Background: Rho iso-alpha acids (RIAA) from hops have been shown to have anti-inflammatory properties. To understand the mechanisms, we evaluated the effect of RIAA in cell signaling pathways and inflammatory markers using various in vitro models. We also investigated their therapeutic effect in mice with collagen-induced arthritis.
Methods: The LPS-stimulated RAW 264.7 macrophages were used to evaluate the effect of RIAA on the NF-kappaB and MAPK signaling pathways; phosphorylation of ERK1/2, p38 and JNK was assessed by western blotting and NF-kappaB binding by electrophoretic mobility shift assays. Effect on the NF-kappaB activity was evaluated by the luciferase reporter assays in LPS-stimulated RAW 264.7 cells. GSK-3alpha/beta kinase activity was measured in cell-free assays. The inhibitory effect of RIAA on inflammatory markers was assessed by measuring nitric oxide in LPS-stimulated RAW 264.7 cells, RANKL-mediated TRAP activity in transformed osteoclasts, and TNF-alpha/IL-1beta-mediated MMP-13 expression in SW1353 cells. Mice with collagen-induced arthritis were fed with RIAA for 2 weeks. Symptoms of joint swelling, arthritic index and joint damage were assessed.
Results: RIAA selectively inhibited the NF-kappaB pathway while having no effect on ERK1/2, p38 and JNK phosphorylation in LPS-stimulated RAW 264.7 cells. RIAA also inhibited GSK-3alpha/beta kinase activity and GSK-3beta dependent phosphorylation of beta-catenin in RAW 264.7 cells. In addition, RIAA inhibited NF-kappaB-mediated inflammatory markers in various cell models, including nitric oxide in LPS-stimulated RAW 264.7 cells, RANKL-mediated TRAP activity in transformed osteoclasts, and TNF-alpha/IL-1beta-mediated MMP-13 expression in SW1353 human chondrosarcoma cells. Finally, in a mouse model of collagen-induced arthritis, RIAA ameliorated joint damage as evidenced by significant reduction of the arthritis index and histology score; at 250 mg/kg-body weight, RIAA had efficacy similar to that of 20 mg/kg-body weight of celecoxib.
Conclusion: RIAA may have potential as an anti-inflammatory therapeutic.