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Extracellular polysaccharides (EPSs) are high-molecular weight sugar-based polymers that are synthesized and secreted by many microorganisms. Recently, EPSs have attracted particular attention due to their multiple biological functions including anti-inflammation. However, studies rarely reported the molecular mechanisms underlying their functions. We previously purified an EPS from an oligotrophic bacteria (Bacillus sp. LBP32) found in Lop Nur Desert, which possesses a potent antioxidant activity, while the anti-inflammatory effects of EPS and signaling mechanisms underlying its action have not been clarified. In this study, we demonstrated that EPS significantly inhibited the LPS-induced release of pro-inflammatory mediators, such as nitric oxide (NO), IL-6 and TNF-alpha, without any significant cytotoxicity. EPS also downregulated the expression of nitric oxide synthase (iNOS) induced by LPS. Furthermore, activation of nuclear factor kappa B (NF-kappa B) was abrogated by EPS through inhibited the phosphorylation of I kappa B kinase (IKK). Activations of Mitogen-activated protein kinases (MAPKs), including p38 MAPK and c-Jun N-terminal kinase (JNK), were also found to be inhibited by EPS. In addition, the level of intracellular reactive oxygen species (ROS) was also significantly decreased with the treatment of EPS. In vivo experiments were conducted and showed that EPS could greatly improve the outcome of mice with LPS-induced endotoxic shock. Taken together, our data indicate that EPS prevents LPS-induced inflammatory response by inhibiting NF-kappa B and MAPKs activation and ROS production. (C) 2013 Elsevier B.V. All rights reserved.