Strong inhibition of crystal-cell attachment by pediatric urinary macromolecules: A close relationship with high urinary citrate secretion

Objectives. To investigate other reasons for the low incidence of pediatric urolithiasis, we evaluated the difference in the crystal-cell adhesion inh ibitory activity of urinary macromolecules (UMMs) between children and adul ts. We also evaluated whether citrates influence the above inhibitory activ ity, because citrates are important in pediatric urine. Methods. Urine samples were collected from children and healthy male adults during a 24-hour period, and urinary components with a molecular weight of 3 kDa or greater were extracted as UMMs to compare their inhibitory activi ty during the adhesion of calcium oxalate monohydrate crystals to cultured Madin-Darby canine kidney cells between children and adults. Subsequently, various concentrations of citrates were added to adult UMMs to evaluate the changes in the crystal-cell adhesion inhibitory activity of UMMs. Results. Pediatric UMMs more strongly inhibited the adhesion of calcium oxa late monohydrate crystals to cultured Madin-Darby canine kidney cells at a concentration of 0.1 mg/mL compared with adult UMMs. In addition, pediatric UMMs contained higher proportions of fibronectin and glycosaminoglycans, b oth of which exhibit crystal-cell adhesion inhibitory activity. When citrat es were added to adult UMMs, the crystal-cell adhesion inhibitory activity of UMMs was increased in a dose-dependent manner. However, citrates alone d id not result in any differences in the inhibitory activity at any of the t hree different concentrations. Conclusions. We speculate that the incidence of pediatric urolithiasis is l ow because pediatric UMMs more potently inhibit the adhesion of calcium oxa late crystals to renal tubular cells or because the higher proportion of ci trates in pediatric urine enhances the crystal-cell adhesion inhibitory act ivity of UMMs in a dose-dependent manner. UROLOGY 58: 493-497, 2001. (C) 20 01, Elsevier Science Inc.