Plasmalogens are plasma-borne antioxidant phospholipid species that provide protection as cellular lipid components during cellular oxidative stress. In this study we investigated plasma plasmalogen levels in human sepsis as well as in rodent models of infection. In humans, levels of multiple plasmenylethanolamine molecular species were decreased in septic patient plasma compared to control subject plasma as well as an age-aligned control subject cohort. Additionally, lysoplasmenylcholine levels were significantly decreased in septic patients compared to the control cohorts. In contrast, plasma diacyl phosphatidylethanolamine and phosphatidylcholine levels were elevated in septic patients. Lipid changes were also determined in rats subjected to cecal slurry sepsis. Plasma plasmenylcholine, plasmenylethanolamine, and lysoplasmenylcholine levels were decreased while diacyl phosphatidylethanolamine levels were increased in septic rats compared to control treated rats. Kidney levels of lysoplasmenylcholine as well as plasmenylethanolamine molecular species were decreased in septic rats. Interestingly, liver plasmenylcholine and plasmenylethanolamine levels were increased in septic rats. Since COVID-19 is associated with sepsis-like acute respiratory distress syndrome and oxidative stress, plasmalogen levels were also determined in a mouse model of COVID-19 (intranasal inoculation of K18 mice with SARS-CoV-2). 3 days following infection, lung infection was confirmed as well as cytokine expression in the lung. Multiple molecular species of lung plasmenylcholine and plasmenylethanolamine were decreased in infected mice. In contrast, the predominant lung phospholipid, dipalmitoyl phosphatidylcholine, was not decreased following SARS-CoV-2 infection. Additionally total plasmenylcholine levels were decreased in the plasma of SARS-CoV-2 infected mice. Collectively, these data demonstrate the loss of plasmalogens during both sepsis and SARS-CoV-2 infection. This study also indicates plasma plasmalogens should be considered in future studies as biomarkers of infection and as prognostic indicators for sepsis and COVID-19 outcomes.

Hypochlorous acid is produced by leukocyte myeloperoxidase activity. 2-Chlorofatty aldehydes (2-ClFALDs) are formed when hypochlorous acid attacks the plasma membrane phospholipid plasmalogen molecular subclass and are thus produced following leukocyte activation as well as in the lungs of mice exposed to chlorine gas. The biological role of 2-ClFALD is largely unknown. Recently, we used an alkyne analog (2-ClHDyA) of the 2-ClFALD molecular species, 2-chlorohexadecanal (2-ClHDA), to identify proteins covalently modified by 2-ClHDyA in endothelial cells and epithelial cells. Here, we demonstrate that 2-ClHDA reduces the metabolic activity of RAW 264.7 cells in a dose-dependent manner. 2-ClHDyA localizes to the mitochondria, endoplasmic reticulum and Golgi in RAW 264.7 cells and modifies many proteins. The thiol-containing precursor of glutathione, N-acetyl cysteine (NAC), was shown to produce an adduct with 2-ClHDA with the loss of Cl− (HDA–NAC). This adduct was characterized in both positive and negative ion modes using LC-MS/MS and electrospray ionization. NAC treatment of neutrophils reduced the 2-ClFALD levels in PMA-stimulated cells with subsequent increases in HDA–NAC. NAC treatments reduced the 2-ClHDA-elicited loss of metabolic activity in RAW 264.7 cells as well as 2-ClHDA protein modification. These studies demonstrate that 2-ClFALD toxic effects can be reduced by NAC, which reduces protein modification.