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

Intermedin alleviates the inflammatory response and stabilizes the endothelial barrier in LPS-induced ARDS through the PI3K/Akt/eNOS signaling pathway

Inflammatory storms and endothelial barrier dysfunction are the central pathophysiological features of acute respiratory distress syndrome (ARDS). Intermedin (IMD), a member of the calcitonin gene-related peptide (CGRP) family, has been reported to alleviate inflammation and protect endothelial cell (EC) integrity. However, the effects of IMD on ARDS have not been clearly elucidated. In the present study, clinical ARDS data were used to explore the relationship between serum IMD levels and disease severity and prognosis, and we then established a model to predict the possibility of hospital survival. Mouse models of ARDS and LPS-challenged endothelial cells were used to analyze the protective effect and underlying mechanism of IMD. We found that in patients with ARDS, increased serum IMD levels were associated with reduced disease severity and increased rates of hospital survival. IMD alleviated the LPS-induced inflammatory response by decreasing proinflammatory cytokines, NF-κB p65 expression and NF-κB p65 nuclear translocation. In addition, IMD stabilized the endothelial barrier by repairing adherens junctions (AJs), cytoskeleton and capillary leakage. IMD exerted protective effects against ARDS on pulmonary endothelial cells, at least partly, through PI3K/Akt/eNOS signaling, while IMD's anti-inflammation effect was mediated through an eNOS-independent mechanism. Our study may provide new therapeutic insight for ARDS treatment.

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.

Inhibition of endoplasmic reticulum stress by intermedin1-53 attenuates angiotensin II-induced abdominal aortic aneurysm in ApoE KO Mice

Endoplasmic reticulum stress (ERS) is involved in the development of abdominal aortic aneurysm (AAA). Since bioactive peptide intermedin (IMD)1-53 protects against AAA formation, here we investigated whether IMD1-53 attenuates AAA by inhibiting ERS. AAA model was induced by angiotensin II (AngII) in ApoE KO mouse background. AngII-treated mouse aortas showed increased ERS gene transcription of caspase12, eukaryotic translation initiation factor 2a (eIf2a) and activating transcription factor 4(ATF4).The protein level of ERS marker glucose regulated protein 94(GRP94), ATF4 and C/EBP homologous protein 10(CHOP) was also up-regulated by AngII. Increased ERS levels were accompanied by severe VSMC apoptosis in human AAA aorta. In vivo administration of IMD1-53 greatly reduced AngII-induced AAA and abrogated the activation of ERS. To determine whether IMD inhibited AAA by ameliorating ERS, we used 2 non-selective ERS inhibitors phenyl butyrate (4-PBA) and taurine (TAU). Similar to IMD, PBA, and TAU significantly reduced the incidence of AAA and AAA-related pathological disorders. In vitro, AngII infusion up-regulated CHOP, caspase12 expression and led to VSMC apoptosis. IMD siRNA aggravated the CHOP, caspase12-mediated VSMC apoptosis, which was abolished by ATF4 silencing. IMD infusion promoted the phosphorylation of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) in aortas in ApoE KO mice, and the AMPK inhibitor compound C abolished the protective effect of IMD on VSMC ERS and apoptosis induced by AngII. In conclusion, IMD may protect against AAA formation by inhibiting ERS via activating AMPK phosphorylation.

Mechanism of adrenomedullin 2/intermedin mediated vasorelaxation in rat main pulmonary artery

Adrenomedullin 2/intermedin (AM2/IMD) is a member of calcitonin related gene peptide family and an important nitric oxide mediated vasorelaxant in various vascular beds. However, the mechanism of post receptor-interaction is not clear and may differ depending on tissue type and species. In this study, we aimed to investigate the exact mechanism and the role of BK_Ca and calcium channels on the vasorelaxant effect of AM2/IMD in rat PA. Changes in the AM2/IMD-mediated vasorelaxation were evaluated in the presence of various inhibitors. CGRP_(8-37) (10^-6 M), L-NAME (10^-4 M), ODQ (10^-5 M), SQ22536 (10^-4 M), H89 (10^-6 M), TEA (10^-2 M), iberiotoxin (3 × 10^-7 M), and verapamil (10^-5 M), all partly or completely inhibited the vasorelaxation. The relaxation was also abolished by removal of the endothelium, or in KCl precontracted PAs. AM2/IMD did not elicit vasorelaxation in the Ca²⁺-free conditions. However, the vasorelaxation was not inhibited with AM_(22-52) (10^-6 M), 4-AP (3 × 10^-3 M), glibenclamide (10^-5 M), apamin (3 × 10^-7 M), TRAM-34 (10^-5 M), and La⁺³ (10^-4 M). AM2/IMD -induced changes in intracellular calcium levels and isometric force were monitored simultaneously in fura-2-loaded, endothelium-intact PAs. The AM2/IMD-induced increase in intracellular Ca²⁺ concentration was inhibited in the presence of iberiotoxin and verapamil, whereas no change was observed with La³⁺ incubation. Our data suggest that the cAMP/PKA pathway is one of the important pathways AM2/IMD-induced vasorelaxation. AM2/IMD acts through activation of endothelial BK_Ca and subsequently causes hyperpolarization of the endothelial cell membrane. The hyperpolarization induces Ca²⁺ influx, which leads to NO production and subsequent vasorelaxation.

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.

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.

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.

Haemodynamic, endocrine and renal actions of adrenomedullin 5 in an ovine model of heart failure

AM5 (adrenomedullin 5), a newly described member of the CGRP (calcitonin gene-related peptide) family, is reported to play a role in normal cardiovascular physiology. The effects of AM5 in HF (heart failure), however, have not been investigated. In the present study, we intravenously infused two incremental doses of AM5 (10 and 100 ng/min per kg of body weight each for 90 min) into eight sheep with pacing-induced HF. Compared with time-matched vehicle control infusions, AM5 produced progressive and dose-dependent increases in left ventricular dP/dt(max) [LD (low dose), +56 mmHg/s and HD (high dose), +152 mmHg/s] and cardiac output (+0.83 l/min and +1.81 l/min), together with decrements in calculated total peripheral resistance (−9.4 mmHg/min per litre and −14.7 mmHg/min per litre), mean arterial pressure (−2.8 mmHg and −8.4 mmHg) and LAP (left atrial pressure; −2.6 mmHg and −5.6 mmHg) (all P<0.001). HD AM5 significantly raised PRA (plasma renin activity) (3.5-fold increment, P<0.001), whereas plasma aldosterone levels were unchanged over the intra-infusion period and actually fell in the post-infusion period (70% decrement, P<0.01), resulting in a marked decrease in the aldosterone/PRA ratio (P<0.01). Despite falls in LAP, plasma atrial natriuretic peptide and B-type natriuretic peptide concentrations were maintained relative to controls. AM5 infusion also induced significant increases in urine volume (HD 2-fold increment, P<0.05) and urine sodium (2.7-fold increment, P<0.01), potassium (1.7-fold increment, P<0.05) and creatinine (1.4-fold increment, P<0.05) excretion and creatinine clearance (60% increment, P<0.05). In conclusion, AM5 has significant haemodynamic, endocrine and renal actions in experimental HF likely to be protective and compensatory in this setting. These results suggest that AM5 may have potential as a therapeutic agent in human HF.

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.