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

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.

In vitro effect of relaxin in the rat corpus cavernosum under hyperglycemic and normoglycemic conditions

Relaxin, an endogenous peptide hormone, elicits vascular relaxation by its direct effect or by modulating the endothelium-dependent relaxation response and is clinically evaluated for the treatment of coronary artery disease. However, its effect on penile tissue has not been explored yet. This study aimed to investigate the effect of serelaxin, recombinant human relaxin-2, on rat corpus cavernosum (CC) under healthy and hyperglycemic conditions. Strips of CC obtained from thirty-nine male Wistar rats weighing 300-350 g were used in organ baths for isometric tension studies to investigate the serelaxin-mediated relaxation (10-12-10-7 M) under normoglycemic conditions and the effect of serelaxin on endothelium-dependent [nitric oxide (NO)- and prostacyclin-mediated] relaxation responses under hyperglycemic conditions. The in vitro hyperglycemia model was created by 3 h of incubation with 44 mM glucose monohydrate +120 μM methylglyoxal. NO-dependent relaxation responses were evaluated by cumulative acetylcholine (10-9-10-4 M) administration in the presence of indomethacin (10-6 M). Prostacyclin-mediated relaxation was evaluated by cumulative administration of iloprost (10-9-10-6 M), a prostacyclin analog. Maximum relaxation responses to serelaxin were not significantly different compared to the time-control (p = 0.480). Three hours of incubation of rat CC in hyperglycemic conditions impaired NO- and prostacyclin-mediated relaxation responses (p = 0.032 and p = 0.047, respectively). Serelaxin coincubation worsened NO-mediated relaxation responses (p = 0.016) but did not affect prostacyclin-mediated responses (p = 0.425). Together, our results demonstrate that in vitro administration of serelaxin does not cause relaxation in penile tissue and short-term in vitro serelaxin treatment in hyperglycemic conditions mimicked diabetes modulates endothelium-dependent responses by worsening NO-mediated responses. Serelaxin exerts different effects via different mechanism on endothelium-dependent responses depending on the dose and duration of exposure. Therefore, proper timing and dosing of serelaxin administration in the penile tissue need to be investigated in further studies in diabetic animal models.

Relaxin-2 Prevents Erectile Dysfunction by Cavernous Nerve, Endothelial and Histopathological Protection Effects in Rats with Bilateral Cavernous Nerve Injury

PURPOSE

Cavernous nerve injury induced erectile dysfunction (ED) is a refractory complication with high incidence in person under radical prostatectomy. Studies have shown that relaxin-2 (RLX-2) plays a vital role of endothelial protection, vasodilation, anti-fibrosis and neuroprotection in a variety of diseases. However, whether penile cavernous erection can benefit from RLX-2 remains unknown. The purpose of the experiment was to explore the effects of RLX-2 on ED in the rat suffering with bilateral cavernous nerve injury (BCNI).

MATERIALS AND METHODS

The rats were divided into three groups: Sham group was underwent sham operation, BCNI+RLX group or BCNI group was underwent bilateral cavernous nerve crush and then randomly treated with RLX-2 (0.4 mg/kg/d) or saline by continuous administration using a subcutaneously implanted micro pump for 4 weeks respectively. Then, erectile function was evaluated by electrical stimulation of cavernous nerves. Cavernous nerves and penile tissues and were collected for histological evaluation.

RESULTS

Erectile function of rats with BCNI was partially improved after RLX-2 treatment. The BCNI group had lower expression of relaxin family peptide receptor (RXFP) 1, p-AKT/AKT, p-eNOS/eNOS ratios than sham operation rats, but RLX-2 could partially reversed these changes. Histologically, the BCNI+RLX group had a significant effect on preservation of neurofilament, neuronal glial antigen 2 of penile tissue and nNOS of cavernous nerves when compared with BCNI group. RLX-2 could inhibited the lever of BCNI induced corporal fibrosis and apoptosis via regulating TGFβ1-Smad2/3-CTGF pathway and the expression of Bax/Bcl-2 ratio, caspase3.

CONCLUSIONS

RLX-2 could improve erectile function of BCNI rats by protecting cavernous nerve and endothelial function and suppressing corporal fibrosis and apoptosis via RXFP1 and AKT/eNOS pathway. Our findings may provide a promising treatment for refractory BCNI induced ED.

Relaxin Inhibits the Cardiac Myofibroblast NLRP3 Inflammasome as Part of Its Anti-Fibrotic Actions via the Angiotensin Type 2 and ATP (P2X7) Receptors

Chronic NLRP3 inflammasome activation can promote fibrosis through its production of interleukin (IL)-1β and IL-18. Conversely, recombinant human relaxin (RLX) can inhibit the pro-fibrotic interactions between IL-1β, IL-18 and transforming growth factor (TGF)-β1. Here, the broader extent by which RLX targeted the myofibroblast NLRP3 inflammasome to mediate its anti-fibrotic effects was elucidated. Primary human cardiac fibroblasts (HCFs), stimulated with TGF-β1 (to promote myofibroblast (HCMF) differentiation), LPS (to prime the NLRP3 inflammasome) and ATP (to activate the NLRP3 inflammasome) (T+L+A) or benzoylbenzoyl-ATP (to activate the ATP receptor; P2X7R) (T+L+Bz), co-expressed relaxin family peptide receptor-1 (RXFP1), the angiotensin II type 2 receptor (AT2R) and P2X7R, and underwent increased protein expression of toll-like receptor (TLR)-4, NLRP3, caspase-1, IL-1β and IL-18. Whilst RLX co-administration to HCMFs significantly prevented the T+L+A- or T+L+Bz-stimulated increase in these end points, the inhibitory effects of RLX were annulled by the pharmacological antagonism of either RXFP1, AT2R, P2X7R, TLR-4, reactive oxygen species (ROS) or caspase-1. The RLX-induced amelioration of left ventricular inflammation, cardiomyocyte hypertrophy and fibrosis in isoproterenol (ISO)-injured mice, was also attenuated by P2X7R antagonism. Thus, the ability of RLX to ameliorate the myofibroblast NLRP3 inflammasome as part of its anti-fibrotic effects, appeared to involve RXFP1, AT2R, P2X7R and the inhibition of TLR-4, ROS and caspase-1.

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.

Decreased NO production in endothelial cells exposed to plasma from ME/CFS patients

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating disease characterized by severe and persistent fatigue. Along with clinical studies showing endothelial dysfunction (ED) in a subset of ME/CFS patients, we have recently reported altered ED-related microRNAs in plasma from affected individuals. Inadequate nitric oxide (NO), mainly produced by the endothelial isoform of nitric oxide synthase (eNOS) in endothelial cells (ECs), is a major cause of ED. In this study, we hypothesized that plasma from that cohort of ME/CFS patients induces eNOS-related ED in vitro. To test this, we cultured human umbilical vein endothelial cells (HUVECs) in the presence of plasma from either ME/CFS patients (ME/CFS-plasma, n = 11) or healthy controls (HC-plasma, n = 12). Then, we measured the NO production in the absence and presence of tyrosine kinase and G protein-coupled receptors agonists (TKRs and GPCRs, respectively), well-known to activate eNOS in ECs. Our data showed that HUVECs incubated with ME/CFS-plasma produced less NO either in the absence or presence of eNOS activators compared to ones in presence of HC-plasma. Also, the NO production elicited by bradykinin, histamine, and acetylcholine (GPCRs agonists) was more affected than the one triggered by insulin (TKR agonist). Finally, inhibitory eNOS phosphorylation at Thr495 was higher in HUVECs treated with ME/CFS-plasma compared to the same treatment with HC-plasma. In conclusion, this study in vitro shows a decreased NO production in HUVECs exposed to plasma from ME/CFS patients, suggesting an unreported role of eNOS in the pathophysiology of this disease.

Nitric oxide inhibits endothelial cell apoptosis by inhibiting cysteine-dependent SOD1 monomerization

Endothelial cell apoptosis is an important pathophysiology in many cardiovascular diseases. The gasotransmitter nitric oxide (NO) is known to regulate cell survival and apoptosis. However, the mechanism underlying the effect of NO remains unclear. In this research, by targeting cytosolic copper/zinc superoxide dismutase (SOD1) monomerization, we aimed to explore how NO inhibited endothelial cell apoptosis. We showed that treatment with the NO synthase (NOS) inhibitor nomega‐nitro‐l‐arginine methyl ester hydrochloride (L‐NAME) significantly decreased the endogenous NO content of endothelial cells, facilitated the formation of SOD1 monomers, inhibited dismutase activity, and promoted reactive oxygen species (ROS) accumulation in human umbilical vein endothelial cells (HUVECs); by contrast, supplementation with the NO donor sodium nitroprusside (SNP) upregulated NO content, prevented the formation of SOD1 monomers, enhanced dismutase activity, and reduced ROS accumulation in L‐NAME‐treated HUVECs. Mechanistically, tris(2‐carboxyethyl) phosphine hydrochloride (TCEP), a specific reducer of cysteine thiol, increased SOD1 monomer formation, thus preventing the NO‐induced increase in dismutase activity and the decrease in ROS. Furthermore, SNP inhibited HUVEC apoptosis caused by the decrease in endogenous NO, whereas TCEP abolished this protective effect of SNP. In summary, our data reveal that NO protects endothelial cells against apoptosis by inhibiting cysteine‐dependent SOD1 monomerization to enhance SOD1 activity and inhibit oxidative stress.

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.

Simultaneous targeting of oxidative stress and fibrosis reverses cardiomyopathy-induced ventricular remodelling and dysfunction

BACKGROUND AND PURPOSE

Oxidative stress and fibrosis are hallmarks of cardiomyopathy-induced heart failure yet are not effectively targeted by current frontline therapies. Here, the therapeutic effects of the anti-oxidant, N-acetylcysteine (NAC), were compared and combined with an acute heart failure drug with established anti-fibrotic effects, serelaxin (RLX), in a murine model of cardiomyopathy.

EXPERIMENTAL APPROACH

Adult male 129sv mice were subjected to repeated isoprenaline (25 mg·kg^-1 )-induced cardiac injury for five consecutive days and then left to undergo fibrotic healing until Day 14. Subgroups of isoprenaline-injured mice were treated with RLX (0.5 mg·kg^-1 ·day^-1 ), NAC (25 mg·kg^-1 ·day^-1 ) or both combined, given subcutaneously via osmotic minipumps from Day 7 to 14. Control mice received saline instead of isoprenaline.

KEY RESULTS

Isoprenaline-injured mice showed increased left ventricular (LV) inflammation (~5-fold), oxidative stress (~1-2.5-fold), cardiomyocyte hypertrophy (~25%), cardiac remodelling, fibrosis (~2-2.5-fold) and dysfunction by Day 14 after injury. NAC alone blocked the cardiomyopathy-induced increase in LV superoxide levels, to a greater extent than RLX. Additionally, either treatment alone only partly reduced several measures of LV inflammation, remodelling and fibrosis. In comparison, the combination of RLX and NAC prevented the cardiomyopathy-induced LV macrophage infiltration, remodelling, fibrosis and cardiomyocyte size, to a greater extent than either treatment alone after 7 days. The combination therapy also restored the isoprenaline-induced reduction in LV function, without affecting systolic BP.

CONCLUSION AND IMPLICATIONS

These findings demonstrated that the simultaneous targeting of oxidative stress and fibrosis is key to treating the pathophysiology and dysfunction induced by cardiomyopathy.

Metabolic Disorder of Extracellular Matrix Mediated by Decorin Upregulation Is Associated With Brain Arteriovenous Malformation Diffuseness

Background and Objective

Diffuse brain arteriovenous malformations (BAVMs) are mixed up with normal brain parenchyma and therefore increase the difficulty of surgical resection, leading to poor surgical prognosis. Since the mechanism underlying BAVM diffuseness remains unknown, a quantitative proteomic analysis was performed to investigate the altered expression of proteins in diffuse BAVMs compared to compact ones.

Methods

We performed proteomic analysis on five diffuse BAVMs and five compact BAVMs. Bioinformatics analysis was conducted to identify potential signals related to BAVM diffuseness. Candidate proteins were then investigated in BAVM specimens using immunofluorescence and Western blot analysis. Tube formation assays were used to investigate the effects of candidate proteins on the angiogenesis of human umbilical endothelial cells (HUVECs). Finally, Masson, Sirius red staining, and immunofluorescence were used to evaluate the characteristics of extracellular matrix (ECM) in BAVM tissues.

Results

A total of 58 proteins were found to be differentially expressed between diffuse and compact BAVMs via proteomic analysis. TGF-β (transforming growth factor-beta) signaling pathway, ECM–receptor pathway, relaxin signaling pathway, and several other pathways were associated with BAVM diffuseness. The TGF-β signaling pathway is associated with angiogenesis; the role of this pathway in the formation of diffuse BAVMs was investigated, and the decorin (DCN) upregulation played an important role in this process. Immunofluorescence showed that DCN was significantly upregulated within and around the malformed vessels of diffuse BAVMs. Functional assays showed that exogenous DCN could promote the tube formation ability of HUVECs through inhibiting the TGF-β signaling pathway and overproducing ECM. Histological staining demonstrated the overproduction of ECM in diffuse BAVMs.

Conclusion

TGF-β signaling pathway inhibited by DCN in vascular endothelial cells is related to BAVM diffuseness. The metabolic disorder of ECM caused by DCN upregulation may significantly contribute to the formation of diffuse BAVMs.

Relaxin reduces endothelium-derived vasoconstriction in hypertension: Revealing new therapeutic insights

BACKGROUND AND PURPOSE

Endothelium-derived vasoconstriction is a hallmark of vascular dysfunction in hypertension. In some cases, an overproduction of endothelium-derived prostacyclin (PGI₂ ) can cause contraction rather than relaxation. Relaxin is well known for its vasoprotective actions, but the possibility that this peptide could also reverse endothelium-derived vasoconstriction has never been investigated. We tested the hypothesis that short-term relaxin treatment mitigates endothelium-derived vasoconstriction in spontaneously hypertensive rats (SHR).

EXPERIMENTAL APPROACH

Male Wistar Kyoto rats (WKY) and SHR were subcutaneously infused with either vehicle (20 mmol·L^-1 sodium acetate) or relaxin (13.3 μg·kg^-1 ·hr^-1 ) using osmotic minipumps for 3 days. Vascular reactivity to the endothelium-dependent agonist ACh was assessed in vitro by wire myography. Quantitative PCR and LC-MS were used to identify changes in gene expression of prostanoid pathways and PG production, respectively.

KEY RESULTS

Relaxin treatment ameliorated hypertension-induced endothelial dysfunction by increasing NO-dependent relaxation and reducing endothelium-dependent contraction. Notably, short-term relaxin treatment up-regulated mesenteric PGI₂ receptor (IP) expression, permitting PGI₂ -IP-mediated vasorelaxation. In the aorta, reversal of contraction was accompanied by suppression of the hypertension-induced increase in prostanoid-producing enzymes and reduction in PGI₂ -evoked contractions.

CONCLUSIONS AND IMPLICATIONS

Relaxin has region-dependent vasoprotective actions in hypertension. Specifically, relaxin has distinct effects on endothelium-derived contracting factors and their associated vasoconstrictor pathways in mesenteric arteries and the aorta. Taken together, these observations reveal the potential of relaxin as a new therapeutic agent for vascular disorders that are associated with endothelium-derived vasoconstriction including hypertension.

The Glucocorticoid Receptor in Cardiovascular Health and Disease

The glucocorticoid receptor is a member of the nuclear receptor family that controls many distinct gene networks, governing various aspects of development, metabolism, inflammation, and the stress response, as well as other key biological processes in the cardiovascular system. Recently, research in both animal models and humans has begun to unravel the profound complexity of glucocorticoid signaling and convincingly demonstrates that the glucocorticoid receptor has direct effects on the heart and vessels in vivo and in vitro. This research has contributed directly to improving therapeutic strategies in human disease. The glucocorticoid receptor is activated either by the endogenous steroid hormone cortisol or by exogenous glucocorticoids and acts within the cardiovascular system via both genomic and non-genomic pathways. Polymorphisms of the glucocorticoid receptor are also reported to influence the progress and prognosis of cardiovascular disease. In this review, we provide an update on glucocorticoid signaling and highlight the critical role of this signaling in both physiological and pathological conditions of the cardiovascular system. With increasing in-depth understanding of glucocorticoid signaling, the future is promising for the development of targeted glucocorticoid treatments and improved clinical outcomes.

Human recombinant relaxin-2 does not attenuate hypertension or renal injury but exacerbates vascular dysfunction in a female mouse model of SLE

Systemic lupus erythematosus (SLE) is an autoimmune disease that disproportionately affects women of reproductive age and increases their risk for developing hypertension, vascular, and renal disease. Relaxin has potential beneficial therapeutic effects in cardiovascular disease through direct actions on the vasculature. The potential therapeutic benefit of relaxin on SLE-associated cardiovascular and renal risk factors like hypertension has not previously been tested. We hypothesized that relaxin would attenuate hypertension, renal injury, and vascular dysfunction in an established female mouse model of SLE (NZBWF1 mice). Serelaxin (human recombinant relaxin-2, 0.5 mg·kg^-1·day^-1) or vehicle was administered via osmotic mini-pump for 4 wk in female control (NZW) or SLE mice between 28 and 31 wk of age. Serelaxin treatment increased uterine weights in both groups, suggesting that the Serelaxin was bioactive. Mean arterial pressure, measured by carotid artery catheter, was significantly increased in vehicle-treated SLE mice compared with vehicle-treated controls, but was not changed by Serelaxin treatment. Albumin excretion rate, measured by ELISA, was similar between vehicle- and Serelaxin-treated SLE mice and between vehicle- and Serelaxin-treated control mice. Wire myography was performed using isolated carotid arteries to assess endothelial-independent and -dependent vasodilation, and data confirm that SLE mice have impaired endothelium-independent and -dependent relaxation compared with control mice. Serelaxin treatment did not affect endothelium-independent vasodilation, but exacerbated the endothelium-dependent dysfunction. These data suggest that, contrary to our hypothesis, Serelaxin infusion does not attenuate hypertension, renal injury, or vascular dysfunction in SLE, but worsens underlying vascular endothelial dysfunction in this experimental model of SLE. These data do not support the use of human recombinant relaxin-2 as an antihypertensive in the SLE patient population. NEW & NOTEWORTHY Relaxin is a peptide hormone commonly known for its role in pregnancy and for its use in recent clinical trials for the treatment of heart failure. Evidence suggests that relaxin has immunomodulatory effects; however, the potential therapeutic impact of relaxin in chronic immune mediated disease is unclear. This study tests whether recombinant human relaxin (Serelaxin) attenuates the progression of autoimmunity, and the associated cardiovascular consequences, in an experimental model of systemic lupus erythematosus.

Relaxin mitigates microvascular damage and inflammation following cardiac ischemia-reperfusion

Microvascular obstruction (MVO) and leakage (MVL) forms a pivotal part of microvascular damage following cardiac ischemia-reperfusion (IR). We tested the effect of relaxin therapy on MVO and MVL in mice following cardiac IR injury including severity of MVO and MVL, opening capillaries, infarct size, regional inflammation, cardiac function and remodelling, and permeability of cultured endothelial monolayer. Compared to vehicle group, relaxin treatment (50 μg/kg) reduced no-reflow area by 38% and the content of Evans blue as a permeability tracer by 56% in jeopardized myocardium (both P < 0.05), effects associated with increased opening capillaries. Relaxin also decreased leukocyte density, gene expression of cytokines, and mitigated IR-induced decrease in protein content of VE-cadherin and relaxin receptor. Infarct size was comparable between the two groups. At 2 weeks post-IR, relaxin treatment partially preserved cardiac contractile function and limited chamber dilatation versus untreated controls by echocardiography. Endothelial cell permeability assay demonstrated that relaxin attenuated leakage induced by hypoxia-reoxygenation, H₂O₂, or cytokines, action that was independent of nitric oxide but associated with the preservation of VE-cadherin. In conclusion, relaxin therapy attenuates IR-induced MVO and MVL and endothelial leakage. This protection was associated with reduced regional inflammatory responses and consequently led to alleviated adverse cardiac remodeling.

Relaxin gene therapy: A promising new treatment option for various diseases with aberrant fibrosis or irregular angiogenesis

Relaxin (RLX) is an insulin-like polypeptide hormone that was initially introduced for its pregnancy-related function. Subsequent studies revealed that RLX possesses anti-fibrotic functions in tumors and nonreproductive tissues, such as skin, lungs, and others. This aspect of the RLX has been explored for the treatment of various illnesses, such as cardiac fibrosis, liver fibrosis, and solid tumors. With gene therapy coming into age with increasing number of products being approved by regulatory bodies in Europe and United States, we aim to discuss how RLX have been utilized in scope of gene therapy for treatment of various illnesses.

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.

Targeting the vascular dysfunction: Potential treatments for preeclampsia

Preeclampsia is a pregnancy-specific disorder, primarily characterized by new-onset hypertension in combination with a variety of other maternal or fetal signs. The pathophysiological mechanisms underlying the disease are still not entirely clear. Systemic maternal vascular dysfunction underlies the clinical features of preeclampsia. It is a result of oxidative stress and the actions of excessive anti-angiogenic factors, such as soluble fms-like tyrosine kinase, soluble endoglin, and activin A, released by a dysfunctional placenta. The vascular dysfunction then leads to impaired regulation and secretion of relaxation factors and an increase in sensitivity/production of constrictors. This results in a more constricted vasculature rather than the relaxed vasodilated state associated with normal pregnancy. Currently, the only effective "treatment" for preeclampsia is delivery of the placenta and therefore the baby. Often, this means a preterm delivery to save the life of the mother, with all the attendant risks and burdens associated with fetal prematurity. To lessen this burden, there is a pressing need for more effective treatments that target the maternal vascular dysfunction that underlies the hypertension. This review details the vascular effects of key drugs undergoing clinical assessment as potential treatments for women with preeclampsia.

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 treatment reduces angiotensin II-induced vasoconstriction in pregnancy and protects against endothelial dysfunction†

The peptide relaxin has gained considerable attention as a new vasoactive drug, largely through its beneficial therapeutic effects in cardiovascular disease. In this study, we tested the hypothesis that relaxin treatment alleviates systemic vascular dysfunction characteristic of hypertensive diseases of pregnancy. We investigated vascular effects and mechanisms of relaxin action in (i) pregnant relaxin-deficient (Rln-/-) mice with enhanced responses to angiotensin II (AngII) and (ii) arteries pre-incubated ex vivo in trophoblast conditioned media (TCM) to induce endothelial dysfunction. Pregnant Rln-/- mice received 0.5 μg/h recombinant human H2 relaxin (rhRLX: n = 5) or placebo (20 nM sodium acetate; n = 7) subcutaneously via osmotic minipumps for 5 days prior to gestational day 17.5. This treatment protocol significantly reduced AngII-mediated contraction of mesenteric arteries and increased plasma 6-keto prostaglandin F1α. These vascular effects were endothelium independent and likely involve smooth muscle-derived vasodilator prostanoids. In the second study, mesenteric arteries were incubated ex vivo for 24 h at 37°C in TCM, which contained high levels of soluble Flt-1 (>20 ng/ml) and soluble Eng (>1 ng/ml). TCM incubation caused significant reduction in endothelium-dependent relaxation and increased sensitivity to AngII. Co-incubation of arteries with rhRLX for 24 h (n = 6-16/treatment) prevented endothelial dysfunction but had no effect on AngII-mediated contraction. In conclusion, relaxin treatment prevents and/or reverses vascular dysfunction in mesenteric arteries, but acts through different vascular pathways depending on duration of relaxin treatment and type of vascular dysfunction. Overall, our data suggest that relaxin is a potential therapeutic to alleviate maternal systemic vascular dysfunction associated with hypertensive diseases in pregnant women.

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.

Oxidative Stress and Renal Fibrosis: Recent Insights for the Development of Novel Therapeutic Strategies

Chronic kidney disease (CKD) is a significant worldwide healthcare problem. Regardless of the initial injury, renal fibrosis is the common final pathway leading to end stage renal disease. Although the underlying mechanisms are not fully defined, evidence indicates that besides inflammation, oxidative stress plays a crucial role in the etiology of renal fibrosis. Oxidative stress results from an imbalance between the production of free radicals that are often increased by inflammation and mitochondrial dysfunction, and reduced anti-oxidant defenses. Several studies have demonstrated that oxidative stress may occur secondary to activation of transforming growth factor β1 (TGF-β1) activity, consistent with its role to increase nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) activity. A number of other oxidative stress-related signal pathways have also been identified, such as nuclear factor erythroid-2 related factor 2 (Nrf2), the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP)-cGMP-dependent protein kinase 1-phosphodiesterase (cGMP-cGK1-PDE) signaling pathway, and the peroxisome proliferator-activated receptor gamma (PPARγ) pathway. Several antioxidant and renoprotective agents, including cysteamine bitartrate, epoxyeicosatrienoic acids (EETs), and cytoglobin (Cygb) have demonstrated ameliorative effects on renal fibrosis in preclinical or clinical studies. The mechanism of action of many traditional Chinese medicines used to treat renal disorders is based on their antioxidant properties, which could form the basis for new therapeutic approaches. This review focuses on the signaling pathways triggered by oxidative stress that lead to renal fibrosis and provides an update on the development of novel anti-oxidant therapies for CKD.

Oral nicotine aggravates endothelial dysfunction and vascular inflammation in diet-induced obese rats: Role of macrophage TNFα

Obesity and cigarette smoke are major cardiovascular (CV) risk factors and, when coexisting in the same individuals, have additive/synergistic effects upon CVD. We studied the mechanisms involved in nicotine enhancement of CVD in Sprague Dawley rats with diet–induced obesity. The rats were fed either a high fat (HFD) or normal rat chow diet with or without nicotine (100 mg/L in drinking water) for 20 weeks. HFD rats developed central obesity, increased systolic blood pressure (SBP), aortic superoxide (O₂^-) production, and impaired endothelial nitric oxide synthase (eNOS) and endothelium-dependent relaxation to acetylcholine (EDR). Nicotine further increased SBP, O₂^- and impaired eNOS and EDR in obese rats. In the peritoneal macrophages from obese rats, tumor necrosis factor (TNF) α, interleukin 1β and CD36 were increased, and were further increased in nicotine-treated obese rats. Using PCR array we found that 3 of 84 target proinflammatory genes were increased by 2–4 fold in the aorta of obese rats, 11 of the target genes were further increased in nicotine-treated obese rats. HUVECs, incubated with conditioned medium from the peritoneal macrophages of nicotine treated-obese rats, exhibited reduced eNOS and increased NADPH oxidase subunits gp91phox and p22phox expression. Those effects were partially prevented by adding anti-TNFα antibody to the conditioned medium. Our results suggest that nicotine aggravates the CV effects of diet–induced obesity including the oxidative stress, vascular inflammation and endothelial dysfunction. The underlying mechanisms may involve in targeting endothelium by enhancement of macrophage-derived TNFα.

Vagal nerve stimulation reduces infarct size via a mechanism involving the alpha-7 nicotinic acetylcholine receptor and downregulation of cardiac and vascular arginase

AIMS

Vagal nerve stimulation (VNS) protects from myocardial and vascular injury following myocardial ischaemia and reperfusion (IR) via a mechanism involving activation of alpha-7 nicotinic acetylcholine receptor (α7 nAChR) and reduced inflammation. Arginase is involved in development of myocardial IR injury driven by inflammatory mediators. The aim of the study was to clarify whether VNS downregulates myocardial and vascular arginase via a mechanism involving activation of α7 nAChR following myocardial IR.

METHODS

Anaesthetized rats were randomized to (i) sham-operated, (ii) control IR (30-min ischaemia and 2-h reperfusion, (iii) VNS throughout IR, (iv) the arginase inhibitor nor-NOHA+IR, (v) nor-NOHA+VNS+IR, (vi) selective α7 nAChR blockade by methyllycaconitine (MLA) followed by VNS throughout IR and (vii) MLA+IR.

RESULTS

Infarct size was reduced by VNS compared to control IR (41 ± 3% vs. 67 ± 2% of the myocardium at risk, P < 0.001). Myocardial IR increased myocardial and aortic arginase activity 1.7- and 3.1-fold respectively (P < 0.05). VNS attenuated the increase in arginase activity compared to control IR both in the myocardium and aorta (P < 0.05). MLA partially abolished the cardioprotective effect of VNS and completely abrogated the effect of VNS on arginase activity. Arginase inhibition combined with VNS did not further reduce infarct size.

CONCLUSION

Vagal nerve stimulation reduced infarct size and reversed the upregulation of arginase induced by IR both in the myocardium and aorta via a mechanism depending on α7 nAChR activation. The data suggest that the cardioprotective effect of VNS is mediated via reduction in arginase activity.

Serelaxin Treatment Reduces Oxidative Stress and Increases Aldehyde Dehydrogenase-2 to Attenuate Nitrate Tolerance

Background: Glyceryl trinitrate (GTN) is a commonly prescribed treatment for acute heart failure patients. However, prolonged GTN treatment induces tolerance, largely due to increased oxidative stress and reduced aldehyde dehydrogenase-2 (ALDH-2) expression. Serelaxin has several vasoprotective properties, which include reducing oxidative stress and augmenting endothelial function. We therefore tested the hypothesis in rodents that serelaxin treatment could attenuate low-dose GTN-induced tolerance.

Methods and Results: Co-incubation of mouse aortic rings ex vivo with GTN (10 μM) and serelaxin (10 nM) for 1 h, restored GTN responses, suggesting that serelaxin prevented the development of GTN tolerance. Male Wistar rats were subcutaneously infused with ethanol (control), low-dose GTN+placebo or low-dose GTN+serelaxin via osmotic minipumps for 3 days. Aortic vascular function and superoxide levels were assessed using wire myography and lucigenin-enhanced chemiluminescence assay respectively. Changes in aortic ALDH-2 expression were measured by qPCR and Western blot respectively. GTN+placebo infusion significantly increased superoxide levels, decreased ALDH-2 and attenuated GTN-mediated vascular relaxation. Serelaxin co-treatment with GTN significantly enhanced GTN-mediated vascular relaxation, reduced superoxide levels and increased ALDH-2 expression compared to GTN+placebo-treated rats.

Conclusion: Our data demonstrate that a combination of serelaxin treatment with low dose GTN attenuates the development of GTN-induced tolerance by reducing superoxide production and increasing ALDH-2 expression in the rat aorta. We suggest that serelaxin may improve nitrate efficacy in a clinical setting.

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.

Vascular actions of relaxin: nitric oxide and beyond

The peptide hormone relaxin regulates the essential maternal haemodynamic adaptations in early pregnancy through direct actions on the renal and systemic vasculature. These vascular actions of relaxin occur mainly through endothelium-derived NO-mediated vasodilator pathways and improvements in arterial compliance in small resistance-size arteries. This work catalysed a plethora of studies which revealed quite heterogeneous responses across the different regions of the vasculature, and also uncovered NO-independent mechanisms of relaxin action. In this review, we first describe the role of endogenous relaxin in maintaining normal vascular function, largely referring to work in pregnant and male relaxin-deficient animals. We then discuss the diversity of mechanisms mediating relaxin action in different vascular beds, including the involvement of prostanoids, VEGF, endothelium-derived hyperpolarisation and antioxidant activity in addition to the classic NO-mediated vasodilatory pathway. We conclude the review with current perspectives on the vascular remodelling capabilities of relaxin.

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.

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.

Anti-atherosclerotic effects of serelaxin in apolipoprotein E-deficient mice

BACKGROUND AND AIMS

Serelaxin (SLX) is a recombinant form of human relaxin-2, a naturally occurring peptide that regulates maternal cardiovascular adaptations to pregnancy. It is unclear whether SLX has a therapeutic effect on atherosclerosis. Therefore, we investigated direct vascular effects of SLX in a mouse model of atherosclerosis.

METHODS

6-8 week-old female apolipoprotein E-deficient mice were fed a high-fat, cholesterol-rich diet for 6 weeks and additionally received a continuous treatment with vehicle or SLX (0.05 or 0.1 μg/h), during the last 4 weeks, via subcutaneously implanted osmotic mini-pumps. Vascular oxidative stress, vasorelaxation and atherosclerotic plaque development were assessed.

RESULTS

Vascular oxidative stress was reduced in SLX-treated mice (vehicle: 322.67 RLU/s, SLX 0.05 μg/h: 119.76 RLU/s (p < 0.001 vs. vehicle), SLX 0.1 μg/h: 109.33 RLU/s (p < 0.001 vs. vehicle; p = 0.967 vs. 0.05 μg/h SLX)). Further SLX improved endothelium-dependent vasodilatation without influencing endothelium-independent vasorelaxation. Atherosclerotic plaque development was significantly reduced by SLX (vehicle: 0.38 ± 0.02 mm(2), 0.05 μg/h SLX: 0.32 ± 0.02 mm(2) (p = 0.047 vs. vehicle), 0.1 μg/h SLX: 0.29 ± 0.02 mm(2) (p = 0.002 vs. vehicle; p = 0.490 vs. 0.05 μg/h SLX)). Neither vascular macrophage, T-cell or neutrophil infiltration, nor collagen/vascular smooth muscle cell content differed between the groups. We observed a significant down-regulation of the angiotensin II type 1a receptor and a decrease in IL-6 and an increase in IL-10 plasma concentrations.

CONCLUSIONS

Our data demonstrates novel pleiotropic effects of SLX on vascular oxidative stress, endothelial dysfunction and atherosclerotic plaque burden. Therefore, SLX could serve as a new drug for the treatment of atherosclerosis-related diseases.

Relaxin-2 improves diastolic function of pressure-overloaded rats via phospholamban by activating Akt

BACKGROUND

Relaxin is a peptide hormone which has been demonstrated to be safe and has a therapeutic effect on acute heart failure in clinic trials. However, its effect on diastolic function is still unknown. The aims of the study were to determine whether relaxin could improve the diastolic function in pressure-overloaded rat model and to analyze potential mechanisms.

METHODS AND RESULTS

In the present study, a pressure-overloaded rat model induced by transaortic constriction (TAC) was established. Four weeks after TAC, echocardiography was performed and then all the rat models were randomly divided into 3 groups: models without intramyocardial injection (TAC), with intramyocardial injection of empty adenoviral vector (TAC+GFP) and adenoviral vector overexpression relaxin-2 gene (TAC+RLN2). A sham group was also included. Twelve days after intramyocardial injection, echocardiography and hemodynamics were carried out to evaluate diastolic function in sham, TAC, TAC+GFP and TAC+RLN2 groups. Then hearts were harvested for subsequent examinations. The results indicated that relaxin-2 had ameliorated diastolic function in the pressure-overloaded rats. Compared with the TAC and TAC+GFP groups, the relaxin-2 gene transfer increased phosphorylation of Akt at both the Ser473 and Thr308 sites. Meanwhile, it increased the Ser16 and Thr17- phosphorylation levels of phospholamban (PLB). Furthermore, SERCA2 activity was enhanced in the TAC+RLN2 group more than in the TAC and TAC+GFP groups.

CONCLUSIONS

These results demonstrated that relaxin-2 gene therapy improved diastolic function in pressure-overloaded rats. The potential mechanism may be that relaxin-2 gene transfer enhances SERCA2 activity in hearts by increasing phospholamban phosphorylation through nuclear-targeted Akt phosphorylation.

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

Protection from cigarette smoke-induced vascular injury by recombinant human relaxin-2 (serelaxin)

Smoking is regarded as a major risk factor for the development of cardiovascular diseases (CVD). This study investigates whether serelaxin (RLX, recombinant human relaxin-2) endowed with promising therapeutic properties in CVD, can be credited of a protective effect against cigarette smoke (CS)-induced vascular damage and dysfunction. Guinea pigs exposed daily to CS for 8 weeks were treated with vehicle or RLX, delivered by osmotic pumps at daily doses of 1 or 10 μg. Controls were non-smoking animals. Other studies were performed on primary guinea pig aortic endothelial (GPAE) cells, challenged with CS extracts (CSE) in the absence and presence of 100 ng/ml (17 nmol/l) RLX. In aortic specimens from CS-exposed guinea pigs, both the contractile and the relaxant responses to phenylephrine and acetylcholine, respectively, were significantly reduced in amplitude and delayed, in keeping with the observed adverse remodelling of the aortic wall, endothelial injury and endothelial nitric oxide synthase (eNOS) down-regulation. RLX at both doses maintained the aortic contractile and relaxant responses to a control-like pattern and counteracted aortic wall remodelling and endothelial derangement. The experiments with GPAE cells showed that CSE significantly decreased cell viability and eNOS expression and promoted apoptosis by sparkling oxygen free radical-related cytotoxicity, while RLX counterbalanced the adverse effects of CSE. These findings demonstrate that RLX is capable of counteracting CS-mediated vascular damage and dysfunction by reducing oxidative stress, thus adding a tile to the growing mosaic of the beneficial effects of RLX in CVD.

Serelaxin: A Novel Therapeutic for Vascular Diseases

Vascular dysfunction is an important hallmark of cardiovascular disease. It is characterized by increased sensitivity to vasoconstrictors, decreases in the endothelium-derived vasodilators nitric oxide (NO) and prostacyclin (PGI2), and endothelium-derived hyperpolarization (EDH). Serelaxin (recombinant human relaxin) has gained considerable attention as a new vasoactive drug, largely through its beneficial therapeutic effects in acute heart failure. In this review we first describe the contribution of endogenous relaxin to vascular homeostasis. We then provide a comprehensive overview of the novel mechanisms of serelaxin action in blood vessels that differentiate it from other vasodilator drugs and explain how this peptide could be used more widely as a therapeutic to alleviate vascular dysfunction in several cardiovascular diseases.

Etanercept improves endothelial function via pleiotropic effects in rat adjuvant-induced arthritis

OBJECTIVES

To determine the effect of etanercept on endothelial dysfunction and on traditional cardiovascular (CV) risk factors in the adjuvant-induced arthritis (AIA) rat model.

METHODS

At the first signs of arthritis, etanercept (10 mg/kg/3 days, s.c.) or saline was administered for 3 weeks in AIA rats. Body weights and arthritis scores were monitored daily. Endothelial function was studied in aortic rings relaxed with acetylcholine (Ach) with or without inhibitors of nitric oxide synthase (NOS), cyclo-oxygenase (COX-2), arginase, endothelium-derived hyperpolarizing factor and superoxide anions (O2 (-)°) production. Aortic expression of endothelial nitic oxide synthase (eNOS), Ser1177-phospho-eNOS, COX-2, arginase-2, p22(phox) and p47(phox) was evaluated by western blotting analysis. Blood pressure, heart rate and blood levels of triglycerides, cholesterol and glucose were measured.

RESULTS

Etanercept significantly reduced arthritis score (P < 0.001). It improved Ach-induced relaxation (P < 0.05) as a result of increased NOS activity, decreased COX-2/arginase activities and decreased O2 (-)° production. These functional effects relied on increased eNOS expression and phosphorylation, and decreased COX-2, arginase-2 and p22(phox) expressions. No correlation was found between arthritis score and Ach-induced relaxation. The treatment did not change triglycerides, cholesterol and glucose levels, but significantly increased systolic blood pressure and heart rate (P < 0.05).

CONCLUSION

Our data demonstrated that efficient dosage of etanercept on inflammatory symptoms improved endothelial function in AIA. This beneficial effect on endothelial function is disconnected from its impact on CV risk factors and relates to pleiotropic effects of etanercept on endothelial pathways. These results suggest that etanercept could be a good choice for patients with rheumatoid arthritis at high risk of CV events.

Serelaxin (recombinant human relaxin-2) prevents high glucose-induced endothelial dysfunction by ameliorating prostacyclin production in the mouse aorta

Diabetes-induced endothelial dysfunction is a critical initiating factor in the development of cardiovascular complications. Treatment with relaxin improves tumour necrosis factor α-induced endothelial dysfunction by enhancing endothelial nitric oxide synthase (eNOS) activity and restoring superoxide dismutase 1 protein in rat aortic rings ex vivo. It is, therefore, possible that relaxin treatment could alleviate endothelial dysfunction in diabetes. This study aimed to test the hypothesis that serelaxin (recombinant human relaxin-2) prevents high glucose-induced vascular dysfunction in the mouse aorta. Abdominal aortae were isolated from C57BL/6 male mice and incubated in M199 media for 3days with either normal glucose (5.5mM) or high glucose (30mM), and co-incubated with placebo (20mM sodium acetate) or 10nM serelaxin at 37°C in 5% CO2. Vascular function was analysed using wire-myography. High glucose significantly reduced the sensitivity to the endothelium-dependent agonist, acetylcholine (ACh) (pEC50; normal glucose=7.66±0.10 vs high glucose=7.29±0.10, n=11-12, P<0.05) and the contraction induced by NOS inhibitor, L-NAME (200μM) (normal glucose=59.9±8.3% vs high glucose=38.7±4.3%, n=6, P<0.05), but had no effect on the endothelium-independent agonist, sodium nitroprusside (SNP)-mediated relaxation. Treatment with serelaxin restored endothelial function (pEC50; 7.83±0.11, n=11) but not NO availability. The presence of the cyclooxygenase (COX) inhibitor, indomethacin (1μM) (pEC50; control=7.29±0.10 vs indo=7.74±0.18, n=6-12, P<0.05) and a superoxide dismutase mimetic, tempol (10μM) (pEC50; control=7.29±0.10 vs tempol=7.82±0.05, n=6-12, P<0.01) significantly improved sensitivity to ACh in high glucose treated aortae, but had no effect in serelaxin treated aortae. This suggests that high glucose incubation alters the superoxide and COX-sensitive pathway, which was normalized by co-incubation with serelaxin. Neither high glucose incubation nor serelaxin treatment had an effect on cyclooxygenase 1 and 2 (Ptgs1, Ptgs2), prostacyclin synthase (PTGIS) and receptor (Ptgir) as well as thromboxane A2 receptor (Tbxa2r) mRNA expression. Importantly, production of prostacyclin was significantly (P<0.05) attenuated in high glucose treated aortae, which was prevented by serelaxin treatment. Our data show that serelaxin treatment for 3 days restores high glucose-induced endothelial dysfunction by ameliorating vasodilator prostacyclin production and possibly through the reduction of superoxide in the mouse aorta.

Time-dependent activation of prostacyclin and nitric oxide pathways during continuous i.v. infusion of serelaxin (recombinant human H2 relaxin)

BACKGROUND AND PURPOSE

In the RELAX-AHF trial, a 48 h i.v. serelaxin infusion reduced systemic vascular resistance in patients with acute heart failure. Consistent with preclinical studies, serelaxin augments endothelial vasodilator function in rat mesenteric arteries. Little is known about the contribution of endothelium-derived relaxing factors after a longer duration of continuous serelaxin treatment. Here we have assessed vascular reactivity and mechanistic pathways in mesenteric arteries and veins and the aorta after 48 or 72 h continuous i.v. infusion of serelaxin.

EXPERIMENTAL APPROACH

Male rats were infused with either placebo or serelaxin (13.3 μg·kg(-1) ·h(-1) ) via the jugular vein using osmotic minipumps. Vascular function was assessed using wire myography. Changes in gene and protein expression and 6-keto PGF1α levels were determined by quantitative PCR, Western blot and ELISA respectively.

KEY RESULTS

Continuous i.v. serelaxin infusion augmented endothelium-dependent relaxation in arteries (mesenteric and aorta) but not in mesenteric veins. In mesenteric arteries, 48 h i.v. serelaxin infusion increased basal NOS activity, associated with increased endothelial NOS (eNOS) expression. Interestingly, phosphorylated-eNOS(Ser1177) , eNOS and basal NOS activity were reduced in mesenteric arteries following 72 h serelaxin treatment. At 72 h, serelaxin treatment improved bradykinin-mediated relaxation through COX2-derived PGI2 production.

CONCLUSIONS AND IMPLICATIONS

Continuous i.v. serelaxin infusion enhanced endothelial vasodilator function in arteries but not in veins. The underlying mediator at 48 h was NO but there was a transition to PGI2 by 72 h. Activation of the PGI2 -dependent pathway is key to the prolonged vascular response to serelaxin treatment.

Relaxin-2 does not ameliorate nephropathy in an experimental model of type-1 diabetes

BACKGROUND/AIMS

In diabetic nephropathy (DN), the current angiotensin-II-blocking pharmacotherapy is frequently failing. For diabetic cardiomyopathy (DC), there is no specific remedy available. Relaxin-2 (Rlx) - an anti-fibrotic, anti-inflammatory, and vasoprotecting peptide – is a candidate drug for both.

METHODS

Low-dose (32 μg/kg/day) and high-dose (320 μg/kg/day) Rlx were tested against vehicle (n = 20 each) and non-diabetic controls (n = 14) for 12 weeks in a model of type-1 diabetes induced in endothelial nitric oxide synthase knock-out (eNOS-KO) mice by intraperitoneal injection of streptozotocin.

RESULTS

Diabetic animals showed normal plasma creatinine, markedly increased albuminuria and urinary malonyldialdehyde, elevated relative kidney weight, glomerulosclerosis, and increased glomerular size, but no relevant interstitial fibrosis. Neither dose of Rlx affected these changes although the drug was active and targeted plasma levels were achieved. Of note, we found no activation of the renal TGF-β pathway in this model. In the hearts of diabetic animals, no fibrotic alterations indicative of DC could be determined which precluded testing of the initial hypothesis.

CONCLUSIONS

We investigated a model showing early DN without overt tubulointerstitial fibrosis and activation of the TGF-β-Smad-2/3 pathway. In this model, Rlx proved ineffective; however, the same may not apply to other models and types of diabetes.

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.

Increased superoxide production and altered nitric oxide-mediated relaxation in the aorta of young but not old male relaxin-deficient mice

The vascular effects of exogenous relaxin (Rln) treatment are well established and include decreased myogenic reactivity and enhanced relaxation responses to vasodilators in small resistance arteries. These vascular responses are reduced in older animals, suggesting that Rln is less effective in mediating arterial function with aging. The present study investigated the role of endogenous Rln in the aorta and the possibility that vascular dysfunction occurs more rapidly with aging in Rln-deficient ( Rln−/−) mice. We compared vascular function and underlying vasodilatory pathways in the aorta of male wild-type ( Rln+/+) and Rln−/− mice at 4 and 16 mo of age using wire myography. Superoxide production, but not nitrotyrosine or NADPH oxidase expression, was significantly increased in the aorta of young Rln−/− mice, whereas endothelial nitric oxide (NO) synthase and basal NO availability were both significantly decreased compared with Rln+/+ mice. In the presence of the cyclooxygenase inhibitor indomethacin, sensitivity to ACh was significantly decreased in young Rln−/− mice, demonstrating altered NO-mediated relaxation that was normalized in the presence of a membrane-permeable SOD or ROS scavenger. These vascular phenotypes were not exacerbated in old Rln−/− mice and, in most cases, did not differ significantly from old Rln+/+ mice. Despite the vascular phenotypes in Rln−/− mice, endothelium-dependent and -independent vasodilation were not adversely affected. Our data show a role for endogenous Rln in reducing superoxide production and maintaining NO availability in the aorta but also demonstrate that Rln deficiency does not compromise vascular function in this artery or exacerbate endothelial dysfunction associated with aging.

Cardiac endothelium-myocyte interaction: clinical opportunities for new heart failure therapies regardless of ejection fraction

Heart failure (HF) is an important global health problem with great socioeconomic burden. Outcomes remain sub-optimal. Endothelium-cardiomyocyte interactions play essential roles in cardiovascular homeostasis, and deranged endothelium-related signalling pathways have been implicated in the pathophysiology of HF. In particular, disturbances in nitric oxide (NO)-mediated pathway and neuregulin-mediated pathway have been shown to contribute to the development of HF. These signalling pathways hold the potential as pathophysiological targets for new HF therapies, and may aid in patient selection for future HF trials.

Tetrahydroxystilbene Glucoside Improves TNF-α-Induced Endothelial Dysfunction: Involvement of TGFβ/Smad Pathway and Inhibition of Vimentin Expression

Endothelial dysfunction plays an important role in the pathogenesis of atherogenesis. 2,3,5,4′-tetrahydroxystilbene-2-O-β-D-glucoside (TSG), an active component of the rhizome extract from Polygonum multiflorum (PM), exhibits significant anti-atherosclerotic activity. Here, we used human umbilical vein endothelial cells (HUVECs) induced by tumor necrosis factor-α (TNF-α) in vitro to investigate the cytoprotective effects of TSG on TNF-α-induced endothelial injury and the related mechanisms. Pretreatment with 50 and 100 μM TSG markedly attenuated TNF-α-induced loss of cell viability and release of lactate dehydrogenase (LDH) and inhibited TNF-α-induced cell apoptosis. The inhibition of vimentin expression was involved in the cytoprotection afforded by TSG. Using inhibitors for PI3K and TGFβ or siRNA for Akt and Smad2, we found that vimentin production in HUVECs is regulated by TGFβ/Smad signaling, but not by PI3K–Akt–mTOR signaling. Meanwhile, TSG inhibited both the expression of TGFβ1 and the phosphorylation of Smad2 and Smad3, and TSG suppressed the nuclear translocation of Smad4 induced by TNF-α. These results suggest that TSG protects HUVECs against TNF-α-induced cell damage by inhibiting vimentin expression via the interruption of the TGFβ/Smad signaling pathway.

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.

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.