Blood Test Can Track the Evolution of COVID-19 Coronavirus Infection

Recreation of the SARS-CoV-2 virus.

A blood test that quantifies the protein ACE2, the cellular protein that allows the coronavirus to enter cells, as well as ACE2 fragments, produced as a result of interaction with the virus, could be a simple and effective method of monitoring SARS-CoV-2 infection, according to a study led by Javier Sáez-Valero, of the UMH-CSIC Neurosciences Institute in Alicante, published in FASEB Journal.

This study, conducted during the first wave of the pandemic, found that patients with COVID-19, in the acute phase of infection, significantly reduced plasma levels of the full-length ACE2 protein, to which SARS-CoV-2 binds. cells, compared to uninfected controls. In addition, the plasma levels of a lower molecular weight (70 kDa) ACE2 fragment generated as a result of interaction with the virus are increased.

These abnormal levels of ACE2 and truncated ACE2 (70 kDa fragment) return to normal upon patient recovery. This suggests that both forms of ACE2 present in plasma can be used as a good biomarker for the evolution of a coronavirus infection. In addition, truncated ACE2 levels served to distinguish between patients infected with SARS-CoV-2 and patients infected with influenza A virus.

“In this work, we have studied the plasma levels of the coronavirus receptor, the ACE2 protein, and we have been able to determine that there are different forms of the protein in plasma, and that some of the soluble ACE2 are proteolytic fragments of the ACE2. receptor, generated after interaction with the virus. The full-length protein is also found in plasma, which provides information about tissue damage during infection,” explains Javier Sáez-Valero, who led the study.

Although the main line of research of Sáez-Valero’s group is Alzheimer’s disease, the “similarities” of ACE2 to core proteins of Alzheimer’s disease, such as beta-amyloid precursor protein (APP), also cell membrane resident proteins, led this expert to think that perhaps ACE2 could be present in plasma, which provides information about its interaction with the coronavirus.

“Our approach to this line of research was the possibility that soluble ACE2 protein could serve as a readout during COVID-19 infection. This hypothesis stems from our expertise in Alzheimer’s disease. In this neurodegenerative disease, we investigate proteins, such as APP, that are present in the cerebrospinal fluid. APP is also a membrane protein that is processed by the same molecular tools as ACE2, enzymes called secretases, which process different membrane proteins into different fragments. This phenomenon was the clue that led us to suspect that ACE2 protein fragments, as well as the entire protein, are present in plasma. So we have the opportunity to investigate this protein as a possible biomarker,” explains Sáez-Valero.

Trial participants

Samples and patient data included in this study were provided by the ISABIAL Biobank, integrated into the Spanish National Biobank Network and the Valencian Biobank Network. Fifty-nine patients with a positive reverse transcription polymerase chain reaction (RT-PCR) test for SARS-CoV-2 in nasopharyngeal swabs were included, including 24 females and 35 males, with a mean age of 64 years). All were hospitalized 7 to 9 days after the onset of symptoms. Of these, 48 SARS-CoV-2 infected patients had a moderate presentation of COVID-19, and 11 were considered severe because they had respiratory failure requiring invasive mechanical ventilation and/or intensive care treatment.

Two additional groups were also analyzed, one of 17 participants (9 women and 8 men), including people aged 34 to 85 with influenza A virus pneumonia. The other group consisted of 26 disease-free controls (14 females and 12 males) aged 34-85 years. For the “influenza A group” samples were also taken in the acute phase, prior to specific hospital treatment.

The ACE2 species in human plasma were identified by immunoprecipitation and western blotting, a technique that allows the detection of a specific protein in a blood or tissue sample, where a complex mixture of forms of the protein is present. Until now, plasma analyzes for the coronavirus have mostly used a different technique called ELISA, which cannot determine the different shapes of the proteins.

Changes in truncated and complete ACE2 species were also examined in serum samples from humanized K18-hACE2 mice inoculated with a lethal dose of SARS-CoV-2. These humanized mice carry the human gene that produces the ACE2 protein, allowing SARS-CoV-2 infection, which does not occur naturally due to a lack of recognition of murine ACE2 by the virus.

The changes in the forms of ACE2 present in plasma after SARS-CoV-2 infection observed in this study warrant further investigation into their potential as biomarkers of the disease process, as well as for assessing efficacy, according to the researchers. of vaccination. The next step will be to investigate what happens to these proteins in asymptomatic PCR-positive or vaccinated individuals.

Reference: “Plasma ACE2 species are differentially altered in COVID-19 patients” by María-Salud García-Ayllón, Oscar Moreno-Pérez, Juan García-Arriaza, José-Manuel Ramos-Rincón, María-Ángeles Cortés-Gómez, Gunnar Brinkmalm, Mariano Andrés, José-Manuel León-Ramírez, Vicente Boix, Joan Gil, Henrik Zetterberg, Mariano Esteban, Esperanza Merino and Javier Sáez-Valero, June 30, 2021, The FASEB Journal.
DOI: 10.1096/fj.202100051R

In this multicenter study led by Javier Sáez-Valero, whose first authors are María Salud García-Ayllón, from the Instituto de Neurosciencias UMH-CSIC, and Óscar Moreno-Pérez, from the Hospital General Universitario de Alicante (HGUA) and the Instituto the Health and Biomedical Research of Alicante (ISABIAL), other participants are Esperanza Merino, José Manuel Ramos-Rincón, Mariano Andrés, José Manuel León-Ramírez, Vicente Boix and Joan Gil of the HGUA-ISABIAL; and María Ángeles Cortés-Gómez of the Institute of Neurosciences UMH-CSIC. The study has the collaboration of prestigious groups, Mariano Esteban and Juan García-Arriaza of CSIC’s National Biotechnology Center; and Henrik Zetterberg and Gunnar Brinkmalm of Sahlgrenska University Hospital in Sweden.

The researchers Javier Sáez-Valero, María Salud García-Ayllón and María Ángeles Cortés-Gómez also belong to the Center for Biomedical Research Network on Neurodegenerative Diseases (CIBERNED).