Stabilization of Calcium Oxalate Suspension by Urinary Macromolecules, Probably an Efficient Protection from Stone Formation

Abstract

Introduction: Crystal aggregation (AGN) destabilizes crystal suspensions and during crystalluria probably favors crystal apposition to kidney calcifications and preexisting stones. We analyzed inhibition of AGN and stabilization of calcium oxalate suspensions by urinary macromolecules (UM), urine and solutions with urinary citrate concentration. Materials and Methods: Solutions of UM (UMS) were obtained by a hemofiltration procedure from urine of 6 healthy men. Calcium oxalate suspensions were prepared in all solutions and urine by adjusting Ca²⁺ to 1.5 mM and by an oxalate titration to 1.0 mM. Crystallization was monitored measuring optical density (OD). Stability of suspensions (SS) was defined as the time without sedimentation and zeta potential (ZP) of crystals was measured. AGN was visualized by scanning electron microscopy and quantified by maximal OD. Results: UMS inhibited AGN and increased ZP and SS. Most inhibitory activity of urine could be attributed to UM. 3.3-fold dilution of UM reduced SS only by 30%. Conclusions: During crystalluria, UM of healthy men are supposed to protect from stone formation by inhibiting AGN and stabilizing crystal suspensions. As a probably important aspect, this protection was found to be limited in time and may favorably be influenced by an increase of diuresis.