DOES URINARY OXALATE INTERFERE WITH THE INHIBITORY ROLE OF GLYCOSAMINOGLYCANS AND SEMISYNTHETIC SULFATED POLYSACCHARIDES IN CALCIUM-OXALATECRYSTALLIZATION

Objectives: Previously it was shown that the polysaccharide G872 in vi tro strongly inhibits calcium oxalate monohydrate crystallization proc esses. However, when rats on a stone-inducing diet of ethylene glycol plus vitamin D-3 are given this polysaccharide, no changes in the urin e capacity for crystallization inhibition were found. We investigated here how the inhibitory action of polysaccharides changes under high o xalate conditions, as they exist in the stone inducing diet. Methods: Calcium oxalate monohydrate (COM) crystals were incubated in a series of 0.05 M PBS buffers containing polysaccharides with increasing oxala te concentrations (0-0.4 mmol/l). The coated crystals were collected, washed and resuspended in an artificial urine. We then measured the ze ta potential of the crystals, using a Coulter DELSA 440, and the initi al rates for crystal growth and agglomeration, using the Coulter Multi sizer II. Results: Addition of oxalate to the medium shifts the negati ve zeta potential distribution of COM crystals coated by polysaccharid es in positive direction. Particle size analysis demonstrated that the initial rates of COM crystal growth and agglomeration responding to o xalate concentration changes (0.1 --> 0.4 mmol/l) in the presence of G 872 (0.2 mg/l) are approximately 2.5 times faster than that in the abs ence of G872. Conclusions: Oxalate interferes with the binding of poly saccharides to crystals. This can be envisioned to occur through chang es in the crystal surface properties or by induction of functional and secondary structural changes of urinary macromolecular inhibitors suc h as GAGs, resulting in a decrease of their inhibitory activity agains t COM crystallization. Thus, in urine, a high oxalate may increase the rate of crystallization both by increasing the supersaturation and by decreasing the inhibitory potential of the urine.