Bikunin prevents adhesion of calcium oxalate crystal to renal tubular cells in human urine

Crystal-renal tubular cell interactions are important factors in crystal re tention and development of kidney stones. It has been reported that human u rine, especially its macromolecular fraction, distinctively prevented calci um oxalate monohydrate (COM) crystal adhesion to tubular cells. This study was designed to find and isolate a specific substance in human urine with a strong inhibitory effect against crystal adhesion. A protein from the urin e was purified by two anion exchange chromatography columns and one gel fil tration column. The inhibition activity for COM crystal adhesion to Madin-D arby canine kidney cells was determined quantitatively. Amino acid sequence of the protein was analyzed and then subjected to homology search in the G enBank protein database. A specific human urine protein that inhibited the COM crystal adhesion to the cells was isolated and identified. Molecular ma ss of the protein was approximately 35 kD. The first 20-amino acid sequence from the N-terminal of the purified protein was structurally homologous wi th the light chain of inter-a-trypsin inhibitor, also called bikunin. The i solated bikunin inhibited crystal adhesion at a minimum concentration of 10 ng/ml, and blocked completely at 200 ng/ml. It is concluded that bikunin m ay contribute to the regulation of crystal adhesion and retention within tu bules during kidney stone formation.