Agonists of MAS oncogene and angiotensin II type 2 receptors attenuate cardiopulmonary disease in rats with neonatal hyperoxia-induced lung injury

Angiotensin II Type 2 Receptor Inhibits M1 Polarization and Apoptosis of Alveolar Macrophage and Protects Against Mechanical Ventilation-Induced Lung Injury

Angiotensin II (Ang II) is associated with macrophage polarization and apoptosis, but the role of the angiotensin type 2 receptor (AT2R) in these processes remains controversial. However, the effect of AT2Rs on alveolar macrophages and mechanical ventilation-induced lung injury has not been determined. Mechanical ventilation-induced lung injury in Sprague‒Dawley (SD) rats and LPS-stimulated rat alveolar macrophages (NR8383) were used to determine the effects of AT2Rs, selective AT2R agonists and selective AT1Rs or AT2R antagonists. Macrophage polarization, apoptosis, and related signaling pathways were assessed via western blotting, QPCR and flow cytometry. AT2R expression was decreased in LPS-stimulated rat alveolar macrophages (NR8383). Administration of the AT2R agonist CGP-42112 was associated with an increase in AT2R expression and M2 polarization, but no effect was observed upon administration of the AT2R antagonist PD123319 or the AT1R antagonist valsartan. In mechanical ventilation-induced lung injury in Sprague‒Dawley (SD) rats, the administration of the AT2R agonist C21 was associated with attenuation of the pathological damage score, lung wet/dry weight, cell count and protein content in BALF. C21 can significantly reduce proinflammatory factor TNF-α, IL-1β levels, increase anti-inflammatory factor IL-4, IL-10 levels in BALF, compared with the model group (p < 0.01). Similarly, compared with those at the same time points, the M1/M2 ratios in alveolar macrophages and apoptosis in peritoneal macrophages at 4 h, 6 h and 8 h in the mechanical ventilation models were lower after C21 administration. These findings indicated that the expression of AT2Rs in alveolar macrophages mediates M1 macrophage polarization and apoptosis and that AT2Rs play a protective role in mediating mechanical ventilation-induced lung injury.

Genetic variants in the renin-angiotensin-aldosterone system: Impact on cancer risk, prognosis, and therapeutic directions

Although renin-angiotensin-aldosterone system (RAAS) is known to maintain blood pressure and electrolyte balance, it has recently been linked to a number of biological processes such as angiogenesis, tumorigenesis, metastasis, and cellular proliferation, increasing the risk of cancer development and progression. Multiple genetic variants have been found to affect the genes encoding RAAS components, altering gene transcription and protein expression. This review provides an up-to-date insight into the role of RAAS in carcinogenesis, as well as the impact of RAAS genetic variants on the risk of cancer development, progression, and patient survival and outcomes, as well as response to treatment. This paves the way for the application of precision medicine in cancer risk assessment and management by implementing preventative programs in individuals at risk and guiding the therapeutic direction in cancer patients.

Hyperoxia-induced airflow restriction and Renin-Angiotensin System expression in a bronchopulmonary dysplasia mouse model

Mechanisms underlying hyperoxia-induced airflow restriction in the pediatric lung disease Bronchopulmonary dysplasia (BPD) are unclear. We hypothesized a role for Renin-Angiotensin System (RAS) activity in BPD. RAS is comprised of a pro-developmental pathway consisting of angiotensin converting enzyme-2 (ACE2) and angiotensin II receptor type 2 (AT2), and a pro-fibrotic pathway mediated by angiotensin II receptor type 1 (AT1). We investigated associations between neonatal hyperoxia, airflow restriction, and RAS activity in a BPD mouse model. C57 mouse pups were randomized to normoxic (FiO2  = 0.21) or hyperoxic (FiO2  = 0.75) conditions for 15 days (P1-P15). At P15, P20, and P30, we measured airflow restriction using plethysmography and ACE2, AT1, and AT2 mRNA and protein expression via polymerase chain reaction and Western Blot. Hyperoxia increased airflow restriction P15 and P20, decreased ACE2 and AT2 mRNA, decreased AT2 protein, and increased AT1 protein expression. ACE2 mRNA and protein remained suppressed at P20. By P30, airflow restriction and RAS expression did not differ between groups. Hyperoxia caused high airflow restriction, increased pulmonary expression of the pro-fibrotic RAS pathway, and decreased expression of the pro-developmental in our BPD mouse model. These associated findings may point to a causal role for RAS in hyperoxia-induced airflow restriction.

Evolving views on the first two ligands of the angiotensin II type 2 receptor. From putative antagonists to potential agonists?

The renin-angiotensin system is one of the most complex regulatory systems that controls multiple organ functions. One of its key components, angiotensin II (Ang II), stimulates two G-protein coupled class A receptors: the Ang II type 1 (AT1) receptor and the Ang II type 2 (AT2) receptor. While stimulation of the AT1 receptor causes G-protein-dependent signaling and arrestin recruitment, the AT2 receptor seems to have a constitutively active-like conformation and appears to act via G-protein-dependent and -independent pathways. Overstimulation of the AT1 receptor may lead to unwanted effects like inflammation and fibrosis. In contrast, stimulation of the AT2 receptor leads to opposite effects thus restoring the balance. However, the role of the AT2 receptor has become controversial due to beneficial effects of putative AT2 receptor antagonists. The two first synthetic AT2 receptor-selective ligands, peptide CGP42112 and small molecule PD123319, were initially both considered antagonists. CGP42112 was subsequently considered a partial agonist and it was recently demonstrated to be a full agonist. Based on the search-term PD123319 in Pubmed, 1652 studies have investigated putative AT2 receptor antagonist PD123319. Here, we put forward literature that shows beneficial effects of PD123319 alone, even at doses too low for antagonist efficacy. These beneficial effects appear compatible with agonist-like activity via the AT2 receptor. Taken together, a more consistent image of a therapeutic role of stimulated AT2 receptor emerges which may clarify current controversies.

AT2 receptor agonist LP2 restores respiratory function in a rat model of bleomycin-induced lung remodelling

This study aimed to evaluate the prophylactic and therapeutic potential of angiotensin II type 2 receptor peptide agonist LP2 in bleomycin-induced airway and cardiac remodeling in rats. Male Wistar rats were intratracheally instillated with bleomycin. Animals of a prophylactic arm received LP2 from day 0 at intraperitoneal doses of 1, 3 or 10 μg/kg/d, whereas animals from a therapeutic arm received this LP2 treatment from day 7. On day 28 direct lung mechanics were determined and cardiac and lung tissues were collected and (histo)morphologically assessed. Prophylactic LP2 at 1 µg/kg/d with bleomycin, versus bleomycin alone, significantly improved the airway pressure responses at fixed inflation of 4 ml (p < 0.05) and 7 ml volume (p < 0.05), static compliance (p < 0.01), inspiratory capacity (p < 0.05), lung tolerance of increased volume (p < 0.0001), right to left ventricular hypertrophy (p < 0.05). Therapeutic regime showed a similar trend as the prophylactic arm but was less effective, mostly lacking significance. However, and importantly, therapeutic LP2 at 1 µg/kg/d significantly decreased mRNA expression of collagen 1A1 (p < 0.01), of Connective Tissue Growth Factor 1 (p < 0.05) and of Tissue MetalloPeptidase inhibitor 1 (p < 0.05). In conclusion, a very low dose of 1 µg/kg/d LP2 has capacity to counter bleomycin-induced impairment of lung functioning and consequent cardiac remodeling.

Effects of the Oral Angiotensin II Type 2 Receptor Agonist C21 in Sugen-Hypoxia Induced Pulmonary Hypertension in Rats

Substantial evidence supports the involvement of the renin-angiotensin system in pulmonary hypertension (PH), and the angiotensin II type 2 receptor (AT₂R) is known to exert tissue protective actions. The effect of the selective AT₂R agonist C21 (also known as Compound 21 or buloxibutid) was evaluated in the rat Sugen-hypoxia PH model. After a single injection of Sugen 5416 and hypoxia for 21 days, C21 (2 or 20 mg/kg) or vehicle was administered perorally twice daily from Day 21 to Day 55. On Day 56, hemodynamic assessments were performed, and lung and heart tissue were prepared for quantification of cardiac and vascular remodeling and fibrosis. Treatment with C21 20 mg/kg improved cardiac output and stroke volume and decreased right ventricular hypertrophy (all p < 0.05). Treatment with C21 2 mg/kg significantly decreased vessel wall and muscular layer thickness and increased the luminal opening in vessels >100 μm (all p < 0.05). There were no significant differences between the two C21 doses on any parameter, and post hoc analyses comparing the merged C21 groups with the vehicle group showed that C21 treatment reduced vascular remodeling (reduced endothelial proliferation and thickening of the vascular wall) in vessels of all sizes; moreover, the diastolic pulmonary artery pressure and right ventricular pressure were reduced along with reduction of right ventricular hypertrophy. Sugen 5416 and hypoxia increased pulmonary collagen deposition, which was counteracted by C21 20 mg/kg. In conclusion, the effects of C21 on vascular remodeling, hemodynamic alterations, and fibrosis suggest that AT₂R agonists may have a role in Group 1 and 3 PH treatment.

LP2, a cyclic angiotensin-(1-7) analog extended with an N-terminal D-lysine, impairs growth of patient-derived xenografts of colorectal carcinoma in mice

LP2 is a 4, 7 D, L lanthionine-stabilized analog of angiotensin-(1-7), with an N-terminal D-lysine, resistant to breakdown by peptidases. It is a specific agonist of the angiotensin II type 2 receptor. Consistent with its high specificity and stability, LP2 has shown excellent safety and pharmacokinetics in a first-in-human clinical phase Ia trial. Here, based on strong rationales, we studied the capacity of LP2 to inhibit the growth of patient-derived xenografts of colorectal cancer in mice. Prior to efficacy studies, immunohistochemistry on an untreated tissue array demonstrated that the AT₂R expression is reduced in human colorectal cancer and in stroma when compared to tumor adjacent tissue. Subsequent studies demonstrated that LP2 at a subcutaneously injected dose as low as 0.2 µg/kg/day inhibited patient-derived xenografts of colorectal carcinoma in mice. Kinome analyses and validation of elected kinase inhibition indicated that LP2-mediated AT₂R stimulation inhibited PI3K/AKT/mTOR which resulted in apoptosis via CDKs. LP2 acted synergistically with 5-FU and the EGFR inhibitor erlotinib. Taken together, the extremely low dose of LP2 at which antitumor activity is exerted, the synergism with selected drugs and, together with its excellent specificity, safety and stability, warrant further evaluation of LP2's inhibitory potential of colorectal cancer.

LP2, a stable lanthipeptide derived from cAng-(1-7), exerts myeloprotective action in mice

OBJECTIVES

Linear unstable angiotensins stimulate hematopoiesis. Here we address: (1) Is cyclic angiotensin-(1-7) myeloprotective in mice? (2) Is cyclic angiotensin-(1-7) stable in rat? (3) Does LP2, a cyclic angiotensin-(1-7) with an N-terminal d-lysine, exert myeloprotective action in tumor-bearing mice?

MATERIALS AND METHODS

Cyclic angiotensin-(1-7)'s capacity to restore levels of blood platelets and white blood cells was studied in gemcitabine-treated mice. The stability of cyclic angiotensin-(1-7) in rat was measured in blood samples taken after injection or infusion. The capacity of LP2 to restore total bone marrow cell levels in mice after treatment with 5-fluoruracil was measured. In addition, the capacity of LP2 to counter anemia in tumor-bearing mice treated with erlotinib was measured.

RESULTS

Cyclic angiotensin-(1-7) dose-dependently restored blood platelet levels in gemcitabine-treated mice, whereas its capacity to restore levels of white blood cells was less. In vivo aminoterminal breakdown of cyclic angiotensin-(1-7) yielded cyclic angiotensin-(2-7) and cyclic angiotensin-(3-7). LP2 significantly (p < .0001 at 100 μg/kg/day) restored bone marrow cell counts in mice after treatment with 5-fluoruracil. LP2 also significantly (p < .05) countered anemia in tumor-bearing mice treated with erlotinib.

CONCLUSIONS

LP2 exerts myeloprotective action with perspectives for continuation of its clinical development.

A Review on COVID-19: Primary Receptor, Endothelial Dysfunction, Related Comorbidities, and Therapeutics

Since December 2019, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused a global pandemic named coronavirus disease-19 (COVID-19) and resulted in a worldwide economic crisis. Utilizing the spike-like protein on its surface, the SARS-CoV-2 binds to the receptor angiotensin-converting enzyme 2 (ACE2), which highly expresses on the surface of many cell types. Given the crucial role of ACE2 in the renin–angiotensin system, its engagement by SARS-CoV-2 could potentially result in endothelial cell perturbation. This is supported by the observation that one of the most common consequences of COVID-19 infection is endothelial dysfunction and subsequent vascular damage. Furthermore, endothelial dysfunction is the shared denominator among previous comorbidities, including hypertension, kidney disease, cardiovascular diseases, etc., which are associated with an increased risk of severe disease and mortality in COVID-19 patients. Several vaccines and therapeutics have been developed and suggested for COVID-19 therapy. The present review summarizes the relationship between ACE2 and endothelial dysfunction and COVID-19, also reviews the most common comorbidities associated with COVID-19, and finally reviews several categories of potential therapies against COVID-19.

Circular RNAs expression profiles and bioinformatics analysis in bronchopulmonary dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) has long been considered the most challenging chronic lung disease for neonatologists and researchers due to its complex pathological mechanisms and difficulty in prediction. Growing evidence indicates that BPD is associated with the dysregulation of circular RNAs (circRNAs). Therefore, we aimed to explore the expression profiles of circRNAs and investigate the underlying molecular network associated with BPD.

METHODS

Peripheral blood was collected from very-low-birth-weight (VLBW) infants at 5-8 days of life to extract PBMCs. Microarray analysis and qRT-PCR tests were performed to determine the differentially expressed circRNAs (DEcircRNAs) between BPD and non-BPD VLBW infants. Simultaneous analysis of GSE32472 was conducted to obtain differentially expressed mRNAs (DEmRNA) from BPD infants. The miRNAs were predicted by DEcircRNAs and DEmRNAs of upregulated, respectively, and then screened for overlapping ones. GO and KEGG analysis was performed following construction of the competing endogenous RNA regulatory network (ceRNA) for further investigation.

RESULTS

A total of 65 circRNAs (52 upregulated and 13 downregulated) were identified as DEcircRNAs between the two groups (FC >2.0 and p.adj <0.05). As a result, the ceRNA network was constructed based on three upregulated DEcircRNAs validated by qRT-PCR (hsa_circ_0007054, hsa_circ_0057950, and hsa_circ_0120151). Bioinformatics analysis indicated these DEcircRNAs participated in response to stimulus, IL-1 receptor activation, neutrophil activation, and metabolic pathways.

CONCLUSIONS

In VLBW infants with a high risk for developing BPD, the circRNA expression profiles in PBMCs were significantly altered in the early post-birth period, suggesting immune dysregulation caused by infection and inflammatory response already existed.

Hypertension in chronic kidney disease: What lies behind the scene

Hypertension is a frequent condition encountered during kidney disease development and a leading cause in its progression. Hallmark factors contributing to hypertension constitute a complexity of events that progress chronic kidney disease (CKD) into end-stage renal disease (ESRD). Multiple crosstalk mechanisms are involved in sustaining the inevitable high blood pressure (BP) state in CKD, and these play an important role in the pathogenesis of increased cardiovascular (CV) events associated with CKD. The present review discusses relevant contributory mechanisms underpinning the promotion of hypertension and their consequent eventuation to renal damage and CV disease. In particular, salt and volume expansion, sympathetic nervous system (SNS) hyperactivity, upregulated renin–angiotensin–aldosterone system (RAAS), oxidative stress, vascular remodeling, endothelial dysfunction, and a range of mediators and signaling molecules which are thought to play a role in this concert of events are emphasized. As the control of high BP via therapeutic interventions can represent the key strategy to not only reduce BP but also the CV burden in kidney disease, evidence for major strategic pathways that can alleviate the progression of hypertensive kidney disease are highlighted. This review provides a particular focus on the impact of RAAS antagonists, renal nerve denervation, baroreflex stimulation, and other modalities affecting BP in the context of CKD, to provide interesting perspectives on the management of hypertensive nephropathy and associated CV comorbidities.

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.

Angiotensin-(1-9) in hypertension

Angiotensin-(1-9) [Ang-(1-9)] is a peptide of the non-canonical renin-angiotensin system (RAS) synthesized from angiotensin I by the monopeptidase angiotensin-converting enzyme type 2 (ACE2). Using osmotic minipumps, infusion of Ang-(1-9) consistently reduces blood pressure in several rat hypertension models. In these animals, hypertension-induced end-organ damage is also decreased. Several pieces of evidence suggest that Ang-(1-9) is the endogenous ligand that binds and activates the type-2 angiotensin II receptor (AT2R). Activation of AT2R triggers different tissue-specific signaling pathways. This phenomenon could be explained by the ability of AT2R to form different heterodimers with other G protein-coupled receptors. Because of the antihypertensive and protective effects of AT2R activation by Ang-(1-9), associated with a short half-life of RAS peptides, several synthetic AT2R agonists have been synthesized and assayed. Some of them, particularly CGP42112, C21 and novokinin, have demonstrated antihypertensive properties. Only two synthetic AT2R agonists, C21 and LP2-3, have been tested in clinical trials, but none of them like an antihypertensive. Therefore, Ang-(1-9) is a promising antihypertensive drug that reduces hypertension-induced end-organ damage. However, further research is required to translate this finding successfully to the clinic.

Angiotensin receptors - affinitiy and beyond

This commentary on the article "Relative affinity of angiotensin peptides and novel ligands at AT1 and AT2 receptors" by Sanja Bosnyak et al. (Clini. Sci. (Lond.) (2011) 121(7): 297-303. https://doi.org/10.1042/CS20110036) summarises the main findings of the study, followed by a discussion of the findings and their relevance for various aspects of the biology of receptors of the renin-angiotensin system in the context of the current state of knowledge.

Stem-Cell Therapy for Bronchopulmonary Dysplasia (BPD) in Newborns

Premature newborns are at a higher risk for the development of respiratory distress syndrome (RDS), acute lung injury (ALI) associated with lung inflammation, disruption of alveolar structure, impaired alveolar growth, lung fibrosis, impaired lung angiogenesis, and development of bronchopulmonary dysplasia (BPD) with severe long-term developmental adverse effects. The current therapy for BPD is limited to supportive care including high-oxygen therapy and pharmacotherapy. Recognizing more feasible treatment options to improve lung health and reduce complications associated with BPD is essential for improving the overall quality of life of premature infants. There is a reduction in the resident stem cells in lungs of premature infants with BPD, which strongly suggests a critical role of stem cells in BPD pathogenesis; this warrants the exploration of the potential therapeutic use of stem-cell therapy. Stem-cell-based therapies have shown promise for the treatment of many pathological conditions including acute lung injury and BPD. Mesenchymal stem cells (MSCs) and MSC-derived extracellular vesicles (EVs) including exosomes are promising and effective therapeutic modalities for the treatment of BPD. Treatment with MSCs and EVs may help to reduce lung inflammation, improve pulmonary architecture, attenuate pulmonary fibrosis, and increase the survival rate.

Renin angiotensin aldosterone system in pulmonary fibrosis: Pathogenesis to therapeutic possibilities

Pulmonary fibrosis is a devastating lung disease with multifactorial etiology characterized by alveolar injury, fibroblast proliferation and excessive deposition of extracellular matrix proteins, which progressively results in respiratory failure and death. Accumulating evidence from experimental and clinical studies supports a central role of the renin angiotensin aldosterone system (RAAS) in the pathogenesis and progression of idiopathic pulmonary fibrosis. Angiotensin II (Ang II), a key vasoactive peptide of the RAAS mediates pro-inflammatory and pro-fibrotic effects on the lungs, adversely affecting organ function. Recent years have witnessed seminal discoveries in the field of RAAS. Identification of new enzymes, peptides and receptors has led to the development of several novel concepts. Of particular interest is the establishment of a protective axis of the RAAS comprising of Angiotensin converting enzyme 2 (ACE2), Angiotensin-(1-7) [Ang-(1-7)], and the Mas receptor (the ACE2/Ang-(1-7)/Mas axis), and the discovery of a functional role for the Angiotensin type 2 (AT₂) receptor. Herein, we will review our current understanding of the role of RAAS in lung fibrogenesis, provide evidence on the anti-fibrotic actions of the newly recognized RAAS components (the ACE2/Ang-(1-7)/Mas axis and AT₂ receptor), discuss potential strategies and translational efforts to convert this new knowledge into effective therapeutics for PF.

Classical and Counter-Regulatory Renin-Angiotensin System: Potential Key Roles in COVID-19 Pathophysiology

In the current COVID-19 pandemic, severe acute respiratory syndrome coronavirus 2 uses angiotensin-converting enzyme-2 (ACE-2) receptors for cell entry, leading to ACE-2 dysfunction and downregulation, which disturb the balance between the classical and counter-regulatory renin-angiotensin system (RAS) in favor of the classical RAS. RAS dysregulation is one of the major characteristics of several cardiovascular diseases; thus, adjustment of this system is the main therapeutic target. RAS inhibitors-particularly angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II type 1 receptor blockers (ARBs)-are commonly used for treatment of hypertension and cardiovascular disease. Patients with cardiovascular diseases are the group most commonly seen among those with COVID-19 comorbidity. At the beginning of this pandemic, a dilemma occurred regarding the use of ACEIs and ARBs, potentially aggravating cardiovascular and pulmonary dysfunction in COVID-19 patients. Urgent clinical trials from different countries and hospitals reported that there is no association between RAS inhibitor treatment and COVID-19 infection or comorbidity complication. Nevertheless, the disturbance of the RAS that is associated with COVID-19 infection and the potential treatment targeting this area have yet to be resolved. In this review, the link between the dysregulation of classical RAS and counter-regulatory RAS activities in COVID-19 patients with cardiovascular metabolic diseases is investigated. In addition, the latest findings based on ACEI and ARB administration and ACE-2 availability in relation to COVID-19, which may provide a better understanding of the RAS contribution to COVID-19 pathology, are discussed, as they are of the utmost importance amid the current pandemic.

Angiotensin II Type 2 Receptor: A Target for Protection Against Hypertension, Metabolic Dysfunction, and Organ Remodeling

The renin-angiotensin system is of vital significance not only in the maintenance of blood pressure but also because of its role in the pathophysiology of different organ systems in the body. Of the 2 Ang II (angiotensin II) receptors, the AT₁R (Ang II type 1 receptor) has been extensively studied for its role in mediating the classical functions of Ang II, including vasoconstriction, stimulation of renal tubular sodium reabsorption, hormonal secretion, cell proliferation, inflammation, and oxidative stress. The other receptor, AT₂R (Ang II type 2 receptor), is abundantly expressed in both immune and nonimmune cells in fetal tissue. However, its expression is increased under pathological conditions in adult tissues. The role of AT₂R in counteracting AT₁R function has been discussed in the past 2 decades. However, with the discovery of the nonpeptide agonist C21, the significance of AT₂R in various pathologies such as obesity, hypertension, and kidney diseases have been examined. This review focuses on the most recent findings on the beneficial effects of AT₂R by summarizing both gene knockout studies as well as pharmacological studies, specifically highlighting its importance in blood pressure regulation, obesity/metabolism, organ protection, and relevance in the treatment of coronavirus disease 2019 (COVID-19).

The Tissue Renin-Angiotensin System and Its Role in the Pathogenesis of Major Human Diseases: Quo Vadis?

Evidence has arisen in recent years suggesting that a tissue renin-angiotensin system (tRAS) is involved in the progression of various human diseases. This system contains two regulatory pathways: a pathological pro-inflammatory pathway containing the Angiotensin Converting Enzyme (ACE)/Angiotensin II (AngII)/Angiotensin II receptor type 1 (AGTR1) axis and a protective anti-inflammatory pathway involving the Angiotensin II receptor type 2 (AGTR2)/ACE2/Ang1–7/MasReceptor axis. Numerous studies reported the positive effects of pathologic tRAS pathway inhibition and protective tRAS pathway stimulation on the treatment of cardiovascular, inflammatory, and autoimmune disease and the progression of neuropathic pain. Cell senescence and aging are known to be related to RAS pathways. Further, this system directly interacts with SARS-CoV 2 and seems to be an important target of interest in the COVID-19 pandemic. This review focuses on the involvement of tRAS in the progression of the mentioned diseases from an interdisciplinary clinical perspective and highlights therapeutic strategies that might be of major clinical importance in the future.

Developing new drugs that activate the protective arm of the renin-angiotensin system as a potential treatment for respiratory failure in COVID-19 patients

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has reached pandemic proportions with negative impacts on global health, the world economy and human society. The clinical picture of COVID-19, and the fact that Angiotensin converting enzyme 2 (ACE2) is a receptor of SARS-CoV-2, suggests that SARS-CoV-2 infection induces an imbalance in the renin–angiotensin system (RAS). We review clinical strategies that are attempting to rebalance the RAS in COVID-19 patients by using ACE inhibitors, angiotensin receptor blockers, or agonists of angiotensin-II receptor type 2 or Mas receptor (MasR). We also propose that the new MasR activator BIO101, a pharmaceutical grade formulation of 20-hydroxyecdysone that has anti-inflammatory, anti-fibrotic and cardioprotective properties, could restore RAS balance and improve the health of COVID-19 patients who have severe pneumonia.

LP2, the first lanthipeptide GPCR agonist in a human pharmacokinetics and safety study

Introduction of a lanthionine into a peptide may enhance target affinity, target specificity and proteolytic resistance. This manuscript reports preclinical safety studies and the first-in-human study with the lanthipeptide AT₂R agonist LP2, a structural analog of cAng-(1-7), whose N-terminus was protected against aminopeptidases by the presence of a d-lysine. None of the preclinical studies, including an in vitro multitarget panel, behavioral, respiratory and cardiovascular measurements, genotoxicity and toxicity studies in rat and dog, posed any safety concern. Due to lack of toxicity the maximum tolerated dose was not reached neither in rat nor in dog. In the human dose escalation study, healthy male volunteers received a single 1 mL subcutaneous injection (0.001 mg, 0.01 mg or 0.1 mg) of LP2 or matching placebo. In contrast to angiotensin II which has a T_1/2 in plasma of < 1 min, LP2 has a T_1/2 of approximately 2.1-2.6 hours. The fraction of the dose excreted unchanged in urine ranged from 84.73 ± 10.4 % at a dose of 0.001 mg to 66.4 ± 3.9 % at 0.1 mg. There were no deaths, serious adverse events or subject withdrawals as a result of an adverse event. The incidence of adverse events was 16.7 %; each was mild in severity. One adverse event, peripheral coldness, was considered to be possibly related to LP2 at 0.001 mg LP2. None of the results was considered to pose a clinically relevant safety concern. This study supports the potential for the therapeutic use of lanthipeptides.

ACE2/Ang-(1-7)/Mas1 axis and the vascular system: vasoprotection to COVID-19-associated vascular disease

The two axes of the renin-angiotensin system include the classical ACE/Ang II/AT1 axis and the counter-regulatory ACE2/Ang-(1-7)/Mas1 axis. ACE2 is a multifunctional monocarboxypeptidase responsible for generating Ang-(1-7) from Ang II. ACE2 is important in the vascular system where it is found in arterial and venous endothelial cells and arterial smooth muscle cells in many vascular beds. Among the best characterized functions of ACE2 is its role in regulating vascular tone. ACE2 through its effector peptide Ang-(1-7) and receptor Mas1 induces vasodilation and attenuates Ang II-induced vasoconstriction. In endothelial cells activation of the ACE2/Ang-(1-7)/Mas1 axis increases production of the vasodilator's nitric oxide and prostacyclin's and in vascular smooth muscle cells it inhibits pro-contractile and pro-inflammatory signaling. Endothelial ACE2 is cleaved by proteases, shed into the circulation and measured as soluble ACE2. Plasma ACE2 activity is increased in cardiovascular disease and may have prognostic significance in disease severity. In addition to its enzymatic function, ACE2 is the receptor for severe acute respiratory syndrome (SARS)-coronavirus (CoV) and SARS-Cov-2, which cause SARS and coronavirus disease-19 (COVID-19) respectively. ACE-2 is thus a double-edged sword: it promotes cardiovascular health while also facilitating the devastations caused by coronaviruses. COVID-19 is associated with cardiovascular disease as a risk factor and as a complication. Mechanisms linking COVID-19 and cardiovascular disease are unclear, but vascular ACE2 may be important. This review focuses on the vascular biology and (patho)physiology of ACE2 in cardiovascular health and disease and briefly discusses the role of vascular ACE2 as a potential mediator of vascular injury in COVID-19.

Regulation of ACE-2 enzyme by hyperoxia in lung epithelial cells by post-translational modification

BACKGROUND

Bronchopulmonary Dysplasia (BPD) occurs in premature neonates with respiratory distress who require supplemental oxygen in the first days after birth. BPD involves uniform arrest of alveolar development and variable interstitial cellularity and/or fibroproliferation. Previous studies by our lab showed that the enzyme, angiotensin converting enzyme-2 (ACE-2) and its product Ang1-7 exerting action on the receptor Mas oncogene in what is known as ACE-2/Mas axis is protective to lung cells. We also showed that ACE-2 is expressed in fetal human lung fibroblasts but is significantly decreased by hyperoxic gas lung injury, an effect caused by ACE-2 enzyme shedding mediated by TNF-alpha-converting enzyme (TACE/ADAM17). However, no reports yet exist about the regulation of ACE-2 in the alveolar epithelia in hyperoxic lung injury.

OBJECTIVE

In this study we aim to define the effects of hyperoxic lung injury on the protective ACE-2 enzyme in the human lung alveolar epithelial cell line A549.

DESIGN/METHODS

Cultured A549 cells were exposed to hyperoxia (95% O2) or normoxia (21% O2) for 3 or 7 days in serum-free nutrient media. Cells were lysed and culture media were collected to test for cellular ACE-2 enzymatic activity and for ACE-2, Mas receptor, TACE/ADAM17, and ubiquitin proteins abundance by immunoblotting. Cells were harvested in Trizol for RNA extraction and ACE-2 qRT-PCR. Whole cell extracts of A549 cell line was used for ACE-2 immunoprecipitation and subsequent ubiquitin immunoblotting.

RESULTS

Total ubiquitinated proteins were increased by hyperoxia treatment, while ACE-2 and Mas receptor proteins abundance and ACE-2 enzymatic activity were decreased significantly in A549 cells exposed to hyperoxia relative to the normoxia controls. The percent decrease in ACE-2 activity corresponded with increased time of hyperoxic gas exposure. However, in contrast to our data from lung fibroblasts, no significant change was noted in ACE-2 protein released into the media or in ACE-2 mRNA levels by the hyperoxic treatment. Ubiquitin immunoreactive bands were detectable in the ACE-2 immunoprecipitate.

CONCLUSIONS

These data suggest that hyperoxic exposure of the lung epithelial cells decreases the protective enzyme ACE-2 by cell type specific mechanisms independent of shedding by TACE/ADAM17. The data also suggest a regulatory level of ACE-2 downstream of transcription may involve ACE-2 ubiquitination and targeting for degradation.

Angiotensin Converting Enzyme-2 (ACE-2) role in disease and future in research

Coronavirus Disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Like the 2002-2003 epidemic severe acute respiratory syndrome coronavirus (SARS-CoV), angiotensin converting enzyme-2 (ACE-2) has been identified as the SARS-CoV-2 receptor.^1-3 The virus docks into host cell via its spike protein binding to ACE-2 and undergoes proteolytic cleavage by TMPRSS2 protease to facilitate membrane fusion. The spike protein binding to ACE-2 has been shown to be stronger in the novel SARS-CoV-2 virus.¹ This review will present an overview of ACE-2 biology.

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.

Emerging Role of Angiotensin AT2 Receptor in Anti-Inflammation: An Update

The hyperactive RAS and inflammation are closely associated. The angiotensin-II/AT1R axis of the RAS has been explored extensively for its role in inflammation and a plethora of pathological conditions. Understanding the role of AT2R in inflammation is an emerging area of research. The AT2R is expressed on a variety of immune and non-immune cells, which upon activation triggers the release of a host of cytokines and has multiple effects that coalesce to anti-inflammation and prevents maladaptive repair. The anti-inflammatory outcomes of AT2R activation are linked to its well-established signaling pathways involving formation of nitric oxide and activation of phosphatases. Collectively, these effects promote cell survival and tissue function. The consideration of AT2R as a therapeutic target requires further investigations.

Biosynthesis of lanthionine-constrained agonists of G protein-coupled receptors

The conformation with which natural agonistic peptides interact with G protein-coupled receptor(s) (GPCR(s)) partly results from intramolecular interactions such as hydrogen bridges or is induced by ligand–receptor interactions. The conformational freedom of a peptide can be constrained by intramolecular cross-links. Conformational constraints enhance the receptor specificity, may lead to biased activity and confer proteolytic resistance to peptidic GPCR agonists. Chemical synthesis allows to introduce a variety of cross-links into a peptide and is suitable for bulk production of relatively simple lead peptides. Lanthionines are thioether bridged alanines of which the two alanines can be introduced at different distances in chosen positions in a peptide. Thioether bridges are much more stable than disulfide bridges. Biosynthesis of lanthionine-constrained peptides exploiting engineered Gram-positive or Gram-negative bacteria that contain lanthionine-introducing enzymes constitutes a convenient method for discovery of lanthionine-stabilized GPCR agonists. The presence of an N-terminal leader peptide enables dehydratases to dehydrate serines and threonines in the peptide of interest after which a cyclase can couple the formed dehydroamino acids to cysteines forming (methyl)lanthionines. The leader peptide also guides the export of the formed lanthionine-containing precursor peptide out of Gram-positive bacteria via a lanthipeptide transporter. An engineered cleavage site in the C-terminus of the leader peptide allows to cleave off the leader peptide yielding the modified peptide of interest. Lanthipeptide GPCR agonists are an emerging class of therapeutics of which a few examples have demonstrated high efficacy in animal models of a variety of diseases. One lanthipeptide GPCR agonist has successfully passed clinical Phase Ia.

Use of Angiotensin-Converting Enzyme Inhibitors and Angiotensin II Receptor Blockers During the COVID-19 Pandemic: A Modeling Analysis

Angiotensin-converting enzyme inhibitors (ACEi) and angiotensin II receptor blockers (ARB) are frequently prescribed for a range of diseases including hypertension, proteinuric chronic kidney disease, and heart failure. There is evidence indicating that these drugs upregulate ACE2, a key component of the renin-angiotensin system (RAS) and is found on the cells of a number of tissues, including the epithelial cells in the lungs. While ACE2 has a beneficial role in many diseases such as hypertension, diabetes, and cardiovascular disease, it also serves as a receptor for both SARS-CoV and SARS-CoV-2 via binding with the spike protein of the virus, thereby allowing it entry into host cells. Thus, it has been suggested that these therapies can theoretically increase the risk of SARS- CoV-2 infection and cause more severe COVID-19. Given the success of ACEi and ARBs in cardiovascular diseases, we seek to gain insights into the implications of these medications in the pathogenesis of COVID-19. To that end, we have developed a mathematical model that represents the RAS, binding of ACE2 with SARS-CoV-2 and the subsequent cell entry, and the host's acute inflammatory response. The model can simulate different levels of SARS-CoV-2 exposure, and represent the effect of commonly prescribed anti-hypertensive medications, ACEi and ARB, and predict tissue damage. Model simulations indicate that whether the extent of tissue damage may be exacerbated by ACEi or ARB treatment depends on a number of factors, including the level of existing inflammation, dosage, and the effect of the drugs on ACE2 protein abundance. The findings of this study can serve as the first step in the development of appropriate and more comprehensive guidelines for the prescription of ACEi and ARB in the current and future coronavirus pandemics.

Dendritic Cells and SARS-CoV-2 Infection: Still an Unclarified Connection

The ongoing pandemic due to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has so far infected about 2.42 × 107 (as at 27 August 2020) subjects with more than 820,000 deaths. It is the third zoonotic coronavirus-dependent outbreak in the last twenty years and represents a major infective threat for public health worldwide. A main aspect of the infection, in analogy to other viral infections, is the so-called "cytokine storm", an inappropriate molecular response to virus spread which plays major roles in tissue and organ damage. Immunological therapies, including vaccines and humanized monoclonal antibodies, have been proposed as major strategies for prevention and treatment of the disease. Accordingly, a detailed mechanistic knowledge of the molecular events with which the virus infects cells and induces an immunological response appears necessary. In this review, we will report details of the initial process of SARS-CoV-2 cellular entry with major emphasis on the maturation of the spike protein. Then, a particular focus will be devoted to describe the possible mechanisms by which dendritic cells, a major cellular component of innate and adaptive immune responses, may play a role in the spread of the virus in the human body and in the clinical evolution of the disease.

Coronavirus Disease 2019 and Hypertension: The Role of Angiotensin-Converting Enzyme 2 and the Renin-Angiotensin System

Hypertension emerged from early reports as a potential risk factor for worse outcomes for persons with coronavirus disease 2019 (COVID-19). Among the putative links between hypertension and COVID-19 is a key counter-regulatory component of the renin-angiotensin system (RAS): angiotensin-converting enzyme 2 (ACE2). ACE2 facilitates entry of severe acute respiratory syndrome coronavirus 2, the virus responsible for COVID-19, into host cells. Because RAS inhibitors have been suggested to increase ACE2 expression, health-care providers and patients have grappled with the decision of whether to discontinue these medications during the COVID-19 pandemic. However, experimental models of analogous viral pneumonias suggest RAS inhibitors may exert protective effects against acute lung injury. We review how RAS and ACE2 biology may affect outcomes in COVID-19 through pulmonary and other systemic effects. In addition, we briefly detail the data for and against continuation of RAS inhibitors in persons with COVID-19 and summarize the current consensus recommendations from select specialty organizations.

Does activation of the protective Renin-Angiotensin System have therapeutic potential in COVID-19?

Infection of lung cells by the corona virus results in a loss of the balance between, on the one hand, angiotensin II-mediated stimulation of the angiotensin II type 1 receptor and, on the other hand, stimulation of the angiotensin II type 2 receptor and/or the Mas receptor. The unbalanced enhanced stimulation of the angiotensin II type 1 receptor causes inflammation, edema and contributes to the pathogenesis of severe acute respiratory distress syndrome. Here we hypothesize that stable, receptor-specific agonists of the angiotensin II type 2 receptor and of the Mas receptor are molecular medicines to treat COVID-19 patients. These agonists have therapeutic potential in the acute disease but in addition may reduce COVID-19-associated long-term pulmonary dysfunction and overall end-organ damage of this disease.

COVID-19 and RAS: Unravelling an Unclear Relationship

The renin-angiotensin system (RAS) plays a main role in regulating blood pressure and electrolyte and liquid balance. Previous evidence suggests that RAS may represent an important target for the treatment of lung pathologies, especially for acute respiratory distress syndrome and chronic fibrotic disease. The scientific community has recently focused its attention on angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor 1 (AT1R) inhibitors and their possible benefit/harms for patients infected by Coronavirus disease (COVID-19) who experience pneumonia, but there are still some doubts about the effects of these drugs in this setting.

Mesenchymal stem/stromal cells stably transduced with an inhibitor of CC chemokine ligand 2 ameliorate bronchopulmonary dysplasia and pulmonary hypertension

Perinatal bronchopulmonary dysplasia (BPD) is defined as lung injury in preterm infants caused by various factors, resulting in serious respiratory dysfunction and high mortality. The administration of mesenchymal stem/stromal cells (MSCs) to treat/prevent BPD has proven to have certain therapeutic effects. However, MSCs can only weakly regulate macrophage function, which is strongly involved in the development of BPD. 7ND-MSCs are MSCs transfected with 7ND, a truncated version of CC chemokine ligand 2 (CCL2) that promotes macrophage activation, using a lentiviral vector. In the present study, we show in a BPD rat model that 7ND-MSC administration, but not MSCs alone, ameliorated the impaired alveolarization evaluated by volume density and surface area in the lung tissue, as well as pulmonary artery remodeling and pulmonary hypertension induced by BPD. In addition, 7ND-MSCs, but not MSCs alone, reduced M1 macrophages and the messenger RNA expressions of interleukin-6 and CCL2 in the lung tissue. Thus, the present study showed the treatment effect of 7ND-MSCs in a BPD rat model, which was more effective than that of MSCs alone.

Mas Receptor Agonist AVE0991 increases surfactant protein expression under hyperoxic conditions in human lung epithelial cells

BACKGROUND

Hyperoxia in pre-term neonates is a known risk factor of bronchopulmonary dysplasia (BPD). Hyperoxia is known to cause oxidative stress, inflammatory changes that leads to surfactant deactivation, and decreased surfactant expression. The previous research has shown short term exposure to hyperoxia increases surfactant protein expression but decreased expression in long term exposure. Local tissue renin-angiotensin system (RAS) is associated with tissue injury and repair and it may play a role in BPD. Endogenous peptide angiotensin 1-7 acts on the MAS receptor. The activation of the MAS receptor was previously shown to have protective pulmonary responses. However, the effect of MAS receptor activation on surfactant proteins in hyperoxic conditions has not been tested.

OBJECTIVE

To determine the effects of hyperoxia with or without MAS receptor activation on Surfactant proteins.

METHODS

Human epithelial cell line A549 and human primary alveolar epithelial cells (AECs) were cultured to sub-confluence (60-75%) and treated with hyperoxia (95% oxygen) and normoxia (21% oxygen) for 72 hours with or without the MAS receptor agonist (AVE0991) in serum-free F-12 nutrient media. Cells were lysed and cell lysates were collected for western blot. The statistical analysis was done using Student-Newman-Keuls Multiple comparison test.

RESULTS

Surfactant protein concentration increased in AVE treated group under the hyperoxic condition when compared to the control group in both A549 cells and human primary AECs. Surfactant protein was in higher concentration in AVE0991 treated cells in both hyperoxic and normoxic conditions when compared to the non-treated control group.

CONCLUSIONS

MAS receptor activation via AVE0991 causes an increase in Surfactant protein concentration in both hyperoxic and normoxic conditions. As per our experiments, hyperoxic conditions decrease the production of surfactant protein when compared to normoxic conditions. These results may reveal a novel potential drug for BPD treatment and decrease its severity.

Oxygen injury in neonates: which is worse? hyperoxia, hypoxia, or alternating hyperoxia/hypoxia

Premature birth results in an increased risk of respiratory distress and often requires oxygen therapy. While the supplemental oxygen has been implicated as a cause of bronchopulmonary dysplasia (BPD), in clinical practice this supplementation usually only occurs after the patient's oxygen saturation levels have dropped. The effect of hyperoxia on neonates has been extensively studied. However, there is an unanswered fundamental question: which has the most impact-hyperoxia, hypoxia or fluctuating oxygen levels? In this review, we will summarize the reported effect of hypoxia, hyperoxia or a fluctuation of oxygen levels (hypoxia/hyperoxia cycling) in preterm neonates, with special emphasis on the lungs.

High affinity rigidified AT2 receptor ligands with indane scaffolds

Rigidification of the isobutyl side chain of drug-like AT2 receptor agonists and antagonists that are structurally related to the first reported selective AT2 receptor agonist 1 (C21) delivered bioactive indane derivatives. Four enantiomer pairs were synthesized and the enantiomers were isolated in an optical purity >99%. The enantiomers 7a, 7b, 8a, 8b, 9a, 9b, 10a and 10b bind to the AT2 receptor with moderate (K i = 54-223 nM) to high affinity (K i = 2.2-7.0 nM). The enantiomer with positive optical rotation (+) exhibited the highest affinity at the receptor. The indane derivatives 7b and 10a are among the most potent AT2 receptor antagonists reported so far. As illustrated by the enantiomer pairs 7a/b and 10a/b, an alteration at the stereogenic center has a pronounced impact on the activation process of the AT2 receptor, and can convert agonists to antagonists and vice versa.

Structural alterations and markers of endothelial activation in pulmonary and bronchial arteries in fatal asthma

Background

There is interest in better understanding vessel pathology in asthma, given the findings of loss of peripheral vasculature associated with disease severity by imaging and altered markers of endothelial activation. To date, vascular changes in asthma have been described mainly at the submucosal capillary level of the bronchial microcirculation, with sparse information available on the pathology of bronchial and pulmonary arteries. The aim of this study was to describe structural and endothelial activation markers in bronchial arteries (BAs) and pulmonary arteries (PAs) of asthma patients who died during a fatal asthma attack.

Methods

Autopsy lung tissue was obtained from 21 smoking and non-smoking patients who died of an asthma attack and nine non-smoking control patients. Verhoeff–Masson trichrome staining was used to analyse the structure of arteries. Using immuno-histochemistry and image analyses, we quantified extracellular matrix (ECM) components (collagen I, collagen III, versican, tenascin, fibronectin, elastic fibres), adhesion molecules [vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1)] and markers of vascular tone/dysfunction [endothelin-1 (ET-1) and angiotensin II type 2 receptor (AT2)] in PAs and BAs.

Results

There were no significant differences in ECM components, ICAM-1, ET-1 or AT2 between asthma patients and controls. Smoking asthma patients presented with decreased content of collagen III in both BA (p = 0.046) and PA (p = 0.010) walls compared to non-smoking asthma patients. Asthma patients had increased VCAM-1 content in the BA wall (p = 0.026) but not in the PA wall.

Conclusion

Our data suggest that the mechanisms linking asthma and arterial functional abnormalities might involve systemic rather than local mediators. Loss of collagen III in the PA was observed in smoking asthma patients, and this was compatible with the degradative environment induced by cigarette smoking. Our data also reinforce the idea that the mechanisms of leukocyte efflux via adhesion molecules differ between bronchial and pulmonary circulation, which might be relevant to understanding and treating the distal lung in asthma.

Counter-regulatory renin-angiotensin system in cardiovascular disease

The renin-angiotensin system is an important component of the cardiovascular system. Mounting evidence suggests that the metabolic products of angiotensin I and II - initially thought to be biologically inactive - have key roles in cardiovascular physiology and pathophysiology. This non-canonical axis of the renin-angiotensin system consists of angiotensin 1-7, angiotensin 1-9, angiotensin-converting enzyme 2, the type 2 angiotensin II receptor (AT₂R), the proto-oncogene Mas receptor and the Mas-related G protein-coupled receptor member D. Each of these components has been shown to counteract the effects of the classical renin-angiotensin system. This counter-regulatory renin-angiotensin system has a central role in the pathogenesis and development of various cardiovascular diseases and, therefore, represents a potential therapeutic target. In this Review, we provide the latest insights into the complexity and interplay of the components of the non-canonical renin-angiotensin system, and discuss the function and therapeutic potential of targeting this system to treat cardiovascular disease.

Activation of mas restores hyperoxia-induced loss of lung epithelial barrier function through inhibition of apoptosis

BACKGROUND

Neonatal therapy with a high concentration of oxygen (hyperoxia) is a known cause of bronchopulmonary dysplasia (BPD). BPD is characterized by increased pulmonary permeability and diffuse infiltration of various inflammatory cells. Disruption of the epithelial barrier may lead to altered pulmonary permeability and airways fluid accumulation. Mas receptor is a component of the renin angiotensin system and is the receptor for the protective endogenous peptide angiotensin 1-7. The activation of the Mas receptor was previously shown to have protective pulmonary responses. However, the effect of Mas receptor activation on epithelial barrier integrity has not been tested.

OBJECTIVE

To determine the effects of hyperoxia with or without Mas receptor activation on epithelial cell barrier integrity.

DESIGN/METHODS

Human epithelial cell line A549 was cultured on transwell polycarbonate porous membrane to confluence and treated with 95% oxygen (hyperoxia) for 72 hours with or without the Mas receptor agonist (AVE0991), or the apoptotic inhibitors Z-VAD-FMK or aurintricarboxylic acid. The cells were then challenged with Rhodamine labeled bovine serum albumin (Rh-BSA) on one side of the membrane. Fluorescent quantitation of Rh-BSA (albumin flux) was performed on the media in the other side of the membrane 3 hours later and was compared with 21% oxygen (Normoxia) control group. A549 cells were also cultured with or without AVE0991 in hyperoxia or normoxia and used for nuclear fragmentation apoptosis assay using propidium iodide staining.

RESULTS

Hyperoxia induced an increase in albumin flux that was significantly prevented by AVE0991 treatment and by the apoptosis inhibitors. AVE0991 also significantly decreased the hyperoxia-induced nuclear fragmentation.

CONCLUSION

These results suggest that hyperoxia causes a disruption in the epithelial barrier integrity, and that this disruption is inhibited by the Mas receptor agonist AVE0991 through inhibition of epithelial apoptosis. These results reveal a novel potential drug for BPD and pulmonary edema treatment.

Efficacy of lanthionine-stabilized angiotensin-(1-7) in type I and type II diabetes mouse models

Native angiotensin-(1-7) exerts many therapeutic effects. However, it is rapidly degraded by ACE and other peptidases. This drawback is largely eliminated for lanthionine-stabilized angiotensin-(1-7), termed cAng-(1-7), which is fully resistant to ACE and has strongly increased resistance to other peptidases. Goal of the present study was to test whether cAng-(1-7) has therapeutic activity in diabetes mouse models: in a multiple low dose streptozotocin-induced model of type I diabetes and / or in a db/db model of type II diabetes. In the type I diabetes model cAng-(1-7) caused in an increase in the insulin level of 133% in week 4 (p < 0.001) compared to vehicle, and in the type II diabetes model an increase of 55% of the insulin level in week 8 (p < 0.05) compared to vehicle. cAng-(1-7) reduced blood glucose levels in the type I model by 37% at day 22 (p < 0.001) and in the type II diabetes model by 17% at day 63 of treatment (p < 0.001) and in an oral glucose tolerance test in a type II diabetes model, by 17% at week 4 (p < 0.01). cAng-(1-7) also caused a reduction of glycated hemoglobin levels in the type II diabetes model of 21% in week 6 (p < 0,001). These data are consistent with therapeutic potential of cAng-(1-7) in type I and II diabetes.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

Human mesenchymal stem cells attenuate hyperoxia-induced lung injury through inhibition of the renin-angiotensin system in newborn rats

Hyperoxia induces activation of the renin-angiotensin system (RAS) in newborn rat lungs. This study investigated the therapeutic effects of human mesenchymal stem cells (MSCs) on lung development and RAS expression in neonatal rats exposed to hyperoxia. Sprague-Dawley rat pups were exposed to either room air (RA) or oxygen-enriched atmosphere (O2) treatment from postnatal days 1 to 14. Human MSCs (1 × 105 cells) in 0.03 mL of normal saline (NS) were administered intratracheally on postnatal day 5, and four study groups were obtained: RA + NS, RA + MSCs, O2 + NS, and O2 + MSCs. The lungs were excised for cytokine, expression of RAS components, and histological analyses on postnatal day 14. Body and lung weights were significantly lower in rats reared in hyperoxia than in those reared in RA. The rats reared in hyperoxia and treated with NS exhibited significantly higher tumor necrosis factor (TNF)-α and interleukin (IL)-6 levels, mean linear intercept (MLI), and expression of angiotensin II, angiotensin II type 1 receptor, and angiotensin-converting enzyme than those reared in RA and treated with NS or MSCs did. Administering MSC to hyperoxia-exposed rats reduced TNF-α and IL-6 levels, improved MLI, and decreased expression of angiotensin II, angiotensin II type 1 receptor, and angiotensin-converting enzyme to normoxic levels. Thus, human MSCs attenuated hyperoxia-induced lung injury through inhibition of the RAS in newborn rats.

Angiotensin peptides in the non-gravid uterus: Paracrine actions beyond circulation

The renin-angiotensin system (RAS) involves a complex network of precursors, peptides, enzymes and receptors comprising a systemic (endocrine) and a local (paracrine/autocrine) system. The local RAS plays important roles in tissue modulation and may operate independently of or in close interaction with the circulatory RAS, acting in a complementary fashion. Angiotensin (Ang) II, its receptor AT₁ and Ang-(1-7) expression in the endometrium vary with menstrual cycle, and stromal cell decidualization in vitro is accompanied by local synthesis of angiotensinogen and prorenin. Mas receptor is unlikely to undergo marked changes accompanying the cyclic ovarian steroid hormone fluctuations. Studies investigating the functional relevance of the RAS in the non-gravid uterus show a number of paracrine effects beyond circulation and suggest that RAS peptides may be involved in the pathophysiology of proliferative and fibrotic diseases. Endometrial cancer is associated with increased expression of Ang II, Ang-converting enzyme 1 and AT₁ in the tumoral tissue compared to neighboring non-neoplastic endometrium, and also with a gene polymorphism that enhances AT₁ signal. Ang II induces human endometrial cells to transdifferentiate into cells with myofibroblast phenotype and to synthetize extracellular matrix components that might contribute to endometrial fibrosis. Altogether, these findings point to a fully operating RAS within the uterus, but since many concepts rely on preliminary evidence further studies are needed to clarify the role of the local RAS in uterine physiology and pathophysiology.

The renin angiotensin system in liver and lung: impact and therapeutic potential in organ fibrosis

Liver and lung fibrosis are two main organ diseases that are of particular importance in both Egypt and the US. Hepatitis C Virus "HCV" infection and idiopathic pulmonary fibrosis (IPF) are fibrotic diseases of the liver and lung respectively. The liver and lung are reported in literature to share many immune/inflammatory responses to damage through the lung-liver axis. Most importantly, HCV was shown to enhance the development of IPF and is considered one of the risk factors for IPF. The renin angiotensin system (RAS) plays a critical role in the fibrogenesis and inflammation damage of many organs including liver and lung. The relatively recently identified component of RAS, angiotensin converting enzyme-2 (ACE-2), has shown a promising therapeutic potential in models of liver and pulmonary fibrosis. This article reviews the role of RAS in organ fibrosis with focus on role of ACE-2 in fibrotic diseases of the liver and the lung.

AT2 receptor agonist Compound 21: A silver lining for diabetic nephropathy

The currently available therapies for diabetic nephropathy, one of the leading causes of renal failure globally are based on inhibition of renin angiotensin system. However, recently, the focus has shifted towards activation of its protective arm rather than the inhibition of deteriorative axis, using specific agonists. Compound 21 (C21), a novel non-peptide Angiotensin II type 2 receptor (AT₂) agonist, recently granted orphan drug status for the treatment of a rare disease, idiopathic pulmonary fibrosis has also shown a potent anti-inflammatory, anti-fibrotic, antioxidant and anti-apoptotic potential in various diseases including heart failure, myocardial infarction, chronic inflammatory diseases, and neurological diseases such as ischemic stroke. A pool of evidences suggest that C21, either alone or in combination with angiotensin receptor blockers could be extremely beneficial in the treatment of diabetic nephropathy, a chronic inflammatory condition sharing its pathogenesis with aforementioned diseases. The review analyses the new therapeutic tool, C21, its mechanisms of action for renoprotection in diabetic nephropathy, and its future perspectives and thereby provides an insight into the potential application of C21 as a novel therapeutic tool in the eradication of diabetic nephropathy.

Human mesenchymal stem cells ameliorate experimental pulmonary hypertension induced by maternal inflammation and neonatal hyperoxia in rats

Pulmonary hypertension is a critical problem in infants with bronchopulmonary dysplasia. This study determined the therapeutic effects of human mesenchymal stem cells (MSCs) on pulmonary hypertension in an animal model. Pregnant Sprague-Dawley rats were intraperitoneally injected with lipopolysaccharide (LPS, 0.5 mg/kg/day) on gestational days 20 and 21. The pups were randomly assigned to two treatment conditions: room air (RA) or an O₂-enriched atmosphere. On postnatal day 5, they were intratracheally transplanted with human MSCs (3 × 10⁵ and 1 × 10⁶ cells) in 0.03 mL of normal saline (NS). Five study groups were examined: normal, LPS+RA+NS, LPS+O₂+NS, LPS+O₂+MSCs (3 × 10⁵ cells), and LPS+O₂+MSCs (1 × 10⁶ cells). On postnatal day 14, the pup lungs and hearts were collected for histological examinations. The LPS+RA+NS and LPS+O₂+NS groups exhibited a significantly higher right ventricle (RV):left ventricle (LV) thickness ratio and medial wall thickness (MWT) and higher β-myosin heavy chain (β-MHC) and toll-like receptor (TLR) 4 expression than did the normal group. Human MSC transplantation in LPS- and O₂-treated rats reduced the MWT, RV:LV thickness ratio, and β-MHC and TLR4 expression to normal levels. Thus, intratracheal human MSC transplantation ameliorates pulmonary hypertension, probably by suppressing TLR4 expression in newborn rats.

Age-Dependent Changes in the Pulmonary Renin-Angiotensin System Are Associated With Severity of Lung Injury in a Model of Acute Lung Injury in Rats

OBJECTIVES

A growing body of evidence suggests that age affects the main pathophysiologic mechanisms of the acute respiratory distress syndrome. This may imply the need for developing age-tailored therapies for acute respiratory distress syndrome. However, underlying molecular mechanisms governing age-related susceptibility first need to be unraveled. In a rat model of acute lung injury, we investigated whether age affects the balance between the two key enzymes of the pulmonary renin-angiotensin system, angiotensin-converting enzyme, and angiotensin-converting enzyme 2. We hypothesized that aging shifts the balance toward the lung injury-promoting angiotensin-converting enzyme, which may form an explanation for the differences in severity of lung injury between different age groups.

DESIGN

Prospective, randomized controlled animal study.

SETTING

University medical research laboratory.

SUBJECTS

Infant (15 ± 2 d), juvenile (37 ± 2 d), adult (4 ± 0.2 mo), and elderly (19.5 ± 0.5 mo) male RCCHan Wistar rats.

INTERVENTIONS

Lung injury was induced by intratracheal administration of lipopolysaccharide (5 mg/kg) and 4 hours of mechanical ventilation (15 mL/kg).

MEASUREMENTS AND MAIN RESULTS

In lipopolysaccharide-exposed and mechanical ventilated rats, angiotensin-converting enzyme activity in bronchoalveolar lavage fluid increased 3.2-fold in elderly when compared with infants. No changes in bronchoalveolar lavage fluid angiotensin-converting enzyme 2 activity were found. In addition, membrane-bound angiotensin-converting enzyme activity decreased. Together with the presence of angiotensin-converting enzyme-sheddase ADAM9 (a disintegrin and metalloproteinase domain-containing protein 9) and an age-dependent increase in tumor necrosis factor-α, an activator of ADAM9, these results indicate increased shedding of angiotensin-converting enzyme in the alveolar compartment, thereby shifting the balance toward the injurious pathway. This imbalance was associated with an increased inflammatory mediator response and more lung injury (wet-to-dry ratio and histology) in elderly rats.

CONCLUSIONS

Increasing age is associated with an imbalance of the pulmonary renin-angiotensin system, which correlates with aggravated inflammation and more lung injury. These changes might form the ground for new therapeutic strategies in terms of dosing and effectiveness of renin-angiotensin system-modulating agents for treatment of acute respiratory distress syndrome.

Significance of angiotensin 1-7 coupling with MAS1 receptor and other GPCRs to the renin-angiotensin system: IUPHAR Review 22

Angiotensins are a group of hormonal peptides and include angiotensin II and angiotensin 1-7 produced by the renin angiotensin system. The biology, pharmacology and biochemistry of the receptors for angiotensins were extensively reviewed recently. In the review, the receptor nomenclature committee was not emphatic on designating MAS1 as the angiotensin 1-7 receptor on the basis of lack of classical G protein signalling and desensitization in response to angiotensin 1-7, as well as a lack of consensus on confirmatory ligand pharmacological analyses. A review of recent publications (2013-2016) on the rapidly progressing research on angiotensin 1-7 revealed that MAS1 and two additional receptors can function as 'angiotensin 1-7 receptors', and this deserves further consideration. In this review we have summarized the information on angiotensin 1-7 receptors and their crosstalk with classical angiotensin II receptors in the context of the functions of the renin angiotensin system. It was concluded that the receptors for angiotensin II and angiotensin 1-7 make up a sophisticated cross-regulated signalling network that modulates the endogenous protective and pathogenic facets of the renin angiotensin system.