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In this study, the adsorption differences of different kinds of amino acids (acidic Lglutamic acid (L-Glu), neutral L-threonine (L-Thr) and alkaline L-histidine (L-His)) onto calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) crystals with sizes of 50 nm, 100 nm, 1 μm, 3 μm and 10 μm were investigated using spectrophotometry. The study of adsorption differences of amino acids on calcium oxalate has rarely been conducted; hence, we studied it with different pH values onto COM and COD crystals. The amount of adsorbed amino acids was determined using the depletion method and the centrifugation method was applied. At pH=7.3, COM crystals mainly adsorbed acidic L-Glu and have less adsorption to L-Thr and L-His, while COD mainly adsorbed alkaline L-His. Results of this study showed that when the size of crystal increases, the adsorption amount of crystals decreased. This was attributed to the decreases of specific surface area of larger crystals. The adsorption amount of COM was greater than that of COD with the same size because the specific surface area of COM is greater than COD. Our results help to further illustrate the formation mechanism of calcium oxalate stones and provide inspiration for inhibiting its recurrence.

This study aims to compare the cytotoxicity and adhesion of calcium oxalate monohydrate (COM) and dehydrate (COD) crystals with a size of 5 μm toward human kidney proximal tubular epithelial (HKC) cells so as to reveal the mechanism of kidney stone formation at cellular level. The measurement of cell viability and Lactate dehydrogenase (LDH) content were used to quantitatively analyze cell injury induced by COM and COD crystals; cell mortality was measured by propidium iodide (PI) staining; the adhesion of crystals on cell surface was observed by SEM. The decrease of cell viability and increase of LDH release of HKC cells caused by COM and COD were concentration-dependent in crystal concentration range of 100∼1600 μg/mL. COM caused more serious injury in HKC than COD. The adhesion amount of COM was significantly greater than COD crystal. The damage of micron COM was larger than COD, and COM was more easily aggregated on HKC. The results in this paper indicated that the presence of COM crystals in urine was more likely to increase the risk of stone formation than COD crystals.