Calcite as a Precursor of Hydroxyapatite in the Early Biomineralization of Differentiating Human Bone-Marrow Mesenchymal Stem Cells

Abstract

Biomineralization is the process by which living organisms generate organized mineral crystals. In human cells, this phenomenon culminates with the formation of hydroxyapatite, which is a naturally occurring mineral form of calcium apatite. The mechanism that explains the genesis within the cell and the propagation of the mineral in the extracellular matrix still remains largely unexplained, and its characterization is highly controversial, especially in humans. In fact, up to now, biomineralization core knowledge has been provided by investigations on the advanced phases of this process. In this study, we characterize the contents of calcium depositions in human bone mesenchymal stem cells exposed to an osteogenic cocktail for 4 and 10 days using synchrotron-based cryo-soft-X-ray tomography and cryo-XANES microscopy. The reported results suggest crystalline calcite as a precursor of hydroxyapatite depositions within the cells in the biomineralization process. In particular, both calcite and hydroxyapatite were detected within the cell during the early phase of osteogenic differentiation. This striking finding may redefine most of the biomineralization models published so far, taking into account that they have been formulated using murine samples while studies in human cell lines are still scarce.

Raman and XANES Spectroscopic Study of the Influence of Coordination Atomic and Molecular Environments in Biomimetic Composite Materials Integrated with Dental Tissue

“…This analytical method allows for characterisation of the speciation (coordination and redox state) of the main elements of mineralised hard tissues (here, Ca and P in calcium phosphates) as well as associated carbonate ions and organic molecules. The combination of XANES and synchrotron radiation, a source of high-intensity polarised X-rays in a given energy range, facilitates studies at the angstrom level, which opens up new horizons for understanding biomineralisation processes [28][29][30].…”

Physical properties, marginal adaptation and bioactivity of an experimental mineral trioxide aggregate-like cement modified with bioactive materials

“…This phase has also been observed on other occasions as a product of hydration in cements that were stored in SBF [8]. Calcium carbonate has been shown to be a precursor for hydroxyapatite [22], carbonate hydroxyapatite was also detected with the highest reflections at planes at 2θ: ca. 26°, 31.8° and 33° corresponding to planes (002), ( 112) and (300) as reported in other studies [8].…”

A guide into the world of high-resolution 3D imaging: the case of soft X-ray tomography for the life sciences

“…Taking advantage of the tunable wavelength obtainable at synchrotron facilities and imaging at different element's K/L-edges, X-ray absorption near-edge spectroscopy (XANES) has also been used alongside SXT to observe, map and quantify elements (such as calcium, oxygen and phosphorus) in cells or materials [ 62 , 63 ]. An example is seen in studies that have surveyed the involvement of calcium in biomineralization processes in bone tissues [ 35 , 62 ].…”

“…Taking advantage of the tunable wavelength obtainable at synchrotron facilities and imaging at different element's K/L-edges, X-ray absorption near-edge spectroscopy (XANES) has also been used alongside SXT to observe, map and quantify elements (such as calcium, oxygen and phosphorus) in cells or materials [ 62 , 63 ]. An example is seen in studies that have surveyed the involvement of calcium in biomineralization processes in bone tissues [ 35 , 62 ]. Also, for the first time to our knowledge, a combination of cryoSXT, nanofocused X-ray fluorescence (XRF) and XANES spectroscopy were used to establish the near-native single-cell chemistry of an anti-cancer compound- photoactivatable diazido platinum (IV) complexes [ 48 ].…”

“…The integration of XANES alongside water window soft X-ray absorption tomography on the same microscope has been implemented at beamline MISTRAL at the ALBA synchrotron [ 62 , 64 , 65 ]. There, they access the full spectral range to 1.5 KeV and with such an expanded spectral range, more structural visualization is enabled to include elemental compositions (K, P, Ca) and imaging deeper into samples already imaged by SXT.…”