Glycosaminoglycans content of stone matrix

The role of urinary glycosaminoglycans (GAGs) in lithogenesis is a topic of current interest in urologic research. One GAG, chondroitin sulfate, has previously been shown to inhibit calcium oxalate crystal formation. It has long been known that the chemical components of GAGs are present in the matrix of urinary concretions, but it has not been determined whether these components exist in free form or as constituents of GAG. This study was undertaken to determine whether GAGs are present in urinary stone matrices and, if so, to characterize them. Matrices of nine single urinary stones of various compositions and of three stone pools (calcium oxalate, magnesium ammonium phosphate) were isolated by exhaustive dialysis. The techniques of cellulose acetate electrophoresis, Alcian blue staining and enzymatic degradation were used to identify various GAGs. Material that stained Alcain blue was present in eleven of twelve samples. GAG was detected as this material in ten samples. The GAGs identified are heparan sulfate, hyaluronic acid and possibly keratan sulfate. The most prominent urinary GAG, chondroitin sulfate, was notably absent from urinary stone matrix. GAG seems to be incorporated into matrix on a selective basis. This finding may be due to differences in the affinities of different GAG species for the crystals which comprise the calculi. It has been proposed that the inhibitory activity of GAGs lies in their ability to bind to (and therefore block) the growth sites of crystals. It is apparent from this study that certain GAG species are incorporated into the structure of the stone and they may be intimately related to stone development and growth.