Effects of adrenomedullin on cultured rat cardiac myocytes and fibroblasts

A Focus on the Pathophysiology of Adrenomedullin Expression: Endothelitis and Organ Damage in Severe Viral and Bacterial Infections

Adrenomedullin (ADM) is a peptide hormone produced primarily in the adrenal glands, playing a crucial role in various physiological processes. As well as improving vascular integrity and decreasing vascular permeability, ADM acts as a vasodilator, positive inotrope, diuretic, natriuretic and bronchodilator, antagonizing angiotensin II by inhibiting aldosterone secretion. ADM also has antihypertrophic, anti-apoptotic, antifibrotic, antioxidant, angiogenic and immunoregulatory effects and antimicrobial properties. ADM expression is upregulated by hypoxia, inflammation-inducing cytokines, viral or bacterial substances, strength of shear stress, and leakage of blood vessels. These pathological conditions are established during systemic inflammation that can result from infections, surgery, trauma/accidents or burns. The ability to rapidly identify infections and the prognostic, predictive power makes it a valuable tool in severe viral and bacterial infections burdened by high incidence and mortality. This review sheds light on the pathophysiological processes that in severe viral or bacterial infections cause endothelitis up to the development of organ damage, the resulting increase in ADM levels dosed through its more stable peptide mid-regional proadrenomedullin (MR-proADM), the most significant studies that attest to its diagnostic and prognostic accuracy in highlighting the severity of viral or bacterial infections and appropriate therapeutic insights.

Cardiac and intestinal tissue conduct developmental and reparative processes in response to lymphangiocrine signaling

Lymphatic vessels conduct a diverse range of activities to sustain the integrity of surrounding tissue. Besides facilitating the movement of lymph and its associated factors, lymphatic vessels are capable of producing tissue-specific responses to changes within their microenvironment. Lymphatic endothelial cells (LECs) secrete paracrine signals that bind to neighboring cell-receptors, commencing an intracellular signaling cascade that preludes modifications to the organ tissue's structure and function. While the lymphangiocrine factors and the molecular and cellular mechanisms themselves are specific to the organ tissue, the crosstalk action between LECs and adjacent cells has been highlighted as a commonality in augmenting tissue regeneration within animal models of cardiac and intestinal disease. Lymphangiocrine secretions have been owed for subsequent improvements in organ function by optimizing the clearance of excess tissue fluid and immune cells and stimulating favorable tissue growth, whereas perturbations in lymphatic performance bring about the opposite. Newly published landmark studies have filled gaps in our understanding of cardiac and intestinal maintenance by revealing key players for lymphangiocrine processes. Here, we will expand upon those findings and review the nature of lymphangiocrine factors in the heart and intestine, emphasizing its involvement within an interconnected network that supports daily homeostasis and self-renewal following injury.

Beraprost sodium attenuates the development of myocardial fibrosis after myocardial infarction by regulating GSK-3β expression in rats

OBJECTIVE

The aim of this study was to elucidate the mechanism of beraprost sodium (BPS) in the intervention of myocardial fibrosis after myocardial infarction (MI) through glycogen synthase kinase-3β (GSK-3β) and to provide new ideas for intervention in myocardial fibrosis.

MATERIALS AND METHODS

MI model rats given BPS and cardiac fibroblasts (CFs) treated with BPS and TGF-β. HE staining and Masson staining were used to detect the pathological changes of myocardial tissue. Fibrotic markers were detected by immunohistochemical staining. The expressions of GSK-3β, cAMP response element binding protein (CREB), and p-CREB were analyzed by qPCR and western blot analysis. EDU staining was used to detect the proliferation of CFs. The promoter activity of GSK-3β was detected by luciferase assay. Chromatin immunoprecipitation assay was used to detect the binding levels of GSK-3β promoter and Y-box binding protein 1 (YBX1). The levels of intracellular cyclic adenosine monophosphate (cAMP) were analyzed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

After operation, BPS improved myocardial fibrosis and upregulated GSK-3β protein expression in male SD rats. BPS can down-regulate α-smooth muscle actin (α-SMA) level and up-regulate GSK-3β protein expression in CFs after TGF-β stimulation. Furthermore, GSK-3β knockdown can reverse the effect of BPS on TGF-β-activated CFs, enhance α-SMA expression, and promote the proliferation of CFs. BPS could regulate GSK-3β expression by promoting the binding of GSK-3β promoter to YBX1. BPS induced upregulation of p-CREB and cAMP, resulting in reduced fibrosis, which was reversed by the knockdown of GSK-3β or prostaglandin receptor (IPR) antagonists.

CONCLUSION

BPS treatment increased the binding of YBX1 to the GSK-3β promoter, and GSK-3β protein expression was upregulated, which further caused the upregulation of p-CREB and cAMP, and finally inhibited myocardial fibrosis.

Clinical Potential of Adrenomedullin Signaling in the Cardiovascular System

Numerous clinical studies have revealed the utility of circulating AM (adrenomedullin) or MR-proAM (mid-regional proAM 45-92) as an effective prognostic and diagnostic biomarker for a variety of cardiovascular-related pathophysiologies. Thus, there is strong supporting evidence encouraging the exploration of the AM-CLR (calcitonin receptor-like receptor) signaling pathway as a therapeutic target. This is further bolstered because several drugs targeting the shared CGRP (calcitonin gene-related peptide)-CLR pathway are already Food and Drug Administration-approved and on the market for the treatment of migraine. In this review, we summarize the AM-CLR signaling pathway and its modulatory mechanisms and provide an overview of the current understanding of the physiological and pathological roles of AM-CLR signaling and the yet untapped potentials of AM as a biomarker or therapeutic target in cardiac and vascular diseases and provide an outlook on the recently emerged strategies that may provide further boost to the possible clinical applications of AM signaling.

Adrenomedullin - Current perspective on a peptide hormone with significant therapeutic potential

The peptide hormone adrenomedullin (ADM) consists of 52 amino acids and plays a pivotal role in the regulation of many physiological processes, particularly those of the cardiovascular and lymphatic system. Like calcitonin (CT), calcitonin gene-related peptide (CGRP), intermedin (IMD) and amylin (AMY), it belongs to the CT/CGRP family of peptide hormones, which despite their low little sequence identity share certain characteristic structural features as well as a complex multicomponent receptor system. ADM, IMD and CGRP exert their biological effects by activation of the calcitonin receptor-like receptor (CLR) as a complex with one of three receptor activity-modifying proteins (RAMP), which alter the ligand affinity. Selectivity within the receptor system is largely mediated by the amidated C-terminus of the peptide hormones, which bind to the extracellular domains of the receptors. This enables their N-terminus consisting of a disulfide-bonded ring structure and a helical segment to bind within the transmembrane region and to induce an active receptor confirmation. ADM is expressed in a variety of tissues in the human body and is fundamentally involved in multitude biological processes. Thus, it is of interest as a diagnostic marker and a promising candidate for therapeutic interventions. In order to fully exploit the potential of ADM, it is necessary to improve its pharmacological profile by increasing the metabolic stability and, ideally, creating receptor subtype-selective analogs. While several successful attempts to prolong the half-life of ADM were recently reported, improving or even retaining receptor selectivity remains challenging.

Contrasting Effects of Inhibition of Phosphodiesterase 3 and 5 on Cardiac Function and Interstitial Fibrosis in Rats With Isoproterenol-Induced Cardiac Dysfunction

Myocardial relaxation and stiffness are influenced by fibrillar collagen content. Cyclic nucleotide signaling regulators have been investigated targeting more effective modulation of collagen deposition during myocardial healing process. To assess the effects of phosphodiesterase type 3 and phosphodiesterase type 5 inhibitors on cardiac function and left ventricular myocardial fibrosis in catecholamine-induced myocardial injury, sildenafil and pimobendan were administered to male Wistar rats 24 hours after isoproterenol injection. Echocardiography and electrocardiogram were performed to assess kinetic and rhythm changes during 45 days of drug administration. At the end of study, type I and type III collagen were measured through immunohistochemistry analysis, and left ventricular pressure was assessed through invasive method. Echocardiography assessment showed increased relative wall thickness at 45 days in pimobendan group with significant diastolic dysfunction and increased collagen I deposition compared with nontreated positive group (3.03 ± 0.31 vs. 2.73 ± 0.28%, P < 0.05). Diastolic pressure correlated positively with type I collagen (r = 0.54, P < 0.05). Type III collagen analysis did not demonstrate difference among the groups. Sildenafil administration attenuated type I collagen deposition (2.15 ± 0.51 vs. positive group, P < 0.05) and suggested to be related to arrhythmic events. Arrhythmic events were not related to the quantity of fibrillar collagen deposition. Although negative modulation of collagen synthesis through cyclic nucleotides signaling have shown promising results, in this study, pimobendan postconditioning resulted in increased collagen type I formation and severe diastolic dysfunction while sildenafil postconditioning reduced collagen type I deposition and attenuated diastolic dysfunction.

The Role of Cyclic AMP Signaling in Cardiac Fibrosis

Myocardial stress and injury invariably promote remodeling of the cardiac tissue, which is associated with cardiomyocyte death and development of fibrosis. The fibrotic process is initially triggered by the differentiation of resident cardiac fibroblasts into myofibroblasts. These activated fibroblasts display increased proliferative capacity and secrete large amounts of extracellular matrix. Uncontrolled myofibroblast activation can thus promote heart stiffness, cardiac dysfunction, arrhythmias, and progression to heart failure. Despite the well-established role of myofibroblasts in mediating cardiac disease, our current knowledge on how signaling pathways promoting fibrosis are regulated and coordinated in this cell type is largely incomplete. In this respect, cyclic adenosine monophosphate (cAMP) signaling acts as a major modulator of fibrotic responses activated in fibroblasts of injured or stressed hearts. In particular, accumulating evidence now suggests that upstream cAMP modulators including G protein-coupled receptors, adenylyl cyclases (ACs), and phosphodiesterases (PDEs); downstream cAMP effectors such as protein kinase A (PKA) and the guanine nucleotide exchange factor Epac; and cAMP signaling organizers such as A-kinase anchoring proteins (AKAPs) modulate a variety of fundamental cellular processes involved in myocardial fibrosis including myofibroblast differentiation, proliferation, collagen secretion, and invasiveness. The current review will discuss recent advances highlighting the role of cAMP and AKAP-mediated signaling in regulating pathophysiological responses controlling cardiac fibrosis.

Adrenomedullin: Continuing to explore cardioprotection

Adrenomedullin (AM), a peptide isolated from an extract of human pheochromocytoma, comprises 52 amino acids with an intramolecular disulfide bond and amidation at the carboxy-terminus. AM is present in various tissues and organs in rodents and humans, including the heart. The peptide concentration increases with cardiac hypertrophy, acute myocardial infarction, and overt heart failure in the plasma and the myocardium. The principal function of AM in the cardiovascular system is the regulation of the vascular tone by vasodilation and natriuresis via cyclic adenosine monophosphate-dependent or -independent mechanism. In addition, AM may possess unique properties that inhibit aldosterone secretion, oxidative stress, apoptosis, and stimulation of angiogenesis, resulting in the protection of the structure and function of the heart. The AM receptor comprises a complex between calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein (RAMP) 2 or 3, and the AM-CLR/RAMP2 system is essential for heart development during embryogenesis. Small-scale clinical trials have proven the efficacy and safety of recombinant AM peptide therapy for heart failure. Gene delivery and a modified AM peptide that prolongs the half-life of the native peptide could be an innovative method to improve the efficacy and benefit of AM in clinical settings. In this review, we focus on the pathophysiological roles of AM and its receptor system in the heart and describe the advances in AM and proAM-derived peptides as diagnostic biomarkers as well as the therapeutic application of AM and modified AM for cardioprotection.

Mesenchymal stem cells overexpressing adrenomedullin improve heart function through antifibrotic action in rats experiencing heart failure

Previous studies of the authors have indicated that the transplantation of mesenchymal stem cells (MSCs) can attenuate cardiac fibrosis through the secretion of antifibrotic factors, such as adrenomedullin (ADM). Therefore, the authors addressed the hypothesis that ADM overexpression could enhance the antifibrotic effect of MSCs transplantation in a rat model of heart failure. The results of the present study demonstrated that, compared with the group that received the GFP-MSCs, the transplantation of ADM-MSCs significantly improved heart function and decreased the percentage of fibrotic area and the expression of matrix metalloproteinase 2. In addition, fluorescence microscopy indicated that the survival of transplanted MSCs also increased significantly in the ADM-MSCs-treated group. Furthermore, the expression of fibrosis-related genes, such as ADM and hepatocyte growth factor, were significantly influenced in the ADM-MSCs-treated group. Based on these findings, it may be concluded that, compared with MSCs, MSCs overexpressing ADM can further improve heart function in rats experiencing heart failure through enhanced antifibrotic activity.

The Role of Adrenomedullin in Cardiovascular Response to Exercise - A Review

Adrenomedullin (ADM), the product of the vascular endothelial and smooth muscle cells, and cardiomyocytes, is considered to be a local factor controlling vascular tone, cardiac contractility and renal sodium excretion. The aim of this article was to review the existing data on the effect of different types of exercise on plasma ADM concentration in healthy men. The results of studies on the effect of dynamic exercise on the plasma ADM are contradictory. Some authors reported an increase in plasma ADM, while others showed a slight decrease or did not observe any changes. The inverse relationship between plasma ADM and mean blood pressure observed during maximal exercise support the concept that ADM might blunt the exercise-induced systemic blood pressure increase. Positive relationships between increases in plasma ADM and those in noradrenaline, atrial natriuretic peptide (ANP) or interleukin-6 observed during prolonged exercise suggest that the sympathetic nervous system and cytokine induction may be involved in ADM release. Increased secretion of ADM and ANP during this type of exercise may be a compensatory mechanism attenuating elevation of blood pressure and preventing deterioration of cardiac function. Studies performed during static exercise have showed an increase in plasma ADM only in older healthy men. Positive correlations between increases in plasma ADM and those in noradrenaline and endothelin-1 may indicate the interaction of these hormones in shaping the cardiovascular response to static exercise. Inverse relationships between exercise-induced changes in plasma ADM and those in cardiovascular indices may be at least partly associated with inotropic action of ADM on the heart. Interactions of ADM with vasoactive peptides, catecholamines and hemodynamic factors demonstrate the potential involvement of this peptide in the regulation of blood pressure and myocardial contractility during exercise.

Endothelium-derived intermedin/adrenomedullin-2 protects human ventricular cardiomyocytes from ischaemia-reoxygenation injury predominantly via the AM₁ receptor

Application of intermedin/adrenomedullin-2 (IMD/AM-2) protects cultured human cardiac vascular cells and fibroblasts from oxidative stress and simulated ischaemia-reoxygenation injury (I-R), predominantly via adrenomedullin AM1 receptor involvement; similar protection had not been investigated previously in human cardiomyocytes (HCM). Expression of IMD, AM and their receptor components was studied in HCM. Receptor subtype involvement in protection by exogenous IMD against injury by simulated I-R was investigated using receptor component-specific siRNAs. Direct protection by endogenous IMD against HCM injury, both as an autocrine factor produced in HCM themselves and as a paracrine factor released from HCMEC co-cultured with HCM, was investigated using peptide-specific siRNA for IMD. IMD, AM and their receptor components (CLR, RAMPs1-3) were expressed in HCM. IMD 1nmol L(-1), applied either throughout ischaemia (3h) and re-oxygenation (1h) or during re-oxygenation (1h) alone, attenuated HCM injury (P<0.05); cell viabilities were 59% and 61% respectively vs. 39% in absence of IMD. Cytoskeletal disruption, protein carbonyl formation and caspase activity followed similar patterns. Pre-treatment (4 days) of HCM with CLR and RAMP2 siRNAs attenuated (P<0.05) protection by exogenous IMD. Pre-treatment of HCMEC with IMD (and AM) siRNA augmented (P<0.05) I-R injury: cell viabilities were 22% (and 32%) vs. 39% untreated HCMEC. Pre-treatment of HCM with IMD (and AM) siRNA did not augment HCM injury: cell viabilities were 37% (and 39%) vs. 39% untreated HCM. Co-culture with HCMEC conferred protection from injury on HCM; such protection was attenuated when HCMEC were pre-treated with IMD (but not AM) siRNA before co-culture. Although IMD is present in HCM, IMD derived from HCMEC and acting in a paracrine manner, predominantly via AM1 receptors, makes a marked contribution to cardiomyocyte protection by the endogenous peptide against acute I-R injury.

Functionalized dendrimer-based delivery of angiotensin type 1 receptor siRNA for preserving cardiac function following infarction

Cardiovascular disease (CVD) is the leading cause of death throughout the world and much pathology is associated with upregulation of inflammatory genes. Gene silencing using RNA interference is a powerful tool in regulating gene expression, but its application in CVDs has been prevented by the lack of efficient delivery systems. We report here the development of tadpole dendrimeric materials for siRNA delivery in a rat ischemia-reperfusion (IR) model. Angiotensin II (Ang II) type 1 receptor (AT1R), the major receptor that mediates most adverse effects of Ang II, was chosen to be the silencing targeting. Among the three tadpole dendrimers synthesized, the oligo-arginine conjugated dendrimer loaded with siRNA demonstrated effective down-regulation in AT1R expression in cardiomyocytes in vitro. When the dendrimeric material was applied in vivo, the siRNA delivery prevented the increase in AT1R levels and significantly improved cardiac function recovery compared to saline injection or empty dendrimer treated groups after IR injury. These experiments demonstrate a potential treatment for dysfunction caused by IR injury and may represent an alternative to AT1R blockade.

The soluble guanylyl cyclase activator bay 58-2667 selectively limits cardiomyocyte hypertrophy

BACKGROUND

Although evidence now suggests cGMP is a negative regulator of cardiac hypertrophy, the direct consequences of the soluble guanylyl cyclase (sGC) activator BAY 58-2667 on cardiac remodeling, independent of changes in hemodynamic load, has not been investigated. In the present study, we tested the hypothesis that the NO(•)-independent sGC activator BAY 58-2667 inhibits cardiomyocyte hypertrophy in vitro. Concomitant impact of BAY 58-2667 on cardiac fibroblast proliferation, and insights into potential mechanisms of action, were also sought. Results were compared to the sGC stimulator BAY 41-2272.

METHODS

Neonatal rat cardiomyocytes were incubated with endothelin-1 (ET(1), 60nmol/L) in the presence and absence of BAY 41-2272 and BAY 58-2667 (0.01-0.3 µmol/L). Hypertrophic responses and its triggers, as well as cGMP signaling, were determined. The impact of both sGC ligands on basal and stimulated cardiac fibroblast proliferation in vitro was also determined.

RESULTS

We now demonstrate that BAY 58-2667 (0.01-0.3 µmol/L) elicited concentration-dependent antihypertrophic actions, inhibiting ET(1)-mediated increases in cardiomyocyte 2D area and de novo protein synthesis, as well as suppressing ET(1)-induced cardiomyocyte superoxide generation. This was accompanied by potent increases in cardiomyocyte cGMP accumulation and activity of its downstream signal, vasodilator-stimulated phosphoprotein (VASP), without elevating cardiomyocyte cAMP. In contrast, submicromolar concentrations of BAY 58-2667 had no effect on basal or stimulated cardiac fibroblast proliferation. Indeed, only at concentrations ≥10 µmol/L was inhibition of cardiac fibrosis seen in vitro. The effects of BAY 58-2667 in both cell types were mimicked by BAY 41-2272.

CONCLUSIONS

Our results demonstrate that BAY 58-2667 elicits protective, cardiomyocyte-selective effects in vitro. These actions are associated with sGC activation and are evident in the absence of confounding hemodynamic factors, at low (submicromolar) concentrations. Thus this distinctive sGC ligand may potentially represent an alternative therapeutic approach for limiting myocardial hypertrophy.

Haemodynamic, endocrine and renal actions of adrenomedullin 5 in an ovine model of heart failure

AM5 (adrenomedullin 5), a newly described member of the CGRP (calcitonin gene-related peptide) family, is reported to play a role in normal cardiovascular physiology. The effects of AM5 in HF (heart failure), however, have not been investigated. In the present study, we intravenously infused two incremental doses of AM5 (10 and 100 ng/min per kg of body weight each for 90 min) into eight sheep with pacing-induced HF. Compared with time-matched vehicle control infusions, AM5 produced progressive and dose-dependent increases in left ventricular dP/dt(max) [LD (low dose), +56 mmHg/s and HD (high dose), +152 mmHg/s] and cardiac output (+0.83 l/min and +1.81 l/min), together with decrements in calculated total peripheral resistance (−9.4 mmHg/min per litre and −14.7 mmHg/min per litre), mean arterial pressure (−2.8 mmHg and −8.4 mmHg) and LAP (left atrial pressure; −2.6 mmHg and −5.6 mmHg) (all P<0.001). HD AM5 significantly raised PRA (plasma renin activity) (3.5-fold increment, P<0.001), whereas plasma aldosterone levels were unchanged over the intra-infusion period and actually fell in the post-infusion period (70% decrement, P<0.01), resulting in a marked decrease in the aldosterone/PRA ratio (P<0.01). Despite falls in LAP, plasma atrial natriuretic peptide and B-type natriuretic peptide concentrations were maintained relative to controls. AM5 infusion also induced significant increases in urine volume (HD 2-fold increment, P<0.05) and urine sodium (2.7-fold increment, P<0.01), potassium (1.7-fold increment, P<0.05) and creatinine (1.4-fold increment, P<0.05) excretion and creatinine clearance (60% increment, P<0.05). In conclusion, AM5 has significant haemodynamic, endocrine and renal actions in experimental HF likely to be protective and compensatory in this setting. These results suggest that AM5 may have potential as a therapeutic agent in human HF.

Association of midregional proadrenomedullin with coronary artery stenoses, soft atherosclerotic plaques and coronary artery calcium

Midregional proadrenomedullin (MR-proADM) is elevated in patients with heart failure and myocardial infarction. The aim of this study was to evaluate the association of MR-proADM with the grade of coronary artery stenosis, presence of coronary artery soft plaques and coronary artery calcification score (CACS), determined by 64-multislice computed tomography (MSCT) in patients without known prior cardiovascular disease. This retrospective study included 107 patients undergoing MSCT for confirmation (or exclusion) of coronary artery disease. MR-proADM levels were measured in all patients. The assessment of coronary artery stenoses, CACS and soft coronary plaques was made by MSCT using known criteria. The MR-proADM [median (25th-75th percentiles)] level was 0.33 (0.21-0.43) nmol/l. The MR-proADM level was 0.28 (0.22-0.40) nmol/l in patients with coronary stenoses ≥50% (n = 23) versus 0.33 (0.27-0.40) nmol/l in patients with coronary stenoses <50% (n = 83, P = 0.59), 0.33 (0.26-0.40) nmol/l in patients with soft plaques (n = 56) versus 0.33 (0.25-0.41) nmol/l in patients without soft plaques (n = 50, P = 0.73) and 0.33 (0.25-0.39) nmol/l in patients with CACS <200 (n = 81) versus 0.32 (0.26-0.44) nmol/l in patients with CACS ≥200 (n = 26, P = 0.77). In multivariate analysis, the MR-proADM level was a significant correlate of coronary artery stenoses [odds ratio (OR) = 0.93; 95% confidence interval (CI) 0.86-0.99; P = 0.026] and soft plaques (OR = 0.94; 95% CI 0.90-0.99; P = 0.015) but not of CACS (OR = 0.98; 95% CI 0.93-1.03; P = 0.36). A decreased MR-proADM level is an independent correlate of the presence of coronary artery disease and of soft atherosclerotic plaques. Patients with decreased MR-proADM levels may need invasive examinations to diagnose more severe forms of coronary artery disease.

Gene silencing of myofibrillogenesis regulator-1 by adenovirus-delivered small interfering RNA suppresses cardiac hypertrophy induced by angiotensin II in mice

Our previous studies proved that myofibrillogenesis regulator (MR)-1 has a close relationship with cardiac hypertrophy induced by ANG II. In the present study, we developed a recombinant adenoviral vector (AdSiR-MR-1) driving small interfering (si)RNA against MR-1 to evaluate its effect on cardiac hypertrophy in vivo. Cardiac hypertrophy was induced by chronic ANG II infusion in mice; AdSiR-MR-1 was administered via the jugular vein through one bolus injection. Thirteen days after the injection, viral DNA was still detectable in the heart, validating the efficiency of gene transfer. Expression levels of MR-1 mRNA and protein were increased by 2.5-fold in the heart after ANG II infusion; AdSiR-control, which contained a scrambled siRNA sequence, had no effect on them. AdSiR-MR-1 treatment abolished the upregulation of MR-1 induced by ANG II. The silencing effect of AdSiR-MR-1 was observed in many other tissues, such as the liver, lung, and kidney, except skeletal muscle. ANG II-induced cardiac hypertrophy was suppressed in mice treated with AdSiR-MR-1, as determined by echocardiography. Morphological and immnohistochemical examinations revealed that interstitial cardiac fibrosis as well as infiltrating inflammatory cells were increased after ANG II infusion; AdSiR-MR-1 greatly ameliorated these disorders. In ANG II-infused mice, MR-1 silencing also blocked the upregulation of other genes related to cardiac hypertrophy or metabolism of the extracellular matrix. In summary, our results demonstrate the feasibility of MR-1 silencing in vivo and suggest that MR-1 could be a potential new target to treat cardiac hypertrophy induced by ANG II.

Mid-regional pro-adrenomedullin is associated with pulse pressure, left ventricular mass, and albuminuria in African Americans with hypertension

BACKGROUND

African Americans with hypertension are prone to target-organ damage and adverse cardiovascular events. Biomarkers for early detection of target-organ damage in this ethnic group are needed. Adrenomedullin (ADM) is a circulating vasoactive peptide with vasodilatory and antiproliferative effects that has been reported to be elevated in adults with hypertension.

METHODS

We investigated the associations of plasma levels of mid-regional pro-ADM (MR-proADM) with pulse pressure, left ventricular mass (LVM), and albuminuria in 1,034 African-American adults (65 +/- 9 years, 72% women) with hypertension. MR-proADM was measured by an immunoluminometric assay, LVM was assessed by 2-dimensional echocardiography, and albuminuria was assessed by urine albumin:creatinine ratio (UACR). Multivariable regression analyses were used to assess whether plasma MR-proADM was independently associated with pulse pressure, LVM indexed by height to the power 2.7 (LVMi), and UACR.

RESULTS

Plasma MR-proADM was significantly correlated (P < 0.001) with pulse pressure, LVMi, and UACR. In separate multivariable linear regression models that adjusted for age and sex, log MR-proADM was associated with greater pulse pressure (P = 0.007), log LVMi (P = 0.001), and log (UACR+1) (P < 0.0001). After additional adjustment for body mass index (BMI), total and high-density lipoprotein (HDL) cholesterol, smoking history, diabetes, estimated glomerular filtration rate (eGFR), history of myocardial infarction (MI) or stroke, and medication use, log MR-proADM remained significantly associated with greater pulse pressure (P = 0.001), log LVMi (P = 0.029), and log (UACR+1) (P = 0.002).

CONCLUSIONS

In African-American adults with hypertension, plasma MR-proADM is independently associated with pulse pressure, LVMi, and albuminuria and is a potential biomarker for target organ damage.

Hemodynamic, hormonal, and renal actions of adrenomedullin 2 in experimental heart failure

BACKGROUND

Adrenomedullin 2 (AM2) is a novel member of the calcitonin gene-related peptide family that is thought to play a regulatory role in circulatory homeostasis under normal physiological conditions. The effects of AM2 in heart failure have not been investigated previously.

METHODS AND RESULTS

Two incremental doses of human AM2 (10 and 100 ng[kg.min] for 90 minutes each) were given by intravenous infusion to 8 sheep with pacing-induced heart failure. Compared with time-matched control infusions, AM2 produced dose-dependent increases in left ventricular dP/dt(max) (control 1168+/-138 mm Hg/s versus AM2 high-dose 1402+/-130 mm Hg/s; P<0.01) and cardiac output (2.09+/-0.66 L/min versus 3.81+/-0.30 L/min; P<0.001) and reductions in calculated total peripheral resistance (40+/-6 mm Hg(L.min) versus 21+/-4 mm Hg(L.min); P<0.001), mean arterial pressure (74.4+/-2.4 mm Hg versus 66.2+/-2.5 mm Hg; P<0.001), and left atrial pressure (23.3+/-1.0 mm Hg versus 18.8+/-1.3 mm Hg; P<0.001). AM2 administration also induced significant elevations in plasma cAMP (P<0.01) in association with rises in atrial (P<0.05) and brain (P<0.01) natriuretic peptides and plasma renin activity (P<0.01). Despite the increase in renin activity, plasma aldosterone levels were not significantly altered, whereas the aldosterone/plasma renin activity ratio was reduced (P=0.08). Plasma vasopressin, endothelin-1, and catecholamines levels were also unchanged by AM2. Renal effects of AM2 included increased excretion of sodium (P<0.05), cAMP (P<0.01), and creatinine (P<0.05), with augmented creatinine clearance (P<0.05), and a trend for urine output to rise (P=0.068).

CONCLUSIONS

These results indicate that AM2 administration has favorable effects on cardiovascular, endocrine, and renal indexes in heart failure and identify the peptide as a potential therapeutic target in this disease.

Adenylyl cyclase activity and function are decreased in rat cardiac fibroblasts after myocardial infarction

Myocardial infarction (MI) results in left ventricular remodeling (e.g., ventricular hypertrophy, dilatation, and fibrosis). Fibrosis contributes to increased myocardial stiffening, impaired ventricular filling and function, and reduced cardiac output. Adenylyl cyclase (AC) expression and activity are reduced in animal models of heart failure. Stimulation of AC can inhibit extracellular matrix production in isolated cardiac fibroblasts; however, a role for reduced AC expression and activity in fibrosis associated with cardiac remodeling after chronic MI has never been determined. We tested the hypothesis that AC expression and activity are reduced in cardiac fibroblasts after chronic (18 wk) MI. Rats underwent coronary artery ligation or sham surgery (control), and echocardiography was used to assess left ventricular remodeling 1, 3, 5, 7, 10, 12, and 18 wk after surgery. Cardiac fibroblasts were isolated from the noninfarcted myocardium and compared for differences in AC activity and collagen synthesis. End-diastolic dimension was increased [control: 0.76 +/- 0.02 cm and MI: 1.0 +/- 0.02 cm (means +/- SE), P < 0.001] and fractional shortening was decreased (control: 44 +/- 2% and MI: 17 +/- 2%, P < 0.001) in MI compared with control rats. Basal and forskolin-stimulated cAMP production were decreased by 90% and 93%, respectively, and AC5/6 expression was decreased 39% in fibroblasts isolated from MI rats compared with sham controls. Serum-stimulated collagen production was increased twofold and forskolin-mediated inhibition of collagen synthesis was reduced in fibroblasts from MI rats compared with controls. Our data demonstrate that AC expression and activity are reduced and collagen production is increased in cardiac fibroblasts of rats after MI.

Globular adiponectin activates nuclear factor-kappaB and activating protein-1 and enhances angiotensin II-induced proliferation in cardiac fibroblasts

Adiponectin is present in the serum as a trimer, hexamer, or high-molecular weight form. A proteolytic cleavage product of adiponectin, known as globular adiponectin (gAd), also circulates in human plasma. The biological activities of these isoforms are not well characterized. Pressure overload in adiponectin-deficient mice results in enhanced concentric cardiac hypertrophy and increased mortality, suggesting that adiponectin inhibits hypertrophic signaling in the myocardium. Therefore, we examined whether gAd exerts the same effects on myocardium signaling. Nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1) activation were examined using cardiac fibroblasts prepared from the ventricles of 1- to 2-day-old Wistar rats and grown in culture. gAd activated NF-kappaB and enhanced tumor necrosis factor-alpha (TNF-alpha)-induced NF-kappaB activity. gAd also activated AP-1 and enhanced angiotensin II (Ang II)-induced AP-1 activity. gAd induced mRNA expression of c-fos and c-jun and activated extracellular signal-regulated kinase. Thus, gAd enhanced Ang II-induced DNA and collagen synthesis. Antibodies against adiponectin receptor (AdipoR)1 and AdipoR2 elicit activation of NF-kappaB or AP-1, two redox-sensitive transcription factors. Thus, rather than having an antihypertrophic effect, gAd might contribute to the activation of myocardium signaling, leading to myocardial hypertrophy.

Attenuation of cardiovascular remodeling in DOCA-salt rats by the vasopeptidase inhibitor, omapatrilat

Omapatrilat, a vasopeptidase inhibitor, inhibits both neutral endopeptidase and angiotensin-converting enzyme with similar potency. The aim of this study was to investigate whether omapatrilat prevents or reverses cardiovascular remodeling and hypertension in deoxycorticosterone acetate (DOCA)-salt rats. Male Wistar rats (313 +/- 2 g, n = 114) were uninephrectomized (UNX) with or without further treatment with DOCA and 1% NaCl in the drinking water. Compared with UNX control rats, DOCA-salt rats developed hypertension, cardiovascular hypertrophy, perivascular and interstitial cardiac fibrosis and inflammation, endothelial dysfunction, and the prolongation of ventricular action potential duration within four weeks. The administration of omapatrilat (40 mg/kg/day po) for two weeks commencing two weeks after surgery attenuated the development of cardiovascular hypertrophy, inflammation, fibrosis, and ventricular action potential prolongation. In contrast, omapatrilat treatment did not lower systolic blood pressure nor improve endothelial dysfunction. This study concludes that the renin-angiotensin-aldosterone, natriuretic peptide, and bradykinin systems are directly involved in the pathogenesis of cardiovascular remodeling in the DOCA-salt model of hypertension in rats, which may be independent of their effects on blood pressure.

Receptor activity-modifying proteins: RAMPing up adrenomedullin signaling

Adrenomedullin (AM) is a 52-amino-acid multifunctional peptide that circulates in the plasma in the low picomolar range and can exert a multitude of biological effects through an autocrine/paracrine mode of action. The mechanism by which AM transduces its signal represents a novel and pharmacologically tractable paradigm in G protein-coupled receptor signaling. Since its discovery in 1993, the study of AM has emerged into a new field of research with nearly 1800 publications that rivals the renown of other common factors like angiopoetin (1015 publications) and ghrelin (1550 publications). Despite the tremendous strides made in recent years toward unveiling the biochemical and cellular functions of AM, we are still lagging in our understanding of the essential roles of AM in normal and disease physiology. As discussed in this current review, a concerted effort to combine information from clinical, genomic, biochemical, and genetic mouse model sources can provide a focused view to help define the physiological functions of AM. Specifically, we find that certain conditions, such as pregnancy, cardiovascular disease, and sepsis, are associated with robust and dynamic changes in the expression of AM and AM receptor proteins, which together represent an elegant mechanism for altering the physiological responsiveness or function of AM. Thus, the modulation of AM signaling may be further exploited for therapeutic strategies in the management and treatment of human disease.

Activation of AMP-activated protein kinase enhances angiotensin ii-induced proliferation in cardiac fibroblasts

AMP-activated kinase (AMPK) is a highly conserved heterotrimeric kinase that functions as a metabolic regulator of cellular enzymes involved in carbohydrate and fat metabolism, which regulate ATP conservation and synthesis. Here, we investigated whether AMPK signaling has a role in the regulation of angiotensin II (Ang II)-induced proliferation in rat cardiac fibroblasts. Aminoimidazole-4-carboxamide-1-beta-ribofuranoside (AICAR) activated AMPK in rat cardiac fibroblasts and increased Ang II-induced extracellular signal-regulated kinase 1/2 phosphorylation and activity. AICAR also increased Ang II-induced c-fos mRNA expression in the cells. [3H]-thymidine and [3H]-proline incorporation by cardiac fibroblasts treated with Ang II was enhanced when the cells were pretreated with AICAR. Inhibition of AMPK by small interfering RNA for AMPKalpha1 suppressed Ang II-induced extracellular signal-regulated kinase activity, c-fos mRNA expression, and cell proliferation. Treatment of rats with AICAR (1 mg/g body weight per day) for 1 week significantly enhanced Ang II-induced hypertrophy of the myocardium. Our findings indicate that AMPK works as a stimulator of the Ang II-induced proliferative pathway in cardiac fibroblasts. Inhibition of AMPK signaling might serve as a new therapeutic target of remodeling of the hypertrophic myocardium.

Different secretion patterns of two molecular forms of cardiac adrenomedullin in pressure- and volume-overloaded human heart failure

BACKGROUND

In the final step of production of adrenomedullin (AM), an inactive intermediate form of glycine-extended AM (AM-glycine) is converted to the active mature form of adrenomedullin (AM-mature) by enzymatic amidation. Recent studies have revealed that AM-mature and AM-glycine circulate in human plasma. In this study, we investigated the differences of the concentrations of cardiac AM between pressure-overloaded (PO) heart failure (HF) and volume-overloaded (VO)-HF in humans.

METHODS AND RESULTS

We measured AM-mature and AM-glycine by immunoradiometric assays in pericardial fluid and plasma in 38 patients who underwent valve replacement surgery (PO-HF: aortic stenosis, n=14; VO-HF: aortic or mitral regurgitation, n=24). Stable coronary artery disease with normal left ventricular function served as the control (n=24). Plasma AM-mature (VO-HF: +59%, PO-HF: +65%, P<.05) and AM-glycine (VO-HF: +43%, PO-HF: +50%, P<0.05) were similarly higher in the 2 HF groups than in the control group. Interestingly, pericardial fluid AM-mature was markedly higher than that in plasma (control: +789%, VO-HF: +1050%, PO-HF: +1745%, all P<.001). Pericardial fluid AM-mature was higher in VO-HF (+106%, P<.01) than in controls and they were further increased in PO-HF (+243%, P<.05). Pericardial fluid molecular forms of AM correlated with left ventricular systolic pressure, but not with left ventricular end-diastolic volume index in PO-HF. In contrast, they correlated with left ventricular end-diastolic volume index, but not with left ventricular systolic pressure in VO-HF.

CONCLUSION

These results suggest that cardiac AM is differently regulated from plasma AM and that cardiac AM production is upregulated in both types of HF in response to each different stimulus.

Adrenomedullin: a new target for the design of small molecule modulators with promising pharmacological activities

Adrenomedullin (AM) is a 52-amino acid peptide with a pluripotential activity. AM is expressed in many tissues throughout the body, and plays a critical role in several diseases such as cancer, diabetes, cardiovascular and renal disorders, among others. While AM is a protective agent against cardiovascular disorders, it behaves as a stimulating factor in other pathologies such as cancer and diabetes. Therefore, AM is a new and promising target for the development of molecules which, through their ability to regulate AM levels, could be used in the treatment of these pathologies.

Up-regulated synthesis of mature-type adrenomedullin in coronary circulation immediately after reperfusion in patients with anterior acute myocardial infarction

OBJECTIVE

Levels of adrenomedullin (AM), a potent vasodilatory peptide, have been shown to increase in the early stage of acute myocardial infarction (AMI). The purpose of this study was to determine whether coronary sinus-aortic step-up of mature forms of AM is accelerated in patients with AMI after reperfusion.

METHODS

The subjects were 29 consecutive patients with a first episode of anterior AMI and 10 normal controls. All patients with AMI underwent balloon reperfusion therapy within 24 h after symptom onset. Plasma levels of two molecular forms of AM (an active, mature form [AM-m] and an intermediate, inactive glycine-extended form [AM-Gly]) in the aorta and coronary sinus (CS) were measured by specific immunoradiometric assay after reperfusion.

RESULTS

Plasma levels of AM-m and AM-Gly in the aorta and CS were higher in AMI patients than in controls. CS-aortic step-up of AM-m, which is an index of myocardial production of AM-m, was significantly greater in AMI patients than in controls (1.7 +/- 1.4 vs. 0.4 +/- 0.3 pmol/L, P < 0.01). However, there was no significant difference in CS-aortic step-up of AM-Gly (P = 0.30). AMI patients with left ventricular dysfunction (n = 10) had a significantly higher CS-aortic AM-m step-up than AMI patients without left ventricular dysfunction (n = 19). AM-m in the aorta and CS negatively correlated with the left ventricular ejection fraction (r = -0.50, r = -0.48, P < 0.01).

CONCLUSIONS

Myocardial synthesis of AM-m is accelerated in patients with reperfused AMI, especially in patients with critical left ventricular dysfunction. Increased myocardial synthesis of active AM may protect against cardiac dysfunction, myocardial remodeling, or both after the onset of AMI.

Effects of adrenomedullin gene overexpression on biological behavior of hepatic stellate cells

AIM: To investigate the effects of adrenomedullin (AM) gene overexpression on the biological characteristics of human hepatic stellate cells (hHSCs) by stable transfection.

METHODS: hHSCs which express low basal levels of AM were stably transfected with an expression construct containing rat AM gene or with an empty expression vector. Expression of AM in hHSCs was determined by reverse transcription (RT)-polymerase chain reaction (PCR) and radioimmunoassay (RIA). Cell proliferation was evaluated by 5-bromo-2’-deoxyuridine (BrdU) incorporation and immunocytochemistry. RT-PCR and Western blot were used to test the expression of procollagen types I and III. Protein expressions of interstitial collagenase (MMP-1), gelatinase (MMP-2) and tissue inhibitors of matrix metalloproteinases-2 (TIMP-2) were assessed by Western blot.

RESULTS: Two cell clones (A-2, A-8) transfected with the AM gene expressed higher levels of AM mRNA (non-transfected group: 0.86±0.11, empty vector group: 1.01±0.11, A-2 clone group: 1.44±0.08 and A-8 clone group: 1.36±0.05) and protein (12.31±0.17, 12.35±0.12, 12.56±0.06 and 12.62±0.07) (P<0.05). AM gene overexpression had inhibitory effects on cell proliferation of hHSCs (29.6%, 30.9%, 18.9% and 21.8%, respectively. P<0.05) and expression of procollagen type I (0.58±0.1, 0.48±0.11, 0.3±0.06 and 0.31±0.07 at mRNA level) (0.27±0.07, 0.3±0.06, 0.14±0.05 and 0.13±0.05 at protein level) (P<0.05) and procollagen type III (0.17±0.04, 0.15±0.03, 0.1±0.02 and 0.09±0.02 at mRNA level) (0.22±0.04, 0.2±0.03, 0.11±0.04 and 0.13±0.03 at protein level) (P<0.05). Compared with cells non-transfected (TIMP2: 2.77±0.03, MMP-2: 0.5±0.04, MMP-1: 0.49±0.07) and transfected with empty vector (TIMP2: 2.79±0.04, MMP-2: 0.48±0.03, MMP-1: 0.45±0.09), these two clones had lower expression levels of TIMP2(A-2 clone group: 2.7±0.02 and A-8 clone group: 2.71±0.02) (P<0.05) and MMP-2(A-2 clone group: 0.15±0.05 and A-8 clone group: 0.13±0.04) (P<0.05) but displayed a higher expression level of MMP-1(A-2 clone group: 0.68±0.06 and A-8 clone group: 0.81±0.09) (P<0.05).

CONCLUSION: AM gene exerts negative influence to some extent on hHSCs by inhibiting proliferation and production of extracellular matrix (ECM) in addition to inducing MMP-1 expression.

Upregulation of intracardiac adrenomedullin and its receptor system in rats with volume overload-induced cardiac hypertrophy

Specific adrenomedullin receptors have been identified as calcitonin receptor-like receptor (CRLR)/receptor activity-modifying proteins (RAMP2 and RAMP3) complexes. Although we have demonstrated that adrenomedullin is increased in volume overload-induced cardiac hypertrophy, it remains unknown whether the adrenomedullin receptor is altered or not. This study sought to investigate the significance of intracardiac adrenomedullin and its receptor system in volume overload-induced cardiac hypertrophy. Left ventricular adrenomedullin levels were higher in aortocaval shunt (ACS) rats than in controls (+58%). The left ventricular gene expressions of adrenomedullin, CRLR, RAMP2 and RAMP3 were increased (+27%, +76%, +108% and +131%, respectively) and the left ventricular collagen gene expressions were also increased (type I: +138%, type III: +87%). The left ventricular adrenomedullin level correlated with the gene expression of type III collagen (R=0.42). These results suggest that intracardiac adrenomedullin and its receptor system are upregulated and may participate in the regulation of cardiac remodeling in volume overload-induced cardiac hypertrophy.

Adrenomedullin induces matrix metalloproteinase-2 activity in rat aortic adventitial fibroblasts

BACKGROUND

The delicate balance of the extracellular matrix (ECM) determines the stiffness of the vascular wall, and adventitial fibroblasts are involved in ECM formation by synthesizing and degrading matrix proteins. In the present study, we examined the effect of the bioactive peptide adrenomedullin (AM) on activity and expression of matrix metalloproteinases (MMPs) in cultured aortic adventitial fibroblasts.

METHODS AND RESULTS

In cultured adventitial fibroblasts isolated from aorta of adult Wistar rats, 10(-6)mol/L angiotensin II (Ang II) significantly (p<0.05) down-regulated MMP-2 activity as determined by in vitro gelatin zymography. In contrast, 10(-7)mol/L synthetic rat AM significantly (p<0.05) stimulated zymographic MMP-2 activity by 23%, increasing intracellular cAMP, and AM abolished the action of Ang II, augmenting the MMP-2 activity. Similarly, Ang II down-regulated MMP-2 protein expression assessed by Western blotting, whereas AM increased it. Furthermore, 8-bromo-cAMP, an analogue of cAMP, mimicked the effect of AM, and H-89, an inhibitor for protein kinase A (PKA), significantly decreased the basal and AM-induced MMP-2 activity.

CONCLUSION

This study provides a new insight into the biological action of AM and its intracellular signaling system of cAMP/PKA stimulating the matrix degrading enzyme MMP-2, suggesting an important role for this molecule in modulating ECM deposition in the adventitial layer.

Production and autocrine/paracrine effects of endogenous insulin-like growth factor-1 in rat cardiac fibroblasts

Insulin-like growth factor (IGF)-1 appears to play an important role in cardiac hypertrophy or remodeling. However, the role of endogenous IGF-1 in the growth of cardiac myocytes and fibroblasts remains unclear. This study investigated the major site of the production of cardiac IGF-1 and the local effects of endogenous IGF-1 secreted from cardiac cells. A significant expression of IGF-1 mRNA was found in cultured neonatal and adult rat cardiac fibroblasts, but not in myocytes. In addition, an in vivo examination by in situ hybridization histochemical analyses demonstrated the IGF-1 transcripts in the interstitial fibrotic tissue of the ventricle. Time-dependent secretion of IGF-1 protein was also observed in cultured cardiac fibroblasts. An antibody against IGF-1 decreased collagen synthesis in cardiac fibroblasts under basal conditions. Fibroblast-conditioned medium, as well as exogenous IGF-1, increased protein synthesis in cardiac myocytes, and this increase was inhibited by antibodies against IGF-1 and IGF-1 receptor, IGF binding protein-3, and IGF-1 receptor antagonist. These observations suggest that IGF-1 is produced and released mainly from cardiac fibroblasts and that endogenous IGF-1 promotes collagen synthesis by cardiac fibroblasts and hypertrophy of myocytes as an autocrine and a paracrine factor. Cardiac IGF-1 may function as an endogenous modulator of cardiac hypertrophy or remodeling.

Inhibition of cardiac myofibroblast formation and collagen synthesis by activation and overexpression of adenylyl cyclase

Transformation of fibroblasts to myofibroblasts, characterized by expression of alpha-smooth muscle actin (alpha-SMA) and production of extracellular matrix (ECM) components, is a key event in connective tissue remodeling. Approaches to inhibit this transformation are needed in tissues, such as the heart, where excessive ECM production by cardiac fibroblasts (CFs) causes fibrosis, myocardial stiffening, and cardiac dysfunction. We tested whether adenylyl cyclase (AC) activation (increased cAMP levels) modulates the transformation of adult rat CF to myofibroblasts, as assessed by immunofluorescent microscopy, immunoblotting, and collagen synthesis. A 24-h incubation of CF with TGF-beta or angiotensin II increased alpha-SMA expression, which was inhibited by the AC agonist forskolin and a cAMP analog that activates protein kinase A. Treatment with forskolin blunted serum-, TGF-beta-, and angiotensin II-stimulated collagen synthesis. CFs engineered to overexpress type 6 AC had enhanced forskolin-promoted cAMP formation, greater inhibition by forskolin of TGF-beta-stimulated alpha-SMA expression, and a decrease in the EC(50) of forskolin to reduce serum-stimulated collagen synthesis. The AC stimulatory agonist adrenomedullin inhibited collagen synthesis in CF that overexpressed AC6 but not in controls. Thus, AC stimulation blunts collagen synthesis and, in parallel, the transformation of adult rat CF to myofibroblasts. AC overexpression enhances these effects, "uncovering" an inhibition by adrenomedullin. These findings implicate cAMP as an inhibitor of ECM formation by means of blockade of the transformation of CF to myofibroblasts and suggest that increasing AC expression, thereby enhancing cAMP generation through stimulation of receptors expressed on CF, could provide a means to attenuate and prevent cardiac fibrosis and its sequelae.

Direct effects of high glucose and insulin on protein synthesis in cultured cardiac myocytes and DNA and collagen synthesis in cardiac fibroblasts

The present study examined the direct effects of high glucose and insulin on protein synthesis in cardiac myocytes and DNA and collagen synthesis in cardiac fibroblasts. Cultured rat cardiac myocytes and fibroblasts were grown in media containing normal glucose, high glucose, or osmotic control, and incubated with or without insulin. In cardiac myocytes, high glucose had no effect, but insulin increased protein synthesis and atrial natriuretic peptide (ANP) secretion and gene expression. The extracellular signal-regulated protein kinase (ERK)/mitogen-activated protein kinase (MAPK) inhibitor and the protein kinase C (PKC) inhibitor blocked insulin-induced protein synthesis. In cardiac fibroblasts, high glucose and osmotic control media increased DNA synthesis. Collagen synthesis and fibronectin and transforming growth factor-beta1 (TGF-beta1) mRNA expression were stimulated by high glucose, but not by osmotic control. Insulin increased DNA and collagen synthesis in fibroblasts, and the insulin-induced increase in DNA synthesis was blocked by the phosphatidylinositol 3 kinase (PI3K) inhibitor. Our findings suggest that cardiomyocyte protein synthesis is mainly regulated by insulin rather than high glucose and both high glucose and insulin contribute to fibroblast DNA and collagen synthesis. High glucose accelerates fibroblast DNA synthesis and collagen synthesis, and fibronectin and TGF-beta1 mRNA expression, dependent or independent of osmotic stress. Insulin regulates myocyte protein synthesis and fibroblast DNA synthesis through different intracellular mechanisms.

Protective effects of endogenous adrenomedullin on cardiac hypertrophy, fibrosis, and renal damage

BACKGROUND

Adrenomedullin (AM) is a novel vasodilating peptide thought to have important effects on cardiovascular function. The aim of this study was to assess the activity of endogenous AM in the cardiovascular system using AM knockout mice.

METHODS AND RESULTS

Mice heterozygous for an AM-null mutation (AM+/-) and their wild-type littermates were subjected to aortic constriction or angiotensin II (Ang II) infusion. The resultant cardiovascular stress led to increases in heart weight/body weight ratios, left ventricular wall thickness, and perivascular fibrosis, as well as expression of genes encoding angiotensinogen, ACE, transforming growth factor-beta, collagen type I, brain natriuretic peptide, and c-fos. In addition, renal damage characterized by decreased creatinine clearance with glomerular sclerosis was noted. In all cases, the effects were significantly more pronounced in AM+/- mice. Hearts from adult mice subjected to aortic constriction showed enhanced extracellular signal-regulated kinase (ERK) activation, as did cardiac myocytes from neonates treated acutely with Ang II. Again the effect was more pronounced in AM+/- mice, which showed increases in cardiac myocyte size, protein synthesis, and fibroblast proliferation. ERK activation was suppressed by protein kinase C inhibition to a greater degree in AM+/- myocytes. In addition, treatment of cardiac myocytes with recombinant AM suppressed Ang II-induced ERK activation via a protein kinase A-dependent pathway.

CONCLUSIONS

Endogenous AM exerts a protective effect against stress-induced cardiac hypertrophy via protein kinase C- and protein kinase A-dependent regulation of ERK activation. AM may thus represent a useful new tool for the treatment of cardiovascular disease.

Chronic Administration of Adrenomedullin Attenuates Transition From Left Ventricular Hypertrophy to Heart Failure in Rats

Acute administration of adrenomedullin (AM) exerts beneficial hemodynamic, renal, and neurohormonal effects in heart failure (HF). However, chronic effects of AM administration on HF remain unknown. This study sought to examine the effect of chronic infusion of AM on progression of HF in rat. Human recombinant AM was administered by osmotic minipump for 7 weeks in the HF model of Dahl salt-sensitive rats. The effect was compared with vehicle and diuretic treatment group. Chronic AM infusion significantly decreased left ventricular end-diastolic pressure, right ventricular systolic pressure, right atrial pressure, and left ventricular weight/body weight ( P <0.01 for all). AM significantly attenuated the increase in circulating renin-aldosterone, endogenous rat AM, and atrial natriuretic peptide levels ( P <0.01 for all). AM also inhibited the myocardial tissue levels of angiotensin II and atrial and brain natriuretic peptide ( P <0.01 for all). These changes were associated with the improvement of cardiac output and systemic vascular resistance (both P <0.05). Furthermore, AM improved left ventricular end-systolic elastance ( P <0.01). These improvements were greater in the AM than in the diuretic group, although both drugs similarly decreased systolic blood pressure and increased urinary sodium excretion. Kaplan-Meier survival analysis showed that AM significantly prolonged survival time compared with diuretic ( P <0.05) and vehicle ( P <0.01) treatment groups. These results suggest that endogenous AM plays a compensatory role in HF and that chronic AM infusion attenuates progression of left ventricular dysfunction and improves survival, at least in part, through inhibition of circulating and myocardial neurohormonal activation.

Gene expression, secretion, and autocrine action of C-type natriuretic peptide in cultured adult rat cardiac fibroblasts

C-type natriuretic peptide (CNP), the third member of the natriuretic peptide family, is known to be synthesized in the central nervous system and vascular endothelial cells, in contrast to atrial natriuretic peptide and brain natriuretic peptide. However, there have been no studies concerning CNP production in cultured cardiac cells. Here, we examined the production and the local effect of CNP in cultured ventricular cells. Under serum-free conditions, adult rat cardiac fibroblasts secreted immunoreactive CNP time dependently. TGF-beta1, basic fibroblast growth factor, and endothelin-1 significantly stimulated CNP secretion. Northern blot analysis detected significant expressions of CNP and its specific receptor (guanylyl cyclase-B) mRNA in cardiac fibroblasts. CNP stimulated intracellular cGMP production in fibroblasts more intensely than atrial and brain natriuretic peptides. CNP inhibited both DNA and collagen syntheses of cardiac fibroblasts, and these inhibitory effects by CNP were stronger than by atrial and brain natriuretic peptides. The inhibition by CNP of DNA and collagen syntheses was reproduced by a cGMP analog, 8-bromo cGMP. The present findings demonstrate that CNP is synthesized in and secreted from cardiac fibroblasts and suggest that CNP has a suppressive effect on fibroblast proliferation and extracellular matrix production, probably via the guanylyl cyclase-B-mediated cGMP-dependent process. CNP produced by cardiac fibroblasts may play a role as an autocrine regulator against excessive cardiac fibrosis.

Upregulation of ligand, receptor system, and amidating activity of adrenomedullin in left ventricular hypertrophy of severely hypertensive rats: effects of angiotensin-converting enzyme inhibitors and diuretic

OBJECT

We investigated the pathophysiological role of the cardiac adrenomedullin (AM) system, including the ligand, receptor and amidating activity in the hypertrophied heart in severe hypertension.

METHOD

We studied the following four groups: control Wistar-Kyoto rats (WKY), spontaneously hypertensive stroke-prone rats (SHR-SP), 8 weeks captopril-treated SHR-SP, and 8 weeks trichlormethiazide-treated SHR-SP. AM precursor is converted to inactive glycine-extended AM (AM-Gly) and subsequently AM-Gly is converted to active mature AM (AM-m) by enzymatic amidation. We measured AM-m, AM-total (AM-T; AM-T = AM-m + AM-Gly), and atrial natriuretic peptide (ANP) in the plasma and left ventricle (LV) by immunoradiometric assay. We also measured gene expression of AM and ANP was and gene expression and protein levels of AM receptor system components such as calcitonin receptor-like receptor (CRLR), receptor-activity modifying protein (RAMP) 2 and RAMP3.

RESULTS

At 7 weeks old, SHR-SP had higher blood pressure and ANP mRNA levels and lower plasma AM-T compared with WKY, however, there were no differences in other indices between the two groups. At 17 weeks old, SHR-SP had increased blood pressure, LV weight, plasma and LV ANP levels and mRNA levels of ANP compared with WKY. AM-m and AM-T levels in plasma (AM-m: + 31%; AM-T: + 56%) and the LV (AM-m: + 84%; AM-T: + 31%) were significantly higher in SHR-SP than in WKY. The LV tissue AM-m/AM-T ratio was significantly higher in SHR-SP (93.2%) than in WKY. The mRNA levels of AM, CRLR, and RAMP2 in the LV were significantly higher in SHR-SP than in WKY. Captopril and trichlormethiazide similarly decreased blood pressure and LV hypertrophy with the reduction of the LV AM-m and AM-T levels and mRNA abundance of AM and its receptor component.

CONCLUSION

These results suggest that cardiac AM system is upregulated in the hypertrophied heart in this hypertension model. Considering that AM acts as an anti-remodeling autocrine and/or paracrine factor, upregulation of the AM system may modulate the pathophysiology in LV hypertrophy.

Omapatrilat induces profound renal vasodilation but does not affect coronary hemodynamics

BACKGROUND

Omapatrilat has potent enzymatic inhibitory effects on the angiotensin-converting enzyme and neutral endopeptidase. The prolonged effects of this inhibition on systemic and regional hemodynamics, cardiovascular mass, and hydroxyproline concentration in spontaneously hypertensive rats were studied. The contribution of endogenous bradykinin on the cardiovascular actions of omapatrilat in this genetic model of hypertension was also investigated.

METHODS AND RESULTS

Systemic and regional hemodynamics (radionuclide-labeled microspheres), left and right ventricular and aortic masses, and hydroxyproline concentration were determined in 35-week-old spontaneously hypertensive rats after 12 weeks of treatment with omapatrilat (40 mg/kg/day), with and without the bradykinin receptor antagonist icatibant (500 microg/kg/day). Omapatrilat decreased mean arterial pressure, reducing total peripheral resistance as well as decreased left ventricular and aortic mass indices. It also induced a profound renovasodilation associated with a decrease renal vascular resistance that markedly increased renal blood flow. Coronary hemodynamics and left ventricular hydroxyproline concentration remained unaltered. Concomitant blockade of bradykinin receptors partially attenuated the hypotensive effect of omapatrilat and its effect on aortic mass; and icatibant did not influence the renovasodilation.

CONCLUSION

Omapatrilat produced profoundly beneficial effects on systemic and renal hemodynamics, as well as on left ventricular and aortic masses, without any effect on coronary hemodynamics. These effects of omapatrilat on arterial pressure and aortic mass, but not on renal hemodynamics and left ventricular mass, may have been at least partially mediated through the action of bradykinin.

Cell and molecular biology of the multifunctional peptide, adrenomedullin

Adrenomedullin (AM) is a recently discovered regulatory peptide involved in many functions including vasodilatation, electrolyte balance, neurotransmission, growth, and hormone secretion regulation, among others. This 52-amino acid peptide is expressed by specific cell types in many organs throughout the body. A complex receptor system has been described for AM; it requires at least the presence of a seven-transmembrane-domain G-protein-coupled receptor, a single-transmembrane-domain receptor activity modifying protein, and a receptor component protein needed to establish the connection with the downstream signal transduction pathway, which usually involves cyclicAMP. In addition, a serum-binding protein regulates the biological actions of AM, frequently by increasing AM functional attributes. Changes in levels of circulating AM correlate with several critical diseases, including cardiovascular and renal disorders, sepsis, cancer, and diabetes. Whether AM is a causal agent, a protective reaction, or just a marker for these diseases is currently under investigation. New technologies seeking to elevate and/or reduce AM levels are being investigated as potential therapeutic avenues.

Altered gene expression of adrenomedullin and its receptor system and molecular forms of tissue adrenomedullin in left ventricular hypertrophy induced by malignant hypertension

To investigate the pathophysiological role of adrenomedullin (AM) in left ventricular hypertrophy (LVH) in hypertension, we measured the plasma level, left ventricle (LV) tissue level, and mRNA abundance of AM and the mRNA abundance of the AM receptor system in the LV. We also analyzed the molecular forms of AM in the plasma and LV tissue and investigated the relationships between AM and the degree of LVH. We studied the following three groups: control Wistar Kyoto rats (WKY), control spontaneously hypertensive rats (SHR), and deoxycorticosterone acetate (DOCA)-salt SHR (D-SHR). We measured AM-mature, active form, and AM-total (active form+inactive form) in plasma and the LV by a newly developed immunoradiometric assay. Gene expression of AM was measured by Northern blot analysis and gene expression of AM receptor system components, such as calcitonin receptor-like receptor (CRLR), receptor activity modifying protein 2 (RAMP2), and RAMP3 was measured by the reverse transcription polymerase chain reaction method. After 3 weeks of DOCA treatment, D-SHR was characterized by higher blood pressure, LV weight, and plasma atrial natriuretic peptide levels compared with those in the other two groups. Plasma AM-mature and AM-total levels were significantly higher in D-SHR than in the other two groups, whereas there were no significant differences in the AM-mature/AM-total ratio among the three groups. On the other hand, LV tissue AM-mature and AM-total levels were also significantly higher in D-SHR than in the other two groups, and the AM-mature/AM-total ratio was significantly higher in LV tissues than in plasma. Furthermore, the LV tissue AM-mature/AM-total ratio was significantly higher in D-SHR compared with the other two groups. The LV tissue AM-mature/AM-total ratio was significantly correlated with LV weight/body weight (r=0.92, p<0.001). The gene expression levels of AM, CRLR, RAMP2, and RAMP3 in the LV were significantly higher in D-SHR than in the other two groups. These results suggest that the AM amidating enzyme activity, ligand, and receptor system are all upregulated in the LV hypertrophy in this malignant hypertensive rat model. Considering that AM serves as a local antihypertrophic autocrine and/or paracrine factor, the induction of AM system observed here may modulate the pathophysiology of LV hypertrophy in certain forms of malignant hypertension.

Adrenomedullin inhibits angiotensin AT1A receptor expression and function in cardiac fibroblasts

Adrenomedullin (AM) is a multifunctional peptide hormone with wide-ranging actions related to cardiovascular homeostasis. AM receptors are highly expressed in the heart and AM has antihypertrophic and antiproliferative effects on cardiac myocytes and fibroblasts, respectively. We have investigated the interaction between AM and angiotensin II (Ang II) signalling in neonatal cardiac fibroblast cultures to determine whether the antagonistic effects of AM are mediated via the modulation of Ang II receptors. Cardiac fibroblasts exclusively expressed the Ang II type 1 receptor (AT(1)R) and binding to this site was downregulated by 35% following an 18-h incubation with 100 nM AM. Levels of AT(1A)R mRNA were dose-dependently lowered by AM, with a maximal 40-50% inhibition by 6 h. The decreases in both AT(1)R binding and AT(1A)R mRNA levels were mimicked by 8-Br-cAMP or forskolin, suggesting that the effects of AM were mediated via an elevation of cAMP. In cardiac fibroblasts pretreated with AM, the Ang II induction of collagen biosynthesis was attenuated, although basal collagen synthesis was unaffected. These data suggest that AM mediates the heterologous downregulation of AT(1)R expression via a relatively rapid decrease in AT(1A)R mRNA pools. This interaction may represent a relevant pathophysiological mechanism for modulating Ang II responsiveness in the diseased heart.

Ventricular adrenomedullin is associated with myocyte hypertrophy in human transplanted heart

Adrenomedullin (ADM) is a vasoactive and natriuretic peptide. While it is known that ADM is increased in failing human ventricles, the expression of ADM in human ventricular allografts remains unknown. The present study was designed to investigate tissue localization and intensity of ADM expression in ventricular biopsy specimens and to characterize ventricular ADM in human cardiac allografts. Thirty-three post-transplant endomyocardial biopsy specimens were examined immunohistochemically. The average score (range: 0-4) of ADM immunoreactivity (IR) was 2.4+/-0.9 (mean+/-standard deviation). Right ventricular (RV) systolic pressure was significantly increased with high ADM-IR (p=0.048) and the ADM-IR positively associated with myocyte size (r(2)=0.23, p=0.010). In contrast, ADM-IR was not associated with systemic blood pressure, serum creatinine, cyclosporine concentration, cardiac fibrosis, or allograft rejection. The present study shows that ADM-IR is present in human ventricular endomyocardium after transplantation, and ADM-IR is associated with the magnitude of RV pressure and myocyte size, suggesting an important role for ventricular ADM in the counteraction against overload as well as in the progress of myocyte hypertrophy after heart transplantation.

Ventricular adrenomedullin system in the transition from LVH to heart failure in rats

We investigated whether adrenomedullin (AM) participates in the pathophysiology during the transition from left ventricular hypertrophy (LVH) to heart failure (HF). We used the Dahl salt-sensitive (DS) rat model, in which systemic hypertension causes LVH at the age of 11 weeks, followed by HF at the age of 18 weeks. Two molecular forms of AM levels in the plasma and myocardium at the LVH stage were significantly elevated compared with those in controls, and they were further increased at the HF stage. Interestingly, the LV tissue AM-mature/AM-total ratio was higher only in the HF group than in controls and LVH. The LV tissue AM-mature/AM-total ratio, AM-mature, and AM-total concentrations had close relations with the LV weight/body weight (r=0.72, r=0.79, and r=0.70, respectively; all P<0.001). AM gene expression was significantly increased at the LVH stage and was further increased at the HF stage. Furthermore, gene expression of AM receptor system components such as calcitonin receptor-like receptor (CRLR), receptor activity-modified protein 2 (RAMP2), and RAMP3 were significantly increased at the stage of LVH and HF. Regarding other neurohumoral factors, plasma renin and aldosterone levels were not increased at the LVH stage but were increased at the HF stage, whereas atrial natriuretic peptide was increased in both the plasma and myocardium at the LVH stage and was further increased at the HF stage. These results suggest that induction of the cardiac AM system, including the ligand, receptor, and amidating activity, may modulate pathophysiology during the transition from LVH to HF in this model.

Cardioprotective effect of adrenomedullin in heart failure

Many neurohumoral factors participate in the pathophysiology of heart failure, and adrenomedullin (AM) may be involved in their derangement. This work reviews the accumulating evidence in support of a compensatory role of AM in heart failure, and describes the possible mechanisms of this role. It has been established that plasma AM levels are increased in patients with heart failure in proportion to the severity of the disease. Furthermore, recent studies suggest that plasma AM level is an independent prognostic indicator of heart failure. Thus, AM may be not only a biochemical marker for evaluating the severity of heart failure, but also a prognostic indicator of this syndrome. In patients with heart failure, AM production is increased not only in the plasma, but also in the heart. AM secretion from the failing human heart is also increased, but this increase is small and responds slowly to the stimulus. This phenomenon may be explained by the fact that AM is secreted via a constitutive pathway and that AM is an autocrine and/or a paracrine factor in the heart. An experiment using cultured myocytes suggested that cytokines and mechanical stress are important stimuli for AM production in the heart. Regarding the action of AM in the heart, recent studies have suggested that AM exerts an inotropic action both in vitro and in vivo. AM also attenuates cardiac hypertrophy in myocytes and inhibits proliferation and collagen production in cardiac fibroblasts. These results suggest that AM may be an antifibrotic, antihypertrophic, and positive inotropic factor in the failing and hypertrophied heart. Because AM has many cardiorenal actions, AM administration may be useful for the treatment of heart failure. Indeed, acute administration of AM has been shown to improve the hemodynamics, renal function, and hormonal parameters in patients with heart failure. Moreover, recent studies have shown that AM gene therapy or long-term AM infusion significantly improved cardiac hypertrophy and fibrosis, and prolonged the survival time in an animal model of hypertension and heart failure. In conclusion, these findings suggest that AM plays a compensatory role in the pathophysiology of heart failure and that administration of AM may be a new and promising approach for the treatment of patients with this syndrome.

Adrenomedullin: a possible autocrine or paracrine hormone in the cardiac ventricles

Adrenomedullin (AM), a potent vasodilator peptide originally isolated from pheochromocytoma, is expressed in cardiovascular tissues such as those of the cardiac atria and ventricles. Cell culture experiments have shown that AM peptide is synthesized and secreted from cardiac myocytes and fibroblasts of neonatal rats. Humoral factors, such as angiotensin II (Ang II) and endothelin-1 (ET-1), and mechanical stress due to pressure and volume overload to the heart have been shown to be involved in AM expression of the myocardium in both in vitro and in vivo studies. The effects of AM on cardiomyocytes and cardiac fibroblasts have been examined in in vitro studies, with the result that AM was shown to exert inhibitory actions on myocyte hypertrophy and on proliferation and collagen production of cardiac fibroblasts in an autocrine or paracrine manner. In rats, experimental therapeutic intervention consisting of transfer of the AM gene or of recombinant AM appears to partly inhibit the progression of cardiac hypertrophy and remodeling. It has been shown that the calcitonin receptor-like receptor (CRLR) and receptor-activity-modifying protein (RAMP) act together to function as AM receptors, although in this regard there are a number of issues, including the cellular mechanism of AM actions, that remain to be addressed. In addition, the role of proadrenomedullin N-terminal 20 peptide (PAMP), which is derived from preproAM, is another topic for future experiments. Collectively, the research data accumulating in this area suggest that AM plays a role as an autocrine or paracrine hormone in the cardiac ventricles, and that AM might be utilized as a therapeutic tool in the treatment of hypertensive or ischemic heart disease.

The effect of pituitary adenylate cyclase activating polypeptide on cultured rat cardiocytes as a cardioprotective factor

In the cardiovascular system, pituitary adenylate cyclase activating polypeptide (PACAP) exhibits not only vasodilation but also positive inotropic action by increasing cardiac output. Then the effect of PACAP in cultured cardiovascular cells was examined. In neonatal rat myocytes, PACAP evoked concentration-dependent increase in intracellular cyclic AMP content more potently than vasoactive intestinal polypeptide (VIP). However, in neonatal rat nonmyocytes, PACAP and VIP showed equal potency. The characterization of the subtype of PACAP/VIP receptors by RT-PCR analysis revealed that PAC1 receptor mRNA is dominantly present in the myocytes, but VPAC2 receptor mRNA is abundant in the nonmyocytes. In the myocytes, PACAP did not change the protein synthesis stimulated by endothelin or by itself. However, PACAP moderately stimulated the secretion of atrial natriuretic polypeptide (ANP). On the other hand, PACAP inhibited the protein synthesis and DNA synthesis of the nonmyocytes. These indicate that PACAP might be involved in the regulation of cardiac hypertrophy and fibrosis as a cardioprotective factor.

Long-term adrenomedullin administration in experimental heart failure

Short-term administration of adrenomedullin, a recently discovered peptide with potent vasodilator, natriuretic, and aldosterone-inhibitory actions, has beneficial effects in experimental and clinical heart failure. The effects of prolonged adrenomedullin administration have not previously been assessed in this setting. Consequently, in 16 sheep with pacing-induced heart failure, we infused either adrenomedullin (10 ng/kg per minute; n=8) or a vehicle control (Hemaccel; n=8) for 4 days. Compared with control data, infusion of adrenomedullin persistently increased circulating levels of the peptide (by approximately 9.5 pmol/L; P<0.001), in association with prompt (15 minutes) and sustained (4 days) increases in cardiac output (day 4, 27%), and reductions in peripheral resistance (30%), mean arterial pressure (13%), and left atrial pressure (24%; all, P<0.001). Adrenomedullin also significantly enhanced urinary sodium excretion (day 4, 3-fold; P<0.05), creatinine excretion (1.2-fold; P<0.001), and creatinine clearance (1.4-fold; P<0.001) over the 4 days of treatment, whereas urine volume and cAMP excretion tended to be elevated (both, 0.1>P>0.05). Plasma renin activity was increased (P<0.05), whereas aldosterone levels were reduced in a sustained fashion (P<0.01). Plasma endothelin rose transiently (hours 1 to 6) after initiation of treatment (P<0.05). Despite substantial cardiac unloading, plasma concentrations of the natriuretic peptides were not significantly different from control. In conclusion, long-term administration of adrenomedullin induces pronounced and sustained cardiovascular and renal effects in experimental heart failure, including reductions in cardiac preload and afterload, as well as augmentation of cardiac output, sodium excretion, and glomerular filtration. These findings support the concept of adrenomedullin as a protective hormone during hemodynamic compromise with therapeutic potential in heart failure.

Multiple roles of adrenomedullin revealed by animal models

The newly identified adrenomedullin (AM) gene codes for a potent, highly conserved vasodilator that is expressed in many tissues. Many biological functions have been ascribed to AM based on its broad expression pattern and numerous in vitro studies, and it is currently viewed as a multifunctional peptide hormone. Recent advances in gene manipulation have permitted the development of experimental animal systems to help distinguish between gene causes and effects in the context of otherwise normal physiology, and so the normal biological function of the AM gene can be studied within the intact physiological milieu of a whole animal. In this review article, we summarize the recent findings from three different types of genetic experiments involving the AM gene.