Effects of adrenomedullin inhalation on hemodynamics and exercise capacity in patients with idiopathic pulmonary arterial hypertension

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.

Prognostic Value for Mortality of Plasma Bioactive Adrenomedullin in Patients with Pulmonary Arterial Hypertension: A Sub Analysis of the Biomarker Study in the COHARD-PH Registry

The adrenomedullin level increases in pulmonary arterial hypertension (PAH, and correlates with a high mortality rate. Its active form, bioactive adrenomedullin (bio-ADM), has been recently developed and has significant prognostic applications in acute clinical settings. Aside from idiopathic/hereditary PAH (I/H-PAH), atrial septal defects-associated pulmonary artery hypertension (ASD-PAH) is still prevalent in developing countries and associated with increased mortality. This study aimed to investigate the mortality-wise prognostic value of the plasma bio-ADM level by comparing subjects with ASD-PAH and I/H-PAH with ASD patients without pulmonary hypertension (PH) as a control group. This was a retrospective, observational cohort study. The subjects were Indonesian adult patients who were recruited from the Congenital Heart Disease and Pulmonary Hypertension (COHARD-PH) registry and divided into three groups: (1) ASD without PH (control group), (2) ASD-PAH and (3) I/H-PAH. During right-heart catheterization at the time of diagnosis, a plasma sample was taken and assayed for bio-ADM using a chemiluminescence immunoassay. Follow-up was performed as a part of the COHARD-PH registry protocol in order to evaluate the mortality rate. Among the 120 subjects enrolled: 20 turned out to have ASD without PH, 85 had ASD-PAH and 15 had I/H-PAH. Compared to the control group (5.15 (3.0-7.95 pg/mL)) and ASD-PAH group (7.30 (4.10-13.50 pg/mL)), bio-ADM levels were significantly higher in the I/H-PAH group (median (interquartile range (IQR)): 15.50 (7.50-24.10 pg/mL)). Moreover, plasma bio-ADM levels were significantly higher in subjects who died (n = 21, 17.5%) compared to those who survived (median (IQR): 11.70 (7.20-16.40 pg/mL) vs. 6.90 (4.10-10.20 pg/mL), p = 0.031). There was a tendency toward higher bio-ADM levels in those who died among the PAH subjects, in both ASD-PAH and I/H-PAH groups. In conclusion, the plasma bio-ADM level is elevated in subjects with PAH from both ASD-PAH and I/H-PAH origins, reaching the highest levels in subjects with the I/H-PAH form. A high bio-ADM level tended to be associated with a high mortality rate in all subjects with PAH, indicating a relevant prognostic value for this biomarker. In patients with I/H-PAH, monitoring bio-ADM could represent a valid tool for predicting outcomes, allowing more appropriate therapeutical choices.

Sustained Activation of CLR/RAMP Receptors by Gel-Forming Agonists

Background: Adrenomedullin (ADM), adrenomedullin 2 (ADM2), and CGRP family peptides are important regulators of vascular vasotone and integrity, neurotransmission, and fetoplacental development. These peptides signal through CLR/RAMP1, 2, and 3 receptors, and protect against endothelial dysfunction in disease models. As such, CLR/RAMP receptor agonists are considered important therapeutic candidates for various diseases. Methods and Results: Based on the screening of a series of palmitoylated chimeric ADM/ADM2 analogs, we demonstrated a combination of lipidation and accommodating motifs at the hinge region of select peptides is important for gaining an enhanced receptor-activation activity and improved stimulatory effects on the proliferation and survival of human lymphatic endothelial cells when compared to wild-type peptides. In addition, by serendipity, we found that select palmitoylated analogs self-assemble to form liquid gels, and subcutaneous administration of an analog gel led to the sustained presence of the peptide in the circulation for >2 days. Consistently, subcutaneous injection of the analog gel significantly reduced the blood pressure in SHR rats and increased vasodilation in the hindlimbs of adult rats for days. Conclusions: Together, these data suggest gel-forming adrenomedullin analogs may represent promising candidates for the treatment of various life-threatening endothelial dysfunction-associated diseases such as treatment-resistant hypertension and preeclampsia, which are in urgent need of an effective drug.

Novel Experimental Therapies for Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive and devastating disease characterized by pulmonary artery vasoconstriction and vascular remodeling leading to vascular rarefaction with elevation of pulmonary arterial pressures and pulmonary vascular resistance. Often PAH will cause death from right heart failure. Current PAH-targeted therapies improve functional capacity, pulmonary hemodynamics and reduce hospitalization. Nevertheless, today PAH still remains incurable and is often refractory to medical therapy, underscoring the need for further research. Over the last three decades, PAH has evolved from a disease of unknown pathogenesis devoid of effective therapy to a condition whose cellular, genetic and molecular underpinnings are unfolding. This article provides an update on current knowledge and summarizes the progression in recent advances in pharmacological therapy in PAH.

The neurohormonal basis of pulmonary hypertension in heart failure with preserved ejection fraction

AIMS

Pulmonary hypertension (PH) represents an important phenotype among the broader spectrum of patients with heart failure with preserved ejection fraction (HFpEF), but its mechanistic basis remains unclear. We hypothesized that activation of endothelin and adrenomedullin, two counterregulatory pathways important in the pathophysiology of PH, would be greater in HFpEF patients with worsening PH, and would correlate with the severity of haemodynamic derangements and limitations in aerobic capacity and cardiopulmonary reserve.

METHODS AND RESULTS

Plasma levels of C-terminal pro-endothelin-1 (CT-proET-1) and mid-regional pro-adrenomedullin (MR-proADM), central haemodynamics, echocardiography, and oxygen consumption (VO2) were measured at rest and during exercise in subjects with invasively-verified HFpEF (n = 38) and controls free of HF (n = 20) as part of a prospective study. Plasma levels of CT-proET-1 and MR-proADM were highly correlated with one another (r = 0.89, P < 0.0001), and compared to controls, subjects with HFpEF displayed higher levels of each neurohormone at rest and during exercise. C-terminal pro-endothelin-1 and MR-proADM levels were strongly correlated with mean pulmonary artery (PA) pressure (r = 0.73 and 0.65, both P < 0.0001) and pulmonary capillary wedge pressure (r = 0.67 and r = 0.62, both P < 0.0001) and inversely correlated with PA compliance (r = -0.52 and -0.43, both P < 0.001). As compared to controls, subjects with HFpEF displayed right ventricular (RV) reserve limitation, evidenced by less increases in RV s' and e' tissue velocities, during exercise. Baseline CT-proET-1 and MR-proADM levels were correlated with worse RV diastolic reserve (ΔRV e', r = -0.59 and -0.67, both P < 0.001), reduced cardiac output responses to exercise (r = -0.59 and -0.61, both P < 0.0001), and more severely impaired peak VO2 (r = -0.60 and -0.67, both P < 0.0001).

CONCLUSION

Subjects with HFpEF display activation of the endothelin and adrenomedullin neurohormonal pathways, the magnitude of which is associated with pulmonary haemodynamic derangements, limitations in RV functional reserve, reduced cardiac output, and more profoundly impaired exercise capacity in HFpEF. Further study is required to evaluate for causal relationships and determine if therapies targeting these counterregulatory pathways can improve outcomes in patients with the HFpEF-PH phenotype.

CLINICAL TRIAL REGISTRATION

NCT01418248; https://clinicaltrials.gov/ct2/results? term=NCT01418248&Search=Search.

The Cardiopulmonary Effects of the Calcitonin Gene-related Peptide Family

Cardiopulmonary diseases are very common among the population. They are high-cost diseases and there are still no definitive treatments. The roles of members of the calcitonin-gene related-peptide (CGRP) family in treating cardiopulmonary diseases have been studied for many years and promising results obtained. Especially in recent years, two important members of the family, adrenomedullin and adrenomedullin2/intermedin, have been considered new treatment targets in cardiopulmonary diseases. In this review, the roles of CGRP family members in cardiopulmonary diseases are investigated based on the studies performed to date.

Plasma adrenomedullin peptides and precursor levels in pulmonary arterial hypertension disease severity and risk stratification

Adrenomedullin is a potent vasodilatory peptide, linked to pulmonary arterial hypertension pathology. Proximity extension assays were utilized to study plasma biomarkers related to vasoregulation, with focus on adrenomedullin peptides and precursor levels, collectively referred to as ADM. ADM was measured in 48 treatment-naïve pulmonary arterial hypertension patients at diagnosis, and in 31 of them at an early treatment follow-up. Plasma ADM was additionally assessed in patients with chronic thromboembolic pulmonary hypertension (n = 20) and pulmonary hypertension due to heart failure with preserved (HFpEF_(PH)) (n = 33) or reduced (HFrEF_(PH)) (n = 36) ejection fraction, as well as healthy controls (n = 16). ADM was studied in relation to pulmonary arterial hypertension hemodynamics, risk assessment, prognosis, treatment response, and differentiation. Plasma ADM levels in pulmonary arterial hypertension patients at diagnosis were higher than in healthy controls (p < 0.001), similar as in chronic thromboembolic pulmonary hypertension patients (p = ns), but lower compared to HFpEF_(PH) (p < 0.03) and HFrEF_(PH) (p < 0.001). In pulmonary arterial hypertension, specifically, plasma ADM at diagnosis correlated mainly to mean right atrial pressure (r = 0.73, p < 0.001), N-terminal prohormone of brain natriuretic peptide (r = 0.75, p < 0.001), six-minute walking distance (r = -0.57, p < 0.001), and venous oxygen saturation (r = -0.57, p < 0.001). ADM also correlated to the ECS/ERS- (r = 0.74, p < 0.001) and REVEAL risk scores (r = 0.54, p < 0.001) at pulmonary arterial hypertension diagnosis. Plasma ADM in pulmonary arterial hypertension patients was unaltered at early treatment follow-up compared to baseline (p = ns). Pulmonary arterial hypertension patients with supra-median ADM at diagnosis showed worse overall survival than those with infra-median levels (median survival 34 versus 66 months, p = 0.0077). In conclusion, the present results suggest that baseline plasma ADM levels mirror disease severity, correlating to both ECS/ERS- and the REVEAL risk scores.

Pulmonary arterial hypertension specific therapy: The old and the new

Pulmonary arterial hypertension (PAH) is a vascular disorder associated with high morbidity and mortality rate and is characterized by pulmonary vascular remodeling and increased pulmonary vascular resistance, ultimately resulting in right ventricular failure and death. Over the past few decades, significant advances in the understanding of the epidemiology, pathogenesis, and pathophysiology of pulmonary arterial hypertension have occured. This has led to the development of disease specific treatment including prostanoids, endothelin receptor antagonists, phosphodiesterase inhibitors, and soluble guanylate cyclase stimulators. These therapies significantly improve exercise capacity, quality of life, pulmonary hemodynamics, but none of the current treatments are actually curative and long-term prognosis remains poor. Thus, there is a clear need to develop new therapies. Several potential pharmacologic agents for the treatment of pulmonary arterial hypertension are under clinical development and some promising results with these treatments have been reported. These agents include tyrosine protein kinase inhibitors, rho-kinase inhibitors, synthetically produced vasoactive intestinal peptide, antagonists of the 5-HT2 receptors, and others. This article will review several of these promising new therapies and will discuss the current evidence regarding their potential benefit in pulmonary arterial hypertension.

Adrenomedullin mediates pro-angiogenic and pro-inflammatory cytokines in asthma and COPD

PURPOSE

Adrenomedullin (AM) is a pluripotent peptide hormone with contradictory effects in human health and disease. In chronic inflammatory lung diseases, such as asthma and COPD, AM has been shown to inhibit inflammation and cell proliferation. In the present study, we aimed to investigate the effect of AM on pro-angiogenic and pro-inflammatory cytokines in asthma and COPD.

PATIENTS AND METHODS

Serum levels of pro-AM were measured in patients with asthma, COPD and matched controls. The effect of AM on intracellular signaling proteins and cytokine secretion was assessed in primary cultures of epithelial cells (EC) and airway smooth muscle cells (ASMC) established from endo-bronchial biopsies of patients with asthma, COPD and controls.

RESULTS

Serum pro-AM was higher in patients with asthma and COPD, compared to controls. AM stimulated cAMP in ASMC but not in EC. In EC, AM decreased Erk1/2 MAPK expression and activation but in ASMC, AM activated Erk1/2. This effect was similar in asthma, COPD and controls. AM stimulated the secretion of pro-angiogenic CXCL1 by EC of controls and CXCL5 by EC of asthma patients. AM did not affect the secretion of IL-6 or IL-8 by EC but stimulated the secretion of IL-6 by ASMC. In EC, AM inhibited the stimulatory effect of TGF-β and IL-4 on the secretion of IL-6 and IL-8 but had an additive stimulatory effect with TGF-β in ASMC.

CONCLUSIONS

These data suggest that AM mediates the secretion of pro-angiogenic and pro-inflammatory cytokines in a cell-type and/or a disease-specific way, explaining its association with clinical outcomes in COPD.

Natural and synthetic peptides in the cardiovascular diseases: An update on diagnostic and therapeutic potentials

Several peptides play an important role in physiological and pathological conditions into the cardiovascular system. In addition to well-known vasoactive agents such as angiotensin II, endothelin, serotonin or natriuretic peptides, the vasoconstrictor Urotensin-II (Uro-II) and the vasodilators Urocortins (UCNs) and Adrenomedullin (AM) have been implicated in the control of vascular tone and blood pressure as well as in cardiovascular disease states including congestive heart failure, atherosclerosis, coronary artery disease, and pulmonary and systemic hypertension. Therefore these peptides, together with their receptors, become important therapeutic targets in cardiovascular diseases (CVDs). Circulating levels of these agents in the blood are markedly modified in patients with specific CVDs compared with those in healthy patients, becoming also potential biomarkers for these pathologies. This review will provide an overview of current knowledge about the physiological roles of Uro-II, UCN and AM in the cardiovascular system and their implications in cardiovascular diseases. It will further focus on the structural modifications carried out on original peptide sequences in the search of analogues with improved physiochemical properties as well as in the delivery methods. Finally, we have overviewed the possible application of these peptides and/or their precursors as biomarkers of CVDs.

Circulating microparticles, protein C, free protein S and endothelial vascular markers in children with sickle cell anaemia

INTRODUCTION

Circulating microparticles (MP) have been described in sickle cell anaemia (SCA); however, their interaction with endothelial markers remains unclear. We investigated the relationship between MP, protein C (PC), free protein S (PS), nitric oxide (NO), endothelin-1 (ET-1) and adrenomedullin (ADM) in a large cohort of paediatric patients.

METHOD

A total of 111 children of African ethnicity with SCA: 51 in steady state; 15 in crises; 30 on hydroxyurea (HU) therapy; 15 on transfusion; 17 controls (HbAA) of similar age/ethnicity. MP were analysed by flow cytometry using: Annexin V (AV), CD61, CD42a, CD62P, CD235a, CD14, CD142 (tissue factor), CD201 (endothelial PC receptor), CD62E, CD36 (TSP-1), CD47 (TSP-1 receptor), CD31 (PECAM), CD144 (VE-cadherin). Protein C, free PS, NO, pro-ADM and C-terminal ET-1 were also measured.

RESULTS

Total MP AV was lower in crisis (1.26×10(6) ml(-1); 0.56-2.44×10(6)) and steady state (1.35×10(6) ml(-1); 0.71-3.0×10(6)) compared to transfusion (4.33×10(6) ml(-1); 1.6-9.2×10(6), p<0.01). Protein C levels were significantly lower in crisis (median 0.52 IU ml(-1); interquartile range 0.43-0.62) compared with all other groups: HbAA (0.72 IU ml(-1); 0.66-0.82, p<0.001); HU (0.67 IU ml(-1); 0.58-0.77, p<0.001); steady state (0.63 IU ml(-1); 0.54-0.70, p<0.05) and transfusion (0.60 IU ml(-1); 0.54-0.70, p<0.05). In addition, levels were significantly reduced in steady state (0.63 IU ml(-1); 0.54-0.70) compared with HbAA (0.72 IU ml(-1); 0.66-0.80, p<0.01). PS levels were significantly higher in HbAA (0.85 IU ml(-1); 0.72-0.97) compared with crisis (0.49 IU ml(-1); 0.42-0.64, p<0.001), HU (0.65 IU ml(-1); 0.56-0.74, p<0.01) and transfusion (0.59 IU ml(-1); 0.47-0.71, p<0.01). There was also a significant difference in crisis patients compared with steady state (0.49 IU ml(-1); 0.42-0.64 vs. 0.68 IU ml(-1); 0.58-0.79, p<0.05). There was high correlation (R>0.9, p<0.05) between total numbers of AV-positive MP (MP AV) and platelet MP expressing non-activation platelet markers. There was a lower correlation between MP AV and MP CD62P (R=0.73, p<0.05) (platelet activation marker), and also a lower correlation between percentage of MP expressing CD201 (%MP CD201) and %MP CD14 (R=0.627, p<0.001). %MP CD201 was higher in crisis (11.6%) compared with HbAA (3.2%, p<0.05); %MP CD144 was higher in crisis (7.6%) compared with transfusion (2.1%, p<0.05); %CD14 (0.77%) was higher in crisis compared with transfusion (0.0%, p<0.05) and steady state (0.0%, p<0.01); MP CD14 was detectable in a higher number of samples (92%) in crisis compared with the rest (40%); %MP CD235a was higher in crisis (17.9%) compared with transfusion (8.9%), HU (8.7%) and steady state (9.9%, p<0.05); %CD62E did not differ significantly across the groups and CD142 was undetectable. Pro-ADM levels were raised in chest crisis: 0.38 nmol L(-1) (0.31-0.49) versus steady state: 0.27 nmol L(-1) (0.25-0.32; p<0.01) and control: 0.28 nmol L(-1) (0.27-0.31; p<0.01). CT-proET-1 levels were reduced in patients on HU therapy: 43.6 pmol L(-1) (12.6-49.6) versus control: 55.1 pmol L(-1) (45.2-63.9; p<0.05). NO levels were significantly lower in chest crisis (19.3 mmol L(-1) plasma; 10.7-19.9) compared with HU (22.2 mmol L(-1) plasma; 18.3-28.4; p<0.05), and HbSC (30.6 mmol L(-1) plasma; 20.8-39.5; p<0.05) and approach significance when compared with steady state (22.5mmol L(-1) plasma; 16.9-28.2; p=0.07).

CONCLUSION

Protein C and free PS are reduced in crisis with lower numbers of platelet MP and higher percentage of markers of endothelial damage and of red cell origin. During chest crisis, ADM and ET-1 were elevated suggesting a role for therapy inhibiting ET-1 in chest crisis.

Bench-to-bedside pharmacology of adrenomedullin

The bioactive peptide adrenomedullin (AM) exerts pleiotropic actions in various organs and tissues. In the heart, AM has an inhibitory effect on ventricular remodeling, suppressing cardiomyocyte hypertrophy and the proliferation of cardiac fibroblasts. This pharmacological property was shown not only in rat models of acute myocardial infarction, but also clinically in patients with this cardiac disease. An originally characterized feature of AM was a potent vasodilatory effect, but this peptide was found to be important for vascular integrity and angiogenesis. AM-induced angiogenesis is involved in tumor growth, while AM inhibits apoptosis of some types of tumor cell. A unique pharmacological property is anti-inflammatory activity, which has been characterized in sepsis and inflammatory bowel diseases; thus, there is an ongoing clinical trial to test the efficacy of AM for patients with intractable ulcerative colitis. These activities are assumed to be mediated via the specific receptor formed by calcitonin receptor-like receptor and receptor activity-modifying protein 2 or 3, while some questions remain to be answered about the molecular mechanisms of this signal transduction system. Taking these findings together, AM is a bioactive peptide with pleiotropic effects, with potential as a therapeutic tool for a wide range of human diseases from myocardial infarction to malignant tumors or inflammatory bowel diseases.

Lungs at high-altitude: genomic insights into hypoxic responses

Hypobaric hypoxia at high altitude (HA) results in reduced blood arterial oxygen saturation, perfusion of organs with hypoxemic blood, and direct hypoxia of lung tissues. The pulmonary complications in the cells of the pulmonary arterioles due to hypobaric hypoxia are the basis of the pathophysiological mechanisms of high-altitude pulmonary edema (HAPE). Some populations that have dwelled at HA for thousands of years have evolutionarily adapted to this environmental stress; unadapted populations may react with excessive physiological responses that impair health. Individual variations in response to hypoxia and the mechanisms of HA adaptation provide insight into physiological responses. Adaptive and maladaptive responses include alterations in pathways such as oxygen sensing, hypoxia signaling, K+- and Ca2+-gated channels, redox balance, and the renin-angiotensin-aldosterone system. Physiological imbalances are linked with genetic susceptibilities, and nonhomeostatic responses in gene regulation that occur by small RNAs, histone modification, and DNA methylation predispose susceptible humans to these HA illnesses. Elucidation of the interaction of these factors will lead to a more comprehensive understanding of HA adaptations and maladaptations and will lead to new therapeutics for HA disorders related to hypoxic lungs.

Ion channels and transporters as therapeutic targets in the pulmonary circulation

Pulmonary circulation is a low pressure, low resistance, high flow system. The low resting vascular tone is maintained by the concerted action of ion channels, exchangers and pumps. Under physiological as well as pathophysiological conditions, they are targets of locally secreted or circulating vasodilators and/or vasoconstrictors, leading to changes in expression or to posttranslational modifications. Both structural changes in the pulmonary arteries and a sustained increase in pulmonary vascular tone result in pulmonary vascular remodeling contributing to morbidity and mortality in pediatric and adult patients. There is increasing evidence demonstrating the pivotal role of ion channels such as K(+) and Cl(-) or transient receptor potential channels in different cell types which are thought to play a key role in vasoconstrictive remodeling. This review focuses on ion channels, exchangers and pumps in the pulmonary circulation and summarizes their putative pathophysiological as well as therapeutic role in pulmonary vascular remodeling. A better understanding of the mechanisms of their actions may allow for the development of new options for attenuating acute and chronic pulmonary vasoconstriction and remodeling treating the devastating disease pulmonary hypertension.

Endogenous α-calcitonin-gene-related peptide promotes exercise-induced, physiological heart hypertrophy in mice

AIM

It is unknown how the heart distinguishes various overloads, such as exercise or hypertension, causing either physiological or pathological hypertrophy. We hypothesize that alpha-calcitonin-gene-related peptide (αCGRP), known to be released from contracting skeletal muscles, is key at this remodelling.

METHODS

The hypertrophic effect of αCGRP was measured in vitro (cultured cardiac myocytes) and in vivo (magnetic resonance imaging) in mice. Exercise performance was assessed by determination of maximum oxygen consumption and time to exhaustion. Cardiac phenotype was defined by transcriptional analysis, cardiac histology and morphometry. Finally, we measured spontaneous activity, body fat content, blood volume, haemoglobin mass and skeletal muscle capillarization and fibre composition.

RESULTS

While αCGRP exposure yielded larger cultured cardiac myocytes, exercise-induced heart hypertrophy was completely abrogated by treatment with the peptide antagonist CGRP(8-37). Exercise performance was attenuated in αCGRP(-/-) mice or CGRP(8-37) treated wild-type mice but improved in animals with higher density of cardiac CGRP receptors (CLR-tg). Spontaneous activity, body fat content, blood volume, haemoglobin mass, muscle capillarization and fibre composition were unaffected, whereas heart index and ventricular myocyte volume were reduced in αCGRP(-/-) mice and elevated in CLR-tg. Transcriptional changes seen in αCGRP(-/-) (but not CLR-tg) hearts resembled maladaptive cardiac phenotype.

CONCLUSIONS

Alpha-calcitonin-gene-related peptide released by skeletal muscles during exercise is a hitherto unrecognized effector directing the strained heart into physiological instead of pathological adaptation. Thus, αCGRP agonists might be beneficial in heart failure patients.

Adrenomedullin alleviates pulmonary artery collagen accumulation in rats with pulmonary hypertension induced by high blood flow

Collagen accumulation is one of the important pathologic changes in the development of pulmonary hypertension. Previous research showed that adrenomedullin (ADM) mitigates the development of pulmonary hypertension. The present study explored the role of ADM in the development of pulmonary artery collagen accumulation induced by high pulmonary blood flow, by investigating the effect of ADM [1.5 μg/(kg h)] subcutaneously administered by mini-osmotic pump on pulmonary hemodynamics, pulmonary vascular structure and pulmonary artery collagen accumulation and synthesis in rats with high pulmonary blood flow induced by aortocaval shunting. The results showed that ADM significantly decreased mean pulmonary artery pressure (mPAP) and the ratio of right ventricular mass to left ventricular plus septal mass [RV/(LV+SP)], attenuated the muscularization of small pulmonary vessels and relative medial thickness (RMT) of pulmonary arteries in rats with high pulmonary blood flow. Meanwhile, ADM ameliorated pulmonary artery collagen deposition represented by a decrease in lung tissue hydroxyproline, collagens I and III content and pulmonary artery collagens I and III expression, reduced collagen synthesis represented by a decrease in lung tissue procollagens I and III mRNA expression. The results suggest that ADM plays a protective role in the development of pulmonary hypertension induced by high blood flow, by inhibiting pulmonary procollagen synthesis and alleviating pulmonary artery collagen accumulation.

Effect of food intake on left ventricular wall stress

Objective

Left ventricular wall stress has been investigated in a variety of populations, but the effect of food intake has not been evaluated. We assessed whether left ventricular wall stress is affected by food intake in healthy subjects.

Methods

Twenty-three healthy subjects aged 25.6 ± 4.5 years were investigated. Meridional end-systolic wall stress (ESS) and circumferential end-systolic wall stress (cESS) were measured before, 30 minutes after, and 110 minutes after a standardised meal.

Results

Both ESS and cESS decreased significantly (P < 0.001) from fasting values 30 minutes after the meal, and had not returned to baseline after 110 minutes. ESS decreased from 65 ± 16 kdynes/cm² (fasting) to 44 ± 12 kdynes/cm² 30 minutes after, and to 58 ± 13 kdynes/cm² 110 minutes after eating. cESS decreased from 98 ± 24 kdynes/cm² to 67 ± 18 kdynes/cm² 30 minutes after, and to 87 ± 19 kdynes/cm² 110 minutes after the meal.

Conclusion

This study shows that left ventricular wall stress is affected by food intake in healthy subjects.

Medical therapeutics for pulmonary arterial hypertension: from basic science and clinical trial design to evidence-based medicine

Pulmonary arterial hypertension is a severe disease with poor prognosis, caused by obliteration of the pulmonary vasculature as a result of pulmonary-vascular remodeling, active vasoconstriction and in situ thrombosis. Left untreated, pulmonary arterial hypertension results in right-ventricular failure and death. There has been dramatic progress in the treatment of pulmonary arterial hypertension during recent years. A remarkable number of randomized-controlled trials with agents known to target specific abnormalities present in pulmonary arterial hypertension have been completed. Most commonly, therapeutic efficacy was judged by the ability of the drug under study to improve exercise capacity and to decrease the rate of severe complications. Completed clinical trials have mainly evaluated patients with relatively advanced disease. Despite these advances, responses to therapy in pulmonary arterial hypertension are not uniformly favorable and frequently incomplete. In addition, the methods of delivery and the adverse effect profile of the currently available pulmonary arterial hypertension-specific drugs create further management difficulties. Based on newly identified pathobiologic abnormalities in the pulmonary vasculature, future studies are likely to focus on the discovery of new therapeutic targets. Clinical trial design will continue to evolve in an attempt to enable inclusion of patients with less advanced disease and evaluation of treatment combinations or comparisons of the currently approved drugs.

Adrenomedullin and adrenotensin regulate collagen synthesis and proliferation in pulmonary arterial smooth muscle cells

To understand the pathophysiological mechanisms of pulmonary arterial smooth muscle cell (PASMC) proliferation and extracellular-matrix accumulation in the development of pulmonary hypertension and remodeling, this study determined the effects of different doses of adrenomedullin (ADM) and adrenotensin (ADT) on PASMC proliferation and collagen synthesis. The objective was to investigate whether extracellular signal-regulated kinase (ERK1/2) signaling was involved in ADM- and ADT-stimulated proliferation of PASMCs in 4-week-old male Wistar rats (body weight: 100-150 g, n=10). The proliferation of PASMCs was examined by 5-bromo-2-deoxyuridine incorporation. A cell growth curve was generated by the Cell Counting Kit-8 method. Expression of collagen I, collagen III, and phosphorylated ERK1/2 (p-ERK1/2) was evaluated by immunofluorescence. The effects of different concentrations of ADM and ADT on collagen I, collagen III, and p-ERK1/2 protein expression were determined by immunoblotting. We also investigated the effect of PD98059 inhibition on the expression of p-ERK1/2 protein by immunoblotting. ADM dose-dependently decreased cell proliferation, whereas ADT dose-dependently increased it; and ADM and ADT inhibited each other with respect to their effects on the proliferation of PASMCs. Consistent with these results, the expression of collagen I, collagen III, and p-ERK1/2 in rat PASMCs decreased after exposure to ADM but was upregulated after exposure to ADT. PD98059 significantly inhibited the downregulation by ADM and the upregulation by ADT of p-ERK1/2 expression. We conclude that ADM inhibited, and ADT stimulated, ERK1/2 signaling in rat PASMCs to regulate cell proliferation and collagen expression.

Adrenomedullin haploinsufficiency predisposes to secondary lymphedema

Secondary lymphedema is a debilitating condition, and genetic factors predisposing to its development remain largely unknown. Adrenomedullin (AM) is peptide encoded, together with proadrenomedullin N-terminal peptide (PAMP), by the Adm gene (adrenomedullin gene). AM and its putative receptor calcitonin receptor-like receptor (CLR) are implicated in angiogenesis and lymphangiogenesis during embryogenesis and wound healing, suggesting their possible involvement in secondary lymphedema. To investigate whether AM deficiency predisposes to secondary lymphedema, we used heterozygous adult mice with Adm gene-knockin stop mutation, which selectively abrogated AM, but preserved PAMP, expression (Adm(AM+/Δ) animals). After hind limb skin incision, Adm messenger RNA expression was upregulated in wounded tissue of both Adm(AM+/+) and Adm(AM+/Δ) mice. However, only Adm(AM+/Δ) animals developed limb swelling and histopathological lymphedematous changes, including epidermal thickening, elevated collagen fiber density, and increased microvessel diameter. Secondary lymphedema was prevented when circulating AM levels in Adm(AM+/Δ) mice were restored by systemic peptide delivery. In human skin, CLR was expressed in tissue components affected by lymphedema, including epidermis, lymphatics, and blood vessels. Our study identified a previously unrecognized role for endogenous AM as a key factor in secondary lymphedema pathogenesis and provided experimental in vivo evidence of an underlying germ-line genetic predisposition to developing this disorder.

Anticipated classes of new medications and molecular targets for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) remains a life-limiting condition with a major impact on the ability to lead a normal life. Although existing therapies may improve the outlook in some patients there remains a major unmet need to develop more effective therapies in this condition. There have been significant advances in our understanding of the genetic, cell and molecular basis of PAH over the last few years. This research has identified important new targets that could be explored as potential therapies for PAH. In this review we discuss whether further exploitation of vasoactive agents could bring additional benefits over existing approaches. Approaches to enhance smooth muscle cell apotosis and the potential of receptor tyrosine kinase inhibition are summarised. We evaluate the role of inflammation, epigenetic changes and altered glycolytic metabolism as potential targets for therapy, and whether inherited genetic mutations in PAH have revealed druggable targets. The potential of cell based therapies and gene therapy are also discussed. Potential candidate pathways that could be explored in the context of experimental medicine are identified.

Regulation of myofibroblast differentiation and bleomycin-induced pulmonary fibrosis by adrenomedullin

Myofibroblast differentiation induced by transforming growth factor-β (TGF-β) is characterized by the expression of smooth muscle α-actin (SMA) and extracellular matrix proteins. We and others have previously shown that these changes are regulated by protein kinase A (PKA). Adrenomedullin (ADM) is a vasodilator peptide that activates cAMP/PKA signaling through the calcitonin-receptor-like receptor (CRLR) and receptor-activity-modifying proteins (RAMP). In this study, we found that recombinant ADM had little effect on cAMP/PKA in quiescent human pulmonary fibroblasts, whereas it induced a profound activation of cAMP/PKA signaling in differentiated (by TGF-β) myofibroblasts. In contrast, the prostacyclin agonist iloprost was equally effective at activating PKA in both quiescent fibroblasts and differentiated myofibroblasts. TGF-β stimulated a profound expression of CRLR with a time course that mirrored the increased PKA responses to ADM. The TGF-β receptor kinase inhibitor SB431542 abolished expression of CRLR and attenuated the PKA responses of cells to ADM but not to iloprost. CRLR expression was also dramatically increased in lungs from bleomycin-treated mice. Functionally, ADM did not affect initial differentiation of quiescent fibroblasts in response to TGF-β but significantly attenuated the expression of SMA, collagen-1, and fibronectin in pre-differentiated myofibroblasts, which was accompanied by decreased contractility of myofibroblasts. Finally, sensitization of ADM signaling by transgenic overexpression of RAMP2 in myofibroblasts resulted in enhanced survival and reduced pulmonary fibrosis in the bleomycin model of the disease. In conclusion, differentiated pulmonary myofibroblasts gain responsiveness to ADM via increased CRLR expression, suggesting the possibility of using ADM for targeting pathological myofibroblasts without affecting normal fibroblasts.

Cyclic guanosine monophosphate signalling pathway in pulmonary arterial hypertension

During the last decade, it emerged that cyclic guanosine monophosphate (cGMP) is a novel drug target for the treatment of pulmonary arterial hypertension (PAH). cGMP regulates many cellular functions, ranging from contractility to growth, of relevance to the disease. Generated from guanylyl cyclases in response to natriuretic peptides or nitric oxide (NO), cGMP transduces its effects through a number of cGMP effectors, including cGMP-regulated phosphodiesterases and protein kinases. Furthermore, the cGMP concentration is modulated by cGMP-degrading phosphodiesterases. Data to date demonstrate that increasing intracellular cGMP through stimulation of GCs, inhibition of PDEs, or both is a valid therapeutic strategy in drug development for PAH. New advances in understanding of cGMP are unravelled, as well as the pathobiology of PAH. cGMP remains an attractive future PAH drug target. This review makes a more detailed examination of cGMP signalling with particular reference to PAH.

Role of adrenomedullin in the growth and differentiation of stem and progenitor cells

Stem cells have captured the imagination of the general public by their potential as new therapeutic tools in the fight against degenerative diseases. This potential is based on their capability for self-renewal and at the same time for producing progenitor cells that will eventually provide the building blocks for tissue and organ regeneration. These processes are carefully orchestrated in the organism by means of a series of molecular cues. An emerging molecule which is responsible for some of these physiological responses is adrenomedullin, a 52-amino acid regulatory peptide which increases proliferation and regulates cell fate of stem cells of different origins. Adrenomedullin binds to specific membrane receptors in stem cells and induces several intracellular pathways such as those involving cAMP, Akt, or MAPK. Regulation of adrenomedullin levels may help in directing the growth and differentiation of stem cells for applications (e.g., cell therapy) both in vitro and in vivo.

Pediatric pulmonary arterial hypertension: current and emerging therapeutic options

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a rare disease in neonates, infants and children that is associated with significant morbidity and mortality. An adequate understanding of the controlling pathophysiologic mechanisms is lacking and although mortality has decreased as therapeutic options have increased over the past several decades, outcomes remain unacceptable.

AREAS COVERED

This review summarizes the currently available therapies for neonates, infants and children with PAH and describes emerging therapies in the context of what is known about the underlying pathophysiology of the disease.

EXPERT OPINION

All of the currently approved PAH therapies impact one of three endothelial-based pathways: nitric oxide-guanosine-3'-5'cyclic monophosphate, prostacyclin or endothelin-1. The beneficial effects of these agents may relate to their impact on pulmonary vascular tone, and/or their antiproliferative and antithrombotic properties. Fundamental advances in PAH therapy are likely to relate to: i) a better understanding of PAH subpopulations, allowing for therapies to be better tailored to individual patients and pathophysiologic processes; and ii) therapies that promote the regression of advanced structural remodeling.

New approaches to the treatment of pulmonary hypertension: from bench to bedside

Pulmonary hypertension (PH) is a severe, life-threatening disease for which there are no effective curative therapies. A diverse group of agents such as prostacyclins, endothelin antagonists, phosphodiesterase inhibitors, calcium channel blockers, diuretics, inotropic agents, and anticoagulants are used to treat PH; however, none of these agents have a marked effect upon survival. Among the new agents that promise treatment of PH are rho-kinase inhibitors and soluble guanylate cyclase stimulators. Although these new classes of agents have beneficial effects in experimental animal models and clinical studies, they are not selective in their actions on the pulmonary vascular bed. This manuscript reviews the actions of rho-kinase inhibitors and soluble guanylate cyclase stimulators on the pulmonary vascular bed. It is our hypothesis that these new agents may be more effective than current therapies in the treatment of PH. Moreover, new methods in the delivery of these agents to the lung need to be developed so that their main effects will be exerted in the pulmonary vascular bed and their systemic effects can be minimized or avoided.

The first clinical pilot study of intravenous adrenomedullin administration in patients with acute myocardial infarction

Adrenomedullin (AM) is a 52-amino-acid vasodilator peptide that was originally isolated from human pheochromocytoma. In the previous experimental study with rat ischemia/reperfusion model, AM reduced infarct size and inhibited myocyte apoptosis. AM also suppressed the production of oxygen-free radicals. The present study was designed to evaluate the feasibility of intravenous administration of AM in patients with acute myocardial infarction. We studied 10 patients with first acute myocardial infarction [male to female ratio: 9 to 1, age: 65 ± 9 (mean ± SD) years, peak creatine phosphokinase level: 4215 ± 1933 (SD) U/L], who were hospitalized within 12 hours of symptom onset. Proceeding reperfusion therapy, AM infusion was initiated and continued at concentration of 0.0125-0.025 μg·kg·min for 12 hours. Follow-up coronary angiography and left ventriculography were performed at 3 months. Cardiac magnetic resonance was examined at 1 month and 3 months after AM therapy. During infusion of AM, hemodynamics kept stable except 2 patients. Wall motion index in the infarct area at 3 months was significantly improved compared with that at baseline, and infarct size evaluated by cardiac magnetic resonance was significantly decreased at 3 months. In conclusion, intravenous administration of AM, which possesses a variety of potential cardiovascular protective actions, can be adjunctive to percutaneous coronary intervention.

New therapies for pulmonary arterial hypertension: an update on current bench to bedside translation

IMPORTANCE OF THE FIELD

Treatments of pulmonary arterial hypertension (PAH) that have so far proven efficacious are all based on the restoration of endothelium control of pulmonary vascular tone and structure, by administration of prostacyclins, endothelin receptor antagonists and phosphodiesterase-5 inhibitors. However, results remain unsatisfactory, with persistent high mortality, insufficient clinical improvement and no convincing report of any reversal of the disease process.

AREAS COVERED IN THIS REVIEW

New antiproliferative approaches that aim to actively limit pulmonary vascular remodeling are being sought. Several such treatments have shown promise in experimental models and in preliminary clinical studies. Noteworthy among these are dichloroacetate, survivin antagonists, nuclear factor of activated T-cell inhibitors, PPAR-gamma agonists, tyrosine kinase inhibitors, Rho-kinase inhibitors, statins, vasoactive intestinal peptide, soluble guanylate cyclase stimulators/activators, adrenomedullin, elastase inhibitors, serotonin reuptake inhibitors, anti-inflammatory agents, and bone marrow-derived progenitor cells.

WHAT THE READER WILL GAIN

Update on various strategies targeting proliferative, inflammatory and regenerating processes currently under evaluation in patients with PAH.

TAKE HOME MESSAGE

In spite of favorable results in experimental models, none of these strategies has achieved the ultimate goal of curing PAH. Further developments will depend on progress made in our pathobiological understanding of the disease and carefully designed randomized, controlled trials.

Emerging therapies for the treatment of pulmonary hypertension

Current treatment of pulmonary arterial hypertension, which includes the use of prostacyclins, endothelin receptor antagonists, and phosphodiesterase type 5 inhibitors, either alone or in combination, often leads to improvements in functional capacity and modest decreases in pulmonary artery pressure. Disappointingly, however, two recent meta-analysis reviewing the controlled trials in pulmonary arterial hypertension, using these three agents, demonstrated little or no increase in survival. Importantly, however, increasing knowledge of the cellular and molecular basis of pulmonary arterial hypertension has led to the development of new agents aimed at either reversing sustained vasoconstriction or stopping/reversing the abnormal cell and extracellular matrix accumulation that, in combination, obstruct pulmonary blood flow and ultimately cause right heart failure. Rho kinase inhibitors, vasodilator peptides (such as vasoactive intestinal peptide and adrenomedullin), and endothelial nitric oxide synthase coupling agents (cicletanine) have been shown sometimes to exert potent pulmonary vasodilatory effects in animal models and in pilot studies in humans. Tyrosine kinase inhibitors (platelet-derived growth factor and epidermal growth factor receptor inhibitors), multikinase inhibitors (tyrosine kinase and serine/threonine kinase), elastase inhibitors, metabolic modulators (e.g., dichloroacetate), survivin inhibitors, and HMG-COA reductase inhibitors have been shown to reverse pulmonary hypertension in rodent models of pulmonary hypertension through inhibition of cell proliferation and induction of apoptosis. Early success in human pulmonary arterial hypertension with tyrosine kinase inhibitors has appeared in case reports. Furthermore, anti-inflammatory/immunomodulatory agents (thiazolidinedinones, rapamycin, cyclosporine, and STAT3 inhibitors) have been demonstrated to be effective at reducing vascular remodeling in animal models. Collectively, these studies are exciting and open potential new avenues for treatment. Caution should be exercised, however, as many agents, which are successful at preventing or reversing pulmonary arterial hypertension in currently used animal models, do not result in similar long-term success in the treatment of human pulmonary arterial hypertension.

Adrenomedullin promotes lung angiogenesis, alveolar development, and repair

Bronchopulmonary dysplasia (BPD) and emphysema are significant global health problems at the extreme stages of life. Both are characterized by alveolar simplification and abnormal distal airspace enlargement due to arrested development or loss of alveoli, respectively. Both lack effective treatments. Mechanisms that inhibit distal lung growth are poorly understood. Adrenomedullin (AM), a recently discovered potent vasodilator, promotes angiogenesis and has protective effects on the cardiovascular and respiratory system. Its role in the developing lung is unknown. We hypothesized that AM promotes lung angiogenesis and alveolar development. Accordingly, we report that lung mRNA expression of AM increases during normal alveolar development. In vivo, intranasal administration of the AM antagonist, AM22-52 decreases lung capillary density (12.4 +/- 1.5 versus 18 +/- 1.5 in control animals; P < 0.05) and impairs alveolar development (mean linear intercept, 52.3 +/- 1.5 versus 43.8 +/- 1.8 [P < 0.05] and septal counts 62.0 +/- 2.7 versus 90.4 +/- 3.5 [P < 0.05]) in neonatal rats, resulting in larger and fewer alveoli, reminiscent of BPD. This was associated with decreased lung endothelial nitric oxide synthase and vascular endothelial growth factor-A mRNA expression. In experimental oxygen-induced BPD, a model of arrested lung vascular and alveolar growth, AM attenuates arrested lung angiogenesis (vessel density, 6.9 +/- 1.1 versus 16.2 +/- 1.3, P < 0.05) and alveolar development (mean linear intercept, 51.9 +/- 3.2 versus 44.4 +/- 0.7, septal counts 47.6 +/- 3.4 versus 67.7 +/- 4.0, P < 0.05), an effect in part mediated by inhibition of apoptosis. AM also prevents pulmonary hypertension in this model, as assessed by decreased right ventricular hypertrophy and pulmonary artery medial wall thickness. Our findings suggest a role for AM during normal alveolar development. AM may have therapeutic potential in diseases associated with alveolar injury.

Intratracheal gene transfer of adrenomedullin using polyplex nanomicelles attenuates monocrotaline-induced pulmonary hypertension in rats

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by progressive PAH and right ventricular failure. Despite recent advances in therapeutic approaches using prostanoids, endothelin antagonists, and so on, PAH remains a challenging condition. To develop a novel therapeutic approach, we have established a nonviral gene delivery system of poly(ethylene glycol) (PEG)-based block catiomers, which form a polyplex nanomicelle with a nanoscaled core-shell structure in the presence of DNA. The polyplex nanomicelle from PEG-b-poly{N-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} (PEG-b-P[Asp(DET)]), having ethylenediamine units at the side chain, showed ~100-fold increase in luciferase transgene expression activity in mouse lung via intratracheal administration with a minimal toxicity compared with the polyplex from linear poly(ethylenimine) (LPEI). The transfection activity was highest on day 3 after administration and remained detectable until day 14. PEG-b-P[Asp(DET)] polyplex nanomicelles were formulated with a therapeutic plasmid bearing the human adrenomedullin (AM) gene and intratracheally administered to rats with monocrotaline-induced pulmonary hypertension. The right ventricular pressure significantly decreased 3 days after administration as confirmed by a notable increase of pulmonary human AM mRNA levels. Intratracheal administration of PEG-b-P[Asp-(DET)] polyplex nanomicelles showed remarkable therapeutic efficacy with PAH animal models without compromising biocompatibility.

Therapeutic targets in pulmonary arterial hypertension

Pulmonary arterial hypertension is a progressive, fatal disease. Current treatments including prostanoids, endothelin-1 (ET-1) antagonists, and phosphodiesterase (PDE) inhibitors, have sought to address the pulmonary vascular endothelial dysfunction and vasoconstriction associated with the condition. These treatments may slow the progression of the disease but do not afford a cure. Future treatments must target more directly the structural vascular changes that impair blood flow through the pulmonary circulation. Several novel therapeutic targets have been proposed and are under active investigation, including soluble guanylyl cyclase, phosphodiesterases, tetrahydrobiopterin, 5-HT2B receptors, vasoactive intestinal peptide, receptor tyrosine kinases, adrenomedullin, Rho kinase, elastases, endogenous steroids, endothelial progenitor cells, immune cells, bone morphogenetic protein and its receptors, potassium channels, metabolic pathways, and nuclear factor of activated T cells. Tyrosine kinase inhibitors, statins, 5-HT2B receptor antagonists, EPCs and soluble guanylyl cyclase activators are among the most advanced, having produced encouraging results in animal models, and human trials are underway. This review summarises the current research in this area and speculates on their likely success.

Adrenomedullin induces lymphangiogenesis and ameliorates secondary lymphoedema

AIMS

Adrenomedullin (AM) is a multifunctional peptide hormone that plays a significant role in vasodilation and angiogenesis. Lymphoedema is a common but refractory disorder that is difficult to be treated with conventional therapy. We therefore investigated whether AM promotes lymphangiogenesis and improves lymphoedema.

METHODS AND RESULTS

The effects of AM on lymphatic endothelial cells (LEC) were investigated. AM promoted proliferation, migration, and network formation of cultured human lymphatic microvascular endothelial cells (HLMVEC). AM increased intracellular cyclic adenosine monophosphate (cAMP) level in HLMVEC. The cell proliferation induced by AM was inhibited by a cAMP antagonist and mitogen-activated protein kinase kinase (MEK) inhibitors. Phosphorylated extracellular signal-regulated kinase (ERK) in HLMVEC was increased by AM. Continuous administration of AM (0.05 microg/kg/min) to BALB/c mice with tail lymphoedema resulted in a decrease in lymphoedema thickness. AM treatment increased the number of lymphatic vessels and blood vessels in the injury site.

CONCLUSION

AM promoted LEC proliferation at least in part through the cAMP/MEK/ERK pathway, and infusion of AM induced lymphangiogenesis and improved lymphoedema in mice.

Review: Therapeutic advances in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by vasoconstriction, in situ thrombosis, and vascular remodeling of small pulmonary arteries inducing increased pulmonary arterial resistance. Conventional treatment is based on life style modification and nonspecific treatment (warfarine, diuretics, oxygen). Calcium channel blockers are vasodilatators that have been shown to be of great efficacy in a very specific subpopulation of patients with PAH. For the majority of patients, specific PAH therapies are still lacking. Numerous studies evaluating prostacyclin agonists, endothelin-receptor antagonists, and phosphodiesterase type 5 inhibitors are now available to guide therapeutic choices. Despite those important advances there is still no cure for PAH. Fortunately, research is ongoing and many drugs show promises.

Adrenomedullin acts in the lateral parabrachial nucleus to increase arterial blood pressure through mechanisms mediated by glutamate and nitric oxide

Adrenomedullin (ADM) acts in a site-specific manner within autonomic centers of the brain to modulate mean arterial pressure (MAP). To determine the role of ADM in the pontine autonomic center, the lateral parabrachial nucleus (LPBN), we used urethane-anesthetized adult Sprague-Dawley male rats to test the hypothesis that ADM increases MAP at this site through glutamate- and nitric oxide (NO)-dependent mechanisms. ADM microinjected into the LPBN increased MAP in a dose-dependent manner. The pressor effect of ADM (0.01 pmol) had a peak value of 11.9 +/- 1.9 mmHg at 2 min and lasted for 7 min. We demonstrated that ADM's effect is receptor mediated by blocking the effect with the ADM receptor antagonist, ADM22-52. We showed that glutamate mediates ADM's pressor response, as this response was blocked using coinjections of ADM with dizolcipine hydrogen maleate or 6-cyano-7-nitroquinoxaline-2,3-dione, N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptor antagonists, respectively. We tested the roles of NO with coinjections of ADM with either N5-(1-iminoethyl)-L-ornithine or 7-nitroindazole monosodium salt, nonspecific and neuronal NO synthase (NOS) inhibitors, respectively; both inhibitors blocked ADM's pressor effect. Finally, we studied the role of calcium influx in ADM's pressor effect, as intracellular calcium is important in both glutamate and NO neurotransmission. ADM's effect was blocked when nifedipine, an L-type calcium channel blocker, was coinjected with ADM into the LPBN. This study is the first to show that ADM acts in the LPBN to increase MAP through mechanisms dependent on activation of ionotropic glutamate receptors, neuronal and endothelial NOS-mediated NO synthesis, and L-type calcium channel activation.

Emerging therapies for pulmonary arterial hypertension

Pulmonary arterial hypertension is characterised by increased pulmonary vascular resistance due to increased vascular tone and structural remodelling of pulmonary vessels. The therapies that are in use so far have been developed to correct endothelial dysfunction and reduce vasomotor tone. These treatments have a limited effect on the remodelling process and, increasingly, the focus is turning to potent strategies for inhibiting vascular proliferation and promoting vascular apoptosis. Multiple novel targets have been uncovered over the last 5 years and several are now in early clinical trials. At present, it is clear that there is no single treatment for the condition. Although this is the case, studies are investigating the role of combining therapies that are already established.

Adrenomedullin ameliorates lipopolysaccharide-induced acute lung injury in rats

Adrenomedullin (AM), an endogenous peptide, has been shown to have a variety of protective effects on the cardiovascular system. However, the effect of AM on acute lung injury remains unknown. Accordingly, we investigated whether AM infusion ameliorates lipopolysaccharide (LPS)-induced acute lung injury in rats. Rats were randomized to receive continuous intravenous infusion of AM (0.1 microg x kg(-1) x min(-1)) or vehicle through a microosmotic pump. The animals were intratracheally injected with either LPS (1 mg/kg) or saline. At 6 and 18 h after intratracheal instillation, we performed histological examination and bronchoalveolar lavage and assessed the lung wet/dry weight ratio as an index of acute lung injury. Then we measured the numbers of total cells and neutrophils and the levels of tumor necrosis factor (TNF)-alpha and cytokine-induced neutrophil chemoattractant (CINC) in bronchoalveolar lavage fluid (BALF). In addition, we evaluated BALF total protein and albumin levels as indexes of lung permeability. LPS instillation caused severe acute lung injury, as indicated by the histological findings and the lung wet/dry weight ratio. However, AM infusion attenuated these LPS-induced abnormalities. AM decreased the numbers of total cells and neutrophils and the levels of TNF-alpha and CINC in BALF. AM also reduced BALF total protein and albumin levels. In addition, AM significantly suppressed apoptosis of alveolar wall cells as indicated by cleaved caspase-3 staining. In conclusion, continuous infusion of AM ameliorated LPS-induced acute lung injury in rats. This beneficial effect of AM on acute lung injury may be mediated by inhibition of inflammation, hyperpermeability, and alveolar wall cell apoptosis.

Combination therapy and new types of agents for pulmonary arterial hypertension

This review assesses the available evidence supporting the use of drug combinations for the management of the various forms of pulmonary arterial hypertension (PAH). Ongoing and forthcoming randomized trials evaluating this strategy are also highlighted. Furthermore, new types of agents to treat PAH in the future are explored.

Hypoxic induction of receptor activity-modifying protein 2 alters regulation of pulmonary endothelin-1 by adrenomedullin: induction under normoxia versus inhibition under hypoxia

The vasodilator adrenomedullin (AM) is up-regulated in pulmonary hypertension, and inhaled AM is beneficial in patients. Therefore, we investigated the effects of AM on pulmonary endothelin-1 (ET-1). In normoxic isolated rat lungs (IRL) and rat pulmonary artery endothelial cells (RPAEC), the calcitonin gene-related peptide type-1 receptor (CGRP1R) antagonist human (h)CGRP(8-37) decreased ET-1 secretion, and the AM receptor antagonist hAM(22-52) had no effect. Exogenous AM (1 and 10 pM) increased ET-1 levels, which was abolished by hCGRP(8-37) and protein kinase A (PKA) inhibition. At 50 and 100 pM, AM decreased ET-1, an effect sensitive to hAM(22-52), NO inhibition, and protein kinase G (PKG) inhibition. In RPAEC, these results were attributed to altered ET-1 gene expression; low exogenous AM also promoted activity of endothelin-converting enzyme, and high AM increased the number of endothelin type-B (ETB) receptor sites. Hypoxia significantly elevated AM and ET-1 levels in IRL and RPAEC, and hAM(22-52), NO inhibition, or PKG inhibitors caused a further ET-1 rise. These interventions also prevented the hypoxia-related increase in ETB sites in RPAEC. In RPAEC, both high AM and hypoxia down-regulated receptor activity-modifying protein (RAMP)1, but they up-regulated RAMP2 protein and AM receptor sites, and RAMP2 silencing by small interference RNA proved its pivotal role for signal switching. In conclusion, endogenous pulmonary AM up-regulates ET-1 and endothelin-converting enzyme activity under physiological conditions, via CGRP1R and PKA. In contrast, hypoxia-induced high AM levels, via AM1 receptor and NO/PKG, down-regulate ET-1 gene expression and promote expression of ETB receptors. This hypoxia-related switch of AM signaling can be attributed to up-regulation of the RAMP2/AM1 receptor system.

Chronic administration of adrenomedullin attenuates hypoxic pulmonary vascular structural remodeling and inhibits proadrenomedullin N-terminal 20-peptide production in rats

Adrenomedullin (ADM) is a novel cardiovascular-active peptide involved in vasodilation, reducing blood pressure and inhibiting vascular smooth muscle cell migration and proliferation. Previous research showed that ADM might be involved in the development of pulmonary hypertension. In this study, we investigated the effect of ADM subcutaneously administered by mini-osmotic pump (300 ng/h) on pulmonary hemodynamics and pulmonary vascular structure in hypoxic rats, as well as the influence of ADM on the proadrenomedullin N-terminal 20-peptide (PAMP) protein and mRNA expressions and its plasma concentrations. The results showed that ADM obviously decreased mean pulmonary artery pressure and the ratio of right ventricular mass to left ventricular plus septal mass in hypoxic rats. Chronic infusion of ADM lessened the muscularization of small pulmonary vessels, attenuated relative medial thickness and relative medial area of pulmonary arteries, and alleviated the ultrastructural changes in pulmonary arteries of hypoxic rats. ADM inhibited the proliferation of pulmonary artery smooth muscle cells, represented by a decrease in the expression of proliferative cell nuclear antigen (PCNA) in the pulmonary artery. Meanwhile, plasma PAMP concentration and the expression of PAMP protein and mRNA by pulmonary arteries in rats of hypoxia with ADM group were markedly decreased compared with those in hypoxic group. The results suggest that ADM ameliorated the development of hypoxic pulmonary vascular structural remodeling. Intramolecular regulation of ADM may play an important role in the regulation of hypoxic pulmonary hypertension by ADM.