title: Scavenging of reactive oxygen species by tryptophan metabolites helps Pseudomonas aeruginosa escape neutrophil killing.
abstract: Pseudomonas aeruginosa is responsible for persistent infections in cystic fibrosis patients, suggesting an ability to circumvent innate immune defenses. This bacterium uses the kynurenine pathway to catabolize tryptophan. Interestingly, many host cells also produce kynurenine, which is known to control immune system homeostasis. We showed that most strains of P. aeruginosa isolated from cystic fibrosis patients produce a high level of kynurenine. Moreover, a strong transcriptional activation of kynA (the first gene involved in the kynurenine pathway) was observed upon contact with immune cells and particularly with neutrophils. In addition, using coculture of human neutrophils with various strains of P. aeruginosa producing no (ΔkynA) or a high level of kynurenine (ΔkynU or ΔkynA pkynA), we demonstrated that kynurenine promotes bacterial survival. In addition, increasing the amount kynurenine inhibits reactive oxygen species production by activated neutrophils, as evaluated by chemiluminescence with luminol or isoluminol or SOD-sensitive cytochrome c reduction assay. This inhibition is due neither to a phagocytosis defect nor to direct NADPH oxidase inhibition. Indeed, kynurenine has no effect on oxygen consumption by neutrophils activated by PMA or opsonized zymosan. Using in vitro reactive oxygen species-producing systems, we showed that kynurenine scavenges hydrogen peroxide and, to a lesser extent, superoxide. Kynurenine׳s scavenging effect occurs mainly intracellularly after bacterial stimulation, probably in the phagosome. In conclusion, the kynurenine pathway allows P. aeruginosa to circumvent the innate immune response by scavenging neutrophil reactive oxygen species production.
authors.affiliation: TIMC/Therex Laboratory, UMR 5525 (CNRS-UJF), Faculty of Medicine, University of Grenoble Alpes, Grenoble F-38041, France.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Genestet
authors.affiliation: TIMC/Therex Laboratory, UMR 5525 (CNRS-UJF), Faculty of Medicine, University of Grenoble Alpes, Grenoble F-38041, France.
authors.forename: Audrey
authors.initials: A
authors.lastname: Le Gouellec
authors.affiliation: TIMC/Therex Laboratory, UMR 5525 (CNRS-UJF), Faculty of Medicine, University of Grenoble Alpes, Grenoble F-38041, France.
authors.forename: Hichem
authors.initials: H
authors.lastname: Chaker
authors.affiliation: TIMC/Therex Laboratory, UMR 5525 (CNRS-UJF), Faculty of Medicine, University of Grenoble Alpes, Grenoble F-38041, France.
authors.forename: Benoit
authors.initials: B
authors.lastname: Polack
authors.affiliation: Recherche translationnelle hôte pathogène, Université Lille 2, Faculté de Médecine, CHRU, Lille, France.
authors.forename: Benoit
authors.initials: B
authors.lastname: Guery
authors.affiliation: TIMC/Therex Laboratory, UMR 5525 (CNRS-UJF), Faculty of Medicine, University of Grenoble Alpes, Grenoble F-38041, France.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Toussaint
authors.affiliation: TIMC/Therex Laboratory, UMR 5525 (CNRS-UJF), Faculty of Medicine, University of Grenoble Alpes, Grenoble F-38041, France; Chronic Granulomatous Disease Diagnosis and Research Center, Pôle Biologie, CHU de Grenoble, Grenoble F-38043, France. Electronic address: mjstasia@chu-grenoble.fr.
authors.forename: Marie José
authors.initials: MJ
authors.lastname: Stasia
mesh_terms: D003550:Cystic Fibrosis / Q000276:immunology / Q000382:microbiology; D016166:Free Radical Scavengers / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D006867:Hydrolases / Q000235:genetics; D057131:Immune Evasion; D007736:Kynurenic Acid / Q000378:metabolism; D007737:Kynurenine / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D009504:Neutrophils / Q000276:immunology*; D010101:Oxygen Consumption; D011552:Pseudomonas Infections / Q000276:immunology; D011550:Pseudomonas aeruginosa / Q000276:immunology* / Q000378:metabolism* / Q000472:pathogenicity; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism
chemical_list: D016166:Free Radical Scavengers; D017382:Reactive Oxygen Species; D007737:Kynurenine; D014364:Tryptophan; D006861:Hydrogen Peroxide; D006867:Hydrolases; C021480:kynureninase; D007736:Kynurenic Acid
keywords: Free radicals; Kynurenine; Neutrophils; P. aeruginosa; Reactive oxygen species; Resistance; Scavenger; Tryptophan metabolites