Bone tissue incorporates in vitro gallium with a local structure similar to gallium-doped brushite

Abstract

During mineral growth in rat bone-marrow stromal cell cultures, gallium follows calcium pathways. The dominant phase of the cell culture mineral constitutes the poorly crystalline hydroxyapatite (HAP). This model system mimics bone mineralization in vivo. The structural characterization of the Ga environment was performed by X-ray absorption spectroscopy at the Ga K-edge. These data were compared with Ga-doped synthetic compounds (poorly crystalline hydroxyapatite, amorphous calcium phosphate and brushite) and with strontium-treated bone tissue, obtained from the same culture model. It was found that Sr(2+) substitutes for Ca(2+) in the HAP crystal lattice. In contrast, the replacement by Ga(3+) yielded a much more disordered local environment of the probe atom in all investigated cell culture samples. The coordination of Ga ions in the cell culture minerals was similar to that of Ga(3+), substituted for Ca(2+), in the Ga-doped synthetic brushite (Ga-DCPD). The Ga atoms in the Ga-DCPD were coordinated by four oxygen atoms (1.90 A) of the four phosphate groups and two oxygen atoms at 2.02 A. Interestingly, the local environment of Ga in the cell culture minerals was not dependent on the onset of Ga treatment, the Ga concentration in the medium or the age of the mineral. Thus, it was concluded that Ga ions were incorporated into the precursor phase to the HAP mineral. Substitution for Ca(2+ )with Ga(3+) distorted locally this brushite-like environment, which prevented the transformation of the initially deposited phase into the poorly crystalline HAP.

Diffraction techniques and vibrational spectroscopy opportunities to characterise bones

“…More precisely regarding HAP, the analysis of EXAFS experiments [75] leads to an environment of Sr atoms composed by six oxygen atoms at a distance of 2.54Å and 2.4 oxygen atoms at 2.70Å. The obtained Sr-O distances were slightly longer than those determined by X-ray crystallography for Ca coordination in HAP, e.g.…”

“…EXAFS studies have been also performed to determine the environment of other cations such Ga [75], Pb [76] or Cd [77] in order to locate these cations inside the mineral. In the case of Sr, its incorporation in several calcium phosphate compounds including apatitic tricalcium phosphate, HAP, OCP and dicalcium phosphate dihydrate have been considered [78].…”

The status of strontium in biological apatites: an XANES investigation

“…Such treatments have been shown also to increase bone mass in postmenopausal osteoporosis patients (Boivin et al, 1996;Farlay et al, 2005;Marie, 2005;Roux, 2007;Rochefort et al, 2010;Roschger et al, 2010). Many studies have been performed to investigate the spatial repartition in tissues as well as the local environment of this oligoelement (Dahl et al, 2001;Verberckmoes et al, 2004;Korbas et al, 2004;Zhang et al, 2005;Ni et al, 2006;Bradley et al, 2007a,b;Zoeger et al, 2008;Zheng et al, 2009;Bellis et al, 2009).…”

O gálio e a patologia óssea

“…This replacement prevents the transformation of the initially deposited phase into HA and inhibiting the growth. Gallium supplementation at the later stages of mineralization does not influence the local environment of the deposited gallium and its ions seem to be loosely bound to the surface of the HA crystals (15) . In conclusion, gallium was shown to act as an inhibitor of bone mineralization in vitro.…”

“…In conclusion, gallium was shown to act as an inhibitor of bone mineralization in vitro. Two different mechanisms of its interaction with bone mineral could be distinguished: (1) substituting for Ca 2+ and (2) rejection of Ga 3+ by the apatite lattice with a possible adsorption on the surface of the HA crystals (14,15) . These data also were corroborated by the affect of gallium on seeded HA growth (16) .…”