Coixol Ameliorates Rheumatoid Arthritis by Regulating Macrophage Polarization by Suppressing the TLR4/NF-κB Pathway

Abstract

Background: Coixol (COI) is derived from C. lacryma-jobi var. ma-yuen (Rom.Caill.) Stapf and has been shown with protective effects on rheumatoid arthritis (RA). However, the detailed mechanisms of COI on RA remain unknown. The current study aimed to assess the therapeutic effect and possible mechanism of COI on RA. Methods: A collagen-induced arthritis (CIA) rat model was established, and COI was administered to CIA rats orally. The therapeutic effects of COI on RA were assessed based on arthritis score and paw volume, pathological staining and the levels of inflammatory factors. Then, the effects of COI on M1 macrophages (Mφ) polarization were evaluated through measuring the levels of M1Mφ-related factors, detecting the proportion of M1Mφ in spleen and synovium. Furthermore, the inhibitory effect of COI on M1Mφ polarization was verified in vitro and the changes in toll-like receptor 4 (TLR4)/nuclear factor-kappaB (NF-κB) pathway in M1Mφ after COI treatment was evaluated through detecting the related levels of proteins and genes. Additionally, the inhibitory effect of COI on NF-κB p65 activation in M1Mφ was assessed through detecting the nucleus transition of NF-κB p65 and the NF-κB transcriptional activity. Results: COI decreased arthritis score and paw volume, improved the pathological changes, and reduced the levels of inflammatory factors in CIA rats (p < 0.01). Besides, COI treatment reduced the proportion of M1Mφ in the spleen and synovium (p < 0.01). In vitro studies suggested that COI decreased the proportion of M1Mφ and reduced the production of pro-inflammatory cytokines (p < 0.05, p < 0.01, respectively). Besides, COI treatment lowered the protein levels of TLR4/NF-κB pathway-related factors and downregulated the gene expression of downstream cytokines (p < 0.05, p < 0.01, respectively). Furthermore, COI treatment inhibited the nucleus transition of NF-κB p65 and diminished the transcriptional activity of NF-κB (p < 0.05). Conclusions: COI exhibits a significant therapeutic effect on RA. The anti-inflammatory mechanism of COI on RA is associated with inhibiting TLR4/NF-κB-mediated M1Mφ polarization.