CoviDrop SARS-CoV-2 Spike-ACE2 Binding Activity/Inhibition Assay Kit

The CoviDrop™ SARS-CoV-2 Spike-ACE2 Binding Activity/Inhibition Assay Kit is a complete set of optimized buffers and reagents designed for measuring SARS-CoV-2-ACE2 binding activity and inhibition using various human samples so that the functional ACE2 binding level from different cells/tissues in different individuals can be identified. The samples can be used immediately or stored at proper conditions for future use.  The kit has the following advantages:

• Fast: Colorimetric assay with easy-to-follow steps for convenience and speed. The entire procedure can be finished within 1 hour and 45 minutes. 
• Robust: Innovative kit composition enables background signals to be extremely low and allows the assay to be simple, accurate, reliable, and consistent.
• Convenient: Biological samples, including plasma, serum, swab samples, other body fluids, and purified proteins, can be used to detect SARS-CoV-2-ACE2 binding activity/inhibition in vivo and in vitro. 
• Sensitive and Specific: The activity can be detected from as low as 0.1 ng of ACE2 binding and only specific for ACE2.  
• Quantitative: The assay standard is included, which allows the bound ACE2 to be quantified.
• Flexible: Strip-well microplate format makes the assay flexible for manual or high throughput analysis.

Background
COVID-19 is an infectious disease caused by SARS-CoV-2, a new member of the same coronavirus family that caused SARS and MERS. Entry of SARS-CoV-2 into human host cells occurs through binding of surface unit S1 of its spike protein to the cell receptor angiotensin-converting enzyme 2 (ACE2). ACE2 is ubiquitous and widely expressed in the lung, heart, kidney, vessels, brain, gut, and testis at different levels. ACE2 is also mostly bound to cell membranes and normally less present in circulation [1]. It was found that increased ACE2 expression in nasal epithelium and lung is associated with higher rates of SARS-CoV-2 infection and severity of COVID-19, respectively [2,3]. A new observation indicates that increased ACE2 concentration in circulation may be associated with increased incidence and fatality rate of COVID-19 [4]. In addition, SARS-CoV-2 invasion degrades ACE2 on cell membranes and may increase soluble ACE2 concentration in circulation [1]. The importance of measuring ACE2 level in various samples is emphasized by the complicated SARS-CoV-2-ACE2 interaction under normal (healthy) and abnormal (pre-existing diseases and viral infection) conditions. 

Fig 1. SARS-Cov-2 binding to ACE2 and entry into cells 

Principles and Procedure
This kit contains all reagents necessary for the measurement SARS-CoV-2 spike-ACE2 binding activity or inhibition. In this assay, a SARS-CoV-2 spike protein is stably pre-coated onto microplate wells. ACE2 contained in the sample is captured by the coated spike protein. The amount of the captured ACE2, which is proportional to ACE2 binding activity, is then recognized by anti-ACE2 antibody and measured through an ELISA-like reaction by reading the absorbance in a microplate spectrophotometer at a wavelength of 450 nm. The binding activity of ACE2 is proportional to the optical density intensity measured.

Starting Materials
Input materials can be cell/tissue extracts, serum, plasma, swab samples, and various body fluids.  

References:
1. Verdecchia P et al:  Eur J Intern Med. 76: 14–20, 2020.
2. Bunyavanich S et al: JAMA. Published online May 20, 2020.
3. Sama IZ et al: Eur Heart l, 41: 1810–1817, 2020. 
4. Pinto BGG et al: medRxiv. Published online March 27, 2020.