URINARY GLYCOSAMINOGLYCANS ARE SELECTIVELY INCLUDED INTO CALCIUM-OXALATE CRYSTALS PRECIPITATED FROM WHOLE HUMAN URINE

Urinary glycosaminoglycans are selectively included into calcium oxalate (CaOx) crystals precipitated from whole human urine: The presence of glycosaminoglycans (GAGs) in the organic matrix of urinary stones, and their known effects on CaOx crystallization have prompted speculation regarding their role in CaOx urolithiasis. The aim of this study was to examine the involvement of GAGs in the early stages of CaOx crystallization in human urine. Urine samples were collected from healthy men and CaOx crystallization was induced by the addition of a sodium oxalate load. The crystals were harvested and demineralized, and the GAG content of the resulting extract analysed by cellulose acetate electrophoresis. Only one GAG, heparan sulphate (HS) was detected in the organic matrix of the crystals; chondroitin sulphate (ChS), the most abundant urinary GAG, was conspicuously absent. Further experiments, in which varying amounts of HS and ChS were added to ultrafiltered (10,000 Da) urine prior to induction of calcium oxalate crystallization, showed that ChS was included into the crystals only when HS was absent from the urine. It was concluded that the selective inclusion of GAGs into crystals and stones is a function related more to relative binding affinity than to ambient GAG concentration and that HS and ChS compete for specific binding sites on the crystal surface.