Registration Dossier

Administrative data

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
24.09.2007 to 28.02.2008
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP.

Data source

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

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): Trimethylsilanol
- Substance type: Silanol
- Physical state: Colourless transparent liquid

The test substance is the hydrolysis product of the registered substance.
- Radiochemical purity (if radiolabelling): 97.6 ±0.03%
- Specific activity (if radiolabelling): 8.653 ±0.11 mCi/g
- Locations of the label (if radiolabelling): 14C
- Expiration date of radiochemical substance (if radiolabelling): No data
- Stability under test conditions: Stable
- Storage condition of test material: Refrigerated at 5 ±4oC
Radiolabelling:
yes
Remarks:
14C-labelled

Test animals

Species:
human
Strain:
other: N/A
Sex:
male/female
Details on test animals and environmental conditions:
Not applicable, in vitro test.

Administration / exposure

Type of coverage:
semiocclusive
Vehicle:
unchanged (no vehicle)
Duration of exposure:
24 hours
Doses:
The average dose applied to the skin samples was 11.1 mg/cm2 of skin and 20.2 µCi/cm2 of skin.
No. of animals per group:
Three skin specimens tested in triplicate
Control animals:
no
Details on study design:
DOSE PREPARATION
- Method for preparation of dose suspensions: The neat 14C-TMS dose solution was prepared by diluting and mixing 14C-TMS with unlabelled TMS. The specific activity of dosing solution was determined on the day of dosing and found to be 1.83 mCi/g by liquid scintillation counting (LSC).

ANALYSIS
- Method type(s) for identification: The radiochemical purity for the dosing solution was verified prior to the dosing day using HPLC with radiomatic detection.
Details on in vitro test system (if applicable):
SKIN PREPARATION
- Source of skin: Human cadavers
- Ethical approval if human skin: No data
- Type of skin: Abdominal skin
- Preparative technique: On the day of the experiment, prior to use, skin samples were cleaned of underlying fat and thawed at room temperature. Excessive hair was only clipped off the skin if required. Each skin sample was sprayed with a mild soap solution, 1% and dermatomed with a mini-dermatone to separate epidermis from most of the dermis. Dermatoned skin samples were placed on a gauze soaked with culture medium while other skin sections are being processed. Three disc shaped pieces, large enough to fit 0.64 cm flow-through diffusion cells, were punched out from the skin of each donor. The thickness of all skin pieces was measured with a digimatic micrometer before placing them in the diffusion flow-through cells.
- Thickness of skin: Dermatoned skin: 250-350 microns
- Membrane integrity check: Each skin sample received an infinite dose of 3H-H2O for 20 minutes in order to determine if the barrier integrity of the skin had been compromised. The 3H-H2O was removed after 20 minutes by blotting and rinsing the application site with reverse osmosis water. After dose removal, aliquots of the receptor fluid continued to be collected in pre-weighed vials for an additional 60±10 minutes. Radioactivity content in the receptor fluid was determined by liquid scintillation analysis and used to determine barrier integrity of the skin samples.
- Storage conditions: In culture medium
- Justification of species: Excised human skin obtained from cadavers is a commonly used and an accepted model for in vitro assessment.

PRINCIPLES OF ASSAY
- Receptor fluid: Physiological buffer, Hank's Balanced Salt Solution with 0.6% HEPES, 0.005% Gentamicin and 4% Bovine Serum Albumin, pH 7.4. Pumped beneath the skin samples through the receptor compartment at the flow rate between 2.0 and 2.2 ml/h and collected using a fraction collector.
- Solubility of test substance in receptor fluid: No data
- Flow-through system: Bronaugh flow-through apparatus
- Test temperature: Receptor fluid temperature 37oC to ensure that the skin surface temperature is kept at 32 ±1oC
- Humidity: No data
- Occlusion: Semi-occlusive
- Other: Sample collection: The receptor fluid was pumped through the individual chambers and collected into vials prefilled with scintillation cocktail at 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 time-points using a fraction collector. Immediately after dose application a charcoal basket was placed in a specially designed holder to collect any test article that volatilised. At termination of the 24 hour exposre period, the air was flushed through the headspace above the skin for approximately two minutes to collect the vapour that might have been present in the space above the skin, into a charcoal basket. Charcoal baskets were removed and the application site was gently blotted using two dry cotton tipped applicators, followed by blotting with three cotton tipped applicators moistened with 1% soap solution and two dry swabs. The holders that were used to hold the charcoal basket over the skin, were removed and the skin was placed on a piece of Saran wrap and tape stripped with D-Squame adhesive tape to remove the stratum corneum and any radioactivity remaining on the skin surface. Tape stripping was discontinued if the epidermis was ruptured. Skin discs were removed and digested in a 35% aqueous solution of tetraethylammonium hydroxide (TEAH). The diffusion cells were removed and rinsed wih ethanol. Radioactivity concentration was measured by LSC in the receptor fluid, solubilised skin samples and extracts.

Results and discussion

Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined
Absorption in different matrices:
Only traces of radioactivity associated with 14C-TMS were found on the skin surface (0.003% of applied dose) after 24 h of exposure. The total % of the dose absorbed was estimated to be 0.08% of the appled dose. The absorption of 14C-TMS is potentially even less than 0.08%, considering presence of radioactive impurities in the dosing solution and their possible contribution to the absorption levels. The majority of the absorbed dose penetrated the skin into the receptor fluid during the initial three hour of exposure. Only traces of radioactivity associated with 14C-TMS (0.001%) remained in the skin after washing and tape stripping the exposure site after 24 h of exposure. The mean cumulative penetration over the 24 hour diffusion period was estimated to be 9.1 ±0.9 µg equivalents of 14C-TMS/cm2 of exposed skin. Steady state flux was established between one and three hours of xposure when TMS is most likely still present on the skin surface and is not depleted in the donor compartment due to evaporation. The permeability coefficient, Kp was estimated to be 4.1 x 10-6 cm/h.
Total recovery:
- Total recovery: The % of applied 14C-TMS recovered from all analysed samples was 93.1%. Almost all (99.9%) of the recovered 14C-TMS volatilised from the skin surface and was captured in the charcoal baskets placed above the exposure sites, demonstrating the high volatility of TMS under these experimental conditions.
- Recovery of applied dose acceptable: Yes
Percutaneous absorption
Dose:
average of 11.1 mg/cm2
Parameter:
percentage
Absorption:
< 0.1 %
Remarks on result:
other: 24 h
Conversion factor human vs. animal skin:
NA

Applicant's summary and conclusion

Conclusions:
In a well conducted guideline study conducted to OECD 428 and GLP (reliability score 1), the total % of the dose of 14C-TMS absorbed was estimated to be <0.08% of the applied dose. Almost all (99.9%) of the recovered 14C-TMS volatilised from the skin surface and was captured in the charcoal baskets placed above the exposure sites. The majority of the absorbed dose penetrated through the skin to the receptor fluid.