Interactions of angiotensin-converting enzyme-2 (ACE2) and SARS-CoV-2 spike receptor-binding domain (RBD): a structural perspective.

BACKGROUND: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has caused millions of infections and deaths worldwide since its discovery in late 2019 in Wuhan, China. The receptor-binding domain (RBD) of the SARS-CoV-2 spike protein binds to the human angiotensin-converting enzyme-2 (ACE2) receptor, a critical component of the renin-angiotensin system (RAS) that initiates the viral transmission. Most of the critical mutations found in SARS-CoV-2 are associated with the RBD of the spike protein. These mutations have the potential to reduce the efficacy of vaccines and neutralizing antibodies. METHODS: In this review, the structural details of ACE2, RBD and their interactions are discussed. In addition, some critical mutations of RBD and their impact on ACE2-RBD interactions are also discussed. CONCLUSION: Preventing the interaction between Spike RBD and ACE2 is considered a viable therapeutic strategy since ACE2 binding by RBD is the first step in virus infection. Because the interactions between the two entities are critical for both viral transmission and therapeutic development, it is essential to understand their interactions in detail.

The spike effect of acute respiratory syndrome coronavirus 2 and coronavirus disease 2019 vaccines on blood pressure.

Among the various comorbidities potentially worsening the clinical outcome in patients hospitalized for the acute respiratory syndrome coronavirus-2 (SARS-CoV-2), hypertension is one of the most prevalent. However, the basic mechanisms underlying the development of severe forms of coronavirus disease 2019 (COVID-19) among hypertensive patients remain undefined and the direct association of hypertension with outcome in COVID-19 is still a field of debate. Experimental and clinical data suggest that SARS-CoV-2 infection promotes a rise in blood pressure (BP) during the acute phase of infection. Acute increase in BP and high in-hospital BP variability may be tied with acute organ damage and a worse outcome in patients hospitalized for COVID-19. In this context, the failure of the counter-regulatory renin-angiotensin-system (RAS) axis is a potentially relevant mechanism involved in the raise in BP. It is well recognized that the efficient binding of the Spike (S) protein to angiotensin converting enzyme 2 (ACE2) receptors mediates the virus entry into cells. Internalization of ACE2, downregulation and malfunction predominantly due to viral occupation, dysregulates the protective RAS axis with increased generation and activity of angiotensin (Ang) II and reduced formation of Ang1,7. Thus, the imbalance between Ang II and Ang1-7 can directly contribute to excessively rise BP in the acute phase of SARS-CoV-2 infection. A similar mechanism has been postulated to explain the raise in BP following COVID-19 vaccination ("Spike Effect" similar to that observed during the infection of SARS-CoV-2). S proteins produced upon vaccination have the native-like mimicry of SARS-CoV-2 S protein's receptor binding functionality and prefusion structure and free-floating S proteins released by the destroyed cells previously targeted by vaccines may interact with ACE2 of other cells, thereby promoting ACE2 internalization and degradation, and loss of ACE2 activities.

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.

The alternative renin-angiotensin-system (RAS) signalling pathway in prostate cancer and its link to the current COVID-19 pandemic.

BACKGROUND: The renin-angiotensin system is known to maintain blood pressure and body fluids. However, it has been found to consist of at least two major constituents, the classic and the alternative pathway, balancing and supporting each other's signalling in a very intricate way. Current research has shown that the renin-angiotensin system is involved in a broad range of biological processes and diseases, such as cancer and infectious diseases. METHODS AND RESULTS: We conducted a literature review on the interaction of the renin-angiotensin system and prostate cancer and explored the research on the possible impact of the SARS-CoV-2 virus in this context. This review provides an update on contemporary knowledge into the alternative renin-angiotensin system, its role in cancer, specifically prostate cancer, and the implications of the current COVID-19 pandemic on cancer and cancer care. CONCLUSION: In this work, we aim to demonstrate how shifting the RAS signalling pathway from the classic to the alternative axis seems to be a viable option in supporting treatment of specific cancers and at the same time demonstrating beneficial properties in supportive care. It however seems to be the case that the infection with SARS-CoV-2 and subsequent impairment of the renin-angiotensin-system could exhibit serious deleterious long-term effects even in oncology.

Immunoglobulin yolk targeting spike 1, receptor binding domain of spike glycoprotein and nucleocapsid of SARS-CoV-2 blocking RBD-ACE2 binding interaction.

Coronavirus disease (COVID)-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has become a global pandemic disease that has social and economic chaos. An alternative mitigation strategy may involve the use of specific immunoglobulin (Ig)-Y derived from chicken eggs. Our study aimed to evaluate the neutralizing potential of specific IgY targeting S1, receptor-binding-domain (RBD) of spike glycoprotein and nucleocapsid (N) of SARS-CoV-2 to inhibit RBD and angiotensin-converting-enzyme-2 (ACE2) binding interaction. Hy-Line Brown laying hens were immunized with recombinant S1, RBD spike glycoprotein, and nucleocapsid (N) of SARS-CoV-2. The presence of specific S1,RBD,N-IgY in serum and egg yolk was verified by indirect enzyme-linked immunosorbent assay (ELISA). Specific S1,RBD,N-IgY was purified and characterized from egg yolk using sodium-dodecyl-sulfate-polyacrylamide-gel-electrophoresis (SDS-PAGE), and was subsequently evaluated for inhibition of the RBD-ACE2 binding interaction in vitro. Specific IgY was present in serum at 1 week post-initial immunization (p.i.i), whereas its present in egg yolk was confirmed at 4 weeks p.i.i. Specific S1,RBD,N-IgY in serum was able to inhibit RBD-ACE2 binding interaction between 4 and 15 weeks p.i.i. The results of the SDS-PAGE revealed the presence of bands with molecular weights of 180 kDa, indicating the presence of whole IgY. Our results demonstrated that S1,RBD,N-IgY was able to inhibit RBD-ACE2 binding interaction in vitro, suggesting its potential use in blocking virus entry. Our study also demonstrated proof-of-concept that laying hens were able to produce this specific IgY, which could block the viral binding and large production of this specific IgY is feasible.

Flap structure within receptor binding domain of SARS-CoV-2 spike periodically obstructs hACE2 Binding subdomain bearing similarities to HIV-1 protease flap.

The SARS-CoV-2 prefusion spike protein is characterized by a high degree of flexibility and temporal transformations associated with its multifunctional behavior. In this study, we have examined the dynamics of the Receptor Binding Domain (RBD) of the SARS-CoV-2 spike protein in detail. Its primary, binding subdomain with human Angiotensin Covering Enzyme II includes a highly conspicuous flap or loop that is part of a beta hairpin loop structural motif. Dynamic details of the RBD obtained through RMSF and Order Parameter calculations are consistent with structural details including the stability of "glue" points or dominant interaction energy residues of the RBD in the Up and Down states with its neighboring N-terminal domain (NTD) protomer. The RBD flap in the Up state protomer periodically obstructs the binding site on an approximate 70 ns time interval and is reminiscent of an HIV-1 protease polypeptide flap that opens and closes to modulate that enzymes activity. No claim is made here regarding the possible modulating role of the flap; however, the flap may be a potential site for therapeutic targeting aimed at keeping it in the closed state, as previously demonstrated in the inhibition of the HIV-1 protease polypeptide. The RBD primary binding subdomain is further shown to have not only similar dynamics but, also, an approximate 30% sequence similarity to the HIV-1 protease polypeptide.

Angiotensin-converting enzyme 1 and voltage-gated potassium channel-interacting protein 4 gene polymorphisms in COVID-19 patients from east of Iran.

BACKGROUND: Coronavirus disease 2019(COVID-19), the infectious respiratory disease caused by a newly discovered pathogen (severe acute respiratory syndrome coronavirus 2), is a pandemic that places a burden on the health care system. Recently, most research on COVID-19 has emphasized its profound impact on specific regions and ethnic groups. A possible explanation for these variations in disease presentation and severity might be differences in the gene pool of populations. This study therefore attempted to clarify possible involvements of genetic factors affecting COVID-19 pathogenesis with a focus on voltage-gated potassium channel-interacting protein 4 (KCNIP4) and angiotensin-converting enzyme 1 (ACE1) gene polymorphisms. MATERIALS AND METHODS: In this case-control study, the polymorphisms were genotyped using PCR in 194 COVID-19 patients and 194 healthy controls. RESULTS: COVID-19 susceptibility and severity appeared to be unaffected by these polymorphisms. However, this study supported the relevance of ACE1 II genotype frequency to a decreased number of deaths due to the infection. We found that COVID-19 patients with the ACE1 II genotype have a statistically significant better chance of survival (p = 0.008). CONCLUSION: This study strengthens the idea that the ACE1 I/D polymorphism can be a novel prognostic factor indicating the outcome of COVID-19.

Biophysical and structural characterizations of the effects of mutations on the structure-activity relationships of SARS-CoV-2 spike protein.

Mutations on the spike (S) protein of SARS-CoV-2 could induce structural changes that help increase viral transmissibility and enhance resistance to antibody neutralization. Here, we report a robust workflow to prepare recombinant S protein variants and its host receptor angiotensin-convert enzyme 2 (ACE2) by using a mammalian cell expression system. The functional states of the S protein variants are investigated by cryo-electron microscopy (cryo-EM) and negative staining electron microscopy (NSEM) to visualize their molecular structures in response to mutations, receptor binding, antibody binding, and environmental changes. The folding stabilities of the S protein variants can be deduced from morphological changes based on NSEM imaging analysis. Differential scanning calorimetry provides thermodynamic information to complement NSEM. Impacts of the mutations on host receptor binding and antibody neutralization are in vitro by kinetic binding analyses in addition to atomic insights gleaned from cryo-electron microscopy (cryo-EM). This experimental strategy is generally applicable to studying the molecular basis of host-pathogen interactions.

Receptor binding domain of SARS-CoV-2 from Wuhan strain to Omicron B.1.1.529 attributes increased affinity to variable structures of human ACE2.

BACKGROUND: COVID-19 is an infectious disease declared as a global pandemic caused by SARS-CoV-2 virus. Genomic changes in the receptor binding domain (RBD) region of SARS-CoV-2 led to an increased, infectivity in humans through interaction with the angiotensin-converting enzyme2 (ACE2) receptor. Simultaneously, the genetic variants in ACE2 provide an opportunity for SARS-CoV-2 infection and severity. We demonstrate the binding efficiencies of RBDs of SARS-CoV-2 strain with ACE2 variants of the human host. METHODOLOGY: A Total of 615 SARS-CoV-2 genomes were retrieved from repository. Eighteen variations were identified contributing to structural changes in RBD that are distributed in 615 isolates. An analyses of 285 single nucleotide variances at the coding region of the ACE2 receptor showed 34 to be pathogenic. Homology models of 34 ACE2 and 18 RBD structures were constructed with 34 and 18 structural variants, respectively. Protein docking of 612 (34 *18) ACE2-RBD complexes showed variable affinities compared to wildtype Wuhan's and other SARS-CoV-2 RBDs, including Omicron B.1.1.529. Finally, molecular dynamic simulation was performed to determine the stability of the complexes. RESULTS: Among 612, the top 3 complexes showing least binding energy were selected. The ACE2 with rs961360700 variant showed the least binding energy (-895.2 Kcal/mol) on binding with the RBD of Phe160Ser variant compared to Wuhan's RBD complex. Interestingly, the binding energy of RBD of Omicron B.1.1.529 with ACE2 (rs961360700) structure showed least binding energy of -1010 Kcal/mol. Additionally, molecular dynamics showed structure stability for all the analysed complexes with the RMSD (0.22-0.26 nm), RMSF (0.11-0.13 nm), and Rg (2.53-2.56 nm). CONCLUSION: In conclusion, our investigation highlights the clinical variants contributing to structural variants in ACE2 receptors that lead to efficient binding of SARS-CoV-2. Therefore, screening of these ACE2 polymorphisms will help detect COVID-19 risk population so as to provide additional care and for safe management.

Inhibitory mechanism of Ambroxol and Bromhexine Hydrochlorides as potent blockers of molecular interaction between SARS-CoV-2 spike protein and human angiotensin-converting Enzyme-2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects the host cells through interaction of its spike protein with human angiotensin-converting enzyme 2 (hACE-2). High binding affinity between the viral spike protein and host cells hACE-2 receptor has been reported to enhance the viral infection. Thus, the disruption of this molecular interaction will lead to reduction in viral infectivity. This study, therefore, aimed to analyze the inhibitory potentials of two mucolytic drugs; Ambroxol hydrochlorides (AMB) and Bromhexine hydrochlorides (BHH), to serve as potent blockers of these molecular interactions and alters the binding affinity/efficiency between the proteins employing computational techniques. The study examined the effects of binding of each drug at the receptor binding domain (RBD) of the spike protein and the exopeptidase site of hACE-2 on the binding affinity (ΔGbind) and molecular interactions between the two proteins. Binding affinity revealed that the binding of the two drugs at the RBD-ACE-2 site does not alter the binding affinity and molecular interaction between the proteins. However, the binding of AMB (-56.931 kcal/mol) and BHH (-46.354 kcal/mol) at the exopeptidase site of hACE-2, significantly reduced the binding affinities between the proteins compared to the unbound, ACE-2-RBD complex (-64.856 kcal/mol). The result further showed the two compounds have good affinity at the hACE-2 site, inferring they might be potent inhibitors of hACE-2. Residue interaction networks analysis further revealed the binding of the two drugs at the exopeptidase site of hACE-2 reduced the number of interacting amino residues, subsequently leading to loss of interactions between the two proteins, with BHH showing better reduction in the molecular interaction and binding affinity than AMB. The result of the structural analyses additionally, revealed that the binding of the drugs considerably influences the dynamic of the complexes when compared to the unbound complex. The findings from this study suggest the binding of the two drugs at the exopeptidase site reduces the binding effectiveness of the proteins than their binding at the RBD site, and consequently might inhibit viral attachment and entry.

Antibodies to the N-Terminal Domain of Angiotensin-Converting Enzyme (ACE2) That Block Its Interaction with SARS-CoV-2 S Protein.

SARS-CoV-2 is a new coronavirus that is the cause of COVID-19 pandemic. To enter the cell, the virus interacts via its surface S protein with angiotensin-converting enzyme 2 (ACE2), the main entry receptor on the cell membrane. Most of protective antibodies, including those induced by vaccinations, target the S protein, preventing its interaction with the ACE2 receptor. We have evaluated an alternative strategy for blocking the S-ACE2 interaction using new antipeptide antibodies to the N-terminus of the ACE2 molecule. These antibodies allow detection of human ACE2 in vitro and ex vivo.

Soluble Neuropilin-1 Response to Hypoglycemia in Type 2 Diabetes: Increased Risk or Protection in SARS-CoV-2 Infection?

Introduction: Neuropilin-1(NRP1) is a cofactor that enhances SARS-CoV-2 coronavirus cell infectivity when co-expressed with angiotensin-converting enzyme 2(ACE2). The Renin-Angiotensin System (RAS) is activated in type 2 diabetes (T2D); therefore, the aim of this study was to determine if hypoglycaemia-induced stress in T2D would potentiate serum NRP1(sNRP1) levels, reflecting an increased risk for SARS-CoV-2 infection. Methods: A case-control study of aged-matched T2D (n = 23) and control (n = 23) subjects who underwent a hyperinsulinemic clamp over 1-hour to hypoglycemia(<40mg/dl) with subsequent timecourse of 4-hours and 24-hours. Slow Off-rate Modified Aptamer (SOMA)-scan plasma protein measurement determined RAS-related proteins: renin (REN), angiotensinogen (AGT), ACE2, soluble NRP1(sNRP1), NRP1 ligands (Vascular endothelial growth factor, VEGF and Class 3 Semaphorins, SEM3A) and NRP1 proteolytic enzyme (A Disintegrin and Metalloproteinase 9, ADAM9). Results: Baseline RAS overactivity was present with REN elevated and AGT decreased in T2D (p<0.05); ACE2 was unchanged. Baseline sNRP1, VEGF and ADAM9 did not differ between T2D and controls and remained unchanged in response to hypoglycaemia. However, 4-hours post-hypoglycemia, sNRP1, VEGF and ADAM9 were elevated in T2D(p<0.05). SEMA3A was not different at baseline; at hypoglycemia, SEMA3A decreased in controls only. Post-hypoglycemia, SEMA3A levels were higher in T2D versus controls. sNRP1 did not correlate with ACE2, REN or AGT. T2D subjects stratified according to ACE inhibitor (ACEi) therapies showed no difference in sNRP1 levels at either glucose normalization or hypoglycaemia. Conclusion: Hypoglycemia potentiated both plasma sNRP1 level elevation and its ligands VEGF and SEMA3A, likely through an ADAM9-mediated mechanism that was not associated with RAS overactivity or ACEi therapy; however, whether this is protective or promotes increased risk for SARS-CoV-2 infection in T2D is unclear. Clinical Trial Registration: https://clinicaltrials.gov, identifier NCT03102801.

Dysregulation of the Renin-Angiotensin-Aldosterone System (RAA) in Patients Infected with SARS-CoV-2-Possible Clinical Consequences.

SARS-CoV-2 impairs the renin-angiotensin-aledosterone system via binding ACE2 enzyme. ACE2 plays a key role in the biosynthesis of angiotensin (1-7), catalyzing the conversion of angiotensin 2 into angiotensin (1-7) and the reaction of angiotensin synthesis (1-9), from which angiotensin is (1-7) produced under the influence of ACE (Angiotensin-Converting Enzyme). Angiotensin 2 is a potent vasoconstrictor and atherogenic molecule converted by ACE2 to reducing inflammation and vasodilating in action angiotensin (1-7). Angiotensin (1-9), that is a product of angiotensin 1 metabolism and precursor of angiotensin (1-7), also exerts cell protective properties. Balance between angiotensin 2 and angiotensin (1-7) regulates blood pressure and ACE2 plays a critical role in this balance. ACE2, unlike ACE, is not inhibited by ACE inhibitors at the doses used in humans during the treatment of arterial hypertension. Membrane ACE2 is one of the receptors that allows SARS-CoV-2 to enter the host cells. ACE2 after SARS-CoV-2 binding is internalized and degraded. Hence ACE2 activity on the cell surface is reduced leading to increase the concentration of angiotensin 2 and decrease the concentration of angiotensin (1-7). Disturbed angiotensins metabolism, changes in ratio between angiotensins with distinct biological activities leading to domination of atherogenic angiotensin 2 can increase the damage to the lungs.

Repurposing of anticancer phytochemicals for identifying potential fusion inhibitor for SARS-CoV-2 using molecular docking and molecular dynamics (MD) simulations.

The viral particle, SARS-CoV-2 is responsible for causing the epidemic of Coronavirus disease 2019 (COVID-19). To combat this situation, numerous strategies are being thought for either creating its antidote, vaccine, or agents that can prevent its infection. For enabling research on these strategies, several target proteins are identified where, Spike (S) protein is of great potential. S-protein interacts with human angiotensin-converting-enzyme-2 (ACE2) for entering the cell. S-protein is a large protein and a portion of it designated as a receptor-binding domain (RBD) is the key region that interacts with ACE2, following to which the viral membrane fuses with the alveolar membrane to enter the human cell. The hypothesis is to identify molecules from the pool of anticancer phytochemicals as a lead possessing the ability to interact and mask the amino acids of RBD, making them unavailable to form associations with ACE2. Such a molecule is termed as 'fusion inhibitor'. We hypothesized to identify fusion inhibitors from the NPACT library of anticancer phytochemicals. For this, all the molecules from the NPACT were screened using molecular docking, the five top hits (Theaflavin, Ginkgetin, Ursolic acid, Silymarin and Spirosolane) were analyzed for essential Pharmacophore features and their ADMET profiles were studied following to which the best two hits were further analyzed for their interaction with RBD using Molecular Dynamics (MD) simulation. Binding free energy calculations were performed using MM/GBSA, proving these phytochemicals containing anticancer properties to serve as fusion inhibitors.Communicated by Ramaswamy H. Sarma.

SARS-CoV-2/human interactome reveals ACE2 locus crosstalk with the immune regulatory network in the host.

Severe acute respiratory syndrome, coronavirus 2 (SARS-CoV-2), remains to be a threat across the globe. SARS-CoV-2 entry into the host is mediated by binding of viral spike protein to the Human angiotensin-converting enzyme 2 (ACE2) receptor. ACE2 is an essential member of the Renin-Angiotensin system (RAS) involved in maintaining the blood pressure and vascular remodelling. Although ACE2 receptor is the entry point to the host, recent studies show activation of ACE2 to modulate the host to develop a suitable environment for its replication. However, the ACE2 activating the immune signals on SARS-CoV-2 attachment is still under investigation. We have used systems biological approach to construct the host regulatory network upon SARS-CoV-2 attachment to the ACE2 receptor. Since lungs are the primary infection site, we integrate human lung gene expression profile along with the host regulatory network to demonstrate the altered host signalling mechanism in viral infection. Further, the network was functionally enriched to determine immune modulation in the network. We also used the proteomic database to assess the occurrence of similar signalling events in other human tissues that exhibit lineage of infection across different organs. The constructed network contains 133 host proteins with 298 interactions that directly or indirectly connect to the ACE2 receptor. Among 133 proteins, 29 were found to be differentially regulated in the host lungs on SARS-CoV-2 infection. Altered proteins connect multiple proteins in a network that modulates kinase, carboxypeptidase and cytokine activity, leading to changes in the host immune system, cell cycle and signal transduction mechanisms. Further investigation showed the presence of similar signalling events in the kidneys, placenta, pancreas, testis, small intestine and adrenal gland as well. Overall, our results will help in understanding the immune molecular regulatory networks influenced by the ACE2 mediated interaction in other body tissues, which may aid in identifying the secondary health complications associated with SARS-CoV-2 infection.

Metabolism of angiotensin peptides by angiotensin converting enzyme 2 (ACE2) and analysis of the effect of excess zinc on ACE2 enzymatic activity.

After decades of notoriety for its adverse cardiovascular, proinflammatory and profibrotic actions, the renin-angiotensin system (RAS) began to be cast in a more favorable light with the discovery of angiotensin-converting enzyme-2 (ACE2) in 2000. This monocarboxypeptidase, best known for its ability to metabolize angiotensin (Ang) II to Ang 1-7, counteracts the adverse effects of Ang II mediated by the AT1 Ang II receptor. Ang peptides are classically considered to be metabolized by aminopeptidases, by which the nomenclature Ang III (des-Asp1Ang II, 2-8 heptapeptide) and Ang IV (des-Asp1des-Arg2Ang II, 3-8 hexapeptide) are derived. This report compares the ability of recombinant human ACE2 (rhACE2) to metabolize Ang III, Ang IV and Ang V, (4-8 pentapeptide) relative to Ang II to form corresponding des-omega-Phe metabolites. rhACE2 has highest affinity (lowest Km) for Ang III, followed by Ang II ∼ Ang V, followed by Ang IV. However, rhACE2 has the highest Kcat for metabolising Ang IV followed by Ang V, Ang III and Ang II. The enzymatic efficiency (Kcat/Km) is highest for Ang V and Ang III followed by Ang IV and is lowest for Ang II. As a gluzincin metallopeptidase, ACE2 requires a zinc molecule at its active site for catalysis. This report also documents inhibition of ACE2 activity by concentrations of zinc exceeding 10 µM. These observations extend the functional significance of ACE2 to include the metabolic inactivation of Ang III, Ang IV and Ang V, reemphasizing the importance of monitoring zinc intake to maintain metabolic homeostasis.

A mechanistic model and therapeutic interventions for COVID-19 involving a RAS-mediated bradykinin storm.

Neither the disease mechanism nor treatments for COVID-19 are currently known. Here, we present a novel molecular mechanism for COVID-19 that provides therapeutic intervention points that can be addressed with existing FDA-approved pharmaceuticals. The entry point for the virus is ACE2, which is a component of the counteracting hypotensive axis of RAS. Bradykinin is a potent part of the vasopressor system that induces hypotension and vasodilation and is degraded by ACE and enhanced by the angiotensin1-9 produced by ACE2. Here, we perform a new analysis on gene expression data from cells in bronchoalveolar lavage fluid (BALF) from COVID-19 patients that were used to sequence the virus. Comparison with BALF from controls identifies a critical imbalance in RAS represented by decreased expression of ACE in combination with increases in ACE2, renin, angiotensin, key RAS receptors, kinogen and many kallikrein enzymes that activate it, and both bradykinin receptors. This very atypical pattern of the RAS is predicted to elevate bradykinin levels in multiple tissues and systems that will likely cause increases in vascular dilation, vascular permeability and hypotension. These bradykinin-driven outcomes explain many of the symptoms being observed in COVID-19.

In late 2019, a new virus named SARS-CoV-2, which causes a disease in humans called COVID-19, emerged in China and quickly spread around the world. Many individuals infected with the virus develop only mild, symptoms including a cough, high temperature and loss of sense of smell; while others may develop no symptoms at all. However, some individuals develop much more severe, life-threatening symptoms affecting the lungs and other parts of the body including the heart and brain. SARS-CoV-2 uses a human enzyme called ACE2 like a 'Trojan Horse' to sneak into the cells of its host. ACE2 lowers blood pressure in the human body and works against another enzyme known as ACE (which has the opposite effect). Therefore, the body has to balance the levels of ACE and ACE2 to maintain a normal blood pressure. It remains unclear whether SARS-CoV-2 affects how ACE2 and ACE work. When COVID-19 first emerged, a team of researchers in China studied fluid and cells collected from the lungs of patients to help them identify the SARS-CoV-2 virus. Here, Garvin et al. analyzed the data collected in the previous work to investigate whether changes in how the body regulates blood pressure may contribute to the life-threatening symptoms of COVID-19. The analyses found that SARS-CoV-2 caused the levels of ACE in the lung cells to decrease, while the levels of ACE2 increased. This in turn increased the levels of a molecule known as bradykinin in the cells (referred to as a 'Bradykinin Storm'). . Previous studies have shown that bradykinin induces pain and causes blood vessels to expand and become leaky which will lead to swelling and inflammation of the surrounding tissue. In addition, the analyses found that production of a substance called hyaluronic acid was increased and the enzymes that could degrade it greatly decreased. Hyaluronic acid can absorb more than 1,000 times its own weight in water to form a hydrogel. The Bradykinin-Storm-induced leakage of fluid into the lungs combined with the excess hyaluronic acid would likely result in a Jello-like substance that is preventing oxygen uptake and carbon dioxide release in the lungs of severely affected COVID-19 patients. Therefore, the findings of Garvin et al. suggest that the Bradykinin Storm may be responsible for the more severe symptoms of COVID-19. Further experiments identified several existing medicinal drugs that have the potential to be re-purposed to treat the Bradykinin Storm. A possible next step would be to carry out clinical trials to assess how effective these drugs are in treating patients with COVID-19. In addition, understanding how SARS-Cov-2 affects the body will help researchers and clinicians identify individuals who are most at risk of developing life-threatening symptoms.

The pivotal link between ACE2 deficiency and SARS-CoV-2 infection.

Angiotensin converting enzyme-2 (ACE2) receptors mediate the entry into the cell of three strains of coronavirus: SARS-CoV, NL63 and SARS-CoV-2. ACE2 receptors are ubiquitous and widely expressed in the heart, vessels, gut, lung (particularly in type 2 pneumocytes and macrophages), kidney, testis and brain. ACE2 is mostly bound to cell membranes and only scarcely present in the circulation in a soluble form. An important salutary function of membrane-bound and soluble ACE2 is the degradation of angiotensin II to angiotensin1-7. Consequently, ACE2 receptors limit several detrimental effects resulting from binding of angiotensin II to AT1 receptors, which include vasoconstriction, enhanced inflammation and thrombosis. The increased generation of angiotensin1-7 also triggers counter-regulatory protective effects through binding to G-protein coupled Mas receptors. Unfortunately, the entry of SARS-CoV2 into the cells through membrane fusion markedly down-regulates ACE2 receptors, with loss of the catalytic effect of these receptors at the external site of the membrane. Increased pulmonary inflammation and coagulation have been reported as unwanted effects of enhanced and unopposed angiotensin II effects via the ACE→Angiotensin II→AT1 receptor axis. Clinical reports of patients infected with SARS-CoV-2 show that several features associated with infection and severity of the disease (i.e., older age, hypertension, diabetes, cardiovascular disease) share a variable degree of ACE2 deficiency. We suggest that ACE2 down-regulation induced by viral invasion may be especially detrimental in people with baseline ACE2 deficiency associated with the above conditions. The additional ACE2 deficiency after viral invasion might amplify the dysregulation between the 'adverse' ACE→Angiotensin II→AT1 receptor axis and the 'protective' ACE2→Angiotensin1-7→Mas receptor axis. In the lungs, such dysregulation would favor the progression of inflammatory and thrombotic processes triggered by local angiotensin II hyperactivity unopposed by angiotensin1-7. In this setting, recombinant ACE2, angiotensin1-7 and angiotensin II type 1 receptor blockers could be promising therapeutic approaches in patients with SARS-CoV-2 infection.