Binding of glycosaminoglycan inhibitors to calcium oxalate crystals in relation to ionic strength

Several inhibitors of calcium oxalate crystallization have been identified and shown to exhibit quantitative and qualitative differences in efficacy. Glycosaminoglycans are potent inhibitors of crystal growth and aggregation, and the efficiency seems to increase with an increasing charge density. In order to investigate the mechanism of inhibition, we performed binding experiments of radioactivity labelled heparin, chondroitin sulphate and the low-molecular mass heparin analogue pentosan polysulphate to calcium oxalate crystals and subsequent displacements by increasing the amounts of non-radioactive ligands or increasing ionic strength. Ligands with a high charge density bound more readily and with a seemingly higher affinity than ligands with a low charge density, but were also more susceptible to displacement when the ionic strength was increased. It is concluded that a higher affinity to the crystals may be the reason why highly charged glycosaminoglycans are more efficient inhibitors of calcium oxalate crystal growth.