Manipulating the angiotensin system – new approaches to the treatment of solid tumours

Angiotensin II (Ang II), a main effector peptide in the renin–angiotensin system (RAS), plays a fundamental role as a vasoconstrictor in controlling cardiovascular function and renal homeostasis. Ang II also acts as a growth promoter or angiogenic factor via type 1 angiotensin II receptors (AT₁Rs) in certain tumour cell lines. Recent studies have shown the activation of the local RAS in various tumour tissues, including the abundant generation of Ang II by angiotensin-converting enzyme (ACE) and the upregulation of AT₁R expression. Thus, considerable attention has been paid to the role of the RAS in cancer and its blockade as a new approach to the treatment of cancer. There is increasing evidence that the Ang II–AT₁R system is involved in tumour growth, angiogenesis and metastasis in experimental models, suggesting the therapeutic potential of an ACE inhibitor and AT₁R blocker, both of which have been used as antihypertensive drugs. In addition, specific Ang II-degrading enzymes are expressed in tumours and play a regulatory role in cell proliferation and invasion. This review focuses on the role of the Ang II–AT₁R system in solid tumours, particularly in the progression of gynaecological cancer, and presents the clinical potential of manipulating the angiotensin system as a novel and promising strategy for cancer treatment.     

Angiotensin 1‐7 protects against ventilator‐induced diaphragm dysfunction

Mechanical ventilation (MV) is a life‐saving instrument used to provide ventilatory support for critically ill patients and patients undergoing surgery. Unfortunately, an unintended consequence of prolonged MV is the development of inspiratory weakness due to both diaphragmatic atrophy and contractile dysfunction; this syndrome is labeled ventilator‐induced diaphragm dysfunction (VIDD). VIDD is clinically important because diaphragmatic weakness is an important contributor to problems in weaning patients from MV. Investigations into the pathogenesis of VIDD reveal that oxidative stress is essential for the rapid development of VIDD as redox disturbances in diaphragm fibers promote accelerated proteolysis. Currently, no standard treatment exists to prevent VIDD and, therefore, developing a strategy to avert VIDD is vital. Guided by evidence indicating that activation of the classical axis of the renin‐angiotensin system (RAS) in diaphragm fibers promotes oxidative stress and VIDD, we hypothesized that activation of the nonclassical RAS signaling pathway via angiotensin 1‐7 (Ang1‐7) will protect against VIDD. Using an established animal model of prolonged MV, our results disclose that infusion of Ang1‐7 protects the diaphragm against MV‐induced contractile dysfunction and fiber atrophy in both fast and slow muscle fibers. Further, Ang1‐7 shielded diaphragm fibers against MV‐induced mitochondrial damage, oxidative stress, and protease activation. Collectively, these results reveal that treatment with Ang1‐7 protects against VIDD, in part, due to diminishing oxidative stress and protease activation. These important findings provide robust evidence that Ang1‐7 has the therapeutic potential to protect against VIDD by preventing MV‐induced contractile dysfunction and atrophy of both slow and fast muscle fibers.

Study Highlights

• WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC?

Prolonged mechanical ventilation results in ventilator‐induced diaphragm dysfunction (VIDD). This is significant because VIDD is a major risk factor for problems in weaning patients from the ventilator. Currently, no standard treatment exists to prevent VIDD. However, emerging evidence reveals that pharmacological inhibition of the classical axis of the renin‐angiotensin system (RAS) protects against VIDD. Although angiotensin 1‐7 (Ang1‐7) activates the nonclassical arm of the RAS and antagonizes classical RAS signaling, the therapeutic potential of Ang1‐7 to protect against VIDD remains unknown.

• WHAT QUESTION DID THIS STUDY ADDRESS?

Is Ang1‐7 a viable therapy to prevent VIDD?

• WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE?

Treatment of animals with Ang1‐7 protected the diaphragm against both MV‐induced diaphragmatic contractile dysfunction and fiber atrophy. Importantly, Ang1‐7 protected against MV‐induced atrophy of both fast and slow‐type fibers and contractile dysfunction.

• HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE?

These new findings provide a foundation for future testing of Ang1‐7, a potential therapy to protect against VIDD.     

Liver fibrosis: a balance of ACEs?

There is an increasing body of evidence to suggest that the RAS (renin-angiotensin system) contributes to tissue injury and fibrosis in chronic liver disease. A number of studies have shown that components of a local hepatic RAS are up-regulated in fibrotic livers of humans and in experimental animal models. Angiotensin II, the main physiological effector molecule of this system, mediates liver fibrosis by stimulating fibroblast proliferation (myofibroblast and hepatic stellate cells), infiltration of inflammatory cells, and the release of inflammatory cytokines and growth factors such as TGF (transforming growth factor)-beta1, IL (interleukin)-1beta, MCP (monocyte chemoattractant protein)-1 and connective tissue growth factor. Furthermore, blockade of the RAS by ACE (angiotensin-converting enzyme) inhibitors and angiotensin type 1 receptor antagonists significantly attenuate liver fibrosis in experimental models of chronic liver injury. In 2000 ACE2 (angiotensin-converting enzyme 2), a human homologue of ACE, was identified. ACE2 efficiently degrades angiotensin II to angiotensin-(1-7), a peptide which has recently been shown to have both vasodilatory and tissue protective effects. This suggests that ACE2 and its products may be part of an alternate enzymatic pathway in the RAS, which counterbalances the generation and actions of angiotensin II, the ACE2-angiotensin-(1-7)-Mas axis. This review focuses on the potential roles of the RAS, angiotensin II and ACE2 in chronic liver injury and fibrogenesis.     

运动训练对慢性心力衰竭大鼠循环血液及骨骼肌肾素-血管紧张素系统的影响

目的 观察运动训练对慢性心力衰竭（CHF）大鼠循环血液及骨骼肌肾素-血管紧张素系统（RAS）的影响。 方法 采用随机数字表法将50只雄性Wistar大鼠分为安静对照组、运动对照组、模型安静组及模型运动组。将模型安静组及模型运动组大鼠制成CHF动物模型,安静对照组及运动对照组给予假手术处理。运动对照组及模型运动组大鼠均进行8周跑台运动,每周运动5次。于干预8周后采用荧光底物法测定大鼠血浆和比目鱼肌血管紧张素转换酶（ACE）及ACE2活性,采用高效液相色谱法检测血浆和比目鱼肌血管紧张素Ⅱ（AngⅡ）及Ang(1-7)含量,采用Western blot法检测大鼠骨骼肌中AngⅡ 1型受体（AT1R）及Mas受体（MasR）蛋白表达情况。 结果 与安静对照组比较,模型安静组血浆ACE活性升高、ACE2活性下降（P<0.05）,模型运动组血浆AngⅡ含量和ACE活性均降低（P<0.05）,Ang-(1-7)/AngⅡ比值升高（P<0.05）;与模型安静组比较,模型运动组ACE活性和血浆AngⅡ含量均降低（P<0.05）,ACE2活性升高（P<0.05）。与安静对照组比较,模型安静组比目鱼肌AngⅡ含量和AT1R蛋白表达量均升高（P<0.05）,模型运动组比目鱼肌MasR蛋白表达量升高（P<0.05）;与模型安静组比较,模型运动组比目鱼肌AngⅡ含量和AT1R蛋白表达量均降低（P<0.05）,Ang-(1-7)/AngⅡ比值升高（P<0.05）。 结论 运动训练能诱导CHF大鼠RAS由ACE-AngⅡ-AT1R轴向ACE2-Ang-(1-7)-MasR轴方向转换,并且血浆、骨骼肌中RAS各组分变化特点各异。     

Manipulating the angiotensin system--new approaches to the treatment of solid tumours

Angiotensin II (Ang II), a main effector peptide in the renin-angiotensin system (RAS), plays a fundamental role as a vasoconstrictor in controlling cardiovascular function and renal homeostasis. Ang II also acts as a growth promoter or angiogenic factor via type 1 angiotensin II receptors (AT1Rs) in certain tumour cell lines. Recent studies have shown the activation of the local RAS in various tumour tissues, including the abundant generation of Ang II by angiotensin-converting enzyme (ACE) and the upregulation of AT1R expression. Thus, considerable attention has been paid to the role of the RAS in cancer and its blockade as a new approach to the treatment of cancer. There is increasing evidence that the Ang II-AT1R system is involved in tumour growth, angiogenesis and metastasis in experimental models, suggesting the therapeutic potential of an ACE inhibitor and AT1R blocker, both of which have been used as antihypertensive drugs. In addition, specific Ang II-degrading enzymes are expressed in tumours and play a regulatory role in cell proliferation and invasion. This review focuses on the role of the Ang II-AT1R system in solid tumours, particularly in the progression of gynaecological cancer, and presents the clinical potential of manipulating the angiotensin system as a novel and promising strategy for cancer treatment.     

Angiotensin II mediates high glucose-induced TGF-beta1 and fibronectin upregulation in HPMC through reactive oxygen species.

OBJECTIVE: To demonstrate the presence of an independent renin-angiotensin system (RAS) in the peritoneum and to determine the role of locally produced angiotensin (Ang) II in high glucose-induced upregulation of transforming growth factor (TGF)-beta1 and fibronectin by human peritoneal mesothelial cells (HPMC). METHODS: In cultured HPMC, the expression of mRNAs for angiotensinogen, angiotensin-converting enzyme (ACE), Ang II type 1 receptor (AT1), and TGF-beta1 was evaluated by real-time polymerase chain reaction; ACE, AT1, and fibronectin proteins by Western blot analysis; and Ang I, Ang II, and TGF-beta1 proteins by ELISA. Dichlorofluorescein (DCF)-sensitive cellular reactive oxygen species (ROS) were measured by fluorometry. RESULTS: HPMC constitutively expressed all the components of RAS, and 50 mmol/L D-glucose (high glucose) significantly increased angiotensinogen, ACE, and AT1 mRNAs and ACE, AT1, and Ang II proteins. Ang II increased TGF-beta1 and fibronectin protein expression and DCF-sensitive cellular ROS. Losartan prevented Ang II-induced increase in cellular ROS. Both losartan and captopril inhibited high glucose-induced upregulation of TGF-beta1 and fibronectin expression in HPMC in a dose-dependent manner. Antioxidant catalase and NADPH oxidase inhibitor diphenyleneiodinium effectively inhibited Ang II-induced TGF-beta1 and fibronectin protein expression. CONCLUSIONS: The present data demonstrate that HPMC constitutively express RAS, that Ang II produced by HPMC mediates high glucose-induced upregulation of TGF-beta1 and fibronectin expression, and that Ang II-induced TGF-beta1 and fibronectin expression in HPMC is mediated by NADPH oxidase-dependent ROS. These data suggest that locally produced Ang II and ROS in the peritoneum may be potential therapeutic targets in peritoneal fibrosis during long-term peritoneal dialysis.     

Pathological roles of angiotensin II produced by mast cell chymase and the effects of chymase inhibition in animal models

The discovery of a new angiotensin II (Ang II) pathway generated by mast cell chymase has highlighted new biological functions for Ang II that is not related to the classic renin-angiotensin system (RAS). The conversion of Ang I to II occurs not only via the plasma angiotensin converting enzyme (ACE) or tissue ACE but also via chymase produced in the mast cells of humans, monkeys, dogs, and hamsters. The conversion by chymase has been especially found in morbid tissues following the migration of mast cells. The newly discovered functions of chymase are discussed in this review. During the vascular narrowing that occurs after vein grafting or balloon injury in dogs, chymase activity and Ang II concentrations along with intimal proliferation are significantly increased and chymase inhibitors completely suppressed these increase, though ACE inhibitors are ineffective. Similar results have also been confirmed in the dog arteriovenous fistula stenosis model. In both human and animal aneurysmal aortas, chymase activity is significantly increased, and chymase inhibitor has been shown to prevent the development of aneurysms in dogs. Chymase is activated in diseased hearts, and chymase inhibitors reduce both the mortality rates after acute myocardial infarction and the cardiac fibrosis that leads to the development of cardiomyopathy in hamsters. Chymase is also a pro-angiogenic factor, since the injection of chymase strongly facilitates angiogenesis in hamsters. We propose that chymase inhibitors are effective in the prevention of multiple cardiovascular disorders, especially at the local event level without any effect on the systemic blood pressure.     

Angiotensin inhibition stimulates PPARγ and the release of visfatin

Background Angiotensin converting enzyme inhibitors (ACE‐I) and angiotensin receptor blockers (ARB) exhibit beneficial antidiabetic effects in patients with type 2 diabetes independent of their blood pressure‐lowering effects. Some antidiabetic properties of ARB and ACE‐I might by exerted by activation of peroxisome proliferator‐activated receptor gamma (PPARγ). However, it is not clear whether this action is drug specific. Materials and methods The binding affinity of telmisartan, valsartan, lisinopril, rosiglitazone and angiotensin II to PPARγ was assessed in a cell‐free assay system. PPARγ signalling was studied in isolated skeletal muscle cells using Western blot analysis of phosphorylated protein kinase B (pAKT) and phosphorylated insulin like growth factor‐1 receptor (pILGF‐1R). Further, the ability of the drugs under study to stimulate the release of the adipocytokine visfatin was investigated in isolated human adipocytes, skeletal muscle cells, and umbilical vein endothelial cells (HUVEC). Results The binding affinity to PPARγ was highest for telmisartan with a half‐maximal effective concentration of 463 nM, followed by lisinopril (2·9 µM) and valsartan (6·2 µM). In skeletal muscle cells phosphorylation of ILGF‐1R was 2‐fold increased after incubation with telmisartan or valsartan and 1·7‐fold with lisinopril. pAKT expression was enhanced after incubation with telmisartan, valsartan and with lisinopril. The release of visfatin from adipocytes was 1·6‐fold increased after treatment with lisinopril and about 2·0‐fold increased with telmisartan and valsartan. Similar results were obtained in skeletal muscle cells and HUVEC. Conclusions Our data confirm agonism of telmisartan, valsartan and lisinopril on PPARγ. Pharmacokinetic differences may explain different potencies of PPARγ stimulation by drugs acting on the renin‐angiotensin system in clinical settings.     

ACE2 and Ang-(1-7) Confer Protection Against Development of Diabetic Retinopathy

Despite evidence that hyperactivity of the vasodeleterious axis (ACE/angiotensin II (Ang II)/AT1 receptor) of the renin–angiotensin system (RAS) is associated with the pathogenesis of diabetic retinopathy (DR) use of the inhibitors of this axis has met with limited success in the control of this pathophysiology. We investigated the hypothesis that enhancing the local activity of the recently established protective axis of the RAS, ACE2/Ang-(1-7), using adeno-associated virus (AAV)-mediated gene delivery of ACE2 or Ang-(1-7) would confer protection against diabetes-induced retinopathy. Genes expressing ACE2 and Ang-(1-7) were cloned in AAV vector. The effects of ocular AAV-ACE2/Ang-(1-7) gene transfer on DR in diabetic eNOS^−/− mice and Sprague–Dawley (SD) rats were examined. Diabetes was associated with approximately tenfold and greater than threefold increases in the ratios of ACE/ACE2 and AT1R/Mas mRNA levels in the retina respectively. Intraocular administration of AAV-ACE2/Ang-(1-7) resulted in significant reduction in diabetes-induced retinal vascular leakage, acellular capillaries, infiltrating inflammatory cells and oxidative damage in both diabetic mice and rats. Our results demonstrate that DR is associated with impaired balance of retinal RAS. Increased expression of ACE2/Ang-(1-7) overcomes this imbalance and confers protection against DR. Thus, strategies enhancing the protective ACE2/Ang-(1-7) axis of RAS in the eye could serve as a novel therapeutic target for DR.     

Analysis of responses to angiotensin I (3-10) and Leu3 angiotensin (3-8) in the pulmonary vascular bed of the cat

Pulmonary vascular responses to angiotensin (3-8) (Ang IV), leu3 angiotensin (3-8) (LeuAng IV), an Ang IV analog and angiotensin I (3-10) [Ang I (3-10)], the precursor for Ang IV, were investigated in the intact-chest cat under conditions of controlled blood flow. Intralobar injections of Ang IV, LeuAng IV, and Ang I (3-10) caused dosage-related increases in lobar arterial pressure. When responses were compared, Ang IV, LeuAng IV, and Ang I (3-10) were equipotent and were approximately 100- to 300-fold less potent than Ang II when dosages are expressed on a nanomolar basis. DuP 753, an angiotensin II type 1 (AT1 ) receptor antagonist, attenuated pulmonary vasoconstrictor responses to LeuAng IV, Ang IV, and its precursor, Ang I (3-10), but did not significantly change pressor responses to serotonin, norepinephrine, or U46619. PD 123319, an angiotensin II type 2 (AT2 ) receptor antagonist, and WSU 3033, a putative angiotensin II type 4 (AT4 ) receptor antagonist, did not significantly change pressor responses to LeuAng IV, Ang IV, and its precursor, Ang I (3-10). Captopril, an angiotensin-converting enzyme (ACE) inhibitor, decreased pulmonary vasoconstrictor responses to Ang I (3-10) but did not significantly change responses to serotonin, norepinephrine, U46619, LeuAng IV, or Ang IV. These data show that LeuAng IV, Ang IV, and its precursor, Ang I (3-10), increase pulmonary vascular resistance by activating AT1 receptors, and that Ang I (3-10) is rapidly and efficiently converted by an ACE-dependent pathway into an active peptide. The present data suggest that Ang IV and LeuAng IV increase pulmonary vascular resistance by activating AT1 receptors and that activation of AT2 or AT4 are not involved in mediating or modulating responses to these peptides. These data provide support for the hypothesis that Ang I (3-10) is converted into an active peptide by ACE at or near the site of action within the pulmonary vascular bed.     

Renin-angiotensin system blockade: a novel therapeutic approach in chronic obstructive pulmonary disease

ACE (angiotensin-converting enzyme) inhibitors and ARBs (angiotensin II receptor blockers) are already widely used for the treatment and prevention of cardiovascular disease and their potential role in other disease states has become increasingly recognized. COPD (chronic obstructive pulmonary disease) is characterized by pathological inflammatory processes involving the lung parenchyma, airways and vascular bed. The aim of the present review is to outline the role of the RAS (renin-angiotensin system) in the pathogenesis of COPD, including reference to results from fibrotic lung conditions and pulmonary hypertension. The review will, in particular, address the emerging evidence that ACE inhibition could have a beneficial effect on skeletal muscle function and cardiovascular co-morbidity in COPD patients. The evidence to support the effect of RAS blockade as a novel therapeutic approach in COPD will be discussed.     

Circulating angiotensin converting enzyme 2 and COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has triggered a widespread outbreak since December 2019. The SARS-CoV-2 infection-related illness has been dubbed the coronavirus disease 2019 (COVID-19) by the World Health Organization. Asymptomatic and subclinical infections, a severe hyper-inflammatory state, and mortality are all examples of clinical signs. After attaching to the angiotensin converting enzyme 2 (ACE2) receptor, the SARS-CoV-2 virus can enter cells through membrane fusion and endocytosis. In addition to enabling viruses to cling to target cells, the connection between the spike protein (S-protein) of SARS-CoV-2 and ACE2 may potentially impair the functionality of ACE2. Blood pressure is controlled by ACE2, which catalyzes the hydrolysis of the active vasoconstrictor octapeptide angiotensin (Ang) II to the heptapeptide Ang-(1-7) and free L-Phe. Additionally, Ang I can be broken down by ACE2 into Ang-(1-9) and metabolized into Ang-(1-7). Numerous studies have demonstrated that circulating ACE2 (cACE2) and Ang-(1-7) have the ability to restore myocardial damage in a variety of cardiovascular diseases and have anti-inflammatory, antioxidant, anti-apoptotic, and anti-cardiomyocyte fibrosis actions. There have been some suggestions for raising ACE2 expression in COVID-19 patients, which might be used as a target for the creation of novel treatment therapies. With regard to this, SARS-CoV-2 is neutralized by soluble recombinant human ACE2 (hrsACE2), which binds the viral S-protein and reduces damage to a variety of organs, including the heart, kidneys, and lungs, by lowering Ang II concentrations and enhancing conversion to Ang-(1-7). This review aims to investigate how the presence of SARS-CoV-2 and cACE2 are related. Additionally, there will be discussion of a number of potential therapeutic approaches to tip the ACE/ACE-2 balance in favor of the ACE-2/Ang-(1-7) axis.     

Chronic blockade of AT2-subtype receptors prevents the effect of angiotensin II on the rat vascular structure.

Angiotensin II (Ang II) is both a vasoactive and a potent growth-promoting factor for vascular smooth muscle cells. Little is known about the in vivo contribution of AT1 and AT2 receptor activation to the biological action of Ang II. Therefore, we investigated the effect of AT1 or AT2 subtype receptor chronic blockade by losartan or PD123319 on the vascular hypertrophy in rats with Ang II-induced hypertension. Normotensive rats received for 3 wk subcutaneous infusions of Ang II (120 ng/kg per min), or Ang II + PD 123319 (30 mg/kg per d), or Ang II + losartan (10 mg/kg per d) or PD 123319 alone, and were compared with control animals. In normotensive animals, chronic blockade of AT2 receptors did not affect the plasma level of angiotensin II and the vascular reactivity to angiotensin II mediated by the AT1 receptor. Chronic blockade of AT1I in rats receiving Ang II resulted in normal arterial pressure, but it induced significant aortic hypertrophy and fibrosis. Chronic blockade of AT2 receptors in Ang II-induced hypertensive rats had no effect on arterial pressure, but antagonized the effect of Ang II on arterial hypertrophy and fibrosis, suggesting that in vivo vasotrophic effects of Ang II are at least partially mediated via AT2 subtype receptors.     

Multiple pathways of angiotensin I conversion and their functional role in the canine penile corpus cavernosum.

Multiple pathways of angiotensin (Ang) I conversion and their functional role in the canine penile corpus cavernosum were investigated. Biochemical analysis revealed high activities of angiotensin-converting enzyme (ACE) (6.9 +/- 1.7 mU/mg of protein, mean +/- S.E.M., n = 8) and chymase-like enzyme (4.0 +/- 1.4 mU/mg of protein). Functional recording of isometric tension showed that Ang I (3 x 10(-7) M) induced a tension of 0.17 +/- 0.05 g (n = 5), which was reduced to about 60% by pretreatment with an ACE inhibitor, lisinopril (10(-6) M), and almost completely blocked by lisinopril in combination with a chymase inhibitor, chymostatin (10(-4) M). Binding sites for ACE and Ang II receptors were studied by in vitro autoradiography using 125I-351A and 125I-[Sar1, Ile8]Ang II as ligands, respectively. Dense binding of ACE appeared in the endothelial layer of the corpus cavernosum penis, and Ang II receptors were localized in the trabecular smooth muscle layer. An AT1 receptor antagonist, CV-11974 (10(-6) M), markedly displaced 125I-[Sar1, Ile8]Ang II bindings, indicating that the corpus cavernosum penis contains AT1 receptors exclusively. Immunohistochemical studies demonstrated ACE in the endothelium of the corpus cavernosum penis. Mast cells that produce chymase were present mainly in the cavernosal area. These results demonstrate that chymase, in addition to ACE, is involved in the contraction of canine penile corpus cavernosum through local Ang II formation.     

Renin-angiotensin system as a therapeutic target in managing atherosclerosis

Clinical and experimental evidence suggests that the pathways by which hypertension and dyslipidemia lead to vascular disease may overlap and that angiotensin II (Ang II) is involved in restructuring of the arterial wall in both atherosclerosis and hypertension. Ang II represents a potent proinflammatory agent promoting recruitment of monocytes into the vascular intima. Ang II also indirectly facilitates transformation of macrophages and smooth muscle cells into foam cells by promoting superoxide radical formation (via NADP/NADPH oxidase stimulation). The oxidative stress produced by Ang II leads to enhanced low-density lipoprotein oxidation and degradation of nitric oxide, an important vascular protective molecule capable of retarding atherosclerosis progression. The importance of the renin-angiotensin system (RAS) in atherogenesis is highlighted by studies in animal models as well as human beings indicating that inhibition of angiotensin-converting enzyme or blockade of type 1 Ang II receptors retards the development of atherosclerotic lesions. In light of a causal and central role of Ang II in atherogenesis, blockade of the RAS represents an important therapeutic consideration in the prevention and treatment of atherosclerotic disease.     

Effects of angiotensin II generated by an angiotensin converting enzyme-independent pathway on left ventricular performance in the conscious baboon.

Human chymase is a serine proteinase that converts angiotensin (Ang) I to Ang II independent of angiotensin converting enzyme (ACE) in vitro. The effects of chymase on systemic hemodynamics and left ventricular function in vivo were studied in nine conscious baboons instrumented with a LV micromanometer and LV minor axis and wall thickness sonomicrometer crystal pairs. Measurements were made at baseline and after [Pro11DAla12] Ang I, a specific substrate for human chymase, was given in consecutive fashion as a 0.1 mg bolus, an hour-long intravenous infusion of 5 mg, a 3 mg bolus, and after 5 mg of an Ang II receptor antagonist. [Pro11DAla12]Ang I significantly increased LV systolic and diastolic pressure, LV end-diastolic and end systolic dimensions and the time constant of LV relaxation and significantly decreased LV fractional shortening and wall thickening. Administration of a specific Ang II receptor antagonist reversed all the hemodynamic changes. In separate studies, similar results were obtained in six of the baboons with ACE blockade (20 mg, intravenous captopril). Post-mortem studies indicated that chymase-like activity was widely distributed in multiple tissues. Thus, in primates, Ang I is converted into Ang II by an enzyme with chymase-like activity. This study provides the first in vivo evidence of an ACE-independent pathway for Ang II production.     

The one-two punch: knocking out angiotensin II in the heart

Ang II plays an important role in the pathophysiology of cardiovascular disease. Angiotensin-converting enzyme (ACE) inhibitors lower Ang II levels by inhibiting conversion of Ang I to Ang II, but Ang II levels have been shown to return to normal with chronic ACE inhibitor treatment. In this issue of the JCI, Wei et al. show that ACE inhibition induces an increase in chymase activity in cardiac interstitial fluid, providing an alternate pathway for Ang II generation. Despite ongoing advances in modern medicine, cardiovascular disease (CVD) remains a major cause of death. Ang II has been implicated in the pathophysiology of atherosclerosis and heart failure (HF) due to its role in regulating multiple renal and cardiovascular functions, including salt/water retention, vasoconstriction, aldosterone secretion, cardiac hypertrophy, thrombosis, fibrosis, and others (1). In the classical renin-angiotensin system (RAS), angiotensinogen (AGT) produced in the liver enters the circulation, where it is cleaved by renin produced in the kidneys to form Ang I. Ang I is converted to Ang II by angiotensin-converting enzyme (ACE) bound to vascular endothelial cells. Ang II then binds to either the Ang II type 1 receptor (AT1), through which it exerts most of its known effects, or to the Ang II type 2 receptor (AT2), which is thought to oppose AT1 (2). However, research conducted over the last few decades has shown that the RAS is much more complex in both mechanism and effect than once thought (Figure ​(Figure1). 1). Open in a separate windowFigure 1The renin-angiotensin system.AGT is cleaved by either renin or cathepsin to form Ang I. Ang I is cleaved by ACE or chymase to form Ang II or by ACE2 to form Ang-(1–9). Ang II binds to one of the Ang II receptors to exert its downstream effects on cardiovascular function, with AT1 and AT2 working in opposition to each other. Ang-(1–12) is an alternative precursor for Ang I and II. Ang-(1–7) is formed through cleavage of Ang II by ACE2 or cleavage of Ang-(1–9) by ACE and binds to the Mas receptor. The ACE–Ang II–AT1 axis and the ACE2–Ang-(1–7)–Mas axis appear to have opposing functions. ACE also degrades BK, serving as a link between the RAS and the kallikrein/kinin system, while chymase is also important in tissue remodeling.Some of this complexity comes from the discovery of nonclassical RAS components. Although Ang II is generally considered to be the main RAS effector molecule, other Ang peptides have been discovered, including Ang-(1–7), Ang-(1–9), Ang-(2–8), Ang-(3–8), and Ang-(1–12) (2, 3). In particular, Ang-(1–7) opposes the effects of Ang II through binding to the Mas receptor (3) and inhibits bradykinin (BK) degradation, possibly through competitive binding to ACE (4), while Ang-(1–12) is an alternative precursor for Ang I and II generation (3). In addition, other enzymes cleave AGT and its products. Cathepsin, like renin, generates Ang I from AGT (5), ACE2, an ACE homolog, and neutral endopeptidases cleave Ang I and II to form Ang-(1–7) (2, 6), and some chymases efficiently cleave Ang I to produce Ang II (7) and may be responsible for generation of Ang II from Ang-(1–12) (3). Furthermore, both ACE and chymase have additional functions besides Ang peptide cleavage. ACE is also a kininase (8), linking the RAS and the kallikrein/kinin system, while chymase activates procollagenase and MMPs and catalyzes degradation of thrombin and plasmin, playing an important role in tissue remodeling (7). How and when these various components come into play depends on the context. Although the RAS was originally thought to function only as a circulatory system, it has since been established that local intracellular and extracellular RAS exist in several tissues, including the heart, kidneys, brain, VSMCs, and BM-derived cells (2, 5, 9). Ang II generated by tissue RAS may function intracellularly to exert an intracrine effect on local RAS function or may contribute to extracellular Ang II levels to exert an autocrine/paracrine effect, depending on the cell type and conditions (2, 5, 9).     

Renin‐angiotensin system gene polymorphisms and diastolic heart failure

Background Diastolic heart failure (DHF) refers to an abnormality of diastolic distensibility, filling or relaxation of the left ventricle. The genetic study of DHF is scarce in the literature. The association of renin‐angiotensin system (RAS) and DHF are well known. We hypothesized that RAS genes might be the susceptible genes for DHF and conducted a case‐control study to prove the hypothesis. Materials and methods A total of 1452 consecutive patients were analysed and 148 patients with a diagnosis of DHF confirmed by echocardiography were recruited. We had two control populations. The first controls consisted of 286 normal subjects while the second were 148 matched controls selected on a 1‐to‐1 basis by age, sex, hypertension, diabetes and medication use. The angiotensin‐converting enzyme (ACE) gene insertion/deletion polymorphism; multilocus polymorphisms of the angiotensinogen gene; and the A1166C polymorphisms of the angiotensin II type I receptor (AT₁R) gene were genotyped. Results In a single‐locus analysis, the odds ratios (ORs) for DHF were significant with the ACE DD genotype and the AT₁R 1166 CC plus AC genotype. In addition, the concomitant presence of ACE DD and AT₁R 1166 CC/AC genotypes synergistically increased the predisposition to DHF. Conclusions Genetic variants in the RAS genes may determine an individual's risk to develop DHF. There is also a synergistic gene‐gene interaction between the RAS genes in the development of DHF.     

Specific immunotherapy for allergic rhinitis to grass and tree pollens in daily medical practice—symptom load with sublingual immunotherapy compared to subcutaneous immunotherapy

The renin-angiotensin-aldosterone system is known to play an essential role in controlling sodium balance and body fluid volumes, and thus blood pressure. In addition to the circulating system which regulates urgent cardiovascular responses, a tissue-localized renin-angiotensin system (RAS) regulates long-term changes in various organs. Many recognized RAS components have also been identified in the human eye. The highly vasoconstrictive angiotensin II (Ang II) is considered the key peptide in the circulatory RAS. However, the ultimate effect of RAS activation at tissue level is more complex, being based not only on the biological activity of Ang II but also on the activities of other products of angiotensinogen metabolism, often exerting opposite effects to Ang II action. In recent studies, orally administered angiotensin II type 1 receptor blockers and angiotensin-converting enzyme inhibitors lower intra-ocular pressure (IOP), likewise topical application of these compounds, the effect being more prominent in ocular hypertensive eyes. Based on previous findings and our own experimental data, it can strongly be suggested that the RAS not only regulates blood pressure but is also involved in the regulation of IOP.