Isoorientin attenuates aging-induced bone deterioration by suppressing M1-mediated TLR4-MAPK-NF-κB inflammatory signaling.

Abstract

Background: Aging disrupts bone remodeling by increasing osteoclast activity, reducing osteogenic capacity, and elevating inflammation. Toll-like receptor 4 (TLR4)-mediated inflammatory signaling has been implicated in bone degeneration, yet its role in age-related skeletal decline remains incompletely understood. Isoorientin, a plant-derived flavonoid with reported anti-inflammatory properties, has not been evaluated in the context of skeletal aging.

Methods: Bone aging was first assessed in C57BL/6 J mice using micro-computed tomography (μCT), histology, TRAP staining, and immunofluorescence. The effects of isoorientin on osteogenesis were examined in senescent hBMSCs by alkaline phosphatase (ALP) activity, mineralization assays, and expression of osteogenesis-related genes. LPS-stimulated RAW264.7 cells were used to evaluate inflammatory responses and M1/M2 polarization. To assess TLR4/ mitogen-activated protein kinase (MAPK)/ nuclear factor-κB (NF-κB) regulation, RAW264.7 cells were treated with TAK-242 or TAK-242 plus isoorientin. Finally, aged mice were treated with isoorientin, TAK-242, or both to evaluate in vivo pathway modulation and bone protection.

Results: Aged mice exhibited reduced trabecular mass, elevated osteoclast activity, and increased osteoclast-associated markers. Isoorientin treatment improved trabecular structure, decreased osteoclast numbers, and lowered osteoclast-associated proteins. In senescent hBMSCs, isoorientin restored ALP activity, enhanced mineral deposition, and increased osteogenic marker expression. Isoorientin also reduced pro-inflammatory cytokines, suppressed M1 polarization, and inhibited TLR4/MAPK/NF-κB activation. The combination of isoorientin and TAK-242 exhibited the most potent suppression of inflammatory signaling and the most significant enhancement in bone microarchitecture.

Conclusion: Isoorientin alleviates age-related bone loss by suppressing TLR4-mediated inflammation, reducing osteoclast activation, and restoring impaired osteogenesis. These findings identify isoorientin as a promising therapeutic candidate for age-associated osteoporosis.