Polyanionic inhibitors of calcium oxalate crystal agglomeration in urine

The excretions and relative potencies of various macromolecular inhibitors of the crystallisation of calcium oxalate (CaOx) were measured in the urines of idiopathic calcium stone-formers and normal subjects. The stone-formers excreted significantly less polyanionic macromolecules in their urine than did the normals, the difference being attributable to the lower excretions of glycosaminoglycans (GAGS), ribonucleic acid (RNA) and Tamm-Horsfall mucoprotein (THM), all of which are precipitable with alcian blue. The relative potencies of the various inhibitors measured under 'whole urine equivalent' conditions using a batch crystallisation system, showed that the order of inhibitory activity towards CaOx crystal agglomeration was RNA greater than GAGS greater than THM greater than pyrophosphate (PPi). This paralleled the order of ability of these inhibitors to produce a high negative zeta potential on the surface of CaOx crystals.