Abstract: BACKGROUND: Rheumatoid arthritis is an inflammatory disease. Many studies have shown that wogonin has a good anti-inflammatory effect on rheumatoid arthritis, but its exact efficacy and specific mechanism of action remain to be clarified.
OBJECTIVE: To investigate the mechanism of wogonin ameliorating joint inflammation by regulating endoplasmic reticulum stress pathway in rats with collagen-induced arthritis.
METHODS: (1) At the animal level: Female Wistar rats were divided into healthy control group, arthritis model group and wogonin treatment group. Rat models of arthritis in the latter two groups were established by subcutaneous injection of bovine type II collagen and adjuvant. In the wogonin group, wogonin was given by gavage for 28 consecutive days after modeling. During this period, the rats in each group were weighed, and arthritis score and ankle swelling were measured every 7 days. After the experiment, the pathological changes of the joint were observed, the mRNA and protein levels of endoplasmic reticulum stress pathway GRP78 and CHOP were detected by qRT-PCR, western blot, and immunohistochemistry. (2) At the cellular level, cell counting kit-8 was used to detect the cytotoxic effect of wogonin on fibroblast-like synoviocytes from rats with collagen-induced arthritis. The fibroblast-like synoviocytes induced by thapsigargin were treated with different concentrations of wogonin. The levels of interleukin-1β and tumor necrosis factor-α in the cell supernatant were detected by ELISA, and the intracellular reactive oxygen species in each group were determined by DCFH-DA probe method. The mRNA and protein levels of GRP78, IRE1α, XBP1s and CHOP were detected by qRT-PCR and western blot, respectively.
RESULTS AND CONCLUSION: Compared with the healthy control group, arthritis index score and ankle swelling degree in the arthritis model group were increased (P < 0.01), synovial hyperplasia, inflammatory cell infiltration, cartilage destruction and bone erosion were observed in pathological sections, and the mRNA and protein expressions of GRP78 and CHOP in the ankle were significantly increased (P < 0.01), which were mainly located in synovial tissue and articular surface. Compared with the arthritis model group, the arthritis index score and ankle swelling degree in the wogonin treatment group were decreased (P < 0.05), synovial hyperplasia and the number of inflammatory cells were decreased, cartilage destruction and bone erosion were alleviated, the mRNA and protein expression levels of GRP78 and CHOP in the ankle were decreased (P < 0.05), particularly in synovial tissue and on the articular surface. There was no significant difference in body mass among the three groups (P > 0.05). In the cell experiment, 200 μmol/L wogonin significantly reduced the survival rate of fibroblast-like synoviocytes (P < 0.01). Compared with the blank control group, the levels of interleukin-1β, tumor necrosis factor-α, content of reactive oxygen species, and mRNA and protein expression of GRP78, IRE1α, XBP1s, and CHOP in the thapsigargin group were significantly increased (P < 0.05); compared with the thapsigargin group, 50 and 100 μmol/L wogonin significantly reduced the levels of interleukin-1β and tumor necrosis factor-α in the cell supernatant (P < 0.05, P < 0.01), and 100 μmol/L wogonin significantly reduced the content of reactive oxygen species (P < 0.01) and down-regulated the mRNA and protein expression levels of GRP78, IRE1α, XBP1s and CHOP (all P < 0.05). These results suggest that wogonin can effectively alleviate joint inflammatory responses in rats with collagen-induced arthritis, and the endoplasmic reticulum stress pathway may be the key target of its intervention.

Key words:  wogonin, endoplasmic reticulum stress, rheumatoid arthritis, fibroblast-like synoviocyte, inflammation