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Toxicological information

Dermal absorption

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Administrative data

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
16 July 2007 - 20 March 2008
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2008
Report date:
2008

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
Version / remarks:
adopted 13 April 2004
GLP compliance:
yes (incl. QA statement)

Test material

Constituent 1
Chemical structure
Reference substance name:
1,3-dihydroxyacetone
EC Number:
202-494-5
EC Name:
1,3-dihydroxyacetone
Cas Number:
96-26-4
Molecular formula:
C3H6O3
IUPAC Name:
1,3-dihydroxyacetone
Details on test material:
Appearance: white powder




Radiolabelling:
yes

Administration / exposure

Type of coverage:
open
Vehicle:
other: O/W emulsion
Duration of exposure:
24h
Doses:
Non-radiolabelled and radiolabelled test material was formulated in a typical O/W emulsion (SK-06-base) at 2.5, 5.0, 7.0 and 10%, respectively. Homogeneity and the actual radioactive concentration of each formulation was verified measuring radioactivity in aliquots using LSC.
The formulations were applied to the skin membranes at a target application rate of 2.0 mg/cm2 (actual mean application rate was in the range of 2.2-2.5 mg/cm2)
Details on in vitro test system (if applicable):
SKIN PREPARATION
- Source of skin: Human (4 donors)
- Ethical approval if human skin: Informed consent was provided by all skin donors
- Type of skin: abdominal surgery
- Preparative technique: Upon arrival of the skin at the laboratory, subcutaneous fat was removed, the skin was cleared from blood residues, carefully dried and then stored wrapped in aluminium foil at <-18°C until use. After thawing, the skin was cut to a recorded thickness.
- Thickness of skin (in mm): 0.4 mm
- Membrane integrity check: Yes, permeability coefficient for tritiated water
- Storage conditions:
- Justification of species, anatomical site and preparative technique: common for this type of test as described in the OECD TG

PRINCIPLES OF ASSAY
- Diffusion cell: flow-through automated diffusion cells (PermeGear Inc., Riegelsville, PA, USA)
- Receptor fluid: Phosphate Buffered Saline (PBS), pH 7.06
- Solubility of test substance in receptor fluid: soluble in aqueous phase of the O/W formulation
- Static system: no
- Flow-through system: yes
- Test temperature: skin surface temperature was 31.8°C (exp. 1, Donor 1 and 2) and 31.6°C (exp. 2, Donor 3 and 4)
- Humidity: ambient
- Occlusion: no

Results and discussion

Percutaneous absorptionopen allclose all
Key result
Time point:
24 h
Dose:
2,56%
Parameter:
percentage
Absorption:
27.5 %
Key result
Time point:
24 h
Dose:
5%
Parameter:
percentage
Absorption:
27.7 %
Key result
Time point:
24 h
Dose:
7%
Parameter:
percentage
Absorption:
31 %
Time point:
24 h
Dose:
10%
Parameter:
percentage
Absorption:
37.2 %

Any other information on results incl. tables

Total radioactivity recovery rates ranged from 95% (2.5% test item) to 97% (5% test item). Between 37% and 45% of the radioactivity applied was removed by skin washing.

The relative absorption of the test item into the receptor fluid was comparable between groups and ranged from 0.89 (2.5% test item) to 1.46 % (7% test item) of the applied dose. Total relative absorption, defined as the summed amounts in the receptor fluid, the receptor compartment wash and skin membrane (epidermis and dermis, excluding tape strips), slightly increased with test item concentration, i.e. values were 27.5 %, 27.7 %, 31.0 % and 37.2 % of the applied dose at DHA concentrations of 2.5, 5, 7 and 10% respectively.

Total absolute absorption values were 18.0, 34.0, 49.5 and 84.4 µg.cm-2 µg.cm-2 at test item concentrations of 2.5, 5, 7 and 10% respectively.

Most of the amounts of DHA considered to be absorbed (i.e. 87 to 91% of the summed amounts in the receptor fluid, the receptor compartment wash and skin membranes) were actually found within the epidermis. This suggests that considerable amounts of the test material might actually be bound to residual parts of the stratum corneum that could not be removed by the ten tape strips performed.

Applicant's summary and conclusion

Conclusions:
In summary, the dermal absorption of the test item contained in typical self tanning formulations was estimated to be 27.5 % (18.0 µg.cm-2), 27.7 %(34.0 µg.cm-2), 31.0 % (49.5 µg.cm-2) and 37.2 % (84.4 µg.cm-2) of the applied dose at test item concentrations of 2.5, 5, 7 and 10% respectively.
Executive summary:

The test item is a cosmetic ingredient that is added to so-called self tanning products in order to generate a superficial skin tanning. The mechanism of tanning is due to substance binding to amino acid residues in the skin.

The present study was designed to examine the in vitro percutaneous absorption of dihydroxyacetone (DHA) through human skin membranes using [14C]-DHA. DHA was tested as an OIW formulation at four concentrations, i.e. 10 %, 7 %, 5 % and 2.5 % in flow-through diffusion cells. The formulations were applied to the skin at a target application rate of 2.0 mg/cm2 (actual mean application rate was in the range of 2.2 - 2.5 mg/cm2) and the contact time was 24 hours. Overall mean recovery rates ranged from 95.0 % (5 % DHA) to 97.4 % (2.5 % DHA).

The relative transdermal absorption of DHA into the receptor fluid was independent of the DI IA concentration applied and narrowly ranged from 0.89 % to 1.46 % of the applied dose. Accordingly, mean values of the absolute transdermal absorption of DHA into the receptor fluid increased with increasing concentrations of DHA in the applied self-tanning creams from 0.77 µg/cm2 (2.5 % DHA) to 2.99 µg/cm2 (10 % DHA) over the 24-hour exposure period.

The relative amounts of DHA in the skin fractions (stratum corneum, epidermis and dermis) were almost comparable between groups. Consequently, the absolute amounts of DHA in each skin fraction equally increased with increasing concentrations of DHA in the applied formulation.

Total relative DHA absorption, defined as the amount in the receptor fluid, the receptor compartment wash and skin membrane (epidermis and dermis), excluding tape strips slightly increased with the applied DHA concentration, being 27.5 % (18.0 µg/cm2) and 27.7 % (34.0 µg/cm2) of the applied dose for the 2.5 % and 5 % DHA formulations, respectively, and 31.0 % (49.5 µg/cm2) and 37.2 % (84.4 µg/cm2) of the applied dose for the 7.5 % and 10 % DHA formulations, respectively.

Most of the amounts of DHA considered being absorbed (i.e. 87 % to 91 % of the amounts in the receptor fluid, the receptor compartment wash and the skin membranes) were actually found within the epidermis. This suggests that considerable amounts of the test material might actually be bound to residual parts of the stratum corneum that could not be removed by the tape stripping as applied.