Excessive crystal agglomeration with low citrate excretion in recurrent stone-formers

Area of Science:

• Nephrology
• Urology
• Biochemistry

Background:

• Calcium oxalate stones are the most common type of kidney stones.
• Recurrent stone formation suggests underlying metabolic or urinary abnormalities.
• Understanding the urinary factors influencing crystal formation is crucial for prevention.

Purpose of the Study:

• To investigate the effects of urine from stone formers and healthy individuals on calcium oxalate monohydrate crystallization processes.
• To identify specific urinary factors, particularly citrate, involved in calcium oxalate stone formation.

Main Methods:

• Studied urine effects on solubility, crystal growth, and crystal agglomeration in 7 stone formers and 10 healthy subjects.
• Assessed urinary citrate levels as a potential metabolic abnormality.
• Investigated the impact of normalizing urinary citrate on crystal agglomeration inhibition in vitro and in vivo.

Main Results:

• Urine from stone formers exhibited low calcium oxalate solubility and normal crystal growth inhibition.
• A key finding was the lack of crystal agglomeration inhibition in stone formers' urine.
• All stone formers presented with hypocitraturia, identified as the sole metabolic abnormality.
• Restoring urinary citrate levels significantly enhanced agglomeration inhibition.

Conclusions:

• Crystal agglomeration inhibition is a critical process in calcium oxalate stone formation.
• Urinary citrate plays a significant, likely regulatory, role in inhibiting crystal agglomeration.
• Hypocitraturia is a key factor contributing to recurrent calcium oxalate stone disease.