Cerium dioxide

Dermal absorption

Administrative data

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2019

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The test substance was not fully characterized for nano characterisation parameters. The methods and results are reported quite briefly.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2019

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: Franz method

Version / remarks:

As published in: Guth, K.; Schäfer-Korting, M.; Fabian, E.; Landsiedel, R.; van Ravenzwaay, B. Suitability of skin integrity tests for dermal absorption studies in vitro. Toxicol. In Vitro 2015, 29, 113–123.

Test guideline 3

Qualifier:

according to guideline

Guideline:

other: EDETOX protocols

Version / remarks:

As published in: Sandt, J.J.; Burgsteden, J.A.; Cage, S.; Carmichael, P.L.; Dick, I.; Kenyon, S.; Korinth, G.; Larese, F.;
Limasset, J.C.; Maas, W.J.; et al. In vitro predictions of skin absorption of caeine, testosterone, and benzoic acid: A multi-centre comparison study. Regul. Toxicol. Pharmacol. 2004, 39, 271–281.

GLP compliance:

not specified

Remarks:

The GLP status was not specified in the article.

Test material

Test material information

Constituent 1

Reference substance name:

Cerium dioxide

EC Number:

215-150-4

EC Name:

Cerium dioxide

Cas Number:

1306-38-3

Molecular formula:

CeO2

IUPAC Name:

cerium dioxide

Test material form:

solid: nanoform

Details on test material:

- State of aggregation: no data
- Particle size distribution: 17 +/- 5 nm (TEM),
- Mass median aerodynamic diameter (MMAD): no data
- Geometric standard deviation (GSD): no data
- Shape of particles: various shapes, ranging from spherical to polyhedral (TEM).
- Surface area of particles: no data
- Crystal structure: yes. Crystalline CeO2 was confirmed by Raman spectroscopy, with the presence of the characteristic peak at 464 cm-1, plus two broad and barely visible peaks at lower
(~255 cm-1) and higher (~590 cm-1) energy. The sharp and symmetric shape of the peak, and its Raman shift (464 cm-1), qualitatively indicated a large size of the ceria particles
- Coating: no data
- Surface properties: no data
- Density: no data
- Moisture content: no data
- Residual solvent: no data
- Activation: no data
- Stabilisation: no data
- Other: in house synthesized by a hydrothermal route using Cerium ammoniumnitrate (purity, 99.99 %) and a synthetic sweat solution as precursors.

Radiolabelling:

no

Test animals

Species:

other: Human

Strain:

other: not applicable

Sex:

female

Details on test animals or test system and environmental conditions:

Not appropriate. See information reported in the section "Details on study design".

Administration / exposure

Type of coverage:

other: no applicable

Vehicle:

other: synthetic sweat

Duration of exposure:

24 hoours

Doses:

0,6 mg cerium dioxide/cm2 corresponding to 0,220 ml of the donor solution (synthetic sweat).

No. of animals per group:

not applicable

Details on in vitro test system (if applicable):

SKIN PREPARATION
- Source of skin: Human abdominal full-thickness skin was obtained as surgical waste from two female donors aged 45–65 years. Others donors were men and women with an age range of 45–71 years.
- Ethical approval if human skin: yes. The study was approved by the Trieste Hospital Ethical Committee n° 236/2007.
- Type of skin: Human abdominal full-thickness skin
- Preparative technique: After the skin excision, subcutaneous fat was removed with a scalpel blade and hair was shaved from the epidermis. Two different experiments were conducted using intact and damaged skin.
- Thickness of skin (in mm): approximately 1 mm.
- Membrane integrity check: Yes. Skin integrity was assessed using the transepidermal water loss (TEWL) method as described by Guth et al. (2015). Cells with a value of >10 g/m2/h were considered to be damaged and rejected.
- Storage conditions: Skin samples were stored at -25 °C for a period up to, but not exceeding, four months. It has been demonstrated that this procedure does not damage skin barrier properties. On the day of the experiment, skin samples were defrosted in a physiological solution at room temperature for a 30-min period and 2 x 2 cm2 pieces were cut from each skin specimen and mounted separately on the diffusion cells.
- Justification of species, anatomical site and preparative technique: no data

PRINCIPLES OF ASSAY
- Diffusion cell: Franz cell
- Receptor fluid: physiological solution. The physiological solution used as the receptor phase was prepared by dissolving 2.38 g of Na2HPO4, 0.19 g of KH2PO4, and 9 g of NaCl into 1 L of Milli-Q water (final pH 7.35). The salt concentration in the receiving fluid was approximately the same as that found in blood.
- Solubility od test substance in receptor fluid: No data.
- Static system: Yes
- Flow-through system:
- Test temperature: 32 ° C
- Humidity: no data
- Occlusion: no
- Reference substance(s): no
- Other
Donor fluid: synthetic sweat solution consisting of 0.5% sodium chloride, 0.1% urea, and 0.1% lactic acid in Milli-Q water, and pH was adjusted to 4.5 using a concentrated ammonia solution. The authors indicated that the cerium concentration in the donor phase, which was collected at the beginning of the test after the removal of the NPs by ultrafiltration, was less than 0.05% of the starting suspensions and did not change at the end of the experiments.

Results and discussion

Signs and symptoms of toxicity:

not examined

Remarks:

in vitro study

Dermal irritation:

not examined

Remarks:

in vitro study

Absorption in different matrices:

- Receptor fluid, receptor chamber, donor chamber (in vitro test system):
The cerium concentration in the donor phase, which was collected at the beginning of the test after the removal of the NPs by ultrafiltration, was less than 0.05% of the starting suspensions and did not change at the end of the experiments.
In the experimental condition, the used Ce did not permeate the intact skin since the concentration in the receiving phase was the same as that of the blank cells (2.0 +/- 0.4 ng/cm2) after 24 hours. However, it reached 3.3 +/- 0.7 ng/ cm2 for damaged skin (p = 0.008).
The amount of Ce (µg/cm2) inside whole skin was 3.64 +/- 0.15 for intact skin, 7.07 +/- 0.78 for damaged skin, and 0.19 +/- 0.06 for blank cells (mean +/- SD). The Ce content was higher in dermal layers of damaged skin compared to intact skin (2.93 +/- 0.71 µg/cm2 and 0.39 +/- 0.16 µg/cm2, respectively).
Microscopic analysis confirmed the low penetration and permeation of CeO2 NPs since only a small signal of Ce was revealed in the epidermis of an intact skin sample but NPs were not
visualized by TEM investigation.

- Skin preparation (in vitro test system): see above in "Details on in vitro test system" and "Any other information on materials and methods incl tables"
- Stratum corneum (in vitro test system): not applicable.

Percutaneous absorption

Percutaneous absorption 1

Key result

Time point:

24 h

Dose:

vehicle (synthetic sweat)

Parameter:

amount

Remarks:

Amount of Ce that penetrate into the whole skin.

Absorption:

ca. 0.19 other: µg/cm2

Remarks on result:

other: For blank cells

Percutaneous absorption 2

Key result

Time point:

24 h

Dose:

0,6 mg CeO2 /cm2

Parameter:

amount

Remarks:

Amount of Ce that penetrate into the whole skin.

Absorption:

ca. 3.64 other: µg/cm2

Remarks on result:

other: for intact skin.

Percutaneous absorption 3

Key result

Time point:

24 h

Dose:

0,6 mg CeO2/cm2

Parameter:

amount

Remarks:

Amount of Ce that penetrate into the whole skin.

Absorption:

ca. 7.07 other: µg/cm2

Remarks on result:

other: For damaged skin

Percutaneous absorption 4

Key result

Time point:

24 h

Dose:

vehicle (synthetic sweat)

Parameter:

amount

Remarks:

Amount of Ce that penetrate into the dermis layer.

Absorption:

> 0 - <= 0.1 other: µg/cm2

Remarks on result:

other: For blank cells

Percutaneous absorption 5

Key result

Time point:

24 h

Dose:

0,6 mg CeO2/cm2

Parameter:

amount

Remarks:

Amount of Ce that penetrate into the dermis layer.

Absorption:

ca. 0.39 other: µg/cm2

Remarks on result:

other: For intact skin

Percutaneous absorption 6

Key result

Time point:

24 h

Dose:

0,6 mg CeO2/cm2

Parameter:

amount

Remarks:

Amount of Ce that penetrate into the dermis layer.

Absorption:

ca. 2.93 other: µg/cm2

Remarks on result:

other: For damaged skin.

Percutaneous absorption 7

Key result

Time point:

24 h

Dose:

vehicle (synthetic sweat)

Parameter:

amount

Remarks:

Ce concentration in the receiving solution

Absorption:

ca. 2 other: ng/cm2

Remarks on result:

other: Blank Cells

Percutaneous absorption 8

Key result

Time point:

24 h

Dose:

0,6 mg CeO2/cm2

Parameter:

amount

Remarks:

Ce concentration in the receiving solution.

Absorption:

ca. 2 other: ng/cm2

Remarks on result:

other: For intact skin.

Percutaneous absorption 9

Key result

Time point:

24 h

Dose:

0,6 mg CeO2/cm2

Parameter:

amount

Remarks:

Ce concentration in the receiving solution

Absorption:

ca. 3.3 other: ng/cm2

Remarks on result:

other: For damages skin.

Applicant's summary and conclusion

Conclusions:

The authors concluded that their data showed a very low dermal absorption and transdermal permeation of cerium dioxide nanoparticles.

Executive summary:

Mauro M. et al, (2019) performed an in vitro investigation of the permeation of in-house syntesized 17-nm CeO2 NPs dispersed in synthetic sweat (1 g/L) using excised human skin on Franz cells. The study was performed according to OECD guideline n° 428, but no information on the GLP status was indicated in the article. Thus, the study was scored as validity 2 according to Klimisch criteria. Experiments were performed using intact and needle-abraded skin, separately.

In intact and damages skin permeation experiments at time 0, the exposure chambers of three Franz dffusion cells were filled with 0.220 mL of the donor solution, corresponding to an amount of CeO2 of 0.6 mg/cm2. The experiment was repeated twice. After the integrity test, the receiving solutions and the skin pieces were removed and analysed for CeO2 content.

After 24 hours, the average amount of Ce into intact and damaged whole skin samples was 3.64 +/- 0.15 and 7.07 +/- 0.78 µg/cm2, respectively. Ce concentration in the receiving solution was 2.0 +/-0.4 (as in the blank cells) and 3.3 +/- 0.7 ng/cm2 after 24 h. The Ce content was higher in dermal layers of damaged skin compared to intact skin (2.93 +/- 0.71 µg/cm2 and 0.39 +/- 0.16 µg/cm2, respectively).

The authors concluded that CeO2 NPs could not permeate intact skin, but this permeation was possible—if at a low level—using an abraded skin protocol. A low amount of cerium was present in intact and damaged skin samples after prolonged exposure (24 h) to CeO2NPs. They further suggested that this behavior is probably due to the very low ionization of these metal oxides in synthetic sweat, resulting in a small concentration of free metal ions in the donor phase being able to cross over the physiological barriers. The NPs’ capability of permeating the dermal layers is lower with respect to the free ions, and depends on their physicochemical characteristics.