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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:
weight of evidence
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: Not performed according to GLP. An equivalent or similar guideline to OECD 428 is used but recovery was not calculated and seems to be very low

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
2003

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
Deviations:
yes
Remarks:
temperature 37°C instead of 32°C
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
not specified
Details on test material:
- Name of test material (as cited in study report): LINALYL ACETATE
Specific details on test material used for the study:
- Name of test material (as cited in study report): linalyl acetate
- Analytical purity: >97%
- Source: Fluka, Buchs, Switzerland
Radiolabelling:
no

Test animals

Species:
other: human
Strain:
other: not relevant
Sex:
female
Details on test animals and environmental conditions:
Human skin was obtained from the region of thorax of one 40-year-old woman

Administration / exposure

Type of coverage:
occlusive
Vehicle:
unchanged (no vehicle)
Duration of exposure:
Absorption: 1, 2, and 4 hours
Elimination: 1 h
Doses:
- Nominal dose: 500 mg
No. of animals per group:
The absorption and elimination experiments were repeated in quadruplicates and triplicates, respectively.
Control animals:
no
Details on study design:
DOSE PREPARATION
Test article applied undiluted

TEST SITE
Skin extracts of 0.65 cm2

REMOVAL OF TEST SUBSTANCE
- Washing procedures and type of cleansing agent: Skin was rinsed shortly with methanol
- Time after start of exposure: 1, 2 or 4 hours

SKIN PREPARATION AFTER EXPOSURE
After 1, 2, or 4 h exposure, the stratum corneum layers were separated using 21 fragments of an adhesive tape, and every fraction of the stratum corneum as well as the remaining skin were extracted with methanol and stored for analysis. The acceptor medium was also collected for analysis.

For the elimination assessment, the acceptor medium was replaced by a fresh portion after 1 h exposure, and its circulation was maintained. The donor chambers remained uncovered. The experiment was terminated after 1, 2, 3 or 4 h, and the skin layers were subjected to the extraction process.

ANALYSIS
- Method type(s) for identification: GC-MS
Details on in vitro test system (if applicable):
SKIN PREPARATION
- Source of skin: 40-year old woman
- Ethical approval if human skin: Yes, ethics committee of the Medical University of Gdansk
- Type of skin: thorax
- Storage conditions: At -20°C

PRINCIPLES OF ASSAY
- Diffusion cell: flow-through Teflon diffusion cells
- Receptor fluid: isotonic phosphate buffer (pH 7.3) preserved with 0.005% sodium azide
- Solubility of test substance in acceptor fluid: 1.34 mg/mL
- Flow-through system: yes, constant rate of 10 mL/h
- Test temperature: 37 +/- 0.5 °C
- Humidity: No data
- Occlusion: Donor compartment occluded with parafilm

Results and discussion

Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined
Absorption in different matrices:
At 1 hour after application (ug/cm2):
- Stratum corneum (tape strips): 61.6 +/- 9.9
- Skin preparation (epidermis + dermis): 62.4 +/- 9.2
- Acceptor fluid: 0

At 2 hours after application (ug/cm2):
- Stratum corneum (tape strips): 98.7 +/- 6.7
- Skin preparation (epidermis + dermis): 87.6 +/- 9.7
- Acceptor fluid: 0

At 4 hours after application (ug/cm2):
- Stratum corneum (tape strips): 86.4 +/- 6.8
- Skin preparation (epidermis + dermis): 129.9 +/- 15.9
- Acceptor fluid: 0
Total recovery:
- Total recovery: 0.028% (216.3/(769.2*1000)
- Recovery of applied dose acceptable: No, not within 100 +/- 10% as stated in the OECD guideline but washed fraction not measured
- Limit of detection (LOD): No data
Conversion factor human vs. animal skin:
Not relevant

Any other information on results incl. tables

Linalyl acetate easily penetrated into the skin, however it was not detected in the acceptor fluid.

The percutaneous absorption of linalyl acetate into the skin layers (ug/cm2), is summarised in the following table. The applied dose was 500 mg/0.65 cm2 (= 769.2 mg/cm2).

Skin layer

Time

1h

2h

4h

Stratum corneum SC1

27.3±7.9

64.1±8.1

54.6±7.4

Stratum corneum SC2

19.5±4.3

19.1±2.5

19.3±0.7

Stratum corneum SC3

14.8±2.9

15.5±2.4

12.5±2.7

Total Stratum corneum

61.6±9.9

98.7±6.7

86.4±6.8

Remaining skin (epidermis and dermis)

62.4±9.2

87.6±9.7

129.9±15.9

Skin total

124.0±5.8

186.3±16.4

216.3±18.5

Elimination of linalool from human skin layers following 1 h absorption is summarised in the following table:

Skin layer

Time   

1h

2h

3h

4h 

Stratum corneum SC1

30.5±4.9

24.1±4.6

17.2±8.0

3.8±1.5

Stratum corneum SC2

22.4±4.0

20.6±5.6

4.2±0.9

0

Stratum corneum SC3

14.2±4.3

11.6±4.6

0

0

Total Stratum corneum

67.1±5.5

56.3±5.3

21.4±7.8

3.8±1.4

Remaining skin (epidermis and dermis)

45.3±6.5

51.6±7.9

71.8±12.6

117.2±15.1

Skin total

112.4±11.3

107.9±2.9

93.2±9.2

121.0±13.6

Applicant's summary and conclusion

Conclusions:
Under the conditions of this in vitro penetration study in human skin, 0.028% of the applied dose could be recovered in epidermis and dermis. The maximum concentration in stratum corneum was reached after only 2 h.
The total amount of linalyl acetate in the skin was unchanged during the elimination phase, but the ratio of the amount in stratum corneum, epidermis and dermis was decreasing, and after 4 h, only 3% of linalyl acetate in total skin was found in stratum corneum.
Executive summary:

The in vitro skin absorption and elimination of linalyl acetate was studied by applying linalyl acetate (500 mg/0.65 cm2) to human skin and determine the amount of linalyl acetate in the stratum corneum and epidermis and dermis after 1, 2, and 4h. Linalyl acetate was analysed using gas chromatography.

Linalyl acetate easily penetrated into the skin, however it was not detected in the acceptor fluid. Additionally, 129.9 ug linalyl acetate/cm2 was found in epidermis and dermis. The percentage of applied dose in epidermis and dermis is therefore calculated to be 0.028%. The maximum concentration in stratum corneum was reached after only 2 h. Considering results of another in vitro penetration study conducted by Green et al (2007), it is likely that most of the applied material is evaporated. The total amount of linalyl acetate in the skin was unchanged during the elimination phase, but the ratio of the amount in stratum corneum, epidermis and dermis was decreasing, and after 4 h, only 3% of linalyl acetate in total skin was found in stratum corneum.