Adrenomedullin stimulates nitric oxide release from SK-N-SH human neuroblastoma cells by modulating intracellular calcium mobilization

Immunomodulatory Role of Neuropeptides in the Cornea

The transparency of the cornea along with its dense sensory innervation and resident leukocyte populations make it an ideal tissue to study interactions between the nervous and immune systems. The cornea is the most densely innervated tissue of the body and possesses both immune and vascular privilege, in part due to its unique repertoire of resident immune cells. Corneal nerves produce various neuropeptides that have a wide range of functions on immune cells. As research in this area expands, further insights are made into the role of neuropeptides and their immunomodulatory functions in the healthy and diseased cornea. Much remains to be known regarding the details of neuropeptide signaling and how it contributes to pathophysiology, which is likely due to complex interactions among neuropeptides, receptor isoform-specific signaling events, and the inflammatory microenvironment in disease. However, progress in this area has led to an increase in studies that have begun modulating neuropeptide activity for the treatment of corneal diseases with promising results, necessitating the need for a comprehensive review of the literature. This review focuses on the role of neuropeptides in maintaining the homeostasis of the ocular surface, alterations in disease settings, and the possible therapeutic potential of targeting these systems.

Adrenomedullin, a Novel Target for Neurodegenerative Diseases

Neurodegenerative diseases represent a heterogeneous group of disorders whose common characteristic is the progressive degeneration of neuronal structure and function. Although much knowledge has been accumulated on the pathophysiology of neurodegenerative diseases over the years, more efforts are needed to understand the processes that underlie these diseases and hence to propose new treatments. Adrenomedullin (AM) is a multifunctional peptide involved in vasodilation, hormone secretion, antimicrobial defense, cellular growth, and angiogenesis. In neurons, AM and related peptides are associated with some structural and functional cytoskeletal proteins that interfere with microtubule dynamics. Furthermore, AM may intervene in neuronal dysfunction through other mechanisms such as immune and inflammatory response, apoptosis, or calcium dyshomeostasis. Alterations in AM expression have been described in neurodegenerative processes such as Alzheimer's disease or vascular dementia. This review addresses the current state of knowledge on AM and its possible implication in neurodegenerative diseases.

Extracellular elevation of adrenomedullin, a gene associated with schizophrenia, suppresses heat shock protein 1A/1B mRNA

Several recent gene expression studies on schizophrenia, including one using monozygotic twins discordant for the disease, have reported the upregulation of adrenomedullin (ADM), which was initially identified as a vasodilator hormone. It has been hypothesized that upregulation of ADM may be a susceptibility factor for schizophrenia, although the exact role of ADM in the central nervous system remains unclear. In this study, we used a microarray analysis to investigate the changes in global gene expression induced by the administration of exogenous ADM in SK-N-SH cells, which allowed us to evaluate the effects of elevated ADM on the central nervous system. A quantitative reverse-transcription PCR study showed that the levels of HSPA1A/1B mRNA, another gene that has been associated with schizophrenia, were significantly suppressed after exogenous ADM treatment. These results indicate that elevated ADM may be involved in the etiology of schizophrenia through the regulation of heat shock protein signaling.

Dysregulation of Cerebellar Adrenomedullin Signaling During Hypertension

Adrenomedullin (AM) is a peptide involved in blood pressure regulation. AM activates three different receptors, the AM type 1 (AM1), type 2 (AM2), and calcitonin gene-related peptide 1 (CGRP1) receptors. AM triggers several signaling pathways such as adenylyl cyclase (AC), guanylyl cyclase (GC), and extracellular signal-regulated kinases (ERK) and modulates reactive oxygen species (ROS) metabolism. Cerebellar AM, AM-binding sites, and its receptor components are altered during hypertension, although it is unknown if these alterations are associated with changes in AM signaling. Thus, we assessed AM signaling pathways in cerebellar vermis of 16-week-old Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Animals were sacrificed by decapitation, and cerebellar vermis was microdissected under stereomicroscopic control. Tissue was stimulated in vitro with AM. Then the production of cyclic guanosine monophosphate (cGMP), nitric oxide (NO) and cyclic adenosine monophosphate (cAMP) were assessed along with ERK1/2 activation and three antioxidant enzymes' activity: glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase (SOD). Our findings demonstrate that in the cerebellar vermis of normotensive rats, AM increases cGMP, NO, cAMP production, and ERK1/2 phosphorylation, while decreases basal antioxidant enzyme activity. In addition, AM antagonizes angiotensin II (ANG II)-induced increment of antioxidant enzyme activity. Hypertension blunts AM-induced cGMP and NO production and AM-induced decrease of antioxidant enzyme activity. Meanwhile, AM-induced effects on cAMP production, ERK1/2 activation, and AM-ANG II antagonism were not altered in SHR rats. Our results support a dysregulation of several AM signaling pathways during hypertension in cerebellar vermis.

5-Substituted 2-amino-4,6-dihydroxypyrimidines and 2-amino-4,6-dichloropyrimidines: synthesis and inhibitory effects on immune-activated nitric oxide production

A series of 5-substituted 2-amino-4,6-dihydroxypyrimidines were prepared by a modified condensation of the corresponding monosubstituted malonic acid diesters with guanidine in an excess of sodium ethoxide. The optimized procedure using Vilsmeier-Haack-Arnold reagent, followed by immediate deprotection of the (dimethylamino)methylene protecting groups, has been developed to convert the 2-amino-4,6-dihydroxypyrimidine analogs to novel 5-substituted 2-amino-4,6-dichloropyrimidines in high yields. Pilot screening for biological properties of the prepared compounds was done in mouse peritoneal cells using the in vitro nitric oxide (NO) assay. Irrespective of the substituent at the 5 position, 2-amino-4,6-dichloropyrimidines inhibited immune-activated NO production. The most effective was 5-fluoro-2-amino-4,6-dichloropyrimidine with an IC 50 of 2 µM (higher activity than the most potent reference compound) while the IC 50s of other derivatives were within the range of 9-36 µM. The 2-amino-4,6-dihydroxypyrimidine counterparts were devoid of any NO-inhibitory activity. The compounds had no suppressive effects on the viability of cells. The Mechanism of action remains to be elucidated.

Involvement of PKA-dependent upregulation of nNOS-CGRP in adrenomedullin-initiated mechanistic pathway underlying CFA-induced response in rats

We have previously shown that intrathecal administration of the adrenomedullin (AM) receptor antagonist AM(22-52) produces a long-lasting anti-hyperalgesia effect. This study examined the hypothesis that AM recruits other pronociceptive mediators in complete Freund's adjuvant (CFA)-induced inflammation. Injection of CFA in the hindpaw of rat produced an increase in the expression of nNOS in dorsal root ganglion (DRG) and the spinal dorsal horn. An intrathecal administration of AM(22-52), but not the CGRP antagonist BIBN4096BS, abolished the CFA-induced increase of nNOS. Moreover, AM-induced increase of CGRP was inhibited by the nNOS inhibitors L-NAME and 7-nitroindazole in cultured ganglion explants. Addition of AM to ganglion cultures induced an increase in nNOS protein, which was attenuated by the PKA inhibitor H-89. Treatment with AM also concentration-dependently increased cAMP content and pPKA protein level, but not its non-phosphorylated form, in cultured ganglia. In addition, nNOS was shown to be co-localized with the AM receptor components calcitonin receptor-like receptor and receptor activity-modifying protein 2- and 3 in DRG neurons. The present study suggests that the enhanced activity of nitric oxide (NO) mediates the biological action of AM at the spinal level and that AM recruits NO-CGRP via cAMP/PKA signaling in a mechanistic pathway underlying CFA-induced hyperalgesia.

Inhibition of the adrenomedullin/nitric oxide signaling pathway in early diabetic retinopathy

The nitric oxide (NO) signaling pathway is integrally involved in visual processing and changes in the NO pathway are measurable in eyes of diabetic patients. The small peptide adrenomedullin (ADM) can activate a signaling pathway to increase the enzyme activity of neuronal nitric oxide synthase (nNOS). ADM levels are elevated in eyes of diabetic patients and therefore, ADM may play a role in the pathology of diabetic retinopathy. The goal of this research was to test the effects of inhibiting the ADM/NO signaling pathway in early diabetic retinopathy. Inhibition of this pathway decreased NO production in high-glucose retinal cultures. Treating diabetic mice with the PKC β inhibitor ruboxistaurin for 5 weeks lowered ADM mRNA levels and ADM-like immunoreactivity and preserved retinal function as assessed by electroretinography. The results of this study indicate that inhibiting the ADM/NO signaling pathway prevents neuronal pathology and functional losses in early diabetic retinopathy.

Calcitonin gene-related peptide- and adrenomedullin-induced facilitation of calcium current in submandibular ganglion

OBJECTIVE

The control of saliva secretion is mainly under parasympathetic control. The submandibular ganglion (SMG) is a parasympathetic ganglion which receives inputs from preganglionic cholinergic neurons, and innervates the submandibular salivary gland to control saliva secretion. The aim of this study was to investigate if adrenomedullin (ADM) and/or calcitonin gene-related peptide (CGRP) modulate voltage-dependent calcium channel (VDCCs) current (I(Ca)) in SMG.

DESIGN

The profile of CGRP and ADM actions in SMG was studied using the whole-cell configuration of the patch-clamp technique.

RESULTS

Both ADM and CGRP facilitated I(Ca). These facilitations were attenuated by intracellular dialysis of the anti-Gα(s)-protein and pretreatment of SQ22536 (an adenylate cyclase inhibitor).

CONCLUSIONS

ADM and CGRP facilitates VDCCs mediated by Gα(s)-protein and adenylate cyclase in SMG.

Calcitonin gene-related peptide- and adrenomedullin-induced facilitation of calcium current by different signal pathways in nucleus tractus solitarius

Calcitonin gene-related peptides (CGRP) and adrenomedullin (ADM) belong to the calcitonin family of peptides and are structurally related. Both peptides are found in the neurons of the CNS and play a role in many neuronal functions, including the control of blood pressure. The nucleus tractus solitarius (NTS) is known to play a major role in the regulation of cardiovascular, respiratory, gustatory, hepatic and swallowing functions. Recently, hypotension and bradycardia were observed after CGRP and ADM injection in the NTS. Voltage-dependent Ca(2+) channels (VDCCs) serve as crucial mediators of membrane excitability and Ca(2+)-dependent functions, such as neurotransmitter release, enzyme activity, and gene expression. The purpose of this study is to investigate the effects of CGRP and ADM on VDCC currents (I(Ca)) carried by Ba(2+) (I(Ba)) in the NTS, using patch-clamp recording methods. Application of CGRP and ADM caused facilitation of I(Ba) in a concentration-dependent manner. Intracellular dialysis of the anti-Galpha(s)-protein antibody attenuated CGRP-induced facilitation of I(Ba). Intracellular dialysis of the anti-Galpha(i)-protein antibody attenuated ADM-induced facilitation of I(Ba). Pretreatment with SQ22536 (an adenylate cyclase inhibitor) and intracellular dialysis of PKI(5-24) (a protein kinase A inhibitor) attenuated CGRP-induced facilitation of I(Ba). In contrast, pretreatment with PD98,059 (a mitogen-activated protein kinas inhibitor) attenuated ADM-induced facilitation of I(Ba). Mainly L-type VDCCs were facilitated by both CGRP and ADM. These results indicate that CGRP facilitates L-type VDCCs via Galpha(s)-protein involving adenylate cyclase and protein kinase A. In contrast, ADM facilitates L-type VDCCs via Galpha(i)-protein involving mitogen-activated protein kinase in the NTS.

Adrenomedullin is expressed during rodent dental tissue development and promotes cell growth and mineralization

BACKGROUND INFORMATION

ADM (adrenomedullin) has pleiotropic effects, including regulation of inflammation, infection, angiogenesis, mineralized-tissue formation and development. Recently, we demonstrated up-regulation of the ADM transcript in diseased pulpal tissue while the protein is sequestered within the dentine extracellular matrix during dentinogenesis. The present study aimed to characterize ADM localization during rodent dental tissue development and determine its potential effects on dental cells. Finally, we sought to profile ADM transcript levels in adult organs and tissues to compare its expression in teeth relative to other tissues.

RESULTS

Immunohistochemical analysis of developmental rat oral tissues indicated that, at E16 (embryonic day 16), ADM was present in dental epithelium and, by E18, ADM localized to the dental papilla and inner and outer dental epithelia. By E20, ADM was detected in secretory odontoblasts and ameloblasts and exhibited a similar expression profile to that of the key dentinogenesis signalling molecule, TGF-beta1 (transforming growth factor-beta1). Cell growth analysis in the dental MDPC-23, OD-21 and control 3T3 cell lines exposed to ADM (range 10(-15)-10(-7) M) together with EDTA-extracted DMPs (dentine matrix proteins) (range 0.00001-1000 mg/ml) containing comparable concentrations of ADM demonstrated that ADM stimulated a biphasic response in dental cell growth, comparable with that of DMPs, with peak stimulation observed at approximately 10(-11) M. For mineralization analysis, cell lines were exposed to combinations of 50 microg/ml ascorbic acid, 10 mM beta-G (beta-glycerophosphate), 10(-8) M DEX (dexamethasone) and ADM (range 10(-15)-10(-7) M). The results demonstrated that ADM could substitute for DEX to stimulate mineralization. Postnatally, multiple tissue expression profiling indicated abundant ADM levels in tongue and pulpal tissues.

CONCLUSIONS

During oral and dental tissue development ADM initially localizes to epithelial tissue, whereas during later stages it is present in mineralized secreting cells, including odontoblasts. ADM may regulate proliferation and mineralization processes during development, whereas, in adulthood, it may be important for maintaining dental tissue homoeostasis.

Adrenomedullin promotes cell cycle transit and up-regulates cyclin D1 protein level in human glioblastoma cells through the activation of c-Jun/JNK/AP-1 signal transduction pathway

Adrenomedullin is a secreted peptide hormone with multiple functions. Although a number of reports have indicated that adrenomedullin may be involved in tumor progression, its mechanism of action remains obscure. In this study, we have analysed the signal transduction pathway activated by adrenomedullin in human glioma cells. Our results revealed that adrenomedullin induced the phosphorylation of both c-Jun and JNK in glioblastoma cells. Silencing JNK expression with siRNA reversed the phosphorylation of c-Jun induced by adrenomedullin, indicating that JNK is responsible of c-Jun activation. In addition, electrophoretic mobility-shift assays showed that the increase in phosphorylation of c-Jun was associated with increased AP-1 DNA binding activity. Supershift assays and co-immunoprecipitation demonstrated that c-Jun and JunD are part of the AP-1 complex, indicating that activated c-Jun is dimerized with JunD in response to adrenomedullin. Furthermore, adrenomedullin was shown to promote cell transit beyond cell cycle phases with a concomittant increase in cyclin D1 protein level, suggesting that adrenomedullin effects cell proliferation through up-regulation of cyclin D1. The inhibition of JNK activation or the suppression of c-Jun or JunD expression with siRNA impaired the effects of adrenomedullin on cell proliferation and on cyclin D1. Taken together, these data demonstrate that activation of cJun/JNK pathway is involved in the growth regulatory activity of adrenomedullin in glioblastoma cells.

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

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

Adrenomedullin in the rostral ventrolateral medulla inhibits baroreflex control of heart rate: a role for protein kinase A

1 The rostral ventrolateral medulla (RVLM) is an essential vasomotor center in the brainstem which participates in maintaining resting levels of arterial pressure and for regulating baroreflex activity. We have demonstrated that microinjections of adrenomedullin (ADM), a vasoactive neuropeptide, into the RVLM cause increased resting mean arterial pressure (MAP) and heart rate (HR). However, the effect of ADM on baroreflex function remains unclear. 2 The purposes of the present study were to investigate the effect of ADM in the RVLM on the regulation of baroreflex activity and to identify the underlying mechanisms. Baroreflex curves were generated with intravenous injections of multiple doses of phenylephrine and nitroprusside. The upper and lower plateaus, reflex range, MAP at the midpoint of HR range (MAP(50)), and gain were evaluated before and after various microinjections were made into the RVLM of urethane-anesthetized rats. 3 Microinjections of ADM decreased the upper plateau, reflex range, and gain, and increased MAP(50), indicating that ADM in the RVLM impairs baroreflex function. 4 ADM(22-52), a putative ADM receptor antagonist, significantly increased the baroreflex gain and upper plateau, demonstrating that endogenous ADM tonically inhibits the baroreflex. Coinjections of ADM(22-52) with ADM blocked the ADM-induced baroreflex responses. 5 ADM's effect was abolished with H-89, a protein kinase A (PKA) inhibitor. 6 Our results show that ADM in the RVLM exerts an inhibitory effect on baroreflex activity via an ADM receptor-mediated mechanism, and that activation of PKA is involved in this event.

Adrenomedullin stimulates nitric oxide production from primary rat hypothalamic neurons: roles of calcium and phosphatases

Adrenomedullin (ADM) in the brain plays important roles in the maintenance of homeostasis. Although in vivo evidence has suggested that nitric oxide (NO) mediates ADM's effects in the brain, mechanisms for ADM stimulation of NO production in neurons have not been identified. In the present study, primary hypothalamic neurons were used to characterize ADM-induced NO production and to study the underlying mechanisms. Using Calcium Orange/4-amino-5-methylamino-2',7'-difluorofluorescein fluorescence live cell imaging, we found that ADM (1 or 10 nM, 5 min) significantly elevated [Ca(2+)](i) and NO production in a concentration-dependent manner. Ca(2+) and NO responses induced by 10 nM ADM were abolished by pretreatment with 50 microM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA-AM), an intracellular Ca(2+) chelator, or protein kinase A (PKA) inhibitors 5 microM N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H-89) and 50 microM Rp-cAMP. Furthermore, the ADM-induced NO production was significantly attenuated by a protein phosphatase 1/2A inhibitor, okadaic acid (OA; 0.1 microM), or calcineurin inhibitors, tacrolimus (FK506) (1 microM) and cyclosporin A (CsA; 0.1 microM). Using Western blotting, we found that ADM significantly decreased phosphorylation of neuronal nitric-oxide synthase (nNOS) at serine 847. This dephosphorylation was inhibited by 0.1 microM OA, 1 microM FK506, 0.1 microM CsA, or 5 microM H-89, and attenuated by 50 microM BAPTA-AM. These results suggest that, in hypothalamic neurons, ADM elevates [Ca(2+)](i) via PKA-associated mechanisms. The PKA/Ca(2+) cascade leads to protein phosphatase (PP) 1/PP2A- and calcineurin-mediated dephosphorylation of nNOS. We hypothesize that the Ca(2+) increase and nNOS dephosphorylation contribute to activation of nNOS and production of NO in hypothalamic neurons.

Participation of adrenomedullin and its relation with vascular endothelial growth factor in androgen regulation of prostatic blood flow in vivo

OBJECTIVES

We had previously reported that androgen-regulated prostatic blood flow and vascular endothelial growth factor (VEGF) were involved in the signal transduction pathway. Adrenomedullin (ADM) is a multifunctional regulatory peptide with mitogenic and angiogenic capabilities that are regulated by androgen. ADM is abundantly expressed in the prostate. We focused on ADM and evaluated its participation and relation with VEGF in androgen prostatic blood flow regulation using a castrated rat model.

METHODS

We examined the effect of locally injected dihydrotestosterone (DHT) and ADM, and the co-administration of DHT with an ADM receptor antagonist (ADM 22-52) on prostatic blood flow. Furthermore, prostatic blood flow was evaluated after ADM and VEGF administration with each other's antagonist, VEGF neutralizing antibody and ADM 22-52, respectively. Changes in the mRNA expression levels of ADM in the prostate after castration and successive androgen stimulation were also evaluated.

RESULTS

The administration of ADM promptly increased prostatic blood flow in a dose-dependent manner within 30 minutes. The DHT-induced increase in prostatic blood flow was completely abolished by co-administration with anti-ADM. Anti-ADM inhibited the VEGF-induced prostatic blood flow elevation, but a VEGF neutralizing antibody did not affect the ADM-mediated blood flow elevation. Furthermore, upregulation of the ADM gene induced by DHT was inhibited by co-administration with a VEGF-neutralizing antibody.

CONCLUSIONS

These results have clearly demonstrated the direct regulation of prostatic blood flow by ADM and its involvement in androgenic prostatic blood flow regulation. Furthermore, ADM was estimated to be a downstream mediator of VEGF action in the signal transduction pathway.

Intermedin1-53 activates l-arginine/nitric oxide synthase/nitric oxide pathway in rat aortas

Intermedin (IMD), a novel member of the calcitonin/calcitonin gene-related peptide (CGRP) family, has similar or more potent vasodilatory and hypotensive actions than adrenomedullin (ADM) and CGRP. The present study was designed to observe the effects of synthetic rat IMD1-53 on L-arginine (L-Arg) cellular transport, nitric oxide synthase (NOS) activity, and nitric oxide (NO) production in the isolated rat aortic ring to illustrate its direct effect on the L-Arg/NOS/NO pathway in vasculature. IMD1-53 significantly increased NO production and cNOS activity in rat aortas and was more potent than equivalent ADM. But the peptides of both IMD and ADM had no effect on inducible NOS expression and activity. Otherwise, IMD1-53 induced a concentration-dependent increase in [3H]L-Arg transport and its effect was more potent than that of an equivalent concentration of ADM. Semiquantitative RT-PCR revealed that IMD1-53 significantly increased cationic amino acid transport (CAT)-1 and CAT-2B mRNA expression, and its effect was similar to that of ADM. All these results suggest that IMD1-53 might regulate vessel function homeostasis via upregulating the L-Arg/NOS/NO pathway.