Effect of adrenomedullin on renal hemodynamics and functions in dogs

Novel Biomarkers of Renal Dysfunction and Congestion in Heart Failure

Heart failure is a major public health problem and, despite the constantly emerging, new, effective treatments, it remains a leading cause of morbidity and mortality. Reliable tools for early diagnosis and risk stratification are crucial in the management of HF. This explains a growing interest in the development of new biomarkers related to various pathophysiological mechanisms of HF. In the course of this review, we focused on the markers of congestion and renal dysfunction in terms of their interference with cardiovascular homeostasis. Congestion is a hallmark feature of heart failure, contributing to symptoms, morbidity, and hospitalizations of patients with HF and has, therefore, become a therapeutic target in AHF. On the other hand, impaired renal function by altering the volume status contributes to the development and progression of HF and serves as a marker of an adverse clinical outcome. Early detection of congestion and an adequate assessment of renal status are essential for the prompt administration of patient-tailored therapy. This review provides an insight into recent advances in the field of HF biomarkers that could be potentially implemented in diagnosis and risk stratification of patients with HF.

Early Biomarkers of Altered Renal Function and Orthostatic Intolerance During 10-day Bedrest

Exposure to actual or simulated microgravity results in alterations of renal function, fluid redistribution, and bone loss, which is coupled to a rise of urinary calcium excretion. We provided evidence that high calcium delivery to the collecting duct reduces local Aquaporin 2 (AQP2)-mediated water reabsorption under vasopressin action, thus limiting the maximal urinary concentration to reduce calcium saturation. To investigate early renal adaptation into simulated microgravity, we investigated the effects of 10 days of strict bedrest in 10 healthy volunteers. We report here that 10 days of inactivity are associated with a transient, significant decrease (day 5) in vasopressin (copeptin) paralleled by a decrease in AQP2 excretion, consistent with an increased central volume to the heart, resulting in reduced water reabsorption. Moreover, bedrest caused a significant increase in calciuria secondary to bone demineralization paralleled by a decrease in PTH. Urinary osteopontin, a glycoprotein exerting a protective effect on stone formation, was significantly reduced during bedrest. Moreover, a significant increase in adrenomedullin (day 5), a peptide with vasodepressor properties, was observed at day 5, which may contribute to the known reduced orthostatic capacity post-bedrest. We conclude that renal function is altered in simulated microgravity and is associated with an early increase in the risk of stone formation and reduced orthostatic capacity post-bedrest within a few days of inactivity.

Pharmacological HIF-PHD inhibition reduces renovascular resistance and increases glomerular filtration by stimulating nitric oxide generation

AIM

Hypoxia-inducible factors (HIFs) are O₂ -sensitive transcription factors that regulate multiple biological processes which are essential for cellular adaptation to hypoxia. Small molecule inhibitors of HIF-prolyl hydroxylase domain (PHD) dioxygenases (HIF-PHIs) activate HIF-dependent transcriptional programs and have broad clinical potential. HIF-PHIs are currently in global late-stage clinical development for the treatment of anaemia associated with chronic kidney disease. Although the effects of hypoxia on renal haemodynamics and function have been studied in animal models and in humans living at high altitude, the effects of pharmacological HIF activation on renal haemodynamics, O₂ metabolism and metabolic efficiency are not well understood.

METHODS

Using a cross-sectional study design, we investigated renal haemodynamics, O₂ metabolism, gene expression and NO production in healthy rats treated with different doses of HIF-PHIs roxadustat or molidustat compared to vehicle control.

RESULTS

Systemic administration of roxadustat or molidustat resulted in a dose-dependent reduction in renovascular resistance (RVR). This was associated with increased glomerular filtration rate (GFR), urine flow and tubular sodium transport rate (T_Na ). Although both total O₂ delivery and T_Na were increased, more O₂ was extracted per transported sodium in rats treated with high-doses of HIF-PHIs, suggesting a reduction in metabolic efficiency. Changes in RVR and GFR were associated with increased nitric oxide (NO) generation and substantially suppressed by pharmacological inhibition of NO synthesis.

CONCLUSIONS

Our data provide mechanistic insights into dose-dependent effects of short-term pharmacological HIF activation on renal haemodynamics, glomerular filtration and O₂ metabolism and identify NO as a major mediator of these effects.

Mid-Regional Proadrenomedullin as a New Biomarker of Kidney and Cardiovascular Diseases-Is It the Future?

The increasing prevalence of cardiovascular disease and concomitant chronic kidney disease among the aging populations is responsible for considerable growth of mortality. Additionally, frequent, prolonged hospitalizations and long-term treatment generates progressive decline in bodily functions as well as substantial public health and economic burden. Accessibility to easy, non-invasive prognostic markers able to detect patients at risk of cardiovascular events may improve effective therapy and mitigate disease progression. Moreover, an early diagnosis allows time for implementation of prophylactic and educational programs that may result in decreased morbidity, improved quality of life and reduced public health expenditure. One of the promising candidates for a novel cardiovascular biomarker is mid-regional proadrenomedullin, a derivative of adrenomedullin. Adrenomedullin is a peptide hormone known for its vasodilatory, antioxidant, antiapoptotic and antifibrotic effects. A remarkable advantage of mid-regional proadrenomedullin is its longer half-life which is a prerequisite for plasma measurements. These review aims to discuss the importance of mid-regional proadrenomedullin with reference to its usefulness as a biomarker of increased cardiovascular risk and kidney disease progression.

Adrenomedullin Inhibits Osmotic Water Permeability in Rat Inner Medullary Collecting Ducts

Adrenomedullin (ADM) is a vasodilator that causes natriuresis and diuresis. However, the direct effect of ADM on osmotic water permeability in the rat inner medullary collecting duct (IMCD) has not been tested. We investigated whether ADM and its ADM receptor components (CRLR, RAMP2, and 3) are expressed in rat inner medulla (IM) and whether ADM regulates osmotic water permeability in isolated perfused rat IMCDs. The mRNAs of ADM, CRLR, and RAMP2 and 3 were detected in rat IM. Abundant protein of CRLR and RAMP3 were also seen but RAMP2 protein level was extremely low. Adding ADM (100 nM) to the bath significantly decreased osmotic water permeability. ADM significantly decreased aquaporin-2 (AQP2) phosphorylation at Serine 256 (pS256) and increased it at Serine 261 (pS261). ADM significantly increased cAMP levels in IM. However, inhibition of cAMP by SQ22536 further decreased ADM-attenuated osmotic water permeability. Stimulation of cAMP by roflumilast increased ADM-attenuated osmotic water permeability. Previous studies show that ADM also stimulates phospholipase C (PLC) pathways including protein kinase C (PKC) and cGMP. We tested whether PLC pathways regulate ADM-attenuated osmotic water permeability. Blockade of either PLC by U73122 or PKC by rottlerin significantly augmented the ADM-attenuated osmotic water permeability and promoted pS256-AQP2 but did change pS261-AQP2. Inhibition of cGMP by L-NAME did not change AQP2 phosphorylation. In conclusion, ADM primarily binds to the CRLR-RAMP3 receptor to initiate signaling pathways in the IM. ADM reduced water reabsorption through a PLC-pathway involving PKC. ADM-attenuated water reabsorption may be related to decreased trafficking of AQP2 to the plasma membrane. cAMP is not involved in ADM-attenuated osmotic water permeability.

Plasma Adrenomedullin and Allelic Variation in the ADM Gene and Kidney Disease in People With Type 2 Diabetes

Production of adrenomedullin (ADM), a vasodilator peptide, increases in response to ischemia and hypoxia in the vascular wall and the kidney. This may be an adaptive response providing protection against organ damage. We investigated the hypothesis that ADM has a nephroprotective effect in two prospective cohorts of patients with type 2 diabetes recruited in France. The highest tertile of plasma MR-proADM (a surrogate for ADM) concentration at baseline was associated with the risk of renal outcomes (doubling of plasma creatinine concentration and/or progression to end-stage renal disease) during follow-up in both cohorts. Four SNPs in the ADM gene region were associated with plasma MR-proADM concentration at baseline and with eGFR during follow-up in both cohorts. The alleles associated with lower eGFR were also associated with lower plasma MR-proADM level. In conclusion, plasma MR-proADM concentration was associated with renal outcome in patients with type 2 diabetes. Our data suggest that the ADM gene modulates the genetic susceptibility to nephropathy progression. Results are consistent with the hypothesis of a reactive rise of ADM in diabetic nephropathy, blunted in risk alleles carriers, and with a nephroprotective effect of ADM. A possible therapeutic effect of ADM receptor agonists in diabetic renal disease would be worth investigating.

Adrenomedullin-RAMP2 system suppresses ER stress-induced tubule cell death and is involved in kidney protection

Various bioactive peptides have been implicated in the homeostasis of organs and tissues. Adrenomedullin (AM) is a peptide with various bioactivities. AM-receptor, calcitonin-receptor-like receptor (CLR) associates with one of the subtypes of the accessory proteins, RAMPs. Among the RAMP subisoforms, only RAMP2 knockout mice (−/−) reproduce the phenotype of embryonic lethality of AM−/−, illustrating the importance of the AM-RAMP2-signaling system. Although AM and RAMP2 are abundantly expressed in kidney, their function there remains largely unknown. We used genetically modified mice to assess the pathophysiological functions of the AM-RAMP2 system. RAMP2+/− mice and their wild-type littermates were used in a streptozotocin (STZ)-induced renal injury model. The effect of STZ on glomeruli did not differ between the 2 types of mice. On the other hand, damage to the proximal urinary tubules was greater in RAMP2+/−. Tubular injury in RAMP2+/− was resistant to correction of blood glucose by insulin administration. We examined the effect of STZ on human renal proximal tubule epithelial cells (RPTECs), which express glucose transporter 2 (GLUT2), the glucose transporter that specifically takes up STZ. STZ activated the endoplasmic reticulum (ER) stress sensor protein kinase RNA-like endoplasmic reticulum kinase (PERK). AM suppressed PERK activation, its downstream signaling, and CCAAT/enhancer-binding homologous protein (CHOP)-induced cell death. We confirmed that the tubular damage was caused by ER stress-induced cell death using tunicamycin (TUN), which directly evokes ER stress. In RAMP2+/− kidneys, TUN caused severe injury with enhanced ER stress. In wild-type mice, TUN-induced tubular damage was reversed by AM administration. On the other hand, in RAMP2+/−, the rescue effect of exogenous AM was lost. These results indicate that the AM-RAMP2 system suppresses ER stress-induced tubule cell death, thereby exerting a protective effect on kidney. The AM-RAMP2 system thus has the potential to serve as a therapeutic target in kidney disease.

Physiology of Kidney Renin

The protease renin is the key enzyme of the renin-angiotensin-aldosterone cascade, which is relevant under both physiological and pathophysiological settings. The kidney is the only organ capable of releasing enzymatically active renin. Although the characteristic juxtaglomerular position is the best known site of renin generation, renin-producing cells in the kidney can vary in number and localization. (Pro)renin gene transcription in these cells is controlled by a number of transcription factors, among which CREB is the best characterized. Pro-renin is stored in vesicles, activated to renin, and then released upon demand. The release of renin is under the control of the cAMP (stimulatory) and Ca2+(inhibitory) signaling pathways. Meanwhile, a great number of intrarenally generated or systemically acting factors have been identified that control the renin secretion directly at the level of renin-producing cells, by activating either of the signaling pathways mentioned above. The broad spectrum of biological actions of (pro)renin is mediated by receptors for (pro)renin, angiotensin II and angiotensin-( 1 – 7 ).

Mid-regional pro-adrenomedullin is associated with pulse pressure, left ventricular mass, and albuminuria in African Americans with hypertension

BACKGROUND

African Americans with hypertension are prone to target-organ damage and adverse cardiovascular events. Biomarkers for early detection of target-organ damage in this ethnic group are needed. Adrenomedullin (ADM) is a circulating vasoactive peptide with vasodilatory and antiproliferative effects that has been reported to be elevated in adults with hypertension.

METHODS

We investigated the associations of plasma levels of mid-regional pro-ADM (MR-proADM) with pulse pressure, left ventricular mass (LVM), and albuminuria in 1,034 African-American adults (65 +/- 9 years, 72% women) with hypertension. MR-proADM was measured by an immunoluminometric assay, LVM was assessed by 2-dimensional echocardiography, and albuminuria was assessed by urine albumin:creatinine ratio (UACR). Multivariable regression analyses were used to assess whether plasma MR-proADM was independently associated with pulse pressure, LVM indexed by height to the power 2.7 (LVMi), and UACR.

RESULTS

Plasma MR-proADM was significantly correlated (P < 0.001) with pulse pressure, LVMi, and UACR. In separate multivariable linear regression models that adjusted for age and sex, log MR-proADM was associated with greater pulse pressure (P = 0.007), log LVMi (P = 0.001), and log (UACR+1) (P < 0.0001). After additional adjustment for body mass index (BMI), total and high-density lipoprotein (HDL) cholesterol, smoking history, diabetes, estimated glomerular filtration rate (eGFR), history of myocardial infarction (MI) or stroke, and medication use, log MR-proADM remained significantly associated with greater pulse pressure (P = 0.001), log LVMi (P = 0.029), and log (UACR+1) (P = 0.002).

CONCLUSIONS

In African-American adults with hypertension, plasma MR-proADM is independently associated with pulse pressure, LVMi, and albuminuria and is a potential biomarker for target organ damage.

Adrenomedullin reduces antioxidant defense system and enhances kidney tissue damage in cadmium and lead exposed rats

Adrenomedullin (AdM) is synthesized and secreted by a number of cells and tissue. AdM is a potent vasodilator but it is also considered a neuromodulator, an angiogenic factor, and a hormone regulator. AdM possess antiapoptotic, antioxidant, and antimicrobial properties. Heavy metals such as cadmium and lead are found widely in the environment and they have important biological functions. Lead (Pb) and cadmium (Cd) can accumulate in the lungs, liver, bone, and kidneys and cause serious organ damage. In the present study, we investigated the effect of AdM, Pb + AdM, and Cd + AdM treatments on superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities as well as the level of malondialdehyde (MDA) in the kidney. Heavy metal accumulation was determined in kidney with and without AdM infusion and kidney damage was evaluated by light and electron microscopy. Increased heavy metal accumulation was observed in the heavy metal and AdM treated groups. SOD, CAT, GSH-Px activities, and MDA levels were significantly different in the treatment groups when compared with the control group. Tubular degeneration, necrosis, cell swelling, mononuclear cell infiltration, and degenerated organelles were observed in the kidney following treatment. Therefore, AdM infusion has no beneficial and/or compensatory role in cadmium and lead toxicity in the kidney. We conclude that heavy metal accumulation in the kidney in conjunction with AdM infusion is cytotoxic despite the known beneficial effects of adrenomedullin.

Differential hormonal profiles of adrenomedullin and proadrenomedullin N-terminal 20 peptide in patients with heart failure and effect of treatment on their plasma levels

BACKGROUND

Adrenomedullin (AM) is a potent vasodilatory peptide discovered in human pheochromocytoma tissue. Proadrenomedullin N-terminal 20 peptide (PAMP) processed from an AM precursor is also a novel hypotensive peptide which inhibits catecholamine secretion from sympathetic nerve endings.

HYPOTHESIS

The present study sought to examine the relationships between the two peptides and other clinical parameters by measuring the plasma AM and PAMP concentrations in 98 patients with heart failure.

METHODS

In all, 98 patients [65 men and 33 women, aged 58.2 +/- 11.0 years, mean +/- standard deviation (SD)] with heart failure and 26 healthy volunteers (12 men and 14 women, aged 54.1 +/- 8.6 years) were examined in this study. Heart failure was secondary to previous myocardial infarction in 58 patients, valvular disease in 28, cardiomyopathy in 9, and congenital heart disease in 3. All patients were classified into two groups of class I or II (Group 1) and class III or IV (Group 2) according to the New York Heart Association (NYHA) functional classification.

RESULTS

Both plasma AM and PAMP concentrations in the patients were significantly higher than those in healthy volunteers. In addition, plasma AM and PAMP concentrations in patients in class III or IV of New York Heart Association (NYHA) classification were significantly higher than those in NYHA class I or II. The elevated plasma concentrations of these peptides in patients in NYHA class III or IV significantly decreased in response to the treatment for 7 days. There was a significant correlation between plasma AM and PAMP, though the plasma concentration of PAMP was one-fifth to one-seventh of that of AM in patients and controls. The plasma AM concentration correlated significantly with the plasma concentrations of atrial and brain natriuretic peptides, epinephrine, and right atrial pressure, whereas such a relationship was not noted for the plasma PAMP concentration.

CONCLUSIONS

Judging from the difference in not only the biological actions but also the hormonal profiles between AM and PAMP, they may differentially modulate the cardiovascular system in patients with heart failure, although they are processed from the same precursor.

Increased renal adrenomedullin expression in rats with ureteral obstruction

Ureteral obstruction is characterized by decreased renal blood flow that is associated with hypoxia within the kidney. Adrenomedullin (AM) is a peptide hormone with tissue-protective capacity that is stimulated through hypoxia. We tested the hypothesis that ureteral obstruction stimulates expression of AM and hypoxia-inducible factor-1 (HIF-1α) in kidneys. Rats were exposed to bilateral ureteral obstruction (BUO) for 2, 6, 12, and 24 h or sham operation and compared with unilateral obstruction (UUO). AM mRNA expression was measured by quantitative PCR in cortex and outer medulla (C+OM) and inner medulla (IM). AM and HIF-1α protein abundance and localization were determined in rats subjected to 24-h BUO. AM mRNA expression in C+OM increased significantly after 12-h BUO and further increased after 24 h. In IM, AM mRNA expression increased significantly in response to BUO for 6 h and further increased after 24 h. AM peptide abundance was enhanced in C+OM and IM after 24-h BUO. Immunohistochemical labeling of kidneys showed a wider distribution and more intense AM signal in 24-h BUO compared with Sham. In UUO rats, AM mRNA expression increased significantly in IM of the obstructed kidney compared with nonobstructed and Sham kidney whereas AM peptide increased in IM compared with Sham. HIF-1α protein abundance increased significantly in IM after 24-h BUO compared with Sham and HIF-1α immunoreactive protein colocalized with AM. In summary, AM and HIF-1α expression increases in response to ureteral obstruction in agreement with expected oxygen gradients. Hypoxia acting through HIF-1α accumulation may be an important pathway for the renal response to ureteral obstruction.

Pathophysiologic and therapeutic implications of adrenomedullin in cardiovascular disorders

Adrenomedullin (AM) is a vasodilator peptide that originally isolated from pheochromocytoma tissue. However, the mRNA is expressed in the normal adrenal gland, heart, kidney and blood vessels. The human AM gene is located in the short arm of chromosome 11 and is composed of 4 exons. There are 2 single nucleotide polymorphisms in introns 1 and 3, and the 3'-end of the AM gene is flanked by a microsatellite marker of cytosine-adenine repeats that is associated with an increased risk of developing hypertension and diabetic nephropathy. AM gene expression is promoted by various stimuli, including inflammation, hypoxia, oxidative stress, mechanical stress and activation of the renin-angiotensin and sympathetic nervous systems. The AM gene promoter region possessed binding site for several transcription factors, including nuclear factor for interleukin-6 expression (NF-IL6) and activator protein 2 (AP-2). Further, plasma AM levels are increased in patients with various cardiovascular diseases, including hypertension, heart failure and renal failure. These findings suggest that AM plays a role in the development of or response to cardiovascular disease. Indeed, experimental and clinical studies have demonstrated that systemic infusion of AM may have a therapeutic effect on myocardial infarction, heart failure and renal failure. Further, vasopeptidase inhibitors which augment the bioactivity of endogenous AM may benefit patients with hypertension and arteriosclerosis. Finally, the angiogenic and cytoprotective properties of AM may have utility in revascularization and infarcted myocardium and ischemic limbs. Because of the potential clinical benefits of AM, indications for use and optimal dosing strategies should be established.

Renoprotective effect of long-term combined treatment with adrenomedullin and omapatrilat in hypertensive rats

BACKGROUND

Previous studies demonstrated that adrenomedullin (AM) is metabolized by neutral endopeptidases and that the renal effect of AM is augmented by the inhibition of neutral endopeptidases. We have recently shown that the long-term administration of AM has renoprotective effects.

OBJECT

This study assessed the chronic renoprotective effects of AM combined with a vasopeptidase inhibitor in hypertensive rats and attempted to elucidate the mechanism involved.

METHODS

We studied the following four groups: control Dahl salt-resistant (DR) rats, untreated Dahl salt-sensitive (DS) rats, omapatrilat (35 mg/kg per day)-treated DS rats; and human AM (500 ng/h) plus omapatrilat-treated DS rats. After 7 weeks' treatment, blood pressure, renal function, neurohumoral factors, gene expression levels, and histological findings were examined.

RESULTS

DS rats were characterized by increased blood pressure, decreased renal function, abnormal histological findings, and increased gene expression of collagen I and III, transforming growth factor beta (TGF-beta), and NADPH oxidase subunits (p40phox, p47phox, and gp91phox) in the renal cortex compared with DR rats. Compared with DS rats, omapatrilat significantly decreased systolic blood pressure (-26 mmHg), improved renal function, histological findings, and messenger RNA expression levels of collagen I, collagen III, and TGF-beta. Combined treatment with omapatrilat and AM further improved renal function, histological findings, and mRNA expression levels of collagen I, collagen III, and TGF-beta, without a further reduction in blood pressure. Only combined treatment decreased mRNA levels of p40phox, p47phox, and gp91phox. There were no differences in plasma AM or atrial natriuretic peptide levels among three DS groups.

CONCLUSION

Our results suggest that combined treatment with omapatrilat and AM provides additional renoprotective effects independent of blood pressure-lowering activity partly via inhibition of gene expressions of oxidative stress and extracellular matrix.

Molecular and functional characterization of adrenomedullin receptors in pufferfish

The receptors for the calcitonin gene-related peptide (CGRP)/adrenomedullin (AM) family peptides were characterized in the mefugu Takifugu obscurus, a euryhaline fugu species very close to Takifugu rubripes, which has as many as five adrenomedullin genes (AM1–5). CGRP and AM share a G protein-coupled core receptor called calcitonin receptor-like receptor (CLR), and the specificity of the CLR is determined by the interaction with receptor activity-modifying proteins (RAMPs). Through database mining, three CLRs (CLR1–3) and five RAMPs (RAMP1–5) were identified, and all of them were cloned by RT-PCR and characterized by functional expression in COS7 cells in every possible combination of CLR-RAMP. The following combinations generated cAMP in response to physiological concentrations of CGRP, AM1 (an ortholog of mammalian AM), AM2, and AM5: CLR1-RAMP1/4 (CGRP), CLR1-RAMP2/3/5 (AM1), CLR2-RAMP2 (AM1), CLR1-RAMP3 (AM2), and CLR1-RAMP3 (AM5). Their expressions were found by Northern blot analysis to be tissue specific and salinity dependent. For example, CLR1-RAMP5 and CLR1-RAMP2 are expressed specifically in the gill and kidney, respectively, suggesting their involvement in osmoregulation. Furthermore, relatively high levels of CLRs and RAMPs were found in the spleen and ovary, suggesting roles in the immune and female reproductive systems. Immunohistochemistry revealed that AM receptors of the following types are expressed in the locations, indicated in brackets, of the mefugu gill and kidney: CLR1-RAMP5 (interlamellar vessels), CLR2-RAMP2 (pillar cells), and CLR1-RAMP2 (apical side of renal proximal tubule cells).

Roles of adrenomedullin 2 in regulating the cardiovascular and sympathetic nervous systems in conscious rats

Recently, a new member of the calcitonin gene-related peptide (CGRP) family, adrenomedullin 2 (AM2) or intermedin (IMD), was identified. AM2/IMD has been shown to have a vasodilator effect in mice and rats and an effect on urine formation in rats. In the present study, we investigated the effects of intravenously infused rat AM2 (rAM2) on blood pressure (BP), heart rate (HR), renal sympathetic nerve activity (RSNA), and renal blood flow (RBF) in conscious unrestrained rats relative to the effects of rat adrenomedullin (rAM) and proadrenomedullin NH2-terminal 20 peptide (rPAMP). Intravenous infusion of rAM2 (5 nmol/kg) significantly decreased BP and increased HR, RSNA, and RBF. These hypotensive and sympathoexcitatory effects diminished after 20 min, and HR returned to control levels 30 min after cessation of the infusion. In contrast, a significant increase in RBF was still evident 60 min after cessation of the peptide infusion. The duration of BP, HR, and RSNA responses was longer with rAM (5 nmol/kg) than with rAM2 infusion, whereas the increases in RBF induced by rAM2 and rAM were similar in their amplitude and duration. Infusion of rPAMP (200 nmol/kg) increased HR and RSNA but had no effect on RBF. Baroreceptor denervation suppressed, but did not diminish, the increases in HR and RSNA to rAM2. These findings indicate that the physiological roles of rAM2 and rAM are similar and that rAM2 also has a long-lasting vasodilator action on the renal vascular bed.

Renal effects of a new member of adrenomedullin family, adrenomedullin2, in rats

A new member of the adrenomedullin family, adrenomedullin2, was identified in mammals. The effects of adrenomedullin2 on renal hemodynamics and urine formation were examined in rats. Intrarenal arterial infusion of adrenomedullin2 at rates of 30, 100 and 300 pmol/kg/min decreased blood pressure and increased heart rate in a dose-dependent fashion. Adrenomedullin2 infusion at 100 pmol/kg/min significantly increased renal blood flow and urine flow. At the higher infusion rate (300 pmol/kg/min), adrenomedullin2 significantly decreased urine flow. Continuous intrarenal infusion of adrenomedullin2 at 100 pmol/kg/min significantly increased renal blood flow from 6.7+/-0.5 to 8.8+/-0.5 ml/min and decreased renal vascular resistance from 16+/-1 to 11+/-1 mm Hg min/ml. Urine flow was significantly increased from 21.5+/-4.9 to 36.2+/-8.5 microl/min and urinary excretion of sodium was increased from 2.3+/-0.9 to 4.9+/-1.4 microEq/min. Blood pressure, heart rate and glomerular filtration rate did not change. Infusion of a similar dose of adrenomedullin also increased renal blood flow (6.8+/-0.4-8.8+/-0.6 ml/min), urine flow (25.4+/-3.2-42.8+/-9.4 microl/min) and urinary excretion of sodium (2.8+/-0.6-6.5+/-1.2 microEq/min), decreased renal vascular resistance (15+/-1-11+/-1 mm Hg min/ml) and did not alter glomerular filtration rate. Thus, the renal actions induced by adrenomedullin2 were similar to those of adrenomedullin. These data suggest that adrenomedullin2 may play an important role in the regulation of renal hemodynamics and urine formation.

Adrenomedullin gene delivery alleviates hypertension and its secondary injuries of cardiovascular system

Adrenomedullin (AM) is a hypotensive peptide that functions as an important regulator in the cardiovascular and renal systems. The current study explored the potential therapeutic effects of delivering the human AM cDNA via a novel double-stranded adeno-associated virus vector (dsAAV) on hypertension and related complications in spontaneously hypertensive rats (SHR). A single dose of dsAAV-AM vector administered by tail vein injection into adult SHR resulted in significant reduction of systolic blood pressure at 2 weeks after gene delivery. This effect was observed through the entire duration of the experiment period (up to 16 weeks). Administration of dsAAV-AM also resulted in a decrease in total urine microalbumin content. Left ventricle and cardiomyocyte hypertrophy, fibrosis in the heart, glomerular sclerosis, and tubular injuries in the kidney were significantly reduced. Moreover, deterioration of hemodynamic variables was prevented in treated rats, as compared with the control groups. We conclude that AAV-mediated AM delivery can render a longterm and stable reduction of hypertension and protect against renal injury and cardiac remodeling in the spontaneously hypertensive rat model. Further preclinical studies are warranted for the development of a gene therapy strategy for human hypertension.

Adrenomedullin: a new target for the design of small molecule modulators with promising pharmacological activities

Adrenomedullin (AM) is a 52-amino acid peptide with a pluripotential activity. AM is expressed in many tissues throughout the body, and plays a critical role in several diseases such as cancer, diabetes, cardiovascular and renal disorders, among others. While AM is a protective agent against cardiovascular disorders, it behaves as a stimulating factor in other pathologies such as cancer and diabetes. Therefore, AM is a new and promising target for the development of molecules which, through their ability to regulate AM levels, could be used in the treatment of these pathologies.

Adrenomedullin: regulator of systemic and cardiac homeostasis in acute myocardial infarction

During and following acute myocardial infarction, a variety of endogenous mediators are elevated, one of which is adrenomedullin (AM). AM is a multifunctional peptide that has been identified as having a putative beneficial role following an ischemic insult at both systemic and local levels. Classically described as a potent vasodilator, natriuretic, and diuretic agent, experimental infarct models also demonstrate AM to exhibit antiproliferative and antiapoptotic functions in the myocardium, counterregulating the effects of mediators such as angiotensin-II and endothelin-1. Less well documented are the angiogenic and inflammatory modulating potentials of AM, which may also contribute toward reducing adverse ventricular remodeling. The review examines clinical and experimental studies, looking at the effects of AM and cellular mechanisms that could be involved in mediating cardioprotective effects and ultimately optimizing left ventricular remodeling. Finally, the possibility of enhancing endogenous actions of AM by pharmacological intervention is considered.

Adrenomedullin enhances invasion by trophoblast cell lines

We have tested the hypothesis that adrenomedullin (ADM), a multifunctional peptide hormone, works as a trophoblast proinvasion factor. Our results showed that ADM receptor components-the mRNA and proteins of calcitonin receptor-like receptor (CALCRL) and receptor activity modifying proteins (RAMPs)-were expressed by human choriocarcinoma JAr cells and first-trimester cytotrophoblast HTR-8/SV neo cells. ADM stimulates both JAr and HTR-8/SV neo cell proliferation. The invasion capabilities of JAr cells and HTR-8/SV neo cells were also enhanced by ADM, and this was associated with increased gelatinolytic activity and reduced plasminogen activator inhibitor-1 mRNA expression (SERPINE1). Our data support the notion that ADM may be involved in the human implantation process via regulating trophoblast proliferation and differentiation.

Brain-derived adrenomedullin controls blood volume through the regulation of arginine vasopressin production and release

Central nervous system-derived adrenomedullin (AM) has been shown to be a physiological regulator of thirst. Administration of AM into the lateral ventricle of the brain attenuated water intake, whereas a decrease in endogenous AM, induced by an AM-specific ribozyme, led to exaggerated water intake. We hypothesized that central AM may control fluid homeostasis, in part by regulating plasma arginine vasopressin (AVP) levels. To test this hypothesis, AM or a ribozyme specific to AM was administered intracerebroventricularly, and alterations in plasma AVP concentrations were examined under basal and stimulated (hypovolemic) conditions. Additionally, we examined changes in blood volume, kidney function, and plasma electrolyte and protein levels, as well as changes in plasma aldosterone concentrations. Intracerebroventricular administration of AM increased plasma AVP levels, whereas AM ribozyme treatment led to decreased plasma AVP levels under stimulated conditions. During hypovolemic challenges, AM ribozyme treatment led to an increased loss of plasma volume compared with control animals. Although overall plasma osmolality did not differ between treatment groups during hypovolemia, aldosterone levels were significantly higher and, consequently, plasma potassium concentrations were lower in AM ribozyme-treated rats than in controls. These data suggest that brain-derived AM is a physiological regulator of vasopressin secretion and, thereby, fluid homeostasis.

Intermedin/adrenomedullin-2 acts within central nervous system to elevate blood pressure and inhibit food and water intake

Intermedin (IMD)/adrenomedullin-2 (AM2) is a novel peptide that was independently discovered by two groups. The 47-amino acid peptide is homologous to adrenomedullin (AM) and can activate both the AM and calcitonin gene-related peptide (CGRP) receptors. IMD should therefore have actions similar to those of AM and CGRP. Indeed, like AM and CGRP, intravenous administration of IMD decreased blood pressure in rats and mice. We demonstrate here that immunoreactive IMD is present in plasma as well as heart, lung, stomach, kidney, pituitary, and brain. Because IMD is present in brain and both AM and CGRP have potent central nervous system (CNS) effects, we examined the ability of IMD within brain to regulate blood pressure and ingestive behaviors. Administration of IMD into the lateral cerebroventricle of rats caused significant, long-lasting elevations in mean arterial pressure and heart rate. These elevations are similar to the effects of CGRP and significantly greater than the effects of AM. IMD-induced elevations in mean arterial pressure were inhibited by intravenous administration of phentolamine, indicating that IMD activates the sympathetic nervous system. Intracerebroventricular administration of IMD also inhibited food and water intake in sated and in food- and water-restricted animals. The effects on feeding are likely related to activation of the CGRP receptor and are independent of the effects on water intake, which are likely through the AM receptor. Our data indicate that IMD has potent actions within the CNS that may be a result of the combined activation of both AM and CGRP receptors.

The clinical relevance of adrenomedullin: a promising profile?

Adrenomedullin (AM) is a peptide that possesses potentially beneficial properties. Since the initial discovery of the peptide by Kitamura et al. in 1993, the literature has been awash with reports describing its novel mechanisms of action and huge potential as a therapeutic target. Strong evidence now exists that AM is able to act as an autocrine, paracrine, or endocrine mediator in a number of biologically significant functions, including the endothelial regulation of blood pressure, protection against organ damage in sepsis or hypoxia, and the control of blood volume through the regulation of thirst. Its early promise as a potential mediator/modulator of disease was not, however, entirely as a result of the discovery of physiological functions but due more to the observation of increasing levels measured in plasma in direct correlation with disease progression. In health, AM circulates at low picomolar concentrations in plasma in 2 forms, a mature 52-amino acid peptide and an immature 53-amino acid peptide. Plasma levels of AM have now been shown to be increased in a number of pathological states, including congestive heart failure, sepsis, essential hypertension, acute myocardial infarction, and renal impairment. These earliest associations have been further supplemented with evidence of a role for AM in other pathologies including, most intriguingly, cancer. In this review, we offer a timely review of our current knowledge on AM and give a detailed account of the putative role of AM in those clinical areas in which the best therapeutic opportunities might exist.

Plasma Levels of Proadrenomedullin N-Terminal 20 Peptide and Adrenomedullin in Patients Undergoing Hemodialysis

BACKGROUND

Proadrenomedullin N-terminal 20 peptide (PAMP) is a novel hypotensive peptide present in the precursor of adrenomedullin (AM), a vasodilative and natriuretic peptide. However, the profile of PAMP in hemodialyzed (HD) patients has not been determined.

METHODS

We measured plasma levels of PAMP, total AM (tAM) and a mature form of AM (mAM, the biologically active form) in HD patients (n = 31) and in normal controls (n = 21).

RESULTS

Plasma concentrations of PAMP before HD were significantly higher than those in controls (4.02 +/- 0.24 vs. 1.64 +/- 0.12 fmol/ml, p < 0.001) and decreased to the control level after HD (2.17 +/- 0.18 vs. 1.64 +/- 0.12 fmol/ml; NS). The plasma PAMP level before HD significantly correlated with weight gain during HD sessions (r = 0.41, p < 0.05), but not with predialysis blood pressure. The concentrations of mAM before and after HD were significantly higher than those in controls. The plasma mAM level before HD significantly correlated with weight gain during HD sessions, but not with predialysis blood pressure. The plasma level of PAMP did not correlate with that of mAM in HD patients.

CONCLUSION

PAMP and AM may be involved in the regulation of blood volume in patients undergoing HD.

Novel fish-derived adrenomedullin in mammals: structure and possible function

Adrenomedullin (AM) has been recognized as a member of the calcitonin (CT)/CT gene-related peptide (CGRP) family. However, an independent AM family consisting of five paralogous peptides exists in teleost fish. Among them, the peptide named AM1 is an ortholog of mammalian AM as determined by the linkage analysis of orthologous genes and the presence of proAM N-terminal 20 peptide (PAMP)-like sequence in the prosegment. Since the peptides named AM2 and 3 are distinct from other members with respect to the precursor sequence, tissue distribution of the transcripts, and exon-intron organization, we searched for their mammalian orthologs from genome databases, which resulted in an identification of AM2 in human, rat, and mouse. AM2 was expressed abundantly in the submaxillary gland, kidney, and some vascular and digestive tissues of mice. AM2 injected in vivo induced potent cardiovascular and renal effects in mice. In the heart and kidney of mice, AM2 was localized in endothelial cells of the coronary vessels and in glomeruli and vasa recta, respectively. AM2 increased cAMP accumulation in cells expressing human CT receptor-like receptor (CRLR) and one of receptor activity-modifying proteins (RAMPs), but it was no more potent than CGRP and AM. AM2 was also less potent than CT in cells expressing CT receptor and RAMP. There remains a possibility that a new AM2-specific receptor or an additional RAMP that enables CRLR to be an AM2-specific receptor, exists in mammals.

Effect of cardiopulmonary bypass on pulmonary clearance of adrenomedullin in humans

BACKGROUND

Adrenomedullin is a potent vasodilatory peptide and its plasma concentration increases after cardiopulmonary bypass. We analyzed the contribution of the lung to the disposition of adrenomedullin before and after cardiopulmonary bypass in humans.

METHODS

Thirty-five patients undergoing cardiac surgery with cardiopulmonary bypass were studied. Bloods were sampled from the pulmonary artery and left atrium at the following times: prior to systemic heparinization, during pulmonary reperfusion and after cardiopulmonary bypass. Plasma concentrations of total and mature adrenomedullin were measured using an immunoradiometric assay kit specific for human adrenomedullin. Intermediate adrenomedullin was calculated as the difference between total adrenomedullin and mature adrenomedullin.

RESULTS

Before cardiopulmonary bypass, mature and intermediate adrenomedullin concentrations were reduced by the pulmonary circulation by approximately 30% and 20%, respectively. However, these effects were not observed during pulmonary reperfusion. Mature, but not intermediate, adrenomedullin was reduced after cardiopulmonary bypass. Furthermore, pulmonary clearance quantity of mature adrenomedullin was significantly enhanced after cardiopulmonary bypass.

CONCLUSION

These results indicate that cardiopulmonary bypass temporally impairs the pulmonary clearance of mature and intermediate adrenomedullin, but clearance of mature, not intermediate adrenomedullin is enhanced after cardiopulmonary bypass.

Expression of adrenomedullin in hypoxic and ischemic rat kidneys and human kidneys with arterial stenosis

To investigate regional aspects of hypoxic regulation of adrenomedullin (AM) in kidneys, we mapped the distribution of AM in the rat kidney after hypoxia (normobaric hypoxic hypoxia, carbon monoxide, and CoCl2 for 6 h), anemia (hematocrit lowered by bleeding) and after global transient ischemia for 1 h (unilateral renal artery occlusion and reperfusion for 6 and 24 h) and segmental infarct (6 and 24 h). AM expression and localization was determined in normal human kidneys and in kidneys with arterial stenosis. Hypoxia stimulated AM mRNA expression significantly in rat inner medulla (CO 13 times, 8% O2 6 times, and CoCl2 8 times), followed by the outer medulla and cortex. AM mRNA level was significantly elevated in response to anemia and occlusion-reperfusion. Immunoreactive AM was associated with the thin limbs of Henle's loop, distal convoluted tubule, collecting ducts, papilla surface epithelium, and urothelium. AM labeling was prominent in the inner medulla after CO and in the outer medulla after occlusion-reperfusion. The infarct border zone was strongly labeled for AM. In cultured inner medullary collecting duct cells, AM mRNA was significantly increased by hypoxia. AM mRNA was equally distributed in human kidney and AM was localized as in the rat kidney. In human kidneys with artery stenosis, AM mRNA was not significantly enhanced compared with controls, but AM immunoreactivity was observed in tubules, vessels, and glomerular cells. In summary, AM expression was increased in the rat kidney in response to hypoxic and ischemic hypoxia in keeping with oxygen gradients. AM was widely distributed in the human kidney with arterial stenosis. AM may play a significant role to counteract hypoxia in the kidney.

The effect of adrenomedullin, amylin fragment 8-37 and calcitonin gene-related peptide on contractile force, heart rate and coronary perfusion pressure in isolated rat hearts

The effect of human adrenomedullin, human amylin fragment 8-37 (amylin 8-37) and rat calcitonin gene-related peptide (CGRP) on contractile force, heart rate and coronary perfusion pressure has been investigated in the isolated perfused rat hearts. Adrenomedullin (2x10(-10), 2x10(-9) and 2x10(-8) M) produced a significant decrease in contractile force and perfusion pressure, but only the peptide caused a decline in heart rate at the highest dose. Amylin (10(-9), 10(-8) and 10(-7) M) significantly increased and then decreased contractile force. Two doses of amylin (10(-8) and 10(-7) M) induced a significant increase in heart rate, however amylin did not change perfusion pressure in all the doses used. Rat alpha CGRP (10(-8), 10(-7) and 10(-6) M) evoked a slight decline in contractile force following a significant increase in contractile force induced by the peptide. CGRP in all the doses raised heart rate and lowered perfusion pressure. Our results suggest that adrenomedullin has negative inotropic, negative chronotropic and coronary vasodilator actions. Amylin produces a biphasic inotropic effect and evokes a positive chronotropy. CGRP causes positive inotropic, positive chronotropic and vasodilatory effects in isolated rat hearts.

Identification of novel adrenomedullin in mammals: a potent cardiovascular and renal regulator

We have identified cDNA encoding a new member of the adrenomedullin (AM) family, AM2, for the first time in mammals (mouse, rat and human). The predicted precursor carried mature AM2 in the C-terminus, which had an intramolecular ring formed by an S-S bond and a possibly amidated C-terminus. Phylogenetic analyses clustered AM2 and AM into two distinct but closely related groups. Similarity of exon-intron structure and synteny of neighboring genes showed that mammalian AM2 is an ortholog of pufferfish AM2 and a paralog of mammalian AM. AM2 mRNA was expressed in submaxillary gland, kidney, stomach, ovary, lymphoid tissues and pancreas of mice, but not in adrenal and testis. Intravenous injection of synthetic mature AM2 decreased arterial pressure more potently than AM, and induced antidiuresis and antinatriuresis in mice. These results show that at least two peptides, AM and AM2, comprise an adrenomedullin family in mammals, and that AM2 may play pivotal roles in cardiovascular and body fluid regulation.

Microsatellite DNA polymorphism of human adrenomedullin gene in type 2 diabetic patients with renal failure

BACKGROUND

Adrenomedullin (AM) is a hypotensive peptide widely produced in the cardiovascular organs and tissues such as the heart, kidney, and the vascular cells. We have previously cloned and sequenced the genomic DNA encoding human AM gene, and determined that the gene is located in the short arm of chromosome 11. The 3'-end of the gene is flanked by the microsatellite marker of cytosine adenine (CA) repeats. In this study, we investigated the association between DNA variations in AM gene and the predisposition to develop nephropathy in type 2 diabetes mellitus.

METHODS

Genomic DNA was obtained from the peripheral leukocytes of 233 normal healthy subjects (NH), 139 type 2 diabetic patients on hemodialysis (DM-HD), 106 control patients with type 2 diabetes without nephropathy (DM-C) and 318 hemodialysis patients due to chronic glomerulonephritis (CGN-HD). The genomic DNA was subject to polymerase chain reaction (PCR) using a fluorescence-labeled primer, and the number of CA repeats were determined by polyacrylamide gel electrophoresis (PAGE).

RESULTS

In our Japanese subjects, there existed four types of alleles with different CA-repeat number; 11, 13, 14, and 19. The frequencies of these alleles were 11: 27.7%, 13: 32.8%, 14: 35.6%, and 19: 3.9% in NH. These allele frequencies were not significantly different in DM-C and CGN-HD. However, DM-HD showed significantly different distribution of allele frequency from other groups (chi 2 = 18.9, P = 0.026). Namely, the frequency of 19-repeat allele in DM-HD was higher (9.0%) than NH, DM-C, and CGN-HD (P = 0.005, 0.041, and 0.004, respectively).

CONCLUSION

The microsatellite DNA polymorphism of AM gene may be associated with the genetic predisposition to develop nephropathy in Japanese patients with type 2 diabetes mellitus.

Cell and molecular biology of the multifunctional peptide, adrenomedullin

Adrenomedullin (AM) is a recently discovered regulatory peptide involved in many functions including vasodilatation, electrolyte balance, neurotransmission, growth, and hormone secretion regulation, among others. This 52-amino acid peptide is expressed by specific cell types in many organs throughout the body. A complex receptor system has been described for AM; it requires at least the presence of a seven-transmembrane-domain G-protein-coupled receptor, a single-transmembrane-domain receptor activity modifying protein, and a receptor component protein needed to establish the connection with the downstream signal transduction pathway, which usually involves cyclicAMP. In addition, a serum-binding protein regulates the biological actions of AM, frequently by increasing AM functional attributes. Changes in levels of circulating AM correlate with several critical diseases, including cardiovascular and renal disorders, sepsis, cancer, and diabetes. Whether AM is a causal agent, a protective reaction, or just a marker for these diseases is currently under investigation. New technologies seeking to elevate and/or reduce AM levels are being investigated as potential therapeutic avenues.

Adrenomedullin influences dissociated rat area postrema neurons

The area postrema (AP) is one of a specialized group of central nervous system (CNS) structures devoid of a significant blood-brain barrier (BBB), collectively known as the circumventricular organs (CVO). While peptides are normally excluded from access to most regions of the CNS, the AP contains neurons with a high density of receptors for many circulating peptides, very likely including those for adrenomedullin (AM). In this study, whole-cell patch-clamp recordings were obtained from 114 dissociated rat AP neurons. The mean resting membrane potential (RMP) of these neurons (n=79) was -54.3+/-0.8 mV, the mean input resistance (IR) was 3.1+/-0.2 GOmega and the spike amplitude of neurons included in this study was always greater than 90 mV. Current-clamp studies showed that bath application of AM depolarized 39.2% (31 of 79) and hyperpolarized 45.6% (36 of 79) of neurons tested. Both effects were found to be concentration dependent from 10(-12) to 10(-7) M. These data support the idea that specific populations of CNS neurons within the AP are directly influenced by AM and support the concept that AM may act at AP to influence central autonomic control. We also examined the roles of specific ion channels in regulating the AM-induced excitability of AP neurons through voltage-clamp studies. These experiments suggest potential actions of AM in modulating voltage gated calcium channels, effects which have the additional consequence of inhibiting calcium activated potassium conductances (I(K(Ca))). These data demonstrate direct effects of AM on dissociated AP neurons and identify ion channels, the modulation of which, may underlie these effects.

Autonomic and neuroendocrine actions of adrenomedullin in the brain: mechanisms for homeostasis

In addition to its role as a potent vasodilator, adrenomedullin (ADM) affects an animal's physiological status through its effects in the brain. We have shown that circulating ADM activates neurons, including nitric oxide (NO)-producing neurons, in autonomic centers of the brain such as the hypothalamic paraventricular nucleus (PVN). Systemic ADM gains access to the brain through the area postrema (AP), a brainstem circumventricular organ, and the PVN is a major target of these ADM-sensitive AP neurons. Neurons expressing the preproADM (ppADM) gene are distributed throughout the brain, with high levels in autonomic centers. Lipopolysaccharide (LPS, immune stress), restraint (psychological stress), and 24 h dehydration all down-regulate ppADM gene expression in different subsets of autonomic centers. Receptor-activity-modifying protein (RAMP) 2 and RAMP3, ADM receptor subunits, are expressed in autonomic centers including the PVN and supraoptic nucleus. Intracerebroventricular injections of ADM increase arterial pressure, heart rate, tyrosine hydroxylase mRNA levels in the locus coeruleus, plasma levels of ACTH, and NO production in the hypothalamus. ADM excites putative GABAergic and cholinergic neurons in dissociated cells from a basal forebrain integrative center, the diagonal band of Broca. These results demonstrate that the signalling components necessary for ADM to influence physiological systems are present in the brain and that ADM is an important transmitter of brain autonomic pathways which are involved in regulating homeostatic balance.

Adrenomedullin improves cardiac function and prevents renal damage in streptozotocin-induced diabetic rats

Adrenomedullin (AM) is a potent vasodilating peptide and is involved in cardiovascular and renal disease. In the present study, we investigated the role of AM in cardiac and renal function in streptozotocin (STZ)-induced diabetic rats. A single tail-vein injection of adenoviral vectors harboring the human AM gene (Ad.CMV-AM) was administered to the rats 1-wk post-STZ treatment (65 mg/kg iv). Immunoreactive human AM was detected in the plasma and urine of STZ-diabetic rats treated with Ad.CMV-AM. Morphological and chemical examination showed that AM gene delivery significantly reduced glycogen accumulation within the hearts of STZ-diabetic rats. AM gene delivery improved cardiac function compared with STZ-diabetic rats injected with control virus, as observed by decreased left ventricular end-diastolic pressure, increased cardiac output, cardiac index, and heart rate. AM gene transfer significantly increased left ventricular long axis (11.69 +/- 0.46 vs. 10.31 +/- 0.70 mm, n = 10, P < 0.05) and rate of pressure rise and fall (+6,090.1 +/- 597.3 vs. +4,648.5 +/- 807.1 mmHg/s), (-4,902.6 +/- 644.2 vs. -3,915.5 +/- 805.8 mmHg/s, n = 11, P < 0.05). AM also significantly attenuated renal glycogen accumulation and tubular damage in STZ-diabetic rats as well as increased urinary cAMP and cGMP levels, along with increased cardiac cAMP and Akt phosphorylation. We also observed that delivery of the AM gene caused an increase in body weight along with phospho-Akt and membrane-bound GLUT4 levels in skeletal muscle. These results suggest that AM plays a protective role in hyperglycemia-induced glycogen accumulation and cardiac and renal dysfunction via Akt signal transduction pathways.

Vasoactive and natriuretic mediators in umbilical cord blood: a report of our observation and review of the literature

BACKGROUND

The relative potency and interrelationship among vasoactive and natriuretic mediators are thought to be important in the transition from fetal to neonatal life. However, little is known about their potential roles in the perinatal setting.

AIM

The aim of this study was to evaluate further the potential roles of vasoactive and natriuretic mediators in the perinatal setting.

STUDY DESIGN

We measured umbilical venous levels of arginine vasopressin, endothelin-1, adrenomedullin, natriuretic peptides and NO(2)(-)/NO(3)(-) in 24 vaginally delivered newborns and examined their possible functions.

RESULTS

Cord levels of vasopressin, endothelin-1 and adrenomedullin were considerably higher compared with normal adult values; the concentrations were more than 10-fold higher for vasopressin, and more than threefold higher for endothelin-1 and adrenomedullin. The levels of natriuretic peptides and NO(2)(-)/NO(3)(-) were almost comparable to those of normal adults. Among the mediators, there was a significant correlation between endothelin-1 and adrenomedullin.

CONCLUSIONS

It appears from other studies that the postnatal fall in vasopressin and endothelin-1 levels is associated with increased levels of natriuretic peptides and NO(2)(-)/NO(3)(-). Based on these observations, we consider that these mediators may play active roles in the initiation, maintenance or both of the transition from fetal to neonatal life.

Large-scale production of functional human adrenomedullin: expression, cleavage, amidation, and purification

Human adrenomedullin (hAM) is a 52-amino-acid regulatory peptide containing a six-membered ring structure and an amidated C-terminus, features that are essential for its biological activity. Here, we describe a simple and effective protocol for producing large quantities of highly pure, functional recombinant hAM. A peptide precursor (hAM-Gly) was expressed in Escherichia coli as a fusion protein with thioredoxin and collected as inclusion bodies. The fusion protein was then digested with BLase, a glutamate-specific endopeptidase, to prepare hAM-Gly. The essential ring structure formed spontaneously, while the terminal amide was generated by conversion of the added glycine residue using peptidylglycine alpha-amidating enzyme. The low solubility of hAM-Gly enabled the use of a selective precipitation/extraction method to generate a product that was 80-90% pure, which was sufficient to proceed with the alpha-amidating enzyme reaction. The resultant hAM was then purified further by column chromatography. The final yield was about 82 mg/L of bacterial culture, and the purity, determined by reverse phase HPLC, was >99.5%. The recombinant hAM was biologically active, eliciting concentration-dependent increases in cAMP in CHO-K1 cells expressing a specific hAM receptor and hypotensive responses when intravenously injected into rats. This new approach to the synthesis of hAM is simpler and more cost-effective for large-scale production than chemical synthesis. It therefore represents a new powerful tool that has the potential to facilitate analysis of the structure and function of hAM, as well as the development of new therapeutic protocols for the treatment of ailments such as hypertension.

High plasma adrenomedullin concentrations in patients with high-renin essential hypertension

Adrenomedullin (AM) is a novel peptide, first isolated from human phaeochromocytoma, which elicits a long-lasting vasorelaxant activity. Recently, it has been reported that endothelial cells produce AM and that immunoreactive AM plasma levels may be elevated in human arterial hypertension, although the exact pathophysiological role of AM remains to be established. The aim of our study was to determine the relationship between the components of the enin-angiotensin-aldosterone system (RAAS) and plasma AM levels in patients with low-, medium- or high- renin essential hypertension. The study groups included 10 patients with low-renin essential hypertension (average age 42+15 years), nine patients with medium-renin essential hypertension (46+13 years), 11 patients with high-renin essential hypertension (42+14 years) and 12 healthy subjects (43+11 years). Our results demonstrated that the mean AM values of all patients with essential hypertension were 10.85+3.14 pg/ml; there was a statistical correlation (r=0.705; p<0.001) between plasma renin activity (PRA) and AM levels in hypertensives. In patients with high-renin essential hypertension, plasma AM levels (14.2+2.2 pg/ml) were significantly higher (p<0.001) than those of healthy subjects (8.7+2.1 pg/ml), patients with medium-renin essential hypertension (8.5+1.4 pg/ml), and patients with low-renin essential hypertension (9.1+1.5 pg/ml). There was no statistical difference in AM concentrations between medium- and low-renin hypertensive patients. In conclusion, we have found that, in hypertensive patients, plasma AM levels were increased only in high-renin individuals, suggesting a role of AM in this particular form of human essential hypertension.

Saturation of adrenomedullin receptors plays an important role in reducing pulmonary clearance of adrenomedullin during the late stage of sepsis

Adrenomedullin (AM) is a potent vasodilator that plays a major role in the cardiovascular response during the progression of sepsis. Although pulmonary clearance of AM (i.e., the primary site of AM clearance) is reduced during the late, hypodynamic stage of sepsis, the role of AM receptors under such conditions remains unclear. This study was carried out to test the hypothesis that saturation of AM receptors is responsible for the decreased clearance of AM in the lungs during sepsis. Polymicrobial sepsis was induced in male adult rats by cecal ligation and puncture (CLP). At 20 h after CLP (i.e., the late phase), 125I-labeled rat AM was administered through the jugular vein, both with (+) and without (-) pre-injection of the human AM fragment AM(22-52) (an AM receptor antagonist). Pulmonary tissue samples were harvested after 30 min and the radioactivity was determined. In addition, lung levels of AM were determined at 5 and 20 h after CLP by radioimmunoassay. Alterations in gene expression of the recently identified AM receptor subunits calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein-2 and -3 (RAMP-2 and -3) were assessed in the lungs by reverse transcription-polymerase chain reaction (RT-PCR) at 5 and 20 h after CLP. The results indicate that there was a significant decrease in pulmonary [125I]AM clearance at 20 h in -AM(22-52) CLP animals. Lung clearance in +AM(22-52) sham animals was significantly lower than in -AM(22-52) sham animals and was not statistically different from the -AM(22-52) CLP group. There was no statistical difference between +AM(22-52) and -AM(22-52) CLP groups. However, there was a significant increase in lung AM levels at 20 but not 5 h after CLP. In addition, RAMP-3 expression was significantly upregulated at 5 but not 20 h after CLP. There were no alterations in the expression of CRLR or RAMP-2 at either time point. These results suggest that pulmonary AM receptors become saturated as more AM enters the bloodstream, thereby reducing the ability of the lungs to clear this peptide during late sepsis. Early upregulation of RAMP-3 may be a compensatory mechanism to help clear the upregulated AM from the bloodstream. The lack of upregulation of RAMP-3 during late sepsis could also contribute to the decreased clearance observed during this phase.

Adrenomedullin functions as an important tumor survival factor in human carcinogenesis

Adrenomedullin (AM) is a pluripotent regulatory peptide initially isolated from a human pheochromocytoma (adrenal tumor) and subsequently shown to play a critical role in cancer cell division, tumor neovascularization, and circumvention of programmed cell death, thus it is an important tumor cell survival factor underlying human carcinogenesis. A variety of neural and epithelial cancers have been shown to produce abundant amounts of AM. Recent findings have implicated elevation of serum AM with the onset of malignant expression. In addition, patients with tumors producing high levels of this peptide have a poor prognostic clinical outcome. Given that most human epithelial cancers display a microenvironment of reduced oxygen tension, it is interesting to note that AM and several of its receptors are upregulated during hypoxic insult. The existence of such a regulatory pathway has been implicated as the basis for the overexpression of AM/AM-R in human malignancies, thereby generating a subsequent autocrine/paracrine growth advantage for the tumor cell. Furthermore, AM has been implicated as a potential immune suppressor substance, inhibiting macrophage function and acting as a newly identified negative regulator of the complement cascade, protective properties which may help cancer cells to circumvent immune surveillance. Hence, AM's traditional participation in normal physiology (cited elsewhere in this issue) can be extended to a primary player in human carcinogenesis and may have clinical relevance as a biological target for the intervention of tumor progression.

Adrenomedullin and the integrative physiology of fluid and electrolyte balance

Adrenomedullin (AM) is hypothesized to be a physiologically relevant regulator in fluid and electrolyte homeostasis. AM acts within the central nervous system to inhibit both water and salt intake. The peptide has direct actions in the hypothalamus to decrease vasopressin secretion and in the pituitary gland to inhibit ACTH release. AM decreases production and release of aldosterone from the adrenal glands and acts directly in the kidneys to increase renal blood flow and cause diuresis and natriuresis. Whether or not these complementary actions in brain, pituitary, adrenal gland, and kidney reflect coordinated regulatory mechanisms is currently unknown. Development of molecular tools to determine the physiologic role of endogenous AM will greatly enhance our understanding of AM and its regulation of fluid and electrolyte homeostasis.

Adrenomedullin in mammalian embryogenesis

Here are summarized data supporting that adrenomedullin (AM) is a multifunctional factor involved in the complex regulatory mechanisms of mammalian development. During rodent embryogenesis, AM is first expressed in the heart, followed by a broader but also defined spatio-temporal pattern of expression in vascular, neural, and skeletal-forming tissues as well as in the main embryonic internal organs. AM pattern of expression is suggestive of its involvement in the control of embryonic invasion, proliferation, and differentiation processes, probably through autocrine or paracrine modes of action. AM levels in fetoplacental tissues, uterus, maternal and umbilical plasma are highly increased during normal gestation. These findings in addition to other physiological and gene targeting studies support the importance of AM as a vasorelaxant factor implicated in the regulation of maternal vascular adaptation to pregnancy, as well as of fetal and fetoplacental circulations. AM is also present in amniotic fluid and milk, which is suggestive of additional functions in the maturation and immunological protection of the fetus. Altered expression of AM has been found in some gestational pathologies, although it is not yet clear whether this corresponds to causative or compensatory mechanisms. Future studies in regard to the distribution and expression levels of the molecules known to function as AM receptors, together with data on the action of complement factor H (an AM binding protein), may help to better define the roles of AM during embryonic development.

Adrenomedullin and PAMP: discovery, structures, and cardiovascular functions

We discovered adrenomedullin (AM) from human pheochromocytoma tissue by monitoring the elevating activity of intracellular cyclic AMP (cAMP) in rat platelets in 1993. Since the discovery of AM, it has attracted intense interest from cardiovascular researchers because AM elicits multiple biological activities, including a potent and powerful hypotensive activity caused by dilatation of resistance vessels. AM is biosynthesized and secreted from tissues, including cardiovascular organs. In addition to AM, "proadrenomedullin N-terminal 20 peptide (PAMP)," another biologically active peptide, was found to be processed from the AM precursor. Plasma AM levels are increased in various cardiovascular and renal diseases. AM, therefore, seems to function as a novel system that controls circulation and body fluid, and may be involved in pathophysiological changes in cardiovascular diseases. Therefore, in this review we will focus on the structure of AM and its gene, distribution, receptor, and the physiological and pathological roles of AM in cardiovascular disease.