Reactive oxygen species (ROS), including hydrogen peroxide (H2O2), are generated in increased amounts in pathological, biological processes and can play a role in signal transduction. Neutrophils often accumulate in acute inflammatory reactions, at sites where elevated concentrations of ROS are present. ROS have been demonstrated to participate in the activation of intracellular signaling pathways, including those involved in modulating nuclear accumulation and transcriptional activity of NF-κB. However, the role of ROS in affecting such events in neutrophils has not been examined. Using exposure of murine bone marrow neutrophils to H2O2 as a model of oxidative stress, we found both strong and persistent activation of ERK1/2, p38, JNK, and PKB, but not the p21-activated kinase. Stimulating the bone marrow-derived neutrophils with H2O2 did not affect nuclear translocation of NF-κB. However, production and secretion of the proinflammatory cytokine TNF-α in LPS-stimulated neutrophils were inhibited by H2O2. Exposure of LPS- or TNF-α-stimulated neutrophils to H2O2 decreased nuclear translocation of NF-κB. LPS-induced activation of the transcriptional factor AP-1 was also inhibited by H2O2. This inhibition of nuclear accumulation of NF-κB by H2O2 was not caused by an impaired capacity of LPS to stimulate the IKK pathway or to direct oxidative effects on NF-κB but rather reflected diminished degradation of IκB-α. These results indicate that oxidative stress, despite being able to selectively activate intracellular kinases in bone marrow-derived neutrophils, also inhibits NF-κB activation and associated TNF-α expression. Such inhibitory effects on neutrophil activation may limit tissue damage produced by oxidative stress.
The immunostimulatory activity of polysaccharides from Glycyrrhiza uralensis