Morphology-dependent titanium dioxide nanoparticle-induced keratinocyte toxicity and exacerbation of allergic contact dermatitis

Abstract

Titanium dioxide (TiO₂) nanoparticles are commonly found in consumer products, such as sunscreens, and human dermal exposures are relatively high. Research suggests potential differences in the toxicity of anatase and rutile crystalline forms of TiO₂. Additionally, transition metal dopants are frequently used to enhance physicochemical properties of TiO₂, and the toxicity of these nanoparticles are not extensively studied. Therefore, this work examined the keratinocyte toxicity and in vivo skin allergy responses after treatment with 30 nm anatase, 30 nm rutile, or <100 nm Mn-doped TiO₂ nanoparticles. After a 24-hour exposure, there were no differences in keratinocyte cytotoxicity; however, Mn-doped TiO₂ nanoparticles induced significant in vitro ROS generation and in vivo skin swelling responses in a model of allergic contact dermatitis.

Figure 1.. TiO₂ physical characterization by TEM

TiO₂ nanoparticles were dispersed in acetone/water prior to deposition on grids for TEM analysis. The images of anatase (A), rutile (B), and 1% Mn-doped (C) particles show evidence for agglomeration. Scale bar 200 nm.

Figure 2.. TiO₂-induced keratinocyte cytotoxicity after 24 hours

HaCaTs were exposed to 0, 5, 10, 50, 100, or 500 μg/mL concentrations of anatase, tile, or 1% Mn-doped TiO₂ nanoparticles for 24 hours. Dose-dependent decreases in cell viability were observed for all TiO₂ particles tested (mean ± SD, n = 3).

Figure 3.. TiO₂-induced keratinocyte ROS generation after 24 hours

HaCaTs were exposed to 0, 5, 10, 50, 100, or 500 μg/mL concentrations of anatase, rutile, or 1% Mn-doped TiO₂ nanoparticles for 24 hours. While there were significant increases in ROS for all TiO₂ nanoparticles, Sigma 1% Mn-doped TiO₂-induced ROS generation was markedly higher (mean ± SD, n = 3).

Figure 4.. TiO₂ exacerbation of DNFB-induced allergic contact dermatitis

Mice were sensitized with 0.05% DNFB five days prior to challenge with either vehicle or 0.2% DNFB. For each mouse, the right ear was exposed to vehicle (gray bars) and the left ear was exposed to 200 μg of TiO₂ nanoparticles (black bars). After 24 hours, the TiO₂ nanoparticles had no effect on skin swelling without DNFB challenge. However, Sigma Mn-doped TiO₂ nanoparticles significantly increased DNFB-induced ear swelling (mean ± SD, n = 3–5).