Severe acute respiratory syndrome coronavirus 2 is responsible for coronavirus disease 2019 (COVID‐19). While COVID‐19 is often benign, a subset of patients develops severe multilobar pneumonia that can progress to an acute respiratory distress syndrome. There is no cure for severe COVID‐19 and few treatments significantly improved clinical outcome. Dexamethasone and possibly aspirin, which directly/indirectly target the biosynthesis/effects of numerous lipid mediators are among those options. Our objective was to define if severe COVID‐19 patients were characterized by increased bioactive lipids modulating lung inflammation. A targeted lipidomic analysis of bronchoalveolar lavages (BALs) by tandem mass spectrometry was done on 25 healthy controls and 33 COVID‐19 patients requiring mechanical ventilation. BALs from severe COVID‐19 patients were characterized by increased fatty acids and inflammatory lipid mediators. There was a predominance of thromboxane and prostaglandins. Leukotrienes were also increased, notably LTB ₄ , LTE ₄ , and eoxin E ₄ . Monohydroxylated 15‐lipoxygenase metabolites derived from linoleate, arachidonate, eicosapentaenoate, and docosahexaenoate were also increased. Finally yet importantly, specialized pro‐resolving mediators, notably lipoxin A ₄ and the D‐series resolvins, were also increased, underscoring that the lipid mediator storm occurring in severe COVID‐19 involves pro‐ and anti‐inflammatory lipids. Our data unmask the lipid mediator storm occurring in the lungs of patients afflicted with severe COVID‐19. We discuss which clinically available drugs could be helpful at modulating the lipidome we observed in the hope of minimizing the deleterious effects of pro‐inflammatory lipids and enhancing the effects of anti‐inflammatory and/or pro‐resolving lipid mediators.

The endocannabinoids 2-arachidonoyl-glycerol and N-arachidonoyl-ethanolamine are lipids regulating many physiological processes, notably inflammation. Endocannabinoid hydrolysis inhibitors are now being investigated as potential anti-inflammatory agents. In addition to 2-arachidonoyl-glycerol and N-arachidonoyl-ethanolamine, the endocannabinoidome also includes other monoacylglycerols and N-acyl-ethanolamines such as 1-linoleoyl-glycerol (1-LG) and N-linoleoyl-ethanolamine (LEA). By increasing monoacylglycerols and/or N-acyl-ethanolamine levels, endocannabinoid hydrolysis inhibitors will likely increase the levels of their metabolites. Herein, we investigated whether 1-LG and LEA were substrates for the 15-lipoxygenase pathway, given that both possess a 1Z,4Z-pentadiene motif, near their omega end. We thus assessed how human eosinophils and neutrophils biosynthesized the 15-lipoxygenase metabolites of 1-LG and LEA. Linoleic acid (LA), a well-documented substrate of 15-lipoxygenases, was used as positive control. N-13-hydroxy-octodecadienoyl-ethanolamine (13-HODE-EA) and 13-hydroxy-octodecadienoyl-glycerol (13-HODE-G), the 15-lipoxygenase metabolites of LEA and 1-LG, were synthesized using Novozym 435 and soybean lipoxygenase. Eosinophils, which express the 15-lipoxygenase-1, metabolized LA, 1-LG, and LEA into their 13-hydroxy derivatives. This was almost complete after five minutes. Substrate preference of eosinophils was LA > LEA > 1-LG in presence of 13-HODE-G hydrolysis inhibition with methyl-arachidonoyl-fluorophosphonate. Human neutrophils also metabolized LA, 1-LG, and LEA into their 13-hydroxy derivatives. This was maximal after 15–30 s. Substrate preference was LA ≫ 1-LG > LEA. Importantly, 13-HODE-G was found in humans and mouse tissue samples. In conclusion, our data show that human eosinophils and neutrophils metabolize 1-LG and LEA into the novel endogenous 15-lipoxygenase metabolites 13-HODE-G and 13-HODE-EA. The full biological importance of 13-HODE-G and 13-HODE-EA remains to be explored.

BACKGROUND: Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) is the infectious agent responsible for Coronavirus disease 2019 (COVID-19). While SARS-CoV-2 infections are often benign, there are also severe COVID-19 cases, characterized by severe bilobar pneumonia that can decompensate to an acute respiratory distress syndrome, notably characterized by increased inflammation and a cytokine storm. While there is no cure against severe COVID-19 cases, some treatments significantly decrease the severity of the disease, notably aspirin and dexamethasone, which both directly or indirectly target the biosynthesis (and effects) of numerous bioactive lipids. OBJECTIVE: Our working hypothesis was that severe COVID-19 cases necessitating mechanical ventilation were characterized by increased bioactive lipid levels modulating lung inflammation. We thus quantitated several lung bioactive lipids using liquid chromatography combined to tandem mass spectrometry. RESULTS: We performed an exhaustive assessment of the lipid content of bronchoalveolar lavages from 25 healthy controls and 33 COVID-19 patients necessitating mechanical ventilation. Severe COVID-19 patients were characterized by increased fatty acid levels as well as an accompanying inflammatory lipid storm. As such, most quantified bioactive lipids were heavily increased. There was a predominance of cyclooxygenase metabolites, notably TXB ₂ >> PGE ₂ ∼ 12-HHTrE > PGD ₂ . Leukotrienes were also increased, notably LTB ₄ , 20-COOH-LTB ₄ , LTE ₄ , and eoxin E ₄ . 15-lipoxygenase metabolites derived from linoleic, arachidonic, eicosapentaenoic and docosahexaenoic acids were also increased. Finally, yet importantly, specialized pro-resolving mediators, notably lipoxin A ₄ and the D-series resolvins, were also found at important levels, underscoring that the lipid storm occurring in severe SARS-CoV-2 infections involves pro- and anti-inflammatory lipids. CONCLUSIONS: Our data unmask the important lipid storm occurring in the lungs of patients afflicted with severe COVID-19. We discuss which clinically available drugs could be helpful at modulating the lipidome we observed in the hope of minimizing the deleterious effects of pro-inflammatory lipids and enhancing the effects of anti-inflammatory and/or pro-resolving lipids.

High eosinophil (EOS) counts are a key feature of eosinophilic asthma. EOS notably affect asthmatic response by generating several lipid mediators. Mice have been utilized in hopes of defining new pharmacological targets to treat asthma. However, many pinpointed targets in mice did not translate into clinics, underscoring that key differences exist between the two species. In this study, we compared the ability of human (h) and mouse (m) EOS to biosynthesize key bioactive lipids derived from arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). hEOS were isolated from the blood of healthy subjects and mild asthmatics, while mEOSs were differentiated from the bone marrow. EOSs were treated with fatty acids and lipid mediator biosynthesis assessed by LC-MS/MS. We found that hEOS biosynthesized leukotriene (LT) C₄ and LTB₄ in a 5:1 ratio while mEOS almost exclusively biosynthesized LTB₄. The biosynthesis of the 15-lipoxygenase (LO) metabolites 15-HETE and 12-HETE also differed, with a 15-HETE:12-HETE ratio of 6.3 for hEOS and 0.727 for mEOS. EOS biosynthesized some specialized pro-resolving mediators, and the levels from mEOS were 9-times higher than those of hEOS. In contrast, hEOS produced important amounts of the endocannabinoid 2-arachidonoyl-glycerol (2-AG) and its congeners from EPA and DHA, a biosynthetic pathway that was up to ~100-fold less prominent in mEOS. Our data show that hEOS and mEOS biosynthesize the same lipid mediators but in different amounts. Compared to asthmatics, mouse models likely have an amplified involvement of LTB₄ and specialized pro-resolving mediators and a diminished impact of the endocannabinoid 2-arachidonoyl-glycerol and its congeners.

Cell-tagging strategies with DNA barcodes have enabled the analysis of clone size dynamics and clone-restricted transcriptomic landscapes in heterogeneous populations. However, isolating a target clone that displays a specific phenotype from a complex population remains challenging. Here we present a multi-kingdom genetic barcoding system, CloneSelect, which enables a target cell clone to be triggered to express a reporter gene for isolation through barcode-specific CRISPR base editing. In CloneSelect, cells are first stably tagged with DNA barcodes and propagated so that their subpopulation can be subjected to a given experiment. A clone that shows a phenotype or genotype of interest at a given time can then be isolated from the initial or subsequent cell pools stored during the experiment using CRISPR base editing. CloneSelect is scalable and compatible with single-cell RNA sequencing. We demonstrate the versatility of CloneSelect in human embryonic kidney 293T cells, mouse embryonic stem cells, human pluripotent stem cells, yeast cells and bacterial cells.

Clonal heterogeneity underlies diverse biological processes, including cancer progression, cell differentiation, and microbial evolution. Cell tagging strategies with DNA barcodes have recently enabled analysis of clone size dynamics and clone-restricted transcriptomic landscapes of heterogeneous populations. However, isolating a target clone that displays a specific phenotype from a complex population remains challenging. Here, we present a new multi-kingdom genetic barcoding system, CloneSelect, in which a target cell clone can be triggered to express a reporter gene for isolation through barcode-specific CRISPR base editing. In CloneSelect, cells are first barcoded and propagated so their subpopulation can be subjected to a given experiment. A clone that shows a phenotype or genotype of interest at a given time can then be isolated from the initial or subsequent cell pools stored throughout the experimental timecourse. This novel CRISPR-barcode genetics platform provides many new ways of analyzing and manipulating mammalian, yeast, and bacterial systems. Teaser A multi-kingdom CRISPR-activatable barcoding system enables the precise isolation of target barcode-labeled clones from a complex cell population.