Octamethylcyclotetrasiloxane

Dermal absorption

Administrative data

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

18.11.1997 to 26.06.1998

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1998

Report date:

1998

Reference 2

Reference Type:

publication

Title:

In Vitro and in Vivo Percutaneous Absorption of 14C-Octamethylcyclotetrasiloxane (14C-D4) and 14C-Decamethylcyclopentasiloxane (14C-D5).

Author:

Jovanovic, ML, JM McMahon, DA McNett, JM Tobin and KP Plotzke

Year:

2008

Bibliographic source:

Regulatory Toxicology and Pharmacology 50: 239-248

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Octamethylcyclotetrasiloxane

EC Number:

209-136-7

EC Name:

Octamethylcyclotetrasiloxane

Cas Number:

556-67-2

Molecular formula:

C8H24O4Si4

IUPAC Name:

2,2,4,4,6,6,8,8-octamethyl-1,3,5,7,2,4,6,8-tetroxatetrasilocane

Radiolabelling:

yes

Remarks:

14C

Test animals

Species:

human

Strain:

other: NA

Sex:

male/female

Details on test animals or test system and environmental conditions:

Not applicable to this study

Administration / exposure

Type of coverage:

semiocclusive

Vehicle:

unchanged (no vehicle)

Duration of exposure:

24 hours

Doses:

8 mg/cm2 (target); 7.0-19.5 mg/cm2 (actual)

No. of animals per group:

Skin samples from six individual humans.

Control animals:

no

Details on study design:

Skin preparation and dosing: Each test preparation was tested in duplicate skin samples from six individual donors. The skin specimens received from the Tissue Banks (US Tissue & Cell, OH and Life Legacy Foundation, AZ) were stored at -80 °C until used in the percutaneous absorption assays. On each day of dosing, skin samples were thawed and dermatomed to thickness between 300 and 500. lm using electrodermatome to separate epidermis from the majority of the dermis. The physiological receptor fluid was pumped beneath the skin samples through the receptor compartment for 24 h at a flow rate between 1.5 and 2.5 ml/h. The skin area available for dosing was 0.64 cm2. Prior to dosing, the barrier properties of skin samples were evaluated by measuring tritiated water penetration into a receptor fluid with a 20-min test. A single dose of either neat or the antiperspirant formulation was applied gravimetrically by weighing dosing device before and after dosing. The average dose of the neat materials was 10.7 mg D4/cm2 of skin. The formulated 14 C-D4 delivered an average dose of 9.5 mg D4/cm2 of skin, respectively.

Sample collection and analysis: Immediately after dosing, charcoal baskets were placed into a custom designed holder approximately 2 cm above the skin to collect any volatilized material. The receptor fluid was collected directly into scintillation cocktail at 1-h intervals for the first 6 h and at 3-h intervals thereafter through 24 h using a fraction collector. After 24 h, the charcoal baskets were removed and exposure sites were gently blotted with cotton-tipped applicators moistened with 1% aqueous solution of hand soap, ethanol and dry swabs, and then tape stripped with five pieces of Scotch tape to remove any radioactivity remaining on the skin surface. Charcoal baskets, holders, cotton-tipped swabs and tape strips were extracted in toluene while the diffusion cells were extracted in absolute ethanol. Skin was digested in a 35% aqueous solution of tetraethylammonium hydroxide (TEAH). All samples were analysed for radioactivity content by liquid scintillation counting (LSC).

Data analysis and statistical methods: Barrier integrity of the skin samples was determined by measuring percent of applied 3H-H2O that penetrated through the skin into the receptor fluid. The integrity of the skin barrier was deemed intact and suitable for analysis of dermal absorption if the mean absorption of 3H-H2O in replicate samples was 60.21% with a coefficient of variation less than 60%. The acceptance criteria were established in the validation study (data not published) that was based on rapid screening procedure introduced by Bronaugh et al., 1986. Skin specimens from individual donors were tested in duplicates.

Penetration of applied 14C-D4 through the skin into receptor fluid was plotted against the time of exposure. The slope of the linear portion of the penetration curve was used to estimate steady state flux (lg/cm2/h), and correspondingly the permeability coefficient (Kp, cm/h) by dividing ''assumed'' steady state flux by the concentration of the test article in the dosing solution. Specific density (g/cm3) was used to represent concentrations of neat materials.

Absorption was reported as the percent of the applied dose that permeated into the receptor fluid and in the skin samples after application site had been washed and tape stripped five times. The absorption data were analysed using a two factor mixed effects analysis of variance with two levels of time and two levels of treatment (neat vs. formulated). A significant treatment effect (p < 0.05) would indicate that the mean percent of D4 absorbed differed between the neat and formulated treatment groups. Statistical analysis of the data was performed using SAS, v. 6.12.

Details on in vitro test system (if applicable):

On day zero skin samples were dermatomed, placed in diffusion cells in duplicate, and dosed with neat 14C-D4. Applied radioactivity ranged from 4.5 to 13.8 µCi per piece of skin. The neat dosing solution was prepared with 14C-D4 and unlabelled D4 to achieve the target specific activity. Prior to use, the skin samples were thawed, the epidermis was separated from dermis. Blemish-free sections of the skin of the appropriate thickness were chosen, and circular pieces measuring approximately 2cm were cut from each skin sample and placed epidermis side up in the diffusion cell. The skin area available for dosing after mounting into the diffusion cell was 0.64 cm2. The receptor fluid, Hank's Balanced Salt Solution with 0.6% HEPES, 0.005% Geneticin and 4% Bovine Serum Albumin was mixed, the pH adjusted to 7.4 and the preparation filtered through a 0.45 micron filter. The receptor fluid was pumped underneath the skin samples for 24 hours and collected using a fraction collector. Immediately after dosing, charcoal baskets were placed above the skin and secured into a custom designed cap to capture any volatilised material.

Barrier integrity test was conducted using 3H-H2O. Only skin samples passing the test were used in the test.

The percent of the dose of 14C-D4 absorbed was determined by analysing the receptor fluid over a 24 hour period and what remained in the skin after washing the skin at the end of the 24 hour period. Radioactivity was measured by liquid scintillation analysis.

Results and discussion

Signs and symptoms of toxicity:

not examined

Remarks:

in vitro study

Dermal irritation:

not examined

Remarks:

in vitro dermal penetration study

Absorption in different matrices:

The percentage of applied dose recovered from all analysed samples for D4, neat and formulated was higher than 91%. The majority of the applied D4 volatilized from the skin surface and was recovered from the charcoal baskets (88.2% for neat D4; 99.3% for the formulated D4). On average, 3.0-4.0% of the applied D4 dose remained on the skin surface indicating that little of the applied dose remained available for absorption. The percent of the applied dose absorbed was estimated to be 0.50% for neat D4. In the antiperspirant formulation, absorption of D4 was estimated to be 0.49% of the applied dose.
There were no significant differences in absorption between neat and antiperspirant formulated dosing solutions of either test article. The main portion of the ''absorbed'' dose was found in the skin, 98% for both neat and formulated D4. The average cumulative penetration through the skin into receptor fluid over 24 h for neat D4 was 1.1 l µg/cm2, and 0.8 µg/cm2 for formulated D4. Based on the results of the regression analysis (R2 > 0.99) the steady state flux for neat D4 of 0.06 µg/ cm2/h was reached between 5 and 15 h and between 6 and 21 h for formulated D4 (0.04 µg/cm2/h). The estimated Kp values were in a range of 10E-9 cm/h for D4 preparations. Only 0.50 % of the applied dose of neat D4 was absorbed at the end of the assay as compared to 0.49 % to the formulated D4. The majority of the dose collected was in the charcoal baskets (88.17 ± 3.38 % ).

Total recovery:

- Total recovery: 91.6% ± 3.4%
- Limit of detection (LOD): Set at one times background values

Percutaneous absorption

Key result

Time point:

24 h

Dose:

8 mg/cm2

Parameter:

percentage

Absorption:

0.5 %

Remarks on result:

other: standard error of 0.07%

Conversion factor human vs. animal skin:

NA

Any other information on results incl. tables

Cumulative penetration over 24 hours for neat D4 was 1.23±0.19 µg/cm² (experiment 1) or 0.91±0.14 µg/cm² (experiment 2). The steady state flux for neat D4 was 0.06 or 0.05 µg/cm²/hr in experiment 1 and 2, respectively. Lag time for the penetration of D4 was approximately 3 hours. After 24 hours, approximately 0.47% of the applied neat D4 remained in the skin.

Applicant's summary and conclusion

Conclusions:

In an in vitro dermal absorption study conducted to OECD 428 and GLP (reliability score 1), 0.50% of topically applied neat 14C-D4 was absorbed. The majority of the absorbed dose remained in the skin (94% of the absorbed dose). The majority (approximately 88%) of the dose evaporated from the skin.