Abstract and Introduction
Abstract
Aim As engineered nanoparticles (ENPs) increasingly enter consumer products, humans become increasingly exposed. The first line of defense against ENPs is the epithelium, the integrity of which can be compromised by wounds induced by trauma, infection, or surgery, but the implications of ENPs on wound healing are poorly understood.
Materials & Methods Herein, we developed an in vitro assay to assess the impact of ENPs on the wound healing of cells from human cornea.
Results & Discussion We show that industrially relevant ENPs impeded wound healing and cellular migration in a manner dependent on the composition, dose and size of the ENPs as well as cell type. CuO and ZnO ENPs impeded both viability and wound healing for both fibroblasts and epithelial cells. Carboxylated polystyrene ENPs retarded wound healing of corneal fibroblasts without affecting viability.
Conclusion Our results highlight the impact of ENPs on cellular wound healing and provide useful tools for studying the physiological impact of ENPs.
Introduction
The global nanotechnology (NT) industry reached over $US1.5 trillion last year, becoming a major economic force of the 21st century. A central ingredient of the NT industry are engineered nanoparticles (ENPs).[1,2] The number of consumer products containing ENPs is growing at a similarly rapid pace, and is expected to reach 10,000 by the year 2020.[3] ENPs can be found in paint coatings with a variety of submicron/nanoscale pigment (metal and oxide) powders;[4] toner formulations;[5] polymer- and carbon-matrix nanocomposites with montmorillonite clays, carbon nanotubes and graphene;[6] and sunscreens/cosmoceuticals. Thus, human exposure to ENPs becomes inevitable and has indeed been demonstrated.[7,8] Compared with micron-sized particulate matter, ENPs have greater potential to cross biological barriers to reach pulmonary connective tissues, lymphatics, blood circulation and critical organs;[5,8–11] they may also enter cells and be more biologically active due to their small size and large surface area.[12–16] Accordingly, potential deleterious effects of ENPs on human health have been reported, mostly focusing on the lung.[9,10,17]
Much less attention has been given to the eye, which is directly exposed to the environment.[18] The cornea possesses an extraordinarily smooth surface, maintains the tear layer, transmits light, and protects the eye from pathogens and particulates. Exposure to air pollutants has been associated with increased conjunctival goblet cell hyperplasia and ocular irritations.[19,20] Although the level of ocular exposure to ENPs remains to be quantified, ENPs are widely present in cosmetic products, such as sunscreens, makeups and contact lenses, which may result in ocular ENP exposure.[8,21] However, the impact of ENPs on the eye and resident cells remains poorly understood. Such impact may be minimal on an intact tissue and cells but exert a toll on a wounded tissue; indeed, humans with pre-existing airway or heart diseases are more susceptible to elevated air pollution.[22] However, a research area of nanotoxicology, which is lagging behind is the effect of ENPs on wounded cells with most of in vitro studies focusing primarily on healthy cells.
Herein, we present the development of a novel cellular bioassay to assess the impact of ENPs on wound healing for diverse types of ENPs and cells. The types of ENPs we used included copper oxide (CuO), zinc oxide (ZnO), silica dioxide (SiO2) and titanium dioxide (TiO2) ENPs, which are industry relevant and commonly used in a variety of products; fluorescent polystyrene (PS) particles were also used to investigate the role of particle size and uptake. The types of cells included human corneal limbal epithelial (HCLE) cells and human corneal fibroblasts (HCFs), which are important for corneal wound healing, and Madin–Darby canine kidney (MDCK) cells, which constitute a widely used model system for investigating wound healing in vitro. Our results establish in vitro wound healing behavior as a physiological end point to evaluate the safety of ENPs.
Nanomedicine. 2014;9(18):2803-2815. © 2014 Future Medicine Ltd.
