REDUCED INHIBITORY ACTIVITY OF URONIC-ACID-RICH PROTEIN IN URINE OF STONE FORMERS

We recently reported that human urine contains a newly identified urin ary glycoprotein acting as a potent inhibitor against calcium oxalate crystallization. This inhibitor is a uronic-acid-rich protein (UAP) wi th a molecular weight of approximately 35 kDa. In the present study, U AP was isolated from urine of stone formers and of subjects without a stone history, and its inhibitory activity was tested in a calcium oxa late crystallization system in vitro. Our results show a weaker inhibi tory activity of UAP extracted from the urine of stone formers than th at extracted from the urine of healthy subjects. Preliminary analyses of amino acid and carbohydrate content showed some differences between the two groups. The main difference was the reduction in sialic acid in UAP isolated from the urine of stone formers. We suggest that UAP c ontributes significantly to total urinary inhibitory activity of calci um oxalate crystallization and that the decrease in this activity in t he urine of recurrent stone formers is due, in part, to the weak inhib itory activity of UAP. A structural abnormality of UAP could explain t he diminution of its inhibitory activity in the urine of stone formers .