Luteolin ameliorates steroid-induced osteonecrosis of the femoral head via a gut microbiota–L-Carnitine–IFIH1 axis

Steroid-induced osteonecrosis of the femoral head (SONFH) lacks effective early-stage interventions, and its systemic drivers remain incompletely defined. Luteolin (Lut) is reported to be protective, but the in vivo mechanism is unclear. We investigated whether Lut acts through a gut microbiota–metabolite–innate immunity axis in SONFH. Male Sprague–Dawley rats underwent SONFH induction using lipopolysaccharide plus methylprednisolone and received oral Lut or L-Carnitine; gut microbiota dependence was examined using a four-antibiotic depletion regimen. Femoral heads were evaluated by histology and micro-computed tomography. Mechanisms were interrogated by integrated 16S rRNA profiling, untargeted serum Liquid Chromatography–Mass Spectrometry metabolomics, and femoral-head transcriptomics. Dexamethasone (Dex)-injuried ROS17/2.8 osteoblasts and HMEC-1 endothelial cells were used for functional validation, and IFIH1 was silenced by shRNA to test pathway necessity. Lut preserved trabecular microarchitecture and reduced empty osteocyte lacunae in vivo, yet minimally rescued Dex-injured osteoblasts and endothelial cells, indicating an indirect mechanism mediated by gut microbiota-derived metabolic changes. Microbiota depletion abolished Lut’s in vivo benefit, establishing microbiota dependence. Metabolomics identified an increase in circulating L-Carnitine that correlated with four bacterial genera. Exogenous L-Carnitine restored cell proliferation, reduced apoptosis, and improved endothelial tube formation, and in vivo improved trabecular indices while lowering inflammatory cytokines (IL-1β, IL-6, TNF-α). Integrated multi-omics highlighted an interferon-stimulated gene module (OAS1A, HERC6, IFIH1, IFI44), with IFIH1 most strongly associated with disease severity. L-Carnitine attenuated Dex-induced IFIH1 expression, and IFIH1 knockdown mimicked L-Carnitine and eliminated its additional anti-inflammatory effect. Lut alleviates SONFH via gut microbiota-driven elevation of L-Carnitine, which constrains IFIH1 expression and inflammation to preserve femoral-head trabecular microarchitecture. Targeting the microbiota–L-Carnitine–IFIH1 axis may enable mechanism-based early intervention strategies for SONFH.