Structure and in vivo anticalcification properties of a polymeric calcium-sodium-phosphocitrate organic-inorganic hybrid

This paper describes the synthesis, characterization and crystal structure of an organic-inorganic polymeric hybrid composed of Ca, Na, and phosphocitrate (CaNaPC). CaNaPC is synthesized by reaction of CaCl2 . 2H(2)O and Na-4(HPC) . 3H(2)O in water, at pH 2. Its structure is polymeric with Ca(PC)(2)(H2O) "monomers" connected through Na+ bridges. The 9-coordinate Ca occupies the center of an irregular polyhedron defined by four phosphate, four carbonyl, and one H2O oxygens. Ca-O(=C) distances are in the 2.446(2)-2.586(2) Angstrom range. There is a short distance of 2.477(1) Angstrom between Ca and the ester O from C-O-PO3H2. All -COOH groups are protonated. There are three dissociated protons per two PC molecules, all coming from -PO3H2. Na ions are six-coordinate surrounded by -COOH's. The anticalcification properties of CaNaPC on plaque growth were studied in vivo using rats as model systems. Na-phosphocitrate is an effective inhibitor, but its effectiveness diminishes when a lower dose is used (9.7 mg as H5PC), resulting in only 30% plaque reduction. Superior inhibition activity becomes evident by following treatment with CaNaPC, at an equal dose (9.6 mg as H5PC) giving nearly quantitative (95%) plaque inhibition. (C) 2003 Elsevier Science B.V. All rights reserved.