Background

Sepsis is a serious and life-threatening syndrome that occurs in intensive care unit patients. Lipopolysaccharide (LPS) has been implicated as one of major causes of sepsis. Nitric oxide (NO) and cytokines are involved in sepsis-induced inflammatory responses. This study is aimed at evaluating the effects of NO on the modulation of pro-and anti-inflammatory cytokines in LPS-activated macrophages and its possible mechanism.

Methods

N-Monomethyl arginine (NMMA), an inhibitor of NO synthase, was used in this study to suppress NO production. Mouse macrophage-like Raw 264.7 cells were exposed to LPS, NMMA, or a combination of NMMA and LPS. Cell viability was determined by the colorimetric 3-(4, 5-dimethylthiazol-2-yl)-2, 5-di-phenyltetrazolium bromide assay. The amounts of nitrite, an oxidative product of NO, in the culture medium were quantified according to the Griess reaction method. Enzyme-linked immunosorbent assay and reverse-transcriptase polymerase chain reaction were carried out to determine the expression of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-10 in macrophages.

Results

Exposure of macrophages to LPS, NMMA, and a combination of NMMA and LPS for 24 hours did not affect cell viability. LPS significantly increased the amounts of nitrite in macrophages (p< 0.01). Treatment with NMMA decreased LPS-enhanced nitrite (p< 0.01) in a concentration-dependent manner. Analyses of enzyme-linked immunosorbent assays and reverse-transcriptase polymerase chain reaction revealed that LPS significantly induced TNF-α, IL-1β, and IL-10 proteins and mRNA (p< 0.01). A combined treatment with NMMA and LPS significantly blocked LPS-induced TNF-α and IL-1β (p< 0.01), but synergistically enhanced LPS-induced IL-10 (p< 0.05) protein and RNA.

Conclusion

This study has shown that NO suppression can inhibit LPS-induced TNF-α and IL-1β but enhance IL-10, and the modulation occurs at a pretranslational level.

Infection-induced sepsis is one of the most important causes of multiple system organ failure and probably leads to a terrible mortality in severely traumatized patients. 1, 2 Lipopolysaccharide (LPS), a gram-negative bacterial outer membrane component, has been implicated as a critical factor contributing to the pathogenesis of sepsis. 3 Exposure of animals or human volunteers to LPS can reproduce inflammatory responses seen in sepsis. 3 A growing body of evidence reports that inflammatory factors such as nitric oxide (NO), tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-10 are involved in LPS-induced sepsis. 4, 5 Modulating these inflammatory factors may influence the LPS-induced septic pathogenesis.