An Alcohol Extract Prepared From the Male Flower of Eucommia Ulmoides Oliv. Promotes Synovial Cell Apoptosis, Inhibits Osteoclast Differentiation and Ameliorates Bone Destruction in Rheumatoid Arthritis

Background: Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease with a complex pathogenesis and is dominated by synovial hyperplasia and bone destruction. Previous research has shown that the male flower of Eucommia ulmoides Oliv. (EF) can exert effect on the inflammation caused by rheumatoid arthritis. However, the effect of EF on synovial cell apoptosis and bone destruction on RA have yet to be investigated. In this study, the effects of the synovial cell apoptosis of the male flower of Eucommia ulmoides Oliv.(EF) on human fibroblast-like synoviocyte -RA (HFLS-RA) cells, the osteoclast differentiation of EF on RAW264.7 cells and the bone destruction of effects of EF on collagen-induced arthritis (CIA) rats were explored.Materials and methods: In vitro, we investigated the anti-proliferative and pro-apoptotic effects of EF on HFLS-RA cells by immunofluorescence assays, flow cytometry, RT-qPCR (Real-time quantitative polymerase chain reaction), and western blotting. We investigated the differentiation into osteoclasts effects of EF on RAW264.7 cells by the TRAP staining and western blotting. In vivo, we used a rat model of collagen-induced arthritis (CIA) to investigate the relative effects of EF on anti-arthritis activity, the toe swelling arthritis score, the serum levels of metabolic bone factors, and pathological conditions. Micro-computed tomography (micro-CT) was used to scan ankle joints while the mRNA and protein levels of factors related to the NF-κB pathway were determined by RT-qPCR and western blotting, respectively. Finally, the main chemical components of EF were identified by HPLC (High Performance Liquid Chromatography). Results: EF inhibited the proliferation of synovial cells and promoted apoptosis in a dose-dependent manner, inhibited the differentiation of osteoclast by inhibiting activation of the NF-κB pathway. We also found that EF reduced articular inflammation in CIA rats, inhibited the expression of pro-angiogenic factors, and delayed the destruction of articular cartilage and bone. Our data indicate that EF acts via a mechanism related to bone metabolism that is induced by the NF-κB pathway. Conclusions: Our findings indicate that EF exerts a potential therapeutic effect on rheumatoid arthritis. Our research will help to elucidate the potential pharmacological mechanisms associated with the beneficial effects of EF and provide an experimental basis for the application of EF in future clinical treatments.