In vitro effect of synthetic pyocyanine on neutrophil superoxide production

Pyocyanine, a low-molecular-weight phenazine pigment produced by Pseudomonas aeruginosa, has previously been shown to strongly inhibit human lymphocyte blastogenesis. We now report that synthetic pyocyanine can also affect the generation of superoxide by human peripheral blood polymorphonuclear leukocytes (PMNs) in a dose-dependent manner. Superoxide production by PMNs stimulated with phorbol myristate acetate (PMA) was measured in the presence and absence of pyocyanine, phenazine, and trifluoperazine, a phenothiazine of similar chemical structure to the phenazine pigments. Pyocyanine at 50 microM inhibited superoxide production to 28.9 +/- 2.8% of PMA control values, whereas at the lower concentration of 1 microM, the production of superoxide was significantly enhanced (203 +/- 31.7% of PMA control values). Phenazine, the tricyclic parent compound of pyocyanine, had only a minor effect. Trifluoperazine had a marked inhibitory effect on superoxide generation at concentrations above 1 microM. None of the compounds induced superoxide generation in the absence of PMA. Pyocyanine at all concentrations, unlike phenothiazines, had very little effect on the release of neutrophil granule enzymes. The effect of P. aeruginosa phenazine pigments on polymorphonuclear phagocytes is of significance, since inhibition of host PMN function at sites of infection could result in ineffective bacterial killing, whereas enhanced PMN function could lead to greater tissue damage. These two possibilities are not mutually exclusive and may coexist depending on local pyocyanine concentrations.