Synthesis, characterization and size-dependent cytotoxicity of magnesium ammonium phosphate hexahydrate crystals of different sizes on renal epithelial cells.

Magnesium ammonium phosphate hexahydrate (MAP) crystals with sizes of 98.5 ± 20.6 nm, 310 ± 67 nm, 1.12 ± 0.34 μm, and 3.23 ± 0.90 μm were synthesized and characterized. These crystals can cause damage to renal tubular epithelial cells (HK-2), which is manifested by crystal-induced cell morphological changes, cell viability, a decrease in superoxide dismutase and mitochondrial membrane potential. In addition, there were crystal-induced increases in reactive oxygen species, lactate dehydrogenase, and malondialdehyde levels, as well as phosphatidylserine ectropion. That is, MAP crystals can lead to cell necrosis and apoptosis, and promote the release of inflammatory cytokines IL-18 and IL-6. The cytotoxicity of MAP crystals has a size effect, that is, the cytotoxicity is: MAP-100 nm > MAP-300 nm > MAP-1 μm > MAP-3 μm. The factors enhancing the cytotoxicity of MAP include small size, large specific surface area, and a more negative crystal surface zeta potential. Nano-crystal MAP-100 nm mainly causes cell death by inducing extensive cell necrosis. When the larger-sized MAP-300 nm, MAP-1 μm and MAP-3 μm crystals acted on HK-2 cells, cell necrosis, apoptosis and autophagy occurred simultaneously. Investigating the relationship between MAP crystal size and cytotoxicity may provide insights into elucidating the mechanism of MAP stone (struvite) formation and preventing its occurrence.