Development of a two-stage model system to investigate the mineralization mechanisms involved in idiopathic stone formation: stage 2 in vivo studies of stone growth on biomimetic Randall’s plaque
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Idiopathic stone formers often form calcium oxalate (CaOx) stones that are attached to calcium phosphate (CaP) deposits in the renal tissue, known as Randall’s plaques (RP). Plaques are suggested to originate in the renal tubular basement membrane and spread into the interstitial regions where collagen fibrils and vesicles become mineralized; if the epithelium is breached, the RP becomes overgrown with CaOx upon exposure to urine. We have developed a two-stage model system of CaP–CaOx composite stones, consisting of Stage (1) CaP mineralized plaque, followed by Stage (2) CaOx overgrowth into a stone. In our first paper in this series (Stage 1), osteopontin (and polyaspartate) were found to induce a non-classical mineralization of porcine kidney tissues, producing features that resemble RP. For the Stage 2 studies presented here, biomimetic RPs from Stage 1 were implanted into the bladders of rats. Hyperoxaluria was induced with ethylene glycol for comparison to controls (water). After 4 weeks, rats were sacrificed and the implants were analyzed using electron microscopy and X-ray microanalyses. Differences in crystal phase and morphologies based upon the macromolecules present in the biomimetic plaques suggest that the plaques have the capacity to modulate the crystallization reactions. As expected, mineral overgrowths on the implants switched from CaP (water) to CaOx (hyperoxaluric). The CaOx crystals were aggregated and mixed with organic material from the biomimetic RP, along with some amorphous and spherulitic CaOx near the “stone” surfaces, which seemed to have become compact and organized towards the periphery. This system was successful at inducing “stones” more similar to human idiopathic kidney stones than other published models.
KeywordsUrolithiasis Randall’s plaque Nephrolithiasis Kidney stones Biomimetic model system PILP
Research reported in this publication was supported by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under Award Number R01DK092311. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We also thank our collaborators who provided the decellularized porcine kidney tissues, Drs. Brad Willenberg and Edward Ross (College of Medicine, University of Central Florida), and Dr. Christopher Batich (Department of Materials Science and Engineering, University of Florida). Data was also gathered from EM core in the College of Medicine, as well as the Research Service Centers within the Herbert Wertheim College of Engineering, so we thank the staff for their training and guidance on these instruments as well.
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Conflict of interest
The authors declare that they have no conflict of interest in this work.
This article does not contain any studies with human participants performed by any of the authors.
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