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* National Institutes of Health, National Institute of Allergy and Infectious Diseases, Laboratory of Host Defenses, Rockville, MD 20852;
Lonza Walkersville, Walkersville, MD 21793; and
Centre National de la Recherche Scientifique, FRE2939, Villejuif, France; Université Paris-Sud 11, Orsay, France; and Institut Gustave Roussy, Villejuif, France
The dual oxidase-thiocyanate-lactoperoxidase (Duox/SCN–/LPO) system generates the microbicidal oxidant hypothiocyanite in the airway surface liquid by using LPO, thiocyanate, and Duox-derived hydrogen peroxide released from the apical surface of the airway epithelium. This system is effective against several microorganisms that infect airways of cystic fibrosis and other immunocompromised patients. We show herein that exposure of airway epithelial cells to Pseudomonas aeruginosa obtained from long-term cultures inhibits Duox1-dependent hydrogen peroxide release, suggesting that some microbial factor suppresses Duox activity. These inhibitory effects are not seen with the pyocyanin-deficient P. aeruginosa strain PA14 Phz1/2. We show that purified pyocyanin, a redox-active virulence factor produced by P. aeruginosa, inhibits human airway cell Duox activity by depleting intracellular stores of NADPH, as it generates intracellular superoxide. Long-term exposure of human airway (primary normal human bronchial and NCI-H292) cells to pyocyanin also blocks induction of Duox1 by Th2 cytokines (IL-4, IL-13), which was prevented by the antioxidants glutathione and N-acetylcysteine. Furthermore, we showed that low concentrations of pyocyanin blocked killing of wild-type P. aeruginosa by the Duox/SCN–/LPO system on primary normal human bronchial epithelial cells. Thus, pyocyanin can subvert Pseudomonas killing by the Duox-based system as it imposes oxidative stress on the host. We also show that lactoperoxidase can oxidize pyocyanin, thereby diminishing its cytotoxicity. These data establish a novel role for pyocyanin in the survival of P. aeruginosa in human airways through competitive redox-based reactions between the pathogen and host.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 This work was supported by funding through the Intramural Research Program of the National Institutes of Health, National Institute of Allergy and Infectious Diseases.
2 Address correspondence and reprint requests to Dr. Thomas L. Leto, National Institutes of Health, National Institute of Allergy and Infectious Diseases, 12441 Parklawn Drive, Bethesda, MD, 20892. E-mail address: tleto{at}nih.gov
3 Abbreviations used in this paper: ASL, airway surface liquid; ALI, air-liquid interface; CF, cystic fibrosis; CFTR, cystic fibrosis transmembrane conductance regulator; DPI, diphenylene iodonium; Duox, dual oxidase; GSH, glutathione; int. RLU, integrated RLU; LB, Luria-Bertani; LPO, lactoperoxidase; MPO, myeloperoxidase; NAC, N-acetylcysteine; NHBE, normal human bronchial epithelial; Nox, NADPH oxidase; OSCN–, hypothiocyanite; PA14, Pseudomonas aeruginosa 14 strain; PAO1, Pseudomonas aeruginosa O1 strain; Pyo, pyocyanin; RLU, relative luminescence unit; ROS, reactive oxygen species; SCN–, thiocyanate; siRNA, small interfering RNA; WT, wild type.
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