Toxicological Aspects of Long‐Term Treatment of Keratinocytes with ZnO and TiO₂ Nanoparticles

Abstract

Sunscreens containing ZnO and TiO(2) nanoparticles (NPs) are increasingly applied to skin over long time periods to reduce the risk of skin cancer. However, long-term toxicological studies of NPs are very sparse. The in vitro toxicity of ZnO and TiO(2) NPs on keratinocytes over short- and long-term applications is reported. The effects studied are intracellular formation of radicals, alterations in cell morphology, mitochondrial activity, and cell-cycle distribution. Cellular response depends on the type of NP, concentration, and exposure time. ZnO NPs have more pronounced adverse effects on keratinocytes than TiO(2). TiO(2) has no effect on cell viability up to 100 μg mL(-1), whereas ZnO reduces viability above 15 μg mL(-1) after short-term exposure. Prolonged exposure to ZnO NPs at 10 μg mL(-1) results in decreased mitochondrial activity, loss of normal cell morphology, and disturbances in cell-cycle distribution. From this point of view TiO(2) has no harmful effect. More nanotubular intercellular structures are observed in keratinocytes exposed to either type of NP than in untreated cells. This observation may indicate cellular transformation from normal to tumor cells due to NP treatment. Transmission electron microscopy images show NPs in vesicles within the cell cytoplasm, particularly in early and late endosomes and amphisomes. Contrary to insoluble TiO(2), partially soluble ZnO stimulates generation of reactive oxygen species to swamp the cell redox defense system thus initiating the death processes, seen also in cell-cycle distribution and fluorescence imaging. Long-term exposure to NPs has adverse effects on human keratinocytes in vitro, which indicates a potential health risk.

Toxicity on Dengue Mosquito Vectors Through Myristica fragrans-Synthesized Zinc Oxide Nanorods, and Their Cytotoxic Effects on Liver Cancer Cells (HepG2)

“…The nano-sized ZnO was found more cytotoxic than the micrometer-sized ZnO with LC 50 values of 15 ± 1 and 29 ± 4 lg, respectively [41]. Prolonged exposure to ZnO nanoparticles at 10 lg ml results in decreased mitochondrial activity, loss of normal cell morphology, and disturbances in cell cycle distribution [42]. A-375 cells were studied for the comparative morphology of untreated and treated ZnO nanoparticles.…”

A review of mammalian toxicity of ZnO nanoparticles

“…41 The NPs were only found inside vesicles within the cytoplasm, particularly in early and late endosomes and amphisomes. Moreover, exposure resulted in ROS generation, decreased mitochondrial activity, loss of normal cell morphology, and a disturbed cellcycle distribution.…”

Zinc oxide nanoparticles-induced epigenetic change and G2/M arrest are associated with apoptosis in human epidermal keratinocytes

“…11,14,15 The characteristics of ZnO NPs, the dose, the treatment time, and the specific cell line selected may affect the results obtained. 48,51 The data presented here showed that the cell cycle was arrested at the G2/M phase after treatment with 50 µg/mL of 100 nm ZnO NPs for 24 hours (Figure 2C), suggesting that the HaCaT cells exposed to ZnO NPs were unable to go through mitosis, leading to the subsequent decreased cell viability at 48 hours.…”

“…10 Long-term exposure to ZnO NPs has been reported to stimulate the generation of ROS, initiating death processes and affecting the cell cycle distribution. 11 ZnO NPs may inhibit cell growth by reducing proliferation. 12,13 Reduced proliferation has been linked to cell cycle arrest at various phases.…”

“…12,13 Reduced proliferation has been linked to cell cycle arrest at various phases. 11,14,15 Cell cycle progression is blocked in response to diverse internal and external cues. The tumor suppressor p53 is able to activate G2/M cell cycle checkpoints, DNA repair, and apoptotic responses to maintain genomic stability.…”