Insights Into the Role of Angiotensin-Converting Enzyme 2 in the Onset of Severe Acute Respiratory Syndrome Coronavirus 2 Pathogenesis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the outbreak of pneumonia which originated in Wuhan, China, at the end of 2019 has turned into a global pandemic—now termed coronavirus diseases 2019 (COVID-19). Like previously reported SARS-CoV strains, the newly discovered SARS-CoV-2 was also found to initiate the pathogenesis by binding with the angiotensin-converting enzyme 2 (ACE2), a receptor produced by various organs in the human body. Hence, COVID-19 is a viral multisystem disease which particularly infects the vascular system expressing ACE2 and reduced the ACE2 function;this further complexed by organ-specific pathogenesis related to the damage of cells expressing ACE2, such as alveolus, glomerulus, endothelium, and cardiac microvasculature. Under these conditions, it was advocated that the upregulation of ACE2 expression in predisposing individuals with aberrant renin–angiotensin system (RAS) level to advanced viral load on infection and relatively a greater number of cell death. Recently, a significant role of decreased ACE2 production and inequality between the RAS and ACE2/angiotensin-(1–7)/ MAS (mitochondrial Ang system) after the onset of SARS-CoV-2 infection was established as a key factor for multiple organ injury in SARS-CoV-2-infected individuals. Furthermore, restoration of this imbalance has been suggested as a therapeutic approach to attenuate organ injuries in SARS-CoV-2 infection. Based on available data, this chapter presents the updated mechanism of the multi-organ diseases causes by COVID-19 via ACE2 which can be further helpful in the development of specific therapeutics. © The Author(s), under exclusive licence to Springer Nature Singapore Pte Ltd. 2021.

Mechanisms of Atrial Fibrillation in Covid-19

Atrial fibrillation (AF) is the most frequent form of cardiac arrhythmia in COVID-19 infected patients. The occurrence of AF paroxysms is often associated with the acute period of infection in time. At the same time, the pathophysiological mechanisms of the occurrence of AF associated with COVID-19 remain insufficiently studied. The review considers the available literature data on the influence of factors such as reduced availability of angiotensin-converting enzyme 2 receptors, interaction of the virus with the cluster of differentiation 147 and sialic acid, increased inflammatory signaling, "cytokine storm", direct viral damage to the endothelium, electrolyte and acid-alkaline balance in the acute phase of severe illness and increased sympathetic activity.Copyright © Autors 2023.

Targeting Angiotensin-converting Enzyme 2 (ACE2) for the Discovery of Anticoronaviral Drugs

Coronaviruses are a leading cause of emerging life-threatening diseases, as evidenced by the ongoing coronavirus disease pandemic (COVID-19). According to complete genome sequence analysis reports, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), which causes COVID-19, has a sequence identity highly similar to the earlier severe acute respiratory syndrome coronavirus (SARS-CoV). The SARS-CoV-2 has the same mode of transmission, replication, and pathogenicity as SARS-CoV. The SARS-CoV-2 spike protein's receptor-binding domain (RBD) binds to host angiotensin-converting enzyme-2 (ACE2). The ACE2 is overexpressed in various cells, most prominently epithelial cells of the lung (surface of type 1 and 2 pneumocytes), intestine, liver, kidney, and nervous system. As a result, these organs are more vulnerable to SARS-CoV-2 infection. Furthermore, renin-angiotensin system (RAS) blockers, which are used to treat cardiovascular diseases, intensify ACE2 expression, leading to an increase in the risk of COVID-19. ACE2 hydrolyzes angioten-sin-II (carboxypeptidase) to heptapeptide angiotensin (1-7) and releases a C-terminal amino acid. By blocking the interaction of spike protein with ACE2, the SARS-CoV-2 entry into the host cell and inter-nalization can be avoided. The pathogenicity of SARS-CoV-2 could be reduced by preventing the RBD from attaching to ACE2-expressing cells. Therefore, inhibition or down-regulation of ACE2 in host cells represents a therapeutic strategy to fight against COVID-19. However, ACE2 plays an essential role in the physiological pathway, protecting against hypertension, heart failure, myocardial infarction, acute respiratory lung disease, and diabetes. Given the importance of ACE's homeostatic role, targeting of ACE2 should be realized with caution. Above all, focusing on the SARS-CoV-2 spike protein and the ACE2 gene in the host cell is an excellent way to avoid viral mutation and resistance. The current review summarises the sequence analysis, structure of coronavirus, ACE2, spike protein-ACE2 complex, essential structural characteristics of the spike protein RBD, and ACE2 targeted approaches for anti-coronaviral drug design and development.Copyright © 2022 Bentham Science Publishers.

The Significance of Angiotensin-Converting Enzyme-2 (ACE2) in SARS-Cov-2 Infection and COVID-19

The new coronavirus was first reported in 2019 (China) and officially announced by the World Health Organization as a pandemic in March 2020. Severe acute respiratory syndrome coro-navirus 2 (SARS-CoV-2) is the causative agent of the pneumonia-associated illnesses and shares structural homology with the related Severe acute respiratory syndrome coronavirus-1 (SARS-CoV--1). One of the mechanisms for SARS-Cov-1 and-2 infection is mediated by the angiotensin-con-verting enzyme-2 (ACE2) cell receptor, enabling the virus to enter the host cells. ACE2 is an iso-form of the angiotensin-converting enzyme 1 (ACE). The actions of ACE2 counterbalance the clas-sic renin-angiotensin system (RAS) axis through the production of Ang 1-7, which promotes car-diovascular, renal, and lung-protective effects. The ACE2 is not the only route for SARS-CoV-2 to enter the host cells. However, due to its roles in the RAS and its participation in the SARS-CoV-2 virulence, ACE2 has gained attention regarding viral mechanisms of pathogenesis, effects of drugs that interfere with the RAS, and as a potential target for therapeutic strategies for the damages caused by SARS-CoV-2 infection. Among other tissues, ACE2 gene expression seems to be in-creased in the lungs upon SARS-CoV-2 infection;however, amid other variables, expression and/or activity of ACE2 is shown as a disease, sex, and age-dependent. The present review covers critical aspects for a comprehensive understanding of ACE2 and its current involvement in SARS-CoV-2 infection and the development of COVID-19.Copyright © 2021 Bentham Science Publishers.

Effect of olmesartan and amlodipine on serum angiotensin-(1-7) levels and kidney and vascular function in patients with type 2 diabetes and hypertension.

BACKGROUND: Recent studies suggest that angiotensin-converting enzyme 2 (ACE2) and angiotensin-(1-7) [Ang-(1-7)] might have beneficial effects on the cardiovascular system. We investigated the effects of olmesartan on the changes in serum ACE2 and Ang-(1-7) levels as well as kidney and vascular function in patients with type 2 diabetes and hypertension. METHODS: This was a prospective, randomized, active comparator-controlled trial. Eighty participants with type 2 diabetes and hypertension were randomized to receive 20 mg of olmesartan (N = 40) or 5 mg of amlodipine (N = 40) once daily. The primary endpoint was changes of serum Ang-(1-7) from baseline to week 24. RESULTS: Both olmesartan and amlodipine treatment for 24 weeks decreased systolic and diastolic blood pressures significantly by > 18 mmHg and > 8 mmHg, respectively. Serum Ang-(1-7) levels were more significantly increased by olmesartan treatment (25.8 ± 34.5 pg/mL → 46.2 ± 59.4 pg/mL) than by amlodipine treatment (29.2 ± 38.9 pg/mL → 31.7 ± 26.0 pg/mL), resulting in significant between-group differences (P = 0.01). Serum ACE2 levels showed a similar pattern (6.31 ± 0.42 ng/mL → 6.74 ± 0.39 ng/mL by olmesartan treatment vs. 6.43 ± 0.23 ng/mL → 6.61 ± 0.42 ng/mL by amlodipine treatment; P < 0.05). The reduction in albuminuria was significantly associated with the increases in ACE2 and Ang-(1-7) levels (r = - 0.252 and r = - 0.299, respectively). The change in Ang-(1-7) levels was positively associated with improved microvascular function (r = 0.241, P < 0.05). Multivariate regression analyses showed that increases in serum Ang-(1-7) levels were an independent predictor of a reduction in albuminuria. CONCLUSIONS: These findings suggest that the beneficial effects of olmesartan on albuminuria may be mediated by increased ACE2 and Ang-(1-7) levels. These novel biomarkers may be therapeutic targets for the prevention and treatment of diabetic kidney disease. TRIAL REGISTRATION: ClinicalTrials.gov NCT05189015.

New Coronavirus Infection Covid-19 and Women's Reproductive Health. Facts and Assumptions

The review presents data on the possible ways in which the SARS-CoV-2 and COVID-19 virus affects the female reproductive system and the already recorded negative consequences. Recommendations on pregnancy planning and the specifics of using hormonal contraceptive methods, as well as approaches to specific prevention of a new coronavirus infection from the standpoint of safety and preserving the reproductive health of women during the COVID-19 pandemic are outlined.

S Protein, ACE2 and Host Cell Proteases in SARS-CoV-2 Cell Entry and Infectivity; Is Soluble ACE2 a Two Blade Sword? A Narrative Review.

Since the spread of the deadly virus SARS-CoV-2 in late 2019, researchers have restlessly sought to unravel how the virus enters the host cells. Some proteins on each side of the interaction between the virus and the host cells are involved as the major contributors to this process: (1) the nano-machine spike protein on behalf of the virus, (2) angiotensin converting enzyme II, the mono-carboxypeptidase and the key component of renin angiotensin system on behalf of the host cell, (3) some host proteases and proteins exploited by SARS-CoV-2. In this review, the complex process of SARS-CoV-2 entrance into the host cells with the contribution of the involved host proteins as well as the sequential conformational changes in the spike protein tending to increase the probability of complexification of the latter with angiotensin converting enzyme II, the receptor of the virus on the host cells, are discussed. Moreover, the release of the catalytic ectodomain of angiotensin converting enzyme II as its soluble form in the extracellular space and its positive or negative impact on the infectivity of the virus are considered.

Delta And Omicron Variants Of SARS-Cov-2 Do Not Stimulate ACE2 Conversion Of Ang II To Ang-(1-7)

The Spike domain of SARS-COV-2 binds ACE2 and induces peptidase internalization removing a key regulatory site within the renin-angiotensin system that may exacerbate the effects of SARS-COV-2. However, a recent study finds that an early Beta variant (D614G) of the SARS-COV-2 Spike protein and its receptor-binding domain (RBD) markedly stimulated ACE2 activity using fluorescent substrates. The more dominant forms of SARS-COV-2 include the Delta and Omicron variants and we determined whether these new variants activate ACE2. Delta (B.1.617.1) and Omicron (B.1.1.529) RBDs, and Beta Spike (B1.351) were incubated with human soluble ACE2 for 10 mins at 37degreeC followed by Ang II [2 muM] and 125I-Ang II [0.5 nM] for up to 20 mins, and the Ang-(1-7)/Ang II ratio quantified by HPLC-gamma detection. Ang-(1-7)/Ang II increased linearly over time and doubled with 10 ng of ACE2 (*P<0.01 vs 5 ng;N=4);however, the Delta or Omicron RBD proteins (1 muM) failed to stimulate ACE2 activity at any time point (A). Varying concentrations of the Delta or Omicron RBDs, as well as Spike protein also failed to stimulate ACE2 activity (5 ng), although 200 nM Omicron RBD was inhibitory (B). The newer Spike variants may not activate ACE2;however, the Spike D614G variant also failed to activate ACE2, which questions whether SARS-COV-2 enhances ACE2 activity to metabolize Ang II. We conclude that Delta and Omicron variants do not stimulate the metabolism of Ang II to Ang-(1-7). Moreover, alterations in circulating ACE2 activity in COVID-19 patients likely reflect changes in protein content through shedding of the peptidase, although the interaction of ACE2 autoantibodies to influence peptidase activity is also possible. (Figure Presented).

Adenosine A2A Receptor (A2AR) Agonist Apadenoson Promotes Survival in K28-hACE2 Mice and Syrian Hamsters Infected with Sars-CoV-2

Purpose: To determine if Apadenoson or Regadenoson has a therapeutic effect in attenuating hyper-inflammation and improving survival rate in K18-hACE2mice or Syrian hamsters infected with SARS-CoV-2. Method(s): 6-8 weeks old male K18-hACE2mice were divided into Control group that received vehicle;Test group 1 that received the drug (Apadenoson or Regadenoson) 24hrs prior to challenge with SARS-CoV-2;and Test Group 2 (Drug-delay), that received the drug with a 5 hr delay post-viral infection (n=6/grp). Viral dose was 1250 PfuHong Kong/VM20001061/2020 delivered via intranasal route. Drug was delivered subcutaneously using 1007D ALZET pumps. 6 weeks old Syrian hamsters were divided into Control group that received Vehicle and Virus (n=4) and 2 test groups (n=5/group) that received Apadenoson+Virus and Regadenoson+Virus. Drugs were delivered by 2ML2 ALZET pumps (4ug/kg/hr). Hamsters were inoculated intratracheally with 750PFU SARS-CoV-2 WA1 strain prior to treatment. Mice were weighed and clinical scores recorded daily. Bronchoalveolar lavage fluid (BALF) and serum were collected along with lungs. Plethysmography was done on days 0, 2, 4 and 7. Result(s): Apadenoson administered post-infection was efficacious in decreasing weight loss, improving clinical score, and increasing the survival rate in K18-hACE2 mice, i.e. 50% survival was observed at Day 5 and at Day 7 post-infection for drug given before or after infection respectively. Apadenoson given post-infection improved the histopathology that was observed in the vehicle control group, decreased pro-inflammatory IL-6, IFN-gamma, MCCP-1, MIP-1beta, IP-10, and Rantes in serum, increased anti-inflammatory Ang1-7 levels, and decreased monocytes in BALF. 42% of mice that received Regadenoson pre-challenge survived infection compared to 6.25% in the vehicle or Drug delay (drug given post-infection) groups. Viral titers in the lungs of Regadenoson-treated mice were found decreased. Treatment also significantly decreased CD4+, CD8+T cells, eosinophils, and neutrophils in BALF. Plethysmography, in hamsters, showed significant improvement of pulmonary function parameters, Rpef and PenH, following treatment with Apadenoson given post-infection. Apadenoson cleared the virus from BALF and maintained Ang1-7 levels. Both drugs decreased plasma IFN-gamma levels. Conclusion(s): Treatment with Apadenoson attenuated inflammation, improved pulmonary function, decreased weight loss, and enhanced survival rate following infection with SARS-CoV-2 virus. The results demonstrate the translational significance of Apadenoson in the treatment of COVID-19.

Sacubitril/Valsartan and Ivabradine Attenuate Left Ventricular Remodelling and Dysfunction in Spontaneously Hypertensive Rats: Different Interactions with the Renin-Angiotensin-Aldosterone System.

This study investigated whether sacubitril/valsartan and ivabradine are able to prevent left ventricular (LV) fibrotic remodelling and dysfunction in a rat experimental model of spontaneous hypertension (spontaneously hypertensive rats, SHRs) and whether this potential protection is associated with RAAS alterations. Five groups of three-month-old male Wistar rats and SHRs were treated for six weeks as follows: untreated Wistar controls, Wistar plus sacubitril/valsartan, SHR, SHR plus sacubitril/valsartan, and SHR plus ivabradine. The SHRs developed a systolic blood pressure (SBP) increase, LV hypertrophy and fibrosis, and LV systolic and diastolic dysfunction. However, no changes in serum RAAS were observed in SHRs compared with the controls. Elevated SBP in SHRs was decreased by sacubitril/valsartan but not by ivabradine, and only sacubitril/valsartan attenuated LV hypertrophy. Both sacubitril/valsartan and ivabradine reduced LV collagen content and attenuated LV systolic and diastolic dysfunction. Sacubitril/valsartan increased the serum levels of angiotensin (Ang) II, Ang III, Ang IV, Ang 1-5, Ang 1-7, and aldosterone, while ivabradine did not affect the RAAS. We conclude that the SHR is a normal-to-low serum RAAS model of experimental hypertension. While the protection of the hypertensive heart in SHRs by sacubitril/valsartan may be related to an Ang II blockade and the protective Ang 1-7, the benefits of ivabradine were not associated with RAAS modulation.

The prognostic importance of the angiotensin II/angiotensin-(1-7) ratio in patients with SARS-CoV-2 infection.

BACKGROUND: Information about angiotensin II (Ang II), angiotensin-converting enzyme 2 (ACE2), and Ang-(1-7) levels in patients with COVID-19 is scarce. OBJECTIVE: To characterize the Ang II-ACE2-Ang-(1-7) axis in patients with SARS-CoV-2 infection to understand its role in pathogenesis and prognosis. METHODS: Patients greater than 18 years diagnosed with COVID-19, based on clinical findings and positive RT-PCR test, who required hospitalization and treatment were included. We compared Ang II, aldosterone, Ang-(1-7), and Ang-(1-9) concentrations and ACE2 concentration and activity between COVID-19 patients and historic controls. We compared baseline demographics, laboratory results (enzyme, peptide, and inflammatory marker levels), and outcome (patients who survived versus those who died). RESULTS: Serum from 74 patients [age: 58 (48-67.2) years; 68% men] with moderate (20%) or severe (80%) COVID-19 were analyzed. During 13 (10-21) days of hospitalization, 25 patients died from COVID-19 and 49 patients survived. Compared with controls, Ang II concentration was higher and Ang-(1-7) concentration was lower, despite significantly higher ACE2 activity in patients. Ang II concentration was higher and Ang-(1-7) concentration was lower in patients who died. The Ang II/Ang-(1-7) ratio was significantly higher in patients who died. In multivariate analysis, Ang II/Ang-(1-7) ratio greater than 3.45 (OR = 5.87) and lymphocyte count ⩽0.65 × 103/µl (OR = 8.43) were independent predictors of mortality from COVID-19. CONCLUSION: In patients with severe SARS-CoV-2 infection, imbalance in the Ang II-ACE2-Ang-(1-7) axis may reflect deleterious effects of Ang II and may indicate a worse outcome.

The Impact of Angiotensin-Converting Enzyme-2/Angiotensin 1-7 Axis in Establishing Severe COVID-19 Consequences.

The COVID-19 pandemic has put a tremendous stress on the medical community over the last two years. Managing the infection proved a lot more difficult after several research communities started to recognize the long-term effects of this disease. The cellular receptor for the virus was identified as angiotensin-converting enzyme-2 (ACE2), a molecule responsible for a wide array of processes, broadly variable amongst different organs. Angiotensin (Ang) 1-7 is the product of Ang II, a decaying reaction catalysed by ACE2. The effects observed after altering the level of ACE2 are essentially related to the variation of Ang 1-7. The renin-angiotensin-aldosterone system (RAAS) is comprised of two main branches, with ACE2 representing a crucial component of the protective part of the complex. The ACE2/Ang (1-7) axis is well represented in the testis, heart, brain, kidney, and intestine. Infection with the novel SARS-CoV-2 virus determines downregulation of ACE2 and interrupts the equilibrium between ACE and ACE2 in these organs. In this review, we highlight the link between the local effects of RAAS and the consequences of COVID-19 infection as they arise from observational studies.

Cross-Talk between the (Endo)Cannabinoid and Renin-Angiotensin Systems: Basic Evidence and Potential Therapeutic Significance.

This review is dedicated to the cross-talk between the (endo)cannabinoid and renin angiotensin systems (RAS). Activation of AT1 receptors (AT1Rs) by angiotensin II (Ang II) can release endocannabinoids that, by acting at cannabinoid CB1 receptors (CB1Rs), modify the response to AT1R stimulation. CB1R blockade may enhance AT1R-mediated responses (mainly vasoconstrictor effects) or reduce them (mainly central nervous system-mediated effects). The final effects depend on whether stimulation of CB1Rs and AT1Rs induces opposite or the same effects. Second, CB1R blockade may diminish AT1R levels. Third, phytocannabinoids modulate angiotensin-converting enzyme-2. Additional studies are required to clarify (1) the existence of a cross-talk between the protective axis of the RAS (Ang II-AT2 receptor system or angiotensin 1-7-Mas receptor system) with components of the endocannabinoid system, (2) the influence of Ang II on constituents of the endocannabinoid system and (3) the (patho)physiological significance of AT1R-CB1R heteromerization. As a therapeutic consequence, CB1R antagonists may influence effects elicited by the activation or blockade of the RAS; phytocannabinoids may be useful as adjuvant therapy against COVID-19; single drugs acting on the (endo)cannabinoid system (cannabidiol) and the RAS (telmisartan) may show pharmacokinetic interactions since they are substrates of the same metabolizing enzyme of the transport mechanism.

Understanding on the possible routes for SARS CoV-2 invasion via ACE2 in the host linked with multiple organs damage.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), accountable for causing the coronavirus diseases 2019 (COVID-19), is already declared as a pandemic disease globally. Like previously reported SARS-CoV strain, the novel SARS-CoV-2 also initiates the viral pathogenesis via docking viral spike-protein with the membranal angiotensin-converting enzyme 2 (ACE2) - a receptor on variety of cells in the human body. Therefore, COVID-19 is broadly characterized as a disease that targets multiple organs, particularly causing acute complications via organ-specific pathogenesis accompanied by destruction of ACE2+ cells, including alveolus, cardiac microvasculature, endothelium, and glomerulus. Under such circumstances, the high expression of ACE2 in predisposing individuals associated with anomalous production of the renin-angiotensin system (RAS) may promote enhanced viral load in COVID-19, which comparatively triggers excessive apoptosis. Furthermore, multi-organ injuries were found linked to altered ACE2 expression and inequality between the ACE2/angiotensin-(1-7)/mitochondrial Ang system (MAS) and renin-angiotensin-system (RAS) in COVID-19 patients. However, the exact pathogenesis of multi-organ damage in COVID-19 is still obscure, but several perspectives have been postulated, involving altered ACE2 expression linked with direct/indirect damages by the virus-induced immune responses, such as cytokinin storm. Thus, insights into the invasion of a virus with respect to ACE2 expression site can be helpful to simulate or understand the possible complications in the targeted organ during viral infection. Hence, this review summarizes the multiple organs invasion by SARS CoV-2 linked with ACE2 expression and their consequences, which can be helpful in the management of the COVID-19 pathogenesis under life-threatening conditions.

Patients with severe COVID-19 have reduced circulating levels of angiotensin-(1-7): A cohort study.

Background and Aims: Angiotensin-converting enzyme 2 (ACE2) acts as a functional receptor for the entry of severe acute respiratory syndrome coronavirus 2 into host cells. Angiotensin (1-7) (Ang (1-7)) obtained from the function of ACE2 improves heart and lung function. We investigated the relationship between Ang (1-7) level and disease severity in patients with coronavirus disease 2019 (COVID-19). Methods: This cohort study was carried out at Masih Daneshvari Hospital in Tehran, Iran from September 2020 to October 2020. To do so, the Ang (1-7) levels of 331 hospitalized COVID-19 patients with and without underlying disease were measured by ELISA kit. The need for oxygen, intubation, and mechanical ventilation were recorded for all the patients. Results: Results showed a significant inverse relationship between the levels of Ang 1-7 and the severity of the disease (needed oxygen, intubation, and mechanical ventilation). According to the results, median (interquartile range) of Ang (1-7) levels was significantly lower in patients who needed oxygen versus those who needed no oxygen (44.50 (91) vs. 82.25 (68), p = 0.002), patients who needed intubation and mechanical ventilation versus those who did not (9.80 (62) vs. 68.70 (102), p < 0.000) and patients hospitalized in an intensive care unit (ICU) than people hospitalized in other wards. We also found that the older patients were more in need of ICU and mechanical ventilation than younger patients. Conclusions: Higher levels of Ang (1-7) have been associated with decreased disease severity. Besides this, we perceived that synthetic Ang 1-7 peptides may be useful to treat and reduce the complications of COVID-19.

Renin-angiotensin system: Basic and clinical aspects-A general perspective.

The renin-angiotensin system (RAS) is one of the most complex hormonal regulatory systems, involving several organs that interact to regulate multiple body functions. The study of this system initially focused on investigating its role in the regulation of both cardiovascular function and related pathologies. From this approach, pharmacological strategies were developed for the treatment of cardiovascular diseases. However, new findings in recent decades have suggested that the RAS is much more complex and comprises two subsystems, the classic RAS and an alternative RAS, with antagonistic effects that are usually in equilibrium. The classic system is involved in pathologies where inflammatory, hypertrophic and fibrotic phenomena are common and is related to the development of chronic diseases that affect various body systems. This understanding has been reinforced by the evidence that local renin-angiotensin systems exist in many tissue types and by the role of the RAS in the spread and severity of COVID-19 infection, where it was discovered that viral entry into cells of the respiratory system is accomplished through binding to angiotensin-converting enzyme 2, which is present in the alveolar epithelium and is overexpressed in patients with chronic cardiometabolic diseases. In this narrative review, preclinical and clinical aspects of the RAS are presented and topics for future research are discussed some aspects are raised that should be clarified in the future and that call for further investigation of this system.

Alternative RAS in Various Hypoxic Conditions: From Myocardial Infarction to COVID-19.

Alternative branches of the classical renin-angiotensin-aldosterone system (RAS) represent an important cascade in which angiotensin 2 (AngII) undergoes cleavage via the action of the angiotensin-converting enzyme 2 (ACE2) with subsequent production of Ang(1-7) and other related metabolites eliciting its effects via Mas receptor activation. Generally, this branch of the RAS system is described as its non-canonical alternative arm with counterbalancing actions to the classical RAS, conveying vasodilation, anti-inflammatory, anti-remodeling and anti-proliferative effects. The implication of this branch was proposed for many different diseases, ranging from acute cardiovascular conditions, through chronic respiratory diseases to cancer, nonetheless, hypoxia is one of the most prominent common factors discussed in conjugation with the changes in the activity of alternative RAS branches. The aim of this review is to bring complex insights into the mechanisms behind the various forms of hypoxic insults on the activity of alternative RAS branches based on the different duration of stimuli and causes (acute vs. intermittent vs. chronic), localization and tissue (heart vs. vessels vs. lungs) and clinical relevance of studied phenomenon (experimental vs. clinical condition). Moreover, we provide novel insights into the future strategies utilizing the alternative RAS as a diagnostic tool as well as a promising pharmacological target in serious hypoxia-associated cardiovascular and cardiopulmonary diseases.