Sinomenine Alleviates Lupus Nephritis in MRL/lpr Mice by Suppressing the Noncanonical NF-kB Pathway

Background: Systemic lupus erythematosus (SLE) is a severe autoimmune disease with significant mortality, often progressing to lupus nephritis (LN), which affects over 50% of patients and can lead to end-stage renal disease. Urgent attention is needed for new drugs in treating LN due to severe complications associated with traditional therapies. Sinomenine, a natural alkaloid with proven anti-inflammatory properties, holds promise for therapeutic efficacy in LN given its success in treating rheumatoid arthritis. Methods: At 10 weeks, MRL/lpr mice were grouped: vehicle (i.g., PBS, n=6), sinomenine (i.g., 50mg/kg/day, n=6), and dexamethasone (i.p., 1mg/kg/day, n=6). MPJ mice served as controls (i.g., PBS, n=5). At week 18, mice were euthanized. Lymph node and spleen size, renal function, histopathology, autoimmune antibodies, inflammatory cell infiltration, and immune complex deposition were assessed. Spleen cell flow cytometry was conducted, and kidneys underwent single-cell RNA sequencing (scRNA-seq) analysis (n=2/group). Sinomenine's binding affinity to target protein was confirmed via molecular docking, cellular thermal shift assay (CESTA), and drug affinity-responsive target stability (DARTS) assay. Results: Sinomenine improved renal function in MRL/lpr mice, reducing UACR and Scr while increasing GFR. It also alleviated renal histological injury and suppressed adaptive immunity, evidenced by reduced splenomegaly, serum anti-dsDNA titers, splenic CD8+ T cells, and splenic Th1/Th2 ratio. scRNA-seq data indicated alleviation of tubule cell inflammation and dedifferentiation in sinomenine treatment group. Dexamethasone exhibited a strong inhibitory effect on immune cells in the kidneys, notably promoting the differentiation of mononuclear cells and macrophages towards an immunosuppressive phenotype in the kidneys. Sinomenine decreased Relb regulon activity, inhibiting the non-canonical NF-kB pathway. In vitro, sinomenine suppressed nuclear translocation of RelB-p52 complex, validated by CESTA and DARTS assays confirming its binding to Relb. Conclusion: Sinomenine protects against LN in MRL/lpr mice by reducing immune cell infiltration and tubular damage through modulating non-canonical NF-kb signaling pathways, suggesting its promise as a therapeutic option for patients with LN. Funding: Government Support – Non-U.S.