Neutrophil-mediated oxidative stress and albumin structural damage predict COVID-19-associated mortality

Human serum albumin (HSA) is the frontline antioxidant protein in blood with established anti-inflammatory and anticoagulation functions. Here we report that COVID-19-induced oxidative stress inflicts structural damages to HSA and is linked with mortality outcome in critically ill patients. We recruited 25 patients who were followed up for a median of 12.5 days (1-35 days), among them 14 had died. Analyzing blood samples from patients and healthy individuals (n=10), we provide evidence that neutrophils are major sources of oxidative stress in blood and that hydrogen peroxide is highly accumulated in plasmas of non-survivors. We then analyzed electron paramagnetic resonance (EPR) spectra of spin labelled fatty acids (SLFA) bound with HSA in whole blood of control, survivor, and non-survivor subjects (n=10-11). Non-survivors HSA showed dramatically reduced protein packing order parameter, faster SLFA correlational rotational time, and greater S/W ratio (strong-binding/weak-binding sites within HSA), all reflecting remarkably fluid protein microenvironments. Stratified at the means, Kaplan-Meier survival analysis indicated that lower values of S/W ratio and accumulated H2O2 in plasma significantly predicted in-hospital mortality (S/W<0.16, 80% (9/12) vs. S/W>0.16, 20% (2/10), p=0.008; plasma [H2O2]>7.1 M, 83.3% (5/6) vs. 16.7% (1/6), p=0.049). When we combined these two parameters as the ratio ((S/W)/[H2O2]) to derive a risk score, the resultant risk score lower than the mean (< 0.0253) predicted mortality with 100% accuracy (100% (6/6) vs. 0% (0/6), logrank {chi}2 = 12.01, p = 5x10-4). The derived parameters may provide a surrogate marker to assess new candidates for COVID-19 treatments targeting HSA replacements.