sEH-derived metabolites of linoleic acid drive pathologic inflammation while impairing key innate immune cell function in burn injury.

Fatty acid composition in the Western diet has shifted from saturated to polyunsaturated fatty acids (PUFAs), and specifically to linoleic acid (LA, 18:2), which has gradually increased in the diet over the past 50 y to become the most abundant dietary fatty acid in human adipose tissue. PUFA-derived oxylipins regulate a variety of biological functions. The cytochrome P450 (CYP450)­formed epoxy fatty acid metabolites of LA (EpOMEs) are hydrolyzed by the soluble epoxide hydrolase enzyme (sEH) to dihydroxyoctadecenoic acids (DiHOMEs). DiHOMEs are considered cardioprotective at low concentrations but at higher levels have been implicated as vascular permeability and cytotoxic agents and are associated with acute respiratory distress syndrome in severe COVID-19 patients. High EpOME levels have also correlated with sepsis-related fatalities; however, those studies failed to monitor DiHOME levels. Considering the overlap of burn pathophysiology with these pathologies, the role of DiHOMEs in the immune response to burn injury was investigated. 12,13-DiHOME was found to facilitate the maturation and activation of stimulated neutrophils, while impeding monocyte and macrophage functionality and cytokine generation. In addition, DiHOME serum concentrations were significantly elevated in burn-injured mice and these increases were ablated by administration of 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), a sEH inhibitor. TPPU also reduced necrosis of innate and adaptive immune cells in burned mice, in a dose-dependent manner. The findings suggest DiHOMEs are a key driver of immune cell dysfunction in severe burn injury through hyperinflammatory neutrophilic and impaired monocytic actions, and inhibition of sEH might be a promising therapeutic strategy to mitigate deleterious outcomes in burn patients.

Plasma Linoleate Diols Are Potential Biomarkers for Severe COVID-19 Infections.

Polyunsaturated fatty acids are metabolized into regulatory lipids important for initiating inflammatory responses in the event of disease or injury and for signaling the resolution of inflammation and return to homeostasis. The epoxides of linoleic acid (leukotoxins) regulate skin barrier function, perivascular and alveolar permeability and have been associated with poor outcomes in burn patients and in sepsis. It was later reported that blocking metabolism of leukotoxins into the vicinal diols ameliorated the deleterious effects of leukotoxins, suggesting that the leukotoxin diols are contributing to the toxicity. During quantitative profiling of fatty acid chemical mediators (eicosanoids) in COVID-19 patients, we found increases in the regioisomeric leukotoxin diols in plasma samples of hospitalized patients suffering from severe pulmonary involvement. In rodents these leukotoxin diols cause dramatic vascular permeability and are associated with acute adult respiratory like symptoms. Thus, pathways involved in the biosynthesis and degradation of these regulatory lipids should be investigated in larger biomarker studies to determine their significance in COVID-19 disease. In addition, incorporating diols in plasma multi-omics of patients could illuminate the COVID-19 pathological signature along with other lipid mediators and blood chemistry.