P. aeruginosa is a common pathogen affecting immunocompromised patients with acute diseases such as pneumonia and vasculitis or chronic diseases such as cystic fibrosis. It produces several phenazine toxic metabolites, in which the most predominant is a blue pigment, pyocyanin. Pyocyanin has been shown to accelerate neutrophil apoptosis in vitro, resulting in resolution of acute inflammation, that is beneficial for bacterial survival. It also induces a 10-fold acceleration of neutrophil apoptosis in vitro. Pyocyanin production results in reduced bacterial clearance from the lungs of immunocompromised patients. It has also been reported to induce apoptosis in human lung epithelial cells and to induce premature cellular senescence in mammalian cells. Pyocyanin undergoes nonenzymatic reduction by NADPH, which produces hydrogen peroxide and depletes intracellular glutathione levels, causing oxidative stress in susceptible cells.
