β-Sitosterol modulates macrophage polarization and attenuates rheumatoid inflammation in mice

Context: beta-Sitosterol (BS), the primary constituent of plants and vegetables, exhibits multiple biological effects. Objective: This study explores its effect of immune-regulation on macrophages and its potential for rheumatoid arthritis (RA) therapy. Materials and methods: In vitro, bone marrow-derived macrophages (BMDMs) were treated with 5, 25 and 50 mu M BS in the M1 or M2 polarization conditions. In vivo, either i.p. injection with 20 or 50 mg/kg BS every 2 d after boost immunization of collagen-induced arthritis (CIA) or adoptive transfer of 2 x 10(6) BS-treated BMDMs (BS-BMDMs) at the day before CIA were adopted in mice to test the therapeutic effect. IL-10 antibody depletion was used in the period of above treatments to discuss the underlying mechanism. Results: The phenotypes and function of BMDMs showed that 5, 25 and 50 mu M BS significantly repressed the M1 polarization and augmented M2 polarization dependent upon concentration. The expression of iNOS, IL-1 beta, CD86 and MHCII in 25 mu M BS-treated M1-polarized BMDMs was reduced by 50.2, 47.1, 87.1 and 31.3%, respectively. In contrast, the expression of arginase-1, IL-10, CD163 and CD206 in 25 mu M BS-treated M2-polarized BMDMs was increased by 65.6, 107.4, 23.5 and 51.3%, respectively. In CIA mice, either i.p. injection with BS or adoptive transfer of BS-BMDMs could alleviate the symptoms of ankle swelling (vehicle group: 3.13 +/- 0.102 mm; 20 mg/kg BS group: 2.64 +/- 0.043 mm; 50 mg/kg BS group: 2.36 +/- 0.084 mm; BMDMs group: 3.09 +/- 0.174 mm; BS-BMDMs group: 2.43 +/- 0.042 mm), reduce the levels of collagen-specific antibodies (IgG and IgG1, but not IgG2c, p < 0.05) and inhibit the production of pro-inflammatory cytokines (p < 0.05). Depletion of IL-10 counteracted the effect of BS treatment (alpha-IL-10 vs. RatIgG1, p < 0.01 on day 16), highlighting the role of IL-10 in the anti-inflammatory response. Conclusions: These results suggested that BS could modulate the functions of macrophages and might be a promising agent for RA therapy.