Effects of silver, zinc oxide and titanium dioxide nanoparticles on differentiated THP-1 cells by transcriptomics and targeted lipidomics approaches

Abstract

Engineered nanomaterials (ENMs) describe any materials sizing between 1 to 100 nm that are deliberately engineered and manufactured by human for desirable properties. Despite the remarkable breakthroughs in product development that they have brought about, health issues are discovered at the same time. The most well-known one conceopen up the biopersistent fibre-like carbon nanotubes (CNTs) that can cause fibrotic symptoms similar to the notorious asbestos. Demands for metal-based nanoparticles on consumer products are huge these days. On the contrary, safety assessment is very much incomplete. This thesis therefore aims to fill this gap and deepen our understanding on the mechanism of toxicity of three commonly used metal-based nanoparticles, n-TiO2, n-ZnO and n-Ag, focusing on the early immunological events that may be triggered. To achieve this, the project was separated into three complementary studies, characterizing the (i) transcriptome (gene expression), (ii) miRNA expression profile (gene regulation), and (iii) eicosadome (oxidative metabolism of polyunsaturated fatty acids (PUFAs)) respectively upon sub-toxic exposures (no more than 15% cell death) to the NMs in PMA-differentiated THP-1 macrophages. Microarray, RNA sequencing and LC-MS were adopted for the analysis respectively, whereas ICP-MS analysis was performed to trace the cellular uptake and particle dissolution. At the transcriptomic level, cellular responses to metal ions, and various immunological events, such as inflammation activation, type I interferon antiviral responses, chemotaxis, macrophage maturation, were induced by n-ZnO and n-Ag to a different extent. Metallothioneins marked the most robustly overexpressed DEGs among the ion-releasing ZnO particles and Ag materials. Among these transcriptomic responses, a co-regulated miR-mRNA cluster was identified by canonical correlation and pathway enrichment analyses, predicted to be highly relevant for cellular response to metal ion homeostasis. These miRs were annotated to be canonical or variant isoforms of hsa-miR-142-5p, -342-3p, -5100, -6087, -6894-3p and -7704. Hsa-miR-5100 was differentially expressed in response to each nanoparticle in both the 6 hours and 24 hours exposures. However, these transcriptomic responses did not seem to generate severe lipidomic changes associated with oxidative stress and inflammation, except a significant increase of 5-HETE production upon exposure to n-Ag. Combining with the ICP-MS analysis, ion releasing potential and the location of ion release seemed to matter a lot for the toxicity of these metal-based nanoparticles. The current thesis presents a NM toxicological assessment that has been carefully planned and executed to yield highly reliable and comparable ‘omics’ data at different layers. With isomiRs annotated, the miRNA data has provided some novel insights on the biological effects of the tested NMs, so as the eicosadome data. These findings characterizing the mode of actions and identifying potential biomarkers of early exposure will benefit the development of the predictive hazard classification of NMs and the safer design of future NMs.