The anti-inflammation effect of baicalin on experimental colitis through inhibiting TLR4/NF-κB pathway activation

Baicalin holds a protective effect on inflammatory responses in several diseases. However, its molecular mechanism of anti-inflammatory activity on ulcerative colitis (UC) remains unknown. The present study was conducted to verify whether the anti-inflammation effect of baicalin on experimental colitis is via inhibiting TLR4/NF-κB pathway activation.

The inflammatory response in RAW264.7 cells was induced by LPS and in rats by intrarectal administration of TNBS. Western blot analysis was carried out to examine toll-like receptor 4 (TLR4), NF-κB, p-NF-κB p65, IκB and p-IκB protein expressions in cells. Furthermore, intercellular adhesion molecule-1 (ICAM-1), monocyte chemoattractant protein-1 (MCP-1), cyclo-oxygenase-2 (Cox-2), tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-6 levels in cell supernatant and rat serum were detected by appropriate kits. An immunohistochemical assay was applied to examine TNF-α and IL-1β protein expression in colon tissues and TLR4 and p-NF-κB p65 protein expressions in RAW264.7 cells.

Baicalin ameliorates the considered inflammatory symptoms of induced colitis. It could also down-regulate pro-inflammatory mediators in the colon mucosa. The decline in the production of pro-inflammatory cytokines was correlated with the decrease in mucosal TLR4 protein expression. The expression of p-NF-κB p65 protein was significantly decreased, which correlated with a similar decrease in p-IκB protein. Consistent with the in vivo results, baicalin blocked LPS-stimulated nuclear translocation of p-NF-κB p65 in mouse macrophage RAW264.7 cells.

The present study indicates for the first time that the mechanism for baicalin on abrogating experimental colitis was targeted inhibition of the TLR4/NF-κB pathway activation.