Materials characterization of calcium oxalate monohydrate kidney stones

Calcium oxalate monohydrate (COM) kidney stones are the most common type of renal calculi. COM kidney stones are shown using polarized optical microscopy (POM) to develop by following a combined mechanism of direct crystal growth from a nidus, and by adsorption of preformed crystals. POM, X-ray diffractometry (XRD) and magnetic resonance imaging demonstrate that stones grow in layers consisting of COM crystals amalgamated with unidentified, optically inactive material. The stones have an intrinsic, non-water permeable core covered with a developing, crystalline COM, water permeable shell. These data provide insight into COM’s variable response to shock wave lithotripsy, the most common surgical treatment. Elmiron® is a commercial drug for the treatment of interstitial cystitis with the active ingredient being pentosan polysulfate (PPS), which is an anionic polysaccharide. Pentosan polysulfate was extracted from Elmiron® and its effects on COM crystal nucleation and growth were examined using a particle size analyzer (PSA), XRD and Infrared (IR) spectroscopy. PSA data suggest that PPS may exhibit an effect at decreasing the crystal size of calcium oxalate particles, but due to statistical variability, the results are inconclusive. SEM images show that PPS favours the formation of COM’s pseudopolymorph, calcium oxalate dihydrate (COD), and it decreased crystal aggregation. The effects of PPS may be due to an interaction between its sulfate groups and calcium oxalate as demonstrated by IR spectroscopy.