Article

Calcified Tissue International

, Volume 75, Issue 5, pp 405-415

First online:

Effects of Strontium on the Physicochemical Characteristics of Hydroxyapatite

  • S. C. VerberckmoesAffiliated withDepartment of Nephrology-Hypertension, University of Antwerp
  • , G. J. BehetsAffiliated withDepartment of Nephrology-Hypertension, University of Antwerp
  • , L. OsteAffiliated withDepartment of Nephrology-Hypertension, University of Antwerp
  • , A. R. BervoetsAffiliated withDepartment of Nephrology-Hypertension, University of Antwerp
  • , L. V. LambertsAffiliated withDepartment of Nephrology-Hypertension, University of Antwerp
  • , M. DrakopoulosAffiliated withEuropean Synchrotron Radiation Facility
  • , A. SomogyiAffiliated withEuropean Synchrotron Radiation Facility
  • , P. CoolAffiliated withDepartment of Chemistry, University of Antwerp
  • , W. DorrinéAffiliated withDepartment of Chemistry, University of Antwerp
    • , M. E. De BroeAffiliated withDepartment of Nephrology-Hypertension, University of Antwerp
    • , P. C. D’HaeseAffiliated withDepartment of Nephrology-Hypertension, University of Antwerp Email author 

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Abstract

In a previous experimental study using a chronic renal failure rat model, a dose-related multiphasic effect of strontium (Sr) on bone formation was found that could be reproduced in an in vitro set-up using primary rat osteoblasts. The results from the latter study allowed us to distinguish between a reduced nodule formation in the presence of an intact mineralization at low Sr-doses (1  Μg/ml) and an interference of the element with the hydroxyapatite (HA) formation at high doses (20–100  Μg/ml). To further investigate the latter effect of Sr on physicochemical bone mineral properties, an in vitro study was set up in which the UMR-106 rat osteosarcoma cell line was exposed to Sr, added to the cell culture medium in a concentration range varying between 0–100  Μg/ml. Temporal growth and functionality of the culture was investigated by measurement of the alkaline phosphatase activity and calcium (Ca) concentration in the culture medium (used as an index of Ca-incorporation, i.e., HA formation) at various time points. At the end of the culture period (14 days post-confluence), samples of the mineralized cultures were taken for further analysis using X-ray diffraction (XRD) and Fourier Transform Infra-Red Spectroscopy (FTIR). Synthetic HA doped with various Sr concentrations (based on the cell culture and previous experimental studies and yielding Sr/(Sr+Ca) ratios ranging from 0–60%), was prepared and examined for crystal growth and solubility. Crystal size was assessed using scanning electron microscopy (SEM). Ca incorporation indicated a reduced mineralization in the 20 and 100  Μg/ml Sr groups vs. controls. Sr-doped synthetic HA showed a significant dose-dependent reduction in crystal growth, as assessed by SEM, and an increase in solubility, apparent from 12.7% Sr/(Sr+Ca) on. Moreover, in both mineralized cultures and synthetic HA, XRD and FTIR analysis showed a reduced crystallinity and altered crystal lattice at similar concentrations. These new data support our previous in vivo and in vitro findings and point to a potential physicochemical interference of Sr with HA formation and crystal properties in vivo.

Keywords

Strontium Hydroxyapatite X-ray diffraction Mineralization Cell culture