Opposing actions of angiotensins on angiogenesis

The renin-angiotensin-aldosterone system (RAAS) signaling pathways and cancer: foes versus allies

The renin-angiotensin-aldosterone system (RAAS), is an old system with new fundamental roles in cancer biology which influences cell growth, migration, death, and metastasis. RAAS signaling enhances cell proliferation in malignancy directly and indirectly by affecting tumor cells and modulating angiogenesis. Cancer development may be influenced by the balance between the ACE/Ang II/AT1R and the ACE2/Ang 1-7/Mas receptor pathways. The interactions between Ang II/AT1R and Ang I/AT2R as well as Ang1-7/Mas and alamandine/MrgD receptors in the RAAS pathway can significantly impact the development of cancer. Ang I/AT2R, Ang1-7/Mas, and alamandine/MrgD interactions can have anticancer effects while Ang II/AT1R interactions can be involved in the development of cancer. Evidence suggests that inhibitors of the RAAS, which are conventionally used to treat cardiovascular diseases, may be beneficial in cancer therapies.Herein, we aim to provide a thorough description of the elements of RAAS and their molecular play in cancer. Alongside this, the role of RAAS components in sex-dependent cancers as well as GI cancers will be discussed with the hope of enlightening new venues for adjuvant cancer treatment.

Is RAS the Link Between COVID-19 and Increased Stress in Head and Neck Cancer Patients?

The COVID-19 pandemic emerged as a largely unexplained outbreak of pneumonia cases, in Wuhan City, China and rapidly spread across the world. By 11th March 2020, WHO declared it as a global pandemic. The resulting restrictions, to contain its spread, demanded a momentous change in the lifestyle of the general population as well as cancer patients. This augmented negative effects on the mental health of patients with head and neck cancer (HNC), who already battle with the stress of cancer diagnosis and treatment. The causative agent of COVID-19, SARS-CoV2, gains entry through the Angiotensin converting enzyme 2 (ACE2) receptor, which is a component of the Renin Angiotensin System (RAS). RAS has been shown to influence cancer and stress such that it can have progressive and suppressive effects on both. This review provides an overview of SARS-CoV2, looks at how the RAS provides a mechanistic link between stress, cancer and COVID-19 and the probable activation of the RAS axis that increase stress (anxiogenic) and tumor progression (tumorigenic), when ACE2 is hijacked by SARS-CoV2. The mental health crises brought about by this pandemic have been highlighted in many studies. The emerging links between cancer and stress make it more important than ever before to assess the stress burden of cancer patients and expand the strategies for its management.

Renin-angiotensin system and cancer: epidemiology, cell signaling, genetics and epigenetics

Day by day, the health and economical burden of cancer increases globally. Indeed it can be considered that there is ''cancer pandemic''. Blocking the renin-angiotensin system (RAS) by angiotensin-converting enzyme (ACE) inhibitors (ACEI) or angiotensin-receptor blockers (ARB) are widely used measures to treat hypertension and heart failure. It has been recently suggested the activation and blocking of RAS has been associated with various types of cancer in epidemiological and experimental studies. Various studies have shown that RAS blockage is protective in some cancers. However, although fewer, contradictory data also showed that RAS blockage is either not related or adversely related to cancer. Although the reasons for these findings are not exactly known, different types of receptors and effectors in RAS may account for these findings. In the current review, we summarize the different RAS receptors and cancer development with regard to epidemiology, and pathogenesis including cell signaling pathways, apoptosis, genetic and epigenetic factors.

Role of Renin-Angiotensin-System in Human Breast Cancer Cells: Is There a Difference in Regulation of Angiogenesis between Hormone-Receptor Positive and Negative Breast Cancer Cells?

Objective This study examined the role of the RAS in human breast cancer cells to question if there are differences between HR-positive and HR-negative cells with regard to regulation of VEGF. Methods Expression of different RAS components in hormone receptor (HR)-positive and HR-negative breast cancer cells was investigated using RT-PCR. Different stimulation protocols with different RAS inhibitors were used to investigate the effect on VEGF expression. Angiotensin II-dependent expression of VEGF was quantified by real time PCR. In addition, the effect of intrinsic RAS was studied performing siRNA knockdown of angiotensinogen (AGT). Statistical analysis were calculated using IBM SPSS Statistics Version 21. Results Expression of AT ₁ R, AT ₂ R, AGT and ACE was shown in HR-positive and HR-negative breast cancer cell lines. Extrinsic stimulation with angiotensin II increased VEGF significantly. After treatment with captopril or AT ₁ R-inhibitor candesartan, VEGF-expression decreased significantly in HR-positive and HR-negative cell lines. However, inhibition of AT ₂ R using PD 123,319 did not show any significant changes of VEGF. After prevention of intrinsic angiotensin II, extrinsic angiotensin II as well as the combination with inhibitors of the receptors caused a significant reduction of VEGF. Surprisingly, the overall effect of the RAS after knockdown of AGT revealed a significant increase of VEGF in HR-positive cells at any time while a significant decrease was observed in HR-negative cells after 144 hours incubation. Conclusion The RAS-dependent regulation of VEGF between HR-positive and HR-negative breast cancer cells seems do be different. These findings provide evidence for a possible future therapeutic strategy.

Retinal angiotensin II and angiotensin-(1-7) response to hyperglycemia and an intervention with captopril

Hypothesis:

Hyperglycemia decreases angiotensin-(1-7), the endogenous counter-regulator of angiotensin II in the retina.

Materials and methods:

The distribution and levels of retinal angiotensin II (Ang II) and angiotensin-(1-7) (Ang-(1-7)) were evaluated by confocal imaging and quantitative immunohistochemistry during the development of streptozotocin-induced diabetes in rats.

Results:

In the nondiabetic eye, Ang II was localized to the endfeet of Müller cells, extending into the cellular processes of the inner plexiform layer and inner nuclear layer; Ang-(1-7) showed a wider distribution, extending from the foot plates of the Müller cells to the photoreceptor layer. Eyes from diabetic animals showed a higher intensity and extent of Ang II staining compared with nondiabetic eyes, but lower intensity with a reduced distribution of Ang-(1-7) immunoreactivity. Treatment of the diabetic animals with the angiotensin-converting enzyme inhibitor (ACEI) captopril showed a reduced intensity of Ang II staining, whereas increased intensity and distribution were evident with Ang-(1-7) staining.

Conclusions:

These studies reveal that pharmacological inhibition with ACEIs may provide a specific intervention for the management of the diabetes-induced decline in retinal function, reversing the profile of the endogenous angiotensin peptides closer to the normal condition.

Measurement of Angiotensin Peptides: HPLC-RIA

The renin-angiotensin system (RAS) is a complex circulating and tissue-based system. There are multiple pathways for the formation and degradation of peptides. In order to understand the functions of the system, characterization of angiotensin peptides (products and substrates) is important. Radioimmunoassays with the requisite specificity and sensitivity have been developed to allow for the characterization and quantification of circulating and tissue angiotensins. Here, we describe the appropriate methods for collecting the tissue and blood, the extractions steps required to partially purify and remove larger molecular weight-interfering proteins from tissue and plasma, and the radioimmunoassay of three of the peptides of this system (Ang I, Ang II, and Ang-(1-7)), as well as the verification of immunoreactive identity for Ang II and Ang-(1-7) by combined high-performance liquid chromatography-RIA analysis.

Phase II Trial of Angiotensin-(1-7) for the Treatment of Patients with Metastatic Sarcoma

Background. Angiotensin-(1-7) [Ang-(1-7)] is an endogenous antiangiogenic hormone with anticancer activity. In a phase I study of Ang-(1-7), two of three patients with metastatic sarcoma experienced disease stabilization. This phase II study examined clinical and biomarker outcomes for patients with metastatic sarcoma. Methods. Ang-(1-7) was administered by subcutaneous injection at a dose of 20 mg daily. If excessive toxicities occurred in the first cohort, a dose deescalation cohort was allowed. Blood samples were obtained to measure changes in biomarkers. Results. Treatment was well-tolerated and the dose deescalation cohort was not required. Plasma PlGF concentrations following treatment were not statistically significantly changed. A significant increase in plasma Ang-(1-7) was observed at 4 hours after injection. The median progression-free survival was 2.7 months (95% CI; 1.4 to 4.1 months), and the median overall survival was 10.2 months (95% CI; 5.3 to 18.3 months). Two patients with vascular sarcomas demonstrated prolonged disease stabilization of 10 months (hemangiopericytoma) and 19 months (epithelioid hemangioendothelioma). Conclusions. Ang-(1-7) at a dose of 20 mg daily was well-tolerated. This prospective phase II study failed to confirm the PlGF biomarker effect identified in the prior phase I study. Prolonged disease stabilization in hemangiopericytoma and epithelioid hemangioendothelioma may warrant further investigation.

Predictive and Prognostic Value of sPRR in Patients with Primary Epithelial Ovarian Cancer

Aim. The purpose of the present study was to analyze the predictive and prognostic role of soluble (pro)renin receptor (sPRR) as a biomarker for clinicopathological outcome in patients with primary epithelial ovarian cancer (EOC). As part of the renin-angiotensin system (RAS) whose activity is known to increase in ovarian cancer patients, the relation of sPRR and ovarian cancer should be further investigated. Patients and Methods. In this study 197 patients with primary EOC in our institution from 2000 to 2011 were included. sPRR was determined by enzyme-linked immunosorbent assay (ELISA) in preoperative taken blood sera. Associations with clinicopathological outcome were analyzed and serum levels of sPRR in patients have been compared to those in healthy specimen. Kaplan-Meier and logistic/Cox regression assessed the impact of the markers on progression-free survival (PFS) and overall survival (OS). Results. There have been no correlations proved of sPRR levels with neither clinicopathological factors nor prognostic data. Also the distribution of sPRR in patients and controls was normal. Conclusion. sPRR seems to have no predictive, prognostic, or diagnostic value in EOC. As several factors of the RAS which might indicate cancer events have been shown, sPRR seems not to be affected.

Renin-angiotensin system blockade for the risk of cancer and death

INTRODUCTION

The effects of renin-angiotensin system blockade with angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II type 1 receptor blockers (ARBs) on cancer remain inconsistent.

METHODS

We searched existing databases from 1960 to August 2015, for randomised controlled trials and observational studies (case-control studies and cohort studies) of ARB/ACEI therapy with a minimal one year of follow-up. Outcomes were incidence and mortality of cancer.

RESULTS

We included 14 randomised controlled trials and 17 observational studies of 3,957,725 participants (350,329 ARB/ACEI users). The users had a lower incidence of cancer in the observational studies (RR 0.82, 95% CI 0.73-0.93) but not in the randomised controlled trials (RR 1.00, 95% CI 0.92-1.08). The protection persisted for lung cancer (RR 0.85, 95% CI 0.75-0.97) but not for other sites of cancer. The relative risk of cancer associated with renin-angiotensin system blockade was reduced along with time of follow-up. Mortality reduction with ARB/ACEI was marginally significant in the observational studies (RR 0.71, 95% CI 0.55-0.93) but not in the randomised controlled trials (RR 0.99, 95% CI 0.89-1.09).

CONCLUSIONS

The significant benefits of renin-angiotensin system blockade observed in case-control studies and cohort studies might diminish in randomised controlled trials. Clinical design, site of cancer and duration of follow-up may affect the clinical outcomes.

Novel long-acting prostacyclin agonist (ONO-1301) with an angiogenic effect: promoting synthesis of hepatocyte growth factor and increasing cyclic AMP concentration via IP-receptor signaling

The purpose of this study was to evaluate the angiogenic potency of ONO-1301, a novel prostacyclin agonist, using a murine sponge model. Solutions of ONO-1301 or hepatocyte growth factor (HGF), as a positive control, were injected into sponges in the backs of mice, daily for 14 days. Hemoglobin and HGF levels in the sponge were increased for up to 14 days on daily treatment with ONO-1301 while on HGF treatment, they peaked on day 7 and had decreased again by day 14. ONO-1301 also upregulated c-Met expression for 14 days in a dose-dependent manner. When the mice were pretreated with an antibody to HGF or the prostaglandin I (IP)-receptor antagonist CAY10441, the angiogenic effect of ONO-1301 was dramatically reduced. Plasma concentrations of cyclic adenosine monophosphate (cAMP) were increased in a dose-dependent manner by once daily treatment with ONO-1301 for 14 days. This effect was reduced by pretreatment with the IP-receptor antagonist. In conclusion, hemoglobin level was increased by repeated treatment with ONO-1301 for 14 days. It is suggested that ONO-1301 induced angiogenesis by promoting the synthesis of HGF and upregulated c-Met expression, followed by an increase in cAMP concentrations mediated by IP-receptor signaling.

Inhibition of central angiotensin II enhances memory function and reduces oxidative stress status in rat hippocampus

While it is now well established that the independent brain renin-angiotensin system (RAS) has some important central functions besides the vascular ones, the relevance of its main bioactive peptide angiotensin II (Ang II) on the memory processes, as well as on oxidative stress status is not completely understood. The purpose of the present work was to evaluate the effects of central Ang II administration, as well as the effects of Ang II inhibition with either AT1 and AT 2 receptor specific blockers (losartan and PD-123177, respectively) or an angiotensin-converting enzyme (ACE) inhibitor (captopril). These effects were studied on the short-term memory (assessed through Y-maze) or long-term memory (as determined in passive avoidance) and on the oxidative stress status of the hippocampus. Our results demonstrate memory deficits induced by the administration of Ang II, as showed by the significant decrease of the spontaneous alternation in Y-maze (p=0.015) and latency-time in passive avoidance task (p=0.001) when compared to saline. On the other side, the administration of all the aforementioned Ang II blockers significantly improved the spontaneous alternation in Y-maze task, while losartan also increased the latency time as compared to saline in step-through passive avoidance (p=0.042). Also, increased oxidative stress status was induced in the hippocampus by the administration of Ang II, as demonstrated by increased levels of lipid peroxidation markers (malondialdehyde-MDA concentration) (p<0.0001) and a decrease in both antioxidant enzymes determined: superoxide dismutase-SOD (p<0.0001) and glutathione peroxidase-GPX (p=0.01), as compared to saline. Additionally, the administration of captopril resulted in an increase of both antioxidant enzymes and decreased levels of lipid peroxidation (p=0.001), while PD-123177 significantly decreased MDA concentration (p>0.0001) vs. saline. Moreover, significant correlations were found between all of the memory related behavioral parameters and the main oxidative stress markers from the hippocampus, which is known for its implication in the processes of memory and also where RAS components are well expressed. This could be relevant for the complex interactions between Ang II, behavioral processes and neuronal oxidative stress, and could generate important therapeutic approaches.

Blockade of cannabinoid receptors reduces inflammation, leukocyte accumulation and neovascularization in a model of sponge-induced inflammatory angiogenesis

OBJECTIVE

Angiogenesis depends on a complex interaction between cellular networks and mediators. The endocannabinoid system and its receptors have been shown to play a role in models of inflammation. Here, we investigated whether blockade of cannabinoid receptors may interfere with inflammatory angiogenesis.

MATERIALS AND METHODS

Polyester-polyurethane sponges were implanted in C57Bl/6j mice. Animals received doses (3 and 10 mg/kg/daily, s.c.) of the cannabinoid receptor antagonists SR141716A (CB1) or SR144528 (CB2). Implants were collected at days 7 and 14 for cytokines, hemoglobin, myeloperoxidase, and N-acetylglucosaminidase measurements, as indices of inflammation, angiogenesis, neutrophil and macrophage accumulation, respectively. Histological and morphometric analysis were also performed.

RESULTS

Cannabinoid receptors expression in implants was detected from day 4 after implantation. Treatment with CB1 or CB2 receptor antagonists reduced cellular influx into sponges at days 7 and 14 after implantation, although CB1 receptor antagonist were more effective at blocking leukocyte accumulation. There was a reduction in TNF-α, VEGF, CXCL1/KC, CCL2/JE, and CCL3/MIP-1α levels, with increase in CCL5/RANTES. Both treatments reduced neovascularization. Dual blockade of cannabinoid receptors resulted in maximum inhibition of inflammatory angiogenesis.

CONCLUSIONS

Blockade of cannabinoid receptors reduced leukocyte accumulation, inflammation and neovascularization, suggesting an important role of endocannabinoids in sponge-induced inflammatory angiogenesis both via CB1 and CB2 receptors.

Angiotensin-(1-7) central administration induces anxiolytic-like effects in elevated plus maze and decreased oxidative stress in the amygdala

There is increasing evidence that besides the well-known angiotensin (Ang) II, other renin-angiotensin system (RAS) peptides, including Ang-(1-7), could have important effects at the central level. However, very few things are known about the central actions of Ang-(1-7), while the effects of its administration alone on anxiety have not been tested to date, to the best of our knowledge. In this way, we were interested in studying the effects of Ang-(1-7) intracerebroventricular administration on anxiety levels, as studied through some main behavioral parameters in the elevated plus maze, as well as the importance of Ang-(1-7) in the oxidative stress status from the amygdala, which is one of the key brain regions involved in mediating anxiety. We report here a possible anxiolytic-like effect of Ang-(1-7) administration, as demonstrated by the increased percentage of time spent and frequency of entries in the open arms of the elevated plus maze, as well as increased head-dipping behavior in the open arms and decreased stretching in closed arms. Also some antioxidant effects of Ang-(1-7) are suggested since a significant increase of GPX specific activity and a decrease of the main peroxidation marker MDA were observed in the amygdala. Moreover, we found a significant correlation between most of the behavioral parameters in the elevated plus maze and the levels of the oxidative stress markers. However, further studies are necessary in order to elucidate the effects of Ang-(1-7) administration on anxiety and oxidative stress status and also on the possible correlation that might exists between these aspects.

Angiotensin-(1-7) attenuates metastatic prostate cancer and reduces osteoclastogenesis

BACKGROUND

Angiotensin-(1-7) [Ang-(1-7)] is an endogenous, heptapeptide hormone with anti-proliferative and anti-angiogenic properties. The primary objective of this study was to determine whether Ang-(1-7) effectively reduces prostate cancer metastasis in mice.

METHODS

Human PC3 prostate cancer cells were injected into the aortic arch via the carotid artery of SCID mice pre-treated with Ang-(1-7) or injected into the tibia of athymic mice, administered Ang-(1-7) for 5 weeks beginning 2 weeks post-injection. Tumor growth and volume were determined by bioluminescent and magnetic resonance imaging. The presence of tumors was confirmed by hematoxylin and eosin staining; TRAP histochemistry was used to identify osteolytic lesions. The effect of Ang-(1-7) on osteoclastogenesis was assessed in differentiated bone marrow cells.

RESULTS

Pre-treatment with Ang-(1-7) prevented metastatic tumor formation following intra-aortic injection of PC3 cells, while 83% of untreated mice developed tumors in metastatic sites. Circulating VEGF was significantly higher in control mice compared to mice administered Ang-(1-7). A 5-week regimen of the heptapeptide hormone attenuated intra-tibial tumor growth; Ang-(1-7) was significantly higher in the tibia of treated mice than in control animals. Osteoclastogenesis was reduced by 50% in bone marrow cells differentiated in the presence of Ang-(1-7), suggesting that the heptapeptide hormone prevents the formation of osteolytic lesions to reduce tumor survival in the bone microenvironment.

CONCLUSIONS

These findings suggest that Ang-(1-7) may serve as an anti-angiogenic and anti-metastatic agent for advanced prostate cancer. By extension, the heptapeptide hormone may provide effective therapy for bone metastasis produced from primary tumors of the lung and breast.

Angiotensin-(1-7) reduces proliferation and angiogenesis of human prostate cancer xenografts with a decrease in angiogenic factors and an increase in sFlt-1

BACKGROUND

Prostate cancer is the most frequently diagnosed malignancy and the second-leading cause of cancer death in men. The purpose of this study was to determine the anti-proliferative and anti-angiogenic efficacy of angiotensin-(1-7) [Ang-(1-7)], an endogenous peptide hormone, in human prostate cancer xenografts.

METHODS

Human LNCaP prostate cancer cells were injected into the flank of athymic mice and tumors were treated with Ang-(1-7) for 54 days. Tumor growth and angiogenesis were determined by immunohistochemistry and western blot hybridization.

RESULTS

Ang-(1-7) markedly reduced the volume and wet weight of LNCaP xenograft tumors. Histological analysis of tumor sections from saline-treated mice showed increased Ki67 immunoreactivity and enhanced phosphorylation of the MAP kinases ERK1/2 compared to tumors from Ang-(1-7)-treated mice, suggesting that the heptapeptide reduces cell proliferation. Intratumoral vessel density was decreased in Ang-(1-7)-treated mice with an associated reduction in vascular endothelial growth factor (VEGF) and placental growth factor (PlGF), suggesting that the heptapeptide attenuates vascularization by reducing angiogenic factors. Ang-(1-7) administration markedly increased the soluble fraction of VEGF receptor 1 (sFlt-1), with a concomitant reduction in VEGF receptors 1 and 2. sFlt-1 serves as a decoy receptor that traps VEGF and PlGF, making the ligands unavailable to membrane-bound VEGF receptors and preventing activation of pro-angiogenic signaling.

CONCLUSIONS

The decrease in PlGF and VEGF coupled with the increase in sFlt-1 suggests that Ang-(1-7) may serve as a novel anti-angiogenic therapy for prostate cancer. Further, the pleiotropic mechanisms of action by Ang-(1-7) may limit angiogenic resistance that occurs with VEGF inhibitors or receptor blockers.

Reverse translation of phase I biomarker findings links the activity of angiotensin-(1-7) to repression of hypoxia inducible factor-1α in vascular sarcomas

Background

In a phase I study of angiotensin-(1–7) [Ang-(1–7)], clinical benefit was associated with reduction in plasma placental growth factor (PlGF) concentrations. The current study examines Ang-(1–7) induced changes in biomarkers according to cancer type and investigates mechanisms of action engaged in vitro.

Methods

Plasma biomarkers were measured prior to Ang-(1–7) administration as well as 1, 2, 3, 4, and 6 hours after treatment. Tests for interaction were performed to determine the impact of cancer type on angiogenic hormone levels. If a positive interaction was detected, treatment-induced biomarker changes for individual cancer types were assessed. To investigate mechanisms of action, in vitro growth assays were performed using a murine endothelioma cell line (EOMA). PCR arrays were performed to identify and statistically validate genes that were altered by Ang-(1–7) treatment in these cells.

Results

Tests for interaction controlled for dose cohort and clinical response indicated a significant impact of cancer type on post-treatment VEGF and PlGF levels. Following treatment, PlGF levels decreased over time in patients with sarcoma (P = .007). Treatment of EOMA cells with increasing doses of Ang-(1–7) led to significant growth suppression at doses as low as 100 nM. PCR arrays identified 18 genes that appeared to have altered expression after Ang-(1–7) treatment. Replicate analyses confirmed significant changes in 8 genes including reduction in PlGF (P = .04) and hypoxia inducible factor 1α (HIF-1α) expression (P < .001).

Conclusions

Ang-(1–7) has clinical and pre-clinical activity for vascular sarcomas that is linked to reduced HIF-1α and PlGF expression.

The genetic deletion of Mas abolishes salt induced hypertension in mice

The G protein-coupled receptor Mas is a physiological antagonist of the angiotensin II type 1 receptor and is associated with angiotensin-(1-7) signaling. We investigated the effect of Mas-deficiency on blood pressure regulation under physiological conditions and salt load using radiotelemetry. Mas-knockout mice and their wild-type controls received a telemetry implant in the carotid artery. One week after surgery, animals were monitored for 3 days receiving normal diet (0.6% NaCl) followed by one-week high-salt diet (8% NaCl). Under same high-salt diet, another set of mice was placed in individual metabolic cages for 4 days. Basal mean arterial pressure, heart rate and locomotor activity displayed normal day-night rhythm in Mas-deficient mice. Mas-knockout mice were normotensive. High dietary NaCl ingestion did not alter heart rate or locomotor activity in both groups, but significantly increased night time mean arterial pressure in control mice whereas this increase was blunted in Mas-deficient mice. Baseline food and water intake and urine osmolality were not different between both genotypes. Under high-salt diet, water consumption and food intake were equally increased in wild-type controls and Mas-knockout, but urinary electrolytes and osmolality were significantly higher in Mas-knockout. Taken together, basal hemodynamic parameters are unchanged in Mas-knockout mice. In contrast to wild-type controls, telemetric mean arterial pressure measurement revealed salt resistance in Mas-deficient animals, probably due to their higher urinary NaCl excretion. This is the first direct proof that Mas blockade might be a new option in the treatment of salt-sensitive hypertension.

The renin–angiotensin system, bone marrow and progenitor cells

Modulation of the RAS (renin–angiotensin system), in particular of the function of the hormones AngII (angiotensin II) and Ang-(1–7) [angiotensin-(1–7)], is an important target for pharmacotherapy in the cardiovascular system. In the classical view, such modulation affects cardiovascular cells to decrease hypertrophy, fibrosis and endothelial dysfunction, and improves diuresis. In this view, excessive stimulation of AT1 receptors (AngII type 1 receptors) fulfils a detrimental role, as it promotes cardiovascular pathogenesis, and this is opposed by stimulation of the AT2 receptor (angiotensin II type 2 receptor) and the Ang-(1–7) receptor encoded by the Mas proto-oncogene. In recent years, this view has been broadened with the observation that the RAS regulates bone marrow stromal cells and stem cells, thus involving haematopoiesis and tissue regeneration by progenitor cells. This change of paradigm has enlarged the field of perspectives for therapeutic application of existing as well as newly developed medicines that alter angiotensin signalling, which now stretches beyond cardiovascular therapy. In the present article, we review the role of AngII and Ang-(1–7) and their respective receptors in haematopoietic and mesenchymal stem cells, and discuss possible pharmacotherapeutical implications.

Angiotensin-(1-7) receptor Mas is an essential modulator of extracellular matrix protein expression in the heart

In this study we investigated the effects of genetic deletion of the Angiotensin-(1-7) receptor Mas or the Angiotensin II receptor AT(2) on the expression of specific extracellular matrix (ECM) proteins in atria, right ventricles and atrioventricular (AV) valves of neonatal and adult mice. Quantification of collagen types I, III and VI and fibronectin was performed using immunofluorescence-labeling and confocal microscopy. Picrosirius red staining was used for the histological assessment of the overall collagen distribution pattern. ECM proteins, metalloproteinases (MMP), ERK1/2 and p38 levels were quantified by western blot analysis. Gelatin zymography was used to evaluate the activity of MMP-2 and MMP-9. We observed that the relative levels of collagen types I and III and fibronectin are significantly higher in both the right ventricle and AV valves of neonatal Mas(-/-) mouse hearts (e.g., collagen type I: 85.28±6.66 vs 43.50±4.41 arbitrary units in the right ventricles of Mas(+/+) mice). Conversely, the level of collagen type VI was lower in the right ventricle and AV valves of Mas(-/-) mice. Adult Mas(-/-) mouse hearts presented similar patterns as observed in neonates. No significant differences in ECM protein level were detected in atria. Likewise, no changes in ECM levels were observed in AT(2) knockout mouse hearts. Although deletion of Mas induced a significant reduction in the level of the active form of MMP-2 in neonate hearts and a reduction of both MMP-2 and MMP-9 in adult Mas(-/-) mice, no significant differences were observed in MMP enzymatic activities when compared to controls. The levels of the active, phosphorylated forms of ERK1/2 and p38 were higher in hearts of both neonatal and adult Mas(-/-) mice. These observations suggest that Mas is involved in the selective expression of specific ECM proteins within both the ventricular myocardium and AV valves. The changes in the ECM profile may alter the connective tissue framework and contribute to the decreased cardiac performance observed in Mas(-/-) mice.

Decidualized pseudopregnant rat uterus shows marked reduction in Ang II and Ang-(1-7) levels

Previous studies showed that angiotensin (Ang) II and Ang-(1-7) concentrations were reduced in the implantation site at day 7 of pregnancy in Sprague-Dawley rats as compared to the site immediately adjacent to it, which does not have the embryo attached, clearly showing the importance of the blastocyst in the regulation of renin-angiotensin system (RAS).

OBJECTIVE

The objective of this study was to evaluate the regulation of the RAS in the decidualized uterus in the pseudopregnant rat, a model without the presence of a conceptus.

METHODS

Ovariectomized, adult female rats were sensitized for the decidual cell reaction with steroid treatments; decidualization was induced by oil-injection of the right horn; the left horn served as a control. The uterine content of Ang I, Ang II, and Ang-(1-7) was examined in the decidualized and non-decidualized uteri.

RESULTS

Both Ang-(1-7) and Ang II and ACE and ACE2 mRNA were significantly reduced in the decidualized horn as compared to the non-decidualized horn. Immunocytochemical characterization of Ang II, Ang-(1-7), ACE and ACE2 demonstrated that Ang-(1-7), Ang II, and ACE2 polarize to the anti-mesometrial pole with decidualization.

CONCLUSION

The decidualization process elicits marked reduction in uterine Ang II and Ang-(1-7) content as compared to the non-decidualized horn. The differential immunocytochemical expression of Ang II and Ang-(1-7) with ACE2, but not ACE in the anti-mesometrial pole of the decidualized horn may favor the formation and action of Ang-(1-7) in the anti-mesometrial pole, an area which plays a role in triggering the decidualization process.

Boswellic acid inhibits inflammatory angiogenesis in a murine sponge model

The aim of the present study was to investigate the effects of boswellic acid (BA) on key components of inflammatory angiogenesis in the murine cannulated sponge implant angiogenesis model. Polyester-polyurethane sponges, used as a framework for fibrovascular tissue growth, were implanted in Swiss albino mice and BA (12.5 or 25mg/kg/day) was given through installed cannulas for nine days. The implants collected at day 9 post-implantation were processed for the assessment of hemoglobin (Hb). Relevant levels of inflammatory, angiogenic and fibrogenic cytokines were also determined. BA treatment resulted in significant decrease in sponge vascularization (Hb content) and in vascular endothelial growth factor (VEGF) and transforming growth factor (TGF-β1) at both doses. Further, BA decreased expression of VEGF and CD31 and reduced % microvessel density (MVD) in sponge implants. A regulatory function of BA on multiple parameters of the main components of inflammatory angiogenesis has been revealed giving an insight into the potential therapeutic use underlying the actions of BA.

Effects of the renin angiotensin system on vasculogenesis-related progenitor cells

The current concept is that there are both cells that integrate into the vasculature, true endothelial progenitor cells (EPC), and cells with hematopoietic markers that support neovascularisation. As identification of the EPC is controversial and studies refer cells that might fall into either pools, we will use the term, vasculogenesis-related progenitor cells (VRPC), for this review. VRPC are considered to be an important target for the treatment of cardiovascular diseases (CVD). Angiotensin II is known to be an important player in neovascularisation and the modulation of renin angiotensin system (RAS) is one of the major pharmacotherapeutic strategies for the treatment of CVD. We will review the effects of different components of the RAS on such VRPC under physiological conditions and in CVD. The reviewed research strongly supports a critical role of the RAS in vasculogenesis and vascular regeneration. Therefore, pharmacological intervention on the components of the RAS does not only target directly end-organ remodelling and blood pressure but also influence tissue healing and/or regeneration by influencing specific progenitor cells. Thus, the interrogation of RAS effects on VRPC will be important in the optimisation of RAS intervention or regenerative therapy.

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.

Liver regeneration and tumour stimulation: implications of the renin-angiotensin system

Liver resection is the most effective treatment for primary liver tumours and metastasis to the liver, and remains the only potentially long-term curative therapy for patients with colorectal cancer (CRC) liver metastases. Nevertheless, there is a significant incidence of tumour recurrence following liver resection. Cellular and molecular changes resulting from resection and the subsequent liver regeneration process may influence the kinetics of tumour growth, contributing to recurrence. Although commonly associated with the systemic homeostasis of blood pressure, fluid and electrolyte, the renin-angiotensin system (RAS) has recently been shown to play a role in regulating cell proliferation, apoptosis and angiogenesis in local organs as well as in malignancies. An electronic search of the English literature on the role of the RAS in liver regeneration and tumourigenesis was performed using PubMed, with additional relevant articles sourced from reference lists. Studies have shown that the blockade of the RAS pathway stimulates liver regeneration and inhibits tumour progression. An understanding of the role of RAS in liver regeneration and tumourigenesis may enable alternative strategies to improve patient outcome and survival after liver resection. This review will discuss the role of the RAS in liver regeneration and in tumour recurrence post-liver resection. The potential of the RAS as a novel therapeutic target for CRC liver metastases patients undergoing liver resection will be outlined.

Changes in the renin angiotensin system during the development of colorectal cancer liver metastases

BACKGROUND

Blockade of the renin angiotensin system (RAS) via angiotensin I converting enzyme (ACE) inhibition reduces growth of colorectal cancer (CRC) liver metastases in a mouse model. In this work we defined the expression of the various components of the RAS in both tumor and liver during the progression of this disease.

METHODS

Immunohistochemistry and quantitative RT-PCR was used to examine RAS expression in a mouse CRC liver metastases model. CRC metastases and liver tissue was assessed separately at key stages of CRC liver metastases development in untreated (control) mice and in mice treated with the ACE inhibitor captopril (750 mg/kg/day). Non-tumor induced (sham) mice indicated the effect of tumors on normal liver RAS. The statistical significance of multiple comparisons was determined using one-way analysis of variance followed by Bonferroni adjustment with SAS/STAT software.

RESULTS

Reduced volume of CRC liver metastases with captopril treatment was evident. Local RAS of CRC metastases differed from the surrounding liver, with lower angiotensin II type 1 receptor (AT1R) expression but increased ANG-(1-7) receptor (MasR) compared to the liver. The AT1R localised to cancer and stromal infiltrating cells, while other RAS receptors were detected in cancer cells only. Tumor induction led to an initial increase in AT1R and ACE expression while captopril treatment significantly increased ACE expression in the final stages of tumor growth. Conversely, captopril treatment decreased expression of AT1R and angiotensinogen.

CONCLUSIONS

These results demonstrate significant changes in RAS expression in the tumor-bearing captopril treated liver and in CRC metastases. The data suggests the existence of a tumor-specific RAS that can be independently targeted by RAS blockade.

Angiostatic activity of human plasminogen fragments is highly dependent on glycosylation

To assess the importance of carbohydrate moieties to the anti-angiogenic activity of plasminogen fragments, we cloned the fragment corresponding to amino acids Val(79) to Thr(346) (Kint3-4) that presents the three glycosylation sites. The activity of glycosylated and unglycosylated Kint3-4 was tested in murine sponge implant model. We observed a significant decrease in the neovascularization on the sponge after treatment with Kint3-4 by histological examination and determination of the hemoglobin levels. The effects were more intense with the glycosylated than the unglycosylated protein. (99m)Technecium-labeled red blood cells confirmed the inhibition of cell infiltration in the implanted sponge. Studies using melanoma B16F1 implanted in a mouse demonstrated that treatment with glycosylated Kint3-4 (0.15 nmol/48 h) during 14 days suppresses tumor growth by 80%. The vascular endothelial growth factor mRNA levels on the tumor were reduced after treatment. Kint3-4 is a potent plasminogen fragment that has been found to inhibit tumor growth.

Peptide hormone regulation of angiogenesis

It is now apparent that regulation of blood vessel growth contributes to the classical actions of hormones on development, growth, and reproduction. Endothelial cells are ideally positioned to respond to hormones, which act in concert with locally produced chemical mediators to regulate their growth, motility, function, and survival. Hormones affect angiogenesis either directly through actions on endothelial cells or indirectly by regulating proangiogenic factors like vascular endothelial growth factor. Importantly, the local microenvironment of endothelial cells can determine the outcome of hormone action on angiogenesis. Members of the growth hormone/prolactin/placental lactogen, the renin-angiotensin, and the kallikrein-kinin systems that exert stimulatory effects on angiogenesis can acquire antiangiogenic properties after undergoing proteolytic cleavage. In view of the opposing effects of hormonal fragments and precursor molecules, the regulation of the proteases responsible for specific protein cleavage represents an efficient mechanism for balancing angiogenesis. This review presents an overview of the actions on angiogenesis of the above-mentioned peptide hormonal families and addresses how specific proteolysis alters the final outcome of these actions in the context of health and disease.

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.

Renin-angiotensin system in the pathogenesis of liver fibrosis

Hepatic fibrosis is considered a common response to many chronic hepatic injuries. It is a multifunctional process that involves several cell types, cytokines, chemokines and growth factors leading to a disruption of homeostatic mechanisms that maintain the liver ecosystem. In spite of many studies regarding the development of fibrosis, the understanding of the pathogenesis remains obscure. The hepatic tissue remodeling process is highly complex, resulting from the balance between collagen degradation and synthesis. Among the many mediators that take part in this process, the components of the Renin angiotensin system (RAS) have progressively assumed an important role. Angiotensin (Ang) II acts as a profibrotic mediator and Ang-(1-7), the newly recognized RAS component, appears to exert a counter-regulatory role in liver tissue. We briefly review the liver fibrosis process and current aspects of the RAS. This review also aims to discuss some experimental evidence regarding the participation of RAS mediators in the pathogenesis of liver fibrosis, focusing on the putative role of the ACE2-Ang-(1-7)-Mas receptor axis.

Role of the chemokines CCL3/MIP-1 alpha and CCL5/RANTES in sponge-induced inflammatory angiogenesis in mice

OBJECTIVE

We examined the potential contribution of CCL3 and CCL5 to inflammatory angiogenesis in mice.

METHODS

Polyester-polyurethane sponges were implanted in mice and blood vessel counting and hemoglobin, myeloperoxidase and N-acetylglucosaminidase measurements used as indexes for vascularization, neutrophil and macrophage accumulation, respectively.

RESULTS

CCL3 and CCL5 were expressed throughout the observation period. Exogenous CCL3 enhanced angiogenesis in WT, but angiogenesis proceeded normally in CCL3(-/-) mice, suggesting that endogenous CCL3 is not critical for sponge-induced angiogenesis in mice. CCL5 expression was detected at day 1, but levels significantly increased thereafter. Exogenous CCL5 reduced angiogenesis in WT mice possible via CCR5 as CCL5 was without an effect in CCR5(-/-) mice. Treatment of WT with the CCR1/CCR5 antagonist, Met-RANTES, prevented neutrophil and macrophage accumulation, but enhanced sponge vascularization.

CONCLUSION

Thus, endogenous CCL3 appears not to play a role in driving sponge-induced inflammatory angiogenesis in mice. The effects of CCL5 were anti-angiogenic and appeared to be mediated via activation of CCR5.

The vasoactive peptide angiotensin-(1-7), its receptor Mas and the angiotensin-converting enzyme type 2 are expressed in the human endometrium

Angiotensin (Ang)-(1-7) is one of the major active components of the renin-angiotensin system, produced from cleavage of Ang II by angiotensin-converting-enzyme type 2 (ACE2), which acts through a specific G protein-coupled receptor, Mas. We have investigated whether the human endometrium expresses these components during menstrual cycle. By radioimmunoassay, Ang-(1-7) was detected in endometrial wash fluid at picomolar concentrations. Using immunofluorescence, both the peptide and its receptor were identified in cultured endometrial epithelial and stromal cells. By immunohistochemistry, Ang(1-7) was localized in the endometrium throughout menstrual cycle, being more concentrated in the glandular epithelium of mid- and late secretory phase. This pattern corresponded to the ACE2 mRNA, which was more abundant in epithelial cells than in stromal cells (2-fold increase, p < 0.05) and in the secretory vs. proliferative phase (6.6-fold increase, p < 0.01). The receptor Mas was equally distributed between epithelial and stromal cells and did not change during menstrual cycle. The physiological role of this peptide system in normal and pathological endometrium warrants further investigation.

Angiotensin metabolites can stimulate receptors of the Mas-related genes family

The Mas protooncogene encodes a G protein-coupled receptor, we identified, also by using the specific angiotensin-(1-7) antagonist A-779, to be associated with intracellular signaling of the angiotensin (Ang) II metabolite Ang-(1-7). Recently, Mas-related genes (Mrg) have been identified coding for the Mrg-receptor family. All family members share high sequence homology to Mas. Most of them are orphan receptors. To proof whether structure similarities of the Mrg receptors with Mas turn them into potential receptors for Ang-(1-7) or other Ang metabolites, we transfected COS or HEK293 cells with an assortment of Mrg receptors and investigated arachidonic acid (AA) release and transcriptional activation by recording serum response factor (SRF) activation after stimulation with Ang II, Ang III, Ang IV, and Ang-(1-7). None of the investigated receptors activated transcription via SRF. Ang-(1-7) stimulated AA release already in control vector-transfected COS cells, indicating the existence of an endogenous receptor (A-779 sensitive). Though less pronounced than for Mas, two of the six studied receptors (MrgD, MRG) initiated significant AA release after stimulation with Ang-(1-7). Interestingly, Mas, MrgD, and MRG mediated Ang IV-stimulated AA release that was highest for Mas. While Ang III activated Mas and MrgX2, Ang II stimulated AA release via Mas and MRG. Thus, we identified other receptors of the Mrg family to respond on Ang-(1-7) stimulation. Furthermore, we describe first an AT(1)-independent direct Ang IV signaling and show that Ang II and Ang III mediate signaling independent of their specific receptors AT(1) and AT(2), whereby the receptor specificity differs.

The renin-angiotensin system and malignancy

The renin-angiotensin system (RAS) is usually associated with its systemic action on cardiovascular homoeostasis. However, recent studies suggest that at a local tissue level, the RAS influences tumour growth. The potential of the RAS as a target for cancer treatment and the suggested underlying mechanisms of its paracrine effects are reviewed here. These include modulation of angiogenesis, cellular proliferation, immune responses and extracellular matrix formation. Knowledge of the RAS has increased dramatically in recent years with the discovery of new enzymes, peptides and feedback mechanisms. The local RAS appears to influence tumour growth and metastases and there is evidence of tissue- and tumour-specific differences. Recent experimental studies provide strong evidence that drugs that inhibit the RAS have the potential to reduce cancer risk or retard tumour growth and metastases. Manipulation of the RAS may, therefore, provide a safe and inexpensive anticancer strategy.

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.

Recent advances in the angiotensin-converting enzyme 2-angiotensin(1-7)-Mas axis

In the past few years, the classical concept of the renin-angiotensin system (RAS) has experienced substantial conceptual changes. The identification of: the renin/prorenin receptor; the angiotensin-converting enzyme homologue, ACE2, as an angiotensin peptide-processing enzyme and a virus receptor for severe acute respiratory syndrome, the Mas as a receptor for angiotensin (1-7) [Ang(1-7)], and the possibility of signaling through ACE have contributed to switch our understanding of the RAS from the classical limited-proteolysis linear cascade to a cascade with multiple mediators, multiple receptors and multifunctional enzymes. With regard to Ang(1-7), the identification of ACE2 and of Mas as a receptor implicated in its actions contributed to decisively establish this heptapeptide as a biologically active member of the RAS cascade. In this review, we will focus on the recent findings related to the ACE2-Ang(1-7)-Mas axis and, in particular, on its putative role as an ACE-Ang II-AT(1) receptor counter-regulatory axis within the RAS.

Reduced circulating levels of angiotensin-(1--7) in systemic sclerosis: a new pathway in the dysregulation of endothelial-dependent vascular tone control

OBJECTIVE

Systemic sclerosis (SSc) impairs endothelium-dependent vasodilatation. Among angiotensin I (Ang I)-derived compounds, vasoconstrictor angiotensin II (Ang II) and vasodilator angiotensin-(1-7) (Ang-(1-7)), cleaved from ACE and neutral endopeptidase (NEP) 24.11, respectively, play an important role in vascular tone regulation. Ang-(1-7) may act independently or by activating other vasodilating molecules, such as nitric oxide (NO) or prostaglandin I2 (PGI2). Our aim was to assess, in patients with SSc, circulating levels of Ang I, Ang II and Ang-(1-7), with their metabolising enzymes ACE and NEP, and levels of NO and PGI2, and to correlate them to the main characteristics of SSc.

METHODS

Levels of Ang I, Ang II, Ang-(1-7), NEP, ACE, NO and PGI2 were measured in 32 patients with SSc, who were also assessed for humoral and clinical characteristics, and 55 controls.

RESULTS

Plasma Ang I, Ang II and Ang-(1-7) levels were lower in patients with SSc than in controls (p<0.001in all cases). When Ang II and Ang-(1-7) levels were expressed as a function of the available Ang I, lower Ang-(1-7) levels in patients with SSc than in controls were confirmed (p<0.001), while no difference was found for Ang II levels. In patients with SSc, the Ang II/Ang-(1-7) ratio indicated a prevalence of Ang II over Ang-(1-7), while in controls Ang-(1-7) was prevalent (p<0.001). Levels of ACE, NEP, NO and PGI2 were lower in patients with SSc than in controls (p<0.05 in all cases).

CONCLUSION

In patients with SSc, prevalence of the vasoconstricting Ang II over the vasodilator Ang-(1-7) suggests a dysfunction of the angiotensin-derived cascade that may contribute to dysregulation of vascular tone.

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) and the renin-angiotensin system

PURPOSE OF REVIEW

In this review we will focus on the recent findings related to angiotensin-(1-7) as an angiotensin II counter-regulatory peptide within the renin-angiotensin system.

RECENT FINDINGS

The identification of the angiotensin-converting enzyme homologue ACE2 as an angiotensin peptide processing enzyme and of Mas as a receptor for angiotensin-(1-7) has contributed to establishing this heptapeptide as a biologically active member of the renin-angiotensin system cascade.

SUMMARY

The previously unsuspected complexity of the renin-angiotensin system, unmasked by novel findings, has revealed new possibilities for exploring its physiological and pathophysiological roles. In addition, the ACE2-angiotensin-(1-7)-Mas axis may be seriously considered as a putative target for the development of new cardiovascular drugs.

Angiotensin II Captopril Cotreatment Augments Angiogenesis in Abdominal Skin Flap in Rats

The effect of captopril, angiotensin-converting enzyme inhibitor, on angiogenesis in several reports remained unclear. Its effect on neovascularization in rat abdominal skin flaps was investigated. Flap elevation, based on the right superficial inferior epigastric artery was performed with or without the administration of captopril (10 mg/kg/d), Ang II (100 microg/kg/d), or captopril and Ang II cotreatment. Mean arterial pressure (MAP), microangiography, capillary density measurement, necrosis area determination, laser Doppler flowmetry (LDF), AT1 and vascular endothelial growth factor (VEGF) immunostaining were used to evaluate the effects of captopril and the interaction between captopril and Ang II on the angiogenesis. Ang II and captopril cotreatment improved angiogenesis more than Ang II or captopril alone. The reduction of necrosis, enhancement of vascular network formation, capillary density, VEGF immunostaining, and local blood flow were evident in the cotreated group. We suggest that Ang II and captopril cotreatment improves ischemia-induced angiogenesis and increased viability and vascularity of skin flap in rats.

The renin-angiotensin system in a rat model of hepatic fibrosis: evidence for a protective role of Angiotensin-(1-7)

BACKGROUND/AIMS

The circulating renin-angiotensin system (RAS) [plasma renin activity (PRA), Angiotensin (Ang) I, Ang II and Ang-(1-7)] was evaluated in a model of hepatic fibrosis in rats. To investigate the pathophysiological involvement of Ang-(1-7), animals were treated with the Ang-(1-7) Mas receptor antagonist, A-779.

METHODS

RAS components, liver function and histology were examined in male Wistar rats (220-300 g). Animals were submitted to sham-surgery or ligature of the bile duct and evaluated 1, 2, 4 and 6 weeks later. Blood samples were obtained to determine biochemical parameters and RAS components. A second group was treated with A-779 or vehicle to measure liver hydroxyproline and total transforming growth factor beta-1 (TGFbeta1).

RESULTS

PRA and Ang I were significantly elevated in rats at 4 and 6 weeks compared to sham-operated animals. Ang II and Ang-(1-7) progressively increased over the 6 weeks. Changes in RAS profile correlated with histological signs of fibrosis and deterioration in liver function. Pharmacological blockade of the Ang-(1-7) receptor aggravated liver fibrosis with a significant elevation in hydroxyproline and total TGFbeta(1).

CONCLUSIONS

Hepatic fibrosis was associated with RAS activation in our model. Our data also suggested that Ang-(1-7) played a protective role in hepatic fibrosis.

Angiotensin-(1-7) Inhibits Growth of Human Lung Adenocarcinoma Xenografts in Nude Mice through a Reduction in Cyclooxygenase-2

Angiotensin-(1-7) [Ang-(1-7)] is an endogenous peptide of the renin-angiotensin system with vasodilator and antiproliferative properties. Our previous studies showed that Ang-(1-7) reduced serum-stimulated growth of human lung cancer cells in vitro through activation of a unique AT((1-7)) receptor. The current study investigates the effect of Ang-(1-7) on lung tumor growth in vivo, using a human lung tumor xenograft model. Athymic mice with tumors resulting from injection of A549 human lung cancer cells were treated for 28 days with either i.v. saline or Ang-(1-7), delivered by implanted osmotic mini-pumps. Treatment with Ang-(1-7) reduced tumor volume by 30% compared with the size before treatment; in contrast, tumor size in the saline-treated animals increased 2.5-fold. These results correlate with a reduction in the proliferation marker Ki67 in the Ang-(1-7)-infused tumors when compared with the saline-infused tumor tissues. Treatment with Ang-(1-7) significantly reduced cyclooxygenase-2 (COX-2) mRNA and protein in tumors of Ang-(1-7)-infused mice when compared with mice treated with saline as well as in the parent A549 human lung cancer cells in tissue culture. These results suggest that Ang-(1-7) may decrease COX-2 activity and proinflammatory prostaglandins to inhibit lung tumor growth. In contrast, the heptapeptide had no effect on COX-1 mRNA in xenograft tumors or A549 cells. Because Ang-(1-7), a peptide with antithrombotic properties, reduces growth through activation of a selective AT((1-7)) receptor, our results suggest that the heptapeptide represents a novel treatment for lung cancer by reducing COX-2.

Angiotensinogen impairs angiogenesis in the chick chorioallantoic membrane

Angiotensinogen shares with other members of the serine protease inhibitor (serpin) family antiangiogenic properties. Angiotensinogen inhibits in vitro endothelial cell proliferation, and is antiangiogenic in ovo in the chick chorioallantoic membrane assay. The cellular mode of action of angiotensinogen has been studied by applying purified human angiotensinogen or Chinese hamster ovary cells producing recombinant angiotensinogen onto the developing chorioallantoic membrane. Vessel density of the control and angiotensinogen-treated areas was quantitated by using Sambucus nigra lectin, a specific endothelial cell marker. After 48 h of angiotensinogen treatment by either applying purified angiotensinogen or angiotensinogen-producing Chinese hamster ovary cells, there was a 70% decrease in mesodermic vessel density in comparison to the control sections. Angiotensinogen treatment induced a strong decrease in endothelial cell proliferation of the chorioallantoic membrane vasculature, as shown by incorporation of bromo-deoxyuridine. Two days after local angiotensinogen treatment, increased apoptosis of endothelial cells of mesodermal blood vessels was detected by transferase-mediated deoxyuridine triphosphate nick end labeling assay. As assessed by in situ hybridization, the gene expression pattern of the main vascular growth factors and their receptors was not altered by angiotensinogen. Angiotensinogen, therefore, impairs angiogenesis without altering the expression level of vascular growth factors through the induction of apoptosis and decreased endothelial cell proliferation.

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.

Angiotensin-(1-7) and its receptor as a potential targets for new cardiovascular drugs

The identification of novel biochemical components of the renin-angiotensin system (RAS) has added a further layer of complexity to the classical concept of this cardiovascular regulatory system. It is now clear that there is a counter-regulatory arm within the RAS that is mainly formed by the angiotensin-converting enzyme 2-angiotensin (1-7)-receptor Mas axis. The functions of this axis are often opposite to those attributed to the major component of the RAS, angiotensin II. This review will highlight the current knowledge concerning the cardiovascular effects of angiotensin-(1-7) through a direct interaction with its receptor Mas or through an indirect interplay with the kallikrein-kinin system. In addition, there will be a discussion of its role in the beneficial effects of angiotensin-converting enzyme inhibitors and angio-tensin receptor type 1 (AT1) antagonists, and the potential of this peptide and its receptor as a novel targets for new cardiovascular drugs.

Angiotensin-(1–7) enhances LTP in the hippocampus through the G-protein-coupled receptor Mas

The renin-angiotensin system not only plays a critical role in blood pressure control but is also involved in learning and memory mechanisms. In addition to angiotensin (Ang) II, Ang-(1-7) may also have important biological activities in the brain. Here, we show for the first time that Ang-(1-7) enhances long-term potentiation (LTP) in the CA1 region of the hippocampus. Our studies with AT1 receptor antagonists and selective Ang-(1-7) receptor antagonists demonstrate the existence of a distinct Ang-(1-7) receptor in the brain, the G-protein-coupled receptor Mas, encoded by the Mas protooncogene. We also show that the genetic deletion of this receptor abolishes the Ang-(1-7)-induced enhancement of LTP. Thus, we firstly demonstrate that Ang-(1-7) influences the induction of LTP in limbic structures implicating its distinct function in learning and memory mechanisms; secondly, we have identified Mas as a functional receptor for Ang-(1-7) in the brain.

Impaired inflammatory angiogenesis, but not leukocyte influx, in mice lacking TNFR1

The majority of biological responses classically attributed to tumor necrosis factor alpha (TNF-alpha) is mediated by p55 receptor (TNFR1). Here, we aimed to clarify the biological role of TNFR1-mediated signals in an in vivo inflammatory angiogenesis model. Polyester-polyurethane sponges, used as a framework for tissue growth, were implanted in C57Bl/6 mice. These implants were collected at days 1, 7, and 14 post-implant for enzyme-linked immunosorbent assay or at days 7 and 14 for hemoglobin, myeloperoxidase, and N-acetylglucosaminidase measurements, used as indexes for angiogenesis, neutrophil, and macrophage accumulation, respectively. In TNFR1-deficient C57Bl/6 mice, there was a significant decrease in sponge vascularization but not in late inflammatory cell influx. It is interesting that levels of vascular endothelial growth factor were significantly lower in TNFR1-deficient than in wild-type mice at days 1 and 7. Levels of angiogenic chemokines, CC chemokine ligand 2/murine homologue of monocyte chemoattractant protein-1 and CXC chemokine ligand 1-3/keratinocyte-derived chemokine, were significantly lower in TNFR1-deficient mice at days 1 and 7 after implantation, respectively. These observations suggest that TNFR1-mediated signals have a critical role in sponge-induced angiogenesis, possibly by influencing the effector state of inflammatory cells and hence, modulating the angiogenic molecular network.