Quantitative monitoring of new coronavirus antibodies with only one blood glucose meter

The blood glucose meter also has a new function-quantitative monitoring of new coronavirus antibodies. Maybe in the near future, we can use a blood glucose meter at home to complete the quantitative monitoring of new coronavirus antibodies without going to the hospital. How is this achieved? Recently, scientists have developed a new fusion protein and successfully combined it with human immunoglobulin G to quantitatively read the level of new coronavirus antibodies in the human body by measuring the amount of glucose produced.
Rapid diagnosis plays a vital role in mitigating the current global COVID-19 pandemic and preventing the large-scale spread of infectious diseases in the future. How to enable more people, especially vulnerable groups, to enjoy safe and universal medical services through rapid, accurate and low-cost diagnosis has become a global issue. Among them, the development of simple, cost-effective and widely applicable detection equipment is also a top priority. Taking the detection of novel coronavirus antigens as an example, the current standard detection method is the enzyme-linked immunosorbent assay (ELISA). Commercial ELISA instruments include portable instruments (eg, manufactured by Samsung, Alere, etc.) and high-throughput, multiplexed clinical analyzers (eg, manufactured by Luminex). However, ELISA requires expensive high-quality optical equipment to achieve the accuracy of antibody measurement, which hinders the application of ELISA in some general hospitals and laboratories; even for ELISA that has been put into use at the point of care, The vast majority are also limited to qualitative measurements. Based on the application defects of the above-mentioned ELISA, it is imminent to develop a simple, cost-effective quantitative detection scheme.
Recently, researchers from Johns Hopkins University (Johns Hopkins University) published a report entitled “Antibody–Invertase Fusion Protein Enables Quantitative” in the Journal of the American Chemical Society (JACS). The paper “Detection of SARS-CoV-2 Antibodies Using Widely Available Glucometers” shows the possibility of using blood glucose meters to quantitatively detect SARS-CoV-2 Antibodies. https://pubs.acs.org/doi/10.1021/jacs.2c02537
Research brief
More recently, invertase-mediated sucrose conversion has been used in molecular diagnostics; however, conjugating the invertase to a detection molecule (eg, a detection antibody) is by no means trivial. Previously, some studies avoided direct attachment of the detection antibody and invertase by coupling the detection antibody and invertase to the same nanoparticle; there were also studies using streptavidin as an intermediate between biotinylated antibody and biotinylated invertase to make the two form a complex. However, these approaches yield very low coupling efficiencies.
In this study, the researchers designed a genetic fusion protein consisting of two invertase molecules and an anti-human immunoglobulin G antibody (anti-hIgG) through genetic fusion. This novel fusion protein overcomes the problem of inefficient chemical coupling between invertase and detection molecules, and retains the binding affinity and catalytic activity of constitutive proteins, and can be used as an accurate reporter gene for immunoassays.
Research key point 1: Design and purification of “anti-human immunoglobulin G antibody (anti-hIgG)-convertase fusion protein”
Four kinds of “anti-human immunoglobulin G antibody (anti-hIgG)-invertase fusion proteins” (hereinafter referred to as Ab+Inv) were produced in the study. The positions and lengths of the peptide linkers to the two invertase molecules differ. These four classes of fusion proteins are all based on anti-hIgG HP6017, an antibody that binds the Fc domain of the human IgG isotype, and were produced by transient transfection of human embryonic kidney (HEK) 293F cells.
Research key point 2: Verify the binding of the new fusion protein (Ab+Inv) to human immunoglobulin G (human IgG)
To demonstrate that this novel fusion protein (Ab + Inv) retains binding to the target antigen (ie, human immunoglobulin G), biolayer interferometry was performed. It was found that compared with unfused antibody (human IgG), the four types of fusion proteins showed similar binding properties to human IgG. Among them, two types of binding proteins showed slightly higher affinity.
Research key point 3: Verify the catalytic activity of the new fusion protein (Ab+Inv)
To determine whether the fusion protein retained the catalytic activity of the component invertase enzyme, a commercial glucose meter was used to perform a glucose inversion assay—incubating the fusion protein with a specific concentration of sucrose to measure post-culturing glucose production Level. The assay showed that the enzymatic activities of the four fusion proteins were almost the same as that of the unfused invertase, and their enzymatic activities were not affected by their binding to human immunoglobulin G.
Research key point 4: Development and application of SARS-CoV-2 antibody detection kits
To demonstrate the diagnostic potential of the fusion protein, the researchers chose a strip-based assay because it is suitable for point-of-care use and meets the goal of cost-effective detection. We accessed confirmed negative and positive patient blood samples from institutional biorepositories and obtained two blinded training sample sets: TS1 contained six confirmed negative patients and six confirmed positive patients. TS2 consisted of 90 longitudinal samples (collected over time) from seven hospitalized patients with confirmed SARS-CoV-2 RT-PCR. The research team did not know the antibody titers of the two TSs until the researchers cross-checked commercial ELISA measurements.
The test strip of this strip detection method has the SARS-CoV-2 spike protein, and when the test strip is immersed in a sample of a COVID-19 patient, the patient’s SARS-CoV-2 antibody binds to the spike protein. This was followed by a washing step – the strip was exposed to the fusion protein solution for 30 minutes to allow the fusion protein to bind to the antibody captured on the strip, followed by washing. Subsequently, the strips were immersed in a 100 mM sucrose solution for 60 minutes to catalyze the conversion of invertase to glucose. Finally, the band was removed and the resulting glucose concentration was determined using a commercial blood glucose meter. Schematic: Quantitative determination of COVID-19-specific antibodies using a commercially available blood glucose meter
future applications
The new fusion protein developed in this research has the advantages of low technology and low cost, which enables the diagnosis method based on blood glucose meter to be extended to a wider population, especially those who do not have access to advanced medical testing. It will also enhance the ability of serial testing, combining the number and diversity of people tested, to provide the high-quality data needed and help provide a clear and detailed understanding of the lifespan of immune protection resulting from vaccination and natural infection. In addition, this technology may be applied to the prevention and detection of cancer and autoimmune diseases—that is, replacing SARS-CoV-2 RBD with cancer diagnostic antigens or self-antigens of autoimmune diseases, so as to quantitatively detect related antibodies , beneficial for immunity testing, disease control, and longitudinal monitoring of progression.

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