| Objective To explore the effect of calcitriol capsule (Cal) on tibial fracture healing in rats through bone morphogenetic protein-2 (BMP-2)/SMAD/Runt-related transcription factor 2 (Runx2) signaling pathway. Methods Fifty-two SD rats were randomly divided into control group (Cont), tibial fracture group, Cal group (gavage 10 ng/mL Cal for 4 consecutive weeks), and Cal + Noggin (BMP specific inhibitor) group (gavage 10 ng/mL Cal+percutaneous injection of 50 ng/mL Noggin for 4 consecutive weeks). X-ray, automatic biochemical analyzer, micro CT, HE staining and Western blotting were used to analyze the treatment effect and possible mechanism. Results After 4 weeks of the fractures, the fracture line in the tibial fracture group was obvious. The fracture line in the Cal group was almost invisible and there was a lot of callus at the broken end. The fracture healing in the Cal+Noggin group was poor. Bone mineral density, bone volume fraction, levels of ALP, OCN, PINP and the protein levels of BMP-2, Runx2, and p-SMAD1/5/8/SMAD1/5/8 in the tibial fracture group were higher than those in the Cont group (P < 0.05), while trabecular separation was lower than that in the Cont Group (P < 0.05). Compared to those in the tibial fracture group, bone mineral density, bone volume fraction, levels of ALP, OCN, PINP, and the protein levels of BMP-2, Runx2, and p-SMAD1/5/8/SMAD1/5/8 in the Cal group increased, and trabecular separation decreased (P < 0.05). Compared to those in the Cal group, bone mineral density, bone volume fraction, levels of ALP, OCN, PINP, and the protein levels of BMP-2, Runx2, and p-SMAD1/5/8/SMAD1/5/8 in the Cal + Noggin group decreased, and trabecular separation increased (P<0.05). Conclusion Cal may improve bone mineral density and microstructure of new callus, and promote the healing of tibial fractures by activating BMP-2/SMAD/Runx2 pathway. |