Effects of Simiao Pill on rheumatoid arthritis complicated with interstitial lung disease via the ATX/LPA/LPA1 and RhoA/ROCK2 signaling pathways

Background: In Traditional Chinese Medicine theory, Simiao Pill represents a traditional herbal formulation used for rheumatoid arthritis (RA) management. Initial research indicates that Simiao Pill might have therapeutic benefits for RA linked with interstitial lung disease (RA-ILD), although the mechanisms are not yet understood. Thus, this research seeks to explore the therapeutic potential of Simiao Pill in treating RA-ILD and uncover its molecular mechanisms. Methods: DBA/1 mice were used as animal models, with a collagen-induced arthritis model (CIA) and a bleomycin (BLM)-induced pulmonary fibrosis model (CIA-BLM). Ultra-high-performance liquid chromatography-tandem mass spectrometry was applied to profile the chemical composition of Simiao Pill. The therapeutic effects on arthritis and pulmonary fibrosis were evaluated through microcomputed tomography, histopathological examination, immunohistochemical staining, Western blot, ELISA assays, etc. Lipidomics analysis was performed to screen potential metabolic targets of Simiao Pill, followed by validation experiments on the identified targets. Results: Simiao Pill significantly reduced the arthritis index and decreased bone and cartilage damage in CIA-BLM mice. Additionally, it inhibited the expression of the inflammatory cytokines TNF-α, IL-6, CXCL1, and CXCL2 and reduced inflammatory cell infiltration in lung tissue. Most importantly, it downregulated the levels of the key profibrotic factor TGF-β1, the myofibroblast marker α-SMA, and fibrotic extracellular matrix components such as fibronectin, collagen-1, and collagen-3. These findings suggest that Simiao Pill may inhibits the transition of pulmonary fibroblasts to pulmonary myofibroblasts. Pulmonary lipidomics analysis revealed that lysophosphatidic acid (LPA) may serve as metabolic targets of Simiao Pill. Further validation experiments demonstrated elevated levels of autotaxin (ATX) and LPA in the serum and bronchoalveolar lavage fluid of CIA-BLM mice, accompanied by upregulation of LPA receptor 1 (LPA1) and downstream RhoA/ROCK2 signaling molecules in lung tissues. Notably, Simiao Pill effectively reversed these pathological alterations. Conclusions: Simiao Pill not only alleviated arthritis and bone destruction but also reduced pulmonary inflammation and fibrosis in CIA-BLM mice. The observed lung-protective properties may be attributed to inhibition of the ATX/LPA/LPA1 cascade and subsequent suppression of the RhoA/ROCK2 signaling axis, suggesting that Simiao Pill has potential therapeutic value for RA-ILD.