Login to Access Video or Poster Abstract: MP12-09
Sources of Funding: Froedtert Foundation_x000D_ Medical College of Wisconsin

Introduction

In general, kidney stones are crystal aggregates held together by an organic matrix, which contains mainly proteins. Little is known about possible differences in the protein distribution between different stone types that likely are critical to stone pathogenesis. Enrichment of highly anionic and highly cationic proteins was observed in calcium oxalate (CaOx) stone matrix compared to urine, suggesting a role for protein aggregation in this stone process. In this study, stone matrix proteins have been quantitatively identified in 3 archival uric acid (UA) stones, and compared to the distribution observed in 8 calcium oxalate stones using a previously reported method.

Methods

Stone matrix proteins were isolated from 3 archival UA stone samples (>95% UA content) by dissolution in sequential washes with an EDTA/SDS solution at pH=8 with dithiothreitol added. The solubilized proteins were combined, then concentrated and desalted by ultradiafiltration. Proteomic analysis was performed at the Medical College of Wisconsin Innovation Center using non-labelled, quantitative mass spectrometry methods, including only proteins with 2 or more peptide matches at >85% confidence, after removing keratin and redundant proteins.

Results

Strong protein signals (>3,000 SC per sample) were obtained from each UA matrix protein sample identifying 342 unique proteins. Of these, 180 proteins were found in both UA and CaOx stone matrix, accounting for 81% of total protein mass of the former and 94% of the latter. Albumin and uromodulin were found in both stone types, but at lower relative abundance than these proteins are found in urine, suggesting non-selective inclusion of these highly abundant urine proteins. Important differences were that none of the 5 predominant proteins in CaOx stone matrix was prominent in UA stone matrix, and highly anionic proteins were not enriched in UA stones. Highly cationic proteins were slightly more prominent in UA stone matrix than in CaOx stone former urine, but much less than observed in CaOx stone matrix. Nuclear proteins were much less strongly represented in UA stone matrix. Conversely, immunoglobulins and complement proteins were predominantly enriched in UA stone matrix and less prominent in CaOx stones.

Conclusions

Stone matrix proteins exhibit distinctly different patterns in UA compared to CaOx stones, implying different underlying pathogenesis. In particular, UA stone formation appears to be more dependent on inflammatory pathways and less dependent on cell injury processes and polyanion-polycation association compared to CaOx stone formation.

Funding

Froedtert Foundation_x000D_ Medical College of Wisconsin