A Fluorometric Method of Measuring Carboxypeptidase Activities for Angiotensin II and Apelin-13

A cell-based assay for rapid assessment of ACE2 catalytic function

Angiotensin-converting enzyme II (ACE2) is a monocarboxypeptidase expressed throughout multiple tissues and its catalysis of bioactive peptides regulates the renin-angiotensin system mediating blood pressure homeostasis. ACE2 is implicated in a variety of diseases, including obesity, diabetes, and cardiovascular diseases, and is the obligate entry receptor for SARS-CoV-2 infection. Disease-associated genetic variants of ACE2 are increasingly being identified but are poorly characterized. To aid this problem, we introduce a fluorometric cell-based assay for evaluating surface-expressed ACE2 catalytic activity that preserves the native glycosylation of the host environment and is amenable to high-throughput analysis of ACE2 variants in multi-well plates. We demonstrate sensitivity to detecting catalysis of the key ACE2 substrates, Angiotensin II, Apelin-13, and des-Arg9-bradykinin, and impact of a catalytically-deficient ACE2 variant. Normalizing catalytic measures to surface ACE2 expression accounts for variability in ACE2 variant transfection, surface delivery or stability. This assay provides a convenient and powerful approach for investigating the catalytic characteristics of ACE2 variants involved in cardiovascular peptide cascades and homeostasis of multiple organs.

Engineered ACE2-Fc counters murine lethal SARS-CoV-2 infection through direct neutralization and Fc-effector activities

Soluble angiotensin-converting enzyme 2 (ACE2) constitutes an attractive antiviral capable of targeting a wide range of coronaviruses using ACE2 as their receptor. Using structure-guided approaches, we developed a series of bivalent ACE2-Fcs harboring functionally and structurally validated mutations that enhance severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor binding domain recognition by up to ~12-fold and remove angiotensin enzymatic activity. The lead variant M81 potently cross-neutralized SARS-CoV-2 variants of concern (VOCs), including Omicron, at subnanomolar half-maximal inhibitory concentration and was capable of robust Fc-effector functions, including antibody-dependent cellular cytotoxicity, phagocytosis, and complement deposition. When tested in a stringent K18-hACE2 mouse model, Fc-enhanced ACE2-Fc delayed death by 3 to 5 days or effectively resolved lethal SARS-CoV-2 infection in both prophylactic and therapeutic settings via the combined effects of neutralization and Fc-effector functions. These data add to the demonstrated utility of soluble ACE2 as a valuable SARS-CoV-2 antiviral and indicate that Fc-effector functions may constitute an important component of ACE2-Fc therapeutic activity.

Renin-Angiotensin System Induced Secondary Hypertension: The Alteration of Kidney Function and Structure

Long-term hypertension is known as a major risk factor for cardiovascular and chronic kidney disease (CKD). The Renin-angiotensin system (RAS) plays a key role in hypertension pathogenesis. Angiotensin II (Ang II) enhancement in Ang II-dependent hypertension leads to progressive CKD and kidney fibrosis. In the two-kidney one-clip model (2K1C), more renin is synthesized in the principal cells of the collecting duct than juxtaglomerular cells (JGCs). An increase of renal Ang I and Ang II levels and a decrease of renal cortical and medullary Ang 1–7 occur in both kidneys of the 2K1C hypertensive rat model. In addition, the activity of the angiotensin-converting enzyme (ACE) increases, while ACE2's activity decreases in the medullary region of both kidneys in the 2K1C hypertensive model. Also, the renal prolyl carboxypeptidase (PrCP) expression and its activity reduce in the clipped kidneys. The imbalance in the production of renal ACE, ACE2, and PrCP expression causes the progression of renal injury. Intrarenal angiotensinogen (AGT) expression and urine AGT (uAGT) excretion rates in the unclipped kidney are greater than the clipped kidney in the 2K1C hypertensive rat model. The enhancement of Ang II in the clipped kidney is related to renin secretion, while the elevation of intrarenal Ang II in the unclipped kidney is related to stimulation of AGT mRNA and protein in proximal tubule cells by a direct effect of systemic Ang II level. Ang II-dependent hypertension enhances macrophages and T-cell infiltration into the kidney which increases cytokines, and AGT synthesis in proximal tubules is stimulated via cytokines. Accumulation of inflammatory cells in the kidney aggravates hypertension and renal damage. Moreover, Ang II-dependent hypertension alters renal Ang II type 1 & 2 receptors (AT₁R & AT₂R) and Mas receptor (MasR) expression, and the renal interstitial fluid bradykinin, nitric oxide, and cGMP response to AT₁R, AT₂R, or BK B₂-receptor antagonists. Based on a variety of sources including PubMed, Google Scholar, Scopus, and Science-Direct, in the current review, we will discuss the role of RAS-induced secondary hypertension on the alteration of renal function.

A Novel Soluble ACE2 Variant with Prolonged Duration of Action Neutralizes SARS-CoV-2 Infection in Human Kidney Organoids

BACKGROUND

There is an urgent need for approaches to prevent and treat SARS-CoV-2 infection. Administration of soluble ACE2 protein acting as a decoy to bind to SARS-CoV-2 should limit viral uptake mediated by binding to membrane-bound full-length ACE2, and further therapeutic benefit should result from ensuring enzymatic ACE2 activity to affected organs in patients with COVID-19.

METHODS

A short variant of human soluble ACE2 protein consisting of 618 amino acids (hACE2 1-618) was generated and fused with an albumin binding domain (ABD) using an artificial gene encoding ABDCon, with improved albumin binding affinity. Human kidney organoids were used for infectivity studies of SARS-CoV-2 in a BSL-3 facility to examine the neutralizing effect of these novel ACE2 variants.

RESULTS

Whereas plasma ACE2 activity of the naked ACE2 1-618 and ACE2 1-740 lasted about 8 hours, the ACE2 1-618-ABD resulted in substantial activity at 96 hours, and it was still biologically active 3 days after injection. Human kidney organoids express ACE2 and TMPRSS2, and when infected with SARS-CoV-2, our modified long-acting ACE2 variant neutralized infection.

CONCLUSIONS

This novel ACE2 1-618-ABD can neutralize SARS-CoV-2 infectivity in human kidney organoids, and its prolonged duration of action should ensure improved efficacy to prevent viral escape and dosing convenience.

A Fluorogenic Assay: Analysis of Chemical Modification of Lysine and Arginine to Control Proteolytic Activity of Trypsin

The chemical modification of amino acids plays an important role in the modulation of proteins or peptides and has useful applications in the activation and stabilization of enzymes, chemical biology, shotgun proteomics, and the production of peptide-based drugs. Although chemoselective modification of amino acids such as lysine and arginine via the insertion of respective chemical moieties as citraconic anhydride and phenyl glyoxal is important for achieving desired application objectives and has been extensively reported, the extent and chemoselectivity of the chemical modification of specific amino acids using specific chemical agents (blocking or modifying agents) has yet to be sufficiently clarified owing to a lack of suitable assay methodologies. In this study, we examined the utility of a fluorogenic assay method, based on a fluorogenic tripeptide substrate (FP-AA1-AA2-AA3) and the proteolytic enzyme trypsin, in determinations of the extent and chemoselectivity of the chemical modification of lysine or arginine. As substrates, we used two fluorogenic tripeptide probes, MeRho-Lys-Gly-Leu(Ac) (lysine-specific substrate) and MeRho-Arg-Gly-Leu(Ac) (arginine-specific substrate), which were designed, synthesized, and evaluated for chemoselective modification of specific amino acids (lysine and arginine) using the fluorogenic assay. The results are summarized in terms of half-maximal inhibitory concentrations (IC50) for the extent of modification and ratios of IC50 values (IC50arginine/IC50lysine and IC50lysine/IC50arginine) as a measure of the chemoselectivity of chemical modification for amino acids lysine and arginine. This novel fluorogenic assay was found to be rapid, precise, and reproducible for determinations of the extent and chemoselectivity of chemical modification.

SARS-CoV-2 spike protein binding selectively accelerates substrate-specific catalytic activity of ACE2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus that has given rise to the devastating global pandemic. In most cases, SARS-CoV-2 infection results in the development of viral pneumonia and acute respiratory distress syndrome, known as ‘coronavirus disease 2019’ or COVID-19. Intriguingly, besides the respiratory tract, COVID-19 affects other organs and systems of the human body. COVID-19 patients with pre-existing cardiovascular disease have a higher risk of death, and SARS-CoV-2 infection itself may cause myocardial inflammation and injury. One possible explanation of such phenomena is the fact that SARS-CoV-2 utilizes angiotensin-converting enzyme 2 (ACE2) as the receptor required for viral entry. ACE2 is expressed in the cells of many organs, including the heart. ACE2 functions as a carboxypeptidase that can cleave several endogenous substrates, including angiotensin II, thus regulating blood pressure and vascular tone. It remains largely unknown if the SARS-CoV-2 infection alters the enzymatic properties of ACE2, thereby contributing to cardiovascular complications in patients with COVID-19. Here, we demonstrate that ACE2 cleavage of des-Arg9-bradykinin substrate analogue is markedly accelerated, while cleavage of angiotensin II analogue is minimally affected by the binding of spike protein. These findings may have implications for a better understanding of COVID-19 pathogenesis.

Fuyuan Xingnao Decoction Promotes Angiogenesis Through the Rab1/AT1R Pathway in Diabetes Mellitus Complicated With Cerebral Infarction

Fuyuan Xingnao decoction (FYXN), a traditional Chinese formula comprised of seven herbs, has been utilized to treat diabetes mellitus complicated with cerebral infarction (DMCI) for years. Yet, its protective and regulatory mechanism is poorly understood. The aim of the study is to investigate the effects of FYXN on DMCI in vitro and in vivo, as well as its mechanism in angiogenesis. For in vivo experiments, FYXN was administered to DMCI rats with streptozotocin (STZ) injection-induced diabetes. Then middle cerebral artery occlusion (MCAO) was conducted and the cerebral cortex sections of the rats were obtained. The ultrastructure of cerebral microvessels and new vessel density of ischemic penumbra were evaluated by the transmission electron microscopy (TEM) assay and immunohistochemistry, respectively. Protein and mRNA expression levels of Rab1/AT1R in cortex were assayed by Western blotting and real-time fluorescence quantitative real-time polymerase chain reaction (RT-qPCR). In vitro, FYXN serum was produced in rats on the fourth day 2 h after the last FYXN administration. Green fluorescence was observed after transfection with lentivirus packaged Rab1-WT or siRNA for 24 h. The activity of brain microvascular endothelial cells (BMECs) treated with sera from these rats was tested by MTT assay and Transwell assays, respectively. The expression of AT1R on the cell membrane and endoplasmic reticulum of BMECs was evaluated by immunofluorescence staining. Protein expression levels of signaling molecules in the Rab1/AT1R pathways were also detected. Results showed that in vivo, FYXN treatment significantly intensified CD31 staining in the cortical areas and enhanced the mRNA and protein levels of AT1R, Ang II, Rab1a, Rab1b and VEGF expression in ischemic cerebral cortex tissues. In vitro, the expression levels of AT1R, Ang II, Rab1a, Rab1b and VEGF in the cerebral infarction model group were significantly higher than those in the control group, with further increases after administration of FYXN drug serum. FYXN promoted the proliferation and migration of BMECs by activating the Rab1/AT1R signaling pathway. In conclusion, FYXN exerts a protective effect against DMCI by promoting angiogenesis via the Rab1/AT1R pathway, which provides strong evidence for the therapeutic effect of FYXN on DMCI.

Designed variants of ACE2-Fc that decouple anti-SARS-CoV-2 activities from unwanted cardiovascular effects

Angiotensin-converting enzyme 2 (ACE2) is the entry receptor for SARS-CoV-2, and recombinant ACE2 decoys are being evaluated as new antiviral therapies. We designed and tested an antibody-like ACE2-Fc fusion protein, which has the benefit of long pharmacological half-life and the potential to facilitate immune clearance of the virus. Out of a concern that the intrinsic catalytic activity of ACE2 may unintentionally alter the balance of its hormonal substrates and cause adverse cardiovascular effects in treatment, we performed a mutagenesis screening for inactivating the enzyme. Three mutants, R273A, H378A and E402A, completely lost their enzymatic activity for either surrogate or physiological substrates. All of them remained capable of binding SARS-CoV-2 and could suppress the transduction of a pseudotyped virus in cell culture. This study established new ACE2-Fc candidates as antiviral treatment for SARS-CoV-2 without potentially harmful side effects from ACE2's catalytic actions toward its vasoactive substrates.

Severe Acute Respiratory Syndrome Coronavirus 2, COVID-19, and the Renin-Angiotensin System: Pressing Needs and Best Research Practices

The coronavirus disease 2019 (COVID-19) pandemic is associated with significant morbidity and mortality throughout the world, predominantly due to lung and cardiovascular injury. The virus responsible for COVID-19-severe acute respiratory syndrome coronavirus 2-gains entry into host cells via ACE2 (angiotensin-converting enzyme 2). ACE2 is a primary enzyme within the key counter-regulatory pathway of the renin-angiotensin system (RAS), which acts to oppose the actions of Ang (angiotensin) II by generating Ang-(1-7) to reduce inflammation and fibrosis and mitigate end organ damage. As COVID-19 spans multiple organ systems linked to the cardiovascular system, it is imperative to understand clearly how severe acute respiratory syndrome coronavirus 2 may affect the multifaceted RAS. In addition, recognition of the role of ACE2 and the RAS in COVID-19 has renewed interest in its role in the pathophysiology of cardiovascular disease in general. We provide researchers with a framework of best practices in basic and clinical research to interrogate the RAS using appropriate methodology, especially those who are relatively new to the field. This is crucial, as there are many limitations inherent in investigating the RAS in experimental models and in humans. We discuss sound methodological approaches to quantifying enzyme content and activity (ACE, ACE2), peptides (Ang II, Ang-[1-7]), and receptors (types 1 and 2 Ang II receptors, Mas receptor). Our goal is to ensure appropriate research methodology for investigations of the RAS in patients with severe acute respiratory syndrome coronavirus 2 and COVID-19 to ensure optimal rigor and reproducibility and appropriate interpretation of results from these investigations.

Development and validation of an LC-MS/MS method for detection and quantification of in vivo derived metabolites of [Pyr1]apelin-13 in humans

[Pyr1]apelin-13 is the predominant apelin peptide isoform in the human cardiovascular system and plasma. To date, few studies have investigated [Pyr1]apelin-13 metabolism in vivo in rats with no studies examining its stability in humans. We therefore aimed to develop an LC-MS/MS method for detection and quantification of intact [Pyr1]apelin-13 and have used this method to identify the metabolites generated in vivo in humans. [Pyr1]apelin-13 (135 nmol/min) was infused into six healthy human volunteers for 120 minutes and blood collected at time 0 and 120 minutes after infusion. Plasma was extracted in the presence of guanidine hydrochloride and analysed by LC-MS/MS. Here we report a highly sensitive, robust and reproducible method for quantification of intact [Pyr1]apelin-13 and its metabolites in human plasma. Using this method, we showed that the circulating concentration of intact peptide was 58.3 ± 10.5 ng/ml after 120 minutes infusion. We demonstrated for the first time that in humans, [Pyr1]apelin-13 was cleaved from both termini but the C-terminal was more susceptible to cleavage. Consequently, of the metabolites identified, [Pyr1]apelin-13(1-12), [Pyr1]apelin-13(1-10) and [Pyr1]apelin-13(1-6) were the most abundant. These data suggest that apelin peptides designed for use as cardiovascular therapeutics, should include modifications that minimise C-terminal cleavage.

Novel Variants of Angiotensin Converting Enzyme-2 of Shorter Molecular Size to Target the Kidney Renin Angiotensin System

ACE2 is a monocarboxypeptidase which generates Angiotensin (1-7) from Angiotensin II (1-8). Attempts to target the kidney Renin Angiotensin System using native ACE2 to treat kidney disease are hampered by its large molecular size, 100 kDa, which precludes its glomerular filtration and subsequent tubular uptake. Here, we show that both urine and kidney lysates are capable of digesting native ACE2 into shorter proteins of ~60-75 kDa and then demonstrate that they are enzymatically very active. We then truncated the native ACE2 by design from the C-terminus to generate two short recombinant (r)ACE2 variants (1-605 and 1-619AA). These two truncates have a molecular size of ~70 kDa, as expected from the amino acid sequence and as shown by Western blot. ACE2 enzyme activity, measured using a specific substrate, was higher than that of the native rACE2 (1-740 AA). When infused to mice with genetic ACE2 deficiency, a single i.v. injection of 1-619 resulted in detectable ACE2 activity in urine, whereas infusion of the native ACE2 did not. Moreover, ACE2 activity was recovered in harvested kidneys from ACE2-deficient mice infused with 1-619, but not in controls (23.1 ± 4.3 RFU/µg creatinine/h and 1.96 ± 0.73 RFU/µg protein/hr, respectively). In addition, the kidneys of ACE2-null mice infused with 1-619 studied ex vivo formed more Ang (1-7) from exogenous Ang II than those infused with vehicle (AUC 8555 ± 1933 vs. 3439 ± 753 ng/mL, respectively, p < 0.05) further demonstrating the functional effect of increasing kidney ACE2 activity after the infusion of our short ACE2 1-619 variant. We conclude that our novel short recombinant ACE2 variants undergo glomerular filtration, which is associated with kidney uptake of enzymatically active proteins that can enhance the formation of Ang (1-7) from Ang II. These small ACE2 variants may offer a potentially useful approach to target kidney RAS overactivity to combat kidney injury.

Ang II (Angiotensin II) Conversion to Angiotensin-(1-7) in the Circulation Is POP (Prolyloligopeptidase)-Dependent and ACE2 (Angiotensin-Converting Enzyme 2)-Independent

The Ang II (Angiotensin II)-Angiotensin-(1-7) axis of the Renin Angiotensin System encompasses 3 enzymes that form Angiotensin-(1-7) [Ang-(1-7)] directly from Ang II: ACE2 (angiotensin-converting enzyme 2), PRCP (prolylcarboxypeptidase), and POP (prolyloligopeptidase). We investigated their relative contribution to Ang-(1-7) formation in vivo and also ex vivo in serum, lungs, and kidneys using models of genetic ablation coupled with pharmacological inhibitors. In wild-type (WT) mice, infusion of Ang II resulted in a rapid increase of plasma Ang-(1-7). In ACE2^-/-/PRCP^-/- mice, Ang II infusion resulted in a similar increase in Ang-(1-7) as in WT (563±48 versus 537±70 fmol/mL, respectively), showing that the bulk of Ang-(1-7) formation in circulation is essentially independent of ACE2 and PRCP. By contrast, a POP inhibitor, Z-Pro-Prolinal reduced the rise in plasma Ang-(1-7) after infusing Ang II to control WT mice. In POP^-/- mice, the increase in Ang-(1-7) was also blunted as compared with WT mice (309±46 and 472±28 fmol/mL, respectively P=0.01), and moreover, the rate of recovery from acute Ang II-induced hypertension was delayed (P=0.016). In ex vivo studies, POP inhibition with ZZP reduced Ang-(1-7) formation from Ang II markedly in serum and in lung lysates. By contrast, in kidney lysates, the absence of ACE2, but not POP, obliterated Ang-(1-7) formation from added Ang II. We conclude that POP is the main enzyme responsible for Ang II conversion to Ang-(1-7) in the circulation and in the lungs, whereas Ang-(1-7) formation in the kidney is mainly ACE2-dependent.

Fluorescence Detection of Prostate Cancer by an Activatable Fluorescence Probe for PSMA Carboxypeptidase Activity

Prostate cancer (PCa) is a common malignant tumor among adult males, and convenient intraoperative detection of PCa would reduce the risk of leaving positive surgical margins, especially during nerve-sparing procedures. To achieve rapid, fluorescence-based visualization of PCa, we focused on the glutamate carboxypeptidase (CP) activity of prostate-specific membrane antigen (PSMA), a type II transmembrane glycoprotein that is attracting attention as a PCa biomarker. Based on our finding that aryl glutamate conjugates with an azoformyl linker are recognized by PSMA and have a sufficiently low LUMO (lowest unoccupied molecular orbital) energy level to quench the fluorophore through photoinduced electron transfer, we designed and synthesized a first-in-class activatable fluorescence probe for CP activity of PSMA. The developed probe allowed us to visualize the CP activity of PSMA in living cells and in clinical specimens from PCa patients and is expected to be useful for rapid intraoperative detection and diagnosis of PCa.

Novel ACE2-Fc chimeric fusion provides long-lasting hypertension control and organ protection in mouse models of systemic renin angiotensin system activation

Angiotensin-converting enzyme 2 (ACE2) is a carboxypeptidase that potently degrades angiotensin II to angiotensin 1-7. Previous studies showed that injection of the enzymatic ectodomain of recombinant ACE2 (rACE2) markedly increases circulatory levels of ACE2 activity, and effectively lowered blood pressure in angiotensin II-induced hypertension. However, due to the short plasma half-life of rACE2, its therapeutic potential for chronic use is limited. To circumvent this, we generated a chimeric fusion of rACE2 and the immunoglobulin fragment Fc segment to increase its plasma stability. This rACE2-Fc fusion protein retained full peptidase activity and exhibited greatly extended plasma half-life in mice, from less than two hours of the original rACE2, to over a week. A single 2.5 mg/kg injection of rACE2-Fc increased the overall angiotensin II-conversion activities in blood by up to 100-fold and enhanced blood pressure recovery from acute angiotensin II induced hypertension seven days after administration. To assess rACE2-Fc given weekly on cardiac protection, we performed studies in mice continuously infused with angiotensin II for 28 days and in a Renin transgenic mouse model of hypertension. The angiotensin II infused mice achieved sustained blood pressure control and reduced cardiac hypertrophy and fibrosis. In chronic hypertensive transgenic mice, weekly injections of rACE2-Fc effectively lowered plasma angiotensin II and blood pressure. Additionally, rACE2-Fc ameliorated albuminuria, and reduced kidney and cardiac fibrosis. Thus, our chimeric fusion strategy for rACE2-Fc is suitable for future development of new renin angiotensin system-based inhibition therapies.

Angiotensin II-derived constrained peptides with antiplasmodial activity and suppressed vasoconstriction

Angiotensin II (Ang II) is a natural mammalian hormone that has been described to exhibit antiplasmodial activity therefore constituting a promising alternative for the treatment of malaria. Despite its promise, the development of Ang II as an antimalarial is limited by its potent induction of vasoconstriction and its rapid degradation within minutes. Here, we used peptide design to perform targeted chemical modifications to Ang II to generate conformationally restricted (disulfide-crosslinked) peptide derivatives with suppressed vasoconstrictor activity and increased stability. Designed constrained peptides were synthesized chemically and then tested for antiplasmodial activity. Two lead constrained peptides were identified (i.e., peptides 1 and 2), each composed of 10 amino acid residues. These peptides exhibited very promising activity in both our Plasmodium gallinaceum (>80%) and Plasmodium falciparum (>40%) models, an activity that was equivalent to that of Ang II, and led to complete suppression of vasoconstriction. In addition, peptide 5 exhibited selective activity towards the pre-erythrocytic stage (98% of activity against P. gallinaceum), thus suggesting that it may be possible to design peptides that target specific stages of the malaria life cycle. The Ang II derived stable scaffolds presented here may provide the basis for development of a new generation of peptide-based drugs for the treatment of malaria.