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To get information on the consequences of adsorption of urinary macromolecules (UMs) on crystals, Ca phosphate (CaP) precipitation was performed in urine of 15 stone patients and 15 controls. In solutions of dissolved precipitates (DPU), Ca oxalate (CaOx) crystallization and aggregation (AGN) of latex beads were spectrophotometrically studied and compared to results obtained in urine and in UMs isolated by hemofilter dialysis (HD). Tests were repeated with a 20 μg/mL albumin solution (AS). Inhibition of CaOx growth and AGN was significantly reduced in DPU as well as in HD. Furthermore, DPU and HD showed an AGN of latex beads which in patients was more pronounced than in controls. Identical effects observed in DPU and HD can be explained by temporary high concentrations of UMs by adsorption on surfaces favoring self AGN. Temporary adsorption of AS on CaP produced polymers of a limited size, significantly reduced the inhibition of CaOx AGN and accelerated latex AGN. In DPU, AGN of latex beads occurred despite a surface potential of -37 mV, which within short distances produces areas of massive electrostatic repulsion and normally inhibits AGN. Such areas might be bridged by self-aggregated UMs. The retardation of CaOx AGN measured in DPU could be decisive whether during crystalluria crystals are washed out from the kidney by diuresis or are attached to kidney calcifications or pre-existing stones.

Objectives: In urine, aggregation (AGN) of crystal occurs although they are coated by negatively charged urinary macromolecules (UM) and isolated at a distance from each other, where attraction forces become extremely weak. Calcium (Ca) bridges or viscous binding by UM could explain this AGN. Methods: Suspensions of Ca oxalate monohydrate (COM) and carboxylated latex (CL) were prepared in buffered water and UM solutions which were obtained from the urine of 6 healthy men. Surface potential or zetapotential (ZP) of the particles was measured at various concentrations of Ca and UM. AGN of CL was monitored determining particle size and optical density. Results: The ZP of COM was neutralized by Ca and stabilized around –15 mV by UM. In CL, a stable ZP of about –20 mV was achieved at >3 mM Ca. However, to induce AGN further addition of Ca was necessary. AGN then increased independently of ZP with increasing Ca and decreased with increasing UM concentration. Conclusions: In CL, two different Ca effects could be distinguished, one on ZP and another on AGN. The latter is probably based on the formation of Ca bridges between particles and is inhibited by a steric barrier of adsorbed UM. A similar mechanism is postulated for crystal aggregation.

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