Elsevier

Metabolism

Volume 53, Issue 4, April 2004, Pages 532-537
Metabolism

Normal matrix mineralization induced by strontium ranelate in MC3T3-E1 osteogenic cells

https://doi.org/10.1016/j.metabol.2003.10.022Get rights and content

Abstract

There is growing evidence that strontium ranelate (SR; S12911-2, PROTELOS; Institut de Recherches Internationales Servier, Courbevoie, France), a compound containing 2 atoms of stable strontium (Sr), influences bone cells and bone metabolism in vitro and in vivo. We previously reported that SR increases bone mass in rats and mice by stimulating bone formation and inhibiting bone resorption. We also showed that short-term treatment with SR enhances osteoblastic cell recruitment and function in short-term rat calvaria cultures. Because Sr incorporates into the bone matrix, it was of interest to determine whether SR may affect matrix mineralization in long-term culture. To this goal, osteogenic mouse calvaria-derived MC3T3-E1 osteoblastic cells were cultured for up to 14 days in the presence of ascorbic acid and phosphate to induce matrix formation and mineralization. Matrix formation was determined by incorporation of tritiated proline during collagen synthesis. Matrix mineralization was quantified by measuring the number and surface of mineralized nodules using a digital image analyzer. In this model, 1,25(OH)2 vitamin D (1 nmol/L) used as internal control, increased alkaline phosphatase (ALP) activity, an early osteoblast marker, on days 4, 10, and 14 of culture. Treatment with SR (1 mmol/L Sr2+) increased ALP activity at days 4 and 14 of culture. SR also increased collagen synthesis at days 4 and 10 of culture. In contrast, 1,25(OH)2 vitamin D (1 nmol/L) inhibited collagen synthesis at 4 to 14 days of culture. Long-term treatment with SR (0.1 to 1 mmol/L Sr2+) dose dependently increased Sr concentration into the calcified nodules, but did not alter matrix mineralization in long-term culture, as shown by the ratio of the surface of mineralized nodules to the number of mineralized nodules on day 14 of culture. These results show that long-term treatment with SR increases collagenous matrix formation by MC3T3-E1 osteoblasts without inducing deleterious effect on matrix mineralization.

Section snippets

Cell cultures and treatment

MC3T3-E1 are clonal osteogenic cells derived from newborn mouse calvaria25 that have a high mineralization potential.25, 26, 27, 28, 29 MC3T3-E1 cultured in the presence of ascorbic acid display a time-dependent and sequential expression of osteoblast characteristics analogous to the bone formation process in vivo.27 The cells actively replicate, then express alkaline phosphatase (ALP) activity and synthesize a collagenous extracellular matrix, which progressively undergoes mineralization.27 In

Sr increases ALP activity

The effects of SR (0.1, 0.5, and 1 mmol/L Sr2+) were first analyzed in MC3T3-E1 cells cultured from 4 to 14 days. In control cells, ALP activity increased transiently at 10 days. Treatment with 1,25(OH)2D (1 nmol/L) significantly increased ALP activity on day 4 (+45%), day 10 (+81%), and day 14 (+100 %) of culture compared with controls. Treatment with SR (1 mmol/L Sr2+) significantly increased ALP activity at day 4 (+45 %) and day 14 (+45 %) of culture compared with control conditions (Fig 1).

Discussion

We previously showed that SR has beneficial effects on bone mass in experimental models of osteopenia (reviewed in Marie31). Because Sr incorporates into bone (reviewed in Dahl et al20), it was important to determine whether SR might alter mineralization of the matrix in long-term culture. The present study shows that long-term in vitro treatment with SR does not hamper matrix mineralization induced by murine osteogenic cells.

MC3T3-E1 are osteogenic cells that are a widely used model to study

Acknowledgements

We thank thank Professor C. Rey for helpful discussions.

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