CeO nanoparticles induce pulmonary fibrosis activating S1P pathway as revealed by metabolomics.

CeO nanoparticles (NPs) have been shown to cause lung fibrosis, however, the exact underlying molecular mechanisms are poorly understood. In this study, we have conducted a mass spectrometry-based global metabolomic analysis of human bronchial epithelial BEAS-2B cells treated by CeO NPs with different aspect ratios and assessed their toxicity on the bronchial epithelial cells by various cell-based functional assays. Although CeO NPs at doses ranging from 12.5 μg/mL to 25 μg/mL displayed low cytotoxicity on the bronchial epithelial cells, the metabolomic analysis revealed a number of metabolites in the cellular metabolic pathways of sphingosine-1-phosphate, fatty acid oxidation, inflammation, . were significantly altered by CeO NPs, especially those with high aspect ratios. More importantly, the robustness of metabolomics findings was further successfully validated in mouse models upon acute and chronic exposures to CeO NPs. Mechanistically, CeO NPs upregulated transforming growth factor beta-1 (TGF-β1) levels in BEAS-2B cells in an aspect ratio-dependent manner through enhancing the expression of early growth response protein 1 (EGR-1). In addition, both and studies demonstrated that CeO NPs significantly induced the expression of sphingosine kinase 1 (SHPK1), phosphorylated Smad2/3 and lung fibrosis markers. Moreover, targeting SPHK1, TGFβ receptor or Smad3 phosphorylation significantly attenuated the fibrosis-promoting effects of CeO NPs, and SPHK1-S1P pathway exerted a greater effect on the TGF-β1-mediated lung fibrosis compared to the conventional Smad2/3 pathway. Collectively, our studies have identified the metabolomic changes in BEAS-2B cells exposed to CeO NPs with different aspect ratios and revealed the subtle changes in metabolic activities that traditional approaches might have missed. More importantly, we have discovered a previously unknown molecular mechanism underlying CeO NP-induced lung fibrosis with different aspect ratios, shedding new insights on the environmental hazard potential of CeO NPs.