The effects of citrate and urine on calcium oxalate crystal aggregation

Abstract

The rate of crystal sedimentation in a suspension of calcium oxalate monohydrate (COM) crystals was determined spectrophotometrically in the presence and absence of dialysed urine and citrate. A reduced rate of crystal sedimentation after stirring was recorded in suspensions containing citrate in concentrations between 0.33 and 1.67 mmol/l. The sedimentation rate was reduced in the presence of a 0.3-3.3% concentration of dialysed urine, with increased inhibition of crystal sedimentation when the concentration of urine was increased. A comparison of the inhibition of COM crystal sedimentation in whole urine and in dialysed urine from normal subjects and stone-formers disclosed significantly higher values (P < 0.05) in the dialysed urine. The results support previous observations that physiological concentrations of citrate might efficiently inhibit the aggregation of COM crystals. Furthermore even low concentrations of both whole urine and dialysed urine are apparently very efficient inhibitors of COM crystal aggregation.

Endogenous oxalogenesis after acute intravenous loading with ethylene glycol or glycine in rats receiving standard and vitamin B6‐deficient diets

“…This process is influenced by the pH of the urine, the solute load, and the various inhibitors of crystallization 25 . Citrate is generally accepted to be an inhibitor of the nucleation of oxalate and calcium phosphate, 26–28 as well as inhibiting crystal aggregation 29,30 and stone growth 29,31 . Thus, hypocitraturia is an important risk factor for renal stone formation.…”

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

“…rather marginal and in the range of 1-3 m M almost independent from concentration. However, crystals being preincubated with citrate during 2 h showed with increasing citrate concentration a marked inhibition of AGN [18] . For stone metaphylaxis it seems to be important to notice that even a 3.3-fold dilution of UM reduced SS only by 30%.…”

“…AGN was measured either by the increase of sedimentation rate or the particle size after incubation. Under such conditions some inhibition of AGN by DU could be demonstrated even at dilution down to a few percent [8,18] . Results of AGN inhibition by DU of stone patients and of healthy subjects were controversial.…”

“…SS is therefore a sensitive measure for the time without AGN. Crystallization of calcium oxalate in dialyzed urine (DU) has been examined in several studies [6,8,9,[15][16][17][18] . Contrary to our approach, where crystals were directly produced in the test medium and the time without measurable AGN was determined, most authors have measured the degree of AGN or even disaggregation [15] of preformed crystals after a given incubation time in the test medium.…”

Aggregation and Dispersion Characteristics of Calcium Oxalate Monohydrate: Effect of Urinary Species

“…Various methods utilizing turbidity/optical density data have been used by other investigators (26,27) to quantify aggregation/dispersion behavior of COM. In this study, optical density data were used to determine an aggregation coefficient (AC, defined in materials and methods section) in both statistical designs.…”