Zinc oxide nanoparticles (ZnO NPs) have been widely used in various materials including sunscreens, cosmetics, over-the-counter topical skin products, and pigments. As traces of the used ZnO NPs have been found in the kidney, it is crucial to uncover their potential risks. The aim of this study is to elucidate detrimental effects of ZnO NPs and the molecular mechanism behind their renal toxicity. Cytotoxic effects were measured by MTT assay after HK2 cells were exposed to ZnO NPs for 24 h and IC₅₀ value was determined. ROS and intracellular Zn²⁺ levels were detected by flow cytometry, and localization of Zn²⁺ and lysosome was determined by confocal microscopy. Occurrence of autophagy and detection of autophagic flux were determined by Western blot and confocal microscopy, respectively. We performed unpaired student t test for two groups, and one-way ANOVA with Tukey’s post hoc for over three groups. ZnO NPs induced cell death in human renal proximal tubule epithelial cells, HK2. Cytosolic Zn²⁺ caused autophagy-mediated cell death rather than apoptosis. Cytosolic Zn²⁺ processed in lysosome was released by TRPML1, and inhibition of TRPML1 significantly decreased autophagic flux and cell death. The findings of this study suggest that ZnO NPs strongly induce autophagy-mediated cell death in human kidney cells. Controlling TRPML1 can be potentially used to prevent the kidney from ZnO NPs-induced toxicity.

Zinc oxide nanoparticles (ZnO NPs) are widely used in versatile applications, from high technology to household products. While numerous studies have examined the toxic gene profile of ZnO NPs across various tissues, the specific lipid species associated with adverse effects and potential biomarkers remain elusive. In this study, we conducted a liquid chromatography-mass spectrometry based lipidomics analysis to uncover potential lipid biomarkers in human kidney cells following treatment with ZnO NPs. Furthermore, we employed lipid pathway enrichment analysis (LIPEA) to elucidate altered lipid-related signaling pathways. Our results demonstrate that ZnO NPs induce cytotoxicity in renal epithelial cells and modulate lipid species; we identified 64 lipids with a fold change (FC) > 2 and p < 0.01 with corrected p < 0.05 in HK2 cells post-treatment with ZnO NPs. Notably, the altered lipids between control HK2 cells and those treated with ZnO NPs were associated with the sphingolipid, autophagy, and glycerophospholipid pathways. This study unveils novel potential lipid biomarkers of ZnO NP nanotoxicity, representing the first lipidomic profiling of ZnO NPs in human renal epithelial cells.

Hyun Pyo Jeon, Jisu Yang, Hana Jo, Eun Kyung Choe, and Sanghun Kim. J Environ Health Sci. 2023;49:312-23. https://doi.org/10.5668/JEHS.2023.49.6.312

This research evaluates standardised size, shape, and dustiness test guidelines for MWCNTs and introduces a novel, non-invasive method for characterising representative carbon nanotube length for regulatory risk assessment.

Applying regulatory-accepted, standardised test guidelines to solid, non-dispersible nanomaterials is challenging, primarily due to the difficulty of generating a homogenous exposure medium. Additional challenges arise from the physicochemical characteristics of multi-walled carbon nanotubes (MWCNTs), which are typically light and exist as entangled bundles. This study evaluated the applicability of available standardised in vitro/in chemico OECD test guidelines (TGs) for animal-free human health testing and explored potential adaptations to make them suitable for MWCNTs. Our focus was on EU-REACH data requirements related to in vitro serious eye damage/irritation, in chemico skin sensitisation, and in vitro gene mutation in mammalian cells. We assessed the applicability of OECD TG 492B, TG 442D/442E, and TG 476 for these endpoints. Our findings indicate that adequate data may only be generated if solid nanomaterials can be applied as such (as in OECD TG 492B), or if nano-specific dispersion protocols are available for an endpoint (as in genotoxicity testing), whereas significant limitations remain for skin sensitisation testing.

This research tackles the challenges of quantifying MWCNTs in environmental media for regulatory risk assessment, examining standardised environmental fate tests and alternative analytical methods.