Differences of Growth and Cytotoxicity of Calcium Oxalate Crystals Formed on HK-2 Cells Under Different Oxalic Acid/Calcium Ratios

We investigated the growth differences of CaOx crystals with different oxalic acid/calcium( Ox/Ca) molar ratios on the surface of human renal proximal tubule epithelial cells (HK-2) before and after injury and the toxicity of the crystals formed on the cells. CaOx supersaturated solution caused further damage to both the normal and damaged cells , resulting in the decrease of cell viability , lysosomal integrity and mitochondrial membrane potential , while the increase of intracellular reactive oxygen species (ROS), cytoskeleton disorder , phosphatidylserine (PS) eversion ratio and osteopontin (OPN) expression. With the increase of Ox/Ca molar ratio in saturated solution, the cell damage increased. Normal cells mainly induce the formation of calcium oxalate dihydrate (COD) crystals, and the percentage of COD is positively correlated with the Ox/Ca ratio. Damaged cells mainly induced calcium oxalate monohydrate (COM), and the number and aggregation of crystals are positively correlated with Ox/Ca molar ratio. Compared with the control group cells, the crystal edges induced by the damaged group cells are sharper, and the damage of sharp crystals to the cells is greater than that of round and blunt crystals. The results of this study suggest that reducing the supersaturation of CaOx, reducing the Ox/Ca molar ratio and repairing the damaged renal epithelial cells are all beneficial to inhibit CaOx stone formation.