The angiotensin II type 2 receptor: what is its clinical significance?

Radiation Induced Skin Fibrosis (RISF): Opportunity for Angiotensin II-Dependent Intervention

Medical procedures, such as radiation therapy, are a vital element in treating many cancers, significantly contributing to improved survival rates. However, a common long-term complication of such exposure is radiation-induced skin fibrosis (RISF), a complex condition that poses substantial physical and psychological challenges. Notably, about 50% of patients undergoing radiation therapy may achieve long-term remission, resulting in a significant number of survivors managing the aftereffects of their treatment. This article delves into the intricate relationship between RISF, reactive oxygen species (ROS), and angiotensin II (Ang II) signaling. It proposes the underlying mechanisms and examines potential treatments for mitigating skin fibrosis. The primary goal is to offer essential insights in order to better care for and improve the quality of life of cancer survivors who face the risk of developing RISF.

Role of angiotensin II in cellular entry and replication of dengue virus

Previous studies have demonstrated the relevance of several soluble molecules in the pathogenesis of dengue. In this regard, a possible role for angiotensin II (Ang II) in the pathophysiology of dengue has been suggested by the observation of a blockade of Ang II in patients with dengue, increased expression of molecules related to Ang II production in the plasma of dengue patients, increased expression of circulating cytokines and soluble molecules related to the action of Ang II, and an apparent relationship between DENV, Ang II effects, and miRNAs. In addition, in ex vivo experiments, the blockade of Ang II AT1 receptor and ACE-1 (angiotensin converting enzyme 1), both of which are involved in Ang II production and its function, inhibits infection of macrophages by DENV, suggesting a role of Ang II in viral entry or in intracellular viral replication of the virus. Here, we discuss the possible mechanisms of Ang II in the entry and replication of DENV. Ang II has the functions of increasing the expression of DENV entry receptors, creation of clathrin-coated vesicles, and increasing phagocytosis, all of which are involved in DENV entry. This hormone also modulates the expression of the Rab5 and Rab7 proteins, which are important in the endosomal processing of DENV during viral replication. This review summarizes the data related to the possible involvement of Ang II in the entry of DENV into cells and its replication.

Angiotensin II and post-streptococcal glomerulonephritis

BACKGROUND

Post-streptococcal glomerulonephritis (PSGN) is a consequence of the infection by group A beta-hemolytic streptococcus. During this infection, various immunological processes generated by streptococcal antigens are triggered, such as the induction of antibodies and immune complexes. This activation of the immune system involves both innate and acquired immunity. The immunological events that occur at the renal level lead to kidney damage with chronic renal failure as well as resolution of the pathological process (in most cases). Angiotensin II (Ang II) is a molecule with vasopressor and pro-inflammatory capacities, being an important factor in various inflammatory processes. During PSGN some events are defined that make Ang II conceivable as a molecule involved in the inflammatory processes during the disease.

CONCLUSION

This review is focused on defining which reported events would be related to the presence of this hormone in PSGN.

Angiotensin II and dengue

Dengue is a disease caused by a flavivirus that is transmitted principally by the bite of an Aedes aegypti mosquito and represents a major public-health problem. Many studies have been carried out to identify soluble factors that are involved in the pathogenesis of this infection. Cytokines, soluble factors, and oxidative stress have been reported to be involved in the development of severe disease. Angiotensin II (Ang II) is a hormone with the ability to induce the production of cytokines and soluble factors related to the inflammatory processes and coagulation disorders observed in dengue. However, a direct involvement of Ang II in this disease has not been demonstrated. This review primarily summarizes the pathophysiology of dengue, the role of Ang II in various diseases, and reports that are highly suggestive of the involvement of this hormone in dengue.

Role of angiotensin II in aging

Aging is an inevitable progressive decline in physiological organ function that increases the chance of disease and death. The renin-angiotensin system (RAS) is involved in the regulation of vasoconstriction, fluid homeostasis, cell growth, fibrosis, inflammation, and oxidative stress. In recent years, unprecedented advancement has been made in the RAS study, particularly with the observation that angiotensin II (Ang II), the central product of the RAS, plays a significant role in aging and chronic disease burden with aging. Binding to its receptors (Ang II type 1 receptor - AT1R in particular), Ang II acts as a mediator in the aging process by increasing free radical production and, consequently, mitochondrial dysfunction and telomere attrition. In this review, we examine the physiological function of the RAS and reactive oxygen species (ROS) sources in detail, highlighting how Ang II amplifies or drives mitochondrial dysfunction and telomere attrition underlying each hallmark of aging and contributes to the development of aging and age-linked diseases. Accordingly, the Ang II/AT1R pathway opens a new preventive and therapeutic direction for delaying aging and reducing the incidence of age-related diseases in the future.

Angiotensin II and human obesity. A narrative review of the pathogenesis

Angiotensin II (Ang II) is a hormone and the main effector of the renin-angiotensin system (RAS). This peptide has crucial pathophysiologi-cal effects on hypertension, cardiac hypertrophy, endothelial proliferation, in-flammation and tissue remodelling through G protein-coupled receptors. The pro-inflammatory role of Ang II has been reported in various inflammatory pro-cesses. Obesity is linked to a chronic inflammatory process which in turn is the cause of some of its morbidities. Ang II is related to the comorbidities related to the comorbidities of obesity, which include alterations in the heart, kid-ney, hypertension and coagulation. In this regard, activation of AT1 receptors by Ang II can induce an inflammatory process mediated by the transcription factor NF-kB, triggering inflammation in various systems that are related to the comorbidities observed in obesity. The aim of this review was to highlight the pro-inflammatory effects of Ang II and the alterations induced by this hor-mone in various organs and systems in obesity. The search was done since 1990 through Medline, EMBASE and PubMed, using the keywords: angiotensin II; an-giotensin II, obesity; angiotensin II, kidney, obesity; angiotensin II, coagulation, obesity; angiotensin II, inflammation, obesity; angiotensin II, adipose tissue, obesity; angiotensin II, hypertension, obesity; angiotensin II, insulin resistance, obesity; angiotensin II, adiponectin, leptin, obesity; angiotensin II, COVID-19, obesity. Angiotensin II through its interaction with its AT1 receptor, can induce alterations in diverse systems that are related to the comorbidities observed in obesity. Therapeutic strategies to decrease the production and action of Ang II could improve the clinical conditions in individuals with obesity.

Renin-Angiotensin System Induced Secondary Hypertension: The Alteration of Kidney Function and Structure

Long-term hypertension is known as a major risk factor for cardiovascular and chronic kidney disease (CKD). The Renin-angiotensin system (RAS) plays a key role in hypertension pathogenesis. Angiotensin II (Ang II) enhancement in Ang II-dependent hypertension leads to progressive CKD and kidney fibrosis. In the two-kidney one-clip model (2K1C), more renin is synthesized in the principal cells of the collecting duct than juxtaglomerular cells (JGCs). An increase of renal Ang I and Ang II levels and a decrease of renal cortical and medullary Ang 1–7 occur in both kidneys of the 2K1C hypertensive rat model. In addition, the activity of the angiotensin-converting enzyme (ACE) increases, while ACE2's activity decreases in the medullary region of both kidneys in the 2K1C hypertensive model. Also, the renal prolyl carboxypeptidase (PrCP) expression and its activity reduce in the clipped kidneys. The imbalance in the production of renal ACE, ACE2, and PrCP expression causes the progression of renal injury. Intrarenal angiotensinogen (AGT) expression and urine AGT (uAGT) excretion rates in the unclipped kidney are greater than the clipped kidney in the 2K1C hypertensive rat model. The enhancement of Ang II in the clipped kidney is related to renin secretion, while the elevation of intrarenal Ang II in the unclipped kidney is related to stimulation of AGT mRNA and protein in proximal tubule cells by a direct effect of systemic Ang II level. Ang II-dependent hypertension enhances macrophages and T-cell infiltration into the kidney which increases cytokines, and AGT synthesis in proximal tubules is stimulated via cytokines. Accumulation of inflammatory cells in the kidney aggravates hypertension and renal damage. Moreover, Ang II-dependent hypertension alters renal Ang II type 1 & 2 receptors (AT₁R & AT₂R) and Mas receptor (MasR) expression, and the renal interstitial fluid bradykinin, nitric oxide, and cGMP response to AT₁R, AT₂R, or BK B₂-receptor antagonists. Based on a variety of sources including PubMed, Google Scholar, Scopus, and Science-Direct, in the current review, we will discuss the role of RAS-induced secondary hypertension on the alteration of renal function.

Obesogenic and Ketogenic Diets Distinctly Regulate the SARS-CoV-2 Entry Proteins ACE2 and TMPRSS2 and the Renin-Angiotensin System in Rat Lung and Heart Tissues

Background: Obesity increases the severity of SARS-CoV-2 outcomes. Thus, this study tested whether obesogenic and ketogenic diets distinctly affect SARS-CoV-2 entry proteins and the renin-angiotensin system (RAS) in rat pulmonary and cardiac tissues. Methods: Male Sprague-Dawley rats were fed either standard chow (SC), a high-fat sucrose-enriched diet (HFS), or a ketogenic diet (KD) for 16 weeks. Afterwards, levels of angiotensin converting enzyme 2 (ACE2), transmembrane protease serine 2 (TMPRSS2), RAS components, and inflammatory genes were measured in the lungs and hearts of these animals. Results: In the lungs, HFS elevated ACE2 and TMPRSS2 levels relative to SC diet, whereas the KD lowered the levels of these proteins and the gene expressions of toll-like receptor 4 and interleukin-6 receptor relative to HFS. The diets did not alter ACE2 and TMPRSS2 in the heart, although ACE2 was more abundant in heart than lung tissues. Conclusion: Diet-induced obesity increased the levels of viral entry proteins in the lungs, providing a mechanism whereby SARS-CoV-2 infectivity can be enhanced in obese individuals. Conversely, by maintaining low levels of ACE2 and TMPRSS2 and by exerting an anti-inflammatory effect, the KD can potentially attenuate the severity of infection and migration of SARS-CoV-2 to other ACE2-expressing tissues.

The role of anti-hypertensive treatment, comorbidities and early introduction of LMWH in the setting of COVID-19: A retrospective, observational study in Northern Italy

BACKGROUND

There is a great deal of debate about the role of cardiovascular comorbidities and the chronic use of antihypertensive agents (such as ACE-I and ARBs) on mortality on COVID-19 patients. Of note, ACE2 is responsible for the host cell entry of the virus.

METHODS

We extracted data on 575 consecutive patients with laboratory-confirmed SARS-CoV-2 infection admitted to the Emergency Department (ED) of Humanitas Center, between February 21 and April 14, 2020. The aim of the study was to evaluate the role of chronic treatment with ACE-I or ARBs and other clinical predictors on in-hospital mortality in a cohort of COVID-19 patients.

RESULTS

Multivariate analysis showed that a chronic intake of ACE-I was associated with a trend in reduction of mortality (OR: 0.53; 95% CI: 0.27-1.03; p = 0.06), differently from a chronic intake of ARB (OR: 1.1; 95% CI: 0.5-2.8; p=0.8). Increased age (ORs ranging from 3.4 to 25.2 and to 39.5 for 60-70, 70-80 and >80 years vs <60) and cardiovascular comorbidities (OR: 1.90; 95% CI: 1.1-3.3; p = 0.02) were confirmed as important risk factors for COVID-19 mortality. Timely treatment with low-molecular-weight heparin (LMWH) in ED was found to be protective (OR: 0.36; 95% CI: 0.21-0.62; p < 0.0001).

CONCLUSIONS

This study can contribute to understand the reasons behind the high mortality rate of patients in Lombardy, a region which accounts for >50% of total Italian deaths. Based on our findings, we support that daily intake of antihypertensive medications in the setting of COVID-19 should not be discontinued and that a timely LMWH administration in ED has shown to decrease in-hospital mortality.

Local ocular renin-angiotensin-aldosterone system: any connection with intraocular pressure? A comprehensive review

The renin-angiotensin system (RAS) is one of the oldest and most extensively studied human peptide cascades, well-known for its role in regulating blood pressure. When aldosterone is included, RAAS is involved also in fluid and electrolyte homeostasis. There are two main axes of RAAS: (1) Angiotensin (1-7), angiotensin converting enzyme 2 and Mas receptor (ACE2-Ang(1-7)-MasR), (2) Angiotensin II, angiotensin converting enzyme 1 and angiotensin II type 1 receptor (ACE1-AngII-AT1R). In its entirety, RAAS comprises dozens of angiotensin peptides, peptidases and seven receptors. The first mentioned axis is known to counterbalance the deleterious effects of the latter axis. In addition to the systemic RAAS, tissue-specific regulatory systems have been described in various organs, evidence that RAAS is both an endocrine and an autocrine system. These local regulatory systems, such as the one present in the vascular endothelium, are responsible for long-term regional changes. A local RAAS and its components have been detected in many structures of the human eye. This review focuses on the local ocular RAAS in the anterior part of the eye, its possible role in aqueous humour dynamics and intraocular pressure as well as RAAS as a potential target for anti-glaucomatous drugs.KEY MESSAGESComponents of renin-angiotensin-aldosterone system have been detected in different structures of the human eye, introducing the concept of a local intraocular renin-angiotensin-aldosterone system (RAAS).Evidence is accumulating that the local ocular RAAS is involved in aqueous humour dynamics, regulation of intraocular pressure, neuroprotection and ocular pathology making components of RAAS attractive candidates when developing new effective ways to treat glaucoma.

Role of angiotensin II type 1 (AT1) and type 2 (AT2) receptors in airway reactivity and inflammation in an allergic mouse model of asthma

Objective: Angiotensin II (Ang II) exerts its effects through two G-protein coupled receptors: angiotensin II type 1 receptors (AT1) and type 2 receptors (AT2). Both these receptor subtypes are poorly understood in asthma. In this study, we investigated effects of AT1 receptor antagonist losartan, novel AT2 receptor agonist novokinin and AT2 receptor antagonist PD 123319 in a mouse model of asthma. Methods: Mice were divided into control (CON) and allergen sensitized (SEN) groups. SEN was sensitized with ovalbumin (OVA) on days 1 and 6 (30 μg; i.p.), followed by 5% OVA aerosol challenge (days 11-13). Treatments included (a) losartan (SEN + LOS; 20 mg/kg i.p., day 14), (b) novokinin (SEN + NOV; 0.3 mg/kg i.p., day 14), and (c) PD 123319 (SEN + PD; 5 mg/kg i.p., day 14). Experiments for airway responsiveness, bronchoalveolar lavage, and tracheal ring reactivity using isolated organ bath were performed. Results: Airway responsiveness to methacholine (MCh) (48 mg/mL) was significantly higher in SEN (563.71 ± 40% vs. 294.3 ± 123.84 in CON). This response was potentiated in SEN + PD group (757 ± 30%; p < .05 compared to SEN). SEN + LOS (247.61 ± 86.85%) and SEN + NOV (352 ± 11%) had significantly lower response compared to SEN. SEN + LOS (26.22 ± 0.29%) and SEN + NOV (46.20 ± 0.76%) treatment significantly (p < .001) attenuated total cell count and eosinophils compared to SEN group (69.38 ± 1.5%), while SEN + PD (73.04 ± 0.69%) had highest number of eosinophils. Tracheal response to MCh was significantly higher in SEN group compared to controls, and this response was significantly lowered with the losartan and novokinin treatments. Conclusions: These data suggest that AT1 and AT2 receptors have opposite effects in modulating airway hyperresponsiveness and inflammation in asthma.

Nanoparticles in Medicine: A Focus on Vascular Oxidative Stress

Nanotechnology has had a significant impact on medicine in recent years, its application being referred to as nanomedicine. Nanoparticles have certain properties with biomedical applications; however, in some situations, they have demonstrated cell toxicity, which has caused concern surrounding their clinical use. In this review, we focus on two aspects: first, we summarize the types of nanoparticles according to their chemical composition and the general characteristics of their use in medicine, and second, we review the applications of nanoparticles in vascular alteration, especially in endothelial dysfunction related to oxidative stress. This condition can lead to a reduction in nitric oxide (NO) bioavailability, consequently affecting vascular tone regulation and endothelial dysfunction, which is the first phase in the development of cardiovascular diseases. Therefore, nanoparticles with antioxidant properties may improve vascular dysfunction associated with hypertension, diabetes mellitus, or atherosclerosis.

Attenuation of angiotensin type 2 receptor function in the rostral ventrolateral medullary pressor area of the spontaneously hypertensive rat

We hypothesized that blockade of angiotensin II type 2 receptors (AT2Rs) in the rostral ventrolateral medullary pressor area (RVLM) may elicit sympathoexcitatory responses which are smaller in hypertensive rats compared to normotensive rats. This hypothesis was tested in urethane-anesthetized, artificially ventilated male 14-week-old spontaneously hypertensive rats (SHR). Age-matched male Wistar-Kyoto rats (WKY) and Wistar rats were used as controls. PD123319 (AT2R antagonist) was microinjected into the RVLM and mean arterial pressure (MAP), heart rate (HR) and greater splanchnic nerve activity (GSNA) were recorded. Increases in MAP, HR and GSNA elicited by unilateral microinjections of PD123319 into the RVLM were significantly smaller in SHR when compared with those in WKY and Wistar rats. Unilateral microinjections of l-glutamate (l-Glu) into the RVLM elicited greater increases in MAP and GSNA in SHR compared to those in WKY. AT2R immunoreactivity was demonstrated in the RVLM neurons which were retrogradely labeled from the intermediolateral cell column (IML) of the spinal cord. These results indicate that AT2Rs are present on the RVLM neurons projecting to the IML and their blockade results in sympathoexcitatory responses. Activation of AT2Rs has an inhibitory influence in the RVLM and these receptors are tonically active. Attenuation of the function of AT2Rs in the RVLM may play a role in genesis and/or maintenance of hypertension in SHR.

Oxidative stress and vascular inflammation in aging

Vascular aging, a determinant factor for cardiovascular disease and health status in the elderly, is now viewed as a modifiable risk factor. Impaired endothelial vasodilation is a early hallmark of arterial aging that precedes the clinical manifestations of vascular dysfunction, the first step to cardiovascular disease and influencing vascular outcomes in the elderly. Accordingly, the preservation of endothelial function is thought to be an essential determinant of healthy aging. With special attention on the effects of aging on the endothelial function, this review is focused on the two main mechanisms of aging-related endothelial dysfunction: oxidative stress and inflammation. Aging vasculature generates an excess of the reactive oxygen species (ROS), superoxide and hydrogen peroxide, that compromise the vasodilatory activity of nitric oxide (NO) and facilitate the formation of the deleterious radical, peroxynitrite. Main sources of ROS are mitochondrial respiratory chain and NADPH oxidases, although NOS uncoupling could also account for ROS generation. In addition, reduced antioxidant response mediated by erythroid-2-related factor-2 (Nrf2) and downregulation of mitochondrial manganese superoxide dismutase (SOD2) contributes to the establishment of chronic oxidative stress in aged vessels. This is accompanied by a chronic low-grade inflammatory phenotype that participates in defective endothelial vasodilation. The redox-sensitive transcription factor, nuclear factor-κB (NF-κB), is upregulated in vascular cells from old subjects and drives a proinflammatory shift that feedbacks oxidative stress. This chronic NF-κB activation is contributed by increased angiotensin-II signaling and downregulated sirtuins and precludes adequate cellular response to acute ROS generation. Interventions targeted to recover endogenous antioxidant capacity and cellular stress response rather than exogenous antioxidants could reverse oxidative stress-inflammation vicious cycle in vascular aging. Lifestyle attitudes such as caloric restriction and exercise training appear as effective ways to overcome defective antioxidant response and inflammation, favoring successful vascular aging and decreasing the risk for cardiovascular disease.

Dopamine and angiotensin type 2 receptors cooperatively inhibit sodium transport in human renal proximal tubule cells

Little is known regarding how the kidney shifts from a sodium and water reclaiming state (antinatriuresis) to a state where sodium and water are eliminated (natriuresis). In human renal proximal tubule cells, sodium reabsorption is decreased by the dopamine D(1)-like receptors (D(1)R/D(5)R) and the angiotensin type 2 receptor (AT(2)R), whereas the angiotensin type 1 receptor increases sodium reabsorption. Aberrant control of these opposing systems is thought to lead to sodium retention and, subsequently, hypertension. We show that D(1)R/D(5)R stimulation increased plasma membrane AT(2)R 4-fold via a D(1)R-mediated, cAMP-coupled, and protein phosphatase 2A-dependent specific signaling pathway. D(1)R/D(5)R stimulation also reduced the ability of angiotensin II to stimulate phospho-extracellular signal-regulated kinase, an effect that was partially reversed by an AT(2)R antagonist. Fenoldopam did not increase AT(2)R recruitment in renal proximal tubule cells with D(1)Rs uncoupled from adenylyl cyclase, suggesting a role of cAMP in mediating these events. D(1)Rs and AT(2)Rs heterodimerized and cooperatively increased cAMP and cGMP production, protein phosphatase 2A activation, sodium-potassium-ATPase internalization, and sodium transport inhibition. These studies shed new light on the regulation of renal sodium transport by the dopaminergic and angiotensin systems and potential new therapeutic targets for selectively treating hypertension.

Angiotensin II type 2 receptor-coupled nitric oxide production modulates free radical availability and voltage-gated Ca2+ currents in NTS neurons

The medial region of the nucleus tractus solitarius (mNTS) is a key brain stem site controlling cardiovascular function, wherein ANG II modulates neuronal L-type Ca(2+) currents via activation of ANG II type 1 receptors (AT(1)R) and production of reactive oxygen species (ROS). ANG II type 2 receptors (AT(2)R) induce production of nitric oxide (NO), which may interact with ROS and modulate AT(1)R signaling. We sought to determine whether AT(2)R-mediated NO production occurs in mNTS neurons and, if so, to elucidate the NO source and the functional interaction with AT(1)R-induced ROS or Ca(2+) influx. Electron microscopic (EM) immunolabeling showed that AT(2)R and neuronal NO synthase (nNOS) are coexpressed in neuronal somata and dendrites receiving synapses in the mNTS. In the presence of the AT(1)R antagonist losartan, ANG II increased NO production in isolated mNTS neurons, an effect blocked by the AT(2)R antagonist PD123319, but not the angiotensin (1-7) antagonist D-Ala. Studies in mNTS neurons of nNOS-null or endothelial NOS (eNOS)-null mice established nNOS as the source of NO. ANG II-induced ROS production was enhanced by PD123319, the NOS inhibitor N(G)-nitro-l-arginine (LNNA), or in nNOS-null mice. Moreover, in the presence of losartan, ANG II reduced voltage-gated L-type Ca(2+) current, an effect blocked by PD123319 or LNNA. We conclude that AT(2)R are closely associated and functionally coupled with nNOS in mNTS neurons. The resulting NO production antagonizes AT(1)R-mediated ROS and dampens L-type Ca(2+) currents. The ensuing signaling changes in the NTS may counteract the deleterious effects of AT(1)R on cardiovascular function.

Role of shear stress and stretch in vascular mechanobiology

Blood vessels are under constant mechanical loading from blood pressure and flow which cause internal stresses (endothelial shear stress and circumferential wall stress, respectively). The mechanical forces not only cause morphological changes of endothelium and blood vessel wall, but also trigger biochemical and biological events. There is considerable evidence that physiologic stresses and strains (stretch) exert vasoprotective roles via nitric oxide and provide a homeostatic oxidative balance. A perturbation of tissue stresses and strains can disturb biochemical homeostasis and lead to vascular remodelling and possible dysfunction (e.g. altered vasorelaxation, tone, stiffness, etc.). These distinct biological endpoints are caused by some common biochemical pathways. The focus of this brief review is to point out some possible commonalities in the molecular pathways in response to endothelial shear stress and circumferential wall stretch.

The role of the renin—angiotensin system in the pathogenesis of intracranial aneurysms

Introduction: Recent work has begun to elucidate the pathogenesis of intracranial aneurysms (IA) and has shown that many genes are involved in the risk for this condition. There has also been increasing research interest in the renin—angiotensin system (RAS) in the brain and its involvement in a range of cardiovascular and neurological disorders. The possibility that the RAS is implicated in the pathogenesis of IA merits further investigation. The aim of this article is to review the literature on the pathogenesis of IA and the pathophysiological significance of the brain RAS, and to identify directions for research into their association.

Methods and results : A survey of the literature in these fields shows that although factors contributing to systemic hypertension predispose to IA, a large number of genes involved in endothelial cell adhesion, smooth muscle activity, extracellular matrix dynamics and the inflammatory and immune responses are also implicated. The brain RAS has a significant role in regulating blood pressure and in maintaining cerebrovascular autoregulation, but angiotensin II receptors are also involved in the maintenance of endothelial cell and vascular smooth muscle function and in the inflammatory response in the brain.

Conclusions: There is strong, albeit largely circumstantial, evidence in the literature for a relationship between the brain RAS and the formation of IA. Research on the association between polymorphisms in RAS-related genes and the incidence of unruptured and ruptured IA is indicated.

Role of the angiotensin II AT2 receptor in inflammation and oxidative stress: opposing effects in lean and obese Zucker rats

Inflammation and oxidative stress are believed to contribute to hypertension in obesity/diabetes. Recently, we reported a role for the AT(2) receptor in blood pressure control in obese Zucker rats. However, the role of AT(2) receptors in inflammation and oxidative stress in obesity is not known. Therefore, in the present study, we tested the effects of the AT(2) receptor agonist CGP-42112A on inflammation and oxidative stress in obese Zucker rats and compared them in their lean counterparts. Rats were systemically treated with either vehicle (control) or CGP-42112A (1 μg·kg(-1)·min(-1); osmotic pump) for 2 wk. Markers of inflammation (CRP, MCP-1, TNF-α, and IL-6) and oxidative stress (HO-1, gp-91(phox)) as well as an antioxidant (SOD) were determined. Control obese rats had higher plasma levels of CRP, MCP-1, TNF-α, IL-6, and HO-1 compared with control lean rats. Conversely, plasma SOD activity was lower in control obese than in control lean rats. Furthermore, the protein levels of TNF-α and gp-91(phox) were higher in the kidney cortex of control obese rats. Interestingly, CGP-42112A treatment in obese rats reduced the plasma and kidney cortex inflammatory (TNF-α, IL-6) and oxidative stress (gp-91(phox)) markers and increased plasma SOD activity to the levels seen in lean control rats. However, CGP-42112A treatment in lean rats increased inflammatory (TNF-α, IL-6) and oxidative stress (gp-91(phox)) markers in the plasma and kidney cortex. Our present studies suggest anti-inflammatory and antioxidative functions of AT(2) receptor in obese Zucker rats but proinflammatory and prooxidative functions in lean Zucker rats.

Angiotensin II revisited: new roles in inflammation, immunology and aging

That the renin–angiotensin system (RAS) is involved in regulation of blood pressure, vasoconstriction, sodium intake and potassium excretion is well established. Studies in the last few years have however documented new roles for this molecule as a pro-inflammatory molecule and more recently as a possible pro-fibrotic agent that contributes to progressive deterioration of organ function in disease. Binding of Ang II to its receptors (in particular AT₁) mediates intracellular free radical generation that contributes to tissue damage by promoting mitochondrial dysfunction. Blocking Ang II signalling protects against neurodegenerative processes and promotes longevity in rodents. Altogether these findings open the unanticipated perspective for exploring Ang II signalling in therapeutic interventions in inflammatory diseases and aging-related tissue injury. This review extends from the discovery of Ang II and its implications in renal and cardiovascular physiology to cover the roles of the system in inflammation, tissue injury, autoimmunity, oxidative stress and aging.

Role of prolylcarboxypeptidase in angiotensin II type 2 receptor-mediated bradykinin release in mouse coronary artery endothelial cells

Activation of angiotensin II type 2 receptors (AT(2)R) causes the release of kinins, which have beneficial effects on the cardiovascular system. However, it is not clear how AT(2)R interact with the kallikrein-kinin system to generate kinins. Prolylcarboxypeptidase is an endothelial membrane-bound plasma prekallikrein activator that converts plasma prekallikrein to kallikrein, leading to generation of bradykinin from high-molecular-weight kininogen. We hypothesized that AT(2)R-induced bradykinin release is at least in part mediated by activation of prolylcarboxypeptidase. Cultures of mouse coronary artery endothelial cells were transfected with an adenoviral vector containing the AT(2)R gene (Ad-AT(2)R) or green fluorescent protein only (Ad-GFP) as control. We found that overexpression of AT(2)R increased prolylcarboxypeptidase mRNA by 1.7-fold and protein 2.5-fold compared with Ad-GFP controls. AT(2)R overexpression had no effect on angiotensin II type 1 receptor mRNA. Bradykinin release was increased 2.2-fold in AT(2)R-transfected cells. Activation of AT(2)R by CGP42112A, a specific AT(2)R agonist, increased bradykinin further in AT(2)R-transfected cells. These effects were diminished or abolished by AT(2)R blockade or a plasma kallikrein inhibitor. Furthermore, blocking prolylcarboxypeptidase with a small interfering RNA partially but significantly reduced bradykinin release by transfected AT(2)R cells either at the basal condition or when stimulated by the AT(2)R agonist CGP42112A. These findings suggest that overexpression of AT(2)R in mouse coronary artery endothelial cells increases expression of prolylcarboxypeptidase, which may contribute to kinin release.

Angiotensin II type-2 (AT2) receptor antagonism alters cardiovascular responses to static exercise and simultaneously changes glutamate/GABA levels within the ventrolateral medulla

Angiotensin II receptors (Ang II), classified into AT1 and AT2 subtypes, are located in different regions of the central nervous system, including the cardiovascular control centers in the medulla oblongata. We previously reported the role of Ang II AT1 receptors within the medulla on cardiovascular responses and glutamate/GABA neurotransmission during the exercise pressor reflex [Patel, D., Böhlke, M., Phattanarudee, S., Kabadi, S., Maher, T.J., Ally, A., 2008. Cardiovascular responses and neurotransmitter changes during blockade of angiotensin II receptors within the ventrolateral medulla. Neurosci. Res. 60 (3), 340-348]. In this study, we investigated the role of the AT2 receptor subtype within the ventrolateral medullary region (VLM) in modulating increases in mean arterial pressure (MAP) and heart rate (HR) in response to static skeletal muscle contraction.

METHODS

Using microdialysis methods in anesthetized rats, we administered AR-AT2 antagonists into the rostral (RVLM) and caudal (CVLM) VLM and determined its effects on cardiovascular responses and glutamate/GABA neurotransmission following muscle contraction. Bilateral microdialysis of a selective AT2 antagonist, PD 123319 (10 microM), for 30 min into the RVLM augmented MAP and HR responses during a static muscle contraction. Simultaneously, the drug increased glutamate and decreased GABA levels within the RVLM. After 60 min of discontinuation of the drug, only MAP and HR values but not the neurotransmitter levels in response to a muscle contraction returned to baseline. In contrast, bilateral microdialysis of the drug into the CVLM attenuated cardiovascular responses during a static muscle contraction, decreased glutamate and increased GABA. However, only the cardiovascular responses recovered after 60 min of discontinuation of the drug. These results demonstrate that AT2 within both RVLM and CVLM plays important differential roles in modulating neurotransmission and cardiovascular function during the exercise pressor reflex.

The renin-angiotensin system modulates inflammatory processes in atherosclerosis: evidence from basic research and clinical studies

Recent evidence shows that the renin-angiotensin system is a crucial player in atherosclerotic processes. The regulation of arterial blood pressure was considered from its first description of the main mechanism involved. Vasoconstriction (mediated by angiotensin II) and salt and water retention (mainly due to aldosterone) were classically considered as pivotal proatherosclerotic activities. However, basic research and animal studies strongly support angiotensin II as a proinflammatory mediator, which directly induces atherosclerotic plaque development and heart remodeling. Furthermore, angiotensin II induces proatherosclerotic cytokine and chemokine secretion and increases endothelial dysfunction. Accordingly, the pharmacological inhibition of the renin-angiotensin system improves prognosis of patients with cardiovascular disease even in settings of normal baseline blood pressure. In the present review, we focused on angiotensin-convertingenzyme (ACE) inhibitors, angiotensin II receptor blockers (ARBs), and renin inhibitors to update the direct activities of the renin-angiotensin system in inflammatory processes governing atherosclerosis.