Assessment of the in vitro dermal irritation potential of cerium, silver, and titanium nanoparticles in a human skin equivalent model

Abstract

Metal nanoparticles can potentially contact human skin during their manufacture and use in commercial products. This study examined the potential of metal nanoparticles to elicit irritant contact dermatitis in a human skin equivalent model (HSEM) derived from keratinocytes. Ag (10-100 nm), TiO₂ (22-214 nm), and CeO₂ (15-40 nm) nanoparticles were studied. The Ag particles were either coated/shelled with silica or capped with citrate or polyvinylpyrrolidone and were in water. The TiO₂ and CeO₂ particles were suspended in media containing 10% fetal bovine serum. The particles (1 mg/ml) were applied to the epidermal surface of the HSEM. Positive (5% sodium dodecyl sulfate (SDS)) and negative controls (saline or media) were included. After 1-h exposure at 37 °C, the HSEM was washed with saline to remove the nanoparticles. Following a 42-h incubation (37 °C), HSEM viability was assessed using the MTT assay. A test substance is considered a dermal irritant if the HSEM viability is < 50%. The mean viability for the SDS-treated HSEM was 7.8%. The viabilities of the nanoparticle-treated HSEM were 91% or greater. The Ag, TiO₂, and CeO₂ nanoparticles examined were not dermal irritants under the conditions used in this study. The stratum corneum of the HSEM may limit penetration of metal nanoparticles to induce toxicity.

Keywords: Inorganic; irritation; metals; nanoparticles; skin.

Figure 1

Human equivalent skin model tissue viability (%) exposed to silver nanoparticles of various sizes and coatings for 1 h. Data represents mean +/− SD, N=4. The concentration of each nanoparticle sample was 1 mg/mL. DPBS (Dulbecco’s phosphate buffered saline) was the negative control. 5% SDS (sodium dodecyl sulfate) was the positive control. PVP (polyvinyl pyrrolidine) is a coating. For Ag 10 nm PVP, two lots were used (L1 and L2). Chemicals with a mean value below the dashed line at 50% viability were considered to be dermal irritants. ***, significantly different from negative control, p < 0.001.

Figure 2

Human equivalent skin model tissue viability (%) exposed to silver nanoparticles of various sizes and coatings for 1 h. Data represents mean ± SD, N=3–4. The concentration of each nanoparticle sample was 1 mg/mL. DPBS (Dulbecco’s phosphate buffered saline) was the negative control. 5% SDS (sodium dodecyl sulfate) was the positive control. PVP (polyvinyl pyrrolidine) is a coating. Chemicals with a mean value below the dashed line at 50% viability were considered to be dermal irritants. ***, significantly different from negative control, p < 0.001. *, % viability for Ag 50 nm PVP nanoparticle significantly greater than that for Ag 50 nm PVP nanoparticle in Fig 3, p < 0.05.

Figure 3

Human equivalent skin model tissue viability (%) exposed to silver nanoparticles of various sizes and coatings for 1 h. Data represents mean ± SD, N=3. The concentration of each nanoparticle sample was 1 mg/mL. DPBS (Dulbecco’s phosphate buffered saline) was the negative control. 5% SDS (sodium dodecyl sulfate) was the positive control. PVP (polyvinyl pyrrolidine) is a coating. Chemicals with a mean value below the dashed line at 50% viability were considered to be dermal irritants. ***, significantly from negative control, p < 0.001. *, % viability for Ag 50 nm PVP nanoparticle significantly less than that for Ag 50 nm PVP nanoparticle in Fig 2, p < 0.05.

Figure 4

Human equivalent skin model tissue viability (%) exposed to titanium dioxide nanoparticles of various sizes for 1 h. Data represents mean ± SD, N=3. The concentration of each nanoparticle sample was 1 mg/mL. DPBS (Dulbecco’s phosphate buffered saline) was the negative control. 5% SDS (sodium dodecyl sulfate) was the positive control. DMEM (Dubelco’s minimum essential medium with 10% fetal bovine serum) was the vehicle for the TiO₂ nanoparticles. Chemicals with a mean value below the dashed line at 50% viability were considered to be dermal irritants. ***, significantly from negative control, p < 0.001.

Figure 5

Human equivalent skin model tissue viability (%) exposed to titanium and cerium dioxide nanoparticles of various sizes and coatings for 1 h. Data represents mean ± SD, N=3. The concentration of each nanoparticle sample was 1 mg/mL. DPBS (Dulbecco’s phosphate buffered saline) was the negative control. 5% SDS (sodium dodecyl sulfate) was the positive control. DMEM (Dubelco’s minimum essential medium with 10% fetal bovine serum) was the vehicle for the TiO₂ and CeO₂ nanoparticles. Chemicals with a mean value below the dashed line at 50% viability were considered to be dermal irritants. ***, significantly from negative control, p < 0.001.