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Sepsis is defined as the systemic, dysregulated host immune response to an infection that leads to injury to host organ systems and, often, death. Complex interactions between pathogens and their hosts elicit microcirculatory dysfunction. Neutrophil myeloperoxidase (MPO) is critical for combating pathogens, but MPO-derived hypochlorous acid (HOCl) can react with host molecular species as well. Plasmalogens are targeted by HOCl, leading to the production of 2-chlorofatty acids (2-CLFAs). 2-CLFAs are associated with human sepsis mortality, decrease in vitro endothelial barrier function, and activate human neutrophil extracellular trap formation. Here, we sought to examine 2-CLFAs in an in vivo rat sepsis model. Intraperitoneal cecal slurry sepsis with clinically relevant rescue therapies led to ∼73% mortality and evidence of microcirculatory dysfunction. Plasma concentrations of 2-CLFAs assessed 8 h after sepsis induction were lower in rats that survived sepsis than in nonsurvivors. 2-CLFA levels were elevated in kidney, liver, spleen, lung, colon, and ileum in septic animals. In vivo, exogenous 2-CLFA treatments increased kidney permeability, and in in vitro experiments, 2-CLFA also increased epithelial surface expression of vascular cell adhesion molecule 1 and decreased epithelial barrier function. Collectively, these studies support a role of free 2-CLFAs as biomarkers of sepsis mortality, potentially mediated, in part, by 2-CLFA-elicited endothelial and epithelial barrier dysfunction.

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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.

Platelet-activating factor (PAF) is a potent biologically active phospholipid that mediates human physiological and pathophysiologic responses. PAF levels increase transiently and are typically assessed by techniques with limitations related to expense, sensitivity, pre-analysis derivatization and interference with isobaric molecules. This study elucidates a facile, accurate liquid chromatography-mass spectrometry analytical method for PAF. In negative ion mode using electrospray ionization, collisionally-activated dissociation analysis showed a unique product ion for acetate adducts of PAF molecular species representing the loss of methyl acetate from the polar head group and loss of a part of the acetate group from the sn-2 position. This product ion was exploited for selected reaction monitoring of PAF molecular species following separation by reversed-phase liquid chromatography. Standard calibration responses were determined, and this method was able to detect as low as 100 fmol of PAF. Finally, PAF molecular species were quantified in human neutrophils and monocytes.