Engeletin attenuates the inflammatory response via inhibiting TLR4-NFκB signaling pathway in Crohn's disease-like colitis

Abstract

Ethnopharmacological relevance: Smilax glabra rhizome has a long history been used for clinical purposes in traditional Chinese medicinal for treating various inflammatory conditions. Engeletin¹ (ENG) is one of the most abundant bioactive compounds found in Smilax glabra rhizome, with anti-inflammatory, antioxidant, and ulcer-preventing activities.

Aim of the study: The purpose of this study was to investigate the ability of ENG to alleviate inflammatory symptoms and improve epithelial barrier integrity utilize a 2,4,6-trinitrobenzene sulfonic acid² (TNBS)-induced murine model in Crohn's disease³ (CD)-like colitis, and to characterize the underlying anti-inflammatory mechanisms of action.

Materials and methods: A colitis model was established in BALB/c mice and treated with ENG for 7 days. RAW264.7 macrophages were pre-treated with ENG and lipopolysaccharide⁴ (LPS) stimulation. The mice's weight and colon length were assessed. qPCR and Western blotting were used to analyze gene expression and TLR4-NFκB pathway. Flow cytometry was used to analyze the polarization states of the macrophages.

Results: Treatment with ENG was sufficient to significantly alleviate symptoms of inflammation and colonic epithelial barrier integrity in treated mice. Significant inhibition of TNF-α, IL-1β, and IL-6 expression was observed following ENG treatment in vivo and in vitro. ENG was also determined to be capable of inhibiting the expression of iNOS and CD86, inhibited M1 macrophage polarization in vitro, as well as the TLR4-NFκB signaling pathway. Molecular docking showed a highly stable binding between ENG and TLR4.

Conclusion: ENG has been proven to alleviate inflammation and ameliorate the damage of epithelial barrier in CD-like colitis. ENG also suppressed the M1 macrophages polarization and the inhibited inflammatory cytokines. TLR4-NFκB signaling pathway, especially TLR4, may be the target of ENG. These data offer a new insight into the therapeutic mechanisms of ENG.

Keywords: CD-Like colitis; Engeletin; M1 polarization; Macrophages; NF-κB signaling.