Abstract
Zinc oxide (ZnO) nanoparticles (NPs) are widely used in cosmetic and sunscreen products which are applied topically to the skin. Despite their widespread use, the safety and biological response of these particles remains an active area of investigation. In this paper we present methods based on in vivo multiphoton microscopy (MPM) in skin to address relevant questions about the potential toxicity and immunological response of ZnO NPs. Registration of time-lapse volumetric MPM images allows the same skin site to be tracked across multiple days for visualizing and quantifying cellular and structural changes in response to NP exposure. Making use of the unique optical properties of ZnO enables high contrast detection of the NPs in the presence of strong autofluorescence and second harmonic generation (SHG) background from the skin. A green fluorescent protein (GFP) bone marrow (BM) transplanted mouse model is used to visualize and assess the dynamic response of BM-derived immune cells. These cells are visualized to assess the potential for ZnO NPs to interact with immune cells and elicit an immune reaction in skin. We investigate both topical and dermal exposure of the ZnO NPs. The methods and findings presented in this paper demonstrate a novel approach for tracking ZnO NPs in vivo and for visualizing the cellular response of the exposed tissue to assess the immunological response and potential toxicity of these particles.
Highlights
The use of nanoparticles (NPs) in consumer products such as cosmetics and sunscreens has become common in recent decades
In this paper we present methods based on in vivo multiphoton microscopy (MPM) in skin to address relevant questions about the potential toxicity and immunological response of Zinc oxide (ZnO) NPs
Registration of time-lapse volumetric MPM images allows the same skin site to be tracked across multiple days for visualizing and quantifying cellular and structural changes in response to NP exposure
Summary
The use of nanoparticles (NPs) in consumer products such as cosmetics and sunscreens has become common in recent decades. The primary safety concern regarding ZnO NPs is their potential for generating free radicals in response to UV illumination, which can result in DNA damage in cells and an immunological response [2, 3]. Despite this potential toxicity, ZnO NPs are generally considered to be safe for use in topically-applied skin products as long as they are not absorbed through the skin or pass through breaches in the protective skin barrier. A primary focus in evaluating the safety of ZnO NPs has been assessing their ability to penetrate skin
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