key: cord-0759959-i3keg077 authors: Almutlaq, Moudhi; Alamro, Abir Abdullah; Alroqi, Fayhan; Barhoumi, Tlili title: Classical and Counter-regulatory Renin-angiotensin System: potential key roles in COVID-19 pathophysiology date: 2021-04-15 journal: CJC Open DOI: 10.1016/j.cjco.2021.04.004 sha: e79e523b0d9e27a0a564e4b2acde7ce2be0968bc doc_id: 759959 cord_uid: i3keg077 In the current coronavirus disease 2019 (COVID-19) pandemic, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uses angiotensin-converting enzyme-2 (ACE-2) receptor for cell entry leading to ACE-2 dysfunction and downregulation which disturbs the balance between classical and counter-regulatory renin-angiotensin system (RAS) in favor of 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 amongst 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 system that is associated with COVID-19 infection and the potential treatment targeting this area has 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 ACEIs and ARBs administration and ACE-2 availability in relation to COVID-19 which may provide a better understanding of RAS contribution to COVID-19 pathology is discussed as it is of the utmost importance amid the current pandemic. with or without cardiovascular diseases cannot be excluded, and reasonable understanding of the crosstalk between COVID-19 and RAS is almost essential for the ideal management of patients with cardiometabolic diseases. In the following review we describe the imbalance of classical RAS and counter-regulatory RAS axes in COVID-19 patients with cardiovascular metabolic diseases and discuss the latest findings based on angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II type 1 receptor blockers (ARBs) administration and ACE-2 availability in relation to COVID-19. RAS plays a pivotal role in the pathophysiology of cardiovascular diseases. Renin (angiotensinogenase) is secreted by the kidney, stimulating angiotensinogen to release angiotensin I (Ang I) peptide. Ang I is then converted to Ang II by the angiotensin-converting enzyme (ACE), which is expressed in high volumes by endothelial and epithelial cells in the vasculature, kidneys, heart, and lungs 12 . Ang II is the major vasoactive peptide, playing a crucial role during normal or pathophysiologic conditions 13 . The binding of Ang II to angiotensin II type 1 receptor (AT1R) is common throughout the cardiovascular system and induces systemic vasoconstriction, proinflammatory and profibrotic effects, and aldosterone secretion 13 Activation of the ACE/Ang II/AT1R axis induces apoptosis in alveolar epithelial cells 14 , promotes ventilator-induced lung injury 15 , increases lung microvascular permeability 16 , stimulates pro-inflammatory cytokine release and, promotes macrophage and neutrophil chemotaxis associated with lung injuries 17 . Moreover, the activation of ACE/Ang II/AT1R axis stimulates both the adaptive and innate immune pro-inflammatory responses leading to inflammation, autoimmune dysfunctions, and cardiovascular damage 18, 19 . A. ACE-2/Ang 1-7 Mas Receptor Angiotensin 1-7 (Ang 1-7) is produced by cleavage of Ang I and II by neprilysin (NEP) and ACE-2 respectively 20 . The RAS regulatory effect of Ang 1-7 is imparted by binding to the Mas receptor (MasR). It was reported that Ang 1-7 plays a protective role in cardiovascular diseases through its central control of blood pressure 21 and serving as an important neuromodulator in the central nervous system to control cardiovascular function and counteract Ang II effects 22 . Ang 1-7 might also act as a local synergistic regulator of kinin-induced vasodilation via inhibiting the generation of ACE and nitric oxide 23 . During vascular inflammation, Ang 1-7 decreases monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), nuclear factor kappa-B (NF-κB), vascular cell adhesion protein 1, reactive oxygen species levels, and apoptosis 24 . Furthermore, activation of angiotensin II type 2 receptor (AT2R) via Ang 1-7 stimulation prevents inflammation and cardiac hypertrophy, as well as reducing vascular remodeling and alveolar septum thickness, whichin a rat with chronic lung diseaseprotects the heart and lungs from damage 25 . Ang 1-7 can also be a source of another counter-regulatory renin-angiotensin pathway when produced from Ang II by ACE-2 and then transformed to alamandine 26 . Alternatively, Ang II can be transformed to angiotensin A (Ang A) by aspartate decarboxylase. Ang A can be converted to alamandine by ACE-2. Recently discovered as part of RAS regulator, alamandinevia binding to Mas-related G protein-coupled receptor member D (MrgD)promotes similar anti-hypertensive and cardioprotective effects as Ang 1-7 27,28 . It was demonstrated in the rat model that angiotensin 1-9 (Ang 1-9) has a cardioprotective effect resulting from the activation of AT2R, improving endothelial function, fibrosis, oxidative stress, collagen deposition 29 , cardiac hypertrophy 30 and, protects against cardiac ischemia/reperfusion injury 31 . It was further reported that Ang 1-9 ameliorates pulmonary arterial hypertension via AT2R by decreasing apoptosis and plasmatic pro-inflammatory cytokines, such as TNF-α, MCP-1, IL-1β, and IL-6 32 . Independently to MasR or AT2R, Ang 1-9 protects against hypertension and cardiovascular damage by decreasing the inflammation in deoxycorticosterone acetate-salt rat test subjects 33 . It was suggested that the Ang 1-9/AT2R axis has a protective effect in vasculature, preventing the heart and kidneys in patients with heart failure and/or hypertension from adverse cardiovascular remodeling 34,35 . It has been observed in vivo that selective activation of AT2 receptors attenuates the progression of pulmonary hypertension and inhibits cardiopulmonary fibrosis 36 . It has also been identified that the stimulation of AT2R using a selective agonist, compound 21(C21), attenuates the progression of lung fibrosis and pulmonary hypertension in an experimental model of a bleomycin-induced lung injury 37 whilst also attenuating pulmonary inflammation in a model of acute lung injury 38 . During pathophysiologic conditions, the ACE/Ang II/AT1R axis is highly activated, yet may be counter-regulated by the activation of the ACE-2/Ang 1-7/MasR and ACE-2/Ang 1-9/AT2R axes. Pharmacological inhibition of the ACE/Ang II/AT1R axis using ACEIs or ARBs induced the upregulation of ACE-2 expression 39 . It was found that ACE-2 inhibits the Ang II/AT1R axis via degradation of Ang I to Ang 1-9 and Ang II into Ang 1-7, which are active biologically through their receptors AT2 and MAS, respectively, and act as anti-inflammatory vasodilators, and anti-fibrotic and anti-proliferative peptides [40] [41] [42] [43] [44] . It was demonstrated that the SARS virus outbreak in 2003 was accompanied by a decrease in ACE-2 expression in the heart 45 , which is posited by some as the possible cause of the myocardial dysfunction and inflammation observed in COVID-19 patients. During COVID-19 infection, the virus uses ACE-2 for cell entry, potentially disturbing RASinduced homeostasis, whilst potentially also affecting the activity of the counter-regulatory RAS system dependent on the ACE-2 availability. This could, in turn, exaggerate the effects of the COVID-19 infection, in terms of RAS homeostasis leading to cardiovascular and pulmonary complications. Recently, it was reported that ACE-2 overexpression counter regulates the inflammatory responses due to RAS activation, by maintaining the balance between the ACE-2/Ang 1-7/MasR and ACE/Ang II/AT1R axes associated with protective effects against lipopolysaccharideinduced acute lung injury in the mice model 46 as well as inhibiting inflammatory response and oxidative stress 47 . More recently, it was reported that the Ang 1-7/MasR axis mediates its anti-inflammatory effects in a murine model of asthma through Src-mediated epidermal growth factor receptor transactivation 48 . In some COVID-19 cases, the immune response to the viral infection intensified due to the upregulation of the ACE/Ang II/AT1R axis, accompanied by ACE-2 depletion, which increases the production of pro-inflammatory cytokines, leading to cytokine storm syndromeassociated with severe cases and death [49] [50] [51] . Most of the deleterious effects following ACE/Ang II/AT1R axis activation that are associated with lung injuries such as acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury are prevented using RAS inhibitors (ACEIs and ARBs) or RAS regulators (AT2R agonist (C21), recombinant soluble human ACE-2 (rhACE-2), Ang 1-7 and MasR agonists) 52,53 ( Figure 1 ). Moreover, the vast majority of protective peptides are dependent on ACE-2 enzyme activity, with this enzymatic pathway representing an endogenous negative regulator of RAS activation. SARS-CoV-2 enters cells via an interaction with ACE-2 54 , which is highly expressed in coronary endothelial cells, cardiomyocytes and cardiac fibroblasts 55 . Furthermore, ACE-2 has been recognized as a major RAS regulator, able to alleviate the deleterious effects mediated by Ang II and AT1R 56 . Current studies on angiotensin peptides such as Ang 1-7, angiotensin 2-8, Ang 1-9, angiotensin 3-7, and angiotensin 3-8 are vital in counteracting the deleterious effects of Ang II 57 . Interestingly, in the midst of ACE-2 deficiency, protective Ang 1-7 can be produced independent of ACE-2, either from Ang I via NEP, thimet oligopeptidase (TOP), or prolyl oligopeptidase (POP), or it can be produced from Ang-II via prolyl carboxypeptidase (PCP), or POP favoring a tilt toward protective Ang1-7/MasR axis 58, 59 (Fig. 1) . Additionally, it has been strongly suggested that ACE-2 deficiency resulting from SARS-COV-2 binding, leads to an increase in bradykinin and des-Arg 9 -bradykinin levels, which in turn causes difficulties seen during COVID-19 infection, such as pulmonary edema 60 , pneumonia, and respiratory failure 61 . TOP and PCP are known to be expressed in endothelial cells and contribute to the metabolism of bradykinin and des-Arg 9 -bradykinin, respectively 59, 62, 63 . Moreover, in addition to the ability of POP to produce anti-fibrotic and anti-inflammatory Ang 1-7, it can convert thymosin β4 to N-acetyl-seryl-aspartyl-lysyl-proline (AC-SDKP), which provides an anti-inflammatory and anti-fibrotic effect during lung and cardiovascular diseases 64 . Activation of the ACE2 compensatory pathways during COVID-19 infection could potentially: i) cause an increase in Ang 1-7 production from accumulated Ang I and Ang II, in order to reconcile the RAS balance; ii) result in the degradation of bradykinin and des-Arg 9 -bradykinin via the actions of TOP and PCP, respectively, for the purpose of managing or alleviating pulmonary edema and respiratory failure; iii) support Ang 1-7 function by increasing AC-SDKP production and reducing Ang-II accumulation 64 . COVID-19 has an acutely harmful effect on patients with cardiovascular diseases. The volume of severe cases and high mortality rates noted in COVID-19 patients is closely correlated with cardiovascular metabolic comorbidities, such as hypertension, cardiovascular diseases, and diabetes 65 . COVID-19 can aggravate any damage to the heart and significantly increase the incidence of acute cardiac injury in ICU/severe patients 65 According to available clinical data from China, 2.5% to 15% of COVID-19 patients also have cardiovascular diseases, whilst 15% to 30% also have hypertension 55, 66 , These values are variable across the countries and, in Italy, according to recent clinical data, the percentage of patients with COVID-19 alongside hypertension (46%-52%), cardiovascular disease (19%-24%), and hypercholesterolemia (16%-20%) is much higher 69 . All these clinical features share a common disorder in RAS activity, where classical RAS is highly activated, leading to an increase in Ang II and upregulation of ACE/Ang II/AT1R axis. A recent study by Osman et al exemplified that RAS components were modulated by SARS-COV-2 in 44 COVID-19 patients. ACE-2 expression was decreased in the blood cells while Ang I and Ang II were increased in the plasma. At the same time, Ang 1-7 levelwhich is supposed to be lowwas not significantly changed compared to the control samples, where it could be explained by the activation ACE-2 independent Ang 1-7 production pathways as a result of Ang I accumulation. That was not, however, enough to prevent the detrimental effects of Ang II accumulation 70 . In order to counteract the deleterious effect of Ang II, RAS is regulated either endogenously by negative feedback to reduce renin secretion 71 or stimulation of AT2R 41 , or exogenously by using ARBs, renin inhibitors, and ACEIs, which are the main drugs used to treat hypertension and vascular diseases 72,73 . Ang 1-7 acts as an antiarrhythmic component in rat cardiac injury-reperfusion, which contributes to the alleviation of reversible and/or irreversible ischemia-reperfusion injury 74 , activates the sodium pump, hyperpolarises the heart cell, and re-establishes impulse conduction 75 . Moreover, Alamandine via the MrgD receptor stimulates the AMP-activated protein kinase pathway to alleviate cardiac hypertrophy that is induced by Ang II in alamandine treated cardiomyocytes from C57BL/6 mice model 76 . In the transverse aortic constriction mice model, the oral administration of alamandine for 2 weeks prevented vascular remodelling and attenuated vascular wall fibrosis. In addition, it was able to elevate MrgD receptor expression and attenuate AT1R expression induced by transverse aortic constriction 77 . In the case of COVID-19, acute cardiac injury, ischemic stroke, acute coronary syndromes, myocarditis, arrhythmias, and heart failure were reported in hospitalized patients [78] [79] [80] . High expression of ACE-2 in heart tissue, cytokine storm, and viral infection-associated hypoxemia are the main potential causes of COVID-19-associated myocardial injury 78, 79 . Recently, it was found that SARS-COV-2 infected the cardiomyocytes in an engineered human heart tissue model of COVID-19 with severe myocarditis, leading to contractile deficits, cytokine production, and cell death 81 . Moreover, critically ill COVID-19 patients showed intense inflammatory syndrome and cardiac complications such as arrhythmia and myocarditis after one week of the infection, while deceased patients showed acute cardiac injury, type I respiratory failure, heart failure, and acute kidney injury. Acute cardiac injury and heart failure were especially common amongst these COVID-19 cases [82] [83] [84] . Increasing interleukin, leukocyte, and neutrophil levels in patients with myocardial injury was correlated with the severity of inflammation during COVID-19 85 . As a result, the administration of alamandine may have therapeutic potential through anti-fibrotic and anti-inflammatory effects, to compensate for the effect of ACE-2 deficiency in cardiovascular diseases during COVID-19 infection. Additionally, ARBs -Telmisartan and Olmesartandemonstrated an antiinflammatory effect in an experimental rat model of autoimmune myocarditis via the reduction of TNF-α, interferon gamma, IL-1β, IL-6 pro-inflammatory cytokines, and increasing antiinflammatory cytokine IL-10 associated with less myocardial fibrosis 86,87 . Disseminated intravascular coagulation and pulmonary embolisms were detected in COVID-19 patients 79 . Furthermore, increasing D-dimer and fibrinogen levels in COVID-19 patients indicates thrombotic formation, where the endothelial damage produced by SARS-CoV-2 infection promotes the coagulation process that leads to the microthrombi formation. This can travel through blood vessels to different internal organs, resulting in pulmonary embolisms in addition to heart, kidney, and liver ischemic injuries. Moreover, frequent activation of the coagulation processwhich is referred to as COVID-19 coagulopathyleads to poor outcomes and high mortality rates 82, [88] [89] [90] [91] . The elevation of proinflammatory cytokines and chemokines during COVID-19 inhibits anticoagulation pathways, thus promoting thrombin formation 92 . Recently, high levels of Ang II were detected in COVID-19 patients, possibly contributing to the thrombosis seen in COVID-19 patients 93 while Ang 1-7 is posited to have an antithrombotic effect similar to losartan 94 , mediating the antithrombotic effect of captopril in addition to losartan 95 . In obese individuals, dysfunctional adipose tissue secretes pro-inflammatory cytokines in the circulatory system, contributing to obesity-related chronic inflammation. SARS-CoV-2 entry via the expression of ACE-2 on adipose tissue could direct adipocyte to produce more proinflammatory cytokines, therefore contributing to the immune dysfunction seen during COVID-19 infection. In addition, IL-6 was identified as more elevated in COVID-19 patients who also have diabetes, particularly when compared to non-diabetic patientsputting them at risk of forming a deadly uncontrolled cytokine storm due to the damage of islets and pancreatic injury caused by SARS-CoV-2 entry 96 . Moreover, diabetes increases the risk of death in COVID-19 patients fourfold, compared to COVID-19 patients without diabetes 97 . In a Korean cohort's observational study of 1,082 COVID-19 patients, diabetes mellitus was found to be risk factor for COVID-19 severity and mortality 98 . The activation of RAS plays a crucial role in inflammation, with the bulk of this system's proinflammatory function being due to Ang II and, more specifically, mediation by AT1R. AT1R, present in most cells, is stimulated by Ang II and activates targeted cells, as well as downstream signaling pathways associated with tissue injury and the inflammatory microenvironment, including fibrosis, oxidative stress, calcium mobilization, adaptive immune cell recruitment, neutrophils and monocyte adhesion, cytokines and chemokines expression, synthesis, and release 18, [99] [100] [101] . It was demonstrated that most of these effects are negatively regulated by ACE-2/Ang 1-7/MasR axis [102] [103] [104] [105] [106] . ACE-2/Ang 1-7/MasR serves as a beneficial antiinflammatory axis in several inflammatory conditions associated with RAS activation and adipokines dysregulation, such as obesity, type 2 diabetes, and cardiovascular diseases 24 . In a model of high-fat, diet-induced obesity, ACE-2 deficiency worsens epicardial adipose tissue inflammation, cardiac dysfunction, myocardial lipotoxicity, and cardiac insulin resistance 107 . In obese patients, the administration of Ang 1−7 improved insulin-stimulated, endotheliumdependent vasodilation and blunted the vasoconstrictor effect of endothelin-1, which may counteract the hemodynamic abnormalities of human obesity 108 . It has been reported that up to 20% of COVID-19 patients suffer from respiratory diseases such as ARDS [66] [67] [68] which are characterized by severe hypoxia, accumulation of inflammatory cells, and increased vascular permeability-dependent pulmonary oedema 109, 110 . ACE/Ang II/AT1R activation and/or expression is significantly upregulated in patients with sepsisone of the most common causes of ARDS. Furthermore, pneumonia that is closely associated with infections such as SARS coronavirus 111, 112 or human influenza viruses 113 represent a predisposing factor for ARDS. Ageing and ARDS are known to be lung fibrosis risk factors, with the two often being identified together in the vast majority of COVID-19 cases. During the inflammatory phase of ARDS, matrix metalloproteinases are produced to contribute to lung injury and fibroproliferation. This is followed by the production of IL-6, TNF-α, and vascular endothelial growth factor, which are implicated in the ARDS conversion to fibrosis. Most COVID-19 patients with ARDS die due to the development of pulmonary fibrosis, the onset of which typically occurred in the first week of infection until the third week, where it is in most of the deceased patient's tissues. Therefore, the importance of anti-fibrotic intervention to counteract early-onset ARDS has been raised 114, 115 . The ACE-2/Ang 1-7/MasR axis protects against lung fibrosis by inhibiting Ang II-induced apoptotic resistance of lung fibroblasts via MAPK/NF-κB pathway and activating the BCL-2-associated X protein/caspase-dependent mitochondrial apoptotic pathway 116, 117 . Interestingly, recent in silico studies noted that the combination of losartanan ARBwith Imatinib 118 or C21 119 has the potential to alleviate ARDS during COVID-19 infection. Increasing evidence has recently demonstrated the existence of local angiotensin systems in the alveolar endothelial cells of the lung 120 . Ang II induces collagen deposition, nucleotide-binding oligomerization, domain-like receptor pyrin domain containing 3 (NLRP3) inflammasome activation, and oxidative stress that promotes pulmonary fibrosis 121, 122 . These effects were inhibited by ACE-2/Ang 1-7/MasR, which decreases lung fibroblast migration and lung fibrosis 122 . Expression and activity of ACE-2 are severely downregulated in both human and experimental lung fibrosis, suggesting that ACE-2 protects against lung fibrogenesis by limiting the local accumulation of the Ang II as a profibrotic peptide 123 . increasing the production of inflammatory cytokines and chemokines such as TNF-α, interferon gamma (IFN-γ), IL-2, IL-6, and IL-8 82, 89, 124 . IL6 acts as a crucial mediator of cytokine storm syndrome, resulting in lung damage and disseminated intravascular coagulation 125, 126 . Moreover, coronaviruses promote NLRP3, increasing the release of IL-18 and IFN-γ. IFN-γ mediates acute lung injury and activates macrophages to release IL-18, IL-6, IL-8, IL-1, and MCP-1, which contribute to alveolar epithelial damage and acute lung injury 124, 126 . Ang II induced-acute lung injury was found to be attenuated by calcitriol/vitamin D receptor signals, reducing the expression of Ang II in endothelial cells and suppressing the Ang II-Tie-2myosin light-chain kinase pathway in the acute lung injury mice model 127 . In a randomized clinical trial of 76 COVID-19 patients, all of whom were treated with a high dose of calcifediol, the severity of the disease decreased, identified via the reduction of admissions to the intensive care unit 128 . As Ang II is known to be elevated in ARDS, most severe form of lung injury, patients 53 , it can be assumed that calcifediol can be converted to the active Vitamin D3 (calcitriol), which blocks the Ang II inflammatory effect and alleviates ARDS in COVID-19 patients. To verify the discovery of calcifediol-indicated effects and the exact mechanism resulting in this, more clinical trials with larger numbers of test subjects to monitor are required. Due to the propensity for patients under ACEIs and ARBs treatment presenting with an upregulation of ACE-2, it was initially suggested that their conditions could be exacerbated by COVID-19. This suggestion renders a huge population of people under RAS inhibitors as highrisk, leading to a debate about the use of this medication. However, the upregulation of ACE-2 in cardiac diseases such as myocardial infraction was considered as a negative regulatory action in response to the increase of ACE/Ang II/AT1R axis. Moreover, that upregulation was suggested to be part of ACE-2 involvement in the inflammatory response during myocardial infraction rather than being ACEIs or ARBs direct effect 129 . Interestingly, high expression of ACE-2 in cardiovascular disorders is unlikely to be a risk factor or responsible for COVID-19 severity. To the best of our knowledge, males are at higher risk of COVID-19 compared to females, but the level of ACE-2 expression was shown to be higher in Asian females compared to males 130 . Moreover, ACE-2 expression level in type-2 diabetic patients tends to decrease as the disease progresses. At the same time, most cardiovascular diseases and type-2 diabetic patients need intensive care once they have COVID-19 regardless to the ACE-2 level before the COVID-19 infection. Therefore, the severity of their cases seems to be due to the fact that they are suffering from metabolic disorders where the balance of RAS already shifted towards the ACE/Ang II/AT1R axis, and alongside that, having the COVID-19 infection augmented the ACE/Ang II/AT1R axis effect which includes vasoconstriction, hypertension, inflammation and myocardial hypertrophy 130 . Various clinical studies and trials have been performed on diverse populations and ages, as well as on those with a range of comorbidities (table1), in order to determine the association between ACEIs/ARBs administration and COVID-19 infection. Most of those studies highlighted the lack of relationship between hypertension or ACEIs/ARBs administration, and the risk of COVID-19 infection, severity, mortality, poor outcomes, and even chance of recovery. Other studies indicate that previous administration of ACEIs/ARBs lowers the risk of COVID-19 infection, as well as the severity and mortality rate (table 2) . This controversy could be attributed to the presence of several competing factors, which were overcame in some studies but not in others, thus limiting the ability to determine the exact relationship with the following: i) missing information about patient lifestyle, Body Mass Index, history of smoking, dose and period of ACEIs/ARBs intake, and ACE-2 activity and expression; ii) the degree of hypertension and its duration, which directly relates to heart failure and, therefore, poor outcomes; iii) the fact that the presence of participants aged 80 years and over could cause an underestimation of the effects of antihypertensive drugs, due to the correlation between COVID-19 severity and mortality in older age patients; iv) due to the nature of retrospective studies, the adherence to antihypertensive drug intake prior to, or during, COVID-19 infection is not fully guaranteed and was based on drug prescriptions recorded in the databases. Furthermore, it is challenging to isolate and analyze the effects of ACEIs and ARBs independently, as they are commonly-used drugs for several comorbidities such as diabetes mellitus, hypertension, and coronary artery disease. At the same time, selection bias cannot be completely excluded, even following statistical analysis such as propensity-score matching. This consideration means that randomized, controlled trials are a necessity in order to delineate the potential effect of ACEIs/ARBs on COVID-19 patientsavoiding the aforementioned factors could help to limit bias in future studies. Despite the relationship between ACE-2 expression level and the susceptibility or severity of COVID-19, ARBs and ACEIs administration should not be discontinued as their detrimental effect has not been approved so at least their administration will protect COVID-19 patients with metabolic disorders from life-threating consequences 130 . Interestingly, in 2014, Deshotels and co-workers demonstrated the effect of increased Ang II level on ACE-2 downregulation during hypertension. The Ang II treatment was able to internalize ACE-2 receptor and promote ACE-2 ubiquitination through AT1R binding while the AT1 receptor in the absence of Ang II was found to be complexed with ACE-2 to prevent ACE-2 internalization. Moreover, the absence of AT1R or AT1R blocking by losartan was found to attenuate the Ang II mediated ACE-2 internalization. In the same context ACEIs prevent Ang II production and up-regulate Ang 1-7 which has an anti-inflammatory effect. Hence, we posit that the use of ACEIs may protect against pulmonary injury while ARBs in particular losartan may prevent ACE-2 internalization and impede viral entry in hypertensive people with COVID-19. All these speculations need further investigation 130, 131 (Figure 2 ). In addition, the depletion of ACE-2 due to the SARS-Cov-2 binding in COVID-19 patients with respiratory problems increases the pulmonary injury. There is a growing evidence to support the administration of ARBs and ACEIs to activate ACE-2/Ang 1-7/MasR axis which ameliorate the deleterious effects of ACE-2 depletion and accelerate disease recovery 130 . As such, targeting the counter-regulatory RAS pathways could be of interest to explain the association between COVID-19 and cardiometabolic diseases and could be a future potential target for treatment. Moreover, conducting randomized, controlled trials with large sample sizes are of utmost importance, in order to determine the definitive effect of ACEIs/ ARBs administration on COVID-19 infection, and the pharmacological mechanisms behind that effect. The administration of several antiviral drugs that intervene with viral-host interaction has been under investigation as a possible COVID-19 treatment 132 . For COVID-19 patients with ARDS, rhACE-2 is suggested as a possible strategy to maintain ACE-2 availability and prevent viral-ACE-2 binding in the lung tissue by saturating SARS-CoV-2 spike protein in the blood before entry to the lung. In addition, the rhACE-2 may shift the balance toward ACE-2/Ang 1-7/MasR axis as the latter was confirmed to increase after rhACE-2 treatment 8 . As recommended by Rello et al. (2020) , COVID-19 treatment by either anti-viral, antiinflammatory, anticoagulant, or anti-fibrotic agents can be personalized based on the main clinical phenotypes that occur in the patient 89 . Ang 1-7 and Ang 1-9 can act as antiinflammatory, anticoagulant, and anti-fibrotic factors 40 , which can cover the majority of clinical phenotypes and thus potentially improve disease outcomes. In light of our hypothesis, the activation of Ang 1-7 without increasing ACE-2 activity may be a promising strategy to rebalance the RAS axes in COVID-19. For example, producing Ang 1-7 from Ang I through NEP activity will promote the protective effect of Ang 1-7 without stimulating ACE-2 which known as virus entry portal. In conclusion, COVID-19 patients share clinical phenotypes similar to those in diseases where the ACE-2/Ang 1-7/MasR axis is downregulated, indicating the pivotal role of RAS balance during SARS-CoV-2 infection. The main issue related to COVID-19 infection is the severity of the cases that lead to organ failure and death. In the majority of these cases, the patient is elderly with at least one comorbidity factor. The majority of these comorbidities are related to cardiovascular diseases and risk factors. When infected with COVID-19, patients with cardiovascular diseases are most likely to develop new cardiac injuries, or worsen their existing pathologies. RASas a crucial aspect in cardiovascular diseaseswill be disturbed during infection. This is firstly because of the lack of ACE-2 function caused by virus binding and, secondly, by the potential imbalance of the RAS classical pathway activation (mainly ACE/Ang II/AT1R) and RAS counter-regulatory pathway (mainly ACE-2/Ang 1-7/MasR and ACE-2/Ang 1-9/AT2R) ( Figure 3 ). Targeting the counter-regulatory pathways using agonists or stimulators such as rhACE-2, MasR agonists, or AT2R agonists may be of interest to boost the function of this system, or to compensate for the poor ACE-2 functionality or availability, due possibly to virus binding and, seems to be a promising therapeutic strategy for COVID-19 treatment. Immune system and cardiovascular disease T regulatory lymphocytes prevent angiotensin II-induced hypertension and vascular injury. Hypertens (Dallas, Tex 1979) CD4(+) Regulatory T Lymphocytes Prevent Impaired Cerebral Blood Flow in Angiotensin II-Induced Hypertension Reduced macrophagedependent inflammation improves endothelin-1-induced vascular injury. Hypertens (Dallas, Tex 1979) Renin-angiotensin system and cardiovascular functions COVID-19 and Older Adults: What We Know The clinical characteristics and prognosis of COVID-19 patients with comorbidities: a retrospective analysis of the infection peak in Wuhan Potential harmful effects of discontinuing ACE-inhibitors and ARBs in COVID-19 patients Three months of COVID-19: A systematic review and meta-analysis WHO Coronavirus Disease COVID-19: angiotensin-converting enzyme 2 (ACE2) expression and tissue susceptibility to SARS-CoV-2 infection Angiotensin converting enzyme defects in shock: Implications for future therapy The vasoprotective axes of the renin-angiotensin system: physiological relevance and therapeutic implications in cardiovascular, hypertensive and kidney diseases Angiotensin II induces apoptosis in human and rat alveolar epithelial cells Losartan Attenuates Ventilator-Induced Lung Injury Losartan attenuates microvascular permeability in mechanical ventilator-induced lung injury in diabetic mice Antagonist of the Type-1 ANG II receptor prevents against LPS-induced septic shock in rats Role of Renin-Angiotensin System in Inflammation, Immunity and Aging γδ T cells mediate angiotensin II-induced hypertension and vascular injury Angiotensin II signal transduction: An update on mechanisms of physiology and pathophysiology Angiotensin-Converting Enzyme 2: SARS-CoV-2 Receptor and Regulator of the Renin-Angiotensin System: Celebrating the 20th Anniversary of the Discovery of ACE2 Covid-19: the renin-angiotensin system imbalance hypothesis Mechanisms of Myocardial Injury in Coronavirus Disease Renin-angiotensin-system, a potential pharmacological candidate, in acute respiratory distress syndrome during mechanical ventilation Angiotensin-converting enzyme 2 protects from severe acute lung failure A pneumonia outbreak associated with a new coronavirus of probable bat origin Coronavirus Disease 2019 (COVID-19) and Cardiovascular Disease: A Viewpoint on the Potential Influence of Angiotensin-Converting Enzyme Inhibitors/Angiotensin Receptor Blockers on Onset and Severity of Severe Acute Respiratory Syndrome Coronavirus 2 Infec Grant and GYO. Role of the ACE2/Angiotensin 1-7 axis of the Renin-Angiotensin System in Heart Failure Novel therapeutic approaches targeting the reninangiotensin system and associated peptides in hypertension and heart failure Identification of prolyl carboxypeptidase as an alternative enzyme for processing of renal angiotensin II using mass spectrometry Angiotensin-(1-7): A bioactive fragment of the renin-angiotensin system Impaired Breakdown of Bradykinin and Its Metabolites as a Possible Cause for Pulmonary Edema in COVID-19 Infection Evaluation of the efficacy and safety of icatibant and C1 esterase/kallikrein inhibitor in severe COVID-19: study protocol for a three-armed randomized controlled trial Regulation of cardiovascular signaling by kinins and products of similar converting enzyme systems-Endopeptidases 3.4. 24.15 and 24.16 in endothelial cells: potential role in vasoactive peptide metabolism Purification and properties of prolylcarboxypeptidase (angiotensinase C) from human kidney Sarah Sarkar N-ER. Tβ4-Ac-SDKP pathway: Any relevance for the cardiovascular system? Prevalence and impact of cardiovascular metabolic diseases on COVID-19 in China Jia'an Xia TY, Xinxin Zhang LZ. Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: a descriptive study Clinical characteristics of coronavirus disease 2019 in China Clinical Characteristics of 138 Hospitalized Patients with 2019 Novel Coronavirus-Infected Pneumonia in Wuhan, China Baseline Characteristics and Outcomes of 1591 Patients Infected with SARS-CoV-2 Admitted to ICUs of the Lombardy Region, Italy Expression of ACE2 receptor soluble ACE2 Angiotensin I Angiotensin II and Angiotensin (1-7) is modulated in COVID-19 patients. medRxiv Atlas A. Steven. The Renin-Angiotensin Aldosterone System: Pathophysiological Role and Pharmacologic Inhibition Faiez Zannad and BP. The past, present and future of renin-angiotensin aldosterone system inhibition Angiotensin-(1-7): cardioprotective effect in myocardial ischemia/reperfusion Angiotensin (1-7) re-establishes impulse conduction in cardiac muscle during ischaemia-reperfusion. The role of the sodium pump Alamandine acts via MrgD to induce AMPK/NO activation against ANG II hypertrophy in cardiomyocytes Alamandine attenuates arterial remodelling induced by transverse aortic constriction in mice Cardiac and arrhythmic complications in patients with COVID-19 Cardiovascular Implications of the COVID-19 Pandemic: A Global Perspective Extrapulmonary manifestations of COVID-19 SARS-CoV-2 Infects Human Engineered Heart Tissues and Models COVID-19 Myocarditis Unraveling the mystery of Covid-19 Cytokine storm: From skin to organ systems Clinical phenotypes of critically ill COVID-19 patients Elisa Col INI of HC-19 mortality group. Clinical Characteristics of Hospitalized Individuals Dying With COVID-19 by Age Group in Italy A Review of Acute Myocardial Injury in Coronavirus Disease Advantages of renin-angiotensin system blockade in the treatment of cardiovascular diseases Angiotensin-(1-7) activates a tyrosine phosphatase and inhibits glucose-induced signalling in proximal tubular cells Vasculopathy and Coagulopathy Associated with SARS-CoV-2 Infection Clinical phenotypes of SARS-CoV-2: implications for clinicians and researchers Clinical and computed tomography characteristics of COVID-19 associated acute pulmonary embolism: A different phenotype of thrombotic disease? Distinct phenotypes require distinct respiratory management strategies in severe COVID-19 Toshiaki Iba JHL. Coagulation abnormalities and thrombosis in patients with COVID-19 Hypertension, Thrombosis, Kidney Failure, and Diabetes: Is COVID-19 an Endothelial Disease? A Comprehensive Evaluation of Clinical and Basic Evidence The antithrombotic effect of angiotensin-(1-7) closely resembles that of losartan Antithrombotic effect of captopril and losartan is mediated by angiotensin-(1-7) Obesity and diabetes as high-risk factors for severe coronavirus disease 2019 (COVID-19) Endocrine-Immune-Vascular Interactions Shapes Clinical Course The clinical characteristics and outcomes of patients with moderate-to-severe coronavirus disease 2019 infection and diabetes in Daegu, South Korea Proinflammatory actions of angiotensins Inflammation and angiotensin II Cardioprotective effects of telmisartan against heart failure in rats in-duced by experimental autoimmune myocarditis through the modulation of Angiotensin-Converting Enzyme-2/Angiotensin 1-7/Mas Receptor axis Prevention of angiotensin II-induced cardiac remodeling by angiotensin-(1-7) ACE2 Overexpression Inhibits Angiotensin II-induced Monocyte Chemoattractant Protein-1 Expression in Macrophages Evidence for angiotensin-converting enzyme 2 as a therapeutic target for the prevention of pulmonary hypertension Telmisartan acts through the modulation of ACE-2/ANG 1-7/mas receptor in rats with dilated cardiomyopathy induced by experimental autoimmune myocarditis ACE2 overexpression in the paraventricular nucleus attenuates angiotensin II-induced hypertension ACE2 deficiency worsens epicardial adipose tissue inflammation and cardiac dysfunction in response to diet-induced obesity Favorable Vascular Actions of Angiotensin-(1-7) in Human Obesity THE ACUTE RESPIRATORY DISTRESS SYNDROME Organ-protective effect of angiotensin-converting enzyme 2 and its effect on the prognosis of COVID-19 Identification of a novel coronavirus in patients with severe acute respiratory syndrome Broad-spectrum coronavirus antiviral drug discovery Avian Influenza A (H5N1) in 10 Patients in Vietnam Pulmonary fibrosis secondary to COVID-19: a call to arms? Pulmonary Fibrosis and COVID-19: The Potential Role for Antifibrotic Therapy Angiotensin-converting enzyme 2/angiotensin-(1-7)/mas axis protects against lung fibrosis by inhibiting the MAPK/NF-κB pathway Disequilibrium Between the Classic Renin-Angiotensin System and Its Opposing Arm in Sars-Cov-2 Related Lung Injury Are losartan and imatinib effective against SARS-CoV2 pathogenesis? A pathophysiologic-based in silico study Combination of C21 and ARBs with rhACE2 as a therapeutic protocol: A new promising approach for treating ARDS in patients with coronavirus infection Exogenous angiotensin (1-7) directly inhibits epithelialmesenchymal transformation induced by transforming growth factor-β1 in alveolar epithelial cells Autophagy attenuates angiotensin II-Induced pulmonary fibrosis by inhibiting redox imbalance-mediated NOD-like receptor family pyrin domain containing 3 inflammasome activation The angiotensin-converting enzyme 2/angiotensin (1-7)/mas axis protects against lung fibroblast migration and lung fibrosis by inhibiting the NOX4-derived ROSmediated RhoA/Rho kinase pathway Angiotensin converting enzyme-2 is protective but downregulated in human and experimental lung fibrosis COVID-19 revisiting inflammatory pathways of arthritis Martina Maritatib PC. A new pharmacological approach based on remdesivir aerosolized administration on SARS-CoV-2 pulmonary inflammation: A possible and rational therapeutic application The amount of cytokine-release defines different shades of Sars-Cov2 infection VDR attenuates acute lung injury by blocking Ang-2-Tie-2 pathway and renin-angiotensin system Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study Myocardial infarction increases ACE2 expression in rat and humans The ACE-2 in COVID-19 : Foe or Friend ? Authors Angiotensin-II mediates ACE2 Internalization and Degradation through an Angiotensin-II type I receptor-dependent mechanism Analysis of the susceptibility to COVID-19 in pregnancy and recommendations on potential drug screening Determinants of healing among patients with coronavirus disease 2019: the results of the SARS-RAS study of the Italian Society of Hypertension Age and multimorbidity predict death among COVID-19 Patients: Results of the SARS-RAS study of the Italian society of hypertension Antihypertensive Drugs and COVID-19 Risk Cardiovascular comorbidities and pharmacological treatments of covid-19 patients not requiring hospitalization COVID-19 In-Hospital Mortality and Use of Renin-Angiotensin System Blockers in Geriatrics Patients Impact of renin-angiotensin system inhibitors use on mortality in severe COVID-19 patients with hypertension: a retrospective observational study Antecedent Administration of Angiotensin-Converting Enzyme Inhibitors or Angiotensin II Receptor Antagonists and Survival After Hospitalization for COVID-19 Syndrome RAAS inhibitors are not associated with mortality in COVID-19 patients: Findings from an observational multicenter study in Italy and a meta-analysis of 19 studies Impact of Treatment with Renin-Angiotensin System Inhibitors on Clinical Outcomes in Hypertensive Patients Hospitalized with COVID-19 Renin-Angiotensin-Aldosterone System Inhibitors and Risk of Covid-19 Hypertension, medications, and risk of severe COVID-19: A Massachusetts community-based observational study Renin-angiotensin system inhibitors improve the clinical outcomes of COVID-19 patients with hypertension Ensieh Zivari HA. Effects of Angiotensin Receptor Blockers (ARBs) on In-Hospital Outcomes of Patients With Hypertension and Confirmed or Clinically Suspected COVID-19. merican Renin-angiotensin system inhibitors and the severity of coronavirus disease 2019 in Kanagawa, Japan: a retrospective cohort study Association of hypertension and antihypertensive treatment with COVID-19 mortality: a retrospective observational study Use of distinct anti-hypertensive drugs and risk for COVID-19 among hypertensive people: A population-based cohort study in Southern Catalonia, Spain The role of anti-hypertensive treatment, comorbidities and early introduction of LMWH in the setting of COVID-19: A retrospective, observational study in Northern Italy Association of Inpatient Use of Angiotensin-Converting Enzyme Inhibitors and Angiotensin II Receptor Blockers With Mortality Among Patients With Hypertension Hospitalized With COVID-19 Renin-Angiotensin-Aldosterone System Blockers and the Risk of Covid-19 Association of Renin-Angiotensin System Inhibitors with Severity or Risk of Death in Patients with Hypertension Hospitalized for Coronavirus Disease 2019 (COVID-19) Infection in Wuhan, China Effect of Discontinuing vs Continuing Angiotensin-Converting Enzyme Inhibitors and Angiotensin II Receptor Blockers on Days Alive and out of the Hospital in Patients Admitted with COVID-19: A Randomized Clinical Trial Continuation versus discontinuation of renin-angiotensin system inhibitors in patients admitted to hospital with COVID-19: a prospective, randomised, open-label trial The authors extend their appreciation to the Medical Core Facility and Research/funding The authors have no conflicts of interest to disclose. T.B. wrote and reviewed the manuscript; M.A. wrote the manuscript; A.A.A. and F.A. edited and reviewed the manuscript.