The status of strontium in biological apatites: an XANES investigation

Abstract

Osteoporosis represents a major public health problem and increases patient morbidity through its association with fragility fractures. Among the different treatments proposed, strontium-based drugs have been shown to increase bone mass in postmenopausal osteoporosis patients and to reduce fracture risk. While the localization of Sr(2+) cations in the bone matrix has been extensively studied, little is known regarding the status of Sr(2+) cations in natural biological apatite. In this investigation the local environment of Sr(2+) cations has been investigated through XANES (X-ray absorption near-edge structure) spectroscopy in a set of pathological and physiological apatites. To assess the localization of Sr(2+) cations in these biological apatites, numerical simulations using the ab initio FEFF9 X-ray spectroscopy program have been performed. The complete set of data show that the XANES part of the absorption spectra may be used as a fingerprint to determine the localization of Sr(2+) cations versus the mineral part of calcifications. More precisely, it appears that a relationship exists between some features present in the XANES part and a Sr(2+)/Ca(2+) substitution process in site (I) of crystal apatite. Regarding the data, further experiments are needed to confirm a possible link between the relationship between the preparation mode of the calcification (cellular activity for physiological calcification and precipitation for the pathological one) and the adsorption mode of Sr(2+) cations (simple adsorption or insertion). Is it possible to draw a line between life and chemistry through the localization of Sr in apatite? The question is open for discussion. A better structural description of these physiological and pathological calcifications will help to develop specific therapies targeting the demineralization process in the case of osteoporosis.

Combining μX-ray fluorescence, μXANES and μXRD to shed light on Zn2+ cations in cartilage and meniscus calcifications

“…Cartilage samples were characterized by use of XRF, XAS and X-ray diffraction (XRD) analyses with the DIFFABS beamline located at the D13-1 bending magnet at the SOLEIL synchrotron facility (France) [23][24][25]. This facility uses a TOP/UP mode with a typical energy for the storage ring of 2.75 GeV and an average current of 400 mA.…”

Flyscan opportunities in medicine: the case of quantum rattle based on gold quantum dots

“…The DiffAbs beamline monochromator provides the energy resolution of ÁE/E = 10 À4 necessary for XANES measurements. Details regarding the experiments have appeared in previous publications on biological tissues including cartilage, kidney and bones (Carpentier et al, 2010;Bazin et al, 2011).…”

Calcifications pathologiques : un diagnostic médical basé sur leurs paramètres physicochimiques

“…La spectroscopie d'absorption différencie ces deux états. Cette technique permet aussi de décrire précisément la première sphère de coordination, c'est à dire de définir la nature et le nombre des atomes voisins de chacun des éléments présents au sein du matériau [112].…”

“…sans affecter la teneur en eau de l'échantillon qui pilote la transition entre la phase apatite amorphe et la phase apatite nanocristalline. Sur la figure 1B, les structures C1 et C2 proviennent de l'existence dans l'apatite de deux sites cristallographiques distincts pour le calcium, présents dans un rapport 2/3 [112]. Lorsque l'on passe d'une apatite très bien cristallisée à une carbapatite biologique puis au PACC, il faut tenir compte des atomes de calcium présents en surface qui altèrent la séparation entre les deux composantes du doublet C1-C2 ( figure 1B).…”