Antagonistic Skin Toxicity of Co-Exposure to Physical Sunscreen Ingredients Zinc Oxide and Titanium Dioxide Nanoparticles

Abstract

Being the main components of physical sunscreens, zinc oxide nanoparticles (ZnO NPs) and titanium dioxide nanoparticles (TiO2 NPs) are often used together in different brands of sunscreen products with different proportions. With the broad use of cosmetics containing these nanoparticles (NPs), concerns regarding their joint skin toxicity are becoming more and more prominent. In this study, the co-exposure of these two NPs in human-derived keratinocytes (HaCaT) and the in vitro reconstructed human epidermis (RHE) model EpiSkin was performed to verify their joint skin effect. The results showed that ZnO NPs significantly inhibited cell proliferation and caused deoxyribonucleic acid (DNA) damage in a dose-dependent manner to HaCaT cells, which could be rescued with co-exposure to TiO2 NPs. Further mechanism studies revealed that TiO2 NPs restricted the cellular uptake of both aggregated ZnO NPs and non-aggregated ZnO NPs and meanwhile decreased the dissociation of Zn2+ from ZnO NPs. The reduced intracellular Zn2+ ultimately made TiO2 NPs perform an antagonistic effect on the cytotoxicity caused by ZnO NPs. Furthermore, these joint skin effects induced by NP mixtures were validated on the epidermal model EpiSkin. Taken together, the results of the current research contribute new insights for understanding the dermal toxicity produced by co-exposure of different NPs and provide a valuable reference for the development of formulas for the secure application of ZnO NPs and TiO2 NPs in sunscreen products.

Heat-Killed Lacticaseibacillus paracasei Ameliorated UVB-Induced Oxidative Damage and Photoaging and Its Underlying Mechanisms

“…In comparison, pure physical sunblock agents based on inorganic UV filters are relatively mild and are often used for children and sensitive skin. Metal oxide-based agents such as TiO 2 and ZnO mainly act as the physical sun-protective ingredients, which have been widely used in commercial sunscreens [ 67 ]. However, they create a white-tinted matte look upon application, which is attributed to a bigger particle size [ 68 ].…”

“…Nanotechnology has been employed to produce nanoparticles (NPs) of TiO 2 and/or ZnO, which gave a transparent appearance upon application. Unfortunately, the safety of these NPs is still a concern, although safety studies carried until now were not evident regarding their penetration into systemic circulation [ 67 ]. When exposed to UV radiation, TiO 2 and ZnO is reported to exhibit photocatalytic activity, causing the formation of potentially harmful free radicals [ 69 ].…”

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“…Here, the viability of HaCaT cells was employed to assess the cytocompatibility of HMNs. 37,38 Compared to the control group, there was a noticeable growth trend of HaCaT cell proliferation in the HMN group, and the Col-HMN group displayed more than 95% cell viability, higher than the blank Col group, indicating the favorable biocompatibility of the prepared HMNs and Col-HMNs (Fig. 4a).…”

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“…The underlying mechanism is that TiO 2 NPs restricted the cellular uptake of ZnO NPs and meanwhile decreased the dissociation of Zn 2+ from ZnO NPs, performing an antagonistic effect on the cytotoxicity caused by ZnO NPs. 330 4.1.2.2 Carbon-based NMs 4.1.2.2.1 Carbon nanotubes. Due to their lightweight and small size, CNTs can be easily inhaled leading to possible harmful effects in the human body.…”