Four-day urocortin-I administration has sustained beneficial haemodynamic, hormonal, and renal effects in experimental heart failure

Urocortin I Protects against Myocardial Ischemia/Reperfusion Injury by Sustaining Respiratory Function and Cardiolipin Content via Mitochondrial ATP-Sensitive Potassium Channel Opening

Objective

Our experiments were aimed at probing whether urocortin I postconditioning was beneficial for maintaining the mitochondrial respiratory function and inhibiting the surging of reactive oxygen species. In addition, our experiments also intended to reveal the relationships between urocortin I postconditioning and mitochondrial ATP-sensitive potassium channel.

Methods

Langendorff and MPA perfusion systems were used to establish myocardial ischemia-reperfusion injury model and cardiomyocytes hypoxia-reoxygenation injury model in rats, respectively. Isolated hearts and cardiomyocytes were randomly divided into normal group, ischemia-reperfusion/hypoxia-reoxygenation group, urocortin I postconditioning group, and 5-hydroxysolanoic acid (5-HD)+urocortin I group. At the end of balance (T₁) and reperfusion (T₂), cardiac functions, mitochondrial state3 respiratory, respiratory control ratio, mitochondrial respiratory enzyme activity, and mitochondrial cardiolipin content were measured. Our experiments also observed the ultrastructure of myocardium. The changes of cardiomyocyte mitochondrial permeability transition pore, mitochondrial membrane potential, reactive oxygen species, expression of apoptosis protein, and cardiomyocytes activity were detected at the end of reoxygenation.

Results

The cardiac functions, mitochondrial respiratory function, and enzyme activity of the normal group were better than other three groups at T₂, and urocortin I postconditioning group was better than the IR group and 5-HD+urocortin I group. LVEDP, +dp/dt_max, mitochondrial respiratory function, and enzyme activity of IR group were worse than 5-HD+urocortin I group. Cardiolipin content of the normal group was higher than the other three groups at T₂, urocortin I postconditioning group was higher than the IR group and 5-HD+urocortin I group, and 5-HD+urocortin I group was still higher than the IR group. The ultrastructure of the normal group maintained the most integrated than the other groups, IR group suffered the most serious damage, and ultrastructure of the urocortin I postconditioning group was better than the IR group and 5-HD+urocortin I group. At the end of reoxygenation, activity of mitochondrial permeability transition pore and generation of reactive oxygen species of normal group were lower than the other groups, HR group and 5-HD+urocortin I group were higher than the urocortin I postconditioning group, and 5-HD+urocortin I group was still higher than the urocortin I postconditioning group. Normal group had the highest level of mitochondrial membrane potential at the end of reoxygenation, and the urocortin I postconditioning group was higher than the HR group and 5-HD+urocortin I group. The normal group had the lowest expression level of Bax and the highest expression level of Bcl-2 at the end of reoxygenation. Urocortin I postconditioning group had lower Bax expression but higher Bcl-2 expression than the HR and 5-HD+urocortin I group. Accordingly, the normal group had the highest activity of cardiomyocytes, and the urocortin I postconditioning group was higher than the HR group and 5-HD+urocortin I group.

Conclusions

Urocortin I postconditioning can protect the activity of cardiomyocytes after hypoxia-reoxygenation injury, improve the mitochondrial respiratory function, and enhance the contractility of isolated heart after myocardial ischemia-reperfusion injury. The alleviation of myocardial injury relates to the opening of mitochondrial ATP-sensitive potassium channel.

Research on the Effects of the Chronic Treatment With Different Doses of Urocortin 2 in Heart Failure Rats

Corticotropin-releasing factor (CRF) receptor type 2 (CRF₂) exists in both cardiomyocytes and neurocytes. The purpose of this research was to explore if chronic treatment with urocortin 2 (UCN2), a CRF₂ receptor agonist, at different doses can improve prognosis and regulate the expression of CRF₂ receptor and calcium handling proteins without any adverse effects on behavior in heart failure. Heart failure was established in Sprague-Dawley rats and was confirmed by echocardiography. Heart failure rats were injected intraperitoneally with UCN2 (5, 10, or 20 µg·kg⁻¹·d⁻¹) for 30 days. Survival rate, cardiac function, expressions of cardiac CRF₂ receptor, RyR2, SERCA2, and hypothalamic and hippocampal c-FOS, CRF receptor type 1 (CRF₁) and CRF₂ receptor were determined. Behavior was evaluated by Morris Water-Maze and Open-Field tests. Results showed that chronic peripheral UCN2 treatment improved survival rate in a dose–response manner and increased cardiac function and expression of CRF₂ receptor and SERCA2 in heart failure, especially at the high dosage. Moreover, cellular-fos (c-FOS), CRF₁ receptor, and CRF₂ receptor expressions of both hypothalamic and hippocampal tissues were significantly increased in high dosage group. Furthermore, the behavior tests suggested that chronic UCN2 treatment did not exacerbate stress/anxiety-like behavior in HF. In conclusion, chronic peripheral treatment with UCN2 increases survival in a dose–response manner in heart failure rats without inducing stress/anxiety-like behavior.

Redefining biomarkers in heart failure

Heart failure (HF) is the end result of many different cardiac and non-cardiac abnormalities leading to a complex clinical entity. In this view, the use of biomarkers in HF should be deeply reconsidered; indeed, the same biomarker may carry a different significance in patients with preserved or reduced EF. The aim of this review is to reconsider the role of biomarkers in HF, based on the different clinical characteristics of this syndrome. The role of cardiac and non-cardiac biomarkers will be reviewed with respect of the different clinical manifestations of this syndrome.

Urocortin attenuates myocardial fibrosis in diabetic rats via the Akt/GSK-3β signaling pathway

OBJECTIVE

Urocortin, a novel identified corticotropin-releasing factor-related endocrinal peptide, has been shown to play an essential role in cardioprotection. Until recently, whether urocortin can protect the heart against diabetic cardiomyopathy (DCM) remained unclear. Herein, we evaluated the cardioprotective effect of urocortin on cardiac dysfunction, inflammation, and fibrosis and demonstrated the potential mechanism in a diabetic rat model.

METHODS

Diabetic rats were randomly divided into 4 groups: diabetic control group, urocortin, urocortin + astressin (a selective CRF receptor 2 antagonist) and urocortin + triciribine (an Akt pathway blocker). Cardiac catheterization was performed to evaluate cardiac function. The levels of creatine phosphokinase isoenzyme (CK-MB), plasma brain natriuretic peptide (BNP), myocardial collagen volume fraction (CVF) and left ventricular mass index (LVWI) were measured. Inflammatory factors (transforming growth factor beta 1, TGF-β1; connective tissue growth factor, CTGF) and activation of signaling proteins (Akt, GSK-3β) were also detected using western blot.

RESULTS

DCM was successfully induced by the injection of streptozotocin (STZ) as evidenced by abnormal heart mass and cardiac function as well as the imbalance of extracellular matrix homeostasis. Rats in the DCM group showed increased mRNA and protein levels of LVWI, BNP, CK-MB, CVF, TGF-β1 and CTGF compared to the control group, which were accompanied with diminished phosphorylation of Akt and GSK-3β. Interestingly, myocardial dysfunction, cardiac fibrosis, and inflammation were suppressed by urocortin in the heart of diabetic rats. Moreover, inhibition of phosphorylation of Akt and GSK-3β was also reversed by urocortin. These effects of urocortin were suppressed by astressin. In addition, triciribine partially reduced the effects of urocortin on myocardial dysfunction, inflammation, and cardiac fibrosis.

CONCLUSIONS

These results suggest that urocortin exhibits a therapeutic benefit in the treatment of DCM by attenuating fibrosis and inflammation. Furthermore, inhibition of the Akt/GSK-3β signaling pathway may be partially responsible for these effects.

The evaluation of the clinical utility of urocortin 1 and adrenomedullin versus proBNP in systolic heart failure

Objective:

Urocortin 1 (UCN1) has vasodilator, diuretic, and natriuretic effects, and its expression increases in heart failure (HF). Adrenomedullin (ADM) increases cardiac output and lowers blood pressure in healthy men and in patients with heart failure. The aim of the study was to determine UCN1 and ADM levels in patients with HF, to evaluate the relationship of UCN1 and ADM with various clinical parameters, and to assess UCN1 and ADM as diagnostic markers in HF, in comparison with pro-brain natriuretic peptide (pro-BNP).

Methods:

We investigated serum levels of UCN1, ADM, and pro-BNP in 86 consecutive patients with systolic HF [ejection fraction (EF) ≤45%] and 85 healthy controls. Serum UCN1, ADM, and pro-BNP levels were measured with the ELISA method. Transthoracic echocardiography was performed to determine left ventricular EF and pulmonary artery systolic pressure.

Results:

UCN1 and ADM levels were higher in HF patients (446.2±145.7 pg/mL, p<0.001; 87.9±4.2 pg/mL, p<0.001 respectively). UCN1 was positively correlated with pro-BNP (r=0.963, p<0.001), ADM (r=0.915, p<0.001), and NYHA (r=0.879, p<0.001); ADM was positively correlated with pro-BNP (r=0.956, p<0.001) and NYHA (r=0.944, p<0.001). Receiver operating characteristic curves yielded an area under the curve of 1.00 (p<0.001) for UCN1, 1.00 (p<0.001) for ADM, and 0.99 (p<0.001) for pro-BNP in the diagnosis of HF.

Conclusion:

UCN1 and ADM increase with worsening HF and left ventricular dysfunction. They may be used as diagnostic biomarkers in systolic HF, but the incremental value of measuring UCN1 and ADM in patients tested for pro-BNP is questionable.

Urocortin ameliorates diabetic cardiomyopathy in rats via the Akt/GSK-3β signaling pathway

Urocortin has been shown to exert powerful protective effects on various cardiovascular disease models. However, the role and mechanism of urocortin in protecting against diabetic cardiomyopathy (DCM) has not yet been elucidated. In the present study, the effects of urocortin on cardiac dysfunction, fibrosis, inflammation and the interrelated signaling pathways were investigated in a diabetic rat model. Diabetes mellitus (DM) was induced in the rats by intraperitoneal injection of streptozotocin. The diabetic rats were randomly divided into four groups: Diabetic control, urocortin, urocortin + astressin treatment and urocortin + triciribine treatment groups. All the experiments were conducted at 16 weeks following the induction of DM. The levels of glycosylated hemoglobin (HbA1c), creatine phosphokinase isoenzyme (CK-MB) and plasma brain natriuretic peptide (BNP), as well as the myocardial collagen volume fraction (CVF) and left ventricular mass index (LVWI), were measured. In addition, levels of inflammatory factors, including transforming growth factor (TGF)-β1, connective tissue growth factor (CTGF) and interrelated proteins, such as Akt and glycogen synthase kinase (GSK)-3β, were detected by biochemical analyses. In the diabetic group, the levels of BNP and CK-MB, as well as the mRNA and protein expression levels of TGF-β1 and CTGF, and the LVWI and CVF, were higher compared with the rats in the control group (P<0.05). This was accompanied by decreased Akt and GSK-3β phosphorylation (P<0.05). Notably, urocortin attenuated myocardial dysfunction, cardiac fibrosis and inflammation in the hearts of the diabetic rats. However, urocortin exhibited no effect on the level of HbA1c. In addition, the inhibited phosphorylation of Akt and GSK-3β was restored with urocortin administration. However, all the effects of urocortin were eliminated with treatment of the corticotropin releasing factor receptor 2 antagonist, astressin. Triciribine, an Akt inhibitor, partially eliminated the effects of urocortin on myocardial dysfunction, inflammation and cardiac fibrosis in the hearts of the diabetic rats. These results indicated that urocortin may exhibit great therapeutic potential in the treatment of DCM by attenuating fibrosis and inflammation. Furthermore, the Akt/GSK-3β signaling pathway may be partially involved in mediating these effects.

Intravenous adeno-associated virus serotype 8 encoding urocortin-2 provides sustained augmentation of left ventricular function in mice

Urocortin-2 (UCn2) peptide infusion increases cardiac function in patients with heart failure, but chronic peptide infusion is cumbersome, costly, and provides only short-term benefits. Gene transfer would circumvent these shortcomings. Here we ask whether a single intravenous injection of adeno-associated virus type 8 encoding murine urocortin-2 (AAV8.UCn2) could provide long-term elevation in plasma UCn2 levels and increased left ventricular (LV) function. Normal mice received AAV8.UCn2 (5×10¹¹ genome copies, intravenous). Plasma UCn2 increased 15-fold 6 weeks and >11-fold 7 months after delivery. AAV8 DNA and UCn2 mRNA expression was persistent in LV and liver up to 7 months after a single intravenous injection of AAV8.UCn2. Physiological studies conducted both in situ and ex vivo showed increases in LV +dP/dt and in LV -dP/dt, findings that endured unchanged for 7 months. SERCA2a mRNA and protein expression was increased in LV samples and Ca²⁺ transient studies showed an increased rate of Ca²⁺ decline in cardiac myocytes from mice that had received UCn2 gene transfer. We conclude that a single intravenous injection of AAV8.UCn2 increases plasma UCn2 and increases LV systolic and diastolic function for at least 7 months. The simplicity of intravenous injection of a long-term expression vector encoding a gene with paracrine activity to increase cardiac function is a potentially attractive strategy in clinical settings. Future studies will determine the usefulness of this approach in the treatment of heart failure.

Bradycardic effects of microinjections of urocortin 3 into the nucleus ambiguus of the rat

The presence of urocortin 3 (UCN3) and CRF2 receptors (CRF2R) has been demonstrated in brain tissue. Nucleus ambiguus (nAmb) is the predominant brain area providing parasympathetic innervation to the heart. On the basis of these reports, it was hypothesized that activation of CRF2Rs in the nAmb may elicit cardiac effects. Experiments were carried out in urethane-anesthetized, artificially ventilated, and adult male Wistar rats. Microinjections of l-glutamate (l-GLU, 5 mM) were used to identify the nAmb. Different concentrations of UCN3 (0.031, 0.062, 0.125, 0.25, and 0.5 mM) microinjected into the nAmb elicited decreases in heart rate (HR) (5.3 ± 1, 22 ± 3.3, 38 ± 4.9, 45.7 ± 2.7, and 27.3 ± 2.3 bpm, respectively). The volume of all microinjections was 30 nl. Blood pressure changes concomitant with decreases in HR were not observed. Bradycardia elicited by microinjections of UCN3 (0.25 mM; maximally effective concentration) into the nAmb was significantly (P < 0.05) attenuated by microinjections of selective CRF2R antagonists (K41498, 0.5 mM, and astressin 2B, 0.25 mM) at the same site. Bilateral vagotomy abolished the bradycardic responses to UCN3. These results indicated that activation of CRF2Rs in the nAmb by UCN3 elicited bradycardia, which was vagally mediated. UCNs have been reported to exert cardioprotective effects in heart failure and ischemia/reperfusion injury. In this situation, centrally induced bradycardia by UCN3 would be beneficial. The results of the present investigation provide a platform for future studies on the role of CRF2Rs in the nAmb in pathological states such as heart failure.

The corticotropin releasing factor system in the kidney: perspectives for novel therapeutic intervention in nephrology

The adaptation to endogenous and exogenous stress stimuli is crucial for survival but also for the onset of various diseases in humans. Corticotropin releasing factor (CRF) system is the major regulator of stress response and homeostasis. The members of this family of peptides extend their actions also outside CNS to the periphery where they may affect various body systems independently, acting via vagal and/or autocrine/paracrine pathways. In search for peripheral targets, kidney has rarely been studied separately, regarding expression and action of CRF and CRF-related peptides. We reviewed the existing literature concerning expression and action of the CRF system in normal and pathological renal tissue and explored possible clinical implications in nephrology. CRF system components are expressed in the kidney of experimental animals and in humans. The intrarenal distribution is reported to be equally extensive, suggesting a physiological or pathophysiological role in renal function and in the occurrence of renal disease. Urocortins have given multiple interesting observations in experimental models of renal disease and clinical studies, showing robust effects in renal regulation mechanisms. We summarize the relevant data and put them in context, proposing applications with clinical significance in the field of hypertension, diabetic nephropathy, chronic kidney disease, cardiorenal syndrome, and peritoneal dialysis.

Clinical perspectives of urocortin and related agents for the treatment of cardiovascular disease

The effects of corticotropin-releasing hormone, also known as corticotropin-releasing factor (CRF), on the cardiovascular system have been intensively researched since its discovery. Moreover, the actions of urocortin (Ucn) I on the cardiovascular system have also been intensively scrutinized following the cloning and identification of its receptor, CRF receptor type 2 (CRFR2), in peripheral tissues including the heart. Given the cardioprotective actions of CRFR2 ligands, the clinical potential of not only Ucn I but also Ucn II and III, which were later identified as more specific ligands for CRFR2, has received considerable attention from researchers. In addition, recent work has indicated that CRF type 1 receptor may be also involved in cardioprotection against ischemic/reperfusion injury. Here we provide a historical overview of research on Ucn I and related agents, their effects on the cardiovascular system, and the clinical potential of the use of such agents to treat cardiovascular diseases.

Emerging biomarkers in heart failure

BACKGROUND

Until recently, biomarker testing in heart failure (HF) syndromes has been viewed as an elective supplement to diagnostic evaluation of patients suspected to suffer from this condition. This approach to the use of biomarker testing contrasts with other cardiovascular diagnoses such as acute myocardial infarction, for which biomarkers are integral to disease process definition, risk stratification, and in some cases treatment decision making.

CONTENT

In this review we consider various perspectives on the evaluation of biomarkers in HF. In addition, we examine recent advances in the understanding of established biomarkers in HF (such as the natriuretic peptides), the elucidation of novel biomarkers potentially useful for the evaluation and management of patients with HF, and the growing understanding of important and relevant comorbidities in HF. We also review candidate biomarkers from a number of classes: (a) myocyte stretch, (b) myocyte necrosis, (c) systemic inflammation, (d) oxidative stress, (e) extracellular matrix turnover, (f) neurohormones, and (g) biomarkers of extracardiac processes, such as renal function.

SUMMARY

Novel applications of established biomarkers of HF as well as elucidation and validation of emerging assays for HF syndromes have collectively led to a growing interest in the more widespread use of such testing in patients affected by the diagnosis.

Prolonged urocortin 2 administration in experimental heart failure: sustained hemodynamic, endocrine, and renal effects

Although acute administration of urocortin 2 has beneficial actions in heart failure, the integrated hemodynamic, hormonal, and renal effects of sustained urocortin 2 treatment in this disease have not been investigated. In the current study, we administered a 4-day infusion of a vehicle control (0.9% saline; n=6) or urocortin 2 (0.75 μg/kg per hour; n=6) to sheep with pacing-induced heart failure. Compared with time-matched controls, infusion of urocortin 2 produced rapid (30-minute) and persistent (4-day) improvements in cardiac contractility (day 4: control 905±73 versus urocortin 2 1424±158 mm Hg/s; P<0.001) and output (2.6±0.1 versus 3.8±0.3 L/min; P<0.001), together with reductions in left atrial pressure (28±1 versus 12±1 mm Hg; P<0.001) and peripheral resistance (30±2 versus 20±2 mm Hg/L per min; P<0.001). In contrast, urocortin 2-induced falls in mean arterial pressure were not established until the second day (day 4: 74±2 versus 72±2 mm Hg; P<0.05). Prolonged urocortin 2 administration was associated with sustained (days 0 to 4) declines in plasma renin activity (day 4: 1.33±0.27 versus 0.73±0.20 nmol/L per hour; P<0.001), aldosterone (970±383 versus 396±96 pmol/L; P<0.05), vasopressin (2.4±0.8 versus 1.3±0.1 pmol/L; P<0.05), endothelin 1 (7.2±0.7 versus 4.5±0.4 pmol/L; P<0.01), and atrial (269±27 versus 150±19 pmol/L; P<0.001) and B-type (65±9 versus 29±6 pmol/L; P<0.001) natriuretic peptides, as well as an acute transient rise in plasma cortisol (day 1: P<0.001). Chronic urocortin 2 also persistently augmented urinary sodium (day 4: 4-fold increase; P<0.001) and creatinine (1.4-fold; P<0.001) excretion and creatinine clearance (1.5-fold; P<0.01) compared with control. Food consumption was temporarily suppressed (P<0.05). In conclusion, 4-day urocortin 2 administration induces sustained improvements in hemodynamics and renal function, in association with inhibition of multiple vasoconstrictor/volume-retaining systems. These findings support the therapeutic potential for urocortin 2 in heart failure.

Microinjections of urocortin1 into the nucleus ambiguus of the rat elicit bradycardia

Urocortins are members of the hypothalamic corticotropin-releasing factor (CRF) peptide family. Urocortin1 (UCN1) mRNA has been reported to be expressed in the brainstem neurons. The present investigation was carried out to test the hypothesis that microinjections of UCN1 into the nucleus ambiguus (nAmb) may elicit cardiac effects. Urethane-anesthetized, artificially ventilated, adult male Wistar rats, weighing between 300-350 g, were used. nAmb was identified by microinjections of l-glutamate (5 mM, 30 nl). Microinjections (30 nl) of different concentrations (0.062, 0.125, 0.25, and 0.5 mM) of UCN1 into the nAmb elicited bradycardic responses (26.5 ± 1, 30.1 ± 1.7, 46.9 ± 1.7, and 40.3 ± 2.6 beats/min, respectively). These heart rate responses were not accompanied by significant changes in mean arterial pressure. The bradycardic responses to maximally effective concentration of UCN1 (0.25 mM) were significantly (P < 0.05) attenuated by prior microinjections of a selective antagonist (NBI 27914, 1.5 mM) for CRF type 1 receptor (CRF1R). Prior microinjections of ionotropic glutamate receptor (iGLUR) antagonists [d-(-)-2-amino-7-phosphono-heptanoic acid and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo-(f)quinoxaline-7-sulfonamide disodium] also attenuated the bradycardia elicited by UCN1 microinjections into the nAmb. Microinjections of NBI 27914 (1.5 mM) into the nAmb did not alter baroreflex responses. Bilateral vagotomy abolished the bradycardic responses to microinjections of UCN1 into the nAmb. These results indicated that 1) microinjections of UCN1 into the nAmb elicited bradycardia, 2) the bradycardia was vagally mediated, 3) activation of CRF1Rs in the nAmb was responsible for the actions of UCN1, and 4) activation of iGLURs in the nAmb also participated in the bradycardia elicited by UCN1.

Corticotropin-releasing factor signaling and visceral response to stress

Stress may cause behavioral and/or psychiatric manifestations such as anxiety and depression and also impact on the function of different visceral organs, namely the gastrointestinal and cardiovascular systems. During the past years substantial progress has been made in the understanding of the underlying mechanisms recruited by stressors. Activation of the corticotropin-releasing factor (CRF) signaling system is recognized to be involved in a large number of stress-related behavioral and somatic disorders. This review will outline the present knowledge on the distribution of the CRF system (ligands and receptors) expressed in the brain and peripheral viscera and its relevance in stress-induced alterations of gastrointestinal and cardiovascular functions and the therapeutic potential of CRF(1) receptor antagonists.

New targets of urocortin-mediated cardioprotection

The urocortin (UCN) hormones UCN1 and UCN2 have been shown previously to confer significant protection against myocardial ischaemia/reperfusion (I/R) injury; however, the molecular mechanisms underlying their action are poorly understood. To further define the transcriptional effect of UCNs that underpins their cardioprotective activity, a microarray analysis was carried out using an in vivo rat coronary occlusion model of I/R injury. Infusion of UCN1 or UCN2 before the onset of reperfusion resulted in the differential regulation of 66 and 141 genes respectively, the majority of which have not been described previously. Functional analysis demonstrated that UCN-regulated genes are involved in a wide range of biological responses, including cell death (e.g. X-linked inhibitor of apoptosis protein), oxidative stress (e.g. nuclear factor erythroid derived 2-related factor 1/nuclear factor erythroid derived 2-like 1) and metabolism (e.g. Prkaa2/AMPK). In addition, both UCN1 and UCN2 were found to modulate the expression of a host of genes involved in G-protein-coupled receptor (GPCR) signalling including Rac2, Gnb1, Dab2ip (AIP1), Ralgds, Rnd3, Rap1a and PKA, thereby revealing previously unrecognised signalling intermediates downstream of CRH receptors. Moreover, several of these GPCR-related genes have been shown previously to be involved in mitogen-activated protein kinase (MAPK) activation, suggesting a link between CRH receptors and induction of MAPKs. In addition, we have shown that both UCN1 and UCN2 significantly reduce free radical damage following myocardial infarction, and comparison of the UCN gene signatures with that of the anti-oxidant tempol revealed a significant overlap. These data uncover novel gene expression changes induced by UCNs, which will serve as a platform to further understand their mechanism of action in normal physiology and cardioprotection.

Expression of urocortin peptides in canine myocardium and plasma

Urocortin (Ucn) peptides are the endogenous ligands for the corticotropin-releasing factor type 2 receptor (CRFR2). They have potentially important roles in cardiovascular physiology in health and disease, and show promise as therapeutics for congestive heart failure. Analysis of canine heart tissue showed mRNA expression of Ucn 1, Ucn 3 and CRFR2 in all heart chambers. Immunohistochemistry also demonstrated Ucns 1 and 3 expression in cardiomyocytes. To assess the potential usefulness of circulating Ucns as markers of heart disease, plasma samples from 45 dogs with cardiac disease and 15 controls were analysed by radioimmunoassay. Both Ucns 1 and 3 were measurable but the presence of cardiac disease did not alter their concentrations. Therefore, whilst Ucns are expressed in canine myocardium (where they may play a role in the endogenous neurohumoral response to cardiac disease or failure) they do not appear to be sensitive biomarkers of cardiac disease in our canine patient population.

Novel biomarkers in heart failure: an overview

Heart failure is a complex systemic syndrome resulting from significant impairment of cardiac function. A vast array of biological pathways is now known to be involved in heart failure, including deleterious pathways promoting its development and progression, as well as compensatory cardioprotective pathways. Some of the components of these pathways are now recognized as biomarkers of this condition, and can aid diagnosis, prognostication and guide management. As the understanding of the pathophysiology of heart failure progresses, further candidate biomarkers are being identified. This article reviews the literature regarding the more recently identified biomarkers and outlines areas requiring further study.

Novel neurohormonal insights with therapeutic potential in chronic heart failure

Despite considerable therapeutic advances over recent years, chronic heart failure remains associated with significant morbidity and mortality. Further improvements in the treatment of this syndrome are therefore needed and this will require advances in the understanding of its underlying pathophysiology. This article reviews the literature regarding recently identified neurohormonal pathways that are declaring themselves as potential therapeutic targets in chronic heart failure.

Corticotropin-releasing factor receptors and urocortins, links between the brain and the heart

Corticotropin-releasing factor (CRF), a 41 amino acid peptide, was discovered as a key signal in mediating neuroendocrine, autonomic, and behavioral responses to stress. It was revealed later that there exist additional CRF-like peptides, termed urocortins. The CRF receptor subtype 1 (CRF1 receptor) is predominant in the brain whereas subtype 2 (CRF2 receptor) is highly expressed in the brain and the heart. Both centrally and peripherally administered CRF and urocortins produce significant hemodynamic effects via activation of CRF receptors in the brain and the heart. CRF and urocortins are important neural and cardioactive hormones, and are potentially useful therapy for heart failure.

Circulating levels of stress associated peptide Urocortin in heart failure patients

The available data suggest that Urocortin (UCN), a cardioprotective and vasoactive peptide known from fish neuroendocrinology, is involved in cardiac regulation. The aim of this study was to determine UCN plasma concentrations in patients with heart failure (HF). Plasma concentrations of UCN, measured in 42 fully treated HF patients. UCN, were determined using a specific ELISA assay after acidic extraction with Sep-Pak C18 columns. Circulating levels of other neurohormones Nt-proBNP, Nt-proANP and Big ET-1 were also determined. Reference values were obtained from 20 healthy age- and sex-matched subjects. In comparison with controls, UCN plasma concentrations (geometric mean [95% CI]) were significantly increased in HF patients (88 pmol/L [75-105] vs 46 [39-54], p<0.001). As expected, the other neurohormones were also significantly increased in HF patients (Nt-proBNP: 3501 pg/ml [2356-5202] vs 35 [24-51], Nt-proANP: 5498 pg/ml [4336-6971] vs 324 [255-411] and Big ET-1: 15.8 pg/ml [13.6-18.4] vs 5.9 [5.2-6.8]; p<0.01 for all vs controls). No significant correlation was observed between UCN and the other HF biomarkers. Our results demonstrate that plasma concentrations of UCN are significantly increased in patients with HF and that UCN may participate in the neurohumoral response of HF.

Urocortin 1 improves renal function in rats with streptozotocin-induced diabetes by inhibiting overproduction of TGF-beta 1 and VEGF

BACKGROUND AND PURPOSE

Renal function can be assessed by measuring albuminuria and glomerular filtration rate, and the latter is often estimated by creatinine clearance rate (Ccr). Transforming growth factor-beta1 (TGF-beta1) and vascular endothelial growth factor (VEGF) are two important factors involved in the progressive loss of renal function in diabetic nephropathy (DN), especially in terms of albuminuria. We investigated the effect of urocortin 1 on renal function of rats with DN and the mechanisms involved.

EXPERIMENTAL APPROACH

A modified rat model of DN (multiple injections of low-dose streptozotocin and complete Freund's adjuvant) and a rat mesangial cell line were used. Albuminuria and Ccr were measured or calculated. Expression and secretion of TGF-beta1 and VEGF were measured by immunohistochemistry, reverse transcription-polymerase chain reaction (RT-PCR) or enzyme-linked immunosorbent assay (R&D System, Inc., Minneapolis, MA, USA). Urocortin 1 and astressin [a non-selective antagonist of corticotrophin-releasing factor (CRF) receptors] were given as daily injections for 8 weeks.

KEY RESULTS

Treatment of DN rats with urocortin 1 decreased albuminuria, renal weight and overexpression of TGF-beta1 and VEGF but enhanced Ccr. Furthermore, VEGF mRNA was increased in kidneys of DN rats, and this increase was reduced by treatment with urocortin 1. The secretion of VEGF induced by TGF-beta1 in mesangial cells was inhibited by urocortin 1 pretreatment. Astressin given with urocortin 1 prevented most of the effects of urocortin 1, in our models, in vivo or in vitro.

CONCLUSION AND IMPLICATIONS

Our results strongly suggest that urocortin 1 improved renal function in rats with DN by inhibiting the overproduction of TGF-beta1 and VEGF.

A novel corticotropin-releasing factor receptor splice variant exhibits dominant negative activity: a putative link to stress-induced heart disease

A growing body of experimental and clinical studies supports a strong association between psychological stress and cardiovascular disease. An important endogenous cardioprotective role in heart physiology has been attributed to corticotropin-releasing factor receptor type 2beta (CRFR2beta). Here, we report the isolation of cDNA from mouse (m) heart encoding a novel CRFR2beta splice variant. Translation of this insertion variant (iv)-mCRFR2beta isoform produces a 421-aa protein that includes a unique C-terminal cytoplasmic tail. Our functional analysis and cellular localization studies demonstrated that when coexpressed with wild-type mCRFR2beta, iv-mCRFR2beta significantly inhibited the wild-type mCRFR2beta membrane expression and its functional signaling by ER-Golgi complex retention, suggesting a dose-dependent dominant negative effect. Interestingly, mice exposed to a 4-wk paradigm of chronic variable stress, a model of chronic psychological stress in humans, presented significantly lower levels of mCRFR2beta and higher levels of iv-mCRFR2beta mRNA expression in their hearts, compared to nonstressed control mice. The dominant-negative effect of iv-mCRFR2beta and its up-regulation by psychological stress suggest a new form of regulation of the mCRFR2beta cardioprotective effect and a potential role for this novel isoform in stress-induced heart disease.

Urocortin 1 exhibits potent inhibition of cardiac sympathetic nerve activity in conscious sheep

OBJECTIVES

Urocortin 1 (Ucn1) and the sympathetic nervous system both participate in cardiac and circulatory regulation, but little is known about their possible interactions.

METHODS

We report the effects of Ucn1 on the cardiac sympathetic nerve activity (CSNA), haemodynamics and plasma catecholamines in normal sheep.

RESULTS

Bolus intravenous administration of Ucn1 at 2.5 and 10 microg in seven sheep had no significant effect on haemodynamic parameters, including heart rate, mean arterial pressure (MAP) and cardiac output. At these doses, however, Ucn1 administration reduced CSNA, with burst frequency (P = 0.011), burst incidence (P = 0.015) and burst area (P = 0.012) all significantly reduced in a dose-related manner compared with a time-matched control. At higher doses (25 and 100 microg; n = 5 sheep), Ucn1 induced significant rises in heart rate (P < 0.001) and cardiac output (P = 0.03) and reduced peripheral resistance (P = 0.03), but had no effect on MAP. Ucn1 administration at the higher doses reduced CSNA, with burst incidence (P < 0.001), burst area/min (P = 0.001) and burst area/100 beats (P < 0.001) all significantly reduced in a dose-related manner compared with a time-matched control. There was no change in plasma catecholamines at any dose.

CONCLUSION

The present study shows that Ucn1 induces potent inhibition of sympathetic traffic to the heart at doses both above and below the threshold for direct actions of Ucn1 on the myocardium. These findings suggest an important role for Ucn1 in cardiovascular homeostasis and warrant further investigation for potential therapeutic applications in acute myocardial injury and heart disease.

Urocortin ameliorates diabetic nephropathy in obese db/db mice

BACKGROUND AND PURPOSE

Hyperglycaemia induces overproduction of mitochondrial reactive oxygen species (ROS) in endothelial cells, which is believed to be a major molecular mechanism underlying complications of diabetes, including diabetic nephropathy. Impairment of endothelium-dependent vasodilatation is found in type 2 diabetes. Urocortin is a 40 amino-acid peptide related to the corticotrophin-releasing factor (CRF) family, which suppresses production of ROS in endothelial cells and sustains endothelium-dependent relaxations of rat coronary artery. However, it is not clear if urocortin has any effect on diabetic nephropathy.

EXPERIMENTAL APPROACH

Possible mechanisms underlying the effects of urocortin on diabetic nephropathy were investigated in db/db mice and cultured rat mesangial cells.

KEY RESULTS

Urocortin decreased body weight, plasma levels of advanced glycation end-products, blood urea nitrogen and creatinine levels. However, food intake, plasma insulin and glucose levels remained unaffected. Superoxide dismutase activity was increased markedly, whereas malonaldehyde levels in kidney homogenate and sorbitol concentrations in red blood cells were decreased significantly in urocortin-treated mice. Urocortin significantly decreased glomerular extracellular matrix expansion and accumulation in kidney. Moreover, urocortin inhibited the overexpression of transforming growth factor-beta 1 and connective tissue growth factor in rat mesangial cells induced by 25 mM glucose. All the effects of urocortin, except sorbitol accumulation, were abolished by the non-selective CRF receptor blocker, astressin.

CONCLUSION AND IMPLICATIONS

Urocortin could significantly ameliorate diabetic nephropathy and this effect was mediated via the CRF receptor.

Residues of corticotropin releasing factor-binding protein (CRF-BP) that selectively abrogate binding to CRF but not to urocortin 1

Corticotropin releasing factor-binding protein (CRF-BP) binds CRF and urocortin 1 (Ucn 1) with high affinity, thus preventing CRF receptor (CRFR) activation. Despite recent progress on the molecular details that govern interactions between CRF family neuropeptides and their cognate receptors, little is known concerning the mechanisms that allow CRF-BP to bind CRF and Ucn 1 with picomolar affinity. We conducted a comprehensive alanine scan of 76 evolutionarily conserved residues of CRF-BP and identified several residues that differentially affected the affinity for CRF over Ucn 1. We determined that both neuropeptides derive their similarly high affinity from distinct binding surfaces on CRF-BP. Alanine substitutions of arginine 56 (R56A) and aspartic acid 62 (D62A) reduce the affinity for CRF by approximately 100-fold, while only marginally affecting the affinity for Ucn 1. The selective reduction in affinity for CRF depends on glutamic acid 25 in the CRF peptide, as substitution of Glu(25) reduces the affinity for CRF-BP by approximately 2 orders of magnitude, but only in the presence of both Arg(56) and Asp(62) in human CRF-BP. We show that CRF-BP(R56A) and CRF-BP(D62A) have lost the ability to inhibit CRFR1-mediated responses to CRF that activate luciferase induction in HEK293T cells and ACTH release from cultured rat anterior pituitary cells. In contrast, both CRF-BP mutants retain the ability to inhibit Ucn 1-induced CRFR1 activation. Collectively our findings demonstrate that CRF-BP has distinct and separable binding surfaces for CRF and Ucn 1, opening new avenues for the design of ligand-specific antagonists based on CRF-BP.

Urocortin 1 administration from onset of rapid left ventricular pacing represses progression to overt heart failure

Urocortin 1 (Ucn1) may be involved in the pathophysiology of heart failure (HF), but the impact of Ucn1 administration on progression of the disease is unknown. The aim of this study was to investigate the effects of Ucn1 in sheep from the onset of cardiac overload and during the subsequent development of HF. Eight sheep underwent two 4-day periods of HF induction by rapid left ventricular pacing (225 beats/min) in conjunction with continuous infusions of Ucn1 (0.1 microg.kg(-1).h(-1) iv) and a vehicle control (0.9% saline). Compared with control, Ucn1 attenuated the pacing-induced decline in cardiac output (2.43 +/- 0.46 vs. 3.70 +/- 0.89 l/min on day 4, P < 0.01) and increases in left atrial pressure (24.9 +/- 1.0 vs. 11.9 +/- 1.1 mmHg, P < 0.001) and peripheral resistance (38.7 +/- 9.4 vs. 25.2 +/- 6.1 mmHg.l(-1).min, P < 0.001). Ucn1 wholly prevented increases in plasma renin activity (4.02 +/- 1.17 vs. 0.87 +/- 0.1 nmol.l(-1).h(-1), P < 0.001), aldosterone (1,313 +/- 324 vs. 413 +/- 174 pmol/l, P < 0.001), endothelin-1 (3.8 +/- 0.5 vs. 2.0 +/- 0.1 pmol/l, P < 0.001), and vasopressin (10.8 +/- 4.1 vs. 1.8 +/- 0.2 pmol/l, P < 0.05) during pacing alone and blunted the progressive increases in plasma epinephrine (2,132 +/- 697 vs. 1,250 +/- 264 pmol/l, P < 0.05), norepinephrine (3.61 +/- 0.73 vs. 2.07 +/- 0.52 nmol/l, P < 0.05), and atrial (P < 0.05) and brain (P < 0.01) natriuretic peptide levels. Ucn1 administration also maintained urine sodium excretion (0.75 +/- 0.34 vs. 1.59 +/- 0.50 mmol/h on day 4, P < 0.05) and suppressed pacing-induced declines in creatinine clearance (P < 0.05). These findings indicate that Ucn1 treatment from the onset of cardiac overload has the ability to repress the ensuing hemodynamic and renal deterioration and concomitant adverse neurohumoral activation, thereby delaying the development of overt HF. These data strongly support a use for Ucn1 as a therapeutic option early in the course of the disease.

Urocortin 1 modulates the neurohumoral response to acute nitroprusside-induced hypotension in sheep

In addition to haemodynamic actions, Ucn1 (urocortin 1) has been reported to affect a number of hormonal systems; however, it remains unclear whether Ucn1 modulates circulating hormones under physiological conditions. Accordingly, in the present study, we have examined the effects of Ucn1 on haemodynamics, hormones and renal indices in normal conscious sheep subjected to a nitroprusside-induced hypotensive stimulus designed to alter hormonal levels within the physiological range. Ucn1 administration did not alter the haemodynamic response to nitroprusside-induced hypotension. However, compared with the rise observed on the control day, plasma ANP (atrial natriuretic peptide; P=0.043), BNP (brain natriuretic peptide; P=0.038) and endothelin-1 (P=0.011) levels were reduced following Ucn1 administration. Associated with this significant reduction in natriuretic peptides, the increase in urinary sodium output associated with rising pressures post-nitroprusside was abolished following Ucn1 administration (P=0.048). Ucn1 had no significant effect on the response of hormones of the renin-angiotensin-aldosterone system or the hypothalamo-pituitary-adrenal axis. In conclusion, Ucn1, administered at physiologically relevant levels during nitroprusside-induced hypotension, attenuates the secretion/release of endothelin-1 and the cardiac natriuretic peptides ANP and BNP. Suppression of ANP and BNP probably led to an attenuated natriuretic response to recovery from acute hypotension. The threshold for the action of Ucn1 on the natriuretic peptides and endothelin-1 appears to be below that of other actions of Ucn1.

Physiology, pharmacology, and therapeutic relevance of urocortins in mammals: ancient CRF paralogs

Urocortins, three paralogs of the stress-related peptide corticotropin-releasing factor (CRF) found in bony fish, amphibians, birds, and mammals, have unique phylogenies, pharmacologies, and tissue distributions. As a result and despite a structural family resemblance, the natural functions of urocortins and CRF in mammalian homeostatic responses differ substantially. Endogenous urocortins are neither simply counterpoints nor mimics of endogenous CRF action. In their own right, urocortins may be clinically relevant molecules in the pathogenesis or management of many conditions, including congestive heart failure, hypertension, gastrointestinal and inflammatory disorders (irritable bowel syndrome, active gastritis, gastroparesis, and rheumatoid arthritis), atopic/allergic disorders (dermatitis, urticaria, and asthma), pregnancy and parturition (preeclampsia, spontaneous abortion, onset, and maintenance of effective labor), major depression and obesity. Safety trials for intravenous urocortin treatment have already begun for the treatment of congestive heart failure. Further understanding the unique functions of urocortin 1, urocortin 2, and urocortin 3 action may uncover other therapeutic opportunities.

Corticotropin-releasing hormone receptor (CRHR)1 and CRHR2 are both trafficking and signaling receptors for urocortin

Transport of urocortin, a potent satiety peptide, occurs at the blood-brain barrier of the mouse. Endocytosis of urocortin by the cerebral microvessel endothelial cells composing the blood-brain barrier is a rate-limiting step of this transport, but the cellular mechanisms involved have not been fully elucidated. The presence of both CRH receptors R1 and R2 in isolated cerebral microvessels shown in this study suggested that both subtypes might mediate urocortin transport. The roles of these two receptors in the endocytosis and signal transduction of urocortin were tested by overexpression studies in human embryonic kidney 293 cells. Both receptors led to a significant increase of binding and endocytosis of radiolabeled urocortin. CRHR1-mediated urocortin endocytosis was blocked by astressin (antagonist for both CRHRs), whereas CRHR2-mediated urocortin endocytosis was also blocked by antisauvagine 30 (selective CRHR2beta antagonist). Chlorpromazine, filipin, and nystatin had no effect on urocortin endocytosis, indicating the lack of significant involvement of clathrin or caveolae membrane microdomains. Both CRHR1 and CRHR2 were able to mediate the ligand-induced increase of cAMP production, suggesting that the overexpressed receptors were biologically active. Elevation of intracellular cAMP by forskolin or dibutyryl-cAMP, however, did not show acute modulation of the binding and endocytosis of urocortin. Despite the substantial intracellular degradation of endocytosed urocortin in cells overexpressing either CRHR1 or CRHR2, intact urocortin could be exocytosed during the 1-h study interval. We conclude that both CRHR1 and CRHR2 play a facilitatory role in the non-clathrin-, non-caveolae-mediated endocytosis and intracellular signal transduction of this potent peptide.

Plasma urocortin 1 in sheep: regional sampling and effects of experimental heart failure

Although urocortin 1 (Ucn-1) has been reported to circulate in human plasma and be raised in heart failure, little, if any, information is available regarding the source of circulating Ucn-1. Accordingly, we have performed trans-organ arteriovenous sampling for measurement of Ucn-1 concentration in anesthetized sheep before and after development of pacing-induced heart failure. Arterial plasma Ucn-1 levels measured 15.2 +/- 0.5 pmol/L in normal sheep and increased significantly following development of heart failure to 19.1 +/- 1.6 (p < 0.05). Small but significant positive arteriovenous gradients were observed across the hepatic and renal tissue beds in both states, with rises across the hind limb significant in normal animals and across the head in heart failure. This is the first report identifying sources of circulating Ucn-1.

Urocortin-induced decrease in Ca2+ sensitivity of contraction in mouse tail arteries is attributable to cAMP-dependent dephosphorylation of MYPT1 and activation of myosin light chain phosphatase

Urocortin, a vasodilatory peptide related to corticotropin-releasing factor, may be an endogenous regulator of blood pressure. In vitro, rat tail arteries are relaxed by urocortin by a cAMP-mediated decrease in myofilament Ca2+ sensitivity through a still unclear mechanism. Here we show that contraction of intact mouse tail arteries induced with 42 mmol/L KCl or 0.5 micromol/L noradrenaline was associated with a approximately 2-fold increase in the phosphorylation of the regulatory subunit of myosin phosphatase (SMPP-1M), MYPT1, at Thr696, which was reversed in arteries relaxed with urocortin. Submaximally (pCa 6.1) contracted mouse tail arteries permeabilized with alpha-toxin were relaxed with urocortin by 39+/-3% at constant [Ca2+], which was associated with a decrease in myosin light chain (MLC20Ser19), MYPT1Thr696, and MYPT1Thr850 phosphorylation by 60%, 28%, and 52%, respectively. The Rho-associated kinase (ROK) inhibitor Y-27632 decreased MYPT1 phosphorylation by a similar extent. Inhibition of PP-2A with 3 nmol/L okadaic acid had no effect on MYPT1 phosphorylation, whereas inhibition of PP-1 with 3 micromol/L okadaic acid prevented dephosphorylation. Urocortin increased the rate of dephosphorylation of MLC20Ser19 approximately 2.2-fold but had no effect on the rate of contraction under conditions of, respectively, inhibited kinase and phosphatase activities. The effect of urocortin on MLC20Ser19 and MYPT1 phosphorylation was blocked by Rp-8-CPT-cAMPS and mimicked by Sp-5,6-DCl-cBIMPS. In summary, these results provide evidence that Ca(2+)-independent relaxation by urocortin can be attributed to a cAMP-mediated increased activity of SMPP-1M which at least in part is attributable to a decrease in the inhibitory phosphorylation of MYPT1.