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

Urinary glycosaminoglycans are selectively included into calcium oxala te (CaOx) crystals precipitated from whole human urine: The presence o f glycosaminoglycans (GAGs) in the organic matrix of urinary stones, a nd their known effects on CaOx crystallization have prompted speculati on regarding their role in CaOx urolithiasis. The aim of this study wa s to examine the involvement of GAGs in the early stages of CaOx cryst allization in human urine. Urine samples were collected from healthy m en and CaOx crystallization was induced by the addition of a sodium ox alate load. The crystals were harvested and demineralized, and the GAG content of the resulting extract analysed by cellulose acetate electr ophoresis. Only one GAG, heparan sulphate (HS) was detected in the org anic matrix of the crystals; chondroitin sulphate (ChS), the most abun dant urinary GAG, was conspicuously absent. Further experiments, in wh ich varying amounts of HS and ChS were added to ultrafiltered (10,000 Da) urine prior to induction of calcium oxalate crystallization, showe d 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 af finity than to ambient GAG concentration and that HS and ChS compete f or specific binding sites on the crystal surface.