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

Multi-biological functions of intermedin in diseases

Intermedin (IMD) is a member of the calcitonin gene-related peptide (CGRP)/calcitonin (CT) superfamily, and it is expressed extensively throughout the body. The typical receptors for IMD are complexes composed of calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein (RAMP), which leads to a biased activation towards Gαs. As a diagnostic and prognostic biomarker, IMD regulates the initiation and metastasis of multiple tumors. Additionally, IMD functions as a proangiogenic factor that can restrain excessive vascular budding and facilitate the expansion of blood vessel lumen, ultimately resulting in the fusion of blood vessels. IMD has protective roles in various diseases, including ischemia-reperfusion injury, metabolic disease, cardiovascular diseases and inflammatory diseases. This review systematically elucidates IMD's expression, structure, related receptors and signal pathway, as well as its comprehensive functions in the context of acute kidney injury, obesity, diabetes, heart failure and sepsis. However, the precise formation process of IMD short peptides in vivo and their downstream signaling pathway have not been fully elucidated yet. Further in-depth studies are need to translate IMD research into clinical applications.

The Role of Sirtuins in Osteogenic Differentiation of Vascular Smooth Muscle Cells and Vascular Calcification

Vascular calcification (VC) is a common pathological change in many chronic diseases, such as diabetes and chronic kidney disease. It is mainly deposited in the intima and media of vessels in the form of hydroxyapatite. Recently, a lot of research has been performed to show that VC is associated with various cellular stresses, such as hyperphosphate, hyperglycemia and oxidative stress. Unfortunately, our understanding of the pathogenesis of calcification is far from comprehensive. Sirtuins belong to a family of class III highly conserved deacetylases that are involved in the regulation of biological and cellular processes including mitochondrial biogenesis, metabolism, oxidative stress, inflammatory response, DNA repair, etc. Numerous studies have shown that sirtuins might play protective roles in VC, and restoring the activity of sirtuins may be a potentially effective treatment for VC. However, the exact mechanism of their vascular protection remains unclear. Here, we reviewed the roles of sirtuins in the osteogenic transformation of vascular smooth muscle cells and the development of VC. We also elucidated the applications of sirtuins agonists for the treatment of VC.

Compensatory role of endogenous sulfur dioxide in nitric oxide deficiency-induced hypertension

OBJECTIVE

This study aimed to determine the communicational pattern of gaseous signaling molecules sulfur dioxide (SO2) and nitric oxide (NO) between vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs), and elucidate the compensatory role and significance of endogenous SO2 in the development of hypertension due to NO deficiency.

APPROACH AND RESULTS

Blood pressure was monitored by the tail-cuff and implantable physiological signal telemetry in L-nitro-arginine methyl ester (l-NAME)-induced hypertensive mice, and structural alterations of mouse aortic vessels were detected by the elastic fiber staining method. l-NAME-treated mice showed decreased plasma NO levels, increased SO2 levels, vascular remodeling, and increased blood pressure, and application of l-aspartate-β-hydroxamate, which inhibits SO2 production, further aggravated vascular structural remodeling and increased blood pressure. Moreover, in a co-culture system of HAECs and HASMCs, NO from HAECs did not influence aspartate aminotransferase (AAT)1 protein expression but decreased AAT1 activity in HASMCs, thereby resulting in the inhibition of endogenous SO2 production. Furthermore, NO promoted S-nitrosylation of AAT1 protein in HASMCs and purified AAT1 protein. Liquid chromatography with tandem mass spectrometry showed that the Cys192 site of AAT1 purified protein was modified by S-nitrosylation. In contrast, dithiothreitol or C192S mutations in HASMCs blocked NO-induced AAT1 S-nitrosylation and restored AAT1 enzyme activity.

CONCLUSION

Endothelium-derived NO inhibits AAT activity by nitrosylating AAT1 at the Cys192 site and reduces SO2 production in HASMCs. Our findings suggest that SO2 acts as a compensatory defense system to antagonize vascular structural remodeling and hypertension when the endogenous NO pathway is disturbed.

Intermedin1-53 attenuates aging-associated vascular calcification in rats by upregulating sirtuin 1

Vascular calcification is a common phenomenon in older adults. Intermedin (IMD) is a cardiovascular bioactive peptide inhibiting vascular calcification. In this study, we aimed to investigate whether IMD_1-53 attenuates aging-associated vascular calcification. Vascular calcification was induced by vitamin D3 plus nicotine (VDN) in young and old rats. The calcification in aortas was more severe in old rats treated with VDN than young control rats, and IMD expression was lower. Exogenous administration of IMD_1-53 significantly inhibited the calcium deposition in aortas and the osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs) in VDN-treated old rats. Moreover, levels of aging-related p16, p21 and β-galactosidase were all greatly decreased by IMD_1-53. These results were further confirmed in rat and human VSMCs in vitro. In addition, IMD-deficient mouse VSMCs showed senescence features coinciding with osteogenic transition as compared with wild-type mouse VSMCs. Mechanistically, IMD_1-53 significantly increased the expression of the anti-aging factor sirtuin 1 (sirt1); the inhibitory effects of IMD_1-53 on calcification and senescence were blocked by sirt1 knockdown. Furthermore, preincubation with inhibitors of PI3K, AMPK or PKA efficiently blunted the upregulatory effect of IMD_1-53 on sirt1. Consequently, IMD_1-53 could attenuate aging-associated vascular calcification by upregulating sirt1 via activating PI3K/Akt, AMPK and cAMP/PKA signaling.

Adrenomedullin 2/intermedin: a putative drug candidate for treatment of cardiometabolic diseases

Adrenomedullin (ADM) 2/intermedin (IMD) is a short peptide that belongs to the CGRP superfamily. Although it shares receptors with CGRP, ADM and amylin, ADM2 has significant and unique functions in the cardiovascular system. In the past decade, the cardiovascular effect of ADM2 has been carefully analysed. In this review, progress in understanding the effects of ADM2 on the cardiovascular system and its protective role in cardiometabolic diseases are summarized.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Intermedin1‑53 enhances angiogenesis and attenuates adverse remodeling following myocardial infarction by activating AMP‑activated protein kinase

Adverse ventricular remodeling is a maladaptive response to acute loss of myocardium and an important risk factor for heart failure following myocardial infarction (MI). Intermedin (IMD) is a novel member of the calcitonin/calcitonin gene‑related peptide family, which may possess potent cardioprotective properties. The aim of the present study was to determine whether IMD1‑53, a mature bioactive form of IMD, may promote therapeutic angiogenesis within the infarcted myocardium, therefore attenuating adverse ventricular remodeling post‑MI. The present study observed that treatment with IMD1‑53 promoted proliferation, migration and tube formation of primary cultured myocardial microvascular endothelial cells (MMVECs). In a rat model of MI, chronic administration of IMD1‑53 increased capillary density in the peri‑infarct zone, attenuated ventricular remodeling and improved cardiac performance post‑MI. Treatment with IMD1‑53 also significantly increased the expression levels of phosphorylated‑AMP‑activated protein kinase (AMPK) and the subsequent activation of endothelial nitric oxide synthase in MMVECs and post‑MI rat myocardium, without a significant influence on the expression of vascular endothelial growth factor. Notably, the in vitro effects of IMD1‑53 on angiogenesis and the in vivo effects of IMD1‑53 on post‑MI ventricular remodeling were largely abrogated by the co‑administration of compound C, an AMPK inhibitor. In conclusion, the present study demonstrated that IMD1‑53 could attenuate adverse ventricular remodeling post‑MI via the promotion of therapeutic angiogenesis, possibly through the activation of AMPK signaling.

Intermedin 1-53 Inhibits Myocardial Fibrosis in Rats by Down-Regulating Transforming Growth Factor-β

BACKGROUND Myocardial fibrosis is the result of persistent anoxia and ischemic myocardial fibers caused by coronary atherosclerotic stenosis, which lead to heart failure, threatening the patient's life. This study aimed to explore the regulatory role of intermedin 1-53 (IMD1-53) in cardiac fibrosis using neonatal rat cardiac fibroblasts and a myocardial infarction (MI) rat model both in vitro and in vivo. MATERIAL AND METHODS The Western blot method was used to detect the protein expression of collagen I and collagen III in myocardial fibroblasts. The SYBR Green I real-time quantitative polymerase chain reaction (PCR) assay was used to detect the mRNA expression of collagen type I and III, IMD1-53 calcitonin receptor-like receptor (CRLR), transforming growth factor-β (TGF-β), and matrix metalloproteinase-2 (MMP-2). Masson staining was used to detect the area changes of myocardial fibrosis in MI rats. RESULTS Results in vivo showed that IMD1-53 reduced the scar area on the heart of MI rats and inhibited the expression of collagen type I and III both in mRNA and protein. Results of an in vitro study showed that IMD1-53 inhibited the transformation of cardiomyocytes into myofibroblasts caused by angiotensin II (Ang II). The further mechanism study showed that IMD1-53 inhibited the expression of TGF-β and the phosphorylation of smad3, which further up-regulated the expression of MMP-2. CONCLUSIONS IMD1-53 is an effective anti-fibrosis hormone that inhibits cardiac fibrosis formation after MI by down-regulating the expression of TGF-β and the phosphorylation of smad3, blocking fibrous signal pathways, and up-regulating the expression of MMP-2, thereby demonstrating its role in regression of myocardial fibrosis.

Plasma Intermedin Level Indicates Severity and Treatment Efficacy of Septic Shock in Sprague-Dawley (SD) Rats

BACKGROUND The aim of this study was to investigate the value of plasma intermedin (IMD) in assessing severity and treatment efficacy of septic shock. MATERIAL AND METHODS Healthy male Sprague-Dawley (SD) rats were chosen and divided into a normal control group (n=15) and a shock model group (n=27) that received intravenous injection of lipopolysaccharide (LPS). Then, 3 specimens were taken from each group. The shock model group rats were divided into an LPS group and a treatment group with 12 rats each. The treatment group received intravenous injection of compound sodium lactate solution. Plasma IMD and IMD1-47 mRNA expressions were compared and analyzed. RESULTS Mean arterial pressure (MAP) was lower while white blood cell count and TNF-α were higher in the shock model group than in the normal control group (P<0.05). After 10 h and 20 h, the treatment group had lower plasma IMD and IMD1-47 mRNA expressions compared with the LPS group (P<0.05). Plasma IMD and IMD1-47 mRNA expressions in the LPS group after 20 h were significantly higher than after 10 h (P<0.05). IMD was positively correlated with interleukins (IL-3, IL-6, and IL-8), white blood cell count, and body temperature (all P<0.05), but were negatively correlated with systolic pressure (r=-0.8474, P=0.0040). CONCLUSIONS Plasma IMD level can effectively reflect the severity of septic shock and can be used as an important indicator of septic shock treatment effectiveness.

Plasma levels of intermedin (adrenomedullin-2) in healthy human volunteers and patients with heart failure

Intermedin/adrenomedullin-2 (IMD) is a member of the adrenomedullin/CGRP peptide family. Less is known about the distribution of IMD than for other family members within the mammalian cardiovascular system, particularly in humans. The aim was to evaluate plasma IMD levels in healthy subjects and patients with chronic heart failure. IMD and its precursor fragments, preproIMD(25-56) and preproIMD(57-92), were measured by radioimmunoassay in 75 healthy subjects and levels of IMD were also compared to those of adrenomedullin (AM) and mid-region proadrenomedullin(45-92) (MRproAM(45-92)) in 19 patients with systolic heart failure (LVEF<45%). In healthy subjects, plasma levels (mean+SE) of IMD (6.3+0.6 pg ml(-1)) were lower than, but correlated with those of AM (25.8+1.8 pg ml(-1); r=0.49, p<0.001). Plasma preproIMD(25-56) (39.6+3.1 pg ml(-1)), preproIMD(57-92) (25.9+3.8 pg ml(-1)) and MRproAM(45-92) (200.2+6.7 pg ml(-1)) were greater than their respective bioactive peptides. IMD levels correlated positively with BMI but not age, and were elevated in heart failure (9.8+1.3 pg ml(-1), p<0.05), similarly to MRproAM(45-92) (329.5+41.9 pg ml(-1), p<0.001) and AM (56.8+10.9 pg ml(-1), p<0.01). IMD levels were greater in heart failure patients with concomitant renal impairment (11.3+1.8 pg ml(-1)) than those without (6.5+1.0 pg ml(-1); p<0.05). IMD and AM were greater in patients receiving submaximal compared with maximal heart failure drug therapy and were decreased after 6 months of cardiac resynchronization therapy. In conclusion, IMD is present in the plasma of healthy subjects less abundantly than AM, but is similarly correlated weakly with BMI. IMD levels are elevated in heart failure, especially with concomitant renal impairment, and tend to be reduced by high intensity drug or pacing therapy.

Induction of adrenomedullin 2/intermedin expression by thyroid stimulating hormone in thyroid

TSH is the important regulator of thyroid function but detailed molecular mechanisms have not been clarified. We first generated the iodine deficient (ID) rat in which goiter is induced by accelerated endogenous TSH secretion. The result of microarray analysis demonstrated markedly increased levels of adrenomedullin 2/intermedin (AM2/IMD) expression in the ID rat thyroid. AM2/IMD is a potent vasodilator. AM2/IMD mRNA expression was induced by TSH in a rat thyroid follicular cell line FRTL-5. Immunohistochemical analysis in human normal and Graves' disease thyroid revealed that AM2/IMD immunoreactivity was detected in follicular cells and more pronounced in Graves' disease. These results indicated that TSH induced AM2/IMD expression in the rat thyroid gland and it could locally work as a potent vasodilator, resulting in the expansion of thyroid inter-follicular capillaries. AM2/IMD could also contribute to facilitate thyroid hormone synthesis possibly via vasodilation effects and/or cAMP stimulating effects in the human thyroid gland.

Cardiac sympathetic afferent reflex response to intermedin microinjection into paraventricular nucleus is mediated by nitric oxide and γ-amino butyric acid in hypertensive rats

Intermedin (IMD) is a member of calcitonin/calcitonin gene-related peptide (CGRP) and involves in the regulation of cardiovascular function in both peripheral tissues and central nervous system (CNS). Paraventricular nucleus (PVN) of hypothalamus is an important site in the control of cardiac sympathetic afferent reflex (CSAR) which participates in sympathetic over-excitation of hypertension. The aim of this study is to investigate whether IMD in the PVN is involved in the inhibition of CSAR and its related mechanism in hypertension. Rats were subjected to two-kidney one-clip (2K1C) surgery to induce renovascular hypertension or sham-operation (Sham). Acute experiments were carried out four weeks later under anesthesia. The CSAR was evaluated with the renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) responses to the epicardial application of capsaicin. The RSNA and MAP were recorded in sinoaortic-denervated, cervical-vagotomized and anesthetized rats. Bilateral PVN microinjection of IMD (25 pmol) caused greater decrease in the CSAR in 2K1C rats than in Sham rats, which was prevented by pretreatment with adrenomedullin (AM) receptor antagonist AM22-52, non-selective nitric oxide (NO) synthase (NOS) inhibitor l-NAME or γ-amino butyric acid (GABA)B receptor blocker CGP-35348. PVN pretreatment with CGRP receptor antagonist CGRP8-37 or GABAA receptor blocker gabazine had no significant effect on the CSAR response to IMD. AM22-52, l-NAME and CGP-35348 in the PVN could increase CSAR in Sham and 2K1C rats. These data indicate that IMD in the PVN inhibits CSAR via AM receptor, and both NO and GABA in the PVN involve in the effect of IMD on CSAR in Sham and renovascular hypertensive rats.

Intermedin in paraventricular nucleus attenuates sympathetic activity and blood pressure via nitric oxide in hypertensive rats

Intermedin (IMD) is a member of calcitonin/calcitonin gene-related peptide family, which shares the receptor system consisting of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMPs). This study investigated the effects of IMD in paraventricular nucleus (PVN) on renal sympathetic nerve activity and mean arterial pressure and its downstream mechanism in hypertension. Rats were subjected to 2-kidney 1-clip (2K1C) surgery to induce renovascular hypertension or sham operation. Acute experiments were performed 4 weeks later under anesthesia. IMD mRNA and protein were downregulated in 2K1C rats. Bilateral PVN microinjection of IMD caused greater decreases in renal sympathetic nerve activity and mean arterial pressure in 2K1C rats than in sham-operated rats, which were prevented by pretreatment with adrenomedullin receptor antagonist AM22-52 or nonselective nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester, and attenuated by selective neuronal NO synthase inhibitor N(ω)-propyl-l-arginine hydrochloride or endothelial NO synthase inhibitor N(5)-(1-iminoethyl)-l-ornithine dihydrochloride. AM22-52 increased renal sympathetic nerve activity and mean arterial pressure in 2K1C rats but not in sham-operated rats, whereas calcitonin/calcitonin gene-related peptide receptor antagonist calcitonin/calcitonin gene-related peptide 8-37 had no significant effect. CRLR and RAMP3 mRNA, as well as CRLR, RAMP2, and RAMP3 protein expressions, in the PVN were increased in 2K1C rats. Microinjection of IMD into the PVN increased the NO metabolites (NOx) level in the PVN in 2K1C rats, which was prevented by AM22-52. Chronic PVN infusion of IMD reduced, but AM22-52 increased, blood pressure in conscious 2K1C rats. These results indicate that IMD in the PVN inhibits sympathetic activity and attenuates hypertension in 2K1C rats, which are mediated by adrenomedullin receptors (CRLR/RAMP2 or CRLR/RAMP3) and its downstream NO.

Effects of intermedin1-53 on myocardial fibrosis

Intermedin (IMD) is a member of the calcitonin/calcitonin gene-related peptide (CGRP) family and has similar or more potent cardiovascular actions than adrenomedullin (ADM) and any other CGRP. The aim of the present work is to study the effects of IMD1-53 on cardiac fibroblast fibrosis in vivo and in vitro. Myocardial infarction model was prepared by ligating rats' left anterior descending coronary artery. Mesenchymal collagen contents in the left ventricle were accessed by Sirius-red stain. Heart functions were explored by hemodynamic changes. Expression of I and III type collagens, IMD1-53, receptor activity-modifying proteins (RAMP)1/2/3, and calcitonin receptor-like receptor (CRLR) in left ventricle were detected by western blot analysis. Cardiac fibroblasts (CFbs) fibrosis was induced by treating the cells with aldosterone (ALD). CFbs proliferation and the hydroxyproline contents in supernatants were determined by 3-[4,5-dimehyl-2-thiazolyl]-2,5-diphenyl-2H-tetrazolium bromide assay and enzyme-linked immunosorbent assay. Heart function was decreased in myocardial infarction model rats. Expression of type I and type III collagens in infarcted zone in myocardial rats was higher than those in the sham-operated group. IMD1-53, RAMP, and CRLR in left ventricle were also up-regulated. In vitro experiment showed that ALD was a powerful stimulator of CFbs activation. IMD1-53 decreased ALD-induced CFbs proliferation in a dose-dependent manner. Moreover, CGRP8-37 and ADM22-52 remarkably blocked the effect of IMD1-53 on ALD-induced myocardial cell fibrosis. IMD could be involved in the onset of cardiac fibrosis. Like ADM, IMD1-53 exerts an antifibrotic effect on CFbs, which might be mediated by CRLR/RAMP complex and ADM receptor.

Effects of continuous intermedin infusion on blood pressure and hemodynamic function in spontaneously hypertensive rats

OBJECTIVE

To examine the effects of exogenously administered intermedin (IMD, adrenomedullin-2) on arterial blood pressure, cardiac function and the cardiovascular IMD receptor system in spontaneously hypertensive rats (SHRs) as well as to investigate the associated mechanisms.

METHODS

Thirteen week-old male rats were divided in Wistar Kyoto (WKY) group (n = 12), SHR group (n = 12), IMD group (SHRs infused with IMD 1-47 500 ng/kg per hour, n = 12), and ADM group (SHRs infused with adrenomedullin 500 ng/kg per hour, n = 12).

RESULTS

A two-week continuous administration of low dose IMD 1-47 via mini-osmotic pumps markedly reduced blood pressure, the maximal rates of increase and decrease of left-ventricle pressure development (LV ± dp/dt(max)), left ventricular systolic pressure and heart rate in SHRs. Furthermore, IMD also inhibited protein over-expression of cardiovascular IMD receptors, myocardial Receptor Activity-Modifying Proteins (RAMP1 and RAMP2), aortic RAMP1, RAMP2, RAMP3, and calcitonin receptor-like receptor (CRLR); suppressed up-regulation of aortic RAMP1, RAMP2, RAMP3 and CRLR gene expression; and markedly elevated the mRNA abundance of myocardial atrial natriuretic peptide (ANP) and myocardial brain natriuretic peptide (BNP). Additionally, IMD 1-47 administration in SHRs increased aortic cAMP concentration and reduced myocardial cAMP concentration.

CONCLUSION

These findings support the speculation that IMD, as a cardiovascular active peptide, is involved in blood pressure reduction and cardiac function amelioration during hypertension. The mechanism underlying this effect may involve IMD binding of a receptor complex formed by RAMPs and CRLR, and consequential regulation of cAMP levels and other cardiovascular active factors, such as ANP and BNP.

The pharmacology of adrenomedullin 2/intermedin

Adrenomedullin 2 (AM2) or intermedin is a member of the calcitonin gene-related peptide (CGRP)/calcitonin family of peptides and was discovered in 2004. Unlike other members of this family, no unique receptor has yet been identified for it. It is extensively distributed throughout the body. It causes hypotension when given peripherally, but when given into the CNS, it increases blood pressure and causes sympathetic activation. It also increases prolactin release, is anti-diuretic and natriuretic and reduces food intake. Whilst its effects resemble those of AM, it is frequently more potent. Some characterization of AM2 has been done on molecularly defined receptors; the existing data suggest that it preferentially activates the AM(2) receptor formed from calcitonin receptor-like receptor and receptor activity modifying protein 3. On this complex, its potency is generally equivalent to that of AM. There is no known receptor-activity where it is more potent than AM. In tissues and in animals it is frequently antagonised by CGRP and AM antagonists; however, situations exist in which an AM2 response is maintained even in the presence of supramaximal concentrations of these antagonists. Thus, there is a partial mismatch between the pharmacology seen in tissues and that on cloned receptors. The only AM2 antagonists are peptide fragments, and these have limited selectivity. It remains unclear as to whether novel AM2 receptors exist or whether the mismatch in pharmacology can be explained by factors such as metabolism.

Intermedin elicits a negative inotropic effect in rat papillary muscles mediated by endothelial-derived nitric oxide

Intermedin (IMD) is a novel vasoactive peptide from the calcitonin gene-related peptide (CGRP) implicated in cardiac regulation, yet the contractile effects of IMD remain controversial, since previous studies in vivo and isolated cardiomyocytes documented contradictory results. We hypothesized cardiac endothelial cells involvement in IMD modulation of cardiac function as an explanation for these opposing observations. With this in mind, we investigated the direct action of increasing concentrations of IMD (10(-8) to 10(-6)M) on myocardial performance parameters in rat left ventricular (LV) papillary muscles with and without endocardial endothelium (EE) and in presence of receptor antagonists and intracellular pathways inhibitors. In LV papillary muscles with intact EE, IMD induced a concentration-dependent negative inotropic action (%decrease relative to baseline, at IMD concentration of 10(-6)M, active tension of 14 ± 4%, and maximum velocity of tension rise of 10 ± 4%). These effects were blunted by EE removal, AM receptor antagonist (AM(22-52)), and CGRP receptor antagonist (CGRP(8-37)). Additionally, nitric oxide (NO) synthase inhibition with N(G)-nitro-l-arginine (l-NAME) in muscles with and without EE and guanylyl cyclase inhibition with {1H-[1,2,4]oxadiazole-[4,4-a]-quinoxalin-1-one} not only blunted the negative inotropic action of IMD but also unmasked IMD-positive inotropic effect dependent on CGRP receptor PKA activation. Western blot quantification of phosphorylated cardiac troponin I (P-cTnI) in IMD-treated papillary muscles revealed a significant increase in P-cTnI when compared with untreated muscles, while in l-NAME-pretreated papillary muscles IMD failed to increase P-cTnI. Finally, we found that stimulation of both EE and microvascular endothelial cells with IMD significantly increased NO production by 40 ± 3 and 38 ± 3%, respectively, suggesting the role of cardiac endothelial cells in NO production upon IMD stimulation. Our findings establish IMD negative inotropic effect in isolated myocardium due to NO/cGMP pathway activation with concomitant thin myofilament desensitization by increase in cTnI phosphorylation and provide a coherent explanation for the previously reported contradictory results.

Effect of intermedin1-53 on angiotensin II-induced hypertrophy in neonatal rat ventricular myocytes

OBJECTIVES

Intermedin (IMD) is coexpressed in the heart with its receptor, which suggests that it may have localized actions as a modulator of cardiac function. The present study was designed to observe the interaction between IMD and cardiac hypertrophy and the possible mechanism involved in the antihypertrophic effects of IMD1-53 in cultured neonatal ventricular myocytes.

METHODS

Myocyte hypertrophy was induced by treating the cells with angiotensin II, and the hypertrophic response was characterized by a significant increase in cell surface area, protein synthesis, and BNP mRNA expression.

RESULTS

Our results showed that angiotensin II led to an obvious decrease in the production, secretion, and mRNA expression of IMD and increase receptor activity modifying proteins 1, 3 mRNA expression. Moreover, IMD1-53 inhibited the angiotensin II-induced hypertrophic response and the effects of IMD1-53 were similar to those of equivalent-dose adrenomedullin and could been blocked by H89. Otherwise, in our study, IMD1-53 resulted in dose-dependent increases of cAMP production in cardiomyocytes.

CONCLUSIONS

Thus, IMD and its receptor system are involved in cardiac hypertrophy, and like adrenomedullin, IMD1-53 exerts an antihypertrophic effect on neonatal cardiomyocytes and the effect can be mediated by the cAMP/PKA pathway.

Mechanisms involved in the regional haemodynamic effects of intermedin (adrenomedullin 2) compared with adrenomedullin in conscious rats

BACKGROUND AND PURPOSE

Intermedin (IMD) is a newly identified member of the calcitonin family of peptides that shares structural and functional homology with adrenomedullin (AM). In vivo cardiovascular effects of AM have been described, but relatively little is known of the in vivo actions of IMD. The purpose of this study was to compare the regional haemodynamic effects of IMD with those of AM in conscious rats, and investigate possible underlying mechanisms.

EXPERIMENTAL APPROACH

Measurements of blood pressure, heart rate and renal, mesenteric and hindquarters haemodynamics were made in conscious, chronically-instrumented rats.

KEY RESULTS

IMD caused tachycardia and vasodilatation in all three vascular beds, associated with modest hypotension. At an equimolar dose (1 nmol.kg(-1)), most of the cardiovascular effects of IMD were greater than those of AM. The AM receptor antagonist, AM(22-52), was equally effective in attenuating the renal and mesenteric vasodilator effects of IMD (1 nmol.kg(-1)) and AM (3 nmol.kg(-1)), but inhibition of NO synthase was more effective at reducing the vasodilator effects of IMD than AM. Vascular K(ATP) channel blockade with U-37883A did not inhibit the vasodilator effects of either peptide.

CONCLUSIONS AND IMPLICATIONS

In vivo, the regional haemodynamic profile of IMD resembles that of AM, and some of the vasodilator effects of IMD are mediated by AM receptors and NO, but not by K(ATP) channels. The cardiovascular effects of AM have been implicated in various pathological conditions, but whether or not endogenous IMD fulfils a similar role remains to be determined.

Upregulated expression of intermedin and its receptor in the myocardium and aorta in spontaneously hypertensive rats

Intermedin (IMD), also called adrenomedullin 2 (ADM2), is a 47-amino acid peptide belonging to the calcitonin/calcitonin gene-related peptide (CGRP) family. IMD has similar or more potent vasodilatory and hypotensive actions compared with adrenomedullin (ADM) and CGRP. This study was designed to explore the role of IMD and its receptor in the pathogenesis of spontaneous hypertension and cardiac hypertrophy. Radioimmunoassay was employed to determine plasma immunoreactive IMD concentration and tissue immunoreactive IMD levels in the myocardium and aorta as well as cAMP concentration in the cardiovascular tissues in 13-week-old Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). The mRNA expression of IMD, its receptor, calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMP)) were determined by semi-quantitative RT-PCR. Protein levels of CRLR and RAMPs were assayed by Western blotting. Our results showed that immunoreactive IMD concentration was enhanced in the SHR myocardium, aortas and plasma. Both the mRNA and protein levels of IMD, as well as those of CRLR and RAMP 1-3 were upregulated in SHRs. IMD affected cAMP generation in the myocardium and aorta, which were not attenuated by prior addition of either CGRP(8-37) or ADM(22-52) alone. These results indicate that the elevation of IMD and its receptor in the cardiovascular tissue may play an important role in the pathogenesis of spontaneous hypertension.

Intermedin ameliorates vascular and renal injury by inhibition of oxidative stress

Intermedin (IMD) is a newly discovered peptide related to calcitonin gene-related peptide and adrenomedullin, and has been shown to reduce blood pressure and reactive oxygen species formation in vivo. In this study, we determined whether IMD exerts vascular and renal protection in DOCA-salt hypertensive rats by intravenous injection of adenovirus harboring the human IMD gene. Expression of human IMD was detected in the rat kidney via immunohistochemistry. IMD administration significantly lowered blood pressure, increased urine volume, and restored creatinine clearance. IMD also dramatically decreased superoxide formation and media thickness in the aorta. Vascular injury in the kidney was reduced by IMD gene delivery as evidenced by the prevention of glomerular and peritubular capillary loss. Moreover, IMD lessened morphological damage of the renal tubulointerstitium and reduced glomerular injury and hypertrophy. Attenuation of inflammatory cell accumulation in the kidney by IMD was accompanied by inhibition of p38MAPK activation and intercellular adhesion molecule 1 expression. In addition, IMD gene transfer resulted in a marked decline in myofibroblast and collagen accumulation in association with decreased transforming growth factor-beta1 levels. Furthermore, IMD increased nitric oxide excretion in the urine and lowered the amount of lipid peroxidation. These results demonstrate that IMD is a powerful renal protective agent with pleiotropic effects by preventing endothelial cell loss, kidney damage, inflammation, and fibrosis in hypertensive DOCA-salt rats via inhibition of oxidative stress and proinflammatory mediator pathways.

Intermedin/adrenomedullin-2 (IMD/AM2) relaxes rat main pulmonary arterial rings via cGMP-dependent pathway: role of nitric oxide and large conductance calcium-activated potassium channels (BK(Ca))

The present study was designed to investigate the effects of rat intermedin/adrenomedullin2 (rIMD), an agonist for calcitonin-like calcitonin receptors (CRLR), on the isolated rat pulmonary arterial rings (PA). When PA were precontracted with 9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F2alpha (U-46619), rIMD (10(-11) to 10(-6)M) induced concentration-dependent relaxation. The pulmonary vasorelaxant response (PVR) to rIMD in PA were completely inhibited by endothelium removal, NG-nitro-L-arginine-methyl-ester (L-NAME), l-N5-(1-iminoethyl)-ornithine hydrochloride (l-NIO) or 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). The PVR to rIMD were also significantly attenuated by a protein kinase inhibitor, Rp-8-bromo-beta-phenyl-1,N2-ethenoguanosine 3':5'-cyclic monophosphorothioate sodium salt hydrate (Rp-8-Br-PETcGMPs), cholera toxin and abolished by tetraethylammonium chloride (TEA), iberiotoxin and precontraction with KCl. The relaxant effect was not affected by 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ22536), (9S,10S,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy 1H diindolo [1,2,3fg:3',2',1'kl] pyrrolo [3,4-i] [1,6] benzodiazocine-10-carboxylic acid hexyl ester (KT5720), meclofenamate, glybenclamide or apamin. In parallel with SQ22536 and KT5720 results rolipram pretreatment did not alter the rIMD-induced PVR. The PVR to rIMD was potentialized either in the presence of zaprinast or sildenafil. Since the PVR to rIMD was also significantly reduced by rCGRP(8-37) and hADM(22-52) and rIMD(17-47), the present data suggest that rIMD produces PVR by acting in an indiscriminant manner on functional, and possibly different, endothelial CRLR. In conclusion, rIMD stimulates endothelial CRLR are coupled to release of nitric oxide, activation of guanylate cyclases, and promotion of hyperpolarization through large conductance calcium-activated K(+) channels in rat main PA.

Differential Effects of an Anti-Oxidant Intervention on Cardiomyocyte Expression of Adrenomedullin and Intermedin and their Receptor Components in Chronic Nitric Oxide Deficiency

BACKGROUND

Chronic inhibition of nitric oxide (NO) synthesis is associated with hypertension, myocardial oxidative stress and hypertrophic remodeling. Up-regulation of the cardiomyocyte adrenomedullin (AM) / intermedin (IMD) receptor signaling cascade is also apparent in NO-deficient cardiomyocytes: augmented expression of AM and receptor activity modifying proteins RAMP2 and RAMP3 is prevented by blood pressure normalization while that of RAMP1 and intermedin (IMD) is not, indicating that the latter is regulated by a pressure-independent mechanism.

AIMS

to verify the ability of an anti-oxidant intervention to normalize cardiomyocyte oxidant status and to investigate the influence of such an intervention on expression of AM, IMD and their receptor components in NO-deficient cardiomyocytes.

METHODS

NO synthesis inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME, 35 mg/kg/day) was given to rats for 8 weeks, with/without con-current administration of antioxidants (Vitamin C (25mg/kg/day) and Tempol (25mg/kg/day)).

RESULTS

In left ventricular cardiomyocytes isolated from L-NAME treated rats, increased oxidative stress was indicated by augmented (3.6 fold) membrane protein oxidation, enhanced expression of catalytic and regulatory subunits of pro-oxidant NADPH oxidases (NOX1, NOX2) and compensatory increases in expression of anti-oxidant glutathione peroxidase and Cu/Zn superoxide dismutases (SOD1, SOD3). Vitamin C plus Tempol did not reduce systolic blood pressure but normalized augmented plasma levels of IMD, but not of AM, and in cardiomyocytes: (i) abolished increased membrane protein oxidation; (ii) normalized augmented expression of prepro-IMD and RAMP1, but not prepro-AM, RAMP2 and RAMP3; (iii) attenuated (by 42%) increased width and normalized expression of hypertrophic markers, skeletal-alpha-actin and prepro-endothelin-1 similarly to blood pressure normalization but in contrast to blood pressure normalization did not attenuate augmented brain natriuretic peptide (BNP) expression.

CONCLUSION

normalization specifically of augmented IMD/RAMP1 expression in NO-deficient cardiomyocytes by antioxidant intervention in the absence of blood pressure reduction indicates that these genes are likely to be induced directly by myocardial oxidative stress. Although oxidative stress contributed to cardiomyocyte hypertrophy, induction of IMD and RAMP1 is unlikely to be secondary to cardiomyocyte hypertrophy.

Intermedin (adrenomedullin-2): a novel counter-regulatory peptide in the cardiovascular and renal systems

Intermedin (IMD) is a novel peptide related to calcitonin gene-related peptide (CGRP) and adrenomedullin (AM). Proteolytic processing of a larger precursor yields a series of biologically active C-terminal fragments, IMD(1-53), IMD(1-47) and IMD(8-47). IMD shares a family of receptors with AM and CGRP composed of a calcitonin-receptor like receptor (CALCRL) associated with one of three receptor activity modifying proteins (RAMP). Compared to CGRP, IMD is less potent at CGRP(1) receptors but more potent at AM(1) receptors and AM(2) receptors; compared to AM, IMD is more potent at CGRP(1) receptors but less potent at AM(1) and AM(2) receptors. The cellular and tissue distribution of IMD overlaps in some aspects with that of CGRP and AM but is distinct from both. IMD is present in neonatal but absent or expressed sparsely, in adult heart and vasculature and present at low levels in plasma. The prominent localization of IMD in hypothalamus and pituitary and in kidney is consistent with a physiological role in the central and peripheral regulation of the circulation and water-electrolyte homeostasis. IMD is a potent systemic and pulmonary vasodilator, influences regional blood flow and augments cardiac contractility. IMD protects myocardium from the deleterious effects of oxidative stress associated with ischaemia-reperfusion injury and exerts an anti-growth effect directly on cardiomyocytes to oppose the influence of hypertrophic stimuli. The robust increase in expression of the peptide in hypertrophied and ischaemic myocardium indicates an important protective role for IMD as an endogenous counter-regulatory peptide in the heart.

Influence of atenolol and nifedipine on nitric-oxide deficient cardiomyocyte hypertrophy and expression of the cardio-endocrine peptide intermedin and its receptor components

BACKGROUND/AIMS

Chronic inhibition of nitric oxide (NO) synthesis is associated with hypertension, myocardial ischemia, oxidative stress and hypertrophy; expression of adrenomedullin (AM) and intermedin (IMD) and their receptor activity modifying proteins (RAMPs 1-3) is augmented in cardiomyocytes, indicating that the myocardial AM/ IMD system may be activated in response to pressure loading and ischemic insult. The aim was to examine effects on (i) parameters of cardiomyocyte hypertrophy and on (ii) expression of AM and IMD and their receptor components in NO-deficient cardiomyocytes of an intervention chosen specifically for ability to alleviate pressure loading and ischemic injury concurrently.

METHODS

The NO synthesis inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME, 35 mg.kg(-1).day(-1)) was given to rats for 8 weeks, with/ without concurrent administration of beta-adrenoceptor antagonist, atenolol (25 mg.kg(-1).day(-1)) / calcium channel blocker, nifedipine (20mg.kg(-1).day(-1)).

RESULTS

In L-NAME treated rats, atenolol / nifedipine abolished increases in systolic blood pressure and plasma AM and IMD levels and in left ventricular cardiomyocytes: (i) normalized increased cell width and mRNA expression of hypertrophic (sk-alpha-actin) and cardio-endocrine (ANP, BNP, ET) genes; (ii) normalized augmented membrane protein oxidation; (iii) normalized mRNA expression of AM, IMD, RAMP1, RAMP2 and RAMP3.

CONCLUSIONS

normalization of blood pressure and membrane oxidant status together with prevention of hypertrophy and normalization of the augmented expression of AM, IMD and their receptor components in NO-deficient cardiomyocytes by atenolol / nifedipine supports involvement of both pressure loading and ischemic insult in stimulating cardiomyocyte hypertrophy and induction of these counter-regulatory peptides and their receptor components. Attenuation of augmented expression of IMD in this model cannot however be explained simply by prevention of cardiomyocyte hypertrophy.

Effect of hyperhomocysteinemia on cardiovascular risk factors and initiation of atherosclerosis in Wistar rats

Hyperhomocysteinemia is considered an independent risk factor for atherosclerosis. The present study was designed to assess the effect of high level of serum homocysteine on other cardiovascular risk factors and markers in rats and to study its mode of action in initiating atherosclerosis. To address this issue, four different doses of methionine (0.1 g/kg, 0.25 g/kg, 0.5 g/kg, 1 g/kg) were orally administered to four groups (Group II, III, IV, V respectively) of rats (6 rats in each group) for a period of 8 weeks to get different level of homocysteine in serum. Group I was administered with saline and served as control. Our results revealed that the level of Total cholesterol, Triglyceride, and Oxidized low-density lipoproteins increased significantly with the increase in the level of serum homocysteine. The levels of Resistin, C-reactive protein and cysteinyl-leukotrienes were found to be significantly high in Group IV (P<0.001 vs Group I) and Group V (P<0.001 vs Group I) at 8 weeks. Total antioxidant capacity and nitrite/nitrate level in serum showed negative correlation with the increased dose of methionine. The mRNA expression and the enzyme activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase significantly increased only in livers of rats of Group V. Furthermore, high mRNA expression of P2 receptors and caveolin were found in aorta of rats administered with high dose of methionine (Group IV and V at 8 weeks). Data obtained from in-vitro effect of homocysteine on isolated aortic arch also showed induction in P2 receptors and caveolin with the increase in the concentration of homocysteine. These findings collectively suggest that hyperhomocysteinemia initiates atherosclerosis by modulating the cholesterol biosynthesis and by significantly inducing the level of other cardiovascular risk factors and markers, which play important role in initiating atherosclerosis.

Adrenomedullin 2 antagonist infusion to rats during midgestation causes fetoplacental growth restriction through apoptosis

Adrenomedullin 2 (ADM2) is a recently discovered member of the calcitonin/calcitonin gene-related peptide family with an exon-intron structure similar to that of ADM. The mRNA of ADM2 is expressed in several tissues, including uterus and ovary. The present study was designed to assess the effects of ADM2 antagonist (ADM2(17-47)) infusion to pregnant rats on fetal and placental growth. On Day 15 of gestation, rats were implanted s.c. with osmotic minipumps delivering 50 and 200 mug per rat per day of ADM2(17-47) and were killed on Gestational Day 18. In ADM2(17-47)-treated rats, placental weights were significantly inhibited in a dose-related manner, with an 11% reduction in the group of rats receiving 200 microg/day, whereas the fetal weights were reduced by 17% without significant differences between the two doses. 2 In ADM2(17-47)-infused rats, increased apoptosis was demonstrated in the labyrinth and junctional zones of rat placenta by the TUNEL method compared with the control animals. Western blot analysis demonstrated that in ADM2(17-47)-treated rats Bcl-2, mitochondrial cytochrome c, and active caspase-9 and caspase-3 were significantly increased compared with the controls. No significant treatment-associated changes were observed in Bax, Bid, p53, and caspase-8 and caspase-10 proteins in the treated placentas. In addition, infusion of ADM2(17-47) caused a significant decline in the transcripts of nitric oxide synthase 3 (NOS3) and NOS2. These findings show that ADM2(17-47) infusion in rats during midpregnancy cause fetoplacental growth restriction through the activation of mitochondrial apoptotic pathways. This study demonstrates for the first time (to our knowledge) a potential role for ADM2 in placental functions during pregnancy.