Jolkinolide B ameliorates rheumatoid arthritis by regulating the JAK2/STAT3 signaling pathway

Jolkinolide B (JB), an ent-abietane-type diterpenoid in Euphorbia plants, has various pharmacological activities, including anticancer, anti-inflammatory, and anti-tuberculosis activities. However, no previous studies have proven whether JB can be regarded as a targeted drug for the treatment of rheumatoid arthritis (RA). This study aimed to evaluate the anti-RA effects of JB and explore the potential mechanisms. Components and targets of JB and RA were identified in different databases, and potential targets and pathways were predicted by protein-protein interaction (PPI) network analysis and pathway enrichment analysis. Then, molecular docking and surface-plasmon resonance (SPR) were used to confirm the predict. The anti-arthritic effects of JB were studied in vivo with collagen-induced arthritis (CIA) rat model and in vitro with lipopolysaccharide (LPS) and interleukin-6 (IL-6)-induced RAW264.7 macrophage. Potential mechanisms were further verified by in vivo and in vitro experiments. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that Th17 cell differentiation, prolactin signaling pathway, and JAK/STAT signaling pathway might be associated with anti-RA effects of JB. Molecular docking and SPR results showed that JB bound effectively to JAK2. JB significantly decreased body weight loss, arthritis index, paw thickness, and synovial thickness in CIA rats. Histomorphological results suggested the protective effects of JB on CIA rats with ankle joint injury. Molecular biology analysis indicated that JB suppressed the mRNA expression of inflammatory factors in ankle joints for CIA mice and reduced the concentration of these factors in LPS- and IL-6 induced RAW264.7 macrophage. The protein expression level of the JAK2/STAT3 pathway was also significantly decreased by JB. JB had a novel inhibitory effect on inflammation and bone destruction in CIA rats, and the mechanism might be related to the JAK2/STAT3 signaling pathway.