Fig. 3.

(Graphical Abstract) The Protein Thiolation Index (PTI), an indicator of the thiol/disulfide balance of extracellular fluids, increases its levels with age, thus mirroring the decline of redox homeostasis systems of tissues. In this study we propose that PTI and extracellular thiol analysis can be utilized to predict the risk of more severe infections and clinical manifestations by higher oxidation of interaction domain Cys that are critical for CoV-2 spike protein and ACE-2 receptor binding. Pro-oxidant conditions of the extracellular environment have been described to promote the physical (protein-protein) interaction of viral proteins and host cell receptors in many other viruses [[16], [19]], thus representing an age-dependent molecular process of increased susceptibility to viral infections and their complications.