Urinary Excretion of Glycosaminoglycans in Patients with Urolithiasis

The interaction between tubular epithelial cells and calcium oxalate crystals or oxalate ions is a very precarious event in the lithogenesis. Urine contains ions, glycoproteins and glycosaminoglycans that inhibit the crystallization process and may protect the kidney against lithogenesis.

Hundred patients (24 women and 76 men) with a history of stone disease and hundred controls (25 women and 75 men) were evaluated for urinary GAG concentration. By using a new dye-binding assay, the total GAG concentration in the urine was measured and corrected to urinary creatinine levels (milligram of GAG per gram creatinine).

There was a preponderance of urinary stones in males; the highest incidence being in Group 2. Excretion of GAGs in 24-hour urine sample was significantly lower in patients compared to controls, for males in all age groups and for females, however, there was no statistically significant difference in the urinary GAGs value between males and females in a given age group for either controls or patients. The urinary GAGs excretion idecreased with age in controls, but the levels in patients were lower.

Conclusion: This study shows that low urinary GAGs are associated with urinary stones in patients. Our study lead us to propose that urinary GAG may play an important role in the prevention and reduction of calculi in patients with urolithiasis. Lower urinary GAG levels are more common in patients with stone formation. This may play a more determinant role in male patients and those with recurrent stone formation. We conclude that uric acid can constitute an important risk factor for calcium oxalate urolithiasis through heterogeneous nucleation and the GAGs can play an important role as preventive agents.