Supplemental exposure to polystyrene nanoplastics synergistically amplifies calcium oxalate crystal–induced injury to renal tubular epithelium, accelerating the formation of calcium oxalate kidney stones

Abstract Background With the escalating issue of polystyrene microplastic pollution, microplastic particles have been detected in human urine. While calcium oxalate (CaOx) crystals are well-established mediators of renal stone formation, the role of microplastics, particularly polystyrene nanoplastics (PS-NPs), in promoting CaOx kidney stone formation remains unclear. This study aims to explore whether PS-NPs interact with CaOx crystals to enhance renal tubular epithelial cell injury and facilitate the formation of kidney stones. Methods Clinical CaOx kidney stone samples were analyzed using pyrolysis—gas chromatography-mass spectrometry (Py-GC/MS), which detected microplastic components. In vitro, human renal proximal tubular epithelial cells (HK-2) were exposed to calcium oxalate monohydrate crystals (1.5 mM), or cells were pretreated with PS-NPs (100 nm, 0.1 mg/mL) for 24 h, followed by the addition of 1.5 mM CaOx for co-treatment. Comprehensive mechanistic assessments, including whole-transcriptome RNA sequencing, crystal adhesion assays, macrophage chemotaxis and polarization analysis, ferroptosis biomarker quantification, lipid peroxidation measurement, and mitochondrial ferrous ion accumulation, were conducted. In vivo, a rat model of CaOx nephrolithiasis was induced by ethylene glycol (EG) with concurrent exposure to PS-NPs (4 mg/Kg·Day) via drinking water. Results Clinical analysis confirmed the presence of PS-NPs and other microplastics in human CaOx kidney stones. In vitro, exposure to PS-NPs significantly altered the morphology of CaOx crystals, promoting aggregation and enhancing adhesion to renal tubular epithelial cells. Combined exposure to PS-NPs and CaOx crystals exacerbated HK-2 cell injury through upregulation of VCAM1, CXCL8-driven macrophage chemotaxis and M1 polarization, and ferroptosis induced by xCT/GPX4 suppression. Transcriptomic analysis revealed LRP6 downregulation as a central regulator in these pathological processes. Overexpression of low-density lipoprotein receptor-related protein 6 (LRP6) alleviated cell damage and attenuated inflammatory responses. In vivo, PS-NPs co-exposure exacerbated renal CaOx deposition, ferroptosis in renal tubular epithelial cells, and inflammatory responses in the rat model. Conclusion Our study identifies PS-NPs as novel lithogenic cofactors that promote CaOx nucleation, enhance crystal adhesion to renal tubular epithelial cells, and amplify inflammation and ferroptosis through LRP6 downregulation. This suggests that microplastic pollution may be an emerging environmental risk factor for kidney stone pathogenesis. Graphical abstract