Crystallization during volume reduction of solutions with a composition corresponding to that in the collecting duct: the influence of hydroxyapatite seed crystals and urinary macromolecules

Abstract

To examine the effect of hydroxyapatite (HAP) seed crystals and urinary macromolecules on the crystallization under conditions similar to those in the collecting duct (CD), we evaporated 100 ml samples of salt solutions with an ioncomposition assumed to correspond to that in the CD without and with HAP seed crystals. The crystallization in seeded solutions was assessed both with and without dialyzed urine (dU). After evaporation, the number and volume of crystals were recorded and the crystal morphology was examined with scanning electron microscopy (SEM) and X-ray crystallography.Addition of HAP crystals was apparently followed by an approximately 15-20% increase in heterogeneous nucleation of calcium oxalate (CaOx). In these experiments, SEM and X-ray crystallography showed a high percentage of CaOx in the precipitate.In samples reduced to 40-69 ml, addition of dU to the CD solution containing HAP seed resulted in a greater mean (SD) number of crystals: 3895(1841) in samples with dU and 1785(583) in samples without. This was mainly explained by an increased mean (SD) number of small crystals. The mean crystal volume was 17.8(1.1) and 34.3(9.1) in samples reduced to 40-69 ml with and without dU, respectively. This might reflect the inhibitory effect of dU on the growth and/ or aggregation of the CaOx-CaP precipitate or a promoted nucleation resulting in a great number of small crystals.It is concluded that calcium phosphate (CaP) formed above the collecting duct might induce heterogeneous nucleation of CaOx at lower levels of the renal collecting system, and that urinary macromolecules are powerful modifiers of these processes.

The Influence of Hydroxyapatite Seed on the Crystallization Induced by Volume Reduction of Solutions with an Ion Composition Corresponding to that in the Distal Tubule at Different pH Levels

“…The present results indicate that CaP formed above the CD, whether in the proximal tubule (1), in the loop of Henle (3,5) or in the distal tubule (1, 2), might induce a heterogeneous nucleation of CaOx in CD urine at pH levels below 6.2. This is in accordance with our previous results (7)(8)(9).…”

“…We have shown previously that CaP is the favoured crystallization product at nephron levels above the CD, and that CaOx forms more easily lower in the nephron (1,2,7,26). The present results indicate that CaP formed above the CD, whether in the proximal tubule (1), in the loop of Henle (3,5) or in the distal tubule (1, 2), might induce a heterogeneous nucleation of CaOx in CD urine at pH levels below 6.2.…”

“…One litre of this solution was given the following ion composition: calcium m m in diameter. Scanning electron microscopy of the HAP seed crystal suspension showed that the majority of the crystals were smaller than 2.4 m m and that larger particles were aggregated crystals (7).…”

“…We have shown previously that CaOx can precipitate in the CD (1,7) and that CaP added to solutions with an ion composition corresponding to that in the CD might induce heterogeneous nucleation of CaOx (7)(8)(9). Several other authors have also shown that CaP can induce a heterogeneous crystallization of CaOx (10)(11)(12).…”

Systematic evaluation for effects of urine pH on calcium oxalate crystallization, crystal-cell adhesion and internalization into renal tubular cells

“…Several previous studies have shown that CaOx crystals can easily form inside distal renal tubules and urine pH is a crucial factor affecting such crystallization 24–27 . The difference of urine pH could generate various CaOx crystal types 14 .…”