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BSP-12
(P)
IDENTIFICATION OF NATURALLY OCCURRING CALCIUM-OXALATE BINDING
PROTEINS IN HUMAN URINE THAT PREVENT CRYSTAL ADHESION IN AN IN
VITRO MODEL OF KIDNEY STONE FORMATION
Paul AUSTIN, Scott MANSON, Joel KOENIG, Qiusha GUO and Katelynn MOORE
Washington University in St. Louis School of Medicine, Urology, Saint Louis, USA
PURPOSE
Approximately one half of renal calculi patients experience at least one recurrence. Calcium oxalate monohydrate (COM)
stone formation requires a combination of supersaturation and crystal adhesion to epithelial cells. We hypothesize that
naturally occurring urinary proteins are capable of binding calcium oxalate crystals and inhibiting stone formation.
MATERIAL AND METHODS
COM crystals and fluorescently-labeled derivatives (COM-FITC) were synthesized in vitro. Stone formation was modeled
in vitro by assessing the adhesion of COM-FITC crystals to confluent monolayers of inner medullary collecting duct
(IMCD) cells. Affinity chromatography was used to isolate calcium oxalate-binding proteins from human urine.
RESULTS
Incubation of IMCD cells with COM-FITC crystals resulted in rapid binding to the cell surface with high affinity. The
addition of urinary proteins purified from human urine inhibited COM-FITC binding by 76.2% and inhibited growth of
COM crystals in a free solution approximating urine composition by 53.5%. Only 16.6% of urinary proteins exhibited
calcium oxalate-binding activity. The bound fraction was eluted, purified by electrophoresis, and four prominent proteins
were identified (97 kD, 69 kD, 56 kD, 45 kD).
CONCLUSIONS
Naturally occurring urinary proteins inhibit COM adhesion to renal epithelium. Isolated calcium oxalate-binding proteins
may provide useful, novel prognostic and therapeutic targets.