INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH
Abstract
Skin absorption and toxicity on keratinocytes of cobalt oxide nanoparticles
(Co3O4NPs) have been investigated. Co3O4NPs are commonly used in industrial products
and biomedicine. There is evidence that these nanoparticles can cause membrane damage
and genotoxicity in vitro, but no data are available on their skin absorption and cytotoxicity
on keratinocytes. Two independent 24 h in vitro experiments were performed using Franz
diffusion cells, using intact (experiment 1) and needle-abraded human skin (experiment 2).
Co3O4NPs at a concentration of 1000 mg/L in physiological solution were used as donor
phase. Cobalt content was evaluated by Inductively Coupled–Mass Spectroscopy.
Co permeation through the skin was demonstrated after 24 h only when damaged skin
protocol was used (57 ± 38 ng·cm−2), while no significant differences were shown between
blank cells (0.92 ± 0.03 ng cm−2) and those with intact skin (1.08 ± 0.20 ng·cm−2).
To further investigate Co3O4NPs toxicity, human-derived HaCaT keratinocytes were
exposed to Co3O4NPs and cytotoxicity evaluated by MTT, Alamarblue® and propidium
iodide (PI) uptake assays. The results indicate that a long exposure time (i.e., seven days)
was necessary to induce a concentration-dependent cell viability reduction (EC50 values:
1.3 × 10−4 M, 95% CL = 0.8–1.9 × 10−4 M, MTT essay; 3.7 × 10−5 M, 95%
CI = 2.2–6.1 × 10−5 M, AlamarBlue® assay) that seems to be associated to necrotic events
(EC50 value: 1.3 × 10−4 M, 95% CL = 0.9–1.9 × 10−4 M, PI assay). This study demonstrated
that Co3O4NPs can penetrate only damaged skin and is cytotoxic for HaCat cells after long
term exposure.