Biochem/physiol Actions
Pyocyanin, a redox-active phenazine, is an electron receptor, which stimulates redox cycling in bacteria, liver cells, and human epithlial cell lines. It enhances oxidative metabolism, which increases the formation of intracellular reactive oxygen species (ROS) via reduction of NADPH. Pyocyanin also increases the release of the neutrophil chemoattractant IL-8 by airway epithelial cells both in vitro and in vivo. This involves signal transduction pathways that include oxidants, protein tyrosin kinases and MAP-kinases. IL-8 secretion by these cells is in synergy with inflammatory cytokines. Pyocyanin accelerates neutrophil apoptosis in vitro. Mice infected with a pyocyanin-deficient strain of P. aeruginosa showed elevated levels of neutrophils and neutrophil chemokines and cytokines, as well as compromised bacterial clearance from the lungs compared with mice infected with a wild type strain. This suggests that pyocyanin production by P. aeruginosa suppresses the acute inflammatory response by pathogen-driven acceleration of neutrophil apoptosis and by reducing local inflammation, and that this is advantageous for bacterial survival.