Characterization of the Protein Components of Matrix Stones Sheds Light on S100-A8 and S100-A9 Relevance in the Inflammatory Pathogenesis of These Rare Renal Calculi

Purpose: Among the different types of kidney stones, matrix stones are uncommon urinary calculi composed of a soft, pliable, amorphous substance with little crystalline content. To gain insight into the pathogenesis we investigated the protein component by analyzing the proteomic profiles of surgically removed matrix stones.Materials and Methods: A total of 5 stones were harvested from 4 patients who underwent surgery for medical reasons at 3 clinical centers during a 7-year period. Matrix stone proteome characterization was performed by mass spectrometry based techniques using an integrated top-down/bottom-up proteomic platform.Results: We identified 142 nonredundant proteins and peptides across all samples. Neutrophil defensin 1, and proteins S100-A8 and S100-A9 were the main components of these renal calculi.Conclusions: The abundance of identified inflammatory molecules points to an inflammatory process as the event that initializes soft calculi formation rather than as a consequence of such formation...