Bruceine A ameliorates ulcerative colitis via macrophage polarization: Targeting HSP90-mediated IL-17 signaling and NF-κB activation.

Background: Bruceine A (BA), a natural quassinoid compound derived from the fruit of Brucea javanica, has demonstrated diverse pharmacological activities. However, the treatment effectiveness of BA against ulcerative colitis (UC) and its underlying mechanisms of action are yet to be fully elucidated.

Purpose: To explore the effects of BA against UC and uncover its underlying mechanisms, with a particular focus on its influence on inhibiting macrophage M1 polarization via the IL-17/NF-κB pathway.

Methods: A murine UC model was constructed using 3 % dextran sulfate sodium (DSS) and treated with BA. Colon length, histopathological damage, inflammatory mediators, and epithelial barrier integrity were assessed to evaluate BA's therapeutic efficacy. In vitro, cell viability and macrophage polarization biomarkers (e.g., iNOS and TNF-α) were quantified to evaluate the cytoprotective effects of BA. The potential mechanisms of BA in combating UC were investigated using network pharmacology, with direct targets validated through biophysical approaches. Furthermore, western blot analysis was employed to confirm BA's regulatory effect on the protein expression of the IL-17/NF-κB pathway in both UC mice and macrophages.

Results: BA treatment effectively restored colon length, attenuated histopathological inflammation, and repaired epithelial barrier via upregulating tight junction proteins (e.g., ZO-1 and Occludin) in UC mice. Although BA failed to enhance cell viability in DSS-injured IEC-6 cells, it potently inhibited M1 macrophage polarization in THP-1 cells, as evidenced by downregulated iNOS and TNF-α. Mechanistically, BA bound to heat shock protein 90 (HSP90), leading to a significant reduction in the expression of IL-17/NF-κB pathway-related proteins, thereby suppressing the IL-17 pathway and the NF-κB cascade activation. Notably, overexpression of HSP90 abrogated BA's inhibition of the IL-17/NF-κB pathway and M1 macrophage polarization.

Conclusions: BA effectively inhibits macrophage M1 polarization, thereby attenuating inflammation in UC by targeting HSP90 and subsequently suppressing the activation of IL-17 and NF-κB pathway. These results imply that BA is a promising therapeutic candidate for UC treatment.