Differences in macrophage pyroptosis and polarization induced by nano-/micro-calcium oxalate crystals.

Objective: This study aimed to compare the differences in pyroptosis and polarization of macrophages induced by different sizes of calcium oxalate monohydrate (COM) crystals and discuss the mechanism of kidney stone formation.

Methods: COM crystals with sizes of about 100 nm, 500 nm, 2.5 μm, and 10 μm were synthesized and characterized. THP-1 cells were induced to differentiate into macrophage-like cells. The damage of COM crystals to Mφs was evaluated by CCK-8 assay. The activation of the pyroptosis signaling pathway, cell morphology, and proportion of pyroptosis cells in Mφs induced by COM crystals were detected. Finally, the proportion of M1/M2 polarization was qualitatively and quantitatively assessed.

Results: COM-100 nm, COM-500 nm, COM-2.5 μm, and COM-10 μm all significantly induced the pyroptosis and polarization of Mφs. Among them, at the same cell viability, COM-10 μm induced the highest pyroptosis rate. The expression of NLRP3 and GSDMD-N induced by COM-10 μm increased by 81.43 ± 11.45% and 112.00 ± 9.87%, respectively, and the rate of caspase-1/PI double-positive pyroptosis cells was 22.2%. Meanwhile, COM-10 μm induced the highest proportion of M1 polarization (M1/M2 ratio was 209.90% ± 2.54%).

Conclusion: COM-10 μm significantly activates the classical caspase-1-mediated pyroptosis pathway and promotes M1 polarization in Mφs. Therefore, at the same cell viability, large-sized micro-COM is more capable of inducing inflammation than nano-COM.