Effects of pyocyanine, a phenazine dye from Pseudomonas aeruginosa, on oxidative burst and bacterial killing in human neutrophils

Abstract

The effects of pyocyanine (phenazinium, 1-hydroxy-5-methyl-hydroxide, inner salt) on oxidative burst in human polymorphonuclear leukocytes were studied by several different approaches. In a cell- and enzyme-free system, pyocyanine oxidized NADPH. The reduced pyocyanine could be measured by its reaction with ferricytochrome c. It was shown by this assay that resting as well as phorbol myristate acetate- or zymosan-stimulated granulocytes reduced pyocyanine. The effect was independent of mitochondria, as cytoplasts were similarly active. Measurement of the hexose monophosphate shunt in intact granulocytes in the presence of pyocyanine indicated a concentration-dependent activation of the shunt without the generation of O2-, suggesting that pyocyanine oxidizes NADPH to NADP+ when it enters granulocytes. Intracellular NADPH in granulocytes was indeed lowered by almost 40% after incubation with pyocyanine. It is by this shuttling of reduction equivalents, leading to the partial depletion of NADPH, that pyocyanine affects the observed concentration-dependent partial inhibition of the phorbol myristate acetate- and zymosan-stimulated generation of O2-. A further consequence was that the intracellular killing of Staphylococcus aureus was also partially suppressed, particularly at higher loads of granulocytes with bacteria. Phagocytosis was not inhibited by pyocyanine concentrations as high as 500 microM. Pyocyanine did not affect the intracellular killing of Pseudomonas aeruginosa. The possible relevance of these findings to the course of mixed hospital infections in immunocompromised patients is discussed.