Although several techniques have been used for the characterization of ex-vivo calcium pyrophosphate (CPP: Ca2P2O7·nH2O) deposits associated to osteoarthritis,1–4 little is known from a chemical point of view on these phases which are difficult to synthesize, could evolve during their formation in vivo and be altered after extraction during conservation, preparation and analysis. The objective of this study was to investigate the stability and evolution properties of synthetic hydrated calcium pyrophosphate phases and finely characterize ex-vivo specimen of meniscii and synovial fluids using laboratory and synchrotron facility in a view to progress in the understanding of the formation, order of appearance and potential evolution of monoclinic and triclinic calcium pyrophosphate dihydrates (m-CPPD and t-CPPD: Ca2P2O7·2H2O), the two phases detected in joints of arthritic patients. Four phases of CPP of biological interest, m-CPPD, t-CPPD and their potential precursor phases (monoclinic calcium pyrophosphate tetrahydrate (m-CPPTb: Ca2P2O7·2H2O) and amorphous calcium pyrophosphate), were synthesized using a protocol established by Gras et al., allowing a one-step and fast synthesis at controlled pH and temperature.5 Synchrotron X-ray diffraction and Raman spectroscopy analyses were conducted on synthetic samples and cryoground meniscii and synovial fluid specimens of arthritic patients to avoid any alteration of the samples. This study highlights the good selectivity of these techniques to detect both of the CPPD phases in complex media such as meniscus and synovial fluid, and to determine their ratio. In accordance with their thermodynamic stability, the data suggests the evolution of CPP in vivo from m-CPPD to t-CPPD. Although precursor phases could be involved their identification seems yet difficult. Progresses in the fine characterization of the different synthetic CPP phases could improve their detection in patients suffering from calcium-salt crystal diseases and could contribute to clarifying the mechanism by which CPP crystals form and evolve in vivo.
References: 1. P. Eliseo et al., Best Pract. Res. Clin. Rheumatol., 2005, 19, 371–86. 2. Y. Z. Liu et al., Osteoarthr. Cartil., 2009, 17, 1333–40. 3. M. Fuerst et al., Rheumatol. Int., 2010, 30, 623–31. 4. C. Nguyen et al., J. Synchrotron Radiat., 2011, 18, 475–80. 5. P. Gras et al., Eur. J. Inorg. Chem., 2013, 2013, 5886–595.