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

Discovery of a First-in-Class Potent Small Molecule Antagonist against the Adrenomedullin-2 Receptor

The hormone adrenomedullin has both physiological and pathological roles in biology. As a potent vasodilator, adrenomedullin is critically important in the regulation of blood pressure, but it also has several roles in disease, of which its actions in cancer are becoming recognized to have clinical importance. Reduced circulating adrenomedullin causes increased blood pressure but also reduces tumor progression, so drugs blocking all effects of adrenomedullin would be unacceptable clinically. However, there are two distinct receptors for adrenomedullin, each comprising the same G protein-coupled receptor (GPCR), the calcitonin receptor-like receptor (CLR), together with a different accessory protein known as a receptor activity-modifying protein (RAMP). The CLR with RAMP2 forms an adrenomedullin-1 receptor, and the CLR with RAMP3 forms an adrenomedullin-2 receptor. Recent research suggests that a selective blockade of adrenomedullin-2 receptors would be therapeutically valuable. Here we describe the design, synthesis, and characterization of potent small-molecule adrenomedullin-2 receptor antagonists with 1000-fold selectivity over the adrenomedullin-1 receptor, although retaining activity against the CGRP receptor. These molecules have clear effects on markers of pancreatic cancer progression in vitro, drug-like pharmacokinetic properties, and inhibit xenograft tumor growth and extend life in a mouse model of pancreatic cancer. Taken together, our data support the promise of a new class of anticancer therapeutics as well as improved understanding of the pharmacology of the adrenomedullin receptors and other GPCR/RAMP heteromers.

Multiple marker approach to risk stratification in patients with stable coronary artery disease

AIMS

multimarker approaches for risk prediction in coronary artery disease have remained inconsistent. We assessed multiple biomarkers representing distinct pathophysiological pathways in relation to cardiovascular events in stable angina.

METHODS AND RESULTS

we investigated 12 biomarkers reflecting inflammation [C-reactive protein, growth-differentiation factor (GDF)-15, neopterin], lipid metabolism (apolipoproteins AI, B100), renal function (cystatin C, serum creatinine), and cardiovascular function and remodelling [copeptin, C-terminal-pro-endothelin-1, mid-regional-pro-adrenomedullin (MR-proADM), mid-regional-pro-atrial natriuretic peptide (MR-proANP), N-terminal-pro-B-type natriuretic peptide (Nt-proBNP)] in 1781 stable angina patients in relation to non-fatal myocardial infarction and cardiovascular death (n = 137) over 3.6 years. Using Cox proportional hazards models and C-indices, the strongest association with outcome for log-transformed biomarkers in multivariable-adjusted analyses was observed for Nt-proBNP [hazard ratio (HR) for one standard deviation increase 1.65, 95% confidence interval (CI) 1.28-2.13, C-index 0.686], GDF-15 (HR 1.59, 95% CI 1.25-2.02, C-index 0.681), MR-proANP (HR 1.46, 95% CI 1.14-1.87, C-index 0.673), cystatin C (HR 1.39, 95% CI 1.10-1.75, C-index 0.671), and MR-proADM (HR 1.63, 95% CI 1.21-2.20, C-index 0.668). Each of these top single markers and their combination (C-index 0.690) added predictive information beyond the baseline model consisting of the classical risk factors assessed by C-index and led to substantial reclassification (P-integrated discrimination improvement <0.05).

CONCLUSION

comparative analysis of 12 biomarkers revealed Nt-proBNP, GDF-15, MR-proANP, cystatin C, and MR-proADM as the strongest predictors of cardiovascular outcome in stable angina. All five biomarkers taken separately offered incremental predictive ability over established risk factors. Combination of the single markers slightly improved model fit but did not enhance risk prediction from a clinical perspective.

Expression and role of adrenomedullin in renal tumors and value of its mRNA levels as prognostic factor in clear-cell renal carcinoma

Antiangiogenic therapies are used for advanced clear-cell renal carcinomas (cRCC), but without curative possibilities, underlining the need for new therapeutic targets. Adrenomedullin (AM), a multifunctional peptide, is highly expressed in several tumors and plays an important role in angiogenesis and tumor growth through its receptors: calcitonin receptor-like receptor/receptor activity-modifying protein 2 and 3 (CLR/RAMP2 and CLR/RAMP3). In this study, real-time quantitative reverse-transcription-PCR showed AM mRNA levels were higher in cRCC and in chromophobe renal carcinomas (chRCC) than in normal renal tissue. Interestingly, AM mRNA expression in cRCC correlated strongly with VEGF-A mRNA expression. Immunohistochemically, AM, CLR and RAMP2 were localized in the carcinomatous epithelial compartment of cRCC. Interestingly, RAMP3 immunostaining was found only in the inflammatory cells that infiltrated tumors, suggesting a cross talk between tumor cells and the microenvironment. We also observed that cRCC cells BIZ and 786-O expressed and secreted AM into the culture medium. In vitro, exogenous AM treatment stimulated cell proliferation, migration and invasion, indicating the cell can respond to AM. The action of AM was specific and was mediated by the CLR/RAMP2 and CLR/RAMP3 receptors. Clinical data showed the prognostic value of AM. High AM mRNA levels were associated with an increased risk of relapse after curative nephrectomy for cRCC. These findings highlight the implication of the AM pathway in the metastatic process and the prognostic relevance of AM in cRCC and point to a potential new therapeutic target.

The renin-angiotensin system, adrenomedullins and urotensin II in the kidney: possible renoprotection via the kidney peptide systems

The incidence of chronic kidney disease, such as diabetic nephropathy, is increasing throughout the world. Many biologically active peptides play important roles in the kidney. The classical example is the renin-angiotensin system (RAS). Angiotensin II plays critical roles in the progression of chronic kidney disease through its vasoconstrictor action, stimulatory action on cell proliferation, and reactive oxygen-generating activity. A renin inhibitor, aliskiren, has recently been shown to be a clinically effective drug to reduce proteinuria in patients with diabetic nephropathy. (Pro)renin receptor, a specific receptor for renin and prorenin, was newly identified as a member of the RAS. When bound to prorenin, (pro)renin receptor activates the angiotensin I-generating activity of prorenin in the absence of cleavage of the prosegment, and directly stimulates the pathway of mitogen-activated protein kinase independently from the RAS. The kidney peptides that antagonize the intrarenal RAS may have renoprotective actions. Adrenomedullins, potent vasodilator peptides, have been shown to have renoprotective actions. On the other hand, urotensin II, a potent vasoconstrictor peptide, may promote the renal dysfunction in chronic kidney disease together with the renal RAS. Thus, in addition to the renin inhibitor and (pro)renin receptor, adrenomedullins and urotensin II may be novel targets to develop therapeutic strategies against chronic kidney disease.

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.

Human cerebral arteriovenous vasoactive exchange during alterations in arterial blood gases

Cerebral blood flow (CBF) is highly regulated by changes in arterial Pco2and arterial Po2. Evidence from animal studies indicates that various vasoactive factors, including release of norepinephrine, endothelin, adrenomedullin, C-natriuretic peptide (CNP), and nitric oxide (NO), may play a role in arterial blood gas-induced alterations in CBF. For the first time, we directly quantified exchange of these vasoactive factors across the human brain. Using the Fick principle and transcranial Doppler ultrasonography, we measured CBF in 12 healthy humans at rest and during hypercapnia (4 and 8% CO2), hypocapnia (voluntary hyperventilation), and hypoxia (12 and 10% O2). At each level, blood was sampled simultaneously from the internal jugular vein and radial artery. With the exception of CNP and NO, the simultaneous quantification of norepinephrine, endothelin, or adrenomedullin showed no cerebral uptake or release during changes in arterial blood gases. Hypercapnia, but not hypocapnia, increased CBF and caused a net cerebral release of nitrite (a marker of NO), which was reflected by an increase in the venous-arterial difference for nitrite: 57 ± 18 and 150 ± 36 μmol/l at 4% and 8% CO2, respectively (both P < 0.05). Release of cerebral CNP was also observed during changes in CO2(hypercapnia vs. hypocapnia, P < 0.05). During hypoxia, there was a net cerebral uptake of nitrite, which was reflected by a decreased venous-arterial difference for nitrite: −96 ± 14 μmol/l at 10% O2( P < 0.05). These data indicate that there is a differential exchange of NO across the brain during hypercapnia and hypoxia and that CNP may play a complementary role in CO2-induced CBF changes.

Role of hypoxia and cAMP in the transdifferentiation of human fetal cardiac fibroblasts: implications for progression to scarring in autoimmune-associated congenital heart block

OBJECTIVE

Identification of isolated congenital heart block (CHB) predicts, with near certainty, the presence of maternal anti-SSA/Ro antibodies; however, the 2% incidence of CHB in first offspring of anti-SSA/Ro+ mothers, 20% recurrence in subsequent pregnancies, and discordance in identical twins suggest that an environmental factor amplifies the effect of the antibody. Accordingly, this study was carried out to explore the hypothesis that hypoxia potentiates a profibrosing phenotype of the fetal cardiac fibroblast.

METHODS

Evidence of an effect of hypoxia was sought by immunohistologic evaluation of CHB-affected fetal heart tissue and by determination of erythropoietin levels in cord blood. The in vitro effect of hypoxia on gene expression and phenotype in fibroblasts derived from fetal hearts and lungs was investigated by Affymetrix arrays, quantitative polymerase chain reaction (PCR), immunofluorescence, and immunoblotting.

RESULTS

In vivo hypoxic exposure was supported by the prominent intracellular fibroblast expression of hypoxia-inducible factor 1alpha in conduction tissue from 2 fetuses in whom CHB led to death. The possibility that hypoxia was sustained was suggested by significantly elevated erythropoietin levels in cord blood from CHB-affected, as compared with unaffected, anti-SSA/Ro-exposed neonates. In vitro exposure of cardiac fibroblasts to hypoxia resulted in transdifferentiation to myofibroblasts (a scarring phenotype), as demonstrated on immunoblots and immunofluorescence by increased expression of smooth muscle actin (SMA), an effect not seen in lung fibroblasts. Hypoxia-exposed cardiac fibroblasts expressed adrenomedullin at 4-fold increased levels, as determined by Affymetrix array, quantitative PCR, and immunofluorescence, thus focusing attention on cAMP as a modulator of fibrosis. MDL12,330A, an adenylate cyclase inhibitor that lowers the levels of cAMP, increased expression of fibrosis-related proteins (mammalian target of rapamycin, SMA, plasminogen activator inhibitor type 1, and type I collagen), while the cAMP activator forskolin attenuated transforming growth factor beta-elicited fibrosing end points in the cardiac fibroblasts.

CONCLUSION

These findings provide evidence that hypoxia may amplify the injurious effects of anti-SSA/Ro antibodies. Modulation of cAMP may be a key component in the scarring phenotype. Further assessment of the susceptibility of cardiac fibroblasts to cAMP modulation offers a new research direction in CHB.

Hypoxia and expression of hypoxia-inducible factor in the aging kidney

Renal senescence is characterized by interstitial fibrosis and loss of peritubular capillaries. In this study, we provided evidence of tubulointerstitial hypoxia and the operation of hypoxia-inducible factor (HIF) in the aging kidney. Using two distinct methods, pimonidazole immunostaining and the expression of the "hypoxia-responsive" reporter of the transgenic rats, we identified the age-related expansion of hypoxia in all areas of the kidney. Expansion was most prominent in the cortex. Clusters of hypoxic tubules were observed in the superficial cortical zones, areas adjacent to the outer nephrons and expanded in the medullary rays. The degree of hypoxia was positively correlated with the age-related tubulointerstitial injury (R(2) = 0.88, p <.01), which was associated with the upregulation of HIF-regulated genes, such as vascular endothelial growth factor (VEGF) and glucose transporter-1 (GLUT1) (real-time polymerase chain reaction). These findings point to the involvement of hypoxia and highlight the pathological relevance of HIF and its target genes in the aging kidney.

Tissue expression and plasma levels of adrenomedullin in renal cancer patients

The peptide AM (adrenomedullin) is stimulated by hypoxia through HIF-1 (hypoxia-inducible factor-1). The majority of human CC-RCCs (clear cell renal cell carcinomas) display mutations in the tumour suppressor protein von Hippel–Lindau, which leads to constitutively elevated HIF-1. We hypothesized that AM is increased in CC-RCC tumours and that AM is a plasma biomarker for CC-RCC. Tumours and non-malignant kidney tissue were obtained from patients that underwent unilateral nephrectomy. Blood samples were drawn at the day of surgery, 3–6 days after surgery and 4–5 weeks after surgery. AM mRNA and peptide expression in tissue and AM plasma concentration were determined. HIF-1α was localized in tissue by immunohistochemistry. AM mRNA was elevated in CC-RCC compared with adjacent renal cortex (6-fold, n=18; P<0.02). There was no difference in AM mRNA between cortex and non-CC-RCC tissue (n=7). AM peptide concentration was elevated in CC-RCC tissue compared with adjacent cortex (4-fold, n=6; P<0.02), whereas there was no difference between cortex and non-CC-RCC tissue (n=5). HIF-1α immunoreactivity was detected in the majority of cell nuclei in 76% of CC-RCC, consistent with constitutive stabilization. In non-CC-RCC, HIF-1α staining was focal. Before surgery there was no difference in plasma AM concentration between tumour types. Nephrectomy increased plasma AM significantly after 3–6 days and a similar pre-surgery level was observed after 4–5 weeks in both groups of tumour patients. We conclude that elevated tissue AM is a distinguishing feature of CC-RCC compared with other kidney tumours. Plasma AM is not suited as a tumour marker for this disease.

A biologic role of HIF-1 in the renal medulla

BACKGROUND

Activation of hypoxia-inducible factor-1 (HIF-1) is the primary defensive mechanism against hypoxia. HIF-1 activation generally occurs in pathologic disruption of tissue oxygenation. However, a biologic role of HIF-1 in the medulla of the kidney, which is considered perpetually hypoxic under physiologic conditions due to its unique circulation, remains to be elucidated.

METHODS

The expression of HIF-1alpha was detected by immunohistochemical analysis. Functional studies of HIF in medulla were carried out by gene transfer of various plasmids by retrograde injection via ureter.

RESULTS

Our immunohistochemical analysis detected HIF-1alpha in the inner stripe and the inner medulla of normal rats. Water deprivation increased the number of HIF-1alpha-positive cells, which may be mediated by an increase in medullar workload and a decrease in local blood flow. To perform functional studies, we performed gene transfer. Efficient expression of the transgene was confirmed using an enhanced green fluorescent protein (E-GFP) expressing vector. Our histologic and immunoblotting analysis detected the transgene product at the inner medulla and the inner stripe 48 hours after injection. Administration of negative-dominant HIF induced severe damage in the medulla of normal rats. In contrast, gene transfer of constitutively active HIF (HIF/VP16) induced expression of various HIF-regulated genes and protected the medulla against ischemic insults.

CONCLUSION

Our studies demonstrated a crucial role of HIF in the renal medulla under normal and hypoxic circumstances.

Expression and regulation of adrenomedullin in renal glomerular podocytes

Adrenomedullin (AM) is postulated to exert organ-protective effects. It is expressed in the renal glomeruli, but its roles in the glomerular podocytes have been poorly elucidated. In the present study, we investigated the expression and regulation of AM in recently established conditionally immortalized mouse podocyte cell line in vitro and podocyte injury model in vivo. The cultured differentiated podocytes expressed AM mRNA and secreted measurable amount of AM. AM secretion from the podocytes was increased by H(2)O(2), hypoxia, puromycin aminonucleoside (PAN), albumin overload, and TNF-alpha. Real-time RT-PCR analysis revealed that AM mRNA expression in the podocytes was enhanced by PAN and TNF-alpha, both of which were suppressed by mitochondrial antioxidants. Furthermore, AM expression was upregulated in the glomerular podocytes of PAN nephrosis rats. These results indicated that AM expression in the podocytes was upregulated by stimuli or condition relevant to podocyte injury, suggesting its potential role in podocyte pathophysiology.

Adrenomedullin expression during hypoxia in fetal sheep

AIM

We asked how adrenomedullin (AM), a vasodilator peptide, was distributed in fetal sheep organs and whether expression of AM would be upregulated in response to moderate acute fetal hypoxia in vivo.

METHODS

In four sheep at day 126-130 of gestation, nitrogen was added to the inspired air by tracheal infusion to reduce fetal arterial oxygen content for a period of 4 h. Control fetuses were from four ewes given a tracheal infusion of room air. Fetal and maternal blood samples were taken prior to and during hypoxia/sham hypoxia. Fetal tissue samples were frozen for RNA analysis and fixed for immunohistochemistry.

RESULTS

In hypoxic fetuses, arterial oxygen content was significantly reduced to 50% compared with sham fetuses with no change in arterial pH in either group. Plasma ACTH levels rose significantly at 2 and 4 h in hypoxic fetuses only. Initial plasma concentrations of AM in control and hypoxic fetuses were 457 +/- 20 and 430 +/- 35 pg mL(-1) and did not change during the experiment. The relative abundance of AM mRNA was placental cotyledons >> lung > cerebral cortex approximately equal to renal cortex > left ventricle approximately equal to right ventricle > adrenal gland > renal medulla > aorta approximately equal to liver. Immunohistochemical staining for AM confirmed distinct labelling in organs with significant expression. AM mRNA level increased significantly in cerebral cortex of hypoxic fetuses.

CONCLUSION

Our results show expression of AM in placenta and in several fetal organs in late gestation sheep. AM may participate in the cerebral vasodilatation that is an integral part of the fetal response to hypoxia.