Crystalline aggregation in vitro: interaction between urinary macromolecules and the micromolecular environment

Area of Science:

• Nephrology
• Biochemistry
• Crystallization

Background:

• Calcium oxalate (CaOx) crystal formation and aggregation are key factors in kidney stone disease.
• Understanding the in vitro formation of CaOx macroaggregates is crucial for elucidating stone pathogenesis.
• The role of the urinary micromolecular environment and macromolecules in CaOx stone formation requires further investigation.

Purpose of the Study:

• To compare in vitro CaOx crystalline macroaggregate formation between healthy individuals and patients with CaOx stones, excluding metabolic abnormalities.
• To assess the influence of the urinary micromolecular environment on macromolecule activity (MW > 10,000 Daltons) in CaOx stone formation.
• To investigate the relationship between CaOx supersaturation, aggregation, nucleation, and the urinary milieu.

Main Methods:

• In vitro induction of CaOx crystalline macroaggregates using increasing oxalate loads.
• Comparison of macroaggregate formation parameters (supersaturation, aggregation-nucleation delta) between control and stone-former groups.
• Analysis of urine composition (citrate, magnesium, calcium, ionic strength) and its correlation with macroaggregate formation.
• Evaluation of macromolecule activity in native urine versus filtered urine and metastable solutions.

Main Results:

• No significant difference was observed in CaOx relative supersaturation or aggregation-nucleation delta between controls and stone formers.
• Urine composition significantly impacts macroaggregate formation; high CaOx saturation, ionic strength, citrate, magnesium, and calcium favor macroaggregate formation.
• A strong positive correlation (r = 0.74, P < 0.0001) was found between aggregation-nucleation delta in filtered urine and in metastable solutions with macromolecules.
• Urinary macromolecules appear to play a role in macroaggregate formation, with their activity preserved even when re-suspended in different media.

Conclusions:

• In vitro formation of CaOx crystalline macroaggregates does not differ between normal subjects and CaOx stone formers without metabolic abnormalities.
• Urinary macromolecules are involved in CaOx crystalline macroaggregate formation.
• The urinary micromolecular environment modulates the activity of these macromolecules, but their intrinsic aggregation-promoting function remains intact.