A new insight into the dissociating effect of strontium on bone resorption and formation

Calcium phosphates are widely used as biomaterials and strontium (Sr) is known to have the ability to modify the bone balance towards osteosynthesis. In the present study we investigated the capacity of Sr-substituted sol–gel calcium phosphate to modify the expression of genes and proteins involved in extracellular matrix synthesis by primary bone cells. We first determined the most effective concentration of strontium using human primary bone cells. Sol–gel biphasic calcium phosphate (BCP) powders were then synthesised to obtain release of the optimal concentration of strontium. Finally, human osteoblasts obtained from explant cultures were cultured in the presence of sol–gel BCP, Sr-substituted BCP (5% Sr-substituted BCP, corresponding to a release of 5 × 10−5 M [Sr2+] under the culture conditions (BCP5%)) and medium containing strontium chloride (SrCl2). Viability, proliferation, cell morphology, protein production and protein activity were studied. We demonstrated that 5 × 10−5 M SrCl2 and BCP5% increased the expression of type I collagen and SERPINH1 mRNA and reduced the production of matrix metalloproteinases (MMP-1 and MMP-2) without modifying the levels of the tissue inhibitors of MMPs (TIMPs). Thus strontium has a positive effect on bone formation.