reduced serum and tissue markers of myocardial injury, cardiomyocyte apoptosis and leukocyte recruitment, resulting in overall improvement in cardiac performance compared with the controls. In in vitro mixed cultures of mouse skeletal myoblasts and adult rat cardiomyocytes, relaxin increased gap junction formation and potentiated gap junction-mediated intercellular exchanges and signaling between the coupled cells. In view of the therapeutic use of myoblast grafting for cardiac repair, relaxin could hence favor the electromechanical coupling of grafted myoblasts with the resident cardiomyocytes and facilitate their transdifferentiation towards a cardiac phenotype. Relaxin, therefore, shows promising therapeutic potential in cardiology and cardiac surgery.

Relaxin-induced reduction of infarct size in male rats receiving MCAO is dependent on nitric oxide synthesis and not estrogenic mechanisms

Relaxins are members of the insulin peptide superfamily. Previous evidence has shown that relaxin pretreatment reduces cortical infarct size in anesthetized, male rats receiving permanent middle cerebral artery occlusion (MCAO). Therefore, the current study was designed to determine if estrogenic mechanisms or nitric oxide production are involved in mediating this relaxin-induced neuroprotection. In separate groups of rats (n=4-6), the following drugs were injected directly into the cortex 30 min prior to MCAO: (a) relaxin, (b) relaxin and estrogen, and (c) relaxin and an estrogen receptor antagonist (ICI 182,780). To investigate the involvement of nitric oxide, relaxin or relaxin and an inhibitor of endothelial nitric oxide synthase (L-NIO) were injected i.v. 30 min prior to MCAO. Saline-treated rats (both intracortical (i.c.) and intravenously (i.v.)) served as controls. Brains were harvested 4h post stroke, coronally sectioned using a brain matrix and stained using 2,3,5-triphenoltetrazolium chloride (TTC). Digital photographs were taken of brain sections and the ratio comparing the area of the infarct to the area of the ipsilateral hemisphere was calculated. Mean ratios were compared using ANOVA and Tukey's test. Intracortical and intravenous relaxin pretreatment significantly reduced the infarct area in the cortex by 33.7 and 58.6%, respectively compared to saline-treated controls. This effect was not dependent on an interaction with estrogenic receptors as co-injection of relaxin and ICI 182,780 did not reverse this effect. However, inhibition of nitric oxide synthase significantly reduced the relaxin-mediated neuroprotection suggesting that relaxin may induce the endothelin-NOS cascade in cerebral vasculature causing vasodilation and improved perfusion of neural tissue.

Novel drug development opportunity for relaxin in acute myocardial infarction: evidences from a swine model

The hormone relaxin has been shown to cause coronary vasodilation and to prevent ischemia/reperfusion-induced cardiac injury in rodents. This study provides evidence that relaxin, used as an adjunctive drug to coronary reperfusion, reduces the functional, biochemical, and histopathological signs of myocardial injury in an in vivo swine model of heart ischemia/reperfusion, currently used to test cardiotropic drugs for myocardial infarction. Human recombinant relaxin, given at reperfusion at doses of 1.25, 2.5, and 5 microg/kg b.wt. after a 30-min ischemia, caused a dose-related reduction of key markers of myocardial damage (serum myoglobin, CK-MB, troponin T) and cardiomyocyte apoptosis (caspase 3, TUNEL assay), as well as of cardiomyocyte contractile dysfunction (myofibril hypercontraction). Compared with the controls, relaxin also increased the uptake of the viability tracer 201Thallium and improved ventricular performance (cardiac index). Relaxin likely acts by reducing oxygen free radical-induced myocardial injury (malondialdehyde, tissue calcium overload) and inflammatory leukocyte recruitment (myeloperoxidase). The present findings show that human relaxin, given as a drug to counteract reperfusion-induced cardiac injury, affords a clear-cut protection to the heart of swine with induced myocardial infarction. The findings also provide background to future clinical trials with relaxin as adjunctive therapy to catheter-based coronary angioplasty in patients with acute myocardial infarction.

Relaxin's physiological roles and other diverse actions

Relaxin has vital physiological roles in pregnant rats, mice, and pigs. Relaxin promotes growth and softening of the cervix, thus facilitating rapid delivery of live young. Relaxin also promotes development of the mammary apparatus, thus enabling normal lactational performance. The actions of relaxin on the mammary apparatus vary among species. Whereas relaxin is required for development of the mammary nipples in rats and mice, it is essential for prepartum development of glandular parenchyma in pregnant pigs. During pregnancy relaxin also inhibits uterine contractility and promotes the osmoregulatory changes of pregnancy in rats. Recent studies with male and nonpregnant female rodents revealed diverse therapeutic actions of relaxin on nonreproductive tissues that have clinical implications. Relaxin has been reported to reduce fibrosis in the kidney, heart, lung, and liver and to promote wound healing. Also, probably through its vasodilatory actions, relaxin protects the heart from ischemia-induced injury. Finally, relaxin counteracts allergic reactions. Knowledge of the diverse physiological and therapeutic actions of relaxin, coupled with the recent identification of relaxin receptors, opens numerous avenues of investigation that will likely sustain a high level of research interest in relaxin for the foreseeable future.