Fuyuan Huoxue Decoction Promotes Lumbar Interbody Fusion in Rats: Role of Macrophage-Driven Inflammation and the TLR9/NF-κB Pathway.

Delayed union and pseudarthrosis remain complications of lumbar interbody fusion. We investigated Fuyuan Huoxue decoction (FY) in a rat extreme lateral interbody fusion model. FY improved bone mineral density and trabecular architecture. Reduced inflammatory macrophage infiltration and nuclear factor kappa B (NF-κB) activation at 4 weeks were accompanied by improved bony bridging at 8 weeks. Transcriptomic and network analyses nominated Toll-like receptor 9 (TLR9)/NF-κB signaling for functional investigation. FY-medicated serum reduced macrophage inflammatory markers and extracellular double-stranded DNA (dsDNA), promoted bone marrow mesenchymal stem cell (BMSC) osteogenesis, and attenuated impairment induced by inflammatory macrophage-conditioned medium. DNase treatment reduced this medium's inhibitory effects, whereas a separate exogenous dsDNA challenge impaired osteogenesis and was attenuated by a TLR9 antagonist. TLR9 agonist and antagonist experiments in BMSCs and a 2-week in vivo agonist intervention supported pathway involvement. Human nonunion single-cell data showed increased phospholipid scramblase 1 and interleukin-6 expression in myeloid cells. These findings support complementary pro-osteogenic and anti-inflammatory actions of FY and identify TLR9/NF-κB as a candidate pathway contributing to fusion repair.