Angiotensin II-induced vasodilation via type 2 receptor: Role of bradykinin and nitric oxide

Direct Vascular Effects of Angiotensin II (A Systematic Short Review)

The octapeptide angiotensin II (Ang II) is a circulating hormone as well as a locally formed agonist synthesized by the angiotensin-converting enzyme (ACE) of endothelial cells. It forms a powerful mechanism to control the amount and pressure of body fluids. All main effects are directed to save body salt and water and ensure blood pressure under basic conditions and in emergencies. All blood vessels respond to stimulation by Ang II; the immediate response is smooth muscle contraction, increasing vascular resistance, and elevating blood pressure. Such effects are conveyed by type 1 angiotensin receptors (AT1Rs) located in the plasma membrane of both endothelial and vascular smooth muscle cells. AT1Rs are heterotrimeric G protein-coupled receptors (GPCRs), but their signal pathways are much more complicated than other GPCRs. In addition to Gq/11, the G12/13, JAK/STAT, Jnk, MAPK, and ERK 1/2, and arrestin-dependent and -independent pathways are activated because of the promiscuous attachment of different signal proteins to the intracellular G protein binding site and to the intracellular C terminal loop. Substantial changes in protein expression follow, including the intracellular inflammation signal protein NF-κB, endothelial contact proteins, cytokines, matrix metalloproteinases (MMPs), and type I protocollagen, eliciting the inflammatory transformation of endothelial and vascular smooth muscle cells and fibrosis. Ang II is an important contributor to vascular pathologies in hypertensive, atherosclerotic, and aneurysmal vascular wall remodeling. Such direct vascular effects are reviewed. In addition to reducing blood pressure, AT1R antagonists and ACE inhibitors have a beneficial effect on the vascular wall by inhibiting pathological wall remodeling.

Muscle mass, muscle strength and the renin-angiotensin system

The renin-angiotensin system (RAS) is a classically known circulatory regulatory system. In addition to the previously known multi-organ circulatory form of the RAS, the existence of tissue RASs in individual organs has been well established. Skeletal muscle has also been identified as an organ with a distinct RAS. In recent years, the effects of RAS activation on skeletal muscle have been elucidated from several perspectives: differences in motor function due to genetic polymorphisms of RAS components, skeletal muscle dysfunction under conditions of excessive RAS activation such as heart failure, and the effects of the use of RAS inhibitors on muscle strength. In addition, the concept of the RAS itself has recently been expanded with the discovery of a 'protective arm' of the RAS formed by factors such as angiotensin-converting enzyme 2 and angiotensin 1-7. This has led to a new understanding of the physiological function of the RAS in skeletal muscle. This review summarizes the diverse physiological functions of the RAS in skeletal muscle and considers the potential of future therapeutic strategies targeting the RAS to overcome problems such as sarcopenia and muscle weakness associated with chronic disease.

Renin-angiotensin system-mediated nitric oxide signaling in podocytes

Nitric oxide (NO) is widely recognized for its role in regulating renal function and blood pressure. However, the precise mechanisms by which NO affects renal epithelial cells remain understudied. Our previous research has shown that NO signaling in glomerular podocytes can be initiated by Angiotensin II (ANG II) but not by ATP. This study aims to elucidate the crucial interplay between the renin-angiotensin system (RAS) and NO production in podocytes. To conduct our research, we used cultured human podocytes and freshly isolated rat glomeruli. A variety of RAS peptides were used, alongside confocal microscopy, to detect NO production and NO/Ca2+ cross talk. Dynamic changes in the podocyte cytoskeleton, mediated by RAS-NO intracellular signaling, were observed using fluorescent labeling for F-actin and scanning probe microscopy. The experiments demonstrated that ANG II and ANG III generated high levels of NO by activating the angiotensin II type 2 receptor (AT2R). We did not detect functional MAS receptor presence in podocytes, and the moderate NO response to ANG 1-7 was also mediated through AT2R. Furthermore, NO production impacted intracellular Ca2+ signaling and correlated with an increase in podocyte volume and growth. Scanning probe experiments revealed that AT2R activation and the corresponding NO generation are responsible for the protrusion of podocyte lamellipodia. Taken together, our data indicate that AT2R activation enhances NO production in podocytes and subsequently mediates changes in Ca2+ signaling and podocyte volume dynamics. These mechanisms may play a significant role in both physiological and pathophysiological interactions between the RAS and podocytes.NEW & NOTEWORTHY The renin-angiotensin system plays a crucial role in the production of intracellular nitric oxide within podocytes. This mechanism operates through the activation of the angiotensin II type 2 receptor, leading to dynamic modifications in intracellular calcium levels and the actin filament network. This intricate process is vital for linking the activity of angiotensin receptors to podocyte function.

The antihypertensive action of C-phycocyanin is related to the prevention of angiotensin II-caused vascular dysfunction in chronic kidney disease

C-phycocyanin (CPC) is a photosynthetic protein found in Arthrospira maxima with a nephroprotective and antihypertensive activity that can prevent the development of hemodynamic alterations caused by chronic kidney disease (CKD). However, the complete nutraceutical activities are still unknown. This study aims to determine if the antihypertensive effect of CPC is associated with preventing the impairment of hemodynamic variables through delaying vascular dysfunction. Twenty-four normotensive male Wistar rats were divided into four groups: (1) sham + 4 mL/kg/d vehicle (100 mM of phosphate buffer, PBS) administered by oral gavage (og), (2) sham + 100 mg/kg/d og of CPC, (3) CKD induced by 5/6 nephrectomy (CKD) + vehicle, (4) CKD + CPC. One week after surgery, the CPC treatment began and was administrated daily for four weeks. At the end treatment, animals were euthanized, and their thoracic aorta was used to determine the vascular function and expression of AT1, AT2, and Mas receptors. CKD-induced systemic arterial hypertension (SAH) and vascular dysfunction by reducing the vasorelaxant response of angiotensin 1-7 and increasing the contractile response to angiotensin II. Also, CKD increased the expression of the AT1 and AT2 receptors and reduced the Mas receptor expression. Remarkably, the treatment with CPC prevented SAH, renal function impairment, and vascular dysfunction in the angiotensin system. In conclusion, the antihypertensive activity of CPC is associated with avoiding changes in the expression of AT1, AT2, and Mas receptors, preventing vascular dysfunction development and SAH in rats with CKD.

Regulation of vascular angiotensin II type 1 and type 2 receptor and angiotensin-(1-7)/MasR signaling in normal and hypertensive pregnancy

Normal pregnancy (Norm-Preg) is associated with a slight reduction in blood pressure (BP) and decreased BP response to vasoconstrictor stimuli such as angiotensin II (Ang II), although the renin-angiotensin-aldosterone system (RAAS) is upregulated. Preeclampsia (PE) is a complication of pregnancy manifested as hypertension-in-pregnancy (HTN-Preg), and dysregulation of angiotensin biosynthesis and signaling have been implicated. Ang II activates vascular Ang II type-1 receptor (AT1R) and Ang II type-2 receptor (AT2R), while angiotensin-(1-7) promotes Ang-(1-7)/MasR signaling. The role of AT1R in vasoconstriction and the activated cellular mechanisms are well-characterized. The sensitivity of vascular AT1R to Ang II and consequent activation of vasoconstrictor mechanisms decrease during Norm-Preg, but dramatically increase in HTN-Preg. Placental ischemia in late pregnancy could also initiate the release of AT1R agonistic autoantibodies (AT1AA) with significant impact on endothelial dysfunction and activation of contraction pathways in vascular smooth muscle including [Ca2+]c and protein kinase C. On the other hand, the role of AT2R and Ang-(1-7)/MasR in vascular relaxation, particularly during Norm-Preg and PE, is less clear. During Norm-Preg, increases in the expression/activity of vascular AT2R and Ang-(1-7)/MasR promote the production of endothelium-derived relaxing factors such as nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factor leading to generalized vasodilation. Aortic segments of Preg rats show prominent endothelial AT2R staining and increased relaxation and NO production in response to AT2R agonist CGP42112A, and treatment with AT2R antagonist PD123319 enhances phenylephrine-induced contraction. Decreased vascular AT2R and Ang-(1-7)/MasR expression and receptor-mediated mechanisms of vascular relaxation have been suggested in HTN-Preg animal models, but their role in human PE needs further testing. Changes in angiotensin-converting enzyme-2 (ACE2) have been observed in COVID-19 patients, and whether ACE2 influences the course of COVID-19 viral infection/immunity in Norm-Preg and PE is an intriguing area for research.

Restoring Angiotensin Type 2 Receptor Function Reverses PFOS-Induced Vascular Hyper-Reactivity and Hypertension in Pregnancy

Perfluorooctane sulfonic acid (PFOS) exposure during pregnancy induces hypertension with decreased vasodilatory angiotensin type-2 receptor (AT2R) expression and impaired vascular reactivity and fetal weights. We hypothesized that AT2R activation restores the AT1R/AT2R balance and reverses gestational hypertension by improving vascular mechanisms. Pregnant Sprague-Dawley rats were exposed to PFOS through drinking water (50 μg/mL) from gestation day (GD) 4-20. Controls received drinking water with no detectable PFOS. Control and PFOS-exposed rats were treated with AT2R agonist Compound 21 (C21; 0.3 mg/kg/day, SC) from GD 15-20. In PFOS dams, blood pressure was higher, blood flow in the uterine artery was reduced, and C21 reversed these to control levels. C21 mitigated the heightened contraction response to Ang II and enhanced endothelium-dependent vasorelaxation in uterine arteries of PFOS dams. The observed vascular effects of C21 were correlated with reduced AT1R levels and increased AT2R and eNOS protein levels. C21 also increased plasma bradykinin production in PFOS dams and attenuated the fetoplacental growth restriction. These data suggest that C21 improves the PFOS-induced maternal vascular dysfunction and blood flow to the fetoplacental unit, providing preclinical evidence to support that AT2R activation may be an important target for preventing or treating PFOS-induced adverse maternal and fetal outcomes.

The Footprint of Kynurenine Pathway in Cardiovascular Diseases

Kynurenine pathway is the main route of tryptophan metabolism and produces several metabolites with various biologic properties. It has been uncovered that several cardiovascular diseases are associated with the overactivation of kynurenine pathway and kynurenine and its metabolites have diagnostic and prognostic value in cardiovascular diseases. Furthermore, it was found that several kynurenine metabolites can differently affect cardiovascular health. For instance, preclinical studies have shown that kynurenine, xanthurenic acid and cis-WOOH decrease blood pressure; kynurenine and 3-hydroxyanthranilic acid prevent atherosclerosis; kynurenic acid supplementation and kynurenine 3-monooxygenase (KMO) inhibition improve the outcome of stroke. Indoleamine 2,3-dioxygenase (IDO) overactivity and increased kynurenine levels improve cardiac and vascular transplantation outcomes, whereas exacerbating the outcome of myocardial ischemia, post-ischemic myocardial remodeling, and abdominal aorta aneurysm. IDO inhibition and KMO inhibition are also protective against viral myocarditis. In addition, dysregulation of kynurenine pathway is observed in several conditions such as senescence, depression, diabetes, chronic kidney disease (CKD), cirrhosis, and cancer closely connected to cardiovascular dysfunction. It is worth defining the exact effect of each metabolite of kynurenine pathway on cardiovascular health. This narrative review is the first review that separately discusses the involvement of kynurenine pathway in different cardiovascular diseases and dissects the underlying molecular mechanisms.

Nitric-Oxide-Mediated Signaling in Podocyte Pathophysiology

Nitric oxide (NO) is a potent signaling molecule involved in many physiological and pathophysiological processes in the kidney. NO plays a complex role in glomerular ultrafiltration, vasodilation, and inflammation. Changes in NO bioavailability in pathophysiological conditions such as hypertension or diabetes may lead to podocyte damage, proteinuria, and rapid development of chronic kidney disease (CKD). Despite the extensive data highlighting essential functions of NO in health and pathology, related signaling in glomerular cells, particularly podocytes, is understudied. Several reports indicate that NO bioavailability in glomerular cells is decreased during the development of renal pathology, while restoring NO level can be beneficial for glomerular function. At the same time, the compromised activity of nitric oxide synthase (NOS) may provoke the formation of peroxynitrite and has been linked to autoimmune diseases such as systemic lupus erythematosus. It is known that the changes in the distribution of NO sources due to shifts in NOS subunits expression or modifications of NADPH oxidases activity may be linked to or promote the development of pathology. However, there is a lack of information about the detailed mechanisms describing the production and release of NO in the glomerular cells. The interaction of NO and other reactive oxygen species in podocytes and how NO-calcium crosstalk regulates glomerular cells’ function is still largely unknown. Here, we discuss recent reports describing signaling, synthesis, and known pathophysiological mechanisms mediated by the changes in NO homeostasis in the podocyte. The understanding and further investigation of these essential mechanisms in glomerular cells will facilitate the design of novel strategies to prevent or manage health conditions that cause glomerular and kidney damage.

Understanding diabetes-induced cardiomyopathy from the perspective of renin angiotensin aldosterone system

Experimental and clinical evidence suggests that diabetic subjects are predisposed to a distinct cardiovascular dysfunction, known as diabetic cardiomyopathy (DCM), which could be an autonomous disease independent of concomitant micro and macrovascular disorders. DCM is one of the prominent causes of global morbidity and mortality and is on a rising trend with the increase in the prevalence of diabetes mellitus (DM). DCM is characterized by an early left ventricle diastolic dysfunction associated with the slow progression of cardiomyocyte hypertrophy leading to heart failure, which still has no effective therapy. Although the well-known "Renin Angiotensin Aldosterone System (RAAS)" inhibition is considered a gold-standard treatment in heart failure, its role in DCM is still unclear. At the cellular level of DCM, RAAS induces various secondary mechanisms, adding complications to poor prognosis and treatment of DCM. This review highlights the importance of RAAS signaling and its major secondary mechanisms involving inflammation, oxidative stress, mitochondrial dysfunction, and autophagy, their role in establishing DCM. In addition, studies lacking in the specific area of DCM are also highlighted. Therefore, understanding the complex role of RAAS in DCM may lead to the identification of better prognosis and therapeutic strategies in treating DCM.

Investigation of proteins important for microcirculation using in vivo microdialysis after glucose provocation: a proteomic study

Insulin has metabolic and vascular effects in the human body. What mechanisms that orchestrate the effects in the microcirculation, and how the responds differ in different tissues, is however not fully understood. It is therefore of interest to search for markers in microdialysate that may be related to the microcirculation. This study aims to identify proteins related to microvascular changes in different tissue compartments after glucose provocation using in vivo microdialysis. Microdialysis was conducted in three different tissue compartments (intracutaneous, subcutaneous and intravenous) from healthy subjects. Microdialysate was collected during three time periods; recovery after catheter insertion, baseline and glucose provocation, and analyzed using proteomics. Altogether, 126 proteins were detected. Multivariate data analysis showed that the differences in protein expression levels during the three time periods, including comparison before and after glucose provocation, were most pronounced in the intracutaneous and subcutaneous compartments. Four proteins with vascular effects were identified (angiotensinogen, kininogen-1, alpha-2-HS-glycoprotein and hemoglobin subunit beta), all upregulated after glucose provocation compared to baseline in all three compartments. Glucose provocation is known to cause insulin-induced vasodilation through the nitric oxide pathway, and this study indicates that this is facilitated through the interactions of the RAS (angiotensinogen) and kallikrein-kinin (kininogen-1) systems.

Differences in the expression of the renin angiotensin system and the kallikrein-kinin system during the course of myocardial infarction in male and female Wistar rats

Background:

There is some evidence that components of the renin-angiotensin system and kallikrein-kinin system are not similarly regulated in both sexes. The aim of this work was to analyze the expression of angiotensin-converting enzyme, angiotensin-converting enzyme 2, angiotensin 1 receptor, angiotensin 2 receptor, beta-1 receptor, and beta-2 receptor during the evolution of myocardial infarction.

Methods:

Thirty-six male and 36 female Wistar rats were used. Myocardial infarction was induced. Six groups of both sexes were formed, (n=6): (a) sham; (b) 48 h myocardial infarction; (c) one week myocardial infarction; (d) two weeks myocardial infarction; (e) three weeks myocardial infarction and (f) four weeks myocardial infarction. The expression was evaluated by real-time polymerase chain reaction on the penumbra of left ventricle.

Results:

The mRNA expression of most biomarkers was lower in females than in males. During acute infarction, an increase of all protein expression was found in female and at two weeks while in the male only biomarker changes occurred at three weeks. In addition, in male biomarkers mRNA expression decreased during chronic infarction while in females it did not.

Conclusions:

The renin-angiotensin system and kallikrein-kinin system biomarkers expression occurs at earlier times in the female than in the male rat. In addition, during chronic myocardial infarction these biomarkers remained unchanged in females while in males they decreased.

Divergent impact of gestational diabetes mellitus between the thoracic and abdominal rat aorta: Influence of endothelium and angiotensin II receptors

Gestational diabetes mellitus (GDM) affects 5-10% of pregnancies and increases the risk of fetal and maternal adverse outcomes. Interestingly, the vascular response to AngII is decreased by pregnancy while the response is increased by diabetes. It remains unclear how GDM affects vascular tone and how angiotensin II receptors contribute to these changes. In this work, we sought to establish the vascular impact of a hypercaloric diet-induced GDM through changes in AT1 and AT2 receptor's expression. Female rats fed for 7 weeks with standard (SD) or hypercaloric (HD) diet were divided at week 4. Half of the rats of each group were mated to become pregnant and those fed with a HD developed GDM. AngII-induced vasoconstriction was measured in thoracic or abdominal aorta rings using a conventional isolated organ bath and AT1 and AT2 receptors were searched by immunohistochemistry. Experiments where conducted on the pregnant standard diet group (PSD) and the pregnant hypercaloric-gestational diabetes mellitus group (PHD-GDM). Vasoconstriction was reduced in the thoracic aorta (P < 0.05 vs PSD) but increased in the abdominal aorta of PHD-GDM rats (P < 0.05 vs PSD). Blockade of AT2 receptors using PD123319 decreased vasoconstriction, particularly in the abdominal aorta of PHD-GDM animals (P < 0.05 vs PSD). PHD-GDM increased AT1 receptors expression (P < 0.05 vs PSD). Also, PHD-GDM reverted physiologic hypoglycemia and hypotension of healthy pregnancy. Findings provide new insight into the hypercaloric diet induced damage on the vasculature during pregnancy.

Role of pregnancy on insulin-induced vasorelaxation: the influence of angiotensin II receptors

Insulin resistance is a feature of pregnancy and is associated with increased levels of angiotensin II (Ang II) and insulin. Therefore, pregnancy may change insulin-induced vasodilation through changes in Ang II receptors. Insulin-induced vasorelaxation was evaluated in phenylephrine-precontracted aortic rings of pregnant and non-pregnant rats, using a conventional isolated organ preparation. Experiments were performed in thoracic or abdominal aorta rings with or without endothelium in the presence and absence of N^G-nitro-L-arginine methyl ester (L-NAME) (10^-5 M), losartan (10^-7 M), or PD123319 (10^-7 M). AT1 and AT2 receptor expressions were detected by immunohistochemistry. Insulin-induced vasodilation was endothelium- and nitric oxide-dependent and decreased in the thoracic aorta but increased in the abdominal segment of pregnant rats. The insulin's vasorelaxant effect was increased by losartan mainly on the thoracic aorta. PD123319 decreased insulin-induced vasorelaxation mainly in the pregnant rat abdominal aorta. AT1 receptor expression was decreased while AT2 receptor expression was increased by pregnancy. In conclusion, pregnancy changes insulin-induced vasorelaxation. Moreover, insulin vasodilation is tonically inhibited by AT1 receptors, while AT2 receptors appear to have an insulin-sensitizing effect. The role of pregnancy and Ang II receptors differ depending on the aorta segment. These results shed light on the role of pregnancy and Ang II receptors on the regulation of insulin-mediated vasodilation.

Activation of angiotensin type 2 receptor attenuates testosterone-induced hypertension and uterine vascular resistance in pregnant rats†

Preeclampsia is a pregnancy-related hypertensive disorder with unclear mechanisms. While hypersensitivity to angiotensin II via vasoconstrictive angiotensin type-1 receptor (AT1R) is observed in preeclampsia, the importance of vasodilatory angiotensin type-2 receptor (AT2R) in the control of vascular dysfunction is less clear. We assessed whether AT1R, AT2R, and endothelial nitric oxide synthase (eNOS) expression are altered in placental vessels of preeclamptic women and tested if ex vivo incubation with AT2R agonist Compound 21 (C21; 1 μM) could restore AT1R, AT2R, and eNOS balance. Further, using a rat model of gestational hypertension induced by elevated testosterone, we examined whether C21 (1 μg/kg/day, oral) could preserve AT1R and AT2R balance and improve blood pressure, uterine artery blood flow, and vascular function. Western blots revealed that AT1R protein level was higher while AT2R and eNOS protein were reduced in preeclamptic placental vessels, and AT2R agonist C21 decreased AT1R and increased AT2R and eNOS protein levels in preeclamptic vessels. In testosterone dams, blood pressure was higher, and uterine artery blood flow was reduced, and C21 treatment reversed these levels similar to those in controls dams. C21 attenuated the exaggerated Ang II contraction and improved endothelium-dependent vasorelaxation in uterine arteries of testosterone dams. These C21-mediated vascular effects were associated with decreased AT1R and increased AT2R and eNOS protein levels. C21 also increased serum nitrate/nitrite and bradykinin production in testosterone dams and attenuated the fetoplacental growth restriction. Thus, AT1R upregulation and AT2R downregulation are observed in preeclampsia and testosterone model, and increasing AT2R activity could help restore AT1R and AT2R balance and improve gestational vascular function.

Exercise training attenuates angiotensin II-induced vasoconstriction in the aorta of normotensive but not hypertensive rats

NEW FINDINGS

What is the central question of this study? What are the effects of exercise on Ang II-induced vasoconstriction in aortas of normotensive rats and how do these effects occur in two-kidney-one-clip hypertensive animals? What is the main finding and its importance? In two-kidney rats, exercise training improves the Ang II-induced vasoconstriction by endothelium-derived NO released through AT₂ R activation. This effect of exercise training on the Ang II-induced vasoconstriction is blunted in two-kidney-one-clip hypertensive animals, possibly as a consequence of oxidative stress.

ABSTRACT

This study investigated the effects of both acute exercise and training on the Ang II-induced vasoconstriction in aorta of normotensive (two-kidney; 2K) and two-kidney-one-clip (2K1C) hypertensive rats, focusing on endothelial mechanisms related to nitric oxide (NO) and prostanoids. Aorta rings of 2K and 2K1C male Wistar rats, sedentary and trained, killed at rest and after acute exercise, were challenged with Ang II in either the absence or the presence of PD 123,319, a selective angiotensin receptor subtype 2 (AT₂ R) antagonist; N^ω -nitro-l-arginine methyl ester (l-NAME), a non-selective inhibitor of nitric oxide synthase; indomethacin, a non-selective inhibitor of cyclooxygenase; or Tiron, an analogue of superoxide dismutase. Aortas of sedentary and trained animals studied at rest were also submitted to histomorphometric analysis. Exercise training reduced the Ang II-induced vasoconstriction in aorta of 2K but not of 2K1C animals. This reduction of Ang II response in aortas of 2K animals was not found after endothelial removal or treatment with PD 123,319 or l-NAME. These results suggest that exercise training improves the modulation of Ang II-induced vasoconstriction in aorta of 2K animals, by endothelium-derived NO released due to the activation of AT₂ R. No exercise-induced change of Ang II response occurred in 2K1C animals, except in the presence of Tiron, which was evidence for reduction of such responses only in resting trained 2K1C animals. In 2K1C animals, NO modulation of Ang II-induced vasoconstriction might be suppressed by local oxidative stress. Moreover, exercise training slightly reduced the media layer thickness in the aortas of the 2K1C, but not 2K animals, which may indicate cardiovascular protection of these animals.

Endoplasmic Reticulum (ER) Stress in Part Mediates Effects of Angiotensin II in Pancreatic Beta Cells

INTRODUCTION

The renin angiotensin aldosterone system (RAAS) is a hormone system known for its role in regulating blood pressure and fluid balance. Numerous RAAS inhibitors routinely prescribed for hypertension have also beneficial effects in type 2 diabetes (T2D) prevention. RAAS components are expressed locally in many tissues, including adipose tissue and pancreas, where they exert metabolic effects through RAAS bioactive hormone angiotensin II (Ang II). Pancreatic beta cells are specialized insulin-producing cells; they have also developed endoplasmic reticulum (ER), which contributes to beta cell dysfunction, when proteins are misfolded in disease states such as T2D. However, no studies have investigated the relationship between RAAS and ER stress in beta cells as a mechanism linking pancreatic RAAS to T2D. Hence, we hypothesized that Ang II treatment of beta cells increases ER stress and inflammation leading to reduced insulin secretion.

METHODS

To test this hypothesis, we treated clonal INS-1E beta cells and human islets with Ang II and assessed changes in ER stress markers. INS-1E beta cells were also used for measuring insulin secretion and for assessing the effects of various RAAS and ER stress inhibitors.

RESULTS

We demonstrated that Ang II significantly increased the expression of ER stress genes such as Chop and Atf4 and reduced insulin secretion. Furthermore, inhibition of Ang II production with an angiotensin converting enzyme inhibitor (ACEi, captopril) significantly reduced ER stress. Moreover, the Ang II receptor blockade reduced ER stress significantly and rescued insulin secretion.

DISCUSSION

This research provides new mechanistic insight into the role of RAAS activation via ER stress on beta cell dysfunction and provides additional evidence for protective effects of RAAS inhibition in T2D.

Cell-Specific Protective Signaling Induced by the Novel AT2R-Agonist NP-6A4 on Human Endothelial and Smooth Muscle Cells

Cardiovascular disease incidence continues to rise and new treatment paradigms are warranted. We reported previously that activation of Angiotensin II receptor (encoded by the X-linked Agtr2 gene) by a new peptide agonist, NP-6A4, was more effective in protecting mouse cardiomyocyte HL-1 cells and human coronary artery vascular smooth muscle cells (hCAVSMCs) from acute nutrient deficiency than other drugs tested. To elucidate further the protective effects of NP-6A4 in human cells, we studied the effects of NP-6A4 treatment on functions of human coronary artery endothelial cells (hCAECs), and hCAVSMCs. In hCAVSMCs, NP-6A4 (1 μM) increased Agtr2 mRNA (sixfold, p < 0.05) after 12-h exposure, whereas in hCAECs, significant increase in Agtr2 mRNA (hCAECs: eightfold) was observed after prolonged exposure. Interestingly, NP-6A4 treatment (1 μM, 12 h) increased AT2R protein levels in all human cells tested. Pre-treatment with AT2R-antagonist PD123319 (20 μM) and anti-AT2R siRNA (1 μM) suppressed this effect. Thus, NP-6A4 activates a positive feedback loop for AT2R expression and signaling in hCAVSMCs and hCAECs. NP-6A4 (1–20 μM) increased cell index (CI) of hCAVSMCs as determined by real time cell analyzer (RTCA), indicating that high concentrations of NP-6A4 were not cytotoxic for hCAVSMCs, rather promoting better cell attachment and growth. Seahorse Extracellular Flux Assay revealed that NP-6A4 (1 μM) treatment for 7 days increased whole cell-based mitochondrial parameters of hCAVSMCs, specifically maximal respiration (p < 0.05), spare respiratory capacity (p < 0.05) and ATP production (p < 0.05). NP-6A4 (1 μM; 7 days) also suppressed Reactive Oxygen Species (ROS) in hCAVSMCs. Exposure to Doxorubicin (DOXO) (1 μM) increased ROS in hCAVSMCs and this effect was suppressed by NP-6A4 (1 μM). In hCAECs grown in complete medium, NP-6A4 (1 μM) and Ang II (1 μM) exerted similar changes in CI. Additionally, NP-6A4 (5 μM: 12 h) increased expression of eNOS (sixfold, p < 0.05) and generation of nitric oxide (1.3-fold, p < 0.05) in hCAECs and pre-treatment with PD123319 (20 μM) suppressed this effect partially (65%). Finally, NP-6A4 decreased phosphorylation of Jun-N-terminal kinase, implicated in apoptosis of ECs in atherosclerotic sites. Taken together, NP-6A4, through its ability to increase AT2R expression and signaling, exerts different cell-specific protective effects in human VSMCs and ECs.

Integrative Physiological Aspects of Brain RAS in Hypertension

PURPOSE OF REVIEW

The renin-angiotensin system (RAS) plays an important role in modulating cardiovascular function and fluid homeostasis. While the systemic actions of the RAS are widely accepted, the role of the RAS in the brain, its regulation of cardiovascular function, and sympathetic outflow remain controversial. In this report, we discuss the current understanding of central RAS on blood pressure (BP) regulation, in light of recent literature and new experimental techniques.

RECENT FINDINGS

Studies using neuronal or glial-specifc mouse models have allowed for greater understanding into the site-specific expression and role centrally expressed RAS proteins have on BP regulation. While all components of the RAS have been identified in cardiovascular regulatory regions of the brain, their actions may be site specific. In a number of animal models of hypertension, reduction in Ang II-mediated signaling, or upregulation of the central ACE2/Ang 1-7 pathway, has been shown to reduce BP, via a reduction in sympathetic signaling and increase parasympathetic tone, respectively. Emerging evidence also suggests that, in part, the female protective phenotype against hypertension may be due to inceased ACE2 activity within cardiovascular regulatory regions of the brain, potentially mediated by estrogen. Increasing evidence suggests the importance of a central renin-angiotensin pathway, although its localization and the mechanisms involved in its expression and regulation still need to be clarified and more precisely defined. All reported studies/experiments with human or animal subjects performed by the authors have been previously published and complied with all applicable ethical standards (including the Helsinki declaration and its amendments, institutional/national research committee standards, and international/national/institutional guidelines).

Association of renin-angiotensin system genetic polymorphisms and aneurysmal subarachnoid hemorrhage

OBJECTIVE

Renin-angiotensin system (RAS) genetic polymorphisms are thought to play a role in cerebral aneurysm formation and rupture. The Cerebral Aneurysm Renin-Angiotensin System (CARAS) study prospectively evaluated common RAS polymorphisms and their relation to aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

The CARAS study prospectively enrolled aSAH patients and controls at 2 academic centers in the United States. A blood sample was obtained from all patients for genetic evaluation and measurement of plasma angiotensin-converting enzyme (ACE) concentration. Common RAS polymorphisms were detected using 5′ exonuclease (TaqMan) genotyping assays and restriction fragment length polymorphism analysis.

RESULTS

Two hundred forty-eight patients were screened, and 149 aSAH patients and 50 controls were available for analysis. There was a recessive effect of the C allele of the angiotensinogen (AGT) C/T single-nucleotide polymorphism (SNP) (OR 1.94, 95% CI 0.912–4.12, p = 0.0853) and a dominant effect of the G allele of the angiotensin II receptor Type 2 (AT2) G/A SNP (OR 2.11, 95% CI 0.972–4.57, p = 0.0590) on aSAH that did not reach statistical significance after adjustment for potential confounders. The ACE level was significantly lower in aSAH patients with the II genotype (17.6 ± 8.0 U/L) as compared with the ID (22.5 ± 12.1 U/L) and DD genotypes (26.6 ± 14.2 U/L) (p = 0.0195).

CONCLUSIONS

The AGT C/T and AT2 G/A polymorphisms were not significantly associated with aSAH after controlling for potential confounders. However, a strong trend was identified for a dominant effect of the G allele of the AT2 G/A SNP. Downregulation of the local RAS may contribute to the formation of cerebral aneurysms and subsequent presentation with aSAH. Further studies are required to elucidate the relevant pathophysiology and its potential implication in treatment of patients with aSAH.

Diabetic Microvascular Disease: An Endocrine Society Scientific Statement

Both type 1 and type 2 diabetes adversely affect the microvasculature in multiple organs. Our understanding of the genesis of this injury and of potential interventions to prevent, limit, or reverse injury/dysfunction is continuously evolving. This statement reviews biochemical/cellular pathways involved in facilitating and abrogating microvascular injury. The statement summarizes the types of injury/dysfunction that occur in the three classical diabetes microvascular target tissues, the eye, the kidney, and the peripheral nervous system; the statement also reviews information on the effects of diabetes and insulin resistance on the microvasculature of skin, brain, adipose tissue, and cardiac and skeletal muscle. Despite extensive and intensive research, it is disappointing that microvascular complications of diabetes continue to compromise the quantity and quality of life for patients with diabetes. Hopefully, by understanding and building on current research findings, we will discover new approaches for prevention and treatment that will be effective for future generations.

Associations of renin-angiotensin system genetic polymorphisms and clinical course after aneurysmal subarachnoid hemorrhage

OBJECTIVE

Renin-angiotensin system (RAS) genetic polymorphisms are thought to play a role in cerebral aneurysm formation and rupture. The Cerebral Aneurysm Renin Angiotensin System (CARAS) study prospectively evaluated associations of common RAS polymorphisms and clinical course after aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

The CARAS study prospectively enrolled aSAH patients at 2 academic centers in the United States. A blood sample was obtained from all patients for genetic evaluation and measurement of plasma angiotensin converting enzyme (ACE) concentration. Common RAS polymorphisms were detected using 5′exonuclease genotyping assays and pyrosequencing. Analysis of associations of RAS polymorphisms and clinical course after aSAH were performed.

RESULTS

A total of 166 patients were screened, and 149 aSAH patients were included for analysis. A recessive effect of allele I (insertion) of the ACE I/D (insertion/deletion) polymorphism was identified for Hunt and Hess grade in all patients (OR 2.76, 95% CI 1.17–6.50; p = 0.0206) with subsequent poor functional outcome. There was a similar effect on delayed cerebral ischemia (DCI) in patients 55 years or younger (OR 3.63, 95% CI 1.04–12.7; p = 0.0439). In patients older than 55 years, there was a recessive effect of allele A of the angiotensin II receptor Type 2 (AT2) A/C single nucleotide polymorphism (SNP) on DCI (OR 4.70, 95% CI 1.43–15.4; p = 0.0111).

CONCLUSIONS

Both the ACE I/D polymorphism and the AT2 A/C single nucleotide polymorphism were associated with an age-dependent risk of delayed cerebral ischemia, whereas only the ACE I/D polymorphism was associated with poor clinical grade at presentation. Further studies are required to elucidate the relevant pathophysiology and its potential implication in the treatment of patients with aSAH.

The High Blood Pressure-Malaria Protection Hypothesis

RATIONALE

A recently proposed hypothesis states that malaria may contribute to hypertension in endemic areas,¹ but the role of angiotensin II (Ang II), a major regulator of blood pressure, was not considered. Elevated levels of Ang II may confer protection against malaria morbidity and mortality, providing an alternative explanation for hypertension in malaria endemic areas.

OBJECTIVE

To discuss a possible alternative cause for hypertension in populations who have been under the selective pressure of malaria.

METHODS AND RESULTS

We reviewed published scientific literature for studies that could establish a link between Ang II and malaria. Both genetic and functional studies suggested that high levels of Ang II may confer protection against cerebral malaria by strengthening the integrity of the endothelial brain barrier. We also describe strong experimental evidence supporting our hypothesis through genetic, functional, and interventional studies.

CONCLUSIONS

A causal association between high levels of Ang II and protection from malaria pathogenesis can provide a likely explanation for the increased prevalence in hypertension observed in populations of African and South Asian origin. Furthermore, this potential causative connection might also direct unique approaches for the effective treatment of cerebral malaria.

A Review of Potential Marine-derived Hypotensive and Anti-obesity Peptides

Bioactive peptides are food derived components, usually consisting of 3-20 amino acids, which are inactive when incorporated within their parent protein. Once liberated by enzymatic or chemical hydrolysis, during food processing and gastrointestinal transit, they can potentially provide an array of health benefits to the human body. Owing to an unprecedented increase in the worldwide incidence of obesity and hypertension, medical researchers are focusing on the hypotensive and anti-obesity properties of nutritionally derived bioactive peptides. The role of the renin-angiotensin system has long been established in the aetiology of metabolic diseases and hypertension. Targeting the renin-angiotensin system by inhibiting the activity of angiotensin-converting enzyme (ACE) and preventing the formation of angiotensin II can be a potential therapeutic approach to the treatment of hypertension and obesity. Fish-derived proteins and peptides can potentially be excellent sources of bioactive components, mainly as a source of ACE inhibitors. However, increased use of marine sources, poses an unsustainable burden on particular fish stocks, so, the underutilized fish species and by-products can be exploited for this purpose. This paper provides an overview of the techniques involved in the production, isolation, purification, and characterization of bioactive peptides from marine sources, as well as the evaluation of the ACE inhibitory (ACE-I) activity and bioavailability.

Renin inhibitor aliskiren exerts beneficial effect on trabecular bone by regulating skeletal renin-angiotensin system and kallikrein-kinin system in ovariectomized mice

SUMMARY

The skeletal renin-angiotensin system contributes to the development of osteoporosis. The renin inhibitor aliskiren exhibited beneficial effects on trabecular bone of osteoporotic mice, and this action might be mediated through angiotensin and bradykinin receptor pathways. This study implies the potential application of renin inhibitor in the management for postmenopausal osteoporosis.

INTRODUCTION

The skeletal renin-angiotensin system plays key role in the pathological process of osteoporosis. The present study is designed to elucidate the effect of renin inhibitor aliskiren on trabecular bone and its potential action mechanism in ovariectomized (OVX) mice.

METHODS

The OVX mice were treated with low dose (5 mg/kg) or high dose (25 mg/kg) of aliskiren or its vehicle for 8 weeks. The bone turnover markers were measured by ELISA. The structural parameters of trabecular bone at lumbar vertebra (LV) and distal femoral metaphysis were measured by micro-CT. The expression of messenger RNA (mRNA) and protein was studied by RT-PCR and immunoblotting, respectively.

RESULTS

Aliskiren treatment reduced urinary excretion of calcium and serum level of tartrate-resistant acid phosphatase in OVX mice. The treatment with aliskiren significantly increased bone volume (BV/TV) and connectivity density (Conn.D) of trabecular bone at LV-2 and LV-5 as well as dramatically enhanced BV/TV, Conn.D, bone mineral density (BMD/BV) and decreased bone surface (BS/BV) at the distal femoral end. Aliskiren significantly down-regulated the expression of angiotensinogen, angiotensin II (Ang II), Ang II type 1 receptor, bradykinin receptor (BR)-1, and osteocytic-specific gene sclerostin as well as the osteoclast-specific genes, including carbonic anhydrase II, matrix metalloproteinase-9, and cathepsin K.

CONCLUSIONS

This study revealed that renin inhibitor aliskiren exhibited the beneficial effects on trabecular bone of ovariectomy-induced osteoporotic mice, and the underlying mechanism for this action might be mediated through Ang II and BR signaling pathways in bone.

Developmental acceleration of bradykinin-dependent relaxation by prenatal chronic hypoxia impedes normal development after birth

Bradykinin-induced activation of the pulmonary endothelium triggers nitric oxide production and other signals that cause vasorelaxation, including stimulation of large-conductance Ca(2+)-activated K(+) (BKCa) channels in myocytes that hyperpolarize the plasma membrane and decrease intracellular Ca(2+). Intrauterine chronic hypoxia (CH) may reduce vasorelaxation in the fetal-to-newborn transition and contribute to pulmonary hypertension of the newborn. Thus we examined the effects of maturation and CH on the role of BKCa channels during bradykinin-induced vasorelaxation by examining endothelial Ca(2+) signals, wire myography, and Western immunoblots on pulmonary arteries isolated from near-term fetal (∼ 140 days gestation) and newborn, 10- to 20-day-old, sheep that lived in normoxia at 700 m or in CH at high altitude (3,801 m) for >100 days. CH enhanced bradykinin-induced relaxation of fetal vessels but decreased relaxation in newborns. Endothelial Ca(2+) responses decreased with maturation but increased with CH. Bradykinin-dependent relaxation was sensitive to 100 μM nitro-L-arginine methyl ester or 10 μM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, supporting roles for endothelial nitric oxide synthase and soluble guanylate cyclase activation. Indomethacin blocked relaxation in CH vessels, suggesting upregulation of PLA2 pathways. BKCa channel inhibition with 1 mM tetraethylammonium reduced bradykinin-induced vasorelaxation in the normoxic newborn and fetal CH vessels. Maturation reduced whole cell BKCa channel α1-subunit expression but increased β1-subunit expression. These results suggest that CH amplifies the contribution of BKCa channels to bradykinin-induced vasorelaxation in fetal sheep but stunts further development of this vasodilatory pathway in newborns. This involves complex changes in multiple components of the bradykinin-signaling axes.

Some Aspects of the Renin-Angiotensin-System in Hemodialysis Patients

Understanding of the renin-angiotensin system (RAS) has changed remarkably over the past decade. Renin, angiotensin converting enzyme (ACE), angiotensin II (Ang II), and Ang II receptors are the main components of the RAS. Recent studies identified the ACE2/Ang 1–7/ Mas receptor axis, which counter-regulates the classical RAS. Many studies have examined the effects of the RAS on the progression of cardiovascular disease and chronic kidney disease (CKD). In addition, many studies have documented increased levels of ACE in hemodialysis (HD) patients, raising concerns about the negative effects of RAS activation on the progression of renal disease. Elevated ACE increases the level of Ang II, leading to vasoconstriction and cell proliferation. Ang II stimulation of the sympathetic system leads to renal and cardiovascular complications that are secondary to uncontrolled hypertension. This review provides an overview of the RAS, evaluates new research on the role of ACE2 in dialysis, and reviews the evidence for potentially better treatments for patients undergoing HD. Further understanding of the role of ACE and ACE2 in HD patients may aid the development of targeted therapies that slow the progression of CKD and cardiovascular disease.

Mas receptor overexpression increased Ang-(1-7) relaxation response in renovascular hypertensive rat carotid

Renin-angiotensin system (RAS) is an important factor in the pathophysiology of hypertension. Mas receptor, Angiotensin-(1-7) [Ang-(1-7)]-activated receptor, is an important RAS component and exerts protective effects in the vasculature. Ang-(1-7) vascular effects and Mas receptor expression in carotid from renovascular hypertensive (2K-1C) rats is not clear. In the present study we investigated Mas receptor vasodilator response activated by Ang-(1-7) in the carotid rings from sham and 2K-1C rats. Changes in isometric tension were recorded on organ chamber. Mas receptors expression was investigated in carotid by Western blot. Nitric oxide production was evaluated by 2,3-diaminonaphthalene (DAN) and eNOS expression and activity by immunofluoresce and western blot, respectively. Ang-(1-7) induced concentration-dependent vasodilator effect in carotid rings from sham and 2K-1C, which the hypertension increased vasodilatation response. In the 2K-1C carotid rings, A-779 (Mas receptor antagonist) reduced but not abolish the vasodilator effect of Ang-(1-7). Corroborating, Mas receptor protein expression was significantly increased in the 2K-1C rats. L-NAME and ibuprofen decreased Ang-(1-7) vasodilator response and L-NAME plus ibuprofen practically abolish the remaining vasodilatation response. Nitric oxide production is increased due increased of eNOS expression and pSer(1177) activity. Our results demonstrated that renovascular hypertension increased Mas receptors expression and nitric oxide production in the rats carotid which, consequently increased Ang-(1-7)-vasorelaxant response.

Role of chymase in the local renin-angiotensin system in keloids: inhibition of chymase may be an effective therapeutic approach to treat keloids

Background

Histologically, keloids contain excess fibroblasts and an overabundance of dermal collagen. Recently, it was reported that chymase induced a profibrotic response via transforming growth factor-β1 (TGF-β1)/Smad activation in keloid fibroblasts (KFs). However, the role of chymase in the local renin-angiotensin system (RAS) in keloids has not been elucidated. This study aims to determine whether chymase plays an important role in the local RAS in keloids.

Methods

We compared the expression and activity of chymase in keloids and normal skin tissues using Western blotting and radioimmunoassay, and studied the expression of TGF-β1, interleukin-1β, collagen I, hydroxyproline, and angiotensin II in KFs after chymase and inhibitors’ treatment.

Results

The results revealed an increased activity of chymase in keloid tissues, and that chymase enhanced the expression of angiotensin II, collagen I, TGF-β1, and interleukin-1β in KFs. Blockade of the chymase pathway involved in the local RAS lowered the expression of these signaling factors.

Conclusion

This research suggests that inhibition of chymase might be an effective therapeutic approach to improve the clinical treatment of keloids.

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.

Experimental gestational diabetes mellitus induces blunted vasoconstriction and functional changes in the rat aorta

Diabetic conditions increase vascular reactivity to angiotensin II in several studies but there are scarce reports on cardiovascular effects of hypercaloric diet (HD) induced gestational diabetes mellitus (GDM), so the objective of this work was to determine the effects of HD induced GDM on vascular responses. Angiotensin II as well as phenylephrine induced vascular contraction was tested in isolated aorta rings with and without endothelium from rats fed for 7 weeks (4 before and 3 weeks during pregnancy) with standard (SD) or hypercaloric (HD) diet. Also, protein expression of AT₁R, AT₂R, COX-1, COX-2, NOS-1, and NOS-3 and plasma glucose, insulin, and angiotensin II levels were measured. GDM impaired vasoconstrictor response (P < 0.05 versus SD) in intact (e+) but not in endothelium-free (e−) vessels. Losartan reduced GDM but not SD e− vasoconstriction (P < 0.01 versus SD). AT₁R, AT₂R, and COX-1 and COX-2 protein expression were significantly increased in GDM vessels (P < 0.05 versus SD). Results suggest an increased participation of endothelium vasodilator mediators, probably prostaglandins, as well as of AT₂ vasodilator receptors as a compensatory mechanism for vasoconstrictor changes generated by experimental GDM. Considering the short term of rat pregnancy findings can reflect early stage GDM adaptations.

Activation of upregulated angiotensin II type 2 receptors decreases carotid pulse pressure in rats with suprarenal abdominal aortic coarctation

Our aim was to determine whether angiotensin type 2 receptors (AT2R) are involved in the depression of carotid pulse pressure (PP) in rats with suprarenal aortic coarctation (SrC). We tested the effects of losartan, PD123319, and CGP42112 on PP in SrC and Sham-operated anesthetized rats. PP increased in SrC rats. Neither losartan nor PD123319 affected PP in SrC and Sham-operated rats. CGP42112 reduced PP, in SrC rats, combined with losartan. Moreover, PD123319 blocked this effect. AT2R protein increased in the thoracic aortas of SrC rats. Thus, upregulated AT2R stimulation by CGP42112 mediates depression of PP in rats under pressure overloading.

Inhibition of PKC-dependent extracellular Ca2+ entry contributes to the depression of contractile activity in long-term pressure-overloaded endothelium-denuded rat aortas

We examined the contractile responsiveness of rat thoracic aortas under pressure overload after long-term suprarenal abdominal aortic coarctation (lt-Srac). Endothelium-dependent angiotensin II (ANG II) type 2 receptor (AT₂R)-mediated depression of contractions to ANG II has been reported in short-term (1 week) pressure-overloaded rat aortas. Contractility was evaluated in the aortic rings of rats subjected to lt-Srac or sham surgery (Sham) for 8 weeks. ANG I and II levels and AT₂R protein expression in the aortas of lt-Srac and Sham rats were also evaluated. lt-Srac attenuated the contractions of ANG II and phenylephrine in the aortas in an endothelium-independent manner. However, lt-Srac did not influence the transient contractions induced in endothelium-denuded aortic rings by ANG II, phenylephrine, or caffeine in Ca²⁺-free medium or the subsequent tonic constrictions induced by the addition of Ca²⁺ in the absence of agonists. Thus, the contractions induced by Ca²⁺ release from intracellular stores and Ca²⁺ influx through stored-operated channels were not inhibited in the aortas of lt-Srac rats. Potassium-elicited contractions in endothelium-denuded aortic rings of lt-Srac rats remained unaltered compared with control tissues. Consequently, the contractile depression observed in aortic tissues of lt-Srac rats cannot be explained by direct inhibition of voltage-operated Ca²⁺ channels. Interestingly, 12-O-tetradecanoylphorbol-13-acetate-induced contractions in endothelium-denuded aortic rings of lt-Srac rats were depressed in the presence but not in the absence of extracellular Ca²⁺. Neither levels of angiotensins nor of AT₂R were modified in the aortas after lt-Srac. The results suggest that, in rat thoracic aortas, lt-Srac selectively inhibited protein kinase C-mediated activation of contraction that is dependent on extracellular Ca²⁺ entry.

Effects of cardiac overexpression of the angiotensin II type 2 receptor on remodeling and dysfunction in mice post-myocardial infarction

The activation of angiotensin II type 2 receptor (AT2R) has been considered cardioprotective. However, there are controversial findings regarding the role of overexpressing AT2R in the heart. Using transgenic mice with different levels of AT2R gene overexpression in the heart (1, 4, or 9 copies of the AT2R transgene: Tg1, Tg4, or Tg9), we studied the effect of AT2R overexpression on left ventricular remodeling and dysfunction post-myocardial infarction (MI). Tg1, Tg4, Tg9, and their wild-type littermates were divided into (1) sham MI, (2) MI plus vehicle, and (3) MI plus AT2R antagonist. Treatments were started 4 weeks after MI and continued for 8 weeks. AT2R protein and mRNA expression in the heart was significantly increased in transgenic mice, and the increase positively correlated with copies of the transgene. AT1R protein and mRNA expression remained unchanged in Tg1 and Tg4 but slightly increased in Tg9 mice. Systolic blood pressure and cardiac phenotypes did not differ among strains under basal conditions. MI caused myocardial hypertrophy, interstitial fibrosis, ventricular dilatation, and dysfunction associated with increased protein expression of Nox2 and transforming growth factor β1. These pathological responses were diminished in Tg1 and Tg4 mice. Moreover, the protective effects of AT2R were abolished by AT2R antagonist and also absent in Tg9 mice. We thus conclude that whether overexpression of AT2R is beneficial or detrimental to the heart is largely dependent on expression levels and possibly via regulations of Nox2 and transforming growth factor β1 signaling pathways.

Modulation of haemodynamics, endogeneous antioxidant enzymes, and pathophysiological changes by selective inhibition of angiotensin II type 1 receptors in pressureoverload rats

Background

Constriction of the thoracic or abdominal aorta provides an experimental model of pressure-overload cardiac hypertrophy. Blockade of AT₁ receptors is beneficial in preventing target-organ damage in hypertension.

Objective

To examine the effect of angiotensin II receptor antagonists on blood pressure, endogenous antioxidant enzyme and histopathological changes in pressure-overload rats.

Methods

Pressure overload was produced by abdominal aortic banding (AAB) using a blunt 22-guage needle in male rats as a model of cardiac hypertrophy. After surgery, the AAB-induced hypertension (AABIH) rats were treated with losartan 40 mg/kg/day, candesartan 10 mg/kg/day, irbesartan 10 mg/kg/day per os for 16 weeks. At 16 weeks of surgery, the rats were observed for general characteristics and mortality, and we determined non-invasive blood pressure (NIBP), endogenous antioxidant enzyme catalase and superoxide dismutase (SOD) activities, and histology of the target organs.

Results

In the AABIH group, significant increase in systolic blood pressure was observed from weeks 3 to 16 compared with the control group, along with reduced serum catalase and SOD activities. The treated groups showed significant reduction in systolic BP and increase in serum SOD and catalase activities. The histological changes induced in the target organs, namely heart, liver, kidneys and thoracic aorta in the AABIH rats were attenuated in the treated rats.

Conclusion

Blockade of the AT₁ receptor caused an improvement in the myocardial antioxidant reserve and decreased oxidative stress in the hypertensive rats, which was evidenced by the protection observed in the treatment groups.

Angiotensin II and oxidative stress in the failing heart

SIGNIFICANCE

Despite recent medical advances, cardiovascular disease and heart failure (HF) continue to be major health concerns, and related mortality remains high. As a result, investigation of the mechanisms involved in the development of HF continues to be an active field of study.

RECENT ADVANCES

The renin-angiotensin system (RAS) and its effector molecule, angiotensin (Ang) II, affect cardiac function through both systemic and local actions, and have been shown to play a major role in cardiac remodeling and dysfunction in the failing heart. Many of the downstream effects of AngII signaling are mediated by elevated levels of reactive oxygen species (ROS) and oxidative stress, which have also been implicated in the pathology of HF.

CRITICAL ISSUES

Inhibitors of the RAS have proven beneficial in the treatment of patients at risk for and suffering from HF, but remain only partially effective. ROS can be generated from several different sources, and the oxidative state is normally tightly regulated in the heart. How AngII increases ROS levels and causes dysregulation of the cardiac oxidative state has been the subject of considerable interest in recent years.

FUTURE DIRECTIONS

A better understanding of this process and the mechanisms involved should lead to the development of more effective HF therapies and improved outcomes.

Plasma kallikrein-kinin system and diabetic retinopathy

Diabetic retinopathy (DR) occurs, to some extent, in most people with at least 20 years' duration of diabetes mellitus. The progression of DR to its sight-threatening stages is usually associated with the worsening of underlying retinal vascular dysfunction and disease. The plasma kallikrein-kinin system (KKS) is activated during vascular injury, where it mediates important functions in innate inflammation, blood flow, and coagulation. Recent findings from human vitreous proteomics and experimental studies on diabetic animal models have implicated the KKS in contributing to DR. Vitreous fluid from people with advanced stages of DR contains increased levels of plasma KKS components, including plasma kallikrein (PK), coagulation factor XII, and high-molecular-weight kininogen. Both bradykinin B1 and B2 receptor isoforms (B1R and B2R, respectively) are expressed in human retina, and retinal B1R levels are increased in diabetic rodents. The activation of the intraocular KKS induces retinal vascular permeability, vasodilation, and retinal thickening, and these responses are exacerbated in diabetic rats. Preclinical studies have shown that the administration of PK inhibitors and B1R antagonists to diabetic rats ameliorates retinal vascular hyperpermeability and inflammation. These findings suggest that components of plasma KKS are potential therapeutic targets for diabetic macular edema.

Role of angiotensin II type 2 receptor during regression of cardiac hypertrophy in spontaneously hypertensive rats

We previously reported that the AT1 receptor antagonist valsartan and the angiotensin converting enzyme (ACE) inhibitor enalapril decrease DNA synthesis and stimulate apoptosis in interstitial fibroblasts and epicardial mesothelial cells during regression of ventricular hypertrophy in spontaneously hypertensive rats (SHR). To examine the role of the AT2 receptor in this model, we studied hearts from SHR treated with valsartan or enalapril either alone or combined with the AT2 antagonist PD123319 for 1 or 2 weeks. Apoptosis was evaluated by quantification of DNA fragmentation or by TUNEL labeling. At 1 week, valsartan significantly increased ventricular DNA fragmentation, increased apoptosis in epicardial mesothelial cells, and decreased DNA synthesis. At 2 weeks, ventricular DNA content and cardiomyocyte cross-sectional area were significantly reduced. These valsartan-induced changes were attenuated by PD123319 co-administration. However, valsartan-induced increases in apoptosis of left ventricular interstitial non-cardiomyocytes was unaffected by the AT2 blocker. Enalapril-induced changes were similar to those observed with valsartan but were not affected by co-treatment with PD123319. These results demonstrate that AT1 and AT2 receptors act in a coordinated yet cell-specific manner to regulate cell growth and apoptosis in the left ventricle of SHR during AT1 receptor blockade but not ACE inhibition.

Phosphorylation of myocardial eNOS is altered in patients suffering from type 2 diabetes

The present study investigated whether endothelial nitric oxide synthase (eNOS) activation may be dysregulated in cardiac tissue of patients suffering from type 2 diabetes (T2D). We performed immunohistochemical measurements of translocated eNOS activation as well as eNOS phosphorylation at Ser1177, Thr495, Ser 635, Ser114, and of the protein kinase B (Akt) in isolated right atrial trabeculae of patients undergoing cardiac bypass or valve surgery with (n = 12, 68.1 ± 2.5 yr) and without T2D (n = 12, 64.7 ± 2.7 yr). In addition, we investigated oxidative (8-isoprostane) and nitrosative stress markers (nitrotyrosine) as well as the effect of pharmacological stimulation of angiotensin (AT)-receptors on eNOS-phosphorylation. Translocation-dependent eNOS activation was similar in both groups. The same holds true for eNOS phosphorylation at Ser114. eNOS phosphorylation at Ser635 was significantly increased, whereas eNOS phosphorylation of Ser1177 was significantly decreased in the diabetic group paralleled by a decrease in phosphorylation of Akt and Thr495. These alterations were accompanied by a significant decrease in nitrotyrosine. After application of angiotensin II (10 μM, 2 min) for investigation of the AT-receptor-dependent eNOS stimulation, we did not find differences between the increases in eNOS Ser1177-phosphorylation in the nondiabetic (+39.7 ± 23.5%) and in the diabetic group (32.22 ± 11.45%). A simultaneous increase in Akt phosphorylation could not be observed. The present study indicates that T2D goes along with a decrease in eNOS phosphorylation at Ser1177 under basal conditions in cardiac tissue. Whether this may be attributed to the insulin resistance of cardiac muscle has to be further investigated. Receptor-stimulated eNOS activation still works at least for angiotensin II-dependent eNOS activation.

Protective role of AT(2) and B(1) receptors in kinin B(2)-receptor-knockout mice with myocardial infarction

AT(2)Rs [AngII (angiotensin II) type 2 receptors] contribute to the cardioprotective effects of angiotensin II receptor blockers, possibly via kinins acting on the B(1)R (B(1) receptor) and B(2)R (B(2) receptor). Recent studies have shown that a lack of B(2)R up-regulates B(1)R and AT(2)R; however, the pathophysiological relevance of such an event remains unclear. We hypothesized that up-regulation of AT(2)R and B(1)R compensates for the loss of B(2)R. Blockade of AT(2)R and/or B(1)R worsens cardiac remodelling and dysfunction following MI (myocardial infarction) in B(2)R(-/-) (B(2)-receptor-knockout mice). B(2)R(-/-) mice and WT (wild-type) controls were subjected to sham MI or MI and treated for 4 weeks with (i) vehicle, (ii) a B(1)R-ant (B(1)R antagonist; 300 μg/kg of body weight per day), (iii) an AT(2)R-ant [AT(2) receptor antagonist (PD123319); 20 mg/kg of body weight per day], or (iv) B(1)R-ant+AT(2)R-ant. B(2)R(-/-) mice had a greater MCSA (myocyte cross-sectional area) and ICF (interstitial collagen fraction) at baseline and after MI compared with WT controls. Cardiac function and increase in macrophage infiltration, TGFβ(1) (transforming growth factor β(1)) expression and ERK1/2 (extracellular-signal-regulated kinase 1/2) phosphorylation post-MI were similar in both strains. Blockade of AT(2)R or B(1)R worsened cardiac remodelling, hypertrophy and dysfunction associated with increased inflammation and ERK1/2 phosphorylation and decreased NO excretion in B(2)R(-/-) mice, which were exacerbated by dual blockade of B(1)R and AT(2)R. No such effects were seen in WT mice. Our results suggest that, in the absence of B(2)R, both B(1)R and AT(2)R play important compensatory roles in preventing deterioration of cardiac function and remodelling post-MI possibly via suppression of inflammation, TGFβ(1) and ERK1/2 signalling.

Angiotensin receptor blockers and tumorigenesis: something to be (or not to be) concerned about?

The possibility of carcinogenic side effects of antihypertensive therapies due to their chronic administration has been raised multiple times in the past. Recently, the issue has again drawn attention, this time in relation to angiotensin receptor blockers (ARBs). This, among others, caused both American and European drug regulation authorities to review the underlying evidence concerning the relationship between this class of medications and potential adverse carcinogenic outcome. A plethora of both basic science and preclinical evidence has been generated, and three meta-analyses and one nationwide cohort have focused on this specific question. The current review aims to summarize the contemporary multidisciplinary evidence on whether ARBs may be associated with an increased risk of tumorigenesis.

Direct stimulation of angiotensin II type 2 receptor enhances spatial memory

We examined the possibility that direct stimulation of the angiotensin II type 2 (AT(2)) receptor by a newly generated direct AT(2) receptor agonist, Compound 21 (C21), enhances cognitive function. Treatment with C21 intraperitoneal injection for 2 weeks significantly enhanced cognitive function evaluated by the Morris water maze test in C57BL6 mice, but this effect was not observed in AT(2) receptor-deficient mice. However, C21-induced cognitive enhancement in C57BL6 mice was attenuated by coadministration of icatibant, a bradykinin B(2) receptor antagonist. Administration of C21 dose dependently increased cerebral blood flow assessed by laser speckle flowmetry and hippocampal field-excitatory postsynaptic potential (f-EPSP) determined by electrophysiological techniques in C57BL6 mice. Furthermore, activation of the AT(2) receptor by C21 promoted neurite outgrowth of cultured hippocampal neurons prepared from fetal transgenic mice expressing green fluorescent protein. Finally, we investigated the pathologic relevance of C21 for spatial learning using an Alzheimer's disease mouse model with intracerebroventricular injection of amyloid-β (1 to 40). We observed that treatment with C21 prevented cognitive decline in this model. These results suggest that a direct AT(2) receptor agonist, C21, enhances cognitive function at least owing to an increase in CBF, enhancement of f-EPSP, and neurite outgrowth in hippocampal neurons.

Vascular mechanisms involved in angiotensin II-induced venoconstriction in hypertensive rats

To investigate the venoconstrictor effect of angiotensin II (Ang II) in spontaneously hypertensive rats (SHR), we used preparations of mesenteric venular beds and the circular muscle of the portal veins. Vessels were tested with Ang II in the presence or absence of losartan, PD 123319, HOE 140, L-NAME, indomethacin, or celecoxib. In the mesenteric venular bed of SHR, the effect of Ang II (0.1 nmol) was nearly abolished by losartan and enhanced by HOE 140, indomethacin, and celecoxib, while PD123319 and L-NAME had no effect. In portal vein preparations, cumulative-concentration response curves (CCRC) to Ang II (0.1-100 nmol/L) exhibited a lower maximal response (E(max)) in SHR compared to Wistar rats. AT(1) receptor expression was similar in the two strains, while AT(2) receptor levels were lower in SHR portal veins when compared to Wistar. In SHR portal veins, losartan shifted the CCRC to Ang II to the right, while indomethacin and HOE 140 increased the E(max) to Ang II. PD 123319, celecoxib, and L-NAME had no effect. Taken together, our results suggest that Ang II-induced venoconstriction in SHR is mediated by activation of AT(1) receptors and this effect may be counterbalanced by kinin B(2) receptor and COX metabolites. Furthermore, our data indicate that there are different cellular and molecular mechanisms involved in the regulation of venous tonus of normotensive and hypertensive rats. These differences probably reflect distinct factors that influence arterial and venous bed in hypertension.

Angiotensin II upregulation of cardiomyocyte adiponectin production is nitric oxide/cyclic GMP dependent

INTRODUCTION

Adiponectin is a circulating cytokine that is now known to be synthesized by cardiomyocytes. Accumulating evidence has shown that adiponectin production is upregulated in patients with heart failure, with activation of the renin-angiotensin system and increased formation of angiotensin (Ang) II playing a critical role in left ventricular remodeling and heart failure. To determine whether Ang II upregulates adiponectin in hypertrophic cardiomyocytes, the authors need to explore the underlying mechanisms that could be involved.

METHODS

To test this hypothesis, neonatal rat ventricular myocytes (NRVMs) were treated with various concentrations of Ang II, and adiponectin expression was measured by quantitative real-time reverse transcription-polymerase chain reaction and Western immunoblotting.

RESULTS

Adiponectin mRNA expression was significantly increased by Ang II at concentrations from 10(-6) to 10(-8) M and was increased in a time-dependent manner at concentrations of 10(-7) M. Angiotensin type-2 receptor activation is required for Ang II-stimulated effects on adiponectin. A nitric oxide synthase inhibitor (Nx-nitro-l-arginine methyl ester hydrochloride) and an analog of cGMP antagonist (Rp-8-Br-CGMP-S) blocked Ang II-mediated upregulation of adiponectin.

CONCLUSIONS

These data suggest a mechanism whereby Ang II upregulates adiponectin in NRVMs via the angiotensin type-2 receptor/nitric oxide/cGMP/ protein kinase G signaling pathway.

Knocking out angiotensin II in the heart

Despite ongoing medical advances, cardiovascular disease continues to be a leading health concern. The renin-angiotensin system (RAS) plays an important role in regulating cardiovascular function, and is, therefore, the subject of extensive study. Several drugs currently used to treat hypertension and heart failure are designed to target angiotensin II synthesis and function, but thus far, none have been able to completely block the effects of RAS signaling. This review discusses current and emerging approaches towards inhibiting cardiac RAS function in order to further improve cardiovascular disease outcomes.