The angiotensin II type 2 receptor agonist Compound 21 is protective in experimental diabetes-associated atherosclerosis

Catch your breath: The protective role of the angiotensin AT2 receptor for the treatment of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease whereby excessive deposition of extracellular matrix proteins (ECM) ultimately leads to respiratory failure. While there have been advances in pharmacotherapies for pulmonary fibrosis, IPF remains an incurable and irreversible disease. There remains an unmet clinical need for treatments that reverse fibrosis, or at the very least have a more tolerable side effect profile than currently available treatments. Transforming growth factor β1(TGFβ1) is considered the main driver of fibrosis in IPF. However, as our understanding of the role of the pulmonary renin-angiotensin system (PRAS) in the pathogenesis of IPF increases, it is becoming clear that targeting angiotensin receptors represents a potential novel treatment strategy for IPF - in particular, via activation of the anti-fibrotic angiotensin type 2 receptor (AT2R). This review describes the current understanding of the pathophysiology of IPF and the mediators implicated in its pathogenesis; focusing on TGFβ1, angiotensin II and related peptides in the PRAS and their contribution to fibrotic processes in the lung. Preclinical and clinical assessment of currently available AT2R agonists and the development of novel, highly selective ligands for this receptor will also be described, with a focus on compound 21, currently in clinical trials for IPF. Collectively, this review provides evidence of the potential of AT2R as a novel therapeutic target for IPF.

Novel AT2R agonist, β-Pro7Ang III, is cardio- and vaso-protective in diabetic spontaneously hypertensive rats

Stimulation of the angiotensin II type 2 receptor (AT2R) evokes protective effects in various cardiovascular diseases. Thus, this study aimed to investigate the effects of AT2R stimulation, with or without AT1R blockade, in a model of hypertension with concomitant type 1 diabetes mellitus (T1DM). Spontaneously hypertensive rats (SHRs) were given either citrate or a single dose of streptozotocin (STZ; 55 mg/kg, i.p.) to induce diabetes. After 4 weeks of diabetes, animals were administered either a vehicle (saline), AT2R agonist, β-Pro7Ang III (0.1 mg/kg/day via osmotic mini-pump), AT1R blocker, candesartan (2 mg/kg/day via drinking water), or a combination of both for a further 8 weeks. β-Pro7Ang III treatment had no effect on blood pressure, but attenuated the significant increase in cardiac interstitial collagen and protein expression of fibrotic and inflammatory markers, and superoxide levels that was evident in diabetic SHRs. These effects were not observed with candesartan, despite its blood pressure lowering effects. Although β-Pro7Ang III had no effect on aortic fibrosis, it significantly attenuated MCP-1 protein expression and superoxide levels when compared to both the non-diabetic and diabetic SHRs, to a similar extent as candesartan. In both the heart and vasculature, the effects of β-Pro7Ang III in combination with candesartan were similar to those of β-Pro7Ang III alone, and superior to candesartan alone. It was concluded that in hypertension with concomitant diabetes, AT2R stimulation with a novel ligand alone, or in combination with AT1R blockade, improved the cardiac and vascular structural changes that were strongly associated with inflammation and oxidative stress, independent of blood pressure regulation.

Effect of liraglutide on atherosclerosis in patients with impaired glucose tolerance: A double‑blind, randomized controlled clinical trial

Glucagon-like peptide-1 receptor agonist liraglutide may have beneficial effects on atherosclerosis development in impaired glucose tolerance (IGT). To the best of our knowledge, however, little conclusive evidence from clinical trials has been presented. The present study aimed to investigate the effect of liraglutide on atherosclerosis progression in patients with IGT. The present study was a double-blind, randomized controlled clinical trial. A total of 39 of patients aged 20-75 years who were overweight or obese (BMI, 27-40 kg/m²) and presented IGT were randomized to receive liraglutide (n=17) or lifestyle interventions (n=22) for 6 months. Serum glucose and insulin (INS) levels, lipid profile, inflammatory biomarkers and carotid intima-media thickness (CIMT) were assessed at the start and end of each treatment. Side effects were also recorded. Liraglutide treatment was found to significantly improve glycaemia, including glycosylated hemoglobin, fasting and postprandial glucose as well as INS levels (all P<0.001). Liraglutide also significantly decreased serum total cholesterol and low-density lipoprotein levels (all P<0.001). Furthermore, serum levels of inflammatory biomarkers, as well as CIMT, were decreased following liraglutide treatment compared with those in the lifestyle intervention group (all P<0.001). Kaplan-Meier analysis showed that the risk of vasculopathy in the liraglutide group was lower than that in the lifestyle intervention group (log-rank test; P=0.041). The monitoring of drug-associated side effects indicated that the dose of liraglutide (0.6 to 1.2 mg/QD via subcutaneous injection) was safe and well-tolerated. The present study suggested that liraglutide may slow atherosclerosis development and improve inflammatory status as well as intimal function in patients with IGT with few side effects. The trial was registered through the Chinese Clinical Trial Registry (ChiCTR; trial registration no. ChiCTR2200063693; retrospectively registered) on Sep 14, 2022.

Dectin-1 Acts as a Non-Classical Receptor of Ang II to Induce Cardiac Remodeling

BACKGROUND

Cardiac remodeling in heart failure involves macrophage-mediated immune responses. Recent studies have shown that a PRR (pattern recognition receptor) called dectin-1, expressed on macrophages, mediates proinflammatory responses. Whether dectin-1 plays a role in pathological cardiac remodeling is unknown. Here, we identified a potential role of dectin-1 in this disease.

METHODS

To model aberrant cardiac remodeling, we utilized mouse models of chronic Ang II (angiotensin II) infusion. In this model, we assessed the potential role of dectin-1 through using D1KO (dectin-1 knockout) mice and bone marrow transplantation chimeric mice. We then used cellular and molecular assays to discover the underlying mechanisms of dectin-1 function.

RESULTS

We found that macrophage dectin-1 is elevated in mouse heart tissues following chronic Ang II administration. D1KO mice were significantly protected against Ang II-induced cardiac dysfunction, hypertrophy, fibrosis, inflammatory responses, and macrophage infiltration. Further bone marrow transplantation studies showed that dectin-1 deficiency in bone marrow-derived cells prevented Ang II-induced cardiac inflammation and dysfunction. Through detailed molecular studies, we show that Ang II binds directly to dectin-1, causing dectin-1 homodimerization and activating the downstream Syk (spleen tyrosine kinase)/NF-κB (nuclear factor kappa B) signaling pathway to induce expression of inflammatory and chemoattractant factors. Mutagenesis studies identified R184 in the C-type lectin domain to interact with Ang II. Blocking dectin-1 in macrophages suppresses Ang II-induced inflammatory mediators and subsequent intercellular cross talk with cardiomyocytes and fibroblasts.

CONCLUSIONS

Our study has discovered dectin-1 as a new nonclassical receptor of Ang II and a key player in cardiac remolding and dysfunction. These studies suggest that dectin-1 may be a new target for treating hypertension-related heart failure.

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

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.

Suppression of Inflammatory Cardiac Cytokine Network in Rats with Untreated Obesity and Pre-Diabetes by AT2 Receptor Agonist NP-6A4

Obesity affects over 42% of the United States population and exacerbates heart disease, the leading cause of death in men and women. Obesity also increases pro-inflammatory cytokines that cause chronic tissue damage to vital organs. The standard-of-care does not sufficiently attenuate these inflammatory sequelae. Angiotensin II receptor AT2R is an anti-inflammatory and cardiovascular protective molecule; however, AT2R agonists are not used in the clinic to treat heart disease. NP-6A4 is a new AT2R peptide agonist with an FDA orphan drug designation for pediatric cardiomyopathy. NP-6A4 increases AT2R expression (mRNA and protein) and nitric oxide generation in human cardiovascular cells. AT2R-antagonist PD123319 and AT2RSiRNA suppress NP-6A4-effects indicating that NP-6A4 acts through AT2R. To determine whether NP-6A4 would mitigate cardiac damage from chronic inflammation induced by untreated obesity, we investigated the effects of 2-weeks NP-6A4 treatment (1.8 mg/kg delivered subcutaneously) on cardiac pathology of male Zucker obese (ZO) rats that display obesity, pre-diabetes and cardiac dysfunction. NP-6A4 attenuated cardiac diastolic and systolic dysfunction, cardiac fibrosis and cardiomyocyte hypertrophy, but increased myocardial capillary density. NP-6A4 treatment suppressed tubulointerstitial injury marker urinary β-NAG, and liver injury marker alkaline phosphatase in serum. These protective effects of NP-6A4 occurred in the presence of obesity, hyperinsulinemia, hyperglycemia, and hyperlipidemia, and without modulating blood pressure. NP-6A4 increased expression of AT2R (consistent with human cells) and cardioprotective erythropoietin (EPO) and Notch1 in ZO rat heart, but suppressed nineteen inflammatory cytokines. Cardiac miRNA profiling and in silico analysis showed that NP-6A4 activated a unique miRNA network that may regulate expression of AT2R, EPO, Notch1 and inflammatory cytokines, and mitigate cardiac pathology. Seventeen pro-inflammatory and pro-fibrotic cytokines that increase during lethal cytokine storms caused by infections such as COVID-19 were among the cytokines suppressed by NP-6A4 treatment in ZO rat heart. Thus, NP-6A4 activates a novel anti-inflammatory network comprised of 21 proteins in the heart that was not reported previously. Since NP-6A4's unique mode of action suppresses pro-inflammatory cytokine network and attenuates myocardial damage, it can be an ideal adjuvant drug with other anti-glycemic, anti-hypertensive, standard-of-care drugs to protect the heart tissues from pro-inflammatory and pro-fibrotic cytokine attack induced by obesity.

Correcting the imbalanced protective RAS in COVID-19 with angiotensin AT2-receptor agonists

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that is responsible for the global corona virus disease 2019 (COVID-19) pandemic enters host cells via a mechanism that includes binding to angiotensin converting enzyme (ACE) 2 (ACE2). Membrane-bound ACE2 is depleted as a result of this entry mechanism. The consequence is that the protective renin-angiotensin system (RAS), of which ACE2 is an essential component, is compromised through lack of production of the protective peptides angiotensin-(1-7) and angiotensin-(1-9), and therefore decreased stimulation of Mas (receptor Mas) and angiotensin AT2-receptors (AT2Rs), while angiotensin AT1-receptors (AT1Rs) are overstimulated due to less degradation of angiotensin II (Ang II) by ACE2. The protective RAS has numerous beneficial actions, including anti-inflammatory, anti-coagulative, anti-fibrotic effects along with endothelial and neural protection; opposite to the deleterious effects caused by heightened stimulation of angiotensin AT1R. Given that patients with severe COVID-19 exhibit an excessive immune response, endothelial dysfunction, increased clotting, thromboses and stroke, enhancing the activity of the protective RAS is likely beneficial. In this article, we discuss the evidence for a dysfunctional protective RAS in COVID and develop a rationale that the protective RAS imbalance in COVID-19 may be corrected by using AT2R agonists. We further review preclinical studies with AT2R agonists which suggest that AT2R stimulation may be therapeutically effective to treat COVID-19-induced disorders of various organ systems such as lung, vasculature, or the brain. Finally, we provide information on the design of a clinical trial in which patients with COVID-19 were treated with the AT2R agonist Compound 21 (C21). This trial has been completed, but results have not yet been reported.

Ameliorative effect of AT2R and ACE2 activation on ischemic renal injury associated cardiac and hepatic dysfunction

This study explored the role of the depressor arm of renin-angiotensin system (RAS) on ischemic renal injury (IRI)-associated cardio-hepatic sequalae under non-diabetic (ND) and diabetes mellitus (DM) conditions. Firstly, rats were injected with Streptozotocin (55 mg/kg i.p.) to develop DM. ND and DM rats underwent Bilateral IRI followed by 24 h of reperfusion. Further, ND and DM rats were subjected to AT2R agonist-Compound 21 (C21) (0.3 mg/kg/day, i.p.) or ACE2 activator- Diminazene Aceturate (Dize), (5 mg/kg/day, p.o.) per se or its combination therapy. As results, IRI caused cardio-hepatic injuries via altered oxidant/anti-oxidant levels, elevated inflammatory events, and altered protein expressions of ACE, ACE2, Ang II, Ang-(1-7) and urinary AGT. However, concomitant therapy of AT2R agonist and ACE2 activator exerts a protective effect in IRI-associated cardio-hepatic dysfunction as evidenced by inhibited oxidative stress, downregulated inflammation, and enhanced cardio-hepatic depressor arm of RAS under ND and DM conditions.

Combination of C21 and ARBs with rhACE2 as a therapeutic protocol: A new promising approach for treating ARDS in patients with coronavirus infection

Background: Coronavirus disease 2019 (COVID-19) is caused by a new severe acute respiratory syndrome Coronavirus. COVID-19 patients are at risk for acute respiratory distress syndrome and death from respiratory failure. Methods: In this study the complete genome of the SARS-CoV-2 reference sequence, geologically isolated types, and Coronavirus related to human diseases were compared by the Molecular Phylogenetic Maximum Likelihood method. The secondary and tertiary structures of the main protease of SARS-CoV were defined as the most similar viruses to SARS-CoV-2, aligned with chimera software. Therefore, considering ineffective antiviral medications used for SARS-CoV and the importance of preventing acute respiratory distress syndrome as the main cause of mortality, 2 strategies were adopted to acquire the most effective drug combination. Results: The results of phylogenic analysis showed that SARS-CoV is the most similar virus to SARS-CoV-2. The secondary structure and superimposing of tertiary structure did not show a significant difference between SARS and SARS-CoV-2 3C-like main protease and the root means square deviation between Cα atoms did not support the difference between the 2 protein structures. Thus, these 2 mechanisms were fostered in accordance with the correlation between acute respiratory distress syndrome-related Coronavirus, angiotensin-converting enzyme 2 on one side and the possible treatments for reducing the respiratory side effects on the other. The analysis of renin-angiotensin system as well as the tested drugs applied to acute respiratory distress syndrome cases, indicated that angiotensin II receptor blockers, angiotensin-converting enzyme inhibitors, and C21 as nonpeptide agonist might possess a promising modality of treatment for acute respiratory distress syndrome. Furthermore, implementing recombinant human ACE2 as a competitive receptor might be an effective way to trap and chelate the SARS-CoV-2 particles. Conclusion: The data suggest that combination therapy of angiotensin II receptor blockers and C21 could be a potential pharmacologic regimen to control and reduce acute respiratory distress syndrome. Moreover, rhACE2 can be recommended as an effective protective antiviral therapy in the treatment of COVID-19 and its complications.

The Other Angiotensin II Receptor: AT2R as a Therapeutic Target

The active hormone of the renin-angiotensin system (RAS), angiotensin II (Ang II), is involved in several human diseases, driving the development and clinical use of several therapeutic drugs, mostly angiotensin I converting enzyme (ACE) inhibitors and angiotensin receptor type I (AT₁R) antagonists. However, angiotensin peptides can also bind to receptors different from AT₁R, in particular, angiotensin receptor type II (AT₂R), resulting in biological and physiological effects different, and sometimes antagonistic, of their binding to AT₁R. In the present Perspective, the components of the RAS and the therapeutic tools developed to control it will be reviewed. In particular, the characteristics of AT₂R and tools to modulate its functions will be discussed. Agonists or antagonists to AT₂R are potential therapeutics in cardiovascular diseases, for agonists, and in the control of pain, for antagonists, respectively. However, controlling their binding properties and their targeting to the target tissues must be optimized.

The Concept of Early Vascular Aging

The age is one of the main non-modified factors which reduces the elasticity of vessels and increases the appearance of atherosclerotic plaques. A number of studies have revealed that in some people, vascular changes occur at a younger age, while the presence of only classical risk factors does not explain the development of cardiovascular events in young people. This phenomenon is described as a syndrome of early, or accelerated, vascular aging (EVA). Aspects of this premature process include endothelial dysfunction, increased arterial stiffness, thickening of the intima-media complex and impaired dilatation of the central arteries, an increase of the reflected wave, hypertrophy of small vessels with a decrease in their lumen. Accelerated aging of the vascular wall increases the frequency of complications, therefore, recently "vascular age” is considered as an important predictor of individual risk of cardiovascular events. The review describes factors and mechanisms that trigger the process of EVA, genetic aspects of vascular damage and the biology of telomeres. Changes in hemodynamics and structural and functional properties of arteries during physiological and accelerated aging are presented. Currently, several indicators have been proposed that indicate arterial wall damaging and progression of vascular aging. The carotid-femoral pulse wave velocity is included in the list of indicators of subclinical target organs damage in ESH-ESC Guidelines for the management of arterial hypertension. The results of studies on the developing the new diagnostic markers for identifying individuals with "normal" or "early" ("accelerated") vascular aging are presented. Therapeutic strategies are aimed at decreasing the influence of factors that provoke EVA and include a non-pharmacological approach and medical intervention. The paper describes methods of therapeutic correction of the EVA syndrome.

AT1R-AT2R-RXFP1 Functional Crosstalk in Myofibroblasts: Impact on the Therapeutic Targeting of Renal and Cardiac Fibrosis

BACKGROUND

Recombinant human relaxin-2 (serelaxin), which has organ-protective actions mediated via its cognate G protein-coupled receptor relaxin family peptide receptor 1 (RXFP1), has emerged as a potential agent to treat fibrosis. Studies have shown that serelaxin requires the angiotensin II (AngII) type 2 receptor (AT₂R) to ameliorate renal fibrogenesis in vitro and in vivo. Whether its antifibrotic actions are affected by modulation of the AngII type 1 receptor (AT₁R), which is expressed on myofibroblasts along with RXFP1 and AT₂R, is unknown.

METHODS

We examined the signal transduction mechanisms of serelaxin when applied to primary rat renal and human cardiac myofibroblasts in vitro, and in three models of renal- or cardiomyopathy-induced fibrosis in vivo.

RESULTS

The AT₁R blockers irbesartan and candesartan abrogated antifibrotic signal transduction of serelaxin via RXFP1 in vitro and in vivo. Candesartan also ameliorated serelaxin's antifibrotic actions in the left ventricle of mice with cardiomyopathy, indicating that candesartan's inhibitory effects were not confined to the kidney. We also demonstrated in a transfected cell system that serelaxin did not directly bind to AT₁Rs but that constitutive AT₁R-RXFP1 interactions could form. To potentially explain these findings, we also demonstrated that renal and cardiac myofibroblasts expressed all three receptors and that antagonists acting at each receptor directly or allosterically blocked the antifibrotic effects of either serelaxin or an AT₂R agonist (compound 21).

CONCLUSIONS

These findings have significant implications for the concomitant use of RXFP1 or AT₂R agonists with AT₁R blockers, and suggest that functional interactions between the three receptors on myofibroblasts may represent new targets for controlling fibrosis progression.

Anti-fibrotic mechanisms of angiotensin AT2 -receptor stimulation

The angiotensin AT₂ -receptor is a main receptor of the protective arm of the renin-angiotensin system. Understanding of this unconventional G-protein coupled receptor has significantly advanced during the past decade, largely because of the availability of a selective non-peptide AT₂ -receptor agonist, which allowed the conduct of a multitude of studies in animal disease models. This article reviews such preclinical studies that in their entirety provide strong evidence for an anti-fibrotic effect mediated by activation of the AT₂ -receptor. Prevention of the development of fibrosis by AT₂ -receptor stimulation has been demonstrated in lungs, heart, blood vessels, kidney, pancreas and skin. In lungs, AT₂ -receptor stimulation was even able to reverse existing fibrosis. The article further discusses intracellular signalling mechanisms mediating the AT₂ -receptor-coupled anti-fibrotic effect, including activation of phosphatases and subsequent interference with pro-fibrotic signalling pathways, induction of matrix-metalloproteinases and hetero-dimerization with the AT₁ -receptor, the TGF-βRII-receptor or the RXFP1-receptor for relaxin. Knowledge of the anti-fibrotic effects of the AT₂ -receptor is of particular relevance because drugs targeting this receptor have entered clinical development for indications involving fibrotic diseases.

Renin-angiotensin system in osteoarthritis: A new potential therapy

Osteoarthritis (OA) is one of the most common chronic joint diseases. However, the mechanism remains unclear. The traditional renin-angiotensin system (RAS) is an important system for regulating homeostasis and controlling balance. In recent years, RAS-related components have played an important role in the occurrence of OA. The purpose of this review is to summarize the research results of RAS-related components that are associated with OA. This study systematically searched e-medical databases such as PubMed, Embase, Medline, and Web of Science. The search targets included English publications describing the effects of RAS-related components in OA, including the role of renin, angiotensin-converting enzyme (ACE), Angiotensin II (Ang II), and angiotensin receptor (ATR). Additionally, this study summarizes the potential pathways for RAS-related components to intervene in OA. This study found that RAS-related components including renin, ACE, Ang II, AT1R and AT2R are involved in inflammation and chondrocyte hypertrophy in OA. RAS is involved in signaling pathways including the NF-κB, JNK, VEGFR/Tie-2, and the Axna2/Axna2R axis ones, which may be potential targets for the treatment of OA. Although there are few studies on RAS in the field of OA, the pathogenic effect of RAS-related components is still an important topic in OA treatment, and great progress may be made in this aspect in future studies.

The Effect of a Nonpeptide Angiotensin II Type 2 Receptor Agonist, Compound 21, on Aortic Aneurysm Growth in a Mouse Model of Marfan Syndrome

Introduction:

Available evidence suggests that the renin–angiotensin–aldosterone (RAA) system is a good target for medical intervention on aortic root dilatation in Marfan syndrome (MFS). The effect of Compound 21 (C21), a nonpeptide angiotensin II type 2 receptor agonist, on aneurysm progression was tested.

Methods:

Mice with a mutation in fibrillin-1 (Fbn1^C1039G/+) and wild-type mice were treated with vehicle, losartan, C21, enalapril, or a combination. Blood pressure, aortic root diameter, and histological slides were evaluated.

Results:

All groups had a comparable blood pressure. Echographic evaluation of the aortic root diameter revealed a protective effect of angiotensin II type 1 receptor antagonist (losartan) and no effect of C21 treatment. None of the treatments had a beneficial effect on the histological changes in MFS.

Discussion:

This study confirms that angiotensin II type 1 receptor antagonism (losartan) decreases aortic aneurysm growth in a mouse model of MFS. A nonpeptide angiotensin II type 2 receptor agonist (C21), at the doses studied, was ineffective. Future studies are warranted to further elucidate the exact role of the RAA system in aneurysm formation in MFS and identify alternative targets for intervention.

Emerging Therapy in Hypertension

PURPOSE OF THE REVIEW

Pharmacology remains the mainstay of treatment for hypertension across the globe. In what may seem like a well-trodden field, there are actually an exciting array of new pathways for the treatment of hypertension on the horizon. This review seeks to discuss the most recent research in ongoing areas of drug development in the field of hypertension.

RECENT FINDINGS

Novel areas of research in the field of hypertension pharmacology include central nervous system regulators, peripheral noradrenergic inhibitors, gastrointestinal sodium modulators, and a counter-regulatory arm of the renin-angiotensin-aldosterone system. This review discusses these pathways in a look into the current status of emerging pharmacological therapies for hypertension.

Protective effect of angiotensin Ⅱ type 1 receptor antagonist against gastric mucosal lesions in rats with cerebral hemorrhage and acute stress gastric mucosal injury

AIM

To analyze the protective effect of angiotensin Ⅱ AT1 receptor blocker (ARB) against gastric mucosal lesions in rats with intracerebral hemorrhage combined with acute stress mucosal injury.

METHODS

Thirty-six healthy male Sprague-Dawley rats were selected from our laboratory Animal Center and randomly divided into either a treatment group (18 rats) or a control group (18 rats). After intracerebral hemorrhage was induced in rats, the treatment group was given telmisartan, and the control group was given equal amount of normal saline. Serum norepinephrine (NE) and epinephrine (E) contents were detected and the gastric mucosal ulcer index (UI) was calculated. Immunohistochemistry was used to detect proliferative cell nuclear antigen (PCNA) in rat gastric mucosa (proliferative cell nuclei). Apoptotic cells were detected by transferase-mediated dUTP nick end labeling (TUNEL).

RESULTS

There was no significant difference in the scores of cerebral apoplexy between the treatment group and the control group (P > 0.05). After 1, 3, and 5 d of treatment, serum E and NE levels in the treatment group were significantly lower than those in the control group (P < 0.05). The UI values of the treatment group on days 1, 3, and 5 were 3.86 ± 1.14, 20.19 ± 1.28, and 13.86 ± 1.25, respectively, which were significantly lower than those of the control group (6.03 ± 1.16, 24.03 ± 1.31, and 17.10 ± 1.28, respectively; P < 0.05). After 1, 3, and 5 d of treatment, the number of PCNA positive cells in the treatment group was significantly higher than that of the control group, while the number of apoptotic cells was significantly lower than that in the control group (P < 0.05).

CONCLUSION

ARB can reduce serum contents of NE and E in rats with intracerebral hemorrhage, decrease apoptotic cells in the gastric mucosa, and increase the number of proliferating cells, thus exerting a therapeutic effect against acute stress gastric mucosal lesions.

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.

Chronic administration of the angiotensin type 2 receptor agonist C21 improves insulin sensitivity in C57BL/6 mice

The renin-angiotensin system modulates insulin action. Angiotensin type 1 receptor exerts a deleterious effect, whereas the angiotensin type 2 receptor (AT2R) appears to have beneficial effects providing protection against insulin resistance and type 2 diabetes. To further explore the role of the AT2R on insulin action and glucose homeostasis, in this study we administered C57Bl/6 mice with the synthetic agonist of the AT2R C21 for 12 weeks (1 mg/kg per day; ip). Vehicle-treated animals were used as control. Metabolic parameters, glucose, and insulin tolerance, in vivo insulin signaling in main insulin-target tissues as well as adipose tissue levels of adiponectin, and TNF-α were assessed. C21-treated animals displayed decreased glycemia together with unaltered insulinemia, increased insulin sensitivity, and increased glucose tolerance compared to nontreated controls. This was accompanied by a significant decrease in adipocytes size in epididymal adipose tissue and significant increases in both adiponectin and UCP-1 expression in this tissue. C21-treated mice showed an increase in both basal Akt and ERK1/2 phosphorylation levels in the liver, and increased insulin-stimulated Akt activation in adipose tissue. This positive modulation of insulin action induced by C21 appeared not to involve the insulin receptor. In C21-treated mice, adipose tissue and skeletal muscle became unresponsive to insulin in terms of ERK1/2 phosphorylation levels. Present data show that chronic pharmacological activation of AT2R with C21 increases insulin sensitivity in mice and indicate that the AT2R has a physiological role in the conservation of insulin action.

The Selective Angiotensin II Type 2 Receptor Agonist, Compound 21, Attenuates the Progression of Lung Fibrosis and Pulmonary Hypertension in an Experimental Model of Bleomycin-Induced Lung Injury

Idiopathic Pulmonary Fibrosis (IPF) is a chronic lung disease characterized by scar formation and respiratory insufficiency, which progressively leads to death. Pulmonary hypertension (PH) is a common complication of IPF that negatively impacts clinical outcomes, and has been classified as Group III PH. Despite scientific advances, the dismal prognosis of IPF and associated PH remains unchanged, necessitating the search for novel therapeutic strategies. Accumulating evidence suggests that stimulation of the angiotensin II type 2 (AT₂) receptor confers protection against a host of diseases. In this study, we investigated the therapeutic potential of Compound 21 (C21), a selective AT₂ receptor agonist in the bleomycin model of lung injury. A single intra-tracheal administration of bleomycin (2.5 mg/kg) to 8-week old male Sprague Dawley rats resulted in lung fibrosis and PH. Two experimental protocols were followed: C21 was administered (0.03 mg/kg/day, ip) either immediately (prevention protocol, BCP) or after 3 days (treatment protocol, BCT) of bleomycin-instillation. Echocardiography, hemodynamic, and Fulton's index assessments were performed after 2 weeks of bleomycin-instillation. Lung tissue was processed for gene expression, hydroxyproline content (a marker of collagen deposition), and histological analysis. C21 treatment prevented as well as attenuated the progression of lung fibrosis, and accompanying PH. The beneficial effects of C21 were associated with decreased infiltration of macrophages in the lungs, reduced lung inflammation and diminished pulmonary collagen accumulation. Further, C21 treatment also improved pulmonary pressure, reduced muscularization of the pulmonary vessels and normalized cardiac function in both the experimental protocols. However, there were no major differences in any of the outcomes measured from the two experimental protocols. Collectively, our findings indicate that stimulation of the AT₂ receptor by C21 attenuates bleomycin-induced lung injury and associated cardiopulmonary pathology, which needs to be further explored as a promising approach for the clinical treatment of IPF and Group III PH.

Angiotensin II AT2 Receptors Contribute to Regulate the Sympathoadrenal and Hormonal Reaction to Stress Stimuli

Angiotensin II, through AT1 receptor stimulation, mediates multiple cardiovascular, metabolic, and behavioral functions including the response to stressors. Conversely, the function of Angiotensin II AT2 receptors has not been totally clarified. In adult rodents, AT2 receptor distribution is very limited but it is particularly high in the adrenal medulla. Recent results strongly indicate that AT2 receptors contribute to the regulation of the response to stress stimuli. This occurs in association with AT1 receptors, both receptor types reciprocally influencing their expression and therefore their function. AT2 receptors appear to influence the response to many types of stressors and in all components of the hypothalamic-pituitary-adrenal axis. The molecular mechanisms involved in AT2 receptor activation, the complex interactions with AT1 receptors, and additional factors participating in the control of AT2 receptor regulation and activity in response to stressors are only partially understood. Further research is necessary to close this knowledge gap and to clarify whether AT2 receptor activation may carry the potential of a major translational advance.

Angiotensin II type 2 receptor inhibits expression and function of insulin receptor in rat renal proximal tubule cells

Both renin-angiotensin systems and insulin participate in kidney-involved blood pressure regulation. Activation of angiotensin II type 2 receptor (AT₂R) decreases sodium reabsorption in renal proximal tubule (RPT) cells, whereas insulin produces the opposite effect. We presume that AT₂R has an inhibitory effect on insulin receptor expression in RPT cells, which may affect renal sodium transport and therefore be of physiological or pathological significance. Our present study found that activation of AT₂R inhibited insulin receptor expression in a concentration and time-dependent manner in RPT cells from Wistar-Kyoto (WKY) rats. In the presence of a protein kinase C (PKC) inhibitor (PKC inhibitor peptide 19-31, 10^-6 mol/L) or a phosphatidylinositol 3 kinase inhibitor (wortmannin, 10^-6 mol/L), the inhibitory effect of AT₂R on insulin receptor was blocked, indicating that both PKC and phosphatidylinositol 3 kinase were involved in the signaling pathway. There was a linkage between AT₂R and insulin receptor which was determined by both laser confocal microscopy and coimmunoprecipitation. However, the effect of AT₂R activation on insulin receptor expression was different in RPT cells from spontaneously hypertensive rats (SHRs). Being contrary to the effect in WKY RPT cells, AT₂R stimulation increased insulin receptor in SHR RPT cells. Insulin (10^-7 mol/L, 15 minutes) enhanced Na⁺-K⁺-ATPase activity in both WKY and SHR RPT cells. Pretreatment with CGP42112 decreased the stimulatory effect of insulin on Na⁺-K⁺-ATPase activity in WKY RPT cells, whereas pretreatment with CGP42112 increased it in SHR RPT cells. It is suggested that activation of AT₂R inhibits insulin receptor expression and function in RPT cells. The lost inhibitory effect of AT₂R on insulin receptor expression may contribute to the pathophysiology of hypertension.

Role of Vitamin D in Cardiovascular Diseases

Vitamin D is critical in mineral homeostasis and skeletal health and plays a regulatory role in nonskeletal tissues. Vitamin D deficiency is associated with chronic inflammatory diseases, including diabetes and obesity, both strong risk factors for cardiovascular diseases (CVDs). CVDs, including coronary artery disease, myocardial infarction, hypertrophy, cardiomyopathy, cardiac fibrosis, heart failure, aneurysm, peripheral arterial disease, hypertension, and atherosclerosis, are major causes of morbidity and mortality. The association of these diseases with vitamin D deficiency and improvement with vitamin D supplementation suggest its therapeutic benefit. The authors review the findings on the association of vitamin D deficiency and CVDs.

Oxidative Stress in Human Atherothrombosis: Sources, Markers and Therapeutic Targets

Atherothrombosis remains one of the main causes of morbidity and mortality worldwide. The underlying pathology is a chronic pathological vascular remodeling of the arterial wall involving several pathways, including oxidative stress. Cellular and animal studies have provided compelling evidence of the direct role of oxidative stress in atherothrombosis, but such a relationship is not clearly established in humans and, to date, clinical trials on the possible beneficial effects of antioxidant therapy have provided equivocal results. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is one of the main sources of reactive oxygen species (ROS) in human atherothrombosis. Moreover, leukocyte-derived myeloperoxidase (MPO) and red blood cell-derived iron could be involved in the oxidative modification of lipids/lipoproteins (LDL/HDL) in the arterial wall. Interestingly, oxidized lipoproteins, and antioxidants, have been analyzed as potential markers of oxidative stress in the plasma of patients with atherothrombosis. In this review, we will revise sources of ROS, focusing on NADPH oxidase, but also on MPO and iron. We will also discuss the impact of these oxidative systems on LDL and HDL, as well as the value of these modified lipoproteins as circulating markers of oxidative stress in atherothrombosis. We will finish by reviewing some antioxidant systems and compounds as therapeutic strategies to prevent pathological vascular remodeling.

Angiotensin II type 2 receptor (AT2R) as a novel modulator of inflammation in rheumatoid arthritis synovium

Despite increasing evidence suggesting that angiotensin II type 2 receptor (AT2R) may regulate tissue inflammation, no study has yet analyzed its possible implication in rheumatoid arthritis (RA) synovitis. In this study, we investigated the expression and function of AT2R in synovial tissue and cultured fibroblast-like synoviocytes (FLS) from RA patients. AT2R expression was strongly increased in RA compared with osteoarthritis (OA) synovium, as well as in in cultured RA-FLS respect to OA-FLS and healthy FLS. Treatment with pro-inflammatory cytokines was able not only to boost AT2R expression in RA-FLS and OA-FLS, but also to induce its de novo expression in healthy FLS. The stimulation of AT2R with the specific agonist CGP42112A significantly reduced gene expression of interleukin (IL)-1β and IL-6 and activation of NF-κB in RA-FLS, while opposite effects were elicited by AT2R small interfering RNA. Moreover, AT2R agonism efficiently decreased RA-FLS proliferation and migration either at baseline or under pro-inflammatory cytokine challenge. In conclusion, AT2R is strongly expressed in key effector cells of rheumatoid synovitis, namely RA-FLS, and the activation of AT2R with a specific agonist may effectively dampen their pro-inflammatory and aggressive behavior. AT2R agonism might represent a novel therapeutic strategy for patients with RA.

Sex and gender differences in hypertensive kidney injury

Hypertension is a complex, multifaceted disorder, affecting ~1 in 3 adults in the United States. Although hypertension occurs in both men and women, there are distinct sex differences in the way in which they develop hypertension, with women having a lower incidence of hypertension until the sixth decade of life. Despite observed sex differences in hypertension, little is known about the molecular mechanisms underlying the development of hypertension in females, primarily because of their underrepresentation in both clinical and experimental animal studies. The first goal of this review is to provide a concise overview of the participation of women in clinical trials, including a discussion of the importance of including females in basic science research, as recently mandated by the National Institutes of Health. The remaining portion of the review is dedicated to identifying clinical and experimental animal studies that concentrate on gender and sex differences in hypertensive kidney disease, ending with a proposed role for T cells in mediating sex differences in blood pressure.

Oleanolic acid alleviates diabetic rat carotid artery injury through the inhibition of NLRP3 inflammasome signaling pathways

The overexpression of inflammasome components is correlated with diabetes‑associated complications. Oleanolic acid is a triterpenoid compound which is important in arterial injury. The present study evaluated whether oleanolic acid improved diabetic rat carotid artery injury through the inhibition of nucleotide‑binding domain, leucine‑rich‑containing family, pyrin domain‑containing‑3 (NLRP3) inflammasomes signaling pathways. A diabetic rat model was induced using streptozotocin (60 mg/kg) and underwent carotid artery injury. Morphometric analysis was performed using hematoxylin and eosin staining. The mRNA and protein levels were assayed by reverse transcription‑quantitative polymerase chain reaction and western blotting, respectively. It was found that oleanolic acid (100 mg/kg/day) improved body weight, glucose metabolic disorders, neointimal hyperplasia and endothelial dysfunction in diabetic rats with carotid artery injury. In addition, oleanolic acid administration significantly downregulated the mRNA and protein expression levels of endothelin 1 in diabetic rats. Oleanolic acid decreased the intimal area and the ratio of neointima to media in diabetic rats. Serum levels of tumor necrosis factor‑α, interleukin (IL)‑1β, IL‑6 and IL‑18 in the oleanolic acid‑treated diabetic rats were downregulated. Consistent with the serum results, it was demonstrated that oleanolic acid administration caused a significant decrease in the levels of NLRP3, caspase‑1 and IL‑1β in the carotid arteries of diabetic rats. Taken together, these observations suggested that oleanolic acid attenuated carotid artery injury in diabetic rats and the underlying mechanism was mediated, at least partially, through the suppression of NLRP3 inflammasome signaling pathways.

Future drug discovery in renin-angiotensin-aldosterone system intervention

INTRODUCTION

Renin-angiotensin-aldosterone system inhibitors (RAASIs), including angiotensin-converting enzyme inhibitors, angiotensin AT1 receptor blockers and mineralocorticoid receptor antagonists (MRAs), are the cornerstone for the treatment of cardiovascular and renal diseases. Areas covered: The authors searched MEDLINE, PubMed and ClinicalTrials.gov to identify eligible full-text English language papers. Herein, the authors discuss AT2-receptor agonists and ACE2/angiotensin-(1-7)/Mas-receptor axis modulators, direct renin inhibitors, brain aminopeptidase A inhibitors, biased AT1R blockers, chymase inhibitors, multitargeted drugs, vaccines and aldosterone receptor antagonists as well as aldosterone synthase inhibitors. Expert opinion: Preclinical studies have demonstrated that activation of the protective axis of the RAAS represents a novel therapeutic strategy for treating cardiovascular and renal diseases, but there are no clinical trials supporting our expectations. Non-steroidal MRAs might become the third-generation of MRAs for the treatment of heart failure, diabetes mellitus and chronic kidney disease. The main challenge for these new drugs is that conventional RAASIs are safe, effective and cheap generics. Thus, the future of new RAASIs will be directed by economical/strategic reasons.

Compound 21 and Telmisartan combination mitigates type 2 diabetic nephropathy through amelioration of caspase mediated apoptosis

The current study aimed to understand the role of novel, highly selective, orally active, non-peptide Angiotensin II type 2 receptor (AT2R) agonist, Compound 21 and its potential additive effect with Telmisartan on apoptosis and underlying posttranslational modifications in a non-genetic murine model for type 2 diabetic nephropathy (T2DN). An experimental model for T2DN was developed by administering low dose Streptozotocin in high fat diet fed male Wistar rats, followed by their treatment with Telmisartan, C21 or their combination. Our results demonstrated that C21 and Telmisartan combination attenuated metabolic and renal dysfunction, renal morphological and micro-architectural aberrations and hemodynamic disturbances in type 2 diabetic rats. The anti-apoptotic and anti-inflammatory effects of Telmisartan were significantly accentuated by C21 indicated by expression of apoptotic markers (Parp1, Caspase 8, Caspase 7, cleaved PARP and cleaved Caspase 3) and NF-κB mediated inflammatory molecules like interleukin 6, tumour necrosis factor alpha; monocyte chemoattractant protein 1 and vascular cell adhesion molecule 1. C21 was found to improve Telmisartan mediated reversal of histone H3 acetylation at lysine 14 and 27 and expression of histone acetyl transferase, p300/CBP-associated factor also known to regulate NF-κB activity and DNA damage response. C21 in combination with Telmisartan markedly mitigates caspase mediated apoptosis and NF-κB signalling in T2D kidney, which could be partially attributed to its influence on PCAF mediated histone H3 acetylation. Hence further research should be done to develop this combination to treat T2DN.

Update on RAAS Modulation for the Treatment of Diabetic Cardiovascular Disease

Since the advent of insulin, the improvements in diabetes detection and the therapies to treat hyperglycemia have reduced the mortality of acute metabolic emergencies, such that today chronic complications are the major cause of morbidity and mortality among diabetic patients. More than half of the mortality that is seen in the diabetic population can be ascribed to cardiovascular disease (CVD), which includes not only myocardial infarction due to premature atherosclerosis but also diabetic cardiomyopathy. The importance of renin-angiotensin-aldosterone system (RAAS) antagonism in the prevention of diabetic CVD has demonstrated the key role that the RAAS plays in diabetic CVD onset and development. Today, ACE inhibitors and angiotensin II receptor blockers represent the first line therapy for primary and secondary CVD prevention in patients with diabetes. Recent research has uncovered new dimensions of the RAAS and, therefore, new potential therapeutic targets against diabetic CVD. Here we describe the timeline of paradigm shifts in RAAS understanding, how diabetes modifies the RAAS, and what new parts of the RAAS pathway could be targeted in order to achieve RAAS modulation against diabetic CVD.