Hypotension and resistance to lipopolysaccharide-induced shock in transgenic mice overexpressing adrenomedullin in their vasculature

Adrenomedullin and its binding protein attenuate the proinflammatory response after hemorrhage

OBJECTIVE

The neuroendocrine response to hemorrhage is to maintain perfusion to the heart and brain, often at the expense of other organ systems. Systemic inflammation and tissue injury are important components of pathophysiologic consequences of hemorrhage. We have recently shown that administration of adrenomedullin (AM, a potent vasodilator peptide) and adrenomedullin binding protein-1 (AMBP-1) prevented the transition from the hyperdynamic to the hypodynamic stage in the progression of sepsis. However, the effect of AM/AMBP-1 on the inflammatory response after hemorrhage remains unknown. We therefore hypothesized that administration of AM/AMBP-1 during fluid resuscitation in hemorrhaged animals (i.e., posttreatment) attenuates tissue injury and the proinflammatory response.

DESIGN

Prospective, controlled, and randomized animal study.

SETTING

A research institute laboratory.

SUBJECTS

Male adult rats.

INTERVENTIONS

Rats were bled, and then a mean arterial pressure was maintained at 40 mm Hg for 90 mins. They were then resuscitated by infusion of four times the volume of shed blood using Ringer's lactate solution for 60 mins.

MEASUREMENTS AND MAIN RESULTS

Fifteen minutes after the beginning of resuscitation, AM (12 microg/kg of body weight) in combination with AMBP-1 (40 microg/kg of body weight) was administered via a femoral venous catheter for 45 mins. Blood samples were collected 4 hrs postresuscitation and assayed for levels of liver enzymes (i.e., alanine aminotransferase and aspartate aminotransferase), lactate, creatinine, proinflammatory cytokines tumor necrosis factor and high mobility group box 1, and anti-inflammatory cytokine interleukin-10. The results indicate that levels of alanine aminotransferase, aspartate aminotransferase, creatinine, lactate, tumor necrosis factor, and high mobility group box 1 markedly elevated after hemorrhage and resuscitation, and AM/AMBP-1 treatment significantly attenuated these increases. In contrast, the serum concentration of anti-inflammatory cytokine interleukin-10 was increased by the treatment of AM/AMBP-1. Moreover, AM/AMBP-1 treatment significantly improved the survival rate from 35% in vehicle-treated animals to 73% in AM/AMBP-1-treated animals in a low-volume resuscitation model of hemorrhage.

CONCLUSION

The combined administration of AM and AMBP-1 effectively suppresses hemorrhage-elicited organ injury and reduces hemorrhage-induced mortality, partly through down-regulation of proinflammatory cytokines (tumor necrosis factor and high mobility group box 1) and up-regulation of the anti-inflammatory cytokine interleukin-10.

Adrenomedullin is both proinflammatory and antiinflammatory: its effects on gene expression and secretion of cytokines and macrophage migration inhibitory factor in NR8383 macrophage cell line

Adrenomedullin (ADM) is a potent vasorelaxant peptide that plays important roles in cardiovascular homeostasis and inflammatory response. ADM derived from macrophages is one of the major sources of ADM that is produced in the inflammatory process. To assess the functions of ADM in inflammation, we studied the temporal changes in ADM production and its effect on secretion of macrophage migration inhibitory factor (MIF) and cytokine response of NR8383 rat macrophages activated by lipopolysaccharide (LPS). NR8383 cells were stimulated by LPS in the absence and presence of exogenous ADM, and the concentrations of ADM, MIF, and proinflammatory cytokines (IL-6, TNF-alpha, and IL-1beta) in the culture media and gene expressions of the cells were measured. We confirmed that the secretion and mRNA expression of ADM in the macrophages were markedly increased by LPS. ADM increased initial secretion of MIF and IL-1beta from both nonstimulated and LPS-stimulated cells, and it also increased basal and LPS-induced IL-6 secretion of the cells by 2- to 15-fold. However, it reduced secretion of TNF-alpha from LPS-stimulated cells by 34-56%. Our results suggest that ADM modulates MIF secretion and cytokine production and plays important roles in both the initiation and propagation of the inflammatory response.

Haplotype-Based Case-Control Study Revealing an Association between the Adrenomedullin Gene and Proteinuria in Subjects with Essential Hypertension

Adrenomedullin (AM) has various physiological actions on the cardiovascular system, including vasodilatation, diuresis, natriuresis, inhibition of aldosterone secretion, and increases of the cardiac output, all of which cause hypotension. Since AM plays a role in the pathophysiology of vascular diseases, genes controlling AM might be involved in the development and etiology of essential hypertension (EH). However, there have been few studies examining the relationship between the AM gene and hypertension. The aims of this study were to genotype some of the genetic markers for the human AM gene in Japanese subjects, and via a haplotype-based case-control study, assess the association between and the AM gene and EH or its risk factors, such as hyperlipidemia, renal damage, and proteinuria. We genotyped 205 EH patients and 210 age-matched normotensive (NT) individuals for two single nucleotide polymorphisms of rs4399321, rs7944706 and a microsatellite polymorphism located approximately 5,400 base pairs downstream of the 3' end of the human AM gene. The overall distribution in each variant and haplotype did not significantly differ between the two groups. However, after dividing the groups into those subjects with and without proteinuria, the haplotype analysis revealed a positive association. In conclusion, a possible mutation linked to the haplotype may indicate a genetic predisposition for proteinuria in EH.

Adrenomedullin expression in a rat model of acute lung injury induced by hypoxia and LPS

Adrenomedullin (ADM) is upregulated independently by hypoxia and LPS, two key factors in the pathogenesis of acute lung injury (ALI). This study evaluates the expression of ADM in ALI using experimental models combining both stimuli: an in vivo model of rats treated with LPS and acute normobaric hypoxia (9% O2) and an in vitro model of rat lung cell lines cultured with LPS and exposed to hypoxia (1% O2). ADM expression was analyzed by in situ hybridization, Northern blot, Western blot, and RIA analyses. In the rat lung, combination of hypoxia and LPS treatments overcomes ADM induction occurring after each treatment alone. With in situ techniques, the synergistic effect of both stimuli mainly correlates with ADM expression in inflammatory cells within blood vessels and, to a lesser extent, to cells in the lung parenchyma and bronchiolar epithelial cells. In the in vitro model, hypoxia and hypoxia + LPS treatments caused a similar strong induction of ADM expression and secretion in epithelial and endothelial cell lines. In alveolar macrophages, however, LPS-induced ADM expression and secretion were further increased by the concomitant exposure to hypoxia, thus paralleling the in vivo response. In conclusion, ADM expression is highly induced in a variety of key lung cell types in this rat model of ALI by combination of hypoxia and LPS, suggesting an essential role for this mediator in this syndrome.

Biological importance of the peptides of the calcitonin family as revealed by disruption and transfer of corresponding genes

The hormone calcitonin (CT) of thyroid C-cell origin, the neuropeptides alpha- and beta-calcitonin gene-related peptide (CGRP), the widely expressed hormone and tissue factor adrenomedullin (AM), and amylin (AMY) that is co-produced with insulin in pancreatic beta-cells, are structurally related peptides. They have in common six or seven amino acid ring structures, linked by disulfide bridges between cysteine residues, and amidated carboxyl termini that are both required for biological activity. The actions of the peptides in vivo have traditionally been studied after intravenous and intracerebroventricular administration. As a result, CT lowers serum calcium and reduces pain perception. alpha- and beta CGRP and AM are highly potent vasodilatory peptides. AMY inhibits food intake through its action in the area postrema of the brain. Physiological actions of the peptides summarized in the present review have been defined through gene knockout and overexpression strategies.

Intermedin, a novel calcitonin family peptide that exists in teleosts as well as in mammals: a comparison with other calcitonin/intermedin family peptides in vertebrates

Endocrine regulation in vertebrates is critical for the adaptation and regulation of homeostasis. The G protein-coupled receptor (GPCR) signaling transduction system represents one of the most ancient forms of cell surface signaling. Recently, comparative sequence analysis has aided in the identification and pairing of a variety of ligand/GPCR signaling systems. Among the ligands of type II GPCRs, the calcitonin family peptides including calcitonin, alpha-calcitonin gene-related peptide (alphaCGRP), betaCGRP, adrenomedullin, and amylin are among the best studied hormones, and the founding member, calcitonin, was originally identified and isolated from teleosts. This unique group of peptides shares a conserved tertiary structure with an N-terminal disulfide-bridged ring. In mammals, these peptides signal through two closely related type II GPCRs and three unique receptor activity-modifying proteins. Recently, based on the analysis of multiple vertebrate genomes, we identified a novel calcitonin/CGRP family peptide named intermedin. Here we show that in humans the five paralogous family genes, calcitonin, CGRP, amylin, adrenomedullin, and intermedin, evolved before the emergence of modern vertebrates, and that teleost genomes carry multiple copies of these co-evolved hormone genes. Sequence comparison showed that each of these genes is highly conserved in different vertebrates and that multiple copies of these peptides in teleosts could be derived from ancient genome duplication and/or lineage-specific intragenic duplications. The present article provides an overview of the calcitonin/intermedin family peptides found in teleost and mammalian genomes, and describes their putative functions. In addition, we demonstrate that one of the intermedin orthologs deduced from the pufferfish (Fugu rubripes) genome shares a conserved signaling activity with mammalian intermedin. The combined results indicate that the physiology associated with each of these family peptides likely evolved during early vertebrate evolution and diverged to serve select physiological functions in different vertebrates.

Novel fish-derived adrenomedullin in mammals: structure and possible function

Adrenomedullin (AM) has been recognized as a member of the calcitonin (CT)/CT gene-related peptide (CGRP) family. However, an independent AM family consisting of five paralogous peptides exists in teleost fish. Among them, the peptide named AM1 is an ortholog of mammalian AM as determined by the linkage analysis of orthologous genes and the presence of proAM N-terminal 20 peptide (PAMP)-like sequence in the prosegment. Since the peptides named AM2 and 3 are distinct from other members with respect to the precursor sequence, tissue distribution of the transcripts, and exon-intron organization, we searched for their mammalian orthologs from genome databases, which resulted in an identification of AM2 in human, rat, and mouse. AM2 was expressed abundantly in the submaxillary gland, kidney, and some vascular and digestive tissues of mice. AM2 injected in vivo induced potent cardiovascular and renal effects in mice. In the heart and kidney of mice, AM2 was localized in endothelial cells of the coronary vessels and in glomeruli and vasa recta, respectively. AM2 increased cAMP accumulation in cells expressing human CT receptor-like receptor (CRLR) and one of receptor activity-modifying proteins (RAMPs), but it was no more potent than CGRP and AM. AM2 was also less potent than CT in cells expressing CT receptor and RAMP. There remains a possibility that a new AM2-specific receptor or an additional RAMP that enables CRLR to be an AM2-specific receptor, exists in mammals.

The role of adrenomedullin and receptors in glomerular hyperfiltration in streptozotocin-induced diabetic rats

BACKGROUND

Since adrenomedullin (AM) elicits vasodilatation by binding to specific AM receptors consisted of calcitonin-receptor-like receptor (CRLR)/receptor-activity-modifying protein 2 (RAMP2) or CRLR/receptor-activity-modifying protein 3 (RAMP3) on endothelial cells and stimulating nitric oxide production, AM possibly involves in glomerular capillary dilatation in early phase of diabetic nephropathy.

METHODS

Streptozotocin (STZ)-induced diabetic Sprague-Dawley rats at 4 weeks after the injection were employed for expression studies of AM, RAPM2, and RAMP3. The measurement of AM peptide levels in kidney tissue, plasma, and urine was performed. Human aortic endothelial cells (HAEC) were used to investigate functional link between glucose-induced AM production and nitric oxide release.

RESULTS

STZ rats showed glomerular hypertrophy and increased urinary NO2- and NO3- excretion. By Northern blot analyses, AM and RAPM2 mRNAs significantly increased in the kidneys of STZ rats, while RAMP3 mRNA was not altered. In STZ rats, AM peptide was actively secreted into urine (1280 +/- 360 fmol/day vs. control 110 +/- 36 fmol/day). AM peptide was mainly detected on cortical and medullary collecting duct cells in control rat kidneys and AM peptide and mRNA were up-regulated on afferent arterioles and glomeruli of STZ rats. RAMP2 expression was detected on afferent arterioles and not in glomeruli in control rats and it was up-regulated on glomerular endothelial cells in STZ rats. In HAEC culture, d-glucose stimulated AM and nitric oxide production and they were suppressed by addition of AM antisense oligodeoxynucleotides.

CONCLUSION

Up-regulated expression of AM and RAMP2 in afferent arterioles and glomeruli may be related to selective dilatation of glomerular capillary in acute phase of type 1 diabetes.

Adrenomedullin and adrenomedullin binding protein-1 attenuate vascular endothelial cell apoptosis in sepsis

OBJECTIVE

To determine whether vascular endothelial cell apoptosis occurs in the late stage of sepsis and, if so, whether administration of a potent vasodilatory peptide adrenomedullin and its newly reported specific binding protein (AM/AMBP-1) prevents sepsis-induced endothelial cell apoptosis.

SUMMARY BACKGROUND DATA

Polymicrobial sepsis is characterized by an early, hyperdynamic phase followed by a late, hypodynamic phase. Our recent studies have shown that administration of AM/AMBP-1 delays or even prevents the transition from the hyperdynamic phase to the hypodynamic phase of sepsis, attenuates tissue injury, and decreases sepsis-induced mortality. However, the mechanisms responsible for the beneficial effects of AM/AMBP-1 in sepsis remain unknown.

METHODS

Polymicrobial sepsis was induced by cecal ligation and puncture in adult male rats. Human AMBP-1 (40 microg/kg body weight) was infused intravenously at the beginning of sepsis for 20 minutes and synthetic AM (12 microg/kg body weight) was continuously administered for the entire study period using an Alzert micro-osmotic pump, beginning 3 hours prior to the induction of sepsis. The thoracic aorta and pulmonary tissues were harvested at 20 hours after cecal ligation and puncture (ie, the late stage of sepsis). Apoptosis was determined using TUNEL assay, M30 Cytodeath immunostaining, and electromicroscopy. In addition, anti-apoptotic Bcl-2 and pro-apoptotic Bax gene expression and protein levels were assessed by RT-PCR and Western blot analysis, respectively.

RESULTS

Vascular endothelial cells underwent apoptosis formation at 20 hours after cecal ligation and puncture as determined by three different methods. Moreover, partial detached endothelial cell in the aorta was observed. Bcl-2 mRNA and protein levels decreased significantly at 20 hours after the onset of sepsis while Bax was not altered. Administration of AM/AMBP-1 early after sepsis, however, significantly reduced the number of apoptotic endothelial cells. This was associated with significantly increased Bcl-2 protein levels and decreased Bax gene expression in the aortic and pulmonary tissues.

CONCLUSION

The above results suggest that vascular endothelial cell apoptosis occurs in late sepsis and the anti-apoptotic effects of AM/AMBP-1 appear to be in part responsible for their beneficial effects observed under such conditions.

Identification of vasoactive nonpeptidic positive and negative modulators of adrenomedullin using a neutralizing antibody-based screening strategy

Adrenomedullin (AM) is a peptide hormone implicated in blood pressure regulation and in the pathophysiology of important diseases, such as hypertension, cancer, and diabetes. However, nonpeptidic modulators of this peptide that could be used to clinically regulate its actions are not available. We present here an efficient new method to screen a large library of small molecules. This technology was applied to the identification of positive and negative modulators of AM function. A two-tier screening strategy was developed in which the first screening entails disruption of the interaction between the peptide and a neutralizing monoclonal antibody. Selected compounds were further characterized by their ability to modulate second messengers in cells containing specific AM receptors. A parallel screen against gastrin-releasing peptide selected a different subset of molecules, confirming the specificity of the screening method. Identified AM-positive regulators reduced blood pressure in vivo, whereas AM-negative regulators mediated vasoconstriction, as predicted by the vasodilatory activity of AM. Binding of the small molecules to immobilized AM was demonstrated by surface plasmon resonance assays, with K(d) values ranging from 7.76 x 10(-9) to 4.14 x 10(-6) m. Preclinical development of AM modulators may result in useful drugs for the prevention and treatment of hypertension, cancer, and diabetes.

Vascular Actions of Calcitonin Gene-Related Peptide and Adrenomedullin

This review summarizes the receptor-mediated vascular activities of calcitonin gene-related peptide (CGRP) and the structurally related peptide adrenomedullin (AM). CGRP is a 37-amino acid neuropeptide, primarily released from sensory nerves, whilst AM is produced by stimulated vascular cells, and amylin is secreted from the pancreas. They share vasodilator activity, albeit to varying extents depending on species and tissue. In particular, CGRP has potent activity in the cerebral circulation, which is possibly relevant to the pathology of migraine, whilst vascular sources of AM contribute to dysfunction in cardiovascular disease. Both peptides exhibit potent activity in microvascular beds. All three peptides can act on a family of CGRP receptors that consist of calcitonin receptor-like receptor (CL) linked to one of three receptor activity-modifying proteins (RAMPs) that are essential for functional activity. The association of CL with RAMP1 produces a CGRP receptor, with RAMP2 an AM receptor and with RAMP3 a CGRP/AM receptor. Evidence for the selective activity of the first nonpeptide CGRP antagonist BIBN4096BS for the CGRP receptor is presented. The cardiovascular activity of these peptides in a range of species and in human clinical conditions is detailed, and potential therapeutic applications based on use of antagonists and gene targeting of agonists are discussed.

Tumor necrosis factor-alpha downregulates adrenomedullin receptors in human coronary artery smooth muscle cells

We examined the effects of tumor necrosis factor (TNF)-alpha on the expression and functionality of adrenomedullin (AM) receptors in cultured human coronary artery smooth muscle cells. Analysis of real-time quantitative polymerase chain reactions showed that these cells abundantly express two AM receptors comprised of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1) or RAMP2. TNF-alpha induced time- and dose-dependent decreases in the expression of CRLR and RAMP1/2 mRNAs, thereby diminishing AM-evoked cAMP production. The suppression of these three mRNAs was unaffected by inhibiting NOS, protein kinase G, protein kinase A, superoxide formation or NF-kappaB activation.

Plasma adrenomedullin concentration is increased in patients with peripheral arterial occlusive disease associated with vascular inflammation

Adrenomedullin (AM), a potent vasodepressor, is known to have anti-atherosclerotic and anti-inflammatory effects. However, there is no information about its level in severe atherosclerotic diseases, such as peripheral arterial occlusive disease (PAOD). The present study investigated the plasma concentration of AM and several inflammatory parameters in 72 patients with and without PAOD. The plasma AM concentration in patients with PAOD was significantly higher than in those without PAOD. Its concentration had significant correlations with ankle-brachial index and Fontaine's stage. The plasma AM level also correlated with high sensitive C-reactive protein and interleukin-6. As an additional study, plasma levels of two forms of AM drawn from the femoral artery and saphenous vein were measured in 27 other subjects. Both mature and intermediate forms of plasma AM in the femoral artery and saphenous vein were higher in patients with PAOD than in those without PAOD. A significant step-up of the mature form of AM from the femoral artery to the saphenous vein was observed. Our findings indicate that the plasma AM concentration was elevated in patients with PAOD in proportion to the severity of the disease and associated with vascular inflammation. An increased production of AM in PAOD may play a protective role against advanced atherosclerosis with an inflammatory signature.

Effects of adrenomedullin on endothelial cells in the multistep process of angiogenesis: Involvement of CRLR/RAMP2 and CRLR/RAMP3 receptors

Recently, we demonstrated that U87 glioblastoma xenograft tumors treated with anti-adrenomedullin (AM) antibody were less vascularized than control tumors, suggesting that AM might be involved in neovascularization and/or vessel stabilization. Angiogenesis, the sprouting of new capillaries from preexisting blood vessels, is a multistep process that involves migration and proliferation of endothelial cells, remodeling of the extracellular matrix and functional maturation of the newly assembled vessels. In our study, we analyzed the role of AM on human umbilical vein endothelial cell (HUVEC) phenotype related to different stages of angiogenesis. Here we report evidence that AM promoted HUVEC migration and invasion in a dose-dependent manner. The action of AM is specific and is mediated by the calcitonin receptor-like receptor/receptor activity-modifying protein-2 and -3 (CRLR/RAMP2; CRLR/RAMP3) receptors. Furthermore, AM was able to induce HUVEC differentiation into cord-like structures on Matrigel. Suboptimal concentrations of vascular endothelial growth factor (VEGF) and AM acted synergistically to induce angiogenic-related effects on endothelial cells in vitro. Blocking antibodies to VEGF did not significantly inhibit AM-induced capillary tube formation by human endothelial cells, indicating that AM does not function indirectly through upregulation of VEGF. These findings suggest that the proangiogenic action of AM on cultured endothelial cells via CRLR/RAMP2 and CRLR/RAMP3 receptors may translate in vivo into enhanced neovascularization and therefore identify AM and its receptors acting as potential new targets for antiangiogenic therapies.

Adrenomedullin: Multiple functions in human pregnancy

Adrenomedullin is a 52 amino acid peptide originally isolated from human phaeochromocytoma in 1993. It was initially demonstrated to have profound effects on the vasculature including vasodilatation and subsequently promotion of angiogenesis. Since then it has become apparent that it has a wide range of other biological actions including regulation of cell growth and differentiation. Successful pregnancy outcome relies on establishing and maintaining throughout gestation an efficient blood supply to the fetus. This allows the exchange of nutrients, oxygenation of fetal blood and removal of cytotoxins from the fetus, such as carbon dioxide. One of the most important local adaptations to pregnancy is the change in maternal blood flow to the implantation site. Evidence now points towards a vital role for adrenomedullin in the regulation of placentation. It appears that adrenomedullin may play important roles in the regulation of fetal perfusion both in normal and in compromised pregnancies. However, most studies have focused on measuring adrenomedullin levels and studying its expression as well as that of its receptors. More functional studies are now required to elucidate the underlying mechanisms involved.

Rôle de la dysfonction endothéliale dans la mortalité liée au sepsis

During the past decade, a unifying hypothesis has been developed to explain the vascular changes that occur in septic shock on the basis of the effect of inflammatory mediators on the vascular endothelium. The vascular endothelium plays a central role in the control of microvascular flow, and it has been proposed that widespread vascular endothelial activation, dysfunction and eventually injury occur in septic shock, ultimately resulting in multiorgan failure. This has been characterised in various models of experimental septic shock. Now, direct and indirect evidence for endothelial cell alteration in humans during septic shock is emerging. The present review details recently published literature on this rapidly evolving topic.

Stimulation of adhesion molecule expression in human endothelial cells (HUVEC) by adrenomedullin and corticotrophin

Adrenomedullin (AM) and corticotrophin (ACTH) are both vasoactive peptides produced by a variety of cell types, including endothelial cells. Although AM and ACTH are considered to be important in the control of blood pressure and the response to stress, respectively, their role in inflammation and the immune response has not been clarified. This study shows, with the use of a cell-based ELISA, that AM and ACTH induce cell surface expression of the adhesion molecules E-selectin, VCAM-1, and ICAM-1 on human umbilical vein endothelial cells (HUVEC). Furthermore, this effect appears to be mediated in part via elevation of cAMP, given that both peptides elevate cAMP, the cell-permeable cAMP analog dibutyryl cAMP is able to mimic induction of all three cell adhesion molecules and the effect of AM and ACTH is inhibited by the adenylyl cyclase inhibitor SQ-22536. These findings demonstrate a role for AM and ACTH in the regulation of the immune and inflammatory response.

Adrenomedullin gene delivery attenuates myocardial infarction and apoptosis after ischemia and reperfusion

Adrenomedullin (AM) has been shown to protect against cardiac remodeling. In this study, we investigated the potential role of AM in myocardial ischemia-reperfusion (I/R) injury through adenovirus-mediated gene delivery. One week after AM gene delivery, rats were subjected to 30-min coronary occlusion, followed by 2-h reperfusion. AM gene transfer significantly reduced the ratio of infarct size to ischemic area at risk and the occurrence of sustained ventricular fibrillation compared with control rats. AM gene delivery also attenuated apoptosis, assessed by both terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay and DNA laddering. The effect of AM gene transfer on infarct size, arrhythmia, and apoptosis was abolished by an AM antagonist, calcitonin gene-related peptide [CGRP(8-37)]. Expression of human AM significantly increased cardiac cGMP levels and reduced superoxide production, superoxide density, NAD(P)H oxidase activity, p38 MAPK activation, and Bax levels. Moreover, AM increased Akt and Bad phosphorylation and Bcl-2 levels, but decreased caspase-3 activation. These results indicate that AM protects against myocardial infarction, arrhythmia, and apoptosis in I/R injury via suppression of oxidative stress-induced Bax and p38 MAPK phosphorylation and activation of the Akt-Bad-Bcl-2 signaling pathway. Successful application of this technology may have a protective effect in coronary artery diseases.

Increased plasma concentrations of the mature form of adrenomedullin during cardiac surgery and hepatosplanchnic hypoperfusion

Adrenomedullin is a potent vasodilatory peptide. Plasma adrenomedullin (AM) concentrations increase during and after cardiopulmonary bypass (CPB). However, the cause of this increase and its site of production have not been identified. We investigated the role of the hepatosplanchnic and cerebral circulations in the increase of plasma AM and investigated whether tissue hypoxygenation is a cause of the AM increase seen during CPB. We measured plasma total AM (AM-T) and the biologically active form of AM, mature AM (AM-m), in seven patients undergoing CPB. Both plasma AM-T and AM-m concentrations increased significantly 60 min after weaning from CPB. At this time point, arterial AM-T and AM-m concentrations were 18-fold and 10-fold larger, respectively, than baseline values measured after the induction of anesthesia. The plasma AM-m concentration and the ratio of AM-m/AM-T in blood from the hepatic vein were significantly larger than those from the radial artery or jugular bulb. The AM-m/AM-T ratio decreased during CPB, suggesting that production of the intermediate form of AM, AM-glycine, is more than that of AM-m. The oxygen tension of the hepatic venous blood (PhvO2) was significantly less during CPB. Plasma AM-m concentrations sampled from the hepatic vein showed a significant negative correlation with PhvO2 at 10 min (r = 0.824; P < 0.02) and 60 min (r = 0.828; P < 0.02) after the onset of CPB. These data suggest that the hepatosplanchnic circulation is an important source of AM-m during CPB. Furthermore, hypoxygenation of the hepatosplanchnic region may be an important cause of this AM-m increase.

Adrenomedullin upregulates M2-muscarinic receptors in cardiomyocytes from P19 cell line

1. The effects of AM on expression of muscarinic (M) receptors from P19-derived cardiomyocytes were examined. 2. RT-PCR experiments revealed expression of M(1)-M(4) receptor genes. Immuno-histochemistry indicated that M(2) expression is restricted to contractile cells. Carbachol inhibition of isoprenaline-induced increase in beating rate was prevented by atropine and methoctramine (pA(2): 8.1). Inhibition of [(3)H]-NMS binding by atropine (pK(i): -8.4+/-0.2) and methoctramine (pK(i): -8.3+/-0.2) suggests that M(2) is the functional expressed isoform. 3. [(3)H]-NMS binding and semiquantitative RT-PCR studies showed a dome shaped time course of M(2) expression with a maximum at 7 days of differentiation followed by a progressive decline. 4. AM concentration-dependently upregulated M(2) receptor mRNA during late differentiation stages in P19 cells but also in rat atrial cardiomyocytes. This effect was potentiated by factor H. AM (100 nM) plus factor H (50 nM) treatment of P19 cells for 24 h significantly increased [(3)H]-NMS-specific binding (B(max): 81+/-7 vs 31+/-6 fmol mg(-1) prot). The effect of AM on mRNA levels was prevented by AM receptor antagonist AM(22-52) (1 micro M) but not by CGRP antagonist, CGRP(8-37) (1 micro M). 5. The mRNA levels encoding CRLR receptor declined with culture duration, whereas those encoding L1/G10D receptor remained stable. 6. Our findings demonstrate that AM regulates M(2) receptors expression in cardiomyocytes probably through a mechanism involving L1/G10D receptors. The 'in vivo' significance of this phenomenon remains to be demonstrated.

Adrenomedullin provokes endothelial Akt activation and promotes vascular regeneration both in vitro and in vivo

We previously reported that adrenomedullin (AM), a vasodilating hormone secreted from blood vessels, promotes proliferation and migration of human umbilical vein endothelial cells (HUVECs). In this study, we examined the ability of AM to promote vascular regeneration. AM increased the phosphorylation of Akt in HUVECs and the effect was inhibited by the AM antagonists and the inhibitors for protein kinase A (PKA) or phosphatidylinositol 3-kinase (PI3K). AM promoted re-endothelialization in vitro of wounded monolayer of HUVECs and neo-vascularization in vivo in murine gel plugs. These effects were also inhibited by the AM antagonists and the inhibitors for PKA or PI3K. The findings suggest that AM plays significant roles in vascular regeneration, associated with PKA- and PI3K-dependent activation of Akt in endothelial cells, and possesses therapeutic potential for vascular injury and tissue ischemia.

Adrenomedullin induces direct (endothelium-independent) vasorelaxations and cyclic adenosine monophosphate elevations that are synergistically enhanced by brain natriuretic peptide in isolated rings of rat thoracic aorta

Our laboratory previously demonstrated that nitric oxide and natriuretic peptides can synergistically enhance cAMP elevations and vasorelaxations in rat aortic rings induced by calcitonin gene-related peptide, likely involving cyclic guanosine monophosphate (cGMP)-mediated inhibition of type-3 phosphodiesterase (PDE3). It was predicted that this cellular mechanism may also serve as a point of synergism between adrenomedullin (ADM) and brain natriuretic peptide (BNP) in aortic smooth muscle cells. The current study shows that ADM (100 nM)-induced vasorelaxations in isolated aortic rings of Sprague-Dawley rats are dependent on endothelium (34.1 +/- 4.2% relaxation with endothelium versus 3.0 +/- 0.6% relaxation without endothelium; P < 0.001). To determine interactions between ADM and BNP in smooth muscle cells without interference from endothelium-derived factors, further studies used aortic rings denuded of endothelium. Pretreatment with BNP (1 nM), which elevated cGMP levels 1.6 fold, uncovered direct vasorelaxant effects of ADM in endothelium-denuded rings, showing 5.6 +/- 1.8%, 20.9 +/- 6.1%, and 55 +/- 9.4% relaxations with ADM at 1, 10, and 100 nM, respectively (n = 6). ADM (100 nM) significantly (P < 0.05) increased cyclic adenosine monophosphate (cAMP) levels in denuded aortic rings pretreated with BNP (1 nM), but not in denuded rings without BNP. Quazinone (20 microM), a PDE3 inhibitor, caused similar enhancement of direct cAMP elevations to ADM (100 nM). The data indicate vasodilatory synergism between ADM and BNP in aorta, likely mediated by enhanced accumulation of cAMP in smooth muscle cells resulting from BNP/cGMP-induced inhibition of PDE3. This synergistic mechanism may be especially important in subjects with dysfunctional endothelium, in which BNP may uncover direct vasorelaxant effects of ADM in arteries that normally require healthy (nitric oxide-releasing) endothelium for ADM-induced vasorelaxations to occur.

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.

Distribution of immunoreactivity for the adrenomedullin binding protein, complement factor H, in the rat brain

Adrenomedullin is a multifunctional amidated peptide that has been found in most nuclei of the CNS, where it plays a neuromodulatory role. An adrenomedullin binding protein has recently been found in plasma and characterized as complement factor H. This regulator of the complement system inhibits the progression of the complement cascade and modulates the function of adrenomedullin. Our study shows the ample distribution of factor H immunoreactivity in neurons of telencephalon, diencephalon, mesencephalon, pons, medulla, and cerebellum in the rat CNS, using immunohistochemical techniques for both light and electron microscopy. Factor H immunoreactivity was found in the cytoplasm, but nuclear staining was also a common finding. Some blood vessels and glial cells were also immunoreactive for factor H. Colocalization studies by double immunofluorescence followed by confocal microscopy revealed frequent coexistence of factor H and adrenomedullin immunoreactivities, thus providing morphological evidence for the potential interaction of these molecules in the CNS. The presence of factor H immunoreactivity in glial cells was confirmed by colocalization with glial fibrillary acidic protein. In summary, factor H is highly expressed in the CNS where it could play important roles in regulating adrenomedullin actions and contributing to an intracerebral complement system.

Adrenomedullin and adrenomedullin binding protein-1: their role in the septic response

Adrenomedullin (AM) is a recently discovered, potent vasodilatory peptide with activities including maintenance of cardiovascular and renal homeostasis. Studies have indicated that AM is important in initiating the hyperdynamic response during the early stage of sepsis, and reduction of the vascular effects of AM marks the transition from the initial hyperdynamic phase to the late hypodynamic phase in experimental sepsis. The decreased AM responsiveness in late sepsis may be related to alterations in the AM receptor binding characteristics and/or signaling pathways. Genetic experiments have provided useful information by enhancing AM gene expression. Moreover, a plasma protein which binds AM, adrenomedullin binding protein-1 (AMBP-1), was reported very recently and is just beginning to be investigated as an important modulator in the biphasic septic response. In this regard, our recent results have demonstrated that AMBP-1 synergistically enhanced AM-induced vascular relaxation in both sham and septic animals. It appears that decreased levels of AMBP-1 play a critical role in producing vascular AM hyporesponsiveness during the late stage of sepsis. Furthermore, administration of AM and AMBP-1 in combination prevented the transition from the hyperdynamic to hypodynamic response during the progression of polymicrobial sepsis. Thus, modulation of vascular responsiveness to AM by AMBP-1 may provide a novel approach for the management of sepsis.

Endothelial responses of the aorta from adrenomedullin transgenic mice and knockout mice

Adrenomedullin (AM) is a potent vascular wall-derived vasorelaxing peptide which induces the release of nitric oxide (NO). To explore the role of endogenous AM in vascular function, we examined the effects of acetylcholine (ACh), AM, and AM receptor antagonists [AM (22-52), and calcitonin gene-related peptide (CGRP) (8-37)] on the isometric tension of aortic rings isolated from AM transgenic (TG) and knockout (KO) mice and wild type littermates (WT). ACh and AM caused a dose-dependent reduction of the isometric tension of aortic rings, but the degree of vasodilatation was smaller in TG than in KO or WT (% delta tension [10(-6) mol/l ACh]: KO -69 +/- 10%, WT -39 +/- 8%, TG -29 +/- 1%, p < 0.01). On the other hand, N(G)-nitro-L-arginine methyl ester, an NO synthase inhibitor, induced greater vasoconstriction in TG (% delta tension 10(-5)mol/l: KO +78 +/- 16%, WT +99 +/- 27%, TG +184 +/- 20%, p < 0.01), whereas E-4021, a cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase inhibitor, caused greater vasodilation in TG mice. Both AM antagonists increased tension in TG to a greater extent than in KO or WT mice (% delta tension [10(-6) mol/l CGRP (8-37)]: KO +24 +/- 5%, WT +51 +/- 6%, TG +75 +/- 7%, p < 0.01). Endothelial denudation of the aorta diminished the vasoconstriction caused by the AM antagonists. In conclusion, the amounts of AM expressed in the aortic endothelium influenced baseline NO release. AM antagonists increased vascular tone in WT as well as in TG, suggesting that endogenous AM plays a physiological role in the regulation of aortic tone.

Adrenomedullin promotes proliferation and migration of cultured endothelial cells

Adrenomedullin (AM) is a vasoactive hormone which exerts its action through cyclic adenosine monophosphate(cAMP) /cAMP-dependent protein kinase (PKA) cascade and intracellular Ca2+ mobilization. Recently, evidence has accumulated that AM plays a critical role in the regulation of vascular tone, remodeling and morphogenesis. And although numerous reports have examined the action of AM on cultured vascular cells, the results have not been consistent and have depended on the experimental conditions used. Accordingly, the purpose of this study was to clarify the effect of AM on the proliferation and migration of cultured endothelial cells. Our results revealed that AM promoted the growth and migration of endothelial cells (ECs). AM significantly promoted the proliferation of human umbilical vein endothelial cells (HUVECs) (56.0 +/- 8.7% over the controls at 10(-9) mol/l) and this stimulative effect was inhibited by two AM antagonists, AM(22-52) and calcitonin gene-related peptide (CGRP) (8-37). The number of HUVECs migrated to the lower surface of the transwell apparatus was also increased dose-dependently in the AM group (30.4 +/- 4.2% over the controls at 10(-7) mol/l), and this increase was suppressed by the two AM antagonists and by two PKA antagonists, adenosine 3'5'-cyclic monophosphorothioate Rp-isomer and myristoylated protein kinase A inhibitor amide 14-22. The promoting action of AM on endothelial migration was also suppressed by LY294002, an inhibitor for phosphatidylinositol 3-kinase, but not by N(G)-nitro-L-arginine-methyl ester (L-NAME), an antagonist for nitric oxide synthase (NOS). These results indicate that AM promotes proliferation and migration of ECs via a cAMP/PKA dependent pathway and lend support to the idea that AM exerts beneficial effects on vascular regeneration and might be used as a novel therapeutic strategy for patients with vascular disease.

Adrenomedullin, an autocrine mediator of blood-brain barrier function

Since the discovery that adrenomedullin gene expression is 20- to 40-fold higher in endothelial cells than even in the adrenal medulla, this peptide has been regarded as an important secretory product of the vascular endothelium, together with nitric oxide, eicosanoids, endothelin-1, and other vasoactive metabolites. Cerebral endothelial cells secrete an exceptionally large amount of adrenomedullin, and the adrenomedullin concentration is about 50% higher in the cerebral circulation than in the peripheral vasculature. The adrenomedullin production of cerebral endothelial cells is induced by astrocyte-derived factors. Adrenomedullin causes vasodilation in the cerebral circulation, may participate in the maintenance of the resting cerebral blood flow, and may be protective against ischemic brain injury. Recent data from our laboratory indicate that adrenomedullin, as an endothelium-derived autocrine/paracrine hormone, plays an important role in the regulation of specific blood-brain barrier properties. Adrenomedullin is suggested to be one of the physiological links between astrocyte-derived factors, cyclic adenosine 3'5'-monophosphate (cAMP), and the induction and maintenance of the blood-brain barrier. Moreover, the role of adrenomedullin in the differentiation and proliferation of endothelial cells and in angiogenesis suggests a more complex function for adrenomedullin in the cerebral circulation and in the development of the blood-brain barrier.

Targeted disruption of adrenomedullin and alphaCGRP genes reveals their distinct biological roles

Adrenomedullin (AM) and calcitonin gene-related peptide (CGRP) share common structural characteristics and receptors and belong to the same peptide family. Both peptides show a diverse set of biological effects including vasodilation. Recent establishment of gene-knockout mice has revealed the physiological importance of these two peptides. AM -/- mice demonstrated defective vascular formation during embryogenesis and did not survive beyond midgestation. AM +/- heterozygous mice showed high blood pressure and susceptibility to tissue injury. On the other hand, alphaCGRP -/- mice demonstrated elevated peripheral vascular resistance and high blood pressure caused by increased peripheral sympathetic activity. Thus, AM and CGRP have distinct physiological roles. AM is indispensable for normal embryonic development, regulation of blood pressure and tissue protection against injury, whereas alphaCGRP contributes to the regulation of cardiovascular function through inhibitory modulation of sympathetic nervous activity.

Organ-protective effects of adrenomedullin

Adrenomedullin (AM), a vasodilatory peptide, has recently been shown to have multipotent properties. Among its other pharmacological actions, AM has been hypothesized to protect organs from hypertension, hypoxia, or infection. In vitro studies have shown that AM has an inhibitory effect on vascular smooth muscle cell proliferation and oxidative stress, but that it enhances nitric oxide (NO) production, which in turn is thought to protect against organ damage. Recent advances in genetic engineering have made it possible to investigate the chronic effects of AM in vivo. Applying genetic engineering, it is revealed that adrenomedullin was shown to protect liver, kidney, vasculature, and heart from septic shock, ischemia and hypertension. However, speculation as to the mechanism of its organ-protective effect varies from report to report. Possible mechanisms include preservation of blood flow, interaction with NO and/or oxidative stress. And although there continue to be technical limitations to the use of these genetically modified models, their application in further investigations should help to clarify the potential efficacy of AM as a new therapeutic agent.

Accelerated Cardiac Hypertrophy and Renal Damage Induced by Angiotensin II in Adrenomedullin Knockout Mice

Adrenomedullin (AM) is a potent vasodilating and natriuretic peptide that is thought to play important roles in cardiovascular function. Whether or not AM is involved in the development of cardiac hypertrophy and renal damage remains controversial. In the present study, using heterozygote knockout mice of the AM gene (AM +/-), we analyzed the physiological and pathological roles of the endogenous AM gene. There were no differences in body size or heart and kidney weight compared with wild-type (AM +/+) mice. However, angiotensin II (Ang II) infusion resulted in more severe cardiac hypertrophy in AM +/- mice. The increases in the heart weight-to-body weight ratio and wall thickness of the left ventricle were more prominent in the AM +/- mice. Renal dysfunction characterized by decreased creatinine clearance (C(cr)) was more severe in AM +/- after Ang II infusion. These results suggest that AM plays critical roles in the defense mechanism against cardiac hypertrophy and renal dysfunction. An improved understanding of these roles may pave the way to a novel pharmacological approach for the prevention of cardiovascular diseases.

Bench-to-bedside review: endothelial cell dysfunction in severe sepsis: a role in organ dysfunction?

During the past decade a unifying hypothesis has been developed to explain the vascular changes that occur in septic shock on the basis of the effect of inflammatory mediators on the vascular endothelium. The vascular endothelium plays a central role in the control of microvascular flow, and it has been proposed that widespread vascular endothelial activation, dysfunction and eventually injury occurs in septic shock, ultimately resulting in multiorgan failure. This has been characterized in various models of experimental septic shock. Now, direct and indirect evidence for endothelial cell alteration in humans during septic shock is emerging. The present review details recently published literature on this rapidly evolving topic.

Mechanisms of the beneficial effect of adrenomedullin and adrenomedullin-binding protein-1 in sepsis: down-regulation of proinflammatory cytokines

OBJECTIVE

Our recent study indicates that administration of adrenomedullin (AM) in combination with AM-binding protein-1 (AMBP-1) before sepsis (i.e., pretreatment) maintains cardiovascular stability and reduces the mortality rate. The aim of the present study was to determine whether administration of AM/AMBP-1 after the onset of sepsis (posttreatment) has any salutary effects on the septic host, and if so, whether AM/AMBP-1 down-regulates proinflammatory cytokines, such as tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6.

DESIGN

Prospective, controlled, randomized animal study.

SETTING

A university research laboratory.

SUBJECTS

Male adult Sprague-Dawley rats.

INTERVENTIONS

Rats were subjected either to polymicrobial sepsis by cecal ligation and puncture or to sham operation followed by the administration of normal saline solution (i.e., fluid resuscitation).

MEASUREMENTS AND MAIN RESULTS

At 5 hrs after cecal ligation and puncture, AM (12 microg/kg body weight) and AMBP-1 (40 microg/kg body weight) were administered intravenously over 1 hr. At 20 hrs after cecal ligation and puncture (i.e., the late, hypodynamic stage of sepsis), cardiac output, stroke volume, total peripheral resistance, systemic oxygen delivery, and organ blood flow were determined by radioactive microspheres, and circulating concentrations of proinflammatory cytokines were measured using enzyme-linked immunosorbent assay kits. Moreover, plasma concentrations of transaminases and lactate were measured. The results indicated that administration of AM/AMBP-1 at 5 hrs after cecal ligation and puncture prevented the decrease in measured systemic and regional hemodynamic variables and reduced plasma concentrations of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 at 20 hrs after the onset of sepsis. Moreover, administration of AM/AMBP-1 attenuated hepatic damage and the increase in plasma lactate and prevented hemoconcentration.

CONCLUSION

Administration of AM/AMBP-1 may provide a novel approach to the treatment of sepsis. Moreover, because AM/AMBP-1 significantly reduced circulating concentrations of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6, down-regulation of those proinflammatory cytokines by AM/AMBP-1 appears to play an important role for the beneficial effects of these agents in polymicrobial sepsis.

Novel approach to prevent the transition from the hyperdynamic phase to the hypodynamic phase of sepsis: role of adrenomedullin and adrenomedullin binding protein-1

OBJECTIVE

To determine whether the combined administration of adrenomedullin and adrenomedullin binding protein-1 (AM/AMBP-1) has any modulatory effects on the cardiovascular response during the progression of sepsis.

SUMMARY BACKGROUND DATA

Polymicrobial sepsis is characterized by an early, hyperdynamic phase followed by a late, hypodynamic phase. Recent studies have shown that AM, a newly reported potent vasodilator peptide, plays a major role in initiating the hyperdynamic response. Moreover, the reduced vascular responsiveness to AM appears to be responsible for the transition from the hyperdynamic phase to the hypodynamic phase of sepsis. Although the novel AMBP-1 augments AM-mediated action in vitro, it remains unknown whether AM/AMBP-1 maintains vascular responsiveness to AM at the late stage of sepsis.

METHODS

Sepsis was induced by cecal ligation and puncture (CLP) in adult male rats. Human AMBP-1 (40 microg/kg body weight) was infused intravenously at the beginning of sepsis for 20 minutes and synthetic AM (12 microg/kg body weight) was continuously administrated for the entire study period using an Alzert micro-osmotic pump, beginning 3 hours before the induction of sepsis. At 20 hours after the onset of sepsis (i.e., the late stage), cardiac output, systemic oxygen delivery, stroke volume, total peripheral resistance, and organ blood flow in the liver, gut, kidneys, and heart were determined using radioactive microspheres. Plasma levels of transaminases (ALT, AST) and lactate were also measured. Additional studies were conducted to determine whether administration of AM alone or AMBP-1 alone alters the cardiovascular response at 20 hours after CLP. In additional rats, the necrotic cecum was excised at 20 hours after CLP following AM/AMBP-1 treatment, the peritoneal cavity irrigated with saline, and the midline incision closed in layers. Survival was then examined for a period of 10 days thereafter.

RESULTS

Administration of AM/AMBP-1 prevented the decrease in the measured systemic and regional hemodynamic parameters at 20 hours after the onset of sepsis. Moreover, AM/AMBP-1 significantly attenuated hepatic damage and the elevation of plasma lactate, and prevented hemoconcentration. Treatment with AM/AMBP-1 reduced the overall 10-day mortality rate from 57% to 7%. Neither AM nor AMBP-1 alone was sufficient to maintain cardiovascular stability at 20 hours after CLP.

CONCLUSIONS

Since AM/AMBP-1 delays or even prevents the transition from the hyperdynamic phase to the hypodynamic phase of sepsis, attenuates tissue injury, and decreases sepsis-induced morality, these agents should provide a novel approach for maintaining cardiovascular stability and preventing cell and organ damage during the progression of polymicrobial sepsis.

Adrenomedullin binding protein-1 modulates vascular responsiveness to adrenomedullin in late sepsis

Adrenomedullin (AM), a potent vasodilatory peptide, plays an important role in initiating the hyperdynamic response during the early stage of sepsis. Moreover, the reduced vascular responsiveness to AM appears to be responsible for the transition from the early, hyperdynamic to the late, hypodynamic phase of sepsis. Although the novel specific AM binding protein-1 (AMBP-1) enhances AM-mediated action in a cultured cell line, it remains to be determined whether AMBP-1 plays any role in modulating vascular responsiveness to AM during sepsis. To study this, adult male rats were subjected to sepsis by cecal ligation and puncture (CLP). The thoracic aorta was harvested for determination of AM-induced vascular relaxation. Aortic levels of AMBP-1 were determined by Western blot analysis, and AM receptor gene expression in the aortic tissue was assessed by RT-PCR. The results indicate that AMBP-1 significantly enhanced AM-induced vascular relaxation in aortic rings from sham-operated animals. Although vascular responsiveness to AM decreased at 20 h after CLP (i.e., the late, hypodynamic stage of sepsis), addition of AMBP-1 in vitro restored the vascular relaxation induced by AM. Moreover, the aortic level of AMBP-1 decreased significantly at 20 h after CLP. In contrast, AM receptor gene expression was not altered under such conditions. These results, taken together, suggest that AMBP-1 plays an important role in modulating vascular responsiveness to AM, and the reduced AMBP-1 appears to be responsible for the vascular AM hyporesponsiveness observed during the hypodynamic phase of sepsis.

Adrenomedullin: a cardiac depressant factor in septic shock

Despite intensive research, septic shock is still the most common cause of death in surgical intensive care, and its incidence keeps increasing. No curative treatment is yet available. The critical aspect of septic shock is the refractory hypotension that develops during its late phase which leads to a progressive deterioration of cell and organ functions, and in most instances, death. During septic shock, following the overproduction of cytokines, many factors such as nitric oxide and adrenomedullin (ADM) are produced in abnormally large quantities, but our understanding of their contribution to the pathophysiology of sepsis is limited. Here we show that adrenomedullin (22-52), an adrenomedullin receptor antagonist, improves the contractility of myocytes isolated from lipopolysaccharide (LPS)-treated rats, whereas in normal myocytes, adrenomedullin, acting through an adrenomedullin (22-52) sensitive receptor, decreases their contractility. In addition, adrenomedullin antiserum and inducible nitric oxide (NO) synthase inhibitor improve the survival of LPS-treated rats. The data indicate that adrenomedullin is a cardiac depressant factor, which along with NO precipitates ventricular failure during septic shock.

Aldosterone augments adrenomedullin production without stimulating pro-adrenomedullin N-terminal 20 peptide secretion in vascular smooth muscle cells

OBJECTIVE

Both adrenomedullin (AM) and pro-adrenomedullin N-terminal 20 peptide (PAMP), processed from the same precursor of prepro-adrenomedullin (preproAM), have differential biological properties; AM dilates blood vessels and presumably affects the vascular remodeling, while PAMP inhibits catecholamine secretion. Since aldosterone has been shown to be involved in vascular remodeling, we examined the effects of aldosterone on AM and PAMP secretion and preproAM gene expression in human aortic vascular smooth muscle cells (VSMC).

METHODS

AM and PAMP secreted from human VSMC incubated with aldosterone were measured by radioimmunoassay, and preproAM gene expression was evaluated by quantitative polymerase chain reaction.

RESULTS

Cultured human VSMC secreted both AM and PAMP into the media, while the secretion rate of AM was much higher than that of PAMP. Aldosterone increased preproAM gene expression in the cultured VSMC in a dose-dependent fashion following incubation for 48 h, with a concomitant increase in AM secretion from the cells, but PAMP secretion remained unchanged. Aldosterone-stimulated AM secretion was significantly reduced by spironolactone. Reverse-phase high-performance liquid chromatography analyses showed that immunoreactive AM secreted from the VSMC untreated or treated with aldosterone emerged at the point of human AM(1-52)-NH2.

CONCLUSIONS

AM production was stimulated by aldosterone in cultured human VSMC without an increase in PAMP secretion, suggesting a possible role of AM in modulating vascular remodeling by aldosterone.

Adrenomedullin expression is up-regulated by ischemia-reperfusion in the cerebral cortex of the adult rat

Changes in the pattern of adrenomedullin expression in the rat cerebral cortex after ischemia-reperfusion were studied by light and electron microscopic immunohistochemistry using a specific antibody against human adrenomedullin (22-52). Animals were subjected to 30 min of oxygen and glucose deprivation in a perfusion model simulating global cerebral ischemia, and the cerebral cortex was studied after 0, 2, 4, 6, 8, 10 or 12 h of reperfusion. Adrenomedullin immunoreactivity was elevated in certain neuronal structures after 6-12 h of reperfusion as compared with controls. Under these conditions, numerous large pyramidal neurons and some small neurons were intensely stained in all cortical layers. The number of immunoreactive pre- and post-synaptic structures increased with the reperfusion time. Neurons immunoreactive for adrenomedullin presented a normal morphology whereas non-immunoreactive neurons were clearly damaged, suggesting a potential cell-specific protective role for adrenomedullin. The number and intensity of immunoreactive endothelial cells were also progressively elevated as the reperfusion time increased. In addition, the perivascular processes of glial cells and/or pericytes followed a similar pattern, suggesting that adrenomedullin may act as a vasodilator in the cerebrocortical circulation. In summary, adrenomedullin expression is elevated after the ischemic insult and seems to be part of CNS response mechanism to hypoxic injury.

Adrenomedullin has multiple roles in disease stress: development and remission of the inflammatory response

The upregulation of adrenomedullin (AM) gene expression and increases in systemic circulatory as well as localized tissue AM concentrations is well coordinated with the onset and progression of trauma, infection, and sepsis. As such, the coordinated change in AM suggests a key role for this peptide in the inflammatory response. By clinical definition, the process of inflammation constitutes an orchestrated cascade of localized tissue and systemic responses to immunological challenges. Classical responses to the onset of disease stresses are manifested in the timely elaboration of humoral, blood-borne signal effectors (such as adrenocortical and locally produced tissue hormones, immune cytokines, and inorganic signals such as nitric oxide) as well as patterned migration and infiltration of circulating bone marrow-derived cells (mononuclear cells such as monocyte-macrophages and polymorphonuclear cells like neutrophils) largely associated with or delivered through the vascular system. The body's attempts to combat acute infection to restore homeostatic equilibrium are further compromised by underlying disease situations. Atherosclerosis, diabetes, and cardiovascular disease, as well as nutritional metabolic derangements and persistent subclinical infection perturb the regulatory feedback loops necessary for proper control of response effectors like hormones and cytokines. When imbalances occur, tissue necrosis can ensue as driven by free radical damage to cell components. A true appreciation of the inflammatory response can only be grasped through an integrative approach in which the relationship between the different physiological systems is viewed in terms of a changing, dynamic interaction. In essence, the inflammatory response can be thought of in three phases: a period of severity assessment, a period of remediation, and a period of homeostatic restoration. Indeed, AM has differential effects on cellular metabolism, immune function, endocrine function, and cardiovascular function. This peptide appears to play a pivotal role in both reprioritizing the biological needs of tissues and organs during the three phases of inflammatory response as well as a role in restoring homeostatic equilibrium to the body.

Regulation of adrenomedullin expression and release

Adrenomedullin (AM) was originally identified in the extracts of human pheochromocytoma tissue, but this peptide is now known to be synthesized and secreted from many kinds of cells in the body, including vascular smooth muscle cells, endothelial cells, fibroblasts, cardiac myocytes, epithelial cells, and cancer cells. In this review, we summarize AM-secreting and AM gene-expressing cells in addition to the regulation of secretion and gene expression of AM. Although the data are still limited to deduce the general features of AM gene expression, synthesis, and secretion, AM is assumed to be classified into the new class of biologically active peptides, which is mainly expressed and secreted from non-endocrine type cells by the stimulation with inflammation-related substances. It is also interesting that serious physiological conditions such as inflammation or hypoxia potently stimulate AM expression and release, suggesting its unique physiological function distinct from other known biologically active peptides.

Cerebral endothelial cells are a major source of adrenomedullin

Adrenomedullin is a peptide hormone with multifunctional biological properties. Its most characteristic effects are the regulation of circulation and the control of fluid and electrolyte homeostasis through peripheral and central nervous system actions. Although adrenomedullin is a vasodilator of cerebral vasculature, and it may be implicated in the pathomechanism of cerebrovascular diseases, the source of adrenomedullin in the cerebral circulation has not been investigated thus far. We measured the secretion of adrenomedullin by radioimmunoassay and detected adrenomedullin mRNA expression by Northern blot analysis in primary cultures of rat cerebral endothelial cells (RCECs), pericytes and astrocytes. We also investigated the expression of specific adrenomedullin receptor components by reverse transcriptase-polymerase chain reaction and intracellular cAMP concentrations in RCECs and pericytes. RCECs had approximately one magnitude higher adrenomedullin production (135 +/- 13 fmol/10(5) cells per 12 h; mean +/- SD, n = 10) compared to that previously reported for other cell types. RCECs secreted adrenomedullin mostly at their luminal cell membrane. Adrenomedullin production was not increased by thrombin, lipopolysaccharide or cytokines, which are known inducers of adrenomedullin release in peripheral endothelial cells, although it was stimulated by astrocyte-derived factors. Pericytes had moderate, while astrocytes had very low basal adrenomedullin secretion. In vivo experiments showed that adrenomedullin plasma concentration in the jugular vein of rats was approximately 50% higher than that in the carotid artery or in the vena cava. Both RCECs and pericytes, which are potential targets of adrenomedullin in cerebral microcirculation, expressed adrenomedullin receptor components, and exhibited a dose-dependent increase in intracellular cAMP concentrations after exogenous adrenomedullin administration. Antisense oligonucleotide treatment significantly reduced adrenomedullin production by RCECs and tended to decrease intraendothelial cAMP concentrations. These findings may suggest an important autocrine and paracrine role for adrenomedullin in the regulation of cerebral circulation and blood-brain barrier functions. Cerebral endothelial cells are a potential source of adrenomedullin in the central nervous system, where adrenomedullin can also be involved in the regulation of neuroendocrine functions.

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.

Adrenomedullin and PAMP: discovery, structures, and cardiovascular functions

We discovered adrenomedullin (AM) from human pheochromocytoma tissue by monitoring the elevating activity of intracellular cyclic AMP (cAMP) in rat platelets in 1993. Since the discovery of AM, it has attracted intense interest from cardiovascular researchers because AM elicits multiple biological activities, including a potent and powerful hypotensive activity caused by dilatation of resistance vessels. AM is biosynthesized and secreted from tissues, including cardiovascular organs. In addition to AM, "proadrenomedullin N-terminal 20 peptide (PAMP)," another biologically active peptide, was found to be processed from the AM precursor. Plasma AM levels are increased in various cardiovascular and renal diseases. AM, therefore, seems to function as a novel system that controls circulation and body fluid, and may be involved in pathophysiological changes in cardiovascular diseases. Therefore, in this review we will focus on the structure of AM and its gene, distribution, receptor, and the physiological and pathological roles of AM in cardiovascular disease.

Evidence for the physiological and pathological roles of adrenomedullin from genetic engineering in mice

Adrenomedullin (AM) has been implicated as having hypotensive as well as protective effects on organs and vessels against different kinds of injuries. To elucidate the in vivo pathophysiological roles of adrenomedullin, we established transgenic mice (AMTg) overexpressing adrenomedullin driven by preproendothelin-1 promoter and adrenomedullin knockout mice (AMKO). Blood pressure in AMTg was significantly lower than that in wild-type mice, and AMTg was significantly resistant to lipopolysaccharide-induced septic shock and vascular injuries. On the other hand, heterozygotes of AMKO, AM(+/-), were fully viable and hypertensive as compared with wild littermates. Mice homozygous for adrenomedullin null mutation (AM-/-) were embryonic lethal, and no embryos could survive beyond the midterm of gestation. Collectively, our findings indicate the indispensable role of adrenomedullin in circulatory homeostasis and the organ protection as well as the fetal morphogenesis and the maintenance of pregnancy.

Adrenomedullin in the cerebral circulation

The central nervous system requires an effective autoregulation of cerebral circulation in order to meet the critical and unusual demands of the brain. In addition, cerebral microvessels has a unique feature, the formation of the blood-brain barrier, which contributes to the stability of the brain parenchymal microenvironment. Many factors are known to be involved in the regulation of cerebral circulation and blood-brain barrier functions. In the last few years a new potential candidate, adrenomedullin, a hypotensive peptide was added to this list. Adrenomedullin has a potent vasodilator effect on the cerebral vasculature, and it may be implicated in the pathologic mechanism of cerebrovascular diseases. In this review, we describe current knowledge about the origin and possible role of adrenomedullin in the regulation of cerebral circulation and blood-brain barrier functions.

Human adrenomedullin gene delivery protects against cardiovascular remodeling and renal injury

We investigated the potential roles of adrenomedullin (AM) in cardiovascular and renal function by somatic gene delivery. We showed that a single intravenous injection of the human AM gene under the control of cytomegalovirus promoter/enhancer induces a prolonged delay in blood pressure rise for several weeks in spontaneously hypertensive rats, Dahl salt-sensitive, DOCA-salt, and two-kidney one-clip hypertensive rats as compared to their respective controls injected with a reporter gene. Expression of the human AM transcript was identified in the heart, kidney, lung, liver and aorta of the rat after adenovirus-mediated AM gene delivery by RT-PCR followed by Southern blot analysis. Immunoreactive human AM levels were measured in rat plasma and urine following AM gene delivery. AM gene delivery induced significant reduction of left ventricular mass in these hypertensive animal models. It also reduces urinary protein excretion and increases glomerular filtration rate, renal blood flow and urinary cAMP levels. AM gene transfer attenuated cardiomyocyte diameter and interstitial fibrosis in the heart, and reduced glomerular sclerosis, tubular disruption, protein cast accumulation and renal cell proliferation in the kidney. In the rat model with myocardial ischemia/reperfusion injury, AM gene delivery significantly reduced myocardial infarction, apoptosis, and superoxide production. Furthermore, local AM gene delivery significantly inhibited arterial thickening, promoted re-endothelialization and increased vascular cGMP levels in rat artery after balloon angioplasty. Collectively, these results indicate that human AM gene delivery attenuates hypertension, myocardial infarction, renal injury and cardiovascular remodeling in animal models via cAMP and cGMP signaling pathways. These findings provide new insights into the role of AM in cardiovascular and renal function.

A review of the biological properties and clinical implications of adrenomedullin and proadrenomedullin N-terminal 20 peptide (PAMP), hypotensive and vasodilating peptides

Adrenomedullin (AM), identified from pheochromocytoma and having 52 amino acids, elicits a long-lasting vasodilatation and diuresis. AM is mainly mediated by the intracellular adenylate cyclase coupled with cyclic adenosine monophosphate (cAMP) and nitric oxide (NO) -cyclic guanosine monophosphate (cGMP) pathway through its specific receptor. The calcitonin receptor-like receptor (CLCR) and receptor-activity modifying protein (RAMP) 2 or RAMP3 models have been proposed as the candidate receptor. AM is produced mainly in cardiovascular tissues in response to stimuli such as shear stress and stretch, hormonal factors and cytokines. Recently established AM knockout mice lines revealed that AM is essential for development of vitelline vessels of embryo. Plasma AM levels elevate in cardiovascular diseases such as heart failure, hypertension and septic shock, where AM may play protective roles through its characteristic biological activities. Human AM gene delivery improves hypertension, renal function, cardiac hypertrophy and nephrosclerosis in the hypertensive rats. AM decreases cardiac preload and afterload and improves cardiac contractility and diuresis in patients with heart failure and hypertension. Advances in gene engineering and receptor studies may contribute to further understandings of biological implication and therapeutic availability of AM.