Signaling via the angiotensin-converting enzyme enhances the expression of cyclooxygenase-2 in endothelial cells

Angiotensin-Converting Enzyme and Hypertension: A Systemic Analysis of Various ACE Inhibitors, Their Side Effects, and Bioactive Peptides as a Putative Therapy for Hypertension

Hypertension is a major risk factor for heart attack, produce atherosclerosis (hardening of the arteries), congestive heart failure, stroke, kidney infection, blindness, end-stage renal infection, and cardiovascular diseases. Many mechanisms are involved in causing hypertension, i.e., via calcium channels, alpha and beta receptors, and the renin-angiotensin system (RAS). RAS has an important role in blood pressure control and is also involved in the metabolism of glucose, homeostasis, and balance of electrolytes in the body. The components of RAS that are involved in the regulation of blood pressure are angiotensinogen, Ang I (angiotensin I), Ang II (angiotensin II), ACE (angiotensin-converting enzyme), and ACE 2 (angiotensin-converting enzyme 2). These components provide for relevant therapeutic targets for the treatment of hypertension, and various drugs are commercially available that target individual components of RAS. Angiotensin receptor blockers (ARBs) and ACE inhibitors are the most popular among these drugs. ACE is chosen in this review as it makes an important target for blood pressure control because it converts Ang I into Ang II and also acts on the vasodilator, bradykinin, to degrade it into inactive peptides. This review highlights various aspects of blood pressure regulation in the body with a focus on ACE, drugs targeting the components involved in regulation, their associated side effects, and a need to shift to alternative therapy for putative hypertension treatment in the form of bioactive peptides from food.

Home pharmacological therapy in early COVID-19 to prevent hospitalization and reduce mortality: Time for a suitable proposal

The COVID‐19 pandemic is a highly dramatic concern for mankind. In Italy, the pandemic exerted its major impact throughout the period of February to June 2020. To date, the awkward amount of more than 134,000 deaths has been reported. Yet, post‐mortem autopsy was performed on a very modest number of patients who died from COVID‐19 infection, leading to a first confirmation of an immune‐thrombosis of the lungs as the major COVID‐19 pathogenesis, likewise for SARS. Since then (June–August 2020), no targeted early therapy considering this pathogenetic issue was approached. The patients treated with early anti‐inflammatory, anti‐platelet, anticoagulant and antibiotic therapy confirmed that COVID‐19 was an endothelial inflammation with immuno‐thrombosis. Patients not treated or scarcely treated with the most proper and appropriate therapy and in the earliest, increased the hospitalization rate in the intensive care units and also mortality, due to immune‐thrombosis from the pulmonary capillary district and alveoli. The disease causes widespread endothelial inflammation, which can induce damage to various organs and systems. Therapy must be targeted in this consideration, and in this review, we demonstrate how early anti‐inflammatory therapy may treat endothelia inflammation and immune‐thrombosis caused by COVID‐19, by using drugs we are going to recommend in this paper.

Angiotensin II-mediated MYH9 downregulation causes structural and functional podocyte injury in diabetic kidney disease

MYH9, a widely expressed gene encoding nonmuscle myosin heavy chain, is also expressed in podocytes and is associated with glomerular pathophysiology. However, the mechanisms underlying MYH9-related glomerular diseases associated with proteinuria are poorly understood. Therefore, we investigated the role and mechanism of MYH9 in diabetic kidney injury. MYH9 expression was decreased in glomeruli from diabetic patients and animals and in podocytes treated with Ang II in vitro. Ang II treatment and siRNA-mediated MYH9 knockdown in podocytes resulted in actin cytoskeleton reorganization, reduced cell adhesion, actin-associated protein downregulation, and increased albumin permeability. Ang II treatment increased NOX4 expression and ROS generation. The Ang II receptor blocker losartan and the ROS scavenger NAC restored MYH9 expression in Ang II-treated podocytes, attenuated disrupted actin cytoskeleton and decreased albumin permeability. Furthermore, MYH9 overexpression in podocytes restored the effects of Ang II on the actin cytoskeleton and actin-associated proteins. Ang II-mediated TRPC6 activation reduced MYH9 expression. These results suggest that Ang II-mediated MYH9 depletion in diabetic nephropathy may increase filtration barrier permeability by inducing structural and functional podocyte injury through TRPC6-mediated Ca²⁺ influx by NOX4-mediated ROS generation. These findings reveal a novel MYH9 function in maintaining urinary filtration barrier integrity. MYH9 may be a potential target for treating diabetic nephropathy.

An Update on the Tissue Renin Angiotensin System and Its Role in Physiology and Pathology

In its classical view, the renin angiotensin system (RAS) was defined as an endocrinesystem involved in blood pressure regulation and body electrolyte balance. However, the emergingconcept of tissue RAS, along with the discovery of new RAS components, increased thephysiological and clinical relevance of the system. Indeed, RAS has been shown to be expressed invarious tissues where alterations in its expression were shown to be involved in multiple diseasesincluding atherosclerosis, cardiac hypertrophy, type 2 diabetes (T2D) and renal fibrosis. In thischapter, we describe the new components of RAS, their tissue-specific expression, and theiralterations under pathological conditions, which will help achieve more tissue- and conditionspecifictreatments.

An Update on the Tissue Renin Angiotensin System and Its Role in Physiology and Pathology

In its classical view, the renin angiotensin system (RAS) was defined as an endocrine system involved in blood pressure regulation and body electrolyte balance. However, the emerging concept of tissue RAS, along with the discovery of new RAS components, increased the physiological and clinical relevance of the system. Indeed, RAS has been shown to be expressed in various tissues where alterations in its expression were shown to be involved in multiple diseases including atherosclerosis, cardiac hypertrophy, type 2 diabetes (T2D) and renal fibrosis. In this chapter, we describe the new components of RAS, their tissue-specific expression, and their alterations under pathological conditions, which will help achieve more tissue- and condition-specific treatments.

The binding of captopril to angiotensin I-converting enzyme triggers activation of signaling pathways

Hypertension is a global health problem, and angiotensin I (ANG I)-converting enzyme (ACE) inhibitors are largely used to control this pathology. Recently, it has been shown that ACE can also act as a transducer signal molecule when its inhibitors or substrates bind to it. This new role of ACE could contribute to understanding some of the effects not explained by its catalytic activity only. In this study, we investigated signaling pathway activation in Chinese hamster ovary (CHO) cells stably expressing ACE (CHO-ACE) under different conditions. We also investigated gene modulation after 4 h and 24 h of captopril treatment. Our results demonstrated that CHO-ACE cells when stimulated with ANG I, ramipril, or captopril led to JNK and ERK1/2 phosphorylation. To verify any physiological role at the endogenous level, we made use of primary cultures of mesangial cells from spontaneously hypertensive rats (SHR) and Wistar rats. Our results showed that ERK1/2 activation occurred mainly in primary cultures of mesangial cells from SHR rats upon captopril stimulation, suggesting that this signaling pathway could be differentially regulated during hypertension. Our results also showed that captopril treatment leads to a decrease of cyclooxygenase 2, interleukin-1β, and β-arrestin2 and a significant increase of AP2 gene expression levels. Our findings strengthen the fact that, in addition to the blockage of enzymatic activity, ACE inhibitors also trigger signaling pathway activation, and this may contribute to their beneficial effects in the treatment of hypertension and other pathologies.

Role of the angiotensin-converting enzyme in the G-CSF-induced mobilization of progenitor cells

In addition to being a peptidase, the angiotensin-converting enzyme (ACE) can be phosphorylated and involved in signal transduction. We evaluated the role of ACE in granulocyte-colony-stimulating factor (G-CSF)-induced hematopoietic progenitor cell (HPC) mobilization and detected a significant increase in mice-lacking ACE. Transplantation experiments revealed that the loss of ACE in the HPC microenvironment rather than in the HPCs increased mobilization. Indeed, although ACE was expressed by a small population of bone-marrow cells, it was more strongly expressed by endosteal bone. Interestingly, there was a physical association of ACE with the G-CSF receptor (CD114), and G-CSF elicited ACE phosphorylation on Ser1270 in vivo and in vitro. A transgenic mouse expressing a non-phosphorylatable ACE (ACE^S/A) mutant demonstrated increased G-CSF-induced HPC mobilization and decreased G-CSF-induced phosphorylation of STAT3 and STAT5. These results indicate that ACE expression/phosphorylation in the bone-marrow niche interface negatively regulates G-CSF-induced signaling and HPC mobilization.

AT1 expression in human urethral stricture tissue

BACKGROUND

Urethral stricture has a high recurrence rate. There is a common doctrine stating that "once a stricture, always a stricture". This fibrotic disease pathophysiology, pathologically characterized by excessive production, deposition and contraction of extracellular matrix is unknown. Angiotensin II type 1 (AT₁) receptor primarily induces angiogenesis, cellular proliferation and inflammatory responses. AT₁ receptors are also expressed in the fibroblasts of hypertrophic scars, whereas angiotensin II (AngII) regulates DNA synthesis in hypertrophic scar fibroblasts through a negative cross talk between AT₁ and angiotensin II type 2 (AT₂) receptors, which might contribute to the formation and maturation of human hypertrophic scars.

OBJECTIVE

This study was conducted to determine the expression of AT₁ receptors in urethral stricture tissues.

METHODS

Urethral stricture tissues were collected from patients during anastomotic urethroplasty surgery. There were 24 tissue samples collected in this study with 2 samples of normal urethra for the control group. Immunohistochemistry study was performed to detect the presence of AT₁ receptor expression. Data were analyzed using Mann-Whitney U test, and statistical analysis was performed with SPSS version 20.

RESULTS

This study showed that positive staining of AT₁ receptor was found in all urethral stricture tissues (n=24). A total of 8.33% patients had low intensity, 41.67% had moderate intensity and 50% had high intensity of AT₁ receptors, while in the control group, 100% patients had no intensity of AT₁ receptors. Using the Mann-Whitney U test, it was found that urethral stricture tissue had a higher intensity of AT₁ receptors than normal urethral tissue with a p-value = 0.012.

CONCLUSION

The results showed that AT₁ receptor had a higher intensity in the urethral stricture tissue and that AT₁ receptor may play an important role in the development of urethral stricture.

The Role of Cyclooxygenase Enzymes in the Effects of Losartan and Lisinopril on the Contractions of Rat Thoracic Aorta

OBJECTIVE

It was suggested that prostaglandins which are synthesized by cyclooxygenase (COX) enzymes contribute to the actions of angiotensin-converting enzyme (ACE) inhibition and angiotensin AT1 receptor antagonism and there is an interaction between ACE signaling pathway and COX enzymes. We aim to investigate the role of COX enzymes in the effects of losartan, an angiotensin II (Ang II) receptor antagonist or lisinopril, an ACE inhibitor, on the contractions of rat thoracic aorta in isolated tissue bath.

MATERIALS AND METHODS

Responses of losartan (10^-6, 10^-5, 10^-4 M), lisinopril (10^-6, 10^-5, 10^-4 M), and non-selective COX inhibitor dipyrone (10^-4, 7 × 10^-4, 2 × 10^-3 M) alone to the contractions induced by phenylephrine (Phe) (10^-7 M), potassium chloride (KCl) (6 × 10^-2 M), Ang II (10^-8 M) and responses of losartan or lisinopril in combination with dipyrone to the contractions induced by Phe or KCl were recorded.

RESULTS

When used alone, dipyrone and losartan inhibited Phe, KCl, and Ang II-induced contractions, whereas lisinopril inhibited only Phe and Ang II-induced contractions. Inhibition of COX enzymes (COX-3, COX-3 + COX-1, COX-1+ COX-2 + COX-3 by dipyrone 10^-4, 7 × 10^-4, 2 × 10^-3 M, respectively) augmented the relaxant effects of losartan or lisinopril. Also, dipyrone potentiated the effect of lisinopril on KCl-induced contractions.

CONCLUSION

We suggest that dipyrone increases the smooth-muscle relaxing effects of losartan or lisinopril and that COX enzyme inhibition may have a role in the enhancement of this relaxation.

Angiotensin Converting Enzyme Regulates Cell Proliferation and Migration

Background

The angiotensin-I converting enzyme (ACE) plays a central role in the renin-angiotensin system, acting by converting the hormone angiotensin-I to the active peptide angiotensin-II (Ang-II). More recently, ACE was shown to act as a receptor for Ang-II, and its expression level was demonstrated to be higher in melanoma cells compared to their normal counterparts. However, the function that ACE plays as an Ang-II receptor in melanoma cells has not been defined yet.

Aim

Therefore, our aim was to examine the role of ACE in tumor cell proliferation and migration.

Results

We found that upon binding to ACE, Ang-II internalizes with a faster onset compared to the binding of Ang-II to its classical AT1 receptor. We also found that the complex Ang-II/ACE translocates to the nucleus, through a clathrin-mediated process, triggering a transient nuclear Ca²⁺ signal. In silico studies revealed a possible interaction site between ACE and phospholipase C (PLC), and experimental results in CHO cells, demonstrated that the β3 isoform of PLC is the one involved in the Ca²⁺ signals induced by Ang-II/ACE interaction. Further studies in melanoma cells (TM-5) showed that Ang-II induced cell proliferation through ACE activation, an event that could be inhibited either by ACE inhibitor (Lisinopril) or by the silencing of ACE. In addition, we found that stimulation of ACE by Ang-II caused the melanoma cells to migrate, at least in part due to decreased vinculin expression, a focal adhesion structural protein.

Conclusion

ACE activation regulates melanoma cell proliferation and migration.

Dihydroartemisinin transiently activates the JNK/SAPK signaling pathway in endothelial cells

Artemisinin and its derivatives are well-known anti-malaria drugs and in the early stages of research for cancer treatment. Dihydroartemisinin (DHA), a more water-soluble derivative of artemisinin, has demonstrated strong anti-angiogenic activity. The purpose of the present study was to investigate the underlying molecular mechanisms of the effect of DHA on angiogenesis. Human umbilical vein endothelial cells (HUVECs) treated with DHA were examined for apoptosis and activation of the c-Jun N-terminal kinase (JNK) signaling pathway, one of the major mitogen-activated protein kinase cascades. It was observed that 20 µM DHA induces transient activation of JNK in HUVECs. DHA also elevates the expression of cyclooxygenase-2 and matrix metalloproteinase-13, which is abolished by treatment with the JNK inhibitor SP600125. Although DHA persistently increases inhibitor of κB-α protein and thus inhibits nuclear factor-κB signaling, it does not affect apoptosis or caspase 3/9 activities in HUVECs. The present study provides key information for understanding the effects of DHA on endothelial cells, which is required for investigating its potential for clinic application as a chemotherapeutic agent.

Angiotensin-converting enzyme inhibition attenuates lipopolysaccharide-induced lung injury by regulating the balance between angiotensin-converting enzyme and angiotensin-converting enzyme 2 and inhibiting mitogen-activated protein kinase activation

Activation of the renin-angiotensin system (angiotensin-converting enzyme [ACE]/angiotensin II [Ang II] and angiotensin-converting enzyme 2 [ACE2]/Ang-1-7) has been implicated in the pathophysiology of inflammatory response and acute lung injury (ALI). Previous studies have shown that the ACE inhibitor captopril (Cap) may be a potent therapeutic drug for ALI. However, the mechanisms of its protective effects on ALI are still largely unknown. In this study, we evaluated the effects of Cap on preventing lipopolysaccharide (LPS)-induced lung injury and further investigated the underlying mechanisms of these protective effects. Rats were intraperitoneally pretreated with Cap (50 mg/kg) 30 min prior to an intravenous administration of LPS (7.5 mg/kg). Furthermore, following a 30-min pretreatment with Cap (10 mol/mL) or combined with the ACE2 inhibitor MLN4760 (10 mol/mL), rat pulmonary microvascular endothelial cells (PMVECs) were stimulated with LPS (1 mg/mL). Captopril pretreatment significantly attenuated LPS-induced pathophysiological changes in the lung, inhibited secretion of tumor necrosis factor α and interleukin 6, reduced the ratio of Ang II to Ang-1-7, and reversed the increased ratio of ACE to ACE2, which was remarkably decreased from 7.07 (LPS only) to 1.71 (LPS + Cap). The protective effects of Cap on ALI were also confirmed by in vitro studies, in which Cap suppressed LPS-induced secretion of proinflammatory cytokines and modulated the expression levels of ACE and ACE2. After Cap pretreatment, the ratio of ACE to ACE2 expression was remarkably decreased from 5.18 (LPS alone) to 1.52 (LPS + Cap). Furthermore, Cap given before LPS administration led to inhibition of p38 mitogen-activated protein kinase (MAPK), ERK (extracellular signal-regulated kinase) 1/2, and JNK (c-Jun N-terminal kinase) phosphorylation in PMVECs, whereas MLN4760 abolished the protective effects of Cap on LPS-induced secretion of proinflammatory cytokines and abolished Cap-induced blockade of p38MAPK, ERK1/2, and JNK phosphorylation. Our findings reveal that Cap exerts protective effects on LPS-induced lung injury and the cytotoxicity of PMVECs, and these effects may, at least in part, regulate the balance of ACE and ACE2 expression and inhibit the activation of MAPKs.

Acute and subchronic exposure to air particulate matter induces expression of angiotensin and bradykinin-related genes in the lungs and heart: Angiotensin-II type-I receptor as a molecular target of particulate matter exposure

Background

Particulate matter (PM) adverse effects on health include lung and heart damage. The renin-angiotensin-aldosterone (RAAS) and kallikrein-kinin (KKS) endocrine systems are involved in the pathophysiology of cardiovascular diseases and have been found to impact lung diseases. The aim of the present study was to evaluate whether PM exposure regulates elements of RAAS and KKS.

Methods

Sprague–Dawley rats were acutely (3 days) and subchronically (8 weeks) exposed to coarse (CP), fine (FP) or ultrafine (UFP) particulates using a particulate concentrator, and a control group exposed to filtered air (FA). We evaluated the mRNA of the RAAS components At1, At2r and Ace, and of the KKS components B1r, B2r and Klk-1 by RT-PCR in the lungs and heart. The ACE and AT₁R protein were evaluated by Western blot, as were HO-1 and γGCSc as indicators of the antioxidant response and IL-6 levels as an inflammation marker.

We performed a binding assay to determinate AT₁R density in the lung, also the subcellular AT₁R distribution in the lungs was evaluated. Finally, we performed a histological analysis of intramyocardial coronary arteries and the expression of markers of heart gene reprogramming (Acta1 and Col3a1).

Results

The PM fractions induced the expression of RAAS and KKS elements in the lungs and heart in a time-dependent manner. CP exposure induced Ace mRNA expression and regulated its protein in the lungs. Acute and subchronic exposure to FP and UFP induced the expression of At1r in the lungs and heart. All PM fractions increased the AT₁R protein in a size-dependent manner in the lungs and heart after subchronic exposure. The AT₁R lung protein showed a time-dependent change in subcellular distribution. In addition, the presence of AT₁R in the heart was accompanied by a decrease in HO-1, which was concomitant with the induction of Acta1 and Col3a1 and the increment of IL-6. Moreover, exposure to all PM fractions increased coronary artery wall thickness.

Conclusion

We demonstrate that exposure to PM induces the expression of RAAS and KKS elements, including AT₁R, which was the main target in the lungs and the heart.

Early pharmacological inhibition of angiotensin-I converting enzyme activity induces obesity in adulthood

We have investigated early programming of body mass in order to understand the multifactorial etiology of obesity. Considering that the renin-angiotensin system (RAS) is expressed and functional in the white adipose tissue (WAT) and modulates its development, we reasoned whether early transitory inhibition of angiotensin-I converting enzyme activity after birth could modify late body mass development. Therefore, newborn Wistar rats were treated with enalapril (10 mg/kg of body mass) or saline, starting at the first day of life until the age of 16 days. Between days ninetieth and hundred and eightieth, a group of these animals received high fat diet (HFD). Molecular, biochemical, histological, and physiological data were collected. Enalapril treated animals presented hyperphagia, overweight, and increased serum level of triglycerides, total cholesterol and leptin, in adult life. Body composition analyses revealed higher fat mass with increased adipocyte size in these animals. Molecular analyses revealed that enalapril treatment increases neuropeptide Y (NPY) and cocaine- and amphetamine-regulated transcript (CART) gene expression in hypothalamus, fatty acid synthase (FAS), and hormone-sensitive lipase (HSL) gene expression in retroperitoneal WAT, and decreases peroxixome proliferators-activated receptor (PPAR)γ, PPARα, uncoupling protein (UCP)2, and UCP3 gene expression in WAT. The results of the current study indicate that enalapril administration during early postnatal development increases body mass, adiposity and serum lipids in adulthood associated with enhanced food intake and decreased metabolic activity in WAT, predisposing to obesity in adulthood.

Unraveling the mechanisms of action of lactoferrin-derived antihypertensive peptides: ACE inhibition and beyond

The characterization of lactoferrin-derived antihypertensive peptides shows that they might act on several molecular targets.

Tissue-specific expression of transgenic secreted ACE in vasculature can restore normal kidney functions, but not blood pressure, of Ace-/- mice

Angiotensin-converting enzyme (ACE) regulates normal blood pressure and fluid homeostasis through its action in the renin-angiotensin-system (RAS). Ace-/- mice are smaller in size, have low blood pressure and defective kidney structure and functions. All of these defects are cured by transgenic expression of somatic ACE (sACE) in vascular endothelial cells of Ace-/- mice. sACE is expressed on the surface of vascular endothelial cells and undergoes a natural cleavage secretion process to generate a soluble form in the body fluids. Both the tissue-bound and the soluble forms of ACE are enzymatically active, and generate the vasoactive octapeptide Angiotensin II (Ang II) with equal efficiency. To assess the relative physiological roles of the secreted and the cell-bound forms of ACE, we expressed, in the vascular endothelial cells of Ace-/- mice, the ectodomain of sACE, which corresponded to only the secreted form of ACE. Our results demonstrated that the secreted form of ACE could normalize kidney functions and RAS integrity, growth and development of Ace-/- mice, but not their blood pressure. This study clearly demonstrates that the secreted form of ACE cannot replace the tissue-bound ACE for maintaining normal blood pressure; a suitable balance between the tissue-bound and the soluble forms of ACE is essential for maintaining all physiological functions of ACE.

Angiotensin-converting enzyme and the tumor microenvironment: mechanisms beyond angiogenesis

The renin angiotensin system (RAS) is a network of enzymes and peptides that coalesce primarily on the angiotensin II type 1 receptor (AT1R) to induce cell proliferation, angiogenesis, fibrosis, and blood pressure control. Angiotensin-converting enzyme (ACE), the key peptidase of the RAS, is promiscuous in that it cleaves other substrates such as substance P and bradykinin. Accumulating evidence implicates ACE in the pathophysiology of carcinogenesis. While the role of ACE and its peptide network in modulating angiogenesis via the AT1R is well documented, its involvement in shaping other aspects of the tumor microenvironment remains largely unknown. Here, we review the role of ACE in modulating the immune compartment of the tumor microenvironment, which encompasses the immunosuppressive, cancer-promoting myeloid-derived suppressor cells, alternatively activated tumor-associated macrophages, and T regulatory cells. We also discuss the potential roles of peptides that accumulate in the setting of chronic ACE inhibitor use, such as bradykinin, substance P, and N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), and how they may undercut the gains of anti-angiogenesis from ACE inhibition. These emerging mechanisms may harmonize the often-conflicting results on the role of ACE inhibitors and ACE polymorphisms in various cancers and call for further investigations into the potential benefit of ACE inhibitors in some neoplasms.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Intracellular signaling controls endothelial cell prostacyclin secretion and regulation of blood clotting time

Blood is constantly in contact with a biological material, the blood vessel wall, without the need for anticoagulants to prevent clot formation on the vessel wall; however, man-made biomaterials require anticoagulants to prevent clot formation on the biomaterial. This study seeks to understand how some biomaterials elicit anticoagulant responses from endothelial cells (ECs), whereas others do not. Partial least squares regression analysis was used to correlate the activity of four relevant signaling molecules [extracellular signal-related kinase (ERK), c-Jun N-terminal kinase (JNK), Akt, and IκB kinase (IKK)] with human umbilical vein EC secretion of prostacyclin and clotting time of whole blood in contact with these cells. Prostacyclin secretion was increased when JNK activity (mean of all time-points) was elevated and IKK activity at 30 min was reduced. In addition, the clotting time, R-time measured by thromboelastography, was increased (reduced coagulability) when activity of both ERK and JNK (mean of all time-points) were increased and when Akt activity was increased at longer contact times (24-72 h after cell contact with material). Inhibition of each signaling molecule with subsequent testing for prostacyclin secretion and R-time confirmed the interrelationship between EC intracellular signaling and prostacyclin secretion. Generally, JNK inhibition decreased and IKK inhibition increased prostacyclin secretion. Inhibition of ERK or JNK generally increased coagulability, and Akt inhibition decreased the R-time of samples normally eliciting reduced coagulability. These findings increase our understanding of the signaling pathways involved in endothelial prostacyclin release and suggest targets for developing EC-seeded biomaterial surfaces that can minimize coagulation.

Zofenopril and incidence of cough: a review of published and unpublished data

OBJECTIVE

Cough is a typical side effect of angiotensin-converting enzyme (ACE) inhibitors, though its frequency quantitatively varies among the different compounds. Data on the incidence of cough with the lipophilic third-generation ACE inhibitor zofenopril are scanty and never systematically analyzed. The purpose of this paper is to give an overview on the epidemiology, pathophysiology, and treatment of ACE inhibitor-induced cough and to assess the incidence of cough induced by zofenopril treatment.

METHODS

Published and unpublished data from randomized and postmarketing zofenopril trials were merged together and analyzed.

RESULTS

Twenty-three studies including 5794 hypertensive patients and three studies including 1455 postmyocardial infarction patients exposed for a median follow-up time of 3 months to zofenopril at doses of 7.5-60 mg once-daily were analyzed. The incidence of zofenopril-induced cough was 2.6% (range 0%-4.2%): 2.4% in the hypertension trials (2.4% in the double-blind randomized studies and 2.4% in the open-label postmarketing studies) and 3.6% in the doubleblind randomized postmyocardial infarction trials. Zofenopril-induced cough was generally of a mild to moderate intensity, occurred significantly (P < 0.001) more frequently in the first 3-6 months of treatment (3.0% vs 0.2% 9-12 months), and always resolved or improved upon therapy discontinuation. Zofenopril doses of 30 mg and 60 mg resulted in significantly (P = 0.042) greater rate of cough (2.1% and 2.6%, respectively) than doses of 7.5 mg and 15 mg (0.4% and 0.7%, respectively). In direct comparison trials (enalapril and lisinopril), incidence of cough was not significantly different between zofenopril and other ACE inhibitors (2.4% vs 2.7%).

CONCLUSION

Evidence from a limited number of studies indicates a relatively low incidence of zofenopril-induced cough. Large head-to-head comparison studies versus different ACE inhibitors are needed to highlight possible differences between zofenopril and other ACE inhibitors in the incidence of cough.

ACE as a mechanosensor to shear stress influences the control of its own regulation via phosphorylation of cytoplasmic Ser(1270)

OBJECTIVES

We tested whether angiotensin converting enzyme (ACE) and phosphorylation of Ser(1270) are involved in shear-stress (SS)-induced downregulation of the enzyme.

METHODS AND RESULTS

Western blotting analysis showed that SS (18 h, 15 dyn/cm(2)) decreases ACE expression and phosphorylation as well as p-JNK inhibition in human primary endothelial cells (EC). CHO cells expressing wild-type ACE (wt-ACE) also displayed SS-induced decrease in ACE and p-JNK. Moreover, SS decreased ACE promoter activity in wt-ACE, but had no effect in wild type CHO or CHO expressing ACE without either the extra- or the intracellular domains, and decreased less in CHO expressing a mutated ACE at Ser(1270) compared to wt-ACE (13 vs. 40%, respectively). The JNK inhibitor (SP600125, 18 h), in absence of SS, also decreased ACE promoter activity in wt-ACE. Finally, SS-induced inhibition of ACE expression and phosphorylation in EC was counteracted by simultaneous exposure to an ACE inhibitor.

CONCLUSIONS

ACE displays a key role on its own downregulation in response to SS. This response requires both the extra- and the intracellular domains and ACE Ser(1270), consistent with the idea that the extracellular domain behaves as a mechanosensor while the cytoplasmic domain elicits the downstream intracellular signaling by phosphorylation on Ser(1270).

Angiotensin-converting enzyme inhibition augments the expression of rat elastase-2, an angiotensin II-forming enzyme

Mounting evidence suggest that tissue levels of angiotensin (ANG) II are maintained in animals submitted to chronic angiotensin-converting enzyme (ACE) inhibitor treatment. We examined the expression levels of transcripts for elastase-2, a chymostatin-sensitive serine protease identified as the alternative pathway for ANG II generation from ANG I in the rat vascular tissue and the relative role of ACE-dependent and -independent pathways in generating ANG II in the rat isolated carotid artery rings of spontaneously hypertensive rats (SHR) and Wistar normotensive rats (WNR) treated with enalapril for 7 days. Enalapril treatment decreased blood pressure of SHR only and resulted in significantly more elastase-2 mRNA expression in carotid artery of both enalapril-treated WNR and SHR. Captopril induced a comparable rightward shift of concentration-response curves to ANG I in vehicle and enalapril-treated rats, although this effect was of lesser magnitude in SHR group. Chymostatin induced a rightward shift of the dose response to ANG I in vehicle-treated and a decrease in maximal effect of 22% in enalapril-treated WNR group. Maximal response induced by ANG I was remarkably reduced by chymostatin in enalapril-treated SHR carotid artery (by 80%) compared with controls (by 23%). Our data show that chronic ACE inhibition was associated with augmented functional role of non-ACE pathway in generating ANG II and increased elastase-2 gene expression, suggesting that this protease may contribute as an alternative pathway for ANG II generation when ACE is inhibited in the rat vascular tissue.

Angiotensin II Binding to Angiotensin I–Converting Enzyme Triggers Calcium Signaling

Angiotensin (Ang) I–converting enzyme (ACE) is involved in the control of blood pressure by catalyzing the conversion of Ang I into the vasoconstrictor Ang II and degrading the vasodilator peptide bradykinin. Human ACE also functions as a signal transduction molecule, and the binding of ACE substrates or its inhibitors initiates a series of events. In this study, we examined whether Ang II could bind to ACE generating calcium signaling. Chinese hamster ovary cells transfected with an ACE expression vector reveal that Ang II is able to bind with high affinity to ACE in the absence of the Ang II type 1 and type 2 receptors and to activate intracellular signaling pathways, such as inositol 1,4,5-trisphosphate and calcium. These effects could be blocked by the ACE inhibitor, lisinopril. Calcium mobilization was specific for Ang II, because other ACE substrates or products, namely Ang 1-7, bradykinin, bradykinin 1-5, and N -acetyl-seryl-aspartyl-lysyl-proline, did not trigger this signaling pathway. Moreover, in Tm5, a mouse melanoma cell line endogenously expressing ACE but not Ang II type 1 or type 2 receptors, Ang II increased intracellular calcium and reactive oxygen species. In conclusion, we describe for the first time that Ang II can interact with ACE and evoke calcium and other signaling molecules in cells expressing only ACE. These findings uncover a new mechanism of Ang II action and have implications for the understanding of the renin-Ang system.

Effects of zofenopril and ramipril on cough reflex responses in anesthetized and awake rabbits

Cough is the most common symptom reported by patients in a primary care setting and is one of the most frequent secondary effects recorded during treatment with angiotensin-converting enzyme (ACE) inhibitors. The aim of the current study was to analyze potential differences in cough induction between 2 structurally different ACE inhibitors, namely zofenopril, which has a sulphydryl moiety, and ramipril, which has a carboxyl moiety. The cough reflex was induced by chemical (citric acid) and/or mechanical stimulation of the tracheobronchial tree in awake and anesthetized rabbits. Intravenous injection of the active compounds of the 2 ACE inhibitors, zofenoprilat (288 nmol/kg) and ramiprilat (129 nmol/kg), caused similar hypotensive effects in anesthetized rabbits. None of the studied cough-related variables changed in response to ACE inhibitor administration, with the exception of the number of coughs. Ramiprilat, but not zofenoprilat, increased the cough response induced by both mechanical and chemical stimulation (1 mol/L citric acid aerosol) of the tracheobronchial tree. In awake animals, zofenoprilat- or vehicle-treated rabbits did not show any significant changes in the number of coughs induced by 1 mol/L citric acid aerosol compared to their respective basal values (from 15.2 ± 2.3 to 13.1 ± 1.3 and from 16.1 ± 4.9 to 15.8 ± 4.3, respectively). Conversely, ramiprilat resulted in a significant increase in the number of coughs (from 21.1 ± 2.6 to 34.9 ± 3.5; P < .01). These findings confirm that there are differences in the cough potentiation effect induced by different ACE inhibitors. The low rate of cough seen with zofenoprilat may be related to its ability to induce a lower accumulation of bradykinin and prostaglandins at the lung level.

Differences between zofenopril and ramipril, two ACE inhibitors, on cough induced by citric acid in guinea pigs: role of bradykinin and PGE2

Dry and persistent cough is one of the commonest side effects experienced by patients treated with angiotensin-converting enzyme (ACE) inhibitors for the therapy of hypertension and congestive heart failure. The present study investigated the effect of zofenopril and ramipril on cough induced by citric acid in guinea pig and the involvement of bradykinin (BK) and prostaglandin E2 (PGE2) in mediating the responses of these drugs. Zofenopril (10 mg/kg) or ramipril (3-10 mg/kg), which is threefold more potent than zofenopril, on a mg basis, in lowering blood pressure, was orally administered daily in drinking water for 2 weeks. At the end of this period, aerosol of citric acid solution (0.1 M) was performed and the number of cough counted for 10 min. The role of the kinin B(2) receptor was also investigated. BK and PGE2 levels in the bronchoalveolar lavage (BAL) fluid were measured after repeated oral treatment with zofenopril or ramipril (10 mg/kg). Ramipril (3-10 mg/kg) increased citric acid-induced cough by 40% and 60%, respectively, as compared to the vehicle control group (15.0 ± 1.8), while zofenopril (10 mg/kg) was without effect. The enhancement of citric acid-induced cough caused by ramipril (10 mg/kg) was reduced by the kinin B(2) receptor antagonist MEN16132 (0.25 mg/kg ip). BK and PGE2 levels in the BAL fluid were increased, in comparison to the control group, after ramipril treatment, while they were unchanged after zofenopril administration. Zofenopril, contrary to ramipril, did not affect either citric acid-induced cough in the guinea pigs or BK and PGE2 production in the airways.

How druggable is protein kinase CK2?

CK2 is a pleiotropic, ubiquitous, and constitutively active protein kinase (PK), with both cytosolic and nuclear localization in most mammalian cells. The holoenzyme is generally composed of two catalytic (alpha and/or alpha') and two regulatory (beta) subunits, but the free alpha/alpha' subunits are catalytically active by themselves and can be present in cells under some circumstances. CK2 catalyzes the phosphorylation of more than 300 substrates characterized by multiple acidic residues surrounding the phosphor-acceptor amino acid, and, consequently, it plays a key role in several physiological and pathological processes. But how can one kinase orchestrate all these tasks faithfully? How is it possible that one kinase can, despite all pleiotropic characteristics of PKs in general, be involved in so many different biochemical events? Is CK2 a druggable target? Several questions are still to be clearly answered, and this review is an occasion for a fruitful discussion.

Signal transduction in CHO cells stably transfected with domain-selective forms of murine ACE

Membrane-bound human angiotensin-converting enzyme (ACE) has been reported to initiate intracellular signaling after interaction with substrates or inhibitors. Somatic ACE is known to contain two distinct, extracellular catalytic centers. We analyzed the signal transduction mechanisms in cells transfected with different forms of murine ACE (mACE) and investigated whether the two domains are similarly involved in these processes. For this purpose, CHO cells were stably transfected with mACE or with its domain-selective mutants. In addition to these modified cellular models, human umbilical vein endothelial cells were used in this study. Signal transduction molecules such as JNK and c-Jun were analyzed after activation of cells with several ACE substrates and inhibitors. ACE-targeting compounds such as substrates, inhibitors, or even the ACE product angiotensin-II induce in mACE-expressing cells a signal transduction response. These processes are also evoked by partially inactivated forms of mACE and finally result in an enhanced cyclooxygenase-2 transcription. Surprisingly, the membrane-bound ACE activity is also influenced by ACE-targeted interventions. Our data suggest that the two catalytic domains of mACE do not function independently but that the signal transduction is influenced by negative cooperativity of the two catalytic domains. This study underlines that ACE indeed has receptor-like properties which occur in a species-specific manner.

MMP-9 inhibition by ACE inhibitor reduces oxidized LDL-mediated foam-cell formation

AIM

Angiotensin-converting enzyme inhibitors (ACEIs) have been shown to block matrix metalloproteinase (MMP)-9 activity, which plays a role in atherogenesis. MMP-9 activity of macrophages is increased during foam cell formation. To investigate the contribution of ACEIs to foam cell formation, we studied the effects of an ACEI, imidaprilat, on THP-1 macrophages and the underlying molecular mechanisms in vitro.

METHODS AND RESULTS

Pre-treatment of THP-1 macrophages with imidaprilat (100 nmol/L, 4 hours) significantly decreased foam cell formation induced by oxidized LDL (OxLDL). Imidaprilat reduced the protein level of MMP-9 in THP-1 macrophages and attenuated OxLDL-induced MMP-9 activity in the culture supernatants. Indeed, pretreatment of THP-1 macrophages with an MMP-2/9 inhibitor (20 micromol/L, 4 hours) attenuated OxLDL-induced foam-cell formation. Imidaprilat or the MMP-2/9 inhibitor blocked OxLDL-induced expressions of LOX-1 and scavenger receptor-A (SR-A), but not that of CD36, in THP-1 macrophages. In addition, OxLDL-induced activation of p38 mitogen-activated protein kinase (MAPK) and ERK, but not JNK, was blunted by imidaprilat or the MMP-2/9 inhibitor. Finally, siRNA against MMP-9 inhibited foam cell formation as well as lipid accumulation in THP-1 macrophages.

CONCLUSION

These findings suggest that imidaprilat reduces OxLDL-triggered foam-cell formation in THP-1 macrophages via modulation of MMP-9 activity and may indicate a novel antiinflamma-tory mechanism of imidaprilat in atherogenesis.

Not just angiotensinases: new roles for the angiotensin-converting enzymes

The renin-angiotensin system (RAS) is a critical regulator of blood pressure and fluid homeostasis. Angiotensin II, the primary bioactive peptide of the RAS, is generated from angiotensin I by angiotensin-converting enzyme (ACE). A homologue of ACE, ACE2, is able to convert angiotensin II to a peptide with opposing effects, angiotensin-(1-7). It is proposed that disturbance of the balance of ACE and ACE2 expression and/or function is important in pathologies in which angiotensin II plays a role. These include cardiovascular and renal disease, lung injury and liver fibrosis. The critical roles of ACE and ACE2 in regulating angiotensin II levels have traditionally focussed attention on their activities as angiotensinases. Recent discoveries, however, have illuminated the roles of these enzymes and of the ACE2 homologue, collectrin, in intracellular trafficking and signalling. This paper reviews the key literature regarding both the catalytic and non-catalytic roles of the angiotensin-converting enzyme gene family.

Cell signaling, internalization, and nuclear localization of the angiotensin converting enzyme in smooth muscle and endothelial cells

The angiotensin converting enzyme (ACE) catalyzes the extracellular formation of angiotensin II, and degradation of bradykinin, thus regulating blood pressure and renal handling of electrolytes. We have previously shown that exogenously added ACE elicited transcriptional regulation independent of its enzymatic activity. Because transcriptional regulation generates from protein-DNA interactions within the cell nucleus we have investigated the initial cellular response to exogenous ACE and the putative internalization of the enzyme in smooth muscle cells (SMC) and endothelial cells (EC). The following phenomena were observed when ACE was added to cells in culture: 1) it bound to SMC and EC with high affinity (K(d) = 361.5 +/- 60.5 pM) and with a low binding occupancy (B(max) = 335.0 +/- 14.0 molecules/cell); 2) it triggered cellular signaling resulting in late activation of focal adhesion kinase and SHP2; 3) it modulated platelet-derived growth factor receptor-beta signaling; 4) it was endocytosed by SMC and EC; and 5) it transited through the early endosome, partially occupied the late endosome and the lysosome, and was localized to the nuclei. The incorporation of ACE or a fragment of it into the nuclei reached saturation at 120 min, and was preceded by a lag time of 40 min. Internalized ACE was partially cleaved into small fragments. These results revealed that extracellular ACE modulated cell signaling properties, and that SMC and EC have a pathway for delivery of extracellular ACE to the nucleus, most likely involving cell surface receptor(s) and requiring transit through late endosome/lysosome compartments.

Reinventing the ACE inhibitors: some old and new implications of ACE inhibition

Since their inception, angiotensin-converting enzyme (ACE) inhibitors have been used as first-line therapy for the treatment of cardiovascular and renal diseases. They restore the balance between the vasoconstrictive salt-retentive and hypertrophy-causing peptide angiotensin II (Ang II) and bradykinin, a vasodilatory and natriuretic peptide. As ACE is a promiscuous enzyme, ACE inhibitors alter the metabolism of a number of other vasoactive substances. ACE inhibitors decrease systemic vascular resistance without increasing heart rate and promote natriuresis. They have been proven effective in the treatment of hypertension, and reduce mortality in congestive heart failure and left ventricular dysfunction after myocardial infarction. They inhibit ischemic events and stabilize plaques. Furthermore, they delay the progression of diabetic nephropathy and neuropathy and act as antioxidants. Ongoing studies have elucidated protective roles for them in both memory-related disorders and cancer. Lastly, N- and C-domain selective ACE inhibitors have led to new uses for ACE inhibitors.

Study of the mechanism of antihypertensive peptides VPP and IPP in spontaneously hypertensive rats by DNA microarray analysis

Many antihypertensive effects of angiotensin-I-converting enzyme (ACE) inhibitory peptides have been studied in spontaneously hypertensive rats (SHRs) and human, however, the mild actions of these peptides expressed by these consecutive uptakes are still not clear. Here, to understand the in vivo antihypertensive effects of well-characterized two peptides, Val-Pro-Pro (VPP) and Ile-Pro-Pro (IPP), DNA microarray was used to analyze gene expression in SHRs fed these peptides for 5 days. By using an Affymetrix analyzer, gene profiling was performed in a target organ, the aorta, of SHRs after repeated administration of VPP and IPP for 5 days. The changes in gene expression were relatively mild; therefore, among the analyzed genes associated with blood pressure, those that showed changes over +/- 5% as compared to the control group were categorized as the renin angiotensin aldosterone system, vascular function, arachidonic acid system, blood coagulation system, and cytokines and growth factors. Significant and marked differences were detected for the endothelial nitric oxide synthase (eNOS) gene (1.89-fold, P<0.05) and the connexin 40 (gap junction 40) gene (2.81-fold, P<0.05). Administration of VPP and IPP led to a slight increase in the expression of the cyclooxigenase (COX-1) gene and a decrease in the expression of both the nuclear factor kappa B subunit (NF-kappaB) gene for vascular function and the peroxisome proliferator activator receptor gamma (PPARgamma) gene. Taken together, these results suggest that VPP and IPP function as ACE inhibitors in the aorta, where they may have a preventive role in cardiovascular function.

The importance of the intrarenal renin-angiotensin system

Evidence suggests that virtually every organ system in the human body possesses a local renin-angiotensin system (RAS). These local systems seem to be independently regulated and compartmentalized from the plasma circulation, perhaps with the exception of the vascular endothelial system, which is responsible for maintaining physiological plasma levels of RAS components. Among these local RASs, the kidney RAS--the focus of this Review--seems to be of critical importance for the regulation of blood pressure and salt balance. Indeed, overactivation of the intrarenal RAS in certain disease states constitutes a pathogenic mechanism that leads to tissue injury, proliferation, fibrosis and ultimately, end-organ damage. Intrarenal levels of angiotensin peptides are considerably higher than those in plasma or any other organ tissue. Moreover, the kidney has a unique capacity to degrade angiotensin peptides, perhaps to maintain its intrinsic homeostasis. Interestingly, each local RAS has a distinct enzymatic profile resulting in different patterns of angiotensin fragment generation in different tissues. A better understanding of the autocrine and paracrine mechanisms involved in the renal RAS and other local RASs might direct future organ-specific therapy.

The novel gaseous vasorelaxant hydrogen sulfide inhibits angiotensin-converting enzyme activity of endothelial cells

OBJECTIVE

Beside NO (nitric monoxide) and CO (carbon monoxide), H2S (hydrogen sulfide) has been identified recently as the third gasotransmitter. By acting directly on KATP-channels on smooth muscle cells (SMC) H2S possesses vasorelaxing properties. It has the potential to react with metal ions (i.e. Cu, Fe, Zn) in metalloproteins. Angiotensin-converting enzyme (ACE), responsible for vasoconstriction, is a zinc (Zn) containing enzyme. We therefore hypothesized that H2S may interact with the Zn in the active center of ACE, modulating (inhibiting) enzyme activity.

METHODS

ACE activity was measured on the surface of human endothelial cells (HUVECs) monolayers in culture, ex-vivo in umbilical veins and in HUVEC protein extracts. Quantitative real-time polymerase chain reaction (PCR) was used to study the effect of H2S on ACE mRNA expression in HUVECs.

RESULTS

H2S inhibited the activity of ACE in HUVEC protein extracts in a dose-dependent manner, and only Zn but not Cd, Ca or Mg could counteract the inhibitory effect. Cell-surface ACE activity was inhibited by H2S on HUVEC monolayers and in ex-vivo umbilical veins. No influence of H2S on ACE mRNA expression was observed.

CONCLUSION

H2S exhibits direct inhibitory action on ACE activity in HUVECs, obviously by interfering with the Zn in the active center of the enzyme. Thus, beside the known influence of H2S on SMC KATP-channels, the observed direct ACE inhibitory effect may add to the vasorelaxant effect of H2S in the vasculature by reducing angiotensin II production and inhibiting bradykinin degradation.

Towards triple vasopeptidase inhibitors for the treatment of cardiovascular diseases

Cardiovascular diseases (CDs) are among the most encountered pathologies in western countries; with obesity reaching pandemic proportions, they are soon to become a worldwide problem. High blood pressure is the main risk factor for CDs, and its tight control is an imperative for the treatment of complications such as renal diseases, heart failure, and atherosclerosis. Blood homeostasis and vascular tone are regulated through at least 3 major closely interrelated pathways in which zinc metallopeptidases modulate the concentration of vasoactive mediators. Those extensively studied vasopeptidases were therefore rapidly targeted with specific inhibitors in order to control the levels of vasoconstrictors [angiotensin II (AII) and endothelin-1 (ET-1)] and vasodilators [bradykinin (BK) and atrial natriuretic peptide (ANP)], thereby controlling blood pressure. The first class of inhibitors to be developed were against angiotensin-converting enzyme (ACE), recently followed by dual inhibitors of ACE/neprylisin (NEP), NEP/endothelin-converting enzyme (ECE), and finally triple ACE/NEP/ECE inhibitors. The dual and triple inhibitors are defined as vasopeptidase inhibitors (VPI). In addition to their ability to effectively lower blood pressure in hypertensive patients, drugs targeting these enzymes also displayed antiinflammatory and antifibrotic activities. The major point emerging from recent studies undertaken to improve the management of CDs is that the combined action of different therapeutic strategies (ie, simultaneous modulation of several neurohumoral mediators) shows better results than conservative therapeutic approaches. In this review, we historically present the advances made in the comprehension of the different mechanisms of blood pressure regulation and some of the drugs that arose from this understanding.

Expression of angiotensin I-converting enzymes and bradykinin B2 receptors in mouse inner medullary-collecting duct cells

We described in mouse inner medullary-collecting duct cells (mIMCD-3) the somatic and the N-domain ACE synthesis and its interaction with the kallikrein-kinin system co-localized in the same cells. We purified two ACE forms from culture medium, M1 (130 kDa) and M2 (N-domain, 60 kDa), and cellular lysate, C1 (130 kDa) and C2 (N-domain, 60 kDa). Captopril and enalaprilat inhibited the purified enzymes. The immunofluorescence studies indicated that ACE is present in the membrane, cytoplasm and in the cell nucleus. Kinin B1 and B2 receptors were detected by immunofluorescence and showed to be activated by BK and DesR9 BK, increasing the acidification rate which was enhanced in the presence of enalaprilat. The presence of secreted and intracellular ACE in mIMCD-3 confirmed the hypothesis previously proposed by our group for a new site of ACE secretion in the collecting duct.

Angiotensin-Converting Enzyme Inhibitor Attenuates Monocyte Adhesion to Vascular Endothelium through Modulation of Intracellular Zinc

To elucidate an anti-inflammatory role of angiotensin-converting enzyme inhibitors (ACEIs) in cardiovascular disease, we studied the effect of ACEIs in monocyte adhesion to endothelial cells and underlying molecular mechanisms. Treatment of human monocytic THP-1 cells with monocyte chemoattractant protein-1 (MCP-1; 100 ng/ml; 10 min) significantly increased their adhesion to human umbilical vein endothelial cells (HUVECs) under flow condition (P < 0.001). Preincubation of THP-1 cells with imidaprilat (50 nM; 4 h), an active metabolite of imidapril, reduced MCP-1-triggered THP-1 cell adhesion (P < 0.01). Similar effects were obtained with experiments using human peripheral monocytes (P < 0.05). MCP-1 activated protein kinase C (PKC)alpha in THP-1 cells, resulting in the up-regulation of alpha4 and beta2 integrin. Imidaprilat attenuated MCP-1-induced PKC activation and integrin up-regulation in THP-1 cells. Imidaprilat also inhibited THP-1 cell adhesion induced by phorbol 12-myristate 13-acetate (PMA), a potent PKC activator. In attempt to elucidate the mechanisms for the modulation of PKC activity by imidaprilat, we found that MCP-1 or PMA increased labile zinc in THP-1 cells, which was canceled by imidaprilat. Indeed, zinc/pyrithione activated PKC and increased THP-1 cell adhesion. Zinc chelator as well as PKC inhibitor inhibited these processes, suggesting the role for labile zinc in PKC activation and THP-1 cell adhesion. Imidaprilat attenuated zinc/pyrithione-induced PKC activation and THP-1 cell adhesion. These data suggest that ACEI reduces MCP-1 or PMA-triggered monocyte adhesion to activated HUVECs by modulating labile zinc in monocytes. Our findings may point out a novel anti-inflammatory mechanism of ACEIs in atherogenesis.

ACE phenotyping as a first step toward personalized medicine for ACE inhibitors. Why does ACE genotyping not predict the therapeutic efficacy of ACE inhibition?

Angiotensin (Ang)-converting enzyme (ACE) inhibitors are widely used for the treatment of cardiovascular diseases. Not all patients respond to ACE inhibitors, and it has been suggested that genetic variation might be a useful marker to predict the therapeutic efficacy of these drugs. In particular, the ACE insertion (I)/deletion (D) polymorphism has been investigated in this regard. Despite a decade of intensive research involving the genotyping of thousands of patients, we still do not know whether ACE genotyping helps in predicting the success of ACE inhibition. This review critically addresses the concept that predictive information on therapeutic efficacy of ACE inhibitors might be obtained based on ACE genotyping. It answers the following questions: Do higher ACE levels really result in higher Ang II levels? Is ACE the only converting enzyme in humans? Does ACE inhibition affect ACE expression? Why does ACE have 2 catalytically active domains? What is the relevance of ACE inhibitor-induced signaling through membrane-bound ACE? The review ends with the proposal that ACE phenotyping may prove to be a better first step toward personalized medicine for ACE inhibitors than ACE genotyping.

Cyclooxygenase-2 and nitric oxide

Nitric oxide (NO) is a simple but pluripotent molecule that is mainly released from vascular endothelial cells where it is formed intracellularly by nitric oxide synthase from L-arginine in response to several stimuli, including shear stress or muscarinic receptor stimulation. NO stimulates guanylyl cyclase to form cyclic guanosine monophosphate, which results in relaxation and vasodilatation of vascular smooth muscle cells (VSMCs). In addition, NO prevents adhesion and aggregation of platelets, and it possesses anti-inflammatory, antiproliferative, and antimigratory effects on leukocytes, endothelial cells, and VSMCs, thus offering protection from atherosclerosis. Dysfunction of the vascular endothelium has been documented in most conditions that promote or are associated with atherosclerosis and is characterized by a reduced bioavailability of NO. The healthy endothelium prevents adhesion and migration of leukocytes, proliferation of VSMCs, and platelet adhesion and aggregation. Maintaining the balance of blood flow and thrombus formation is also a major task of the vascular endothelium. It has been shown that both NO and prostacyclin, a cyclooxygenase-derived relaxing factor, inhibit activation of platelets and regulate vasomotion. Reduced NO and prostacyclin levels can result in endothelial dysfunction, which is recognized as the first step in the atherogenic process. It is of note that chronic inflammation conditions, such as rheumatoid arthritis, are associated with endothelial dysfunction. The reduced NO bioavailability may therefore explain the increased risk for cardiovascular events in patients with chronic low-grade inflammation, such as rheumatoid arthritis and osteoarthritis. Thus, this article provides an overview of the impact of inflammation and anti-inflammatory treatment with cyclooxygenase inhibitors on endothelial function.

Human ACE and bradykinin B2 receptors form a complex at the plasma membrane

To investigate how angiotensin I-converting enzyme (ACE) inhibitors enhance the actions of bradykinin (BK) on B2 receptors independent of blocking BK inactivation, we expressed human somatic ACE and B2 receptors in CHO cells. Bradykinin and its ACE-resistant analog were the receptor agonists. B2 fused with green fluorescent protein (GFP) and ACE were coprecipitated with antisera to GFP or ACE shown in Western blots. Immunohistochemistry of fixed cells localized ACE by red color and B2-GFP by green. Yellow on plasma membranes of coexpressing cells also indicated enzyme-receptor complex formation. Using ACE-fused cyan fluorescent protein donor and B2-fused yellow fluorescent protein (YFP) acceptor, we registered fluorescence resonance energy transfer (FRET) by the enhanced fluorescence of donor on acceptor photobleaching, establishing close (within 10 nm) positions of B2 receptors and ACE. Bradykinin stimulation cointernalized ACE and B2 receptors. We expressed ACE fused to N terminus of B2 receptors, anchoring only receptors to plasma membranes. Here, in contrast to cells, where both ACE and B2 receptors are separately anchored, ACE inhibitors neither enhance activation of chimeric B2 nor resensitize desensitized B2 receptors. Heterodimer formation between ACE and B2 receptors can be a mechanism for ACE inhibitors to augment kinin activity at cellular level.

Fibroblast Growth Factor-2 Mediates Angiotensin-Converting Enzyme Inhibitor-Induced Angiogenesis in Coronary Endothelium

The beneficial effect exerted by angiotensin-converting enzyme inhibitors (ACEI) on vascular endothelium has been attributed to restoration of endothelial cell survival properties and improvement of angiogenesis. Fibroblast growth factor (FGF)-2 is an angiogenic factor for the microvascular endothelium, which tonically promotes endothelial cell growth and survival through an autocrine/paracrine mechanism. Here, we formulate the hypothesis that FGF-2 might contribute to the prosurvival/proangiogenic effect of ACEI. We investigated zofenoprilat and, in selected experiments, lisinopril, as representatives of ACEI. These compounds induced formation of pseudocapillaries in vessel fragments isolated from porcine coronary and human umbilical arteries by increasing endothelial cell growth up to 5-fold. Angiogenesis was abolished by inhibitors of nitric-oxide synthase (NOS) pathway and by anti-FGF-2 antibodies. Consistently, in cultured coronary endothelial cells (CVECs), ACEI up-regulated endothelial NOS (eNOS) and FGF-2 and induced mitogen-activated protein kinase extracellular signal-regulated kinase 1/2 activation. The overexpression of eNOS/FGF-2 produced, at the functional level, enhanced cell proliferation and migration, the latter effect being dose-dependent and maximal at 0.1 microM zofenoprilat. The importance of FGF-2 for the acquisition of the angiogenic phenotype elicited by ACEI was clearly demonstrated by the impairment of endothelial functions following transfection of CVECs with small interference RNA for FGF-2. Moreover, FGF-2 silencing greatly affected the nuclear translocation of the FGF receptor (FGFR)-1, highlighting the autocrine mode of action of FGF-2. At the endothelial membrane level, zofenoprilat appeared to activate the bradykinin B1 receptor, a known stimulant of FGF-2 expression. In conclusion, we show that ACEI exert protective/proangiogenic effects in microvascular coronary endothelial cells by activating the endogenous FGF-2/FGFR-1 system.