Understanding the sub-lethal effects of ZNO nanoparticles and its implications to skin repair

• Main Author: Wu, Zhuoran
• Other Authors: Dalton Tay Chor Yong
• Format: Theses and Dissertations
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering::Nanotechnology
• Online Access: http://hdl.handle.net/10356/74852
• Institution: Nanyang Technological University

Understanding the cellular responses to nano zinc oxide particles (Nano-ZnO) (<100 nm) is key to its successful novel exploitation in nanomedicine and bio-nanotechnology. Unlike other conventional inorganic compounds, zinc is an essential co-factor for numerous enzymes that are known to regulate a wide spectrum of fundamental cellular activities such as redox homeostasis, metabolism and signal transductions. In human, as many as 3000 proteins have been revealed to contain Zn2+. In this regard, Nano-ZnO can be considered as a unique class of biologically active nanomaterials that can either disrupt (at toxic concentration) or support (at non-toxic concentration) cellular functions. While studies have shown that high concentrations of Nano-ZnO can trigger oxidative stress-mediated cell death via the generation of reactive oxygen species (ROS), little is known about the effects of Nano-ZnO and its role in mediating ROS signalling in the low-dose range. Inspired by recent demonstrations of biological systems capable of reciprocating to low level of oxidative stress via the process of cell adaptation, this project seeks to examine whether (i) cells can adapt to low dose of Nano-ZnO, (ii) understand the underlying mechanism underpinning the adaption process and (iii) conduct proof-of-concept studies to unveil the biological consequences of Nano-ZnO mediated adaption. Herein, using a “conditioning and challenge” (2Cs) experimental regime, it is showed that long term (48h – 144h) exposure of sub-lethal dose of Nano-ZnO (~ 100nm) (0.5 µg/ml) to human keratinocytes (HaCaTs), could induce adaptive response and dramatically improve the overall fitness of HaCaTs to cope with toxic level of oxidative stress. As Nano-ZnO is limiting in the low dose range, it was observed a generation of discrete ROS “hotspots” (~2%) in the HaCaTs cells, which could correspond to Nano-¬ZnO Loaded Keratinocytes (Nano-ZLKs). Interestingly, the occurrence of these ROS “hotspots” is sufficient to trigger a population wide activation of the nuclear factor (erythroid-derived 2)-like 2 (Nrf-2) stress response pathway via a complex cross-talk between the Nano-ZLK and the “bystander” cells through paracrine signalling. Transcriptome analysis revealed that the cross-talk between these two sub-population of cells were mediated primarily via interleukins (1α, 1β, 6, 8, 15, 18, 23, 33). Further mechanistic studies revealed that it is the Nrf-2 mediated enhancement in proteolytic activity of the Nano-ZnO conditioned cells, but not the anti-oxidant effects that accounts for the cyto-protective adaption process. Importantly, this study provides a first account depicting the capability of Nano-ZnO to induce a cross adaptive effect in the Nano-ZnO conditioned HaCaTs to alleviate the DNA damage and compromised cell viability induced by Ultraviolet-A (UVA) irradiation. Taken together, this study shows that the formation and cross talk of Nano-ZLK and the bystander cells via the ROS-Nrf2 stress response pathway is a pervasive feature in the low dose Nano-ZnO exposure range. These findings not only provide critical information regarding the nano-safety of Nano-ZnO in the context sunscreen products, but also shed light on the unique and exploitable bio-activity of Nano-ZnO for skin protection against oxidative damage.