The effect of heparan sulphate on the crystallization of calcium oxalate in undiluted, ultrafiltered human urine

Abstract

To determine the effect of physiological concentrations of heparan sulphate (HS) on the crystallization of CaOx in undiluted, ultrafiltered human urine. Urine was collected from normal male volunteers and ultrafiltered at a nominal molecular weight threshold of 10 kDa. Calcium oxalate (CaOx) crystallization was induced by the addition of a standard load of oxalate above an experimentally determined metastable limit and the effect of added HS tested at concentrations of 0, 1, 2 and 10 micrograms/mL using a Coulter Counter particle analyser and scanning electron microscopy. The metastable limit of the urine for CaOx was unaffected by HS at any concentration, as was the total volume of crystalline material deposited. However, HS strongly inhibited the formation of crystal aggregates with a response dependent on the dose and completely prevented the formation of crystal aggregates at a final concentration of 10 micrograms/mL. These findings were confirmed by scanning electron microscopy. HS is a potent inhibitor of CaOx crystallization in human urine and may protect against CaOx stone formation by reducing the degree of aggregation and thereby, the size of particles precipitated in the urinary tract.