Unveiling potential natural promoters of calcium oxalate kidney stones in the urine via anion-exchange chromatography, crystal assays, and proteomics.

Knowledge of natural stone promoters in the urine was previously limited, but is essential to develop new targets for better management of calcium oxalate (CaOx) kidney stones. This work, therefore, unveils such information in the urine of CaOx stone formers (patients with stones). Urinary proteins were fractionated by DEAE/GigaQ anion-exchange chromatography, and individual fractions were subjected to multiple crystal assays. The fractions with the summed crystal-promoting score ≥ 3 were subjected to proteomic analysis using nanoLC-ESI-Qq-TOF tandem mass spectrometry (MS/MS). Almost all of the chromatographic fractions (SFQ1-SFQ9) showed promoting effects on CaOx crystallization, growth, aggregation and crystal-cell adhesion. Among them, SFQ2, SFQ8 and SFQ9 provided the greatest summed crystal-promoting score, implicating their roles in stone promotion. MS/MS successfully identified 12, 38 and 6 proteins in fractions SFQ2, SFQ8 and SFQ9, respectively. Among all proteins identified, CD44 antigen, galectin-3-binding protein, kallikrein-1, and protein AMBP were found in more than one fraction, suggesting that they might serve as candidates for the stone promoters. These findings narrow the gap to better understand the pathogenesis and offer opportunities to define new therapeutic targets for better management of CaOx kidney stones.