Even after almost two years of the coronavirus disease 2019 (COVID-19) pandemic and extensive research, many aspects that could curb the pandemic remain unknown. The causal agent of this pandemic is severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), which has evolved with time, and some of the variants are more virulent with a higher rate of transmission and mortality rate.

Study: Precise blood proteome profiling in an undiagnosed population with COVID-19. Image Credit: Fotomay/ Shutterstock

COVID-19 infection affects an individual’s respiratory system and damages many other physiological systems, including cardiovascular, digestive, and nervous systems. Researchers stated that one of the primary factors of COVID-19 pathogenesis is the over-activation of the innate immune response, which causes the cytokine storm.

Previous studies have helped understand the molecular mechanism behind SARS-CoV-2 infection or the factors contributing to severe infection. However, the long-term effects related to mild or asymptomatic COVID-19 infection are still not clear. Some studies using computed tomography revealed that even mild or asymptomatic infection could cause subclinical lung abnormalities.

Background

Scientists have highlighted the need for population-based studies to understand heterogeneous phenotypes, genetic and environmental factors, and their association with disease severity, mortality, and long-term effects of its health. Some large-scale population studies have been conducted, but their results contain biases. The main problem in conducting large-scale population studies is proper sampling. Biased results may be obtained by including undetected or non-hospitalized individuals affected by COVID-19 infection with mild or no symptoms.

To reduce bias, scientists have come up with a possibility to reach a population that is typically hard to reach, i.e., via home-sampled dried blood spots (DBS). Some of the advantages of the DBS system include the collection of samples without direct contact or requiring a skilled person. Further, this system also prevents visiting a healthcare center. The shortcoming of the DBS approach has recently been corrected by a new microfluidic-based DBS device that can collect the precise volume of blood in a controlled manner.

During the first pandemic wave, scientists have used a volumetric DBS home-sampling device to collect 878 samples from Stockholm, Sweden, randomly. This study helped determine the presence of IgG and IgM antibodies against several proteins from the SARS-CoV-2 virus in a multi-analyte assay. The same group of researchers currently collected DBS samples in the Stockholm population to conduct more analyses to understand the molecular effects of the infection. This study is available on the medRxiv* preprint server.

In this study, scientists have profiled 276 circulating proteins that are associated with cardiovascular and metabolic functions. These proteins were present in the eluates previously prepared for the serological survey. The main focus of this study has been to gather a comprehensive picture of the biological processes along with the diverse immune responses associated with SARS-CoV-2 infection in a random population.

Proteomic survey

The authors claim that this study is the first proteomics survey conducted in a general population. The main strength of this study is the integrity of the home sample that enabled obtaining high-quality molecular data with large cohorts. Scientists used proximity extension assays (PEA) for the proteomics analyses owing to their low sample volume requirement. PEA assays are also highly sensitive and specific. Previous studies have also used PEAs to quantify proteins from filter paper-based DBS samples collected from clinical settings.

This study validated the DBS sampling system by comparing the protein profiles generated using venous blood draw and DBS sample via finger pricking. Researchers found comparable results in both sampling systems. This study revealed that a higher abundance of protein was found in the DBS samples from the skin, intracellular, and blood cells due to cell lysis. Researchers have conducted variability analysis and found that BLMH, THOP1, SOD1, and BAG6 are among the least variable proteins.

Generally, assessment of circulating proteins helps monitor disease progression and determines the response to therapy in severely infected and hospitalized patients. It also helps understand the causes behind the long-term symptoms experienced by the individuals affected with mild COVID-19 symptoms. Previous studies have reported that overproduction of pro-inflammatory cytokines causes multi-organ failure and increases levels of cardiac biomarkers such as Troponin, BNP, and MBL2, which are the predictors of mortality.

Compared to seronegative individuals, those with mild symptoms showed high levels of MBL2, IL2RA MMP3, and FCGR2A protein, which were previously associated with ICU mortality. Proteins, such as CRTAC and CHRDL2, involved with the active proliferation of cells and adaptive immune responses, were also found. The authors also indicated the presence of GP1BA, VWF, SDC4, ANG, and CHL1 in the sample.

Future studies

In the future, the authors aim to quantify stable proteins occurring at lower abundance, such as IL6 or TNF, and inflammatory biomarkers in circulation. Also, a more sensitive quantitative method is required to analyze proteins from DBS samples. This study has provided valuable insights into the molecular effects of SARS-CoV-2 infection.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.