Effects Of Nd³⁺ And Sm³⁺ On Proliferation, Differentiation And Mineralized Function Of Primary Osteoblasts In Vitro

A series of methods including 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method, alkaline phosphatase (ALP) activity measurement, Oil Red O stain and measurement, mineralized function and quantitative real-time PCR (qPCR) were employed to assess the effect of Nd³⁺ and Sm³⁺ on the proliferation, differentiation and mineralized function of primary osteoblasts (OBs) in vitro at cell and molecular levels. The results showed that:Nd³⁺ and Sm³⁺ suppressed the proliferation of OBs at tested concentrations, moreover, the inhibitory effect of Sm³⁺ was stronger than that of Nd³⁺. As to the ALP activity, Nd³⁺ and Sm³⁺ showed similar effects, they increased the ALP activity at a higher concentration of 1×10^-5 mol/L. However, the ALP activity was sharply decreased at a concentration of 1×10^-6 mol/L and gradually increased as concentration decreasing, they turned to increase the ALP activity at a concentration of 1×10^-8 mol/L. Nd³⁺ promoted the formation of mineralized matrix nodules at a higher concentration of 1×10^-5 mol/L, inhibited the formation of mineralized matrix nodules at concentrations of 1×10-7 and 1×10^-6 mol/L, but had no effect at a concentration of 1×10^-8 mol/L. Sm³⁺ inhibited the formation of mineralized matrix nodules of OBs at tested concentrations. Nd³⁺ and Sm³⁺ exhibited distinctive effects on the adipogenic transdifferentiation of OBs. Sm³⁺ (1×10-7, 1×10^-6, and 1×10^-5 mol/L) promoted the adipogenic transdifferentiation. Nd³⁺ suppressed the adipogenic transdifferentiation at tested concentrations. Moreover, we observed the gene expression of runt-related transcription factor-2 (Runx-2) and peroxisome proliferators activated receptor-γ(PPAR-γ) during differentiation of OBs. The expression of the mRNA for Runx-2 was significantly down-regulated in the presence of 1×10^-6 mol/L Sm³⁺ and Nd³⁺. The expression of the mRNA for PPAR-γwas slightly down-regulated by 1×10^-6 mol/L Nd³⁺, but significantly up-regulated by 1×10^-6 mol/L Sm³⁺.Our findings suggested that the effects of Nd³⁺ and Sm³⁺ on the proliferation, differentiation and mineralization function of primary OBs in vitro depended on the concentration, culture time and ion species. These ?ndings may be valuable for better understanding the mechanism of the effect of rare earth ions on the metabolism of bone.