Effects of strontium on the physicochemical characteristics of hydroxyapatite.
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 microg/ml) and an interference of the element with the hydroxyapatite (HA) formation at high doses (20-100 microg/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 microg/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 microg/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.
Verberckmoes
S C
SC
Department of Nephrology-Hypertension, University of Antwerp, Antwerp, Belgium.
Behets
G J
GJ
Oste
L
L
Bervoets
A R
AR
Lamberts
L V
LV
Drakopoulos
M
M
Somogyi
A
A
Cool
P
P
Dorriné
W
W
De Broe
M E
ME
D'Haese
P C
PC
D000469:Alkaline Phosphatase / Q000187:drug effects; D000818:Animals; D002113:Calcification, Physiologic / Q000187:drug effects*; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D045744:Cell Line, Tumor; D003460:Crystallization; D003470:Culture Media / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D017886:Durapatite / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D012995:Solubility / Q000187:drug effects; D017550:Spectroscopy, Fourier Transform Infrared; D013324:Strontium / Q000494:pharmacology*; D013997:Time Factors; D014961:X-Ray Diffraction
D003470:Culture Media; D017886:Durapatite; D000469:Alkaline Phosphatase; D002118:Calcium; D013324:Strontium