Interaction of glucuronic acid and iduronic acid-rich glycosaminoglycans and their modified forms with hydroxyapatite

Proteoglycans and their spatial arms, glycosaminoglycans (GAGs), are known to interact with hydroxyapatite (HAP) and have been implicated as important modulators of mineralisation. In the present study isotherm data (0.02M so dium acetate, pH 6.8) revealed that the iduronic-rich GAGs heparan sulphate , heparin and dermatan sulphate showed greater binding onto HAP with higher adsorption maxima compared with the glucuronic acid-rich GAGs chondroitin- 4-sulphate, chondroitin-6-sulphate and hyaluronan. Chemically desulphated c hondroitin showed no adsorption onto HAP. With the exception of hyaluronan, the GAGs studied showed no desorbability in sodium acetate buffer only, wh ereas in di-sodium orthophosphate, desorption occurred much more readily. T he data indicates that GAG chemistry and conformation in solution greatly i nfluence the interaction of these molecules with HAP. The conformational fl exibility of iduronic acid residues may be an important determinant in the strong binding of iduronic acid-rich GAGs to HAP, increasing the possibilit y of the appended anionic groups matching calcium sites on the HAP surface, compared with more rigid glucuronic acid residues. This work provides impo rtant information concerning interfacial adsorption phenomena between the o rganic inorganic phases of mineralised systems. (C) 2001 Elsevier Science L td. All rights reserved.