Biological effects of titanium dioxide, zinc oxide and silver nanoparticles in mouse skin, gut and lungs by transcriptomic and microbiome profiling

Abstract

Advancement of nanotechnology has spurred tremendous interests and creativity for innovative design of commercial and industrial goods. Engineered nanomaterials (ENMs) are seen in arrays of applications in everyday life, ranging from electronics, biomedical and diagnostic equipment, environmental remediation devices to personal care products, pharmaceuticals, textile, food and agricultural materials. Miniaturization lies at the heart of nanotechnology. It not only improves or confers new properties to the obsolete bulk-sized materials, but also controls their ultimate behaviour in human body. The past research on the detrimental effect of fibrous carbon nanotubes raises health concern over exposures to nanoparticles (NPs) in consumers and workers. This thesis sought to ascertain the biological modulatory ability of three most popular metallic nanosized (n) particles, nTiO2, nZnO and nAg via three major exposure routes, dermal contact, ingestion, and inhalation. Varying degrees of immunosuppression or immunostimulation, in addition to oxidative stress, protein mis-/un-folding and DNA injury, were caused by the studied NPs in murine models with or without immunological perturbations in skin, gut or lungs. Firstly, the main findings after dermal exposure in the context of oxazolone-induced contact hypersensitivity (CHS) were that nZnO completely decreased local skin-swelling, infiltration of inflammatory cells and production of pro-inflammatory cytokines via a full abrogation of global innate and adaptive immune responses such as downregulation of antigen-hapten presentation and immune cell chemotaxis, as evidenced in the skin transcriptome profile. On the other hand, nZnO did not interfere with the sensitization phase of CHS development. These results suggest a strong immunosuppressive role of nZnO during elicitation of CHS response. Secondly, we found that although oral exposure to nAg did not seem to significantly affect the phenotypes of mice with dextran sodium sulphate (DSS)-induced colitis, it modulated pathways of apoptosis, RNA metabolism and cellular lipid catabolism based on colonic transcriptome and shifted the composition of gut microbiota. NTiO2 particles, in contrast to nAg, were seen to aggravate inflammatory hallmarks in colon histology including hyperplasia and deeper infiltration of inflammatory cells, in addition to increasing the abundance of colonic mucus and Akkermansia spp. in stool. Lastly, both nZnO and nAg were found to be pro-inflammatory in lungs of healthy mice upon single pulmonary exposure via oropharyngeal aspiration. While they demonstrated shared dose- and endpoint-dependent effects, nAg induced more severe and persistent inflammatory responses than nZnO and triggered adaptive immunity via Th cell activation. This work advances the current understanding of biological responses evoked by nTiO2, nZnO and nAg particles that are highly relevant to real-life exposure scenarios, via a combined approach of conventional assessment and omics techniques (transcriptomic and microbiome sequencing). Our findings highlight the complex and context-dependent bioactivities of the studied NPs, with an emphasis on a highly informative role of multi-omics data in elucidating NPs’ potential beneficial or harmful effects, and the mechanisms involved. Our data provide solid evidence that accelerates the establishment of future predictive models for impacts of NPs in biological systems.