Predictive Metabolomic Signatures for Safety Assessment of Metal Oxide Nanoparticles

Abstract

The widespread use of metal oxide nanoparticles (MOx NPs) poses a risk of exposure that may lead to adverse health effects on humans. Even though a number of toxicological methodologies are available for assessing nanotoxicity, the effect of MOx NPs on cell metabolism in vitro and in vivo remains largely unknown, especially under the exposure to low-dose or supposedly low-toxicity MOx NPs. In this study, liquid chromatography−mass spectrometry (LC-MS) based metabolomics was used to reveal significantly altered metabolites and metabolic pathways in human bronchial epithelial cells exposed to four different types of MOx NPs (ZnO, SiO 2 , TiO 2 , and CeO 2 ) at both high (25 μg/mL) and low (12.5 μg/mL) doses. We demonstrated that high-dose ZnO NPs caused severe cytotoxicity with altered metabolism of amino acids, nucleotides, nucleosides, tricarboxylic acid cycle, lipids, inflammation/redox, and fatty acid oxidation, as well as the elevation of toxic and DNA damage related metabolites. Fewer metabolomic alterations were induced by low-dose ZnO NPs. However, most metabolites significantly altered by high-dose ZnO NPs were also slightly changed by low-dose ZnO NPs. On the other hand, the cells exposed to SiO 2 , TiO 2 , and CeO 2 NPs at either high or low dose displayed low cytotoxicity with similar metabolomic alterations, although each type of NPs induced distinct changes of certain metabolites. These three NPs significantly affected the metabolic pathways of sphingosine-1-phosphate, fatty acid oxidation, folate cycle, inflammation/redox, and lipid metabolism. In addition, dose-dependent effects were observed for a number of metabolites significantly altered by respective MOx NPs. Representative metabolites of the significantly altered metabolic pathways were successfully validated in vitro using enzymatic assays. More importantly, these representative metabolites were further validated in a mouse model after lung exposure to respective NPs, indicating that in vitro metabolomic findings may be used to effectively predict the toxicological effects in vivo. Despite functional assay results demonstrating that the changes in cellular functions were largely reflected by the metabolomic alterations, LC-MS-based metabolomics was sensitive enough to detect the subtle metabolomic changes when functional cellular assays showed no significant difference. Collectively, our studies have unveiled potential metabolic mechanisms of MOx NP-induced nanotoxicity in lung epithelial cells and demonstrated the sensitivity and feasibility of using metabolomic signatures to understand and predict nanotoxicity in vivo.

Continued Efforts on Nanomaterial‐Environmental Health and Safety Is Critical to Maintain Sustainable Growth of Nanoindustry

“…that discovers new mode of action, especially at lower dose range that has higher environmental relevance. [18][19][20] Over the years, much progress has been achieved by the nanosafety community, which has greatly enhanced our understanding on the major physicochemical properties that could lead to toxicity, molecular and cellular mechanisms of toxicity induced by ENMs, different exposure routes and dosimetry, animal models, as well as implications to human health (Figure 1), however, there are many knowledge gaps and challenges still remain. [11,[21][22][23][24]…”

“…[39][40][41][42][43] However, it is worth noting that despite the high doses used in vitro and in vivo studies, valuable information has been obtained on the mechanism of toxicity and potential adverse effects for ENMs, and measures have been taken to cover a wider dose range for in vitro and in vivo studies and use more sensitive methods such as toxicogenomics to study ENM effects at lower doses. [18,20] To better predict the realistic concentrations of ENMs, models and approaches have been developed based on the estimation of global and regional production, application, and life-cycle of ENMs. [44,45] Further improvement and fine-tuning of these models by taking into account the real-life measurements would facilitate the development of ENM hazard assessment under environmentally relevant conditions.…”

“…Moreover, additional alternative test strategies and multiomics technology should be utilized more for nano-EHS assessment, which includes high throughput screening, predictive toxicology, genomics/epigenetics/metabolomics, and in silico approaches, to move nano-EHS from descriptive science to mechanism-based toxicology. [11,13,18,20,87] Especially, it is important to link the physicochemical properties of ENMs to the toxicological outcomes. [10][11][12]16,87,88] iii) After years of development, there are still enormous obstacles and limitations for the current computational models to precisely characterize nano toxicology.…”

Landscape of Lipidomic Metabolites in Gut-liver Axis of Sprague-Dawley Rats after Oral Exposure to Titanium Dioxide Nanoparticles

“…Meanwhile, pathological change of fatty degeneration in hepatocytes was found in rats after oral exposure to TiO 2 NPs [38]. Other studies also indicated that lipid metabolism disorder may be one of the obvious toxic effects of TiO 2 NPs [39][40][41]. The link between the gut microbiota and adipose tissue has been recently identi ed.…”

“…In recent years, lipidomics provides a highly sensitive and high-resolution method for analyzing the structure and function of the complete set of lipids as well as their interactions [43]. It is sensitive enough to detect the subtle metabolomic changes when functional cellular assays showed no signi cant difference [40]. Research on lipid metabolism using lipidomics will contribute to the safety assessment of nanomaterials.…”