Neutralization of SARS-CoV-2 spike pseudotyped virus by recombinant ACE2-Ig.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in Wuhan, China, at the end of 2019, and there are currently no specific antiviral treatments or vaccines available. SARS-CoV-2 has been shown to use the same cell entry receptor as SARS-CoV, angiotensin-converting enzyme 2 (ACE2). In this report, we generate a recombinant protein by connecting the extracellular domain of human ACE2 to the Fc region of the human immunoglobulin IgG1. A fusion protein containing an ACE2 mutant with low catalytic activity is also used in this study. The fusion proteins are then characterized. Both fusion proteins have a high binding affinity for the receptor-binding domains of SARS-CoV and SARS-CoV-2 and exhibit desirable pharmacological properties in mice. Moreover, the fusion proteins neutralize virus pseudotyped with SARS-CoV or SARS-CoV-2 spike proteins in vitro. As these fusion proteins exhibit cross-reactivity against coronaviruses, they have potential applications in the diagnosis, prophylaxis, and treatment of SARS-CoV-2.

Pharmacokinetics and pharmacodynamics of recombinant human angiotensin-converting enzyme 2 in healthy human subjects.

BACKGROUND AND OBJECTIVES: Angiotensin-converting enzyme 2 (ACE2) converts angiotensin II (Ang1-8) to angiotensin 1-7 (Ang1-7), a functional antagonist of Ang1-8, with vasodilatory, antiproliferative, antiangiogenic, and anti-inflammatory properties. In conditions with an unbalanced renin-angiotensin-aldosterone system with elevated Ang1-8, administration of ACE2 has shown promising effects in a variety of animal models. Enhancing ACE2 activity by exogenous administration of ACE2 might also be beneficial in human diseases with pathologically elevated Ang1-8. As a first step we performed a first-in-man study to determine pharmacokinetics, pharmacodynamics, safety, and tolerability of recombinant ACE2 in healthy volunteers. METHODS: Recombinant human ACE2 (rhACE2) was administered intravenously to healthy human subjects in a randomized, double-blind, placebo-controlled, single-dose, dose-escalation study followed by an open-label multiple-dose study. ACE2 concentrations were determined by quantifying ACE2 activity and ACE2 content in plasma samples. Concentrations of the angiotensin system effector peptides Ang1-8, Ang1-7, and Ang1-5 were determined using a liquid chromatography-tandem mass spectrometry method. RESULTS: Single rhACE2 doses of 100-1,200 µg/kg caused a dose-dependent increase of systemic exposure with biphasic elimination and a dose-independent terminal half-life of 10 h. In all single-dose cohorts, Ang1-8 decreased within 30 min postinfusion, angiotensin 1-7 (Ang1-7) either increased (100 and 200 µg/kg doses), decreased, or remained unchanged (400-1,200 µg/kg doses), whereas angiotensin 1-5 (Ang1-5) transiently increased for all doses investigated. With the exception of the lowest rhACE2 dose, the decrease in Ang1-8 levels lasted for at least 24 h. Repeated dosing (400 µg/kg for 3 or 6 days) caused only minimal accumulation of ACE2, and Ang1-8 levels were suppressed over the whole application period. CONCLUSIONS: Administration of rhACE2 was well tolerated by healthy human subjects. Exposure was dose dependent with a dose-independent terminal elimination half-life in the range of 10 h. Despite marked changes in angiotensin system peptide concentrations, cardiovascular effects were absent, suggesting the presence of effective compensatory mechanisms in healthy volunteers.

Immunotargeting of antioxidant enzyme to the pulmonary endothelium.

Oxidative injury to the pulmonary endothelium has pathological significance for a spectrum of diseases. Administration of antioxidant enzymes, superoxide dismutase (SOD) and catalase (Cat), has been proposed as a method to protect endothelium. However, neither these enzymes nor their derivatives possess specific affinity to endothelium and do not accumulate in the lung. Previously we have described a monoclonal antibody to angiotensin-converting enzyme (ACE) that accumulates selectively in the lung after systemic injection in rats, hamsters, cats, monkeys, and humans. In the present work we describe a system for selective intrapulmonary delivery of CuZn-SOD and Cat conjugated with biotinylated anti-ACE antibody mAb 9B9 (b-mAb 9B9) by a streptavidin (SA)-biotin bridge. Both enzymes biotinylated with biotin ester at biotin/enzyme ratio 20 retain enzymatic activity and bind SA without loss of activity. We have constructed tri-molecular heteropolymer complexes consisting of b-mAb 9B9, SA, and biotinylated SOD or biotinylated Cat and have studied biodistribution and pulmonary uptake of these complexes in the rat after i.v. injection. Biodistribution of biotinylated enzymes was similar to that of nonmodified enzymes. Binding of SA markedly prolonged lifetime of biotinylated enzymes in the circulation. In contrast to enzymes conjugated with nonspecific IgG, other enzyme derivatives, and nonmodified enzymes, biotinylated enzymes conjugated with b-mAb 9B9 accumulated specifically in the rat lung (9% of injected SOD/g of lung tissue and 7.5% of injected Cat/g of lung tissue). Pulmonary uptake of nonmodified enzymes or derivatives with nonspecific IgG did not exceed 0.5% of injected dose/g. Both SOD and Cat conjugated with b-mAb 9B9 were retained in the rat lung for at least several hours. Trichloracetic acid-precipitable radiolabeled Cat was associated with microsomal and plasma membrane fractions of the lung tissue homogenate. Thus, modification of antioxidant enzymes with biotin and SA-mediated conjugation with b-mAb 9B9 prolongs the circulation of enzymes resulting in selective accumulation in the lung and intracellular delivery of enzymes to the pulmonary endothelium. These results provide the background for an approach to provide protection of pulmonary endothelium against oxidative insults.

Kidney angiotensin II receptors and converting enzyme in neonatal and adult Wistar-Kyoto and spontaneously hypertensive rats.

The aim of the present study was to correlate the development of the renin angiotensin system (RAS) in the kidney of the rat with the development of genetic hypertension. Immature (1-week-old) and adult (12-week-old) normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive kidney rats (SHR) were used for quantification of angiotensin II (ANG II) receptors and angiotensin converting enzyme (ACE) binding sites using quantitative autoradiography. In both neonatal and adult animals of either strain, ANG II receptors were of AT1 subtype. In all kidney areas of 1-week-old rats. ANG II receptor density was higher in SHR than WKY. Binding density increased with age in WKY rats; thus, in the glomeruli and the outer stripe of the outer medulla of 12-week-old WKY, binding was significantly higher than that present in age-matched SHR. [125I]351A binding to ACE was highest in the outer medulla and not detectable in glomeruli. In 1-week-old rats, binding to ACE was higher in WKY than in SHR strain. No differences in ACE binding were found between adult SHR and WKY rats, with the exception of the inner stripe of the outer medulla, where no binding was detected in SHR. Our results support the hypothesis that the RAS in kidney is developmentally regulated and is involved in the development and maintenance of genetic hypertension in SHR.

Tissue angiotensin converting enzyme inhibition. Relevant to clinical practice?

Accumulating data indicate that tissue and systemic renin-angiotensin systems may coexist. Evidence supporting the existence of local regulatory systems derives from several sources. Firstly, it has been clearly demonstrated that all components of the renin-angiotensin system are detectable in the tissues of organs such as the brain, heart, lung, kidney, testis, and blood vessels. Secondly, many diverse actions of angiotensin II have been defined in different tissues, all of which have a common mechanism: maintaining or increasing vascular tone, blood volume, or both. Evidence supporting the concept that the local and systemic renin-angiotensin systems are functionally independent includes the discrepancy in the time courses of hemodynamic changes and enzyme inhibition following administration of angiotensin-converting enzyme (ACE) inhibitors; and the observation that ACE inhibitor treatment results in decreases in blood pressure in anephric subjects, who have extremely low circulating concentrations of angiotensin II. These and other data suggest that inhibition of tissue ACE may be as, or more, important than its effects on the more easily measured circulating ACE. This raises the question of whether there are differences among ACE inhibitors in their selectivity for one or more organ systems. Some experimental data indicate that the binding affinity and time course of ACE inhibition can vary from one tissue to another, and among individual agents.(ABSTRACT TRUNCATED AT 250 WORDS)