To investigatethe inhibitory effect and mechanisms of curcumin on lipopolysaccharide (LPS) -induced inflammation of nerve cells.

Microglia (BV2) was used in current study and named control group (without any treatment), model group (treated with LPS 100 ng/mL for 24 h) and treatment group (curcumin at 1, 5, 10 μmol/L concentration plus 100 ng/ml LPS for 24 h). The expression levels of interleukin-6 (IL-6), IL-10, p-NF-κB, NLRP3, Bax and Bcl-2 in BV2 cells were detected by immunofluorescence assay. Western blot was used to detect the protein expression of NF-κB/NLRP3 signaling pathway. The contents of tumor necrosis factor α (TNF-α), IL-1β and iNOS were detected by ELISA. In addition, the expression levels of IL-6, IL-10, Bax and Bcl-2 proteins in BV2 cells were detected after administration of NF-κB inhibitor BAY 11-7082. The experimental data were analyzed by t test, one-way ANOVA and Dunnett-t test.

Compared with the control group, the inflammatory cytokines TNF-α (398.80 ± 11.39 vs 113.00 ± 5.93), IL-1β (592.40 ± 11.32 vs 206.70 ± 6.81), IL-6 (1.73 ± 0.09 vs 0.99 ± 0.03), iNOS (88.39 ± 2.14 vs 32.48 ± 1.71), p-NF-κB (1.92 ± 0.02 vs 1.02 ± 0.05), INOS (88.39 ± 2.14 vs 32.48 ± 1.71), NLRP3 (10.33 ± 0.61 vs 1.02 ± 0.05) and apoptosis-related protein Bax (2.68 ± 0.10 vs 1.05 ± 0.08) in the model group were increased. IL-10 (0.82 ± 0.03 vs 1.01 ± 0.06) and Bcl-2 protein expression levels (0.70 ± 0.02 vs 1.11 ± 0.06) were decreased (P < 0.05). Western blot results showed that compared with the control group, the protein expression levels of p-NF-κB (2.65 ± 0.06 vs 1.04 ± 0.05) and NLRP3 (4.38 ± 0.08 vs 1.07 ± 0.04) in the model group were increased (P < 0.001). Compared to the model group, the expression levels of TNF-α (207.90 ± 7.37 vs 398.80 ± 11.39), IL-1β (405.40 ± 6.56 vs 592.40 ± 11.32), IL-6 (1.09 ± 0.05 vs 1.73 ± 0.09), iNOS (39.52 ± 1.32 vs 88.39 ± 2.14), p-NF-κB (01.21 ± 0.05 vs 1.92 ± 0.02) and NLRP3 (1.51 ± 0.11 vs 10.33 ± 0.61) were decreased, and the expression levels of IL-10 (2.61 ± 0.03 vs 0.82 ± 0.03) were increased after treatment with high concentration of curcumin. Compared with the model group, the expression level of Bax protein was decreased (0.80 ± 0.04 vs 2.68 ± 0.10), while the expression level of Bcl-2 protein was increased after high concentration curcumin treatment (1.93 ± 0.02 vs 0.70 ± 0.02) (P < 0.001). Compared with the model group, the expression levels of IL-6 (0.88 ± 0.06 vs 2.70 ± 0.12) and Bax protein (1.14 ± 0.04 vs 3.63 ± 0.16) were decreased, while the expression levels of IL-10 (1.58 ± 0.03 vs 0.52 ± 0.04) and Bcl-2 protein (1.48 ± 0.11 vs 0.53 ± 0.05) were increased after NF-κB inhibitor treatment (P < 0.001). Western blot results showed that compared with the model group, the expression levels of p-NF-κB and NLRP3 protein were decreased after curcumin treatment with 1, 5 and 10 μmol/L concentration in dose-dependent manner (0.40 ± 0.02 vs 2.65 ± 0.06, 0.21 ± 0.02 vs 4.38 ± 0.08, P < 0.001) .

Curcumin could reduce LPS-induced neuroinflammatory damage in microglia, and its mechanism may be related to down-regulating NF-κB/NLRP3 signaling pathway, inhibiting inflammation and apoptosis.