Composition and inhibitory properties of endogenous urinary GAGS are different in subjects from two race groups with different occurrence rates of kidney stones: Pilot studies provide unique evidence in support of an inhibitory role for this group of compounds

Abstract

BackgroundCalcium oxalate (CaOx) kidney stone disease is common in South African whites (W) but is rare in the black population (B). The possible role of endogenous urinary glycosaminoglycans (GAGs) has not been previously investigated in this context. AimTo determine concentration, composition, structure and CaOx crystal-inhibiting properties of this group of compounds in ultrafiltered urine of healthy subjects from both groups. Materials and methodsGAGS were isolated from 24 h urine samples and were quantified and characterized by sequential precipitation, Bradford protein assay, high performance liquid chromatography, and anion exchange high performance chromatography. CaOx crystal inhibition was determined in ultrafiltered urinary fractions to which purified GAGS (PG) from each group (PGB and PGW) had been added. Nucleation, growth and aggregation were measured by Coulter particle counting, spectrophotometric assay and [14C]-oxalate deposition. ResultsHigher concentrations of chondroitin sulfate (CS) were found in PGB than in PGW. PGB inhibited crystallization to a greater extent than PGW. ConclusionsWe attribute the stronger inhibitory effect of PGB to its higher content of CS and suggest that the superior inhibition of CaOx crystallization by PGB relative to PGW might be a contributory factor in accounting for the lower stone occurrence rate in B.