Targeted MRM-analysis of plasma proteins in frozen whole blood samples from patients with COVID-19

The COVID-19 pandemic has exposed a number of key challenges that need to be urgently addressed. In particular, rapid identification and validation of prognostic markers is required. Mass spectrometric studies of blood plasma proteomics provide a deep understanding of the relationship between the severe course of infection and activation of specific pathophysiological pathways. Analysis of plasma proteins in whole blood may also be relevant for the pandemic as it requires minimal sample preparation. Here, for the first time, frozen whole blood samples were used to analyze 189 plasma proteins using multiple reaction monitoring (MRM) mass spectrometry and stable isotope-labeled peptide standards (SIS). A total of 128 samples (FRCC, Russia) from patients with mild (n=40), moderate (n=36) and severe (n=19) COVID-19 infection and healthy controls (n=33) were analyzed. Levels of 114 proteins were quantified and compared. Significant differences between all of the groups were revealed for 61 proteins. Changes in the levels of 30 reproducible COVID-19 markers (SERPING1, CRP, C9, ORM1, APOA1, SAA1/SAA2, LBP, AFM, IGFALS, etc.) were consistent with studies performed with serum/plasma samples. Levels of 70 proteins correlated between whole blood and plasma samples. The best-performing classifier built with 13 significantly different proteins achieved the best combination of ROC-AUC (0.93-0.95) and accuracy (0.87-0.93) metrics and distinguished patients from controls, as well as patients by severity and risk of mortality. Overall, the results support the use of frozen whole blood for MRM analysis of plasma proteins and assessment of the status of patients with COVID-19.