Adrenomedullin and the microvasculature

Quantitative proteomics reveals CLR interactome in primary human cells

The G protein-coupled receptor (GPCR) calcitonin receptor-like receptor (CLR) mediates essential functions in several cell types and is implicated in cardiovascular pathologies, skin diseases, migraine, and cancer. To date, the network of proteins interacting with CLR ("CLR interactome") in primary cells, where this GPCR is expressed at endogenous (physiologically relevant) levels, remains unknown. To address this knowledge gap, we established a novel integrative methodological workflow/approach for conducting a comprehensive/proteome-wide analysis of Homo sapiens CLR interactome. We used primary human dermal lymphatic endothelial cells and combined immunoprecipitation utilizing anti-human CLR antibody with label-free quantitative nano LC-MS/MS and quantitative in situ proximity ligation assay. By using this workflow, we identified 37 proteins interacting with endogenously expressed CLR amongst 4902 detected members of the cellular proteome (by quantitative nano LC-MS/MS) and revealed direct interactions of two kinases and two transporters with this GPCR (by in situ proximity ligation assay). All identified interactors have not been previously reported as members of CLR interactome. Our approach and findings uncover the hitherto unrecognized compositional complexity of the interactome of endogenously expressed CLR and contribute to fundamental understanding of the biology of this GPCR. Collectively, our study provides a first-of-its-kind integrative methodological approach and datasets as valuable resources and robust platform/springboard for advancing the discovery and comprehensive characterization of physiologically relevant CLR interactome at a proteome-wide level in a range of cell types and diseases in future studies.

Endometrial Angiogenesis of Abnormal Uterine Bleeding and Infertility in Patients with Uterine Fibroids-A Systematic Review

Uterine fibroids are the most common benign tumors in women, with abnormal uterine bleeding (AUB) as the main reported symptom. Additionally, an association between fibroids and infertility has been established, especially if the fibroid protrudes in the uterine cavity. Hormonal therapy is associated with side-effects and as well as hysterectomy, which is incompatible with a desire to conceive. To improve treatment, it is essential to unravel the etiology of fibroid-related symptoms. We aim to evaluate endometrial angiogenesis in women with fibroids, with and without AUB, and the influence of pharmaceutical therapies in these patients. Furthermore, we explore the possible role of altered angiogenesis in patients with fibroids and infertility. We performed a systematic review according to PRISMA-guidelines (PROSPERO: CRD42020169061), and included 15 eligible studies. Endometrial expression of vascular endothelial growth factor (VEGF) and adrenomedullin was increased in patients with fibroids. This suggests aberrant angiogenesis, potentially involving disturbed vessel maturation, resulting in immature and fragile vessels. Treatment with gonadotropin-releasing hormone agonist, ulipristal acetate, and continuous oral contraception pills reduced several angiogenic parameters, including VEGF. If infertile and fertile patients with fibroids were compared, a significant decreased expression of the bone morphogenetic protein/Smad-protein pathway was found, possibly caused by the increased expression of transforming growth factor-beta. For future therapeutic development, these different angiogenic pathways could be of interest as possible targets to treat fibroid-related symptoms.

Melatonin: Manager of psychosomatic and metabolic disorders in polymorbid cardiovascular pathology

Objectives

To investigate the relationship between changes in circadian patterns of melatonin and clinical manifestations of polymorbid cardiovascular pathology (PCVP) in young men and to analyze the effectiveness of their complex treatment.

Materials and methods

We made the immunohistochemical (IHC) analysis of epiphysis tissues from autopsies of 25 men aged 32–44 with PCVP and metabolic syndrome (MS) who had died as a result of ischemic cardiomyopathy (IC) and 25 persons after the car accident as a control group. Then, 93 young men aged 35–44 with PCVP, metabolic syndrome, and depressive spectrum disorders (DSD) were divided into three groups: (1) standard therapy; (2) standard therapy and psychotherapy sessions; (3) standard therapy in combination with psychotherapeutic and psychophysiological visual and auditory correction sessions. The control group included 24 conditionally healthy male volunteers. Before and after the treatment, we studied the anthropometric status, lipid and carbohydrate metabolism indicators, the level of urinary 6-hydroxymelatonin sulfate, the degree of nocturnal decrease in blood pressure (BP), and the relationship of these indicators with circadian variations of melatonin excretion.

Results

Young polymorbid patients who died from IC have a lower expression of melatonin type 1 and 2 receptors. All patients with PCVP showed a decrease in the nocturnal melatonin excretion fraction and a correlation with higher severity of depressive (r = −0.72) and anxiety (r = −0.66) symptoms. Reduced values of the 6-hydroxymelatonin sulfate (6-SM) in the 1st (r = 0.45), 2nd (r = 0.39), and 3rd (r = 0.51) groups before treatment was associated with periods of increased BP. The achievement of melatonin excretion reference values and normalization of biochemical parameters of carbohydrate and lipid metabolism, daily BP profile, and psychophysiological state were noted in all three patients’ groups, with a more pronounced effect in group 3.

Conclusion

Low nocturnal melatonin excretion levels are associated with greater severity of clinical symptoms and a higher risk of death in patients with PCVP. Therefore, comprehensive therapy may be more effective for correcting this disease.

Obesity and Circadian Cycle of Sleep and Wakefulness: Common Points and Prospects of Therapy

The prevalence of obesity in recent years has assumed the character of a non-communicable epidemic. Wherein, the standard approaches for its treatment are not always successful. Meanwhile, obesity remains one of the main causes of the formation of a number of some serious diseases, such as cardiovascular, diabetes, cancer, etc. and death from them. In search of alternative and more adequate methods of obesity treatment and preventing its complications, recent studies are aimed at further identifying new associations and revealing the pathophysiological mechanisms underlying excessive weight gain. It should be noted an increasing amount of chronobiological studies that raised awareness of the key role of the body’s circadian rhythms and its main regulator, melatonin, responsible for the temporary organization of the main physiological (including metabolism) processes throughout the 24-h day, in the development and progression of obesity. This review is devoted to the consideration of mutually directed interactions between the circadian system and metabolism; attempts have been made to explain the role of sleep-wake cycle disruptions in the excess accumulation of adipose tissue and the formation of obesity and its comorbidities, as well as detailed therapeutic principles based on normalizing disruption of body clocks using time-coordinated approaches to food intake, physical activity, the effects of non-drug methods and pharmacological substances (chronobiotics), which represents a novel and promising ways to prevent or treat obesity and associated diseases.

Adrenomedullin haploinsufficiency predisposes to secondary lymphedema

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

Plasma adrenomedullin level in Egyptian children and adolescents with type 1 diabetes mellitus: relationship to microvascular complications

BACKGROUND

Adrenomedullin (AM) is known to be elevated in different clinical situations including diabetes mellitus (DM), but its potential role in the pathogenesis of vascular complications in diabetic children and adolescents is to be clarified. Hence, the study aimed at assessment of plasma adrenomedullin levels in children and adolescents with type 1 DM and correlation of these levels with metabolic control and diabetic microvascular complications (MVC).

METHODS

The study was performed in the Diabetes Specialized Clinic, Children's Hospital of Ain Shams University in Cairo, Egypt. It included 55 diabetic children and adolescents (mean age 13.93 +/- 3.15 years) who were subdivided into 40 with no MVC and 15 with MVC. Thirty healthy subjects, age-and sex-matched, were included as control group (mean age 12.83 +/- 2.82 years). Patients and controls were assessed for glycosylated hemoglobin (HbA1c) and plasma adrenomedullin assay using ELISA technique.

RESULTS

Mean plasma AM levels were significantly increased in patients with and without MVC compared to control group, (110.6 pg/mL, 60.25 pg/mL and 39.2 pg/mL respectively) (P < 0.01) with higher levels in those with MVC (P < 0.05). Plasma AM levels were positively correlated with both duration of diabetes (rho = 0.703, P < 0.001) and glycemic control (HbA1c) (rho = 0.453, P < 0.001).

CONCLUSION

Higher plasma AM levels in diabetics particularly in those with MVC & its correlation with diabetes duration and metabolic control may reflect the role of AM in diabetic vasculopathy in the pediatric age group.

Angiogenesis therapies for cardiovascular disease

PURPOSE OF REVIEW

The purpose was to summarize the findings of the proangiogenic clinical trials using protein and gene therapy, with analysis of the problems and an interpretation of the results.

RECENT FINDINGS

Recent findings include several new large clinical trials, using both gene and protein therapies. There has been development of new basic science concepts, especially with regard to endothelial activation and stabilization of newly formed microvessels. This review provides a critical analysis of the most recent clinical trials, both in efforts to understand the pitfalls of earlier clinical trials, and also to focus on requirements for future studies.

SUMMARY

This article reviews many of the clinical trials utilizing proangiogenic therapy, assesses the pitfalls seen within the current trials, and discusses the conclusions drawn and the future of angiogenesis therapy.

Nonclassic endogenous novel [corrected] regulators of angiogenesis

Angiogenesis, the process through which new blood vessels arise from preexisting ones, is regulated by several "classic" factors, among which the most studied are vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2). In recent years, investigations showed that, in addition to the classic factors, numerous endogenous peptides play a relevant regulatory role in angiogenesis. Such regulatory peptides, each of which exerts well-known specific biological activities, are present, along with their receptors, in the blood vessels and may take part in the control of the "angiogenic switch." An in vivo and in vitro proangiogenic effect has been demonstrated for erythropoietin, angiotensin II (ANG-II), endothelins (ETs), adrenomedullin (AM), proadrenomedullin N-terminal 20 peptide (PAMP), urotensin-II, leptin, adiponectin, resistin, neuropeptide-Y, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and substance P. There is evidence that the angiogenic action of some of these peptides is at least partly mediated by their stimulating effect on VEGF (ANG-II, ETs, PAMP, resistin, VIP and PACAP) and/or FGF-2 systems (PAMP and leptin). AM raises the expression of VEGF in endothelial cells, but VEGF blockade does not affect the proangiogenic action of AM. Other endogenous peptides have been reported to exert an in vivo and in vitro antiangiogenic action. These include somatostatin and natriuretic peptides, which suppress the VEGF system, and ghrelin, that antagonizes FGF-2 effects. Investigations on "nonclassic" regulators of angiogenesis could open new perspectives in the therapy of diseases coupled to dysregulation of angiogenesis.

Vasodilator effects of adrenomedullin on retinal arterioles in streptozotocin-induced diabetic rats

PURPOSE

The aim of this study was to examine whether diabetes changes the in vivo effects of adrenomedullin (ADM) on diameter of retinal arteriole and blood pressure in rats.

METHODS

Male Wistar rats were treated with streptozotocin (65 mg/kg, intravenously [i.v.]) and experiments were performed 6-8 weeks later. Under artificial ventilation, rats were injected with tetrodotoxin (50 microg/kg, i.v.) to eliminate any nerve activity and prevent movement of the eye. A mixture solution of norepinephrine and epinephrine (1:9) was used to maintain adequate systemic circulation. Diameters of retinal vessels were measured from the fundus images and were captured by a digital camera that was equipped with a special objective lens.

RESULTS

ADM dose-dependently increased diameters of retinal arterioles and decreased blood pressure in streptozotocin-induced diabetic rats and the age-matched controls. The depressor responses, but not vasodilator responses of retinal arterioles, to ADM were reduced in diabetic rats.

CONCLUSIONS

These results suggest that mechanism(s) of ADM-induced vasodilation of retinal arterioles is preserved in diabetes, even when depressor effects of ADM are impaired. ADM may play a role as a regulatory mechanism of retinal circulation in nondiabetic and diabetic conditions.

Adrenomedullin and tumour angiogenesis

The angiogenic activity of peptide adrenomedullin (AM) was first shown in 1998 . Since then, a number of reports have confirmed the ability of AM to induce the growth and migration of isolated vascular endothelial and smooth muscle cells in vitro and to promote angiogenesis in xenografted tumours in vivo. In addition, knockout murine models point to an essential role for AM in embryonic vasculogenesis and ischaemic revascularisation. AM expression is upregulated by hypoxia (a typical feature of solid tumours) and a potential role as a regulator of carcinogenesis and tumour progression has been proposed based on studies in vitro and in animal models. Nevertheless, translational research on AM, and in particular, confirmation of its importance in the vascularisation of human tumours has lagged behind. In this commentary, we review current progress and potential directions for future research into the role of AM in tumour angiogenesis.

Comparison of hypoxia transcriptome in vitro with in vivo gene expression in human bladder cancer

Hypoxia-inducible genes have been linked to the aggressive phenotype of cancer. However, nearly all work on hypoxia-regulated genes has been conducted in vitro on cell lines. We investigated the hypoxia transcriptome in primary human bladder cancer using cDNA microarrays to compare genes induced by hypoxia in vitro in bladder cancer cell line EJ28 with genes upregulated in 39 bladder tumour specimens (27 superficial and 12 invasive). We correlated array mRNA fold changes with carbonic anhydrase 9 (CA IX) staining of tumours as a surrogate marker of hypoxia. Of 6000 genes, 32 were hypoxia inducible in vitro more than two-fold, five of which were novel, including lactate transporter SLC16A3 and RNAse 4. Eight of 32 hypoxia-inducible genes in vitro were also upregulated on the vivo array. Vascular endothelial growth factor mRNA was upregulated two-fold by hypoxia and 2–18-fold in 31 out of 39 tumours. Glucose transporter 1 was also upregulated on both arrays mRNA, and fold changes on the in vivo array significantly correlated with CA IX staining of tumours (P=0.008). However, insulin-like growth factor binding protein 3 mRNA was the most strongly differentially expressed gene in both arrays and this confirmed its upregulation in urine of bladder cancer patients (n=157, P<0.01). This study defines genes suitable for an in vivo hypoxia ‘profile’, shows the heterogeneity of the hypoxia response and describes new hypoxia-regulated genes.

The role of adrenomedullin in angiogenesis

Adrenomedullin (AM) is a 52 amino acid peptide originally isolated from human pheochromocytoma. It was initially demonstrated to have profound effects in vascular cell biology, since AM protects endothelial cells from apoptosis, promotes angiogenesis and affects vascular tone and permeability. This review article summarizes the literature data concerning the relationship between AM and angiogenesis and describes the relationship between vascular endothelial growth factor, hypoxia and AM and tumor angiogenesis. Finally, the role of AM as a potential target of antiangiogenic therapy is discussed.

Adrenomedullin reduces Staphylococcus aureus alpha-toxin-induced rat ileum microcirculatory damage

OBJECTIVE

Increased microvascular permeability and perfusion mismatch are hallmarks of sepsis or septic shock. The intestinal mucosa is very sensitive to tissue hypoxia. Intestinal mucosa dysfunction may allow translocation of bacteria and their products, thereby perpetuating sepsis and inflammation. Staphylococcus aureus alpha-toxin is a major pathogenicity determinant of this bacterium, provoking cardiovascular collapse. Current evidence suggests that the endogenous peptide adrenomedullin stabilizes circulatory homeostasis in systemic inflammatory response. Using alpha-toxin as a well-defined strong initiator of an inflammatory reaction, we tested the hypothesis that exogenously applied adrenomedullin stabilizes gut microcirculation.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Isolated, perfused ileum from male Sprague-Dawley rats and human umbilical vein endothelial cells.

INTERVENTIONS

Administration of S. aureus alpha-toxin before or after infusion of adrenomedullin.

MEASUREMENTS AND MAIN RESULTS

Injection of a bolus of 1 microg of alpha-toxin in the superior mesenteric artery in a constant-flow, blood-perfused preparation of rat ileum increased perfusion pressure and relative hemoglobin concentration and decreased mucosal hemoglobin oxygen saturation. Continuous infusion of adrenomedullin (0.1 micromol/L) significantly reduced these alpha-toxin-related effects. Severe microvascular hyperpermeability observed in alpha-toxin-exposed ileum was abolished by adrenomedullin pretreatment. In addition, adrenomedullin blocked alpha-toxin-induced endothelial myosin light chain phosphorylation, endothelial cell contraction, and subsequent loss of endothelial barrier function in vitro. Treatment of alpha-toxin (infusion of 0.05 microg/mL)-exposed ileum with adrenomedullin (0.1 micromol/L) started 10 mins after onset of toxin application also significantly reduced superior mesenteric artery pressure and permeability increase.

CONCLUSIONS

In summary, these data suggest that exogenous adrenomedullin protects ileum by reducing alpha-toxin-induced microcirculatory disturbances and by stabilizing endothelial barrier function.

Tissue and plasma expression of the angiogenic peptide adrenomedullin in breast cancer

Adrenomedullin (ADM) is an angiogenic factor that has also been shown to be a mitogen and a hypoxia survival factor for tumour cells. These properties point to ADM as a potential promoter of human malignancies, but little data are available concerning the expression of ADM in human breast cancer. In the present work, we have examined ADM peptide expression in a series of malignant breast tumours by immunohistochemistry using a newly developed anti-ADM monoclonal antibody. In addition, ADM plasma concentrations in breast cancer patients and healthy controls were determined by radioimmunoassay. Of the examined breast cancer samples, 27/33 (82%) showed a moderate to strong staining intensity. ADM-peptide expression in breast tumours was significantly correlated with axillary lymph node metastasis (P=0.030). Analysis of ADM plasma concentrations showed no significant difference between the circulating ADM levels of breast cancer patients and healthy controls. However, a significant positive correlation was found between tumour size and plasma ADM levels (r=0.641, P=0.017). Moreover, ADM levels in breast cancer patients correlated with the presence of lymph node metastasis (P=0.002). In conclusion, we have shown for the first time that ADM peptide is widely expressed in breast cancer and that the degree of expression is associated with lymph node metastasis. ADM peptide in plasma of breast cancer patients reflects the size of the primary tumour, but is unlikely to be a useful tumour marker for the detection of breast cancer. Plasma ADM might represent an independent predictor of lymph node metastasis. The clinical implications of these findings remain to be evaluated.

Relationship between the Contents of Adrenomedullin and Distributions of Neutral Endopeptidase in Blood and Tissues of Spontaneously Hypertensive Rats

Adrenomedullin (ADM) is a multifunctional peptide with important roles in the cardiovascular system, especially in the adjustment of cardiovascular and renal homeostasis. ADM is present in plasma, organs and tissues, and its activity increases during hypertension. It remains unknown whether the clearance of this peptide is altered during hypertension. Neutral endopeptidase (NEP) is the major enzyme in ADM's degradation. We observed the activity and distribution of NEP and the expression of its mRNA in the plasma, cardiac ventricle, aorta, jejunum and kidney of spontaneously hypertensive rats (SHRs) in order to study the possible role of NEP in elevating tissue ADM concentrations during hypertension. ADM and NEP were diffuse in all tissues studied. The level of tissue ADM was generally higher in SHR tissues than in control tissues, except in the renal medulla, and its mRNA expression was higher in all tissues. Plasma NEP activity, general NEP activity and the expression of NEP mRNA in the left ventricle, aorta and jejunum in SHRs was lower than that of controls, and the level of ADM was inversely correlated with NEP activity. NEP activity and mRNA and protein expression in SHR kidneys were higher than in control kidneys; moreover, the ADM content was positively correlated with NEP activity in the renal cortex. NEP activity in the lung of SHRs did not differ from that of controls. Thus, in SHRs, the local concentration and action of ADM in the tissues may be differentially regulated by NEP.

CL/RAMP2 and CL/RAMP3 produce pharmacologically distinct adrenomedullin receptors: a comparison of effects of adrenomedullin22-52, CGRP8-37 and BIBN4096BS

Adrenomedullin (AM) has two known receptors formed by the calcitonin receptor-like receptor (CL) and receptor activity-modifying protein (RAMP) 2 or 3: we report the effects of the antagonist fragments of human AM and CGRP (AM22-52 and CGRP8-37) in inhibiting AM at human (h), rat (r) and mixed species CL/RAMP2 and CL/RAMP3 receptors transiently expressed in Cos 7 cells or endogenously expressed as rCL/rRAMP2 complexes by Rat 2 and L6 cells. AM22-52 (10 microM) antagonised AM at all CL/RAMP2 complexes (apparent pA2 values: 7.34+/-0.14 (hCL/hRAMP2), 7.28+/-0.06 (Rat 2), 7.00+/-0.05 (L6), 6.25+/-0.17 (rCL/hRAMP2)). CGRP8-37 (10 microM) resembled AM22-52 except on the rCL/hRAMP2 complex, where it did not antagonise AM (apparent pA2 values: 7.04+/-0.13 (hCL/hRAMP2), 6.72+/-0.06 (Rat2), 7.03+/-0.12 (L6)). On CL/RAMP3 receptors, 10 microM CGRP8-37 was an effective antagonist at all combinations (apparent pA2 values: 6.96+/-0.08 (hCL/hRAMP3), 6.18+/-0.18 (rCL/rRAMP3), 6.48+/-0.20 (rCL/hRAMP3)). However, 10 microM AM22-52 only antagonised AM at the hCL/hRAMP3 receptor (apparent pA2 6.73+/-0.14). BIBN4096BS (10 microM) did not antagonise AM at any of the receptors. Where investigated (all-rat and rat/human combinations), the agonist potency order on the CL/RAMP3 receptor was AM approximately betaCGRP>alphaCGRP. rRAMP3 showed three apparent polymorphisms, none of which altered its coding sequence. This study shows that on CL/RAMP complexes, AM22-52 has significant selectivity for the CL/RAMP2 combination over the CL/RAMP3 combination. On the mixed species receptor, CGRP8-37 showed the opposite selectivity. Thus, depending on the species, it is possible to discriminate pharmacologically between CL/RAMP2 and CL/RAMP3 AM receptors.

Vinblastine inhibits the angiogenic response induced by adrenomedullin in vitro and in vivo

Adrenomedullin (ADM) is protumorigenic by stimulating tumor cell growth and angiogenesis. In this context, ADM is identified as a novel target for antiangiogenic therapy. In this study, we addressed the possibility that vinblastine (VBL), as demonstrated in other experimental conditions, may act as an angiostatic molecule in the angiogenic response induced by ADM in two assays, such as Matrigel tube formation in vitro and angiogenesis in the chick embryo chorioallantoic membrane (CAM) in vivo. When tested on Matrigel, ADM caused a morphogenetic effect. In fact, endothelial cells spread and aligned with each other to form branching anastomosing tubes with multicentric junctions that gave rise to a meshwork of capillary-like structures. When ADM was administered in the presence of VBL, the capillary-like tubes were interrupted, most cells were spherical, either isolated or aggregated in small clumps. In the CAM assay, ADM induced a strong angiogenic response, which was counteracted by the treatment with VBL. Overall, these observations implicate ADM as a promoter of tumor growth and a possible target for anticancer strategies, such as the use of VBL at very low, nontoxic doses. Nevertheless, the antiangiogenic activity of low-dose VBL deserves further investigation, alone or together with other antiangiogenic agents for the treatment of tumors characterized by enhanced angiogenesis.

Secretory and vascular effects of adrenomedullin in gastric ulcer: role of CGRP- and adrenomedullin-receptors

Adrenomedullin prevents damage of gastric mucosa in either reserpine-treated or pylorus-ligated rats. Pre-treatment with CGRP(8-37) resulted in a decrease of the gastro-protective effect of adrenomedullin in both models and reversed the inhibitory effect of adrenomedullin on gastric acid output in the pylorus-ligated rats. These adrenomedullin actions were less effectively modified by pre-treatment with adrenomedullin(22-52). These data suggest that the anti-ulcer effect of adrenomedullin is mainly related to its anti-secretory action, presumably mediated through CGRP-receptors.

Transcriptional regulation of the CRLR gene in human microvascular endothelial cells by hypoxia

Adrenomedullin is a 52 amino acid peptide that shows a remarkable range of effects on the vasculature that include inter alia, vasodilatation, regulation of permeability, inhibition of endothelial cell apoptosis, and promotion of angiogenesis. Recently the G-protein coupled receptor (GPCR) calcitonin receptor-like receptor (CRLR), and receptor activity modifying proteins (RAMPs) have become recognized as integral components of the adrenomedullin signaling system. However, mechanisms of regulation of CRLR expression are still largely unknown. This is in part due to lack of information on the gene promoter. In this study we have determined the transcriptional start of human CRLR cDNA by 5'-RACE and cloned the proximal 5'-flanking region of the gene by PCR. The 2318 bp genomic fragment contains the basal promoter of human CRLR, including potential TATA-boxes and several GC boxes. Regulatory elements binding known transcription factors, such as Sp-1, Pit-1, glucocorticoid receptor, and hypoxia-inducible factor-1 alpha (HIF-1alpha) were also identified. When cloned into reporter gene vectors, the genomic fragment showed significant promoter activity, indicating that the 5'-flanking region isolated by PCR contains the gene promoter of human CRLR. Of significance is that the cloned promoter fragments were activated by hypoxia when transfected in primary microvascular endothelial cells. Site-directed mutagenesis of the consensus hypoxia-response element (HRE) in the 5'-flanking region abolished such a response. We also demonstrated by semi-quantitative RT-PCR that transcription of the gene is activated by hypoxia in microvascular endothelial cells. In contrast, expression of RAMPs 1, 2, and 3 was unaffected by low oxygen tension. We conclude that simultaneous transcriptional up-regulation of CRLR and its ligand adrenomedullin in endothelial cells could lead to a potent survival loop and therefore might play a significant role in vascular responses to hypoxia and ischemia.

Regulation of pancreatic physiology by adrenomedullin and its binding protein

Adrenomedullin (AM) is a 52 amino acid, multifunctional hormone. It is expressed in many tissues of the human body including the pancreas, where it is mainly localized to the periphery of the islets of Langerhans and specifically to the pancreatic polypeptide-expressing cells. The AM receptor, a complex formed by calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMPs), and the recently discovered AM-binding protein, complement factor H (fH), are expressed in the insulin-producing beta-cells. The colocalization of these key elements of the AM system in the endocrine portion of the pancreas implicates AM in the control of both normal and altered pancreatic physiologies. AM inhibits insulin secretion both in vitro (isolated rat islets) and in vivo (oral glucose tolerance test in rats) in a dose-dependent manner. The addition of fH to isolated rat islets produces a further reduction of insulin secretion in the presence of AM. Furthermore, AM is elevated in plasma from patients with pancreatic dysfunctions such as type 1 or type 2 diabetes and insulinoma. Using a diabetic model in rats, we have shown that AM increases circulating glucose levels whereas a blocking monoclonal antibody against AM has the opposite effect and improves postprandial recovery. Such experimental evidence implicates AM as a fundamental factor in maintaining insulin homeostasis and normoglycemia, and suggests the implication of AM as a possible causal agent in diabetes. Further investigation focused on the development of blocking agents for AM could result in new treatments for pancreatic AM-related disorders.

Adrenomedullin reduces endothelial hyperpermeability

Endothelial hyperpermeability induced by inflammatory mediators is a hallmark of sepsis and adult respiratory distress syndrome. Increased levels of the regulatory peptide adrenomedullin (ADM) have been found in patients with systemic inflammatory response. We analyzed the effect of ADM on the permeability of cultured human umbilical vein endothelial cell (HUVEC) and porcine pulmonary artery endothelial cell monolayers. ADM dose-dependently reduced endothelial hyperpermeability induced by hydrogen peroxide (H2O2), thrombin, and Escherichia coli hemolysin. Moreover, ADM pretreatment blocked H2O2-related edema formation in isolated perfused rabbit lungs and increased cAMP levels in lung perfusate. ADM bound specifically to HUVECs and porcine pulmonary artery endothelial cells and increased cellular cAMP levels. Simultaneous inhibition of cAMP-degrading phosphodiesterase isoenzymes 3 and 4 potentiated ADM-dependent cAMP accumulation and synergistically enhanced ADM-dependent reduction of thrombin-induced hyperpermeability. However, ADM showed no effect on endothelial cGMP content, basal intracellular Ca2+ levels, or the H2O2-stimulated, thrombin-stimulated, or Escherichia coli hemolysin-stimulated Ca2+ increase. ADM diminished thrombin- and H2O2-related myosin light chain phosphorylation as well as stimulus-dependent stress fiber formation and gap formation in HUVECs, suggesting that ADM may stabilize the barrier function by cAMP-dependent relaxation of the microfilament system. These findings identify a new function of ADM and point to ADM as a potential interventional agent for the reduction of vascular leakage in sepsis and adult respiratory distress syndrome.