Angiotensin-(1-7) does not affect vasodilator or TPA responses to bradykinin in human forearm

Counter-regulatory renin-angiotensin system in hypertension: Review and update in the era of COVID-19 pandemic

Cardiovascular disease is the major cause of mortality and disability, with hypertension being the most prevalent risk factor. Excessive activation of the renin-angiotensin system (RAS) under pathological conditions, leading to vascular remodeling and inflammation, is closely related to cardiovascular dysfunction. The counter-regulatory axis of the RAS consists of angiotensin-converting enzyme 2 (ACE2), angiotensin (1-7), angiotensin (1-9), alamandine, proto-oncogene Mas receptor, angiotensin II type-2 receptor and Mas-related G protein-coupled receptor member D. Each of these components has been shown to counteract the effects of the overactivated RAS. In this review, we summarize the latest insights into the complexity and interplay of the counter-regulatory RAS axis in hypertension, highlight the pathophysiological functions of ACE2, a multifunctional molecule linking hypertension and COVID-19, and discuss the function and therapeutic potential of targeting this counter-regulatory RAS axis to prevent and treat hypertension in the context of the current COVID-19 pandemic.

Angiotensin-(1-7) as a Potential Therapeutic Strategy for Delayed Cerebral Ischemia in Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is a substantial cause of mortality and morbidity worldwide. Moreover, survivors after the initial bleeding are often subject to secondary brain injuries and delayed cerebral ischemia, further increasing the risk of a poor outcome. In recent years, the renin-angiotensin system (RAS) has been proposed as a target pathway for therapeutic interventions after brain injury. The RAS is a complex system of biochemical reactions critical for several systemic functions, namely, inflammation, vascular tone, endothelial activation, water balance, fibrosis, and apoptosis. The RAS system is classically divided into a pro-inflammatory axis, mediated by angiotensin (Ang)-II and its specific receptor AT₁R, and a counterbalancing system, presented in humans as Ang-(1-7) and its receptor, MasR. Experimental data suggest that upregulation of the Ang-(1-7)/MasR axis might be neuroprotective in numerous pathological conditions, namely, ischemic stroke, cognitive disorders, Parkinson's disease, and depression. In the presence of SAH, Ang-(1-7)/MasR neuroprotective and modulating properties could help reduce brain damage by acting on neuroinflammation, and through direct vascular and anti-thrombotic effects. Here we review the role of RAS in brain ischemia, with specific focus on SAH and the therapeutic potential of Ang-(1-7).

The Impact of the Renin-Angiotensin-Aldosterone System on Inflammation, Coagulation, and Atherothrombotic Complications, and to Aggravated COVID-19

Atherosclerosis is considered a disease caused by a chronic inflammation, associated with endothelial dysfunction, and several mediators of inflammation are up-regulated in subjects with atherosclerotic disease. Healthy, intact endothelium exhibits an antithrombotic, protective surface between the vascular lumen and vascular smooth muscle cells in the vessel wall. Oxidative stress is an imbalance between anti- and prooxidants, with a subsequent increase of reactive oxygen species, leading to tissue damage. The renin-angiotensin-aldosterone system is of vital importance in the pathobiology of vascular disease. Convincing data indicate that angiotensin II accelerates hypertension and augments the production of reactive oxygen species. This leads to the generation of a proinflammatory phenotype in human endothelial and vascular smooth muscle cells by the up-regulation of adhesion molecules, chemokines and cytokines. In addition, angiotensin II also seems to increase thrombin generation, possibly via a direct impact on tissue factor. However, the mechanism of cross-talk between inflammation and haemostasis can also contribute to prothrombotic states in inflammatory environments. Thus, blocking of the renin-angiotensin-aldosterone system might be an approach to reduce both inflammatory and thrombotic complications in high-risk patients. During COVID-19, the renin-angiotensin-aldosterone system may be activated. The levels of angiotensin II could contribute to the ongoing inflammation, which might result in a cytokine storm, a complication that significantly impairs prognosis. At the outbreak of COVID-19 concerns were raised about the use of angiotensin converting enzyme inhibitors and angiotensin receptor blocker drugs in patients with COVID-19 and hypertension or other cardiovascular comorbidities. However, the present evidence is in favor of continuing to use of these drugs. Based on experimental evidence, blocking the renin-angiotensin-aldosterone system might even exert a potentially protective influence in the setting of COVID-19.

Angiotensin-(1-7) oral formulation improves physical performance in mountain bike athletes: a double-blinded crossover study

BACKGROUND

The ECA2/Ang-(1-7)/Mas axis is shown to be involved in effects mediated by physical exercise, as it can induce the release of nitric oxide (ON) and bradykinin (BK), which are potent vasodilators. The vasodilating action the NO/BK can contribute to increased metabolic efficiency in muscle tissue and central nervous system. The formulation HPβ-CD-Ang-(1-7) through its mechanisms of action can be a promising supplement to aid in the maintenance and improvement of performance and may also favor recovery during competitions. The premise of this study was to investigate the effects of acute oral supplementation HPβ-CD-Ang-(1-7) on the performance of mountain bike (MTB) practitioners.

METHODS

Fourteen recreational athletes, involved in training programs for at least one year, participated in this crossover design study. Subjects underwent two days of testing with a seven-day interval. HPβ-CD-Ang-(1-7) (1.75 mg) and HPβCD-Placebo were provided in capsules three hours prior to tests. To determine the safety of the HPβ-CD-Ang-(1-7) formulation associated with physical effort, cardiovascular parameters heart rate (HR) and blood pressure (BP) were analyzed. Physical performance was measured using maximal oxygen uptake (VO2), total exercise time (TET), mechanical work (MW), mechanical efficiency (ME), and rating of perceived exertion (RPE). Respiratory exchange coefficient (REC), lactate and non-esterified fatty acids (NEFAs) were measured. Maximal incremental tests were performed on a progressively loaded leg cycle ergometer.

RESULTS

There were no significant differences in terms of HR or BP at rest and maximum effort between the HPβ-CD-Ang-(1-7) and placebo groups. The VO2max showed significant differences (p = 0.04). It was higher in the Ang-(1-7)condition (66.15 mlO2.kg- 1.min- 1) compared to the placebo (60.72 mlO2.kg- 1.min- 1). This was also observed for TET (Ang-(1-7) 39.10 min vs. placebo 38.14 min; p = 0.04), MW (Ang-(1-7) 156.7 vs. placebo 148.2; p = 0.04), and at the lowest RPE (Ang-(1-7) vs. placebo; p = 0.009). No significant differences were observed for REC, NEFAs, or Lactate.

CONCLUSIONS

These results suggest that HPβ-CD-Ang-(1-7) improves the physical performance of MTB recreational athletes and could be a promising supplement.

TRIAL REGISTRATION

RBR-2 × 56pw8, registered January 15th, 2021. The study was prospectively registered.

ACE2/Ang-(1-7)/Mas1 axis and the vascular system: vasoprotection to COVID-19-associated vascular disease

The two axes of the renin-angiotensin system include the classical ACE/Ang II/AT1 axis and the counter-regulatory ACE2/Ang-(1-7)/Mas1 axis. ACE2 is a multifunctional monocarboxypeptidase responsible for generating Ang-(1-7) from Ang II. ACE2 is important in the vascular system where it is found in arterial and venous endothelial cells and arterial smooth muscle cells in many vascular beds. Among the best characterized functions of ACE2 is its role in regulating vascular tone. ACE2 through its effector peptide Ang-(1-7) and receptor Mas1 induces vasodilation and attenuates Ang II-induced vasoconstriction. In endothelial cells activation of the ACE2/Ang-(1-7)/Mas1 axis increases production of the vasodilator's nitric oxide and prostacyclin's and in vascular smooth muscle cells it inhibits pro-contractile and pro-inflammatory signaling. Endothelial ACE2 is cleaved by proteases, shed into the circulation and measured as soluble ACE2. Plasma ACE2 activity is increased in cardiovascular disease and may have prognostic significance in disease severity. In addition to its enzymatic function, ACE2 is the receptor for severe acute respiratory syndrome (SARS)-coronavirus (CoV) and SARS-Cov-2, which cause SARS and coronavirus disease-19 (COVID-19) respectively. ACE-2 is thus a double-edged sword: it promotes cardiovascular health while also facilitating the devastations caused by coronaviruses. COVID-19 is associated with cardiovascular disease as a risk factor and as a complication. Mechanisms linking COVID-19 and cardiovascular disease are unclear, but vascular ACE2 may be important. This review focuses on the vascular biology and (patho)physiology of ACE2 in cardiovascular health and disease and briefly discusses the role of vascular ACE2 as a potential mediator of vascular injury in COVID-19.

An update on ACE2 amplification and its therapeutic potential

The renin angiotensin system (RAS) plays an important role in the pathogenesis of variety of diseases. Targeting the formation and action of angiotensin II (Ang II), the main RAS peptide, has been the key therapeutic target for last three decades. ACE‐related carboxypeptidase (ACE2), a monocarboxypeptidase that had been discovered 20 years ago, is one of the catalytically most potent enzymes known to degrade Ang II to Ang‐(1‐7), a peptide that is increasingly accepted to have organ‐protective properties that oppose and counterbalance those of Ang II. In addition to its role as a RAS enzyme ACE2 is the main receptor for SARS‐CoV‐2. In this review, we discuss various strategies that have been used to achieve amplification of ACE2 activity including the potential therapeutic potential of soluble recombinant ACE2 protein and novel shorter ACE2 variants.

Angiotensin-(1-7): Translational Avenues in Cardiovascular Control

Despite decades of research and numerous treatment approaches, hypertension and cardiovascular disease remain leading global public health problems. A major contributor to regulation of blood pressure, and the development of hypertension, is the renin-angiotensin system. Of particular concern, uncontrolled activation of angiotensin II contributes to hypertension and associated cardiovascular risk, with antihypertensive therapies currently available to block the formation and deleterious actions of this hormone. More recently, angiotensin-(1-7) has emerged as a biologically active intermediate of the vasodilatory arm of the renin-angiotensin system. This hormone antagonizes angiotensin II actions as well as offers antihypertensive, antihypertrophic, antiatherogenic, antiarrhythmogenic, antifibrotic and antithrombotic properties. Angiotensin-(1-7) elicits beneficial cardiovascular actions through mas G protein-coupled receptors, which are found in numerous tissues pivotal to control of blood pressure including the brain, heart, kidneys, and vasculature. Despite accumulating evidence for favorable effects of angiotensin-(1-7) in animal models, there is a paucity of clinical studies and pharmacokinetic limitations, thus limiting the development of therapeutic agents to better understand cardiovascular actions of this vasodilatory peptide hormone in humans. This review highlights current knowledge on the role of angiotensin-(1-7) in cardiovascular control, with an emphasis on significant animal, human, and therapeutic research efforts.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

Kallikrein-kinin system as the dominant mechanism to counteract hyperactive renin-angiotensin system

The renin-angiotensin system (RAS) generates, maintains, and makes worse hypertension and cardiovascular diseases (CVDs) through its biologically active component angiotensin II (Ang II), that causes vasoconstriction, sodium retention, and structural alterations of the heart and the arteries. A few endogenous vasodilators, kinins, natriuretic peptides, and possibly angiotensin (1-7), exert opposite actions and may provide useful therapeutic agents. As endothelial autacoids, the kinins are potent vasodilators, active natriuretics, and protectors of the endothelium. Indeed, the kallikrein-kinin system (KKS) is considered the dominant mechanism for counteracting the detrimental effects of the hyperactive RAS. The 2 systems, RAS and KKS, are controlled by the angiotensin-converting enzyme (ACE) that generates Ang II and inactivates the kinins. Inhibitors of ACE can reduce the impact of Ang II and potentiate the kinins, thus contributing to restore the cardiovascular homeostasis. In the last 20 years, ACE-inhibitors (ACE-Is) have become the drugs of first choice for the treatments of the major CVDs. ACE-Is not only reduce blood pressure, as sartans also do, but by protecting and potentiating the kinins, they can reduce morbidity and mortality and improve the quality of life for patients with CVDs. This paper provides a brief review of the literature on this topic.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Vascular Actions of Angiotensin 1-7 in the Human Microcirculation: Novel Role for Telomerase

OBJECTIVE

This study examined vascular actions of angiotensin 1-7 (ANG 1-7) in human atrial and adipose arterioles.

APPROACH AND RESULTS

The endothelium-derived hyperpolarizing factor of flow-mediated dilation (FMD) switches from antiproliferative nitric oxide (NO) to proatherosclerotic hydrogen peroxide in arterioles from humans with coronary artery disease (CAD). Given the known vasoprotective properties of ANG 1-7, we tested the hypothesis that overnight ANG 1-7 treatment restores the NO component of FMD in arterioles from patients with CAD. Endothelial telomerase activity is essential for preserving the NO component of vasodilation in the human microcirculation; thus, we also tested whether telomerase activity was necessary for ANG 1-7-mediated vasoprotection by treating separate arterioles with ANG 1-7±the telomerase inhibitor 2-[[(2E)-3-(2-naphthalenyl)-1-oxo-2-butenyl1-yl]amino]benzoic acid. ANG 1-7 dilated arterioles from patients without CAD, whereas dilation was significantly reduced in arterioles from patients with CAD. In atrial arterioles from patients with CAD incubated with ANG 1-7 overnight, the NO synthase inhibitor NG-nitro-l-arginine methyl ester abolished FMD, whereas the hydrogen peroxide scavenger polyethylene glycol catalase had no effect. Conversely, in vessels incubated with ANG 1-7+2-[[(2E)-3-(2-naphthalenyl)-1-oxo-2-butenyl1-yl]amino]benzoic acid, NG-nitro-l-arginine methyl ester had no effect on FMD, but polyethylene glycol catalase abolished dilation. In cultured human coronary artery endothelial cells, ANG 1-7 significantly increased telomerase activity. These results indicate that ANG 1-7 dilates human microvessels, and dilation is abrogated in the presence of CAD. Furthermore, ANG 1-7 treatment is sufficient to restore the NO component of FMD in arterioles from patients with CAD in a telomerase-dependent manner.

CONCLUSIONS

ANG 1-7 exerts vasoprotection in the human microvasculature via modulation of telomerase activity.

Hemodynamic responses to angiotensin-(1-7) in women in their third trimester of pregnancy

BACKGROUND

To understand the role of Angiotensin-(1-7) (Ang-(1-7)) in vasculature of pregnant women, we compared cardiac output (CO), total peripheral resistance (TPR) and forearm blood flow (FBF) responses to Ang-(1-7) infusion between normotensive pregnant women in their third trimester and healthy age matched non-pregnant women. The responses of skin microcirculation to Ang-(1-7) were tested in preeclamptic, normotensive pregnant and non-pregnant women. Responses to Angiotensin II (Ang II) were also determined.

METHODS

Non-invasive methods for systemic (bioimpedance and VascuMAP), FBF (venous occlusion strain gauge plethysmography), and skin (laser Doppler) hemodynamics assessments were used.

RESULTS

Compared to non-pregnant women, systemic infusion of Ang-(1-7) (2000 pmol/min) resulted in a greater increase in CO (9.4 ± 6.4 versus -3.3 ± 2.1%, n = 9-10) in normotensive pregnant women. Brachial local infusion of Ang-(1-7) had no effect on FBF in either group. In non-pregnant and normotensive pregnant women, local Ang II induced a dose-dependent decrease in FBF and increase in forearm resistance at 50 and 100 pmol/min (p < 0.05 versus corresponding baseline, n = 7-10). Following iontophoretic application of 5 mmol/l dose of Ang-(1-7), the change in skin flow was higher in normotensive pregnant versus preeclamptic women (182.5 ± 93 versus 15.76 ± 19.46%, n = 14-15). Skin flow was lower in normotensive pregnant versus preeclamptic women (-46.5 ± 48.7 versus 108.7 ± 49.1%, n = 14-15) following Ang II infusion at 1.0 pmol/min.

CONCLUSION

In the third trimester of pregnancy, Ang-(1-7) induces alterations in CO and differentially regulates micro- and macro-circulations, depending on the dose. Dysregulation in skin vasculature may contribute to the development of vascular dysfunction and hypertension in preeclampsia.

A systematic review to investigate whether Angiotensin-(1-7) is a promising therapeutic target in human heart failure

Context. Heart failure (HF) is a common condition causing much morbidity and mortality despite major advances in pharmacological and device therapies. Preclinical data suggest a cardioprotective role of Angiotensin-(1-7) in animal models of HF. Objective. Perform a systematic review on the effects of Angiotensin-(1-7) on humans, focusing on HF. Results. 39 studies were included in the review (4 in human HF and (35) in non-HF patients). There is only one intervention study on 8 patients with human HF, using Angiotensin-(1-7), with forearm blood flow (FBF) as the endpoint. Angiotensin-(1-7) caused no significant effect on FBF in this HF study but caused vasodilation in 3 out of 4 non-HF studies. In one other non-HF study, Angiotensin-(1-7) infusion led to a significant increase in blood pressure in normal men; however, effects were <0.03% that of angiotensin II. Cardioprotective effects seen in non-HF studies include for instance beneficial actions against atherosclerosis and myocardial fibrosis. Conclusions. The main finding of our systematic review is that Angiotensin-(1-7) plays an important cardioprotective role in HF in animals and in patients without heart failure. More research is required to test the hypothesis that Angiotensin-(1-7) benefits patients with heart failure.

Chronic angiotensin-(1-7) prevents cardiac fibrosis in DOCA-salt model of hypertension

Cardiac remodeling is a hallmark hypertension-induced pathophysiology. In the current study, the role of the angiotensin-(1-7) fragment in modulating cardiac remodeling was examined. Sprague-Dawley rats underwent uninephrectomy surgery and were implanted with a deoxycorticosterone acetate (DOCA) pellet. DOCA animals had their drinking water replaced with 0.9% saline solution. A subgroup of DOCA-salt animals was implanted with osmotic minipumps, which delivered angiotensin-(1-7) chronically (100 ng.kg(-1).min(-1)). Control animals underwent sham surgery and were maintained on normal drinking water. Blood pressure was measured weekly with the use of the tail-cuff method, and after 4 wk of treatment, blood pressure responses to graded doses of angiotensin II were determined by direct carotid artery cannulation. Ventricle size was measured, and cross sections of the heart ventricles were paraffin embedded and stained using Masson's Trichrome to measure interstitial and perivascular collagen deposition and myocyte diameter. DOCA-salt treatment caused significant increases in blood pressure, cardiac hypertrophy, and myocardial and perivascular fibrosis. Angiotensin-(1-7) infusion prevented the collagen deposition effects without any effect on blood pressure or cardiac hypertrophy. These results indicate that angiotensin-(1-7) selectively prevents cardiac fibrosis independent of blood pressure or cardiac hypertrophy in the DOCA-salt model of hypertension.

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.

Cardiovascular actions of angiotensin-(1-7)

Angiotensin-(1-7) (Ang-(1-7)) is now considered to be a biologically active member of the renin-angiotensin system. The functions of Ang-(1-7) are often opposite to those attributed to the main effector component of the renin-angiotensin system, Ang II. Chronic administration of angiotensin-converting enzyme inhibitors (ACEI) increases 10- to 25-fold the plasma levels of this peptide, suggesting that part of the beneficial effects of ACEI could be mediated by Ang-(1-7). Ang-(1-7) can be formed from Ang II or directly from Ang I. Other enzymatic pathways for Ang-(1-7) generation have been recently described involving the novel ACE homologue ACE2. This enzyme can form Ang-(1-7) from Ang II or less efficiently by the hydrolysis of Ang I to Ang-(1-9) with subsequent Ang-(1-7) formation. The biological relevance of Ang-(1-7) has been recently reinforced by the identification of its receptor, the G-protein-coupled receptor Mas. Heart and blood vessels are important targets for the formation and actions of Ang-(1-7). In this review we will discuss recent findings concerning the biological role of Ang-(1-7) in the heart and blood vessels, taking into account aspects related to its formation and effects on these tissues. In addition, we will discuss the potential of Ang-(1-7) and its receptor as a target for the development of new cardiovascular drugs.

Angiotensin-(1-7) antagonist A-779 attenuates the potentiation of bradykinin by captopril in rats

We evaluated the possibility that endogenous angiotensin-(1-7) [Ang-(1-7)] could participate in the potentiation of bradykinin (BK) by the angiotensin-converting enzyme inhibitor (ACEI) captopril in conscious Wistar rats. Catheters were introduced into descending aorta (through the left carotid artery) for BK injection, femoral artery for arterial pressure measurement, and both femoral veins for BK injection and vehicle or Ang-(1-7) antagonist, A-779 infusion. Infusion of vehicle or A-779 started 40 to 45 minutes after captopril administration. Sequential BK dose-response curves were made before, 10 minutes after captopril, and within 10 minutes of infusion of vehicle or A-779. To evaluate angiotensin I conversion, dose-response curves for angiotensin I and angiotensin II were made following the same protocol used for BK. Captopril treatment markedly increased the BK hypotensive effect and significantly decreased angiotensin I conversion. Infusion of A-779 did not modify the angiotensin II pressor effect or the effect of captopril on angiotensin I conversion. However, A-779 significantly reduced the potentiating effect of captopril on the hypotensive effect of BK administered intravenously or intra-arterially. These results suggest that endogenous Ang-(1-7) and/ or an Ang-(1-7)-related peptide plays an important role in the BK potentiation by ACEI through a mechanism not dependent upon inhibition of ACE hydrolytic activity.

Endothelial release of tissue-type plasminogen activator in the human forearm: role of nitric oxide

Release of tissue-type plasminogen activator (t-PA) from the vascular endothelium is paramount to endogenous thrombolysis potential. In addition to its vasodilator effects, nitric oxide (NO) has important antithrombotic properties, such as inhibition of platelet aggregation. It is currently not clear whether NO influences the capacity of the endothelium to release t-PA. The authors determined whether net endothelial t-PA release is regulated, at least in part, by NO. Endothelial t-PA release was determined, in vivo, in response to intrabrachial infusions of bradykinin (12.5-50.0 ng.100 mL tissue-1.min-1) in the presence and absence of the NO synthase inhibitor, NG-monomethyl-l-arginine (l-NMMA; 5 mg/min) in 12 healthy men. Net release of t-PA across the forearm vascular bed was calculated as the product of arteriovenous concentration gradient and forearm plasma flow. The vasodilator response to bradykinin was significantly blunted ( approximately 30%) with l-NMMA. Although there was no effect of l-NMMA on basal t-PA release, acute release of t-PA to bradykinin was higher (P < 0.01) after (from -0.2 +/- 0.5 to 105.2 +/- 9.4 ng.100 mL tissue-1.min-1) versus before (from -0.4 +/- 0.7 to 48.7 +/- 7.3 ng.100 mL tissue-1.min-1) the administration of l-NMMA. Thus, in the absence of NO endothelial t-PA release was enhanced. These results suggest a potential regulatory influence of NO on bradykinin induced endothelial t-PA release.

Angiotensin-(1-7) inhibits angiotensin II-induced signal transduction

The inhibitory effects of angiotensin-(1-7) on angiotensin II-induced vasoconstriction, growth of vascular smooth muscle cells, stimulation of protein kinase C, extracellular signal-regulated kinases (ERK), and angiotensin subtype 1 receptor (AT1) and subtype 2 receptor (AT2) mRNA expression were investigated. The hemodynamic effects of angiotensin-(1-7) were measured in Wistar rats. Vasoconstriction was measured using aortic rings. DNA synthesis or protein synthesis was measured in cultured vascular smooth muscle cells using [3H] thymidine or [3H] leucine incorporation, respectively. Angiotensin II stimulated protein kinase C and ERK1/2 were measured by Western blot analysis using phosphospecific protein kinase C and ERK1/2 antibodies. AT1 and AT2 receptor mRNA expression was measured using reverse-transcription polymerase chain reaction. Infusion of angiotensin II significantly increased whereas infusion of angiotensin-(1-7) had no effects on mean arterial blood pressure in Wistar rats. Angiotensin-(1-7) dose-dependently showed partial antagonism on angiotensin II-induced contraction of aortic rings. Angiotensin-(1-7) showed partial antagonism on angiotensin II-induced DNA synthesis and protein synthesis. Angiotensin-(1-7) showed partial antagonism on angiotensin II-induced activation of protein kinase C and ERK1/2. The administration of angiotensin-(1-7) showed partial antagonism on angiotensin II-induced downregulation of AT1 receptor mRNA expression, whereas AT2 receptor mRNA expression was unchanged. Angiotensin-(1-7) showed partial antagonism on angiotensin II-induced intracellular signal transduction and may play a crucial role in the adaptation process of AT1 receptors to sustained stimulation of angiotensin II.

In vivo release of tissue-type plasminogen activator antigen from the human brachial artery

The rate of secretion of t-PA from vascular endothelial cells has been proposed as a good marker of endothelial function. Our aim was to measure the rate of in vivo t-PA antigen release from the human brachial artery and not from the combined vascular pool of the upper extremity. In 10 healthy male volunteers, we have occluded the forearm by a sphygmomanometer cuff for 5-7 min in order to reduce the blood flow in the brachial artery. Arterial blood samples were taken from the cubital artery above the occlusion and from the contralateral artery that served as the control. The arterial t-PA antigen concentrations were significantly higher after forearm occlusion than in the non-occluded contralateral arteries: median 3.3 (range between first and third quartile 2.1-3.6) vs. 2.5 (2.0-3.2) ng/ml, p=0.03. The PAI-1 antigen concentrations did not change significantly: 6.9 (2.3-18.6) ng/ml in the contralateral artery vs. 5.4 (1.8-8.0) ng/ml after occlusion, p=0.09. The average forward blood flow in the distal 15 cm of the brachial artery that was measured by duplex ultrasound decreased from 107 (97-118) ml/min at baseline to 25 ml/min (19-33) ml/min during occlusion. The release rate of circulating t-PA antigen was calculated as the product of the increment in arterial t-PA concentration and the average plasma flow in the arterial segment of interest with a volume of 2 ml. The median release rate of t-PA antigen under conditions of reduced blood flow in the brachial artery was 3.3 (1.1-11.5) ng/min. We conclude that the secretion of t-PA antigen from arterial endothelium of healthy subjects is substantial, whereas the arterial wall is not an important source of PAI-1 in vivo.

Biological properties of the angiotensin peptides other than angiotensin II: implications for hypertension and cardiovascular diseases

Several peptides of the RAS other than angiotensin (1-8) have been identified. They are generally referred as 'angiotensin fragments': Ang (2-8), Ang (3-8) and Ang (1-7) and have been detected in human tissues. There is evidence that they may play a functional role in humans by acting in concert with angiotensin (1-8) and aldosterone. Available knowledge on the pathways leading to synthesis and degradation of angiotensin fragments, as well as on their interactions with receptors and on their possible role in cardiovascular homeostasis and disease are reviewed.

The angiotensin-converting enzyme gene family: genomics and pharmacology

Modulation of the renin-angiotensin system (RAS), and particularly inhibition of angiotensin-converting enzyme (ACE), a zinc metallopeptidase, has long been a prime strategy in the treatment of hypertension. However, other angiotensin metabolites are gaining in importance as our understanding of the RAS increases. Recently, genomic approaches have identified the first human homologue of ACE, termed ACEH (or ACE2). ACEH differs in specificity and physiological roles from ACE, which opens a potential new area for discovery biology. The gene that encodes collectrin, a homologue of ACEH, is upregulated in response to renal injury. Collectrin lacks a catalytic domain, which indicates that there is more to ACE-like function than simple peptide hydrolysis.

Multiple interactions between the renin-angiotensin and the kallikrein-kinin systems: role of ACE inhibition and AT1 receptor blockade

The investigation of therapeutic actions of angiotensin type 1 (AT1) receptor antagonists and ACE inhibitors (ACEI) demonstrated complex interactions between the renin-angiotensin system (RAS) and the kallikrein-kinin system (KKS) in several experimental and clinical studies. They are evidenced by the fact that (1) ACE efficiently catabolizes kinins; (2) angiotensin-derivatives such as ANG-(1-7) exert kininlike effects; and (3) kallikrein probably serves as a prorenin-activating enzyme. (4) Several authors have demonstrated experimentally that the protective effects of ACEI are at least partly mediated by a direct potentiation of kinin receptor response on BK stimulation. (5) Furthermore, studies on AT1 antagonists, which do not directly influence kinin degradation, and studies on angiotensin-receptor transgenic mice have revealed additional interactions between the RAS and the KKS. There is mounting evidence that an autocrine cascade including kinins, nitric oxide, prostaglandins, and cyclic GMP is involved in at least some of the angiotensin type 2 receptor effects. This review discusses multiple possibilities of cross-talks between the RAS and KKS in vascular and cardiac physiology and pathology after ACE inhibition and AT1 receptor blockade.

Angiotensin(1-7) potentiates bradykinin-induced vasodilatation in man

BACKGROUND

It has been clearly demonstrated that angiotensin(1-7) potentiates the vasodilating effect of bradykinin in isolated vessels of animals.

OBJECTIVE

To investigate the interaction between angiotensin(1-7) Ang(1-7) and bradykinin in human forearm resistant vessels of normotensive healthy men in vivo, by the measurement of forearm blood flow using venous occlusion, strain-gauge plethysmography with intra-arterial infusions of peptides in a placebo-controlled, double-blind, cross-over design.

METHODS

In eight men, bradykinin was infused intra-arterially twice; placebo, Ang(1-7), or angiotensin II was co-infused with the second infusion. The effect of inhibition of nitric oxide synthase on the interaction between Ang(1-7) and bradykinin was also tested in eight other individuals. The effects of Ang(1-7) were analyzed by analysis of variance (ANOVA) and by the ratios of individually derived areas under the dose-response curves (AUC) of bradykinin, adjusted for changes in the AUCs by repeated infusions of bradykinin with placebo.

RESULTS

Ang(1-7) (1000 pmol/min) significantly potentiated the vasodilating effect of bradykinin compared with the effect of saline (P = 0.0471, ANOVA) and in a dose-dependent manner (adjusted AUC ratio [95% confidence interval (CI)] 2.75 (1.72 to 3.78) with 1000 pmol/min, 1.62 (1.31 to 1.93) with 100 pmol/min, and 0.98 (0.80, to 1.09) with 10 pmol/min). This effect was completely abolished by co-infusion of NG-monomethyl-l-arginine [AUC ratio 0.98 (0.90 to 1.04)]. Ang(1-7) did not affect the vasodilating effects of either acetylcholine or sodium nitroprusside.

CONCLUSIONS

Ang(1-7) potentiates the vasodilating effect of bradykinin, possibly through a mechanism(s) involving nitric oxide release, in human forearm resistance vessels.