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1 Department of Research Service, VA Medical Center, Iowa City, IA, USA; Department of Internal Medicine, University of Iowa, Iowa City, IA, USA; Department of Research Service, VA Medical Center, Iowa City, IA, USA
2 Department of Research Service, VA Medical Center, Iowa City, IA, USA; The Free Radical and Radiation Biology Program of the Department of Radiation Oncology, The Roy G. and Lucille A. Carver College of Medicine of The University of Iowa, Iowa City, IA, USA; Department of Internal Medicine, VA Medical Center, Iowa City, IA, USA
3 The Free Radical and Radiation Biology Program of the Department of Radiation Oncology, The Roy G. and Lucille A. Carver College of Medicine of The University of Iowa, Iowa City, IA, USA; The Free Radical and Radiation Biology Program of the Department of Radiation Oncology, The Roy G. and Lucille A. Carver College of Medicine of The University of Iowa, Iowa City, IA, USA
4 Department of Internal Medicine, VA Medical Center, Iowa City, IA, USA; Department of Research Service, VA Medical Center, Iowa City, IA, USA; Department of Internal Medicine, University of Iowa, Iowa City, IA, USA
* To whom correspondence should be addressed. E-mail: bradley-britigan{at}uiowa.edu.
Pyocyanin, produced by Pseudomonas aeruginosa, has many deleterious effects on human cells that relate to its ability to generate reactive oxygen species (ROS), such as superoxide and hydrogen peroxide. Human cells possess several mechanisms to protect themselves from ROS, including manganese superoxide dismutase (MnSOD), copper zinc superoxide dismutase (CuZnSOD), and catalase. Given the link between pyocyaninmediated epithelial cell injury and oxidative stress, we assessed pyocyanin's affect on MnSOD, CuZnSOD, and catalase levels in the A549 human alveolar epithelial cell line and in normal human bronchial epithelial (NHBE) cells. In both cell types, CuZnSOD and MnSOD was unaltered, but over 24 h pyocyanin significantly decreased cellular catalase activity and protein content. Pyocyanin also decreased catalase mRNA. Overexpression of MnSOD in A549 cells prevented pyocyanin-mediated loss of catalase protein, but catalase activity still declined. Furthermore, pyocyanin decreased catalase activity, but not protein, in A549 cells overexpressing human catalase. These data suggest a direct effect of pyocyanin on catalase activity. Addition of pyocyanin to catalase in a cell-free system also decreased catalase activity. Mammalian catalase binds four NADPH molecules, helping maintain enzyme activity. Spin trapping data suggest that pyocyanin directly oxidizes this NADPH, producing superoxide. We conclude that pyocyanin may decrease cellular catalase activity via both transcriptional regulation and direct inactivation of the enzyme. Decreased cellular catalase activity and failure to augment MnSOD could contribute to pyocyanin-dependent cytotoxicity.
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