Recombinant Human Angiotensin-converting Enzyme 2 Research Articles

Perindopril decreases angiotensin-converting enzyme 2 (ACE2) expression in human adipocytes exposed to SARS-CoV-2 S1 spike protein

The expression of angiotensin-converting enzyme 2 (ACE2) in the adipose tissues of obese patients needs further study, as it may aid infection and serve as a viral reservoir. There has been controversy over whether to use ACE inhibitors to prevent coronavirus disease 2019 (COVID-19) severity. Perindopril, an ACE2 inhibitor, has been proposed; however, its relationship with COVID-19 has not yet been clear. The aim of this study was to investigate the effect of perindopril to reduce the expression of ACE2 and pro-inflammatory cytokine in adipocytes exposed to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Enzymatic isolation of adipose tissues was performed from obese male donor patients aged 30–50 years, then exposed it with SARS-CoV-2 S1 spike protein. This study also included human recombinant ACE2 (hrsACE2) as a comparison to perindopril. The expression of ACE2 was evaluated using ELISA. Our data indicated that SARS-CoV-2 Spike protein exposure increased ACE2 expression significantly. Administration of perindopril decreased ACE2 expression (43.37 µg/mL) significantly compared to the positive group (80.31 µg/mL) (p<0.001). Perindopril administration also decreased IL-6 levels significantly compared to positive group(p<0.001). This study highlights that perindopril could reduce the ACE2 expression and pro-inflammatory cytokine levels in adipocytes exposed to SARS-CoV-2 S1 spike protein.

Expression and purification of truncated recombinant human angiotensin converting enzyme 2 (trhACE2) capable of binding spike protein of SARS-CoV-2

SARS-CoV-2 infects the host through the interaction be-tween spike protein and the ACE2 (Angiotensin convert-ing enzyme 2) receptor on the host cell surface. There-fore, ACE2 is considered as a key target in drug devel-opment against COVID-19. In this study, we generated the truncated recombinant human ACE2 (trhACE2) expressed on Escherichia coli and evaluated its binding activity to spike protein of SARS-CoV-2. The sequence of ACE2 (18-119 aa) was cloned into pET28a(+) plasmid and transformed into E. coli DH5α strain and finally was transferred to E. coli BL21 (DE3) cells for protein expression. Protein trhACE2 was purified by affinity chromatography using a HisTrap HP column. Protein purity was above 95% and production yield was 75 mg/l. The purified protein was refolded by dialysis method. trhACE2 was evaluated for its ability to bind the spike protein by sandwich ELISA assay and surface plasmon resonance (SPR). The results showed that trhACE2 has the ability to bind spike protein of SARS-CoV-2 with the equilibrium dissociation constant Kd=15.7 nM. With a relatively simple and inexpensive expression and purifi-cation process on E. coli system, there is the potential to develop trhACE2 for preventive and supportive thera-pies against COVID-19.

Phase I dose-escalation study to assess the safety, tolerability, pharmacokinetics and pharmacodynamics of an inhaled recombinant human ACE2.

APN01 is a soluble recombinant human angiotensin-converting enzyme 2 (rhACE2), a key player in the renin-aldosterone-angiotensin system (RAAS). In clinical studies, APN01 was administered intravenously only, so far. The aim of this study (ClinicalTrials.gov: NCT05065645) was to evaluate the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of inhaled APN01. This was a phase I, double-blind, placebo-controlled, dose-escalation study. Inhalation was conducted via a nebuliser over 15 min in three single ascending dose (SAD) cohorts (n=24) and two multiple ascending dose (MAD) cohorts (n=16: every 12 h for 7 days). Doses in the SAD cohort were 1.25, 2.5 and 5 mg·mL-1; doses in the MAD cohort were 2.5 and 5 mg·mL-1. Safety (including adverse events (AEs), laboratory findings and lung function results), PK and PD data were assessed. In the SAD and MAD cohorts, treatment-related AEs were slightly more frequent in the active treatment group than in the placebo group. AEs were mild to moderate, with no dose-limiting toxicities. No clinically relevant changes in lung function and laboratory results were observed. The mean maximum observed plasma concentration (Cmax) values after single and multiple doses of 5 mg·mL-1 APN01 were 1.88 and 6.61 ng·mL-1, respectively. Among the PD variables, significance was found for ACE2 and angiotensin 1-5. The application of aerosolised APN01 is safe and well tolerated after single and multiple doses. By achieving a high local concentration in the lungs and low systemic bioavailability, inhaled rhACE2 may present a therapeutic option in ACE2-related diseases.

Efficient Expression in the Prokaryotic Host System, Purification and Structural Analyses of the Recombinant Human ACE2 Catalytic Subunit as a Hybrid Protein with the B Subunit of Cholera Toxin (CTB-ACE2).

Angiotensin-converting enzyme 2 (ACE2) has a specific interaction with the coronavirus spike protein, enabling its entry into human cells. This membrane enzyme converts angiotensin II into angiotensin 1-7, which has an essential role in protecting the heart and improving lung function. Many therapeutic properties have been attributed to the human recombinant ACE2 (hrACE2), especially in combating complications related to diabetes mellitus and hypertension, as well as, preventing the coronavirus from entering the target tissues. In the current study, we designed an appropriate gene construct for the hybrid protein containing the ACE2 catalytic subunit and the B subunit of cholera toxin (CTB-ACE2). This structural feature will probably help the recombinant hybrid protein enter the mucosal tissues, including the lung tissue. Optimization of this hybrid protein expression was investigated in BL21 bacterial host cells. Also, the hybrid protein was identified with an appropriate antibody using the ELISA method. A large amount of the hybrid protein (molecular weight of ~ 100kDa) was expressed as the inclusion body when the induction was performed in the presence of 0.25mM IPTG and 1% sucrose for 10h. Finally, the protein structural features were assessed using several biophysical methods. The fluorescence emission intensity and oligomeric size distribution of the CTB-ACE2 suggested a temperature-dependent alteration. The β-sheet and α-helix were also dominant in the hybrid protein structure, and this protein also displays acceptable chemical stability. In overall, according to our results, the efficient expression and successful purification of the CTB-ACE2 protein may pave the path for its therapeutic applications against diseases such as covid-19, diabetes mellitus and hypertension.

Mapping immunological and host receptor binding determinants of SARS-CoV spike protein utilizing the Qubevirus platform

The motifs involved in tropism and immunological interactions of SARS-CoV spike (S) protein were investigated utilizing the Qubevirus platform. We showed that separately, 14 overlapping peptide fragments representing the S protein (F1-14 of 100 residues each) could be inserted into the C-terminus of A1 on recombinant Qubevirus without affecting its viability. Additionally, recombinant phage expression resulted in the surface exposure of different engineered fragments in an accessible manner. The F6 from S425-525, was found to contain the binding determinant of the recombinant human angiotensin converting enzyme 2 (rhACE2), with the shortest active binding motif situated between residues S437-492. Upstream, another fragment, F7, containing an overlapping portion of F6 would not bind to rhACE2, confirming that a contiguous stretch of residues could adopt the appropriate structural orientation of F6 as an insertion within the Qubevirus. The F6 (S441-460) and other inserts, including F7/F8 (S601-620) and F10 (S781-800), were demonstrated to contain important immunological determinants through recognition and binding of S protein specific (anti-S) antibodies. An engineered chimeric insert bearing the fusion of all three anti-S reactive epitopes, improved substantially the recognition and binding to their cognate antibodies. These results provide insights into humoral immune relevant epitopes and tropism characteristics of the S protein with implications for the development of subunit vaccines or other biologics against SARS-CoV.

Molecular PET/CT mapping of rhACE2 distribution and quantification in organs to aid in SARS-CoV-2 targeted therapy.

Coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, poses a significant threat to public health. Angiotensin-converting enzyme 2 (ACE2) is a key receptor for SARS-CoV-2 infection. Recombinant human ACE2 (RhACE2), as a soluble supplement for human ACE2, can competitively block SARS-CoV-2 infection. In this study, a mouse organ in situ rhACE2high aggregation model was constructed for the first time, and in vivo real-time positron emission tomography (PET) imaging of rhACE2 in the mouse model was performed using an ACE2-specific agent 68 Ga-HZ20. This radiotracer exhibits reliable radiochemical properties in vitro and maintains a high affinity for rhACE2 in vivo. In terms of probe uptake, 68 Ga-HZ20 showed a good target-to-nontarget ratio and was rapidly cleared from the circulatory system and excreted by the kidneys and urinary system. PET imaging with this radiotracer can noninvasively and accurately monitor the content and distribution of rhACE2 in the body, which clarifies that rhACE2 can aggregate in multiple organs, suggesting the preventive and therapeutic potential of rhACE2 for SARS-CoV-2 and COVID-19.

Losartan Has a Comparable Effect to Human Recombinant ACE2 in Reducing Interleukin-6 (IL-6) Levels on Human Adipocytes Exposed to SARS-CoV-2 Spike Protein

BACKGROUND: High angiotensin-converting enzyme 2 (ACE2) expression in adipocyte cells facilitates the initiation of SARS-CoV-2 infection and triggers a cytokine storm. This finding suggests that obesity is an independent risk factor for the severity of the symptoms caused by COVID-19. The use of cardiovascular medications that focus on ACE2, such as angiotensin II receptor blockers, remains controversial, and their effects on inflammatory cytokine production and ACE2 expression in cells, especially adipocytes, remain inconsistent.METHODS: The human adipocytes were isolated from obese donor subcutaneous adipose tissue and infected with the subunit S1 spike protein from SARS-Cov-2. The adipocytes were later treated with either hrsACE2 or losartan. The levels of ACE2 and inflammatory cytokines interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α were measured using enzyme linked immunosorbent assay (ELISA). ACE2 and S1 spike protein binding assays were also performed. RESULTS: ACE2, IL-6, and TNF-α levels were significantly increased in human adipocyte cells infected with SARS-Cov-2 but not IL-1β. There was a statistically significant positive correlation between ACE2 and IL-6 (r=0.878, p<0.001). Administration of losartan and hrsACE2 was shown to reduce ACE2 levels and its binding to the SARS-CoV-2 S1 spike protein, and IL-6 levels were statistically significant, but had no significant effect on IL-1β or TNF-α levels.CONCLUSION: This study shows that the administration of losartan in COVID-19 may not be harmful, but instead has a protective effect similar to that of hrsACE2 in preventing a cytokine storm, especially IL-6.KEYWORDS: obesity, SARS-CoV-2, losartan, IL-6, ACE2

Lung Surfactant Protein B Peptide Mimics Interact with the Human ACE2 Receptor

Lung surfactant is a complex mixture of phospholipids and surfactant proteins that is produced in alveolar type 2 cells. It prevents lung collapse by reducing surface tension and is involved in innate immunity. Exogenous animal-derived and, more recently, synthetic lung surfactant has shown clinical efficacy in surfactant-deficient premature infants and in critically ill patients with acute respiratory distress syndrome (ARDS), such as those with severe COVID-19 disease. COVID-19 pneumonia is initiated by the binding of the viral receptor-binding domain (RBD) of SARS-CoV-2 to the cellular receptor angiotensin-converting enzyme 2 (ACE2). Inflammation and tissue damage then lead to loss and dysfunction of surface activity that can be relieved by treatment with an exogenous lung surfactant. Surfactant protein B (SP-B) is pivotal for surfactant activity and has anti-inflammatory effects. Here, we study the binding of two synthetic SP-B peptide mimics, Super Mini-B (SMB) and B-YL, to a recombinant human ACE2 receptor protein construct using molecular docking and surface plasmon resonance (SPR) to evaluate their potential as antiviral drugs. The SPR measurements confirmed that both the SMB and B-YL peptides bind to the rhACE2 receptor with affinities like that of the viral RBD–ACE2 complex. These findings suggest that synthetic lung surfactant peptide mimics can act as competitive inhibitors of the binding of viral RBD to the ACE2 receptor.

Computational and Enzymatic Studies of Sartans in SARS-CoV-2 Spike RBD-ACE2 Binding: The Role of Tetrazole and Perspectives as Antihypertensive and COVID-19 Therapeutics.

This study is an extension of current research into a novel class of synthetic antihypertensive drugs referred to as "bisartans", which are bis-alkylated imidazole derivatives bearing two symmetric anionic biphenyltetrazoles. Research to date indicates that bisartans are superior to commercially available hypertension drugs, since the former undergo stronger docking to angiotensin-converting enzyme 2 (ACE2). ACE2 is the key receptor involved in SARS-CoV-2 entry, thus initiating COVID-19 infection and in regulating levels of vasoactive peptides such as angiotensin II and beneficial heptapeptides A(1-7) and Alamandine in the renin-angiotensin system (RAS). In previous studies using in vivo rabbit-iliac arterial models, we showed that Na+ or K+ salts of selected Bisartans initiate a potent dose-response inhibition of vasoconstriction. Furthermore, computational studies revealed that bisartans undergo stable binding to the vital interfacial region between ACE2 and the SARS-CoV-2 "receptor binding domain" (i.e., the viral RBD). Thus, bisartan homologs are expected to interfere with SARS-CoV-2 infection and/or suppress disease expression in humans. The primary goal of this study was to investigate the role of tetrazole in binding and the network of amino acids of SARS-CoV-2 Spike RBD-ACE2 complex involved in interactions with sartans. This study would, furthermore, allow the expansion of the synthetic space to create a diverse suite of new bisartans in conjunction with detailed computational and in vitro antiviral studies. A critical role for tetrazole was uncovered in this study, shedding light on the vital importance of this group in the binding of sartans and bisartans to the ACE2/Spike complex. The in silico data predicting an interaction of tetrazole-containing sartans with ACE2 were experimentally validated by the results of surface plasmon resonance (SPR) analyses performed with a recombinant human ACE2 protein.

Extracts of plant-based yogurts inhibit recombinant human angiotensin converting enzyme 2 (rhACE2) activity

Little is known about how diet and nutraceuticals modulate Angiotensin-converting enzyme 2 (ACE2). Plant-based yogurts (PBYs) are potential sources of functional components and are made from a variety of plant-milks with varying cultures and protein sources. This study assessed the recombinant human (rh)ACE2 inhibitory activity of PBYs available in the United States. Extracts from 21 almond, cashew, coconut, oat and soy PBYs were screened for rhACE2 inhibitory activity. Among these samples, 9 PBYs inhibited recombinant human (rh)ACE2 by 50% at less than 50 mg/mL (dry weight (dw) PBY basis). Extracts of soy, almond, and oat PBYs were among the most active inhibitors, from 4-11 mg/mL IC50 (dw PBY). Among plant milks, soy milk extracts were more active rhACE2 inhibitors than oat or almond milks. Isoflavones contributed to activity, as purified isoflavones inhibited rhACE2. Therefore, rhACE2 inhibition by PBY varies considerably between products. These results suggest that there are a variety of nutraceuticals in PBYs that inhibit ACE2, and their bioactivity depends on the method of manufacturing and ingredient selection.

Recombinant human angiotensin-converting enzyme 2 plays a protective role in mice with sepsis-induced cardiac dysfunction through multiple signaling pathways dependent on converting angiotensin II to angiotensin 1-7.

Sepsis-induced cardiac dysfunction (SICD) is a common complication of sepsis and contributes to mortality and the complexity of management in patients with sepsis. Recombinant human angiotensin-converting enzyme 2 (rhACE2) has been reported to protect the heart from injury and dysfunction in conditions which involve increased angiotensin II (Ang II). In this study, we aimed to detect the effects of rhACE2 on SICD. A SICD model was developed in male C57/B6 mice by lipopolysaccharide (LPS) intraperitoneal injection. When cardiac dysfunction was confirmed by echocardiography 3 hours after LPS administration, mice were treated with either saline, rhACE2, or rhACE2 + A779. All mice received echocardiographic examination at 6 hours after LPS injection and then were sacrificed for serum and myocardial tissues collection. Angiotensin, cardiac troponin I (cTnI), and inflammatory markers in serum were measured. Histopathology features were examined by hematoxylin and eosin (HE) and terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) staining to evaluate structure injury and cell pyroptosis rate in heart tissue respectively. Pyroptosis-related proteins and signaling pathways involved in nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome activation in heart tissue were investigated by western blot (WB). RhACE2 relieved myocardial injury and improved cardiac function in mice with SICD accompanied by decrease of Ang II and increase of angiotensin 1-7 (Ang 1-7) in serum. RhACE2 diminished activation of NLRP3 inflammasome, inflammatory response, and cell pyroptosis induced by LPS. In addition, rhACE2 partly inhibited activation of nuclear factor κB (NF-κB), the p38 mitogen-activated protein kinase (MAPK) pathway, and promoted activation of the AMP-activated protein kinase-α1 (AMPK-α1) pathway in heart tissue. Administration of A779 offset the inhibitive effects of rhACE2 on NLRP3 expression and protective role on cardiac injury and dysfunction in mice with SICD. RhACE2 plays a protective role in SICD, ameliorating cardiac injury and dysfunction through NF-κB, p38 MAPK, and the AMPK-α1/NLRP3 inflammasome pathway dependent on converting Ang II to Ang 1-7.

Effects of Two Soluble ACE2-Fc Variants on Blood Pressure and Albuminuria in Hypertensive Mice: Research Letter.

Angiotensin-converting enzyme 2 (ACE2) hydrolyzes angiotensin (Ang) II to Ang-(1-7), promoting vasodilatation, and inhibiting oxidative stress and inflammation. Plasma membrane ACE2 is the receptor for all known SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) viral variants. In COVID-19 infection, soluble ACE2 variants may act as decoys to bind and neutralize the coronavirus, reducing its tissue infectivity. Furthermore, soluble ACE2 variants have been proposed as potential therapeutics for kidney disease and hypertensive disorders. Soluble ACE2 variants conjugated to human Fc domains and selected for high-potency viral SARS-CoV-2 neutralization were prepared and evaluated for ACE2 activity in vitro. Lead candidates were then tested for systemic ACE2 activity, stability, and effects on blood pressure and albuminuria in mice with Ang II-induced hypertension. ACE2 activity of 10 soluble ACE2 variants was first assessed in cell-free conditions using a fluorogenic substrate, or by Ang II hydrolysis to Ang-(1-7). Hypertension was induced in male or female mice by implantation of osmotic minipumps containing Ang II. Two lead ACE2 variants were injected intravenously (i.v.) into hypertensive mice, followed by measurements of blood pressure (tail-cuff plethysmography), albuminuria, and tissue ACE2 activity and protein (immunoblots). Soluble ACE2-Fc variants demonstrated significant ACE2 enzymatic activity, with kinetics comparable with human recombinant ACE2. In hypertensive mice, single dose i.v. injection of ACE2-Fc variant K (10 mg/kg) significantly decreased systolic blood pressure at 24 hours, with partial lowering sustained to 48 hours, and tendency to reduce albuminuria at 72 hours. By contrast, ACE2-Fc variant I had no effect on blood pressure or albuminuria in hypertensive mice; ACE2-Fc variant K was detected by immunoblotting in plasma, kidney, heart, lung, liver, and spleen lysates 72 hours after injection, associated with significantly increased ACE2 activity in all tissues except kidney and spleen. Angiotensin-converting enzyme 2-Fc variant I had no effect on plasma ACE2 activity. Soluble ACE2-Fc variant K reduces blood pressure and tends to lower albuminuria in hypertensive mice. Furthermore, soluble ACE2-Fc variant K has prolonged tissue retention, associated with increased tissue ACE2 activity. The results support further studies directed at the therapeutic potential of soluble ACE2-Fc variant K for cardiovascular and kidney protection.

Is targeting angiotensin-converting enzyme 2 (ACE2) a prophylactic strategy against COVID-19?

Prophylaxis against COVID-19 is greatly needed for vulnerable populations who have a higher risk of developing severe disease. Vaccines and neutralizing antibodies against SARS-CoV-2 are currently the main approaches to preventing the virus infection. However, the constant mutation of SARS-CoV-2 poses a huge challenge to the effectiveness of these prophylactic strategies. A recent study suggested that downregulation of angiotensin-converting enzyme 2 (ACE2), the receptor of SARS-CoV-2 entry into human cells, can decrease susceptibility to viral infection in vitro, in vivo, and in human lungs and livers perfused ex situ. These findings indicate the potential to use agents to reduce ACE2 expression to prevent COVID-19, but the efficacy and safety should be verified in clinical trials. Considering ACE2 performs physiological functions, risks due to its downregulation and benefits from prophylaxis against SARS-CoV-2 infection should be carefully weighed. In the future, updating vaccines against variants of SARS-CoV-2 might still be an important strategy for prophylaxis against COVID-19. Soluble recombinant human ACE2 that acts as a decoy receptor might be an option to overcome the mutation of SARS-CoV-2.

Circulating angiotensin converting enzyme 2 and COVID-19.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has triggered a widespread outbreak since December 2019. The SARS-CoV-2 infection-related illness has been dubbed the coronavirus disease 2019 (COVID-19) by the World Health Organization. Asymptomatic and subclinical infections, a severe hyper-inflammatory state, and mortality are all examples of clinical signs. After attaching to the angiotensin converting enzyme 2 (ACE2) receptor, the SARS-CoV-2 virus can enter cells through membrane fusion and endocytosis. In addition to enabling viruses to cling to target cells, the connection between the spike protein (S-protein) of SARS-CoV-2 and ACE2 may potentially impair the functionality of ACE2. Blood pressure is controlled by ACE2, which catalyzes the hydrolysis of the active vasoconstrictor octapeptide angiotensin (Ang) II to the heptapeptide Ang-(1-7) and free L-Phe. Additionally, Ang I can be broken down by ACE2 into Ang-(1-9) and metabolized into Ang-(1-7). Numerous studies have demonstrated that circulating ACE2 (cACE2) and Ang-(1-7) have the ability to restore myocardial damage in a variety of cardiovascular diseases and have anti-inflammatory, antioxidant, anti-apoptotic, and anti-cardiomyocyte fibrosis actions. There have been some suggestions for raising ACE2 expression in COVID-19 patients, which might be used as a target for the creation of novel treatment therapies. With regard to this, SARS-CoV-2 is neutralized by soluble recombinant human ACE2 (hrsACE2), which binds the viral S-protein and reduces damage to a variety of organs, including the heart, kidneys, and lungs, by lowering Ang II concentrations and enhancing conversion to Ang-(1-7). This review aims to investigate how the presence of SARS-CoV-2 and cACE2 are related. Additionally, there will be discussion of a number of potential therapeutic approaches to tip the ACE/ACE-2 balance in favor of the ACE-2/Ang-(1-7) axis.

An albumin-angiotensin converting enzyme 2-based SARS-CoV-2 decoy with FcRn-driven half-life extension

The emergence of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mutants and breakthrough infections despite available coronavirus disease 2019 (COVID-19) vaccines calls for antiviral therapeutics. The application of soluble angiotensin converting enzyme 2 (ACE2) as a SARS-CoV-2 decoy that reduces cell bound ACE2-mediated virus entry is limited by a short plasma half-life. This work presents a recombinant human albumin ACE2 genetic fusion (rHA-ACE2) to increase the plasma half-life by an FcRn-driven cellular recycling mechanism, investigated using a wild type (WT) albumin sequence and sequence engineered with null FcRn binding (NB). Binding of rHA-ACE2 fusions to SARS-CoV-2 spike protein subdomain 1 (S1) was demonstrated (WT-ACE2 KD = 32.8 nM and NB-ACE2 KD = 31.7 nM) using Bio-Layer Interferometry and dose-dependent in vitro inhibition of host cell infection of pseudotyped viruses displaying surface SARS-CoV-2 spike (S) protein. FcRn-mediated in vitro recycling was translated to a five times greater plasma half-life of WT-ACE2 (t½ β = 13.5 h) than soluble ACE2 (t½ β = 2.8 h) in humanised FcRn/albumin double transgenic mice. The rHA-ACE2-based SARS-CoV-2 decoy system exhibiting FcRn-driven circulatory half-life extension introduced in this work offers the potential to expand and improve the anti-COVID-19 anti-viral drug armoury. Statement of significanceThe COVID-19 pandemic has highlighted the need for rapid development of efficient antiviral therapeutics to combat SARS-CoV-2 and new mutants to lower morbidity and mortality in severe cases, and for people that are unable to receive a vaccine. Here we report a therapeutic albumin ACE2 fusion protein (rHA-ACE2), that can bind SARS-CoV-2 S protein decorated virus-like particles to inhibit viral infection, and exhibits extended in vivo half-life compared to ACE2 alone. Employing ACE2 as a binding decoy for the virus is expected to efficiently inhibit all SARS-CoV-2 mutants as they all rely on binding with endogenous ACE2 for viral cell entry and, therefore, rHA-ACE2 constitutes a versatile addition to the therapeutic arsenal for combatting COVID-19.

Is Diminazene an Angiotensin-Converting Enzyme 2 (ACE2) Activator? Experimental Evidence and Implications.

Antiprotozoal veterinary drug diminazene aceturate (DIZE) has been proposed to be an angiotensin-converting enzyme 2 (ACE2) activator. Since then, DIZE was used in dozens of experimental studies, but its mechanism of action attributed to ACE2 activation and enhanced formation of angiontensin-(1-7) [Ang-(1-7)] from Ang II was not carefully verified. The aim of this study was to confirm the effect of DIZE on catalytic activity of ACE2 and extend it to other peptidases involved in formation and degradation of Ang-(1-7). Concentration-dependent effect of DIZE on the initial rate of a fluorogenic substrate hydrolysis by human and mouse recombinant ACE2 was measured at assay conditions imitating that of the original report, but no activation of ACE2 was documented. Similar results were obtained with a more physiologically relevant assay buffer. In addition, DIZE did not affect activity of recombinant neprilysin, neurolysin, thimet oligopeptidase, and ACE. Efficiency of the fluorogenic substrate hydrolysis (Vmax/Km value) by ACE2 in response to different concentrations of DIZE was also measured, but no substantial effects were documented. Likewise, DIZE failed to enhance the hydrolysis of ACE2 endogenous substrate Ang II. Identity of the commercial recombinant ACE2 variants used in these experiments was confirmed by inhibition with two well characterized inhibitors (DX600 and MLN4760), activation by NaCl, and Western Blotting using validated antibodies. These observations challenge the widely accepted notion about the molecular mechanism of DIZE action and call for not ascribing this molecule as an ACE2 activator. SIGNIFICANCE STATEMENT: DIZE has been proposed and widely used in experimental studies as an ACE2 activator. The detailed in vitro pharmacological studies failed to confirm that DIZE is an ACE2 activator. In addition, DIZE did not substantially affect the activity of other peptidases involved in formation and degradation of angiotensin-(1-7). Researchers should refrain from calling DIZE an ACE2 activator. Other mechanisms are responsible for the therapeutic benefits attributed to DIZE.

Study to Explore the Association of the Renin-Angiotensin System and Right Ventricular Function in Mechanically Ventilated Patients.

Background: Right ventricular (RV) dysfunction is associated with pulmonary vasoconstriction in mechanically ventilated patients. Enhancing the activity of angiotensin-converting enzyme 2 (ACE2), a key enzyme of the renin-angiotensin system (RAS), using recombinant human ACE2 (rhACE2) could alleviate RAS-mediated vasoconstriction and vascular remodeling. Methods: This prospective observational study investigated the association between concentrations of RAS peptides (Ang II or Ang(1–7)) and markers of RV function, as assessed by echocardiography (ratio of RV to left ventricular end-diastolic area, interventricular septal motion, and pulmonary arterial systolic pressure (PASP)). Results: Fifty-seven mechanically ventilated patients were enrolled. Incidence rates of acute cor pulmonale (ACP) and pulmonary circulatory dysfunction (PCD) were consistent with previous studies. In the 45 evaluable participants, no notable or consistent changes in RAS peptides concentration were observed over the observation period, and there was no correlation between Ang II concentration and either PASP or RV size. The model of the predicted posterior distributions for the pre- and post-dose values of Ang II demonstrated no change in the likelihood of PCD after hypothetical dosing with rhACE2, thus meeting the futility criteria. Similar results were observed with the other RAS peptides evaluated. Conclusions: Pre-defined success criteria for an association between PCD and the plasma RAS peptides were not met in the mechanically ventilated unselected patients.

ACE2-like enzyme B38-CAP suppresses abdominal sepsis and severe acute lung injury.

Angiotensin-converting enzyme 2 (ACE2) is the carboxypeptidase to degrade angiotensin II (Ang II) to angiotensin 1–7 (Ang 1–7) and improves the pathologies of cardiovascular disease and acute respiratory distress syndrome (ARDS)/acute lung injury. B38-CAP is a bacteria-derived ACE2-like carboxypeptidase as potent as human ACE2 and ameliorates hypertension, heart failure and SARS-CoV-2-induced lung injury in mice. Recombinant B38-CAP is prepared with E. coli protein expression system more efficiently than recombinant soluble human ACE2. Here we show therapeutic effects of B38-CAP on abdominal sepsis- or acid aspiration-induced acute lung injury. ACE2 expression was downregulated in the lungs of mice with cecal ligation puncture (CLP)-induced sepsis or acid-induced lung injury thereby leading to upregulation of Ang II levels. Intraperitoneal injection of B38-CAP significantly decreased Ang II levels while upregulated angiotensin 1–7 levels. B38-CAP improved survival rate of the mice under sepsis. B38-CAP suppressed the pathologies of lung inflammation, improved lung dysfunction and downregulated elevated cytokine mRNA levels in the mice with acute lung injury. Thus, systemic treatment with an ACE2-like enzyme might be a potential therapeutic strategy for the patients with severe sepsis or ARDS.

Utilization of SUMO Tag and Freeze-thawing Method for a High-level Expression and Solubilization of Recombinant Human Angiotensinconverting Enzyme 2 (rhACE2) Protein in E. coli

SARS-CoV-2 uses angiotensin-converting enzyme 2 (ACE2) as a receptor for entering the host cells. Production of the ACE2 molecule is important because of its potency to use as a blocker and therapeutic agent against SARS-CoV-2 for the prophylaxis and treatment of COVID-19. The recombinant human ACE2 (rhACE2) is prone to form an inclusion body when expressed in the bacterial cells. We used the SUMO tag fused to the rhACE2 molecule to increase the expression level and solubility of the fusion protein. Afterward, the freeze-thawing method plus 2 M urea solubilized aggregated proteins. Subsequently, the affinity of solubilized rhACE2 to the receptor binding domain (RBD) of the SARS-CoV-2 spike was assayed by ELISA and SPR methods. SUMO protein succeeded in increasing the expression level but not solubilization of the fusion protein. The freeze-thawing method could solubilize and recover the aggregated fusion proteins significantly. Also, ELISA and SPR assays confirmed the interaction between solubilized rhACE2 and RBD with high affinity. The SUMO tag and freeze- Conclusion: The SUMO tag and freeze-thawing method would be utilized for high-level expression and solubilization of recombinant rhACE2 protein.

Restoration of Brain Angiotensin-Converting Enzyme 2 Alleviates Neurological Deficits after Severe Traumatic Brain Injury via Mitigation of Pyroptosis and Apoptosis.

Clinically, the renin-angiotensin-aldosterone system is activated intensely in patients with moderate to severe traumatic brain injury (TBI). Increased angiotensin II in circulatory blood after TBI can enter the brain through the disrupted blood-brain barrier. Angiotensin-converting enzyme 2 (ACE2) is an enzyme that metabolizes angiotensin II into angiotensin (1-7), which has been shown to have neuroprotective results. The expression and role of ACE2 in the brain after TBI remains elusive, however. We found that ACE2 protein abundance was downregulated around the contusional area in the brains of both humans and mice. Endogenous ACE2 was expressed in neurons, astrocytes, and microglia in the cortex of the mouse brain. Administration of recombinant human ACE2 intracerebroventricularly alleviated neurological defects after TBI in mice. Treatment of recombinant human ACE2 suppressed TBI-induced increase of angiotensin II and the decrease of angiotensin (1-7) in the brain, mitigated neural cell death, reduced the activation of NLRP3 and caspase3, decreased phosphorylation of mitogen-activated protein kinases, and nuclear factor kappa B, and reduced inflammatory cytokines tumor necrosis factor alpha and interleukin-1β. Administration of ACE2 enzyme activator diminazene aceturate intraperitoneally rescued downregulation of ACE2 enzymatic activity and protein abundance in the brain. Diminazene aceturate treatment once per day in the acute stage after TBI alleviated long-term cognitive defects and neuronal loss in mice. Collectively, these results indicated that restoration of ACE2 alleviated neurological deficits after TBI by mitigation of pyroptosis and apoptosis.