This study is to investigate alkaline phosphatase activity, calcium nodules formation and proliferation of alendronate combination with calcitriol on osteoblast.

Bone marrow mesenchymal stem cells were differentiated into osteoblast. Different concentration of alendronate (1×10^-10, 1×10^-9, 1×10^-8, 1×10^-7, 1×10^-6, 1×10^-5, and 1×10^-4 mmol/L) and calcitriol (1×10^-8, 1×10^-7, 1×10^-6, 1×10^-5, 1×10^-4, 1×10^-3, and 1×10^-2 mmol/L) were added, and alkaline phosphatase (AKP) activity and calcium nodules formation were determined. The effect of mono intervention and combined intervention on AKP activity, calcium nodules formation, proliferation, and protein expression levels of OPG/RANKL were compared. Comparison of AKP activity among groups were applied by ANOVA followed by q test. Ratio comparison was achieved by χ² test.

Osteoblast was successfully differentiated. Alendronate of 1×10^-6mmol/L and calcitriol of 1×10^-4mmol/L were the best concentration for osteoblast differentiation. Compared with control group or osteoinduction group, the alkaline phosphatase activity and alizarin red staining level have been significantly improved in combination therapy group. Combination therapy of alendronate and calcitriol can significantly promote proliferation, increase the expression level of OPG, and decrease the expression level of RANKL. These effects in combination were better than calcitriol and alendronate alone.

The combination therapy of alendronate and calcitriol has significant regulatory effects on alkaline phosphatase activity, calcium nodules formation, proliferation of osteoblast, which is associated with the protein expression profile of OPG/RANKL.