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A methodology developed by researchers from the University of Sao Paulo (USP) allows you to predict, with a simple blood test, the risk that a patient diagnosed with Covid-19 will develop complications and have to be hospitalized. The technique consists in analyzing the set of proteins present in the blood plasma to find out if it corresponds to a standard classified by the authors as “high risk”. The details of the work, which was supported by FAPESP (São Paulo State Research Support Foundation), have been published on the medRxiv platform, in an article still without peer review.
“We have identified a group of molecules whose level is significantly higher in the plasma of patients with severe Covid-19, with emphasis on SAA1 proteins. [proteína amiloide A1 sérica] and to SAA2 [proteína amiloide A2 sérica]. Our proposal is that this plasma analysis be performed as soon as the person has the diagnosis confirmed by the RT-PCR test. And, if he has a high-risk profile, the doctor may already be adopting a more targeted approach ”, says Giuseppe Palmisano, professor at the Institute of Biomedical Sciences (ICB-USP) and project coordinator.
The researcher points out, however, that it is still necessary to confirm the prognostic power of the method and its clinical utility in studies with larger patient groups in Brazil and abroad.
The conclusions presented in the article are based on analyzes carried out with samples of 117 patients with Covid-19 treated at Instituto do Coração (InCor) at the Hospital das Clínicas of the Medical School of USP (HCFMUSP), thanks to the collaboration with the doctors Rinaldo Focaccia Siciliano and José Carlos Nicolau.
Volunteers who had samples included in the study were matched for age, gender, and comorbidities (associated diseases, such as diabetes, obesity, or hypertension), so that the results were comparable.
To identify the set of proteins existing in the samples, the researchers used a mass spectrometer of the MALDI-TOF type (acronym for time of flight by ionization and matrix-assisted laser desorption) – relatively common equipment in Brazilian hospitals and widely used in microbiological analyzes. With it it is possible to identify, for example, the presence of fungi or bacteria in blood or urine samples, as well as determine the species of microorganisms.
“It’s an inexpensive technology that’s already in the clinic. It could, therefore, have a rapid application in the prognosis of Covid-19 ”, Palmisano assesses. “With this equipment it is possible to analyze the protein profile with only 1 microliter of plasma and the result would have come out in less than half an hour. Additionally, you can automate the process and evaluate samples from multiple people at the same time. “
Artificial intelligence
Six different machine learning algorithms were used to determine the plasma protein pattern corresponding to high- and low-risk patients. The researchers used 88 of the 117 samples to train the software to identify which of them belonged to hospitalized individuals (high risk) and which were from people who had only mild symptoms at the time of collection (low risk). The other 29 samples were used in a blind test to validate the method, ie to confirm that the program was performing the evaluation correctly. In the end, the methodology showed an accuracy of 93.1% (probability of offering a correct result), sensitivity of 87.5% (probability of a true positive result) and specificity of 100% (probability of a true negative result).
“We found that the plasma protein profile was different enough to separate the two patient groups [hospitalizados e sintomas leves], which made us very excited. So we tried to identify which proteins were most abundant in the high-risk group and came up with SAA1 and SAA2. The levels of these proteins in the plasma of high-risk patients were also evaluated with other techniques, confirming the result obtained ”, says Palmisano.
As the researcher explains, both SAA1 and SAA2 are produced in the liver and have inflammatory potential. “There is a correlation between the level of these proteins and that of some cytokines [moléculas pró-inflamatórias liberadas por células de defesa]. It has been reported that when the level of interleukin 1 increases [IL-1] and interleukin 6 [IL-6] in the blood also increases the level of these proteins, which are involved in the inflammatory response of the acute phase, ”he explains.
In addition to validating the test on a larger number of samples, from InCor patients and also from other groups, Palmisano believes it is important to study how the level of these inflammatory proteins evolves during infection. “One of the things we intend to understand is whether the concentration of these molecules decreases in patients who can cope with the disease and recover,” he says.
Biomarkers
In another study conducted by groups of the Faculty of Philosophy, Sciences and Letters of Ribeirão Preto (FFCLRP-USP) and the Federal University of São Carlos (UFSCar) the sTREM-1 protein has been identified as a potential gravitational biomarker for Covid-19. In this case, the level of the molecule in the patient’s circulation was measured by a test known as the ELISA (acronym for Enzyme Immunoassorption Assay), which is based on the interactions between antigen and antibody detectable through enzymatic reactions.
In analyzes performed by MALDI-TOF mass spectrometry by the Palmisano group, sTREM-1 did not appear among the differently regulated proteins in high-risk patients.
“We may not have found the same biomarkers because the technologies used in the studies are different. But it would be interesting to combine the two methodologies to try to reach a wider set of biomarkers, which could provide an even more accurate result, ”says Palmisano.
The article Prognostic accuracy of MALDI mass spectrometric analysis of plasma in Covid-19 can be read on www.medrxiv.org/content/10.1101/2020.10.01.20205310v1.full.pdf.
(With information from Karina Toledo | Agência FAPESP)
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