| Objective NLRP3 inflammasome is an important component of innate immunity.Its’aberrant activation and subsequent IL-1βsecretion plays a vital role in the development of inflammatory bowel diseases(IBD).Curcumin,as a kind of natural polyphenols,possesses potent anti-inflammatory and immunoregulatory effects.In this study,we sought to clarify the inhibitory effect and possible mechanisms of curcumin on the DSS-induced NLRP3 inflammasome activation and IL-1βproduction,and to investigate the protective role of curcumin against dextran sulfate sodium(DSS)-induced colitis.Methods LPS-primed murine macrophages(bone marrow-derived macrophages or peritoneal macrophages)or colonic epithelial cells were treated with different concentrations of DSS,and DSS-untreated cells were regarded as control.Mature IL-1β,a pivotal pro-inflammatory cytokine associated with inflammasome activation,was detected by ELISA.Then specific inhibitors of caspase-1 or NLRP3 were administrated to the DSS-stimulated cells respectively,the secretion of mature IL-1βwas measured to confirm the effect of DSS on the activation of NLRP3 inflammasome.Meanwhile,curcumin was added prior to DSS in some groups,and its’inhibitory effect on DSS-induced NLRP3 inflammasome activation was evaluated by the measurement of released IL-1βas well as the observation of ASC oligomerization.Three common mechanisms are involved in the NLRP3 inflammasomes activation:potassium(K~+)efflux,cathepsin B leakage and reactive oxygen species(ROS)generation.Thus,to explore the possible mechanisms of the inhibitory effect of curcumin on DSS-induced NLRP3 inflammasome activation,LPS-primed murine macrophages were treated with DSS in the presence or absence of curcumin.Fluorescence staining and flow cytometry were conducted to analyze ROS formation;Lysosomal cathepsin B leakage was measured by fluorescence staining and cathepsin B activity assay;ICP-OES、fluorescence staining and flow cytometry were performed to assess the changes of intracellular K~+levels.To explore the protective effect of curcmin on DSS-induced colitis through suppressing NLRP3inflammasomes activation,wild-type C57BL/6 mice were randomly divided into five groups:control group,DSS group,DSS-curcumin group,DSS-MCC950(NLRP3-specific inhibitor)group and DSS-curcumin-MCC950 group.Colitis was induced in mice with 3%DSS for 7 days,the changes of body weight and stool properties were recorded daily and disease activity index(DAI)was evaluated.On day 8,mice were sacrificed then the colon length was measured;HE staining of colon sections was performed and histopathological damage score was assessed.In addition,mature IL-1βas well as MPO and caspase-1 activity of colonic tissue homogenate were detected.Results DSS could induce the NLRP3 inflammasomes activation and mature IL-1βsecretion in LPS-primed murine macrophages and colonic epithelial cells.While the effect of DSS could be drammatically inhibited by curcumin in a dose-dependent fashion.Curcumin suppresssed DSS-induced NLRP3 inflammasome activation through inhibiting K~+efflux,cathepsin B leakage and ROS generation.In vivo,curcumin administration significantly ameliorated DSS-induced colitis,as evidenced by reduced hematochezia score,weight loss and colon length shortening,meanwhile,mature IL-1βlevel as well as MPO and caspase-1 activity in the colonic tissue were also strongly decreased.Furthermore,the inhibitory effect of curcumin on intestinal inflammation was comparable with the specific NLRP3 inhibitor,and the blockage of NLRP3 inflammasome activation with specific NLRP3 inhibitor almost completely abrogated the further inhibitory effect of curcumin on DSS-induced colitis.Conclusion Curcumin could potently inhibit DSS-induced NLRP3 inflammasome activation and proinflammatory cytokine secretion,thus contributing to the amelioration of DSS-induced colitis in mice.Curcumin may be served as a potential candidate drug in clinical application for IBD therapy. |
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