Antigen test detects spike proteins of SARS-CoV-2

The COVID-19 pandemic has increased the demand for rapid, accurate, user-friendly and cost-effective antigen tests to diagnose people infected with the SARS-CoV-2 virus. Polymerase chain reaction (PCR)-based antigen tests are widely used, but are time-consuming, costly and technically difficult to perform. In a paper published Aug. 14, 2020, in Diagnostics, researchers in Japan describe a de novo antigen test that combines sandwich enzyme-linked immunosorbent assay and thio-nicotinamide adenine dinucleotide (thio-NAD) cycling. The test takes advantage of the spike proteins peculiar to SARS-CoV-2, and has a limit of detection of 2.3 x 1-18 moles/assay, the team said. For example, if the virus has about 25 spike proteins on its surface, the method should detect on an order of 10-20 moles of virus per assay, corresponding to ~105 copies of the virus RNA per assay. The detection sensitivity is close to that of PCR assays, which have an average virus RNA load of ~105 copies per oro- or nasopharyngeal swab sample. “To our knowledge, this is the first ultrasensitive antigen test for SARS-CoV-2 spike proteins that can be performed with an easy-to-use microplate reader,” the authors wrote. “Sufficient sensitivity can be achieved within 10 min of thio-NAD cycling.” While the test only requires a microplate reader, the team said they are working to produce an automated instrument for use with its method. The researchers also noted their study detected SARS-CoV-2 spike proteins at the attomole level and emphasized the need to demonstrate their system can detect live SARS-CoV-2 in specimens obtained from patients positive for COVID-19.

Blood volume assessment study to use Daxor device

New York-based Daxor Corp. is taking part in a trial, alongside NYU Langone Health, to assess blood volume in patients infected with SARS-CoV-2, the virus that causes COVID-19. Little is known currently about the state of intravascular volume, the characteristics of blood components and risk of developing a vascular leak in patients with SARS-CoV-2 infection who are admitted to the intensive care unit. The prospective, observational, 30-patient study will describe the blood volume, the volume of blood components and the capillary leak and their trajectory during the early phase of patients infected with SARS-CoV-2 utilizing Daxor’s FDA-cleared BVA-100 blood volume analyzer. The test helps to guide care teams in balancing the level of fluids they give patients to maintain normal circulation. In a prospective, randomized, controlled trial, the BVA-100 test reduced ICU deaths by 66% and led to a 44% change in blood volume treatment strategy. The study kicked off on Aug. 1, 2020, and has an estimated completion date of Feb. 1, 2021.

Gaining insights into loss of function

Researchers at Johns Hopkins University have identified a link between the density of CpG islands in promoters and the severity of loss-of-function mutations of their downstream genes. As next-generation sequencing uncovers even more genetic variation with every greater ease and accuracy, an important clinical question is which variants are functionally important. One way to gauge a gene’s importance is by assessing an organism’s tolerance to loss of function of that gene. However, small genes in particular may have few loss-of-function variants in populations, because they are very important, or because they are small. In their work, the authors looked at CpG islands, a genomic feature that prevents gene silencing through methylation, and thus loss of function, via regulatory mechanisms rather than mutations. They showed that genes with many CpG islands in their promoters were much more sensitive to loss-of-function mutations, suggesting that CpG islands could be used to indirectly gauge the clinical importance of variants of unknown significance in their downstream genes. They reported their results in the Aug. 14, 2020, issue of the American Journal of Human Genetics.

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