Bovine aortic endothelial cells contain an angiotensin-(1-7) receptor

The angiotensin-(1-7)/MasR axis improves pneumonia caused by Pseudomonas aeruginosa: Extending the therapeutic window for antibiotic therapy

Pseudomonas aeruginosa is a frequent cause of antimicrobial-resistant hospital-acquired pneumonia, especially in critically ill patients. Inflammation triggered by P. aeruginosa infection is necessary for bacterial clearance but must be spatially and temporally regulated to prevent further tissue damage and bacterial dissemination. Emerging data have shed light on the pro-resolving actions of angiotensin-(1-7) [Ang-(1-7)] signaling through the G protein-coupled receptor Mas (MasR) during infections. Herein, we investigated the role of the Ang-(1-7)/Mas axis in pneumonia caused by P. aeruginosa by using genetic and pharmacological approach and found that Mas receptor-deficient animals developed a more severe form of pneumonia showing higher neutrophilic infiltration into the airways, bacterial load, cytokines, and chemokines production and more severe pulmonary damage. Conversely, treatment of pseudomonas-infected mice with Ang-(1-7) was able to decrease neutrophilic infiltration in airways and lungs, local and systemic levels of pro-inflammatory cytokines and chemokines, and increase the efferocytosis rates, mitigating lung damage/dysfunction caused by infection. Notably, the therapeutic association of Ang-(1-7) with antibiotics improved the survival rates of mice subjected to lethal inoculum of P. aeruginosa, extending the therapeutic window for imipenem. Mechanistically, Ang-(1-7) increased phagocytosis of bacteria by neutrophils and macrophages to accelerate pathogen clearance. Altogether, harnessing the Ang-(1-7) pathway during infection is a potential strategy for the development of host-directed therapies to promote mechanisms of resistance and resilience to pneumonia.

MasR and pGCA receptor activation protects primary vascular smooth muscle cells and endothelial cells against oxidative stress via inhibition of intracellular calcium

Cardiovascular diseases (CVDs) are associated with vascular smooth muscle cell (VSMC) and endothelial cell (EC) damage. Angiotensin1-7 (Ang1-7) and B-type natriuretic peptide (BNP) are responsible for vasodilation and regulation of blood flow. These protective effects of BNP are primarily mediated by the activation of sGCs/cGMP/cGKI pathway. Conversely, Ang1-7 inhibits Angiotensin II-induced contraction and oxidative stress via Mas receptor activation. Thus, the aim of the study was to determine the effect of co-activation of MasR and particulate guanylate cyclase receptor (pGCA) pathways by synthesized novel peptide (NP) in oxidative stress-induced VSMCs and ECs. MTT and Griess reagent assay kits were used for the standardization of the oxidative stress (H₂ O₂ ) induced model in VSMCs. The expression of targeted receptors in VSMC was done by RT-PCR and Western blot analysis. Protective effect of NP in VSMC and EC was determined by immunocytochemistry, FACS analysis, and Western blot analysis. Underlying mechanisms of EC-dependent VSMC relaxation were done by determining downstream mRNA gene expression and intracellular calcium imaging of cells. Synthesized NP significantly improved oxidative stress-induced injury in VSMCs. Remarkably, the actions of NP were superior to that of the Ang1-7 and BNP alone. Further, a mechanistic study in VSMC and EC suggested the involvement of upstream mediators of calcium inhibition for the therapeutic effect. NP is reported to possess vascular protective activities and is also involved in the improvement of endothelial damage. Moreover, it is highly effective than that of individual peptides BNP and Ang1-7 and therefore it may represent a promising strategy for CVDs.

Novel Experimental Therapies for Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive and devastating disease characterized by pulmonary artery vasoconstriction and vascular remodeling leading to vascular rarefaction with elevation of pulmonary arterial pressures and pulmonary vascular resistance. Often PAH will cause death from right heart failure. Current PAH-targeted therapies improve functional capacity, pulmonary hemodynamics and reduce hospitalization. Nevertheless, today PAH still remains incurable and is often refractory to medical therapy, underscoring the need for further research. Over the last three decades, PAH has evolved from a disease of unknown pathogenesis devoid of effective therapy to a condition whose cellular, genetic and molecular underpinnings are unfolding. This article provides an update on current knowledge and summarizes the progression in recent advances in pharmacological therapy in PAH.

Cirrhotic portal hypertension: From pathophysiology to novel therapeutics

Portal hypertension and bleeding from gastroesophageal varices is the major cause of morbidity and mortality in patients with cirrhosis. Portal hypertension is initiated by increased intrahepatic vascular resistance and a hyperdynamic circulatory state. The latter is characterized by a high cardiac output, increased total blood volume and splanchnic vasodilatation, resulting in increased mesenteric blood flow. Pharmacological manipulation of cirrhotic portal hypertension targets both the splanchnic and hepatic vascular beds. Drugs such as angiotensin converting enzyme inhibitors and angiotensin II type receptor 1 blockers, which target the components of the classical renin angiotensin system (RAS), are expected to reduce intrahepatic vascular tone by reducing extracellular matrix deposition and vasoactivity of contractile cells and thereby improve portal hypertension. However, these drugs have been shown to produce significant off-target effects such as systemic hypotension and renal failure. Therefore, the current pharmacological mainstay in clinical practice to prevent variceal bleeding and improving patient survival by reducing portal pressure is non-selective -blockers (NSBBs). These NSBBs work by reducing cardiac output and splanchnic vasodilatation but most patients do not achieve an optimal therapeutic response and a significant proportion of patients are unable to tolerate these drugs. Although statins, used alone or in combination with NSBBs, have been shown to improve portal pressure and overall mortality in cirrhotic patients, further randomized clinical trials are warranted involving larger patient populations with clear clinical end points. On the other hand, recent findings from studies that have investigated the potential use of the blockers of the components of the alternate RAS provided compelling evidence that could lead to the development of drugs targeting the splanchnic vascular bed to inhibit splanchnic vasodilatation in portal hypertension. This review outlines the mechanisms related to the pathogenesis of portal hypertension and attempts to provide an update on currently available therapeutic approaches in the management of portal hypertension with special emphasis on how the alternate RAS could be manipulated in our search for development of safe, specific and effective novel therapies to treat portal hypertension in cirrhosis.

Blockade of Mas Receptor or Mas-Related G-Protein Coupled Receptor Type D Reduces Portal Pressure in Cirrhotic but Not in Non-cirrhotic Portal Hypertensive Rats

Portal hypertension (PHT) resulting from splanchnic vasodilatation is a major cause of morbidity and mortality in patients with cirrhosis. The renin-angiotensin system (RAS) plays an important role in splanchnic vasodilatation in cirrhosis. This study investigated whether acute blockade of the vasodilatory receptors of the alternate RAS, Mas (MasR), Mas-related G-protein coupled receptor type D (MrgD), and angiotensin II type-2 receptor (AT2R) improves PHT in cirrhotic and non-cirrhotic portal hypertensive rats and counteracts systemic hypotension associated with angiotensin II type 1 receptor (AT1R) blockade. Cirrhotic bile duct ligated (BDL) or carbon tetrachloride (CCl₄) injected and non-cirrhotic partial portal vein ligated (PPVL) rats were used for measurement of portal pressure (PP) and mean arterial pressure before and after an intravenous bolus injection of the MasR, MrgD, and AT2R blockers, A779, D-Pro⁷-Ang-(1-7) (D-Pro) and PD123319, respectively. Separate groups of rats received a combined treatment with A779 or D-Pro given 20 min after AT1R blocker losartan. Mesenteric expression of MasR, MrgD, and AT2R and circulating levels of peptide blockers were also measured. Treatment with A779 and D-Pro significantly reduced PP in cirrhotic rat models. Despite rapid degradation of A779 and D-Pro in the rat circulation, the PP lowering effect of the blockers lasted for up to 25 min. We also found that PD123319 reduced PP in CCl₄ rats, possibly by blocking the MasR and/or MrgD since AT2R expression in cirrhotic mesenteric vessels was undetectable, whereas the expression of MasR and MrgD was markedly elevated. While losartan resulted in a marked reduction in PP, its profound systemic hypotensive effect was not counteracted by the combination therapy with A779 or D-Pro. In marked contrast, none of the receptor blockers had any effect on PP in non-cirrhotic PPVL rats whose mesenteric expression of MasR and MrgD was unchanged. We conclude that in addition to MasR, MrgD, a newly discovered receptor for Angiotensin-(1-7), plays a key role in splanchnic vasodilatation in cirrhosis. This implies that both MasR and MrgD are potential therapeutic targets to treat PHT in cirrhotic patients. We also conclude that the alternate RAS may not contribute to the development of splanchnic vasodilatation in non-cirrhotic PHT.

A potential therapeutic role for angiotensin-converting enzyme 2 in human pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a deadly disease with no cure. Alternate conversion of angiotensin II (AngII) to angiotensin-(1-7) (Ang-(1-7)) by angiotensin-converting enzyme 2 (ACE2) resulting in Mas receptor (Mas1) activation improves rodent models of PAH. Effects of recombinant human (rh) ACE2 in human PAH are unknown. Our objective was to determine the effects of rhACE2 in PAH.We defined the molecular effects of Mas1 activation using porcine pulmonary arteries, measured AngII/Ang-(1-7) levels in human PAH and conducted a phase IIa, open-label pilot study of a single infusion of rhACE2 (GSK2586881, 0.2 or 0.4 mg·kg^-1 intravenously).Superoxide dismutase 2 (SOD2) and inflammatory gene expression were identified as markers of Mas1 activation. After confirming reduced plasma ACE2 activity in human PAH, five patients were enrolled in the trial. GSK2586881 was well tolerated with significant improvement in cardiac output and pulmonary vascular resistance. GSK2586881 infusion was associated with reduced plasma markers of inflammation within 2-4 h and increased SOD2 plasma protein at 2 weeks.PAH is characterised by reduced ACE2 activity. Augmentation of ACE2 in a pilot study was well tolerated, associated with improved pulmonary haemodynamics and reduced markers of oxidant and inflammatory mediators. Targeting this pathway may be beneficial in human PAH.

Role of the ACE2‑Ang‑(1‑7)‑Mas axis in blood pressure regulation and its potential as an antihypertensive in functional foods (Review)

The renin‑angiotensin system (RAS) serves a critical role in blood pressure regulation and prevention of cardiovascular diseases. Efforts to develop functional foods that enhance the RAS have focused on inhibition of angiotensin‑converting enzyme (ACE) activity in the ACE‑angiotensin II (Ang II)‑Ang II type 1 receptor axis. ACE2 and the Mas receptor are important components of this axis. ACE2 catalyzes Ang II into Ang‑(1‑7), which then binds to the G‑protein‑coupled receptor Mas. In addition, it induces nitric oxide release from endothelial cells and exerts antiproliferative, vasodilatory and antihypertensive effects. The present review examined recent findings regarding the physiological and biological roles of the ACE2‑Ang‑(1‑7)‑Mas axis in the cardiovascular system, discussed potential food‑derived ACE2‑activating agents, and highlighted initiatives, based on this axis, that aim to develop functional foods for the treatment of hypertension.

Ang (1-7) is a modulator of the vasoconstrictor actions of Ang I and Ang II

INTRODUCTION

The role of angiotensin (Ang) (1-7) on the vasoconstrictor effect induced by angiotensins could be different in the presence of an ACE inhibitor or an ARB because Ang II is formed through several pathways. Therefore, the role of Ang (1-7) in Ang I and Ang II contraction was evaluated in aortas from Wistar rats after 48-hour coronary occlusion treated with captopril or losartan.

METHODS

Concentration-response curves to Ang I or Ang II were conducted in the absence or presence of Ang (1-7) and A779: a) sham group; b) 48-hour coronary occlusion; c) treated with captopril or d) losartan (3.1 mg/kg, i.m.).

RESULTS

Captopril caused a significant increase in the contractile effect of Ang I and Ang II, while losartan reduced it. The presence of Ang (1-7) in the captopril group showed a reduction of the contraction compared to the sham group, while the treatment with losartan did not show a significant difference. Ang (1-7) presents effects different from Ang I or Ang II.

CONCLUSION

Ang (1-7) showed a modulatory role, suggesting Ang I did as well after treatment with an ACE inhibitor but not with an AT1 receptor antagonist.

Modulation of the action of insulin by angiotensin-(1-7)

The prevalence of Type 2 diabetes mellitus is predicted to increase dramatically over the coming years and the clinical implications and healthcare costs from this disease are overwhelming. In many cases, this pathological condition is linked to a cluster of metabolic disorders, such as obesity, systemic hypertension and dyslipidaemia, defined as the metabolic syndrome. Insulin resistance has been proposed as the key mediator of all of these features and contributes to the associated high cardiovascular morbidity and mortality. Although the molecular mechanisms behind insulin resistance are not completely understood, a negative cross-talk between AngII (angiotensin II) and the insulin signalling pathway has been the focus of great interest in the last decade. Indeed, substantial evidence has shown that anti-hypertensive drugs that block the RAS (renin-angiotensin system) may also act to prevent diabetes. Despite its long history, new components within the RAS continue to be discovered. Among them, Ang-(1-7) [angiotensin-(1-7)] has gained special attention as a counter-regulatory hormone opposing many of the AngII-related deleterious effects. Specifically, we and others have demonstrated that Ang-(1-7) improves the action of insulin and opposes the negative effect that AngII exerts at this level. In the present review, we provide evidence showing that insulin and Ang-(1-7) share a common intracellular signalling pathway. We also address the molecular mechanisms behind the beneficial effects of Ang-(1-7) on AngII-mediated insulin resistance. Finally, we discuss potential therapeutic approaches leading to modulation of the ACE2 (angiotensin-converting enzyme 2)/Ang-(1-7)/Mas receptor axis as a very attractive strategy in the therapy of the metabolic syndrome and diabetes-associated diseases.

Activation of the MAS receptor by angiotensin-(1-7) in the renin-angiotensin system mediates mesenteric vasodilatation in cirrhosis

BACKGROUND & AIMS

Splanchnic vascular hypocontractility with subsequent increased portal venous inflow leads to portal hypertension. Although the renin-angiotensin system contributes to fibrogenesis and increased hepatic resistance in patients with cirrhosis, little is known about its effects in the splanchnic vasculature, particularly those of the alternate system in which angiotensin (Ang) II is cleaved by the Ang-converting enzyme-2 (ACE2) to Ang-(1-7), which activates the G-protein-coupled Mas receptor (MasR). We investigated whether this system contributes to splanchnic vasodilatation and portal hypertension in cirrhosis.

METHODS

We measured levels of renin-angiotensin system messenger RNA and proteins in splanchnic vessels from patients and rats with cirrhosis. Production of Ang-(1-7) and splanchnic vascular reactivity to Ang-(1-7) was measured in perfused mesenteric vascular beds from rats after bile-duct ligation. Ang-(1-7) and MasR were blocked in rats with cirrhosis to examine splanchnic vascular hemodynamics and portal pressure response.

RESULTS

Levels of ACE2 and MasR were increased in splanchnic vessels from cirrhotic patients and rats compared with healthy controls. We also observed an ACE2-dependent increase in Ang-(1-7) production. Ang-(1-7) mediated splanchnic vascular hypocontractility in ex vivo splanchnic vessels from rats with cirrhosis (but not control rats) via MasR stimulation. Identical effects were observed in the splanchnic circulation in vivo. MasR blockade reduced portal pressure, indicating that activation of this receptor in splanchnic vasculature promotes portal inflow to contribute to development of portal hypertension. In addition, the splanchnic effects of MasR required nitric oxide. Interestingly, Ang-(1-7) also decreased hepatic resistance.

CONCLUSIONS

In the splanchnic vessels of patients and rats with cirrhosis, increased levels of ACE2 appear to increase production of Ang-(1-7), which leads to activation of MasR and splanchnic vasodilatation in rats. This mechanism could cause vascular hypocontractility in patients with cirrhosis, and might be a therapeutic target for portal hypertension.

Predominance of AT(1) blockade over mas-mediated angiotensin-(1-7) mechanisms in the regulation of blood pressure and renin-angiotensin system in mRen2.Lewis rats

BACKGROUND

We investigated whether the antihypertensive actions of the angiotensin II (Ang II) receptor (AT(1)-R) blocker, olmesartan medoxomil, may in part be mediated by increased Ang-(1-7) in the absence of significant changes in plasma Ang II.

METHODS

mRen2.Lewis congenic hypertensive rats were administered either a vehicle (n = 14) or olmesartan (0.5 mg/kg/day; n = 14) by osmotic minipumps. Two weeks later, rats from both groups were further randomized to receive either the mas receptor antagonist A-779 (0.5 mg/kg/day; n = 7 per group) or its vehicle (n = 7 per group) for the next 4 weeks. Blood pressure was monitored by telemetry, and circulating and tissue components of the renin-angiotensin system (RAS) were measured at the completion of the experiments.

RESULTS

Antihypertensive effects of olmesartan were associated with an increase in plasma renin concentration, plasma Ang I, Ang II, and Ang-(1-7), whereas serum aldosterone levels and kidney Ang II content were reduced. Preserved Ang-(1-7) content in kidneys was associated with increases of ACE2 protein but not activity and no changes on serum and kidney ACE activity. There was no change in cardiac peptide levels after olmesartan treatment. The antihypertensive effects of olmesartan were not altered by concomitant administration of the Ang-(1-7) receptor antagonist except for a mild further increase in plasma renin concentration.

CONCLUSIONS

Our study highlights the independent regulation of RAS among plasma, heart, and kidney tissue in response to AT(1)-R blockade. Ang-(1-7) through the mas receptor does not mediate long-term effects of olmesartan besides counterbalancing renin release in response to AT(1)-R blockade.

Altered regional blood flow distribution in Mas-deficient mice

BACKGROUND

We have recently shown that the acute infusion of angiotensin-(1-7) [Ang-(1-7)] or chronic increase in plasma Ang-(1-7) produces important changes in regional blood flow in rats.

METHODS

To further assess whether these changes are related to Mas, in this study hemodynamic measurements were performed in Ang-(1-7) receptor Mas knockout C57BL/6 (Mas-KO) mice and age-matched wild type (WT) control mice, using fluorescent microspheres.

RESULTS

Mean arterial pressure in urethane-anesthetized Mas-KO mice (12-16 weeks old) did not differ from that in WT mice (79 ± 2 and 80 ± 2 mmHg respectively). However, pronounced differences were observed in other hemodynamic measurements. Mas-KO mice exhibited a significant decrease in stroke volume (0.03 ± 0.01 versus 0.05 ± 0.01 ml/beat in WT) and decreased cardiac index (0.81 ± 0.08 versus 1.24 ± 0.24 ml/min/g in WT). Strikingly, Mas-KO mice exhibited a marked increase in vascular resistance and a decrease in blood flow in the kidney, lung, adrenal gland, mesentery, spleen and brown fat tissue. The decrease in blood flow ranged from 34% (spleen) to 55% (brown fat tissue).

CONCLUSION

These results suggest that the Ang-(1-7)/Mas axis plays an important role in regional and systemic hemodynamic adjustments in mice.

Angiotensin II and angiotensin-(1-7) decrease sFlt1 release in normal but not preeclamptic chorionic villi: an in vitro study

BACKGROUND

During preeclampsia, placental angiogenesis is impaired. Factors released from the placenta including vascular endothelial growth factor (VEGF), placental growth factor (PLGF), soluble VEGF receptor 1 (sFlt1), and soluble endoglin (sEng) are regulatory molecules of placental development and function. While the renin angiotensin system has been shown to regulate angiogenic factors in other research fields, these mechanisms have not been extensively studied during pregnancy.

METHODS

We evaluated the effects of angiotensin II (Ang II) and angiotensin-(1-7) [Ang-(1-7)] on the release of VEGF, PLGF, sFlt1, and sEng from placental chorionic villi (CV). CV were collected from nulliparous third-trimester normotensive and preeclamptic subjects. CV were incubated for 0, 2, 4, and 16 hours with or without Ang II (1 nM and 1 microM) or Ang-(1-7) (1 nM and 1 microM). The release of VEGF, PLGF, sFlt1, sEng, lactate dehydrogenase (LDH), and human placenta lactogen (HPL) was measured by ELISA.

RESULTS

The release of sFlt1, PLGF, sEng from normal and preeclamptic CV increased over time. Release of sFlt1 and sEng was significantly higher from preeclamptic CV. VEGF was below the detectable level of the assay in normal and preeclamptic CV. After 2 hours, sFlt1 release from normal CV was significantly inhibited with Ang II (1 nM and 1 microM) and Ang-(1-7) (1 nM and 1 microM). There was a time-dependent increase in HPL indicating that the CV were functioning normally.

CONCLUSIONS

Our study demonstrates a critical inhibitory role of angiotensin peptides on sFlt1 in normal pregnancy. Loss of this regulation in preeclampsia may allow sFlt1 to increase resulting in anti-angiogenesis and end organ damage in the mother.

New pathways of the renin-angiotensin system: the role of ACE2 in cardiovascular pathophysiology and therapy

IMPORTANCE OF THE FIELD

The renin-angiotensin system (RAS) is nowadays an important target in cardiovascular diseases and we are currently on the verge of a new interpretation of its role in cardiovascular homeostasis, mainly due to the identification of the new axis ACE2/angiotensin 1 - 7/Mas receptor.

AREAS COVERED IN THIS REVIEW

The main aspects related to ACE2 role in cardiovascular physiology and possible pathological and therapeutic implications are reviewed.

WHAT THE READER WILL GAIN

A description of the new view of the RAS, along with the key findings that support it. In the cardiovascular system, the ACE2/angiotensin 1 - 7/Mas axis, mainly through the inhibition of fibrosis, inflammation, thrombosis and cell proliferation, modulates RAS activity with significant pathophysiological implications in clinical conditions such as hypertension, myocardial ischemia and heart failure. A more complete understanding of this axis has significant therapeutic relevance and a major effort is being carried out in order to pursue this objective.

TAKE HOME MESSAGE

There is increasing evidence that ACE2/angiotensin 1 - 7/Mas receptor axis has a key role in RAS activity regulation with significant pathophysiological implications in several disease states. A therapeutic intervention at this level may open new doors and change the current approach to RAS targeting.

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 ).

Phase I and pharmacokinetic study of angiotensin-(1-7), an endogenous antiangiogenic hormone

PURPOSE

Angiotensin-(1-7) [Ang-(1-7)] is an endogenous peptide hormone of the renin-angiotensin system with antiproliferative and antiangiogenic properties. The primary objective of this study was to establish the recommended phase II dose of Ang-(1-7) for treating patients with advanced cancer. Secondary objectives were to assess toxicities, pharmacokinetics, clinical activity, and plasma biomarkers.

EXPERIMENTAL DESIGN

Patients with advanced solid tumors refractory to standard therapy were treated with escalating doses of Ang-(1-7) in cohorts of three patients. Ang-(1-7) was administered by s.c. injection once daily for 5 days on a 3-week cycle. Tumor measurements were done every two cycles and treatment was continued until disease progression or unacceptable toxicity.

RESULTS

Eighteen patients were enrolled. Dose-limiting toxicities encountered at the 700 microg/kg dose included stroke (grade 4) and reversible cranial neuropathy (grade 3). Other toxicities were generally mild. One patient developed a 19% reduction in tumor measurements. Three additional patients showed clinical benefit with stabilization of disease lasting more than 3 months. On day 1, Ang-(1-7) administration led to a decrease in plasma placental growth factor (PlGF) levels in patients with clinical benefit (P = 0.04) but not in patients without clinical benefit (P = 0.25). On day 5, PlGF levels remained lower in patients with clinical benefit compared with patients without clinical benefit (P = 0.04).

CONCLUSIONS

Ang-(1-7) is a first-in-class antiangiogenic drug with activity for treating cancer that is linked to reduction of plasma PlGF levels. The recommended phase II dose is 400 microg/kg for this administration schedule.

Angiotensin-(1-7) inhibits tumor angiogenesis in human lung cancer xenografts with a reduction in vascular endothelial growth factor

Angiotensin-(1-7) [Ang-(1-7)] is an endogenous seven-amino acid peptide hormone with antiproliferative properties. Our previous studies showed that Ang-(1-7) inhibits the growth of human lung cancer cells in vitro and reduces the size of human lung tumor xenografts in vivo. In the current study, s.c. injection of Ang-(1-7) not only caused a significant reduction in human A549 lung tumor growth but also markedly decreased vessel density, suggesting that the heptapeptide inhibits angiogenesis to reduce tumor size. A decrease in human endothelial cell tubule formation in Matrigel was observed following a 16 h incubation with Ang-(1-7), with a maximal reduction at a 10 nmol/L concentration. Ang-(1-7) had similar antiangiogenic effects in the chick chorioallantoic membrane, causing a >50% decrease in neovascularization. The Ang-(1-7)-induced reduction in both endothelial cell tubule formation and vessel formation in the chick was completely blocked by the specific Ang-(1-7) receptor antagonist [d-proline(7)]-Ang-(1-7), suggesting that these biological actions are mediated by an AT((1-7)) receptor. Ang-(1-7) significantly reduced vascular endothelial growth factor-A protein and mRNA in tumors from mice treated with the heptapeptide compared with saline controls as well as in the parent A549 human lung cancer cells in culture. These results suggest that Ang-(1-7) may attenuate tumor angiogenesis by reducing vascular endothelial growth factor-A, a primary proangiogenic protein. Taken together, this study shows that Ang-(1-7) exhibits significant antiangiogenic activity and may be a novel therapeutic agent for lung cancer treatment targeting a specific AT((1-7)) receptor.

Endogenous angiotensin-(1-7) reduces cardiac ischemia-induced dysfunction in diabetic hypertensive rats

Angiotensin-(1-7) [Ang-(1-7)] is a vasodilator peptide with cardiac and vascular protective properties. We examined the influence of Ang-(1-7), both endogenous and after chronic treatment with the peptide (576microg/(kgday)), on ischemia/reperfusion (I/R)-induced cardiac dysfunction in streptozotocin-treated spontaneously hypertensive rats (diabetic SHR). In isolated perfused hearts, recovery of left ventricular function from 40min of global ischemia was improved significantly in Ang-(1-7)- or captopril-treated diabetic SHR and worsened in animals treated with A779, an Ang-(1-7) receptor (AT((1-7))) antagonist. The beneficial effect of captopril on cardiac recovery was reduced when co-administered with A779. Cardiac NF-kappaB activity appears to be higher in diabetic SHR and treatment with Ang-(1-7) or captopril decreased NF-kappaB activity in diabetic SHR, an effect partially reversed by co-administration of A779. Real-time PCR-based gene array analysis of cardiac tissue revealed that Ang-(1-7) or captopril treatment may reduce expression of several genes of inflammation involved in the NF-kappaB signalling pathway. The data provide for the first time a role for endogenous Ang-(1-7) as well as confirmation that exogenous treatment with the peptide produces cardioprotection. Whether potential anti-inflammatory and transcriptional factor changes are directly linked to the cardioprotection produced by Ang-(1-7) in diabetic SHR remains to be determined.

New angiotensins

Accumulation of a large body of evidence during the past two decades testifies to the complexity of the renin–angiotensin system (RAS). The incorporation of novel enzymatic pathways, resulting peptides, and their corresponding receptors into the biochemical cascade of the RAS provides a better understanding of its role in the regulation of cardiovascular and renal function. Hence, in recent years, it became apparent that the balance between the two opposing effector peptides, angiotensin II and angiotensin-(1-7), may have a pivotal role in determining different cardiovascular pathophysiologies. Furthermore, our recent studies provide evidence for the functional relevance of a newly discovered rat peptide, containing two additional amino acid residues compared to angiotensin I, first defined as proangiotensin-12 [angiotensin-(1-12)]. This review focuses on angiotensin-(1-7) and its important contribution to cardiovascular function and growth, while introducing angiotensin-(1-12) as a potential novel angiotensin precursor.

Angiotensin receptor subtype mediated physiologies and behaviors: new discoveries and clinical targets

The renin-angiotensin system (RAS) mediates several classic physiologies including body water and electrolyte homeostasis, blood pressure, cyclicity of reproductive hormones and sexual behaviors, and the regulation of pituitary gland hormones. These functions appear to be mediated by the angiotensin II (AngII)/AT(1) receptor subtype system. More recently, the angiotensin IV (AngIV)/AT(4) receptor subtype system has been implicated in cognitive processing, cerebroprotection, local blood flow, stress, anxiety and depression. There is accumulating evidence to suggest an inhibitory influence by AngII acting at the AT(1) subtype, and a facilitory role by AngIV acting at the AT(4) subtype, on neuronal firing rate, long-term potentiation, associative and spatial learning, and memory. This review initially describes the biochemical pathways that permit synthesis and degradation of active angiotensin peptides and three receptor subtypes (AT(1), AT(2) and AT(4)) thus far characterized. There is vigorous debate concerning the identity of the most recently discovered receptor subtype, AT(4). Descriptions of classic and novel physiologies and behaviors controlled by the RAS are presented. This review concludes with a consideration of the emerging therapeutic applications suggested by these newly discovered functions of the RAS.

Angiotensin-(1-7) inhibits in vitro endothelial cell tube formation in human umbilical vein endothelial cells through the AT(1-7) receptor

Angiotensin-(1-7) is increased in the circulation during human pregnancy, but its functional role is unknown. Recent studies suggested that it opposes angiotensin II mediated vascular growth. Because angiogenesis is critical to normal embryonic development during human pregnancy, this study assessed the in vitro effects of angiotensin-(1-7) on human umbilical vein endothelial cell tube formation. The blocking effects of the angiotensin-(1-7) receptor antagonist, D-[Alanine7]-Ang-(1-7), and angiotensin II receptor AT1 and AT2 antagonists, losartan and PD123319, on tube formation were measured by counting tube branch points. Human umbilical vein endothelial cells were cultured in EGM-2 medium and treated with angiotensin-(1-7) (0.17 nM-17 microM) for 18 h. Angiotensin-(1-7) inhibited tube formation by 24% (P < 0.01) at all doses tested. Treatment with 1.7 microM angiotensin-(1-7) plus 17 microM D-[Alanine7]-Ang-(1-7) resulted in the reversal of angiotensin-(1-7) mediated inhibition of tube formation (P < 0.05). Losartan (17 microM) also reversed the angiotensin-(1-7) mediated inhibition of tube formation (P < 0.05). Tube formation was unaffected by PD123319. These results suggest that angiotensin-(1-7) has an anti-angiogenic effect on human umbilical vein endothelial cells through a unique AT(1-7) receptor that is sensitive to losartan, indicating that angiotensin-(1-7) may play an important role in the regulation of vascular growth in the placenta during pregnancy.

Angiotensin-(1-7): pharmacology and new perspectives in cardiovascular treatments

Many advances have been made in the cardiovascular field in the last several decades. Among them is the progress completed to date on the heptapeptide member of the renin-angiotensin system (RAS), angiotensin-(1-7) [Ang-(1-7)]. The peptide's beneficial actions against pathophysiological processes, such as cardiac arrhythmia, heart failure, hypertension, renal disease, preeclampsia, and even cancer are continuously being uncovered. This review encompasses the pharmacology of Ang-(1-7) and expounds upon the peptide's potential as a therapeutic agent against pathological processes both within and outside the cardiovascular continuum.

Angiotensin, bradykinin and the endothelium

Angiotensins and kinins are endogenous peptides with diverse biological actions; as such, they represent current and future targets of therapeutic intervention. The field of angiotensin biology has changed significantly over the last 50 years. Our original understanding of the crucial role of angiotensin II in the regulation of vascular tone and electrolyte homeostasis has been expanded to include the discovery of new angiotensins, their important role in cardiovascular inflammation and the development of clinically useful synthesis inhibitors and receptor antagonists. While less applied progress has been achieved in the kinin field, there are continuous discoveries in bradykinin physiology and in the complexity of kinin interactions with other proteins. The present review focuses on mechanisms and interactions of angiotensins and kinins that deal specifically with vascular endothelium.

Angiotensin-(1-7) potentiates responses to bradykinin but does not change responses to angiotensin I

Angiotensin-(1-7) (Ang-(1-7)), a bioactive peptide in the renin-angiotensin system, has counterregulatory actions to angiotensin II (Ang II). However, the mechanism by which Ang-(1-7) enhances vasodepressor responses to bradykinin (BK) is not well understood. In the present study, the effects of Ang-(1-7) on responses to BK, BK analogs, angiotensin I (Ang I), and Ang II were investigated in the anesthetized rat. The infusion of Ang-(1-7) (55 pmol/min i.v.) enhanced decreases in systemic arterial pressure in response to i.v. injections of BK and the BK analogs [Hyp3, Tyr(Me)8]-bradykinin (HT-BK) and [Phe8psi (CH2-NH) Arg9]-bradykinin (PA-BK) without altering pressor responses to Ang I or II, or depressor responses to acetylcholine and sodium nitroprusside. The angiotensin-converting enzyme (ACE) inhibitor enalaprilat enhanced responses to BK and the BK analog HT-BK without altering responses to PA-BK and inhibited responses to Ang I. The potentiating effects of Ang-(1-7) and enalaprilat on responses to BK were not attenuated by the Ang-(1-7) receptor antagonist A-779. Ang-(1-7)- and ACE inhibitor-potentiated responses to BK were attenuated by the BK B2 receptor antagonist Hoe 140. The cyclooxygenase inhibitor sodium meclofenamate had no significant effect on responses to BK or Ang-(1-7)-potentiated BK responses. These results suggest that Ang-(1-7) potentiates responses to BK by a selective B2 receptor mechanism that is independent of an effect on Ang-(1-7) receptors, ACE, or cyclooxygenase product formation. These data suggest that ACE inhibitor-potentiated responses to BK are not mediated by an A-779-sensitive mechanism and are consistent with the hypothesis that enalaprilat-induced BK potentiation is due to decreased BK inactivation.

Evidence for a new angiotensin-(1-7) receptor subtype in the aorta of Sprague-Dawley rats

We have recently described, in the mouse aorta, the vasodilator effect of angiotensin-(1-7) (Ang-(1-7)) was mediated by activation of the Mas Ang-(1-7) receptor and that A-779 and D-Pro7-Ang-(1-7) act as Mas receptor antagonists. In this work we show pharmacological evidence for the existence of a different Ang-(1-7) receptor subtype mediating the vasodilator effect of Ang-(1-7) in the aorta from Sprague-Dawley (SD) rats. Ang-(1-7) induced an endothelium-dependent vasodilator effect in aortic rings from SD rats which was inhibited by removal of the endothelium and by L-NAME (100 microM) but not by indomethacin (10 microM). The Ang-(1-7) receptor antagonist D-Pro7-Ang-(1-7) (0.1 microM) abolished the vasodilator effect of the peptide. However, the other specific Ang-(1-7) receptor antagonist, A-779 in concentrations up to 10 microM, did not affect vasodilation induced by Ang-(1-7). The Ang II AT1 and AT2 receptors antagonists CV11974 (0.01 microM) and PD123319 (1 microM), respectively, the bradykinin B2 receptor antagonist HOE 140 (1 microM) and the inhibitor of ACE captopril (10 microM) did not change the effect of Ang-(1-7). Our results show that in the aorta of SD rats, the vasodilator effect of Ang-(1-7) is dependent on endothelium-derived nitric oxide. This effect is mediated by the activation of Ang-(1-7) receptors sensitive to D-Pro7-Ang-(1-7), but not to A-779, which suggests the existence of a different Ang-(1-7) receptor subtype.

Effects of angiotensin 1-7 on the actions of angiotensin II in the renal and mesenteric vasculature of hypertensive and streptozotocin-induced diabetic rats

Angiotensin 1-7, a heptapeptide derived from metabolism of either angiotensin I or angiotensin II, is a biologically active peptide of the renin-angiotensin system. The present study investigated the effect of angiotensin 1-7 on the vasopressor action of angiotensin II in the renal and mesenteric vasculature of Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHR) and streptozotocin-induced diabetic rats. Angiotensin II-induced dose-dependent vasoconstrictions in the renal vasculature. The pressor response was enhanced in the SHR and reduced in the streptozotocin-diabetic rat compared to WKY rats. Angiotensin 1-7 attenuated the angiotensin II pressor responses in the renal vasculature of WKY and SHR rats. However, the ability to reduce angiotensin II response was diminished in diabetic-induced rat kidneys. The effect of angiotensin 1-7 was not inhibited by 1-[(4-(Dimethylamino)-3-methylphenyl] methyl]-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid ditrifluoroacetate (PD123319), an angiotensin AT(2) receptor antagonist. (D-ALA(7))-Angiotensin I/II (1-7) (D-ALA) (an angiotensin 1-7 receptor antagonist), indomethacin (a cyclo-oxygenase inhibitor), and N(omega)-Nitro-L-Arginine Methyl Ester (L-NAME)(a nitric oxide synthetase inhibitor) abolished the attenuation by angiotensin 1-7 in both WKY rats and SHR, indicating that its action is mediated by angiotensin 1-7 receptor that is either coupled to the release of prostaglandins and/or nitric oxide. The vasopressor responses to angiotensin II in mesenteric vasculature bed was also dose-dependent but smaller in magnitude compared to the renal vasculature. The responses to angiotensin II were relatively smaller in SHR but no significant difference was observed between WKY and streptozotocin-induced diabetic rats. Angiotensin 1-7 attenuated the angiotensin II pressor responses in WKY, SHR and diabetic-induced mesenteric bed. The attenuation was observed at the lower concentrations of angiotensin II in WKY and diabetic-induced rats but at higher concentrations in SHR. Similar observation as in the renal vasculature was seen with PD123319, D-ALA, and L-NAME. Indomethacin reversed the attenuation by angiotensin 1-7 only in the SHR mesenteric vascular bed. The present findings support the regulatory role of angiotensin 1-7 in the renal and mesenteric vasculature, which is differentially altered in hypertension and diabetes.

Regulation of Cardiovascular Control Mechanisms by Angiotensin-(1–7) and Angiotensin-Converting Enzyme 2

Among the molecular forms of angiotensin peptides generated by the action of renin on angiotensinogen (Aogen), both angiotensin II (Ang II) and the amino terminal heptapeptide angiotensin-(1–7) [Ang-(1–7)] are critically involved in the long-term control of tissue perfusion, cell-cell communication, development, and growth. Whereas an impressive body of literature continues to uncover pleiotropic effects of Ang II in the regulation of cell function, research on Ang-(1–7) has a shorter history as it was only 16 yr ago that a biological function for this heptapeptide was first demonstrated in the isolated rat neuro-hypophysial explant preparation (1). On the contrary, the synthesis of angiotonin/ hypertensin (now Ang II) was first obtained in 1957 (2), three decades ahead of the discovery of Ang-(1–7) biological properties.

Angiotensin-(1-7) inhibits angiotensin II-stimulated phosphorylation of MAP kinases in proximal tubular cells

Angiotensin-converting enzyme 2 (ACE2) is a homolog of ACE, which is not blocked by ACE inhibitors. High amounts of ACE2 are present in the proximal tubule, and ACE2 catalyzes generation of angiotensin 1-7 (Ang-(1-7)) by this segment. Ang-(1-7) binds to a receptor distinct from the AT1 or AT2 Ang II receptor, identified as the mas receptor. We studied the effects of Ang-(1-7) on Ang II-mediated cell signaling pathways in proximal tubule. In primary cultures of rat proximal tubular cells, activation of mitogen-activated protein kinases (MAPK) was detected by immunoblotting, in the presence or absence of agonists/antagonists. Transforming growth factor-beta1 (TGF-beta1) was measured by enzyme-linked immunosorbent assay. Ang II (5 min, 10(-7) M) stimulated phosphorylation of the three MAPK (p38, extracellular signal-related kinase (ERK 1/2), and c-Jun N-terminal kinase (JNK)). While incubation of proximal tubular cells with Ang-(1-7) alone did not significantly affect MAPK phosphorylation, Ang-(1-7) (10(-7) M) completely inhibited Ang II-stimulated phosphorylation of p38, ERK 1/2, and JNK. This inhibitory effect was reversed by the Ang-(1-7) receptor antagonist, D-Ala7-Ang-(1-7). Ang II significantly increased production of TGF-beta1 in proximal tubular cells, an effect that was partly inhibited by Ang-(1-7). Ang-(1-7) had no significant effect on cyclic 3',5'-adenosine monophosphate production in these cells. In summary, Ang-(1-7) inhibits Ang II-stimulated MAPK phosphorylation in proximal tubular cells. Generation of Ang-(1-7) by proximal tubular ACE2 could thereby serve a protective role by counteracting the effects of locally generated Ang II.

The endothelium-dependent vasodilator effect of the nonpeptide Ang(1-7) mimic AVE 0991 is abolished in the aorta of mas-knockout mice

Recently, we demonstrated that the endothelium-dependent vasodilator effect of angiotensin(1-7) in the mouse aorta is abolished by genetic deletion of the G protein-coupled receptor encoded by the Mas protooncogene. To circumvent the limitations posed by the possible metabolism of Ang(1-7) in this vessel, in this work we studied the mechanism underlying the vasorelaxant effect of AVE 0991, a nonpeptide mimic of the effects of Ang(1-7), using wild-type and Mas-deficient mice. Ang(1-7) and AVE 0991 induced an equipotent concentration-dependent vasodilator effect in aortic rings from wild-type mice that was dependent on the presence of endothelium. The vasodilator effect of Ang(1-7) and AVE 0991 was completely blocked by 2 specific Ang(1-7) receptor antagonists, A-779 and D-Pro-Ang(1-7), and by inhibition of NO synthase with L-NAME. Moreover, in aortic rings from Mas-deficient mice, the vasodilator effect of both Ang(1-7) and AVE 0991 was abolished. In contrast, the vasodilator effect of acetylcholine and substance P were preserved in Mas-null mice. In addition, the vasoconstriction effect induced by Ang II was slightly increased, and the vasodilation induced by the AT2 agonist CGP 42112A was not altered in Mas-deficient mice. Our results show that Ang(1-7) and AVE 0991 produced an NO-dependent vasodilator effect in the mouse aorta that is mediated by the G protein-coupled receptor Mas.

In vivo characterization of the angiotensin-(1-7)-induced dopamine and gamma-aminobutyric acid release in the striatum of the rat

The effect of angiotensin (Ang)-1-7 on dopamine, gamma-aminobutyric acid (GABA) and glutamate release in the striatum of the rat was examined using in vivo microdialysis. Ang-(1-7) was administered locally in the striatum through the microdialysis probe. At a concentration of 100 microm, Ang-(1-7) caused a significant increase in extracellular dopamine and GABA but had no effect on glutamate release. The Ang-(1-7)-induced dopamine release was blocked by EC33, an inhibitor of aminopeptidase A, an enzyme which converts Ang-(1-7) into Ang-(3-7), suggesting that this effect occurs after metabolism into Ang-(3-7). Indeed, administration of Ang-(3-7) (10-100 microm) into the striatum caused a more potent increase in the striatal dopamine release than Ang-(1-7). Because Ang-(3-7) is an inhibitor of insulin-regulated aminopeptidase (IRAP) and because Ang IV, another IRAP inhibitor, also causes a concentration-dependent increase in dopamine in the rat striatum, IRAP may be involved in this effect. In contrast, EC33 had no effect on the Ang-(1-7)-induced GABA increase but the GABA release was blocked by the putative AT(1-7) receptor antagonist A779 (0.1 microm) and by the nitric oxide synthase inhibitor L-NAME (1 mm). These drugs could not block the effect of Ang-(1-7) on the striatal dopamine release suggesting that only the observed effects on GABA release are mediated by the AT(1-7) receptor and/or are associated with a release of nitric oxide.

Pharmacological concentration of angiotensin-(1-7) activates NADPH oxidase after ischemia-reperfusion in rat heart through AT1 receptor stimulation

The cardiovascular role of angiotensin-(1-7), especially in the functional and metabolic alterations associated with ischemia-reperfusion (IR), is still not clearly defined. Our objective was to evaluate the cardiac effects of angiotensin-(1-7), the receptors involved, and their relationships with NADPH oxidase activation under non-ischemic conditions and, during an ischemia-reperfusion sequence. Isolated perfused rat hearts underwent 45 min of non-ischemic perfusion, or 30 min of global ischemia followed by 30 min of reperfusion. Angiotensin-(1-7) and/or AT1 receptor blocker losartan or angiotensin-(1-7) receptor antagonist (D-Ala7)-angiotensin-(1-7) were perfused. Our results showed that angiotensin-(1-7) was without effect at low concentrations (10(-10) to 10(-7) M). At a pharmacological concentration, 0.5 microM angiotensin-(1-7) induced vasoconstriction, which was antagonised by losartan. After ischemia, we noted a partial recovery of functional parameters, which was not modified by any of the treatments. The expression of AT1 receptor mRNA was increased by ischemia-reperfusion, except in (D-Ala7)-angiotensin-(1-7) treated hearts. Angiotensin-(1-7) further increased the AT1 expression. NADPH oxidase activity was enhanced in 0.5 microM angiotensin-(1-7)-treated hearts subjected to ischemia-reperfusion, this effect was totally reversed by losartan. This is the first time that it has been shown that, in the heart, angiotensin-(1-7) at pharmacological concentration activates NADPH oxidase, an enzyme thought to be involved in several angiotensin II effects.

Angiotensin-(1-7) binds to specific receptors on cardiac fibroblasts to initiate antifibrotic and antitrophic effects

ANG-(1-7) improves the function of the remodeling heart. Although this peptide is generated directly within the myocardium, the effects of ANG-(1-7) on cardiac fibroblasts that play a critical role in cardiac remodeling are largely unknown. We tested the hypothesis that specific binding of ANG-(1-7) to cardiac fibroblasts regulates cellular functions that are involved in cardiac remodeling. 125I-labeled ANG-(1-7) binding assays identified specific binding sites of ANG-(1-7) on adult rat cardiac fibroblasts (ARCFs) with an affinity of 11.3 nM and a density of 131 fmol/mg protein. At nanomolar concentrations, ANG-(1-7) interacted with specific sites that were distinct from ANG II type 1 and type 2 receptors without increasing cytosolic Ca2+ concentration. At these concentrations, ANG-(1-7) had inhibitory effects on collagen synthesis as assessed by [3H]proline incorporation and decreased mRNA expression of growth factors in ARCFs. These effects of ANG-(1-7) contrasted with effects of ANG II. Pretreatment of ARCFs with ANG-(1-7) inhibited ANG II-induced increases in collagen synthesis and in mRNA expression of growth factors, including endothelin-1 and leukemia inhibitory factor. ANG-(1-7) pretreatment also inhibited the stimulatory effects of conditioned medium from ANG II-treated ARCFs on [3H]leucine incorporation and atrial natriuretic factor mRNA expression, markers of hypertrophy, in cardiomyocytes. Thus ANG-(1-7) interacted with specific receptors on ARCFs to exert potential antifibrotic and antitrophic effects that could reverse ANG II effects. These results suggest that ANG-(1-7) may play an important role in the heart in regulating cardiac remodeling.

Histological evaluation of the effects of angiotensin peptides on wound repair in diabetic mice

Recent studies have shown that angiotensin peptides accelerate dermal repair. Histological observation of samples taken at the termination of studies showed that the wounds treated with peptides were mature and organized by day 25 after full thickness excision in diabetic mice. However, the mechanisms by which this acceleration occurs has not been determined. In the experiments described here, the effect of angiotensin peptides (AII, A(1-7) and NorLeu (3)-A(1-7) on the quality of the healing wound was evaluated histologically. Administration of the peptides accelerated collagen deposition, re-epithelialization and new blood vessels formation. By day 4, the percentage of the wound with collagen increased two- to six-fold depending upon the peptide. The increase by angiotensin peptides continued throughout the experimental period. On days 4 and 7 9 (only) after injury, exposure to angiotensin peptides increased the number of blood vessels at wound site two-to three-fold. Finally, the percentage of the wound site covered with new epithelium increased after administration of angiotensin peptides. Re-epithelialization was observed as early as day 4 in wounds treated ith angiotensin peptides. The increase was greater at later time points (up to 8-fold ar day 14 with NorLeu(3)-A(1-7) had an increase in neutrophils and macrophages on day 4 after wounding. Overall, administration of these peptides resulted in a healing site that was more mature, including reorganization of the collagen into a basket-weave appearance. Further, these studies confirm the superiority of NorLeu(3)-A(1-7) to AII and A(1-7) in wound healing evaluated at a microscopic level.

Neutral endopeptidase expression in mesangial cells

In the kidney, neutral endopeptidase (NEP) is implicated in the metabolism of several peptides involved in blood pressure and sodium homeostasis control, such as the atrial natriuretic peptide, bradykinin and angiotensin I. Due to its physiological importance in the modulation of pressor responses, the presence of NEP in mouse mesangial cells has been investigated, since these cells control glomerular function and are able to synthesise components of the renin-angiotensin system. A NEP-like activity (NEP-like) that cleaves the fluorogenic substrates Abz-BKQ-EDDnp and Abz-DRRL-EDDnp was purified from mesangial cell lysate by ion-exchange, followed by gel filtration chromatography. The enzyme was able to hydrolyse bradykinin at the G4-F5 peptide bond and was inhibited by thiorphan. A pH study established that enzyme activity was maximal at pH 7.5 and the determined K(m) was 4.86 M using Abz-DRRL-EDDnp as substrate. NEP-like was recognised by monoclonal anti-NEP and had a molecular mass of 95 kDa. The purified enzyme was sequenced and showed similarity with human, rat, mouse and rabbit NEPs. We isolated, for the first time, NEP-like from mesangial cells. This enzyme could have an important role in the renal physiology by its action upon different peptides that are able to alter renal haemodynamics.

Novel roles of neuropeptide processing enzymes: EC3.4.24.15 in the neurome

Neuropeptide processing metalloenzymes, such as angiotensin converting enzyme, neprilysin, endothelin converting enzyme, neurolysin, and EC3.4.24.15 (EP24.15), are central to the formation and degradation of bioactive peptides. We present EP24.15 as a paradigm for novel functions ascribed to these enzymes in the neurome. Although the neurome typically encompasses proteomes of the brain and central nervous system, exciting new roles of these neuropeptidases have been demonstrated in other organ systems. We discuss the involvement of EP24.15 with clinical sequelae involving the use of gonadotropin-releasing hormone (GnRH; LHRH) analogs that act as enzyme inhibitors, in vascular physiology (blood pressure regulation), and in the hematologic system (immune surveillance). Hemodynamic forces, such as cyclic strain and shear stress, on vascular cells, induce an increase in EP24.15 transcription, suggesting that neuropeptidase-mediated hydrolysis of pressor/depressor peptides is likely regulated by changes in hemodynamic force and blood pressure. Lastly, EP24.15 regulates surface expression of major histocompatibility complex Class I proteins in vivo, suggesting that EP24.15 may play an important role in maintenance of immune privilege in sites of increased endogenous expression. In these extraneural systems, regulation of both neuropeptide and other peptide substrates by neuropeptidases indicates that the influence of these enzymes may be more global than was anticipated previously, and suggests that their attributed role as neuropeptidases underestimates their physiologic actions in the neural system.

Pregnancy enhances the angiotensin (Ang)-(1-7) vasodilator response in mesenteric arteries and increases the renal concentration and urinary excretion of Ang-(1-7)

The vasoactive effect of angiotensin (Ang)-(1-7) in mesenteric resistance arteries together with its plasma and kidney concentration and urinary excretion was assessed in pregnant and virgin rats. Mesenteric arteries (230-290 microm) were mounted in a pressurized myograph system and Ang-(1-7) concentration-dependent response curves (10(-10)-10(-5) M) were determined in arteries preconstricted with endothelin-1 (10(-7) M). The Ang-(1-7) response was investigated in vessels with and without pretreatment with the Ang-(1-7) antagonist [D-[Ala(7)]-Ang-(1-7)] (10(-7) M). Ang-(1-7) caused a significantly enhanced, concentration-dependent dilation of mesenteric vessels (EC(50) = 2.7 nM) from pregnant compared with virgin female rats. D-[Ala(7)]-Ang-(1-7) eliminated the vasodilator effect of Ang-(1-7). There was no significant change in plasma concentration of Ang-(1-7) in pregnant animals. On the other hand, 24 h urinary excretion and kidney concentration of Ang-(1-7) were significantly higher in pregnant animals. The increased mesenteric dilation to Ang-(1-7) with enhanced kidney concentration and 24 h urinary excretion rate of Ang-(1-7) suggests an important role for this peptide in cardiovascular regulation during pregnancy.

Effects of angiotensin-(1-7) and other bioactive components of the renin-angiotensin system on vascular resistance and noradrenaline release in rat kidney

OBJECTIVE

Angiotensin (Ang) is broken down enzymatically to several different metabolites which, in addition to Ang II, may have important biological effects in the kidney. This study investigates the role of Ang metabolites on vascular resistance and noradrenaline release in the rat kidney.

METHODS AND RESULTS

In rat isolated kidney Ang I, Ang II, Ang III, Ang IV and des-Asp-Ang I induced pressor responses and enhanced noradrenaline release to renal nerve stimulation (RNS) in an concentration-dependent manner, with the following rank order of potency (EC(50)): Ang II >or= Ang III > Ang I = des-Asp-Ang I > Ang IV. All effects were blocked by the AT(1)-receptor antagonist EXP 3174 (0.1 micromol/l) but not by the AT(2)-receptor antagonist PD 123319 (1 micromol/l). Angiotensin-converting enzyme (ACE) inhibition by captopril (10 micromol/l) abolished the effect of Ang I and des-Asp-Ang I but had no influence on the effect of the other metabolites. Ang-(1-7) blocked the effects of Ang I and Ang II, being 10 times more potent against Ang I than Ang II. The selective Ang-(1-7) receptor blocker d-Ala7-Ang-(1-7) (10 micromol/l) did not influence the inhibitory effects of Ang-(1-7). Ang-(1-7) (10 micromol/l) by itself had no influence on vascular resistance and RNS-induced noradrenaline release.

CONCLUSION

Ang I, Ang II, Ang III, Ang IV and des-Asp-Ang I regulate renal vascular resistance and noradrenaline release by activation of AT(1) receptors. In the case of Ang I and des-Asp-Ang I this depends on conversion by ACE. Ang-(1-7) may act as a potent endogenous inhibitor/antagonist of ACE and the AT(1)-receptors, respectively.

Bradykinin, angiotensin-(1-7), and ACE inhibitors: how do they interact?

The beneficial effect of ACE inhibitors in hypertension and heart failure may relate, at least in part, to their capacity to interfere with bradykinin metabolism. In addition, recent studies have provided evidence for bradykinin-potentiating effects of ACE inhibitors that are independent of bradykinin hydrolysis, i.e. ACE-bradykinin type 2 (B(2)) receptor 'cross-talk', resulting in B(2) receptor upregulation and/or more efficient activation of signal transduction pathways, as well as direct activation of bradykinin type 1 receptors by ACE inhibitors. This review critically reviews the current evidence for hydrolysis-independent bradykinin potentiation by ACE inhibitors, evaluating not only the many studies that have been performed with ACE-resistant bradykinin analogues, but also paying attention to angiotensin-(1-7), a metabolite of both angiotensin I and II, that could act as an endogenous ACE inhibitor. The levels of angiotensin-(1-7) are increased during ACE inhibition, and most studies suggest that its hypotensive effects are mediated in a bradykinin-dependent manner.

Biphasic effects of angiotensin (1-7) and its interactions with angiotensin II in rat aorta

Using isolated rat aortic rings perfused with Krebs-Henseleit saline, the vascular effects of angiotensin (1-7) (Ang [1-7]) and its interactions with angiotensin II (Ang II) were investigated. Ang (1-7) induced endothelium-dependent relaxation and vasodilating effects in preparations precontracted with phenylephrine. Without preconstriction, Ang (1-7) at high doses (10(-6) 10(-5) M) produced either a significant inhibition of Ang II-induced vasoconstriction or a non-tachyphylactic vasopressor response. While losartan inhibited the vasoconstriction induced by Ang (1-7), A779 blocked only its relaxation. Unlike losartan, blockade of AT(2)-receptors with PD 123319 had no effect. Taking into account the biphasic effects of angiotensin (1-7), we propose that it is one of the active components of the renin-angiotensin system, which is involved as a modulator both in the counter-regulatory actions of Ang II and in the self-regulation of its own vasodilating effects.

Systemic and regional hemodynamic effects of angiotensin-(1-7) in rats

The systemic and regional hemodynamics effects of ANG-(1-7) were examined in urethane-anesthetized rats. The blood flow distribution (kidneys, skin, mesentery, lungs, spleen, brain, muscle, and adrenals), cardiac output, and total peripheral resistance were investigated by using fluorescent microspheres. Blood pressure and heart rate were recorded from the brachial artery. ANG-(1-7) infusion (110 fmol x min(-1) x 10 min(-1) iv) significantly increased blood flow to the kidney (5.10 +/- 1.07 to 8.30 +/- 0.97 ml x min(-1) x g(-1)), mesentery (0.73 +/- 0.16 to 1.17 +/- 0.49 ml x min(-1) x g(-1)), brain (1.32 +/- 0.44 to 2.18 +/- 0.85 ml x min(-1) x g(-1)), and skin (0.07 +/- 0.02 to 0.18 +/- 0.07 ml x min(-1) x g(-1)) and the vascular conductance in these organs. ANG-(1-7) also produced a significant increase in cardiac index (30%) and a decrease in total peripheral resistance (2.90 +/- 0.55 to 2.15 +/- 0.28 mmHg x ml(-1) x min x 100 g). Blood flow to the spleen, muscle, lungs, and adrenals, as well as the blood pressure and heart rate, were not altered by the ANG-(1-7) infusion. The selective ANG-(1-7) antagonist A-779 reduced the blood flow in renal, cerebral, mesenteric, and cutaneous beds and blocked the ANG-(1-7)-induced vasodilatation in the kidney, mesentery, and skin, suggesting a significant role of endogenous ANG-(1-7) in these territories. The effects of ANG-(1-7) on the cerebral blood flow, cardiac index, systolic volume, and total peripheral resistance were partially attenuated by A-779. A high dose of ANG-(1-7) (11 pmol x min(-1) x 10 min(-1)) caused an opposite effect of that produced by the low dose. Our results show for the first time that ANG-(1-7) has a previously unsuspected potent effect in the blood flow distribution and systemic hemodynamics.

Characterization of angiotensin-(1-7) receptor subtype in mesenteric arteries

Mesenteric arteries from male Sprague-Dawley rats were mounted in a pressurized myograph system. Ang-(1-7) concentration-dependent responses were determined in arteries preconstricted with endothelin-1 (10(-7)M). The receptor(s) mediating the Ang-(1-7) evoked dilation were investigated by pretreating the mesenteric arteries with specific antagonists of Ang-(1-7), AT(1) or AT(2) receptors. The effects of Ang-(3-8) and Ang-(3-7) were also determined. Ang-(1-7) caused a concentration-dependent dilation (EC(50): 0.95 nM) that was blocked by the selective Ang-(1-7) receptor antagonist D-[Ala(7)]-Ang-(1-7). Administration of a specific antagonist to the AT(2) receptor (PD123319) had no effect. On the other hand, losartan and CV-11974 attenuated the Ang-(1-7) effect. These results demonstrate that Ang-(1-7) elicits potent dilation of mesenteric resistance vessels mediated by a D-[Ala(7)]-Ang-(1-7) sensitive site that is also sensitive to losartan and CV-11974.

Angiotensin-(1-7) reduces renal angiotensin II receptors through a cyclooxygenase-dependent mechanism

In the kidney, angiotensin-(1-7) [Ang-(1-7)] exhibits diuretic and natriuretic properties associated with an increase in prostaglandin production. The prohypertensive effects of Ang II are attenuated in rats infused with Ang-(1-7), consistent with recent work showing that Ang-(1-7) downregulates AT1 receptors in Chinese hamster ovary-AT1A or vascular smooth muscle cells. To determine whether exposure to Ang-(1-7) reduces AT1 receptors in the kidney through an increase in prostaglandin production, kidney slices from Sprague-Dawley rats were incubated with 10 n -1 microM Ang-(1-7) in the presence or absence of 5 microM meclofenamate, a cyclooxygenase inhibitor. Following these treatments, the kidney slices were retrieved, frozen, and sectioned for determination of [125I]-Ang II binding using in vitro receptor autoradiography. Greater than 90% of the specific binding was competed for by losartan, indicating that the majority of binding was to the AT1 receptor. Incubation of kidney slices with 1 microM Ang-(1-7) caused a 20% reduction in [125I]-Ang II binding (n = 8) in the cortical tubulointerstitium, which was prevented when Ang-(1-7)-treated slices were incubated in the presence of 5 microM meclofenamate (1 +/- 2% increase, n = 8; p < 0.05). Incubation with 5 microM meclofenamate alone had no effect on [125I]-Ang II binding (-3 +/- 3%). The decrease in [125I]-Ang II binding with Ang-(1-7) was also blocked by the Ang-(1-7) antagonist [d-Ala7]-Ang-(1-7). Treatment with 1 microM [d-Ala7]-Ang-(1-7) alone had no effect on [125I]-Ang II binding (-3 +/- 6% of control). Pretreatment with 1 microM Ang II caused a similar reduction in [125I]-Ang II binding in the cortical tubulointerstitium. Neither Ang-(1-7) nor Ang II had any effect on [125I]-Ang II binding in the glomeruli and the area of the vasa recta of the kidney. These original findings suggest that prior exposure to Ang-(1-7) or Ang II causes a modest decrease in the number of AT1 receptors in the cortical tubulointerstitial area of the kidney. The reduction in Ang II binding by Ang-(1-7) was blocked by meclofenamate and [d-Ala7]-Ang-(1-7), suggesting that cyclooxygenase products released through activation of a novel receptor participate in this effect.

Cellular targets for angiotensin II fragments: pharmacological and molecular evidence

Although angiotensin II has long been considered to represent the end product of the renin-angiotensin system (RAS), there is accumulating evidence that it encompasses additional effector peptides with diverse functions. In this respect, angiotensin IV (Ang IV) formed by deletion of the two N terminal amino acids, has sparked great interest because of its wide range of physiological effects. Among those, its facilitatory role in memory acquisition and retrieval is of special therapeutic relevance. High affinity binding sites for this peptide have been denoted as AT(4)- receptors and, very recently, they have been proposed to correspond to the membrane-associated OTase/ IRAP aminopeptidase. This offers new opportunities for examining physiological roles of Ang IV in the fields of cognition, cardiovascular and renal metabolism and pathophysiological conditions like diabetes and hypertension. Still new recognition sites may be unveiled for this and other angiotensin fragments. Recognition sites for Ang-(1-7) (deletion of the C terminal amino acid) are still elusive and some of the actions of angiotensin III (deletion of the N terminal amino acid) in the CNS are hard to explain on the basis of their interaction with AT(1)-receptors only. A more thorough cross-talk between in vitro investigations on native and transfected cell lines and in vivo investigations on healthy, diseased and transgenic animals may prove to be essential to further unravel the molecular basis of the physiological actions of these small endogenous angiotensin fragments.

Vasodilator effect of angiotensin-(1-7) in mature and sponge-induced neovasculature

Angiotensin-(1-7) (Ang-(1-7)), a peptide constituent of the renin-angiotensin system, has been shown to act as a vasodilator mediator in pre-existing (skin) and newly formed vasculatures (14-day-old sponge implants). Blood flow was determined by the outflow rate of sodium fluorescein applied intradermally or intraimplant and the results were expressed in t(1/2) values (time taken for the fluorescence to reach 50% of the peak in the systemic circulation). We showed that the t(1/2) value was significantly lower (4.1+/-0.46) in the implants compared with the cutaneous vasculature (5.7+/-0.5). Ang-(1-7) 20 ng was able to decrease t(1/2) values in both vasculatures. The specific receptor antagonist, D-Ala7-Ang-(1-7) (A-779), prevented Ang-(1-7)-induced vasodilation and altered the basal vascular tone of the implants. The vasodilator effect was also abolished by nitric oxide (NO) synthase inhibitors in both vasculatures and by indomethacin in the implant. Selective AT(1) and AT(2) receptor antagonists did not alter the vasodilation induced by the peptide. These results establish the vasodilator effect of Ang-(1-7) in the cutaneous and implant vasculature and that the peptide is produced endogenously by the fibrovascular tissue, and suggest that this peptide contributes for the vasodilation found in newly formed vascular beds (wound healing, chronic inflammatory processes and tumors).