Crude triterpenoid saponins from Anemone flaccida (Di Wu) exert anti-arthritic effects on type II collagen-induced arthritis in rats

BACKGROUND: Anemone flaccida Fr . Schmidt (Ranunculaceae) (Di Wu in Chinese) is used to treat punch injury and rheumatoid arthritis (RA). However, the active compounds and underlying mechanism of action mediating the anti-arthritic effects of A. flaccida remain unclear. This study aims to evaluate the underlying action mechanism of A. flaccida crude triterpenoid saponins (AFS) on RA using a type II collagen (CII)-induced arthritis (CIA) rat model, and to assess the anti-inflammatory effects of the main active compounds of AFS, namely flaccidoside II, anhuienoside E, glycoside St-I4a, hemsgiganoside B, hederasaponin B, and 3-O-α-l-rhamnopyranosyl (1 → 2)-β-d-glucopyranosyl oleanolic acid 28-O-β-d-glucopyranosyl (1 → 6)-β-d-glucopyranosyl ester. METHODS: Male Wistar rats (n = 50) were randomly separated into five groups (n = 10) and immunized by CII injection. AFS (200 or 400 mg/kg) and dexamethasone were orally administered for 30 days after establishing the model. The arthritis severity was assessed by paw volume using a plethysmometer. After 30 days of treatment, the right hind paws of the rats were obtained. Paw histology was analyzed by hematoxylin and eosin staining, and radiologic imaging was performed by micro-computed tomography. MTT assays were used to evaluate the cytotoxicity of AFS and its main compounds in RAW264.7 cells. Enzyme-linked immunosorbent assay kits were used to measure interleukin (IL)-6 and tumor necrosis factor (TNF)-α in serum and supernatants from AFS- and main AFS compound-treated RAW264.7 cells stimulated by lipopolysaccharide (LPS). RESULTS: Anemone flaccida crude triterpenoid saponins inhibited redness and swelling of the right hind paw in the CIA model. Radiological and histological examinations indicated that inflammatory responses were reduced by AFS treatment. Moreover, comparing with untreated rats, serum TNF-α (P = 0.0035 and P < 0.001) and IL-6 (P = 0.0058 and P = 0.0087) were lower in AFS-treated CIA rats at the dose of 200 and 400 mg/kg/day. AFS and its main compounds, including hederasaponin B, flaccidoside II, and hemsgiganoside B, significantly inhibited TNF-α (P = 0.0022, P = 0.013, P = 0.0015, and P = 0.016) and IL-6 (P = 0.0175, P < 0.001, P < 0.001, and P < 0.001) production in LPS-treated RAW264.7 cells, respectively. CONCLUSIONS: Anemone flaccida crude triterpenoid saponins and its main bioactive components, including hederasaponin B, flaccidoside II, and hemsgiganoside B, decreased pro-inflammatory cytokine levels in a CIA rat model and LPS-induced RAW264.7 cells.