Adrenomedullin as a novel antimigration factor of vascular smooth muscle cells

Adrenomedullin Ameliorates Pulmonary Fibrosis by Regulating TGF-ß-Smads Signaling and Myofibroblast Differentiation

Pulmonary fibrosis is an irreversible, potentially fatal disease. Adrenomedullin (AM) is a multifunctional peptide whose activity is regulated by receptor activity-modifying protein 2 (RAMP2). In the present study, we used the bleomycin (BLM)-induced mouse pulmonary fibrosis model to investigate the pathophysiological significance of the AM-RAMP2 system in the lung. In heterozygous AM knockout mice (AM+/-), hydroxyproline content and Ashcroft scores reflecting the fibrosis severity were significantly higher than in wild-type mice (WT). During the acute phase after BLM administration, FACS analysis showed significant increases in eosinophil, monocyte, and neutrophil infiltration into the lungs of AM+/-. During the chronic phase, fibrosis-related molecules were upregulated in AM+/-. Notably, nearly identical changes were observed in RAMP2+/-. AM administration reduced fibrosis severity. In the lungs of BLM-administered AM+/-, the activation level of Smad3, a receptor-activated Smad, was higher than in WT. In addition, Smad7, an antagonistic Smad, was downregulated and microRNA-21, which targets Smad7, was upregulated compared to WT. Isolated AM+/- lung fibroblasts showed less proliferation and migration capacity than WT fibroblasts. Stimulation with TGF-β increased the numbers of α-SMA-positive myofibroblasts, which were more prominent among AM+/- cells. TGF-β-stimulated AM+/- myofibroblasts were larger and exhibited greater contractility and extracellular matrix production than WT cells. These cells were α-SMA (+), F-actin (+), and Ki-67(-) and appeared to be nonproliferating myofibroblasts (non-p-MyoFbs), which contribute to the severity of fibrosis. Our findings suggest that in addition to suppressing inflammation, the AM-RAMP2 system ameliorates pulmonary fibrosis by suppressing TGF-β-Smad3 signaling, microRNA-21 activity and differentiation into non-p-MyoFbs.

Adrenomedullin-Receptor Activity-Modifying Protein 2 System Ameliorates Subretinal Fibrosis by Suppressing Epithelial-Mesenchymal Transition in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of visual impairment. Anti-vascular endothelial growth factor drugs used to treat AMD carry the risk of inducing subretinal fibrosis. We investigated the use of adrenomedullin (AM), a vasoactive peptide, and its receptor activity-modifying protein 2, RAMP2, which regulate vascular homeostasis and suppress fibrosis. The therapeutic potential of the AM-RAMP2 system was evaluated after laser-induced choroidal neovascularization (LI-CNV), a mouse model of AMD. Neovascular formation, subretinal fibrosis, and macrophage invasion were all enhanced in both AM and RAMP2 knockout mice compared with those in wild-type mice. These pathologic changes were suppressed by intravitreal injection of AM. Comprehensive gene expression analysis of the choroid after LI-CNV with or without AM administration revealed that fibrosis-related molecules, including Tgfb, Cxcr4, Ccn2, and Thbs1, were all down-regulated by AM. In retinal pigment epithelial cells, co-administration of transforming growth factor-β and tumor necrosis factor-α induced epithelial-mesenchymal transition, which was also prevented by AM. Finally, transforming growth factor-β and C-X-C chemokine receptor type 4 (CXCR4) inhibitors eliminated the difference in subretinal fibrosis between RAMP2 knockout and wild-type mice. These findings suggest the AM-RAMP2 system suppresses subretinal fibrosis in LI-CNV by suppressing epithelial-mesenchymal transition.

Adrenomedullin and truncated peptide adrenomedullin(22-52) affect chondrocyte response to apoptotis in vitro: downregulation of FAS protects chondrocyte from cell death

Chondrocyte apoptosis may have a pivotal role in the development of osteoarthritis. Interest has increased in the use of anti-apoptotic compounds to protect against osteoarthritis development. In this work, we investigated the effect of adrenomedullin (AM), a 52 amino-acid hormone peptide, and a 31 amino-acid truncated form, AM(22-52), on chondrocyte apoptosis. Bovine articular chondrocytes (BACs) were cultured under hypoxic conditions to mimic cartilage environment and then treated with Fas ligand (Fas-L) to induce apoptosis. The expression of AM and its calcitonin receptor-like receptor (CLR)/receptor activity-modifying protein (RAMP) (receptor/co-receptor) was assessed by immunostaining. We evaluated the effect of AM and AM(22-52) on Fas-L-induced chondrocyte apoptosis. FAS expression was appreciated by RT-qPCR and immunostainings. The expression of hypoxia-inducible factor 1α (HIF-1α), CLR and one co-receptor (RAMP2) was evidenced. With BACs under hypoxia, cyclic adenosine monophosphate production increased dose-dependently with AM stimulation. AM significantly decreased caspase-3 activity (mean 35% decrease; p = 0.03) as a marker of Fas-L-induced apoptosis. Articular chondrocytes treated with AM showed significantly reduced cell death, along with downregulated Fas expression and production, as compared with AM(22-52). AM decreased articular chondrocyte apoptosis by downregulating a Fas receptor. These findings may pave the way for novel therapeutic approaches in osteoarthritis.

Uremic Toxins and Vascular Calcification-Missing the Forest for All the Trees

The cardiorenal syndrome relates to the detrimental interplay between the vascular system and the kidney. The uremic milieu induced by reduced kidney function alters the phenotype of vascular smooth muscle cells (VSMC) and promotes vascular calcification, a condition which is strongly linked to cardiovascular morbidity and mortality. Biological mechanisms involved include generation of reactive oxygen species, inflammation and accelerated senescence. A better understanding of the vasotoxic effects of uremic retention molecules may reveal novel avenues to reduce vascular calcification in CKD. The present review aims to present a state of the art on the role of uremic toxins in pathogenesis of vascular calcification. Evidence, so far, is fragmentary and limited with only a few uremic toxins being investigated, often by a single group of investigators. Experimental heterogeneity furthermore hampers comparison. There is a clear need for a concerted action harmonizing and standardizing experimental protocols and combining efforts of basic and clinical researchers to solve the complex puzzle of uremic vascular calcification.

Adrenomedullin has a cytoprotective role against endoplasmic reticulum stress for pancreatic β-cells in autocrine and paracrine manners

AIMS/INTRODUCTION

Pancreatic β-cells are sensitive to endoplasmic reticulum (ER) stress, which has a major role in the context of β-cell death. Adrenomedullin (ADM) has been shown to exert a cytoprotective effect under various pathophysiological conditions. Several studies have suggested that thiazolidinediones have protective effects on β-cells. During the course to elucidate the molecular mechanisms by which pioglitazone prevents β-cell death, ADM emerged as a candidate. Here, we studied the regulation of ADM expression, including the effects of pioglitazone, and its role in pancreatic islets.

MATERIALS AND METHODS

We analyzed ADM expression in islet cell lines treated with pioglitazone. The effects of ER stress on ADM and ADM receptor expressions were investigated by analyzing thapsigargin-treated MIN6 cells and islets isolated from Wfs1-/- and db/db mice. To study the anti-apoptotic effect of ADM, ER stress-exposed MIN6 cells were treated with ADM peptides or transfected with ADM expression plasmid.

RESULTS

Pioglitazone increased the production and secretion of ADM in islets through peroxisome-proliferator activated receptor-γ-dependent mechanisms. Thapsigargin treatment increased expressions of both ADM and ADM receptor, composed of Ramp2, Ramp3 and Crlr, in MIN6 cells. ADM and ADM receptor expressions were also increased in isolated islets from Wfs1-/- and db/db mice. ADM peptides and ADM overexpression protected MIN6 cells from thapsigargin-induced apoptosis.

CONCLUSIONS

ER stress stimulates ADM production and secretion in islets. ADM signaling might protect β-cells from ER stress-induced apoptosis, and might be one of the self-protective mechanisms. β-Cell protection by pioglitazone is partly through induction of ADM. ADM-based therapy could be a novel strategy for treating diabetes.

Equine Chorionic Gonadotropin Modulates the Expression of Genes Related to the Structure and Function of the Bovine Corpus Luteum

We hypothesized that stimulatory and superovulatory treatments, using equine chorionic gonadotropin (eCG), modulate the expression of genes related to insulin, cellular modelling and angiogenesis signaling pathways in the bovine corpus luteum (CL). Therefore, we investigated: 1—the effect of these treatments on circulating insulin and somatomedin C concentrations and on gene and protein expression of INSR, IGF1 and IGFR1, as well as other insulin signaling molecules; 2—the effects of eCG on gene and protein expression of INSR, IGF1, GLUT4 and NFKB1A in bovine luteal cells; and 3—the effect of stimulatory and superovulatory treatments on gene and protein expression of ANG, ANGPT1, NOS2, ADM, PRSS2, MMP9 and PLAU. Serum insulin did not differ among groups (P = 0.96). However, serum somatomedin C levels were higher in both stimulated and superovulated groups compared to the control (P = 0.01). In stimulated cows, lower expression of INSR mRNA and higher expression of NFKB1A mRNA and IGF1 protein were observed. In superovulated cows, lower INSR mRNA expression, but higher INSR protein expression and higher IGF1, IGFR1 and NFKB1A gene and protein expression were observed. Expression of angiogenesis and cellular modelling pathway-related factors were as follows: ANGPT1 and PLAU protein expression were higher and MMP9 gene and protein expression were lower in stimulated animals. In superovulated cows, ANGPT1 mRNA expression was higher and ANG mRNA expression was lower. PRSS2 gene and protein expression were lower in both stimulated and superovulated animals related to the control. In vitro, eCG stimulated luteal cells P4 production as well as INSR and GLUT4 protein expression. In summary, our results suggest that superovulatory treatment induced ovarian proliferative changes accompanied by increased expression of genes providing the CL more energy substrate, whereas stimulatory treatment increased lipogenic activity, angiogenesis and plasticity of the extracellular matrix (ECM).

Effect of vasoactive peptides in Tetrahymena: chemotactic activities of adrenomedullin, proadrenomedullin N-terminal 20 peptide (PAMP) and calcitonin gene-related peptide (CGRP)

Adrenomedullin (AMD), proadrenomedullin N-terminal 20 peptide (PAMP) and calcitonin gene-related peptide (CGRP) were studied for chemotaxis, chemotactic selection and G-actin/F-actin transition in Tetrahymena. The aim of the experiments was to study the effects of two different peptides encoded by the same gene compared to a peptide related to one of the two, but encoded by a different gene, at a low level of phylogeny. The positive, chemotactic effect of ADM and the strong negative, chemorepellent effect of PAMP suggest that in Tetrahymena, the two peptides elicit their chemotactic effects via different signalling mechanisms. The complexity of swimming behaviour modulated by the three peptides underlines that chemotaxis, chemokinesis and some characteristics of migratory behaviour (velocity, tortuosity) are working as a sub-population level complex functional unit. Chemotactic responsiveness to ADM and CGRP is short-term, in contrast to PAMP, which as a chemorepellent ligand, has the ability to select sub-populations with negative chemotactic responsiveness. The different effects of ADM and PAMP on the polymerization of actin networks show that the microtubular structure of cilia is more essential to chemotactic response than are transitions of the actin network. The results draw attention to the characteristic effects of vasoactive peptides at this low level of phylogeny.

The Renal Protective Effect of Jiangya Tongluo Formula, through Regulation of Adrenomedullin and Angiotensin II, in Rats with Hypertensive Nephrosclerosis

We investigated the effect of Jiangya Tongluo (JYTL) formula on renal function in rats with hypertensive nephrosclerosis. A total of 21 spontaneously hypertensive rats (SHRs) were randomized into 3 groups: valsartan (10 mg/kg/d valsartan), JYTL (14.2 g/kg/d JYTL), and a model group (5 mL/kg/d distilled water); Wistar Kyoto rats comprised the control group (n = 7, 5 mL/kg/d distilled water). Treatments were administered by gavage every day for 8 weeks. Blood pressure, 24-h urine protein, pathological changes in the kidney, serum creatinine, and blood urea nitrogen (BUN) levels were estimated. The contents of adrenomedullin (ADM) and angiotensin II (Ang II) in both the kidney and plasma were evaluated. JYTL lowered BP, 24-h urine protein, serum creatinine, and BUN. ADM content in kidneys increased and negatively correlated with BP, while Ang II decreased and negatively correlated with ADM, but there was no statistically significant difference of plasma ADM between the model and the treatment groups. Possibly, activated intrarenal renin-angiotensin system (RAS) plays an important role in hypertensive nephrosclerosis and the protective function of ADM via local paracrine. JYTL may upregulate endogenous ADM level in the kidneys and antagonize Ang II during vascular injury by dilating renal blood vessels.

Adrenomedullin and cardiovascular diseases

The cardiovascular system is regulated by the autonomic nervous system, the renin-angiotensin-aldosterone system, nitric oxide (NO) and other factors including neuropeptides. Research in neurohumoral factors has led to the development of many cardiovascular drugs. Adrenomedullin (ADM), initially isolated from the adrenal gland, has diverse physiological and pathophysiological functions in the cardiovascular system. It is produced in many organs and tissues including the vasculature. ADM has numerous actions, including vasodilation, natriuresis, antiapoptosis and stimulation of NO production. It might play a protective role in various cardiovascular pathologies, and its plasma level is elevated in patients with hypertension and heart failure. Administration of ADM is a possible therapeutic approach for treating cardiovascular diseases. A number of studies have investigated the infusion of ADM in humans, which seems to be benficial in heart failure and myocardial infarction. Instead of ADM infusion, augmentation of its endogenous level is another possible strategy. Gene therapy is feasible in animal models, but its application in humans is limited. At present, the most promising clinical application of ADM is the use of the plasma level of mid-regional proadrenomedullin as a biomarker in cardiovascular diseases. It is a good marker of prognosis and survival in patients with coronary aretery disease or heart failure.

Chronic ethanol consumption reduces adrenomedullin-induced relaxation in the isolated rat aorta

Adrenomedullin (AM) is a peptide that displays cardiovascular protective activity. We investigated the effects of chronic ethanol consumption on vascular reactivity to AM and the expression of AM system components in the rat aorta. Male Wistar rats were treated with ethanol (20% vol/vol) for 6 weeks. Vascular reactivity experiments were performed in the isolated rat aorta. Metalloproteinase-2 (MMP-2) levels were determined by gelatin zymography. Nitrite and nitrate generation was measured by chemiluminescence. Protein and mRNA levels of pre-pro-AM, calcitonin receptor-like receptor (CRLR) and RAMP1, 2, and 3 (receptor-activity-modifying proteins) were assessed by western blot and quantitative real-time polymerase chain reaction, respectively. Ethanol intake reduced AM-induced relaxation in endothelium-intact rat aortas, whereas calcitonin gene-related peptide-, acetylcholine-, and sodium nitroprusside-induced relaxation were not affected by ethanol intake. N(G)-nitro-l-arginine-methyl-ester (l-NAME), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, and tetraethylammonium reduced AM-induced relaxation in aortic rings from both control and ethanol-treated rats. Ethanol consumption did not alter basal levels of nitrate and nitrite, nor did it affect the expression of MMP-2 in the rat aorta. Ethanol consumption increased mRNA levels of pre-pro-AM and RAMP1. Protein levels of AM, CRLR, and RAMP1, 2, and 3 were not affected by ethanol consumption. The major findings of the present study are that ethanol consumption reduces the vascular relaxation induced by AM and changes the mRNA expression of the components of the AM system in the vasculature. This response could be one of the mechanisms by which ethanol predisposes individuals to vascular dysfunction and hypertension.

Treating pulmonary arterial hypertension: current treatments and future prospects

Pulmonary arterial hypertension (PAH) consists of a group of heterogeneous but distinct disorders characterized by complex proliferation of the pulmonary vascular endothelium and progressive pulmonary vascular remodeling that leads to right ventricular failure and death. Over the past two decades, significant advances in our understanding of the pathobiology of PAH have led to the development of several therapeutic targets in this disease. Besides conservative therapeutic strategies such as anticoagulation and diuretics, the current treatment paradigm for PAH targets the mediators of the three main biologic pathways that are critical for its pathogenesis and progression: endothelin receptor antagonists inhibit the upregulated endothelin pathway by blocking the biologic activity of endothelin-1; phosphodiesterase-5 inhibitors prevent breakdown and increase the endogenous availability of cyclic guanosine monophosphate, which signals the vasorelaxing effects of the downregulated mediator nitric oxide; and prostacyclin derivatives provide an exogenous supply of the deficient mediator prostacyclin. In addition to these established current therapeutic options, a large number of potential therapeutic targets are being investigated. These novel therapeutic targets include soluble guanylyl cyclase, phosphodiesterases, tetrahydrobiopterin, 5-hydroxytryptamine (serotonin) receptor 2B, 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. This review provides an overview of the current therapeutic options and potential therapeutic targets for PAH.

Adrenomedulline improves ischemic left colonic anastomotic healing in an experimental rodent model

BACKGROUND

Leakage from colonic anastomosis is a major complication causing increased mortality and morbidity. Ischemia is a well-known cause of this event. This study was designed to investigate the effects of adrenomedullin on the healing of ischemic colon anastomosis in a rat model.

METHODS

Standardized left colon resection 3 cm above the peritoneal reflection and colonic anastomosis were performed in 40 Wistar rats that were divided into four groups. To mimic ischemia, the mesocolon was ligated 2 cm from either side of the anastomosis in all of the groups. The control groups (1 and 2) received no further treatment. The experimental groups (3 and 4) received adrenomedullin treatment. Adrenomedullin therapy was started in the perioperative period in group 3 and 4 rats (the therapeutic groups). Group 1 and group 3 rats were sacrificed on postoperative day 3. Group 2 and group 4 rats were sacrificed on postoperative day 7. After careful relaparotomy, bursting pressure, hydroxyproline, malondialdehyde, interleukin 6, nitric oxide, vascular endothelial growth factor, and tumor necrosis factor alpha levels were measured. Histopathological characteristics of the anastomosis were analyzed.

RESULTS

The group 3 animals had a significantly higher bursting pressure than group 1 (p<0.05). Hydroxyproline levels in group 1 were significantly lower than in group 3 (p<0.05). The mean bursting pressure was significantly different between group 2 and group 4 (p<0.05). Hydroxyproline levels in groups 3 and 4 were significantly increased by adrenomedullin therapy relative to the control groups (p<0.05). When all groups were compared, malondialdehyde and nitric oxide were significantly lower in the control groups (p<0.05). When vascular endothelial growth factor levels were compared, no statistically significant difference between groups was observed. Interleukin 6 and tumor necrosis factor alpha were significantly decreased by adrenomedullin therapy (p<0.05). The healing parameters and inflammatory changes (e.g., granulocytic cell infiltration, necrosis, and exudate) were significantly different among all groups (p<0.05).

CONCLUSION

Adrenomedullin had positive effects on histopathologic anastomotic healing in this experimental model of ischemic colon anastomosis.

Adrenomedullin increases fibroblast-like synoviocyte adhesion to extracellular matrix proteins by upregulating integrin activation

Introduction

Rheumatoid arthritis (RA) is characterized by bone and cartilage invasion by fibroblast-like synoviocytes (FLSs). Adrenomedullin, a peptide with anabolic and antiapoptotic properties, is secreted by rheumatoid FLSs. Adrenomedullin also increases the expression of adhesion molecules in endothelial cells and keratinocytes. Here, we investigated whether adrenomedullin mediated FLS adhesion to extracellular matrix (ECM) proteins.

Methods

FLSs were isolated from synovial tissues from RA and osteoarthritis (OA) patients. Plates were coated overnight with the ECM proteins vitronectin, fibronectin, and type I collagen (Coll.I). Adrenomedullin was used as a soluble FLS ligand before plating. We tested interactions with the adrenomedullin receptor antagonist (22-52)adrenomedullin and with the protein kinase A (PKA) inhibitor H-89, and inhibition of co-receptor RAMP-2 by siRNA. Cell adhesion was measured by using color densitometry. Activation of α₂ and β₁ integrins was evaluated by fluorescent microscopy; integrin inhibition, by RGD peptides; and the talin-integrin interaction, by immunoprecipitation (IP).

Results

Adrenomedullin specifically increased RA-FLS adhesion to vitronectin, fibronectin, and Coll.I; no such effect was found for OA-FLS adhesion. Basal or adrenomedullin-stimulated RA-FLS adhesion was inhibited by (22-52)adrenomedullin, H-89, and RAMP-2 siRNA. Adrenomedullin-stimulated adhesion was inhibited by RGD peptides, and associated with α₂ and β₁ integrin activation. This activation was shown with IP to be related to an integrin-talin interaction and was significantly decreased by (22-52)adrenomedullin.

Conclusions

Adrenomedullin-stimulated RA-FLS adhesion was specific for ECM proteins and mediated by α₂ and β₁ integrins. This effect of adrenomedullin was dependent on adrenomedullin receptors. These results support a new role for adrenomedullin in rheumatoid synovial fibroblast pathobiology.

Adrenomedullin ameliorates the development of atherosclerosis in apoE-/- mice

Adrenomedullin (ADM) is a multifunctional peptide regulating cardiovascular homeostasis. We studied the role of ADM in the pathogenesis of atherosclerosis by investigating changes in ADM and its receptors - calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMPs) - in aorta of apoE-/- mice and the effect of exogenous ADM administration. ApoE-/- mice were fed an atherogenic diet for 4 weeks, and apoE-/-+ADM mice were additionally given subcutaneous injections of ADM, 300ng/kg/h, for 4 weeks. ApoE-/- mice fed an atherogenic diet showed hyperlipidemia, a large plaque area and increased vessel wall thickness. The mRNA expression and protein level of ADM/ADM receptors were increased in the aorta, compared with C57BL/6J mice. The elevated mRNA level of CRLR and RAMPs correlated positively with ADM mRNA level. Radioimmunoassay revealed a higher plasma and aorta ADM content, by 61.6% and 285% (both P<0.01), respectively, in apoE-/- mice than that in C57BL/6J mice. Exogenous ADM significantly ameliorated dyslipidemia in apoE-/- mice. ADM-treated mice showed fewer aortic plaques, decreased plaque area, by 76% (P<0.01), and reduced ratio of plaque area to luminal area, by 65% (P<0.01), and ultrasonography revealed significantly reduced intima-media thickness of the ascending branch and abdominal aorta. The results suggest that atherosclerotic apoE-/- mice fed an atherogenic diet showed upregulated endogenous ADM and its receptors, and exogenous ADM treatment ameliorated the dyslipidemia and vascular atherosclerotic lesions. ADM/ADM receptors might be an important protective system against atherosclerosis and could become a new target of prevention and therapy for atherosclerosis.

Lack of adrenomedullin affects growth and differentiation of adult neural stem/progenitor cells

Adrenomedullin (AM) is a peptide hormone involved in the modulation of cellular growth, migration, apoptosis, and angiogenesis. These characteristics suggest that AM is involved in the control of neural stem/progenitor cell (NSPC) biology. To explore this hypothesis, we have obtained NSPC from the olfactory bulb of adult wild-type animals and brain conditional knockouts for adm, the gene that produces AM. Knockout NSPC contain higher levels of hyperpolymerized tubulin and more abundant filopodia than adm-containing cells, resulting in a different morphology in culture, whereas the size of the knockout neurospheres is smaller than that of the wild-types. Proliferation studies have demonstrated that adm-null NSPC incorporate less 5'-bromodeoxyuridine (BrdU) than their wild-type counterparts. In contrast, BrdU studies in the olfactory bulb of adult animals show more labeled cells in adm-null mice that in wild-types, suggesting that a compensatory mechanism exists that guarantees the sufficient production of neural cells in this organ. In NSPC differentiation tests, lack of adm results in significantly lower proportions of neurons and astrocytes and higher proportions of oligodendrocytes. The oligodendrocytes produced from adm-null neurospheres present an immature phenotype with fewer and shorter processes than adm-containing oligodendrocytes. Thus, AM is an important factor in regulating the proliferation and differentiation of adult NSPC and might be used to modulate stem cell renewal and fate in protocols destined to produce neural cells for regenerative therapies.

Adrenomedullin is induced by hypoxia and enhances pancreatic cancer cell invasion

Adrenomedullin (ADM) is synthesized by different types of cells and acts by binding calcitonin receptor-like receptor (CRLR) and members of the receptor activity-modifying protein (RAMP) family. In this study, the expression and functional role of ADM and its signaling components were investigated in pancreatic adenocarcinoma (PDAC). By QRT-PCR, median mRNA levels of ADM and CRLR were 1.5- and 2.4-fold higher, respectively, in PDAC tissues compared to normal pancreatic tissues. By immunohistochemistry, ADM, CRLR, RAMP1 and RAMP2, but not RAMP3, were expressed in pancreatic cancer cells. ADM serum levels were significantly increased in PDAC patients compared to healthy controls and chronic pancreatitis (CP) patients, with an area under the ROC curve of 0.83 and 0.98, respectively. At a cut-off level of 30.6 ng/ml, the specificity of ADM to differentiate PDAC from controls and CP patients was 85.5 and 83.6%, with a sensitivity of 80 and 100%. All 5 evaluated pancreatic cancer cells lines expressed ADM, CRLR, RAMP1 and RAMP2, whereas RAMP3 was expressed in only 1/5 pancreatic cancer cell lines. ADM was strongly induced by hypoxia and significantly increased invasiveness in 3/5 human pancreatic cancer cells. Blocking of CRLR decreased invasiveness in 4/5 human pancreatic cancer cells. In addition, rADM slightly up-regulated vascular endothelial growth factor secretion in 3/5 cell lines. In conclusion, ADM is induced by hypoxia and over-expressed in PDAC and might therefore serve as a potential tumor marker. Furthermore, ADM increases invasiveness of some pancreatic cancer cells and might influence angiogenesis, suggesting that blocking this pathway might have a therapeutic potential.

Adrenomedullin is a novel adipokine: adrenomedullin in adipocytes and adipose tissues

Adrenomedullin (AM) is a multifunctional regulatory peptide that is produced and secreted by various types of cells. The production and the secretion of AM have been demonstrated in cultured adipocytes and adipose tissues. Inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and lipopolysaccharide are strong stimulators for AM expression in adipocytes. Furthermore, AM expression in the adipose tissue is increased in obesity, and plasma concentrations of AM are increased in obese subjects. One possible (patho)physiological role of AM secreted by adipose tissue may be actions against complications of the metabolic syndrome characterized by obesity, type 2 diabetic mellitus and hypertension, via its antioxidant and potent vasodilator effects. These findings indicate that AM is a new member of the adipokine family.

Adrenomedullin antagonizes angiotensin II-stimulated proliferation of human aortic smooth muscle cells

The vasodilating peptide adrenomedullin has been reported to regulate vascular tone as well as proliferation and differentiation of various cell types in an autocrine/paracrine manner. Conflicting data have been reported on the adrenomedullin (AM) effect on vascular smooth muscle cell proliferation, a process involved in the progression of vascular remodeling and atherosclerotic lesion. In this paper we investigate the effect of AM on proliferation of human aorta smooth muscle cell (HASMC). AM showed a potent dose-dependent inhibiting effect on angiotensin II (AngII) induced-proliferation and a stimulatory effect on proliferation of quiescent cells. The cAMP/PKA pathway was involved in the AM inhibitory effect of AngII-induced proliferation in HASMC. PI3K/Akt and ERK pathways were involved in the proliferative effect exerted by AM per se. Our results suggest that AM plays a role in the regulation of HASMC growth antagonizing the AngII effect and may be involved in conditions of altered regulation of the blood vessels.

Adrenomedullin gene transfer induces neointimal apoptosis and inhibits neointimal hyperplasia in injured rat artery

Arterial wall injury leads to inflammatory reaction and release of growth factors that may mediate intimal regrowth. It is hypothesized that the neointimal cells may originate from adventitial myofibroblasts, medial smooth muscle cells, or differentiated bone marrow derived cells. Adrenomedullin (AM), an auto/paracrine cardiovascular peptide that is secreted from fibroblasts, endothelial cells, and vascular smooth muscle cells, may have a regulatory role in the intimal regeneration. In order to investigate the role of AM in neointimal growth, stimulation of stem cell migration, and apoptosis, we overexpressed AM with recombinant adenovirus in a rat arterial injury model. The intimae were significantly thinner in the arteries treated with AM adenovirus compared to the control group. Intima/media ratios were 0.48 +/- 0.18 and 1.01 +/- 0.20 (P < 0.05) in the AM group and the control group, respectively. In addition, a significantly higher apoptotic index of neointimal cells was seen in the AM gene transfer group compared to the control (2.78 +/- 0.5 vs. 0.57 +/- 0.20, P < 0.01). The neointimal cells stained positive for alpha-smooth muscle actin and negative for desmin suggesting possible myofibroblast origin. Very few c-Kit+ or MDR1+ cells were detected 2 weeks after the injury. We conclude that AM overexpression inhibits neointimal growth. The inhibition is associated with enhanced apoptosis of the neointimal cells which may be of myofibroblast origin.

Pathophysiologic and therapeutic implications of adrenomedullin in cardiovascular disorders

Adrenomedullin (AM) is a vasodilator peptide that originally isolated from pheochromocytoma tissue. However, the mRNA is expressed in the normal adrenal gland, heart, kidney and blood vessels. The human AM gene is located in the short arm of chromosome 11 and is composed of 4 exons. There are 2 single nucleotide polymorphisms in introns 1 and 3, and the 3'-end of the AM gene is flanked by a microsatellite marker of cytosine-adenine repeats that is associated with an increased risk of developing hypertension and diabetic nephropathy. AM gene expression is promoted by various stimuli, including inflammation, hypoxia, oxidative stress, mechanical stress and activation of the renin-angiotensin and sympathetic nervous systems. The AM gene promoter region possessed binding site for several transcription factors, including nuclear factor for interleukin-6 expression (NF-IL6) and activator protein 2 (AP-2). Further, plasma AM levels are increased in patients with various cardiovascular diseases, including hypertension, heart failure and renal failure. These findings suggest that AM plays a role in the development of or response to cardiovascular disease. Indeed, experimental and clinical studies have demonstrated that systemic infusion of AM may have a therapeutic effect on myocardial infarction, heart failure and renal failure. Further, vasopeptidase inhibitors which augment the bioactivity of endogenous AM may benefit patients with hypertension and arteriosclerosis. Finally, the angiogenic and cytoprotective properties of AM may have utility in revascularization and infarcted myocardium and ischemic limbs. Because of the potential clinical benefits of AM, indications for use and optimal dosing strategies should be established.

Adrenomedullin: molecular mechanisms and its role in cardiac disease

Adrenomedullin (AM) is a potent, long-lasting vasoactive peptide originally isolated from human pheochromocytoma. Since its discovery, serum and tissue AM expression have been shown to be increased in experimental models and in patients with cardiac hypertrophy, myocardial infarction and end-stage heart failure with several beneficial effects. Considerable evidence exists for a wide range of autocrine, paracrine and endocrine mechanisms for AM which include vasodilatory, anti-apoptotic, angiogenic, anti-fibrotic, natriuretic, diuretic and positive inotropic. Thus, through regulation of body fluid or direct cardiac mechanisms, AM has additive and beneficial effects in the context of heart disease. Notable molecular mechanisms of AM include cyclic adenosine monophosphate, guanosine-3',5'-monophosphate, PI3K/Akt and MAPK-ERK-mediated cascades. Given the endogenous and multifunctional nature of AM, we consider this molecule to have great potential in the treatment of cardiovascular diseases. In agreement, early experimental and preliminary clinical studies suggest that AM is a new and promising therapy for cardiovascular diseases.

Significant changes of peripheral perfusion and plasma adrenomedullin levels in N-acetylcysteine long term treatment of patients with sclerodermic Raynauds phenomenon

The unclear pathogenesis of scleroderma vascular lesions makes treatment of Raynaud's phenomenon (RP) in Systemic Sclerosis (SSc) patients very difficult and a new effective treatment is requested. Recently, a powerful antioxidant agent, the N-acetylcysteine (NAC) has been shown to decrease the frequency and severity of RP in SSc patients. Subsequently, using functional infrared imaging, we showed that a single 1-hour NAC infusion in these patients caused a significant increase of skin temperature. The aim of this study was to demonstrate the efficacy of long term therapy with NAC in an open clinical trial evaluating clinical, instrumental and laboratory parameters. Patients started the treatment receiving for two years, from October to May, intravenous NAC infusions of 15 mg/kg per hour each, for 5 consecutive hours, every two weeks. Before and after each infusion, patients underwent both Laser Doppler perfusion Imaging (LDPI) for the evaluation of the digital perfusion and a blood test to ascertain the plasma adrenomedullin (AM) levels. The NAC infusion increased global hands perfusion and induced a significant decreasing of plasma AM concentrations. Side effects were negligible, easy to control and reversible. Reduction of frequency and severity of RP attacks was recorded. In conclusion, NAC seems to act as an effective vasodilatator in the treatment of RP secondary to SSc and, in addition, it induced significant changes in plasma levels of AM, a potent vasodilator endothelial-derived peptide.

EXPERIMENTAL THERAPIES FOR HYPOXIA-INDUCED PULMONARY HYPERTENSION DURING ACUTE LUNG INJURY

Hypoxic pulmonary vasoconstriction (HPV) and pulmonary hypertension present a common and formidable clinical problem for practicing thoracic, transplant, and trauma surgeons. The recent discovery of efficacious drugs that are selective for the pulmonary vasculature has brought about the potential for very powerful therapeutic agents. Inhaled nitric oxide (NO) therapy has already found broad clinical utility, yet its use is limited by potential toxicities. Rho kinase (ROK) has been discovered to play a very central role in the formation of hypoxia induced pulmonary hypertension, and the advent of very specific ROK inhibitors has shown positive clinical results. Finally, phosphodiesterase-5 inhibitors have been found to selectively vasodilate the pulmonary vasculature in the midst of HPV. The purposes of this review are to: 1) discuss the advantages and disadvantages of inhaled preparations of NO; 2) address experimental alternatives to inhaled preparations of NO to treat HPV; 3) explore potential therapeutic avenues associated with inhibition of Rho-kinase; and, 4) examine the use of phosphodiesterase-5 (PDE-5) inhibitors and combination therapy in the treatment of HPV.

Inhaled tolafentrine reverses pulmonary vascular remodeling via inhibition of smooth muscle cell migration

BACKGROUND

The aim of the study was to assess the chronic effects of combined phosphodiesterase 3/4 inhibitor tolafentrine, administered by inhalation, during monocrotaline-induced pulmonary arterial hypertension (PAH) in rats.

METHODS

CD rats were given a single subcutaneous injection of monocrotaline to induce PAH. Four weeks after, rats were subjected to inhalation of tolafentrine or sham nebulization in an unrestrained, whole body aerosol exposure system. In these animals (i) the acute pulmonary vasodilatory efficacy of inhaled tolafentrine (ii) the anti-remodeling effect of long-term inhalation of tolafentrine (iii) the effects of tolafentrine on the expression profile of 96 genes encoding cell adhesion and extracellular matrix regulation were examined. In addition, the inhibitory effect of tolafentrine on ex vivo isolated pulmonary artery SMC cell migration was also investigated.

RESULTS

Monocrotaline injection provoked severe PAH (right ventricular systolic pressure increased from 25.9 +/- 4.0 to 68.9 +/- 3.2 after 4 weeks and 74.9 +/- 5.1 mmHg after 6 weeks), cardiac output depression and right heart hypertrophy. The media thickness of the pulmonary arteries and the proportion of muscularization of small precapillary resistance vessels increased dramatically, and the migratory response of ex-vivo isolated pulmonary artery smooth muscle cells (PASMC) was increased. Micro-arrays and subsequent confirmation with real time PCR demonstrated upregulation of several extracellular matrix regulation and adhesion genes, such as matrixmetalloproteases (MMP) 2, 8, 9, 10, 11, 12, 20, Icam, Itgax, Plat and serpinb2. When chronically nebulized from day 28 to 42 (12 daily aerosol maneuvers), after full establishment of severe pulmonary hypertension, tolafentrine reversed about 60% of all hemodynamic abnormalities, right heart hypertrophy and monocrotaline-induced structural lung vascular changes, including the proportion of pulmonary artery muscularization. The upregulation of extracellular matrix regulation and adhesion genes was reduced by nearly 80% by inhalation of the tolafentrine. When assessed in vitro, tolafentrine blocked the enhanced PASMC migratory response.

CONCLUSION

In conclusion, we demonstrate for the first time that inhalation of combined PDE3/4 inhibitor reverses pulmonary hypertension fully developed in response to monocrotaline in rats. This "reverse-remodeling" effect includes structural changes in the lung vascular wall and key molecular pathways of matrix regulation, concomitant with 60% normalization of hemodynamics.

Cyclic AMP induces morphological changes of vascular smooth muscle cells by inhibiting a Rac-dependent signaling pathway

Cyclic AMP (cAMP) is a pleiotropic second messenger that regulates numerous cellular processes. In vascular smooth muscle cells (VSMCs), these include cell proliferation, migration, and contractility. Here we show that cAMP-elevating agents induce dramatic morphological changes in VSMCs, characterized by cell rounding and formation of long branching processes. The stellate morphology is associated with disassembly of actin stress fibers and lamellipodia, loss of focal adhesions, and the formation of small F-actin rings. Because of the importance of Rho family GTPases in regulating actin dynamics, we analyzed their individual roles in the cAMP phenotype. We found that pharmacological or genetic inhibition of Rac mimics cAMP effect in inducing a stellate morphology of VSMCs. Expression of activated Rac1 prevents forskolin-induced cAMP stellation, suggesting that cAMP affects cell morphology by inhibiting Rac function. Consistent with this, treatment with forskolin inhibits agonist-stimulated Rac activation in VSMCs. We further show that activated Rac1 containing the F37A effector loop substitution fails to rescue the cAMP phenotype. Our results suggest that cAMP modulates the morphology of VSMCs by inhibiting a Rac-dependent signaling pathway.

Inhibition of Rac activation as a mechanism for negative regulation of actin cytoskeletal reorganization and cell motility by cAMP

cAMP has been found to play a role in mediating the negative regulation of cell motility, although its underlying molecular mechanism remains poorly understood. By using CHO (Chinese-hamster ovary) cells that express the EP2 subtype of PGE2 (prostaglandin E2) receptors, we provide evidence that an increase in cellular cAMP content leads to inhibition of cellular Rac activity, which serves as a mechanism for this negative regulation. In CHO cells expressing EP2, but not in vector control cells, PGE2 dose-dependently inhibited chemotaxis towards IGF-I (insulin-like growth factor-I), which is a Rac-dependent process, with the maximal 75% inhibition observed at 10(-8) M PGE2. EP2 stimulation failed to inhibit tyrosine phosphorylation either of IGF-I receptor or IRS-1 (insulin receptor substrate-1), or activation of phosphoinositide 3-kinase or Akt in response to IGF-I, but potently and dose-dependently inhibited IGF-I-induced activation of cellular Rac activity and membrane ruffling. However, PGE2 failed to inhibit Val12-Rac-induced membrane ruffling. Similar to the case of CHO cells, PGE2 inhibited PDGF (platelet-derived growth factor)-induced Rac activation and chemotaxis in vascular smooth muscle cells endogenously expressing EP2. The inhibitory effects of PGE2 on IGF-I-induced chemotaxis, membrane ruffling and Rac activation were faithfully reproduced by a low concentration of forskolin, which induced a comparable extent of cAMP elevation as with 10(-8) M PGE2, and were potentiated by isobutylmethylxanthine. The protein kinase A inhibitor Rp isomer of adenosine 3',5'-cyclic monophosphorothioate reduced PGE2 inhibition of Rac activation and chemotaxis. These results indicate that EP2 mediates Rac inhibition through a mechanism involving cAMP and protein kinase A, thereby inhibiting membrane ruffling and chemotaxis.

The Proinflammatory Cytokine Interleukin 1β and Hypoxia Cooperatively Induce the Expression of Adrenomedullin in Ovarian Carcinoma Cells through Hypoxia Inducible Factor 1 Activation

Adrenomedullin (ADM) is a potent hypotensive peptide produced by macrophages and endothelial cells during ischemia and sepsis. The molecular mechanisms that control ADM gene expression in tumor cells are still poorly defined. It is known, however, that hypoxia potently increases ADM expression by activation of the transcription factor complex hypoxia inducible factor 1 (HIF-1). Proinflammatory cytokines produced by tumor invading macrophages likewise activate expression of ADM. Herein, we show that apart from hypoxia, the proinflammatory cytokine interleukin 1beta (IL-1beta) induced the expression of ADM mRNA through activation of HIF-1 under normoxic conditions and enhanced the hypoxia-induced expression in the human ovarian carcinoma cell line OVCAR-3. IL-1beta significantly increased accumulation and nuclear translocation of HIF-1alpha under normoxic conditions and amplified hypoxic HIF-1 activation. IL-1beta treatment affected neither HIF-1alpha mRNA levels nor the hydroxylation status of HIF-1alpha and, thus, stability of the protein. Instead cycloheximide effectively prevented the increase in HIF-1alpha protein, indicating a stimulatory effect of IL-1beta on HIF-1alpha translation. Finally, treatment of HIF-1alpha with short interfering RNA revealed a significant role for HIF-1 in the IL-1beta-dependent stimulation of ADM expression.

Distinct signaling mechanisms for apoE inhibition of cell migration and proliferation

Over the years, the vascular protective role of apolipoprotein (apo) E has been attributed to the ability of apoE to induce cholesterol efflux from macrophage foam cells and its transport of extrahepatic cholesterol to the liver for excretion out of the body. Recently, apoE has been shown to protect against vascular disease by additional mechanisms that are independent of its cholesterol transport functions. This review summarizes data demonstrating apoE binding to specific cell surface receptors and proteoglycans in smooth muscle cells triggers distinct signalling pathways that result in inhibition of cell migration, proliferation, and excessive extracellular matrix deposition. apoE binding to the low density lipoprotein receptor-related protein is responsible for inhibition of cell migration, due to the induction of cyclic AMP accumulation and protein kinase A activation. apoE inhibition of cell proliferation is mediated by its binding to proteoglycans and the resulting activation of inducible nitric oxide synthase. apoE also inhibits excessive extracellular matrix protein synthesis. The receptor responsible for this latter apoE function remains to be identified.

The clinical relevance of adrenomedullin: a promising profile?

Adrenomedullin (AM) is a peptide that possesses potentially beneficial properties. Since the initial discovery of the peptide by Kitamura et al. in 1993, the literature has been awash with reports describing its novel mechanisms of action and huge potential as a therapeutic target. Strong evidence now exists that AM is able to act as an autocrine, paracrine, or endocrine mediator in a number of biologically significant functions, including the endothelial regulation of blood pressure, protection against organ damage in sepsis or hypoxia, and the control of blood volume through the regulation of thirst. Its early promise as a potential mediator/modulator of disease was not, however, entirely as a result of the discovery of physiological functions but due more to the observation of increasing levels measured in plasma in direct correlation with disease progression. In health, AM circulates at low picomolar concentrations in plasma in 2 forms, a mature 52-amino acid peptide and an immature 53-amino acid peptide. Plasma levels of AM have now been shown to be increased in a number of pathological states, including congestive heart failure, sepsis, essential hypertension, acute myocardial infarction, and renal impairment. These earliest associations have been further supplemented with evidence of a role for AM in other pathologies including, most intriguingly, cancer. In this review, we offer a timely review of our current knowledge on AM and give a detailed account of the putative role of AM in those clinical areas in which the best therapeutic opportunities might exist.

Effect of Adrenomedullin on Adrenergic Vasoconstriction in Mesenteric Resistance Arteries of the Rat

Adrenomedullin (AM) is a hypotensive peptide that belongs to a family of peptides structurally related to calcitonin gene-related peptide (CGRP). The present study examined the effect of AM on adrenergic nerve-mediated vasoconstriction in rat perfused mesenteric vascular beds without endothelium. Perfusion of AM at 0.1 nM but not 10 nM increased vasoconstrictor responses to periarterial nerve stimulation (PNS) (1-4 Hz), while AM at 10 nM significantly attenuated vasoconstriction induced by bolus injection of norepinephrine (NE). In preparations treated with capsaicin (a CGRP depletor), pressor responses to both PNS and NE injection were markedly attenuated by AM. Perfusion of CGRP(8-37) (a CGRP-receptor antagonist) significantly potentiated the PNS- but not the NE-induced vasoconstriction. Combined perfusion of CGRP(8-37) and AM had no effect on the PNS-induced response and antagonized the inhibitory effect of AM on the NE-induced response. AM(2-52) (an AM-receptor antagonist) did not influence the effect of AM. These findings suggest that AM facilitates adrenergic vasoconstriction by inhibiting neurotransmission of CGRP-containing nerves, which counteract adrenergic nerve-mediated vasoconstriction.

Concomitant expression of adrenomedullin and its receptor components in rat adipose tissues

Adrenomedullin (AM) expressed by and secreted from a variety of cells plays pluripotent roles in an autocrine/paracrine fashion. The present study was undertaken to explore the expression of AM and its receptor genes in adipose tissues, their changes during the development of obesity, and the process of preadipocyte differentiation. Both mature adipocytes and stromal vascular cells constituting adipose tissue expressed AM transcript. AM and its receptor component [calcitonin receptor-like receptor and receptor activity-modifying protein-2 (CRLR/RAMP2)] mRNAs were expressed in a variety of rat adipose tissues, including epididymal, mesenteric, retroperitoneal, and subcutaneous adipose tissue. AM mRNA levels in rat and human epididymal adipose tissue were about one-tenth of those in the kidney. Steady-state mRNA levels of AM and CRLR/RAMP2 in epididymal, mesenteric, and retroperitoneal adipose tissues in rats fed a high-fat diet for 4 wk were far greater than those in rats with normal diet accompanied by increased plasma AM levels, whereas steady-state AM mRNA levels conversely decreased in other organs, such as kidney and liver. AM mRNA expressed in a mouse preadipocyte cell line (3T3-L1) transiently decreased by day 3, returned to basal level by day 6, and then increased by day 9 during preadipocyte differentiation, which paralleled AM secretion from the cells. However, the addition of either exogenous AM or AM receptor antagonist calcitonin gene-related peptide-(8-37), to block endogenous AM did not affect lipid droplet accumulation during preadipocyte differentiation. The present study demonstrates for the first time that AM and its receptor component (CRLR/RAMP2) mRNAs were concomitantly expressed in various adipose tissues, whose tissue-specific upregulation was induced during the development of obesity. These data suggest that AM may act as a new member of adipokines, although its functional role, as well as its pathophysiological significance in obesity, remains to be determined.

Adrenomedullin in the treatment of pulmonary hypertension

Adrenomedullin (AM) is a potent, long-lasting pulmonary vasodilator peptide. Plasma AM level is elevated in patients with primary pulmonary hypertension (PPH), and circulating AM is partially metabolized in the lungs. These findings suggest that AM plays an important role in the regulation of pulmonary vascular tone and vascular remodeling. We have demonstrated the effects of three types of AM delivery systems: intravenous administration, inhalation, and cell-based gene transfer. Despite endogenous production of AM, intravenously administered AM at a pharmacologic level decreased pulmonary vascular resistance in patients with PPH. Inhalation of AM improved hemodynamics with pulmonary selectivity and exercise capacity in patients with PPH. Cell-based AM gene transfer ameliorated pulmonary hypertension rats. These results suggest that additional administration of AM may be effective in patients with pulmonary hypertension. AM may be a promising endogenous peptide for the treatment of pulmonary hypertension.

Increased adrenomedullin immunoreactivity and mRNA expression in coronary plaques obtained from patients with unstable angina

OBJECTIVE

To examine the expression and localisation of adrenomedullin in human coronary atherosclerotic lesions from patients with unstable angina (UAP) and stable angina (SAP), and to study the relation between adrenomedullin expression and plaque instability.

DESIGN

A retrospective observational study.

PATIENTS

Directional coronary atherectomy samples were obtained from 15 patients with UAP and 12 with SAP.

METHODS

The localisation of adrenomedullin was examined by immunohistochemistry, and adreno-medullin mRNA expression was measured by quantitative polymerase chain reaction.

RESULTS

Adrenomedullin immunoreactivity was preferentially localised in macrophages, intimal smooth muscle cells, and proliferated microvessels. The mean number of adrenomedullin positive cells in five high power fields (x 400) per specimen was higher in patients with UAP than in those with SAP (mean (SEM), 110 (13) v 76 (7); p < 0.05); and the ratio of adrenomedullin positive to total cells was higher in patients with UAP (43.0 (2.2)% v 34.2 (2.0)%; p < 0.01). More adrenomedullin mRNA was expressed in the plaque of patients with UAP than in those with SAP (60.4 (16.9)% v 9.7 (3.3)%; p < 0.01).

CONCLUSIONS

The findings suggest that adrenomedullin is involved in the development of atherosclerosis and plaque instability in human coronary arteries, in an autocrine or paracrine manner.

Plasma adrenomedullin and carotid atherosclerosis in atherothrombotic ischemic stroke

OBJECTIVE

Adrenomedullin is known to exert anti-atherosclerotic actions by inhibiting proliferation and migration of smooth muscle cells in vitro. Here we examine the relationship between the plasma concentration of adrenomedullin and ultrasonographic characteristics of carotid arteries both in ischemic stroke and in the absence of cerebrovascular disease.

METHODS

We studied 61 patients with atherothrombotic ischemic stroke in the chronic phase and 50 patients without any cerebrovascular disease. Intima-media thickness and vascular lumen diameters were evaluated by carotid ultrasonography. Plasma mature-adrenomedullin was determined by radioimmunoassay.

RESULTS

Plasma mature-adrenomedullin in the patients with atherothrombotic ischemic stroke in the chronic phase (2.01 +/- 0.58 fmol/ml) was significantly higher than that in the patients without any cerebrovascular disease (1.24 +/- 0.18 fmol/ml, P < 0.001). With multiple regression analysis, plasma mature-adrenomedullin was found to be predicted by: stroke status (atherothrombotic ischemic stroke versus no cerebrovascular disease), diabetes status (yes/no), left ventricular ejection fraction, internal carotid artery intima-media thickness, and common carotid artery pressure strain elastic modulus (R = 0.79; F5,105 = 85.39, P < 0.0001).

CONCLUSION

Plasma mature-adrenomedullin showed significantly positive associations with carotid atherosclerosis and atherothrombotic ischemic stroke, independent of systolic blood pressure.

Adrenomedullin as a sensitive marker for coronary and peripheral arterial complications in patients with atherosclerotic risks

Plasma adrenomedullin (AM) levels are elevated in various pathological states including cardiovascular and inflammatory diseases. The present study investigated whether an increased AM level is a marker of vascular complications in patients with atherosclerotic risks. In 114 patients with cardiovascular risks and/or diseases including ischemic heart disease (IHD) and peripheral arterial disease (PAD), plasma AM concentration and other inflammatory markers such as high sensitive C-reactive protein (CRP) and interleukin (IL)-6 were examined. The plasma AM level was not altered by the absence or presence of each of four major risk factors, i.e., hypertension, diabetes mellitus, hyperlipidemia, and smoking and its level was not significantly correlated with blood pressure, plasma glucose, or serum lipid levels. The patients with IHD had a significantly higher concentration of plasma AM than those without IHD. The AM level in subjects with PAD was also increased significantly compared with those without PAD. The plasma AM was strongly correlated with inflammatory parameters such as CRP and IL-6. Among AM, CRP, and IL-6, however, only AM was an independent predictor for both IHD and PAD by multiple logistic regression analysis. Our findings suggest the possibility that plasma AM is a novel sensitive marker for the presence of vascular lesions in patients with atherosclerotic risks.

Antioxidant effect of adrenomedullin on angiotensin II-induced reactive oxygen species generation in vascular smooth muscle cells

Recent adrenomedullin (AM) gene-targeting studies have proposed a novel concept that AM plays a protective role against oxidative stress in vivo. The present study was undertaken to explore the underlying molecular mechanism of the putative antioxidant action of AM against angiotensin II (Ang II)induced reactive oxygen species (ROS) generation in rat vascular smooth muscle cells (VSMCs). Intracellular ROS levels were measured by dichlorofluoroscein fluorescence. Redox-sensitive c-Jun amino-terminal kinase (JNK) and ERK1/2 activation and gene expression induced by Ang II in VSMCs were also studied. AM dose-relatedly (10(-8)-10(-7) m) inhibited intracellular ROS generation stimulated by Ang II (10(-7) m), as mimicked by dibutyl-cAMP, the effect of which was inhibited by the pretreatment with N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide hydrochloride, a protein kinase A inhibitor, and calcitonin gene-related peptide(8-37), an AM/calcitonin gene-related peptide receptor antagonist. Ang II induced JNK and ERK1/2 activation via a redox-sensitive manner, whereas AM inhibited JNK, but not ERK1/2, activation by Ang II. Furthermore, AM inhibited Ang II-induced redox-sensitive gene expression (plasminogen activator inhibitor-1 and monocyte chemoattractant protein-1) in the same manner as N-acetyl-l-cysteine, a potent antioxidant. AM also inhibited Ang II-induced up-regulation of Nox1, a critical membrane-bound component of reduced nicotinamide adenine dinucleotide phosphate oxidase in VSMCs, in the same degree as N-acetyl-l-cysteine. Our study demonstrates for the first time that AM directly inhibits intracellular ROS generation via an AM receptor-mediated and c-AMP-protein kinase A-dependent mechanism in VSMCs and that AM with its potent antioxidant action inhibits redox-sensitive JNK activation and gene expression induced by Ang II. These data suggest that AM plays a protective role as an endogenous antioxidant in Ang II-induced vascular injury.

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 C-reactive protein on atherogenic mediators and adrenomedullin in human coronary artery endothelial and smooth muscle cells

We examined the effects of recombinant human C-reactive protein (rhCRP) on atherosclerosis-related factors in cultured human coronary artery endothelial and smooth muscle cells (HCAECs and HCASMCs). After removing endotoxin from commercial rhCRP preparations using the appropriate column, the purified (P)-rhCRP retained the ability to Ca(2+)-dependently bind to phosphorylcholine, but did not augment the secretion of interleukin-6 and MCP-1 from HCAECs, as non-purified (NP)-rhCRP did. By contrast, P-rhCRP elicited 2- to 3-fold increases in the secretion of both hormones from HCASMCs, though the effect was smaller than that obtained with NP-rhCRP. Production of PAI-1 and endothelin-1 was little affected by either rhCRP preparation in either cell type. In addition, P-rhCRP dose-dependently diminished adrenomedullin release from both cell types, but did not affect adrenomedullin receptor expression or function. Our findings highlight the importance of removing endotoxin from commercial rCRP preparations and show that hCRP elicits atherogenic responses from HCASMCs, but not HCAECs.

Significance of recently identified peptides in hypertension: endothelin, natriuretic peptides, adrenomedullin, leptin

Arterial hypertension is one of the major risk factors in cardiovascular and renal disease. Advances in the study of pathophysiologic mechanisms and the relationship between several regulatory systems provide the basis for development of more selective therapeutic strategies. The increasing understanding of the role played by ETs, natriuretic peptides, AM, and leptin opens new frontiers in the care of hypertension and its complications, coronary artery disease and heart failure and other forms of cardiovascular disease.

Repeated inhalation of adrenomedullin ameliorates pulmonary hypertension and survival in monocrotaline rats

Adrenomedullin (AM) is a potent vasodilator peptide. We investigated whether inhalation of aerosolized AM ameliorates monocrotaline (MCT)-induced pulmonary hypertension in rats. Male Wistar rats given MCT (MCT rats) were assigned to receive repeated inhalation of AM ( n = 8) or 0.9% saline ( n = 8). AM (5 μg/kg) or saline was inhaled as an aerosol using an ultrasonic nebulizer for 30 min four times a day. After 3 wk of inhalation therapy, mean pulmonary arterial pressure and total pulmonary resistance were markedly lower in rats treated with AM than in those given saline [mean pulmonary arterial pressure: 22 ± 2 vs. 35 ± 1 mmHg (–37%); total pulmonary resistance: 0.048 ± 0.004 vs. 0.104 ± 0.006 mmHg · ml–1 · min–1 · kg–1 (–54%), both P < 0.01]. Neither systemic arterial pressure nor heart rate was altered. Inhalation of AM significantly attenuated the increase in medial wall thickness of peripheral pulmonary arteries in MCT rats. Kaplan-Meier survival curves demonstrated that MCT rats treated with aerosolized AM had a significantly higher survival rate than those given saline (70% vs. 10% 6-wk survival, log-rank test, P < 0.01). In conclusion, repeated inhalation of AM inhibited MCT-induced pulmonary hypertension without systemic hypotension and thereby improved survival in MCT rats.

Angiogenic role of adrenomedullin through activation of Akt, mitogen-activated protein kinase, and focal adhesion kinase in endothelial cells

Adrenomedullin (AM) is a multifunctional peptide in human pheochromocytoma. To evaluate whether AM could be an angiogenic factor, we examined its effect on kinases and angiogenic processes. AM induced tyrosine phosphorylation of Akt and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase1/2 (ERK1/2) by using distinct signaling pathways in human umbilical vein endothelial cells (HUVECs). AM also phosphorylated focal adhesion kinase, and phosphatidylinositol 3'-kinase inhibitor inhibited AM-induced focal adhesion kinase phosphorylation. Pretreatment with high concentrations of AM22-52, a putative AM receptor antagonist, partially suppressed AM-induced phosphorylation of Akt, ERK1/2, and focal adhesion kinase. AM and vascular endothelial growth factor produced increases in DNA synthesis and migration in HUVECs. AM induced tube formation in HUVECs, and its effect was inhibited by pretreatment with phosphatidylinositol 3'-kinase inhibitor or ERK1/2 inhibitor. AM induced sprouting in porcine pulmonary arterial endothelial cells and promoted neovessel formation in a mouse Matrigel plug assay. Inhibitors of phosphatidylinositol 3'-kinase and ERK1/2 inhibited AM-induced endothelial sprouting in vitro and angiogenesis in vivo. AM exerts angiogenic activity through activation of Akt, MAPK, and focal adhesion kinase in endothelial cells.

Apolipoprotein E binding to low density lipoprotein receptor-related protein-1 inhibits cell migration via activation of cAMP-dependent protein kinase A

Smooth muscle cell migration and proliferation contribute to neointimal hyperplasia and vascular stenosis after endothelial denudation. Previous studies revealed that apolipoprotein E (apoE) is an effective inhibitor of platelet-derived growth factor-directed smooth muscle cell migration and proliferation and that the anti-migratory function is mediated via apoE binding to low density lipoprotein receptor-related protein-1 (LRP-1). This study was undertaken to identify the intracellular pathway by which apoE binding to LRP-1 results in inhibition of smooth muscle cell migration. The results showed that apoE increased intracellular cAMP levels 3-fold after 5 min, and the increase was sustained for more than 1 h. As a consequence, apoE also increased protein kinase A (PKA) activity in smooth muscle cells. Importantly, suppression of PKA activity with a cell-permeable peptide inhibitor of PKA abolished the inhibitory effect of apoE on smooth muscle cell migration. These results indicated that apoE inhibition of smooth muscle cell migration is mediated via the activation of cAMP-dependent PKA. Additional experiments revealed that apoE also inhibited fibroblasts migration toward platelet-derived growth factor by a similar mechanism of cAMP-dependent PKA activation. It is noteworthy that apoE failed to increase cAMP levels or inhibit migration of LRP-1-negative mouse embryonic fibroblasts and LRP-1-deficient smooth muscle cells. Taken together, these findings established the mechanism by which apoE inhibits cell migration, i.e. via cAMP-dependent protein kinase A activation as a consequence of its binding to LRP-1.

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.

Lessons from the adrenomedullin knockout mouse

Because vasolidator peptide adrenomedullin (AM) exhibits complicated action, we developed AM knockout mice in order to elucidate the physiological and pathophysiological role of AM. The AM(-/-) mice were embryonic lethal, so we could not evaluate directly the role of AM in this mutant mice. Thus, we loaded angiotensin II (AngII) and salt in AM(+/-) mice, which were viable and fertile. As a result, AngII and salt loading caused coronary vascular damage and left ventricular hypertrophy in AM(+/-) mice more greatly than AM(+/+) mice. Moreover, cuff placement of femoral artery stimulated intimal thickening more severely. This treatment increased local AM levels in AM(+/+) mice but not in AM(+/-) mice. The accelerated organ damage in AM(+/-) mice was accompanied with enhanced production of oxidative stress. Thus, our data suggest that intrinsic AM play a vascular protective role.