INVESTIGATION OF THE POSSIBLE ROLE OF SIALIC-ACID IN CALCIUM-OXALATE UROLITHIASIS

Objective: It is considered that sialic acid in urine comprises two di fferent types of sialic acid, that is, the free sialic acid and the bo und one which exists as a basic component of urinary macromolecules. T he present studies were performed to clarify the role of sialic acid i n urine and compare the excretion and concentrations of sialic acid in urine between calcium oxalate (CaOx) stone formers and healthy subjec ts. Methods: First, we prepared the crystal surface binding substances from whole human urine. The crystal surface binding substances were d igested with sialidase and both the inhibitory activity on CaOx crysta l growth and concentrations of sialic acid before and after sialidase digestion were measured. The inhibitory activity of free sialic acid i n ultrafiltered urine was also measured. The excretion and concentrati on of sialic acid in urine from patients with CaOx urolithiasis and he althy controls were determined and compared. Results: The inhibitory a ctivity of crystal surface binding substances on CaOx crystal growth d id not show any significant difference before and after sialidase dige stion. The free sialic acid had also no effect on CaOx crystal growth. There was no statistically significant difference between CaOx stone formers and healthy controls on the excretion and concentration of sia lic acid in urine. The free:bound sialic acid ratio in urine was consi dered 1:0.97 and 1:1.33 for healthy controls and CaOx stone formers re spectively (p = NS). Conclusions: It is suggested that neither the fre e sialic acid nor the bound one in urine has a significant inhibitory effect on CaOx crystal growth.