A betulinic acid derivative SH479 inhibits collagen-induced arthritis by modulating T cell differentiation and cytokine balance

The ideal therapeutic drug for rheumatoid arthritis (RA) should not only inhibit inflammation, but also prevent articular joint damage and particularly inhibit osteoclastogenesis. Betulinic acid (BA) is a natural pentacyclic triterpene that has displayed moderate anti-inflammatory and anti-osteoclastogenesis activities in various experimental systems, suggesting that BA or its derivatives could have an inhibitory effect on RA. In this study, we screened BA derivatives and found a heterocyclic ring-fused BA derivative, SH479, which had greater inhibitory effect than BA on Th17 differentiation. Moreover, we investigated the immune regulatory activity and potential therapeutic effects of SH479 in an experimental model of rheumatoid arthritis, the collagen-induced arthritis (CIA) mouse model. SH479 significantly inhibited Th1 and Th17 polarization, antigen-specific T cell proliferation and splenic lymphocyte-induced osteoclastogenesis. Furthermore, it diminished arthritis scores as well as bone destruction and cartilage depletion in the CIA mouse model. The protective effect of SH479 was accompanied by decreased levels of pro-inflammatory cytokines IL-17 and IFN-γ, together with enhanced anti-inflammatory cytokine expression including IL-10 and IL-4, as well as elevated CD4⁺ Foxp3⁺ cell number. At the molecular level, our results indicated that SH479 alleviated CIA through regulation of CD4⁺ T cell subtypes by JAK-STAT pathways. In conclusion, this study demonstrates that SH479 has therapeutic potential for rheumatoid arthritis through an anti-inflammatory effect by shifting a pathogenic Th17/Th1 response to a Th2/Treg phenotype, and also through an additional articular bone protection effect.