Objective: To explore the effects of safflower yellow (SY) on the angiogenesis and fracture healing in
osteoporotic fracture (OPF) rats through activation of the hypoxia-inducible growth factor-1α (HIF-1α)/vascular
endothelial growth factor (VEGF) signaling pathway. Methods: An ORF model of rats was established and randomly
divided into five groups: sham operation group, model group, SY group (15.75 mg/kg), inhibitor group (HIF-1α
inhibitor-digoxin, 0.05 mg/kg), SY (15.75 mg/kg) + inhibitor (0.05 mg/kg) group. After the administration, X-ray
examination was conducted to assess the fracture and healing status of the rats; the changes in bone mineral
density (BMD) and bone mineral content (BMC) in callus tissue were detected; H-E staining was used to observe
the histopathological changes in rat callus tissue; ELISA was performed to detect the levels of serum biochemical
indicators of rats-bone morphogenetic protein-2 (BMP-2) and insulin-like growth factor-1 (IGF-1); Western blotting
and RT-qPCR were employed to determine the expression of HIF-1α and VEGF proteins and mRNA in rat callus
tissue. Results: Compared with the sham operation group, the model group exhibited clear fracture lines, less callus
growth and no connection, disorganized and sparse bone trabeculae, a few osteoblasts and newly formed blood
vessels. The fracture healing score, BMD, BMC, HIF-1α, VEGF protein and mRNA expression, BMP-2, and IGF-1
levels were significantly reduced. Compared with the model group, the histopathological changes in the callus tissue
and fracture healing of the rats in the SY group were
improved, with fracture healing score, BMD, BMC,
HIF-1α, VEGF protein and mRNA expression, BMP-2,and IGF-1 levels significantly increased. Compared with the model group, the inhibitor group showed poorer
histopathological changes in the callus tissue and the fracture healing, with significant reductions in fracture healing
score, BMD, BMC, HIF-1α, VEGF protein and mRNA expression, BMP-2, and IGF-1 levels. Compared with the SY
group, the fracture healing score, BMD, BMC, HIF-1α, VEGF protein and mRNA expression, BMP-2, and IGF-1
levels in the SY + inhibitor group were significantly reduced. Conclusion: SY can promote angiogenesis at the
fracture site, improve the morphology of bone tissue in osteoporotic rats by activating the HIF-1α/VEGF signaling
pathway, thereby accelerating the process of fracture healing.