Anti-inflammatory potential of pyocyanin in LPS-stimulated murine macrophages

Context: Pyocyanin is a typical Pseudomonas aeruginosa virulence factor, a common Gram-negative rod responsible for a wide range of severe nosocomial infections. There is evidence indicating that pyocyanin has multiple biological activities, but little is known about anti-inflammatory properties.Objective: This study investigated pyocyanin effect on nitric oxide and cytokine production in lipopolysaccharide (LPS)-activated murine peritoneal macrophages.Materials and methods: Macrophages were incubated in the presence and absence of pyocyanin (1, 5, 10, 50, and 100 mu M) with and without LPS (1 mu g/mL). Nitric oxide production was determined by Griess reagent and tumor necrosis factor (TNF)- and interleukin (IL)-1 production was assessed by enzyme-linked immunosorbent assay. In addition, pyocyanin effects on zymosan A-induced peritonitis in mice were evaluated.Results: Pyocyanin (5 and 10 mu M) decreased nitric oxide, TNF-, and IL-1 production independent of macrophage death. On the other hand, in vivo, pyocyanin (5 mg/kg) was not able to affect leukocyte migration into the site of inflammation.Discussion and conclusion: Thus, our findings suggest that pyocyanin exerts anti-inflammatory effects on murine peritoneal macrophages, downregulating nitric oxide, TNF-, and IL-1 levels, which seems to be independent of cell migration. These effects may represent a mechanism of immune evasion; nevertheless more detailed studies should be performed to confirm this hypothesis.