Intermedin 1-53 inhibits rat cardiac fibroblast activation induced by angiotensin II

Intermedin1-53 Inhibits NLRP3 Inflammasome Activation by Targeting IRE1α in Cardiac Fibrosis

Intermedin (IMD), a paracrine/autocrine peptide, protects against cardiac fibrosis. However, the underlying mechanism remains poorly understood. Previous study reports that activation of nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) inflammasome contributes to cardiac fibrosis. In this study, we aimed to investigate whether IMD mitigated cardiac fibrosis by inhibiting NLRP3. Cardiac fibrosis was induced by angiotensin II (Ang II) infusion for 2 weeks in rats. Western blot, real-time PCR, histological staining, immunofluorescence assay, RNA sequencing, echocardiography, and hemodynamics were used to detect the role and the mechanism of IMD in cardiac fibrosis. Ang II infusion resulted in rat cardiac fibrosis, shown as over-deposition of myocardial interstitial collagen and cardiac dysfunction. Importantly, NLRP3 activation and endoplasmic reticulum stress (ERS) were found in Ang II-treated rat myocardium. Ang II infusion decreased the expression of IMD and increased the expression of the receptor system of IMD in the fibrotic rat myocardium. IMD treatment attenuated the cardiac fibrosis and improved cardiac function. In addition, IMD inhibited the upregulation of NLRP3 markers and ERS markers induced by Ang II. In vitro, IMD knockdown by small interfering RNA significantly promoted the Ang II-induced cardiac fibroblast and NLRP3 activation. Moreover, silencing of inositol requiring enzyme 1 α (IRE1α) blocked the effects of IMD inhibiting fibroblast and NLRP3 activation. Pre-incubation with PKA pathway inhibitor H89 blocked the effects of IMD on the anti-ERS, anti-NLRP3, and anti-fibrotic response. In conclusion, IMD alleviated cardiac fibrosis by inhibiting NLRP3 inflammasome activation through suppressing IRE1α via the cAMP/PKA pathway.

CGRP derived from cardiac fibroblasts is an endogenous suppressor of cardiac fibrosis

AIMS

Aberrant activation of cardiac fibroblasts leads to cardiac fibrosis, and evolving evidences suggest that endogenous bioactive substances derived from cardiac fibroblasts regulate cardiac fibroblasts activation in an autocrine/paracrine manner. Here we first presented evidence that cardiac fibroblasts can synthesize and secrete calcitonin gene-related peptide (CGRP), therefore, this study aimed to investigate the role of cardiac fibroblasts-derived CGRP in cardiac fibroblasts activation and its regulative mechanism.

METHODS AND RESULTS

The abundantly expression of CGRP in rat, mouse, and human myocardium allowed us to explore the cellular origin of CGRP, and found that the cardiac CGRP was mainly derived from cardiac fibroblasts. Activating TRPA1 with a specific agonist allyl isothiocyanate promoted the synthesis and secretion of CGRP, as well as intracellular Ca2+. These effects were reversed by TRPA1-specific antagonist HC030031 and Ca2+ chelator BAPTA-AM. TGF-β1 was applied to induce the activation of cardiac fibroblasts, and found that TGF-β1 can increase the mRNA expression and secretion levels of CGRP in cardiac fibroblasts. Either CGRP8-37 (CGRP receptor antagonist) or α-CGRP small interfering RNA (siRNA) aggravated TGF-β1-induced proliferation, differentiation, collagen production, and instigated inflammation in cardiac fibroblasts. Moreover, TGF-β1-induced NF-κB activation including IκBα phosphorylation and p65 nuclear translocation were also promoted by CGRP8-37 and α-CGRP siRNA. NF-κB inhibitor pyrrolidinedithiocarbamate ammonium (PDTC) reversed the effects of CGRP8-37 on NF-κB activation. The promotive effects of CGRP8-37 on TGF-β1-induced activation of cardiac fibroblasts were all reversed by PDTC. Monocrotaline (MCT) induces pulmonary arterial hypertension, progressively leading to right ventricular fibrosis. This model of cardiac fibrosis was developed here to test the potentially beneficial effects of TRPA1 activation in vivo. The non-toxic TRPA1 agonist Cinnamaldehyde (CA) inhibited MCT-induced elevation in right ventricle systolic pressure, RV/LV + S, and right ventricular collagen accumulation, as well as down-regulation of CGRP. CA increased the synthesis and secretion of CGRP, and inhibited TGF-β1-induced activation in cardiac fibroblasts.

CONCLUSION

Our data suggested an autocrine role for cardiac fibroblasts-derived CGRP in suppressing activation of cardiac fibroblasts through inhibiting NF-κB activation. Increasing autocrine CGRP by activating TRPA1 can ameliorate cardiac fibrosis. These findings support the notion that CGRP derived from cardiac fibroblasts is an endogenous suppressor of cardiac fibrosis.

The Cardiopulmonary Effects of the Calcitonin Gene-related Peptide Family

Cardiopulmonary diseases are very common among the population. They are high-cost diseases and there are still no definitive treatments. The roles of members of the calcitonin-gene related-peptide (CGRP) family in treating cardiopulmonary diseases have been studied for many years and promising results obtained. Especially in recent years, two important members of the family, adrenomedullin and adrenomedullin2/intermedin, have been considered new treatment targets in cardiopulmonary diseases. In this review, the roles of CGRP family members in cardiopulmonary diseases are investigated based on the studies performed to date.

The Role of Cyclic AMP Signaling in Cardiac Fibrosis

Myocardial stress and injury invariably promote remodeling of the cardiac tissue, which is associated with cardiomyocyte death and development of fibrosis. The fibrotic process is initially triggered by the differentiation of resident cardiac fibroblasts into myofibroblasts. These activated fibroblasts display increased proliferative capacity and secrete large amounts of extracellular matrix. Uncontrolled myofibroblast activation can thus promote heart stiffness, cardiac dysfunction, arrhythmias, and progression to heart failure. Despite the well-established role of myofibroblasts in mediating cardiac disease, our current knowledge on how signaling pathways promoting fibrosis are regulated and coordinated in this cell type is largely incomplete. In this respect, cyclic adenosine monophosphate (cAMP) signaling acts as a major modulator of fibrotic responses activated in fibroblasts of injured or stressed hearts. In particular, accumulating evidence now suggests that upstream cAMP modulators including G protein-coupled receptors, adenylyl cyclases (ACs), and phosphodiesterases (PDEs); downstream cAMP effectors such as protein kinase A (PKA) and the guanine nucleotide exchange factor Epac; and cAMP signaling organizers such as A-kinase anchoring proteins (AKAPs) modulate a variety of fundamental cellular processes involved in myocardial fibrosis including myofibroblast differentiation, proliferation, collagen secretion, and invasiveness. The current review will discuss recent advances highlighting the role of cAMP and AKAP-mediated signaling in regulating pathophysiological responses controlling cardiac fibrosis.

Structure-function analyses reveal a triple β-turn receptor-bound conformation of adrenomedullin 2/intermedin and enable peptide antagonist design

The cardioprotective vasodilator peptide adrenomedullin 2/intermedin (AM2/IMD) and the related adrenomedullin (AM) and calcitonin gene-related peptide (CGRP) signal through three heterodimeric receptors comprising the calcitonin receptor-like class B G protein-coupled receptor (CLR) and a variable receptor activity-modifying protein (RAMP1, -2, or -3) that determines ligand selectivity. The CGRP receptor (RAMP1:CLR) favors CGRP binding, whereas the AM₁ (RAMP2:CLR) and AM₂ (RAMP3:CLR) receptors favor AM binding. How AM2/IMD binds the receptors and how RAMPs modulate its binding is unknown. Here, we show that AM2/IMD binds the three purified RAMP-CLR extracellular domain (ECD) complexes with a selectivity profile that is distinct from those of CGRP and AM. AM2/IMD bound all three ECD complexes but preferred the CGRP and AM₂ receptor complexes. A 2.05 Å resolution crystal structure of an AM2/IMD antagonist fragment-bound RAMP1-CLR ECD complex revealed that AM2/IMD binds the complex through a unique triple β-turn conformation that was confirmed by peptide and receptor mutagenesis. Comparisons of the receptor-bound conformations of AM2/IMD, AM, and a high-affinity CGRP analog revealed differences that may have implications for biased signaling. Guided by the structure, enhanced-affinity AM2/IMD antagonist variants were developed, including one that discriminates the AM₁ and AM₂ receptors with ∼40-fold difference in affinities and one stabilized by an intramolecular disulfide bond. These results reveal differences in how the three peptides engage the receptors, inform development of AM2/IMD-based pharmacological tools and therapeutics, and provide insights into RAMP modulation of receptor pharmacology.

Intermedin attenuates high-glucose exacerbated simulated hypoxia/reoxygenation injury in H9c2 cardiomyocytes via ERK1/2 signaling

Objective:

This study investigated whether and how intermedin (IMD) exerted a protective effect against simulated hypoxia/reoxygenation (H/R) injury in high-glucose-treated H9c2 cells.

Methods:

Cellular viability was assessed via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Oxidative stress was determined by malondialdehyde and superoxide dismutase content in the culture medium supernatant. Flow cytometry with Annexin V/propidium iodide staining was used to detect the cardiomyocyte apoptosis rate. The protein expression of Bax, Bcl-2, caspase-3, and ERK1/2 was determined by western blot.

Results:

IMD administration to H9c2 cells during H/R injury decreased oxidative stress product generation and inhibited apoptosis ( P < 0.05 or P < 0.01) while these effects were blocked by the ERK1/2 inhibitor ( P < 0.05 or P < 0.01). Through the application of a specific ERK1/2 inhibitor, it was demonstrated that IMD mitigates high-glucose-induced oxidative stress and apoptosis via ERK1/2 signaling.

Conclusion:

Intermedin may be a novel therapeutic agent for mitigating diabetic cardiovascular injury in the clinical setting.

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 Protects Against Myocardial Fibrosis by Inhibiting Endoplasmic Reticulum Stress and Inflammation Induced by Homocysteine in Apolipoprotein E-Deficient Mice

AIM

Endoplasmic reticulum stress (ERS) and inflammation participate in cardiac fibrosis. Importantly, a novel paracrine/autocrine peptide intermedin_1-53 (IMD_1-53) in the heart inhibits myocardial fibrosis in rats. However, the mechanisms are yet to be fully elucidated.

METHODS

Myocardial fibrosis in apolipoprotein E-deficient (ApoE -/-) mice and neonatal rat cardiac fibroblasts (CFs) were induced using homocysteine (Hcy).

RESULTS

IMD_1-53 inhibited myocardial fibrosis in vivo and in vitro. Picrosirius red staining showed that IMD_1-53 reduced myocardial interstitial collagen deposition in ApoE-/- mice treated with Hcy and decreased the expression of myocardial collagen I and III, which was further verified in rat CFs. IMD_1-53 attenuated myocardial hypertrophy, as shown by cardiomyocyte cross-sectional area, ratio of heart weight to body weight, and mRNA levels of atrial natriuretic peptide and brain natriuretic peptide. IMD_1-53 inhibited the upregulation of ERS hallmarkers such as glucose-regulated protein 78 (GRP78), GRP94, activating transcription factor 6 (ATF6), ATF4, inositol-requiring enzyme 1α, spliced-X-box-binding protein-1, protein kinase receptor-like ER kinase, and eukaryotic translation initiation factor 2α in mouse myocardium and rat CFs treated with Hcy. In addition, IMD_1-53 decreased the production of inflammatory factors such as tumor necrosis factor-α, monocyte chemotactic protein-1, interleukin-6 (IL-6), and IL-1β in the mouse myocardium and rat CFs treated with Hcy. Concurrently, IMD_1-53 ameliorated the expression of nuclear factor-κB, transforming growth factor-β1, and c-Jun N-terminal kinase in the mouse myocardium and rat CFs treated with Hcy.

CONCLUSIONS

IMD potentially protects against myocardial fibrosis induced by Hcy in ApoE-/- mice, possibly via attenuating myocardial ERS and inflammation.

Endothelium-derived intermedin/adrenomedullin-2 protects human ventricular cardiomyocytes from ischaemia-reoxygenation injury predominantly via the AM₁ receptor

Application of intermedin/adrenomedullin-2 (IMD/AM-2) protects cultured human cardiac vascular cells and fibroblasts from oxidative stress and simulated ischaemia-reoxygenation injury (I-R), predominantly via adrenomedullin AM1 receptor involvement; similar protection had not been investigated previously in human cardiomyocytes (HCM). Expression of IMD, AM and their receptor components was studied in HCM. Receptor subtype involvement in protection by exogenous IMD against injury by simulated I-R was investigated using receptor component-specific siRNAs. Direct protection by endogenous IMD against HCM injury, both as an autocrine factor produced in HCM themselves and as a paracrine factor released from HCMEC co-cultured with HCM, was investigated using peptide-specific siRNA for IMD. IMD, AM and their receptor components (CLR, RAMPs1-3) were expressed in HCM. IMD 1nmol L(-1), applied either throughout ischaemia (3h) and re-oxygenation (1h) or during re-oxygenation (1h) alone, attenuated HCM injury (P<0.05); cell viabilities were 59% and 61% respectively vs. 39% in absence of IMD. Cytoskeletal disruption, protein carbonyl formation and caspase activity followed similar patterns. Pre-treatment (4 days) of HCM with CLR and RAMP2 siRNAs attenuated (P<0.05) protection by exogenous IMD. Pre-treatment of HCMEC with IMD (and AM) siRNA augmented (P<0.05) I-R injury: cell viabilities were 22% (and 32%) vs. 39% untreated HCMEC. Pre-treatment of HCM with IMD (and AM) siRNA did not augment HCM injury: cell viabilities were 37% (and 39%) vs. 39% untreated HCM. Co-culture with HCMEC conferred protection from injury on HCM; such protection was attenuated when HCMEC were pre-treated with IMD (but not AM) siRNA before co-culture. Although IMD is present in HCM, IMD derived from HCMEC and acting in a paracrine manner, predominantly via AM1 receptors, makes a marked contribution to cardiomyocyte protection by the endogenous peptide against acute I-R injury.

Intermedin ameliorates IgA nephropathy by inhibition of oxidative stress and inflammation

IgA nephropathy (IgAN) is the most frequent form of glomerulonephritis worldwide. The role of oxidative stress and inflammation in the pathogenesis of IgAN has been reported. Intermedin (IMD) is a newly discovered peptide that is closely related to adrenomedullin. We have recently reported that IMD can significantly reduce renal ischemia/reperfusion injury by diminishing oxidative stress and suppressing inflammation. The present study was designed to explore whether IMD ameliorates IgAN via oxidative stress- and inflammation-dependent mechanisms. Our results showed that IMD administration resulted in the prevention of albuminuria and ameliorated renal pathomorphological changes. These findings were associated with (1) decreased renal TGF-β1 and collagen IV expression, (2) an increased SOD level and reduced MDA level, (3) the inhibition of the renal activation of NF-κB p65 and (4) the downregulation of the expression of inflammatory factors (TNF-α, MCP-1 and MMP-9) in the kidney. These results indicate that IMD in the kidney protects against IgAN by reducing oxidative stress and suppressing inflammation.

Intermedin in the paraventricular nucleus attenuates cardiac sympathetic afferent reflex in chronic heart failure rats

Background and Aim

Intermedin (IMD) is a member of calcitonin/calcitonin gene-related peptide (CGRP) family together with adrenomedullin (AM) and amylin. It has a wide distribution in the central nervous system (CNS) especially in hypothalamic paraventricular nucleus (PVN). Cardiac sympathetic afferent reflex (CSAR) is enhanced in chronic heart failure (CHF) rats. The aim of this study is to determine the effect of IMD in the PVN on CSAR and its related mechanisms in CHF rats.

Methodology/Principal Findings

Rats were subjected to left descending coronary artery ligation to induce CHF or sham-operation (Sham). Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) were recorded. CSAR was evaluated by the RSNA and MAP responses to epicardial application of capsaicin. Acute experiments were carried out 8 weeks after coronary ligation or sham surgery under anesthesia. IMD and angiotensin II (Ang II) levels in the PVN were up-regulated in CHF rats. Bilateral PVN microinjection of IMD caused greater decreases in CSAR and the baseline RSNA and MAP in CHF rats than those in Sham rats. The decrease of CSAR caused by IMD was prevented by pretreatment with AM receptor antagonist AM22-52, but not CGRP receptor antagonist CGRP8-37. Ang II in the PVN significantly enhanced CSAR and superoxide anions level, which was inhibited by PVN pretreatment with IMD or tempol (a superoxide anions scavenger) in Sham and CHF rats.

Conclusion

IMD in the PVN inhibits CSAR via AM receptor, and attenuates the effects of Ang II on CSAR and superoxide anions level in CHF rats. PVN superoxide anions involve in the effect of IMD on attenuating Ang II-induced CSAR response.

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.

Intermedin enhances sympathetic outflow via receptor-mediated cAMP/PKA signaling pathway in nucleus tractus solitarii of rats

Direct administration of intermedin (IMD) into the brain elicits cardiovascular effects different from the systemic administration. Nucleus tractus solitarii (NTS) is an important region for the cardiovascular regulation. The present study was designed to determine the effect of IMD on modulating the sympathetic outflow and its related molecular mechanism in the NTS. Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded in anesthetized rats. Site-specific microinjection of IMD (20pmol) bilaterally into the NTS significantly increased RSNA and MAP. IMD-evoked increases of RSNA and MAP were almost abolished by pretreatment with receptor antagonist ADM22-52, an adenylyl cyclase (AC) inhibitor SQ22536, or a protein kinase A (PKA) inhibitor Rp-cAMP. However, pretreatment with another receptor antagonist calcitonin gene-related peptide (CGRP)8-37 did not suppress the increases of RSNA and MAP induced by IMD. Furthermore, IMD increased the cyclic adenosine monophosphate (cAMP) level, which was inhibited by ADM22-52 pretreatment in the NTS. These results suggest that IMD participates in the sympathetic nerve activity and central regulation of the cardiovascular system and a receptor-mediated cAMP/PKA signaling pathway is involved in IMD-induced effects in the NTS.

Intermedin protects against myocardial ischemia-reperfusion injury in diabetic rats

Background

Diabetic patients, through incompletely understood mechanisms, endure exacerbated ischemic heart injury compared to non-diabetic patients. Intermedin (IMD) is a novel calcitonin gene-related peptide (CGRP) superfamily member with established cardiovascular protective effects. However, whether IMD protects against diabetic myocardial ischemia/reperfusion (MI/R) injury is unknown.

Methods

Diabetes was induced by streptozotocin in Sprague–Dawley rats. Animals were subjected to MI via left circumflex artery ligation for 30 minutes followed by 2 hours R. IMD was administered formally 10 minutes before R. Outcome measures included left ventricular function, oxidative stress, cellular death, infarct size, and inflammation.

Results

IMD levels were significantly decreased in diabetic rats compared to control animals. After MI/R, diabetic rats manifested elevated intermedin levels, both in plasma (64.95 ± 4.84 pmol/L, p < 0.05) and myocardial tissue (9.8 ± 0.60 pmol/L, p < 0.01) compared to pre-MI control values (43.62 ± 3.47 pmol/L and 4.4 ± 0.41). IMD administration to diabetic rats subjected to MI/R decreased oxidative stress product generation, apoptosis, infarct size, and inflammatory cytokine release (p < 0.05 or p < 0.01).

Conclusions

By reducing oxidative stress, inflammation, and apoptosis, IMD may represent a promising novel therapeutic target mitigating diabetic ischemic heart injury.

Increased plasma levels of intermedin and brain natriuretic peptide associated with severity of coronary stenosis in acute coronary syndrome

Intermedin (IMD) is a newly discovered peptide with increased levels in plasma and cardiac tissue in mice with ischemia/reperfusion. Continuous administration of low dose IMD markedly elevated the mRNA abundance of myocardial BNP in rats. Plasma BNP levels may reflect the severity of degree of coronary stenosis in patients with acute coronary syndrome (ACS). However, the role of circulating IMD in coronary heart disease remains unclear. We aimed to examine the plasma content of IMD and brain natriuretic peptide (BNP) and its clinical significance in patients with ACS. We collected plasma samples from 41 patients with ACS and 31 controls and measured IMD and BNP levels by radioimmunoassay. The severity of coronary artery stenosis for patients with ACS was measured by coronary angiography. Plasma IMD and BNP levels were markedly higher in ACS patients than that in controls (P<0.05). The increased plasma IMD and BNP were positively correlated with degree of coronary stenosis in ACS patients (r=0.263 and r=0.238, respectively, both P<0.05). In addition, plasma levels of IMD were positively correlated with BNP levels.

Reverse myocardial effects of intermedin in pressure-overloaded hearts: role of endothelial nitric oxide synthase activity

Intermedin (IMD) is a cardiac peptide synthesized in a prepro form, which undergoes a series of proteolytic cleavages and amidations to yield the active forms of 47 (IMD(1-47)) and 40 amino acids (IMD(8-47)). There are several lines of evidence of increased IMD expression in rat models of cardiac pathologies, including congestive heart failure and ischaemia; however, its myocardial effects upon cardiac disease remain unexplored. With this in mind, we investigated the direct effects of increasing concentrations of IMD(1-47) (10(-10) to10(-6) m) on contraction and relaxation of left ventricular (LV) papillary muscles from two rat models of chronic pressure overload, one induced by transverse aortic constriction (TAC), the other by nitric oxide (NO) deficiency due to chronic NO synthase inhibition (NG-nitro-l-arginine, l-NAME), and respective controls (Sham and Ctrl). In TAC and l-NAME rats, exogenous administration of IMD(1-47) elicited concentration-dependent positive inotropic and lusitropic effects. By contrast, in Sham and Ctrl rats, IMD(1-47) induced a negative inotropic response without a significant effect on relaxation. Both TAC and l-NAME rats presented LV hypertrophy, elevated LV systolic pressures, preserved systolic function and elevated peroxynitrite levels. In the normal myocardium (Ctrl and Sham), IMD(1-47) induced a 3-fold increase of endothelial nitric oxide synthase (eNOS) phosphorylation at Ser(1177), indicating enhanced eNOS activity. In TAC and l-NAME rats, eNOS phosphorylation was increased at baseline, and its response to IMD(1-47) was blunted. In addition, the distinct myocardial response to IMD(1-47) was accompanied by distinct subcellular mechanisms. While in Sham rats the addition of IMD(1-47) induced the phosphorylation of cardiac troponin I due to NO/cGMP activation, in TAC rats IMD(1-47) induced phospholamban phosphorylation possibly associated with cAMP/protein kinase A activation. Therefore, we demonstrated for the first time a reversed myocardial response to IMD(1-47) neurohumoral stimulation due to impairment of eNOS activation in TAC and l-NAME rats. These results not only reveal the distinct myocardial effects and subcellular mechanisms for IMD(1-47) in normal and hypertrophic hearts, but also highlight the potential pathophysiological relevance of cardiac endothelial dysfunction in neurohumoral myocardial action.

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.

AM₁-receptor-dependent protection by intermedin of human vascular and cardiac non-vascular cells from ischaemia-reperfusion injury

Intermedin (IMD) protects rodent heart and vasculature from oxidative stress and ischaemia. Less is known about distribution of IMD and its receptors and the potential for similar protection in man. Expression of IMD and receptor components were studied in human aortic endothelium cells (HAECs), smooth muscle cells (HASMCs), cardiac microvascular endothelium cells (HMVECs) and fibroblasts (v-HCFs). Receptor subtype involvement in protection by IMD against injury by hydrogen peroxide (H₂O₂, 1 mmol l⁻¹) and simulated ischaemia and reperfusion were investigated using receptor component-specific siRNAs. IMD and CRLR, RAMP1, RAMP2 and RAMP3 were expressed in all cell types.When cells were treated with 1 nmol l⁻¹ IMD during exposure to 1 mmol l⁻¹ H₂O₂ for 4 h, viability was greater vs. H2O2 alone (P<0.05 for all cell types). Viabilities under 6 h simulated ischaemia differed (P<0.05) in the absence and presence of 1 nmol l⁻¹ IMD: HAECs 63% and 85%; HMVECs 51% and 68%; v-HCFs 42% and 96%. IMD 1 nmol l⁻¹ present throughout ischaemia (3 h) and reperfusion (1 h) attenuated injury (P<0.05): viabilities were 95%, 74% and 82% for HAECs, HMVECs and v-HCFs, respectively, relative to those in the absence of IMD (62%, 35%, 32%, respectively). When IMD 1 nmol l⁻¹ was present during reperfusion only, protection was still evident (P<0.05, 79%, 55%, 48%, respectively). Cytoskeletal disruption and protein carbonyl formation followed similar patterns. Pre-treatment (4 days) of HAECs with CRLR or RAMP2, but not RAMP1 or RAMP3, siRNAs abolished protection by IMD (1 nmol l⁻¹) against ischaemia-reperfusion injury. IMD protects human vascular and cardiac non-vascular cells from oxidative stress and ischaemia-reperfusion,predominantly via AM1 receptors.

Inhibition of endoplasmic reticulum stress by intermedin(1-53) protects against myocardial injury through a PI3 kinase-Akt signaling pathway

Intermedin (IMD) is a novel member of the calcitonin/calcitonin gene-related peptide family. We aimed to explore whether the cardioprotective effect of IMD is mediated by inhibiting myocardial endoplasmic reticulum (sarcoplasmic reticulum) stress (ERS). In vitro, IMD(1-53) (10(-9), 10(-8), and 10(-7) mol/l) directly inhibited the upregulation of ERS markers such as glucose-regulated protein 78, CCAAT/enhancer binding protein homologous protein, and caspase-12 induced by the ERS inducers tunicamycin (Tm, 10 mg/ml) or dithiothreitol (DTT, 2 mmol/l) in cardiac tissue. IMD(1-53) also inhibited Tm- or DTT-induced upregulation of cleaved activating transcription factor 6 and 4. These inhibitory effects of IMD(1-53) were abolished by the IMD receptor antagonist IMD(17-47) (10(-6) mol/l) and phosphoinositide 3-kinase inhibitor LY294002 (10 μmol/l). However, preincubation with PD98059 (20 μmol/l), an extracellular signal-regulated protein kinase inhibitor, and H89 (10 μmol/l), a protein kinase A inhibitor, could not block the ERS-inhibiting effects of IMD(1-53). Furthermore, in an in vivo model of myocardium ischemia/reperfusion (I/R) in rats, administration of IMD(1-53) (20 nmol/kg, intravenously) greatly attenuated ERS and ameliorated myocardium impairment induced by I/R. IMD(1-53) could exert its cardioprotective effect by inhibiting myocardial ERS, which might be mediated by the phosphoinositide 3-kinase/Akt signaling pathway.

Influence of adrenomedullin 2/intermedin gene polymorphism on blood pressure, renal function and silent cerebrovascular lesions in Japanese: the Ohasama study

Adrenomedullin 2/intermedin (AM2/IMD) is a novel vasodilator peptide with various effects on the renal function and cardiovascular system. An exonic insertion (I)/deletion (D) polymorphism (rs3840963) may influence generation of AM2/IMD-53, due to its location within the N-terminal sequence. We investigated the association of this polymorphism with blood pressure, renal function and the risk of silent cerebrovascular lesions in a Japanese population recruited from the Ohasama study. We recorded 24 h ambulatory blood pressure (ABP), estimated glomerular filtration rate (eGFR) and proteinuria of 1073 individuals over 40 years of age. Silent cerebrovascular lesions (lacunar infarction and white matter hyperintensity (WMH)) were recorded in 794 individuals over 55 years of age. Chronic kidney disease (CKD) was diagnosed in individuals with proteinuria and/or decreased eGFR ≤60 ml min(-1) per 1.73 m(2). DD carriers, compared with II and ID carriers, displayed significantly higher 24 h ABP (127.4 vs. 122.0 and 122.9 mm Hg, respectively, in systolic ABP, P=0.009; and 74.8 vs. 71.3 and 72.5 mm Hg, respectively, in diastolic ABP, P=0.002), and lower eGFR (75.4 vs. 82.6 and 82.9 ml min(-1) per 1.73 m(2), respectively, P=0.04). DD carriers also had a significantly higher odds ratio (OR) for prevalence of CKD (OR: 2.7, P=0.003), presence of lacunar infarction (OR: 2.4, P=0.01) and WMH (OR: 2.7, P=0.003), compared with II carriers. The AM2/IMD I/D polymorphism is associated with renal dysfunction, blood pressure regulation and asymptomatic cerebrovascular diseases in the Japanese general population.