Abstract: Objective To explore the inhibitory effect of Sidaxue (SX), a traditional Guizhou Miao herbal medicine formula, on necrotic apoptosis and synovial angiogenesis in rats with collagen-induced arthritis (CIA) and the role of the RIPK1/RIPK3/MLKL pathway in mediating this effect. Methods Forty-two SD rats were randomized into 6 groups (n=7), including a normal control group, a CIA model group, 3 SX treatment groups at low (10 g/kg), moderate (20 g/kg) and high (40 g/kg) doses, and a GTW treatment group. CIA rat models were established by subcutaneous injections of bovine type II collagen, and the treatments were administered daily by gavage for 21 days. The rats were observed for swelling of the hind limb joints, which was rated using the arthritis index (AI) score on a weekly basis. Serum levels of TNF-α, IL-1β and IL-17 in the rats were detected using ELISA, and the pathological changes in the synovium were observed with HE staining. Real-time PCR was performed to detect the mRNA expression levels of VEGF, MMP- 9, Ang- 1, RIPK1, RIPK3, and caspase- 8 in the synovial tissues, and the protein expressions of VEGF, MMP9, Ang-1, Stat-3, RIPK1, RIPK3, MLKLl, p-MLKL and caspase-8 were detected using Western blotting. Results Compared with those in CIA model group, the rats receiving treatment with GTW and SX showed milder swelling of the hind limb joints with significantly lower AI scores (P<0.05). In CIA model group, a large number of inflammatory cells were observed in the synovium with obvious damages of the tissue structure. In the drug treatment groups, inflammatory cell infiltration, synovial angiogenesis and synovial hyperplasia were alleviated, and the therapeutic effects were obviously enhanced as SX dose increased. Compared with those in the model group, the rats treated with GTW and high-dose SX showed significantly decreased serum levels of IL-1β, IL-17 and TNF-α (P<0.05), lower mRNA and protein expressions of RIPK1, RIPK3, VEGF, Ang-1, and MMP9 (P<0.05), higher expressions of caspase-8 (P<0.01), and obviously lowered expression of Stat-3 protein and phosphorylation level of MLKL (P<0.05). Conclusion SX can improve synovial angiogenesis in CIA rats possibly by inhibiting the activation of RIP1/RIP3/MLKL signaling pathway and down- regulating the expression of the vascular growth actors VEGF, Ang-1, MMP9, and Stat-3.

Key words: Miao medicine Sidaxue formula; rheumatoid arthritis; RIPK1/RIPK3/MLKL pathway; inflammation; pannus