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 µM) with and without LPS (1 µg/mL). Nitric oxide production was determined by Griess reagent and tumor necrosis factor (TNF)-α and interleukin (IL)-1β 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 µM) decreased nitric oxide, TNF-α, and IL-1β 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-α, and IL-1β 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.